• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Challenges for cysteamine stabilization,quantification,and biological effects improvement

    2021-01-21 03:02:04CarlaAtallahCatherineCharcossetneGreigeGerges
    Journal of Pharmaceutical Analysis 2020年6期

    Carla Atallah,Catherine Charcosset,Hélène Greige-Gerges

    aBioactive Molecules Research Laboratory,Doctoral School of Sciences and Technologies,Faculty of Sciences,Lebanese University,Lebanon

    bLaboratory of Automatic Control,Chemical and Pharmaceutical Engineering,Claude Bernard Lyon 1 University,France

    ABSTRACT

    Keywords:

    Cysteamine

    Detection

    Encapsulation

    Skin

    Stability

    1.Introduction

    Cysteamine(cys)or 2-mercaptoethylamine is an aminothiol endogenously synthesized by human body cells during the coenzyme A metabolism cycle(Fig.1).

    In 1953,cys was found to be one of the most potent thiol derivatives in the protection against ionizing radiation[1].Numerous studies have tested the radioprotective effect and the mechanism of action of this compound using human cell lines[2,3],bacteria[4],and mice models[5].

    In 1976,cys was first used for the treatment of cystinosis,approved by the US Food and Drug Administration(FDA),and commercialized in the 1990s[6].Till now,cys is the only specific targeted therapy available for patients with cystinosis.The latter is a rare autosomal recessive metabolic disease,characterized by the accumulation and crystallization of cystine within the lysosome,which eventually results in apoptosis and tissue damage in all organ systems including the cornea[7].Following oral administration,cys enters the lysosome by an unknown transporter and breaks down cystine into cysteine and cysteine-cys disulfide,which are removed by specific transporters.Consequently,cys rapidly depletes cells and tissues of lysosomal cystine.

    Another interesting application was recently discovered for cys,as it was shown to be clinically efficient in treating hyperpigmentation disorders[8,9].Despite the presence of many potent depigmenting agents,namely hydroquinone and derivatives and kojic acid,they were found to possess local side effects(irritation,permanent depigmentation,etc.)and presented mutagenic and carcinogenic potentials[10].Cys has shown to be a well-tolerated compound,demonstrating its non-mutagenicity and non-carcinogenicity criteria[11].Interestingly,it may inhibit the mutagenic effect of some potent mutagens.Besides,it may exert an anti-cancer effect in several cancers,such as melanoma,in in vivo studies[12].

    Fig.1.Structure of cys.

    Fig.2.Oxidation of cys to cystamine.

    Regardless of its numerous and remarkable biological applications,the efficacy of cys may be limited by its unpleasant organoleptic properties,strong hygroscopicity,chemical instability,and its poor pharmacokinetic profile(T1/2=1.75 h)[13].Moreover,cys is often susceptible to degradation through its rapid oxidation in air or aqueous solution to its disulfide form cystamine(Fig.2).

    Consequently,the encapsulation of this molecule into delivery systems has been commonly used as a good approach to overcoming these problems[14-16].Cys was mainly incorporated into three different types of encapsulating agents:liposomes,cyclodextrin(CDs),and emulsions.For example,its encapsulation in liposomes was used to selectively release cys in lysosomes[17]and to enhance its gastrointestinal absorption[15].Besides,CDs and emulsions were successfully shown to remove cys odor[13]and to improve cys stability[18],respectively.On the other hand,cys was employed to modify the surface of encapsulation systems for many purposes.For example,cys was linked to the surface of CDs to improve intra-oral drug delivery[19,20],and to the surface of gold nanoparticles to enhance the colorimetric detection of compounds by these particles[21,22].

    This review highlights the biosynthesis,the physicochemical properties,and the stability of cys.The quantification of this compound using different analytical methods,as well as the challenges encountered in these techniques,will be for the first time analyzed.Then,we will discuss the biological activities of this compound emphasizing its topical effects.Finally,the encapsulation of cys in different encapsulation systems and the use of cys to modify the surface of these carriers will be presented.

    2.Metabolism of cys

    Cys is an aminothiol derived from coenzyme A(CoA)degradation.The degradation of CoA leads to the formation of pantetheine,which is hydrolyzed by pantetheinase to obtain cys and pantothenic acid(Fig.3)[23,24].Then,the oxidation of cys by cys dioxygenase produces hypotaurine.Later,cys is eliminated by the taurine pathway in the form of bile salts[25].After the administration of a high dose of cys,an alternative catabolic route is manifested,involving its conversion to S-methylcys by a thiolmethyltransferase,which is consequently metabolized into methanethiol and acetamide by cytochrome P450.Then,methanethiol is converted to dimethylsulfide by another thiol-methyltransferase[26,27].

    3.Physicochemical properties and stability of cys

    Cys possesses high aqueous solubility(23.5g/L),a pKa1(SH)=8.19 and pKa2(NH2)=10.75 with a melting point of 67.3℃(Table 1[16,28-31]).This molecule exists in three ionic forms:the positively charged form(cys+),the zwitterionic form(cys-ZW),and the negatively charged form(cys-)(Fig.4)[32].

    Besides,cys,as a thiol compound,has a very offensive odor that makes it difficult to be used as a depigmenting agent[9].Different forms of cys have been used:cys hydrochloride(HCl),phosphocys,and cys bitartrate.Cys hydrochloride forms a eutectic equilibrium with water with a low eutectic temperature of-33.15℃.A eutectic mixture is composed of two or three components with a melting point significantly lower than that of its one component[33].This low temperature causes the rapid dissolution of cys in the presence of water.The presence of a minor quantity of water vapor does not affect the stability state of cys hydrochloride,and cys mass remains stable until a 35% relative humidity.In fact,above this water vapor pressure,cys hydrochloride melts immediately to form a very concentrated saturated solution of 0.85 mass fraction or 0.47 mol fraction of cys hydrochloride[31].

    Cys is unstable in aqueous solution;a rapid conversion to cystamine occurs due to the rapid oxidation of the sulfhydryl group.The reactions of oxygen with thiols in aqueous solutions are presented in Eqs.(1)and(2),according to which the reactions give disulfides and hydrogen peroxide or water.

    Alkaline pH stimulates the oxidation of cys because the thiolate anion(cys-)is more reactive.Moreover,this reaction is catalyzed by metal ions such as Cu2+,Fe3+,and Zn2+.In fact,the reduction reaction of cys by metal ions produces the reduced ion(Eq.(3));the latter reacts with oxygen and peroxide.The following series of reactions would explain this fact.

    The reaction between Cu+and oxygen produces superoxide(Eq.(4)),then superoxide reacts with a thiol to generate thiol radical(Eq.(5))that reacts with itself to produce the disulfide(Eq.(6)).

    On the other hand,oxygen consumption is stimulated by a reaction of a reduced metal ion with peroxide,producing,the potent hydroxyl radical(Eq.(7));the latter reacts with a thiol group,leading to the formation of a water molecule(Eq.(8)).The thiol radical reacts with itself to produce the disulfide(Eq.(6))as described previously.Therefore,the use of a chelating agent,such as diethyldithiocarbamate,inhibits this reaction[34].

    The degradation of cys is a zero-order reaction,indicating that the concentration of cys decreases linearly with time[35].The removal of oxygen from a solution of cys by packing under nitrogen and the presence of ascorbic acid(antioxidant)increase the stability of the molecule,but show a lower efficacy in comparison with chelating agents such as disodium edetate[36].

    Pescina et al.[16]examined the stability of cys after being dissolved in 0.9% NaCl at different pH,temperature,and in the presence of α-CD,ethylenediaminetetraacetic acid(EDTA),and sodium phosphate.They showed that cys oxidation is a pH-dependent reaction.It is very fast at pH 7.4 because of the presence of the ionized thiol groups while the oxidation decreases at an acidic pH of 4.2.As for the influence of the temperature(-20,4,and 25℃),they found that the stability decreases when the temperature increases.While EDTA plays a crucial role in preventing cys oxidation,the presence of α-CD or sodium phosphate does not affect its stability.

    Fig.3.Metabolism of cys[24](with permission from John Wiley and Sons).

    The degradation of 0.1 mg/mL cys has been reached within 18 h in phosphate buffer saline(PBS)with a rate of degradation of 126 μg/h.A similar rate(132 μg/h)was also observed but with a higher concentration(4.4 mg/mL)[18].In order to improve the stability of cys,the addition of different types of antioxidant to 0.1 mg/mL cys has been evaluated to out-compete cys for oxygen consumption and compared to the degradation rate of free cys(126 μg/h).Nevertheless,the presence of the hydrophilicantioxidant vitamin C increased the degradation rate of cys(523μg/h).This rate was not also influenced by the presence of the hydrophobic antioxidants,vitamin E,and soybean oil since they are scarcely soluble in aqueous solution.Tween 80 surfactant induced a reduction in degradation rate to 112μg/h,suggesting some interactions with either dissolved cys or oxygen molecules.While,an emulsion of vitamin E,soybean oil,and Tween 80 surfactant resulted in a greater decrease in cys degradation(101μg/h).However,these results are not significant because the degradation rate of cys was not well decreased.The use of catalase enzyme,which can revert peroxide species to diatomic oxygen and potentially scavenging the system of radicals essential to oxidize cys,reduced the degradation rate to 58μg/h.On the other hand,a decline in the cys degradation rate to 20%-30% was obtained after the addition of hydrophobic film(a soybean oil layer)to slow oxygen diffusion[18].

    Table 1Physicochemical properties of cys.

    4.Analytical methods for cys detection

    Fig.4.Chemical structures of cys forms obtained at different pHs.

    Different analytical methods have been suggested to detect and quantify cys in biological samples(i.e.,plasma and urine)in the literature,including enzymatic assay,high-voltage electrophoresis,ion-exchange column chromatography,high-performance liquid chromatography(HPLC)with fluorescence and ultraviolet(UV)detection,and gas chromatography with flame ionization and photometric detection.These methods will be for the first time presented in this review.

    4.1.Cys derivatization

    Due to the lack of a chromophore in cys structure,the quantifi cation of this compound using conventional analytical methods with UV absorbance or fluorescence detection is a challenging mission.Therefore,the derivatization of cys is used for cys separation or quantification.For this purpose,numerous derivatization agents were utilized and optimized according to the analytical method used.In Table 2,the structures of all these agents,as well as the derivatization reactions with cys,are presented[37-53].

    4.1.1.Pivaldehyde

    Cys is derivatized with pivaldehyde before its analysis with gas chromatography[37].

    4.1.2.Bis(trimethylsilyl)trifluoroacetamide(BSTFA)

    The sample containing cys is placed in a screw-capped reaction vial,followed by the addition of dimethylformamide and BSTFA.The mixture is allowed to stand overnight before the analysis[38].

    4.1.3.Monobromobimane(mBBr)or monobromotrimethylammoniobimane(qBBr)

    mBBr or qBBr were dissolved in methanol,stored at 4℃,and protected from light for up to 4 months.This agent was used to quantify cys in plasma,red blood cells,and urine.A certain volume of this agent was added to cys solution and incubated for 15 min in the dark.For biological samples,perchloric acid was added to allow protein precipitation[39-42].

    4.1.4.Ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate(SBD-F)

    SBD-F was prepared in borate buffer.Borate buffer(125 mM;pH 9.5)containing 4 mM EDTA was added to cys sample solution.After vortex-mixing for 30 s,the reaction mixture was heated at 60°C for 60 min and then cooled at 4°C for 15 min to stop the labeling reaction[43,44].

    4.1.5.o-Phthalaldehyde

    Cys solution was mixed with sodium hypochlorite followed by the addition of o-phthalaldehyde in the presence of 2-mercaptoethanol.The latter was used as an antioxidant.Sodium hypochlorite increased several times the fluorescence intensity of cys coupled to o-phthalaldehyde[45].

    4.1.6.Isobutyl chloroformate(isoBCF)

    IsoBCF and NaOH were added to cys sample,and the mixture was shaken at 300 rpm for 5 min at room temperature.The mixture was extracted with n-pentane,and the pentane extract was evaporated to dryness at 80℃.The residue was dissolved in ethyl acetate[46,47].

    4.1.7.2-Chloro-1-methylquinolinium tetrafluoroborate(CMQT)

    CMQT was synthetized as follows:2-chloroquinoline,nitromethane,and trimethyloxonium tetrafluoroborate were mixed.Then,diethyl ether was added to the reaction mixture.The white precipitate was filtered off,washed with diethyl ether,and dried over phosphorus pentoxide under vacuum.Unfortunately,the synthesis reaction of CMQT was not presented.

    Cys was derivatized by an excess of CMQT in tris buffer solution(pH 8.2),and hydrochloric acid was added to the mixture[48].

    4.1.8.N-(1-pyrenyl)maleimide(NPM)

    NPM solution was prepared in acetonitrile.Cys solutions were derivatized with 1.0 mM NPM solution and left to stand for 5 min at room temperature.HCl solution(2 M)was added to stop the reaction and stabilize the adducts at the end of the reaction time.The final pH of the solution was kept at about 2,which is necessary for the stability of the NPM-cys adduct[49].

    4.1.9.7-Chloro-N-[2-(dimethylamino)ethyl]-2,1,3-benzoxadiazole-4-sulfonamide(DAABD-Cl)

    DAABD-Cl was synthesized as follows(Fig.5):4-chlorosulfonyl-7-chloro-2,1,3-benzoxadiazole was dissolved in CH3CN.After the addition of N,N-dimethylethylenediamine and triethylamine,the mixture was stirred at room temperature for 10 min.The reaction mixture was evaporated to dryness under reduced pressure to form DAABD-Cl[50].

    DAABD-Cl was prepared in acetonitrile.A mixture of tris(2-carboxyethyl)phosphine hydrochloride,EDTA,and 3-[(3-cholamidoproryl)dimethylammonio]propanesulfonic acid was prepared in borate buffer.This mixture was added to cys solution,borate buffer,and DAABD-Cl.The reaction mixture was heated at 40℃,and aliquots of the reaction mixture were taken out at intervals of 5-20 min,followed by the addition of 20% trifluoroacetic acid to stop the derivatization reaction[51].

    4.1.10.4-Fluoro-7-sulfamoyl benzofurazan(ABD-F)

    Cys solutions were directly derivatized with ABD-F reagent.The alkylation reaction was completed at 55℃for 15 min and stopped with HCl 12 N[52].

    4.1.11.6-Aminoquinolyl-N-hydroxysuccinimidyl carbamate(ACQ)

    Cys solutions were derivatized with ACQ in the presence of borate buffer and heated at 55℃for 10 min.The mixture was allowed to cool at room temperature before HPLC analysis[53].

    4.2.Analytical methods

    4.2.1.Enzymatic assay

    This assay consists of the inhibition of D-amino acid oxidase enzyme activity by the product of the reaction occurring between cys and bromopyruvate(Eq.(9)).The enzyme activity is proportional to the amount of cys[54].

    Table 2Structure and reaction of derivatization agents with cys.

    Table 2(continued)

    Fig.5.Synthetic route for DAABD-Cl(7-chloro-N-[2-(dimethylamino)ethyl]-2,1,3-benzoxadiazole-4-sulfonamide).

    Another method described by Duffel et al.[55]involved the oxidation of cys to hypotaurine by cys dioxygenase(Eq.(10)).Therefore,the quantification of oxygen uptake is proportional to cys concentration with standard solutions between 10 and 100 nmol.

    4.2.2.Ion-exchange column chromatography

    Hsiung et al.[56]worked on the detection of cys by ionexchange column chromatography using an amino acid analyzer with a short column of Beckman analyzer.Cys was detected after 268 min,a long time that may lead to the oxidation of the product during the analysis and therefore,an underestimation of the product concentration.

    Derivatization of cys with qBBr and mBBr has been realized by Fahey et al.[39],followed by separation of the derivatives by cationexchange chromatography and detection by fluorometry.The principal limitation of this method was the time required for sample analysis,3-4 h,for each of the bromobimane derivatives.

    Later,Ida et al.[45]used o-phthalaldehyde as the derivatization agent in the presence of 2-mercaptoethanol and sodium hypochlorite.Cation-exchange chromatography,using cation exchange resin(ISC-05/S0504),sodium borate buffer(pH 11.10)as mobile phase,70℃as temperature and with a linearity range of 2-200 pmol,was used to separate the derivatives,and the elution time was decreased to attain 7.5 min based on a fluorometric detection.For the application of this assay method to biological materials,the pretreatment with a cation exchange column(Dowex 5OWX8)was essential for removing interfering o-phthalaldehydereactive substances.This method was found to be suitable for evaluating the cys plus cystamine content in various organs and tissues because cys was quantitatively converted to cystamine in biological materials during these sampling procedures.

    4.2.3.HPLC

    The detection of cys by HPLC was performed using fluorescence,UV,and electrochemical detections.Electrochemical detection does not require any derivatization,while cys needs to be derivatized when using fluorescence and UV detections (Table 3[40-44,48,49,51-53]).Herein,we will present two methods of HPLC that use derivatization agents.

    4.2.3.1.Fluorescence detection.HPLC using fluorescence detection is widely used to detect cys.Many derivatization agents are used inducing different analysis conditions and eluting time.For example,mBBr[40-42],qBBr[43,44],NPM[49],DAABD-Cl[51],ABD-F[52],and ACQ[53]were all selected to detect cys.Table 3 resumes the analytical conditions and elution time for each derivatization agent.

    4.2.3.2.UV detection.CMQT was synthesized and used as a derivatization agent for UV detection of cys.The elution time was 25 min,the limit of detection was 0.1 and 0.2μmol/L,and the detection wavelength was 355 nm.This method is highly sensitive and specific.But,it is labor-intensive,as the derivatization reagent has to be synthesized initially for the preparation of stablederivatives[48].

    Table 3Detection of cys by HPLC.

    Table 4Gas chromatography detection of cys.

    Table 5UHPLC-ESI-MS/MS detection of cys.

    Fig.6.Reaction between bis(p-nitrophenyl)disulfide and mercaptan anion[59].

    4.2.4.Gas chromatography

    Gas chromatography with flame ionization and photometric detection were used to quantify cys(Table 4[37,38,46,47]).

    4.2.4.1.Flame ionization.Pivaldehyde(2,2-dimethylpropanal)[37]and(trimethylsilyl)trifluoracetamide[38]were used as derivative agents of cys.The conditions used in the analysis are presented in Table 4.

    4.2.4.2.Flame photometric detection.The detection of cys in mouse tissues[46],in urine,and plasma samples[47]using isoBCF as a derivatization agent was studied.It is a sensitive and selective method but requires the preparation of stable derivatives,which is a time-consuming procedure.

    4.2.5.Ultra-high performance liquid chromatography-electrospray ionization tandem mass spectrometry(UHPLC-ESI-MS/MS)

    5-Aminoisoquinolyl-N-hydroxysuccinimidyl carbamate (5-AIQC)and N-(acridin-9-yl)-2-bromoacetamide(AYBA)were used as derivatization agents for cys quantification using UHPLC-ESI-MS/MS.The different conditions of the analysis are described in Table 5[57,58].

    Fig.7.Structure difference between bis(p-nitrophenyl)disulfide and DTNB.

    4.2.6.Colorimetric method using Ellman's reagent

    In 1958,George Ellman[59]described a method for the determination of mercaptan based on interchange of bis(p-nitrophenyl)disulfide and mercaptan anions(S-)at pH 8.0(Fig.6).The kinetics of the reaction between cys and bis(p-nitrophenyl)disulfide showed that the full absorbance was settled after 60-90 min.

    In 1959,bis(p-nitrophenyl)disulfide was replaced by its carboxylated derivative DTNB(5,5′-dithiobis(2-nitrobenzoique acid))because of its poor solubility in water(Fig.7)[60].

    An easy and rapid method was developed by Ellman[60]to quantify sulfhydryl groups based on colorimetric detection after a reaction between sulfhydryl groups and DTNB,resulting in a yellow-colored product(2-nitro-5-thiobenzoic acid).The absorbance of the latter was measured spectrophotometrically at a wavelength of 412 nm,reflecting the concentration of cys.

    The detection and quantification of cys using Ellman's reagent can be achieved using many techniques such as UV-visible spectroscopy[15],HPLC[61],ultra-performance liquid chromatography-tandem mass spectrometer[62],and using microtiter plate[63].This methodis easy to be applied sinceit does not need any synthesis of the reactive agent,can be used with different analytical techniques from the simplest to the most complicated ones,and the reaction between the reactive and the sulfhydryl group is rapid without the requirement of heat or enzyme(Fig.8).

    Some difficulties could be encountered in the detection of cys by this method in some samples,for example in cloudy solutions such as liposomes loading cys.This issue is not well elaborated in the literature.However,Butler et al.[17]tried to overcome this problem by adding 2% deoxycholate solution in the assay buffer to solubilize liposomes and/or by using matching amounts of liposomes suspension in the reference cuvette.This method is not selective since many compounds possessing a sulfhydryl group may react with DTNB.

    4.2.7.Ion pair and micellar chromatography

    The quantification of cys was also assessed with the addition of a surfactant into the mobile phase which interacts with cys,affecting its retention through a reversed-phase column.The addition of sodium dodecyl phosphate(40 mM)using micellar chromatography and sodium 1-heptanesulfonate(4 mM)using the ion pair chromatography to the mobile phase were able to separate and quantify cys and cystamine(Table 6[16,64]).

    4.2.8.Electrochemical detection of cys

    Electrochemical reactions involve the loss or gain of electrons followed by subsequent rearrangements or reactions.If these reactions occur on physically separated metals in a conducting medium,a difference in electrical potential is generated;the electrical signal depends on the analyte concentration[65].Cys is known for its oxidation to cystamine and therefore can be detected electrochemically.This was realized in literature using different types of electrodes.Cys was first analyzed by HPLC with an electrochemical detector using platinum electrode[66]or a single gold/mercury electrode[67,68].However,the use of unmodified electrodes has proved a high overpotential and low electrical signal.Therefore,the electrochemical determination of cys was assessed using modified electrodes such as single-wall carbon nanotube modified glassy carbon electrode[69],carbon paste electrode[70-74],multiwall carbon nanotubes paste electrode[75-78],and screen-printed electrode[79].The electrooxidation of cys was catalyzed using different types of mediators cited in Table 7[69-79].The electrocatalytic mechanism for cys determination at the surface of an electrode in the presence of the mediator is illustrated in Fig.9.Each method was applied in a certain range of cys concentration where the catalytic oxidation peak current showed a linear relationship with the concentration of cys.The limit of detection was determined for each method and the quantification was evaluated in different biological samples such as urine,tablet,capsules and serum.

    Fig.8.Reaction between cys and Ellman's reagent.DTNB:5,5′-dithiobis(2-nitrobenzoique acid),TNB:5'-thio-2-nitrobenzoic acid.

    Table 6Cys detection using ion pair and micellar chromatography.

    Herein,we present the different methods of cys quantification.The choice of an adequate method is hard,and it is based on various parameters.First,the type of sample used should be widely considered.For example,the Ellman method cannot be applied to plasma samples because of the interference of other thiol compounds during cys detection.Moreover,some derivatization agents(CMQT and cystine thiosulfonate)are not commercialized,and thus they should be synthesized.Additionally,the time required to detect cys seems to be crucial.For instance,the use of ACQ as a derivatization agent elutes cys after 29 min while SBD-F elutes cys after 5 min using HPLC with fluorescence detection.

    5.Pharmacokinetics of cys

    Limited information is available on the pharmacokinetics of cys.The bioavailability of cys is less than 10%.After the ingestion of cys(15 mg/kg)by children with nephropathic cystinosis,a peak concentration(0.03-0.07 mM)in plasma is reached around 1 h later[80].The absorption of this molecule in the small intestine is much better than in the stomach or colon[81].In addition,this bioavailability can be affected by the type of food administered as this drug can potentially bind to food such as fats and high-protein meals.A study showed that taking cys with foods may reduce its absorption by 30%,particularly with a high-protein diet[82].Cys absorption is enhanced by iron in the proximal duodenum,iron loading accelerates,and iron depletion slows[14C]cys uptake in intestinal epithelial cells[83].Armas et al.[84]showed that the pharmacokinetics of cys bitartrate delayed-release capsules are not affected by co-administration with orange juice,water only,or omeprazole(with water).

    Fig.9.Electrocatalytic mechanism for cys determination at the surface of an electrode in the presence of a mediator.

    Cys,after oral administration in rats,is primarily distributed in the kidney,the gastrointestinal tract(mainly the duodenum),and the liver.Regardless of the route of administration,cys uptake reaches a maximum in the duodenum after 6 h,which is maintained for up to 12 h,and the efflux is observed only after 24 h.At a concentration higher than 20 mM,cys uptake is blocked,suggesting that the uptake system is saturable.Two studies suggested a carrier-mediated system for cys uptake.Based on an in vitro system,the first study suggested the presence of an unknown cys carrier for the human fibroblast lysosomes[85].The second one confirmed that cys uptake by intestinal epithelial cells is mediated by an organic cation transport(OCT)system.The latter is inhibited by cys analogs and modulated by inhibitors of the OCTs and by suppression of OCT gene expression[83].Moreover,these studies showed that cellular uptake of cys is more favorable at alkaline pH,compared to pH 5,due to the reason of pKaof NH2;the protonated form is presumably less well transported into the lysosome and intestinal epithelial cells,compared to its thiolate form[83,85].

    After being metabolized to taurine and bile salts,cys is eliminated from the body after 6 h of administration,and this is the main reason of cys administration every 6 h for patients with cystinosis.The problem of repeated administration of cys was resolved in 2013,where Cystagon?,an immediate release cys approved by FDA in 1994,was replaced by PROCYSBI?(Horizon Pharma),an entericcoated delayed-release cys bitartrate formulation.This formulation bypasses absorption in the stomach,resulting in sustained absorption in the small intestine and thus improving gastro-intestinaltolerability[82].Consequently,the drug is eliminated after 12 h,reducing the drug administration and thus the treatment side effects[86].

    Table 7The different electrochemical detection methods.

    Table 8 shows the pharmacokinetic parameters after the oral and gastrointestinal administration of cys in human body cells.Tmaxis the time corresponding to Cmax,half-life(t1/2),the area under the curve between time 0 and the last sample(AUC0-∞),and clearance(CL)are represented in this table[87,88].The best pharmacokinetic values were obtained for gastro-intestinal administration in humans,more specifically in the small intestine.

    6.Biological applications of cys

    A low concentration of cys induces the transport of cysteine into cells.The latter is a precursor of glutathione(GSH)synthesis,an important antioxidant,thus influencing the oxidative state of a cell[89].The oxidative state regulates several signaling pathways involved in cell proliferation and influences the gene expression of several redox-sensitive genes[90].Moreover,the thiol group of cys can react with free thiol or the disulfide bonds of peptides and proteins,ending by interference with their function[91].The alteration in gene expression and the interference with the protein function are the main causes behind the ability of cys to treat Huntington and Parkinson diseases.At high concentration,the oxidation of cys in the presence of transition metals produces hydrogen peroxide(H2O2)molecules,responsible for oxidative stress.Additionally,it induces the inhibition of GSH peroxidase responsible for cys toxicity at high concentrations(10-4to 10-3M)[92].Therefore,the dose selection is very important to avoid any complications in the treatment of any diseases by cys.

    Cys has shown several biological applications:treatment of cystinosis,Huntington and Parkinson diseases,malaria,neuropsychiatric disorders,cancer,and non-alcoholic fatty liver disease,and is used as a radioprotective agent(Fig.10).Many reviews have profoundly discussed these applications[7,23,24].We will focus on the main applications of cys as a radioprotective agent,in the treatment of cystinosis,and for anti-tumor proliferation.However,the topical application of cys,for the treatment of hyperpigmentation,has not yet been well elaborated and reviewed.Consequently,all the data in the literature concerning this topic are collected and described below.

    6.1.Radioprotective effect

    Cys was first used in 1954 as a radioprotective agent[1].This radioprotective effect is attributed to its sulfhydryl group.It is a great scavenger of hydroxyl radical(.OH).It also reacts slowly with hydrogen peroxide(H2O2),but this reaction can lead to significant rates of H2O2removal if high concentrations of cys are present[93].Cys enters the cells rapidly and provides the maximum level of protection within 10 min[94].Cys radioprotection in vitro is based on three different mechanisms[4].First,cys can undergo an oxidation reaction with molecular oxygen in the cells,leading to hypoxia.Besides,cys donates hydrogen atoms to hydroxyl radicals(?OH),decreasing the indirect effect of radiation.Moreover,cys activates specific repressor molecules that interrupt the DNA templates activity necessary for DNA replication.A metabolically active DNA molecule is more sensitive to ionizing radiation;thus cys leads to the diminishment of radiation injury to the DNA molecule[5,95].

    6.2.Treatment of cystinosis

    Cystinosis is a rare autosomal recessive metabolic disorder characterized by a defect in lysosomal cystine transport,leading to the intralysosomal accumulation of cystine crystals in many tissues(kidneys,bone marrow,intestine,etc.)including the eye(retina,conjunctiva,iris,and cornea)[96],affecting muscles and the central nervous system[86].This disease can cause a generalized proximal tubular damage(called renal Fanconi syndrome),resulting in polyuria,polydipsia,and a development failure within the first year of life[97].If left untreated,cystinosis can cause end-stage renal disease around the age of ten.

    In 1976,cys in the form of cys bitartrate was introduced as a treatment of cystinosis[98].Cys is a weak base that enters the lysosome and reacts with cystine to form a mixed disulfide of halfcystine and cys.The mixed disulfide has a stearic resemblance to the amino acid lysine;consequently,it rapidly leaves the lysosomes via lysine transporter[99].However,this treatment presents many side effects such as gastrointestinal complaints,disagreeable breath,sweat odor,development of lupus nephritis,proliferative vascular lesions on their elbows,skin striae,and bone and muscular pain[23].These side effects are mainly caused by the metabolism of 3% of cys to dimethyl sulfide(Fig.3)[100].

    6.3.Treatment of cancer

    Cys has been shown to inhibit gastric[101]and mammary[12]tumors formation.Besides,a study conducted by Wan et al.[102]demonstrated that cys caused autophagosome accumulation in cancer cells and sensitized doxorubicin-elicited chemotherapeutic killing in HeLa,B16 melanoma,doxorubicin-resistant MCF-7 cells,and in a mouse melanoma model.Besides,cys inhibits matrix metalloproteinases conducting to the suppression of invasion,metastasis,and prolonging survival in a mouse model of human pancreatic cancer[103]and human ovarian cancer[104].

    6.4.Treatment of hyperpigmentation

    There are three types of skin color alteration:darkening,lightening,and the occurrence of unusual skin color[105].Eumelanin and pheomelanin are the two forms of melanin.Eumelanin is responsible for the brown pigmentation of the skin while pheomelanin produces yellow and red colorations[106].Pigmentary disorders can occur after an increase or decrease in melanocyte activity.They are divided into two different categories:hyperpigmentation and hypopigmentation[107].Hyperpigmentation is divided into three main types:melasma,post-inflammatoryhyperpigmentation,and sun damage or sunspots.Melasma is a psychologically distressing skin disorder divided into three types:epidermal,dermal,and mixed melasma.Epidermal and dermal melasma is the accumulation of melanin in the epidermis and the dermis,respectively,and mixed melasma is a combination of epidermal and dermal melasma[108].Post-inflammatory hyperpigmentation is an acquired hypermelanosis occurring after cutaneous inflammation or injury that can arise in all skin types[109],and sunspots are usually light brown(generally called freckles)and appear mostly on the face,neck,chest,and hands,which are primarily exposed to UV rays[110].

    Table 8Pharmacokinetic parameters of cys after different routes of administration.

    Fig.10.Cys pharmacodynamics.

    Several natural and synthetic skin depigmenting agents have been developed.Their mechanisms of action may occur before,during or after the melanin synthesis.Moreover,depigmentation by any exogenous agent is induced by the destruction or the loss of melanocytes,alteration of the melanin present in melanosomes,and the interference with(i)the biosynthesis of premelanosomes and melanosomes,(ii)the conversion of tyrosine to 3,4-dihydroxyphenylalanine(DOPA)to melanin,(iii)the biosynthesis of tyrosinase or the active center of the enzyme,and(iv)the transfer of melanosomes to keratinocytes(Fig.11)[111].

    Cys hydrochloride has been known to be a potent depigmenting molecule for over 5 decades.Chavin et al.[112]examined,for the first time,the ability of several compounds(quinhydrone,cys,N-(2 mercaptoethyl)-dimethylamine HCI,sodium cys-S-phosphate,cystamine,3-methylcatechol,fluphenazine,hydroquinone,etc.),to induce a specific destructive effect in the melanin synthesizing cells(melanocytes and melanophores).These compounds were injected by subcutaneous injection in black goldfish.They found that all the molecules induced lysis of melanophores and melanocytes locally and systemically;however,hydroquinone was the most potent anti-pigmentary compound.Another study demonstrated that cys was an effective depigmenting agent when applied to the skin of black guinea pigs,and conversely to the previous result,was shown to be more potent than hydroquinone[113].In fact,melanocytes are the specific target of cys since a noticeable decrease of the epidermal melanocyte was observed after the topical application of this compound to the skin of black guinea pigs.The treatment with cys did not affect the keratinocytes cells adjacent to melanocytes cells[114].The minimum dose required for depigmentation is 100μM,and this concentration decreases the percentage of melanin by 21%[11].

    Fig.11.Schematic illustration of the mechanism of action of skin whitening agents[111](with permission from Elsevier).

    The mechanism of cys as a depigmenting agent is not yet deeply studied.It may act through the inhibition of tyrosinase and peroxidase and the increase of intracellular GSH levels.

    6.4.1.Inhibition of tyrosinase and peroxidase activity

    Tyrosinase is responsible for the conversion of tyrosine to DOPA and of DOPA to DOPA quinone.As for peroxidase,it catalyzes the final step of the oxidative polymerization reaction of the formed indoles to eumelanin pigments[115].Thiolic depigmenting agents such as cys and GSH[116]are known to be inhibitors of tyrosinase and peroxidase,the two key enzymes involved in melanin biosynthesis[117].The inhibition of tyrosinase will produce the scavenging of DOPA quinone affecting the production of melanin.Arbutin,azelaic acid,flavonoids,kojic acid resveratrol,tretinoin,and vitamins C and E act by the same mechanism[111].Qiu et al.[11]reported that the depigmenting action of cys is due to its interaction with the products of the reactions catalyzed by tyrosinase activity(DOPA oxidation products are isolated)inhibiting pigment synthesis.They confirmed that the cys mechanism of action is a melanogenesis inhibition,but not melanocytotoxicity,in contrast to hydroquinone.

    6.4.2.Increase in the level of intracellular GSH

    The interaction of DOPA-quinone with the thiol groups of GSH or cysteine shifts the melanogenesis from eumelanin to phaeomelanin synthesis(Fig.10)[118].Cys enhances the intracellular levels of GSH,thus delaying the melanogenesis procedure.Among the different depigmenting agents,only vitamin E exhibited this action as well[111].Djurhuus et al.[119]demonstrated the enhancement of GSH content in C3H/10T1/2 cells after the addition of cys.De Matos and Furnus[89]proved that the addition of cys to the culture medium during in vitro maturation of bovine oocytes increased the GSH levels in the mature oocytes,while Wilmer et al.[120]showed that cys increased total GSH and restored GSH redox status in a renal cystinosis cell mode[89,119-121].Cys stimulates GSH synthesis by increasing the rate of cellular cysteine uptake through the formation of mixed disulfides with cysteine.Mixed disulfides of cysteine and cys enter cells via transport system L and are reduced intracellularly to release both thiol compounds.The cysteine is then used in GSH synthesis[122].

    Several skin whitening agents such as retinoic acid,kojic acid or hydroquinone proved high efficacy.However,they present numerous side effects like hypersensitivity to the sun,skin irritation,inhibition of new melanin formation,and they are responsible for itching,peeling,dryness,and redness of the skin[123].Cysteamine is a natural skin whitening agent as powerful as hydroquinone,does not present any risk,and is compatible with light exposure.The main obstacle in the use of cys as a depigmenting agent is its fast oxidation once in contact with air as well as the strongly unpleasant organoleptic features of this molecule[13],which can not be covered by perfumes[124].Recently,Scientis Pharma?developed a new technology that stabilizes cys molecules and significantly reduces its odor.Cys Cream?is eventually the first and only depigmenting agent commercially available based on cys molecule.Hsu et al.[124]applied cys cream?to the ear of black female guinea pigs.Evaluation with dermatoscopic,chromametric,and histologic instruments was performed,and the cys cream?showed a potent depigmenting effect in guinea pig skin.Then,Mansouri et al.[9]evaluated the efficacy and safety of cys cream?for the treatment of epidermal melasma in a randomized,doubleblind vehicle-controlled clinical trial.After an evaluation of melanin content and erythema levels,they concluded that the treatment with cys cream?decreased the content of melanin and consequently it was a good treatment for epidermal melasma[8,9].

    7.Cys and encapsulation systems

    Cys encapsulation into liposomes,CDs,and emulsions was conducted to enhance its effects;studies dealing with encapsulation are addressed in this section.Moreover,the conjugation of cys to the surface of CD induces the formation of disulfide bonds with cysteine-rich substructures of the ocular and glycoproteins mucus,providing a prolonged residence time of the incorporated drugs at the site of action.On the other hand,the conjugation of cys to the surface of gold nanoparticles improves the colorimetric detection of compounds using the gold nanoparticles aggregation method by decreasing the electrostatic repulsion force between the nanoparticles.

    7.1.Liposomes

    Liposomes are enclosed spherical vesicles organized in one or several concentric phospholipidic bilayers with an internal aqueous phase.Liposomes can entrap lipophilic drugs within the lipid membrane,hydrophilic agents in their internal aqueous compartment,or amphiphilic ones at the water-lipid interface[125].These carriers are biodegradable,biocompatible,and non-immunogenic[126].Since liposomes mimic natural membranes,their use in topical applications is generally favorable[127].Liposomes can be prepared by classical and large-scale techniques[125,128].In fact,cys was first encapsulated in liposomes by Butler et al.[17],to reduce cystine accumulation in cells.Since cys is a water-soluble compound,it can be incorporated in the internal aqueous cavity of the liposomes,thus facilitating the selective uptake of cys by endocytic target cells.The authors compared different types of liposomes formed from saturated and unsaturated or positively and negatively charged lipids.The best type of liposomes selected for subsequent experiments was those containing saturated dipalmitoyl phosphatidylcholine and negative charge by the inclusion of phosphatidic acid.This is explained as follows:saturated fatty acids are not subject to autoxidation as are unsaturated ones;the use of dipalmitoylphosphatidylcholine liposomes avoids some of the toxic effects of peroxides or epoxides on cells in tissue culture and negatively charged liposomes made with phosphatidic do not present any aggregation contrary to those with positive charge.The encapsulation of cys in liposomes provides a better efficacy to reduce cystine in cystinotic cells in tissue culture[17].In addition,liposomes serve as a targeting agent to the lysosome since cys incorporated into liposomes will be mainly taken up by phagocytic cells and concentrated in lysosomes.They confirmed that the liposomes were disrupted by lysosomal enzymes releasing cys intralysosomally,followed by the diffusion of mixed disulfide from lysosome[17].

    Roman et al.[129]reported the encapsulation of cys in liposomes.It was delivered orally in mice with an evaluation of its radioprotective effect.They found that the liposome encapsulating cys protected the drug up to 3 h after administration in contrast to free cys.In order to investigate the effect of liposome-encapsulation on cys absorption through the intestinal wall,the distribution of the molecule after in vivo administration was studied by Jaskierowicz et al.[15].They used mixed egg yolk lecithin and cholesterol(4:1,mol/mol)and reported that radioactivity was higher and more persistent in blood,plasma,liver,and spleen in encapsulated cys than that in the free form.The digestive absorption of cys was more important when entrapped,and the drug was protected from digestive degradation.

    On the other hand,the encapsulation of cys in liposomes formed from egg yolk phospholipid and cholesterol(4:1)extended the presence and duration of action of cys in pituitary glands,after oral administration.It led to reduce tumor proliferation through the modification of hormone status where cys could reduce somatostatin and/or prolactin levels near the tumor.10.8% of the initial cys was encapsulated in liposomes.Cys loaded liposomes were stable during storage for six days[130].Table 9 shows the different studies conducted to encapsulate cys in liposomes[15,17,130].

    Unfortunately,liposome's characteristics(size,shape,homogeneity,encapsulation efficiency,and loading rate)were not investigated in these studies.

    7.2.Cyclodextrins

    CDs are a family of cyclic oligosaccharides composed of α-(1,4)linked glucopyranose subunits[131].Three native CDs are known as follows:α-CD,β-CD,and γ-CD,composed of six,seven,and eight α-units,respectively[132].CDs possess a lipophilic inner cavity and a hydrophilic outer surface that allow the formation of noncovalent inclusion complexes with numerous types of guests[133].

    Table 10 shows the methods of preparation and the effects of different molar ratios of cys to CD on cys properties.In fact,the presence of hydroxyl groups(OH)outside the molecule prevents the inclusion of hydrophilic drugs in CDs.To evaluate if the complexation between cys and CDs can be realized,Lahiani-Skiba et al.[13]studied interactions between cys hydrochloride and α-CD in lyophilized inclusion complexes.Inclusion complexes were prepared from solutions obtained by the dissolution of cys hydrochloride in α-CD solution.Lyophilized products were obtained with molar ratios of 1:1,2:1,3:1,and 4:1(cys hydrochloride:α-CD).After the analysis of the lyophilized products by differential scanning calorimetry,mass spectrometry analysis,1H nuclear magnetic resonance(NMR),and Fourier transform infrared spectroscopy,they confirmed the complex formation.The nuclear over Hauser effect spectroscopy technique showed the proximity of the methylene groups of cys protons with protons H2 and H4,located at the outside of α-CD(Fig.12).They obtained odorless powder of cys with moderate flavor,storable at room temperature[13].

    Pescina et al.[16]reported the encapsulation of cys in α-CD to improve the trans-corneal permeation of cys.An increase of permeation was observed when CD concentration was added to the range between 3% and 5.5%.The increase of permeation was CD concentration-dependent;for example,a 5.5% concentration of CD increased the amount permeated up to 20 times compared to free cys[16].

    7.3.Emulsions

    Emulsions are metastable colloids made out of two immiscible fluids,one being dispersed in the other,in the presence of surfaceactive agents[134].

    Gresham et al.[14]reported the use of sustained-release multiple emulsion to extend the period of cys radioprotection.They compared the radioprotective effect in irradiated mice protected by cys with those unprotected.They found that emulsions prolonged the radioprotective effect of cys from 15 min obtained using free cys to 1.5 h when cys was administered in an emulsion[14].

    Recently,Dixon et al.[18]tried to enhance cys stability using an emulsion of vitamin E,soybean oil,and Tween 80 surfactants,since emulsions have been shown to decrease the transport of oxygen and increase the stability of other hydrophilic antioxidants[135].Vitamin E and/or soybean oil were prepared at the solubility limit by adding an excess of the hydrophobic component(s)to PBS and stirring at 300 rpm for 24 h,followed by the addition of cys(0.1 mg/mL).The emulsion formulation was prepared by first mixing vitamin E(0.45 mg/mL)and soybean oil(0.45 mg/mL),followed by the addition of the surfactant solution Tween 80(0.1 mg/mL)with sonication for 30 min.The degradation rate of cys decreased from 126μg/h for freecys(0.1 mg/mL)to 111μg/h forcys,oil,and vitamin E at the solubility limit in PBS.This rate was decreased to 101μg/h for cys in the emulsion.The solubilization of the antioxidantsincreased their concentrations in the formulation and consequently allowed the stabilization of cys[18].

    Table 9Liposomes prepared by thin lipid film hydration method encapsulating cys.

    Table 10Interaction of cys with CDs.

    Fig.12.Representation proposed for the interaction between cys and α-CD according to the results of NMR technique(A)interactions of CH2of cys with H2 and H4 of two different glucopyranose(B)interactions of CH2of cys with H2 and H4 of a same glucopyranose[13](with permission from Springer).

    7.4.Modification of encapsulation systems by cys

    7.4.1.Cyclodextrins

    The synthesis and characterization of thiolated β-and α-CD[19,20]as a novel mucoadhesive excipient for intra-oral drug delivery was studied.The synthesis of the thiolated CD was achieved in two steps:the oxidation of CD and the covalent coupling of cys via reductive amination(Fig.13).α-CD-cys and β-CD-cys conjugates displayed an increase in the retention time of cetirizine on the ocular mucosal surface and miconazole nitrate on porcine intestinal and buccal mucosa.This could be due to the improvement of CD drug encapsulation properties after being thiolated,where the solubility of miconazole nitrate was enhanced.In addition,local mucosal irritating effects of cetirizine were significantly reduced after being complexed withα-CD-cys and applied on the rabbit's ocular mucosa(Table 10).These findings could be a promising tool for the delivery of poorly water-soluble therapeutic agents.

    7.4.2.Gold nanoparticles

    Fig.13.Synthetic pathway for the generation of thiolated α-CD.cys:cysteamine,CD:cyclodextrins.

    Fig.14.Colorimetric detection strategy of molecules based on cys modified AuNPs.cys:cysteamine,AuNPs:gold nanoparticles.

    7.4.2.1.Synthesis.Gold nanoparticles(AuNPs)are a diverse group of nanomaterials ranging in size from 5 to 110 nm with different forms,including spheres,cubes,nanorods,and nanoribbons[136].There are a variety of methods to synthesize AuNPs.We can find chemical methods of synthesis based on the chemical reduction of gold salt in aqueous or/and organic phase.The physical methods involve the γ-irradiation technique,the technique of microwave irradiation,and heat or photochemical reduction.Finally,the biological method was also reported using citrus fruit juice extracts or edible mushrooms[137].Cys modified AuNPs were prepared by the attachment of cys mercapto group to the surface of the AuNPs by the formation of Au-S bonds with the-NH2 groups exposed on the outer surface of the citrate-capped AuNPs[138].

    7.4.2.2.Colorimetric detection of compounds via cys-AuNPs.The use of AuNPs as a colorimetric reporter to detect several compounds of large numbers of samples,such as milk products,eggs,and feeds,has received great attention in the last few years,to substitute the classical techniques like HPLC and gas chromatography which are expensive and need dedicated instruments.This method was developed since AuNPs possess a surface plasmon resonance changing from red to blue corresponding to their dispersion or aggregation state.The development of a more sensitive assay involves the modification of the AuNPs surface bycys to decrease the electrostatic repulsion force between AuNPs.The cys-AuNPs solution is wine-red and displays an absorption peak at 524 nm.An electrostatic repulsion occurs because of the positive charge of cys-AuNPs inhibiting the aggregation of the latter.When the compound is added to the cys-AuNPs solution,the absorption spectrum exhibits an obvious decrease at 524 nm and a strong increase at 650 nm.The color of the conjugates changes from winered to purple within several minutes,indicating the aggregation of cys-AuNPs(Fig.14)[21,22].The colorimetric detection of gentamycin melamine[21,139],heparin[139],lipopolysaccharides[140],mercury(II)[21],glyphosate[22],trinitrotoluene[141],clenbuterol[142],and sulfate[143]using cys modified AuNPs has been reported.This method presents a lot of advantages like simplicity of preparation and manipulation and high sensitivity.It is more robust and less expensive than the conventional methods.

    8.Conclusion and perspectives

    Due to the important role of cys in medical and cosmetic fields,it has been extensively studied in literature.However,this molecule suffers from different drawbacks mainly related to instability,organoleptic and pharmacokinetic properties.The quantification of this agent is also challenging because of its low absorptivity.This review presents a broad overview of cys characteristics;it can serve as a reference for novel works focusing on the improvement of cys properties through encapsulation in delivery systems which may enlarge cys application.

    Declaration of competing interest

    The authors declare that there are no conflicts of interest.

    Acknowledgments

    Authors thank the Research Funding Program at the Lebanese University and the“Agence Universitaire de la Francophonie,projet PCSI”for supporting the project(2018-2020).

    一级作爱视频免费观看| 亚洲精品国产一区二区精华液| 国产人伦9x9x在线观看| 超碰成人久久| 亚洲国产精品sss在线观看| 欧美激情极品国产一区二区三区| 精品欧美国产一区二区三| 色尼玛亚洲综合影院| 欧美日本视频| 男女午夜视频在线观看| 国产成人精品在线电影| 日韩高清综合在线| 日韩欧美在线二视频| 一本大道久久a久久精品| 大型黄色视频在线免费观看| 亚洲精品美女久久av网站| 一边摸一边抽搐一进一小说| 国产人伦9x9x在线观看| 中文亚洲av片在线观看爽| 日本 av在线| 一夜夜www| 免费在线观看亚洲国产| 久久精品国产综合久久久| 成人av一区二区三区在线看| 99国产精品免费福利视频| 在线观看午夜福利视频| av天堂久久9| 国产乱人伦免费视频| 一级a爱片免费观看的视频| 大陆偷拍与自拍| 精品国产一区二区久久| 91九色精品人成在线观看| 亚洲成人久久性| 欧美激情 高清一区二区三区| 国产精品久久久久久人妻精品电影| 中出人妻视频一区二区| 手机成人av网站| 免费少妇av软件| 免费观看人在逋| 亚洲免费av在线视频| 午夜日韩欧美国产| 女人高潮潮喷娇喘18禁视频| 久久久精品欧美日韩精品| 18禁黄网站禁片午夜丰满| 免费观看精品视频网站| 亚洲精品在线观看二区| 18禁美女被吸乳视频| 成年女人毛片免费观看观看9| 在线观看舔阴道视频| 亚洲少妇的诱惑av| 欧美成人性av电影在线观看| 婷婷丁香在线五月| 国产精品1区2区在线观看.| 男人舔女人下体高潮全视频| a在线观看视频网站| www.熟女人妻精品国产| 国产99白浆流出| 亚洲久久久国产精品| 如日韩欧美国产精品一区二区三区| 精品第一国产精品| 亚洲 国产 在线| 国产精品日韩av在线免费观看 | 久久欧美精品欧美久久欧美| 一夜夜www| 亚洲欧美精品综合久久99| 超碰成人久久| 亚洲激情在线av| 大香蕉久久成人网| 精品高清国产在线一区| 亚洲国产毛片av蜜桃av| 日本 欧美在线| 国产片内射在线| 女同久久另类99精品国产91| 变态另类丝袜制服| 97超级碰碰碰精品色视频在线观看| 黑人操中国人逼视频| 女人高潮潮喷娇喘18禁视频| 久久久久久久久久久久大奶| 日本在线视频免费播放| 少妇粗大呻吟视频| 国内毛片毛片毛片毛片毛片| 性欧美人与动物交配| 欧美性长视频在线观看| 亚洲激情在线av| 亚洲五月婷婷丁香| 色综合婷婷激情| 涩涩av久久男人的天堂| 亚洲av第一区精品v没综合| 色av中文字幕| 精品国产超薄肉色丝袜足j| 中文字幕人妻丝袜一区二区| 很黄的视频免费| 亚洲 欧美一区二区三区| 纯流量卡能插随身wifi吗| 成人免费观看视频高清| 国产亚洲欧美精品永久| 中文字幕高清在线视频| 黄色丝袜av网址大全| 好男人在线观看高清免费视频 | 啦啦啦韩国在线观看视频| 999久久久国产精品视频| 琪琪午夜伦伦电影理论片6080| 非洲黑人性xxxx精品又粗又长| 国产亚洲精品综合一区在线观看 | 久久久久久人人人人人| 一夜夜www| svipshipincom国产片| 亚洲电影在线观看av| 在线天堂中文资源库| 久久这里只有精品19| 熟妇人妻久久中文字幕3abv| 欧美黑人精品巨大| 在线观看日韩欧美| 少妇熟女aⅴ在线视频| 国产高清激情床上av| 一区二区三区精品91| 看免费av毛片| 久久国产精品男人的天堂亚洲| 亚洲一码二码三码区别大吗| 国产精品一区二区在线不卡| 亚洲av成人不卡在线观看播放网| 夜夜爽天天搞| 欧美久久黑人一区二区| av中文乱码字幕在线| 高清黄色对白视频在线免费看| 成人18禁在线播放| 亚洲中文字幕一区二区三区有码在线看 | 十分钟在线观看高清视频www| 不卡av一区二区三区| 久热这里只有精品99| 午夜精品在线福利| 搞女人的毛片| 久久精品国产清高在天天线| 中文字幕人妻熟女乱码| 老司机在亚洲福利影院| 亚洲熟妇中文字幕五十中出| 老司机午夜福利在线观看视频| 9热在线视频观看99| 黄片小视频在线播放| 日本一区二区免费在线视频| 欧美乱色亚洲激情| www.999成人在线观看| 国产成人一区二区三区免费视频网站| 国产乱人伦免费视频| 天堂动漫精品| 一卡2卡三卡四卡精品乱码亚洲| 麻豆成人av在线观看| 老汉色av国产亚洲站长工具| 熟女少妇亚洲综合色aaa.| 动漫黄色视频在线观看| 国产亚洲精品久久久久5区| 多毛熟女@视频| 动漫黄色视频在线观看| 日本a在线网址| 国产av一区在线观看免费| 一进一出抽搐gif免费好疼| 国内毛片毛片毛片毛片毛片| 亚洲欧美日韩高清在线视频| 欧美在线黄色| 亚洲一卡2卡3卡4卡5卡精品中文| 欧美国产精品va在线观看不卡| 亚洲成人国产一区在线观看| 精品久久蜜臀av无| 12—13女人毛片做爰片一| 极品教师在线免费播放| 夜夜躁狠狠躁天天躁| 亚洲精品在线观看二区| 欧美乱妇无乱码| 久久精品国产综合久久久| 日本 av在线| 别揉我奶头~嗯~啊~动态视频| 热re99久久国产66热| 亚洲 国产 在线| 亚洲专区中文字幕在线| 欧美不卡视频在线免费观看 | 久久人妻福利社区极品人妻图片| 国产熟女午夜一区二区三区| 色av中文字幕| 欧美绝顶高潮抽搐喷水| 91成人精品电影| av在线天堂中文字幕| 亚洲人成伊人成综合网2020| 亚洲自偷自拍图片 自拍| 巨乳人妻的诱惑在线观看| 亚洲人成77777在线视频| 一级作爱视频免费观看| 人妻丰满熟妇av一区二区三区| 一二三四在线观看免费中文在| 日本 av在线| 日本 欧美在线| 午夜久久久久精精品| 亚洲一区二区三区不卡视频| 亚洲成人久久性| 日韩三级视频一区二区三区| 国产精品美女特级片免费视频播放器 | 欧美日韩亚洲国产一区二区在线观看| 中文字幕精品免费在线观看视频| 成人三级黄色视频| 久久中文字幕一级| 老司机午夜十八禁免费视频| 怎么达到女性高潮| 成人av一区二区三区在线看| 久久香蕉国产精品| 久久香蕉激情| 级片在线观看| 日韩精品中文字幕看吧| 亚洲全国av大片| 99国产精品免费福利视频| 国内毛片毛片毛片毛片毛片| 国产av又大| 国产成人精品久久二区二区免费| 亚洲 欧美 日韩 在线 免费| 国产精品久久久久久亚洲av鲁大| 视频区欧美日本亚洲| 女警被强在线播放| 法律面前人人平等表现在哪些方面| 中文字幕精品免费在线观看视频| 国产又爽黄色视频| 色播亚洲综合网| 非洲黑人性xxxx精品又粗又长| 亚洲av成人不卡在线观看播放网| 亚洲熟妇中文字幕五十中出| 久99久视频精品免费| 免费在线观看日本一区| 午夜福利高清视频| avwww免费| 亚洲一区中文字幕在线| 天天躁狠狠躁夜夜躁狠狠躁| 亚洲国产欧美日韩在线播放| 国产欧美日韩一区二区三区在线| 久久精品人人爽人人爽视色| 国产精华一区二区三区| 国内精品久久久久久久电影| 免费观看精品视频网站| 又黄又爽又免费观看的视频| 日本免费一区二区三区高清不卡 | 久久久精品国产亚洲av高清涩受| 99国产精品99久久久久| 久久久久亚洲av毛片大全| 90打野战视频偷拍视频| 桃色一区二区三区在线观看| 国语自产精品视频在线第100页| 1024香蕉在线观看| 久99久视频精品免费| 真人做人爱边吃奶动态| 久久久国产欧美日韩av| www.www免费av| 亚洲色图综合在线观看| 精品人妻1区二区| 欧美在线一区亚洲| 午夜久久久久精精品| 老熟妇仑乱视频hdxx| 成在线人永久免费视频| 久久草成人影院| 99国产精品一区二区三区| 老司机靠b影院| 在线观看免费视频网站a站| 亚洲国产精品成人综合色| 高清在线国产一区| 成人av一区二区三区在线看| 亚洲狠狠婷婷综合久久图片| 精品日产1卡2卡| 日本黄色视频三级网站网址| 久久久精品欧美日韩精品| 欧美另类亚洲清纯唯美| 亚洲中文字幕一区二区三区有码在线看 | 国产免费av片在线观看野外av| 成年人黄色毛片网站| 国产日韩一区二区三区精品不卡| 老汉色∧v一级毛片| 免费高清视频大片| 亚洲人成电影免费在线| 超碰成人久久| av在线播放免费不卡| 久久久久国内视频| 国产精品野战在线观看| 免费少妇av软件| 母亲3免费完整高清在线观看| 国产人伦9x9x在线观看| 日本黄色视频三级网站网址| 国产精品,欧美在线| 亚洲色图 男人天堂 中文字幕| 国产伦一二天堂av在线观看| 国产蜜桃级精品一区二区三区| 日本一区二区免费在线视频| 亚洲专区字幕在线| 欧美黑人精品巨大| 午夜精品在线福利| 欧美日韩瑟瑟在线播放| 精品乱码久久久久久99久播| 欧美日韩亚洲综合一区二区三区_| 夜夜夜夜夜久久久久| 女性被躁到高潮视频| 亚洲,欧美精品.| 久9热在线精品视频| 在线国产一区二区在线| 久久欧美精品欧美久久欧美| 亚洲一码二码三码区别大吗| 伦理电影免费视频| 在线观看www视频免费| 久久精品人人爽人人爽视色| 成人亚洲精品av一区二区| 亚洲精品在线美女| 精品久久久久久久毛片微露脸| 伦理电影免费视频| av中文乱码字幕在线| 亚洲精华国产精华精| 麻豆一二三区av精品| 国产一区在线观看成人免费| 久久性视频一级片| 色综合婷婷激情| 久久精品aⅴ一区二区三区四区| 99riav亚洲国产免费| 久久久久久久久中文| 亚洲视频免费观看视频| 精品熟女少妇八av免费久了| 国产激情欧美一区二区| 97人妻精品一区二区三区麻豆 | 欧美精品亚洲一区二区| 午夜福利一区二区在线看| 亚洲五月天丁香| 中文字幕最新亚洲高清| 在线观看www视频免费| 在线天堂中文资源库| 国产欧美日韩综合在线一区二区| 久久精品亚洲熟妇少妇任你| 十八禁网站免费在线| 午夜老司机福利片| 久久久久国产精品人妻aⅴ院| 国产欧美日韩一区二区三| 可以在线观看的亚洲视频| 韩国av一区二区三区四区| 无遮挡黄片免费观看| 黄片大片在线免费观看| 亚洲av成人一区二区三| 欧美在线黄色| 一进一出抽搐动态| 欧美乱码精品一区二区三区| 1024香蕉在线观看| 日韩一卡2卡3卡4卡2021年| 国语自产精品视频在线第100页| 久久久久久国产a免费观看| 亚洲人成伊人成综合网2020| 亚洲一区中文字幕在线| 久久亚洲精品不卡| 操出白浆在线播放| 日韩国内少妇激情av| 国产91精品成人一区二区三区| 午夜老司机福利片| 国产99久久九九免费精品| 99国产极品粉嫩在线观看| 久久亚洲真实| 国产99久久九九免费精品| 欧美黑人精品巨大| 亚洲人成伊人成综合网2020| 69av精品久久久久久| 精品午夜福利视频在线观看一区| 亚洲色图综合在线观看| 两个人免费观看高清视频| 桃红色精品国产亚洲av| 亚洲一区二区三区不卡视频| 欧美激情 高清一区二区三区| 成人国语在线视频| 嫩草影视91久久| 男人的好看免费观看在线视频 | 高清黄色对白视频在线免费看| 成人欧美大片| 久久精品国产清高在天天线| 欧美黄色淫秽网站| 亚洲精品国产区一区二| 国产精品av久久久久免费| 精品久久蜜臀av无| 老司机靠b影院| 久久中文字幕人妻熟女| www.熟女人妻精品国产| 一进一出抽搐gif免费好疼| 久久人妻福利社区极品人妻图片| 日本三级黄在线观看| 老熟妇仑乱视频hdxx| 色播亚洲综合网| 91在线观看av| 亚洲熟妇熟女久久| 亚洲国产精品久久男人天堂| 老司机靠b影院| 久久久久久久久久久久大奶| 香蕉久久夜色| 国产精品一区二区三区四区久久 | 亚洲一码二码三码区别大吗| 亚洲av片天天在线观看| АⅤ资源中文在线天堂| 丰满人妻熟妇乱又伦精品不卡| 男女午夜视频在线观看| 国产色视频综合| www日本在线高清视频| 国产一区二区在线av高清观看| 国产片内射在线| 一区二区三区高清视频在线| 一级片免费观看大全| 国产免费男女视频| 国产一区二区激情短视频| 亚洲国产精品久久男人天堂| 久久人人97超碰香蕉20202| 国产一区二区在线av高清观看| 精品久久蜜臀av无| 国产精品综合久久久久久久免费 | 美女 人体艺术 gogo| 身体一侧抽搐| 一本久久中文字幕| 又黄又爽又免费观看的视频| 亚洲九九香蕉| 我的亚洲天堂| 亚洲片人在线观看| 美女 人体艺术 gogo| 不卡一级毛片| www.www免费av| 色老头精品视频在线观看| 51午夜福利影视在线观看| 波多野结衣巨乳人妻| 1024香蕉在线观看| 午夜福利成人在线免费观看| 久久人人97超碰香蕉20202| 两性夫妻黄色片| 久久精品亚洲熟妇少妇任你| 美女高潮到喷水免费观看| 正在播放国产对白刺激| 久久久国产欧美日韩av| 国内毛片毛片毛片毛片毛片| 久久青草综合色| 亚洲精品久久成人aⅴ小说| 三级毛片av免费| 美女国产高潮福利片在线看| 老汉色av国产亚洲站长工具| 国产精品永久免费网站| 亚洲成人精品中文字幕电影| 操出白浆在线播放| 国产精品99久久99久久久不卡| 亚洲欧美一区二区三区黑人| 国产成人免费无遮挡视频| 男女做爰动态图高潮gif福利片 | 久久久久亚洲av毛片大全| 性欧美人与动物交配| 日本 av在线| 免费久久久久久久精品成人欧美视频| 在线免费观看的www视频| 99精品在免费线老司机午夜| 91老司机精品| 精品少妇一区二区三区视频日本电影| 中文字幕另类日韩欧美亚洲嫩草| 9191精品国产免费久久| 国产一区二区三区综合在线观看| 婷婷丁香在线五月| 亚洲 国产 在线| 两性夫妻黄色片| 91字幕亚洲| 欧美中文日本在线观看视频| 色综合亚洲欧美另类图片| 亚洲欧美日韩高清在线视频| 国产精品av久久久久免费| 一边摸一边抽搐一进一出视频| 在线观看午夜福利视频| 国产成人欧美| 老司机午夜十八禁免费视频| 欧美黑人精品巨大| 99精品在免费线老司机午夜| 性色av乱码一区二区三区2| 国产乱人伦免费视频| 亚洲成av人片免费观看| 男女午夜视频在线观看| 丰满人妻熟妇乱又伦精品不卡| 十八禁网站免费在线| 欧美日本视频| 中国美女看黄片| 亚洲中文字幕一区二区三区有码在线看 | 久久精品亚洲精品国产色婷小说| 18美女黄网站色大片免费观看| 妹子高潮喷水视频| av片东京热男人的天堂| 久久精品国产亚洲av香蕉五月| 精品国产乱子伦一区二区三区| 亚洲精品粉嫩美女一区| 亚洲色图综合在线观看| 日韩三级视频一区二区三区| 色av中文字幕| 国产精品久久久av美女十八| 夜夜夜夜夜久久久久| 天天躁狠狠躁夜夜躁狠狠躁| 欧美成人免费av一区二区三区| 久久婷婷人人爽人人干人人爱 | 婷婷精品国产亚洲av在线| 精品一区二区三区四区五区乱码| av中文乱码字幕在线| 大码成人一级视频| 亚洲欧美日韩无卡精品| 可以免费在线观看a视频的电影网站| 亚洲全国av大片| 性少妇av在线| 少妇粗大呻吟视频| 国产欧美日韩综合在线一区二区| 欧美+亚洲+日韩+国产| 人人妻人人澡人人看| 动漫黄色视频在线观看| 国产成人系列免费观看| 性少妇av在线| 亚洲自拍偷在线| 国产成人一区二区三区免费视频网站| 韩国精品一区二区三区| 欧美人与性动交α欧美精品济南到| 成人国产综合亚洲| 欧美黑人欧美精品刺激| 黄片播放在线免费| 丰满的人妻完整版| svipshipincom国产片| 色在线成人网| 午夜精品久久久久久毛片777| 少妇熟女aⅴ在线视频| 国产精品九九99| 精品高清国产在线一区| av有码第一页| 亚洲在线自拍视频| 男女床上黄色一级片免费看| 精品国内亚洲2022精品成人| 久久久久久久午夜电影| 亚洲午夜理论影院| 亚洲九九香蕉| 欧美 亚洲 国产 日韩一| 欧美在线一区亚洲| 亚洲精品一卡2卡三卡4卡5卡| 啪啪无遮挡十八禁网站| 国语自产精品视频在线第100页| 日韩av在线大香蕉| 老司机在亚洲福利影院| 69av精品久久久久久| 亚洲一区中文字幕在线| 中国美女看黄片| 国产亚洲av高清不卡| 91国产中文字幕| 国产精品综合久久久久久久免费 | 一级毛片精品| 午夜福利免费观看在线| 热re99久久国产66热| 中文字幕另类日韩欧美亚洲嫩草| 9热在线视频观看99| 久久久久国内视频| 激情视频va一区二区三区| 后天国语完整版免费观看| 亚洲 国产 在线| 女人被狂操c到高潮| 一区二区日韩欧美中文字幕| 正在播放国产对白刺激| www.999成人在线观看| 99国产精品99久久久久| av在线天堂中文字幕| 日韩精品中文字幕看吧| 久久精品91无色码中文字幕| 欧美日韩黄片免| 亚洲人成电影免费在线| 欧美日本亚洲视频在线播放| 国产亚洲欧美精品永久| 丰满的人妻完整版| 亚洲在线自拍视频| 色综合站精品国产| 中文字幕精品免费在线观看视频| 夜夜爽天天搞| 在线观看www视频免费| 99久久国产精品久久久| 在线视频色国产色| 在线播放国产精品三级| 长腿黑丝高跟| 9191精品国产免费久久| 久久精品国产亚洲av高清一级| 激情在线观看视频在线高清| 电影成人av| 国产亚洲av高清不卡| 麻豆av在线久日| 精品一区二区三区视频在线观看免费| 好男人在线观看高清免费视频 | 午夜影院日韩av| 国内精品久久久久久久电影| 日韩成人在线观看一区二区三区| 日本三级黄在线观看| 国产欧美日韩精品亚洲av| 久久精品国产综合久久久| 亚洲国产精品成人综合色| 在线观看www视频免费| 精品无人区乱码1区二区| 日韩 欧美 亚洲 中文字幕| 两个人看的免费小视频| 欧美日韩中文字幕国产精品一区二区三区 | 欧美激情久久久久久爽电影 | 麻豆久久精品国产亚洲av| 日韩一卡2卡3卡4卡2021年| 在线观看免费视频网站a站| 九色国产91popny在线| 90打野战视频偷拍视频| 日韩精品中文字幕看吧| 十八禁人妻一区二区| 久久人人97超碰香蕉20202| 久久精品国产99精品国产亚洲性色 | 久久婷婷人人爽人人干人人爱 | 欧美日本中文国产一区发布| 看黄色毛片网站| 亚洲精品中文字幕一二三四区| 亚洲欧美激情在线| 操出白浆在线播放| 美女免费视频网站| 欧美久久黑人一区二区| 成人免费观看视频高清| 搞女人的毛片| 黄色视频,在线免费观看| 97人妻天天添夜夜摸| 亚洲人成电影观看| 久久欧美精品欧美久久欧美| 婷婷丁香在线五月| 国产精品一区二区三区四区久久 | 欧美另类亚洲清纯唯美|