ABSTRACT Gamma-tocopherol along with the other forms of vitamin E plays a vital role in maintaining tissue homeostasis and protecting against oxidative stress and lipid peroxidation. Recent evidences suggest that gamma-tocopherol has characteristics that are not shared by alpha-tocopherol. In present study, based on the significant role of gamma-tocopherol as a particular antioxidant and its substantial effect on the mitochondria, a new derivative of gamma-tocopherol for improved penetration in mitochondrial matrix and also enhanced anti oxidative activity was synthesized and its protective effects were evaluated. Our results showed that this derivative protected mitochondria more efficiently than gamma tocopherol against oxidative damage caused by arsenic. As mitochondria are presumably the involved organelle in the pathogenesis of many chronic diseases including diabetes and cancer, our results may perhaps open a new view for treatment or prevention of those disorders. Keywords: gamma-tocopherol; mitochondria; reactive oxygen species; arsenic; glutathione Received23.11.2014 Revised30.12.2014 Accepted11.01.2015
INTRODUCTION Oxidative damage considered to be a major predisposing factor in causing chronic diseases includingcancer, cardiovascular and neurodegenerative disorders [1,2]. Oxygen free radicals can damage cellularcomponentsthatnormallyhaveimportantbiologicalfunctionsformaintaininghomeostasis[1,3].Forthisreason,variousnaturalantioxidantsandtheirderivativeswerestudiedorareinclinicalusefortreatmentor prevention of several disorders [4,5]. Studies showed that natural products such as tocopherolderivativesbesidetheiroverallantioxidantproperties,affectedotherorganellesofthecell.Interestingly,the effect of tocopherol on the mitochondrial electron transport chain is considered to be a promisingtherapeutic target in the treatment of cancer [6]. For instance, a vitamin E derivative, alpha tocopherylsuccinate,exhibitedapotentialanti‐canceractivity[7]. Vitamin E is a fat‐soluble antioxidant found in the cell membrane and other lipophilic components ofmammaliancellsandplays a vital role inmaintainingtissuehomeostasis, protectingthe organismfromfree radicals, oxidative stress and lipid peroxidation [8‐10]. Generally, Vitamin E family includes fourtocopherolsandfourtocotrienolsandbasedonthenumberandpositionofmethylgroupsonthearomaticringlabeledasα,β,γandδisomers[11].Asantioxidant,ahydrogenatomthroughthephenolichydroxylgroupiseasilytransferstolipidperoxylradicaltostoptheprogressofthelipidperoxidationchain[12].
The major types of the vitamin E family in diet are α and γ‐tocopherol (GT) partly due to their higherbioavailabilityandvitamincharacteristics.Whilebioavailability,bioactivityandplasmaconcentrationsofγ‐tocopherolarelowerthanα‐tocopherol,ithasdistinctivepropertiesthatareveryimportantforhumanhealth[1,13]. It isa majorpartof tocopherols in theNorthAmerican dietand thesecondmostcommon
tocopherol in human serum (10‐20%) [14]. Furthermore, epidemiological studies suggested that γ‐tocopheroldeficiencycomparetoα‐tocopherolmayprovidearisk factorforcertaintypesofcancerandmyocardial infarction. These findings have encouraged further research on vitamin E and consequently,manyinvivostudieshavebeenconductedontocopherolderivatives[15].Recentevidenceillustratedthatgamma‐tocopherol has characteristics that are not shared by alpha‐tocopherol. Chemical reactivity andinterferencewiththecellmetabolismareamongthoseuniquebiologicalactivities[16].One interesting role of gamma‐tocopherol supposed to be achieved by mitochondrial exploitation.Mitochondria are organelles found in eukaryotic cells and generate a large number of ATP required fortheirlife[17].Mitochondriaarealsoamajorsourceofintracellularreactiveoxygenspecies(ROS)andarepotentially vulnerable to oxidative stress. When ROS production exceeds the cellular capacity fordetoxificationandrepair,oxidativedamagetoproteins,DNA,andphospholipidscouldensue.Impairmentofmitochondrialoxidative phosphorylation, potentially leads tocelldysfunctionanddeath.Beside theirpathological role, ROS can also act as signal for cell redox capacity [18,19]. Studies have shown that inmany chronic states including type 2 diabetes, neurodegenerative disorders, cancer, and also aging,mitochondrial dysfunction may be presented [20]. Interestingly, a number of mitochondrial dysfunctioninduced toxicants including arsenic (As) were linked to aforementioned diseases. Conversely, there aremanyreportsthatconnectedarsenicexposuretodiabetesandcancer[21‐24].BecauseofdistinctiveroleofmitochondriaforintracellularROSproductionandtheirvulnerabilitytodeleteriousROSaction,severalvitamin E derived antioxidants have rigorously been tested to protect mitochondrion[25‐30]. In thepresent study a new gamma‐tocopherolderivative (GTD) was synthesized and its protective effects onmitochondria were evaluated.Firstly, we focused on gamma tocopherol (GT), the recently rediscoveredformofvitaminEbecauseofitsamazingeffectsontheregulationofcellsignalinginvolvedinproliferationand/ordegeneration.Wechemicallymodified itsstructure for improvedpenetrationandalsoenhancedantioxidativeactivityinthemitochondrialmatrix.Rationally,improvedpenetrationwouldbeachievedbyshortening the hydrocarbon residue compared to parent molecule and more efficient anti oxidantpropertywouldbeconferredbyaddinganunsaturatedbondtothemodifiedderivative.
MATERIALS AND METHODS Materials: As2O3, 4‐2‐hydroxyethyl‐1‐piperazineethanesulfonic acid (HEPES), D‐mannitol, 3‐(4,5‐dimethylthiazol‐2‐yl)‐ 2,5diphenyltetrazolium bromide (MTT), dithiobis‐2‐nitrobenzoic acid (DTNB), 2/,7/‐dichlorofluoresceindiacetate (DCFH‐DA), sucrose, rhodamine 123 (Rh 123), Coomassie blue, ethyleneglycol‐bis(2‐aminoethylether)‐N,N,N/,N/‐tetra acetic acid (EGTA), bovine serum albumin (BSA), bovineserum albumin (BSA), dimethyl sulfoxide (DMSO), n‐hexan, ethyl acetate, buthyl acetate, propylenecarbonate,‐Butyrolactone, isobutylmethyl ketone, diethyl ketone, toluene, formic acid, p‐Toluenesulfonicacid,FeCl2,AlCl3,P2O5,BF3,TiCl4,SnBr2,SilicaSulfuricacid(SiO2‐OSO3H),aceticacid,wereobtainedfromMerck, Fluka, Sigma‐Aldrich (Darmstadt, Germany). The progress of the reaction was followed with TLCusingsilica‐gelSILG/UV254plate.MerckSilicagel(100‐200mesh)wasusedforcolumnchromatography.The IR spectra were recorded on PerkinElmer BX II FT IR spectrophotometer with KBr pellets. 1H NMRspectrawererecordedbyaBrukerAC300MHzspectrometer.13CNMRspectrawererecordedbyaBrukerDPX400MHzspectrometer.MassspectraweredeterminedbyaFINNIGAN‐MAT8430massspectrometeroperatingatanionizationpotentialof70eV.Preparation of 2RS,7,8-Trimethyl-2-(4-methylpent-3-en-1-yl)-6-hydroxy-3-Chromane (GTD):The experimental procedure involved charging the reactor with 0.69 gr (0.005mole) of 2,3‐dimethylhydroquinone,0.272gr(0.002mole)ofZnCl2and50mlofbutylacetate.Reactionmixturewasstirredfor2 hours, flushed with nitrogen and heated up to about 130 °C, so that the azeotropic mixture of butylacetateandwaterwasdistilledoff.Next0.77g(0.005mole)oflinaloolalcoholwasaddeddropwise.Aftercompletion of the reaction, as indicated by TLC (5 hours) and cooling down the reaction mixture, thecatalyst(zincdichloride)wasremoved.Themixturethenextracted(3times)byaqueousNaOH(8%wt.),followedbyaqueousHCl(5%wt.)andfinallybywater.Subsequenttothelastwashing,organiclayerwascarefully separated, dried over anhydrous MgSO4, filtered and the solvent was removed under lowpressure. The product was purified by column chromatography using eluent mixture of hexane: ethylacetate(5:1v:v). Finally,pureproduct (component3 (GTD), figure2and3)asa yellowish‐brownoil (70% yield) was obtained; FTIR (KBr, cm−1 ): 3392, 3026, 2933, 2869, 1618, 1493, 1454, 1223; 13CNMR(400MHz,CDCl3):δ147.38,146.75,130.61,123.17,120.97,116.81,114.37,113.42,74.68,38.13,29.86,24.65,23.12,22.40,21.24,19.57,18.72,16.56.Animals: Male Wistar rats (200–250 g) were kept in polypropylene cages and were fed with standard chow anddrinkingwaterad libitum.Theanimalsweremaintainedatacontrolledconditionoftemperature(25±2
Heidari et al
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◦C)witha12hlight:12hdarkcycle.AllexperimentscarriedaccordingtothestandardsoutlinedblocalUniversity'sEthicalCommittee.Mitochondrial isolation: Mitochondria were prepared from Wistar rat’s liver using differential centrifugation. The liver wasremovedandmincedwithasmallscissorinacoldmannitolsolutioncontaining200mMDmMsucrose,1mMEGTA,0.1%(w/v)BSAwas gently homogenized in a glass homogenizer. Nuclei and cell debris were sedimented throughcentrifugation (600×g, 10 min, 4ºC) and the supernatSupernatant was carefully discarded and the pellet (mitochondria) washed gently by suspending in theisolation medium and centrifuged again for 15 min at 10,000×g. Finally, pellet was suspended in themannitol solution. For each test, mitochondria were prepared freshly and used within 2 h of isolation.Protein concentrations were determined through the Coomassie blue proteinexplained by Bradford, 1976 [31various concentrations of GTD (1, 5, and 10 µM) (as illustrated below, figure 1) forfollowed byAs2O3(20,40and100µM) exposure for30min.AliquotsofmitochondrialsuspensionwereusedtodeterminetheprotectiveeffectsofGTDagainstarsenictoxicity.Allexperimentswereperformedandrepeatedatleastthreetimes.
Figure 1.
ROS determination:The mitochondrial ROS measurement was performed using the fluorescent probe DCFHisolated mitochondria suspensions (0.5 mg protein/ml) were incubated with various concentrGTD, and then incubated with different concentrations of Arsenic. 10 µM of DCFHmitochondrial solution. The fluorescence was measured using PerkinElmer LSfluorescence spectrophotometer at the excitation and emirespectively[32].Mitochondrial damage determination:The mitochondrial uptake of the cdeterminationofmitochondrialmembranepotential.Themitochondrialsuspensions(0.5mgprotein/ml)wereincubatedwithvariousconcentrationsofGTD,andthenincubatedwithdifferentconcentratArsenic. 10 µM of rhodamine123 was added to the mitochondrial solution. Themeasured using PerkinElmer LS‐wavelengthsof490and535nm,respectively[Mitochondrial dehydrogenase activity (MTT assay):The activity of mitochondrial complex II (succinate dehydrogenase) was assayed through themeasurement of MTT reduction. Brieincubated with different concentrations of GTD, and then incubated with different concentrations ofArsenic. suspensionwascentrifugedat 10,621×g for1 min. pellet wassuspended in970µLof isolationmediumand500µLof0.5µMMTTandincubatedat37formedweredissolvedin800µLDMSO,andtheabsorbancemeasuredat570nmspectrophotometrically(UV‐1650PC,Shimadzu,Japan)[34
Mitochondria were prepared from Wistar rat’s liver using differential centrifugation. The liver wasremovedandmincedwithasmallscissorinacoldmannitolsolutioncontaining200mMDmMsucrose,1mMEGTA,0.1%(w/v)BSA,10mMHEPES‐KOH,pH7.4preparefreshly.Themincedliverwas gently homogenized in a glass homogenizer. Nuclei and cell debris were sedimented throughcentrifugation (600×g, 10 min, 4ºC) and the supernatants were centrifuged at10,000×g for 15 min.Supernatant was carefully discarded and the pellet (mitochondria) washed gently by suspending in theisolation medium and centrifuged again for 15 min at 10,000×g. Finally, pellet was suspended in the
olution. For each test, mitochondria were prepared freshly and used within 2 h of isolation.Protein concentrations were determined through the Coomassie blue protein
31]. Mitochondrial samples (500 µg protein/ml) were incubated withvarious concentrations of GTD (1, 5, and 10 µM) (as illustrated below, figure 1) for
The mitochondrial ROS measurement was performed using the fluorescent probe DCFHisolated mitochondria suspensions (0.5 mg protein/ml) were incubated with various concentrGTD, and then incubated with different concentrations of Arsenic. 10 µM of DCFH
fluorescence was measured using PerkinElmer LSfluorescence spectrophotometer at the excitation and emission wavelengths of 490 and 535 nm,
Mitochondrial damage determination: The mitochondrial uptake of the cationic fluorescent dye, rhodamine123, has been used for thedeterminationofmitochondrialmembranepotential.Themitochondrialsuspensions(0.5mgprotein/ml)wereincubatedwithvariousconcentrationsofGTD,andthenincubatedwithdifferentconcentratArsenic. 10 µM of rhodamine123 was added to the mitochondrial solution. The
‐50B Luminescence spectrofluorometer at the excitation and emissionwavelengthsof490and535nm,respectively[33].Mitochondrial dehydrogenase activity (MTT assay): The activity of mitochondrial complex II (succinate dehydrogenase) was assayed through themeasurement of MTT reduction. Briefly, 1mL of mitochondrial suspensions (0.5 mg protein/ml) waincubated with different concentrations of GTD, and then incubated with different concentrations ofArsenic. suspensionwascentrifugedat 10,621×g for1 min. pellet wassuspended in970µLof isolationmediumand500µLof0.5µMMTTandincubatedat37Cfor45min.Thepurpleformazancrystalswhichformedweredissolvedin800µLDMSO,andtheabsorbancemeasuredat570nmspectrophotometrically
Mitochondria were prepared from Wistar rat’s liver using differential centrifugation. The liver wasremovedandmincedwithasmallscissorinacoldmannitolsolutioncontaining200mMD‐mannitol,70
KOH,pH7.4preparefreshly.Themincedliverwas gently homogenized in a glass homogenizer. Nuclei and cell debris were sedimented through
ants were centrifuged at10,000×g for 15 min.Supernatant was carefully discarded and the pellet (mitochondria) washed gently by suspending in theisolation medium and centrifuged again for 15 min at 10,000×g. Finally, pellet was suspended in the
olution. For each test, mitochondria were prepared freshly and used within 2 h of isolation.Protein concentrations were determined through the Coomassie blue protein‐binding method as
]. Mitochondrial samples (500 µg protein/ml) were incubated withvarious concentrations of GTD (1, 5, and 10 µM) (as illustrated below, figure 1) for 30 min at 37 C
The mitochondrial ROS measurement was performed using the fluorescent probe DCFH‐DA. Briefly,isolated mitochondria suspensions (0.5 mg protein/ml) were incubated with various concentrations ofGTD, and then incubated with different concentrations of Arsenic. 10 µM of DCFH‐DA was added to the
fluorescence was measured using PerkinElmer LS‐50B Luminescencession wavelengths of 490 and 535 nm,
fluorescent dye, rhodamine123, has been used for thedeterminationofmitochondrialmembranepotential.Themitochondrialsuspensions(0.5mgprotein/ml)wereincubatedwithvariousconcentrationsofGTD,andthenincubatedwithdifferentconcentrationsofArsenic. 10 µM of rhodamine123 was added to the mitochondrial solution. The fluorescence was
50B Luminescence spectrofluorometer at the excitation and emission
The activity of mitochondrial complex II (succinate dehydrogenase) was assayed through thefly, 1mL of mitochondrial suspensions (0.5 mg protein/ml) was
incubated with different concentrations of GTD, and then incubated with different concentrations ofArsenic. suspensionwascentrifugedat 10,621×g for1 min. pellet wassuspended in970µLof isolation
Mitochondrial glutathione content: GSH content was determined using DTNB reagent by spectrophotometric method in isolatedmitochondria. The developed yellowish color was read at 412 nm using a spectrophotometer (UV‐1650PC,Shimadzu,Japan).GSHcontentwasexpressedasµg/mgprotein[35].Statistical Analysis: Results were presented as mean ± SD. All assays performed triplicate, and the mean was used for thestatisticalanalysis.Statisticalsignificancewasestablishedusingtheone‐wayANOVAtest,accompaniedbytheposthocTukeyˊstest.StatisticalsignificancehasbeensetatP<0.05. RESULTS 2RS,7,8-Trimethyl-2-(4-methylpent-3-en-1-yl)-6 hydroxy-3-Chromane (GTD) preparation: Treatment of methyl hydroquinone with isoprenoid alcohol in the presence of Lewis acid catalystsappears to be appropriate route for chromane structure preparation. Thus in order to investigate thepossibilityandlimitationsofthisroute,thereactionof2,3‐dimethylhydroquinonewithlinaloolalcoholinthe presence of variety catalysts (Lewis and Brϕnsted acids) and solvents were tested. The resultsobtainedaresummarizedinTable1andTable2.Amongthevariouscatalystsandsolventsused,twowereparticularlyhelpfultoformcompound3,entries8and4(Table1,2).ThenareactionusingdifferentquantitiesofZnCl2wasperformed.Withloweramountof ZnCl2 at molar ratio of 2,3‐dimethyl hydroquinone : linalool : ZnCl2 = 1 :1 : 0.2, the yield of productdecreasedto55%andwithhigheramountofZnCl2atmolarratioof2,3‐dimethylhydroquinone:linalool:ZnCl2=1:1:0.6,theyieldofproductincreasedto72%.aReaction condition: 2,3‐dimethyl hydroquinone=1 mole, linalool alcohol= 1 mole, catalyst= 0.4moleisolatedyieldAsshowninfigure2,fourproductswererecognizedbytheirspectroscopicdatainthesereactions:3,4,5and6,ofwhichonlycompound3whichwasproducedinallreactionsindifferentyieldswasthegoal.Thiscompoundseparatedandpurifiedbycolumnchromatographyinreportedyields(Tables1and2)at130°CinthepresenceofZnCl2for7hours.Compound3wasisolatedfromthecrudereactionmixturebycolumnchromatographyandidentifiedbyNMR,MS,andIRspectroscopy.Compound4,5and6areallderivativesofthemajorproduct3andareformedindifferentratiosdependingonthereactionconditions.Theyweretentatively identified by spectroscopic analysis of crude reaction mixtures. No attempts were made forisolatingthesecompounds.Structureof(3)wasestablishedbyitsspectroscopydata:mass,IR,1HNMRand13CNMR.Thefragmentationobserved in the mass spectrum of compound 3 followed familiar courses reported for tocopherols [36].This spectrum provided useful structural information for compound 3 (figure 2).1HNMR spectrum(300MHz,CDCl3),exhibitsresonancesignalsatδ6.57–6.69(2H,H5,H3
In order to determine the biological activity of compound (3) (GTD), we conducted the followingexperiments:GTD role in the decrease of As-induced Fig.4ashowsthe increased levelofoxygenradicalsuponarsenicexposurewere increased byhigherconcentrationofarsenicsignificant lower levels of oxygen free radical were detected. The results indicated that GTinfluence on ROS formation attenuation has been achieved by 5 and 10 μM at concentrations of 20 and40μMarsenicrespectively.ROSreductionnotas farasthenegativecontrolreductionofROSwereobtained(P<0.05).Asshowninfig.4b,gammatocopherolderivative(GTD)hasalsobeenablepresence of arsenic. Unlike the GT
increased byhigherconcentrationofarsenic.Whengammatocopherol(GT)pretreatmentapplied,er levels of oxygen free radical were detected. The results indicated that GT
influence on ROS formation attenuation has been achieved by 5 and 10 μM at concentrations of 20 andreductionbytheuseofdifferentconcentrationsofgamma
Asshowninfig.4b,gammatocopherolderivative(GTD)hasalsobeenabletoreduceROSformationintheUnlike the GT, GTD even at concentration as low as 1μM, reduced ROS formation
er levels of oxygen free radical were detected. The results indicated that GTˊs highestinfluence on ROS formation attenuation has been achieved by 5 and 10 μM at concentrations of 20 and
toreduceROSformationintheat concentration as low as 1μM, reduced ROS formation
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significantly. In thepresenceofarsenic,GTD reducedthe levelofROSdoseeffectwasaccomplishedataconcentrationof10μMofGTDreducedROSlevelsformedunderAs shown in fig.5a, b and c at 40 μM of arsenic, GTD in comparison with GT, reduced the level of ROSdrastically (P <0.05). Decrease in ROS achieved by 10 μM gammayieldedbyGTDatthesameconcentration(P<0.05).Fig.5bshowssignificantdifferencesforROSamountswith1,5and10μMofGTDcomparedtoGT.Atthehighestconcentrationofarsenic(100μM),again,GTcouldneverbethesameasGTDininhibitingtheformationoffreeradicals(P<0.05).
Figure 4.Gammatocopherol(GT)anditsderivative(GTD)reducedmitochondrialROSgenerationunderdifferentconcentrationsofAs2O3. Reactiveoxygenspecies(ROS)determinedusingHreflects different ROS amount in different groups. Rat liver mitochondria were isolated, purified(0.5mg/ml protein) and incubated in buffer contains mannitol, sucrose, HEPES and EGTA (pH 7.4)followed by 1 hour exposure to Asλemission=520nm.(P<0.05)GTD0µMtocomparedasdifferenceSignificant٭**SignificantdifferenceascomparedtoGTD1µM(P<0.05)$SignificantdifferenceascomparedtoGTD5µM(P<0.05)
Figure 5.Gamma tocopherol (GT) and its derivative (GTD) reduced mitochondrial ROS generationcomparativelyatdifferentAs2O3concentrations.
48 | P a g e
In thepresenceofarsenic,GTD reducedthe levelofROSdose‐dependentlyandeffectwasaccomplishedataconcentrationof10μMofGTD.Incontrast toGT,GTDat1μMsignific
under40μMofarseniccomparedtothecontrol(P<0.05).As shown in fig.5a, b and c at 40 μM of arsenic, GTD in comparison with GT, reduced the level of ROSdrastically (P <0.05). Decrease in ROS achieved by 10 μM gamma‐tocopherol was comparable to thatyieldedbyGTDatthesameconcentration(P<0.05).Fig.5bshowssignificantdifferencesforROSamountswith1,5and10μMofGTDcomparedtoGT.Atthehighestconcentrationofarsenic(100μM),again,GT
Reactiveoxygenspecies(ROS)determinedusingH2DCF‐DAoxidation.RelativeDCFfluorescenceintensityreflects different ROS amount in different groups. Rat liver mitochondria were isolated, purified(0.5mg/ml protein) and incubated in buffer contains mannitol, sucrose, HEPES and EGTA (pH 7.4)
by 1 hour exposure to As2O3. Fluorimetric measurements were made at λ
P<0.05).As shown in fig.5a, b and c at 40 μM of arsenic, GTD in comparison with GT, reduced the level of ROS
opherol was comparable to thatyieldedbyGTDatthesameconcentration(P<0.05).Fig.5bshowssignificantdifferencesforROSamountswith1,5and10μMofGTDcomparedtoGT.Atthehighestconcentrationofarsenic(100μM),again,GT
DAoxidation.RelativeDCFfluorescenceintensityreflects different ROS amount in different groups. Rat liver mitochondria were isolated, purified(0.5mg/ml protein) and incubated in buffer contains mannitol, sucrose, HEPES and EGTA (pH 7.4)
. Fluorimetric measurements were made at λexcitation=500,
Gamma tocopherol (GT) and its derivative (GTD) reduced mitochondrial ROS generation
BEPLS Vol 4 [3] February 2015
Reactiveoxygenspecies(ROS)determinedusingHreflects different ROS amount in different groups. Rat liver mitochondria were isolated, purified(0.5mg/ml protein) and incubated in buffer contains mannitol, sucrose, HEPES and EGTA (pH 7.4)followed by 1 hour exposure to Asλemission=520nm.(P<0.05)concentrationGTcorrespondingtocomparedasdifferenceSignificant٭GTD role in preventing oxidation of glutathione:Glutathione levels were measured in isolated mitochodifferent concentrations of arsenic (40, 20 and 100) using DTNB as an indicator. Fig.6 demonstrates asignificant depletion of glutathione for all three applied arsenic concentrations (P <0.05) in aconcentration dependent manner. The results showed that mitochondrial GSH levels increased with theuseofGTDinwhich5and10μMofGTDinthepresenceofarseniccontributedthehigherlevels.
Glutathione contents determined using DTNB. Rat liver mitochondria were isolated, purified (0.5mg/mlprotein)andincubatedinbuffercontainsmannitol,sucrose,HEPESandEGTA(pH7.4)followedby1hourexposuretoAs2O3.Theyellowishcolordevelopedwasreadat412nmspectrophoto(P<0.05)GTD0µMtocomparedasdifferenceSignificant٭**SignificantdifferenceascomparedtoGTD1µM(P<0.05)$SignificantdifferenceascomparedtoGTD5µM(P<0.05)GTD role in preventing mitochondrial membrane potential collapse:As seen in Fig.7a mitochondrial membrane collapse was concentrationthearsenicconcentrationelevated.GTprotectedthemitochondrialmembranewhenexposedtoarsenic.However,exceptfor10μMGTat20and100μMofarsenic,resultsshowedn<0.05). In the absence of arsenic, gammaconcentration affected the membrane potential (Fig.7b). Using the GTD pretreatment, the damage wasdiminishedandtheGTDhighestimpactinreducingmitochondrialmembranedamageachievedby5and10μMat40μMofarsenic.As shown in Fig.8a, b and c, GTD more effectively reduced vulnerability of mitochondrial membrane toarsenicthantheGTparticularlyatarsenicconcentrationresults did not show any significant differences between GT and GTD (P <0.05). In this context, Fig.8bshowssignificantdifferenceattheconcentrationof5μM(P<0.05).Sameresultswereobtainedfor1ofGTDat100μMarsenicconcentration.Collectively,theresultsshowedthatatthesamevaluesused,GTDprotectedmitochondrialmembranemoreeffectivelythanGT.
49 | P a g e
Reactiveoxygenspecies(ROS)determinedusingH2DCF‐DAoxidation.RelativeDCFfluorescenceintensityROS amount in different groups. Rat liver mitochondria were isolated, purified
(0.5mg/ml protein) and incubated in buffer contains mannitol, sucrose, HEPES and EGTA (pH 7.4)followed by 1 hour exposure to As2O3. Fluorimetric measurements were made at λ
SignificantdifferenceascomparedtocorrespondingGTconcentration(P<0.05)GTD role in preventing oxidation of glutathione: Glutathione levels were measured in isolated mitochondria by spectrophotometric assay under thedifferent concentrations of arsenic (40, 20 and 100) using DTNB as an indicator. Fig.6 demonstrates asignificant depletion of glutathione for all three applied arsenic concentrations (P <0.05) in a
dependent manner. The results showed that mitochondrial GSH levels increased with theTDinwhich5and10μMofGTDinthepresenceofarseniccontributedthehigherlevels.
Gamma tocopherol derivative (GTD) modified mitochondrial glutathione contents affected by
ed using DTNB. Rat liver mitochondria were isolated, purified (0.5mg/mlprotein)andincubatedinbuffercontainsmannitol,sucrose,HEPESandEGTA(pH7.4)followedby1hour
GTD role in preventing mitochondrial membrane potential collapse: itochondrial membrane collapse was concentration‐dependently increased following
thearsenicconcentrationelevated.GTprotectedthemitochondrialmembranewhenexposedtoarsenic.However,exceptfor10μMGTat20and100μMofarsenic,resultsshowednosignificantdifferences(P<0.05). In the absence of arsenic, gamma‐tocopherol derivative (GTD) in comparison with GT, at highconcentration affected the membrane potential (Fig.7b). Using the GTD pretreatment, the damage was
As shown in Fig.8a, b and c, GTD more effectively reduced vulnerability of mitochondrial membrane toarsenicthantheGTparticularlyatarsenicconcentrationsof40and100μM(P<0.05).At20μMofarsenic,results did not show any significant differences between GT and GTD (P <0.05). In this context, Fig.8bshowssignificantdifferenceattheconcentrationof5μM(P<0.05).Sameresultswereobtainedfor1ofGTDat100μMarsenicconcentration.Collectively,theresultsshowedthatatthesamevaluesused,GTDprotectedmitochondrialmembranemoreeffectivelythanGT.
DAoxidation.RelativeDCFfluorescenceintensityROS amount in different groups. Rat liver mitochondria were isolated, purified
(0.5mg/ml protein) and incubated in buffer contains mannitol, sucrose, HEPES and EGTA (pH 7.4). Fluorimetric measurements were made at λexcitation=500,
ndria by spectrophotometric assay under thedifferent concentrations of arsenic (40, 20 and 100) using DTNB as an indicator. Fig.6 demonstrates asignificant depletion of glutathione for all three applied arsenic concentrations (P <0.05) in a
dependent manner. The results showed that mitochondrial GSH levels increased with theTDinwhich5and10μMofGTDinthepresenceofarseniccontributedthehigherlevels.
Gamma tocopherol derivative (GTD) modified mitochondrial glutathione contents affected by
ed using DTNB. Rat liver mitochondria were isolated, purified (0.5mg/mlprotein)andincubatedinbuffercontainsmannitol,sucrose,HEPESandEGTA(pH7.4)followedby1hour
osignificantdifferences(Ptocopherol derivative (GTD) in comparison with GT, at high
concentration affected the membrane potential (Fig.7b). Using the GTD pretreatment, the damage wasstimpactinreducingmitochondrialmembranedamageachievedby5and
As shown in Fig.8a, b and c, GTD more effectively reduced vulnerability of mitochondrial membrane tosof40and100μM(P<0.05).At20μMofarsenic,
results did not show any significant differences between GT and GTD (P <0.05). In this context, Fig.8bshowssignificantdifferenceattheconcentrationof5μM(P<0.05).Sameresultswereobtainedfor1μMofGTDat100μMarsenicconcentration.Collectively,theresultsshowedthatatthesamevaluesused,GTD
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Figure 7.Gamma tocopherol and its derivative (GTD) reduced mitochondrial damage underconcentrationsofAs2O3.
Mitochondrial membrane potential (MMP) (ΔΨm) determined using Rhodamine 123. Relativefluorescence intensityreflectsdifferent(MMP)amountindifferentgroups.Rat livermitochondrialwereisolated, purified (0.5mg/ml protein) and incubated in buffer contains mannitol, sucrose, HEPPES andEGTA(pH7.4)for2hr.Fluorimetricmeasurementsweremadeatλ
*significantdifferenceascomparedtoGTD0µM(P**SignificantdifferenceascomparedtoGTD1µM(P<0.05)Activity of mitochondrial dehydrogenases:DehydrogenasesactivityexaminedusingtheMTTassay100 μM) (Fig.9). Arsenic alone caused a concentrationwhile GTD in the absence of arsenic significantly increased the activity of complex II. MitochondrialcomplexIIordehydrogenaseactivityimprovedbyGTDandthemaximumeffectobtainedfrom1and10μMforarsenicconcentrationsof100or40μMrespectively.
Mitochondrial viability (total dehydrogenase activity) was assayed by determining the amount of MTTconversion. Rat liver mitochondria were isolated, purified (0.5mg/ml protein) and incubated in buffercontains mannitol, sucrose, HEPES and EGTA (pH 7.4) followed by 1 hour exposure to Asabsorbanceat570nmwasmeasuredwithaspectrophotometer.(P<0.05)GTD0µMtocomparedasdifferenceSignificant٭**SignificantdifferenceascomparedtoGTD1µM(P<0.05)$SignificantdifferenceascomparedtoGTD5µM(P<0.05)DISCUSSIONMitochondrial dysfunction has been implicated indiabetes, cardiovascular disease and agefunctionofmitochondriaanditsroleincellulartoxicityinducedbyvarioustoxicantsprovidedanumberofimportant targets for treatment and prevention of some related diseases. Besides the nature ofmitochondrial genome and its sensitivity to mutations, enzyme activation and also detoxification ofdifferent toxicants and xenobiotics in the mitochondrion and its membrane swellinjurieshaveenormouslyevaluated[Mitochondrion not only plays a key role in generating energy through the process called OxidativePhosphorylation(OXPHOS),italsoplaysacentralroleinapoptosis,cellularstressresponsesandgeneticdiseases [38].DisruptionofOXPHOS leads tochanges in the intracellularRedOxstatesand intracellularorganelles,ATPproduction,theformationofreactiveoxygenspecieapoptosis[39].
Mitochondria are believed to be as target for environmental pollutants including heavy metals. In thiscontext, mitochondrial dysfunction started a noxious process thdevelopmentofmanydiseases[40and its dysfunction were shown to have devastating consequences, in this study, we synthesized a newderivative of gamma‐tocopherol and tested its potential prarsenic.Recent studies have suggested that gammamainlybyitsdistinctivefeatureswhichdistinguishitfromothermembersofthetocopherolfamily[Gamma‐tocopherol found to be advanta
51 | P a g e
*significantdifferenceascomparedtoGTD0µM(P˂0.05) **SignificantdifferenceascomparedtoGTD1µM(P<0.05)Activity of mitochondrial dehydrogenases: DehydrogenasesactivityexaminedusingtheMTTassayatdifferentconcentrationsofarsenic(20,40and100 μM) (Fig.9). Arsenic alone caused a concentration‐dependent inhibition of dehydrogenases activitywhile GTD in the absence of arsenic significantly increased the activity of complex II. Mitochondrial
Gamma tocopherol derivative (GTD) potently retained mitochondrial viability affected by
Mitochondrial viability (total dehydrogenase activity) was assayed by determining the amount of MTTconversion. Rat liver mitochondria were isolated, purified (0.5mg/ml protein) and incubated in buffer
sucrose, HEPES and EGTA (pH 7.4) followed by 1 hour exposure to Asabsorbanceat570nmwasmeasuredwithaspectrophotometer.
Mitochondrial dysfunction has been implicated in pathogenesis of various conditions such as cancer,diabetes, cardiovascular disease and age‐related neurodegenerative diseases. Understanding the precisefunctionofmitochondriaanditsroleincellulartoxicityinducedbyvarioustoxicantsprovidedanumberof
for treatment and prevention of some related diseases. Besides the nature ofmitochondrial genome and its sensitivity to mutations, enzyme activation and also detoxification ofdifferent toxicants and xenobiotics in the mitochondrion and its membrane swelling due to the diverseinjurieshaveenormouslyevaluated[37].
Mitochondrion not only plays a key role in generating energy through the process called OxidativePhosphorylation(OXPHOS),italsoplaysacentralroleinapoptosis,cellularstressresponsesandgenetic
].DisruptionofOXPHOS leads tochanges in the intracellularRedOxstatesand intracellularorganelles,ATPproduction,theformationofreactiveoxygenspeciesandeventuallytocelldeathincluding
Mitochondria are believed to be as target for environmental pollutants including heavy metals. In thiscontext, mitochondrial dysfunction started a noxious process that is believed to be involved in
40].Sincemitochondriaplayimportantroleinthenormalfunctionofcelland its dysfunction were shown to have devastating consequences, in this study, we synthesized a new
tocopherol and tested its potential protective effects against damage caused by
Recent studies have suggested that gamma‐tocopherol might be essential for maintaining healthy bodymainlybyitsdistinctivefeatureswhichdistinguishitfromothermembersofthetocopherolfamily[
tocopherol found to be advantageous in the control of diseases associated with chronic
atdifferentconcentrationsofarsenic(20,40anddependent inhibition of dehydrogenases activity
while GTD in the absence of arsenic significantly increased the activity of complex II. MitochondrialomplexIIordehydrogenaseactivityimprovedbyGTDandthemaximumeffectobtainedfrom1and10
Gamma tocopherol derivative (GTD) potently retained mitochondrial viability affected by
Mitochondrial viability (total dehydrogenase activity) was assayed by determining the amount of MTTconversion. Rat liver mitochondria were isolated, purified (0.5mg/ml protein) and incubated in buffer
sucrose, HEPES and EGTA (pH 7.4) followed by 1 hour exposure to As2O3. The
onditions such as cancer,related neurodegenerative diseases. Understanding the precise
functionofmitochondriaanditsroleincellulartoxicityinducedbyvarioustoxicantsprovidedanumberoffor treatment and prevention of some related diseases. Besides the nature of
mitochondrial genome and its sensitivity to mutations, enzyme activation and also detoxification ofing due to the diverse
Mitochondrion not only plays a key role in generating energy through the process called OxidativePhosphorylation(OXPHOS),italsoplaysacentralroleinapoptosis,cellularstressresponsesandgenetic
].DisruptionofOXPHOS leads tochanges in the intracellularRedOxstatesand intracellularsandeventuallytocelldeathincluding
Mitochondria are believed to be as target for environmental pollutants including heavy metals. In thisat is believed to be involved in
].Sincemitochondriaplayimportantroleinthenormalfunctionofcelland its dysfunction were shown to have devastating consequences, in this study, we synthesized a new
otective effects against damage caused by
tocopherol might be essential for maintaining healthy bodymainlybyitsdistinctivefeatureswhichdistinguishitfromothermembersofthetocopherolfamily[13].
geous in the control of diseases associated with chronic
inflammation,includingarthritis,cancer,cardiovascularandneurodegenerativediseases(Alzheimer)[41‐45]. As a result, mechanisms beyond the absorption of oxygen free radicals have been proposed forgamma‐tocopherol. Nucleophilically, this form is more potent than alpha‐tocopherol and can neutralizeelectrophilicmutagensinthelipophilicpartsofthecell[46‐48].Thisneutralizingactivityiscomparabletoinhibitingtheelectrophilicmutagensbyglutathioneinthehydrophilicportionofthecell.Inthisway,oneimportant reaction is the neutralization of peroxynitrite by gamma‐tocopherol which inhibits theformationoflipidradicalsandprotectsDNAandproteins.Efficiencyofgamma‐tocopheroltoscavengingoxygenfreeradicalsbelievedtobemorethanalpha‐tocopherol.Thisfeaturemaybeassociatedwiththestructure of gamma‐tocopherol since the unsubstituted C‐5 position of gamma‐tocopherol (Fig. 2), is anucleophiliccenterandcanpotentlyscavengeoxygenandnitrogenradicals[49].
Today'sadvances inresearchonmitochondria providedatool todesignnewdrugsforvariousdiseasesand conditions related to mitochondrial abnormality. Study on isolated mitochondria has led to betterunderstandingofmolecularmechanismsofxenobiotics[32,38,50].Purifiedmitochondriahavebeenusedfor assessing the toxicity and mechanism of injury caused by heavy metals. Such studies revealed thatarsenicinducedapoptosisandnecrosisthroughreleaseofcytochromec.Mitochondriaaresupposedtobethe main targets for arsenic toxicity. Arsenic exposure through disruption of mitochondrial electrontransferchainleadtomitochondrialswelling[51].ArsenicincancercelllinesinducedMPT(mitochondrialpermeability transition) and apoptosis [52,53]. Studies show that arsenic increases ROS, lipidperoxidation,andimpairmentofmitochondrialmembranepotential[54,55].strongevidenceshavelinkedarsenic‐induced oxidative stress to endothelial inflammation, the major complication in atherosclerosis[52,56].Althoughhighlevelsofarsenicinhibitedangiogenesis,atlowerconcentrationsinsomestudiesithas been stimulated angiogenesis and it seems that mitochondrial disruption caused by arsenic oroxidativestressplaysakeyroleintheangiogenesis[57,58].The results of the present study indicated that mitochondrial ROS overproduction was significantlyinducedbyarsenic inaconcentrationdependentmannerthatwithregardtothemechanismsdescribedabovecanbecausedbyimpairedelectrontransportchainandmitochondrialmembrane(Fig.4a).Whenmitochondria were pretreated with gamma‐tocopherol or its derivative (GTD) the amounts of ROSformationwereconsiderablyreduced(Fig.4a‐b).Giventheroleofgamma‐tocopherolinscavengingfreeradicals inthelipophilicphase,theseresultswereexpected. Interestingly,gamma‐tocopherolderivative,compared to parent tocopherol, inhibited arsenic induced oxygen free radicals production in a moreeffectivemanner.Thisisespeciallyevidentfor40µMarsenic.Thepresenceofunsaturateddoublebondinthemodifiedderivativemaycontributetothishigherefficiency.Besidesthedoublebondcontributiontoantioxidant property, fluidity also plays a significant role. Here the higher fluidity leads to enhancedpenetrationacrossthemembranes.Oursynthesizedcompoundaccordingtoitsunsaturabilityhasfurtherfluidity and perhaps cross the membrane easier (Fig. 2). In this regard we can take a look at sometocotrienols derivatives which contain three unsaturated double bonds and the antioxidant propertiesthatconferredreportedtobehigherthangamma‐tocopherol[59,60].
Asmentionedgamma‐tocopheroleffectsonvariousdiseasessuchascancerarenotdirectlyrelatedtoitsantioxidant effects. Studies revealed that tocopherols with similar antioxidant activities have differentantiproliferative properties. Lots of evidences suggested that tocopherols alongside their antioxidantproperties were also involved in signaling and regulation of gene expression in animals [13,39,61]. Tosomeextent,theseeffectspossiblyrelatedtomitochondrialexploitationbygamma‐tocopherol.Therefore,in this study, mitochondrial membrane potential in the presence of arsenic, gamma‐ tocopherol and itsderivativehavebeenstudied(Fig.7a‐b).Gamma‐tocopherolonlyathighconcentrations(10μM)reducedmitochondrialdamagewhileGTDatlesserconcentrationshowedprotectiveeffectonmitochondria.Intheotherwords,GTDprotectedmitochondriamoreefficientlywhichmaybeduetothehigherROSinhibitoryeffectofthisderivative(Fig.8a‐c).Arsenic‐induced damage to the mitochondria thought to be through its stimulation for reactive oxygenspecies generation. Naturally, 1‐2% of oxygen consumed by mitochondria are converted to superoxideradicals [62]. At the presence of arsenic, the formation of superoxide increased and resulted inmitochondrial glutathione oxidation and depletion (Fig. 6). In our study, mitochondrial glutathionedepletioninaconcentrationdependentmannerobservedforarsenicexposure.GTderivativewithrespecttoitshigherantioxidantandpenetrationrateneutralizedthefreeradicalsandpreventedtheoxidationofmitochondrial glutathione (Fig.6). On the other hand, mitochondrial dehydrogenase activity graduallydecreases with increasing arsenic concentrations (Fig.8) and GTD profoundly maintained mitochondrialdehydrogenase activity in such a way that at the highest concentration (10μM) dehydrogenase activityapproximatelyrestoredtoitsnormalvalues(controlgroup).Inconclusion,ourresultsshowedthatthechemicallymodifiedderivativeofgammatocopherolprotectedmitochondria more efficiently against oxidative damage induced by arsenic. As mitochondria are
presumably the affected organelle in the pathogenesis of many chronic diseases including diabetes andcancer,ourresultsmayperhapsopenanewviewfortreatmentorpreventionofthosedisorders.
Figure 10. Mitochondrial view of gamma tocopherol derivative (GTD) action
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CITATION OF THIS ARTICLE MohammadH,RashidB,MohsenR,MohammadRS,AliRK.MitochondrialProtectionagainstArsenicToxicitybyaNovelGammaTocopherolAnalogueinRat.Bull.Env.Pharmacol.LifeSci.,Vol4[3]February2015:43‐55
