Chiang Mai J. Sci. 2014; 41(1) 105

Chiang Mai J. Sci. 2014; 41(1) : 105-116http://epg.science.cmu.ac.th/ejournal/Contributed Paper

Antioxidant and Antiglycation Activities of SomeEdible and Medicinal PlantsKhwanta Kaewnarin [a,b], Hataichanoke Niamsup [a,b], Lalida Shank [a,b] andNuansri Rakariyatham [a,b]*[a] The Center of Excellence for Innovation in Chemistry (PERCH-CIC), Commission on Higher Education,

Ministry of Education, Department of Chemistry, Faculty of Science, Chiang Mai University,Chiang Mai 50200, Thailand.

[b] Division of Biotechnology, Graduate School, Chiang Mai University, Chiang Mai 50200, Thailand.*Author for correspondence; e-mail: nuansri1@yahoo.com

Received: 14 November 2012Accepted: 19 March 2013

ABSTRACTProtein glycation and oxidative stress caused by chronic hyperglycemia are the

major factors in diabetic complications. In the attempt to search for natural remedies,ethyl acetate and ethanol extracts from twenty Thai edible and medicinal plants wereassessed in terms of their phenolic and flavonoid contents as well as their antioxidantand antiglycation activities. The highest amounts of phenolic and flavonoid compoundswere found in the ethanolic extract of the young leaves of Punica granatum followed bythose of Dimorcarpus longan and Mangifera indica, respectively. These three plant extractsalso exhibited the highest antioxidant activity. A high correlation between the antiglycationactivity and the phenolic and flavonoid contents was observed in all extracts. In addition,five ethanolic extracts−−from Tamarindus indica, Psidium guajava, Mangifera indica,Dimocarpus longan and Punica granatum young leaves−−were determined for theirconcentrations required to inhibit 50% (IC50) of either glucose or methyl glyoxal-derivedglycation. P.granatum, M.indica and P.guajava extracts showed high antiglycation activityin the BSA-glucose model, with IC50 values of 110.4, 214.4 μg/mL and 243.3 μg/mL,respectively. The IC50 values of antiglycation activity in the BSA-methylglyoxal modelof M.indica (54.1 μg/mL), P.granatum (69.1 μg/mL) and D.longan (74.2 μg/mL) werehigher than that of the standard AGE inhibitor, aminoguanidine (91.2 μg/mL). Theseresults indicated that some Thai edible and medicinal plants possessed high contents ofphenolic and flavonoid and have potential applications towards the prevention ofglycation-associated diabetic complications.

Keywords: antioxidant, antiglycation, diabetic complications

1. INTRODUCTIONAt the present, the number of diabetic

patients has rapidly increased, especially inthe Asia-Pacific region [1]. Diabetes mellitus,a disorder characterized by hyperglycemia,

is caused by insulin deficiency and/orinsulin resistance. Prolonged hyperglycemiaplays a vital role in the development of chronicdiabetic complications such as retinopathy,

106 Chiang Mai J. Sci. 2014; 41(1)

cataracts, atherosclerosis, neuropathy, impairedwounding and aging [2-4]. Numerous studieson diabetes have reported that hyperglycemiainvolves oxidative stress via glucoseautooxidation and an interruption ofthe electron transport chain. Glucoseautooxidation catalyzed by transition metalscan generate superoxide radical (O2

⋅⋅⋅⋅⋅-) andketoaldehyde; by which the superoxideradical will be converted to hydroxyl radical(OH⋅⋅⋅⋅⋅) through the Fenton reaction [5-8].The accelerated oxidation can result in celldamage and induction of specific signalingpathway, for example, the nuclear factor-κB(NF-κB) leading to pro-inflammatorycytokines [9-10]. The protein glycation is a keymolecular basis of diabetic complicationswhich results from chronic hyperglycemia.In terms of the glycation mechanism, thecarbonyl group of reducing sugars reactsnon-enzymatically with the amino group ofproteins, nucleic acids and others molecules[11-12] in order to initiate glycation (Amadorior fructosamine products). Subsequently,Amadori products undergo a series ofirreversible reactions forming highly reactivecarbonyl species (RCS), such as glyoxal,methylglyoxal and 3-deoxy-glucosone [13].Finally, these reactive carbonyls react with theamino, sulfhydryl and guanidine functionalgroups of intracellular and extracellularproteins to form the stable advancedglycation endproducts (AGEs). The reactivecarbonyl species can also be produced fromsugar glyoxidation contributing to theAGE formation [14-15]. AGE products cancross-link with long-lived proteins such ascollagen, lens crystallins, and otherbiological molecules---haemoglobin, low-density lipoprotein---leading to the alteredstructures and functions of these proteinsin vivo [16-17]. Ahmed [18] reported thatthe glycation of lens crystallins has beenconsidered as one of the major factors in

causing diabetic cataracts. Furthermore, oneof the most well-known AGEs contributingtowards diabetic atherosclerosis is glycated-low density lipoprotein (LDL) [8, 19].

In recent years, many synthetic AGEsinhibitors have been found to beeffective against AGEs formation, such asaminoguanidine (AG), the most well-knownsynthetic prodrug. However, their practicalapplications are limited because of theirtoxicity and severe side effects [12, 20].Besides, some AGEs inhibitors contribute tothe pyridoxal sequestration causing vitaminB6 deficiency in diabetic patients [11].Currently, many plant extracts and purifiedconstituents have been demonstrated as ableto suppress AGE formation. Procyanidins,extracted from cinnamon [12], as well ascaffeic acid and chlorogenic acid from matetea extracts [21], were shown to be the activeconstituents responsible for the antiglycationeffect. Additionally, several scientific reportshave revealed that the antiglycation of plantextracts can be attributed to the phenoliccompounds, which are correlated with theirfree radical scavenging activities [12, 17,22-25]. In previous studies, our teams haveinvestigated several Thai edible plantswhich contain large amounts of bioactivecompounds, particularly phenolic compoundsthat exhibit strong antioxidant activities[26-27]. However, phytochemical dataof compounds involved in alleviating orpreventing diabetic complications are stillneeded. For these reasons, this study aims toevaluate the antioxidant and antiglycationactivities of various edible and medicinal plantsincluding the correlations with their totalphenolic and flavonoid contents.

2. MATERIALS AND METHODS2.1 Plant Materials and the Preparationof Crude Extracts

Plant materials (Table 1) were purchased

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from the local market in Chiang Mai,Thailand during the period of April toAugust, 2011. The plant materials were driedat 50°C and powdered. The extraction wasprepared as described by Harborne [28]with slight modifications. Three grams ofeach sample were extracted with ethylacetate (50 mL, x3) over 1 h in a shaker at

room temperature. Ethyl acetate (EA) extractwas filtered through Whatman’s no. 1filter paper. The dried residue was thensuccessively extracted with 80% (v/v)ethanol (50 mL, x3). After filtration, the ethylacetate and ethanolic extracts (ET) werefiltered and allowed to evaporate andlyophillize.

Table 1. Edible and medicinal plants used in this study.

Allium cepaAllium ascalonicumAllium sativumGynura divaricataGymnema inodorumCoccinia grandisGynostemma pentaphyllumCoriandrum sativumApium graveolensEryngium foetidumCentella asiatica UrbanCissus quadrangularisAndrographis paniculata Wallex NeesClitoria ternateaMusa sapientumTamarindus indicaPsidium guajavaMangifera indicaDimocarpus longanPunica granatum

Common nameOnionShallotGarlic

--

ivy gourdjiaogulancoriander

chinese celeryfalse coriander

Asiatic pennywort-

king of bitterblue peabanana

tamarindguavamangolongan

pomegranate

Extracted partWhole bulbWhole bulbWhole bulb

LeavesLeavesLeavesLeavesLeavesLeavesLeavesLeavesStemsLeavesFlowersFlowers

Young leavesYoung leavesYoung leavesYoung leavesYoung leaves

2.2 Determination of Total PhenolicContent

The total phenolic content of each extractwas assessed by the Folin-Ciocalteu methodwith some modifications [26] and gallic acidwas used as the standard phenolic compound.The extract which was redissolved in ethanol(100 μL) was transferred to a test tubecontaining 7.9 mL of distilled water.The samples were mixed with 500 μL of theFolin-Ciocalteu reagent and left to react for5 min. The reaction mixture was neutralized

with the addition of 1.5 mL of 200g/Lsodium carbonate (Na2CO3), followed by2 h incubation with constant shaking.The absorbance was then measured at 760nm. The total phenolic content was expressedas mg gallic acid equivalent (GAE)/g sample.

2.3 Determination of Total FlavonoidContent

Total flavonoid content was determinedby a colorimetric method [29] with slightmodifications and quercetin was used as

108 Chiang Mai J. Sci. 2014; 41(1)

the standard flavonoid. One half mL of theextract was mixed with 2 mL of distilledwater, followed by addition of 0.15 mL of50 g/L sodium nitrite (NaNO2). After 5 minof reaction, 0.15 ml of 100 g/L aluminiumchloride (AlCl3) solution was added. Thereaction solution was mixed well andincubated at room temperature for 15 min,and the absorbance at 415 nm was measured.Total flavonoid content was expressed as μgquercetin equivalent (QE)/g sample.

2.4 In vitro Determination of AntioxidantActivity by Using DPPH RadicalScavenging Activity

1,1-Diphenyl-2-picrylhydrazyl (DPPH)radical scavenging activity of different sampleextracts was determined [27]. One mL ofDPPH radical solution (0.1 mM DPPH⋅⋅⋅⋅⋅ inmethanol) was well mixed with 3 mL of theextract and incubated for 30 min at roomtemperature. The decrease in absorbancecaused by the proton donating property ofthe active compounds was measured at517nm. The percent DPPH radical scavengingactivity was calculated using the followingformula:

DPPH radical scavenging effect (%) =[(Ao - A1)/Ao] × 100

where Ao represented the absorbance ofthe control solution and A1 represented theabsorbance of the extract solutions.

2.5 In vitro Determination ofAntiglycation Activity in BSA-glucoseModel

Inhibition of Protein glycation methodwas performed according to Matsuura et al.[30] with some modifications. The reactionmixture (2 mL) contained 800 μg/mL bovineserum albumin (BSA), 200 mM D-glucoseand with/without the extract (1 mg/mL) in

phosphate buffer (50 mM, pH 7.4) in thepresence of 0.2g/L of sodium azide (NaN3).The reaction mixture was incubated at37°C for 7 days. The fluorescence intensitywas measured at an excitation wavelength of370 nm and an emission wavelength of440 nm with a Perkin Elmer LS-50Bspectrofluorometer. Aminoguanidine (AG)(1 mg/mL) was used as a positive control.Results were expressed as percent AGEinhibition calculated using the followingequation:

Inhibition (%) = [(F0 - Ft )/F0 ] × 100

where Ft and F0 represent the fluorescenceintensity of the sample and the controlmixtures, respectively. Different extractconcentrations (50-500 μg/mL) providing50% AGE inhibition (IC50) were calculatedfrom the graph of inhibition percentageagainst the extract concentration.

2.6 In vitro Determination ofAntiglycation Activity in the BSA-methylglyoxal Model

The evaluation for the inhibition of themiddle stage of protein was performedaccording to Peng et al. [12]. Thirty microlitersof 500 mM methylglyoxal (MGO) weremixed with 300 μL of 10 mg/mL BSA inthe presence of 0.2 g/L of NaN3. TheBSA-methylglyoxal reaction mixture wasincubated at 37°C for 3 days with/withoutvarious concentrations (50-500 μg/mL) ofthe selected plant extracts. Aminoguanidine(AG) (10-100 μg/mL) was used as a positivecontrol. The fluorescence intensity wasmeasured at an excitation wavelength of370 nm and an emission wavelength of420 nm with a Perkin Elmer LS-50B.The percentage of the AGE inhibition wascalculated using the same equation as in theBSA-glucose model.

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2.7 Statistical AnalysisAll experimental results were presented

as means ± SD in triplicate. One way analysisof variance (ANOVA) was appliedfor comparison of the mean values. P value< 0.05 was regarded as significant. Thecorrelation (r) between the two variants wasanalyzed using the Pearson test. All statisticalanalyses were performed using SPSSsoftware (SPSS 17.0 for windows; SPSS Inc.,Chicago).

3. RESULTS AND DISCUSSION3.1 Total Phenolic and Total FlavonoidContents

This study involved twenty Thai edibleand medicinal plants that are regularlyconsumed and applied in traditional formsof medicines in Thailand. Total phenolicand flavonoid contents, antioxidant andantiglycation activities of the extracts ofthese plants were determined. The phenoliccontent was determined by the Folin-Ciocalteu method and expressed as mg gallicacid equivalent (GAE) per g of dry sample.Table 2 shows the content of phenoliccompounds in various plant extracts rangingfrom 0.02 to 3.13 mg/g sample. Significantdifferences (p<0.05) were found in all of

these amounts. High amounts of phenoliccompounds were found in ethanolic (ET)fractions of P.granatum (3.13 mg/g), D.longan(1.68 mg/g), M.indica (1.51 mg/g) andthe ethyl acetate (EA) fractions of D.longan(1.20 mg/g) and P.granatum (1.11 mg/g),respectively. The total flavonoid content in eachplant extract was also determined using acolorimetric method and reported as the μgquercetin equivalent (QE) per g of driedsample. The results showed that the contentof the flavonoid range from 1.39 to 237 mg/g. Significantly, the highest amount offlavonoids was shown (p<0.05) in the ETfraction of P.granatum (237 mg/g) followedby D.longan (160 mg/g), M.indica (151 mg/g)and EA fractions of D.longan (136 mg/g) andM.indica (135 mg/g). It could be observedthat the young leaf extract of P.granatumexhibited the highest amounts of totalphenolics and flavonoids. Moreover, theethanolic extracts of P.granatum, D.longanand M.indica contained higher amounts ofphenolic compounds and flavonoids thantheir ethyl acetate (EA) extracts. The resultscorrespond with Harborne’s work [28]which reported that alcohol is a suitableorganic solvent for phenolic and flavonoidextraction.

Table 2. Total phenolic and total flavonoid contents in the ethyl acetate (EA) and ethanolic(ET) extracts of edible and medicinal plants.

Plants

A.cepaA.ascalonicumA.sativumG.divaricataG.inodorumC.grandisG.pentaphyllumC.sativumA.graveolensE.foetidum

Total phenolic content(mg GAE/g)

Total flavonoid content(μg QE/g )

EA extract0.04±0.00.04±0.0

ND0.16±0.00.08±0.00.07±0.00.16±0.00.05±0.00.03±0.00.05±0.0

ET extract0.04±0.00.10±0.00.02±0.00.40±0.00.38±0.00.18±0.00.13±0.00.09±0.00.14±0.00.07±0.0

EA extract2.96±0.23.82±1.02.96±0.448.3±6.550.4±1.468.4±4.349.0±5.122.2±0.827.8±1.419.0±1.0

ET extract8.49±0.26.16±0.21.39±0.078.6±7.2d

159±6.4b,c

51.3±4.926.3±3.215.4±0.440.5±0.79.26±2.0

110 Chiang Mai J. Sci. 2014; 41(1)

3.2 Antioxidant Activity1,1-Diphenyl-2-picrylhydrazyl (DPPH) is

a stable free radical which is frequently usedin measuring antioxidant activities due to thefollowing strengths: its direct measurementof inhibition, simplicity and quick analysis[31]. Both solvent extracts were assessedfor the antioxidant activity using the DPPHradical method and expressed as percentDPPH⋅⋅⋅⋅⋅ inhibition (Table 3). Significantdifferences (p<0.05) were found in theantioxidant activity of the plant extracts.Strong antioxidant activity was found inboth EA and ET fractions, especially thoseof P.granatum (94.1% and 95.7%), D.longan(94.3% and 95.5%), M.indica (93.9% and94.8%) and P.guajava (94.6% and 93.5%).The strong antioxidant activities of theseplant extracts are possible a result of the highcontents of phenolics and flavonoids whichhave been shown to be highly antioxidant[32-35]. Correlations between the antioxidantactivity and the phenolic and flavonoidcontents were investigated (Table 4).There were strong correlations (r ET = 0.779and r EA = 0.866, p<0.05) between antioxidant

activity and phenolic content for allethanolic (ET) and ethyl acetate (EA) extracts.This relationship indicated that the freeradical scavenging activity of the plant extractswas associated with the phenolic compounds.This result agreed with previous studiesreporting that phenolic compounds in variousplant extracts are the major constituents withfree radical scavenging property to donate ahydrogen atom from their phenolic hydroxylgroups [25, 36-39]. This is similar to the resultspresented in Thitilertdecha’s research [27],which suggested that the antioxidant activitiesof rambutan extracts were remarkably relatedto their phenolic contents. Additionally, highcorrelation (rET = 0.796) was observedbetween antioxidant activity and the flavonoidcontent in the ethanolic fractions of all plants.Moderate correlation (rEA = 0.583) wasobserved for their ethyl acetate (EA) fractions.The findings showed that ethanol was a goodsolvent for the extraction of antioxidantsubstances. These correlations suggest that thestrong antioxidant activity present in theseplants possibly come from the phenoliccompounds.

Table 2. (Continue)

- Values are expressed as means ± SD.- a-d Means in the column followed by different letters are significantly different (p<0.05)- ND = not determined

Plants

C.asiatica UrbanC.quadrangularisA.paniculata Wallex NeesC.ternateaM.sapientumT.indicaP.guajavaM.indicaD.longanP.granatum

Total phenolic content(mg GAE/g)

Total flavonoid content(μg QE/g )

EA extract0.04±0.00.03±0.00.03±0.00.12±0.00.03±0.00.29±0.0d

0.14±0.00.74±0.0c

1.20±0.1a

1.11±0.1b

ET extract0.16±0.00.04±0.00.05±0.00.26±0.00.11±0.00.15±0.00.69±0.1d

1.51±0.0c

1.68±0.2b

3.13±0.1a

EA extract19.9±1.718.2±1.4118±0.6c

50.3±1.69.46±0.9130±3.9b

93.6±2.6d

135±4.6a,b

136±5.5a

33.2±1.9

ET extract34.5±5.15.54±1.013.5±0.576.6±2.88.67±1.369.3±1.773.4±5.3151±4.7c

160±2.1b

237±5.5a

Chiang Mai J. Sci. 2014; 41(1) 111

Table 3. Antioxidant and antiglycation activities of EA and ET plant extracts.

Plants

A.cepaA.ascalonicumA.sativumG.divaricataG.inodorumC.grandisG.pentaphyllumC.sativumA.graveolensE.foetidumC.asiatica UrbanC.quadrangularisA.paniculata Wallex NeesC.ternateaM.sapientumT.indicaP.guajavaM.indicaD.longanP.granatum

EA extract1.73±0.42.91±0.3

ND31.3±0.187.9±0.7b

ND11.0±0.66.64±0.11.91±0.18.82±0.49.64±0.34.00±0.20.64±0.112.6±1.06.12±0.123.4±1.894.6±0.2a

93.9±0.5a

94.3±0.1a

94.1±0.3a

ET extract3.34±0.83.04±0.8

ND60.7±3.4b

53.3±1.335.2±2.7

ND28.6±0.418.7±0.68.87±0.559.7±4.8b

6.45±1.711.5±0.428.3±0.515.8±3.117.6±1.193.5±0.9a

94.8±0.2a

95.5±0.2a

95.7±0.2a

EA extract58.1±6.649.8±1.77.19±1.4

97.6±0.7b,c

97.6±0.1b,c

99.6±0.3a

98.5±0.5a,b

82.3±2.988.0±0.681.0±1.182.2±4.780.6±0.689.6±0.6d

98.4±0.2a,b

45.7±1.399.4±0.4a

99.8±0.1a

99.8±0.1a

99.9±0.0a

99.8±0.0a

ET extract71.7±0.478.7±1.38.06±1.891.6±0.7d

99.5±0.2a

95.9±2.1c

96.3±0.2a

85.7±2.4d

99.6±0.2a

61.8±1.695.6±1.8c

56.3±3.196.5±0.9b,c

99.9±0.4a

70.7±0.796.2±0.1c

99.8±0.0a

99.9±0.0a

99.8±0.0a

99.0±0.0a

DPPH radical scavenging activity(% Inhibition)

Antiglycation activity(% Inhibition)

- Values are expressed as means ± SD.- a-d Means in the column followed by different letters are significantly different (p<0.05)- ND = not determined

Table 4. The Pearson correlation coefficient of total phenolic and flavonoid contents withantioxidant and antiglycation activities of plant extracts.

Phenolic contentFlavonoid content

CorrelationAntioxidant activity Antiglycation activity

EA extract0.8660.583

ET extract0.7790.796

EA extract0.8490.879

ET extract0.8640.796

112 Chiang Mai J. Sci. 2014; 41(1)

3.3 Antiglycation ActivityThe antiglycation activity of plant extracts

was evaluated for the inhibition of advancedglycation endproducts(AGEs) formationbased on the BSA/glucose system. The resultsindicated that sixteen plants exhibited potentialantiglycation activity (> 80% inhibition)(Table 3). Similarly to the antioxidant activity,strong antiglycation activity was foundstatistically in both the EA and ET extracts(p<0.05), especially those of T.indica (99.4%and 96.2%), P.guajava (99.8% and 99.8%),M.indica (99.8% and 99.9%), D.longan (99.9%and 99.8%) and P.granatum (99.8% and 99.0%).This correlation was also evaluated (Table 4).Data revealed substantial correlation of theantiglycation activity of the plant extractswith the phenolic(rET = 0.864 and rEA = 0.849)and flavonoid contents (rET = 0.796 and rEA=0.879, p<0.05). These results are noteworthynot only because the phenolic and flavonoidcontents of these extracts show a positiverelationship with the antioxidant activity,but also with the antiglycation property.Many published studies have suggested thatthe phenolic and flavonoid compounds inplant extracts are responsible for theantiglycation activity [12, 17, 22-25]. Forexample, it has been reported that cinnamonbark extract could inhibit the formation ofAGEs which is mainly attributed to its phenolicconstituents, such as catechin, epicatechin, andprocyanidin B2.

As a result of their strong antioxidantand antiglycation activities, the ethanolic youngleaf extracts of 5 plants (T.indica, P.guajava,M.indica, D.longan and P.granatum) were selectedfor further investigation of their antiglycationactivity against glucose and methylglyoxal

models. In the BSA-glucose model, it wasfound that P.granatum (IC50= 110 μg/mL) hadsignificantly stronger inhibitory activity thanM.indica and P.guajava extract (IC50= 214 μg/mL and 243 μg/mL), respectively (p<0.05).However, these extracts were found to be lesseffective than aminoguanidine (IC50= 50.2 μg/mL) which is the positive control.

The inhibitory effect of the selected plantextracts on a BSA-methylglyoxal (MGO)model was also reported (Figure 1(B)).BSA-methylglyoxal model represented themiddle stage of protein glycation in whichsugar is oxidized to α-dicarbonyl compoundssuch as methylglyoxal, glyoxal and 3-deoxyglucosome, which are more reactive inreacting with amino group of protein leadingto AGE formation [17]. The IC50 valuesshowed that M.indica extract (54.1 μg/mL) hadstatistically higher antiglycation activity thanP.granatum and D.longan extract (69.1 μg/mLand 74.2 μg/mL, respectively) (p<0.05).In addition, these results indicated that theethanolic extracts of M.indica, P.granatum andD.longan had significantly higher inhibitoryactivity-against AGE formation induced bymethylglyoxal than aminoguanidine (IC50=91.2 μg/mL) (p<0.05). This is likely the resultof the high contents of phenolic andflavonoid compounds in these plant extracts.It has been that reported P.granatum leavescontain high amounts of tannins and phenoliccompounds [40], whereas Gil [41] hasreported the presence of phenolic apigeninand luteolin glycosides in pomegranateleaves [41]. This fact suggests that P.granatumleave extracts were responsible for theinhibition of AGE formation in the BSA-methylglyoxal model.

Chiang Mai J. Sci. 2014; 41(1) 113

These results were consistent with aprevious study [12] on the correlation ofthe antiglycation activities and the totalphenolic contents of bean extracts.Interestingly, the young leaf extracts ofM.indica, P.granatum and D.longa displayedsignificantly greater inhibitory activities thanamionguanidine aminoguanidine in theBSA-methylglyoxal model which is likelyone of their principle mechanisms of theinhibition in the AGE formation [39]. Theprevious study demonstrated that severalphenolic compounds, such as catechin,

epicatechin, and procyanidin B2, andphenol polymers, identified from thesubfractions of the aqueous cinnamonextract displayed significant inhibitoryeffects on the formation of AGEs [12]. Theirantiglycation activities were related to theirtrapping abilities of the reactive carbonylspecies, such as methylglyoxal (MGO), anintermediate reactive carbonyl of AGEformation, of which proanthocyanidins(condensed tannins) were shown to be moreeffective scavenging reactive carbonylspecies than other isolated compounds.

Figure 1. Inhibitory effect of the selected plant extracts (A) on the formation of glycation inBSA- glucose model (B) on the formation of glycation in BSA- methylglyoxal model.Aminoguanidine was used as a positive control. Different superscripts indicate statisticallysignificant differences (p<0.05).

114 Chiang Mai J. Sci. 2014; 41(1)

Besides, Wu [24] has reported that flavonoids,especially, luteolin and rutin, developed a moresignificant inhibitory effect on methylglyoxal-medicated protein modification. While, rutin,quercetin and kaempferol were reported tobe effective at the last stage of proteinglycation in the BSA-glucose model.

4. CONCLUSIONSThe present study shows an evaluation

of the antiglycation and antioxidantproperties present in the extracts of 20edible and medicinal plants. Most of theethanolic extracts from the plants containedhigher phenolics and flavonoids than theirethyl acetate extracts. In addition, thecorrelation was found between thephytochemical compositions of the extractsand their antiglycation and antioxidantactivities. Among these extracts, the ethanolicextracts of T.indica, P.guajava, M.indica, D.longanand P.granatum young leaves exhibited bothstrong antiglycation and strong antioxidantactivities in vitro. The ethanolic extracts ofP.granatum, D.longan and M.indica showedhigher antiglycation activity in the BSA-methylglyoxal model than the positive control,aminoguanidine. Therefore, it is possible thatthese edible and medicinal plants mightprovide effective natural sources of treatmentagainst the glycation reaction and oxidativestress found in diabetic patients.

ACKNOWLEDGEMENTThe authors are grateful to the Center

of Excellence for Innovation in Chemistry(PERCH-CIC), the Commission on HigherEducation, Ministry of Education,Department of Chemistry, Faculty of Scienceand the Graduate School, Chiang MaiUniversity, Chiang Mai, Thailand for thefinancial support of this research.

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