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BMC Complementary and Alternative Medicine

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In vitro antioxidant and, α-glucosidase inhibitory activities and comprehensive metabolite profiling of methanol extract and its fractions from Clinacanthus nutans

  • Md. Ariful Alam1,
  • I.S.M. Zaidul1Email author,
  • Kashif Ghafoor2,
  • F. Sahena3,
  • M. A. Hakim4,
  • M.Y. Rafii4,
  • H.M. Abir5,
  • M.F. Bostanudin6,
  • V Perumal1 and
  • A. Khatib1
BMC Complementary and Alternative MedicineBMC series – open, inclusive and trusted201717:181

https://doi.org/10.1186/s12906-017-1684-5

Received: 25 August 2016

Accepted: 15 March 2017

Published: 31 March 2017

Abstract

Background

This study was aimed to evaluate antioxidant and α-glucosidase inhibitory activity, with a subsequent analysis of total phenolic and total flavonoid content of methanol extract and its derived fractions from Clinacanthus nutans accompanied by comprehensive phytochemical profiling.

Methods

Liquid-liquid partition chromatography was used to separate methanolic extract to get hexane, ethyl acetate, butanol and residual aqueous fractions. The total antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazy (DPPH) radical scavenging and ferric reducing antioxidant power assay (FRAP). The antidiabetic activity of methanol extract and its consequent fractions were examined by α-glucosidase inhibitory bioassay. The chemical profiling was carried out by gas chromatography coupled with quadrupole time-of-flight mass spectrometry (GC Q-TOF MS).

Results

The total yield for methanol extraction was (12.63 ± 0.98) % (w/w) and highest fractionated value found for residual aqueous (52.25 ± 1.01) % (w/w) as compared to the other fractions. Significant DPPH free radical scavenging activity was found for methanolic extract (63.07 ± 0.11) % and (79.98 ± 0.31) % for ethyl acetate fraction among all the fractions evaluated. Methanol extract was the most prominent in case of FRAP (141.89 ± 0.87 μg AAE/g) whereas most effective reducing power observed in ethyl acetate fraction (133.6 ± 0.2987 μg AAE/g). The results also indicated a substantial α-glucosidase inhibitory activity for butanol fraction (72.16 ± 1.0) % and ethyl acetate fraction (70.76 ± 0.49) %. The statistical analysis revealed that total phenolic and total flavonoid content of the samples had the significant (p < 0.05) impact on DPPH free radical scavenging and α-glucosidase inhibitory activity.

Conclusion

Current results proposed the therapeutic potential of Clinacanthus nutans, especially ethyl acetate and butanol fraction as chemotherapeutic agent against oxidative related cellular damages and control the postprandial hyperglycemia. The phytochemical investigation showed the existence of active constituents in Clinacanthus nutans extract and fractions.

Keywords

Clinacanthus nutansAntioxidant activityα-glucosidase inhibitory activityReducing powerTotal phenolicTotal flavonoidActivity phytochemical profiling

Background

The chemotherapeutic uses of medicinal plants are a result of ancient people’s belief in their protective effects. Many plants have abundant active secondary metabolites that exhibit certain pharmacological effects in humans. Thus plant based traditional remedies have been developed from these chemotherapeutic agents to prevent certain ailments [1]. These active constituents are varied in their chemical structure, chemical composition, protective activity, and mode of action, hence, medicinal herbs have been used in traditional medicine. Antioxidant-rich natural products in the form of herbal formulations are able to interrupt cellular damage, mainly through the mechanism of free radical scavenging [2, 3]. Free radical causes oxidative stress related-complications in the human body owing to a physiological imbalance of free radicals and antioxidants, which is related to the impairment of primary metabolites, and consequently result in a number of health impediments [4, 5]. Phenolic and flavonoid compounds are the most common antioxidant metabolites in plants and include saponins, alkaloids, coumarins, tannins, lignin, terpenoids, stilbenes, quinones, amines and betalains [6, 7]. These compounds are important active natural products, which possess various biological actions, such as anti-diabetic, anti-inflammatory, hepatoprotective, anti-allergic, anti-carcinogenic, anti-thrombotic, anti-microbial activities, anti-atherosclerotic, anti-tumor and anti-mutagenic activity [8, 9].

Diabetes is a pandemic endocrine disorder characterized by hyperglycemia resulting from insulin resistance or overall insulin dysfunction [10, 11]. Modern synthetic hypoglycemic agents can cause side effects, are costly and decline in efficiency with long term uses [12, 13]. The inhibition of the α-glucosidase enzyme can control the intestinal carbohydrate metabolism by retarding the cleavage of polysaccharides to glucose [14, 15]. Therefore, the best strategy is to reduce the postprandial upsurge of blood glucose level and prevent late diabetic complications. Thus natural product based α-glucosidase inhibitors are the key targets to identify new compounds for the therapeutic management of diabetes [16]. The extensive literature reported more than four hundred natural products isolated from various herbal plants that exhibited digestive enzyme inhibitory activity [17], a majority of the compounds were flavonoid, terpene, and phenylpropanoid ring containing compounds [17].

Clinacanthus nutans Lindau is a medicinal plant from Acantheceae family widely distributed throughout tropical Asia. For a long time, this shrub has been used to prevent skin infections, insect bites and lesions caused by the herpes simplex and varicella-zoster viruses [18, 19]. Many beneficial effects of this plant have been reported, including antidiabetic, antioxidant, anti-proliferative, immunomodulatory, wound healing, anti-inflammatory, analgesic activities and anti-viral activities [2023]. However, its efficacy is yet to be proven scientifically and more research needs to be carried out, especially with regard to the antidiabetic effects of this plant. Our analysis of the current literature ascertained that- the free radical scavenging activity, ferric reducing antioxidant power, and α-glucosidase inhibitory activity of the methanol extract and its different polar, non-polar fractions from C. nutans have not been previously determined. Moreover, the complete phytochemical profile of this plant remains unestablished. Therefore, this study aimed to investigate the in vitro antioxidant and α-glucosidase inhibitory activities of methanol extract and its different fractions from C. nutans. Our research also identified the various chemical constituents of the extract and fractions by GC Q-TOF MS, in addition to bioactivity correlation.

Methods

Sample collection and preparation

The stem of C. nutans was obtained from TKC Herbal Nursery SDN BHD, Pusat Pertanian Pantai Baru, Pantai Negeri Sembilan, Malaysia in September 2014. The plant material was identified by Dr. Alfi Khatib, Associate Professor, Department of Pharmaceutical Chemistry, International Islamic University, Kuantan, Pahang, Malaysia. A voucher specimen (PIIUM 0238–1) was deposited in the herbarium of the Faculty of Pharmacy, International Islamic University, Kuantan, Pahang, Malaysia. The C. nutans stem was dried, in an airy place under shade. When dry the samples were ground in a cutting mill (FRITSCH, Pulverisette 19, Germany), sieved, and fractionated by a vibratory sieve shaker (AS 700, BASIC, RETSCH, Germany) to obtain fine particles. The extracts and fractions were freeze dried before analysis of the pharmacological activity and chemical profile (Alpha 1–2 LD plus CHRIST, Freeze dryer, UK).

Chemicals

Ethanol (99.5%, analytical grade), Folin-Ciocalteu phenol reagent, potassium acetate, aluminum chloride, sodium carbonate, methanol, hexane, ethyl acetate and butanol were obtained from Merck Germany (Darmstadt, Germany). α-Glucosidase enzyme (Saccharomyces cerevisiae) and 4-nitrophenyl β-D-glucopyranoside substrate were obtained from the Sigma Chemical Co (St. Louis, Mo., U. S. A.). 2, 2-Diphenyl-1-picrylhydrazyl (DPPH), methoxyamine hydrochloride, pyridine, N-Methyl-N-(trimethylsilyl) trifluoroacetamide, quercetin (≥95% HPLC, solid), and rutin hydrate (≥94% HPLC, powder) were obtained from Malaysia Sigma-Aldrich (M), Sdn. Bhd. Kuala Lumpur, Malaysia. All other chemicals used were of analytical grade.

Extraction and fractionation

The solvent extraction of the air-dried stem of C. nutans was performed by maceration technique using methanol as the initial solvent in an Erlenmeyer flask. After maceration, the mixture was sonicated for 15 min, and set aside for 24 h, filtered, and evaporated in a rotary evaporator at 40 °C under reduced pressure. The extract was freeze dried and stored ready for pharmacological analysis and fractionation.

The fractionation of dried methanolic extract was achieved by liquid-liquid partition chromatography in a separating funnel using hexane, methanol, and water (13:2:5) with a final volume of 2 L, based on the amount of extract. After vigorous shaking, the mixture was set aside until two layers were formed. To obtain the hexane fraction, the was separated and then concentrated in rotary evaporator at 40 °C under reduced pressure. To obtain the ethyl acetate fraction, the remaining fraction in the separating funnel was added to ethyl acetate and the evaporation procedure was repeated. Similarly, butanol was added to obtain the butanol fraction; the remaining material in the separating funnel was considered as the residual aqueous fraction. The residual solvent was removed from the extract and fractions by freeze drying. The methanol extract and its four fractions were then freeze-dried and stored at −80 °C freezer until use.

Total phenolic content

The total phenolic content (TPC) of the methanol extract and the derived fractions from C. nutans were determined spectrophotometrically according to the Folin-Ciocalteu method [24]. The reaction mixture was prepared by mixing 20 μL of the extract solution (at 5 mg/mL in DMSO), 100 μL Folin-Ciocalteu reagent (1 mL of Folin-Ciocalteu reagent in 9 mL of distilled water) and 80 μL 7.5% Na2CO3 solution in deionized water. The solution was incubated for 30 min in a dark place at 26.8 °C and the absorbance was measured at 765 nm. The total phenolic concentration was calculated from a gallic acid (GA) calibration curve 10–100 mg/L; y = 0.0005x + 0.0779, R2 = 0.9943. Data were expressed as gallic acid equivalent/g of extract averaged from three measurements.

Total flavonoid content

The total flavonoid content (TFC) of the C. nutans extract and fractions were estimated according to the aluminum chloride spectrophotometric method based on the formation of aluminum-flavonoid complexes [25]. To prepare the reaction solutions, approximately 2 mL extract solution (0.3 mg in 1 mL of methanol), 0.1 mL aluminum chloride hexahydrate solution (10% aqueous AlCl3 solution), 0.1 mL 1 M potassium acetate and 2.8 mL of deionized water were mixed together. The mixture was shaken and incubated at 26.8 °C for 10 min. After incubation, the solution was subjected to spectral analysis at 415 nm. A standard curve was constructed of the absorbance of rutin between 0.005 and 0.1 mg/mL and the total flavonoid content calculated as mg rutin equivalent per g dry extract. The absorbance at 415 nm = 14.171x + 0.0461, R2 = 0.9991.

DPPH free radical scavenging activity

The free radical scavenging capacity of the methanol extract and each derived fractions from C. nutans were analyzed by using a 96-well microplate and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) as the free radical source [26]. For sample preparation, 5 mg freeze dried sample was added to 1 mL of DMSO, which was vortexed and sonicated to produce a homogenized solution. The sample solution was transferred (100 μL) to a 96well plate and 50 μL of this sample was diluted with 50 μL DMSO. Then, 100 μL DPPH (5.9 mg in 100 mL 100% ethanol) was added to each of dilutions, suspended and incubated in a dark place for 30 min. Blank samples were prepared following the same procedure, but used using 100 μL 100% ethanol instead of DPPH. A reagent blank which contained 50 μL DMSO and 100 μL DPPH, but no sample was, also subjected to the sample preparation process. Quercetin was used as a positive control to observe the reaction of inhibition. The absorbance was recorded at 517 nm and the percentage inhibition was calculated by using the following equation-
$$ \% Inhibition=\frac{R_b-\left({S}_a- B{S}_a\right)}{R_b}\times 100 $$
(1)

R b  = Reagent blank absorbance

S a  = Sample absorbance

BS a  = Blank sample absorbance

Ferric reducing antioxidant power assay

The total antioxidant capacity of methanol extract and other derived fractions were examined by using the FRAP method adapted by Szd lowska Czerniak et al., with some modifications [27]. FRAP reagent (10 mM TPTZ solution) (2.5 mL) in 40 mM HCl, 20 mM FeCl3 (2.5 mL), and 0.1 M acetate buffer pH 3.6 (25 mL) was freshly prepared and incubated for 10 min at 37 °C in an oven. Then 20 μL of different concentration (0%, 20%, 40%, 60%, 80% and 100%) of methanol extract and fractions of C. nutans and ascorbic acid (standard) and 40 μL FRAP reagent were added to 140 μL of distilled water in a 96 wells plate. The samples were stored at 26.8 °C for 20 min in dark and the blue color was quantified through measurement of the absorbance at 593 nm relative to a reagent blank (40 μL FRAP reagents and 160 μL distilled water) using microplate reader. Ascorbic acid was used as a standard compound to create a calibration curve. The total antioxidant capacity of the samples was expressed in ascorbic acid equivalents as (AAE) in μg/g of dried sample.

α-Glucosidase inhibitory assay

The α-glucosidase inhibitory activity of the C. nutans extract and each of the fractions from liquid-liquid partition chromatography was determined following the method by Collins et al., [28]. In this assay, the formation of p-nitrophenol that resulted from the cleavage of p-nitrophenyl-α-D-glucopyranose was estimated for the evaluation of α-glucosidase inhibitory activity. To prepare the stock solution, 5 mg of the extract and fractions were dissolved in 1 mL of DMSO. Additionally, 5 mg quercetin was dissolved in 1 mL of DMSO to form a positive control [29]. For the dilution, 10 μL prepared stock solutions were added to 115 μL 30 mM phosphate buffer (pH 6.5). The enzyme (α-glucosidase type 1 from Saccharomyces cerevisiae) (Sigma G5003) solution was prepared using 1 mg enzyme with 13.9 mL 50 mM phosphate buffer (pH 6.5). The substrate containing 3 mg p-nitrophenyl-α- D-glucopyranose (Sigma-Aldrich, N1377-1G) was dissolved in 10 mL of a 50 mM phosphate buffer (pH 6.5) and incubated at 26.8 °C for 15 min. The diluted samples were mixed with 15 μL of enzyme and 75 μL of substrate in the microplate, and incubated for 15 min at 26.8 °C. A blank sample, positive control, negative control, and blank positive control were prepared according to the mentioned method. Glycine solution was prepared as a reaction-stopping reagent by the dissolution of 15 g with 100 mL of cold water (pH 10). The optical densities (ODs) were read at 405 nm in a multi-detection micro-plate reader (Infinite M200, Tecan, Switzerland) [30]. The inhibitory activity was calculated according to the following equation
$$ \textcolor[rgb]{0.07450980392156862,0.0784313725490196,0.07450980392156862}{\kern0.75em }\% Inhibition\ of\ sample=\frac{a_n-{a}_s}{a_n}\times 100 $$
(2)
where a n  = negative control and a p  = (Sample Absorbance-Blank Sample Absorbance).

Derivatization for GC Q-TOF MS analysis

Derivatization of the methanol extract and the derived polar-nonpolar fractions from C. nutans were performed by methoxyamination and trimethylsilylation (TMS) for GC Q-TOF MS chemical profiling according to the method mentioned by Robinson et al. [31]. The methoxyamine hydrochloride was dissolved in pyridine to produce a concentration of 20 mg/mL. Exactly 2.5 mg of sample was mixed with 50 μL pyridine in a 2-mL centrifuge tube and sonicated for 10 min at 30 °C. Then, 100 μL methoxyamine hydrochloride (20 mg/mL in pyridine) was added to the sample solution and incubated for 2 h at 60 °C. After the incubation 300 μL MSTFA (N-Methyl-N-(trimethylsilyl) trifluoroacetamide) was mixed and incubated for a further 30 min at 60 °C. The prepared sample was stored overnight at 23 °C for the completion of chemical reaction. The mixture was then filtered by syringe filter for the separation of any solid particles.

GC Q-TOF MS determination

The GC-MS Agilent system of model 7200 accurate-mass GC QTOF equipped with a 7890A GC system connected to a detector quadrupole time of flight mass spectrometer was used to acquire mass spectral data. Exactly, 1 μL of derivatized sample was injected into the inlet of the Agilent GC column (J &W Scientific, Folsom, CA, USA) model, HP-5MS; dimensions 30 m × 0.25 mm × 0.25 μm), with 50:1 split mode and ratio. The injector temperature was maintained at 280 °C and the detector was maintained at 290 °C. The oven temperature profile was as follows: an increase from set to 70 to 135 °C with a 2 °C/min, hold for 10 min, an increase from 135 to 220 °C with 4 °C/min, hold for 10 min, an increase from 220 to 270 °C at 3.5 °C/min and then a final hold for 20 min. Helium was used as carrier gas at a constant flow rate of 1.9 mL/min. GC Q-TOF MS, and Auto MS-MS data were processed with Mass Hunter qualitative analysis software (v. B.06.00 SP1, Agilent Technologies Inc., USA). Agilent Mass Profiler Professional (MPP) software was used to eliminate the molecular features produce from background by deduction of data from the blank spectrum. The mass spectral deconvolution was performed by Mass Hunter Unknown Analysis Software (version B.06.00) which automatically detected peaks and deconvoluted the spectra using model ion traces.

Statistical analysis

The results were calculated as the mean ± SD from three separate experiments (n = 3). The IC50 values of the extract and fractions for DPPH free radical scavenging and α-glucosidase inhibitory activity were determined by Graph Pad Prism 5 software. The significant differences between the means were established by ANOVA with Bonferroni post tests and Newman-Keuls multiple comparison test. Values of P < 0.05 were considered statistically significant.

Results

Yield

The average yield of methanol extract from solvent extraction by the maceration technique was found to be 12.63 ± 0.98 (as % w/w of C. nutans on a dry weight basis). The fractionation of methanolic extract produced the hexane, ethyl acetate, butanol, and residual aqueous fractions with average yields of 29.08 ± 0.070, 1.23 ± 0.03, 8.558 ± 0.0305 and 52.25 ± 1.013 (as the percentage of total methanol extract; the white precipitation from the butanol fraction was excluded from this study), respectively (Table 1)
Table 1

Total yield, total phenolic content and total flavonoid content of methanol extract and its different fractions

 

Yield%

TPC (mg GAE/g)

TFC (mg RE/g)

Methanol

12.63 ± 0.92

7.54 ± 0.52

16.83 ± 0.85

Hexane

29.08 ± 0.70

13.31 ± 0.36

22.78 ± 0.10

Ethyl Acetate

1.23 ± 0.03

17.403 ± 0.25

13.29 ± 0.04

Butanol

8.558 ± 0.30

4.105 ± 0.75

10.04 ± 0.56

R. Aqueous

52.25 ± 1.01

1.32 ± 0.02

9.53 ± 0.088

Each value in the table is represented as mean ± SD (n = 3)

.

Total phenolic content (TPC) and total flavonoid content (TFC)

The total phenolic content of the extract and all the fractions were, reported as gallic acid equivalents per g of dried sample. The TPC of the methanol extract was 7.54 ± 0.02 mg GAE/g, whereas the ethyl acetate fraction had the highest TPC (17.403 ± 0.025 mg GAE/g) among all the fractions. The methanolic extract had a TFC of 16.83 ± 0.085 mg Rutin Equivalent/g of dried materials and the hexane fraction contained the maximum TFC (22.78 ± 0.01 mg RE/g) compared with all other fractions. The TPC and TFC of methanolic extract and the different fractions are presented in Table 1.

DPPH free radical scavenging activity

The DPPH free radical scavenging is a commonly used method to assess antioxidant activity in plant samples. The antioxidant activity of the samples was examined at six different concentrations (31.25, 62.5, 125, 250, 500 and 1000 μg/mL). In this study, all the samples dose- dependently scavenged DPPH radicals, except for the residual aqueous fraction. The ethyl acetate fraction showed the highest DPPH scavenging activity, at 79.98 ± 0.31% (IC50: 0.2691 mg/mL) whereas the lowest scavenging ability was observed in the methanol extract, at 63.07 ± 0.118% (IC50: 0.3302 mg/mL). The antioxidant activity of the methanol extract and its derived fractions was ranked as follows: ethyl acetate > butanol > hexane > methanol > residual aqueous fraction. The DPPH free radical scavenging activity at different concentration of methanol extract and fractions is shown in Fig. 1.
Fig. 1

DPPH Free Radical Scavenging Activity at Different Concentration of Methanol Extract and its Fractions. The IC50 values of Methanol Extract and its Hexane, EoAC, BuOH, R. aqueous Fractions are 0.3302 mg/ml, 0.1527 mg/ml, 0.2691 mg/ml, 0.2517 mg/ml, 0.585 mg/ml and 0.1927 mg/ml, respectively. Legends: MeOH, Hexane, EoAC, BuOH, R. Aqueous, Quercitin

Ferric reducing antioxidant power assay

The donation of electrons by the reduction of ferric cyanide complex in the ferrous form specifies the reducing capacity of experimental samples. Essentially, this method considers the total antioxidant capacity of a sample through the oxidation-reduction potential. The methanol extract and ethyl acetate fraction exhibited the highest FRAP values of 141.89 ± 0.874 and 133.6 ± 0.29 AAE μg/g respectively (Table 2). The reducing power of the extract and fractions was ranked as follows: methanol > ethyl acetate > butanol > hexane > residual aqueous.
Table 2

DPPH scavenging activity, ferric reducing antioxidant power and α-Glucosidase inhibitory activity of methanol extract and its different fractions

 

DPPH%

FRAP (μg AAE/g)

AGI%

Methanol

63.07 ± 0.11a

141.89 ± 3.87**/*

58.21 ± 0.8a

Hexane

66.35 ± 0.09b

130.56 ± 2.43*/*

69.94 ± 0.81b

Ethyl Acetate

79.98 ± 0.31c

133.6 ± 3.29*/*

70.76 ± 0.49c

Butanol

78.47 ± 0.26c

132.76 ± 3.72**/*

72.16 ± 1.12d

R. Aqueous

28.32 ± 0.27d

12.11 ± 0.31ns

41.86 ± 0.37e

Each value in the table is represented as mean ± SD (n = 3). Means within each column with different letters (a-e) differ significantly (p < 0.05) according to ANOVA with Newman-keuls multiple comparison test when compared with standard. For FRAP compared total phenolic and total flavonoid content where **P < 0.01, *P < 0.05, ns P > 0.05 according to ANOVA with Bonferroni posttests

α-Glucosidase inhibitory activity

The α-glucosidase inhibitory activity of the methanol extract and the fractions was assessed at six different dilutions (6.25, 12.5, 25, 50, 100 and 200 μg/mL) (Fig. 2). The highest potential α-glucosidase inhibitory activities were found in the butanol and ethyl acetate fractions with inhibition of 72.16 ± 1.0041% (IC50: 37.47 μg/mL) and 70.76 ± 0.4974% (IC50: 53.69 μg/mL) (Table 2). The efficacy of the α-glucosidase inhibition of the extract and various fractions was ranked as follows: butanol > ethyl acetate > hexane > methanol > residual aqueous. The standard quercetin was used as positive control and showed a maximum α-glucosidase inhibitory activity of 94.63 ± 1.21% (IC50: 38.54 μg/mL).
Fig. 2

α-Glucosidase Inhibitory Activity at Different Concentration of Methanol Extract and its Fractions. The IC50 values of Methanol Extract and its Hexane, EoAC, BuOH, R. aqueous Fractions are 0.06139 mg/ml, 0.04457 mg/ml, 0.05369 mg/ml, 0.3747 mg/ml, 0.0635 mg/ml and 0.03854 mg/ml, Respectively. Legends: MeOH, Hexane, EoAC, BuOH, R. Aqueous, Quercitin

GC Q-TOF MS analysis

GC Q-TOF MS analysis was conducted to identify the phytoconstituents of the methanol extract and the four fractions. The spectral data were integrated with mass retention index of NIST14.L library. This study only considered those compounds with matching library scores with similarity index of 70%. The biological potential of the identified compounds was compared with previously reported results (Table 3). The major phytochemicals were found in the methanol extract and the fractions, except residual aqueous. The identified phytochemicals belonged mainly to the classes of α-hydroxyl acids, dicarboxylic acids, terpenes, phenolics, inositols, fatty acids, coumarins, glycosides, phytosterols, polysiloxanes and polyols. The phytochemical profiling of C. nutans revealed that experimental samples were abundant in the phenolic and terpenoids compounds.
Table 3

Identified metabolites in methanol extract and its different fractions

MeOH

Mass

Formula (DB)

Score (Lib)

m/z

RT

Glyceric acid rq

322.145

C12H30O4

82.1

73.03153

22.04

Malic acid hex, rq

350.14

C13H30O

82.63

73.03153

31.411

Erythritol hex, bu., rq

410.216

C16H42O4

83.96

73.03153

33.044

Ribitol hex

512.266

C20H52O5

90.44

73.03153

49.243

Neophytadiene

278.297

C20H38

81.5

67.0393

53.357

Mannitol bu

614.316

C24H62O6

86.43

73.03153

56.957

Gluconic acid

628.295

C24H60O7

72.71

73.03153

58.972

Palmitic acid rq

328.28

C19H40O2

75.99

117.0168

59.131

Rhamnose ea., bu., rq

452.227

C18H44O5

71.07

73.03153

59.918

Myo-Inositol hex, ea., bu

612.301

C24H60O6

81.27

73.03153

61.069

Oleic Acid hex

354.295

C21H42O2

74.58

75.01034

63.292

Stearic acid hex, ea., bu., rq

356.311

C21H44O2

75.89

117.0168

63.921

1-Monopalmitin hex, ea., bu., rq

474.356

C25H54O4

86.25

371.2661

76.818

Hexane

Mass

Formula (DB)

Score (Lib)

m/z

RT

Glycolic acid ea., bu., rq

220.095

C8H20O3

78.81

147.0445

8.457

Glycerol hex, bu

308.166

C12H32O3

86.8

73.03193

18.785

Myristic acid

300.248

C17H36O2

77.37

117.0175

53.071

Hexadecanoic acid bu

270.256

C17H34O2

80.98

87.02704

55.509

Cyclononasiloxane ea., bu

666.169

C18H54O9

78.42

73.03193

64.886

Squalene

410.391

C30H50

76.25

81.05419

83.616

Sulfurous acid

376.301

C21H44O3

79.63

57.05663

85.537

β-Tocopherol

488.405

C31H56O2

78.3

488.3697

87.803

1-Tetracosanol

426.426

C27H58O

74.64

411.3688

87.824

γ-Tocopherol

488.405

C31H56O2

76.32

73.03193

88.004

Lupeol

426.386

C30H50O

78.1

189.1404

98.854

EoAC

Mass

Formula (DB)

Score (Lib)

m/z

RT

Lactic Acid rq

234.111

C9H22O3

70.76

73.03193

7.867

Hexanoic acid

188.123

C9H20O2

82.18

73.03193

8.127

Oxalic acid

234.074

C8H18O4

74.24

147.0437

11.408

Benzoic acid

194.076

C10H14O2

89.19

135.0956

16.142

Benzeneacetic acid

208.092

C11H16O2

82.37

73.03193

19.06

Tyrosol

282.147

C14H26O2

83.45

179.063

35.281

Arabinitol bu., rq

512.266

C20H52O5

87.01

73.03193

49.249

Vanillic acid

312.121

C14H24O4

81.66

297.1034

49.77

4-Coumaric acid

308.126

C15H24O3

81.65

293.1079

50.764

p-Coumaric alcohol

294.147

C15H26O2

75.26

73.03193

51.005

Azelaic acid

332.184

C15H32O4

85.4

73.03193

51.378

Tryptophol

305.163

C16H27NO

73.32

202.1438

54.561

Syringic acid

342.132

C15H26O5

76.23

327.0037

55.145

Heptasiloxane

532.184

C16H48O6

70.08

355.0375

87.993

D-Xylose bu

438.211

C17H42O5

74.23

191.0664

88.537

BuOH

Mass

Formula (DB)

Score (Lib)

m/z

RT

Propylene glycol

220.131

C9H24O2

72.85

73.03256

13.928

Dulcitol

614.316

C24H62O6

73.74

73.03256

56.96

Octadecanoic acid

284.272

C18H36O2

71.73

87.02775

62.021

Residual Aqueous

Mass

Formula (DB)

Score (Lib)

m/z

RT

Butanedioic acid

262.106

C10H22O4

78.34

147.0448

20.507

Xylitol

512.266

C20H52O5

75.32

73.0321

49.24

Subscript with hex-hexane fraction, ea.- ethyl acetate fraction, bu.-butanol fraction, rq-residual aqueous fraction represents the identified compound in that fraction

Discussion

In the current study, we fractionated the crude extract of C. nutans using polar and non-polar solvents to obtain phytoconstituent rich biologically active standardized fractions and produced a comprehensive metabolite profiling. The average yield, TPC, and TFC of different samples are presented in Table 1. In order to achieve high quality fractionation, the purification of the extract essentially be purified to remove undesirable components could, enhance the biological activity for future pharmaceutical applications. Therefore, it is crucial to select an appropriate extraction process, as affects the characterization of secondary metabolites [32]. Plant phenolics are one of the most abundant vital group of phytochemicals and are widely known for their antioxidant and radical scavenging activity with potential impacts on human health. The phenolics are natural antioxidants which can control oxidative stress-related degenerative diseases. The adverse effects of oxidative stress have been found to be controlled by the antioxidant activities of this group of bioactive compounds. Therefore, numerous experimental studies have been designed to elucidate the antioxidant and other activities of these compounds that can inhibit certain pathological and degenerative complications [33].

As presented in Fig. 1, dose-dependent DPPH radical scavenging capacity was examined in the methanol extract and fractions, in which the standard compound (quercetin) produced the maximum antioxidant activity (IC50: 0.1927 mg/mL). The methanol extract, hexane and residual aqueous fractions were statistically significant when compared with quercetin (Table 2). This research work also revealed a strong agreement between the antioxidant activity of samples when measured by the TPC and TFC. Among all the fractions, the ethyl acetate fraction had the highest DPPH free radical scavenging activity and was rich in phenolic and flavonoid content (P < 0.05) (Table 2). The TPC, TFC of butanol, and TPC of the hexane fraction also shown a significant correlation with antioxidant activity (P < 0.05) (Fig. 3). Hence, these findings support the antioxidant function of phenolics and are also in good agreement with previous research [34].
Fig. 3

Effect of TPC and TFC on DPPH Free Radical Scavenging Activity. Bars with **P < 0.01, *P < 0.05 are Significantly Correlated whereas ns P > 0.05 Denotes Non significant Correlation According to Bonferroni Posttests (The Numerator on Bar Represent the Correlation with TPC and Denominator with TFC)

To determine the reducing power, the ferric reducing antioxidant power (FRAP), was studied for the methanol extract and the fractions of C. nutans to determine the reducing power; this provides a substantial indicator of antioxidant capacity. The presence of reducing agents in the samples is associated with the exertion of antioxidant activity by the cleavage of free radical chains through the donation of hydrogen atom. The statistically significant TPC and TFC values (P < 0.05), showed a positive correlation with the FRAP of methanol extract and fractions, except for the residual aqueous (Table 2). The methanol extract showed the highest reducing power, with a value of 141.89 ± 0.87 μg AAE/g followed by the ethyl acetate (133.6 ± 0.29), butanol (132.76 ± 0.72), hexane (130.56 ± 0.43) fractions.

An effective approach for the management of carbohydrate metabolic disorders, including diabetes mellitus type II is the inhibition of the α-glucosidase enzyme [35]. A delay in the digestion of carbohydrate plays an important role in the control of postprandial hyperglycemia, hyper insulinemia and decreases the risk of cardiovascular disease [36]. The α-glucosidase inhibitory activity of the methanol extract and fractions were significantly to the standard compound (Table 2).

Natural bioactive compounds regulate blood glucose level through obstructing the degradation of polysaccharides [37]. Plant phenolics are natural α-glucosidase inhibitors because they inhibit intestinal carbohydrate digesting enzymes owing to their protein-binding capability [38]. Recent researchers have reported the α-glucosidase inhibitory activity of numerous flavonoid compounds [39]. As shown in Fig. 2, the α-glucosidase inhibitory activity of methanol extract and the obtained fractions were evaluated at different concentrations: the strongest inhibitory concentration (IC50 37.47 μg/mL) was found in the butanol fraction compared with the standard compound. A multiple range test, between the extract, fractions and positive control is shown in Table 2; the extract and fractions were significantly different from the control (P < 0.05).

The current study also revealed a significant (P < 0.05) correlation between the TPC and TFC with an α-glucosidase inhibitory activity of the samples (Fig. 4). The higher concentration phenolics, flavonoids and higher antioxidant activity, resulted in a higher enzyme inhibitory capacity (Table 2). The results from the current study are in good agreement with other research works, which have reported the ability of phenolic rich extracts that exhibited a high antioxidant and α-glucosidase inhibitory effect [40]. Furthermore, these results revealed a direct correlation between antioxidant activity and α-glucosidase inhibitory activity. Butanol, ethyl acetate and hexane fractions revealed similar α-glucosidase inhibitory activities of 72.16 ± 1.0041%, 70.76 ± 0.4974% and 69.94 ± 0.8115% whereas the methanol extract showed moderate inhibitory activity 58.21 ± 0.08%. The butanol fraction had significantly higher (P < 0.05) α-glucosidase inhibitory activity, with an IC50 value of 37.47 μg/mL, which is close to the standard quercetin compound (IC50: 38.54 μg/mL). The higher phytochemical content and antioxidant activity significantly influenced the α-glucosidase inhibitory activity of the samples (P < 0.05).
Fig. 4

Effect of TPC and TFC on α-Glucosidase Inhibitory Activity. Bars with ***P < 0.01, **P < 0.01, *P < 0.05 are Significantly Correlated whereas ns P > 0.05 Denotes Non significant Correlation According to Bonferroni Posttests (The Numerator on Bar Represent the Correlation with TPC and Denominator with TFC)

The most abundant identified phytoconstituents were neophytadiene, squalene, lupeol, tocopherols, vanillic acid, syringic acid, myo-inositol, glycolic acid, butanedioic acid, 4-coumaric acid, and stigmasterol. Extensive literature searches documented that the identified compounds were responsible for various biological activities, including antioxidants, antidiabetic, and anti-inflammatory chemotherapeutic agents [41]. The structural orientation of the polyphenolic compounds owing to the lactones/quinones or 4-oxo-pyrane moiety responsible for the digestive enzyme inhibitory activity [42]. It was also reported that phenolic compounds help to reduce the intestinal digestive enzymes and were able to oxidize the body fat owing to their thermogenic properties [43], whereas the terpenes and terpenoids class of compounds can act as anti-hyperglycemic agents [44].

Conclusion

The methanol extract of C. nutans and the obtained solvent fractions exhibited a significant range of biological activities. The ethyl acetate and butanol fractions of the methanol extract had the highest antioxidant and α-glucosidase inhibitory activity which showed a significant correlation with the total phenolic and total flavonoid contents of the fractions. In addition, there was a strong correlation of the antioxidant activity with the α-glucosidase inhibitory potency of different samples. GC Q-TOF MS analysis showed that the presence of major phytoconstituents might be responsible for the potential antioxidant and α-glucosidase inhibitory activities of C. nutans extract and fractions. However, further toxicological study of the antioxidant rich fractions is necessary to verify their suitability for future pharmaceutical applications.

Abbreviations

CN: 

Clinacanthus nutans

GC Q-TOF-MS: 

Gas Chromatography Quadrupole Time of Flight Mass Spectroscopy

DPPH: 

2, 2-dyphenyl-1-picrylhydrazyl

TPC: 

Total Phenolic Content

TFC: 

Total Flavonoid Content

DMSO: 

Dimethyl sulfoxide

FRAP: 

Ferric Reducing Antioxidant Power

TPTZ: 

2,4,6-Tripyridyl-s-Triazine

AAE: 

Ascorbic Acid Equivalent

ANOVA: 

Analysis of Variance

Declarations

Acknowledgement

We would like to acknowledge the Malaysian International Scholarship, Ministry of Higher Education, Malaysia. We extend our appreciation to the International Scientific Partnership Program ISPP at King Saud University, Riyadh, Saudi Arabia, for funding this research work (ISPP# 0026).

The study was also supported partially by the special postdoc program under Research Initiative Grant Scheme (RIGS16-397-0561).

Funding

This study is supported and financed by the research grant of Ministry of Higher Education Malaysia through International Islamic University of Malaysia.

Availability of data and materials

Publicly available repositories

Authors’ contributions

Study design, experimental and analytical work done by MA under supervision of MZI, co-supervision of SF, AK. Article written by MA and revised by KG, HA, RM. Data interpretation and assistance provided by AM, BM. Special assistance by PV. All authors read and approved the final manuscript.

Competing interest

The authors declare that they have no competing interests.

Consent for publication

Not applicable

Ethics approval and consent to participate

Not applicable

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
Faculty of Pharmacy, International Islamic University Malaysia (IIUM)
(2)
Department of Food Science and Nutrition, King Saud University
(3)
Faculty of Science, International Islamic University Malaysia (IIUM)
(4)
Institute of Tropical Agriculture, University Putra Malaysia
(5)
Faculty of Agricultural Engineering and Technology, Bangladesh Agricultural University
(6)
Department of Pharmaceutical Technology and Industry, Faculty of Pharmacy, Cyberjaya University College of Medical Science

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Copyright

© The Author(s). 2017

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