<i>In Vitro</i> Alpha-Glucosidase Inhibitory Effect of <i>Etlingera Elatior</i> Ethanol Extract Growing in Gayo Highland, Aceh Province, Indonesia

Zumaidar Zumaidar; Nuzul Asmilia; Saudah Saudah; Milda Husnah

doi:10.12688/f1000research.149029.2

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Research Article

Revised

In Vitro Alpha-Glucosidase Inhibitory Effect of Etlingera Elatior Ethanol Extract Growing in Gayo Highland, Aceh Province, Indonesia

[version 2; peer review: 2 approved]

Zumaidar Zumaidar ¹, Nuzul Asmilia², Saudah Saudah³, Milda Husnah⁴

PUBLISHED 04 Sep 2024

Author details Author details

¹ Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Syiah Kuala, Banda Aceh, Aceh, 23111, Indonesia
² Clinical Laboratory, Faculty of Veterinary Medicine, Universitas Syiah Kuala, Banda Aceh, Aceh, 23111, Indonesia
³ Faculty of Teacher Training and Education, Universitas Serambi Mekkah, Banda Aceh, Aceh, 23245, Indonesia
⁴ Graduate School of Mathematics and Applied Science, Universitas Syiah Kuala, Banda Aceh, Aceh, 23111, Indonesia

Zumaidar Zumaidar
Roles: Conceptualization, Formal Analysis, Funding Acquisition, Methodology, Project Administration, Resources, Supervision, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Nuzul Asmilia
Roles: Data Curation, Formal Analysis, Investigation, Methodology, Validation

Saudah Saudah
Roles: Conceptualization, Data Curation, Formal Analysis, Investigation, Software, Validation, Writing – Original Draft Preparation

Milda Husnah
Roles: Data Curation, Writing – Original Draft Preparation, Writing – Review & Editing

OPEN PEER REVIEW

REVIEWER STATUS

This article is included in the Plant Science gateway.

Abstract

Background

The prevalence of diabetes mellitus (DM) is increasing overtime, potentially leading to various severe health complications and mortality. Despite therapeutic agents have currently been developed, unexpected adverse effects are inevitable. Hence, safe and effective medications such as those of plant origin are critical to prevent unexpected complication in DM sufferers. Etlingera elatior has been widely used as spice and traditional medicine to treat diabetes in Aceh Province, Indonesia. However, study regarding α-glucosidase inhibitory effect of E. elatior growing in Gayo highlands, Aceh, Indonesia, is completely lacking. The aim of this study was to evaluate in vitro α-glucosidase inhibitory effect of E. elatior ethanol extracts (EEEE) growing in Gayo highlands, Aceh Province, Indonesia.

Methods

Antioxidant activity was determined using DPPH procedure, whereas α-glucosidase inhibition assay was carried out using spectrophotometric method. Data analysis was performed using One-Way Analysis of Variance (ANOVA), followed by Duncan’s multiple range test at α=0.05.

Results

Phytochemical analysis revealed the presence of total phenolic (TPC), total flavonoid (TFC), and total tannin (TTC) content in all E. elatior plant parts, in which the highest TPC was found in the stem (158.38 GAE/g), whereas the highest TFC and TTC was obtained in the rhizome extracts. The extract of fruit showed the strongest antioxidant activities, followed by the stem and leaf, with IC50 of 2.381 μg/mL, 6.966 μg/mL, and 19.365 μg/mL, respectively. All E. elatior extracts revealed a significant inhibitory activity against α-glucosidase at the concentration of 500 μg/mL, in which the stem extract showed the most effective α-glucosidase inhibitory effect with IC50 value of 5.15 μg/mL, suggesting its promising potential as antidiabetic agent.

Conclusions

This study highlights E. elatior potency as a novel source of antioxidant and natural antidiabetic compounds that are useful for the prevention and treatment of diabetes.

Keywords

Antidiabetic, anti-hyperglycemic, α-glucosidase inhibitor, antioxidant activity, Etlingera elatior

Corresponding author: Zumaidar Zumaidar

Competing interests: No competing interests were disclosed.

Grant information: This study was funded by the Research and Community Service Institution of Universitas Syiah Kuala for funding our study through the Directorate of Research, Technology, and Community Service, Ministry of Education, Culture, Research, and Technology, Research Program Fiscal Year 2023 (Ref Number: 168/E5/PG.02.00.PL/2023).
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Copyright: © 2024 Zumaidar Z et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

How to cite: Zumaidar Z, Asmilia N, Saudah S and Husnah M. In Vitro Alpha-Glucosidase Inhibitory Effect of Etlingera Elatior Ethanol Extract Growing in Gayo Highland, Aceh Province, Indonesia [version 2; peer review: 2 approved]. F1000Research 2024, 13:489 (https://doi.org/10.12688/f1000research.149029.2) First published: 17 May 2024, 13:489 (https://doi.org/10.12688/f1000research.149029.1) Latest published: 04 Sep 2024, 13:489 (https://doi.org/10.12688/f1000research.149029.2)

Revised Amendments from Version 1

There was a change in references (reference number 9 was excluded from the manuscript).

See the authors' detailed response to the review by Arif Nur Muhammad Ansori

Introduction

Diabetes mellitus (DM) has been considered one of the leading causes of death worldwide.¹ Approximately 415 million adults suffer from diabetes globally, and the number is estimated to increase up to 642 million by the year of 2040.² In the Southeast Asian regions, around 11.3% prevalence of DM has been reported and Indonesia occupies the 7th most DM sufferers, which is considered a major contributor of diabetes cases in Southeast Asia.³ DM often leads to various health complications such as blindness, stroke, heart disease, and kidney failure.⁴ According to the World Health Organization (WHO) report, around 422 million people suffer from DM at the age of 20-70 years worldwide. Several factors, including age, obesity, lifestyle, and unhealthy diets are among risk factors for diabetes.⁵

Most of diabetic patients use oral preparations and insulin injections as therapy; however, taking long-term oral medications may result in unexpected adverse effects.⁶^,⁷ This condition has urged the need for searching and developing new therapeutic approaches that are safer and easier for users,⁸ including the use of α-glucosidase inhibitors, especially those of plant origin. Αlpha-glucosidase inhibitors are oral antidiabetics that act by inhibiting α-glucosidase enzyme responsible for catabolizing complex polysaccharide into monosaccharides, causing a reduction in glucose absorption and postprandial blood sugar levels.⁹

Identification of potent natural compounds effectively inhibiting α-glucosidase has been extensively carried out as an effort in searching for new antidiabetic agents.¹⁰ Some α-glucosidase inhibitors have been isolated from medicinal plants, offering the potential for alternative medications with greater efficacy and fewer side effects compared to current treatments.¹¹ Among the traditionally favored source of alternative medicines for the treatment of diabetes is Etlingera elatior.¹² Research on E. elatior flower extract revealed a strong inhibitory activity against α-glucosidase, making it a promising candidate for diabetes treatment.¹³ Rhizome of E. elatior was also reported to exhibit antidiabetic effect attributed to its flavonoid compounds.¹⁴ However, there is currently lack of information regarding antioxidant and antidiabetic properties of E. elatior extracts growing in Gayo highlands, Aceh, Indonesia. Therefore, the aim of this study was to evaluate antioxidant and α-glucosidase inhibitory activities of E. elatior extracts growing in this specific region.

Methods

Materials

The materials used in this study included technical ethanol 96%, Folin-Ciocalteu’s reagent (Merck-1.09001.0100, Germany), sodium carbonate (Na₂CO₃) (Merck-1.06392.0500, Germany), gallic acid (Merck-8.42649.0025, Germany), sodium nitrite (NaNO₂) (Merck-1.06549.0500, Germany), aluminium chloride (AlCl₃) (Merck-8.01081.0500, Germany), sodium hydroxide (NaOH) (Merck-1.06498.1000, Germany), quercetin (Sigma Aldrich-Q4951, USA), vanillin (Merck-8.18718.0100, Germany), hydrochloric acid fuming (HCl) (Merck-1.00317.2500, Germany), tannic acid (Sigma Aldrich-1643328-2G, USA), 1,1-Diphenyl-2-picrylrazyl (DPPH) powder (Tokyo Chemical Industry Co., Ltd. (JP)-D4313, Japan), ascorbic acid (Merck-1.00468.0100, Germany), phosphate buffer saline (PBS) (Oxoid-BR0014G, England), dimethyl sulfoxide (DMSO) (Merck-1.02952.1000, Germany), α-glucosidase powder (CDH-105265, India), bovine serum albumin (Himedia-MB083-25G, India), p-nitrophenyl-D-glucopyranose (p-NPG) (Sigma-N1377-5g, USA), and acarbose.

Sample collection

Etlingera elatior plant was obtained from Gayo Highlands of Aceh Province, Indonesia. The plant was identified and preserved at Acehense Herbarium, Department of Biology, Universitas Syiah Kuala, Indonesia. Based on the International Union for Conservation of Nature (IUCN), the plant is classified into “data deficient (DD)” species due to inadequate information for its conservation status assessment. Meanwhile, this plant widely grows in various areas in Aceh, including forest, garden, or at the backyard of Acehnese houses since it has been traditionally used as traditional medicine, spice, and food.¹⁵

Extracts preparation

Samples of E. elatior plant parts consisting of rhizomes, stems, leaves, flowers, and fruits were washed thoroughly under running tap water. The samples were then air-dried for 6 days and diligently grinded to obtain powder. Extraction was carried out by the maceration method. In brief, a 100 gram of simplicial was placed into a maceration container, filled with ethanol 96% until submerged, homogenized, sealed, and let stand for 24 hours with occasional stirring. The mixture was then filtered yielding macerate and lees. The macerate was stored and the lees underwent the same maceration procedure until the solvent became colourless. The obtained macerate was evaporated by vacuum rotary evaporator (Buchi R-300, Swiss) at 50°C to obtain concentrated (100%) stem, leaf, fruit, flower, and rhizome extracts.¹⁶ The extracts were then stored at 20°C for further analysis.

Total Phenolic Content (TPC)

Each EEEE samples (stems, leaf, fruit, flower, and rhizome) (0.2 mL) with a concentration of 300 μg/mL was mixed with 2.5 mL of 10% (v/v) Folin-Ciocalteu’s reagent and 2 mL of 7.5% (v/v) Na₂CO₃. After being incubated for 10 minutes at 45°C, the absorbance of the solution was measured using a UV-Vis spectrophotometer at a wavelength of 765 nm (UV-1800, Shimadzu, Japan) for the determination of TPC. Standard solution of gallic acid (concentrations of 10 – 100 μg/mL; R²= 0.9237) was used to make a calibration curve, and TPC was expressed as mg (+)- of gallic acid equivalent per gram of dry weight of the extracts (GAE/g).¹⁷^,¹⁸ The assay was performed in triplicate.

Total Flavonoids Content (TFC)

Each extract sample (5 mL) with a concentration of 500 μg/mL was mixed with 0.3 mL of 5% (v/v) NaNO₂ and 0.3 mL of 10% v/v AlCl₃. After incubation for 5 minutes, 2 mL of 1 M NaOH was added to the concoction. The absorbance of the solution was measured using UV-Vis spectrophotometer at a wavelength of 510 nm (UV-1800, Shimadzu, Japan). The calibration curve of standard quercetin (concentrations of 10 – 400 μg/mL; R²= 0.9282) was used for quantification of TFC in the extracts, which was expressed as mg (+)- quercetin equivalent per gram of dry extract (QE/g).¹⁸^,¹⁹ The assay was performed in triplicate.

Total Tannin Content (TTC)

Condensed tannins (proanthocyanidins) were determined by mixing 50 μL of the diluted EEEE sample with 3 mL of 4% vanillin in methanol and 1.5 mL of concentrated HCl. The mixture was allowed to stand for 15 minutes and the absorption was measured using UV-Vis spectrophotometer (UV-1800, Shimadzu, Japan) at a wavelength of 500 nm with respect to methanol as a blank control. Quantification of total tannin in the extracts was based on tannic acid (concentrations of 1.5 – 20 μg/mL; R² = 0.9705) calibration curve, and the total amount of condensed tannins was expressed as mg (+)- tannic acid equivalent per gram of dry extracts (TAE/g).¹⁸^,²⁰ The assay was performed in triplicate.

1,1-Diphenyl-2-picrylrazyl (DPPH) assay

DPPH assay was employed to assess free radical-scavenging activity of EEEE. Briefly, 3.5 mL of DPPH solution and 0.5 mL of each sample extract (concentrations of 1000, 500, 250, 125, 62.5, and 31.5 μg/mL) were mixed, homogenized, and incubated at 27°C for 20 minutes. The absorbance of the solution was then measured at a wavelength of 517 nm using UV-Vis spectrophotometer (UV-1800, Shimadzu, Japan). The ascorbic acid of various concentrations (2, 4, 6, and 8 μg/mL) was used as the positive control.¹⁹ The percentage of DPPH inhibition was calculated using the following formula²¹:

DPPH inhibition (%) = \frac{A_{contol} - A_{sample}}{A_{control}} \times 100 %

Alpha-glucosidase inhibitory assay

Briefly, each EEEE sample was dissolved in dimethyl sulfoxide (DMSO) to obtain a concentration of 500 μg/mL. The enzyme solution was prepared by dissolving 1.0 mg of α-glucosidase in a phosphate buffer saline (PBS) (pH 7) containing 200 mg of serum bovine albumin. Before use, 1 mL of the enzyme was pre-diluted 25 times with PBS (pH 7.0). The reaction was initiated by mixing 10 μL of the sample solution (concentration of 500 μg/mL) with 25 μL of 0.04 U/mL α-glucosidase, 50 μL of 0.1 mM PBS (pH 7.0), and 25 μL of p-nitrophenyl-D-glucopyranose (p-NPG). The mixture was incubated at 37°C for 30 minutes. A 100 μL of 0.2 M sodium carbonate (Na₂CO₃) was then added to terminate the reaction, and the absorbance of p-nitrophenol was measured at a wavelength of 410 nm using a UV-Vis spectrophotometer (UV-1800, Shimadzu, Japan).²²

Positive control was prepared by dissolving acarbose tablets in PBS (pH 7.0) and HCl 2N. To make a 1% acarbose standard solution, the acarbose tablets was diluted in distilled water and 2N HCl at 1:100 ratio. The solution was then centrifuged at 10.000 rpm for 10 minutes and the supernatant was used as a standard. Each test was performed in triplicate, and the inhibitory activity of the extract against α-glucosidase was quantified in % inhibition using the following formula:

% inhibition = \frac{A_{control -} A_{sample}}{A_{control}} \times 100 %

$A_{control}$ is the solution absorbance in the absence of the extracts and A_sample is the solution absorbance in the presence of the extracts. The IC₅₀ value was obtained by plotting the log concentration against the percent (%) inhibition using a regression equation. The IC₅₀ represent a concentration inhibiting 50% of the enzyme activity. Based on the IC₅₀ values, antioxidant activities are categorized as very strong (IC₅₀ value of <50 μg/mL), strong (IC₅₀ value of 50-100 μg/mL), weak (IC₅₀ of >100 μg/mL), and not active (IC₅₀: >250 μg/mL).²³

Data analysis

The IC₅₀ of antioxidant activity was determined using a linear regression between concentration (X-axis) and percent inhibition (Y-axis) trough the probit analysis of concentration log data with the probit free radical scavenger (DPPH) percentage. A parametric One-Way Analysis of Variance (ANOVA) was employed to identify significance of differences of the percent inhibition between extracts, followed by Duncan’s multiple range test. All statistical analysis was performed using IBM SPSS software version 25 (IBM Corp., New York, USA), and a p-value of ≤0.05 was considered statistically significant.

Results

Total phenolic, total flavonoid, and total tannin contents

The result of EEEE phytochemical analysis is presented in Table 1. TPC was expressed in mg GAE/g extract using a standard gallic acid curve (R² = 0.9237), TFC in mg QE/g extract using a standard quercetin curve (R² = 0.9282), and TTC in mg TAE/gr extract using a standard tannic acid curve (R² = 0.9705). The highest TPC was found in the extract of the stem (158.38 mg GAE/g), whereas the lowest was observed in the extract of the leaves (31.35 mg GAE/g). The highest of both TFC (37.91 mg QE/g) and TTC (48.71 TAE/gr) were recorded in the rhizome extract, whereas the lowest were obtained in the leaf extract (TFC: 6.10 QE/g; TTC: 2.13 TAE/gr).

Table 1. Total phenolic, total flavonoid, and total tannin content of EEEE.

E. elatior Extracts	TPC (mg GAE/g)	TFC (mg QE/g)	TTC (mg TAE/gr)
Rhizome	56.76	37.91	48.71
Stem	158.38	8.31	46.08
Leaf	31.35	6.10	2.13
Flower	127.30	22.79	34.24
Fruit	126.49	22.44	35.82

Antioxidant activity of EEEE

The result of antioxidant activity of EEEE is presented in Table 2. The most effective radical scavenging activity was shown by the extract of fruit (IC₅₀ value of 2.81 μg/mL), whereas the least effective effect was exhibited by the extract of rhizome (IC₅₀ value of 188.056 μg/mL). The extracts of stem and leaf showed a very strong antioxidant activity (IC₅₀ value of less 50 μg/mL), whereas the extract of flower indicated a strong activity (IC₅₀ of 50-100 μg/mL).

Table 2. IC₅₀ values of EEEE antioxidant activity.

E. elatior Extracts	IC₅₀ (μg/mL)
Rhizome	188.056^*
Stem	6.966^***
Leaf	19.365^***
Flower	83.095^**
Fruit	2.381^***
Ascorbic acid standard	16.426^***

*** Very strong.

** Strong.

* Weak.

Alpha-glucosidase inhibition assay of EEEE

Alpha-glucosidase inhibitory activity of EEEE is presented in Figure 1. All the extracts (rhizome, stem, leaf, flower, and fruit) exhibited a statistically significant inhibitory effect on α-glucosidase activity at the concentration of 500 μg/mL (p < 0.05). The result of Duncan test suggested that the percent of inhibition were significantly different among E. elatior plant parts, except between the stem and fruit extracts. The extracts of the leaf and flower accounted for more than 50.0% of inhibition, suggesting a promising anti-diabetic potential of E. elatior. On the other hand, the lowest inhibition percentage was shown by the stem extract (14.23±3.9%).

Figure 1. Inhibition of α-glucosidase by EEEE at the concentration of 500 μg/mL.

Different superscripts above each bar indicated statistically significant different based on Duncan test (α = 0.05).

The IC₅₀ values of EEEE against α-glucosidase are presented in Table 3. The flower extract exhibited the highest IC₅₀ values (100 μg/mL), followed by the rhizome, leaf, and fruit extracts. Meanwhile, the lowest IC₅₀ values was observed in the extract of stem (5.15 μg/mL), which was comparable to that of acarbose (4.45 μg/mL), highlighting a strong anti α-glucosidase potential of E. elatior stem.

Table 3. IC₅₀ value of EEEE ethanol extracts against α-glucosidase.

E. elatior ethanol extracts	IC₅₀ (μg/mL)
Rhizome	85.33
Stem	5.15
Leaf	15.25
Flower	100
Fruit	10.07
Acarbose	4.45

Discussion

The prevalence of type 2 DM (T2DM) is increasing, accounting for approximately 95% of all diabetes cases worldwide.¹ This condition can lead to severe complications, such as retinopathy, neuropathy and coronary heart disease if left untreated for a long period of time.²⁴^,²⁵ Therefore, a proper, safe, and effective medication is critical to prevent unexpected complication among sufferers. Medicinal plants have been widely used for the treatment of DM and become a preferable source in the search of novel natural anti-diabetic drugs. In the present study, we evaluated α-glucosidase inhibitory effect of EEEE as a new source of antidiabetic agent.

Phytochemical screening of EEEE indicated the presence of phenolics, flavonoids and tannins. Phenolics represented the most abundant secondary metabolites in EEEE and the content varied among E. elatior plant parts. The highest amount was found in the stem extract, followed by flower, fruit, rhizome, and leaf. Phenolics are the most commonly found secondary metabolites in plants synthesized as a response to biotic and abiotic stresses such as temperature, pH, heavy metal stress, and UV radiation.²⁶ Phenolics have been reportedly able to inhibit α-glucosidase activity, justifying its potency for antidiabetic agent.²⁷^,²⁸ Other useful pharmacological properties of phenolic compounds included their ability to treat chronic diseases related to oxidative stress, such as diabetes, cancer, and cardiovascular disorders.²⁸^–³²

DPPH radical scavenging assay suggested that the fruit, stem, and leaf extracts of E. elatior exhibited a very strong antioxidant activity (Table 2), which was assumingly attributed to their secondary metabolites such as phenolic and flavonoid content. Phenolics have been reported to facilitate superoxide dismutase (SOD) and glutathione biosynthesis, thus resulting in the prevention and reduction of oxidative stress which has been associated with pancreatic-cell dysfunction exacerbation.³³^,³⁴ The ability of phenolic compounds to react with the peroxyl radical (ROO^-), donate electron or hydrogen to neutralize free radicals, and act as prooxidant and metal ion chelation has made these compounds as potential antioxidant agents.³⁵^,³⁶ Flavonoids in E. elatior also responsible for antioxidant activities by either causing a direct reactive oxygen species (ROS) scavenging, antioxidant enzyme activation, metal chelation, oxidase inhibition, tocopheryl radical reduction, or nitric-oxide-associated oxidative stress attenuation.³⁶ Among all E. elatior plant parts evaluated in the present study, the fruits exhibited the most effective antioxidant activity, assumingly associated with the presence of quercetin in the fruits of this plant.³⁷ Antioxidant properties of plant extracts have often been associated with various pharmacological activities including immunomodulatory, antitumor, anti-inflammatory, and antidiabetic potentials.¹²^,³⁸

We found that all E. elatior plant parts significantly inhibited α-glucosidase activity at the concentration of 500 μg/mL. The highest inhibitory percentage was observed in the leaf extract (70.67±2.3%), whereas the lowest was noted in the stem extract (14.23±3.9%). The ability of E. elatior leaves to interfere with α-glucosidase activity was assumingly attributed to its chlorogenic compounds that inhibit glucose transporter through their interaction with glucose absorption in the intestine,²⁸ which is similar to the mechanism of action of acarbose, a pharmaceutical drugs used in the treatment of type 2 diabetes.³⁹^–⁴¹ In terms of effectivity, the stem extract was found to be the most effective α-glucosidase inhibitor among all E. elatior plant parts as it possessed the lowest IC₅₀ value (5.15 μg/mL), which was comparable to that of acarbose (4.45 μg/mL). Similar finding was also reported in a previous study, suggesting antihyperglycemic effect of E. elatior stem extract in vivo.³² This superior α-glucosidase inhibitory effect of the stem was in consistent with the dominant levels of phenolic contents in this part of the plant. Plant-derived polyphenols have been reportedly able to inhibit α-glucosidase activity by interacting with the active sites of this enzyme receptors with a high binding affinity.⁴²

The extract of E. elatior flower also exhibited more than 50.0% of α-glucosidase inhibition in vitro, suggesting its antidiabetic potential. This finding was in accordance with that of a former study, reporting a high percentage (52.39%) of α-glucosidase inhibition by E. elatior flower extract at a concentration of 100 μg/mL in vitro and reduced blood glucose level by 57.07% at a concentration of 1000 mg/kg against induced type-2 DM animals model.¹³ This part of the plant is rich in fiber that might be potential to reduce cholesterol levels and treat various diseases such as hypertension, heart disease, constipation, and diabetes.³⁶ Anti-hyperglycemic activity E. elatior flower has been closely related to its antioxidant properties, such as phenolic and flavonoid compounds,²⁸ which have been evidenced to effectively reduce free radicals.⁴³ In addition, alkaloids, flavonoid glucosides, and saponins, which are also found in E. elatior flowers, are among other potential hypoglycemic agents that play a crucial role in the prevention of diabetes by hindering α-glucosidase enzyme activity.²⁸^,⁴⁴^–⁴⁷ In Indonesian society, young flowers of this plant have been widely used as food ingredients in traditional dishes and empirically used as traditional medicine.¹⁵

In addition to the leaves and flowers, the extract of fruit was another E. elatior plant part effectively hindering α-glucosidase activity, with percent inhibition of almost 40.0% and IC₅₀ value of less than 50 μg/mL. It has been traditionally used as an antidiabetic drug and is rich in anthocyanins constituent.³⁶ Anthocyanins, compounds found in dark colored fruits, has been reported to exhibit anti-inflammatory, antimicrobial, and antidiabetic potentials.⁴⁸ The synergistic effect of anthocyanins and phenolic compounds is responsible for enzyme inhibitory, antioxidant, and anti-inflammatory activities.⁴⁹ These findings can lead to future research on the therapeutic use of the E. elatior plant in preventing diabetes.

This study possesses several limitations that should be addressed. We employed spectrophotometric method to obtain data, which could have a relatively limited sensitivity and selectivity. Detecting extremely low concentrations of an analyte or distinguishing the analyte from other substances with similar absorption wavelength might be challenging, potentially leading to data bias.

Conclusion

Ethanol extracts of different E. elatior plant parts significantly inhibited α-glucosidase activity in vitro. Stem extract showed the most effective α-glucosidase inhibitory effect, highlighting its potential as a future antidiabetic agent. Further study assessing anti α-glucosidase activity of E. elatior extracts using non-polar solvents, as well as identification of specific bioactive constituent responsible for α-glucosidase inhibition should be carried out as an effort to develop effective novel anti-diabetic drugs of natural origin.

Author contributions

Conceptualization: ZZ, SS; data curation: NA, SS, MH; formal analysis: ZZ, NA, SS; funding acquisition: ZZ; investigation: SS, NA; methodology: ZZ, NA; project administration: ZZ; resources: ZZ; software: SS; supervision: ZZ; validation: ZZ, NA, SS; writing – original draft preparation: ZZ, SS, MH; writing – review & editing: ZZ, MH.

Data availability

Underlaying data

Figshare: ‘In Vitro Alpha-Glucosidase Inhibitory Effect of Etlingera elatior Ethanol Extract Growing in Gayo Highland, Aceh Province. https://doi.org/10.6084/m9.figshare.25333411.v1.⁵⁰

This project contains the following underlaying data:

1. OD value and percent inhibition (%) of EEEE against DPPH radical scavenging.xlsx
2. OD value and percent inhibition (%) of EEEE against α-glucosidase.xlsx

Data are available under the terms of the Creative Commons Attribution 4.0 International licence (CC-BY 4.0).

Acknowledgment

We would like to thank the community members of Gayo Highland for their assistance during the plant sample collection in Gayo Highland, as well as Biology Laboratory assistant at Universitas Riau (UNRI) and Pharmacy Laboratory assistant at Universitas Syiah Kuala for their assistance during the study.

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Version 2

VERSION 2 PUBLISHED 17 May 2024

Author details Author details

Nuzul Asmilia
Roles: Data Curation, Formal Analysis, Investigation, Methodology, Validation

Saudah Saudah
Roles: Conceptualization, Data Curation, Formal Analysis, Investigation, Software, Validation, Writing – Original Draft Preparation

Milda Husnah
Roles: Data Curation, Writing – Original Draft Preparation, Writing – Review & Editing

Competing interests

No competing interests were disclosed.

Grant information

This study was funded by the Research and Community Service Institution of Universitas Syiah Kuala for funding our study through the Directorate of Research, Technology, and Community Service, Ministry of Education, Culture, Research, and Technology, Research Program Fiscal Year 2023 (Ref Number: 168/E5/PG.02.00.PL/2023).
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Zumaidar Z, Asmilia N, Saudah S and Husnah M. In Vitro Alpha-Glucosidase Inhibitory Effect of Etlingera Elatior Ethanol Extract Growing in Gayo Highland, Aceh Province, Indonesia [version 2; peer review: 2 approved]. F1000Research 2024, 13:489 (https://doi.org/10.12688/f1000research.149029.2)

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Reviewer Report 17 Oct 2024

Dora Dayu Rahma Turista, Universitas Mulawarman, Samarinda, East Kalimantan, Indonesia

Approved

https://doi.org/10.5256/f1000research.171238.r330766

The introduction has been described sharply. the research method is very clear and detailed so that it makes it easier for readers to understand. The results obtained are in accordance with the method used. The discussion is described in detail ... Continue reading

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Natural Resources

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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Reviewer Report 13 Sep 2024

Arif Nur Muhammad Ansori, Universitas Airlangga, Surabaya, East Java, Indonesia; Division of Research and Development, Jalan Tengah, Surabaya, Indonesia

Approved

https://doi.org/10.5256/f1000research.171238.r320734

The revised manuscript provides a well-structured and comprehensive evaluation of the alpha-glucosidase inhibitory activity and antioxidant properties of Etlingera elatior ethanol extract. The study presents significant data on the phytochemical content and its implications in diabetes treatment. The objectives are clear, the ... Continue reading

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Reviewer Report 29 Aug 2024

Arif Nur Muhammad Ansori, Universitas Airlangga, Surabaya, East Java, Indonesia; Division of Research and Development, Jalan Tengah, Surabaya, Indonesia

Approved with Reservations

https://doi.org/10.5256/f1000research.163430.r288676

First of all, this manuscript is good and well-written. However, I may require some comments on the following issues. Basically, this manuscript is acceptable.
Language can be improved for the readability of the paper.
Title: The title is easy to follow and no mistakes.
Abstract: This section was well-written and easy to understand. In addition, the study's objective and the state of the art of the study is clear. Furthermore, the keywords should represent the study.
Discussion: To develop a systematic discussion, the authors should mention the limitation(s) of the study.
Conclusion: In this part of the paper, the authors have established the conclusion of this study.
References: Many references are out of guidelines. Please kindly check the references again, do not include the old references, and check the abbreviation of the journals/proceedings. Please mention many high-quality related publications. References number 14, 15, 16, 24, and 33 should be changed.

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

I cannot comment. A qualified statistician is required.
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests: No competing interests were disclosed.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

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Author Response 04 Sep 2024

zumaidar zumaidar, Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia

04 Sep 2024

Author Response

Thank you for reviewing our manuscript. The comments and suggestions have improved the quality of our current manuscript significantly.

References: Many references are out of guidelines. Please kindly check ... Continue reading Thank you for reviewing our manuscript. The comments and suggestions have improved the quality of our current manuscript significantly.

References: Many references are out of guidelines. Please kindly check the references again, do not include the old references, and check the abbreviation of the journals/proceedings. Please mention many high-quality related publications. References number 14, 15, 16, 24, and 33 should be changed.

RESPONSE: Thank you for the suggestions.
1. We agree to exclude reference number 9 (old reference) as it is not strongly relevant to our study. Since it supports general information in the introduction, it will not affect any specific content in our manuscript.

2. We sincerely appreciate the suggestion to exclude older references from the manuscript. However, we believe that several of these references are crucial to our study. Some provide essential information on the phytochemical content and pharmacological activities of Etlingera elatior, which serve as the foundational basis for our research. Therefore, we have chosen to retain these references, especially for reference.

3. We appreciate the reviewer's suggestion regarding the exclusion of references number 14, 15, 16, 24, and 33. However, we believe these references are highly relevant to our study as they provide essential information that directly supports our findings. Therefore, we kindly request to retain these references in the manuscript.
Thank you for reviewing our manuscript. The comments and suggestions have improved the quality of our current manuscript significantly.

References: Many references are out of guidelines. Please kindly check the references again, do not include the old references, and check the abbreviation of the journals/proceedings. Please mention many high-quality related publications. References number 14, 15, 16, 24, and 33 should be changed.

RESPONSE: Thank you for the suggestions.
1. We agree to exclude reference number 9 (old reference) as it is not strongly relevant to our study. Since it supports general information in the introduction, it will not affect any specific content in our manuscript.

2. We sincerely appreciate the suggestion to exclude older references from the manuscript. However, we believe that several of these references are crucial to our study. Some provide essential information on the phytochemical content and pharmacological activities of Etlingera elatior, which serve as the foundational basis for our research. Therefore, we have chosen to retain these references, especially for reference.

3. We appreciate the reviewer's suggestion regarding the exclusion of references number 14, 15, 16, 24, and 33. However, we believe these references are highly relevant to our study as they provide essential information that directly supports our findings. Therefore, we kindly request to retain these references in the manuscript.
Competing Interests: No competing interests were disclosed. Close
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Author Response 04 Sep 2024

zumaidar zumaidar, Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia

04 Sep 2024

Author Response

Thank you for reviewing our manuscript. The comments and suggestions have improved the quality of our current manuscript significantly.

References: Many references are out of guidelines. Please kindly check ... Continue reading Thank you for reviewing our manuscript. The comments and suggestions have improved the quality of our current manuscript significantly.

References: Many references are out of guidelines. Please kindly check the references again, do not include the old references, and check the abbreviation of the journals/proceedings. Please mention many high-quality related publications. References number 14, 15, 16, 24, and 33 should be changed.

RESPONSE: Thank you for the suggestions.
1. We agree to exclude reference number 9 (old reference) as it is not strongly relevant to our study. Since it supports general information in the introduction, it will not affect any specific content in our manuscript.

2. We sincerely appreciate the suggestion to exclude older references from the manuscript. However, we believe that several of these references are crucial to our study. Some provide essential information on the phytochemical content and pharmacological activities of Etlingera elatior, which serve as the foundational basis for our research. Therefore, we have chosen to retain these references, especially for reference.

3. We appreciate the reviewer's suggestion regarding the exclusion of references number 14, 15, 16, 24, and 33. However, we believe these references are highly relevant to our study as they provide essential information that directly supports our findings. Therefore, we kindly request to retain these references in the manuscript.
Thank you for reviewing our manuscript. The comments and suggestions have improved the quality of our current manuscript significantly.

References: Many references are out of guidelines. Please kindly check the references again, do not include the old references, and check the abbreviation of the journals/proceedings. Please mention many high-quality related publications. References number 14, 15, 16, 24, and 33 should be changed.

RESPONSE: Thank you for the suggestions.
1. We agree to exclude reference number 9 (old reference) as it is not strongly relevant to our study. Since it supports general information in the introduction, it will not affect any specific content in our manuscript.

2. We sincerely appreciate the suggestion to exclude older references from the manuscript. However, we believe that several of these references are crucial to our study. Some provide essential information on the phytochemical content and pharmacological activities of Etlingera elatior, which serve as the foundational basis for our research. Therefore, we have chosen to retain these references, especially for reference.

3. We appreciate the reviewer's suggestion regarding the exclusion of references number 14, 15, 16, 24, and 33. However, we believe these references are highly relevant to our study as they provide essential information that directly supports our findings. Therefore, we kindly request to retain these references in the manuscript.
Competing Interests: No competing interests were disclosed. Close
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Arif Nur Muhammad Ansori, Universitas Airlangga, Surabaya, Indonesia; Jalan Tengah, Surabaya, Indonesia
Dora Dayu Rahma Turista, Universitas Mulawarman, Samarinda, Indonesia

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17 Oct 2024 | for Version 2

Dora Dayu Rahma Turista, Universitas Mulawarman, Samarinda, East Kalimantan, Indonesia

9 Views Cite this report Responses(0)

Approved

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests

No competing interests were disclosed.

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Natural Resources

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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13 Sep 2024 | for Version 2

Arif Nur Muhammad Ansori, Universitas Airlangga, Surabaya, East Java, Indonesia; Division of Research and Development, Jalan Tengah, Surabaya, Indonesia

6 Views Cite this report Responses(0)

Approved

Competing Interests

No competing interests were disclosed.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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23 Views

29 Aug 2024 | for Version 1

Arif Nur Muhammad Ansori, Universitas Airlangga, Surabaya, East Java, Indonesia; Division of Research and Development, Jalan Tengah, Surabaya, Indonesia

23 Views Cite this report Responses(1)

Approved With Reservations

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

I cannot comment. A qualified statistician is required.
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests

No competing interests were disclosed.

Respond to this report

Responses (1)

Author Response

04 Sep 2024

zumaidar zumaidar, Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Syiah Kuala, Banda Aceh, 23111, Indonesia

Thank you for reviewing our manuscript. The comments and suggestions have improved the quality of our current manuscript significantly.

References: Many references are out of guidelines. Please kindly check the references again, do not include the old references, and check the abbreviation of the journals/proceedings. Please mention many high-quality related publications. References number 14, 15, 16, 24, and 33 should be changed.

RESPONSE: Thank you for the suggestions.
1. We agree to exclude reference number 9 (old reference) as it is not strongly relevant to our study. Since it supports general information in the introduction, it will not affect any specific content in our manuscript.

2. We sincerely appreciate the suggestion to exclude older references from the manuscript. However, we believe that several of these references are crucial to our study. Some provide essential information on the phytochemical content and pharmacological activities of Etlingera elatior, which serve as the foundational basis for our research. Therefore, we have chosen to retain these references, especially for reference.

3. We appreciate the reviewer's suggestion regarding the exclusion of references number 14, 15, 16, 24, and 33. However, we believe these references are highly relevant to our study as they provide essential information that directly supports our findings. Therefore, we kindly request to retain these references in the manuscript.

View more View less

Competing Interests

No competing interests were disclosed.

Alongside their report, reviewers assign a status to the article:

Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions

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[14] 14. Fitrianita A, Yardi Y, Musir A: Uji efek antihiperglikemia ekstrak etanol 70% daun kecombrang (Etlingera elatior) pada tikus sprague dawley dengan penginduksi aloksan. Jurnal Ilmiah Farmasi. 2018; 14(1): 9–16. Publisher Full Text

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[16] 16. Sruthi D, Indira G: A comparative evaluation of maceration, soxhlation and ultra sound assisted extraction for the phytochemical screening of the leaves of Nephelium lappaceum. L.(Sapindaceae). J. Pharmacogn. Phytochem. 2016; 5(5): 386–389.

[17] 17. Jayaprakasha G, Girennavar B, Patil BS: Radical scavenging activities of rio red grapefruits and sour orange fruit extracts in different in vitro model systems. Bioresour. Technol. 2008; 99(10): 4484–4494. PubMed Abstract | Publisher Full Text

[18] 18. Ojha S, Raj A, Roy A, et al.: Extraction of total phenolics, flavonoids and tannins from Paederia foetida L. Leaves and their relation with antioxidant activity. Pharm. J. 2018; 10(3): 541–547. Publisher Full Text

[19] 19. Ghasemzadeh A, Jaafar HZ, Rahmat A, et al.: Secondary metabolites constituents and antioxidant, anticancer and antibacterial activities of Etlingera elatior (Jack) RM Sm grown in different locations of Malaysia. BMC Complement. Altern. Med. 2015; 15: 1–10.

[20] 20. Medini F, Fellah H, Ksouri R, et al.: Total phenolic, flavonoid and tannin contents and antioxidant and antimicrobial activities of organic extracts of shoots of the plant Limonium delicatulum. J. Taibah Univ. Sci. 2014; 8(3): 216–224. Publisher Full Text

[21] 21. Molyneux P: The use of the stable free radical diphenylpicrylhydrazyl (DPPH) for estimating antioxidant activity. Songklanakarin J. Sci. Technol. 2004; 26(2): 211–219.

[22] 22. Dwitasari O, Seno DSH, Safithri M: Identification of bioactive compounds and α-glucosidase inhibition activity of Caesalpinia Bonduc seed extract in vitro. Curr. Biochem. 2018; 5(2): 12–20. Publisher Full Text

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In Vitro Alpha-Glucosidase Inhibitory Effect of Etlingera Elatior Ethanol Extract Growing in Gayo Highland, Aceh Province, Indonesia

Abstract

Background

Methods

Results

Conclusions

Keywords

Revised Amendments from Version 1

Introduction

Methods

Materials

Sample collection

Extracts preparation

Total Phenolic Content (TPC)

Total Flavonoids Content (TFC)

Total Tannin Content (TTC)

1,1-Diphenyl-2-picrylrazyl (DPPH) assay

Alpha-glucosidase inhibitory assay

Data analysis

Results

Total phenolic, total flavonoid, and total tannin contents

Table 1. Total phenolic, total flavonoid, and total tannin content of EEEE.

Antioxidant activity of EEEE

Table 2. IC50 values of EEEE antioxidant activity.

Alpha-glucosidase inhibition assay of EEEE

Figure 1. Inhibition of α-glucosidase by EEEE at the concentration of 500 μg/mL.

Table 3. IC50 value of EEEE ethanol extracts against α-glucosidase.

Discussion

Conclusion

Author contributions

Data availability

Underlaying data

Acknowledgment

References

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Table 2. IC₅₀ values of EEEE antioxidant activity.

Table 3. IC₅₀ value of EEEE ethanol extracts against α-glucosidase.