In vitro screening of α-glucosidase, DPP-IV, and pancreatic lipase inhibitory activity of extracts from 181 coastal island plants of Korea

All plant extracts derived from coastal island plants were obtained from the Honam National Institute of Biological Resources (Mokpo, Korea). The reagents used in this study included Bovine Serum Albumin (BSA), sodium azide (NaN₃), α-glucosidase (from Saccharomyces cerevisiae), p-nitrophenyl-α-D-glucopyranoside (pNPG), acarbose, dipeptidyl peptidase-IV (DPP-IV; human recombinant), Gly-Pro-p-nitroanilide hydrochloride (Gly-Pro-pNA), Ile-Pro-Ile (Diprotin A), sodium acetate, lipase (from porcine pancreas), and p-nitrophenyl butyrate, all of which were purchased from Sigma-Aldrich (St. Louis, MO, USA). 10X MOPS buffer was obtained from Bioneer (Daejeon, Korea).

The α-glucosidase inhibitory activity was determined using a modified method from (Indrianingsih et al., 2015). 10 μL of each plant extract or positive control Acarbose was added to a 96-well plate to reach a final concentration of 100 μg/mL. Then, 50 μL of 0.7 U/mL α-glucosidase solution in phosphate buffered saline (PBS) was added, and the initial absorbance at 405 nm was measured. The plate was incubated at room temperature for 5 minutes, followed by the addition of 50 μL of 5 mM pNPG in PBS. After an additional 5 minutes of incubation, the absorbance at 405 nm was measured to determine enzyme activity.

The DPP-IV inhibitory activity was determined using a modified method from (Parmar et al., 2012). 25 μL of each plant extract or positive control Ile-Pro-Ile (Diprotin A) was added to a 96-well plate to reach a final concentration of 100 μg/mL. Then, 25 μL of 0.8 mM Gly-Pro-p-NA in 0.1 M Tris-HCl buffer (pH 8.0) was added, and the plate was incubated at 37°C for 10 minutes. After this, 50 μL of 5 mU/mL DPP-IV enzyme solution in the same tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer was added. The plate was incubated for 60 minutes at 37°C, and the reaction was stopped by adding 100 μL of 3% acetic acid. The absorbance at 405 nm was measured to determine enzyme activity.

The pancreatic lipase inhibitory activity was determined using a modified method from (Wei et al., 2015). 20 μL of each plant extract or positive control (orlistat) was added to a 96-well plate to reach a final concentration of 100 μg/mL. Then, 169 μL of 0.1 M Tris-HCl buffer (pH 7.0) containing 5 mM CaCl² was added, followed by 6 μL of 2.5 mg/mL lipase from porcine pancreas solution prepared in 1X MOPS buffer. The plate was incubated at 37°C for 15 minutes. After this, 5 μL of 10 mM p-nitrophenyl butyrate dissolved in dimethyl sulfoxide (DMSO) was added, and the plate was incubated for an additional 30 minutes at 37°C. The absorbance at 405 nm was then measured to determine enzyme activity.

To correct for potential color interference from plant extracts, a blank control was included for each assay. The blank was prepared under the same conditions as the test samples but without the enzyme. The inhibition rate was calculated using the following formula:

All experiments were performed in triplicate and data are presented as mean ± SD. For each enzyme assay, differences between each extract (n = 181) and the control were assessed by one-way analysis of variance (ANOVA) followed by Dunnett’s multiple comparisons test in GraphPad Prism. Adjusted p-values are reported, statistical significance is denoted as ^*p < 0.05, ^**p < 0.01, ^***p < 0.001, and ^****p < 0.0001.

α-Glucosidase is an enzyme that breaks down disaccharides into monosaccharides in the small intestine, facilitating glucose absorption (Kumar et al., 2011). Inhibiting this enzyme can delay carbohydrate digestion and reduce postprandial blood glucose levels, making it a promising target for type 2 diabetes management (Hossain et al., 2020; Kumar et al., 2011). This inhibitory activity is known to be mediated by various bioactive compounds, including flavonoids (e.g., quercetin), polyphenols, tannins, and triterpenoids, which are commonly found in many medicinal and edible plants (Hossain et al., 2020; Martin & Montgomery, 1996).

Therefore, this study analyzed the α-glucosidase inhibitory activities of 181 extracts from coastal island plants in Korea. The 181 plant extracts were found to have different levels of α-glucosidase inhibitory activity, ranging from 0 ± 0.31% to 85 ± 0.56% (Table 2). Among the 181 plant extracts, Acer okamotoanum Nakai exhibited the highest α-glucosidase inhibitory activity (85 ± 0.56%). Furthermore, the next most potent α-glucosidase inhibitory capacities (> 75%) were found in the following extracts: Tsuga sieboldii Carriere (84 ± 1.31%), Elaeagnus glabra Thunb. (84 ± 0.48%), Acer tataricum subsp. ginnala (83 ± 0.41%), and Staphylea bumalda DC. (75 ± 0.35%). The inhibitory activity of the five extracts listed above was greater than that of the commercial α-glucosidase inhibitor acarbose (69%) (Martin & Montgomery, 1996).

These findings suggest that the identified extracts could be promising candidates for controlling postprandial hyperglycemia, supporting the development of new α-glucosidase inhibitors for the treatment of type 2 diabetes (Kumar et al., 2011).

DPP-IV is an enzyme that degrades GLP-1 and GIP, which are incretin hormones that stimulate insulin secretion and help regulate blood glucose levels (Barnett, 2006). Inhibiting DPP-IV prolongs GLP-1 activity, enhances insulin release and improves glycemic control, making DPP-IV a valuable target for type 2 diabetes therapy (Kumar & Chauhan, 2021). The inhibitory activity of DPP-IV is influenced by various bioactive compounds, including polyphenols (e.g., catechins), flavonoids and alkaloids, which are found in abundance in medicinal plants (Ansari et al., 2022; Singh et al., 2021).

This study evaluated the DPP-IV inhibitory activities of various plant extracts as illustrated in Table 3. The 181 plant extracts were found to have different levels of DPP-IV inhibitory activity, ranging from 0 ± 0.41% to 56 ± 2.76% (Table 3). Of the 181 extracts tested, Elaeagnus macrophylla Thunb. exhibited the highest DPP-IV inhibition (56 ± 2.76%). The next most potent DPP-IV inhibitory activities were observed in Camellia japonica L. (55 ± 5.97%), Farfugium japonicum (L.) Kitam. (55 ± 1.59%), Bidens pilosa L. (55 ± 1.20%), and Solidago altissima L. (54 ± 0.92%). Although these extracts demonstrated notable inhibitory activity, their inhibition rates did not exceed that of the positive control (Ile-Pro-Ile, 86%) (Singh et al., 2021).

These findings suggest that the identified extracts could be used to modulate incretin activity, supporting the development of new DPP-IV inhibitors for treating type 2 diabetes (Lin et al., 2019).

Pancreatic lipase is an enzyme that plays a crucial part in digesting and absorbing dietary fats (Subramaniyan & Hanim, 2025). Inhibiting this enzyme reduces fat absorption and promotes weight loss, making it a promising target for obesity management (Lunagariya et al., 2014). Various natural compounds have been found to exhibit this inhibitory activity, including catechins, polyphenols, saponins and triterpenoids, which are commonly found in numerous edible and medicinal plants (de La Garza et al., 2011).

Therefore, this study analyzed the pancreatic lipase inhibitory activities of 181 extracts from coastal island plants in Korea. The 181 plant extracts were found to have different levels of pancreatic lipase inhibitory activity, ranging from 12 ± 6.84% to 105 ± 1.63% (Table 4). Among the 181 plant extracts, Ilex macropoda Miq. exhibited the highest pancreatic lipase inhibitory activity (105 ± 1.63%). Furthermore, the next most potent pancreatic lipase inhibitory capacities (> 90%) were found in the following extracts: Lilium lancifolium Thunb. (93 ± 5.02%), Mallotus japonicus (L. f.) Müll. (93 ± 2.50%), Viburnum japonicum (Thunb.) C. K. Spreng. (91 ± 2.35%), and Suaeda japonica Makino (90 ± 1.93%). The inhibitory activity of the five extracts listed above was greater than that of the commercial pancreatic lipase inhibitor orlistat (87%) (Rajan et al., 2020).

These findings suggest that the identified extracts could be promising candidates for reducing fat absorption, supporting the development of new anti-obesity agents (Hou et al., 2022).

MetS is a complex health condition in which multiple metabolic disorders, including obesity, hyperglycemia, and dyslipidemia, occur simultaneously, and it is recognized as a major cause of cardiovascular disease and type 2 diabetes (Heindel et al., 2017). The increasing prevalence of MetS, primarily driven by reduced physical activity, high-calorie diets, and the widespread adoption of Westernized eating habits, is considered a significant public health concern worldwide, leading to an increasing demand for effective therapeutic strategies (Asghari et al., 2015; Dziegielewska-Gesiak, 2021). Various mechanisms have been investigated for the treatment of MetS, and among them, enzyme inhibitors targeting α-glucosidase, DPP-IV, and pancreatic lipase have been demonstrated to be effective in the management of type 2 diabetes and obesity (Hossain et al., 2020; Kumar & Chauhan, 2021; Lunagariya et al., 2014).

Acarbose, a well-known α-glucosidase inhibitor, reduces glucose absorption in the intestinal lumen and enhances insulin sensitivity, thereby effectively controlling postprandial hyperglycemia and hyperinsulinemia (Altay, 2022). It is considered a safe and effective therapeutic agent for managing postprandial blood glucose levels, as it does not increase the risk of hypoglycemia or weight gain (Uuh Narvaez & Segura Campos, 2022). However, acarbose has been associated with gastrointestinal adverse effects, such as gas, bloating, and diarrhea (Hollander, 1992), and its efficacy has not been confirmed in cardiovascular outcome trials (Altay, 2022). Similarly, Ile-Pro-Ile, also known as diprotin A, is a well-known DPP-IV inhibitor that effectively prevents the degradation of GLP-1 in vitro (Holst et al., 1998). However, its in vivo efficacy remains limited, and several adverse effects, including nasopharyngitis, headache, nausea, hypersensitivity, dermatological reactions, and pancreatitis, have been reported (Juillerat-Jeanneret, 2014). Likewise, orlistat is a well-known pancreatic lipase inhibitor that reduces fat absorption by binding to the active site of the enzyme during the digestive process, thereby promoting the excretion of undigested dietary fat (Bülbül & Çokdinleyen, 2024). However, orlistat has been reported to induce gastrointestinal side effects, including bloating, loose stools, or diarrhea (Morales et al., 2016). Given these concerns, the long-term use of synthetic drugs targeting these enzymes may lead to adverse effects and reduced patient compliance (Asliddin & Gulnaz, 2025). Accordingly, there is a need for effective and sustainable alternative treatments that can overcome the limitations of current pharmacological approaches.

In this context, natural product-based therapeutics, known for their generally greater safety than synthetic drugs, are increasingly regarded as promising alternatives, owing to their structural diversity, favorable biocompatibility, and potential for multi-target activity (Meier & Lappas, 2016; Wu et al., 2025). Especially, coastal plants represent a promising resource due to their capacity to produce diverse bioactive metabolites in response to environmental stresses such as high salinity, ultraviolet radiation, and nutrient limitations (Saba Nazir et al., 2018; Sadeghi et al., 2024). To adapt to such environmental stresses, coastal plants are known to produce a wide array of secondary metabolites, including potent antioxidants such as phenolic compounds (Stanković et al., 2023). These bioactive constituents may act as valuable enzyme inhibitors, highlighting their therapeutic potential for potential in the management of MetS.

In this study, the inhibitory activities of 181 natural extracts derived from coastal island were evaluated against α-glucosidase, DPP-IV, and pancreatic lipase in vitro. Several extracts exhibited inhibitory activities that were comparable to or even exceeded those of commercially available positive controls. Notably, certain extracts, including Hypochaeris radicata, Vaccinium bracteatum Thunb., Sorbus ulleungensis Chin. S. Chang, Lonicera insularis Nakai, and Trachelospermum asiaticum (Siebold & Zucc.) Nakai, exhibited potent inhibitory activity across all three enzyme assays, highlighting their potential as multifunctional natural therapeutics for the simultaneous regulation of carbohydrate and lipid metabolism. Given that MetS is characterized by a multifactorial pathophysiology involving the dysregulation of multiple metabolic pathways, therapeutic strategies that simultaneously modulate multiple targets are increasingly recognized as being more efficacious than those focusing on a single enzyme or pathway (Lillich et al., 2021). Accordingly, the simultaneous inhibition of α-glucosidase, DPP-IV, and pancreatic lipase by these extracts suggests a broader modulatory potential on the metabolic disturbances underlying MetS, thereby conferring therapeutic advantages over agents targeting a single enzymatic pathway. Moreover, these extracts present as high-value natural therapeutic candidates, offering potential advantages over conventional drugs, which often face challenges such as high costs, adverse side effects, and resistance.

In conclusion, this study provides robust scientific evidence supporting the potential of island-derived natural resources as sustainable and effective therapeutic agents for managing MetS. These findings provide a strong basis for the development of natural product-based alternatives to conventional pharmacological treatments. To facilitate clinical translation into pharmacotherapy, functional food development, and preventive strategies, future studies should aim to isolate the active constituents and validate their efficacy and safety through vivo and clinical trials.