Mechanistic in vitro study of the effect of <i>Cucurbita moschata</i> (Cucurbitaceae) on carbohydrate digestive enzymes

Diabetes is marked by postprandial hyperglycemia (PHG), an abnormal rise in blood glucose after meals. A key therapeutic goal to reduce PHG is the inhibition of α-amylase (αAM) and α-glucosidase (αGL), enzymes that break down carbohydrates into sugars. Cucurbita moschata has been shown to inhibit both enzymes. However, its inhibition mechanism has not been explored. This study investigated the in vitro inhibition mechanisms of αAM and αGL and conducted a metabolomic analysis of C. moschata (edible part) water-extract (CME), aiming to preliminarily identify its bioactive compounds (BCs). The inhibitory mechanisms were determined using Lineweaver-Burk plots. The BCs were identified and quantified using HPLC-QTOF-MS, employing both targeted and untargeted metabolomic approaches. CME had a significant higher effect (p < 0.05) on αAM activity than against αGL with IC₅₀ of 28.99 and 698.42 mg/mL, respectively. The extract showed mixed and uncompetitive type inhibitions on αAM and αGL, respectively. The lowest inhibition constant (K_i) was 47.68 mg/mL on αAM activity at 20 mg/mL. Untargeted metabolic profiling by UPLC-MS-ESI-QTOF putatively identified 30 compounds in CME, such as amino acids, vitamins, phytohormones, fatty acids, cucurbitacins and phenolic acids, and flavonoids. Functional analysis of CME identified significant pathways, including pantothenate and CoA biosynthesis and phenylpropanoids, among others. The targeted analysis by UPLC-MS-ESI-QqQ allowed us to identify 12 compounds, with l-phenylalanine, p-hydroxybenzoic, and p-coumaric acid as majors. This study demonstrated the inhibitory potential of CME on αAM and αGL activities, which may be attributed to its metabolites. Thus, this plant represents a valuable source of BC against PHG. Practical Application: The research highlights that Cucurbita moschata has significant potential in managing postprandial hyperglycemia in diabetic patients by inhibiting enzymes like α-amylase and α-glucosidase. In addition, the identification of its compounds emphasizes its importance as a source of bioactive compounds. Therefore, C. moschata could be effectively utilized in the development of nutraceuticals or as an ingredient in functional foods specifically designed for postprandial hyperglycemia management. Thus, integrating C. moschata as part of the daily diet could offer patients with diabetes a natural alternative to control their blood glucose levels after eating.