Alleviation of adverse effects associated with α-glucosidase inhibitors by Ocimum basilicum L., Matricaria chamomilla L., and Salvia officinalis L. reveals novel selective inhibition of Bacillus α-glucosidase by acarbose

Abstract

Ocimum basilicum L., Matricaria chamomilla L., and Salvia officinalis L. have literature-supported ethnobotanical claims of reducing hyperglycaemia and gastrointestinal discomfort. Thus, they contain potent potential for reducing gastrointestinal adverse side effects associated with the use of the type 2 diabetes medication, acarbose. The adverse effects are predominantly theorised to be caused by excess carbohydrate fermentation by gut bacteria. Therefore, the aim of this study was to subject herbal extracts as well as compounds identified in the herbs to in silico and in vitro investigation for selective inhibition of a gut bacterial enzyme, Bacillus α-glucosidase, compared with human α-glucosidase. In silico molecular docking was employed to filter and select top performing compounds that exhibited the highest selective Bacillus α-glucosidase inhibition, followed by pharmacokinetic examination of the selected compounds. In vitro enzyme kinetics, hepatocellular carcinoma cell line cytotoxicity and the reduction of hepatic lipid accumulation in a hepatocellular carcinoma/oleic acid cellular model of metabolic dysfunction-associated fatty liver disease was examined. A metabolomic study on the concentration of the selected compounds in the herbs as well as a comparative analysis on abundant metabolites between herbs were analysed through an ultra-performance liquid chromatography-mass spectrometry-based study. Molecular docking revealed cinnamic acid, coumaric acid, epicatechin, hesperetin, linalool, menthol, octenol, terpineol, umbelliferone, and vanillic acid as the top predicted compounds with the highest predicted selective inhibition of Bacillus α-glucosidase. These findings were validated through in vitro assessment, in which the primary finding and the most unexpected result was obtained through enzyme kinetics, where compared with all compounds, acarbose exhibited the most potent inhibition and selectivity towards Bacillus α-glucosidase. Only umbelliferone significantly reduced cell viability and therefore validated its predicted toxicity that was obtained through pharmacokinetic studies. O. basilicum, M. chamomilla, and S. officinalis were evaluated against Camellia sinensis (L.) Kuntze for cytotoxic effects, where only M. chamomilla produced a significantly higher EC50, substantiating the herbs potent anti-cancerous abilities. Compounds and herb extracts were not found to reduce hepatic lipid accumulation. The novel finding was related to acarbose inhibition and specifically its potent selectivity of Bacillus α-glucosidase which discredits and disproves the theory that excess bacterial fermentation is the cause behind acarbose's reported adverse effects. Thus, this research study rather proves that acarbose negatively affects gut bacterial enzymes, promoting microbiome dysbiosis and therefore future research should at the forefront focus on the rehabilitation of diabetic patients' gut microbiome and intestinal health.

HIGHLIGHTS • Type 2 diabetes (T2D) medication, acarbose, causes adverse gastrointestinal side effects. • It is theorised this is due to excess carbohydrate fermentation by gut bacteria. • However, acarbose proved potent selective inhibition towards Bacillus α-glucosidase. • Disproving the theory, showing acarbose negatively affect gut bacterial enzymes. • Leading to possible future pathogenic Bacillus α-glucosidase inhibition by acarbose.