Unveiling the potential of naturally occurring rosmarinic acid inspired analogues as pancreatic lipase inhibitors: In silico, in vitro and in vivo evaluation as anti-obesity agents

Abstract

Pancreatic Lipase (PL) is a prime enzyme responsible for the digestion of dietary fat and is considered a safer and more efficient target for managing obesity. Orlistat is the only approved drug for the long-term management of obesity. In this study, using a molecular docking study, various inhibitors were designed via structural optimization of one of the moderately active natural products, namely, rosmarinic acid. A total of 17 acrylate-linked chromone analogues were synthesized, followed by structure elucidation via NMR spectroscopy and HR-MS. To confirm the stereochemistry of the analogues, a single-crystal XRD spectroscopy was performed for analogue 5ab. Among all the synthesized analogues, six analogues were found to exhibit IC50 values in the range of 1.24–2.76 µM. The analogue 5gb was the most potent among the series with IC50 of 1.24 ± 0.296 µM. The enzyme kinetics study revealed a competitive inhibitory mechanism, with Ki values of 0.554 and 0.488 for 5gb and orlistat, respectively. The number of binding sites (n) and binding constant values were obtained through a fluorescence quenching study and found to be 0.57 and 2.97 × 105 L mol−1, respectively, confirming the single binding site of analogue 5gb in the PL enzyme. Through in vivo screening, 5gb was found to exhibit significant weight reduction and normalization of the serum parameters (triglycerides, total cholesterol, HDL, and LDL cholesterol) at a dose of 20 mg/kg. Through a faecal triglyceride quantification study, the PL inhibitory mechanism was confirmed. Further, the histopathological changes (that occurred in obese animals) in liver and adipose tissue were normalized in the case of 5gb treatment groups. Thus, 5gb possessed a comparable anti-obesity activity to that of orlistat.