Inhibitory effect of Mexican oregano (Lippia graveolens Kunth) extracts on digestive enzymes in vitro, and beneficial impact on carbohydrates and lipids absorption in vivo

Abstract

Ethnopharmacological relevance: Although Mexican oregano inhibits digestive enzymes in vitro its effect on the absorption of carbohydrates and lipids in vivo has not been addressed.

Aim of the study: Assess the effect of Mexican oregano (Lippia graveolens Kunth) on carbohydrates and lipids absorption in vivo. The antioxidant activity also was investigated.

Materials and methods: Enzymatic inhibitory action of lipase, α-amylase, and α-glucosidase was evaluated in vitro. Oral lipid (OLTT) and starch tolerance tests (OSTT) were conducted with L. graveolens acetone (O-A) and ethanol (O-E) extracts (at 102 mg/kg body weight equivalent to a 1 g human doses) in male Wistar rats. The antioxidant activity was evaluated through inhibition of lipid peroxidation and scavenging radical.

Results: Both extracts exhibited higher inhibitory median concentration (IC₅₀) of lipase activity (1.9 μg/μL for O-E and 1.8 μg/μL for O-A) than the positive control (Orlistat) (0.07 μg/μL). The IC₅₀ of α-amylase was higher (41.8 μg/μL for O-E and 25.2 μg/μL for O-A) than the Acarbose (2.5 μg/μL); while α-glucosidase results showed not statistically differences between groups (∼1.7 μg/μL). The OLTT results showed that both extracts significantly reduced serum triglycerides (∼147 mg/dL for O-E and ∼155 mg/dL for O-A) as compared with negative control group (only lipid load). In the OSTT, glucose levels showed a significant decrease (∼31 mg/dL for O-E and ∼17 mg/dL for O-A) than the negative control group (only starch load). About in vitro antioxidant evaluation, not statistically differences between extracts and positive control (Trolox) were observed for scavenged free radicals (∼2.0 μg/μL); whereas O-A inhibited lipid peroxidation similar to the Trolox (∼0.8 μg/μL IC₅₀). The main chemical composition of both extracts was coumaric acid, luteolin, rutinoside, naringenin, and carvacrol.

Conclusions: Both extracts reduce lipid absorption; whereas O-E decreases carbohydrate absorption in vivo. Both extracts inhibit lipid peroxidation and scavenging free radicals in vitro.

Keywords: Antioxidant; Enzymatic starch digestion; Hypoglycemic; Hypolipidemic; Mexican oregano.