Abstract:
Essential oils from scent and curry leaves have been used in folk medicine for the
treatment/management of several ailments for centuries with limited information on the scientific backing. Hence, this study sought to investigate the possible mechanisms of antidiabetic and antihypertensive properties of essential oils from scent and curry leaves in vitro. The essential oils were obtained by hydro-distillation and phytoconstituents were analysed using Gas Chromatography. The phenolic contents, antioxidant properties and inhibitory effect of the oils on pancreatic α-amylase, intestinal α-glucosidase and angiotensin-I converting enzyme (ACE) were determined in vitro. Furthermore, ability of the oils to prevent some pro-oxidants induced lipid peroxidation in selected mammalian tissues was investigated. The essential oils inhibited αamylase, α-glucosidase and ACE activities dose-dependently. As revealed by the EC50 values, essential oil from curry leaves had higher α-amylase (7.59 ml/L), α-glucosidase (6.85 ml/L) and ACE (2.66 ml/L) inhibitory ability than that of scent leaves α-amylase (8.83 ml/L), α-glucosidase
(10.50 ml/L) and ACE (3.10ml/L). The total phenol ranged from 126.20 (scent) to 163.15 mg GAE/100 g (curry), and total flavonoid ranged from 30.25 (scent) to 45.20 mg QE/100 g (curry).
The oil exhibit strong antioxidant properties as exemplified by their reducing power, Fe2+ chelating and their radical scavenging abilities. Furthermore, the essential oils inhibited lipid peroxidation induced by sodium nitroprusside and FeSO4 in isolated rat’s pancreas, heart and lungs homogenates. The GC characterization revealed the presence of phytochemicals such as limonene, α-terpineol, neral, borneol, β-caryophellene, mycrene, α-thujene, 1,8-cineole, β-elemene, linalool, α-pinene, γ-terpinene, terpinen-4-ol and geranial, as the most abundant phytochemicals in the essential oils. Thus, inhibition of key enzymes linked with type-2 diabetes (α-amylase and αglucosidase) and hypertension (ACE), and the antioxidant properties of the oils may be due to constituent phytochemicals of the oils, and may also suggest possible mechanism underlying their antidiabetic and antihypertensive properties. Nevertheless, essential oil from curry leaves appeared more potent than that of scent leaves.
