In vitro angiotensin-converting enzyme inhibitory activity of Hibiscus sabdariffa (Linn.) and Allium sativum (Linn.) as potential alternatives to captopril for hypertension management
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Abstract
Hypertension is a major global public health challenge affecting over 1.28 billion adults worldwide. Although synthetic angiotensin-converting enzyme (ACE) inhibitors such as captopril are widely used, their adverse effects and cost have prompted interest in plant-derived alternatives. Fresh Hibiscus sabdariffa calyces and Allium sativum bulbs were collected in January 2026 from Kawo market, Kaduna, Nigeria, and authenticated, with voucher specimens (NDA/BIOH/202644 and NDA/BIOH/202645, respectively) deposited at the Nigerian Defence Academy Herbarium. This study evaluated the in vitro ACE inhibitory activity of Hibiscus sabdariffa (Roselle) and Allium sativum (Garlic) extracts and fractions using a modified gelatin-ninhydrin assay with cow lung as the enzyme source. Qualitative phytochemical screening revealed saponins, alkaloids, flavonoids, tannins, cardiac glycosides, and terpenes in both plants. Quantitative analysis showed that roselle contained higher levels of alkaloids (876.78 mg/g), flavonoids (288.63 mg QE/g), polyphenols (6.61 mg GAE/g), and tannins (13.88 mg TAE/g) compared to garlic. Column chromatography yielded five fractions from garlic (G1–G5) and seven from roselle (R1–R7). ACE inhibition assays showed that nine of twelve fractions (75%) exhibited strong inhibitory activity with IC50 values ≤25 µg/mL. The most potent plant fraction was garlic fraction G4 (IC50 = 15 µg/mL), followed by roselle fractions R5 (18 µg/mL), R6 and R7 (both 20 µg/mL). Captopril demonstrated an IC50 of 5 µg/mL, validating the assay. GC-MS analysis of the most active fractions identified squalene, 2,4-di-tert-butylphenol, stearic acid, and fatty acid derivatives as pharmacologically relevant compounds. These findings provide scientific validation for the traditional use of both plants in hypertension management and demonstrate that they contain bioactive compounds with significant ACE inhibitory potential.
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