ABSTRACT

Angiotensin I Converting Enzyme (ACE) is a glycoprotein with peptidyl dipeptide hydrolase

activity which cleaves Angiotensin I to produce Angiotensin II. Angiotensin II is a powerful

vasoconstrictor that as well regulates the synthesis of aldosterone that consequently interferes

with blood pressure regulation. This study evaluates the effect of aqueous extract of

Combretummicranthum leaves and its fractions on the in vitro activity of rabbit ACE and the

possible antioxidant potentials fractions. C. micranthum leaves were extracted using aqueous

as solvent. Consequently, the in vitro ACE inhibitory activity of the extract was conducted

using cushman and cheng method and the aqueous extract was further subjected to

chromatographic fractionation where the fractions obtained were assayed for in

vitroinhibitory activity against rabbit ACE and their possible antioxidant potentials. Aqueous

extract of C. micranthumleaves produced 59.43±4.00 % inhibitory activity comparable to

captopril which produced 83.02±2.67% activity. The chromatographic fractions A, B, C and

D were able to inhibit the in vitro activity of rabbit ACE with the inhibitory percentages of

8.21±41.19, 97.69±8.57, 78.32±7.14 and 98.32±2.66 % respectively. Phenolic compounds

were found in the various fractions of the aqueous extract of C. micranthum with fraction B

having the highest amount of these phenolics. The antioxidant potency of these fractions was

evident in their free radical scavenging IC50, reducing power ability and total antioxidant

capacity which all showed that fraction B may possibly exhibit the highest antioxidant

potency as compared to fractions C and D. The bioactive phytochemical constituents from the

GC-MS analysis of fraction B of the aqueous extract of C. micranthum where found to be

Megastigmatrienone, 3,5-Dimethoxy-4-hydroxyphenylacetic acid and Estra-1,3,5(10)-trien-

17β-ol. Hence, the results demonstrated that aqueous extract of C. micranthum has shown the

tendency to inhibit the in vitro activity of ACE which could be attributed to its antioxidant

activity demonstrated by the reduction power and the total antioxidant capacity of the various

fractions.

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