Angiotensin-1-converting enzyme inhibition, antioxidant activity, and modulation of cerebral Na+/K+ ATPase by free phenolics of African locust bean (Parkia biglobosa).

Aims: To investigate the antioxidant activities and effects of free phenols (FPPB) and bound phenols (BPPB) of Parkia biglobosa leaves on some enzymes of neuro-cardiovascular relevance.

Methods And Results: HPLC-DAD fingerprinting of FPPB and BPPB, and the antihemolytic, radical (1,1-diphenyl-2 picrylhydrazyl, DPPH; 2,2-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), ABTS) scavenging and ferric reducing antioxidant properties of extracts, were assessed. In addition, the effects of the phenolics on angiotensin-1-converting enzyme (ACE), cerebral acetylcholinesterase/butyrylcholinesterase (AChE/BuChE), and Na/KATPase were determined in vitro. FPPB was more potent than BPPB in terms of ABTS (EC:4.06 ± 0.3 vs 24.07 ± 2.1 μg/mL) and DPPH (EC:3.82 ± 0.2 vs 10.22 ± 0.1 μg/mL) radicals scavenged, respectively. The free phenolic extract was a better DPPH scavenger than ascorbic acid (EC = 12.58 ± 0.4 μg/mL; DPPH reference) and compared well with Trolox (EC:4.44 ± 0.08 μg/mL; ABTS reference). The anti-hemolytic effect of FPPB (36%) and BPPB (53%) was highest at 15 μg/mL but lower than that recorded for ascorbic acid (67% at 10 μg/mL). Even though FPPB (IC = 15.35 ± 4.0 μg/mL) and BPPB (IC = 46.85 ± 3.3 μg/mL) showed considerably lower ACE-inhibitory effect than ramipril (IC:0.173 ± 0.04 μg/mL), both extracts demonstrated dose-dependent, significant (p < 0.01/p < 0.05) inhibition of the enzyme. FPPB increased cerebral Na+/K+ATPase activity but neither phenolic extract affects cerebral AChE/BuChE activities. HPLC-DAD revealed catechin, caffeic acid, and quercetin, respectively, as the major phenolics (mg/g) in FPPB (29.85, 30.29, and 17.10) and BPPB (32.70, 30.51, and 19.25).

Conclusion: The effects of P biglobosa on ACE and cerebral ATPase are related to its constituent phenolics. ACE inhibition could be an important mechanism underlying the documented hypotensive effect of the plant.