Bio-assay guided fractionation and identification of antihypertensive compounds from syzygium polyanthum (wight) walp. (serai kayu) leaves

Abstract

Hypertension is commonly known as a silent killer disease. There are several available antihypertensive drugs, yet expensive and have side effects. Syzygium polyanthum (Wight) Walp. (Serai Kayu) leaf has been reported for its antihypertensive effect and regularly consumed by the locals as fresh salad. However, the responsible bioactive compounds were still unknown. The present study aimed to screen the potential antihypertensive compound(s) from the most active crude extract of S.polyanthum leaves and to examine correlation between total phenolic content and antioxidant activities with their magnitude of antihypertensive effect. S. polyanthum leaves were partitioned by extractions with hexane, ethyl acetate, methanol and water to obtain crude hexane extract (HSP), ethyl acetate extract (ESP), methanol extract (MSP) and aqueous extract (ASP). These four extracts were intravenously administered in pentobarbital-anaesthetized Spontaneously Hypertensive Rats (SHR) (n=5) for measurement of blood pressure as well as the heart rate. The most active crude extract was then fractionated in a column chromatography using binary solvent system of ethyl acetate and methanol. Thin layer chromatography (TLC) profiling was done to pool out nine fractions derived from the active crude extract into 3 final fractions (F1ASP, F2ASP and F3ASP). These fractions were then intravenously administered in anaesthetized SHR (n=5) for measurement of blood pressure and heart rate and then compared with the effect of 5 mg/kg of captopril, a standard antihypertensive drug. Chemical profiling of the fractions were analyzed using Liquid Chromatography Mass Spectrometry (LC-MS). In addition, analysis of TPC and antioxidant FRAP assay were conducted on the fractions. Statistical analyses conducted were one-way and two-way ANOVA for in vivo animal study while the correlation between antihypertensive and antioxidant activity was tested using Pearson?s Correlation test. This study showed that ASP as the most prominent antihypertensive crude extract. F2ASP was found to be the most active fraction, and its antihypertensive effect was actually more potent compared to other fractions as well as the crude ASP extract and comparable with captopril. Several potential antihypertensive compounds identified by LC-MS are 1-galloyl-glucose, polydatin, sesamol, brazilin, eugenol, ellagic acid, kukoamine A and cyclocurcumin. TPC and antioxidant activities of ASP crude extract and the three derived fractions were positively correlated. However, these activities were not significantly correlated with their antihypertensive activity. In conclusion, this study showed ASP crude extract and F2ASP fraction have the most prominent antihypertensive effect of S. polyanthum leaves with identification of several potential antihypertensive compounds but the magnitude of the effect was not correlated with either TPC content or antioxidant activities of S.polyanthum leaves. Potential antihypertensive compounds from S.polyanthum leaves can be further isolate in order to generate other alternative antihypertensive drugs that are more cost-effective and fewer side effects.