An evaluation of the chemical composition and the in vitro and in vivo antihypertensive activity of extracts of Tulbaghia acutiloba Harv. in an L-NAME induced hypertensive model.

Abstract

The increasing prevalence of hypertension over the years has been identified as a major contributor to high morbidity and mortality, globally and locally, in Africa, posing a serious global health threat. The demand for novel therapeutic strategies has become increasingly important, given that conventional options may be inaccessible and costly, and are often associated with side effects, hampering patient compliance. The scientific validation of alternative strategies, such as phytotherapy has, therefore, become a major focus in the treatment and management of hypertension, as it is perceived as being cheap, accessible, and possessing minimal side effects. Hence the investigation of medicinal plants, within the field of novel drug discovery, is of interest as plants possess various phytochemicals displaying biological activities, which may be beneficial in hypertension, and it’s associated complications. Since there is no existing scientific data available to validate its medicinal usage, this study, therefore, evaluated the in vitro and in vivo antihypertensive effects of Tulbaghia acutiloba. The hydro-methanolic extracts of the plant parts (i.e. leaves, flowers, rhizomes and roots) were initially evaluated in vitro for their phytochemistry, antioxidant potential, angiotensin-converting enzyme (ACEI) inhibition activities, and heavy metal content. The phytochemical investigation of the various parts of the plants showed the presence of phenols, amino acids and alkaloids in all parts, with the leaves exhibiting a higher total phenolic content, in comparison to the other parts. Further analysis, using gas chromatography–mass spectrometry (GC-MS), revealed the presence of bioactive compounds, such as α-linolenic acid, which was found only in the leaves. Other compounds such as oleic acid and palmitic acid were found in all the parts of the plants. All parts of the plant showed antioxidant activity in vitro. Heavy metal toxicity analysis revealed the safety profile for all parts of the plants. All parts also showed a potential ACE inhibitory effect of greater than 50%, with the leaves showing the most significant effects, comparable to the conventional drug, Ramipril. We further investigated the effect of the hydro-methanolic leaf extract on oxidative stress, endothelial function, cardiovascular, renal and haematological parameters, associated with hypertension, in an L-NAME induced hypertensive rat model. The administration of the hydro-methanolic leaf extract of Tulbaghia acutiloba at different concentrations of 40, 60 and 80mg/kg b.w., reduced systolic, diastolic and mean arterial pressure in the model, with a pronounced effect at the dosage of 80mg/kg b.w. Additionally, the leaves of T. acutiloba significantly enhanced bradykinin receptor levels (B1 and B2), nitric oxide (NO) availability, promoted antioxidant activities and significantly reduced ACE activity in serum and cardiac tissues in hypertensive rats. Cardioprotection was significantly enhanced at 80mg/kg b.w. of T.acutiloba, as depicted by the cardiac function and morphology, and cardiac gene expression in experimental rats. There was no evidence of toxicity as depicted in the liver enzymatic activity after the administration of T.acutiloba in the hypertensive rats. Administration of T. acutiloba improved renal function as evidenced by the increased creatinine clearance (Ccr), improved

fractional excretion of sodium and decreased urine protein-creatinine ratio (UPr/UCr). Additionally, decreased levels of leucocyte infiltration, decrease in both, neutrophil to lymphocyte ratio (NLR) and lymphocyte to monocyte ratio (LMR), was found after administration of T.acutiloba, with a maximal effect occurring at a dose of 80mg/kg b.w. Together, these findings provide scientific validation for T.acutiloba as a medicinal plant that has cardioprotective and antihypertensive properties, and is able to improve renal function and haematological parameters in an L-NAME induced hypertensive rat model. Overall, the data also provides substantive evidence for the possible usage of T.acutiloba as an alternate antihypertensive agent, in resource limited areas where conventional drugs are inaccessible. Key Words: Tulbaghia acutiloba, phytotherapy, cardioprotection, L-NAME, renal function, haematology.