Selected physiological activities and in vitro toxicological evaluation of essential oils and crude extracts of Helichrysum odoratissimum (L.) Sweet used for the treatment of diabetes in Eastern Cape Province, South Africa

Abstract

Diabetes mellitus is a multifactorial glucose metabolic disorder with detrimental effect on the economic and health status of individuals in South Africa. Plant medicine has become the alternative healing power of this disease due to its availability and affordability with little or no side effect compared with synthetic drugs. However a few of these medicinal plants have not been scientifically studied to ascertain their effectiveness and safety. This research work evaluated the extracts of H. odoratissimum leaves and stems for their anti-diabetic property using selected physiological investigations to validate its folkloric usage in the management of diabetes in Eastern Cape Province of South Africa. In this study aqueous extracts of H. odoratissimum leaves and stem were investigated for enzyme inhibitory activities against alpha-amylase and alpha glucosidase using porcine pancreatin and p Nitrophenyl α D glucopyranoside p NP-Gluc enzyme assays respectively. Acarbose and epigallocatechin gallate served as reference drugs respectively. The anti inflammatory activity was performed using inhibition of 5 Lipoxygenase activity and inhibition of inducible nitric oxide synthase iNOS from nitric oxide NO production in lipopolysaccharide LPS activated macrophages RAW 264.7 with nordihydroguaiaretic acid NDGA and aminoguanidine AG as reference drugs while 3 4 5 dimethylthiazol 2 yl 2 5 diphenyltetrazolium bromide MTT assay was used to assess cell viability. The aqueous leaves and stem extract exhibited weak inhibitory potency against 5 LOX activity .The IC50 values of 1.88 ugmL and 4.64 ug mL for leaf and stem extracts, respectively, is significantly different p 0.05 from that of the standard NDGA with IC50 14.49 ug mL. For inhibition of iNOS activity by the extracts aqueous stem extract exhibited a high inhibitory effect of 16.27 μg mL on NO production compared to 20.83 μgmL displayed by leaf aqueous extract. However the percentage cell viability using MTT assay was 86.07 percent and 90.51 percent for aqueous leaf and stem extracts respectively. The percentage inhibition of aqueous leaf and stem extracts against alpha amylase activity was 0.2 percent and 0.04 percent respectively. These cannot be compared with the standard drug acarbose which exhibited 96 percent inhibitory effect against alpha amylase activity. However the aqueous leaf extract exhibited strong percentage inhibition of 90.05 percent over 45.48 percent displayed by aqueous stem extract against alpha glucosidase activity. This is compared favourably with 86.09 percent of the standard, epigallocatechin gallate EGCG. Alkaloids flavonoids and terpenoids were present in appreciable amounts in both leaves and stem extracts. The result of radical scavenging showed that all the assay models exhibited significant influence over inhibition activity of the extracts assayed. In respect to the IC50 values aqueous stem extract had good DPPH radical scavenging activity while leaf aqueous extract had good nitric oxide NO and hydrogen peroxide H2O2 inhibition potential. Aqueous stem extracts exhibited effective antimicrobial activity against the tested pathogenic species with minimum inhibitory concentrations values ranging from 0.1 5.0 mg mL for bacteria and 0. 5 5.000 mg mL for fungi respectively. The antioxidant activity thus indicates the potential modulatory utility of the leaf and stem extracts of H. odoratissimum against oxidative stress-induced chronic diseases. This discovery demonstrated that aqueous leaf and stem extracts contain bioactive components with anti diabetic potential.Thesis (PhD) -- Faculty of Science and Agriculture, 202