Pharmacological, Chemical, Chromatographic and Spectroscopic Profiles of Extracts and Bioactive Compounds from Selected Kenyan Ruellia Species

Abstract

The growing challenge of non-communicable diseases (NCDs) especially in developing world necessitates search for novel drugs that are not only efficacious but also affordable. Plants have traditionally provided a rich source of medicine, and therefore, there is a need to explore the untapped reservoir of medicinal plants for the management of NCDs. Ruellia (Acanthaceae) species are wild perennial creepers which have been reported to possess anti-inflammatory, analgesic, antinociceptive, and antipyretic activities. Therefore, the main objective of this study was to investigate the pharmacological, chemical, chromatographic, and spectroscopic profiles of the bioactive compounds present in three Kenyan Ruellia species. The selected species viz. R. prostrata (RPM), R. bignoniiflora (RBK) and R. lineari-bracteolata (RLB), were studied with special emphasis to antioxidant, analgesic, anti-inflammatory and anti-arthritic activities. Whole plant parts were collected from their natural habitats and both aqueous extracts (hot maceration) and organic extracts (cold maceration) were obtained. The acute toxicity study categorized the aqueous extract of R. prostrata to be in Category 5 (>2000-5000mg/kg) as per Globally Harmonised System. The sub-chronic toxicity studies revealed that the oral aqueous extract of R. prostrata (1000mg/kg per os) had no adverse effects on the internal organs, haematological parameters, and blood biochemistry in Wistar albino rats. The methanolic extract of RLB showed the highest antioxidant activity [1,1-diphenyl-2-picrylhydrazyl radical (DPPH)], scavenging activity, of IC50, 2.9±3.21 μg/mL, comparable to ascorbic acid standard (2.1±0.10 μg/mL). The aqueous extract of RPM showed the highest analgesic activity (Tail flick method) of ED50, 358.90±20.90 mg/kg. The aqueous extract of R. prostrata showed the highest anti- antinociceptive activity (Formalin test) in phase-1 (ED50 22.22±0.52 mg/kg), and phase-2 (ED50 7.07±4.10 mg/kg). The aqueous extract of RPM also showed the highest anti-inflammatory activity (Carrageenan test) of ED50, 168.05±3.25 mg/kg. In vivo anti-arthritic studies (Complete Freund’s Adjuvant-induced arthritis) revealed no differences (p˃0.05) compared to the untreated control in hind paw swelling (mL), hind joint thickness (cm), arthritis score on a scale of 0-16, and inhibition of loss of grip strength (secs) as observed on a rotating rotarod. Aqueous extract of RPM did not suppress the bone marrow unlike methotrexate standard. Chemical profiling revealed the presence of terpenoids, saponins, flavonoids, phenolics, and glycosides. No alkaloids were detected in all the three species. Fourier transform infra-red profiling revealed the presence of -OHstr, C-Hstr, C=Cstr and C-O-C linkages. Some of the compounds in Gas Chromatography-Mass Spectrometry profiling were β-sitosterol, stigmasterol, lupeol, and triterpenes. 13-Docosenamide, (Z)-, l-(+)-Ascorbic acid 2,6-dihexadecanoate, α-D-Glucopyranose, 4-O-. β -D-galactopyranosyl-, squalene, 9-Hexadecenoic acid, methyl ester, (Z), 9-Octadecenamide, (Z)-, 9-Octadecenoic acid (Z)-, methyl ester. These compounds have been documented to possess antioxidant, anti-inflammatory and analgesic activities. The present study concluded that extracts from Ruellia species studied possess antioxidant, analgesic, antinociceptive, anti-inflammatory and anti-arthritic activities, with the aqueous extract of RPM showing the highest activities, followed by the aqueous extract of RBK. This is the first scientific report regarding the efficacy of RPM in a rheumatoid arthritis animal model. The antioxidant, analgesic, antinociceptive and anti-inflammatory activities of R. bignoniiflora and R. linear-bracteolata were reported for the first time. Some compounds identified from the selected Kenyan Ruellia species, such as flavonoids, saponins, phenolics, glycosides, terpenes, β-sitosterol, stigmasterol, and lupeol have been reported in other Ruellia species. The present study recommends that the bioactive compounds present in R. prostrata and R. bignoniiflora should undergo further pre- clinical studies as analgesic and anti-arthritic drugs in a non-human primate before use in man.