Pharmacognostic profiles, evaluation of analgesic, anti-inflammatory and anticonvulsant activities of Newbouldia laevis (P. Beauv.) Seem. ex Bureau leaf and root extracts in Wistar rats

Abstract

Ethnopharmacological relevance: Newbouldia laevis is a popular medicinal plant whose leaves and roots are used in Nigeria as ethnomedicinal prescriptions for pain, inflammation, convulsion, and epilepsy. These claims have not been scientifically verified prior to this study. Aim of the study: To determine pharmacognostic profiles of the leaves and roots and evaluate the analgesic, antiinflammatory, and anticonvulsant activities of methanol leaf and root extracts in Wistar rats. Material and methods: The pharmacognostic profiles of the leaves and roots were determined using standard procedures to serve as fingerprints for the plant. The methanol leaf and root extracts of Newbouldia laevis were tested for acute toxicity using the OECD’s up and down method at the maximum dose of 2000 mg/kg (orally) in Wistar rats. Analgesic studies were carried out in acetic acid-induced writhing in rats and tail immersion. The anti-inflammatory activity of the extracts was evaluated using carrageenan-induced rat paw-oedema and formalin-induced inflammation in rats’ mode. The anticonvulsant activity was determined using strychnineinduced, pentylenetetrazol-induced, and maximal electroshock-induced rat convulsion models. For each of these studies, the extracts doses of 100, 200 and 400 mg/kg were administered to the rats following the oral route. Results: The pharmacognostic profiles showed that the leaves possessed deep-sunken paracytic stomata (5-8-16 mm2 ; adaxial, 8-11-24 mm2 ; abaxial epidermis), vein islets (2-4-10 mm2 ; adaxial), vein terminations (10-14-18 mm2 ; adaxial), palisade ratio (8.3-12.5-16.4 mm2 ; adaxial, 2.5-6.8-12.2 mm2 ; adaxial), covering unicellular trichome (8–14; adaxial), spheroidal calcium oxalate crystals (3–5 μm), and oval-shaped striated starch grain with no hilum (0.5–4.3 μm). The transverse section of the leaf showed the presence of spongy and palisade parenchyma as well as a closed vascular bundle. The root powder showed the presence of brachy sclereid, fibers without lumen, and lignin. All physicochemical parameters fall within the acceptable limits, phytochemical contents showed mainly glycosides, alkaloids, and steroids while acute oral toxicity (LD50) of the parts for 14 days did not produce any toxicity signs or mortality in the rats. The extracts produced dose-dependent (100–400 mg/kg) analgesic involving opioid receptors, anti-inflammatory, and anticonvulsant activities in the rats which were significant (p ≤ 0.05) when compared to the standard drugs. The leaf extract possessed the most potent analgesic and anti-inflammatory effects in the rats, while the most anticonvulsant effects were observed in ratstreated with the leaf extract. Both extracts showed elevated levels of protection against strychnine-induced, pentylenetetrazol-induced, and maximal electroshock-induced seizure in rats. Conclusion: Our study revealed some pharmacognostic profiles of Newbouldia laevis leaves and roots that are vital for its identification from closely related species often used for adulteration in traditional medicine. The study further showed that the leaf and root extracts of the plant possessed dose-dependent analgesics, antiinflammatory and anti-convulsant activities in rats, thus, justifying its use for the treatment of these diseases in Nigerian traditional medicine. There is a need to further study its mechanisms of action towards drug discovery.