The imbalance in homeostatic process between oxidants and antioxidants in the body caused by reactive oxygen and nitrogen species (free radicals) leads to oxidative stress. Cellular enzymes such as myeloperoxidase, nicotinamide adenine dinucleotide phosphate-oxidase (NADPH-oxidase) and nitric oxide synthase (NOS) produce these reactive oxygen and nitrogen species (RONS). Oxidative stress is considered to be the primary cause of aging and a wide variety of human diseases such as cancers, diabetes, neurodegenerative disorders (Alzheimer's disease, Parkinson's disease), rheumatoid arthritis etc. Invariably, to maintain a healthy biological system the balance between oxidation and antioxidation is a critical requirement. Antioxidants are any substances that significantly delay, prevent or inhibit oxidative damage to target molecules. They are widely distributed throughout plants and animals and are found to be at low concentrations compared with that of oxidizable substrates. Natural and synthetic antioxidants have been reported to prevent or treat various human diseases. This article presents a comprehensive account of free radical generation, oxidative stress and its consequences, antioxidants including sources, classification, chemical structures, mechanisms of action, physicochemical properties. The study also dealt with applications of antioxidants in pharmaceutical and food industries, their therapeutic properties and pharmacokinetic features.

Coronavirus disease 2019 (COVID-19) is an infection caused by a newly discovered coronavirus which was identified in Wuhan, China. The race is on globally to repurpose drugs for COVID-19 and develop a safe and effective vaccine against the disease. There is an urgent need to search for effective remedies against COVID-19 from the rich and extensive flora of Africa and the world. A literature search was conducted to obtain information on drugs with the potential for effectiveness in the treatment of COVID-19 based mostly on outcomes of preclinical studies and a few clinical investigations. This was considered important to this perspective as some of the identified mechanisms of action may be related to potential anti-COVID-19 actions of phytomedicines. The findings from the literature search were also used to establish the need for exploration of phytomedicines in the fight against COVID-19. This perspective identifies the need to preserve the rich tradition of herbal medicine in Africa, repositioning it by inculcating all aspects of discovery, development, and chemical evaluation of pharmaceuticals from medicinal plants for effective management of prevalent diseases. The identified mechanisms of action of current drugs under consideration for the treatment of COVID-19 include preventing fusion of SARS-CoV-2 with human cells; decrease acidity in endosomes, cell membrane-derived vesicles for transportation of the virus within the host cell and within which the virus can replicate; and blockade of the production of proinflammatory cytokines. Phytomedicines may possibly elicit either one or a combination of these effects. The case for the exploration of phytomedicines against COVID-19 is strengthened by the emergence of a number of conventional drugs from medicinal plants and the emergence of botanicals with proven efficacy for some medical conditions. Caution against indiscriminate use of medicinal plants in the guise of treating COVID-19 has been highlighted and the need for reliable preclinical and clinical studies.

The emergence of the novel coronavirus (SARS-CoV-2) that emanated from Wuhan in China in 2019 has become a global concern. The current situation warrants ethnomedicinal drug discovery and development for delivery of phytomedicines with potential for the treatment of COVID-19. The aim of this review is to provide a detailed evaluation of available information on plant species used in African traditional medicines with antiviral, anti-inflammatory, immunomodulatory, and COVID-19 symptoms relieving effects. Literature from scientific databases such as Scopus, PubMed, Google scholar, African Journals OnLine (AJOL), Science Direct, and Web of Science were used for this review. A total of 35 of the 38 reviewed plants demonstrated a wide range of antiviral activities. Bryophyllum pinnatum, Aframomum melegueta, Garcinia kola, Sphenocentrum jollyanum, Adansonia digitata, Sutherlandia frutescens, Hibiscus sabdariffa, Moringa oleifera, and Nigella sativa possess a combination of antiviral, immunomodulatory, anti-inflammatory, and COVID-19 symptoms relieving activities. Nine, 13, and 10 of the plants representing 23.7%, 34.2%, and 26.3% of the plants studied had antiviral activity with 3 other activities, antiviral activity with 2 other activities, and antiviral with one pharmacological activity alone, respectively. The plants studied were reported to be relatively safe at the subchronic toxicity level, except for 2. The study provides baseline information on the pharmacological activities, toxicity, and chemical components of 9 African medicinal plants with antiviral, immunomodulatory, anti-inflammatory, and symptoms relieving activities, thereby making the plants candidates for further investigation for effectiveness against COVID-19.

Pawpaw root (Carica papaya), Guava leaf (Psidium guajava) and Bush Mango leaf (Irvingia gabonensis) are commonly used locally to treat diarrhoea. The present study evaluated the anti-diarrhoeal effects of these plant extracts on E. coli -induced diarrhoea in albino rats. Fresh tender roots and leaves of these plants were collected, air dried, powdered and percolated in n-hexane, Methanol and aqueous solvents. Qualitative phytochemical analysis was done using different standard methods. Diarrhoea was induced with Ecoli in albino rats using standard procedures. Qualitative phytochemical analysis confirmed the presence of various phytochemicals like saponins, alkaloids, flavonoids, cardiac glycosides, tannins, phytates, oxalates and phenols. The extracts, in a dose dependent manner, significantly protected the rats against diarrhoea induced experimentally by E. coli in terms of the nature of stool passage; there was no significant difference when compared with the control drug (loperamide) (P> 0.05). Generally, methanol extract of Irvingia gabonensis was more effective at low (100 ml/kg) and high (200 ml/kg) doses. The study justifies the ethno pharmacological uses of these medicinal plants for treatments of diarrhoeal disease.

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