An overview of anti-diabetic plants used in Gabon: Pharmacology and toxicology

ETHNOPHARMACOLOGICAL RELEVANCE

The management of diabetes mellitus management in African communities, especially in Gabon, is not well established as more than 60% of population rely on traditional treatments as primary healthcare. The aim of this review was to collect and present the scientific evidence for the use of medicinal plants that are in currect by Gabonese traditional healers to manage diabetes or hyperglycaemia based here on the pharmacological and toxicological profiles of plants with anti-diabetic activity. There are presented in order to promote their therapeutic value, ensure a safer use by population and provide some bases for further study on high potential plants reviewed.

MATERIALS AND METHODS

Ethnobotanical studies were sourced using databases such as Online Wiley library, Pubmed, Google Scholar, PROTA, books and unpublished data including Ph.D. and Master thesis, African and Asian journals. Keywords including 'Diabetes', 'Gabon', 'Toxicity', 'Constituents', 'hyperglycaemia' were used.

RESULTS

A total of 69 plants currently used in Gabon with potential anti-diabetic activity have been identified in the literature, all of which have been used in in vivo or in vitro studies. Most of the plants have been studied in human or animal models for their ability to reduce blood glucose, stimulate insulin secretion or inhibit carbohydrates enzymes. Active substances have been identified in 12 out of 69 plants outlined in this review, these include Allium cepa and Tabernanthe iboga. Only eight plants have their active substances tested for anti-diabetic activity and are suitables for further investigation. Toxicological data is scarce and is dose-related to the functional parameters of major organs such as kidney and liver.

CONCLUSION

An in-depth understanding on the pharmacology and toxicology of Gabonese anti-diabetic plants is lacking yet there is a great scope for new treatments. With further research, the use of Gabonese anti-diabetic plants is important to ensure the safety of the diabetic patients in Gabon.

Effect of Tephrosia vogelii and Justicia extensa on Tilapia nilotica in vivo

According to our and other ethnobotanic studies (Walker, R., 1951. Une Nouvelle Légumineuse du Gabon servant à narcotiser le poisson. Rev. Bot. Appl. 31, 327; Walker, R., Sillans, R., 1961. Les plantes utiles du Gabon. Encyclopédie Biologique. P. Chevalier, Paris; Halle, N., 1970. Flore du Gabon 17, Famille des Rubiacées. Museum National d'Histoire Naturelle, Paris; Mounzeo, H., et al., 1997. Quelques plantes utilisées comme poisons de pêches chez les Punu du Gabon. Le Flamboyant 44. Décembre, Bulletin de Liaison des membres du réseau 'Arbres Tropicaux'), Tephrosia vogelii and Justicia extensa are two plants whose leaves are particularly used for the catching of fish in Gabonese rivers. The leaf extracts of those plants have been tested on Tilapia nilotica in order to observe their toxicity. At a given dose, the small fish are the first to be poisoned. This toxicity is more important for J. extensa and increased in a dose-dependent manner. After boiling for 90 min, those leaf extracts and rotenone (10(-6) M) taken as a control retain their toxicity at high dose (625 mg/l), although the latency period is higher. With the same temperature condition, at weak doses (37.5 and 62.5 mg/l), T. vogelii loses its toxicity, whereas J. extensa preserves it at 62.5 mg/l. As shown in our results, the fact that the extracts preserve their toxicity at high dose after boiling requires particular attention be given to the doses used for fishing and to the type of plants used.