African diet: A toxic/protective dilemma
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Date
2009
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Transworld Research Network, Kerala, India
Abstract
Food shortages and high prevalence of poverty-related chronic diseases including HIV/AIDS, malaria and tuberculosis have culminated in health crisis in African continent. The diet of the majority of African populations consists largely of maize and cassava flour. Apart from being deficient in essential amino-acids, important vitamins and micronutrients, maize and cassava flour are prone to fungal infestation and thus to contamination by mycotoxins which increases the risk of cancer development mostly in HIV/AIDS individuals. In addition, digestive cancers and especially squamous cell carcinoma of the oesophagus (SCCE) are become the most common cancers in Southern African black men (incidence: 14.5%). Among other factors including hepatitis B and C, excessive intake of dietary iron as a result of drinking homebrewed in iron pots constitutes one of the most important factors leading into hepatocellular carcinoma (HCC). Alcohol consumption has been also implicated in the aetiology of both SCCE associated with cigarette smoking, low intake of dietary antioxidants, consumption of compounds such as polycyclic hydrocarbons, nitrosamines, heterocyclic amines found in African diet and HCC associated with increased hepatic iron stores inducing successively fibrosis and cirrhosis which finally progress into liver cancer. Despite our progress in antioxidant, environmental, genetic and carcinogenic studies, the mechanism of induction of those two types of cancer is still not fully understood. Our histological findings and the immuno-histochemistry evidence of DNA damage by the presence in situ (biopsies) of 8-hydroxy-deoxyguanosine (8-OHdG) and that of lipid peroxidation by the presence in situ of 4-hydroxy-nonenal (4-HNE) increasing with the disease progression, have provided a consistent correlation between low intake of dietary antioxidant and the occurrence of carcinoma. In contrast to those toxicological aspects of African diet leading to the occurrence of digestive and liver cancers in African populations, an expanding body of evidence from epidemiological and laboratory studies demonstrated that edible plant as whole, or their ingredients have substantial protective effects on human carcinogenesis. We have recently demonstrated the anti-oxidative and anti-mutagenic properties of some African indigenous edible plants: Bambara groundnut (Vignea subterranean) and beverage: Rooi bos tea (Aspalathus linearis). Their chemo-preventive and antiinflammatory activities have been tested in cell culture using human breast epithelial (MCF-10A) cells and in animal model using mouse skin. Methanolic extracts of some other African plants (Sutherlandia fructescens and Harpagophytum procumbens) used
as beverages showed inhibition of 12-O-tetradecanoyl-phorbol-13 acetate (TPA)- induced cyclo-oxygenase (COX-2) expression in mouse skin, which appears to be mediated through blocking of catalytic activity of extracellular signal-regulated protein kinase (ERK) and through inhibition of activator protein-1 (AP-1) and cylic AMP response element binding (CREB) protein activation, suggesting their chemopreventive and chemo-protective activities. Due to the fact that inhibition of COX-2 is now regarded as an effective and promising strategy for prevention of anti-inflammatory process precluding the initiation and tumor stage, more research on African food plants and beverages should be conducted using this strategy in order to understand the molecular mechanism underlying those specific activities. In the light of these data, the extensive use of African foodstuffs and beverage bearing preventive and protective factors should be recommend in the diet of African populations for reducing the incidence of digestive and liver cancers in those areas.
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In: E. Olatunde Farombi (ed). Nutritional Antioxidants in Cancer and Degenerative Diseases, pp 185-212