S. J. Van Rensburg

Hepatocellular carcinoma and dietary aflatoxin in Mozambique and Transkei

Estimations of the incidence of hepatocellular carcinoma (HCC) for the period 1968-74 in the Province of Inhambane, Mozambique, have been calculated and together with rates observed in South Africa among mineworkers from the same Province indicate very high levels of incidence in certain districts of Inhambane. Exceptionally high incidence levels in adolescents and young adults are not sustained at older ages and suggest the existence of a subgroup of highly susceptible individuals. A sharp decline in incidence occurred during the period of study. Concurrently with the studies of incidence, 2183 samples of prepared food were randomly collected from 6 districts of Inhambane as well as from Manhica-Magude, a region of lower HCC incidence to the south. A further 623 samples were taken during 1976-77 in Transkei, much further south, where an even lower incidence had been recorded. The mean aflatoxin dietary intake values for the regions studied were significantly related to HCC rates. Furthermore, data on aflatoxin B1 contamination of prepared food from 5 different countries showed overall a highly significant relationship with crude HCC rates. In view of the evidence that chronic hepatitis B virus (HBV) infection may be a prerequisite for the development of virtually all cases of HCC and given the merely moderate prevalence of carrier status that has been observed in some high incidence regions, it is likely that an interaction between HBV and aflatoxin is responsible for the exceptionally high rates evident in parts of Africa and Asia. Various indications from Mozambique suggest that aflatoxin may have a late stage effect on the development of HCC. This points to avenues for intervention that could be more rapidly implemented than with vaccination alone.

Mutagenicity to Salmonella typhimurium of some Aspergillus and Penicillium mycotoxins

17 mycotoxins produced by various Aspergillus and Penicillium species were screened for their mutagenic activity to Salmonella typhimurium strains TA98, TA100, TA1535 and TA1537, both with and without metabolic activation. Austdiol, austocystins A and D, kojic acid and viridicatumtoxin were found to be mutagenic after metabolic activation, while austdiol was also mutagenic per se. Aflatoxin B1, sterigmatocystin and versicolorin A, which were used as positive controls were also mutagenic. No mutagenic activity was evident in the case of citrinin, cyclopiazonic acid, fumitremorgen B, griseofulvin, luteoskyrin, O-methylsterigmatocystin, mycophenolic acid, ochratoxin A, patulin, penicillic acid, secalonic acid D and TR2-toxin. A good relationship was found between the mutagenic activity, or lack of it, of most of the mycotoxins with existing data on carcinogenicity. Inadequate information on the carcinogenicity of austdiol, austocystins A and D, kojic acid and viridicatumtoxin precluded correlations with mutagenicity to S. typhimurium. The relationship between chemical structure and mutagenicity of the mycotoxins is discussed.

Oesophageal cancer in Zulu men, South Africa: a case-control study.

The high rate of oesophageal cancer amongst southern African blacks has also been recorded amongst the Zulus. Data embracing a wide spectrum of factors pertaining to socio-economic status, nutrition, exposure to carcinogens, tobacco and alcohol usage and traditional health practices were obtained from 211 hospitalized oesophageal cancer patients and compared with hospital population controls matched for age and urban-rural background. Stepwise logistic regression analysis with adjustment for age effects showed that four of the many factors could adequately model the odds of being a cancer case. They were the daily consumption of purchased maize meal (relative risk (RR) 5.7) currently smoking commercial cigarettes (RR 2.6), pipe smoking (RR 2.1), and a reduction of risk in those using butter or margarine daily (RR 0.51). Further significant differences (P less than 0.05) in 12 other factors suggest that those with rural assets but an ability to earn a modest income external to the subsistence economy are at highest risk. They represent a transitional state of Westernisation which is characterised by excessive smoking habits and a diet having a low vitamin and mineral density. These results provide further evidence for the need to combat smoking and for a program of nutrient enrichment of maize meal.

Mutagenicity of marijuana and Transkei tobacco smoke condensates in the salmonella/microsome assay

Extracts and smoke condensates of marijuana, Transkei home-grown tobacco and also commercial cigarette tobaccos were assayed for their mutagenic activity to Salmonella typhimurium strains TA98, TA100, TA1535, TA1537 and TA1538, both with and without metabolic activation. No mutagenic activity was detected in dichloromethane extracts of marijuana and tobacco per se, but all the smoke condensates exhibited mutagenicity with metabolic activation. The only strain not mutated by any of the pyrolyzates was TA1535. Transkei tobacco pyrolyzate proved to be the most mutagenic, followed by marijuana, pipe and cigarette tobacco. Mutagenicity was positively associated with the nitrogen content of the various products. The potent mutagenic action of marijuana smoke condensate, coupled with a condensate yield of more than 50% higher than that of cigarette and pipe tobacco, indicates a high carcinogenic risk associated with marijuana smoking.

Subacute toxicity of the mycotoxin cyclopiazonic acid

Abstract Cyclopiazonic acid (CA) is known to contaminate processed foods, maize and peanuts. Since previously available toxicity data were limited to the effects of single doses, Wistar-derived rats were given weekly doses of 0, 12 or 21 mg CA/kg body weight in 1 n -sodium bicarbonate, using a dosage volume of 2.5 ml/kg body weight, and subgroups of eight were killed 1 wk after doses 2, 5, 9 and 14. Males on the highest dose level showed mild growth retardation initially and 25% died suddenly during wk 4. No abnormal signs were observed in the surviving males or in any of the females throughout the 15 wk of the experiment. CA induced mild cellular degenerative changes in the myocardium and in several other organs where ballooning of nuclei, especially in ductal epithelia, was also characteristic. The changes were only weakly related to dose level, sex and the number of doses given. The findings suggest that CA is probably a metabolic inhibitor requiring considerable concentrations to exert toxicity. The limited data currently available do not elicit concern in terms of human risk or warrant any particular control procedures.

Mycotoxicological investigations on Zambian maize.

Abstract In Zambia there is a statutory requirement that visually diseased kernels should not constitute more than 2% of maize intended for human consumption. Four samples of Zambian maize containing 1·8, 5·4, 13·0 and 20·3% visually diseased kernels were subjected to mycological and chemical analyses and to toxicity trials in ducklings and rats. For all the samples the dominant fungi isolated from surface-sterilized kernels were Fusarium moniliforme Sheldon and Diplodia macrospora Earle, and the most prevalent fungus isolated from prepared maize meals was F. moniliforme . The level of fungal invasion of both kernels and meal was significantly lower for the 1·8%-diseased sample than for the other three. Protein and essential amino acid content tended to increase as the level of diseased kernels increased. None of the samples contained chemically detectable amounts of aflatoxins, ochratoxins, sterigmatocystin, cyclopiazonic acid or zearalenone. Although no samples were lethal to either ducklings or rats, body-weight gains were higher in male and female rats fed the 1·8%-diseased sample for 6 months than in those given the other test diets, the difference being statistically significant in the males. Of seven pure cultures of fungi isolated from the maize samples, five, including F. moniliforme and D. macrospora , were acutely toxic to ducklings and rats. In view of the indications that unidentified Fusarium and Diplodia toxins present in Zambian maize containing more than 1·8% visually diseased kernels reduce the growth rate of rats fed such samples for 6 months, it is recommended that the 2% maximum level of visually diseased kernels acceptable in Zambian maize for human consumption should be maintained.

Hepatic and Renal Pathology Induced in Mice by Feeding Fungal Cultures

Our search for toxic fungi originated from the concept that mycotoxins may be responsible for liver cancer in certain tribes in Africa. In order to provide a practical screening technique for the toxicity of fungal cultures, ducklings have frequently been used because of their known susceptibility to aflatoxin and because they will eat foods which are unpalatable to mammals. The drawback of these acute toxicity tests is that death (or weight loss) is the only criterion on which to judge toxicity and that acute toxicity is used as an index for carcinogenicity. The economic implications of using very longterm screening tests for carcinogens and the fact that the vast majority of carcinogens are also acutely toxic have so far prevented large-scale chronic toxicity studies. The only practical way of overcoming the objection to using death as the only end point is to examine animals fed fungal cultures for pathological lesions. We have found that the histopathological examination of organs from ducklings consuming fungal cultures is unrewarding except in a few cases such as Aspergillus flavus toxicity.