Malnutrition and experimental oral carcinogenesis
The work was undertaken to examine the effects of nutritional deficiencies on cancer induction. Two of the most common and widely distributed nutrients, iron and folic acid, were examined to evaluate the effects of their deficiency on animals. The Syrian golden hamster was the animal model for all experimental work. In the first part of the study an attempt was made to induce iron deficiency in young adult male hamsters by feeding iron deficient diet coupled with repeated venesection of 1.5ml every two weeks. Following twelve weeks on this regime a superficial biopsy was taken, on week 13, from the medial wall of one pouch in each hamster in order to evaluate the effect of iron depletion on the epithelial compartment thicknesses. After allowing the biopsy sites to heal for two weeks, a solution of 0.25% DMBA in acetone was painted, three times per week, for eight weeks, on a defined one square centimetre area in each pouch of each hamster of the experimental and control groups. The hamsters were then maintained on the same dietary regimes for twelve weeks before being killed at the beginning of week 37 for analysis. Iron deficiency anaemia could not be induced in the experimental animals of this study. The effect of the iron deficient diet on epithelial compartment thicknesses at the stage of the biopsy was not clear. However, restriction of iron intake did cause animals to develop significantly fewer grossly seen tumours and histologically identified carcinomas than control animals. In the second part of this thesis an attempt was made to investigate alternative hamster dietary components that have less iron contamination than the diet given in the first part of this thesis. Casein and calcium lactate were the main contributers to iron in the hamster diet. Casein could not be substituted by another source of protein for hamsters. However, other sources for calcium with less iron contamination were available and therefore investigated in this part of the study. Three groups of young adult male and female hamsters were given the fully nourishing powdered diet used in previous studies. However, calcium lactate was substituted for by either calcium acetate, calcium chloride or calcium sulphate in each group. None of the three diets was accepted by the animals and many of them died of starvation. When calcium salts were replaced by calcium lactate the surviving animals accepted the diet and recovered quickly afterwards. This study proved that calcium lactate could not be substituted by any other calcium salt with less iron content and therefore iron contamination in the hamster diet could not be further reduced by this method. In the third part of this thesis the effect of nutritional folate deficiency on cancer induction was studied. A group of young adult female hamsters was given folate deficient diet for four weeks. On week 5, DMBA in acetone at a concentration of 0.25% was painted on a defined one square centimetre area of the medial wall of each pouch in each hamster in folate deficient and control groups. The carcinogen was applied three times per week for eight weeks following which animals were maintained on the same dietary regimes for a further 13 weeks before being killed at the beginning of week 27 for the final analysis of the study. It was found that nutritional folate deficiency had significantly reduced the number of animals developing grossly counted tumours and histologically identified carcinomas. The folate deficient animals also developed significantly less tumours and carcinomas compared to control groups. In the last part of this thesis, the effect of combined iron and folate deficiency was examined for its role in carcinogenesis of the hamster cheek pouch. Two groups of young adult male hamsters were fed powdered diet lacking iron and folic acid and a third group was fed diet lacking iron only. One of the combined deficiency groups and the iron deficiency group were bled 1.0-1.3ml every week. On week 6 of the study DMBA in acetone at a concentration of 0.25% was painted three times per week for eight weeks on the same area of the pouch used in the previous studies. The animals were then maintained on the same experimental regimes for a further eleven weeks before being sacrificed, on week 25, for the final analysis of the study. In this study, iron deficiency anaemia was induced in animals of the bleeding groups. Animals in the group with combined iron and folate deficiency without bleeding showed low normal folate levels and normal haemoglobin levels. The two groups that were bled repeatedly showed iron deficiency anaemia. In all groups, the numbers of tumours counted grossly and the numbers of carcinomas identified histologically were significantly reduced compared to control animals in the previous studies. The folate deficient diet did not appear to influence the induction of iron deficiency. The studies reported in this thesis proved that nutritional folate deficiency not only reduces the incidence, but it also reduces the numbers of tumours and carcinomas in the hamster cheek pouch. Iron deficiency anaemia was also found to significantly reduce the numbers of tumours and carcinomas of the hamster cheek pouch. It was not possible to produce combined iron and folate deficiency under the conditions of these studies. However, animals fed on a diet lacking iron and folic acid had significantly reduced numbers of grossly seen tumours and histologically identified carcinomas in the cheek pouch in response to DMBA applications. In each of the reported studies, the nutritional deficiency of iron and folic acid, whether individually or combined was found to significantly reduce the growth rate of affected animals.