Rarity of colorectal adenomas in the African black population

Emergence of Colorectal Cancer in West Africa: Accepting the Inevitable

It seems not too long ago that colon and rectal cancer is a "rare" disease in rural Africa; however, over the last 30 years in West Africa, published evidence has shown decade by decade increases in the incidence of colorectal cancer (CRC). Therefore, CRC should now be accepted as a recognized disease in native Africans; nevertheless, we must acknowledge that the incidence is a fraction of what obtains in the developed countries of Europe and America. This presentation will attempt to examine the emergence of CRC within the West African axis over the last four decades.

Colorectal carcinogenesis: a cellular response to sustained risk environment

The current models for colorectal cancer (CRC) are essentially linear in nature with a sequential progression from adenoma through to carcinoma. However, these views of CRC development do not explain the full body of published knowledge and tend to discount environmental influences. This paper proposes that CRC is a cellular response to prolonged exposure to cytotoxic agents (e.g., free ammonia) as key events within a sustained high-risk colonic luminal environment. This environment is low in substrate for the colonocytes (short chain fatty acids, SCFA) and consequently of higher pH with higher levels of free ammonia and decreased mucosal oxygen supply as a result of lower visceral blood flow. All of these lead to greater and prolonged exposure of the colonic epithelium to a cytotoxic agent with diminished aerobic energy availability. Normal colonocytes faced with this unfavourable environment can transform into CRC cells for survival through epigenetic reprogramming to express genes which increase mobility to allow migration and proliferation. Recent data with high protein diets confirm that genetic damage can be increased, consistent with greater CRC risk. However, this damage can be reversed by increasing SCFA supply by feeding fermentable fibre as resistant starch or arabinoxylan. High protein, low carbohydrate diets have been shown to alter the colonic environment with lower butyrate levels and apparently greater mucosal exposure to ammonia, consistent with our hypothesis. Evidence is drawn from in vivo and in vitro genomic and biochemical studies to frame experiments to test this proposition.

Colorectal carcinoma: why is there a lower incidence in Nigerians when compared to Caucasians?

Carcinoma of the colon and rectum is the 2nd commonest cancer in the United States; the leading cancer being lung cancer. It has been estimated that 130,200 new cases of colorectal cancer will be diagnosed annually while 56,300 sufferers will die from the disease (Murphy et al., 2000). In developing countries especially West Africa, the rate has not yet reached such magnitude. This suggests that there may be factors either anthropomorphic or environmental which may be responsible for this. The paper acknowledges the reduced incidence of colorectal cancer in native West Africans living in Africa and endeavours to highlight the various factors that produce this observation in medical literature. A diligent search through available literature on the aetiology, epidemiology and comparative anthropology of colorectal cancer was done. Internet search using PubMed, British Library Online and Google Scholar was also utilized. The rarity of adenomatous polyposis syndromes in the native West African contributes to the reduced incidence of colorectal cancer. Cancer prevention and cancer-protective factors are deemed to lie in the starchy, high-fiber, spicy, peppery foodstuff low in animal protein which many West African nations consume.

Modification by N-acetyltransferase 1 genotype on the association between dietary heterocyclic amines and colon cancer in a multiethnic study

OBJECTIVE

Colorectal cancer incidence is greater among African Americans, compared to whites in the U.S., and may be due in part to differences in diet, genetic variation at metabolic loci, and/or the joint effect of diet and genetic susceptibility. We examined whether our previously reported associations between meat-derived heterocyclic amine (HCA) intake and colon cancer were modified by N-acetyltransferase 1 (NAT1) or 2 (NAT2) genotypes and whether there were differences by race.

METHODS

In a population-based, case-control study of colon cancer, exposure to HCAs was assessed using a food-frequency questionnaire with a meat-cooking and doneness module, among African Americans (217 cases and 315 controls) and whites (290 cases and 534 controls).

RESULTS

There was no association with NAT1*10 versus NAT1-non*10 genotypes for colon cancer. Among whites, there was a positive association for NAT2-"rapid/intermediate" genotype [odds ratio (OR)=1.4; 95% confidence interval (CI)=1.0, 1.8], compared to the NAT2-"slow" that was not observed among African Americans. Colon cancer associations with HCA intake were modified by NAT1, but not NAT2, regardless of race. However, the "at-risk" NAT1 genotype differed by race. For example, among African Americans, the positive association with 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) was confined to those with NAT1*10 genotype (OR=1.8; 95% CI=1.0, 3.3; P for interaction=0.02, comparing highest to lowest intake), but among whites, an association with 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was confined to those with NAT1-non*10 genotype (OR=1.9; 95% CI=1.1, 3.1; P for interaction=0.03).

CONCLUSIONS

Our data indicate modification by NAT1 for HCA and colon cancer associations, regardless of race. Although the at-risk NAT1 genotype differs by race, the magnitude of the individual HCA-related associations in both race groups are similar. Therefore, our data do not support the hypothesis that NAT1 by HCA interactions contribute to differences in colorectal cancer incidence between African Americans and whites.

Health potential of polyols as sugar replacers, with emphasis on low glycaemic properties

Abstract Polyols are hydrogenated carbohydrates used as sugar replacers. Interest now arises because of their multiple potential health benefits. They are non-cariogenic (sugar-free tooth-friendly), low-glycaemic (potentially helpful in diabetes and cardiovascular disease), low-energy and low-insulinaemic (potentially helpful in obesity), low-digestible (potentially helpful in the colon), osmotic (colon-hydrating, laxative and purifying) carbohydrates. Such potential health benefits are reviewed. A major focus here is the glycaemic index (GI) of polyols as regards the health implications of low-GI foods. The literature on glycaemia and insulinaemia after polyol ingestion was analysed and expressed in the GI and insulinaemic index (II) modes, which yielded the values: erythritol 0, 2; xylitol 13, 11; sorbitol 9, 11; mannitol 0, 0; maltitol 35, 27; isomalt 9, 6; lactitol 6, 4; polyglycitol 39, 23. These values are all much lower than sucrose 65, 43 or glucose 100, 100. GI values on replacing sucrose were independent of both intake (up to 50 g) and the state of carbohydrate metabolism (normal, type 1 with artificial pancreas and type 2 diabetes mellitus). The assignment of foods and polyols to GI bands is considered, these being: high (> 70), intermediate (> 55–70), low (> 40–55), and very low (< 40) including non-glycaemic; the last aims to target particularly low-GI-carbohydrate-based foods. Polyols ranged from low to very low GI. An examination was made of the dietary factors affecting the GI of polyols and foods. Polyol and other food GI values could be used to estimate the GI of food mixtures containing polyols without underestimation. Among foods and polyols a departure of II from GI was observed due to fat elevating II and reducing GI. Fat exerted an additional negative influence on GI, presumed due to reduced rates of gastric emptying. Among the foods examined, the interaction was prominent with snack foods; this potentially damaging insulinaemia could be reduced using polyols. Improved glycated haemoglobin as a marker of glycaemic control was found in a 12-week study of type 2 diabetes mellitus patients consuming polyol, adding to other studies showing improved glucose control on ingestion of low-GI carbohydrate. In general some improvement in long-term glycaemic control was discernible on reducing the glycaemic load via GI by as little as 15–20 g daily. Similar amounts of polyols are normally acceptable. Although polyols are not essential nutrients, they contribute to clinically recognised maintenance of a healthy colonic environment and function. A role for polyols and polyol foods to hydrate the colonic contents and aid laxation is now recognised by physicians. Polyols favour saccharolytic anaerobes and aciduric organisms in the colon, purifying the colon of endotoxic, putrefying and pathological organisms, which has clinical relevance. Polyols also contribute towards short-chain organic acid formation for a healthy colonic epithelium. Polyol tooth-friendliness and reduced energy values are affirmed and add to the potential benefits. In regard to gastrointestinal tolerance, food scientists and nutritionists, physicians, and dentists have in their independent professional capacities each now described sensible approaches to the use and consumption of polyols.

Colorectal adenomas with a low frequency of ki-ras mutations: a sample from a population with a low mortality rate from colorectal cancer

OBJECTIVE

To detect and analyse ki-ras point mutations in colorectal adenomas and carcinomas in patients from Greece, where mortality rate from colorectal cancer is lower than that in other European countries and the USA.

PATIENTS AND METHODS

As a method we used PCR-RFLP technique, to examine ki-ras codons 12 and 13 mutations in 450 paraffin embedded tissues, consisting of 141 normal mucosas, 165 adenomas and 144 sporadic colorectal cancers taken from 141 patients.

RESULTS

Frequency of ki-ras mutations was 3.2% (3/93) in small adenomas, 5.2% (3/57) in greater than 1 cm adenomas, 20% (3/15) in tissues where adenoma and cancer coexisted and 39.5% (57/144) in colorectal cancer.

CONCLUSION

These data showed that the frequency of ki-ras mutations was low in all sizes of polyps and high in carcinomas in a sample of a population, characterized by a low mortality rate from colorectal cancer. Ki-ras mutations were not an early event of colon carcinogenesis in these patients and the low frequency of ki-ras mutations in adenomas may probably have some relevance to the low mortality rate. Our findings could be explained, not by the dietary habits of this population, but by the presence of other hitherto unknown environmental factors.

Fecal levels of short-chain fatty acids and bile acids as determinants of colonic mucosal cell proliferation in humans

We studied the correlation between fecal levels of short-chain fatty acids (SCFA), bile acids (BA), and colonic mucosal proliferation in humans on a free diet. Subjects [n = 43: 27 men and 16 women; 61 +/- 7 and 59 +/- 6 (SE) yr old, respectively] were outpatients who previously underwent resection of at least two sporadic colon polyps. Mucosal proliferation was determined by [3H]thymidine incorporation in vitro in three colorectal biopsies obtained without cathartics and was expressed as labeling index (LI). BA were analyzed in feces by mass spectrometry and SCFA by gas chromatography. We found that increasing levels of BA in feces did not correlate with higher LI. On the contrary, higher levels of SCFA were significantly associated with lower LI in the colonic mucosa (P for trend = 0.02). In conclusion, in humans on a free diet, intestinal proliferation seems to be regulated by the levels of SCFA in feces and not by BA. Because a lower intestinal proliferation is associated with a decreased colon cancer risk, treatments or diets that increase colonic levels of SCFA might be beneficial for colonic mucosa.

Differences in N-acetylation genotypes between Caucasians and Black South Africans: implications for cancer prevention

Polymorphic N-acetyltransferase genes (NAT1 and NAT2) determine rapid or slow acetylation phenotypes, which are believed to affect cancer risk related to environmental exposure. Black South Africans have a unique incidence pattern of environment-related cancers, but genetic characteristics of this population are mostly unknown. In this study, we compared NAT1 and NAT2 allele distributions in 101 Black South Africans and 112 UK Caucasians. Frequencies of the rapid alleles were significantly higher in Black South Africans for both NAT1 and NA72. Putative rapid NAT1 genotypes due to the presence of either NAT1*10 or NAT1*11 were found in 74.3% of Black South Africans (only NAT1*10) and 42.0% of UK Caucasians (P < 0.0001). Similarly, NAT2 analysis showed that the presence of NA12*4, NAT2*12A, NAT2*12B, NA72*12C, and NAT2*13 alleles provided significantly higher (P = 0.0001) frequency of rapid acetylation genotypes among Black South Africans (60.4%) than in the Caucasian group (33.9%). The rapid acetylation genotype in Caucasians usually depended on the NAT2*4 allele presence. The significant differences in N-acetylation genotypes can be among the factors determining a distinctive cancer morbidity and mortality pattern observed in Black South Africans. Both further genetic characterization of different populations and development of preventive strategies adopted for ethnicities with different genetic backgrounds are needed to deal adequately with the emerging health care problems in developing multiethnic societies.

Colorectal cancer in an African city population in transition

An enquiry has been made on a series of African patients with colorectal cancer who were admitted in 1995-1999 to Chris Hani Baragwanath Hospital (3200 beds), and who lived in Soweto (population about 1 million), Johannesburg, South Africa. In the urban context described, Africans have considerably more advantages, socio-economically, dietarily and in other respects, than their rural counterparts. The 126 patients comprised 58 males and 68 females, giving calculated incidence rates in their communities for colorectal cancer of 1.7 and 2.0, respectively, per 100,000 'world' population. In contrast, as indicated in the South African Cancer Registry for 1993-1995, the corresponding rates for white males and females were 24.7 and 19.3, respectively, per 100,000. The proportion of African patients under 40 years was 19.0%; but was only 4.0% in the white population. In contrast to this major disparity, there was only a minor interethnic disparity regarding cancers that are very common in Africans, namely, those of the oesophagus and lung. Hence, with ongoing transitional changes - in diet and other respects - the relatively high proportion of younger African patients probably indicates a rising occurrence of colorectal cancer in the urban African population.