Role of bacteria in human carcinogenesis

The bacterial hydrolysis of conjugated carcinogens, production of potential carcinogens from amino acid metabolism, formation of N-nitroso-compounds, and production of carcinogens from bile salt metabolism are discussed. The limited evidence implicating these compounds in the causation of bowel, gastric, bladder, biliary tract and cervical cancer is presented. Although there is no example of a proven role for bacteria in the causation of any human cancer, there are many leads currently under investigation. They have exciting implications for prevention.

The inability of nuclear dehydrogenating clostridia to oxidize bile salt hydroxyl groups

In a survey of the intracellular bile salt oxidoreductase activity in fecal bacteria, 16 strains of nuclear dehydrogenating clostridia and 2 strains of non-nuclear dehydrogenating C. paraputrificum were demonstrated unable to oxidize cholate at any of the 3 OH groups. Since nuclear dehydrogenation at the delta-1 and delta-4 position requires a 3-oxo precursor steroid, it appears that these organisms require the presence of a 3 alpha-hydroxysteroid dehydrogenating organism for nuclear dehydrogenation.

The digestion of pectin in the human gut and its effect on calcium absorption and large bowel function

1. The effect of dietary fibre digestion in the human gut on its ability to alter bowel habit and impair mineral absorption has been investigated using the technique of metablic balance. 2. Five healthy male students were studied for 9 weeks under controlled dietary conditions and during the last 6 weeks they took 36 g pectin/d. Bowel habit, transit through the gut, faecal fibre excretion, calcium balance and faecal composition were measured. 3. During the control period only 15% of the dietary fibre ingested was excreted in the stools and when pectin was added to the diet there was no increase in fibre excretion. Stool frequency and mean transit time were unchanged by pectin but stool wet weight increased by 33% and faecal excretion increased (%) for fatty acids 80, nitrogen 47, total dry matter 28 and bile acids 35. Ca balance remained unchanged. 4. It may be concluded from these results that dietary fibre is largely metabolized in the human gut and dietary pectin completely so. This could explain its lack of effect on bowel habit and Ca balance. Other changes in the faeces may be related to an increase in bacterial mass.

The effects of phthalylsulphathiazole on the bacteria of the colonic mucosa and intestinal contents as revealed by the examination of surgical samples

The isolation of a bacterial flora specifically associated with the colonic mucosa of patients undergoing large-bowel surgery is described. This flora differed from that of faeces in both the numbers and the types of bacteria isolated. The most striking difference was the reduction in the number of anaerobic bacteria isolated from the colonic mucosa. The ratio of anaerobic to aerobic was approximately 1:1 for mucosa compared with 100:1 for faeces.

Influence of diets high and low in animal fat on bowel habit, gastrointestinal transit time, fecal microflora, bile acid, and fat excretion

Epidemiological observations and animal experiments suggest that large bowel cancer is related to serveral factors. Among them, high dietary intakes of animal fat, the presence in the colon of relatively high levels of bile acids, specific patterns of intestinal microflora, slow transit through the gut, and low stool weights. Under metabolic conditions we have observed the effect on these variables of dietes containing 62 or 152 g/day of fat mainly of animal origin in six healthy young men over 4-wk periods. No change attributable to the diet was observed in the subjects' bowel habit, fecal weight, mean transit time through the gut, or in the excretion of dry matter. Total fecal bile acid excretion was significantly higher on the high fat diet (320 +/- 120 mg/day) than on the low fat diet (139.7) +/- 63 mg/day) t test = 7.78 P less than 0.001 as also was the total fecal fatty acid excretion, 3.1+/-0.71 and 1.14+/-0.35 g/day, respectively t test = 11.4 P less than 0.001). The fecal microflora including the nuclear dehydrogenating clostridia were unaltered by the dietary changes as was fecal beta-glucuronidase activity. Dietary changes which increase animal fat intake clearly influence fecal bile acid excretion in a way that would favor the development of large bowel cancer if current theories prove to be true. Dietary fat however has no effect on overall colonic function so other components of the diet must be responsible for the observed associations of bowel cancer with slow transit and reduced fecal bulk.

Pathogenesis of gastric cancer in pernicious anaemia

A pathogenetic mechanism to explain the increased incidence of gastric cancer in patients with pernicious anaemia (P.A.) is proposed. Mean nitrite concentration in gastric juice from thirteen fasting patients with P.A. was nearly fiftyfold greater than that of age-matched controls. The number of bacteria in the gastric juice of P.A. patients was also greatly increased. Small amounts of volatile nitrosamines were detected in simulated P.A. gastric juice in vitro, after addition of nitrite to achieve a concentration approximating to that found in vivo. If similar nitrosation occurs in vivo, the intragastric production of carcinogenic N-nitroso compounds could explain the high incidence of gastric cancer in patients with P.A.

Aetiology of adenoma--carcinoma sequence in large bowel

A hypothesis, based on epidemiological and histopathological data, is proposed to account for the aetiology of colorectal adenomas and carcinomas. Adenomas are initially caused by an environmental agent which acts on the colorectal cells of adenoma-prone persons, a further environmental agent causes small adenomas to grow, and a carcinogen causes malignancy in a high proportion of large adenomas.

The effects of two dietary fiber supplements on gastrointestinal transit, stool weight and frequency, and bacterial flora, and fecal bile acids in normal subjects

The effect of dietary supplements of sugar-cane fiber (bagasse), on stool weight, solids, and water content were studied in normal ambulant volunteers over a 9-mo period; a second inpatient study was done with bran supplements. The addition on 10.5 g of bagasse containing 5.1 g of crude fiber to a normal diet containing 3.7 g of crude dietary fiber daily raised the mean fecal weight from 88.3 +/- 6.4 g to 139.7 +/- 10.2 g/day (p less than 0.005). There was also a significant rise in fecal solids and fecal water, although the percentage of water in the stools remained unchanged. Bagasse supplements accelerated gastrointestinal transit when measured by the carmine marker technique. Radiopaque "shapes" showed a trend toward more rapid transit with bagasse supplements. Daily supplements of 39 g of wheat bran or 10.5 g of bagasse increased the total daily excretion of fecal bacteria, but there were no changes in bacteria excreted per gram of feces. The composition of the bacterial flora showed no change. There was increased excretion of fecal acid sterols on the bagasse supplement, but this failed to occur with bran. No changes attributable to fiber supplements occurred in the plasma triglycerides or cholesterol. Future work may define specific dietary fiber supplements for different therapeutic purposes. One fiber may be used as a bulk expander in diverticular disease and another as a hypocholesteremic fiber.

Changes in fecal composition and colonic function due to cereal fiber

The effect on colonic function of adding wheat fiber for 3 weeks to the metabolically-controlled diets of six healthy volunteers has been studied. Increasing dietary fiber intake from 17 to 45 g/day increased fecal weight from 79 +/- 6.6 g/day to 228 +/- 29.9 g/day and shortened mean transit time, measured by a continuous marker method, from 57.8 +/- 8.3 hr to 40.3 +/- 8.9 hr. The increase in fecal weight was largely due to water. Fiber caused a dilution of fecal marker and an increase in fecal fat, nitrogen, and calcium output. Fecal sodium, potassium, and chloride showed only small changes but volatile fatty acid output increased significantly without concentrations changing. Fecal bile acid output increased from 199 +/- 46 mg/day to 279 +/- 46 mg/day. These changes are discussed in light of current views of the role of dietary fiber in protecting against colon cancer.

Gastric-juice nitrite. A risk factor for cancer in the hypochlorhydric stomach?

Nitrite and hydrogen ion concentrations have been measured in the fasting gastric juice of 69 patients undergoing routine gastrointestinal investigations. There was an inverse relationship between nitrite concentration and hydrogen ion concentration, with a highly significant increase in gastric-juice nitrite in hypochlorhydric subjects. Thiocyanate was also found in all specimens in concentrations likely to increase nitrosamine formation, if nitrosation of amines occurs in the fasting stomach. Neutral gastric juice contains metabolically active bacteria capable both of generating nitrite from nitrate and of catalysing nitrosation. In this way an intragastric environment suitable for the formation of carcinogenic nitrosamines exists in the hypochlorhydric and achlorhydric stomach, providing a possible mechanism for the high incidence of gastric cancer in these subjects.

Metabolic responses to dietary supplements of bran

During a metabolic ward study, the addition of dietary fiber in the form of wheat bran biscuits to the diet of five volunteer subjects resulted in an increase in the stool wet weight and fecal solids. The excretion of fecal solids was highly correlated with the intake of unavailable carbohydrates, and fecal losses of water were similarly correlated with fecal excretion of these constituents. The major component of the increase in fecal solids was due to the noncellulosic polysaccharide fraction of dietary fiber. There was an increased fecal excretion of nitrogen fat and energy by most subjects when the supplement was eaten. However, the increased loss of energy in the feces was only 40-80 kcal/day, and therefore a large supplemental intake of dietary fiber had only minor effects on energy metabolism. Supplemental fiber is thus unlikely to induce a useful loss of calories in the management of obesity. The addition of dietary fiber caused an increased excretion of most inorganic constituents, particularly sodium and phosphorus; increased excretion of iron and magnesium was also found in two subjects.

Faecal steroids and bacteria and large bowel cancer in Hong Kong by socio-economic groups

In a study of three socio-economic groups in Hong Kong, the high income group had a high faecal concentration of bile acids, especially the dihydroxy bile acids, compared to the low income group. The faecal bile acids were also more highly degraded. The faecal flora contained more bacteroides and fewer eubacteria. Very few of the clostridia able to dehydrogenate the steroid nucleus were isolated. An epidemiological study based on street blocks indicated that the high income group also have a higher incidence of cancer of the large bowel and of the breast. The results are discussed in terms of theories on the aetiology of large bowel cancer.

The role of colon anaerobes in the metabolism of bile acids and steroids, and its relation to colon cancer

The principle enzymes in the metabolism of both the substituent groups and the nucleus of the bile acids and of cholesterol are reviewed, together with their possible relevence to the etiology of large bowel cancer. Since the incidence of the disease appears to be related to the bile acid concentration and the activity of the 7-dehydroxylase and the delta4-dehydrogenase enzymes, the study of bile acids with a 4,6-dien-3-one structure is strongly recommended.

Metabolic epidemiology of dietary factors in large bowel cancer

According to the hypothesis being tested by this laboratory, bacteria (in particular, certain clostridia) metabolize the bile acids to give unsaturated products that are important in the causation of colorectal cancer. In this paper, various dietary regimens are discussed in terms of their effect on the fecal steroid concentration and on the gut bacterial flora. The diets considered include high- and low-fiber, high- and low-meat, and high- and low-fat diets.

Effects of two types of dietary fibre on faecal steroid and lipid excretion

Fibre supplements from wheat bran and sugar cane residue (bagasse) were added to the normal diet of volunteers for 12-week periods in a controlled metabolic study. Stool weights and stool fat excretion increased on both dietary fibres. Bagasse increased the daily loss of acid steroids, but bran failed to affect bile acid excretion. Decreased transit time without alteration in faecal flora occurred with bagasse. The raised excretion of bile acids and fatty acids failed to lower the plasma cholesterol and triglycerides after 12 weeks. Thus different fibre sources with variable components have dissimilar metabolic effects.

The nuclear dehydrogenation of steroids by intestinal bacteria

We have postulated that bacteria able to dehydrogenate the bile-acid nucleus are important in the aetiology of cancer of the colon. In this paper we report on screening for the ability to carry out two such reactions. The relevant enzymes are produced by a high proportion of strains of Clostridium paraputrificum, C. tertium and C. indolis, and by small numbers of strains in other clostridial species, but not by organisms of the other genera tested. Strains able to dehydrogenate the bile-acid nucleus represent a high proportion of the lecithinase-negative clostridia isolated from faeces of people living in Britain but a low proportion of those from people living in Uganda or Hong Kong.

Effects of two types of dietary fibre on faecal steroid and lipid excretion

Fibre supplements from wheat bran and sugar cane residue (bagasse) were added to the normal diet of volunteers for 12-week periods in a controlled metabolic study. Stool weights and stool fat excretion increased on both dietary fibres. Bagasse increased the daily loss of acid steroids, but bran failed to affect bile acid excretion. Decreased transit time without alteration in faecal flora occurred with bagasse. The raised excretion of bile acids and fatty acids failed to lower the plasma cholesterol and triglycerides after 12 weeks. Thus different fibre sources with variable components have dissimilar metabolic effects.

Gut bacteria and their metabolic activities in familiar polyposis

Earlier work had suggested that patients with large-bowel cancer can be characterized by carriage of clostridia capable of dehydrogenating the nucleus of steroids and by high faecal bile-acid concentrations. Familial polyposis is an inherited disease which untreated, will progress to cancer of the large bowel, and those affected might be expected to have these metabolic characteristics. However, enviromental factors seem to play no part in polyposis. Investigation of as yet unaffected children of known polyposis patients revealed that the gut flora of half of them did not degrade cholesterol in vivo andnor did flora from patients in whom polyposis had already been diagnosed. The reason for this is unknown, but if the same patients develop polyposis (i.e., they carry the abnormal gene) we would have a simple diagnostic test which could replace the continuing follow-up now required for the siblings and children of patients with polyposis.

Faecal bile-acids and clostridia in patients with cancer of the large bowel

Of 44 patients with cancer of the large bowel, 36 ( 82%) had high faecal bile-acid concentrations compared with only 15 (17%) out of 90 patients with other diseases. 31 (70%) of the 44 patients with large-bowel cancer had high faecal bile-acid concentrations in the presence of faecal clostridia able to dehydrogenate the bile-acid nucleus, compared with only 8 (9%) out of 90 patients with other diseases. Thes findings support the hypothesis that cancer of the large bowel is caused by high concentrations of bile-acid derivatives produced by certain anaerobic bacteria.

Effects of sulphasalazine (Salazopyrin) on faecal flora in patients with inflammatory bowel disease

The faecal flora of 21 patients with proctocolitis and five patients with Crohn's disease of the large bowel was examined both while sulphasalazine was being administered and during control periods. Patients with proctocolitis and Crohn's disease who were not receiving sulphasalazine had a similar flora which did not differ in any way from the normal. The effect of sulphasalazine was to decrease the numbers of opalescent-negative clostridia, enterobacteria, and total non-sporing anaerobes. It is suggested that this antibacterial effect of sulphasalazine, which has not been previously demonstrated, may be related to the beneficial effects of this drug in proctocolitis and should be investigated further.

The in vivo formation of N-nitrosamines in the rat bladder and their subsequent absorption

Experiments are described which demonstrate the production of nitrosamine in vivo in the bladder of rats with experimental bladder infections. The absorption of nitrosamines from the bladder into the circulating blood is also described.

Bacteria, nitrosamines and cancer of the stomach

Until recently the public water supply to Worksop contained high concentrations of nitrate. An epidemiological study has revealed that, compared with low nitrate control towns, Worksop has an increased death rate from gastric cancer. The possible role of the bacterial production of nitrosamines in the aetiology of these stomach cancer deaths is discussed.

The effect of a chemically defined diet on the faecal flora and faecal steroid concentration

The consumption of a chemically defined diet altered both the faecal flora and faecal steroids. Enterobacteria increased while enterococci and other lactic acid bacteria decreased in number. No other obvious change occurred. However, the alteration in the degree of degradation of the faecal neutral steroids may reflect some alteration in the anaerobic flora. Total excretion of both acid and neutral steroids was also reduced. On cessation of the diet both faecal flora and faecal steroids reverted to levels before the diet.