Functional significance of histologic alterations induced by Escherichia coli pig-specific, mouse-negative, heat-stable enterotoxin (STb)

In contrast to cholera enterotoxin and other Escherichia coli enterotoxins, a pig-specific, heat-stable E. coli enterotoxin (STb) causes morphologic lesions (loss of villous epithelial cells and partial villous atrophy). These lesions reflect a loss of absorptive cells and thus suggest that STb causes impaired absorption as well as inducing net secretion. The present studies assess functional significance of morphologic changes induced by STb. Net fluid movement, mucosal surface area, sucrase activity and the electrical response induced by alanine were measured in swine jejunal loops exposed to E. coli culture filtrates with and without STb. Net fluid secretion (-11.1 +/- 1.1 ml) occurred in some STb loops (secretors) and net absorption (2.7 +/- 0.3 ml) in others (nonsecretors), but net absorption occurred in all control loops (4.9 +/- 0.2 ml). The mucosal surface area of STb loops was about 20% less than that of controls (P less than 0.01). Sucrase activity was also lower (about 15%) in STb loops than in control loops (P less than 0.01). The electrical response induced by alanine in mucosa from nonsecreting STb loops did not differ from that induced in mucosa from control loops. However, the response to alanine in mucosa from secreting STb loops was reduced about 70% from that in mucosa from nonsecreting STb loops or from control loops (P less than 0.05). It is concluded that reduced sucrase activity is a functional correlate to villous atrophy induced by STb, that STb impairs alanine absorption in some loops (secretors), and that the impaired alanine absorption is independent of the decreased surface area caused by STb. Because the impaired alanine absorption occurred independent of the decreases in surface area, it is suggested that the secretory response to STb is associated with an impairment of active absorption of alanine.

Hydrogen peroxide-inducible proteins in Salmonella typhimurium overlap with heat shock and other stress proteins

Hydrogen peroxide treatment induces the synthesis of 30 proteins in Salmonella typhimurium. Five of these proteins are also induced by heat shock, including the highly conserved DnaK protein. The induction of one of these five proteins by heat shock is dependent on oxyR, a positive regulator of hydrogen peroxide-inducible genes, while the induction of the other four by heat shock is oxyR independent. Five of the 30 hydrogen peroxide-inducible proteins have been identified, and their structural genes have been mapped. Other stresses such as nalidixic acid, ethanol, or cumene hydroperoxide treatment also induce subsets of the 30 hydrogen peroxide-inducible proteins as well as additional proteins. Hydrogen peroxide-inducible proteins are shown to be largely different from those proteins induced by aerobiosis. In addition, the expression of the katG (catalase) gene is shown to be regulated by oxyR at the level of mRNA.

An epidemiological study of petroleum refinery employees

A cohort study of 14179 current and former Chevron USA employees at the Richmond and El Segundo, California, refineries was conducted. The cohort consisted of everyone working at either refinery for a minimum of one year. The observed mortality of the cohort, by cause, was compared with the expected based on the United States mortality rates, standardised for age, race, sex, and calendar time. Analyses by refinery, job category, hire date, duration of employment, and latency were performed. For the entire cohort, mortality from all causes was 72.4% of that expected, a deficit that was statistically significant. In addition, a significantly lower mortality was found for all forms of cancer combined, digestive cancer, lung cancer, heart disease, non-malignant respiratory disease, diseases of the digestive system, and accidents. Only lymphopoietic cancer showed a pattern of increased risk suggestive of a possible relation to an occupational exposure. The excess appears confined to cancer of lymphatic tissue (not leukaemias) at Richmond, and only among those hired before 1948. A follow up case analysis of the deaths from lymphatic cancer failed to identify a common exposure pattern.

Mortality among members of a heavy construction equipment operators union with potential exposure to diesel exhaust emissions

A historical prospective mortality study was conducted on a cohort of 34 156 male members of a heavy construction equipment operators union with potential exposure to diesel exhaust emissions. This cohort comprised all individuals who were members of the International Union of Operating Engineers, Locals 3 and 3A, for at least one year between 1 January 1964 and 31 December 1978. The mortality experience of the entire cohort and several subcohorts was compared with that of United States white men, adjusted for age and calendar time. The comparison statistic was the commonly used standardised mortality ratio (SMR). Historical environmental measurements did not exist, but partial work histories were available for some cohort members through the union dispatch computer tapes. An attempt was made to relate mortality experience to the union members' dispatch histories. Overall mortality for the entire cohort and several subgroups was significantly lower than expected. When cause specific mortality was examined, however, the study provided suggestive evidence for the existence of several potential health problems in this cohort. Mortality from liver cancer for the entire cohort was significantly high. Although mortality from lung cancer for the entire cohort was similar to expected, a positive trend by latency was observed for lung cancer. A significant excess of mortality from lung cancer was found among the retirees and the group for whom no dispatch histories were available. Other dispatch groups showed no evidence of lung cancer excess. In addition, the total cohort experienced significant mortality excess from emphysema and accidental deaths.

Asbestos and gastrointestinal cancer. A review of the literature

Exposure to asbestos is among several factors cited as possible causes of esophageal, gastric and colorectal cancer. More than 45 published studies have presented mortality data on asbestos-exposed workers. For each cohort, we listed the observed and expected rates of deaths from types of gastrointestinal cancer based on the latest published follow-up. Summary standardized mortality ratios (SMRs) were then derived. Finally, we calculated summary SMRs for total gastrointestinal tract cancer for three occupational groups: asbestos factory workers, insulators/shipyard workers and asbestos miners. Statistically significant elevations in summary SMRs were found for esophageal, stomach and total gastrointestinal tract cancer in all asbestos-exposed workers. Esophageal cancer summary SMRs remained significantly elevated when data were reanalyzed to include only those cohorts with death certificate diagnoses for cause of observed deaths. However, summary SMRs were not statistically significant for stomach and total gastrointestinal tract cancer after reanalysis. Summary SMRs by occupational group showed a significant elevation for total gastrointestinal cancer in insulators/shipyard workers. The elevation was not significant after reanalysis. Based on the results after reanalysis, the elevations in summary SMRs for stomach and total gastrointestinal tract cancer are of a magnitude that could result from diagnostic and investigator error. We conclude that more studies are required before stomach and colorectal cancers are documented as asbestos-related diseases.

Mortality of paint and coatings industry workers. A follow-up study

Extensive follow-up of production workers in the paint and coatings industry failed to indicate any important hazard that was previously unsuspected. The authors are more confident of the results of their original study since studying a subsample of persons lost to follow-up in the original study. Some efforts to investigate certain diseases (skin and liver cancer) more vigorously met with failure, which illustrates the problem of attempting retrospective studies by using death certificates for case ascertainment. Of the successful studies, the leukemia case-control analysis showed a possible relationship to lacquer production, which probably included benzene exposure. For lung cancer, no exposure category was associated with increased risk. The bowel cancer excesses, concentrated in three plants, are probably not job related and in any case do not represent an industry-wide problem. Cerebrovascular accidents showed a mild elevation of risk for vehicle workers. Although strong statements concerning the safety of this industry probably await more studies or further follow-up of this cohort, there is every indication that it is an industry without a major excess of any job-related disease. In drawing this conclusion, however, one must be aware that an individual job or individual plant could harbor health problems that would not be detected by a study of this type.

A review of epidemiological studies on artificial sweeteners and bladder cancer

Next to tobacco, saccharin may be the substance that has been most studied epidemiologically. Over 5000 patients with bladder cancer have participated in case-control studies; over 27,000 diabetics have been observed for 234,000 person-years. The summary relative risk from combining all case-control studies is less than 0.98, the standardized mortality ratio for bladder cancer in diabetics is only 70. Analysis of these studies leads to the conclusion that saccharin is not related to human bladder cancer.

An epidemiologic surveillance program for evaluating occupational reproductive hazards

A noninvasive and inexpensive epidemiologic program for evaluating the possible effects of occupational exposures on fertility is proposed. This surveillance program utilizes reproductive information obtainable from a short questionnaire (1-2 pages in length) or directly from existing medical, employment, or insurance records, and results can be generated readily on a routine basis. This program examines the reproductive experience of the exposed workers in terms of live births compared with that of the US general population with the proper statistical adjustments. It calculates the standardized birth ratios (SBR), adjusting for maternal age, parity, calendar time, and race. Such an analysis will detect whether there is a significant decrease in fertility among a group of employees, and is, therefore, a useful surveillance tool. The proposed method should be viewed as a mechanism to provide an early signal for any potential hazard and to direct priority for other more in-depth epidemiologic or physiologic studies. The procedure is illustrated with data from individuals exposed to EDB, DBCP, and waste-water treatment plant processes. The method can be modified to compare the reproductive performance of an exposed group to that of an internal control group. With an internal control group, additional confounding factors can be taken into consideration. The relative merits of this approach compared to another method of fertility evaluation, semen analysis, are discussed.

Fetal loss and work in a waste water treatment plant

We investigated pregnancy outcomes in 101 wives of workers employed in a waste water treatment plant (WWTP), and verified fetal losses by hospital records. Paternal work histories were compiled and each of the 210 pregnancies was assigned a paternal exposure category. The relative risk of fetal loss was increased when paternal exposure to the WWTP occurred around the time of conception.

Review: putative mutagens and carcinogens in foods. V. Cycad azoxyglycosides

Cycasin is a member of a family of azoxyglycosides produced by cycads. It is mutagenic and carcinogenic only when deglucosylated to release its principal metabolite, methylazoxymethanol (MAM). Methylazoxymethanol is also the aglycone of other cycad azoxyglycosides and is responsible for their toxicologic properties. The way in which people can be exposed to cycad azoxyglycosides is through the consumption of foods prepared from cycads. MAM induces genetic alterations in various test systems in bacteria, yeast, plants, Drosophila, and mammalian cells. An important aspect of the biological activities of cycasin and MAM is the intimate connection between their metabolism and their toxicologic effects. In adult mammals, the deglucosylation of cycasin is catalyzed only by enzymes of the microflora of the gut. Cycasin is therefore active when administered orally but not when administered parenterally. In contrast, MAM is active regardless of the route of exposure. Major uncertainties remain regarding the intermediates generated from MAM spontaneously and metabolically. More knowledge of these intermediates is required for a better understanding of the molecular mechanisms underlying the toxicity of cycasin, MAM, and related compounds.

Exogenous estrogens and development of breast and endometrial cancer

The risk of breast cancer and endometrial cancer in 1483 menopausal and postmenopausal women who had received estrogen therapy for other than contraceptive use was examined. The incidence and mortality rates of the study cohort (cohort A) were compared with the age-specific cancer incidence and mortality rates of the female populations of Ontario (cohort B) and of Saskatchewan (cohort C). A significant difference was found in each of the two comparisons between the observed and expected survival curves for breast cancer incidence and breast cancer mortality. However, the incidence rate of endometrial cancer in the study cohort (cohort A) did not differ significantly from the rates of the reference populations (cohorts B and C). The results suggest that the women in the study may have received some protective effect against breast cancer by taking estrogens, but the estrogens did not protect them against endometrial cancer and may indeed have predisposed them to this cancer.

Age at menarche, probability of ovulation and breast cancer risk

An analysis is undertaken of the frequency of ovulation in 17 groups of women aged 15 to 19 who had been the subjects of other studies. A urine specimen of at least 8 h accumulation had been provided on the 20th or 21st day of a menstrual cycle by 681 women. Analysis is restricted to 431 specimens which had been collected between 11 and 3 days prior to the onset of the subsequent menstrual period. A pregnanediol concentration of less than 1 mg per litre in such a specimen was taken as evidence that the cycle was anovular. The probability of a cycle being anovular was inversely and significantly related to the number of years since menarche, and, with years since menarche held constant, was positively but not significantly associated with age at menarche. This observation indicates that women with early menarche do not have a longer duration of exposure to anovular cycles than do those whose menarche is delayed, and that variation in the duration of exposure to post-menarcheal anovular cycles does not explain the association of breast cancer risk with early age at menarche. The 17 groups of women were classified into four categories according to ethnic origin and breast cancer incidence in the populations from which they derived. Anovular cycles were not more common in the high-risk groups; indeed, the two centers in the lowest risk category had the highest proportion of anovular cycles.

Smoking as a risk factor in cancer of the cervix: additional evidence from a case-control study

The results of a case-control study in Toronto, Canada, demonstrated a two-fold risk of invasive squamous cell carcinoma of the cervix among current smokers relative to women who had never smoked. This significant effect of smoking was not diminished by simultaneously adjusting for age, education, and indices of sexual behavior. This association was further supported by the observations that ex-smokers were at a lower risk than current smokers (1.7 versus 2.3), and that the risk increased with the amount of cigarettes smoked (2.2 for less than half a pack per day to 2.9 for more than one pack per day).

Aroclor 1254-induced intestinal metaplasia and adenocarcinoma in the glandular stomach of F344 rats

Ingestion of diets containing Aroclor 1254, a mixture of polychlorinated biphenyls, for 2 years led to a dose-related increase in the incidence of focal lesions in the glandular stomachs of male and female F344 rats. The incidence of stomach lesions was 6% in control specimens and in specimens from rats fed a diet containing 25, 50, or 100 ppm Aroclor 1254, the incidences of stomach lesions were 10, 17, and 35%, respectively. The majority of gastric lesions in treated rats were histologically identified as intestinal metaplasia characterized by an architecture resembling that of intestinal crypts and particularly by goblet cells, which stained with Alcian blue and periodic acid-Schiff reagent. Adenocarcinomas were found in six specimens. Most (88%) of the lesions were located in the pyloric region of the glandular stomach. No multiple lesions were observed among 47 control specimens examined; however, nine cases of multiple lesions were observed in 30 lesion-containing specimens from Aroclor 1254-treated rats. Although the exact relationship between gastric intestinal metaplasia and adenocarcinoma remains to be established, they commonly coexist and may share initiating mechanisms.

Mortality among ethylene oxide workers

Because of reports linking an increased risk of leukemia with exposure to ethylene oxide, a mortality study of workers with potential exposure to ethylene oxide at the Texaco Chemical Company Plant in Port Neches, Tex., was undertaken. A total of 767 males with potential exposure to ethylene oxide were identified. Forty-six deaths occurred in this cohort with 80 expected (standardized mortality ratio; SMR = 58). No deaths from leukemia were seen, nor were there any statistically significant excesses from any specific causes of death.

Mortality study of fibrous glass production workers

This retrospective cohort study examines the mortality experience of 6,536 male employees engaged in fibrous glass production for 10 or more years. A special component of this investigation was an analysis of a long-term cohort involving 1,222 individuals who were employed 20 or more years and who experienced 30 or more years latency. There was no marked excess of statistically significant increase in mortality for any cause of death. In fact, the pattern of mortality for fibrous glass production workers appeared considerably lower than comparable U.S. patterns, perhaps reflecting both a "health worker" effect, and the life style of the steadily employed person. Long-term workers' mortality experience was similar to those individuals employed for shorter periods.

Detection of mutagens-carcinogens: carcinogen-induced lesions pinpointed by alkaline phosphatase activity in fixed gastric specimens from rats

Alkaline phosphatase (AP) activity was not detectable by histochemical staining in the glandular stomachs of normal rats. However, AP activity was present at high levels in the brush borders of the intestine and persisted after fixation of the tissues in Formalin at room temperature. Foci of AP activity were detected in gross Formalin-fixed specimens of glandular stomachs of male and female inbred F344 rats exposed to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and killed over 6 years ago. The incidence of AP-positive foci increased in proportion to the dose of the carcinogen MNNG. Histologically, most of the grossly visible AP-positive foci corresponded to areas of intestinal metaplasia and adenocarcinoma. AP-positive foci localized sites of pathologic significance for microscopic examination and pinpointed gastric sites containing very early tumors that were missed by standard examination.

Airborne carcinogens and human cancer

There is as yet little convincing evidence that air pollution contributes to cancer risk, save for the strong suspicion of an increase in risk for persons living adjacent to arsenic emitters. The lack of any demonstrated direct and strong relationship between pollution and cancer, as well as the absence of any easily identifiable cancer epidemic in polluted areas, leads us to suspect that if a relationship exists, it is relatively weak and contributes little to the total cancer burden, especially in comparison to hazards such as cigarette smoking. There is a need for further research to verify our conclusions.

A general mortality study of production workers in the paint and coatings manufacturing industry. A preliminary report

Information has been obtained on a cohort of 16,243 men employed for at least one year in the manufacture of paint or vanish after January 1, 1946, and for seven subgroups on the basis of exposure. These workers experienced a level of mortality that compares favorably with that of the U.S. white male population. The workers' pattern of mortality differed somewhat from the U.S. pattern, with considerably reduced mortality from psychiatric, metabolic, respiratory, and violent causes. There was an increased mortality due to bowel and rectal cancer. While the numbers are smaller, there are also increased rates for liver and skin cancer. Lung cancer rates, while not in excess of the national average, did not match the low mortality from nonmalignant, noninfectious respiratory disease. The authors have concluded that work in this industry presents no major health hazard.

Exercise prescription: a clinical trial

To assess the effectiveness of physician prescribed exercise, health education, and patient self-monitoring, 124 firefighters were medically screened and randomly allocated to a control and two treatment groups. Physiologic and reporting methods were employed to assess adherence to regular exercise at three months and six months after the initial exercise prescription. Addition of a health education program significantly improved compliance over that achieved by a physician consultation. Self-monitoring did not produce a further increase in compliance. Improvement in the treatment groups was limited to three months after prescription; at six months, the treatment and control populations had similar exercise patterns.

Effects of chemical and physical mutagens on the frequency of a large genetic duplication in Salmonella typhimurium. I. Induction of duplications

In Salmonella typhimurium a simple selection has been described to detect bacteria that are merodiploid for almost one-third of the chromosome. The selective procedure is based upon improved utilization of L-malate as the sole carbon source in merodiploid strains. The spontaneous frequency of the duplication in haploid strains is approximately 10(-4) per cell plated. Following the exposure of a haploid strain to mutagenic agents, there is a dose-dependent increase in the duplication frequency above the spontaneous level. In this paper we describe the induction of genetic duplications in Salmonella typhimurium by X-rays, ultraviolet light (UV), ethyl methanesulfonate (EMS), nitrous acid, and the azaacridine half mustard, ICR-372.