Inhibitory effect of sorbitol on sugar metabolism of Streptococcus mutans in vitro and on acid production in dental plaque in vivo.

This study was conducted to find out whether sorbitol inhibits the sugar metabolism of Streptococcus mutans in vitro and the acid production in dental plaque in vivo. S. mutans NCIB 11723 was anaerobically grown in sorbitol-containing medium. The rate of acid production from sugars was estimated with a pH stat. The rate of acid production from glucose or sucrose was not changed at various concentrations of oxygen. By the addition of sorbitol to sugar, however, the acid production was decreased with increasing levels of oxygen. Intracellular NADH/NAD+ ratio and (dihydroxyacetone-phosphate+glyceraldehyde-phosphate)/3-phosphoglycerate ratio were high whenever the acid production was inhibited by sorbitol. Sorbitol also inhibited the acid production in dental plaque in vivo. These results suggest that the increased NADH/NAD+ ratio during sorbitol metabolism through the inactivation of pyruvate formate-lyase by oxygen inhibited glyceraldehyde-phosphate dehydrogenase and then the acid production of S. mutans and the one in dental plaque.

Rate-limiting steps of glucose and sorbitol metabolism in Streptococcus mutans cells exposed to air.

It has been supposed that rate of sorbitol metabolism in the air-exposed streptococcal cells could be limited by the low capacity to regenerate nicotinamide adenine dinucleotide (NAD) from reduced NAD (NADH) following inactivation of pyruvate formate-lyase by oxygen. The rate-limiting steps, however, have not been identified. The aim of this study was to examine the effect of temporary exposure of the streptococcal cells to air on the intracellular flux of glucose and sorbitol metabolism by measuring acid excretion, fluorescence dependent on cellular level of NADH, glycolytic intermediates and enzyme activities. The exposure of cells to air decreased the acid excretions during glucose and sorbitol metabolism. The analysis of the glycolytic intermediates and the fluorescence suggested that the reduced level of acid excretion in the air-exposed glucose metabolizing cells resulted from the decrease in pyruvate catabolism. In the presence of sorbitol, the decreased acid production resulted from the reduced rates of the reactions catalyzed by sorbitol-phosphoenolpyruvate phosphotransferase and sorbitol 6-phosphate dehydrogenase because of shortage of substrates for these enzymes in addition to the decrease in pyruvate catabolism.

Cloning and sequence analysis of the pfl gene encoding pyruvate formate-lyase from Streptococcus mutans.

We have isolated a sorbitol-negative mutant of Streptococcus mutans GS-5 following random mutagenesis with plasmid pVA891 clone banks. This mutant did not metabolize sorbitol anaerobically but did so aerobically. A 10-kb chromosomal DNA fragment flanking the pVA891 insertion was deleted in this mutant. The corresponding region from the parental strain GS-5 was then recovered by a marker rescue method with Escherichia coli. The pyruvate formate-lyase gene, pfl, was identified within a 3-kb PstI-XbaI fragment located in the middle of the deleted region of the chromosome, and its inactivation in S. mutans produced the same sorbitol-negative phenotype. Nucleotide sequence analysis of the pfl gene revealed a 2.3-kb open reading frame (ORF) preceded by potential ribosome-binding and promoter-like sequences. The ORF specified a putative protein of 775 amino acid residues with a calculated molecular weight of 87,533. The amino acid sequence deduced from the ORF exhibited significant similarity to that of the E. coli pfl gene.

Acid production by streptococci growing at low pH in a chemostat under anaerobic conditions.

Streptococcus mutans and other oral streptococci were grown in continuous culture under strictly anaerobic conditions. When the cultural pH was kept at 7.0, the main acid products were formate and acetate, as reported previously. However, more lactate was produced at pH values of 5.5 or 6.0, with a concomitant decrease in formate and acetate production. This change in fermentation products could partly be ascribed to a change in intracellular pH and difference in the pH optima between pyruvate formate-lyase (PFL) and lactate dehydrogenase (LDH). At extracellular pH values of 7.0 and 5.5, the intracellular pH values of S. mutans NCIB 11723 were 7.5 and 6.6, respectively. The pH optima of PFL and LDH were 7.8 and 5.5-6.3, respectively. The cells had also a larger amount of LDH during growth at pH 5.5 than at pH 7.0.

Colon cancer in Argentina. II: Risk from fibre, fat and nutrients.

A case-control study has been conducted to investigate the relationship between total energy intake, fibre and nutrients and colon cancer in Argentina. Cases are 110 newly diagnosed patients from 10 hospitals between 1985 and 1986. Two neighbourhood controls per case were matched on age, sex and place of residence. The intake of calories, fibre and nutrients was estimated from the information collected on food consumption during the 5-year period up to 6 months prior to interview of subjects, based on a pilot study and standard portion sizes in Argentina. In conditional regression models, dietary fibre is highly protective (odds ratio (OR) = 0.07 per 19.02 g/day; 95% confidence interval (CI): 0.02 to 0.25) and total energy intake increases risk (RR = 1.82 per 1000 kcal/day; 95% CI: 1.20 to 2.77), each with adjustment for the other. Analysis of caloric components (fat, protein and carbohydrates) reveals that carbohydrates are the most important factor driving the total energy effect. Other nutrients make little apparent contribution to risk.

Colon cancer in Argentina. I: Risk from intake of dietary items.

A case-control study has been conducted to investigate the relationship between dietary components and risk of colon cancer in the La Plata area of Argentina. Cases are 110 patients newly diagnosed with colon cancer in 10 major hospitals between 1985 and 1986. Two neighbourhood controls per case were individually matched by age, sex and place of residence. Personal interviews elicited information on frequency of consumption of 140 food items during the 5-year period up to 6 months prior to interview. Risk is analyzed by quartiles of individual food items and groups of items. Multivariate conditional logistic regression modelling indicates that consumption of eggs is associated with increased risk for colon cancer (odds ratios by quartile: 1.0, 1.58, 2.02, 4.66), as are some dairy products (ORs of 1.93 for the highest quartile of consumption of cheese). Intake of vegetables, fish and poultry is associated with statistically significant decreasing risk (ORs of 0.075, 0.39 and 0.39, for the highest categories of consumption of vegetables, fish and poultry, respectively). The risk for red meat does not consistently increase as consumption increases. Risks are not altered by the inclusion of potential confounders such as education or body mass index. These findings confirm those of several previous studies and are of particular interest, since the Argentinean diet typically includes a high intake of red meat.

Oral contraceptives and risk of benign proliferative epithelial disorders of the breast.

In a case-control study conducted in Adelaide, South Australia, we investigated the hypothesis that use of oral contraceptives is associated with increased risk of benign proliferative epithelial disorders (BPED) of the breast, conditions strongly associated with increased risk of breast cancer and thought to have pre-malignant potential. The study was restricted to women with no prior history of breast biopsy, and involved 383 cases of biopsy-confirmed BPED, 192 controls whose biopsy did not show epithelial proliferation, and 383 unbiopsied community controls individually matched to cases by age and socio-economic grading of area of residence. When cases were compared with community controls, the adjusted odds ratio (OR) for the association between ever-use of oral contraceptives and risk of BPED was 1.1 (95% CI 0.7 to 1.7), while when cases were compared with biopsy controls, the adjusted OR was 0.9 (95% CI 0.5 to 1.5). There was little variation in risk of BPED with total duration of use of oral contraceptives, and with duration of use before first pregnancy, while current users had a statistically significant 60% reduction in risk, irrespective of the control group used for comparative purposes. Also, there was little variation in risk with years since first and last use of oral contraceptives, and there was no trend in the association between ever-use of oral contraceptives and risk of BPED by degree of cytological atypia.

Incorporating variations in the quality of individual randomized trials into meta-analysis.

Meta-analysis is a method of synthesizing evidence from multiple sources. It has been increasingly applied to combine results from randomized trials of therapeutic strategies. Unfortunately there is often variation in the quality of the trials that are included in meta-analyses, limiting the value of combining the results in an overview. This variation in quality can lead to both bias and reduction in precision of the estimate of the therapy's effectiveness. There are a number of methods for quantifying the quality of trials including the detailed Chalmers system and simple scales. The nature of the relationship between these quality scores and the true estimate of effectiveness is unknown at this time. We discuss four methods of incorporating quality into meta-analysis: threshold score as inclusion/exclusion criterion, use of quality score as a weight in statistical pooling, visual plot of effect size against quality score and sequential combination of trial results based on quality score. The last method permits an examination of the relation between quality and both bias and precision on the pooled estimates. We conclude that while it is possible to incorporate the effect of variation of quality of individual trials into overviews, this issue requires more study.

Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols.

Epidemiological studies have revealed an increased risk of cancer, notably soft-tissue sarcomas and non-Hodgkin's lymphomas, in people occupationally exposed to chlorophenoxy herbicides, including those contaminated by 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). We report here a historical cohort study of mortality in an international register of 18,910 production workers or sprayers from ten countries. Exposure was reconstructed through questionnaires, factory or spraying records, and job histories. Cause-specific national death rates were used as reference. No excess was observed in all-cause mortality, for all neoplasms, for the most common epithelial cancers, or for lymphomas. A statistically non-significant two-fold excess risk, based on 4 observed deaths, was noted for soft-tissue sarcoma with a standardised mortality ratio (SMR) of 196 and 95% confidence interval (Cl) 53-502; this was concentrated as a six-fold statistically significant excess, occurring 10-19 years from first exposure in the cohort as a whole (SMR = 606 [165-1552]) and, for the same time period, as a nine-fold excess among sprayers (SMR = 882 [182-2579]). Risks appeared to be increased for cancers of the testicle, thyroid, other endocrine glands, and nose and nasal cavity, based on small numbers of deaths. The excess of soft-tissue sarcomas among sprayers is compatible with a causal role of chlorophenoxy herbicides but the excess does not seem to be specifically associated with those herbicides probably contaminated by TCDD.

A collaborative study of cancer incidence and mortality among vinyl chloride workers.

A large European multicentric cohort study has been coordinated by the International Agency for Research on Cancer with the objectives of investigating the dose-response relationship between liver cancer and exposure to vinyl chloride and assessing cancer risk for sites other than the liver. A nearly threefold increase in liver cancer was detected on the basis of 24 observed deaths and 8.4 expected (standardized mortality ratio 286, 95% confidence interval 186-425). The excess from liver cancer was clearly related to time since first exposure, duration of employment, and estimated ranked and quantitative exposures. Other cancer sites investigated on the basis of a priori hypotheses were either not in excess (lung) or apparently unrelated to the exposure variables (brain and lymphoma).

Liver cancer in Thailand. I. A case-control study of cholangiocarcinoma.

Potential risk factors for cholangiocarcinoma were investigated in a case-control study among inhabitants of north-east Thailand, which included 103 cases from 3 hospitals, with age- and sex-matched controls. A clear association with past or present infection with Opisthorchis viverrini, as indicated by raised serum antibodies, was found (o.r. 5.0), and at least two-thirds of cases can be attributed to this cause. The results suggest that males may be at higher risk than females. There was no association with hepatitis B infection, with aflatoxin intake as estimated from albumin adducts in serum or with any particular dietary patterns. Alcohol consumption was very low in the population, and the risk associated with regular drinking was non-significant. Regular users of betel nut-predominantly female-had a high risk (o.r. 6.4), a possible mechanism being through their increased exposure to nitrosamines.

Liver cancer in Thailand. II. A case-control study of hepatocellular carcinoma.

Potential risk factors for hepatocellular carcinoma were investigated in a case-control study among inhabitants of north east Thailand. Sixty-five cases from 3 hospitals, with matched controls, were included. Infection with hepatitis-B virus was the major risk factor-chronic carriers of HB surface antigen had an estimated relative risk of 15.2. Infection with hepatitis-C virus appeared to be rare. No increase in risk was found with recent aflatoxin intake, as estimated by consumption of possibly contaminated foods, or by measuring aflatoxin-albumin adducts in serum. Regular use of alcohol (2 or more glasses of spirits per week) was associated with a non-significant elevation in risk (o.r. = 3.4, 95% c.i. 0.8-14.6), but the number of regular drinkers in the population was small. The meaning of an apparent protection conferred by certain food items is uncertain, but a possible role of betel nut in the aetiology deserves further investigation.

Radon exposure, cigarette smoking, and other mining experience in the beaverlodge uranium miners cohort.

A nested case-control study within the Beaverlodge Uranium Miners Cohort was undertaken to assess any possible contribution of confounding by smoking and other mining experience to the risk estimate derived from the original cohort study. Next of kin have been interviewed for 46 lung cancer cases and 95 controls enrolled in the Beaverlodge Uranium Miners Cohort Study who died between 1950 and 1980. Confounding by cigarette smoking and other mining experience appears unlikely to have contributed to the relative risk coefficient for exposure to Rn decay products derived in the parent study. Data for smoking and exposure to Rn decay products are consistent with a multiplicative model, although considerable caution must be applied to this interpretation.

Oxygen and the sugar metabolism in oral streptococci.

Streptococci have several ways of adapting themselves to the constantly changing environment of the human oral cavity. This paper discusses the adaptation of sugar metabolism to variations in oxygen levels. In all streptococci the Embden-Meyerhof pathway of glycolysis works under aerobic as well as anaerobic conditions, but pyruvate is converted into different metabolic end products depending on the oxygen levels. Under anaerobic conditions all streptococci form formate, acetate, and ethanol by a pyruvate formate-lyase pathway. If sugar is in excess, they also form lactate using a lactate dehydrogenase. Under aerobic conditions pyruvate formate-lyase is inactivated. This enzyme is then replaced by a pyruvate oxidase in some streptococci and by a pyruvate dehydrogenase in others. The characteristics of these enzymes help streptococci like S. sanguis, S. oralis, S. gordonii, and S. mitis to compete successfully with other bacteria in those sites of the oral cavity that are freely exposed to saliva, while mutans streptococci have to colonize anaerobic sites such as those in-between the teeth and in the occlusal fissures of the teeth.

Interaction between human carcinogens.

In the absence of direct information on the carcinogenicity of a complex mixture, assessment of its risk requires not only knowledge of the risks due to the separate components, but also assumptions about the interaction between the components. A formal definition of interaction is given, followed by a discussion of the theoretical basis for different kinds of interactions. Epidemiological studies which have considered the simultaneous effect of two chemical carcinogens are reviewed, and shown to provide examples of additivity, multiplicativity and interaction both intermediate between the two and greater than multiplicative. Finally, implications for the risk assessment of mixtures are discussed.

Visits to physicians before and after exposure to urea formaldehyde foam insulation.

The average number of visits to a physician made by a sample of 351 residents of homes insulated with urea formaldehyde foam insulation in Montreal in the one year period before exposure was 5.25, and in the year following 5.62, an increase of 7 per cent (odds ratio 1.07, 95% CI = 1.00, 1.15). The increase in visits in the post insulation year was limited to subjects who had the product installed in the winter (OR = 1.48, 95% CI = 1.18,1.85), and was not seen for study subjects who insulated their homes during other seasons of the year.

Meta-analysis in clinical research.

Meta-analysis is the process of combining study results that can be used to draw conclusions about therapeutic effectiveness or to plan new studies. We review important design and statistical issues of this process. The design issues include protocol development, objectives, literature search, publication bias, measures of study outcomes, and quality of the data. The statistical issues include consistency (homogeneity) of study outcomes, and techniques for pooling results from several studies. Guidelines are provided to assess the quality of meta-analyses based on our discussion of the design and statistical issues. Limitations and areas for further development of this approach are discussed; researchers should come to a general agreement on how to conduct meta-analysis. As an explicit strategy for summarizing results, meta-analysis may help clinicians and researchers better understand the findings of clinical studies.

Oxygen sensitivity of sugar metabolism and interconversion of pyruvate formate-lyase in intact cells of Streptococcus mutans and Streptococcus sanguis.

Pyruvate formate-lyase (PFL) (formate acetyltransferase; EC 2.3.1.54) of oral streptococci is essential for metabolizing sugar into volatile compounds (formate, acetate, and ethanol). This enzyme is extremely sensitive to oxygen, and its activity is irreversibly inactivated by oxygen. When Streptococcus sanguis was anaerobically starved, a part of the active form of PFL was converted into a reversible inactive form that was tolerant of oxygen. This reversible inactive enzyme could be reactivated to the active enzyme by anaerobic sugar metabolism, with the recovery of volatile compound production. The PFL in Streptococcus mutans was not converted into an oxygen-tolerant inactive form by anaerobic starvation, and after exposure of the cells to oxygen the PFL could not be reactivated. These findings suggest that S. mutans can produce acids rapidly under anaerobic conditions because of its capacity to keep PFL active and that S. sanguis can protect its sugar metabolism from oxygen impairment because of its interconversion of PFL.

Role of NADH oxidase in the oxidative inactivation of Streptococcus salivarius fructosyltransferase.

A cell-associated fructosyltransferase produced by Streptococcus salivarius was irreversibly inactivated in a time-dependent manner when resting or permeabilized cell suspensions were incubated with low concentrations (less than 1.0 microM) of copper. In addition to copper, the inactivation was dependent on oxygen and on a fermentable carbon source (endogenous intracellular polysaccharide or glucose). In starved, permeabilized cell suspensions, the fermentable carbon source could be replaced by NADH but not by NADPH or ATP. Of several other S. salivarius enzymes tested, only fructosyltransferase was inactivated under these conditions. The available evidence indicated that NADH oxidase is the enzyme responsible for fructosyltransferase inactivation. Results from oxygen radical scavenger studies implicated one or more species of oxygen radicals and hydrogen peroxide in the inactivation reaction.

Do interns and residents order more tests than attending staff? Results of a house staff strike.

Between October 30 and November 5, 1980, the Professional Association of Interns and Residents of Ontario called a strike of house staff in Ontario's teaching hospitals. The authors obtained data concerning utilization of laboratory tests and radiology procedures during that period and for the same days 2 weeks before and after the strike. During the strike period, the number of tests performed per patient day decreased by only 8.3%. After accounting for proportional changes in emergency and nonemergency admissions, there was no significant change in the number of tests or relative value units performed per patient day as a result of the strike. These results suggest that the volume of tests performed in teaching hospitals is more likely related to the case mix and severity of illness of patients admitted to these institutions than to a pure "teaching effect."