Silica, compensated silicosis, and lung cancer in Western Australian goldminers

OBJECTIVES

Silica has recently been reclassified as carcinogenic to humans based largely on the observed increase in rates of lung cancer in subjects with silicosis. Other recent reviews have arrived at different conclusions as to whether silicosis or silica itself is carcinogenic. This study aims to examine exposure-response relations between exposure to silica and subsequent silicosis and lung cancer in a cohort of goldminers.

METHODS

2,297 goldminers from Kalgoorlie in Western Australia were examined in 1961, 1974, and 1975. Data were collected on respiratory symptoms, smoking habits, and employment history. Subjects were followed up to the end of 1993. Survival analyses for lung cancer mortality and incidence of compensated silicosis were performed with age and year matched conditional logistic regression analyses.

RESULTS

89% of the cohort were traced to the end of 1993. 84% of the men had smoked at some time and 66% were current smokers. 1386 deaths occurred during the follow up period, 138 from lung cancer, and 631 subjects were compensated for silicosis. A strong effect of smoking on mortality from lung cancer, and a smaller effect on the incidence of compensated silicosis was found. There was a strong effect of duration and intensity of exposure on the incidence of silicosis. The risk of mortality from lung cancer increased after compensation for silicosis. Of all direct measures of exposure to silica, only log cumulative exposure was significantly related to incidence of lung cancer, but this effect disappeared once the onset of silicosis was taken into account.

CONCLUSIONS

The incidence of silicosis was clearly related to exposure to silica and the onset of silicosis conferred a significant increase in risk for subsequent lung cancer, but there was no evidence that exposure to silica caused lung cancer in the absence of silicosis.

Vitamin A and cancer prevention I: observations in workers previously exposed to asbestos at Wittenoom, Western Australia

Our aim was to describe a vitamin A-based cancer prevention program for former asbestos workers and to check for possible harmful effects by comparing rates of disease and death in study subjects with subjects who chose not to join. All subjects had been occupationally exposed to crocidolite at Wittenoom Gorge between 1943 and 1966; 1,677 subjects indicated interest in the program and 1,203 joined between June 1990 and May 1995. Comparison subjects consisted of 996 former workers known to be alive in Western Australia in 1990 who did not join the program. Program subjects were provided with annual supplies of vitamin A (either synthetic beta-carotene or retinol), help in quitting smoking and dietary advice. The comparison group received only mail contact. Both groups were followed up to December 1994 for vital status and cancer information, and rates of cancer and death from various causes were compared. Mortality in both groups was higher than expected (standardised mortality ratio 1.23 in program subjects and 1.67 in comparison subjects). After adjustment for age, smoking and asbestos exposure, the relative rates in participants compared with non-participants was below I for all examined cancers and causes of death. For mesothelioma and lung cancer, group differences increased with time from entry, whereas other differences dissipated with time. No significant side effects were reported. In conclusion, program participants had significantly lower mortality than non-participants, but the rates of the 2 groups converged with time.

Vitamin A and cancer prevention II: comparison of the effects of retinol and beta-carotene

Former blue asbestos workers known to be at high risk of asbestos-related diseases, particularly malignant mesothelioma and lung cancer, were enrolled in a chemo-prevention program using vitamin A. Our aims were to compare rates of disease and death in subjects randomly assigned to beta-carotene or retinol. Subjects were assigned randomly to take 30 mg/day beta-carotene (512 subjects) or 25,000 IU/day retinol (512 subjects) and followed up through death and cancer registries from the start of the study in June 1990 till May 1995. Comparison between groups was by Cox regression in both intention-to-treat analyses and efficacy analyses based on treatment actually taken. Median follow-up time was 232 weeks. Four cases of lung cancer and 3 cases of mesothelioma were observed in subjects randomised to retinol and 6 cases of lung cancer and 12 cases of mesothelioma in subjects randomised to beta-carotene. The relative rate of mesothelioma (the most common single cause of death in our study) for those on retinol compared with those on beta-carotene was 0.24 (95% CI 0.07-0.86). In the retinol group, there was also a significantly lower rate for death from all causes but a higher rate of ischaemic heart disease mortality. Similar results were found with efficacy analyses. Our results confirm other findings of a lack of any benefit from administration of large doses of synthetic beta-carotene. The finding of significantly lower rates of mesothelioma among subjects assigned to retinol requires further investigation.

A genome scan for loci influencing total serum immunoglobulin levels: possible linkage of IgA to the chromosome 13 atopy locus

Immunoglobulins play an essential part in the immune system, and immunoglobulin deficiencies can have profound medical consequences. The genetic control and regulation of the immunoglobulin response is therefore of interest. Previous investigations have identified a number of loci influencing total and specific IgE levels. In this study, 80 nuclear families have been examined for linkage of total serum IgA, IgG and IgM levels to a genome-wide panel of microsatellite markers. Potential quantitative trait loci influencing IgA levels have been identified on chromosomes 10 and 13, and possible loci influencing IgG levels were found on chromosomes 3 and 13. No significant linkages to IgM levels were found. The linkage of IgA on chromosome 13 was to a marker previously linked to IgE responses (atopy). Linkage to IgG was in the same region but to a more distal marker. None of the factors known to influence immunoglobulin expression map to the loci identified in the present study. These loci are therefore likely to contain previously unrecognized components of the immunoregulatory system.

Environmental exposure to crocidolite and mesothelioma: exposure-response relationships

This study aimed to estimate exposure-response relationships for mesothelioma and environmental exposure to crocidolite. All 4,659 former residents of Wittenoom, Western Australia (WA) who lived there between 1943 and 1993 for at least 1 mo and were not directly employed in the crocidolite industry, were followed-up through the WA death, cancer and mesothelioma registries, electoral rolls, and telephone books. In 1992, all subjects who should be traced were sent a questionnaire. Exposure levels were estimated from results of periodic environmental surveys and duration of residence. Incidence rates were standardized to the World Population and Cox Regression was used to estimate the effects of exposure on incidence. To the end of 1993, 27 cases of mesothelioma were diagnosed. Mesothelioma cases stayed longer at Wittenoom, had a higher average intensity of exposure, and a higher cumulative exposure to crocidolite than control subjects. The standardized incidence of mesothelioma was 260 per million person-years, and was similar for males and females. The rate increased significantly with time from first exposure, duration of exposure and cumulative exposure. At these levels of crocidolite exposure, there is a significantly increased risk of mesothelioma, which is dose-dependent.

Risk factors for the development of non-response to first-line treatment for tuberculosis in southern Vietnam

BACKGROUND

Acquired resistance to standard chemotherapy for tuberculosis (TB) is an increasing problem worldwide. Vietnam has one of the highest incidences of TB and also has a large population of potential migrants to other countries. Since 1979 the International Organisation for Migration (IOM) has been running a supervised programme of TB treatment for intending migrants from Vietnam where few facilities for bacteriological culture and sensitivity testing exist. This study aimed to assess the most important factors for predicting non-response to first-line treatment as treatment starts and whether any further indicators occur during the course of treatment which may enable more accurate prediction of non-response.

METHODS

In all, 130 subjects failing to respond to first-line therapy (cases) between 1990 and 1995 were compared with 673 subjects who responded to therapy (controls) on various demographic and clinical characteristics using logistic regression to create a prognostic index. Variables analysed included the patient history of past TB treatment, weight, age, sex and radiological and bacteriological findings. All subjects also tested negative for HIV status.

RESULTS

The chief markers of successful response were x-ray signs and degree of sputum smear positivity. These markers provided a prognostic index with an optimal cutoff providing about 70% sensitivity and 80% specificity. Incorporating further measures obtained through the first 3 months of treatment improved the sensitivity to 80%.

CONCLUSION

While this study enabled prediction of the majority of subjects failing to respond to first-line therapy, other factors need to be assessed before recommendations for altering treatment regimens can be made. The prognostic index could be useful in assessing subjects for closer supervision.

Fc epsilon R1-beta polymorphism and total serum IgE levels in endemically parasitized Australian aborigines

Endemic helminthic infection is a major public-health problem and affects a large proportion of the world's population. In Australia, helminthic infection is endemic in Aboriginal communities living in tropical northern regions of the continent. Such infection is associated with nonspecific (polyclonal) stimulation of IgE synthesis and highly elevated total serum IgE levels. There is evidence that worm-infection variance (i.e., human capacity of resistance) and total serum IgE levels may be related to the presence of a major codominant gene. The beta chain of the high-affinity IgE receptor, Fc epsilon R1-beta, has been previously identified as a candidate for the close genetic linkage of the 11q13 region to IgE responses in several populations. We show a biallelic RsaI polymorphism in Fc epsilon R1-beta to be associated with total serum IgE levels (P = .0001) in a tropical population of endemically parasitized Australian Aborigines (n = 234 subjects). The polymorphism explained 12.4% of the total residual variation in serum total IgE and showed a significant (P = .0000) additive relationship with total serum IgE levels, across the three genotypes. These associations were independent of familial correlations, age, gender, racial admixture, or smoking status. Alleles of a microsatellite repeat in intron 5 of the same gene showed similar associations. The results suggest that variation in Fc epsilon R1-beta may regulate IgE-mediated immune responses in this population.

Comparison of oral bambuterol and terbutaline in elderly patients with chronic reversible airflow obstruction

Bambuterol, a carbamate prodrug of terbutaline, is the first once-daily oral beta 2-agonist. The effect/side effect ratio of bambuterol oral solution was compared with terbutaline mixture in elderly patients with chronic reversible obstructive airways disease. The study was of a double-blind, crossover, randomized design and consisted of a 4-7-day run-in period followed by four consecutive treatment periods each of 2 weeks. The treatments were bambuterol solution 20 mg nocte (B20), 10 mg nocte (B10), terbutaline mixture 3 mg t.i.d., (T), and placebo solution (P). Patients measured daily peak expiratory flow rate (PEFR), asthma symptoms, use of inhaled beta 2-agonist, and tremor. Of 84 patients, 66 completed all periods. Mean age was 67 years (60-90), basal FEV1 1.49 L, and reversibility of FEV1 30%. Ninety-four percent of the patients used inhaled/oral steroids in constant dosage. All treatments were significantly more effective than placebo. B20 resulted in higher morning PEFR than T (306 +/- 2.9 L/min vs. 297 +/- 2.9 L/min), while B10 gave equivalent results to T. No differences were seen in the use of inhaled beta 2-agonist. Less shortness of breath was experienced during the night with B20 and during the day with B10 compared with placebo. Both B20 and T produced more tremor than B10 and P. In elderly patients with chronic reversible airways obstruction once-daily bambuterol (10-20 mg) has a better effect/side effect ratio than 3 mg terbutaline thrice daily.

Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia

Determinations of exposure-response relationships between crocidolite and the major asbestos-related diseases in the Wittenoom cohort have previously depended on the validity of estimates of airborne exposure to asbestos. This work aims to validate the airborne exposure measurements by obtaining measurements of the concentrations of uncoated crocidolite fibers and asbestos bodies retained in the lungs of individual workers, and to estimate the half-life of crocidolite fibers in the lungs. Samples of lung tissue, excluding tumor, of all former Wittenoom workers known to have died in Western Australia (WA) were sought from teaching hospitals, pathology departments, and the Coroner's pathologist. The lung specimens were processed using Pooley's method with TEM for counts of fibers of all types and using Smith and Naylor's method with conventional light microscopy for asbestos bodies (AB). Multiple linear regression was utilized to examine the associations between crocidolite concentrations in the lung and duration of employment at Wittenoom, time since last employed at Wittenoom, nature of job, estimated average fiber concentration at the worksite, and estimated cumulative crocidolite exposure (CCE) in fiber-years/ml for each subject. Lung tissue from 90 cases was processed and there was good agreement between counts of crocidolite fibers, asbestos bodies, and CCE. Correlations were 0.77 for AB and fibers, 0.54 for AB and CCE, and 0.58 for CCE and fibers, after log transformation. The half-life of crocidolite fibers in the lung was estimated at 92 months (95% CI 55-277 months). Previous estimates of airborne exposure to Wittenoom crocidolite have been reasonably reliable. The relatively simple technique of light microscopy for counting ABs in lung tissue also provides a useful and reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. The half-life of crocidolite fibers in the lungs of former Wittenoom workers is about 7-8 years.

A genome-wide search for quantitative trait loci underlying asthma

Asthma now affects one child in seven in the United Kingdom. Most cases (95%) of childhood asthma are associated with atopy, the immunoglobulin E (IgE)-mediated familial syndrome of allergic asthma, eczema and rhinitis. Segregation analysis has consistently suggested the presence of major genes influencing atopy and IgE levels, with the expectation that these genes may be identified by positional cloning or the examination of candidate genes. Here we report the results of a genome-wide search for linkage to one qualitative and four quantitative traits associated with allergic (atopic) asthma. We have identified six potential linkages (P<0.001), five of which are to quantitative traits. Monte Carlo simulations show that 1.6 false-positive linkages at this level of significance would be expected from the data. One linkage, to chromosome 11q13, has been established previously. Three of the new loci show evidence of linkage to a second panel of families, in which maternal effects and pleiotropy of linked phenotypes are seen. The results demonstrate the extent and the complexity of the genetic predisposition to asthma.

Exposure to crocidolite and the incidence of different histological types of lung cancer

OBJECTIVES

To estimate the relations between exposure to both tobacco smoke and crocidolite and the incidence of various histological types of lung cancer.

METHODS

In 1979 all former workers from the Wittenoom asbestos industry who could be traced were sent a questionnaire on smoking history. Of 2928 questionnaires sent, satisfactory replies were received from 2400 men and 149 women. Of the men, 80% had smoked at some time and 50% still smoked. Occupational exposure to crocidolite was known from employment records and follow up was maintained through death and cancer registries in Australia with histological diagnoses obtained from the relevant State Cancer Registry. Conditional logistic regression was used to estimate the effects of tobacco and asbestos exposure on incidence of different cell types of lung cancer in a nested case-control design.

RESULTS

Between 1979 and 1990, 71 cases of lung cancer occurred among men in this cohort: 27% squamous cell carcinoma, 31% adenocarcinoma, 18% small cell carcinoma, 11% large cell carcinoma, and 13% unclassified or indeterminate. Two of the classified cases and one unclassified case had never smoked. The incidence of both squamous and adenocarcinoma types of lung cancer were greatest in ex-smokers and in those subjects with the highest levels of exposure to crocidolite. After adjustment for smoking habit, the increase in incidence of lung cancer with increasing exposure to crocidolite was greater for squamous cell carcinoma than for adenocarcinoma.

CONCLUSIONS

The results from this study have shown significant exposure-response effects for exposure to crocidolite, and both adenocarcinoma and squamous cell carcinoma of the lung. They also provide some further evidence against the theory that parenchymal fibrosis induced by asbestos is a necessary precursor to asbestos induced lung cancer.

Asbestos bodies in lung tissue following exposure to crocidolite

A series of 206 necropsies in Western Australia (WA) have had routine counts made of asbestos bodies in samples of lung tissue using conventional light microscopy. Thirty-two cases had worked in the asbestos industry at Wittenoom, WA and (log) counts of asbestos bodies in their lung tissue correlated well with estimates of their (log) cumulative airborne exposure to crocidolite fibers (r = 0.60). There was no association between the number of asbestos bodies and time since exposure to asbestos ceased. In subjects without known exposure to asbestos, there was a weak but nonsignificant increase in number of asbestos bodies with increasing age, with 26% of cases having no asbestos bodies present. It is concluded that the relatively simple technique of light microscopy for counting of asbestos bodies in lung tissue provides a reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. This could be extremely useful in follow-up studies of cohorts that lack reliable measures of airborne exposure to crocidolite asbestos.

Malignant mesothelioma in Pilbara Aborigines

Malignant mesothelioma occurred in a female Aborigine after environmental exposure to asbestos. All known cases of the disease in Aborigines in Western Australia were reviewed; all occurred in Pilbara residents. Most were exposed while involved in the transport of asbestos from the Wittenoom crocidolite operation. Based on recent estimates of the size of the Aboriginal population in the Pilbara region, their incidence of this disease (250 per million for ages 15 and over) is one of the highest population-based rates recorded.

Fc epsilon RI-beta polymorphism and risk of atopy in a general population sample

OBJECTIVE

To establish the prevalence of Fc epsilon RI-beta polymorphisms Leu181 and Leu181/Leu183 on chromosome 11q13 in the general population and to examine whether when maternally inherited they confer a risk of atopy.

DESIGN

A population based survey for measures of atopy (skin prick test reactions, specific IgE titres, total serum IgE concentration), bronchial hyperresponsiveness, and carriage of Fc epsilon RI-beta Leu181 and Leu181/Leu183.

SETTING

The rural coastal town of Busselton, Western Australia.

SUBJECTS

1004 members of 230 two generation families identified through adults aged under 55.

RESULTS

Fc epsilon RI-beta Leu181/Leu183 was identified in 45 subjects (4.5%). All 13 children who had inherited the variant maternally were atopic. Six had asthma and nine rhinitis. The odds ratio of a positive skin prick test reaction to house dust mite or grass pollen in these children compared with the other 523 children was 7.37 (95% confidence interval 1.62 to 33.60). The 95% confidence interval for the odds ratio of a positive specific IgE response (radio-allergosorbent test) was 3.00 to infinity, and the odds ratio for bronchial hyperresponsiveness was 3.70 (1.21 to 11.60). By contrast, the eight children who had derived the variant paternally had negative skin prick and radioallergosorbent test results and did not have increased bronchial responsiveness.

CONCLUSION

Fc epsilon RI"' beta Leu181/Leu183 when inherited maternally identifies a genetic risk factor for atopy and bronchial hyperresponsiveness.

Potential for interferon-alpha-based therapy in mesothelioma: assessment in a murine model

Malignant mesothelioma is an aggressive tumor, usually induced by asbestos exposure, that has a poor prognosis and is unresponsive to conventional therapy. The present study was aimed at assessing the potential for interferon-alpha (IFN-alpha)-based therapies in a murine model for malignant mesothelioma. The effect of recombinant human IFN-alpha B/D on tumor growth, alone and in combination with either of two immunomodulatory and antiproliferative agents beta-carotene or alpha-difluoromethylornithine (DFMO), was assessed. The data suggest that IFN-alpha treatment is most efficacious when commenced early in tumor development. Combination of IFN-alpha with either DFMO or dietary beta-carotene supplementation improved the effect of an otherwise suboptimal IFN-alpha therapy regimen. Both IFN-alpha and beta-carotene had in vivo stimulatory effects on immune cells, perhaps indirectly by inhibiting TGF-beta generation. The immunomodulatory effects may contribute, at least in part, to the positive antitumor and clinical activities of the treatments in this model.

Detection of a recessive major gene for high IgE levels acting independently of specific response to allergens

The genetic control of the total IgE, the immunoglobulins E involved in allergy, remains still unclear. Although high IgE levels were found to be determined by a recessive major gene in several studies, other modes of inheritance were also reported. Moreover, at least two different genetic mechanisms controlling the IgE regulation have been suggested: one involved in the specific IgE response and the other one in the nonspecific response. To better understand the genetic mechanisms controlling IgE variation, we performed segregation analysis of IgE levels by ignoring or taking into account the specific response to allergens (SRA). Analyses were conducted using the class D regressive model, in a sample of 234 Australian nuclear families randomly selected during the winter months, when IgE levels are the lowest (basal). SRA, when included as a covariate in the model, was defined by one of the three following criteria: (1) raised specific IgE level for one or more allergens, (2) positive skin test for one or more allergens, and (3) at least one of the (1) or (2) criteria. When the presence of SRA is ignored, the familial transmission of total IgE level is compatible with the segregation of a recessive major gene and residual familial correlations. When the presence of SRA is accounted for in the analysis, whether defined by criteria (1), (2), or (3), there is still evidence for a recessive major gene controlling IgE levels but residual familial correlations are no longer significant. In addition, no interaction between this major gene and SRA is shown here. Our results suggest that this gene, which accounts for 28% of the variation of the trait, may be involved in the control of basal IgE production, independently of specific response to allergens.

Genetic linkage of T-cell receptor alpha/delta complex to specific IgE responses

IgE responses to inhaled proteins underlie the clinical syndrome of allergic (atopic) asthma and rhinitis. We have investigated genetic linkage between specific IgE reactions to highly purified major allergens and the T-cell receptor (TCR) alpha and beta gene complexes on chromosome 14 and 7, respectively. Antigens tested included highly purified proteins from the housedust mite Dermatophagoides pteronyssinus, the domestic cat and dog, grass pollen, and the mould Alternaria alternata. Affected sibling-pair methods were used in two independent sets of families, one in the UK and one in Australia. No linkage of IgE serotypes to TCR-beta was detected, but significant linkage to TCR-alpha was seen in both family groups. For several of the IgE phenotypes investigated (positive responses to whole allergen sources or purified antigens or serum IgE above the 70th percentile in the population) the affected sibling-pairs showed significant sharing of TCR-alpha microsatellite alleles from both parents. The results show that a gene (or genes) in the TCR-alpha region modifies specific IgE responses.

Progress on smoking control in Western Australia

In 1990, 20 years of campaigning by the Western Australian branch of the Australian Council on Smoking and Health succeeded in getting tobacco advertising banned in Western Australia and a fund set up to replace the sponsorship of sport by tobacco companies. The council coordinated the activities of the mainly professional medical organisations that formed its members, ensuring that messages about the dangers of tobacco were consistently presented from different angles. The campaigners also ensured that medical data were reworked for presentation to decision makers and public, invaded the corporate world, and minimised opposition by enlisting the support of sportspeople opposed to tobacco sponsorship. The council hopes now that elimination of advertising will reduce the prevalence of smoking.