Prevention of hepatic fibrosis with liver microsomal triglyceride transfer protein deletion in liver fatty acid binding protein null mice.

Blocking hepatic very low-density lipoprotein secretion through genetic or pharmacologic inhibition of microsomal triglyceride transfer protein (Mttp) causes hepatic steatosis, yet the risks for developing hepatic fibrosis are poorly understood. We report that liver-specific Mttp knockout mice (Mttp-LKO) exhibit both steatosis and fibrosis, which is exacerbated by a high-transfat/fructose diet. When crossed into germline liver fatty acid (FA) binding protein null mice (Mttp-LKO, i.e., double knockout mice) hepatic steatosis was greatly diminished and fibrosis prevented, on both low-fat and high-fat diets. The mechanisms underlying protection include reduced long chain FA uptake, shifts in FA distribution (lipidomic profiling), and metabolic turnover, specifically decreased hepatic 18:2 FA and triglyceride species and a shift in 18:2 FA use for oxidation versus incorporation into newly synthesized triglyceride. Double knockout mice were protected against fasting-induced hepatic steatosis (a model of enhanced exogenous FA delivery) yet developed steatosis upon induction of hepatic de novo lipogenesis with fructose feeding. Mttp-LKO mice, on either the liver FA binding protein null or Apobec-1 null background (i.e., apolipoprotein B100 only) exhibited only subtle increases in endoplasmic reticulum stress, suggesting that an altered unfolded protein response is unlikely to account for the attenuated phenotype in double knockout mice. Acute, antisense-mediated liver FA binding protein knockdown in Mttp-LKO mice also reduced FA uptake, increased oxidation versus incorporation of 18:2 species with complete reversal of hepatic steatosis, increased hepatic injury, and worsened fibrosis. CONCLUSION: Perturbing exogenous hepatic FA use modulates both hepatic steatosis and fibrosis in the setting of hepatic Mttp deletion, adding new insight into the pathophysiological mechanisms and consequences of defective very low-density lipoprotein secretion. (Hepatology 2017;65:836-852).

Cd36 knockout mice are protected against lithogenic diet-induced gallstones.

The scavenger receptor and multiligand transporter CD36 functions to promote cellular free fatty acid uptake and regulates aspects of both hepatic and intestinal cholesterol metabolism. However, the role of CD36 in regulating canalicular and biliary cholesterol transport and secretion is unknown. Here, we show that germline Cd36 knockout (KO) mice are protected against lithogenic diet (LD)-induced gallstones compared with congenic (C57BL6/J) controls. Cd36 KO mice crossed into congenic L-Fabp KO mice (DKO mice) demonstrated protection against LD-induced gallstones, reversing the susceptibility phenotype observed in L-Fabp KO mice. DKO mice demonstrated reduced biliary cholesterol secretion and a shift into more hydrophophilic bile acid species, without changes in either BA pool size or fecal excretion. In addition, we found that the mean and maximum force of gallbladder contraction was increased in germline Cd36 KO mice, and gallbladder lipid content was reduced compared with wild-type controls. Finally, whereas germline Cd36 KO mice were protected against LD-induced gallstones, neither liver- nor intestine-specific Cd36 KO mice were protected. Taken together, our findings show that CD36 plays an important role in modifying gallstone susceptibility in mice, at least in part by altering biliary lipid composition, but also by promoting gallbladder contractility.

Liver fatty acid binding protein (L-Fabp) modulates murine stellate cell activation and diet-induced nonalcoholic fatty liver disease.

UNLABELLED: Activation of hepatic stellate cells (HSCs) is crucial to the development of fibrosis in nonalcoholic fatty liver disease. Quiescent HSCs contain lipid droplets (LDs), whose depletion upon activation induces a fibrogenic gene program. Here we show that liver fatty acid-binding protein (L-Fabp), an abundant cytosolic protein that modulates fatty acid (FA) metabolism in enterocytes and hepatocytes, also modulates HSC FA utilization and in turn regulates the fibrogenic program. L-Fabp expression decreased 10-fold following HSC activation, concomitant with depletion of LDs. Primary HSCs isolated from L-FABP(-/-) mice contain fewer LDs than wild-type (WT) HSCs, and exhibit up-regulated expression of genes involved in HSC activation. Adenoviral L-Fabp transduction inhibited activation of passaged WT HSCs and increased both the expression of prolipogenic genes and also augmented intracellular lipid accumulation, including triglyceride and FA, predominantly palmitate. Freshly isolated HSCs from L-FABP(-/-) mice correspondingly exhibited decreased palmitate in the free FA pool. To investigate whether L-FABP deletion promotes HSC activation in vivo, we fed L-FABP(-/-) and WT mice a high-fat diet supplemented with trans-fatty acids and fructose (TFF). TFF-fed L-FABP(-/-) mice exhibited reduced hepatic steatosis along with decreased LD abundance and size compared to WT mice. In addition, TFF-fed L-FABP(-/-) mice exhibited decreased hepatic fibrosis, with reduced expression of fibrogenic genes, compared to WT mice. CONCLUSION: L-FABP deletion attenuates both diet-induced hepatic steatosis and fibrogenesis, despite the observation that L-Fabp paradoxically promotes FA and LD accumulation and inhibits HSC activation in vitro. These findings highlight the importance of cell-specific modulation of hepatic lipid metabolism in promoting fibrogenesis in nonalcoholic fatty liver disease. (Hepatology 2013).

Decreased body weight and hepatic steatosis with altered fatty acid ethanolamide metabolism in aged L-Fabp -/- mice.

The tissue-specific sources and regulated production of physiological signals that modulate food intake are incompletely understood. Previous work showed that L-Fabp(-/-) mice are protected against obesity and hepatic steatosis induced by a high-fat diet, findings at odds with an apparent obesity phenotype in a distinct line of aged L-Fabp(-/-) mice. Here we show that the lean phenotype in L-Fabp(-/-) mice is recapitulated in aged, chow-fed mice and correlates with alterations in hepatic, but not intestinal, fatty acid amide metabolism. L-Fabp(-/-) mice exhibited short-term changes in feeding behavior with decreased food intake, which was associated with reduced abundance of key signaling fatty acid ethanolamides, including oleoylethanolamide (OEA, an agonist of PPARα) and anandamide (AEA, an agonist of cannabinoid receptors), in the liver. These reductions were associated with increased expression and activity of hepatic fatty acid amide hydrolase-1, the enzyme that degrades both OEA and AEA. Moreover, L-Fabp(-/-) mice demonstrated attenuated responses to OEA administration, which was completely reversed with an enhanced response after administration of a nonhydrolyzable OEA analog. These findings demonstrate a role for L-Fabp in attenuating obesity and hepatic steatosis, and they suggest that hepatic fatty acid amide metabolism is altered in L-Fabp(-/-) mice.

Occupational exposure influences on gender differences in respiratory health.

BACKGROUND: The aim of this study was to evaluate gender differences in the respiratory health of workers exposed to organic and inorganic dusts. METHODS: Meta-analysis techniques incorporating logistic regression were applied to a combined file of 12 occupational health studies. RESULTS: Meta-analysis of data on 1,367 women and 4,240 men showed that women had higher odds of shortness of breath whether exposed to inorganic dust or having no occupational exposure, with an overall odds ratio (OR) of 2.07 (95% confidence interval [CI] = 1.57-2.73) adjusted for smoking status, age, body mass index (BMI), ethnic status, atopy, and job duration. Inorganic dust exposure was associated with the highest odds of asthma (adjusted OR = 8.38, 95% CI = 1.72-40.89) for women compared to men, but no differences were found for unexposed workers. With organic dust exposure, men had elevated odds for occasional wheeze and worse lung function compared to women. CONCLUSION: Within the limitations of this analysis, gender differences in respiratory health, as suggested by population-based studies, were confirmed in our analysis of occupational health studies, with the general type of exposure, organic or inorganic, generally determining the extent of differences. The higher risks for women compared to men for shortness of breath were robust regardless of work exposure category, with the highest odds ratios found for asthma.

Altered hepatic triglyceride content after partial hepatectomy without impaired liver regeneration in multiple murine genetic models.

UNLABELLED: Liver regeneration is impaired following partial hepatectomy (PH) in mice with genetic obesity and hepatic steatosis and also in wild-type mice fed a high-fat diet. These findings contrast with other data showing that liver regeneration is impaired in mice in which hepatic lipid accumulation is suppressed by either pharmacologic leptin administration or by disrupted glucocorticoid signaling. These latter findings suggest that hepatic steatosis may actually be required for normal liver regeneration. We have reexamined this relationship using several murine models of altered hepatic lipid metabolism. Liver fatty acid (FA) binding protein knockout mice manifested reduced hepatic triglyceride (TG) content compared to controls, with no effect on liver regeneration or hepatocyte proliferation. Examination of early adipogenic messenger RNAs revealed comparable induction in liver from both genotypes despite reduced hepatic steatosis. Following PH, hepatic TG was reduced in intestine-specific microsomal TG transfer protein deleter mice, which fail to absorb dietary fat, increased in peroxisome proliferator activated receptor alpha knockout mice, which exhibit defective FA oxidation, and unchanged (from wild-type mice) in liver-specific FA synthase knockout mice in which endogenous hepatic FA synthesis is impaired. Hepatic TG increased in the regenerating liver in all models, even in animals in which lipid accumulation is genetically constrained. However, in no model -- and over a >90-fold range of hepatic TG content -- was liver regeneration significantly impaired following PH. CONCLUSION: Although hepatic TG content is widely variable and increases during liver regeneration, alterations in neither exogenous or endogenous lipid metabolic pathways, demonstrated to promote or diminish hepatic steatosis, influence hepatocyte proliferation.

Diet-induced alterations in intestinal and extrahepatic lipid metabolism in liver fatty acid binding protein knockout mice.

Liver fatty acid binding protein (L-FABP) is highly expressed in both enterocytes and hepatocytes and binds multiple ligands, including saturated (SFA), unsaturated fatty acids (PUFA), and cholesterol. L-fabp (-/-) mice were protected against obesity and hepatic steatosis on a high saturated fat (SF), high cholesterol "Western" diet and manifested a similar phenotype when fed with a high SF, low cholesterol diet. There were no significant differences in fecal fat content or food consumption between the genotypes, and fatty acid (FA) oxidation was reduced, rather than increased, in SF-fed L-fabp (-/-) mice as evidenced by decreased heat production and serum ketones. In contrast to mice fed with a SF diet, L-fabp (-/-) mice fed with a high PUFA diet were not protected against obesity and hepatic steatosis. These observations together suggest that L-fabp (-/-) mice exhibit a specific defect in the metabolism of SFA, possibly reflecting altered kinetics of FA utilization. In support of this possibility, microarray analysis of muscle from Western diet-fed mice revealed alterations in genes regulating glucose uptake and FA synthesis. In addition, intestinal cholesterol absorption was decreased in L-fabp (-/-) mice. On the other hand, and in striking contrast to other reports, female L-fabp (-/-) mice fed with low fat, high cholesterol diets gained slightly less weight than control mice, with minor reductions in hepatic triglyceride content. Together these data indicate a role for L-FABP in intestinal trafficking of both SFA and cholesterol.

Biomarkers of airway acidity and oxidative stress in exhaled breath condensate from grain workers.

RATIONALE: Grain workers report adverse respiratory symptoms due to exposures to grain dust and endotoxin. Studies have shown that biomarkers in exhaled breath condensate (EBC) vary with the severity of airway inflammation. OBJECTIVES: The purpose of the study was to evaluate biomarkers of airway acidity (pH and ammonium [NH(4)(+)]) and oxidative stress (8-isoprostane) in the EBC of grain workers. METHODS: A total of 75 workers from 5 terminal elevators participated. In addition to EBC sampling, exposure monitoring for inhalable grain dust and endotoxin was performed; spirometry, allergy testing, and a respiratory questionnaire derived from that of the American Thoracic Society were administered. MEASUREMENTS AND MAIN RESULTS: Dust and endotoxin levels ranged from 0.010 to 13 mg/m(3) (median, 1.0) and 8.1 to 11,000 endotoxin units/m(3) (median, 610) respectively. EBC pH values varied from 4.3 to 8.2 (median, 7.9); NH(4)(+) values from 22 to 2,400 microM (median, 420); and 8-isoprostane values from 1.3 to 45 pg/ml (median, 11). Univariate and multivariable analyses revealed a consistent effect of cumulative smoking and obesity with decreased pH and NH(4)(+), and intensity of grain dust and endotoxin with increased 8-isoprostane. Duration of work on the test day was associated with decreased pH and NH(4)(+), whereas duration of employment in the industry was associated with decreased 8-isoprostane. CONCLUSIONS: Chronic exposures are associated with airway acidity, whereas acute exposures are more closely associated with oxidative stress. These results suggest that the collection of EBC may contribute to predicting the pathological state of the airways of workers exposed to acute and chronic factors.

The healthy worker effect in asthma: work may cause asthma, but asthma may also influence work.

Despite the increasing attention to the relationship between asthma and work exposures, occupational asthma remains underrecognized and its population burden underestimated. This may be due, in part, to the fact that traditional approaches to studying asthma in populations cannot adequately take into account the healthy worker effect (HWE). The HWE is the potential bias caused by the phenomenon that sicker individuals may choose work environments in which exposures are low; they may be excluded from being hired; or once hired, they may seek transfer to less exposed jobs or leave work. This article demonstrates that population- and workplace-based asthma studies are particularly subject to HWE bias, which leads to underestimates of relative risks. Our objective is to describe the HWE as it relates to asthma research, and to discuss the significance of taking HWE bias into account in designing and interpreting asthma studies. We also discuss the importance of understanding HWE bias for public health practitioners and for clinicians. Finally, we emphasize the timeliness of this review in light of the many longitudinal "child to young adult" asthma cohort studies currently underway. These prospective studies will soon provide an ideal opportunity to examine the impact of early workplace environments on asthma in young adults. We urge occupational and childhood asthma epidemiologists collaborate to ensure that this opportunity is not lost.

Longitudinal analysis of respiratory symptoms in population studies with a focus on dyspnea in marine transportation workers.

PURPOSE: Longitudinal respiratory symptoms are rarely studied in occupational epidemiology. We investigated dyspnea change over time and predictors of change over time using two longitudinal modeling techniques, a semi-parametric group-based approach (SAS® Proc Traj) and a generalized linear mixed model (SAS® Proc Glimmix), and compared the two techniques for use in longitudinal studies of respiratory symptoms. METHODS: Data were previously collected from a lung health surveillance study of marine transportation workers. Subjects were seen two to four times over 12 years (1987-1999). At each visit the American Thoracic Society questionnaire was administered and lung function was tested. The semi-parametric group-based model and the generalized linear mixed model were applied to the data. RESULTS: The group-based trajectory model supported two groups of dyspnea change over time. Group 1 (73%) had a steady low-level probability of reporting dyspnea over follow-up, while Group 2 (27%) had an increasing probability of reporting dyspnea over follow-up. The generalized linear mixed model (random intercept) estimated that the probability of reporting dyspnea was increasing over time in the population. Current smoking, female sex, lower lung function and older age were associated with increased probability of reporting dyspnea in both models. CONCLUSIONS: Results from both models indicate that the probability of reporting dyspnea was increasing over time in this occupational cohort. The group-based model is capable of identifying multiple patterns of linear and non-linear change while the generalized linear mixed model is preferable when the population mean change (linear) is of interest. Both approaches were able to identify similar characteristics associated with longitudinal dyspnea symptoms.

Occupational noise exposure and hearing protector use in Canadian lumber mills.

Noise exposure is probably the most ubiquitous of all occupational hazards, and there is evidence for causal links between noise and both auditory and nonauditory health effects. Noise control at source is rarely considered, resulting in reliance on hearing protection devices to reduce exposure. A comprehensive noise survey of four lumber mills using a randomized sampling strategy was undertaken, resulting in 350 full-shift personal dosimetry measurements. Sound frequency spectrum data and information on hearing protector usage was collected. A determinants-of-exposure regression model for noise was developed. Mean (L(eq,8hr)) exposure level was 91.7 dBA, well above the exposure British Columbia (BC) limit of 85 dBA. Of 52 jobs for which more than a single observation was made, only 4 were below the exposure limit. Twenty-eight jobs had means over 90 dBA, and four jobs had means over 100 dBA. The sawmill and by-products departments of the lumber mills had the highest exposure to low frequency noise, while the planing and saw filing areas had the highest exposure to high frequency noise. Hearing protector use was greatest among those exposed above 95 dBA, and among those exposed between 85 and 95 dBA, self-reported use was 84% for 73% of the time. The determinants of exposure model had an R(2) of 0.52, and the within-participant correlation was 0.07. Key predictors in the final model were mill; enclosure and enclosure construction material; and certain departments, jobs, and noise sources. The study showed that workers in lumber mills are highly exposed to noise, and although the prevalence of the use of hearing protection is high, their use is unlikely to provide complete protection again noise-induced hearing loss at the observed exposures. Determinants of noise exposure modeling offers a good method for the quantitative estimation of noise exposure.

Within- and between-person variability of exhaled breath condensate pH and NH4+ in never and current smokers.

Recent studies have suggested that the collection of exhaled breath condensate (EBC) may be a viable method in occupational field studies to sample secretions of the lower airway because it is simple to perform and non-invasive. However, there are unresolved questions about whether certain laboratory conditions may influence the analysis of EBC biomarker measurements. A total of 12 subjects performed 116 EBC tests. The effect of short and long-term sample storage and sample volume on two biomarkers of acid stress, pH and NH4+, in EBC were investigated and did not significantly influence either marker measurement after argon deaeration. We also investigated the variability and the effect of smoking on the biomarkers by collecting six samples each from five adult never smokers and five adult current smokers over a period of 1 month (n=60 total). For pH, the within-person and between-person variability was larger in current smokers compared to never smokers. Similar results were found for NH4+. Cigarette packs smoked per day now was also associated with both pH (p=0.01) and NH4+ (p=0.04) using mixed effects regression analysis. The variability and smoking results suggest that repeated measurements of EBC pH and NH4+ from the same individual may accurately predict the biological state of the airways of current smokers when compared to never smokers.

Assessment of pesticide exposure control practices among men and women on fruit-growing farms in British Columbia.

Exposure to pesticides can be reduced by wearing personal protective equipment (PPE) or by implementing alternative pest control techniques, such as Integrated Pest Management (IPM). A cross-sectional telephone survey was conducted to explore the prevalence of these practices and the factors that may be associated with them among men and women involved in fruit growing in British Columbia (BC), Canada. Survey variables were developed using a framework that incorporated aspects of farm structure, health promotion, and risk perception theories. Three hundred and eighty people took part in the survey (response rate 75%). Of those who applied pesticides (n = 119), 63% indicated that they usually wore PPE during application. Individual equipment use varied. Gloves were worn most frequently (84%), followed by a spray suit (77%) and breathing protection (75%). Peer-related factors and farm-specific characteristics such as the type of crops grown were most strongly associated with PPE use, whereas perception of pesticide risk was only weakly associated with this practice. IPM techniques had been tried on 62% of the conventional farms in the study. A range of factors was significantly associated with the use of IPM, including cultural, attitudinal, experiential, and risk-based and farm-specific variables. These results suggest that decisions to adopt exposure control practices may reflect consideration from the multiple dimensions that make up farm life, including structural characteristics of the farm as well as the attributes of the individuals who live on farms. These findings provide a better understanding of current practices and may help in the development of programs to promote pesticide exposure control practices in the BC farming community.

Work organization and musculoskeletal injuries among a cohort of health care workers.

OBJECTIVES: This study investigated the relationship between work-organization factors (job control, job demands, and workload measures) and the risk of lower-body musculoskeletal injury among health care workers. METHODS: A four-year, retrospective cohort study of 3769 health care workers was carried out in one acute care hospital in the Canadian province of British Columbia. A job-exposure matrix was constructed for the work-organization factors from survey and administrative data and assigned to workers on the basis of their occupation and department of employment. Musculoskeletal injuries resulting in workers' compensation claims were ascertained from the injury database of the hospital's Occupational Health and Safety Department. RESULTS: In the final Poisson models adjusted for demographic and biomechanical factors, an increased risk for compensated musculoskeletal injuries of the lower back and lower limb was related to low job control [relative risk (RR) 1.64, 95% confidence interval (95% CI) 1.08-2.49] and workload defined by working during periods of high absenteeism within a department (RR 2.10, 95% CI 1.61-2.98). The risk also increased with more biomechanical demands in an occupation and with a recent previous injury. CONCLUSIONS: The results indicate that work-organization characteristics (job control and workload) were associated with an increased risk of musculoskeletal injuries resulting in a compensation claim. These associations remained after the effect of demographic and biomechanical factors was taken into consideration. The association with workload measured by departmental levels of absenteeism should be explored further in future studies as reverse causality (musculoskeletal symptoms resulting in absenteeism) could not be fully ruled out in the current study.

Monoclonal antibody 5C3 raised against formalin fixed paraffin-embedded invasive breast tumour tissue: characterisation of its reactive antigen via immunoprecipitation and internal sequencing.

Monoclonal antibodies (MAbs) provide a powerful tool for the identification of novel tumour associated antigens. In an attempt to identify such an antigen, MAbs were generated by immunization with paraffin wax-embedded formalin-fixed invasive ductal breast tumour tissue from a patient who relapsed following an initial response to adjuvant chemotherapy. Extensive immunocytochemical and Western blot analysis of a range of cell lines and tissues including a series of pre- and post-chemotherapy treated invasive ductal breast carcinomas, with one of these MAbs, antibody 5C3, indicated that the 5C3 reactive antigen displayed a wide spectrum of reactivity amongst various human tumours. A reduced level of 5C3 expression was observed in non-cancerous archival breast tissues and breast cell lines and normal murine tissues compared to the expression observed in infiltrating breast tumour cells. Immunoprecipitation studies using the human ductal breast carcinoma cell line, ZR-75-1 resulted in the isolation of a 175 kDa reactive band which was excised from an SDS-PAGE gel and subjected to internal sequencing. Sequencing analysis and database searching revealed that this 175 kDa band represented a cytokeratin heteropolymer, composed of type I cytokeratin 9 and type II cytokeratin 6. Further studies confirmed that antibody 5C3 recognised this heteropolymer of cytokeratin 9 and 6 but not the individual cytokeratins. This novel method of MAb generation may facilitate the isolation of further potentially interesting cellular antigens. Characterisation of these novel antigens may identify specific disease targets with possible prognostic or predictive significance.

Novel APC promoter and exon 1B deletion and allelic silencing in three mutation-negative classic familial adenomatous polyposis families.

BACKGROUND: The overwhelming majority (approximately 80%) of individuals with classic familial adenomatous polyposis (FAP) exhibit mutations in the coding sequence of the adenomatous polyposis coli (APC) tumor suppressor gene. Families without detectable APC mutations are unable to benefit from the use of genetic testing for clinical management of this autosomal dominant syndrome. METHODS: We used exome sequencing and linkage analysis, coupled with second-generation sequencing of the APC locus including non-coding regions to investigate three APC mutation-negative classical FAP families. RESULTS: We identified a novel ~11 kb deletion localized 44 kb upstream of the transcription start site of APC that encompasses the APC 1B promoter and exon. This deletion was present only in affected family members of one kindred with classical FAP. Furthermore, this same deletion with identical breakpoints was found in the probands of two additional APC mutation-negative classical FAP kindreds. Phasing analysis of single nucleotide polymorphisms (SNPs) around the deletion site in the three probands showed evidence of a shared haplotype, suggesting a common founder deletion in the three kindreds. SNP analysis within the coding sequence of APC, revealed that this ~11 kb deletion was accompanied by silencing of one of the APC alleles in blood-derived RNA of affected individuals. CONCLUSIONS: These results support the causal role of a novel promoter deletion in FAP and suggest that non-coding deletions, identifiable using second-generation sequencing methods, may account for a significant fraction of APC mutation-negative classical FAP families.

Women and occupational lung disease: sex differences and gender influences on research and disease outcomes.

We have attempted to describe the current state of knowledge regarding occupational lung disease in women. A large section of this article was devoted to describing the methodologic challenges that face researchers when evaluating gender differences in occupational lung disease. The findings of the presented studies are likely limited by many of the methodologic problems that were identified earlier. To accurately identify the true risk of occupational lung disease in women workers, these findings must be replicated in future studies with special attention paid to the various aspects of occupational lung disease research that are susceptible to gender-related bias.

Evaluation of specific occupational asthma risks in a community-based study with special reference to single and multiple exposures.

OBJECTIVES: To compare two job exposure matrices (JEMs) for the evaluation of asthma risks related to specific occupational exposures in a community-based study. METHODS: A questionnaire on self-reported asthma, respiratory symptoms and current occupation was sent to the participants of the European Community Respiratory Health Survey in five areas in Spain. Both an asthma-specific JEM, including expert judgment steps and a general JEM, were applied to occupational codes. Risks of current asthma symptoms and wheeze in the last year associated with the obtained exposure estimates were evaluated. Correlations between specific exposures were investigated using explanatory factor analysis. RESULTS: Occupational exposures to the high-molecular-weight (MW) agents flour dust, enzymes, mites and animal-derived proteins as obtained by the asthma-specific JEM were positively associated with asthma outcomes. The effect of additional expert judgment steps was limited. High exposures to biological dust assessed by the general JEM without expert judgment was also associated with asthma. Many of the exposed individuals worked in environments with multiple exposures. CONCLUSIONS: Asthma risks associated with occupational exposures to specific high-MW agents could be identified from a population-based study using an asthma-specific JEM. Application of JEMs can be a useful tool to estimate asthma risks attributable to specific occupational exposures in the general population. However, these specific exposure risks should be interpreted in connection with the whole of concomitant exposures constituting the work environment.

Truncating the dose range for methacholine challenge tests: three occupational studies.

The methacholine challenge test protocol was assessed in the reanalysis of three occupational studies. We evaluated the impact of truncating the range of methacholine on responsiveness, as defined by slope and PC(20). In original analysis, reactivity was similar for apprentices and auto body shop workers, whereas boilermakers were more responsive. Truncating high concentrations did not change the classification of subjects with PC(20) <8 or 16 in any population. However, when responsiveness was measured by slope, the mean responsiveness increased, from -7.9 to -15.3 for apprentices and -7.2 to -10.0 for auto-body shop workers. Results support the American Thoracic Society's recommended maximum of 16 mg/ml and provide evidence that extending the dose range beyond that does not increase sensitivity, whereas stopping before 16 may exaggerate response. Furthermore, to ensure validity, neither slope nor PC(20) should be extrapolated beyond data.

Beta(1-->3)-glucan exposure levels among workers in four British Columbia sawmills.

Beta(1-->3)-glucans were extracted from wood dust samples taken during the summer of 1997 at four British Columbia sawmills. Personal dust samples were collected using a GSP-sampler for inhalable dust and the sampling strategy targeted all production and maintenance jobs at least once at each mill. Potential exposure determinants data were documented concurrently, including weather conditions, log storage methods, wood conditions, species, production level, jobs and tasks. beta(1-->3)-glucans were measured by enzyme inhibition immunoassay (EIA). A total of 223 personal beta(1-->3)-glucan samples were analyzed. 45.7% were below the limit of detection (LOD). Geometric mean concentration ranged from 3.5 to 18.9 micro g/m(3) across the four mills. The highest levels were measured at the Interior mills, particularly in the log processing and sawmill areas. Multivariate regression models indicated that land-based log storage, clean-up jobs, high wood dust concentration, lumber yard department and the interaction between land-based log storage method and log processing department were associated with increased beta(1-->3)-glucan concentration.