D-penicillamine for primary sclerosing cholangitis

BACKGROUND

Primary sclerosing cholangitis is a cholestatic disease. D-penicillamine is suggested as a treatment option due to its copper reducing and immunomodulatory potential.

OBJECTIVES

To evaluate the beneficial and harmful effects of D-penicillamine for patients with primary sclerosing cholangitis.

SEARCH STRATEGY

Eligible trials were identified through searches of The Cochrane Hepato-Biliary Group Controlled Trials Register (August 2005), The Cochrane Central Register of Controlled Trials in The Cochrane Library (Issue 3, 2005), MEDLINE (1950 to August 2005), EMBASE (1980 to August 2005), Science Citation Index EXPANDED (1945 to August 2005), and reference lists of relevant articles. Authors of trials and pharmaceutical companies known to produce D-penicillamine were also contacted.

SELECTION CRITERIA

Randomised clinical trials comparing D-penicillamine in any dose, duration, and route of administration versus placebo, no intervention, or other intervention(s). Trials were included irrespective of publication status, year of publication, language, or blinding.

DATA COLLECTION AND ANALYSIS

Both authors selected the trials, extracted data, and evaluated the methodological quality of the trials with respect to the generation of allocation sequence, allocation concealment, blinding, and follow-up. The results were reported by intention-to-treat analysis. The outcomes were presented as relative risk (RR) or weighted mean difference (WMD), both with 95% confidence intervals (CI).

MAIN RESULTS

One randomised trial was identified and included in the review. It was of low methodological quality. The trial compared D-penicillamine versus placebo in 70 patients with primary sclerosing cholangitis. Compared with placebo, D-penicillamine therapy had no significant effect on mortality (RR 1.14, 95% CI 0.49 to 2.64), liver transplantation (RR 1.11, 95% CI 0.39 to 3.17), hepatic histologic progression (RR 1.17, 95% CI 0.79 to 1.74), or cholangiographic deterioration (RR 0.87, 95% CI 0.43 to 1.79). D-penicillamine led to a significant improvement in the serum aspartate aminotransferase (WMD -23.00 U/L; 95% CI -30.66 to -15.34), but not in serum bilirubin level (WMD 0.40 mg/L; 95% CI -0.19 to 0.99) and serum alkaline phosphatases activity (WMD 44.00 U/L; 95% CI -37.89 to 125.89). There were significantly more adverse events in patients receiving D-penicillamine (P = 0.013).

AUTHORS' CONCLUSIONS

There is not sufficient evidence to support or refute the use of D-penicillamine for patients with primary sclerosing cholangitis. We do not recommend the use of D-penicillamine for patients with primary sclerosing cholangitis outside randomised trials.

First Report of Sclerotinia Stem Rot of Chickpea Caused by Sclerotinia sclerotiorum in North Dakota and Washington

Chickpea (Cicer arietinum L.) is cultivated as a rotational crop in the cereal-based production system in the U.S. Pacific Northwest (PNW) and its production is expanding to other northern tier states. During July 2005, symptoms of Sclerotinia stem rot were observed on chickpea cv. Dwelley and Dylan in fields near Spangle, WA and Carrington, ND, respectively, with disease incidence of approximately ≤1% in affected areas at both locations. Symptoms included stem whitening, wilting, and stem breakage. Occasionally, white fluffy mycelium was observed; however, production of sclerotia on infected plants was rarely observed. Sclerotinia sclerotiorum was isolated from diseased stems collected from both states. The isolates produced a ring of sclerotia near the edge of potato dextrose agar (PDA) plates in 7 days and produced neither conidia nor other fruiting bodies in culture after 30 days. PCR amplification of the rDNA internal transcribed spacer region from two representative isolates and subsequent digestion with restriction enzymes, Mbo I and Taq I, produced identical banding patterns to previously identified isolates of S. sclerotiorum from pea from the PNW (2). Chickpea cvs. Dwelley and Spanish White (eight plants of each) were inoculated by fastening mycelial agar plugs from an actively growing colony on PDA onto the stems with Parafilm. Symptoms of stem whitening were observed as early as 2 days after inoculation, and the lesions extended upward and downward from the inoculation site. Wilting and stem breakage were also observed. Control inoculations of four plants of each cultivar with PDA plugs without mycelium produced no visible symptoms. S. sclerotiorum was consistently reisolated from inoculated plants but not from control plants. Chickpea had been grown in the PNW for more than 20 years without any reported incidence of Sclerotinia stem rot although the disease has been reported from Arizona (3) and Asian countries (1). This is likely because of the upright growth habit of the chickpea plant coupled with relatively dry conditions late in the growing season. Previous chickpea cultivars were very susceptible to Ascochyta blight, an early-season disease of chickpea in the PNW that reduced chickpea stands and canopy coverage. Current cultivars possess much improved resistance to Ascochyta blight, allowing greater vegetative growth to occur and creating microenvironmental conditions conducive to Sclerotinia stem rot. In North Dakota, where humid conditions prevail late in the growing season, symptoms of Sclerotinia stem rot had been observed in previous years but had not been documented because of a recent history of chickpea cultivation there. To our knowledge, this is the first report of confirmed Sclerotinia stem rot of chickpea in North Dakota and Washington. References: (1) G. J. Boland and R. Hall. Can. J. Plant Pathol. 16:93, 1994. (2) I. Jimenez-Hidalgo et al. Phytopathology (Abstr.) 94(suppl.):S47, 2004. (3) M. E. Matheron and M. Porchas. Plant Dis. 84:1250, 2000.

Quantification of quantum dots in HUVECs by confocal laser scanning microscopy

Quantum dots (QDs) are emerged as a new class of fluorescent probes for many biological and biomedical applications. Comparing with conventional fluorescent probes, they have substantial advantages such as bright fluorescence, narrow emission, broad excitation band and high photostability. However, little is known about the toxicity of nanoscale particles to biological systems. In this study, the interaction between 3-Mercaptopropionic acid capped CdTe QDs and HUVECs was studied quantitatively in vitro. Fluorescent intensity of QDs in cells was measured by confocal fluorescence laser scanning microscopy. The results showed that the amount of QDs absorbed by cells is dependent on concentration and incubation time. Further, the viability of cells incubated with QDs was investigated using MTT assay. Dramatic dose-dependent decrease in cellular viability was observed.

Vaccines for preventing hepatitis B in health-care workers

BACKGROUND

Hepatitis B virus (HBV) causes acute and chronic liver diseases. Hepatitis B vaccination is recommended for health-care workers.

OBJECTIVES

To assess the beneficial and harmful effects of hepatitis B vaccination in health-care workers.

SEARCH STRATEGY

We searched the trial registers of The Cochrane Hepato-Biliary Group, The Cochrane Library, MEDLINE, and EMBASE to February 2003.

SELECTION CRITERIA

Randomised trials comparing any dose, injection route, injection site, or schedule of hepatitis B plasma-derived vaccines (PDV) or recombinant vaccines (RV) versus placebo, no intervention, or another hepatitis B vaccine in health-care workers.

DATA COLLECTION AND ANALYSIS

Two reviewers extracted the data independently. The reviewers assessed the methodological quality of the trials regarding generation of the allocation sequence, allocation concealment, double blinding, and follow-up. The results were presented as relative risk (RR) with 95% confidence intervals (CI).

MAIN RESULTS

We identified 21 randomised trials, all with one or more methodological weaknesses. Four trials demonstrated that PDV versus placebo significantly decreased hepatitis B events at maximum follow-up (RR 0.51, 95% CI 0.35 to 0.73). RV did not differ significantly from PDV in eliciting a protective hepatitis B surface antibody (anti-HBs) level in two trials. Both vaccines were well tolerated. Low-dose vaccine (1 or 2 microg) by the intradermal route resulted in significantly more participants without protective anti-HBs level compared with high-dose (10 or 20 microg) by the intramuscular route (RR 1.41, 95% CI 1.13 to 1.76). The intradermal route caused significantly more local adverse events, while the intramuscular route caused significantly more systemic adverse events. The gluteal injection produced significantly more participants without protective anti-HBs level than the deltoid injection. The prevalence of anti-HBs seroconversion by rapid vaccination (0, 1, and 2 months) was significantly lower than that by standard vaccination (0, 1, and 6 months). Booster vaccinations with different RV doses (2.5, 5, 10, 20, or 40 microg) produced similar prevalence of anti-HBs seroconversion in three trials assessing participants who did not respond to previous HBV vaccination.

AUTHORS' CONCLUSIONS

PDV significantly prevents hepatitis B events. RV seems to be able to elicit similar protective anti-HBs levels. The intramuscular route with 20 microg RV was significantly more effective compared with the intradermal route with 2 microg RV as was the standard schedule compared with a rapid schedule and deltoid intramuscular injection compared with the gluteal intramuscular injection. It is unclear if booster vaccination of non-responders offers higher anti-HBs seroconversion and hepatitis B vaccine prevents the infection of hepatitis B mutants in health-care workers.

Pneumonia in lambs inoculated with Bordetella parapertussis: clinical and pathological studies

Eight one-week-old, colostrum-deprived lambs were inoculated intratracheally with ovine isolates of Bordetella parapertussis. After inoculation, the lambs showed slight depression and anorexia. The total circulating leucocyte counts in these animals rose gradually to a peak five days post-inoculation. Neutrophil counts also increased and were highest at Day 3. Lesions grossly and histologically similar to those of naturally-occurring ovine chronic non-progressive pneumonia were seen in the majority of infected animals. Grossly, they consisted of many small areas of collapse and dull-red consolidation. Histologically, B. parapertussis caused mild acute tracheobronchitis, severe alveolar collapse and acute bronchopneumonia, which was most severe from Days 1 to 3. Pure cultures of B. parapertussis were consistently recovered from nasal swabs of infected lambs throughout the study. Viable bacterial counts of bronchoalveolar lavage fluid showed a rapid elimination of this organism from the lower respiratory tract between Days 1 to 5. Bordetella parapertussis infection in the respiratory tract of lambs has the potential to compromise pulmonary defence mechanisms and allow other pathogenic organisms to become established in the lower respiratory tract.

Mortality following development of breast cancer while using oestrogen or oestrogen plus progestin: a computer record-linkage study

The literature on the relationship between breast cancer mortality and postmenopausal oestrogen and combined oestrogen/progestin therapy is seemingly contradictory. This study explored survival after exposure to oestrogen or oestrogen plus progestin at or in the year prior to breast cancer diagnosis. Information on patients first diagnosed with invasive breast cancer between 1993 and 1998 was linked with outpatient pharmacy data from 1992 to 2000. Patients were classified according to use of oestrogen alone or oestrogen plus progestin at or in the year prior to diagnosis. Compared to nonusers, and adjusting for age at diagnosis, race/ethnicity, tumour size and grade, oestrogen receptor status, surgery status, and chemotherapy and hormone therapy for breast cancer treatment, oestrogen plus progestin users had lower all-cause mortality (stage I hazard ratio (HR)=0.69, 95% confidence interval (CI)=0.48–0.99; stage II HR=0.53, 95% CI=0.39–0.72) and breast cancer mortality (stage I HR=0.52, 95% CI=0.26–1.04; stage II HR=0.69, 95% CI=0.48–0.98). Oestrogen users experienced little or no survival benefit for all-cause mortality (stage I HR=1.04, 95% CI=0.77–1.42; stage II HR=0.86, 95% CI=0.65–1.14) or breast cancer mortality (stage I HR=1.23, 95% CI 0.72–2.10; stage II HR=1.01, 95% CI 0.72–1.41). Our findings suggest, relative to nonusers, a lower risk of death from all causes and from breast cancer in patients who were diagnosed with breast cancer while exposed to oestrogen plus progestin, but not in patients exposed to oestrogen only.

MUC1 oncoprotein is targeted to mitochondria by heregulin-induced activation of c-Src and the molecular chaperone HSP90

The MUC1 heterodimeric transmembrane glycoprotein is aberrantly overexpressed by most human carcinomas. The MUC1 C-terminal subunit localizes to mitochondria and blocks stress-induced activation of the intrinsic apoptotic pathway. How MUC1 is delivered to mitochondria is not known. The present studies demonstrate that MUC1 forms intracellular complexes with HSP70 and HSP90. We show that the MUC1 cytoplasmic domain binds directly to HSP70 in vitro. By contrast, binding of MUC1 to HSP90 in vitro is induced by c-Src-mediated phosphorylation of the MUC1 cytoplasmic domain. c-Src also increases binding of MUC1 to HSP90 in cells. In concert with these results, we show that heregulin (HRG), a ligand for ErbB receptors, activates c-Src and, in turn, stimulates binding of MUC1 to HSP90. We also show that inhibitors of c-Src or HSP90 block HRG-induced targeting of MUC1 to mitochondria and integration of MUC1 into the mitochondrial outer membrane. These findings indicate that MUC1 is delivered to mitochondria by a mechanism involving activation of the ErbB receptor-->c-Src pathway and transport by the molecular chaperone HSP70/HSP90 complex.

Enhancing effect of taurine on CYP7A1 mRNA expression in Hep G2 cells

Taurine has been reported to enhance cholesterol 7alpha-hydroxylase (CYP7A1) mRNA expression in animal models. However, no in vitro studies of this effect have been reported. The Hep G2 human hepatoma cell line has been recognized as a good model for studying the regulation of human CYP7A1. This work characterizes the effects of taurine on CYP7A1 mRNA levels of Hep G2 cells in a dose- and time-dependent manner. In the dose-dependent experiment, Hep G2 cells were treated with 0, 2, 10 or 20 mM taurine in the presence or absence of cholesterol 0.2 mM for 48 h. In the time-dependent experiment, Hep G2 cells were treated with 0 or 20 mM taurine for 4, 24 and 48 h with and without cholesterol 0.2 mM. Our data revealed that taurine showed time- and dose-response effects on CYP7A1 mRNA levels in Hep G2 cells. However, glycine - a structural analogue of taurine - did not have an effect on CYP7A1 gene expression. These results show that, in agreement to previous studies on animal models, taurine induces the mRNA levels of CYP7A1 in Hep G2 cells, which could enhance cholesterol conversion into bile acids. Also, Hep G2 cell line may be an appropriate model to study the effects of taurine on human cholesterol metabolism.

The novel triterpenoid CDDO-Me suppresses MAPK pathways and promotes p38 activation in acute myeloid leukemia cells

Development of novel therapeutic strategies is a continuing challenge for the treatment of acute myeloid leukemia (AML). The novel triterpenoid, C-28 methyl ester of 2-cyano-3,12-dioxoolen-1,9-dien-28-oic acid (CDDO-Me), induces apoptosis in myeloid leukemic cell lines and in primary AML samples. In this report, the effects of CDDO-Me on CD34(+) AML progenitor cells in vitro were examined. CDDO-Me induced apoptosis in all but one of ten AML samples. CDDO-Me is known to inhibit the activation of ERK1/2. In this series of primary AML samples, ERK was expressed and phosphorylated in all patient samples studied and CDDO-Me inhibited ERK phosphorylation in five of 10 samples. However, CDDO-Me induced apoptosis in four of five samples without decreasing pERK levels, suggesting that pERK is not the sole target of the compound. CDDO-Me induced phosphorylation of p38 in AML-derived U937 cells. Pretreatment of U937 cells with a p38 inhibitor protected cells from the cyto-toxic effects of CDDO-Me. These findings suggest a role for p38 in CDDO-Me-induced apoptosis. In preliminary studies, CDDO-Me induced p38 phosphorylation in seven of eight primary AML samples. These findings suggest that CDDO-Me treatment shifts cell signaling away from cyto-protective pathways and thus CDDO-Me may be effective for the treatment of AML.

siRNA targeting the leader sequence of SARS-CoV inhibits virus replication

SARS-CoV (the SARS-Associated Coronavirus) was reported as a novel virus member in the coronavirus family, which was the cause of severe acute respiratory syndrome. Coronavirus replication occurs through a unique mechanism employing Leader sequence in the transcripts when initiating transcription from the genome. Therefore, we cloned the Leader sequence from SARS-CoV(BJ01), which is identical to that identified from SARS-CoV(HKU-39849), and constructed specific siRNA targeting the Leader sequence. Using EGFP and RFP reporter genes fused with the cloned SARS-CoV Leader sequence, we demonstrated that the siRNA targeting the Leader sequence decreased the mRNA abundance and protein expression levels of the reporter genes in 293T cells. By stably expressing the siRNA in Vero E6 cells, we provided data that the siRNA could effectively and specifically decrease the mRNA abundance of SARS-CoV genes as analyzed by RT-PCR and Northern blot. Our data indicated that the siRNA targeting the Leader sequence inhibited the replication of SARS-CoV in Vero E6 cells by silencing gene expression. We further demonstrated, via transient transfection experiments, that the siRNA targeting the Leader sequence had a much stronger inhibitory effect on SARS-CoV replication than the siRNAs targeting the Spike gene or the antisense oligodeoxynucleotides did. This report provides evidence that targeting Leader sequence using siRNA could be a powerful tool in inhibiting SARS-CoV replication.

Bile acids for liver-transplanted patients

BACKGROUND

Liver transplantation has become a widely accepted form of treatment for numerous end-stage liver diseases. Bile acids may decrease the degree of allograft rejection after liver transplantation by changing the expression of major histocompatibility complex class molecules in bile duct epithelium and central vein endothelium.

OBJECTIVES

To assess the beneficial and harmful effects of bile acids for liver-transplanted patients.

SEARCH STRATEGY

We performed searches of the Cochrane Hepato-Biliary Group Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and EMBASE to April 2003. We also searched The Chinese Biomedical Database to May 2002.

SELECTION CRITERIA

Randomised clinical trials comparing any dose of bile acids or duration of treatment in liver-transplanted patients versus placebo, no intervention, or another intervention. We included randomised clinical trials irrespective of blinding, language, and publication status.

DATA COLLECTION AND ANALYSIS

W Chen extracted the data and C Gluud validated them. We evaluated the methodological quality of the trials from the method for generation of the allocation sequence, allocation concealment, double blinding, and follow-up. We used the intention-to-treat principle to perform meta-analyses and presented the outcomes as relative risk (RR) or weighted mean difference (WMD), both with 95% confidence intervals (CI).

MAIN RESULTS

We identified seven randomised trials (six evaluating ursodeoxycholic acid versus placebo or no intervention and one evaluating tauro-ursodeoxycholic acid versus no intervention) with a total of 335 liver-transplanted patients. The administration of bile acids began one day or more after liver transplantation. All patients received the standard triple-drug immunosuppressive regimen (steroids, azathioprine, and cyclosporine or tacrolimus) to suppress the allograft rejection response after liver transplantation. Bile acids did not significantly reduce all-cause mortality, mortality related to allograft rejection, retransplantation, acute cellular rejection, or number of patients with steroid-resistant rejection. Bile acids significantly reduced the number of patients who had chronic rejection in a fixed-effect model but not in a random-effects model. Bile acids were safe and well tolerated by liver-transplanted patients.

AUTHORS' CONCLUSIONS

Bile acids do not seem to have significant beneficial effects in liver-transplanted patients.

Mutation of COL11A2 causes autosomal recessive non-syndromic hearing loss at the DFNB53 locus

BACKGROUND

Allele variants of COL11A2, encoding collagen type XI alpha2, cause autosomal dominant non-syndromic hearing loss (ARNSHL) at the DFNA13 locus (MIM 601868) and various syndromes that include a deafness phenotype.

OBJECTIVE

To describe a genome-wide scan carried out on a consanguineous Iranian family segregating ARNSHL.

RESULTS

Genotyping data identified a novel locus for ARNSHL on chromosome 6p21.3, which was designated DFNB53. Homozygosity for the P621T mutation of COL11A2 was present in all deaf persons in this family; this same variation was absent in 269 Iranian controls. Sequence comparison of collagen type XI alpha1 and alpha2 peptides across species shows that the replaced proline is an evolutionarily conserved amino acid.

CONCLUSIONS

The P621T mutation of COL11A2 affects the Y position of the canonical -Gly-X-Y- repeat in collagens. It lies near the amino-terminus of the triple helical region and causes ARNSHL. This finding suggests that mutation type and location are critical determinants in defining the phenotype of COL11A2 associated diseases.

Single-crystal neutron diffuse scattering and Monte Carlo study of the relaxor ferroelectric PbZn1/3Nb2/3O3(PZN)

Full three-dimensional diffuse neutron scattering data have been recorded from a single crystal of Pb(Zn1/3Nb2/3)O3(PZN) at 300 K using the time-of-flight Laue technique on the SXD single-crystal instrument at ISIS. The data show a series of diffuse rods of scattering oriented parallel to each of the six 〈1 1 0〉 crystal directions. Monte Carlo simulation has been used to demonstrate that the diffuse rods are caused by planar nanodomains oriented normal to the 〈1 1 0〉 directions. Within these domains, there are correlated displacements of the atoms away from their average site positions. In order to explain the systematic absence of some rods of scattering in the (h k 1) data but the presence of all rods in the (h k 0) data, it is necessary that the displacement of an O atom is of opposite sign to that of its neighbouring Pb atoms. This is explained in terms of a model based on the fact that Pb2+possesses a lone pair of electrons, giving the Pb ion directionality.

Risk of silicosis in cohorts of Chinese tin and tungsten miners and pottery workers (II): Workplace-specific silica particle surface composition

BACKGROUND

It is hypothesized that surface occlusion by alumino-silicate affects the toxic activity of silica particles in respirable dust. In conjunction with an epidemiological investigation of silicosis disease risk in Chinese tin and tungsten mine and pottery workplaces, we analyzed respirable silica dusts using a multiple-voltage scanning electron microscopy-energy dispersive X-ray spectroscopy (MVSEM-EDS).

METHODS

Forty-seven samples of respirable sized dust were collected on filters from 13 worksites and were analyzed by MVSEM-EDS using high (20 keV) and low (5 keV) electron beam accelerating voltages. Changes in the silicon-to-aluminum X-ray line intensity ratio between the two voltages are compared particle-by-particle with the 90th percentile value of the same measurements for a ground glass homogeneous control sample. This provides an index that distinguishes a silica particle that is homogeneously aluminum-contaminated from a clay-coated silica particle.

RESULTS

The average sample percentages of respirable-sized silica particles alumino-silicate occlusion were: 45% for potteries, 18% for tin mines, and 13% for tungsten mines. The difference between the pottery and the metal mine worksites accounted for one third of an overall chi-square statistic for differences in change in measured silicon fraction between the samples.

CONCLUSION

The companion epidemiological study found lower silicosis risk per unit cumulative respirable silica dust exposure for pottery workers compared to metal miners. Using these surface analysis results resolves differences in risk when exposure is normalized to cumulative respirable surface-available silica dust.

The prevalence of PD in a nutritionally deficient rural population in China

OBJECTIVES

In most reports, the prevalence of PD in mainland China is lower than in western populations. To estimate PD prevalence in China, we performed a cross-sectional study in a rural population in Linxian County, China.

PRIMARY OUTCOMES

Clinical diagnosis of PD.

RESULTS

Among the 16,488 participants examined, the overall age- and gender-adjusted prevalence rate of PD was 522/100,000 (95% CI: 477-567) assuming no cases of PD would be found among those younger than 50 years of age. The gender-adjusted prevalence rates were 103 (95% CI: 83-123), 621 (95% CI: 572-670), 902 (95% CI: 843-961), and 1744 (95% CI: 1662-1826) per 100,000 in age groups 50-59, 60-69, 70-79, and 80 and above, respectively.

CONCLUSIONS

The estimated prevalence of PD in Linxian, China is higher than most of those reported from other areas in China, and similar to those reported from non-Asian populations.

Risk of silicosis in cohorts of Chinese tin and tungsten miners, and pottery workers (I): an epidemiological study

BACKGROUND

Epidemiological evaluations of the risk of silicosis in relation to exposure to crystalline silica have raised the question of whether different types of silica dust exposures vary with respect to their ability to cause silicosis. The aim of this study is to compare the risk of silicosis among cohorts of silica dust-exposed Chinese tin miners, tungsten miners, and pottery workers and to assess whether gravimetric measurements of respirable silica dust sufficiently determine the risk of silicosis or whether other factors of exposure may play a significant role.

METHODS

Cohorts were selected from 20 Chinese mines and potteries. Inclusion criteria were starting employment after January 1, 1950 and being employed for at least 1 year during 1960-1974 in one of the selected workplaces. Radiological follow-up for silicosis onset was from January 1, 1950 through December 31, 1994. Silicosis was assessed according to the Chinese radiological criteria for diagnosis of pneumoconiosis (as suspect, Stage I, II, or III). Exposure-response relationships were estimated for silicosis of Stage I or higher. Silica dust exposure was estimated in terms of cumulative total dust exposure, calculated from a workplace, job title, and calendar year exposure matrix, and individual occupational histories. Cumulative total dust exposure was converted in two steps into cumulative respirable dust exposure and cumulative respirable silica dust exposure using conversion factors estimated from side-by-side measurements conducted in 1988-89.

RESULTS

The male cohorts included 4,028 tin miners, 14,427 tungsten miners, and 4,547 pottery workers who had similar onset of employment and duration of follow-up. For a given exposure level, the risk of silicosis was higher for the tin and tungsten than the pottery workers.

CONCLUSION

The observed differences in the risk of silicosis among the three cohorts suggest that silica dust characteristics, in addition to cumulative respirable silica dust exposure, may affect the risk of silicosis.