Osteopontin, asbestos exposure and pleural plaques: a cross-sectional study

Our plain-English summary of Osteopontin, asbestos exposure and pleural plaques: a cross-sectional study, by G. Mastrangelo, G. Marangi, M.N. Ballarin, et al (BMC Public Health, 2011).

The study

• Authors: G. Mastrangelo, G. Marangi, M.N. Ballarin, S. Michilin, A.S. Fabricio, F. Valentini, J.H. Lange, U. Fedeli, L. Cegolon, M. Gion
• Journal: BMC Public Health
• Published: 2011;11:220
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Osteopontin (OPN) is a plasma protein/cytokine produced in excess in several malignancies. In a recent study OPN was reported as being related to the duration of asbestos exposure and presence of benign asbestos-related diseases; however, it was unclear whether this protein was an indicator of exposure or effect.

Methods: In 193 workers, 50 with pleural plaques (PP), in whom different indicators of past asbestos exposure were estimated, OPN plasma levels were assessed using commercial quantitative sandwich enzyme immunoassays according to the manufacturer's instructions.

Results: Osteopontin increased with increasing age and several aspects of asbestos exposure, without differences related to the presence of pleural plaques. At multivariable regression analysis, the explanatory variables with a significant independent influence on OPN were length of exposure (positive correlation) and time elapsed since last exposure (positive correlation).

Conclusions: Since asbestos in lung tissue tends to wane over time, OPN should decrease (rather than increase) with time since last exposure. Therefore, OPN cannot be a reliable biomarker of exposure nor effect (presence of pleural plaques).

In plain English

This cross-sectional study in Venice, Italy, tested whether plasma osteopontin, a blood protein, could indicate past asbestos exposure or pleural plaques. From 904 former asbestos workers at a local occupational health service, 263 were randomly sampled by stratum and invited. One hundred and ninety-two agreed, and 8 more workers with plaques were added. After 7 with missing data were dropped, 193 were analysed: 50 with plaques and 143 without. Past exposure was estimated retrospectively with a structured job questionnaire. Mean osteopontin was similar in workers with plaques (55.25 ng/ml) and without (53.89 ng/ml; p = 0.872). Looking at one factor at a time, osteopontin was associated with age, time since first and last exposure, and cumulative exposure. When factors were analysed together, time since last exposure and length of exposure were independently linked to higher osteopontin, and age was a strong confounder. The authors reasoned that because lung asbestos wanes over time, an exposure marker should fall, not rise, with time since last exposure. They concluded osteopontin cannot serve as a marker of exposure or of plaques. They noted no asbestosis cases, a possibly unrepresentative sample, and no objective exposure measurements.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: cross-sectional study
• Who was studied: Former asbestos workers examined at the Occupational Health Service of Primary Care Trust 12, Venice, Veneto Region, Italy. A 30% stratified random sample (263) was drawn from 904 workers. One hundred and ninety-two of the 263 agreed to be examined, and 8 additional workers with pleural plaques were added, giving 200. After 7 were discarded for missing values, 193 were analysed: 50 with and 143 without pleural plaques. The year of observation was 2008.
• Exposure: Past occupational asbestos exposure, estimated retrospectively with a job-specific modules (JSM) questionnaire; fibre types were not specified for the workers. The measures were cumulative exposure (fibres/ml × years), peak exposure (fibres/ml), length of exposure, time since first exposure and time since last exposure.
• Main results:
  • Plasma osteopontin did not differ significantly between groups. Workers without pleural plaques had a mean of 53.89 ng/ml (SD 19.57), and workers with pleural plaques had a mean of 55.25 ng/ml (SD 20.86); Wilcoxon p = 0.872.
  • The trend of osteopontin with age and with each exposure measure was not significantly different between workers with and without pleural plaques (Chow test), so the two groups were pooled.
  • In univariable analysis of all 193 workers, osteopontin was positively associated with:
• age (b = 0.94, p = 0.000)
• time since last exposure (b = 0.83, p = 0.000)
• time since first exposure (b = 0.99, p = 0.000)
• cumulative exposure (b = 0.03, p = 0.009)
  Length of exposure (p = 0.090), peak exposure (p = 0.150) and smoking (p = 0.746) were not statistically significant.
  • In multivariable Model 1, only time since last exposure (b = 1.13, p = 0.000) and length of exposure (b = 0.77, p = 0.000) entered the model, both positively associated with osteopontin. In Model 2, with age forced in:
• time since last exposure: b = 0.98, p = 0.005
• length of exposure: b = 0.68, p = 0.014
• age: b = 0.19, p = 0.570
  • The coefficient for age fell from 0.94 in simple regression to 0.19 in Model 2, which the authors interpreted as strong confounding by age.
  • When the reciprocal of osteopontin was used as the outcome, only time since first exposure entered Model 1.
• The authors' conclusion: The authors concluded that plasma osteopontin cannot be used as a surrogate of asbestos exposure and does not differentiate workers with or without pleural plaques. They reasoned that because asbestos in the lungs declines over time, a true exposure marker should not rise with time since last exposure.
• Limitations the authors state:
  • The study included no cases of asbestosis.
  • Adding 8 workers with pleural plaques who were not in the original sample may have limited the sample's representativeness.
  • There was no objective measure of asbestos concentrations over time; exposure was estimated retrospectively.
  • Leaving age out of the model improved precision but may have increased bias from inadequate control of confounding.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Osteopontin, Asbestos Exposure, Pleural Plaques, Cytokine, Biomarker.

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