Subclinical nephrotoxicity caused by smoking and occupational silica exposure among Egyptian industrial workers

The aim of the present work was to investigate early signs of subclinical renal alterations due to silica exposure and smoking among non-silicotics and silicotics by measuring urinary indicators of nephrotoxicity.

The subjects comprised 29 non-silicotics (9 non-smokers, 20 smokers), 24 silicotics (9 non-smokers, 15 smokers), and 28 referents (9 non-smokers, 19 smokers). Measured urinary parameters were concentrations of total protein, microalbumin, retinol-binding protein, and activities of N-acetyl-beta-D-glucosaminidase and glutathione S-transferase. In addition, we measured levels of urinary silicon and creatinine.

Compared with referents, both non-silicotics and silicotics excreted significant high levels of all measured parameters. Smokers in each investigated group also showed increased levels (although not significant) of renal parameters in comparison to corresponding non-smokers. Among non-silicotics, the present results showed that elevation of measured urinary parameters was significantly associated with work duration, while only urinary excretion of glutathione S-transferase was associated with work duration among silicotics.

The study confirms that silica may lead to subclinical signs of nephrotoxicity, and that smoking also has a nephrotoxic effect on kidney and is synergistic to nephrotoxicity of silica exposure. Additionally, the study suggests that renal alterations may occur prior to pulmonary involvement.