Influence of smoking on metallothionein level and other proteins binding essential metals in human milk

Abstract

To assess the influence of smoking on the level of total protein, metallothionein (MT), albumin and lactoferrin in human breast milk. Samples of whole milk and supernatants of milk after centrifugation at 10 000 x g and 105 000 x g were analysed. Cadmium was determined by graphite furnace atomic absorption spectrometry (GFAAS). The concentration measurements employed the following methods: total protein by Lowry, albumin by colorimetry, cotinine and lactoferrin by ELISA tests, metallothionein by 109Cd/haemoglobin assay. The assessment of tobacco smoke exposure was based on concentrations of cotinine in breast milk (197 +/- 98 ng/ml in smokers and 23 +/- 11 ng/ml in non-smokers; p < or = 0.001) and serum (179 +/- 87 ng/ml and 32 +/- 19 ng/ml, respectively; p < or = 0.001). The level of cadmium was four times higher in the milk of smoking women than in non-smokers. The concentration of total protein was lower in smoking (37.3 +/- 10.6 mg/ml) than in non-smoking mothers (51.8 +/- 13.8 mg/ml; p < or = 0.02). No significant differences between albumin and lactoferrin concentrations were observed. The level of metallothionein was over twice as low in smokers (5.1 +/- 1.9 microg/ml) than in non-smokers (13.4 +/- 3.0 microg/ml; p < or = 0.001), and an inverse correlation between MT level and cadmium concentration (r = -0.86; p = 0.001) was noticed. The breast milk of smoking mothers might be of lower nutritive value. The amount of MT transported by milk to the mammary gland is smaller in smokers than in non-smokers, which may prove to be advantageous to an infant because of the higher toxicity of the Cd-MT complex than that of inorganic Cd salts.