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

Aim: To assess the influence of smoking on the level of total protein, metallothionein (MT), albumin and lactoferrin in human breast milk. Methods: Samples of whole milk and supernatants of milk after centrifugation at 10 000×g and 105 000×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. Results: 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≤0.001) and serum (179±87 ng/ml and 32±19 ng/ml, respectively; p≤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≤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 μg/ml) than in non-smokers (13.4±3.0 μg/ml; p≤0.001), and an inverse correlation between MT level and cadmium concentration (r=-0.86; p=0.001) was noticed.

Conclusions: 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.