Uptake of copper from brass vessels by bovine milk and its relevance to Indian childhood cirrhosis

Abstract

To mimic the infant feeding practice associated with Indian childhood cirrhosis (ICC), bovine milk was stored for 6 h in indigenous brass vessels. The milk copper concentration rose from 27 +/- 4 to 621 +/- 65 micrograms/dl, whereas zinc concentration was not significantly changed. Copper in bovine milk was associated with casein (67%), whey proteins (7%), less than 10 kDa molecules (11%), and fat (7%). Addition of copper sulphate to a concentration of 600 micrograms/dl produced a 102-fold rise in copper content of the casein fraction, a 47-fold increase for whey, and 15-fold for the less than 10 kDa fraction. Analysis by sepharose gel chromatography confirmed that casein was the major copper-binding fraction in control and copper-loaded milk. To mimic intragastric conditions, the pH of copper-loaded milk was lowered to 4.5 to precipitate casein, resulting in a rise in less than 10 kDa bound copper (10.7 +/- 4.0 to 104.3 +/- 7.5 micrograms Cu/100 ml) and whey-bound copper (53.1 +/- 4.5 to 118.4 +/- 19.1 micrograms Cu/100 ml). Copper/casein complex (3 micrograms Cu/mg protein, pH 6.6) was dialysed against low-MW metal chelating agents, including picolinate and citrate, which are present in the duodenum. Picolinate 1 mM and citrate 1 mM were able to remove 84% and 29% of copper, respectively. Thus, copper, though not zinc, is avidly taken up from brass and bound largely to casein, from which it is partly liberated by acid precipitation and almost completely removed by picolinate chelation. Milk is an effective carrier of copper from brass utensil to infant enterocyte.