Immunoglobulins associated with elevated riboflavin binding by plasma from cancer patients

Plasma from 182 patients with different malignant diseases was tested for riboflavin binding by immunoglobulins, which have been recently identified as major carriers of this micronutrient. A wide range of binding (5.9 to 130 pmole/ml plasma) was observed, and significant elevations were found for patients having breast cancer (21.2 +/- 1.9, P less than 0.05) and melanoma (25.7 +/- 1.9, P less than 0.001) compared to controls (15.5 +/- 1.9). The proteins responsible for a majority of the higher binding were identified as immunoglobulins, based on their elution from gel filtration columns and the removal of 57-88% of the non-albumin binding by treating of plasma with Protein A-agarose. The binding was only weakly related to the total concentration of immunoglobulins (r = 0.11 by linear regression analysis), however, and is apparently due to a subclass that is elevated in some types of cancer. Elevated levels of these immunoglobulins may contribute to the lower urinary levels and clearance of riboflavin in cancer.