Biotransformation of Formaldehyde in Cultured Human Bronchus

Biotransformation of formaldehyde to formic acid was studied to investigate the capacity of human bronchial epithelial cells to detoxicate formaldehyde. Normal human bronchial explants and normal primary bronchial epithelial cells were grown in medium containing 0.5 to 5 mM formaldehyde for up to 48 h. Formic acid was quantitated by analytical isotachophoresis. Explants were cultured with up to 5 mM formaldehyde for 48 h with approximately linear turnover, but at 5 mM the cells showed reduced biotransformation relative to the lower concentrations. The mean Km values for explants were 1.4 and 5.1 mM for cells and the mean Vmax values were 3.3 nmol/mg protein•min for the explants and 6.1 nmol/mg protein•min for the cells. By using the same technique with hepatocytes we found Km 1.25 mM and Vmax 4.2 nmol/mg protein•min, indicating that human bronchial epithelium cells have formaldehyde biotransforming activity similar to that of hepatocytes. Our results indicate that human bronchial epithelial cells oxidize formaldehyde at a relatively fast rate at concentrations up to 3 mM formaldehyde in the medium over a period up to 48 h.