Binding of formaldehyde to human and rat nasal mucus and bovine serum albumin

Abstract

The function of the nasal mucociliary apparatus, an important airway defense mechanism, is inhibited by inhaled formaldehyde. Nasal mucus, which contains significant concentrations of glycoprotein and soluble proteins, is an integral component of this system. This investigation addresses some reactions of formaldehyde with human and rat mucus in vitro in comparison with a model protein, bovine serum albumin. [ 14C]Formaldehyde was incubated with reconstituted preparations of human and rat nasal mucus or bovine serum albumin. Formaldehyde adducts, stabilized by sodium cyanoborohydride reduction to methylamines, were separated by Sepharose 2B gel filtration. [ 14C]Formaldehyde bound exclusively to one component of nasal mucus which had an elution volume identical to that of albumin. There was no detectable binding to the large molecular weight glycoproteins. The time course of reaction of formaldehyde to free amino groups was then measured using the fluorescamine technique. Formaldehyde binding was characterized by an initial fast phase (< 2 min) followed by a slower phase which appeared to approach equilibrium (> 60 min). The rate of binding to human and rat nasal mucus was similar to albumin. Irreversible binding of formaldehyde to albumin was insignificant within the first 60 min indicating the reversibility of binding during this time. These data indicate that within the first 60 min, formaldehyde reacts rapidly and reversibly with nasal mucus and that it binds primarily to one component of nasal mucus. Gel filtration analysis suggests this component may be albumin although other low molecular weight proteins cannot be ruled out.