N-phenyl-p-phenylenediamine uptake onto reconstituted collagen fibrils

N-Phenyl-p-phenylenediamine (N-PPDA) is known to cause strong skin irritation and a sensitization reaction in exposed persons. In a previous in vitro study with portions of skin, N-PPDA exhibited appreciable binding affinity, which suggests a likely involvement of collagen. The present study was therefore undertaken to assess the potential and kinetics of N-PPDA uptake onto collagen. A linear relationship between t-PPDA concentration and its uptake on collagen fibrils was observed. The higher the exposure or contact time the greater the uptake, until a saturation of available sites was reached. The binding was dependent on temperature, with greatest uptake noted at 35 degrees C, and a sharp decline observed at about 50 degrees C. The importance of the intact helical structure of collagen fibrils in offering optimal binding sites was evident from the diminished binding response of collagen denaturated by heat and urea and from the limited affinity towards gelatin. There appeared to be no involvement of sulphydryl groups in the N-PPDA uptake on collagen. A striking resemblance between the binding kinetics of t-PPDA onto collagen and that observed previously with skin portions in vitro, suggests that the collagen fibril model may have a use as a simple preliminary tool to screen chemicals that show binding potential towards skin, in order to make predictions about their dermal toxicity.