Human epidermal growth factor—on molecular forms present in urine and blood

Abstract

A sensitive enzyme-linked immunosorbent assay (ELISA) for quantitation of human epidermal growth factor (EGF) was employed to study EGF in urine and blood. The EGF/creatinine ratio in urine was significantly higher for women (range and (median); 0.20–0.83 (0.50) nmol EGF/mmol creatinine) than for men (0.17–0.63 (0.30) nmol EGF/mmol creatinine). We were not able to demonstrate EGF in plasma (median plasma EGF < 0.01 nmol/l) whereas serum contained a range and (median) of 0.02–0.31 (0.12) nmol EGF/l. The amount of EGF in serum showed a weak correlation to the platelet count ( r = 0.327). EGF was partly purified by affinity chromatography from urine (urine EGF) and from activated platelets in platelet rich plasma (blood EGF). Both blood and urine contained a high molecular weight form of EGF (HMW EGF) as well as 6 kDa EGF. HMW EGF from blood was similar to HMW EGF from urine concerning behaviour upon gel filtration, p I and apparent affinity constant for binding to the EGF receptor. However, HMW EGF constituted approx. 40% of blood EGF but only 10% of urinary EGF. The 6 kDa EGF from both blood and urine contained two isopeptides with p I around 4.40 and 4.15 but in various proportions. The apparent affinity constant for binding to the EGF receptor for blood 6 kDa EGF was 1.8·10 10 l/mol compared to 1.0·10 10 l/mol for urinary 6 kDa EGF and 0.8·10 10 l/mol for HMW EGF from both blood and urine. The present study suggests that the processing of the EGF precursor differs in the blood and in the kidneys and that 6 kDa EGF from blood and urine binds to the EGF receptor with a higher apparent affinity constant than does HMW EGF.