Alanine aminopeptidase in serum: biological variations and reference limits

Abstract

We studied the effect of various factors on the biological variation of alanine aminopeptidase (AAP, EC 3.4.11.2) in serum in a population of 2178 apparently healthy subjects and in subjects taking specific drugs. To measure AAP, we used an automated assay, with alanyl-4-nitroanilide as substrate. AAP activity concentrations were significantly higher in males than in females in all age groups between 10 and 55 years. The highest mean AAP values were found for children between 10 and 14 years. In male heavy smokers, AAP values were 8% higher than in moderate or nonsmokers (P less than 0.001); in females, this effect was less pronounced. AAP concentrations were higher in subjects consuming over 44 g of ethanol a day than in those consuming less (P less than 0.01 for men, P less than 0.05 for women). The use of oral contraceptives increased AAP values by 12% (P less than 0.001). Hypolipidemic drugs caused lower values for AAP in men (P less than 0.001). Subjects showing induction of gamma-glutamyltransferase (EC 2.3.2.2) by anticonvulsant drugs had also higher AAP activities (by 23%). Taking these data into account, we established reference limits for AAP in serum.

PIP: The aim of this study was to describe the major factors producing variation in levels of serum alanine aminopeptidase. The study population consisted of 1065 men and 1113 women screened at the Center for Preventive Medicine in Vandoeuvre-les-Nancy in 1987. Mean values were significantly higher for men than for women between age 10 and age 55. Alanine aminopeptidase activity was higher in prepubertal children than in adults and decreased with age, but increased again in postmenopausal women. Overweight status had no effect, nor did systolic blood pressure below 160 mmHg. Serum levels fell by 10% for men over this limit, but increased by 15% for women above this limit. Enzyme levels rose with alcohol consumption for both men and women. Men who were heavy smokers (over 20 cigarettes/day) had elevated levels of serum alanine aminopeptidase. In women oral contraceptives and antihypertensive drugs increased enzyme levels. Mean levels increased by 23% in both men and women taking anticonvulsant drugs who also had increased gamma-glutamyltransferase activity. Factors affecting serum alanine aminopeptidase levels, in decreasing order of importance, were sex, age, alcohol consumption, and cigarette smoking.