Noninvasive assessment of microsomal enzyme activity in occupational medicine: present state of knowledge and future perspectives

Abstract

The activity of the hepatic microsomal enzyme system, which may be of great importance for metabolic activation and deactivation of hepatotoxic agents and carcinogens, is changed by exposure to commonly used industrial chemicals. The antipyrine test is the most widely used method for assessing microsomal enzyme activity in man. The clearance of antipyrine can be accurately calculated from one sample of saliva obtained about 24 h after an oral dose of the drug. By measuring antipyrine metabolism during exposure to industrial chemicals and at the end of 3-4 weeks free from exposure, the impact of industrial chemicals on antipyrine metabolism can be estimated, provided the chemicals are eliminated within 3-4 weeks. This test can be performed by skilled and unskilled workers using written instructions. This has broadened the application of the test. Other noninvasive indices of microsomal enzyme activity include the aminopyrine and caffeine breath tests and the urinary excretion of 6-beta-hydroxycortisol and D-glucaric acid. These tests probably reflect the activity of different but overlapping parts of the microsomal enzyme system and may be of value in research in occupational medicine. Previous studies indicate that chlorinated hydrocarbon insecticides, phenoxyacids, chlorophenols, polychlorinated biphenyles, some organic solvents and high concentrations of inhalation anaesthetics may stimulate microsomal enzyme activity, while styrene, toluene and inhalation anaesthetics in concentrations at about the allowed safety limit values have no effect. Lead, chemicals used by spray painters, and carbon disulphide probably inhibit the activity. While the short-term consequences of these changes include altered metabolism of hormones, vitamins, drugs, and other microsomally metabolized compounds, the possible impact on health on a long-term scale is unknown. It is now possible to study this with the use of the available noninvasive simple indices of microsomal enzyme activity. The potentially useful applications include biological monitoring of environmental carcinogenesis and hepatotoxicity.