The Center for Alternatives to Animal Testing is an academic center affiliated with the Division of Toxicological Sciences in the Department of Environmental Health Sciences of the Johns Hopkins University Bloomberg School of Public Health.

 

Johns Hopkins School of Public Health

Research Grants 1983-1984

Specific Protein Synthesis as an Indicator of Cellular Injury

John M. Frazier, PhD
Johns Hopkins School of Public Health, Baltimore, Maryland

Problem

Exposure of cells to toxic chemicals results in a sequence of cellular events which is initiated by the molecular interaction of the toxicant with cellular components. At the biochemical level the initiation of the toxic response is expressed as alterations in normal patterns of biochemical functions. One such alteration is the de novo synthesis of new cellular proteins which are probably involved in cellular defense.

A well-studied example of this induction process is the synthesis of a unique protein, metallothionein, following exposure of many different cell types to Class II B metals (zinc, cadmium and mercury). This protein is quite small, having a molecular weight of approximately 6,600, a high content of the sulfur-containing amino acid cysteine (about 30%) and containing no aromatic amino acids. Metallothionein binds the Class II B metals very strongly and is thought to participate in metal detoxification processes via this function.

The objective of the research program is to develop a model system using isolated rat hepatocytes to evaluate the process of protein induction as an index of the cellular toxicity of chemicals. The initial aim is to investigate the induction of metallothionein and heat-shock protein in response to metals as a first prototype. Following exposure of isolated rat hepatocytes to cadmium, the general metallothionein and heat shock separately. The design of these experiments allows us to distinguish between specific protein synthesis and general protein synthesis.

Impact of the Research

The quantitating of specific protein induction will establish the basis for a chemical toxicity test. Such a test would significantly reduce the number of animals involved in hepatotoxicity screening since one rat liver provides sufficient cells to generate a complete dose response curve.