Proteomics and toxicology 8/1/03. By Richard Twyman Large-scale protein analysis can identify proteins whose expression is altered by the administration of drugs.

One of the greatest hurdles in drug development is the occurrence of adverse drug responses (side effects), the unwanted physiological effects of drug toxicity. Such responses cannot generally be predicted. They reveal themselves late in the drug development process, either in pre-clinical trials on animal models or in clinical trials on human patients. In many cases, the candidate drug has to be abandoned at this stage.

A major application of proteomics , the large-scale study of proteins, is the prediction and investigation of adverse drug responses. This field has even been given its own name: toxicoproteomics.

The predominant technology platform in proteomics, two-dimensional gel electrophoresis , is used to separate complex protein mixtures allowing individual protein spots on the gel to be identified by mass spectrometry .

If two samples are compared, in this case tissue from an untreated patient and tissue from a patient treated with a candidate drug, differences in the abundances of particular proteins may be evident. These differentially expressed proteins may be useful as biological markers for drug toxicity. If they can be identified, the mechanism of toxicity may also become clear.

Much toxicoproteomic research has focussed on the liver and kidneys because these break down and excrete drugs and are therefore the major sites of toxicity in the body. Many drugs that have been investigated in this manner including some of the medicines we take for granted, such as paracetmol and the antibiotic gentamicin.

Another such drug is the immunosuppressant drug cyclosporin A. This is widely used to prevent rejection following grafts or organ transplants, especially in children.

One of the major side effects of cyclosporin A is kidney toxicity, which occurs in nearly 40 per cent of patients. The toxicity is associated with the loss of calcium in the urine and resulting calcification of the kidney tubules.

Proteomic analysis of rat, and subsequently human, kidneys from untreated patients and those treated with cyclosporin A showed a striking difference in the level of one particular protein, the calcium-binding protein calbindin. This protein was much less abundant in the kidneys of humans and rats treated with cyclosporin A, and immediately suggested the mechanism of cyclosporin A toxicity.

Interestingly, while many humans show kidney toxicity in response to this drug, monkeys generally do not. Furthermore, the investigation of monkey kidneys using showed that expression of the monkey calbindin protein is not affected by cyclosporin A treatment.

Image credit: Nicoletta Baloyianni

Further reading

Benito B, et al. Effects of cyclosporine A on the rat liver and kidney protein pattern, and the influence of vitamin E and C coadministration. Electrophoresis 1995, 16: 1273-83. Abstract

Steiner S, et al. Cyclosporine A decreases the protein level of the calcium-binding protein calbindin-D 28kDa in rat kidney. Biochem Pharmacol 1996, 51: 253-8. Abstract

Aicher L, et al. Decrease in kidney calbindin-D 28kDa as a possible mechanism mediating cyclosporine A- and FK-506-induced calciuria and tubular mineralization. Biochem Pharmacol 1997, 53: 723-31. Abstract

Reviewed: Aicher L, et al. New insights into cyclosporine A nephrotoxicity by proteome analysis. Electrophoresis 1998, 19: 1998-2003. Abstract