Biomarkers of tissue injury.

Biomarkers of tissue injury have evolved empirically over the last 50-100 years. With the advent of immunoassays and discovery tools such as RNA expression and proteomics, more systematic approaches to the discovery of biomarkers can be expected in the future. This review discusses the evolution of biomarkers of muscle, liver, heart and brain injury and illustrates that a modern discovery tool, such as mRNA profiling, would have predicted the biomarkers for cardiac injury (heart attacks) that actually evolved over 50 years by empiric approaches. We also discuss how novel biomarkers for brain injury were identified using RNA expression approaches. It is our prediction that there will be a growth in the number of valuable biomarkers for identifying cell and organ injury in the next 5-10 years.

Identification of novel brain biomarkers.

BACKGROUND: The diagnosis of diseases leading to brain injury, such as stroke, Alzheimer disease, and Parkinson disease, can often be problematic. In this study, we pursued the discovery of biomarkers that might be specific and sensitive to brain injury. METHODS: We performed gene array analyses on a mouse model to look for biomarkers that are both preferentially and abundantly produced in the brain. Via bioinformatics databases, we identified the human homologs of genes that appeared abundant in brain but not in other tissues. We then confirmed protein production of the genes via Western blot of various tissue homogenates and assayed for one of the markers, visinin-like protein 1 (VLP-1), in plasma from patients after ischemic stroke. RESULTS: Twenty-nine genes that were preferentially and abundantly expressed in the mouse brain were identified; of these 29 genes, 26 had human homologs. We focused on 17 of these genes and their protein products on the basis of their molecular characteristics, novelty, and/or availability of antibodies. Western blot showed strong signals in brain homogenates for 13 of these proteins. Tissue specificity was tested by Western blot on a human tissue array, and a sensitive and quantitative sandwich immunoassay was developed for the most abundant gene product observed in our search, VLP-1. VLP-1 was detected in plasma of patients after stroke and in cerebrospinal fluid of a rat model of stroke. CONCLUSIONS: The use of relative mRNA production appears to be a valid method of identifying possible biomarkers of tissue injury. The tissue specificity suggested by gene expression was confirmed by Western blot. One of the biomarkers identified, VLP-1, was increased in a rat model of stroke and in plasma of patients after stroke. More extensive, prospective studies of the candidate biomarkers identified appear warranted.