An enzyme-linked immunosorbent assay for glial fibrillary acidic protein as an indicator of the presence of brain or spinal cord in meat

Abstract

The current methods to detect central nervous system (CNS) tissue in blood, lungs, or meat are cumbersome, time consuming, and costly. The objective of this study was to use glial fibrillary acidic protein (GFAP), which is restricted to the CNS, in an enzyme-linked immunosorbent assay (ELISA) for the detection of CNS tissue in blood and muscle from beef cattle. Bovine brain, cerebral cortex, spinal cord, sciatic nerve, diaphragm, blood clots, and other skeletal muscle were obtained from three animals at slaughter. The limit for detection of GFAP was approximately 1.0 ng and the standard curve was linear up to 40 ng. Tissue samples gave responses parallel to the GFAP standard, suggesting that standard and unknown samples were immunoreactively identical. No GFAP was detected in skeletal muscle (ground beef, shoulder clod, and diaphragm) and blood clots. Trace amounts (13.5 to 51 ng/mg) were present in sciatic nerve. In contrast, high levels of GFAP (55 to 220 μg/mg) were present in spinal cord, cerebral cortex (17 μg/mg), and whole brain (9 to 55 μg/mg). In a storage study using two animals in two separate studies, immunoreactive GFAP was detectable for up to 8 days at 4°C in all tissues containing neural elements. Thus, mixtures of muscle with spinal cord or brain retained almost 80% of their immunoreactivity after 8 days at 4°C, while brain and spinal cord alone retained approximately 50% and 25%, respectively, of their initial activities. In a repeat experiment, 80 to 100% of the initial activity was retained in these tissues after 8 days at 4°C. The results of the current study demonstrate that the GFAP ELISA provides a valid and repeatable method to detect CNS tissue contamination in meat.