Neuronal death in brain infarcts in man

The mechanism of neuronal death in brain ischaemia remains unclear. Morphol ogy, terminal transferase-mediated dUTP-digoxigenin nick end-labelling (TUN EL) and immunohistochemistry for the pro-apoptotic enzyme caspase-3 (CASP3) , for its substrates poly(ADP-ribose) polymerase (PARP) and the DNA-depende nt protein kinase catalytic subunit (DNA-PKCS) and for poly(ADP-ribose) (PA R), an end-product of PARP activity, were used to investigate neuronal deat h in brain infarcts from 15 men and 20 women, aged 46-95 years. The infarct s varied in age from 18 h to several months. Neuronal death was characteriz ed morphologically by cell shrinkage, cytoplasmic hypereosinophilia and mod erate nuclear pyknosis with later chromatin dispersal and disintegration, b ut not features of apoptosis. Occasional apoptotic bodies were seen but the se appeared to be related to inflammatory cells, endothelial cells and occa sional glia, including satellite cells. Neurones within infarcts showed str ong nuclear and cytoplasmic labelling for CASP3 during the first 2 days aft er infarction. Neuronal DNA-PKCS, PARP and poly(ADP-ribose) immunoreactivit y was demonstrable in scattered neurones in and adjacent to infarcts for 18 -24 h but thereafter declined to below detectable levels in most cases. TUN EL labelled cells towards the edge of the infarcts, particularly at 2-4 day s, but most of the labelling could be prevented by preincubation of the sec tions in diethyl pyrocarbonate to inactivate endogenous nucleases. Between 3 days and 3 weeks, CASP3 and DNA-PKCS were detected in proliferating capil laries and CASP3, PARP and poly(ADP-ribose) in infiltrating macrophages. Ou r findings indicate that neuronal death in human brain infarcts has some of the early biochemical features of programmed cell death, with upregulation of CASP3 and rapid disappearance of DNA-PKCS and PARP. However, the morpho logical changes are not those of apoptosis, the DNA cleavage occurs relativ ely late, and some of the TUNEL is probably mediated by the release of endo genous endonucleases during protease or microwave pretreatment of the damag ed tissue.