Sequence of metabolic changes during X-ray-induced apoptosis

A cell population undergoing apoptosis usually contains varying proportions of cells in the diverse stages of the process, from very early continuousl y through to secondary necrosis. This heterogeneity acts as a confounding f actor in metabolic studies if a general population is investigated. Using f luorescent probes and multiparameter flow cytometry, we report on metabolic changes occurring during X-ray-induced apoptosis in human peripheral blood lymphocytes and relate the observed alterations to cells at various phases of the process assessed by monitoring the progressive loss of selective pl asma membrane permeability, Data show that alterations of mitochondria card iolipin and a reduction of plasma membrane potential are rather early event s as they commence in cells which still possess an impermeable plasma membr ane. Conversely, mitochondrial transmembrane potential is impaired only whe n plasma membrane permeability starts to be altered, that is, in relatively later apoptotic cells, thereby reflecting the complexity of mitochondria d emise during apoptosis. The prooxidant/antioxidant balance is altered in ce lls in early apoptosis with a correlated increase of prooxidants and deplet ion of thiols, the latter indicative for the progressive impairment of this detoxifying mechanism. The imbalance in prooxidant/antioxidant remained ev ident through apoptosis suggesting that oxidative damage starts early and t hen continues, eventually leading to cellular disruption. Assessing cell tr ansit through the apoptotic process and coupling the observed metabolic cha nges to selected stages of the process enables one to improve the understan ding of the temporary sequence of biochemical phenomena occurring in a give n model. (C) 1999 Academic Press.