Adenosine deaminase inhibition induces apoptosis in a human astrocytoma cell line

It is known that inborn errors of purine metabolism are often associated with psychomotor dysfunctions, but the molecular link between the metabolic disorders and the neurological manifestations remains in most cases unclear. The deficiency of adenosine deaminase (ADA), the enzyme that catalyzes the hydrolytic deamination of adenosine and deoxyadenosine, is associated with severe immune deficiency and abnormalities in the functioning of many organs such as bone, liver, kidney and nervous system. We have mimicked an ADA-deficient situation by incubating a human astrocytoma cell line (ADF) in the presence of the strong ADA inhibitor deoxycoformycin (dCF) and deoxyadenosine (dAdo), which accumulates in vivo when the enzyme is deficient, and have monitored the effect of the combination on cell viability, mitochondrial functions, and other metabolic features. Cells incubated in the presence of dAdo and dCF in combination, but not those incubated with dAdo or dCF alone, underwent apoptotic death, which appears to proceed through a mitochondrial pathway, since release of cytochrome c and caspase-3 activation have been observed. The inhibition of ADA affects mitochondrial functionality as well, because an alteration in mitochondrial reactive oxygen species level has been revealed. A surprising effect of dAdo and dCF in combination is the significant reduction in lactate production, which is suggestive of a reduced glycolytic capacity, not ascribable to an alteration in NAD+/NADH ratio. This is a hitherto unknown effect presenting early during the incubation with dAdo and dCF, which precedes their effect on cell viability. We are presently investigating on the possible connection between lactate decrease and induction of the apoptotic program.