<atl>Anoxia-induced changes in purine nucleoside metabolism of in vitro aged human fibroblasts

Inosine deriving from the metabolism of adenosine or inosine monophosphate (IMP) in the fibroblast provides the substrate for xanthine oxidase and is, therefore, an important source of toxic oxygen free radicals. With well-oxygenated medium, adenosine release appears to be greater for aged than young fibroblasts. In that the adenosine release by young cells is enhanced by reduced oxygenation, the effect anoxic stress on the release of the purine nucleosides adenosine and inosine by low-passage (PDL23-26; young) vs. high-passage (PDL 43–51; aged) human lung fibroblasts (IMR-90) was studied. Cultures of confluent fibroblasts were incubated for 16 hr under normoxic (NF) or anoxic (AF) atmospheres. The release of adenosine and inosine was determined by HPLC at 0, 3, 6 and 24 hr after termination of the 16-hr period. Immediately following anoxia (time 0), adenosine release by young AF was 29% greater than for young NF, whereas both the young AF and aged AF displayed a 34- and 21-fold greater inosine release, respectively, as compared to NF. With continued normoxic incubation for 3 hours inosine release by young and aged AF returned to levels observed with NF. However, with further normoxic incubation inosine release by aged AF again became elevated at 6 and 24 hr post-anoxia to values 3.0- to 5.3-fold those of NF. Deamination of the released adenosine was not the primary source of inosine. These data suggest that in the aged, but not young, fibroblast, anoxia initiates the induction of changes in purine metabolism which may potentially enhance the production of toxic peroxides and oxygen radicals upon return to normoxic conditions following an anoxic stress. [Copyright &y& Elsevier]