Biochemical characterization of ADP-ribose polymer metabolism in SLE

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Abstract
The metabolism of poly(ADP-ribose) in peripheral blood mononuclear (PBM) cells was studied in 13 patients with systemic lupus erythematosus (SLE) and in 12 age and sex matched controls. Poly(ADP-ribose) polymerase activity was measured as the net accumulation of ADP-ribose polymers during the conversion of 32P-NAD to poly(ADP-ribose) in PBM cells in vitro. The control population showed a mean activity of 418 ± 91(s.d.) pmol ADP-ribose/10 min/106 cells. The SLE population was more heterogeneous and showed a lower mean of 225 ± 147(s.d.) pmol ADP-ribose/ 10 min/106 cells. The mechanism of decreased ADP-ribose polymer accumulation was investigated. Measurements of turnover of the ADP-ribose polymers and its substrate, NAD+, showed that diminished ADP-ribose polymer accumulation in SLE subjects resulted from decreased poly(ADP- ribose) synthesis and not from altered rates of polymer turnover or NAD utilization. Western blot analyses of enzyme protein levels, kinetic studies of poly(ADP-ribose) polymerase activity and analyses of polymer size distribution suggested that the mechanism of poly(ADP-ribose) synthesis in SLE cells is not altered but that the number of active poly(ADP-ribose) polymerase molecules is reduced.