Minocycline inhibits poly(ADP-ribose) polymerase-1 at nanomolar concentrations

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Abstract
Poly(ADP-ribose) polymerase-1 (PARP-1), when activated by DNA damage, promotes both cell death and inflammation. Here we report that PARP-1 enzymatic activity is directly inhibited by minocycline and other tetracycline derivatives that have previously been shown to have neuroprotective and anti-inflammatory actions. These agents were evaluated by using cortical neuron cultures in which PARP-1 activation was induced by the genotoxic agents N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or 3-morpholinosydnonimine (SIN-1). In both conditions, neuronal death was reduced by >80% either by 10 muM 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone, an established PARP inhibitor, or by 100 nM minocycline. Neuronal NAD(+) depletion and poly(ADP-ribose) formation, which are biochemical markers of PARP-1 activation, were also blocked by 100 nM minocycline. A direct, competitive inhibition of PARP-1 by minocycline (K(i) = 13.8 +/- 1.5 nM) was confirmed by using recombinant PARP-1 in a cell-free assay. Comparison of several tetracycline derivatives showed a strong correlation (r(2) = 0.87) between potency as a PARP-1 inhibitor and potency as a neuroprotective agent during MNNG incubations, with the rank order of potency being minocycline > doxycycline > demeclocycline > chlortetracycline. These compounds are known to have other actions that could contribute their neuroprotective effects, but at far higher concentrations than shown here to inhibit PARP-1. The neuroprotective and antiinflammatory effects of minocycline and other tetracycline derivatives may be attributable to PARP-1 inhibition in some settings.