Poly(ADP-ribosyl)ation enhancement in brain cell nuclei is associated with diabetic neuropathy.
The study has been undertaken to evaluate the effect of streptozotocin (STZ)-induced diabetes on rat brain poly(ADP-ribose)polymerase (Parp) activity and assess whether and how a Parp inhibitor, nicotinamide (NAm), may potentially regulate the diabetes-induced changes. Experiments were carried out after 4 weeks of diabetes duration in rats treated with or without NAm (100 or 200 mg kg(-1) day(-1), injected intraperitonally for 2 weeks). Assays were performed in purified brain cell nuclei to determine Parp activity by incorporation of radiolabeled ADP-ribose moieties from nicotinamide adenine dinucleotide (NAD+) into nuclear proteins. NAD+ and ATP levels were measured by enzymatic procedures. DNA damage was detected spectrophotometrically.


RESULTS
Parp activity but not NAD-glycohydrolase (NADase) was stimulated by 21% in diabetes vs. control while lowering effects of diabetes on NAD+ and ATP levels were observed. Increase in Parp activity was accompanied by accumulation of malondialdehyde (MDA) and increase in DNA breakage. Treatment with either 100 or 200 mg/kg NAm dose diminished both DNA damage and Parp activity and partially restored the NAD+ and ATP contents, which is probably associated with direct competitive inhibition of Parp as well as with NAm's ability to block diabetes induced oxidative stress.


CONCLUSIONS
Poly(ADP-ribosyl)polymerase overactivation is involved in the development of brain dysfunction in diabetic neuropathy. The mechanism of brain disorders seems to be at least partially connected with a decrease in cellular content and altered subcellular distribution of Parp substrate, NAD+, which, in turn, results in a reduction of ATP level that leads to a total failure of oxidative metabolism. NAm in both doses is effective for the inhibition of poly(ADP-ribosyl)ation.
Kuchmerovska
Tamara
T
Department of Coenzymes, A.V. Palladin Institute of Biochemistry, National Academy of Science, 9, Leontovich Street, 01601 Kyiv, Ukraine. kuch@biochem.kiev.ua
Shymanskyy
Ihor
I
Donchenko
Georgiy
G
Kuchmerovskyy
Mykola
M
Pakirbaieva
Larysa
L
Klimenko
Arkadiy
A
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000648:ultrastructure*; D002467:Cell Nucleus / Q000201:enzymology*; D004249:DNA Damage; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D003929:Diabetic Neuropathies / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D008315:Malondialdehyde / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009536:Niacinamide / Q000494:pharmacology; D011064:Poly Adenosine Diphosphate Ribose / Q000378:metabolism*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D004791:Enzyme Inhibitors; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D009243:NAD; D009536:Niacinamide; D011064:Poly Adenosine Diphosphate Ribose; D008315:Malondialdehyde; D000255:Adenosine Triphosphate; D011065:Poly(ADP-ribose) Polymerases