Effects of nicotinamide supplementation on liver and serum contents of amino acids in diabetic rats.
OBJECTIVE
Diabetes-related metabolic impairments may be associated with altered protein and amino acid turnover. The goal of the current research was to estimate possible changes in amino acid profiles in rat serum and liver. We also studied whether nicotinamide (NAm), as a drug with the wide range of metabolic effects, can influence metabolic impairments associated with diabetes.


METHODS
After 4 weeks of streptozotocin-induced diabetes (60 mg/kg, i.p.), male Wistar rats were injected for 14 days with or without NAm (100 mg/kg, i.p.). The free amino acids were assayed by cation exchange chromatography. The thiol-active reagent, 5,5'-dithiobis(2-nitrobenzoic acid), was used to determine reduced glutathione (GSH).


RESULTS
Diabetes was associated with derangement of protein and amino acid metabolism as evidenced by 1.72- and 1.16-fold increase in the total amount of free amino acids in liver and serum and Fischer index (Leu+ILe+Val/Tyr+Phe) raised in serum (3.58 vs. 1.73 in control). This was accompanied by increased ratio of essential/nonessential free amino acids, which was more profound in serum. Diabetes led to elevation of hepatic glutamine content, whereas the activity of glutamine synthetase was shown to be decreased. It was also shown a considerable reduction of brain GSH level. Diabetes-related changes in compositions of free amino acids and the ratio of essential/ nonessential free amino acids were partially reversed towards normalisation after NAm supplementation with the efficacy greater in liver than in serum. Furthermore, Fisher index in blood serum was not influenced by drug treatment. NAm exerted slight glucose lowering effect without any effect on decreased body weight in diabetes.


CONCLUSIONS
The study confirms diabetes-induced derangements in protein and amino acid metabolism in animals. The beneficial effects of NAm on these processes, additionally with other possible contributing factors, may be attributed to metabolic improvements in type I diabetes.
Department of Coenzymes, O.V. Palladin Institute of Biochemistry of National Academy of Science, Kyiv, Ukraine. kuch@biochem.kiev.ua
Tamara
T
Kuchmerovska
I
I
Shymanskyy
L
L
Bondarenko
A
A
Klimenko
D000596:Amino Acids / Q000097:blood* / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D003921:Diabetes Mellitus, Experimental / Q000097:blood* / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D009536:Niacinamide / Q000627:therapeutic use*; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014803:Vitamin B Complex / Q000627:therapeutic use
D000596:Amino Acids; D011506:Proteins; D013438:Sulfhydryl Compounds; D014803:Vitamin B Complex; D009536:Niacinamide; D005978:Glutathione