NAD+ biosynthesis and metabolic fluxes of tryptophan in hepatocytes isolated from rats fed a clofibrate-containing diet.
Hepatocytes were isolated from rats fed a diet with or without 0.25% clofibrate, and NAD+ synthesis by the hepatocytes was determined using either [carboxyl-14C]nicotinic acid or [5-3H]tryptophan. NAD+ and total pyridine nucleotides synthesized from [14C]nicotinic acid by the clofibrate-treated cells were not significantly different from those synthesized by the control cells when expressed on the basis of nanomoles per hour per milligram of DNA. On the contrary, NAD+ synthesized from [3H]tryptophan was significantly higher in the clofibrate-treated cells (158% of the control cells) on the basis of nanomoles per hour per milligram of DNA. Clofibrate was inhibitory to tryptophan metabolism as a whole, affecting the glutarate pathway more (decreased to 37% of control) than the kynureninase flux (decreased to 64% of control). As a result, the quinolinate-NAD flux, estimated as the difference in the amounts of tryptophan metabolized by the two metabolic pathways, increased in the clofibrate-treated hepatocytes. The increase in quinolinate during the incubation was 8 times more in the clofibrate-treated cells than in the control cells, which confirmed alteration in the metabolic fluxes of tryptophan in the clofibrate-treated cells. Hepatic quinolinate phosphoribosyltransferase (EC 2.4.2.19) activity increased with dietary clofibrate and returned to the control level 1 week after removing clofibrate from the diet. Nicotinate phosphoribosyltransferase (EC 2.4.2.11) and NAD+ glycohydrolase (EC 3.2.2.5) activities remained unchanged with dietary clofibrate.
Shin
M
M
School of Pharmacy, Kobe Gakuin University, Japan.
Mori
Y
Y
Kimura
A
A
Fujita
Y
Y
Yoshida
K
K
Sano
K
K
Umezawa
C
C
D000818:Animals; D002478:Cells, Cultured; D002994:Clofibrate / Q000008:administration & dosage*; D004032:Diet; D008099:Liver / Q000378:metabolism*; D008297:Male; D009243:NAD / Q000096:biosynthesis*; D009525:Niacin / Q000378:metabolism; D010430:Pentosyltransferases / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014364:Tryptophan / Q000378:metabolism*; D000098553:Nicotinate-Nucleotide Diphosphorylase (Carboxylating)
D009243:NAD; D009525:Niacin; D014364:Tryptophan; D010430:Pentosyltransferases; D000098553:Nicotinate-Nucleotide Diphosphorylase (Carboxylating); D002994:Clofibrate