The kynurenine pathway enzymes in healthy and hyperlipidemic rabbits

Tryptophan metabolism along the kynurenine pathway in normolipidemic and diet-induced hyperlipidemic New Zealand rabbits was studied. The activities of liver tryptophan 2,3-dioxygenase small intestine indole 2,3-dioxygenase, liver and kidney kynurenine 3-monooxygenase, kynurenine-oxoglutarate transaminase, kynureninase, 3-hydroxyanthranilate 3,4-dioxygenase and aminocarboxymuconate semialdehyde decarboxylase (picolinic carboxylase) were determined. Liver tryptophan 2,3-dioxygenase (TDO) was present only as a holoenzyme. In fact, similar results were found in the absence or presence of the cofactor haematin. In addition, TDO activity was higher in normolipidemic than in hyperlipidemic rabbits. Small intestine indole 2,3-dioxygenase did not change significantly among the two groups of animals, but was higher than liver TDO. Liver and kidney kynurenine 3-monooxygenase activities did not change significantly whereas kynurenine-oxoglutarate transaminase activity decreased only per g of fresh kidney in hyperlipidemic rabbits. Kynureninase activity decreased significantly per g of fresh tissue only in liver. 3-Hydroxyanthranilate 3,4-dioxygenase, both as specific activity and per g of fresh tissue and aminocarboxymuconate-semialdehyde decarboxylase activities showed significantly lower values per g of fresh kidney in hyperlipidemic rabbits compared with controls. Therefore, hyperlipidemia can influence enzyme activities along the kynurenine pathway, leading to a reduction in the biosynthesis of NAD coenzymes.