Tryptophan-NAD+ pathway metabolites as putative biomarkers and predictors of peroxisome proliferation

• Published in: Archives of toxicology 2005-04, Vol.79 (4), p.208-223
• Main Authors: DELANEY, Jane, HODSON, Mark P, WATERFIELD, Catherine J, THAKKAR, Hansa, CONNOR, Susan C, SWEATMAN, Brian C, KENNY, Steve P, MCGILL, Paul J, HOLDER, Julie C, HUTTON, Kathryn A, HASELDEN, John N
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Biomarkers; Carboxy-Lyases - metabolism; Chromatography, High Pressure Liquid; Gene Expression; Hepatocytes - ultrastructure; Hypolipidemic Agents - pharmacology; Immunohistochemistry; Lipids - blood; Lipoproteins - blood; Liver Function Tests; Magnetic Resonance Spectroscopy; Male; Mass Spectrometry; Medical research; Medical sciences; Metabolites; Microscopy, Electron, Transmission; Models, Statistical; NAD - metabolism; NMR; Nuclear magnetic resonance; Organ Size - drug effects; Pentosyltransferases - metabolism; Peroxisome Proliferators - metabolism; Peroxisomes - ultrastructure; Rats; Rats, Sprague-Dawley; RNA, Messenger - biosynthesis; Toxicology; Tryptophan - metabolism
• ISSN: 0340-5761; 1432-0738
• DOI: 10.1007/s00204-004-0625-5

The present study was designed to provide further information about the relevance of raised urinary levels of N-methylnicotinamide (NMN), and/or its metabolites N-methyl-4-pyridone-3-carboxamide (4PY) and N-methyl-2-pyridone-3-carboxamide (2PY), to peroxisome proliferation by dosing rats with known peroxisome proliferator-activated receptor alpha (PPARalpha) ligands [fenofibrate, diethylhexylphthalate (DEHP) and long-chain fatty acids (LCFA)] and other compounds believed to modulate lipid metabolism via PPARalpha-independent mechanisms (simvastatin, hydrazine and chlorpromazine). Urinary NMN was correlated with standard markers of peroxisome proliferation and serum lipid parameters with the aim of establishing whether urinary NMN could be used as a biomarker for peroxisome proliferation in the rat. Data from this study were also used to validate a previously constructed multivariate statistical model of peroxisome proliferation (PP) in the rat. The predictive model, based on 1H nuclear magnetic resonance (NMR) spectroscopy of urine, uses spectral patterns of NMN, 4PY and other endogenous metabolites to predict hepatocellular peroxisome count. Each treatment induced pharmacological (serum lipid) effects characteristic of their class, but only fenofibrate, DEHP and simvastatin increased peroxisome number and raised urinary NMN, 2PY and 4PY, with simvastatin having only a transient effect on the latter. These compounds also reduced mRNA expression for aminocarboxymuconate-semialdehyde decarboxylase (ACMSDase, EC 4.1.1.45), the enzyme believed to be involved in modulating the flux of tryptophan through this pathway, with decreasing order of potency, fenofibrate (-10.39-fold) >DEHP (-3.09-fold) >simvastatin (-1.84-fold). Of the other treatments, only LCFA influenced mRNA expression of ACMSDase (-3.62-fold reduction) and quinolinate phosphoribosyltransferase (QAPRTase, EC 2.4.2.19) (-2.42-fold) without any change in urinary NMN excretion. Although there were no correlations between urinary NMN concentration and serum lipid parameters, NMN did correlate with peroxisome count (r2=0.63) and acyl-CoA oxidase activity (r2=0.61). These correlations were biased by the large response to fenofibrate compared to the other treatments; nevertheless the data do indicate a relationship between the tryptophan-NAD+ pathway and PPARalpha-dependent pathways, making this metabolite a potentially useful biomarker to detect PP. In order to strengthen the observed link between the me