Metabolism of 1-nitro[¹⁴C]pyrene in vivo in the rat and mutagenicity of urinary metabolites

Abstract

The metabolic fate of the bacterial mutagen, environmental pollutant and potential carcinogen 1-nitropyrene (NP) has been investigated in the rat. Over half of an i.p. dose (10 mg/kg) of 1-nitro[14C]pyrene was excreted within 24 h of dosing, 15% of the dose in urine and 40% in the faeces. After 96 h greater than 80% of the dose had been recovered. The urinary and fecal metabolites of NP were separated and quantitated by h.p.l.c., then identified by high resolution gas chromatography/mass spectrometry (h.r.g.c./m.s.) and comparison with synthetic reference compounds, where available. Very little (less than 5%) of the dose was excreted unchanged. Urinary metabolites were all excreted in conjugate form, mainly with glucuronic acid. Among the principal metabolite fractions identified were 3-hydroxy-1-nitropyrene and 8-hydroxy-1-nitropyrene (already known as hepatic in vitro metabolites of 1-nitropyrene) and the hitherto unreported metabolites 6-hydroxy-N-acetyl-1-aminopyrene and 8-hydroxy-N-acetyl-1-aminopyrene. Mutagenic activity was detected, by means of the Ames Salmonella (strain TA 98) plate incorporation assay, in the urine of rats dosed with NP. This mutagenicity, unlike that of NP itself, required exogenous metabolic activation. It was predominantly associated with 6-hydroxy-N-acetyl-1-aminopyrene and with the nitropyrene phenols (specific mutagenicity 600 and 700 rev/nmol respectively in the presence of 0.6 mg of S9 protein per plate). The majority of the residual metabolites were polar, refractory to enzymic hydrolysis, and of low mutagenicity. The major proportion of the 14C in feces was not extractable or amenable to enzymic hydrolysis; the extractable fecal metabolites were similar in nature to those in urine.

Identification and Quantification of 1-Nitropyrene Metabolites in Human Urine as a Proposed Biomarker for Exposure to Diesel Exhaust

“…This may be because some of the subjects had extremely low concentrations of urinary OHNAAPs. In studies with rats, ring hydroxylation in the liver seems to be the predominant route of 1-NP biotransformation, whereas nitroreduction occurs only to a small extent in the liver (17). Biotransformation by nitroreduction occurs mainly by intestinal bacteria (18,45).…”

“…1-NAAP was prepared by acetylation of 1-AP with acetic anhydride in ethyl acetate. To identify the synthesized compounds, their GC-MS and proton NMR spectra were compared with data in the literature (17,34,35). Similar procedures were applied to synthesize deuterated OHNPs and OHNAAPs from pyrene-d 10 for use as internal standards.…”

Evaluation of Endocrine Disrupting Activities of Monohydroxylated Derivatives of 1-nitropyrene by Yeast Two-hybrid Assay

“…1) in the presence of cytochrome P450 enzymes. 3,4) Additionally, OHNPs were observed in airborne particles 5,6) and diesel exhaust particles. 7,8) The mutagenicity of OHNPs has been investigated by several groups, and they concluded that most of OHNP isomers showed lower activity than the parent 1-NP.…”

Mutagenicities and Endocrine-disrupting Activities of 1-Hydroxy-2-nitropyrene and 1-Hydroxy-5-nitropyrene

“…1), such as 1-hydroxy-3-nitropyrene (1-OH-3-NP), 1-hydroxy-6-nitropyrene (1-OH-6-NP), and 1-hydroxy-8-nitropyrene (1-OH-8-NP) in the presence of cytochrome P450 enzymes. 4,5) We recently found that these OHNP isomers were also produced from a photoreaction of 1-NP in the atmosphere as well as the other isomers, 1-hydroxy-2-nitropyrene (1-OH-2-NP) and 1-hydroxy-5-nitropyrene (1-OH-5-NP). 6) Several groups reported that 1-OH-3-NP, 1-OH-6-NP, and 1-OH-8-NP are weakly muta- The Pharmaceutical Society of Japan genic, [7][8][9][10] but the mutagenicities of 1-OH-2-NP and 1-OH-5-NP are unknown.…”