Impact of hepatic P450-mediated biotransformation on the disposition and respiratory tract toxicity of inhaled naphthalene

Abstract

We determined whether a decrease in hepatic microsomal cytochrome P450 activity would impact lung toxicity induced by inhalation exposure to naphthalene (NA), a ubiquitous environmental pollutant. The liver-Cpr-null (LCN) mouse showed decreases in microsomal metabolism of NA in liver, but not lung, compared to wild-type (WT) mouse. Plasma levels of NA and NA-glutathione conjugates (NA-GSH) were both higher in LCN than in WT mice after a 4-h nose-only NA inhalation exposure at 10ppm. Levels of NA were also higher in lung and liver of LCN, compared to WT, mice, following exposure to NA at 5 or 10ppm. Despite the large increase in circulating and lung tissue NA levels, the level of NA-GSH, a biomarker of NA bioactivation, was either not different, or only slightly higher, in lung and liver tissues of LCN mice, relative to that in WT mice. Furthermore, the extent of NA-induced acute airway injury, judging from high-resolution lung histopathology and morphometry at 20h following NA exposure, was not higher, but lower, in LCN than in WT mice. These results, while confirming the ability of extrahepatic organ to bioactivate inhaled NA and mediate NA's lung toxicity, suggest that liver P450-generated NA metabolites also have a significant, although relatively small, contribution to airway toxicity of inhaled NA. This hepatic contribution to the airway toxicity of inhaled NA may be an important risk factor for individuals with diminished bioactivation activity in the lung.

The Cellular and Molecular Determinants of Naphthoquinone-Dependent Activation of the Aryl Hydrocarbon Receptor

“…1,2-NQ and 1,4-NQ have been shown to influence oxidative status in rodent models and cells in culture, and have been linked to toxicity [1,2,6,53,54]. Their potential to activate the AhR signaling pathway in vivo could lead to increased production of reactive metabolites as a result of the induction of expression of AhR-responsive CYPs (e.g., CYP1A1, CYP1B1, CYP1A2, CYP2A5, etc.)…”

Toxicokinetic Interaction between Hepatic Disposition and Pulmonary Bioactivation of Inhaled Naphthalene Studied Using Cyp2abfgs-Null and CYP2A13/2F1-Humanized Mice with Deficient Hepatic Cytochrome P450 Activity

“…The reaction was quenched by transferring the incubation tubes to an ice bath and adding 0.2 ml ice-cold methanol containing the internal standard AP-GSH to the uncapped tubes. The resultant mixtures were centrifuged twice to remove precipitated proteins and aliquots of supernatants were injected into an ultra-performance liquid chromatography-tandem mass spectrometry system for analysis, as previously described (Kovalchuk et al, 2017). NADPH, GSH, or NA were omitted, or boiled microsomes were used, in negative control incubations.…”

“…Two-to three-month-old male mice were used for the study. NA inhalation exposure settings were the same as described in detail elsewhere (Kovalchuk et al, 2017). Mice were nose-only exposed to a single 4-hour session of 10 ppm NA (U.S. Occupational Safety and Health Administration-established exposure limit for occupational settings) or high-efficiency particulate air-filtered air (sham-exposure control) in an Oro-Nasal and Respiratory Exposure System (CH Technologies, Westwood, NJ).…”

“…Several P450 isoforms with the ability to metabolize NA are also identified in the human liver, including CYP1A2, CYP2A6, CYP3A4, and CYP2D6 (Cho et al, 2006;Shimada et al, 2016). Hepatic P450mediated NA metabolism has a major impact on the in vivo disposition of inhaled or intraperitoneally administered NA, as indicated by studies comparing wild type (WT) and liver-Cpr-null (LCN) mice (Li et al, 2011;Kovalchuk et al, 2017). However, both hepatic and extrahepatic P450-mediated NA metabolism also contributed to toxicity in lung airways after inhalation exposure to NA at occupationally relevant concentrations (Kovalchuk et al, 2017).…”

“…Hepatic P450mediated NA metabolism has a major impact on the in vivo disposition of inhaled or intraperitoneally administered NA, as indicated by studies comparing wild type (WT) and liver-Cpr-null (LCN) mice (Li et al, 2011;Kovalchuk et al, 2017). However, both hepatic and extrahepatic P450-mediated NA metabolism also contributed to toxicity in lung airways after inhalation exposure to NA at occupationally relevant concentrations (Kovalchuk et al, 2017). These seemingly opposing actions of hepatic P450-mediated NA metabolism make it complicated to predict consequences of alterations in hepatic NA metabolism on risks of lung toxicity.…”