Compensatory changes in CYP expression in three different toxicology mouse models: CAR-null, Cyp3a-null, and Cyp2b9/10/13-null mice

Abstract

Targeted mutant models are common in mechanistic toxicology experiments investigating the absorption, metabolism, distribution, or elimination (ADME) of chemicals from individuals. Key models include those for xenosensing transcription factors and cytochrome P450s (CYP). Here we investigated changes in transcript levels, protein expression, and steroid hydroxylation of several xenobiotic detoxifying CYPs in constitutive androstane receptor (CAR)-null and two CYP-null mouse models that have subfamily members regulated by CAR; the Cyp3a-null and a newly described Cyp2b9/10/13-null mouse model. Compensatory changes in CYP expression that occur in these models may also occur in polymorphic humans, or may complicate interpretation of ADME studies performed using these models. The loss of CAR causes significant changes in several CYPs probably due to loss of CAR-mediated constitutive regulation of these CYPs. Expression and activity changes include significant repression of Cyp2a and Cyp2b members with corresponding drops in 6α- and 16β-testosterone hydroxylase activity. Further, the ratio of 6α-/15α-hydroxylase activity, a biomarker of sexual dimorphism in the liver, indicates masculinization of female CAR-null mice, suggesting a role for CAR in the regulation of sexually dimorphic liver CYP profiles. The loss of Cyp3a causes fewer changes than CAR. Nevertheless, there are compensatory changes including gender-specific increases in Cyp2a and Cyp2b. Cyp2a and Cyp2b were down-regulated in CAR-null mice, suggesting activation of CAR and potentially PXR following loss of the Cyp3a members. However, the loss of Cyp2b causes few changes in hepatic CYP transcript levels and almost no significant compensatory changes in protein expression or activity with the possible exception of 6α-hydroxylase activity. This lack of a compensatory response in the Cyp2b9/10/13-null mice is probably due to low CYP2B hepatic expression, especially in male mice. Overall, compensatory and regulatory CYP changes followed the order CAR-null > Cyp3a-null > Cyp2b-null mice.

Cyp2b‐Knockdown Mice Poorly Metabolize Corn Oil and Are Age‐Dependent Obese

“…Obesity, increased abdominal fat deposition, and increased serum triacylglycerols are all key symptoms of prediabetic conditions and associated with metabolic syndromes and indicate that the lack or inhibition of Cyp2b has metabolic consequences. Taken together, males with low Cyp2b levels appear to be more susceptible to age‐onset obesity even though they express less Cyp2b enzymes (Hernandez et al, ; Kumar et al, ).…”

“…Furthermore, db/db mice also show increased Car and Cyp2b10 expression (Yoshinari et al, 2006). Interestingly, the older Cyp2b-KD mice lost their RNAi-mediated Cyp2b repression and this may be lipid-mediated induction or compensation that is consistent with induction of Cyp2b members following exposure to corn oil (Finn et al, 2009), a high-fat diet (Leung et al, 2016;McGregor et al, 2013), or a compensatory mechanism due to changes in key metabolites (Hernandez et al, 2009b;Kumar et al, 2017;Mota et al, 2011). Taken together, Cyp2b9, Cyp2b10, and the transcription factors they are regulated by (Foxa2/CAR) are associated with obesity and age-onset obesity.…”

“…They are expressed in the kidney (Jarukamjorn et al, 2001), small intestine (Zhang et al, 2003), brain (Hersman and Bumpus, 2014;Johri et al, 2007), lungs (Hersman and Bumpus, 2014), heart (Isensee et al, 2007), testes, skeletal muscle (Finger et al, 2011), skin (Du et al, 2005;Keeney et al, 1998b), adipose (Yoshinari et al, 2004), and prostate (Kumagai et al, 2007). Five Cyp2b isoforms have been identified in mice (Cyp2b9, 2b10, 2b13, 2b19, and 2b23) compared to only one in humans (CYP2B6) (Kumar et al, 2017). However, only three Cyp2b isoforms are primarily expressed in the liver with Cyp2b9, Cyp2b10, and to a lesser extent Cyp2b13 being the major hepatic Cyp2b isoforms (Mota et al, 2010;Peng et al, 2012).…”

Use of Oral Citrulline Administration as a Mitigation Strategy for Fescue Toxicosis in Sheep

“…Western blots. A subset of lambs (n = 4/treatment) was selected for analysis of cytochrome P450 subfamily 3A (CYP3A) activity using 30 µg microsomal protein from neonatal livers according to the procedures of Kumar et al (2017). Due to the ability to recognize several proteins, CYP3A subfamily was assessed rather than individual proteins (Acevedo et al, 2005;Damiri et al, 2012).…”

Hepatic gene expression variations in response to high-fat diet-induced impaired glucose tolerance using RNAseq analysis in collaborative cross mouse population

“…A notable change is the additional reduction in Cyp2b13 in health versus disease. Based on a recent study using the Cyp2b9/10/13-null mouse model, CypB hepatic expression is lower in males, which might be mediated by the constitutive androstane receptor (CAR) (Kumar et al 2017). An additional gene with greater FC in diabetic condition is the Cyp7b1 gene, 7-alpha hydroxylase of steroid nucleus, playing a role in bile acid biosynthesis.…”