Role of signalling systems in the effects of dietary factors on the expression of mammalian CYPs

Dietary lipids differentially modulate the initiation of experimental breast carcinogenesis through their influence on hepatic xenobiotic metabolism and DNA damage in the mammary gland

Breast cancer is the most common malignancy among women worldwide. In addition to reproductive factors, environmental factors such as nutrition and xenobiotic exposure have a role in the etiology of this malignancy. A stimulating and a potentially protective effect on experimental breast cancer has been previously described for high corn oil and high extra-virgin olive oil diets, respectively. This work investigates the effect of these lipids on the metabolism of 7,12-dimethylbenz(a)anthracene (DMBA), a polycyclic aromatic hydrocarbon that can initiate carcinogenesis and its consequences in an experimental rat breast cancer model. The PUFA n-6-enriched diet increased expression of Phase I enzymes prior to DMBA administration and raised the activity of CYP1s in the hours immediately after induction, while reducing the activity of Phase II enzymes, mainly NQO1. The levels of reactive metabolites measured in plasma by GC-MS and DMBA-DNA adducts in the mammary gland of the animals fed the high corn oil diet were also higher than in the other groups. On the other hand, the high extra-virgin olive oil diet and the control low-fat diet exhibited better coordinated Phase I and Phase II activity, with a lower production of reactive metabolites and less DNA damage in the mammary gland. The concordance between these effects and the different efficacy of the carcinogenesis process due to the dietary treatment suggest that lipids may differently modify mammary gland susceptibility or resistance to cancer initiation over the exposure to environmental carcinogens.

SUMMARY

Dietary lipids influence the initiation of DMBA-induced mammary cancer through the modulation of liver xenobiotic metabolism, formation of reactive metabolites and subsequent DNA damage in the target tissue.

EPMA position paper in cancer: current overview and future perspectives

At present, a radical shift in cancer treatment is occurring in terms of predictive, preventive, and personalized medicine (PPPM). Individual patients will participate in more aspects of their healthcare. During the development of PPPM, many rapid, specific, and sensitive new methods for earlier detection of cancer will result in more efficient management of the patient and hence a better quality of life. Coordination of the various activities among different healthcare professionals in primary, secondary, and tertiary care requires well-defined competencies, implementation of training and educational programs, sharing of data, and harmonized guidelines. In this position paper, the current knowledge to understand cancer predisposition and risk factors, the cellular biology of cancer, predictive markers and treatment outcome, the improvement in technologies in screening and diagnosis, and provision of better drug development solutions are discussed in the context of a better implementation of personalized medicine. Recognition of the major risk factors for cancer initiation is the key for preventive strategies (EPMA J. 4(1):6, 2013). Of interest, cancer predisposing syndromes in particular the monogenic subtypes that lead to cancer progression are well defined and one should focus on implementation strategies to identify individuals at risk to allow preventive measures and early screening/diagnosis. Implementation of such measures is disturbed by improper use of the data, with breach of data protection as one of the risks to be heavily controlled. Population screening requires in depth cost-benefit analysis to justify healthcare costs, and the parameters screened should provide information that allow an actionable and deliverable solution, for better healthcare provision.

DNA methylation dynamics in the hepatic CYP3A4 gene promoter

The CYP3A4 gene, encoding the major drug metabolizing enzyme in humans, exhibits a high interindividual variation in hepatic expression that can lead to interindividual differences in drug metabolism and associated adverse drug effects. Much of the interindividual variability in CYP3A4 remains unexplained. In the present study we investigated the role of DNA methylation in influencing the interindividual CYP3A4 expression. Individual CpG methylation within the ∼12 kb CYP3A4 regulatory region was investigated in 72 adult as well as in 7 fetal human livers using bisulfite sequencing. We identified highly variable CpG methylation sites in adult livers, which correspond to important CYP3A4 transcription factor binding sites including the proximal promoter, XREM and CLEM4 as well as in separate C/EBP and HNF4α binding regions. CpG hypermethylation within these regulatory regions was observed in fetal livers when compared to adult livers. This data suggests that dynamic DNA methylation elements are likely associated with key regulatory CYP3A4 promoter regions and may potentially contribute to the commonly observed interindividual expression of CYP3A4 as well as the hepatic developmental shift in its expression. The findings provide novel insight to CYP3A4 regulation with possible implications for understanding interindividual differences in drug response.

Nutrition and human health from a sex-gender perspective

Nutrition exerts a life-long impact on human health, and the interaction between nutrition and health has been known for centuries. The recent literature has suggested that nutrition could differently influence the health of male and female individuals. Until the last decade of the 20th century, research on women has been neglected, and the results obtained in men have been directly translated to women in both the medicine and nutrition fields. Consequently, most modern guidelines are based on studies predominantly conducted on men. However, there are many sex-gender differences that are the result of multifactorial inputs, including gene repertoires, sex steroid hormones, and environmental factors (e.g., food components). The effects of these different inputs in male and female physiology will be different in different periods of ontogenetic development as well as during pregnancy and the ovarian cycle in females, which are also age dependent. As a result, different strategies have evolved to maintain male and female body homeostasis, which, in turn, implies that there are important differences in the bioavailability, metabolism, distribution, and elimination of foods and beverages in males and females. This article will review some of these differences underlying the impact of food components on the risk of developing diseases from a sex-gender perspective.

Quantitative shot-gun proteomics and MS-based activity assay for revealing gender differences in enzyme contents for rat liver microsome

Liver microsomes are subcellular fractions that contain many metabolizing enzymes for drugs and endogeneous compounds. Some of these enzymes are regulated by sex hormonal control and exhibit sex-dependent expression pattern and metabolizing speed. Studying these enzymes, however, are complicated by the presence of isoforms such as cytochrome P450 (CYP450), which families share more than 50% amino acid identities. In this study, we applied quantitative shot-gun proteomics approach coupled with stable-isotope dimethyl labeling, two-dimensional reversed-phase peptide separation and tandem mass spectrometry (MS) to explore the gender-dependent expression of rat liver microsomal proteins. A total of 391 proteins were identified and quantified by this approach, and 56% of quantified proteins were enzymes. Although shot-gun approach is rarely used for identifying protein isoforms, we identified 53 isoforms by at least one unique peptide including 21 isoforms of CYP450s. Moreover, by quantitative and statistics assessment, we were able to classify them into 28 male dominant enzymes including CYP2C12 CYP2C11, CYP2C13, CYP2B3, CYP2C11, CYP2C70 and CYP3A2 which are known to be male specific, 21 female dominant enzymes including CYP2A1, CYP2C7, CYP2C12, CYP2D26, alcohol dehydrogenase 1, carboxylesterase 3, glutathione S-transferase, liver carboxylesterase 4, UDP-glucuronosyltransferase 2B1, and glyceraldehyde-3-phosphate dehydrogenase which are known to be female specific; and 125 sex-independent enzymes. However, most of the sex specificities revealed from this study, such as the male specificity of CYP2D1, were novel and not yet reported. We then conducted a mass spectrometry-multiple reaction mode (MS-MRM) based enzyme activity method to determine the catalyzing rate of CYP2D1 in male and female liver microsomes using carteolol as its specific substrate. The reaction rate catalyzed by CYP2D1 in female rats was determined to differ significantly with the rate in male rats. Moreover, the ratio (female/male) of reaction rate (0.68) was found to correlate with their relative protein abundance (0.72). This study revealed novel sex dependences of many rat liver enzymes and also demonstrated a unique MS-based analytical platform that could identify novel iso-enzymes and further quantify their abundance and enzyme activity.

Enhanced expression and glucocorticoid-inducibility of hepatic cytochrome P450 3A involve recruitment of the pregnane-X-receptor to promoter elements in rats fed soy protein isolate

Previous studies and Expt. 1 of the current study demonstrate that diets made with soy protein isolate (SPI) enhance the glucocorticoid-inducibility of hepatic cytochrome P450 (CYP)3A-dependent monooxygenase activities (P < 0.05) compared with diets made with casein (CAS). To determine the underlying molecular mechanism, in a second experiment, we analyzed the time course of dexamethasone (DEX)-induction of hepatic CYP3A mRNA expression on postnatal d (PND) 25 and PND60 in male and female rats fed SPI- or CAS-based diets. After 50 mg(/)kg DEX, CYP3A1 mRNA expression increased >200-fold in SPI-fed males and females at PND25 compared with a 100-fold increase in CAS-fed rats (P < 0.05). The DEX-induced increase in CYP3A1 mRNA in SPI-fed rats on PND60 was also greater than that in CAS-fed rats. The induction by DEX of CYP3A2 mRNA was 1- to 3-fold greater in rats fed SPI compared with those fed CAS on PND25 (P < 0.05). Quantitation of newly synthesized CYP3A1 RNA transcripts by nuclear run-on analysis demonstrated a greater rate of basal transcription in SPI-fed compared with CAS-fed rats on PND60 accompanied by greater binding of the pregnane X receptor (PXR) to a response element on the CYP3A1 promoter in SPI-fed compared with CAS-fed rats (P < 0.05). These data suggest that increased hepatic CYP3A expression and inducibility following SPI feeding involves recruitment of PXR to its response element and suggests that soy consumption has potential effects on metabolism and transport of a wide variety of drugs and on bile acid homeostasis via proteins regulated by this transcription factor.

Sex differences in the expression of hepatic drug metabolizing enzymes

Sex differences in pharmacokinetics and pharmacodynamics characterize many drugs and contribute to individual differences in drug efficacy and toxicity. Sex-based differences in drug metabolism are the primary cause of sex-dependent pharmacokinetics and reflect underlying sex differences in the expression of hepatic enzymes active in the metabolism of drugs, steroids, fatty acids and environmental chemicals, including cytochromes P450 (P450s), sulfotransferases, glutathione transferases, and UDP-glucuronosyltransferases. Studies in the rat and mouse liver models have identified more than 1000 genes whose expression is sex-dependent; together, these genes impart substantial sexual dimorphism to liver metabolic function and pathophysiology. Sex differences in drug metabolism and pharmacokinetics also occur in humans and are due in part to the female-predominant expression of CYP3A4, the most important P450 catalyst of drug metabolism in human liver. The sexually dimorphic expression of P450s and other liver-expressed genes is regulated by the temporal pattern of plasma growth hormone (GH) release by the pituitary gland, which shows significant sex differences. These differences are most pronounced in rats and mice, where plasma GH profiles are highly pulsatile (intermittent) in male animals versus more frequent (nearly continuous) in female animals. This review discusses key features of the cell signaling and molecular regulatory mechanisms by which these sex-dependent plasma GH patterns impart sex specificity to the liver. Moreover, the essential role proposed for the GH-activated transcription factor signal transducer and activator of transcription (STAT) 5b, and for hepatic nuclear factor (HNF) 4alpha, as mediators of the sex-dependent effects of GH on the liver, is evaluated. Together, these studies of the cellular, molecular, and gene regulatory mechanisms that underlie sex-based differences in liver gene expression have provided novel insights into the physiological regulation of both xenobiotic and endobiotic metabolism.