Psychophysiological stress: a significant parameter in drug pharmacokinetics

Age-related modifications in CYP-dependent drug metabolism: role of stress

Accumulating clinical evidence indicates extensive inter-individual variations in the effectiveness and adverse effects of standard treatment protocols, which are largely attributed to the multifactorial regulation of the hepatic CYP-dependent drug metabolism that is connected with either transcriptional or post-translational modifications. Age and stress belong to the most important factors in CYP gene regulation. Alterations in neuroendocrine responses to stress, which are associated with modified hypothalamo-pituitary-adrenal axis function, usually accompany ageing. In this light, ageing followed by a decline of the functional integrity of organs, including liver, a failure in preserving homeostasis under stress, increased morbidity and susceptibility to stress, among others, holds a determinant role in the CYP-catalyzed drug metabolism and thus, in the outcome and toxicity of pharmacotherapy. Modifications in the drug metabolizing capacity of the liver with age have been reported and in particular, a decline in the activity of the main CYP isoforms in male senescent rats, indicating decreased metabolism and higher levels of the drug-substrates in their blood. These factors along with the restricted experience in the use of the most medicines in childhood and elderly, could explain at an extent the inter-individual variability in drug efficacy and toxicity outcomes, and underscore the necessity of designing the treatment protocols, accordingly.

Quantitative determination of LY-404,039, a metabotropic glutamate 2/3 receptor agonist, in rat plasma using chemical derivatization and HPLC-MRM/MS

A rapid, selective and sensitive method was developed and validated for the determination of LY-404,039 concentration in rat plasma using a butylation derivatization step to improve chromatographic characteristics and enhance signal intensity. The method consisted of a protein precipitation extraction followed by derivatization with butanol/HCl and analysis by high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The separation was achieved using a 100 × 2.1 mm (2.6 μm) Thermo Scientific Accucore RP-MS column combined with an isocratic mobile phase composed of 40:60 acetonitrile-0.1% formic acid in water. An analytical range of 2.0-1,000 ng/ml was validated and used to quantify LY-404,039 in rat plasma. The novel method met all of the requirements of specificity, sensitivity, linearity, precision, accuracy and stability. A pharmacokinetic study was performed in rats and the novel analytical method was used as a routine analysis method to provide enhanced measurements of plasma concentrations of LY-404,039. The plasma pharmacokinetic results indicate very short terminal half-life (0.27 h ± 0.8) and high clearance (0.97 L/h/kg ± 0.12), suggesting that LY-404,039 is rapidly eliminated in the rat. Dose-dependent pharmacokinetics were observed following subcutaneous administration of LY-404,039 at doses of 0.1, 0.3 and 1.0 mg/kg.

The role of cytochromes P450 in metabolism of selected antidepressants and anxiolytics under psychological stress

In today's modern society, it seems to be more and more challenging to cope with life stresses. The effect of psychological stress on emotional and physical health can be devastating, and increased stress is associated with increased rates of heart attack, hypertension, obesity, addiction, anxiety and depression. This review focuses on the possibility of an influence of psychological stress on the metabolism of selected antidepressants (TCAs, SSRIs, SNRIs, SARIs, NDRIs a MMAs) and anxiolytics (benzodiazepines and azapirone), as patients treated with antidepressants and/or anxiolytics can still suffer from psychological stress. Emphasis is placed on the drug metabolism mediated by the enzymes of Phase I, typically cytochromes P450 (CYPs), which are the major enzymes involved in drug metabolism, as the majority of psychoactive substances are metabolized by numerous CYPs (such as CYP1A2, CYP2B6, CYP2C19, CYP2C9, CYP2A6, CYP2D6, CYP3A4). As the data on the effect of stress on human enzymes are extremely rare, modulation of the efficacy and even regulation of the biotransformation pathways of drugs by psychological stress can be expected to play a significant role, as there is increasing evidence that stress can alter drug metabolism, hence there is a risk of less effective drug metabolism and increased side effects.

The mechanisms of interactions of psychotropic drugs with liver and brain cytochrome P450 and their significance for drug effect and drug-drug interactions

Cytochrome P450 (CYP) plays an important role in psychopharmacology. While liver CYP enzymes are responsible for the biotransformation of psychotropic drugs, brain CYP enzymes are involved in the local metabolism of these drugs and endogenous neuroactive substances, such as neurosteroids, and in alternative pathways of neurotransmitter biosynthesis including dopamine and serotonin. Recent studies have revealed a relation between the brain nervous system and cytochrome P450, indicating that CYP enzymes metabolize endogenous neuroactive substances in the brain, while the brain nervous system is engaged in the central neuroendocrine and neuroimmune regulation of cytochrome P450 in the liver. Therefore, the effect of neuroactive drugs on cytochrome P450 should be investigated not only in vitro, but also at in vivo conditions, since only in vivo all mechanisms of drug-enzyme interaction can be observed, including neuroendocrine and neuroimmune modulation. Psychotropic drugs can potentially affect cytochrome P450 via a number of mechanisms operating at the level of the nervous, hormonal and immune systems, and the liver. Their effect on cytochrome P450 in the brain is often different than in the liver and region-dependent. Since psychotropic drugs can affect cytochrome P450 both in the liver and brain, they can modify their own pharmacological effect at both pharmacokinetic and pharmacodynamic level. The article describes the mechanisms by which psychotropic drugs can change the expression/activity of cytochrome P450 in the liver and brain, and discusses the significance of those mechanisms for drug action and drug-drug interactions. Moreover, the brain CYP2D6 is considered as a potential target for psychotropics.

Oleuropein-Induced Acceleration of Cytochrome P450-Catalyzed Drug Metabolism: Central Role for Nuclear Receptor Peroxisome Proliferator-Activated Receptor α

Oleuropein (OLE), the main constituent of Olea europaea, displays pleiotropic beneficial effects in health and disease, which are mainly attributed to its anti-inflammatory and cardioprotective properties. Several food supplements and herbal medicines contain OLE and are available without a prescription. This study investigated the effects of OLE on the main cytochrome P450s (P450s) catalyzing the metabolism of many prescribed drugs. Emphasis was given to the role of peroxisome proliferator-activated receptor α (PPARα), a nuclear transcription factor regulating numerous genes including P450s. 129/Sv wild-type and Ppara-null mice were treated with OLE for 6 weeks. OLE induced Cyp1a1, Cyp1a2, Cyp1b1, Cyp3a14, Cyp3a25, Cyp2c29, Cyp2c44, Cyp2d22, and Cyp2e1 mRNAs in liver of wild-type mice, whereas no similar effects were observed in Ppara-null mice, indicating that the OLE-induced effect on these P450s is mediated by PPARα. Activation of the pathways related to phosphoinositide 3-kinase/protein kinase B (AKT)/forkhead box protein O1, c-Jun N-terminal kinase, AKT/p70, and extracellular signal-regulated kinase participates in P450 induction by OLE. These data indicate that consumption of herbal medicines and food supplements containing OLE could accelerate the metabolism of drug substrates of the above-mentioned P450s, thus reducing their efficacy and the outcome of pharmacotherapy. Therefore, OLE-induced activation of PPARα could modify the effects of drugs due to their increased metabolism and clearance, which should be taken into account when consuming OLE-containing products with certain drugs, in particular those of narrow therapeutic window. SIGNIFICANCE STATEMENT: This study indicated that oleuropein, which belongs to the main constituents of the leaves and olive drupes of Olea europaea, induces the synthesis of the major cytochrome P450s (P450s) metabolizing the majority of prescribed drugs via activation of peroxisome proliferator-activated receptor α. This effect could modify the pharmacokinetic profile of co-administered drug substrates of the P450s, thus altering their therapeutic efficacy and toxicity.

The Influence of Long-Term Treatment with Asenapine on Liver Cytochrome P450 Expression and Activity in the Rat. The Involvement of Different Mechanisms

Therapy of schizophrenia requires long-term treatment with a relevant antipsychotic drug to achieve a therapeutic effect. The aim of the present study was to investigate the influence of prolonged treatment with the atypical neuroleptic asenapine on the expression and activity of rat cytochrome P450 (CYP) in the liver. The experiment was carried out on male Wistar rats. Asenapine (0.3 mg/kg s.c.) was administered for two weeks. The levels of CYP mRNA protein and activity were determined in the liver and hormone concentrations were measured in the pituitary gland and blood serum. Asenapine significantly decreased the activity of CYP1A (caffeine 8-hydroxylation and 3-N-demethylation), CYP2B, CYP2C11 and CYP3A (testosterone hydroxylation at positions 16β; 2α and 16α; 2β and 6β, respectively). The neuroleptic did not affect the activity of CYP2A (testosterone 7α-hydroxylation), CYP2C6 (warfarin 7-hydroxylation) and CYP2E1 (chlorzoxazone 6-hydroxylation). The mRNA and protein levels of CYP1A2, CYP2B1, CYP2C11 and CYP3A1 were decreased, while those of CYP2B2 and CYP3A2 were not changed. Simultaneously, pituitary level of growth hormone-releasing hormone and serum concentrations of growth hormone and corticosterone were reduced, while that of triiodothyronine was enhanced. In conclusion, chronic treatment with asenapine down-regulates liver cytochrome P450 enzymes, which involves neuroendocrine mechanisms. Thus, chronic asenapine treatment may slow the metabolism of CYP1A, CYP2B, CYP2C11 and CYP3A substrates (steroids and drugs). Since asenapine is metabolized by CYP1A and CYP3A, the neuroleptic may inhibit its own metabolism, therefore, the plasma concentration of asenapine in patients after prolonged treatment may be higher than expected based on a single dose.

Circadian Effects of Drug Responses

Circadian rhythms describe physiological systems that repeat themselves with a cycle of approximately 24 h. Our understanding of the cellular and molecular origins of these oscillations has improved dramatically, allowing us to appreciate the significant role these oscillations play in maintaining physiological homeostasis. Circadian rhythms allow living organisms to predict and efficiently respond to a dynamically changing environment, set by repetitive day/night cycles. Since circadian rhythms underlie almost every aspect of human physiology, it is unsurprising that they also influence the response of a living organism to disease, stress, and therapeutics. Therefore, not only do the mechanisms that maintain health and disrupt homeostasis depend on our internal circadian clock, but also the way drugs are perceived and function depends on these physiological rhythms. We present a holistic view of the therapeutic process, discussing components such as disease state, pharmacokinetics, and pharmacodynamics, as well as adverse reactions that are critically affected by circadian rhythms. We outline challenges and opportunities in moving toward personalized medicine approaches that explore and capitalize on circadian rhythms for the benefit of the patient.

Pharmacokinetics of Intravenous, Intramuscular, Oral, and Transdermal Administration of Flunixin Meglumine in Pre-wean Piglets

Castration and tail-docking of pre-wean piglets are common procedures that are known to induce pain and would benefit from pain mitigation. Flunixin meglumine (FM) is a non-steroidal anti-inflammatory drug currently approved in the United States for pyrexia in swine and lameness pain in cattle. The objective of this study was to establish the pharmacokinetic (PK) parameters resulting from intravenous (IV), intramuscular (IM), oral (PO) and transdermal (TD) administration of FM in pre-wean piglets. FM was administered to thirty-nine pre-wean piglets at a target dose of 2.2 mg/kg for IV and IM and 3.3 mg/kg for PO and TD route. Plasma was collected at twenty-seven time points from 0 to 9 days after FM administration and concentrations were determined using ultra-high performance liquid chromatography coupled with mass spectrometry (UPLC-MS). Pharmacokinetic data were analyzed using noncompartmental analysis (NCA) methods and nonlinear mixed-effects (NLME). Initial plasma concentration for IV (C₀) 11,653 μg/L and mean peak plasma concentrations (C_max) 6,543 μg/L (IM), 4,883 μg/L (PO), and 31.5 μg/L (TD) were measured. The time points of peak FM concentrations (t_max) were estimated 30 min, 1 h, and 24 h for IM, PO, and TD, respectively. The bioavailability (F) of PO and IM FM was estimated at >99%, while the bioavailability of TD FM was estimated to be 7.8%. The reported C_max of FM after IM and PO administration is consistent with therapeutic concentration ranges that mitigate pain in other species and adult pigs. However, the low estimated concentration of FM after TD dosing is not expected to mitigate pain in pre-wean piglets. The low F of TD FM suggests that expanding the surface area of application is unlikely to be sufficient to establish an effective TD dose for pain, while the high bioavailability for PO FM should allow for an effective dose regimen to be established.

The effects of agomelatine and imipramine on liver cytochrome P450 during chronic mild stress (CMS) in the rat

BACKGROUND

The aim of our research was to determine the effects of chronic treatment with the atypical antidepressant agomelatine on the expression and activity of liver cytochrome P450 (CYP) in the chronic mild stress (CMS) model of depression, and to compare the results with those obtained for the first-generation antidepressant imipramine.

METHODS

Male Wistar rats were subjected to CMS for 7 weeks. Imipramine (10 mg/kg ip/day) or agomelatine (40 mg/kg ip/day) was administered to nonstressed or stressed animals for 5 weeks (weeks 3-7 of CMS). The levels of cytochrome P450 mRNA, protein and activity were measured in the liver.

RESULTS

Agomelatine and imipramine produced different broad-spectrum effects on cytochrome P450. Like imipramine, agomelatine increased the expression/activity of CYP2B and CYP2C6, and decreased the CYP2D activity. Unlike imipramine, agomelatine raised the expression/activity of CYP1A, CYP2A and reduced that of CYP2C11 and CYP3A. CMS modified the effects of antidepressants at transcriptional/posttranscriptional level; however, the enzyme activity in stressed rats remained similar to that in nonstressed animals. CMS alone decreased the CYP2B1 mRNA level and increased that of CYP2C11.

CONCLUSION

We conclude the following: (1) the effects of agomelatine and imipramine on cytochrome P450 are different and involve both central and peripheral regulatory mechanisms, which implicates the possibility of drug-drug interactions; (2) CMS influences the effects of antidepressants on cytochrome P450 expression, but does not change appreciably their effects on the enzyme activity. This suggests that the rate of antidepressant drug metabolism under CMS is similar to that under normal conditions.

Quantitative proteomic analysis of the liver reveals antidepressant potential protein targets of Sinisan in a mouse CUMS model of depression

In traditional Chinese medicine, the role of the liver in depression is highly valued, and liver-relieving drugs, such as Sinisan, are often used to treat depression; however, the mechanism whereby these drugs work remains unclear. The present study aimed to reveal possible antidepressant mechanisms of Sinisan (SNS) by analyzing hepatic proteomics in chronic unpredictable mild stress (CUMS) mice. Using the CUMS mouse model of depression, the antidepressant effects of SNS were assessed by the sucrose preference test (SPT) and forced swimming test (FST). Hepatic differentially expressed proteins (DEPs) after SNS treatment were investigated by tandem mass tag (TMT) based quantitative proteomics analysis. Then, a bioinformatics analysis of DEPs was conducted through hierarchical clustering, Venn analysis, Gene Ontology (GO) annotation enrichment, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment. DEP genes were further validated by quantitative real-time polymerase chain reaction (qRT-PCR) analysis and western blotting. Behavioral results demonstrated that SNS significantly increased sucrose intake in SPT and shortened the immobility time in FST in model mice. Eighty-two DEPs were identified, including 37 upregulated and 45 downregulated proteins, between model and SNS groups. Enrichment analysis of GO annotations indicated that SNS primarily maintained cellular iron ion homeostasis by iron ion transportation and regulated expression of some extracellular structural proteins for oxidation-reduction processes. KEGG and Venn analysis showed that mineral absorption, steroid hormone biosynthesis and metabolism might be the principal pathways through which SNS acts on depression. Furthermore, several proteins involved in the biosynthesis and metabolism of steroid hormone pathways were significantly up/downregulated by SNS, including CYP2B19, CYP7B1 (validated by qRT-PCR) and HSD3b5 (validated by qRT-PCR and western blotting). Our results indicate that SNS plays important roles in antidepressant actions by restoring DEPs, resulting in the biosynthesis and metabolism of steroid hormones. The current results provide novel perspectives for revealing potential protein targets of SNS in depression.

Epigallocatechin-3-gallate protects immunity and liver drug-metabolism function in mice loaded with restraint stress

(-)-Epigallocatechin-3-gallate (EGCG) is the most abundant polyphenolic compound present in green tea and has been shown to possess bio-activities. In this study, we investigated the protective effects of EGCG against restraint stress (RS)-induced liver injury and immunosuppression. EGCG (10, 20 and 40 mg/kg) was orally administered to mice daily for 7 days before modeling the restraint stress. lood, liver and broncho-alveolar lavage fluid (BALF) samples were collected and tested. We found that EGCG significantly reduced the release of stress hormones to weak restraint stress response. EGCG effectively improved hepatic damage by decreas the serum levels of alanine aminotransaminase (ALT) and aspartate transaminase (AST) in restraint-challenged mice. Furthermore, EGCG also significantly prevented the release of H₂O₂, NOS and 8-isoprostane, and reduced the levels of interleukin (IL)-1β, IL-2,and IL-6 restrained mice. EGCG can normal the level of cytochrome P450 (CYP450) 1A2, 2D22, 2E1 and 3A11 that induced by restraint stress., the inhibition status of T cells subsets in serum and gA in BALF were significantly relieved EGCG pretreatment. Taken together, our data suggest that EGCG possesse hepatic- and immune-protective properties against restraint stress through its anti-oxidant, anti-inflammatory and immunomodulatory activities.

Modeling inter-sex and inter-individual variability in response to chronopharmacological administration of synthetic glucocorticoids

Endogenous glucocorticoids have diverse physiological effects and are important regulators of metabolism, immunity, cardiovascular function, musculoskeletal health and central nervous system activity. Synthetic glucocorticoids have received widespread attention for their potent anti-inflammatory activity and have become an important class of drugs used to augment endogenous glucocorticoid activity for the treatment of a host of chronic inflammatory conditions. Chronic use of synthetic glucocorticoids is associated with a number of adverse effects as a result of the persistent dysregulation of glucocorticoid sensitive pathways. A failure to consider the pronounced circadian rhythmicity of endogenous glucocorticoids can result in either supraphysiological glucocorticoid exposure or severe suppression of endogenous glucocorticoid secretion, and is thought be a causal factor in the incidence of adverse effects during chronic glucocorticoid therapy. Furthermore, given that synthetic glucocorticoids have potent feedback effects on the hypothalamic-pituitary-adrenal (HPA) axis, physiological factors which can give rise to individual variability in HPA axis activity such as sex, age, and disease state might also have substantial implications for therapy. We use a semi-mechanistic mathematical model of the rodent HPA axis to study how putative sex differences and individual variability in HPA axis regulation can influence the effects of long-term synthetic exposure on endogenous glucocorticoid circadian rhythms. Model simulations suggest that for the same drug exposure, simulated females exhibit less endogenous suppression than males considering differences in adrenal sensitivity and negative feedback to the hypothalamus and pituitary. Simulations reveal that homeostatic regulatory variability and chronic stress-induced regulatory adaptations in the HPA axis network can result in substantial differences in the effects of synthetic exposure on the circadian rhythm of endogenous glucocorticoids. In general, our results provide insight into how the dosage and exposure profile of synthetic glucocorticoids could be manipulated in a personalized manner to preserve the circadian dynamics of endogenous glucocorticoids during chronic therapy, thus potentially minimizing the incidence of adverse effects associated with long-term use of glucocorticoids.

The engagement of brain cytochrome P450 in the metabolism of endogenous neuroactive substrates: a possible role in mental disorders

The current state of knowledge indicates that the cerebral cytochrome P450 (CYP) plays an important role in the endogenous metabolism in the brain. Different CYP isoenzymes mediate metabolism of many endogenous substrates such as monoaminergic neurotransmitters, neurosteroids, cholesterol, vitamins and arachidonic acid. Therefore, these enzymes may affect brain development, susceptibility to mental and neurodegenerative diseases and may contribute to their pathophysiology. In addition, they can modify the therapeutic effects of psychoactive drugs at the place of their target action in the brain, where the drugs can act by affecting the metabolism of endogenous substrates. The article focuses on the role of cerebral CYP isoforms in the metabolism of neurotransmitters, neurosteroids, and cholesterol, and their possible involvement in animal behavior, as well as in stress, depression, schizophrenia, cognitive processes, learning, and memory. CYP-mediated alternative pathways of dopamine and serotonin synthesis may have a significant role in the local production of these neurotransmitters in the brain regions where the disturbances of these neurotransmitter systems are observed in depression and schizophrenia. The local alternative synthesis of neurotransmitters may be of great importance in the brain, since dopamine and serotonin do not pass the blood-brain barrier and cannot be supplied from the periphery. In vitro studies indicate that human CYP2D6 catalyzing dopamine and serotonin synthesis is more efficient in these reactions than the rat CYP2D isoforms. It suggests that these alternative pathways may have much greater significance in the human brain but confirmation of these assumptions requires further studies.

In Vivo Toxicity of Solasonine and Its Effects on cyp450 Family Gene Expression in the Livers of Male Mice from Four Strains

Solasonine was reported to inhibit tumour cell growth in several different models. The in vivo toxicity of solasonine, the effects of genetic background on its toxicity, and its possible roles in regulating the expression of cyp450 family genes were still unclear and required characterisation. Here, Horn’s assays were performed on male mice from four different strains, and the expression of cyp450 family genes in their livers was examined by RT-PCR and ELISA. Mice treated by intraperitoneal injection with high levels of solasonine showed immediate post-excitatory depression, intraperitoneal tissue adhesion, and dissolving of cells in the liver. Furthermore, these four mouse strains showed different toxicological sensitivity to solasonine. The strains, in decreasing order of LD50 value, rescuing speed of body weight, and more severe pathological symptoms, were KM, ICR, C57BL/6, and BALB/c. Interestingly, more cyp450 genes were downregulated at the mRNA and/or protein level in the livers of male mice from C57BL/6 or BALB/c strains than those from KM or ICR strains. These results suggest that (1) Solasonine has hepatic toxicity and downregulates cyp450 genes expression at transcriptional and/or post-transcriptional levels; (2) Genetic background is an important factor which can affect the in vivo toxicity; (3) Downregulation of cyp450 gene expression in the liver may be a clue to help understand whether or not a given strain is sensitive to solasonine; (4) Influences on the expression of cyp450 genes should be considered when using solasonine alone, or in combination with other drugs.

Chronic unpredicted mild stress-induced depression alter saxagliptin pharmacokinetics and CYP450 activity in GK rats

Background. This study was to explore the pharmacokinetics of saxagliptin (Sax) in Goto–Kakizaki (GK) rats complicated with depression induced by chronic unpredicted mild stress (CUMS). The comorbidity of diabetic patients with depression is becoming more and more epidemic. Whether depression mental disorder alters the pharmacokinetics of hypoglycemic drugs in diabetes patients is not clear.

Methods. Five-week-old male GK rats were kept in the cage for 7 weeks in a specific pathogen free (SPF)-grade lab until the emergence of diabetes and were then divided into two groups: control group and depression model group. Rats in the CUMS-induced depression group were exposed to a series of stressors for 8 weeks. Plasma serotonin and dopamine levels and behavior of open-field test were used to confirm the establishment of the depression model. All rats were given 0.5 mg/kg Sax orally after 8 weeks and blood samples were collected at different time points. The Sax concentration was assayed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The CYP450 activity of the liver microsomes was determined by using cocktails of probe drugs in which the activities of CYP enzymes were assessed through the determination of the production of the probe drugs.

Results. Statistically significant differences in Sax pharmacokinetics were observed for area under curve, clearance, peak concentration, peak time and mean residence time between the depression rats and the control rats, while no statistical differences were observed for half-time and distribution volume by HPLC-MS/MS analysis. The CYP450 activity had different changes in the depression group.

Conclusions. These results indicated that CUMS-induced depression alters the drug metabolic process of Sax and CYP450 activity of the liver microsomal enzymes in GK rats.

Dopamine D2-Receptor Antagonists Down-Regulate CYP1A1/2 and CYP1B1 in the Rat Liver

Dopaminergic systems regulate the release of several hormones including growth hormone (GH), thyroid hormones, insulin, glucocorticoids and prolactin (PRL) that play significant roles in the regulation of various Cytochrome P450 (CYP) enzymes. The present study investigated the role of dopamine D₂-receptor-linked pathways in the regulation of CYP1A1, CYP1A2 and CYP1B1 that belong to a battery of genes controlled by the Aryl Hydrocarbon Receptor (AhR) and play a crucial role in the metabolism and toxicity of numerous environmental toxicants. Inhibition of dopamine D₂-receptors with sulpiride (SULP) significantly repressed the constitutive and benzo[a]pyrene (B[a]P)-induced CYP1A1, CYP1A2 and CYP1B expression in the rat liver. The expression of AhR, heat shock protein 90 (HSP90) and AhR nuclear translocator (ARNT) was suppressed by SULP in B[a]P-treated livers, whereas the AhRR expression was increased by the drug suggesting that the SULP-mediated repression of the CYP1 inducibility is due to inactivation of the AhR regulatory system. At signal transduction level, the D₂-mediated down-regulation of constitutive CYP1A1/2 and CYP1B1 expression appears to be mediated by activation of the insulin/PI3K/AKT pathway. PRL-linked pathways exerting a negative control on various CYPs, and inactivation of the glucocorticoid-linked pathways that positively control the AhR-regulated CYP1 genes, may also participate in the SULP-mediated repression of both, the constitutive and induced CYP1 expression. The present findings indicate that drugs acting as D₂-dopamine receptor antagonists can modify several hormone systems that regulate the expression of CYP1A1, CYP1A2 and CYP1B1, and may affect the toxicity and carcinogenicity outcome of numerous toxicants and pre-carcinogenic substances. Therefore, these drugs could be considered as a part of the strategy to reduce the risk of exposure to environmental pollutants and pre-carcinogens.