Phytosterols activating nuclear receptors are involving in steroid hormone-dependent cancers: Myth or fact?

Nuclear receptors (NRs) represent intracellular proteins that function as a signaling network of transcriptional factors to control genes in response to a variety of environmental, dietary, and hormonal stimulations or serve as orphan receptors lacking a recognized ligand. They also play an essential role in normal development, metabolism, cell growth, cell division, physiology, reproduction, and homeostasis and function as biological markers for tumor subclassification and as targets for hormone therapy. NRs, including steroid hormone receptors (SHRs), have been studied as tools to examine the fundamentals of transcriptional regulation within the development of mammals and human physiology, in addition to their links to disturbances. In this regard, it is widely recognized that aberrant NR signaling is responsible for the pathological growth of hormone-dependent tumors in response to SHRs dysregulation and consequently represents a potential therapeutic candidate in a range of diseases, as in the case of prostate cancer and breast cancer. On the other hand, phytosterols are a group of plant-derived compounds that act directly as ligands for NRs and have proven their efficacy in the management of diabetes, heart diseases, and cancers. However, these plants are not suggested in cases of hormone-dependent cancer since a certain group of plants contains molecules with a chemical structure similar to that of estrogens, which are known as phytoestrogens or estrogen-like compounds, such as lignans, coumestans, and isoflavones. Therefore, it remains an open and controversial debate regarding whether consuming a phytosterol-rich diet and adopting a vegetarian lifestyle like the Mediterranean diet may increase the risk of developing steroid hormone-dependent cancers by constitutively activating SHRs and thereby leading to tumor transformation. Overall, the purpose of this review is to better understand the relevant mechanistic pathways and explore epidemiological investigations in order to establish that phytosterols may contribute to the activation of NRs as cancer drivers in hormone-dependent cancers.

[A lipid exchange market : vectorial cholesterol transport by the protein OSBP]. / Un marché d'échange de lipides - Transport vectoriel du cholestérol par la protéine OSBP.

Cholesterol is synthesized in the endoplasmic reticulum (RE) and then transported to cellular compartments whose functions require high cholesterol levels. Here, we describe the mechanism by which cholesterol is transported from the RE to the trans-Golgi network (TGN) by the protein OSBP (Oxysterol-Binding Protein). OSBP has two complementary activities. First, it tethers the RE to the TGN by forming a contact site where the two membranes are about twenty nanometers away. Then, it exchanges RE cholesterol for a TGN lipid, phosphatidylinositol 4-phosphate (PI4P). Eventually, PI4P is hydrolyzed at the RE, making the exchange cycle irreversible. Thus, OSBP is at the center of a lipid exchange market where a transported cholesterol "costs" a PI4P. Antiviral or anti-cancer molecules target OSBP, suggesting the importance of the OSBP cycle in different physiopathological contexts. The general principles of this cycle are shared by other lipid-transfer proteins.

TITLE: Un marché d'échange de lipides - Transport vectoriel du cholestérol par la protéine OSBP. ABSTRACT: Le cholestérol est synthétisé dans le réticulum endoplasmique (RE) puis transporté vers les compartiments cellulaires dont la fonction en nécessite un taux élevé. Nous décrivons ici le mécanisme de transport du cholestérol du RE vers le réseau trans golgien (TGN) par la protéine OSBP (oxysterol binding protein). Celle-ci présente deux activités complémentaires : elle arrime les deux compartiments, RE et TGN, en formant un site de contact où les deux membranes sont à une vingtaine de nanomètres de distance ; puis elle échange le cholestérol du RE avec un lipide présent dans le TGN, le phosphatidylinositol 4-phosphate (PI4P). Dans le RE, le PI4P est hydrolysé, rendant le cycle d'échange irréversible. OSBP est donc au cœur d'un marché d'échange de lipides dans lequel un cholestérol transporté « coûte ¼ un PI4P. Des molécules à activités antivirales ou anticancéreuses ont pour cible OSBP, suggérant une importance dans différents contextes physiopathologiques du cycle d'OSBP, dont les bases générales sont partagées par d'autres protéines transporteurs de lipides.

Dose-dependent difference of nuclear receptors involved in murine liver hypertrophy by piperonyl butoxide.

Nuclear receptors play important roles in chemically induced liver hypertrophy in rodents. To clarify the involvement of constitutive androstane receptor (CAR) and other nuclear receptors in mouse liver hypertrophy induced by different doses of piperonyl butoxide (PBO), wild-type and CAR-knockout mice were administered PBO (200, 1,000, or 5,000 ppm) in the basal diet for 1 week. Increased liver weight and diffuse hepatocellular hypertrophy were observed at 5,000 ppm for both genotypes, accompanied by increased Cyp3a11 mRNA and CYP3A protein expression, suggesting that CAR-independent pathway, possibly pregnane X receptor (PXR), plays a major role in the induction of hypertrophy. Moreover, wild-type mice at 5,000 ppm showed enhanced hepatocellular hypertrophy and strong positive staining for CYP2B in the centrilobular area, suggesting the localized contribution of CAR. At 1,000 ppm, only wild-type mice showed liver weight increase and centrilobular hepatocellular hypertrophy concurrent with elevated Cyp2b10 mRNA expression and strong CYP2B staining, indicating that CAR was essential at 1,000 ppm. We concluded that high-dose PBO induced hypertrophy via CAR and another pathway, while lower dose of PBO induced a pathway mediated predominantly by CAR. The dose-responsiveness on liver hypertrophy is important for understanding the involvement of nuclear receptors.

Nigramide C is a natural agonist of human pregnane x receptor.

Pregnane X receptor (PXR) is known as a xenosensor, playing a key role in response to xenochemical stimuli. Activation of PXR enhanced expression of various drug-metabolizing enzymes and transporters such as cytochrome P450 3A4 (CYP3A4). During a screening of a natural compounds library for novel ligands of human xenosensing receptors by the mammalian one-hybrid assay, two cyclohexene-type amide alkaloids were isolated, with nigramide C (NigC) showing the most potent activation of human PXR (hPXR). NigC-mediated hPXR activation was enhanced by overexpression of steroid receptor coactivator 1 (SRC1), peroxisome proliferator-activated receptor γ, coactivator 1α, and protein arginine methyltransferase 1. A direct interaction between the ligand-binding domain of hPXR and the receptor interaction domain of SRC1 was observed. NigC induced the expression of endogenous CYP3A4 mRNA and protein in both cultured hepatoma cells and primary hepatocytes. However, in primary hepatocytes, the relative agonist activity of NigC was not as potent as that of rifampicin, probably because of lower metabolic stability of NigC in these cells. In conclusion, NigC was found to be an effective agonist of hPXR. NigC is a useful tool for investigation of hPXR function.

Calcium-calmodulin dependent protein kinase I from Macrobrachium nipponense: cDNA cloning and involvement in molting.

Calcium-calmodulin dependent protein kinase I is a component of a calmodulin-dependent protein kinase cascade and involved in many physiological processes. The full-length cDNA of calcium-calmodulin dependent protein kinase I (MnCaMKI) was cloned from the freshwater prawn Macrobrachium nipponense and its expression pattern during the molt cycle and after eyestalk ablation is described. The full-length cDNA of MnCaMKI is 3,262 bp in length and has an open reading frame (ORF) of 1,038 bp, encoding a 345 amino acid protein. The expression of MnCaMKI in three examined tissues was upregulated in the premolt stage of the molt cycle. Its expression was induced after eyestalk ablation (ESA): the highest expression level was reached 1 day after ESA in hepatopancreas, and 3 days after ESA in muscle. By dsRNA-mediated RNA interference assay, expression of MnCaMKI and ecydone receptor gene (MnEcR) was significantly decreased in prawns treated by injection of dsMnCaMKI, while expression of these two genes was also significantly decreased in prawns treated by injection of dsMnEcR, demonstrating a close correlation between the expression of these two genes. These results suggest that CaMKI in M. nipponense is involved in molting.

Pregnane X receptor (PXR)--a contributor to the diabetes epidemic?

Pregnane X receptor (PXR), a ligand-activated nuclear receptor, was originally identified as a regulator of drug and bile acid metabolism. Studies in experimental animals and humans within the last decade have revealed PXR as a regulator of energy metabolism repressing gluconeogenesis and hepatic lipid oxidation. The most recent in vivo studies demonstrate that PXR activation has a detrimental role in the regulation of glucose metabolism. The prevalence of many PXR agonists in low concentrations in our environments as well as the PXR-activating properties of numerous commonly used medications and herbal remedies may have unanticipated health effects. It could be speculated that, due to its dual role as a xenosensor and a regulator of energy metabolism, PXR, in concert with a mixture of PXR agonists in the environment, contributes to the present-day type 2 diabetes epidemic. With this hypothesis in mind, we review the current literature on PXR as a regulator of glucose and hepatic lipid metabolism and the association of exposure to PXR agonists with diabetes susceptibility.

Pregnane X receptor and yin yang 1 contribute to the differential tissue expression and induction of CYP3A5 and CYP3A4.

The hepato-intestinal induction of the detoxifying enzymes CYP3A4 and CYP3A5 by the xenosensing pregnane X receptor (PXR) constitutes a key adaptive response to oral drugs and dietary xenobiotics. In contrast to CYP3A4, CYP3A5 is additionally expressed in several, mostly steroidogenic organs, which creates potential for induction-driven disturbances of the steroid homeostasis. Using cell lines and mice transgenic for a CYP3A5 promoter we demonstrate that the CYP3A5 expression in these organs is non-inducible and independent from PXR. Instead, it is enabled by the loss of a suppressing yin yang 1 (YY1)-binding site from the CYP3A5 promoter which occurred in haplorrhine primates. This YY1 site is conserved in CYP3A4, but its inhibitory effect can be offset by PXR acting on response elements such as XREM. Taken together, the loss of YY1 binding site from promoters of the CYP3A5 gene lineage during primate evolution may have enabled the utilization of CYP3A5 both in the adaptive hepato-intestinal response to xenobiotics and as a constitutively expressed gene in other organs. Our results thus constitute a first description of uncoupling induction from constitutive expression for a major detoxifying enzyme. They also suggest an explanation for the considerable tissue expression differences between CYP3A5 and CYP3A4.

Irinotecan induces steroid and xenobiotic receptor (SXR) signaling to detoxification pathway in colon cancer cells.

BACKGROUND: Resistance to chemotherapy remains one of the principle obstacles to the treatment of colon cancer. In order to identify the molecular mechanism of this resistance, we investigated the role of the steroid and xenobiotic receptor (SXR) in the induction of drug resistance. Indeed, this nuclear receptor plays an important role in response to xenobiotics through the upregulation of detoxification genes. Following drug treatments, SXR is activated and interacts with the retinoid X receptor (RXR) to induce expression of some genes involved in drug metabolism such as phase I enzyme (like CYP), phase II enzymes (like UGT) and transporters (e.g. MDR1). RESULTS: In this study, we have shown that endogenous SXR is activated in response to SN-38, the active metabolite of the anticancer drug irinotecan, in human colon cancer cell lines. We have found that endogenous SXR translocates into the nucleus and associates with RXR upon SN-38 treatment. Using ChIP, we have demonstrated that endogenous SXR, following its activation, binds to the native promoter of the CYP3A4 gene to induce its expression. RNA interference experiments confirmed SXR involvement in CYP3A4 overexpression and permitted us to identify CYP3A5 and MRP2 transporter as SXR target genes. As a consequence, cells overexpressing SXR were found to be less sensitive to irinotecan treatment. CONCLUSIONS: Altogether, these results suggest that the SXR pathway is involved in colon cancer irinotecan resistance in colon cancer cell line via the upregulation of select detoxification genes.

Anatomy of the kisspeptin neural network in mammals.

Kisspeptin has been recognized as a key regulator of GnRH secretion during puberty and adulthood, conveying the feedback influence of endogenous gonadal steroids onto the GnRH system. Understanding the functional roles of this peptide depends on knowledge of the anatomical framework in which it acts, including the location of kisspeptin-expressing cells in the brain and their connections. In this paper, we review current data on the anatomy of the kisspeptin neuronal network, including its colocalization with gonadal steroid hormone receptors, anatomical sites of interaction with the GnRH system, and recent evidence of neurochemical heterogeneity among different kisspeptin neuronal populations. Evidence to date suggests that kisspeptin cells in mammals comprise an interconnected network, with reciprocal connections both within and between separate cell populations, and with GnRH neurons. At the same time, there is more functional and anatomical heterogeneity in this system than originally thought, and many unanswered questions remain concerning anatomical relationships of kisspeptin neurons with other neuroendocrine and neural systems in the brain.

Modulation of orphan nuclear receptor Nur77-mediated apoptotic pathway by acetylshikonin and analogues.

Shikonin derivatives, which are the active components of the medicinal plant Lithospermum erythrorhizon, exhibit many biological effects including apoptosis induction through undefined mechanisms. We recently discovered that orphan nuclear receptor Nur77 migrates from the nucleus to the mitochondria, where it binds to Bcl-2 to induce apoptosis. Here, we report that certain shikonin derivatives could modulate the Nur77/Bcl-2 apoptotic pathway by increasing levels of Nur77 protein and promoting its mitochondrial targeting in cancer cells. Structural modification of acetylshikonin resulted in the identification of a derivative 5,8-diacetoxyl-6-(1'-acetoxyl-4'-methyl-3'-pentenyl)-1,4-naphthaquinones (SK07) that exhibited improved efficacy and specificity in activating the pathway. Unlike other Nur77 modulators, shikonins increased the levels of Nur77 protein through their posttranscriptional regulation. The apoptotic effect of SK07 was impaired in Nur77 knockout cells and suppressed by cotreatment with leptomycin B that inhibited Nur77 cytoplasmic localization. Furthermore, SK07 induced apoptosis in cells expressing the COOH-terminal half of Nur77 protein but not its NH(2)-terminal region. Our data also showed that SK07-induced apoptosis was associated with a Bcl-2 conformational change and Bax activation. Together, our results show that certain shikonin derivatives act as modulators of the Nur77-mediated apoptotic pathway and identify a new shikonin-based lead that targets Nur77 for apoptosis induction.

Neurosteroids are excitatory in supraoptic neurons but inhibitory in the peripheral nervous system: it is all about oxytocin and progesterone receptors.

Neuroactive steroids synthesized from the brain or peripheral sources are called neurosteroids. Beside their common nuclear effects, they are considered to be potent neuromodulators, acting rapidly mainly in a non-genomic manner, either through allosteric regulation of ionic channels, or through membrane-bound steroid receptors. In contrast to the situation in the adult, the neurotransmitter GABA is excitatory during development and plays a trophic role, in particular inducing calcium signals necessary for the regulation of excitability and neuronal maturation. We demonstrated that the primary metabolite of progesterone (Proges), allopregnanolone (Allo), evoked a robust Ca(2+) influx in foetal hypothalamic neurons and in postnatal supraoptic nucleus (SON) neurons. In the latter, this led to oxytocin and arginine vasopressin release. Interestingly, these responses were GABA(A) and oxytocin-receptor-dependent. Allo is a well-known positive allosteric modulator of GABA(A) receptors. It is noteworthy that two other steroids, Proges and 17-beta-estradiol, displayed the same effect on Ca(2+) and oxytocin release but to a lesser extent. Importantly, no effect was observed in adult neurons from the SON, or in neurohypophysial axon terminals, regardless of the stage. The molecular mechanisms of the neurosteroid actions are multifaceted and depend on the type of cells, and are thus extremely interesting and challenging. In the peripheral nervous system, Allo and Proges surprisingly inhibited the GABA-induced Ca(2+) increases in embryonic dorsal root ganglion neurons. We propose that this rapid, reversible and dose-dependent phenomenon (at very low concentrations) was mediated by membrane Proges receptors, since transcripts for a newly discovered receptor protein, 25-Dx, were detected in our model. Recently, novel families of membrane steroid receptors, activating intracellular-signalling pathways such as MAP kinases, have been identified and described. This opens new perspectives to understand the intracellular machinery involved in the interaction between neuropeptides and neurosteroids, two major regulators of hypothalamo-neurohypophysial system development.

Machine learning methods and docking for predicting human pregnane X receptor activation.

The pregnane X receptor (PXR) regulates the expression of genes involved in xenobiotic metabolism and transport. In vitro methods to screen for PXR agonists are used widely. In the current study, computational models for human PXR activators and PXR nonactivators were developed using recursive partitioning (RP), random forest (RF), and support vector machine (SVM) algorithms with VolSurf descriptors. Following 10-fold randomization, the models correctly predicted 82.6-98.9% of activators and 62.0-88.6% of nonactivators. The models were validated using separate test sets. The overall ( n = 15) test set prediction accuracy for PXR activators with RP, RF, and SVM PXR models is 80-93.3%, representing an improvement over models previously reported. All models were tested with a second test set ( n = 145), and the prediction accuracy ranged from 63 to 67% overall. These test set molecules were found to cover the same area in a principal component analysis plot as the training set, suggesting that the predictions were within the applicability domain. The FlexX docking method combined with logistic regression performed poorly in classifying this PXR test set as compared with RP, RF, and SVM but may be useful for qualitative interpretion of interactions within the LBD. From this analysis, VolSurf descriptors and machine learning methods had good classification accuracy and made reliable predictions within the model applicability domain. These methods could be used for high throughput virtual screening to assess for PXR activation, prior to in vitro testing to predict potential drug-drug interactions.

Variability in PXR-mediated induction of CYP3A4 by commercial preparations and dry extracts of St. John's wort.

St. John's wort (SJW, Hypericum perforatum) is a well-tolerated herbal medicine widely used for the treatment of mild and moderate depressions. In the last 5 years, SJW has been implicated in drug interactions, which are largely mediated by the induction of the drug metabolizing enzymes, especially CYP3A4. There is still some controversy regarding the exact mechanism of induction and the identity of the SJW constituents involved. We investigated in LS174T cells the induction of CYP3A4 by ten SJW extracts, six commercial preparations, and the purified SJW constituent hyperforin. The content of hyperforin among the commercial preparations of SJW varied 62-fold (range 0.49-30.57 mg/dose). The CYP3A4 induction was mediated by PXR, but not by CAR. The magnitude of the induction correlated statistically significantly with the content of hyperforin in commercial SJW preparations (R = 0.87, p = 0.004) and in dry extracts (R = 0.65, p = 0.03), but not with their content of flavonoids or hypericin. Most of the CYP3A4 induction response occurred in the hyperforin range encountered in the blood of patients treated with SJW preparations. A temperature-induced decrease in the hyperforin content of a selected dry SJW extract abolished the induction of CYP3A4. In conclusion, commercial SJW preparations still exhibit an enormous variability in CYP3A4 induction, which is mediated by hyperforin and PXR. SJW preparations with lower hyperforin content should reduce the frequency of clinical interactions involving this herbal drug.

Vitamin B6 conjugation to nuclear corepressor RIP140 and its role in gene regulation.

Pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, is an important cofactor in amino acid metabolism, and supplementary vitamin B6 has protective effects in many disorders. Other than serving as a cofactor, it can also modulate the activities of steroid hormone receptors and transcription factors. However, the molecular basis of this modulation is unclear. Here, we report that mouse nuclear receptor interacting protein 140 (RIP140) can be modified by PLP conjugation. We mapped the modification site to Lys613 by LC-ESI-MS/MS analysis. This modification enhanced its transcriptional corepressive activity and its physiological function in adipocyte differentiation. We attribute this effect to increased interaction of RIP140 with histone deacetylases and nuclear retention of RIP140. This study uncovers a new physiological role of vitamin B6 in gene regulation by PLP conjugation to a transcriptional coregulator, which represents a new function of an old form of protein post-translational modification that has important biological consequences.

Effects of alterations in CAR on bilirubin detoxification in mouse collagen-induced arthritis.

Nuclear receptors such as constitutive androstane receptor (CAR) and pregnane X receptor (PXR) regulate the transcription of cytochromes P450 and transporters. We investigated whether quantitative and functional changes in CAR and PXR could affect bilirubin detoxification in chronic arthritis. The CAR mRNA level was significantly decreased in the liver of mice with collagen-induced arthritis (CIA) compared with control mice. In normal mice treated with CAR agonists, relatively rapid elimination of bilirubin was observed after its intravenous injection. Next, we investigated the effects of CAR on bilirubin-detoxifying enzymes and transporters in arthritis. The mRNA levels of organic anion transporter peptide (OATP) 2, glutathione S-transferase (GST) A1, and GSTA2 were decreased in CIA mice, whereas the mRNA levels of OATP4, UDP-glucuronosyl-transferase 1A1, and multidrug resistance-associated protein 2 remained unchanged. The protein levels and transport activities of OATP2 were also decreased in CIA mice. Furthermore, the CIA mice actually exhibited retarded elimination of bilirubin after its intravenous injection. These results indicate that alterations to CAR during arthritis affect the elimination of bilirubin because of changes in multiple bilirubin-detoxifying enzymes and transporters.

The ratio of constitutive androstane receptor to pregnane X receptor determines the activity of guggulsterone against the Cyp2b10 promoter.

Guggulsterone is the active ingredient in gugulipid, an organic extract of the Commiphora mukul plant. Gugulipid has been used for nearly 3000 years in Ayurvedic medicine, mainly as a treatment for arthritis. Herbal practitioners currently use gugulipid therapy in conditions as diverse as rheumatism, coronary artery disease, arthritis, hyperlipidemia, acne, and obesity. The active ingredient in gugulipid is guggulsterone, a plant sterol compound recently identified as a pregnane X receptor (PXR; NR1I2) ligand. We show herein that guggulsterone treatment represses the expression of cytochrome P450 2b10 (Cyp2b10) gene expression by inhibiting constitutive androstane receptor (CAR; NR1I3) activity in hepatocytes lacking functional PXR (PXR-knockout). We also show that PXR-CAR cross-talk determines the net activity of guggulsterone treatment toward Cyp2b10 gene expression. Using mammalian two-hybrid assays, we show that treatment with guggulsterone differentially affects protein cofactor recruitment to these two nuclear receptors. These data identify guggulsterone as an inverse agonist of the nuclear receptor CAR. When viewed together with the data showing that PXR and CAR expression is highly variable in different ethnic populations and that CAR expression is under the control of a circadian rhythm, our data provide important insight into the molecular mechanism of interindividual variability of drug metabolism. These data, together with the recent resolution of the crystal structures of PXR and CAR, will likely aid in the rational design of more specific CAR inverse agonists that are currently viewed as potential antiobesity drugs.

Oxysterols inhibit phosphatidylcholine synthesis via ERK docking and phosphorylation of CTP:phosphocholine cytidylyltransferase.

Surfactant deficiency contributes to acute lung injury and may result from the elaboration of bioactive lipids such as oxysterols. We observed that the oxysterol 22-hydroxycholesterol (22-HC) in combination with its obligate partner, 9-cis-retinoic acid (9-cis-RA), decreased surfactant phosphatidylcholine (PtdCho) synthesis by increasing phosphorylation of the regulatory enzyme CTP:phosphocholine cytidylyltransferase-alpha (CCTalpha). Phosphorylation of CCTalpha decreased its activity. 22-HC/9-cis-RA inhibition of PtdCho synthesis was blocked by PD98059 or dominant-negative ERK (p42 kinase). Overexpression of constitutively active MEK1, the kinase upstream of p42 kinase, increased CCTalpha phosphorylation. Expression of truncated CCTalpha mutants lacking proline-directed sites within the C-terminal phosphorylation domain partially blocked oxysterol-mediated inhibition of PtdCho synthesis. Mutagenesis of Ser315 within CCTalpha was both required and sufficient to confer significant resistance to 22-HC/9-cis-RA inhibition of PtdCho synthesis. A novel putative ERK-docking domain N-terminal to this phosphoacceptor site was mapped within the CCTalpha membrane-binding domain (residues 287-300). The results are the first demonstration of a physiologically relevant phosphorylation site and docking domain within CCTalpha that serve as targets for ERKs, resulting in inhibition of surfactant synthesis.

Guggulsterone activates multiple nuclear receptors and induces CYP3A gene expression through the pregnane X receptor.

Gugulipid is an extract of the guggul tree, Commiphora mukul, that is used to treat hyperlipidemia in humans. The lipid-lowering activity is found in the stereoisomers and plant sterols Z-guggulsterone and E-guggulsterone. The molecular basis for the lipid-lowering action of guggulsterone has been suggested to be antagonism of the farnesoid X receptor, a member of the nuclear receptor superfamily of ligand-activated transcription factors. To determine whether guggulsterone has the ability to function as an agonist of other nuclear receptor family members, we screened a panel of these proteins for their ability to transactivate reporter genes. Here, we show that guggulsterones activate the estrogen receptor alpha isoform, progesterone receptor, and pregnane X receptor. Concentration-response analysis using reporter gene assays indicate that guggulsterones activate these three receptors with EC(50) values in the low micromolar range. Furthermore, we show that guggulsterone-mediated activation of the pregnane X receptor induces the expression of CYP3A genes in both rodent and human hepatocytes. Protein interaction assays indicate that guggulsterones interact directly with pregnane X receptor, thereby modulating interaction with protein cofactors. We introduce a novel method to screen herbal remedies for their ability to activate pregnane X receptor. Pregnane X receptor activation is known to cause herb-drug interactions, and our data suggest that gugulipid therapy should be used cautiously in patients taking prescription medications that are metabolized by CYP3A family members. Moreover, our data suggest the need for additional studies of guggulsterones agonist activity against estrogen receptor alpha isoform and the progesterone receptor.

Hormones, brain and stress.

The stress system orchestrates body and brain responses to the environment. This action exerted by the mediators of the stress system has two modes of operation. The immediate response mode driven by corticotropin-releasing hormone (CRH) organises via CRH-1 receptors the behavioural, sympathetic and hypothalamic-pituitary-adrenal (HPA) responses to a stressor. In the other - slower - mode, which facilitates behavioural adaptation, the urocortins acting through CRH-2 receptors seem prominent. Corticosteroid hormones secreted by the adrenal cortex are implicated in both modes through their high affinity type 1 (mineralocorticoid receptors - MR) and lower affinity type 2 (glucocorticoid receptors - GR) receptors that are co-localised in limbic neural circuitry. Current data suggest that MR controls in specific afferents the threshold or sensitivity of the fast CRH-1 driven stress system mode and thus prevents disturbance of homeostasis, while GR facilitates its recovery by restraining in these very same circuits stress responses and by mobilising energy resources. In preparation for future events GR facilitates behavioural adaptation and promotes storage of energy. The balance in the two stress system modes is thought to be essential for cell homeostasis, mental performance and health. Imbalance induced by genetic modification or chronic stressors changes specific neural signalling pathways underlying psychic domains of cognition and emotion, anxiety and aggression. This Yin-Yang stress concept is fundamental for genomic strategies to understand the mechanistic underpinning of cortisol-induced stress-related disorders such as i.e. severe forms of depression and co-morbid diseases.