Nuclear receptors as targets for drug development: the role of nuclear receptors during neural stem cell proliferation and differentiation

The fate of stem cells, such as neural stem cells and hematopoietic stem cells, depends on strictly regulated signaling events including activation of nuclear receptors, resulting in subsequent gene induction. Recently, we demonstrated that PPARgamma, a ligand-activated nuclear receptor, plays an important role in regulating the proliferation and differentiation of murine neural stem cell (NSC). NSC prepared from heterozygous PPARgamma-deficient mouse exhibited a slower growth rate compared with that of wild-type mouse, which was also demonstrated in PPARgamma-knockdown NSC that was generated by the lentiviral-vector-mediated RNA interference approach. These studies have important implications for understanding central nervous system functions and developing a therapy for neurodegenerative disorders. In this review, recent findings on stem cell biology, especially focusing on nuclear receptors in NSCs, including our current study, will be discussed.     

Adenosine receptors as targets for drug development

Adenosine is a ubiquitous autacoid that acts on four defined receptors, named A(1), A(2A), A(2B) and A(3). Although the biological activity of adenosine has been known for more than 70 years and the existence of specific receptors for more than 25 years, it is only now that the full potential for drug development is becoming clear. Among some of the conditions for which adenosine receptor-based therapy might be used are Parkinson's disease, hypoxia/ischemia, epilepsy, kidney disease and asthma.     

以核受体为靶标的胆汁淤积治疗药物研究进展

胆汁淤积的治疗药物匮乏,熊去氧胆酸是目前唯一被FDA通过的治疗原发性胆汁性肝硬化的药物,但其药效却限于疾病早期,因此迫切需要开发新的胆汁淤积治疗药物。核受体能调控胆汁酸稳态,它作为胆汁淤积治疗的靶标是目前研究的热点。该综述对目前报道最多的核受体进行总结,分析其作为胆汁淤积药物治疗靶标的利弊及应用前景。     

Nuclear receptors as potential targets for modulating reverse cholesterol transport

This review describes the role of nuclear receptors in the regulation of genes involved in cholesterol transport and synthetic modulators of these receptors. Increasing the efflux of cholesterol from peripheral cells, such as lipid-laden macrophages, through a process called reverse cholesterol transport (RCT) requires HDL. Increasing the circulating levels of HDL, as well as the efficiency of the RCT process, could result in a reduction in the development of coronary artery disease and atherosclerosis. Nuclear receptors of the RXR heterodimer family have recently been shown to regulate key genes involved in HDL metabolism and reverse cholesterol transport. These include the PPARs (peroxisome proliferator activated receptors), the LXR (liver X receptor) and the farnesoid X receptor (FXR). The synthesis of specific and potent ligands for these receptors has aided in ascertaining the physiological role of these receptors as lipid sensors and the potential therapeutic utility of modulators of these receptors in dyslipidemias and cardiovascular disease.     

Metabotropic glutamate receptors as targets for new drug development

The review is devoted to experimental investigations of metabotropic glutamate receptors and the properties of drugs (ligands) belonging to agonists, antagonists, and modulators of the activity of these receptors. Possibilities of the treatment of neurodegenerative disorders, cognitive disturbances in schizophrenia patients, and narcotic dependency by using drugs of this class are considered.     

NPY receptors as potential targets for anti-obesity drug development

The neuropeptide Y system has proven to be one of the most important regulators of feeding behaviour and energy homeostasis, thus presenting great potential as a therapeutic target for the treatment of disorders such as obesity and at the other extreme, anorexia. Due to the initial lack of pharmacological tools that are active in vivo, functions of the different Y receptors have been mainly studied in knockout and transgenic mouse models. However, over recent years various Y receptor selective peptidic and non-peptidic agonists and antagonists have been developed and tested. Their therapeutic potential in relation to treating obesity and other disorders of energy homeostasis is discussed in this review.     

Enzymes of the trypanothione metabolism as targets for antitrypanosomal drug development

Trypanosomatids are the causative agents of African sleeping sickness, Chagas' disease and the three forms of leihmaniasis. New drugs against these parasitic protozoa are urgently needed since the currently available chemotherapy is not at all satisfying. One promising approach towards the development of new drugs is based on the design of specific enzyme inhibitors. Trypanosomes and leishmania possess a unique thiol metabolism in which the ubiquitous glutathione/glutathione reductase system is replaced by trypanothione and trypanothione reductase. The dithiol trypanothione is the key molecule for the synthesis of DNA precursors, the homeostasis of ascorbate, the detoxification of hydroperoxides, and the sequestration/export of thiol conjugates. Synthesis and reduction of trypanothione are essential for the maintenance of a reducing intracellular milieu which renders the respective enzymes attractive drug target molecules. Here we present the current state of knowledge of the thiol metabolism of trypanosomatids, comprising the trypanothione/tryparedoxin, thioredoxin, and ovothiol systems of the parasites. The most effective inhibitors of the enzymes known to date, their mode of action, and the (dis)advantages of different types of inhibitors as potential drug candidates will be discussed.     

Neuropeptide Y receptors as targets for anti-obesity drug development: perspective and current status

Neuropeptide Y is a widely distributed neuropeptide that elicits a plethora of physiological effects via interaction with six different receptors (Y₁–y₆). Recent attention has focused on the role of neuropeptide Y in the regulation of energy homeostasis. Neuropeptide Y stimulates food intake, inhibits energy expenditure, increases body weight and increases anabolic hormone levels by activating the neuropeptide Y Y₁ and Y₅ receptors in the hypothalamus. Based on these findings, several neuropeptide Y Y₁ and Y₅ receptor antagonists have been developed recently as potential anti-obesity agents. In addition, mice lacking neuropeptide Y, the neuropeptide Y Y₁ receptor or the neuropeptide Y Y₅ receptor have been generated. The data obtained to date with these newly developed tools suggests that neuropeptide Y receptor antagonists, particularly neuropeptide Y Y₁ receptor antagonists, may be useful anti-obesity agents. However, the redundancy of the neurochemical systems regulating energy homeostasis may limit the effect of ablating a single pathway. In addition, patients in whom the starvation response is activated, such as formerly obese patients who have lost weight or patients with complete or partial leptin deficiency, may be the best candidates for treatment with a neuropeptide Y receptor antagonist.     

Peripheral TRPV1 receptors as targets for drug development: new molecules and mechanisms

Based on the painful effects of exposure to capsaicin, TRPV1 (transient receptor potential vanilloid subfamily member 1) localization is most readily associated with peripheral sensory neurons, however, TRPV1 is now known to be expressed, albeit at lower levels, in the spinal cord, brain and a wide-range of non-neuronal cells. The latter includes epithelial cells (e.g. keratinocytes, urothelium, gastric epithelial cells, enterocytes, and pneumocytes) through vascular endothelium and cells of the immune system (e.g. T-cells and mast cells) to smooth muscle, fibroblasts and hepatocytes. Despite extensive research, the physiological function of TRPV1 in the brain and in non-neuronal tissues remains elusive. The preliminary results are exciting, but many are unconfirmed and/or contradictory. As yet, studies with TRPV1 knock-out mice have proven unhelpful in clarifying such biological roles. Now that a range of potent and selective TRPV1 antagonists are available in this rapidly expanding research field, further understanding of the biological roles of TRPV1 throughout the body is within reach. In this article, we will summarize the known roles of peripheral TRPV1 receptors in physiology and disease and review the current perspectives for the therapeutic potential of TRPV1 agonists and antagonists in the treatment of a wide range of conditions such as pain, cancer, migraine, chronic cough, asthma, rectal hypersensitivity, inflammatory bowel disease, obesity, overactive bladder and diabetes. New applications of targeting central TRPV1 receptors are reviewed in the accompanying article by Starowicz et al. (in this issue).     

Nuclear receptors as drug targets: new developments in coregulators, orphan receptors and major therapeutic areas

Nuclear receptors (NRs) are ideal targets for drug discovery. Not only do they control a myriad of biological and disease processes, but they are also regulated by small lipophilic molecules that can be easily exchanged with a drug of choice. All 48 of the NR genes in the human genome have been identified, many of their structures have been solved and their ligands identified. Their mechanism of action has been elucidated and many of their target genes have been identified. Nonetheless, presentations at the recent conference sponsored by IBC Life Sciences indicated that, while many NRs already have marketable drugs, the latest tools in robotics, genomics, proteomics, and informatics are helping to identify more selective drugs.     

Nuclear receptors as therapeutic targets for Alzheimer's disease

INTRODUCTION: Alzheimer's disease (AD) is characterized by the accumulation and extensive deposition of amyloid β (Aβ) in the parenchyma of the brain. This accumulation of amyloid is associated with perturbations in synaptic function, impairments in energy metabolism and induction of a chronic inflammatory response which acts to promote neuronal loss and cognitive impairment. AREAS COVERED: Currently, there are no drugs that target the underlying mechanisms of AD. Here, we propose a class of nuclear receptors as novel and promising new therapeutic targets for AD. This review summarizes the literature on nuclear receptors and their effects on AD-related pathophysiology. EXPERT OPINION: Nuclear receptors are attractive targets for the treatment of AD due to their ability to facilitate degradation of Aβ, affect microglial activation and suppress the inflammatory milieu of the brain. Liver X receptor agonists have proven difficult to move into clinical trials as long-term treatment results in hepatic steatosis. It is our view that PPAR-γ activation remains a promising avenue for the treatment for AD; however, the poor BBB permeability of the currently available agonists and the negative outcome of the Phase III clinical trials are likely to diminish interest in pursuing this target.     

Coordinate regulation of drug metabolism by xenobiotic nuclear receptors: UGTs acting together with CYPs and glucuronide transporters

Xenobiotic nuclear receptors (PXR, CAR, and the Ah receptor) coordinately induce genes involved in all phases of xenobiotic metabolism including oxidative metabolism, conjugation, and transport. The comment--dedicated to honor the memory of Herbert Remmer, mentor of the author K. W. B.--discusses mechanistic, functional, and evolutionary aspects of xenobiotic nuclear receptors which induce UGTs together with CYPs and glucuronide transporters in human and rodent liver and intestine. Recent findings on regulation of CYPs, UGTs, and transporters suggest that while nuclear receptor signaling induces different CYPs, regulation may converge on single UGTs and transporters. Functional consequences of co-regulation are discussed using examples from the metabolism of xeno- and endobiotics (drugs, bilirubin, bile salts, steroid hormones, and carcinogens). Animal-plant interactions may have been a major driving force in the evolutionary divergence of CYPs and UGTs in mammals and insects as well as in their regulation by nuclear receptors. In addition, regulation by nuclear receptors was probably shaped by the need for homeostatic control of endobiotic signals in the evolution of multicellular organisms.