Differential and Isomer-Specific Modulation of Vitamin A Transport and the Catalytic Activities of the RBP Receptor by Retinoids

Retinoids are vitamin A derivatives with diverse biological functions. Both natural and artificial retinoids have been used as therapeutic reagents to treat human diseases, but not all retinoid actions are understood mechanistically. Plasma retinol binding protein (RBP) is the principal and specific carrier of vitamin A in the blood. STRA6 is the membrane receptor for RBP that mediates cellular vitamin A uptake. The effects of retinoids or related compounds on the receptor’s vitamin A uptake activity and its catalytic activities are not well understood. In this study, we dissected the membrane receptor-mediated vitamin A uptake mechanism using various retinoids. We show that a subset of retinoids strongly stimulates STRA6-mediated vitamin A release from holo-RBP. STRA6 also catalyzes the exchange of retinol in RBP with certain retinoids. The effect of retinoids on STRA6 is highly isomer-specific. This study provides unique insights into the RBP receptor’s mechanism and reveals that the vitamin A transport machinery can be a target of retinoid-based drugs.     

Thematic Review Series: Bile Acids: Bile acids: regulation of apoptosis by ursodeoxycholic acid

Bile acids are a group of molecular species of acidic steroids with peculiar physical-chemical and biological characteristics. At high concentrations they become toxic to mammalian cells, and their presence is pertinent in the pathogenesis of several liver diseases and colon cancer. Bile acid cytoxicity has been related to membrane damage, but also to nondetergent effects, such as oxidative stress and apoptosis. Strikingly, hydrophilic ursodeoxycholic acid (UDCA), and its taurine-conjugated form (TUDCA), show profound cytoprotective properties. Indeed, these molecules have been described as potent inhibitors of classic pathways of apoptosis, although their precise mode of action remains to be clarified. UDCA, originally used for cholesterol gallstone dissolution, is currently considered the first choice therapy for several forms of cholestatic syndromes. However, the beneficial effects of both UDCA and TUDCA have been tested in other experimental pathological conditions with deregulated levels of apoptosis, including neurological disorders, such as Alzheimer''s, Parkinson''s, and Huntington''s diseases. Here, we review the role of bile acids in modulating the apoptosis process, emphasizing the anti-apoptotic effects of UDCA and TUDCA, as well as their potential use as novel and alternate therapeutic agents for the treatment of apoptosis-related diseases.     

Potential agents for cancer and obesity treatment with herbal medicines from the green garden

Many classes of bioactive drug-like molecules derived from traditional herbal plants are becoming attractive as alternative medicines for the treatment of severe chronic diseases such as cancer and obesity. A set of chemically synthesized drugs that is capable of both inhibiting cancer growth and reducing body weight for treatment of obesity have severe side effects including nausea, vomiting, diarrhea as well as producing increased blood pressure and headache, respectively. For decades, drug candidates from herbal plants have been considered as potential therapeutic agents because they are generally safer, less toxic, and have fewer lethal side effects than chemically synthesized or semi-synthetic drugs. Understanding the key factors affecting pharmacological effects and clinical outcomes has been a critical theme of natural product research. However, standardized sample preparation methods, well-controlled scientific studies, and validation studies are needed before herbal therapeutics can be introduced into the global market. This review will address the current advances in using traditional herbal plants, including the pharmacological effects and the challenges faced during the development of new drugs. The safety issues associated with toxicity and the effectiveness of the herbs in specific diseases such as cancer and obesity are also discussed.     

Model systems: modeling human staphylococcal arthritis and sepsis in the mouse.

The staphylococci have been recognized as serious pathogens for over a century and are the etiological agent of a variety of diseases ranging from mild cutaneous infections to often fatal forms of septic arthritis, endocarditis, toxic shock syndrome and sepsis. Despite intensive efforts to halt their spread, they remain the most common cause of community- and nosocomially acquired bacteremia. Murine models of Staphylocococus aureus-mediated arthritis and sepsis exist and are being used to gain a better understanding of the host-bacterium relationship as well to develop better methods of prevention and treatment.     

Mechanisms of action of retinoids in gastrointestinal mucosal protection in animals, human healthy subjects and patients.

Retinoids prevent chemically induced gastric mucosal damage without inhibiting gastric acid secretion ("nutritional gastric cytoprotection"). The gastroprotective effects of retinoids do not depend on 1) vitamin A activity; 2) number of unsaturated double bonds; 3) the presence of a characteristic chemical structure of their terminal components; however, they depend on 1) intact vagal nerve and 2) adrenals in experimental animals. The gastric cytoprotective effect of retinoids produces a dose-dependent inhibition of ATP-transformation into ADP. It also increases the transformation of ATP into cAMP. Other features of these gastric cytoprotective effects of retinoids include: 1) The retinoid-induced gastric mucosal protection differs from that of PGs; 2) The cAMP is an intracellular signal in the development of gastric mucosal damage produced by chemicals (e.g., ethanol, HCl, indomethacin) and in the protection of gastric mucosa induced by retinoids (but not by PGs); 3) The gastric mucosal protection induced by retinoids and gastric mucosal permeability can be separated in time. The existence of gastric mucosal protection can be demonstrated in healthy persons (against indomethacin treatment), in patients with gastric ulcer (GU) and duodenal ulcer (DU) without any inhibition of gastric acid secretion. The serum levels of vitamin A and zeaxanthin were significantly decreased in patients with chronic gastrointestinal (GI) inflammatory diseases (e.g., terminal ileitis, ulcerative colitis), colorectal polyposis, and different (e.g., esophageal, gastric, pancreatic, hepatocellular and colorectal) malignant diseases. The serum levels of vitamin A provitamins were unchanged and their GI mucosal protective effects do not depend on vitamin A activity. Conclusions: 1) Abundant experimental and human observations clearly proved the defensive role of retinoids in the GI tract; 2) There is a correlation between the a) scavenger properties of retinoids vs. intact vagal nerve; b) scavenging properties vs. intact adrenals. 3) The GI mucosal protective effect of retinoids is correlated with biochemical changes in the GI mucosa.     

Vitamin neurotoxicity

Vitamins contain reactive functional groups necessary to their established roles as coenzymes and reducing agents. Their reactive potential may produce injury if vitamin concentration, distribution, or metabolism is altered. However, identification of vitamin toxicity has been difficult. The only well-established human vitamin neurotoxic effects are those due to hypervitaminosis A (pseudotumor cerebri) and pyridoxine (sensory neuropathy). In each case, the neurological effects of vitamin deficiency and vitamin excess are similar. Closely related to the neurological symptoms of hypervitaminosis A are symptoms including headache, pseudotumor cerebri, and embryotoxic effects reported in patients given vitamin A analogs or retinoids. Most tissues contain retinoic acid (RA) and vitamin D receptors, members of a steroid receptor superfamily known to regulate development and gene expression. Vitamin D3 effects on central nervous system (CNS) gene expression are predictable, in addition to the indirect effects owing to its influence on calcium and phosphorus homeostasis. Folates and thiamine cause seizures and excitation when administered in high dosage directly into the brain or cerebrospinal fluid (CSF) of experimental animals but have rarely been reported to cause human neurotoxicity, although fatal reactions to i.v. thiamine are well known. Ascorbic acid influences CNS function after peripheral administration and influences brain cell differentiation and 2-deoxyglucose accumulation by cultured glial cells. Biotin influences gene expression in animals that are not vitamin-deficient and alters astrocyte glucose utilization. The multiple enzymes and binding proteins involved in regeneration of retinal vitamin A illustrate the complexity of vitamin processing in the body. Vitamin A toxicity is also a good general model of vitamin neurotoxicity, because it shows the importance of the ratio of vitamin and vitamin-binding proteins in producing vitamin toxicity and of CNS permeability barriers. Because vitamin A and analogs enter the CNS better than most vitamins, and because retinoids have many effects on enzyme activity and gene expression, Vitamin A neurotoxicity is more likely than that of most, perhaps all other vitamins. Megadose vitamin therapy may cause injury that is confused with disease symptoms. High vitamin intake is more hazardous to peripheral organs than to the nervous system, because CNS vitamin entry is restricted. Vitamin administration into the brain or CSF, recommended in certain disease states, is hazardous and best avoided. The lack of controlled trials prevents us from defining the lowest human neurotoxic dose of any vitamin. Large differences in individual susceptibility to vitamin neurotoxicity probably exist, and ordinary vitamin doses may harm occasional patients with genetic disorders.(ABSTRACT TRUNCATED AT 400 WORDS)     

Control of cell fate by Hsp70: more than an evanescent meeting

During their lifetime, proteins inevitably expose hydrophobic segments within the polypeptide chains on a molecule's surface, which may be otherwise buried inside the molecules in the proper conformation. This potentially dangerous situation is managed with the aid of the 70-kDa heat shock proteins (Hsp70s) and other molecular chaperones. Although a major function of Hsp70 is assisting in efficient folding of anonymous proteins in unfolded states, recent studies have revealed that Hsp70 plays a variety of specific roles, sometimes deciding the cell fate. These multiple activities are based on the specific binding of Hsp70 to proteins in native states, which regulate cell growth and/or death. It is now well recognized that unfolding of some proteins may cause serious diseases, especially those associated with neurodegeneration, such as Alzheimer's disease. It is suggested that Hsp70 might be a potential drug against these diseases, but caution should be taken because Hsp70 exerts multiple effects by binding to specific proteins.     

Microtubule-targeting agents are clinically successful due to both mitotic and interphase impairment of microtubule function

Microtubules undergo continual dynamic changes in mitotic cells as the mitotic spindle forms and is broken down and in interphase cells where they play a central role in intracellular trafficking, cell signaling, cell migration, and angiogenesis. Compounds that target the microtubule have been hugely successful in the clinic as chemotherapeutics, and this success is likely due to their ability to target cells regardless of their cell cycle stage. Additionally, new generation antibody-conjugated microtubule-targeting agents are improving the targeting of these drugs to tumors. Microtubule-targeting agents have been shown to have anti-angiogenic and vascular-disrupting properties as well as effects on cellular migration, intracellular trafficking, and cell secretion. There are a number of these compounds in development that target the vasculature, and different formulations of clinically used drugs are being developed to take advantage of these anti-angiogenic properties. Microtubule-targeting agents have also been shown to have the potential to treat neurodegenerative diseases, such as Alzheimer’s disease. Thus, drugs that target the microtubule will continue to have a major impact in oncology not only as anti-mitotics but also as potent inhibitors of interphase functions, and in future may also prove to be effective in reducing the consequences of neurodegenerative disease.     

Optimization of treatment conditions for studying the anticancer effects of retinoids using pancreatic adenocarcinoma as a model

Retinoids are natural differentiation-inducing compounds that are promising as anticancer agents. Cancer cell lines are valuable in the investigation of the potential of retinoids for the treatment of specific cancers. However, using different treatment conditions but the same cell lines, investigators have produced markedly contradictory results for the effectiveness of retinoids. The present study examined different factors in the treatment conditions that may have masked or interfered with the effects of retinoids and, thereby, resulted in this conflict. Our studies revealed that the effects of retinoids on cancer cell proliferation were influenced by serum, the choice of vehicle (DMSO vs ethanol) and its concentration, phenol red, the degree of cellular confluence, and the method of assessing proliferation (cell number or [3H]thymidine uptake vs the MTT assay). Optimized conditions were the use of serum-free, ethanol-free, and phenol red-free media, investigating cells in the log phase of growth, using 相似文献   

Retinoid-induced expression and activity of an immediate early tumor suppressor gene in vascular smooth muscle cells

Retinoids are used clinically to treat a number of hyper-proliferative disorders and have been shown in experimental animals to attenuate vascular occlusive diseases, presumably through nuclear receptors bound to retinoic acid response elements (RARE) located in target genes. Here, we show that natural or synthetic retinoids rapidly induce mRNA and protein expression of a specific isoform of A-Kinase Anchoring Protein 12 (AKAP12β) in cultured smooth muscle cells (SMC) as well as the intact vessel wall. Expression kinetics and actinomycin D studies indicate Akap12β is a retinoid-induced, immediate-early gene. Akap12β promoter analyses reveal a conserved RARE mildly induced with atRA in a region that exhibits hyper-acetylation. Immunofluorescence microscopy and protein kinase A (PKA) regulatory subunit overlay assays in SMC suggest a physical association between AKAP12β and PKA following retinoid treatment. Consistent with its designation as a tumor suppressor, inducible expression of AKAP12β attenuates SMC growth in vitro. Further, immunohistochemistry studies establish marked decreases in AKAP12 expression in experimentally-injured vessels of mice as well as atheromatous lesions in humans. Collectively, these results demonstrate a novel role for retinoids in the induction of an AKAP tumor suppressor that blocks vascular SMC growth thus providing new molecular insight into how retiniods may exert their anti-proliferative effects in the injured vessel wall.     

丁酸盐与β-羟基丁酸盐在脊髓损伤中的抗炎作用

脊髓损伤是一种严重的疾病,目前尚无有效的治疗方法。炎症反应在脊髓损伤后数h内开始,在几d内达到峰值,并可能持续数y。减轻脊髓损伤后的炎症反应是重要的治疗策略之一。丁酸盐与β-羟基丁酸盐是2种密切相关的物质,2者结构相似,仅有1个羟基不同,因在多种疾病中显现出良好的抗炎特性而引起广泛关注。近期有基础研究发现,丁酸盐与β-羟基丁酸盐可以抑制NF-κB/ NLRP3炎性小体信号通路活性,降低促炎因子表达;或通过增加抗氧化分子的水平,减轻脊髓损伤后炎症反应。因此,丁酸盐与β-羟基丁酸盐可能是脊髓损伤后有前景的治疗方法。本文拟对丁酸盐与β-羟基丁酸盐的结构与产生、在脊髓损伤中发挥抗炎作用的机制、治疗前景进行综述,以期为该领域科研人员提供理论参考。     

Topical ‘dual-soft’ glucocorticoid receptor agonist for dermatology

Steroidal glucocorticoids (GR agonists) have been widely used for the topical treatment of skin disorders, including atopic dermatitis. They are a very effective therapy, but they are associated with both unwanted local effects in the skin (skin thinning/atrophy) and systemic side effects. These effects can limit the long-term utility of potent steroids.Here we report on a topically delivered non-steroidal GR agonist, that has the potential to deliver high efficacy in the skin, but due to rapid metabolism in the blood & liver (“dual-soft”) it should have greater systemic safety than existing treatments. In addition, compared to less selective steroidal GR agonists, the new non-steroidal Selective Glucocorticoid Agonists (SEGRAs) have the potential to avoid the skin atrophy observed with existing topical steroids.Due to its potential for reduced skin atrophy and low systemic exposure, LEO 134310 (17) may be suitable for long term topical treatment of skin diseases such as atopic dermatitis and psoriasis.     

Cell-based therapies for the preterm infant

The severely preterm infant receives a multitude of life-saving interventions, many of which carry risks of serious side effects. Cell therapy is an important and promising arm of regenerative medicine that may address a number of these problems. Most forms of cellular therapy use stem/progenitor cells or stem-like cells, which have the capacity to migrate, engraft and exert anti-inflammatory effects. Although some of these cell-based therapies have made their way to clinical trials in adults, little headway has been made in the neonatal patient group. This review discusses the efficacy of cell therapy in preclinical studies to date and their potential applications to diseases that afflict many prematurely born infants. Specifically, we identify the major hurdles that must be overcome before cell therapies can be safely used in the neonatal intensive care unit.     

Bacterial diseases of crabs: a review

Bacterial diseases of crabs are manifested as bacteremias caused by organisms such as Vibrio, Aeromonas, and a Rhodobacteriales-like organism or tissue and organ tropic organisms such as chitinoclastic bacteria, Rickettsia intracellular organisms, Chlamydia-like organism, and Spiroplasma. This paper provides general information about bacterial diseases of both marine and freshwater crabs. Some bacteria pathogens such as Vibrio cholerae and Vibrio vulnificus occur commonly in blue crab haemolymph and should be paid much attention to because they may represent potential health hazards to human beings because they can cause serious diseases when the crab is consumed as raw sea food. With the development of aquaculture, new diseases associated with novel pathogens such as spiroplasmas and Rhodobacteriales-like organisms have appeared in commercially exploited crab species in recent years. Many potential approaches to control bacterial diseases of crab will be helpful and practicable in aquaculture.     

Retinoic acid and its receptors in limb regeneration

The effects of retinoids on the regenerating amphibian limb are described: the mesenchymal cells of the blastema can be proximalized, posteriorized and ventralized. Ectopic limbs are also induced after retinoid treatment of regenerating tails, but not during limb development unless the limb bud is damaged. The cellular and molecular alterations induced by retinoids are reported as well as experiments which have revealed the importance of endogenous retinoids for normal limb regeneration. Various retinoic acid receptors are expressed in the regeneration blastema and the experiments which have revealed functions for individual isoforms are described. These experiments reveal that retinoids are a crucial component of the normal, regenerating limb and demonstrate the value of the regenerating limb as an experimental system for providing functional data on individual retinoic acid receptors.     

Fruit Peels: Food Waste as a Valuable Source of Bioactive Natural Products for Drug Discovery

Fruits along with vegetables are crucial for a balanced diet. These not only have delicious flavors but are also reported to decrease the risk of contracting various chronic diseases. Fruit by-products are produced in huge quantity during industrial processing and constitute a serious issue because they may pose a harmful risk to the environment. The proposal of employing fruit by-products, particularly fruit peels, has gradually attained popularity because scientists found that in many instances peels displayed better biological and pharmacological applications than other sections of the fruit. The aim of this review is to highlight the importance of fruit peel extracts and natural products obtained in food industries along with their other potential biological applications.     

Retinoic acid promotes the development of Th2-like human myelin basic protein-reactive T cells

To determine if retinoids might be beneficial in the treatment of multiple sclerosis (MS), all-trans-retinoic acid (tRA) was tested for its effects on proliferation and cytokine expression in human autoreactive T cells. tRA decreased human lymphocyte proliferation in vitro in a dose-dependent manner. In addition, tRA induced IL-4 gene expression in myelin basic protein (MBP)-specific T cell lines which had previously expressed a Th1-like phenotype. MBP-specific T cell lines generated in the presence of tRA had a Th2-like phenotype. Retinoids have previously been shown to have a similar effect on encephalitogenic T cells in experimental allergic encephalomyelitis (EAE; an animal model for MS) and treatment of EAE with retinoids stabilizes the disease. Since several oral retinoids have been shown to be safe in humans, retinoids may be beneficial in the treatment of MS.