Retinoic acid suppresses endothelin-1 gene expression at the transcription level in endothelial cells

Potential Therapeutic Effect of All-Trans Retinoic Acid on Atherosclerosis

Atherosclerosis is a major risk factor for myocardial infarction and ischemic stroke, which are the leading cause of death worldwide. All-trans retinoic acid (ATRA) is a natural derivative of essential vitamin A. Numerous studies have shown that ATRA plays an important role in cell proliferation, cell apoptosis, cell differentiation, and embryonic development. All-trans retinoic acid (ATRA) is a ligand of retinoic acid receptors that regulates various biological processes by activating retinoic acid signals. In this paper, the metabolic processes of ATRA were reviewed, with emphasis on the effects of ATRA on inflammatory cells involved in the process of atherosclerosis.

Association between serum retinol and overall and cause-specific mortality in a 30-year prospective cohort study

How retinol as a clinical indicator of vitamin A status is related to long-term mortality is unknown. Here we report the results of a prospective analysis examining associations between serum retinol and risk of overall and cause-specific mortality. During a 30-year cohort follow-up, 23,797 deaths were identified among 29,104 men. Participants with higher serum retinol experienced significantly lower overall, CVD, heart disease, and respiratory disease mortality compared to men with the lowest retinol concentrations, reflecting 17–32% lower mortality risk (P_trend < 0.0001). The retinol-overall mortality association is similar across subgroups of smoking intensity, alcohol consumption, body mass index, trial supplementation, serum alpha-tocopherol and beta-carotene concentrations, and follow-up time. Mediation analysis indicated that <3% of the effects of smoking duration and diabetes mellitus on mortality were mediated through retinol concentration. These findings indicate higher serum retinol is associated with lower overall mortality, including death from cardiovascular, heart, and respiratory diseases.

Vitamin A, of which retinol is the major form in the circulation, is a determinant of human health but whether vitamin A status is associated with mortality is not well understood. Here the authors report that in a prospective observational analysis of 29 104 men, higher serum retinol associates with lower risk of overall and cause-specific mortality.

All‑trans retinoic acid reduces endothelin‑1 expression and increases endothelial nitric oxide synthase phosphorylation in rabbits with atherosclerosis

All-trans retinoic acid (ATRA) is a natural derivative of vitamin A that ameliorates atherosclerosis (AS) by regulating inflammatory factors. However, studies concerning the role of retinoic acid in artery endothelial function are rare. Therefore, the present study investigated its role in regulating the production of endothelin‑1 (ET‑1) and nitric oxide (NO) in rabbits with AS. The rabbits were randomly divided into 3 groups: The control group was administered an ordinary diet, while the high fat group and the ATRA drug intervention group were administered a high fat diet. After 12 weeks, the blood lipid levels of rabbits, the morphological structure of the arterial wall, the arterial intimal permeability, the activity of blood endothelial nitric oxide synthase (eNOS) and the level of plasma NO were investigated. Western blot analysis was used to detect the levels of ET‑1, eNOS and eNOS phosphorylation at Ser‑1177 (p‑eNOS), and a radioimmunoassay was performed to detect the level of ET‑1 in the plasma. It was identified that plaque formation was alleviated in the ATRA group compared with the high fat group, as revealed by hematoxylin and eosin and oil red O staining, and a similar trend was reflected in the immunofluorescence results for endothelial permeability. Western blotting demonstrated significantly decreased ET‑1 expression levels in the arterial tissue of rabbits in the ATRA group compared with the high fat group, together with increased p‑eNOS level (P<0.05), however, no difference was observed in the expression of eNOS (P>0.05). The trends observed for ET‑1 and the activity of eNOS in plasma were similar to those for arterial tissue. Therefore, the present study demonstrated that ATRA may regulate the grade of AS by the reduction of ET‑1 secretion and increased NO formation via increased phosphorylation of eNOS. ATRA provides a potential novel method for the treatment of atherosclerosis.

Regulatory T-Cell Augmentation or Interleukin-17 Inhibition Prevents Calcineurin Inhibitor-Induced Hypertension in Mice

The immunosuppressive calcineurin inhibitors cyclosporine A and tacrolimus alter T-cell subsets and can cause hypertension, vascular dysfunction, and renal toxicity. We and others have reported that cyclosporine A and tacrolimus decrease anti-inflammatory regulatory T cells and increase proinflammatory interleukin-17-producing T cells; therefore, we hypothesized that inhibition of these effects using noncellular therapies would prevent the hypertension, endothelial dysfunction, and renal glomerular injury induced by calcineurin inhibitor therapy. Daily treatment of mice with cyclosporine A or tacrolimus for 1 week significantly decreased CD4⁺/FoxP3⁺ regulatory T cells in the spleen and lymph nodes, as well as induced hypertension, vascular injury and dysfunction, and glomerular mesangial expansion in mice. Daily cotreatment with all-trans retinoic acid reported to increase regulatory T cells and decrease interleukin-17-producing T cells, prevented all of the detrimental effects of cyclosporine A and tacrolimus. All-trans retinoic acid also increased regulatory T cells and prevented the hypertension, endothelial dysfunction, and glomerular injury in genetically modified mice that phenocopy calcineurin inhibitor-treated mice (FKBP12-Tie2 knockout). Treatment with an interleukin-17-neutralizing antibody also increased regulatory T-cell levels and prevented the hypertension, endothelial dysfunction, and glomerular injury in cyclosporine A-treated and tacrolimus-treated mice and FKBP12-Tie2 knockout mice, whereas an isotype control had no effect. Augmenting regulatory T cells and inhibiting interleukin-17 signaling using noncellular therapies prevents the cardiovascular and renal toxicity of calcineurin inhibitors in mice.

A novel bidirectional interaction between endothelin-3 and retinoic acid in rat enteric nervous system precursors

BACKGROUND

Signaling through the endothelin receptor B (EDNRB) is critical for the development of the enteric nervous system (ENS) and mutations in endothelin system genes cause Hirschsprung's aganglionosis in humans. Penetrance of the disease is modulated by other genetic factors. Mutations affecting retinoic acid (RA) signaling also produce aganglionosis in mice. Thus, we hypothesized that RA and endothelin signaling pathways may interact in controlling development of the ENS.

METHODS

Rat immunoselected ENS precursor cells were cultured with the EDNRB ligand endothelin-3, an EDNRB-selective antagonist (BQ-788), and/or RA for 3 or 14 days. mRNA levels of genes related to ENS development, RA- and EDNRB-signaling were measured at 3 days. Proliferating cells and cells expressing neuronal, glial, and myofibroblast markers were quantified.

RESULTS

Culture of isolated ENS precursors for 3 days with RA decreases expression of the endothelin-3 gene and that of its activation enzyme. These changes are associated with glial proliferation, a higher percentage of glia, and a lower percentage of neurons compared to cultures without RA. These changes are independent of EDNRB signaling. Conversely, EDNRB activation in these cultures decreases expression of RA receptors β and γ mRNA and affects the expression of the RA synthetic and degradative enzymes. These gene expression changes are associated with reduced glial proliferation and a lower percentage of glia in the culture. Over 14 days in the absence of EDNRB signaling, RA induces the formation of a heterocellular plexus replete with ganglia, glia and myofibroblasts.

CONCLUSIONS

A complex endothelin-RA interaction exists that coordinately regulates the development of rat ENS precursors in vitro. These results suggest that environmental RA may modulate the expression of aganglionosis in individuals with endothelin mutations.

Nuclear Receptors in atherosclerosis: a superfamily with many 'Goodfellas'

Nuclear Receptors form a superfamily of 48 transcription factors that exhibit a plethora of functions in steroid hormone signaling, regulation of metabolism, circadian rhythm and cellular differentiation. In this review, we describe our current knowledge on the role of Nuclear Receptors in atherosclerosis, which is a multifactorial disease of the vessel wall. Various cell types are involved in this chronic inflammatory pathology in which multiple cellular processes and numerous genes are dysregulated. Systemic risk factors for atherosclerosis are among others adverse blood lipid profiles, enhanced circulating cytokine levels, as well as increased blood pressure. Since many Nuclear Receptors modulate lipid profiles or regulate blood pressure they indirectly affect atherosclerosis. In the present review, we focus on the functional involvement of Nuclear Receptors within the atherosclerotic vessel wall, more specifically on their modulation of cellular functions in endothelial cells, smooth muscle cells and macrophages. Collectively, this overview shows that most of the Nuclear Receptors are athero-protective in atherosclerotic lesions.

Endothelin Type A Receptor Genotype is a Determinant of Quantitative Traits of Metabolic Syndrome in Asian Hypertensive Families: A SAPPHIRe Study

Co-heritability of hypertension and insulin resistance (IR) within families not only implies genetic susceptibility may be responsible for these complex traits but also suggests a rational that biological candidate genes for hypertension may serve as markers for features of the metabolic syndrome (MetS). Thus we determined whether the T323C polymorphism (rs5333) of endothelin type A (ETA) receptor, a predominant receptor evoking potent vasoconstrictive action of endothelin-1, contributes to susceptibility to IR-associated hypertension in 1694 subjects of Chinese and Japanese origins. Blood pressures (BPs) and biochemistries were measured. Fasting insulin level, insulin-resistance homeostasis model assessment (HOMAIR) score, and area under curve of insulin concentration (AUCINS) were selected for assessing insulin sensitivity. Genotypes were obtained by methods of polymerase chain reaction-restriction fragment length polymorphism. Foremost findings were that minor allele frequency of the T323C polymorphism was noticeable lower in our overall Asian subjects compared to multi-national population reported in gene database; moreover both the genotypic and allelic frequencies of the polymorphism were significantly different between the two ethnic groups we studied. The genotype distributions at TT/TC/CC were 65, 31, 4% in Chinese and 51, 41, 8% in Japanese, respectively (p < 0.0001). Additionally, carriers of the C homozygote revealed characteristics of IR, namely significantly higher levels of fasting insulin, HOMAIR score, and AUCINS at 29.3, 35.3, and 39.3%, respectively, when compared to their counterparts with TT/TC genotypes in Chinese. Meanwhile, the CC genotype was associated with a higher level of high density lipoprotein cholesterol in Japanese. No association of the polymorphism with BP was observed. This study demonstrated for the first time that T323C polymorphism of ETA receptor gene was associated with an adverse insulin response in Chinese and a favorite atherogenic index in Japanese.

Prevention of Retinoic Acid-Induced Early Craniofacial Abnormalities by Vitamin B12 in Mice

Objective

The purpose of the present study was to identify the potential effect of prenatal vitamin B12 administration on retinoic acid (RA)-induced early craniofacial abnormalities in mice and to investigate the possible mechanisms by which vitamin B12 reduces malformations.

Design

In our study, whole embryo culture was used to explore the effect of vitamin B12 on mouse embryos during the critical period of organogenesis. All embryos were exposed to 0.4 μM RA and different concentrations of vitamin B12 and scored for their growth in the branchial region at the end of a 48-hour culture period. The endothelin-1 (ET-1)/dHAND protein expression levels in the first branchial arch were investigated using an immunohistochemical method.

Results

In the whole embryo culture, 100 and 10 μM vitamin B12 dose-dependently prevented branchial region malformations and decreased craniofacial defects by 90.5% and 77.3%, respectively. ET-1 and dHAND protein levels were significantly increased in vitamin B12-supplemented embryos compared to the RA-exposed group in embryonic branchial region.

Conclusions

These results suggest that vitamin B12 may prevent RA-induced craniofacial abnormalities via prevention of an RA-induced decrease of ET-1 and dHAND protein levels in the branchial region during the organogenic period. This study may shed new light on preventing craniofacial abnormalities.

Irreversible effects of retinoic acid pulse on Xenopus jaw morphogenesis: new insight into cranial neural crest specification

Jaws are formed by cephalic neural crest (CNCCs) and mesodermal cells migrating to the first pharyngeal arch (PA1). A complex signaling network involving different PA1 components then establishes the jaw morphogenetic program. To gather insight on this developmental process, in this study, we analyze the teratogenic effects of brief (1-15 min) pulses of low doses of retinoic acid (RA: 0.25-2 µM) or RA agonists administered to early Xenopus laevis (X.l.) embryos. We show that these brief pulses of RA cause permanent craniofacial defects specifically when treatments are performed during a 6-hr window (developmental stages NF15-NF23) that covers the period of CNCCs maintenance, migration, and specification. Earlier or later treatments have no effect. Similar treatments performed at slightly different developmental stages within this temporal window give rise to different spectra of malformations. The RA-dependent teratogenic effects observed in Xenopus can be partially rescued by folinic acid. We provide evidence suggesting that in Xenopus, as in the mouse, RA causes craniofacial malformations by perturbing signaling to CNCCs. Differently from the mouse, where RA affects CNCCs only at the end of their migration, in Xenopus, RA has an effect on CNCCs during all the period ranging from their exit from the neural tube until their arrival in the PA1. Our findings provide a conceptual framework to understand the origin of individual facial features and the evolution of different craniofacial morphotypes.

Endothelin-1 gene regulation

Over two decades of research have demonstrated that the peptide hormone endothelin-1 (ET-1) plays multiple, complex roles in cardiovascular, neural, pulmonary, reproductive, and renal physiology. Differential and tissue-specific production of ET-1 must be tightly regulated in order to preserve these biologically diverse actions. The primary mechanism thought to control ET-1 bioavailability is the rate of transcription from the ET-1 gene (edn1). Studies conducted on a variety of cell types have identified key transcription factors that govern edn1 expression. With few exceptions, the cis-acting elements bound by these factors have been mapped in the edn1 regulatory region. Recent evidence has revealed new roles for some factors originally believed to regulate edn1 in a tissue or hormone-specific manner. In addition, other mechanisms involved in epigenetic regulation and mRNA stability have emerged as important processes for regulated edn1 expression. The goal of this review is to provide a comprehensive overview of the specific factors and signaling systems that govern edn1 activity at the molecular level.

Anti-pigmentary activity of fucoxanthin and its influence on skin mRNA expression of melanogenic molecules

OBJECTIVES

Carotenoids and retinoic acid derivatives are topically applied for sun-protective and whitening purposes. Fucoxanthin is a carotenoid derived from edible sea algae, but its effect on melanogenesis has not been established. Therefore, we examined the effect of fucoxanthin on melanogenesis.

METHODS

Inhibitory effects on tyrosinase activity, melanin formation in B16 melanoma and skin pigmentation in UVB-irradiated guinea-pigs were evaluated. To elucidate the action of fucoxanthin on melanogenesis, its effect on skin melanogenic mRNA expression was evaluated in UVB-irradiated mice. Fucoxanthin was given topically or orally to mice once a day and UVB irradiation was applied for 14 days. The effect of fucoxanthin on skin melanogenic mRNA expression was evaluated by real time reverse transcription polymerase chain reaction.

KEY FINDINGS

Fucoxanthin inhibited tyrosinase activity, melanogenesis in melanoma and UVB-induced skin pigmentation. Topical application of fucoxanthin (1%) significantly suppressed mRNA expression of cyclooxygenase (COX)-2, endothelin receptor A, p75 neurotrophin receptor (NTR), prostaglandin E receptor 1 (EP1), melanocortin 1 receptor (MC1R) and tyrosinase-related protein 1. The suppression of p75NTR, EP1 and MC1R expressions was observed at 0.01% application. Also, oral application of fucoxanthin (10 mg/kg) significantly suppressed expression of COX-2, p75NTR, EP1 and MC1R.

CONCLUSIONS

These results suggest that fucoxanthin exhibits anti-pigmentary activity by topical or oral application in UVB-induced melanogenesis. This effect of fucoxanthin may be due to suppression of prostaglandin (PG) E(2) synthesis and melanogenic stimulant receptors (neurotrophin, PGE(2) and melanocyte stimulating hormone expression).

Molecular dynamics of retinoic acid-induced craniofacial malformations: implications for the origin of gnathostome jaws

Background

Intake of retinoic acid (RA) or of its precursor, vitamin A, during early pregnancy is associated with increased incidence of craniofacial lesions. The origin of these teratogenic effects remains enigmatic as in cranial neural crest cells (CNCCs), which largely contribute to craniofacial structures, the RA-transduction pathway is not active. Recent results suggest that RA could act on the endoderm of the first pharyngeal arch (1stPA), through a RARß-dependent mechanism.

Methodology/Principal Findings

Here we show that RA provokes dramatically different craniofacial malformations when administered at slightly different developmental times within a narrow temporal interval corresponding to the colonization of the 1^st PA by CNCCs. We provide evidence showing that RA acts on the signalling epithelium of the 1^st PA, gradually reducing the expression of endothelin-1 and Fgf8. These two molecular signals are instrumental in activating Dlx genes in incoming CNCCs, thereby triggering the morphogenetic programs, which specify different jaw elements.

Conclusions/Significance

The anatomical series induced by RA-treatments at different developmental times parallels, at least in some instances, the supposed origin of modern jaws (e.g., the fate of the incus). Our results might provide a conceptual framework for the rise of jaw morphotypes characteristic of gnathostomes.

Regulation of dHAND protein expression by all-trans retinoic acid through ET-1/ETAR signaling in H9c2 cells

dHAND is thought to be a cardiac-restricted transcription factor during embryonic development. Vertebrate heart development involves many transcription factors such as Nkx2.5, GATA, and tbx5. All-trans retinoic acid (AtRA), the oxidative metabolite of vitamin A, can regulate the expression of these factors to affect embryonic heart development. However, the action of atRA on the expression of dHAND is rarely reported. To clarify whether atRA regulate the dHAND expression, we exposed cultured H9c2 cells (rat embryonic cardiomyocytes) to atRA and detected the protein expression of dHAND by Western blot analysis. We observed atRA can regulate the dHAND expression in a dose- and time-dependent manner. AtRA also inhibited endothelin-1 (ET-1) expression in a time-dependent manner. Further studies revealed that pretreatment with 10 microM BQ-123, a selective endothelin-1 receptor (ETAR) antagonist, for 2 h can significantly counteract the inhibition of 5 microM atRA treatment for 2 h of dHAND mRNA and protein expression. Taken together, these results suggest that atRA regulates dHAND expression by ET-1/ETAR signal transduction pathway in H9c2 cells. The mechanism of ET-1/ETAR signaling in controlling the level of dHAND protein is to reduce the levels of dHAND mRNA. It is possible for atRA to exert its cardiac teratogenesis during vertebrate embryonic development in this way.

Downregulation of endothelin-1 by farnesoid X receptor in vascular endothelial cells

The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily that is highly expressed in liver, kidney, adrenals, and intestine. FXR may play an important role in the pathogenesis of cardiovascular diseases via regulating the metabolism and transport of cholesterol. In this study, we report that FXR is also expressed in rat pulmonary artery endothelial cells (EC), a "nonclassical" bile acid target tissue. FXR is functional in EC, as demonstrated by induction of its target genes such as small heterodimer partner (SHP) after treatment with chenodeoxycholic acid, a FXR agonist. Interestingly, activation of FXR in EC led to downregulation of endothelin (ET)-1 expression. Reporter assays showed that activation of FXR inhibited transcriptional activation of the human ET-1 gene promoter and also repressed the activity of a heterologous promoter driven by activator protein (AP)-1 response elements. Electrophoretic mobility-shift and chromatin immunoprecipitation assays indicated that FXR reduced the binding activity of AP-1 transcriptional factors, suggesting that FXR may suppress ET-1 expression via negatively interfering with AP-1 signaling. These studies suggest that FXR may play a role in endothelial homeostasis and may serve as a novel molecular target for manipulating ET-1 expression in vascular EC.

Retinoic acid down-regulates Tbx1 expression in vivo and in vitro

Both Tbx1 and retinoic acid (RA) are key players in embryonic pharyngeal development; loss of Tbx1 produces DiGeorge syndrome-like phenotypes in mouse models as does disruption of retinoic acid homeostasis. We have demonstrated that perturbation of retinoic acid levels in the avian embryo produces altered Tbx1 expression. In vitamin A-deficient quails, which lack endogenous retinoic acid, Tbx1 expression patterns were disrupted early in development and expression was subsequently lost in all tissues. "Gain-of-function" experiments where RA-soaked beads were grafted into the pharyngeal region produced localized down-regulation of Tbx1 expression. In these embryos, analysis of Shh and Foxa2, upstream control factors for Tbx1, suggested that the effect of RA was independent of this regulatory pathway. Real-time polymerase chain reaction analysis of retinoic acid-treated P19 cells showed a dose-dependent repression of Tbx1 by retinoic acid. Repression of Tbx1 transcript levels was first evident after 8-12 hr in culture in the presence of retinoic acid, and to achieve the highest levels of repression, de novo protein synthesis was required.

Heparin Regulates Transcription of Endothelin-1 Gene in Endothelial Cells

Heparin, which is widely used as an anticoagulant, has been shown to have antiatherosclerotic and antihypertensive effects in animals and humans. These effects are mediated by the inhibition of endothelin-1 (ET-1) production in endothelial cells. To clarify the mechanism of this inhibition, we investigated the effect of heparin on transcriptional regulation of the ET-1 gene in bovine aortic endothelial cells (BAEC) cultured in fetal calf serum. ET-1 mRNA expression was significantly suppressed by heparin in a dose-dependent manner. Promoter analysis revealed that the minimum ET-1 promoter containing only the GATA and AP-1 sequences as positive cis-acting sites in the ET-1 promoter is sufficient for this suppression. Gel mobility shift assays using oligonucleotides encoding the ET-1 AP-1 and ET-1 GATA sites confirmed that both AP-1 and GATA binding activities in BAEC nuclear extract were markedly inhibited by heparin. Western blot analyses indicated that heparin completely blocked extracellular signal-regulated kinase (ERK) activation, and inhibiting ERK activity resulted in loss of heparin-dependent inhibition of the ET-1 gene. These data indicate that the ET-1 mRNA level is negatively regulated by heparin at the transcription level, through modification of AP-1 and GATA protein binding activities, which direct the ET-1 promoter in BAEC. This effect may be mediated, at least in part, through inhibition of ERK activity.

À quoi sert le système endothéline ?

Endothelins are a family of three peptides of 21 amino acids with strong vasoconstrictor effects. The three peptides are encoded by three different genes and derived from precursors (" big endothelins") which are cleaved by metalloproteases, named endothelin-converting enzyme. Two receptors have been cloned, ET-A and ET-B which bind the three endothelins with various affinities. The diverse expression pattern of the endothelin system (ET) components is associated with a complex pharmacology and its counteracting physiological actions. New modulators of the ET system have been described : retinoic acid, leptin, prostaglandins, hypoxia. Endothelins can be considered as regulators working in paracrine and autocrine fashion in a variety of organs in different cellular types. The ET system has beneficial and detrimental roles in mammals. The different components have been shown to be essential for a normal embryonic and neonatal development, for renal homeostasis and maintenance of basal vascular tone. They are involved in physiological and tumoral angiogenesis. They affect the physiology and pathophysiology of the liver, muscle, skin, adipose tissue and reproductive tract. The endothelin system participates in the development of atherosclerosis as well as pulmonary hypertension, and mediates cardiac remodeling in heart failure. Elaboration of new animal models (knock-out, pathophysiological models em leader ) will allow the clear genetic dissection of physiological and pathophysiological roles of the endothelin system.

Endothelin-1 Gene Expression in Endothelial Cells Is Potently Inhibited by a Vasodilator, Dilazep

Endothelin-1 (ET-1) is considered to be involved in various cardiovascular and renal disorders. The objective of this study was to investigate whether a vasodilator and antiplatelet agent, 1,4-bis[3-(3,4,5-trimethoxybenzoyloxy) propyl]perhydro-1,4-diazepine dihydrochloride monohydrate (dilazep, DZ), has an ET-1-inhibiting effect in vitro. Bovine aortic endothelial cells (BAEC) and human umbilical vein endothelial cells (HUVEC) pretreated with fetal calf serum were treated with DZ and preproET-1 (PpET-1) transcription was evaluated by Northern blot analysis. ET-1 peptide release in culture medium was evaluated by radioimmunoassay. The effect of DZ on the ET-1 promoter/enhancer apparatus was evaluated in transfection experiments using -5 kb ET-1 promoter/enhancer constructs. Modest inhibition of PpET-1 gene transcription was detected after 30 min of DZ treatment (0.56+/-0.19 vs. 1 , p<0.01) and more marked inhibition was seen at 24 h (0.04+/-0.04 vs. 1, p<0.0001). ET-1 peptide release was suppressed strongly after 3 h (382.5+/-2.9 vs. 673.5+/-74.5pg/ml, p< 0.001) and 24 h (38.8+/-9.8 vs. 5,075+/-52.0pg/ml, p<0.0001). DZ potently inhibited PpET-1 transcription in a concentration-dependent manner (0.42+/-0.18 vs. 1, p<0.001, at 100micromol/l). DZ suppressed PpET-1 transcription in confluent HUVEC at 3 h (0.41 +/-0.11 vs. 1, p<0.0001). DZ strongly inhibited PpET-1 transcription after 1 h of thrombin (TH) treatment (0.30+/-0.01 vs. 1.51+/-0.03, p<0.0001). Transfection experiments using the 5 kb ET-1 promoter-luciferase plasmid revealed that DZ strongly suppressed ET-1 promoter activity by 99% (p<0.01). DZ potently inhibited ET-1 gene expression at the transcription level in serum- or TH-treated endothelial cells.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.