Effects of all-trans retinoic acid on angiotensin II-induced myocyte hypertrophy

Role of cellular retinol-binding protein, type 1 and retinoid homeostasis in the adult mouse heart: A multi-omic approach

The main active metabolite of Vitamin A, all-trans retinoic acid (RA), is required for proper cellular function and tissue organization. Heart development has a well-defined requirement for RA, but there is limited research on the role of RA in the adult heart. Homeostasis of RA includes regulation of membrane receptors, chaperones, enzymes, and nuclear receptors. Cellular retinol-binding protein, type 1 (CRBP1), encoded by retinol-binding protein, type 1 (Rbp1), regulates RA homeostasis by delivering vitamin A to enzymes for RA synthesis and protecting it from non-specific oxidation. In this work, a multi-omics approach was used to characterize the effect of CRBP1 loss using the Rbp1^-/- mouse. Retinoid homeostasis was disrupted in Rbp1^-/- mouse heart tissue, as seen by a 33% and 24% decrease in RA levels in the left and right ventricles, respectively, compared to wild-type mice (WT). To further inform on the effect of disrupted RA homeostasis, we conducted high-throughput targeted metabolomics. A total of 222 metabolite and metabolite combinations were analyzed, with 33 having differential abundance between Rbp1^-/- and WT hearts. Additionally, we performed global proteome profiling to further characterize the impact of CRBP1 loss in adult mouse hearts. More than 2606 unique proteins were identified, with 340 proteins having differential expression between Rbp1^-/- and WT hearts. Pathway analysis performed on metabolomic and proteomic data revealed pathways related to cellular metabolism and cardiac metabolism were the most disrupted in Rbp1^-/- mice. Together, these studies characterize the effect of CRBP1 loss and reduced RA in the adult heart.

Multi-omic Analysis of Non-human Primate Heart after Partial-body Radiation with Minimal Bone Marrow Sparing

ABSTRACT

High-dose radiation exposure results in hematopoietic and gastrointestinal acute radiation syndromes followed by delayed effects of acute radiation exposure, which encompasses multiple organs, including heart, kidney, and lung. Here we sought to further characterize the natural history of radiation-induced heart injury via determination of differential protein and metabolite expression in the heart. We quantitatively profiled the proteome and metabolome of left and right ventricle from non-human primates following 12 Gy partial body irradiation with 2.5% bone marrow sparing over a time period of 3 wk. Global proteome profiling identified more than 2,200 unique proteins, with 220 and 286 in the left and right ventricles, respectively, showing significant responses across at least three time points compared to baseline levels. High-throughput targeted metabolomics analyzed a total of 229 metabolites and metabolite combinations, with 18 and 22 in the left and right ventricles, respectively, showing significant responses compared to baseline levels. Bioinformatic analysis performed on metabolomic and proteomic data revealed pathways related to inflammation, energy metabolism, and myocardial remodeling were dysregulated. Additionally, we observed dysregulation of the retinoid homeostasis pathway, including significant post-radiation decreases in retinoic acid, an active metabolite of vitamin A. Significant differences between left and right ventricles in the pathology of radiation-induced injury were identified. This multi-omic study characterizes the natural history and molecular mechanisms of radiation-induced heart injury in NHP exposed to PBI with minimal bone marrow sparing.

Cyanide Poisoning Compromises Gene Pathways Modulating Cardiac Injury in Vivo

Smoke inhalation from a structure fire is a common route of cyanide poisoning in the U.S. Cyanide inhibits cellular respiration, often leading to death. Its rapid distribution throughout the body can result in injuries to multiple organs, and cyanide victims were reported to experience myocardial infarction and other cardiac complications. However, molecular mechanisms of such complications are yet to be elucidated. While FDA-approved CN antidotes such as sodium thiosulfate and hydroxocobalamin are clinically used, they have foreseeable limitations during mass casualty situations because they require intravenous administration. To facilitate the development of better antidotes and therapeutic treatments, a global view of molecular changes induced by cyanide exposure is necessary. As an exploratory pursuit, we performed oligonucleotide microarrays to establish cardiac transcriptomes of an animal model of nose-only inhalation exposure to hydrogen cyanide (HCN), which is relevant to smoke inhalation. We also profiled cardiac transcriptomes after subcutaneous injection of potassium cyanide (KCN). Although the KCN injection model has often been used to evaluate medical countermeasures, this study demonstrated that cardiac transcriptomes are largely different from that of the HCN inhalation model at multiple time points within 24 h after exposure. Pathway analysis identified that HCN-induced transcriptomes were enriched with genes encoding mediators of pathways critical in modulation of cardiac complications and that a large number of such genes were significantly decreased in expression. We utilized the upstream regulatory analysis to propose drugs that can be potentially employed to treat cyanide-induced cardiac complications.

Vitamin A as a Transcriptional Regulator of Cardiovascular Disease

Vitamin A is a micronutrient and signaling molecule that regulates transcription, cellular differentiation, and organ homeostasis. Additionally, metabolites of Vitamin A are utilized as differentiation agents in the treatment of hematological cancers and skin disorders, necessitating further study into the effects of both nutrient deficiency and the exogenous delivery of Vitamin A and its metabolites on cardiovascular phenotypes. Though vitamin A/retinoids are well-known regulators of cardiac formation, recent evidence has emerged that supports their role as regulators of cardiac regeneration, postnatal cardiac function, and cardiovascular disease progression. We here review findings from genetic and pharmacological studies describing the regulation of both myocyte- and vascular-driven cardiac phenotypes by vitamin A signaling. We identify the relationship between retinoids and maladaptive processes during the pathological hypertrophy of the heart, with a focus on the activation of neurohormonal signaling and fetal transcription factors (Gata4, Tbx5). Finally, we assess how this information might be leveraged to develop novel therapeutic avenues.

Rosuvastatin and retinoic acid may act as 'pleiotropic agents' against β-adrenergic agonist-induced acute myocardial injury through modulation of multiple signalling pathways

Cardiovascular disorders constitute the principal cause of deaths worldwide and will continue as the major disease-burden by the year 2060. A significant proportion of heart failures occur because of use and misuse of drugs and most of the investigational agents fail to achieve any clinical relevance. Here, we investigated rosuvastatin and retinoic acid for their "pharmacological pleiotropy" against high dose β-adrenergic agonist (isoproterenol)-induced acute myocardial insult. Rats were pretreated with rosuvastatin and/or retinoic acid for seven days and the myocardial injury was induced by administering isoproterenol on the seventh and eighth day. After induction, rats were anaesthetized for electrocardiography, then sacrificed and different samples were collected/stored for various downstream assays. Myocardial injury with isoproterenol resulted in increased cardiac mass, decreased R-wave amplitude, increased QRS and QT durations; elevated levels of cardiac markers like cTnI, CK-MB, ALT and AST; increased lipid peroxidation, protein carbonylation and tissue nitric oxide levels; decreased endogenous antioxidants like SOD, CAT, GR, GST, GPx and total antioxidant activity; increased inflammatory markers like TNF-α and IL-6; decreased the mRNA expression of Nrf2 and Bcl-2; increased the mRNA expression of Bax, eNOS and iNOS genes. Pretreatment with rosuvastatin and/or retinoic acid mitigated many of the above biochemical and pathological alterations. Our results demonstrate that rosuvastatin and retinoic acid exert cardioprotective effects and may act as potential agents in the prevention of β-adrenergic agonist-induced acute myocardial injury in rats. Cardioprotective potential of rosuvastatin and retinoic acid could be attributed to their influence on the redox pathways, immunomodulation, membrane stability, Nrf2 preservation, iNOS and Bax expression levels. Thus, they may act directly or indirectly at various steps, the breakpoints, in the pathophysiological cascade responsible for cardiac injury. Our study gives insights about the pharmacological pleiotropism of rosuvastatin and retinoic acid.

Chondroitin Sulfate-Linked Prodrug Nanoparticles Target the Golgi Apparatus for Cancer Metastasis Treatment

Metastasis is a multistep biological process regulated by multiple signaling pathways. The integrity of the Golgi apparatus plays an important role in these signaling pathways. Inspired by the mechanism and our previous finding about accumulation of chondroitin sulfate in Golgi apparatus in hepatic stellate cells, we developed a Golgi apparatus-targeting prodrug nanoparticle system by synthesizing retinoic acid (RA)-conjugated chondroitin sulfate (CS) (CS-RA). The prodrug nanoparticles appeared to accumulate in the Golgi apparatus in cancer cells and realized RA release under an acidic environment. We confirmed that CS-RA exhibited successful inhibition of multiple metastasis-associated proteins expression in vitro and in vivo by disruption of the Golgi apparatus structure. Following loading with paclitaxel (PTX), the CS-RA based nanoformulation (PTX-CS-RA) inhibited migration, invasion, and angiogenesis in vitro and suppressed tumor growth and metastasis in 4T1-Luc bearing mice. This multistep targeted nanoparticle system potentially enhanced the effect of antimetastasis combined with chemotherapy.

All-trans retinoic acid attenuates isoproterenol-induced cardiac dysfunction through Crabp1 to dampen CaMKII activation

Inhibiting Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) over activation can decrease detrimental cardiac remodeling that leads to dilated cardiomyopathy, cell death, and heart failure. We previously showed that cellular retinoic acid binding protein 1 (Crabp1) knockout mice (CKO) exhibited a more severe isoproterenol (ISO)-induced heart failure and cardiac remodeling phenotype with elevated CaMKII activity in the heart, suggesting a cardiac-protective function of Crabp1 through modulating CaMKII activity. Here we examine whether the highly selective, endogenous ligand of Crabp1, all-trans retinoic acid (RA), can attenuate ISO-induced cardiac dysfunction. We also examine if this attenuation involves Crabp1 and the inhibition of CaMKII. RA pre-treatment followed by ISO challenge effectively restores ejection fraction in wild type, but not in CKO mice. This is correlated with reduced CaMKII auto-phosphorylation at T287 and phospholamban phosphorylation at T17, a substrate of CaMKII. RA pretreatment also reduces ISO-induced apoptosis in WT heart. Cell culture experiments confirm that RA inhibits CaMKII phosphorylation, which requires Crabp1. Molecular data reveal interaction of Crabp1 with the kinase and regulatory domains of CaMKII, and that RA selectively enhances Crabp1 interaction with the regulatory domain, suggesting a potential regulatory role for holo-Crabp1 in CaMKII activation. Together, these data demonstrate that RA bound Crabp1 plays a protective role in β-adrenergic stimulated cardiac remodeling, which is partially attributed to its dampening CaMKII activation. Targeting Crabp1 provides a potentially new therapeutic strategy for managing heart diseases.

Zeaxanthin Isolated from Dunaliella salina Microalgae Ameliorates Age Associated Cardiac Dysfunction in Rats through Stimulation of Retinoid Receptors

Retinoids are essential during early cardiovascular morphogenesis. However, recent studies showed their important role in cardiac remodeling in rats with hypertension and following myocardial infarction. The present study aimed to investigate the effect of zeaxanthin heneicosylate (ZH); a carotenoid ester isolated from Dunaliella salina microalgae, on cardiac dysfunction ensuing d-galactose injection in rats. Rats injected with d-GAL (200 mg/kg; I.P) for 8 weeks were orally treated with ZH (250 μg/kg) for 28 consecutive days. Results showed that d-GAL injection caused dramatic electrocardiographic changes as well as marked elevation in serum levels of homocysteine, creatinine kinase isoenzyme and lactate dehydrogenase. A reduction in the cardiac contents of glucose transporter-4 and superoxide dismutase along with the elevation of inducible nitric oxide synthetase and interleukin-6 was also noticed. Oral administration of ZH significantly improved the above mentioned cardiac aging manifestations; this was further emphasized through histopathological examinations. The effect of ZH is mediated through the interaction with retinoid receptor alpha (RAR-α) as evidenced through a significant elevation of RAR-α expression in cardiac tissue following the lead of an in silico molecular docking study. In conclusion, zeaxanthin heneicosylate isolated from D. salina ameliorated age-associated cardiac dysfunction in rats through the activation of retinoid receptors.

Increased plasma RBP4 concentration in older hypertensives is related to the decreased kidney function and the number of antihypertensive drugs-results from the PolSenior substudy

Increased plasma retinol-binding protein 4 (RBP4), a novel adipokine, has been associated in previous studies with obesity, type 2 diabetes, dyslipidemia, hypertension (HT), atherosclerosis, and coronary artery disease. This study aimed to analyze the relationship between HT occurrence and its treatment, and plasma RBP4 concentrations in the older polish population. The study sample consisted of 1728 (890 men and 838 women) PolSenior study participants aged 65 years and older with available plasma samples and NT-proBNP values below 2000 pg/mL. The analysis included body mass index, waist circumference, blood pressure, antihypertensive medication, estimated glomerular filtration rate, serum glucose and insulin (and the homeostatic model assessment of insulin resistance), and plasma RBP4 levels. RBP4 plasma concentrations were higher in hypertensive (N = 645) than normotensive (N = 236) men (43.4 [30.4-64.8] vs. 38.1 [27.1-54.4] ng/mL, respectively; P < .01) but not in women (44.6 [29.6-63.5] vs. 40.7 [29.1-58.1] ng/mL, respectively; P = .21). In the subanalysis, higher plasma RBP4 levels were observed in women with treated than untreated HT and in subjects taking four of more antihypertensive drugs. The linear regression shown that estimated glomerular filtration rate (β = -0.015), thiazide diuretics (β = 0.041), and α-blockers (β = 0.049) were explaining log₁₀RBP4 plasma levels variability in the study group. Older male Caucasians with HT are characterized by elevated plasma RBP4 levels. This increase is proportional to the number of antihypertensive drugs and decreased glomerular filtration rate. Among the antihypertensive drugs, only thiazide diuretics and α-blockers had a significant influence on RBP4 levels.

Triptolide Upregulates Myocardial Forkhead Helix Transcription Factor p3 Expression and Attenuates Cardiac Hypertrophy

The forkhead/winged helix transcription factor (Fox) p3 can regulate the expression of various genes, and it has been reported that the transfer of Foxp3-positive T cells could ameliorate cardiac hypertrophy and fibrosis. Triptolide (TP) can elevate the expression of Foxp3, but its effects on cardiac hypertrophy remain unclear. In the present study, neonatal rat ventricular myocytes (NRVM) were isolated and stimulated with angiotensin II (1 μmol/L) to induce hypertrophic response. The expression of Foxp3 in NRVM was observed by using immunofluorescence assay. Fifty mice were randomly divided into five groups and received vehicle (control), isoproterenol (Iso, 5 mg/kg, s.c.), one of three doses of TP (10, 30, or 90 μg/kg, i.p.) for 14 days, respectively. The pathological morphology changes were observed after Hematoxylin and eosin, lectin and Masson's trichrome staining. The levels of serum brain natriuretic peptide (BNP) and troponin I were determined by enzyme-linked immunosorbent assay and chemiluminescence, respectively. The mRNA and protein expressions of α- myosin heavy chain (MHC), β-MHC and Foxp3 were determined using real-time PCR and immunohistochemistry, respectively. It was shown that TP (1, 3, 10 μg/L) treatment significantly decreased cell size, mRNA and protein expression of β-MHC, and upregulated Foxp3 expression in NRVM. TP also decreased heart weight index, left ventricular weight index and, improved myocardial injury and fibrosis; and decreased the cross-scetional area of the myocardium, serum cardiac troponin and BNP. Additionally, TP markedly reduced the mRNA and protein expression of myocardial β-MHC and elevated the mRNA and protein expression of α-MHC and Foxp3 in a dose-dependent manner. In conclusion, TP can effectively ameliorate myocardial damage and inhibit cardiac hypertrophy, which is at least partly related to the elevation of Foxp3 expression in cardiomyocytes.

Loss of myocardial retinoic acid receptor α induces diastolic dysfunction by promoting intracellular oxidative stress and calcium mishandling in adult mice

Retinoic acid receptor (RAR) has been implicated in pathological stimuli-induced cardiac remodeling. To determine whether the impairment of RARα signaling directly contributes to the development of heart dysfunction and the involved mechanisms, tamoxifen-induced myocardial specific RARα deletion (RARαKO) mice were utilized. Echocardiographic and cardiac catheterization studies showed significant diastolic dysfunction after 16wks of gene deletion. However, no significant differences were observed in left ventricular ejection fraction (LVEF), between RARαKO and wild type (WT) control mice. DHE staining showed increased intracellular reactive oxygen species (ROS) generation in the hearts of RARαKO mice. Significantly increased NOX2 (NADPH oxidase 2) and NOX4 levels and decreased SOD1 and SOD2 levels were observed in RARαKO mouse hearts, which were rescued by overexpression of RARα in cardiomyocytes. Decreased SERCA2a expression and phosphorylation of phospholamban (PLB), along with decreased phosphorylation of Akt and Ca²⁺/calmodulin-dependent protein kinase II δ (CaMKII δ) was observed in RARαKO mouse hearts. Ca²⁺ reuptake and cardiomyocyte relaxation were delayed by RARα deletion. Overexpression of RARα or inhibition of ROS generation or NOX activation prevented RARα deletion-induced decrease in SERCA2a expression/activation and delayed Ca²⁺ reuptake. Moreover, the gene and protein expression of RARα was significantly decreased in aged or metabolic stressed mouse hearts. RARα deletion accelerated the development of diastolic dysfunction in streptozotocin (STZ)-induced type 1 diabetic mice or in high fat diet fed mice. In conclusion, myocardial RARα deletion promoted diastolic dysfunction, with a relative preserved LVEF. Increased oxidative stress have an important role in the decreased expression/activation of SERCA2a and Ca²⁺ mishandling in RARαKO mice, which are major contributing factors in the development of diastolic dysfunction. These data suggest that impairment of cardiac RARα signaling may be a novel mechanism that is directly linked to pathological stimuli-induced diastolic dysfunction.

Retinoic acid and sodium butyrate suppress the cardiac expression of hypertrophic markers and proinflammatory mediators in Npr1 gene-disrupted haplotype mice

The objective of the present study was to examine the genetically determined differences in the natriuretic peptide receptor-A (NPRA) gene (Npr1) copies affecting the expression of cardiac hypertrophic markers, proinflammatory mediators, and matrix metalloproteinases (MMPs) in a gene-dose-dependent manner. We determined whether stimulation of Npr1 by all-trans retinoic acid (RA) and histone deacetylase (HDAC) inhibitor sodium butyric acid (SB) suppress the expression of cardiac disease markers. In the present study, we utilized Npr1 gene-disrupted heterozygous (Npr1(+/-), 1-copy), wild-type (Npr1(+/+), 2-copy), gene-duplicated (Npr1(++/+), 3-copy) mice, which were treated intraperitoneally with RA, SB, and a combination of RA/SB, a hybrid drug (HB) for 2 wk. Untreated 1-copy mice showed significantly increased heart weight-body weight (HW/BW) ratio, blood pressure, hypertrophic markers, including beta-myosin heavy chain (β-MHC) and proto-oncogenes (c-fos and c-jun), proinflammatory mediator nuclear factor kappa B (NF-κB), and MMPs (MMP-2, MMP-9) compared with 2-copy and 3-copy mice. The heterozygous (haplotype) 1-copy mice treated with RA, SB, or HB, exhibited significant reduction in the expression of β-MHC, c-fos, c-jun, NF-κB, MMP-2, and MMP-9. In drug-treated animals, the activity and expression levels of HDAC were significantly reduced and histone acetyltransferase activity and expression levels were increased. The drug treatments significantly increased the fractional shortening and reduced the systolic and diastolic parameters of the Npr1(+/-) mice hearts. Together, the present results demonstrate that a decreased Npr1 copy number enhanced the expression of hypertrophic markers, proinflammatory mediators, and MMPs, whereas an increased Npr1 repressed the cardiac disease markers in a gene-dose-dependent manner.

Retinoid X receptor agonists inhibit hypertension-induced myocardial hypertrophy by modulating LKB1/AMPK/p70S6K signaling pathway

BACKGROUND

Retinoid X receptor (RXR) has been demonstrated to play an important role in cardiac development and has been implicated in cardiovascular diseases. This study aimed to examine the effects of RXRα agonist bexarotene on pathological left ventricular hypertrophy (LVH) in a spontaneously hypertensive rat (SHR) model and the underlying mechanism.

METHODS

WKY rats served as controls. SHRs were randomized into 3 groups at the age of 4 weeks and were treated (once daily for 12 weeks) with either bexarotene (30 or 100mg/kg body weight) or vehicle alone. Echocardiography was performed to determine cardiac structure and function. Neonatal cardiomyocytes were treated with AngII (10(-7) mmol/L) with or without the indicated concentration of RXRα ligand 9-cis-RA. The protein abundances of β-actin, RXRα, LKB1, phospho-LKB1, AMPK, phospho-AMPK, P70S6K, phospho-P70S6K, ACE, and AT1 receptor were measured along with blood pressure, body weight and angiotensin II (Ang II) levels. The effects of LKB1 downregulation by LKB1 small, interfering RNA were examined.

RESULTS

Treatment of SHRs with bexarotene resulted in significant inhibition of LVH without eliminating hypertension. Immunoblot with heart tissue homogenates from SHRs revealed that bexarotene activated the LKB1/AMPK signaling pathway and inhibited p70S6K. However, the increased Ang II levels in SHR serum and heart tissue were not reduced by bexarotene treatment. Treatment of cardiomyocytes with Ang II resulted in significantly reduced LKB1/AMPK activity and increased p70S6K activity. 9-cis-RA antagonized Ang II-induced LKB1/AMPK and p70S6K activation changes in vitro.

CONCLUSIONS

RXR agonists prevent the inhibition of the LKB1/AMPK/p70S6K pathway and regulate protein synthesis to reduce LVH. This antihypertrophic effect of bexarotene is independent of blood pressure.

Molecular Mechanisms of Retinoid Receptors in Diabetes-Induced Cardiac Remodeling

Diabetic cardiomyopathy (DCM), a significant contributor to morbidity and mortality in diabetic patients, is characterized by ventricular dysfunction, in the absence of coronary atherosclerosis and hypertension. There is no specific therapeutic strategy to effectively treat patients with DCM, due to a lack of a mechanistic understanding of the disease process. Retinoic acid, the active metabolite of vitamin A, is involved in a wide range of biological processes, through binding and activation of nuclear receptors: retinoic acid receptors (RAR) and retinoid X receptors (RXR). RAR/RXR-mediated signaling has been implicated in the regulation of glucose and lipid metabolism. Recently, it has been reported that activation of RAR/RXR has an important role in preventing the development of diabetic cardiomyopathy, through improving cardiac insulin resistance, inhibition of intracellular oxidative stress, NF-κB-mediated inflammatory responses and the renin-angiotensin system. Moreover, downregulated RAR/RXR signaling has been demonstrated in diabetic myocardium, suggesting that impaired RAR/RXR signaling may be a trigger to accelerate diabetes-induced development of DCM. Understanding the molecular mechanisms of retinoid receptors in the regulation of cardiac metabolism and remodeling under diabetic conditions is important in providing the impetus for generating novel therapeutic approaches for the prevention and treatment of diabetes-induced cardiac complications and heart failure.

All-trans retinoic acid stimulates gene expression of the cardioprotective natriuretic peptide system and prevents fibrosis and apoptosis in cardiomyocytes of obese ob/ob mice

In hypertensive rodents, retinoic acid (RA) prevents adverse cardiac remodelling and improves myocardial infarction outcome, but its role in obesity-related changes of cardiac tissue are unclear. We hypothesized that all-trans RA (ATRA) treatment will improve the cardioprotective oxytocin-natriuretic peptides (OT-NP) system, preventing apoptosis and collagen accumulation in hearts of ob/ob mice, a mouse model of obesity and insulin resistance. Female 9-week-old B6.V-Lep/J ob/ob mice (n = 16) were divided into 2 groups: 1 group (n = 8) treated with 100 μg of ATRA dissolved in 100 μL of corn oil (vehicle) delivered daily (∼2 μg·g body weight(-1)·day(-1)) by stomach intubation for 16 days, and 1 group (n = 8) that received the vehicle alone. A group of nonobese littermate mice (n = 9) served as controls. Ob/ob mice exhibited obesity, hyperglycaemia, and downregulation of the cardiac OT-NP system, including the mRNA for the transcription factor GATA4, OT receptor and brain NP, and the protein expression for endothelial nitric oxide synthase. Hearts from ob/ob mice also demonstrated increased apoptosis and collagen accumulation. ATRA treatment induced weight loss and decreased adipocytes diameter in the visceral fat, thus reducing visceral obesity, which is associated with a high risk for cardiovascular disease. RA treatment was associated with a reduction in hyperglycemia and a normalization of the OT-NP system's expression in the hearts of ob/ob mice. Furthermore, ATRA treatment prevented apoptosis and collagen accumulation in hearts of ob/ob mice. The present study indicates that ATRA treatment was effective in restoring the cardioprotective OT-NP system and in preventing abnormal cardiac remodelling in the ob/ob mice.

Retinoid signaling in pathological remodeling related to cardiovascular disease

Retinoids, the active derivatives of vitamin A, are critical signaling molecules in crucial biological processes such as embryonic development, the maintenance of immune function, and cellular differentiation and proliferation. Preclinical studies have shown that retinoids also regulate morphological changes during the progression of cardiovascular disease (CVD). CVD is complexly formed in a mutual chain reaction of various modern lifestyle-related risk factors such as dyslipidemia, hypertension, diabetes, and obesity. These factors induce the pathological remodeling of adipose tissue, the vasculature, and the ventricles, which are a potential target for retinoid signaling. This perspective highlights emerging topics and future prospectives on the relationship between CVD and retinoid signaling.

Retinoic acid signalling is activated in the postischemic heart and may influence remodelling

Background

All-trans retinoic acid (atRA), an active derivative of vitamin A, regulates cell differentiation, proliferation and cardiac morphogenesis via transcriptional activation of retinoic acid receptors (RARs) acting on retinoic acid response elements (RARE).We hypothesized that the retinoic acid (RA) signalling pathway is activated in myocardial ischemia and postischemic remodelling.

Methods and Findings

Myocardial infarction was induced through ligating the left coronary artery in mice. In vivo cardiac activation of the RARs was measured by imaging RARE-luciferase reporter mice, and analysing expression of RAR target genes and proteins by real time RT-PCR and western blot. Endogenous retinoids in postinfarcted hearts were analysed by triple-stage liquid chromatography/tandem mass spectrometry. Cardiomyocytes (CM) and cardiofibroblasts (CF) were isolated from infarcted and sham operated RARE luciferase reporter hearts and monitored for RAR activity and expression of target genes. The effect of atRA on CF proliferation was evaluated by EdU incorporation. Myocardial infarction increased thoracic RAR activity in vivo (p<0.001), which was ascribed to the heart through ex vivo imaging (p = 0.002) with the largest signal 1 week postinfarct. This was accompanied by increased cardiac gene and protein expression of the RAR target genes retinol binding protein 1 (p = 0.01 for RNA, p = 0,006 for protein) and aldehyde dehydrogenase 1A2 (p = 0.04 for RNA, p = 0,014 for protein), while gene expression of cytochrome P450 26B1 was downregulated (p = 0.007). Concomitantly, retinol accumulated in the infarcted zone (p = 0.02). CM and CF isolated from infarcted hearts had higher luminescence than those from sham operated hearts (p = 0.02 and p = 0.008). AtRA inhibited CF proliferation in vitro (p = 0.02).

Conclusion

The RA signalling pathway is activated in postischemic hearts and may play a role in regulation of damage and repair during remodelling.

High glucose-induced repression of RAR/RXR in cardiomyocytes is mediated through oxidative stress/JNK signaling

The biological actions of retinoids are mediated by nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs). We have recently reported that decreased expression of RARα and RXRα has an important role in high glucose (HG)-induced cardiomyocyte apoptosis. However, the regulatory mechanisms of HG effects on RARα and RXRα remain unclear. Using neonatal cardiomyocytes, we found that ligand-induced promoter activity of RAR and RXR was significantly suppressed by HG. HG promoted protein destabilization and serine-phosphorylation of RARα and RXRα. Proteasome inhibitor MG132 blocked the inhibitory effect of HG on RARα and RXRα. Inhibition of intracellular reactive oxidative species (ROS) abolished the HG effect. In contrast, H(2)O(2) stimulation suppressed the expression and ligand-induced promoter activity of RARα and RXRα. HG promoted phosphorylation of ERK1/2, JNK and p38 MAP kinases, which was abrogated by an ROS inhibitor. Inhibition of JNK, but not ERK and p38 activity, reversed HG effects on RARα and RXRα. Activation of JNK by over expressing MKK7 and MEKK1, resulted in significant downregulation of RARα and RXRα. Ligand-induced promoter activity of RARα and RXRα was also suppressed by overexpression of MEKK1. HG-induced cardiomyocyte apoptosis was potentiated by activation of JNK, and prevented by all-trans retinoic acid and inhibition of JNK. Silencing the expression of RARα and RXRα activated the JNK pathway. In conclusion, HG-induced oxidative stress and activation of the JNK pathway negatively regulated expression/activation of RAR and RXR. The impaired RAR/RXR signaling and oxidative stress/JNK pathway forms a vicious circle, which significantly contributes to hyperglycemia induced cardiomyocyte apoptosis.

13-cis-Retinoic acid specific down-regulation of angiotensin type 1 receptor in rat liver epithelial and aortic smooth muscle cells

Transcriptional repression through cis- and trans-acting factors enabling an alternate approach to control angiotensin type 1 receptor (AT1 or AGTR1 as listed in the MGI database) expression has not been studied. In previous investigations, treatment with retinoic acid was found to be associated with enhanced insulin sensitivity. In our previous study, expression of AT1 was found to be inversely correlated with intracellular glucose concentrations. Therefore, we hypothesized that 13-cis-retinoic acid (13cRA), an antioxidant, enhances insulin-sensitive glucose-mediated down-regulation of the AT1. In this study, we used continuously passaged rat liver epithelial cells. Our study shows that cells exposed to 13cRA specifically down-regulated the AT1 protein in a dose- and time-dependent manner, independently of any change in receptor affinity. Down-regulation of the AT1 expression leads to reduced AngII-mediated intracellular calcium release, a hallmark of receptor-mediated intracellular signaling. Similarly with receptor down-regulation, we observed a significant reduction in AT1 mRNA; however, the AT1 down-regulation was independent of insulin-sensitive glucose uptake and retinoic acid receptor activation (RAR/RXR). Treatment with 13cRA resulted in phosphorylation of p42/p44 MAP kinases in these cells. Subsequent studies using MEK inhibitor PD98059 prevented 13cRA-mediated AT1 down-regulation and restored AngII-mediated intracellular calcium response. Furthermore, 13cRA-mediated inhibitory effects on AT1 were validated in primary rat aortic smooth muscle cells. In summary, our results demonstrate for the first time that 13cRA has a glucose- and RAR/RXR-independent mechanism for transcriptional inhibition of AT1, suggesting its therapeutic potential in systems in which AT1 expression is deregulated in insulin-sensitive and -insensitive tissues.

Transient expression of cellular retinol-binding protein-1 during cardiac repair after myocardial infarction

Retinoic acid (RA) is a vitamin A derivative that exerts pleiotropic biological effects. Intracellular transport and metabolism of RA are regulated by cellular retinol-binding proteins (CRBP). CRBP-1 is transiently expressed in granulation tissue fibroblasts during wound healing; however, its role in cardiac remodeling remains unknown. A rat myocardial infarction (MI) model was established by ligation of the left coronary artery, and hearts were obtained at 3, 6, 15, 30 and 45 days after operation. Heart sections were examined immunohistochemically using anti-vimentin, anti-α-smooth muscle actin (α-SMA), anti-matrix metalloproteinase (MMP)-2, anti-MMP-9 and anti-CRBP-1 antibodies. Infarction involved 48.8 ± 3.6% of the left ventricle and was followed by an important cardiac remodeling. Vimentin-positive fibroblastic cells including α-SMA-positive myofibroblasts expressed CRBP-1 at 3-, 6-, and 15-days after MI. Expression of CRBP-1 reached a maximum at 6-days after infarction. Thereafter, CRBP-1 expression was dramatically decreased, showing a similar tendency to MMP expression. Human heart specimens of individuals with a recent myocardial infarction demonstrated presence of CRBP-1-positive fibroblasts by immunohistochemistry. We have demonstrated that CRBP-1 is transiently expressed by fibroblasts during cardiac remodeling. Our results suggest that CRBP-1 plays a role in ventricular remodeling after MI allegedly through its RA binding activity.

Acute effects of all-trans-retinoic acid in ischemic injury

All-trans-retinoic acid (ATRA) is a vitamin A derivative that is important in neuronal patterning, survival, and neurite outgrowth. Neuroprotective effects of ATRA in ischemia have been demonstrated but its effects on glial swelling are not known. We investigated the relatively acute effects of ATRA on cell swelling in ischemic injury and on key features hypothesized to contribute to cell swelling including increased reactive oxygen species/reactive nitrogen species (ROS/RNS), depolarization of the inner mitochondrial membrane potential (ΔΨm), and increased intracellular calcium ([Ca2+]i). C6 glial cultures were subjected to 5 hr oxygen-glucose deprivation (OGD). ATRA was added to separate groups after the end of OGD. OGD increased cell volume by 43%, determined at 90 min after the end of OGD, but this increase was significantly attenuated by ATRA. OGD induced an increase in ROS/RNS production in the whole cell and mitochondria, as assessed by the fluorescent dyes CM-H2DCFDA and MitoTracker CM-H2-XROS at the end of OGD. The increase in mitochondrial ROS, but not cellular ROS, was significantly attenuated by ATRA. OGD also induced a 67% decline in mitochondrial ΔΨm but this decline was significantly attenuated by ATRA. OGD-induced increase in [Ca2+]i was also significantly attenuated by ATRA. Taken together with our previous results where calcium channel blockers reduced cell swelling, the effects of ATRA in attenuating swelling are possibly mediated through its effects in regulating [Ca2+]i. Considering the paucity of agents in attenuating brain edema in ischemia, ATRA has the potential to reduce brain edema and associated neural damage in ischemic injury.

Retinoic acid receptor-mediated signaling protects cardiomyocytes from hyperglycemia induced apoptosis: role of the renin-angiotensin system

Diabetes mellitus (DM) is a primary risk factor for cardiovascular diseases and heart failure. Activation of the retinoic acid receptor (RAR) and retinoid X receptor (RXR) has an anti-diabetic effect; but, a role in diabetic cardiomyopathy remains unclear. Using neonatal and adult cardiomyocytes, we determined the role of RAR and RXR in hyperglycemia-induced apoptosis and expression of renin-angiotensin system (RAS) components. Decreased nuclear expression of RARα and RXRα, activation of apoptotic signaling and cell apoptosis was observed in high glucose (HG) treated neonatal and adult cardiomyocytes and diabetic hearts in Zucker diabetic fatty (ZDF) rats. HG-induced apoptosis and reactive oxygen species (ROS) generation was prevented by both RAR and RXR agonists. Silencing expression of RARα and RXRα, by small interference RNA, promoted apoptosis under normal conditions and significantly enhanced HG-induced apoptosis, indicating that RARα and RXRα are required in regulating cell apoptotic signaling. Blocking angiotensin type 1 receptor (AT(1) R); but, not AT(2) R, attenuated HG-induced apoptosis and ROS generation. Moreover, HG induced gene expression of angiotensinogen, renin, AT(1) R, and angiotensin II (Ang II) synthesis were inhibited by RARα agonists and promoted by silencing RARα. Activation of RXRα, downregulated the expression of AT(1) R; and RXRα silencing accelerated HG induced expression of angiotensinogen and Ang II synthesis, whereas there was no significant effect on renin gene expression. These results indicate that reduction in the expression of RARα and RXRα has an important role in hyperglycemia mediated apoptosis and expression of RAS components. Activation of RAR/RXR signaling protects cardiomyocytes from hyperglycemia, by reducing oxidative stress and inhibition of the RAS.

Vitamin A metabolism: an update

Retinoids are required for maintaining many essential physiological processes in the body, including normal growth and development, normal vision, a healthy immune system, normal reproduction, and healthy skin and barrier functions. In excess of 500 genes are thought to be regulated by retinoic acid. 11-cis-retinal serves as the visual chromophore in vision. The body must acquire retinoid from the diet in order to maintain these essential physiological processes. Retinoid metabolism is complex and involves many different retinoid forms, including retinyl esters, retinol, retinal, retinoic acid and oxidized and conjugated metabolites of both retinol and retinoic acid. In addition, retinoid metabolism involves many carrier proteins and enzymes that are specific to retinoid metabolism, as well as other proteins which may be involved in mediating also triglyceride and/or cholesterol metabolism. This review will focus on recent advances for understanding retinoid metabolism that have taken place in the last ten to fifteen years.

The histopathalogical effects of retinoic acid on the tissues

The aim of this study is to sum up the important information that has emerged from the last 10 years of experimental investigations over the effects of retinoic acid (RA) on embryonic structure and adult tissues. Administration of exogenous RA can affect the connective tissues including enhancement of myeloid compartment and suppression of erythroid cells and conversion of hematopoietic stem cells to erythroid progenitors. Also, it is able to induce osteogenic differentiation of stem cells derived from adipose tissues and etc. Examining the neural tissue highlighted that disruption of RA signaling in the adult leads to degeneration of motor neurons and development of some diseases. In vitro administration of All-Trans Retinoic Acid (ATRA) increased dendritic growth and synaptophysin puncta intensity and increased expressions of neuronal nuclei, neuron specific enolase, synaptophysin. RA also promotes expression of a marker of mature astrocytes. On muscular tissue, it can inhibit proliferation of smooth muscle cells (SMC) while promoting differentiation of SMC in vitro instead. The ATRA stimulates skeletal myogenesis while inhibiting cardiomyogenesis and hypertrophy and proliferation of cultured neonatal cardiomyocytes and cardiofibroblasts. In addition, differences in levels of embryonic RA may contribute to variability in great artery anomalies. In epithelial tissue, the squamous epithelium exposed to ATRA showed the columnar differentiation independent to proliferation. Also RA seems able to rescue the regeneration process of injured gut and revealing a better wound healing of the intestine undergone intra-operative radiotherapy. It can interrupt the process of progressive fibrosis, enhancements of the langerhans islets, exocrine pancreas, modulate the health of the mammary glands and repairs the lung cell. Thus, differences in levels of endogenous RA in embryonic and adult tissues may contribute to anomalies and pathogenesis of disease, furthermore RA has paradoxical effects on the parts forming the connective and muscles tissue in equal conditions.

Beneficial effect of all-trans retinoic acid (ATRA) on glomerulosclerosis rats via the down-regulation of the expression of alpha-smooth muscle actin: a comparative study between ATRA and benazepril

Although ATRA is a potent renoprotective agent, relatively little is known regarding the mechanisms of its action. The present study was designed to further elucidate the mechanisms of ATRA's action to GS rats and compare that with the beneficial effect of benazepril. Male SD rats weighting 160 to 200g were used in this study. GS was induced by unilateral nephrectomy and intravenous injection of adriamycin (6mg/kg). They were divided randomly 20 ones per group into GS group, GS treated with ATRA (20mg/kg/day) group, and GS treated with benazepril (10mg/kg/day) group. The other 20 ones were taken as sham-operation group, injected normal saline into caudal vein. 12weeks later, all rats were subjected to sacrifice. As expected, the GS group exhibited significant lower serum TP and Alb, and higher BUN, Cr and proteinuria than those of the sham group. Administration of ATRA or benazepril did ameliorate these above disorders of biochemical parameters in GS rats. Extensive renal damage was observed in the GS group, such as mononuclear infiltration, mesangial proliferation, focal segment glomerular sclerosis, and tubulointerstitial fibrosis. The pathological changes in both ATRA and benazepril group were alleviated remarkably. Semiquantitative GSI was used to evaluate the degree of GS in all groups. GSI was significantly higher in the GS group than in sham group. GSI decreased from 21.9+/-6.7 in the GS group to 6.9+/-2.8 in the ATRA group and 7.0+/-2.7 in benazepril group respectively. However, no significant difference in GSI between rats treated with ATRA and rats treated with benazepril was found. RT-PCR analysis revealed the renal expression of alpha-SMA mRNA was induced substantially in GS group as compared to sham group, which could be offset completely by ATRA or benazepril administration. However, expression level of alpha-SMA mRNA in GS rats treated with ATRA was identical to that in GS rats treated with benazepril. We also examined immunohistochemical staining for renal alpha-SMA, TGF-beta1, Col IV, and FN in this model. Weak staining was observed in some glomerulus, mesangial cells, and tubular interstitium of sham rats. Staining was markedly enhanced in the majority of glomerulus, mesangial cells, and tubular interstitium of untreated GS rats. Compared with untreated GS animals, intensity and extent of staining for renal alpha-SMA, TGF-beta1, Col IV, and FN were markedly reduced in glomerulus, mesangial cells, and tubular interstitium of GS rats treated with either ATRA or benazepril. However, no significant differences existed between ATRA and benazepril with respect to the glomerular and tubulointerstitial staining scores. Interestingly, our data documented some differences of therapeutic capacities between ATRA and benazepril. In comparison with benazepril, ATRA exerted no improvement in hypoproteinemia, but more significant decrease in serum Cr level in GS rats. The reasons leading to these variations are unclear. Whatever they are, the properties of down-regulate inflammatory/proliferative programs may make ATRA an attractive potential candidate for future therapeutic use in kidney disease.

Effect of Targeting Mitogen-Activated Protein Kinase on Cardiac Remodeling in Rats

Background: Increasing evidence suggests that the activation of p38 mitogen-activated protein kinase (p38MAPK) plays a role in cardiac remodeling. Targeting p38MAPK using drugs reported to interfere with its phosphorylation, namely statins and all-trans retinoic acid (atRA), might play a role in ameliorating this remodeling. Methods and Results: Cardiac remodeling was induced in male albino rats by chronic inhibition of nitric oxide (NO) synthesis by N-nitro L-arginine methyl ester (L-NAME). Daily oral administration of L-NAME for 4 weeks resulted in the elevation of mean arterial blood pressure (MABP) together with cardiac remodeling evidenced by an increase in left ventricular-body weight ratio together with an increase in cardiac hydroxyproline concentration and a decrease in left ventricular papillary muscle-developed tension. An elevation in cardiac phosphorylated p38MAPK concentration, tumor necrosis factor alpha concentration and in cardiac caspase 3 activity was also observed. Administration of either rosuvastatin or all-trans retinoic acid (atRA), starting 4 weeks after L-NAME administration, ameliorated remodeling and improved all studied parameters. Conclusions: Targeting MAPK might represent a useful therapeutic avenue to ameliorate cardiac remodeling and support the notion that atRA and statins are potential candidates for the prevention and therapy of cardiac remodeling.

Dimethylarginine dimethylaminohydrolase regulation: a novel therapeutic target in cardiovascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase, with consequent reduced synthesis of nitric oxide. ADMA is metabolised to L-citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). The modulation of DDAH activity and expression plays a pivotal role in regulating intracellular ADMA concentrations, with important effects on vascular homeostasis. For example, impairment in DDAH activity, resulting in elevated ADMA concentrations and reduced nitric oxide synthesis, can promote the onset and progression of atherosclerosis in experimental models. This review discusses the current role of ADMA and DDAH in vascular health and disease, the techniques used to assess DDAH activity and expression, and the results of recent studies on pharmacological and biological agents modulating DDAH activity and expression. Suggestions for future basic and clinical research directions are also discussed.

Retinoic acid and the heart

Retinoic acid (RA), the active derivative of vitamin A, by acting through retinoid receptors, is involved in signal transduction pathways regulating embryonic development, tissue homeostasis, and cellular differentiation and proliferation. RA is important for the development of the heart. The requirement of RA during early cardiovascular morphogenesis has been studied in targeted gene deletion of retinoic acid receptors and in the vitamin A-deficient avian embryo. The teratogenic effects of high doses of RA on cardiovascular morphogenesis have also been demonstrated in different animal models. Specific cardiovascular targets of retinoid action include effects on the specification of cardiovascular tissues during early development, anteroposterior patterning of the early heart, left/right decisions and cardiac situs, endocardial cushion formation, and in particular, the neural crest. In the postdevelopment period, RA has antigrowth activity in fully differentiated neonatal cardiomyocytes and cardiac fibroblasts. Recent studies have shown that RA has an important role in the cardiac remodeling process in rats with hypertension and following myocardial infarction. This chapter will focus on the role of RA in regulating cardiomyocyte growth and differentiation during embryonic and the postdevelopment period.

All-trans retinoic acid prevents angiotensin II- and mechanical stretch-induced reactive oxygen species generation and cardiomyocyte apoptosis

Cardiomyocyte apoptosis has an important role in the transition from compensatory cardiac remodeling to heart failure. All-trans retinoic acid (RA), a bioactive vitamin A derivative, prevents stretch- and angiotensin II (Ang II)-induced cardiac hypertrophy. However, the anti-apoptotic potential of RA in the heart remains unexplored. Here, we demonstrate that stretch- and Ang II-induced apoptosis is prevented by RA in neonatal cardiomyocytes. RA improved mitochondrial function by inhibiting the stretch- and Ang II-induced reduction in mitochondrial membrane potential, cytochrome c release and by increasing the Bcl2/Bax ratio. RA inhibited stretch- and Ang II-induced intracellular reactive oxygen species (ROS) generation and upregulated the SOD2 level. Hydrogen peroxide-induced increases in the number of TUNEL-positive cells and percentage of Annexin V positive cells, were dose-dependently inhibited by RA. The thiol antioxidant, N-acetyl cysteine (NAC), completely inhibited stretch- and Ang II-induced apoptosis. Using diazoxide (mitochondrial ATP-sensitive K(+) channel opener) and SDS (NADPH oxidase activator), we confirmed that RA suppressed both mitochondrial- and NADPH oxidase-derived ROS. We also observed that both RAR and RXR were involved in preventing Ang II- and stretch-induced ROS production and apoptosis, by using selective retinoid receptor agonists and antagonists. Our data provide the first evidence that RA prevents Ang II and stretch induced apoptosis, by inhibiting ROS generation and increasing the anti-oxidant defense system, suggesting that RA-mediated signaling may provide a new therapeutic target for the prevention of the cardiac remodeling process.

All-trans retinoic acid prevents development of cardiac remodeling in aortic banded rats by inhibiting the renin-angiotensin system

This study was designed to determine the effect of all-trans retinoic acid (RA) on the development of cardiac remodeling in a pressure overload rat model. Male Sprague-Dawley rats were subjected to sham operation and the aortic constriction procedure. A subgroup of sham control and aortic constricted rats were treated with RA for 5 mo after surgery. Pressure-overloaded rats showed significantly increased interstitial and perivascular fibrosis, heart weight-to-body weight ratio, and gene expression of atrial natriuretic peptide and brain natriuretic peptide. Echocardiographic analysis showed that pressure overload induced systolic and diastolic dysfunction, as evidenced by decreased fractional shortening, ejection fraction, stroke volume, and increased E-to-E(a) ratio and isovolumic relaxation time. RA treatment prevented the above changes in cardiac structure and function and hypertrophic gene expression in pressure-overloaded rats. RA restored the ratio of Bcl-2 to Bax, inhibited cleavage of caspase-3 and -9, and prevented the decreases in the levels of SOD-1 and SOD-2. Pressure overload-induced phosphorylation of ERK1/2, JNK, and p38 was inhibited by RA, via upregulation of mitogen-activated protein kinase phosphatase (MKP)-1 and MKP-2. The pressure overload-induced production of angiotensin II was inhibited by RA via upregulation of expression of angiotensin-converting enzyme (ACE)2 and through inhibition of the expression of cardiac and renal renin, angiotensinogen, ACE, and angiotensin type 1 receptor. Similar results were observed in cultured neonatal cardiomyocytes in response to static stretch. These results demonstrate that RA has a significant inhibitory effect on pressure overload-induced cardiac remodeling, through inhibition of the expression of renin-angiotensin system components.

Survivin mediates the anti-apoptotic effect of delta-opioid receptor stimulation in cardiomyocytes

Survivin is known to be essential for cell division and to inhibit apoptosis during embryonic development and in adult cancerous tissues. However, the cardiovascular role of survivin is unknown. We observed that in cardiomyocytes cultured under conditions of serum and glucose deprivation (DEPV), the levels of survivin, Bcl-2 and extracellular signal-regulated kinase (ERK) were positively correlated with the anti-apoptotic action of a delta-opioid receptor agonist, [D-Ala2, D-Leu5]-enkephalin acetate (DADLE). By contrast, Bax translocation, mitochondrial membrane damage and reactive oxygen species (ROS) production were inversely correlated with the changes of survivin and Bcl-2. The use of RNA interference (RNAi) targeting survivin increased DEPV-induced cardiomyocyte apoptosis, whereas the anti-apoptotic effect of DADLE was blunted by survivin RNAi. Moreover, survivin transfection and overexpression provided protection against DEPV-induced cardiomyocyte apoptosis. Inhibition of ERK prevented the DADLE-induced decrease in apoptosis and Bax translocation, and increase in survivin and Bcl-2. DADLE-induced increase in survivin was also blunted by phosphoinositol 3-kinase (PI 3-kinase) inhibition. In conclusion, the present study provides the first direct evidence of an anti-apoptotic role of survivin mediating the anti-apoptotic effect of delta-opioid receptor activation in cardiomyocytes. ERK and PI 3-kinase were found to be upstream regulators of survivin. Mitochondrial membranes as well as ROS, Bcl-2 and Bax were also involved in this anti-apoptotic action.

All-trans retinoic acid inhibited angiotensin II-induced increase in cell growth and collagen secretion of neonatal cardiac fibroblasts

AIM

To determine whether all-trans retinoic acid (atRA) acts to modulate angiotensin II (Ang II)-induced cardiac fibroblast cell growth and collagen secretion.

METHODS

Cultured neonatal rat cardiac fibroblasts (CF) were used in the experiment. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was used to detect cell growth of the CF; and immunocytochemistry and Western blotting were used to measure the production and secretion of collagen and the expression of transforming growth factor-beta1 (TGF-beta1) by the CF.

RESULTS

atRA (10(-7) to 10(-5) mol/L) inhibited the Ang II-induced increase in cell growth of CF (P<0.05). Ang II stimulated the secretion of collagen types I and III by the CF. This effect was blocked by AT(1) receptor antagonist losartan (10(-6) mol/L), but not by AT2 receptor antagonist PD123319 (up to 10(-6) mol/L). Exposure of CF to atRA (10(-5) mol/L) attenuated the Ang II-induced increase in the secretion of collagen types I and III (P<0.05). atRA (10(-5) mol/L) also blocked the Ang II-induced increase in the expression of TGF-beta1.

CONCLUSION

atRA inhibits the Ang II-induced increase in cell growth and collagen secretion of neonatal rat CF. The effect of atRA is possibly mediated by lowering the TGF-beta1 level. These observations support the notion that atRA is a potential candidate for the prevention and therapy of cardiac remodeling.

Retinoic acid supplementation attenuates ventricular remodeling after myocardial infarction in rats

The objective of this study was to evaluate the role of retinoic acid in experimental postinfarction myocardial remodeling. Wistar rats were subjected to myocardial infarction (MI) and treated with retinoic acid (RA), 0.3 mg/(kg x d) (MI-RA, n = 29), or fed a control diet (MI, n = 34). After 6 mo, the surviving rats (MI-RA = 18 and MI = 22) underwent echocardiograms, and isolated hearts were tested for function in vitro. The cross-sectional area of the myocyte (CSA) and interstitial collagen fraction (IC) were measured in a cross section of the heart stained by hematoxylin-eosin and picrosirius red, respectively. The CSA was smaller in the MI-RA group [229 (220,234) microm2] [medians (lower quartile, upper quartile)] than in the MI group [238 (232,241) microm2] (P = 0.01) and IC was smaller in the MI-RA group [2.4 (1.7, 3.1)%] than in the MI group [3.5 (2.6, 3.9)%] (P = 0.05). The infarct size did not differ between the groups [MI = 44.6 (40.8, 48.4)%, MI-RA = 45 (38.6, 47.2)%]. Maximum rate of rise of left ventricular pressure (+dp/dt) was greater in the MI-RA group (2645 +/- 886 mm Hg/s) than in the MI group (2081 +/- 617 mm Hg/s) (P = 0.05). The other variables tested did not differ between groups. Retinoic acid supplementation of rats for 6 mo attenuates the ventricular remodeling process after MI.

Isotretinoin (13‐ Cis ‐Retinoic Acid) Associated Atrial Tachycardia

We describe a 16-year-old boy who presented with palpitations for 1 week while being on isotretinoin treatment for nodulocystic facial acne for 3 months. Twenty four-hour Holter monitoring showed frequent premature atrial beats and episodes of nonsustained atrial tachycardia. He never had any episodes of palpitations previously. His complaints almost disappeared within a week after stopping the treatment. He remained asymptomatic since the discontinuation of the drug. The temporal relationship between isotretinoin treatment and patient's symptoms in the presence of documented arrhythmia suggests a drug-related cause. As a result, clinicians should be aware of the possible arrhythmogenic effect of isotretinoin.

Mitogen-activated protein kinases and mitogen-activated protein kinase phosphatases mediate the inhibitory effects of all-trans retinoic acid on the hypertrophic growth of cardiomyocytes

All-trans retinoic acid (RA) has been implicated in mediation of cardiac growth inhibition in neonatal cardiomyocytes. However, the associated signaling mechanisms remain unclear. Utilizing neonatal cardiomyocytes, we demonstrated that RA suppressed the hypertrophic features induced by cyclic stretch or angiotensin II (Ang II). Cyclic stretch- or Ang II-induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAP kinase) was dose- and time-dependently inhibited by RA. Significant inhibition was observed by 5 microm RA, from 8 to 24 h of pretreatment. This inhibitory effect was not mediated at the level of mitogen-activated protein kinase kinases (MKKs), because RA had no effect on stretch- or Ang II-induced phosphorylation of MEK1/2, MKK4, and MKK3/6. However, the phosphatase inhibitor vanadate reversed the inhibitory effect of RA on MAP kinases and protein synthesis. RA up-regulated the expression level of MAP kinase phosphatase-1 (MKP-1) and MKP-2, and the time course was correlated with the inhibitory effect of RA on activation of MAP kinases. Overexpression of wild-type MKP-1 inhibited the phosphorylation of JNK and p38 in cardiomyocytes. These data indicated that MKPs were involved in the inhibitory effect of RA on MAP kinases. Using specific RAR and RXR antagonists, we demonstrated that both RARs and RXRs were involved in regulating stretch- or Ang II-induced activation of MAP kinases. Our findings provide the first evidence that the anti-hypertrophic effect of RA is mediated by up-regulation of MKPs and inhibition of MAP kinase signaling pathways.

Role of angiotensin AT1 and AT2 receptors in cardiac hypertrophy and cardiac remodelling

1. Left ventricular hypertrophy (LVH) is an independent cardiovascular risk factor. Angiotensin AT1 receptor antagonism has been considered as a specific approach to block the renin-angiotensin system and been demonstrated to be able to prevent or regress LVH by interfering with the remodelling process of the heart. 2. Angiotensin AT1 receptor blockade induces a marked increase in angiotensin (Ang) II, which may stimulate the AT2 receptors. Gene expression of AT1 and AT2 receptors increases in a time-dependent manner in cardiac remodelling following myocardial infarction. 3. Considerable efforts have been made to clarify the role of AT2 receptors in cardiac hypertrophy and remodelling since the mid-1990s, resulting in controversial reports: the AT2 receptor mediates actions either opposite to or in coordination with those of the AT1 receptor. Moreover, there are many reports of no significant effects mediated by AT2 receptors. 4. Based on the studies reviewed in the present article, we assume that the predominant effect of AngII in cardiac hypertrophy and cardiac remodelling is growth promoting and that this effect is mediated mainly via AT1 receptors. The AT2 receptors may affect the hypertrophic process by interacting with other cardiac membrane proteins, enzymes and autacoids. Before coming to a conclusion as to whether AT2 receptor stimulation or antagonism is beneficial to the heart, more studies should be performed in different LVH models, especially long-term treatment protocols in vivo.

Chronic all-trans retinoic acid treatment prevents medial thickening of intramyocardial and intrarenal arteries in spontaneously hypertensive rats

There are in vitro data linking all-trans retinoic acid (atRA) with inhibition of hypertrophy and hyperplasia in cardiomyocytes, vascular smooth muscle cells, and fibroblasts. In the present study, we tested the hypothesis that chronic treatment with atRA may blunt the process of myocardial remodeling in spontaneously hypertensive rats (SHR). Four-week-old male SHR were treated with atRA (5 or 10 mg.kg-1.day-1) given daily for 3 mo by gavage; age- and sex-matched Wistar-Kyoto rats (WKY) and placebo-treated SHR served as controls. At the end of the treatment period, cardiac geometry and function were assessed by Doppler echocardiography. Histological examination and RIA were performed to evaluate medial thickening of intramyocardial and renal arteries, perivascular and interstitial collagen content, and atrial natriuretic peptide (ANP) and IGF-I in the heart, respectively. The novel finding of the present study is that atRA prevented hypertrophy of intramyocardial and intrarenal arteries and ventricular fibrosis. However, atRA treatment did not lower blood pressure or left ventricular weight and left ventricular weight-to-body weight ratio in SHR. atRA did not change cardiac geometry and function as assessed by Doppler echocardiography. atRA showed no influence on either ANP or IGF-I levels. In conclusion, the present study suggests that chronic atRA treatment prevents medial thickening of intramyocardial and intrarenal arteries and ventricular fibrosis during the development of hypertension. Left ventricular hypertrophy and cardiac geometry and function are not changed by atRA treatment.

Ventricular remodeling induced by retinoic acid supplementation in adult rats

Retinoic acid (RA) plays a role in regulating cardiac geometry and function throughout life. The aim of this study was to analyze the cardiac effects of RA in adult rats. Wistar rats were randomly allocated to a control group (n = 18) receiving standard rat chow and a group treated with RA (n = 14) receiving standard rat chow supplemented with RA for 90 days. All animals were evaluated by echocardiography, isolated papillary muscle function, and morphological studies. Whereas the RA-treated group developed an increase in both left ventricular (LV) mass and LV end-diastolic diameter, the ratio of LV wall thickness to LV end-diastolic diameter remained unchanged when compared with the control group. In the isolated papillary muscle preparation, RA treatment decreased the time to peak developed tension and increased the maximum velocity of isometric relengthening, indicating that systolic and diastolic function was improved. Although RA treatment produced an increase in myocyte cross-sectional area, the myocardial collagen volume fraction was similar to controls. Thus our study demonstrates that small physiological doses of RA induce ventricular remodeling resembling compensated volume-overload hypertrophy in rats.