Bile acids (BA) are classically known as an important agent in lipid absorption and cholesterol metabolism. Nowadays, their role in glucose regulation and energy homeostasis are widely reported. BAs are involved in various cellular signaling pathways, such as protein kinase cascades, cyclic AMP (cAMP) synthesis, and calcium mobilization. They are ligands for several nuclear hormone receptors, including farnesoid X-receptor (FXR). Recently, BAs have been shown to bind to muscarinic receptor and Takeda G-protein-coupled receptor 5 (TGR5), both G-protein-coupled receptor (GPCR), independent of the nuclear hormone receptors. Moreover, BA signals have also been elucidated in other nonclassical BA pathways, such as sphingosine-1-posphate and BK (large conductance calcium- and voltage activated potassium) channels. Hydrophobic BAs have been proven to affect heart rate and its contraction. Elevated BAs are associated with arrhythmias in adults and fetal heart, and altered ratios of primary and secondary bile acid are reported in chronic heart failure patients. Meanwhile, in patients with liver cirrhosis, cardiac dysfunction has been strongly linked to the increase in serum bile acid concentrations. In contrast, the most hydrophilic BA, known as ursodeoxycholic acid (UDCA), has been found to be beneficial in improving peripheral blood flow in chronic heart failure patients and in protecting the heart against reperfusion injury. This review provides an overview of BA signaling, with the main emphasis on past and present perspectives on UDCA signals in the heart.

ABSTRACT. Ursodeoxycholic acid (UDCA) is used to treat liver diseases and demonstrates cardioprotective effects. Accumulation of the plasma membrane sphingolipid sphingomyelin in the heart can lead to atherosclerosis and coronary artery disease. Sphingomyelinases (SMases) break down sphingomyelin, producing ceramide, and inhibition of SMases activity can promote cell survival. We hypothesized that UDCA regulates activation of ERK and Akt survival signaling pathways and SMases in protecting cardiac cells against hypoxia. Neonatal cardiomyocytes were isolated from 0-to 2-day-old Sprague Dawley rats, and given 100 µM CoCl 2 , 150 µM H 2 O 2 , or placed in a hypoxia chamber for 24 h. The ameliorative effects of 100-µM UDCA treatment for 12 h were then assessed using MTS, QuantiGene Plex (for Smpd1 and Smpd2), and SMase assays, beating rate assessment, and western blotting (for ERK and Akt). Data were analyzed by the paired Student t-tests and one-way analyses of variance. Cell viability decreased significantly after H 2 O 2 (85%), CoCl 2 (50%), and hypoxia chamber (52%) treatments compared to the untreated control (100%). UDCA significantly counteracted the effects of chamber-and CoCl 2 -induced hypoxia on viability and beating rate. However, no significant differences were observed in acid SMase gene and protein expression between the untreated, CoCl 2 , and UDCA-CoCl 2 groups. In contrast, neutral SMase gene and protein expression did significantly differ between the latter two groups. ERK and Akt phosphorylation was higher in hypoxic cardiomyocytes treated with UDCA than those given CoCl 2 alone. In conclusion, UDCA regulates the activation of survival signaling proteins and SMases in neonatal rat cardiomyocytes during hypoxia.

In hepatocytes, ursodeoxycholic acid (UDCA) activates cell signalling pathways such as p53, intracellular calcium ([Ca ] ), and sphingosine-1-phosphate (S1P)-receptor via Gα -coupled-receptor. Recently, UDCA has been shown to protect the heart against hypoxia-reoxygenation injury. However, it is not clear whether UDCA cardioprotection against hypoxia acts through a transcriptional mediator of cells stress, HIF-1α and p53. Therefore, in here, we aimed to investigate whether UDCA could protect cardiomyocytes (CMs) against hypoxia by regulating expression of HIF-1α, p53, [Ca ] , and S1P-Gα -coupled-receptor. Cardiomyocytes were isolated from newborn rats (0-2 days), and hypoxia was induced by using cobalt chloride (CoCl ). Cardiomyocytes were treated with UDCA and cotreated with either FTY720 (S1P-receptor agonist) or pertussis toxin (PTX; Gα inhibitor). Cells were subjected for proliferation assay, beating frequency, QuantiGene Plex assay, western blot, immunofluorescence, and calcium imaging. Our findings showed that UDCA counteracted the effects of CoCl on cell viability, beating frequency, HIF-1α, and p53 protein expression. We found that these cardioprotection effects of UDCA were similar to FTY720, S1P agonist. Furthermore, we observed that UDCA protects CMs against CoCl -induced [Ca ] dynamic alteration. Pharmacological inhibition of the Gα -sensitive receptor did not abolish the cardioprotection of UDCA against CoCl detrimental effects, except for cell viability and [Ca ] . Pertussis toxin is partially effective in inhibiting UDCA protection against CoCl effects on CM cell viability. Interestingly, PTX fully inhibits UDCA cardioprotection on CoCl -induced [Ca ] dynamic changes. We conclude that UDCA cardioprotection against CoCl -induced hypoxia is similar to FTY720, and its actions are not fully mediated by the Gα -coupled protein sensitive pathways. Ursodeoxycholic acid is the most hydrophilic bile acid and is currently used to treat liver diseases. Recently, UDCA is shown to have a cardioprotection effects; however, the mechanism of UDCA cardioprotection is still poorly understood. The current data generated were the first to show that UDCA is able to inhibit the activation of HIF-1α and p53 protein during CoCl -induced hypoxia in cardiomyocytes. This study provides an insight of UDCA mechanism in protecting cardiomyocytes against hypoxia.

Ursodeoxycholic acid (UDCA) is known as a therapeutic agent in treating cholestasis and liver diseases. Recently, UDCA has been suggested as a therapeutic drug for heart related diseases. Cardioprotective effect of UDCA against the development of ischemia has been studied. Yet, the mechanism of UDCA-cardioprotection is not clearly understood. Therefore, this study aimed to elucidate the mechanisms of UDCA cardioprotection against hypoxia by investigating the expression of caspase -3/-9 and ROS generation using an in vitro hypoxic heart model. A newborn (0-2 days old) rat heart was isolated for primary cell culture of cardiomyocytes. Hypoxia was chemically induced by using CoCl2. Cardiomyocytes were then incubated with UDCA. The treated cardiomyocytes were subjected for ROS generation detection assay, QuantiGene Plex assay for caspase-3/-9 gene expression and ELISA for caspase-3/-9 protein expression. The data were analyzed by using sample paired t-test and One-way ANOVA. Our results showed that UDCA abolishes the effects on CoCl2 in ROS production and UDCA downregulates caspase-9 protein  expression in CoCl2 treated cardiomyocytes. This study provides an insight of UDCA in protecting cardiomyocytes against hypoxia mediated by anti-apoptosis mechanism.