Mast Cells Play an Important Role in the Pathogenesis of Hyperglycemia-Induced Atrial Fibrillation.

BACKGROUND AND OBJECTIVES: Recently, it was reported that mast cells (MCs) could underlie the mechanisms of several cardiovascular diseases. However, the role of MCs in diabetes-induced atrial fibrillation (AF) has not been notably investigated. We tested the hypothesis that MC deficiency attenuates hyperglycemia-induced AF in mice. METHODS AND RESULTS: Mast cell-deficient W/W(v)  mice, and congenic +/+ littermates (WT) were divided into either the vehicle (VEH)-injection group or the streptozotocin (STZ)-injection group (MCKO-VEH, MCKO-STZ, WT-VEH, and WT-STZ groups). On day 28 of our studies, we observed that (1) STZ-induced hyperglycemia increased MC infiltration in the left atrium (LA) in WT mice (P < 0.01), (2) atrium isolated from the WT-STZ group showed inhomogeneous interstitial fibrosis, abundant infiltration of macrophages, and enhanced apoptosis compared to the WT-VEH group (P < 0.01, P < 0.01, P < 0.05, respectively). However, the changes observed in the WT-STZ group were significantly attenuated in the MCKO-STZ mice. In addition, we observed that (3) messenger RNA levels of tumor necrosis factor-α, monocyte chemoattractant protein-1, interleukin-1ß, transforming growth factor-ß, and collagen-1 in the LA were increased in the WT-STZ group, but not in the MCKO-STZ group, (4) STZ-induced hyperglycemia increased AF induction and prolonged interatrial conduction time in the WT mice, which were not observed in the MCKO mice, and that (5) hyperglycemia-enhanced atrial production of reactive oxygen species (ROS) was equally observed in the WT and MCKO mice. CONCLUSIONS: Our results suggest that MCs contribute to the pathogenesis of hyperglycemia-induced AF via enhancement of inflammation and fibrosis.

Candesartan restored cardiac Hsp72 expression and tolerance against reperfusion injury in hereditary insulin-resistant rats.

AIMS: We tested the hypothesis that candesartan, an angiotensin II (AII) type 1 receptor antagonist, would restore the depressed phosphatidylinositol 3 (PI3) kinase-dependent Akt phosphorylation, an essential signal to induce heat-shock protein 72 (Hsp72) in response to hyperthermia, in Otsuka Long-Evans Tokushima fatty (OLETF) rats. METHODS AND RESULTS: At 14 weeks of age, male OLETF rats and Long-Evans Tokushima Otsuka (LETO) rats were treated with candesartan (0.25 mg/kg/day) for 2 weeks. Thereafter, hyperthermia (43°C for 20 min) was applied. We observed the following: (i) Candesartan did not improve insulin sensitivity in OLETF rats. (ii) Candesartan restored depressed PI3 kinase-dependent Akt phosphorylation and Hsp72 expression in OLETF rat hearts. (iii) Cardiac ventricular tissue contents of AII were greater in OLETF rats, which were suppressed by candesartan. (iv) Cardiac levels of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) phosphorylation were greater in OLETF rats, which were suppressed by candesartan. In cultured cardiomyocytes, application of AII induced PTEN phosphorylation, which was suppressed by candesartan. (v) In high-fat diet insulin-resistant rats, similar results were observed with respect to Hsp72 expression, Akt phosphorylation and PTEN phosphorylation. (vi) In isolated, perfused heart experiments, reperfusion-induced cardiac functional recovery was suppressed in OLETF rat hearts, which was improved by candesartan. CONCLUSION: Our results suggest that the depression of PI3 kinase-dependent Akt activation in response to hyperthermia in OLETF rats can be restored by candesartan. Substantial activation of the renin-angiotensin system, represented by increased myocardial AII content and subsequent PTEN phosphorylation, may underlie the pathogenesis which is ameliorated by candesartan.

Pioglitazone attenuates inflammatory atrial fibrosis and vulnerability to atrial fibrillation induced by pressure overload in rats.

BACKGROUND: Inflammatory processes are involved in the pathogenesis of atrial fibrillation (AF). OBJECTIVE: The purpose of this study was to test the hypothesis that atrial fibrosis and enhanced vulnerability to AF evoked by pressure overload can be attenuated by pioglitazone, a peroxisome proliferator-activated receptor-γ agonist, via suppression of inflammatory profibrotic signals. METHODS: Male Sprague-Dawley rats were subjected to abdominal aortic constriction (AAC). Pioglitazone 3 mg/kg/day or vehicle was orally administered for 4 weeks. RESULTS: Western blot analysis revealed that AAC enhanced expression of monocyte chemoattractant protein (MCP)-1, transforming growth factor-ß1 and α-smooth muscle actin in the left atrium (LA), which was suppressed by pioglitazone. Messenger RNA expression of collagen type 1 and atrial natriuretic peptide in the LA was increased by AAC, which was suppressed by pioglitazone. Gelatin zymography demonstrated that activity of matrix metalloproteinase-9 was increased by AAC, which was suppressed by pioglitazone. Pioglitazone attenuated AAC-induced LA fibrosis. In isolated-perfused heart experiments, AAC did not alter the refractory period of the LA or the right atrium (RA), but it did prolong the interatrial conduction time. Programmed extrastimuli from the RA induced AF in all of the AAC-treated rats (8/8 [100%]). This was suppressed by pioglitazone (2/8 [25%], P <.05) with normalization to interatrial conduction time. CONCLUSION: The results of this study suggest that inflammatory profibrotic mechanisms are involved in this pressure-overloaded AF model. The results also suggest that pioglitazone is effective at attenuating atrial fibrosis, possibly via suppression of MCP-1-mediated inflammatory profibrotic processes.

High-glucose condition reduces cardioprotective effects of insulin against mechanical stress-induced cell injury.

AIMS: Mechanical stress induces cardiomyocyte injury and contributes to the progression of heart failure in patients with hypertension. In this study, we investigated whether insulin exerts cardioprotective effects against mechanical stretching-induced cell injury, and whether the protective effect is influenced by high-glucose condition. MAIN METHODS: Cultured neonatal rat cardiomyocytes were plated on silicone chambers, and the cells were mechanically stretched by 15% to induce cell injury. KEY FINDINGS: Mechanical stretching increased reactive oxygen species (ROS) and decreased mitochondrial inner membrane potential (DeltaPsi(m)), eventually leading to cell death by apoptosis and necrosis. Insulin activated the phosphoinositide 3 (PI3) kinase/Akt pathway and reduced apoptosis and necrosis by suppressing ROS increase and preserving DeltaPsi(m). However, high-glucose condition attenuated the insulin-induced Akt phosphorylation and cardioprotection. To investigate the mechanisms that attenuated the effects of insulin in high-glucose condition, we examined the expression of tensin homologue deleted on chromosome 10 (PTEN), which is a negative regulator of the PI3 kinase/Akt pathway. The expressions of PTEN and phosphorylated PTEN were significantly decreased by insulin, and those effects were attenuated in high-glucose condition. SIGNIFICANCE: The present results suggest that insulin prevents mechanical stress-induced cell injury which otherwise lead to heart failure. Furthermore, we found that high-glucose condition prevented the decrease in PTEN expression and the cardioprotective effects induced by insulin.

Mitochondrial K(ATP) channels-derived reactive oxygen species activate pro-survival pathway in pravastatin-induced cardioprotection.

Reactive oxygen species (ROS) are important intracellular signaling molecules and are implicated in cardioprotective pathways including ischemic preconditioning. Statins have been shown to have cardioprotective effects against ischemia/reperfusion injury, however, the precise mechanisms remain to be elucidated. We hypothesized that ROS-mediated signaling cascade may be involved in pravastatin-induced cardioprotection. Cultured rat cardiomyocytes were exposed to H(2)O(2) for 30 min to induce cell injury. Pravastatin significantly suppressed H(2)O(2)-induced cell death evaluated by propidium iodide staining and the MTT assay. Incubation with pravastatin activated catalase, and prevented a ROS burst induced by H(2)O(2), which preserved mitochondrial membrane potential. Protective effects were induced very rapidly within 10 min, which was concordant with the up-regulation of phosphorylated ERK1/2. L-NAME, 5HD, N-acetylcysteine (NAC) and staurosporine inhibited ERK1/2 phosphorylation and also reduced pravastatin-induced cardioprotection, suggesting NO, mitochondrial K(ATP) (mitoK(ATP)) channels, ROS and PKC should be involved in the cardioprotective signaling. We also demonstrated that pravastatin moderately up-regulated ROS generation in a 5HD-inhibitable manner. In isolated perfused rat heart experiments, pravastatin administered 10 min prior to no-flow global ischemia significantly improved left ventricular functional recovery, and also reduced infarct size, which were attenuated by the treatment with NAC, 5HD, L-NAME or staurosporine. Administration of pravastatin from the beginning of reperfusion also conferred cardioprotection. Pravastatin protected the cardiomyocytes against oxidative stress by preventing the ROS burst and preserving mitochondrial function. Moderately up-regulated ROS production by mitoK(ATP) channels opening is involved in the pro-survival signaling cascade activated by pravastatin.

Adrenomedullin improves cardiac expression of heat-shock protein 72 and tolerance against ischemia/reperfusion injury in insulin-resistant rats.

We recently reported that long-term treatment with pioglitazone restored cardiac Akt phosphorylation in response to hyperthermia (HT) and subsequent cardiac heat-shock protein 72 (HSP72) expression, in heredity insulin resistance rats via improvement of insulin sensitivity. Because adrenomedullin (AM) promotes Akt phosphorylation and attenuates myocardial ischemia/reperfusion injury, we tested the hypothesis that pretreatment with AM before HT could restore depressed Akt activation and cardiac HSP72 expression, thereby enhancing protection against ischemia/reperfusion injury in this model. At 16 wk of age, male insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rats and control Long-Evans Tokushima Otsuka (LETO) rats were treated with AM (0.05 microg/kg . /min iv) or vehicle for 60 min. Thereafter, HT (43 C for 20 min) or normothermia (NT; 37 C for 20 min) was applied. The heart was isolated 1 and 24 h after HT. 1) Either AM or HT induced myocardial Akt phosphorylation in a phosphatidylinositol 3-kinase-dependent manner, which was augmented by their combination. 2) Akt phosphorylation induced by HT, or a combination of HT and AM, was attenuated in insulin-resistant OLETF rat hearts. 3) The levels of Akt phosphorylation in response to AM and/or HT correlated with reperfusion-induced left ventricular functional recovery and amount of released creatine kinase during reperfusion. 4) AM protected the hearts of OLETF rats and LETO rats. Our results suggest that AM pretreatment could enhance HT-induced myocardial Akt phosphorylation and subsequent HSP72 expression in a phosphatidylinositol 3-kinase-dependent manner, in association with tolerance against ischemia/reperfusion injury. This intervention was effective even in insulin-resistant hearts.

Mitochondria are targets for geranylgeranylacetone-induced cardioprotection against ischemia-reperfusion in the rat heart.

It has been shown that orally administered geranylgeranylacetone (GGA), an anti-ulcer drug, induces expression of heat shock protein 72 (HSP72) and provides protection against ischemia-reperfusion in rat hearts. The underlying protective mechanisms, however, remain unknown. Mitochondria have been shown to be a selective target for heat stress-induced cardioprotection. Therefore, we hypothesized that preservation of mitochondrial function, owing to an opening of a putative channel in the inner mitochondrial membrane, the mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel, could be involved in GGA- or heat stress-induced cardioprotection against ischemia-reperfusion. Rats were treated with oral GGA or vehicle. Twenty-four hours later, each heart was isolated and perfused with a Langendorff apparatus. GGA-treated hearts showed better functional recovery, and less creatine kinase was released during a 30-min reperfusion period, after 20 min of no-flow ischemia. Concomitant perfusion with 5-hydroxydecanoate (5-HD, 100 microM) or glibenclamide (10 microM) abolished the GGA-induced cardioprotective effect. GGA also showed preserved mitochondrial respiratory function, isolated at the end of the reperfusion period, which was abolished with 5-HD treatment. GGA prevented destruction of the mitochondrial structure by ischemia-reperfusion, as shown by electron microscopy. In cultured cardiomyocytes, GGA induced HSP72 expression and resulted in less damage to cells, including less apoptosis in response to hypoxia-reoxygenation. Treatment with 5-HD abolished the GGA-induced cardioprotective effects but did not affect HSP72 expression. Our results indicate that preserved mitochondrial respiratory function, owing to GGA-induced HSP72 expression, may, at least in part, have a role in cardioprotection against ischemia-reperfusion. These processes may involve opening of the mitoK(ATP) channel.

Selenium deficiency in a patient with Crohn's disease receiving long-term total parenteral nutrition.

We report a case of selenium deficiency in a patient with Crohn's disease on long-term total parenteral nutrition (TPN). She manifested lassitude of the legs, discoloration of the nail beds, and macrocytosis. Since her plasma selenium level was found to be below the measurable level, we diagnosed this case as selenium deficiency. After intravenous administration of sodium selenite, her symptoms were reversed. Careful attention should be paid to selenium deficiency when a patient receives long-term TPN; supplementary administration of selenium via TPN may be required because selenium is often not routinely added to TPN formulations.