Inhibition of glycogen synthase kinase-3beta improves tolerance to ischemia in hypertrophied hearts

Bibliometric and visual analysis of RAN methylation in cardiovascular disease

Background

RNA methylation is associated with cardiovascular disease (CVD) occurrence and development. The purpose of this study is to visually analyze the results and research trends of global RNA methylation in CVD.

Methods

Articles and reviews on RNA methylation in CVD published before 6 November 2022 were searched in the Web of Science Core Collection. Visual and statistical analysis was performed using CiteSpace 1.6.R4 advanced and VOSviewer 1.6.18.

Results

There were 847 papers from 1,188 institutions and 63 countries/regions. Over approximately 30 years, there was a gradual increase in publications and citations on RNA methylation in CVD. America and China had the highest output (284 and 259 papers, respectively). Nine of the top 20 institutions that published articles were from China, among which Fudan University represented the most. The International Journal of Molecular Sciences was the journal with the most studies. Nature was the most co-cited journal. The most influential writers were Zhang and Wang from China and Mathiyalagan from the United States. After 2015, the primary keywords were cardiac development, heart, promoter methylation, RNA methylation, and N6-methyladenosine. Nuclear RNA, m6A methylation, inhibition, and myocardial infarction were the most common burst keywords from 2020 to the present.

Conclusions

A bibliometric analysis reveals research hotspots and trends of RNA methylation in CVD. The regulatory mechanisms of RNA methylation related to CVD and the clinical application of their results, especially m6A methylation, are likely to be the focus of future research.

Epi-Drugs in Heart Failure

Unveiling the secrets of genome's flexibility does not only foster new research in the field, but also gives rise to the exploration and development of novel epigenetic-based therapies as an approach to alleviate disease phenotypes. A better understanding of chromatin biology (DNA/histone complexes) and non-coding RNAs (ncRNAs) has enabled the development of epigenetic drugs able to modulate transcriptional programs implicated in cardiovascular diseases. This particularly applies to heart failure, where epigenetic networks have shown to underpin several pathological features, such as left ventricular hypertrophy, fibrosis, cardiomyocyte apoptosis and microvascular dysfunction. Targeting epigenetic signals might represent a promising approach, especially in patients with heart failure with preserved ejection fraction (HFpEF), where prognosis remains poor and breakthrough therapies have yet to be approved. In this setting, epigenetics can be employed for the development of customized therapeutic approaches thus paving the way for personalized medicine. Even though the beneficial effects of epi-drugs are gaining attention, the number of epigenetic compounds used in the clinical practice remains low suggesting that more selective epi-drugs are needed. From DNA-methylation changes to non-coding RNAs, we can establish brand-new regulations for drug targets with the aim of restoring healthy epigenomes and transcriptional programs in the failing heart. In the present review, we bring the timeline of epi-drug discovery and development, thus highlighting the emerging role of epigenetic therapies in heart failure.

Lithium enhances exercise-induced glycogen breakdown and insulin-induced AKT activation to facilitate glucose uptake in rodent skeletal muscle

The purpose of this study was to investigate the effect of lithium on glucose disposal in a high-fat diet-induced type 2 diabetes mellitus (T2DM) and streptozotocin-induced type 1 diabetes mellitus (T1DM) animal model along with low-volume exercise and low-dose insulin. Lithium decreased body weight, fasting plasma glucose, and insulin levels when to treat with low-volume exercise training; however, there were no adaptive responses like an increase in GLUT4 content and translocation factor levels. We discovered that lithium enhanced glucose uptake by acute low-volume exercise-induced glycogen breakdown, which was facilitated by the dephosphorylation of serine 473-AKT (Ser473-AKT) and serine 9-GSK3β. In streptozotocin-induced T1DM mice, Li/low-dose insulin facilitates glucose uptake through increase the level of exocyst complex component 7 (Exoc7) and Ser473-AKT. Thus, lithium enhances acute exercise-induced glycogen breakdown and insulin-induced AKT activation and could serve as a candidate therapeutic target to regulate glucose level of DM patients.

Citric acid promoted melanin synthesis in B16F10 mouse melanoma cells, but inhibited it in human epidermal melanocytes and HMV-II melanoma cells via the GSK3β/β-catenin signaling pathway

Melanin, a pigment synthesized by melanocytes in the skin, resists the damage caused by ultraviolet rays to cells. Citric acid, a well-known food additive, is commonly used as an antioxidant and is an important part of the tricarboxylic acid (TCA) cycle for energy production during cellular metabolism. Here, we aimed to investigate whether the addition of excess citric acid regulates melanin synthesis, and to delineate the underlying mechanism. First, we observed that citric acid exerts opposite redox effects on mouse and human cells. Interestingly, treatment with excess citric acid increased the melanin content in mouse cells but decreased it in human cells. Furthermore, the expression of factors important for melanin synthesis, such as microphthalmia-associated transcription factor (MITF), was also regulated by citric acid treatment-it was promoted in mouse cells and suppressed in human cells. Citric acid also impacted the upstream regulators of MITF, glycogen synthase kinase 3β (GSK3β), and β-catenin. Second, we determined the importance of GSK3β in the citric acid-mediated regulation of melanin synthesis, using a GSK3β inhibitor (BIO). To the best of our knowledge, this is the first study to show that citric acid regulates melanin synthesis via the GSK3β/β-catenin signaling pathway, and that equal amounts of exogenous citric acid exert opposing effects on mouse and human cells.

Lithium interacts with cardiac remodeling: the fundamental value in the pharmacotherapy of bipolar disorder

Patients with bipolar disorder (BD) have an increased risk of cardiovascular morbidity and mortality during the course of their illness. For over half a century, lithium has been the gold-standard medication used to treat the mood burdens of BD. In addition, lithium possesses several biological effects that may modulate cardiovascular risk in patients with BD. In this review, we update the current knowledge of cellular and molecular mechanisms underlying the possible cardiac actions of lithium. The mechanistic insights suggest that lithium at therapeutic levels potentially exerts cardioprotective effects on ischemic hearts by modulating structural and electrical remodeling. The possible cardioprotective actions of lithium may involve an extensive range of signaling pathways, including the Wnt/glycogen synthase kinase-3β, phosphatidylinositol-3-kinase/protein kinase B, phosphoinositide/protein kinase C, and mitogen-activated protein kinase/extracellular signal-regulated kinase cascades. Accordingly, understanding the cardioprotective effects of lithium may lead to the development of a potential strategy for reducing cardiovascular morbidity in patients with BD.

Food Bioactive HDAC Inhibitors in the Epigenetic Regulation of Heart Failure

Approximately 5.7 million U.S. adults have been diagnosed with heart failure (HF). More concerning is that one in nine U.S. deaths included HF as a contributing cause. Current HF drugs (e.g., β-blockers, ACEi) target intracellular signaling cascades downstream of cell surface receptors to prevent cardiac pump dysfunction. However, these drugs fail to target other redundant intracellular signaling pathways and, therefore, limit drug efficacy. As such, it has been postulated that compounds designed to target shared downstream mediators of these signaling pathways would be more efficacious for the treatment of HF. Histone deacetylation has been linked as a key pathogenetic element for the development of HF. Lysine residues undergo diverse and reversible post-translational modifications that include acetylation and have historically been studied as epigenetic modifiers of histone tails within chromatin that provide an important mechanism for regulating gene expression. Of recent, bioactive compounds within our diet have been linked to the regulation of gene expression, in part, through regulation of the epi-genome. It has been reported that food bioactives regulate histone acetylation via direct regulation of writer (histone acetyl transferases, HATs) and eraser (histone deacetylases, HDACs) proteins. Therefore, bioactive food compounds offer unique therapeutic strategies as epigenetic modifiers of heart failure. This review will highlight food bio-actives as modifiers of histone deacetylase activity in the heart.

Enhancing Mitochondrial Health to Treat Hypertension

PURPOSE OF REVIEW

This review summarizes literature pertaining to the dawning field of therapeutic targeting of mitochondria in hypertension and discusses the potential of these interventions to ameliorate hypertension-induced organ damage.

RECENT FINDINGS

In recent years, mitochondrial dysfunction has been reported as an important contributor to the pathogenesis of hypertension-related renal, cardiac, and vascular disease. This in turn prompted development of novel mitochondria-targeted compounds, some of which have shown promising efficacy in experimental studies and safety in clinical trials. In addition, drugs that do not directly target mitochondria have shown remarkable benefits in preserving these organelles in experimental hypertension. Enhancing mitochondrial health is emerging as a novel feasible approach to treat hypertension. Future perspectives include mechanistic experimental studies to establish a cause-effect relationship between mitochondrial dysfunction and hypertension and further clinical trials to confirm the reno-, cardio-, and vasculo-protective properties of these compounds in hypertension.

1-Deoxynojirimycin Alleviates Liver Injury and Improves Hepatic Glucose Metabolism in db/db Mice

The present study investigated the effect of 1-Deoxynojirimycin (DNJ) on liver injury and hepatic glucose metabolism in db/db mice. Mice were divided into five groups: normal control, db/db control, DNJ-20 (DNJ 20 mg·kg⁻¹·day⁻¹), DNJ-40 (DNJ 40 mg·kg⁻¹·day⁻¹) and DNJ-80 (DNJ 80 mg·kg⁻¹·day⁻¹). All doses were treated intravenously by tail vein for four weeks. DNJ was observed to significantly reduce the levels of serum triglyceride (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C) and liver TG, as well as activities of serum alanine aminotransferase (ALT), and aspartate transaminase (AST); DNJ also alleviated macrovesicular steatosis and decreased tumor necrosis factor α (TNF-α), interleukin-1 (IL-1), interleukin-6 (IL-6) levels in liver tissue. Furthermore, DNJ treatment significantly increased hepatic glycogen content, the activities of hexokinase (HK), pyruvate kinase (PK) in liver tissue, and decreased the activities of glucose-6-phosphatase (G6Pase), glycogen phosphorylase (GP), and phosphoenolpyruvate carboxykinase (PEPCK). Moreover, DNJ increased the phosphorylation of phosphatidylinositol 3 kinase (PI3K) on p85, protein kinase B (PKB) on Ser473, glycogen synthase kinase 3β (GSK-3β) on Ser9, and inhibited phosphorylation of glycogen synthase (GS) on Ser645 in liver tissue of db/db mice. These results demonstrate that DNJ can increase hepatic insulin sensitivity via strengthening of the insulin-stimulated PKB/GSK-3β signal pathway and by modulating glucose metabolic enzymes in db/db mice. Moreover, DNJ also can improve lipid homeostasis and attenuate hepatic steatosis in db/db mice.

Tolerance to ischaemic injury in remodelled mouse hearts: less ischaemic glycogenolysis and preserved metabolic efficiency

AIMS

Post-infarction remodelled failing hearts have reduced metabolic efficiency. Paradoxically, they have increased tolerance to further ischaemic injury. This study was designed to investigate the metabolic mechanisms that may contribute to this phenomenon and to examine the relationship between ischaemic tolerance and metabolic efficiency during post-ischaemic reperfusion.

METHODS AND RESULTS

Male C57BL/6 mice were subjected to coronary artery ligation (CAL) or SHAM surgery. After 4 weeks, in vivo mechanical function was assessed by echocardiography, and then isolated working hearts were perfused in this sequence: 45 min aerobic, 15 min global no-flow ischaemia, and 30 min aerobic reperfusion. Left ventricular (LV) function, metabolic rates, and metabolic efficiency were measured. Relative to SHAM, both in vivo and in vitro CAL hearts had depressed cardiac function under aerobic conditions (45 and 36%, respectively), but they had a greater recovery of LV function during post-ischaemic reperfusion (67 vs. 49%, P < 0.05). While metabolic efficiency (LV work per ATP produced) was 50% lower during reperfusion of SHAM hearts, metabolic efficiency in CAL hearts did not decrease. During ischaemia, glycogenolysis was 28% lower in CAL hearts, indicative of lower ischaemic proton production. There were no differences in mitochondrial abundance, calcium handling proteins, or key metabolic enzymes.

CONCLUSION

Compared with SHAM, remodelled CAL hearts are more tolerant to ischaemic injury and undergo no further deterioration of metabolic efficiency during reperfusion. Less glycogen utilization in CAL hearts during ischaemia may contribute to increased ischaemic tolerance by limiting ischaemic proton production that may improve ion homeostasis during early reperfusion.

Cordycepin, 3'-deoxyadenosine, prevents rat hearts from ischemia/reperfusion injury via activation of Akt/GSK-3β/p70S6K signaling pathway and HO-1 expression

Cordycepin (3'-deoxyadenosine) isolated from Cordyceps militaris, a species of the fungal genus Cordyceps, has been shown to exhibit many pharmacological functions, such as anticancer, anti-inflammatory, and antioxidant activities. In this study, we investigated the preventive role of cordycepin in ischemic/reperfusion (I/R) injury of isolated rat hearts and anesthetized rats. After Sprague-Dawley rats received cordycepin (3, 10, and 30 mg/kg) or control (0.5 % carboxyl methylcellulose) orally once a day for a week, hearts were isolated and mounted on Langendorff heart perfusion system. Isolated hearts were perfused with Krebs-Henseleit buffer for 15-min pre-ischemic stabilization period and subjected to 30-min global ischemia and 30-min reperfusion. Cordycepin administration (10 mg/kg, p.o.) significantly increased left ventricular developed pressure during the reperfusion period compared to that in the control group, but without any effect on coronary flow. Cordycepin (10 mg/kg, p.o.) significantly increased the phosphorylation of Akt/GSK-3β/p70S6K pathways, which are known to modulate multiple survival pathways. In addition, cordycepin decreased Bax and cleaved caspase-3 expression while increasing Bcl-2 expression, Bcl-2/Bax ratio, and heme oxygenase (HO-1) expression in isolated rat hearts. In anesthetized rats subjected to 30 min occlusion of left anterior descending coronary artery/2.5-h reperfusion, cordycepin (1, 3, and 10 mg/kg, i.v.) administered 15 min before the onset of ischemia dose-dependently decreased the infarct size in left ventricle. In conclusion, cordycepin could be an attractive therapeutic candidate with oral activity against I/R-associated heart diseases such as myocardial infarction.

Gsk-3β inhibitors mimic the cardioprotection mediated by ischemic pre- and postconditioning in hypertensive rats

The aim of this study was to examine the effects of GSK-3β inhibitors compared with PRE and POS in spontaneously hypertensive rats (SHR). Isolated hearts were submitted to the following protocols: IC: 45 min global ischemia (GI) and 1-hour reperfusion (R); PRE: a cycle of 5 min GI and 10 minutes of R prior to 45 min GI; POS: three cycles of 30 sec GI/30 sec R at the start of R. Other hearts received lithium chloride (LiCl) or indirubin-3′-monoxime,5-iodo-(IMI) as GSK-3β inhibitors. All interventions reduced the infarct size observed in IC group. The expressions of P-GSK-3β and P-Akt decreased in IC and were restored after PRE, POS, and GSK-3β inhibitors treatments. An increase of cytosolic MnSOD activity and lipid peroxidation and a decrease of GSH content observed in IC hearts were attenuated in PRE, POS, and LiCl or IMI treatments. An increase of P-GSK-3β/VDAC physical association and a partial recovery of mitochondrial permeability were also detected after interventions. These data show that, in SHR hearts, GSK-3β inhibitors mimic the cardioprotection afforded by PRE and POS and suggest that a decrease in mitochondrial permeability mediated by P-GSK-3β/VDAC interaction is a crucial event.

Chronic lithium treatment protects against liver ischemia/reperfusion injury in rats

Lithium has long been widely used in the treatment of bipolar mood disorders. Recent studies have demonstrated that lithium is able to decrease ischemia/reperfusion (I/R) injury in the brain, kidneys, and heart. Because lithium may act on a number of stress and survival pathways, it is of great interest to explore this compound also in the setting of liver I/R injury. In this study, we aimed to evaluate the effects of lithium in a model of liver I/R injury in rats. Chronic treatment with lithium (2 mmol/kg for 3 days before ischemia) decreased I/R injury, whereas acute treatment with a single dose of lithium (2 mmol/kg 1 hour before ischemia) did not confer any protection in a partial hepatic I/R model. Furthermore, rats subjected to chronic lithium treatment had a significantly better survival rate (60%) than saline-treated rats (27%) in a total hepatic I/R survival model. Chronic lithium treatment protected against liver I/R injury, as indicated by lower serum aminotransferase levels, fewer I/R-associated histopathological changes, lower hepatic inflammatory cytokine levels, less neutrophil infiltration, and lower hepatic high-mobility group box expression and serum levels. The mechanism of action of lithium appears to involve its ability to inhibit glycogen synthase kinase 3β activation, modulate mitogen-activated protein kinase activation, inhibit hepatic apoptosis, and induce autophagy. On the basis of these data, we conclude that lithium treatment may be a simple and applicable preconditioning intervention for protecting against liver I/R injury.

Lithium exacerbates hepatic ischemia/reperfusion injury by inhibiting GSK-3β/NF-κB-mediated protective signaling in mice

Lithium (an inhibitor of GSK-3β activity) has beneficial effects on ischemia/reperfusion (I/R) injury in the central nervous system, heart and kidney. However, the role of lithium in hepatic I/R injury is unknown. The aim of this study was to assess the effects of lithium on hepatic I/R injury in a mouse model of partial hepatic I/R. Previous studies showed that lithium chloride (LiCl) can phosphorylate residue Ser9, inhibit GSK-3β activity, and improve I/R injury in other organs. In the present study, mice were pretreated with either vehicle or LiCl, which had similar effects on GSK-3β activity. Surprisingly, treatment with LiCl significantly exacerbated hepatic I/R injury, which was determined by serological and histological analyses. Acute and chronic LiCl treatment caused serious damage in hepatic I/R injury, including increased apoptosis and oxidative stress. To gain insight into the mechanism involved in this damage, the activity of nuclear factor-κB (NF-κB) (GSK-3β can regulate the transcriptional complex of NF-κB) was analyzed, which revealed that LiCl treatment significantly down-regulated the activity of NF-κB. The NF-κB-mediated protective genes were then further evaluated, including anti-apoptotic genes (RAF2, cIAP 2, Bfl-1 and cFLIP) and the antioxidant gene MnSOD. The expression of these protective genes was obviously suppressed compared with the vehicle group. Taken together, these findings show that lithium exacerbates hepatic I/R injury by suppressing the expression of GSK-3β/NF-κB-mediated protective genes.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Involvement of GSK-3β in attenuation of the cardioprotective effect of ischemic preconditioning in diabetic rat heart

Ischemic preconditioning (IPC) produces cardioprotection by phosphorylation of glycogen synthase kinase-3β (GSK-3β) that inhibits the opening of mitochondrial permeability transition pore (MPTP). The activity of glycogen GSK-3β is elevated during diabetes mellitus (DM). This study investigated the role of GSK-3β in attenuation of cardioprotective effect of IPC in diabetic rat. DM was induced by single administration of streptozotocin (STZ, 50 mg/kg, i.p.). Isolated perfused heart was subjected to 30 min of ischemia followed by 120 min of reperfusion. Myocardial infarct size was estimated by triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) was analyzed in coronary effluent. IPC significantly decreased myocardial infarct size and release of LDH and CK-MB from normal rat heart. The cardioprotective effect of IPC was significantly attenuated in diabetic rat. Four episodes of preconditioning by either of GSK-3β inhibitors, lithium chloride (LiCl, 20 mM), indirubin-3 monooxime (1 μM), and SB216763 (3 μM) significantly reduced the LDH and CK-MB release and decreased infarct size in diabetic rat heart. Perfusion of atractyloside, an opener of MPTP, significantly attenuated, the cardioprotective effect of IPC in normal rat heart, and of GSK-3β inhibitor induced preconditioning in the DM rat heart. Our results suggest that preconditioning with GSK-3β inhibitors in diabetic rat heart may provide a more consistent cardioprotection, as compared to IPC. Also, the mechanism of diabetes mellitus-induced attenuation of cardioprotective effect of IPC involves activation of GSK-3β, due to impaired protective upstream signaling pathways and opening of MPTP during reperfusion.

Effect of GSK-3 activity, enzymatic inhibition and gene silencing by RNAi on tick oviposition and egg hatching

Glycogen synthase kinase-3 (GSK-3) is classically described as a key enzyme involved in glycogen metabolism in mammals. It has been shown to be highly conserved among several organisms, mainly in the catalytic domain region. This enzyme has already been described in Rhipicephalus (Boophilus) microplus and the ovaries of females appeared to be the major site of GSK-3 transcription. The treatment with GSK-3 specific inhibitor (alsterpaullone, bromo-indirubin-oxime 6 and indirubin-3-oxime) caused a reduction in oviposition and egg hatching in completely engorged female ticks. The effect was more pronounced in partially engorged females when alsterpaullone was administrated by artificial capillary feeding. Moreover, GSK-3 gene silencing by RNAi in partially engorged females reduced significantly both oviposition and hatching. The study of tick embryogenesis and proteins that participate in this process has been suggested as an important means for the development of novel strategies for parasite control. GSK-3 is an essential protein involved in embryonic processes and for this reason it has already been suggested as a possible antigen candidate for tick control.

Indirubin-3'-oxime prevents hepatic I/R damage by inhibiting GSK-3beta and mitochondrial permeability transition

Indirubin-3'-oxime is an indirubin analogue that shows favorable inhibitory activity targeting glycogen synthase kinase 3beta (GSK-3beta). In this study, we evaluated if acute treatment with indirubin-3'-oxime (Ind) prevents hepatic ischemia/reperfusion (I/R) damage. Wistar rats were subjected to 150 min of 70% warm ischemia and 16 h of reperfusion. In the treated group 1 microM indirubin-3'-oxime was administered in the hepatic artery 30 min before ischemia. Acute treatment with Ind decreased serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels, comparatively to I/R livers. Bax translocation to the mitochondria and cytochrome c release were higher in I/R livers. Ind treatment significantly attenuated Bax translocation and preserved mitochondrial cytochrome c content. Ind also protected mitochondria from calcium-induced mitochondrial permeability transition (MPT), as well as the decrease in state 3 mitochondrial respiration, the delay in the repolarization after a phosphorylative cycle and the decrease in ATP content caused by I/R. By addressing GSK-3beta activity and phosphorylated GSK-3beta at Ser(9) content in liver homogenates and isolated mitochondria, data suggests that inhibition of GSK-3beta by indirubin-3'-oxime prevents the increase in mitochondrial phosphorylated GSK-3beta at Ser(9) induced by I/R, thus correlating with MPT inhibition and preservation of cytochrome c content. Pre-treatment with indirubin-3'-oxime in conditions of hepatic I/R, protects the liver by maintaining mitochondrial function and hepatic energetic balance.

Cardioprotection by GSK-3 inhibition: role of enhanced glycogen synthesis and attenuation of calcium overload

AIMS

Glycogen synthase kinase-3 (GSK-3) is a multi-functional kinase that regulates signalling pathways affecting glycogen metabolism, protein synthesis, mitosis, and apoptosis. GSK-3 inhibition limits cardiac ischaemia-reperfusion (IR) injury, but mechanisms are not clearly defined. This study tested the hypothesis that acute GSK-3 inhibition stimulates glycogen synthesis, repartitions glucose away from glycolysis, reduces proton (H+) production from glucose metabolism, and attenuates intracellular Ca2+ (Ca2+(i)) overload.

METHODS AND RESULTS

In isolated perfused working rat hearts subjected to global ischaemia and reperfusion, the selective GSK-3 inhibitor, SB-216763 (SB, 3 micromol/L), when added either prior to ischaemia or at the onset of reperfusion, improved recovery of left-ventricular (LV) work. SB increased glycogen synthesis during reperfusion while glycolysis and H+ production were reduced. Rates of glucose and palmitate oxidation were improved by SB. Measurement of Ca2+(i) concentration by rapid acquisition indo-1 fluorescence imaging showed that SB, when added either prior to ischaemia or at the onset of reperfusion, reduced diastolic Ca2+(i) overload during reperfusion. In aerobic hearts depleted of glycogen by substrate-free perfusion to a level similar to that measured at the onset of reperfusion, SB accelerated glycogen synthesis and reduced glycolysis and H+ production independent of changes in LV work.

CONCLUSION

Our study indicates that reduction in H+ production by GSK-3 inhibition is an early and upstream event that lessens Ca2+(i) overload during ischaemia and early reperfusion independent of LV work which enhances the recovery of post-ischaemic LV function and that may ultimately contribute to previously observed reductions in cell death and infarction.

Review of lithium effects on brain and blood

Clinicians have long used lithium to treat manic depression. They have also observed that lithium causes granulocytosis and lymphopenia while it enhances immunological activities of monocytes and lymphocytes. In fact, clinicians have long used lithium to treat granulocytopenia resulting from radiation and chemotherapy, to boost immunoglobulins after vaccination, and to enhance natural killer activity. Recent studies revealed a mechanism that ties together these disparate effects of lithium. Lithium acts through multiple pathways to inhibit glycogen synthetase kinase-3beta (GSK3 beta). This enzyme phosphorylates and inhibits nuclear factors that turn on cell growth and protection programs, including the nuclear factor of activated T cells (NFAT) and WNT/beta-catenin. In animals, lithium upregulates neurotrophins, including brain-derived neurotrophic factor (BDNF), nerve growth factor, neurotrophin-3 (NT3), as well as receptors to these growth factors in brain. Lithium also stimulates proliferation of stem cells, including bone marrow and neural stem cells in the subventricular zone, striatum, and forebrain. The stimulation of endogenous neural stem cells may explain why lithium increases brain cell density and volume in patients with bipolar disorders. Lithium also increases brain concentrations of the neuronal markers n-acetyl-aspartate and myoinositol. Lithium also remarkably protects neurons against glutamate, seizures, and apoptosis due to a wide variety of neurotoxins. The effective dose range for lithium is 0.6-1.0 mM in serum and >1.5 mM may be toxic. Serum lithium levels of 1.5-2.0 mM may have mild and reversible toxic effects on kidney, liver, heart, and glands. Serum levels of >2 mM may be associated with neurological symptoms, including cerebellar dysfunction. Prolonged lithium intoxication >2 mM can cause permanent brain damage. Lithium has low mutagenic and carcinogenic risk. Lithium is still the most effective therapy for depression. It "cures" a third of the patients with manic depression, improves the lives of about a third, and is ineffective in about a third. Recent studies suggest that some anticonvulsants (i.e., valproate, carbamapazine, and lamotrigene) may be useful in patients that do not respond to lithium. Lithium has been reported to be beneficial in animal models of brain injury, stroke, Alzheimer's, Huntington's, and Parkinson's diseases, amyotrophic lateral sclerosis (ALS), spinal cord injury, and other conditions. Clinical trials assessing the effects of lithium are under way. A recent clinical trial suggests that lithium stops the progression of ALS.

Drug development targeting the glycogen synthase kinase-3beta (GSK-3beta)-mediated signal transduction pathway: role of GSK-3beta in myocardial protection against ischemia/reperfusion injury

Although reperfusion is required to salvage ischemic myocardium from necrosis, reperfusion per se induces myocardial necrosis. In this "lethal reperfusion injury", opening of the mitochondrial permeability transition pore (mPTP) upon reperfusion is crucially involved. The mPTP primarily consists of adenine nucleotide translocator (ANT) and voltage-dependent anion channel, and its opening is triggered by binding of cyclophilin-D (CyP-D) to ANT, which increases Ca(2+) sensitivity of the mPTP. Recent studies have shown that inactivation of glycogen synthase kinase-3beta (GSK-3beta) suppresses mPTP opening and protects cardiomyocytes. Multiple intracellular signals relevant to cardiomyocyte protection converge to GSK-3beta and inactivate this kinase by phosphorylation. Although the effect of GSK-3beta phosphorylation on mPTP structure and function remains unclear, suppression of ANT-CyP-D interaction by binding of phospho-GSK-3beta to ANT and reduction in GSK-3beta-mediated phosphorylation of p53 may contribute to elevation of the threshold for mPTP opening. Furthermore, a significant inverse correlation was observed between level of phospho-GSK-3beta at the time of reperfusion and the extent of myocardium infarction in heart. Together with the infarct size-limiting effect of GSK-3beta inhibitors, this finding indicates that phospho-GSK-3beta is a determinant of myocardial tolerance against reperfusion-induced necrosis. Thus, GSK-3beta appears to be a target of novel therapy for cardioprotection upon reperfusion.

Indirubin-3'-oxime impairs mitochondrial oxidative phosphorylation and prevents mitochondrial permeability transition induction

Indirubin, a red colored 3,2'-bisindole isomer, is a component of Indigo naturalis and is an active ingredient used in traditional Chinese medicine for the treatment of chronic diseases. The family of indirubin derivatives, such as indirubin-3'-oxime, has been suggested for various therapeutic indications. However, potential toxic interactions such as indirubin effects on mitochondrial bioenergetics are still unknown. This study evaluated the action of indirubin-3'-oxime on the function of isolated rat liver mitochondria contributing to a better understanding of the biochemical mechanisms underlying the multiple effects of indirubin. Indirubin-3'-oxime incubated with isolated rat liver mitochondria, at concentrations above 10microM, significantly depresses the phosphorylation efficiency of mitochondria as inferred from the decrease in the respiratory control and ADP/O ratios, the perturbations in mitochondrial membrane potential and in the phosphorylative cycle induced by ADP. Furthermore, indirubin-3'-oxime at up to 25microM stimulates the rate of state 4 respiration and inhibits state 3 respiration. The increased lag phase of repolarization was associated with a direct inhibition of the mitochondrial ATPase. Indirubin-3'-oxime significantly inhibited the activity of complex II and IV thus explaining the decreased FCCP-stimulated mitochondrial respiration. Mitochondria pre-incubated with indirubin-3'-oxime exhibits decreased susceptibility to calcium-induced mitochondrial permeability transition. This work shows for the first time multiple effects of indirubin-3'-oxime on mitochondrial bioenergetics thus indicating a potential mechanism for indirubin-3'-oxime effects on cell function.

The intrinsic resistance of female hearts to an ischemic insult is abrogated in primary cardiac hypertrophy

Important sex differences in cardiovascular disease outcomes exist, including conditions of hypertrophic cardiomyopathy and cardiac ischemia. Studies of sex differences in the extent to which load-independent (primary) hypertrophy modulates the response to ischemia-reperfusion (I/R) damage have not been characterized. We have previously described a model of primary genetic cardiac hypertrophy, the hypertrophic heart rat (HHR). In this study the sex differences in HHR cardiac function and responses to I/R [compared to control normal heart rat (NHR)] were investigated ex vivo. The ventricular weight index was markedly increased in HHR female (7.82 +/- 0.49 vs. 4.80 +/- 0.10 mg/g; P < 0.05) and male (5.76 +/- 0.22 vs. 4.62 +/- 0.07 mg/g; P < 0.05) hearts. Female hearts of both strains exhibited a reduced basal contractility compared with strain-matched males [maximum first derivative of pressure (dP/dt(max)): NHR, 4,036 +/- 171 vs. 4,258 +/- 152 mmHg/s; and HHR, 3,974 +/- 160 vs. 4,540 +/- 259 mmHg/s; P < 0.05]. HHR hearts were more susceptible to I/R (I = 25 min, and R = 30 min) injury than NHR hearts (decreased functional recovery, and increased lactate dehydrogenase efflux). Female NHR hearts exhibited a significantly greater recovery (dP/dt(max)) post-I/R relative to male NHR (95.0 +/- 12.2% vs. 60.5 +/- 9.4%), a resistance to postischemic dysfunction not evident in female HHR (29.0 +/- 5.6% vs. 25.9 +/- 6.3%). Ventricular fibrillation was suppressed, and expression levels of Akt and ERK1/2 were selectively elevated in female NHR hearts. Thus the occurrence of load-independent primary cardiac hypertrophy undermines the intrinsic resistance of female hearts to I/R insult, with the observed abrogation of endogenous cardioprotective signaling pathways consistent with a potential mechanistic role in this loss of protection.