Cardiac abnormalities in diabetic patients with neuropathy: effects of aldose reductase inhibitor administration

Randomized Trial of a Selective Aldose Reductase Inhibitor in Patients With Diabetic Cardiomyopathy

BACKGROUND

Progression to symptomatic heart failure is a complication of type 2 diabetes; heart failure onset in this setting is commonly preceded by deterioration in exercise capacity.

OBJECTIVES

This study sought to determine whether AT-001, a highly selective aldose reductase inhibitor, can stabilize exercise capacity among individuals with diabetic cardiomyopathy (DbCM) and reduced peak oxygen uptake (Vo2).

METHODS

A total of 691 individuals with DbCM meeting inclusion and exclusion criteria were randomized to receive placebo or ascending doses of AT-001 twice daily. Stratification at inclusion included region of enrollment, cardiopulmonary exercise test results, and use of sodium-glucose cotransporter 2 inhibitors or glucagon-like peptide-1 receptor agonists. The primary endpoint was proportional change in peak Vo2 from baseline to 15 months. Subgroup analyses included measures of disease severity and stratification variables.

RESULTS

The mean age was 67.5 ± 7.2 years, and 50.4% of participants were women. By 15 months, peak Vo2 fell in the placebo-treated patients by -0.31 mL/kg/min (P = 0.005 compared to baseline), whereas in those receiving high-dose AT-001, peak Vo2 fell by -0.01 mL/kg/min (P = 0.21); the difference in peak Vo2 between placebo and high-dose AT-001 was 0.30 (P = 0.19). In prespecified subgroup analyses among those not receiving sodium-glucose cotransporter 2 inhibitors or glucagon-like peptide-1 receptor agonists at baseline, the difference between peak Vo2 in placebo vs high-dose AT-001 at 15 months was 0.62 mL/kg/min (P = 0.04; interaction P = 0.10).

CONCLUSIONS

Among individuals with DbCM and impaired exercise capacity, treatment with AT-001 for 15 months did not result in significantly better exercise capacity compared with placebo. (Safety and Efficacy of AT-001 in Patients With Diabetic Cardiomyopathy [ARISE-HF]; NCT04083339).

Aldose reductase inhibition alleviates diabetic cardiomyopathy and is associated with a decrease in myocardial fatty acid oxidation

BACKGROUND

Cardiovascular diseases, including diabetic cardiomyopathy, are major causes of death in people with type 2 diabetes. Aldose reductase activity is enhanced in hyperglycemic conditions, leading to altered cardiac energy metabolism and deterioration of cardiac function with adverse remodeling. Because disturbances in cardiac energy metabolism can promote cardiac inefficiency, we hypothesized that aldose reductase inhibition may mitigate diabetic cardiomyopathy via normalization of cardiac energy metabolism.

METHODS

Male C57BL/6J mice (8-week-old) were subjected to experimental type 2 diabetes/diabetic cardiomyopathy (high-fat diet [60% kcal from lard] for 10 weeks with a single intraperitoneal injection of streptozotocin (75 mg/kg) at 4 weeks), following which animals were randomized to treatment with either vehicle or AT-001, a next-generation aldose reductase inhibitor (40 mg/kg/day) for 3 weeks. At study completion, hearts were perfused in the isolated working mode to assess energy metabolism.

RESULTS

Aldose reductase inhibition by AT-001 treatment improved diastolic function and cardiac efficiency in mice subjected to experimental type 2 diabetes. This attenuation of diabetic cardiomyopathy was associated with decreased myocardial fatty acid oxidation rates (1.15 ± 0.19 vs 0.5 ± 0.1 µmol min-1 g dry wt-1 in the presence of insulin) but no change in glucose oxidation rates compared to the control group. In addition, cardiac fibrosis and hypertrophy were also mitigated via AT-001 treatment in mice with diabetic cardiomyopathy.

CONCLUSIONS

Inhibiting aldose reductase activity ameliorates diastolic dysfunction in mice with experimental type 2 diabetes, which may be due to the decline in myocardial fatty acid oxidation, indicating that treatment with AT-001 may be a novel approach to alleviate diabetic cardiomyopathy in patients with diabetes.

Emerging Therapy for Diabetic Cardiomyopathy: From Molecular Mechanism to Clinical Practice

Diabetic cardiomyopathy is characterized by abnormal myocardial structure or performance in the absence of coronary artery disease or significant valvular heart disease in patients with diabetes mellitus. The spectrum of diabetic cardiomyopathy ranges from subtle myocardial changes to myocardial fibrosis and diastolic function and finally to symptomatic heart failure. Except for sodium–glucose transport protein 2 inhibitors and possibly bariatric and metabolic surgery, there is currently no specific treatment for this distinct disease entity in patients with diabetes. The molecular mechanism of diabetic cardiomyopathy includes impaired nutrient-sensing signaling, dysregulated autophagy, impaired mitochondrial energetics, altered fuel utilization, oxidative stress and lipid peroxidation, advanced glycation end-products, inflammation, impaired calcium homeostasis, abnormal endothelial function and nitric oxide production, aberrant epidermal growth factor receptor signaling, the activation of the renin–angiotensin–aldosterone system and sympathetic hyperactivity, and extracellular matrix accumulation and fibrosis. Here, we summarize several important emerging treatments for diabetic cardiomyopathy targeting specific molecular mechanisms, with evidence from preclinical studies and clinical trials.

Rationale and design of the Aldose Reductase Inhibition for Stabilization of Exercise Capacity in Heart Failure Trial (ARISE-HF) in patients with high-risk diabetic cardiomyopathy

BACKGROUND

Diabetic cardiomyopathy (DbCM) is a specific form of heart muscle disease that may result in substantial morbidity and mortality in individuals with type 2 diabetes mellitus (T2DM). Hyperactivation of the polyol pathway is one of the primary mechanisms in the pathogenesis of diabetic complications, including development of DbCM. There is an unmet need for therapies targeting the underlying metabolic abnormalities that drive this form of Stage B heart failure (HF).

METHODS

Aldose reductase (AR) catalyzes the first and rate-limiting step in the polyol pathway, and AR inhibition has been shown to reduce diabetic complications, including DbCM in animal models and in patients with DbCM. Previous AR inhibitors (ARIs) were limited by poor specificity resulting in unacceptable tolerability and safety profile. AT-001 is a novel investigational highly specific ARI with higher binding affinity and greater selectivity than previously studied ARIs. ARISE-HF (NCT04083339) is an ongoing Phase 3 randomized, placebo-controlled, double blind, global clinical study to investigate the efficacy of AT-001 (1000 mg twice daily [BID] and 1500 mg BID) in 675 T2DM patients with DbCM at high risk of progression to overt HF. ARISE-HF assesses the ability of AT-001 to improve or prevent decline in exercise capacity as measured by functional capacity (changes in peak oxygen uptake [peak VO₂]) over 15 (and possibly 27) months of treatment. Additional endpoints include percentage of patients progressing to overt HF, health status metrics, echocardiographic measurements, and changes in cardiacbiomarkers.

RESULTS

The ARISE-HF Trial is fully enrolled.

CONCLUSIONS

This report describes the rationale and study design of ARISE-HF.

Troponin T Is Negatively Associated With 3 Tesla Magnetic Resonance Peripheral Nerve Perfusion in Type 2 Diabetes

OBJECTIVE

The pathogenesis of diabetic polyneuropathy (DN) is poorly understood and given the increasing prevalence of DN, there is a need for clinical or imaging biomarkers that quantify structural and functional nerve damage. While clinical studies have found evidence of an association between elevated levels of troponin T (hsTNT) and N-terminal pro brain natriuretic peptide (proBNP) with microvascular compromise in type 2 diabetes (T2D), their implication in mirroring DN nerve perfusion changes remains unclear. The objective of this study was, therefore, to investigate whether hsTNT and proBNP assays are associated with MRI nerve perfusion in T2D.

METHODS

In this prospective cross-sectional single-center case-control study, 56 participants (44 with T2D, 12 healthy control subjects) consented to undergo magnetic resonance neurography (MRN) including dynamic contrast-enhanced (DCE) perfusion imaging of the right leg. Using the extended Tofts model, primary outcome parameters that were quantified are the sciatic nerve's microvascular permeability (K^trans), the extravascular extracellular volume fraction (v_e), and the plasma volume fraction (v_p), as well as hsTNT and proBNP values from serological workup. Further secondary outcomes were clinical, serological, and electrophysiological findings.

RESULTS

In T2D patients, hsTNT was negatively correlated with K^trans (r=-0.38; p=0.012) and v_e (r=-0.30; p=0.048) but not with v_p (r=-0.16; p=0.294). HsTNT, K^trans, and v_e were correlated with peroneal nerve conduction velocities (NCVs; r=-0.44; p=0.006, r=0.42; p=0.008, r=0.39; p=0.014), and tibial NCVs (r=-0.38;p=0.022, r=0.33; p=0.048, r=0.37; p=0.025). No such correlations were found for proBNP.

CONCLUSIONS

This study is the first to find that hsTNT is correlated with a decrease of microvascular permeability and a reduced extravascular extracellular volume fraction of nerves in patients with T2D. The results indicate that hsTNT may serve as a potential marker for the assessment of nerve perfusion in future studies on DN.

Diet and Obesity-Induced Methylglyoxal Production and Links to Metabolic Disease

The obesity rate in the United States is 42.4% and has become a national epidemic. Obesity is a complex condition that is influenced by socioeconomic status, ethnicity, genetics, age, and diet. Increased consumption of a Western diet, one that is high in processed foods, red meat, and sugar content, is associated with elevated obesity rates. Factors that increase obesity risk, such as socioeconomic status, also increase consumption of a Western diet because of a limited access to healthier options and greater affordability of processed foods. Obesity is a public health threat because it increases the risk of several pathologies, including atherosclerosis, diabetes, and cancer. The molecular mechanisms linking obesity to disease onset and progression are not well understood, but a proposed mechanism is physiological changes caused by altered lipid peroxidation, glycolysis, and protein metabolism. These metabolic pathways give rise to reactive molecules such as the abundant electrophile methylglyoxal (MG), which covalently modifies nucleic acids and proteins. MG-adducts are associated with obesity-linked pathologies and may have potential for biomonitoring to determine the risk of disease onset and progression. MG-adducts may also play a role in disease progression because they are mutagenic and directly impact protein stability and function. In this review, we discuss how obesity drives metabolic alterations, how these alterations lead to MG production, the association of MG-adducts with disease, and the potential impact of MG-adducts on cellular function.

Asymptomatic Diabetic Cardiomyopathy: an Underrecognized Entity in Type 2 Diabetes

PURPOSE OF REVIEW

Type 2 diabetes (T2D) is associated with an increased risk of heart failure (HF), with diabetic cardiomyopathy (DbCM) referring to abnormal heart structure in the absence of other driving cardiac factors such as hypertension, coronary artery disease (CAD), and valvular heart disease. Stage B DbCM is commonly asymptomatic and represents a form of stage B HF; DbCM thus represents a transitional phenotype prior to onset of symptomatic HF. The pathogenesis of DbCM is not fully elucidated but involves hyperglycemia, insulin resistance, increased free fatty acids (FFA), lipotoxicity, oxidative stress, advanced glycation end product (AGE) formation, activation of the renin-angiotensin-aldosterone system (RAAS) with an increase in angiotensin II, and dyshomeostasis of calcium, which all contribute to left ventricular hypertrophy (LVH) and cardiac systolic and diastolic dysfunction. Although DbCM is an established pathogenic process, it is underrecognized clinically due to its commonly asymptomatic nature. Raising awareness to identify high-risk individuals with stage B HF due to DbCM, who may subsequently progress to overt HF (stage C/D HF), as well as identifying new pharmacological agents and approaches to prevent functional decline, may help reduce this global health problem. The aim of this review is to focus on stage B DbCM; provide data on diagnostic approaches, current therapies, and potential therapies under investigation; and highlight the need to raise awareness and interdisciplinary dialogue among clinicians and researchers.

RECENT FINDINGS

There are no currently approved therapeutic strategies to treat or prevent progression of stage B DbCM, but multiple attempts are being made to target different pathogenic mechanisms involved in the development of DbCM. Recent cardiovascular (CV) outcome trials (CVOTs) have identified newer therapeutic agents with CV benefit, such as sodium-glucose cotransporter-2 (SGLT-2) inhibitors that reduce hospitalization for HF and glucagon-like peptide-1 (GLP-1) receptor agonists that reduce major adverse CV events (MACE), though without consistent effect on HF outcomes. Recent clinical practice guidelines recommend screening patients at high risk for HF. Further definition and interdisciplinary discussion of high-yield populations to screen, appropriate subsequent evaluation and intervention are needed to advance this area. DbCM is a complex entity that results from multiple pathogenic mechanisms triggered by impairment of glucose and lipid metabolism over many years. DbCM is commonly asymptomatic and represents a form of stage B HF. It is an underrecognized process that may progress to functional decline and overt HF. Although newer medications approved for the treatment of T2D may play an important role in reducing the risk of HF complications, less focus has been placed on earlier recognition and treatment of DbCM while asymptomatic. Additional efforts should be made to further study and target this stage in order to decrease the overall burden of HF.

Fructose Metabolism and Cardiac Metabolic Stress

Cardiovascular disease is one of the leading causes of mortality in diabetes. High fructose consumption has been linked with the development of diabetes and cardiovascular disease. Serum and cardiac tissue fructose levels are elevated in diabetic patients, and cardiac production of fructose via the intracellular polyol pathway is upregulated. The question of whether direct myocardial fructose exposure and upregulated fructose metabolism have potential to induce cardiac fructose toxicity in metabolic stress settings arises. Unlike tightly-regulated glucose metabolism, fructose bypasses the rate-limiting glycolytic enzyme, phosphofructokinase, and proceeds through glycolysis in an unregulated manner. In vivo rodent studies have shown that high dietary fructose induces cardiac metabolic stress and functional disturbance. In vitro, studies have demonstrated that cardiomyocytes cultured in high fructose exhibit lipid accumulation, inflammation, hypertrophy and low viability. Intracellular fructose mediates post-translational modification of proteins, and this activity provides an important mechanistic pathway for fructose-related cardiomyocyte signaling and functional effect. Additionally, fructose has been shown to provide a fuel source for the stressed myocardium. Elucidating the mechanisms of fructose toxicity in the heart may have important implications for understanding cardiac pathology in metabolic stress settings.

Development of Aldose Reductase Inhibitors for the Treatment of Inflammatory Disorders and Cancer: Current Drug Design Strategies and Future Directions

Aldose Reductase (AR) is an enzyme that converts glucose to sorbitol during the polyol pathway of glucose metabolism. AR has been shown to be involved in the development of secondary diabetic complications due to its involvement in causing osmotic as well as oxidative stress. Various AR inhibitors have been tested for their use to treat secondary diabetic complications, such as retinopathy, neuropathy, and nephropathy in clinical studies. Recent studies also suggest the potential role of AR in mediating various inflammatory complications. Therefore, the studies on the development and potential use of AR inhibitors to treat inflammatory complications and cancer besides diabetes are currently on the rise. Further, genetic mutagenesis studies, computer modeling, and molecular dynamics studies have helped design novel and potent AR inhibitors. This review discussed the potential new therapeutic use of AR inhibitors in targeting inflammatory disorders and cancer besides diabetic complications. Further, we summarized studies on how AR inhibitors have been designed and developed for therapeutic purposes in the last few decades.

Aldose Reductase: An Emerging Target for Development of Interventions for Diabetic Cardiovascular Complications

Diabetes is a leading cause of cardiovascular morbidity and mortality. Despite numerous treatments for cardiovascular disease (CVD), for patients with diabetes, these therapies provide less benefit for protection from CVD. These considerations spur the concept that diabetes-specific, disease-modifying therapies are essential to identify especially as the diabetes epidemic continues to expand. In this context, high levels of blood glucose stimulate the flux via aldose reductase (AR) pathway leading to metabolic and signaling changes in cells of the cardiovascular system. In animal models flux via AR in hearts is increased by diabetes and ischemia and its inhibition protects diabetic and non-diabetic hearts from ischemia-reperfusion injury. In mouse models of diabetic atherosclerosis, human AR expression accelerates progression and impairs regression of atherosclerotic plaques. Genetic studies have revealed that single nucleotide polymorphisms (SNPs) of the ALD2 (human AR gene) is associated with diabetic complications, including cardiorenal complications. This Review presents current knowledge regarding the roles for AR in the causes and consequences of diabetic cardiovascular disease and the status of AR inhibitors in clinical trials. Studies from both human subjects and animal models are presented to highlight the breadth of evidence linking AR to the cardiovascular consequences of diabetes.

Elevated myocardial fructose and sorbitol levels are associated with diastolic dysfunction in diabetic patients, and cardiomyocyte lipid inclusions in vitro

Diabetes is associated with cardiac metabolic disturbances and increased heart failure risk. Plasma fructose levels are elevated in diabetic patients. A direct role for fructose involvement in diabetic heart pathology has not been investigated. The goals of this study were to clinically evaluate links between myocardial fructose and sorbitol (a polyol pathway fructose precursor) levels with evidence of cardiac dysfunction, and to experimentally assess the cardiomyocyte mechanisms involved in mediating the metabolic effects of elevated fructose. Fructose and sorbitol levels were increased in right atrial appendage tissues of type 2 diabetic patients (2.8- and 1.5-fold increase respectively). Elevated cardiac fructose levels were confirmed in type 2 diabetic rats. Diastolic dysfunction (increased E/e’, echocardiography) was significantly correlated with cardiac sorbitol levels. Elevated myocardial mRNA expression of the fructose-specific transporter, Glut5 (43% increase), and the key fructose-metabolizing enzyme, Fructokinase-A (50% increase) was observed in type 2 diabetic rats (Zucker diabetic fatty rat). In neonatal rat ventricular myocytes, fructose increased glycolytic capacity and cytosolic lipid inclusions (28% increase in lipid droplets/cell). This study provides the first evidence that elevated myocardial fructose and sorbitol are associated with diastolic dysfunction in diabetic patients. Experimental evidence suggests that fructose promotes the formation of cardiomyocyte cytosolic lipid inclusions, and may contribute to lipotoxicity in the diabetic heart.

COVID-19 and the Heart and Vasculature: Novel Approaches to Reduce Virus-Induced Inflammation in Patients With Cardiovascular Disease

The coronavirus disease 2019 (COVID-19) pandemic presents an unprecedented challenge and opportunity for translational investigators to rapidly develop safe and effective therapeutic interventions. Greater risk of severe disease in COVID-19 patients with comorbid diabetes mellitus, obesity, and heart disease may be attributable to synergistic activation of vascular inflammation pathways associated with both COVID-19 and cardiometabolic disease. This mechanistic link provides a scientific framework for translational studies of drugs developed for treatment of cardiometabolic disease as novel therapeutic interventions to mitigate inflammation and improve outcomes in patients with COVID-19.

The Role of Nonglycolytic Glucose Metabolism in Myocardial Recovery Upon Mechanical Unloading and Circulatory Support in Chronic Heart Failure

BACKGROUND

Significant improvements in myocardial structure and function have been reported in some patients with advanced heart failure (termed responders [R]) following left ventricular assist device (LVAD)-induced mechanical unloading. This therapeutic strategy may alter myocardial energy metabolism in a manner that reverses the deleterious metabolic adaptations of the failing heart. Specifically, our previous work demonstrated a post-LVAD dissociation of glycolysis and oxidative-phosphorylation characterized by induction of glycolysis without subsequent increase in pyruvate oxidation through the tricarboxylic acid cycle. The underlying mechanisms responsible for this dissociation are not well understood. We hypothesized that the accumulated glycolytic intermediates are channeled into cardioprotective and repair pathways, such as the pentose-phosphate pathway and 1-carbon metabolism, which may mediate myocardial recovery in R.

METHODS

We prospectively obtained paired left ventricular apical myocardial tissue from nonfailing donor hearts as well as R and nonresponders at LVAD implantation (pre-LVAD) and transplantation (post-LVAD). We conducted protein expression and metabolite profiling and evaluated mitochondrial structure using electron microscopy.

RESULTS

Western blot analysis shows significant increase in rate-limiting enzymes of pentose-phosphate pathway and 1-carbon metabolism in post-LVAD R (post-R) as compared with post-LVAD nonresponders (post-NR). The metabolite levels of these enzyme substrates, such as sedoheptulose-6-phosphate (pentose phosphate pathway) and serine and glycine (1-carbon metabolism) were also decreased in Post-R. Furthermore, post-R had significantly higher reduced nicotinamide adenine dinucleotide phosphate levels, reduced reactive oxygen species levels, improved mitochondrial density, and enhanced glycosylation of the extracellular matrix protein, α-dystroglycan, all consistent with enhanced pentose-phosphate pathway and 1-carbon metabolism that correlated with the observed myocardial recovery.

CONCLUSIONS

The recovering heart appears to direct glycolytic metabolites into pentose-phosphate pathway and 1-carbon metabolism, which could contribute to cardioprotection by generating reduced nicotinamide adenine dinucleotide phosphate to enhance biosynthesis and by reducing oxidative stress. These findings provide further insights into mechanisms responsible for the beneficial effect of glycolysis induction during the recovery of failing human hearts after mechanical unloading.

Effects of Inhibition of the Polyol Pathway during Chronic Peritoneal Exposure to a Dialysis Solution

♦ Background

Peritoneal dialysis with glucose- and lactate-containing dialysis solutions stimulates peritoneal angiogenesis and fibrosis. These serious side effects can also be induced by chronic peritoneal exposure to dialysis solutions in nonuremic rats. The high glucose concentrations of the dialysis solutions may saturate physiological glucose metabolism pathways and stimulate the polyol pathway that has been described to damage nerves and vessels in diabetes mellitus. To investigate the role of the polyol pathway in the development of fibrosis and angiogenesis during chronic peritoneal exposure, the rate-limiting aldose reductase activity in the polyol pathway was inhibited in a chronic peritoneal exposure model in the rat, in which different administration routes were compared.

♦ Experimental Procedures

Three groups of rats received daily intraperitoneal infusion with lactate/glucose (3.86%)- containing dialysate via a peritoneal catheter with a subcutaneous puncture device, for 14 weeks: group 1 received only the dialysis solution, groups 2 and 3 received, in addition, zopolrestat, administered either orally (group 2) or intraperitoneally (group 3). After sacrifice, omental tissue was examined by histology for the presence of fibrosis (Picro Sirius Red) and the number of blood vessels (CD31).

♦ Results

Histology revealed significantly less Picro Sirius Red-positive tissue in perivascular areas of both experimental groups and submesothelial areas of the oral group in comparison to the control group. There were significantly fewer CD31-positive vessels per field in both groups treated with zopolrestat compared to the infusion-only group: group 2, 9 (7 – 12); group 3, 17 (13 – 38), compared to group 1, 37 (32 – 39), p < 0.05.

♦ Conclusion

The combination of peritoneal exposure to dialysis fluids and administration of zopolrestat, a newly developed inhibitor of aldose reductase activity, resulted in less fibrosis and fewer peritoneal vessels than exposure to dialysis fluids only, in a long-term exposure model in the rat. Inhibition of the polyol pathway may thus offer an important contribution to allow long-term continuation of peritoneal dialysis.

Investigations on the structural, vibrational, computational, and molecular docking studies on potential antidiabetic chemical agent Diosmetin

In the present study, the harmonic vibrational frequencies of Diosmetin(5, 7 dihydroxy-2(3-hydroxy-4 methoxyphenyl) chromen-4-one) have been investigated by both experimental (FTIR and FT-Raman) and theoretical (HF and DFT/B3LYP) method. The calculated harmonic vibrational frequencies were compared with experimental data. A detailed interpretation of the vibrational spectra of the compound has been made on the basis of the calculated potential energy distribution (PED). The ¹ H, ¹³ C NMR chemical shifts and TD-DFT calculations of the molecule were calculated and compared with the available experimental observations. A study on the molecular electrostatic potential surface (MEP) of the compound was performed, and the electrophilic and nucleophilic reactive sites were identified. Furthermore, the inhibition effect of compound against aldose reductase enzyme has been analyzed by molecular docking method, and the results were compared with the standard drug. The docking study indicates that the investigated compound shows better inhibitory activity toward aldose reductase enzyme than the standard drug, and hence this study may be supportive in the field of drug discovery to design more potential antidiabetic agents.

Vitamin K1 prevents diabetic cataract by inhibiting lens aldose reductase 2 (ALR2) activity

This study investigated the potential of vitamin K1 as a novel lens aldose reductase inhibitor in a streptozotocin-induced diabetic cataract model. A single, intraperitoneal injection of streptozotocin (STZ) (35 mg/kg) resulted in hyperglycemia, activation of lens aldose reductase 2 (ALR2) and accumulation of sorbitol in eye lens which could have contributed to diabetic cataract formation. However, when diabetic rats were treated with vitamin K1 (5 mg/kg, sc, twice a week) it resulted in lowering of blood glucose and inhibition of lens aldose reductase activity because of which there was a corresponding decrease in lens sorbitol accumulation. These results suggest that vitamin K1 is a potent inhibitor of lens aldose reductase enzyme and we made an attempt to understand the nature of this inhibition using crude lens homogenate as well as recombinant human aldose reductase enzyme. Our results from protein docking and spectrofluorimetric analyses clearly show that vitamin K1 is a potent inhibitor of ALR2 and this inhibition is primarily mediated by the blockage of DL-glyceraldehyde binding to ALR2. At the same time docking also suggests that vitamin K1 overlaps at the NADPH binding site of ALR2, which probably shows that vitamin K1 could possibly bind both these sites in the enzyme. Another deduction that we can derive from the experiments performed with pure protein is that ALR2 has three levels of affinity, first for NADPH, second for vitamin K1 and third for the substrate DL-glyceraldehyde. This was evident based on the dose-dependency experiments performed with both NADPH and DL-glyceraldehyde. Overall, our study shows the potential of vitamin K1 as an ALR2 inhibitor which primarily blocks enzyme activity by inhibiting substrate interaction of the enzyme. Further structural studies are needed to fully comprehend the exact nature of binding and inhibition of ALR2 by vitamin K1 that could open up possibilities of its therapeutic application.

Cardiorespiratory Fitness and Cardiac Autonomic Function in Diabetes

PURPOSE OF REVIEW

This review summarizes the current knowledge on the relationship of physical activity, exercise, and cardiorespiratory fitness (CRF) with cardiovascular autonomic neuropathy (CAN) based on epidemiological, clinical, and interventional studies.

RECENT FINDINGS

The prevalence of CAN increases with age and duration of diabetes. Further risk factors for CAN comprise poor glycemic control, dyslipidemia, abdominal obesity, hypertension, and the presence of diabetic complications. CAN has been also linked to reduced CRF. We recently showed that CRF parameters (e.g., maximal oxidative capacity or oxidative capacity at the anaerobic threshold) are associated with cardiac autonomic function in patients recently diagnosed with type 1 or type 2 diabetes. Exercise interventions have shown that physical activity can increase cardiovagal activity and reduce sympathetic overactivity. In particular, long-term and regularly, but also supervised, performed endurance and high-intense and high-volume exercise improves cardiac autonomic function in patients with type 2 diabetes. By contrast, the evidence in those with type 1 diabetes and also in individuals with prediabetes or metabolic syndrome is weaker. Overall, the studies reviewed herein addressing the question whether favorably modulating the autonomic nervous system may improve CRF during exercise programs support the therapeutic concept to promote physical activity and to achieve physical fitness. However, high-quality exercise interventions, especially in type 1 diabetes and metabolic syndrome including prediabetes, are further required to better understand the relationship between physical activity, fitness, and cardiac autonomic function.

Corticosteroids and aldose reductase inhibitor Epalrestat modulates cardiac action potential via Kvβ1.1 (AKR6A8) subunit of voltage-gated potassium channel

We previously demonstrated the role of Kvβ1.1 subunit of voltage-activated potassium channel in heart for its sensory roles in detecting changes in NADH/NAD and modulation of ion channel. However, the pharmacological role for the association of Kvβ1 via its binding to ligands such as cortisone and its analogs remains unknown. Therefore, we investigated the significance of Kvβ1.1 binding to cortisone analogs and AR inhibitor epalrestat. In addition, the aldose reductase (AR) inhibitor epalrestat was identified as a pharmacological target and modulator of cardiac activity via binding to the Kvβ1 subunit. Using a combination of ex vivo cardiac electrophysiology and in silico binding, we identified that Kvβ1 subunit binds and interacts with epalrestat. To identify the specificity of the action potential changes, we studied the sensitivity of the action potential prolongation by probing the electrical changes in the presence of 4-aminopyridine and evaluated the specificity of pharmacological effects in the hearts from Kvβ1.1 knock out mouse. Our results show that pharmacological modulation of cardiac electrical activity by cortisone analogs and epalrestat is mediated by Kvβ1.1.

Exercise mediated protection of diabetic heart through modulation of microRNA mediated molecular pathways

Hyperglycaemia, hypertension, dyslipidemia and insulin resistance collectively impact on the myocardium of people with diabetes, triggering molecular, structural and myocardial abnormalities. These have been suggested to aggravate oxidative stress, systemic inflammation, myocardial lipotoxicity and impaired myocardial substrate utilization. As a consequence, this leads to the development of a spectrum of cardiovascular diseases, which may include but not limited to coronary endothelial dysfunction, and left ventricular remodelling and dysfunction. Diabetic heart disease (DHD) is the term used to describe the presence of heart disease specifically in diabetic patients. Despite significant advances in medical research and long clinical history of anti-diabetic medications, the risk of heart failure in people with diabetes never declines. Interestingly, sustainable and long-term exercise regimen has emerged as an effective synergistic therapy to combat the cardiovascular complications in people with diabetes, although the precise molecular mechanism(s) underlying this protection remain unclear. This review provides an overview of the underlying mechanisms of hyperglycaemia- and insulin resistance-mediated DHD with a detailed discussion on the role of different intensities of exercise in mitigating these molecular alterations in diabetic heart. In particular, we provide the possible role of exercise on microRNAs, the key molecular regulators of several pathophysiological processes.

Cardiac autonomic neuropathy in patients with diabetes mellitus: current perspectives

Cardiac autonomic neuropathy (CAN) is a common and often-underdiagnosed complication of diabetes mellitus (DM). CAN is associated with increased mortality, cardiovascular disease, chronic kidney disease, and morbidity in patients with DM, but despite these significant consequences CAN often remains undiagnosed for a prolonged period. This is commonly due to the disease being asymptomatic until the later stages, as well as a lack of easily available screening strategies. In this article, we review the latest developments in the epidemiology, pathogenesis, diagnosis, consequences, and treatments of CAN in patients with DM.

Cardiovascular autonomic neuropathy

Cardiovascular autonomic neuropathy often goes unrecognized. We present a case of a 22-year-old man with multiple manifestations of this disease, including weakness, dizziness, fatigue, tachycardia, abnormal QTc, and orthostasis, which occurred 2 years after his type 1 diabetes diagnosis. He exhibited parasympathetic denervation with resting tachycardia and exercise intolerance but also had evidence of orthostatic hypotension, which suggests sympathetic denervation. He did not have complete cardiovascular autonomic reflex testing, which would have been helpful, but improved with aggressive diabetes treatment and the increase of beta-blockade. It is important to identify these patients to understand their signs and symptoms and consider appropriate therapies.

Cardiac autonomic neuropathy in patients with diabetes mellitus

Cardiac autonomic neuropathy (CAN) is an often overlooked and common complication of diabetes mellitus. CAN is associated with increased cardiovascular morbidity and mortality. The pathogenesis of CAN is complex and involves a cascade of pathways activated by hyperglycaemia resulting in neuronal ischaemia and cellular death. In addition, autoimmune and genetic factors are involved in the development of CAN. CAN might be subclinical for several years until the patient develops resting tachycardia, exercise intolerance, postural hypotension, cardiac dysfunction and diabetic cardiomyopathy. During its sub-clinical phase, heart rate variability that is influenced by the balance between parasympathetic and sympathetic tones can help in detecting CAN before the disease is symptomatic. Newer imaging techniques (such as scintigraphy) have allowed earlier detection of CAN in the pre-clinical phase and allowed better assessment of the sympathetic nervous system. One of the main difficulties in CAN research is the lack of a universally accepted definition of CAN; however, the Toronto Consensus Panel on Diabetic Neuropathy has recently issued guidance for the diagnosis and staging of CAN, and also proposed screening for CAN in patients with diabetes mellitus. A major challenge, however, is the lack of specific treatment to slow the progression or prevent the development of CAN. Lifestyle changes, improved metabolic control might prevent or slow the progression of CAN. Reversal will require combination of these treatments with new targeted therapeutic approaches. The aim of this article is to review the latest evidence regarding the epidemiology, pathogenesis, manifestations, diagnosis and treatment for CAN.

Efficacy and safety of aldose reductase inhibitor for the treatment of diabetic cardiovascular autonomic neuropathy: systematic review and meta-analysis

Background

Aldose reductase inhibitors (ARIs) can block the metabolism of the polyol pathway, and have been used to slow or reverse the progression of diabetic cardiovascular autonomic neuropathy (DCAN). The purpose of this study was to review the effectiveness and safety of ARIs in the treatment of DCAN as determined by five cardiac autonomic neuropathy function tests.

Methods

CENTRAL, MEDLINE, EMBASE, Scopus databases (inception to May 2012) were searched to identify randomized controlled trials (RCTs) and non-randomized controlled trials (non-RCTs) investigating ARIs for the treatment of DCAN with an English-language restriction. The data were analyzed using RevMan 5.0, and the heterogeneity between the trials was evaluated using the Cochrane's Q-test as well as the I² test. The type of model (random or fixed) used for analysis was based on heterogeneity. Weighted mean differences (WMD) with 95% confidence intervals (CI) were computed for the five cardiac automatic neuropathy function tests to evaluate the effects.

Results

Ten articles met the prerequisites for this review. Analysis of the results showed that ARIs significantly improved function in at least three of the five automatic neuropathy tests, including the resting heart rate variation coefficients (WMD = 0.25, 95%CI 0.02 to 0.48, P = 0.040); the 30∶15 ratio (WMD = 0.06, 95%CI 0.01 to 0.10, P = 0.010) and the postural systolic blood pressure change (WMD = −5.94, 95%CI −7.31 to −4.57, P = 0.001). The expiration/inspiration ratio showed a marginally significant benefit (WMD = 0.05, 95%CI 0.00 to 0.09, P = 0.040). Glycaemic control was not significantly affected by ARIs. Adverse effects of ARIs except for Tolerestat were minimal.

Conclusions

Based on these results, we conclude that ARIs could ameliorate cardiac automatic neuropathy especially mild or asymptomatic DCAN but need further investigation.

Cardiac metabolism and its interactions with contraction, growth, and survival of cardiomyocytes

The network for cardiac fuel metabolism contains intricate sets of interacting pathways that result in both ATP-producing and non-ATP-producing end points for each class of energy substrates. The most salient feature of the network is the metabolic flexibility demonstrated in response to various stimuli, including developmental changes and nutritional status. The heart is also capable of remodeling the metabolic pathways in chronic pathophysiological conditions, which results in modulations of myocardial energetics and contractile function. In a quest to understand the complexity of the cardiac metabolic network, pharmacological and genetic tools have been engaged to manipulate cardiac metabolism in a variety of research models. In concert, a host of therapeutic interventions have been tested clinically to target substrate preference, insulin sensitivity, and mitochondrial function. In addition, the contribution of cellular metabolism to growth, survival, and other signaling pathways through the production of metabolic intermediates has been increasingly noted. In this review, we provide an overview of the cardiac metabolic network and highlight alterations observed in cardiac pathologies as well as strategies used as metabolic therapies in heart failure. Lastly, the ability of metabolic derivatives to intersect growth and survival are also discussed.

Left ventricular systolic and diastolic function in normotensive type 2 diabetic patients with or without autonomic neuropathy: a radionuclide ventriculography study

We investigated the relation between diabetic autonomic neuropathy (DAN) and left ventricular (LV) function in 59 patients with type 2 diabetes mellitus (T2DM) free of coronary artery disease (CAD) or hypertension. Diabetic autonomic neuropathy was established by ≥2 abnormal autonomic nervous function tests. Left ventricular systolic and diastolic functions were assessed by resting radionuclide ventriculography. Compared with non-DAN patients (n=24), patients with DAN (n=35) had an increased adjusted atrial contribution to ventricular filling (A/V%, 30.1%±8.2% vs 26.5%±5.1%; P=.031), suggestive of diastolic dysfunction (DD). There were no differences between the 2 groups in peak filling rate, first 1/3 filling fraction, ejection fraction, cardiac output, and cardiac index. Patients with diabetic autonomic neuropathy had an increased heart rate (77.8±6.3 vs 69.3±3.3 bpm; P<.0001) and a higher rest LV workload (10,072±1165 vs 8606±1075 bpm mm Hg; P<.0001). Patients with DAN T2DM without CAD or hypertension have DD, increased A/V index, and a higher LV working load than non-DAN patients.

Diabetic cardiovascular autonomic neuropathy: clinical implications

Diabetic cardiovascular autonomic neuropathy (DCAN), the impairment of the autonomic balance of the cardiovascular system in the setting of diabetes mellitus (DM), is frequently observed in both Type 1 and 2 DM, has detrimental effects on the quality of life and portends increased mortality. Clinical manifestations include: resting heart rate disorders, exercise intolerance, intraoperative cardiovascular lability, orthostatic alterations in heart rate and blood pressure, QT-interval prolongation, abnormal diurnal and nocturnal blood pressure variation, silent myocardial ischemia and diabetic cardiomyopathy. Clinical tests for autonomic nervous system evaluation, heart rate variability analysis, autonomic innervation imaging techniques, microneurography and baroreflex analysis are the main diagnostic tools for DCAN detection. Aldose reductase inhibitors and antioxidants may be helpful in DCAN therapy, but a regular, more generalized and multifactorial approach should be adopted with inclusion of lifestyle modifications, strict glycemic control and treatment of concomitant traditional cardiovascular risk factors, in order to achieve the best therapeutic results. In the present review, the authors provide aspects of DCAN pathophysiology, clinical presentation, diagnosis and an algorithm regarding the evaluation and management of DCAN in DM patients.

Aldose reductase, oxidative stress, and diabetic mellitus

Diabetes mellitus (DM) is a complex metabolic disorder arising from lack of insulin production or insulin resistance (Diagnosis and classification of diabetes mellitus, 2007). DM is a leading cause of morbidity and mortality in the developed world, particularly from vascular complications such as atherothrombosis in the coronary vessels. Aldose reductase (AR; ALR2; EC 1.1.1.21), a key enzyme in the polyol pathway, catalyzes nicotinamide adenosine dinucleotide phosphate-dependent reduction of glucose to sorbitol, leading to excessive accumulation of intracellular reactive oxygen species (ROS) in various tissues of DM including the heart, vasculature, neurons, eyes, and kidneys. As an example, hyperglycemia through such polyol pathway induced oxidative stress, may have dual heart actions, on coronary blood vessel (atherothrombosis) and myocardium (heart failure) leading to severe morbidity and mortality (reviewed in Heather and Clarke, 2011). In cells cultured under high glucose conditions, many studies have demonstrated similar AR-dependent increases in ROS production, confirming AR as an important factor for the pathogenesis of many diabetic complications. Moreover, recent studies have shown that AR inhibitors may be able to prevent or delay the onset of cardiovascular complications such as ischemia/reperfusion injury, atherosclerosis, and atherothrombosis. In this review, we will focus on describing pivotal roles of AR in the pathogenesis of cardiovascular diseases as well as other diabetic complications, and the potential use of AR inhibitors as an emerging therapeutic strategy in preventing DM complications.

A 41-year-old man with polyarthritis and severe autonomic neuropathy

Orthostasis due to autonomic neuropathy can cause severe debilitation and prove refractory to treatment. This report describes a case of severe sympathetic and parasympathetic autonomic dysfunction as a consequence of acetylcholine receptor antibodies and Sjogren’s syndrome. Symptomatic management, plasma fluid expanders, and IVIG therapy failed to offer a salutary response to the condition. Etanercept therapy provided improvement of the orthostasis and autonomic function measured as high and low frequency respiratory effects on heart rate variability as well as enhancement of skin blood flow using Laser Doppler. It would be of considerable interest to determine the effectiveness of etanercept in other autoimmune neuropathies.

Glucose metabolism and cardiac hypertrophy

The most notable change in the metabolic profile of hypertrophied hearts is an increased reliance on glucose with an overall reduced oxidative metabolism, i.e. a reappearance of the foetal metabolic pattern. In animal models, this change is attributed to the down-regulation of the transcriptional cascades promoting gene expression for fatty acid oxidation and mitochondrial oxidative phosphorylation in adult hearts. Impaired myocardial energetics in cardiac hypertrophy also triggers AMP-activated protein kinase (AMPK), leading to increased glucose uptake and glycolysis. Aside from increased reliance on glucose as an energy source, changes in other glucose metabolism pathways, e.g. the pentose phosphate pathway, the glucosamine biosynthesis pathway, and anaplerosis, are also noted in the hypertrophied hearts. Studies using transgenic mouse models and pharmacological compounds to mimic or counter the switch of substrate preference in cardiac hypertrophy have demonstrated that increased glucose metabolism in adult heart is not harmful and can be beneficial when it provides sufficient fuel for oxidative metabolism. However, improvement in the oxidative capacity and efficiency rather than the selection of the substrate is likely the ultimate goal for metabolic therapies.

Aldose reductase and cardiovascular diseases, creating human-like diabetic complications in an experimental model

Hyperglycemia and reduced insulin actions affect many biological processes. One theory is that aberrant metabolism of glucose via several pathways including the polyol pathway causes cellular toxicity. Aldose reductase (AR) is a multifunctional enzyme that reduces aldehydes. Under diabetic conditions AR converts glucose into sorbitol, which is then converted to fructose. This article reviews the biology and pathobiology of AR actions. AR expression varies considerably among species. In humans and rats, the higher level of AR expression is associated with toxicity. Flux via AR is increased by ischemia and its inhibition during ischemia reperfusion reduces injury. However, similar pharmacological effects are not observed in mice unless they express a human AR transgene. This is because mice have much lower levels of AR expression, probably insufficient to generate toxic byproducts. Human AR expression in LDL receptor knockout mice exacerbates vascular disease, but only under diabetic conditions. In contrast, a recent report suggests that genetic ablation of AR increased atherosclerosis and increased hydroxynonenal in arteries. It was hypothesized that AR knockout prevented reduction of toxic aldehydes. Like many in vivo effects found in genetically manipulated animals, interpretation requires the reproduction of human-like physiology. For AR, this will require tissue specific expression of AR in sites and at levels that approximate those in humans.

Polyol pathway and RAGE: a central metabolic and signaling axis in diabetic complications

There are multiple metabolic and molecular consequences of hyperglycemia. This review will focus on the roles of the polyol pathway and the receptor for advanced glycation end products (RAGE) in the pathogenesis of diabetic complications. The lead enzyme of the polyol pathway, aldose reductase, transduces maladaptive effects of hyperglycemia by multiple mechanisms, at least in part via the generation of the products of nonenzymatic glycation of proteins, the advanced glycation end products (AGEs). Furthermore, seminal shifts in metabolic flux in the intracellular space stimulated by aldose reductase action activate signal transduction pathways, which alter gene expression and change cellular phenotype. Among the ligands of the multi-ligand receptor RAGE are the AGEs. AGE-RAGE stimulation mediates vascular and target cell dysfunction. The intersection and interdependence of the polyol pathway-RAGE connection suggest that targeting this axis may provide benefit in reducing the complications of diabetes.

Diabetic myocardial disease: pathophysiology, early diagnosis and therapeutic options

Diabetes mellitus is a powerful risk factor for cardiovascular disease associated with high morbidity and mortality rates. Diabetic patients also have an increased incidence of heart failure which has been traditionally attributed to the concurrent presence of ischemic or hypertensive heart disease. Yet, nowadays, according to recent scientific evidence, diabetic myocardial disease (DMD) is more and more being considered as a distinct nosologic entity, independent of the co-existence of coronary artery disease, arterial hypertension or other risk factors, with the potential to lead to a self-existent progressive development of heart failure. In this article, we review the possible pathophysiologic mechanisms involved in the development of DMD as well as the structural and functional changes in the diabetic heart. We emphasize the importance of early detection of the syndrome, especially by novel echocardiographic techniques. Finally, we refer to the various therapeutic options for the optimal management of DMD according to the recent literature.

Uncomplicated type 1 diabetes and preclinical left ventricular myocardial dysfunction: insights from echocardiography and exercise cardiac performance evaluation

OBJECTIVES

Left ventricular (LV) diastolic dysfunction is considered the earliest manifestation of diabetic cardiomyopathy. Whether LV abnormalities identified at rest by echocardiography predict peak exercise LV performance in uncomplicated type 1 diabetes mellitus (DM1) is largely unknown.

RESEARCH DESIGN AND METHODS

We evaluated LV size, mass, and functions and peak exercise LV performance in 25 subjects with uncomplicated DM1 (median disease duration 13.5 years, 1-30 years) and in 56 non-DM subjects (24 hypertensive (HT) and 32 normotensive (NT)). Overt coronary heart disease, significant microangiopathy and central autonomic neuropathy were minimized by exclusion criteria. Peak exercise LV stroke index (SVi), cardiac index (COi), LV ejection fraction (EF), LV end-diastolic and end-systolic volumes were assessed noninvasively. No subject was on cardiovascular medications at the time of evaluation.

RESULTS

In our study, DM1 did not show LV hypertrophy or impaired LV systolic function at rest. Prevalence of diastolic dysfunction was 8% among DM1, 18% among NT and 50% among HT. Pre-exercise heart rate, SVi, COi, and peak exercise blood pressure (BP) and heart rate were comparable among the three groups, but peak exercise LV EF, SVi and COi were lower in DM1 than in HT and NT independent to covariates (p<0.05). In separate analyses, DM1 predicted lower peak exercise SVi (B=-6.2) and COi (B=-1.6, both p<0.05) independently. Within DM1, glycated haemoglobin (HbA1c) and disease duration did not predict peak exercise LV systolic function.

CONCLUSIONS

Our study suggests that uncomplicated DM1 may be associated with subnormal LV contractility reserve, which might not be predicted by LV dysfunction evaluated at rest.

Aldose reductase inhibition prevents endotoxin-induced uveitis in rats

PURPOSE

The purpose of the present study was to elucidate the role of the polyol pathway enzyme aldose reductase (AR) in the mediation of ocular inflammation in a rat model of endotoxin-induced uveitis (EIU).

METHODS

EIU was induced by a subcutaneous injection of 200 microg lipopolysaccharide (LPS) in male Lewis rats treated with the AR inhibitor, zopolrestat (25 mg/kg body weight, intraperitoneally) or its carrier. The rats were killed 24 hours after LPS injection, the eyes were enucleated immediately, and aqueous humor (AqH) was collected. The number of infiltrating cells, protein concentration, and levels of nitric oxide (NO), tumor necrosis factor (TNF)-alpha, and prostaglandin E(2) (PGE(2)) in the AqH were determined. Immunohistochemical analysis was performed in paraformaldehyde-fixed eye sections by staining with antibodies against iNOS, COX-2, TNF-alpha, NF-kappaB, and AR. The levels of reactive oxygen species (ROS) in rat eye sections were determined by dihydroethidium (hydroethidine) fluorescence staining.

RESULTS

In the EIU rat eye AqH, both the number of infiltrating cells and protein concentrations of the inflammatory markers, TNF-alpha, NO, and PGE(2) were significantly higher than in the control rats, and inhibition of AR by zopolrestat suppressed the LPS-induced increases. The LPS-induced increased expression of AR, TNF-alpha, iNOS, and COX-2 proteins in the ciliary body, corneal epithelium, and retinal wall was also significantly inhibited by zopolrestat. Furthermore, AR inhibition prevented the LPS-induced increased levels of ROS and activation of NF-kappaB in the ciliary body, corneal epithelium, and retinal wall of the rat eye. AR inhibition also prevented the LPS-induced activation of NF-kappaB and expression of COX-2 and iNOS in the human monocyte cell line U-937.

CONCLUSIONS

The results indicate that AR inhibition suppresses the inflammation in EIU by blocking the expression and release of inflammatory markers in ocular tissues, along with the attenuation of NF-kappaB activation. This finding suggests that AR inhibition could be a novel therapeutic target for the treatment of uveitis and associated ocular inflammation.

Continuous positive airway pressure therapy improves cardiovascular autonomic function for persons with sleep-disordered breathing

BACKGROUND

Sleep-disordered breathing (SDB) is an independent risk factor for cardiovascular morbidity. Dysfunction of the cardiovascular autonomic nervous system may be a potential mechanism whereby SDB is linked to cardiovascular disease. Repetitive sympathetic activation during apneic episodes may impair cardiovascular reflex function, and increased sympathetic activity can stimulate renin release. Given that patients with SDB may have reduced cardiovascular autonomic function, the purpose of this study was to determine whether treatment with continuous positive airway pressure (CPAP) for 6 weeks would improve autonomic function.

METHODS

Twenty-nine participants with a diagnosis of SDB, who completed 6 weeks of CPAP therapy, were evaluated for cardiovascular autonomic nerve fiber function at baseline and post therapy. Autonomic function tests included the following: R-R interval variation during deep breathing measured by vector analysis (ie, mean circular resultant [MCR]) and expiration/inspiration (E/I) ratio; and the Valsalva maneuver. Participants were also evaluated prior to CPAP therapy for plasma renin activity levels.

RESULTS

Participants in this study showed improved cardiovascular autonomic function after 6 weeks of treatment (baseline vs follow-up) as assessed by the mean (+/- SD) MCR (33.2 +/- 22.5 vs 36.9 +/- 24.2, respectively; p < 0.05) and E/I ratio (1.20 +/- 0.12 vs 1.24 +/- 0.14, respectively; p < 0.01). Improved vagal tone was also noted for subjects with elevated renin levels.

CONCLUSIONS

Treatment of SDB with CPAP for 6 weeks improved vagal tone and may be beneficial in reducing the risk of developing clinical manifestations of cardiovascular autonomic dysfunction (eg, increased risk of mortality).

Aldose reductase inhibitors for the treatment of diabetic polyneuropathy

BACKGROUND

Polyneuropathy, a common complication of diabetes mellitus, causes pain and sensory and motor deficits in the limbs, and is also an important independent predictor of foot ulceration. Inhibiting the metabolism of glucose by the polyol pathway using aldose reductase inhibitors is a potential mechanism to slow or reverse the neuropathy's progression.

OBJECTIVES

To assess the effects of aldose reductase inhibitors on the progression of symptoms, signs or functional disability in diabetic polyneuropathy.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Trials Register, MEDLINE (from January 1966 to May 2007), EMBASE (from January 1980 to May 2007) and LILACS (from 1982 to May 2007). We reviewed bibliographies of randomized trials identified, and contacted authors and experts in the field.

SELECTION CRITERIA

We included randomized controlled trials comparing an aldose reductase inhibitor with control, and lasting at least six months. The primary outcome measure was change in neurological function, measured in various ways, including strength testing, sensory examination, and composite scores of neurological examination. Secondary outcome measures were nerve conduction studies, neuropathic symptoms, quality of life, occurrence of foot ulcers and adverse effects.

DATA COLLECTION AND ANALYSIS

Trials included in the review were selected and assessed independently by at least two of us. Methodological criteria and study results were recorded on data extraction forms.

MAIN RESULTS

Thirty-two randomized controlled trials meeting the inclusion criteria were identified. Many had significant methodological flaws. Change in neurological function, our primary outcome measure, was assessed in 29 trials, but sufficient data for meta-analysis were only available in 13 studies, involving 879 treated participants and 909 controls. There was no overall significant difference between the treated and control groups (SMD -0.25, 95% CI -0.56 to 0.05), although one subgroup analysis (four trials using tolrestat) favored treatment. A benefit for neuropathic symptoms was suggested by a group of trials using a dichotomized endpoint (improvement or not), but this was contradicted by another group of trials which measured symptoms on a continuous scale. There was no overall benefit on nerve conduction parameters (27 studies) or foot ulceration (one study). Quality of life was not assessed in any of the studies. While most adverse events were infrequent and minor, three compounds had dose limiting adverse events that lead to their withdrawal from human use: severe hypersensitivity reactions with sorbinil, elevation of creatinine with zenarestat, and alteration of liver function with tolrestat.

AUTHORS' CONCLUSIONS

We found no statistically significant difference between aldose reductase inhibitors and placebo in the treatment of diabetic polyneuropathy. Any future clinical trials of aldose reductase inhibitors should be restricted to compounds proven to have substantial biological or preclinical advantages over previously tested agents.

Fidarestat improves cardiomyocyte contractile function in db/db diabetic obese mice through a histone deacetylase Sir2-dependent mechanism

BACKGROUND

Fidarestat, an aldose reductase (AR) inhibitor, displays promise for the treatment of diabetic neuropathy, although the underlying mechanism of action remains unclear. Histone modification, especially histone acetylation, has been implicated in the pathogenesis of diabetes and its complications.

OBJECTIVE

The aim of this study was two-fold: to examine the impact of fidarestat on diabetic cardiomyopathy; and to evaluate the role of histone acetylation in the fidarestat-elicited effect, if any.

METHODS

Cardiomyocytes from db/db diabetic obese and control mice were exposed to fidarestat (0.1-10 mumol/l) for 60 min in the absence or presence of splitomicin, an inhibitor of the NAD-dependent histone deacetylase Sir2. Superoxide levels were measured by dihydroethidium fluorescence. Expression of Sir2, IkappaB (inhibitor of kappaB) and phosphorylated IkappaB was evaluated by western blotting.

RESULTS

Myocytes from db/db mice exhibited greater cross-sectional area, depressed peak shortening and maximal velocity of shortening/re-lengthening, and prolonged duration of re-lengthening (TR90). Myocytes from db/db mice displayed a reduced rise in intracellular Ca and prolonged intracellular Ca decay. All abnormalities were attenuated by fidarestat. The beneficial effects of fidarestat on db/db cardiomyocytes were nullified by splitomicin with the exception of intracellular Ca decay rate and TR90. Intracellular superoxide was enhanced in db/db myocytes, which was attenuated by fidarestat. Protein expression of Sir2 was decreased in db/db mouse hearts. Phosphorylated IkappaB: IkappaB ratio was increased in db/db mouse. Fidarestat reduced the elevated phosphorylated IkappaB: IkappaB ratio, the effect of which was abolished by splitomicin.

CONCLUSIONS

Collectively, these results suggest that fidarestat may protect against cardiomyocyte dysfunction in db/db mice through a Sir2-dependent pathway.

Diabetic vascular disease: an experimental objective

It is well known that humans with diabetes have more atherosclerosis and its complications. The causes of this relationship are, however, unclear. Although recent data show that improved glycemic control reduces arterial disease in type 1 diabetes, other studies have shown that subjects with "prediabetes" have more cardiovascular disease before the development of hyperglycemia. Thus, either hyperglycemia and/or lack of insulin actions are toxic to arteries, or metabolic derangements exclusive of hyperglycemia are atherogenic. For >50 years animal models of diabetes and atherosclerosis have been used to uncover potential mechanisms underlying diabetes associated cardiovascular disease. Surprisingly, diabetes alone increases vascular disease in only a few select animal models. Increased atherosclerosis has been found in several animals and lines of genetically modified mice; however, diabetes often also leads to greater hyperlipidemia. This makes it difficult to separate the toxic effects of insulin lack and/or hyperglycemia from those caused by the lipids. These studies are reviewed, as well as more recent investigations using new methods to create diabetic-atherosclerotic models.

Permeability characteristics of novel aldose reductase inhibitors using rat jejunum in vitro

The aim of this study was to estimate in vivo permeability and bioavailability of epalrestat and newly synthesized compounds with possible therapeutic activity as aldose enzyme inhibitors (ARIs). For this purpose permeability in vitro using rat jejunum mounted in side-by-side diffusion cells was determined. Tested substances were found to be low and moderately permeable and some of them were also substrates for efflux transporters. It was shown, that the higher efflux for some derivatives was due to MRP-2, but not Pgp involvement. Tested ARIs do not share the same efflux transporter with epalrestat, the only ARI currently on the market in Japan. The most permeable compound, a 2,6-difluoro-4-pyrrol-1ylphenol derivative, is not a substrate for efflux transporters and would therefore be the most promising lead compound for further investigation of potent ARIs.

High-resolution Crystal Structure of Aldose Reductase Complexed with the Novel Sulfonyl-pyridazinone Inhibitor Exhibiting an Alternative Active Site Anchoring Group

The crystal structure of a novel sulfonyl-pyridazinone inhibitor in complex with aldose reductase, the first enzyme of the polyol pathway, has been determined to 1.43 angstroms and 0.95 angstroms resolution. The ternary complex of inhibitor, cofactor and enzyme has been obtained by soaking of preformed crystals. Supposedly due to low solubility in the crystallisation buffer, in both structures the inhibitor shows reduced occupancy of 74% and 46% population, respectively. The pyridazinone head group of the inhibitor occupies the catalytic site, whereas the chloro-benzofuran moiety penetrates into the opened specificity pocket. The high-resolution structure provides some evidence that the pyridazinone group binds in a negatively charged deprotonated state, whereas the neighbouring His110 residue most likely adopts a neutral uncharged status. Since the latter structure is populated by the ligand to only 46%, a second conformation of the C-terminal ligand-binding region can be detected. This conformation corresponds to the closed state of the specificity pocket when no or only small ligands are bound to aldose reductase. The two conformational states are in good agreement with frames observed along a molecular dynamics trajectory describing the transition from closed to open situation. Accordingly, both geometries, superimposed in the averaged crystal structure, correspond to snapshots of the ligand-bound and the unbound state. Isothermal titration calorimetry has been applied to determine the binding constants of the investigated pyridazinone in comparison to the hydantoin sorbinil and the carboxylate-type inhibitors IDD 594 and tolrestat. The pyridazinone exhibits a binding affinity similar to those of tolrestat and sorbinil, and shows slightly reduced affinity compared to IDD 594. These studies elucidating the binding mode and providing information about protonation states of protein side-chains involved in binding of this novel class of inhibitors establish the platform for further structure-based drug design.

Aldose Reductase and AGE-RAGE Pathways: Key Players in Myocardial Ischemic Injury

Cardiovascular disease represents the major cause of morbidity and mortality in patients with diabetes mellitus. The impact of cardiac disease includes increased sensitivity of diabetic myocardium to ischemic episodes and diabetic cardiomyopathy, manifested as a subnormal functional response of the diabetic heart independent of coronary artery disease. In this context, we were to our knowledge the first to demonstrate that diabetes increases glucose flux via the first and key enzyme, aldose reductase, of the polyol pathway, resulting in impaired glycolysis under normoxic and ischemic conditions in diabetic myocardium. Our laboratory has been investigating the role of the polyol pathway in mediating myocardial ischemic injury in diabetics. Furthermore, the influence of the aldose reductase pathway in facilitating generation of key potent glycating compounds has led us to investigate the impact of advanced glycation end products (AGEs) in myocardial ischemic injury in diabetics. The potent impact of increased flux via the aldose reductase pathway and the increased AGE interactions with its receptor (RAGE) resulting in cardiac dysfunction will be discussed in this chapter.

Effect of quinapril or losartan alone and in combination on left ventricular systolic and diastolic functions in asymptomatic patients with diabetic autonomic neuropathy

OBJECTIVE

To investigate the effect of angiotensin converting enzyme inhibition (ACE-I) or angiotensin receptor blockade (ARB), and their combination, on both diabetic autonomic neuropathy (DAN) and left ventricular (LV) diastolic dysfunction (LVDD) in asymptomatic patients with diabetes mellitus (DM).

MATERIALS AND METHODS

Sixty-two patients (34 women) with long-term DM (24 with Type 1) and DAN, aged 51.7+/-13.9 years, free of coronary artery disease (CAD) or arterial hypertension (HT) at baseline, were studied for a 12-month period. Diagnosis of DAN was established if two or more of the standard cardiovascular reflex tests (CRT) were abnormal. Patients were randomly allocated to quinapril (20 mg/day), losartan (100 mg/day), or quinapril plus losartan (20 mg/day+100 mg/day). LV systolic and diastolic function was assessed using radionuclide ventriculography (RNV) at baseline and after 12 months of treatment.

RESULTS

In all three treatment groups, abnormal CRT values were improved. In the quinapril group, the first third filling fraction (1/3FF, 48.9+/-17.8% vs. 39.2+/-12.9% at baseline, P=.005) was increased and the atrial contribution to ventricular filling (25.1+/-6.3 vs. 30.1+/-7.8, P=.027) was reduced in the losartan group; the peak filling rate (PFR) was improved (3.41+/-.62 vs. 3.11+/-.44 volumes/s, P=.05), and in the combination group, the 1/3FF (39.4+/-11.8% vs. 29.6+/-11.9%, P=.018) was markedly increased, while the time to peak filling (TPF; 147+/-42 vs. 184+/-33 ms, P=.02) and the TPF/filling time (TPF/FT; 32.5+/-6.2% vs. 38.2+/-5.7%, P=.016) were reduced.

CONCLUSIONS

Early ACE-I or ARB improve both DAN and LVDD in asymptomatic patients with Type 1 or 2 DM, after 1 year of treatment. Their combination may be slightly better than monotherapies on DAN and LVDD. The clinical importance of these effects should be validated by larger studies.