Supplemental ferulic acid does not affect metabolic markers and improves some oxidative damage parameters in diabetic rats.

This study investigated the differences in health outcomes associated with ferulic acid (FA) supplementation in animals before the induction of diabetes with streptozotocin (STZ) treatment and post-STZ treatment. 18 male Wistar rats were equally distributed into three groups: groups 1 and 2 received FA (50 mg/kg body weight) supplementation one week before STZ treatment (60 mg/kg body weight, intraperitoneal) and one week after STZ treatment, respectively; group 3 received STZ without FA supplementation. FA supplementation was continued for 12 weeks after STZ treatment. The results indicated no difference in glucose and lipid profile with FA supplementation. However, FA supplementation reduced lipid and protein oxidative damage in the heart, liver and pancreas and increased glutathione in the pancreas. The results indicate that while oxidative damages were positively affected by FA, it was not sufficient to improve metabolic markers of diabetes.

Transient receptor potential vanilloid 1 (TRPV1)-independent actions of capsaicin on cellular excitability and ion transport.

Capsaicin is a naturally occurring alkaloid derived from chili pepper that is responsible for its hot pungent taste. Capsaicin is known to exert multiple pharmacological actions, including analgesia, anticancer, anti-inflammatory, antiobesity, and antioxidant effects. The transient receptor potential vanilloid subfamily member 1 (TRPV1) is the main receptor mediating the majority of the capsaicin effects. However, numerous studies suggest that the TRPV1 receptor is not the only target for capsaicin. An increasing number of studies indicates that capsaicin, at low to mid µM ranges, not only indirectly through TRPV1-mediated Ca2+ increases, but also directly modulates the functions of voltage-gated Na+ , K+ , and Ca2+ channels, as well as ligand-gated ion channels and other ion transporters and enzymes involved in cellular excitability. These TRPV1-independent effects are mediated by alterations of the biophysical properties of the lipid membrane and subsequent modulation of the functional properties of ion channels and by direct binding of capsaicin to the channels. The present study, for the first time, systematically categorizes this diverse range of non-TRPV1 targets and discusses cellular and molecular mechanisms mediating TRPV1-independent effects of capsaicin in excitable, as well as nonexcitable cells.

Invited review: Potential effects of short- and long-term intake of fermented dairy products on prevention and control of type 2 diabetes mellitus.

The consumption of fermented dairy products has been linked with lowering the risk of type 2 diabetes mellitus (T2DM), but studies have yet to demonstrate a definite association. We evaluated evidence from a cross-sectional analysis of longitudinal studies and human and animal experimental trials to further understand the current knowledge linking short- and long-term consumption of fermented dairy products to T2DM. Most cohort studies revealed a protective effect of fermented dairy products on T2DM development, with yogurt noted as the most consistent food item protecting against the disease. Human experimental trials and animal studies revealed improvements in biomarkers of glycemic control with short-term monitored intake of fermented dairy products from various sources. Therefore, fermented dairy products may offer protection against the development and may have therapeutic benefits for individuals with T2DM. This could influence on dietary recommendations and the development of functional foods aiming to minimize the risk of T2DM.

Capsaicin Is a Negative Allosteric Modulator of the 5-HT3 Receptor.

In this study, effects of capsaicin, an active ingredient of the capsicum plant, were investigated on human 5-hydroxytryptamine type 3 (5-HT3) receptors. Capsaicin reversibly inhibited serotonin (5-HT)-induced currents recorded by two-electrode voltage clamp method in Xenopus oocytes. The inhibition was time- and concentration-dependent with an IC50 = 62 µM. The effect of capsaicin was not altered in the presence of capsazepine, and by intracellular BAPTA injections or trans-membrane potential changes. In radio-ligand binding studies, capsaicin did not change the specific binding of the 5-HT3 antagonist [3H]GR65630, indicating that it is a noncompetitive inhibitor of 5-HT3 receptor. In HEK-293 cells, capsaicin inhibited 5-HT3 receptor induced aequorin luminescence with an IC50 of 54 µM and inhibition was not reversed by increasing concentrations of 5-HT. In conclusion, the results indicate that capsaicin acts as a negative allosteric modulator of human 5-HT3 receptors.

Effects of prolactin on ventricular myocyte shortening and calcium transport in the streptozotocin-induced diabetic rat.

The physiological role of prolactin (PRL) in the heart, and in particular the diabetic heart, are largely unknown. The effects of PRL on ventricular myocyte shortening and Ca2+ transport in the streptozotocin (STZ) - induced diabetic and in age-matched control rats were investigated. PRL receptor protein, myocyte shortening, intracellular [Ca2+], L-type Ca2+ current were measured by Western blot, cell imaging, fluorescence photometry and whole-cell patch-clamp techniques, respectively. Compared to normal Tyrode solution (NT), PRL (50 ng/ml) significantly (p < 0.05) increased the amplitude of shortening in myocytes from control (7.43 ± 0.38 vs. 9.68 ± 0.46 %) and diabetic (6.57 ± 0.24 vs. 8.91 ± 0.44 %) heart (n = 44-49 cells). Compared to NT, PRL (50 ng/ml) significantly increased the amplitude of Ca2+ transients in myocytes from control (0.084 ± 0.004 vs. 0.115 ± 0.007 Fura-2 ratio units) and diabetic (0.087 ± 0.007 vs. 0.112 ± 0.006 Fura-2 ratio units) heart (n = 36-50 cells). PRL did not significantly alter the amplitude of caffeine-evoked Ca2+ transients however, PRL significantly increased the fractional release of Ca2+ in myocytes from control (21 %) and diabetic (14 %) and heart. The rate of Ca2+ transient recovery following PRL treatment was significantly increased in myocytes from diabetic and control heart. Amplitude of L-type Ca2+ current was not significantly altered by diabetes or by PRL. PRL increased the amplitude of shortening and Ca2+ transients in myocytes from control and diabetic heart. Increased fractional release of sarcoplasmic reticulum Ca2+ may partly underlie the positive inotropic effects of PRL in ventricular myocytes from control and STZ-induced diabetic rat.

Oxytocin induces intracellular Ca2+ release in cardiac fibroblasts from neonatal rats.

Pituitary neuropeptide oxytocin is increasingly recognised as a cardiovascular hormone, in addition to its many regulatory roles in other organ systems. Studies in atrial and ventricular myocytes from the neonatal and adult rats have identified synthesis of oxytocin and the expression of oxytocin receptors in these cells. In cardiac fibroblasts, the most populous non-myocyte cell type in mammalian heart, the oxytocin receptors have not been described before. In the present study, we have investigated the direct effects of oxytocin on intracellular Ca2+ dynamics in ventricular myocytes and fibroblasts from new born rats. In myocytes, oxytocin increased the frequency of spontaneous Ca2+ transients and decreased their amplitude. Our data suggest that oxytocin receptors are also present and functional in the majority of cardiac fibroblasts. We used selective oxytocin receptor inhibitor L-371,257 and a number of intracellular Ca 2+ release blockers to investigate the mechanism of oxytocin induced Ca2+ signalling in cardiac fibroblasts. Our findings suggest that oxytocin induces Ca2+ signals in cardiac fibroblasts by triggering endoplasmic reticulum Ca2+ release via inositol trisphosphate activated receptors. The functional significance of the oxytocin induced Ca2+ signalling in cardiac fibroblasts, especially for their activation into secretory active myofibroblasts, remains to be investigated.

Type 1 diabetes mellitus induces structural changes and molecular remodelling in the rat kidney.

There is much evidence that diabetes mellitus (DM)-induced hyperglycemia (HG) is responsible for kidney failure or nephropathy leading to cardiovascular complications. Cellular and molecular mechanism(s) whereby DM can damage the kidney is still not fully understood. This study investigated the effect of streptozotocin (STZ)-induced diabetes (T1DM) on the structure and associated molecular alterations of the isolated rat left kidney following 2 and 4 months of the disorder compared to the respective age-matched controls. The results revealed hypertrophy and general disorganized architecture of the kidney characterized by expansion in glomerular borders, tubular atrophy and increased vacuolization of renal tubular epithelial cells in the diabetic groups compared to controls. Electron microscopic analysis revealed ultrastructural alterations in the left kidney highlighted by an increase in glomerular basement membrane width. In addition, increased caspase-3 immunoreactivity was observed in the kidney of T1DM animals compared to age-matched controls. These structural changes were associated with elevated extracellular matrix (ECM) deposition and consequently, altered gene expression profile of ECM key components, together with elevated levels of key mediators (MMP9, integrin 5α, TIMP4, CTGF, vimentin) and reduced expressions of Cx43 and MMP2 of the ECM. Marked hypertrophy of the kidney was highlighted by increased atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) gene expression. These changes also correlated with increased TGFß1 activity, gene expression in the left kidney and elevated active TGFß1 in the plasma of T1DM rats compared to control. The results clearly demonstrated that TIDM could elicit severe structural changes and alteration in biochemical markers (remodelling) in the kidney leading to diabetic nephropathy (DN).

Curcumin potentiates the function of human α7-nicotinic acetylcholine receptors expressed in SH-EP1 cells.

Effects of curcumin, a biologically active ingredient of turmeric, were tested on the Ca2+ transients induced by the activation of α7 subunit of the human nicotinic acetylcholine (α7 nACh) receptor expressed in SH-EP1 cells. Curcumin caused a significant potentiation of choline (1 mM)-induced Ca2+ transients with an EC50 value of 133 nM. The potentiating effect of curcumin was not observed in Ca2+ transients induced by high K+ (60 mM) containing solutions or activation of α4ß2 nACh receptors and the extent of curcumin potentiation was not altered in the presence of Ca2+ channel antagonists nifedipine (1 µM), verapamil (1 µM), ω-conotoxin (1 µM), and bepridil (10 µM). Noticeably the effect of curcumin was not observed when curcumin and choline were co-applied without curcumin pre-incubation. The effect of curcumin on choline-induced Ca2+ transients was not reversed by pre-incubation with inhibitors of protein C, A, and CaM kinases. Metabolites of curcumin such as tetrahydrocurcumin, demethylcurcumin, and didemethylcurcumin also caused potentiation of choline-induced Ca2+ transients. Notably, specific binding of [125I]-bungarotoxin was not altered in the presence of curcumin. Collectively, our results indicate that curcumin allosterically potentiate the function of the α7-nACh receptor expressed in SH-EP1 cells.

Hyperglycemia-induced cardiac contractile dysfunction in the diabetic heart.

The development of a diabetic cardiomyopathy is a multifactorial process, and evidence is accumulating that defects in intracellular free calcium concentration [Ca2+]i or its homeostasis are related to impaired mechanical performance of the diabetic heart leading to a reduction in contractile dysfunction. Defects in ryanodine receptor, reduced activity of the sarcoplasmic reticulum calcium pump (SERCA) and, along with reduced activity of the sodium-calcium exchanger (NCX) and alterations in myofilament, collectively cause a calcium imbalance within the diabetic cardiomyocytes. This in turn is characterized by cytosolic calcium overloading or elevated diastolic calcium leading to heart failure. Numerous studies have been performed to identify the cellular, subcellular, and molecular derangements in diabetes-induced cardiomyopathy (DCM), but the precise mechanism(s) is still unknown. This review focuses on the mechanism behind DCM, the onset of contractile dysfunction, and the associated changes with special emphasis on hyperglycemia, mitochondrial dysfunction in the diabetic heart. Further, management strategies, including treatment and emerging therapeutic modalities, are discussed.

Cellular and Molecular Targets of Menthol Actions.

Menthol belongs to monoterpene class of a structurally diverse group of phytochemicals found in plant-derived essential oils. Menthol is widely used in pharmaceuticals, confectionary, oral hygiene products, pesticides, cosmetics, and as a flavoring agent. In addition, menthol is known to have antioxidant, anti-inflammatory, and analgesic effects. Recently, there has been renewed awareness in comprehending the biological and pharmacological effects of menthol. TRP channels have been demonstrated to mediate the cooling actions of menthol. There has been new evidence demonstrating that menthol can significantly influence the functional characteristics of a number of different kinds of ligand and voltage-gated ion channels, indicating that at least some of the biological and pharmacological effects of menthol can be mediated by alterations in cellular excitability. In this article, we examine the results of earlier studies on the actions of menthol with voltage and ligand-gated ion channels.

Regional effects of streptozotocin-induced diabetes on shortening and calcium transport in epicardial and endocardial myocytes from rat left ventricle.

In the heart, the left ventricle pumps blood at higher pressure than the right ventricle. Within the left ventricle, the electromechanical properties of ventricular cardiac myocytes vary transmurally and this may be related to the gradients of stress and strain experienced in vivo across the ventricular wall. Diabetes is also associated with alterations in hemodynamic function. The aim of this study was to investigate shortening and Ca2+ transport in epicardial (EPI) and endocardial (ENDO) left ventricular myocytes in the streptozotocin (STZ)-induced diabetic rat. Shortening, intracellular Ca2+ and L-type Ca2+ current (ICa,L) were measured by video detection, fura-2 microfluorimetry, and whole-cell patch clamp techniques, respectively. Time to peak (TPK) shortening was prolonged to similar extents in ENDO and EPI myocytes from STZ-treated rats compared to ENDO and EPI myocytes from controls. Time to half (THALF) relaxation of shortening was prolonged in ENDO myocytes from STZ-treated rats compared to ENDO controls. TPK Ca2+ transient was prolonged in ENDO myocytes from STZ-treated rats compared to ENDO controls. THALF decay of the Ca2+ transient was prolonged in ENDO myocytes from STZ-treated rats compared to ENDO controls. Sarcoplasmic reticulum (SR) fractional release of Ca2+ was reduced in EPI myocytes from STZ-treated rats compared to EPI controls. ICa,L activation, inactivation, and recovery from inactivation were not significantly altered in EPI and ENDO myocytes from STZ-treated rats or controls. Regional differences in Ca2+ transport may partly underlie differences in ventricular myocyte shortening across the wall of the healthy and the STZ-treated rat left ventricle.

Exercise-induced alterations in pancreatic oxidative stress and mitochondrial function in type 2 diabetic Goto-Kakizaki rats.

Progressive metabolic complications accompanied by oxidative stress are the hallmarks of type 2 diabetes. The precise molecular mechanisms of the disease complications, however, remain elusive. Exercise-induced nontherapeutic management of type 2 diabetes is the first line of choice to control hyperglycemia and diabetes associated complications. In this study, using 11-month-old type 2 Goto-Kakizaki (GK) rats, we have investigated the effects of exercise on mitochondrial metabolic and oxidative stress in the pancreas. Our results showed an increase in theNADPHoxidase enzyme activity and reactive oxygen species (ROS) production inGKrats, which was inhibited after exercise. Increased lipid peroxidation and protein carbonylation andSODactivity were also inhibited after exercise. Interestingly, glutathione (GSH) level was markedly high in the pancreas ofGKdiabetic rats even after exercise. However,GSH-peroxidase andGSH-reductase activities were significantly reduced. Exercise also induced energy metabolism as observed by increased hexokinase and glutamate dehydrogenase activities. A significant decrease in the activities of mitochondrial ComplexesII/IIIandIVwere observed in theGKrats. Exercise improved only ComplexIVactivity suggesting increased utilization of oxygen. We also observed increased activities of cytochrome P450s in the pancreas ofGKrats which was reduced significantly after exercise.SDS-PAGEresults have shown a decreased expression ofNF-κB, Glut-2, andPPAR-ϒ inGKrats which was markedly increased after exercise. These results suggest differential oxidative stress and antioxidant defense responses after exercise. Our results also suggest improved mitochondrial function and energy utilization in the pancreas of exercisingGKrats.

Chronic effects of mild hyperglycaemia on left ventricle transcriptional profile and structural remodelling in the spontaneously type 2 diabetic Goto-Kakizaki rat.

Heart failure in chronic type 2 diabetes mellitus is partly attributable to adverse structural remodelling of the left ventricle (LV), but the contribution of hyperglycaemia (HG) per se in remodelling processes is debated. In this study, we examined the molecular signature of LV remodelling in 18-month-old spontaneously diabetic male Goto-Kakizaki (GK) rats that represent a long-term mildly diabetic phenotype, using histological, immunoblotting and quantitative gene expression approaches. Relative to age-matched Wistar controls, mildly diabetic GK rats presented with LV hypertrophy, increased expression of natriuretic peptides and phosphorylation of pro-hypertrophic Akt. Fibrosis proliferation in the GK LV paralleled increased transcriptional and biologically active pro-fibrogenic transforming growth factor-ß1 (TGFß1) in the LV with upregulated mRNA abundance for key extracellular matrix (ECM) components such as fibronectin, collagen type(s) 1 and 3α and regulators including matrix metalloproteinases 2 and 9, and their tissue inhibitor (TIMP) 4, connexin 43 and α5-integrin. GK rats also presented with altered mRNA expression for cardiac sarcoplasmic reticulum Ca(2+)ATPase, Na(+)/Ca(2+) exchanger and the L-type Ca(2+) channels which may contribute to the altered Ca(2+) transient kinetics previously observed in this model at 18 months of age (t test, p < 0.05 vs. age-matched Wistar control for all parameters). The results indicate that chronic mild HG can produce the molecular and structural correlates of a hypertrophic myopathy. Diffuse ECM proliferation in this model is possibly a product of HG-induced TGFß1 upregulation and altered transcriptional profile of the ECM.

Menthol inhibits 5-HT3 receptor-mediated currents.

The effects of alcohol monoterpene menthol, a major active ingredient of the peppermint plant, were tested on the function of human 5-hydroxytryptamine type 3 (5-HT3) receptors expressed in Xenopus laevis oocytes. 5-HT (1 µM)-evoked currents recorded by two-electrode voltage-clamp technique were reversibly inhibited by menthol in a concentration-dependent (IC50 = 163 µM) manner. The effects of menthol developed gradually, reaching a steady-state level within 10-15 minutes and did not involve G-proteins, since GTPγS activity remained unaltered and the effect of menthol was not sensitive to pertussis toxin pretreatment. The actions of menthol were not stereoselective as (-), (+), and racemic menthol inhibited 5-HT3 receptor-mediated currents to the same extent. Menthol inhibition was not altered by intracellular 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid injections and transmembrane potential changes. The maximum inhibition observed for menthol was not reversed by increasing concentrations of 5-HT. Furthermore, specific binding of the 5-HT3 antagonist [(3)H]GR65630 was not altered in the presence of menthol (up to 1 mM), indicating that menthol acts as a noncompetitive antagonist of the 5-HT3 receptor. Finally, 5-HT3 receptor-mediated currents in acutely dissociated nodose ganglion neurons were also inhibited by menthol (100 µM). These data demonstrate that menthol, at pharmacologically relevant concentrations, is an allosteric inhibitor of 5-HT3 receptors.

Menthol binding and inhibition of α7-nicotinic acetylcholine receptors.

Menthol is a common compound in pharmaceutical and commercial products and a popular additive to cigarettes. The molecular targets of menthol remain poorly defined. In this study we show an effect of menthol on the α7 subunit of the nicotinic acetylcholine (nACh) receptor function. Using a two-electrode voltage-clamp technique, menthol was found to reversibly inhibit α7-nACh receptors heterologously expressed in Xenopus oocytes. Inhibition by menthol was not dependent on the membrane potential and did not involve endogenous Ca(2+)-dependent Cl(-) channels, since menthol inhibition remained unchanged by intracellular injection of the Ca(2+) chelator BAPTA and perfusion with Ca(2+)-free bathing solution containing Ba(2+). Furthermore, increasing ACh concentrations did not reverse menthol inhibition and the specific binding of [(125)I] α-bungarotoxin was not attenuated by menthol. Studies of α7- nACh receptors endogenously expressed in neural cells demonstrate that menthol attenuates α7 mediated Ca(2+) transients in the cell body and neurite. In conclusion, our results suggest that menthol inhibits α7-nACh receptors in a noncompetitive manner.

Alterations in glutathione redox metabolism, oxidative stress, and mitochondrial function in the left ventricle of elderly Zucker diabetic fatty rat heart.

The Zucker diabetic fatty (ZDF) rat is a genetic model in which the homozygous (FA/FA) male animals develop obesity and type 2 diabetes. Morbidity and mortality from cardiovascular complications, due to increased oxidative stress and inflammatory signals, are the hallmarks of type 2 diabetes. The precise molecular mechanism of contractile dysfunction and disease progression remains to be clarified. Therefore, we have investigated molecular and metabolic targets in male ZDF (30--34 weeks old) rat heart compared to age matched Zucker lean (ZL) controls. Hyperglycemia was confirmed by a 4-fold elevation in non-fasting blood glucose (478.43 ± 29.22 mg/dL in ZDF vs. 108.22 ± 2.52 mg/dL in ZL rats). An increase in reactive oxygen species production, lipid peroxidation and oxidative protein carbonylation was observed in ZDF rats. A significant increase in CYP4502E1 activity accompanied by increased protein expression was also observed in diabetic rat heart. Increased expression of other oxidative stress marker proteins, HO-1 and iNOS was also observed. GSH concentration and activities of GSH-dependent enzymes, glutathione S-transferase and GSH reductase, were, however, significantly increased in ZDF heart tissue suggesting a compensatory defense mechanism. The activities of mitochondrial respiratory enzymes, Complex I and Complex IV were significantly reduced in the heart ventricle of ZDF rats in comparison to ZL rats. Western blot analysis has also suggested a decreased expression of IκB-α and phosphorylated-JNK in diabetic heart tissue. Our results have suggested that mitochondrial dysfunction and increased oxidative stress in ZDF rats might be associated, at least in part, with altered NF-κB/JNK dependent redox cell signaling. These results might have implications in the elucidation of the mechanism of disease progression and designing strategies for diabetes prevention.

Modulation of excitability, membrane currents and survival of cardiac myocytes by N-acylethanolamines.

N-acylethanolamines (NAE) are endogenously produced lipids playing important roles in a diverse range of physiological and pathological conditions. In the present study, using whole-cell patch clamp technique, we have for the first time investigated the effects of the most abundantly produced NAEs, N-stearoylethanolamine (SEA) and N-oleoylethanolamine (OEA), on electric excitability and membrane currents in cardiomyocytes isolated from endocardial, epicardial, and atrial regions of neonatal rat heart. SEA and OEA (1-10µM) attenuated electrical activity of the myocytes from all regions of the cardiac muscle by hyperpolarizing resting potential, reducing amplitude, and shortening the duration of the action potential. However, the magnitudes of these effects varied significantly depending on the type of cardiac myocyte (i.e., endocardial, epicardial, atrial) with OEA being generally more potent. OEA and to a lesser extent SEA suppressed in a concentration-dependent manner currents through voltage-gated Na(+) (VGSC) and L-type Ca(2+) (VGCC) channels, but induced variable cardiac myocyte type-dependent effects on background K(+) and Cl(-) conductance. The mechanisms of inhibitory action of OEA on cardiac VGSCs and VGCCs involved influence on channels' activation/inactivation gating and partial blockade of ion permeation. OEA also enhanced the viability of cardiac myocytes by reducing necrosis without a significant effect on apoptosis. We conclude that SEA and OEA attenuate the excitability of cardiac myocytes mainly through inhibition of VGSCs and VGCC-mediated Ca(2+) entry. Since NAEs are known to increase during tissue ischemia and infarction, these effects of NAEs may mediate some of their cardioprotective actions during these pathological conditions.

Structural lesions and changing pattern of expression of genes encoding cardiac muscle proteins are associated with ventricular myocyte dysfunction in type 2 diabetic Goto-Kakizaki rats fed a high-fat diet.

Given the clinical prevalence of type 2 diabetes and obesity and their association with high mortality linked to cardiovascular disease, the aim of the study was to investigate the effects of feeding type 2 diabetic Goto-Kakizaki (GK) rats either high- or low-fat diets on cardiomyocyte structure and function. The GK rats were fed either a high-fat diet (HFD) or a low-fat diet (LFD) from the age of 2 months for a period of 7 months. The GK-HFD rats gained more weight, ate less food and drank less water compared with GK-LFD rats. At 7 months, non-fasting blood glucose was higher in GK-LFD (334 ± 35 mg dl(-1)) compared with GK-HFD rats (235 ± 26 mg dl(-1)). Feeding GK rats with a HFD had no significant effect on glucose clearance following a glucose challenge. Time-to-peak (t(peak)) shortening was reduced in myocytes from GK-HFD (131.8 ± 2.1 ms) compared with GK-LFD rats (144.5 ± 3.0 ms), and time-to-half (t(1/2)) relaxation of shortening was also reduced in myocytes from GK-HFD (71.7 ± 6.9 ms) compared with GK-LFD rats (86.1 ± 3.6 ms). The HFD had no significant effect on the amplitude of shortening. The HFD had no significant effect on t(peak), t(1/2) decay, amplitude of the Ca(2+) transient, myofilament sensitivity to Ca(2+), sarcoplasmic reticulum Ca(2+) content, fractional release of Ca(2+) and the rate of Ca(2+) uptake. Structurally, ventricular myocytes from GK-HFD rats showed extensive mitochondrial lesions, including swelling, loss of cristae, and loss of inner and outer membranes, resulting in gross vacuolarization and deformation of ventricular mitochondria with a subsequent reduction in mitochondrial density. Expression of genes encoding various L-type Ca(2+) channel proteins (Cacnb2) and cardiac muscle proteins (Myl2 and Atp2a1) were downregulated in GK-HFD compared with GK-LFD rats. Structural lesions and changed expression of genes encoding various cardiac muscle proteins might partly underlie the altered time course of myocyte shortening and relaxation in myocytes from GK-HFD compared with GK-LFD rats.

Left ventricle structural remodelling in the prediabetic Goto-Kakizaki rat.

This study tested the hypothesis that experimental prediabetes can elicit structural remodelling in the left ventricle (LV). Left ventricles isolated from 8-week-old male Goto-Kakizaki (GK) rats and age-matched male Wistar control rats were used to assess remodelling changes and underlying transforming growth factor ß1 (TGFß1) activity, prohypertrophic Akt-p70S6K1 signalling and gene expression profile of the extracellular matrix (ECM) using histological, immunohistochemical, immunoblotting and quantitative gene expression analyses. Prediabetes in GK rats was confirmed by impaired glucose tolerance and modestly elevated fasting blood glucose. Left ventricle remodelling in the GK rat presented with marked hypertrophy of cardiomyocytes and increased ECM deposition that together translated into increased heart size in the absence of ultrastructural changes or fibre disarray. Molecular derangements underlying this phenotype included recapitulation of the fetal gene phenotype markers B-type natriuretic peptide and α-skeletal muscle actin, activation of the Akt-p70S6K1 pathway and altered gene expression profile of key components (collagen 1α and fibronectin) and modulators of the ECM (matrix metalloproteinases 2 and 9 and connective tissue growth factor). These changes were correlated with parallel findings of increased TGFß1 transcription and activation in the LV and elevated active TGFß1 in plasma of GK rats compared with control animals (Student's t test, P < 0.05 versus age-matched Wistar control animals for all parameters). This is the first report to describe LV structural remodelling in experimental prediabetes. The results suggest that ventricular decompensation pathognomonic of advanced diabetic cardiomyopathy may have possible origins in profibrotic and prohypertrophic mechanisms triggered before the onset of type 2 diabetes mellitus.

Pathogenesis and pathophysiology of accelerated atherosclerosis in the diabetic heart.

It has been established that atherosclerotic coronary artery disease is more frequent and more severe in diabetic compared to non-diabetic subjects, but the reason for the excess risk of developing coronary macroangiopathy in diabetes remains incompletely characterized. Various biochemical mechanisms speculated to being at the "heart" of diabetic cardiac and coronary macroangiopathy are reviewed in the present article. In doing so, this article presents evidence that the labyrinthine interactions of hyperglycemia, insulin resistance, and dyslipidemia in diabetes result in a pro-atherogenic phenotype. Furthermore, the diabetic milieu yields a complex (dys)metabolic environment characterized by chronic inflammation, procoagulability, impaired fibrinolysis, neovascularization abnormalities, and microvascular defects that cumulatively alter blood rheology, artery structure, and homeostasis of the endothelium. The contributory influences of these factors in the pathophysiology of coronary artery disease in diabetes are also discussed.