Nair Sreejayan

Cardiac contractile dysfunction in Lep/Lep obesity is accompanied by NADPH oxidase activation, oxidative modification of sarco(endo)plasmic reticulum Ca2+-ATPase and myosin heavy chain isozyme switch.

Aims/hypothesisObesity is an independent risk factor for heart diseases but the underlying mechanism is not clear. This study examined cardiac contraction, oxidative stress, oxidative modification of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) and the myosin heavy chain (MHC) isoform switch in obese mice.MethodsMechanical properties were evaluated in ventricular myocytes from C57BL/6J lean and Lep/Lep obese mice (formerly known as ob/ob mice), including peak shortening (PS), time to 50 or 90% PS, time to 50 or 90% relengthening (TR50, TR90), maximal velocity of shortening/relengthening (±dL/dt), intracellular Ca2+ and its decay (τ). Oxidative stress, lipid peroxidation, protein damage and SERCA activity were assessed by glutathione/glutathione disulfide, malondialdehyde, protein carbonyl and 45Ca2+ uptake, respectively. NADPH oxidase was determined by immunoblotting.ResultsMyocytes from Lep/Lep mice displayed depressed PS and ± dL/dt, prolonged TR50, TR90, elevated resting [Ca2+]i, prolonged τ, reduced contractile capacity at high stimulus frequencies and diminished responsiveness to extracellular Ca2+ compared with lean controls. Cardiac glutathione/glutathione disulfide was decreased whereas malondialdehyde, protein carbonyl, membrane p47phox and membrane gp91phox were increased in the Lep/Lep group. SERCA isoenzyme 2a was markedly modified by oxidation in Lep/Lep hearts and associated with decreased 45Ca2+ uptake. The MHC isozyme displayed a shift from the α to the β isoform in Lep/Lep hearts. Short-term incubation of angiotensin II with myocytes mimicked the mechanical defects, SERCA oxidation and 45Ca2+ uptake seen in Lep/Lep myocytes. Incubation of the NADPH oxidase inhibitor apocynin with Lep/Lep myocytes alleviated contractile defects without reversing SERCA oxidation or activity.Conclusions/interpretationThese data indicate that obesity-related cardiac defects may be related to NADPH oxidase activation, oxidative damage to SERCA and the MHC isozyme switch.

Metallothionein prolongs survival and antagonizes senescence-associated cardiomyocyte diastolic dysfunction: role of oxidative stress

Senescence is accompanied by oxidative stress and cardiac dysfunction, although the link between the two remains unclear. This study examined the role of antioxidant metallothionein on cardiomyocyte function, superoxide generation, the oxidative stress biomarker aconitase activity, cytochrome c release, and expression of oxidative stress‐related proteins, such as the GTPase RhoA and NADPH oxidase protein p47phox in young (5–6 mo) and aged (26–28 mo) FVB wild‐type (WT) and cardiac‐specific metallothionein transgenic mice. Metallothionein mice showed a longer life span (by ∼4 mo) than FVB mice evaluated by the Kaplan‐Meier survival curve. Compared with young cardiomyocytes, aged myocytes displayed prolonged TR90, reduced tolerance to high stimulus frequency, and slowed intracellular Ca2+ decay, all of which were nullified by metallothionein. Aging increased superoxide generation, active RhoA abundance, cytochrome c release, and p47phox expression and suppressed aconitase activity without affecting protein nitrotyrosine formation in the hearts. These aging‐induced changes in oxidative stress and related protein biomarkers were attenuated by metallothionein. Aged metallothionein mouse myocytes were more resistant to the superoxide donor pyrogallol‐induced superoxide generation and apoptosis. In addition, aging‐associated prolongation in TR90 was blunted by the Rho kinase inhibitor Y‐27632. Collectively, our data demonstrated that metallothionein may alleviate aging‐induced cardiac contractile defects and oxidative stress, which may contribute to prolonged life span in metallothionein transgenic mice.—Yang, X., Doser, T. A., Fang, C. X., Nunn, J. M., Janardhanan, R., Zhu, M., Sreejayan, N., Quinn, M. T., Ren, J. Metallothionein prolongs survival and antagonizes senescence‐associated cardiomyocyte diastolic dysfunction: role of oxidative stress FASEB J. 20, E260–E270 (2006)

Metallothionein Prevents High-Fat Diet–Induced Cardiac Contractile Dysfunction: Role of Peroxisome Proliferator–Activated Receptor γ Coactivator 1α and Mitochondrial Biogenesis

Obesity is associated with oxidative stress and mitochondrial and myocardial dysfunction, although interaction among which remains elusive. This study was designed to evaluate the impact of the free radical scavenger metallothionein on high-fat diet–induced myocardial, intracellular Ca2+, and mitochondrial dysfunction. FVB and metallothionein transgenic mice were fed a high- or low-fat diet for 5 months to induce obesity. Echocardiography revealed decreased fractional shortening, increased end-systolic diameter, and cardiac hypertrophy in high-fat–fed FVB mice. Cardiomyocytes from high-fat–fed FVB mice displayed enhanced reactive oxygen species (ROS) production, contractile and intracellular Ca2+ defects including depressed peak shortening and maximal velocity of shortening/relengthening, prolonged duration of relengthening, and reduced intracellular Ca2+ rise and clearance. Transmission microscopy noted overt mitochondrial damage with reduced mitochondrial density. Western blot analysis revealed enhanced phosphorylation of nuclear factor Foxo3a without changes in Foxo3a, Foxo1a, pFoxo1a, silent information regulator (Sirt), and Akt and pAkt in hearts of high-fat diet–fed FVB mice. The peroxisome proliferator–activated receptor γ coactivator-1α (PGC-1α), a key regulator of mitochondrial biogenesis, was significantly depressed by high-fat diet feeding and in vitro palmitic acid treatment. RT-PCR further depicted reduced levels of the PGC-1α downstream nuclear respiratory factors 1 and 2, mitochondrial transcription factor A, and mitochondrial DNA copy number in hearts of high-fat–fed FVB mice. Intriguingly, the high-fat diet–induced alterations in ROS, myocardial contractile, and mitochondrial and cell signaling were negated by metallothionein, with the exception of pFoxo3a. These data suggest that metallothionein may protect against high-fat diet–induced cardiac dysfunction possibly associated with upregulation of PGC-1α and preservation of mitochondrial biogenesis.

Curcumin Inhibits Platelet-Derived Growth Factor–Stimulated Vascular Smooth Muscle Cell Function and Injury-Induced Neointima Formation

Objective—Vascular smooth muscle cell (VSMC) migration, proliferation, and collagen synthesis are key events involved in the pathogenesis of cardiovascular disease. Growth factors, such as platelet-derived growth factor (PDGF) and fibroblast growth factor, released during vascular injury plays a pivotal role in regulating these events. Curcumin (diferuloyl methane), a major component of the spice turmeric (Curcuma longa), has been shown recently to have beneficial effects in chronic conditions, such as inflammation, cancer, cystic fibrosis, and Alzheimer’s disease. The objective of this study was to investigate the ability of curcumin to inhibit PDGF-stimulated migration, proliferation, and collagen synthesis in cultured VSMCs and neointima formation after carotid artery injury in rats. Methods and Results—Curcumin (1 to 25 &mgr;M) produced a concentration-dependent inhibition of PDGF-elicited VSMC migration, proliferation, and collagen synthesis assessed by chemotaxis, [3H]thymidine incorporation, and [3H]-l-proline incorporation, respectively. Curcumin blocked PDGF-induced VSMC actin-cytoskeleton reorganization, attenuated PDGF signal transduction, and inhibited the binding of PDGF to its receptors. Carotid artery neointima formation was significantly attenuated by perivascular curcumin compared with vehicle controls 14 days after injury, characterized by reduced DNA synthesis, collagen synthesis, and PDGF receptor phosphorylation. Conclusions—These data suggest that curcumin is a potent inhibitor of key PDGF-stimulated VSMC functions and may play a critical role in regulating these events after vascular injury.

Aging induces cardiac diastolic dysfunction, oxidative stress, accumulation of advanced glycation endproducts and protein modification

Evidence suggests that aging, per se, is a major risk factor for cardiac dysfunction. Oxidative modification of cardiac proteins by non‐enzymatic glycation, i.e. advanced glycation endproducts (AGEs), has been implicated as a causal factor in the aging process. This study was designed to examine the role of aging on cardiomyocyte contractile function, cardiac protein oxidation and oxidative modification. Mechanical properties were evaluated in ventricular myocytes from young (2‐month) and aged (24–26‐month) mice using a MyoCam® system. The mechanical indices evaluated were peak shortening (PS), time‐to‐PS (TPS), time‐to‐90% relengthening (TR90) and maximal velocity of shortening/relengthening (± dL/dt). Oxidative stress and protein damage were evaluated by glutathione and glutathione disulfide (GSH/GSSG) ratio and protein carbonyl content, respectively. Activation of NAD(P)H oxidase was determined by immunoblotting. Aged myocytes displayed a larger cell cross‐sectional area, prolonged TR90, and normal PS, ± dL/dt and TPS compared with young myocytes. Aged myocytes were less tolerant of high stimulus frequency (from 0.1 to 5 Hz) compared with young myocytes. Oxidative stress and protein oxidative damage were both elevated in the aging group associated with significantly enhanced p47phox but not gp91phox expression. In addition, level of cardiac AGEs was ∼2.5‐fold higher in aged hearts than young ones determined by AGEs‐ELISA. A group of proteins with a molecular range between 50 and 75 kDa with pI of 4–7 was distinctively modified in aged heart using one‐ or two‐dimension SDS gel electrophoresis analysis. These data demonstrate cardiac diastolic dysfunction and reduced stress tolerance in aged cardiac myocytes, which may be associated with enhanced cardiac oxidative damage, level of AGEs and protein modification by AGEs.

Molecular Mechanisms of Chromium in Alleviating Insulin Resistance

Type 2 diabetes is often associated with obesity, dyslipidemia and cardiovascular anomalies and is a major health problem approaching global epidemic proportions. Insulin resistance, a prediabetic condition, precedes the onset of frank type 2 diabetes and offers potential avenues for early intervention to treat the disease. Although lifestyle modifications and exercise can reduce the incidence of diabetes, compliance has proved to be difficult, warranting pharmacological interventions. However, most of the currently available drugs that improve insulin sensitivity have adverse effects. Therefore, attractive strategies to alleviate insulin resistance include dietary supplements. One such supplement is chromium, which has been shown to reduce insulin resistance in some, but not all, studies. Furthermore, the molecular mechanisms of chromium in alleviating insulin resistance remain elusive. This review examines emerging reports on the effect of chromium, as well as molecular and cellular mechanisms by which chromium may provide beneficial effects in alleviating insulin resistance.

Endoplasmic reticulum chaperon tauroursodeoxycholic acid alleviates obesity-induced myocardial contractile dysfunction

ER stress is involved in the pathophysiology of obesity although little is known about the role of ER stress on obesity-associated cardiac dysfunction. This study was designed to examine the effect of ER chaperone tauroursodeoxycholic acid (TUDCA) on obesity-induced myocardial dysfunction. Adult lean and ob/ob obese mice were treated with TUDCA (50mg/kg/day, p.o.) or vehicle for 5 weeks. Oral glucose tolerance test (OGTT) was performed. Echocardiography, cardiomyocyte contractile and intracellular Ca(2+) properties were assessed. Sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) activity and protein expression of intracellular Ca(2+) regulatory proteins were measured using (45)Ca(2+) uptake and Western blot analysis, respectively. Insulin signaling, ER stress markers and HSP90 were evaluated. Our results revealed that chronic TUDCA treatment lowered systolic blood pressure and lessened glucose intolerance in obese mice. Obesity led to increased diastolic diameter, cardiac hypertrophy, compromised fractional shortening, cardiomyocyte contractile (peak shortening, maximal velocity of shortening/relengthening, and duration of contraction/relaxation) and intracellular Ca(2+) properties, all of which were significantly attenuated by TUDCA. TUDCA reconciled obesity-associated decrease in SERCA activity and expression, and increase in serine phosphorylation of IRS, total and phosphorylated cJun, ER stress markers Bip, peIF2α and pPERK. Obesity-induced changes in phospholamban and HSP90 were unaffected by TUDCA. In vitro finding revealed that TUDCA ablated palmitic acid-induced cardiomyocyte contractile dysfunction. In summary, these data depicted a pivotal role of ER stress in obesity-associated cardiac contractile dysfunction, suggesting the therapeutic potential of ER stress as a target in the management of cardiac dysfunction in obesity.

A newly synthetic chromium complex - chromium(phenylalanine)3 improves insulin responsiveness and reduces whole body glucose tolerance

Low‐molecular‐weight organic chromium complexes such as chromium picolinate are often used as dietary supplements to improve insulin sensitivity and to correct dyslipidemia. However, toxicity associated with such chromium compounds has compromised their therapeutic value. The aim of this study was to evaluate the impact of a newly synthesized complex of chromium with phenylalanine, Cr(pa)3 on insulin‐signaling and glucose tolerance. Cr(pa)3 was synthesized by chelating chromium(III) with d‐phenylalanine ligand in aqueous solution. In mouse 3T3‐adipocytes, Cr(pa)3 augmented insulin‐stimulated glucose‐uptake as assessed by a radioactive‐glucose uptake assay. At the molecular level, Cr(pa)3 enhanced insulin‐stimulated phosphorylation of Akt in a time‐ and concentration‐dependent manner without altering the phosphorylation of insulin receptor. Oral treatment with Cr(pa)3 (150 μg/kg/d, for six weeks) in ob/ob(+/+) obese mice significantly alleviated glucose tolerance compared with untreated obese mice. Unlike chromium picolinate, Cr(pa)3 does not cleave DNA under physiological reducing conditions. Collectively, these data suggest that Cr(pa)3 may represent a novel, less‐toxic chromium supplement with potential therapeutic value to improve insulin sensitivity and glycemic control in type II diabetes.

Chromium Alleviates Glucose Intolerance, Insulin Resistance, and Hepatic ER Stress in Obese Mice

Objective: Chromium has gained popularity as a nutritional supplement for diabetic patients. This study evaluated the effect of chronic administration of a chromium complex of d‐phenylalanine (Cr(d‐phe)3) on glucose and insulin tolerance in obese mice. The study tested the hypothesis that Cr(d‐phe)3 suppresses endoplasmic reticulum (ER) stress and insulin resistance in these animals.

Inhibition of radiation-induced lipid peroxidation by curcumin

Abstract The ability of curcumin, a natural antioxidant from turmeric, to inhibit radiation-induced lipid peroxidation in rat liver microsomes was examined. Curcumin was incorporated into microsomes during ultracentrifugation. The antioxidant has significant time- and concentration-dependent inhibitory effect on lipid peroxidation induced by r-radiation. Inhibition of lipid peroxidation was also observed in microsomes samples previously saturated with N 2 O. Curcumin also inhibited lipid peroxidation during the post-irradiation incubation.