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.

AMP-activated protein kinase (AMPK) cross-talks with canonical Wnt signaling via phosphorylation of beta-catenin at Ser 552.

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism; its activity is regulated by a plethora of physiological conditions, exercises and many anti-diabetic drugs. Recent studies show that AMPK involves in cell differentiation but the underlying mechanism remains undefined. Wingless Int-1 (Wnt)/beta-catenin signaling pathway regulates the differentiation of mesenchymal stem cells through enhancing beta-catenin/T-cell transcription factor 1 (TCF) mediated transcription. The objective of this study was to determine whether AMPK cross-talks with Wnt/beta-catenin signaling through phosphorylation of beta-catenin. C3H10T1/2 mesenchymal cells were used. Chemical inhibition of AMPK and the expression of a dominant negative AMPK decreased phosphorylation of beta-catenin at Ser 552. The beta-catenin/TCF mediated transcription was correlated with AMPK activity. In vitro, pure AMPK phosphorylated beta-catenin at Ser 552 and the mutation of Ser 552 to Ala prevented such phosphorylation, which was further confirmed using [gamma-(32)P]ATP autoradiography. In conclusion, AMPK phosphorylates beta-catenin at Ser 552, which stabilizes beta-catenin, enhances beta-catenin/TCF mediated transcription, expanding AMPK from regulation of energy metabolism to cell differentiation and development via cross-talking with the Wnt/beta-catenin signaling pathway.

Tauroursodeoxycholic acid attenuates lipid accumulation in endoplasmic reticulum-stressed macrophages.

BACKGROUND/AIM: Recent evidence suggests that endoplasmic reticulum (ER) stress provoked under diabetic conditions augments the expression of scavenger receptors on macrophages, promoting the uptake of oxidized low-density lipoprotein uptake and atherogenesis. The aim of the present study was to test the hypothesis that the chemical chaperone tauroursodeoxycholic acid (TUDCA) attenuates lipid accumulation in macrophages subjected to ER stress. METHODS: Cultured human macrophages were subjected to ER stress by treating them with tunicamycin. Lipid uptake by macrophages subjected to ER stress in the presence or absence of TUDCA was assessed by oil red O staining and by assessing the cellular uptake of Dil-oxidized low-density lipoprotein by fluorescence measurement. Protein levels and phosphorylation status of ER stress markers, insulin-signaling molecules, and scavenger receptor were assessed by Western blotting. RESULTS: Treatment of cultured human macrophages with the ER stressor tunicamycin caused an increase in the protein levels of cluster of differentiation 36 (CD-36) and augmentation of lipid uptake both of which were inhibited by TUDCA. TUDCA treatment inhibited tunicamycin-induced ER stress as evidenced by the attenuation of phosphorylation of eukaryotic translation initiation factor-2a and glucose reactive protein-78. In addition, TUDCA improved insulin signaling in macrophages by augmenting Akt phosphorylation and blunting c-Jun N-terminal kinase activity. CONCLUSIONS: Inhibition of macrophage ER stress may represent a potential strategy in preventing atherogenesis under diabetic conditions.

Safety and toxicological evaluation of a novel chromium(III) dinicocysteinate complex.

Chromium(III) is an essential trace element required for normal protein, fat and carbohydrate metabolism. It also helps in energy production and increasing lean body mass. Chromium(III) dinicocysteinate (CDNC) is a unique form of bioavailable chromium(III). This study was focused on determining the broad spectrum safety of CDNC. Acute oral, acute dermal, primary dermal and eye irritation studies, Ames' bacterial reverse mutation assay, mammalian erythrocyte micronucleus test, and a 90-day dose-dependent oral toxicity study were conducted. Acute oral and dermal LD(50) of CDNC was found to be greater than 2000 mg/kg in Sprague-Dawley rats. A primary skin irritation study in New Zealand Albino rabbits demonstrated CDNC as slightly irritating. An eye irritation study exhibited that CDNC is moderately irritating. Ames' bacterial reverse mutation assay and mammalian erythrocyte micronucleus test demonstrated CDNC as non-mutagenic. A dose-dependent 90-day oral toxicity study demonstrated no significant toxicity of CDNC. Body weight, food and water consumption, selected organ weights (expressed as percentages of body or brain weights), ocular health, hematology, blood chemistry, and histopathology showed no abnormal changes. Clinical and histopathological evaluation of CDNC identified a dose level of 5.7 mg/kg/day as the no observed adverse effect level (NOAEL). Overall, these results demonstrate the broad spectrum safety of CDNC.

Chromium (D-phenylalanine)3 supplementation alters glucose disposal, insulin signaling, and glucose transporter-4 membrane translocation in insulin-resistant mice.

Chromium has gained popularity as a nutritional supplement for diabetic and insulin-resistant subjects. This study was designed to evaluate the effect of chronic administration of a novel chromium complex of d-phenylalanine [Cr(D-phe)(3)] in insulin-resistant, sucrose-fed mice. Whole-body insulin resistance was generated in FVB mice by 9 wk of sucrose feeding, following which they were randomly assigned to be unsupplemented (S group) or to receive oral Cr(D-phe)(3) in drinking water (SCr group) at a dose of 45 mug.kg(-1).d(-1) ( approximately 3.8 mug of elemental chromium.kg(-1).d(-1)). A control group (C) did not consume sucrose and was not supplemented. Sucrose-fed mice had an elevated serum insulin concentration compared with controls and this was significantly lower in sucrose-fed mice that received Cr(D-phe)(3), which did not differ from controls. Impaired glucose tolerance in sucrose-fed mice, evidenced by the poor glucose disposal rate following an intraperitoneal glucose tolerance test, was significantly improved in mice receiving Cr(D-phe)(3). Chromium supplementation significantly enhanced insulin-stimulated Akt phosphorylation and membrane-associated glucose transporter-4 in skeletal muscles of sucrose-fed mice. In cultured adipocytes rendered insulin resistant by chronic exposure to high concentrations of glucose and insulin, Cr(D-phe)(3) augmented Akt phosphorylation and glucose uptake. These results indicate that dietary supplementation with Cr(D-phe)(3) may have potential beneficial effects in insulin-resistant, prediabetic conditions.

Antioxidant properties of argpyrimidine.

Argpyrimidine, the product of non-enzymatic protein glycation by methylglyoxal, has been implicated in the pathophysiology of diabetes mellitus and neurodegenerative diseases. Chemically, argpyrimidine is a substituted pyrimidinol with structural features common to known antioxidants. The objective of this study was to investigate the antioxidant properties of argpyrimidine. Argpyrimidine was synthesized by mixing L-arginine with 3-acetoxypentane-2,4-dione under acidic conditions and purified by chromatography. Argpyrimidine inhibited lipid peroxidation of rat brain homogenates catalyzed by hydroxyl radicals, metal ions, and autooxidation in a concentration- and time-dependent manner. In addition, argpyrimidine scavenged superoxide anion, 1,1-diphenyl 2-picryl-hydrazyl-stable free radical, intracellular-hydrogen peroxide, and inhibited free-radical-mediated nicking of plasmid-DNA. Taken together, our data suggest that argpyrimidine has antioxidant properties and may therefore have biological relevance in pathophysiologies associated with diabetes mellitus and neurodegenerative diseases.

Inhibitory effect of dehydrozingerone on vascular smooth muscle cell function.

BACKGROUND/AIMS: Growth factor and oxidative stress-mediated migration and proliferation of vascular smooth muscle cells (VSMCs) play a key role in the pathogenesis of atherosclerosis. The objective of this study was to assess the ability of dehydrozingerone, a structural analog of curcumin, to inhibit PDGF-stimulated vascular functions in VSMCs. METHODS: VSMCs isolated from adult rats were treated with dehydrozingerone (0 to 50 microM) before challenge with PDGF (10 ng/mL) and migration, proliferation, and collagen synthesis were assayed by transwell-migration, thymidine-, and L-proline-incorporation assays, respectively. Phosphorylation of PDGF-receptor (PDGFR) and Akt were assessed by Western blotting. Cellular protein tyrosine phosphatase (PTP) activity was determined by the extent of p-nitro-phenyl phosphate hydrolysis. RESULTS: Dehydrozingerone elicited a concentration-dependent inhibition of PDGF-stimulated VSMC migration, proliferation, collagen synthesis, and PDGF/H2O2-stimulated phosphorylation of PDGFR-beta and downstream Akt. Dehydrozingerone also inhibited H2O2-mediated oxidation of PTP. CONCLUSIONS: Dehydrozingerone is a potent inhibitor of growth factor/ H2O2-stimulated VSMC functions and may play a critical role in regulating these events after vascular injury. Inhibition of oxidation of cellular phosphatases may represent one of the mechanisms by which dehydrozingerone inhibits these VSMC functions. Inability of the structural analog isoeugenol to inhibit PDGF-signaling suggests that the carbonyl side chain may be necessary for activity.

Metallothionein antagonizes aging-induced cardiac contractile dysfunction: role of PTP1B, insulin receptor tyrosine phosphorylation and Akt.

Aging is often accompanied by reduced insulin sensitivity and cardiac dysfunction. However, the causal relationship between the two remains poorly understood. This study was designed to determine the impact of cardiac-specific overexpression of antioxidant metallothionein (MT) on aging-associated cardiac dysfunction and impaired insulin signaling. Contractile and intracellular Ca(2+) properties were evaluated in left ventricular myocytes including peak shortening (PS), maximal velocity of shortening/relengthening (+/- dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR(90)), fura-2 fluorescence intensity change (DeltaFFI) and intracellular Ca(2+) decay rate. Expression of insulin receptor, protein-tyrosine phosphatase 1B (PTP1B), phosphorylation of insulin receptor (Tyr1146) and Akt were evaluated by Western blot analysis. Aged wild-type FVB and MT transgenic mice (26-28 months old) displayed glucose intolerance and hyperinsulinemia. Cardiomyocytes from aged FVB mice exhibited prolonged TR(90) and intracellular Ca(2+) decay associated with normal PS, +/- dL/dt, TPS and DeltaFFI compared with those from young (2-3 months old) mice. Western blot analysis revealed reduced Akt expression and insulin (5 mU g(-1))-stimulated Akt phosphorylation, elevated PTP1B expression and diminished basal insulin receptor tyrosine phosphorylation associated with comparable insulin receptor expression in aged FVB mouse hearts. All of these aging-related defects in cardiac contractile function and insulin signaling (although not hyperinsulinemia and glucose intolerance) were significantly attenuated or ablated by MT transgene. These data indicate that enhanced antioxidant defense is beneficial for aging-induced cardiac contractile dysfunction and alteration in insulin signaling.

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 approximately 4 mo) than FVB mice evaluated by the Kaplan-Meier survival curve. Compared with young cardiomyocytes, aged myocytes displayed prolonged TR(90), 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.

Insulin-like growth factor I deficiency prolongs survival and antagonizes paraquat-induced cardiomyocyte dysfunction: role of oxidative stress.

Interruption of insulin-like growth factor I (IGF-1) signaling has been demonstrated to prolong life span although the underlying mechanism has not been elucidated. The aim of this study was to examine the influence of severe IGF-1 deficiency on survival rate, cardiomyocyte viability, contractile function, and intracellular Ca(2+) property in response to challenge with the pro-oxidant paraquat. C57 negative and liver IGF-1 deficient (LID) transgenic mice were administrated paraquat (75 mg/kg) and survival was monitored. LID mice displayed a significantly improved survival than did C57 mice evaluated by the Kaplan-Meier curve. MTT assay revealed that in vitro IGF-1 treatment significantly sensitized paraquat-induced cell death in both C57 and LID groups, with significantly better cell viability in LID cardiomyocytes. Compared to C57 mouse cardiomyocytes, LID myocytes displayed reduced peak shortening (PS), decreased maximal velocity of shortening/relengthening (+/- dL/dt), prolonged time-to-90% relengthening (TR(90)), and comparable tolerance to high stimulus frequency and intracellular Ca(2+) homeostasis. Paraquat treatment for 48 hours reduced PS, +/- dL/dt, tolerance to high stimulus frequency, resting and rise in intracellular Ca(2+), and prolonged TR(90), all of which were nullified or masked by IGF-1 deficiency. Paraquat increased reactive oxygen species and carbonyl production upregulated the Ca(2+) regulating protein SERCA2a, and downregulated Na(+) -Ca(2+) exchanger, the effects of which were nullified or masked by IGF-1 deficiency. Although LID mice displayed reduced whole body glucose clearance, cardiomyocytes from LID mice exhibited dramatically enhanced insulin-stimulated phosphorylation of insulin receptor and Akt. These data demonstrated that IGF-1 deficiency may antagonize or mask the paraquat-induced decrease in survival, cardiomyocyte dysfunction, oxidative stress, and change in Ca(2+) regulating proteins.

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 microM) 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.

Impact of insulin-like growth factor-I on migration, proliferation and Akt-ERK signaling in early and late-passages of vascular smooth muscle cells.

Migration and proliferation of vascular smooth muscle cells (VSMCs) are important events in the progression of atherosclerosis. Insulin-like growth factor I (IGF-1) possesses both antiapoptotic and mitogenic/motogenic effects in VSMCs although the influence of life cycle on IGF-1-induced effects is unclear. This study was designed to evaluate the effect of IGF-1 on migration, proliferation, and signaling mechanisms in VSMCs from early (3-5) to late (20-22) passages. Migration, proliferation, and cell survival were measured using monolayer wounding, 3[H]-thymidine incorporation and MTT assay, respectively. Akt and ERK, which are critical to proliferation, differentiation and migration, were examined using Western blot analysis. DCF-DA fluorescence was used to quantify Reactive Oxygen Species (ROS) production. Late-passage VSMCs exhibited significantly higher basal cell proliferation and enhanced sensitivity to IGF-1-stimulated migration compared to cells from early-passages. Phosphorylated Akt and ERK levels were significantly higher in late-passage cells compared to early-passage, which was further enhanced by IGF-1 treatment. Late-passage cells exhibited higher levels of ROS production compared to early-passage, cells. IGF-1 did not significantly alter ROS levels in either passage. Expression of the cell cycle regulator p53, p21, and p16 was not affected by repeated passaging of cells. These results indicated that repeated passaging of VSMCs exhibits a phenotype which has higher proliferative capacity. Activation of trophic signaling molecules such as ERK1/2 and Akt and generation of ROS may represent the mechanisms by which repeated passages of VSMCs acquire a motogenic and mitogenic phenotype.

Isolation and functional studies of rat aortic smooth muscle cells.

Migration, proliferation, and collagen synthesis by vascular smooth muscle cells are thought to be key events involved in the pathogenesis of cardiovascular disease. Following endothelial injury, smooth muscle cells (SMCs) in the intima of the blood vessels assume a synthetic, promitogenic phenotype resulting in their migration, proliferation, and deposition of extracellular matrix within the neointimal tissue. This chapter describes a method of isolation of SMCs from rat aorta and in vitro assays to characterize these abnormal SMC functions.

Metallothionein alleviates cardiac dysfunction in streptozotocin-induced diabetes: role of Ca2+ cycling proteins, NADPH oxidase, poly(ADP-Ribose) polymerase and myosin heavy chain isozyme.

Diabetic cardiomyopathy contributes to high morbidity and mortality in diabetic populations. It is manifested by compromised ventricular contraction and prolonged relaxation attributable to multiple causative factors including oxidative stress. This study was designed to examine the effect of cardiac overexpression of the heavy metal scavenger metallothionein (MT) on cardiac contractile function, intracellular Ca(2+) cycling proteins, stress-activated signaling molecules and the myosin heavy chain (MHC) isozyme in diabetes. Adult male wild-type (FVB) and MT transgenic mice were made diabetic by a single injection of streptozotocin (STZ). Contractile properties were evaluated in cardiomyocytes including peak shortening (PS), time-to-PS (TPS), time-to-relengthening (TR(90)), maximal velocity of shortening/relengthening (+/-dL/dt) and intracellular Ca(2+) fluorescence. Diabetes significantly depressed PS, +/-dL/dt, prolonged TPS, TR(90) and intracellular Ca(2+) clearing, elevated resting intracellular Ca(2+), reduced caffeine-induced sarcoplasmic reticulum Ca(2+) release and dampened stress tolerance at high stimulus frequencies. MT itself exhibited little effect on myocyte mechanics but it significantly alleviated STZ-induced myocyte contractile dysfunctions. Diabetes enhanced expression of the AT(1) receptor, phospholamban, the p47(phox) NADPH oxidase subunit and poly(ADP-ribose) polymerase (PARP), depressed the level of SERCA2a, Na(+)-Ca(2+) exchanger and triggered a beta-MHC isozyme switch. All of these STZ-induced alterations with the exception of depressed SERCA2a and enhanced phospholamban were reconciled by MT. Collectively, these data suggest a beneficial effect of MT in the therapeutics of diabetic cardiomyopathy, possibly through a mechanism related to NADPH oxidase, PARP and MHC isozyme switch.

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 approximately 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.

Nitric oxide-induced motility in aortic smooth muscle cells: role of protein tyrosine phosphatase SHP-2 and GTP-binding protein Rho.

We have previously reported that SHP-2 upregulation is necessary for NO-stimulated motility in differentiated rat aortic smooth muscle cells. We now test the hypothesis that upregulation of SHP-2 is necessary and sufficient to stimulate cell motility. Overexpression of SHP-2 via recombinant adenoviral vector stimulated motility to the same extent as NO, whereas the expression of C463S-SHP-2, the dominant-negative SHP-2 allele, blocked the motogenic effect of NO. On the basis of previous studies, we next tested the hypothesis that NO decreases RhoA activity and that this event is necessary and sufficient to explain NO-induced motogenesis. We found that NO decreased RhoA activity in a concentration-dependent manner. Moreover, a dominant-negative SHP-2 allele, DSH2, blocked the NO-induced inhibition of RhoA activity, indicating that upregulation of SHP-2 is necessary for this event. Expression of G14V-RhoA, the constitutively active RhoA allele, decreased cell motility and blocked the motogenic effect of NO, whereas the expression of T19N-RhoA, the dominant-negative RhoA allele, increased cell motility to an extent similar to that induced by NO. Dominant-negative RhoA reversed the effect of dominant-negative SHP-2, indicating that RhoA functions downstream from SHP-2. To investigate events downstream from RhoA, we treated cells with fasudil, a selective Rho kinase inhibitor, and found that it increased cell motility. These results indicate that upregulation of SHP-2, leading to downregulation of RhoA, which is followed by decreased Rho kinase activity, is a sequence of events necessary and sufficient to explain NO-induced cell motility in differentiated aortic smooth muscle cells. The results may be of relevance to in vivo events such as neointimal formation, angiogenesis, and vasculogenesis.

Insulin-sensitizing and cholesterol-lowering effects of chromium (D-Phenylalanine)3.

Low-molecular weight organic chromium complexes are thought to play a key role in carbohydrate and lipid metabolism and therefore have been gaining popularity as nutritional supplement for patients with diabetes and concomitant lipid disorders. The aim of the present study was to evaluate the effects of a novel synthetic chromium (d-phenylalanine)(3) complex on insulin-sensitivity, plasma lipid-profile and oxidant stress in a mouse model of type II diabetes. Plasma glucose levels following intraperitoneal insulin-challenge (1U/kg) to obese ob/ob(+/+) mice treated with Cr(d-Phe)(3) (150 microg/kg/day for 6 weeks) were significantly lower compared to vehicle-control (control: 175.8+/-43.2mg/dL versus Cr(d-Phe)(3) 115.3+/-18.0mg/dL, p<0.01, n=12). Total serum cholesterol to high-density lipoprotein ratio was significantly reduced following Cr(d-Phe)(3)-treatment (control: 2.19+/-0.08 versus Cr(d-Phe)(3) 1.63+/-0.05; p<0.05). Hepatic oxidant stress, assessed as malondialdehyde equivalents and protein-carbonyl content were significantly attenuated following Cr(d-Phe)(3) treatment. The complex also inhibited lipid-peroxidation in vitro, in a concentration dependent manner. Taken together, these data suggest that Cr(d-Phe)(3) may be of potential value in the therapy or prophylaxis of insulin-resistance and dyslipidemia associated with 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 microg/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.

NO attenuates insulin signaling and motility in aortic smooth muscle cells via protein tyrosine phosphatase 1B-mediated mechanism.

OBJECTIVE: Hyperinsulinemia is a significant risk factor for the pathogenesis of vascular disease. Protein tyrosine phosphatase 1B (PTP1B) has been recognized as a modulator of insulin signaling in nonvascular cells, and we have recently reported that NO increases the activity of PTP1B in rat vascular smooth muscle cells. In the present study, we tested the hypothesis that NO attenuates insulin-stimulated cell motility via a PTP1B-mediated mechanism involving downregulation of insulin signal transduction. METHODS AND RESULTS: Treatment of primary aortic smooth muscle cells from newborn rats with the NO donor S-nitroso-N-acetylpenicillamine reduced cell motility, tyrosine phosphorylation levels of insulin receptor beta subunit and insulin receptor substrate-1, and extracellular signal-regulated kinase activity. Overexpression of wild-type PTP1B via an adenoviral vector blocked the capacity of insulin to stimulate cell motility and insulin receptor phosphorylation, whereas expression of a dominant-negative mutant of PTP1B attenuated the capacity of NO to decrease cell motility. CONCLUSIONS: Our findings indicate that activation of PTP1B is necessary and sufficient to account for the capacity of NO to decrease insulin-stimulated signal transduction and cell motility in cultured aortic smooth muscle cells. The results could explain the capacity of NO to oppose neointima formation in states of hyperinsulinemia.