Reduced vasorelaxant effect of carbon monoxide in diabetes and the underlying mechanisms

Diabetic Nephropathy and Gaseous Modulators

Diabetic nephropathy (DN) remains the leading cause of vascular morbidity and mortality in diabetes patients. Despite the progress in understanding the diabetic disease process and advanced management of nephropathy, a number of patients still progress to end-stage renal disease (ESRD). The underlying mechanism still needs to be clarified. Gaseous signaling molecules, so-called gasotransmitters, such as nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), have been shown to play an essential role in the development, progression, and ramification of DN depending on their availability and physiological actions. Although the studies on gasotransmitter regulations of DN are still emerging, the evidence revealed an aberrant level of gasotransmitters in patients with diabetes. In studies, different gasotransmitter donors have been implicated in ameliorating diabetic renal dysfunction. In this perspective, we summarized an overview of the recent advances in the physiological relevance of the gaseous molecules and their multifaceted interaction with other potential factors, such as extracellular matrix (ECM), in the severity modulation of DN. Moreover, the perspective of the present review highlights the possible therapeutic interventions of gasotransmitters in ameliorating this dreaded disease.

Gasotransmitter signaling in energy homeostasis and metabolic disorders

Gasotransmitters are small molecules of gases, including nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). These three gasotransmitters can be endogenously produced and regulate a wide range of pathophysiological processes by interacting with specific targets upon diffusion in the biological media. By redox and epigenetic regulation of various physiological functions, NO, H₂S, and CO are critical for the maintenance of intracellular energy homeostasis. Accumulated evidence has shown that these three gasotransmitters control ATP generation, mitochondrial biogenesis, glucose metabolism, insulin sensitivity, lipid metabolism, and thermogenesis, etc. Abnormal generation and metabolism of NO, H₂S, and/or CO are involved in various abnormal metabolic diseases, including obesity, diabetes, and dyslipidemia. In this review, we summarized the roles of NO, H₂S, and CO in the regulation of energy homeostasis as well as their involvements in the metabolism of dysfunction-related diseases. Understanding the interaction among these gasotransmitters and their specific molecular targets are very important for therapeutic applications.

A new mitochondrion targetable fluorescent probe for carbon monoxide-specific detection and live cell imaging

A new mitochondrion targetable molecular probe for carbon monoxide (CO)-specific detection based on palladium-free mediated opening of spirolactam was designed. The turn-on red fluorescence caused by CO enables a safe and powerful method for unravelling the function of CO in biological systems to be established.

Gasotransmitters in Vascular Complications of Diabetes

In the past decades three gaseous signaling molecules-so-called gasotransmitters-have been identified: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S). These gasotransmitters are endogenously produced by different enzymes in various cell types and play an important role in physiology and disease. Despite their specific functions, all gasotransmitters share the capacity to reduce oxidative stress, induce angiogenesis, and promote vasorelaxation. In patients with diabetes, a lower bioavailability of the different gasotransmitters is observed when compared with healthy individuals. As yet, it is unknown whether this reduction precedes or results from diabetes. The increased risk for vascular disease in patients with diabetes, in combination with the extensive clinical, financial, and societal burden, calls for action to either prevent or improve the treatment of vascular complications. In this Perspective, we present a concise overview of the current data on the bioavailability of gasotransmitters in diabetes and their potential role in the development and progression of diabetes-associated microvascular (retinopathy, neuropathy, and nephropathy) and macrovascular (cerebrovascular, coronary artery, and peripheral arterial diseases) complications. Gasotransmitters appear to have both inhibitory and stimulatory effects in the course of vascular disease development. This Perspective concludes with a discussion on gasotransmitter-based interventions as a therapeutic option.

A pharmacological investigation of Hippophae salicifolia (HS) and Hippophae rhamnoides turkestanica (HRT) against multiple stress (C-H-R): an experimental study using rat model

Hippophae salicifolia (HS) and Hippophae rhamnoides turkestanica (HRT) are abundantly found species of Hippophae in Himalayan region of India. As these plants thrive under extreme climatic conditions, it is suspected that these plants must have a unique adaptogenic property against high-altitude stress. To keeping these views in our mind, the present study was planned to evaluate the mechanism of action of aqueous extract of HS and aqueous extract of HRT against multiple stress [cold-hypoxia-restraint (C-H-R)] for their adaptogenic activity. The present study reported the adaptogenic activity of HS in facilitating tolerance to multiple stress, CHR in rats. Pre-treatment with aqueous extract of HS significantly attenuated reactive oxygen species (ROS) production, protein oxidation, and lipid peroxidation and also showed role in maintaining antioxidant status as similar to control rats. Since protein oxidation was decreased by pre-treatment of HS, protein homeostasis was also sustained by regulation of heat shock proteins (HSP70 and HSP60). Interestingly, heme oxygenase-1 (HO-1), Vascular Endothelial Growth Factor (VEGF), and nitric oxide (NO) level was also increased in HS pre-treated rats depicted its adaptogenic activity against multiple stress, CHR. Conclusively, aqueous extract of HS could use an adaptogen for high altitude-associated multiple stress (CHR).

Haeme oxygenase signalling pathway: implications for cardiovascular disease

Evidence now points to the haeme oxygenase (HO) pathway as a possible actor in modulating risk for cardiovascular disease (CVD). In particular, the HO pathway may represent a key endogenous modulator of oxidative, inflammatory, and cytotoxic stress while also exhibiting vasoregulatory properties. In this review, we summarize the accumulating experimental and emerging clinical data indicating how activity of the HO pathway and its products may play a role in mechanisms underlying the development of CVD. We also identify gaps in the literature to date and suggest future directions for investigation. Because HO pathway activity can be influenced not only by genetic traits and environmental stimuli but also by a variety of existing pharmacologic interventions, the pathway could serve as a prime target for reducing the overall burden of CVD. Further work is needed to determine the role of HO pathway products as possible prognostic markers of risk for clinical CVD events and the extent to which therapeutic augmentation or inhibition of HO pathway activity could serve to modify CVD risk.

Carbon monoxide stimulates Ca2+ -dependent big-conductance K channels in the cortical collecting duct

We used the patch-clamp technique to examine the role of carbon monoxide (CO) in regulating Ca(2+)-activated big-conductance K (BK) channels in the principal cell of the cortical collecting duct (CCD). Application of CORM3 or CORM2, a CO donor, activated BK channels in the CCD, whereas adding inactivated CORM2/3 had no effect. Superfusion of the CCD with CO-bubbled bath solution also activated the BK channels in the cell-attached patches. The effect of CO on BK channels was not dependent on nitric oxide synthase (NOS) because the effect of CORM3 was also observed in the CCD treated with l-NAME, an agent that inhibits the NOS. Adding a membrane-permeable cGMP analog, 8-bromo-cGMP, significantly increased the BK channel in the CCD. However, inhibition of soluble guanylate cyclase failed to abolish the stimulatory effect of CORM3 on BK channels. Moreover, inhibition of cGMP-dependent protein kinase G did not block the stimulatory effect of CORM3 on the BK channels, suggesting that the stimulatory effect of CO on the BK channels was, at least partially, induced by a cGMP-independent mechanism. Western blot demonstrated that heme oxygenase type 1 (HO-1) and HO-2 were expressed in the kidney. Moreover, a high-K (HK) intake increased the expression of HO-1 but not HO-2 in the kidney. A HK intake also increased renal HO activity defined by NADPH-dependent CO generation following addition of heme in the cell lysate from renal cortex and outer medulla. The role of HO in regulating BK channel activity in the CCD was also suggested by experiments in which application of hemin increased the BK channels. The stimulatory effect of hemin on the BK channels was blocked by SnMP, a HO inhibitor. But, adding CORM3 was still able to activate the BK channels in the presence of SnMP. We conclude that CO activates the BK channels, at least partially, through a NO-cGMP-independent pathway and that HO plays a role in mediating the effect of HK intake on the BK channels in the CCD.

Function and regulation of large conductance Ca(2+)-activated K+ channel in vascular smooth muscle cells

Large conductance Ca(2+)-activated K(+) (BK(Ca)) channels are abundantly expressed in vascular smooth muscle cells. Activation of BK(Ca) channels leads to hyperpolarization of cell membrane, which in turn counteracts vasoconstriction. Therefore, BK(Ca) channels have an important role in regulation of vascular tone and blood pressure. The activity of BK(Ca) channels is subject to modulation by various factors. Furthermore, the function of BK(Ca) channels are altered in both physiological and pathophysiological conditions, such as pregnancy, hypertension and diabetes, which has dramatic impacts on vascular tone and hemodynamics. Consequently, compounds and genetic manipulation that alter activity and expression of the channel might be of therapeutic interest.

Functional dissection of Nrf2-dependent phase II genes in vascular inflammation and endotoxic injury using Keap1 siRNA

Keap1 is a cytoplasmic repressor of the transcription factor Nrf2, and its degradation induces Nrf2 activation, leading to upregulation of antioxidant phase II genes. We investigated the roles of phase II genes in vascular inflammation and septic injury using Keap1 siRNA and elucidated its underlying mechanism. Selective knockdown of Keap1 with siRNA promoted Nrf2-dependent expression of phase II genes in endothelial cells, such as heme oxygenase-1 (HO-1), glutamate-cysteine ligase (GCL), and peroxiredoxin-1 (Prx1), resulting in the elevation of cellular glutathione levels and suppression of tumor necrosis factor (TNF)-α-induced intracellular H(2)O(2) accumulation. Keap1 knockdown inhibited TNF-α-induced expression of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) by suppressing NF-κB activation via inhibition of its upstream modulators, Akt, NIK, and IKK, resulting in the elevation of monocyte adhesion to endothelial cells. Importantly, these events were reversed by HO-1 and GCL inhibitors and Prx1-specific siRNA. Keap1 knockdown also inhibited endotoxin-induced expression of inducible nitric oxide synthase (iNOS) and TNF-α by upregulating HO-1, GCL, and Prx1 expression in macrophages. Moreover, in vivo Keap1 knockdown increased the expression of phase II genes and suppressed the expression of ICAM-1, VCAM-1, iNOS, and TNF-α in an endotoxemic mouse model, resulting in significant protection against liver and lung injuries and lethality. Our results indicate that Keap1 knockdown prevents NF-κB-mediated vascular inflammation and endotoxic shock by suppressing NF-κB-mediated inflammatory gene expression via upregulation of Nrf2-mediated antioxidant genes. Thus, siRNA targeting Keap1 may provide a new therapeutic approach for inflammation-associated vascular diseases and sepsis.

The endothelium: influencing vascular smooth muscle in many ways

The endothelium, although only a single layer of cells lining the vascular and lymphatic systems, contributes in multiple ways to vascular homeostasis. Subsequent to the 1980 report by Robert Furchgott and John Zawadzki, there has been a phenomenal increase in our knowledge concerning the signalling molecules and pathways that regulate endothelial - vascular smooth muscle communication. It is now recognised that the endothelium is not only an important source of nitric oxide (NO), but also numerous other signalling molecules, including the putative endothelium-derived hyperpolarizing factor (EDHF), prostacyclin (PGI(2)), and hydrogen peroxide (H(2)O(2)), which have both vasodilator and vasoconstrictor properties. In addition, the endothelium, either via transferred chemical mediators, such as NO and PGI(2), and (or) low-resistance electrical coupling through myoendothelial gap junctions, modulates flow-mediated vasodilatation as well as influencing mitogenic activity, platelet aggregation, and neutrophil adhesion. Disruption of endothelial function is an early indicator of the development of vascular disease, and thus an important area for further research and identification of potentially new therapeutic targets. This review focuses on the signalling pathways that regulate endothelial - vascular smooth muscle communication and the mechanisms that initiate endothelial dysfunction, particularly with respect to diabetic vascular disease.

Chronic tempol treatment attenuates the renal hemodynamic effects induced by a heme oxygenase inhibitor in streptozotocin diabetic rats

Heme oxygenase-1 (HO-1) is induced by oxidative stress and plays an important role in protecting the kidney from oxidant-mediated damage in the streptozotocin (STZ) rat model of type-1 diabetes mellitus (DM-1). HO-derived metabolites, presumably carbon monoxide (CO), mediate vasodilatory influences in the renal circulation, particularly in conditions linked to elevated HO-1 protein expression or diminished nitric oxide (NO) levels. We tested the hypothesis that diabetes increases oxidative stress and induces HO-1 protein expression, which contributes to regulate renal hemodynamics in conditions of low NO bioavailability. Two weeks after the induction of diabetes with STZ (65 mg/kg iv), Sprague-Dawley rats exhibited higher renal HO-1 protein expression, hyperglycemia, and elevated renal nitrotyrosine levels than control normoglycemic animals. In anesthetized diabetic rats, renal vascular resistance (RVR) was increased, and in vivo cortical NO levels were reduced ( P < 0.05) compared with control animals. Acute administration of the HO inhibitor Stannous mesoporphyrin (SnMP; 40 μmol/kg iv) did not alter renal hemodynamics in control rats, but greatly decreased glomerular filtration rate and renal blood flow, markedly increasing RVR in hyperglycemic diabetic rats. Chronic oral treatment with the SOD mimetic tempol prevented the elevation of nitrotyrosine, the HO-1 protein induction, and the increases in RVR induced by SnMP in the diabetic group, without altering basal NO concentrations or RVR. Increasing concentrations of a CO donor (CO-releasing molecule-A1) on pressurized renal interlobar arteries elicited a comparable relaxation in vessels taken from control or diabetic animals. These results suggest that oxidative stress-induced HO-1 exerts vasodilatory actions that partially maintain renal hemodynamics in uncontrolled DM-1.

Corpus cavernosal smooth muscle relaxation effect of a novel AMPK activator, beta-lapachone

INTRODUCTION

Adenosine monophosphate-activated protein kinase (AMPK) activation is suggested to relax smooth muscle by endothelial nitric oxide synthase (eNOS) phosphorylation.

AIM

To assess the mechanism and effect of a novel AMPK activator, beta-lapachone, upon cavernosal smooth muscle relaxation and the therapeutic potential for erectile dysfunction.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with beta-lapachone. The lysates were blotted with specific antibodies for phosphorylated AMPK (p-AMPK) or phosphorylated eNOS (p-eNOS). The membranes were re-blotted for total AMP total eNOS, or beta-actin. The eNOS activity was measured by the conversion of L-14C-arginine to L-14C-citrulline in HUVECs lysates. In a separated experiment, cavernosal strips from New Zealand white rabbits were harvested for organ bath study and the relaxation effect of beta-lapachone on phenylephrine-induced contracted strips was evaluated and compared with sodium nitroprusside, zaprinast, metformin, and aminoimidazole carboxamide ribonucleotide (AICAR). Methylene blue and L-NAME were used to assess the inhibition of cyclic guanosine monophosphate/nitric oxide pathway. Zinc-protoporphyrin-IX (ZnPP) was also used to investigate the contribution of mevalonate pathway.

MAIN OUTCOME MEASURES

The expression of p-AMPK, p-eNOS, AMPK and eNOS induced by beta-lapachone in HUVECs study and the percent relaxation of cavernosal tissue in organ bath study.

RESULTS

Beta-lapachone clearly induced AMPK phosphorylation and, as a consequence, eNOS phosphorylation in HUVECs. Beta-lapachone-induced upregulation of eNOS activity was also observed in HUVECs and steadily increased up to 1 hour. In organ bath study, beta-lapachone significantly relaxed the phenylephrine pretreated strips in a dose-dependent manner. This relaxation effect was not totally blocked by methylene blue or L-NAME. After removing endothelium, the relaxation was totally blocked by ZnPP.

CONCLUSIONS

A novel AMPK activator, beta-lapachone has a strong relaxation effect on precontracted cavernosal smooth muscle strips in the rabbit. And phosphorylation of AMPK and eNOS strongly related to the action of beta-lapachone. Mevalonate pathway also might be considered as a suggestive mechanism.

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Heme oxygenase: the key to renal function regulation

Heme oxygenase (HO) plays a critical role in attenuating the production of reactive oxygen species through its ability to degrade heme in an enzymatic process that leads to the production of equimolar amounts of carbon monoxide and biliverdin/bilirubin and the release of free iron. The present review examines the beneficial role of HO-1 (inducible form of HO) that is achieved by increased expression of this enzyme in renal tissue. The influence of the HO system on renal physiology, obesity, vascular dysfunction, and blood pressure regulation is reviewed, and the clinical potential of increased levels of HO-1 protein, HO activity, and HO-derived end products of heme degradation is discussed relative to renal disease. The use of pharmacological and genetic approaches to investigate the role of the HO system in the kidney is key to the development of therapeutic approaches to prevent the adverse effects that accrue due to an impairment in renal function.

Tricarbonyldichlororuthenium (II) dimer (CORM2) activates non-selective cation current in human endothelial cells independently of carbon monoxide releasing

Tricarbonyldichlororuthenium (II) dimer (CORM2) has been developed as carbon monoxide (CO) donor. We found that CORM2 activated a type of specific current which was distinct from the big-conductance Ca(2+)-activated K(+) current activated by CO in human umbilical vein endothelial cells (HUVECs). So the aim of the present study was to characterize the CORM2-induced current and to access the relation with CO releasing. CORM2 (100 microM) activated a kind of bi-directional current in HUVECs when the ramp protocol (holding potential 0 mV, from -120 mV to +120 mV) was applied. The current was not blocked by apamin, TRAM-34 and iberiotoxin, the small, intermediate and big-conductance Ca(2+) -activated K(+) channel blockers, and it was not sensitive to the pipette solution chelated with EGTA. CORM2 still activated the current when the chloride in the pipette solution was substituted by equal mol gluconic acid. Substitution of the sodium in the bath with choline significantly reduced the current activated by CORM2. The current was regarded as the non-selective cation current. The current showed slightly inward rectifier property and was not sensitive to Gd(3+) (100 microM), La(3+) (10 microM) or 2-aminoethoxydiphenyl borate (100 microM). CO (10 microM), CORM3 (100, 200 microM) and RuCl(3) (100 microM) were used as controls and showed no effect of the current activation. In conclusion, CORM2 activated the non-selective cation current in HUVECs independently of its CO releasing.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.

Functional and molecular evidence for impairment of calcium-activated potassium channels in type-1 diabetic cerebral artery smooth muscle cells

Cerebral vascular dysfunction and associated diseases often occur in type-1 diabetes, but the underlying mechanisms are largely unknown. In this study, we sought to determine whether big-conductance, Ca(2+)-activated K(+) (BK) channels were impaired in vascular (cerebral artery) smooth muscle cells (CASMCs) from streptozotocin-induced type-1 diabetic mice using patch clamp, molecular biologic, and genetic approaches. Our data indicate that the frequency and amplitude of spontaneous transient outward currents (STOCs) are significantly decreased, whereas the activity of spontaneous Ca(2+) sparks is increased, in diabetic CASMCs. The sensitivity of BK channels to voltage, Ca(2+), and the specific inhibitor iberiotoxin are all reduced in diabetic myocytes. Diabetic mice show increased myogenic tone and decreased contraction in response to iberiotoxin in cerebral arteries and elevated blood pressure. The expression of the BK channel beta1, but not alpha-subunit protein, is markedly decreased in diabetic cerebral arteries. Diabetic impairment of BK channel activity is lost in CASMCs from BK channel beta1-subunit gene deletion mice. In conclusion, the BK channel beta1-subunit is impaired in type-1 diabetic vascular SMCs, resulting in increased vasoconstriction and elevated blood pressure, thereby contributing to vascular diseases in type-1 diabetes.

Carbon monoxide stimulates the Ca2(+)-activated big conductance k channels in cultured human endothelial cells

We used the whole-cell patch-clamp technique to study K channels in the human umbilical vein endothelial cells and identified a 201 pS K channel, which was blocked by tetraethylammonium and iberiotoxin but not by TRAM34 and apamin. This suggests that the Ca(2+)-activated big-conductance K channel (BK) is expressed in endothelial cells. Application of carbon monoxide (CO) or tricarbonylchloro(glycinato)ruthenium(II), a water soluble CO donor, stimulated the BK channels. Moreover, application of hemin, a substrate of heme oxygenase, mimicked the effect of CO and increased the BK channel activity. The stimulatory effect of hemin was significantly diminished by tin mesoporphyrin, an inhibitor of heme oxygenase. To determine whether the stimulatory effect of CO on the BK channel was mediated by NO and the cGMP-dependent pathway, we examined the effect of CO on BK channels in cells treated with, N(G)-nitro-l-arginine methyl ester, 1H(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one, an inhibitor of soluble guanylate cyclase, or KT5823, an inhibitor of protein kinase G. Addition of either diethylamine NONOate or sodium nitroprusside significantly increased BK channel activity. Inhibition of endogenous NO synthesis with N(G)-nitro-l-arginine methyl ester, blocking soluble guanylate cyclase or protein kinase G, delayed but did not prevent the CO-induced activation of BK channels. Finally, application of an antioxidant agent, ebselen, had no effect on CO-mediated stimulation of BK channels in human umbilical vein endothelial cells. We conclude that BK channels are expressed in human umbilical vein endothelial cells and that they are activated by both CO and NO. CO activates BK channels directly, as well as via a mechanism involving NO or the cGMP-dependent pathway.

Accumulation of endogenous methylglyoxal impaired insulin signaling in adipose tissue of fructose-fed rats

Increased accumulation of methylglyoxal (MG) has been linked to different insulin resistance states including diabetes and hypertension. In this study, the effects of MG on insulin signaling pathway were investigated. Following 9 weeks of fructose treatment, an insulin resistance state was developed in Sprague-Dawley (SD) rats, demonstrated as increased triglyceride and insulin levels, high blood pressure, and decreased insulin-stimulated glucose uptake by adipose tissue. More importantly, we observed a close correlation between the development of insulin resistance and elevated MG level in serum and adipose tissue. Both insulin resistance state and the elevated MG level were reversed by the MG scavenger, N-acetyl cysteine (NAC). When 3T3-L1 adipocytes were treated directly with MG, the impaired insulin signaling was also observed, indicated by decreased insulin-induced insulin-receptor substrate-1 (IRS-1) tyrosine phosphorylation and the decreased kinase activity of phosphatidylinositol (PI) 3-kinase (PI3K). The ability of NAC to block MG-impairment of PI3K activity and IRS-1 phosphorylation further confirmed the role of MG in the development of insulin resistance. In conclusion, the increase in endogenous MG accumulation impairs insulin-signaling pathway and decreases insulin-stimulated glucose uptake in adipose tissue, which may contribute to the development of insulin resistance.

Carbon Monoxide: Endogenous Production, Physiological Functions, and Pharmacological Applications

Over the last decade, studies have unraveled many aspects of endogenous production and physiological functions of carbon monoxide (CO). The majority of endogenous CO is produced in a reaction catalyzed by the enzyme heme oxygenase (HO). Inducible HO (HO-1) and constitutive HO (HO-2) are mostly recognized for their roles in the oxidation of heme and production of CO and biliverdin, whereas the biological function of the third HO isoform, HO-3, is still unclear. The tissue type-specific distribution of these HO isoforms is largely linked to the specific biological actions of CO on different systems. CO functions as a signaling molecule in the neuronal system, involving the regulation of neurotransmitters and neuropeptide release, learning and memory, and odor response adaptation and many other neuronal activities. The vasorelaxant property and cardiac protection effect of CO have been documented. A plethora of studies have also shown the importance of the roles of CO in the immune, respiratory, reproductive, gastrointestinal, kidney, and liver systems. Our understanding of the cellular and molecular mechanisms that regulate the production and mediate the physiological actions of CO has greatly advanced. Many diseases, including neurodegenerations, hypertension, heart failure, and inflammation, have been linked to the abnormality in CO metabolism and function. Enhancement of endogenous CO production and direct delivery of exogenous CO have found their applications in many health research fields and clinical settings. Future studies will further clarify the gasotransmitter role of CO, provide insight into the pathogenic mechanisms of many CO abnormality-related diseases, and pave the way for innovative preventive and therapeutic strategies based on the physiologic effects of CO.

Impaired arachidonic acid-mediated activation of large-conductance Ca2+-activated K+ channels in coronary arterial smooth muscle cells in Zucker Diabetic Fatty rats

We studied the arachidonic acid (AA)-mediated modulation of large-conductance Ca2+-activated K+ (BK) channels in coronary arterial smooth myocytes from lean control and Zucker Diabetic Fatty (ZDF) rats. A total of 1 micromol/l AA enhanced BK current by 274% in lean and by 98% in ZDF rats. After incubation with 10 micromol/l indomethacin, 1 micromol/l AA increased BK currents by 80% in lean and by 70% in ZDF rats. Vasoreactivity studies showed that the dilation of small coronary arteries produced by 1 micromol/l AA was reduced by 44% in ZDF rats. [3H]6-keto-prostagladin F1alpha ([3H]6-keto-PGF1alpha,), the stable metabolite of prostacyclin (PGI2), was the major [3H]AA metabolite produced by coronary arteries of lean vessels, but ZDF vessels produced only 15% as much [3H]6-keto-PGF1alpha. BK channel activation and vasorelaxation by iloprost were similar in lean and ZDF rats. Immunoblots showed a 73% reduction in PGI2 synthase (PGIS) expression in ZDF vessels compared with lean vessels, and there was no change in cyclooxygenase (COX) and BK channel expressions. Real-time PCR studies showed that mRNA levels of PGIS, COX-1, and COX-2 were similar between lean and ZDF vessels. We conclude that PGI2 is the major AA metabolite in lean coronaries, and AA-mediated BK channel activation is impaired in ZDF coronaries due to reduced PGIS activity.

Overexpression of human heme oxygenase-1 attenuates endothelial cell sloughing in experimental diabetes

Heme oxygenase (HO)-1 represents a key defense mechanism against oxidative injury. Hyperglycemia produces oxidative stress and various perturbations of cell physiology. The effect of streptozotocin (STZ)-induced diabetes on aortic HO activity, heme content, the number of circulating endothelial cells, and urinary 8-epi-isoprostane PGF2alpha (8-Epi) levels in control rats and rats overexpressing or underexpressing HO-1 was measured. HO activity was decreased in hyperglycemic rats. Hyperglycemia increased urinary 8-Epi, and this increase was augmented in rats underexpressing HO-1 and diminished in rats overexpressing HO-1. The number of detached endothelial cells and O2- formation increased in diabetic rats and in hyperglycemic animals underexpressing HO-1 and decreased in diabetic animals overexpressing HO-1 compared with controls. These data demonstrate that HO-1 gene transfer in hyperglycemic rats brings about a reduction in O2- production and a decrease in endothelial cell sloughing. Upregulation of HO-1 decreases oxidant production and endothelial cell damage and shedding and may attenuate vascular complications in diabetes.

Dietary approach to attenuate oxidative stress, hypertension, and inflammation in the cardiovascular system

Imbalance between production and scavenging of superoxide anion results in hypertension by the inactivation of nitric oxide, and the increased oxidative stress from the resultant peroxynitrite that is produced promotes inflammatory processes such as atherosclerosis. Induction of phase 2 proteins promotes oxidant scavenging. We hypothesized that intake of dietary phase 2 protein inducers would ameliorate both hypertension and atherosclerotic changes in the spontaneously hypertensive stroke-prone rat. For 5 days/week for 14 weeks, we fed rats 200 mg/day of dried broccoli sprouts that contained glucoraphanin, which is metabolized into the phase 2 protein-inducer sulforaphane (Group A), sprouts in which most of the glucoraphanin was destroyed (Group B), or no sprouts (Group C). After 14 weeks of treatment, no significant differences were seen between rats in Groups B and C. Rats in Group A had significantly decreased oxidative stress in cardiovascular and kidney tissues, as shown by increased glutathione (GSH) content and decreased oxidized GSH, decreased protein nitrosylation, as well as increased GSH reductase and GSH peroxidase activities. Decreased oxidative stress correlated with better endothelial-dependent relaxation of the aorta and significantly lower (20 mm Hg) blood pressure. Tissues from Groups B and C had considerable numbers of infiltrating activated macrophages, indicative of inflammation, whereas animals in Group A had few detectable infiltrating macrophages. There is interest in dietary phase 2 protein inducers as means of reducing cancer incidence. We conclude that a diet containing phase 2 protein inducers also reduces the risk of developing cardiovascular problems of hypertension and atherosclerosis.

Heme oxygenase-1 prevents superoxide anion-associated endothelial cell sloughing in diabetic rats

Heme oxygenase-1 (HO-1) represents a key defense mechanism against oxidative injury. Hyperglycemia has been linked to increased oxidative stress, leading to endothelial dysfunction, delayed cell replication, and enhanced apoptosis. The effect of streptozotocin (STZ)-induced diabetes on HO activity, HO-1 promoter activity, superoxide anion (O*-2, and the number of circulating endothelial cells was measured. The expression of HO-1/HO-2 protein was unchanged, but HO activity was decreased in aortas of diabetic rats compared with control (p < 0.05). High glucose decreased HO-1 promoter activity (p < 0.05). Hyperglycemia increased O*-2 and this increase was augmented with HO-1 inhibition and diminished with HO-1 upregulation (p < 0.05). Circulating endothelial cells were significantly higher in diabetic rats and were decreased or increased with administration of the HO-1 inducer (CoPP) or inhibitor (SnMP), respectively (p<0.05). In conclusion, HO-1 upregulation in diabetic rats brings about an increase in serum bilirubin, a reduction in O*-2 production, and a decrease in endothelial cell sloughing.

Interaction of selective amino acid residues of K(ca) channels with carbon monoxide

The activation of big-conductance K(Ca) channels in vascular smooth muscle cells by carbon monoxide (CO) has been demonstrated previously. One specific target of CO on K(Ca) channel proteins is the histidine residue. The roles of other amino acid residues on the functionality of K(Ca) channels, as well as their reactions to CO, have been unclear. In the present study, the cell-free single channel recording technique was used to investigate the chemical modification of K(Ca) channels by CO and other chemical agents. The modification of negatively charged carboxyl groups and the epsilon -amino group of lysine did not affect the open probability, but decreased single-channel conductance of K(Ca) channels. When sulfhydryl groups of cysteine were modified with N-ethylmaleimide, the open probability of K(Ca) channels was decreased, but single-channel conductance was not affected. None of the above chemical modifications affected the CO-induced increase in the open probability of K(Ca) channels. However, N-ethylmaleimide treatment reduced the stimulatory effect of nitric oxide (NO) on K(Ca) channels. Finally, pretreatment of smooth muscle cells with NO abolished the effects of subsequently applied CO on K(Ca) channel proteins. Our study demonstrates that CO and NO acted on different amino acid residues of K(Ca) channel proteins. The interaction of CO and NO determines the functional status of K(Ca) channels in vascular smooth muscle cells

Selective regulation of blood pressure by heme oxygenase-1 in hypertension

Heme oxygenase (HO) and carbon monoxide (CO) participate in the homeostatic control of cardiovascular functions, including the regulation of blood pressure (BP). Upregulation of the HO/CO system has been shown to lower BP in young (8 weeks) but not in adult (20 weeks) spontaneously hypertensive rats (SHR). The underlying mechanism for this selective effect, however, has been unknown and was investigated in the present study. The administration of hemin resulted in a marked decrease in BP (from 148.6+/-3.2 to 125.8+/-2.6 mm Hg, P<0.01) in young but not in prehypertensive (4 weeks) or adult SHR or Wistar-Kyoto rats at all ages. The inhibition of HO with chromium mesoporphyrin abrogated the BP-lowering effect of hemin. Significantly lower expression levels of HO-1 and soluble gyanylyl cyclase (sGC) as well as reduced cGMP content were detected in 8-week SHR but not in adult SHR or Wistar-Kyoto rats of all ages. These deficiencies were all corrected by hemin treatment. The expression of HO-2 protein was not different among all animal groups tested and not affected by hemin treatment. Desensitization of the sGC/cGMP pathway in adult SHR was demonstrated by the reduced vasorelaxant potency of the sGC activator 3-(5' -hydroxymethyl-2-'furyl)-1-benzylindazole. Thus, in young and prehypertensive SHR, a defective HO/CO-sGC/cGMP system might constitute a pathogenic mechanism for the development of hypertension. The HO/CO-sGC/cGMP system appears normal in adult SHR, but desensitization of the downstream targets of the system to sGC/cGMP may endow SHR at this stage a persistent hypertension status.

Carbon monoxide and bile pigments: surprising mediators of vascular function

Heme oxygenase (HO) catalyzes the degradation of heme to CO, iron, and biliverdin. Biliverdin is subsequently metabolized to bilirubin by the enzyme biliverdin reductase. Although long considered irrelevant byproducts of heme catabolism, recent studies indicate that CO and the bile pigments biliverdin and bilirubin may play an important physiological role in the circulation. The release of CO by vascular cells may modulate blood flow and blood fluidity by inhibiting vasomotor tone, smooth muscle cell proliferation, and platelet aggregation. CO may also maintain the integrity of the vessel wall by directly blocking vascular cell apoptosis and by inhibiting the release of pro-apoptotic inflammatory cytokines from the vessel wall. These effects of CO are mediated via multiple pathways, including activation of soluble guanylate cyclase, potassium channels, p38 mitogen-activated protein kinase, or inhibition of cytochrome P450. In addition, the release of bile pigments may serve to sustain vascular homeostasis by protecting vascular cells from oxidative stress and by inhibiting the adhesion and infiltration of leukocytes into the vessel wall. Induction of HO-1 gene expression and the subsequent release of CO and bile pigments are observed in numerous vascular disorders and may provide an important adaptive mechanism to preserve homeostasis at sites of vascular injury. Thus, the HO-catalyzed formation of CO and bile pigments by vascular cells may function as a critical endogenous vasoprotective system. Moreover, pharmacological or genetic approaches targeting HO-1 to the vessel wall may represent a novel therapeutic approach in treating vascular disease.

The impaired glutathione system and its up-regulation by sulforaphane in vascular smooth muscle cells from spontaneously hypertensive rats

The glutathione (GSH) system plays an important role in reducing oxidative stress, the increase of which has been linked to the pathogenesis of hypertension. The aims of this study were to investigate: (1) whether the GSH system was impaired in aortic smooth muscle cells (SMCs) from spontaneously hypertensive rats (SHR), and (2) whether this system could be up-regulated by the phase-2 enzyme inducers, sulforaphane and t-butylhydroquinone (t-BHQ). Basal levels of cellular GSH, GSH-reductase and GSH-peroxidase were significantly lower in SMCs from SHR than from normotensive Wistar-Kyoto (WKY) rats. Heme oxygenase-1 (HO-1) was significantly higher in SHR SMCs, which correlated with the higher oxidative stress experienced by these cells. No differences were observed in the basal activity of GSH-S-transferase nor in the ability to synthesize GSH between SMCs from these two strains. Sulforaphane (0.05-1 micromol/l) and t-BHQ (10-100 micromol/l) induced significant and concentration-dependent increases in cellular GSH levels, HO-1 protein content and activities of GSH-reductase and GSH-peroxidase in SMCs from both rat strains. Upregulation of phase 2 enzymes correlated with a decrease in oxidative stress experienced by the SMCs, particularly with SHR. We conclude that SHR SMCs experience greater oxidative stress than WKY SMCs and that malfunction of the GSH system contributes to the enhanced oxidative stress in SHR SMCs.