Glucose-induced changes in Na+/H+ antiport activity and gene expression in cultured vascular smooth muscle cells. Role of protein kinase C

Inhibition of c-MYC-miRNA 19 Pathway Sensitized CML K562 Cells to Etoposide via NHE1 Upregulation

As a previously discovered target of DNA damage, Na⁺/H⁺ exchanger 1 (NHE1) plays a role in regulation of intracellular pH (pH_i) through the extrusion of intracellular proton (H⁺) in exchange for extracellular sodium (Na⁺). Its abnormal expression and dysfunction have been reported in solid tumor and hematopoietic malignancies. Here, we reported that suppression of NHE1 in BCR-ABL⁺ hematopoietic malignancies' K562 cells treated with Etoposide was manipulated by miR-19 and c-MYC. Inhibition of miR-19 or c-MYC enhanced the expression of NHE1 and sensitized K562 cells to Etoposide in vitro. The in vivo nude mouse transplantation model was also performed to confirm the enhanced sensitivity of K562 cells to Etoposide by inhibiting the miR-19 or c-MYC pathway. TCGA analysis conferred a negative correlation between miR-19 level and leukemia patients' survival. Thus, our results provided a potential management by which the c-MYC-miRNA 19 pathway might have a crucial impact on sensitizing K562 cells to Etoposide in the therapeutic approaches.

Dysregulated Erythroid Mg2+ Efflux in Type 2 Diabetes

Hyperglycemia is associated with decreased Mg²⁺ content in red blood cells (RBC), but mechanisms remain unclear. We characterized the regulation of Mg²⁺ efflux by glucose in ex vivo human RBC. We observed that hemoglobin A_1C (HbA_1C) values correlated with Na⁺-dependent Mg²⁺ efflux (Na⁺/Mg²⁺ exchange) and inversely correlated with cellular Mg content. Treatment of cells with 50 mM D-glucose, but not with sorbitol, lowered total cellular Mg (2.2 ± 0.1 to 2.0 ± 0.1 mM, p < 0.01) and enhanced Na⁺/Mg²⁺ exchange activity [0.60 ± 0.09 to 1.12 ± 0.09 mmol/10¹³ cell × h (flux units, FU), p < 0.05]. In contrast, incubation with selective Src family kinase inhibitors PP2 or SU6656 reduced glucose-stimulated exchange activation (p < 0.01). Na⁺/Mg²⁺ exchange activity was also higher in RBC from individuals with type 2 diabetes (T2D, 1.19 ± 0.13 FU) than from non-diabetic individuals (0.58 ± 0.05 FU, p < 0.01). Increased Na⁺/Mg²⁺ exchange activity in RBC from T2D subjects was associated with lower intracellular Mg content. Similarly increased exchange activity was evident in RBC from the diabetic db/db mouse model as compared to its non-diabetic control (p < 0.03). Extracellular exposure of intact RBC from T2D subjects to recombinant peptidyl-N-glycosidase F (PNGase F) reduced Na⁺/Mg²⁺ exchange activity from 0.98 ± 0.14 to 0.59 ± 0.13 FU (p < 0.05) and increased baseline intracellular Mg content (1.8 ± 0.1 mM) to normal values (2.1 ± 0.1 mM, p < 0.05). These data suggest that the reduced RBC Mg content of T2D RBC reflects enhanced RBC Na⁺/Mg²⁺ exchange subject to regulation by Src family kinases and by the N-glycosylation state of one or more membrane proteins. The data extend our understanding of dysregulated RBC Mg²⁺ homeostasis in T2D.

Alterations of sodium-hydrogen exchanger 1 function in response to SGLT2 inhibitors: what is the evidence?

This review summarizes and describes the current evidence addressing how sodium-glucose cotransporter 2 (SGLT2) inhibitors alter the function of sodium-hydrogen exchanger 1 (NHE-1), in association with their protective effects against adverse cardiovascular events. In the heart, SGLT2 inhibitors modulate the function of NHE-1 (either by direct inhibition or indirect attenuation of protein expression), which promotes cardiac contraction and an enhanced energy supply, in association with improved mitochondrial function, reduced inflammation/oxidative/endoplasmic reticulum stress, and attenuated fibrosis and apoptotic/autophagic cell death. The vasodilating effect of SGLT2 inhibitors has also been proposed due to NHE-1 inhibition. Moreover, platelet-expressed NHE-1 might serve as a target for SGLT2 inhibitors, since these drugs and selective NHE-1 inhibitors produce comparable activity against adenosine diphosphate-stimulated platelet activation. Overall, it is promising that the modulation of the functions of NHE-1 on the heart, blood vessels, and platelets may act as a contributing pathway for the cardiovascular benefits of SGLT2 inhibitors in diabetes and heart failure.

Towards an Integral Therapeutic Protocol for Breast Cancer Based upon the New H+-Centered Anticancer Paradigm of the Late Post-Warburg Era

A brand new approach to the understanding of breast cancer (BC) is urgently needed. In this contribution, the etiology, pathogenesis, and treatment of this disease is approached from the new pH-centric anticancer paradigm. Only this unitarian perspective, based upon the hydrogen ion (H+) dynamics of cancer, allows for the understanding and integration of the many dualisms, confusions, and paradoxes of the disease. The new H+-related, wide-ranging model can embrace, from a unique perspective, the many aspects of the disease and, at the same time, therapeutically interfere with most, if not all, of the hallmarks of cancer known to date. The pH-related armamentarium available for the treatment of BC reviewed here may be beneficial for all types and stages of the disease. In this vein, we have attempted a megasynthesis of traditional and new knowledge in the different areas of breast cancer research and treatment based upon the wide-ranging approach afforded by the hydrogen ion dynamics of cancer. The concerted utilization of the pH-related drugs that are available nowadays for the treatment of breast cancer is advanced.

Another Consequence of the Warburg Effect? Metabolic Regulation of Na+/H+ Exchangers May Link Aerobic Glycolysis to Cell Growth

To adjust cell growth and proliferation to changing environmental conditions or developmental requirements, cells have evolved a remarkable network of signaling cascades that integrates cues from cellular metabolism, growth factor availability and a large variety of stresses. In these networks, cellular information flow is mostly mediated by posttranslational modifications, most notably phosphorylation, or signaling molecules such as GTPases. Yet, a large body of evidence also implicates cytosolic pH (pHc) as a highly conserved cellular signal driving cell growth and proliferation, suggesting that pH-dependent protonation of specific proteins also regulates cellular signaling. In mammalian cells, pHc is regulated by growth factor derived signals and responds to metabolic cues in response to glucose stimulation. Importantly, high pHc has also been identified as a hall mark of cancer, but mechanisms of pH regulation in cancer are only poorly understood. Here, we discuss potential mechanisms of pH regulation with emphasis on metabolic signals regulating pHc by Na⁺/H⁺-exchangers. We hypothesize that elevated NHE activity and pHc in cancer are a direct consequence of the metabolic adaptations in tumor cells including enhanced aerobic glycolysis, generally referred to as the Warburg effect. This hypothesis not only provides an explanation for the growth advantage conferred by a switch to aerobic glycolysis beyond providing precursors for accumulation of biomass, but also suggests that treatments targeting pH regulation as a potential anti-cancer therapy may effectively target the result of altered tumor cell metabolism.

A New and Integral Approach to the Etiopathogenesis and Treatment of Breast Cancer Based upon Its Hydrogen Ion Dynamics

Despite all efforts, the treatment of breast cancer (BC) cannot be considered to be a success story. The advances in surgery, chemotherapy and radiotherapy have not been sufficient at all. Indeed, the accumulated experience clearly indicates that new perspectives and non-main stream approaches are needed to better characterize the etiopathogenesis and treatment of this disease. This contribution deals with how the new pH-centric anticancer paradigm plays a fundamental role in reaching a more integral understanding of the etiology, pathogenesis, and treatment of this multifactorial disease. For the first time, the armamentarium available for the treatment of the different types and phases of BC is approached here from a Unitarian perspective-based upon the hydrogen ion dynamics of cancer. The wide-ranged pH-related molecular, biochemical and metabolic model is able to embrace most of the fields and subfields of breast cancer etiopathogenesis and treatment. This single and integrated approach allows advancing towards a unidirectional, concerted and synergistic program of treatment. Further efforts in this line are likely to first improve the therapeutics of each subtype of this tumor and every individual patient in every phase of the disease.

Exacerbated brain edema in a rat streptozotocin model of hyperglycemic ischemic stroke: Evidence for involvement of blood-brain barrier Na-K-Cl cotransport and Na/H exchange

Cerebral edema is exacerbated in diabetic ischemic stroke through poorly understood mechanisms. We showed previously that blood-brain barrier (BBB) Na-K-Cl cotransport (NKCC) and Na/H exchange (NHE) are major contributors to edema formation in normoglycemic ischemic stroke. Here, we investigated whether hyperglycemia-exacerbated edema involves changes in BBB NKCC and NHE expression and/or activity and whether inhibition of NKCC or NHE effectively reduces edema and injury in a type I diabetic model of hyperglycemic stroke. Cerebral microvascular endothelial cell (CMEC) NKCC and NHE abundances and activities were determined by Western blot, radioisotopic flux and microspectrofluorometric methods. Cerebral edema and Na in rats subjected to middle cerebral artery occlusion (MCAO) were assessed by nuclear magnetic resonance methods. Hyperglycemia exposures of 1-7d significantly increased CMEC NKCC and NHE abundance and activity. Subsequent exposure to ischemic factors caused more robust increases in NKCC and NHE activities than in normoglycemic CMEC. MCAO-induced edema and brain Na uptake were greater in hyperglycemic rats. Intravenous bumetanide and HOE-642 significantly attenuated edema, brain Na uptake and ischemic injury. Our findings provide evidence that BBB NKCC and NHE contribute to increased edema in hyperglycemic stroke, suggesting that these Na transporters are promising therapeutic targets for reducing damage in diabetic stroke.

The Role of Sodium in Diabetic Cardiomyopathy

Cardiovascular complications are the major cause of mortality and morbidity in diabetic patients. The changes in myocardial structure and function associated with diabetes are collectively called diabetic cardiomyopathy. Numerous molecular mechanisms have been proposed that could contribute to the development of diabetic cardiomyopathy and have been studied in various animal models of type 1 or type 2 diabetes. The current review focuses on the role of sodium (Na⁺) in diabetic cardiomyopathy and provides unique data on the linkage between Na⁺ flux and energy metabolism, studied with non-invasive ²³Na, and ³¹P-NMR spectroscopy, polarography, and mass spectroscopy. ²³Na NMR studies allow determination of the intracellular and extracellular Na⁺ pools by splitting the total Na⁺ peak into two resonances after the addition of a shift reagent to the perfusate. Using this technology, we found that intracellular Na⁺ is approximately two times higher in diabetic cardiomyocytes than in control possibly due to combined changes in the activity of Na⁺–K⁺ pump, Na⁺/H⁺ exchanger 1 (NHE1) and Na⁺-glucose cotransporter. We hypothesized that the increase in Na⁺ activates the mitochondrial membrane Na⁺/Ca²⁺ exchanger, which leads to a loss of intramitochondrial Ca²⁺, with a subsequent alteration in mitochondrial bioenergetics and function. Using isolated mitochondria, we showed that the addition of Na⁺ (1–10 mM) led to a dose-dependent decrease in oxidative phosphorylation and that this effect was reversed by providing extramitochondrial Ca²⁺ or by inhibiting the mitochondrial Na⁺/Ca²⁺ exchanger with diltiazem. Similar experiments with ³¹P-NMR in isolated superfused mitochondria embedded in agarose beads showed that Na⁺ (3–30 mM) led to significantly decreased ATP levels and that this effect was stronger in diabetic rats. These data suggest that in diabetic cardiomyocytes, increased Na⁺ leads to abnormalities in oxidative phosphorylation and a subsequent decrease in ATP levels. In support of these data, using ³¹P-NMR, we showed that the baseline β-ATP and phosphocreatine (PCr) were lower in diabetic cardiomyocytes than in control, suggesting that diabetic cardiomyocytes have depressed bioenergetic function. Thus, both altered intracellular Na⁺ levels and bioenergetics and their interactions may significantly contribute to the pathology of diabetic cardiomyopathy.

Intracellular acidosis via activation of Akt-Girdin signaling promotes post ischemic angiogenesis during hyperglycemia

AIMS

The impaired angiogenesis is the major cause of diabetic delayed wound healing. The molecular insight remains unknown. Previous study has shown that high glucose (HG) activates Na⁺/H⁺ exchanger 1 (NHE1) and induces intracellular alkalinization, resulting in endothelial dysfunction. The aim of this study is to investigate whether activation of NHE1 in endothelial cells by HG damages the angiogenesis in vitro and in vivo.

METHODS AND RESULTS

We used western blot to detect the phosphorylations of both Akt and Girdin, and pH-sensitive BCECF fluorescence to assay NHE1 activity and pHi value, respectively. The angiogenesis was evaluated by measuring the number of tube formation in vitro, and blood perfusion by laser doppler and neovascularization by staining CD31 in vivo. Our results indicated that induction of intracellular acidosis (IA) increased p-Akt and p-Girdin in human umbilical vein endothelial cells (HUVEC). HG activated NHE1 and increased pHi value in a time-dependent manner, associated with the decreased phosphorylations of both Akt and Gridin, while inhibition of NHE1 by amiloride abolished the HG-induced reductions of p-Akt and p-Girdin. However, silence of Akt by siRNA transfection or pharmacological inhibitors (wortmannin and LY294002) bypassed IA-induced Girdin phosphorylation. Overexpression of constitutively active Akt abolished HG-reduced Girdin phosphorylation. In addition, upregulation of Akt or inhibition of NHE1 remarkably attenuated HG-impaired tube formation in HUVEC. In vivo study revealed that amiloride dramatically rescued hyperglycemia-delayed blood perfusion and neovascularization by augmenting ischemia-induced angiogenesis.

CONCLUSION

IA promotes ischemia-induced angiogenesis via Akt-dependent Girdin phosphorylation in diabetic mice.

Cellular acidification as a new approach to cancer treatment and to the understanding and therapeutics of neurodegenerative diseases

During the last few years, the understanding of the dysregulated hydrogen ion dynamics and reversed proton gradient of cancer cells has resulted in a new and integral pH-centric paradigm in oncology, a translational model embracing from cancer etiopathogenesis to treatment. The abnormalities of intracellular alkalinization along with extracellular acidification of all types of solid tumors and leukemic cells have never been described in any other disease and now appear to be a specific hallmark of malignancy. As a consequence of this intracellular acid-base homeostatic failure, the attempt to induce cellular acidification using proton transport inhibitors and other intracellular acidifiers of different origins is becoming a new therapeutic concept and selective target of cancer treatment, both as a metabolic mediator of apoptosis and in the overcoming of multiple drug resistance (MDR). Importantly, there is increasing data showing that different ion channels contribute to mediate significant aspects of cancer pH regulation and etiopathogenesis. Finally, we discuss the extension of this new pH-centric oncological paradigm into the opposite metabolic and homeostatic acid-base situation found in human neurodegenerative diseases (HNDDs), which opens novel concepts in the prevention and treatment of HNDDs through the utilization of a cohort of neural and non-neural derived hormones and human growth factors.

Simulated diabetic ketoacidosis therapy in vitro elicits brain cell swelling via sodium-hydrogen exchange and anion transport

A common complication of type 1 diabetes mellitus is diabetic ketoacidosis (DKA), a state of severe insulin deficiency. A potentially harmful consequence of DKA therapy in children is cerebral edema (DKA-CE); however, the mechanisms of therapy-induced DKA-CE are unknown. Our aims were to identify the DKA treatment factors and membrane mechanisms that might contribute specifically to brain cell swelling. To this end, DKA was induced in juvenile mice with the administration of the pancreatic toxins streptozocin and alloxan. Brain slices were prepared and exposed to DKA-like conditions in vitro. Cell volume changes were imaged in response to simulated DKA therapy. Our experiments showed that cell swelling was elicited with isolated DKA treatment components, including alkalinization, insulin/alkalinization, and rapid reductions in osmolality. Methyl-isobutyl-amiloride, a nonselective inhibitor of sodium-hydrogen exchangers (NHEs), reduced cell swelling in brain slices elicited with simulated DKA therapy (in vitro) and decreased brain water content in juvenile DKA mice administered insulin and rehydration therapy (in vivo). Specific pharmacological inhibition of the NHE1 isoform with cariporide also inhibited cell swelling, but only in the presence of the anion transport (AT) inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid. DKA did not alter brain NHE1 isoform expression, suggesting that the cell swelling attributed to the NHE1 was activity dependent. In conclusion, our data raise the possibility that brain cell swelling can be elicited by DKA treatment factors and that it is mediated by NHEs and/or coactivation of NHE1 and AT.

Resistance to cancer chemotherapy: failure in drug response from ADME to P-gp

Cancer chemotherapy resistance (MDR) is the innate and/or acquired ability of cancer cells to evade the effects of chemotherapeutics and is one of the most pressing major dilemmas in cancer therapy. Chemotherapy resistance can arise due to several host or tumor-related factors. However, most current research is focused on tumor-specific factors and specifically genes that handle expression of pumps that efflux accumulated drugs inside malignantly transformed types of cells. In this work, we suggest a wider and alternative perspective that sets the stage for a future platform in modifying drug resistance with respect to the treatment of cancer.

Metabolic alterations induce oxidative stress in diabetic and failing hearts: different pathways, same outcome

SIGNIFICANCE

Several authors have proposed a link between altered cardiac energy substrate metabolism and reactive oxygen species (ROS) generation. A cogent evidence of this association has been found in diabetic cardiomyopathy (dCM); however, experimental findings in animal models of heart failure (HF) and in human myocardium also seem to support the coexistence of the two alterations in HF.

CRITICAL ISSUES

Two important questions remain open: whether pathological changes in metabolism play an important role in enhancing oxidative stress and whether there is a common pathway linking altered substrate utilization and activation of ROS-generating enzymes, independently of the underlying cardiac pathology. In this regard, the comparison between dCM and HF is intriguing, in that these pathological conditions display very different cardiac metabolic phenotypes.

RECENT ADVANCES

Our literature review on this topic indicates that a vast body of knowledge is now available documenting the relationship between the metabolism of energy substrates and ROS generation in dCM. In some cases, biochemical mechanisms have been identified. On the other hand, only a few and relatively recent studies have explored this phenomenon in HF and their conclusions are not consistent.

FUTURE DIRECTIONS

Better methods of investigation, especially in vivo, will be necessary to test whether the metabolic fate of certain substrates is causally linked to ROS production. If successful, these studies will place a new emphasis on the potential clinical relevance of metabolic modulators, which might indirectly mitigate cardiac oxidative stress in dCM, HF, and, possibly, in other pathological conditions.

Blood-brain barrier Na transporters in ischemic stroke

Blood-brain barrier (BBB) endothelial cells form a barrier that is highly restrictive to passage of solutes between blood and brain. Many BBB transport mechanisms have been described that mediate transcellular movement of solutes across the barrier either into or out of the brain. One class of BBB transporters that is all too often overlooked is that of the ion transporters. The BBB has a rich array of ion transporters and channels that carry Na, K, Cl, HCO3, Ca, and other ions. Many of these are asymmetrically distributed between the luminal and abluminal membranes, giving BBB endothelial cells the ability to perform vectorial transport of ions across the barrier between blood and brain. In this manner, the BBB performs the important function of regulating the volume and composition of brain interstitial fluid. Through functional coupling of luminal and abluminal transporters and channels, the BBB carries Na, Cl, and other ions from blood into brain, producing up to 30% of brain interstitial fluid in healthy brain. During ischemic stroke cerebral edema forms by processes involving increased activity of BBB luminal Na transporters, resulting in "hypersecretion" of Na, Cl, and water into the brain interstitium. This review discusses the roles of luminal BBB Na transporters in edema formation in stroke, with an emphasis on Na-K-Cl cotransport and Na/H exchange. Evidence that these transporters provide effective therapeutic targets for reduction of edema in stroke is also discussed, as are recent findings regarding signaling pathways responsible for ischemia stimulation of the BBB Na transporters.

Production of reactive oxygen species in the diabetic heart. Roles of mitochondria and NADPH oxidase

Reactive oxygen species (ROS) are the main facilitators of cardiovascular complications in diabetes mellitus (DM), and the ROS level is increased in cultured cells exposed to high glucose concentrations or in diabetic animal models. Emerging evidence shows that mitochondria and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase are dominant mechanisms of ROS production in the diabetic heart. Hyperpolarization of the mitochondrial inner membrane potentials and impaired mitochondrial function promote ROS production in the mitochondria of the diabetic heart. Uncoupling proteins are upregulated and may reduce the ROS level by depolarizing the mitochondrial inner membrane potential. NADPH oxidase is another major site of ROS production and its contribution to DM-induced ROS increase has been elucidated not only in vascular smooth muscle cells and endothelial cells, but also in cardiomyocytes. Protein kinase C, angiotensin II, and advanced glycation endproducts (AGEs)/receptor for AGEs can activate NADPH oxidase. Increased intracellular calcium level mediated via the Na(+)-H(+) exchanger and subsequent activation of Ca(2+)/calmodulin-dependent protein kinase II may also activate NADPH oxidase. This review presents the current understanding of the mechanisms of ROS production, focusing especially on the roles of mitochondria and NADPH oxidase. 

Protein Kinase C Inhibitors as Modulators of Vascular Function and their Application in Vascular Disease

Blood pressure (BP) is regulated by multiple neuronal, hormonal, renal and vascular control mechanisms. Changes in signaling mechanisms in the endothelium, vascular smooth muscle (VSM) and extracellular matrix cause alterations in vascular tone and blood vessel remodeling and may lead to persistent increases in vascular resistance and hypertension (HTN). In VSM, activation of surface receptors by vasoconstrictor stimuli causes an increase in intracellular free Ca(2+) concentration ([Ca(2+)]i), which forms a complex with calmodulin, activates myosin light chain (MLC) kinase and leads to MLC phosphorylation, actin-myosin interaction and VSM contraction. Vasoconstrictor agonists could also increase the production of diacylglycerol which activates protein kinase C (PKC). PKC is a family of Ca(2+)-dependent and Ca(2+)-independent isozymes that have different distributions in various blood vessels, and undergo translocation from the cytosol to the plasma membrane, cytoskeleton or the nucleus during cell activation. In VSM, PKC translocation to the cell surface may trigger a cascade of biochemical events leading to activation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK), a pathway that ultimately increases the myofilament force sensitivity to [Ca(2+)]i, and enhances actin-myosin interaction and VSM contraction. PKC translocation to the nucleus may induce transactivation of various genes and promote VSM growth and proliferation. PKC could also affect endothelium-derived relaxing and contracting factors as well as matrix metalloproteinase (MMPs) in the extracellular matrix further affecting vascular reactivity and remodeling. In addition to vasoactive factors, reactive oxygen species, inflammatory cytokines and other metabolic factors could affect PKC activity. Increased PKC expression and activity have been observed in vascular disease and in certain forms of experimental and human HTN. Targeting of vascular PKC using PKC inhibitors may function in concert with antioxidants, MMP inhibitors and cytokine antagonists to reduce VSM hyperactivity in certain forms of HTN that do not respond to Ca(2+) channel blockers.

Evolution of Tumor Metabolism might Reflect Carcinogenesis as a Reverse Evolution process (Dismantling of Multicellularity)

Carcinogenesis occurs through a series of steps from normal into benign and finally malignant phenotype. This cancer evolutionary trajectory has been accompanied by similar metabolic transformation from normal metabolism into Pasteur and/or Crabtree-Effects into Warburg-Effect and finally Cannibalism and/or Lactate-Symbiosis. Due to lactate production as an end-product of glycolysis, tumor colonies acquire new phenotypes that rely on lactate as energetic fuel. Presence of Warburg-Effect indicates that some tumor cells undergo partial (if not complete) de-endosymbiosis and so cancer cells have been become unicellular microorganism (anti-Dollo's Law) specially when they evolve to develop cannibalism as way of metabolism while oxidative types of cells that rely on lactate, as their energetic fuel, might represent extra-endosymbiosis. Thus, at the end, the cancer colony could be considered as integrated metabolic ecosystem. Proper understanding of tumor metabolism will contribute to discover potential anticancer agents besides conventional chemotherapy.

The vasorelaxant effect of hydrogen sulfide is enhanced in streptozotocin-induced diabetic rats

Hydrogen sulfide (H₂S) is an endogenous gas which has potent relaxant effect in vascular and nonvascular smooth muscles. In the present study, we have investigated how streptozotocin (STZ)-induced diabetes affected the relaxant effect of H₂S in rat isolated thoracic aorta and mesenteric and pulmonary arteries. Diabetes was induced by IV injection of STZ (35 mg/kg). Insulin treatment was applied by using insulin implants. At the end of 4 and 12 weeks, the thoracic aorta and mesenteric and pulmonary arteries were isolated, and the relaxation responses to sodium hydrogen sulfide (NaHS), diazoxide, and acetylcholine were evaluated. The mRNA and protein levels of H₂S-synthesizing enzymes were also examined by RT-PCR and Western Blot. The relaxation response to NaHS in the arteries isolated from both 4 and 12 week-diabetic rats was increased when compared with that obtained from the control group. Glibenclamide inhibited the relaxation response to NaHS in the arteries isolated from either diabetic or non-diabetic group of rats. Concurrent treatment of insulin to STZ-injected rats prevented the potentiation of the relaxant effect of NaHS in the arteries. However, acetylcholine and diazoxide-induced relaxation responses were not altered in diabetic group of rats. The mRNA and protein levels of H₂S-synthesizing enzymes were also not altered in diabetic rats. STZ-induced experimental diabetes in rats resulted in the potentiation of the relaxation response to H₂S in vascular tissues. The potentiated relaxation to H₂S in diabetic arteries may play a role in vascular complications frequently seen in severe diabetes.

Protein kinase C upregulates intercellular adhesion molecule-1 and leukocyte-endothelium interactions in hyperglycemia via activation of endothelial expressed calpain

OBJECTIVE

We tested the hypothesis of a role for the calcium-dependent protease calpain in the endothelial dysfunction induced by hyperglycemic activation of protein kinase C (PKC).

METHODS AND RESULTS

Chronic hyperglycemia with insulin deficiency (type 1 diabetes) was induced in rats by streptozotocin. Total PKC and calpain activities, along with activity and expression level of the 2 endothelial-expressed calpains isoforms, μ- and m-calpain, were measured in vascular tissue homogenates by enzymatic assays and Western blot analysis, respectively. Intravital microscopy was used to measure and correlate leukocyte-endothelium interactions with calpain activity in the microcirculation. Expression levels and endothelial localization of the inflammatory adhesion molecule intercellular adhesion molecule-1 were studied by Western blot analysis and immunofluorescence, respectively. The mechanistic role of hyperglycemia alone in the process of PKC-induced calpain activation and actions was also investigated. We found that in the type 1 diabetic vasculature, PKC selectively upregulates the activity of the μ-calpain isoform. Mechanistic studies confirmed a role for hyperglycemia and PKCβ in this process. The functional implications of PKC-induced calpain activation were upregulation of endothelial expressed intercellular adhesion molecule-1 and leukocyte-endothelium interactions.

CONCLUSIONS

Our results uncover the role of μ-calpain in the endothelial dysfunction of PKC. Calpain may represent a novel molecular target for the treatment of PKC-associated diabetic vascular disease.

NA+/H+ Exchanger 1-and Aquaporin-1-Dependent Hyperosmolarity Changes Decrease Nitric Oxide Production and Induce VCAM-1 Expression in Endothelial Cells Exposed to High Glucose

Since diabetic hyperglycaemia causes hyperosmolarity, we investigated the contribution of hyperosmolarity in the proinflammatory endothelial effects of hyperglycemia, and sought to unravel the mechanisms involved. Human aortic endothelial cells (HAEC) were incubated for short-term (1–3 days) or long-term (1–2 weeks) exposures to 5.5 mmol/L glucose (normoglycemia, basal), high glucose (25 and 45 mmol/L, HG), or a hyperosmolar control (mannitol 25 and 45 mmol/L, HM), in the presence or absence of the aquaporin-1 (AQP1) inihibitor dimethylsulfoxide (DMSO), the Na+/H+ exchanger 1 (NHE-1) inihibitor cariporide (CA), the protein kinase C (PKC) inihibitor calphostin C or the PKCβ isoform inhibitor LY379196 (LY). Both short- and long-term exposures to HG and HM decreased the expression of the active, phosphorylated form of endothelial nitric oxide synthase (Ser1146-eNOS) and, in parallel, increased vascular cell adhesion molecule(VCAM)-1 protein at immunoblotting. After 24 h incubation with HG/HM, we observed a significant similar and concentration-dependent enhancement of AQP1 expression. DMSO and CA inhibited hyperosmolarity-induced VCAM-1 expressions, while increasing nitrite levels and Ser1146-eNOS expression. Gene silencing by small interfering RNA reduced the expression of AQP1, and suppressed HG- and HM-stimulated VCAM-1 expression. Calphostin C and LY blunted hyperosmolarity-induced VCAM-1 expression, while increasing the expression of Ser1146-eNOS and nitrite production. Thus HG decreases eNOS activation and induces total VCAM-1 expression in HAEC through a hyperosmolar mechanism. These effects are mediated by activation of the water channels AQP1 and NHE-1, and a PKCβ-mediated intracellular signaling pathway. Targeting osmosignaling pathways may represent a novel strategy to reduce vascular effects of hyperglycemia.

Na+/H+ exchanger is required for hyperglycaemia-induced endothelial dysfunction via calcium-dependent calpain

AIMS

Recent studies have reported that the calcium-dependent protease calpain is involved in hyperglycaemia-induced endothelial dysfunction and that the Na(+)/H(+) exchanger (NHE) is responsible for an increase in the intracellular calcium (Ca(2+)(i)) concentration in diabetes. We hypothesized that activation of NHE mediates hyperglycaemia-induced endothelial dysfunction via calcium-dependent calpain.

METHODS AND RESULTS

Exposure of human umbilical vein endothelial cells (HUVECs) to high glucose (HG, 30 mM d-glucose) time dependently increased both the Ca(2+)(i) concentration and calpain activity. Chelation of free Ca(2+)(i) with 1,2-bis (2-aminophenoxy) ethane-N, N, N',N'-tetraacetic acid abolished the HG-increased calpain activity. In addition, HG activated NHE in a time-dependent manner, but cariporide, an NHE inhibitor, blocked the HG-induced increase in NHE activity. Furthermore, cariporide or NHE siRNA (small interfering ribonucleic acid) attenuated the HG-induced increases of both Ca(2+)(i) concentration and calpain activity. All of these HG-induced effects in HUVECs, including decreased endothelial nitric oxide synthase (eNOS) activity and NO (nitric oxide) production and increased dissociation of heat shock protein (hsp90) from eNOS, were NHE or calpain reversible. In vivo experiments showed that cariporide treatment via inhibition of NHE activity significantly attenuated the hyperglycaemia-induced impairment of acetylcholine-induced endothelium-dependent relaxation in streptozotocin-injected diabetic rats.

CONCLUSION

Activation of NHE via calcium-dependent calpain contributes to hyperglycaemia-induced endothelial dysfunction through dissociation of hsp90 from eNOS.

Acute hyperglycaemia disturbs cardiac repolarization in Type 1 diabetes

AIMS

Patients with Type 1 diabetes have an increased risk of cardiovascular mortality. Notably, a prolonged heart rate adjusted QT interval (QTc) is a predictor of sudden cardiovascular death. Therefore, the objectives of this study were to investigate whether acute hyperglycaemia affects the QTc duration and the QTc dispersion in patients with Type 1 diabetes and in healthy volunteers.

METHODS

Acute hyperglycaemia (15 mmol/l) for 120 min was induced in 35 males (22 men with Type 1 diabetes and 13 age-matched non-diabetic volunteers). All participants were non-smokers without any diabetic complications. Electrocardiogram recordings were performed at normoglycaemia and at 0, 60 and 120 min of hyperglycaemia.

RESULTS

Compared with normoglycaemia, acute hyperglycaemia increased the QTc interval in both patients with Type 1 diabetes (390 +/- 6 vs. 415 +/- 5 ms, P < 0.001) and in healthy volunteers (378 +/- 5 vs. 412 +/- 8 ms, P < 0.01). During hyperglycaemia, the QTc dispersion was prolonged in healthy volunteers (36 +/- 4 ms vs. 54 +/- 7 ms, P < 0.05) but not in patients with Type 1 diabetes (45 +/- 3 ms at baseline vs. 48 +/- 5 ms, NS).

CONCLUSIONS

Acute hyperglycaemia alters myocardial ventricular repolarization in patients with Type 1 diabetes and in healthy volunteers and might consequently be an additional risk factor for cardiovascular events.

Role of endothelin-1, sodium hydrogen exchanger-1 and mitogen activated protein kinase (MAPK) activation in glucose-induced cardiomyocyte hypertrophy

BACKGROUND

Cardiac hypertrophy is a key structural feature of diabetic cardiomyopathy. Previous studies have shown that diabetes-induced endothelin-1 (ET-1) and sodium hydrogen exchanger-1 (NHE-1) mediate structural and functional deficits in the heart. In order to gain a mechanistic understanding of the role of ET-1 and NHE-1 in cardiomyocyte hypertrophy, we have utilized an in vitro endothelial-myocyte co-culture system to reveal cellular interactions that may arbitrate cardiomyocyte deficits in diabetes.

METHODS AND RESULTS

Rat ventricular cardiomyocytes were cultured in high glucose levels, which caused cellular hypertrophy. Hypertrophic markers, atrial natruritic peptide (ANP) and angiotensinogen (Agt), as well as inducible nitric oxide synthase (iNOS) were upregulated by high glucose. Treatment of cells with ET antagonist bosentan and NHE-1 inhibitor cariporide prevented glucose-induced cardiomyocyte hypertrophy and expression of ANP, Agt, and iNOS. Bosentan and cariporide treatment of cardiomyocytes co-cultured with endothelial cells produced a more pronounced normalization of glucose-induced changes as compared to cardiomyocyte cultured alone. To further explore the signaling mechanisms involved, we investigated the mitogen activated protein kinase (MAPK) pathway and its cross-interaction with signaling proteins known to be altered in diabetes. Our results indicate that MAPK activation is associated with cardiomyocyte hypertrophy and is inhibited by bosentan, cariporide, as well as protein kinase C inhibiton. Furthermore, MAPK activation was found to be upstream of the transcription factors, nuclear factor-kappaB and activating protein-1.

CONCLUSION

These results demonstrate that ET-1 and NHE-1 may mediate cardiomyocyte hypertrophy via MAPK activation and provide an insight into the pathogenesis of diabetic cardiomyopathy.

Cariporide inhibits high glucose-mediated adhesion of monocyte–endothelial cell and expression of intercellular adhesion molecule-1

The aim of this study was to examine whether cariporide, a new inhibitor of Na(+)/H(+) exchanger 1 (NHE-1), may inhibit high glucose-induced monocyte-endothelial cell adhesion and the expression of intercellular adhesion molecule-1 (ICAM-1). Cultured endothelial cells were incubated with normal glucose control (5.5 mM), cariporide control (5.5 mM glucose plus 10 microM cariporide), hyperosmolarity (5.5 mM glucose plus 16.5 mM mannitol), high glucose (HG, 22 mM), low-concentration cariporide (22 mM glucose plus 0.1 microM cariporide), medium-concentration cariporide (22 mM glucose plus 1 muM cariporide), and high-concentration cariporide (22 mM glucose plus 10 microM cariporide) for 24 h. Monocytes were isolated from peripheral human blood. Adhered monocytes were quantified by measuring their protein content. ICAM-1 expression and NHE-1 activity was determined with enzyme-linked immunosorbent assay (ELISA) and pH-sensitive fluorescent spectrophotometry. Exposure of endothelial cells to HG for 24 h caused an increase of adhesion of monocytes to endothelial cells and an increased expression of ICAM-1. However, these effects were reversed by treatment with cariporide (0.1, 1, 10 microM) in a concentration-dependent manner. Furthermore, cariporide (1 microM) was able to inhibit the activation of NHE-1 induced by HG in endothelial cells. These findings suggest that cariporide might inhibit HG-mediated monocyte-endothelial cell adhesion and expression of ICAM-1 by inhibiting the activation of NHE-1.

Apelin stimulates myosin light chain phosphorylation in vascular smooth muscle cells

OBJECTIVE

Physiological roles of apelin and its specific receptor APJ signaling were investigated in vascular smooth muscle cells (VSMCs). The present study determined whether apelin activates myosin light chain (MLC), a major regulatory event in initiating smooth muscle contraction.

METHODS AND RESULTS

To assess MLC activation, we performed Western blot and immunohistochemical studies using an antibody against the phospho-MLC. In VSMCs, apelin induces the phosphorylation of MLC in a concentration-dependent manner with a peak at 2 minutes. Pretreatment of VSMCs with pertussis toxin abolishes the apelin-induced phosphorylation of MLC. Inhibition of protein kinase C (PKC) with GF-109203X markedly attenuated the apelin-induced MLC phosphorylation. In addition, methylisobutyl amiloride, a specific inhibitor of the Na+/H+ exchanger (NHE), and KB-R7943, a potent inhibitor for the reverse mode of the Na+/Ca2+ exchanger (NCX), significantly suppressed the action of apelin. In wild-type mice, apelin phosphorylates MLC in vascular tissue, whereas it had no response in APJ-deficient mice by Western blot and immunohistochemistry. Apelin-induced phosphorylation of MLC was accompanied with myosin phosphatase target subunit phosphorylation.

CONCLUSIONS

These results provide the first evidence to our knowledge for apelin-mediated MLC phosphorylation in vitro and in vivo, which is a potential mechanism of apelin-mediated vasoconstriction.

Diabetes induces Na/H exchange activity and hypertrophy of rat mesenteric but not basilar arteries

Experimental hyperglycemia produces a marked hypertrophic response in rat mesenteric arteries, accompanied by activation of Na/H exchange (NHE) in medial smooth muscle. This study asked if other vascular beds are similarly affected by examining the hypertrophic and NHE response of the basilar artery. Sections of mesenteric and basilar arteries from adult rats were analysed by standard morphometric techniques at 1 and 3 weeks after streptozotocin injection. NHE activity was assessed as changes in intracellular pH in isolated intact vessels using concurrent myography and fluorescence spectroscopy. Mesenteric arteries showed a significant increase in lumenal (47%), medial (51%) and adventitial (17%) area. In contrast, these parameters were not increased in basilar arteries from the same set of animals. Maximal NHE activity was significantly increased at 1 week (24%) and 3 weeks (20%) in mesenteric arteries, but in basilar arteries there was no change in basal intracellular pH, maximal NHE activity or kinetic properties of the transporter. NHE plays a central role in vascular changes in diabetes. As the mesenteric hypertrophy is amenable to therapeutic intervention these findings add further to the potential of NHE as a therapeutic target for ameliorating vascular disease in diabetes.

M40403 prevents myocardial injury induced by acute hyperglycaemia in perfused rat heart

M40403 is a low-molecular-weight, synthetic manganese-containing biscyclohexylpyridine superoxide dismutase mimetic (SODm) that removes superoxide anions (O(2)(-)) without interfering with other reactive species known to be involved in cardiovascular alterations (e.g. nitric oxide [NO] and peroxynitrite [ONOO(-)]). As such, M40403 represents an important pharmacological tool to dissect the roles of O(2)(-) in functional and biochemical cardiovascular alterations induced by perfusion of high glucose concentrations into the heart. Perfusion of a high glucose concentration of glucose into the heart elicited important cardiovascular alterations characterized by QT interval prolongation, increase in coronary perfusion pressure (CPP), lipid peroxidation, decrease in MnSOD activity and DNA damage. All parameters of cardiovascular alteration were attenuated by M40403 (1-10 mg/l). Furthermore, perfusion of a high of glucose concentration induced a significant formation of nitrotyrosine as well as an activation of poly(adenosine diphosphate [ADP]-ribose) synthetase (PARS), as determined by immunohistochemical analysis of heart tissue. The extent of staining for nitrotyrosine and PARS was reduced by M40403. These results clearly indicate that O(2)(-) plays a critical role in the development of the functional and biochemical cardiovascular alterations induced by perfusion of a high concentration of glucose into the heart. Therefore, synthetic enzymes of SOD, such as M40403, offer a novel therapeutic approach for the management of various cardiovascular diseases where these radicals have been postulated to play a role.

Na+/H+ Exchanger Inhibitor Prevented Endothelial Dysfunction Induced by High Glucose

The aims of this study were to examine whether cariporide, a selective Na+/H+ exchanger inhibitor, has protective effects against endothelial dysfunction induced by high glucose in vitro and to investigate the potential mechanisms. Exposure of rat aorta rings to high glucose (44 mmol/L) for 6 hours caused an inhibition of acetylcholine-induced endothelium-dependent relaxation but had no effect on sodium nitroprusside-induced endothelium-independent relaxation. Treatment with cariporide (0.01, 0.1, 1 micromol/L) of aortic rings incubated with high-glucose medium attenuated the impaired endothelium-dependent relaxation in a dose-dependent manner. Furthermore, high glucose resulted in an increase of malondialdehyde and a decrease of superoxide dismutase activity in rat aorta rings, and these effects were reversed by cariporide. In addition, cariporide was able to inhibit the activation of Na+/H+ exchanger induced by high glucose in cultured endothelial cells. These findings suggest that the endothelial dysfunction induced by high glucose in vitro is caused by the activation of Na+/H+ exchanger.

Protective effects of cariporide on endothelial dysfunction induced by high glucose

AIM

To explore the effects of cariporide, a selective sodium-hydrogen antiporter inhibitor, on endothelial dysfunction induced by high glucose.

METHODS

Acetylcholine (ACh)-induced endothelium-dependent relaxation (EDR), sodium nitroprusside (SNP)-induced endothelium-independent relaxation and biochemical parameters including malondialdehyde (MDA), superoxide dismutase (SOD), and nitric oxide (NO) were measured in rat isolated aorta.

RESULTS

A 6-h incubation of aortic rings with high glucose (44 mmol/L) resulted in a significant inhibition of EDR, but had no effects on endothelium-independent relaxation. After the 6-h incubation of aortic rings in the co-presence of cariporide (0.01, 0.1, and 1 micromol/L) with high glucose, cariporide prevented the inhibition of EDR caused by high glucose in concentration-dependent manners. Similarly, high glucose decreased SOD activity and contents of NO, and increased MDA concentration in aortic tissue. Cariporide (1 micromol/L) significantly resisted the decrease of NO content and SOD activity, and elevation of MDA concentration caused by high glucose in aortic tissues. Mannitol (44 mmol/L) or cariporide (1 micromol/L) alone had no effect on EDR, endothelium-independent relaxation and biochemical parameters.

CONCLUSION

Cariporide significantly prevented endothelial dysfunction induced by high glucose. The mechanisms of endothelial dysfunction induced by high glucose may involve the activation of sodium-hydrogen antiporter and the generation of oxygen-free radicals, but it is not related to the change of osmolarity.

Ascites from patients with encapsulating peritoneal sclerosis augments NIH/3T3 fibroblast proliferation

Encapsulating peritoneal sclerosis (EPS) remains one of the major causes of dropout in continuous ambulatory peritoneal dialysis by reducing ultrafiltration capacity. To demonstrate whether ascites from patients with EPS (EPS ascites) has fibroblast proliferation activity, we used NIH/3T3 fibroblasts to examine the effects of EPS ascites on fibroblast proliferation activity by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Encapsulating peritoneal sclerosis ascites dose-dependently augmented NIH/3T3 fibroblast proliferation. The protein kinase C inhibitors and the tyrosine kinase inhibitors partially inhibited the stimulatory effects of EPS ascites on fibroblast proliferation activity. In EPS ascites, levels of interleukin (IL)-1beta, IL-6, IL-8, transforming growth factor (TGF)-beta1, hepatocyte growth factor (HGF), and platelet-derived growth factor (PDGF)-AB were elevated. The treatment with IL-1beta, HGF, TGF-beta1, and PDGF-AB alone or in combination at similar concentrations to those in EPS ascites exhibited small but significant fibroblast proliferation activities. We conclude that EPS ascites stimulate NIH/3T3 fibroblast proliferation via protein kinase C and tyrosine kinase. The elevated cytokine and growth factors partly contribute to the EPS ascites-induced fibroblast proliferation.

Contributions of endothelin-1 and sodium hydrogen exchanger-1 in the diabetic myocardium

BACKGROUND

Endothelin-1 (ET-1) and sodium hydrogen exchanger-1 (NHE-1) are important mediators of several disease processes affecting the heart, especially relating to myocardial ischemia. There is evidence that their actions may be interrelated. Their contributions to diabetic heart disease have not been extensively documented. Accordingly, the aim of this study was to investigate the interactive roles of ET-1 and NHE-1 in the pathogenesis of diabetic cardiomyopathy, a significant cause of morbidity in diabetic patients.

METHODS

Streptozotocin-induced diabetic Sprague Dawley rats were treated with NHE-1 blocker cariporide or dual ET(A)/ET(B) blocker bosentan and were subsequently studied one, three and six months after induction of diabetes. These animals were compared with nondiabetic rats as well as with diabetic rats on poor blood glucose control.

RESULTS

Diabetes leads to hyperglycemia, reduced body weight gain and increased glycated hemoglobin levels. These animals exhibited focal myocardial fibrosis and increased ejection fraction, in association with a tendency to increased left ventricular wall thickness and heart weight, after six months of follow-up, both bosentan and cariporide prevented these responses. Diabetes also caused significant increases in ET-1 mRNA and protein expression in the heart at all time points, which was further augmented by cariporide treatment for three months. Diabetes did not affect either mRNA or protein expression of NHE-1, although these did decrease in hearts of diabetic animals treated with bosentan for six months.

CONCLUSIONS

These results indicate an important contribution of both ET-1 and NHE-1 in the pathogenesis of diabetic cardiomyopathy. These data suggest that NHE-1 may act as a downstream mediator in the production of ET-induced functional and structural changes in the myocardium in diabetes.

Na+ effects on mitochondrial respiration and oxidative phosphorylation in diabetic hearts

Intracellular Na+ is approximately two times higher in diabetic cardiomyocytes than in control. We hypothesized that the increase in Na+i activates the mitochondrial membrane Na+/Ca2+ exchanger, which leads to loss of intramitochondrial Ca2+, with a subsequent alteration (generally depression) in bioenergetic function. To further evaluate this hypothesis, mitochondria were isolated from hearts of control and streptozotocin-induced (4 weeks) diabetic rats. Respiratory function and ATP synthesis were studied using routine polarography and 31P-NMR methods, respectively. While addition of Na+ (1-10 mM) decreased State 3 respiration and rate of oxidative phosphorylation in both diabetic and control mitochondria, the decreases were significantly greater for diabetic than for control. The Na+ effect was reversed by providing different levels of extramitochondrial Ca2+ (larger Ca2+ levels were needed to reverse the Na+ depressant effect in diabetes mellitus than in control) and by inhibiting the Na+/Ca2+ exchanger function with diltiazem (a specific blocker of Na+/Ca2+ exchange that prevents Ca2+ from leaving the mitochondrial matrix). On the other hand, the Na+ depressant effect was enhanced by Ruthenium Red (RR, a blocker of mitochondrial Ca2+ uptake, which decreases intramitochondrial Ca2+). The RR effect on Na+ depression of mitochondrial bioenergetic function was larger in diabetic than control. These findings suggest that intramitochondrial Ca2+ levels could be lower in diabetic than control and that the Na+ depressant effect has some relation to lowered intramitochondrial Ca2+. Conjoint experiments with 31P-NMR in isolated superfused mitochondria embedded in agarose beads showed that Na+ (3-30 mM) led to significantly decreased ATP levels in diabetic rats, but produced smaller changes in control. These data support our hypothesis that in diabetic cardiomyocytes, increased Na+ leads to abnormalities of oxidative processes and subsequent decrease in ATP levels, and that these changes are related to Na+ induced depletion of intramitochondrial Ca2+.

Hyperglycemia and the O-GlcNAc transferase in rat aortic smooth muscle cells: elevated expression and altered patterns of O-GlcNAcylation

Hyperglycemia leads to vascular disease specific to diabetes mellitus. This pathology, which results from abnormal proliferation of smooth muscle cells in arterial walls, may lead to cataract, renal failure, and atherosclerosis. The hexosamine biosynthetic pathway is exquisitely responsive to glucose concentration and plays an important role in glucose-induced insulin resistance. UDP-GlcNAc: polypeptide O-N-acetylglucosaminyltransferase (O-GlcNAc transferase; OGTase) catalyzes the O-linked attachment of single GlcNAc moieties to serine and threonine residues on many cytosolic or nuclear proteins. Polyclonal antibody against OGTase was used to examine the expression of OGTase in rat aorta and aortic smooth muscle (RASM) cells. OGTase enzymatic activity and expression at the mRNA and protein levels were determined in RASM cells cultured at normal (5 mM) and at high (20 mM) glucose concentrations. OGTase mRNA and protein are expressed in both endothelial cells and smooth muscle cells in the aorta of normal rats. In both cell types, the nucleus is intensely stained, while the cytoplasm stains diffusely. Immunoelectron microscopy shows that OGTase is localized to euchromatin and around the myofilaments of smooth muscle cells. In RASM cells grown in 5 mM glucose, OGTase is also located mainly in the nucleus. Hyperglycemic RASM cells also display a relative increase in OGTase's p78 subunit and an overall increase protein and activity for OGTase. Biochemical analyses show that hyperglycemia qualitatively and quantitatively alters the glycosylation or expression of many O-GlcNAc-modified proteins in the nucleus. These results suggest that the abnormal O-GlcNAc modification of intracellular proteins may be involved in glucose toxicity to vascular tissues.

Troglitazone, but not rosiglitazone, inhibits Na/H exchange activity and proliferation of macrovascular endothelial cells

Diabetes is associated with a high level of mortality due to cardiovascular disease resulting from accelerated coronary artery atherosclerosis. A current focus for investigation of atherosclerotic mechanisms is the vascular endothelium since physical or functional injury may represent an initiating step for atherogenesis. Thiazolidinediones (TZDs) are the newest class of drugs for the treatment of insulin resistance and its metabolic consequences; they are peroxisome proliferator-activating receptor (PPAR)-gamma ligands that act as insulin-sensitizing agents. We are interested in the contribution of direct vascular actions to the clinical utility of these agents. We investigated the effect troglitazone and rosiglitazone on endothelial cell proliferation in low- and high-glucose media and further explored their action on the ubiquitous membrane transport system, the Na/H exchanger (NHE), which has been implicated in regulating the growth of vascular cells. Experiments were conducted in cultured bovine aortic endothelial cells (BAECs). Cell proliferation was assessed by cell counting, and NHE activity was determined in cells loaded with the pH-sensitive fluorescent dye, 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF-AM). Troglitazone caused a dose-dependent inhibition of endothelial cell proliferation with approximately 50% inhibition at 10 microM. Troglitazone inhibited endothelial cell proliferation with similar potency under low- (5 mM) and high-glucose (25 mM) concentrations. Rosiglitazone had no significant effect on endothelial cell proliferation at concentrations of up to 100 microM under low- or high-glucose concentrations. The NHE inhibitor, 3-metlylsulfonyl-4-piperidinobenzoyl guanidine (HOE 694), caused dose dependent inhibition of BAEC proliferation, which was independent of the media glucose concentration. Acute exposure of cells to troglitazone (10 microM) and rosiglitazone (30 microM) during recovery from acidosis showed slight but significant (P<.05) inhibition of NHE activity by troglitazone, but no significant (P>.05) effect by rosiglitazone. Exposure of cells to either drug for 24 h revealed no chronic regulation of NHE activity. Our data demonstrate that troglitazone has similar actions in endothelial cells as in vascular smooth muscle. The absence of rosiglitazone effects, a more potent PPAR-gamma activator, suggests that the observed actions of troglitazone may be at least partially independent of PPAR-gamma. The effects of troglitazone and rosiglitazone on endothelial cell proliferation and NHE activity, although contrasting, are consistent with a central signalling role of this transporter in cell proliferation.

Regulation of B(2)-kinin receptors by glucose in vascular smooth muscle cells

The development of vascular disease is accelerated in hyperglycemic states. Vascular injury plays a pivotal role in the progression of atherosclerotic vascular disease in diabetes, which is characterized by increased vascular smooth muscle cell (VSMC) proliferation and extracellular matrix accumulation. We previously reported that diabetes alters the activity of the kallikrein-kinin system and results in the upregulation of kinin receptors in the vessel wall. To determine whether glucose can directly influence the regulation of kinin receptors, the independent effect of high glucose (25 mM) on B(2)-kinin receptors (B2KR) in VSMC was examined. A threefold increase in B2KR protein levels and a 40% increase in B2KR surface receptors were observed after treatment with high glucose after 24 h. The mRNA levels of B2KR were also significantly increased by high glucose as early as 4 h later. To elucidate the cellular mechanisms by which glucose regulates B2KR, we examined the role of protein kinase C (PKC). High glucose increased total PKC activity and resulted in the translocation of conventional PKC isoforms (beta(1) and beta(2)), novel (epsilon), and atypical (zeta) PKC isoforms into the membrane. Inhibition of PKC activity prevented the increase in B2KR levels induced by ambient high glucose. These findings provide the first evidence that glucose regulates the expression of B(2) receptors in VSMC and provide a rationale to further study the interaction between glucose and kinins on the pathogenesis of atherosclerotic vascular disease in diabetes.

Diabetes-induced vascular hypertrophy is accompanied by activation of Na(+)-H(+) exchange and prevented by Na(+)-H(+) exchange inhibition

Vascular disease often involves vessel hypertrophy with underlying cellular hypertrophy or hyperplasia. Experimental diabetes stimulates hypertrophy of the rat mesenteric vasculature, and we investigated the hypothesis that this hypertrophy is associated with activation of Na(+)-H(+) exchange (NHE) activity. We measured the NHE activity in isolated, intact blood vessels from control and streptozotocin-induced diabetic adult rats using concurrent myography and fluorescence spectroscopy. The role of inhibiting NHE activity in preventing the development of the mesenteric hypertrophy in streptozotocin-diabetic rats was investigated by administration of cariporide (100 mg/kg body weight per day in 3 doses by gavage) after induction of diabetes and subsequently determining vessel weight and structure. The weight of the mesenteric vasculature was not increased 1 week after streptozotocin treatment but was significantly increased by an average of 56% at 3 weeks. NHE activity in mesenteric arteries showed an enhanced maximal velocity (V:(max)) in diabetic vessels at 1 and 3 weeks (0.246+/-0.006 and 0. 238+/-0.007 versus 0.198+/-0.007 pH U/min) with no change in the apparent K:(m). Moreover, NHE-1 mRNA in mesenteric arterioles at 3 weeks after streptozotocin treatment was increased by >60% (55.8+/-6. 4 versus 91.3+/-12.3 fg). Administration of cariporide significantly reduced mesenteric vascular weight, the wall/lumen ratio, and mesenteric extracellular matrix accumulation in the diabetic animals. Our study shows that diabetes in vivo correlates with elevated NHE activity and mRNA in the mesenteric vasculature and furthermore that inhibition of this system prevents the hypertrophic response. These data suggest that NHE may be a target for therapeutic modulation of vascular changes in diabetes.

Hyperglycemia inhibits vascular smooth muscle cell apoptosis through a protein kinase C-dependent pathway

We hypothesized that the pathogenesis of diabetic vasculopathy involves the abnormal regulation of vascular smooth muscle cell (VSMC) apoptosis. In nondiabetic mice, a reduction in carotid artery blood flow resulted in a significant loss of medial VSMCs via apoptosis (normal flow 84+/-1 viable VSMCs, reduced flow 70+/-5 viable VSMCs; n=12, P:<0.01). In contrast, flow-induced VSMC apoptosis was markedly attenuated in streptozotocin-induced diabetic mice (normal flow 85+/-2 viable VSMC, reduced flow 82+/-4 viable VSMC; n=13, NS). In accord with our in vivo findings, the exposure of cultured rat and human VSMCs to high glucose (17.5 mmol/L) significantly attenuated the induction of apoptosis in response to serum withdrawal (rat VSMCs in normal [5.5 mmol/L] glucose 28+/-1%, high D-glucose 19+/-2%; P:<0.0001). High glucose also inhibited apoptosis induced by Fas ligand (100 ng/mL) (normal 23+/-2%, high D-glucose 13+/-2%; P:<0.006). Supplementation with the nonmetabolized enantiomer L-glucose had no effect. We confirmed reports that high glucose activates protein kinase C (PKC) and demonstrated that PKC blockade with long-term phorbol ester treatment or calphostin C prevented the antiapoptotic effect (P:<0. 001). Moreover, the upregulation of either PKCalpha or PKCbetaII expression was sufficient to inhibit serum withdrawal-induced apoptosis (control 25+/-2%, PKCalpha 11+/-2%, PKCbetaII 8+/-2%; P:<0. 0001), whereas the upregulation of PKCdelta had no significant effect. Taken together, these findings demonstrate that hyperglycemia inhibits VSMC apoptosis via a PKC-dependent pathway.

High glucose induces the activity and expression of Na(+)/H(+) exchange in glomerular mesangial cells

Changes in activity or expression of transporters may account for alterations in cell behavior in diabetes. We sought to ascertain if mesangial cells (MC) grown in different glucose concentrations exhibit changes in activity and expression of acid-extruding transporters, the Na(+)/H(+) and Na(+)-dependent Cl(-)/HCO(-)(3) exchanger. pH(i) was determined by the use of the fluorescent pH-sensitive dye BCECF. In MCs grown in 5 mM glucose (control), the Na(+)/H(+) exchanger was responsible for 31.8 +/- 5.1% of steady-state pH(i), whereas Na(+)-dependent Cl(-)/HCO(-)(3) contributed 62.9 +/- 4.0% (n = 11). In MCs grown in high glucose for 2 wk, Na(+)/H(+) exchange contribution to acid-extrusion increased as follows: 42.3 +/- 4.6% [n = 8, 10 mM, not significant (NS)], 51.1 +/- 5.1% (n = 8, 20 mM, P < 0.01), and 64.8 +/- 5.5% (n = 7, 30 mM, P < 0.001). The Na(+)-dependent Cl(-)/HCO(-)(3) exchanger contributed less [47.0 +/- 4.6, 38.6 +/- 5.8, and 21.1 +/- 3.8%, for 10, 20, and 30 mM glucose, respectively (n > 7)]. We sought to ascertain if the magnitude of the acute stimulated response to ANG II by the Na(+)/H(+) and Na(+)-dependent Cl(-)/HCO(-)(3) exchanger is changed. Na(+)/H(+) exchanger (1.89-fold increase in 30 vs. 5 mM, P < 0.002), but not Na(+)-dependent Cl(-)/HCO(-)(3) exchange (0. 17-fold, NS), exhibited an enhanced response to ANG II (1 microM). Na(+)/H(+) exchange (NHE1) expression was significantly different (1. 72-fold) after prolonged exposure to high glucose. These results suggest that the Na(+)/H(+) exchanger, but not Na(+)-dependent Cl(-)/HCO(-)(3) exchanger, may play an early role in the response to hyperglycemia in the diabetic state.

Differential expression of protein kinase C isoforms in streptozotocin-induced diabetic rats

BACKGROUND

The cellular effects of hyperglycemia are mediated by protein kinase C (PKC). However, PKC consists of several distinct isoforms, and their contribution to the pathogenesis of diabetic complications in different organs is not clear. We investigated the expression and translocation of PKC isoforms alpha, betaI, betaII, delta, epsilon, and zeta in kidney, heart, and aorta from diabetic rats.

METHODS

Hyperglycemia was induced with streptozotocin (70 mg/kg) in the rat. After four weeks, PKC isoform expression was assessed by Western blot after tissue fractionation and by immunohistochemistry.

RESULTS

Streptozotocin increased blood glucose from 117.0 +/- 3.6 to 510.0 +/- 19.4 mg/dl (N = 8, P < 0.01) and induced albuminuria. PKC isoforms alpha, beta, delta, epsilon, and zeta were all detected in control animals. Western blot showed increased PKC alpha expression in kidney and heart (160% and 170%, respectively). PKC betaI, betaII, and delta expression was not influenced by hyperglycemia. PKC zeta was decreased in diabetic animals in both tissues by 60%. The membrane association of PKC alpha and PKC epsilon was increased; however, the relative amount of PKC in the particulate fraction was not influenced by hyperglycemia. Immunohistochemistry revealed a marked increase in PKC alpha immunoreactivity in renal glomeruli and interstitial capillaries, cardiac capillaries, and skeletal muscle, as well as in the endothelial cells of larger arteries. PKC beta showed a small decrease in the glomeruli. PKC epsilon was increased in renal tubules in diabetic rats but was decreased in the myocardium. PKC zeta was expressed in both myocardial and glomerular cells but was decreased during hyperglycemia. Our results demonstrate that PKC isoforms are differentially regulated in kidney and heart in diabetes. High glucose increases PKC alpha expression, whereas PKC zeta is down-regulated. The finding that PKC alpha is mostly increased in endothelial cells supports a role for PKC alpha in functional endothelial disturbances observed in diabetes.

Aldosterone activates Na+/H+ exchange in vascular smooth muscle cells by nongenomic and genomic mechanisms

BACKGROUND

In vascular smooth muscle cells (VSMCs), Na+/H+ exchange (NHE) plays an important role in intracellular pH (pHi) regulation. Recently, nongenomic effect of aldosterone (ALDO) on NHE activity has been suggested in VSMCs. However, the nongenomic and genomic effects of ALDO on NHE and the intracellular signaling mechanisms for these effects have not fully been determined in VSMCs.

METHODS

The effects of short- (3 hr) and long- (24 hr) term exposure to ALDO on NHE activity were examined in cultured VSMCs from rat thoracic aortae by using single-cell pHi measurement with the pH-sensitive dye 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. The NHE activity was calculated from the initial rate of Na+-dependent pHi recovery after acid load.

RESULTS

The NHE activity significantly increased after short- and long-term exposure of VSMCs to ALDO (10(-6) M). The inhibitors of gene transcription (actinomycin D) and of protein synthesis (cycloheximide) had no effect on the short-term ALDO effect, but inhibited the long-term ALDO effect. The antagonists of the mineralocorticoid receptor (MR) (spironolactone) and of the glucocorticoid receptor (GR) (RU38486) caused no effect on the short-term ALDO effect, but inhibited the long-term ALDO effect. Two protein kinase C (PKC) inhibitors (staurosporine A and calphostin C) and PKC down-regulation (24 hr pre-exposure to phobol 12-myristate 13-acetate, PMA) inhibited both the short- and long-term ALDO effects. Exposure of VSMCs to PMA for 3 hours mimicked the short-term effect of ALDO on NHE activity. ALDO significantly increased PKC activity in VSMCs. The short-term ALDO effect was inhibited by disruptors of microtubule (colchicine) and of filamentous-actin (cytochalasin B). Long-term exposure of ALDO caused a threefold increase in NHE (NHE-1) mRNA levels.

CONCLUSIONS

The short-term effect of ALDO on NHE activity is not mediated through either MR or GR, occurs independent of gene transcription and protein synthesis, and occurs through a mechanism involving the structural elements of cytoskeleton. The long-term effect of ALDO on NHE activity occurs through both MR and GR and requires gene transcription and protein synthesis. Both short- and long-term effects of ALDO are mediated through PKC activation. Therefore, ALDO activates NHE by nongenomic and genomic mechanisms in VSMCs.

Acidosis antagonizes intracellular calcium response to kappa-opioid receptor stimulation in the rat heart

To study the effects of kappa-opioid receptor stimulation on intracellular Ca2+ concentration ([Ca2+]i) homeostasis during extracellular acidosis, we determined the effects of kappa-opioid receptor stimulation on [Ca2+]i responses during extracellular acidosis in isolated single rat ventricular myocytes, by a spectrofluorometric method. U-50488H (10-30 microM), a selective kappa-opioid receptor agonist, dose dependently decreased the electrically induced [Ca2+]i transient, which results from the influx of Ca2+ and the subsequent mobilization of Ca2+ from the sarcoplasmic reticulum (SR). U-50488H (30 microM) also increased the resting [Ca2+]i and inhibited the [Ca2+]i transient induced by caffeine, which mobilizes Ca2+ from the SR, indicating that the effects of the kappa-opioid receptor agonist involved mobilization of Ca2+ from its intracellular pool into the cytoplasm. The Ca2+ responses to 30 microM U-50488H were abolished by 5 microM nor-binaltorphimine, a selective kappa-opioid receptor antagonist, indicating that the event was mediated by the kappa-opioid receptor. The effects of the agonist on [Ca2+]i and the electrically induced [Ca2+]i transient were significantly attenuated when the extracellular pH (pHe) was lowered to 6.8, which itself reduced intracellular pH (pHi) and increased [Ca2+]i. The inhibitory effects of U-50488H were restored during extracellular acidosis in the presence of 10 microM ethylisopropyl amiloride, a potent Na+/H+ exchange blocker, or 0.2 mM Ni2+, a putative Na+/Ca2+ exchange blocker. The observations indicate that acidosis may antagonize the effects of kappa-opioid receptor stimulation via Na+/H+ and Na+/Ca2+ exchanges. When glucose at 50 mM, known to activate the Na+/H+ exchange, was added, both the resting [Ca2+]i and pHi increased. Interestingly, the effects of U-50488H on [Ca2+]i and the electrically induced [Ca2+]i transient during superfusion with glucose were significantly attenuated; this mimicked the responses during extracellular acidosis. When a high-Ca2+ (3 mM) solution was superfused, the resting [Ca2+]i increased; the increase was abolished by 0.2 mM Ni2+, but the pHi remained unchanged. Like the responses to superfusion with high-concentration glucose and extracellular acidosis, the responses of the [Ca2+]i and electrically induced [Ca2+]i transients to 30 microM U-50488H were also significantly attenuated. Results from the present study demonstrated for the first time that extracellular acidosis antagonizes the effects of kappa-opioid receptor stimulation on the mobilization of Ca2+ from SR. Activation of both Na+/H+ and Na+/Ca2+ exchanges, leading to an elevation of [Ca2+]i, may be responsible for the antagonistic action of extracellular acidosis against kappa-opioid receptor stimulation.

Regulation of the Na+/H+ antiporter in patients with mild chronic renal failure: effect of glucose

BACKGROUND

The aim of this study was to determine the glucose-dependent regulation of the sodium-proton-antiporter (Na+/H+ antiporter) in patients with mild chronic renal failure (CRF).

METHODS

We measured plasma glucose concentrations, plasma insulin concentrations, plasma C peptide concentrations, arterial blood pressure, cytosolic pH (pHi), cellular Na+/H+ antiporter activity, and cytosolic sodium concentration ([Na+]i) in 19 patients with CRF and 41 age-matched healthy control subjects (control) during a standardized oral glucose tolerance test. Intracellular pHi, [Na+]i, and Na+/H+ antiporter activity was measured in lymphocytes using fluorescent dye techniques.

RESULTS

Under resting conditions, the pHi was significantly lower, whereas the Na+/H+ antiporter activity was significantly higher in CRF patients compared with controls (each P < 0.0001). The oral administration of 100 g glucose significantly increased the Na+/H+ antiporter activity in CRF patients from 13.35 +/- 1.26 x 10-3 pHi/second to 16.44 +/- 1.37 x 10-3 pHi/second after one hour and to 14.06 +/- 1.36 x 10-3 pHi/second after two hours (mean +/- SEM, P = 0.008 by Friedmans's two-way analysis of variance). In controls, the administration of 100 g glucose significantly increased the Na+/H+ antiporter activity from 4.23 +/- 0.20 x 10-3 pHi/second to 6.00 +/- 0.56 x 10-3 pHi/second after one hour and to 6.65 +/- 0.64 x 10-3 pHi/second after two hours (P = 0.0003). The glucose-induced enhancement of the Na+/H+ antiporter activity was more pronounced in CRF patients compared with controls (P = 0.011). Resting [Na+]i was not significantly different between the two groups.

CONCLUSIONS

CRF patients show an intracellular acidosis leading to an increased Na+/H+ antiporter activity. In addition, high glucose levels exaggerate the differences in Na+/H+ antiporter activity already present between cells from patients with mild CRF and those from control subjects.

Regulation of Na+/H+ exchanger gene expression: mitogenic stimulation increases NHE1 promoter activity

We examined factors important in regulation of expression of the Na+/H+ exchanger gene in NIH/3T3 cells. A stable fibroblast cell line was generated that contained a 1.1-kb proximal fragment of the mouse NHE1 promoter. The addition of serum to serum-starved cells resulted in an increase in activity of the NHE1 promoter. The mitogenic agonists insulin, thrombin, and epidermal growth factor also increased transcription from the NHE1 promoter. Phorbol esters also increased NHE1 promoter-directed transcription, whereas the serine/threonine protein kinase inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine inhibited this stimulation. The protein kinase inhibitors GF-109203X, PD-98059, and genistein all stimulated promoter activity. Promoter deletion analysis and gel mobility shift assays showed that a region between 0.9 and 1.1 kb from the start site was involved in mediating the effect of mitogenic stimulation. The results show that a variety of mitogenic factors can activate the NHE1 promoter during cell growth and proliferation.

Chronic hyperosmolality increases NHE3 activity in OKP cells

This study investigated the effect of chronic hypertonicity on the OKP cell Na/H antiporter, encoded by Na/H exchanger 3 (NHE3). Chronic (48 h) increases in extracellular glucose, mannitol, or raffinose concentration caused a significant increase in Na/H antiporter activity, while increases in urea concentration were without effect. This effect was seen with changes in osmolality of only 20 mOsm/liter, a magnitude that is observed clinically in poorly controlled diabetes mellitus. Increases in mannitol concentration acutely inhibited and chronically stimulated Na/H antiporter activity. The increase in Na/H antiporter activity induced by hypertonic incubation was resistant to 10(-7) and 5 x 10(-6) M but inhibited by 10(-4) M ethylisopropyl amiloride, consistent with regulation of NHE3. In addition, hypertonicity increased total cellular and plasma membrane NHE3 protein abundance twofold, with only a small increase in NHE3 mRNA abundance. We conclude that chronic pathophysiologically relevant increases in tonicity lead to increases in NHE3 protein abundance and activity. This may be responsible for increased proximal tubule apical membrane Na/H antiporter activity in poorly controlled diabetes mellitus, which could then contribute to hypertension, glomerular hyperfiltration and diabetic nephropathy.

Changes in protein kinase C in early cardiomyopathy and in gracilis muscle in the BB/Wor diabetic rat

Hyperglycemia can upregulate protein kinase C (PKC), which may be an important mediator of the progression from normal heart and muscle function to diabetic myopathy in the myocardium and skeletal muscle in type 1 insulin-dependent diabetes mellitus (IDM). We evaluated this possibility during the early stage of IDM in BB/Wor diabetic (D) rats and age-matched BB/Wor diabetes-resistant (DR) rats. Interventricular septal thickness, E wave peak velocity of tricuspid inflow (both minimum and maximum), and left ventricular (LV) weight index were increased, and the rate of change in LV pressure (LV dP/dt) decreased in D rats subjected to M-mode and two-dimensional echocardiography and hemodynamic recording of heart rate, LV pressure (LVP), + LV dP/dt, -LV dP/dt, and LV end-diastolic pressure (LVEDP) in vivo and in vitro 41 days after the onset of hyperglycemia. Whole ventricle basal PKC activity was increased by 44.4 and 18.4% in the particulate and soluble fractions, respectively, from D rats compared with that from DR rats using r-32P phosphorylation of appropriate peptide substrates. When measured by Western blot gel densitometry, particulate PKC-alpha and PKC-delta content increased by 89 and 24%, respectively, but soluble PKC-beta and soluble and particulate PKC-epsilon were unchanged compared with that of DR rats. Similarly, gracilis muscle PKC activity and PKC-alpha and PKC-delta were elevated in the gracilis muscle, whereas that of the circulating neutrophil did not differ between the D and DR rats. Thus, in vivo, the early diabetic cardiomyopathy of the D rat is characterized by a restrictive LV with increased septal thickness and is associated with elevated PKC activity and increased amounts of myocardial particulate PKC-alpha and PKC-delta, which are also seen in the skeletal muscle. We conclude that increased PKC isozymes may play a pivotal role during IDM in the development of diabetic cardiomyopathy and skeletal muscle myopathy.