Ronald G. Tilton

Hyperglycemic Pseudohypoxia and Diabetic Complications

Vasodilation and increased blood flow are characteristic early vascular responses to acute hyperglycemia and tissue hypoxia. In hypoxic tissues these vascular changes are linked to metabolic imbalances associated with impaired oxidation of NADH to NAD+ and the resulting increased ratio of NADH/NAD+. In hyperglycemic tissues these vascular changes also are linked to an increased ratio of NADH/NAD+, in this case because of an increased rate of reduction of NAD+ to NADH. Several lines of evidence support the likelihood that the increased cytosolic ratio of free NADH/NAD+ caused by hyperglycemia, referred to as pseudohypoxia because tissue partial pressure oxygen is normal, is a characteristic feature of poorly controlled diabetes that mimics the effects of true hypoxia on vascular and neural function and plays an important role in the pathogenesis of diabetic complications. These effects of hypoxia and hyperglycemia-induced pseudohypoxia on vascular and neural function are mediated by a branching cascade of imbalances in lipid metabolism, increased production of superoxide anion, and possibly increased nitric oxide formation.

Aminoguanidine, a Novel Inhibitor of Nitric Oxide Formation, Prevents Diabetic Vascular Dysfunction

Increased blood flow and vascular leakage of proteins preferentially affect tissues that are sites of diabetic complications in humans and animals. These vascular changes in diabetic rats are largely prevented by aminoguanidine. Glucose-induced vascular changes in nondiabetic rats are also prevented by aminoguanidine and by NG-monomethyl-L-arginine (NMMA), an established inhibitor of nitric oxide (NO·) formation from L-arginine. Aminoguanidine and NMMA are equipotent inhibitors of interleukin-1 β-induced 1) nitrite formation (an oxidation product of NO·) and cGMP accumulation by the rat β-cell insulinoma cell line RINm5F, and 2) inhibition of glucose-stimulated insulin secretion and formation of iron-nitrosyl complexes by islets of Langerhans. In contrast, NMMA is ∼ 40 times more potent than aminoquanidine in elevating blood pressure in nondiabetic rats. These results demonstrate that aminoguanidine inhibits NO. production and suggest a role for NO· in the pathogenesis of diabetic vascular complications.

An adventitial IL-6/MCP1 amplification loop accelerates macrophage-mediated vascular inflammation leading to aortic dissection in mice

Vascular inflammation contributes to cardiovascular diseases such as aortic aneurysm and dissection. However, the precise inflammatory pathways involved have not been clearly defined. We have shown here that subcutaneous infusion of Ang II, a vasopressor known to promote vascular inflammation, into older C57BL/6J mice induced aortic production of the proinflammatory cytokine IL-6 and the monocyte chemoattractant MCP-1. Production of these factors occurred predominantly in the tunica adventitia, along with macrophage recruitment, adventitial expansion, and development of thoracic and suprarenal aortic dissections. In contrast, a reduced incidence of dissections was observed after Ang II infusion into mice lacking either IL-6 or the MCP-1 receptor CCR2. Further analysis revealed that Ang II induced CCR2+CD14hiCD11bhiF4/80- macrophage accumulation selectively in aortic dissections and not in aortas from Il6-/- mice. Adoptive transfer of Ccr2+/+ monocytes into Ccr2-/- mice resulted in selective monocyte uptake into the ascending and suprarenal aorta in regions of enhanced ROS stress, with restoration of IL-6 secretion and increased incidence of dissection. In vitro, coculture of monocytes and aortic adventitial fibroblasts produced MCP-1- and IL-6-enriched conditioned medium that promoted differentiation of monocytes into macrophages, induced CD14 and CD11b upregulation, and induced MCP-1 and MMP-9 expression. These results suggest that leukocyte-fibroblast interactions in the aortic adventitia potentiate IL-6 production, inducing local monocyte recruitment and activation, thereby promoting MCP-1 secretion, vascular inflammation, ECM remodeling, and aortic destabilization.

Production of stem cells with embryonic characteristics from human umbilical cord blood

Abstract.  When will embryonic stem cells reach the clinic? The answer is simple – not soon! To produce large quantities of homogeneous tissue for transplantation, without feeder layers, and with the appropriate recipients immunological phenotype, is a significant scientific hindrance, although adult stem (ADS) cells provide an alternative, more ethically acceptable, source. The annual global 100 million human birth rate proposes umbilical cord blood (UCB) as the largest untouched stem cell source, with advantages of naive immune status and relatively unshortened telomere length. Here, we report the worlds first reproducible production of cells expressing embryonic stem cell markers, – cord‐blood‐derived embryonic‐like stem cells (CBEs). UCB, after elective birth by Caesarean section, has been separated by sequential immunomagnetic removal of nucleate granulocytes, erythrocytes and haemopoietic myeloid/lymphoid progenitors. After 7 days of high density culture in microflasks, (105 cells/ml, IMDM, FCS 10%, thrombopoietin 10 ng/ml, flt3‐ligand 50 ng/ml, c‐kit ligand 20 ng/ml). CBE colonies formed adherent to the substrata; these were maintained for 6 weeks, then were subcultured and continued for a minimum 13 weeks. CBEs were positive for TRA‐1‐60, TRA‐1‐81, SSEA‐4, SSEA‐3 and Oct‐4, but not SSEA‐1, indicative of restriction in the human stem cell compartment. The CBEs were also microgravity–bioreactor cultured with hepatocyte growth medium (IMDM, FCS 10%, HGF 20 ng/ml, bFGF 10 ng/ml, EGF 10 ng/ml, c‐kit ligand 10 ng/ml). After 4 weeks the cells were found to express characteristic hepatic markers, cytokeratin‐18, α‐foetoprotein and albumin. Thus, such CBEs are a viable human alternative from embryonic stem cells for stem cell research, without ethical constraint and with potential for clinical applications.

Inhibition of Sorbitol Dehydrogenase: Effects on Vascular and Neural Dysfunction in Streptozocin-Induced Diabetic Rats

These experiments were undertaken to assess the role of sorbitol dehydrogenase in mediating sorbitol pathway-linked neural and vascular dysfunction in rats with strep-tozocin-induced diabetes. 2-methyl-4-[N N-dimethylsulfamoyl-piperazino]-pyrimidine (S-0773), a putative inhibitor of sorbitol dehydrogenase, was given in the drinking water to control and diabetic rats. After 5 weeks of diabetes, glycosylated hemoglobin levels were increased twofold and were unaffected by S-0773. Sorbitol levels in diabetic rats were increased 11- to 14-fold in ocular tissues and sciatic nerve; S-0773 increased sorbitol levels another 4-fold or more in these same tissues but had much smaller effects in other tissues. Diabetes-associated increases in fructose levels and lactate:pyruvate ratios in retina and in sciatic nerve were markedly attenuated by S-0773. S-0773 also attenuated, but did not completely normalize, impaired caudal nerve conduction and vascular dysfunction in ocular tissues, sciatic nerve, and aorta in diabetic rats. These observations, together with other evidence, suggest that sorbitol pathway-linked vascular dysfunction (in ocular tissues, peripheral nerve, and aorta) and electrophysiological dysfunction (in peripheral nerve) induced by diabetes are more closely linked to increased oxidation of sorbitol to fructose than to putative osmotic effects of elevated sorbitol levels or redox and metabolic imbalances associated with reduction of glucose to sorbitol by aldose reductase.

Klotho Depletion Contributes to Increased Inflammation in Kidney of the db/db Mouse Model of Diabetes Via RelA (Serine)536 Phosphorylation

OBJECTIVE Klotho is an antiaging hormone present in the kidney that extends the lifespan, regulates kidney function, and modulates cellular responses to oxidative stress. We investigated whether Klotho levels and signaling modulate inflammation in diabetic kidneys. RESEARCH DESIGN AND METHODS Renal Klotho expression was determined by quantitative real-time PCR and immunoblot analysis. Primary mouse tubular epithelial cells were treated with methylglyoxalated albumin, and Klotho expression and inflammatory cytokines were measured. Nuclear factor (NF)-κB activation was assessed by treating human embryonic kidney (HEK) 293 and HK-2 cells with tumor necrosis factor (TNF)-α in the presence or absence of Klotho, followed by immunoblot analysis to evaluate inhibitor of κB (IκB)α degradation, IκB kinase (IKK) and p38 activation, RelA nuclear translocation, and phosphorylation. A chromatin immunoprecipitation assay was performed to analyze the effects of Klotho signaling on interleukin-8 and monocyte chemoattractant protein-1 promoter recruitment of RelA and RelA serine (Ser)536. RESULTS Renal Klotho mRNA and protein were significantly decreased in db/db mice, and a similar decline was observed in the primary cultures of mouse tubule epithelial cells treated with methylglyoxal-modified albumin. The exogenous addition of soluble Klotho or overexpression of membranous Klotho in tissue culture suppressed NF-κB activation and subsequent production of inflammatory cytokines in response to TNF-α stimulation. Klotho specifically inhibited RelA Ser536 phosphorylation as well as promoter DNA binding of this phosphorylated form of RelA without affecting IKK-mediated IκBα degradation, total RelA nuclear translocation, and total RelA DNA binding. CONCLUSIONS These findings suggest that Klotho serves as an anti-inflammatory modulator, negatively regulating the production of NF-κB–linked inflammatory proteins via a mechanism that involves phosphorylation of Ser536 in the transactivation domain of RelA.

Directed engineering of umbilical cord blood stem cells to produce C-peptide and insulin

Abstract.  Objectives: In this study, we investigated the potential of umbilical cord blood stem cell lineages to produce C‐peptide and insulin. Materials and methods: Lineage negative, CD133+ and CD34+ cells were analyzed by flow cytometry to assess expression of cell division antigens. These lineages were expanded in culture and subjected to an established protocol to differentiate mouse embryonic stem cells (ESCs) toward the pancreatic phenotype. Phase contrast and fluorescence immunocytochemistry were used to characterize differentiation markers with particular emphasis on insulin and C‐peptide. Results: All 3 lineages expressed SSEA‐4, a marker previously reported to be restricted to the ESC compartment. Phase contrast microscopy showed all three lineages recapitulated the treatment‐dependent morphological changes of ESCs as well as the temporally restricted expression of nestin and vimentin during differentiation. After engineering, each isolate contained both C‐peptide and insulin, a result also obtained following a much shorter protocol for ESCs. Conclusions: Since C‐peptide can only be derived from de novo synthesis and processing of pre‐proinsulin mRNA and protein, we conclude that these results are the first demonstration that human umbilical cord blood‐derived stem cells can be engineered to engage in de novo synthesis of insulin.

Vascular endothelial growth factor is crucial for erythropoietin-induced improvement of cardiac function in heart failure

AIMS We intended to delineate the mechanisms of erythropoietin (EPO)-induced cardiac vascular endothelial growth factor (VEGF) production and to establish if VEGF is crucial for EPO-induced improvement of cardiac performance. METHODS AND RESULTS The effects of EPO on VEGF expression were studied in cultured cardiac cells and EPO-treated hearts. The role of VEGF in EPO-induced neovascularization was studied with two distinct VEGF-neutralizing antibodies or irrelevant control IgG in an aortic sprouting assay and in rats with heart failure (HF) after myocardial infarction (MI) treated with EPO. EPO-alfa (10 IU/mL) was used in vitro and darbepoetin alfa (40 microg/kg/3 weeks, starting 3 weeks after MI) in vivo. EPO stimulated VEGF mRNA expression through the signal transducers and activators of transcription-3 (STAT-3) pathway in neonatal rat cardiomyocytes, but not in endothelial cells or fibroblasts. Similarly, the direct effects of EPO on endothelial sprouting were modest and VEGF independent. In rats with HF, EPO increased VEGF protein expression predominantly in cardiomyocytes, associated with a 37% increase in capillary density and improved cardiac performance. Administration of VEGF-neutralizing antibodies abrogated the salutary effects of EPO on cardiac microvascularization and function. VEGF neutralization attenuated EPO-induced proliferation of myocardial endothelial cells and reduced myocardial incorporation of endothelial progenitor cells (EPCs) in rats with alkaline phosphatase-labelled bone marrow cells. CONCLUSION VEGF is crucial for EPO-induced improvement of cardiac function in HF. EPO fosters VEGF expression predominantly in cardiomyocytes, which in turn stimulates myocardial endothelial proliferation and incorporation of EPCs.

RhoA Mediates Angiotensin II–Induced Phospho-Ser536 Nuclear Factor κB/RelA Subunit Exchange on the Interleukin-6 Promoter in VSMCs

The vasoconstrictor angiotensin II (Ang II) accelerates atherosclerosis by inducing vascular gene expression programs, producing monocyte recruitment, and vascular remodeling. In vascular smooth muscle cells (VSMCs), Ang II signaling activates interleukin (IL)-6 expression, a cytokine producing acute-phase inflammation, mediated by the transcription factor nuclear factor &kgr;B (NF-&kgr;B). The classical NF-&kgr;B activation pathway involves cytoplasmic-to-nuclear translocation of the potent RelA transactivating subunit; however, because nuclear RelA is present in VSMCs, the mechanism by which NF-&kgr;B activity is controlled is incompletely understood. In this study, we focus on early activation steps controlling RelA activation. Although Ang II only weakly induces ≈1.5-fold RelA nuclear translocation, RelA is nevertheless required because short interfering RNA–mediated RelA knockdown inhibits inducible IL-6 expression. We find instead that Ang II stimulation rapidly induces RelA phosphorylation at serine residue 536, a critical regulatory site in its transactivating domain. Chromatin immunoprecipitation assays indicate no significant changes in total RelA binding to the native IL-6 promoter, but an apparent increase in fractional binding of phospho-Ser536 RelA. Inactivation of RhoA by treatment with Clostridium botulinum exoenzyme C3 exotoxin or expression of dominant negative RhoA blocks Ang II–inducible RelA Ser536 phosphorylation and IL-6 expression. Finally, enhanced phospho-Ser536 RelA formation in the aortae of rats chronically infused with Ang II was observed. Together, these data indicate a novel mechanism for Ang II–induced NF-&kgr;B activation in VSMCs, mediated by RhoA-induced phospho-Ser536 RelA formation, IL-6 expression, and vascular inflammation.

Roles of IL-6-gp130 Signaling in Vascular Inflammation

Interleukin-6 (IL-6) is a well-established, independent indicator of multiple distinct types of cardiovascular disease and all-cause mortality. In this review, we present current understanding of the multiple roles that IL-6 and its signaling pathways through glycoprotein 130 (gp130) play in cardiovascular homeostasis. IL-6 is highly inducible in vascular tissues through the actions of the angiotensin II (Ang II) peptide, where it acts in a paracrine manner to signal through two distinct mechanisms, the first being a classic membrane receptor initiated pathway and the second, a trans-signaling pathway, being able to induce responses even in tissues lacking the IL-6 receptor. Recent advances and new concepts in how its intracellular signaling pathways operate via the Janus kinase (JAK)-Signal Transducer and Activator of Transcription (STAT) are described. IL-6 has diverse actions in multiple cell types of cardiovascular importance, including endothelial cells, monocytes, platelets, hepatocytes and adipocytes. We discuss central roles of IL-6 in endothelial dysfunction, cellular inflammation by affecting monocyte activation/differentiation, cellular cytoprotective functions from reactive oxygen species (ROS) stress, modulation of pro-coagulant state, myocardial growth control, and its implications in metabolic control and insulin resistance. These multiple actions indicate that IL-6 is not merely a passive biomarker, but actively modulates adaptive and pathological responses to cardiovascular stress. Summary: IL-6 is a multifunctional cytokine whose presence in the circulation is linked with diverse types of cardiovascular disease and is an independent risk factor for atherosclerosis. In this review, we examine the mechanisms by which IL-6 signals and its myriad effects in cardiovascular tissues that modulate the manifestations of vascular inflammation.