CLINICAL CHARACTERIZATION OF AQUEOUS AND VITREOUS RETINOL-BINDING PROTEIN 3 CONCENTRATIONS IN RELATION TO DIABETIC RETINOPATHY SEVERITY, RETINAL STRUCTURES, AND SYSTEMIC COMPLICATIONS

PURPOSE

To evaluate Retinol-Binding Protein 3 (RBP3) from photoreceptors in aqueous and its association with vitreous concentrations, diabetic retinopathy (DR) severity, retinal layer thickness, and clinical characteristics in people with diabetes.

METHODS

RBP3 concentration was measured by custom-developed enzyme-linked immunosorbent assay in aqueous and correlated with vitreous concentrations in patients from the 50-Year Medalist study and Beetham Eye Institute at Joslin Diabetes Center.

RESULTS

Aqueous RBP3 concentration (N = 131) was elevated in eyes with no to mild DR (mean ± SD 0.7 nM ± 0.2) and decreased in eyes with moderate to severe DR (0.65 nM ± 0.3) and proliferative DR (0.5 nM ± 0.2, P < 0.001) compared to eyes without diabetes. Aqueous and vitreous RBP3 concentrations correlated with each other (r = 0.34, P = 0.001) and between fellow eyes (P < 0.0001). History of retinal surgery did not affect aqueous RBP3 concentrations, but cataract surgery affected both vitreous and aqueous levels. Elevated aqueous RBP3 concentration associated with increased thickness of the outer nuclear layer (P = 0.004) and correlated with hemoglobin A1c, whereas vitreous RBP3 concentrations correlated with diabetic systemic complications.

CONCLUSION

These findings suggest that aqueous RBP3 concentration may be an important endogenous clinical retinal protective factor, a biomarker for DR severity, and a promising VEGF-independent clinical intervention target in DR.

Endothelial Insulin Resistance Exacerbates Experimental Periodontitis

Epidemiological studies suggest that the severity of periodontitis is higher in people with diabetes than in healthy individuals. Insulin resistance might play a crucial role in the pathogenesis of multiple diabetic complications and is reportedly induced in the gingiva of rodents with type 2 diabetes; however, the molecular mechanisms underlying the pathogenesis of diabetes-related periodontitis remain unclear. Therefore, we aimed to investigate whether endothelial insulin resistance in the gingiva may contribute to the pathogenesis of periodontitis as well as elucidate its underlying molecular mechanisms. We demonstrated that insulin treatment downregulated lipopolysaccharide (LPS)-induced or tumor necrosis factor α (TNFα)-induced VCAM1 expression in endothelial cells (ECs) via the PI3K/Akt activating pathway, resulting in reduced cellular adhesion between ECs and leukocytes. Hyperglycemia-induced selective insulin resistance in ECs diminished the effect of insulin on LPS- or TNFα-stimulated VCAM1 expression. Vascular endothelial cell-specific insulin receptor knockout (VEIRKO) mice exhibited selective inhibition of the PI3K/Akt pathway in the gingiva and advanced experimental periodontitis-induced alveolar bone loss via upregulation of Vcam1, Tnfα, Mcp-1, Rankl, and neutrophil migration into the gingiva compared with that in the wild-type (WT) mice despite being free from diabetes. We also observed that insulin-mediated activation of FoxO1, a downstream target of Akt, was suppressed in the gingiva of VEIRKO and high-fat diet (HFD)-fed mice, hyperglycemia-treated ECs, and primary ECs from VEIRKO. Further analysis using ECs transfected with intact and mutated FoxO1, with mutations at 3 insulin-mediated phosphorylation sites (T24A, S256D, S316A), suggested that insulin-mediated regulation of VCAM1 expression and cellular adhesion of ECs with leukocytes was attenuated by mutated FoxO1 overexpression. These results suggest that insulin resistance in ECs may contribute to the progression of periodontitis via dysregulated VCAM1 expression and cellular adhesion with leukocytes, resulting from reduced activation of the PI3K/Akt/FoxO1 axis.

Dysregulation of CXCL1 expression and neutrophil recruitment in insulin resistance and diabetes-related periodontitis in male mice

Insulin resistance and hyperglycemia are risk factors for periodontitis and poor wound healing in diabetes, which have been associated with selective loss of insulin- activation of the PI3K/Akt pathway in the gingiva. This study showed that insulin resistance in the mouse gingiva due to selective deletion of smooth muscle and fibroblast insulin receptor (SMIRKO mice) or systemic metabolic changes induced by high fat diet (HFD) in HFD-fed mice exacerbated periodontitis-induced alveolar bone loss, preceded by delayed neutrophil and monocyte recruitment and impaired bacterial clearance compared to their respective controls. The immunocytokines, CXCL1, CXCL2, MCP-1, TNFα, IL-1β and IL-17A exhibited delayed maximal expression in the gingiva of male SMIRKO and HFD-fed mice compared to controls. Targeted overexpression of CXCL1 in the gingiva by adenovirus normalized neutrophil and monocyte recruitment and prevented bone loss in both mouse models of insulin resistance. Mechanistically, insulin enhanced bacterial lipopolysaccharide-induced CXCL1 production in mouse and human gingival fibroblasts (GFs), via Akt pathway and NF-κB activation, which were reduced in GFs from SMIRKO and HFD-fed mice. These results provided the first report that insulin signaling can enhance endotoxin induced CXCL1 expression to modulate neutrophil recruitment, suggesting CXCL1 as a new therapeutic direction for periodontitis or wound healing in diabetes.

Elevated Retinol Binding Protein 3 Concentrations Are Associated With Decreased Vitreous Inflammatory Cytokines, VEGF, and Progression of Diabetic Retinopathy

OBJECTIVE

To correlate inflammatory cytokines and vascular endothelial growth factor (VEGF) in vitreous and plasma with vitreous retinol binding protein 3 (RBP3), diabetic retinopathy (DR) severity, and DR worsening in a population with type 1 and type 2 diabetes.

RESEARCH DESIGN AND METHODS

RBP3, VEGF, and inflammatory cytokines were measured in plasma and vitreous samples (n = 205) from subjects of the Joslin Medalist Study and Beetham Eye Institute.

RESULTS

Higher vitreous RBP3 concentrations were associated with less severe DR (P < 0.0001) and a reduced risk of developing proliferative DR (PDR) (P < 0.0001). Higher RBP3 correlated with increased photoreceptor segment thickness and lower vitreous interleukin-12 (IL-12), tumor necrosis factor-α (TNF-α), and TNF-β (P < 0.05). PDR was associated with lower vitreous interferon-γ and IL-10 and higher VEGF, IL-6, and IL-15 (P < 0.05), but was not associated with their plasma concentrations.

CONCLUSIONS

Higher vitreous RBP3 concentrations are associated with less severe DR and slower rates of progression to PDR, supporting its potential as a biomarker and therapeutic agent for preventing DR worsening, possibly by lowering retinal VEGF and inflammatory cytokines.

Endothelial Cells Induced Progenitors Into Brown Fat to Reduce Atherosclerosis

BACKGROUND

Insulin resistance (IR) can increase atherosclerotic and cardiovascular risk by inducing endothelial dysfunction, decreasing nitric oxide (NO) production, and accelerating arterial inflammation. The aim is to determine the mechanism by which insulin action and NO production in endothelial cells can improve systemic bioenergetics and decrease atherosclerosis via differentiation of perivascular progenitor cells (PPCs) into brown adipocytes (BAT).

METHODS

Studies used various endothelial transgenic and deletion mutant ApoE-/- mice of insulin receptors, eNOS (endothelial NO synthase) and ETBR (endothelin receptor type B) receptors for assessments of atherosclerosis. Cells were isolated from perivascular fat and micro-vessels for studies on differentiation and signaling mechanisms in responses to NO, insulin, and lipokines from BAT.

RESULTS

Enhancing insulin's actions on endothelial cells and NO production in ECIRS1 transgenic mice reduced body weight and increased systemic energy expenditure and BAT mass and activity by inducing differentiation of PPCs into beige/BAT even with high-fat diet. However, positive changes in bioenergetics, BAT differentiation from PPCs and weight loss were inhibited by N(gamma)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of eNOS, in ECIRS1 mice and eNOSKO mice. The mechanism mediating NO's action on PPC differentiation into BAT was identified as the activation of solubilized guanylate cyclase/PKGIα (cGMP protein-dependent kinase Iα)/GSK3β (glycogen synthase kinase 3β) pathways. Plasma lipidomics from ECIRS1 mice with NO-induced increased BAT mass revealed elevated 12,13-diHOME production. Infusion of 12,13-diHOME improved endothelial dysfunction and decreased atherosclerosis, whereas its reduction had opposite effects in ApoE-/-mice.

CONCLUSIONS

Activation of eNOS and endothelial cells by insulin enhanced the differentiation of PPC to BAT and its lipokines and improved systemic bioenergetics and atherosclerosis, suggesting that endothelial dysfunction is a major contributor of energy disequilibrium in obesity.

Endothelial Cell Insulin Signaling Regulates CXCR4 (C-X-C Motif Chemokine Receptor 4) and Limits Leukocyte Adhesion to Endothelium

BACKGROUND

An activated, proinflammatory endothelium is a key feature in the development of complications of obesity and type 2 diabetes and can be caused by insulin resistance in endothelial cells.

METHODS

We analyzed primary human endothelial cells by RNA sequencing to discover novel insulin-regulated genes and used endothelial cell culture and animal models to characterize signaling through CXCR4 (C-X-C motif chemokine receptor 4) in endothelial cells.

RESULTS

CXCR4 was one of the genes most potently regulated by insulin, and this was mediated by PI3K (phosphatidylinositol 3-kinase), likely through FoxO1, which bound to the CXCR4 promoter. CXCR4 mRNA in CD31+ cells was 77% higher in mice with diet-induced obesity compared with lean controls and 37% higher in db/db mice than db/+ controls, consistent with upregulation of CXCR4 in endothelial cell insulin resistance. SDF-1 (stromal cell-derived factor-1)-the ligand for CXCR4-increased leukocyte adhesion to cultured endothelial cells. This effect was lost after deletion of CXCR4 by gene editing while 80% of the increase was prevented by treatment of endothelial cells with insulin. In vivo microscopy of mesenteric venules showed an increase in leukocyte rolling after intravenous injection of SDF-1, but most of this response was prevented in transgenic mice with endothelial overexpression of IRS-1 (insulin receptor substrate-1).

CONCLUSIONS

Endothelial cell insulin signaling limits leukocyte/endothelial cell interaction induced by SDF-1 through downregulation of CXCR4. Improving insulin signaling in endothelial cells or inhibiting endothelial CXCR4 may reduce immune cell recruitment to the vascular wall or tissue parenchyma in insulin resistance and thereby help prevent several vascular complications.

Regenerating glomerular metabolism and function by podocyte pyruvate kinase M2 in diabetic nephropathy

Diabetic nephropathy (DN) arises from systemic and local changes in glucose metabolism and hemodynamics. We have reported that many glycolytic and mitochondrial enzymes, such as pyruvate kinase M2 (PKM2), were elevated in renal glomeruli of DN-protected type 1 and type 2 diabetic patients. Here, mice with PKM2-specific overexpression in podocytes (PPKM2Tg) were generated to uncover its renal protective function as potential therapeutic target, which prevented elevated albumin-creatinine ratio (ACR), mesangial expansion, basement membrane thickness and podocyte foot process effacement after 7-months of STZ-induced diabetes. Further, diabetes-induced impairment of glycolytic rate and mitochondrial function were normalized in diabetic PPKM2Tg glomeruli, in concordance with elevated Ppargc1a and Vegf expressions. Restored VEGF expression improved glomerular maximal mitochondrial function in diabetic PPKM2Tg and WT mice. Elevated VEGF levels were observed in the glomeruli of DN-protected patients with chronic type 1 diabetes, and clinically correlated with estimated GFR, but not glycemic control. Mechanistically, the preservations of mitochondrial function and VEGF expression were dependent on tetrameric structure and enzymatic activities of PKM2 in podocyte. These findings demonstrated that PKM2 structure and enzymatic activation in podocytes can preserve entire glomerular mitochondrial function against toxicity of hyperglycemia via paracrine factors such as VEGF and prevent DN progression.

Association of Coding Variants in Hydroxysteroid 17-beta Dehydrogenase 14 (HSD17B14) with Reduced Progression to End Stage Kidney Disease in Type 1 Diabetes

BACKGROUND

Rare variants in gene coding regions likely have a greater impact on disease-related phenotypes than common variants through disruption of their encoded protein. We searched for rare variants associated with onset of ESKD in individuals with type 1 diabetes at advanced kidney disease stage.

METHODS

Gene-based exome array analyses of 15,449 genes in five large incidence cohorts of individuals with type 1 diabetes and proteinuria were analyzed for survival time to ESKD, testing the top gene in a sixth cohort (n=2372/1115 events all cohorts) and replicating in two retrospective case-control studies (n=1072 cases, 752 controls). Deep resequencing of the top associated gene in five cohorts confirmed the findings. We performed immunohistochemistry and gene expression experiments in human control and diseased cells, and in mouse ischemia reperfusion and aristolochic acid nephropathy models.

RESULTS

Protein coding variants in the hydroxysteroid 17-β dehydrogenase 14 gene (HSD17B14), predicted to affect protein structure, had a net protective effect against development of ESKD at exome-wide significance (n=4196; P value=3.3 × 10^-7). The HSD17B14 gene and encoded enzyme were robustly expressed in healthy human kidney, maximally in proximal tubular cells. Paradoxically, gene and protein expression were attenuated in human diabetic proximal tubules and in mouse kidney injury models. Expressed HSD17B14 gene and protein levels remained low without recovery after 21 days in a murine ischemic reperfusion injury model. Decreased gene expression was found in other CKD-associated renal pathologies.

CONCLUSIONS

HSD17B14 gene is mechanistically involved in diabetic kidney disease. The encoded sex steroid enzyme is a druggable target, potentially opening a new avenue for therapeutic development.

Selective modulation by PARP-1 of HIF-1α-recruitment to chromatin during hypoxia is required for tumor adaptation to hypoxic conditions

BACKGROUND

The adaptation to hypoxia is mainly controlled by the HIF transcription factors. Increased expression/activity of HIF-1α correlates with poor prognosis in cancer patients. PARP-1 inhibitors are used in the clinic to treat BRCAness breast/ovarian cancer and have been shown to regulate the hypoxic response; therefore, their use could be expanded.

METHODS

In this work by integrating molecular/cell biology approaches, genome-wide ChIP-seq, and patient samples, we elucidate the extent to which PARP-1 exerts control over HIF-1-regulated genes.

RESULTS

In human melanoma, PARP-1 and HIF-1α expression are strongly associated. In response to a hypoxic challenge poly(ADP-ribose) (PAR) is synthesized, HIF-1α is post-transcriptionally modified (PTM) and stabilized by PARylation at specific K/R residues located at its C-terminus. Using an unbiased ChIP-seq approach we demonstrate that PARP-1 dictates hypoxia-dependent HIF-recruitment to chromatin in a range of HIF-regulated genes while analysis of HIF-binding motifs (RCGTG) reveals a restriction on the recognition of hypoxia responsive elements in the absence of PARP-1. Consequently, the cells are poorly adapted to hypoxia, showing a reduced fitness during hypoxic induction.

CONCLUSIONS

These data characterize the fine-tuning regulation by PARP-1/PARylation of HIF activation and suggest that PARP inhibitors might have therapeutic potential against cancer types displaying HIF-1α over-activation.

Insulin's actions on vascular tissues: Physiological effects and pathophysiological contributions to vascular complications of diabetes

Background

Insulin has been demonstrated to exert direct and indirect effects on vascular tissues. Its actions in vascular cells are mediated by two major pathways: the insulin receptor substrate 1/2-phosphoinositide-3 kinase/Akt (IRS1/2/PI3K/Akt) pathway and the Src/mitogen-activated protein kinase (MAPK) pathway, both of which contribute to the expression and distribution of metabolites, hormones, and cytokines.

Scope of review

In this review, we summarize the current understanding of insulin's physiological and pathophysiological actions and associated signaling pathways in vascular cells, mainly in endothelial cells (EC) and vascular smooth muscle cells (VSMC), and how these processes lead to selective insulin resistance. We also describe insulin's potential new signaling and biological effects derived from animal studies and cultured capillary and arterial EC, VSMC, and pericytes. We will not provide a detailed discussion of insulin's effects on the myocardium, insulin's structure, or its signaling pathways' various steps, since other articles in this issue discuss these areas in depth.

Major conclusions

Insulin mediates many important functions on vascular cells via its receptors and signaling cascades. Its direct actions on EC and VSMC are important for transporting and communicating nutrients, cytokines, hormones, and other signaling molecules. These vascular actions are also important for regulating systemic fuel metabolism and energetics. Inhibiting or enhancing these pathways leads to selective insulin resistance, exacerbating the development of endothelial dysfunction, atherosclerosis, restenosis, poor wound healing, and even myocardial dysfunction. Targeted therapies to improve selective insulin resistance in EC and VSMC are thus needed to specifically mitigate these pathological processes.

•

Insulin's actions in vascular cells have a significant influence on systemic metabolism.

•

Insulin exerts its vascular effects through its receptors and signaling cascades.

•

Inhibition or enhancement of different insulin signaling leads to selective insulin resistance.

•

Loss of insulin's actions causes endothelial dysfunction and vascular complications in diabetes.

Association of Cognitive Function and Retinal Neural and Vascular Structure in Type 1 Diabetes

CONTEXT

Cognitive dysfunction is a growing and understudied public health issue in the aging type 1 diabetic population and is difficult and time-consuming to diagnose. Studies in long duration type 1 diabetes have reported the presence of proliferative diabetic retinopathy was associated with cognitive dysfunction.

OBJECTIVE

This study assessed whether structural and vascular abnormalities of the retina, representing an extension of the central nervous system, are associated with cognitive impairment and other complications of type 1 diabetes.

METHODS

An observational cross-sectional study of individuals with 50 or more years of type 1 diabetes (Joslin Medalist Study) was conducted at a university hospital in the United States. The study included 129 participants with complete cognitive testing. Validated cognitive testing measures included psychomotor speed, and immediate, and delayed memory. Optical coherence tomography (OCT) and OCT angiography (OCTA) were performed to obtain neural retinal layer thicknesses and vascular density for superficial (SCP) and deep retinal capillary plexus (DCP). Multivariable modeling was adjusted for potential confounders associated with outcomes in unadjusted analyses.

RESULTS

Decreased vessel density of the SCP and DCP was associated with worse delayed memory (DCP: P = .002) and dominant hand psychomotor speed (SCP: P = .01). Thinning of the retinal outer nuclear layer was associated with worse psychomotor speed both in nondominant and dominant hands (P = .01 and P = .05, respectively). Outer plexiform layer thickness was associated with delayed memory (P = .04).

CONCLUSION

These findings suggest that noninvasive retinal imaging using OCT and OCTA may assist in estimating the risks for cognitive dysfunction in people with type 1 diabetes.

Retinol binding protein 3 is increased in the retina of patients with diabetes resistant to diabetic retinopathy

The Joslin Medalist Study characterized people affected with type 1 diabetes for 50 years or longer. More than 35% of these individuals exhibit no to mild diabetic retinopathy (DR), independent of glycemic control, suggesting the presence of endogenous protective factors against DR in a subpopulation of patients. Proteomic analysis of retina and vitreous identified retinol binding protein 3 (RBP3), a retinol transport protein secreted mainly by the photoreceptors, as elevated in Medalist patients protected from advanced DR. Mass spectrometry and protein expression analysis identified an inverse association between vitreous RBP3 concentration and DR severity. Intravitreal injection and photoreceptor-specific overexpression of RBP3 in rodents inhibited the detrimental effects of vascular endothelial growth factor (VEGF). Mechanistically, our results showed that recombinant RBP3 exerted the therapeutic effects by binding and inhibiting VEGF receptor tyrosine phosphorylation. In addition, by binding to glucose transporter 1 (GLUT1) and decreasing glucose uptake, RBP3 blocked the detrimental effects of hyperglycemia in inducing inflammatory cytokines in retinal endothelial and Müller cells. Elevated expression of photoreceptor-secreted RBP3 may have a role in protection against the progression of DR due to hyperglycemia by inhibiting glucose uptake via GLUT1 and decreasing the expression of inflammatory cytokines and VEGF.

The Role of Protein Kinase C Activation in the Pathogenesis of Diabetic Vascular Complications

Many vascular diseases in diabetes are known to be associated with the activation of the diacylglycerol (OAG)protein kinase C (PKC) pathway. The major source of OAG that is elevated in diabetes is de novo synthesis from glycolytic intermediates. Among the various PKC isoforms, the β-isoform has been shown to be persistently activated in diabetic animals. Multiple lines of evidence have shown that many vascular alterations in diabetes such as a decrease in the activity of Na+-K+ -adenosine triphosphatase (Na+-K+-ATPase), and increases in extracellular matrix, cytokines, permeability, contractility, and cell proliferation -are caused by activation of PKC. Inhibition of PKC by two different kinds of PKC inhibitors, LY333531, a selective PKC-β-isoform inhibitor, and d-α-tocopherol, were able to prevent or reverse the various vascular dysfunctions in diabetic rats. These results have also provided in vivo evidence that OAG-PKC activation could be responsible for the hyperglycemia-induced vascular dysfunctions in diabetes. Clinical studies are now being performed to clarify the pathogenic roles of the OAG-PKC pathway in developing vascular complications in diabetic patients.

High Concentration of Medium-Sized HDL Particles and Enrichment in HDL Paraoxonase 1 Associate With Protection From Vascular Complications in People With Long-standing Type 1 Diabetes

OBJECTIVE

A subset of people with long-standing type 1 diabetes (T1D) appears to be protected from microvascular and macrovascular complications. Previous studies have focused on improved abilities to respond to glucose and its downstream effects as protective mechanisms. It is unclear whether lipoproteins play a role in the vascular health of these people. We therefore determined whether HDL particle concentration, size, function, and/or protein composition associate with protection from vascular complications.

RESEARCH DESIGN AND METHODS

We studied two independent cross-sectional cohorts with T1D: the T1D Exchange Living Biobank (n = 47) and the Joslin Medalist Study (n = 100). Some of the subjects had vascular complications, whereas others never exhibited vascular complications, despite an average duration of diabetes in the cohorts of 45 years. We assessed HDL particle size and concentration by calibrated ion mobility analysis, the HDL proteome by targeted mass spectrometry, and HDL function ex vivo by quantifying cholesterol efflux capacity and inhibition of monocyte adhesion to endothelial cells.

RESULTS

In both cohorts, people without vascular complications exhibited significantly higher concentrations of medium-sized HDL particles (M-HDL) independently of total and HDL cholesterol levels. While no consistent differences in HDL functions were observed ex vivo, people without vascular complications had higher levels of HDL-associated paraoxonase 1 (PON1), an enzyme that inhibits atherosclerosis in animal models.

CONCLUSIONS

Elevated concentrations of M-HDL particles and elevated levels of HDL-associated PON1 may contribute to long-term protection from the vascular complications of diabetes by pathways that are independent of total cholesterol and HDL cholesterol.

Characterization of Glycolytic Enzymes and Pyruvate Kinase M2 in Type 1 and 2 Diabetic Nephropathy

OBJECTIVE

Elevated glycolytic enzymes in renal glomeruli correlated with preservation of renal function in the Medalist Study, individuals with ≥50 years of type 1 diabetes. Specifically, pyruvate kinase M2 (PKM2) activation protected insulin-deficient diabetic mice from hyperglycemia-induced glomerular pathology. This study aims to extend these findings in a separate cohort of individuals with type 1 and type 2 diabetes and discover new circulatory biomarkers for renal protection through proteomics and metabolomics of Medalists' plasma. We hypothesize that increased glycolytic flux and improved mitochondrial biogenesis will halt the progression of diabetic nephropathy.

RESEARCH DESIGN AND METHODS

Immunoblots analyzed selected glycolytic and mitochondrial enzymes in postmortem glomeruli of non-Medalists with type 1 diabetes (n = 15), type 2 diabetes (n = 19), and no diabetes (n = 5). Plasma proteomic (SOMAscan) (n = 180) and metabolomic screens (n = 214) of Medalists with and without stage 3b chronic kidney disease (CKD) were conducted and significant markers validated by ELISA.

RESULTS

Glycolytic (PKM1, PKM2, and ENO1) and mitochondrial (MTCO2) enzymes were significantly elevated in glomeruli of CKD- versus CKD+ individuals with type 2 diabetes. Medalists' plasma PKM2 correlated with estimated glomerular filtration rate (r ² = 0.077; P = 0.0002). Several glucose and mitochondrial enzymes in circulation were upregulated with corresponding downregulation of toxic metabolites in CKD-protected Medalists. Amyloid precursor protein was also significantly upregulated, tumor necrosis factor receptors downregulated, and both confirmed by ELISA.

CONCLUSIONS

Elevation of enzymes involved in the metabolism of intracellular free glucose and its metabolites in renal glomeruli is connected to preserving kidney function in both type 1 and type 2 diabetes. The renal profile of elevated glycolytic enzymes and reduced toxic glucose metabolites is reflected in the circulation, supporting their use as biomarkers for endogenous renal protective factors in people with diabetes.

Characterization of periodontitis in people with type 1 diabetes of 50 years or longer duration

BACKGROUND

Periodontitis is more common and severe in people with diabetes than the general population. We have reported in the Joslin Medalist Study that people with type 1 diabetes of ≥50 years (Medalists) may have endogenous protective factors against diabetic nephropathy and retinopathy.

METHODS

In this cross-sectional study, the prevalence of periodontitis according to the Centers for Disease Control/American Academy of Periodontology classification in a subset (n = 170, mean age = 64.6 ± 6.9 years) of the Medalist cohort, and its associations to various criteria of periodontitis and diabetic complications were assessed.

RESULTS

The prevalence of severe periodontitis in Medalists was only 13.5% which was lower than reported levels in diabetic patients of similar ages. Periodontal parameters, including bleeding on probing, plaque index, gingival index, and demographic traits, including male sex, chronological age, and age at diagnosis were significantly associated with severity of periodontitis, which did not associate with diabetes duration, hemoglobin A1c (HbA1c), body mass index, and lipid profiles. Random serum C-peptide levels inversely associated with severity of periodontitis (P = 0.03), lower probing depth (P = 0.0002), and clinical attachment loss (P = 0.03). Prevalence of cardiovascular diseases (CVD) and systemic inflammatory markers, plasma interleukin-6 (IL-6), and serum immunoglobulin G titer against Porphyromonas gingivalis positively associated with severity of periodontitis (P = 0.002 and 0.02, respectively). Antibody titer to P. gingivalis correlated positively and significantly with CVD, serum IL-6, and high-sensitivity C-reactive protein.

CONCLUSIONS

Some Medalists could be protected from severe periodontitis even with hyperglycemia. Endogenous protective factors for periodontitis could possibly be related to residual insulin production and lower levels of chronic inflammation.

Cognitive Function Deficits Associated With Long-Duration Type 1 Diabetes and Vascular Complications

OBJECTIVE

Patients with type 1 diabetes now live long enough to experience cognitive decline. During middle age, they show mild cognitive deficits, but it is unknown whether severity increases with aging or whether cognitive profiles are similar to those of age-matched peers with and without diabetes.

RESEARCH DESIGN AND METHODS

We tested and compared cognition in 82 individuals with 50 or more years of type 1 diabetes (Medalists), 31 age-matched individuals with type 2 diabetes, and 30 age-matched control subjects without diabetes. Medical histories and biospecimens were collected. We also evaluated the association of complications with cognition in Medalists only.

RESULTS

Compared with control subjects, both individuals with type 1 diabetes and individuals with type 2 diabetes performed worse on immediate and delayed recall (P ≤ 0.002) and psychomotor speed in both hands (P ≤ 0.01) and showed a trend toward worse executive function (P = 0.05). In Medalists, cardiovascular disease was associated with decreased executive function and proliferative diabetic retinopathy with slower psychomotor speed.

CONCLUSIONS

Both patients with type 1 and patients with type 2 diabetes showed overall worse cognition than control subjects. Further, in Medalists, a relationship between complications and cognition was seen. Although both groups with diabetes showed similar deficit patterns, the underlying mechanisms may be different. Now that patients with type 1 diabetes are living longer, efforts should be made to evaluate cognition and to identify modifying behaviors to slow decline.

Meta-genome-wide association studies identify a locus on chromosome 1 and multiple variants in the MHC region for serum C-peptide in type 1 diabetes

AIMS/HYPOTHESIS

The aim of this study was to identify genetic variants associated with beta cell function in type 1 diabetes, as measured by serum C-peptide levels, through meta-genome-wide association studies (meta-GWAS).

METHODS

We performed a meta-GWAS to combine the results from five studies in type 1 diabetes with cross-sectionally measured stimulated, fasting or random C-peptide levels, including 3479 European participants. The p values across studies were combined, taking into account sample size and direction of effect. We also performed separate meta-GWAS for stimulated (n = 1303), fasting (n = 2019) and random (n = 1497) C-peptide levels.

RESULTS

In the meta-GWAS for stimulated/fasting/random C-peptide levels, a SNP on chromosome 1, rs559047 (Chr1:238753916, T>A, minor allele frequency [MAF] 0.24-0.26), was associated with C-peptide (p = 4.13 × 10^-8), meeting the genome-wide significance threshold (p < 5 × 10^-8). In the same meta-GWAS, a locus in the MHC region (rs9260151) was close to the genome-wide significance threshold (Chr6:29911030, C>T, MAF 0.07-0.10, p = 8.43 × 10^-8). In the stimulated C-peptide meta-GWAS, rs61211515 (Chr6:30100975, T/-, MAF 0.17-0.19) in the MHC region was associated with stimulated C-peptide (β [SE] = - 0.39 [0.07], p = 9.72 × 10^-8). rs61211515 was also associated with the rate of stimulated C-peptide decline over time in a subset of individuals (n = 258) with annual repeated measures for up to 6 years (p = 0.02). In the meta-GWAS of random C-peptide, another MHC region, SNP rs3135002 (Chr6:32668439, C>A, MAF 0.02-0.06), was associated with C-peptide (p = 3.49 × 10^-8). Conditional analyses suggested that the three identified variants in the MHC region were independent of each other. rs9260151 and rs3135002 have been associated with type 1 diabetes, whereas rs559047 and rs61211515 have not been associated with a risk of developing type 1 diabetes.

CONCLUSIONS/INTERPRETATION

We identified a locus on chromosome 1 and multiple variants in the MHC region, at least some of which were distinct from type 1 diabetes risk loci, that were associated with C-peptide, suggesting partly non-overlapping mechanisms for the development and progression of type 1 diabetes. These associations need to be validated in independent populations. Further investigations could provide insights into mechanisms of beta cell loss and opportunities to preserve beta cell function.

Differential Association of Microvascular Attributions With Cardiovascular Disease in Patients With Long Duration of Type 1 Diabetes

OBJECTIVE

Independent association of chronic kidney disease (CKD) and proliferative diabetic retinopathy (PDR) with cardiovascular disease (CVD) has not been established. In the Joslin 50-Year Medalist study, characterizing individuals with type 1 diabetes for 50 years or more, we examined the associations of CKD and PDR with CVD, which was validated by another cohort with type 1 diabetes from Finland.

RESEARCH DESIGN AND METHODS

This cross-sectional study characterized U.S. residents (n = 762) with type 1 diabetes of 50 years or longer (Medalists) at a single site by questionnaire, clinical, ophthalmic, and laboratory studies. A replication cohort (n = 675) from the longitudinal Finnish Diabetic Nephropathy Study (FinnDiane) was used. CKD and PDR were defined as estimated glomerular filtration rate <45 mL/min/1.73 m² (CKD stage 3b) and according to the Early Treatment Diabetic Retinopathy Study (ETDRS) protocol, respectively. CVD was based on questionnaires and/or hospital discharge registers. Associations of CVD status with CKD and PDR were analyzed by multivariable logistic regression.

RESULTS

CVD prevalence in the Medalists with CKD and without PDR (+CKD/-PDR) (n = 30) and CVD prevalence in the -CKD/+PDR group (n = 339) were half the prevalence in the +CKD/+PDR group (n = 66) (34.5% and 42.8% vs. 68.2%, P = 0.002). PDR status was independently associated with CVD (odds ratio 0.21 [95% CI 0.08-0.58], P = 0.003) in patients with CKD. Among the Finnish cohort, a trend toward a lower prevalence of CVD in the +CKD/-PDR group (n = 21) compared with the +CKD/+PDR group (n = 170) (19.1% vs. 37.1%, P = 0.10) was also observed.

CONCLUSIONS

Absence of PDR in people with type 1 diabetes and CKD was associated with a decreased prevalence of CVD, suggesting that common protective factors for PDR and CVD may exist.

Obesity-associated glomerular inflammation increases albuminuria without renal histological changes

Obesity is one of risk factors for chronic kidney disease (CKD), but the precise mechanism involved is unclear. This study characterizes the effect of obesity-induced glomerular inflammation, oxidative stress, and albuminuria in obese rats. Glomerular samples were collected from fatty (ZF) and lean (ZL) Zucker rats. After 2 months of feeding, body weight and albuminuria were significantly increased in ZF rats when compared to ZL rats. Expression of the inflammatory markers TNF-α and CCR2 was significantly increased in the glomeruli of ZF rats. However, expression of IL-6 mRNA was not increased. Analysis of renal pathology showed no glomerular expansion. As inflammatory and oxidative stress markers are associated with NF-κB, we evaluated whether NF-κB activation was increased in the glomeruli of mice on a high-fat diet. Immunohistochemistry showed increased NF-κB activation in the glomeruli when transgenic mice overexpressing an NF-κB-dependent enhanced green fluorescent protein were fed with a high-fat diet. These results suggest that obesity of only 2 months duration can cause albuminuria, due to increased inflammation or oxidative stress, but may not be long enough to develop renal pathological changes.

Diabetic Microvascular Disease: An Endocrine Society Scientific Statement

Both type 1 and type 2 diabetes adversely affect the microvasculature in multiple organs. Our understanding of the genesis of this injury and of potential interventions to prevent, limit, or reverse injury/dysfunction is continuously evolving. This statement reviews biochemical/cellular pathways involved in facilitating and abrogating microvascular injury. The statement summarizes the types of injury/dysfunction that occur in the three classical diabetes microvascular target tissues, the eye, the kidney, and the peripheral nervous system; the statement also reviews information on the effects of diabetes and insulin resistance on the microvasculature of skin, brain, adipose tissue, and cardiac and skeletal muscle. Despite extensive and intensive research, it is disappointing that microvascular complications of diabetes continue to compromise the quantity and quality of life for patients with diabetes. Hopefully, by understanding and building on current research findings, we will discover new approaches for prevention and treatment that will be effective for future generations.

Exogenous Insulin Infusion Can Decrease Atherosclerosis in Diabetic Rodents by Improving Lipids, Inflammation, and Endothelial Function

OBJECTIVE

The objective of this study is to evaluate whether exogenously induced hyperinsulinemia may increase the development of atherosclerosis.

APPROACH AND RESULTS

Hyperinsulinemia, induced by exogenous insulin implantation in high-fat fed (60% fat HFD) apolipoprotein E-deficient mice (ApoE^-/-) mice, exhibited insulin resistance, hyperglycemia, and hyperinsulinemia. Atherosclerosis was measured by the accumulation of fat, macrophage, and extracellular matrix in the aorta. After 8 weeks on HFD, ApoE^-/- mice were subcutaneously implanted with control (sham) or insulin pellet, and phlorizin, a sodium glucose cotransporters inhibitor (1/2)inhibitor, for additional 8 weeks. Intraperitoneal glucose tolerance test showed that plasma glucose levels were lower and insulin and IGF-1 (insulin-like growth factor-1) levels were 5.3- and 3.3-fold higher, respectively, in insulin-implanted compared with sham-treated ApoE^-/- mice. Plasma triglyceride, cholesterol, and lipoprotein levels were decreased in mice with insulin implant, in parallel with increased lipoprotein lipase activities. Atherosclerotic plaque by en face and complexity staining showed significant reductions of fat deposits and expressions of vascular adhesion molecule-1, tumor necrosis factor-α, interleukin 6, and macrophages in arterial wall while exhibiting increased activation of pAKT and endothelial nitric oxide synthase (P<0.05) comparing insulin-implanted versus sham HFD ApoE^-/- mice. No differences were observed in atherosclerotic plaques between phlorizin-treated and sham HFD ApoE^-/- mice, except phlorizin significantly lowered plasma glucose and glycated hemoglobin levels while increased glucosuria. Endothelial function was improved only by insulin treatment through endothelial nitric oxide synthase/nitric oxide activations and reduced proinflammatory (M1) and increased anti-inflammatory (M2) macrophages, which were inhibited by endothelial nitric oxide synthase inhibitor.

CONCLUSIONS

Exogenous insulin decreased atherosclerosis by lowering inflammatory cytokines, macrophages, and plasma lipids in HFD-induced hyperlipidemia, insulin resistant and mildly diabetic ApoE^-/- mice.

Association of Glycemic Control With Reduced Risk for Large-Vessel Disease After More Than 50 Years of Type 1 Diabetes

Context

Previously we demonstrated, in individuals who have had type 1 diabetes (T1D) for 50 or more years (Medalists), that glycemic control was unrelated to diabetic complications, with the exception of cardiovascular disease (CVD), contrary to what has been documented in registry-based studies.

Objective

The purpose of this study is to validate these initial findings and identify contributors to mortality on an individual basis in a large cohort.

Design

Cross-sectional and longitudinal study.

Setting

Joslin Diabetes Center (JDC), Boston, Massachusetts.

Patients

50-year Medalists presenting to JDC for study participation.

Interventions

None.

Main Outcomes Measures

Microvascular and macrovascular complications of diabetes and mortality.

Results

Glycemic control was not significantly associated with small-vessel complications in Medalists but was associated with CVD in the overall cohort, yet with varying effect by tertile of cohort duration. CVD was the largest contributor to mortality, whereas hemoglobin A1c was not an independent predictor of mortality either overall or substantially by diagnosis interval. Additionally, exercise mitigated mortality risk imparted by CVD.

Conclusions

Few large populations with long duration of (T1D) have been available to examine the effects of long-term exposure to hyperglycemia. These data indicate that an association of glycemic control, complications, and mortality may change in an older population with T1D. These results suggest that careful control is still warranted in older populations with T1D.

High density lipoprotein modulates osteocalcin expression in circulating monocytes: a potential protective mechanism for cardiovascular disease in type 1 diabetes

Background

Cardiovascular disease (CVD) is a major cause of mortality in type 1 diabetes (T1D). A pro-calcific drift of circulating monocytes has been linked to vascular calcification and is marked by the surface expression of osteocalcin (OCN). We studied OCN+ monocytes in a unique population with ≥50 years of T1D, the 50-Year Joslin Medalists (J50M).

Methods

CD45 bright/CD14+/OCN+ cells in the circulating mononuclear blood cell fraction were quantified by flow cytometry and reported as percentage of CD45 bright cells. Mechanisms were studied by inducing OCN expression in human monocytes in vitro.

Results

Subjects without history of CVD (n = 16) showed lower levels of OCN+ monocytes than subjects with CVD (n = 14) (13.1 ± 8.4% vs 19.9 ± 6.4%, p = 0.02). OCN+ monocytes level was inversely related to total high density lipoprotein (HDL) cholesterol levels (r = −0.424, p = 0.02), large (r = −0.413, p = 0.02) and intermediate (r = −0.445, p = 0.01) HDL sub-fractions, but not to small HDL. In vitro, incubation with OxLDL significantly increased the number of OCN+ monocytes (p < 0.01). This action of OxLDL was significantly reduced by the addition of HDL in a concentration dependent manner (p < 0.001). Inhibition of the scavenger receptor B1 reduced the effects of both OxLDL and HDL (p < 0.05).

Conclusions

Low OCN+ monocytes levels are associated with lack of CVD in people with long duration T1D. A possible mechanism for the increased OCN+ monocytes could be the elevated levels of oxidized lipids due to diabetes which may be inhibited by HDL. These findings suggest that circulating OCN+ monocytes could be a marker for vascular disease in diabetic patients and possibly modified by HDL elevation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-017-0599-2) contains supplementary material, which is available to authorized users.

Regulation of Macrophage Apoptosis and Atherosclerosis by Lipid-Induced PKCδ Isoform Activation

RATIONALE

Activation of monocytes/macrophages by hyperlipidemia associated with diabetes mellitus and obesity contributes to the development of atherosclerosis. PKCδ (protein kinase C δ) expression and activity in monocytes were increased by hyperlipidemia and diabetes mellitus with unknown consequences to atherosclerosis.

OBJECTIVE

To investigate the effect of PKCδ activation in macrophages on the severity of atherosclerosis.

METHODS AND RESULTS

PKCδ expression and activity were increased in Zucker diabetic rats. Mice with selective deletion of PKCδ in macrophages were generated by breeding PKCδ flox/flox mice with LyzM-Cre and ApoE^-/- mice (MPKCδKO/ApoE^-/- mice) and studied in atherogenic (AD) and high-fat diet (HFD). Mice fed AD and HFD exhibited hyperlipidemia, but only HFD-fed mice had insulin resistance and mild diabetes mellitus. Surprisingly, MPKCδKO/ApoE^-/- mice exhibited accelerated aortic atherosclerotic lesions by 2-fold versus ApoE^-/- mice on AD or HFD. Splenomegaly was observed in MPKCδKO/ApoE^-/- mice on AD and HFD but not on regular chow. Both the AD or HFD increased macrophage number in aortic plaques and spleen by 1.7- and 2-fold, respectively, in MPKCδKO/ApoE^-/- versus ApoE^-/- mice because of decreased apoptosis (62%) and increased proliferation (1.9-fold), and not because of uptake, with parallel increased expressions of inflammatory cytokines. Mechanisms for the increased macrophages in MPKCδKO/ApoE^-/- were associated with elevated phosphorylation levels of prosurvival cell-signaling proteins, Akt and FoxO3a, with reduction of proapoptotic protein Bim associated with PKCδ induced inhibition of P85/PI3K.

CONCLUSIONS

Accelerated development of atherosclerosis induced by insulin resistance and hyperlipidemia may be partially limited by PKCδ isoform activation in the monocytes, which decreased its number and inflammatory responses in the arterial wall.

Pyruvate kinase M2 activation may protect against the progression of diabetic glomerular pathology and mitochondrial dysfunction

Diabetic nephropathy (DN) is a major cause of end-stage renal disease, and therapeutic options for preventing its progression are limited. To identify novel therapeutic strategies, we studied protective factors for DN using proteomics on glomeruli from individuals with extreme duration of diabetes (ł50 years) without DN and those with histologic signs of DN. Enzymes in the glycolytic, sorbitol, methylglyoxal and mitochondrial pathways were elevated in individuals without DN. In particular, pyruvate kinase M2 (PKM2) expression and activity were upregulated. Mechanistically, we showed that hyperglycemia and diabetes decreased PKM2 tetramer formation and activity by sulfenylation in mouse glomeruli and cultured podocytes. Pkm-knockdown immortalized mouse podocytes had higher levels of toxic glucose metabolites, mitochondrial dysfunction and apoptosis. Podocyte-specific Pkm2-knockout (KO) mice with diabetes developed worse albuminuria and glomerular pathology. Conversely, we found that pharmacological activation of PKM2 by a small-molecule PKM2 activator, TEPP-46, reversed hyperglycemia-induced elevation in toxic glucose metabolites and mitochondrial dysfunction, partially by increasing glycolytic flux and PGC-1α mRNA in cultured podocytes. In intervention studies using DBA2/J and Nos3 (eNos) KO mouse models of diabetes, TEPP-46 treatment reversed metabolic abnormalities, mitochondrial dysfunction and kidney pathology. Thus, PKM2 activation may protect against DN by increasing glucose metabolic flux, inhibiting the production of toxic glucose metabolites and inducing mitochondrial biogenesis to restore mitochondrial function.

Beta 2-adrenergic receptor agonists are novel regulators of macrophage activation in diabetic renal and cardiovascular complications

Macrophage activation is increased in diabetes and correlated with the onset and progression of vascular complications. To identify drugs that could inhibit macrophage activation, we developed a cell-based assay and screened a 1,040 compound library for anti-inflammatory effects. Beta2-adrenergic receptor (β2AR) agonists were identified as the most potent inhibitors of phorbol myristate acetate-induced tumor necrosis factor-α production in rat bone marrow macrophages. In peripheral blood mononuclear cells isolated from streptozotocin-induced diabetic rats, β2AR agonists inhibited diabetes-induced tumor necrosis factor-α production, which was prevented by co-treatment with a selective β2AR blocker. To clarify the underlying mechanisms, THP-1 cells and bone marrow macrophages were exposed to high glucose. High glucose reduced β-arrestin2, a negative regulator of NF-κB activation, and its interaction with IκBα. This subsequently enhanced phosphorylation of IκBα and activation of NF-κB. The β2AR agonists enhanced β-arrestin2 and its interaction with IκBα, leading to downregulation of NF-κB. A siRNA specific for β-arrestin2 reversed β2AR agonist-mediated inhibition of NF-κB activation and inflammatory cytokine production. Treatment of Zucker diabetic fatty rats with a β2AR agonist for 12 weeks attenuated monocyte activation as well as pro-inflammatory and pro-fibrotic responses in the kidneys and heart. Thus, β2AR agonists might have protective effects against diabetic renal and cardiovascular complications.

SHP-1 activation inhibits vascular smooth muscle cell proliferation and intimal hyperplasia in a rodent model of insulin resistance and diabetes

AIMS/HYPOTHESIS

Accelerated migration and proliferation of vascular smooth muscle cells (VSMCs) enhances arterial restenosis after angioplasty in insulin resistance and diabetes. Elevation of Src homology 2-containing protein tyrosine phosphatase 1 (SHP-1) induces apoptosis in the microvasculature. However, the role of SHP-1 in intimal hyperplasia and restenosis has not been clarified in insulin resistance and diabetes.

METHODS

We used a femoral artery wire injury mouse model, rodent models with insulin resistance and diabetes, and patients with type 2 diabetes. Further, we modulated SHP-1 expression using a transgenic mouse that overexpresses SHP-1 in VSMCs (Shp-1-Tg). SHP-1 agonists were also employed to study the molecular mechanisms underlying the regulation of SHP-1 by oxidised lipids.

RESULTS

Mice fed a high-fat diet (HFD) exhibited increased femoral artery intimal hyperplasia and decreased arterial SHP-1 expression compared with mice fed a regular diet. Arterial SHP-1 expression was also decreased in Zucker fatty rats, Zucker diabetic fatty rats and in patients with type 2 diabetes. In primary cultured VSMCs, oxidised LDL suppressed SHP-1 expression by activating Mek-1 (also known as Map2k1) and increased DNA methylation of the Shp-1 promoter. VSMCs from Shp-1-Tg mice exhibited impaired platelet-derived growth factor (PDGF)-stimulated tyrosine phosphorylation with a concomitant decrease in PDGF-stimulated VSMC proliferation and migration. Similarly, HFD-fed Shp-1-Tg mice and mice treated with the SHP-1 inducer, Icariside II, were protected from the development of intimal hyperplasia following wire injury.

CONCLUSIONS/INTERPRETATION

Suppression of SHP-1 by oxidised lipids may contribute to the excessive VSMC proliferation, inflammatory cytokine production and intimal hyperplasia observed in arteries from diabetes and insulin resistance. Augmenting SHP-1 levels is a potential therapeutic strategy to maintain stent patency in patients with insulin resistance and diabetes.

Overexpressing IRS1 in Endothelial Cells Enhances Angioblast Differentiation and Wound Healing in Diabetes and Insulin Resistance

The effect of enhancing insulin's actions in endothelial cells (ECs) to improve angiogenesis and wound healing was studied in obesity and diabetes. Insulin receptor substrate 1 (IRS1) was overexpressed in ECs using the VE-cadherin promoter to create ECIRS1 TG mice, which elevated pAkt activation and expressions of vascular endothelial growth factor (VEGF), Flk1, and VE-cadherin in ECs and granulation tissues (GTs) of full-thickness wounds. Open wound and epithelialization rates and angiogenesis significantly improved in normal mice and high fat (HF) diet-induced diabetic mice with hyperinsulinemia in ECIRS1 TG versus wild type (WT), but not in insulin-deficient diabetic mice. Increased angioblasts and EC numbers in GT of ECIRS1 mice were due to proliferation in situ rather than uptake. GT in HF-fed diabetic mice exhibited parallel decreases in insulin and VEGF-induced pAkt and EC numbers by >50% without changes in angioblasts versus WT mice, which were improved in ECIRS1 TG mice on normal chow or HF diet. Thus, HF-induced diabetes impaired angiogenesis by inhibiting insulin signaling in GT to decrease the differentiation of angioblasts to EC, which was normalized by enhancing insulin's action targeted to EC, a potential target to improve wound healing in diabetes and obesity.

Selective Insulin Resistance and the Development of Cardiovascular Diseases in Diabetes: The 2015 Edwin Bierman Award Lecture

The Edwin Bierman Award Lecture is presented in honor of the memory of Edwin L. Bierman, MD, an exemplary scientist, mentor, and leader in the field of diabetes, obesity, hyperlipidemia, and atherosclerosis. The award and lecture recognizes a leading scientist in the field of macrovascular complications and contributing risk factors in diabetes. George L. King, MD, of the Section of Vascular Cell Biology and Complications, Dianne Nunnally Hoppes Laboratory for Diabetes Complications, Joslin Diabetes Center, Harvard Medical School, Boston, MA, received the prestigious award at the American Diabetes Association's 75th Scientific Sessions, 5-9 June 2015, in Boston, MA. He presented the Edwin Bierman Award Lecture, "Selective Insulin Resistance and the Development of Cardiovascular Disease in Diabetes," on Sunday, 7 June 2015.This review is focused on the factors and potential mechanisms that are causing various cardiovascular pathologies. In diabetes, insulin's actions on the endothelium and other vascular cells have significant influence on systemic metabolisms and the development of cardiovascular pathologies. Our studies showed that insulin receptors on the endothelium are important for insulin transport across the endothelial barrier and mediate insulin's actions in muscle, heart, fat, and the brain. Insulin actions on the vascular cells are mediated by two pathways involving the actions of either IRS/PI3K/Akt or Grb/Shc/MAPK. Insulin's activation of IRS/PI3K/Akt results in mostly antiatherogenic actions, as this pathway induces activation of eNOS, the expressions of HO-1 and VEGF, and the reduction of VCAM-1. In contrast, insulin's activation of the Grb/Shc/MAPK pathway mediates the expressions of ET-1 and PAI-1 and migration and proliferation of contractile cells, which have proatherogenic actions. Elevated levels of glucose, free fatty acids, and inflammatory cytokines due to diabetes and insulin resistance selectively inhibit insulin's antiatherogenic actions via the IRS/PI3K/Akt pathway. This review provides evidence to support the importance of insulin actions in preventing cardiovascular pathology that can be selectively inhibited via the IRS/PI3K/Akt cascade in diabetes.

Insulin decreases atherosclerosis by inducing endothelin receptor B expression

Endothelial cell (EC) insulin resistance and dysfunction, caused by diabetes, accelerates atherosclerosis. It is unknown whether specifically enhancing EC-targeted insulin action can decrease atherosclerosis in diabetes. Accordingly, overexpressing insulin receptor substrate-1 (IRS1) in the endothelia of Apoe^-/- mice (Irs1/Apoe^-/-) increased insulin signaling and function in the aorta. Atherosclerosis was significantly reduced in Irs1/ApoE^-/- mice on diet-induced hyperinsulinemia and hyperglycemia. The mechanism of insulin's enhanced antiatherogenic actions in EC was related to remarkable induction of NO action, which increases endothelin receptor B (EDNRB) expression and intracellular [Ca²⁺]. Using the mice with knockin mutation of eNOS, which had Ser1176 mutated to alanine (AKI), deleting the only known mechanism for insulin to activate eNOS/NO pathway, we observed that IRS1 overexpression in the endothelia of Aki/ApoE^-/- mice significantly decreased atherosclerosis. Interestingly, endothelial EDNRB expression was selectively reduced in intima of arteries from diabetic patients and rodents. However, endothelial EDNRB expression was upregulated by insulin via P13K/Akt pathway. Finally EDNRB deletion in EC of Ldlr^-/- and Irs1/Ldlr^-/- mice decreased NO production and accelerated atherosclerosis, compared with Ldlr^-/- mice. Accelerated atherosclerosis in diabetes may be reduced by improving insulin signaling selectively via IRS1/Akt in the EC by inducing EDNRB expression and NO production.

PKCδ inhibition normalizes the wound-healing capacity of diabetic human fibroblasts

Abnormal fibroblast function underlies poor wound healing in patients with diabetes; however, the mechanisms that impair wound healing are poorly defined. Here, we evaluated fibroblasts from individuals who had type 1 diabetes (T1D) for 50 years or more (Medalists, n = 26) and from age-matched controls (n = 7). Compared with those from controls, Medalist fibroblasts demonstrated a reduced migration response to insulin, lower VEGF expression, and less phosphorylated AKT (p-AKT), but not p-ERK, activation. Medalist fibroblasts were also functionally less effective at wound closure in nude mice. Activation of the δ isoform of protein kinase C (PKCδ) was increased in postmortem fibroblasts from Medalists, fibroblasts from living T1D subjects, biopsies of active wounds of living T1D subjects, and granulation tissues from mice with streptozotocin-induced diabetes. Diabetes-induced PKCD mRNA expression was related to a 2-fold increase in the mRNA half-life. Pharmacologic inhibition and siRNA-mediated knockdown of PKCδ or expression of a dominant-negative isoform restored insulin signaling of p-AKT and VEGF expression in vitro and improved wound healing in vivo. Additionally, increasing PKCδ expression in control fibroblasts produced the same abnormalities as those seen in Medalist fibroblasts. Our results indicate that persistent PKCδ elevation in fibroblasts from diabetic patients inhibits insulin signaling and function to impair wound healing and suggest PKCδ inhibition as a potential therapy to improve wound healing in diabetic patients.

Associations between metabolic dysregulation and circulating biomarkers of fibrosis: the Cardiovascular Health Study

AIM

Fibrosis is one postulated pathway by which diabetes produces cardiac and other systemic complications. Our aim was to determine which metabolic parameters are associated with circulating fibrosis-related biomarkers transforming growth factor-β (TGF-β) and procollagen type III N-terminal propeptide (PIIINP).

METHODS

We used linear regression to determine the cross-sectional associations of diverse metabolic parameters, including fasting glucose, fasting insulin, body mass index, fatty acid binding protein 4, and non-esterified fatty acids, with circulating levels of TGF-β (n = 1559) and PIIINP (n = 3024) among community-living older adults in the Cardiovascular Health Study.

RESULTS

Among the main metabolic parameters we examined, only fasting glucose was associated with TGF-β (P = 0.03). In contrast, multiple metabolic parameters were associated with PIIINP, including fasting insulin, body mass index, and non-esterified fatty acids (P<0.001, P<0.001, P=0.001, respectively). These associations remained statistically significant after mutual adjustment, except the association between BMI and PIIINP.

CONCLUSIONS

Isolated hyperglycemia is associated with higher serum concentrations of TGF-β, while a broader phenotype of insulin resistance is associated with higher serum PIIINP. Whether simultaneous pharmacologic targeting of these two metabolic phenotypes can synergistically reduce the risk of cardiac and other manifestations of fibrosis remains to be determined.

PKC-β activation inhibits IL-18-binding protein causing endothelial dysfunction and diabetic atherosclerosis

AIMS

Clinical observations showed a correlation between accelerated atherosclerosis in diabetes and high plasmatic level of IL-18, a pro-inflammatory cytokine. IL-18 enhances the production of inflammatory cytokines and cellular adhesion molecules contributing to atherosclerotic plaque formation and instability. Previous studies indicated that protein kinase C (PKC)-β inhibition prevented macrophage-induced cytokine expression involved in diabetic (DM) atherosclerotic plaque development. However, the role of PKC-β activation on IL-18/IL-18-binding protein (IL-18BP) pathway causing endothelial dysfunction and monocyte adhesion in diabetes has never been explored.

METHODS AND RESULTS

Apoe(-/-) mice were rendered DM and fed with western diet containing ruboxistaurin (RBX), a PKC-β inhibitor. After 20 weeks, atherosclerotic plaque composition was quantified. Compared with non-diabetic, DM mice exhibited elevated atherosclerotic plaque formation, cholestoryl ester content and macrophage infiltration, as well as reduced IL-18BP expression in the aorta which was prevented with RBX treatment. Endothelial cells (ECs) and macrophages were exposed to normal or high glucose (HG) levels with or without palmitate and recombinant IL-18 for 24 h. The combined HG and palmitate condition was required to increase IL-18 expression and secretion in macrophages, while it reduced IL-18BP expression in EC causing up-regulation of the vascular cell adhesion molecule (VCAM)-1 and monocyte adhesion. Elevated VCAM-1 expression and monocyte adherence were prevented by siRNA, RBX, and IL-18 neutralizing antibody.

CONCLUSION

Our study unrevealed a new mechanism by which PKC-β activation promotes EC dysfunction caused by the de-regulation of the IL-18/IL-18BP pathway, leading to increased VCAM-1 expression, monocyte/macrophage adhesion, and accelerated atherosclerotic plaque formation in diabetes.

Improvement of insulin sensitivity by isoenergy high carbohydrate traditional Asian diet: a randomized controlled pilot feasibility study

The prevalence of diabetes is rising dramatically among Asians, with increased consumption of the typical Western diet as one possible cause. We explored the metabolic responses in East Asian Americans (AA) and Caucasian Americans (CA) when transitioning from a traditional Asian diet (TAD) to a typical Western diet (TWD), which has not been reported before. This 16-week randomized control pilot feasibility study, included 28AA and 22CA who were at risk of developing type 2 diabetes. Eight weeks of TAD were provided to all participants, followed by 8 weeks of isoenergy TWD (intervention) or TAD (control). Anthropometric measures, lipid profile, insulin resistance and inflammatory markers were assessed. While on TAD, both AA and CA improved in insulin AUC (-960.2 µU/mL × h, P = 0.001) and reduced in weight (-1.6 kg; P<0.001), body fat (-1.7%, P<0.001) and trunk fat (-2.2%, P<0.001). Comparing changes from TAD to TWD, AA had a smaller weight gain (-1.8 to 0.3 kg, P<0.001) than CA (-1.4 to 0.9 kg, P = 0.001), but a greater increase in insulin AUC (AA: -1402.4 to 606.2 µU/mL × h, P = 0.015 vs CA: -466.0 to 223.5 µU/mL × h, P = 0.034) and homeostatic static model assessment-insulin resistance (HOMA-IR) (AA: -0.3 to 0.2, P = 0.042 vs CA: -0.1 to 0.0, P = 0.221). Despite efforts to maintain isoenergy state and consumption of similar energy, TAD induced weight loss and improved insulin sensitivity in both groups, while TWD worsened the metabolic profile.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00379548.

Characterization of circulating and endothelial progenitor cells in patients with extreme-duration type 1 diabetes

OBJECTIVE

We characterized and correlated endothelial progenitor cells (EPCs) and circulating progenitor cells (CPCs) with lack of vascular complications in the Joslin Medalist Study in patients with type 1 diabetes for 50 years or longer.

RESEARCH DESIGN AND METHODS

EPC and CPC levels were ascertained by flow cytometry and compared among Medalists (n = 172) with or without diabetic retinopathy (DR; n = 84 of 162), neuropathy (n = 94 of 165), diabetic nephropathy (DN; n = 18 of 172), cardiovascular disease (CVD; n = 63 of 168), age-matched controls (n = 83), type 2 diabetic patients (n = 36), and younger type 1 diabetic patients (n = 31). Mitogens, inflammatory cytokines, and oxidative markers were measured in blood or urine. Migration of cultured peripheral blood mononuclear cells (PBMCs) from Medalists and age-matched controls were compared.

RESULTS

Medalists' EPC and CPC levels equaled those of their nondiabetic age-matched controls, were 10% higher than those in younger type 1 diabetic patients, and were 20% higher than those in age-matched type 2 diabetic patients. CPC levels were 15% higher in Medalists without CVD and nephropathy than in those affected, whereas EPC levels were significantly higher in those without peripheral vascular disease (PVD) than those with PVD. Stromal-derived factor 1 (SDF-1) levels were higher in Medalists with CVD, DN, and DR than in those not affected and their controls. IGF-I levels were lower in Medalists and correlated inversely with CPC levels. Additionally, cultured PBMCs from Medalists migrated more than those from nondiabetic controls.

CONCLUSIONS

Normal levels of EPC and CPC in the Medalists, unlike other groups with diabetes, especially those without CVD, support the idea that endogenous factors exist to neutralize the adverse effects of metabolic abnormalities of diabetes on vascular tissues.

Molecular mechanisms of diabetic vascular complications

Diabetic complications are the major causes of morbidity and mortality in patients with diabetes. Microvascular complications include retinopathy, nephropathy and neuropathy, which are leading causes of blindness, end‐stage renal disease and various painful neuropathies; whereas macrovascular complications involve atherosclerosis related diseases, such as coronary artery disease, peripheral vascular disease and stroke. Diabetic complications are the result of interactions among systemic metabolic changes, such as hyperglycemia, local tissue responses to toxic metabolites from glucose metabolism, and genetic and epigenetic modulators. Chronic hyperglycemia is recognized as a major initiator of diabetic complications. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on vascular tissues. These include increased polyol pathway, activation of the diacylglycerol/protein kinase C pathway, increased oxidative stress, overproduction and action of advanced glycation end products, and increased hexosamine pathway. In addition, the alterations of signal transduction pathways induced by hyperglycemia or toxic metabolites can also lead to cellular dysfunctions and damage vascular tissues by altering gene expression and protein function. Less studied than the toxic mechanisms, hyperglycemia might also inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, platelet‐derived growth factor and activated protein C, which play important roles in maintaining vascular homeostasis. Thus, effective therapies for diabetic complications need to inhibit mechanisms induced by hyperglycemia’s toxic effects and also enhance the endogenous protective factors. The present review summarizes these multiple biochemical pathways activated by hyperglycemia and the potential therapeutic interventions that might prevent diabetic complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00018.x, 2010)

A high-fiber, low-fat diet improves periodontal disease markers in high-risk subjects: a pilot study

Periodontal disease is related to aging, smoking habits, diabetes mellitus, and systemic inflammation. However, there remains limited evidence about causality from intervention studies. An effective diet for prevention of periodontal disease has not been well established. The current study was an intervention study examining the effects of a high-fiber, low-fat diet on periodontal disease markers in high-risk subjects. Forty-seven volunteers were interviewed for recruitment into the study. Twenty-one volunteers with a body mass index of at least 25.0 kg/m(2) or with impaired glucose tolerance were enrolled in the study. After a 2- to 3-week run-in period, subjects were provided with a test meal consisting of high fiber and low fat (30 kcal/kg of ideal body weight) 3 times a day for 8 weeks and followed by a regular diet for 24 weeks. Four hundred twenty-five teeth from 17 subjects were analyzed. Periodontal disease markers assessed as probing depth (2.28 vs 2.21 vs 2.13 mm; P < .0001), clinical attachment loss (6.11 vs 6.06 vs 5.98 mm; P < .0001), and bleeding on probing (16.2 vs 13.2 vs 14.6 %; P = .005) showed significant reductions after the test-meal period, and these improvements persisted until the follow-up period. Body weight (P < .0001), HbA1c (P < .0001), and high-sensitivity C-reactive protein (P = .038) levels showed improvement after the test-meal period; they returned to baseline levels after the follow-up period. In conclusion, treatment with a high-fiber, low-fat diet for 8 weeks effectively improved periodontal disease markers as well as metabolic profiles, at least in part, by effects other than the reduction of total energy intake.

Obesity-associated Gingival Vascular Inflammation and Insulin Resistance

Obesity is a risk factor for periodontitis, but the pathogenic mechanism involved is unclear. We studied the effects of insulin in periodontal tissues during the state of obesity-induced insulin resistance. Gingival samples were collected from fatty (ZF) and lean (ZL, control) Zucker rats. Endothelial nitric oxide synthase (eNOS) expression was decreased, and activities of protein kinase C (PKC) α, ß2, δ, and ϵ isoforms were significantly increased in the gingiva from ZF rats compared with those from ZL rats. Expression of oxidative stress markers (mRNA) and the p65 subunit of NF-κB was significantly increased in ZF rats. Immunohistochemistry revealed that NF-κB activation was also increased in the gingival endothelial cells from transgenic mice overexpressing NF-κB-dependent enhanced green fluorescent protein (GFP) and on a high-fat vs. normal chow diet. Analysis of the gingiva showed that insulin-induced phosphorylation of IRS-1, Akt, and eNOS was significantly decreased in ZF rats, but Erk1/2 activation was not affected. General PKC inhibitor and an anti-oxidant normalized the action of insulin on Akt and eNOS activation in the gingiva from ZF rats. This provided the first documentation of obesity-induced insulin resistance in the gingiva. Analysis of our data suggested that PKC activation and oxidative stress may selectively inhibit insulin-induced Akt and eNOS activation, causing endothelial dysfunction and inflammation.

Willow bark extract increases antioxidant enzymes and reduces oxidative stress through activation of Nrf2 in vascular endothelial cells and Caenorhabditis elegans

Willow bark extract (WBE) is listed in the European Pharmacopoeia and has been traditionally used for treating fever, pain, and inflammation. Recent studies have demonstrated its clinical usefulness. This study investigated the antioxidative effects of WBE in human umbilical vein endothelial cells (HUVECs) and Caenorhabditis elegans. WBE prevented oxidative-stress-induced cytotoxicity of HUVECs and death of C. elegans. WBE dose-dependently increased mRNA and protein expression levels of the nuclear factor erythroid 2-related factor 2 (Nrf2) target genes heme oxygenase-1, γ-glutamylcysteine ligase modifier and catalytic subunits, and p62 and intracellular glutathione (GSH) in HUVECs. In the nematode C. elegans, WBE increased the expression of the gcs-1::green fluorescent protein reporter, a well-characterized target of the Nrf2 ortholog SKN-1, in a manner that was SKN-1-dependent. WBE increased intranuclear expression and DNA binding of Nrf2 and the activity of an antioxidant response element (ARE) reporter plasmid in HUVECs. WBE-induced expression of Nrf2-regulated genes and increased GSH levels in HUVECs were reduced by Nrf2 and p38 small interfering (si) RNAs and by the p38-specific inhibitor SB203580. Nrf2 siRNA reduced the cytoprotective effect of WBE against oxidative stress in HUVECs. Salicin, a major anti-inflammatory ingredient of WBE, failed to activate ARE-luciferase activity, whereas a salicin-free WBE fraction showed intensive activity. WBE induced antioxidant enzymes and prevented oxidative stress through activation of Nrf2 independent of salicin, providing a new potential explanation for the clinical usefulness of WBE.

Sexual dysfunction as a marker of cardiovascular disease in males with 50 or more years of type 1 diabetes

OBJECTIVE

Vascular dysfunction is a major contributor to diabetes complications. It is also the primary physiologic cause of erectile dysfunction and considered an independent predictor of cardiovascular disease (CVD) in males over age 40 years. A cohort of individuals with 50 or more years of type 1 diabetes, Joslin Medalists, have low rates of small but not large vessel complications. This study aims to identify the prevalence and longitudinal association of sexual dysfunction (SD) with CVD in Joslin Medalists.

RESEARCH DESIGN AND METHODS

Description and association of self-assessment of SD in males of the Medalist cohort by self-reported sexual problems with CVD. SD is validated through the use of the abbreviated International Index of Erectile Dysfunction (IIEF).

RESULTS

Of 301 males in the Medalist Study, 69.8% reported a history of SD. Unadjusted risk factors included elevated glycated hemoglobin (HbA1c) (P=0.02), elevated BMI (P=0.03), higher total cholesterol (P=0.02), lower HDL (P<0.01), and increased levels of interleukin-6 (P=0.03). SD was independently associated with CVD (age-, HbA1c-, and BMI-adjusted OR 1.9 [95% CI 1.0-3.5]). In adjusted analyses, retinal, neural, and renal complications were not associated (P>0.05) with SD. Current report of SD (IIEF score≤17) in a subset of Medalists was significantly correlated with self-reported longitudinal SD.

CONCLUSIONS

SD in those with extreme-duration type 1 diabetes is independently associated with CVD, representing a large-vessel pattern. The findings suggest that SD may predict CVD in those with type 1 diabetes of long duration. These individuals have also been found to be relatively free of microvascular complications.

Characterization of factors affecting attainment of glycemic control in Asian Americans with diabetes in a culturally specific program

PURPOSE

The purpose of this study is to examine the effectiveness of a culturally specific pilot clinic for Asian Americans (AA) in reaching glycemic target and to characterize factors affecting the attainment of glycemic control in comparison with white counterparts.

METHODS

This electronic health record review included all new AA patients with type 2 diabetes (n = 109) in a culturally specific program and a randomly selected sample of new white patients with type 2 diabetes (n = 218) in the adult clinic within the same time period and diabetes center.

RESULTS

AA and whites had a comparable proportion of patients with A1C ≤7% (32.1%, 34.9%; P = .621) at baseline and after 12 months of care (48.6%, 56.0%; P = .210), with a similar A1C decline (-0.9% ± 1.6%, -0.8% ± 1.7%, P = .710) by 12 months. Factors associated with the lack of success in reaching target in AA but not in whites included older age, lower educational attainment, less likelihood of having health insurance, and a need for more educational visits. The percentage of AA reaching A1C ≤7%, as compared to whites, worsened among those with highest initial A1C when stratified by ascending quartiles (96.7% vs 85.2%, P = .101; 61.9% vs 58.9%, P = .813; 24.0% vs 37.7%, P = .230; 15.2% vs 35.4%, P = .044).

CONCLUSION

While a culturally specific diabetes program in a specialty setting achieved a similar glycemic outcome for AA compared with whites, reasons for not reaching glycemic target differed. The findings suggest that the elimination of diabetes disparities requires not only culturally and linguistically specific programs, but must also identify and address the socio-environmental differences unique to each population.

Induction of vascular insulin resistance and endothelin-1 expression and acceleration of atherosclerosis by the overexpression of protein kinase C-β isoform in the endothelium

RATIONALE

Loss of insulin action in the endothelium can cause endothelial dysfunction and atherosclerosis. Hyperglycemia and elevated fatty acids induced by diabetes mellitus can activate protein kinase C-β isoforms and selectively inhibit insulin signaling via phosphatidylinositol 3-kinase/Akt pathway to inhibit the activation of endothelial nitric oxide synthase and metabolic actions.

OBJECTIVE

To demonstrate that overexpressing protein kinase C-β2 isoform in endothelial cells can cause selective insulin resistance and exacerbate atherosclerosis in the aorta.

METHODS AND RESULTS

Protein kinase C-β2 isoform was overexpressed in endothelial cells using a promoter of vascular endothelial cell cadherin. These mice were cross-bred with apoE-/- mice [Tg (Prkcb)apoE-/-]. On a Western diet, Tg(Prkcb)apoE-/- and apoE-/- mice did not differ in systemic insulin sensitivity, glucose tolerance, plasma lipid, or blood pressure. Insulin action in endothelial cells and femoral artery from Tg(Prkcb)apoE-/- mice was impaired by ≈40% with respect to Akt/endothelial nitric oxide synthase activation, and leukocyte-endothelial cell binding increased in cultured lung endothelial cells from Tg(Prkcb)apoE-/- mice compared with that from apoE-/- mice. Basal and angiotensin-stimulated big endothelin-1 levels were elevated in Tg(Prkcb)apoE-/- mice compared with apoE-/- mice. The severity of atherosclerosis in the aorta from Tg(Prkcb)apoE-/- mice increased by ≈70% as measured by en face fat staining and plaque content of the number of smooth muscle cells, macrophages, and extracellular matrix.

CONCLUSIONS

Specific protein kinase C-β2 activation in the endothelial cells caused dysfunction and accelerated atherosclerosis because of loss of insulin-stimulated Akt/endothelial nitric oxide synthase activation and angiotensin-induced increases in endothelin-1 expression.