The unique hypusine modification of eIF5A promotes islet beta cell inflammation and dysfunction in mice

In both type 1 and type 2 diabetes, pancreatic islet dysfunction results in part from cytokine-mediated inflammation. The ubiquitous eukaryotic translation initiation factor 5A (eIF5A), which is the only protein to contain the amino acid hypusine, contributes to the production of proinflammatory cytokines. We therefore investigated whether eIF5A participates in the inflammatory cascade leading to islet dysfunction during the development of diabetes. As described herein, we found that eIF5A regulates iNOS levels and that eIF5A depletion as well as the inhibition of hypusination protects against glucose intolerance in inflammatory mouse models of diabetes. We observed that following knockdown of eIF5A expression, mice were resistant to beta cell loss and the development of hyperglycemia in the low-dose streptozotocin model of diabetes. The depletion of eIF5A led to impaired translation of iNOS-encoding mRNA within the islet. A role for the hypusine residue of eIF5A in islet inflammatory responses was suggested by the observation that inhibition of hypusine synthesis reduced translation of iNOS-encoding mRNA in rodent beta cells and human islets and protected mice against the development of glucose intolerance the low-dose streptozotocin model of diabetes. Further analysis revealed that hypusine is required in part for nuclear export of iNOS-encoding mRNA, a process that involved the export protein exportin1. These observations identify the hypusine modification of eIF5A as a potential therapeutic target for preserving islet function under inflammatory conditions.

12-Lipoxygenase Products Reduce Insulin Secretion and {beta}-Cell Viability in Human Islets

CONTEXT

Inflammation is increasingly recognized as an important contributing factor in diabetes mellitus. Lipoxygenases (LOs) produce active lipids that promote inflammatory damage by catalyzing the oxidation of linoleic and arachidonic acid, and LO is expressed in rodent and human islets. Little is known about the differential effect of the various hydroxyeicosatetraenoic acids (HETEs) that result from LO activity in human islets.

OBJECTIVE

We compared the effects of 12-LO products on human islet viability and function.

DESIGN

Human islets were treated with stable compounds derived from LOs: 12(S)-HETE, 15HETE, 12HPETE, and 12RHETE and then examined for insulin secretion and islet viability. The p38-MAPK (p38) and JNK stress-activated pathways were investigated as mechanisms of 12-LO-mediated islet inhibition in rodent and human islets.

RESULTS

Insulin secretion was consistently reduced by 12(S)-HETE and 12HPETE. 12(S)-HETE at 1 nm reduced viability activity by 32% measured by MTT assay and increased cell death by 50% at 100 nm in human islets. These effects were partially reversed with lisofylline, a small-molecule antiinflammatory compound that protects mitochondrial function. 12(S)-HETE increased phosphorylated p38-MAPK (pp38) protein activity in human islets. Injecting 12-LO siRNA into C57BL/6 mice reduced 12-LO and pp38-MAPK protein levels in mouse islets. The addition of proinflammatory cytokines increased pp38 levels in normal mouse islets but not in siRNA-treated islets.

CONCLUSIONS

These data suggest that 12(S)-HETE reduces insulin secretion and increases cell death in human islets. The 12-LO pathway is present in human islets, and expression is up-regulated by inflammatory cytokines. Reduction of 12-LO activity could thus provide a new therapeutic approach to protect human beta-cells from inflammatory injury.

Valsartan protects pancreatic islets and adipose tissue from the inflammatory and metabolic consequences of a high-fat diet in mice

Obesity, hypertension, cardiovascular disease, and inflammation are closely associated with the rising incidence of diabetes mellitus. One pharmacological target that may have significant potential to lower the risk of obesity-related diseases is the angiotensin type 1 receptor (AT1R). We examined the hypothesis that the AT1R blocker valsartan reduces the metabolic consequences and inflammatory effects of a high-fat (Western) diet in mice. C57BL/6J mice were treated by oral gavage with 10 mg/kg per day of valsartan or vehicle and placed on either a standard chow or Western diet for 12 weeks. Western diet-fed mice given valsartan had improved glucose tolerance, reduced fasting blood glucose levels, and reduced serum insulin levels compared with mice fed a Western diet alone. Valsartan treatment also blocked Western diet-induced increases in serum levels of the proinflammatory cytokines interferon-gamma and monocyte chemotactic protein 1. In the pancreatic islets, valsartan enhanced mitochondrial function and prevented Western diet-induced decreases in glucose-stimulated insulin secretion. In adipose tissue, valsartan reduced Western diet-induced macrophage infiltration and expression of macrophage-derived monocyte chemotactic protein 1. In isolated adipocytes, valsartan treatment blocked or attenuated Western diet-induced changes in expression of several key inflammatory signals: interleukin 12p40, interleukin 12p35, tumor necrosis factor-alpha, interferon-gamma, adiponectin, platelet 12-lipoxygenase, collagen 6, inducible NO synthase, and AT1R. Our findings indicate that AT1R blockade with valsartan attenuated several deleterious effects of the Western diet at the systemic and local levels in islets and adipose tissue. This study suggests that AT1R blockers provide additional therapeutic benefits in the metabolic syndrome and other obesity-related disorders beyond lowering blood pressure.

Improved survival and reduced vascular permeability by eliminating or blocking 12/15-lipoxygenase in mouse models of acute lung injury (ALI)

Acute lung injury (ALI) is a prevalent disease associated with high mortality. 12/15-lipoxygenase (12/15-LO) is an enzyme producing 12-hydroxyeicosatetraenoic acid (HETE) and 15-HETE from arachidonic acid. To test whether 12/15-LO is involved in increasing vascular permeability in the lung, we investigated the role of 12/15-LO in murine models of LPS-induced pulmonary inflammation and clinically relevant acid-induced ALI. The vascular permeability increase upon LPS inhalation was abolished in Alox15(-/-) mice lacking 12/15-LO and in wild-type mice after pharmacological blockade of 12/15-LO. Alox15(-/-) mice also showed improved gas exchange, reduced permeability increase, and prolonged survival in the acid-induced ALI model. Bone marrow chimeras and reconstitution experiments revealed that 12-HETE produced by hematopoietic cells regulates vascular permeability through a CXCR2-dependent mechanism. Our findings suggest that 12/15-LO-derived 12-HETE is a key mediator of vascular permeability in acute lung injury.

12/15-lipoxygenase products induce inflammation and impair insulin signaling in 3T3-L1 adipocytes

Inflammation and insulin resistance associated with visceral obesity are important risk factors for the development of type 2 diabetes, atherosclerosis, and the metabolic syndrome. The 12/15-lipoxygenase (12/15-LO) enzyme has been linked to inflammatory changes in blood vessels that precede the development of atherosclerosis. The expression and role of 12/15-LO in adipocytes have not been evaluated. We found that 12/15-LO mRNA was dramatically upregulated in white epididymal adipocytes of high-fat fed mice. 12/15-LO was poorly expressed in 3T3-L1 fibroblasts and was upregulated during differentiation into adipocytes. Interestingly, the saturated fatty acid palmitate, a major component of high fat diets, augmented expression of 12/15-LO in vitro. When 3T3-L1 adipocytes were treated with the 12/15-LO products, 12-hydroxyeicosatetranoic acid (12(S)-HETE) and 12-hydroperoxyeicosatetraenoic acid (12(S)-HPETE), expression of proinflammatory cytokine genes, including tumor necrosis factor-alpha (TNF-alpha), monocyte chemoattractant protein 1 (MCP-1), interleukin 6 (IL-6), and IL-12p40, was upregulated whereas anti-inflammatory adiponectin gene expression was downregulated. 12/15-LO products also augmented c-Jun N-terminal kinase 1 (JNK-1) phosphorylation, a known negative regulator of insulin signaling. Consistent with impaired insulin signaling, we found that insulin-stimulated 3T3-L1 adipocytes exhibited decreased IRS-1(Tyr) phosphorylation, increased IRS-1(Ser) phosphorylation, and impaired Akt phosphorylation when treated with 12/15-LO product. Taken together, our data suggest that 12/15-LO products create a proinflammatory state and impair insulin signaling in 3T3-L1 adipocytes. Because 12/15-LO expression is upregulated in visceral adipocytes by high-fat feeding in vivo and also by addition of palmitic acid in vitro, we propose that 12/15-LO plays a role in promoting inflammation and insulin resistance associated with obesity.

Murine 12/15-lipoxygenase regulates ATP-binding cassette transporter G1 protein degradation through p38- and JNK2-dependent pathways

12/15-Lipoxygenase (12/15LO) plays a role in the pathogenesis of atherosclerosis and diabetes and has been implicated in low density lipoprotein oxidation. Murine macrophages express high levels of 12/15LO and are key cells involved in the accumulation and efflux of oxidized low density lipoprotein in the arterial wall. During this process, macrophages up-regulate scavenger receptors that regulate lipid uptake, and ATP-binding cassette (ABC) transporters, that regulate lipid efflux. We have previously demonstrated that 12/15LO enhances the turnover and serine phosphorylation of ABCG1. In the current study, we further elucidate the mechanisms by which 12/15LO regulates ABCG1. Proteasomal inhibitors blocked the down-regulation of ABCG1 expression and resulted in accumulation of phosphorylated ABCG1. Macrophages that lack 12/15LO have enhanced transporter expression, reduced ABCG1 phosphorylation, and increased cholesterol efflux. Conversely, macrophages that overexpress 12/15LO have reduced ABCG1 expression, increased transporter phosphorylation, and reduced cholesterol efflux. 12/15LO plays a key role in activating the MAPK pathway. Inhibition of the p38 or JNK pathways with pharmacological inhibitors or dominant negative constructs blocked 12S-hydroxyeicosatetranoic acid-mediated degradation of ABCG1. Moreover, we isolated macrophages from JNK1-, JNK2-, and MKK3-deficient mice to analyze the involvement of specific MAPK pathways. JNK2- and MKK3-, but not JNK1-deficient macrophages were resistant to the down-regulation of ABCG1 protein, reduction in efflux, and increase in serine phosphorylation by 12S-hydroxyeicosatetranoic acid. These findings provide evidence that 12/15LO regulates ABCG1 expression and function through p38- and JNK2-dependent mechanisms, and that targeting these pathways may provide novel approaches for regulating cholesterol homeostasis.

Noninvasive assessment of pancreatic beta-cell function in vivo with manganese-enhanced magnetic resonance imaging

Loss of beta-cell function in type 1 and type 2 diabetes leads to metabolic dysregulation and inability to maintain normoglycemia. Noninvasive imaging of beta-cell function in vivo would therefore provide a valuable diagnostic and research tool for quantifying progression to diabetes and response to therapeutic intervention. Because manganese (Mn(2+)) is a longitudinal relaxation time (T1)-shortening magnetic resonance imaging (MRI) contrast agent that enters cells such as pancreatic beta-cells through voltage-gated calcium channels, we hypothesized that Mn(2+)-enhanced MRI of the pancreas after glucose infusion would allow for noninvasive detection of beta-cell function in vivo. To test this hypothesis, we administered glucose and saline challenges intravenously to normal mice and mice given high or low doses of streptozotocin (STZ) to induce diabetes. Serial inversion recovery MRI was subsequently performed after Mn(2+) injection to probe Mn(2+) accumulation in the pancreas. Time-intensity curves of the pancreas (normalized to the liver) fit to a sigmoid function showed a 51% increase in signal plateau height after glucose stimulation relative to saline (P < 0.01) in normal mice. In diabetic mice given a high dose of STZ, only a 9% increase in plateau signal intensity was observed after glucose challenge (P = not significant); in mice given a low dose of STZ, a 20% increase in plateau signal intensity was seen after glucose challenge (P = 0.02). Consistent with these imaging findings, the pancreatic insulin content of high- and low-dose STZ diabetic mice was reduced about 20-fold and 10-fold, respectively, compared with normal mice. We conclude that Mn(2+)-enhanced MRI demonstrates excellent potential as a means for noninvasively monitoring beta-cell function in vivo and may have the sensitivity to detect progressive decreases in function that occur in the diabetic disease process.

12-Lipoxygenase-knockout mice are resistant to inflammatory effects of obesity induced by Western diet

Inflammation is a key pathological process in the progression of atherosclerosis and type 2 diabetes. 12/15-lipoxygenase (12-LO), an enzyme involved in fatty acid metabolism, may contribute to inflammatory damage triggered by stressors such as obesity and insulin resistance. We hypothesized that mice lacking 12-LO are protected against inflammatory-mediated damage associated with a "western" diet. To test this hypothesis, age-matched male 12-LO knockout (12-LOKO) and wild-type C57BL/6 (B6) mice were fed either a standard chow or western diet and assessed for several inflammatory markers. Western-fed B6 mice showed expected reductions in glucose and insulin tolerance compared with chow-fed mice. In contrast, western-fed 12-LOKO mice maintained glucose and insulin tolerance similar to chow-fed mice. Circulating proinflammatory cytokines, tumor necrosis factor-alpha and interleukin-6, were increased in western B6 mice but not 12-LOKO mice, whereas the reported protective adipokine, adiponectin, was decreased only in western B6 mice. 12-LO activity was significantly elevated by western diet in islets from B6 mice. Islets from 12-LOKO mice did not show western-diet-induced islet hyperplasia or increases in caspase-3 apoptotic staining observed in western-fed B6 mice. Islets from 12-LOKO mice were also protected from reduced glucose-stimulated insulin secretion observed in islets from western-fed B6 mice. In visceral fat, macrophage numbers and monocyte chemoattractant protein-1 expression were elevated in western B6 mice but not 12-LOKO mice. These data suggest that 12-LO activation plays a role in western-diet-induced damage in visceral fat and islets. Inhibiting 12-LO may provide a new therapeutic approach to prevent inflammation-mediated metabolic consequences of excess fat intake.

12/15-Lipoxygenase activity increases the degradation of macrophage ATP-binding cassette transporter G1

OBJECTIVE

The purpose of this study was to evaluate the effect of 12/15-lipoxygenase (12/15LO) in macrophage ABCG1 expression and function associated with cholesterol efflux.

METHODS AND RESULTS

12/15LO was stably overexpressed in J774 macrophages. 12/15LO-overexpressing macrophages had a 30% reduction in HDL-mediated cholesterol efflux, corresponding with significantly reduced ABCG1 protein expression. Treatment of 12/15LO-overexpressing macrophages with a 12/15LO ribozyme to reduce 12/15LO restored HDL-mediated efflux and ABCG1 protein expression. Treating macrophages with 12/15LO unsaturated fatty acid substrates or eicosanoid products also reduced HDL-mediated cholesterol efflux. Additionally, both 12/15LO overexpression in macrophages and incubation of macrophages with eicosanoids reduced ABCG1 protein, but not mRNA, expression. However, incubation of macrophages with linoleic or arachidonic acids significantly reduced both ABCG1 mRNA and protein expression, suggesting that 12/15LO substrates and eicosanoid products differentially regulate ABCG1 expression. 12/15LO fatty acids did not decrease ABCG1 translation; however, 12/15LO fatty acids increased ABCG1 degradation when blocked by cyclohexidmide. ABCG1 degradation may be regulated through posttranslational modifications. Treatment with the 12/15LO eicosanoid product 12SHETE increased serine phosphorylation of ABCG1.

CONCLUSIONS

We conclude that serine phosphorylation may increase the degradation rate of ABCG1, and as a result cause macrophage cholesterol accumulation. These findings provide evidence that 12/15LO activity in the vessel wall contributes to atherogenesis by impairing the macrophage ABCG1 cholesterol efflux pathway.

5-Lipoxygenase, but not 12/15-lipoxygenase, contributes to degeneration of retinal capillaries in a mouse model of diabetic retinopathy

OBJECTIVE

Lipoxygenases are regulators of chronic inflammation and oxidative stress generation. We evaluated the role of 5- and 12-lipoxygenases in the development of diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Wild-type mice, 5-lipoxygenase-deficient mice, and 12/15-lipoxygenase-deficient mice were assessed 1) after 9 months of diabetes for retinal histopathology and leukotriene receptor expression and 2) after 3 months of diabetes for leukostasis and retinal superoxide generation.

RESULTS

Diabetic wild-type mice developed the expected degeneration of retinal capillaries and pericytes and increases in both leukostasis and superoxide production (P < 0.006). We found no evidence of diabetes-induced degeneration of retinal ganglion cells in these animals. The vascular histopathology was significantly inhibited in 5-lipoxygenase-deficient mice, but not in 12/15-lipoxygenase-deficient mice. Retinas from diabetic 5-lipoxygenase-deficient mice also had significantly less leukostasis, superoxide production, and nuclear factor-kappaB (NF-kappaB) expression (all P < 0.006), whereas retinas from diabetic 12/15-lipoxygenase-deficient mice had significantly less leukostasis (P < 0.005) but not superoxide production or NF- kappaB expression. Retinas from diabetic wild-type mice were enriched with receptors for the 5-lipoxygenase metabolite leukotriene B(4). Diabetes-induced histological and biochemical alterations were significantly reduced in 5-lipoxygenase-deficient mice, but not 12/15-lipoxygenase-deficient mice.

CONCLUSIONS

5-Lipoxygenase represents a novel pathway for therapeutic intervention of diabetic retinopathy.

Role of 12/15-lipoxygenase in the expression of MCP-1 in mouse macrophages

Monocyte chemoattractant protein (MCP)-1 plays a key role in atherosclerosis and inflammation associated with visceral adiposity by inducing mononuclear cell migration. Evidence shows that mouse peritoneal macrophages (MPM) express a 12-lipoxygenase (12/15-LO) that has been clearly linked to accelerated atherosclerosis in mouse models and increased monocyte endothelial interactions in both rodent and human cells. However, the role of 12/15-LO products in regulating MCP-1 expression in macrophages has not been clarified. In this study, we tested the role of 12/15-LO products using MPM and the mouse macrophage cell line, J774A.1 cells. We found that 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] increased MCP-1 mRNA and protein expression in J774A.1 cells and MPM. In contrast, 12(R)-HETE, a lipid not derived from 12/15-LO, did not affect MCP-1 expression. 15(S)-HETE also increased MCP-1 mRNA expression, but the effect was less compared with 12(S)-HETE. MCP-1 mRNA expression was upregulated in a macrophage cell line stably overexpressing 12/15-LO (Plox-86 cells) and in MPM isolated from a 12/15-LO transgenic mouse. In addition, the expression of MCP-1 was downregulated in MPM isolated from 12/15-LO knockout mice. 12(S)-HETE-induced MCP-1 mRNA expression was attenuated by specific inhibitors of protein kinase C (PKC) and p38 mitogen-activated protein kinase (p38). 12(S)-HETE also directly activated NADPH oxidase activity. Two NADPH oxidase inhibitors, apocynin and diphenyleneiodonium chloride, blocked 12(S)-HETE-induced MCP-1 mRNA. Apocynin attenuated 12(S)-HETE-induced MCP-1 protein secretion. These data show that 12(S)-HETE increases MCP-1 expression by inducing PKC, p38, and NADPH oxidase activity. These results suggest a potentially important mechanism linking 12/15-LO activation to MCP-1 expression that induces inflammatory cell infiltration.

Nonobese diabetic (NOD) mice congenic for a targeted deletion of 12/15-lipoxygenase are protected from autoimmune diabetes

OBJECTIVE

12/15-lipoxygenase (12/15-LO), one of a family of fatty acid oxidoreductase enzymes, reacts with polyenoic fatty acids to produce proinflammatory lipids. 12/15-LO is expressed in macrophages and pancreatic beta-cells. It enhances interleukin 12 production by macrophages, and several of its products induce apoptosis of beta-cells at nanomolar concentrations in vitro. We had previously demonstrated a role for 12/15-LO in beta-cell damage in the streptozotocin model of diabetes. Since the gene encoding 12/15-LO (gene designation Alox15) lies within the Idd4 diabetes susceptibility interval in NOD mice, we hypothesized that 12/15-LO is also a key regulator of diabetes susceptibility in the NOD mouse.

RESEARCH DESIGN AND METHODS

We developed NOD mice carrying an inactivated 12/15-LO locus (NOD-Alox15(null)) using a "speed congenic" protocol, and the mice were monitored for development of insulitis and diabetes.

RESULTS

NOD mice deficient in 12/15-LO develop diabetes at a markedly reduced rate compared with NOD mice (2.5 vs. >60% in females by 30 weeks). Nondiabetic female NOD-Alox15(null) mice demonstrate improved glucose tolerance, as well as significantly reduced severity of insulitis and improved beta-cell mass, when compared with age-matched nondiabetic NOD females. Disease resistance is associated with decreased numbers of islet-infiltrating activated macrophages at 4 weeks of age in NOD-Alox15(null) mice, preceding the development of insulitis. Subsequently, islet-associated infiltrates are characterized by decreased numbers of CD4(+) T cells and increased Foxp3(+) cells.

CONCLUSIONS

These results suggest an important role for 12/15-LO in conferring susceptibility to autoimmune diabetes in NOD mice through its effects on macrophage recruitment or activation.

High-fat diet induced neuropathy of pre-diabetes and obesity: effects of "healthy" diet and aldose reductase inhibition

OBJECTIVE

Subjects with dietary obesity and pre-diabetes have an increased risk for developing both nerve conduction slowing and small sensory fiber neuropathy. Animal models of this type of neuropathy have not been described. This study evaluated neuropathic changes and their amenability to dietary and pharmacological interventions in mice fed a high-fat diet (HFD), a model of pre-diabetes and alimentary obesity.

RESEARCH DESIGN AND METHODS

Female C57BL6/J mice were fed normal diets or HFDs for 16 weeks.

RESULTS

HFD-fed mice developed obesity, increased plasma FFA and insulin concentrations, and impaired glucose tolerance. They also had motor and sensory nerve conduction deficits, tactile allodynia, and thermal hypoalgesia in the absence of intraepidermal nerve fiber loss or axonal atrophy. Despite the absence of overt hyperglycemia, the mice displayed augmented sorbitol pathway activity in the peripheral nerve, as well as 4-hydroxynonenal adduct nitrotyrosine and poly(ADP-ribose) accumulation and 12/15-lipoxygenase overexpression in peripheral nerve and dorsal root ganglion neurons. A 6-week feeding with normal chow after 16 weeks on HFD alleviated tactile allodynia and essentially corrected thermal hypoalgesia and sensory nerve conduction deficit without affecting motor nerve conduction slowing. Normal chow containing the aldose reductase inhibitor fidarestat (16 mg x kg(-1) x day (-1)) corrected all functional changes of HFD-induced neuropathy.

CONCLUSIONS

Similar to human subjects with pre-diabetes and obesity, HFD-fed mice develop peripheral nerve functional, but not structural, abnormalities and, therefore, are a suitable model for evaluating dietary and pharmacological approaches to halt progression and reverse diabetic neuropathy at the earliest stage of the disease.

Effects of lifestyle intervention on health care costs: Improving Control with Activity and Nutrition (ICAN)

OBJECTIVE

To evaluate program and health care costs of a lifestyle intervention in a high-risk obese population.

DESIGN

Twelve-month randomized controlled trial comparing lifestyle case management to usual care.

SUBJECTS/SETTING

Health plan members (n=147) with obesity (body mass index >/=27) and type 2 diabetes.

INTERVENTION

Lifestyle case management entailed individual and group education, support, and referrals by registered dietitians. Those in the usual-care group received educational material.

MAIN OUTCOME MEASURES

Medical and pharmaceutical health care costs reimbursed by the participant's primary insurance company.

STATISTICAL ANALYSIS

Total costs were modeled using the four-equation model using previous year cost as a predictor.

RESULTS

Net cost of the intervention was $328 per person per year. After incorporating program costs, mean health plan costs were $3,586 (95% confidence interval [CI]: -$8,036, -$25, P<0.05) lower in case management compared to usual care. The difference was driven by group differences in medical (-$3,316, 95% CI: -$7,829 to -$320, P<0.05) but not pharmaceutical costs (-$239, 95% CI: -$870 to $280, not statistically significant), with fewer inpatient admissions and costs among case management compared with usual care (admission prevalence: 2.8% vs 22.5% respectively, P<0.001).

CONCLUSION

Addition of a modest-cost, registered dietitian-led lifestyle case-management intervention to usual medical care did not increase health care costs and suggested modest cost savings among obese patients with type 2 diabetes. Larger trials are needed to determine whether these results can be replicated in a broader population. The findings can be judiciously applied to support that the addition of a registered dietitian-led lifestyle case-management program to medical care does not increase health care costs.

Inflammatory mechanisms of diabetic complications

Activation of inflammatory processes may contribute to the development of type 2 diabetes mellitus. In addition, inflammation appears to be a major mechanism responsible for vascular damage leading to the clinically well-recognized complications of diabetes. Inflammatory cytokine and chemokine mediators released from visceral fat contribute to atherosclerotic plaque formation and increased risk for myocardial infarction and stroke. Activation of growth factors and adhesion molecules may promote the movement of inflammatory cells into the renal microvasculature, predisposing to the development of diabetic nephropathy. Emerging evidence also indicates that markers of inflammation are associated with the more severe forms of diabetic retinopathy. Future approaches to the treatment of diabetic complications may involve regulation of inflammatory processes, specifically targeting factors that contribute to vascular damage.

The role of 12/15-lipoxygenase in the expression of interleukin-6 and tumor necrosis factor-alpha in macrophages

12/15-lipoxygenase (12/15-LO) enzyme and products have been associated with inflammation and atherosclerosis. However, the mechanism of effects of the 12/15-LO products has not been fully clarified. To study the role of 12/15-LO in cytokine expression, experiments with direct additions of the12/15-LO products, 12(S)-hydroxyeicosa tetraenoic acid or 12(S)-hydroperoxyeicosa-5Z, 8Z, 10E, or 14Z-tetraenoic acid to macrophages were first carried out, and results showed that the 12/15-LO products stimulated mRNA and protein expression of IL-6 and TNF-alpha in a dose-dependent manner. In contrast, an inactive analogue of 12(S)-hydroxyeicosa tetraenoic acid had no effect. To further explore the role of endogenous 12/15-LO in cytokine expression, we used an in vitro and in vivo model to test the effect of 12/15-LO overexpression. The models included Plox-86 cells, a J774A.1 cell line that stably overexpresses leukocyte-type 12/15-LO and primary mouse peritoneal macrophages (MPMs) from 12/15-LO transgenic mice. The results showed a clear increase in IL-6 and TNF-alpha expression in Plox-86 cells and MPMs from 12/15-LO transgenic mice, compared with mock-transfected J774A.1 cells and MPMs from control C57BL6 mice. IL-1beta, IL-12, and monocyte chemoattractant protein (MCP)-1 mRNA were also increased in Plox-86 cells. These data clearly suggest a clear role of 12/15-LO pathway in cytokine production. We also demonstrated that signaling pathways including protein kinase C, p38 MAPK (p38), c-jun NH(2)-terminal kinase as well as nicotinamide adenine dinucleotide phosphate oxidase are important for 12-(S)-hydroxyeicosatetraenoic acid-induced increases in IL-6 and TNF-alpha gene expression. These results suggest a potentially important mechanism linking 12/15-LO activation to chronic inflammation and atherosclerosis.

Mechanisms by which diabetes increases cardiovascular disease

Diabetes mellitus is one of the major risk factors for cardiovascular disease which is the leading cause of death in the U.S. Increasing prevalence of diabetes and diabetic atherosclerosis makes identification of molecular mechanisms by which diabetes promotes atherogenesis an important task. Targeting common pathways may ameliorate both diseases. This review focuses on well known as well as newly discovered mechanisms which may represent promising therapeutic targets.

Insulin and glucose play a role in foam cell formation and function

Background

Foam cell formation in diabetic patients often occurs in the presence of high insulin and glucose levels. To test whether hyperinsulinemic hyperglycemic conditions affect foam cell differentiation, we examined gene expression, cytokine production, and Akt phosphorylation in human monocyte-derived macrophages incubated with two types of oxidized low density lipoprotein (LDL), minimally modified LDL (mmLDL) and extensively oxidized LDL (OxLDL).

Methods and results

Using Affymetrix GeneChip^® arrays, we found that several genes directly related to insulin signaling were changed. The insulin receptor and glucose-6-phosphate dehydrogenase were upregulated by mmLDL and OxLDL, whereas insulin-induced gene 1 was significantly down-regulated. In hyperinsulinemic hyperglycemic conditions, modified LDL upregulated Akt phosphorylation and expression of the insulin-regulated aminopeptidase. The level of proinflammatory cytokines, IL-lβ, IL-12, and IL-6, and of a 5-lipoxygenase eicosanoid, 5-hydroxyeicosatetraenoic acid (5-HETE), was also increased.

Conclusion

These results suggest that the exposure of macrophages to modified low density lipoproteins in hyperglycemic hyperinsulinemic conditions affects insulin signaling and promotes the release of proinflammatory stimuli, such as cytokines and eicosanoids. These in turn may contribute to the development of insulin resistance.

Lifestyle intervention in obese patients with type 2 diabetes: impact of the patient's educational background

OBJECTIVE

To determine whether people with different educational backgrounds respond differently to a lifestyle intervention program for obese patients with type 2 diabetes.

RESEARCH METHODS AND PROCEDURES

The study consisted of a 12-month randomized controlled trial of 147 health plan members with type 2 diabetes who were overweight or obese (BMI > or = 27 kg/m(2)). Participants were randomized to lifestyle case management or usual care. Case management (CM) involved group and individual education, support, and referral by registered dietitians. Usual care (UC) participants received educational material. Both groups received ongoing primary care. A post hoc analysis was performed, evaluating the impact of education level on intervention group differences with respect to change in weight and waist circumference.

RESULTS

There was a significant education by group interaction for both changes in weight (p = 0.02) and waist circumference (p = 0.01) during the study period. Contrary to expectations, CM participants with less formal education had greater risk reductions compared with more educated participants. Models predicted that, by 12 months, those with less education in the UC group gained 1.71 kg more in weight and 3.67 cm more in waist circumference than those with greater education. However, by 12 months, those in the CM group with less education lost a model-predicted 3.30 kg more in weight and 4.95 cm more in waist circumference than those with more formal education.

DISCUSSION

People with varied educational backgrounds may respond differently to a lifestyle intervention for weight management and diabetes control.

Combined treatment with lisofylline and exendin-4 reverses autoimmune diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease leading to near complete pancreatic beta-cell destruction. New evidence suggests that beta-cell regeneration is possible, but ongoing autoimmune damage prevents restoration of beta-cell mass. We tested the hypothesis that simultaneously blocking autoimmune cytokine damage and supplying a growth-promoting stimulus for beta-cells would provide a novel approach to reverse T1DM. Therefore, in this study we combined lisofylline to suppress autoimmunity and exendin-4 to enhance beta-cell proliferation for treating autoimmune-mediated diabetes in the non-obese diabetic (NOD) mouse model. We found that this combined therapy effectively reversed new-onset diabetes within a week of therapy, and even maintained euglycemia up to 145 days after treatment withdrawal. The therapeutic effect of this regimen was associated with improved beta-cell metabolism and insulin secretion, while reducing beta-cell apoptosis. It is possible that such combined therapy could become a new strategy to defeat T1DM in humans.

Synthesis and biological evaluation of lisofylline (LSF) analogs as a potential treatment for Type 1 diabetes

Lisofylline (LSF, 1-(5-R-hydroxyhexyl)-3,7-dimethylxanthine) is an anti-inflammatory agent that protects beta-cells from Th1 cytokine-induced dysfunction and reduces the onset of Type 1 diabetes in non-obese diabetic (NOD) mice. Due to its low potency, poor oral bioavailability, and short half-life, the widespread clinical utility of LSF may be limited. Our goal has been to develop new agents based on the LSF structural motif that resolve the potency and pharmacokinetic liabilities of LSF. In this study, we have generated a focused library of LSF analogs that maintain the side chain (5-R-hydroxyhexyl) constant, while substituting a variety of nitrogen-containing heterocyclic substructures for the xanthine moiety of LSF. This library includes the xanthine-like (5-aza-7-deazaxanthine), as well as non-xanthine-like skeletons. The LSF analogs were evaluated in a pancreatic beta-cell line for the effects on apoptosis protection and insulin release. The metabolic stability of selected compounds was also tested.

Elevated glucose and diabetes promote interleukin-12 cytokine gene expression in mouse macrophages

Inflammation is emerging as an important mechanism for micro- and macrovascular complication of diabetes. The macrophage plays a key role in the chronic inflammatory response in part by generating particular cytokines. IL-1beta, IL-6, IL12, IL-18, TNFalpha, and interferon-gamma are produced primarily in macrophages and have been associated with accelerated atherosclerosis and altered vascular wall function. In this study, we evaluated the effect and mechanism of high glucose (HG) on gene expression of these cytokines in mouse peritoneal macrophages (MPM). HG led to a 2-fold increase in the mRNA expression of these cytokines, with IL-12 showing the highest activation (5.4-fold) in a time-dependent (3-12 h) and dose-dependent (10, 17.5, and 25 mmol/liter) manner. The effects were specific to HG because mannitol and 3-O-methyl-glucose had no effect on cytokine mRNA expression. HG also increased IL-12 protein accumulation from MPM. We also explored the role of induced and spontaneous diabetes on inflammatory cytokine expression in MPM. Increases in expression in MPM of multiple inflammatory cytokines, including a 20-fold increase in IL-12 mRNA, were observed in streptozotocin-induced type 1 diabetic mice as well as type 2 diabetic db/db mice, suggesting that cytokine gene expression is increased by hyperglycemia in vivo. We next explored potential mechanisms of HG-induced increases in IL-12 mRNA. HG increased the activity of protein kinase C, p38 MAPK (p38), c-Jun terminal kinase, and inhibitory-kappaB kinase in MPM. Furthermore, inhibitors of these signaling pathways significantly reduced HG-induced IL-12 mRNA expression in MPM. These results provide evidence for a potentially important mechanism linking elevated glucose and diabetes to inflammation.