Role of 12-lipoxygenase and oxidant stress in hyperglycaemia-induced acceleration of atherosclerosis in a diabetic pig model

Emerging Roles and Therapeutic Applications of Arachidonic Acid Pathways in Cardiometabolic Diseases

Cardiometabolic disease has become a major health burden worldwide, with sharply increasing prevalence but highly limited therapeutic interventions. Emerging evidence has revealed that arachidonic acid derivatives and pathway factors link metabolic disorders to cardiovascular risks and intimately participate in the progression and severity of cardiometabolic diseases. In this review, we systemically summarized and updated the biological functions of arachidonic acid pathways in cardiometabolic diseases, mainly focusing on heart failure, hypertension, atherosclerosis, nonalcoholic fatty liver disease, obesity, and diabetes. We further discussed the cellular and molecular mechanisms of arachidonic acid pathway-mediated regulation of cardiometabolic diseases and highlighted the emerging clinical advances to improve these pathological conditions by targeting arachidonic acid metabolites and pathway factors.

Challenges of aortic valve tissue culture - maintenance of viability and extracellular matrix in the pulsatile dynamic microphysiological system

BACKGROUND

Calcific aortic valve disease (CAVD) causes an increasing health burden in the 21st century due to aging population. The complex pathophysiology remains to be understood to develop novel prevention and treatment strategies. Microphysiological systems (MPSs), also known as organ-on-chip or lab-on-a-chip systems, proved promising in bridging in vitro and in vivo approaches by applying integer AV tissue and modelling biomechanical microenvironment. This study introduces a novel MPS comprising different micropumps in conjunction with a tissue-incubation-chamber (TIC) for long-term porcine and human AV incubation (pAV, hAV).

RESULTS

Tissue cultures in two different MPS setups were compared and validated by a bimodal viability analysis and extracellular matrix transformation assessment. The MPS-TIC conjunction proved applicable for incubation periods of 14-26 days. An increased metabolic rate was detected for pulsatile dynamic MPS culture compared to static condition indicated by increased LDH intensity. ECM changes such as an increase of collagen fibre content in line with tissue contraction and mass reduction, also observed in early CAVD, were detected in MPS-TIC culture, as well as an increase of collagen fibre content. Glycosaminoglycans remained stable, no significant alterations of α-SMA or CD31 epitopes and no accumulation of calciumhydroxyapatite were observed after 14 days of incubation.

CONCLUSIONS

The presented ex vivo MPS allows long-term AV tissue incubation and will be adopted for future investigation of CAVD pathophysiology, also implementing human tissues. The bimodal viability assessment and ECM analyses approve reliability of ex vivo CAVD investigation and comparability of parallel tissue segments with different treatment strategies regarding the AV (patho)physiology.

Genetic and Epigenetic Regulation of Lipoxygenase Pathways and Reverse Cholesterol Transport in Atherogenesis

Atherosclerosis is one of the most important medical and social problems of modern society. Atherosclerosis causes a large number of hospitalizations, disability, and mortality. A considerable amount of evidence suggests that inflammation is one of the key links in the pathogenesis of atherosclerosis. Inflammation in the vascular wall has extensive cross-linkages with lipid metabolism, and lipid mediators act as a central link in the regulation of inflammation in the vascular wall. Data on the role of genetics and epigenetic factors in the development of atherosclerosis are of great interest. A growing body of evidence is strengthening the understanding of the significance of gene polymorphism, as well as gene expression dysregulation involved in cross-links between lipid metabolism and the innate immune system. A better understanding of the genetic basis and molecular mechanisms of disease pathogenesis is an important step towards solving the problems of its early diagnosis and treatment.

Key Role of 12-Lipoxygenase and Its Metabolite 12-Hydroxyeicosatetraenoic Acid (12-HETE) in Diabetic Retinopathy

PURPOSE

Abnormal lipid metabolism has been proved to be implicated in the complex pathogenesis of diabetic retinopathy (DR). 12-lipoxygenase (12-LOX) is a member of lipoxygenase family responsible for the oxygenation of cellular polyunsaturated fatty acids to produce lipid mediators which modulate cell inflammation. This review explores the role of 12-lipoxygenase and its products in the pathogenesis of DR.

METHODS

A comprehensive medical literature search was conducted on PubMed till September 2021.

RESULTS

Emerging evidence has demonstrated that 12-LOX and its main product 12- hydroxyeicosatetraenoic acid (12-HETE) activate retinal cells, especially retinal vascular endothelial cells, through the activation of NADPH oxidase and the subsequent generation of reactive oxygen species (ROS), mediating multiple pathological changes during DR. Genetic deletion or pharmacological inhibition models of 12-LOX in mice show protection from DR.

CONCLUSION

12-LOX and its product 12-HETE take important part in DR pathogenesis and show their potential as future therapeutic targets for DR. Further studies are needed on the specific mechanism including 12-LOX pathway related molecules, 12-HETE receptors and downstream signaling pathways.

Unraveling the Role of 12- and 20- HETE in Cardiac Pathophysiology: G-Protein-Coupled Receptors, Pharmacological Inhibitors, and Transgenic Approaches

ABSTRACT

Arachidonic acid-derived lipid mediators play crucial roles in the development and progression of cardiovascular diseases. Eicosanoid metabolites generated by lipoxygenases and cytochrome P450 enzymes produce several classes of molecules, including the epoxyeicosatrienoic acid (EET) and hydroxyeicosatetraenoic acids (HETE) family of bioactive lipids. In general, the cardioprotective effects of EETs have been documented across a number of cardiac diseases. In contrast, members of the HETE family have been shown to contribute to the pathogenesis of ischemic cardiac disease, maladaptive cardiac hypertrophy, and heart failure. The net effect of 12(S)- and 20-HETE depends upon the relative amounts generated, ratio of HETEs:EETs produced, timing of synthesis, as well as cellular and subcellular mechanisms activated by each respective metabolite. HETEs are synthesized by and affect multiple cell types within the myocardium. Moreover, cytochrome P450-derived and lipoxygenase- derived metabolites have been shown to directly influence cardiac myocyte growth and the regulation of cardiac fibroblasts. The mechanistic data uncovered thus far have employed the use of enzyme inhibitors, HETE antagonists, and the genetic manipulation of lipid-producing enzymes and their respective receptors, all of which influence a complex network of outcomes that complicate data interpretation. This review will summarize and integrate recent findings on the role of 12(S)-/20-HETE in cardiac diseases.

Regulation of Tissue Inflammation by 12-Lipoxygenases

Lipoxygenases (LOXs) are lipid metabolizing enzymes that catalyze the di-oxygenation of polyunsaturated fatty acids to generate active eicosanoid products. 12-lipoxygenases (12-LOXs) primarily oxygenate the 12th carbon of its substrates. Many studies have demonstrated that 12-LOXs and their eicosanoid metabolite 12-hydroxyeicosatetraenoate (12-HETE), have significant pathological implications in inflammatory diseases. Increased level of 12-LOX activity promotes stress (both oxidative and endoplasmic reticulum)-mediated inflammation, leading to damage in these tissues. 12-LOXs are also associated with enhanced cellular migration of immune cells-a characteristic of several metabolic and autoimmune disorders. Genetic depletion or pharmacological inhibition of the enzyme in animal models of various diseases has shown to be protective against disease development and/or progression in animal models in the setting of diabetes, pulmonary, cardiovascular, and metabolic disease, suggesting a translational potential of targeting the enzyme for the treatment of several disorders. In this article, we review the role of 12-LOXs in the pathogenesis of several diseases in which chronic inflammation plays an underlying role.

Epigenetic Mechanisms in Diabetic Vascular Complications and Metabolic Memory: The 2020 Edwin Bierman Award Lecture

Macrovascular complications such as atherosclerosis, myocardial infarction and stroke, and microvascular complications such as nephropathy, retinopathy, and neuropathy are the major causes of increased morbidity and mortality in both type 1 and type 2 diabetes. Increased inflammation, oxidative stress, and fibrosis are common features in most diabetes complications. Although extensive studies have examined the biochemical pathways leading to the expression of inflammatory, profibrotic, and other pathological genes, as well as genetic factors related to diabetes and associated complications, much less is known about the contribution of epigenetic changes that occur without alterations in the DNA sequence. Environmental factors, lifestyles, and improper diet implicated in diabetes can affect epigenetic states. Epigenetic modifications, including DNA methylation and histone modifications, can alter gene transcription in response to environmental stimuli and cooperate with noncoding RNAs. These epigenetic modifications have been observed in various target cells under diabetic conditions. Moreover, epigenetics has also been implicated in the phenomenon of metabolic memory observed in clinic trials and animal studies, in which prior episodes of poor glycemic control can confer continued risk of complications despite subsequent glucose normalization. Epigenome-wide association studies in cohorts with diabetes are uncovering epigenotype variations that provide new insights into diabetic vascular complications. Here, I discuss the role of epigenetics and noncoding RNAs in diabetes complications and metabolic memory, and their translation potential to serve as biomarkers and drug targets to improve clinical management of diabetic vascular complications.

Eicosanoids and Oxidative Stress in Diabetic Retinopathy

Oxidative stress is an important factor to cause the pathogenesis of diabetic retinopathy (DR) because the retina has high vascularization and long-time light exposition. Cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes can convert arachidonic acid (AA) into eicosanoids, which are important lipid mediators to regulate DR development. COX-derived metabolites appear to be significant factors causative to oxidative stress and retinal microvascular dysfunction. Several elegant studies have unraveled the importance of LOX-derived eicosanoids, including LTs and HETEs, to oxidative stress and retinal microvascular dysfunction. The role of CYP eicosanoids in DR is yet to be explored. There is clear evidence that CYP-derived epoxyeicosatrienoic acids (EETs) have detrimental effects on the retina. Our recent study showed that the renin-angiotensin system (RAS) activation augments retinal soluble epoxide hydrolase (sEH), a crucial enzyme degrading EETs. Our findings suggest that EETs blockade can enhance the ability of RAS blockade to prevent or mitigate microvascular damage in DR. This review will focus on the critical information related the function of these eicosanoids in the retina, the interaction between eicosanoids and reactive oxygen species (ROS), and the involvement of eicosanoids in DR. We also identify potential targets for the treatment of DR.

Atherosclerosis and the Capillary Network; Pathophysiology and Potential Therapeutic Strategies

Atherosclerosis and associated ischemic organ dysfunction represent the number one cause of mortality worldwide. While the key drivers of atherosclerosis, arterial hypertension, hypercholesterolemia and diabetes mellitus, are well known disease entities and their contribution to the formation of atherosclerotic plaques are intensively studied and well understood, less effort is put on the effect of these disease states on microvascular structure an integrity. In this review we summarize the pathological changes occurring in the vascular system in response to prolonged exposure to these major risk factors, with a particular focus on the differences between these pathological alterations of the vessel wall in larger arteries as compared to the microcirculation. Furthermore, we intend to highlight potential therapeutic strategies to improve microvascular function during atherosclerotic vessel disease.

Development and Genome Sequencing of a Laboratory-Inbred Miniature Pig Facilitates Study of Human Diabetic Disease

Pig has been proved to be a valuable large animal model used for research on diabetic disease. However, their translational value is limited given their distinct anatomy and physiology. For the last 30 years, we have been developing a laboratory Asian miniature pig inbred line (Bama miniature pig [BM]) from the primitive Bama xiang pig via long-term selective inbreeding. Here, we assembled a BM reference genome at full chromosome-scale resolution with a total length of 2.49 Gb. Comparative and evolutionary genomic analyses identified numerous variations between the BM and commercial pig (Duroc), particularly those in the genetic loci associated with the features advantageous to diabetes studies. Resequencing analyses revealed many differentiated gene loci associated with inbreeding and other selective forces. These together with transcriptome analyses of diabetic pig models provide a comprehensive genetic basis for resistance to diabetogenic environment, especially related to energy metabolism.

12(S)-hydroxyeicosatetraenoic acid impairs vascular endothelial permeability by altering adherens junction phosphorylation levels and affecting the binding and dissociation of its components in high glucose-induced vascular injury

AIMS/INTRODUCTION

Diabetes is an important risk factor for atherosclerotic disease. The initiating factor of atherosclerosis is local endothelial cell injury. The arachidonic acid metabolite, 12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE), might be involved in this process. In recent years, some studies have discussed the effect of 12(S)-HETE on vascular endothelial cell function. In the present study, we investigated the effect of 12(S)-HETE on vascular endothelial cell function in high-glucose conditions and the mechanisms involved.

MATERIALS AND METHODS

Human umbilical vein endothelial cells were cultured in conventional M199 medium and high-glucose M199 medium. Human umbilical vein endothelial cells were stimulated with 12(S)-HETE and cinnamyl-3,4-dihydroxy-α-cyanocinnamate (a 12/15-lipoxygenases inhibitor). A type 1 diabetes mellitus model was established in C57BL/6 or 12/15-lipoxygenases knockout mice with streptozotocin. Aortic tissue was harvested for subsequent testing. The transmembrane transport of dextran and human acute monocytic leukaemia cell line (THP-1) cells was measured. The adherens junction protein, IkBα, nuclear factor kappa Bp65 (P65), intercellular adhesion molecule 1 and vascular cell adhesion protein 1 expression and phosphorylation, and the binding/dissociation of endothelial cell components were observed.

RESULTS

Transendothelial migration of dextran and THP-1 cells was significantly increased by stimulation of human umbilical vein endothelial cell monolayers with high glucose and 12(S)-HETE (P < 0.05). High glucose and 12(S)-HETE altered the vascular endothelial cadherin and β-catenin phosphorylation level, and promoted the dissociation of β-catenin and vascular endothelial cadherin. Expression levels of P-Ikbα, P-P65, intercellular adhesion molecule 1 and vascular cell adhesion protein 1 were elevated in high glucose and 12(S)-HETE treated cells and diabetic mice compared with controls (P < 0.05).

CONCLUSIONS

The lipoxygenases metabolite, 12(S)-HETE, can impair vascular endothelial permeability by altering adherens junction phosphorylation levels, and affecting the binding and dissociation of its components in high-glucose conditions.

12(S)-Hydroxyeicosatetraenoic acid downregulates monocyte-derived macrophage efferocytosis: New insights in atherosclerosis

The involvement of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a 12-lipooxygenase product of arachidonic acid, has been suggested in atherosclerosis. However, its effect on macrophage functions is not completely understood, so far. The uptake of apoptotic cells (efferocytosis) by macrophages is an anti-inflammatory process, impaired in advanced atherosclerotic lesions. This process induces the release of the anti-inflammatory cytokine interleukin-10 (IL-10), and it is regulated by Rho-GTPases, whose activation involves the isoprenylation, a modification inhibited by statins. We assessed 12-HETE levels in serum of coronary artery disease (CAD) patients, and explored 12(S)-HETE in vitro effect on monocyte-derived macrophage (MDM) efferocytosis. Sixty-four CAD patients and 24 healthy subjects (HS) were enrolled. Serum 12-HETE levels were measured using a tandem mass spectrometry method. MDMs, obtained from a spontaneous differentiation of adherent monocytes, were treated with 12(S)-HETE (10-50 ng/mL). Efferocytosis and RhoA activation were evaluated by flow cytometry. IL-10 was measured by ELISA. CAD patients showed increased 12-HETE serum levels compared to HS (665.2 [438.1-896.2] ng/mL and 525.1 [380.1-750.1] ng/mL, respectively, p < 0.05) and reduced levels of IL-10. MDMs expressed the 12(S)-HETE cognate receptor GPR31. CAD-derived MDMs displayed defective efferocytosis vs HS-MDMs (9.4 [7.7-11.3]% and 11.1 [9.6-14.1]% of MDMs that have engulfed apoptotic cells, respectively, p < 0.01). This reduction is marked in MDMs obtained from patients not treated with statin (9.3 [7.4-10.6]% statin-free CAD vs HS, p = 0.01; and 9.9 [8.6-11.6]% statin-treated CAD vs HS, p = 0.07). The in vitro treatment of MDMs with 12(S)-HETE (20 ng/mL) induced 20% decrease of efferocytosis (p < 0.01) and 71% increase of RhoA activated form (p < 0.05). Atorvastatin (0.1 μM) counteracted these 12(S)-HETE-mediated effects.These results show a 12(S)-HETE pro-inflammatory effect and suggest a new potential contribution of this mediator in the development of atherosclerosis.

Activation of Lipid Mediator Formation Due to Lipoprotein Apheresis

Lipoprotein apheresis reliably reduces low-density lipoprotein (LDL) cholesterol in patients with atherosclerotic disease and therapy-refractory hypercholesterolemia or elevated lipoprotein (a) (Lp(a)). Besides lowering lipoproteins and triglycerides, apheresis also decreases levels of essential omega-6 and omega-3 polyunsaturated fatty acids (n-6 and n-3 PUFAs) in blood plasma. In contrast, heparin-induced extracorporeal low-density lipoprotein precipitation (HELP) lipid apheresis might increase the formation of potentially pro-inflammatory and pro-thrombotic lipid mediators derived from n-6 and n-3 PUFAs. The study presented here analyzed lipid mediator profiles in the plasma of patients with hyperlipidemia treated by one of three different apheresis methods, either HELP, direct absorption (DA), or membrane filtration (MDF), in a direct pre- and post-apheresis comparison. Using gas chromatography and liquid chromatography tandem mass spectrometry (LC-MS/MS) we were able to analyze fatty acid composition and the formation of lipid mediators called oxylipins. Our data illustrate—particularly in HELP-treated patients—significant decreases of essential omega-6 and omega-3 polyunsaturated fatty acids in blood plasma but significant increases of PUFA-derived lipoxygenase-, as well as cyclooxygenase- and cytochrome P450-derived lipid mediators. Given that n-3 PUFAs in particular are presumed to be cardioprotective and n-3 PUFA-derived lipid mediators might limit inflammatory reactions, these data indicate that n-3 PUFA supplementation in the context of lipid apheresis treatment might have additional benefits through apheresis-triggered protective n-3 PUFA-derived lipid mediators.

Effect of Omega-3 Fatty Acid Supplementation on Oxylipins in a Routine Clinical Setting

Omega-6 polyunsaturated fatty acid (n-6 PUFA) is the predominant polyunsaturated fatty acid (PUFA), especially in Western diet. A high omega-6/omega-3 ratio in Western diets is implicated in the development of cardiovascular diseases and inflammatory processes. Studies in animal models and in humans have demonstrated beneficial effects of omega-3 PUFA (n-3 PUFA) in a variety of diseases, including cardiac arrhythmias and inflammatory diseases, as well as breast and colon cancer. The molecular mechanisms underlying the effects of n-3 PUFA are still not well understood. Possible mechanisms include competition between n-3 and n-6 PUFAs at the cyclooxygenase (COX) and lipoxygenase (LOX) and cytochrome P450 levels, and subsequent formation of oxylipins with specific anti-inflammatory or anti-arrhythmic effects. In this study, we report the impact of routine long-term treatment with prescription-grade n-3 PUFA (either 840 mg or 1680 mg per day) on blood cell membrane fatty acid composition, as well as plasma oxylipin patterns, in a patient population with severe hyperlipidemia and cardiovascular disease who are on standard lipid-lowering and cardioprotective medications. Lipidomics analyses were performed by LC/ESI-MS/MS. Supplementation led to a dose-dependent increase in n-3 PUFA eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the blood cell fraction. We also observed a dose-dependent increase in EPA- and DHA-derived epoxy metabolites, whereas the effect of n-3 PUFA supplementation on LOX-dependent EPA- and DHA-derived hydroxy metabolites was less pronounced, with a tendency towards lower metabolites in subjects with higher n-3 PUFA levels. These data thus generally confirm effects of n-3 PUFA supplementation observed previously in healthy individuals. Additionally, they indicate a suppressive effect of high n-3 PUFA supplementation on the formation of LOX metabolites in the context of concomitant aspirin medication.

Targeting of 12/15-Lipoxygenase in retinal endothelial cells, but not in monocytes/macrophages, attenuates high glucose-induced retinal leukostasis

AIMS

Our previous studies have established a role for 12/15-lipoxygenase (LO) in mediating the inflammatory response in diabetic retinopathy (DR). However, the extent at which the local or systemic induction of 12/15-LO activity involved is unclear. Thus, the current study aimed to characterize the relative contribution of retinal endothelial versus monocytic/macrophagic 12/15-LO to inflammatory responses in DR.

MATERIALS & METHODS

We first generated a clustered heat map for circulating bioactive lipid metabolites in the plasma of streptozotocin (STZ)-induced diabetic mice using liquid chromatography coupled with mass-spectrometry (LC-MS) to evaluate changes in circulating 12/15-LO activity. This was followed by comparing the in vitro mouse endothelium-leukocytes interaction between leukocytes isolated from 12/15-LO knockout (KO) versus those isolated from wild type (WT) mice using the myeloperoxidase (MPO) assay. Finally, we examined the effects of knocking down or inhibiting endothelial 12/15-LO on diabetes-induced endothelial cell activation and ICAM-1 expression.

RESULTS

Analysis of plasma bioactive lipids' heat map revealed that the activity of circulating 12/15-LO was not altered by diabetes as evident by no significant changes in the plasma levels of major metabolites derived from 12/15-lipoxygenation of different PUFAs, including linoleic acid (13-HODE), arachidonic acid (12- and 15- HETEs), eicosapentaenoic acid (12- and 15- HEPEs), or docosahexaenoic acid (17-HDoHE). Moreover, leukocytes from 12/15-LO KO mice displayed a similar increase in adhesion to high glucose (HG)-activated endothelial cells as do leukocytes from WT mice. Furthermore, abundant proteins of 12-LO and 15-LO were detected in human retinal endothelial cells (HRECs), while it was undetected (15-LO) or hardly detectable (12-LO) in human monocyte-like U937 cells. Inhibition or knock down of endothelial 12/15-LO in HRECs blocked HG-induced expression of ICAM-1, a well-known identified important molecule for leukocyte adhesion in DR.

CONCLUSION

Our data support that endothelial, rather than monocytic/macrophagic, 12/15-LO has a critical role in hyperglycemia-induced ICAM-1 expression, leukocyte adhesion, and subsequent local retinal barrier dysfunction. This may facilitate the development of more precisely targeted treatment strategies for DR.

An anti-αVβ3 antibody inhibits coronary artery atherosclerosis in diabetic pigs

BACKGROUND AND AIMS

Diabetes is a major risk factor for the development of atherosclerosis. Hyperglycemia stimulates vascular smooth muscle cells (VSMC) to secrete ligands that bind to the αVβ3 integrin, a receptor that regulates VSMC proliferation and migration. This study determined whether an antibody that had previously been shown to block αVβ3 activation and to inhibit VSMC proliferation and migration in vitro, inhibited the development of atherosclerosis in diabetic pigs.

METHODS

Twenty diabetic pigs were maintained on a high fat diet for 22 weeks. Ten received injections of anti-β3 F(ab)₂ and ten received control F(ab)₂ for 18 weeks.

RESULTS

The active antibody group showed reduction of atherosclerosis of 91 ± 9% in the left main, 71 ± 11%, in left anterior descending, 80 ± 10.2% in circumflex, and 76 ± 25% in right coronary artery, (p < 0.01 compared to lesions areas from corresponding control treated arteries). There were significant reductions in both cell number and extracellular matrix. Histologic analysis showed neointimal hyperplasia with macrophage infiltration, calcifications and cholesterol clefts. Antibody treatment significantly reduced number of macrophages contained within lesions, suggesting that this change contributed to the decrease in lesion cellularity. Analysis of the biochemical changes within the femoral arteries that received the active antibody showed a 46 ± 12% (p < 0.05) reduction in the tyrosine phosphorylation of the β3 subunit of αVβ3 and a 40 ± 14% (p < 0.05) reduction in MAP kinase activation.

CONCLUSIONS

Blocking ligand binding to the αVβ3 integrin inhibits its activation and attenuates increased VSMC proliferation that is induced by chronic hyperglycemia. These changes result in significant decreases in atherosclerotic lesion size in the coronary arteries. The results suggest that this approach may have efficacy in treating the proliferative phase of atherosclerosis in patients with diabetes.

Genome-Wide Association Analysis for Blood Lipid Traits Measured in Three Pig Populations Reveals a Substantial Level of Genetic Heterogeneity

Serum lipids are associated with myocardial infarction and cardiovascular disease in humans. Here we dissected the genetic architecture of blood lipid traits by applying genome-wide association studies (GWAS) in 1,256 pigs from Laiwu, Erhualian and Duroc × (Landrace × Yorkshire) populations, and a meta-analysis of GWAS in more than 2,400 pigs from five diverse populations. A total of 22 genomic loci surpassing the suggestive significance level were detected on 11 pig chromosomes (SSC) for six blood lipid traits. Meta-analysis of GWAS identified 5 novel loci associated with blood lipid traits. Comparison of GWAS loci across the tested populations revealed a substantial level of genetic heterogeneity for porcine blood lipid levels. We further evaluated the causality of nine polymorphisms nearby or within the APOB gene on SSC3 for serum LDL-C and TC levels. Of the 9 polymorphisms, an indel showed the most significant association with LDL-C and TC in Laiwu pigs. But the significant association was not identified in the White Duroc × Erhualian F2 resource population, in which the QTL for LDL-C and TC was also detected on SSC3. This indicates that population-specific signals may exist for the SSC3 QTL. Further investigations are warranted to validate this assumption.

Minireview: 12-Lipoxygenase and Islet β-Cell Dysfunction in Diabetes

The insulin producing islet β-cells have increasingly gained attention for their role in the pathogeneses of virtually all forms of diabetes. Dysfunction, de-differentiation, and/or death of β-cells are pivotal features in the transition from normoglycemia to hyperglycemia in both animal models of metabolic disease and humans. In both type 1 and type 2 diabetes, inflammation appears to be a central cause of β-cell derangements, and molecular pathways that modulate inflammation or the inflammatory response are felt to be prime targets of future diabetes therapy. The lipoxygenases (LOs) represent a class of enzymes that oxygenate cellular polyunsaturated fatty acids to produce inflammatory lipid intermediates that directly and indirectly affect cellular function and survival. The enzyme 12-LO is expressed in all metabolically active tissues, including pancreatic islets, and has received increasing attention for its role in promoting cellular inflammation in the setting of diabetes. Genetic deletion models of 12-LO in mice reveal striking protection from metabolic disease and its complications and an emerging body of literature has implicated its role in human disease. This review focuses on the evidence supporting the proinflammatory role of 12-LO as it relates to islet β-cells, and the potential for 12-LO inhibition as a future avenue for the prevention and treatment of metabolic disease.

Lean and obese pig breeds exhibit differences in prenatal gene expression profiles of muscle development

Muscle development in domesticated animals is important for meat production. Furthermore, intramuscular fat content is an important trait of meat intended for consumption. Here, we examined differences in the expression of factors related to myogenesis, adipogenesis and skeletal muscle growth during fetal muscle development of lean (Yorkshire) and obese (Chenghua) pig breeds. At prenatal days 50 (d50) and 90 (d90), muscles and sera were collected from pig fetuses. Histology revealed larger diameters and numbers of myofibers in Chenghua pig fetuses than those in Yorkshire pig fetuses at d50 and d90. Yorkshire fetuses had higher serum concentrations of myostatin (d90), a negative regulator for muscle development, and higher mRNA expression of the growth hormone receptor Ghr (d90), myogenic MyoG (d90) and adipogenic LPL (d50). By contrast, Chenghua fetuses exhibited higher serum concentration of growth hormone (d90), and higher mRNA expression of myogenic MyoD (d90) as well as adipogenic PPARG and FABP4 (d50). Our results revealed distinct expression patterns in the two pig breeds at each developmental stage before birth. Compared with Chenghua pigs, development and maturation of fetal skeletal muscles may occur earlier in Yorkshire pigs, but the negative regulatory effects of myostatin may suppress muscle development at the later stage.

Intrauterine growth retarded piglet as a model for humans--studies on the perinatal development of the gut structure and function

The overall acceptance of pig models for human biomedical studies is steadily growing. Results of rodent studies are usually confirmed in pigs before extrapolating them to humans. This applies particularly to gastrointestinal and metabolism research due to similarities between pig and human physiology. In this context, intrauterine growth retarded (IUGR) pig neonate can be regarded as a good model for the better understanding of the IUGR syndrome in humans. In pigs, the induction of IUGR syndrome may include maternal diet intervention, dexamethasone treatment or temporary reduction of blood supply. However, in pigs, like in humans, circa 8% of neonates develop IUGR syndrome spontaneously. Studies on the pig model have shown changes in gut structure, namely a reduced thickness of mucosa and muscle layers, and delayed kinetic of disappearance of vacuolated enterocytes were found in IUGR individuals in comparison with healthy ones. Functional changes include reduced dynamic of gut mucosa rebuilding, decreased activities of main brush border enzymes, and changes in the expression of proteins important for carbohydrate, amino acids, lipid, mineral and vitamin metabolism. Moreover, profiles of intestinal hormones are different in IUGR and non-IUGR piglets. It is suggested that supplementation of the mothers during the gestation and/or the IUGR offspring after birth can help in restoring the development of the gastrointestinal tract. The pig provides presumably the optimal animal model for humans to study gastrointestinal tract structure and function development in IUGR syndrome.

Vascular endothelial tight junctions and barrier function are disrupted by 15(S)-hydroxyeicosatetraenoic acid partly via protein kinase C ε-mediated zona occludens-1 phosphorylation at threonine 770/772

Disruption of tight junctions (TJs) perturbs endothelial barrier function and promotes inflammation. Previously, we have shown that 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), the major 15-lipoxygenase 1 (15-LO1) metabolite of arachidonic acid, by stimulating zona occludens (ZO)-2 tyrosine phosphorylation and its dissociation from claudins 1/5, induces endothelial TJ disruption and its barrier dysfunction. Here, we have studied the role of serine/threonine phosphorylation of TJ proteins in 15(S)-HETE-induced endothelial TJ disruption and its barrier dysfunction. We found that 15(S)-HETE enhances ZO-1 phosphorylation at Thr-770/772 residues via PKCε-mediated MEK1-ERK1/2 activation, causing ZO-1 dissociation from occludin, disrupting endothelial TJs and its barrier function, and promoting monocyte transmigration; these effects were reversed by T770A/T772A mutations. In the arteries of WT mice ex vivo, 15(S)-HETE also induced ZO-1 phosphorylation and endothelial TJ disruption in a PKCε and MEK1-ERK1/2-dependent manner. In line with these observations, in WT mice high fat diet feeding induced 12/15-lipoxygenase (12/15-LO) expression in the endothelium and caused disruption of its TJs and barrier function. However, in 12/15-LO(-/-) mice, high fat diet feeding did not cause disruption of endothelial TJs and barrier function. These observations suggest that the 12/15-LO-12/15(S)-HETE axis, in addition to tyrosine phosphorylation of ZO-2, also stimulates threonine phosphorylation of ZO-1 in the mediation of endothelial TJ disruption and its barrier dysfunction.

12/15-lipoxygenase contributes to platelet-derived growth factor-induced activation of signal transducer and activator of transcription 3

We showed previously that the small molecule indirubin-3′-monoxime (I3MO) prevents vascular smooth muscle cell (VSMC) proliferation by selectively inhibiting signal transducer and activator of transcription 3 (STAT3). Looking for the underlying upstream molecular mechanism, we here reveal the important role of reactive oxygen species (ROS) for PDGF-induced STAT3 activation in VSMC. We show that neither NADPH-dependent oxidases (Noxes) nor mitochondria, but rather 12/15-lipoxygenase (12/15-LO) are pivotal ROS sources involved in the redox-regulated signal transduction from PDGFR to STAT3. Accordingly, pharmacological and genetic interference with 12/15-LO activity selectively inhibited PDGF-induced Src activation and STAT3 phosphorylation. I3MO is able to blunt PDGF-induced ROS and 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) production, indicating an inhibitory action of I3MO on 12/15-LO and consequently on STAT3. We identify 12/15-LO as a hitherto unrecognized signaling hub in PDGF-triggered STAT3 activation and show for the first time a negative impact of I3MO on 12/15-LO.

Multi-targeted mechanisms underlying the endothelial protective effects of the diabetic-safe sweetener erythritol

Diabetes is characterized by hyperglycemia and development of vascular pathology. Endothelial cell dysfunction is a starting point for pathogenesis of vascular complications in diabetes. We previously showed the polyol erythritol to be a hydroxyl radical scavenger preventing endothelial cell dysfunction onset in diabetic rats. To unravel mechanisms, other than scavenging of radicals, by which erythritol mediates this protective effect, we evaluated effects of erythritol in endothelial cells exposed to normal (7 mM) and high glucose (30 mM) or diabetic stressors (e.g. SIN-1) using targeted and transcriptomic approaches. This study demonstrates that erythritol (i.e. under non-diabetic conditions) has minimal effects on endothelial cells. However, under hyperglycemic conditions erythritol protected endothelial cells against cell death induced by diabetic stressors (i.e. high glucose and peroxynitrite). Also a number of harmful effects caused by high glucose, e.g. increased nitric oxide release, are reversed. Additionally, total transcriptome analysis indicated that biological processes which are differentially regulated due to high glucose are corrected by erythritol. We conclude that erythritol protects endothelial cells during high glucose conditions via effects on multiple targets. Overall, these data indicate a therapeutically important endothelial protective effect of erythritol under hyperglycemic conditions.

Randomized placebo-controlled intervention with n-3 LC-PUFA-supplemented yoghurt: effects on circulating eicosanoids and cardiovascular risk factors

BACKGROUND & AIMS

The study examined the value of n-3 LC-PUFA-enriched yogurt as means of improving cardiovascular health.

DESIGN

Fifty three mildly hypertriacylglycerolemic subjects (TAG ≥ 1.7 mmol/L) participated in a randomized, placebo-controlled, double-blind, parallel designed study. The subjects consumed 1) control yoghurt; 2) yoghurt enriched with 0.8 g n-3 LC-PUFA/d; or 3) yoghurt enriched with 3 g n-3 LC-PUFA/d for a period of 10 wks. Blood samples were taken at the beginning and the end of the study period.

RESULTS

Following daily intake of 3 g n-3 LC-PUFA for 10 weeks, n-3 LC-PUFA levels increased significantly in plasma and red blood cells (RBC) with concomitant increase in the EPA-derived mediators (PGE₃, 12-, 15-, 18-HEPE) in plasma whilst cardiovascular risk factors such as HDL, TAG, AA/EPA ratio, and n-3 index were improved (P < 0.05); the decrease of TAG and increase in HDL were associated with the CD36 genotype.

CONCLUSION

The observed increase of n-3 LC-PUFA in RBC and plasma lipids due to intake of n-3 LC-PUFA enriched yoghurt resulted in a reduction of cardiovascular risk factors and inflammatory mediators showing that daily consumption of n-3 PUFA enriched yoghurt can be an effective way of supplementing the daily diet and improving cardiovascular health.

Examining the role of lipid mediators in diabetic retinopathy

Diabetic retinopathy is the most disabling complication of diabetes, affecting 65% of patients after 10 years of the disease. Current treatment options for diabetic retinopathy are highly invasive and fall short of complete amelioration of the disease. Understanding the pathogenesis of diabetic retinopathy is critical to the development of more effective treatment options. Diabetic hyperglycemia and dyslipidemia are the main metabolic insults that affect retinal degeneration in diabetes. Although the role of hyperglycemia in inducing diabetic retinopathy has been studied in detail, much less attention has been paid to dyslipidemia. Recent clinical studies have demonstrated a strong association between dyslipidemia and development of diabetic retinopathy, highlighting the importance of understanding the exact changes in retinal lipid metabolism in diabetes. This review describes what is known on the role of dyslipidemia in the development of diabetic retinopathy, with a focus on retinal-specific lipid metabolism and its dysregulation in diabetes.

Effect of captopril and the bradykinin-PKC pathway on ROS production in type 1 diabetic rats

The aim of this study was to investigate the possible effects of captopril as a promoter in modulating the oxidant-antioxidant balance in rats with type 1 diabetes, and the influence of protein kinase C (PKC) pathways in the production of reactive oxygen species (ROS) induced by bradykinin in type 1 diabetic rats. This study evaluated the redox status in both the cardiac tissue and at the cellular level (neutrophils). Two concentrations of captopril were utilized: (i) 5 mg·(kg body mass)(-1), which was considered a therapeutic dose; and (ii) 10 mg·(kg body mass)(-1). Body mass, plasma glucose, and serum insulin were evaluated. To investigate the redox status of the cardiac tissue, we analyzed lipid peroxidation, concentration of carbonylated protein, catalase activity, and the concentration of glutathione. For a more accurate assessment of the possible antioxidant effect of captopril, we also analyzed ROS in neutrophils (in vivo), and ROS production induced by bradykinin and the influence of the PKC pathway in this production (in vitro). Our data show that the hearts of diabetic animals have increased oxidative damage, exemplified by the increased concentration of carbonylated protein and thiobarbituric acid reactive substances (TBARS). However, animals treated with captopril at both concentrations showed lower concentrations of carbonylated protein compared with untreated diabetic animals. We found an increase of catalase activity in the heart of diabetic rats, which was reversed by captopril treatment at both of the dosages tested. Our data showed that captopril was able to reduce ROS production in the neutrophils of diabetic rats at a dose of 10 mg captopril·(kg body mass)(-1). However, the antioxidant effect of captopril is independent of bradykinin. Diabetes induces oxidative stress, and these results suggest that captopril has an antioxidant effect and can modulate the production of ROS in circulating neutrophils.

Animal models of calcific aortic valve disease

Calcific aortic valve disease (CAVD), once thought to be a degenerative disease, is now recognized to be an active pathobiological process, with chronic inflammation emerging as a predominant, and possibly driving, factor. However, many details of the pathobiological mechanisms of CAVD remain to be described, and new approaches to treat CAVD need to be identified. Animal models are emerging as vital tools to this end, facilitated by the advent of new models and improved understanding of the utility of existing models. In this paper, we summarize and critically appraise current small and large animal models of CAVD, discuss the utility of animal models for priority CAVD research areas, and provide recommendations for future animal model studies of CAVD.

Increased expression and activity of 12-lipoxygenase in oxygen-induced ischemic retinopathy and proliferative diabetic retinopathy: implications in retinal neovascularization

OBJECTIVE

Arachidonic acid is metabolized by 12-lipoxygenase (12-LOX) to 12-hydroxyeicosatetraenoic acid (12-HETE) and has an important role in the regulation of angiogenesis and endothelial cell proliferation and migration. The goal of this study was to investigate whether 12-LOX plays a role in retinal neovascularization (NV).

RESEARCH DESIGN AND METHODS

Experiments were performed using retinas from a murine model of oxygen-induced ischemic retinopathy (OIR) that was treated with and without the LOX pathway inhibitor, baicalein, or lacking 12-LOX. We also analyzed vitreous samples from patients with and without proliferative diabetic retinopathy (PDR). Western blotting and RT-PCR were used to assess the expression of 12-LOX, vascular endothelial growth factor (VEGF), and pigment epithelium-derived factor (PEDF). Liquid chromatography-mass spectrometry was used to assess the amounts of HETEs in the murine retina and human vitreous samples. The effects of 12-HETE on VEGF and PEDF expression were evaluated in Müller cells (rMCs), primary mouse retinal pigment epithelial cells, and astrocytes.

RESULTS

Retinal NV during OIR was associated with increased 12-LOX expression and 12-, 15-, and 5-HETE production. The amounts of HETEs also were significantly higher in the vitreous of diabetic patients with PDR. Retinal NV was markedly abrogated in mice treated with baicalein or mice lacking 12-LOX. This was associated with decreased VEGF expression and restoration of PEDF levels. PEDF expression was reduced in 12-HETE-treated rMCs, astrocytes, and the retinal pigment epithelium. Only rMCs and astrocytes showed increased VEGF expression by 12-HETE.

CONCLUSIONS

12-LOX and its product HETE are important regulators of retinal NV through modulation of VEGF and PEDF expression and could provide a new therapeutic target to prevent and treat ischemic retinopathy.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.

Aminoguanidine inhibits aortic hydrogen peroxide production, VSMC NOX activity and hypercontractility in diabetic mice

Background

Dysfunctionally uncoupled endothelial nitric oxide synthase (eNOS) is involved in producing reactive oxygen species (ROS) in the diabetic endothelium. The present study investigated whether anti-diabetes drug Aminoguanidine (AG) has any effect on eNOS function and vascular oxidant stress.

Methods and Results

Blood glucose levels were increased to 452.0 ± 15.1 mg/dl in STZ-treated male C57BL/6J mice (148.4 ± 3.2 mg/dl in untreated controls). Aortic productions of NO^• and O₂^•- were measured specifically and sensitively using electron spin resonance. Diabetic mice had a marked increase in aortic O₂^•- production. Aortic hydrogen peroxide (H₂O₂) production was also increased in diabetic aortas and significantly attenuated by AG. AG however had only a marginal effect in reducing aortic O₂^•- production, which corresponded to a minimal effect in improving aortic nitric oxide (NO^•) bioavailability. The endothelium-dependent vasodilatation however was modestly but significantly improved by AG, likely consequent to AG-induced reduction in hyper-contractility. NAD(P)H oxidase (NOX)-dependent O₂^•- production was completely attenuated by AG in endothelium-denuded diabetic aortas.

Conclusion

In summary, despite that AG is not an effective eNOS recoupling agent presumably consequent to its ineffectiveness in preventing endothelial NOX activation, it is inhibitory of aortic H₂O₂ production, VSMC NOX activity, and hypercontractility in diabetes.

Role of Src tyrosine kinase in the atherogenic effects of the 12/15-lipoxygenase pathway in vascular smooth muscle cells

OBJECTIVE

The 12/15-Lipoxygenase (12/15-LO) and its metabolite 12(S)-Hydroxyeicosatetraenoic acid [12(S)-HETE] mediate proatherogenic responses in vascular smooth muscle cells (VSMCs). We examined the role of the nonreceptor tyrosine kinase Src in the signaling and epigenetic chromatin mechanisms involved in these processes.

METHODS AND RESULTS

Rat VSMCs (RVSMCs) were stimulated with 12(S)-HETE (0.1 micromol/L) in the presence or absence of the Src inhibitor PP2 (10 micromol/L). Src activation and downstream signaling events including inflammatory gene expression and chromatin histone H3-Lys-9/14 acetylation were examined by immunoblotting, RT-PCR, and chromatin immunoprecipitation assays, respectively. 12(S)-HETE significantly activated Src, focal adhesion kinase, Akt, p38MAPK, and CREB. Expression of monocyte chemoattractant protein-1 and interleukin-6 genes and histone H3-Lys-9/14 acetylation on their promoters were also increased by 12(S)-HETE. PP2 inhibited these responses as well as 12(S)-HETE-induced VSMC migration. Furthermore, dominant negative mutants of Src, CREB, and a histone acetyltransferase p300 significantly blocked 12(S)-HETE-induced inflammatory gene expression. In addition, growth factor induced Src signaling and downstream events including H3-Lys-9/14 acetylation and migration were significantly attenuated in VSMCs derived from 12/15-LO(-/-) mice relative to WT.

CONCLUSIONS

Src kinase signaling plays a central role in the proatherogenic responses mediated by 12/15-LO and its oxidized lipid metabolite 12(S)-HETE in VSMCs.

Sphingosine-1-phosphate inhibits high glucose-mediated ERK1/2 action in endothelium through induction of MAP kinase phosphatase-3

Endothelial activation is a key early event in vascular complications of Type 1 diabetes. The nonobese diabetic (NOD) mouse is a well-characterized model of Type 1 diabetes. We previously reported that Type 1 diabetic NOD mice have increased endothelial activation, with increased production of monocyte chemoattractant protein (MCP)-1 and IL-6, and a 30% increase of surface VCAM-1 expression leading to a fourfold increase in monocyte adhesion to the endothelium. Sphingosine-1-phosphate (S1P) prevents monocyte:endothelial interactions in these diabetic NOD mice. Incubation of diabetic NOD endothelial cells (EC) with S1P (100 nmol/l) reduced ERK1/2 phosphorylation by 90%, with no significant changes in total ERK1/2 protein. In the current study, we investigated the mechanism of S1P action on ERK1/2 to reduce activation of diabetic endothelium. S1P caused a significant threefold increase in mitogen-activated kinase phosphatase-3 (MKP-3) expression in EC. MKP-3 selectively regulates ERK1/2 activity through dephosphorylation. Incubation of diabetic NOD EC with S1P and the S1P(1)-selective agonist SEW2871 significantly increased expression of MKP-3 and reduced ERK1/2 phosphorylation, while incubation with the S1P(1)/S1P(3) antagonist VPC23019 decreased the expression of MKP-3, both results supporting a role for S1P(1) in MKP-3 regulation. To mimic the S1P-mediated induction of MKP-3 diabetic NOD EC, we overexpressed MKP-3 in human aortic endothelial cells (HAEC) cultured in elevated glucose (25 mmol/l). Overexpression of MKP-3 in glucose-cultured HAEC decreased ERK1/2 phosphorylation and resulted in decreased monocyte:endothelial interactions in a static monocyte adhesion assay. Finally, we used small interfering RNA to MKP-3 and observed increased monocyte adhesion. Moreover, S1P was unable to inhibit monocyte adhesion in the absence of MKP-3. Thus, one mechanism for the anti-inflammatory action of S1P in diabetic EC is inhibition of ERK1/2 phosphorylation through induction of MKP-3 expression via the S1P-S1P(1) receptor axis.

Influence of ketone bodies on oxidative stress parameters in brain of developing rats in vitro

Pro-oxidant and antioxidant properties have been found for acetoacetate (AcAc) and beta-hydroxybutyrate (BHB) in peripheral tissues. In the present study we investigated the role of AcAc and BHB at concentrations found in diabetic patients during ketoacidotic crises and in individuals affected by succinyl CoA: 3-oxoacid CoA transferase and acetoacetyl-CoA thiolase deficiencies, disorders clinically characterized by neurological symptoms, on a large number of oxidative stress parameters in fresh cerebral cortex of developing rats. Lipid peroxidation (chemiluminescence and thiobarbituric acid-reactive substances levels), protein oxidative damage (carbonyl formation and sulfhydryl oxidation), 2',7'-dichlorofluorescin diacetate oxidation and the non-enzymatic (total antioxidant reactivity and glutathione levels) and enzymatic (glutathione peroxidase, superoxide dismutase and catalase activities) antioxidant defenses were not changed by doses of BHB and AcAc as high as 25 mM in cortical supernatants under basal conditions. Furthermore, BHB did not affect the increased thiobarbituric acid-reactive substances levels provoked by 3-hydroxy-3-methylglutaric and 3-methylglutaconic acids and by a hydroxyl-induced generation system. Finally, BHB and AcAc were not able to oxidize sulfhydryl groups from a commercial GSH solution. Therefore, under basal conditions or under situations with high production of free radicals, AcAc and BHB were not able to reduce or increase the oxidative stress parameters in the brain. Taken together, our present results do not support the hypothesis that BHB and AcAc act as potent direct or indirect pro-oxidants or antioxidants in the CNS.

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.

Regulation of renal 12(S)-hydroxyeicosatetraenoic acid in diabetes by angiotensin AT1 and AT2 receptors

Diabetes is associated with increased production of 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE]. The mechanisms involved in this process remain unclear. We hypothesized that hyperglycemia and angiotensin II (ANG II) regulate renal 12(S)-HETE production via a balance between angiotensin AT(1) and AT(2) receptors activities. Using a microdialysis technique, renal interstitial fluid (RIF) levels of ANG II and 12(S)-HETE were monitored in normal control and streptozotocin-induced diabetic rats at baseline and then weekly thereafter for 12 wk. In a second group of normal and diabetic rats, 3 wk after development of diabetes, we monitored RIF 12(S)-HETE levels in response to acute AT(1) receptor blockade with valsartan or AT(2) receptor blockade with PD123319 individually or combined. Two weeks after induction of diabetes there was a 404% increase in ANG II (P < 0.05), a 149% increase in 12S-HETE (P < 0.05), and a 649% increase in urinary albumin excretion (P < 0.05). These levels remained elevated throughout the study. PD123319 given alone had no effect on 12(S)-HETE. Valsartan decreased 12(S)-HETE by 61.6% (P < 0.0001), a response that was abrogated when PD123319 was given with valsartan. These data demonstrate that hyperglycemia increases renal ANG II and 12(S)-HETE levels. The increase in 12(S)-HETE is mediated via AT(1) receptor. The attenuation of the effects of AT(1) receptor blockade by PD123319 suggests that AT(2) receptor contributes to the downregulation of renal 12(S)-HETE production.

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.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

Products of 12/15-lipoxygenase upregulate the angiotensin II receptor

Angiotensin II and its type 1 receptor (AT1R) play important roles in the pathogenesis of renal disease and diabetic nephropathy. The 12/15-lipoxygenase pathway of arachidonate metabolism and its lipid products have also been implicated in diabetic nephropathy. However, it is unclear whether 12/15-lipoxygenase regulates expression of AT1R. In cultured rat mesangial cells, we found that the 12/15-lipoxygenase product 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) increased AT1R mRNA and protein expression, primarily by stabilizing AT1R mRNA. Pretreatment with 12(S)-HETE also amplified the signaling effects of angiotensin II, likely due to the increased AT1R expression. Levels of AT1R protein expression decreased when 12/15-lipoxygenase was knocked down with specific short hairpin RNA (shRNA) compared with control cells. Similarly, levels of the AT1 receptor, but not the AT2 receptor, were significantly lower in mesangial cells and glomeruli derived from 12/15-lipoxygenase knockout mice compared with control mice. Reciprocally, stable overexpression of 12/15-lipoxygenase increased AT1R expression in cultured mesangial cells. In vivo, modified siRNA targeting 12/15-lipoxygenase reduced glomerular AT1R expression in a diabetic mouse model. Interestingly, angiotensin II induced greater levels of 12/15-lipoxygenase, TGF-beta1, and fibronectin (FN) in AT1R-overexpressing mesangial cells compared with control cells. Therefore, oxidized lipids generated by the 12/15-lipoxygenase-mediated metabolism of arachidonic acid can enhance AT1R expression in mesangial cells and augment the profibrotic effects of angiotensin II.

Evaluation of beta-cell mass and function in the Göttingen minipig

Increased knowledge about beta-cell mass and function is important for our understanding of the pathophysiology of type 2 diabetes (T2DM). The relationship between the two is difficult to study in humans, whereas animal models allow studies of consequences of, for example, reduction of beta-cell mass and induction of obesity and procurement of the pancreas for histological examination. An overview of results obtained in the Göttingen minipig in relation to beta-cell function, and mass is provided here. Effects of a primary reduction of beta-cell mass have indicated that not all of the defects of pulsatile insulin secretion in human T2DM can be explained by reduced beta-cell mass. Furthermore, induction of obesity has shown deterioration of beta-cell function and morphological changes in the pancreas. As in humans, obesity leads to an increased beta-cell volume in the minipig, and based on the increased number of islets, neogenesis of islets is an important factor in expansion of beta-cell mass in this species. Measurement of beta-cell function as an estimate of beta-cell mass is, at present, the only method possible in humans, and this approach has been validated using lean and obese minipigs with a range of beta-cell mass. The effects on beta-cell function and mass of obesity of longer duration and/or more pronounced hyperglycaemia remains to be determined, but the models developed so far represent a valuable tool for such investigations.

Viral vector-mediated 12/15-lipoxygenase overexpression in vascular smooth muscle cells enhances inflammatory gene expression and migration

Increased expression and activity of 12/15-lipoxygenase (12/15-LO) in vascular smooth muscle cells (VSMCs) play a key role in the pathogenesis of diabetes and vascular complications. However, the consequences of 12/15-LO overexpression for VSMC migration and inflammatory gene expression are not known. In this study, 12/15-LO was overexpressed using adeno- and baculoviral vectors in human VSMC (HVSMCs) and proatherogenic responses compared with control enhanced green fluorescent protein (EGFP)-expressing cells. HVSMCs transduced with 12/15-LO viruses expressed high levels of enzymatically active protein and produced increased levels of the LO product, 12(S)-hydroxyeicosatetraenoic acid. 12/15-LO-overexpressing HVSMCs exhibited increased oxidant stress, activation of p38 mitogen-activated protein kinase, migration and inflammatory gene expression relative to HVSMCs expressing EGFP. Furthermore, inflammatory gene expression induced by 12/15-LO overexpression was abolished by anti-oxidants, siRNAs targeting p65 (nuclear factor-kappaB), or new-generation baculoviruses expressing inhibitory IkappaBalpha or IkappaBalpha superrepressor mutant. Thus, we have used novel viral vector delivery systems, including baculoviruses, for the first time to deliver foreign genes into VSMCs and thereby demonstrated that 12/15-LO overexpression increases oxidant stress, mitogen-activated protein kinase activation, migration and inflammatory genes in VSMCs and that NF-kappaB is a key downstream effector. Enhanced proatherogenic responses in VSMCs triggered by increased 12/15-LO levels under pathological conditions may contribute to vascular dysfunction.

12(S)-hydroperoxyeicosatetraenoic acid (12-HETE) increases mitochondrial nitric oxide by increasing intramitochondrial calcium

12(S)-hydroxyeicosatetraenoic acid (12-HETE) is one of the metabolites of arachidonic acid involved in pathological conditions associated with mitochondria and oxidative stress. The present study tested effects of 12-HETE on mitochondrial functions. In isolated rat heart mitochondria, 12-HETE increases intramitochondrial ionized calcium concentration that stimulates mitochondrial nitric oxide (NO) synthase (mtNOS) activity. mtNOS-derived NO causes mitochondrial dysfunctions by decreasing mitochondrial respiration and transmembrane potential. mtNOS-derived NO also produces peroxynitrite that induces release of cytochrome c and stimulates aggregation of mitochondria. Similarly, in HL-1 cardiac myocytes, 12-HETE increases intramitochondrial calcium and mitochondrial NO, and induces apoptosis. The present study suggests a novel mechanism for 12-HETE toxicity.