Increased production of 12/15 lipoxygenase eicosanoids accelerates monocyte/endothelial interactions in diabetic db/db mice

12(S)-hydroxyeicosatetraenoic acid is significantly increased in diabetic kidney disease and associated with renal function decline

AIMS

12(S)-hydroxyeicosatetraenoic (12(S)-HETE), an alternate arachidonic acid metabolite, has been recently examined in metabolic disease. However, the role of 12(S)-HETE in diabetic kidney disease (DKD) remains unclear. We studied for the first time the relationship of serum 12(S)-HETE and DKD and renal function parameters in a Chinese population.

MATERIALS AND METHODS

We recruited 275 subjects who were diagnosed with type 2 diabetes (T2DM) for more than 10 years, including 149 DKD patients and 126 T2DM patients without DKD. Serum 12(S)-HETE was measured using the enzyme-linked immunosorbent assay.

RESULTS

Serum 12(S)-HETE was significantly higher in DKD patients than controls [384.69 (77.54, 1003.05) pg/ml and 17.77 (8.11, 75.13) pg/ml, respectively, p < 0.0001]. Compared to controls, 12(S)-HETE was significantly increased in both macroalbuminuria and microalbuminuria groups (p < 0.0001). Further, the macroalbuminuria group also had a higher serum 12(S)-HETE level compared to the microalbuminuria group (p = 0.0063). Moreover, serum 12(S)-HETE was positively correlated with the albuminuria level (r = 0.5833, p < 0.0001), serum creatinine (r = 0.2725, p < 0.0001), and was negatively associated with the estimated glomerular filtration rate (r = -0.2085, p = 0.0005). Further, receiver operating characteristic analysis (ROC) revealed that 12(S)-HETE had a good performance of distinguishing DKD from controls (AUC 0.828) with a sensitivity of 0.913 and a specificity of 0.711.

CONCLUSION

Our findings revealed that serum 12(S)-HETE significantly associated with DKD and disease severity, suggesting that serum 12(S)-HETE may be used as a potential biomarker for the early diagnosis of DKD.

Growth State-Dependent Expression of Arachidonate Lipoxygenases in the Human Endothelial Cell Line EA.hy926

Endothelial cells regulate vascular homeostasis through the secretion of various paracrine molecules, including bioactive lipids, but little is known regarding the enzymes responsible for generating these lipids under either physiological or pathophysiological conditions. Arachidonate lipoxygenase (ALOX) expression was therefore investigated in confluent and nonconfluent EA.h926 endothelial cells, which represent the normal quiescent and proliferative states, respectively. mRNAs for ALOX15, ALOX15B, and ALOXE3 were detected in EA.hy926 cells, with the highest levels present in confluent cells compared to nonconfluent cells. In contrast, ALOX5, ALOX12, and ALOX12B mRNAs were not detected. At the protein level, only ALOX15B and ALOXE3 were detected but only in confluent cells. ALOXE3 was also observed in confluent human umbilical artery endothelial cells (HUAEC), indicating that its expression, although previously unreported, may be a general feature of endothelial cells. Exposure to laminar flow further increased ALOXE3 levels in EA.hy926 cells and HUAECs. The evidence obtained in this study indicates that proliferative status and shear stress are both important factors that mediate endothelial ALOX gene expression. The presence of ALOX15B and ALOXE3 exclusively in quiescent human endothelial cells suggests their activity likely contributes to the maintenance of a healthy endothelium.

The Emerging Role of COX-2, 15-LOX and PPARγ in Metabolic Diseases and Cancer: An Introduction to Novel Multi-target Directed Ligands (MTDLs)

Emerging evidence supports an intertwining framework for the involvement of different inflammatory pathways in a common pathological background for a number of disorders. Of importance are pathways involving arachidonic acid metabolism by cyclooxygenase-2 (COX-2) and 15-lipoxygenase (15-LOX). Both enzyme activities and their products are implicated in a range of pathophysiological processes encompassing metabolic impairment leading to adipose inflammation and the subsequent vascular and neurological disorders, in addition to various pro- and antitumorigenic effects. A further layer of complexity is encountered by the disparate, and often reciprocal, modulatory effect COX-2 and 15-LOX activities and metabolites exert on each other or on other cellular targets, the most prominent of which is peroxisome proliferator-activated receptor gamma (PPARγ). Thus, effective therapeutic intervention with such multifaceted disorders requires the simultaneous modulation of more than one target. Here, we describe the role of COX-2, 15-LOX, and PPARγ in cancer and complications of metabolic disorders, highlight the value of designing multi-target directed ligands (MTDLs) modifying their activity, and summarizing the available literature regarding the rationale and feasibility of design and synthesis of these ligands together with their known biological effects. We speculate on the potential impact of MTDLs in these disorders as well as emphasize the need for structured future effort to translate these early results facilitating the adoption of these, and similar, molecules in clinical research.

Pemafibrate, A Novel Selective Peroxisome Proliferator-Activated Receptor α Modulator, Reduces Plasma Eicosanoid Levels and Ameliorates Endothelial Dysfunction in Diabetic Mice

Aims: Various pathological processes related to diabetes cause endothelial dysfunction. Eicosanoids derived from arachidonic acid (AA) have roles in vascular regulation. Fibrates have recently been shown to attenuate vascular complications in diabetics. Here we examined the effects of pemafibrate, a selective peroxisome proliferator-activated receptor α modulator, on plasma eicosanoid levels and endothelial function in diabetic mice.

Methods: Diabetes was induced in 7-week-old male wild-type mice by a single injection of streptozotocin (150 mg/kg). Pemafibrate (0.3 mg/kg/day) was administered orally for 3 weeks. Untreated mice received vehicle. Circulating levels of eicosanoids and free fatty acids were measured using both gas and liquid chromatography-mass spectrometry. Endothelium-dependent and endothelium-independent vascular responses to acetylcholine and sodium nitroprusside, respectively, were analyzed.

Results: Pemafibrate reduced both triglyceride and non-high-density lipoprotein-cholesterol levels ( P ＜0.01), without affecting body weight. It also decreased circulating levels of AA ( P ＜0.001), thromboxane B ₂ ( P ＜0.001), prostaglandin E ₂ , leukotriene B ₄ ( P ＜0.05), and 5-hydroxyeicosatetraenoic acid ( P ＜0.001), all of which were elevated by the induction of diabetes. In contrast, the plasma levels of 15-deoxy-Δ ^12,14 -prostaglandin J ₂ , which declined following diabetes induction, remained unaffected by pemafibrate treatment. In diabetic mice, pemafibrate decreased palmitic acid (PA) and stearic acid concentrations ( P ＜0.05). Diabetes induction impaired endothelial function, whereas pemafibrate ameliorated it ( P ＜0.001). The results of ex vivo experiments indicated that eicosanoids or PA impaired endothelial function.

Conclusion: Pemafibrate diminished the levels of vasoconstrictive eicosanoids and free fatty acids accompanied by a reduction of triglyceride. These effects may be associated with the improvement of endothelial function by pemafibrate in diabetic mice.

Plasma metabolites, especially lipid metabolites, are altered in pregnant women with gestational diabetes mellitus

BACKGROUND AND AIMS

Gestational diabetes mellitus (GDM) is a pathological condition of glucose intolerance associated with adverse pregnancy outcomes and increased risk of developing maternal type 2 diabetes later in life. Metabolomics is finding increasing use in the study of GDM. To date, GDM-specific metabolomic changes have not been completely elucidated.

MATERIALS AND METHODS

In this pilot study, metabolomics fingerprinting data, obtained by ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF-MS), of 54 healthy pregnant women and 49 patients with GDM at the second and third gestational trimesters were analyzed. Multilevel statistical methods were used to process complex metabolomic data from the retrospective cohorts.

RESULTS

Using univariate analysis (p < 0.05), 41 metabolites were identified as having the most significant differences between these two groups. Lipid metabolites, particularly glycerophospholipids, were the most prevalent class of altered compounds. In addition, metabolites with previously unknown connection to GDM - such as monoacylglycerol, dihydrobiopterin, and 13S-hydroxyoctadecadienoic acid - were identified with strong discriminative power. The main metabolic pathways affected by GDM included glycerophospholipid metabolism, linoleic acid metabolism, and D-arginine and D-ornithine metabolism.

CONCLUSION

Our data provide a comprehensive overview of metabolite changes at different stages of pregnancy, which offers further insights into the pathogenesis of GDM.

Effect of renal replacement therapy on selected arachidonic acid derivatives concentration

BACKGROUND

Platelet activation is an important side effect of dialysis, resulted in a subsequent release of arachidonic acid (AA) from activated platelets. AA is involved in many pathologic conditions, such as inflammation, asthma, cancer, diabetes, hypertension, and the pathogenesis of kidney disease. The aim of this study was to define whether the dialysis type affects the concentration of AA derivatives in patients with chronic kidney disease.

METHODS

117 patients were qualified to the study group. Based on the type of renal replacement therapy, patients were divided into the following groups: hemodialysis (HD A - before/HD B - after hemodialysis), peritoneal dialysis (PD), kidney transplant patients (TE - before/TE A - after transplantation) and conservative treatment (CT) (30; 30; 27; 30 patients, respectively). The control group consisted of 30 healthy volunteers (NK). The ELISA methods were used to measure the concentrations of TXB2, 5-HETE, 12-HETE, and 15-HETE in the blood serum.

RESULTS

Renal replacement therapy significantly influences the concentration of TXB₂ (mean ± SD [ng/mL]: HD A- 34.6 ± 9; HD B- 28.3 ± 15.2; PD- 28.3 ± 15.2; CT- 34.2 ± 8.0; TE- 36.7 ± 42.9; TE A- 27.9 ± 8.8; NK- 19.6 ± 15; p = 0.010), 5-HETE (mean ± SD [ng/mL]: HD A- 284.2 ± 428.4; HD B- 304.8 ± 516.2; PD - 530.0 ± 553.3; CT- 318.7 ± 366.0; TE- 525.6 ± 358.0; TE A - 409.8 ± 377.1; NK 838.1 ± 497.8; p < 0.001) and 15-HETE (HD A-18.1 ± 8.7; HD B- 42.2 ± 14; PD - 36.3 ± 13.8; CT- 33.7 ± 14.0; TE- 19.5 ± 10.2; TE A - 34.4 ± 16.3; NK 22.2 ± 17.8; p < 0,001). There was a significant relationship between the type of renal replacement therapy and the duration of dialysis, and the concentration of TXB₂, 12-HETE acid, and 15-HETE.

CONCLUSIONS

The type of renal replacement therapy significantly affects the concentration of AA derivatives. Peritoneal dialysis is the best method of dialysis, taking into account the concentration of arachidonic acid derivatives.

Emerging role of 12/15-Lipoxygenase (ALOX15) in human pathologies

12/15-lipoxygenase (12/15-LOX) is an enzyme, which oxidizes polyunsaturated fatty acids, particularly omega-6 and -3 fatty acids, to generate a number of bioactive lipid metabolites. A large number of studies have revealed the importance of 12/15-LOX role in oxidative and inflammatory responses. The in vitro studies have demonstrated the ability of 12/15-LOX metabolites in the expression of various genes and production of cytokine related to inflammation and resolution of inflammation. The studies with the use of knockout and transgenic animals for 12/15-LOX have further shown its involvement in the pathogenesis of a variety of human diseases, including cardiovascular, renal, neurological and metabolic disorders. This review summarizes our current knowledge on the role of 12/15-LOX in inflammation and various human diseases.

Altered Protein Expression of Cardiac CYP2J and Hepatic CYP2C, CYP4A, and CYP4F in a Mouse Model of Type II Diabetes-A Link in the Onset and Development of Cardiovascular Disease?

Arachidonic acid can be metabolized by cytochrome P450 (CYP450) enzymes in a tissue- and cell-specific manner to generate vasoactive products such as epoxyeicosatrienoic acids (EETs-cardioprotective) and hydroxyeicosatetraenoic acids (HETEs-cardiotoxic). Type II diabetes is a well-recognized risk factor for developing cardiovascular disease. A mouse model of Type II diabetes (C57BLKS/J-db/db) was used. After sacrifice, livers and hearts were collected, washed, and snap frozen. Total proteins were extracted. Western blots were performed to assess cardiac CYP2J and hepatic CYP2C, CYP4A, and CYP4F protein expression, respectively. Significant decreases in relative protein expression of cardiac CYP2J and hepatic CYP2C were observed in Type II diabetes animals compared to controls (CYP2J: 0.80 ± 0.03 vs. 1.05 ± 0.06, n = 20, p < 0.001); (CYP2C: 1.56 ± 0.17 vs. 2.21 ± 0.19, n = 19, p < 0.01). In contrast, significant increases in relative protein expression of both hepatic CYP4A and CYP4F were noted in Type II diabetes mice compared to controls (CYP4A: 1.06 ± 0.09 vs. 0.18 ± 0.01, n = 19, p < 0.001); (CYP4F: 2.53 ± 0.22 vs. 1.10 ± 0.07, n = 19, p < 0.001). These alterations induced by Type II diabetes in the endogenous pathway (CYP450) of arachidonic acid metabolism may increase the risk for cardiovascular disease by disrupting the fine equilibrium between cardioprotective (CYP2J/CYP2C-generated) and cardiotoxic (CYP4A/CYP4F-generated) metabolites of arachidonic acid.

Dietary Linoleic Acid and Its Oxidized Metabolites Exacerbate Liver Injury Caused by Ethanol via Induction of Hepatic Proinflammatory Response in Mice

Alcoholic liver disease is a major human health problem leading to significant morbidity and mortality in the United States and worldwide. Dietary fat plays an important role in alcoholic liver disease pathogenesis. Herein, we tested the hypothesis that a combination of ethanol and a diet rich in linoleic acid (LA) leads to the increased production of oxidized LA metabolites (OXLAMs), specifically 9- and 13-hydroxyoctadecadienoic acids (HODEs), which contribute to a hepatic proinflammatory response exacerbating liver injury. Mice were fed unsaturated (with a high LA content) or saturated fat diets (USF and SF, respectively) with or without ethanol for 10 days, followed by a single binge of ethanol. Compared to SF+ethanol, mice fed USF+ethanol had elevated plasma alanine transaminase levels, enhanced hepatic steatosis, oxidative stress, and inflammation. Plasma and liver levels of 9- and 13-HODEs were increased in response to USF+ethanol feeding. We demonstrated that primarily 9-HODE, but not 13-HODE, induced the expression of several proinflammatory cytokines in vitro in RAW264.7 macrophages. Finally, deficiency of arachidonate 15-lipoxygenase, a major enzyme involved in LA oxidation and OXLAM production, attenuated liver injury and inflammation caused by USF+ethanol feeding but had no effect on hepatic steatosis. This study demonstrates that OXLAM-mediated induction of a proinflammatory response in macrophages is one of the potential mechanisms underlying the progression from alcohol-induced steatosis to alcoholic steatohepatitis.

Modified citrus pectin inhibits galectin-3 function to reduce atherosclerotic lesions in apoE-deficient mice

Galectin-3 is a carbohydrate-binding lectin, which has been implicated in the modulation of atherosclerotic pathophysiology, and is highly expressed in monocytes, macrophages and endothelial cells within atherosclerotic plaques. Modified citrus pectin (MCP) is produced from citrus pectin via pH and temperature modifications, which break it into shorter, non‑branched, galactose‑rich carbohydrate chains. MCP is able to tightly bind with galectin‑3, via recognition of its carbohydrate recognition domain, and facilitates the modulation of galectin‑3‑induced bioactivity. The present study explored the effects of MCP on the initiation of atherosclerosis. Eight‑week‑old apolipoprotein E‑deficient mice were treated with 1% MCP and fed an atherogenic diet for 4 weeks. The effects of MCP on atherosclerotic initiation were determined by pathological analysis and scanning electron microscope (SEM) imaging. MCP treatment reduced the size of atherosclerotic lesion areas, which was accompanied by decreased numbers of macrophages and smooth muscle cells (SMCs). Furthermore, SEM examination of the surface of the atheroma‑prone vessel wall indicated that MCP treatment reduced endothelial injury. To analyze the effects of MCP on monocyte adhesion, firstly, oxidized‑low density lipoprotein and various concentrations of MCP (0.025, 0.05, 0.1 and 0.25%) were incubated with the human umbilical vein endothelial cells (HUVECs) for stimulation and following this, the U937 cells were plated onto the HUVECs. The results revealed that MCP reduced the adhesion of U937 monocytes to HUVECs, indicating the adhesion-inhibiting effects of MCP. In conclusion, the present study revealed that MCP, a galectin‑3 inhibitor, reduced the size of atherosclerotic lesions by inhibiting the adhesion of leucocytes to endothelial cells. Inhibition of galectin‑3 function may be a therapeutic strategy for the treatment of atherosclerosis.

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.

DPP-4 inhibition improves early mortality, β cell function, and adipose tissue inflammation in db/db mice fed a diet containing sucrose and linoleic acid

BACKGROUND

Diabetes therapy that not only lowers glucose levels but also lengthens life spans is required. We previously demonstrated that DPP-4 inhibition ameliorated β cell apoptosis and adipose tissue inflammation in β cell-specific glucokinase haploinsufficient mice fed a diet containing a combination of sucrose and linoleic acid (SL).

METHODS

In this study, we investigated the effects of DPP-4 inhibition in obese diabetic db/db mice fed an SL diet or a control diet containing sucrose and oleic acid (SO). We also examined the effects of DPP-4 inhibition in IRS-1-deficient mice fed an SL or SO diet as a model of insulin resistance.

RESULTS

DPP-4 inhibition efficiently increases the active GLP-1 levels in db/db mice. Unexpectedly, the SL diet, but not the SO diet, markedly increases mortality in the db/db mice. DPP-4 inhibition reduces the early lethality in SL-fed db/db mice. DPP-4 inhibition improves glucose tolerance, β cell function, and adipose tissue inflammation in db/db mice fed either diet. No significant changes in glycemic control or β cell mass were observed in any of the IRS-1-deficient mouse groups.

CONCLUSIONS

A diet containing a combination of sucrose and linoleic acid causes early lethality in obese diabetic db/db mice, but not in lean and insulin resistant IRS-1 knockout mice. DPP-4 inhibition has protective effects against the diet-induced lethality in db/db mice.

Reactive Oxygen Species (ROS) Mediate p300-dependent STAT1 Protein Interaction with Peroxisome Proliferator-activated Receptor (PPAR)-γ in CD36 Protein Expression and Foam Cell Formation

Previously, we have demonstrated that 15(S)-hydroxyeicosatetranoic acid (15(S)-HETE) induces CD36 expression involving STAT1. Many studies have shown that peroxisome proliferator-activated receptor (PPAR)-γ mediates CD36 expression. Therefore, we asked the question whether these transcriptional factors interact with each other in the regulation of CD36 expression by 15(S)-HETE. Here, we show that STAT1 interacts with PPARγ in the induction of CD36 expression and foam cell formation by 15(S)-HETE. In addition, using molecular biological approaches such as EMSA, supershift EMSA, ChIP, re-ChIP, and promoter-reporter gene assays, we demonstrate that the STAT1 and PPARγ complex binds to the STAT-binding site at -107 nucleotides in the CD36 promoter and enhances its activity. Furthermore, the interaction of STAT1 with PPARγ depends on STAT1 acetylation, which is mediated by p300. In addition, our findings show that reactive oxygen species-dependent Syk and Pyk2 stimulation is required for p300 tyrosine phosphorylation and activation. Together, these results demonstrate that an interaction between STAT1, p300, and peroxisome proliferator-activated receptor-γ is required for 15(S)-HETE-induced CD36 expression, oxidized low density lipoprotein uptake, and foam cell formation, critical events underlying the pathogenesis of atherosclerosis.

12/15-Lipoxygenase-dependent ROS production is required for diet-induced endothelial barrier dysfunction

To understand the mechanisms of 15(S)-HETE-induced endothelial cell (EC) barrier dysfunction, we examined the role of xanthine oxidase (XO). 15(S)-HETE induced junction adhesion molecule A (JamA) phosphorylation on Y164, Y218, and Y280 involving XO-mediated reactive oxygen species production and Src and Pyk2 activation, resulting in its dissociation from occludin, thereby causing tight junction (TJ) disruption, increased vascular permeability, and enhanced leukocyte and monocyte transmigration in vitro using EC monolayer and ex vivo using arteries as models. The phosphorylation of JamA on Y164, Y218, and Y280 appears to be critical for its role in 15(S)-HETE-induced EC barrier dysfunction, as mutation of any one of these amino acid residues prevented its dissociation from occludin and restored TJ integrity and barrier function. In response to high-fat diet (HFD) feeding, WT, but not 12/15-lipoxygenase (LO)(-/-), mice showed enhanced XO expression and its activity in the artery, which was correlated with increased aortic TJ disruption and barrier permeability with enhanced leukocyte adhesion and these responses were inhibited by allopurinol. These observations provide novel insights on the role of XO in 12/15-LO-induced JamA tyrosine phosphorylation and TJ disruption leading to increased vascular permeability in response to HFD.

ROS-dependent Syk and Pyk2-mediated STAT1 activation is required for 15(S)-hydroxyeicosatetraenoic acid-induced CD36 expression and foam cell formation

15(S)-Hydroxyeicosatetraenoic acid (15(S)-HETE), the major 15-lipoxygenase 1/2 (15-LO1/2) metabolite of arachidonic acid (AA), induces CD36 expression through xanthine oxidase and NADPH oxidase-dependent ROS production and Syk and Pyk2-dependent STAT1 activation. In line with these observations, 15(S)-HETE also induced foam cell formation involving ROS, Syk, Pyk2, and STAT1-mediated CD36 expression. In addition, peritoneal macrophages from Western diet-fed ApoE(-/-) mice exhibited elevated levels of xanthine oxidase and NADPH oxidase activities, ROS production, Syk, Pyk2, and STAT1 phosphorylation, and CD36 expression compared to those from ApoE(-/-):12/15-LO(-/-) mice and these events correlated with increased lipid deposits, macrophage content, and lesion progression in the aortic roots. Human atherosclerotic arteries also showed increased 15-LO1 expression, STAT1 phosphorylation, and CD36 levels as compared to normal arteries. Together, these findings suggest that 12/15-LO metabolites of AA, particularly 12/15(S)-HETE, might play a crucial role in atherogenesis by enhancing foam cell formation.

Importance of sulfur-containing metabolites in discriminating fecal extracts between normal and type-2 diabetic mice

A metabolic disorder such as Type-2 Diabetes mellitus (T2DM) is a complex disease induced by genetic, environmental, and nutritional factors. The db/db mouse model, bearing a nonfunctional leptin receptor, is widely used to investigate the pathophysiology of T2DM. Fecal extracts of db/db and wild-type littermates were studied to unravel a broad spectrum of new and relevant metabolites related to T2DM as proxies of the interplay of gut microbiome and murine metabolomes. The nontargeted metabolomics approach consists of an integrated analytical concept of high-resolution mass spectrometry FT-ICR-MS, followed by UPLC-TOF-MS/MS experiments. We demonstrate that a metabolic disorder such as T2DM affects the gastrointestinal tract environment, thereby influencing different metabolic pathways and their respective metabolites in diabetic mice. Fatty acids, bile acids concerning cholic and deoxycholic acid, and steroid metabolism were highly discriminative comparing fecal meta-metabolomes of wt and db/db mice. Furthermore, sulfur-(S)-containing metabolites including N-acyl taurines were altered in diabetic mice, enabling us to focus on S-containing metabolites, especially the sulfate and taurine conjugates of bile and fatty acids. Different sulfate containing bile acids including sulfocholic acid, oxocholic acid sulfate, taurocholic acid sulfate, and cyprinol sulfate were significantly altered in diabetic mice. Moreover, we identified 12 new sulfate and taurine conjugates of hydroxylated fatty acids with significant importance in T2DM metabolism in db/db mice.

MyD88-dependent interplay between myeloid and endothelial cells in the initiation and progression of obesity-associated inflammatory diseases

MyD88-dependent GM-CSF production by endothelial cells plays a role in the initiation of obesity-associated inflammation by promoting adipose macrophage recruitment and M1-like polarization.

Low-grade systemic inflammation is often associated with metabolic syndrome, which plays a critical role in the development of the obesity-associated inflammatory diseases, including insulin resistance and atherosclerosis. Here, we investigate how Toll-like receptor–MyD88 signaling in myeloid and endothelial cells coordinately participates in the initiation and progression of high fat diet–induced systemic inflammation and metabolic inflammatory diseases. MyD88 deficiency in myeloid cells inhibits macrophage recruitment to adipose tissue and their switch to an M1-like phenotype. This is accompanied by substantially reduced diet-induced systemic inflammation, insulin resistance, and atherosclerosis. MyD88 deficiency in endothelial cells results in a moderate reduction in diet-induced adipose macrophage infiltration and M1 polarization, selective insulin sensitivity in adipose tissue, and amelioration of spontaneous atherosclerosis. Both in vivo and ex vivo studies suggest that MyD88-dependent GM-CSF production from the endothelial cells might play a critical role in the initiation of obesity-associated inflammation and development of atherosclerosis by priming the monocytes in the adipose and arterial tissues to differentiate into M1-like inflammatory macrophages. Collectively, these results implicate a critical MyD88-dependent interplay between myeloid and endothelial cells in the initiation and progression of obesity-associated inflammatory diseases.

Lipids and the endothelium: bidirectional interactions

The endothelium is often viewed solely as the barrier that prevents the penetration of circulating lipoproteins into the arterial wall. However, recent research has demonstrated that the endothelium has an important part in regulating circulating fatty acids and lipoproteins, and is in turn affected by these lipids/lipoproteins in ways that appear to have important repercussions for atherosclerosis. Thus, a number of potentially toxic lipids are produced during lipolysis of lipoproteins at the endothelial cell surface. Catabolism of triglyceride-rich lipoproteins creates free fatty acids that are readily taken up by endothelial cells, and, likely through the action of acyl-CoA synthetases, exacerbate inflammatory processes. In this article, we review how the endothelium participates in lipoprotein metabolism, how lipids alter endothelial functions, and how lipids are internalized, processed, and transported into the subendothelial space. Finally, we address the many endothelial changes that might promote atherogenesis, especially in the setting of diabetes.

Involvement of fibrinolytic regulators in adhesion of monocytes to vascular endothelial cells induced by glycated LDL and to aorta from diabetic mice

Diabetes mellitus accelerates the development of atherosclerotic cardiovascular diseases. Monocyte adhesion is an early cellular event of atherogenesis. Elevated levels of glyLDL were common in diabetic patients. Our previous studies indicated that HSF1 and p22-phox (a subunit of the NOX complex) were involved in glyLDL-induced up-regulation of PAI-1 in vascular EC. The present study demonstrated that glyLDL significantly increased the adhesion of monocytes to the surface of cultured human umbilical vein or PAEC. Transfection of siRNA for PAI-1, p22-phox, or HSF1 in EC prevented glyLDL-induced monocyte adhesion to EC. uPA siRNA increased monocyte adhesion to EC. Exogenous uPA reduced monocyte adhesion induced by glyLDL or uPA siRNA. Exogenous PAI-1 restored monocyte adhesion to EC inhibited by PAI-1 siRNA or uPA. GlyLDL-induced monocyte adhesion to EC was inhibited by treatment of EC with RAP, an antagonist for LRP, and enhanced by uPAR antibody. The adhesion of monocytes to aorta from leptin db/db diabetic mice was significantly greater than to that from control mice, which was associated with elevated contents of PAI-1, uPA, p22-phox, and HSF1 in hearts of db/db mice. The results suggest that oxidative stress and fibrinolytic regulators (PAI-1, uPA, and uPAR) are implicated in the modulation of glyLDL-induced monocyte adhesion to vascular endothelium, which may play a crucial role in vascular inflammation under diabetes-associated metabolic disorder.

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.

The transcription factor CREB enhances interleukin-17A production and inflammation in a mouse model of atherosclerosis

The enzyme 15-lipoxygenase (15-LO) plays a role in atherogenesis (also known as atherosclerosis), but the underlying mechanisms are unclear. We found that 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], the major 15-LO-dependent metabolite of arachidonic acid, stimulated the production of reactive oxygen species (ROS) by monocytes through the xanthine oxidase-mediated activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. ROS production led to the Syk-, Pyk2-, and mitogen-activated protein kinase (MAPK)-dependent production of the proinflammatory cytokine interleukin-17A (IL-17A) in a manner that required the transcription factor CREB (cyclic adenosine monophosphate response element-binding protein). In addition, this pathway was required for the 15(S)-HETE-dependent migration and adhesion of monocytes to endothelial cells. Consistent with these observations, we found that peritoneal macrophages from apolipoprotein E-deficient (ApoE-/-) mice fed a high-fat diet (a mouse model of atherosclerosis) exhibited increased xanthine oxidase and NADPH oxidase activities; ROS production; phosphorylation of Syk, Pyk2, MAPK, and CREB; and IL-17A production compared to those from similarly fed ApoE-/-:12/15-LO-/- mice. These events correlated with increased lipid deposits and numbers of monocytes and macrophages in the aortic arches of ApoE-/- mice, which resulted in atherosclerotic plaque formation. Together, these observations suggest that 15(S)-HETE exacerbates atherogenesis by enhancing CREB-dependent IL-17A production and inflammation.

12/15-lipoxygenase expressed in non-epithelial cells causes airway epithelial injury in asthma

The mechanisms underlying asthmatic airway epithelial injury are not clear. 12/15-lipoxygenase (an ortholog of human 15-LOX-1), which is induced by IL-13, is associated with mitochondrial degradation in reticulocytes at physiological conditions. In this study, we showed that 12/15-LOX expressed in nonepithelial cells caused epithelial injury in asthma pathogenesis. While 12/15-LOX overexpression or IL-13 administration to naïve mice showed airway epithelial injury, 12/15-LOX knockout/knockdown in allergic mice reduced airway epithelial injury. The constitutive expression of 15-LOX-1 in bronchial epithelia of normal human lungs further indicated that epithelial 15-LOX-1 may not cause epithelial injury. 12/15-LOX expression is increased in various inflammatory cells in allergic mice. Though non-epithelial cells such as macrophages or fibroblasts released 12/15-LOX metabolites upon IL-13 induction, bronchial epithelia didn't release. Further 12-S-HETE, arachidonic acid metabolite of 12/15-LOX leads to epithelial injury. These findings suggested 12/15-LOX expressed in non-epithelial cells such as macrophages and fibroblasts leads to bronchial epithelial injury.

12/15-Lipoxygenase mediates high-fat diet-induced endothelial tight junction disruption and monocyte transmigration: a new role for 15(S)-hydroxyeicosatetraenoic acid in endothelial cell dysfunction

A convincing body of evidence suggests that 12/15-lipoxygenase (12/15-LO) plays a role in atherosclerosis. However, the mechanisms of its involvement in the pathogenesis of this disease are not clear. Therefore, the purpose of this study is to understand the mechanisms by which 12/15-LO mediates endothelial dysfunction. 15(S)-Hydroxyeicosatetraenoic acid (15(S)-HETE), the major 12/15-LO metabolite of arachidonic acid (AA), induced endothelial barrier permeability via Src and Pyk2-dependent zonula occluden (ZO)-2 tyrosine phosphorylation and its dissociation from the tight junction complexes. 15(S)-HETE also stimulated macrophage adhesion to the endothelial monolayer in Src and Pyk2-dependent manner. Ex vivo studies revealed that exposure of arteries from WT mice to AA or 15(S)-HETE led to Src-Pyk2-dependent ZO-2 tyrosine phosphorylation, tight junction disruption, and macrophage adhesion, whereas the arteries from 12/15-LO knock-out mice are protected from these effects of AA. Feeding WT mice with a high-fat diet induced the expression of 12/15-LO in the arteries leading to tight junction disruption and macrophage adhesion and deletion of the 12/15-LO gene disallowed these effects. Thus, the findings of this study provide the first evidence of the role of 12/15-LO and its AA metabolite, 15(S)-HETE, in high-fat diet-induced endothelial tight junction disruption and macrophage adhesion, the crucial events underlying the pathogenesis of atherosclerosis.

Role of epigenetic mechanisms in the vascular complications of diabetes

Diabetes and metabolic disorders are leading causes of micro- and macrovascular complications. Furthermore, efforts to treat these complications are hampered by metabolic memory, a phenomenon in which prior exposure to hyperglycemia predisposes diabetic patients to the continued development of vascular diseases despite subsequent glycemic control. Persistently increased levels of oxidant stress and inflammatory genes are key features of these pathologies. Biochemical and molecular studies showed that hyperglycemia induced activation of NF-κB, signaling and actions of advanced glycation end products and other inflammatory mediators play key roles in the expression of pathological genes. In addition, epigenetic mechanisms such as posttranslational modification of histones and DNA methylation also play central roles in gene regulation by affecting chromatin structure and function. Recent studies have suggested that dysregulation of such epigenetic mechanisms may be involved in metabolic memory leading to persistent changes in the expression of genes associated with diabetic vascular complications. Further exploration of these mechanisms by also taking advantages of recent advances in high throughput epigenomics technologies will greatly increase our understanding of epigenetic variations in diabetes and its complications. This in turn can lead to the development of novel new therapies.

12/15-lipoxygenase during the regulation of inflammation, immunity, and self-tolerance

12/15-Lipoxygenase (12/15-LO) catalyzes the oxidation of free and esterified fatty acids thereby generating a whole spectrum of bioactive lipid mediators. This enzyme is involved in the regulation of various homeostatic processes as well as in the pathogenesis of multiple diseases. During the innate and adaptive immune response, 12/15-LO and its products exert both pro- and anti-inflammatory effects. Likewise, this enzyme has been implicated in the pathogenesis of autoimmune disease as well as in the maintenance of self-tolerance. This review will summarize our current knowledge about the role of 12/15-LO and will try to examine the two faces of this enzyme within the context of inflammation and immunity.

Eliminating or blocking 12/15-lipoxygenase reduces neutrophil recruitment in mouse models of acute lung injury

INTRODUCTION

Acute lung injury (ALI) is a common disease in critically ill patients with a high morbidity and mortality. 12/15-lipoxygenase (12/15-LO) is an enzyme generating 12-hydroxy-eicosatetraenoic acid (12-HETE) and 15-HETE from arachidonic acid. It has been shown that 12/15-LO is involved in the regulation of vascular permeability during ALI.

METHODS

To test whether 12/15-LO participates in leukocyte recruitment into the lung, we investigated the role of 12/15-LO in mouse models of lipopolysaccharide (LPS)-induced pulmonary inflammation and acid-induced ALI, a clinically relevant model of acute lung injury.

RESULTS

The increase in neutrophil recruitment following LPS inhalation was reduced in 12/15-LO-deficient (Alox15(-/-)) mice and in wild-type (WT) mice after the blocking of 12/15-LO with a pharmacological inhibitor. Bone marrow chimeras revealed that 12/15-LO in hematopoietic cells regulates neutrophil accumulation in the interstitial and alveolar compartments, whereas the accumulation of neutrophils in the intravascular compartment is regulated by 12/15-LO in non-hematopoietic and hematopoietic cells. Mechanistically, the increased plasma levels of the chemokine CXCL1 in Alox15(-/-) mice led to a reduced response of the neutrophil chemokine receptor CXCR2 to stimulation with CXCL1, which in turn abrogated neutrophil recruitment. Alox15(-/-) mice also showed decreased edema formation, reduced neutrophil recruitment and improved gas exchange in an acid-induced ALI model.

CONCLUSIONS

Our findings suggest that 12/15-LO modulates neutrophil recruitment into the lung by regulating chemokine/chemokine receptor homeostasis.

Reciprocal regulation of HIF-1α and 15-LO/15-HETE promotes anti-apoptosis process in pulmonary artery smooth muscle cells during hypoxia

15-Hydroxyeicosatetraenoic acid, a predominant metabolic product of arachidonic acid (AA) catalyzed by 15-lipoxygenase (15-LO), plays an important role in hypoxic pulmonary arterial hypertension (PAH). Hypoxia-inducible factor-1α (HIF-1α) as a critical oxygen-sensitive transcriptional factor participates in many physiological and pathological processes including PAH. Therefore, it is possible that there may be some connections between HIF-1α and 15-LO/15-HETE in hypoxic pulmonary artery smooth muscle cells. Our results showed that HIF-1α inhibitor or siRNA reduced hypoxia-induced upregulation of 15-LO and endogenous 15-HETE, meanwhile HIF-1α expression and transcriptional activity were induced by 15-HETE under both normoxic and hypoxic conditions. It suggests there exists a potential positive feedback regulatory loop between HIF-1α and 15-LO/15-HETE. Furthermore, cell viability assay and several cell apoptosis assays, including TUNEL assay, Western blot, nuclear morphology determination, mitochondrial potential analysis, indicated that blocking HIF-1α induced apoptosis, decreased cell viability and suppressed the anti-apoptosis effects of 15-HETE. Taken together, our data indicate that upregulation of 15-LO/15-HETE in response to hypoxia may be partially mediated by HIF-1α which is also regulated by 15-HETE in a positive feedback manner, and HIF-1α can effectively inhibit pulmonary artery smooth muscle cells apoptosis which leads to vascular remodeling. The feedback loop between HIF-1α and 15-LO/15-HETE would obviously reinforce hypoxia-induced anti-apoptosis effect and may become a novel target of therapy in PAH.

The dimeric platelet collagen receptor GPVI-Fc reduces platelet adhesion to activated endothelium and preserves myocardial function after transient ischemia in mice

Platelets play a critical role in the pathophysiology of reperfusion, sepsis, and cardiovascular diseases. In a multiple step process, they adhere to activated endothelium and release proinflammatory cytokines thereby promoting the inflammatory process. Glycoprotein VI (GPVI) is the major collagen receptor on the platelet surface and triggers platelet activation and primary hemostasis. Activation of GPVI leads to stable platelet adhesion and degranulation of platelet granules. However, GPVI is critically involved in platelet adhesion to activated endothelium without exposure of subendothelial matrix. Earlier studies show that the soluble GPVI-Fc binds to collagen and protects mice from atherosclerosis and decreases neointima proliferation after arterial injury. Here, we show for the first time that recombinant GPVI-Fc binds to activated endothelium mainly via vitronectin and prevents platelet/endothelial interaction. Administration of GPVI-Fc reduced infarct size and preserved cardiac function in a mouse model of myocardial infarction. This process was associated with reduced GPVI-induced platelet degranulation and release of proinflammatory cytokines in vitro and in vivo. Taken together, administration of GPVI-Fc offers a novel strategy to control platelet-mediated inflammation and to preserve myocardial function following myocardial infarction.

Inhibition of renin release by arachidonic acid metabolites, 12(s)-HPETE and 12-HETE: role of TRPV1 channels

We test the hypothesis that 12-hydroperoxyeicosatetraenoic acid (12(s)-HPETE) and 12-hydroxyeicosatetraenoic acid (12-HETE) perfused into the renal pelvis increase afferent renal nerve activity (ARNA) and suppress renin release in rats fed a low-salt (LS) diet via activation of the transient receptor potential vanilloid type 1 (TRPV1) expressed in renal sensory nerves. 12(s)-HPETE or 12-HETE given into the left renal pelvis dose-dependently increased ARNA, which was abolished by AMG9810, a selective TRPV1 antagonist, or by RP67580, a selective neurokinin 1 receptor antagonist, in normal salt or LS-treated rats. 12(s)-HPETE, 12-HETE, or substance P perfused into the left renal pelvis suppressed plasma angiotensin I (Ang I) levels in LS rats, which was abolished by AMG9810 or attenuated by ipsilateral renal denervation (RD). 12(s)-HPETE or 12-HETE increased release of substance P and calcitonin gene-related peptide from the ipsilateral kidney, which was abolished by AMG9810 but not RP67580, RD, or RP67580 plus RD. Immunofluorescence staining showed that TRPV1-positive nerve fibers located in the renal cortex, medulla, and pelvis, and that the sympathetic nerve marker, neuropeptide Y, but not neurokinin 1 receptors expressed in the juxtaglomerular region colocalized with renin. Thus, our data show that 12(s)-HPETE and 12-HETE enhance ARNA and substance P/calcitonin gene-related peptide release but suppress renin activity in LS rats, and these effects are abolished when TRPV1 is blocked. These results indicate that TRPV1 mediates 12(s)-HPETE and 12-HETE action in the kidney in such a way that dysfunction in TRPV1 may lead to disintegrated regulation of renin and renal function.

Effect of gestational hypercholesterolemia and maternal immunization on offspring plasma eicosanoids

OBJECTIVE

Maternal immunization with oxidized low-density lipoprotein prior to pregnancy prevents pathogenic in utero programming by gestational hypercholesterolemia, but it is unknown whether gestational hypercholesterolemia and maternal immunization affect similar pathways.

STUDY DESIGN

A lipidomic approach was used for unbiased plasma eicosanoid profiling in adult offspring of immunized and nonimmunized normocholesterolemic or hypercholesterolemic rabbit mothers.

RESULTS

Gestational hypercholesterolemia was associated with increased levels of some eicosanoids formed by the cyclooxygenase and 12-lipoxygenase pathways only (including thromboxane B2, prostaglandin [PG] F2α, PGE2, and PGD2). Immunization of hypercholesterolemic or normocholesterolemic mothers reduced 9 of 14 eicosanoids of the cyclooxygenase pathway, 21 of 23 eicosanoids of the 5- and 12-lipoxygenase pathways (eg, 5-hydroxyeicosatetraenoic acid, hepoxilin B3, 12-hydroxyeicosatetraenoic acid), 8 of 19 eicosanoids of the cytochrome P-450 pathway, and all metabolites of the nonenzymatic pathway.

CONCLUSION

Maternal immunization not only counteracts in utero programming by gestational hypercholesterolemia but reduces a broad range of eicosanoid modulators of immunity and inflammation in offspring.

Eicosanoids, β-cell function, and diabetes

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in diverse diseases, including type 1 and type 2 diabetes. During the last 30 years, evidence has been accumulated that suggests important functions for eicosanoids in the control of pancreatic β-cell function and destruction. AA metabolites of the COX pathway, especially prostaglandin E(2) (PGE(2)), appear to be significant factors to β-cell dysfunction and destruction, participating in the pathogenesis of diabetes and its complications. Several elegant studies have contributed to the sorting out of the importance of 12-LOX eicosanoids in cytokine-mediated inflammation in pancreatic β cells. The role of CYP eicosanoids in diabetes is yet to be explored. A recent publication has demonstrated that stabilizing the levels of epoxyeicosatrienoic acids (EETs), CYP eicosanoids, by inhibiting or deleting soluble epoxide hydrolase (sEH) improves β-cell function and reduces β-cell apoptosis in diabetes. In this review we summarize recent findings implicating these eicosanoid pathways in diabetes and its complications. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of diabetes and its complications.

Diet-induced adipose tissue inflammation and liver steatosis are prevented by DPP-4 inhibition in diabetic mice

OBJECTIVE

Diet composition alters the metabolic states of adipocytes and hepatocytes in diabetes. The effects of dipeptidyl peptidase-4 (DPP-4) inhibition on adipose tissue inflammation and fatty liver have been obscure. We investigated the extrapancreatic effects of DPP-4 inhibition on visceral fat and the liver.

RESEARCH DESIGN AND METHODS

We investigated diet-induced metabolic changes in β-cell-specific glucokinase haploinsufficient (Gck(+/-)) diabetic mice. We challenged animals with a diet containing a combination of sucrose and oleic acid (SO) or sucrose and linoleic acid (SL). Next, we assessed the effects of a DPP-4 inhibitor, des-fluoro-sitagliptin, on adipose tissue inflammation and hepatic steatosis.

RESULTS

The epididymal fat weight and serum leptin level were significantly higher in Gck(+/-) mice fed SL than in mice fed SO, although no significant differences in body weight or adipocyte size were noted. Compared with SO, SL increased the numbers of CD11c(+) M1 macrophages and CD8(+) T-cells in visceral adipose tissue and the expression of E-selectin, P-selectin, and plasminogen activator inhibitor-1 (PAI-1). DPP-4 inhibition significantly prevented adipose tissue infiltration by CD8(+) T-cells and M1 macrophages and decreased the expression of PAI-1. The production of cytokines by activated T-cells was not affected by DPP-4 inhibition. Furthermore, DPP-4 inhibition prevented fatty liver in both wild-type and Gck(+/-) mice. DPP-4 inhibition also decreased the expressions of sterol regulatory element-binding protein-1c, stearoyl-CoA desaturase-1, and fatty acid synthase, and increased the expression of peroxisome proliferator-activated receptor-α in the liver.

CONCLUSIONS

Our findings indicated that DPP-4 inhibition has extrapancreatic protective effects against diet-induced adipose tissue inflammation and hepatic steatosis.

Epigenetic mechanisms in diabetic vascular complications

There has been a rapid increase in the incidence of diabetes as well the associated vascular complications. Both genetic and environmental factors have been implicated in these pathologies. Increasing evidence suggests that epigenetic factors play a key role in the complex interplay between genes and the environment. Actions of major pathological mediators of diabetes and its complications such as hyperglycaemia, oxidant stress, and inflammatory factors can lead to dysregulated epigenetic mechanisms that affect chromatin structure and gene expression. Furthermore, persistence of this altered state of the epigenome may be the underlying mechanism contributing to a 'metabolic memory' that results in chronic inflammation and vascular dysfunction in diabetes even after achieving glycaemic control. Further examination of epigenetic mechanisms by also taking advantage of recently developed next-generation sequencing technologies can provide novel insights into the pathology of diabetes and its complications and lead to the discovery of much needed new drug targets for these diseases. In this review, we highlight the role of epigenetics in diabetes and its vascular complications, and recent technological advances that have significantly accelerated the field.

Modulating Notch signaling to enhance neovascularization and reperfusion in diabetic mice

Diabetes can diminish the responsiveness to angiogenic factors (e.g., VEGF) important for wound healing and the treatment of ischemic diseases, and this study investigated the hypothesis that this effect can be reversed by altering Notch signaling. Aortic endothelial cells (ECs) isolated from diabetic mice demonstrated reduced sprouting capability in vitro, but adding a Notch inhibitor (DAPT) led to cell-density and VEGF-dose dependent enhancement of proliferation, migration and sprouting, in both 2-D and 3-D cultures, as compared to VEGF alone. The in vivo effects of VEGF and DAPT were tested in the ischemic hind limbs of diabetic mice. Combining VEGF and DAPT delivery resulted in increased blood vessel density (∼150%) and improved tissue perfusion (∼160%), as compared to VEGF alone. To examine if DAPT would interfere with vessel maturation, DAPT was also delivered with a combination of VEGF and platelet derived growth factor (PDGF). DAPT and PDGF did not interfere with the effects of the other, and highly functional and mature networks of vessels could be formed with appropriate delivery. In summary, modulating Notch signaling enhances neovascularization and perfusion recovery in diabetic mice suffering from ischemia, suggesting this approach could have utility for human diabetics.

Human lipoxygenase pathway gene variation and association with markers of subclinical atherosclerosis in the diabetes heart study

Aims. Genes of the 5-lipoxygenase pathway are compelling candidates for atherosclerosis. We hypothesize that polymorphisms in ALOX12, ALOX15, ALOX5, and ALOX5AP genes are associated with subclinical atherosclerosis in multiple vascular beds. Methods. Families with two or more siblings with type 2 diabetes and their nondiabetic siblings were studied as part of the Diabetes Heart Study (DHS). European American diabetic (n = 828) and nondiabetic (n = 170) siblings were genotyped for SNPs in the ALOX12, ALOX15, ALOX5, and ALOX5AP genes. Subclinical measures of atherosclerosis (IMT, coronary (CorCP), carotid (CarCP) and aortic (AorCP) calcified plaque) were obtained. Results. Associations were observed between ALOX12 with CorCP, ALOX5 with CorCP, AorCP, and IMT, and ALOX5AP with CorCP and CarCP, independent of known epidemiologic risk factors. Further, lipoxygenase pathway SNPs that were associated with measures of atherosclerosis were associated with markers of inflammation (CRP, ICAM-1) and calcification (MGP). Conclusions. Polymorphisms within ALOX12, ALOX5, and ALOX5AP are genetically associated with subclinical atherosclerosis and with biomarkers of disease in families with type 2 diabetes. These results suggest that variants in lipoxygenase pathway genes may have pleiotropic effects on multiple components that determine risk of cardiovascular disease.

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 is required for the early onset of high fat diet-induced adipose tissue inflammation and insulin resistance in mice

BACKGROUND

Recent understanding that insulin resistance is an inflammatory condition necessitates searching for genes that regulate inflammation in insulin sensitive tissues. 12/15-lipoxygenase (12/15LO) regulates the expression of proinflammatory cytokines and chemokines and is implicated in the early development of diet-induced atherosclerosis. Thus, we tested the hypothesis that 12/15LO is involved in the onset of high fat diet (HFD)-induced insulin resistance.

METHODOLOGY/PRINCIPAL FINDINGS

Cells over-expressing 12/15LO secreted two potent chemokines, MCP-1 and osteopontin, implicated in the development of insulin resistance. We assessed adipose tissue inflammation and whole body insulin resistance in wild type (WT) and 12/15LO knockout (KO) mice after 2-4 weeks on HFD. In adipose tissue from WT mice, HFD resulted in recruitment of CD11b(+), F4/80(+) macrophages and elevated protein levels of the inflammatory markers IL-1beta, IL-6, IL-10, IL-12, IFNgamma, Cxcl1 and TNFalpha. Remarkably, adipose tissue from HFD-fed 12/15LO KO mice was not infiltrated by macrophages and did not display any increase in the inflammatory markers compared to adipose tissue from normal chow-fed mice. WT mice developed severe whole body (hepatic and skeletal muscle) insulin resistance after HFD, as measured by hyperinsulinemic euglycemic clamp. In contrast, 12/15LO KO mice exhibited no HFD-induced change in insulin-stimulated glucose disposal rate or hepatic glucose output during clamp studies. Insulin-stimulated Akt phosphorylation in muscle tissue from HFD-fed mice was significantly greater in 12/15LO KO mice than in WT mice.

CONCLUSIONS

These results demonstrate that 12/15LO mediates early stages of adipose tissue inflammation and whole body insulin resistance induced by high fat feeding.

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.

12/15-lipoxygenase counteracts inflammation and tissue damage in arthritis

Eicosanoids are essential mediators of the inflammatory response and contribute both to the initiation and the resolution of inflammation. Leukocyte-type 12/15-lipoxygenase (12/15-LO) represents a major enzyme involved in the generation of a subclass of eicosanoids, including the anti-inflammatory lipoxin A(4) (LXA(4)). Nevertheless, the impact of 12/15-LO on chronic inflammatory diseases such as arthritis has remained elusive. By using two experimental models of arthritis, the K/BxN serum-transfer and a TNF transgenic mouse model, we show that deletion of 12/15-LO leads to uncontrolled inflammation and tissue damage. Consistent with these findings, 12/15-LO-deficient mice showed enhanced inflammatory gene expression and decreased levels of LXA(4) within their inflamed synovia. In isolated macrophages, the addition of 12/15-LO-derived eicosanoids blocked both phosphorylation of p38MAPK and expression of a subset of proinflammatory genes. Conversely, 12/15-LO-deficient macrophages displayed significantly reduced levels of LXA(4), which correlated with increased activation of p38MAPK and an enhanced inflammatory gene expression after stimulation with TNF-alpha. Taken together, these results support an anti-inflammatory and tissue-protective role of 12/15-LO and its products during chronic inflammatory disorders such as arthritis.

Effects of vitamin E on mitochondrial dysfunction and asthma features in an experimental allergic murine model

We showed recently that IL-4 causes mitochondrial dysfunction in allergic asthma. IL-4 is also known to induce 12/15-lipoxygenase (12/15-LOX), a potent candidate molecule in asthma. Because vitamin E (Vit-E) reduces IL-4 and inhibits 12/15-LOX in vitro, here we tested the hypothesis that Vit-E may be effective in restoring key mitochondrial dysfunctions, thus alleviating asthma features in an experimental allergic murine model. Ovalbumin (OVA)-sensitized and challenged male BALB/c mice showed the characteristic features of asthma such as airway hyperresponsiveness (AHR), airway inflammation, and airway remodeling. In addition, these mice showed increase in the expression and metabolites of 12/15-LOX, reduction in the activity and expression of the third subunit of mitochondrial cytochrome-c oxidase, and increased cytochrome c in lung cytosol, which indicate that OVA sensitization and challenge causes mitochondrial dysfunction. Vit-E was administered orally to these mice, and 12/15-LOX expression, key mitochondrial functions, ultrastructural changes of mitochondria in bronchial epithelia, and asthmatic parameters were determined. Vit-E treatment reduced AHR, Th2 response including IL-4, IL-5, IL-13, and OVA-specific IgE, eotaxin, transforming growth factor-beta1, airway inflammation, expression and metabolites of 12/15-LOX in lung cytosol, lipid peroxidation, and nitric oxide metabolites in the lung, restored the activity and expression of the third subunit of cytochrome-c oxidase in lung mitochondria and bronchial epithelia, respectively, reduced the appearance of cytochrome c in lung cytosol, and also restored mitochondrial ultrastructural changes of bronchial epithelia. In summary, these findings show that Vit-E reduces key mitochondrial dysfunctions and alleviates asthmatic features.

Cardiac 12/15 lipoxygenase-induced inflammation is involved in heart failure

To identify a novel target for the treatment of heart failure, we examined gene expression in the failing heart. Among the genes analyzed, Alox15 encoding the protein 12/15 lipoxygenase (LOX) was markedly up-regulated in heart failure. To determine whether increased expression of 12/15-LOX causes heart failure, we established transgenic mice that overexpressed 12/15-LOX in cardiomyocytes. Echocardiography showed that Alox15 transgenic mice developed systolic dysfunction. Cardiac fibrosis increased in Alox15 transgenic mice with advancing age and was associated with the infiltration of macrophages. Consistent with these observations, cardiac expression of monocyte chemoattractant protein 1 (MCP-1) was up-regulated in Alox15 transgenic mice compared with wild-type mice. Treatment with 12-hydroxy-eicosatetraenoic acid, a major metabolite of 12/15-LOX, increased MCP-1 expression in cardiac fibroblasts and endothelial cells but not in cardiomyocytes. Inhibition of MCP-1 reduced the infiltration of macrophages into the myocardium and prevented both systolic dysfunction and cardiac fibrosis in Alox15 transgenic mice. Likewise, disruption of 12/15-LOX significantly reduced cardiac MCP-1 expression and macrophage infiltration, thereby improving systolic dysfunction induced by chronic pressure overload. Our results suggest that cardiac 12/15-LOX is involved in the development of heart failure and that inhibition of 12/15-LOX could be a novel treatment for this condition.

Rapid sample preparation and simultaneous quantitation of prostaglandins and lipoxygenase derived fatty acid metabolites by liquid chromatography-mass spectrometry from small sample volumes

BACKGROUND

Fatty acid metabolites play a key role in numerous physiological and pathological processes. A rapid liquid chromatography-mass spectrometry assay for the simultaneous determination of prostanoids, isoprostane and lipoxygenase (LOX) derived fatty acid metabolites in a small biological sample of only 20 microL was developed.

METHODS

Human plasma samples were applied to a filter spot, extracted without prior derivatization and analyzed within 13 min. Detection of metabolites was performed on a triple quadrupole mass spectrometer in negative multiple-reaction monitoring detection mode. Application of this assay to various biological matrices was performed.

RESULTS

The validated assay was linear over the concentration range of 5-500 nmol/L for prostanoids and isoprostane, 50-5000 nmol/L for LOX-derived metabolites and 400-40,000 nmol/L for fatty acids. Limits of quantitation were 0.4-233 nmol/L, depending on the metabolite. Plasma samples from diabetic patients and controls showed significant increases in (+/-)9-HODE and 15(S)-HETE with p-values of 0.019 and 0.024, respectively.

CONCLUSIONS

The small amount of 20 microL sample volume used in this assay and the demonstrated application to various sample types makes it an ideal routine analysis method for fatty acid metabolites. The resulting values for LOX-derived metabolites in diabetes mellitus type 2 samples support earlier findings about the role of lipid oxidation products in diabetes.

Inhibitory activity of salicylic acid on lipoxygenase-dependent lipid peroxidation

BACKGROUND

Since iron is essential for lipoxygenase activity and salicylic acid (SA) can interact with the metal, possible lipoxygenase inhibition by SA was investigated.

METHODS

Kinetic spectrophotometric evaluation of enzymatic lipid peroxidation catalyzed by soybean lipoxygenase (SLO), rabbit reticulocyte 15-lipoxygenase (RR15-LOX), porcine leukocyte 12-lipoxygenase (PL12-LOX) and human recombinant 5-lipoxygenase (HR5-LOX) with and without SA.

RESULTS

SA inhibited linoleic, arachidonic and docosahexaenoic acid or human lipoprotein peroxidation catalyzed by SLO with IC50 of, respectively, 107, 153, 47 and 108 microM. Using the same substrates, SA inhibited RR15-LOX with IC50 of, respectively, 49, 63, 27 and 51 microM. Further, arachidonic acid peroxidation catalyzed by PL12-LOX and HR5-LOX was inhibited by SA with IC50 of 101 and 168 microM, respectively. Enzymatic inhibition was complete, reversible and non-competitive. Conceivably due to its lower hydrophobicity, aspirin was less effective, indicating acetylation-independent enzyme inhibition. SA and aspirin were ineffective peroxyl radical scavengers but readily reduced Fe3+, i.e. FeCl3, to Fe2+, suggesting their capacity to reduce Fe3+ at the enzyme active site. Indeed, similar to the catecholic redox inhibitor nordihydroguaiaretic acid, SA inhibited with the same efficiency both ferric and the native ferrous SLO form, indicating that these compounds reduce the active ferric enzyme leading to its inactivation.

GENERAL SIGNIFICANCE

SA can inhibit lipoxygenase-catalyzed lipid peroxidation at therapeutic concentrations, suggesting its possible inhibitory activity against enzymatic lipid peroxidation in the clinical setting.