Angiotensin II type 1 receptor expression is increased via 12-lipoxygenase in high glucose-stimulated glomerular cells and type 2 diabetic glomeruli

Elevated ALOX12 in renal tissue predicts progression in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the major causes of end-stage renal disease and one of the significant complications of diabetes. This study aims to identify the main differentially expressed genes in DKD from transcriptome sequencing results and analyze their diagnostic value. The present study sequenced db/m mouse and db/db mouse to determine the ALOX12 genetic changes related to DKD. After preliminary validation, ALOX12 levels were significantly elevated in the blood of DKD patients, but not during disease progression. Moreover, urine ALOX12 was increased only in macroalbuminuria patients. Therefore, to visualize the diagnostic efficacy of ALOX12 on the onset and progression of renal injury in DKD, we collected kidney tissue from patients for immunohistochemical staining. ALOX12 was increased in the kidneys of patients with DKD and was more elevated in macroalbuminuria patients. Clinical chemical and pathological data analysis indicated a correlation between ALOX12 protein expression and renal tubule injury. Further immunofluorescence double staining showed that ALOX12 was expressed in both proximal tubules and distal tubules. Finally, the diagnostic value of the identified gene in the progression of DKD was assessed using receiver operating characteristic (ROC) curve analysis. The area under the curve (AUC) value for ALOX12 in the diagnosis of DKD entering the macroalbuminuria stage was 0.736, suggesting that ALOX12 has good diagnostic efficacy. During the development of DKD, the expression levels of ALOX12 in renal tubules were significantly increased and can be used as one of the predictors of the progression to macroalbuminuria in patients with DKD.

Sex Difference in MasR Expression and Functions in the Renal System

Renin-angiotensin system (RAS), as a critical system for controlling body fluid and hemostasis, contains peptides and receptors, including angiotensin 1-7 (Ang 1-7) and Mas receptor (MasR). Ang 1-7 implements its function via MasR. Ang II is another peptide in RAS that performs its actions via two Ang II type 1 and 2 receptors (AT1R and AT2R). The functions of AT2R and MasR are very similar, and both have a vasodilation effect, while AT1R has a vasoconstriction role. MasR affects many mechanisms in the brain, heart, blood vessels, kidney, lung, endocrine, reproductive, skeletal muscle, and liver and probably acts like a paracrine hormone in these organs. The effect of Ang 1-7 in the kidney is complex according to the hydroelectrolyte status, the renal sympathetic nervous system, and the activity level of the RAS. The MasR expression and function seem more complex than Ang II receptors and have interacted with Ang II receptors and many other factors, including sex hormones. Also, pathological conditions including hypertension, diabetes, and ischemia-reperfusion could change MasR expression and function. In this review, we consider the role of sex differences in MasR expression and functions in the renal system under physiological and pathological conditions.

Angiotensin II type 1 receptor blockers favorably affect renal angiotensin II and MAS receptor expression in patients with diabetic nephropathy

Introduction:

The aims of this study were to assess the renal expression of angiotensin II type 1 receptor (AT1R), angiotensin II type 2 receptor (AT2R), and MAS receptor in human type 2 diabetic nephropathy (DN).

Materials and methods:

In total, 115 patients diagnosed with DN by renal biopsy were enrolled in this study. The protein expression levels of the AT1R, AT2R, and MAS receptors were assessed by immunohistochemistry.

Results:

The protein expression levels of AT1R, AT2R, and MAS receptor in the renal biopsy tissue were correlated with the pathologic classification of DN. Tubulointerstitial AT1R expression in patients of class IIb was significantly stronger than control samples (p < 0.05). Expression of AT2R and MAS receptors were highest with class IIb DN patients. When DN patients were treated with AT1R blocker (ARB), the expression of AT1R was downregulated (p < 0.05), and the MAS receptor was upregulated in tubular interstitial (p < 0.05).

Conclusions:

Our results directly observed that renal expression levels of AT1R increase during the early stages of DN, ARB reducing AT1R while increasing MAS receptor. Therefore, ARB should be used as soon as possible in patients with DN.

The Treatment Effectiveness Evaluation for Slowing the Progression of Diabetic Nephropathy During Stage 4 Chronic Kidney Disease

INTRODUCTION

People with advanced diabetic nephropathy (DN) are at high risk for development of end-stage renal disease (ESRD) or death. Whether renin-angiotensin system inhibitors and some concomitant drugs could still continue to delay the onset of ESRD in the later stage of DN needs to be clarified. This study aimed to evaluate the relationship of the therapeutic methods as well as clinicopathologic variables with prognosis of patients with biopsy-proven DN during stage 4 of chronic kidney disease (CKD).

METHODS

Forty-six DN patients who underwent renal biopsy in stage 4 CKD were enrolled from January 1, 2002, to December 31, 2019. Clinical data were abstracted retrospectively from the time of renal biopsy. Follow-up data were collected until April 1, 2020, or from the day of renal biopsy to either the occurrence of ESRD or death. The primary outcome was the composite of ESRD or death. Treatment effectiveness and the prognostic ability of clinicopathologic data were evaluated using multivariate Cox regression analyses.

RESULTS

The median renal survival duration was 17.3 (95% confidence interval, 7.4-27.3 months). Primary endpoint events occurred in 29 individuals (63.0%) during follow-up, including 24 who reached ESRD and 5 who died before progression to ESRD. None of the clinicopathologic data, including pathologic cass of DN, were statistically independent prognostic factors for renal survival. Conventional therapies, such as use of renin-angiotensin system (RAS) inhibitors, a level of glycated hemoglobin (HbA1c) < 7%, and blood pressure < 130/80 mmHg, were also not statistically different between the stable and progressive groups.

CONCLUSION

Specific therapies including targeting blood pressure < 130/80 mmHg, HbA1c concentration < 7%, and use of RAS inhibitors could not effectively delay the onset of ESRD in the later stage of DN. Therefore, efforts to slow the progression of DN should focus on early diagnosis and treatment.

Inhibition of STAT3 in tubular epithelial cells prevents kidney fibrosis and nephropathy in STZ-induced diabetic mice

Recent evidences indicate that signal transducer and activator of transcription 3 (STAT3) is one of the crucial signaling pathways in the progression of diabetic nephropathy (DN). Here, we investigated the hypothesis that pharmacological blockade of STAT3 limits the progression of DN. Treatment with selective STAT3 inhibitor, S3I-201 for 16 weeks significantly attenuated kidney injuries in streptozotocin (STZ) induced diabetic mice, associated with downregulated expression of TGF-β1, ACE/AT1, and VEGF in diabetic mouse kidneys. Similar results were confirmed using genetic knockdown of STAT3 in mouse kidneys by injections of AAV2 expressing STAT3 shRNA in diabetic mouse. Further, STAT3 localization in kidney tissue was evaluated using immunofluorescent double-staining analysis, which indicated that STAT3 expression was mainly in the tubular epithelial cells. As expected, in renal tubular epithelial NRK-52E cells, high glucose (HG)-induced overexpression of TGF-β1, ACE/AT1, and VEGF were abrogated by S3I-201 pretreatment, as well as by genetic knockdown of STAT3 using specific siRNA sequence. This study found that renal tubular epithelial cells contributed to STAT3-mediated progression of DN and provided the first evidence that pharmacological inhibition of STAT3 attenuates DN.

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.

Role of the 12-lipoxygenase pathway in diabetes pathogenesis and complications

12-lipoxygenase (12-LOX) is one of several enzyme isoforms responsible for the metabolism of arachidonic acid and other poly-unsaturated fatty acids to both pro- and anti-inflammatory lipid mediators. Mounting evidence has shown that 12-LOX plays a critical role in the modulation of inflammation at multiple checkpoints during diabetes development. Due to this, interventions to limit pro-inflammatory 12-LOX metabolites either by isoform-specific 12-LOX inhibition, or by providing specific fatty acid substrates via dietary intervention, has the potential to significantly and positively impact health outcomes of patients living with both type 1 and type 2 diabetes. To date, the development of truly specific and efficacious inhibitors has been hampered by homology of LOX family members; however, improvements in high throughput screening have improved the inhibitor landscape. Here, we describe the function and role of human 12-LOX, and mouse 12-LOX and 12/15-LOX, in the development of diabetes and diabetes-related complications, and describe promise in the development of strategies to limit pro-inflammatory metabolites, primarily via new small molecule 12-LOX inhibitors.

Low-protein diet supplemented with ketoacids ameliorates proteinuria in 3/4 nephrectomised rats by directly inhibiting the intrarenal renin-angiotensin system

Low-protein diet plus ketoacids (LPD+KA) has been reported to decrease proteinuria in patients with chronic kidney diseases (CKD). However, the mechanisms have not been clarified. As over-activation of intrarenal renin-angiotensin system (RAS) has been shown to play a key role in the progression of CKD, the current study was performed to investigate the direct effects of LPD+KA on intrarenal RAS, independently of renal haemodynamics. In this study, 3/4 subtotal renal ablated rats were fed 18 % normal-protein diet (Nx-NPD), 6 % low-protein diet (Nx-LPD) or 5 % low-protein diet plus 1 % ketoacids (Nx-LPD+KA) for 12 weeks. Sham-operated rats fed NPD served as controls. The level of proteinuria and expression of renin, angiotensin II (AngII) and its type 1 receptors (AT1R) in the renal cortex were markedly higher in Nx-NPD group than in the sham group. LPD+KA significantly decreased the proteinuria and inhibited intrarenal RAS activation. To exclude renal haemodynamic impact on intrarenal RAS, the serum samples derived from the different groups were added to the culture medium of mesangial cells. It showed that the serum from Nx-NPD directly induced higher expression of AngII, AT1R, fibronectin and transforming growth factor-β1 in the mesangial cells than in the control group. Nx-LPD+KA serum significantly inhibited these abnormalities. Then, proteomics and biochemical detection suggested that the mechanisms underlying these beneficial effects of LPD+KA might be amelioration of the nutritional metabolic disorders and oxidative stress. In conclusion, LPD+KA could directly inhibit the intrarenal RAS activation, independently of renal haemodynamics, thus attenuating the proteinuria in CKD rats.

12-Lipoxygenase Inhibition on Microalbuminuria in Type-1 and Type-2 Diabetes Is Associated with Changes of Glomerular Angiotensin II Type 1 Receptor Related to Insulin Resistance

(1) BACKGROUND: 12-lipoxygenase (12-LO) is involved in the development of diabetic nephropathy (DN). In the present study, we investigated whether 12-LO inhibition may ameliorate type-2 DN (T2DN) by interfering with insulin resistance (IR); (2) METHODS: Rat glomerular mesangial cells, glomeruli and skeletal muscles were isolated and used in this study. Kidney histological changes were confirmed by periodic-acid Schiff staining; mRNA expression was detected by competitive reverse transcription polymerase chain reaction; and the protein level was determined by Western blot and the enzyme-linked immunosorbent assay, respectively; (3) RESULTS: The inhibition of 12-LO attenuated microalbuminuria (MAU) increases in type-2 diabetic rats, but not in type-1 diabetic rats. Infusion of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) significantly increased the expression of angiotensin II (Ang II) and Ang II type 1 receptor (AT1R), but decreased the expression of AT1R-associated protein (ATRAP) in rat glomeruli, compared to the control. An in vitro study revealed that both 12(S)-HETE and insulin upregulated AT1R expression in rat mesangial cells. In the presence of p38 mitogen-activated protein kinase (MAPK) inhibitor, SB202190, the 12(S)-HETE-induced ATRAP reduction was significantly abolished. Interestingly, 12-LO inhibition did not influence AT1R expression in type-1 diabetic rats, but significantly abolished the increased AT1R and Ang II expression in glomeruli of type-2 diabetic rats. Furthermore, the inhibition of 12-LO significantly corrected impaired insulin sensitivity and fast serum insulin level, as well as the p-AMP-activated protein kinase (AMPK) reduction in skeletal muscle of type-2 diabetic rats; (4) CONCLUSION: The inhibition of 12-LO potentially ameliorated MAU by preventing IR through the downregulation of glomerular AT1R expression in T2DN.

Effect of angiotensin II type 1 receptor blocker on 12-lipoxygenase activity and slit diaphragm protein expression in type 2 diabetic rat glomeruli

BACKGROUND

The 12-lipoxygenase (12-LO) and angiotensin II (Ang II) interaction plays an important role in diabetic nephropathy (DN). Proteinuria in DN is associated with decreased slit diaphragm proteins including nephrin and P-cadherin. Therefore, we investigated whether Ang II type 1 receptor (AT1) blocker (ARB) regulates 12-LO activity and slit diaphragm protein expression in diabetic rat glomeruli.

METHOD

Glomeruli were isolated with the sieving method, and classified into small glomeruli (SG; 75-μm sieve) and large glomeruli (LG; 125-μm sieve).

RESULTS

12(S)-HETE, a lipid product of 12-LO, was increased by Ang II in the glomeruli. Infusion of 12(S)-HETE and Ang II significantly decreased nephrin expression in LG, but increased it in SG compared to control. Glomerular P-cadherin expression was reduced after Ang II and 12(S)-HETE treatment without differences between LG and SG. ARB did not influence glycemic levels but completely abolished the increases in 12(S)-HETE, AT1 expression, and proteinuria in diabetic rats. Nephrin expression was significantly reduced in LG but increased in SG in diabetic rats compared to control. P-cadherin expression decreased in both diabetic LG and SG. The abnormalities of nephrin and P-cadherin were partially but significantly reversed by ARB.

CONCLUSION

ARB potentially ameliorates DN via the up-regulation of glomerular nephrin and P-cadherin expression through the inhibition of 12-LO activation in the glomeruli of rats with DN.

Epigenetic Histone Modifications Involved in Profibrotic Gene Regulation by 12/15-Lipoxygenase and Its Oxidized Lipid Products in Diabetic Nephropathy

AIMS

Epigenetic mechanisms, including histone post-translational modifications and DNA methylation, are implicated in the pathogenesis of diabetic nephropathy (DN), but the mediators are not well known. Moreover, although dyslipidemia contributes to DN, epigenetic changes triggered by lipids are unclear. In diabetes, increased expression of 12/15-lipoxygenase (12/15-LO) enhances oxidized lipids such as 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], which promote oxidant stress, glomerular and mesangial cell (MC) dysfunction, and fibrosis, and mediate the actions of profibrotic growth factors. We hypothesized that 12/15-LO and its oxidized lipid products can regulate epigenetic mechanisms mediating profibrotic gene expression related to DN.

RESULTS

12(S)-HETE increased profibrotic gene expression and enrichment of permissive histone lysine modifications at their promoters in MCs. 12(S)-HETE also increased protein levels of SET7, a histone H3 lysine 4 methyltransferase, and promoted its nuclear translocation and enrichment at profibrotic gene promoters. Furthermore, SET7 (Setd7) gene silencing inhibited 12(S)-HETE-induced profibrotic gene expression. 12/15-LO (Alox15) gene silencing or genetic knockout inhibited transforming growth factor-β1 (TGF-β1)-induced expression of Setd7 and profibrotic genes and histone modifications in MCs. Furthermore, 12/15-LO knockout in mice ameliorated key features of DN and abrogated increases in renal SET7 and profibrotic genes. Additionally, 12/15-LO siRNAs in vivo blocked increases in renal SET7 and profibrotic genes in diabetic mice.

INNOVATION AND CONCLUSION

These novel results demonstrate for the first time that 12/15-LO-derived oxidized lipids regulate histone modifications associated with profibrotic gene expression in MCs, and 12/15-LO can mediate similar actions of TGF-β1 and diabetes. Targeting 12/15-LO might be a useful strategy to inhibit key epigenetic mechanisms involved in DN.

p16ink4a Expression Is Increased through 12-Lipoxygenase in High Glucose-Stimulated Glomerular Mesangial Cells and Type 2 Diabetic Glomeruli

BACKGROUND/AIMS

Arachidonic acid-metabolizing enzyme, 12-lipoxygenase (12-LO), is involved in the glomerular hypertrophy of diabetic nephropathy (DN), in which cyclin-dependent kinase inhibitors (CKIs) play important roles. However, it is unclear whether 12-LO regulates the expression of the CKI p16(ink4a) in DN.

METHODS

Primary glomerular mesangial cells (MCs) and glomeruli isolated from rats were used in this study. The rats were fed a high-fat diet and given low-dose streptozotocin to induce type 2 diabetes. The 12-LO product, 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), was infused through an osmotic minipump. Enzyme-linked immunosorbent assay, Western blot, and morphometric analyses were performed.

RESULTS

High glucose (HG) increased the p16(ink4a) protein expression in MCs, but this increase was prevented by the 12-LO inhibitor, cinnamyl-3,​4-dihydroxy-α-cynanocinnamate (CDC). The levels of p-p38MAPK and p16(ink4a) in MCs were significantly elevated after the 12(S)-HETE treatment, whereas the p38MAPK inhibitor SB203580 prevented these increases. Compared with levels in control MCs, marked increases in p38MAPK activation and p16(ink4a) expression were observed in MCs plated on collagen IV, while the CDC treatment prevented these changes. Subcutaneous injection of CDC did not affect glucose levels, but completely attenuated the diabetes-related increases in the 12(S)-HETE content, p16(ink4a) expression, p-p38MAPK levels, glomerular volume, and the kidney/body weight ratio. Compared with levels in controls, p16(ink4a) and p-p38MAPK in the glomeruli derived from 12(S)-HETE-treated rats were significantly higher.

CONCLUSIONS

12-LO-p38MAPK mediates the upregulation of p16(ink4a) in HG-stimulated MCs and type 2-diabetic glomeruli, and new therapies aimed at 12-LO inhibition may prove beneficial in ameliorating diabetes-induced glomerular hypertrophy.

Progesterone ameliorates diabetic nephropathy in streptozotocin-induced diabetic Rats

BACKGROUND

Previous studies reported that 17β-estradiol may influence the progression of diabetic renal disease in females. The present study was intended to provide an insight into the specific effects of progesterone, the other female sex hormone, in the diabetic renal complications.

METHODS

Adult female wistar rats were divided into four groups (n = 6/group): intact control (non-diabetic, ND), intact diabetic (D), ovariectomized diabetic (D-OVX) and ovariectomized diabetic which were treated with progesterone (D-OVX + P; 10 mg/kg, s.c, every second day) for 10 weeks. Diabetes was induced by a single dose injection of 55 mg/kg streptozotocin. Expressions of transforming growth factor-β (TGF-β), fibronectin, vascular endothelial growth factor-A (VEGF-A), angiotensin II type 1 receptor (ATR1) and podocyte markers (nephrin and podocin) were assessed by immunohistochemistry and real-time PCR.

RESULTS

The treatment of D-OVX rats with progesterone attenuated diabetic-associated increases in the urinary albumin to creatinine ratio, glomerulosclerosi and the expression of profibrotic and angiogenic factors (TGF-β, Fibronectin and VEGF-A). Furthermore, progesterone supplementation prevented diabetes-induced downregulation of nephrin and podocin while the overexpression of ATR1 in the diabetic rats was inhibited by the progesterone supplementation.

CONCLUSION

These results provided evidence, for the first time, that the replacement of progesterone can ameliorate the renal damage in the experimental models of diabetic nephropathy through improving the renal function; the inhibition of renal fibrosis and abnormal angiogenesis; along with the amelioration of podocyte injury. Additionally, the blocking of renin-angiotensin system through the down-regulation of ATR1 expression may also account for the reno-protective effect of progesterone.

3,4-DGE is cytotoxic and decreases HSP27/HSPB1 in podocytes

Hyperglycemia is the key driver of diabetic complications and increased concentrations of glucose degradation products. The study of peritoneal dialysis solution biocompatibility has highlighted the adverse biological effects of glucose degradation products. Recently, 3,4-dideoxyglucosone-3-ene (3,4-DGE) was identified as the most toxic glucose degradation product in peritoneal dialysis fluids. In addition, 3,4-DGE is present in high-fructose corn syrup, and its precursor 3-deoxyglucosone is increased in diabetes. The role of 3,4-DGE in glomerular injury had not been addressed. We studied the effects of 3,4-DGE on cultured human podocytes and in vivo in mice. 3,4-DGE induced apoptosis in podocytes in a dose- and time-dependent manner. 3,4-DGE promoted the release of cytochrome c from mitochondria and activation of caspase-3. While high glucose concentrations increased the levels of the podocyte intracellular antiapoptotic protein HSP27/HSPB1, 3,4-DGE decreased the expression of podocyte HSP27/HSPB1. Apoptosis induced by 3,4-DGE was caspase-dependent and could be prevented by the broad-spectrum caspase inhibitor zVAD-fmk. Antagonism of Bax by a Ku-70-derived peptide also prevented apoptosis. Intravenous administration of 3,4-DGE to healthy mice resulted in a decreased expression of HSP27/HSPB1 and caspase-3 activation in whole kidney and in podocytes in vivo. In conclusion, 3,4-DGE induces apoptotic cell death in cultured human podocytes, suggesting a potential role in glomerular injury resulting from metabolic disorders.

12- and 15-lipoxygenases in adipose tissue inflammation

The lipoxygenases (LOs) are principal enzymes involved in the oxidative metabolism of polyunsaturated fatty acids, including arachidonic acid. 12- and 15-LO and their lipid metabolites have been implicated in the development of insulin resistance and diabetes. Adipose tissue, and in particular visceral adipose tissue, plays a primary role in the development of the inflammation seen in these conditions. 12- and 15-LO and their lipid metabolites act as upstream regulators of many of the cytokines involved in the inflammatory response in adipose tissue. While the role that 12- and 15-LO play in chronically inflamed adipose tissue is becoming clearer, there are still many questions that remain unanswered regarding their activation, signaling pathways, and roles in healthy fat. 12- and 15-LO also generate products with anti-inflammatory properties that are under investigation. Therefore, 12- and 15-LO have the potential to be very important targets for therapeutics aimed at reducing insulin resistance and the comorbid conditions associated with obesity.

12S-hydroxyeicosatetraenoic acid levels link to coronary artery disease in Type 2 diabetic patients

BACKGROUND

12(S)-Hydroxyeicosatetraenoic acid (12(S)-HETE) is a metabolite of arachidonic acid. 12(S)-HETE is involved in the pathogenesis of atherosclerosis and diabetes. However, the correlation between 12(S)-HETE and coronary artery disease (CAD) in the diabetic patient is unclear.

AIMS

The study investigated the relationship between 12(S)-HETE and CAD in Type 2 diabetes (T2D).

METHODS

Plasma 12(S)- HETE levels were detected by enzyme-linked immunosorbent assay in 103 healthy controls (control), 109 diabetic patients without CAD (diabetic), and 152 diabetic patients with CAD (diabetic-CAD).

RESULTS

12(S)-HETE levels were higher in both diabetic and diabetic-CAD groups compared to control and in the diabetic-CAD group compared to the diabetic group. In the multiple linear stepwise regression analysis, 12(S)-HETE levels correlated independently with CAD, systolic blood pressure, and glycated hemoglobin.

CONCLUSIONS

These results indicate that 12(S)-HETE levels are increased in diabetic patients with CAD, suggesting a role for atherosclerosis in T2D.

The arrestin-selective angiotensin AT1 receptor agonist [Sar1,Ile4,Ile8]-AngII negatively regulates bradykinin B2 receptor signaling via AT1-B2 receptor heterodimers

The renin-angiotensin and kallikrein-kinin systems are key regulators of vascular tone and inflammation. Angiotensin II, the principal effector of the renin-angiotensin system, promotes vasoconstriction by activating angiotensin AT1 receptors. The opposing effects of the kallikrein-kinin system are mediated by bradykinin acting on B1 and B2 bradykinin receptors. The renin-angiotensin and kallikrein-kinin systems engage in cross-talk at multiple levels, including the formation of AT1-B2 receptor heterodimers. In primary vascular smooth muscle cells, we find that the arrestin pathway-selective AT1 agonist, [Sar(1),Ile(4),Ile(8)]-AngII, but not the neutral AT1 antagonist, losartan, inhibits endogenous B2 receptor signaling. In a transfected HEK293 cell model that recapitulates this effect, we find that the actions of [Sar(1),Ile(4), Ile(8)]-AngII require the AT1 receptor and result from arrestin-dependent co-internalization of AT1-B2 heterodimers. BRET50 measurements indicate that AT1 and B2 receptors efficiently heterodimerize. In cells expressing both receptors, pretreatment with [Sar(1),Ile(4),Ile(8)]-AngII blunts B2 receptor activation of Gq/11-dependent intracellular calcium influx and Gi/o-dependent inhibition of adenylyl cyclase. In contrast, [Sar(1),Ile(4),Ile(8)]-AngII has no effect on B2 receptor ligand affinity or bradykinin-induced arrestin3 recruitment. Both radioligand binding assays and quantitative microscopy-based analysis demonstrate that [Sar(1),Ile(4),Ile(8)]-AngII promotes internalization of AT1-B2 heterodimers. Thus, [Sar(1),Ile(4),Ile(8)]-AngII exerts lateral allosteric modulation of B2 receptor signaling by binding to the orthosteric ligand binding site of the AT1 receptor and promoting co-sequestration of AT1-B2 heterodimers. Given the opposing roles of the renin-angiotensin and kallikrein-kinin systems in vivo, the distinct properties of arrestin pathway-selective and neutral AT1 receptor ligands may translate into different pharmacologic actions.

The renin-angiotensin-aldosterone system in podocytes

The renin-angiotensin-aldosterone system (RAAS) plays a critical role in kidney function and its inhibition reduces proteinuria and preserves kidney function in patients with chronic kidney disease. Recent studies have shown that podocytes generate many components of the RAAS and they express receptors of RAAS, including angiotensin II, mineralocorticoid, and prorenin receptors. Crucial functions of podocytes, such as contraction, apoptosis, autophagocytosis, and cytoskeletal organization, have been shown to be regulated by the angiotensin II type 1 receptors. An activation of the glomerular RAAS and protection from podocyte injury by RAAS inhibitors have been shown in many glomerular diseases. Exploring the interaction between the local RAAS and the signaling involved in RAAS activation in podocytes will lead to new therapeutic strategies of podocyte protection.

Dietary fish oil reduces glomerular injury and elevated renal hydroxyeicosatetraenoic acid levels in the JCR:LA-cp rat, a model of the metabolic syndrome

We have previously shown nutritional intervention with fish oil (n-3 PUFA) to reduce numerous complications associated with the metabolic syndrome (MetS) in the JCR:LA-corpulent (cp) rat. In the present study, we sought to explore the potential role of fish oil to prevent glomerulosclerosis in JCR:LA-cp rats via renal eicosanoid metabolism and lipidomic analysis. Male lean and MetS JCR:LA-cp rats were fed a lipid-balanced diet supplemented with fish oil (5 or 10 % of total fat). After 16 weeks of feeding, albuminuria was significantly reduced in MetS rats supplemented with 5 or 10 % fish oil ( − 53 and − 70 %, respectively, compared with the untreated MetS rats). The 5 % fish oil diet resulted in markedly lower glomerulosclerosis ( − 43 %) in MetS rats and to a lesser extent in those supplemented with 10 % fish oil. Interestingly, untreated MetS rats had higher levels of 11- and 12-hydroxyeicosatetraenoic acids (HETE) v. lean rats. Dietary fish oil reduced these levels, as well as other (5-, 9- and 15-) HETE. Whilst genotype did not alter prostanoid levels, fish oil reduced endogenous renal levels of 6-keto PGF1α (PGI2 metabolite), thromboxane B2 (TxB2), PGF2α and PGD2 by approximately 60 % in rats fed 10 % fish oil, and TxB2 ( − 50 %) and PGF2α ( − 41 %) in rats fed 5 % fish oil. In conclusion, dietary fish oil prevented glomerular damage in MetS rats and mitigated the elevation in renal HETE levels. These results suggest a potential role for dietary fish oil to improve dysfunctional renal eicosanoid metabolism associated with kidney damage during conditions of the MetS.

12-lipoxygenase: a potential target for novel anti-platelet therapeutics

Platelets play an essential role in the regulation of hemostasis and thrombosis and controlling their level of activation is central to prevention of occlusive clot formation and stroke. Although a number of anti-platelet targets have been identified to address this issue including COX-1, the P2Y(12) receptor, the integrin αIIbβ3, and more recently the protease-activated receptor-1, these targets often result in a significant increased risk of bleeding which may lead to pathologies as serious as the thrombosis they were meant to treat including intracranial hemorrhage and gastrointestinal bleeding. Therefore, alternative approaches to treat uncontrolled platelet activation are warranted. Platelet-type 12-lipoxygenase is an enzyme which oxidizes the free fatty acid in the platelet resulting in the production of the stable metabolite 12-hydroxyeicosatetraenoic acid (12-HETE). The role of 12-HETE in the platelet has been controversial with reports associating its function as being both anti- and pro-thrombotic. In this review, the role of 12-lipoxygenase and its bioactive metabolites in regulation of platelet reactivity, clot formation, and hemostasis is described. Understanding the mechanisms by which 12-lipoxygenase and its metabolites modulate platelet function may lead to the development of a novel class of anti-platelet therapies targeting the enzyme in order to attenuate injury-induced clot formation, vessel occlusion and pathophysiological shifts in hemostasis.

HSP27/HSPB1 as an adaptive podocyte antiapoptotic protein activated by high glucose and angiotensin II

Apoptosis is a driving force of diabetic end-organ damage, including diabetic nephropathy (DN). However, the mechanisms that modulate diabetes-induced cell death are not fully understood. Heat shock protein 27 (HSP27/HSPB1) is a cell stress protein that regulates apoptosis in extrarenal cells and is expressed by podocytes exposed to toxins causing nephrotic syndrome. We investigated the regulation of HSPB1 expression and its function in podocytes exposed to factors contributing to DN, such as high glucose and angiotensin (Ang) II. HSPB1 expression was assessed in renal biopsies from patients with DN, minimal change disease or focal segmental glomerulosclerosis (FSGS), in a rat model of diabetes induced by streptozotocin (STZ) and in Ang II-infused rats. The regulation of HSPB1 was studied in cultured human podocytes and the function of HSPB1 expressed in response to pathophysiologically relevant stimuli was explored by short interfering RNA knockdown. Total kidney HSPB1 mRNA and protein expression was increased in rats with STZ-induced diabetes and in rats infused with Ang II. Upregulation of HSPB1 protein was confirmed in isolated diabetic glomeruli. Immunohistochemistry showed increased glomerular expression of HSPB1 in both models and localized glomerular HSPB1 to podocytes. HSPB1 protein was increased in glomerular podocytes from patients with DN or FSGS. In cultured human podocytes HSPB1 mRNA and protein expression was upregulated by high glucose concentrations and Ang II. High glucose, but not Ang II, promoted podocyte apoptosis. HSPB1 short interfering RNA (siRNA) targeting increased apoptosis in a high-glucose milieu and sensitized to Ang II or TGFβ1-induced apoptosis by promoting caspase activation. In conclusion, both high glucose and Ang II contribute to HSPB1 upregulation. HSPB1 upregulation allows podocytes to better withstand an adverse high-glucose or Ang II-rich environment, such as can be found in DN.

Role of 12-lipoxygenase in decreasing P-cadherin and increasing angiotensin II type 1 receptor expression according to glomerular size in type 2 diabetic rats

12-lipoxygenase (12-LO) was implicated in the development of diabetic nephropathy (DN), in which the proteinuria was thought to be associated with a decreased expression of glomerular P-cadherin. Therefore, we investigated the role of 12-LO in the glomerular P-cadherin expression in type 2 diabetic rats according to the glomerular sizes. Rats fed with high-fat diet for 6 wk were treated with low-dose streptozotocin. Once diabetes onset, diabetic rats were treated with 12-LO inhibitor cinnamyl-3,4-dihydroxy-cyanocinnamate (CDC) for 8 wk. Then glomeruli were isolated from diabetic and control rats with a sieving method. RT-PCR, Western blotting, and immunofluorescent staining were used for mRNA and protein expressions of P-cadherin and angiotensin II (Ang II) type 1 receptor (AT1). We found that CDC did not affect the glucose levels but completely attenuated diabetic increases in glomerular volume and proteinuria. Diabetes significantly decreased the P-cadherin mRNA and protein expressions and increased the AT1 mRNA and protein expressions in the glomeruli. These changes were significantly prevented by CDC and recaptured by direct infusion of 12-LO product [12(S)-HETE] to normal rats for 7 days. The decreased P-cadherin expression was similar between large and small glomeruli, but the increased AT1 expression was significantly higher in the large than in the small glomeruli from diabetic and 12(S)-HETE-treated rats. Direct infusion of normal rats with Ang II for 14 days also significantly decreased the glomerular P-cadherin expression. These results suggest that diabetic proteinuria is mediated by the activation of 12-LO pathway that is partially attributed to the decreased glomerular P-cadherin expression.

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.

Flow cytometric analysis of circulating microparticles in plasma

Microparticles, which include exosomes, micro-vesicles, apoptotic bodies and apoptotic microparticles, are small (0.05 - 3 mum in diameter), membranous vesicles that can contain DNA, RNA, miRNA, intracellular proteins and express extracellular surface markers from the parental cells. They can be secreted from intracellular multivesicular bodies or released from the surface of blebbing membranes. Circulating microparticles are abundant in the plasma of normal individuals and can be derived from circulating blood cells such as platelets, red blood cells and leukocytes as well as from tissue sources, such as endothelial and placental tissues. Elevated levels of microparticles are associated with various diseases such as thrombosis (platelet microparticles), congestive heart failure (endothelial microparticles), breast cancer patients (leukocyte microparticles) and women with preeclampsia (syncytiotrophoblast microparticles). Although microparticles can be detected by microscopy, enzyme-linked immunoassays and functional assays, flow cytometry is the preferred method because of the ability to quantitate (fluorescent bead- or flow rate-based method) and because of polychromatic capabilities. However, standardization of pre-analytical and analytical modus operandi for isolating, enumerating and fluorescent labeling of microparticles remains a challenge. The primary focus of this article is to review the preliminary steps required to optimally study circulating in vivo microparticles which include: 1) centrifugation speed used, 2) quantitation of microparticles before antibody labeling, 3) levels of fluorescence intensity of antibody-labeled microparticles, 4) polychromatic flow cytometric analysis of microparticle sub-populations and 5) use of polyclonal antibodies designed for Western blotting for flow cytometry. These studies determine a roadmap to develop microparticles as biomarkers for a variety of conditions.

Age is a determinant of acute hemodynamic responses to hyperglycemia and angiotensin II in humans with uncomplicated type 1 diabetes mellitus

Hyperglycemia is associated with hemodynamic changes in type 1 diabetes (DM), acting in part through renin-angiotensin system activation. Since aging is associated with vascular dysfunction in DM, we hypothesized that acute hemodynamic responses to clamped hyperglycemia and infused ANG II would be exaggerated in older adults compared with a group of adolescent/young adults with type 1 DM. Renal hemodynamic function, blood pressure, and arterial stiffness were assessed in adolescent/young adults ( n = 34; mean age: 18 ± 3 yr) and older adults ( n = 32; mean age: 45 ± 9 yr). Studies were performed during clamped euglycemia (4–6 mmol/l) and hyperglycemia (9–11 mmol/l). Renal and systemic hemodynamic responses to ANG II were measured during clamped euglycemia in diabetic subjects. ANG II responses were also assessed in a cohort of non-DM subjects ( n = 97; mean age: 26; age range: 18–40 yr). Older DM adults exhibited higher baseline blood pressure, arterial stiffness, and renal vascular resistance, and lower glomerular filtration rate (GFR) and effective renal plasma flow, compared with adolescent/young DM adults ( P < 0.05). Clamped hyperglycemia was associated with exaggerated peripheral and renal hemodynamic responses uniquely in older DM adults; only GFR increased in adolescent/young DM adults. ANG II infusion also produced exaggerated vasoconstrictive responses in older DM adults vs. adolescent/young DM adults ( P < 0.05). The independent effect of age on hemodynamic responses to hyperglycemia and ANG II was confirmed using multivariate regression analysis in DM subjects ( P < 0.05), and results were still significant when participants were matched for DM duration. Age-related alterations in hemodynamic function and ANG II response were not observed in healthy non-DM control subjects. Acute hemodynamic responses to clamped hyperglycemia and ANG II were exaggerated in older subjects with type 1 DM, highlighting an important interaction between age and factors that contribute to the pathogenesis of acute vascular dysfunction in DM.

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

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