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

UHPLC-MS-Based Serum and Urine Metabolomics Reveals the Anti-Diabetic Mechanism of Ginsenoside Re in Type 2 Diabetic Rats

Panax ginseng was employed in the treatment of “Xiao-Ke” symptom, which nowadays known as diabetes mellitus, in traditional Chinese medicine for more than a thousand years. Ginsenoside Re was the major pharmacologic ingredient found abundantly in ginseng. However, the anti-diabetic of Ginsenoside Re and its underlying mechanism in metabolic level are still unclear. Serum and urine metabolomic method was carried out to investigate the anti-diabetic pharmacological effects and the potential mechanism of Ginsenoside Re on high-fat diet combined streptozotocin-induced type 2 diabetes mellitus (T2DM) rats based on ultra-high-performance liquid chromatography coupled with quadrupole exactive orbitrap mass spectrometry (UHPLC-Q-Exactive Orbitrap/MS). Serum and urine samples were collected from the control group (CON), T2DM group, metformin (MET) treatment group, and ginsenoside Re treatment group after intervention. The biochemical parameters of serum were firstly analyzed. The endogenous metabolites in serum and urine were detected by UHPLC-MS. The potential metabolites were screened by multivariate statistical analysis and identified by accurate mass measurement, MS/MS, and metabolite databases. The anti-diabetic-related metabolites were analyzed by KEGG metabolic pathway, and its potential mechanism was discussed. The treatment of ginsenoside Re significantly reduced the blood glucose and serum lipid level improved the oxidative stress caused by T2DM. Biochemical parameters (urea nitrogen, uric acid) showed that ginsenoside Re could improve renal function in T2DM rats. Respective 2 and 6 differential metabolites were found and identified in serum and urine of ginsenoside Re compared with T2DM group and enriched in KEGG pathway. Metabolic pathways analysis indicated that the differential metabolites related to T2DM were mainly involved in arachidonic acid metabolism, Vitamin B6, steroid hormone biosynthesis, and bile secretion metabolic pathways. This study verified the anti-diabetic and anti-oxidation effects of ginsenoside Re, elaborated that ginsenoside Re has a good regulation of the metabolic disorder in T2DM rats, which could promote insulin secretion, stimulated cannabinoid type 1 receptor (CB₁), and CaMKK β to activate AMPK signaling pathway, inhibited insulin resistance, and improved blood glucose uptake and diabetic nephropathy, so as to play the role of anti-diabetic.

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

ABSTRACT

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

Interaction of the renin angiotensin and cox systems in the kidney

Cyclooxygenase-2 (COX-2) plays an important role in mediating actions of the renin-angiotensin system (RAS). This review sheds light on the recent developments regarding the complex interactions between components of RAS and COX-2; and their implications on renal function and disease. COX-2 is believed to counter regulate the effects of RAS activation and therefore counter balance the vasoconstriction effect of Ang II. In kidney, under normal conditions, these systems are essential for maintaining a balance between vasodilation and vasoconstriction. However, recent studies suggested a pivotal role for this interplay in pathology. COX-2 increases the renin release and Ang II formation leading to increase in blood pressure. COX-2 is also associated with diabetic nephropathy, where its upregulation in the kidney contributes to glomerular injury and albuminuria. Selective inhibition of COX-2 retards the progression of renal injury. COX-2 also mediates the pathologic effects of the (Pro)renin receptor (PRR) in the kidney. In summary, this review discusses the interaction between the RAS and COX-2 in health and disease.

Angiotensin II-mediated GFR decline in subtotal nephrectomy is due to acid retention associated with reduced GFR

BACKGROUND

Angiotensin II (AII) mediates glomerular filtration rate (GFR) decline in animals with subtotal nephrectomy (Nx), but the mechanisms for increased AII activity are unknown. Because reduced GFR of Nx is associated with acid (H(+)) retention that increases kidney AII, AII-mediated GFR decline might be induced by H(+) retention.

METHODS

We measured GFR and kidney microdialyzate H(+) and AII content in Sham and 2/3 Nx rats in response to amelioration of H(+) retention with dietary NaHCO3, to AII receptor antagonism and to both.

RESULTS

GFR was lower in Nx than that in Sham. Nx but not Sham GFR was lower at Week 24 than that at Week 1. Despite no differences in plasma acid-base parameters or urine net acid excretion, kidney H(+) content was higher in Nx than that in Sham, consistent with H(+) retention. Plasma and kidney microdialyzate AII were higher in Nx than that in Sham and dietary NaHCO3 reduced each in Nx but not in Sham. AII receptor antagonism was associated with higher Week 24 GFR in Nx with H(+) retention but not in Sham or in Nx in which H(+) retention had been corrected with dietary NaHCO3. Week 24 GFR after dietary NaHCO3 was higher than after AII receptor antagonism. Week 24 GFR was not different after adding AII receptor antagonism to dietary NaHCO3.

CONCLUSIONS

AII-mediated GFR decline in 2/3 Nx was induced by H(+) retention and its amelioration with dietary HCO3 conserved GFR better than AII receptor antagonism in this CKD model. H(+) retention might induce AII-mediated GFR decline in patients with reduced GFR, even without metabolic acidosis.

Hypertension in the elderly: unique challenges and management

Elderly individuals, worldwide, are on the rise, posing new challenges to care providers. Hypertension is highly prevalent in elderly individuals, and multiple challenges face care providers while managing it. In addition to treating hypertension, the physician must treat other modifiable cardiovascular risk factors in patients with or without diabetes mellitus or chronic kidney disease to reduce cardiovascular events and mortality. This review discusses some of the unique characteristics of high blood pressure in the elderly and provides an overview of the challenges facing care providers, as well as the current recommendations for management of hypertension in the elderly.

High glucose activates the alternative ACE2/Ang-(1-7)/Mas and APN/Ang IV/IRAP RAS axes in pancreatic β-cells

The activation of the classical angiotensin (Ang)-converting enzyme (ACE)/Ang II/Ang II type 1 receptor (AT1R) axis of the renin-angiotensin system (RAS) has been associated with islet dysfunction and insulin resistance. Hyperglycaemia, hypertension and obesity, major components of metabolic syndrome, are all associated with increased systemic and tissue levels of Ang II. Whereas it is well established that Ang II, by binding to AT1R, impairs glucose-stimulated insulin secretion and insulin signaling, the contribution of alternative RAS axes to β-cell function remains to be fully elucidated. In this study, using the BRIN-BD11 rat insulinoma cell line, we i) examined the basal expression levels of components of classical and alternative RAS axes and ii) investigated the effects of normal (5.5 mM) and elevated (11, 15, 25 mM) glucose concentrations on their expression and/or enzymatic activity by means of reverse transcription quantitative PCR (RT-qPCR), immunoblot analysis and enzymatic activity assays. The results correlated with the insulin production and release. Essential components of all RAS axes were found to be expressed in the BRIN-BD11 cells. Components of the alternative RAS axes, ACE2, neutral endopeptidase 24.11, Mas receptor (Mas), aminopeptidases A (APA) and N (APN) and insulin-regulated aminopeptidase (IRAP) showed an increased expression/activity in response to high glucose. These alterations were paralleled by the glucose-dependent increase in insulin production and release. By contrast, components of the classical RAS axis, ACE, AT1R and Ang II type 2 receptor (AT2R), remained largely unaffected under these conditions. Glucose induced the activation of the alternative ACE2/Ang-(1-7)/Mas and APN/Ang IV/IRAP RAS axes simultaneously with the stimulation of insulin production/release. Our data suggest the existence of a functional link between the local RAS axis and pancreatic β-cell function; however, further studies are required to confirm this hypothesis.

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.

Emerging targets in lipid-based therapy

The use of prostaglandins and NSAIDS in the clinic has proven that lipid mediators and their associated pathways make attractive therapeutic targets. When contemplating therapies involving lipid pathways, several basic agents come to mind. There are the enzymes and accessory proteins that lead to the metabolism of lipid substrates, provided through diet or through actions of lipases, the subsequent lipid products, and finally the lipid sensors or receptors. There is abundant evidence that molecules along this lipid continuum can serve as prognostic and diagnostic indicators and are in fact viable therapeutic targets. Furthermore, lipids themselves can be used as therapeutics. Despite this, the vernacular dialog pertaining to "biomarkers" does not routinely include mention of lipids, though this is rapidly changing. Collectively these agents are becoming more appreciated for their respective roles in diverse disease processes from cancer to preterm labor and are receiving their due appreciation after decades of ground work in the lipid field. By relating examples of disease processes that result from dysfunction along the lipid continuum, as well as examples of lipid therapies and emerging technologies, this review is meant to inspire further reading and discovery.

Angiotensin II receptors mediate increased distal nephron acidification caused by acid retention

Patients with a moderately reduced glomerular filtration rate (GFR) typically have no metabolic acidosis and a urine net acid excretion comparable to those with normal GFR, supporting greater per nephron acidification with moderately reduced GFR. We modeled such patients using rats with a surgical reduction of 2/3 kidney mass, yielding animals with reduced GFR without metabolic acidosis. We then tested the hypothesis that reduction of nephron mass augments distal nephron acidification in remnant nephrons mediated by increased angiotensin II activity, and that the latter is induced by underlying acid retention. Nephron mass reduction yielded lower GFR than controls (sham operation), higher acid retention (measured by microdialysis of kidney cortex), higher distal nephron acidification, and higher plasma and kidney levels of angiotensin II, but plasma total CO(2) and urine net acid excretion were not different. Angiotensin II receptor antagonism reduced distal nephron acidification to levels similar to control. Dietary alkali that lowered acid retention to that of control also reduced plasma and kidney levels of angiotensin II and reduced distal nephron acidification to control. Angiotensin II receptor antagonism with dietary alkali had no significant added effect on distal nephron acidification. Thus, nephron reduction that moderately reduced GFR with no metabolic acidosis is characterized by increased angiotensin II activity. This mediates increased distal nephron acidification and is induced by acid retention.

Renin-angiotensin-aldosterone system blockade effects on the kidney in the elderly: benefits and limitations

The proportion of the population that is elderly (age>or=65 years) is growing across the world. The increasing longevity of humans results in a higher number of elderly patients' presenting with multiple chronic diseases such as hypertension, diabetes, and chronic kidney disease (CKD). These problems increase morbidity and mortality in the elderly. Overactivity of the renin-angiotensin-aldosterone system (RAAS) is associated with the development of hypertension, cardiovascular events, and CKD, so targeting the RAAS is a logical therapeutic approach. Elderly patients present special concerns regarding the benefits versus risks of using RAAS blockers. Plasma renin activity declines with age, which has been attributed to the effect of age-associated nephrosclerosis. Plasma aldosterone is also reduced with age, resulting in a greater risk for hyperkalemia in older individuals, especially when coupled with the age-associated decline in GFR. Moreover, the elderly have a higher frequency of concurrent conditions and are on many medications, which may further increase the risk for adverse effects of RAAS blocking agents. Unfortunately, there is a paucity of literature that is specifically aimed at studying elderly using the RAAS blockers. We present in our in-depth review data regarding benefits and limitations of the use of the RAAS blockades on the various sites along the RAAS pathway for elderly patients. Specific attention was given to the role of combination RAAS blockade therapy and higher monotherapy dosing in the treatment of hypertension in the elderly.

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

CONTEXT

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSIONS

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

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

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