Top-Down Lipidomics Reveals Ether Lipid Deficiency in Blood Plasma of Hypertensive Patients

Background

Dyslipoproteinemia, obesity and insulin resistance are integrative constituents of the metabolic syndrome and are major risk factors for hypertension. The objective of this study was to determine whether hypertension specifically affects the plasma lipidome independently and differently from the effects induced by obesity and insulin resistance.

Methodology/Principal Findings

We screened the plasma lipidome of 19 men with hypertension and 51 normotensive male controls by top-down shotgun profiling on a LTQ Orbitrap hybrid mass spectrometer. The analysis encompassed 95 lipid species of 10 major lipid classes. Obesity resulted in generally higher lipid load in blood plasma, while the content of tri- and diacylglycerols increased dramatically. Insulin resistance, defined by HOMA-IR >3.5 and controlled for BMI, had little effect on the plasma lipidome. Importantly, we observed that in blood plasma of hypertensive individuals the overall content of ether lipids decreased. Ether phosphatidylcholines and ether phosphatidylethanolamines, that comprise arachidonic (20∶4) and docosapentaenoic (22∶5) fatty acid moieties, were specifically diminished. The content of free cholesterol also decreased, although conventional clinical lipid homeostasis indices remained unaffected.

Conclusions/Significance

Top-down shotgun lipidomics demonstrated that hypertension is accompanied by specific reduction of the content of ether lipids and free cholesterol that occurred independently of lipidomic alterations induced by obesity and insulin resistance. These results may form the basis for novel preventive and dietary strategies alleviating the severity of hypertension.     

Hyperinsulinemia, insulin resistance and essential hypertension.

Glucose intolerance and noninsulin-dependent diabetes are commonly associated with hypertension. Epidemiological data suggest that this association is independent of age and obesity. Much evidence indicates that the link between diabetes and essential hypertension is hyperinsulinemia. When hypertensive patients whether obese or of normal weight are compared with matched normotensive control subjects, an increased plasma insulin response to a glucose challenge is consistently observed. Studies using insulin glucose clamp techniques in combination with tracer glucose infusion and indirect calorimetry have demonstrated that the insulin resistance in hypertensive subjects is located in muscles and restricted to glycogen synthesis. The relations between hyperinsulinemia and blood pressure do not prove that the relationship is a causal one. However, at least four mechanisms may link hyperinsulinemia with hypertension: Na+ retention, sympathetic nervous system overactivity, disturbed membrane ion transport and proliferation of vascular smooth muscle cells. Diuretics and beta-blockers may enhance insulin resistance, which is not affected by calcium antagonists, but decreased by the ACE inhibitor captopril. Weight reduction and regular physical exercise can improve insulin sensitivity and decrease blood pressure values. These nonpharmacological interventions should be more strongly recommended to diabetic and nondiabetic hypertensive patients.     

Novel qualitative aspects of tissue fatty acids related to metabolic regulation: lessons from Elovl6 knockout

Insulin resistance, often associated with obesity, precipitates metabolic syndrome, type 2 diabetes, and finally, atherosclerosis. Sources of excess energy cause abnormal accumulation of tissue lipids leading to cellular dysfunction through cellular stress and inflammation. This process is often referred to as lipotoxicity. Until date, effective approaches that aim to overcome insulin resistance involve amelioration of obesity by caloric restriction and/or exercise. Quantitative control of lipids, especially triglycerides and fatty acids in adipose and other tissues, and plasma can be addressed using these measures. However, altering tissue lipid composition may provide another strategy to prevent or control lipotoxicity. Endogenous fatty acid synthesis plays a crucial role in determining tissue energy states. As a target gene of SREBP-1 that controls lipogenesis we identified a unique enzyme, Elovl6, which is responsible for the final step in endogenous saturated fatty acid synthesis, thereby controlling tissue fatty acid composition. Elovl6-deficient mice become obese and develop hepatosteatosis when fed a high-fat diet or when mated to leptin-deficient ob/ob mice. However, the mice exhibited marked protection from hyperinsulinemia, hyperglycemia, and hyperleptinemia. Hepatic fatty acid composition is a novel determinant of insulin sensitivity independent of cellular energy balance. Inhibiting Elovl6 activity may provide a novel therapeutic approach for treating insulin resistance, diabetes, metabolic syndrome, and cardiovascular risks by circumventing obesity problems. In this review, we consider fatty acid metabolism and lipotoxicity, and discuss the role of Elovl6 in newly recognized aspects of metabolic regulation.     

Cardiovascular disease in diabetes mellitus type 2: a potential role for novel cardiovascular risk factors

A major consequence of diabetes mellitus type 2 is the accelerated development of atherosclerosis. Assessment of conventional risk factors such as plasma lipids, lipoproteins and hypertension only partly account for the excessive risk of developing cardiovascular disease in this population. Increasing evidence has emerged suggesting that conditions associated with diabetes mellitus type 2, such as insulin resistance, hyperinsulinemia and hyperglycemia, may also play a significant role in regulating 'novel' cardiovascular risk factors. These factors and their potential roles in the development of atherosclerosis and cardiovascular events are discussed in this review.     

Elevated plasma total homocysteine levels in hyperinsulinemic obese subjects

Homocysteine has been associated with the oxidative stress in the pathogenesis of atherosclerosis. Oxidative stress caused by triglycerides and free fatty acids is known to cause insulin resistance and hyperinsulinemia. On the other hand, insulin resistance may increase homocysteine levels. Since obesity is associated with insulin resistance and hyperinsulinemia, we aimed to study the possible association of homocysteine with hyperinsulinemia in obese subjects. 20 obese male subjects (body mass index >29), aged 33--55 (mean 45 years old) were studied. A fasting blood sample was obtained for the study and the subjects undertook an oral glucose tolerance test with samples taken at 1 and 2 h after glucose. Subjects were divided in two groups according to the fasting insulin levels, < 9 &mgr;U/ml or normoinsulinemic (group 1) and >9 &mgr;U/ml or hyperinsulinemic (group 2). Glucose, insulin, homocysteine, folate, B(12,) total cholesterol, HDL-cholesterol and triglycerides levels were determined in fasting blood samples. In oral glucose tolerance test, glucose, insulin and homocysteine levels were measured. Hyperinsulinemic obese subjects (group 2) had higher levels of insulin and glucose at 1 h and 2 h postglucose, compared with group 1. Fasting total homocysteine and triglyceride levels were also increased in this group, whereas folate and B(12) levels were similar in both groups. Fasting homocysteine significantly correlated with fasting insulin (r = 0.6, p <0.01). Homocysteine levels slightly but significantly decreased after glucose loading in normoinsulinemic but not in hyperinsulinemic obese subjects. These results show that higher homocysteine levels are observed in the hyperinsulinemic obese subjects and suggest that homocysteine could play a role in the higher risk of cardiovascular disease in obesity.     

Fasting Plasma Insulin at 5 Years of Age Predicted Subsequent Weight Increase in Early Childhood over a 5-Year Period—The Da Qing Children Cohort Study

Background

The association between hyperinsulinemia and obesity is well known. However, it is uncertain especially in childhood obesity, if initial fasting hyperinsulinemia predicts obesity, or obesity leads to hyperinsulinemia through insulin resistance.

Objective

To investigate the predictive effect of fasting plasma insulin on subsequent weight change after a 5-year interval in childhood.

Methods

424 Children from Da Qing city, China, were recruited at 5 years of age and followed up for 5 years. Blood pressure, anthropometric measurements, fasting plasma insulin, glucose and triglycerides were measured at baseline and 5 years later.

Results

Fasting plasma insulin at 5 years of age was significantly correlated with change of weight from 5 to 10 years (ΔWeight). Children in the lowest insulin quartile had ΔWeight of 13.08±0.73 kg compare to 18.39±0.86 in the highest insulin quartile (P<0.0001) in boys, and similarly 12.03±0.71 vs 15.80±0.60 kg (P<0.0001) in girls. Multivariate analysis showed that the predictive effect of insulin at 5 years of age on subsequent weight gain over 5 years remained statistically significant even after the adjustment for age, sex, birth weight, TV-viewing time and weight (or body mass index) at baseline. By contrast, the initial weight at 5 years of age did not predict subsequent changes in insulin level 5 years later. Children who had both higher fasting insulin and weight at 5 years of age showed much higher levels of systolic blood pressures, fasting plasma glucose, the homeostasis model assessment for insulin resistance (HOMA-IR) and triglycerides at 10 years of age.

Conclusions

Fasting plasma insulin at 5 years of age predicts weight gain and cardiovascular risk factors 5 year later in Chinese children of early childhood, but the absolute weight at 5 years of age did not predict subsequent change in fasting insulin.     

The complexities of obesity and diabetes with the development and progression of pancreatic cancer

Pancreatic cancer (PC) is one of the most lethal malignant diseases with the worst prognosis. It is ranked as the fourth leading cause of cancer-related deaths in the United States. Many risk factors have been associated with PC. Interestingly, large numbers of epidemiological studies suggest that obesity and diabetes, especially type-2 diabetes, are positively associated with increased risk of PC. Similarly, these chronic diseases (obesity, diabetes, and cancer) are also a major public health concern. In the U.S. population, 50 percent are overweight, 30 percent are medically obese, and 10 percent have diabetes mellitus (DM). Therefore, obesity and DM have been considered as potential risk factors for cancers; however, the focus of this article is restricted to PC. Although the mechanisms responsible for the development of these chronic diseases leading to the development of PC are not fully understood, the biological importance of the activation of insulin, insulin like growth factor-1 (IGF-1) and its receptor (IGF-1R) signaling pathways in insulin resistance mechanism and subsequent induction of compensatory hyperinsulinemia has been proposed. Therefore, targeting insulin/IGF-1 signaling with anti-diabetic drugs for lowering blood insulin levels and reversal of insulin resistance could be useful strategy for the prevention and/or treatment of PC. A large number of studies have demonstrated that the administration of anti-diabetic drugs such as metformin and thiazolidinediones (TZD) class of PPAR-γ agonists decreases the risk of cancers, suggesting that these agents might be useful anti-tumor agents for the treatment of PC. In this review article, we will discuss the potential roles of metformin and TZD anti-diabetic drugs as anti-tumor agents in the context of PC and will further discuss the complexities and the possible roles of microRNAs (miRNAs) in the pathogenesis of obesity, diabetes, and PC.     

Disease model: hyperinsulinemia and insulin resistance. Part A-targeted disruption of insulin signaling or glucose transport.

Insulin resistance and hyperinsulinemia are common pathophysiological features of several metabolic diseases, obesity and diabetes being two notable examples. In this article we review how the use of animal models has increased our understanding of insulin resistance and hyperinsulinemia, with a particular emphasis on the use of mice with targeted disruptions of the insulin signaling pathway.     

Leukotriene Production Is Increased in Abdominal Obesity

Obesity is a major risk factor for insulin resistance and type-2 diabetes. A chronic low grade inflammatory state has been described during obesity and associated with insulin resistance pathogenesis. Results from animal studies are in favor of a role of the leukotriene (LT) pathway in obesity induced-insulin resistance. However, there is a paucity of data regarding this association in human obesity. Therefore, the aim of this study was to investigate whether LT production was associated with insulin resistance and other metabolic parameters in a cohort of obese subjects. Forty-six (70% females) obese subjects (BMI≧30 kg/m²) without known diabetes and without inflammatory disease (CRP<10 mg/l) were included. Median age was 44 years (16–80) with a median BMI of 36.8 kg/m² (30–51). Insulin resistance was evaluated by HOMA-IR index and glucose tolerance test. Urinary LTE₄ (U-LTE₄) concentration was measured by enzyme immune assay. Screening for obstructive sleep apnea was performed. There was a positive association of U-LTE₄ with waist to hip ratio, systolic blood pressure and HOMA-IR in univariate analysis. Further, waist to hip ratio remained the only parameter significantly correlated with U-LTE₄, in adjusted multivariate analysis. Taken together, these results confirm the previously established notion of chronic low grade inflammation in obesity and further suggests a role for the LT pathway in obesity-associated development of insulin resistance in humans.     

Chronic insulin treatment causes insulin resistance in 3T3-L1 adipocytes through oxidative stress

Insulin resistance and hyperinsulinemia are commonly present in obesity and pre-diabetes, and hyperinsulinemia is both a marker and a cause for insulin resistance. However, the molecular link between hyperinsulinemia and insulin resistance remains elusive. The present study examined the effect of chronic insulin treatment on the reactive oxygen species (ROS) production, insulin signalling and insulin-stimulated glucose uptake in 3T3-L1 adipocytes. The results showed that chronic insulin treatment significantly increased the intracellular generation of superoxide anion, hydrogen peroxide and hydroxyl radical. ROS induced by chronic insulin treatment inhibited insulin signalling and glucose uptake, induced endoplasmic reticulum (ER) stress and JNK activation. Furthermore, these effects were reversed by antioxidants N-acetylcysteine, superoxide dismutase or catalase. These results suggested that ROS, ER stress and JNK pathway are involved in insulin resistance induced by chronic insulin treatment. Therefore, oxidative stress could be a potential interventional target for hyperinsulinemia-induced insulin resistance and related diseases.     

Chronic insulin treatment causes insulin resistance in 3T3-L1 adipocytes through oxidative stress

Insulin resistance and hyperinsulinemia are commonly present in obesity and pre-diabetes, and hyperinsulinemia is both a marker and a cause for insulin resistance. However, the molecular link between hyperinsulinemia and insulin resistance remains elusive. The present study examined the effect of chronic insulin treatment on the reactive oxygen species (ROS) production, insulin signalling and insulin-stimulated glucose uptake in 3T3-L1 adipocytes. The results showed that chronic insulin treatment significantly increased the intracellular generation of superoxide anion, hydrogen peroxide and hydroxyl radical. ROS induced by chronic insulin treatment inhibited insulin signalling and glucose uptake, induced endoplasmic reticulum (ER) stress and JNK activation. Furthermore, these effects were reversed by antioxidants N-acetylcysteine, superoxide dismutase or catalase. These results suggested that ROS, ER stress and JNK pathway are involved in insulin resistance induced by chronic insulin treatment. Therefore, oxidative stress could be a potential interventional target for hyperinsulinemia-induced insulin resistance and related diseases.     

Pathway-selective Insulin Resistance and Metabolic Disease: The Importance of Nutrient Flux

Hepatic glucose and lipid metabolism are altered in metabolic disease (e.g. obesity, metabolic syndrome, and Type 2 diabetes). Insulin-dependent regulation of glucose metabolism is impaired. In contrast, lipogenesis, hypertriglyceridemia, and hepatic steatosis are increased. Because insulin promotes lipogenesis and liver fat accumulation, to explain the elevation in plasma and tissue lipids, investigators have suggested the presence of pathway-selective insulin resistance. In this model, insulin signaling to glucose metabolism is impaired, but insulin signaling to lipid metabolism is intact. We discuss the evidence for the differential regulation of hepatic lipid and glucose metabolism. We suggest that the primary phenotypic driver is altered substrate delivery to the liver, as well as the repartitioning of hepatic nutrient handling. Specific alterations in insulin signaling serve to amplify the alterations in hepatic substrate metabolism. Thus, hyperinsulinemia and its resultant increased signaling may facilitate lipogenesis, but are not the major drivers of the phenotype of pathway-selective insulin resistance.     

肥胖诱发胰岛素抵抗的炎性机制

肥胖可诱发一系列慢性代谢性疾病,如2型糖尿病、血脂障碍、高血压和非酒精性脂肪肝等.这些疾病构成了当今世界人类健康的极大威胁.胰岛素抵抗是这些疾病的共有特征.胰岛素抵抗的发生与慢性低度系统炎性密切相关,涉及多条炎性信号通路的激活和胰岛素信号转导的缺陷.本文综述了肥胖、炎性与胰岛素抵抗之间的本质联系,以及肥胖诱发胰岛素抵抗的炎性机制,以期为肥胖相关疾病的防治提供重要参考.     

Leptin Expression in Hypothalamic PVN Reverses Dietary Obesity and Hyperinsulinemia but Stimulates Ghrelin*

Objective: In order to circumvent the multiple peripheral effects of hyperleptinemia and leptin resistance, the efficacy of leptin transgene expression in the hypothalamic paraventricular nucleus (PVN) to reinstate the central energy homeostasis in obesity was examined. Research Methods and Procedures: A recombinant adeno‐associated viral vector encoding either leptin (rAAV‐lep) or green fluorescent protein (rAAV‐GFP) was microinjected into the PVN of obesity‐prone rats consuming a high‐fat diet (HFD). Results: rAAV‐lep, and not rAAV‐GFP, microinjection significantly reduced energy intake and enhanced energy expenditure, thereby resulting in normalization of weight and blood levels of leptin, insulin, free fatty acids, and glucose concomitant with enhanced ghrelin secretion during the extended period of observation. Discussion: Thus, we show, for the first time, that amelioration of leptin insufficiency with enhanced localized leptin availability in the PVN alone can reverse dietary obesity and the attendant hyperinsulinemia and concurrently block the central stimulatory effects of elevated endogenous ghrelin on food intake and adiposity.     

Insulin and C-peptide levels in patients with idiopathic arterial hypertension]

Insulinemia in patients with essential hypertension and normal glucose tolerance was assessed. The study involved 25 patients divided into subgroups according body weight and 9 of control subjects. It was found, that hyperinsulinemia seen in hypertensive patients seems to be associated with obesity. Moreover, hyperinsulinemia does not depend primarily on hypersecretion of insulin but may reflect resistance to insulin and ab normal metabolism in the liver.     

Low-dose naltrexone rescues inflammation and insulin resistance associated with hyperinsulinemia

The incidence of diabetes, obesity, and metabolic diseases has reached an epidemic status worldwide. Insulin resistance is a common link in the development of these conditions, and hyperinsulinemia is a central hallmark of peripheral insulin resistance. However, how hyperinsulinemia leads to systemic insulin resistance is less clear. We now provide evidence that hyperinsulinemia promotes the release of soluble pro-inflammatory mediators from macrophages that lead to systemic insulin resistance. Our observations suggest that hyperinsulinemia induces sirtuin1 (SIRT1) repression and stimulates NF-κB p65 nuclear translocation and transactivation of NF-κB to promote the extracellular release of pro-inflammatory mediators. We further showed that low-dose naltrexone (LDN) abrogates hyperinsulinemia-mediated SIRT1 repression and prevents NF-κB p65 nuclear translocation. This, in turn, attenuates the hyperinsulinemia-induced release of pro-inflammatory cytokines and reinstates insulin sensitivity both in in vitro and in vivo diet-induced hyperinsulinemic mouse model. Notably, our data indicate that Sirt1 knockdown or inhibition blunts the anti-inflammatory properties of LDN in vitro. Using numerous complementary in silico and in vitro experimental approaches, we demonstrated that LDN can bind to SIRT1 and increase its deacetylase activity. Together, these data support a critical role of SIRT1 in inflammation and insulin resistance in hyperinsulinemia. LDN improves hyperinsulinemia-induced insulin resistance by reorienting macrophages toward anti-inflammation. Thus, LDN treatment may provide a novel therapeutic approach against hyperinsulinemia-associated insulin resistance.     

Relationship among hyperinsulinemia,insulin resistance,and hypertension is dependent on sex

Hyperinsulinemia and insulin resistance have been linked to hypertension; however, the influence of sex on this relationship has not been well studied. The purpose of this experiment was to compare the effects of chronic insulin treatment on insulin sensitivity and blood pressure in male and female rats. Male and female Wistar rats were treated with insulin (2 U/day) via subcutaneous sustained release implants for 5 wk. Systolic blood pressure was measured via the tail-cuff method before and after treatment, and insulin sensitivity was assessed with an oral glucose tolerance test. The insulin sensitivity of female rats was 4.5-fold greater than male rats. Chronic insulin treatment impaired insulin sensitivity in both sexes; however, this occurred to a greater degree in male rats. Blood pressure increased in male rats treated with insulin only. The results demonstrate that hyperinsulinemia and insulin resistance are associated with hypertension in male rats only. Therefore, the link between these conditions appears to depend on sex.     

Insulin Regulates Nitric Oxide Production in the Kidney Collecting Duct Cells

The kidney is an important organ for arterial blood pressure (BP) maintenance. Reduced NO generation in the kidney is associated with hypertension in insulin resistance. NO is a critical regulator of vascular tone; however, whether insulin regulates NO production in the renal inner medullary collecting duct (IMCD), the segment with the greatest enzymatic activity for NO production in kidney, is not clear. Using an NO-sensitive 4-amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) fluorescent dye, we found that insulin increased NO production in mouse IMCD cells (mIMCD) in a time- and dose-dependent manner. A concomitant dose-dependent increase in the NO metabolite (NOx) was also observed in the medium from insulin-stimulated cells. NO production peaked in mIMCD cells at a dose of 100 nm insulin with simultaneously increased NOx levels in the medium. At this dose, insulin significantly increased p-eNOS^Ser1177 levels in mIMCD cells. Pretreatment of cells with a PI 3-kinase inhibitor or insulin receptor silencing with RNA interference abolished these effects of insulin, whereas insulin-like growth factor-1 receptor (IGF-1R) silencing had no effect. We also showed that chronic insulin infusion to normal C57BL/6J mice resulted in increased endothelial NOS (eNOS) protein levels and NO production in the inner medulla. However, insulin-infused IRKO mice, with targeted deletion of insulin receptor from tubule epithelial cells of the kidney, had ∼50% reduced eNOS protein levels in their inner medulla along with a significant rise in BP relative to WT littermates. We have previously reported increased baseline BP and reduced urine NOx in IRKO mice. Thus, reduced insulin receptor signaling in IMCD could contribute to hypertension in the insulin-resistant state.     

Cerebral Blood Flow Links Insulin Resistance and Baroreflex Sensitivity

Insulin resistance confers risk for diabetes mellitus and associates with a reduced capacity of the arterial baroreflex to regulate blood pressure. Importantly, several brain regions that comprise the central autonomic network, which controls the baroreflex, are also sensitive to the neuromodulatory effects of insulin. However, it is unknown whether peripheral insulin resistance relates to activity within central autonomic network regions, which may in turn relate to reduced baroreflex regulation. Accordingly, we tested whether resting cerebral blood flow within central autonomic regions statistically mediated the relationship between insulin resistance and an indirect indicator of baroreflex regulation; namely, baroreflex sensitivity. Subjects were 92 community-dwelling adults free of confounding medical illnesses (48 men, 30-50 years old) who completed protocols to assess fasting insulin and glucose levels, resting baroreflex sensitivity, and resting cerebral blood flow. Baroreflex sensitivity was quantified by measuring the magnitude of spontaneous and sequential associations between beat-by-beat systolic blood pressure and heart rate changes. Individuals with greater insulin resistance, as measured by the homeostatic model assessment, exhibited reduced baroreflex sensitivity (b = -0.16, p < .05). Moreover, the relationship between insulin resistance and baroreflex sensitivity was statistically mediated by cerebral blood flow in central autonomic regions, including the insula and cingulate cortex (mediation coefficients < -0.06, p-values < .01). Activity within the central autonomic network may link insulin resistance to reduced baroreflex sensitivity. Our observations may help to characterize the neural pathways by which insulin resistance, and possibly diabetes mellitus, relates to adverse cardiovascular outcomes.