Tissue angiotensinogen gene expression induced by lipopolysaccharide in hypertensive rats

Renin-Angiotensin System Induced Secondary Hypertension: The Alteration of Kidney Function and Structure

Long-term hypertension is known as a major risk factor for cardiovascular and chronic kidney disease (CKD). The Renin-angiotensin system (RAS) plays a key role in hypertension pathogenesis. Angiotensin II (Ang II) enhancement in Ang II-dependent hypertension leads to progressive CKD and kidney fibrosis. In the two-kidney one-clip model (2K1C), more renin is synthesized in the principal cells of the collecting duct than juxtaglomerular cells (JGCs). An increase of renal Ang I and Ang II levels and a decrease of renal cortical and medullary Ang 1–7 occur in both kidneys of the 2K1C hypertensive rat model. In addition, the activity of the angiotensin-converting enzyme (ACE) increases, while ACE2's activity decreases in the medullary region of both kidneys in the 2K1C hypertensive model. Also, the renal prolyl carboxypeptidase (PrCP) expression and its activity reduce in the clipped kidneys. The imbalance in the production of renal ACE, ACE2, and PrCP expression causes the progression of renal injury. Intrarenal angiotensinogen (AGT) expression and urine AGT (uAGT) excretion rates in the unclipped kidney are greater than the clipped kidney in the 2K1C hypertensive rat model. The enhancement of Ang II in the clipped kidney is related to renin secretion, while the elevation of intrarenal Ang II in the unclipped kidney is related to stimulation of AGT mRNA and protein in proximal tubule cells by a direct effect of systemic Ang II level. Ang II-dependent hypertension enhances macrophages and T-cell infiltration into the kidney which increases cytokines, and AGT synthesis in proximal tubules is stimulated via cytokines. Accumulation of inflammatory cells in the kidney aggravates hypertension and renal damage. Moreover, Ang II-dependent hypertension alters renal Ang II type 1 & 2 receptors (AT₁R & AT₂R) and Mas receptor (MasR) expression, and the renal interstitial fluid bradykinin, nitric oxide, and cGMP response to AT₁R, AT₂R, or BK B₂-receptor antagonists. Based on a variety of sources including PubMed, Google Scholar, Scopus, and Science-Direct, in the current review, we will discuss the role of RAS-induced secondary hypertension on the alteration of renal function.

Insulin Resistance the Hinge Between Hypertension and Type 2 Diabetes

Epidemiological studies have documented a high incidence of diabetes in hypertensive patients.Insulin resistance is defined as a less than expected biologic response to a given concentration of the hormone and plays a pivotal role in the pathogenesis of diabetes. However, over the last decades, it became evident that insulin resistance is not merely a metabolic abnormality, but is a complex and multifaceted syndrome that can also affect blood pressure homeostasis. The dysregulation of neuro-humoral and neuro-immune systems is involved in the pathophysiology of both insulin resistance and hypertension. These mechanisms induce a chronic low grade of inflammation that interferes with insulin signalling transduction. Molecular abnormalities associated with insulin resistance include the defects of insulin receptor structure, number, binding affinity, and/or signalling capacity. For instance, hyperglycaemia impairs insulin signalling through the generation of reactive oxygen species, which abrogate insulin-induced tyrosine autophosphorylation of the insulin receptor. Additional mechanisms have been described as responsible for the inhibition of insulin signalling, including proteasome-mediated degradation of insulin receptor substrate 1/2, phosphatase-mediated dephosphorylation and kinase-mediated serine/threonine phosphorylation of both insulin receptor and insulin receptor substrates. Insulin resistance plays a key role also in the pathogenesis and progression of hypertension-induced target organ damage, like left ventricular hypertrophy, atherosclerosis and chronic kidney disease. Altogether these abnormalities significantly contribute to the increase the risk of developing type 2 diabetes.

The effects of captopril on lipopolysaccharide induced learning and memory impairments and the brain cytokine levels and oxidative damage in rats

AIM

Renin-angiotensin system has a role in inflammation and also involves in learning and memory. In the present study, the effects of captopril on lipopolysaccharide (LPS) induced learning and memory impairments, hippocampal cytokine levels and brain tissues oxidative damage was investigated.

MATERIALS AND METHODS

The rats were divided and treated : [1] saline (Control), [2] LPS (1mg/kg), [3-5] 10, 50 or 100mg/kg captopril 30min before LPS. The treatment was started since six days before the behavioral experiments and continued during the behavioral tests (LPS injection two h before each behavioral experiment).

RESULTS

Administration of LPS prolonged the escape latency and traveled path to find the platform in Morris water maze (MWM) test (P<0.01-P<0.001) while, shortened the latency to enter the dark compartment in passive avoidance (PA) test (P<0.001). Pretreatment by all doses of captopril improved performances of the rats in MWM (P<0.05-P<0.001) and also prolonged the latency to enter the dark in PA test (P<0.001). LPS also increased IL-6, TNF-α, malondialdehyde (MDA) and nitric oxide(NO) metabolites in the hippocampal tissues (P<0.05-P<0.001) which were prevented by captopril (P<0.05-P<0.001). The thiol, superoxide dismutase(SOD) and catalase(CAT) in the hippocampus of LPS group were lower than the control (P<0.001) while, they were enhanced when the aniamls were pretraeted by captopril (P<0.01-P<0.001).

CONCLUSION

The results of present study showed that captopril improved the LPS-induced learning and memory impairments in rats which were accompanied with attenuating hippocampal cytokine levels and improving the brain tissues oxidative damage criteria.

Maternal high-fat diet programs rat offspring hypertension and activates the adipose renin-angiotensin system

OBJECTIVE

A maternal high-fat diet creates an increased risk of offspring obesity and systemic hypertension. Although the renal renin-angiotensin system (RAS) is known to regulate blood pressure, it is now recognized that the RAS is also activated in adipose tissue during obesity. We hypothesized that programmed offspring hypertension is associated with the activation of the adipose tissue RAS in the offspring of obese rat dams.

STUDY DESIGN

At 3 weeks of age, female rats were weaned to a high-fat diet (60% k/cal; n = 6) or control diet (10% k/cal; n = 6). At 11 weeks of age, these rats were mated and continued on their respective diets during pregnancy. After birth, at 1 day of age, subcutaneous adipose tissue was collected; litter size was standardized, and pups were cross-fostered to either control or high-fat diet dams, which created 4 study groups. At 21 days of age, offspring were weaned to control or high-fat diet. At 6 months of age, body fat and blood pressure were measured. Thereafter, subcutaneous and retroperitoneal adipose tissue was harvested from male offspring. Protein expression of adipose tissue RAS components were determined by Western blotting.

RESULTS

The maternal high-fat diet induced early and persistent alterations in offspring adipose RAS components. These changes were dependent on the period of exposure to the maternal high-fat diet, were adipose tissue specific (subcutaneous and retroperitoneal), and were exacerbated by a postnatal high-fat diet. Maternal high-fat diet increased adiposity and blood pressure in offspring, regardless of the period of exposure.

CONCLUSION

These findings suggest that programmed adiposity and the activation of the adipose tissue RAS are associated with hypertension in offspring of obese dams.

Expression of angiotensin II and its receptors in cyclosporine-induced gingival overgrowth

BACKGROUND AND OBJECTIVES

The renin-angiotensin system (RAS) is considered as a hormonal circulatory system involved in maintaining blood pressure, electrolyte and fluid homeostasis. RAS components can be synthesized in local tissues and are found to play a role in gingival overgrowth. The drug-induced gingival overgrowth (DIGO) is a fibrotic condition, which is associated with multiple factors, including inflammation and adverse drug effects such as cyclosporine A. This study was directed forward to the identification of the angiotensinogen, angiotensin II (Ang II) and its receptors AT₁ /AT₂ expression in DIGO tissues and cyclosporine-treated human gingival fibroblast cells.

MATERIAL AND METHODS

Gingival samples were obtained from patients with cyclosporine-induced gingival overgrowth, chronic periodontitis and normal healthy subjects. The total RNA was isolated and reverse transcription-polymerase chain reaction was performed for angiotensinogen, Ang II and AT₁ /AT₂ receptor. Ang II protein was estimated from tissue by enzyme immunoassay. The expression of Ang II and its receptors were also examined in gingival fibroblast cells treated with cyclosporine.

RESULTS

Ang II mRNA and protein expression was significantly higher in patients with DIGO than in patients with periodontitis and healthy subjects. The AT₁ mRNA was expressed more than AT₂ in all examined tissues. In gingival fibroblasts, Ang II and AT₁ expressions were increased with cyclosporine incorporation compared to controls.

CONCLUSION

These results suggest that cyclosporine can modulate local expression of RAS components such as angiotensinogen, Ang II and its receptors in gingival tissues and gingival fibroblast cells.

The adipose tissue renin-angiotensin system and metabolic disorders: a review of molecular mechanisms

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. In this system, angiotensinogen (Agt), the obligate precursor of all bioactive angiotensin peptides, undergoes two enzymatic cleavages by renin and angiotensin converting enzyme (ACE) to produce angiotensin I (Ang I) and angiotensin II (Ang II), respectively. The contemporary view of RAS has become more complex with the discovery of additional angiotensin degradation pathways such as ACE2. All components of the RAS are expressed in and have independent regulation of adipose tissue. This local adipose RAS exerts important auto/paracrine functions in modulating lipogenesis, lipolysis, adipogenesis as well as systemic and adipose tissue inflammation. Mice with adipose-specific Agt overproduction have a 30% increase in plasma Agt levels and develop hypertension and insulin resistance, while mice with adipose-specific Agt knockout have a 25% reduction in Agt plasma levels, demonstrating endocrine actions of adipose RAS. Emerging evidence also points towards a role of RAS in regulation of energy balance. Because adipose RAS is overactivated in many obesity conditions, it is considered a potential candidate linking obesity to hypertension, insulin resistance and other metabolic derangements.

Tumor necrosis factor-{alpha} suppresses angiotensinogen expression through formation of a p50/p50 homodimer in human renal proximal tubular cells

Angiotensinogen (AGT) expression in renal proximal tubular cells (RPTCs) and intrarenal tumor necrosis factor-α (TNF-α) levels are increased in hypertension and renal diseases However, the contribution of TNF-α to AGT expression in RPTCs has not been established. Therefore, the objective of the present study was to determine influence of TNF-α on AGT expression in RPTCs. Human kidney-2 (HK-2) cells, immortalized human RPTCs, were treated with several concentrations of TNF-α up to 24 h. AGT mRNA and protein expression were evaluated by RT-PCR and ELISA, respectively. Activation of nuclear factor-κB (NF-κB) by TNF-α was evaluated by Western blot analysis, immunocytochemistry, and electrophoretic mobility shift assay (EMSA). TNF-α suppressed AGT mRNA expression in a dose- and time-dependent manner. Maximum AGT mRNA reduction was caused by 40 ng/ml of TNF-α (0.52 ± 0.09, ratio to control, at 24 h) and at 24 h (0.66 ± 0.05, ratio to control, by 10 ng/ml TNF-α). TNF-α reduced AGT protein accumulation in the medium between 8 and 24 h (0.62 ± 0.13 by 40 ng/ml TNF-α, ratio to control). TNF-α activated and induced translocalization of p50 and p65, which are NF-κB subunits. Elevated formation of p50/p65 and p50/p50 dimers by TNF-α were observed by EMSA and supershift assay. Gene silencing of p50, but not p65, attenuated the effect of TNF-α on reduction of AGT expression in RPTCs. These results indicate that TNF-α suppresses AGT expression through p50/p50 homodimer formation in human RPTCs, suggesting a possible counteracting mechanism that limits excessive intrarenal AGT production.

Adipose tissue-specific dysregulation of angiotensinogen by oxidative stress in obesity

Adipose tissue expresses all components of the renin-angiotensin system including angiotensinogen (AGT). Recent studies have highlighted a potential role of AGT in adipose tissue function and homeostasis. However, some controversies surround the regulatory mechanisms of AGT in obese adipose tissue. In this context, we here demonstrated that the AGT messenger RNA (mRNA) level in human subcutaneous adipose tissue was significantly reduced in obese subjects as compared with nonobese subjects. Adipose tissue AGT mRNA level in obese mice was also lower as compared with their lean littermates; however, the hepatic AGT mRNA level remained unchanged. When 3T3-L1 adipocytes were cultured for a long period, the adipocytes became hypertrophic with a marked increase in the production of reactive oxygen species. Expression and secretion of AGT continued to decrease during the course of adipocyte hypertrophy. Treatment of the 3T3-L1 and primary adipocytes with reactive oxygen species (hydrogen peroxide) or tumor necrosis factor alpha caused a significant decrease in the expression and secretion of AGT. On the other hand, treatment with the antioxidant N-acetyl cysteine suppressed the decrease in the expression and secretion of AGT in the hypertrophied 3T3-L1 adipocytes. Finally, treatment of obese db/db mice with N-acetyl cysteine augmented the expression of AGT in the adipose tissue, but not in the liver. The present study demonstrates for the first time that oxidative stress dysregulates AGT in obese adipose tissue, providing a novel insight into the adipose tissue-specific interaction between the regulation of AGT and oxidative stress in the pathophysiology of obesity.

IL-6 augments angiotensinogen in primary cultured renal proximal tubular cells

In human kidneys, the mechanisms underlying angiotensinogen (AGT) augmentation by interleukin 6 (IL-6) are poorly understood and the only information available is in HK-2, immortalized human renal proximal tubular epithelial cells. Therefore, the present study was performed to elucidate the effects of IL-6 on AGT expression in primary cultured human renal proximal tubular epithelial cells (RPTEC) after characterization of HK-2 and RPTEC. RPTEC showed low basal AGT mRNA (11+/-1%) and protein (7.0+/-0.9%) expression, high IL-6 receptor (IL-6R) expression (282+/-17%), and low basal NF-kappaB (43+/-7%) and STAT3 (43+/-7%) activities compared to those in HK-2. In RPTEC, AGT mRNA and protein expressions were enhanced by IL-6 (172+/-31% and 378+/-39%, respectively). This AGT augmentation was attenuated by an IL-6R antibody. STAT3 phosphorylation (366+/-55% at 30min) and translocation were enhanced by IL-6. The AGT augmentation was attenuated by a STAT3 inhibitor. These data indicate that IL-6 increases AGT expression via STAT3 pathway in RPTEC.

Localization of the novel angiotensin peptide, angiotensin-(1-12), in heart and kidney of hypertensive and normotensive rats

A low expression of angiotensinogen in the heart has been construed as indicating a circulating uptake mechanism to explain the local effects of angiotensin II on tissues. The recent identification of angiotensin-(1-12) in an array of rat organs suggests this propeptide may be an alternate substrate for local angiotensin production. To test this hypothesis, tissues from 11-wk-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats (n = 14) were stained with purified antibodies directed to the COOH terminus of angiotensin-(1-12). Robust angiotensin-(1-12) staining was predominantly found in ventricular myocytes with less staining found in the medial layer of intracoronary arteries and vascular endothelium. In addition, angiotensin-(1-12) immunoreactivity was present in the proximal, distal, and collecting renal tubules within the deep cortical and outer medullary zones in both strains. Preadsorption of the antibody with angiotensin-(1-12) abolished staining in both tissues. Corresponding tissue measurements by radioimmunoassay showed 47% higher levels of angiotensin-(1-12) in the heart of SHR compared with WKY rats (P < 0.05). In contrast, renal angiotensin-(1-12) levels were 16.5% lower in SHR compared with the WKY rats (P < 0.05). This study shows for first time the localization of angiotensin-(1-12) in both cardiac myocytes and renal tubular components of WKY and SHR. In addition, we show that increased cardiac angiotensin-(1-12) concentrations in SHR is associated with a small, but statistically significant, reduction in renal angiotensin-(1-12) levels.

Effects of central injection of angiotensin-converting-enzyme inhibitor and angiotensin type 1 receptor antagonist on the brain NF-kappaB and AP-1 activities of rats given LPS

Angiotensin II (ANG II) activation of the angiotensin type 1 (AT1) receptor facilitates the production of brain interleukin-1beta (IL-1beta) and contributes to the induction of the fever following the intracerebroventricular (i.c.v.) injection of lipopolysaccharide (LPS). The purpose of the present study was to investigate whether proinflammatory transcription factors [nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1)] contribute to the ANG II-dependent production of cytokines within the brain. Interestingly, we found that a single i.c.v. injection of LPS had no effect on NF-kappaB and AP-1 activities in the hypothalamus, hippocampus, and cerebellum at either 1 or 3 h post-injection (except for a decrease in hypothalamic AP-1 activity at 1 h). Furthermore, both an angiotensin-converting-enzyme (ACE) inhibitor and an AT1 receptor antagonist enhanced (rather than reduced) the NF-kappaB and AP-1 activities in the hippocampus and/or cerebellum of rats given LPS. In contrast, an i.c.v. injection of ANG II increased the NF-kappaB activity in the hypothalamus. These results suggest that while "endogenous" ANG II exerts (via AT1 receptors) inhibitory effects on the activation of transcription factors in the brain of rats given LPS, a large dose of exogenous ANG II produces effects opposite to those induced by the presumably small amount of endogenous ANG II released locally by LPS. Our results seem not to support the idea that NF-kappaB and AP-1 play key roles in the ANG II-induced enhancement of the production of proinflammatory cytokines that is induced by LPS in the rat's brain.

LPS induces permeability injury in lung microvascular endothelium via AT1 receptor

Lipopolysaccharide (LPS) is known to stimulate the circulation and local production of angiotensin II (Ang II). To assess whether Ang II plays a role in LPS-induced acute lung injury, rats were injected with LPS, the microvascular endothelial permeability injury was evaluated by histological changes, increased pulmonary wet/dry weight ratio, and pulmonary microvascular protein leak. Besides, increased rat pulmonary microvascular endothelial cell monolayer permeability coefficient (K(f)) was measured after treatment with LPS and/or Ang II, respectively. LPS/Ang II, treatment resulted in a significant increase in K(f). Ang II cooperates with LPS to further increase K(f). Hence, LPS increases pulmonary microvascular endothelial permeability both in vitro and in vivo. Local lung Ang II was increased in response to LPS challenge, and elevated Ang II ulteriorly exacerbates LPS-induced endothelium injury. [Sar(1),Ile(8)]Ang II, a selective block of Ang II type 1 (AT(1)) receptors, eliminated these changes significantly. Our conclusion is that the LPS-induced lung injury may be mediated by the AT(1) receptor.

Human adipose angiotensinogen gene expression and secretion are stimulated by cyclic AMP via increased DNA cyclic AMP responsive element binding activity

Components of the adipose renin-angiotensin system (RAS) have been suggested as providing a potential path-way linking obesity to hypertension. In adipose cells, the biological responses to beta-adrenergic stimulation are mediated by an increase in intracellular cAMP. Because an association exists among body fat mass, hypertension, and increased sympathetic stimulation, we examined the influence of cAMP on angiotensinogen (ATG) expression and secretion in human adipose tissue and in parallel we studied the DNA binding activity of CRE transcriptional factors. A 24 h exposure to the cAMP analog 8Br-cAMP resulted in significant increases in ATG mRNA levels (+176+/-60%) and protein secretion (+40+/-27%). The ability of 8Br-cAMP to promote ATG gene expression was unaltered by H89, a protein kinase A inhibitor, because H89 per se was found to stimulate ATG mRNA levels and protein secretion. Moreover, 8Br-cAMP stimulated the specific CRE DNA binding activity (+115+/-14%) in human adipocyte nuclear extracts as assessed by electrophoretic mobility shift assays. These results indicate that cAMP upregulates in vitro ATG expression and secretion in human adipose tissue and that the induction in ATG mRNA levels appears to result, at least in part, from positive effects on the DNA binding activity of CRE transcription factors. Further studies are required to determine whether this regulatory pathway is activated in human obesity and to elucidate the importance of adipose ATG to the elevated blood pressure observed in this pathological state.

The effect of central injection of angiotensin-converting enzyme inhibitor and the angiotensin type 1 receptor antagonist on the induction by lipopolysaccharide of fever and brain interleukin-1beta response in rats

We recently reported an involvement of peripheral angiotensin II (ANG II) in the development of both the fever and the peripheral interleukin (IL)-1beta production induced in rats by a systemic injection of lipopolysaccharide (LPS). The present study was performed to investigate whether brain ANG II contributes to the fever and IL-1beta production in the rat brain induced by i.c.v. injection of LPS. LPS (0.2 and 2 microg i.c.v.) induced dose-related fevers and increases in the brain (hypothalamus, hippocampus, and cerebellum) concentrations of IL-1beta. These effects were significantly inhibited by i.c.v. administration of either an angiotensin-converting-enzyme (ACE) inhibitor or an angiotensin type 1 (AT(1)) receptor antagonist. By contrast, the ACE inhibitor had no effect on the IL-1beta (i.c.v.)-induced fever, whereas the AT(1) receptor antagonist enhanced (rather than reduced) it. The AT(1) receptor antagonist had no effect on the brain levels of prostaglandin E(2) in rats given an i.c.v. injection of IL-1beta. These results suggest that in rats, brain ANG II and AT(1) receptors are involved in the LPS-induced production of brain IL-1beta, thus contributing to the fever induced by the presence of LPS within the brain.

The angiotensin II receptor blocker candesartan improves survival and mesenteric perfusion in an acute porcine endotoxin model

BACKGROUND

Blockade of the angiotensin II type 1 (AT1) receptor has been demonstrated to ameliorate splanchnic hypoperfusion in acute experimental circulatory failure. This study focused on hemodynamic changes and survival in pigs treated with AT1 blockade prior to or during acute endotoxinemia.

METHODS

Escherichia coli lipopolysaccharide endotoxin was infused in anesthetized and mechanically ventilated pigs. Systemic, renal, mesenteric and jejunal mucosal perfusion as well as systemic oxygen and acid-base balance were monitored. The selective AT1 receptor blocker candesartan was administered prior to as well as during endotoxinemia. Control animals received the saline vehicle.

RESULTS

Pre-treatment with candesartan resulted in higher survival rate (83%, 10 out of 12 animals) compared with 50% (6 of 12) in control animals and 27% (3 of 11) in animals treated during endotoxinemia. Pre-treatment with candesartan resulted in higher cardiac output, mixed venous oxygen saturation, arterial standard base-excess, portal venous blood flow during endotoxin infusion compared with controls and animals treated during endotoxinemia. No adverse effects were found on neither systemic nor renal circulation.

CONCLUSION

The favorable results of AT1 receptor blockade prior to endotoxinemia are lost when blockade is established during endotoxinemia demonstrating the importance of the renin-angiotensin system and its dynamic involvement in acute endotoxinemic shock.

Insulin resistance and chronic cardiovascular inflammatory syndrome

Insulin resistance is increasingly recognized as a chronic, low-level, inflammatory state. Hyperinsulinemia and insulin action were initially proposed as the common preceding factors of hypertension, low high-density lipoprotein cholesterol, hypertriglyceridemia, abdominal obesity, and altered glucose tolerance, linking all these abnormalities to the development of coronary heart disease. The similarities of insulin resistance with another inflammatory state, atherosclerosis, have been described only in the last few decades. Atherosclerosis and insulin resistance share similar pathophysiological mechanisms, mainly due to the actions of the two major proinflammatory cytokines, TNF-alpha and IL-6. Genetic predisposition to increased transcription rates of these cytokines is associated with metabolic derangement and simultaneously with coronary heart disease. Dysregulation of the inflammatory axis predicts the development of insulin resistance and type 2 diabetes mellitus. The knowledge of how interactions between metabolic and inflammatory pathways occur will be useful in future therapeutic strategies. The effective administration of antiinflammatory agents in the treatment of insulin resistance and atherosclerosis is only the beginning of a promising approach in the management of these syndromes.

The adipose-tissue renin-angiotensin-aldosterone system: role in the metabolic syndrome?

Overfeeding of rodents leads to increased local formation of angiotensin II due to increased secretion of angiotensinogen from adipocytes. Whereas angiotensin II promotes adipocyte growth and preadipocyte recruitment, increased secretion of angiotensinogen from adipocytes also directly contributes to the close relationship between adipose-tissue mass and blood pressure in mice. In contrast, angiotensin II acts as an antiadipogenic substance in human adipose tissue, and the total increase in adipose-tissue mass may be more important in determining human plasma angiotensinogen levels than changes within the single adipocyte. However, as increased local formation of angiotensin II in adipose tissue may be increased especially in obese hypertensive subjects, a contribution of the adipose-tissue renin-angiotensin system to the development of insulin resistance and hypertension is conceivable in humans, but not yet proven. Insulin resistance may be aggravated by the inhibition of preadipocyte recruitment, which results in the redistribution of triglycerides to the liver and skeletal muscle, and blood pressure may be influenced by local formation of angiotensin II in perivascular adipose tissue. Thus, although the mechanisms are still speculative, the beneficial effects of ACE-inhibition and angiotensin-receptor blockade on the development of type 2 diabetes in large clinical trials suggest a pathophysiological role of the adipose-tissue renin-angiotensin system in the metabolic syndrome.

Impact of exercise and angiotensin converting enzyme inhibition on tumor necrosis factor-alpha and leptin in fructose-fed hypertensive rats

The aim of this study was to evaluate the effects of moderate-intensity regular exercise and/or an angiotensin converting enzyme (ACE) inhibition on tumor necrosis factor-alpha (TNF-alpha) and glucose and lipid metabolism parameters. Spontaneously hypertensive rats (SHRs) were fed a fructose-rich diet during 16 weeks of either exercise training (Ex group: 20 m/min, 0% grade, 60 min/day, 5 days/week), administration of an ACE inhibitor (TM group: temocapril, 10 mg/kg/day), or a combination of both (TM+Ex group). The systolic blood pressure was reduced exclusively in the TM and TM+Ex group. Epididymal fat pads (EPI) weighed less in the TM+Ex group than in the single-treatment (TM) group. The serum leptin level was significantly and directly correlated with the EPI weight (p < 0.001). The TNF-alpha content per gram of EPI was the highest in the TM+Ex group. In addition, the EPI TNF-alpha level was negatively correlated with both the EPI weight and the serum leptin level (p < 0.001, respectively). In contrast, the TNF-alpha level of skeletal muscles was identical among the groups. The extensor digitorum longus had a significantly higher abundance of TNF-alpha protein than the soleus muscle. These data indicate that the local TNF-alpha expression is tissue-specific, and that upregulation of TNF-alpha in EPI by exercise training and/or ACE inhibition may have contributed to the reduction in fat cell volume via the induction of apoptosis and/or the regulation of metabolic homeostasis.

Shedding of TNF-alpha receptors, blood pressure, and insulin sensitivity in type 2 diabetes mellitus

Tumor necrosis factor-alpha (TNF-alpha) is increasingly recognized as a key component in the development of insulin resistance and increased blood pressure. In a sample of 368 individuals, the ratio of soluble TNF-alpha receptors (sTNFR2/sTNFR1) correlated positively with systolic and diastolic blood pressure (P < 0.01). This ratio was significantly greater in type 2 diabetic subjects (DM-2) than in type 1 diabetic patients and was greater than in control nondiabetic subjects (P < 0.00001). The TNF-alpha receptor 1 (TNFR1) density in peripheral blood monocytes was similar in DM-2 patients and in nondiabetic subjects. After phorbol 12-myristate 13-acetate, TNFR1 shedding was significantly decreased in DM-2 compared with control subjects, and it was directly associated with insulin sensitivity (r = 0.54, P = 0.03). Serum sTNFR1 concentration was also linked to the vasodilatory response to glyceryltrinitrate (P = 0.01). Conversely, TNF-alpha receptor 2 shedding was negatively associated with insulin sensitivity (r = -0.54, P = 0.03), whereas shedding of L-selectin showed no significant association. After exercise-induced lowering of blood pressure, a parallel decrease in sTNFR2/sTNFR1 was observed in DM-2 patients. Our findings suggest that insulin resistance and blood pressure are linked to altered shedding of TNF-alpha receptors in DM-2. The latter seems reversible and is not genetically determined.

Suppression of endotoxin-induced renal tumor necrosis factor-alpha and interleukin-6 mRNA by renin-angiotensin system inhibitors

The present study was designed to clarify the role of angiotensin II (Ang II) in modulating renal tumor necrosis factor (TNF)-alpha and interleukin-6 (IL-6) production and to investigate the effect of one dose of Ang II inhibitor on cytokines production following lipopolysaccharide (LPS) to cause endotoxemia. Two studies were performed: 1) Ang II was infused intravenously at a rate of 0.2 microg/kg per minute for 4 h in rats and then kidneys were collected to assay TNF-alpha and IL-6 mRNA levels; 2) Four-week-old Wistar rats pre-treated with angiotensin-converting enzyme inhibitor, enalapril, or type I Ang II-receptor antagonist, TCV-116, were injected with LPS (0.1, 0.5, 1.0 mg, i.p.), and then 2 or 4 h later, kidneys were collected to assay TNF-alpha, IL-6, renin and angiotensinogen mRNA levels. After a 4-h intravenous infusion of Ang II, renal TNF-alpha or IL-6 mRNA level significantly increased 1.9-fold or 2.1-fold (each P<0.05) to the control level, respectively. LPS stimulated TNF-alpha, IL-6 and angiotensinogen mRNA levels in the kidney but in rats given enalapril or TCV-116, LPS-induced IL-6 and TNF-alpha mRNA levels were completely suppressed (each P<0.05). This suggests that a single dose of renin-angiotensin system inhibitor suppressed renal IL-6 and TNF-alpha production and may prevent cytokine-induced renal damage during endotoxemia.

Tumor necrosis factor-alpha--308 G/A polymorphism in obese Caucasians

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) is expressed primarily in adipocytes, and elevated levels of this cytokine have been linked to obesity and insulin resistance. Recently, the A allele of a polymorphism in the 5'-flanking region of the TNF-alpha gene (G-308A) has been reported to be more frequent in obese than in lean subjects and has also been associated with increased expression of this cytokine in fat tissue and influences fat mass and insulin resistance. We, therefore, examined the relationship between this variant and obesity in a German Caucasian population.

SUBJECTS AND METHODS

We genotyped 176 index subjects recruited within the framework of the BErG (Berlin Ernährung Geschwister)- Study for the TNF-alpha-G-308A polymorphism. Subjects were characterized for weight, height, waist and hip circumference, body mass index (BMI), body composition, glucose tolerance, leptin and angiotensinogen levels.

RESULTS

The frequency of the -308A allele (0.18) was similar to that reported previously and genotype distribution was in Hardy-Weinberg equilibrium (GG, n=118; GA, n=53; AA, n=5). There was a significant difference in allele frequencies of the polymorphism by BMI quartiles (I,<27.3 kg/m2; II, 27.3-31.9 kg/m2; III, 31.9-36.5 kg/m2; IV,>36.5 kg/m2, in each quartile n=44) with -308A allele carriers having a higher BMI than G allele carriers (P=0.013). Despite previous smaller studies that have related insulin resistance to the G-308A polymorphism, we found no relationship between glucose and insulin response during an oral glucose tolerance test (OGTT) and the polymorphism. Furthermore, none of the plasma parameters were related to the polymorphism.

CONCLUSION

Our findings support the hypothesis that the G-308A polymophism of the TNF-alpha gene is associated with BMI. The G-308A polymorphism may, therefore, represent a genetic marker for increased susceptibility for obesity in Caucasians.

Circulating tumor necrosis factor-alpha concentrations in a native Canadian population with high rates of type 2 diabetes mellitus

Recent research suggests that tumor necrosis factor-alpha (TNF alpha) may play an important role in obesity-associated insulin resistance and diabetes. We studied the relationship between TNF alpha and the anthropometric and physiological variables associated with insulin resistance and diabetes in an isolated Native Canadian population with very high rates of type 2 diabetes mellitus (DM). A stratified random sample (n = 80) of participants was selected from a population-based survey designed to determine the prevalence of type 2 DM and its associated risk factors. Fasting blood samples for glucose, insulin, triglyceride, leptin, and TNF alpha were collected; a 75-g oral glucose tolerance test was administered, and a second blood sample was drawn after 120 min. Insulin resistance was estimated using the homeostasis assessment (HOMA) model. Systolic and diastolic blood pressure (BP), height, weight, and waist and hip circumferences were determined, and percent body fat was estimated using biological impedance analysis. The relationship between circulating concentrations of TNF alpha and the other variables was assessed using Spearman correlation coefficients, analysis of covariance, and multiple linear regression. The mean TNF alpha concentration was 5.6 pg/mL (SD = 2.18) and ranged from 2.0-12.9 pg/mL, with no difference between men and women (P = 0.67). There were moderate, but statistically significant, correlations between TNF alpha and fasting insulin, HOMA insulin resistance (HOMA IR) waist circumference, fasting triglyceride, and systolic BP (r = 0.23-0.34; all P < 0.05); in all cases, coefficients for females were stronger than those for males. Individuals with normal glucose tolerance had lower log TNF alpha concentrations than those with impaired glucose tolerance or type 2 DM (both P = 0.03, adjusted for age and sex), although differences were not significant after adjustment for HOMA IR (both P > 0.25). Regression analysis indicated that log HOMA IR and log systolic BP were significant independent contributors to variations in log TNF alpha concentration (model r2 = 0.32). We conclude that in this homogeneous Native Canadian population, circulating TNF alpha concentrations are positively correlated with insulin resistance across a spectrum of glucose tolerance. The data suggest a possible role for TNF alpha in the pathophysiology of insulin resistance.

Activation of angiotensinogen gene in cardiac myocytes by angiotensin II and mechanical stretch

Circulating and cardiac renin-angiotensin systems (RAS) play important roles in the development of cardiac hypertrophy. Mechanical stretch of cardiac myocytes induces secretion of ANG II and evokes hypertrophic responses. Angiotensinogen is a unique substrate of the RAS. This study was performed to examine the regulation of the angiotensinogen gene in cardiac myocytes in response to ANG II and stretch. ANG II and stretch significantly increased the levels of angiotensinogen mRNA in cardiac myocytes. Actinomycin D completely inhibited ANG II- and stretch-mediated increases in angiotensinogen mRNA. Although CV-11974 abolished ANG II-mediated increases in mRNA level and promoter activity of the angiotensinogen gene, the inhibition of stretch-mediated activation by CV-11974 was significant but not complete. These results indicate that ANG II activates transcription of the angiotensinogen gene exclusively via ANG II type 1-receptor pathway and that stretch activates such transcription mainly via the same pathway in cardiac myocytes. Furthermore, factors other than ANG II may also be involved in stretch-mediated activation of the angiotensinogen gene in cardiac myocytes.

gp130 is involved in stretch-induced MAP kinase activation in cardiac myocytes

We have recently reported that mitogen activated protein kinase (MAP kinase) is activated by the stretch of the cultured cardiac myocytes in the angiotensin II deficient state in the angiotensinogen-deficient mice (Atg-/-), suggesting that factors other than the cardiac renin-angiotensin system are involved in the stretch-induced MAP kinase activation. We examined the contribution of cytokines using RX435, an anti-gp130 antibody. Leukemia inhibitory factor, which is one of the cytokines and has the common receptor subunit gp130, activated MAP kinase and the response was completely blocked by pretreatment of the Atg-/- cardiac myocytes with RX435. RX435 pretreatment greatly reduced stretch-induced activation of MAP kinase in Atg-/- cardiac myocytes. Interestingly, the same results were obtained in the cardiac myocytes of control mice. These results suggest that cytokine-gp130 may play a role in the stretch-induced MAP kinase activation independently of Ang II in cardiac myocytes.