Selective aspects of the insulin resistance syndrome

Sex and body-type interactions in the regulation of renal sodium transporter levels, urinary excretion, and activity in lean and obese zucker rats

BACKGROUND

Female humans and rodents are relatively protected against the development of hypertension and renal disease. Whether this protection is modified during insulin resistance and obesity, however, is not known.

OBJECTIVE

Because renal sodium reabsorption has a central role in determining blood pressure, we hypothesized that lean female rats would bave reduced renal expression, activity, and urinary excretion of 8 major sodium transporters/channels.

METHODS

Lean and obese, male and female Zucker rats (n = 4-8 per group) were fed progressively higher levels of dietary NaCl over a period of 54 days. Urinary excretion of renal sodium transport proteins was determined for 3 different dietary levels (0.04%, 0.4%, and 4%) of NaCl. With the high-NaCl diet, natriuretic responses to benzamil, furosemide, and thiazide were used as in vivo markers for activity of the epithelial sodium channel (ENaC), the bumetanide-sensitive Na-K-2C1 cotransporter (NKCC2), and the thiazide-sensitive NaCl cotransporter (NCC), respectively.

RESULTS

Female rats (of both body types) had lower plasma renin activity and insulin levels than their male counterparts. Likewise, immunoblotting revealed female rats had increased whole kidney abundance of NCC and of the alpha, beta, and gamma subunits of ENaC, as well as decreased abundance of the type 3 sodium hydrogen exchanger (NHE3), type 2 sodium phosphate cotransporter (NaPi-2), and alpha-1 sodium-potassium-adenosine triphosphatase (Na-K-ATPase), compared with males. Obese rats had reduced levels of NKCC2, NHE3, and gamma-ENaC, but higher levels of NaPi-2 and NCC. Urine excretion of sodium transporters in lean female rats was nearly undetectable, whereas obese rats of both sexes excreted markedly more NKCC2 and NCC, which agreed with greater natriuretic responses to thiazide and furosemide.

CONCLUSIONS

Obese female rats are similar to lean female rats with regard to the sex-distinct pattern of renal sodium transporters. However, obese female rats are more like obese male rats with regard to increased natriuretic response tofurosemide and thiazide, and to urine excretion of several transporters including NCC. Our results suggest that, with obesity, there is some loss of the protective female advantage.

Should we quantify insulin resistance in patients with renal disease?

Cardiovascular disease is a major cause of morbidity and mortality in dialysis patients. Vascular disease develops before the initiation of dialysis, and it is now recognized that chronic kidney disease (CKD) is an independent risk factor for cardiovascular disease. Death from cardiovascular disease is a more common endpoint of CKD than progression to dialysis. There are multiple mechanisms that contribute to the increased vascular risk of CKD, one of which is the presence of insulin resistance (IR). CKD is characterised by many features of the metabolic syndrome, and features of IR are also observed in dialysis and transplant patients. IR may be quantified by several different methods. One such method is homeostatic model assessment (HOMA) technique, which derives a measurement of IR from fasting plasma glucose and insulin concentrations. The HOMA index has been demonstrated to be an independent predictor of survival in dialysis patients. CKD is characterised by a chronic inflammatory response and abnormalities in the production and regulation of adipose tissue derived proteins, which may contribute to the development of IR. There are a range of interventions including diet and exercise programmes or medications that may influence IR; however, the impact of these interventions in the context of CKD has not been systematically evaluated.

The management of short-term intestinal failure in obese patients

The prevalence of obesity in the general population is high and it is inevitable that artificial feeding will be needed from time to time in the obese patient, particularly in the critical care setting. Against a background of generous endogenous stores of energy as adipose tissue and the ability of obese individuals to survive starvation longer than non-obese individuals, emphasis is placed on preserving lean body mass and optimizing physiological function. Insulin resistance is typical of the obese individual and is exacerbated by stress; overfeeding is dangerous, particularly if it results in hyperglycaemia. Refeeding syndrome also has to be avoided. Weight may be difficult to measure and lean body mass difficult to assess. Calculation of energy requirements is therefore problematic in practice in the obese individual and there is substantial evidence from controlled clinical trials of the safety of feeding at or below resting energy expenditure. If this approach is taken it is wise to provide a more generous than normal protein intake and to beware of patients with a very high baseline urinary N excretion.

Acute and "chronic" phase reaction-a mother of disease

The world is increasingly threatened by a global epidemic of chronic diseases. Almost half of the global morbidity and almost two thirds of global mortality is due to these diseases-approximately 35 million die each year from chronic diseases. And they continue to increase. Increasing evidence suggest that these diseases are associated with lifestyle, stress, lack of physical exercise, over-consumption of calorie-condensed foods rich in saturated fat, sugar and starch, but also under-consumption of antioxidant-rich fruits and vegetables. As a result the function of the innate immune system is severe impaired. This review discusses the changes induced in response to mental and physical stress and their association with the subsequent development of metabolic syndrome, and its association with various chronic diseases. The endothelial cells and their function appears to be of great importance, and the function of their cellular membranes of special importance to the function of the underlying cells; their ability to obtain nutrients and antioxidants and to eliminate waste products. The abdominal adipocytes seen to play a key role, as they have the ability to in stressful situations release much of proinflammatory cytokines, PAI-1 and free fatty acids compared to elsewhere in the body. The load on the liver of these various substances in often of greater magnitude than the liver can handle. Some of the most common chronic diseases and their potential association with acute and "chronic" phase response, and with metabolic syndrome are discussed separately. The need for studies with lifestyle modifications is especially emphasized.

What is the relationship between exercise and metabolic abnormalities? A review of the metabolic syndrome

Prevention of the metabolic syndrome and treatment of its main characteristics are now considered of utmost importance in order to combat the epidemic of type 2 diabetes mellitus and to reduce the increased risk of cardiovascular disease and all-cause mortality. Insulin resistance/hyperinsulinaemia are consistently linked with a clustering of multiple clinical and subclinical metabolic risk factors. It is now widely recognised that obesity (especially abdominal fat accumulation), hyperglycaemia, dyslipidaemia and hypertension are common metabolic traits that, concurrently, constitute the distinctive insulin resistance or metabolic syndrome. Cross-sectional and prospective data provide an emerging picture of associations of both physical activity habits and cardiorespiratory fitness with the metabolic syndrome. The metabolic syndrome, is a disorder that requires aggressive multi-factorial intervention. Recent treatment guidelines have emphasised the clinical utility of diagnosis and an important treatment role for 'therapeutic lifestyle change', incorporating moderate physical activity. Several previous narrative reviews have considered exercise training as an effective treatment for insulin resistance and other components of the syndrome. However, the evidence cited has been less consistent for exercise training effects on several metabolic syndrome variables, unless combined with appropriate dietary modifications to achieve weight loss. Recently published randomised controlled trial data concerning the effects of exercise training on separate metabolic syndrome traits are evaluated within this review. Novel systematic review and meta-analysis evidence is presented indicating that supervised, long-term, moderate to moderately vigorous intensity exercise training, in the absence of therapeutic weight loss, improves the dyslipidaemic profile by raising high density lipoprotein-cholesterol and lowering triglycerides in overweight and obese adults with characteristics of the metabolic syndrome. Lifestyle interventions, including exercise and dietary-induced weight loss may improve insulin resistance and glucose tolerance in obesity states and are highly effective in preventing or delaying the onset of type 2 diabetes in individuals with impaired glucose regulation. Randomised controlled trial evidence also indicates that exercise training decreases blood pressure in overweight/obese individuals with high normal blood pressure and hypertension. These evidence-based findings continue to support recommendations that supervised or partially supervised exercise training is an important initial adjunctive step in the treatment of individuals with the metabolic syndrome. Exercise training should be considered an essential part of 'therapeutic lifestyle change' and may concurrently improve insulin resistance and the entire cluster of metabolic risk factors.

A dietary and exercise intervention slows menopause-associated progression of subclinical atherosclerosis as measured by intima-media thickness of the carotid arteries

OBJECTIVES

The object of this study was to assess the effects of menopause and a diet/exercise intervention on subclinical atherosclerosis progression.

BACKGROUND

Subclinical atherosclerosis has been linked to higher coronary heart disease and stroke rates and is greater among postmenopausal women according to cross-sectional analyses. Whether menopause is associated with an accelerated progression of subclinical disease is unknown, as is the extent to which lifestyle intervention can alter the course of progression.

METHODS

Intima-media thickness (IMT) measures of the common carotid artery (CCA), internal carotid artery (ICA), and bulb segments of the carotid arteries were measured twice during the course of 4 years in 353 women from the Women's Healthy Lifestyle Project, a dietary and exercise clinical trial designed to prevent adverse risk factor changes through the menopause. A third measure was obtained 2.5 years later for 113 women.

RESULTS

The progression of IMT was observed for the average of all segments (AVG), the CCA, and the bulb (0.007 mm/year, 0.008 mm/year, and 0.012 mm/year; p < 0.01 for all), but not for the ICA. Among controls, menopause was associated with accelerated IMT progression (0.003 mm/year for premenopausal women vs. 0.008 mm/year for perimenopausal/postmenopausal women for AVG IMT; p = 0.049). Additionally, among the 160 perimenopausal/postmenopausal women, the intervention slowed IMT progression (0.008 mm/year for the control group vs. 0.004 mm/year for the intervention group for AVG IMT; p = 0.02). Similar results were found for the CCA and bulb segments.

CONCLUSIONS

These data demonstrate that the menopause transition is associated with accelerated subclinical atherosclerosis progression and that a diet/exercise intervention slows menopause-related atherosclerosis progression.

Prophecies of childhood: how children's social environments and biological propensities affect the health of populations

During the past decade, important steps have been taken globally to improve the status of children. Concurrently, significant advances have been made toward understanding how child development is shaped by transactions between biological and environmental influences. Despite such advances, ongoing adversities in the lives of children worldwide undermine the development of individuals and thus the health of nations. The primary tenets of this paper are that: children continue to suffer a disproportionate share of the world's adversities; exposure to early adversities is not only associated with increased morbidity during childhood, but also across the lifespan; and recent advances in understanding the operation and ontogeny of stress-response systems can help explain how adversity is translated into lifelong effects on health. Acknowledging the long-lasting sequelae of childhood adversity has important implications for public health and society.

Genotype, obesity and cardiovascular disease--has technical and social advancement outstripped evolution?

Teleologically, our ancestors were highly adapted hunter-gatherers. In recent history, the environment in which Homo sapiens exists has altered drastically and humans are exposed to environments for which the hunter-gatherer genotype is ill-suited. The adoption of a sedentary Western lifestyle, and the case of obtaining food of a high calorific content imposed upon a thrifty genotype, have resulted in the current global epidemic of obesity, Type 2 diabetes and the Metabolic Syndrome. The ramification of this epidemic is that cardiovascular disease is becoming a global healthcare problem, which will have its greatest impact on the developing nations. A global strategy is required to reduce the impact of the Western lifestyle on the health of developing nations and prevent obesity and Type 2 diabetes. Such an approach needs to be culturally sensitive, integrated, and multidisciplinary and involve a range of interventions that work at the individual and community levels. If lifestyle measures fail, then pharmacological intervention may be necessary. For this, novel agents such as dual PPARalpha/gamma agonists may be the therapy of the future.

Differential transcriptional regulation by human immunodeficiency virus type 1 and gp120 in human astrocytes

Astrocytes may be infected with the human immunodeficiency virus type 1 (HIV-1) or exposed to the HIV protein gp120, yet their role in the pathogenesis of HIV dementia is largely unknown. To characterize the effects of HIV on astrocytic transcription, microarray analysis and ribonuclease protection assays (RPA) were performed. Infection of astrocytes by HIV or treatment with gp120 had differential and profound effects on gene transcription. Of the 1153 oligonucleotides on the immune-based array, the expression of 108 genes (53 up; 55 down) and 82 genes (32 up; 50 down) were significantly modulated by gp120 and HIV infection respectively. Of the 1153 oligonucleotides on the neuro-based array, 58 genes (25 up; 33 down) and 47 genes (17 up; 30 down) were significantly modulated by gp120 and HIV infection respectively. Chemokine and cytokine induction occurred predominantly by HIV infection, whereas gp120 had no significant effect. These results were confirmed by RPA. The authors conclude that profound alterations of astrocytic function occur in response to HIV infection or interaction with viral proteins, suggesting that astrocytes may play an important role in the pathogenesis of HIV dementia.

A novel antiinflammatory maintains glucocorticoid efficacy with reduced side effects

Glucocorticoids (GCs) are commonly used to treat inflammatory disease; unfortunately, the long-term use of these steroids leads to a large number of debilitating side effects. The antiinflammatory effects of GCs are a result of GC receptor (GR)-mediated inhibition of expression of proinflammatory genes as well as GR-mediated activation of antiinflammatory genes. Similarly, side effects are most likely due to both activated and repressed GR target genes in affected tissues. An as yet unachieved pharmaceutical goal is the development of a compound capable of separating detrimental side effects from antiinflammatory activity. We describe the discovery and characterization of AL-438, a GR ligand that exhibits an altered gene regulation profile, able to repress and activate only a subset of the genes normally regulated by GCs. When tested in vivo, AL-438 retains full antiinflammatory efficacy and potency comparable to steroids but its negative effects on bone metabolism and glucose control are reduced at equivalently antiinflammatory doses. The mechanism underlying this selective in vitro and in vivo activity may be the result of differential cofactor recruitment in response to ligand. AL-438 reduces the interaction between GR and peroxisomal proliferator-activated receptor gamma coactivator-1, a cofactor critical for steroid-mediated glucose up-regulation, while maintaining normal interactions with GR-interacting protein 1. This compound serves as a prototype for a unique, nonsteroidal alternative to conventional GCs in treating inflammatory disease.

Inflammatory status and insulin resistance

PURPOSE OF REVIEW

The inflammatory response is essential in the response to pathogens. TNF-alpha, IL-1 and IL-6 are key mediators of the response. They initiate metabolic changes to provide nutrients for the immune system, from host tissues. These changes include hyperlipidemia and increased gluconeogenesis. Insulin resistance and disordering of lipid metabolism occur in obesity, diabetes mellitus, atherosclerosis. This review examines recent research that links inflammation to insulin insensitivity.

RECENT FINDINGS

Population studies show a strong association between indices of inflammation, and abnormal lipid and carbohydrate metabolism, obesity and atherosclerosis. TNF-alpha is produced, by cells of the immune system and by adipocytes. It may provide the link between inflammation and insulin sensitivity. TNF-alpha results in insulin insensitivity, indirectly by stimulating stress hormone production and directly by sustained induction of SOCS-3 which decreases insulin-induced insulin receptor substrate 1 (IRS1) tyrosine phosphorylation and its association with the p85, regulatory subunit of phosphatidylinositol-3 kinase; and by negative regulation of PPAR gamma. Adipose tissue produces both TNF-alpha and leptin. Production of the latter relates positively to adipose tissue mass and through its actions on immune function exerts a pro-inflammatory influence.

SUMMARY

Recent studies on diseases which involve insulin insensitivity (e.g. obesity, type 2 diabetes and atherosclerosis) also show increased cytokine production and markers of inflammation. Evidence at present favours chronic inflammation as a trigger for chronic insulin insensitivity, rather than the reverse situation.

Part 1. Uric acid and losartan

PURPOSE OF REVIEW

To characterize the mechanism and clinical impact of the angiotensin-receptor blocker losartan on both renal uric acid handling and thereby serum uric acid.

RECENT FINDINGS

Losartan effect on serum uric acid has been demonstrated at various stages of renal failure including most recently observations obtained in end-stage renal disease patients. Other angiotensin-receptor blockers do not alter renal handling of uric acid. The uricosuria, which accompanies losartan administration, has not been associated with adverse renal consequences, in part, because of the increase in urinary pH that follows its administration.

SUMMARY

Hyperuricemia is closely linked to both hypertension and cardiovascular disease. The development of hyperuricemia and its persistence are clearly renal processes. Likewise, the correction of hyperuricemia is often accomplished by increasing its renal excretion. A number of medications, by way of varying mechanisms, can alter renal urate handling and thereby influence serum uric acid values. Most recently, the angiotensin-receptor blocker losartan has been shown to reduce serum uric acid. The mechanism of this process relates to losartan alone and does not involve the E-3174 metabolite of this compound. This probenecid-like effect of losartan occurs shortly after drug administration, and is both transient and dose-dependent. This property of losartan, touted by some as a meaningful pharmacological distinction among the angiotensin-receptor blockers, remains to be proved, since, to date, the hypothesis that a reduction in serum uric acid alters the natural history of cardiovascular disease has not been formally tested.

Decreases in serum uric acid by amelioration of insulin resistance in overweight hypertensive patients: effect of a low-energy diet and an insulin-sensitizing agent

BACKGROUND

Hyperuricemia and hyperinsulinemia/insulin resistance are commonly seen in obese subjects and hypertensive patients. To clarify whether the insulin resistance plays a role in hyperuricemia, we investigated alterations in serum uric acid (UA) concentrations during treatment with a low-energy diet or an insulin-sensitizing agent in overweight hypertensive patients.

METHODS

Twenty-eight overweight hypertensive patients (14 men and 14 women, mean age 61 +/- 2 years) were assigned to a weight reduction program with a low-energy diet (3360 kJ/day for 3 weeks, n = 14) and to treatment with troglitazone (200 mg twice daily for 8 weeks, n = 14). Measurements of body weight, blood pressure (BP), serum UA, and a 75-g oral glucose tolerance test were performed at baseline and the end of the intervention periods.

RESULTS

Body weight and BP decreased significantly in the diet group but not in the troglitazone group at the end of the intervention periods. Levels of blood glucose, plasma insulin, and homeostasis model assessment-insulin resistance index (HOMA-R) improved similarly in the two groups. Serum UA concentration decreased by treatment both in the diet (0.4 +/- 0.2 mg/dL, P < .05) and troglitazone groups (1.0 +/- 0.2 mg/dL, P < .001).

CONCLUSIONS

The amelioration of insulin resistance by either a low-energy diet or troglitazone decreased the serum UA level in overweight hypertensive patients. Insulin resistance or hyperinsulinemia, independent of body weight and BP, may play an important role in UA metabolism in multiple risk factor syndrome.

Role of dopamine receptors in the kidney in the regulation of blood pressure

Regulation by dopamine of cardiovascular function, renal function and systemic blood pressure regulation is multifaceted. Each of the five dopamine receptor subtypes participates in the regulation of blood pressure by mechanisms specific for the subtype. Some receptors regulate blood pressure by influencing the central or peripheral nervous system; others influence epithelial transport and regulate the secretion and receptors of several humoral agents. The D1, D3, and D4 receptors interact with the renin-angiotensin system, while the D2 and D5 receptors interact with the sympathetic nervous system to regulate blood pressure.