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In order to better understand the mechanisms leading to insulin resistance, the number of fat tissue insulin receptors, their affinity and insulin receptor protein in rats with monosodium glutamate-induced obesity were studied. Obese rats displayed significantly lower number of insulin receptors with high affinity. Surprisingly, the amount of insulin receptor protein was significantly elevated in these animals. The same relations have been already reported for angiotensin II binding and AT1 receptor protein in the same model of obesity. Therefore we suggest an existence of general defect of adipocyte cell membrane in monosodium glutamate-induced obesity characterized by the presence of high quantity of impaired receptor protein.
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PMID:Low number of insulin receptors but high receptor protein content in adipose tissue of rats with monosodium glutamate-induced obesity. 1511 27

More than 20 syndromes among the significant and increasing number of degenerative diseases of neuronal tissues are known to be associated with diabetes mellitus, increased insulin resistance and obesity, disturbed insulin sensitivity, and excessive or impaired insulin secretion. This review briefly presents such syndromes, including Alzheimer disease, ataxia-telangiectasia, Down syndrome/trisomy 21, Friedreich ataxia, Huntington disease, several disorders of mitochondria, myotonic dystrophy, Parkinson disease, Prader-Willi syndrome, Werner syndrome, Wolfram syndrome, mitochondrial disorders affecting oxidative phosphorylation, and vitamin B(1) deficiency/inherited thiamine-responsive megaloblastic anemia syndrome as well as their respective relationship to malignancies, cancer, and aging and the nature of their inheritance (including triplet repeat expansions), genetic loci, and corresponding functional biochemistry. Discussed in further detail are disturbances of glucose metabolism including impaired glucose tolerance and both insulin-dependent and non-insulin-dependent diabetes caused by neurodegeneration in humans and mice, sometimes accompanied by degeneration of pancreatic beta-cells. Concordant mouse models obtained by targeted disruption (knock-out), knock-in, or transgenic overexpression of the respective transgene are also described. Preliminary conclusions suggest that many of the diabetogenic neurodegenerative disorders are related to alterations in oxidative phosphorylation (OXPHOS) and mitochondrial nutrient metabolism, which coincide with aberrant protein precipitation in the majority of affected individuals.
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PMID:Neurodegenerative disorders associated with diabetes mellitus. 1517 61

The renin-angiotensin system plays a critical role in the pathogenesis of obesity, obesity-associated hypertension, and insulin resistance. However, the biological actions of angiotensin II (AII) on insulin sensitivity remain controversial. Because angiotensinogen and AII receptors are expressed on adipose tissue, we investigated the effect of AII on the insulin sensitivity of isolated rat adipocytes. The results of a receptor binding assay showed the maximal AII binding capacity of adipocytes to be 8.3 +/- 0.9 fmol/7 x 10(6) cells and the dissociation constant to be 2.72 +/- 0.11 nM. Substantial expression of both type 1 and 2 AII (AT1 and AT2) receptors was detected by RT-PCR. AII had no effect on basal glucose uptake, but significantly potentiated insulin-stimulated glucose uptake; this effect was abolished by the AT1 antagonist, losartan. In addition, AII did not alter the insulin binding capacity of adipocytes, but increased insulin-stimulated tyrosine phosphorylation of the insulin receptor beta-subunit, Akt phosphorylation, and translocation of glucose transporter 4 to the plasma membrane. AII potentiated insulin-stimulated glucose uptake through the AT1 receptor and by alteration of the intracellular signaling of insulin. Intraperitoneal injection of Sprague Dawley rats with AII increased insulin sensitivity in vivo. In conclusion, we have shown that AII enhances insulin sensitivity both in vitro and in vivo, suggesting that dysregulation of the insulin-sensitizing effect of AII may be involved in the development of insulin resistance.
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PMID:Angiotensin II enhances insulin sensitivity in vitro and in vivo. 1570 82

Increased renal sodium retention is considered a major risk factor contributing to hypertension associated with chronic hyperinsulinemia and obesity. However, the molecular mechanism involved is not understood. The present study investigates the effect of insulin treatment on AT1 receptor expression and ANG II-induced stimulation of Na/H exchanger (NHE) and Na-K-ATPase (NKA) in opossum kidney (OK) cells, a proximal tubule cell line. The presence of the AT1 receptors in OK cells was confirmed by the specific binding of 125I-sar-ANG II and by detecting approximately 43-kDa protein on Western blot analysis with AT1 receptor antibody and blocking peptide as well as by expression of AT1 receptor mRNA as determined by RT-PCR. Insulin treatment (100 nM for 24 h) caused an increase in 125I-sar-ANG II binding, AT1 receptor protein content, and mRNA levels. The whole cell lysate and membrane showed similar insulin-induced increase in the AT1 receptor protein expression, which was blocked by genistein (100 nM), a tyrosine kinase inhibitor, and cycloheximide (1.5 microg/ml), a protein synthesis inhibitor. Determination of ethyl isopropyl amiloride-sensitive 22Na+ uptake, a measure of the NHE activity, revealed that ANG II (1-100 pM)-induced stimulation of NHE in insulin-treated cells was significantly greater than in the control cells. Similarly, ANG II (1-100 pM)-induced stimulation of ouabain-sensitive 86Rb+ uptake, a measure of NKA activity in insulin-treated cells, was significantly greater than in the control cells. ANG II stimulation of both the transporters was blocked by AT1 receptor antagonist losartan, suggesting the involvement of AT1 receptors. Thus chronic insulin treatment causes upregulation of AT1 receptors, which evoked ANG II-induced stimulation of NHE and NKA. We propose that insulin-induced increase in the renal AT1 receptor function serves as a mechanism responsible for the increased renal sodium reabsorption and thus may contribute to development of hypertension in conditions associated with hyperinsulinemia.
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PMID:Insulin treatment enhances AT1 receptor function in OK cells. 1571 8

Breast cancer is the most frequent cancer in women and represents the second leading cause of cancer death among women (after lung cancer). The etiology of breast cancer is still poorly understood with known breast cancer risk factors explaining only a small proportion of cases. Risk factors that modulate the development of breast cancer discussed in this review include: age, geographic location (country of origin) and socioeconomic status, reproductive events, exogenous hormones, lifestyle risk factors (alcohol, diet, obesity and physical activity), familial history of breast cancer, mammographic density, history of benign breast disease, ionizing radiation, bone density, height, IGF- 1 and prolactin levels, chemopreventive agents. Additionally, we summarized breast cancer risk associated with the following genetic factors: breast cancer susceptibility high-penetrance genes (BRCA1, BRCA2, p53, PTEN, ATM, NBS1 or LKB1) and low-penetrance genes such as cytochrome P450 genes (CYP1A1, CYP2D6, CYP19), glutathione S-transferase family (GSTM1, GSTP1), alcohol and one-carbon metabolism genes (ADH1C and MTHFR), DNA repair genes (XRCC1, XRCC3, ERCC4/XPF) and genes encoding cell signaling molecules (PR, ER, TNFalpha or HSP70). All these factors contribute to a better understanding of breast cancer risk. Nonetheless, in order to evaluate more accurately the overall risk of breast tumorigenesis, novel genetic and phenotypic traits need to be identified.
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PMID:Understanding breast cancer risk -- where do we stand in 2005? 1578 78

Breast and ovarian cancers are the second and fifth leading causes of cancer death, respectively, among women in the United States. Individuals with breast cancer have a 20--30% chance of having at least one relative with the disease. However, only 5--10% of the cases are a direct result of germline mutations in highly penetrable genes, such as BRCA1 and BRCA2 (BRCA1/2) as well as genes TP53 and PTEN. Since 1996, genetic testing for these mutations has been clinically available. A strategy for the management of women at increased familial risk of breast and ovarian cancers is described, which includes genetic assessment, chemoprevention, radiologic screening, and clinical and self-examination. Genetic testing should occur within a cancer genetic clinic after genetic counseling. A blood sample allows determination of the presence of the BRCA1 and BRCA2 genes, the TP53 gene, the PTEN gene, and the ATM gene. Tumor examination has identified a growth factor receptor gene, human epidermal growth factor receptor (HER-2). With regard to diet and lifestyle, women at increased risk of breast cancer could be advised to reduce dietary fat, avoid obesity, decrease alcohol consumption, and take regular exercise. Although chemoprotection is a valuable consideration, it is important to emphasize that the use of Tamoxifen in BRCA1 and BRCA2 mutation carriers is not established, nor is the optimum duration of benefit. An overview of the main outcomes of the current published studies confirms a 38% decrease in breast cancer incidence with Tamoxifen but recommends its use be restricted to women at high risk of breast cancer and low risk for potential side effects. The role of bilateral risk-reducing mastectomy or prophylactic mastectomy has been controversial for several reasons, including the psychosocial significance of the breast in Western cultures, the wide acceptance of breast conservation in surgery for early breast cancer, and the previous lack of data on its efficacy. The surgical procedure should aim to remove substantially all at-risk breast tissue. However, there is a balance between reduction of cancer risk and cosmetic outcome. Bilateral prophylactic oophorectomy can significantly decrease ovarian cancer risk in women who carry BCRA1 mutations. Oophorectomy lowers the risk of breast cancer, even in women who have previously used hormone replacement therapy. There are no published randomized controlled trials examining the effectiveness of mammographic screening in women under 50 years of age with a family history of breast cancer. However, the published studies do suggest that mammographic screening of a high-risk group of women under 50 years of age may detect cancer at a rate equivalent to that seen in women 10 years older with normal risk. Other initial studies also support MRI as having a greater sensitivity than mammography in high-risk women. Breast clinical and self-examination is often advocated, but its effectiveness is unproved, and only one randomized study has been undertaken in women at risk. On the basis of this study as well as one nonrandomized study, it can be concluded that clinical examination as well as mammography are essential in detecting breast cancer. under 50 years of age with a family history of breast cancer. However, the published studies do suggest that mammographic screening of a high-risk group of women under 50 years of age may detect cancer at a rate equivalent to that seen in women 10 years older with normal risk. Other initial studies also support MRI as having a greater sensitivity than mammography in high-risk women. Breast clinical and self-examination is often advocated, but its effectiveness is unproved, and only one randomized study has been undertaken in women at risk. On the basis of this study as well as one nonrandomized study, it can be concluded that clinical examination as well as mammography are essential in detecting breast cancer.
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PMID:Breast cancer and ovarian cancer genetics. 1621 1

The level of proteinuria is one of the most important risk factors for progressive renal function loss in renal diseases. Any therapeutic measure that reduces proteinuria will slow or halt the progression of proteinuric nephropathies. Blockade of the renin-angiotensin-aldosterone system (RAAS) with angiotensin-converting enzyme (ACE) inhibitors or AT1-receptor antagonists (ARA) is currently the most powerful available antiproteinuric treatment. Recent investigations point out that blockade of RAAS at other levels (e.g., aldosterone or renin antagonists) could also induce a significant decrease in proteinuria. Because angiotensin II is also generated from angiotensin I by enzymes other than ACE, ARA would provide a more effective blockade of angiotensin II; however, ACE inhibition increases plasma levels of substances such as bradykinin and N-acetyl-seryl-aspartyl-lysyl-proline, which have strong antifibrotic properties. These differential effects of ACE inhibitors and ARA are the rationale for combined administration of both agents, which in clinical studies has demonstrated a significantly higher antiproteinuric and renoprotective effect than by either drug alone. Salt and protein restriction, as well as cautious use of diuretics, can also increase the antiproteinuric effect of RAAS blockade. Treatment with statins or other lipid-lowering agents leads to reduction in proteinuria levels, as some meta-analyses have demonstrated. Smoking is associated with an increased risk for the appearance of proteinuria, so cessation of smoking should be mandatory in proteinuric renal diseases. Recent studies have highlighted an epidemic increase of obesity-related proteinuric glomerulopathies; weight loss is effective not only in this condition, but also in overweight patients with proteinuric nephropathies of other etiologies.
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PMID:Therapeutic measures in proteinuric nephropathy. 1633 67

Renal angiotensin II (AII) is suggested to play a role in the enhanced sodium reabsorption that causes a shift in pressure natriuresis in obesity related hypertension; however, the mechanism is not known. Therefore, to assess the influence of AII on tubular sodium transport, we determined the effect of AII on the Na+, K+-ATPase activity (NKA), an active transporter regulated by the AT1 receptor activity, in the isolated proximal tubules of lean and obese Zucker rats. Also, we determined the levels of the tubular AT1 receptor and associated signal transducing G proteins, as the initial signaling components that mediate the effects of AII on Na+, K+-ATPase activity. In the isolated proximal tubules, AII produced greater stimulation of the NKA activity in obese compared with lean rats. Determination of the AT1 receptors by Scatchard analysis of the [125I] Sar-Ang II binding and Western blot analysis in the basolateral (BLM) and brush border membrane (BBM) revealed a modest but significant increase (23%) in the AT1 receptor number mainly in the BLM of obese compared with lean rats. The AII affinity for AT1 receptors, as determined by IC50 values of AII to displace [125I] Sar-Ang II binding in BLM and BBM were similar in lean and obese rats. Western blot analysis revealed significant increases in Gialpha1, Gialpha2, Gialpha3, and Gq/11alpha in BLM and Gialpha1, Gialpha3, and Gq/11alpha in BBM of obese as compared with lean rats. The increase in the levels of the AT1 receptor and G proteins, mainly in the BLM, may be contributing to the enhanced AII-induced activation of NKA in the proximal tubules of obese rats. This phenomenon, in part, may be responsible for the increased sodium reabsorption and the development of hypertension in obese Zucker rats.
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PMID:Enhanced angiotensin II-induced activation of Na+, K+-ATPase in the proximal tubules of obese Zucker rats. 1644 62

Patients with high blood pressure are often overweight or even obese. Conversely, some 43% of overweight and obese patients suffer from hypertension. Diabetes (16.7%), coronary heart disease (15.0%) and nephropathy (7.8%) are common additional findings. The cardiac risk in these patients is thus appreciably elevated. Currently, a prospective medical care study "Best practice with irbesartan in overweight and obese patients" (BIG) - is being conducted throughout Germany. In this study obese hypertensive patients of general practitioners are receiving the AT1 blocker irbesartan, as monotherapy or in fixed combination with the diuretic hydrochlorothiazide over a period of 3 months. Obese patients and nonobese patients are compared with regard to the following variables: drug utilization, blood pressure decrease, responder rates, normalization rates, decrease in the number of patients with (micro)albuminurea, changes in patient risk profile (e.g. after SCORE), and tolerability. The study is expected to provide new information on the efficacy, tolerability and safety of irbesartan in regard to pressure reduction and its protective effect on the kidneys and heart in overweight patients.
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PMID:[Arterial hypertension in obese patients. Rationale for a prospective medical care study in the family doctor's practice]. 1673 58

Hypertension is often associated with an impairment of glucose tolerance and is a risk factor for the development of type 2 diabetes mellitus. The occurrence of diabetes may be also influenced by the selection of the type of antihypertensive treatment. While it has been shown that the use of older type antihypertensives - diuretics and beta-blockers - may precipitate diabetes, newer drugs which inhibit the renin-angiotensin system have a positive effect on glucose tolerance. Several recent clinical trials of ACE-inhibitors and AT1-blockers have demonstrated a decreased risk of the occurrence of diabetes in comparison with placebo or conventional antihypertensive drugs. The mechanisms responsible for the antidiabetic effect of these newer antihypertensive agents remain largely speculative. Insulin resistance may be improved in several ways, e.g. by changes in microcirculation or direct effects on insulin response and glucose transport in target organ cells. However, as shown in experimental studies, improved islet function and insulin secretion may also have role due to an inhibitory effect on the local renin-angiotensin system in the pancreas. Ongoing prospective clinical trials having the occurrence of diabetes as a primary specified endpoint should confirm the preventive potential of the inhibitors of the renin-angiotensin system. Since direct comparisons are lacking, current data are inconclusive as to the superiority of one of the two classes of these inhibitors or of any single drug. Nevertheless, inhibitors of the renin-angiotensin system should definitely represent first choice antihypertensive agents for persons with additional risk factors such as family history of diabetes, obesity or impaired glucose tolerance.
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PMID:[Prevention of type 2 diabetes mellitus due to antihypertensive treatment affecting renin-angiotensin system]. 1709 2


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