Shahla Riazi

Reduced Expression of Insulin Receptors in the Kidneys of Insulin-Resistant Rats

Insulin resistance is accompanied by hyperinsulinemia and activation of the renin-angiotensin system, both of which are associated with hypertension. Because the kidney plays a major role in the regulation of blood pressure, we studied the regulation of insulin receptor expression in the kidney during states of insulin resistance. Using two rat models of insulin resistance, Western blot analysis demonstrated a significant reduction in the expression of insulin receptor subunits in the kidney compared to lean control rats. Treatment of insulin resistance in Zucker rats with the insulin-sensitizing drug rosiglitazone partially restored renal insulin receptor levels. Conversely, treatment with the angiotensin II type 1 receptor (AT1) antagonist candesartan increased renal insulin receptor expression compared to untreated rats. Streptozotocin-induced hyperglycemia, which results from hypoinsulinemia, reduced expression of renal insulin receptors. Hyperinsulinemia induced by insulin infusion, however, did not produce a similar effect. In conclusion, insulin receptors are downregulated in the kidneys of insulin resistant rats, possibly mediated by hyperglycemia and angiotensin II.

Rosiglitazone Regulates ENaC and Na-K-2Cl Cotransporter (NKCC2) Abundance in the Obese Zucker Rat

Background/Aims: Progressive diabetes is associated renal remodeling, which we previously showed correlated to reduced protein abundance of several major renal sodium transporters and channel subunits in the obese Zucker rat. Here we test whether rosiglitazone (RGZ), a peroxisome proliferator-activated subtype γ receptor agonist, would be protective and attenuate these changes. Methods: Male, obese and lean Zucker rats (9 weeks old) were randomly divided (n = 6/group) to receive control diet with or without RGZ at 3 mg/kg·bw/day for 12 weeks. Results: RGZ normalized blood glucose and plasma fructosamine levels in obese rats. Obese control rats had relatively increased fractional excretion of sodium (FENa, sodium excretion relative to creatinine). Nonetheless, both obese and RGZ-treated rats had relatively higher 24-hour net sodium balances. Immunoblotting revealed obese rats had significantly reduced renal cortical protein abundances of the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2) and the sodium hydrogen exchanger (NHE3). RGZ normalized NKCC2 abundance and increased the abundance of the α-subunit of the epithelial sodium channel (ENaC). In contrast, in the outer medulla, obese rats had increased abundance of NKCC2, γ-ENaC (85-kDa), and endothelial NOS. Furthermore, RGZ caused a decrease in the abundance of cortical β- and γ-ENaC (85-kDa). Finally, the whole kidney abundances of α-1 Na-K-ATPase, α- β-, and γ-ENaC (70-kDa band) positively correlated with net sodium balance, whereas NKCC2 was negatively correlated to FENa. Conclusion: Chronic RGZ treatment of obese Zucker rats may preserve renal sodium reabsorptive capacity by its indirect actions to attenuate hyperglycemia as well as direct effects on transporter abundance and activity.

Chronic candesartan alters expression and activity of NKCC2, NCC, and ENaC in the obese Zucker rat

The obese Zucker rat reportedly has increased activity of the intrarenal renin-angiotensin-aldosterone system, which conceptually could contribute to elevated salt sensitivity and blood pressure (BP). Our aim was to determine whether there was increased angiotensin II type 1 receptor (AT(1)R)-mediated upregulation of expression or activity of the bumetanide-sensitive Na-K-2Cl cotransporter, the thiazide-sensitive Na-Cl cotransporter (NCC), and/or the epithelial sodium channel (ENaC) in obese vs. lean Zucker rats. Male obese and lean Zucker rats (10-wk old) were fed either 1) control chow (1% NaCl) or 2) chow with candesartan (CAN), an AT(1)R antagonist (25 mg/kg.diet) for 14 wk (n = 8/treatment/body type). BP measured by radiotelemetry, was markedly reduced by CAN ( approximately 20-25 mmHg) in both lean and obese rats with no body-type differences. Obese rats had significantly greater net natriuretic response to single injections of hydrochlorothiazide and benzamil, suggesting increased activity of NCC and ENaC, respectively; however, only the response to benzamil was reduced by CAN. CAN led to a significant reduction in whole kidney levels of NCC and gamma-ENaC (70-kDa band) in both lean and obese rats. However, it significantly increased alpha-ENaC and Na-K-2Cl cotransporter levels, and these increases were greater in obese rats. These studies suggest that relatively increased ENaC, but not NCC activity, in obese rats is due to enhanced AT(1)R activity. CAN attenuated the reduction of several renal transporters in the obese rat kidney. Finally, differences in intrarenal AT(1)R activity do not seem directly responsible for BP differences between lean and obese rats.

Abundance of the Na-K-2Cl cotransporter NKCC2 is increased by high-fat feeding in Fischer 344 X Brown Norway (F1) rats

Insulin resistance is associated with hypertension by mechanisms likely involving the kidney. To determine how the major apical sodium transporter of the thick ascending limb, the bumetanide-sensitive Na-K-2Cl cotransporter (NKCC2) is regulated by high-fat feeding, we treated young male, Fischer 344 X Brown Norway (F344BN) rats for 8 wk with diets containing either normal (NF, 4%) or high (HF, 36%) fat, by weight, primarily as lard. HF-fed rats had impaired glucose tolerance, increased urine excretion of 8-isoprostane (a marker of oxidative stress), increased protein levels for NKCC2 (50-125%) and the renal outer medullary potassium channel (106%), as well as increased natriuretic response to furosemide (20-40%). To test the role of oxidative stress in this response, in study 2, rats were fed the NF or HF diet plus plain drinking water, or water containing N(G)-nitro-l-arginine methyl ester (l-NAME), a nitric oxide synthase inhibitor (100 mg/l), or tempol, a superoxide dismutase mimetic (1 mmol/l). The combination of tempol with HF nullified the increase in medullary NKCC2, while l-NAME with HF led to the highest expression of medullary NKCC2 (to 498% of NF mean). However, neither of these drugs dramatically affected the elevated natriuretic response to furosemide with HF. Finally, l-NAME led to a marked increase in blood pressure (measured by radiotelemetry), which was significantly enhanced with HF. Mean arterial blood pressure at 7 wk was as follows (mmHg): NF, 100 +/- 2; NF plus l-NAME, 122 +/- 3; and HF plus l-NAME, 131 +/- 2. Overall, HF feeding increased the abundance of NKCC2. Inappropriately high sodium reabsorption in the thick ascending limb via NKCC2 may contribute to hypertension with insulin resistance.

Sex and age result in differential regulation of the renal thiazide-sensitive NaCl cotransporter and the epithelial sodium channel in angiotensin II-infused mice.

Background/Aims: We determined the effects of age and sex on the blood pressure (BP) response to angiotensin II (Ang II) infusion and evaluated the potential mechanistic role of the thiazide-sensitive NaCl cotransporter (NCC) and the epithelial sodium channel (ENaC). Methods: Male and female mice (∼3 or 21 months of age) were infused with Ang II or control for 7 days. Results: Males had a greater BP response to Ang II, somewhat enhanced by aging. Mean systolic BPs (at 7 days) were (mm Hg): 161, 143, 172, and 157 in young male, young female, old male, and old female mice, respectively. Immunoblotting changes in the whole kidney that supported this BP profile included a 51 and 52% increase in NCC band density in the old females and old males (as compared to sex-respective controls) with Ang II infusion, while the young males and young females showed an increase of 40 and 0%, respectively. Young males also had a greater reduction in major bands of β- and γ-ENaC, than did young female mice. The natriuretic response to hydrochlorothiazide supported an increase in activity of NCC with Ang II in aged mice only. Conclusions: Increased sensitivity to Ang II in aging and male mice may involve overactivity of NCC.

Sex differences in adaptive downregulation of pre-macula densa sodium transporters with ANG II infusion in mice

An increase in blood pressure (BP) due to angiotensin II (ANG II) infusion or other means is associated with adaptive pressure natriuresis due to reduced sodium reabsorption primarily in proximal tubule (PT) and thick ascending limb (TAL). We tested the hypothesis that male and female mice would show differential response to ANG II infusion with regard to the regulation of the protein abundance of sodium transporters in the PT and TAL and that these responses would be modulated by aging. Young (approximately 3 mo) and old (approximately 21 mo) male and female mice were infused with ANG II at 800 ng x kg body wt(-1) x min(-1) by osmotic minipump for 7 days or received a sham operation. ANG II increased mean arterial pressure (MAP), measured by radiotelemetry, significantly more in male mice of both ages (increased approximately 30-40 mmHg), compared with females (increased approximately 15-25 mmHg). On day 1, MAP was also significantly increased in old mice, relative to young (P = 0.01). ANG II infusion was associated with a significant decline in plasma testosterone (to <30% of control male) in male mice and rise in young female mice (to 478% of control female). No sex differences were found in the upregulation of the sodium hydrogen exchanger abundance on Western blots observed with ANG II infusion or the downregulation of the sodium phosphate cotransporter; however, aging did impact on some of these changes. Male mice (especially young) also had significantly reduced levels of the TAL bumetanide-sensitive Na-K-2Cl cotransporter (to 60% of male control), while young females showed an increase (to 126% of female control) with ANG II infusion. These sex differences do not support impaired pressure natriuresis in male mice, but might reflect a greater need and attempt to mount an appropriately BP-metered natriuretic response by additional downregulation of TAL sodium reabsorption.

Rapid diagnosis of Mycobacterium tuberculosis infection in children using interferon-gamma release assays (IGRAs).

Diagnosis of tuberculosis (TB) in children by the tuberculin skin test (TST) poses a diagnostic challenge for physicians due to its low specificity and cross-reactivity with nontuberculous mycobacteria and bacille Calmette-Guerin (BCG). Although interferon-gamma release assays (IGRAs) have been shown as novel TST alternatives for diagnosis of latent TB infection (LTBI) in adults, their effectiveness is less clear in children. The present study examined QuantiFERON-TB Gold (QFT-G) responses and IFN-gamma production capacity of TST-positive children, younger children ≤5 years. A total of 517 children of whom 434 were TST positive ranging in age from 1 month to 18 years were evaluated by the QFT-G. Of the 517 children, 434 (84%) were TST positive, 25 (5.8%) of whom were found to be QFT-G positive and 25 (5.4%) with an indeterminate response. Of the 517 children, 355 (68.7%) were previously BCG immunized and 310/355 (87.3%) were TST positive including 18/27 (66.7%) QFT-positive children. Adequate IFN-gamma production by purified TB peptides or mitogen was observed in 92.8% of children, 29.6% of whom were <5 years. This study shows that the QFT-G assay is useful for diagnosis of LTBI. The finding of 5.8% positive QFT-G in 434 TST-positive children underscores the superior specificity of the QFT-G than the TST and its greater cost effectiveness in preventing unnecessary and potentially toxic treatment in children. The study suggests that the majority of positive TST in children represent false-positive reactions and supports the use of IGRAs for diagnosis of LTBI in children, including those <5 years of age.

The child’s immune system and pediatric tuberculosis

That children are more likely develop a severe form of TB is reflective of the differences in the maturational stages of their immune systems, but a paucity of data is available about how this system matures and what the relationship of these developmental immune deficiencies are with infection. Maturational deficiencies in the adaptive and innate immune systems in infants and young children may result in immature macrophage and DC function; Th1-type responses to pathogens; and a propensity to develop Th2-type CD4 T-cells in response to immunogens. In vitro responses of two groups of TST positive children at risk for TB were examined by comparing Enzyme-Linked ImmunoSorbent Assay (ELISA)-based IGRAs with clinical and TST findings. Age-related changes in the immune capacity for specific and mitogen-induced IFN-γ production was also examined in these two groups. In the original guidelines for the use of QFT-G, the US Centers for Disease Control and Prevention recommended that additional studies were needed, especially in children under five years of age, both to establish the validity of the assay as a diagnostic tool in the younger age group and to compare the accuracy of the test with the TST for diagnosing active and latent TB. Of TST positive US children, 10 of the 196 (5%) were found to be QFT-G positive; nine had an indeterminate response; of the 130 children from the Philippines who had been immunized with BCG, 115 were TST positive, and seven were also QFT-G positive. In BCG immunized children, all were TST positive and BCG-immunized and because of a presumptive diagnosis of TB, all had received anti-TB therapy; of the 30 children, 14 (47%) were found to be QFT-G-IT positive and one had an indeterminate response. For the study of variations in age-related immune capacity, the capacity of IFN-γ production was measured in various age groups of children in response to specific TB peptides (ESAT-6, CFP-10 and TB7.7) as well as to mitogen in amounts used in the QFT-G and the QFT-G-IT assay kits that had been provided. Both studies suggest that ELISA QFT-G and QFT-G-IT assays are useful for diagnosing TB in children and that adequate IFN-γ production was observed in all children in both groups following lymphocyte stimulation by either purified TB peptides or mitogen including those less than 5 years of age.

Consultants for the American Journal of Nephrology 2009

Glenn Chertow Robert Chevalier Monique Cho Kai-Ming Chow Felix Claverie-Martin Mark Cooper Fernando Cordido Daniel Coyne Farhad Danesh Robert Danziger John Daugirdas Prasad Devarajan Francis Dumler Thomas Easterling Tevfik Ecder Paul Eggers Randa El Zein Kathrin Eller Murray Epstein Sahar Fathallah-Shaykh Gal Finer Jeffrey Fink Michael Fischer Agnes Fogo Barry Freedman Eli Friedman Verica Garaj-Vrhovac Richard Glassock Glenda Gobe Stuart Goldstein Harvest Gu Krishnamurthy Gudehithlu Martha Gulati Michael Haase Melisha Hanna Peter Hart Kitamura Harumi Marion Hofmann-Bowman Yao Huang Adrian Iaina Narita Ichiei Zaid Abassi Kevin Abbott Rajiv Agarwal Adesuyi Ajayi Charambolos Antoniades Natarajan Aravindan Gema Ariceta Jose Arruda Arif Asif John Asplin Jonas Axelsson Mindy Banks Vinod Bansal Amy Barton Pai David Basile Alexei Basnakian Srinivasan Beddhu Enrico Benedetti Carsten Bergmann Daniel Berlowitz Judith Beto Rajendra Bhimma Erhard Bieberich Geoffrey Block Amy Bobrowski Neil Boudville Michael Braun Carolyn Brecklin Ellen Brooks Rebecca Brown Steve Brunelli Nigel Brunskill Emmanuel Burdmann Michel Burnier Hui Cai David Calhoun Niels Camara Vito Campese Thomas Carpenter Tak Mao Chan Arelene Chapman