Macrophage and epithelial cell H-ferritin expression regulates renal inflammation.

Inflammation culminating in fibrosis contributes to progressive kidney disease. Cross-talk between the tubular epithelium and interstitial cells regulates inflammation by a coordinated release of cytokines and chemokines. Here we studied the role of heme oxygenase-1 (HO-1) and the heavy subunit of ferritin (FtH) in macrophage polarization and renal inflammation. Deficiency in HO-1 was associated with increased FtH expression, accumulation of macrophages with a dysregulated polarization profile, and increased fibrosis following unilateral ureteral obstruction in mice: a model of renal inflammation and fibrosis. Macrophage polarization in vitro was predominantly dependent on FtH expression in isolated bone marrow-derived mouse monocytes. Using transgenic mice with conditional deletion of FtH in the proximal tubules (FtH(PT-/-)) or myeloid cells (FtH(LysM-/-)), we found that myeloid FtH deficiency did not affect polarization or accumulation of macrophages in the injured kidney compared with wild-type (FtH(+/+)) controls. However, tubular FtH deletion led to a marked increase in proinflammatory macrophages. Furthermore, injured kidneys from FtH(PT-/-) mice expressed significantly higher levels of inflammatory chemokines and fibrosis compared with kidneys from FtH(+/+) and FtH(LysM-/-) mice. Thus, there are differential effects of FtH in macrophages and epithelial cells, which underscore the critical role of FtH in tubular-macrophage cross-talk during kidney injury.

DDAVP is effective in preventing and reversing inadvertent overcorrection of hyponatremia.

BACKGROUND AND OBJECTIVES: Adherence to therapeutic guidelines for the treatment of hyponatremia becomes difficult when water diuresis emerges during therapy. The objective of this study was to assess the effectiveness and safety of desmopressin acetate as a therapeutic agent to avoid overcorrection of hyponatremia and to lower the plasma sodium concentration again after inadvertent overcorrection. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Retrospective chart review was conducted of all patients who were given desmopressin acetate during the treatment of hyponatremia during 6 yr in a 528-bed community teaching hospital. RESULTS: Six patients (group 1) were given desmopressin acetate after the 24-h limit of 12 mmol/L had already been reached or exceeded; correction was prevented from exceeding the 48-h limit of 18 mmol/L in five of the six. Fourteen patients (group 2) were given desmopressin acetate in anticipation of overcorrection after the plasma sodium concentration had increased by 1 to 12 mmol/L. In all 14 patients who were treated with desmopressin acetate as a preventive measure, correction was prevented from exceeding either the 24- or 48-h limits. After desmopressin acetate was administered, the plasma sodium concentration of 14 of the 20 patients fell by 2 to 9 mmol/L. In all six group 1 patients and in five of the group 2 patients, the plasma sodium concentration was actively lowered again by the concurrent administration of desmopressin acetate and 5% dextrose in water; no serious adverse consequences from this maneuver were observed. CONCLUSION: Desmopressin acetate is effective in preventing and reversing inadvertent overcorrection of hyponatremia.

AMPK activation with AICAR provokes an acute fall in plasma [K+].

AMP-activated protein kinase (AMPK), activated by an increase in intracellular AMP-to-ATP ratio, stimulates pathways that can restore ATP levels. We tested the hypothesis that AMPK activation influences extracellular fluid (ECF) K(+) homeostasis. In conscious rats, AMPK was activated with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) infusion: 38.4 mg x kg bolus then 4 mg x kg(-1) x min(-1) infusion. Plasma [K(+)] and [glucose] both dropped at 1 h of AICAR infusion and [K(+)] dropped to 3.3 +/- 0.04 mM by 3 h, linearly related to the increase in muscle AMPK phosphorylation. AICAR treatment did not increase urinary K(+) excretion. AICAR lowered [K(+)] whether plasma [K(+)] was chronically elevated or lowered. The K(+) infusion rate needed to maintain baseline plasma [K(+)] reached 15.7 +/- 1.3 micromol K(+) x kg(-1) x min(-1) between 120 and 180 min AICAR infusion. In mice expressing a dominant inhibitory form of AMPK in the muscle (Tg-KD1), baseline [K(+)] was not different from controls (4.2 +/- 0.1 mM), but the fall in plasma [K(+)] in response to AICAR (0.25 g/kg) was blunted: [K(+)] fell to 3.6 +/- 0.1 in controls and to 3.9 +/- 0.1 mM in Tg-KD1, suggesting that ECF K(+) redistributes, at least in part, to muscle ICF. In summary, these findings illustrate that activation of AMPK activity with AICAR provokes a significant fall in plasma [K(+)] and suggest a novel mechanism for redistributing K(+) from ECF to ICF.

Modest dietary K+ restriction provokes insulin resistance of cellular K+ uptake and phosphorylation of renal outer medulla K+ channel without fall in plasma K+ concentration.

Extracellular K(+) concentration ([K(+)]) is closely regulated by the concerted regulatory responses of kidney and muscle. In this study, we aimed to define the responses activated when dietary K(+) was moderately reduced from a control diet (1.0% K(+)) to a 0.33% K(+) diet for 15 days. Although body weight and baseline plasma [K(+)] (4.0 mM) were not reduced in the 0.33% K(+) group, regulatory responses to conserve plasma [K(+)] were evident in both muscle and kidney. Insulin-stimulated clearance of K(+) from the plasma was estimated in vivo in conscious rats with the use of tail venous and arterial cannulas. During infusion of insulin.(50 mU.kg(-1).min(-1)), plasma [K(+)] level fell to 3.2 +/- 0.1 mM in the 1.0% K(+) diet group and to only 3.47 +/- 0.07 mM in the 0.33% K(+) diet group (P < 0.01) with no reduction in urinary K(+) excretion, which is evidence of insulin resistance to cellular K(+) uptake. Insulin-stimulated cellular K(+) uptake was quantitated by measuring the K(+) infusion rate necessary to clamp plasma K(+) at baseline (in micromol.kg(-1).min(-1)) during 5 mU of insulin.kg(-1).min(-1) infusion: 9.7 +/- 1.5 in 1% K(+) diet was blunted to 5.2 +/- 1.7 in the 0.33% K(+) diet group (P < 0.001). Muscle [K(+)] and Na(+)-K(+)-ATPase activity and abundance were unchanged during the 0.33% K(+) diet. Renal excretion, which was measured overnight in metabolic cages, was reduced by 80%, from 117.6 +/- 10.5 micromol/h/animal (1% K(+) diet) to 24.2 +/- 1.7 micromol/h/animal (0.33% K(+) diet) (P < 0.001). There was no significant change in total abundance of key renal K(+) transporters, but 50% increases in both renal PTK cSrc abundance and ROMK phosphorylation in the 0.33% K(+) vs. 1% K(+) diet group, previously established to be associated with internalization of ROMK. These results indicate that plasma [K(+)] can be maintained during modest K(+) restriction due to a decrease in insulin-stimulated cellular K(+) uptake as well as renal K(+) conservation mediated by inactivation of ROMK, both without a detectable change in plasma [K(+)]. The error signals inciting and maintaining these responses remain to be identified.

Dexamethasone treatment causes resistance to insulin-stimulated cellular potassium uptake in the rat.

Patients treated with glucocorticoids have elevated skeletal muscle ouabain binding sites. The major Na(+)-K(+)-ATPase (NKA) isoform proteins found in muscle, alpha2 and beta1, are increased by 50% in rats treated for 14 days with the synthetic glucocorticoid dexamethasone (DEX). This study addressed whether the DEX-induced increase in the muscle NKA pool leads to increased insulin-stimulated cellular K+ uptake that could precipitate hypokalemia. Rats were treated with DEX or vehicle via osmotic minipumps at one of two doses: 0.02 mg.kg(-1).day(-1) for 14 days (low DEX; n = 5 pairs) or 0.1 mg.kg(-1).day(-1) for 7 days (high DEX; n = 6 pairs). Insulin was infused at a rate of 5 mU.kg(-1).min(-1) over 2.5 h in conscious rats. Insulin-stimulated cellular K+ and glucose uptake rates were assessed in vivo by measuring the exogenous K+ infusion (K+(inf)) and glucose infusion (Ginf) rates needed to maintain constant plasma K+ and glucose concentrations during insulin infusion. DEX at both doses decreased insulin-stimulated glucose uptake as previously reported. Ginf (in mmol.kg(-1).h(-1)) was 10.2 +/- 0.6 in vehicle-treated rats, 5.8 +/- 0.8 in low-DEX-treated rats, and 5.2 +/- 0.6 in high-DEX-treated rats. High DEX treatment also reduced insulin-stimulated K+) uptake. K+(inf) (in mmol.kg(-1).h(-1)) was 0.53 +/- 0.08 in vehicle-treated rats, 0.49 +/- 0.14 in low-DEX-treated rats, and 0.27 +/- 0.08 in high-DEX-treated rats. DEX treatment did not alter urinary K+ excretion. NKA alpha2-isoform levels in the low-DEX-treated group, measured by immunoblotting, were unchanged, but they increased by 38 +/- 15% (soleus) and by 67 +/- 3% (gastrocnemius) in the high-DEX treatment group. The NKA alpha1-isoform level was unchanged. These results provide novel evidence for the insulin resistance of K+ clearance during chronic DEX treatment. Insulin-stimulated cellular K+ uptake was significantly depressed despite increased muscle sodium pump pool size.

Mechanism of action in dogs of slow-acting insulin analog O346.

We compared metabolic effects as well as plasma and interstitial fluid kinetics of fatty acid-acylated insulin, Lys(B29)(N(epsilon)-omega-carboxynonadecanoyl)-des(B30) human insulin (O346), with previously determined kinetics of native insulin and insulin detemir. Euglycemic clamps with iv injection of O346 (90 pmol/kg) or saline control were performed in 10 male mongrel dogs under inhalant anesthesia. The t(1/2) for the clearance of O346 from plasma was 375.7 +/- 26.7 min; the t(1/2) for the appearance of O346 in interstitial fluid was 137 +/- 20 min (mean +/- SEM). Glucose disposal with O346 injection was increased 4-fold (t = 480 min, 8.3 +/- 1.42 mg/min/kg) compared with preinjection (t = 0 min, 2.1 +/- 0.13 mg/min/kg; P < 0.05) or saline control (t = 480 min, 2.09 +/- 0.22 mg/min/kg; P < 0.05). O346 plasma elimination and transendothelial transport were 0.3% and 3.5% of regular insulin and 3% and 50% of insulin detemir, respectively. Combination of in vivo results and compartmental modeling suggests that the duration of action of O346 after iv injection is about 25-fold and 10-fold longer compared with regular human insulin and insulin detemir, respectively. This study demonstrates that O346 stimulates glucose disposal very slowly, but when injected iv, its effect may be maintained for as long as 48 h as estimated from simulation analysis. The data suggest that O346 bound to albumin in plasma acts as a storage compartment for O346 from which the analog is slowly released to insulin-sensitive tissues. Reduced liver clearance of O346 is suggested to be the major mechanism for the protracted action.

Chronic renal injury-induced hypertension alters renal NHE3 distribution and abundance.

Renal cortical phenol injection provokes acute sympathetic nervous system-dependent hypertension and a shift of proximal tubule Na(+)/H(+) exchanger isoform 3 (NHE3) and Na(+)-P(i) cotransporter type 2 (NaPi2) to apical microvilli. This study aimed to determine whether proximal tubule (PT) Na(+) transporter redistribution persists chronically and whether the pool sizes of renal Na(+) transporters are altered. At 5 wk after a 50-microl 10% phenol injection, blood pressure is elevated: 154 +/- 8 vs. 113 +/- 11 mmHg after saline injection. Cortical membranes were fractionated into three "windows" enriched in apical brush border (WI), mixed apical and intermicrovillar cleft (WII), and intracellular membranes (WIII). NHE3 relative distribution in these windows, assessed by immunoblots and expressed as %total, remained shifted to apical from intracellular membranes (WI: 25.3 +/- 3 in phenol vs.12.7 +/- 3% in saline and WIII: 9.1 +/- 1.3 in phenol vs. 18.9 +/- 3% in saline). NaPi2 and dipeptidyl-peptidase IV also remained shifted to WI, and alkaline phosphatase activity increased 100.9 +/- 29.7 (WI) and 51.4 +/- 17.5% (WII) in phenol-injected membranes. Na(+) transporter total abundance [NHE3, NaPi2, thiazide-sensitive Na-Cl cotransporter, bumetanide-sensitive Na-K-2Cl cotransporter, Na-K-ATPase alpha(1)- and beta(1)-subunits, and epithelial Na(+) channel (ENaC) alpha- and beta-subunits] was profiled by immunoblotting. Only cortical NHE3 abundance was altered, decreasing to 0.56 +/- 0.06. The results demonstrate that phenol injury provokes a persistant shift of PT NHE3 and NaPi2 to the apical microvilli, along with a 44% decrease in total NHE3, evidence for an escape mechanism that would counteract the redistribution of a larger fraction of NHE3 to the apical surface by normalizing the total amount of NHE3 in apical membranes.