No abstract

In the kidney nitric oxide (NO) has numerous important functions including the regulation of renal haemodynamics, maintenance of medullary perfusion, mediation of pressure-natriuresis, blunting of tubuloglomerular feedback, inhibition of tubular sodium reabsorption and modulation of renal sympathetic neural activity. The net effect of NO in the kidney is to promote natriuresis and diuresis. Significantly, deficient renal NO synthesis has been implicated in the pathogenesis of hypertension. All three isoforms of nitric oxide synthase (NOS), namely neuronal NOS (nNOS or NOS1), inducible NOS (iNOS or NOS2) and endothelial NOS (eNOS or NOS3) are reported to contribute to NO synthesis in the kidney. The regulation of NO synthesis in the kidney by NOSs is complex and incompletely understood. Historically, many studies of NOS regulation in the kidney have emphasized the role of variations in gene transcription and translation. It is increasingly appreciated, however, that the constitutive NOS isoforms (nNOS and eNOS) are also subject to rapid regulation by post-translational mechanisms such as Ca 2+ flux, serine/threonine phosphorylation and protein-protein interactions. Recent studies have emphasized the role of post-translational regulation of nNOS and eNOS in the regulation of NO synthesis in the kidney. In particular, a role for phosphorylation of nNOS and eNOS at both activating and inhibitory sites is emerging in the regulation of NO synthesis in the kidney. This review summarizes the roles of NO in renal physiology and discusses recent advances in the regulation of eNOS and nNOS in the kidney by post-translational mechanisms such as serine/threonine phosphorylation.

The ultrasensitive energy sensor AMP-activated protein kinase (AMPK) orchestrates the regulation of energy-generating and energy-consuming pathways. AMPK is highly expressed in the kidney where it is reported to be involved in a variety of physiological and pathological processes including ion transport, podocyte function, and diabetic renal hypertrophy. Sodium transport is the major energy-consuming process in the kidney, and AMPK has been proposed to contribute to the coupling of ion transport with cellular energy metabolism. Specifically, AMPK has been identified as a regulator of several ion transporters of significance in renal physiology, including the cystic fibrosis transmembrane conductance regulator (CFTR), the epithelial sodium channel (ENaC), the Na(+)-K(+)-2Cl(-) cotransporter (NKCC), and the vacuolar H(+)-ATPase (V-ATPase). Identified regulators of AMPK in the kidney include dietary salt, diabetes, adiponectin, and ischemia. Activation of AMPK in response to adiponectin is described in podocytes, where it reduces albuminuria, and in tubular cells, where it reduces glycogen accumulation. Reduced AMPK activity in the diabetic kidney is associated with renal accumulation of triglyceride and glycogen and the pathogenesis of diabetic renal hypertrophy. Acute renal ischemia causes a rapid and powerful activation of AMPK, but the functional significance of this observation remains unclear. Despite the recent advances, there remain significant gaps in the present understanding of both the upstream regulating pathways and the downstream substrates for AMPK in the kidney. A more complete understanding of the AMPK pathway in the kidney offers potential for improved therapies for several renal diseases including diabetic nephropathy, polycystic kidney disease, and ischemia-reperfusion injury.

Background: Denosumab, a RANK-ligand inhibitor, is an effective treatment for osteoporosis in postmenopausal women and men. Unlike the bisphosphonates, it is not excreted by the kidney. Little is known, however, about its efficacy and safety in patients with severe chronic kidney disease (CKD). Methods: A retrospective study was performed in CKD 4-5D patients from a tertiary referral hospital who were treated with denosumab between 1st January 2011 and 31st March 2014. Data collected included information about the following: CKD stage, fracture history, bone mineral density, serum calcium levels pre and post denosumab treatment, episodes of hypocalcemia, relevant medications and adverse events. Results: Eight patients with CKD-5 and 6 patients with CKD-4 were identified (all female, mean age 77.1 ± 9.9). The mean pre-denosumab calcium value was 2.42 ± 0.12 mmol/l, PTH 20.2 ± 14.7 pmol/l and 25-OH vitamin D 69.1 ± 30.1 nmol/l. After denosumab treatment, 6/8 patients with CKD-5/5D, and 2/5 patients with CKD-4 developed severe hypocalcemia. Two patients developed direct adverse complications of hypocalcemia (seizure, laryngospasm, prolonged QT_c). Among the patients who developed hypocalcemia, the median time to serum calcium nadir was 21 days and the median time to correction of hypocalcemia was 71 days. Treatment of hypocalcemia required large doses of oral calcium and calcitriol, and increases in dialysate calcium concentration. Conclusions: A high rate of severe hypocalcemia was observed in patients with advanced CKD treated with denosumab. If denosumab is used in patients with severe CKD, close monitoring and aggressive replacement of calcium and calcitriol is required to avoid the development of hypocalcemia.

These data indicate that reduced phosphorylation of ACC after renal injury contributes to the development of TIF, and that phosphorylation of ACC is required for metformin's antifibrotic action in the kidney.

The AMP-activated protein kinase (AMPK) is a key controller of cellular energy metabolism. We studied its expression and regulation by salt handling in the kidney. Immunoprecipitation and Western blots of protein lysates from whole rat kidney using subunit-specific antibodies showed that the alpha1-catalytic subunit is expressed in the kidney, associated with the beta2- and either gamma1- or gamma2-subunits. Activated AMPK, detected by immunohistochemical staining for phospho-Thr172 AMPK (pThr172), was expressed on the apical surface of the cortical thick ascending limb of the loop of Henle, including the macula densa, and some parts of the distal convoluted tubule. Activated AMPK was also expressed on the basolateral surface of the cortical and medullary collecting ducts as well as some portions of the distal convoluted tubules. AMPK activity was increased by 25% in animals receiving a high-salt diet, and this was confirmed by Western blotting for pThr172. Low-salt diets were associated with reduced levels of the alpha-subunit of AMPK, which was highly phosphorylated on Thr172. Surprisingly, both low- and high-salt media transiently activated AMPK in the macula densa cell line MMDD1, an effect due to changes in osmolality, rather than Na+ or Cl- concentration. This study, therefore, demonstrates regulation of AMPK by both a high- and a low-salt intake in vivo and suggests a role for the kinase in the response to changes in osmolality within the kidney.

Background: A new class of dialysis membrane, the mid cutoff (MCO) dialyzer, has been developed to improve the clearance of uremic toxins in hemodialysis (HD). The a tRial Evaluating Mid cutOff Value membrane clearance of Albumin and Light chains in HemoDialysis patients (REMOVAL-HD) study aimed to determine if regular use of MCO dialyzer was safe and specifically did not result in a significant loss of albumin. Methods: This investigator initiated, crossover, longitudinal , device study was conducted across 9 centers in Australia and New Zealand (n = 89). Participants had a 4-week wash-in with high-flux HD, followed by 24-week intervention with MCO HD and a subsequent 4-week wash-out with high-flux HD. The primary outcome was change in serum albumin between weeks 4 and 28. Secondary outcomes included trends in serum albumin, changes in kappa-and lambda-free light chains (FLC), 6-min walk test (6MWT), malnutrition inflammation score (MIS), restless legs score and quality of life. Results: Participants had a mean age of 66 ± 14 years, 62% were men, 45% were anuric, and 51% had diabetes. There was no reduction in serum albumin following treatment with MCO HD (mean reduction-0.7 g/L, 95% CI-1.5 to 0.1). A sustained, unexplained reduction in serum REMOVAL-HD Study 469

AMG 416 (velcalcetide), a novel peptide agonist of the calcium-sensing receptor, lowers plasma parathyroid hormone in preclinical uremic animal models and in normal healthy individuals. Here, we studied its efficacy in hemodialysis patients suffering from secondary hyperparathyroidism. Major inclusion criteria were hemodialysis for at least 3 months, serum parathyroid hormone over 300 pg/ml, a corrected serum calcium of 9.0 mg/dl or more, and stable doses of vitamin D analogs for at least 3 weeks prior to screening. Twenty-eight patients were enrolled in one of five cohorts (5, 10, 20, 40, 60 mg). Cohorts 1-3 (four patients each) were treated in a two-period crossover design, while cohorts 4 and 5 (eight patients each) were randomized 1:1 to AMG 416 or placebo. Patients were admitted to a clinical research unit following hemodialysis and studied for 3 days prior to discharge for hemodialysis. Single intravenous doses of AMG 416 from 5 to 60 mg were well tolerated, and plasma levels increased in a dose-related manner. AMG 416 treatment was associated with significant, dose-dependent reductions in serum parathyroid hormone and fibroblast growth factor 23. Compared with placebo, all dose groups of 10 mg or more were associated with attenuation in the rise in serum phosphate during the interdialytic period. Dose-dependent reductions in serum calcium were observed and were well tolerated. Thus, AMG 416 represents a novel therapeutic approach for the treatment of secondary hyperparathyroidism in hemodialysis patients.