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 QTc). 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.

Obesity is an independent risk factor for chronic kidney disease (CKD). The mechanisms linking obesity and CKD include systemic changes such as high blood pressure and hyperglycemia, and intrarenal effects relating to lipid accumulation. Normal lipid metabolism is integral to renal physiology and disturbances of renal lipid and energy metabolism are increasingly being linked with kidney disease. AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) are important regulators of fatty acid oxidation, which is frequently abnormal in the kidney with CKD. A high fat diet reduces renal AMPK activity, thereby contributing to reduced fatty acid oxidation and energy imbalance, and treatments to activate AMPK are beneficial in animal models of obesity-related CKD. Studies have found that the specific cell types affected by excessive lipid accumulation are proximal tubular cells, podocytes, and mesangial cells. Targeting disturbances of renal energy metabolism is a promising approach to addressing the current epidemic of obesity-related kidney disease.

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 α₁-catalytic subunit is expressed in the kidney, associated with the β₂- and either γ₁- or γ₂-subunits. Activated AMPK, detected by immunohistochemical staining for phospho-Thr¹⁷²AMPK (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 α-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.