Potassium Magnesium Citrate Is Superior to Potassium Chloride in Reversing Metabolic Side Effects of Chlorthalidone.

BACKGROUND: Thiazide diuretics (TD) are the first-line treatment of hypertension because of its consistent benefit in lowering blood pressure and cardiovascular risk. TD is also known to cause an excess risk of diabetes, which may limit long-term use. Although potassium (K) depletion was thought to be the main mechanism of TD-induced hyperglycemia, TD also triggers magnesium (Mg) depletion. However, the role of Mg supplementation in modulating metabolic side effects of TD has not been investigated. Therefore, we aim to determine the effect of potassium magnesium citrate (KMgCit) on fasting plasma glucose and liver fat by magnetic resonance imaging during TD therapy. METHODS: Accordingly, we conducted a double-blinded RCT in 60 nondiabetic hypertension patients to compare the effects of KCl versus KMgCit during chlorthalidone treatment. Each patient received chlorthalidone alone for 3 weeks before randomization. Primary end point was the change in fasting plasma glucose after 16 weeks of KCl or KMgCit supplementation from chlorthalidone alone. RESULTS: The mean age of subjects was 59±11 years (30% Black participants). Chlorthalidone alone induced a significant rise in fasting plasma glucose, and a significant fall in serum K, serum Mg, and 24-hour urinary citrate excretion (all P<0.05). KMgCit attenuated the rise in fasting plasma glucose by 7.9 mg/dL versus KCl (P<0.05), which was not observed with KCl. There were no significant differences in liver fat between the 2 groups. CONCLUSIONS: KMgCit is superior to KCl, the common form of K supplement used in clinical practice, in preventing TD-induced hyperglycemia. This action may improve tolerability and cardiovascular safety in patients with hypertension treated with this drug class.

Phosphate and Cellular Senescence.

Cellular senescence is one type of permeant arrest of cell growth and one of increasingly recognized contributor to aging and age-associated disease. High phosphate and low Klotho individually and synergistically lead to age-related degeneration in multiple organs. Substantial evidence supports the causality of high phosphate in cellular senescence, and potential contribution to human aging, cancer, cardiovascular, kidney, neurodegenerative, and musculoskeletal diseases. Phosphate can induce cellular senescence both by direct phosphotoxicity, and indirectly through downregulation of Klotho and upregulation of plasminogen activator inhibitor-1. Restriction of dietary phosphate intake and blockage of intestinal absorption of phosphate help suppress cellular senescence. Supplementation of Klotho protein, cellular senescence inhibitor, and removal of senescent cells with senolytic agents are potential novel strategies to attenuate phosphate-induced cellular senescence, retard aging, and ameliorate age-associated, and phosphate-induced disorders.

Control of metabolic predisposition to cardiovascular complications of chronic kidney disease by effervescent calcium magnesium citrate: a feasibility study.

AIMS: Cardiovascular (CV) complications are common in chronic kidney disease (CKD). Numerous metabolic disturbances including hyperphosphatemia, high circulating calciprotein particles (CPP), hyperparathyroidism, metabolic acidosis, and magnesium deficiency are associated with, and likely pathogenic for CV complications in CKD. The goal of this feasibility study was to determine whether effervescent calcium magnesium citrate (EffCaMgCit) ameliorates the aforementioned pathogenic intermediates. METHODS: Nine patients with Stage 3 and nine patients with Stage 5D CKD underwent a randomized crossover study, where they took EffCaMgCit three times daily for 7 days in one phase, and a conventional phosphorus binder calcium acetate (CaAc) three times daily for 7 days in the other phase. Two-hour postprandial blood samples were obtained on the day before and on the 7th day of treatment. RESULTS: In Stage 5D CKD, EffCaMgCit significantly increased T50 (half time for conversion of primary to secondary CPP) from baseline by 63% (P = 0.013), coincident with statistically non-significant declines in serum phosphorus by 25% and in saturation of octacalcium phosphate by 35%; CaAc did not change T50. In Stage 3 CKD, neither EffCaMgCit nor CaAc altered T50. With EffCaMgCit, a significant increase in plasma citrate was accompanied by statistically non-significant increase in serum Mg and phosphate. CaAc was without effect in any of these parameters in Stage 3 CKD. In both Stages 3 and 5D, both drugs significantly reduced serum parathyroid hormone. Only EffCaMgCit significantly increased serum bicarbonate by 3 mM (P = 0.015) in Stage 5D. CONCLUSIONS: In Stage 5D, EffCaMgCit inhibited formation of CPP, suppressed PTH, and conferred magnesium and alkali loads. These effects were unique, since they were not observed with CaAc. In Stage 3 CKD, neither of the regimens have any effect. These metabolic changes suggest that EffCaMgCit might be useful in protecting against cardiovascular complications of CKD by ameliorating pathobiologic intermediates.

Cisplatin nephrotoxicity as a model of chronic kidney disease.

Cisplatin (CP)-induced nephrotoxicity is widely accepted as a model for acute kidney injury (AKI). Although cisplatin-induced chronic kidney disease (CKD) in rodent has been reported, the role of phosphate in the cisplatin-induced CKD progression is not described. In this study, we gave a single peritoneal injection of CP followed by high (2%) phosphate diet for 20 weeks. High dose CP (20 mg/Kg) led to high mortality; whereas a lower dose (10 mg/Kg) resulted in a full spectrum of AKI with tubular necrosis, azotemia, and 0% mortality 7 days after CP injection. After consuming a high phosphate diet, mice developed CKD characterized by low creatinine clearance, interstitial fibrosis, hyperphosphatemia, high plasma PTH and FGF23, low plasma 1,25(OH)2 Vitamin D3 and αKlotho, and classic uremic cardiovasculopathy. The CP model was robust in demonstrating the effect of aging, sexual dimorphism, and dietary phosphate on AKI and also AKI-to-CKD progression. Finally, we used the CP-high phosphate model to examine previously validated methods of genetically manipulated high αKlotho and therapy using exogenous soluble αKlotho protein supplementation. In this CP CKD model, αKlotho mitigated CKD progression, improved mineral homeostasis, and ameliorated cardiovascular disease. Taken together, CP and high phosphate nephrotoxicity is a reproducible and technically very simple model for the study of AKI, AKI-to-CKD progression, extrarenal complications of CKD, and for evaluation of therapeutic efficacy.

The Hormone FGF21 Stimulates Water Drinking in Response to Ketogenic Diet and Alcohol.

Alcohol and ketogenic diets increase water consumption. Here, we show that the hormone FGF21 is required for this drinking response in mice. Circulating levels of FGF21 are increased by alcohol consumption in humans and by both alcohol and ketogenic diets in mice. Pharmacologic administration of FGF21 stimulates water drinking behavior in mice within 2 hr. Concordantly, mice lacking FGF21 fail to increase water intake in response to either alcohol or a ketogenic diet. The effect of FGF21 on drinking is mediated in part by SIM1-positive neurons of the hypothalamus and is inhibited by ß-adrenergic receptor antagonists. Given that FGF21 also is known to suppress alcohol intake in favor of pure water, this work identifies FGF21 as a fundamental neurotropic hormone that governs water balance in response to specific nutrient stresses that can cause dehydration.

Association of serum magnesium with all-cause mortality in patients with and without chronic kidney disease in the Dallas Heart Study.

Background: Low serum magnesium (SMg) has been linked to increased mortality and cardiovascular disease (CVD) in the general population. We examined whether this association is similar in participants with versus without prevalent chronic kidney disease (CKD) in the multiethnic Dallas Heart Study (DHS) cohort. Methods: SMg was analyzed as a continuous variable and divided into tertiles. Study outcomes were all-cause death, cardiovascular (CV) death or event, and CVD surrogate markers, evaluated using multivariable Cox regression models adjusted for demographics, comorbidity, anthropometric and biochemical parameters including albumin, phosphorus and parathyroid hormone, and diuretic use. Median follow-up was 12.3 years (11.9-12.8, 25th percentile-75th percentile). Results: Among 3551 participants, 306 (8.6%) had prevalent CKD. Mean SMg was 2.08 ± 0.19 mg/dL (0.85 ± 0.08 mM, mean ± SD) in the CKD and 2.07 ± 0.18 mg/dL (0.85 ± 0.07 mM) in the non-CKD subgroups. During the follow-up period, 329 all-cause deaths and 306 CV deaths or events occurred. In a fully adjusted model, every 0.2 mg/dL decrease in SMg was associated with ∼20-40% increased hazard for all-cause death in both CKD and non-CKD subgroups. In CKD participants, the lowest SMg tertile was also independently associated with all-cause death (adjusted hazard ratio 2.31; 95% confidence interval 1.23-4.36 versus 1.15; 0.55-2.41; for low versus high tertile, respectively). Conclusions: Low SMg levels (1.4-1.9 mg/dL; 0.58-0.78 mM) were independently associated with all-cause death in patients with prevalent CKD in the DHS cohort. Randomized clinical trials are important to determine whether Mg supplementation affects survival in CKD patients.

Global kidney health 2017 and beyond: a roadmap for closing gaps in care, research, and policy.

The global nephrology community recognises the need for a cohesive plan to address the problem of chronic kidney disease (CKD). In July, 2016, the International Society of Nephrology hosted a CKD summit of more than 85 people with diverse expertise and professional backgrounds from around the globe. The purpose was to identify and prioritise key activities for the next 5-10 years in the domains of clinical care, research, and advocacy and to create an action plan and performance framework based on ten themes: strengthen CKD surveillance; tackle major risk factors for CKD; reduce acute kidney injury-a special risk factor for CKD; enhance understanding of the genetic causes of CKD; establish better diagnostic methods in CKD; improve understanding of the natural course of CKD; assess and implement established treatment options in patients with CKD; improve management of symptoms and complications of CKD; develop novel therapeutic interventions to slow CKD progression and reduce CKD complications; and increase the quantity and quality of clinical trials in CKD. Each group produced a prioritised list of goals, activities, and a set of key deliverable objectives for each of the themes. The intended users of this action plan are clinicians, patients, scientists, industry partners, governments, and advocacy organisations. Implementation of this integrated comprehensive plan will benefit people who are at risk for or affected by CKD worldwide.

Recombinant α-Klotho may be prophylactic and therapeutic for acute to chronic kidney disease progression and uremic cardiomyopathy.

α-Klotho is highly expressed in the kidney, and its extracellular domain is cleaved and released into the circulation. Chronic kidney disease (CKD) is a state of α-Klotho deficiency, which exerts multiple negative systemic effects on numerous organs including the cardiovascular system. Since acute kidney injury (AKI) greatly escalates the risk of CKD development, we explored the effect of α-Klotho on prevention and treatment on post-AKI to CKD progression and cardiovascular disease. Therein, ischemia reperfusion injury-induced AKI was followed by early administration of recombinant α-Klotho or vehicle starting one day and continued for four days after kidney injury (CKD prevention protocol). A CKD model was generated by unilateral nephrectomy plus contralateral ischemia reperfusion injury. Late administration of α-Klotho in this model was started four weeks after injury and sustained for 12 weeks (CKD treatment protocol). The prevention protocol precluded AKI to CKD progression and protected the heart from cardiac remodeling in the post-AKI model. One important effect of exogenous α-Klotho therapy was the restoration of endogenous α-Klotho levels long after the cessation of exogenous α-Klotho therapy. The treatment protocol still effectively improved renal function and attenuated cardiac remodeling in CKD, although these parameters did not completely return to normal. In addition, α-Klotho administration also attenuated high phosphate diet-induced renal and cardiac fibrosis, and improved renal and cardiac function in the absence of pre-existing renal disease. Thus, recombinant α-Klotho protein is safe and efficacious, and might be a promising prophylactic or therapeutic option for prevention or retardation of AKI-to-CKD progression and uremic cardiomyopathy.

Effect of urine pH and magnesium on calcium oxalate saturation.

Hypomagnesiuria is a common biochemical finding in patients with calcium oxalate (CaOx) nephrolithiasis. Clinical trials using Mg supplements as therapy against CaOx stones have shown mixed results. We tested the effect of Mg administration in healthy subjects under conditions of controlled urine pH (UpH) on urinary Ca excretion rate (UCaV) and CaOx saturation. This is a 4-phase, double blind, placebo-controlled, metabolic crossover study performed in healthy volunteers. Mg lactate (MgLact2) was used as Mg supplement. High UpH and low UpH were achieved by administration of potassium citrate (K3Citrate) and ammonium chloride (NH4Cl), respectively, with potassium balance maintained by KCl. Eight participants completed 4 phases of study. The interventions successfully modulated 24-h UpH (7.0 ± 0.4 vs. 5.7 ± 0.6 in high vs low pH phases; P<0.001). Administration of MgLact2 increased UMgV [175.8 ± 40.2 vs 93.4 ± 39.7 mg/day (7.2 ± 1.7 vs 3.8 ± 1.6 mmol/day), high vs low Mg phase; P<0.001], and increased pH both at low (5.6 ± 0.5 to 5.8 ± 0.7; P = 0.02) and high UpH (6.9 ± 0.4 to 7.0 ± 0.3; P = 0.01). At a given urine pH, Mg supplementation marginally increased UCaV, but did not alter UOxV or CaOx saturation. Provision of an alkali load significantly lowered UCaV and saturation of CaOx at any level of UMgV. Compared to changes in UMgV, changes in UpH play a more significant role in determining urine CaOx saturation in healthy subjects. Mg supplements are likely to reduce CaOx saturation if they also raise urine pH.

Metabolic diagnosis and medical prevention of calcium nephrolithiasis and its systemic manifestations: a consensus statement.

BACKGROUND: Recently published guidelines on the medical management of renal stone disease did not address relevant topics in the field of idiopathic calcium nephrolithiasis, which are important also for clinical research. DESIGN: A steering committee identified 27 questions, which were proposed to a faculty of 44 experts in nephrolithiasis and allied fields. A systematic review of the literature was conducted and 5216 potentially relevant articles were selected; from these, 407 articles were deemed to provide useful scientific information. The Faculty, divided into working groups, analysed the relevant literature. Preliminary statements developed by each group were exhaustively discussed in plenary sessions and approved. RESULTS: Statements were developed to inform clinicians on the identification of secondary forms of calcium nephrolithiasis and systemic complications; on the definition of idiopathic calcium nephrolithiasis; on the use of urinary tests of crystallization and of surgical observations during stone treatment in the management of these patients; on the identification of patients warranting preventive measures; on the role of fluid and nutritional measures and of drugs to prevent recurrent episodes of stones; and finally, on the cooperation between the urologist and nephrologist in the renal stone patients. CONCLUSIONS: This document has addressed idiopathic calcium nephrolithiasis from the perspective of a disease that can associate with systemic disorders, emphasizing the interplay needed between urologists and nephrologists. It is complementary to the American Urological Association and European Association of Urology guidelines. Future areas for research are identified.

Effects of Potassium Magnesium Citrate Supplementation on 24-Hour Ambulatory Blood Pressure and Oxidative Stress Marker in Prehypertensive and Hypertensive Subjects.

Diet rich in fruits, vegetables, and dairy products, known as the Dietary Approaches to Stop Hypertension (DASH) diet, is known to reduce blood pressure (BP) in hypertensive patients. More recently, the DASH diet was shown to reduce oxidative stress in hypertensive and nonhypertensive humans. However, the main nutritional components responsible for these beneficial effects of the DASH diet remain unknown. Because the DASH diet is rich in potassium (K), magnesium (Mg), and alkali, we performed a randomized, double-blinded, placebo-controlled study to compare effects of potassium magnesium citrate (KMgCit), potassium chloride (KCl), and potassium citrate (KCit) to allow dissociation of the three components of K, Mg, and citrate on 24-hour ambulatory BP and urinary 8-isoprostane in hypertensive and prehypertensive subjects, using a randomized crossover design. We found that KCl supplementation for 4 weeks induced a significant reduction in nighttime SBP compared with placebo (116 ± 12 vs 121 ± 15 mm Hg, respectively, p <0.01 vs placebo), whereas KMgCit and KCit had no significant effect in the same subjects (118 ± 11 and 119 ± 13 mm Hg, respectively, p >0.1 vs placebo). In contrast, urinary 8-isoprostane was significantly reduced with KMgCit powder compared with placebo (13.5 ± 5.7 vs 21.1 ± 10.5 ng/mgCr, respectively, p <0.001), whereas KCl and KCit had no effect (21.4 ± 9.1 and 18.3 ± 8.4, respectively, p >0.1 vs placebo). In conclusion, our study demonstrated differential effects of KCl and KMgCit supplementation on BP and the oxidative stress marker in prehypertensive and hypertensive subjects. Clinical significance of the antioxidative effect of KMgCit remains to be determined in future studies.

Effects of sex and postmenopausal estrogen use on serum phosphorus levels: a cross-sectional study of the National Health and Nutrition Examination Survey (NHANES) 2003-2006.

BACKGROUND: Elevation of serum phosphorus concentrations has been associated with cardiovascular events in older women and men. Whether age, sex, or estrogen therapy is associated with different phosphorus levels is unknown. STUDY DESIGN: Cross-sectional study. SETTING & PARTICIPANTS: 7,005 participants in the National Health and Nutrition Examination Survey (NHANES) 2003-2006. PREDICTORS: Demographic data; body measurement indexes; dietary intake by 24-hour dietary recall and food-frequency questionnaire; data for reproductive health, prescription medication, cardiovascular disease, osteoporosis, and diabetes mellitus obtained by questionnaire; and blood chemistry indexes. OUTCOMES & MEASUREMENTS: Serum phosphorus concentrations. RESULTS: In both males and premenopausal females, serum phosphorus levels decline progressively with age. In males, the decline continues over the entire age range of 21-85 years. In contrast, in females, serum phosphorus levels increase between ages 46-60 years (sex×age interaction; P<0.001). The increase in serum phosphorus levels in older women is independent of changes in serum parathyroid hormone levels, daily dietary phosphorus intake, and estimated glomerular filtration rate. In analysis of covariance, we show that postmenopausal women receiving estrogen therapy have significantly lower serum phosphorus levels than non-estrogen users after adjusting for age, race, body mass index, daily dietary phosphorus intake, and serum albumin, serum parathyroid hormone, and 25-hydroxyvitamin D levels (3.83 vs 3.98mg/dL; P<0.001). LIMITATIONS: The study was cross-sectional in design and estrogen therapy was not randomly assigned or concealed. Important phosphorus regulatory factors such as serum fibroblast growth factor 23 and klotho were not available in the study. CONCLUSIONS: Estrogen status may account for the difference in serum phosphorus levels in postmenopausal women.

Klotho and chronic kidney disease.

Through alternative splicing, Klotho protein exists both as a secreted and a membrane form whose extracellular domain could be shed from the cell surface by secretases and released into the circulation to act as endocrine factor. Unlike membrane Klotho which functions as a coreceptor for fibroblast growth factor-23 (FGF23) to modulate FGF23 signal transduction, soluble Klotho is a multifunction protein present in the biological fluids including blood, urine and cerebrospinal fluid and plays important roles in antiaging, energy metabolism, inhibition of Wnt signaling, antioxidation, modulation of ion transport, control of parathyroid hormone and 1,25(OH)2VD3 production, and antagonism of renin-angiotensin-aldosterone system. Emerging evidence from clinical and basic studies reveal that chronic kidney disease is a state of endocrine and renal Klotho deficiency, which may serve as an early biomarker and a pathogenic contributor to chronic progression and complications in chronic kidney disease including vascular calcification, cardiac hypertrophy, and secondary hyperparathyroidism. Supplementation of exogenous Klotho and/or upregulation of endogenous Klotho production by using rennin angiotensin system inhibitors, HMG CoA reductase inhibitors, vitamin D analogues, peroxisome proliferator-activated receptors-gamma agonists, or anti-oxidants may confer renoprotection from oxidation and suppression of renal fibrosis, and also on prevention or alleviation of complications in chronic kidney disease. Therefore, Klotho is a highly promising candidate on the horizon as an early biomarker, and as a novel therapeutic agent for chronic kidney disease.

Clinical assessment of phosphorus status, balance and renal handling in normal individuals and in patients with chronic kidney disease.

PURPOSE OF REVIEW: The concepts of steady state, external balance, total body status and internal distribution are not always appreciated or even considered in clinical practice. The current tests available for clinical assessment of phosphorus physiology and pathophysiology are valid in some aspects, but also have many limitations. The purpose of this review is to clarify the above concepts and discuss the utility of the currently available tests to assess phosphorus disorders. RECENT FINDINGS: Both epidemiologic and preclinical data have shown that disturbances in mineral metabolism contribute significantly to the morbidity and mortality in chronic kidney disease. There are also emerging data supporting the notion that phosphotoxicity may exist even in individuals with normal renal function. In chronic kidney disease (CKD), hyperphosphatemia is a relative late event and is a suboptimal indicator of phosphorus balance and status. The judicious use of plasma and urine chemistry and hormonal biomarkers such as fibroblast growth factor 23 should be considered. SUMMARY: There is a dire need to increase awareness of what physiologic parameters should be monitored in terms of phosphorus pathophysiology. Although the current available tests in the clinical armamentarium are not ideal, understanding their implications and limitations will improve patient care and motivate practitioners and investigators to develop better tests.

Renal and extrarenal actions of Klotho.

Klotho is a single-pass transmembrane protein highly expressed in the kidney. Membrane Klotho protein acts as a co-receptor for fibroblast growth factor-23. Its extracellular domain is shed from the cell surface and functions as an endocrine substance that exerts multiple renal and extrarenal functions. An exhaustive review is beyond the scope and length of this article; thus, only effects with pertinence to mineral metabolism and renoprotection are highlighted here. Klotho participates in mineral homeostasis via interplay with other calciophosphoregulatory hormones (parathyroid hormone, fibroblast growth factor-23, and 1,25-[OH]2 vitamin D3) in kidney, bone, intestine, and parathyroid gland. Klotho also may be involved in acute and chronic kidney disease development and progression. Acute kidney injury is a temporary and reversible state of Klotho deficiency and chronic kidney disease is a sustained state of systemic Klotho deficiency. Klotho deficiency renders the kidney more susceptible to acute insults, delays kidney regeneration, and promotes renal fibrosis. In addition to direct renal effects, Klotho deficiency also triggers and aggravates deranged mineral metabolism, secondary hyperparathyroidism, vascular calcification, and cardiac hypertrophy and fibrosis. Although studies examining the therapeutic effect of Klotho replacement were performed in animal models, it is quite conceivable that supplementation of exogenous Klotho and/or up-regulation of endogenous Klotho production may be a viable therapeutic strategy for patients with acute or chronic kidney diseases.

Comparison of insulin action on glucose versus potassium uptake in humans.

BACKGROUND AND OBJECTIVES: Insulin has several physiologic actions that include stimulation of cellular glucose and potassium uptake. The ability of insulin to induce glucose uptake by cells is impaired in type 2 diabetes mellitus, but whether potassium uptake is similarly impaired is not known. This study examines whether the cellular uptake of these molecules is regulated in concert or independently. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Thirty-two nondiabetic and 13 type 2 diabetic subjects with normal GFR were given a similar, constant metabolic diet for 8 days. On day 9, they were subjected to a hyperinsulinemic euglycemic clamp for 2 hours. Serum and urinary chemistry were obtained before and during the clamp. Glucose disposal rate was calculated from glucose infusion rate during hyperinsulinemic euglycemia. Intracellular potassium and phosphate uptake were calculated by the reduction of extracellular potassium or phosphate content corrected for urinary excretion. RESULTS: Although glucose disposal rate tended to be lower in type 2 diabetics, cellular potassium uptake was similar between diabetics and nondiabetics. Additionally, although glucose disposal rate was lower with increasing body mass index (R² = 0.362), cellular potassium (R² = 0.052), and phosphate (R² = 0.002), uptake rates did not correlate with body mass index. There was also no correlation between glucose disposal rate and potassium (R² = 0.016) or phosphate uptake (R² = 0.053). Conclusions Insulin-stimulated intracellular uptake of glucose and potassium are independent of each other. In type 2 diabetes, potassium uptake is preserved despite impaired glucose disposal.

Klotho: a novel regulator of calcium and phosphorus homeostasis.

Klotho which was originally identified as an anti-aging protein is emerging as a substance with multiple effects on many systems including mineral homeostasis. In addition to its membrane-bound function as a co-receptor for fibroblast growth factor-23, soluble Klotho exerts effects as a circulating substance in plasma and urine. Novel features of this system include its autocrine-paracrine-endocrine glycan-modifying enzymatic function in the urinary lumen on calcium and phosphate transporters. Klotho induces phosphaturia by inhibiting the proximal tubule Na-coupled phosphate transporter. The action of Klotho is enzymatic in nature which includes alteration of transport activity and the more traditional means of regulation by trafficking. Klotho reduces calciuria by its distal as a sialidase directly on the apical calcium channel. Desialidation of the channel exposes glycan residues that promote binding to galectin-1, resulting in stabilization of residence on the plasma membrane. Through its systematic as well as renal actions, Klotho is emerging as a principal calciophosphoregulatory hormone.

Metabolic basis for low urine pH in type 2 diabetes.

BACKGROUND AND OBJECTIVES: Type 2 diabetes is associated with excessively low urine pH, which increases the risk for uric acid nephrolithiasis. This study was conducted to assess the metabolic basis responsible for the excessive urinary acidity of individuals with type 2 diabetes. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Nine non-stone-forming patients who had type 2 diabetes and low urine pH and 16 age- and body mass index-matched non-stone-forming volunteers without type 2 diabetes were maintained on a constant metabolic diet for 7 days, and 24-hour urine was collected on the last 2 days of the diet. RESULTS: Urine dietary markers (potassium, sulfate, phosphorus, and urea nitrogen) were not different between the two groups. Patients with type 2 diabetes exhibited a significantly lower 24-hour urine pH (5.45+/-0.27 versus 5.90+/-0.42; P<0.01) and higher net acid excretion (NAE; 57+/-12 versus 38+/-18 mEq/d; P<0.01) compared with control subjects. The proportion of NAE excreted as ammonium (NH4+/NAE) was significantly lower in patients with type 2 diabetes than in control subjects (0.70+/-0.12 versus 0.94+/-0.36; P<0.01); however, the greater NAE in patients with type 2 diabetes was not accounted for by the differences in unmeasured urinary anions. CONCLUSIONS: The overly acidic urine in patients with type 2 diabetes persists after controlling for dietary factors, body size, and age. The lower pH is due to a combination of greater NAE and lower use of ammonia buffers in patients with diabetes, which predisposes them to uric acid urolithiasis.

Biochemical and histological assessment of alkali therapy during high animal protein intake in the rat.

The Westernized diet is acidogenic due to the high content of sulfur-containing amino acids and relative deficiency of potassium organic anions. Chronic acid loads result in hypercalciuria and negative calcium balance often associated with loss of bone mineral. Alkali therapy tends to reverse the hypercalciuria but little is known regarding its effect on bone as assessed by bone histomorphometry. The present study utilized dynamic bone histomorphometry to evaluate the effects of alkali therapy on acid-induced changes in bone turnover. Serum and urine analyses and bone histomorphometry were assessed in adult rats after 2 months of either a low casein (LC) or high casein (HC) diet supplemented with either potassium chloride (KCl) or potassium citrate (KCit). Compared to animals on LC-KCl diet, HC-KCl diet delivered a substantial acid load as shown by significant increases in urinary sulfate, ammonium, and net acid excretion, and a lower urinary pH and citrate excretion without detectable changes in serum parameters. The acid load also resulted in hypercalciuria. Dynamic and static bone histomorphometry disclosed a significant reduction in cancellous bone volume and trabecular number associated with a 2.5-fold increase in eroded and a 3.5-fold increase in osteoclastic surfaces. There was also a near 2-fold increase in bone formation rate in rats on the HC-KCl diet. When animals on the HC diet were given KCit instead of KCl, all of the aforementioned changes in urine biochemistry and bone turnover were significantly attenuated or entirely prevented. These findings underscore the deleterious effects of high animal protein intake in promoting hypercalciuria and increasing bone turnover. Co-administration of potassium alkali attenuates or prevents these changes. In this animal model of high dietary animal protein intake, the major skeletal effect of alkali therapy is to reduce bone resorption, with little or no effect on bone formation.

Klotho variants and chronic hemodialysis mortality.

Patients with end-stage renal disease (ESRD) suffer exceptionally high mortality rates in their first year of chronic hemodialysis. Both vitamin D and fibroblast growth factor (FGF)-23 levels correlate with survival in these patients. Klotho is a protein in the vitamin D/FGF-23 signaling pathway that has been linked with accelerated aging and early mortality in animal models. We therefore hypothesized that genetic variation in the Klotho gene might be associated with survival in subjects with ESRD. We tested the association between 12 single nucleotide polymorphisms (SNPs) in the Klotho gene and mortality in a cohort of ESRD patients during their first year on hemodialysis (n = 1307 white and Asian). We found a significant association between the CC genotype of one tag SNP, rs577912, and increased risk for 1-yr mortality (RR, 1.76; 95% CI, 1.19-2.59; p = 0.003). This effect was even more marked among patients who were not treated with activated vitamin D supplementation (HR, 2.51; 95% CI, 1.18-5.34; p = 0.005). In lymphoblastoid cell lines derived from HapMap subjects, the CC genotype was associated with a 16-21% lower Klotho expression compared with the AA/AC genotype. Our data suggest that a specific Klotho variant (rs577912) is linked to survival in ESRD patients initiating chronic hemodialysis and that therapy with activated vitamin D may modify this risk.