Connexin43 in mesenchymal lineage cells regulates body adiposity and energy metabolism in mice.

Connexin43 (Cx43) is the most abundant gap junction protein present in the mesenchymal lineage. In mature adipocytes, Cx43 mediates white adipose tissue (WAT) beiging in response to cold exposure and maintains the mitochondrial integrity of brown adipose tissue (BAT). We found that genetic deletion of Gja1 (Cx43 gene) in cells that give rise to chondro-osteogenic and adipogenic precursors driven by the Dermo1/Twist2 promoter led to lower body adiposity and partial protection against the weight gain and metabolic syndrome induced by a high-fat diet (HFD) in both sexes. These protective effects were related to increased locomotion, fuel utilization, energy expenditure, nonshivering thermogenesis, and better glucose tolerance in conditionally Gja1-ablated mice. Accordingly, Gja1-mutant mice exhibited reduced adipocyte hypertrophy, partially preserved insulin sensitivity, increased BAT lipolysis, and decreased whitening under HFD. This metabolic phenotype was not reproduced with more restricted Gja1 ablation in differentiated adipocytes, suggesting that Cx43 in adipocyte progenitors or other targeted cells restrains energy expenditures and promotes fat accumulation. These results reveal what we believe is a hitherto unknown action of Cx43 in adiposity, and offer a promising new pharmacologic target for improving metabolic balance in diabetes and obesity.

Normal Levels of Ionized Calcium Despite Persistent Increase in Total Calcium in a Patient With IgA Paraproteinemia.

Approximately half of the calcium in the blood circulates in the ionized, free form; which is critical for cellular function. As a result, its levels are tightly regulated by homeostatic mechanisms dependent on hormones such as PTH, vitamin D, and fibroblast growth factor-23. The other half of the total calcium is in a complex with anions, predominantly albumin. Clinically, the levels of albumin are known to influence the relationship of total calcium to free calcium. However, the relevance of changes in other serum proteins on calcium homeostasis is less appreciated. We present the case of a 70-year-old woman who was followed over 5 years with persistently elevated total calcium levels but with normal ionized calcium levels. Her evaluation was notable for IgA paraprotein, which paralleled her history of elevated total serum calcium. Extensive clinical investigations did not reveal hyperparathyroidism or cancer-mediated hypercalcemia. Additional in vitro analyses comparing the plasma containing the IgA paraprotein against a healthy control revealed that a high-molecular-weight IgA paraprotein in the patient has increased capacity to reduce the amount of free calcium in solution, thus providing a direct mechanistic explanation for the clinical findings.

1,25-Dihydroxyvitamin D3 regulates furin-mediated FGF23 cleavage.

Intact fibroblast growth factor 23 (iFGF23) is a phosphaturic hormone that is cleaved by furin into N-terminal and C-terminal fragments. Several studies have implicated vitamin D in regulating furin in infections. Thus, we investigated the effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D] and the vitamin D receptor (VDR) on furin-mediated iFGF23 cleavage. Mice lacking VDR (Vdr-/-) had a 25-fold increase in iFGF23 cleavage, with increased furin levels and activity compared with wild-type (WT) littermates. Inhibition of furin activity blocked the increase in iFGF23 cleavage in Vdr-/- animals and in a Vdr-knockdown osteocyte OCY454 cell line. Chromatin immunoprecipitation revealed VDR binding to DNA upstream of the Furin gene, with more transcription in the absence of VDR. In WT mice, furin inhibition reduced iFGF23 cleavage, increased iFGF23, and reduced serum phosphate levels. Similarly, 1,25(OH)2D reduced furin activity, decreased iFGF23 cleavage, and increased total FGF23. In a post hoc analysis of a randomized clinical trial, we found that ergocalciferol treatment, which increased serum 1,25(OH)2D, significantly decreased serum furin activity and iFGF23 cleavage, compared with placebo. Thus, 1,25(OH)2D inhibits iFGF23 cleavage via VDR-mediated suppression of Furin expression, thereby providing a mechanism by which vitamin D can augment phosphaturic iFGF23 levels.

Altered Signaling and Desensitization Responses in PTH1R Mutants Associated with Eiken Syndrome.

The parathyroid hormone receptor type 1 (PTH1R) is a G protein-coupled receptor that plays key roles in regulating calcium homeostasis and skeletal development via binding the ligands, PTH and PTH-related protein (PTHrP), respectively. Eiken syndrome is a rare disease of delayed bone mineralization caused by homozygous PTH1R mutations. Of the three mutations identified so far, R485X, truncates the PTH1R C-terminal tail, while E35K and Y134S alter residues in the receptor's amino-terminal extracellular domain. Here, using a variety of cell-based assays, we show that R485X increases the receptor's basal rate of cAMP signaling and decreases its capacity to recruit ß-arrestin2 upon ligand stimulation. The E35K and Y134S mutations each weaken the binding of PTHrP leading to impaired ß-arrestin2 recruitment and desensitization of cAMP signaling response to PTHrP but not PTH. Our findings support a critical role for interaction with ß-arrestin in the mechanism by which the PTH1R regulates bone formation.

Intravenous Sodium Thiosulphate for Calciphylaxis of Chronic Kidney Disease: A Systematic Review and Meta-analysis.

Importance: Calciphylaxis is a rare disease with high mortality mainly involving patients with chronic kidney disease (CKD). Sodium thiosulphate (STS) has been used as an off-label therapeutic in calciphylaxis, but there is a lack of clinical trials and studies that demonstrate its effect compared with those without STS treatment. Objective: To perform a meta-analysis of the cohort studies that provided data comparing outcomes among patients with calciphylaxis treated with and without intravenous STS. Data Sources: PubMed, Embase, Cochrane Library, Web of Science, and ClinicalTrials.gov were searched using relevant terms and synonyms including sodium thiosulphate and calci* without language restriction. Study Selection: The initial search was for cohort studies published before August 31, 2021, that included adult patients diagnosed with CKD experiencing calciphylaxis and could provide a comparison between patients treated with and without intravenous STS. Studies were excluded if they reported outcomes only from nonintravenous administration of STS or if the outcomes for CKD patients were not provided. Data Extraction and Synthesis: Random-effects models were performed. The Egger test was used to measure publication bias. Heterogeneity was assessed using the I2 test. Main Outcomes and Measures: Skin lesion improvement and survival, synthesized as ratio data by a random-effects empirical Bayes model. Results: Among the 5601 publications retrieved from the targeted databases, 19 retrospective cohort studies including 422 patients (mean age, 57 years; 37.3% male) met the eligibility criteria. No difference was observed in skin lesion improvement (12 studies with 110 patients; risk ratio, 1.23; 95% CI, 0.85-1.78) between the STS and the comparator groups. No difference was noted for the risk of death (15 studies with 158 patients; risk ratio, 0.88; 95% CI, 0.70-1.10) and overall survival using time-to-event data (3 studies with 269 participants; hazard ratio, 0.82; 95% CI, 0.57-1.18). In meta-regression, lesion improvement associated with STS negatively correlated with publication year, implying that recent studies are more likely to report a null association compared with past studies (coefficient = -0.14; P = .008). Conclusions and Relevance: Intravenous STS was not associated with skin lesion improvement or survival benefit in patients with CKD experiencing calciphylaxis. Future investigations are warranted to examine the efficacy and safety of therapies for patients with calciphylaxis.

Physiopathology of Phosphate Disorders.

Intracellular phosphate is critical for cellular processes such as signaling, nucleic acid synthesis, and membrane function. Extracellular phosphate (Pi) is an important component of the skeleton. Normal levels of serum phosphate are maintained by the coordinated actions of 1,25-dihydroxyvitamin D3, parathyroid hormone and fibroblast growth factor-23, which intersect in the proximal tubule to control the reabsorption of phosphate via the sodium-phosphate cotransporters Npt2a and Npt2c. Furthermore, 1,25-dihydroxyvitamin D3 participates in the regulation of dietary phosphate absorption in the small intestine. Clinical manifestations associated with abnormal serum phosphate levels are common and occur as a result of genetic or acquired conditions affecting phosphate homeostasis. For example, chronic hypophosphatemia leads to osteomalacia in adults and rickets in children. Acute severe hypophosphatemia can affect multiple organs leading to rhabdomyolysis, respiratory dysfunction, and hemolysis. Patients with impaired kidney function, such as those with advanced CKD, have high prevalence of hyperphosphatemia, with approximately two-thirds of patients on chronic hemodialysis in the United States having serum phosphate levels above the recommended goal of 5.5 mg/dL, a cutoff associated with excess risk of cardiovascular complications. Furthermore, patients with advanced kidney disease and hyperphosphatemia (>6.5 mg/dL) have almost one-third excess risk of death than those with phosphate levels between 2.4 and 6.5 mg/dL. Given the complex mechanisms that regulate phosphate levels, the interventions to treat the various diseases associated with hypophosphatemia or hyperphosphatemia rely on the understanding of the underlying pathobiological mechanisms governing each patient condition.

Intravenous sodium thiosulphate for vascular calcification of hemodialysis patients-a systematic review and meta-analysis.

BACKGROUND: Vascular calcification (VC) is a common comorbidity among patients with chronic kidney disease (CKD), indicating major cardiovascular events. This study aimed to evaluate the effects and safety of intravenous sodium thiosulphate (STS) for VC in CKD patients. METHODS: Electronic databases were searched for clinical trials that provided data comparing outcomes among patients treated with and without STS. The PRISMA guidelines were followed. Efficacy was assessed using calcification scores and arterial stiffness. Safety was examined by analyzing adverse symptoms, electrolytes and bone mineral density (BMD). Random-effects models were performed. Meta-regression and sensitivity analysis were done. The risk of bias was assessed using the Cochrane tools. RESULTS: Among the 5601 publications, 6 studies involving 305 participants (mean age: 56 years, male: 56.6%) with all participants on maintenance hemodialysis met eligibility criteria. For efficacy, the progression in Agatston scores in the coronary arteries [107 patients, mean difference (MD): -241.27, 95% confidence interval (95% CI): -421.50 to -61.03] and iliac arteries (55 patients, MD: -382.00, 95% CI: -751.07 to -12.93) was lower in the STS treated group compared with controls. The increase in pulse wave velocity was lower in the STS group (104 patients, MD: -1.29 m/s, 95% CI: -2.24 to -0.34 m/s). No association was found between the change in calcification scores and STS regimen. For safety, gastrointestinal symptoms (e.g. nausea) and increased anion gap acidosis were noted. No reduction in BMD by STS was observed. CONCLUSIONS: Intravenous STS may attenuate the progression of VC and arterial stiffness in hemodialysis patients. Large and well-designed randomized controlled trials are warranted.

PTH, FGF-23, Klotho and Vitamin D as regulators of calcium and phosphorus: Genetics, epigenetics and beyond.

The actions of several bone-mineral ion regulators, namely PTH, FGF23, Klotho and 1,25(OH)2 vitamin D (1,25(OH)2D), control calcium and phosphate metabolism, and each of these molecules has additional biological effects related to cell signaling, metabolism and ultimately survival. Therefore, these factors are tightly regulated at various levels - genetic, epigenetic, protein secretion and cleavage. We review the main determinants of mineral homeostasis including well-established genetic and post-translational regulators and bring attention to the epigenetic mechanisms that affect the function of PTH, FGF23/Klotho and 1,25(OH)2D. Clinically relevant epigenetic mechanisms include methylation of cytosine at CpG-rich islands, histone deacetylation and micro-RNA interference. For example, sporadic pseudohypoparathyroidism type 1B (PHP1B), a disease characterized by resistance to PTH actions due to blunted intracellular cAMP signaling at the PTH/PTHrP receptor, is associated with abnormal methylation at the GNAS locus, thereby leading to reduced expression of the stimulatory G protein α-subunit (Gsα). Post-translational regulation is critical for the function of FGF-23 and such modifications include glycosylation and phosphorylation, which regulate the cleavage of FGF-23 and hence the proportion of available FGF-23 that is biologically active. While there is extensive data on how 1,25(OH)2D and the vitamin D receptor (VDR) regulate other genes, much more needs to be learned about their regulation. Reduced VDR expression or VDR mutations are the cause of rickets and are thought to contribute to different disorders. Epigenetic changes, such as increased methylation of the VDR resulting in decreased expression are associated with several cancers and infections. Genetic and epigenetic determinants play crucial roles in the function of mineral factors and their disorders lead to different diseases related to bone and beyond.

Functional Properties of Two Distinct PTH1R Mutants Associated With Either Skeletal Defects or Pseudohypoparathyroidism.

Consistent with a vital role of parathyroid hormone (PTH) receptor type 1 (PTH1R) in skeletal development, homozygous loss-of-function PTH1R mutations in humans results in neonatal lethality (Blomstrand chondrodysplasia), whereas such heterozygous mutations cause a primary failure of tooth eruption (PFE). Despite a key role of PTH1R in calcium and phosphate homeostasis, blood mineral ion levels are not altered in such cases of PFE. Recently, two nonlethal homozygous PTH1R mutations were identified in two unrelated families in which affected members exhibit either dental and skeletal abnormalities (PTH1R-V204E) or hypocalcemia and hyperphosphatemia (PTH1R-R186H). Arg186 and Val204 map to the first transmembrane helix of the PTH1R, and thus to a critical region of this class B G protein-coupled receptor. We used cell-based assays and PTH and PTH-related protein (PTHrP) ligand analogs to assess the impact of the R186H and V204E mutations on PTH1R function in vitro. In transiently transfected HEK293 cells, PTH1R-R186H mediated cyclic adenosine monophosphate (cAMP) responses to PTH(1-34) and PTHrP(1-36) that were of comparable potency to those observed on wild-type PTH1R (PTH1R-WT) (half maximal effective concentrations [EC50s] = 0.4nM to 1.2nM), whereas the response-maxima were significantly reduced for the PTH1R-V204E mutant (maximum effect [Emax] = 81%-77% of PTH1R-WT, p ≤ 0.004). Antibody binding to an extracellular hemagglutinin (HA) tag was comparable for PTH1R-R186H and PTH1R-WT, but was significantly reduced for PTH1R-V204E (maximum binding level [Bmax] = 44% ± 11% of PTH1R-WT, p = 0.002). The potency of cAMP signaling induced by a PTH(1-11) analog was reduced by ninefold and threefold, respectively, for PTH1R-R186H and PTH1R-V204E, relative to PTH1R-WT, and a PTH(1-15) radioligand analog that bound adequately to PTH1R-WT exhibited little or no specific binding to either mutant receptor. The data support a general decrease in PTH1R surface expression and/or function as a mechanism for PFE and a selective impairment in PTH ligand affinity as a potential PTH1R-mutation-based mechanism for pseudohypoparathyroidism. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Zoledronic Acid-Associated Fanconi Syndrome in Patients With Cancer.

Zoledronic acid (ZA) is an antiresorptive agent typically used for fracture prevention in postmenopausal osteoporosis, malignancy-associated metastatic bone lesions, and as a treatment for hypercalcemia. ZA is excreted almost entirely by the kidney; as a result, a reduction in renal clearance can lead to its accumulation and potential renal toxicity. Although uncommon, acute kidney injury (AKI) from intravenous bisphosphonates has been described, with different patterns including tubulointerstitial nephritis, acute tubular necrosis, as well as focal segmental glomerulosclerosis. Here we present 4 patients with an underlying malignancy who each developed evidence of generalized proximal tubular dysfunction, also known as Fanconi syndrome, approximately 1 week after receiving treatment with ZA. On presentation, all patients had AKI, low serum bicarbonate levels, abnormal urinary acidification, hypophosphatemia, hypokalemia, and increased urine amino acid excretion or renal glycosuria. Based on the temporal association between ZA infusion and the development of these electrolyte abnormalities, each case is highly suggestive of ZA-associated Fanconi syndrome. Due to the severity of presentation, all required discontinuation of ZA and ongoing electrolyte repletion. Nephrologists and oncologists should be aware of this complication and consider ZA as a possible trigger of new-onset Fanconi syndrome.

Conventional Chemotherapy Nephrotoxicity.

Conventional chemotherapies remain the mainstay of treatment for many malignancies. Kidney complications of these therapies are not infrequent and may have serious implications for future kidney function, cancer treatment options, eligibility for clinical trials, and overall survival. Kidney adverse effects may include acute kidney injury (via tubular injury, tubulointerstitial nephritis, glomerular disease and thrombotic microangiopathy), long-term kidney function loss and CKD, and electrolyte disturbances. In this review, we summarize the kidney complications of conventional forms of chemotherapy and, where possible, provide estimates of incidence, and identify risk factors and strategies for kidney risk mitigation. In addition, we provide recommendations regarding kidney dose modifications, recognizing that these adjustments may be limited by available supporting pharmacokinetic and clinical outcomes data. We discuss management strategies for kidney adverse effects associated with these therapies with drug-specific recommendations. We focus on frequently used anticancer agents with established kidney complications, including platinum-based chemotherapies (cisplatin, carboplatin, oxaliplatin), cyclophosphamide, gemcitabine, ifosfamide, methotrexate and pemetrexed, among others.

Beta-2 Microglobulin Amyloidosis: Past, Present, and Future.

Almost half a century has elapsed since the first description of dialysis-related amyloidosis (DRA), a disorder caused by excessive accumulation of ß-2 microglobulin (B2M). Within that period, substantial advances in RRT occurred. These improvements have led to a decrease in the incidence of DRA. In many countries, DRA is considered a "disappearing act" or complication. Although the prevalence of patients living with RRT increases, not all will have access to kidney transplantation. Consequently, the number of patients requiring interventions for treatment of DRA is postulated to increase. This postulate has been borne out in Japan, where the number of patients with ESKD requiring surgery for carpal tunnel continues to increase. Clinicians treating patients with ESKD have treatment options to improve B2M clearance; however, there is a need to identify ways to translate improved B2M clearance into improved quality of life for patients undergoing long-term dialysis.

Allostasis and the Clinical Manifestations of Mild to Moderate Chronic Hyponatremia: No Good Adaptation Goes Unpunished.

When homeostatic regulatory systems are unable to maintain a normal serum sodium concentration, the organism must adapt to demands of a disordered internal environment, a process known as "allostasis." Human cells respond to osmotic stress created by an abnormal serum sodium level with the same adaptations used by invertebrate organisms that do not regulate body fluid osmolality. To avoid intolerable changes in their volume, cells export organic osmolytes when exposed to a low serum sodium concentration and accumulate these intracellular solutes when serum sodium concentration increases. The brain's adaptation to severe hyponatremia (serum sodium < 120 mEq/L) has been studied extensively. However, adaptive responses occur with less severe hyponatremia and other tissues are affected; the consequences of these adaptations are incompletely understood. Recent epidemiologic studies have shown that mild (sodium, 130-135 mEq/L) and moderate (sodium, 121-129 mEq/L) chronic hyponatremia, long thought to be inconsequential, is associated with adverse outcomes. Adaptations of the heart, bone, brain, and (possibly) immune system to sustained mild to moderate hyponatremia may adversely affect their function and potentially the organism's survival. This review explores what is known about the consequences of mild to moderate chronic hyponatremia and the potential benefits of treating this condition.

Calciphylaxis-as a drug induced adverse event.

INTRODUCTION: Calciphylaxis is a rare but devastating disease with a mortality rate up to 50% in 1 year. It is characterized by profoundly painful ischemic skin lesions and vascular calcification that affects predominantly patients with end stage renal disease. The use of certain medications is an important modifiable risk factor in calciphylaxis and discontinuation of these is a mainstay of treatment. AREAS COVERED: This review will provide an overview of calciphylaxis and will focus on how certain therapeutic agents can affect the risk of calcification and associated thrombosis, key processes involved in the development of calciphylaxis. EXPERT OPINION: Calciphylaxis treatment requires a multi-modal approach including prevention, risk factor management, wound care, reperfusion, and use of fibrinolytics and antioxidants. Patients with end stage renal disease represent the most affected population. This population often has multiple medications prescribed, some worth reconsidering before starting or continuing them. When possible, we recommend stopping all potentially contributing medications in patients with calciphylaxis, including warfarin, active vitamin D, calcium supplements, and iron.

Where Do the Salt and Water Go? A Case of Profound Hyponatremia.

Treatment of profound hyponatremia is challenging. Severe symptoms mandate correction by 4 to 6 mEq/L within hours, but with risk factors for osmotic demyelination, daily correction should be <8 mEq/L. With a therapeutic window this narrow, clinicians would like to know how serum sodium (SNa) concentration will respond to their therapy. Based on isotopic measurements, Edelman showed SNa level to be a function of exchangeable sodium and potassium divided by total-body water. Edelman defined this relationship with linear regression yielding an equation of the form y = mx + b, where y is SNa level, x is exchangeable sodium and potassium divided by total-body water, m is the slope, and b is the intercept. Edelman said that the intercept of his regression "probably is a measure of the quantity of osmotically inactive exchangeable sodium and potassium per unit of body water." Predictive formulas are derived from Edelman's original linear regression, some including and some omitting the regression's intercept. We illustrate the performance and limitations of these formulas using comprehensive data for electrolyte and fluid balance obtained during the treatment of a critically patient who presented with an SNa concentration of 101 mEq/L.