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1.
The Effect of Extended Release Niacin on Markers of Mineral Metabolism in CKD.
Malhotra, R, Katz, R, Hoofnagle, A, Bostom, A, Rifkin, DE, Mcbride, R, Probstfield, J, Block, G, Ix, JH
Clinical journal of the American Society of Nephrology : CJASN. 2018;(1):36-44
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Abstract
BACKGROUND AND OBJECTIVES Niacin downregulates intestinal sodium-dependent phosphate transporter 2b expression and reduces intestinal phosphate transport. Short-term studies have suggested that niacin lowers serum phosphate concentrations in patients with CKD and ESRD. However, the long-term effects of niacin on serum phosphate and other mineral markers are unknown. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS The Atherothrombosis Intervention in Metabolic Syndrome with Low HDL/High Triglycerides: Impact on Global Health Trial was a randomized, double-blind, placebo-controlled trial testing extended release niacin in persons with prevalent cardiovascular disease. We examined the effect of randomized treatment with niacin (1500 or 2000 mg) or placebo on temporal changes in markers of mineral metabolism in 352 participants with eGFR<60 ml/min per 1.73 m2 over 3 years. Changes in each marker were compared over time between the niacin and placebo arms using linear mixed effects models. RESULTS Randomization to niacin led to 0.08 mg/dl lower plasma phosphate concentrations per year of treatment compared with placebo (P<0.01) and 0.25 mg/dl lower mean phosphate 3 years after baseline (3.32 versus 3.57 mg/dl; P=0.03). In contrast, randomization to niacin was not associated with statistically significant changes in plasma intact fibroblast growth factor 23, parathyroid hormone, calcium, or vitamin D metabolites over 3 years. CONCLUSIONS The use of niacin over 3 years lowered serum phosphorous concentrations but did not affect other markers of mineral metabolism in participants with CKD.
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2.
[GENETIC DISORDERS OF RENAL PHOSPHATE HANDLING].
Magen, D
Harefuah. 2017;(10):654-658
Abstract
Hereditary disorders of renal phosphate handling comprise a diverse group of genetic diseases, usually characterized by excessive urinary phosphate wasting and a negative phosphate balance. In the minority of cases, perturbations of renal phosphate handling are associated with excessive urinary phosphate reabsorption, leading to pathological hyperphosphatemia. Inorganic phosphate is an essential mineral in the human body, playing a crucial role in cellular metabolism and skeletal mineralization. Whole body phosphate balance is maintained by a highly controlled equilibrium between intestinal uptake, skeletal deposition and renal excretion. The human kidney plays a crucial role in phosphate homeostasis. The bulk filtered phosphate is reabsorbed in the renal proximal tubule by two specialized phosphate transporters, NaPi-IIa and NaPi-IIc. Phosphate balance is regulated by dietary phosphate intake, and by the action of the parathyroid hormone, vitamin D3 and fibroblast growth factor-23 (FGF-23). All these regulators exert their effect by modulating the activity of the proximal-tubular phosphate transporters, NaPi-IIa and NaPi-IIc. Based on the versatile molecular mechanism underlying various renal phosphate wasting disorders, these diseases can be divided into three main subgroups: (1) primary impairment of proximal tubular phosphate transporters; (2) disorders of FGF-23 metabolism; (3) generalized dysfunction of the proximal tubule, also known as renal Fanconi syndrome. The clinical similarity between various renal phosphate wasting disorders, combined with their rarity, pose a diagnostic and therapeutic challenge. Recent advancement in molecular biology has led to the identification of the genetic basis of many disorders in this group, has improved our understanding of underlying disease mechanisms, and enables accurate genetic diagnosis. Nevertheless, the current therapy of most renal phosphate wasting disorders is mainly supportive, with limited capacity to change their natural course.
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Osteomalacia-Inducing Tumors of the Brain: A Case Report, Review and a Hypothesis.
Fathalla, H, Cusimano, M, Di Ieva, A, Karamchandani, J, Fung, R, Kovacs, K
World neurosurgery. 2015;(1):189.e1-5
Abstract
BACKGROUND Osteomalacia-inducing tumors (OIT) are mesenchymal tumors that characteristically secrete fibroblast growth factor 23, resulting in a paraneoplastic syndrome of hypophosphatemic osteomalacia. These tumors are known to occur in soft tissues and bones in various sites. It is very unusual for OITs to occur intracranially, with only 10 reported intracranial cases since their discovery in 1959. The most common intracrainal OITs are phosphaturic mesenchymal tumors and hemangiopericytomas. We report a case of hypophosphatemic osteomalacia caused by a tumor in the right anterior cranial fossa. We also hypothesize, based on our review of the literature, that this entity is underdiagnosed. CASE DESCRIPTION A 49-year-old woman had a history of a nonhealing ankle fracture that required repeated surgery over 3 years. She subsequently was found to have severe hypophosphatemia and evidence of osteomalacia together with multiple occult fractures. A diagnosis of tumor-induced osteomalacia was suspected. An elevated serum fibroblast growth factor 23 level confirmed the diagnosis. An octreotide scan that was performed to locate the responsible tumor revealed an area of avid uptake in the right frontal lobe. Magnetic resonance imaging showed a large right anterior fossa extra-axial mass. The patient was referred for surgical intervention and was cured clinically after surgical removal of the tumor. Pathologic examination revealed a phosphaturic mesenchymal OIT. Her phosphate levels returned to normal 3 weeks after surgery. CONCLUSIONS The diagnosis of OIT should be considered in a case of severe hypophosphatemia and metabolic bone disease that is not explained by any other metabolic or hereditary disease. These tumors can occur intracranially and may be confused with a meningioma or a hemangiopericytoma. Taking OIT into consideration in such cases could lead to a shorter time to diagnosis and management, which in our case took 4 years.
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Serum phosphate predicts early mortality in adults starting antiretroviral therapy in Lusaka, Zambia: a prospective cohort study.
Heimburger, DC, Koethe, JR, Nyirenda, C, Bosire, C, Chiasera, JM, Blevins, M, Munoz, AJ, Shepherd, BE, Potter, D, Zulu, I, et al
PloS one. 2010;(5):e10687
Abstract
BACKGROUND Patients starting antiretroviral therapy (ART) for acquired immunodeficiency syndrome (AIDS) in sub-Saharan Africa have high rates of mortality in the initial weeks of treatment. We assessed the association of serum phosphate with early mortality among HIV-infected adults with severe malnutrition and/or advanced immunosuppression. METHODOLOGY/PRINCIPAL FINDINGS An observational cohort of 142 HIV-infected adults initiating ART in Lusaka, Zambia with body mass index (BMI) <16 kg/m(2) or CD4(+) lymphocyte count <50 cells/microL, or both, was followed prospectively during the first 12 weeks of ART. Detailed health and dietary intake history, review of systems, physical examination, serum metabolic panel including phosphate, and serum ferritin and high-sensitivity C-reactive protein (hsCRP) were monitored. The primary outcome was mortality. Baseline serum phosphate was a significant predictor of mortality; participants alive at 12 weeks had a median value of 1.30 mmol/L (interquartile range [IQR]: 1.04, 1.43), compared to 1.06 mmol/L (IQR: 0.89, 1.27) among those who died (p<0.01). Each 0.1 mmol/L increase in baseline phosphate was associated with an incremental decrease in mortality (AHR 0.83; 95% CI 0.72 to 0.95). The association was independent of other metabolic parameters and known risk factors for early ART-associated mortality in sub-Saharan Africa. While participant attrition represented a limitation, it was consistent with local program experience. CONCLUSIONS/SIGNIFICANCE Low serum phosphate at ART initiation was an independent predictor of early mortality among HIV patients starting ART with severe malnutrition or advanced immunosuppression. This may represent a physiologic phenomenon similar to refeeding syndrome, and may lead to therapeutic interventions that could reduce mortality.
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Refeeding syndrome: an important aspect of supportive oncology.
Marinella, MA
The journal of supportive oncology. 2009;(1):11-6
Abstract
Refeeding syndrome (RFS) is an underappreciated, yet common and potentially dangerous, constellation of metabolic derangements that can occur upon reinstitution of any type of nutritional intervention. The typical patient who experiences RFS has been malnourished for days to weeks and develops hypophosphatemia and, occasionally, hypokalemia and hypomagnesemia when administered a carbohydrate load in the form of glucose-containing fluids, total parenteral nutrition (TPN), tube feedings, or an oral diet. The pathophysiology of RFS is complex but mainly results from an acute intracellular shift in electrolytes, increased phosphate demand during tissue anabolism, and formation of high-energy phosphate bonds. Potential complications of RFS include fatal cardiac arrhythmia, systolic heart failure, respiratory insufficiency, and hematologic derangements. Because supportive care of the cancer patient often involves nutritional and metabolic support, any clinician involved with providing acute or palliative oncologic care should be familiar with the risks, manifestations, and treatment of RFS.
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The journey from vitamin D-resistant rickets to the regulation of renal phosphate transport.
Levine, BS, Kleeman, CR, Felsenfeld, AJ
Clinical journal of the American Society of Nephrology : CJASN. 2009;(11):1866-77
Abstract
In 1937, Fuller Albright first described two rare genetic disorders: Vitamin D resistant rickets and polyostotic fibrous dysplasia, now respectively known as X-linked hypophosphatemic rickets (XLH) and the McCune-Albright syndrome. Albright carefully characterized and meticulously analyzed one patient, W.M., with vitamin D-resistant rickets. Albright subsequently reported additional carefully performed balance studies on W.M. In this review, which evaluates the journey from the initial description of vitamin D-resistant rickets (XLH) to the regulation of renal phosphate transport, we (1) trace the timeline of important discoveries in unraveling the pathophysiology of XLH, (2) cite the recognized abnormalities in mineral metabolism in XLH, (3) evaluate factors that may affect parathyroid hormone values in XLH, (4) assess the potential interactions between the phosphate-regulating gene with homology to endopeptidase on the X chromosome and fibroblast growth factor 23 (FGF23) and their resultant effects on renal phosphate transport and vitamin D metabolism, (5) analyze the complex interplay between FGF23 and the factors that regulate FGF23, and (6) discuss the genetic and acquired disorders of hypophosphatemia and hyperphosphatemia in which FGF23 plays a role. Although Albright could not measure parathyroid hormone, he concluded on the basis of his studies that showed calcemic resistance to parathyroid extract in W.M. that hyperparathyroidism was present. Using a conceptual approach, we suggest that a defect in the skeletal response to parathyroid hormone contributes to hyperparathyroidism in XLH. Finally, at the end of the review, abnormalities in renal phosphate transport that are sometimes found in patients with polyostotic fibrous dysplasia are discussed.
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[Hyperphosphatemia and cardiovascular risk in patients on dialysis].
Basić-Jukić, N, Kes, P
Acta medica Croatica : casopis Hravatske akademije medicinskih znanosti. 2004;(3):207-13
Abstract
Cardiovascular diseases are the leading causes of mortality among patients with end-stage renal disease (ESRD), with arterial disease and left ventricular hypertrophy being the two principal factors of the high mortality rate in this population. In addition to traditional risk factors (age, gender, diabetes, hypertension, lifestyle, hyperlipidemia, smoking, hyperhomocystinemia), inflammation, oxidative stress and disorders of mineral metabolism may contribute to cardiovascular risk in patients with uremic syndrome. High serum phosphate may influence vascular calcifications directly and indirectly, by worsening secondary hyperparathyroidism. Several treatment options are available for the treatment of hyperphosphatemia and secondary hyperparathyroidism in patients with ESRD. The treatment approach includes a diet low in phosphorus, with less than 1 g/kg/day of protein. Vitamin D supplementation is an important part of treatment. Phosphate binding agents are in most of the patients necessary in addition to diet. Aluminum hydroxide has been widely used for many years. It is very potent, but also very toxic, with severe encephalopathy as the most dangerous side effect. Calcium salts are less potent, and were considered safe for use in patients on dialysis. However, improvement in the understanding of vascular calcifications has demonstrated that calcium overload significantly contributes to widespread atherosclerosis in patients with ESRD. Sevelamer-hydrochloride is a novel non-aluminum, non-calcium containing phosphate binder, which is capable of reducing the levels of phosphorus as well as of low-density lipoprotein cholesterol, and increasing high-density lipoprotein cholesterol.
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8.
Disorders of phosphate metabolism--pathomechanisms and management of hypophosphataemic disorders.
Ritz, E, Haxsen, V, Zeier, M
Best practice & research. Clinical endocrinology & metabolism. 2003;(4):547-58
Abstract
Hypophosphataemia does not necessarily indicate phosphate (Pi) depletion. In acute emergencies such as septicaemia, alkalosis or re-feeding, hypophosphataemia may result from redistribution of Pi from the extracellular to the intracellular space. Hypophosphataemia from true Pi depletion gives rise to skeletal (osteomalacia) and extraskeletal (myopathy, cardiomyopathy) disorders. It is practically never the result of diminished nutritional intake. The most severe syndromes of Pi depletion result from diminished tubular Pi re-absorption and renal Pi wasting. In the differential diagnosis mainly four conditions have to be considered: (i) tumour-associated osteomalacia, (ii) X-linked hypophosphataemia (XLH), (iii) autosomal dominant hypophosphataemia, and (iv) hypercalcaemic renal phosphate wasting. Recent molecular insight has put fibroblast growth factor (FGF-23) into the centre of pathophysiological considerations because of (i) overproduction (tumour-associated osteomalacia) or (ii) hypothetically, accumulation resulting from mutations causing resistance to processing or degradation (autosomal dominant hypophosphataemia) or (iii) loss-of-function of a protease (PHEX) interfering with FGF-23 breakdown (XLH). In oncogenic osteomalacia the treatment of choice is resection of the tumour. Recently, pharmacological treatment has also become possible, i.e. administration of octreotide. XLH and autosomal dominant hypophosphataemia must be managed by oral administration of phosphate and calcitriol. In patients with gastrointestinal intolerance to phosphate or with severely symptomatic bone disease, prolonged intravenous administration of Pi is necessary.
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Phosphate, the renal tubule, and the musculoskeletal system.
Laroche, M
Joint bone spine. 2001;(3):211-5
Abstract
A component of ATP, phosphate is at the hub of the energy-related mechanisms operative in muscle cells. Together with calcium, phosphate is involved in bone tissue mineralization: thus, a chronic alteration in the metabolism of phosphate can induce bone and joint disorders. Diagnosis of chronic hypophosphatemia. Serum phosphate, calcium, and creatinine should be assayed simultaneously. Serum calcium is increased in hypophosphatemia caused by hyperparathyroidism and decreased in osteomalacia. Urinary phosphate excretion should be measured in patients with a normal serum calcium level and a serum phosphate level lower than 0.80 mmol/L. A decrease in urinary phosphate excretion to less than 10 mmol/24 h strongly suggests a gastrointestinal disorder, such as malabsorption, antacid use, or chronic alcohol abuse. In patients with a urinary phosphate excretion greater than 20 mmol/24 h, the maximal rate of tubular reabsorption of phosphate (TmPO4) and the ratio of TmPO4 over glomerular filtration rate (GFR) should be determined to look for phosphate diabetes. Manifestations and causes of phosphate diabetes in adults. Moderately severe phosphate diabetes in adults manifests as chronic fatigue, depression, spinal pain, and polyarthralgia, with osteoporosis ascribable to increased bone resorption. Although many cases are idiopathic, investigations should be done to look for X-linked vitamin D-resistant rickets missed during childhood, a mesenchymatous tumor, or Fanconi's syndrome with renal wasting of phosphate, glucose, and amino acids. Management of phosphate diabetes. Phosphate supplementation and, in patients with normal urinary calcium excretion, calcitriol produce some improvement in the symptoms and increase the bone mineral density. Whether dipyramidole is clinically effective remains unclear.