Emerging drugs for hyperphosphatemia.

Cardiovascular mortality is the leading cause of death in the uremic patient. Hyperphosphatemia is considered an independent risk factor associated with cardiovascular morbidity and mortality in dialysis patients. As phosphate control is not efficient with diet or dialysis, phosphate binders are commonly prescribed in patients with chronic renal failure. Aluminum salts, the first phosphate binders, even if effective, have several side effects due to their deposition in CNS, bone and hematopoietic cells. Calcium-containing phosphate binders, used in the last 15 years, increase total body calcium load and may exacerbate metastatic calcification, thus, increasing the risk of cardiovascular mortality. Recently two new compounds non-aluminum and non-calcium phosphate binders, sevelamer hydrochloride and lanthanum carbonate, have been introduced. Sevelamer, besides the effect on phosphate, has been associated with reduction of coronary and aortic calcification and with other pleiotropic effects especially on lipid metabolism. Lanthanum carbonate has similar phosphate control to calcium-based binders with less incidence of hypercalcemia but long-term clinical studies are needed for testing long-term exposure. Recently the authors found in dialysis patients, that salivary phosphorus correlated with serum phosphorus. Therefore, they supposed that the use of salivary phosphate binders could reduce its absorption and represent a chance for reducing the serum phosphate concentration in uremic patients.

The clinical management of hyperphosphatemia.

As renal function declines in patients with end-stage renal disease (ESRD), excess dietary phosphorus accumulates in the bloodstream. Routine dialysis removes up to 70% of absorbed phosphorus; therefore, hyperphosphatemia is found in the majority of patients with ESRD. The consequences of this imbalance include secondary hyperparathyroidism and osteodystrophy. Recent studies have also documented that hyperphosphatemia can lead to soft-tissue and vascular calcification; the latter is strongly associated with cardiovascular disease and, thus, increased mortality and morbidity. The reduction of phosphorus levels is, therefore, an important therapeutic target in this patient group. Management of hyperphosphatemia using conventional phosphate binders is not always successful. However, emerging therapies aim to reduce the incidence of hyperparathyroidism, bone disease, and calcification in this patient population. In this article, the consequences of hyperphosphatemia are reviewed, and recent developments in the treatment of the condition are discussed.

The role of sevelamer in achieving the kidney disease outcomes quality initiative (K/DOQI) guidelines for hyperphosphatemia.

BACKGROUND: End-stage renal disease (ESRD) is a chronic health care problem associated with multiple co-morbidities and escalating costs. Disregulation of mineral metabolism (principally hyperphosphatemia and hypercalcemia) contributes to substantial morbidity and mortality. Accordingly, new and more-aggressive Kidney Disease Outcomes Quality Initiative (K/DOQI) Guidelines from the National Kidney Foundation promote lower serum phosphorus (3.5-5.5 mg/dL), lower calcium (8.4-9.5 mg/dL), and lower calcium-phosphorus product (< 55 mg(2)/dL(2)) targets. REVIEW FINDINGS: Traditional calcium-based and metal-based phosphate binders are effective but are associated with side effects and toxicity that limit their use. Achieving rigorous K/DOQI goals demands higher therapeutic doses of phosphate binders and may require more-aggressive use of calcium-free and metal-free phosphate binders. Sevelamer hydrochloride is a calcium- and metal-free polymer that binds phosphate effectively without contributing to calcium load or metal accumulation. In the Treat-to-Goal trial, sevelamer-treated dialysis patients had less progression of coronary and aortic calcification than patients treated with calcium-based binders. This offers the potential promise of reducing cardiovascular morbidity and mortality. The 800-mg tablet (Renagel) increases the daily sevelamer dose while reducing the number of tablets required per meal. Nine of the 800-mg tablets per day (3 x 800-mg tablets tid with meals) of sevelamer monotherapy have been shown to achieve K/DOQI serum phosphorus and calcium-phosphorus product targets. CONCLUSION: In summary, this review of the current evidence-base concludes that the new, more-aggressive, K/DOQI goals limit the use of metal-based and calcium-based phosphate binders. Sevelamer offers the advantages of lowering serum phosphorus without the risks of calcium or metal accumulation - and offers the promise of slowing the progression of vascular calcification and potentially reducing the morbidity and mortality of hemodialysis patients.

Mineral metabolism and aging: the fibroblast growth factor 23 enigma.

PURPOSE OF REVIEW: The regulation of phosphate homeostasis was thought to be passively mediated by the calciotrophic hormones parathyroid hormone and 1,25(OH)2D3. This article summarizes the emerging trends that show an active regulation of phosphate homeostasis by fibroblast growth factor 23 (FGF-23) - a process fairly independent of calcium homeostasis - and how altered mineral ion metabolism may affect the aging process. RECENT FINDINGS: A major breakthrough in FGF-23 biology has been achieved by the demonstration of strikingly similar physical/biochemical phenotypes of Fgf-23(-/-) and klotho hypomorph mice, which eventually led to the identification of klotho as a cofactor in FGF-23 and its receptor interactions. Furthermore, FGF-23 has emerged as a counter regulator of the renal 1alpha(OH)ase and sodium-phosphate cotransporter activities to modulate phosphate homeostasis. Finally, studies point towards a role of dentine matrix protein 1 in affecting phosphate homeostasis, in coordination with FGF-23. SUMMARY: Recent mouse genetic studies have broadened our understanding of biochemical/molecular pathways involved in phosphate homeostasis, and linked FGF-23 to such regulation. Understanding the molecular interactions of essential calcium and phosphate regulators will enhance our knowledge of the coordinated regulation of mineral ion metabolism, and will help to redefine the molecular pathology of age-associated lesions accompanied by abnormal mineral ion metabolism such as vascular calcifications and osteoporosis.

Phosphate metabolism in the setting of chronic kidney disease: significance and recommendations for treatment.

Phosphorus is an essential mineral that plays a crucial role in cell structure and metabolism. In living organisms, phosphorus exists surrounded by four oxygen atoms to form phosphate (PO(4)). Within cells, PO(4) regulates enzymatic activity and serves as an essential component of nucleic acids, adenosine triphosphate, and phospholipid membranes. Outside cells, PO(4) primarily resides in bone and teeth as hydroxyapatite. A small amount of inorganic PO(4) circulates in serum, with levels balanced by gastrointestinal intake, renal excretion, and a set of specific hormones. Under normal conditions, PO(4) is excreted through the kidneys. Among patients with end stage renal disease (ESRD) receiving chronic dialysis, circulating PO(4) levels typically rise to levels well above the normal laboratory range. Higher serum PO(4) levels are strongly associated with arterial calcification and mortality in this setting. Among predialysis patients with chronic kidney disease (CKD), phosphaturic hormones enhance renal PO(4) excretion to maintain serum PO(4) levels within the high-normal laboratory range. Recently, high-normal serum PO(4) levels have been associated with cardiovascular (CV) events and mortality among individuals who have CKD and among those who have normal kidney function. This review discusses PO(4) metabolism in the context of CKD, examines associations of PO(4) levels with adverse outcomes in the CKD setting, and suggests treatment strategies for moderating serum PO(4) levels.

[The systemic environment and dental development. From the clinical to the molecular approach]. / Environnement systémique et développement dentaire. De la clinique à l'approche moléculaire.

Clinical observation of patients with disordered phosphocalcium metabolism has demonstrated that dyschromia and/or dental dysplasias systematically accompany such disorders. A certain action of this steroid on dental buds has been demonstrated after analysis of the effects of experimental vitamin D deficiency in the rat: vitamin D would seem to control the behaviour of cells undergoing differentiation and also after this process is complete. Dentinogenesis and amelogenesis would appear principally to be affected. Two proteins, calbindins D-9K and -28K, may constitute the molecular mediators of this ameloblastic regulation.

Head and neck manifestations of tumoral calcinosis.

Intraoral facial and laryngeal features of tumoral calcinosis are reviewed in six patients of Jewish-Yemenite descent. Extraoral features included calcified masses, erythematous patches, and angular cheilitis. Oral soft tissue findings included papillary hyperplasia of the lip vermilion and velvety-red macules on the tongue, palate, and buccal mucosa. Gingival findings included advanced periodontitis and an erythematous marginal gingivitis. In all patients, orthognathic evaluation revealed a concave profile, retruded maxilla, and relative mandibular prognathism. Although previously reported clinical dental abnormalities were not present, extracted teeth demonstrated abnormal dentin. Hoarseness was present in all patients and was the earliest appearing feature in two patients. The appearance of these head and neck findings preceded the classical manifestations of tumoral calcinosis and may be helpful in the early diagnosis of this entity. The varied reported features of tumoral calcinosis support the notion that this disease may present multiple formes frustes with variable clinical expressivity.