Calcium and phosphorus
Hyperphosphatemia and vascular calcification in end-stage renal disease

https://doi.org/10.1053/j.jrn.2004.09.027Get rights and content

Vascular calcification is a common finding in atherosclerosis and a serious problem in uremic patients. Because of the correlation of hyperphosphatemia and vascular calcification, the ability of extracellular inorganic phosphate levels to regulate human aortic smooth muscle cell (HSMC) culture mineralization in vitro was examined. HSMC cultured in media containing normal physiologic levels of inorganic phosphate (1.4 mM) did not mineralize. In contrast, HSMC cultured in media containing phosphate levels comparable with those seen in hyperphosphatemic individuals (>1.4 mM) showed dose-dependent increases in mineral deposition. Mechanistic studies showed that elevated phosphate treatment of HSMC also enhanced the expression of the osteoblastic differentiation markers osteocalcin and osf2/Cbfa-1. The effects of elevated phosphate on HSMC were mediated by a sodium-dependent phosphate cotransporter (NPC) as indicated by the ability of the specific NPC inhibitor phosphonoformic acid to dose-dependently inhibit phosphate-induced calcium deposition as well as osteocalcin and Cbfa-1 gene expression. The NPC in HSMC was identified as Pit-1, a member of the novel type III NPCs. These data suggest that elevated phosphate may directly stimulate HSMC to undergo phenotypic changes that predispose to calcification and offers a novel explanation of the phenomenon of vascular calcification under hyperphosphatemic conditions. Furthermore, we examined the factors affecting peripheral vascular calcification in 332 nondiabetic hemodialysis patients. There were 45 nondiabetic patients with vascular calcification. In multivariate logistic regression, the significant factors affecting vascular calcification were advanced age, longer duration of hemodialysis, increased phosphate concentrations, male gender, and lower predialysis diastolic pressure. Our findings suggest that an elevated phosphate level may directly stimulate HSMC to undergo phenotypic changes that predispose to calcification and offer a novel explanation of the phenomenon of vascular calcification under hyperphosphatemic conditions.

Section snippets

Inorganic phosphate levels as an important regulator of vascular calcification

The molecular mechanisms regulating vascular calcification remain obscure. A clue to this process, however, is suggested by several observations linking serum phosphate levels with a tendency toward vascular calcification. First, a high serum phosphate level is highly correlated with the extent of vascular calcification and vascular disease.15, 16 One of the most common causes of hyperphosphatemia is chronic renal failure and subsequent kidney dialysis, in which serum inorganic phosphate levels

Inorganic phosphate levels regulate vascular smooth muscle cell calcification

We hypothesized that vascular smooth muscle cells (HSMC) might respond to elevated extracellular Pi levels by increasing promineralizing molecules, thereby leading to vascular calcification. The role of inorganic phosphate in vascular HSMC mineralization was investigated using an in vitro model system that was shown to mimic many of the features seen in human metastatic vascular calcification in vivo. We found that HSMC cultured in media containing normal serum phosphate levels do not

Evidence for a sodium-dependent phosphate cotransporter system in HSMC

How might HSMC sense elevated phosphate levels? To determine the mechanism by which HSMC sense elevated Pi levels, we examined phosphate uptake in the HSMC using radiolabeled Pi. HSMC took up Pi in a sodium-dependent and Pi gradient-dependent manner. These properties are consistent with the presence of a sodium-dependent phosphate cotransporter (NPC). Three types of NPCs have been identified to date and are grouped according to homology. Type I and type II NPCs are predominantly restricted to

HSMC culture mineralization is dependent on NPC function

To determine whether NPC function was important in HSMC culture calcification, we used the NPC inhibitor phosphonoformic acid (PFA). In the presence of PFA, HSMC Pi uptake was almost completely abolished. Inhibition of transport was dose-dependent, and half-maximal inhibition occurred between 0.1 and 0.5 mmol/L PFA. Consistent with a role in culture mineralization, PFA completely inhibited HSMC calcification. PFA effects were dose-dependent and half-maximal between 0.1 and 0.5 mmol/L PFA.

How

Increased phosphate level is associated with vascular calcification in dialysis patients

Vascular calcification, which significantly increases cardiovascular and other causes of mortality,28 is highly prevalent in dialysis patients. Factors affecting vascular calcification in dialysis patients include advanced age, derangement of calcium-phosphate metabolism,29 and diabetes.30 We examined 332 nondiabetic patients (192 male and 140 female, 59 ± 13 years). Hand roentgenography was performed, and visible vascular calcification of the hand arteries was evaluated. There were 45

References (30)

  • H.T. Blumenthal et al.

    Calcification of the media of the human aorta and its relationship to intimal arteriosclerosis, aging and disease

    Am J Pathol

    (1944)
  • R.J. Frink et al.

    Significance of calcification of the coronary arteries

    Am J Cardiol

    (1970)
  • P.J. Fitzgerald et al.

    Contribution of localized calcium deposits to dissection after angioplasty. An observational study using intravascular ultrasound

    Circulation

    (1992)
  • T.H. Loecker et al.

    Fluoroscopic coronary artery calcification and associated coronary disease in asymptomatic young men

    J Am Coll Cardiol

    (1992)
  • C.M. Giachelli

    Ectopic calcificationGathering hard facts about soft tissue mineralization

    Am J Pathol

    (1999)
  • K.E. Watson et al.

    TGF-b1 and 25-hydroxycholesterol stimulate osteoblast-like vascular cells to calcify

    J Clin Invest

    (1994)
  • A. Shioi et al.

    Beta-glycerophosphate accelerates calcification in cultured bovine vascular smooth muscle cells

    Arterioscler Thromb Vasc Biol

    (1995)
  • T. Wada et al.

    Calcification of vascular smooth muscle cell culturesInhibition by osteopontin

    Circ Res

    (1999)
  • G. Luo et al.

    Spontaneous calcification of arteries and cartilage in mice lacking matrix GLA protein

    Nature

    (1997)
  • O.M. Kuro et al.

    Mutation of the mouse klotho gene leads to a syndrome resembling ageing

    Nature

    (1997)
  • S.S. Spicer et al.

    Mice carrying a CAR-2 null allele lack carbonic anhydrase II immunohistochemically and show vascular calcification

    Am J Pathol

    (1989)
  • L.E. Thornell et al.

    Null mutation in the desmin gene gives rise to a cardiomyopathy

    J Mol Cell Cardiol

    (1997)
  • N. Bucay et al.

    Osteoprotegerin-deficient mice develop early onset osteoporosis and arterial calcification

    Genes Dev

    (1998)
  • F. Parhami et al.

    Role of molecular regulation in vascular calcification

    J Atheroscler Thromb

    (1996)
  • A.C. Alfrey et al.

    Role of phosphate and pyrophosphate in soft tissue calcification

    Adv Exp Med Biol

    (1978)

    • Cited by (40)

    • Advances in diagnosis and management of secondary and tertiary hyperparathyroidism

      2019, Advances in Treatment and Management in Surgical Endocrinology

    • Phosphate metabolism, hyperphosphatemia, and hypophosphatemia

      2018, Encyclopedia of Endocrine Diseases

    • Relationship between serum osteoprotegerin and vascular calcifications in hemodialysis patients

      2017, Egyptian Heart Journal
      Citation Excerpt :

      Also, Nigel et al.2 reported that the presence and severity of AAC were related to age, duration of dialysis and the presence of cardiovascular disease, but there was no significant relationship between AACS and serum markers of mineral metabolism (phosphate, calcium, PTH, 25-hydroxy vitamin D), lipids, C-reactive protein or the presence of diabetes. Moreover, Nishizawa et al.49 concluded that the significant factors affecting vascular calcification were advanced age, longer duration of hemodialysis, increased phosphate concentrations and lower predialysis diastolic pressure. In the current study, CACS directly correlated with age, duration of hemodialysis, phosphorus, calcium, PTH, alkaline phosphatase and CRP, cholesterol, triglycerides, LDL, and inversely with HDL.

    • Complete resolution of calciphylaxis after kidney transplantation

      2013, American Journal of Kidney Diseases
      Citation Excerpt :

      Many theories emphasize the effect of hyperphosphatemia, which leads to soft-tissue mineralization of vascular smooth muscle. It has yet to be proved whether this effect, which has been shown in large vessels,7-9 also occurs in small arterioles. In the case of a well-functioning transplant, the patient's tubular function is restored and parathyroid hormone concentration decreases, which causes serum phosphate concentrations to normalize within months.10-12

    • Serum phosphate and hip bone mineral density as additional factors for high vascular calcification scores in a community-dwelling: The São Paulo Ageing & Health Study (SPAH)

      2013, Bone
      Citation Excerpt :

      Interestingly, we observed an association of high AACS and serum phosphate, even within normal range. It has been hypothesized that serum phosphate is an important additional regulator of vascular calcification, since high serum phosphate in uremic patients is a well-known risk factor for vascular calcification [16]. The phosphate increased in these patients promotes mineralization of smooth muscle cells (SMC), in vivo and in vitro, leading to vascular calcification [35].

    • Knowledge of haemodialysis patients about Nutrition: a cross-sectional study from Palestine

      2022, Palestinian Medical and Pharmaceutical Journal
    View all citing articles on Scopus
    View full text
    Copyright © 2005 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.