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Cardiovascular calcification is a common consequence of aging, diabetes, hypercholesterolemia, mechanically abnormal valve function, and chronic renal insufficiency. Although vascular calcification may appear to be a uniform response to vascular insult, it is a heterogenous disorder, with overlapping yet distinct mechanisms of initiation and progression. A minimum of four histoanatomic variants-atherosclerotic (fibrotic) calcification, cardiac valve calcification, medial artery calcification, and vascular calciphylaxis-arise in response to metabolic, mechanical, infectious, and inflammatory injuries. Common to the first three variants is a variable degree of vascular infiltration by T cells and macrophages. Once thought benign, the deleterious clinical consequences of calcific vasculopathy are now becoming clear; stroke, amputation, ischemic heart disease, and increased mortality are portended by the anatomy and extent of calcific vasculopathy. Along with dystrophic calcium deposition in dying cells and lipoprotein deposits, active endochondral and intramembranous (nonendochondral) ossification processes contribute to vascular calcium load. Thus vascular calcification is subject to regulation by osteotropic hormones and skeletal morphogens in addition to key inhibitors of passive tissue mineralization. In response to oxidized lipids, inflammation, and mechanical injury, the microvascular smooth muscle cell becomes activated. Orthotopically, proliferating stromal myofibroblasts provide osteoprogenitors for skeletal growth and fracture repair; however, in valves and arteries, vascular myofibroblasts contribute to cardiovascular ossification. Current data suggest that paracrine signals are provided by bone morphogenetic protein-2, Wnts, parathyroid hormone-related polypeptide, osteopontin, osteoprotegerin, and matrix Gla protein, all entrained to endocrine, metabolic, inflammatory, and mechanical cues. In end-stage renal disease, a "perfect storm" of vascular calcification often occurs, with hyperglycemia, hyperphosphatemia, hypercholesterolemia, hypertension, parathyroid hormone resistance, and iatrogenic calcitriol excess contributing to severe calcific vasculopathy. This brief review recounts emerging themes in the pathobiology of vascular calcification and highlights some fundamental deficiencies in our understanding of vascular endocrinology and metabolism that are immediately relevant to human health and health care.
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PMID:Osteogenic regulation of vascular calcification: an early perspective. 1510 15

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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PMID:[Hyperphosphatemia and cardiovascular risk in patients on dialysis]. 1550 84

Patients with end-stage renal disease have greatly elevated risks of atherosclerotic disease. Vascular calcification in advanced atherosclerosis is a common feature in ESRD patients. Risk factors of atherosclerosis in ESRD patients are coronary risk factors such as hypertension, diabetes and hyperlipidemia and hyperphosphatemia. Bone associated proteins including osteopontin, matrix Gla protein and osteoprotegerin may be involved in the progression of atherosclerosis.
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PMID:[Risk factors of atherosclerosis in end-stage renal disease patients]. 1557 49

Dialysis, in its routine 3 x week manifestation, undoubtedly is life saving. The therapy is limited by a number of factors that persist despite the development of safe machines and highly efficient dialyzers. The turnover of known, and very likely, many unknown uremic toxins, is rapid so that 3 x week dialysis is accompanied by relatively high levels of these substances. Only the lower part of the range of molecular weights of those putative uremic toxins, which are small proteins, are removed by current therapies. For substances such as phosphorus, long dialysis is successful in removing the excess retained dietary phosphorus, perhaps the only proven uremic toxin. The difficulty of achieving a normal extracellular volume is probably a major factor in the progression and poor outcomes of cardiovascular disease despite the potential improvement with management of hyperlipidemia, inflammation, potential arrhythmias, and cardiac failure due to other pathogenetic mechanisms. New developments in understanding of Vitamin D metabolism, Ca receptor inhibitor drugs, and control of hyperphosphatemia may reduce the problems of kidney bone disease and the adverse cardiovascular effect of calcium phosphorus disposition. Dialysis more frequent than 3 x week is already routinely, if only infrequently, used to deal with the very large volume or overhydrated patient. However, daily dialysis--whether short or long-is now beginning as a therapy with a large randomized NIH trial in the offing. Currently, the net growth of dialysis is approximately 4% a year, but it would not be surprising if there were a gradual increase in growth rates as CKD patients live longer due to control of cardiac disease. Eventually, the treatment of early kidney disease should reduce the dialysis population, particularly if diabetes can be better controlled or even prevented. The dialysis aspect of nephrology as a profession for physicians, nurses, and technicians appears to be on a long course with increasing demand and the need for applying what is already known, while awaiting new technical developments. Wearable artificial kidneys, involving the application of technology and use of new materials, are currently being investigated. The presence of nephrologists during the actual dialysis treatment is certainly not as evident as it was in the past. Reimbursement methodology has ensured at least a minimum of documented visits by nephrologists or nurse practitioners to the dialysis patient during treatment. It is controversial as to the value of this, but evidence has been presented that certain outcomes, such as use of appropriate dialysis dose and blood chemistries, are improved by more frequent visits. The present is over.
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PMID:Technology: kidneys--the present of dialysis. 1567 76

Vascular calcifications are more frequent in dialysis patients than in the general population or in patients with cardiovascular disease (CVD) and normal renal function. The reasons for this high incidence are multiple; they include traditional factors such as hypertension, diabetes, dyslipidemia, and specific factors such as sodium overload, hyperomocysteinemia, chronic inflammation and oxidative stress, as well as mineral metabolism disturbances. Specifically, hyperphosphatemia and the elevated calcium (Ca) x phosphate product have been associated with an increased risk for the development of vascular calcification and death. Treatment with Ca salts can induce hypercalcemia, increased Ca x phosphate product and Ca overload. Sevelamer substitution for Ca salts has been documented to attenuate the progression of coronary artery and aortic calcification. A possible mechanism explaining this observation could be ongoing Ca loading related to oral Ca ingestion. Treatment with Ca salts could induce Ca overload, particularly in patients dialyzed against a high dialysate Ca (>1.5 mmol/L) solution, which is known to determine a positive dialysis balance. Conversely, an overall negative Ca balance can result from low Ca dialysate use (1.25 mmol/L) when the patients do not receive Ca supplements or vitamin D metabolites. Maintaining normal Ca and phosphate balances remains a primary goal in the management of dialysis patients. Control of hyperphopshataemia should be achieved either using Ca and aluminum-free phosphate binders, such as sevelamer, or Ca salts, alone or in combination, provided that a daily oral elemental Ca intake of 1.5 g is not exceeded.
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PMID:[Control of calcium and phosphate metabolism and prevention of vascular calcifications in uremic patients]. 1578 2

Renal osteodystrophy is an important complication of chronic kidney disease characterized by abnormal bone turnover with varied bone histologic changes. Etiology is multifactorial including abnormalities of serum calcium, phosphorus, and 1,25(OH)(2)-vitamin D deficiency; secondary hyperparathyroidism; age; cause of kidney disease; diet; renal replacement therapy; and drug therapy. In addition, there is evidence that there may be ethnic differences. Our study is a description of a case series of hormonal and biochemical abnormalities of bone disease in end-stage renal disease patients in South India. A total of 115 patients were studied; 86% were on hemodialysis and 14% were on peritoneal dialysis (age, 47.31 +/- 14.66 years). Sixty-eight percent were men. Diabetes was the cause of end-stage renal disease in 29.5%. Intact parathyroid hormone (PTH) level was 124.6 +/- 174.9 pg/mL and less than twice normal in 69.5% of patients. Hypocalcemia was present in 16.5% and hyperphosphatemia in 35.7% of patients. Empirical vitamin D was prescribed in 40% of patients. Age, sex, diabetic status, and vitamin D use were similar in patients with high PTH (130 pg/mL) and low PTH levels (< 130 pg/mL). Bone histologic studies were not performed owing to economic limitation. But the biochemical and hormonal results are suggestive of a mild form of osteodystrophy in Indian patients. Etiology remains uncertain but differences in dietary intake, tropical climate, vitamin D activation, vitamin D receptor polymorphism, parathyroid gland sensitivity, and PTH target organ sensitivity may account for the difference in pattern in bone disease.
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PMID:Parathyroid hormone and biochemical profile in chronic kidney disease patients in South India. 1619 Oct 55

Soft-tissue and vascular calcification are highly prevalent in end-stage renal disease (ESRD). Vascular calcifications manifest as both medial and intimal calcification of arteries and are a hallmark of the accelerated atherosclerosis observed in uremia. The nature of vascular calcification is progressive, and is associated with arterial stiffness and increased cardiovascular mortality. Age, duration of dialysis, and diabetes mellitus are clear determinants of the severity of vascular calcification; however, more recently novel insights into the pathomechanisms of unwanted calcification processes have been gained. Disturbances of mineral metabolism such as hyperphosphatemia and hypercalcemia appear to contribute to progressive calcification, not only by passive precipitation but by actively inducing changes in vascular smooth muscle cell behavior toward an osteoblast-like phenotype. Specific calcium-regulatory proteins may act locally or systemically as calcification inhibitors. Dysregulations of calcification inhibitors, including fetuin-A, matrix Gla protein, osteoprotegerin, and pyrophosphates may also be pathophysiologically relevant factors in the context of uremic extraosseous calcification. In this context, low serum fetuin-A levels were recently found to be associated with increased mortality in cohorts of dialysis patients. This overview intends to summarize current knowledge of the scientific concepts involved in the pathogenesis of extraosseous calcification in ESRD.
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PMID:Pathogenesis of vascular calcification in dialysis patients. 1636 52

Vascular calcification is often encountered in advanced atherosclerotic lesions and is a common consequence of aging. Calcification of the coronary arteries has been positively correlated with coronary atherosclerotic plaque burden, increased risk of myocardial infarction, and plaque instability. Chronic kidney disease (CKD) patients have two to five times more coronary artery calcification than healthy age-matched individuals. Vascular calcification is a strong prognostic marker of cardiovascular disease mortality in CKD patients. Vascular calcification has long been considered to be a passive, degenerative, and end-stage process of atherosclerosis and inflammation. However, recent evidence indicates that bone matrix proteins such as osteopontin, matrix Gla protein (MGP), and osteocalcin are expressed in calcified atherosclerotic lesions, and that calcium-regulating hormones such as vitamin D3 and parathyroid hormone-related protein regulate vascular calcification in in vitro vascular calcification models based on cultured aortic smooth muscle cells. These findings suggest that vascular calcification is an actively regulated process similar to osteogenesis, and that bone-associated proteins may be involved in the development of vascular calcification. The pathogenesis of vascular calcification in CKD is not well understood and is almost multifactorial. In CKD patients, several studies have found associations of both traditional risk factors, such as hypertension, hyperlipidemia, and diabetes, and uremic-specific risk factors with vascular calcification. Most patients with progressive CKD develop hyperphosphatemia. An elevated phosphate level is an important risk factor for the development of calcification and cardiovascular mortality in CKD patients. Thus, it is hypothesized that an important regulator of vascular calcification is the level of inorganic phosphate. In order to test this hypothesis, we characterized the response of human smooth muscle cell (HSMC) cultures to inorganic phosphate levels. Our findings indicate that inorganic phosphate directly regulates HSMC calcification through a sodium-dependent phosphate transporter mechanism. After treatment with elevated phosphate, there is a loss of smooth muscle lineage markers, such as alpha-actin and SM-22alpha, and a simultaneous gain of osteogenic markers such as cbfa-1 and osteocalcin. Elevated phosphate 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. Furthermore, putative calcification inhibitory molecules have been identified using mouse mutational analyses, including MGP, beta-glucosidase, fetuin-A, and osteoprotegerin. Mutant mice deficient in these molecules present with enhanced cardiovascular calcification, demonstrating that specific molecules are normally important in suppressing vascular calcification. These findings suggest that the balance of inducers, such as phosphate, and inhibitors, such as MGP, fetuin-A, and others, are likely to control whether or not calcification occurs under pathological conditions.
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PMID:Vascular calcification in chronic kidney disease. 1650 29

Cardiovascular complications are a major clinical problem in patients with chronic kidney disease and end-stage renal failure; cardiac death accounts for approximately 40-50% of all deaths in these patients. Death from cardiovascular causes is up to 20 times more common in uremic patients than in the general population with the risk being even higher than in patients with diabetes mellitus. A high rate of myocardial infarction and excessive cardiac mortality have repeatedly been documented in patients with kidney disease and renal failure. Not only is the prevalence of myocardial infarction high, but also the case fatality rate is significantly higher in uremic patients with and without diabetes, respectively, compared to nonuremic patients. This is of particular interest since the prevalence of coronary atheroma in uremic patients was shown to be approximately 30% by autopsy and coronary angiography studies. Thus, coronary factors, i.e. atherosclerosis, and non-coronary factors may play an important role in the genesis of cardiac complications in the renal patient. In addition, renal failure recently has also be identified as a predictor of mortality in different stages of peripheral vascular disease. In particular, marked differences in the pathogenesis, morphology and course of atherosclerosis and arteriosclerosis under the conditions of renal failure have been documented. Among others increased plaque formation and particularly higher proportion and intensity of vascular calcification have been found in clinical and autopsy studies. In addition to the so-called classical or traditional risk factors, an important role for nonclassical risk factors such as microinflammation, hyperphosphatemia and oxidative stress has been documented in patients with renal failure and is discussed in detail.
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PMID:Atherosclerosis and vascular calcification in chronic renal failure. 1653 22

Vascular calcification increasingly afflicts our aging and dysmetabolic population. Once considered a passive process, it has emerged as an actively regulated form of calcified tissue metabolism, resembling the mineralization of endochondral and membranous bone. Executive cell types familiar to bone biologists, osteoblasts, chondrocytes, and osteoclasts, are seen in calcifying macrovascular specimens. Lipidaceous matrix vesicles, with biochemical and ultrastructural "signatures" of skeletal matrix vesicles, nucleate vascular mineralization in diabetes, dyslipidemia, and uremia. Skeletal morphogens (bone morphogenetic protein-2 (BMP) and BMP4 and Wnts) divert aortic mesoangioblasts, mural pericytes (calcifying vascular cells), or valve myofibroblasts to osteogenic fates. Paracrine signals provided by these molecules mimic the epithelial-mesenchymal interactions that induce skeletal development. Vascular expression of pro-osteogenic morphogens is entrained to physiological stimuli that promote calcification. Inflammation, shear, oxidative stress, hyperphosphatemia, and elastinolysis provide stimuli that: (1) promote vascular BMP2/4 signaling and matrix remodeling; and (2) compromise vascular defenses that limit calcium deposition, inhibit osteo/chondrogenic trans-differentiation, and enhance matrix vesicle clearance. In this review, we discuss the biology of vascular calcification. We highlight how aortic fibrofatty tissue expansion (adventitia, valve interstitium), the adventitial-medial vasa, vascular matrix, and matrix vesicle metabolism contribute to the regulation of aortic calcium deposition, with greatest emphasis placed on diabetic vascular disease.
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PMID:Molecular mechanisms of vascular calcification: lessons learned from the aorta. 1660 Dec 33


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