[Prevention of extraskeletal calcifications in uremia]. / Prevenzione delle calcificazioni extrascheletriche nel paziente uremico.

Secondary hyperparathyroidism (HPTH) is a common feature in end-stage renal disease (ESRD) patients. The three main factors involved in secondary HPTH pathogenesis are high phosphate levels, hypocalcemia and vitamin D deficiency. Recently, many studies demonstrated a strong association between bone disease and cardiovascular events in chronic kidney disease patients. In addition, cardiovascular events are the most frequent cause of death in patients with chronic renal failure. Increased levels of serum phosphorus and calcium-phosphate product are directly involved in the pathogenesis of extraskeletal calcifications (blood vessels, soft tissues, etc) in dialyzed patients compared to the non-uremic population. Recent studies suggested that vascular calcification is due not only to a passive calcium-phosphate deposition on atherosclerotic arteries, but also to active mechanisms regulated by bone-associated genes. In particular, fetuin and matrix Gla-protein are two 'protective' proteins associated with reduced vascular calcification and could be the regulatory keys in preventing this process in renal failure. The limitations of calcium salts as phosphate-binders in patients with advanced renal failure have been thoroughly evaluated in the last 5 yrs. New phosphate binders, which do not contain aluminum or calcium, have been developed to reduce the risk of extraskeletal calcifications in ESRD.

Potassium-based dilutional method to measure hemodialysis access recirculation.

BACKGROUND: Assessment of access recirculation (AR) is crucial to dialysis efficiency and there is thus a need for a method yielding a highly accurate, fast, easy and economical measurement that can be applied in any busy dialysis clinic. Non-urea based dilutional methods are more accurate than urea based methods and avoid problems with cardiopulmonary recirculation, but they require expensive specialized devices, which limit their applicability. METHODS: We developed a simple dilutional method of AR which does not require any specific device, based on the determination of serum potassium [K+] in two samples. Briefly, a basal sample is drawn at the time of needle insertion (basal [K+]); needles are connected to blood lines and blood flow rate is quickly increased to 300 ml/mm; a second sample (arterial [K+]) is drawn from the arterial line port within 5 to 10 seconds, to avoid errors due to cardiopulmonary recirculation of the normal saline entering the blood stream. At this time, if recirculation is present, part of the normal saline will enter the arterial line and dilute the serum [K+]. The AR formula is: AR (%) = 100 x [1 - arterial K+/basal K+]. We compared our method with the two-needle urea and ultrasound velocity dilution methods. RESULTS: AR values by the ultrasound method > 10% were hypothesized as gold standard for AR, against which values obtained with the potassium method were compared. The potassium based method showed: sensitivity (100%,); specificity (95%); predictive value, positive (91%); predictive value, negative (100%). In addition, the potassium based method appears to be more reliable than the two-needle urea based method. CONCLUSION: Our method, similar to other dilutional methods, is not influenced by cardiopulmonary recirculation or veno-venous disequilibrium and is fast and accurate. Moreover it is very simple, economical, and can easily be performed in any dialysis unit.

Sevelamer reduces calcium load and maintains a low calcium-phosphorus ion product in dialysis patients.

BACKGROUND: Sevelamer HCl, a non-aluminum, non-calcium containing hydrogel, has proved an effective phosphate binder in North American hemodialysis patients. This single-center, open-label, dose titration study assessed the efficacy of sevelamer in a cohort of European hemodialysis patients with different dietary habits, in particular with lower phosphate intake. The aim of the study was to obtain a calcium x phosphate product lower than 60 mg2/dL2 in all patients. METHODS: Administration of calcium- or aluminum-based phosphate binders was discontinued during a two-week washout period. Nineteen patients whose serum phosphate level at the end of washout was greater than 5.5 mg/dL (1.78 mmol/L) qualified to receive sevelamer for six weeks. Based on the degree of hyperphosphatemia during washout, patients were started on 403 mg sevelamer capsules with a dose schedule different from previous studies. Only one capsule was administered at breakfast, and the rest of the phosphate binder was divided equally at the two main meals. Sevelamer could be increased by two capsules per day every two weeks, if necessary. A second two-week washout period followed. RESULTS: Mean serum phosphorus rose from a baseline of 5.3 +/- 1.0 to 7.4 +/- 1.4 mg/dL at the end of washout, then declined to 5.4 +/- 0.8 mg/dL (p < 0.001) by the end of the six-week treatment period and rebounded significantly to 7.1 +/- 1.1 mg/dL after the second two-week washout. Calcium x phosphate product showed a similar pattern, decreasing significantly from 64.1 +/- 14.1 to 46.9 +/- 7.4 mg2/dL2 (p < 0.001) after six weeks of sevelamer. A level of less than 50 mg2/dL2 was reached by 68% of patients, and 95% had less than 60 mg2/dL2. The mean dose of sevelamer at the end of treatment was 3.1 +/- 0.6 g per day. As expected, calcium declined from 9.2 +/- 0.5 to 8.7 mg/dL (p < 0.01) during the initial washout after stopping calcium-based phosphate binders, but remained stable thereafter. Ionized calcium did not change significantly throughout the washout and sevelamer treatment. However, interruption of calcium salts led to a 81% reduction of total calcium intake. CONCLUSIONS: We confirmed in an European sample of hemodialysis patients that sevelamer can reduce phosphate levels without inducing hypercalcemia. The drug can also be successfully used to reduce mean calcium x phosphate levels below 50 mg2/dL2, closer to normal values. Although similar results can be obtained with other phosphate binders, a concomitant accumulation of aluminum, calcium or magnesium could be detrimental to patients.

Deposition of kappa and lambda light chains in amyloid filaments of dialysis-related amyloidosis.

beta 2-Microglobulin (beta 2m) is considered to be the amyloidogenic precursor in dialysis-related amyloidosis, although the implication of other relevant cofactors in the pathogenesis of this disease has also been hypothesized. It is conceivable that substances found in amyloid deposits might represent something more than simple codeposition, possibly playing a pathogenic role in amyloidogenesis. Along these lines, a detailed analysis of the protein composition of amyloid fibrils purified from synovial material surgically obtained from nine patients on long-term dialysis was carried out. By the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, several other protein components, in addition to beta 2m, were found. These were characterized by NH2 amino-terminal sequencing and immunoblotting. In fibrils obtained by water extraction, which fulfill the electron microscopy criteria of highly pure amyloid material, polyclonal kappa and lambda light chains were detected with a concentration of 15 micrograms/mL in the water extraction material; the beta 2m concentration was 200 micrograms/mL. Light microscopy immunohistochemistry was performed on samples from five patients. Amyloid deposits reacted with anti-beta 2m, and anti-light (kappa, lambda), chain antibodies. The immunoreaction of amyloid filaments to anti-beta 2m, anti-lambda, and anti-kappa light chain antibodies was also tested by electron microscopy by use of the immunogold staining procedure. Amyloid filaments were labeled by the three antibodies and showed a different intensity of immunostaining apparently related to their different aggregation pattern. These observations demonstrate that polyclonal immunoglobulin light chains (kappa and lambda) are not contaminants but, together with beta 2m, represent a major constituent of amyloid deposits in dialysis-related osteoarticular amyloidosis, thus indicating their possible role in amyloidogenesis.

Complement activation in dialysis: effects on cytokines, lymphocyte activation and beta 2 microglobulin.

Anaphylatoxins generated by complement activation by filter membranes are present in plasma during hemodialysis (HD). In the presence of endotoxins which may contaminate the dialysate, they can trigger monocytes to produce interleukin-1 (IL-1) and tumor necrosis factor (TNF), with detrimental effects for the patients. We have investigated whether or not the use of complement activating (cuprophan) and non- (or less-) activating membranes (polysulfone, polymethylmethacrylate or polyacrylonitrile) per se influences cytokine levels in HD patients. Our results indicate that if a sterile bicarbonate solution is used as dialysate, there are no significant increases in IL-1, TNF, interleukin-2 (IL-2) and soluble IL-2 receptors (sIL-2r) throughout HD, even with cuprophan membranes. Moreover even a prolonged use of this membrane (three months) did not change pre-dialysis levels of cytokines and receptors. Use of complement activating membranes also does not influence beta 2 microglobulin levels.

CO binding to hemoglobin and myoglobin in equilibrium with a gas phase of low PO2 value.

The aim of this paper was to measure the binding of CO to myoglobin and hemoglobin at various PO2 values. For this purpose we have studied an "in vitro" system made up of solutions of hemoglobin and myoglobin equilibrated in two connected tonometers with the same gas phase of various PO2 and PCO. The results indicate that a significant proportion of CO is released by hemoglobin and binds myoglobin at low PO2 values (approximately 2-3 Torr), in qualitative agreement with the predictions of a previous computer simulation of the "in vivo" system.