Temporin G, an amphibian antimicrobial peptide against influenza and parainfluenza respiratory viruses: Insights into biological activity and mechanism of action

Treatment of respiratory viral infections remains a global health concern, mainly due to the inefficacy of available drugs. Therefore, the discovery of novel antiviral compounds is needed; in this context, antimicrobial peptides (AMPs) like temporins hold great promise. Here, we discovered that the harmless temporin G (TG) significantly inhibited the early life-cycle phases of influenza virus. The in vitro hemagglutinating test revealed the existence of TG interaction with the viral hemagglutinin (HA) protein. Furthermore, the hemolysis inhibition assay and the molecular docking studies confirmed a TG/HA complex formation at the level of the conserved hydrophobic stem groove of HA. Remarkably, these findings highlight the ability of TG to block the conformational rearrangements of HA2 subunit, which are essential for the viral envelope fusion with intracellular endocytic vesicles, thereby neutralizing the virus entry into the host cell. In comparison, in the case of parainfluenza virus, which penetrates host cells upon a membrane-fusion process, addition of TG to infected cells provoked ~1.2 log reduction of viral titer released in the supernatant. Nevertheless, at the same condition, an immunofluorescent assay showed that the expression of viral hemagglutinin/neuraminidase protein was not significantly reduced. This suggested a peptide-mediated block of some late steps of viral replication and therefore the impairment of the extracellular release of viral particles. Overall, our results are the first demonstration of the ability of an AMP to interfere with the replication of respiratory viruses with a different mechanism of cell entry and will open a new avenue for the development of novel therapeutic approaches against a large variety of respiratory viruses, including the recent SARS-CoV2.

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.

The mechanisms of hyperphosphatemia-induced vascular calcification

Extensive calcification of the arterial wall and soft tissues is a frequent feature of patients with end-stage chronic kidney disease (CKD stage 5). Hyperphosphatemia and secondary hyperparathyroidism have been extensively investigated as inducing factors in cardiovascular calcification. In fact, cardiovascular disease in renal failure is associated with bone metabolism alterations. Together with passive deposition of calcium-phosphate in extraskeletal tissues, it has recently been demonstrated that inorganic phosphate induces arterial calcification directly through a real “ossification” of the tunica media in the vasculature of CKD patients. Therefore, control of serum phosphate in CKD patients becomes crucial in preventing increases in calcium × phosphate product, secondary hyperparathyroidism, and ultimately vascular calcification.

Facial Changes in Adult Uremic Patients on Chronic Dialysis: Possible Role of Hyperparathyroidism

Background

Uremic patients on regular dialytic treatment (RDT) are often affected by a complex metabolic syndrome leading to osteodystrophy. Bone changes are primarily due to high bone turn over, often combined with a mineralization defect leading to increased bone fractures and bone deformities. Although rarely considered, the craniofacial skeleton represents one of the peculiar targets of this complex metabolic disease whose more dramatic pattern is a form of leontiasis ossea. This complication, although described, has never been evaluated in depth nor quantitatively assessed. In order to assess facial deformities in uremic conditions and to understand the possible relation with hyperparathyroidism, we undertook a quantitative evaluation of soft facial structures in a cohort of uremic patients undergoing RDT.

Methods

The three-dimensional coordinates of 50 soft-tissue facial landmarks were obtained by an electromagnetic digitizer in 10 male and 10 female patients with chronic renal insufficiency aged 53–81 years, and in 34 healthy individuals of the same age, ethnicity and sex. Uremic patients were enrolled according to hyperparathyroid status (PTH < 300 pg/mL and PTH > 500 pg/mL). From the landmarks, facial distances, angles and volumes were calculated according to a geometrical face model.

Results

Overall, the uremic patients had significantly larger facial volumes than the reference subjects. The effect was particularly evident in the facial middle third (maxilla), leading to an inversion of the mandibular-maxillary ratio. Facial dimensions were increased in all three spatial directions: width (skull base, mandible, nose), length (nose, mandible), and depth (mid face, mandible). The larger maxilla was accompanied by a tendency to more prominent lips (reduced interlabial angle). Some of the facial modifications (nose, lips, mandible) were significantly related to the clinical characteristics of the patients (age, duration of renal insufficiency and PTH levels).

Conclusions

This report, the first in the literature, shows that facial structures of uremic patients are enlarged in comparison with matched normal subjects and that increased bone turnover could be responsible – at least in part – for facial bone changes.

Salvage Insertion of Tunneled Central Venous Catheters in the Internal Jugular Vein after Accidental Catheter Removal

Purpose

Tunneled catheters are widely used for intermediate to long-term hemodialysis (HD) access, but are prone to several complications that can require catheter replacement. Replacing malfunctioning catheters with a new line, placed in a different access site, can lead to problems with multiple vein occlusions. This has led many nephrologists to continue using the same vein as long as possible by guidewire catheter exchanges, to preserve other veins for future use. We describe a guidewire exchange technique for the Ash-Split catheter in the internal jugular vein.

Methods

In three patients, the exchange was performed because of partial catheter removal, as evidenced by the outward dislocation of the Dacron cuff. In these patients, the guidewire was inserted through the catheter. In two additional patients, the catheter had been completely removed by accident: the replacement of the dislodged tunneled venous catheters was attempted 5 hr and 1 day after accidental removal. In these patients, the guidewire was inserted through the previous tunnel. After guidewire placement, a skin incision was made in the supraclavicular region. The metal guidewire was easily located inside the fibrous structure that had previously surrounded the catheter. The guidewire was then extracted from the subcutaneous tunnel and used to insert a new catheter safely and easily after creating a new tunnel. Patients were routinely given antibiotic prophylaxis (1 g of cefazolin) immediately before the procedure. A strict aseptic technique was used, including several sterile glove changes.

Results

No infections developed following this procedure, which has the potential for bacterial contamination. All procedures were successful. Only in one patient did we have to convert to a different catheter: it was not possible to replace the old Ash-Split catheter with the same dual-lumen catheter because of difficulties in inserting the peel away introducer-catheter complex. In this patient, rather than forcing it with larger dilators or trying to disrupt the fibrin sheath with balloon dilatation, a single lumen Tesio catheter was successfully placed. In both patients who completely lost the previous catheter, the guidewire was readily reinserted through the subcutaneous tunnel into the vein. Catheter function was excellent in all patients, with a test blood flow rate on the 1st catheter use >350 ml/min.

Conclusions

We described a new method for catheter exchange, which allows the easy insertion of a new catheter and the creation of a new and safer subcutaneous tunnel. In addition, we demonstrated that in cases of complete catheter removal, it is possible to reinsert a catheter in the same vein through a guidewire, even when reinsertion was attempted up to 1 day later.

How to avoid and manage a pneumothorax

Pneumothorax is one of the most frequent complications during percutaneous central vascular cannulation. When choosing a site for central vascular access, the internal jugular vein is preferable to other vessels, for the lower frequency of related complications, including pneumothorax. This review intends to summarize the current state of the art on how to avoid and, if it occurs, to manage this rare but relevant complication. In order to prevent pneumothorax, as well as other relevant complications of central vein cannulation, it is advisable to use ultrasound guidance whenever possible. If pneumothorax occurs, it is important to recognize its signs and symptoms. To exclude the presence of asymptomatic pneumothorax, in the normal clinical routine a chest X-ray should be obtained within 4 hours from the procedure of central vein cannulation of subclavian and internal jugular veins. If promptly recognized, pneumothorax can be managed quickly and in a relatively easy way. Depending on its size and symptoms, and in particular when a tension pneumothorax is supected, treatment can vary from simple observation to a chest tube insertion or, in the latter case, to an emergency thoracentesis needle insertion in the pleural space.

Hyperphosphatemia in Dialysis Patients: The Therapeutic Role of Lanthanum Carbonate

Phosphate overload is a dramatic consequence in end-stage renal disease (ESRD) patients. Recent studies have well documented that abnormalities in mineral and bone metabolism in these patients are associated with increased cardiovascular morbidity and mortality. Elevated serum phosphate and calcium-phosphate product levels play an important role in the pathogenesis of secondary hyperparathyroidism and extra-skeletal calcification in dialysis patients. Furthermore, inorganic phosphate may cause vascular calcification directly through a real “ossification” of the tunica media in the vasculature of ESRD patients.

The “classical” treatment of secondary hyperparathyroidism and hyperphosphatemia in ESRD patients consists of either calcium- or aluminum-based phosphate binders and calcitriol administration. Unfortunately, this “old generation” therapy is not free of complications. This review paper suggests that new calcium- and aluminum-free phosphate binders, such as lanthanum carbonate, can be used to treat hyperphosphatemia and secondary hyperparathyroidism in ESRD patients.

[Prevention and treatment of secondary hyperparathyroidism in non-dialyzed patients with stage 3-5 chronic kidney diease]

Deficiencies in vitamin D and vitamin D receptor (VDR) activation adversely affect cardiovascular health in the general population and in people at high risk of cardiovascular disease, as well as contributing to secondary hyperparathyroidism in patients with chronic kidney disease (CKD). Furthermore, epidemiological and observational data indicate that there is a close interrelationship between progressive renal dysfunction in CKD, cardiovascular disease, and mortality. The causes of death in patients even with only moderate kidney dysfunction are commonly associated with cardiovascular events. Modulation of vitamin D levels results in correlative regulatory effects on mineral homeostasis, hypertension, vascular disease, and calcification, as well as a number of other endpoints in cardiac and renal disease. The use of VDR activators to treat these and other parameters outside of cardiovascular and renal disease not only results in enhanced patient health but significantly lowers the risk of mortality in CKD and non-CKD patients with low systemic activity of vitamin D. The cardiovascular and renal systems continue to demonstrate their interrelated effects on each other, particularly when vitamin D and VDR signaling are considered.

[Cardiovascular effects of VDR and CaSR activation]

Cardiovascular complications are the most common cause of death in uremic patients, especially those on chronic dialysis. One of the major findings is massive calcium deposition in the vessel walls. There is general consensus about the correlation between the distribution of vascular calcification and increased risk of death due to cardiovascular disease. An emerging issue is the possible beneficial role of vitamin D receptor (VDR) activation in reducing the morbidity and mortality rates in patients on chronic dialysis, as shown in large, although retrospective, studies. Still open is the possible role of CaSR activators in ameliorating the clinical course of patients on dialysis, although calcimimetics are able to improve the Ca-P-PTH serum profile and increase the number of patients within the international guidelines parameters. This review has been structured to give the readers an updated opinion on the possible positive impact of VDR and CaSR activators in terms of all-cause and cardiovascular morbidity and mortality in dialysis patients.

[Pathogenesis and treatment of vascular calcification in CKD]

Increased vascular calcification is a major cause of cardiovascular events in patients with chronic kidney disease (CKD). It is the result of an active ossification process counteracted by ''bone'' proteins such as osteopontin, alkaline phosphatase, osteoprotegerin, and osteocalcin. Chronic kidney disease - mineral and bone disorder (CKD-MBD) is a systemic disorder of mineral and bone metabolism that occurs in CKD. In addition to abnormalities in the serum calcium and phosphate profile, CKD-MBD is characterized by abnormalities of bone turnover, mineralization, volume and growth as well as vascular calcification. Considering that the presence and extent of vascular calcification in CKD portend a poor prognosis, many efforts have been made to shed light on this complicated phenomenon to prevent vascular calcium deposition and its progression. Indeed, careful control of calcium load, serum phosphate and parathyroid hormone along with the use of calcium-free phosphate binders and vitamin D receptor activators represent a new therapeutic armamentarium to improve quality of life and reduce mortality in CKD.

Impaired brachial artery endothelial flow-mediated dilation and orthostatic stress in hemodialysis patients

PURPOSE

Chronic kidney disease (CKD) is associated with an impaired endothelial function, which may contribute to cardiovascular events. Whether impairment in endothelial function is involved in the circulatory response to orthostatic stress is unknown. We assessed endothelial function via brachial artery flow-mediated dilation (BAFMD), an index of endothelial-dependent vasodilation.

METHODS

We measured changes in brachial artery diameter (BAD) and blood flow by Doppler ultrasound in 35 CKD patients on hemodialysis, 37 young healthy controls (HC) and 50 non-uremic matched controls (MC), in the supine position and after 60 degrees head-up tilting (HUT).

RESULTS

In the supine position, endothelial flow-mediated BAD was significantly increased in HC (p<0.001) and MC (p<0.01) while no significant changes were detected in CKD. Mean percent blood flow changes were HC+323.5%, MC+195.1% and CKD+158.8% (HC vs. CKD p<0.001; HC vs. MC p<0.001; MC vs. CKD p=0.04). Similarly, during HUT mean BAD and blood flow increases were significantly impaired in CKD patients.

CONCLUSION

In CKD patients, an impaired response in the physiologic vascular reactivity, suggesting endothelial dysfunction, was found in the supine position and after orthostasis by BAFMD. Our results are in favor of a possible adjunctive role of uremia in the abnormal brachial artery response.

[Therapeutic options for mineral metabolism disorders in dialysis patients: a case report]

Mineral metabolism disorders are well-recognized complications in patients with chronic kidney disease (CKD). Furthermore, hyperphosphatemia and secondary hyperparathyroidism are associated with both renal osteodystrophy and cardiovascular disease. During the last 5 years, new therapeutic options have become available to treat these conditions in CKD. We describe the case of a 70-year-old lady with a dialysis history of 5 years and a number of cardiovascular risk factors (hypertension, hypercholesterolemia and obesity). Unfortunately, the patient was poorly compliant with any pharmaceutical treatment. After 2 years, a pharmacological approach with a low dosage of calcium salts and sevelamer HCl, subsequently changed to lanthanum carbonate, intravenous paricalcitol, and cinacalcet HCl reached the goals suggested by the current guidelines. Every nephrologist should look at the pathogenesis and treatment of hyperphosphatemia and secondary hyperparathyroidism. New options are now available and may help the clinician to obtain satisfactory short- and long-term outcomes in the treatment of this disease.

[The bone-vasculature-axis interaction: new insights into the pathogenesis of vascular calcification.]

It is commonly accepted that the first cause of morbidity and mortality in chronic kidney disease (CKD) is the cardiovascular (CV) disease, in which vascular calcification (VC) plays a central pathogenetic role. In CKD population, mineral metabolism disorders have been recently investigated not only as key factors on renal osteodystrophy but also as inducing players on extra-skeletal calcification. Clearly, either high phosphate (P) or high calcium (Ca) concentration induce vascular smooth muscle cells mineralization in vitro studies. In fact, VC is induced by a cell-mediated process, which actively accompanies the traditional and passive Ca-P deposition in arterial walls. Interestingly, lack of inhibitory proteins, such as fetuin-A (alpha2-HS glycoprotein, AHSG), matrix GLA protein (MGP), osteoprotegerin (OPG), and bone morphogenetic protein 7 (BMP-7) are the regulatory key factors in preventing VC in uremic conditions.

[Avascular jaw osteonecrosis in a hemodialysis patient treated with bisphosphonates]

Bisphosphonates are molecules derived from pyrophosphates,but, unlike pyrophosphates, they are resistant to enzymatic hydrolysis. Bisphosphonates are used in the treatment of Paget's disease, cancer-related osteolysis, myeloma, primary hyperparathyroidism, and osteoporosis. In dialysis patients bisphosphonates may be used to reduce bone pain due to renal osteodystrophy. We describe the case of a 60-year-old woman with a history of breast cancer who had been on dialysis for 8 years. She had been receiving clodronic acid at 100 mg per week intravenously for the last 2 years. A year ago, the patient underwent surgical extraction of the lower right second molar. Her jaw pain increased in the following days. An orthopanthograph and a CT scan of the head showed osteolysis, and a surgical osteotomy was performed. Histological examination led to a diagnosis of avascular osteonecrosis of the jaw. Avascular osteonecrosis is typically described in the jaw. In this case, prolonged bisphosphonate treatment may have worsened the osteonecrosis.

Lanthanum carbonate: Time to abandon prejudices?

Since lanthanum carbonate has become available there has been much interest in its use as a non-calcium-containing phosphate binder, but also much speculation among scientists about possible aluminum-like toxicity. This Commentary focuses on the major aspects of this scientific controversy, confirming the safety and efficacy of this new phosphate binder.

[New insights in the pathogenesis of secondary hyperparathyroidism]

Parathyroid gland growth is a major cause of secondary hyperparathyroidism in renal failure. It is well known that high serum phosphate levels, low serum calcium levels and vitamin D deficiency are the three promoters of parathyroid hyperplasia in renal failure. Recent studies have investigated in depth the potential role of growth factors (transforming growth factor alpha) and their receptors (epidermal growth factor receptor) in the pathogenesis of parathyroid cell hyperplasia in chronic renal failure. The identification of molecular mechanisms involved in calcium, phosphate and vitamin D manipulations in an experimental renal failure model could help design more effective therapy for secondary hyperparathyroidism in uremic patients.

[Prevention of extraskeletal calcifications in uremia]

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.

[Mechanism of uremic osteodystrophy and prevention of hyperparathyroidism in the uremic patient]

The management of secondary hyperparathyroidism is of crucial importance in the treatment of end stage renal disease (ESRD) patients. In particular, hypercalcemia, hyperphosphatemia, and elevated calcium x phosphate (Ca x P) product should be taken into consideration during administration of vitamin D metabolites for the control of PTH secretion. During the last 10 years, many authors have been studying the efficacy of new non-calcemic vitamin D analogs on suppressing secondary hyperparathyroidism in ESRD patients. In this brief review, we analyzed three new vitamin D analogs: 22-oxacalcitriol (Maxacalcitriol), 19-nor-1a, 25(OH)2D2 (Paracalcitriol), and 1a (OH)2D2 (Doxacalciferol). In addition, calcimimetic agents may represent a new pharmacologic choice to the treatment of secondary hyperparathyroidism, binding parathyroid calcium sensing receptors (CaSR) and reducing PTH secretion. These compounds may represent an important tool for the treatment of both secondary hyperparathyroidism and soft tissue calcifications in ESRD patients. In conclusion, a combined use of non calcemic phosphate binders, new vitamin D analogs and calcimimetics should be seriously considered to further improve the already known therapy of secondary hyperparathyroidism in ESRD patients.

Cardiac and pulmonary calcification in a hemodialysis patient: partial regression 4 years after parathyroidectomy

AIMS

The reversibility of extraskeletal calcifications in dialysis patients is an important and unresolved issue. Although periarticular calcifications have been shown to be reversible, little data are available on vascular or parenchymal calcifications.

CASE HISTORY

A patient on maintenance hemodialysis with severe hyperparathyroidism, hypercalcemia and hyperphosphatemia was admitted to undergo parathyroidectomy. A preoperative total body bone scintigraphy was performed to better evaluate a lytic lesion in the pelvis, the histology of which proved to be a "brown tumor". The scan showed the typical findings of renal osteodystrophy, but also a diffuse extra-skeletal uptake of bone tracer in the lungs, kidneys, femoral arteries and myocardium. After surgery, good control of serum calcium, phosphate (Ca x P product < 50 mg2/dl2) and PTH levels was maintained during 4 years of follow-up. Bone scans were repeated after 2 and 4 years, showing marked improvement of periarticular uptake at the ends of long bones. Extraosseous calcium deposition was still markedly evident, but progressively decreased (at 4 years: heart -36%, lungs -18%).

CONCLUSION

In this dialysis patient, extraskeletal calcification of visceral organs (particularly in the heart and the lungs) due to prolonged hypercalcemia and hyperphosphatemia was partially reversible by parathyroidectomy followed by good long-term control of serum phosphate and calcium.

Placement, performance and complications of the Ash Split Cath hemodialysis catheter

A tunneled catheter is the alternative vascular access for those patients in need of hemodialysis who cannot undergo dialysis through an arterio-venous fistula or a vascular graft. This study was undertaken to evaluate the performance of the Ash Split Cath, a 14 French chronic hemodialysis catheter with D-shaped lumens and a Dacron cuff. After tunneling through a transcutaneous portion the catheter enters the venous system, where it splits into two separate limbs. Data regarding catheter positioning, function and adequacy of dialysis were collected from two hemodialysis facilities. Twenty-eight Ash-split catheters were placed in 28 patients, with no complications, and immediate technical success was 100%. Patients were followed up for a total of 7,286 catheter days. No catheter-related infections were observed. Only one catheter failed after 15 days, with a primary catheter patency of 96% for the whole study length. Mean blood flow was 303 +/- 20 ml/min at 1 week after insertion, 306 +/- 17 ml/min at 3 months, 299 +/- 44 ml/min at 6 months, and 308 +/- 16 ml/min at 12 months. With a mean dialysis session duration of 234 +/- 25 minutes, adequate dialysis dose was observed for 96% of catheters, as reflected by a mean urea reduction ratio (URR) of 71% +/- 8 or a mean urea kinetic modeling, or Kt/V, value of 1.51 +/- 0.3 during follow up. In conclusion, compared with previous studies we report the best permanent catheter performance, confirming that the Ash-split catheter is a good alternative for vascular access in hemodialysis patients who are not candidates for surgical A-V fistula or graft placement.

Vascular calcifications as a footprint of increased calcium load and chronic inflammation in uremic patients: a need for a neutral calcium balance during hemodialysis?

Cardiovascular complications caused by an accelerated atherosclerotic disease represent the largest single cause of mortality in chronic renal failure patients. The rapidly developing atherosclerosis of the uremic syndrome appears to be caused by a synergism of different mechanisms, such as malnutrition, oxidative stress and genetic factors. Recent studies provide evidence that chronic inflammation plays an important role in the pathogenesis of cardiovascular diseases. Hyperphosphatemia and an increased calcium-phosphate ion product have also been associated with an increased risk of death. Cardiovascular calcifications secondary to increases in phosphate and calcium load in dialysis patients might exert an important contribution to the excess cardiovascular mortality and morbidity in dialysis patients. Elevated serum levels of plasma C-reactive protein (CRP) are associated with the extent and severity of the atherosclerotic processes as well as with an increased risk of experiencing myocardial infarction and sudden cardiac death in apparently healthy subjects. In patients affected by pre-dialytic renal failure increased levels of CRP and IL-6 were recorded in 25% of our population; CRP and IL-6 were inversely related with renal function. These data suggest the activation--even in the predialytic phase of renal failure--of mechanisms known to contribute to the enhanced cardiovascular morbidity and mortality of the uremic syndrome. In recent years we have investigated the hypothesis that the chronic inflammatory state of the uremic patient could be at least in part due to the dialytic technique. We have shown that the increase of CRP in stable dialysis patients may be due to the stimulation of monocyte/macrophage by backfiltration of dialysate contaminants. During conventional dialysis, a positive calcium balance and a concomitant inflammatory state may act as cofactors in the development of cardiovascular calcifications. We suggest that this hypothesis should be verified by clinical studies. A reevaluation of the ideal calcium levels in the dialysate is warranted: a neutral intradialytic calcium balance is probably more appropriate, although not easily attainable.

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.

Dynamic of beta(2)-microglobulin fibril formation and reabsorption: the role of proteolysis

Dialysis-related amyloidosis (DRA) is caused by the deposition, in target tissues, of beta(2)-microglobulin (beta(2)M) in fibrillar conformation. Several reports indicate that fibrillar beta(2)M is chemically heterogeneous and such heterogeneity is partially related to the presence of truncated species of the protein. In association with the full-length species, a beta(2)M isoform lacking six N-terminal residues is present in all the samples of our collection of ex vivo fibrils. The pattern of proteolytic cleavage in amyloidosis and in other diseases is completely different, as demonstrated by the absence in fibrillar beta(2)M of the cleavage at lysine 58, which is contrary to that described in rheumatoid arthritis and other diseases. The role of limited proteolysis of beta(2)M in the pathogenesis of the disease is uncertain. However, we have shown that the apparently minor modification of the intact protein, such as the removal of N-terminal hexapeptide, is capable of dramatically affecting its stability, protection from proteolytic digestion, and enhance its capacity to make in vitro amyloid fibrils. The structure, folding dynamic, and function of the truncated species of beta(2)M, peculiar of DRA, could shed new light on the mechanism of beta(2)M fibril formation and reabsorption.

Twice versus thrice weekly administration of intravenous calcitriol in dialysis patients: a randomized prospective trial. Gruppo Italiano di Studio dell'Osteodistrofia Renale

BACKGROUND

Administration of intravenous (i.v.) calcitriol three times weekly effectively controls the synthesis and secretion of PTH in most uremic patients. Administration of a single dose of 1.25(OH)2D3 reduces synthesis of PTH-mRNA for 6 days in rats. Moreover, it can lower PTH levels for up to 4 days in chronic hemodialysis patients. Therefore, a good response to the administration of i.v. calcitriol two times weekly can be expected. We studied - in a multicenter randomized study in patients with moderate to severe secondary hyperparathyroidism - the effects of the same doses of intravenous calcitriol, administered two or three times weekly.

METHODS

Twenty-two hemodialysis patients were randomized into two frequencies of treatment groups: two times (G-2/w) and three times weekly (G-3/w). Both groups were treated with increasing doses of intravenous calcitriol for 3 months (first month 3 microg, second month 4 microg, third month 6 microg weekly).

RESULTS

After 12 weeks of therapy with intravenous calcitriol the G-2/w group showed a significant reduction in serum PTH levels (from 821 +/- 392 to 350 +/- 246 pg/ml; mean reduction = 57.4%) comparable to the decrease observed in the G-3/w group (from 632 +/- 116 to 246 +/- 190 pg/ml; mean reduction = 61.2%). Ionized calcium (G-2/w from 1.13 +/-0.10 to 1.14 +/- 0.08 and G-3/w 1.21 +/- 0.13 to 1.26 +/- 0.18 mmol/l) and phosphate levels (G-2/w from 4.99 +/- 1.01 to 5.99 +/- 1.78 and G-3/w 5.31 +/- 0.73 to 5.81 +/- 1.18 mg/dl) did not change significantly and phosphate binders were not modified during the study.

CONCLUSION

This study confirms that intravenous calcitriol is an effective therapy for moderate to severe secondary hyperparathyroidism. The administration of two doses per week of intravenous calcitriol is as efficacious as three doses per week in suppressing PTH secretion.

Hyperparathyroidism and anemia in renal failure

Patients with severe secondary hyperparathyroidism, usually associated with osteitis fibrosa on bone histology, show considerable resistance to Epoetin, partly because of replacement of the cellular components of the bone marrow by fibrous tissue. In case of unexplained resistance to Epoetin, investigation of secondary hyperparathyroidism is strongly recommended, with measurement of serum parathyroid hormone, calcium, phosphate, and alkaline phosphatase levels and, where needed, skeletal radiology and bone biopsy. Treatment of severe secondary hyperparathyroidism consists of active vitamin D metabolites or parathyroidectomy, although the marrow fibrosis, if present, may be irreversible. The finding of a progressive inability of the bone marrow to respond to Epoetin treatment with higher levels of parathyroid hormone suggests the importance to prevent metabolic bone disease and in particular secondary hyperparathyroidism. Moreover, there are several reports of a beneficial action on hemoglobin levels of an effective treatment of hyperparathyroidism. Larger, controlled studies are necessary to confirm these preliminary and exciting findings, and to elucidate the mechanisms underlying the improvement in anemia after medical or surgical treatment of hyperparathyroidism.

Ultrastructural localization of advanced glycation end products and beta2-microglobulin in dialysis amyloidosis

BACKGROUND

beta2-microglobulin (beta2m) is considered to be the amyloidogenic precursor in dialysis-related amyloidosis (DRA, Abeta2M amyloidosis). beta2m modified with advanced glycation end products (AGE) may be an important factor in the pathogenesis of DRA. The presence of AGE in beta2m-positive amyloid deposits and surrounding macrophages has been demonstrated by immunohistochemical techniques in light microscopy.

METHODS

In order to better define the localization of beta2m and AGE in amyloid deposits and in cells, carpal tunnel connective tissues obtained from surgical specimens in six patients with DRA were studied by immunohistochemistry and electron microscopy, using the avidine-biotine complex and immunogold staining procedures, respectively. A polyclonal rabbit anti-human beta2m and two monoclonal mouse anti-AGE antibodies [AG-1 anti-imidazolone and AG-10 anti-N(epsilon)-carboxymethyl-lysine] enabled us to label their respective antigens at the optical and ultrastructural level.

RESULTS

with both techniques, extracellular amyloid deposits strongly reacted with anti-beta2m and anti-AGE antibodies, although the immunoreactivity of beta2m was more intense. Macrophage-like synovial cells (CD-68 positive) surrounding amyloid deposits were also immunoreactive for beta2m and AGE, which were detected in lysosomes and in intracellular fibrillar material. Anti-AGE reactivity was also evident in collagenous structures in the absence of beta2m or amyloid deposits, supporting the proposal that AGE modification of collagen might have pathogenic relevance in the development of DRA.

CONCLUSIONS

The co-localization of AGE and beta2m, both intra- and extra-cellularly, in amyloid fibrils was confirmed by immunoelectron microscopy; however, the positivity of collagen to anti-AGE antibodies and a different pattern of intracellular localization suggest that molecules other than beta2m may also be modified by AGE and may be involved in the pathogenesis of DRA.

[Assessment of geometric, biomechanical, and osteodensitometric properties of the ultradistal radius with peripheral quantitative computerized tomography in uremic patients with severe hyperparathyroidism]

INTRODUCTION

Bone integrity and mineral status were studied with a noninvasive method in uremic patients with severe secondary hyperparathyroidism undergoing maintenance hemodialysis.

MATERIAL AND METHODS

Volumetric cortical and trabecular mineral density (cBMD, tBMD) and bone geometrical properties were evaluated in 16 patients (11 women and 5 men) candidate to parathyroidectomy. Peripheral quantitative Computed Tomography (pQCT) was used to make measurements at the distal radius of the nondominant forearm. Thirty-two age-matched healthy subjects were chosen as a control group. Cortical area (CA), cross-sectional area (Total A), cortical thickness (CThk) and stress strain index (SSI) were assessed as biomechanical parameters. Serum intact PTH levels were assessed with a radioimmunoassay method (IRMA).

RESULTS

Both cBMD and tBMD were decreased in all patients and the difference was more significant in women (p < .0004 and p < .009) than in the smaller group of men (p < .01 and p < .01). Serum PTH levels correlated negatively with cBMD (r = .52; p < .01), CThk (r = .51; p < .04), CA (r = .52; p < .03) and SSI (r = .54; p < .02), as well as tBMD (r = .34), though not significantly. Dialysis duration did not significantly correlate with cBMD (r = .33), tBMD (r = .20), CA (r = .31), CThk (r = .40) and SSI (r = .35). As for geometrical and biomechanical parameters, CA, CThk and SSI were significantly different in both male and female uremic patients in comparison with the relative controls. Bone quantitative analysis and three-dimensional (3D) representation with the paraboloid revolution model also demonstrated osteopenia.

CONCLUSIONS

pQCT shows significant cortical and trabecular osteopenia in uremic patients with severe secondary hyperparathyroidism. Osteopenia is associated with geometrical and mechanical impairment with consequently increased bone fragility and thus a higher risk of fracture. Prolonged PTH hyperexpression seems to be mainly associated with intracortical porosity and cortical-endosteal resorption. Bone quantitative analysis and 3D representation provide rapid automated information on the cortex mineral status.