Tubular palladium-based catalysts enhancing direct ethanol electrooxidation.

Direct ethanol fuel cell (DEFC) has the advantages of high power density, high energy conversion efficiency and environmental friendliness, but its commercialization is restricted by factors such as insufficient activity and low anti-poisoning ability of anode catalyst for incomplete oxidation of ethanol. It is of great significance to design and prepare anode catalyst with high activity and high anti-poisoning ability that can be recycled. In this work, tubular palladium-based (Pd-based) catalysts with abundant lattice defect sites were prepared by simple and reproducible electro-displacement reactions using Cu nanowires as sacrificial template. Pd is the main catalytic element which provides adsorption sites for ethanol oxidation. Ag and Cu introduced facilitates the formation of hydroxyl groups to oxidize toxicity intermediates, and changes the d-band center position of Pd, so as to adjust the adsorption and desorption of ethanol and its intermediates on the Pd surface. At the same time, Au introduced with high potential maintains the stability of the catalyst structure. The tubular structure exposes more active sites, improves the atomic utilization rate and enhances the ability of the catalyst resisting dissolution and aggregation. The series of PdAuAgCu tubular catalysts with outer layer dendrites were prepared by electro-displacement reactions using the mixture (ethylene glycol : ultra-pure water = 3 : 1) as the reaction solvent and fivefold twinned Cu nanowires as sacrificial template. The performance evaluation of ethanol electrocatalytic oxidation showed that the Pd17Au40Ag11Cu32 tubular catalysts were prepared at 120 °C and 10 mM CTAB had excellent overall performance, with a peak mass activity of 6335 mA mgPd-1, which was 9.6 times of Pd/C (JM). The residual current density after the stability test of 3000 s was 249 mA mgPd-1, which was 3.3 times of Pd/C (JM).

Magnesium carbonate for phosphate control in patients on hemodialysis. A randomized controlled trial.

BACKGROUND: Magnesium salts bind dietary phosphorus, but their use in renal patients is limited due to their potential for causing side effects. The aim of this study was to evaluate the efficacy and safety of magnesium carbonate (MgCO(3)) as a phosphate-binder in hemodialysis patients. METHODS: Forty-six stable hemodialysis patients were randomly allocated to receive either MgCO(3) (n=25) or calcium carbonate (CaCO(3)), (n=21) for 6 months. The concentration of Mg in the dialysate bath was 0.30 mmol/l in the MgCO(3) group and 0.48 mmol/l in the CaCO(3) group. RESULTS: Only two of 25 patients (8%) discontinued ingestion of MgCO(3) due to complications: one (4%) because of persistent diarrhea, and the other (4%) because of recurrent hypermagnesemia. In the MgCO(3) and CaCO(3) groups, respectively, time-averaged (months 1-6) serum concentrations were: phosphate (P), 5.47 vs. 5.29 mg/dl, P=ns; Ca, 9.13 vs. 9.60 mg/dl, P<0.001; Ca x P product, 50.35 vs. 50.70 (mg/dl)(2), P=ns; Mg, 2.57 vs. 2.41 mg/dl, P=ns; intact parathyroid hormone (iPTH), 285 vs. 235 pg/ml, P<0.01. At month 6, iPTH levels did not differ between groups: 251 vs. 212 pg/ml, P=ns. At month 6 the percentages of patients with serum levels of phosphate, Ca x P product and iPTH that fell within the Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines were similar in both groups, whereas more patients in the MgCO(3) group (17/23; 73.91%) than in the CaCO(3) group (5/20, 25%) had serum Ca levels that fell within these guidelines, with the difference being significant at P<0.01. CONCLUSION: Our study shows that MgCO(3) administered for a period of 6 months is an effective and inexpensive agent to control serum phosphate levels in hemodialysis patients. The administration of MgCO(3) in combination with a low dialysate Mg concentration avoids the risk of severe hypermagnesemia.

Factors related to erythropoietin hypo-responsiveness in patients on chronic peritoneal dialysis.

BACKGROUND: The present study was aimed at investigating the factors related to hypo-responsiveness to erythropoietin in patients on chronic peritoneal dialysis (PD). METHODS: We studied 44 patients with end-stage renal disease who had been on PD for more than 6 months and on erythropoietin (EPO) >/=6,000 U/week for more than 3 months. We expressed EPO resistance index (ERI) as weekly EPO dose per hematocrit (Hct) per body weight. The dose of EPO was titrated to maintain a target Hct level between 33% and 36%. Patients were divided into two groups according to weekly EPO dose. We compared the various factors in those two groups and, by using correlation and linear regression analysis, investigated factors that might predict EPO resistance. RESULTS: There were 13 patients in the EPO <150 U/kg per week group and 31 patients in the EPO >/=150 U/kg per week group. Among those 31 patients, there were five patients on EPO >/=300 U/kg per week. Compared to the EPO <150 U/kg per week group, the EPO >/=150 U/kg per week group had a lower normalized protein catabolic rate (nPCR), lower level of serum albumin and higher C-reactive protein (CRP). Correlation analysis showed that the ERI had a statistically significant correlation with CRP (r = 0.303, P < 0.05), serum albumin (r = -0.26, P < 0.05), parathyroid hormone (PTH) (r = -0.307, P < 0.05) and nPCR (r = -0.259, P < 0.05). These results show that CRP, serum albumin, PTH and nPCR are factors related to hypo-responsiveness. Multiple stepwise linear regression analysis showed that CRP was the most important independent predictor of EPO hypo-responsiveness. CONCLUSION: CRP, serum albumin, nPCR and PTH are factors related to hypo-responsiveness. Inflammation contributes significantly to EPO hypo-responsiveness.

Relationship between serum magnesium, parathyroid hormone, and vascular calcification in patients on dialysis: a literature review.

Secondary hyperparathyroidism is present in most patients with end-stage renal disease and has been linked to uremic bone disease, vascular calcification, and mortality. Current literature suggests an association between hypomagnesemia and cardiovascular disease in the general population. We reviewed all published studies on the relationship between serum magnesium and parathyroid hormone and the relationship between serum Mg and vascular calcification in dialysis patients. Of these, 10 of 12 studies of patients on hemodialysis and 4 of 5 studies of patients on peritoneal dialysis showed a significantinverse relationship between serum Mg and serum intact parathyroid hormone. Hyperparathyroidism develops in peritoneal dialysis patients dialyzed with a solution containing normal calcium (1.25 mmol/L) and low Mg (0.25 mmol/L), even though serum calcium is maintained at a normal level. Four of the hemodialysis studies and one of the peritoneal dialysis studies indicated that there is an inverse relationship between serum Mg and vascular calcification in these patients. Potential benefits have been attributed to magnesium carbonate as a phosphate binder and it may possibly be an effective, less toxic, less expensive phosphate binder. We believe that the role of Mg in secondary hyperparathyroidism and vascular calcification merits further investigation.

25(OH) vitamin D3 in patients with chronic kidney disease and those on dialysis: rediscovering its importance.

In terms of both exogenous sources (diet), and endogenous production (activation through exposure to ultraviolet light), vitamin D is unique. Few foods naturally contain vitamin D and only a few are fortified with vitamin D. Most people get more than 90% of their vitamin D requirements from exposure to sunlight. Those who protect their skin from ultraviolet-B radiation with clothing or sunscreen, the elderly, and dark-skinned individuals have limited capacity to produce vitamin D. Vitamin D deficiency is common in the general population and even more common in patients with chronic renal failure (CKD). Increased use of sun-blocking agents and decreased exposure to sunlight, to reduce the risk of skin cancer, attributed to exposure to UV radiation, may contribute to the increase in vitamin D deficiency in the population. These issues are particularly important in the dialysis population who are at particular risk because these, mostly elderly, individuals have an inactive life style and have reduced exposure to sunshine and UV light, thus limiting the actinic synthesis of vitamin D. The nephrology community seems to have overlooked the importance of vitamin D for overall health and well being in patients with CKD. Recently however, several authors have called attention to the role of plasma 25(OH)D3 levels in mineral metabolism dysregulation in patients with chronic kidney diseases, and those on dialysis. Vitamin D not only contributes to skeletal health but also plays a major role in the health of a wide variety of other organ systems. It seems that vitamin D supplementation is the most effective way of preventing vitamin D deficiency.

Inverse correlation between serum magnesium and parathyroid hormone in peritoneal dialysis patients: a contributing factor to adynamic bone disease?

BACKGROUND: Secondary hyperparathyroidism (SHPTH) is present in many patients with end-stage renal disease (ESRD) and has been linked to uremic bone disease. Parathyroid hormone (PTH) levels are affected by calcium, vitamin D, and phosphorus. Recent data suggests that serum magnesium may also modulate PTH levels. OBJECTIVE: The aim of this retrospective study was to investigate the impact of different calcium (Ca) and magnesium (Mg) concentrations of dialysis solutions on serum Mg and serum PTH levels in peritoneal dialysis (PD) patients. PATIENTS AND METHODS: Two groups of PD patients-group A (n = 17) on "standard" Ca and Mg dialysis solution (SCa-MgD) (Ca: 1.62 mmol/l, Mg: 0.75 mmol/l and Lactate 35 mmol/l), and group B (n = 29) on "low" Ca and Mg dialysis solution (LCa-MgD) (Ca: 1.25 mmol/l, Mg: 0.25 mmol/l and Lactate 40 mmol/l), on PD for more than 6 months, were studied. Calcium carbonate (CaCO3) was used as the phosphate (P) binder in 87% (40/46) of the patients. Biochemical parameters were evaluated every 1-2 months over 6 months and the mean values were computed. RESULTS: No significant differences were found between the two groups in all parameters except for serum Mg and PTH. Serum Mg was higher in SCa-MgD group compared to those in the LCa-MgD group (1.05 +/- 0.19 vs 0.90 +/- 0.23 mmol/l, respectively) and serum PTH was higher in LCa-MgD group compared to those in SCa-MgD group (72.3 +/- 64.2 vs 31.1 +/- 39.0 pmol/l, respectively) even though serum Ca was not different. There was a statistically significant inverse correlation between serum Mg and PTH levels (r = -0.357, p < 0.05). CONCLUSION: Serum Mg is lower and serum PTH higher in patients dialyzed with lower Mg concentration dialysis solution compared to those with higher Mg concentration dialysis solution. Our study confirms previous reports that serum Mg may have a suppressive role on PTH synthesis and/or secretion, and thus may play a role in pathogenesis of adynamic bone disease that often develops in patients on chronic PD with high calcium and high magnesium concentrations.

K/DOQI guideline requirements for calcium, phosphate, calcium phosphate product, and parathyroid hormone control in dialysis patients: can we achieve them?

BACKGROUND: Mineral metabolism has emerged as an important predictor of morbidity and mortality in dialysis patients. Kidney Disease Outcomes Quality Initiative (K/DOQI) clinical practice guidelines for bone metabolism and disease in chronic kidney disease (CKD) recommend that, in Stage 5 CKD, the target levels for calcium (Ca) (corrected for serum albumin), phosphate (P), calcium x phosphate (CaxP) product and parathyroid hormone (PTH) levels should be maintained at 8.4-9.5 mg/dl, 3.5-5.5 mg/dl, <55 mg2/dl2 and 150-300 pg/ml, respectively. OBJECTIVES: To evaluate our ability to achieve K/DOQI guidelines for bone metabolism and disease targets in our patients and to compare them between patients on hemodialysis (HD) and peritoneal dialysis (PD) and also with those reported in the literature. METHODS: We reviewed bone metabolism laboratory parameters in 57 HD patients and 69 PD patients, who had been on dialysis for more than 9 months. RESULTS: The percentage of patients whose serum Ca, P, CaxP product and PTH were within K/DOQI recommended target ranges were 46%, 53%, 77% and 28% in HD patients and 52%, 65%, 77% and 23% in PD patients, respectively. There were no significant differences between HD and PD patients in the percentage of all parameters that were within K/DOQI recommended target ranges. The percentage of our HD patients who had Ca, P, and PTH levels within recommended target range was similar to those in previous reports. CONCLUSION: In our unit, the management of bone and mineral metabolism in HD and PD patients is still far short of meeting K/DOQI guidelines. These findings appear similar in HD and PD patients. Our findings resemble those reported in the literature.