Uremic Subjects Research Articles

Plasma Adiponectin Concentration and Insulin Resistance: Role of Successful Kidney Transplantation

Adiponectin (ADPN) has been reported to be inversely correlated with insulin resistance (IR) in uremic subjects and following kidney transplantation. Kidneys have been suggested to play a part in ADPN clearance. This study sought to evaluate this hypothesis. We enrolled 67 candidates with end-stage renal disease (ESRD) along with 30 healthy unrelated donors. Plasma ADPN, IR (based on the homeostasis model assessment for IR index), and glomerular filtration rates were compared between control and patient groups. The correlations of the aforementioned variables were also compared in the patient group 1 day before and 14 days following transplantation. The changes in measured parameters were also compared with control group values. The glomerular filtration rate was significantly decreased among recipients. ADPN levels were remarkably higher in the patient group before transplantation when compared with healthy subjects (P < .001) and remained significantly higher thereafter (P < .001). Insulin resistance was higher, albeit not significantly, among ESRD patients compared with controls (P > .05) and it increased following transplantation (P = .03). There was no correlation between ADPN, IR, and glomerular filtration rate in normal individuals or ESRD patients before or after transplantation. It is our assumption that mechanisms other than kidney function are probably involved in ADPN metabolism in ESRD patients and in the immediate phase following transplantation. It does not seem that ADPN substantially affects IR either in ESRD or transplantation patients.

Dialysis Initiation and Survival in Patients with Refractory Congestive Heart Failure

It has been reported that more than 30% of patients present with congestive heart failure at the initiation of renal replacement therapy (RRT). We followed up a cohort of patients with refractory congestive heart failure (RCHF) who started dialysis between 2005 and 2006 and conducted an observational cohort study in order to evaluate the clinical features at the time RRT was started, and the survival rate of patients with RCHF METHODS: Data were collected on 33 uremic subjects (24 male) with RCHF, referred by cardiologists, who started dialysis between 2005 and 2006 and were followed-up for 42 months. The following parameters were derived from clinical records: age, sex, history of ischemic heart disease (IHD), cerebrovascular disease (CVD), peripheral vascular disease (PVD), diabetes, smoking, hypertension, myeloma or malignancies, the cause for dialysis and procedure used to initiate treatment. RCHF was the cause of initial RRT in 15 patients in 2005 and in 18 the following year with an incidence of 27 out of 100 patients per year. Diabetes was diagnosed in 51% (n = 17) of cases. More than 80% of patients with RCHF had histories of hypertension and smoking. IHD, CVD and PVD were present in 66%, 30% and 54% of cases, respectively. Cancers were recorded in 36% of subjects. Fluid overload was the cause of urgent dialysis in 73% of cases; a central venous catheter (CVC) was placed in 75% of patients. Mean survival of patients with RCHF was 23 months. Eighteen patients died because of cardiovascular events after a mean follow-up of 365 +/- 387 days; they had higher prevalence of a smoking history (100% vs. 73%, p = 0.02) and CVD (44% vs. 13%, p = 0.05) than the survivors. In uremic patients starting dialysis, RCHF appears to be a frequent condition, comorbidity is high and they require urgent treatment by CVC because of fluid overload. Since RCHF is time- and resource-consuming, nephrologists need to ameliorate its management.

The clearance of unidentified uremic solutes (with molecular weight under 5 kDa) plays an important role in hemodialyzer selection

The purpose of this study was to evaluate two commercial hemodialyzers (F100 and P21) through the clearance of identified and unidentified uremic solutes. We investigated plasma samples from healthy and uremic subjects. We found three unidentified uremic solutes (P1, P2, and P3) after HPLC analysis of plasma samples. Then, we determined the clearance of four identified and the three unidentified uremic solutes in patients with F100 and P21. There was no significance between F100 and P21 in clearance of four identified uremic solutes. By contrast, the clearance of P1 and P2 with F100 was superior with the P21 (P < 0.05). Our data suggest that selection of a hemodialyzer based on the clearance of identified uremic solutes might not be sufficient. Application of external techniques to determine additional external factors (i.e., clearance of unidentified uremic solutes) can facilitate a better decision in the selection of the ideal hemodialyzer.

Increased Asymmetric Dimethylarginine Serum Levels are Associated With Acute Rejection in Kidney Transplant Recipients

Asymmetric dimethylarginine (ADMA) has been identified as a marker of endothelial dysfunction and an independent risk factor for cardiovascular events in uremic subjects. This study evaluated ADMA plasma levels in kidney transplant recipients. ADMA levels were serially measured during the first year posttransplantation in 41 recipients treated with cyclosporine regimen (CY), sirolimus (SIR), or low-dose cyclosporine plus everolimus (E). Homocysteine, C reactive protein (CRP), nitric oxide (NO), and standard routine laboratory analyses were determined serially. ADMA significantly increased at 6 months posttransplantation, but was significantly lower among patients on SIR or E. NO was only slightly reduced in patients with increased ADMA levels. Interestingly, ADMA was significantly increased during the first 4 days posttransplantation in patients who experienced acute rejection during the first 6 months after transplantation. The same group of patients demonstrated higher levels of CRP and systolic blood pressure before transplantation. Our results demonstrated that ADMA was increased in patients on CY at 6 months. When increased soon after transplantation ADMA may be associated with episodes of acute rejection in kidney transplant recipients. The presence of elevated systolic blood pressure, as well as CRP and ADMA levels, suggested a role for endothelial dysfunction in the development of acute rejection episodes among deceased donor kidney transplant recipients.

Uremia impairs monocyte and monocyte-derived dendritic cell function in hemodialysis patients

Patients with chronic renal failure maintained on intermittent hemodialysis have frequent infections and a suboptimal response to vaccinations. Dendritic cells are potent antigen-presenting cells essential for the initiation and maintenance of innate and adaptive immunity. In this study we used uremic sera from hemodialysis patients to measure its impact on monocyte and monocyte-derived dendritic cell function in vitro. Monocytes from healthy and uremic subjects were isolated using immunomagnetic beads and differentiated into dendritic cells in the presence of either complete sera or sera from hemodialysis patients. Dendritic cells from normal patients cultured in uremic sera had decreased endocytosis and impaired maturation. These cells, however, had enhanced IL-12p70 production and increased allogeneic T-cell proliferation compared to cells of normal subjects cultured in normal sera. Monocyte derived dendritic cells of hemodialysis patients cultured in either normal or uremic sera were functionally impaired for endocytosis and maturation but had enhanced IL-12p70 production and allogeneic T-cell proliferation only when cultured with uremic sera. High concentrations of urea in normal sera inhibited all aspects of normal dendritic cell function in vitro. Our study suggests that hemodialysis regimes tailored to remove uremic toxins more efficiently may improve immune functions of these patients.

Are PTH serum levels predictive of coronary calcifications in haemodialysis patients?

Cardiac calcifications are a frequent occurrence in uraemic subjects and are probably connected to the increased cardiovascular mortality of haemodialysis patients. There is substantial support to the hypothesis that low levels of serum PTH in haemodialysis patients are associated with increased vascular and cardiac calcium deposits, due to decreased buffering capacity of bone in low turnover osteodystrophy. The present study has been carried out on a cohort of patients on haemodialysis, with exclusion of previously parathyroidectomized patients, with the aim to evaluate the association between PTH serum levels and coronary calcifications. The study has been carried out in a cohort of 197 haemodialysis patients. There were 133 males and 64 females. Twenty-two patients had diabetes mellitus. Average age was 58.6 +/- 12.9 years. Patients were divided into groups of intact PTH levels, 0-150 (A), 150-300 (B), 300-600 (C) and >600 (D) pg/ml. The values of coronary scores in the PTH groups were as follows: (A) 624.7 +/- 939, (B) 866.4 +/- 1080, (C) 1202.8 +/- 1742.3 and (D) 1872.7 +/- 2961.9. The difference between coronary calcium scores was significant (P < 0.01). A general linear model identified serum calcium and dialysis age as independent factors of calcium deposits in the high PTH group. No prominent association between low PTH serum levels and the severity of coronary calcium deposits in haemodialysis patients was found while increased levels of PTH, with special regard to very elevated levels, associated with more frequent hypercalcaemia and hyperphosphataemia, should be considered a major risk factor of coronary calcifications and cardiac events.

Gastro-Duodenal Lesions and Helicobacter pylori Infection in Uremic Patients and Renal Transplant Recipients

Background Upper gastrointestinal (UGI) symptoms are common in uremic patients, and higher serum levels of urea have been suggested to be related to Helicobacter pylori (HP) colonization and UGI mucosal inflammation. Aim The aim of this study was to compare HP infection and UGI endoscopic findings between uremic patients, renal transplant (RT) recipients, and controls. Methods A total of 474 subjects (71 chronic renal failure [CRF], 73 hemodialysis [HD], 25 Tx, and 305 controls) from Baqyiatallah Hospital, Tehran, Iran were recruited between April 2002 and March 2004 for evaluation of dyspepsia, excluding those receiving any HP-eradication therapy. All subjects were examined for esophagus, stomach and duodenum mucosa, and infection with HP on 2 distinct tissue samples of the anthral region. Results Four groups of subjects (mean ± 2 se; age, 45 ± 1.6 years; 62.9% male) were studied. Duodenal ulcer in the uremic patients (CRF, 16.1%; HD, 13.7%) was more common than that in the RT-recipients (8%) and controls (6.5%); P = .038. Erosive gastritis and duodenal bulb deformity were also more common in the uremic subjects (CRF, 23.9%, 36.9%; HD, 30.1%, 20.5%, respectively) than those in the other subjects (RT recipients, 16%, 8%; controls, 8.2%; 0%, respectively); P < .001. HP infection was found to be higher in the uremic patients (CRF, 66.2%; HD, 63%) than in the RT recipients (40%) and controls (34.8%); P < .001. Conclusion Higher rates of gastric and duodenal mucosal lesions and HP infection in the uremic patients in comparison with the subjects with normal renal function may have resulted from higher serum levels of urea, anemia, and fluctuations in the gastric blood supply in the CRF and HD patients. However, more tenable evidence from controlled trials is required for the eradication of HP in all uremic patients and transplantation candidates.

The Relationship between Carotid and Coronary Atherosclerotic Damage in Dialysis Patients

Data relating carotid ultrasound (CU) to atherosclerotic damage evaluated by coronary angiography in hemodialysis patients are scarce. We carried out a cross-sectional study in 33 uremic subjects (age 55 +/- 12 years, 22 male, 7 diabetic), who have been on dialysis for 41 +/- 48 months (range 2-192). Twenty-two underwent a coronary angiography in order to complete clinical evaluation for inclusion on the kidney transplantation waiting list, and 11 because of coronary artery disease (CAD); Gensini's score was calculated. Intima-media thickness (IMT) and presence of plaques were related to the degree of coronary stenosis and to cardiovascular risk factors. Patients were divided into two groups depending on mean IMT (group 1 IM <or= 0.9 mm, n=18; group 2 IMT>0.9 mm, n=15). Group 2 was older (60 +/- 8 vs 50 +/- 12 year, p=0.01), had higher frequency of CAD (53 vs 16%, p=0.02) and had higher prevalence of coronary artery stenosis >or= 75% in the right (60 vs 22%, p=0.02), left anterior descending (46 vs 16%, p=0.06) and left circumflex coronary arteriers (60 vs 11%, p=0.05) than group 1. IMT was not related to the degree of CAD evaluated by Gensini's score. IMT sensibility and specificity in detecting the presence of hemodynamically significant coronary stenosis were 64% and 68%, respectively. Coronary narrowing was correlated with the degree of stenosis of common, internal and external carotid arteries (Spearman's rank correlation coefficient). During two years of follow-up, six major cardiac events were recorded and they were related to Gensini's score. In uremic patients, ultrasonographic evaluation of carotid arteries is a simple, noninvasive examination that could be a helpful tool in detecting coronary atherosclerotic damage, but IMT does not appear to add more information regarding risk stratification of CAD.

Oxidative stress and cellular stress response in diabetic nephropathy

Oxidative stress has been suggested to play a main role in the pathogenesis of type 2 diabetes mellitus and its complications. As a consequence of this increased oxidative status, a cellular-adaptive response occurs requiring functional chaperones, antioxidant production, and protein degradation. This study was designed to evaluate systemic oxidative stress and cellular stress response in patients suffering from type 2 diabetes-induced nephropathy and in age-matched healthy subjects. Systemic oxidative stress has been evaluated by measuring advanced glycation end-products (pentosidine), protein oxidation (protein carbonyls [DNPH]), and lipid oxidation (4-hydroxy-2-nonenal [HNE] and F2-isoprostanes) in plasma, lymphocytes, and urine, whereas the lymphocyte levels of the heat shock proteins (Hsps) heme oxygenase-1 (HO-1), Hsp70, and Hsp60 as well as thioredoxin reductase-1 (TrxR-1) have been measured to evaluate the systemic cellular stress response. We found increased levels of pentosidine (P < 0.01), DNPH (P < 0.05 and P < 0.01), HNE (P < 0.05 and P < 0.01), and F2-isoprostanes (P < 0.01) in all the samples from type 2 diabetic patients with nephropathy with respect to control group. This was paralleled by a significant induction of cellular HO-1, Hsp60, Hsp70, and TrxR-1 (P < 0.05 and P < 0.01). A significant upregulation of both HO-1 and Hsp70 has been detected also in lymphocytes from type 2 diabetic patients without uraemia. Significant positive correlations between DNPH and Hsp60, as well as between the degree of renal failure and HO-1 or Hsp70, also have been found in diabetic uremic subjects. In conclusion, patients affected by type 2 diabetes complicated with nephropathy are under condition of systemic oxidative stress, and the induction of Hsp and TrxR-1 is a maintained response in counteracting the intracellular pro-oxidant status.

Premature aging in uremia

Guanidinosuccinic acid is an aberrant metabolite isolated 40 years ago in the blood and urine of uremic subjects and a suspect in the toxicity associated with renal failure. It plays a minor role in the bleeding diathesis of uremia, contributes to the methyl group deficiency of dialysis patients, and is a factor in the premature atherosclerosis of end stage renal disease through the induction of hyperhomocysteinemia. As a major player, however, in the diversity and severity of uremic symptoms, it is a disappointment. Recently its source has been identified. It results from the superoxidation of argininosuccinic acid, which leads, also, to the production of gamma glutamic semialdehyde, an advanced glycation end product (AGE), which normally results from from the Maillard reaction, the non-enzymatic browning of protein. AGEs stimulate cross-linkages in protein that lead ultimately to loss of function, phagocytosis, and removal, and are important elements in the premature aging characteristic of renal disease, and diabetes.

Defense mechanisms in hemodialysis-dependent patients

Defense mechanisms are automatic psychological processes that protect the individual against anxiety and from the awareness of internal or external dangers or stressors. The influence of defense mechanisms in patients on chronic hemodialysis treatment was studied. There were 53 uremic subjects (37 males and 16 females), aged between 22 and 88 years (mean age 60.11, SD 15.03), on chronic dialysis and 50 healthy subjects as controls have been enrolled in the study. According to the duration of dialysis, uremic patients were divided in two subgroups: 21 patients with less than 5 years and 19 patients with more than 10 years of dialytic treatment. Assessment was conducted using the Defense Mechanisms Inventory DMI. The inventory identifies five defensive styles: turning against the object (TAO), projection (PRO), principalization (PRN), turning against the self (TAS) and reversal (REV). Results showed DMI scores within the normal range both for uremics and controls with significant differences in TAO (t = -3.053, p = 0.003) and REV (t = 5.067, p < 0.0001) between groups. No significant differences in the use of defensive styles related to the duration of dialytic treatment were observed. Besides other psychological features, the assessment of defense mechanisms in patients with chronic and invalidating diseases may contribute to ameliorate the knowledge of the adjustment processes and of the psychological well-being of the patients.

Vitamin E-coated filter decreases levels of free 4-hydroxyl-2-nonenal during haemodialysis sessions

Uraemic subjects undergoing chronic haemodialysis show increased oxidative stress. The use of non-biocompatible filters and reduced antioxidative defences are important sources of reactive oxygen species (ROS) release. The highly oxidative environment accelerates the onset and progression of tissue damage and atherosclerotic cardiovascular disease. The aldehyde 4-hydroxyl-2-nonenal (HNE) is probably the best marker of oxidative stress. In this study, the concentration of plasma HNE was evaluated in eight uremic subjects during two sessions of haemodialysis: the first using a standard biocompatible filter and the second using a filter coated with vitamin E. Baseline plasma levels of HNE were elevated, and dropped during haemodialysis. At the end of the session, however, low levels were maintained only when the vitamin E-modified filter was used. By contrast, a marked increase in HNE was recorded at the end of the session in all subjects who underwent haemodialysis with the conventional filter. This study provides evidence that the vitamin E-coated filter plays a role in counteracting oxidative stress. The chronic use of vitamin E-modified filters in haemodialysed subjects might help to counterbalance oxidative attack and, consequently, contribute to preventing cardiovascular disease.

Nitric oxide– and EDHF-mediated arteriolar tone in uremia is unaffected by selective inhibition of vascular cytochrome P450 2C9

Uremia is a state of endothelial dysfunction as demonstrated by a reduced agonist-induced endothelium-dependent vasodilatation. Recent studies suggest that an endothelial cytochrome P450 (CYP) epoxygenase (CYP 2C9) can modulate endothelium-dependent vasodilatation in two different ways: (1) by the production of epoxyeicosatrienoic acids (EETs), which elicit hyperpolarization and relaxation; and (2) by the release of oxygen-derived free radicals, which compromise the bioavailability of nitric oxide. We therefore determined whether one of these pathways is involved in endothelial dysfunction of uremia. Using venous occlusion plethysmography, we measured forearm blood flow (FBF) in response to the intrabrachial infusion of acetylcholine (ACh; endothelium-dependent vasodilator; 1, 5, 10, 50, 100, and 300 nmol/min) and sodium nitroprusside (SNP; endothelium-independent vasodilator; 2.5, 5 and 10 microg/min) in 10 stable patients on hemodialysis (HD) and 9 healthy control subjects. In HD patients, ACh infusions were repeated together with sulfaphenazole (SPZ, 6 mg/min), a highly selective inhibitor of CYP 2C9 with and without concomitant blockade of the nitric oxide synthase (NOS) by N(omega)monomethyl L-arginine (L-NMMA, 16 microumol/min). Endothelium-dependent vasodilatation to ACh was reduced in HD compared to control subjects (P= 0.002), indicating endothelial dysfunction in the patients examined. Endothelium-independent vascular responses to SNP were attenuated in HD, but not significantly different to control. SPZ failed to modulate both baseline FBF and Ach-induced vasodilatation in HD. Furthermore, SPZ had no effect on baseline FBF and ACh-mediated vasodilatation in the presence of L-NMMA in HD. Our results do not support a major role for CYP 2C9-derived products in the regulation of arteriolar tone in early endothelial dysfunction of uremic subjects.

The C677T methylenetetrahydrofolate reductase gene mutation does not influence cardiovascular risk in the dialysis population: results of a multicentre prospective study

Although the methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism has been identified as an independent cardiovascular risk factor (CRF) in the general population and among uraemic subjects, the validity of this association remains controversial. To verify this hypothesis, we enrolled all subjects on maintenance dialysis treatment from a specific Italian district. We also enrolled, from the same area, 1307 subject to serve as controls. Genomic DNA was obtained and MTHFR C677T gene polymorphisms were determined. After a baseline evaluation, patients were followed-up for 37+/-13 months, and all cardiovascular events and causes of mortality were recorded. A total of 461 patients (417 on haemodialysis and 44 on peritoneal dialysis) were investigated, and these included patients with and without cardiovascular diseases at baseline. At enrollment, mean age was 58.8+/-15.6 years and dialytic age was 82+/-69 months. Genotype frequencies were not different between controls and uraemics. During the follow-up, the mean mortality rate was 8.81%/year, with cardiovascular events as the most frequent cause of death (n = 68, 56.6%). There was no relationship between the MTHFR genotype and cardiovascular morbidity, overall mortality or cardiovascular mortality. In end-stage renal disease, MTHFR C677T polymorphisms were not associated with cardiovascular disease or mortality.

Body Composition in Diabetic Subjects with Chronic Kidney Disease: Interest of Bio-Impedance Analysis, and Anthropometry

Background/Aims: Lean body mass (LBM) is reduced in uremia, but this has not been reported in diabetic nephropathy. Subjects and Methods: We compared predicted % LBM to DEXA measurements in 10 non-diabetic uremic, 10 non-uremic diabetic and 10 uremic diabetic subjects matched for age, gender and BMI. We also measured % LBM by anthropometry, bio-impedance analysis (BIA) and compared them with DEXA in 49 diabetic subjects with a wide range of renal failure. The results were compared and a Bland & Altman procedure was performed. Associations between glomerular filtration rate (GFR) and % LBM were tested. Results: In matched groups, predicted % LBM values were overestimated in non-diabetic uremic subjects, and underestimated in non-uremic diabetic subjects. In uremic diabetic subjects, the error was intermediary. As compared to DEXA (% LBM: 69.0 ± 7.1%), measurement of % LBM by anthropometry (71.4 ± 8.0%, p < 0.05) and BIA (67.2 ± 7.6%, p < 0.05) were biased in the 49 diabetic subjects. The mean of anthropometric and BIA (Ant+BIA) were similar to DEXA results (69.3 ± 6.8%, p = 0.64), with best correlation coefficients and Bland & Altman plots. GFR was correlated to % LBM assessed by DEXA, BIA and Ant+BIA. Conclusion: In diabetic subjects with chronic kidney disease, LBM should be measured, rather than predicted. A good evaluation is possible, even without DEXA.

Impaired release of interleukin-6 from human osteoblastic cells in the uraemic milieu

Osteoblast-derived interleukin-6 (IL-6) affects bone metabolism and is linked with a number of pathological states characterized by increased bone resorption, including osteoporosis and renal osteodystrophy. To examine the possibility that uraemia directly influences the release of this cytokine in bone, we have investigated the effect of human uraemic serum on the release of IL-6 from human osteoblast-like cells. Individual serum samples collected from healthy male volunteers or male haemodialysis patients prior to and during a dialysis treatment were assayed for IL-6, interleukin-1beta (IL-1beta) and soluble IL-6 receptor (sIL-6R) using specific enzyme-linked immunosorbent assays. MG-63 and SaOS-2 cells were cultured in media containing pooled sera from both groups and alongside matching charcoal-stripped sera. IL-6 concentrations were determined in harvested cell supernatants after 24 h. In further experiments, media containing individual sera obtained from five patients at regular intervals during their haemodialysis treatment were incubated with MG-63 cells to determine the effects of the dialysis process on IL-6 secretion. Haemodialysis patients had significantly higher (n = 10, P < 0.001) circulating concentrations of IL-6 (7.0 +/- 1.6 pg/ml) than normal subjects (0.4 +/- 0.1 pg/ml), but there were no significant differences in the concentrations of either IL-1beta or sIL-6R. These serum concentrations did not change significantly during 80 min of dialysis. IL-6 release by MG-63 cells incubated with charcoal-stripped serum from normal or from uraemic subjects was similar. Incubation with untreated sera from normal subjects increased IL-6 release by approximately 6-fold above the charcoal-stripped control, whereas sera from uraemic subjects increased IL-6 release by only approximately 2- to 3-fold (normal vs uraemic of 6878 +/- 595 and 2579 +/- 169 pg/ml, respectively, P < 0.001). Similar results were seen with SaOS-2 cells. Haemodialysis did not restore the capacity of uraemic serum to augment IL-6 release to the same degree as normal serum. These data show that the augmentation of IL-6 release from human osteoblastic cells after incubation with normal serum is greater than after uraemic serum. This may indicate the presence of an inhibitor of IL-6 release in uraemic serum that is involved in the deranged bone turnover of uraemic patients.

Protein thiol oxidation and lipid peroxidation in patients with uraemia

Background: Patients with uraemia are exposed to increased oxidative stress. In this study, a series of oxidative stress markers were measured in patients with chronic renal failure (CRF) and patients with CRF on haemodialysis (HD) compared to normal controls to establish whether there is enhanced oxidative stress on HD therapy in uraemic subjects. Methods: Protein thiol oxidation, lipid hydroperoxides, albumin and uric acid concentrations were estimated in patients receiving HD and patients with CRF and compared with those in healthy controls. Results: There was a significant decrease in the level of protein thiols in CRF (p=0.0001) and HD patients (p=0.0001) compared with that in controls. Lipid hydroperoxides were significantly higher in CRF (p=0.026) and HD patients (p=0.003) than in controls. However, there was no significant difference in protein thiols and lipid hydroperoxides between CRF and HD patients. Serum protein thiols correlated negatively with lipid hydroperoxides and positively with serum albumin. Conclusions: These findings suggest that both CRF and HD patients have increased plasma protein oxidation and lipid peroxidation. However, HD therapy per se did not contribute to oxidative stress already present in uraemia. Owing to the variability in lipid peroxidation products as markers of oxidative stress and the vital role played by thiol antioxidants in the biological system, it is suggested that protein thiol oxidation may be a better marker of oxidative stress.

Increased platelet phosphatidylserine exposure and caspase activation in chronic uremia

Platelet activation is associated with exposure of the aminophospholipid phosphatidylserine (PS) to the outer hemi-leaflet of the plasma membrane bilayer, which seems to be involved in the coagulation process. Because platelet activation may occur in patients suffering from chronic uremia, which is frequently associated with a thrombophilic tendency, we studied whether uremic platelets show an increased propensity to expose PS on the outer membrane leaflet and whether this process is linked with important functional and molecular changes. Flow cytometric percentage of annexin V-positive platelets, a measure of PS externalization, was significantly elevated (P < 0.001) in uremic patients when compared to normal controls under both unstimulated and agonist-stimulated conditions. Uremic platelet procoagulant activity, as measured by thrombin generation, was more than twice as high (4.13 +/- 0.3 micro mL(-1)) as that found in normal controls (1.86 +/- 0.2 micro mL(-1)). Two independent assays showed that the enzymatic activity of caspase-3, a protease involved in the loss of membrane PS asymmetry, was significantly greater in the platelets of uremic subjects than in those of healthy controls. PS exposure in agonist-stimulated platelets was markedly reduced by inhibition of caspase-3 activity but was not affected by inhibition of calpain activity. These results support the view that the thrombophilic susceptibility of uremic patients may be partly ascribed to increased PS exposure to the outer membrane leaflet of platelets. This process seems to be causally linked to an increase in caspase-3 activity, particularly during platelet activation.

Resting energy expenditure in uremic, diabetic, and uremic diabetic subjects

We compared Harris and Benedict [H&B; Harris, J. A., & Benedict, F. G. (1919). A biometric study of basal metabolism in man. Washington, DC: Carnegie Institution of Washington. p. 279.] predicted resting energy expenditure (REE) to values measured by indirect calorimetry in normal, uremic, diabetic, and uremic diabetic subjects. Predicted REE were overestimated (+9.2%, P<.005) in uremic subjects, and underestimated (−8.5%, P<.0001) in diabetic subjects. Uremic diabetic subjects were submitted to the opposite influences of diabetes and uremia on REE. Differences in body composition (lower fat-free mass in uremia and higher fat-free mass in diabetes) played a major role in these influences. In uremic diabetic subjects, predicted REE seemed well fitted to measured REE (biases <2%), but they were less correlated, and limits of agreement between predicted and measured REE were large. Although their mean REE seems normal, prediction by the H&B equation leads to important individual errors in uremic diabetic subjects: direct measurement of energy expenditure by indirect calorimetry may be helpful to precise the adequate energy content of a diet for these subjects.

Nitric oxide and hemodialysis.

Nitric oxide (NO), previously thought of as a noxious gas, is now recognized as an important mediator of vascular responsiveness. Soon after its discovery, it was realized that the actions of NO are similar to the previously described endothelium-derived relaxing factor (EDRF). It is synthesized in the vascular endothelium utilizing the enzyme nitric oxide synthase (NOS) and diffuses in the adjacent vascular media, where it has a vasodilatory action. Opposing actions of NO and vasoconstrictor agents (such as endothelin-1, angiotensin IotaIota, and others) maintain the vascular tone of the renal arteries. The same balance at the level of the macula densa maintains glomerular filtration rate (GFR) during varying levels of salt excretion. Lack of NO can result in disruption of this fine balance, with resultant vasoconstriction and disease progression, hypertension, and accelerated atherosclerosis. In addition, hypertension may result from positive salt balance that occurs when macula densa NOS is inhibited. While most investigators report low levels of NO in uremic subjects, the levels in hemodialysis (HD) patients have not been characterized adequately. This is primarily because HD patients are exposed to both stimulatory and inhibitory factors for NO synthesis. Retention of inhibitors of NOS tends to decrease NO levels, whereas production of NO will be increased by cytokines generated during blood-dialyzer interaction. There is less disagreement, however, over the finding of elevated levels in those with dialyzer reactions and dialysis-induced hypotension. Recent developments in the isolation of inducible and constitutive forms of NOS makes understanding of its pathophysiologic effects more complete. Newer treatment directed at inhibiting only the inducible forms of NOS (sparing the constitutive forms) may soon be found useful for the treatment and prevention of hypotension and dialyzer reactions in HD patients.