Urea induces macrophage proliferation by inhibition of inducible nitric oxide synthesis

Metabolites and growth factors produced by airway epithelial cells induce tolerance in macrophages

Macrophages play a role in preventing inflammation in the respiratory tract. To investigate the mechanisms that lead to tolerance in macrophages, we examined the crosstalk between airway epithelial cells (AECs) and macrophages using a 2D coculture model. Culture of macrophages with AECs led to a significant inhibition of LPS induced pro-inflammatory responses. More importantly, AECs induced the secretion of TGF-β and IL-10 from macrophages even in the absence of LPS stimulation. In addition, the expression of inhibitory molecule, CD200R was also upregulated on AEC exposed macrophages. Furthermore, the AECs exposed macrophages induced significantly increased level of T regulatory cells. Investigation into the possible mechanisms indicated that a combination of growth factor, G-CSF, and metabolites, Kynurenine and lactic acid produced by AECs is responsible for inducing tolerance in macrophages. Interestingly, all these molecules had differential effect on macrophages with G-CSF inducing TGF-β, Kynurenine elevating IL-10, and lactic acid upregulating CD200R. Furthermore, a cocktail of these factors/metabolites induced similar changes in macrophages as AEC exposure. Altogether, these data identify factors secreted by AECs that enhance tolerance in the respiratory tract. These mediators thus have the potential to be used for therapeutic purposes to modulate respiratory inflammation following local viral infections and lung diseases.

Modeling of Tumor Growth with Input from Patient-Specific Metabolomic Data

Advances in omic technologies have provided insight into cancer progression and treatment response. However, the nonlinear characteristics of cancer growth present a challenge to bridge from the molecular- to the tissue-scale, as tumor behavior cannot be encapsulated by the sum of the individual molecular details gleaned experimentally. Mathematical modeling and computational simulation have been traditionally employed to facilitate analysis of nonlinear systems. In this study, for the first time tumor metabolomic data are linked via mathematical modeling to the tumor tissue-scale behavior, showing the capability to mechanistically simulate cancer progression personalized to omic information obtainable from patient tumor core biopsy analysis. Generally, a higher degree of metabolic dysregulation has been correlated with more aggressive tumor behavior. Accordingly, key parameters influenced by metabolomic data in this model include tumor proliferation, vascularization, aggressiveness, lactic acid production, monocyte infiltration and macrophage polarization, and drug effect. The model enables evaluating interactions of interest between these parameters which drive tumor growth based on the metabolomic data. The results show that the model can group patients consistently with the clinically observed outcomes of response/non-response to chemotherapy. This modeling approach provides a first step towards evaluation of tumor growth based on tumor-specific metabolomic data.

Sexual Dimorphism in Alternative Metabolic Pathways of L-Arginine in Circulating Leukocytes in Young People with Type 1 Diabetes Mellitus

Background: Sexual dimorphism in specific biochemical pathways and immune response, underlies the heterogeneity of type 1 diabetes mellitus (T1DM) and affects the outcome of immunotherapy. Arginase and nitric oxide (NO) synthase (NOS) metabolize L-arginine and play opposite roles in the immune response and autoimmune processes.Objective: We hypothesized that the above mentioned enzymes can be involved in sex and age differences in T1DM and its treatment. Based on this, the enzymes have been studied in peripheral blood leukocytes (PBL) and plasma of young people with T1DM.Methods: Patients were recruited from Muratsan University Hospital (Yerevan, Armenia) and were divided into groups: girls and boys by age, from children to adolescents and adolescents/young adults with recent-onset T1DM (RO-T1DM) (0.1-1 years) and long-term T1DM (LT-T1DM) (1.6-9.9 years). Arginase activity was assessed by L-arginine-dependent production of L-ornithine, and the NOS activity was assessed by NO/nitrite production. Glycemic control was assessed using hemoglobin A1c test. Plasma HbA1c concentration below 7.5% (median (range) 6.7 [6.2-7.5]) was taken as good glycemic control (+) and above 7.5% (median (range) 10.5 [7.6-13]) as poor glycemic control (-). Healthy volunteers with corresponding sex and age were used as the control group.Results: All the patients with RO-T1DM, with poor glycemic control, had increased arginase activity in the cytoplasm (cARG) and mitochondria (mARG) in PBL. In girls with RO-T1DM, with good glycemic control, the subcellular arginase activity decreased, and normalized in LT-T1DM, regardless of age. In contrast, boys from both age groups showed high arginase activity, regardless of glycemic control and duration of T1DM along with insulin therapy. At the same time, a significant decrease in the subcellular production of bioavailable NO was observed in children/preadolescents, regardless of glycemic control and duration of diabetes. In adolescents/young adult boys with RO-T1DM, with (-), the subcellular production of NO decreased significantly, and with LT-T1DM, the decrease was attenuated, but even with (+) remained lower than in healthy people. In contrast, in the group of same age girls with RO-T1DM, NO production increased above normal in both cellular compartments, while with LT-T1DM it normalized in the cytoplasm. In adolescents/young adults with LT-T1DM, NO production in PBL mitochondria decreased by almost a half, regardless of glycemic control and gender. Changes in the metabolic pathways of L-arginine in plasma differed and were less substantial than in the PBL cellular compartments in T1DM.Conclusions: Glycemic status and duration of T1DM along with insulin therapy affect the activity of arginase and NOS-dependent production of bioavailable NO in the cytoplasm and mitochondria in PBL of young patients with T1DM, depending on sex and age. Arginase and NOS can directly affect the processes occurring in the pancreas and the outcome of therapy through infiltrated leukocytes. Obtained data can be useful for understanding the heterogeneity of T1DM and using it to develop available criteria for assessing the severity and treatment of autoimmune diabetes.

UT-A1/A3 knockout mice show reduced fibrosis following unilateral ureteral obstruction

Renal fibrosis is a major contributor to the development and progression of chronic kidney disease. A low-protein diet can reduce the progression of chronic kidney disease and reduce the development of renal fibrosis, although the mechanism is not well understood. Urea reabsorption into the inner medulla is regulated by inner medullary urea transporter (UT)-A1 and UT-A3. Inhibition or knockout of UT-A1/A3 will reduce interstitial urea accumulation, which may be beneficial in reducing renal fibrosis. To test this hypothesis, the effect of unilateral ureteral obstruction (UUO) was compared in wild-type (WT) and UT-A1/A3 knockout mice. UUO causes increased extracellular matrix associated with increases in transforming growth factor-β, vimentin, and α-smooth muscle actin (α-SMA). In WT mice, UUO increased the abundance of three markers of fibrosis: transforming growth factor-β, vimentin, and α-SMA. In contrast, in UT-A1/A3 knockout mice, the increase following UUO was significantly reduced. Consistent with the Western blot results, immunohistochemical staining showed that the levels of vimentin and α-SMA were increased in WT mice with UUO and that the increase was reduced in UT-A1/A3 knockout mice with UUO. Masson's trichrome staining showed increased collagen in WT mice with UUO, which was reduced in UT-A1/A3 knockout mice with UUO. We conclude that reduced UT activity reduces the severity of renal fibrosis following UUO.

Metabolomic study on the faecal extracts of atherosclerosis mice and its application in a Traditional Chinese Medicine

The intestinal microbiota and their metabolites are closely related to the formation of atherosclerosis (AS). In this study, a metabolomic approach based on the reversed-phase liquid chromatography/quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) platform was established to analyze the metabolic profiling of fecal extracts from AS mice model. The established metabolomic platform was also used for clearing the effective mechanism of a Traditional Chinese Medicine (TCM) named Sishen granule (SSKL). Totally, sixteen potential biomarkers in faeces of AS mice were identified and 5 of them could be reversed by SSKL. Through functional analysis of these biomarkers and the established network, lipid metabolism, cholesterol metabolism, energy cycle, and inflammation reaction were considered as the most relevant pathological changes in gastrointestinal tract of AS mice. The metabolomic study not only revealed the potential biomarkers in AS mice' faeces but also supplied a systematic view of the pathological changes in gastrointestinal metabolite in AS mice. This metabolomic study also demonstrated that SSKL had the therapeutic effectiveness on AS through partly reversing the lipid metabolism, inflammation and energy metabolism.

Effect of time on dialysis and renal transplantation on endothelial function: a longitudinal analysis

Background

Soluble vascular cell adhesion molecule-1 (sVCAM-1) is a marker of endothelial injury and a potent predictor of cardiovascular mortality in patients with kidney failure on dialysis. The longitudinal effects of dialysis on endothelial dysfunction and in particular the effects of renal transplantation on markers of endothelial function including sVCAM-1 have not been well characterized.

Methods

We used the Transplant Manitoba registry and biobank to assemble a retrospective cohort of all patients receiving a first kidney transplant between January 1, 2000, and December 31, 2005 (n=186). One hundred seventy-four patients had at least two serum samples pretransplant and at least two samples posttransplant. In total, 1,004 serial samples (median 5/patient) were analyzed. Factors associated with sVCAM-1 were examined using mixed linear models.

Results

The sVCAM-1 levels increased progressively on dialysis (0.15 [0.10 to 0.20] ng/mL/day; P<0.0001), fell significantly within 1 month after transplantation (−625 ng/mL/day; P<0.0001) and continued to fall thereafter (−0.23 [−0.34 to −0.12] ng/mL/day). Smoking and heart failure were associated with higher sVCAM-1 levels, whereas transplantation was associated with lower sVCAM-1 levels. The relationship between sVCAM-1 and transplantation was not changed by multivariate adjustment.

Conclusion

Endothelial injury worsens over time on dialysis but improves significantly after renal transplantation.

Supplemental digital content is available in the article.

Arginase II inhibited lipopolysaccharide-induced cell death by regulation of iNOS and Bcl-2 family proteins in macrophages

Arginase II catalyzes the conversion of arginine to urea and ornithine in many extrahepatic tissues. We investigated the protective role of arginase II on lipopolysaccharide-mediated apoptosis in the macrophage cells. Adenoviral gene transfer of full length of arginase II was performed in the murine macrophage cell line RAW264.7. The role of arginase II was investigated with cell viability, cytoplasmic histone-associated DNA fragmentation assay, arginase activity, nitric oxide production, and Western blot analysis. Arginase II is localized in mitochondria of macrophage cells, and the expression of arginase II was increased by lipopolysaccharide (LPS). LPS significantly increased cell death which was inhibited by AMT, a specific inducible nitric oxide synthase (iNOS) inhibitor. In contrast, LPS-induced cell death and nitric oxide production were increased by 2-boronoethyl-L-cysteine, a specific inhibitor of arginase. Adenoviral overexpression of arginase II significantly inhibited LPS-induced cell death and cytoplasmic histone-associated DNA fragmentation. LPS-induced iNOS expression and poly ADP-ribose polymerase cleavage were significantly suppressed by arginase II overexpression. Furthermore, arginase II overexpression resulted in a decrease in the Bax protein level and the reverse induction of Bcl-2 protein. Our data demonstrated that inhibition of NO production by arginase II may be due to arginine depletion as well as iNOS suppression though its reaction products. Moreover, arginase II plays a protective role of LPS-induced apoptosis in RAW264.7 cells.

Model-driven multi-omic data analysis elucidates metabolic immunomodulators of macrophage activation

Macrophages are central players in immune response, manifesting divergent phenotypes to control inflammation and innate immunity through release of cytokines and other signaling factors. Recently, the focus on metabolism has been reemphasized as critical signaling and regulatory pathways of human pathophysiology, ranging from cancer to aging, often converge on metabolic responses. Here, we used genome-scale modeling and multi-omics (transcriptomics, proteomics, and metabolomics) analysis to assess metabolic features that are critical for macrophage activation. We constructed a genome-scale metabolic network for the RAW 264.7 cell line to determine metabolic modulators of activation. Metabolites well-known to be associated with immunoactivation (glucose and arginine) and immunosuppression (tryptophan and vitamin D3) were among the most critical effectors. Intracellular metabolic mechanisms were assessed, identifying a suppressive role for de-novo nucleotide synthesis. Finally, underlying metabolic mechanisms of macrophage activation are identified by analyzing multi-omic data obtained from LPS-stimulated RAW cells in the context of our flux-based predictions. Our study demonstrates metabolism's role in regulating activation may be greater than previously anticipated and elucidates underlying connections between activation and metabolic effectors.

Effect of moderate-to-severe chronic kidney disease on flow-mediated dilation and progenitor cells

A reduction in progenitor cell populations that help preserve vascular continuity and induce vascularization may accentuate endothelial cell apoptosis and dysfunction, ultimately contributing to organ failure and increased cardiovascular disease in chronic kidney disease (CKD). We hypothesized that CD45+ myeloid and CD34+ hematopoietic circulating progenitor cell (CPC) subpopulations would be reduced, peripheral blood mononuclear cell (PBMNC) colony-forming units (CFU) would be impaired, and flow-mediated dilation (FMD) would be impaired in patients with moderate-to-severe CKD as compared with healthy controls. Eleven moderate-to-severe CKD patients (mean estimated glomerular filtration rate [eGFR]: 36 ± 5) and 14 healthy controls were studied; blood was drawn and FMD was assessed by brachial artery FMD. CPCs were quantified via flow cytometry, and isolated PBMNCs were cultured for the colony-forming assay. CKD patients had significantly impaired FMD; lower CD34+, CD34+/KDR+, CD34+/CD45- and CD34+/KDR+/CD45- hematopoietic CPCs; lower CD45+, CD45+/KDR+, CD34+/CD45+ and CD34+/KDR+/CD45+ myeloid CPCs; and impaired CFUs as compared with healthy controls. Regression analysis revealed that CD34+, CD34+/KDR+ and CD34+/CD45- hematopoietic CPCs were associated positively with eGFR and negatively with blood urea nitrogen and serum creatinine. The CD45+/KDR+ myeloid CPCs also were associated positively with eGFR and negatively with serum creatinine. CD34+ hematopoietic CPCs and CD45+/KDR+ as well as CD34+/CD45+ myeloid CPCs were associated positively with FMD. In conclusion, myeloid and hematopoietic CPCs are reduced and associated with renal function as well as FMD in CKD. Therefore, reductions in CPCs may be a potential mechanism by which vascular integrity is compromised, increasing cardiovascular disease risk and contributing to renal disease progression in CKD.

Nitrergic response to cyclophosphamide treatment in blood and bone marrow

Daily intraperitoneal injection of cyclophosphamide (CPA) (50 mgkg(-1) of body weight) for 5 days resulted in reduced levels of marrow and blood cellularity, which was most pronounced in 18 days post-treatment (pt). On day 18 after CPA treatment the enhancedlevels of nitric oxide (NO) precursors and metabolites (L-arginine, L-citrulline, reactive nitrogen species (RNS)) of marrow and blood cells (platelet, neutrophil, lymphocyte and monocyte) resulted from up-regulation of Ca(II)/calmodulin(CaM)-independent "inducible" NO synthase (iNOS), with a lessercontribution of Ca(II)/CaM-dependent "constitutive" cNOS isoforms to systemic NO.Biphasic response to CPA of marrow nitrergic system, i.e. both iNOS and cNOS showed significantly depressed activities, as well as diminished levels of NO metabolites on day 9 pt, suggested that signals in addition to NO might be involved in CPA-induced inhibition of hematopoesis, while a gradual increase of neutrophil and platelet NOS activity appeared to be contributed to a CPA-induced development of granulopenia, thrombocytopenia and hemorrhage.

Hypochlorite-oxidized low density lipoproteins reduce production and bioavailability of nitric oxide in RAW 264.7 macrophages by distinct mechanisms

Oxidative modification of low density lipoproteins is thought to play a pivotal role in the development and exacerbation of atherosclerosis and atherogenesis, and is believed to be closely associated with alterations in the vascular production of nitric oxide (NO). Previous work has shown that several products emerging from lipid peroxidation (e.g. lipid hydroperoxides, lysophospholipids, oxidized cholesterol) are able to reduce NO production in macrophages. The naturally occurring oxidant hypochlorite has been shown to be responsible for the in vivo formation of hypochlorite-oxidized LDL and such OxLDL are known to lack lipid peroxidation products. In this work we demonstrate that hypochlorite-oxidized LDL mediate profound effects on lipopolysaccharide-induced nitric oxide production in RAW 264.7 macrophages. By means of the membrane-permeable NO indicator 4,5-diaminofluorescein diacetate, we are able to show decreased levels of intracellular authentic nitric oxide following incubation with hypochlorite-oxidized LDL. The observed effects are dose-dependent and comparable to results obtained in the presence of the NOS inhibitor NG-monomethyl-L-arginine. This marked reduction of intracellular NO is accompanied by a dose-dependent inhibition of inducible nitric oxide synthase (iNOS) protein and mRNA expression. Furthermore, hyp-OxLDL lead to the generation of peroxynitrite, thereby also reducing bioavailability of NO. By mediating these effects on production and bioavailability of NO, hyp-OxLDL might also contribute to atherogenesis by reducing the antiatherogenic effects of nitric oxide.

Cellular Response to Hyperosmotic Stresses

Cells in the renal inner medulla are normally exposed to extraordinarily high levels of NaCl and urea. The osmotic stress causes numerous perturbations because of the hypertonic effect of high NaCl and the direct denaturation of cellular macromolecules by high urea. High NaCl and urea elevate reactive oxygen species, cause cytoskeletal rearrangement, inhibit DNA replication and transcription, inhibit translation, depolarize mitochondria, and damage DNA and proteins. Nevertheless, cells can accommodate by changes that include accumulation of organic osmolytes and increased expression of heat shock proteins. Failure to accommodate results in cell death by apoptosis. Although the adapted cells survive and function, many of the original perturbations persist, and even contribute to signaling the adaptive responses. This review addresses both the perturbing effects of high NaCl and urea and the adaptive responses. We speculate on the sensors of osmolality and document the multiple pathways that signal activation of the transcription factor TonEBP/OREBP, which directs many aspects of adaptation. The facts that numerous cellular functions are altered by hyperosmolality and remain so, even after adaptation, indicate that both the effects of hyperosmolality and adaptation to it involve profound alterations of the state of the cells.

Design and synthesis of urea and thiourea derivatives and their inhibitory activities on lipopolysaccharide-induced NO production

Series of ureas and thioureas were designed and synthesized, and their inhibitory activities of NO production in lipopolysaccharide-activated macrophages were evaluated. We found several essential moieties in the structure of the prepared compounds for the activity. Thiourea derivatives revealed higher inhibitory activity than the corresponding urea derivatives. Among these compounds, 7e having carboxymethyl group at N3 position of thiourea was the most potent in the inhibition of NO production. They inhibited NO production through the suppression of iNOS protein and mRNA expression.

Renal failure after percutaneous coronary intervention is associated with high mortality

Renal failure is a marker of poor outcome in the general population. Renal failure after percutaneous coronary artery intervention (PCI) is associated with an increased hazard of in-hospital mortality. We hypothesized that post-PCI renal insufficiency would be a predictor of long-term mortality in patients undergoing PCI who survive for over 30 days after the procedure. A retrospective analysis was conducted from a registry of 9,067 patients undergoing PCI at our center from 1997 to 2001. A rise in creatinine by 1 mg/dl from baseline was defined as post-PCI renal insufficiency. Vital status was assessed using Social Security Death Index. There were a total of 996 deaths over a mean follow-up period of 3.2 years. In a multivariate analysis, history of recent acute myocardial infarction, older age, insulin-dependent diabetes, baseline creatinine greater than 1.5 mg/dl, and presence of mitral regurgitation were associated with post-PCI renal insufficiency. Developing post-PCI renal insufficiency was associated with a 4.31-fold hazard of mortality in univariate analysis and a 1.77-fold hazard after adjustment for known predictors of mortality after PCI. The 1-year survival in patients with renal failure was 70.3% +/- 3.91%, compared to a survival of 93.6% +/- 0.27% in those without any post-PCI renal insufficiency (P < 0.0001). Acute renal insufficiency after PCI is a strong and independent predictor of long-term mortality in patients who survived for 30 days after the procedure.

Low water-soluble uremic toxins

The uremic syndrome is the result of the retention of solutes, which under normal conditions are cleared by the healthy kidneys. Uremic retention products are arbitrarily subdivided according to their molecular weight. Low-molecular-weight molecules are characterized by a molecular weight below 500 D. The purpose of the present publication is to review the main water soluble, nonprotein bound uremic retention solutes, together with their main toxic effects. We will consecutively discuss creatinine, glomerulopressin, the guanidines, the methylamines, myo-inositol, oxalate, phenylacetyl-glutamine, phosphate, the polyamines, pseudouridine, the purines, the trihalomethanes, and urea per se.

[Atherosclerosis and uremia: signifance of non-traditional risk factors]

Arteriosclerosis, atherosclerosis and vascular calcification are causally related to the high morbidity and mortality of patients with chronic renal failure. Oxidative stress and carbonyl stress of uremia, dialysis procedure and/or intravenous iron therapy result in AGE (advanced glycation end-product), ALE (advanced lipoxidation end-product) and AOPP (advanced oxidation protein product) formation, favouring together with elevated CRP (C-reactive protein) levels the development of cardiovascular and cerebrovascular complications. Enhanced plasma levels of homocysteine and ADMA (asymmetric dimethylarginine) contribute to this process. In addition, in chronic renal insufficiency hyperphosphatemia and an enhanced calcium x phosphorus ion product are associated with the morbidity and mortality of the patients, particularly in the presence of fetuin deficiency. Phosphorus, AGEs and AOPPs, beside other factors, catalyze the conversion of vascular smooth muscle cells to osteoblast--like cells (particularly in the presence of monocytes/macrophages), resulting in bone matrix protein formation. Other risk factors, such as age, male sex, smoking, hypertension, diabetes, chronic inflammation, insulin resistance or dyslipidemia (enhanced non-HDL-cholesterol) also contribute to the atherosclerotic risk profile of the patient with chronic renal insufficiency. While there is growing understanding of the mechanisms involved in arteriosclerosis, atherosclerosis and vascular calcification in uremia, we are still missing effective therapeutic maneuvers for reduction of excess mortality in uremic patients.

Urea percentiles in children with chronic renal failure. Data from the ItalKid project

In chronic renal failure high serum urea levels (sUrea) are correlated with the onset of uremic symptoms. Urea has generally been considered relatively non-toxic, functioning more as a surrogate for other toxic solutes; however, it has been recently reported that it can contribute to uremic toxicity. Clinically sUrea are often difficult to interpret because of the wide range of kidney functions. To obtain a practical and easily accessible tool to evaluate sUrea, we have produced percentile curves for different ranges of chronic renal failure, defined with creatinine clearance ( C(Cr)) obtained with the Schwartz formula. Data were obtained from the Italian Pediatric Registry of Chronic Renal Failure (ItalKid); its inclusion criteria are: (1) C(Cr )<75 ml/min per 1.73 m(2), (2) age <20 years at time of registration, and (3) conservative treatment. To obtain the percentiles, the following patients were excluded: patients with an underlying disease, a concomitant treatment, or a disorder that could affect urea metabolism, per se, and/or food intake, and patients aged <2 years. The study group included 690 subjects (mean age 9.56+/-4.54 years, 485 males). In total, 2,085 observations (C(Cr )and sUrea) were available for the construction of the percentile curves. A median of 258 (range 99-380) observations was obtained for each of the eight different categories of C(Cr )(intervals of 10 ml/min per 1.73 m(2)). The 10th, 25th, 50th, 75th, and 90th percentiles were calculated and a graph was produced. Patients with the highest urea percentiles showed significantly higher plasma levels of phosphorus and parathyroid hormone and significantly lower hemoglobin concentrations and bicarbonate levels. Our percentile curves may help to identify subjects with inappropriate sUrea for a given C(Cr).

Evolution of oxidative stress and inflammation during hemodialysis and their contribution to cardiovascular disease

End-stage renal disease patients have increased cardiovascular morbidity and mortality. These patients have many unique risk factors, such as an accumulation of uremic toxins, electrolyte imbalances, metabolic disturbances, anemia, chronic inflammation, and thrombogenic disturbances. Oxidative stress has been implicated in many of these disturbances. This review will focus on some of the factors that may accelerate cardiovascular disease in uremic patients, with an emphasis on mechanisms and interactions of various components of oxidative stress and inflammation. Understanding the mechanisms of these pathways may be useful in developing effective prevention and treatment strategies.

Human uremic plasma increases microvascular permeability to water and proteins in vivo

BACKGROUND

The risk of cardiovascular disease is significantly higher in patients with long-term uremia than in otherwise healthy adults. This is true even before patients proceed to dialysis, but the reason why cardiovascular risk is increased is unknown. Transvascular transport of lipids and other macromolecules in both large vessels and the microcirculation has been implicated in generation of cardiovascular disease.

METHODS

To determine whether patients with long-term uremia have circulating factors that promote increased vascular permeability, we measured the effect of perfusing microvessels with uremic plasma in a non-mammalian model of vascular permeability measurement.

RESULTS

Perfusion of frog mesenteric microvessels with dialyzed normal plasma did not result in an increase in either hydraulic conductivity (Lp, permeability of the vessel wall to water) or oncotic reflection coefficient (sigma, permeability to macromolecules, particularly proteins). Perfusion with dialyzed uremic plasma resulted in a very significant increase in vascular permeability to both water (Lp increased 8.8-fold from 4.1 to 36.4 x 10(-7) cm x s(-1) cm H2O(-1)) and proteins (sigma reduced from 0.93 to 0.53).

CONCLUSIONS

These results suggest that one or more circulating macromolecules in uremic plasma are able to increase transvascular solute and fluid flux, and may underlie the increased cardiovascular risk found in these patients.

Dissociation between dialysis adequacy and Kt/V

Since the initiation of dialysis, nephrologists have sought an index (or indices) for the adequacy of toxic solute removal. This quest has been characterized by a gradual shift in thinking, ending with a preference for dynamic parameters such as clearances normalized for body size (Kt/V). The threshold Kt/V, however, has changed over the years. While present guidelines suggest 1.2 with single-pool kinetics, higher levels might be proposed in the future. In spite of the known relation between Kt/V and survival, the accuracy of this parameter as a representative of the removal of the whole spectrum of compounds that are responsible for uremia is problematic. Kt/V only assesses the removal of a water-soluble compound from the body water through mostly hydrophilic membranes to the dialysate water. Furthermore, the small size of urea means that convective and/or diffusive transfer through a given semipermeable membrane is unlikely to be representative of larger molecules, especially if dialyzers with a small pore size are applied. Urea kinetics are also poorly representative of the removal of small protein-bound molecules and intracellular solutes with cell membrane-limited clearance. Finally, it should be realized that the Kt/V concept has been developed in a specific population, that is, a group of renal failure patients with few comorbidities, submitted to short intermittent hemodialysis with small-pore bioincompatible membranes very likely using dialysate of lower quality than that used today. Kt/V might well become less accurate and useful in predicting outcomes as different dialysis conditions are pursued, such as dialysis with biocompatible and/or large-pore membranes, (ultra) pure dialysate, alternative time frames, high levels of convection, and/or in populations with a different distribution of body mass.

Uremic levels of BUN do not cause nitric oxide deficiency in rats with normal renal function

In vitro, 7 days of high blood urea nitrogen (BUN) inhibits endothelial L-arginine transport and nitric oxide synthase (NOS) activity. The present study investigates whether 7 days of high BUN in vivo influences renal hemodynamics, blood pressure (BP), and/or the nitric oxide (NO) system. Normal rats were fed low-nitrate food containing 30% urea for 7 days, which increased BUN (15 +/- 1 to 69 +/- 4 mg/100 ml, P < 0.001). High BUN did not reduce 24-hour urinary nitrite/nitrate excretion (a measure of total NO production). Baseline BP and renal hemodynamics were unaffected by high BUN as were the pressor and renal vasoconstrictor responses to acute NOS inhibition with N(G)-nitro-L-arginine-methyl ester. In addition, high BUN had no impact on renal cortical L-arginine concentration, density of either endothelial NOS or neuronal NOS protein, or renal cortical NOS activity. NOS activity in the brain cerebellum was also unaffected. In conclusion, high BUN did not lead to vasoconstriction or NO deficiency in rats with normal renal function. Further studies are needed to evaluate the effect of high BUN on the NO system in rats with progressive renal functional insufficiency.

Lipopolysaccharide-induced cell cycle arrest in macrophages occurs independently of nitric oxide synthase II induction

Lipopolysaccharide (LPS, a Gram-negative bacterium cell wall component) is a potent macrophage activator that inhibits macrophage proliferation and stimulates production of nitric oxide (NO) via NO synthase II (NOSII). We investigated whether NO mediates the LPS-stimulated cell cycle arrest in mouse bone marrow-derived macrophages (BMM). The addition of the NO donor DETA NONOate (200 microM) inhibited BMM proliferation by approx. 80%. However, despite NO being an antimitogen, LPS was as potent at inhibiting proliferation in BMM derived from NOSII-/- mice as from wild-type mice. Consistent with these findings, LPS-induced cell cycle arrest in normal BMM was not reversed by the addition of the NOSII inhibitor S-methylisothiourea. Moreover, in both normal and NOSII-/- BMM, LPS inhibited the expression of cyclin D1, a protein that is essential for proliferation in many cell types. Despite inhibiting proliferation DETA NONOate had no effect on cyclin D1 expression. Our data indicate that while both LPS and NO inhibit BMM proliferation, LPS inhibition of BMM proliferation can occur independently of NOSII induction.

Macrophage proliferation in atherosclerosis

Oxidized LDL can induce an increase in intracellular calcium concentration and the activation of protein kinase C in mouse peritoneal macrophages. The activation of protein kinase C leads to the release into the culture medium of granulocyte-macrophage colony-stimulating factor, which plays a priming role in oxidized LDL-induced macrophage proliferation. The expression of granulocyte-macrophage colony-stimulating factor in macrophages by oxidized LDL is positively regulated in the 5'-flanking region of granulocyte-macrophage colony-stimulating factor gene from sequence -169 to -160, but negatively regulated from -91 to -82. Granulocyte-macrophage colony-stimulating factor released by oxidized LDL from macrophages induces proliferation in autocrine or paracrine fashion via the activation of phosphatidylinositol 3-kinase. The capacity of oxidized LDL to induce macrophage proliferation in vitro may be involved in the enhanced progression of atherosclerosis in vivo.

Inhibition of inducible nitric oxide synthesis by oxidized lipoprotein(a) in a murine macrophage cell line

Increased plasma levels of human lipoprotein(a) (Lp(a)) are highly correlated with the development of atherosclerotic lesions. During our study, we investigated the effects of native and hypochlorite oxidized lipoprotein(a) (ox-Lp(a)) on nitric oxide production by the inducible nitric oxide synthase (iNOS) in lipopolysaccharide/interferon stimulated mouse macrophages (J774A.1). Ox-Lp(a) (0-2 microg/ml) induces a dose dependent inhibition of inducible nitric oxide synthesis. iNOS protein expression showed a dose dependent reduction as revealed by immunoblotting when cells were incubated with increasing amounts of ox-Lp(a). Ox-Lp(a) decreases iNOS mRNA synthesis as shown by reverse transcription-polymerase chain reaction. Ox-Lp(a) induced iNOS inhibition might contribute to the development of atherosclerotic lesions by reducing the anti-atherogenic effects of nitric oxide.

Quantitating urea removal in patients with acute renal failure: lost art or forgotten science?

A 67-year-old woman is admitted to the surgical service with a high fever, a painful and distended abdomen, jaundice, and almost complete anuria. A urinalysis revealed dark red-brown urine notable for albuminuria, erythrocytes, leukocytes, and casts. The patient was treated with antibiotics, but continued to have oligoanuria. On the eighth day of hospitalization, the following laboratory tests were obtained: serum potassium, 13.7 mEq/L; BUN, 396 mg/dl. At this time the patient was noted to be encephalopathic with deteriorating clinical condition. Renal replacement therapy was initiated. The characteristics of the initial dialysis treatment are described in Table 1. After the initial dialysis treatment, the patient went on to become nonoliguric, followed by gradual recovery of urea clearance. She survived her acute illness, left the hospital, and at 7 months posthospitalization was doing quite well.