Monocytes as Targets for Immunomodulation by Regional Citrate Anticoagulation.

Immune alterations in end-stage renal patients receiving hemodialysis are complex and predispose patients to infections. Anticoagulation may also play an immunomodulatory role in addition to the accumulation of uremic toxins and the effects of the dialysis procedure. Accordingly, it has been recently shown that the infection rate increases in patients under regional citrate anticoagulation (RCA) compared with systemic heparin anticoagulation (SHA). We hypothesized that RCA affects the immune status of hemodialysis patients by targeting monocytes. In a cohort of 38 end-stage renal patients undergoing hemodialysis, we demonstrated that whole blood monocytes of patients receiving RCA-but not SHA-failed to upregulate surface activation markers, like human leukocyte antigen class II (HLA-DR), after stressful insults, indicating a state of deactivation during and immediately after dialysis. Additionally, RNA sequencing (RNA-seq) data and gene set enrichment analysis of pre-dialysis monocytes evidenced a great and complex difference between the groups given that, in the RCA group, monocytes displayed a dramatic transcriptional change with increased expression of genes related to the cell cycle regulation, cellular metabolism, and cytokine signaling, compatible with the reprogramming of the immune response. Transcriptomic changes in pre-dialysis monocytes signalize the lasting nature of the RCA-related effects, suggesting that monocytes are affected even beyond the dialysis session. Furthermore, these findings demonstrate that RCA-but not SHA-impairs the response of monocytes to activation stimuli and alters the immune status of these patients with potential clinical implications.

The Soluble Fms-like Tyrosine Kinase-1 Contributes to Structural and Functional Changes in Endothelial Cells in Chronic Kidney Disease.

Endothelial cells are a critical target of the soluble Fms-like tyrosine kinase-1 (sFlt-1), a soluble factor increased in different diseases with varying degrees of renal impairment and endothelial dysfunction, including chronic kidney disease (CKD). Although the mechanisms underlying endothelial dysfunction are multifactorial and complex, herein, we investigated the damaging effects of sFlt-1 on structural and functional changes in endothelial cells. Our results evidenced that sera from patients with CKD stiffen the endothelial cell cortex in vitro, an effect correlated with sFlt-1 levels and prevented by sFlt-1 neutralization. Besides, we could show that recombinant sFlt-1 leads to endothelial stiffening in vitro and in vivo. This was accompanied by cytoskeleton reorganization and changes in the endothelial barrier function, as observed by increased actin polymerization and endothelial cell permeability, respectively. These results depended on the activation of the p38 MAPK and were blocked by the specific inhibitor SB203580. However, sFlt-1 only minimally affected the expression of stiffness-sensitive genes. These findings bring new insight into the mechanism of action of sFlt-1 and its biological effects that cannot be exclusively ascribed to the regulation of angiogenesis.

Symmetric dimethylarginine in dysfunctional high-density lipoprotein mediates endothelial glycocalyx breakdown in chronic kidney disease.

Dysfunctional high-density lipoprotein (d-HDL) in chronic kidney disease is known to have a change in composition towards an endothelial-damaging phenotype, amongst others, via the accumulation of symmetric dimethylarginine. The endothelial glycocalyx, a carbohydrate-rich layer lining the endothelial luminal surface, is a first line defense against vascular diseases including atherosclerosis. Here we conducted a translational, cross-sectional study to determine the role of symmetric dimethylarginine in d-HDL as a mediator of glycocalyx damage. Using confocal and atomic force microscopy, intact HDL from healthy donors was found to maintain the glycocalyx while isolated HDL from hemodialysis patients and exogenous symmetric dimethylarginine caused significant damage to the glycocalyx in endothelial cells in vitro in a dose-dependent manner. Symmetric dimethylarginine triggered glycocalyx deterioration via molecular pathways mediated by toll-like-receptor 2 and matrix metalloprotease-9. Corresponding intravital microscopy revealed that exogenous symmetric dimethylarginine and d-HDL from hemodialysis patients caused glycocalyx breakdown, which subsequently contributed to alterations in leukocyte rolling. Biologically effective HDL, which estimates the functionality of HDL, was calculated from circulating HDL-cholesterol and symmetric dimethylarginine, as described in the literature. Biologically effective HDL was the only parameter that could independently predict glycocalyx damage in vivo. Thus, our data suggest that symmetric dimethylarginine in d-HDL mediates glycocalyx breakdown in chronic kidney disease.

Treatment of established left ventricular hypertrophy with fibroblast growth factor receptor blockade in an animal model of CKD.

BACKGROUND: Activation of fibroblast growth factor receptor (FGFR)-dependent signalling by FGF23 may contribute to the complex pathogenesis of left ventricular hypertrophy (LVH) in chronic kidney disease (CKD). Pan FGFR blockade by PD173074 prevented development of LVH in the 5/6 nephrectomy rat model of CKD, but its ability to treat and reverse established LVH is unknown. METHODS: CKD was induced in rats by 5/6 nephrectomy. Two weeks later, rats began treatment with vehicle (0.9% NaCl) or PD173074, 1 mg/kg once-daily for 3 weeks. Renal function was determined by urine and blood analyses. Left ventricular (LV) structure and function were determined by echocardiography, histopathology, staining for myocardial fibrosis (Sirius-Red) and investigating cardiac gene expression profiles by real-time PCR. RESULTS: Two weeks after inducing CKD by 5/6 nephrectomy, rats manifested higher (mean ± SEM) systolic blood pressure (208 ± 4 versus 139 ± 3 mmHg; P < 0.01), serum FGF23 levels (1023 ± 225 versus 199 ± 9 pg/mL; P < 0.01) and LV mass (292 ± 9 versus 220 ± 3 mg; P < 0.01) when compared with sham-operated animals. Thereafter, 3 weeks of treatment with PD173074 compared with vehicle did not significantly change blood pressure, kidney function or metabolic parameters, but significantly reduced LV mass (230 ± 14 versus 341 ± 33 mg; P < 0.01), myocardial fibrosis (2.5 ± 0.7 versus 5.4 ± 0.95% staining/field; P < 0.01) and cardiac expression of genes associated with pathological LVH, while significantly increasing ejection fraction (18 versus 2.5% post-treatment increase; P < 0.05). CONCLUSIONS: FGFR blockade improved cardiac structure and function in 5/6 nephrectomy rats with previously established LVH. These data support FGFR activation as a potentially modifiable, blood pressure-independent molecular mechanism of LVH in CKD.

High phosphate directly affects endothelial function by downregulating annexin II.

Hyperphosphatemia is associated with increased cardiovascular risk in patients with renal disease and in healthy individuals. Here we tested whether high phosphate has a role in the pathophysiology of cardiovascular events by interfering with endothelial function, thereby impairing microvascular function and angiogenesis. Protein expression analysis found downregulation of annexin II in human coronary artery endothelial cells, an effect associated with exacerbated shedding of annexin II-positive microparticles by the cells exposed to high phosphate media. EAhy926 endothelial cells exposed to sera from hyperphosphatemic patients also display decreased annexin II, suggesting a negative correlation between serum phosphate and annexin II expression. By using endothelial cell-based assays in vitro and the chicken chorioallantoic membrane assay in vivo, we found that angiogenesis, vessel wall morphology, endothelial cell migration, capillary tube formation, and endothelial survival were impaired in a hyperphosphatemic milieu. Blockade of membrane-bound extracellular annexin II with a specific antibody mimicked the effects of high phosphate. In addition, high phosphate stiffened endothelial cells in vitro and in rats in vivo. Thus, our results link phosphate and adverse clinical outcomes involving the endothelium in both healthy individuals and patients with renal disease.

Influence of erythropoietin on arterial stiffness and endothelial function in renal transplant recipients.

BACKGROUND/AIMS: Recent retrospective studies suggest an association of therapy with erythropoiesis-stimulating agents (ESAs) and increased mortality in renal transplant recipients (RTR). Large artery structure and function are significantly impaired in RTR which contributes to their high cardiovascular morbidity and could be altered by erythropoietin. We aimed to examine the influence of ESA therapy on large artery stiffness and endothelial function in RTR. METHODS: 63 RTR with chronic allograft dysfunction and renal anemia were randomized to a group receiving darbepoetin alfa (Dar) and a control group (Co). At baseline and after 8 months of treatment (cumulative Dar dose 11.1 µg/kg b.w.) brachial and common carotid artery distensibility coefficients, aortic pulse wave velocity, brachial artery flow-mediated and nitroglycerin-mediated vasodilation were measured as well as the following biomarkers of vascular function: vWF, sVCAM, sICAM, E-selectin, t-PA and PAI-1. RESULTS: 23 patients in the Dar group and 17 patients in the Co group were available for per-protocol analysis. Hemoglobin increased significantly from 10.9 to 12.6 g/dl after 8 months in the Dar group, whereas it remained stable at 11.3 g/dl in the Co group. Effects on large artery stiffness, endothelial function and biomarkers of vascular function did not differ significantly between the two groups. CONCLUSION: Therapy with Dar during 8 months did not significantly impact parameters of large artery stiffness and endothelial function in RTR. These data suggest that therapy with erythropoietin does not deteriorate arterial stiffness and endothelial function in RTR.

FGF23/FGFR4-mediated left ventricular hypertrophy is reversible.

Fibroblast growth factor (FGF) 23 is a phosphaturic hormone that directly targets cardiac myocytes via FGF receptor (FGFR) 4 thereby inducing hypertrophic myocyte growth and the development of left ventricular hypertrophy (LVH) in rodents. Serum FGF23 levels are highly elevated in patients with chronic kidney disease (CKD), and it is likely that FGF23 directly contributes to the high rates of LVH and cardiac death in CKD. It is currently unknown if the cardiac effects of FGF23 are solely pathological, or if they potentially can be reversed. Here, we report that FGF23-induced cardiac hypertrophy is reversible in vitro and in vivo upon removal of the hypertrophic stimulus. Specific blockade of FGFR4 attenuates established LVH in the 5/6 nephrectomy rat model of CKD. Since CKD mimics a form of accelerated cardiovascular aging, we also studied age-related cardiac remodeling. We show that aging mice lacking FGFR4 are protected from LVH. Finally, FGF23 increases cardiac contractility via FGFR4, while known effects of FGF23 on aortic relaxation do not require FGFR4. Taken together, our data highlight a role of FGF23/FGFR4 signaling in the regulation of cardiac remodeling and function, and indicate that pharmacological interference with cardiac FGF23/FGFR4 signaling might protect from CKD- and age-related LVH.

NADPH oxidase and enhanced superoxide generation in intrauterine undernourished rats: involvement of the renin-angiotensin system.

OBJECTIVE: We previously reported that intrauterine undernutrition increased the oxidative stress by decreasing superoxide dismutase activity. In the present study, we tested whether NADPH oxidase, xanthine oxidase, cyclooxygenase or nitric oxide synthase are responsible for the increased O(2)(-) generation observed in rats submitted to intrauterine undernutrition. In addition, we investigated the effect of angiotensin II (ANG II) on O(2)(-) production via activation of NADPH oxidase. METHODS: Female pregnant Wistar rats were fed either normal or 50% of the normal intake diets, during the whole gestational period. At 16 weeks of age, the rats were used for the study of intravital fluorescence microscopy; microvascular reactivity, local ANG II concentration and AT(1), p22(phox) and gp91(phox) gene expression. In this study only the male offspring was used. RESULTS: Treatment of mesenteric arterioles with the xanthine oxidase inhibitor oxypurinol, the nitric oxide synthase inhibitor L-NAME or the cyclooxygenase inhibitor diclofenac did not significantly change superoxide production. Thus, these vascular sources of superoxide were not responsible for the increased superoxide concentration. In contrast, treatment with the NADPH oxidase inhibitor apocynin significantly decreased superoxide generation and improved vascular function. On the other hand, intrauterine undernutrition did not alter the gene expression for p22(phox) and gp91(phox). The fact that the local ANG II concentration was increased and the attenuation of oxidative stress by blocking AT(1) receptor with losartan, led us to suggest that ANG II induces O(2)(-) generation in intrauterine undernourished rats. CONCLUSION: Our study shows that NADPH oxidase inhibition attenuated superoxide anion generation and ameliorated vascular function in rats submitted to intrauterine undernutrition. Although it is not clear which mechanisms are responsible for the increase in NADPH oxidase activity, a role for ANG II-mediated superoxide production via activation of NADPH oxidase is suggested.

Activation of Cardiac Fibroblast Growth Factor Receptor 4 Causes Left Ventricular Hypertrophy.

Chronic kidney disease (CKD) is a worldwide public health threat that increases risk of death due to cardiovascular complications, including left ventricular hypertrophy (LVH). Novel therapeutic targets are needed to design treatments to alleviate the cardiovascular burden of CKD. Previously, we demonstrated that circulating concentrations of fibroblast growth factor (FGF) 23 rise progressively in CKD and induce LVH through an unknown FGF receptor (FGFR)-dependent mechanism. Here, we report that FGF23 exclusively activates FGFR4 on cardiac myocytes to stimulate phospholipase Cγ/calcineurin/nuclear factor of activated T cell signaling. A specific FGFR4-blocking antibody inhibits FGF23-induced hypertrophy of isolated cardiac myocytes and attenuates LVH in rats with CKD. Mice lacking FGFR4 do not develop LVH in response to elevated FGF23, whereas knockin mice carrying an FGFR4 gain-of-function mutation spontaneously develop LVH. Thus, FGF23 promotes LVH by activating FGFR4, thereby establishing FGFR4 as a pharmacological target for reducing cardiovascular risk in CKD.

Urinary neopterin quantification by reverse-phase high-performance liquid chromatography with ultraviolet detection.

Neopterin plays an important role in the malignant disease diagnostics. However, the methods employed in neopterin determination are generally difficult and/or time consuming. The aim of this work was to standardize a practical method to quantify neopterin using high-performance liquid chromatography-ultraviolet (HPLC-UV) and quantify it in patients with systemic lupus erythematosus (SLE). Urine was collected from healthy subjects (n= 49), patients with inactive (n= 15), active (n= 28), and highly active SLE (n= 6). The HPLC was performed using two coupled reverse-phase columns eluted with 150 mM sodium phosphate, pH 4.0, under a flow rate of 0.8 ml/min, with UV detector set at 353 nm and 100-fold diluted urines. The inter- and intra-assay studies presented an imprecision of 12.5% and 12.9% for quality controls of 3.94 and 1.1 micromol/ml, respectively. Recovery from 79.5% to 82% was observed throughout the assay's linear range. Subjects with active (874.2 +/- 165.38 micromol/mol creatinin) and highly active SLE (1753.8 +/- 453.9 micromol/mol creatinin) showed three- and sixfold increased neopterin levels, respectively, compared to subjects with inactive SLE (314.3 +/- 121.3 micromol/mol creatinin) and healthy subjects (294.6 +/- 178.6 micromol/mol creatinin) (P< 0.05). Briefly, the proposed method was precise, specific, and reproducible, not invasive and allows the urinary neopterin quantification only with UV detection.

Neutral endopeptidase expression in mesangial cells.

In the kidney, neutral endopeptidase (NEP) is implicated in the metabolism of several peptides involved in blood pressure and sodium homeostasis control, such as the atrial natriuretic peptide, bradykinin and angiotensin I. Due to its physiological importance in the modulation of pressor responses, the presence of NEP in mouse mesangial cells has been investigated, since these cells control glomerular function and are able to synthesise components of the renin-angiotensin system. A NEP-like activity (NEP-like) that cleaves the fluorogenic substrates Abz-BKQ-EDDnp and Abz-DRRL-EDDnp was purified from mesangial cell lysate by ion-exchange, followed by gel filtration chromatography. The enzyme was able to hydrolyse bradykinin at the G4-F5 peptide bond and was inhibited by thiorphan. A pH study established that enzyme activity was maximal at pH 7.5 and the determined K(m) was 4.86 M using Abz-DRRL-EDDnp as substrate. NEP-like was recognised by monoclonal anti-NEP and had a molecular mass of 95 kDa. The purified enzyme was sequenced and showed similarity with human, rat, mouse and rabbit NEPs. We isolated, for the first time, NEP-like from mesangial cells. This enzyme could have an important role in the renal physiology by its action upon different peptides that are able to alter renal haemodynamics.

Damage of the endothelial glycocalyx in chronic kidney disease.

BACKGROUND AND OBJECTIVES: The endothelial glycocalyx (eGC), a mesh of anionic biopolymers covering the luminal surface of endothelial cells, is considered as an intravascular compartment that protects the vessel wall against pathogenic insults in cardiovascular disease. We hypothesized that chronic kidney disease (CKD) is associated with reduced eGC integrity and subsequent endothelial dysfunction. METHODS & RESULTS: Shedding of two major components of the eGC, namely syndecan-1 (Syn-1) and hyaluronan (HA), was measured by ELISA in 95 patients with CKD (stages 3-5) and 31 apparently healthy controls. Plasma levels of Syn-1 and HA increased steadily across CKD stages (5- and 5.5-fold, respectively P < 0.001) and were independently associated with impaired renal function after multivariate adjustment. Furthermore, Syn-1 and HA correlated tightly with plasma markers of endothelial dysfunction such as soluble fms-like tyrosine kinase-1 (sFlt-1), soluble vascular adhesion molecule-1 (sVCAM-1), von-Willebrand-Factor (vWF) and angiopoietin-2 (P < 0.001). Experimentally, excessive shedding of the eGC, evidenced by 11-fold increased Syn-1 plasma levels, was also observed in an established rat model of CKD, the 5/6-nephrectomized rats. Consistently, an atomic force microscopy-based approach evidenced a significant decrease in eGC thickness (360 ± 79 vs. 157 ± 29 nm, P = 0.001) and stiffness (0.33 ± 0.02 vs. 0.22 ± 0.01 pN/nm, P < 0.001) of aorta endothelial cell explants isolated from CKD rats. CONCLUSION: Our findings provide evidence for damage of the atheroprotective eGC as a consequence of CKD and potentially open a new avenue to pathophysiology and treatment of cardiovascular disease in renal patients.

FGF23 induces left ventricular hypertrophy.

Chronic kidney disease (CKD) is a public health epidemic that increases risk of death due to cardiovascular disease. Left ventricular hypertrophy (LVH) is an important mechanism of cardiovascular disease in individuals with CKD. Elevated levels of FGF23 have been linked to greater risks of LVH and mortality in patients with CKD, but whether these risks represent causal effects of FGF23 is unknown. Here, we report that elevated FGF23 levels are independently associated with LVH in a large, racially diverse CKD cohort. FGF23 caused pathological hypertrophy of isolated rat cardiomyocytes via FGF receptor-dependent activation of the calcineurin-NFAT signaling pathway, but this effect was independent of klotho, the coreceptor for FGF23 in the kidney and parathyroid glands. Intramyocardial or intravenous injection of FGF23 in wild-type mice resulted in LVH, and klotho-deficient mice demonstrated elevated FGF23 levels and LVH. In an established animal model of CKD, treatment with an FGF-receptor blocker attenuated LVH, although no change in blood pressure was observed. These results unveil a klotho-independent, causal role for FGF23 in the pathogenesis of LVH and suggest that chronically elevated FGF23 levels contribute directly to high rates of LVH and mortality in individuals with CKD.

Catecholamine production along the nephron.

The present work proposes an extra neural site of catecholamine production along the nephron. LLC-PK(1), MDCK, and mIMCD-3 (proximal and distal tubules and inner medullary collecting duct, respectively) presented the following amine concentrations in the cell homogenates: Norepinephrine = 275+/-34, 56+/-16 and 255+/-21; Epinephrine = 161+/-20, 83+/-17 and 53+/-7; and Dopamine = 63+/-15, 39+/-6 and 36+/-7 pg/mg cell protein (Means +/- SEM), respectively. The culture medium showed Norepinephrine = 168+/-25, 22+/-3 and 135+/-8; Epinephrine = 32+/-6, 152+/-17 and 39+/-5; and Dopamine = 27+/-9, 241+/-34 and 26+/-5 pg/mg cell protein, respectively. The synthesis enzymes as tyrosine hydroxylase, dopa decarboxylase and dopamine beta-hydroxylase were detected by Western blotting. Biopterin, the enzymatic cofactor of tyrosine hydroxylase, was quantified in the intracellular and medium of mIMCD-3 cells (17+/-4 and 24+/-3 nmol/mg cell protein, respectively) and in the medium of MDCK cells (19+/-4 nmol/mg cell protein). The data confirmed that the proximal tubule is an important source of dopa decarboxilase and Dopamine and epithelial cell along the nephron express the biochemical pathway for catecholamine production.

Expression and localization of N-domain ANG I-converting enzymes in mesangial cells in culture from spontaneously hypertensive rats.

The angiotensin-converting enzyme (ACE) profile in urine of hypertensive patients and spontaneously hypertensive rats (SHR; 90- and 65-kDa N-domain ACEs) is different from that of healthy subjects and Wistar rats (190 and 65 kDa). In addition, four ACE isoforms were purified from mesangial cells (MC) of Wistar rats in the intracellular compartment (130 and 68 kDa) and as secreted forms (130 and 60 kDa). We decided to characterize ACE forms from SHR MC in culture. Analysis of the ACE gene showed that SHR MC are able to express ACE mRNA. The concentrated medium and cell homogenate were separately purified by gel filtration and then subjected to lisinopril-Sepharose chromatography. The molecular masses of purified enzymes, 90 kDa for ACEm1A and 65 kDa for ACEm2A (secreted enzymes) and 90 kDa for ACEInth1A and 65 kDa for ACEInth2A (intracellular), were different from those of Wistar MC. The purified enzymes are Cl- dependent, inhibited by enalaprilat and captopril, and able to hydrolyze AcSDKP. Immunofluorescence and cell fractionation followed by Western blotting showed predominant immunoreaction of the 9B9 antiserum for N-domain ACE in the nuclei. The N-domain ACE was localized in the glomerulus from Wistar rats and SHR. ANG II and ANG-(1-7) were localized in the cell cytoplasm and nuclei. The 90-kDa N-domain ACE, described recently as a possible genetic marker of hypertension, was found inside the cell nuclei of SHR MC colocalized with ANG II and ANG-(1-7). The presence of ANG II in the cell nuclei could suggest an important role for this peptide in the transcription of new genes.

Sirolimus quantification by high-performance liquid chromatography with ultraviolet detection.

The need to adapt optimal conditions of sirolimus blood level monitoring in laboratories led us to optimize an high-performance liquid chromatography-ultraviolet method and compare the elution performances using the mobile phase A, 68% MeOH/2% acetonitrile (ACN)/30% H(2)O and mobile phase B, 30% MeOH/42% ACN/28% H(2)O. Samples were assayed with 1-chlorobutane, redissolved in MeOH/water and injected onto a C-18 column at 50 degrees C. The assay achieved sensitivity of 2.5-150 ng/ml (CV = 10.6%) and recovery of 92-103.6%. The intra- and interassay precisions ranged from 3.3% to 13% and from 5.9% to 15% for quality controls of 7.5, 60 and 120 ng/ml. The mobile phase A was unable to elute and recover sirolimus and internal standard in the expected retention time and concentration. Under our working conditions, the assay was precise, accurate and sensible, stressing the importance of establishing for the best working conditions according to the staff and demands of the laboratory.

Cyclosporine A and NAC on the inducible nitric oxide synthase expression and nitric oxide synthesis in rat renal artery cultured cells.

BACKGROUND: The immunosuppressor cyclosporine A (CsA) presents the nephrotoxicity as its major side effect that is mostly attributed to a renal vasoconstriction. This may be due to an excessive generation of vasoconstrictors like reactive oxygen species (ROS), or due to a reduction of vasodilators such as the nitric oxide, which in turn, can be caused by increased amounts of ROS. We evaluated the effect of CsA and the antioxidant N-acetylcysteine (NAC) on inducible nitric oxide synthase (iNOS) mRNA expression and nitric oxide synthesis, in rat renal artery vascular smooth muscle cells (rVSMCs) primary culture. METHODS: In cells treated during 72 hours with CsA (10 microg/mL), its vehicle (control) (10 microL/mL), Escherichia coli lipopolysaccharide (LPS) (100 microg/mL), CsA + LPS, NAC (6.13 mmol/L), or CsA + NAC, we determined the nitric oxide synthesis (Griess and chemiluminescence methods), iNOS expression [reverse transcription-polymerase chain reaction (RT-PCR)] and cell viability (acridine orange method). RESULTS: In rVSMCs, LPS increased nitric oxide and iNOS expression; CsA decreased basal and LPS-induced nitric oxide and iNOS expression; NAC increased nitric oxide and blunted the nitric oxide reduction caused by CsA, with no effect on iNOS. CsA reduced cell viability. CONCLUSION: In this study, CsA reduced nitric oxide synthesis in rVSMCs, both through iNOS down-regulation and reduction of cell viability, which could be responsible for the vasoconstrictive effect of the CsA. In the effect of CsA on nitric oxide, probably a role is also played by free radical production, as this effect was blunted by NAC.

Purification and characterization of the active form of tyrosine hydroxylase from mesangial cells in culture.

The capacity of mesangial cells (MC) to produce catecholamines (CAs) has been investigated in our laboratory. To study the CA cascade, it is necessary to examine some steps in their metabolic pathway. Tyrosine hydroxylase (TH) catalyzes the rate-limiting step in the biosynthesis of these biogenic amines (dopamine (DA), norepinephrine (NE), and epinephrine (EPI)). Since the glomerular mesangium is their target in the regulation of renal sodium transport and renin secretion, the aim of the study was to determine the presence of TH in these cells in culture. The CA levels were detected in immortalized MC by high-performance liquid chromatography with electrochemical detection. The following concentrations were found in the intracellular region and in the medium, respectively: NE = 284 +/- 31 and 134 +/- 22, EPI = 75 +/- 14 and 22 +/- 5, and DA = 42 +/- 14, 40 +/- 20 pg/mg cell protein. The enzymatic activity of the cell lysate and medium was measured based on L-dopa formation. In the presence of o-phenanthroline, both samples presented 39% inhibition. The biopterin was detected in the intracellular and in the medium (64.87 and 631.99 pmol/mg protein, respectively) using high-performance liquid chromatography with ultraviolet detection. The cell lysate was submitted to a DEAE-Sephacel column, followed by gel filtration, and Heparin-Sepharose. TH was purified 613.16-fold with a specific activity of 466.0 pg/mg cell protein. Immunoblotting using monoclonal antibody revealed the presence of TH in the different purification steps. Purified TH was sequenced, presenting an alignment with amino-terminal sequence of mouse enzyme. Our results demonstrated the presence of active TH in MC, suggesting that these cells are able to produce CA "in vivo", and establishing a convenient purification method for TH that can be applied to the study of the molecular properties of the enzyme modified "in vivo" by different physiological and pathophysiological stimuli.

Mesangial cells are able to produce catecholamines in vitro.

Mesangial cells (MC) participate in the control of the glomerular function due to their ability to synthesize hormones and induce cell contraction. Since MC can produce various kinds of hormones, the purpose of the present study was to determine if they are able to synthesize catecholamines. For this evaluation, the levels of norepinephrine, epinephrine, dopamine, and biopterin, the enzymatic cofactor of tyrosine hydroxylase (TH), were analyzed by HPLC in the intracellular compartment and in the medium of primary cultured MC. To identify and locate the enzymes responsible for monoamine synthesis, TH, dopa decarboxylase, and dopamine beta-hydroxylase, Western blotting and immunocytochemistry were employed using monoclonal and polyclonal antibodies. Concentrations of NE = 57 +/- 8, EPI = 82 +/- 10, and DA = 52 +/- 9 pg/mg protein (X +/- SEM) were found in the cell homogenate. The culture medium showed concentrations of NE = 25 +/- 3, EPI = 33 +/- 3, and DA = 62 +/- 15 pg/mg protein. Western blotting analysis and immunocytochemistry evidenced the presence of all enzymes. Moreover, biopterin was also detected in the intracellular compartment and in the medium (0.28 +/- 0.03 and 5.70 +/- 2 nmol/mg cell protein, respectively). Overall, the data indicate that MC have the biosynthetic machinery necessary to produce catecholamines, suggesting that they can act as a paracrine/autocrine hormone system, contributing to the regulation of glomerular hemodynamic and renal microcirculation.