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Biomedical subjects

T Sitter

Publications and source records attributed to T Sitter.

51 records · Page 3Linked to original sources
PubMed1995

Involvement of retinoic acid receptor alpha in the stimulation of tissue-type plasminogen-activator gene expression in human endothelial cells.

Retinoids stimulate tissue-type plasminogen-activator (t-PA) gene expression in human endothelial cells, and are likely to do so by binding to one or more nuclear retinoid receptors. The present study was initiated to identify the retinoid receptor(s) involved in this process. Expression and regulation of retinoic acid receptors (RARs) and retinoid X receptors (RXRs) were analyzed by Northern-blot analysis of total or poly(A)-rich RNA prepared from cultured human umbilical vein endothelial cells (HUVEC). Prior to any exposure to retinoids, HUVEC express two transcripts for RAR-alpha (3.6 kb and 2.8 kb), and low levels of transcripts for RAR-beta (3.4 kb and 3.2 kb) and RAR-gamma (3.3 kb and 3.1 kb). Two RXR subtypes were identified, RXR-alpha (4.8 kb) and, at a much lower concentration, RXR-beta (2.4 kb); no evidence for the presence of RXR-gamma was found. Furthermore, HUVEC express cellular retinol-binding protein I (CRBP-I) and cellular retinoic-acid-binding protein I (CRABP-I) mRNA. Exposure of HUVEC to 1 microM retinoic acid or the retinobenzoic acid, Ch55, led to the induction of the two RAR-beta mRNAs, RXR-alpha mRNA and CRBP-I mRNA, whereas the expression of the other receptor and CRABP-I transcripts did not change appreciably. Using retinoid analogues that bind preferentially to one of the RAR or RXR subtypes, we found evidence that RAR-alpha is involved in the retinoid-induced t-PA expression in HUVEC. This conclusion was strengthened by experiments in which blocking of RAR-alpha with a specific RAR-alpha antagonist, Ro 41-5253, was demonstrated to suppress the induction of t-PA by retinoids.

Benzoates↗
PubMed1995

Limitations of pulse oral calcitriol therapy in continuous ambulatory peritoneal dialysis patients.

Calcitriol is increasingly used for therapy of secondary hyperparathyroidism in patients with end-stage renal disease. Its therapeutic efficacy, however, often has been limited by the associated increase in intestinal calcium and phosphorus absorption. Previous studies reported that these side effects could be avoided by intermittent administration of calcitriol in high doses, subsequently referred to as pulse therapy. The present study was designed to investigate pulse oral calcitriol therapy in a patient subgroup especially susceptible to the development of hypercalcemia and hyperphosphatemia under standard continuous calcitriol treatment. We examined 15 peritoneal dialysis patients with moderate degrees of hyperparathyroidism (intact parathyroid hormone [iPTH] levels, 150 to 903 pg/mL) ingesting between 1.5 and 6 g of calcium salts as the sole phosphate binders. Treatment consisted of 0.5 microgram calcitriol twice weekly. Eight of these patients had been previously converted to low calcium dialysate to tolerate the necessary doses of phosphate-binding calcium salts. During the study period, comprising 8 pretreatment weeks and 8 weeks of therapy, dialysates and doses of calcium salts were not changed, so that only calcitriol influenced the determined parameters. As expected, iPTH levels decreased rapidly in all patients (P < 0.0001). However, within 4 weeks of treatment a marked increase in calcium phosphorus products was observed (P < 0.0001). Overt hypercalcemia developed in five patients. We concluded that pulse oral calcitriol has to be carefully monitored in peritoneal dialysis patients receiving high doses of calcium salts because of the increased risk for hypercalcemia and hyperphosphatemia.

Administration, Oral↗
PubMed1995

Imbalance between intraperitoneal coagulation and fibrinolysis during peritonitis of CAPD patients: the role of mesothelial cells.

We compared peritoneal dialysis effluents from 18 CAPD patients who had not suffered from peritonitis during the last 6 months (group 1) with the effluents from five patients with acute peritonitis (group 2), measuring activation markers of coagulation and fibrinolysis. These markers included prothrombin fragment F1 + 2 (F1 + 2), thrombin-antithrombin III complex (TAT), fibrin monomer (FM), and fibrin degradation products (FbDP). In the dialysate of group 1 we found remarkably high levels of F1 + 2, TAT and FM concomitant with a high concentration of FbDP, indicating a high rate of intraperitoneal fibrin turnover. The balance between peritoneal generation and degradation of fibrin was disturbed in untreated patients of group 2, who had significantly higher levels of coagulation markers and a higher ratio between FM and FbDP. Seven days after treatment with intraperitoneal administration of antibiotics and heparin, F1 + 2, TAT, FM and FbDP decreased significantly. To evaluate the role of mesothelial cells (MC) in the high peritoneal fibrin turnover we investigated the expression of tissue-type plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA), plasminogen activator inhibitor type-1 (PAI-1), and tissue factor in cultured human peritoneal MC under basal conditions and after exposure to tumour necrosis factor alpha (TNF alpha), interleukin-1 alpha (IL-1 alpha), or bacterial lipopolysaccharide (LPS). The exposure of MC to TNF alpha or to a lesser extent IL-1 alpha or LPS reduced their fibrinolytic activity by decreasing t-PA production and increasing PAI-1 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1993

Hypertension secondary to early-stage kidney disease: the pathogenetic role of altered cytosolic calcium (Ca2+) homeostasis of vascular smooth muscle cells.

We have examined cardiovascular pressor responsiveness to infused norepinephrine (NE) as related to endogenous plasma NE and plasma renin and to platelet free cytosolic (Ca2+) in 36 patients with early-stage kidney disease and 27 matched normal subjects. The 27 hypertensive patients and the normal subjects did not differ in blood volume, plasma renin, and NE; however, the hypertensive patients had a higher exchangeable body sodium content. Basal plasma NE levels, the relationship between plasma NE measured during NE infusion and the corresponding NE infusion rate, as well as the total plasma clearance for NE did also not differ significantly between the two study groups. In contrast, the threshold or pressor doses of infused NE significantly decreased in the patients with kidney disease. Antihypertensive pharmacotherapy with (Ca2+) channel blockers and/or loop diuretics normalized blood pressure and cardiovascular NE hyperresponsiveness and reduced blood volume, exchangeable body sodium, and platelet free cytosolic (Ca2+). In contrast, experimental digitalisation as a model for in vivo sodium/potassium adenosine triphosphatase inhibition augmented NE responsiveness and raised platelet free cytosolic (Ca2+). Incubation of platelets from normal subjects with plasma ultrafiltrate from hypertensive patients gave evidence for an endogenous factor capable to raise free cytosolic (Ca2+) and to act synergistically with digoxin. Hypertension secondary to early-stage kidney disease is related to an impairment of sodium excretion leading to an expansion of blood volume and exchangeable body sodium. This may result in increased secretion of endogenous factors, leading to alterations of cytosolic (Ca2+) homeostasis of vascular smooth muscle cells followed by elevated peripheral resistance and thus blood pressure.

Adult↗
PubMed1992

[Acute aortic insufficiency following endocarditis due to infection with Campylobacter fetus subspecies fetus].

A 50-year-old male alcoholic addict, examined because of diarrhoea with fever was found to have Campylobacter jejuni in blood and stool cultures. After administration of broad-spectrum penicillin all acute symptoms disappeared but he lost 8 kg within 3 months and his general state health gradually deteriorated. After 3 months he suddenly developed leg oedema, dyspnoea and bouts of fever up to 38.8 degrees C. A loud cardiac murmur was now heard. Echocardiography demonstrated vegetations on the regurgitant aortic valve. Endocarditis being suspected he was at first treated with penicillin G (15 mega IU/d) and gentamycin (160 mg/d). The fever regressed, but after 8 days the blood culture grew Campylobacter fetus subspecies fetus. Antibiotic treatment was switched to imipenem, twice daily 500 mg, in accordance with sensitivity test results. Further blood cultures were sterile. Despite this the cardiac status deteriorated, the aortic regurgitation reaching grade IV. The valve was replaced with a bioprosthesis and the patient quickly improved postoperatively. Antibiotic treatment was stopped and the cardiovascular status became normal. The patient has now been free of symptoms and recurrence for 7 months.

Acute Disease↗
PubMed1992

Anticardiolipin antibodies and lupus anticoagulant in patients treated with different methods of renal replacement therapy in comparison to patients with systemic lupus erythematosus.

Antiphospholipid antibodies were found to be associated with certain clinical manifestations such as recurrent venous thrombosis or arterial occlusions in a wide spectrum of immune disorders [6]. We analyzed the plasma concentration of two isotypes (IgG, IgM) of anticardiolipin antibodies (ACA) and lupus anticoagulant (LAC) activity in 84 patients with end-stage renal disease. They were receiving different types of renal replacement therapy and had a high frequency of thrombotic vascular complications. The prevalence of positive tests and the mean ACA concentration obtained in the plasma of renal patients were compared with those in patients with systemic lupus erythematosus (SLE) and in healthy controls. When analyzed as a whole group, renal patients maintained on dialysis (n = 45: hemodialysis, n = 20; peritoneal dialysis) or with a functioning kidney transplant (n = 19) did not differ in mean ACA concentration and LAC activity (n = 84, ACA: IgG 10 +/- 7 U/ml, IgM 2 +/- 1 U/ml, LAC ratio: 1.0 +/- 0.2) from healthy subjects (n = 50, ACA: IgG 10 +/- 3, IgM 2 +/- 1 U/ml, LAC ratio: 1.0 +/- 0.1) but they had a higher incidence of raised IgG-ACA titers (renal replacement 14% vs. normal controls 4%, p less than 0.05). No significant correlation was found between thrombotic events and raised ACA or LAC activity in dialysis patients. In contrast, the proportion of SLE patients (n = 51) with a raised concentration of ACA was significantly higher (IgG: 69%, IgM: 29%) than that among patients with renal replacement therapy (IgG: 14%, IgM: 4%) or normal controls (IgG: 4%, IgM: 2%, p less than 0.002). Moreover, recurrent manifestations of thrombosis in SLE were associated with very high IgG-ACA (n = 11, IgG 117 +/- 91 U/ml) and LAC activity (LAC ratio: 2.4 +/- 0.7) in comparison to SLE patients without thrombotic events (n = 40, ACA: IgG 23 +/- 13). The results of our investigations demonstrate that the pathogenetic role of these phospholipid antibodies in end-stage renal disease is far from established.

Adult↗
PubMed1989

Leflunomide (HWA 486) inhibits experimental autoimmune tubulointerstitial nephritis in rats.

Experimental tubulointerstitial nephritis (TIN), induced in Brown Norway rats, is an autoimmune disorder in which afflicted animals display high levels of serum autoantibodies directed against antigens present on the tubular basement membrane (TBM). Serious functional damage, due to lesions of the kidney cortex, is evident 10 days after disease initiation. In an earlier study, we could show that cyclosporin A (CsA), an immunosuppressive drug, effectively prevented the onset of this illness, although it did not inhibit the formation of TBM autoantibodies. In the present study, the protective effects of CsA in autoimmune TIN was compared to those of drugs currently used to combat inflammatory ailments (i.e. prednisolone, indomethacin, naproxen, azathioprine) and a novel immunomodulating agent, leflunomide (HWA 486). Leflunomide is known to specifically inhibit the formation of T-dependent antibodies and is effective in preventing and curing animal autoimmune diseases, i.e. adjuvant arthritis disease of rats and murine lupus-like disorders. We found that not only could leflunomide inhibit TIN, but the drug-effects seemed to be more effective than those of CsA. Further, leflunomide was extremely effective in inhibiting the formation of autoantibodies to TBM, whereas CsA displayed only partial suppression. Neither prednisolone, indomethacin nor naproxen were effective in reducing the autoantibody titer, and did not offer any protection to the development of this disease. Together with the known effects on other autoimmune diseases we conclude that leflunomide is a novel immunointerventive drug protecting against several types of autoimmunity.

Animals↗
PubMed1987

Cyclosporin A inhibits autoimmune experimental tubulointerstitial nephritis.

Tubulointerstitial nephritis, regularly induced in Brown Norway rats by autosensitization with tubular basement membranes, appeared acutely at about 10 days and was completely inhibited by Cyclosporin A (CyA) when this was given before and at the time of onset of the disease. It did not recur after the end of therapy. In spite of this disease inhibition, autoantibodies against tubular basement membranes persisted in the circulation and in the kidney. It is therefore suggested that it is not so much the antibodies that are the decisive factors in the pathogenesis of this and other autoimmune diseases but, rather cellular factors that are directly influenced by CyA. Although in this model CyA application was a preventive measure, the experiments provide a cogent reason for the application of CyA as early as possible in acute and seriously damaging diseases.

Animals↗
PubMedDate not supplied

Bioincompatible membranes place patients with acute renal failure at increased risk of infection.

The mortality of critically ill patients with acute renal failure (ARF) requiring hemodialysis remains high (> 50%), even though major improvements in the management of this disorder have been made. Sepsis has been identified as a major cause of death in ARF. Experimental data have suggested that bioincompatible membranes aggravate uremia induced neutrophil dysfunction. In the following two combined prospective, randomized, clinical studies, the effects of the biocompatibility of dialysis membranes on the susceptibility to infection were compared in 72 surgical and medical patients with ARF. The group of patients treated with biocompatible polyacrylonitrile membranes had a significantly lower incidence of bacterial infections and a lower relative and absolute mortality rate due to sepsis, compared to patients treated with bioincompatible cuprophane membranes. These investigations identified bioincompatibility as a factor that adversely affects the prognosis of critically ill patients with ARF.

Acrylic Resins↗
PubMedDate not supplied

Thrombin upregulates production of plasminogen activator inhibitor type 1 in human peritoneal mesothelial cells.

OBJECTIVE: To determine the influence of thrombin, which is generated intraperitoneally during peritoneal dialysis, on the synthesis of fibrinolytic system components in human peritoneal mesothelial cells (HMC). METHODS: Confluently grown HMC, isolated from the omental tissue, were used in the experiments. Conditioned media were obtained by incubating cells with serum-free M199 containing the appropriate concentration of the test compound. Tissue type plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1) antigen concentrations were measured by ELISA. Northern blot analysis was conducted for mRNA expression experiments. To test thrombin specificity, we used the thrombin inhibitor hirudin. The protein kinase C (PKC) inhibitor Ro 31-8220 was inserted to examine whether the effect of thrombin depends on PKC activity. RESULTS: Thrombin increased PAI-1 antigen in the conditioned media of HMC in a time- and concentration-dependent manner. After 24 hours incubation, PAI-1 levels increased from 350+/-30 ng/10(5) cells in control conditions to 620+/-30 ng/10(5) cells in HMC exposed to 5 U/mL thrombin (n = 8, p < 0.05). In contrast, there was no effect of thrombin on tPA antigen levels. An increase of PAI-1 mRNA expression was also observed by Northern blot hybridization. Hirudin (10 U/mL) inhibited the thrombin-induced increase in PAI-1 synthesis. In addition, a complete inhibition of the stimulating effect of thrombin on PAI-1 synthesis was obtained by blocking PKC activity with Ro 31-8220 (3 micromol/L). CONCLUSIONS: Thrombin increases PAI-1 synthesis in HMC via a PKC-dependent mechanism. Thereby the synthesis of tPA is not affected. Thus, thrombin may not only promote fibrin formation in the peritoneal cavity, but may also inhibit fibrin degradation by release of free PAI-1 from HMC.

Antithrombins↗
PubMedDate not supplied

Thrombin suppresses matrix metalloproteinase 2 activity and increases tissue inhibitor of metalloproteinase 1 synthesis in cultured human peritoneal mesothelial cells.

OBJECTIVE: Recently, high levels of intraperitoneally generated thrombin were found in the effluent of patients treated with continuous ambulatory peritoneal dialysis (CAPD). The aim of the present study was to investigate in human peritoneal mesothelial cells (HMCs) the effect of thrombin on the activity and synthesis of matrix metalloproteinases (MMPs), which regulate the degradation of basement membrane collagen. METHODS: Cultured HMCs were isolated from omental tissue and used at confluence for the experiments. Conditioned media were obtained by incubating cells with serum-free M199 containing the relevant doses of thrombin. Activity of MMP-2 and MMP-9 were determined by an activity assay system. The antigen levels of MMPs and of the specific tissue inhibitor of metalloproteinases 1 (TIMP-1) were measured by ELISA. Northern blot analysis was applied to analyze mRNA expression of MMP-2 and TIMP-1. RESULTS: Incubation of HMCs with increasing doses of thrombin resulted in a concentration- and time-dependent suppression of MMP-2 activity. No changes in MMP-9 activity were seen. After a 48-hour stimulation period with thrombin (5 U/mL), MMP-2 activity decreased to 53% of that seen in control conditions. Antigen measurements revealed that this decrease was paralleled by a slight reduction in MMP-2 levels, which became significant at a thrombin dose of 5 U/mL [50.65 +/- 7.5 ng/10(5) cells (48 hours, 5 U/mL) vs 64.6 +/- 10.1 ng/10(5) cells (control)]. Under the same conditions, TIMP-1 levels were considerably increased [3.9 +/- 0.46 microg/10(5) cells (48 hours, 5 U/mL) vs 1.2 +/- 0.14 microg/10(5) cells (control)]. Hirudin (10 U/mL) completely inhibited the thrombin-induced effects on MMP-2 and TIMP-1 synthesis. These results were also reflected by Northern blot hybridization, where a slight decrease in MMP-2 and an increase in TIMP-1 mRNA expression were observed in response to thrombin. CONCLUSIONS: Our results suggest that high thrombin levels suppress MMP-2 activity through decreased MMP-2 and increased TIMP-1 synthesis. Thus, thrombin may promote the accumulation of basement membrane collagen. In addition to fibrin formation, this mechanism may represent a further contribution by thrombin to peritoneal thickening during CAPD.

Cells, Cultured↗
PubMedDate not supplied

Reversible MRI changes in a patient with uremic encephalopathy.

A 19-year-old patient on chronic ambulatory peritoneal dialysis experienced severe neurologic disturbances caused by uremia. Increased signal intensity was seen bilaterally in the cortical and subcortical areas of the occipital and parietal lobe on cranial magnetic resonance imaging (MRI). Insufficient peritoneal dialysis efficacy was documented and the patient was switched from peritoneal to hemodialysis. Cranial MRI indicated a marked regression of the lesions to nearly normal, confirming the diagnosis of uremic encephalopathy.

Adult↗
PubMedDate not supplied

Early glycated albumin, but not advanced glycated albumin, methylglyoxal, or 3-deoxyglucosone increases the expression of PAI-1 in human peritoneal mesothelial cells.

OBJECTIVE: The continuous contact of glucose-containing peritoneal dialysis (PD) fluids with the peritoneum results in the intraperitoneal formation of early and advanced glycation end-products. This nonenzymatic glycation of proteins may cause morphological and functional alterations to the peritoneum, which may contribute to patient dropout from PD therapy. Because fibrinolytic system components have been demonstrated to play an important role in the balance of intraperitoneal generation and degradation of fibrin, we studied the effect of early and advanced glycated human serum albumin, methylglyoxal, and 3-deoxyglucosone on the synthesis of tissue-type plasminogen activator (tPA), as well as its specific inhibitor (PAI-1), in human peritoneal mesothelial cells (HPMC). METHODS: Antigen concentrations in the supernatants of cultured HPMC were measured by ELISA. Northern blot analysis was conducted for mRNA expression. Electrophoretic mobility shift assays were applied to demonstrate the involvement of the transcription factors nuclear factor kappa B (NF-kappaB) and activator protein-1 (AP-1) in signal transduction. RESULTS: Incubation of HPMC with early glycated albumin (GHSA) resulted in a time- and concentration-dependent increase in PAI-1 mRNA expression and antigen secretion. In contrast, no changes in PAI-1 synthesis occurred after stimulation with either the 1,2-dicarbonyl compounds methylglyoxal and 3-deoxyglucosone, or with late advanced glycation end-products. tPA synthesis was not affected by any of the tested components. Furthermore, HPMC exposed to GHSA induced NF-kappaB and AP-1 DNA binding activity, suggesting that GHSA-induced overexpression of PAI-1 is transcriptionally regulated by both transcription factors. CONCLUSIONS: We conclude that Amadori modified glycated albumin upregulates PAI-1 synthesis in HPMC, possibly mediated through the activation of the transcription factors NF-kappaB and AP-1. The present data support the clinical relevance of the formation of glycated proteins and their involvement in pathological processes in PD patients. Thus, glycated albumin may contribute to an imbalance between intraperitoneal formation and degradation of fibrin that causes peritoneal structural alterations, with subsequent membrane failure.

Albumins↗
PubMedDate not supplied

Coagulation- and fibrinolysis-related antigens in plasma and dialysate of CAPD patients.

OBJECTIVE: The present study is aimed at gaining insight into coagulation and fibrinolysis in the peritoneal cavity of patients on continuous ambulatory peritoneal dialysis (CAPD). For this purpose we measured coagulation- and fibrinolysis-related antigens in plasma and dialysate, comparing patients with and without peritonitis. DESIGN: Markers of activated coagulation and fibrinolysis in plasma and dialysate of CAPD patients were determined at different time points (0 hr, 2 hr, 4 hr) after infusion of the dialysis solution in the peritoneal cavity. Prothrombin fragment (F1 + 2), thrombin-antithrombin III complex (TAT), and fibrin monomer (FM) were chosen as parameters of activated coagulation. Fibrin degradation products (FbDP), D-dimer (DD), tissue-type plasminogen activator (t-PA), and plasminogen activator inhibitor type 1 (PAI-1) were measured as parameters for ongoing fibrinolysis. Beta 2-microglobulin, albumin, and IgG were used as marker proteins for the diffusion of proteins of intravascular origin into the peritoneal cavity. PATIENTS: Eleven clinically stable CAPD patients, who had not suffered from peritonitis during the last six months, and 5 CAPD patients with an acute episode of bacterial peritonitis were studied. RESULTS: In the dialysate of stable CAPD patients (n = 11) the concentration of activation markers of coagulation and fibrinolysis increased continuously with dwell time. After four hours we found remarkably high levels of the coagulation markers F1 + 2 (0.4 +/- 0.1 nmol/L), TAT (6.5 +/- 1.0 ng/mL), and FM (24.5 +/- 7.1 micrograms/mL), and the fibrinolysis markers DD (851 +/- 26 ng/mL), FbDP (1.0 +/- 0.3 microgram/mL), t-PA (3.3 +/- 0.8 ng/mL), and PAI-1 (2.6 +/- 1.2 ng/mL). The dialysate-to-plasma (D/P) ratios of all of these antigens were significantly higher compared to the D/P ratios of proteins with similar molecular weight, which are not produced intraperitoneally (beta 2-microglobulin, albumin, and IgG). These findings point to a local, thrombin-induced intraperitoneal fibrin generation during regular CAPD. Compared with clinically stable CAPD patients, the patients with bacterial peritonitis (n = 5) had significantly higher levels of F1 + 2 (5.3 +/- 1.6 nmol/L), TAT (57.8 +/- 10.7 ng/mL), FM (972 +/- 3.2 micrograms/L), FbDP (16.4 +/- 2.9 micrograms/L), and PAI-1 (7.3 +/- 2.4 ng/mL) in the dialysate (4-hr dwell time), and a 2.4-times higher ratio between FM and FbDP. These results can be interpreted as an intraperitoneal imbalance between coagulation and fibrinolysis during peritonitis. CONCLUSION: Our study demonstrates a high intraperitoneal fibrin formation, not only during peritonitis but also in clinically stable CAPD patients. The remarkably high levels of coagulation (F1 + 2, TAT, FM) and fibrinolysis (FbDP, DD, t-PA, PAI-1) related antigens in the dialysate of patients without peritonitis cannot be explained by transport from plasma into the peritoneal cavity and may reflect a high rate of intraperitoneal fibrin turnover. The balance between peritoneal generation and degradation of fibrin is obviously disturbed in CAPD patients with peritonitis, who had significantly higher levels of coagulation markers in the dialysate and a higher ratio between FM and FbDP.

Acute Disease↗