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Biomedical subjects

C Tetta

Publications and source records attributed to C Tetta.

At least 55 records · Page 3Linked to original sources
PubMed1992

Urinary protein excretion induced by exercise: effect of a mountain agonistic footrace in healthy subjects. Renal function and mountain footrace.

The increase in albuminuria induced by exercise in healthy subjects is variably dependent on an increased glomerular filtration and/or to a decreased tubular reabsorption of albumin, in relation to the intensity of muscular work. Membrane anionic charges and haemodynamic changes have been implicated in exercise-induced albuminuria. We evaluated in 12 healthy subjects albumin and beta-2-microglobulin excretion rate and the presence in urine of cationic compounds before and after an agonistic mountain footrace. Albumin excretion rate increased significantly (3.7 +/- 1.3 vs 43.7 +/- 10.0 micrograms/min) (p less than 0.001) and beta-2-microglobulin excretion rate (16.5 +/- 4.4 vs 37.9 +/- 7.4 micrograms/min) (p less than 0.025), too. In 3/4 subjects, urines revealed a peak of highly cationic proteins, sharing antigenic and biological characteristics with platelet-derived cationic proteins. The increase in albuminuria induced by strenuous exercise of an agonistic mountain footrace is of mixed type (both glomerular and tubular) and is associated to the urinary excretion of cationic proteins.

Adult↗
PubMed1992

Platelet-activating factor biosynthesis by cultured mesangial cells is modulated by proteinase inhibitors.

Rat mesangial cells stimulated with calcium ionophore A23187 and phagocytosis were shown to produce platelet-activating factor (PAF), a mediator of inflammation and endotoxic shock. In the study presented here, the cultured human mesangial but not epithelial cells synthetized PAF not only in response to calcium ionophore A23187 and phagocytosis of immunoglobulin G-coated latex beads, but also after stimulation with cytokines such as tumor necrosis factor-alpha and interleukin-1 beta. PAF synthetized after stimulation with A23187 and to a lesser extent with phagocytosis was partially released. In contrast, PAF synthesized by stimulation with tumor necrosis factor-alpha and interleukin-1 beta remained cell associated. Experiments with labeled precursors demonstrated that PAF was synthetized via the remodeling pathway that involves the activation of phospholipase A2 and of an acetyl-coenzymeA:2-lyso-PAF acetyltransferase. Synthetic inhibitors of serine proteases as well as plasma alpha 1-proteinase inhibitor inhibited the activation of phospholipase A2 detected as release of (14C) arachidonic acid and the activation of acetyl-CoA:2-lyso-PAF acetyltransferase at concentrations 100-fold lower than those present in plasma. This raises the question about the ability of mesangial cells to synthetize PAF in vivo. However, the inhibitory effect of plasma alpha 1-proteinase inhibitor may be abrogated by oxidative inactivation due to a concomitant stimulation of mesangial cell respiratory burst or in zones of close contact among cells or matrix, which have been shown to exclude antiproteinases.

Acetyltransferases↗
PubMed1991

The molecular action of tumor necrosis factor-alpha.

Tumor necrosis factor-alpha (TNF-alpha) is a polypeptide hormone newly synthesized by different cell types upon stimulation with endotoxin, inflammatory mediators (C5a anaphylatoxin), or cytokines such as interleukin-1 and, in an autocrine manner, TNF itself. The net biological effect of TNF-alpha may vary depending on relative concentration, duration of cell exposure and presence of other mediators which may act in synergism with this cytokine. TNF-alpha may be relevant either in pathological events occurring in cachexia and endotoxic shock and inflammation or in beneficial processes such as host defense, immunity and tissue homeostasis. The biological effects of TNF-alpha are triggered by the binding to specific cell surface receptors. The formation of TNF-alpha-receptor complex activates a variety of biochemical pathways that include the transduction of the signal at least in part controlled by guanine-nucleotide-binding regulatory proteins (G proteins), its amplification through activation of adenyl cyclase, phospholipases and protein kinases with the generation of second messenger pathways. The transduction of selected genes in different cell types determines the characteristics of the cell response to TNF-alpha. The full understanding of the molecular mechanisms of TNF-alpha will provide the basis for a pharmacological approach intended to inhibit or potentiate selected biological actions of this cytokine.

Free Radicals↗
PubMed1991

Inhibition of the synthesis of platelet-activating factor by anti-inflammatory peptides (antiflammins) without methionine.

Antiflammins are synthetic peptides corresponding to a region of similarity between uteroglobin and lipocortin I. These peptides inhibit synthesis of platelet-activating factor and release of arachidonic acid from neutrophils and macrophages stimulated by phagocytosis or tumor necrosis factor. Antiflammins containing methionine are inactivated readily in the absence of reducing agents. Novel antiflammins containing alanine or norleucine in place of methionine are inhibitory without added reducing agents, but only when stock solutions are heated to 45 degrees C. Heating may favor hydrophobic interactions between peptide molecules, thereby activating the antiflammins. These peptides are less inhibitory when added after cell stimulation, suggesting that they interfere with the activation of phospholipase A2.

Alanine↗
PubMed1990

An anti-inflammatory protein secreted from the rat seminal vesicle epithelium inhibits the synthesis of platelet-activating factor and the release of arachidonic acid and prostacyclin.

Platelet-activating factor (PAF), a 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, is a mediator of inflammation and endotoxic shock produced by a variety of stimulated cells. Since the main biosynthetic pathway of PAF involves acetylation of 1-O-alkyl-sn-glycero-3-phosphocholine (lyso-PAF) generated from 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine by phospholipase A2, we suggest a general physiological role played by steroid-induced anti-(phospholipase A2) proteins in the modulation of PAF synthesis. The results of the present study support this hypothesis since an androgen-induced anti-inflammatory protein, SV-IV, secreted from rat seminal vesicles, inhibits PAF synthesis in stimulated polymorphonuclear neutrophils, macrophages and endothelial cells. SV-IV impairs PAF synthesis by inhibiting the activation of phospholipase A2, that also results in the inhibition of arachidonic acid and prostacyclin release, and of acetyl-CoA:lyso-PAF acetyltransferase.

Acetyltransferases↗
PubMed1990

Antiinflammatory peptides (antiflammins) inhibit synthesis of platelet-activating factor, neutrophil aggregation and chemotaxis, and intradermal inflammatory reactions.

Synthetic peptides corresponding to the region of highest similarity between human lipocortin I and rabbit uteroglobin inhibit phospholipase A2 and show potent antiinflammatory activity on the carrageenan-induced rat footpad edema. The peptide HDMNKVLDL (antiflammin-2) inhibits the synthesis of platelet-activating factor (PAF) induced by TNF or phagocytosis in rat macrophages and human neutrophils, and by thrombin in vascular endothelial cells. The peptide MQMKKVLDS (antiflammin-1) is less inhibitory than antiflammin-2 for macrophages and not inhibitory for neutrophils after a 5-min preincubation. This finding suggests that antiflammin-1 is inactivated by neutrophils secretory products, possibly oxidizing agents. Synthesis of PAF is inhibited by antiflammin-2 without an appreciable lag, but this inhibition is reversed when neutrophils or macrophages are washed and incubated in fresh medium. Therefore, antiflammins must be continuously present to inhibit PAF synthesis. Antiflammins block activation of the acetyltransferase required for PAF synthesis, suggesting that this enzyme is another target for the inhibitory activity of antiflammins. These peptides inhibit neutrophil aggregation and chemotaxis induced by complement component C5a. Antiflammin-2 suppresses the increase in vascular permeability and the leukocyte infiltration induced in rats by an Arthus reaction or by intradermal injection of rTNF and C5a.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1990

Tumor necrosis factor induces contraction of mesangial cells and alters their cytoskeletons.

Cultures of human mesangial cells (MC) were established from the renal cortex of surgical specimen. The characteristic spindle-shaped or stellate appearance of MC was altered after treatment with tumor necrosis factor (TNF). After two hours, the MC retracted and lost reciprocal contacts. Furthermore, this treatment altered the cytoskeletal organization of MC, since a peripheral band of actin and stress fibers disappeared while the streaks of vinculin at focal contacts decreased. These changes were reversible when the MC were cultured in fresh medium. After five minutes of treatment with platelet activating factor (PAF), changes similar to those induced by TNF were observed. Inhibitors of PAF synthesis, such as plasma alpha 1-proteinase inhibitor and an anti-inflammatory peptide, blocked changes induced by TNF, PAF receptor antagonists inhibited changes induced by PAF and also by TNF. These results and the finding that MC are stimulated to produce PAF by TNF suggest that PAF is a secondary mediator of the changes in cell shape and cytoskeletal organization induced by this cytokine.

Cells, Cultured↗
PubMed1990

Effect of leukocyte stimulation on rabbit immune complex glomerulonephritis.

Phytohemagglutinin (PHA), a leukocyte mitogen, induces a lymphocyte and blast cell glomerulonephritis in rat renal allografts (Cell Immunol 13:146, 1974). The aim of this study was to assess whether PHA similarly enhances rabbit monocyte-dependent experimental, acute immune complex glomerulonephritis, and whether this effect is associated with local release of interleukin-1 (IL-1) and tumor necrosis factor (TNF). Rabbits with experimental acute serum sickness (AcSS: Group I) had focal proliferative and exudative glomerulonephritis with immune deposits, scattered subepithelial electron-dense deposits (humps), mild and transient proteinuria, normal creatinine clearance and slightly increased production of IL-1 and TNF from isolated glomeruli. Rabbits with AcSS and injected with PHA (Group II) developed severe lymphocyte and blast cell glomerulonephritis with diffuse endothelial damage; immune deposits were significantly reduced, focal subepithelial electron-dense deposits were absent, proteinuria was increased, creatinine clearance was decreased and production of IL-1 and TNF was markedly augmented as compared to rabbits in Group I. Rabbits with AcSS and injected with IL-1 beta and TNF alpha (Group V) had lesions comparable to those seen in Group II. These results show that PHA, IL-1 and TNF enhance the severity of acute immune complex glomerulonephritis, presumably by activating glomerular endothelial and mesangial cells and resident or infiltrated leukocytes.

Animals↗
PubMed1990

Tumour necrosis factor in serum and synovial fluid of patients with active and severe rheumatoid arthritis.

Fifteen serum samples and 29 synovial fluids of patients with rheumatoid arthritis (RA) were examined for the presence of tumour necrosis factor (TNF). The assay for TNF was based on the cytotoxic activity of this cytokine for human melanoma cells in tissue culture. High concentrations of TNF were found in serum samples of patients with severe RA, who had increased erythrocyte sedimentation rate and serum alpha 2 macroglobulin, but decreased haemoglobin and serum iron concentrations. Tumour necrosis factor was also found in the synovial fluid of 16 out of 29 patients. High TNF concentrations were found in fluids with greater than 10(10) leucocytes/l. Tumour necrosis factor was not detected in the serum of normal subjects or in synovial fluid of patients with osteoarthritis. A mediator of inflammation, such as TNF, may contribute to the severity of RA.

Arthritis, Rheumatoid↗
PubMed1990

Production of cytokines in hemodialysis.

Tumor necrosis factor (TNF-alpha) and interleukin-1 (IL-1 beta) are cytokines primarily produced by monocytes/macrophages when stimulated by endotoxin, complement-derived anaphylatoxins and the specific antigen. In the present study, the plasma levels of TNF-alpha and IL-1 beta were evaluated before and after hemodialysis with cuprophane membrane (in 9 patients) and hemodiafiltration (in 9 patients) using three high-permeability membranes such as polymethylmethacrylate, polyacrylonitrile (AN-69) and polysulfone. In vitro spontaneous production of TNF-alpha and IL-1 beta was evaluated in the supernatants from short-term cultured monocytes obtained before and after treatment. The predialytic levels of TNF-alpha and IL-1 beta were significantly higher (p less than 0.05) in the uremic population than in 21 healthy subjects taken as controls. The analysis of the uremic population regarding the mode of therapy indicated that in hemodialysis the predialytic plasma levels of TNF-alpha and IL-1 beta did not significantly differ from those of healthy subjects. In contrast, in hemodiafiltration with polymethylmethacrylate and AN-69, but not with polysulfone, the predialytic plasma levels of both cytokines were significantly (p less than 0.05) increased. No significant variation in plasma levels of both cytokines was observed after hemodialysis with cuprophane membranes. Hemodiafiltration with polymethylmethacrylate and AN-69, but not with polysulfone, brought about a consistent reduction in plasma levels of both cytokines. Detectable amounts of TNF-alpha and IL-1 beta were spontaneously produced by peripheral-blood monocytes 6 h after the end of hemodialysis but not of hemodiafiltration. These studies suggest a possible role of TNF-alpha and IL-1 beta in the biocompatibility of different extracorporeal treatments.

Acrylic Resins↗
PubMed1990

Release of platelet-activating factor in systemic lupus erythematosus.

The biologically active 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (platelet-activating factor; PAF) is inactivated in plasma mainly by a specific PAF acetylhydrolase (1-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine acetylhydrolase; EC 3.1.1.48). In the present study, PAF was released in detectable amounts (5.4 +/- 2.9 ng/ml; mean +/- 1 SD) in the plasma of 8 out of 10 patients with systemic lupus erythematosus (SLE) during the most active phases of the disease. PAF was never detectable in the plasma of patients with inactive SLE or of healthy subjects. PAF acetylhydrolase activity was markedly reduced in sera of 10 patients with active SLE as compared to 7 patients with inactive SLE, 16 patients with rheumatoid arthritis (RA), 5 patients with nephrotic syndrome (NS) and 15 healthy subjects. A kinetic study of the enzyme in patients with active SLE suggested an overall reduced activity rather than an intrinsic defect of the enzyme. PAF acetylhydrolase in sera of patients with active SLE shared with that of healthy subjects the same substrate specificity, sensitivity to enzymatic and chemicophysical treatments and association to low-density lipoprotein (LDL), acting as carrier of PAF acetylhydrolase in plasma. However, the protein concentration of LDL was significantly reduced in patients with active SLE as compared to patients with inactive SLE, RA and NS and to healthy subjects, thereby suggesting that the reduction of PAF acetylhydrolase activity in active SLE might be due at least in part to a carrier defect related to the activity of the disease. In addition, experiments in which serum of patients with active SLE and serum of healthy subjects were mixed in different combinations indicated the absence of factors inhibiting PAF acetylhydrolase activity in SLE patients.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1990

Regulation of platelet-activating factor synthesis by acetyl-coenzyme A.

Human neutrophils (PMN) stimulated by tumor necrosis factor (TNF) synthesize and release platelet-activating factor (PAF) transiently. In the present investigation, we have examined the mechanism responsible for the down-regulation of PAF synthesis. The response of PMN is proportional to the occupancy of high-affinity TNF receptors on the PMN plasma membrane, as shown by binding assays with [125I]TNF. These receptors are down-regulated within 10 min of the addition of TNF; the receptors reappear after 60 min, but the PMN do not resume PAF synthesis. Further PAF synthesis is obtained by adding acetyl-coenzyme A (CoA) to the culture medium. However, this compound does not diffuse into PMN, as shown by incubating these cells with labeled acetyl-CoA. This finding suggests that PAF synthesis is regulated by the amount of acetyl-CoA available to the lyso-PAF: acetyltransferase on the cell plasma membrane. This acetyl-CoA is accessible to chemicals in the culture medium, since it is hydrolysed by hydroxylamine. The inhibition of PAF synthesis by hydroxylamine is reversed by adding acetyl-CoA. PAF synthesis in TNF-treated cells appears to be regulated either by the amount of acetyl-CoA available or by the ability to transfer acetyl-CoA from the cellular pool to the lyso-PAF: acetyltransferase.

Acetyl Coenzyme A↗
PubMed1990

Selected cytokines promote the synthesis of platelet-activating factor in vascular endothelial cells: comparison between tumor necrosis factor alpha and beta and interleukin-1.

Tumor necrosis factor (TNF alpha and TNF beta) and interleukin-1 (IL-1) are mediators of immunity and inflammation that induce different, but partially overlapping responses in human endothelial cells (HEC). We compared the effect of purified recombinant human TNF alpha, TNF beta and IL-1 on the production of platelet-activating factor (PAF) in HEC. After 30-60 min of treatment with TNF alpha or TNF beta, HEC produce and partially release considerable amounts of PAF, which reach a maximum after 4-6 h. In HEC treated with IL-1 PAF production is detectable after 2 h and peaks at 8-12 h. More than twice as much PAF is produced in response to optimal concentrations of TNF alpha than in response to TNF beta or IL-1. However, PAF synthesis is stimulated by lower molar concentrations of IL-1 than TNF alpha and TNF beta. The ability to induce PAF synthesis in HEC seems to be restricted to these three cytokines, as shown by negative results obtained with other cytokines that activate HEC (interferons, granulocyte- and granulocyte-macrophage colony-stimulating factor, epithelial growth factor, fibroblast growth factor, transforming growth factor beta), or participate in the inflammatory process (IL-6, platelet-derived growth factor).

Cells, Cultured↗
PubMed1990

Involvement of cytokines and platelet-activating factor in renal pathology.

Platelet-activating factor (PAF) is a phospholipid that exhibits a wide range of biological activities as a secondary mediator of inflammation and anaphylaxis. Primary mediators of inflammation, such as interleukin-1 and tumor necrosis factor, stimulate PAF release by monocytes/macrophages, neutrophils and endothelial cells. PAF has also been implicated in cell-mediated hypersensitivity reactions. This review will focus on recent data suggesting that the local production of these mediators in glomeruli by infiltrating inflammatory cells or resident cells may influence the clinicopathological expression of glomerular disease. Results from in vitro and experimental studies suggest that these mediators alter the growth pattern of glomerular cells and the composition of secreted matrix, leading to scar formation and eventually to glomerulosclerosis.

Acute Kidney Injury↗