Low levels of nitric oxide (NO) in systemic sclerosis: inducible NO synthase production is decreased in cultured peripheral blood monocyte/macrophage cells.

OBJECTIVE: To investigate nitric oxide (NO) production and inducible NO synthase expression by cultured peripheral blood mononuclear cells (PBMC) in patients with systemic sclerosis (SSc). METHODS: Eighteen patients with SSc were compared with two control groups: 16 patients with rheumatoid arthritis (RA) and 23 patients with mechanical sciatica. Nitrate was determined by fluorimetry in plasma and by spectrophotometry in supernatants. Inducible NO synthase (iNOS) was detected in cultured PBMC by immunofluorescence, immunoblotting and flow cytometry with or without treatment of the cells with interleukin (IL) 1beta+ tumour necrosis factor alpha (TNF-alpha), IL-4 or interferon gamma (IFN-gamma) from day 1 to day 5. RESULTS: NO metabolite concentrations were lower in SSc patients (mean+/-s.e.m. 34.3+/-2.63 micromol/l) than in RA (48.3+/-2.82 micromol/l; P<0.02) and sciatica (43.3+/-5.24 micromol/l; P<0.03) patients. iNOS was detected in cultured monocytes in all three groups but induction occurred on day 1 in RA, day 2 in sciatica and only on day 3 in SSc, whatever the stimulus. CONCLUSIONS: The concentrations of NO metabolites are decreased in SSc patients and the metabolism of these compounds in PBMC is altered. Low levels of NO, a vasodilator, may be involved in vasospasm, which is critical in SSc. This may have therapeutic implications.

Tetracyclines inhibit nitrosothiol production by cytokine-stimulated osteoarthritic synovial cells.

OBJECTIVE AND DESIGN: To evaluate the capacity of doxycycline and minocycline to inhibit NO production and N-nitrosation reactions in vitro. METHODS: Synovial cells obtained from 6 patients with osteoarthritic joint disease were incubated for 24 hours with (i) or without (ii) IL-1beta (1 ng/ml), TNF-alpha (500 pg/ml), IFN-gamma (10(4) U/ml) plus minocycline or doxycycline (10(-4) to 10(-6) M), diclofenac (10(-5) M), or cortisol (10(-5) M). Nitrosothiols were determined by fluorimetry, nitrite by the Griess reaction, nitrate by a spectrophotometric assay using oxidation by nitrate reductase and iNOS by immunoblotting. RESULTS: After 24 hours of stimulation, the level of NO production was much higher than that in untreated cells: about 5.5 times higher for nitrosothiols, 5.2 times higher for nitrate and about 3.5 times higher for nitrite. Doxycycline and minocycline induced a dose-dependent decrease in the production of nitrosothiols, nitrate and nitrite, and inhibited the synthesis of the iNOS protein. Doxycycline and minocycline inhibited the N-nitrosation reaction of DAN effectively, with IC50 values close to 100 microM. Diclofenac and cortisol had no effect. CONCLUSION: This study provides new information on the mechanism by which tetracyclines exert anti-inflammatory effects, via inhibiting nitrosothiols.

[Inducible nitric oxide synthase expression and nitric oxide production by monocytes in systemic sclerosis]. / Expression de la NO synthase inductible et production du monoxyde d'azote par les cellules mononucléées sanguines dans la sclérodermie systémique.

We investigated nitric oxide (NO) production and inducible NO synthase (iNOS) expression by cultured peripheral blood mononuclear cells (PBMC) in systemic sclerosis (SSc). Eighteen patients with SSc were compared to two control groups: 16 rheumatoid arthritis patients (RA) and 23 mechanical sciatica patients. The sum of nitrites and nitrates was determined by fluorimetry in sera and spectrophotometry in supernatants. Inducible iNOS was detected in cultured PBMC by immunofluorescence, immunoblot and flow cytometry with or without IL-1 beta + TNF alpha, IL-4 or IFN gamma from day 1 to day 5. NO metabolite concentrations in the plasma were lower in SSc (34.3 mumol/l +/- 2.63 SEM) than in RA (48.3 mumol/l +/- 2.2; p < 0.02) and sciatica (43.3 mumol/l +/- 5.24; p < 0.03) patients. iNOS was detected in cultured monocytes in the 3 groups but induction occurred on day 1 in RA, day 2 in sciatica and only on day 3 in SSc, whatever the stimulus. The concentrations of NO metabolites are decreased in SSc patients and the induction of iNOS in PBMC is delayed. Low levels of NO, a vasodilator, may be involved in vasospasm, which is critical in SSc. This may suggest therapeutic implications.

Inhibition of the nitrosothiol production of cultured osteoarthritic chondrocytes by rhein, cortisol and diclofenac.

OBJECTIVE: Nitric oxide (NO degrees ) is a free molecule produced by NO synthases which acts as a mediator in inflammatory processes. NO degrees can react with thiol groups of proteins to produce nitrosothiols. Increased concentrations of these bioactive compounds have been found in sera and synovial fluids from patients with osteoarthritis (OA). The aim of this study was to assess the ability of human osteoarthritic chondrocytes to synthesize nitrosothiols and to compare the in vitro effects of rhein, cortisol and diclofenac on nitrosothiol and nitrite production. METHODS: Osteoarthritic chondrocytes were incubated for 24 h with 1 ng/ml of recombinant human interleukin-1beta (IL-1beta) in the presence or absence of rhein (1.3x10(-5) M, 6.5x10(-6) M, or 1.3x10(-6) M), cortisol (10(-5) M) or diclofenac (10(-5) M or 10(-6) M). Nitrite levels were measured in cell supernatants by the Griess method; nitrosothiol levels were determined in supernatants and cellular lysates by fluorimetry. RESULTS: At the basal level, nitrosothiols represented 80% of the total of nitrite and nitrosothiol production. After IL-1beta stimulation, NO degrees production was highly increased in the supernatants (45-fold increase in nitrite, 60-fold increase in nitrosothiols) as well as in cell lysates (35-fold increase in nitrosothiols). Rhein caused a dose-dependent decrease in nitrosothiol and nitrite production. In comparison, diclofenac (10(-5) M) moderately decreased nitrite and nitrosothiol levels in the supernatants but had no effect on lysate nitrosothiol. Cortisol had no significant effect on NO degrees production. CONCLUSIONS: The IL-1beta stimulation increased nitrosothiol production by osteoarthritic chondrocytes. These results demonstrate the need to measure nitrosothiol as well as nitrite production. Rhein inhibited the IL-1beta induced NO degrees production, and may be a suitable treatment for osteoarthritis.

Nitric oxide modifies glycolytic pathways in cultured human synoviocytes.

Nitric oxide (NO) is a free radical produced during inflammation following activation of an inducible NO synthase by pro-inflammatory cytokines such as IL-1beta. Since both NO and IL-1beta are involved in the physiopathology of inflammatory arthropathies, we investigated the effects of exogenous NO on glycolytic pathways in cultured human osteoarthritic synovial cells. NO generated from S-nitroso-N-acetyl penicillamine (SNAP) or sodium nitroprusside (SNP) inhibited glucose uptake (by 50% after 1 h of incubation) and lactate production by 16% (SNAP) and 8.5% (SNP) after 3 h. Both NO donors also reduced production of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), an enzyme of the glycolytic pathway. This effect was reversed by haemoglobin, a NO scavenger with higher affinity for the radical. In contrast, the effect on glucose uptake appeared to be irreversible.

System A neutral amino acid transporter regulation by interleukin-1beta in human osteoarthritic synovial cells: evidence for involvement of prostaglandin E(2) as a second messenger.

We studied the long-terms effects of interleukin-1beta (IL-1beta; 3 to 6 h) on alpha-(methylamino) isobutyric acid (MeAIB), a nonmetabolizable amino acid transported by system A. We found that IL-1beta induced a large decrease in MeAIB uptake by human osteoarthritic synovial cells and a concomitant increase in prostaglandin E(2) (PGE(2)) synthesis. Therefore, we investigated whether PGE(2) acts as a mediator for the long-term action of IL-1beta. We found that exogenous PGE(2) inhibited MeAIB uptake, and that AH6809, a PGE(2) receptor antagonist, inhibited IL-1beta-mediated MeAIB uptake. To identify the enzymes involved in the IL-1beta-mediated synthesis of PGE(2) that inhibits MeAIB uptake, we studied the expression of secreted (s) and cytosolic (c) phospholipase A(2) (PLA(2)). Because both were expressed, we selected a broad spectrum of inhibitors to determine which of the two PLA(2)s was involved. We used AACOCF3, a cPLA(2) inhibitor, and dithiothreitol (DTT) and bromophenacyl bromide (BPB), which are sPLA(2) inhibitors. Our results suggest that the PLA(2) involved in the IL-1beta-mediated synthesis of PGE(2) was sPLA(2). We also showed the expression of cyclooxygenase (COX)-2 and its partial involvement using a potent selective COX-2 inhibitor, L-745337. These findings provide insight into the mechanisms underlying the IL-1beta-mediated regulation of transport system A. The Il-1beta-induced inhibition of MeAIB uptake in human osteoarthritic synovial cells thus seems to be essentially mediated by PGE(2) production via the activation of sPLA(2) and the partial activation of COX-2.

Nitric oxide synthase is expressed in the lymphomononuclear cells of synovial fluid in patients with rheumatoid arthritis.

OBJECTIVE: To investigate the expression of inducible nitric oxide synthase (iNOS) in subpopulations of peripheral blood and synovial fluid (SF) leukocytes in patients with rheumatoid arthritis (RA). METHODS: iNOS was detected in peripheral blood and SF samples after cell permeabilization, by 2 color immunofluorescence flow cytometry. Samples from 14 patients with RA and 8 with osteoarthritis (OA) were studied. Nitrite concentration was determined by Griess reaction, interleukin 1beta and tumor necrosis factor alpha by an immunoenzymatic assay, and C-reactive protein (CRP) by an immunonephelometric method. RESULTS: In SF, iNOS was detected in 11 of 14 patients with RA and 2 of 8 with OA. In blood cells, iNOS was detected in 8 of 14 patients with RA and none of the OA group. iNOS was consistently detected in monocytes and was not detected in granular cells. In RA, there was no correlation between the number of iNOS positive mononuclear cells and cytokine concentrations. CRP concentration was correlated with the number of iNOS positive mononuclear cells in RA SF samples. CONCLUSION: SF mononuclear cells from patients with RA express iNOS and are involved in NO production in the joint. The number of positive cells is correlated with CRP concentration, suggesting the implication of NO production in the inflammatory process.

[Inhibition by rhein of nitrosothiol production of human chondrocytes from osteoarthritis in culture]. / Inhibition par la rhéine de la production des nitrosothiols des chondrocytes humains arthrosiques en culture.

Nitric oxide (NOo) is an inorganic radical produced after the activation of a NO synthase involved in inflammatory and immune reactions. It can react with protein thiols to form nitrosothiols, a bioactive molecule or can generate in nitrite or nitrate. High concentrations of these metabolites have been found in sera and synovial fluids from patients with osteoarthritis, the higher synovial concentrations suggesting NOo intra-articular production. The aim of this study was to evaluate the capacity of osteoarthritic chondrocytes to produce bioactive NOo metabolites and to study the inhibitory effect of rhein, the active form of diacerhein. Chondrocytes were stimulated by interleukin-1 beta (1 ng/ml) during 24 hours in presence or absence of rhein (1.3 x 10-5, 6.5 x 10-6, 1.3 x 10-6 M) or diclofenac (10-5, 10-6 M). After 24 hours, nitrite and nitrosothiols were measured in the supernatants and nitrosothiols were also determined in cell lysats. After interleukin-1 beta stimulation chondrocytes produced great quantities of nitrosothiols and nitrite. This effect was inhibited in a dose dependent manner by rhein but not by diclofenac. In conclusion, chondrocytes produce high quantities of nitrosothiols after IL-1 beta stimulation and this effect is inhibited by rhein. This drug could be beneficial to prevent the destruction of osteoarthritic cartilage.

Apoptosis induced by nitric oxide is associated with nuclear p53 protein expression in cultured osteoarthritic synoviocytes.

OBJECTIVE: Nitric oxide (NO) is a free radical molecule endogenously produced by NO synthases that may play a critical role in inflammation. It inhibits cell proliferation and may be involved in the induction of apoptosis in various cellular models. Recently, the presence of apoptotic cells was reported in the synovium of osteoarthritic (OA) patients. The aim of this study was to determine whether synovial fibroblasts are target cells for NO-induced apoptosis. The expression of p53 protein was also studied to evaluate the ability of synovial cells to repair DNA fragmentation. METHODS: Synoviocytes from OA patients were treated with two NO donors: sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP). Apoptosis was analysed by transmission electron microscopy. DNA content was evaluated by flow cytometric analysis after propidium iodide staining and recognition of DNA strand break determined by the TUNEL (TdT-mediated dUTP nick end labeling) method. P53 protein expression was studied by immunofluorescence using a monoclonal antibody. RESULTS: After 6 hours, cells treated with NO donors (1.25 mM) showed a cytoplasmic condensation and vacuolization. DNA strand break analysis by the TUNEL method confirmed the presence of a DNA fragmentation after 24 hours of NO treatment. There was also a progressive decrease in the DNA diploid peak in response to NO donors. In parallel, p53 protein, constitutively expressed in cytoplasmic synovial cells, showed markedly increased expression after a 6-hour NO exposure and displayed prominent nuclear staining after 12 hours. CONCLUSIONS: This study demonstrates the potential role of NO for the induction of synoviocyte apoptosis in OA. The increased expression of p53 in the nucleus may play a protective role in the control of apoptosis.

Sedimentation field-flow fractionation of cellular species.

More than 15 years ago a pioneering report on the separation of cellular material using sedimentation field-flow fractionation (SdFFF) was published. Surprisingly, only a few reports on SdFFF applications to cell separations are available as yet. The major limitations which seemed to slow the development of SdFFF applications in biology appeared to be related to the development of specific instrumentation. Therefore, guidelines are given for setting up a biocompatible SdFFF apparatus. SdFFF elution of cells with different characteristics was performed to demonstrate the efficiency, completeness, and rapidity of cell separations by this method. Retention data describing the effect of lifting forces on nucleated cells are compared to those for red blood cells (RBC). The effects of flow rates, field intensity, and injection protocol were studied using normal human RBC eluted in isotonic medium as a probe for retention conditions. When possible, data were also compared to previously published reports. Guidelines for elution and separation optimization are given. Using mixtures of nucleated and living red blood cells, viability studies showed a surprisingly high recovery of each type of material.

Nitric oxide as S-nitrosoproteins in rheumatoid arthritis.

OBJECTIVE: Nitric oxide (NO) is a free radical involved in inflammation and immune reactions. The presence of NO is usually assessed by assaying its degradation products, nitrite and nitrate. NO binds to thiol-containing proteins to form S-nitrosoproteins (S-NP). The aim of this study was to investigate the presence of S-NP, together with nitrite and nitrate, in patients with rheumatoid arthritis (RA). METHODS: Forty patients with RA were studied and compared with 24 patients with osteoarthritis (OA) and 21 control subjects. Fourteen patients were treated with 3 consecutive pulses of methylprednisolone for flares of RA. Nitrite was measured by the Griess reaction, and nitrate by a spectrophotometric assay using nitrate reductase. Spectrofluorometry coupled with the inner filter effect was used for the measurement of S-NP. RESULTS: S-NP was detected in all RA samples, both in serum and synovial fluid (SF). Serum and articular S-NP concentrations were correlated (P < 0.03). In RA, nitrite and S-NP levels were higher in SF than in serum; higher SF levels of the 3 compounds were observed in RA than in OA. S-NP levels in RA patients decreased significantly (P < 0.03) after pulse methylprednisolone treatment, in parallel with the clinical improvement. CONCLUSION: S-NP, a biologically active form of NO, was consistently present in RA, with higher concentrations within the arthritic joint. S-NP assays should be added to nitrite and nitrate assays for the evaluation of NO metabolism. S-NP could be a stable storage form of active NO in RA, and its measurement could be useful in evaluating pharmacologic interventions that modulate NO generation.

IL-1 modifies system A transport activity in human rheumatoid synovial cells.

Given the importance of interleukin-1 in both rheumatic diseases and the modulation of cell metabolic activities, we studied the action of this cytokine on the neutral amino acid transport A system on rheumatoid synovial cells. In these cells IL-1 (1 ng/ml) induced amino transport stimulation from 5 min to 5 h. This effect was obtained only after a starvation period. No concentration-related effect was found for IL-1-stimulated MeAIB uptake, and the IL-1-mediated MeAIB uptake stimulation is independent of protein synthesis. Neosynthesis or post-translational maturation of protein transport is a prerequisite for obtaining this effect. In conclusion, rheumatoid synovial cells exhibit a higher sensitivity for IL-1 than osteoarthritic ones, probably related to their intense metabolic activity.

Increased serum concentration of IgA2 subclass and IgA2/IgA1 ratio: specific markers of chronic alcoholic abuse?

Enhanced serum IgA concentrations are common in alcoholic liver cirrhosis, but functional differences between IgA subclasses and their relation with interleukin-6 (IL-6) have not been described. Distinct immunoregulatory mechanisms may exist that selectively affect one subclass. This possibility prompted us to investigate the distribution of IgA1 and IgA2 subclasses in the serum of 25 heavy alcohol drinkers (alcohol: 80 to 200 g per day) without clinical disorders, in comparison with 35 patients affected by alcoholic liver cirrhosis, 29 viral hepatitis patients and 33 social drinkers as a control group. Mean (+/- SD) IgA2 concentration (0.56 +/- 0.31 g/l) was significantly increased (p < 0.01) in heavy alcohol drinkers, with an IgA2/IgA1 ratio of 0.33 +/- 0.12, while the mean total IgA concentration was similar to the control group. Mean IgA1 and IgA2 concentrations were significantly increased (p < 0.001) in alcoholic liver cirrhosis patients (6.13 +/- 4.52 g/l and 1.83 +/- 1.93 g/l respectively, with an IgA2/IgA1 ratio of 0.32 +/- 0.19) and viral hepatitis patients (3.66 +/- 2.59 g/l and 0.69 +/- 0.67 g/l respectively, with an IgA2/IgA1 ratio of 0.21 +/- 0.14) High serum IL-6 concentrations (34 +/- 33 ng/l) were correlated with elevated IgA1 and IgA2 concentrations only in patients with alcoholic liver cirrhosis. IgA2 subclass and IgA2/IgA1 ratio could therefore be used as markers of chronic alcohol abuse directly related to the extent and duration of the alcohol abuse and the effectiveness of alcohol withdrawal.

Action of anti-inflammatory drugs on interleukin-1 beta-mediated glucose uptake by synoviocytes.

Synovial cell cultures prepared from samples taken from osteoarthritic and rheumatoid patients were treated with different anti-inflammatory agents (cortisol, indomethacin, ibuprofen and piroxicam) to determine their 'anti-interleukin-1 beta' action, using inhibition of interleukin-1 beta-mediated glucose uptake stimulation as a biological test. Confluent cells were treated for 24 h with different concentrations of these drugs (10(-5), 10(-6) and 10(-7) mol/l) to study their effect on the inflammation process. 6 h before glucose uptake studies, interleukin-1 beta (1 ng/ml) was added. Whereas non-steroid anti-inflammatory agents were inefficient, cortisol inhibited the action of interleukin-1 beta on glucose uptake. In osteoarthritic cells, cortisol, 10(-5) mol/l, reduced interleukin-1 beta-mediated glucose uptake by 27% after a 24-h incubation. In rheumatoid cells, stimulated 2-deoxy-D-glucose uptake was reduced by 40.6%. Results were similar when interleukin-1 beta and cortisol were added simultaneously, 6 h before glucose uptake was measured. This rapid effect of cortisol was protein synthesis-dependent (inhibited by cycloheximide). Cortisol decreased glucose uptake by synoviocytes by acting on basal and interleukin-1 beta-mediated glucose uptake. This effect was more pronounced in rheumatoid synovial cells. The inhibition of interleukin-1 beta-mediated glucose uptake could be proposed as a new model for studying the anti-interleukin-1 beta effects of anti-rheumatic drugs.

Dependence of adaptative regulation for IL-1 beta action on system A activity in human synovial cells.

Human synovial cells are a suitable model for estimating the physiopathological effects of IL-1 beta (IL-1) in joint. Given the importance of this cytokine in the modulation of cell metabolic activities, we set out to study the action of IL-1 on the neutral amino acid transport A system, using the methyl (aminoisobutyric) acid (MeAIB), the most highly specific and nonmetabolizable substrate for the A system. Stimulation of system A activity by adaptative regulation is a prerequisite to obtain an increase of MeAIB uptake in IL-1-treated cells, since cells which had been grown in a normal medium did not express stimulation of system A activity when IL-1 was added. The IL-1-mediated MeAIB uptake is independent of protein synthesis, since cycloheximide (CHX) did not inhibit MeAIB uptake, and characterized by a decrease in the Michaelis constant K(m) (0.147 vs. 0.270 mmol/l, IL-1 vs. control) and a slight increase in maximal velocity (Vmax) (4.59 vs. 3.89 nmol/mg prot/10 min, IL-1 vs. control). These observations indicate that IL-1 induces modifications in both system A transporter affinity and number. Moreover, we indicate that system A should be responsive in vivo to IL-1 in the same way since derepression and IL-1 action occurred in the presence of human synovial fluid.

Interleukin-1 beta-mediated glucose uptake by chondrocytes. Inhibition by cortisol.

The aim of this study was to investigate the in vitro effects of interleukin-1 beta (IL-1 beta) on cultured human articular chondrocytes from patients with osteoarthritis, by the evaluation of glucose uptake. We also investigated the inhibitory effect of cortisol on IL-1 beta-mediated glucose uptake. Experiments were performed by using 2-deoxy-D-[1-3H]glucose (2-DOG) and confluent monolayer cells at first passage. Confluent cells were also treated for 24 h with different concentrations of cortisol (10(-5), 10(-6) and 10(-7) mol/l). IL-1 beta (100 pg/ml) was added 6 h before glucose uptake studies. Glucose uptake stimulation was observed 3 h after the addition of 100 pg/ml IL-1 beta (+70%) and increased up to 24 h (+145%). The sensitivity and responsiveness of chondrocytes to IL-1 beta, studied after a 6 h association time, appeared to be dose-dependent from 0.1 pg/ml IL-1 beta (+50%) to 100 pg/ml (+130%) over basal values. The effect of the cytokine was protein synthesis-dependent, as demonstrated by using cycloheximide. Cortisol inhibited the action of IL-1 beta on glucose uptake because it reduced stimulating effects by 28% at concentrations as weak as 10(-6) mol/l. Results appeared similar when IL-1 beta and cortisol were added simultaneously 6 h before 2-DOG uptake. The rapid effect of cortisol was protein-synthesis dependent, as indicated by inhibition by cycloheximide. These results suggest that IL-1 beta stimulates chondrocyte metabolic activity. The inhibition of IL-1 beta-mediated glucose uptake is suggested for studying the anti-IL-1 effect of other anti-rheumatic drugs.

Stimulation of alpha-(methylamino) isobutyric acid uptake by interleukin-1 in human synovial cells. Involvement of a cAMP dependent pathway.

After one hour incubation with interleukin-1 beta (IL-1 beta), the uptake of alpha-(methylamino) isobutyric acid (MeAIB) by human osteoarthritic synovial cells appeared significantly increased. This effect, observed with 0.1 to 5 ng/ml of cytokine, was inhibited by cycloheximide, indicating that protein synthesis is involved. In addition, this effect seems mediated by a pertussis toxin-sensitive G protein. Finally, intracellular cAMP concentration measurements, the use of a phorbol ester, protein kinase inhibitors and forskolin+3-isobutyl-1-methylxantine (IBMX) provided evidence that a cAMP-dependent protein kinase is associated with interleukin-1 beta-mediated alpha-(methylamino) isobutyric acid uptake.

Cytokine response to burn injury: relationship with protein metabolism.

Plasma levels of interleukin 1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha), interleukin 6 (IL-6), and markers of protein metabolism were determined in 12 burn patients throughout the healing period (day 2 to 21 post-injury) to determine the pattern of variations in plasma cytokine concentration. To establish the relationship between cytokine production and the nutritional status a wide range of severity standpoints (burn surface area ranging from 9% to 82%) was chosen. Interleukin 6 levels were increased in all patients throughout the study period; maximum concentrations (615 +/- 198 pg/mL) were reached on day 4 and correlated (p < 0.01) with the extent of burn injury. Tumor necrosis factor alpha levels were also elevated; they were significantly higher on day 7 in the patients who developed sepsis than in the other patients (67 +/- 21 pg/mL vs. 20 +/- 7 pg/mL; p < 0.05) but did not correlate with the extent of burn injury. Interleukin 1 beta was rarely detected. Cortisolemia on day 7 was inversely correlated with levels of TNF alpha but not with those of IL-6. Interleukin 6 levels correlated positively with protein turnover (phenylalaninemia) and catabolism (3-methylhistidine/creatinine ratio) and negatively with levels of fibronectin and transthyretin. Our data indicate that the systemic cytokine response to burn injury is mainly represented by IL-6. These data also support the hypothesis that IL-6 is a key mediator of the variations in protein metabolism following burn injury.

Tumor necrosis factor alpha, a cytokine coregulating sugar uptake by cultured human synovial cells.

Confluent cultures of osteoarthritic and rheumatoid human synovial cells were treated with human recombinant tumor necrosis factor alpha (TNF-alpha). The cytokine increased uptake of 2-deoxy-D-[1-3H]-glucose (2-DOG) in a time- and concentration-dependent manner. In synovial cells obtained from osteoarthritic patients (OA cells), the stimulation of 2-DOG uptake occurred 3 hours following addition of TNF-alpha (1 ng/ml) and was maximal by 24 hours. Rheumatoid synovial cells (RA cells) appeared less sensitive to the cytokine: 2-DOG uptake stimulation was only significant after 6 hours of incubation. In both OA and RA cells, the effect was protein synthesis-dependent, and was not secondary to prostaglandin E2 synthesis or cell growth. Interleukin-1 beta was more efficient than TNF-alpha for 2-DOG uptake stimulation. The two cytokines seemed to act in an additive manner.