Tumor Necrosis Factor: Function, Release and Clearance.

Tumor Necrosis Factor (TNF) is a multifunctional cytokine. It plays an important role in the pathophysiology of several diseases. Recently, it has been discovered that TNF is circulating in two different forms, a bioactive form and an immunologically detectable form. These two forms of TNF show different clearance kinetics. The immunological form is supposed to be an inactivated TNF protein. For this inactivation, proteolytic degradation or TNF binding by inactivating proteins is necessary. In this review we have focused on TNF inactivation by TNF binding proteins. Recent data show that there are soluble TNF receptors circulating which can bind and inactivate TNF. These receptors are membrane-bound TNF receptors which have been proteolytically cleaved from the cell membrane. Two TNF receptors are circulating, the soluble TNF receptor of 55 kDa (P55) and the receptor of 75 kDa (P75). The receptors are held responsible not only for inactivation of the TNF, but also for the clearance of TNF. Recent data show that the kidney is the most important organ for TNF clearance, followed by the liver. All other organs are of less importance. In this review, function, release, and clearance of TNF are discussed.

Autoantibodies against oxidized low-density lipoprotein and lipid profile in patients with chronic periaortitis: case-control study.

Chronic periaortitis is thought to result from an autoallergic reaction to oxidized low-density lipoprotein (OxLDL). No data exist on lipid profile and atherosclerotic biomarkers. We investigated circulating levels of OxLDL and of anti-OxLDL (aOxLDL) antibodies in patients with chronic periaortitis using the cross-sectional case-control study on 20 patients with chronic periaortitis. Patients were compared to 20 age- and sex-matched controls. aOxLDL antibodies were measured by ELISA and expressed as mean optical density values at 450 nm from duplicate measurements (OD(450)). aOxLDL antibody titers (median [interquartile range]) did not differ significantly between patients and controls (aOxLDL-IgM: 0.70 [0.24-1.08] vs. 0.54 [0.25-0.73] OD(450); aOxLDL-IgG: 0.59 [0.38-0.75] vs. 0.41[0.33-0.63]OD(450)). Female patients had higher aOxLDL-IgM levels than male patients (1.02 [0.46-1.38] vs. 0.29 [0.22-0.84] OD(450); P = 0.05). aOxLDL-IgM titers were lower in patients with cardiovascular disease (CVD) than in patients without CVD (0.22 [0.16-0.37] vs. 0.92 [0.70-1.30] OD(450); P = 0.003) and correlated positively with HDL-cholesterol (r = 0.47, 95% CI 0.02-0.69; P = 0.03) and inversely with diastolic blood pressure (r = -0.46, 95% CI -0.75 to -0.01; P = 0.03) and OxLDL/apoB ratio (r = -0.41, 95% CI -0.73 to 0.04; P = 0.06). No differences or associations were found between aOxLDL-IgG titers and other variables between or within patients and/or controls. In patients OxLDL levels correlated with smoking pack-years (r = 0.58, 95% CI 0.17-0.81; P = 0.007). Data suggest a differing innate immune response to OxLDL in patients with chronic periaortitis compared to controls. Whether this response is causally related to chronic periaortitis development remains to be clarified.

Oxidized LDL enhances pro-inflammatory responses of alternatively activated M2 macrophages: a crucial role for Krüppel-like factor 2.

OBJECTIVE: Macrophages are key players in atherogenesis because of their properties to form foam cells that produce a large variety of pro-inflammatory mediators. We addressed the potency of phenotypic different macrophages to accumulate oxidized LDL. METHODS AND RESULTS: Surprisingly, anti-inflammatory M2 macrophages but not pro-inflammatory M1 macrophages rapidly accumulated oxidized LDL. Simultaneously, expression of Krüppel-like factor 2, a nuclear transcription factor known to suppress inflammation in endothelial cells and monocytes, decreased and the functional phenotype of M2 macrophages shifted towards a pro-inflammatory profile, characterized by higher production of IL-6, IL-8 and MCP-1 and lower expression of IL-10 upon stimulation with LPS. In contrast, Krüppel-like factor 2 expression and the phenotype of M1 macrophages remained largely unchanged upon oxidized LDL exposure. Downregulation of Krüppel-like factor 2 expression of M2 macrophages using siRNA technology led to a significant increase of LPS-induced MCP-1 secretion. CONCLUSIONS: We show that (1) anti-inflammatory M2 macrophages are more susceptible to foam cell formation than pro-inflammatory M1 macrophages, (2) exposure to oxidized LDL renders M2 macrophages pro-inflammatory, and (3) Krüppel-like factor 2 is involved in the enhanced secretion of MCP-1 by M2 macrophages loaded with oxidized LDL. The phenotype switch of M2 macrophages from an anti- to a pro-inflammatory profile may play an important role in pathogenesis of atherosclerosis, and could represent a novel therapeutic target.

Anti-inflammatory therapy with tumour necrosis factor alpha inhibitors improves high-density lipoprotein cholesterol antioxidative capacity in rheumatoid arthritis patients.

OBJECTIVE: High-density lipoprotein (HDL) antiatherogenic functions seem to be diminished during inflammatory conditions such as rheumatoid arthritis (RA). The aim of this study was to investigate the effects of tumour necrosis factor (TNF) inhibition on the antioxidative capacity of HDL in RA. METHODS: Plasma lipids and paraoxonase (PON-1) activity were investigated in 45 RA patients, before and during 6 months of anti-TNF therapy. In addition, HDL was isolated and tested for its ability to inhibit copper-induced oxidation of low-density lipoprotein in vitro. RESULTS: Plasma HDL concentrations did not change considerably after 6 months of therapy. However, stable increases of PON-1 activities were observed throughout the same period (p<0.03). The increases were more obvious when related to HDL or apolipoprotein AI concentrations. HDL total antioxidative capacity significantly improved 6 months after the initiation of anti-TNF therapy (p = 0.015). The initial improvement of PON-1 activity paralleled a decrease in the inflammatory status, whereas specific TNF blockade was likely to be responsible for the long-term effects. CONCLUSIONS: Anti-TNF therapy with infliximab has beneficial effects on lipids through changes in HDL antioxidative capacity, which might be clinically relevant and contribute to the reported protective effect of anti-TNF on cardiovascular morbidity in RA. This emphasises the importance of HDL antiatherogenic capacity for cardiovascular risk in chronic inflammatory conditions.

Cholesterol in end-stage renal disease: the good, the bad or the ugly?

The incidence of cardiovascular disease is markedly increased in patients with end-stage renal disease (ESRD). High serum cholesterol is widely recognised as a cardiovascular risk factor in the general population. However, in patients with ESRD high concentrations of cholesterol are associated with a better survival. This reverse epidemiology is, amongst others, caused by confounding due to malnutrition and chronic inflammation. In this population, treatment with statins to lower the serum cholesterol remains a matter of debate. In ESRD, LDL cholesterol is modified by increased oxidative stress. These altered LDL particles play a pivotal role in the development of atherosclerosis. Treatment with the antioxidant vitamin E has not equivocally been shown to be beneficial in this population. This review tries to put data from literature on dyslipidaemia and oxidative stress in ESRD in perspective.

Endothelial function in familial combined hyperlipidaemia.

BACKGROUND: Familial combined hyperlipidaemia (FCH) is characterized by dyslipidaemia, visceral obesity and insulin resistance, and is associated with an increased intima-media thickness (IMT) and an increased risk for cardiovascular disease. In the present study, we investigated whether FCH is associated with early functional vascular wall changes, as represented by endothelial dysfunction, and we determined whether endothelial function in FCH is related to any of the cardiovascular risk factors associated with the FCH phenotype, or to the (increased) IMT. DESIGN: In 98 patients with FCH [mean age 51 (48-54) years, 43% male] and 230 unaffected relatives [mean age 44 (42-46) years, 48% male], venous blood was drawn in the fasting state after discontinuation of lipid lowering drugs for at least 4 weeks (if used). IMT was measured by B-mode ultrasound and endothelial function was assessed by determination of flow mediated dilation (FMD) and by measurement of plasma concentrations of various soluble adhesion molecules, including soluble vascular cell adhesion molecule (sVCAM), soluble intercellular adhesion molecule (sICAM) and soluble E-selectin. RESULTS: There were no significant differences between FCH patients and their non-affected relatives in FMD [2.9 (2.3-3.6%) vs. 2.8 (2.5-3.2%)] or in the plasma concentrations of the various adhesion molecules. None of the individual clinical and biochemical cardiovascular risk factors was an independent predictor of endothelial function in patients with FCH, nor was IMT. However, subgroup analysis revealed that IMT was an independent and powerful predictor of FMD in subjects with carotid artery plaques (St. beta = 4.11, P < 0.004), whereas IMT was no significant predictor in subjects without plaques. CONCLUSIONS: FCH patients have no impaired endothelial function when compared to their unaffected relatives. IMT is an important predictor of FMD when advanced morphological wall changes are present. Our results question the value of FMD measurements for cardiovascular risk stratification in populations with an anticipated high cardiovascular risk.

Non-transferrin-bound iron is associated with plasma level of soluble intercellular adhesion molecule-1 but not with in vivo low-density lipoprotein oxidation.

BACKGROUND: Excess body iron is associated with increased cardiovascular disease risk, possibly via non-transferrin-bound iron (NTBI)-mediated enhancement of inflammation and oxidation of low-density lipoprotein (LDL). METHODS: We assessed this proposed atherosclerotic mechanism of body iron by determining the relationship of levels of serum iron parameters, including NTBI, with plasma markers of inflammation and LDL oxidation in 232 subjects who visited the outpatient clinic for hemochromatosis family screening. RESULTS: Plasma level of soluble intercellular adhesion molecule-1 (sICAM-1) was positively related to ferritin (standardized beta coefficient 0.16) and to NTBI (0.185) and negatively to total iron-binding capacity (TIBC, -0.166). Significant higher levels of sICAM-1 were found for subjects in the highest quartile of NTBI compared to the lowest quartile of NTBI (122 microg/L (107-141) and 106 microg/L (89-125), median (interquartile range), p<0.001). Odds ratio of subjects having sICAM-1 level above 134 microg/L (75th percentile) in the highest and lowest quartile of NTBI amounted 2.3. White blood cell count was positively related to ferritin (0.149). High-sensitivity C-reactive protein, interleukin-6, interleukin-8, oxidized LDL, oxidized LDL/apolipoprotein B and IgG and IgM antibodies to oxidized LDL were not related to any of the markers of iron status. CONCLUSION: Excess body iron, reflected by elevated serum ferritin and NTBI and decreased TIBC, is associated with increased plasma level of sICAM-1 but not with markers of in vivo LDL oxidation.

The story of PON1: how an organophosphate-hydrolysing enzyme is becoming a player in cardiovascular medicine.

Since the discovery of human serum paraoxonase (PON1), the enzyme has been the subject of various fields of research. Initially, PON1 was identified as an enzyme capable of hydrolysing organophosphate compounds, but there is a growing body of evidence that PON1 plays a role in lipid metabolism and the onset of cardiovascular disease. Still, the precise mechanism by which PON1 functions in vivo remains to be clarified. Here we will briefly review developments in the field of PON1 research which merit further attention.

Proportion of oxidized LDL relative to plasma apolipoprotein B does not change during statin therapy in patients with heterozygous familial hypercholesterolemia.

OBJECTIVE: Circulating oxidized low-density lipoprotein (LDL) has been shown to be a useful marker for identifying patients with coronary heart disease (CHD) and persons at high cardiovascular risk. The effect of cholesterol-lowering therapy on plasma level of oxidized LDL is not clear. METHODS AND RESULTS: We investigated effects of cholesterol lowering by therapeutic intervention (2 years) with atorvastatin (80 mg daily) and simvastatin (40 mg daily) on circulating oxidized LDL (absolute level and in proportion to plasma apolipoprotein B) in relation to atherosclerosis progression (carotid intima-media thickness, carotid IMT) and to inflammation (high-sensitivity C-reactive protein, hsCRP) in 115 stable patients with heterozygous familial hypercholesterolemia (FH). Atorvastatin and simvastatin reduced plasma-oxidized LDL (-43 and -35%, respectively) in proportion to the decrease in plasma apolipoprotein B. Neither absolute nor relative level of oxidized LDL correlated with carotid IMT or hsCRP at baseline. Also changes in levels of circulating oxidized LDL were not related to changes in carotid IMT and hsCRP. CONCLUSIONS: In familial hypercholesterolemia-oxidized LDL carried in plasma is strongly associated with apolipoprotein B but not with inflammation nor with carotid IMT, and statin treatment does not reduce oxidized LDL relative to apolipoprotein B.

The effect of statin therapy on plasma high-density lipoprotein cholesterol levels is modified by paraoxonase-1 in patients with familial hypercholesterolaemia.

OBJECTIVES: Statins reduce low-density lipoprotein cholesterol (LDL-C) and can raise high-density lipoprotein cholesterol (HDL-C). HDL-bound paraoxonase-1 (PON1) is associated with variations in plasma HDL-C, and may, therefore, contribute to changes of HDL-C during statin therapy. DESIGN: The effects of baseline PON1 status to HDL-C changes because of statin therapy were investigated. PON1 status was determined with (i) PON1 -107C>T and 192Q>R genotype, (ii) PON1 levels and (iii) PON1 paraoxonase, diazoxonase and arylesterase activity. SETTING: Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands. SUBJECTS: A total of 134 familial hypercholesterolaemia (FH) patients undergoing atorvastatin or simvastatin therapy. RESULTS: PON1 levels and activities significantly modified the HDL-C increment (P=0.002 for PON1 levels and arylesterase activity and P=0.001 for diazoxonase activity). The effects were even more evident amongst subgroup classifications based on PON1 status and baseline HDL-C concentrations: the HDL-C increment was more pronounced in subgroups of -107CT/TT or 192QR/RR genotype combined with low baseline HDL-C (+13.9%, P<0.001, respectively+15.4%, P<0.001). In contrast, the -107CC or 192QQ genotype in combination with high baseline HDL-C, did not show a significant increase of HDL-C. CONCLUSIONS: PON1 status in conjunction with baseline HDL-C levels predicts HDL-C increment during statin therapy in FH patients.

Anti-inflammatory effects of troglitazone in nondiabetic obese subjects independent of changes in insulin sensitivity.

BACKGROUND: Obesity is characterised by insulin resistance and by elevated levels of proinflammatory markers. We investigated whether, in the absence of changes in glucose, thiazolidinediones (TZDs) have anti-inflammatory effects and whether improvement of insulin sensitivity correlates with suppression of inflammatory markers. METHODS: We performed a randomised double-blind placebo-controlled crossover study with troglitazone (400 mg daily for eight weeks) in 15 normoglycaemic obese subjects. We measured plasma high-sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), leptin, tissue-type plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1) and tumour necrosis factor-alpha (TNF-alpha) after each of the two treatment periods and in 13 age- and sex-matched lean individuals. RESULTS: Obese subjects were insulin resistant (decreased glucose infusion rate (GIR) during euglycaemic hyperinsulinaemic clamp) and had higher plasma levels of hsCRP, IL-6, leptin, tPA, and PAI-1 compared with lean subjects. TNF-alpha also tended to be higher. Troglitazone improved insulin sensitivity (mean increase in whole body glucose uptake 23.1 +/- 10.5% (p = 0.047)) and normalised plasma concentrations of hsCRP, tPA and TNF-alpha, whereas it did not significantly change IL-6, leptin and PAI-1. Changes in GIR did not correlate with changes in inflammatory markers. CONCLUSION: Troglitazone induces suppression of some of the inflammatory markers that are elevated in normoglycaemic obese subjects. The suppression of inflammatory markers, however, does not correlate with improvement in insulin sensitivity, suggesting involvement of partially differential mechanisms in these effects of TZDs.

Effect of lowering of homocysteine levels on inflammatory markers: a randomized controlled trial.

BACKGROUND: Elevated concentrations of homocysteine and low concentrations of folate may lead to a proinflammatory state that could explain their relation to vascular disease risk. We investigated the effect of lowering homocysteine concentrations by means of folic acid supplementation on markers of inflammation. METHODS: In a double-blind, randomized, placebo-controlled trial among 530 men and postmenopausal women with homocysteine concentrations of 1.8 mg/L or higher (>/=13 micromol/L) at screening, we investigated the effect of folic acid supplementation (0.8 mg/d) vs placebo for 1 year on serum concentrations of C-reactive protein, soluble intercellular adhesion molecule-1, oxidized low-density lipoprotein, and autoantibodies against oxidized low-density lipoprotein. RESULTS: After 1 year of supplementation, concentrations of serum folate increased by 400% (95% confidence interval [CI], 362%-436%), and those of homocysteine decreased by 28% (95% CI, 24%-36%) in the folic acid group compared with the placebo group. However, no changes in plasma concentrations of the inflammatory markers were observed. CONCLUSIONS: Although homocysteine is associated with vascular disease risk in the general population, marked lowering of slightly elevated homocysteine concentrations by means of 1-year folic acid supplementation does not influence inflammatory responses involving C-reactive protein, soluble intercellular adhesion molecule-1, oxidized low-density lipoprotein, and autoantibodies against oxidized low-density lipoprotein.

Stability studies of ubiquinol in plasma.

BACKGROUND: Ubiquinol is a sensitive redox marker in the first line of the antioxidative defence mechanism and is increasingly being measured in oxidation studies. Because of its apparent instability during storage and processing, we compared various storage conditions. METHOD: Blood was collected from three volunteers into tubes containing EDTA; it was then separated at 4 degrees C and cryopreserved with saccharose (final concentration 6 g/L). Aliquots were stored with or without glutathione or butylated hydroxytoluene at -20 degrees C and -80 degrees C. RESULTS AND CONCLUSION: Ubiquinol in samples stored at -20 degrees C was not stable; however, it was stable when stored at -80 degrees C, even without addition of antioxidant. By contrast, alpha-tocopherol was stable under all conditions studied.