The Inter-Relationship of Platelets with Interleukin-1ß-Mediated Inflammation in Humans.

BACKGROUND: Inflammation and coagulation are key processes in cardiovascular diseases (CVDs). The Canakinumab Anti-inflammatory Thrombosis Outcome Study trial affirmed the importance of inflammation in CVD by showing that inhibition of the interleukin (IL)-1ß pathway prevents recurrent CVD. A bi-directional relationship exists between inflammation and coagulation, but the precise interaction of platelets and IL-1ß-mediated inflammation is incompletely understood. We aimed to determine the inter-relationship between platelets and inflammation-and especially IL-1ß-in a cohort of healthy volunteers. METHODS: We used data from the 500-Human Functional Genomics cohort, which consists of approximately 500 Caucasian, healthy individuals. We determined associations of plasma levels of IL-1ß and other inflammatory proteins with platelet number and reactivity, the association of platelet reactivity with ex vivo cytokine production as well as the impact of genetic variations through a genome-wide association study (GWAS). RESULTS: Platelets were associated with IL-1ß on different levels. First, platelet number was positively associated with plasma IL-1ß concentrations (p = 8.9 × 10-9) and inversely with concentrations of α-1-anti-trypsin (p = 1.04 × 10-18), which is a known antagonist of IL-1ß. Second, platelet degranulation capacity, as determined by agonist-induced P-selectin expression, was associated with ex vivo IL-1ß and IL-6 production. Third, several platelet single-nucleotide polymorphisms (SNPs) were associated with cytokine production and there was a significant platelet SNP enrichment in specific biological important pathways. Finally, platelet SNPs were enriched among SNPs earlier identified in GWAS studies in blood-related diseases and immune-mediated diseases. CONCLUSION: This comprehensive assessment of factors associated with platelet number and reactivity reinforces the important inter-relationship of platelets and IL-1ß-mediated inflammation.

Host and Environmental Factors Influencing Individual Human Cytokine Responses.

Differences in susceptibility to immune-mediated diseases are determined by variability in immune responses. In three studies within the Human Functional Genomics Project, we assessed the effect of environmental and non-genetic host factors of the genetic make-up of the host and of the intestinal microbiome on the cytokine responses in humans. We analyzed the association of these factors with circulating mediators and with six cytokines after stimulation with 19 bacterial, fungal, viral, and non-microbial metabolic stimuli in 534 healthy subjects. In this first study, we show a strong impact of non-genetic host factors (e.g., age and gender) on cytokine production and circulating mediators. Additionally, annual seasonality is found to be an important environmental factor influencing cytokine production. Alpha-1-antitrypsin concentrations partially mediate the seasonality of cytokine responses, whereas the effect of vitamin D levels is limited. The complete dataset has been made publicly available as a comprehensive resource for future studies. PAPERCLIP.

Suppression of monosodium urate crystal-induced cytokine production by butyrate is mediated by the inhibition of class I histone deacetylases.

OBJECTIVES: Acute gouty arthritis is caused by endogenously formed monosodium urate (MSU) crystals, which are potent activators of the NLRP3 inflammasome. However, to induce the release of active interleukin (IL)-1ß, an additional stimulus is needed. Saturated long-chain free fatty acids (FFAs) can provide such a signal and stimulate transcription of pro-IL-1ß. In contrast, the short-chain fatty acid butyrate possesses anti-inflammatory effects. One of the mechanisms involved is inhibition of histone deacetylases (HDACs). Here, we explored the effects of butyrate on MSU+FFA-induced cytokine production and its inhibition of specific HDACs. METHODS: Freshly isolated peripheral blood mononuclear cells (PBMCs) from healthy donors were stimulated with MSU and palmitic acid (C16.0) in the presence or absence of butyrate or a synthetic HDAC inhibitor. Cytokine responses were measured with ELISA and quantitative PCR. HDAC activity was measured with fluorimetric assays. RESULTS: Butyrate decreased C16.0+MSU-induced production of IL-1ß, IL-6, IL-8 and IL-1ß mRNA in PBMCs from healthy donors. Similar results were obtained in PBMCs isolated from patients with gout. Butyrate specifically inhibited class I HDACs. The HDAC inhibitor, panobinostat and the potent HDAC inhibitor, ITF-B, also decreased ex vivo C16.0+MSU-induced IL-1ß production. CONCLUSIONS: In agreement with the reported low inhibitory potency of butyrate, a high concentration was needed for cytokine suppression, whereas synthetic HDAC inhibitors showed potent anti-inflammatory effects at nanomolar concentrations. These novel HDAC inhibitors could be effective in the treatment of acute gout. Moreover, the use of specific HDAC inhibitors could even improve the efficacy and reduce any potential adverse effects.

Soluble uric acid primes TLR-induced proinflammatory cytokine production by human primary cells via inhibition of IL-1Ra.

OBJECTIVES: The study of the proinflammatory role of uric acid has focused on the effects of its crystals of monosodium urate (MSU). However, little is known whether uric acid itself can directly have proinflammatory effects. In this study, we investigate the priming effects of uric acid exposure on the cytokine production of primary human cells upon stimulation with gout-related stimuli. METHODS: Peripheral blood mononuclear cells (PBMCs) were harvested from patients with gout and healthy volunteers. Cells were pretreated with or without uric acid in soluble form for 24 h and then stimulated for 24 h with toll-like receptor (TLR)2 or TLR4 ligands in the presence or absence of MSU crystals. Cytokine production was measured by ELISA; mRNA levels were assessed using qPCR. RESULTS: The production of interleukin (IL)-1ß and IL-6 was higher in patients compared with controls and this correlated with serum urate levels. Proinflammatory cytokine production was significantly potentiated when cells from healthy subjects were pretreated with uric acid. Surprisingly, this was associated with a significant downregulation of the anti-inflammatory cytokine IL-1 receptor antagonist (IL-1Ra). This effect was specific to stimulation by uric acid and was exerted at the level of gene transcription. Epigenetic reprogramming at the level of histone methylation by uric acid was involved in this effect. CONCLUSIONS: In this study we demonstrate a mechanism through which high concentrations of uric acid (up to 50 mg/dL) influence inflammatory responses by facilitating IL-1ß production in PBMCs. We show that a mechanism for the amplification of IL-1ß consists in the downregulation of IL-1Ra and that this effect could be exerted via epigenetic mechanisms such as histone methylation. Hyperuricaemia causes a shift in the IL-1ß/IL-1Ra balance produced by PBMCs after exposure to MSU crystals and TLR-mediated stimuli, and this phenomenon is likely to reinforce the enhanced state of chronic inflammation.

Circulating leptin and adiponectin concentrations during tumor necrosis factor blockade in patients with active rheumatoid arthritis.

OBJECTIVE: Adipocytokines, including leptin and adiponectin, may play an important role in the pathogenesis of rheumatoid arthritis (RA). We investigated the effects of longterm therapeutic tumor necrosis factor (TNF) blockade on adipocytokine concentrations in patients with RA. METHODS: We studied 58 RA patients starting anti-TNF therapy and 58 healthy controls matched for age, sex, and body mass index (BMI). Fasting blood samples were drawn at baseline, 2 weeks, and 6 months after the start of anti-TNF therapy and serum levels of leptin and adiponectin were measured. RESULTS: Patients with RA had increased adiponectin (p<0.001) and similar leptin concentrations compared with the controls. Leptin concentrations were significantly higher in patients with high BMI (p<0.001) and correlated positively with BMI at all timepoints (r>0.75). In contrast, serum adiponectin tended to be higher in lean RA patients and did not correlate with BMI at any timepoint. There were no clear correlations between serum concentrations of adipocytokines and disease activity (Disease Activity Score 28). Short or longterm TNF blockade alone had no influence on circulating leptin and adiponectin concentrations. Patients treated with anti-TNF and concomitant corticosteroids on a stable basis showed a significant decrease in adiponectin levels after 6 months of therapy (p<0.025). CONCLUSION: In patients with RA, chronic inflammation and its suppression during anti-TNF therapy have limited influence on plasma leptin concentrations, while significantly decreasing circulating adiponectin levels. Our findings question the suggested key role of inflammatory markers in regulating adipocytokine patterns in RA.