Uric acid as a danger signal in gout and its comorbidities. Nat Rev Rheumatol. 2013;9:13-23. [PMID: 22945591 DOI: 10.1038/nrrheum.2012.143]

Uric acid is released in the brain during seizure activity and increases severity of seizures in a mouse model for acute limbic seizures

Recent evidence points at an important role of endogenous cell-damage induced pro-inflammatory molecules in the generation of epileptic seizures. Uric acid, under the form of monosodium urate crystals, has shown to have pro-inflammatory properties in the body, but less is known about its role in seizure generation. This study aimed to unravel the contribution of uric acid to seizure generation in a mouse model for acute limbic seizures. We measured extracellular levels of uric acid in the brain and modulated them using complementary pharmacological and genetic tools. Local extracellular uric acid levels increased three to four times during acute limbic seizures and peaked between 50 and 100 min after kainic acid infusion. Manipulating uric acid levels through administration of allopurinol or knock-out of urate oxidase significantly altered the number of generalized seizures, decreasing and increasing them by a twofold respectively. Taken together, our results consistently show that uric acid is released during limbic seizures and suggest that uric acid facilitates seizure generalization.

Targeting the inflammasome in rheumatic diseases

Activation of the inflammasome, a protein complex responsible for many cellular functions, including the activation of the proinflammatory cytokines interleukin (IL)-1β and IL-18, has been identified as a key participant in many rheumatic diseases including autoimmune, inflammatory, and autoinflammatory syndromes. This review will discuss the recent advances in understanding the role of this complex in various rheumatic diseases. Furthermore, it will focus on available therapies, which directly and indirectly target the inflammasome and its downstream cytokines to quiet inflammation and possibly dampen autoimmune processes.

An Independent Risk of Gout on the Development of Deep Vein Thrombosis and Pulmonary Embolism: A Nationwide, Population-Based Cohort Study

Previous studies indicated that gout is a risk factor of cardiovascular diseases. This study aimed to determine if patients with gout have an increased risk of deep vein thrombosis (DVT) or pulmonary embolism (PE).We used the Longitudinal Health Insurance Database, a subset of the national insurance claim dataset, which enrolled 1 million Taiwanese to identify 57,981 patients with gout and 115,961 reference subjects matched by sex, age, and entry date of diagnosis. The risk of DVT and PE was analyzed using the Cox proportional hazards model.In this Taiwanese dataset observed from 2000 to 2010, we found the incidence of DVT was 5.26 per 10 person-years in the gout cohort, which was twofold higher than the incidence of 2.63 per 10 person-years in the reference cohort. After adjusting for age, sex, and 9 comorbidities, the hazard ratio (HR) of developing DVT was 1.66 (95% confidence interval [CI] = 1.37-2.01). Among patients with gout, the youngest age group had the highest increase in the risk of developing DVT (HR [95% CI] = 2.04 [1.24-3.37] for ages 20 to 49 years, 1.80 [1.28-2.51] for ages 50 to 64 years, and 1.45 [1.11-1.91] for ages ≥65 years). The incidence of PE was about one-fifth that of DVT in gout patients, but the effect of gout on the risk was similar (HR [95% CI] = 1.53 [1.01-2.29]).Our analysis confirmed that gout increased the risk of DVT and PE. Further exploration is needed in the future.

Hyperuricemia is a biomarker of early mortality in patients with chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) are often at high risk of early death. Identification of prognostic biomarkers for COPD may aid in improving their survival by providing early strengthened therapy for high-risk patients. In the present study, we investigated the prognostic role of hyperuricemia at baseline on the prognosis of patients with COPD. Thirty-four patients with COPD with hyperuricemia were matched (1:2) to 68 patients with COPD without hyperuricemia and of similar age and sex. Data from those patients with COPD were evaluated retrospectively. The role of hyperuricemia on mortality was first analyzed using the Kaplan-Meier method, and multivariate Cox regression model was then used to evaluate the prognostic significance of hyperuricemia in patients with COPD. Hyperuricemia was not associated with other baseline characteristics in patients with COPD. Kaplan-Meier survival curve showed that patients with COPD with hyperuricemia had higher risk of mortality compared with patients with normouricemia, and the P-value for log-rank test was 0.005. In univariate analysis, hyperuricemia was associated with higher risk of mortality in patients with COPD (hazard ratio =2.29, 95% CI =1.07-4.88, P=0.032). In the multivariate analysis, hyperuricemia was independently associated with higher risk of mortality in patients with COPD (hazard ratio =2.68, 95% CI =1.18-6.09, P=0.019). In conclusion, hyperuricemia is a promising biomarker of early mortality in patients with COPD.

Transmembrane TNF-α is sufficient for articular inflammation and hypernociception in a mouse model of gout

Gout manifests as recurrent episodes of acute joint inflammation and pain due to the deposition of monosodium urate (MSU) crystals within the affected tissue in a process dependent on NLRP3 inflammasome activation. The synthesis, activation, and release of IL-1β are crucial for MSU-induced inflammation. The current study evaluated the mechanism by which TNF-α contributed to MSU-induced inflammation. Male C57BL/6J or transgenic mice were used in this study and inflammation was induced by the injection of MSU crystals into the joint. TNF-α was markedly increased in the joint after the injection of MSU. There was inhibition in the infiltration of neutrophils, production of CXCL1 and IL-1β, and decreased hypernociception in mice deficient for TNF-α or its receptors. Pharmacological blockade of TNF-α with Etanercept or pentoxyfylline produced similar results. Mechanistically, TNF-α blockade resulted in lower amounts of IL-1β protein and pro-IL-1β mRNA transcripts in joints. Gene-modified mice that express only transmembrane TNF-α had an inflammatory response similar to that of WT mice and blockade of soluble TNF-α (XPro™1595) did not decrease MSU-induced inflammation. In conclusion, TNF-α drives expression of pro-IL-1β mRNA and IL-1β protein in experimental gout and that its transmembrane form is sufficient to trigger MSU-induced inflammation in mice.

EGCG Attenuates Uric Acid-Induced Inflammatory and Oxidative Stress Responses by Medicating the NOTCH Pathway

Background. The aim of this study is to investigate whether (-)-epigallocatechin-3-gallate (EGCG) can prevent the UA-induced inflammatory effect of human umbilical vein endothelial cells (HUVEC) and the involved mechanisms in vitro. Methods. HUVEC were subjected to uric acid (UA) with or without EGCG treatment. RT-PCR and western blots were performed to determine the level of inflammation marker. The antioxidant activity was evaluated by measuring scavenged reactive oxygen species (ROS). Functional studies of the role of Notch-1 in HUVEC lines were performed using RNA interference analyses. Results. UA significantly increased the expressions of IL-6, ICAM-1, TNF-α, and MCP-1 and the production of ROS in HUVEC. Meanwhile, the expression of Notch-1 and its downstream effects significantly increased. Using siRNA, inhibition of Notch-1 signaling significantly impeded the expressions of inflammatory cytokines under UA treatment. Interestingly, EGCG suppressed the expressions of inflammatory cytokines and the generation of ROS. Western blot analysis of Notch-1 showed that EGCG significantly decreased the expressions of inflammatory cytokines through Notch-1 signaling pathways. Conclusions. In summary, our findings indicated that Notch-1 plays an important role in the UA-induced inflammatory response, and the downregulation of Notch-1 by EGCG could be an effective approach to decrease inflammation and oxidative stress induced by UA.

Human β Defensin-3 Increases CD86 Expression on Monocytes by Activating the ATP-Gated Channel P2X7

Human β defensin-3 (hBD-3), an epithelial cell-derived antimicrobial peptide, mediates chemotaxis and activation of myeloid cells. In this study, we provide evidence that hBD-3 induces the costimulatory molecule CD86 on primary human monocytes by a mechanism involving autocrine activation of ionotropic P2X7 receptors (P2X7R) by ATP. Incubation of monocytes with hBD-3 resulted in increased expression of both the CD80 and CD86 costimulatory molecules. Treatment of monocytes with a selective P2X7R antagonist inhibited the ability of hBD-3 to induce expression of CD86 but not CD80. The hBD-3-dependent upregulation of CD86 was also attenuated in monocytes incubated with apyrase, a potent scavenger of extracellular ATP. Finally, direct activation of monocyte P2X7R by exogenous ATP mimicked the ability of hBD-3 to induce CD86 expression. These data suggest that hBD-3 induces monocyte activation by both P2X7-dependent (CD86 upregulation) and P2X7-independent (CD80 upregulation) signaling mechanisms and raise the possibility that activation of P2X7R could play an important role in shaping the inflammatory microenvironment in conditions where hBD-3 is highly expressed, such as psoriasis or oral carcinoma.

Inflammasome activation in the liver: Focus on alcoholic and non-alcoholic steatohepatitis

Upregulation of the inflammatory cascade is a major element both in the progression of steatohepatitis to severe alcoholic hepatitis as well as in the progression of NASH to advanced NASH with fibrosis. The mechanisms underpinning these changes are only partially understood. Activation of the inflammatory cascade requires multiple stimuli and in this report, we discuss the role of inflammasomes that activate IL-1β as well as the sterile and pathogen-derived danger signals that results in inflammasome activation and inflammation in alcoholic and non-alcoholic steatohepatitis. The dynamics of inflammasome activation, the cell types involved and the trigger signals appear to be somewhat different between ASH and NASH. Further studies are needed to dissect the pathology-related differences between these two major forms of steatohepatitis. Clinical and therapeutic implications of inflammasome activation in steatohepatitis are also discussed.

Hyperuricemia has an adverse impact on the prognosis of patients with osteosarcoma

Patients with osteosarcoma have poor prognosis and are often at high risk of death. Identification of prognostic biomarkers for osteosarcoma may aid in improving the survival. Hyperuricemia had been suggested as a poor prognostic factor of several cancers, but the prognostic role of hyperuricemia in osteosarcoma patients had not been assessed. In the present study, we investigated the prognostic role of hyperuricemia at baseline on the overall survival of patients with osteosarcoma. Sixty osteosarcoma patients with hyperuricemia were matched (1:2) to 120 osteosarcoma patients without hyperuricemia with similar age and gender. Data from those patients with osteosarcoma were evaluated retrospectively. The role of hyperuricemia on overall survival was firstly analyzed using the Kaplan-Meier method. Univariate and multivariate Cox regression models were also used to further evaluate the prognostic significance of hyperuricemia. None of the clinicopathological parameters except distant metastasis was associated with hyperuricemia. Kaplan-Meier method showed that patients with hyperuricemia had shorter overall survival compared with those with normouricemia (P < 0.0001, log-rank test). In univariate analysis, hyperuricemia was associated with poorer overall survival in osteosarcoma patients (HR = 2.71, 95 % CI 1.75-4.20; P < 0.0001). In the multivariate analysis, after adjusting for age, gender, serum alkaline phosphatase, stage, tumor size, and metastasis, hyperuricemia was independently associated with poorer overall survival in osteosarcoma patients (HR = 2.28, 95 % CI 1.41-3.69; P = 0.001). In conclusion, hyperuricemia at baseline is associated with poorer overall survival in osteosarcoma patients, and it has an adverse impact on the prognosis of osteosarcoma patients.

Inflammasome activation and function in liver disease

Inflammation contributes to the pathogenesis of most acute and chronic liver diseases. Inflammasomes are multiprotein complexes that can sense danger signals from damaged cells and pathogens and assemble to mediate caspase-1 activation, which proteolytically activates the cytokines IL-1β and IL-18. In contrast to other inflammatory responses, inflammasome activation uniquely requires two signals to induce inflammation, therefore setting an increased threshold. IL-1β, generated upon caspase-1 activation, provides positive feed-forward stimulation for inflammatory cytokines, thereby amplifying inflammation. Inflammasome activation has been studied in different human and experimental liver diseases and has been identified as a major contributor to hepatocyte damage, immune cell activation and amplification of liver inflammation. In this Review, we discuss the different types of inflammasomes, their activation and biological functions in the context of liver injury and disease progression. Specifically, we focus on the triggers of inflammasome activation in alcoholic steatohepatitis and NASH, chronic HCV infection, ischaemia-reperfusion injury and paracetamol-induced liver injury. The application and translation of these discoveries into therapies promises novel approaches in the treatment of inflammation in liver disease.

Effect of Urate-lowering Therapy on the Risk of Cardiovascular Disease and All-cause Mortality in Patients with Gout: A Case-matched Cohort Study

Objective.

To examine (1) the risk of death from cardiovascular disease (CVD) and from all causes in patients with gout who do not undergo urate-lowering therapy (ULT), and (2) the effect of ULT on mortality risk in patients with gout.

Methods.

In this prospective case-matched cohort study, 40,623 Taiwanese individuals aged ≥ 17 years were followed for 6.5 years. Mortality rate was compared between 1189 patients with gout who did not receive ULT and reference subjects (no gout, no ULT) matched for age, sex, and the index date of gout diagnosis (1:3 patients with gout/reference subjects), and between 764 patients with gout who received ULT and 764 patients with gout who did not receive ULT matched 1-to-1 based on their propensity score and the index date of ULT prescription. Cox proportional hazard modeling was used to estimate the respective risk of CVD (International Classification of Diseases, 9th ed. code 390–459) and all-cause mortality.

Results.

After adjustment, patients with gout not treated with ULT had an increased risk of CVD mortality (HR 2.43, 95% CI 1.33–4.45) and all-cause mortality (1.45, 1.05–2.00) relative to the matched reference subjects (no gout, no ULT). Patients with gout treated with ULT had a lower risk of CVD (0.29, 0.11–0.80) and all-cause mortality (0.47, 0.29–0.79) relative to patients with gout not treated with ULT. This survival benefit persisted for users of either allopurinol or benzbromarone.

Conclusion.

Patients with gout who received ULT had significantly better survival rates than those who did not. Thus, undertreatment of gout has serious negative consequences.

Endogenous and Uric Acid-Induced Activation of NLRP3 Inflammasome in Pregnant Women with Preeclampsia

Preeclampsia (PE) is a specific syndrome of pregnancy, characterized by hypertension and proteinuria. This pathology is associated with hyperuricemia and elevated serum levels of inflammatory cytokines. Uric acid crystals may activate an intracellular complex called inflammasome, which is important for processing and release of inflammatory cytokines. This study investigated the state of monocyte activation, both endogenous and stimulated with monosodium urate (MSU), by gene expression of NLRP1 and NLRP3 receptors as well as their association with inflammatory cytokines expression. Monocytes were obtained from peripheral blood of 23 preeclamptic pregnant women, 23 normotensive pregnant women (NT) and 23 healthy non-pregnant women (NP). Inflammasome activation was evaluated by the gene expression of NLRP1, NLRP3, caspase-1, IL-1β, IL-18 and TNF-α by RT-qPCR in unstimulated monocytes (endogenous expression), or after cell stimulation with MSU (stimulated expression). The concentration of cytokines was assessed by ELISA. In preeclamptic pregnant women, gene expression of NLRP1, NLRP3, caspase-1, IL-1β and TNF-α by monocytes stimulated or not with MSU was significantly higher than in NT and NP groups. Stimulation of monocytes from preeclamptic and non-pregnant women with MSU induced increased gene expression of NLRP3, caspase-1 and TNF-α in relation to the endogenous expression in these groups, while this was not observed in the NT group. The cytokine determination showed that monocytes from women with PE produced higher endogenous levels of IL-1β, IL-18 and TNF-α compared to the other groups, while the stimulus with MSU led to higher production of these cytokines in preeclamptic group than in the NT group. In conclusion, the results showed increased basal gene expression of NLRP1 and NLRP3 receptors in monocytes from PE group. These cells stimulation with MSU demonstrates that uric acid plays a role in NLRP3 inflammasome activation, suggesting the participation of this inflammatory complex in the pathogenesis of preeclampsia.

Upregulation of NLRP3 Inflammasome in the Tears and Ocular Surface of Dry Eye Patients

PURPOSE

To evaluate the mRNA and protein expressions of NLRP3 inflammasome and its downstream inflammatory factors in human dry eye.

METHODS

We recruited 54 patients with Sjögren's syndrome dry eye (SSDE), 50 patients with non-Sjögren's syndrome dry eye (NSSDE), and 46 healthy controls. Tear film breakup time (TBUT), Schirmer I test, and fluorescein staining (FL) were performed on all subjects. Tear samples were obtained to analyze the inflammatory cytokine levels of IL-1β and IL-18 via enzyme-linked immunosorbent (ELISA). Conjunctival impression cytology (CIC) specimens were collected to detect the mRNA expression of NLRP3, caspase-1, IL-1β, and IL-18 using quantitative RT-PCR, and the protein expression of NLRP3 and caspase-1 by Western blotting.

RESULTS

NLRP3 mRNA expression showed higher levels in both dry eye groups compared with controls, with a comparably significant elevation in the SSDE group (relative 2.47-fold upregulation, p<0.05). NLRP3 protein expression was also increased in SSDE group (relative1.94-fold upregulation) compared with the controls. mRNA expression of caspase-1 was significantly upregulated in both SSDE (relative 1.44-fold upregulation, p<0.05) and NSSDE (relative 1.32-fold upregulation, p<0.05). Procaspase-1 protein level was increased in SSDE (relative 1.84-fold upregulation) and NSSDE (relative 1.12-fold upregulation) versus controls; and caspase-1 protein expression was also increased in SSDE (relative 1.49-fold upregulation) and NSSDE (relative 1.17-fold upregulation) compared with the controls. The patients with SSDE and NSSDE had higher IL-1β and IL-18 mRNA values and protein expressions than the controls did. The relative mRNA expression of IL-1β upregulated 3.59-fold (p<0.001) in SSDE and 2.13-fold (p<0.01) in NSSDE compared with the controls. IL-1β protein level also showed significant upregulation in SSDE (p=0.01; vs. controls groups). IL-18 mRNA expression levels were significantly upregulated in the SSDE (relative 2.97-fold upregulation, p=0.001) and NSSDE (relative 2.05-fold upregulation, p=0.001) groups compared with the controls; tear IL-18 concentrations were also significantly increased in the SSDE (p<0.001) and NSSDE (p<0.05) groups.

CONCLUSIONS

In the current study, we found that mRNA and protein expressions of NLRP3 inflammasome were upregulated in human dry eyes, especially in SSDE; the downstream inflammatory factors caspase-1, IL-1β, and IL-18 were also elevated in dry eye patients. These observations suggest the involvement of NLRP3 inflammasome in the onset and development of the inflammation in dry eye.

The inflammasome and lupus: another innate immune mechanism contributing to disease pathogenesis?

PURPOSE OF REVIEW

The role of innate immunity in systemic lupus erythematosus (SLE) has been a rapidly expanding area of research over the last decade. Included in this rubric is the concept that activation of the inflammasome, a molecular complex that activates caspase-1 and in turn the cytokines IL-1β and IL-18, is important in lupus pathogenesis. This review will summarize the recent discoveries exploring the role of the inflammasome machinery in SLE.

RECENT FINDINGS

Immune complexes can activate the NLRP3 inflammasome, and SLE-derived macrophages are hyper-responsive to innate immune stimuli, leading to enhanced activation of the inflammasome and production of inflammatory cytokines. Work in several murine models suggests an important role for the NLRP3 inflammasome in mediating lupus nephritis. Caspase-1, the central enzyme of the inflammasome, is essential for the development of type I interferon responses, autoantibody production, and nephritis in the pristane model of lupus. The absence of melanoma 2 inflammasome may have protective and pathogenic roles in SLE.

SUMMARY

Recent evidence suggests that the inflammasome machinery is dysregulated in SLE, plays an important role in promotion of organ damage, and may mediate cross-talk between environmental triggers and the development of lupus. Further research should focus on whether inhibition of inflammasome components may serve as a viable target for therapeutic development in SLE.

Processing of Neutrophil α-Defensins Does Not Rely on Serine Proteases In Vivo

The α-defensins, human neutrophil peptides (HNPs) are the predominant antimicrobial peptides of neutrophil granules. They are synthesized in promyelocytes and myelocytes as proHNPs, but only processed in promyelocytes and stored as mature HNPs in azurophil granules. Despite decades of search, the mechanisms underlying the posttranslational processing of neutrophil defensins remain unidentified. Thus, neither the enzyme that processes proHNPs nor the localization of processing has been identified. It has been hypothesized that proHNPs are processed by the serine proteases highly expressed in promyelocytes: Neutrophil elastase (NE), cathepsin G (CG), and proteinase 3 (PR3), all of which are able to process recombinant proHNP into HNP in vitro. We investigated whether serine proteases are in fact responsible for processing of proHNP in human bone marrow cells and in human and murine myeloid cell lines. Subcellular fractionation of the human promyelocytic cell line PLB-985 demonstrated proHNP processing to commence in fractions containing endoplasmic reticulum. Processing of ³⁵S-proHNP was insensitive to serine protease inhibitors. Simultaneous knockdown of NE, CG, and PR3 did not decrease proHNP processing in primary human bone marrow cells. Furthermore, introduction of NE, CG, and PR3 into murine promyelocytic cells did not enhance the proHNP processing capability. Finally, two patients suffering from Papillon–Lefèvre syndrome, who lack active neutrophil serine proteases, demonstrated normal levels of fully processed HNP in peripheral neutrophils. Contradicting earlier assumptions, our study found serine proteases dispensable for processing of proHNPs in vivo. This calls for study of other protease classes in the search for the proHNP processing protease(s).

Comprehensive metabolomics identifies the alarmin uric acid as a critical signal for the induction of peanut allergy

BACKGROUND

Food allergy, in particular peanut allergy, is a growing concern in Western countries. The prevalence of allergy to peanut, which currently stands at 1.4%, nearly tripled between 1997 and 2008. Allergic sensitization is a particularly difficult process to study as it is clinically silent. We sought to identify key pathways and mediators critically involved in the induction of allergic sensitization to peanut.

METHODS

Comprehensive metabolomics analysis with liquid chromatography-mass spectrometry was used to detect metabolite changes in mice (C57BL/6) undergoing sensitization. Loss-of-function and gain-of-function studies were performed in mice subjected to two models of peanut sensitization and anaphylaxis that involved either oral or epicutaneous sensitization. Flow cytometric analyses on dendritic cells (DCs) in vitro and in vivo were used to investigate the mechanisms of immune activation.

RESULTS

Elevated levels of uric acid (UA) were detected in mice undergoing sensitization as well as in peanut-allergic children who were not challenged with peanut. In mice, the depletion of UA during sensitization prevented the development of peanut-specific immunoglobulins IgE and IgG1 as well as anaphylaxis while exogenous delivery of UA crystals (monosodium urate, MSU) restored the allergic phenotype. Monosodium urate enhanced CD86 and OX40L expression on DCs, independent of Toll-like receptors 2 and 4, the NLRP3 inflammasome, and IL-1β, via a PI3K signaling pathway.

CONCLUSION

Overproduction of the UA alarmin in the local microenvironment plays a critical role in the induction of peanut-allergic sensitization, likely due to its ability to activate DCs. These finding suggest that cellular damage or tissue injury may be an essential requisite for the development of allergic sensitization to foods.

Role of the NLRP3 inflammasome in the transient release of IL-1β induced by monosodium urate crystals in human fibroblast-like synoviocytes

BACKGROUND

To investigate whether monosodium urate (MSU) crystals induce interleukin (IL)-1β in human fibroblast-like synoviocytes (FLS), and whether the NLRP3 inflammasome is involved in the inflammatory mechanism.

METHODS

Human FLS isolated from explants of synovial tissue were stimulated with MSU crystals (0.001 to 0.5 mg/ml) for different time course (6 hours to 48 hours). The expressions of IL-1β, IL-6, TNF-α and NLRP3 were evaluated with ELISA, Western blot and quantitative real-time PCR.

RESULTS

Exposure of FLS to MSU crystals transiently induced a significant increase in IL-1β expression in culture medium with a peak at 6 h. The mRNA level of IL-1β in the FLS cells had a similar pattern at this time point. Changes in IL-6 and TNF-α expression were not observed. Simultaneously, intercellular pro-IL-1β was detected at 6 h. Furthermore, MSU crystals also induced NLRP3 mRNA and protein expression at 6 h to 48 h after MSU treatment.

CONCLUSIONS

MSU crystals directly increased IL-1β and intercellular NLRP3 expression in FLS cells. It is suggested that the NLRP3 inflammasome may be associated with IL-1β in FLS treated with MSU. Altogether, MSU could induce production and release of IL-1β through the NLRP3 inflammasome in human synoviocytes.

Soluble uric acid increases NALP3 inflammasome and interleukin-1β expression in human primary renal proximal tubule epithelial cells through the Toll-like receptor 4-mediated pathway

Urate crystals activate innate immunity through Toll like receptor 4 (TLR4) activation, leading to the formation of the NACHT, LRR and PYD domains-containing protein 3 [NALP3; also known as NOD-like receptor family, pyrin domain containing 3 (NALP3) and cryopyrin] inflammasome, caspase-1 activation and interleukin (IL)-1β expression in gout. However, whether elevated serum uric acid (UA) levels are associated with the development and progression of renal diseases without renal urate crystal deposition remains unknown. In the present study, human primary renal proximal tubule epithelial cells were incubated with soluble UA (100 µg/ml) with or without the TLR4 inhibitor, TAK242 (1 µM). The gene expression and protein synthesis of TLR4, NALP3, caspase-1, IL-1β and intercellular adhesion molecule-1 (ICAM-1) were detected by real-time PCR, ELISA, western blot analysis and fluorescence-activated cell sorting (FACS), respectively. Soluble UA significantly enhanced TLR4, NALP3, caspase-1, IL-1β and ICAM-1 expression in the human primary renal proximal tubule epithelial cells. The TLR4 inhibitor, TAK242 effectively blocked the soluble UA-induced upregulation of TLR4, NALP3, caspase-1, IL-1β and ICAM-1 expression in the human primary renal proximal tubule epithelial cells. Our findings indicate that soluble UA enhances NALP3 expression, caspase-1 activation, IL-1β and ICAM-1 production in renal proximal tubule epithelial cells in a TLR4-dependent manner, suggesting the activation of innate immunity in human primary renal proximal tubule epithelial cells by soluble UA.

Uric Acid and Cardiovascular Events: A Mendelian Randomization Study

Obesity and diets rich in uric acid-raising components appear to account for the increased prevalence of hyperuricemia in Westernized populations. Prevalence rates of hypertension, diabetes mellitus, CKD, and cardiovascular disease are also increasing. We used Mendelian randomization to examine whether uric acid is an independent and causal cardiovascular risk factor. Serum uric acid was measured in 3315 patients of the Ludwigshafen Risk and Cardiovascular Health Study. We calculated a weighted genetic risk score (GRS) for uric acid concentration based on eight uric acid-regulating single nucleotide polymorphisms. Causal odds ratios and causal hazard ratios (HRs) were calculated using a two-stage regression estimate with the GRS as the instrumental variable to examine associations with cardiometabolic phenotypes (cross-sectional) and mortality (prospectively) by logistic regression and Cox regression, respectively. Our GRS was not consistently associated with any biochemical marker except for uric acid, arguing against pleiotropy. Uric acid was associated with a range of prevalent diseases, including coronary artery disease. Uric acid and the GRS were both associated with cardiovascular death and sudden cardiac death. In a multivariate model adjusted for factors including medication, causal HRs corresponding to each 1-mg/dl increase in genetically predicted uric acid concentration were significant for cardiovascular death (HR, 1.77; 95% confidence interval, 1.12 to 2.81) and sudden cardiac death (HR, 2.41; 95% confidence interval, 1.16 to 5.00). These results suggest that high uric acid is causally related to adverse cardiovascular outcomes, especially sudden cardiac death.

Mechanistic insights into xanthine oxidoreductase from development studies of candidate drugs to treat hyperuricemia and gout

Xanthine oxidoreductase (XOR), which is widely distributed from humans to bacteria, has a key role in purine catabolism, catalyzing two steps of sequential hydroxylation from hypoxanthine to xanthine and from xanthine to urate at its molybdenum cofactor (Moco). Human XOR is considered to be a target of drugs not only for therapy of hyperuricemia and gout, but also potentially for a wide variety of other diseases. In this review, we focus on studies of XOR inhibitors and their implications for understanding the chemical nature and reaction mechanism of the Moco active site of XOR. We also discuss further experimental or clinical studies that would be helpful to clarify remaining issues.

Case study: a case of debilitating gout in the 1st metatarsophalangeal joint

Gout is a painful arthritic condition that affects many people worldwide. The disease has been associated with hyperuricaemia and life style risk factors such as obesity, alcohol intake, meat and seafood consumption. We present a case of a 67-year-old male with a history of gout, who attended the clinic with a painful 1st metatarsophalangeal joint, which had progressively worsened in pain, mobility and deformity in the last 20 years. Although lifestyle changes had been advised by the GP some years earlier such as a low purine based diet, management had only consisted of NSAID's, which had not significantly improved symptoms. Surgical excision of chalky white material from around the 1st metatarsophalangeal joint rendered the patient symptom free with increased mobility after 6 weeks. Histopathology confirmed the excised tissue as gouty tophus. Following this, the patient was placed on allopurinol, a xanthine oxidase inhibitor to prevent recurrent attacks. This case study highlights the importance of early recognition and prophylactic management in gout sufferers. In joints where the disease process is well-established surgical excision of the gouty tophus may help mitigate further disease progression, and restore quality of life to individuals.

Inflammation: a possible mechanism for a causative role of hyperuricemia/gout in cardiovascular disease

Hyperuricemia and gout are independent risk factors associated with the development of hypertension, metabolic syndrome, vascular damage, and renal disease. Whether these risk factors are causally related to these important chronic co-morbidities remains uncertain, but inflammation may provide a mechanistic explanation. Hyperuricemia and gout negatively affect vascular function by exerting pro-oxidant effects and by decreasing nitric oxide bioavailability, thus inducing inflammation and endothelial dysfunction, which may promote hypertension, metabolic syndrome, and cardiovascular (CV) disease. This paper presents and discusses current understanding of the diverse influences promoting hyperuricemia and gout and the basis of acute and chronic hyperuricemia/gout-related inflammation. This review is based on a PubMed/Embase database search for articles on hyperuricemia and its impact on cardiovascular and renal function.

Contribution of mast cell-derived interleukin-1β to uric acid crystal-induced acute arthritis in mice

OBJECTIVE

Gouty arthritis is caused by the precipitation of monosodium urate monohydrate (MSU) crystals in the joints. While it has been reported that mast cells (MCs) infiltrate gouty tophi, little is known about the actual roles of MCs during acute attacks of gout. This study was undertaken to assess the role of MCs in a mouse model of MSU crystal-induced acute arthritis.

METHODS

We assessed the effects of intraarticular (IA) injection of MSU crystals in various strains of mice with constitutive or inducible MC deficiency or in mice lacking interleukin-1β (IL-1β) or other elements of innate immunity. We also assessed the response to IA injection of MSU crystals in genetically MC-deficient mice after IA engraftment of wild-type or IL-1β(-/-) bone marrow-derived cultured MCs.

RESULTS

MCs were found to augment acute tissue swelling following IA injection of MSU crystals in mice. IL-1β production by MCs contributed importantly to MSU crystal-induced tissue swelling, particularly during its early stages. Selective depletion of synovial MCs was able to diminish MSU crystal-induced acute inflammation in the joints.

CONCLUSION

Our findings identify a previously unrecognized role of MCs and MC-derived IL-1β in the early stages of MSU crystal-induced acute arthritis in mice.

The xanthine oxidase inhibitor Febuxostat reduces tissue uric acid content and inhibits injury-induced inflammation in the liver and lung

Necrotic cell death in vivo induces a robust neutrophilic inflammatory response and the resulting inflammation can cause further tissue damage and disease. Dying cells induce this inflammation by releasing pro-inflammatory intracellular components, one of which is uric acid. Cells contain high levels of intracellular uric acid, which is produced when purines are oxidized by the enzyme xanthine oxidase. Here we test whether a non-nucleoside xanthine oxidase inhibitor, Febuxostat (FBX), can reduce intracellular uric acid levels and inhibit cell death-induced inflammation in two different murine tissue injury models; acid-induced acute lung injury and acetaminophen liver injury. Infiltration of inflammatory cells induced by acid injection into lungs or peritoneal administration of acetaminophen was evaluated by quantification with flow cytometry and tissue myeloperoxidase activity in the presence or absence of FBX treatment. Uric acid levels in serum and tissue were measured before giving the stimuli and during inflammation. The impact of FBX treatment on the peritoneal inflammation caused by the microbial stimulus, zymosan, was also analyzed to see whether FBX had a broad anti-inflammatory effect. We found that FBX reduced uric acid levels in acid-injured lung tissue and inhibited acute pulmonary inflammation triggered by lung injury. Similarly, FBX reduced uric acid levels in the liver and inhibited inflammation in response to acetaminophen-induced hepatic injury. In contrast, FBX did not reduce inflammation to zymosan, and therefore is not acting as a general anti-inflammatory agent. These results point to the potential of using agents like FBX to treat cell death-induced inflammation.

The role of kinin B1 receptor and the effect of angiotensin I-converting enzyme inhibition on acute gout attacks in rodents

OBJECTIVE

Verify the role of the kinin B1 receptors (B1R) and the effect of ACE inhibitors (ACEi) on acute gout induced by monosodium urate (MSU) crystals in rodents.

METHODS

Painful (overt pain and allodynia) and inflammatory parameters (joint oedema, leukocyte trafficking, interleukin-1β levels) of acute gout attacks were assessed several hours after an intra-articular injection of MSU (1.25 or 0.5 mg/articulation) into the ankle of rats or mice, respectively. The role of B1R was investigated using pharmacological antagonism or gene deletion. Additionally, B1R immunoreactivity in ankle tissue and sensory neurons, kininase I activity and des-Arg(9)-bradykinin synovial levels were also measured. Similar tools were used to investigate the effects of ACEi on a low dose of MSU (0.0125 mg/articulation)-induced inflammation.

RESULTS

Kinin B1R antagonism or gene deletion largely reduced all painful and inflammatory signs of gout. Furthermore, MSU increased B1R expression in articular tissues, the content of the B1 agonist des-Arg(9)-bradykinin and the activity of the B1 agonist-forming enzyme kininase I. A low dose of MSU crystals, which did not induce inflammation in control animals, caused signs of acute gout attacks in ACEi-treated animals that were B1R-dependent.

CONCLUSIONS

Kinin B1R contributes to acute gouty attacks, including the ones facilitated by ACEi. Therefore, B1R is a potential therapeutic target for the treatment and prophylaxis of gout, especially in patients taking ACEi.

Inflammasomes

Inflammasomes are large cytosolic multiprotein complexes that assemble in response to detection of infection- or stress-associated stimuli and lead to the activation of caspase-1-mediated inflammatory responses, including cleavage and unconventional secretion of the leaderless proinflammatory cytokines IL-1β and IL-18, and initiation of an inflammatory form of cell death referred to as pyroptosis. Inflammasome activation can be induced by a wide variety of microbial pathogens and generally mediates host defense through activation of rapid inflammatory responses and restriction of pathogen replication. In addition to its role in defense against pathogens, recent studies have suggested that the inflammasome is also a critical regulator of the commensal microbiota in the intestine. Finally, inflammasomes have been widely implicated in the development and progression of various chronic diseases, such as gout, atherosclerosis, and metabolic syndrome. In this perspective, we discuss the role of inflammasomes in infectious and noninfectious inflammation and highlight areas of interest for future studies of inflammasomes in host defense and chronic disease.

HDL functionality and crystal-based sterile inflammation in atherosclerosis

Change is inevitable. In early evolution, due to the limited availability of resources, the sole purpose of living organisms was to survive long enough to transmit their genes to the next generation. During their short lifetime, organisms used pathogen-associated and damage-associated molecular pattern pathways as an inflammatory response against pathogens (exogenous factors) and tissue damage (endogenous factors), respectively. Despite advances in human lifespan, it appears that an increasing number of diseases such as atherosclerosis are associated with inflammation. Excessive glucose, lipid and protein intake leads to the formation of endogenous crystals, i.e., cholesterol, which can induce a sterile inflammatory immune response that manifests as a vicious cycle. In this review, we evaluate the possible relationship between crystal-based sterile inflammatory response and HDL functionality.

Artefactual nanoparticle activation of the inflammasome platform: in vitro evidence with a nano-formed calcium phosphate

AIM

To determine whether in vitro experimental conditions dictate cellular activation of the inflammasome by apatitic calcium phosphate nanoparticles.

MATERIAL & METHODS

The responses of blood-derived primary human cells to in situ-formed apatite were investigated under different experimental conditions to assess the effect of aseptic culture, cell rest and duration of particle exposure. Cell death and particle uptake were assessed, while IL-1β and caspase 1 responses, with and without lipopolysaccharide prestimulation, were evaluated as markers of inflammasome activation.

RESULTS

Under carefully addressed experimental conditions, apatitic nanoparticles did not induce cell death or engage the inflammasome platform, although both could be triggered through artefacts of experimentation.

CONCLUSION

In vitro studies often predict that engineered nanoparticles, such as synthetic apatite, are candidates for inflammasome activation and, hence, are toxic. However, the experimental setting must be very carefully considered as it may promote false-positive outcomes.

Uric acid accumulation in an Arabidopsis urate oxidase mutant impairs seedling establishment by blocking peroxisome maintenance

Purine nucleotides can be fully catabolized by plants to recycle nutrients. We have isolated a urate oxidase (uox) mutant of Arabidopsis thaliana that accumulates uric acid in all tissues, especially in the developing embryo. The mutant displays a reduced germination rate and is unable to establish autotrophic growth due to severe inhibition of cotyledon development and nutrient mobilization from the lipid reserves in the cotyledons. The uox mutant phenotype is suppressed in a xanthine dehydrogenase (xdh) uox double mutant, demonstrating that the underlying cause is not the defective purine base catabolism, or the lack of UOX per se, but the elevated uric acid concentration in the embryo. Remarkably, xanthine accumulates to similar levels in the xdh mutant without toxicity. This is paralleled in humans, where hyperuricemia is associated with many diseases whereas xanthinuria is asymptomatic. Searching for the molecular cause of uric acid toxicity, we discovered a local defect of peroxisomes (glyoxysomes) mostly confined to the cotyledons of the mature embryos, which resulted in the accumulation of free fatty acids in dry seeds. The peroxisomal defect explains the developmental phenotypes of the uox mutant, drawing a novel link between uric acid and peroxisome function, which may be relevant beyond plants.

Angiogenic and innate immune responses triggered by PRP in tendon cells are not modified by hyperuricemia

BACKGROUND

hyperuricemia is becoming a critical medical problem, and a current focus of research. Uric acid is also a death cell associated stressor that may trigger innate immune responses via the synthesis of inflammatory and angiogenic proteins.

PURPOSE

to investigate the angiogenic/inflammatory protein profile of tendon cells treated with Platelet Rich Plasma (PRP), and to assess if there are any differences in synthesis of angiogenic/inflammatory cytokines between PRP-treated or hyperuricemic PRP-treated cells.

METHODS

tendon cells were treated with PRP or hyperuricemic PRP and cell culture supernatants examined using glass based protein arrays for inflammation and angiogenesis. Relevant proteins were subsequently quantified by ELISA or EASIA methods.

RESULTS

the impact of PRP on angiogenesis and inflammation is evidenced by relevant cytokine synthesis including: Monocyte Chemoattractant Protein (MCP-1/CCL2), Regulated upon Activation Normally T cells Expressed and Secreted (RANTES/CCL5), IL-6/CXCL6, IL-8/CXCL8, Vascular Endothelial Growth Factor (VEGF), Growth Regulated Protein (GRO-a/CXCL1) and Hepatocyte Growth Factor (HGF). IL-1beta was not detected in these conditions. Taken together these data suggest an initial angiogenetic and innate immune responses driven by chemokines that is not altered by the presence of hyperuricemia, at this point, except for IL-8 secretion, p= 0.042.

Inflammasomes and metabolic disorders: old genes in modern diseases

Modern medical and hygienic practices have greatly improved human health and longevity; however, increased human life span occurs concomitantly with the emergence of metabolic and age-related diseases. Studies over the past decade have strongly linked host inflammatory responses to the etiology of several metabolic diseases including atherosclerosis, type 2 diabetes (T2D), obesity, and gout. A common immunological factor to these diseases is the activation of the inflammasome and release of proinflammatory cytokines that promote disease progression. Here we review the molecular mechanism(s) of inflammasome activation in response to metabolic damage-associated molecular patterns (DAMPs) and discuss potential targets for therapeutic intervention.

Possible implication of bacterial infection in acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Graft-versus-host disease (GVHD) is still one of the major causes of morbidity and mortality in allogeneic hematopoietic stem cell transplantation (HSCT). In the pathogenesis of acute GVHD, it has been established that donor-derived T-cells activated in the recipient play a major role in GVHD in initiation and maintenance within an inflammatory cascade. To reduce the risk of GVHD, intensification of GVHD prophylaxis like T-cell depletion is effective, but it inevitably increases the risk of infectious diseases and abrogates beneficial graft-versus-leukemia effects. Although various cytokines are considered to play an important role in the pathogenesis of GVHD, GVHD initiation is such a complex process that cannot be prevented by means of single inflammatory cytokine inhibition. Thus, efficient methods to control the whole inflammatory milieu both on cellular and humoral view are needed. In this context, infectious diseases can theoretically contribute to an elevation of inflammatory cytokines after allogeneic HSCT and activation of various subtypes of immune effector cells, which might in summary lead to an aggravation of acute GVHD. The appropriate treatments or prophylaxis of bacterial infection during the early phase after allogeneic HSCT might be beneficial to reduce not only infectious-related but also GVHD-related mortality. Here, we aim to review the literature addressing the interactions of bacterial infections and GVHD after allogeneic HSCT.

Psoriasis, psoriatic arthritis and risk of gout in US men and women

BACKGROUND AND OBJECTIVE

Individuals with psoriasis have increased blood levels of uric acid. However, there is no prospective data on the association between psoriasis and uric acid levels and subsequent development of gout. In this study, we examined the risk of gout among individuals with psoriasis and psoriatic arthritis (PsA) in two cohorts of men and women, the Health Professionals Follow-up Study (HPFS) (1986-2010) and Nurses' Health Study (NHS) (1998-2010).

METHODS

27 751 men and 71 059 women were included in the analysis. Lifetime history of physician-diagnosed incident psoriasis and PsA was confirmed by validated supplementary questionnaires. Incident gout diagnoses were confirmed based on the American College of Rheumatology survey criteria. We used Cox proportional hazards models controlling for potential risk factors to calculate the HRs with 95% CIs of incident gout while simultaneously adjusting for several common risk factors.

RESULTS

We documented 2217 incident cases of gout during follow-up. Psoriasis was associated with an increased risk of subsequent gout with a multivariate HR of 1.71 (95% CI 1.36 to 2.15) in the pooled analysis. Risk of gout was substantially augmented among those with psoriasis and concomitant PsA (pooled multivariate HR: 4.95, 95% CI 2.72 to 9.01) when compared to participants without psoriasis.

CONCLUSIONS

In this prospective study of US women and men, psoriasis and PsA were associated with an increased risk of gout.

Clec12a is an inhibitory receptor for uric acid crystals that regulates inflammation in response to cell death

Recognition of cell death by the innate immune system triggers inflammatory responses. However, how these reactions are regulated is not well understood. Here, we identify the inhibitory C-type lectin receptor Clec12a as a specific receptor for dead cells. Both human and mouse Clec12a could physically sense uric acid crystals (monosodium urate, MSU), which are key danger signals for cell-death-induced immunity. Clec12a inhibited inflammatory responses to MSU in vitro, and Clec12a-deficient mice exhibited hyperinflammatory responses after being challenged with MSU or necrotic cells and after radiation-induced thymocyte killing in vivo. Thus, we identified a negative regulatory MSU receptor that controls noninfectious inflammation in response to cell death that has implications for autoimmunity and inflammatory disease.

Danger signals - damaged-self recognition across the tree of life

Multicellular organisms suffer injury and serve as hosts for microorganisms. Therefore, they require mechanisms to detect injury and to distinguish the self from the non-self and the harmless non-self (microbial mutualists and commensals) from the detrimental non-self (pathogens). Danger signals are "damage-associated molecular patterns" (DAMPs) that are released from the disrupted host tissue or exposed on stressed cells. Seemingly ubiquitous DAMPs are extracellular ATP or extracellular DNA, fragmented cell walls or extracellular matrices, and many other types of delocalized molecules and fragments of macromolecules that are released when pre-existing precursors come into contact with enzymes from which they are separated in the intact cell. Any kind of these DAMPs enable damaged-self recognition, inform the host on tissue disruption, initiate processes aimed at restoring homeostasis, such as sealing the wound, and prepare the adjacent tissues for the perception of invaders. In mammals, antigen-processing and -presenting cells such as dendritic cells mature to immunostimulatory cells after the perception of DAMPs, prime naïve T-cells and elicit a specific adaptive T-/B-cell immune response. We discuss molecules that serve as DAMPs in multiple organisms and their perception by pattern recognition receptors (PRRs). Ca(2+)-fluxes, membrane depolarization, the liberation of reactive oxygen species and mitogen-activated protein kinase (MAPK) signaling cascades are the ubiquitous molecular mechanisms that act downstream of the PRRs in organisms across the tree of life. Damaged-self recognition contains both homologous and analogous elements and is likely to have evolved in all eukaryotic kingdoms, because all organisms found the same solutions for the same problem: damage must be recognized without depending on enemy-derived molecules and responses to the non-self must be directed specifically against detrimental invaders.

Hyperuricaemia in the Pacific: why the elevated serum urate levels?

Pacific Island populations, particularly those of Polynesian descent, have a high prevalence of hyperuricaemia and gout. This is due to an inherently higher urate level among these populations with a demonstrated genetic predisposition. While an excess of urate can cause pathology, urate is also important for human health. It has been implicated as an antioxidant, has a neuroprotective role and is involved in innate immune responses. This paper provides a brief review of urate levels worldwide, with a particular focus on island Southeast Asia and the Pacific. We then present possible evolutionary explanations for the elevated serum urate levels among Pacific populations in the context of the physiological importance of urate and of the settlement history of the region. Finally, we propose that ancestry may play a significant role in hyperuricaemia in these populations and that exposure to malaria prior to population expansion into the wider Pacific may have driven genetic selection for variants contributing to high serum urate.