Suppression of monosodium urate crystal-induced inflammation by inhibiting TGF-ß-activated kinase 1-dependent signaling: role of the ubiquitin proteasome system.

Monosodium urate (MSU) crystals activate inflammatory pathways that overlap with interleukin-1ß (IL-1ß) signaling. However, the post-translational mechanisms involved and the role of signaling proteins in this activation are unknown. In the present study, we investigated the intracellular signaling mechanisms involved in MSU-induced activation of THP-1 macrophages and human nondiseased synovial fibroblasts (NLSFs) and the in vivo efficacy of an inhibitor of tumor growth factor-ß (TGF-ß)-activated kinase 1 (TAK1), 5Z-7-oxozeaenol, in MSU-induced paw inflammation in C57BL/6 mice. THP-1 macrophage activation with MSU crystals (25-200 µg/ml) resulted in the rapid and sustained phosphorylation of interleukin-1 receptor-activated kinase 1 (IRAK1 Thr209) and TAK1 (Thr184/187) and their association with the E3 ubiquitin ligase TRAF6. At the cellular level, MSU inhibited the deubiquitinases A20 and UCHL2 and increased 20s proteasomal activity, leading to a global decrease in K63-linked ubiquitination and increase in K48-linked ubiquitination in THP-1 macrophages. While MSU did not stimulate cytokine production in NLSFs, it significantly amplified IL-1ß-induced IL-6, IL-8, and ENA-78/CXCL5 production. Docking studies and MD simulations followed by TAK1 in vitro kinase assays revealed that uric acid molecules are capable of arresting TAK1 in an active-state conformation, resulting in sustained TAK1 kinase activation. Importantly, MSU-induced proinflammatory cytokine production was completely inhibited by 5Z-7-oxozeaenol but not IRAK1/4 or TRAF6 inhibitors. Administration of 5Z-7-oxozeaenol (5 or 15 mg/kg; orally) significantly inhibited MSU-induced paw inflammation in C57BL/6 mice. Our study identifies a novel post-translational mechanism of TAK1 activation by MSU and suggests the therapeutic potential of TAK1 in regulating MSU-induced inflammation.

Xanthine oxidase inhibitory peptides derived from tuna protein: virtual screening, inhibitory activity, and molecular mechanisms.

BACKGROUND: There has been growing interest in the use of xanthine oxidase (XO) as a therapeutic agent to prevent gout and hyperuricemia. In the present study, XO inhibitory peptides were identified from tuna protein by virtual screening, and molecular docking was used to elicit the interaction mechanism between XO and peptides. RESULTS: A novel tetrapeptide, EEAK, exhibited high XO inhibitory activity with an IC50 of 173.00 ± 0.06 µM. Molecular docking analysis revealed that EEAK bound with the pivotal residues of XO's active sites (i.e., Glu802, Arg880, Glu1261) through two conventional hydrogen bond interactions, two attractive charge interactions, and one salt bridge. EEAK could also bind with the residues Phe649, Leu648, Lys771, Ser876, Phe914, and Thr1010 of XO. CONCLUSION: This study suggested that conventional hydrogen bond interactions and electrostatic interactions play an important role in XO inhibition. The novel XO inhibitory peptide EEAK from tuna protein could be used as potential candidate for controlling gout and hyperuricemia. © 2020 Society of Chemical Industry.

Xanthine oxidase inhibitors: patent landscape and clinical development (2015-2020).

INTRODUCTION: Xanthine oxidase (XO) is a molybdoflavoprotein that catalyzes the oxidative hydroxylation of purines to produce uric acid and reactive oxygen species. These reaction products can cause severe disease conditions like hyperuricemia which makes XO enzyme, an important therapeutic target in diseases like gout. AREAS COVERED: Herein, patents from 2015 to 2020 are discussed to disclose the synthetic, as well as natural compounds, claimed to inhibit XO enzyme. The article also presents the last five years of clinical progression of some prominent XO inhibitors. EXPERT OPINION: There has been considerable creativity in the discovery of novel XO inhibitors in the last five years that falls outside the purine scaffold. Along with the evaluation of synthetic compounds, natural compounds can also be an area of interest for the discovery of novel XO inhibitors. Based on the patent literature of last five years, we can expect a burst of novel alternate compounds in the near future which could have the ability to reduce the uric acid level, by inhibiting XO enzyme in patients, which at the moment are striving hard to fight against the dreadful disease condition like gout.

The net clinical benefits of febuxostat versus allopurinol in patients with gout or asymptomatic hyperuricemia - A systematic review and meta-analysis.

BACKGROUND AND AIMS: Systemic reviews and meta-analyses suggest hyperuricemia is a cardiovascular risk factor. The effects of xanthine oxidase inhibitors on cardiac outcomes remain unclear. We assessed the effects of febuxostat and allopurinol on mortality and adverse reactions in adult patients with hyperuricemia. METHODS AND RESULTS: PubMed and EMBASE were searched to retrieve randomized controlled trials of febuxostat and allopurinol from January 2005 to July 2018. The meta-analysis consisted of 13 randomized controlled trials with a combined sample size of 13,539 patients. Febuxostat vs. allopurinol was not associated with an increased risk of cardiac-related mortality in the overall population (OR: 0.72, 95% CI: 0.24-2.13, P = 0.55). Regarding adverse skin reactions, the patients receiving febuxostat had significantly fewer adverse skin reactions than those receiving allopurinol treatment (OR: 0.50, 95% CI: 0.30-085, P = 0.01). Compared with allopurinol, febuxostat was associated with an improved safety outcome of cardiac-related mortality and adverse skin reactions (OR: 0.72, 95% CI: 0.55-0.96, P = 0.02). The net clinical outcome, composite of incident gout and the safety outcome, was not different significantly in the patients receiving febuxostat or allopurinol (OR: 1.04, 95% CI: 0.76-0.1.42, P = 0.79). In sensitivity analyses, a borderline significance was found in the patients randomized to febuxostat vs. allopurinol regarding cardiac-related mortality (OR: 1.29, 95% CI: 1.00-1.67, P = 0.05) after the CARES study was included. CONCLUSION: Febuxostat vs. allopurinol was associated with the improved safety outcome and have comparable mortality and net clinical outcome in patients with hyperuricemia. REGISTRATION NUMBER: PROSPERO(CRD42018091657).

Gout in males: a possible role for COMT hypomethylation.

OBJECTIVE: Gout is a common inflammatory disease, and the prevalence of gout in men is significantly higher than in women. Catechol-O-methyltransferase (COMT) regulates dopamine activity and metabolism, thereby participating in the uric acid metabolism, which in turn affects the occurrence of gout. Our study aimed to investigate the association between COMT methylation and gout in men. METHODS: This study involved 57 male gout patients and 103 age-matched healthy men. We used quantitative methylation-specific polymerase chain reaction (qMSP) to determine DNA methylation levels in the blood. The COMT methylation level was represented by the percentage of methylation reference (PMR). RESULTS: Our results showed that COMT methylation levels were significantly lower in gout patients than in the control group (median PMR 9.50 vs 31.34, p = 3E-5). The area under the curve (AUC) was 0.701 (95% CI 0.611-0.790, p = 2.7E-5) with a sensitivity of 68% and a specificity of 68.4%. CONCLUSION: Our study found that there was a significant correlation between COMT hypomethylation and the risk of gout in males, and this provides an epigenetic mechanism of COMT in gout. COMT hypomethylation might be used as a potential diagnostic biomarker for gout in the future.

Xanthine oxidase inhibitors for prevention of cardiovascular events: a systematic review and meta-analysis of randomized controlled trials.

BACKGROUND: Xanthine oxidase inhibitors (XOI), classified as purine-like (allopurinol and oxypurinol) and non-purine (febuxostat and topiroxostat) XOI, present antioxidant properties by reducing the production of reactive oxygen species derived from purine metabolism. Oxidative stress is an important factor related to endothelial dysfunction and ischemia-reperfusion injury, and may be implicated in the pathogenesis of heart failure, hypertension, and ischemic heart disease. However, there is contradictory evidence regarding the possible cardiovascular (CV) protective effect exerted by XOI. Our objective is to compare the incidence of major adverse cardiovascular events (MACE), mortality, total (TCE) and specific CV events in randomized controlled trials (RCTs) testing XOI against placebo or no treatment. METHODS: PubMed, EMBASE, Web of Science, Cochrane Central, Lilacs databases were searched from inception to Dec 30 2016, along with hand searching. RCTs including exclusively adult individuals, lasting ≥ 4 weeks, with no language restriction, were eligible. Independent paired researchers selected studies and extracted data. Considering the expected rarity of events, Peto and DerSimonian/Laird odds ratios (OR), the latter in case of heterogeneity, were used for analysis. Random-effects meta-regression was used to explore heterogeneity. RESULTS: The analysis of MACE included 81 articles (10,684 patients, 6434 patient-years). XOI did not significantly reduce risk of MACE (ORP = 0.71, 95% CI 0.46-1.09) and death (0.89, 0.59-1.33), but reduced risk of TCE (0.60, 0.44-0.82; serious TCE: 0.64, 0.46 to 0.89), and hypertension (0.54, 0.37 to 0.80). There was protection for MACE in patients with previous ischemic events (0.42, 0.23-0.76). Allopurinol protected for myocardial infarction (0.38, 0.17-0.83), hypertension (0.32, 0.18-0.58), TCE (0.48, 0.31 to 0.75, I2 = 55%) and serious TCE (0.56, 0.36 to 0.86, I2 = 44%). Meta-regression associated increasing dose of allopurinol with higher risk of TCE and serious TCE (P < 0.05). Accordingly, lower doses (≤ 300 mg/day) of allopurinol reduced the risk of TCE, unlike higher doses. Non-purine-like XOI did not significantly reduce or increase the risk of adverse CV events, but confidence intervals were wide. Quality of evidence was generally low to moderate. CONCLUSIONS: Purine-like XOI may reduce the incidence of adverse CV outcomes. However, higher doses of allopurinol (> 300 mg/day) may be associated with loss of CV protection.

Synthesis and evaluation of sulfonamide derivatives as potent Human Uric Acid Transporter 1 (hURAT1) inhibitors.

This letter presents synthesis and structure-activity relationship study of sulfonamide derivatives as inhibitors of Human Uric Acid Transporter 1 (hURAT1). Among all tested sulfonamide derivatives, compounds 9b, 16i and 19b exhibited excellent inhibition activity with IC50 value of 10, 2, and 83nM, respectively. In addition, compounds 9b and 19b demonstrated moderate PK profile in rats.

COX-2/mPGES-1/PGE2 cascade activation mediates uric acid-induced mesangial cell proliferation.

Hyperuricemia is not only the main feature of gout but also a cause of gout-related organ injuries including glomerular hypertrophy and sclerosis. Uric acid (UA) has been proven to directly cause mesangial cell (MC) proliferation with elusive mechanisms. The present study was undertaken to examined the role of inflammatory cascade of COX-2/mPGES-1/PGE2 in UA-induced MC proliferation. In the dose- and time-dependent experiments, UA increased cell proliferation shown by the increased total cell number, DNA synthesis rate, and the number of cells in S and G2 phases in parallel with the upregulation of cyclin A2 and cyclin D1. Interestingly, UA-induced cell proliferation was accompanied with the upregulation of COX-2 and mPGES-1 at both mRNA and protein levels. Strikingly, inhibition of COX-2 via a specific COX-2 inhibitor NS-398 markedly blocked UA-induced MC proliferation. Meanwhile, UA-induced PGE2 production was almost entirely abolished. Furthermore, inhibiting mPGES-1 by a siRNA approach in MCs also ameliorated UA-induced MC proliferation in line with a significant blockade of PGE2 secretion. More importantly, in gout patients, we observed a significant elevation of urinary PGE2 excretion compared with healthy controls, indicating a translational potential of this study to the clinic. In conclusion, our findings indicated that COX-2/mPGES-1/PGE2 cascade activation mediated UA-induced MC proliferation. This study offered new insights into the understanding and the intervention of UA-related glomerular injury.

An updated patent review: xanthine oxidase inhibitors for the treatment of hyperuricemia and gout (2011-2015).

INTRODUCTION: Xanthine oxidase (XO) is a versatile molybdoflavoprotein, widely distributed, occurring in milk, kidney, lung, heart, and vascular endothelium. Catalysis by XO to produce uric acid and reactive oxygen species leads to many diseases. Anti hyperuricemic therapy by xanthine oxidase inhibitors has been mainly employed for the treatment of gout. Area covered: This review covers the patent literature (2011-2015) and also presents the interesting strategies/rational approaches employed for the design of xanthine oxidase inhibitors reported recently. Expert opinion: Recent literature indicates that various non purine scaffolds have been extensively investigated for xanthine oxidase inhibition. The significant potential endowed by heteroaryl based compounds, in particularly fused heterocycles clearly highlights their clinical promise and the need for detailed investigation. Studies by various research groups have also revealed that the flavone framework is open for isosteric replacements and structural modifications for yielding potent non purine xanthine oxidase inhibitors. In addition, various plant extracts recently reported to possess significant xanthine oxidase inhibitory potential presents enough promise to initiate a screening program for the identification of other plant extracts and phytoconstituents possessing inhibitory potential towards the enzyme.

Xanthine oxidoreductase and its inhibitors: relevance for gout.

Xanthine oxidoreductase (XOR) is the rate-limiting enzyme in purine catabolism and converts hypoxanthine to xanthine, and xanthine into uric acid. When concentrations of uric acid exceed its biochemical saturation point, crystals of uric acid, in the form of monosodium urate, emerge and can predispose an individual to gout, the commonest form of inflammatory arthritis in men aged over 40 years. XOR inhibitors are primarily used in the treatment of gout, reducing the formation of uric acid and thereby, preventing the formation of monosodium urate crystals. Allopurinol is established as first-line therapy for gout; a newer alternative, febuxostat, is used in patients unable to tolerate allopurinol. This review provides an overview of gout, a detailed analysis of the structure and function of XOR, discussion on the pharmacokinetics and pharmacodynamics of XOR inhibitors-allopurinol and febuxostat, and the relevance of XOR in common comorbidities of gout.

Intercritical circulating levels of neo-epitopes reflecting matrixmetalloprotease-driven degradation as markers of gout and frequent gout attacks.

OBJECTIVE: Recurrent flares constitute the main clinical burden of gout. Our aim was to assess whether biomarkers measuring MMP tissue degradation could be used as markers of frequent gout flares. METHODS: Fasting plasma samples from 112 men with gout and 170 controls, along with serum samples from 447 men with gout collected at baseline from an ongoing clinical trial, were analysed by ELISA for neo-epitopes from MMP degradation of collagens type I (C1M) and type III (C3M). The log10 levels of both markers were compared between cases and controls and between gout patients with three or more gout attacks in the past year and those with two or less attacks. RESULTS: The circulating levels of C1M and C3M correlated with gout status in the case-control study. Levels of both markers were associated with frequent gout flares (⩾3 attacks in the past year) in both cohorts (odds ratio, OR = 3.1; 95% CI: 1.4, 6.8; P = 0.0056 for log10C1M, and OR = 6.7; 95% CI: 2.3, 19.3; P = 0.0005 for log10C3M). The area under the curve in a receiver operating characteristic analysis of frequent flares increased from 0.68 to 0.74 in one cohort and from 0.60 to 0.66 in the other when log10C1M and log10C3M were added to clinical variables of the model. CONCLUSION: C1M and C3M, reflective of interstitial matrix destruction, are associated with gout status and with frequent gout flares in men, suggesting that increased MMP activity may contribute to gout flares. Further research is needed to find out whether this is independent of dietary and lifestyle risk factors for acute gout.

AMP-activated protein kinase suppresses urate crystal-induced inflammation and transduces colchicine effects in macrophages.

OBJECTIVE: AMP-activated protein kinase (AMPK) is metabolic biosensor with anti-inflammatory activities. Gout is commonly associated with excesses in soluble urate and in nutrition, both of which suppress tissue AMPK activity. Gout is driven by macrophage-mediated inflammation transduced partly by NLRP3 inflammasome activation and interleukin (IL)-1ß release. Hence, we tested the hypothesis that AMPK activation limits monosodium urate (MSU) crystal-induced inflammation. METHODS: We studied bone marrow-derived macrophages (BMDMs) from AMPKα1 knockout and wild-type mice, and assessed the selective AMPK pharmacological activator A-769662 and a low concentration (10 nM) of colchicine. We examined phosphorylation (activation) of AMPKα Thr172, NLRP3 mRNA expression, and caspase-1 cleavage and IL-1ß maturation using western blot and quantitative RT-PCR approaches. We also assessed subcutaneous murine air pouch inflammatory responses to MSU crystals in vivo. RESULTS: MSU crystals suppressed phosphorylation of AMPKα in BMDMs. Knockout of AMPKα1 enhanced, and, conversely, A-769662-inhibited MSU crystal-induced inflammatory responses including IL-1ß and CXCL1 release in vitro and in vivo. A-769662 promoted AMPK-dependent macrophage anti-inflammatory M2 polarisation and inhibited NLRP3 gene expression, activation of caspase-1 and IL-1ß. Colchicine, at low concentration (10 nM) achieved in gout flare prophylaxis dosing, promoted phosphorylation of AMPKα and macrophage M2 polarisation, and reduced activation of caspase-1 and release of IL-1ß and CXCL1 by MSU crystals in BMDMs in vitro. CONCLUSIONS: AMPK activity limits MSU crystal inflammation in vitro and in vivo, and transduces multiple anti-inflammatory effects of colchicine in macrophages. Targeting increased and sustained AMPK activation in inflammatory cells merits further investigation for enhancing efficacy of prophylaxis and treatment of gouty inflammation.

Increase in thyroid stimulating hormone levels in patients with gout treated with inhibitors of xanthine oxidoreductase.

Increase in thyroid stimulating hormone (TSH) levels over the upper normal limit has been reported in a small percentage of patients treated with febuxostat in clinical trials, but a mechanistic explanation is not yet available. In an observational parallel longitudinal cohort study, we evaluated changes in TSH levels in patients with gout at baseline and during urate-lowering treatment with febuxostat. Patients to be started on allopurinol who had a measurement of TSH in the 6-month period prior to baseline evaluation were used for comparison. TSH levels and change in TSH levels at 12-month follow-up were compared between groups. Patients with abnormal TSH levels or previous thyroid disease or on amiodarone were not included for analysis. Eighty-eight patients treated with febuxostat and 87 with allopurinol were available for comparisons. Patients to be treated with febuxostat had higher urate levels and TSH levels, more severe gout, and poorer renal function, but were similar regarding other characteristics. A similar rise in TSH levels was observed in both groups (0.4 and 0.5 µUI/mL for febuxostat and allopurinol, respectively); at 12-mo, 7/88 (7.9 %) of patients on febuxostat and 4/87 (3.4 %) of patients on allopurinol showed TSH levels over 0.5 µUI/mL. Doses prescribed (corrected for estimated glomerular filtration rate in the case if patients on allopurinol) and baseline TSH levels were determinants of TSH levels at 12-month follow-up. No impact on free T4 (fT4) levels was observed. Febuxostat, but also allopurinol, increased TSH levels in a dose-dependent way, thus suggesting rather a class effect than a drug effect, but with no apparent impact on either clinical or fT4 levels.

[Association of single nucleotide polymorphisms of cytochrome P450 gene with susceptibility to gout in ethnic Han males from coastal regions of Shandong province].

OBJECTIVE: To assess the association of cytochrome P450 gene single nucleotide polymorphisms (SNPs) with susceptibility to gout in ethnic Han males from coastal regions of Shandong province. METHODS: Four hundred and eighty male patients with gout and 480 healthy male controls were included. Genotyping was carried out with a custom Illumina GoldenGate Genotyping assay to detect SNP rs2275620 of CYP2C8 gene, SNP rs2070676 of CYP2E1 gene, SNP rs837395 of CYP4B1 gene, and SNP rs194150 of TBXAS1 gene. The association was assessed with chi-square test. RESULTS: No significant difference has been found between the two groups in regard to the genotypic and allelic frequencies of the TT, AT, AA genotypes and A, T alleles of the SNP rs2275620 of the CYP2C8 gene (P=0.88; P=0.97), the CC, CG, GG genotypes and C,G alleles of SNP rs2070676 of the CYP2E1 gene (P=0.24; P=0.09), the TT, AT, AA genotypes and A, T alleles of SNP rs837395 of the CYP4B1 (P=0.88; P=0.97), and TT, AT, AA genotypes and the A,T alleles of SNP rs194150 of TBXAS1 gene (P=0.15; P=0.06). CONCLUSION: This study has identified no association of SNP loci rs2275620(A/T) of CYP2C8, rs2070676(C/G) of CYP2E1, rs837395(A/T) of CYP4B1 and rs194150(A/T) of TBXAS1 with gout in ethnic Han males from coastal regions in Shandong province. However, our result needs to be replicated in larger sets of patients collected from other regions and populations.

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.

An allopurinol-controlled, multicenter, randomized, double-blind, parallel between-group, comparative study of febuxostat in Chinese patients with gout and hyperuricemia.

AIM: Febuxostat, a novel non-purine selective inhibitor of xanthine oxidase, has been identified as a potential alternative to allopurinol in patients with hyperuricemia. The purpose of this study was to compare the urate-lowering (UL) efficacy and safety of daily febuxostat and allopurinol in Chinese gout patients with hyperuricemia. METHODS: Gout patients (n = 512) with serum uric acid (sUA) concentrations of at least 8.0 mg/dL were randomized to receive daily febuxostat 40 mg or 80 mg or allopurinol 300 mg for 28 weeks. Prophylaxis against gout flares with meloxicam or colchicine was provided during weeks 1 through 8. The primary endpoint was the percentage of subjects achieving a sUA concentration of <6.0 mg/dL at the last three monthly measurements. RESULTS: The primary endpoint was reached in 44.77% of patients receiving 80 mg of febuxostat, 27.33% of those receiving 40 mg of febuxostat, and 23.84% of those receiving allopurinol. The UL efficacy in the febuxostat 80 mg group was higher than in the allopurinol (P < 0.0001) and febuxostat 40 mg (P = 0.0008) groups. The UL efficacy of the febuxostat 40 mg group was statistically non-inferior to that of the allopurinol group. No significant change in the number of tophi was observed during the final visit relative to baseline in each treatment group. The rate of gout flares requiring treatment from weeks 9 through 28 and the incidence of adverse events was similar among treatment groups. CONCLUSIONS: The UL efficacy of daily febuxostat 80 mg was greater than that of febuxostat 40 mg and allopurinol 300 mg, which exhibited comparable UL efficacy. Safety of febuxostat and allopurinol was comparable at the doses tested.

Caspase-1 level in synovial fluid is high in patients with spondyloarthropathy but not in patients with gout.

Activation of caspase-1 by NALP3 inflammasomes has been shown to be important in initiating acute gouty arthritis. The objectives of this study were to measure the levels of caspase-1 in synovial fluid in gout and various arthritides, and to elucidate the clinical significance of caspase-1 levels in synovial fluid. Caspase-1, IL-1ß, IL-18, and uric acid were measured in synovial fluid from 112 patients with gout and other arthritides, such as rheumatoid arthritis, osteoarthritis, and spondyloarthropathy. Caspase-1 in synovial fluid from patients with crystal-induced arthritis, inflammatory arthritis, osteoarthritis, and spondyloarthropathy was 35.9 ± 86.7, 49.7 ± 107.7, 2.1 ± 7.0, and 152.6 ± 155.7 pg/mL, respectively. The mean level and the frequency of high levels (≥125 pg/mL) of caspase-1 in spondyloarthropathy were significantly higher than those in the other arthritides including gout. Caspase-1 was detectible in the synovial fluid of patients with the various arthritides. Contrary to our hypothesis, the caspase-1 level in the synovial fluid of patients with gout was not higher than in that of other arthritides. High levels of caspase-1 may be helpful in differentiating spondyloarthropathy from other arthritides.

A small disturbance, but a serious disease: the possible mechanism of D52H-mutant of human PRS1 that causes gout.

Phosphoribosyl pyrophosphate synthetase isoform 1 (PRS1) has an essential role in the de novo and salvage synthesis of human purine and pyrimidine nucleotides. The dysfunction of PRS1 will dramatically influence nucleotides' concentration in patient's body and lead to different kinds of disorders (such as hyperuricemia, gout and deafness). The D52H missense mutation of PRS1 will lead to a conspicuous phosphoribosyl pyrophosphate content elevation in the erythrocyte of patients and finally induce hyperuricemia and serious gout. In this study, the enzyme activity analysis indicated that D52H-mutant possessed similar catalytic activity to the wild-type PRS1, and the 2.27 Å resolution D52H-mutant crystal structure revealed that the stable interaction network surrounding the 52 position of PRS1 would be completely destroyed by the substitution of histidine. These interaction variations would further influence the conformation of ADP-binding pocket of D52H-mutant and reduced the inhibitor sensitivity of PRS1 in patient's body.

ALDH16A1 is a novel non-catalytic enzyme that may be involved in the etiology of gout via protein-protein interactions with HPRT1.

Gout, a common form of inflammatory arthritis, is strongly associated with elevated uric acid concentrations in the blood (hyperuricemia). A recent study in Icelanders identified a rare missense single nucleotide polymorphism (SNP) in the ALDH16A1 gene, ALDH16A1*2, to be associated with gout and serum uric acid levels. ALDH16A1 is a novel and rather unique member of the ALDH superfamily in relation to its gene and protein structures. ALDH16 genes are present in fish, amphibians, protista, bacteria but absent from archaea, fungi and plants. In most mammalian species, two ALDH16A1 spliced variants (ALDH16A1, long form and ALDH16A1_v2, short form) have been identified and both are expressed in HepG-2, HK-2 and HK-293 human cell lines. The ALDH16 proteins contain two ALDH domains (as opposed to one in the other members of the superfamily), four transmembrane and one coiled-coil domains. The active site of ALDH16 proteins from bacterial, frog and lower animals contain the catalytically important cysteine residue (Cys-302); this residue is absent from the mammalian and fish orthologs. Molecular modeling predicts that both the short and long forms of human ALDH16A1 protein would lack catalytic activity but may interact with the hypoxanthine-guanine phosphoribosyltransferase (HPRT1) protein, a key enzyme involved in uric acid metabolism and gout. Interestingly, such protein-protein interactions with HPRT1 are predicted to be impaired for the long or short forms of ALDH16A1*2. These results lead to the intriguing possibility that association between ALDH16A1 and HPRT1 may be required for optimal HPRT activity with disruption of this interaction possibly contributing to the hyperuricemia seen in ALDH16A1*2 carriers.