Expert opinion on emerging urate-lowering therapies

Hyperuricemia and its related diseases: mechanisms and advances in therapy

Hyperuricemia, characterized by elevated levels of serum uric acid (SUA), is linked to a spectrum of commodities such as gout, cardiovascular diseases, renal disorders, metabolic syndrome, and diabetes, etc. Significantly impairing the quality of life for those affected, the prevalence of hyperuricemia is an upward trend globally, especially in most developed countries. UA possesses a multifaceted role, such as antioxidant, pro-oxidative, pro-inflammatory, nitric oxide modulating, anti-aging, and immune effects, which are significant in both physiological and pathological contexts. The equilibrium of circulating urate levels hinges on the interplay between production and excretion, a delicate balance orchestrated by urate transporter functions across various epithelial tissues and cell types. While existing research has identified hyperuricemia involvement in numerous biological processes and signaling pathways, the precise mechanisms connecting elevated UA levels to disease etiology remain to be fully elucidated. In addition, the influence of genetic susceptibilities and environmental determinants on hyperuricemia calls for a detailed and nuanced examination. This review compiles data from global epidemiological studies and clinical practices, exploring the physiological processes and the genetic foundations of urate transporters in depth. Furthermore, we uncover the complex mechanisms by which the UA induced inflammation influences metabolic processes in individuals with hyperuricemia and the association with its relative disease, offering a foundation for innovative therapeutic approaches and advanced pharmacological strategies.

Discovery of digallic acid as XOD/URAT1 dual target inhibitor for the treatment of hyperuricemia

The development of XOD/URAT1 dual target inhibitors has emerged as a promising therapeutic strategy for the management of hyperuricemia. Here, through virtual screening, we have identified digallic acid as a novel dual target inhibitor of XOD/URAT1 and subsequently evaluated its pharmacological properties, pharmacokinetics, and toxicities. Digallic acid inhibited URAT1 with an IC50 of 5.34 ± 0.65 μM, which is less potent than benzbromarone (2.01 ± 0.36 μM) but more potent than lesinurad (10.36 ± 1.23 μM). Docking and mutation analysis indicated that residues S35, F241 and R477 of URAT1 confer a high affinity for digallic acid. Digallic acid inhibited XOD with an IC50 of 1.04 ± 0.23 μM. Its metabolic product, gallic acid, inhibited XOD with an IC50 of 0.91 ± 0.14 μM. Enzyme kinetic studies indicated that both digallic acid and gallic acid act as mixed-type XOD inhibitors. It shares the same binding mode as digallic acid, and residues E802, R880, F914, T1010, N768 and F1009 contribute to their high affinity. The anion group (carboxyl) of digallic acid contribute significantly to its inhibition activity on both XOD and URAT1 as indicated by docking analysis. Remarkably, at a dosage of 10 mg/kg in vivo, digallic acid exhibited a stronger urate-lowering and uricosuric effect compared to the positive drug benzbromarone and lesinurad. Pharmacokinetic study indicated that digallic acid can be hydrolyzed into gallic acid in vivo and has a t1/2 of 0.77 ± 0.10 h. Further toxicity evaluation indicated that digallic acid exhibited no obvious renal toxicity, as reflected by CCK-8, biochemical analysis (CR and BUN) and HE examination. The findings of our study can provide valuable insights for the development of XOD/URAT1 dual target inhibitors, and digallic acid deserves further investigation as a potential anti-hyperuricemic drug.

Design, synthesis, and biological evaluation of 3-phenyl substituted pyridine derivatives as potential dual inhibitors of XOR and URAT1

Xanthine oxidoreductase (XOR) and uric acid transporter 1 (URAT1) are two most widely studied targets involved in production and reabsorption of uric acid, respectively. Marketed drugs almost target XOR or URAT1, but sometimes, single agents might not achieve aim of lowering uric acid to ideal value in clinic. Thus, therapeutic strategies of combining XOR inhibitors with uricosuric drugs were proposed and implemented. Based on our initial work of virtual screening, A and B were potential hits for dual-targeted inhibitors on XOR/URAT1. By docking A/B with XOR/URAT1 respectively, compounds I1-7 were designed to get different degree of inhibition effect on XOR and URAT1, and I7 showed the best inhibitory effect on XOR (IC50 = 0.037 ± 0.001 μM) and URAT1 (IC50 = 546.70 ± 32.60 μM). Further docking research on I7 with XOR/URAT1 led to the design of compounds II with the significantly improved inhibitory activity on XOR and URAT1, such as II11 and II15. Especially, for II15, the IC50 of XOR is 0.006 ± 0.000 μM, superior to that of febuxostat (IC50 = 0.008 ± 0.000 μM), IC50 of URAT1 is 12.90 ± 2.30 μM, superior to that of benzbromarone (IC50 = 27.04 ± 2.55 μM). In acute hyperuricemia mouse model, II15 showed significant uric acid lowering effect. The results suggest that II15 had good inhibitory effect on XOR/URAT1, with the possibility for further investigation in in-vivo models of hyperuricemia.

Discovery of Novel Biphenyl Carboxylic Acid Derivatives as Potent URAT1 Inhibitors

Urate transporter 1 (URAT1) is a clinically validated target for the treatment of hyperuricemia and gout. Due to the absence of protein structures, the molecular design of new URAT1 inhibitors generally resorts to ligand-based approaches. Two series of biphenyl carboxylic acids were designed based on the structures of URAT1 inhibitors Epaminurad and Telmisartan via a strategy of pharmacophore fusion. Fifty-one novel compounds were synthesized and most of them showed obvious inhibition against human URAT1. A1 and B21 were identified as the most potent URAT1 inhibitors in series A and B, respectively. They exhibited IC50 values of 0.93 μM and 0.17 μM, which were comparable or superior to the clinical uricosuric drug benzbromarone. The results confirmed the effectiveness of ligand-based approaches in identifying novel and potent URAT1 inhibitors.

Outcome reporting in randomized trials in gout: A systematic scoping review from the OMERACT gout working group assessing the uptake of the core outcome set

OBJECTIVE

The selection and reporting of core outcome measures in clinical trials is essential for patients, researchers, and healthcare providers for clinical research to have an impact on healthcare. In this systematic scoping review, we aimed to quantify the extent to which gout clinical trials are collecting and reporting data in accordance with the core outcome domains from Outcome Measures in Rheumatology (OMERACT) published in 2009 applicable for both acute and chronic trials and evaluate the reporting according to the core domains before and after the 2009 OMERACT endorsement.

METHODS

We searched multiple databases PubMed, EMBASE, the Cochrane Library including the Cochrane Central Register of Controlled Trials (CENTRAL), and Cochrane Database of Systematic Reviews (CDSR) and www.

CLINICALTRIALS

gov for randomized controlled trials (RCTs) allocating people with gout versus an active pharmacological gout treatment or a control comparator (no date limitation). We extracted the data in accordance with the core outcome sets, focusing individually on core outcome domains and the core outcome measurements for acute and chronic trials, respectively. In this study 'Acute trials' reflect studies that describe interventions for short term management of gout flares, and 'chronic trials' describe interventions for long-term urate lowering therapy in the management of gout.

RESULTS

From 8,522 records identified in the database search, 134 full text papers were reviewed, and 71 trials were included, of which 36 were acute and 35 were chronic. Only 3 of 36 (8%) acute trials reported all five core domains and none of the 35 included chronic trials reported all 7 core domains. In the acute trials, twenty-seven unique measurement instruments across the 5 core domains were identified. For chronic trials there were 31 unique measurement instruments used across the 7 core domains. Serum urate was reported in 100% of the chronic trials and gout flares in 80%. However, other core domains were reported in <30% of chronic trials. In particular the patient-important domains such as HR-QOL, patient global assessment and activity limitations were rarely reported. A broad variety of different measurement instruments were used to assess each endorsed core domain, a minority of trials used the OMERACT endorsed instruments. For acute trials, the number reporting on all core domains was consistently low and no change was detected before and after the endorsement of the core domains in 2009. None of the included chronic trials reported on all 7 endorsed core domains at any time.

CONCLUSION

In this study we found a low adherence with the intended endorsed (i.e., core) outcome domains for acute and chronic gout studies which represents a poor uptake of the global OMERACT efforts for the minimum of what should be measured in clinical trials. In addition, there is a significant variation in how the OMERACT endorsed outcome domains have been measured. This systematic review demonstrates the need for continuous encouragement among gout researchers to adhere to OMERACT core domains as well as further guidance on outcome measurements reporting.

REGISTRATION

Prospero: CRD42019151316.

Novel urate transporter 1 (URAT1) inhibitors: a review of recent patent literature (2020-present)

INTRODUCTION

The urate transporter 1 (URAT1) is a membrane transporter located in the apical membrane of human renal proximal tubule epithelial cells, which mediates most of the reabsorption of urate. Hyperuricemia (HUA) is a common disease caused by metabolic disorders, which has been considered as the key factor of gout. Approximately 90% of patients suffer from hyperuricemia due to insufficient or poor uric acid excretion. Therefore, the drug design of URAT1 inhibitors targeting improve the renal urate excretion by reducing the reabsorption of urate anions represent a hot topic in searching for anti-gout drugs currently.

AREAS COVERED

In this review, we summarize URAT1 inhibitors patents reported since 2020 to present through the public database at https://worldwide.espacenet.com and some medicinal chemistry strategies employed to develop novel drug candidates.

EXPERT OPINION

Ligand-based drug design (LBDD) strategies have been frequently used developing new URAT1 inhibitors. Meanwhile, the discovery of dual drugs targeting both inhibition of xanthine oxidase (XOD) and URAT1 may be an emerging horizon for designing novel uric acid-lowering candidates in future. Furthermore, advanced techniques in the field of molecular biology and computer science can increase the chances to discover and/or optimize URAT1 inhibitors, contributing to the development of novel drug candidates.

The Role of Uric Acid in Acute and Chronic Coronary Syndromes

Uric acid (UA) is the final product of the catabolism of endogenous and exogenous purine nucleotides. While its association with articular gout and kidney disease has been known for a long time, new data have demonstrated that UA is also related to cardiovascular (CV) diseases. UA has been identified as a significant determinant of many different outcomes, such as all-cause and CV mortality, and also of CV events (mainly Acute Coronary Syndromes (ACS) and even strokes). Furthermore, UA has been related to the development of Heart Failure, and to a higher mortality in decompensated patients, as well as to the onset of atrial fibrillation. After a brief introduction on the general role of UA in CV disorders, this review will be focused on UA's relationship with CV outcomes, as well as on the specific features of patients with ACS and Chronic Coronary Syndrome. Finally, two issues which remain open will be discussed: the first is about the identification of a CV UA cut-off value, while the second concerns the possibility that the pharmacological reduction of UA is able to lower the incidence of CV events.

Bmk9 and Uricase Nanoparticle Complex for the Treatment of Gouty Arthritis and Uric Acid Nephropathy

Uric acid is the final product of purine metabolism, and excessive serum uric acid can cause gouty arthritis and uric acid nephropathy. Therefore, lowering the uric acid level and alleviating inflammation in the body are the key points to treating these diseases. A stable nanosuspension of peptide BmK9 was prepared by the precipitation-ultrasonication method. By combining uricase on the surface of a positively charged carrier, a complex consisting of neutral rod-shaped BmK9 and uricase nanoparticles (Nplex) was formed to achieve the delivery of BmK9 and uricase, respectively. The formulation of Nplex has a diameter of 180 nm and drug loading up to 200%, which releases BmK9 and uricase slowly and steadily in drug release tests in vitro. There was significantly improved pharmacokinetic behavior of the two drugs because Nplex prolonged the half-life and increased tissue accumulation. Histological assessments showed that the dual drug Nplex can reduce the inflammation response in acute gouty arthritis and chronic uric acid nephropathy in vivo. In the macrophage system, there was lower toxicity and increased beneficial effect on inflammation with Nplex than free BmK9 or uricase. Collectively, this novel formulation provides a dual drug delivery system that can treat gouty arthritis and uric acid nephropathy.

Aotearoa New Zealand Māori and Pacific Population-amplified Gout Risk Variants: CLNK Is a Separate Risk Gene at the SLC2A9 Locus

OBJECTIVE

The Māori and Pacific (Polynesian) population of Aotearoa New Zealand has a high prevalence of gout. Our aim was to identify potentially functional missense genetic variants in candidate inflammatory genes amplified in frequency that may underlie the increased prevalence of gout in Polynesian populations.

METHODS

A list of 712 inflammatory disease-related genes was generated. An in silico targeted exome set was extracted from whole genome sequencing data in people with gout of various ancestral groups (Polynesian, European, East Asian; n = 55, 780, 135, respectively) to identify Polynesian-amplified common missense variants (minor allele frequency > 0.05). Candidate functional variants were tested for association with gout by multivariable-adjusted regression analysis in 2528 individuals of Polynesian ancestry.

RESULTS

We identified 26 variants common in the Polynesian population and uncommon in the European and East Asian populations. Three of the 26 population-amplified variants were nominally associated with the risk of gout (rs1635712 [KIAA0319], OR_meta = 1.28, P _meta = 0.03; rs16869924 [CLNK], OR_meta = 1.37, P _meta = 0.002; rs2070025 [fibrinogen A alpha chain (FGA)], OR_meta = 1.34, P _meta = 0.02). The CLNK variant, within the established SLC2A9 gout locus, was genetically independent of the association signal at SLC2A9.

CONCLUSION

We provide nominal evidence for the existence of population-amplified genetic variants conferring risk of gout in Polynesian populations. Polymorphisms in CLNK have previously been associated with gout in other populations, supporting our evidence for the association of this gene with gout.

Clinical Effects of Xanthine Oxidase Inhibitors in Hyperuricemic Patients

This review aims to critically present the available clinical evidence supporting the treatment of chronic hyperuricemia with xanthine oxidase inhibitors. For this reason, the studies published on uric acid (UA)-lowering drugs in the English language from 2000 to August 2019 have been carefully reviewed. The terms "serum uric acid," "xanthine oxidase," "allopurinol," "febuxostat," and "topiroxostat" were incorporated into an electronic search strategy, alone and in combinations, in both MEDLINE (National Library of Medicine, Bethesda, MD) and the Cochrane Register of Controlled Trials (The Cochrane Collaboration, Oxford, UK). Even if new urate-lowering drugs seem of particular efficacy for acute treatment of refractory hyperuricemia, their use is supported by relatively small clinical evidence. On the contrary, large long-term clinical trials have demonstrated that xanthine oxidase inhibitors (XOIs, namely, allopurinol and febuxostat) are effective, safe, and relatively well-tolerated in most of the patients. They have mainly been tested in the elderly, in patients affected by chronic diseases such as heart failure and cancer, and in patients taking a large number of drugs, confirming their safety profile. Recent data also show that they could exert some positive effects on vascular health, renal function, and glucose metabolism. Their cost is also low. In conclusion, XOIs remain the first choice of UA-lowering drug for chronic treatment.

The role of interleukin-1 family members in hyperuricemia and gout

BACKGROUND

Interleukin (IL)-1 family cytokines and their receptors have important roles in innate and partly in adaptive immunity. The family consists of 11 members of which IL-1α, IL-1β, IL-18, IL-33, IL-36α, IL-36β and IL-36γ are considered pro-inflammatory and IL-1Ra, IL-36Ra, IL-37 and IL-38 anti-inflammatory. Whereas IL-1β has a known pivotal role in gout, increasing evidence suggests other IL-1 family members are also involved in the pathogenesis of hyperuricemia and gout flares.

FINDINGS

Studies indicate IL-1α, like IL-1β, plays an essential role in the pathogenesis of gout flares. IL-18, although elevated in patients with gout, does not contribute to MSU crystal-induced inflammation, but may be involved in the subsequent development of cardiovascular disease in individuals with gout. The role of the pro-inflammatory cytokine IL-36 in gout remains elusive. In contrast, IL-1Ra, IL-33, IL-37 and IL-38 inhibit MSU crystal-induced inflammation and therefore have therapeutic potential for treatment of gout flares. In addition to existing IL-1β blockers, several new therapeutics to treat gout are being developed either inhibiting the transcription or maturation of IL-1β.

CONCLUSION

In this review, IL-1 family cytokines are discussed in the context of hyperuricemia and gout. Finally, current and novel therapeutic options for targeting IL-1 are reviewed.

Bucillamine Inhibits UVB-Induced MAPK Activation and Apoptosis in Human HaCaT Keratinocytes and SKH-1 Hairless Mouse Skin

Ultraviolet B (UVB) radiation is known as a culprit in skin carcinogenesis. We have previously reported that bucillamine (N-[2-mercapto-2-methylpropionyl]-L-cysteine), a cysteine derivative with antioxidant and anti-inflammatory capacity, protects against UVB-induced p53 activation and inflammatory responses in mouse skin. Since MAPK signaling pathways regulate p53 expression and activation, here we determined bucillamine effect on UVB-mediated MAPK activation in vitro using human skin keratinocyte cell line HaCaT and in vivo using SKH-1 hairless mouse skin. A single low dose of UVB (30 mJ cm^-2 ) resulted in increased JNK/MAPK phosphorylation and caspase-3 cleavage in HaCaT cells. However, JNK activation and casaspe-3 cleavage were inhibited by pretreatment of HaCaT cells with physiological doses of bucillamine (25 and 100 µm). Consistent with these results, bucillamine pretreatment in mice (20 mg kg^-1 ) inhibited JNK/MAPK and ERK/MAPK activation in skin epidermal cells at 6-12 and 24 h, respectively, after UVB exposure. Moreover, bucillamine attenuated UVB-induced Ki-67-positive cells and cleaved caspase-3-positive cells in mouse skin. These findings demonstrate that bucillamine inhibits UVB-induced MAPK signaling, cell proliferation and apoptosis. Together with our previous report, we provide evidence that bucillamine has a photoprotective effect against UV exposure.

Hyperuricemia and Risk of Cardiovascular Outcomes: The Experience of the URRAH (Uric Acid Right for Heart Health) Project

The latest European Guidelines of Arterial Hypertension have officially introduced uric acid evaluation among the cardiovascular risk factors that should be evaluated in order to stratify patient's risk. In fact, it has been extensively evaluated and demonstrated to be an independent predictor not only of all-cause and cardiovascular mortality, but also of myocardial infraction, stroke and heart failure. Despite the large number of studies on this topic, an important open question that still need to be answered is the identification of a cardiovascular uric acid cut-off value. The actual hyperuricemia cut-off (> 6 mg/dL in women and 7 mg/dL in men) is principally based on the saturation point of uric acid but previous evidence suggests that the negative impact of cardiovascular system could occur also at lower levels. In this context, the Working Group on uric acid and CV risk of the Italian Society of Hypertension has designed the Uric acid Right for heArt Health project. The primary objective of this project is to define the level of uricemia above which the independent risk of CV disease may increase in a significantly manner. In this review we will summarize the first results obtained and describe the further planned analysis.

Mangiferin Ameliorates Hyperuricemic Nephropathy Which Is Associated With Downregulation of AQP2 and Increased Urinary Uric Acid Excretion

Hyperuricemia is characterized by abnormally high level of circulating uric acid in the blood and is associated with increased risk of kidney injury. The pathophysiological mechanisms leading to hyperuricemic nephropathy (HN) involve oxidative stress, endothelial dysfunction, inflammation, and fibrosis. Mangiferin is a bioactive C-glucoside xanthone, which has been exerting anti-inflammatory, anti-fibrotic, and antioxidative effects in many diseases. This study aimed to evaluate the effect of mangiferin treatment in HN. In a mouse model of HN, we observed lower circulating urate levels and ameliorated renal dysfunction with mangiferin treatment, which was associated with reduced renal inflammation and fibrosis. We next investigated the mechanism of urate lowering effect of mangiferin. Metabolic cage experiment showed that mangiferin-administrated mice excreted significantly more urinary uric acid due to elevated urine output, but no marked change in urine uric acid concentration. Expressions of water channels and urate transporters were further assessed by western blot. Renal AQP2 expression was decreased, yet urate transporters URAT1, GLUT9, and OAT1 expressions were not affected by mangiferin in HN mice. Moreover, mangiferin treatment also normalized xanthine oxidase and SOD activity in HN mice, which would decrease uric acid synthesis and improve oxidative stress, respectively. Therefore, our results reveal a novel mechanism whereby mangiferin can reduce serum uric acid levels by promoting AQP2-related urinary uric acid excretion. This study suggested that mangiferin could be a multi-target therapeutic candidate to prevent HN via mechanisms that involve increased excretion and decreased production of uric acid and modulation of inflammatory, fibrotic, and oxidative pathways.

Polydatin and Resveratrol Inhibit the Inflammatory Process Induced by Urate and Pyrophosphate Crystals in THP-1 Cells

Resveratol (RES) and its natural precursor polydatin (PD) are polyphenols that may display a broad variety of beneficial effects including anti-inflammatory properties. This study aimed to investigate the role of RES and PD in the inflammatory process induced by monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals in vitro. A monocytic cell line (THP-1) was primed for 3 hours with phorbol myristate acetate (100 ng/mL) and stimulated with synthetic MSU (0.05 mg/mL) and CPP (0.025 mg/mL) crystals. RES and PD were added to cultures concurrently with the crystals, or as 2-hour pretreatment. The effect of the two polyphenols was evaluated on intracellular and extracellular IL-1β levels, NACHT-LRRPYD-containing protein-3 (NLRP3) inflammasome expression, reactive oxygen species (ROS) and nitric oxide (NO) production, and the assessment of crystal phagocytosis. RES and PD strongly inhibited IL-1β induced by crystals after cell pretreatment. Cell pretreatment was effective also in reducing IL-1 mRNA expression while no effect was observed on NLRP3 gene expression. RES and PD had no effect on crystal phagocytosis when used as pretreatment. Both polyphenols were significantly effective in inhibiting ROS and NO production. Our results demonstrated that RES and PD are effective in inhibiting crystal-induced inflammation. Data obtained after cell pretreatment allow us to hypothesize that these polyphenols act on specific signaling pathways, preventing inflammation.

Pharmacological urate-lowering approaches in chronic kidney disease

Chronic kidney disease (CKD) has become a global public health issue and uric acid (UA) remains a major risk factor of CKD. As the main organ for the elimination of UA, kidney owned a group of urate transporters in tubular epithelium. Kidney disease hampered the UA excretion, and the accumulation of serum UA in return harmed the renal function. Commercially, there are three kinds of agents targeting at urate-lowering, xanthine oxidoreductase inhibitor which prevents the production of UA, uricosuric which increases the concentration of UA in urine thus decreasing serum UA level, and uricase which converts UA to allantoin resulting in the dramatic decrement of serum UA. Of note, in patients with CKD, administration of above-mentioned agents, alone or combined, needs special attention. New evidence is emerging for the efficacy of several urate-lowering drugs for the treatment of hyperuricemia in patients with CKD. Besides, loads of novel and promising drug candidates and phytochemicals are in the different phases of research and development. As of today, there is insufficient evidence to recommend the widespread use of UA-lowering therapy to prevent or slow down the progression of CKD. The review summarized the evidence and perspectives about the treatment of hyperuricemia with CKD for medicinal chemist and nephrologist.