Gout: The last 50 years

Monosodium urate crystals in inflammation and immunity

Uric acid crystals [monosodium urate (MSU)] have emerged as an important factor for both gouty arthritis and immune regulation. This simple crystalline structure appears to activate innate host defense mechanisms in multiple ways and triggers robust inflammation and immune activation. The recognition mechanisms of MSU following its phase change from soluble uric acid are diverse, involving both protein receptors and non-specific plasma membrane attachment. Upon contact with host cells, MSU induces a set of membrane events that trigger Syk and PI3K activation, phagocytosis, and cytokine production. Having entered the cell, MSU further triggers NALP3 inflammasome activation and induces the production of IL-1 beta, likely inducing a full spectrum of inflammation. This review describes the recognition mechanisms and activation pathways involved in MSU-mediated inflammation and adjuvanticity and hypothesizes that direct membrane binding by solid surfaces, such as MSU, may function as a generic mechanism in tissue responses to particulate and crystalline structures.

Uric acid changes in urine and plasma: an effective tool in screening for purine inborn errors of metabolism and other pathological conditions

Purine inborn errors of metabolism (IEM) are serious hereditary disorders, which should be suspected in any case of neonatal fitting, failure to thrive, recurrent infections, neurological deficit, renal disease, self-mutilation and other manifestations. Investigation usually starts with uric acid (UA) determination in urine and plasma. UA, the final product of purine metabolism in humans, may be altered not only in purine IEM, but also in other related pathologies and clinical conditions. However, data and information about abnormal UA levels are scattered in the literature, often being controversial and confusing. A comprehensive overview has been elaborated, according to abnormal UA levels in urine and plasma, which associates these alterations with purine IEM. Other possible diseases, clinical conditions, diet and drug intake, related to the metabolism of uric acid, are also presented. The article includes tables that classify the disorders according to different patterns of UA alterations, with pertinent enzymes, clinical symptoms, inheritance and comments. Additionally, summarized pathophysiological mechanisms of important disorders are described. The overview is intended to assist in the interpretation of the results of UA analyses. It demonstrates that variation of UA concentrations in urine and plasma may constitute an effective tool in screening for purine IEM and other related pathological conditions.

Pharmacokinetics, Pharmacodynamics and Safety of Febuxostat, a Non-Purine Selective Inhibitor of Xanthine Oxidase, in a Dose Escalation Study in Healthy Subjects

BACKGROUND

Febuxostat is a novel non-purine selective inhibitor of xanthine oxidase currently being developed for the management of hyperuricemia in patients with gout.

OBJECTIVE

To investigate the pharmacokinetics, pharmacodynamics and safety of febuxostat over a range of oral doses in healthy subjects.

METHODS

In a phase I, dose-escalation study, febuxostat was studied in dose groups (10, 20, 30, 40, 50, 70, 90, 120, 160, 180 and 240 mg) of 12 subjects each (10 febuxostat plus 2 placebo). In all groups, subjects were confined for 17 days and were administered febuxostat once daily on day 1, and days 3-14. During the course of the study, blood and urine samples were collected to assess the pharmacokinetics of febuxostat and its metabolites, and its pharmacodynamic effects on uric acid, xanthine and hypoxanthine concentrations after both single and multiple dose administration. Safety measurements were also obtained during the study.

RESULTS

Orally administered febuxostat was rapidly absorbed with a median time to reach maximum plasma concentration following drug administration of 0.5-1.3 hours. The pharmacokinetics of febuxostat were not time dependent (day 14 vs day 1) and remained linear within the 10-120 mg dose range, with a mean apparent total clearance of 10-12 L/h and an apparent volume of distribution at steady state of 33-64 L. The harmonic mean elimination half-life of febuxostat ranged from 1.3 to 15.8 hours. The increase in the area under the plasma concentration-time curve of febuxostat at doses >120 mg appeared to be greater than dose proportional, while the febuxostat maximum plasma drug concentration was dose proportional across all the doses studied. Based on the urinary data, febuxostat appeared to be metabolised via glucuronidation (22-44% of the dose) and oxidation (2-8%) with only 1-6% of the dose being excreted unchanged via the kidneys. Febuxostat resulted in significant decreases in serum and urinary uric acid concentrations and increases in serum and urinary xanthine concentrations. The percentage decrease in serum uric acid concentrations ranged from 27% to 76% (net change: 1.34-3.88 mg/dL) for all doses and was dose linear for the 10-120 mg/day dosage range. The majority of adverse events were mild-to-moderate in intensity.

CONCLUSION

Febuxostat was well tolerated at once-daily doses of 10-240 mg. There appeared to be a linear pharmacokinetic and dose-response (percentage decrease in serum uric acid) relationship for febuxostat dosages within the 10-120 mg range. Febuxostat was extensively metabolised and renal function did not seem to play an important role in its elimination from the body.

A literature review of the epidemiology and treatment of acute gout

BACKGROUND

Gout is the most common cause of inflammatory arthritis in men aged >40 years and is frequently encountered in clinical practice.

OBJECTIVE

The goal of this article was to review the published literature on the epidemiology, treatment, and estimated burden of illness of acute gout.

METHODS

Articles on gout published in English between 1980 and June 2002 were identified through a MEDLINE search. Relevant clinical studies and review articles were found using the text- and keyword-search term gout alone and in combination with epidemiology, prevalence, incidence, complications, outcome, quality of life, economics, cost, prevention or drug therapy. The reference lists of identified articles, especially review articles, were checked for any additional studies that might have been missed in the original MEDLINE search.

RESULTS

The epidemiology of gout in various geographic regions has been well documented. Data suggest that environmental, racial, and hereditary factors may influence the development of gout, and that the prevalence of gout appears to be on the rise worldwide. Evidence from well-designed clinical studies evaluating drug therapies for gout is limited. Therapies for acute gout include corticotropin, corticosteroids, colchicine or, more often, nonsteroidal anti-inflammatory drugs (NSAIDs), which have shown comparable efficacy. A recent study suggests that etoricoxib, a new cyclooxygenase-2-selective inhibitor, may be as effective as and better tolerated than traditional NSAIDs in the treatment of gout. Urate-lowering therapy, prophylactic colchicine, and low-dose NSAIDs are used for the long-term prophylaxis of gout. However, all acute and prophylactic therapies are associated with adverse events. Using an economic model for gout, the annual direct burden of illness for new cases of acute gout can be estimated at 27,378,494 US dollars in the United States.

CONCLUSIONS

Gout is an increasingly prevalent condition worldwide and creates a heavy economic burden. Available treatments are generally effective; however, they are not devoid of adverse events. Well-designed, long-term, controlled clinical trials evaluating the comparative efficacy and tolerability of treatments for gout are needed.