Hyperalgesia, synovitis and multiple biomarkers of inflammation are suppressed by interleukin 1 inhibition in a novel animal model of gouty arthritis

BACKGROUND

Monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystal-induced interleukin 1 beta (IL1beta) release contributes to inflammation in subcutaneous air pouch and peritoneal models of acute gout and pseudogout. However, consequences of IL1 inhibition have not been explored in more clinically relevant models of crystal-induced arthritis.

OBJECTIVE

To develop a novel mouse model of acute gouty ankle arthritis and use it to assess the effects of genetic deletion of IL1 receptor type (IL1R1) and of exogenous mIL1 Trap (a high-affinity blocker of mouse IL1alpha and IL1beta) on pain, synovitis and systemic inflammatory biomarkers.

METHODS

MSU crystals were injected into the mouse ankle joint and pain and ankle swelling were measured over 4 days. The effects of IL1 inhibition were determined in this model, and in the comparator models of crystal-induced peritonitis and subcutaneous air pouch inflammation.

RESULTS

Both IL1R1-null mice and mice pretreated with mIL1 Trap showed reduced neutrophil influx in MSU and CPPD crystal-induced peritonitis and air pouch models (p<0.05). In the ankle joint model, both IL1R1 knockout mice and pretreatment with mIL1 Trap were associated with significant reductions in MSU crystal-induced elevations in hyperalgesia, inflammation, serum amyloid A and the levels of multiple inflammatory cytokines and chemokines (p<0.05). Additionally, it was found that administration of mIL1 Trap after MSU crystal injection reduced established hyperalgesia and ankle swelling.

CONCLUSIONS

IL1 inhibition both prevented and relieved pain and ankle joint inflammation in response to intra-articular MSU crystals in mice. Results suggested that IL1 Trap has the potential to both prevent and treat gouty arthritis.

Overview of Hyperuricaemia and Gout

In most mammals purine degradation ultimately leads to the formation of allantoin. Humans lack the enzyme uricase, which catalyzes the conversion of uric acid to allantoin. The resulting higher level of uric acid has been hypothesized to play a role as an antioxidant. Hyperuricaemia is usually an asymptomatic condition which is hypothesized to play a role in cardiovascular disease and hypertension. Some hyperuricaemic individuals develop gout, an inflammatory arthritis caused by the deposition of monosodium urate crystals in joints. Over time, acute intermittent gouty arthritis can develop into a chronic condition with deposits of monosodium urate (MSU) crystals in joints and as tophi. The mechanisms by which MSU crystals lead to an acute inflammatory arthritis are under investigation and current knowledge is reviewed here. Treatment of gout includes management of acute flares with anti-inflammatory medications such as non-steroidal anti-inflammatory drugs or corticosteroids and long term management with urate-lowering therapy when indicated. Future directions in the treatment of gout, in part guided by a better understanding of pathophysiology, are discussed.