Hyperuricemia is a metabolic disorder characterized by abnormally elevated levels of uric acid (UA) in the blood. Uric acid, the end product of purine metabolism, may crystallize as urate in joints, leading to gouty arthritis or form stones in the kidneys when its concentration is excessively high. The clinical manifestations of gout include hyperuricemia, recurrent acute gouty arthritis, deposition of tophi, chronic tophaceous arthritis, and joint deformities. It commonly affects the kidneys, causing chronic interstitial nephritis and uric acid nephrolithiasis ^[1-3]. By 2020, the global prevalence of hyperuricemia and gout surpassed 1.1 billion cases. In China, the number of patients is projected to reach 200 million for hyperuricemia and 43.25 million for gout by 2024 ^[2-3]. With the increasing disease burden, the demand for pharmacological interventions for hyperuricemia and gout continues to grow.

Hyperuricemia is closely related to uric acid levels in the body, and current therapeutic agents mainly target the reduction of uric acid synthesis or the promotion of uric acid excretion to manage the condition. Xanthine oxidoreductase (XOR) plays a critical role in purine metabolism by catalyzing the oxidation of hypoxanthine to xanthine and subsequently to uric acid. It is thus a key regulatory point in uric acid synthesis and an important target for hyperuricemia treatment ^[4-5]. XOR exists in two forms: the reduced xanthine dehydrogenase (XDH) and the oxidized xanthine oxidase (XO). XDH, in its reduced state, catalyzes the conversion of hypoxanthine to xanthine and uric acid, generating reduced nicotinamide adenine dinucleotide (NADH). In contrast, XO, in its oxidized state, converts xanthine to uric acid and hydrogen peroxide. The inhibition of XO by xanthine oxidase inhibitors (XOIs) to reduce uric acid production is a widely adopted therapeutic strategy for hyperuricemia and gout ^[6]. However, safety concerns remain with existing XOIs, highlighting the urgent need for novel therapeutics with improved safety profiles. Small interfering RNA (siRNA) represents a promising research focus in this area.

This strain is a humanized mouse model of the Xdh gene, generated by replacing the mouse Xdh gene with the complete human XDH gene sequence, including its untranslated regions (UTRs), exons, and introns. The B6-hXDH mice express the human XDH gene and xanthine oxidase protein in a pattern similar to the endogenous Xdh gene in mice, making their genetic, protein expression, and biochemical features highly comparable to humans. This strain serves as an ideal preclinical platform for studying the pathological mechanisms of hyperuricemia and gout and for developing novel xanthine oxidase inhibitors and nucleic acid therapies.