Urinary 4-pyridoxic acid as a non-invasive biomarker for evaluating osteoarthritis severity: findings from the ROAD study.

BACKGROUND: The early detection of osteoarthritis (OA) requires reliable biomarkers; however, reports identifying such biomarkers remain limited. AIMS: This study aimed to evaluate the potential of urinary 4-pyridoxic acid (4PA) as a biomarker for the severity of knee osteoarthritis (KOA) and lumbar spondylosis (LS) in Japanese adults, using data from the population-based cohort study. METHODS: Data were analysed from 1566 participants (510 men and 1,056 women) aged ≥ 40 years, who were enrolled in the Research on Osteoarthritis/Osteoporosis against Disability (ROAD) cohort, a population-based study initiated in 2005. Participants underwent radiographic assessments of the knees and lumbar spine, and urinary 4PA levels were measured using high-performance liquid chromatography. Logistic regression analyses were performed to evaluate the association between urinary 4PA levels and the Kellgren-Lawrence (KL) grade of KOA and LS, adjusting for age, sex, body mass index (BMI), and lifestyle factors. RESULTS: Urinary 4PA levels were significantly higher in participants with KL grade 4 KOA compared to those with lower KL grades (p < 0.001). This association remained significant after adjusting for confounding factors. In contrast, no significant differences in 4PA levels were observed across the KL grades for LS, although a slight increase in 4PA levels was noted in KL grade 4 cases. DISCUSSION AND CONCLUSIONS: These findings suggest that urinary 4PA could serve as a biomarker for assessing KOA severity, particularly in advanced stages. While the detection of early OA using 4PA remains challenging, the significant increase in KL grade 4 cases highlights its potential role in guiding treatment decisions, such as surgical intervention.