Circulating Neopterin Is Independently Associated with Autonomic Neuropathy in Type 2 Diabetes, but Not with Other Microvascular Complications

Background: Chronic low-grade inflammation plays a central role in the pathogenesis of type 2 diabetes (T2DM) and its complications. Neopterin, a marker of macrophage activation and Th1-mediated immune response, has been associated with cardiovascular disease and metabolic disorders. However, its relationship with diabetic autonomic neuropathy remains insufficiently investigated. Methods: We conducted a cross-sectional study including 129 participants (93 with T2DM and 36 with obesity without carbohydrate disturbances). Clinical, anthropometric, and biochemical assessments were performed. Cardiovascular autonomic neuropathy was evaluated using Ewing cardiovascular reflex tests and sudomotor dysfunction scoring. Neopterin concentrations were measured in serum. Correlation, ROC, and logistic regression analyses were performed. Results: Neopterin levels were not significantly different between T2DM and obesity groups. No differences were observed in patients with versus without peripheral neuropathy, nephropathy, or retinopathy. However, neopterin levels were significantly higher in individuals with cardiovascular autonomic neuropathy (p = 0.013). Neopterin correlated with cardiovascular autonomic neuropathy score, sudomotor dysfunction, fasting glucose, fasting insulin, and HOMA-IR. It showed a moderate negative monotonic correlation with eGFR (Spearman’s rho = −0.41, p< 0.001). In multivariable logistic regression adjusted for age, HbA1c, BMI, eGFR, and diabetes duration, each 1-SD increase in neopterin was associated with 2.67-fold higher odds of cardiovascular autonomic neuropathy (95% CI 1.21–5.89; p = 0.015). Conclusions: Circulating neopterin is independently associated with cardiovascular autonomic neuropathy in T2DM but not with classical microvascular complications. These findings suggest a potential role of immune-mediated mechanisms in the pathogenesis of diabetic cardiovascular autonomic neuropathy.