Role of Anti-Inflammatory Cytokines in the Development of Diabetic Peripheral Neuropathy in Male UCD-Type 2 Diabetic Rats

Diabetic peripheral neuropathy (DPN) is a debilitating complication of type 2 diabetes (T2D) and is often diagnosed only after irreparable nerve damage has occurred. Mechanical allodynia, previously nonpainful stimuli that becomes painful, presents early in the disease, and precedes irreparable nerve damage. Previous studies suggest the development of DPN is associated with increased inflammation, which can result from elevated pro-inflammatory and/or reduced anti-inflammatory cytokines. OBJECTIVE: To investigate the role of anti-inflammatory cytokines in the development of DPN. We hypothesized that reduced interleukin (IL)-4 and IL-10 levels would precede the development of mechanical allodynia in a diabetic rat model. METHODS: Bimonthly hemoglobin A1c (HbA1c) measures were obtained from male University of California Davis-T2D rats, ≥ 5.6% used as diagnostic criteria. Age-matched, healthy Sprague-Dawley rats were used as controls. Mechanical allodynia was assessed monthly using von Frey filaments (North Coast Medical, Morgan Hill, CA) and is presented as 50% paw withdrawal threshold. Tail vein blood draws were also performed monthly. Serum IL-4 and IL-10 concentrations were assessed using a rat multiplex kit (Millipore, RECYTMAG, Burlington, MA). Data are presented as mean ± SD and were analyzed using a two-way, repeated measures ANOVA with Holm-Sidak post hoc analyses. Von Frey data were converted to a logarithmic scale for parametric statistical analyses. RESULTS: 50% paw withdrawal threshold was significantly decreased at both 3 and 4 mo relative to onset in T2D rats (n=18; Onset: 1.48±0.2 log(g); 3 mo: 1.28±0.3 log(g), P=0.033; 4 mo: 1.31±0.3 log(g), P=0.023). The same comparisons in control rats demonstrated a significant increase (n=20; Onset: 1.67±0.2 log(g); 3 mo: 1.91±0.1 log(g), P<0.001; 4 mo: 1.92±0.1 log(g), P<0.001). Although no significant interaction was found for IL-4 (P=0.613), there was a main group effect such that IL-4 was significantly lower in T2D rats (n=10; IL-4: 372±125 pg/mL) relative to control rats (n=11; 471±153 pg/mL; P=0.019). There was no significant interaction (P=0.438) or main group effect (P=0.208) for IL-10, though there was a significant main effect of time (P=0.003). CONCLUSIONS: Our findings suggest that mechanical allodynia is present 3 mo post diabetes onset in UCD-T2D rats and that IL-4, but not IL-10, concentration is decreased in T2D compared to control rats regardless of the time point of the disease. Although anti-inflammatory cytokines are reduced in T2D, they do not appear to play a role in the development of DPN. This project was supported by NIH R01 HL144723. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.