Omega‐3‐Fatty Acids Prevent Mechanical Hypersensitivity but Do Not Alter Nerve Fiber Density in a High Fat‐Fed Murine Model of Prediabetic Neuropathy

Abstract

Diabetic peripheral neuropathy (DPN) is a chronic complication of diabetes, affecting patients with both Type 1 and Type 2 diabetes. Loss of nerve fibers in the skin and increased sensitivity to touch is a characteristic sign of painful neuropathy in human patients. Similarly, high fat‐fed prediabetic mice exhibit signs of neuropathy including hindpaw hypersensitivity accompanied by neuronal inflammation. In contrast to loss of epidermal innervation in humans with painful neuropathy, high fat‐fed mice exhibit increased overall intraepidermal nerve fiber density (IENFD) which is primarily due to increased peptidergic nociceptive nerve fibers (TrkA). Although omega‐3‐fatty acids are known for anti‐inflammatory properties, the effects of omega‐3‐fatty acids on high fat diet‐induced neuropathy have not been evaluated.PURPOSEAssess how diet composition affects mechanical sensitivity (a behavioral indicator of neuropathy) and nerve fiber density. We hypothesized that omega‐3‐fatty acids would prevent hindpaw hypersensitivity and prevent the increase in IENF and TrkA nerve fiber density in high fat‐fed mice. We expect these effects may be mediated by attenuated neuronal inflammation.METHODSC57BL/6 mice were randomized into four diet groups (n = 12/group): 10% low fat‐fish oil (LFFO), 41% high fat‐fish oil (HFFO), 10% low fat‐lard (LFL), or 41% high fat‐lard (HFL). The von Frey behavioral test for hindpaw mechanical sensitivity was utilized to characterize neuropathy at baseline then biweekly for 32 weeks. At end study, a glucose tolerance test was performed and the trapezoidal method was employed to calculate total area under the curve (AUC). Fasting glucose and insulin values were used to calculate the homeostatic model assessment of insulin resistance (HOMA‐IR). IENF and TrkA nerve fiber density was quantified using fluorescence immunohistochemistry.RESULTSAt 32 wks, HFL had greater body weight and HOMA‐IR compared to all other groups, but glucose AUC was only greater in HFL compared to LFFO. Both HFL and HFFO had greater fasting glucose compared to LFFO. Percent paw withdrawal was greater in HFL compared to HFFO and LFFO, but there were no significant differences for LF vs. HF for fish oil or lard. There were no significant differences in IENFD or TrkA nerve fiber density among groups.CONCLUSIONMice fed a HFL diet displayed hindpaw hypersensitivity, indicating neuropathy. Despite elevated fasting glucose and similarly impaired glucose tolerance in HFFO, fish oil protected high fat‐fed mice from hindpaw hypersensitivity. This suggests diet composition, rather than glycemic control, may play a larger role in the development of painful neuropathy. None of the diets had a significant effect on IENF or TrkA nerve fiber density, thus the protective effects of omega‐3‐fatty acids do not appear to be mediated by changes in nerve fiber density. To further assess the protective effects of omega‐3‐fatty acids on high fat dietinduced neuropathy, we will assess the effects of these diets on neuronal and adipose inflammation.Support or Funding InformationSupported by NIH R21NS090282‐01 Low Fat Fish Oil (LFFO) High Fat Fish Oil (HFFO) Low Fat Lard (LFL) High Fat Lard (HFL) Body weight (g) 34.3 ± 0.6 39.5 ± 1.6a 37.2 ± 1.1 44.3 ± 1.7ga,b,c Fasting glucose (mg/dl) 129.1 ± 5.6 152.0 ±7.7a 148.1 ± 5.2 158.8 ± 8.8a Glucose AUC total (ms · 120 min · dl −1) 5368.1 ± 678.9 7282.6 ± 1144.4 7384.3 ± 685.4 9149.6 ± 1013.8a HOMA‐1R 4.8 ± 1.0 5.7 ± 1.3 5.5 ± 0.8 20.1 ± 4.3a,b,c Percent paw withdrawal (%) 22.5 ± 4.5% 29.2 ± 6.4% 37.5 ± 7.2 54.2 ± 5.7a,b Intraepidermal nerve fiber density (fibers/mm) 32.1 ±2.0 33.2 ± 1.9 30.7 ± 1.6 30.9 ± 2.0 TrkA nerve fiber density (fibers/mm) 28.0 ± 1.4 28.2 ± 1.6 26.2 ± 1.3 27.5 ± 1.7 P < 0.05 vs. LFFO; P < 0.05 vs. HFFO; and P < 0.05 vs. LFL This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.