Omega-3 Fatty Acids Prevent Peripheral Neuropathy and Pro Inflammatory Adipose Tissue Macrophage Phenotype in High-Fat-Fed Mice

Abstract

Obesity and/or consumption of a high fat diet is associated with the development of peripheral neuropathy (PN) which is characterized by changes in epidermal innervation and increased sensitivity in the extremities. Evidence indicates that omega-3 fatty acids prevent the development of PN and attenuate adipose inflammation, but the interaction of PN and adipose tissue macrophage (ATMΦ) phenotype have not been investigated. We hypothesized that a diet high in unsaturated fatty acids may prevent PN and adipose inflammation, despite the high fat content. PURPOSE: Assess the effects of omega-3 fatty acids on signs of PN and ATMΦ phenotype in high-fat-fed mice. Methods: Male C57Bl/6 mice were randomized to (n = 12-14/group): 10% low fat fish oil (10% FO); 54% high fat fish oil (54% FO); 10% low fat lard (10% L); or 54% high fat lard (54% L) for 14 weeks. PN was characterized by the von Frey test for hindpaw sensitivity at baseline then biweekly through week 14. After 14 weeks, intraepidermal nerve fiber density (IENFD) was quantified by immunohistochemistry of the hindpaw footpad skin using anti-PGP 9.5. The relative percentage of total macrophage cells (F4/80+CD11b+) and M1 (CD206-CD11c+) and M2 (CD206+CD11c-) cell populations in epididymal adipose were identified using flow cytometry. Group differences were identified by 2 x 2 factorial ANOVA. Pearson correlations were used to assess the relationship between hindpaw withdrawal threshold and ATMΦ. Results: 54% L (35.3 ± 1.0 g) had greater body mass compared to all other groups: 10% FO (26.5 ± 0.7, p < 0.001); 10% L (27.8 ± 0.6, p = 0.001); and 54% L (35.3 ± 1.0, p < 0.001). Similarly, fasting insulin was greater in 54% L (3.1 ± 0.4 ng/mL) compared to all other groups: 10% FO (1.0 ± 1.0, p < 0.001); 10% L (1.6 ± 0.2, p < 0.001), and 54% FO (1.0 ± 0.1, p < 0.001). Fasting glucose was greater in 54% L (225.8 ± 7.5 mg/dl) compared to 10% FO (216.1 ± 7.7, p =0.04) and 54% FO (182.6 ± 6.6, p = 0.03), but not 10% L (180.7 ± 17.1, p = 0.483). Following the same pattern as body mass and insulin, homeostatic model assessment of insulin resistance (HOMA-IR) was greater in 54% L (8.1 ± 1.1) compared to all other groups: 10% FO (2.2 ± 0.4, p < 0.001); 10% L (4.1 ± 0.6, p < 0.001); and 54% FO (2.2 ± 0.3, p < 0.001). Hindpaw sensitivity was greater in 54% L (0.08 ± 0.02 g) compared to 54% FO (0.19 ± 0.03, p = 0.02). IENFD was greater in 54% L (52.5 ± 2.2 fibers per mm) compared to 10% FO (44.1 ± 1.5, p = 0.04), but was not different from 10% L (49.7 ± 2.8, p = 0.47) or 54% FO (48.1 ± 3.0, p = 0.24). M1 ATMΦ percentage was greater in 54% L (11.7 ± 2.5 %) compared to all other groups: 10% L (3.8 ± 0.8, p = 0.001), 10% FO (5.2 ± 0.7, p = 0.014), and 54% FO (5.1 ± 0.6 %, p = 0.016). M2 ATMΦ percentage was greater in 10% L (59.7 ± 4.5 %) compared to all other groups: 10% FO (42.1 ± 5.0, p = 0.036), 54% L (41.4 ± 3.9, p = 0.027), and 54% FO (31.4 ± 3.6 %, p < 0.001), but there were no significant differences in M2 ATMΦ percentage in 54% L vs. 54% FO. There were no significant correlations between hindpaw sensitivity and M1 ATMΦ percentage, M2 ATMΦ percentage, or M1:M2 ratio. CONCLUSION: The negative metabolic effects of a high fat lard diet on body mass, glucose, insulin, and insulin resistance were prevented when the dietary fat source was omega-3 fatty acids instead of lard. Notably, mice fed a high fat lard diet had a higher percentage of the pro inflammatory M1 ATMΦ phenotype and developed signs of painful PN including hindpaw hypersensitivity and increased IENFD but these effects were prevented by omega-3 fatty acids in the 54% FO group, despite the high dietary fat content. Supported by the Southern Illinois University Edwardsville Vaughnie Lindsay New Investigator Award. This is the full abstract presented at the American Physiology Summit 2024 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.