Effect of dietary oils on peripheral neuropathy-related endpoints in dietary obese rats

Abstract

Purpose

This study aimed to determine the effect of dietary oils (olive, safflower, evening primrose, flaxseed, or menhaden) enriched in different mono unsaturated fatty acids or polyunsaturated fatty acids on peripheral neuropathies in diet-induced obese Sprague-Dawley rats.

Materials and methods

Rats at 12 weeks of age were fed a high-fat diet (45% kcal) for 16 weeks. Afterward, the rats were fed diets with 50% of the kilocalories of fat derived from lard replaced by the different dietary oils. In addition, a control group fed a standard diet (4% kcal fat) and a high fat fed group (45% kcal) were maintained. The treatment period was 32 weeks. The endpoints evaluated included motor and sensory nerve conduction velocity, thermal sensitivity, innervation of sensory nerves in the cornea and skin, and vascular relaxation by epineurial arterioles.

Results

Menhaden oil provided the greatest benefit for improving peripheral nerve damage caused by dietary obesity. Similar results were obtained when we examined acetylcholine-mediated vascular relaxation of epineurial arterioles of the sciatic nerve. Enriching the diets with fatty acids derived from the other oils provided minimal to partial improvements.

Conclusion

These studies suggest that omega-3 polyunsaturated fatty acids derived from fish oil could be an effective treatment for neural and vascular complications associated with obesity.

Keywords:

• peripheral neuropathy
• fish oil
• omega-3 polyunsaturated fatty acids
• omega-6 polyunsaturated fatty acids
• vascular reactivity
• nerve conduction velocity

Acknowledgments

Research reported in this publication was supported by the Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development Merit award (RX000889-05), by a National Institute of Diabetes and Digestive and Kidney Diseases of the NIH award (DK107339), and by a National Heart, Lung, and Blood Institute of the NIH award (T35HL007485). The abstract of this paper was presented at two meetings as a poster presentation with interim findings; first, at the annual NEURODIAB 2017 meeting held on September 9–11 in Coimbra, Portugal and second at the University of Iowa Medical Student Research Conference, held on September 13–15, 2017. The poster’s abstract was for the NEURODIAB meeting published on the NEURODIAB2017 website (http://www.neurodiab2017. com/AbstractBook.aspx). For the University of Iowa Medical Student Research Conference, the abstract was published on the Carver College of Medicine website (https://medicine.uiowa.edu/md/sites/medicine.uiowa.edu.md/files/2017%20Abstract%20Book.pdf).

Author contributions

LC, EC, HS, and MET assisted in design, performance of the studies, and data analysis as well as preparation of the manuscript. MET was also responsible for animal care. ED was involved in the preparation of figures. MAY was responsible for the overall projects including design of the studies, overseeing the performance of the studies, data analysis, and writing the manuscript. All authors contributed toward data analysis, drafting and revising the paper and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.

Supplementary materials

Figure S1 Effect of dietary oils on glucose clearance in DIO Sprague-Dawley rats.

Notes: Rats were fed a standard or high-fat diet for 16 weeks. Afterward, 50% kcal derived from lard in the high-fat diet was replaced with olive oil, safflower oil, flaxseed oil, evening primrose oil, or menhaden oil. Rats were maintained on these diets as well as on standard and high-fat diets for an additional 32 weeks. Glucose utilization was determined as described in the “Materials and methods” section. Data are presented as the mean±standard error of mean in mg/dL. The area under the curve was significantly different (p<0.05) for high-fat-fed rats and high-fat-fed rats treated with olive oil, safflower oil, or menhaden oil versus control. The number of rats in each group was the same as shown in Table 1.
Abbreviation: DIO, diet-induced obese.

Table S1 Fatty acid % composition of diets

Table S2 Effect of dietary lipids on fatty acid % composition of serum measured by gas chromatography

Table S3 Effect of dietary lipids on fatty acid % composition of liver measured by gas chromatography

Table S4 Fatty acid unsaturation indices of liver and serum measured by gas chromatography

Table S5 Ratio of n-6 to n-3 fatty acids of liver and serum measured by gas chromatography