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

Figure 1

Effect of dietary oils on motor and sensory nerve conduction velocity in DIO Sprague-Dawley rats. Notes: Motor and sensory nerve conduction velocities were examined as described in the “Materials and methods” section. Data are presented as the mean±standard error of mean in m/s. The number of rats in each group was the same as shown in Table 1. ^*p<0.05 compared to control rats; ⁺p<0.05 compared to DIO rats. Abbreviations: MNCV, motor nerve conduction velocity; SNCV, sensory nerve conduction velocity; DIO, diet-induced obese; OO, olive oil; SO, safflower oil; FO, flaxseed oil; EPO, evening primrose oil; MO, menhaden oil.

Figure 2

Effect of dietary oils on intraepidermal nerve fiber density and thermal nociception in DIO Sprague-Dawley rats. Notes: Intraepidermal nerve fiber density and thermal nociception were examined as described in the “Materials and methods” section. Data are presented as the mean±standard error of mean for intraepidermal nerve fiber profiles per mm and thermal nociception in seconds. The number of rats in each group was the same as shown in Table 1. ^*p<0.05 compared to control rats; ⁺p<0.05 compared to DIO rats. Abbreviations: IENF, intraepidermal nerve fiber density; DIO, diet-induced obese; OO, olive oil; SO, safflower oil; FO, flaxseed oil; EPO, evening primrose oil; MO, menhaden oil.

Figure 3

Effect of dietary oils on cornea nerve fiber length and cornea sensitivity in DIO Sprague-Dawley rats. Notes: Innervation of the subepithelial layer of the cornea and corneal sensitivity were determined by using corneal confocal microscopy and Cochet–Bonnet filament esthesiometer, respectively, as described in the “Materials and methods” section. The number of rats in each group was the same as shown in Table 1. Data are presented as the mean±standard error of mean for innervation of the cornea in mm/mm² and for corneal sensitivity in centimeters. ^*p<0.05 compared to control rats; ⁺p<0.05 compared to DIO rats. Abbreviations: DIO, diet-induced obese; OO, olive oil; SO, safflower oil; FO, flaxseed oil; EPO, evening primrose oil; MO, menhaden oil.

Figure 4

Effect of dietary oils on vascular relaxation by acetylcholine in epineurial arterioles of the sciatic nerve in DIO Sprague-Dawley rats. Notes: Pressurized arterioles (40 mm Hg and ranging from 60 to 100 µm luminal diameters) were constricted with phenylephrine (30%–50%) and incremental doses of acetylcholine were added to the bathing solution while recording steady state vessel diameter. The number of rats in each group was the same as shown in Table 1. Data are presented as the mean of % relaxation±standard error of mean. ^*p<0.05 compared to control rats; ⁺p<0.05 compared to DIO rats. Abbreviation: DIO, diet-induced obese.