Low Phytanic Acid-Concentrated DHA Prevents Cognitive Deficit and Regulates Alzheimer Disease Mediators in an ApoE-/- Mice Experimental Model

Abstract

Alzheimer's disease (AD) is the main cause of dementia and cognitive impairment. It has been associated with a significant diminution of omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) levels in the brain. Clinical trials with DHA as a treatment in neurological diseases have shown inconsistent results. Previously, we reported that the presence of phytanic acid (PhA) in standard DHA compositions could be blunting DHA's beneficial effects. Therefore, we aimed to analyze the effects of a low PhA-concentrated DHA and a standard PhA-concentrated DHA in Apolipoprotein E knockout (ApoE^-/-) mice. Behavioral tests and protein expression of pro-inflammatory, pro-oxidant, antioxidant factors, and AD-related mediators were evaluated. Low PhA-concentrated DHA decreased Aβ, ß-amyloid precursor protein (APP), p-tau, Ca²⁺/calmodulin-dependent protein kinase II (CAMKII), caspase 3, and catalase, and increased brain derived neurotrophic factor (BDNF) when compared to standard PhA-concentrated DHA. Low PhA-concentrated DHA decreased interleukin (IL)-6 and tumor necrosis factor alpha (TNF-α) protein expression in ApoE^-/- mice when compared to standard PhA-concentrated DHA. No significant differences were found in p22phox, inducible nitric oxide synthase (iNOS), glutathione peroxidase (GPx), superoxide dismutase 1 (SOD-1), and tau protein expression. The positive actions of a low PhA-concentrated DHA were functionally reflected by improving the cognitive deficit in the AD experimental model. Therefore, reduction of PhA content in DHA compositions could highlight a novel pathway for the neurodegeneration processes related to AD.

Keywords: Alzheimer’s; ApoE−/−; DHA; inflammation; neuroprotection; oxidation; phytanic acid.

Figure 1

Effects of docosahexaenoic acid (DHA)(PhA:50) and DHA (PhA:1000) on spontaneous mouse locomotor activity in ApoE^−/− and wild-type mice. Data shown as mean ± SEM. *** p < 0.0001 compared between genotypes. (n = 8 or 9).

Figure 2

Effects of DHA (PhA:50) and DHA (PhA:1000) on the curve learning (A,B), spatial memory (C,D), and visual cue localization (E,F) in the Morris Water Maze (MWM) test in ApoE^−/− and wild-type mice. Data shown as mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^$ p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8 or 9).

Figure 2

Effects of DHA (PhA:50) and DHA (PhA:1000) on the curve learning (A,B), spatial memory (C,D), and visual cue localization (E,F) in the Morris Water Maze (MWM) test in ApoE^−/− and wild-type mice. Data shown as mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^$ p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8 or 9).

Figure 3

Effects of DHA (PhA:50) and DHA (PhA:1000) on relative protein expression of (A) amyloid precursor protein (APP) and (B) amyloid beta (Aß) in hippocampus of ApoE^−/− and wild-type mice. Data show mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^$ p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8).

Figure 4

Effects of DHA (PhA:50) and DHA (PhA:1000) on relative protein expression of (A) Total tau, (B) p-Tau^s-396 and (C) Ca²⁺/calmodulin-dependent protein kinase II (CaMK II) in hippocampus of ApoE^−/− and wild-type mice. Data show mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^& p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in wild-type mice; ^$ p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8).

Figure 5

Effects of DHA (PhA:50) and DHA (PhA:1000) on relative protein expression brain derived neurotrophic factor (BDNF) in hippocampus of ApoE^−/− and wild-type mice. Data show mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^$ p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8).

Figure 6

Effects of DHA (PhA:50) and DHA (PhA:1000) on relative protein expression of (A) interleukin-6 (IL-6), (B) tumor necrosis factor alpha (TNF-α) and (C) inducible nitric oxide synthase (iNOS) in hippocampus of ApoE^−/− and wild-type mice. Data shown as mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^& p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in wild-type mice; ^$ p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8).

Figure 7

Effects of DHA (PhA:50) and DHA (PhA:1000) on relative protein expression of NADPH oxidase subunit p22phox (p22phox) in hippocampus of ApoE^−/− and wild-type mice. Data shown as mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice. (n = 8).

Figure 8

Effects of DHA (PhA:50) and DHA (PhA:1000) on relative protein expression of (A) superoxide dismutase 1 (SOD-1), (B) catalase, and (C) glutathione peroxidase (GPx) in hippocampus of ApoE^−/− and wild-type mice. Data show mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^& p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in wild-type mice; ^$ p<0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8).

Figure 9

Effects of DHA (PhA:50) and DHA (PhA:1000) on relative protein expression of caspase-3 (cas-3) in hippocampus of ApoE^−/− and wild-type mice. Data shown as mean ± SEM. * p < 0.05 compared to control wild-type mice; ^# p < 0.05 compared to control ApoE^−/− mice; ^& p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in wild-type mice; ^$ p < 0.05 compared between DHA (PhA:50) and DHA (PhA:1000) in ApoE^−/− mice. (n = 8).