Promising Effects of Neurorestorative Diets on Motor, Cognitive, and Gastrointestinal Dysfunction after Symptom Development in a Mouse Model of Parkinson's Disease

Abstract

Parkinson's disease (PD) is characterized by the progressive degeneration of dopaminergic nigrostriatal neurons, with reductions in the function and amount of dopaminergic synapses. Therefore, synapse loss and membrane-related pathology provide relevant targets for interventions in PD. We previously showed the beneficial preventive effects of a dietary intervention containing uridine and DHA, two precursors for membrane synthesis, in the intrastriatal rotenone model for PD. Here, we examined the therapeutic potential of the same dietary intervention on motor, cognitive, and gastrointestinal symptoms. In addition, we tested the effects of an extended nutritional formula based on the same precursors plus other nutrients that increase membrane phospholipid synthesis as well as prebiotic fibers. C57BL/6J mice received a unilateral rotenone injection in the striatum. Dietary interventions started 28 days after surgery, when motor-symptoms had developed. Readout parameters included behavioral tasks measuring motor function and spatial memory as well as intestinal function and histological examination of brain and gut to assess PD-like pathology. Our results show that rotenone-induced motor and non-motor problems were partially alleviated by the therapeutic dietary interventions providing uridine and DHA. The extended nutritional intervention containing both precursors and other nutrients that increase phospholipid synthesis as well as prebiotic fibers was more effective in normalizing rotenone-induced motor and non-motor abnormalities. The latter diet also restored striatal DAT levels, indicating its neurorestorative properties. This is the first study demonstrating beneficial effects of specific dietary interventions, given after full development of symptoms, on a broad spectrum of motor and non-motor symptoms in a mouse model for PD.

Keywords: Rotenone Parkinson's model; docosahexaenoic acid; motor-symptoms; non-motor symptoms; uridine.

Figures

Figure 1

Effects of the dietary interventions that were started after development of full motor dysfunction on motor symptoms;(A) rotarod performance, (B) inverted screen test, and (C) forelimb grip strength test. Unilateral rotenone injection induced motor dysfunction and grip strength loss. Dietary interventions had beneficial effects on motor function and grip strength. The extended nutritional intervention (Diet2) was more effective than Diet1 for all the tests. Data are shown as mean ± SEM. *p < 0.05, **p < 0.01, ****p < 0.0001. (n = 10 per group).

Figure 2

Effects of dietary interventions that were started after development of full motor dysfunction on (A) the number of dopaminergic cells indicated by the number of tyrosine hydroxylase (TH) immunoreactive cells in the substantia nigra and (B) dopamine transporter (DAT) expression in the striatum. Photographs show typical examples of TH and DAT immunostaining of substantia nigra and striatum, respectively, from all treatment groups. Rotenone injection decreased the number of dopaminergic cells in the substantia nigra and the level of DAT expression in the striatum. No differences were found in the number of TH positive cells and DAT expression between hemispheres after unilateral injection of rotenone. Dietary interventions had no effect on the number of TH positive cells but Diet2 increased DAT expression. Data are shown as mean ± SEM. *p < 0.05, ***p < 0.001. (Scale bar: 200 μm applies to all panels). (n = 6 for TH immunostaining and n = 4 for DAT immunostaining).

Figure 3

Effects of dietary interventions that were started after development of full motor dysfunction on spatial object recognition test. Sham-operated animals selectively re-explored the displace object (DO) as compared to the non-displaced object (NDO) throughout the experiment. Rotenone decreased animals' ability to react to a spatial novelty from day 42 after surgery onwards. On day 70 after surgery, rotenone-injected animals on Diet2 showed better spatial discrimination abilities compared to rotenone-injected animals on control diet. Data are shown as mean ± SEM. **p < 0.01, ****p < 0.0001 compared to Sham + Control food. ##p < 0.01 compared to Rotenone + Control food (n = 10 per group).

Figure 4

Effects of dietary interventions that were started after development of full motor dysfunction on: (A) intestinal transit indicated by the total distance traveled by the Evans blue dye in the GI tract 30 min after its injection by oral gavage, (B) alpha-synuclein expression in the colon and (C) on enteric glial cells expression in the colon as indicated by the glial fibrillary acidic protein (GFAP). Rotenone injection reduced intestinal transit time and increased alpha-synuclein (shown in green) and GFAP (shown in red) expression in the myenteric and submucosal plexus of the colon. Dietary interventions improved rotenone-induced delayed intestinal transit and reduced rotenone-induced alpha-synuclein and GFAP overexpression in the colon. The beneficial effect of Diet2 on intestinal transit after rotenone exposure was more pronounced that the effect of Diet1. The Corrected Total Fluorescence (CTF) was calculated with the formula: integrated density-(area × mean fluorescence of background reading). Data are shown as mean ± SEM. *p < 0.05, ***p < 0.001, ****p < 0.0001. (Scale bar: 50 μm applies to all panels) (n = 9 or 10 per group).

Figure 5

Effects of dietary interventions that were started after development of full motor dysfunction on (A) colon length and (B) the number of T-cells in the colon. Photographs show typical examples of T-cell immunostaining in the colon from all treatment groups. Rotenone reduced the length of the colon and increased the number of T-cells (shown in brown). Both dietary interventions increased rotenone-induced reduction of the colon and reduced T-cell infiltration. Diet2 was more effective in normalizing rotenone induced T-cell infiltration than Diet1. Data are shown as mean ± SEM. *p < 0.05, ***p < 0.001, ****p < 0.0001. (Scale bar: 50 μm applies to all panels). (n = 10 per group for colon length and n = 7 for T-cell infiltration 10).