The impact of dextran sodium sulphate and probiotic pre-treatment in a murine model of Parkinson's disease

Abstract

Background: Recent work has established that Parkinson's disease (PD) patients have an altered gut microbiome, along with signs of intestinal inflammation. This could help explain the high degree of gastric disturbances in PD patients, as well as potentially be linked to the migration of peripheral inflammatory factors into the brain. To our knowledge, this is the first study to examine microbiome alteration prior to the induction of a PD murine model.

Methods: We presently assessed whether pre-treatment with the probiotic, VSL #3, or the inflammatory inducer, dextran sodium sulphate (DSS), would influence the PD-like pathology provoked by a dual hit toxin model using lipopolysaccharide (LPS) and paraquat exposure.

Results: While VSL #3 has been reported to have anti-inflammatory effects, DSS is often used as a model of colitis because of the gut inflammation and the breach of the intestinal barrier that it induces. We found that VSL#3 did not have any significant effects (beyond a blunting of LPS paraquat-induced weight loss). However, the DSS treatment caused marked changes in the gut microbiome and was also associated with augmented behavioral and inflammatory outcomes. In fact, DSS markedly increased taxa belonging to the Bacteroidaceae and Porphyromonadaceae families but reduced those from Rikencellaceae and S24-7, as well as provoking colonic pro-inflammatory cytokine expression, consistent with an inflamed gut. The DSS also increased the impact of LPS plus paraquat upon microglial morphology, along with circulating lipocalin-2 (neutrophil marker) and IL-6. Yet, neither DSS nor VSL#3 influenced the loss of substantia nigra dopamine neurons or the astrocytic and cytoskeleton remodeling protein changes that were provoked by the LPS followed by paraquat treatment.

Conclusions: These data suggest that disruption of the intestinal integrity and the associated microbiome can interact with systemic inflammatory events to promote widespread brain-gut changes that could be relevant for PD and at the very least, suggestive of novel neuro-immune communication.

Keywords: Inflammatory neurodege5neration; Microbiota; Microglia; Probiotic.

Fig. 1

Timeline of experimental treatments, behaviors, and sample collections.

Fig. 2

Microbiota sequencing revealed that LPS and paraquat treatment did not alter the composition of the gut microbiome. However, VSL#3 administration increased levels of Streptococcaceae family bacteria but had no other impact, whereas DSS treatment had the biggest effects. Specifically, DSS significantly increased levels of the Verrucomicrobaceae, Bacteriodaceae, Clostridiaceae, and Porphyromonadaceae families and decreased levels of the S24-7 and Rikencellaceae families, relative to cornstarch-treated controls

Fig. 3

Weight changes and survival throughout the experiment. a DSS treatment (red lines with either saline control (Con) or LPS-paraquat co-administration) caused marked sickness and mice reached endpoint in 7 days following cessation of DSS treatment (25–30% reached endpoint). b DSS-treated animals lost weight 48 h after cessation of DSS treatment (pre-surgery weight) (p < 0.001) and c by the end of the experiment, the VSL#3-treated animals recovered, while LPS and paraquat treatment reduced weight gain in control and DSS administered mice (p < 0.01). **p < 0.01 compared to controls. ***p < 0.001 compared to other water treatment groups

Fig. 4

Behavioral motor disturbances were observed in the DSS and LPS + paraquat-treated animals. As shown in panel a, all DSS-treated mice exhibited reduced time spent on rotarod, relative to all other animals. Panel b illustrates that the DSS treatment initially (prior to LPS and paraquat) reduced home-cage locomotor activity. Thereafter, panel c illustrates that by the time of sacrifice, the home-cage locomotor activity was significantly diminished by the LPS-paraquat treatment. However, this decrement was most apparent in the mice that also received DSS earlier. *p < 0.05 compared to non-treated control mice. ***p < 0.001 compared to other water treatment groups

Fig. 5

Stereological counts of TH+ neurons in the SNc ipsilateral to the intra-nigral LPS infusion. Clearly, the LPS infusion coupled with systemic paraquat (i.p. 10 mg/kg, six injections over 2 weeks) administration significantly reduced the number of viable TH+ neurons within the SNc. But no significant differences whatsoever were observed concerning the VSL#3 and DSS treatments. ***p < 0.001 compared to saline-treated animals

Fig. 6

Microglial activation was assessed using a validated semi-quantitative rating scale for morphology on ×20 images of SNc sections with IBA-1 (red) and TH (green) immunofluorescence. The DSS treatment alone significantly increased ratings of activation scoring (p < 0.05), as did the LPS and paraquat combination treatment (p < 0.001). But the VSL#3 treatment was without significant effect on microglial morphological ratings. *p < 0.05 compared to saline treated animals ***p < 0.001 compared to either: a control water-treated mice that received LPS + PQ infusion or b saline-infused mice that received DSS treatment

Fig. 7

Pro-inflammatory cytokine expression in the colon was quantified by qRT PCR and normalized against GAPDH expression. Both TNF-α and IL-1β levels were found to be elevated in DSS-treated mice following sacrifice. *p < 0.05 compared to water intake control animals

Fig. 8

As shown in panel a, plasma lipocalin-2 (LCN-2) levels were significantly elevated by DSS treatment, whereas panel b shows that circulating IL-6 levels significantly increased in the LPS- and paraquat-treated mice. Both IL-1β (p = 0.30; panel c) and IL-10 (p = 0.26; panel d) levels were modestly but not significantly elevated in DSS-treated mice that also received LPS + paraquat. *p < 0.05 compared to control animals, ***p < 0.001 compared to other water treatment groups

Fig. 9

Western blot assessment of SNc tissue revealed increased levels of GFAP (a) and WAVE2 (b) in LPS and paraquat-treated mice. *p < 0.05 compared to saline-treated animals, **p < 0.01 compared to control animals