Prolonged administration of pyridostigmine impairs neuromuscular function with and without down-regulation of acetylcholine receptors

Induction of distinct neuroinflammatory markers and gut dysbiosis by differential pyridostigmine bromide dosing in a chronic mouse model of GWI showing persistent exercise fatigue and cognitive impairment

AIMS

To characterize neuroinflammatory and gut dysbiosis signatures that accompany exaggerated exercise fatigue and cognitive/mood deficits in a mouse model of Gulf War Illness (GWI).

METHODS

Adult male C57Bl/6N mice were exposed for 28 d (5 d/wk) to pyridostigmine bromide (P.O.) at 6.5 mg/kg/d, b.i.d. (GW1) or 8.7 mg/kg/d, q.d. (GW2); topical permethrin (1.3 mg/kg), topical N,N-diethyl-meta-toluamide (33%) and restraint stress (5 min). Animals were phenotypically evaluated as described in an accompanying article [124] and sacrificed at 6.6 months post-treatment (PT) to allow measurement of brain neuroinflammation/neuropathic pain gene expression, hippocampal glial fibrillary acidic protein, brain Interleukin-6, gut dysbiosis and serum endotoxin.

KEY FINDINGS

Compared to GW1, GW2 showed a more intense neuroinflammatory transcriptional signature relative to sham stress controls. Interleukin-6 was elevated in GW2 and astrogliosis in hippocampal CA1 was seen in both GW groups. Beta-diversity PCoA using weighted Unifrac revealed that gut microbial communities changed after exposure to GW2 at PT188. Both GW1 and GW2 displayed systemic endotoxemia, suggesting a gut-brain mechanism underlies the neuropathological signatures. Using germ-free mice, probiotic supplementation with Lactobacillus reuteri produced less gut permeability than microbiota transplantation using GW2 feces.

SIGNIFICANCE

Our findings demonstrate that GW agents dose-dependently induce differential neuropathology and gut dysbiosis associated with cognitive, exercise fatigue and mood GWI phenotypes. Establishment of a comprehensive animal model that recapitulates multiple GWI symptom domains and neuroinflammation has significant implications for uncovering pathophysiology, improving diagnosis and treatment for GWI.

Persistent exercise fatigue and associative learning deficits in combination with transient glucose dyshomeostasis in a GWI mouse model

Aims:

To characterize exercise fatigue, metabolic phenotype and cognitive and mood deficits correlated with brain neuroinflammatory and gut microbiome changes in a chronic Gulf War Illness (GWI) mouse model. The latter have been described in an accompanying paper [1].

Main methods:

Adult male C57Bl/6N mice were exposed for 28 days (5 days/week) to pyridostigmine bromide: 6.5 mg/kg, b.i.d., P.O. (GW1) or 8.7 mg/kg, q.d., P.O. (GW2); topical permethrin (1.3 mg/kg in 100% DMSO) and N,N-diethyl-meta-toluamide (DEET 33% in 70% EtOH) and restraint stress (5 min). Exercise, metabolic and behavioral endpoints were compared to sham stress control (CON/S).

Key findings:

Relative to CON/S, GW2 presented persistent exercise intolerance (through post-treatment (PT) day 161), deficient associative learning/memory, and transient insulin insensitivity. In contrast to GW2, GW1 showed deficient long-term object recognition memory, milder associative learning/memory deficit, and behavioral despair.

Significance:

Our findings demonstrate that GW chemicals dose-dependently determine the presentation of exercise fatigue and severity/type of cognitive/mood-deficient phenotypes that show persistence. Our comprehensive mouse model of GWI recapitulates the major multiple symptom domains characterizing GWI, including fatigue and cognitive impairment that can be used to more efficiently develop diagnostic tests and curative treatments for ill Gulf War veterans.

Increased Cholinergic Tone Causes Pre-synaptic Neuromuscular Degeneration and is Associated with Impaired Diaphragm Function

In vertebrates, muscle activity is dependent on acetylcholine (ACh) released from neuromuscular junctions (NMJs), and changes in cholinergic neurotransmission are linked to a variety of neuromuscular diseases, including congenital myasthenic syndromes (CMS). The storage and release of ACh depends on the activity of the Vesicular Acetylcholine Transporter (VAChT), a rate-limiting step for cholinergic neurotransmission whose loss of function mutations was shown to cause human congenital myasthenia. However, we know much less about increased VAChT activity, due to copy number variations, for example. Therefore, here we investigated the impact of increased VAChT expression and consequently ACh levels at the synaptic cleft of the diaphragm NMJs. We analyzed structure and function of nerve and muscles from a mouse model of cholinergic hyperfunction (ChAT-ChR2-EYFP) with increased expression of VAChT. Our results showed a significant increase of ACh released under evoked stimuli. However, we observed deleterious changes in synaptic vesicles cycle (impaired endocytosis and decrease in vesicles number), together with structural alterations of NMJs. Interestingly, ultrastructure analyses showed that synaptic vesicles from ChAT-ChR2-EYFP mice NMJs were larger, which might be related to increased ACh load. We also observed that these larger synaptic vesicles were less rounded in comparison with control. Finally, we showed that ChAT-ChR2-EYFP mice NMJs have compromised safety factor, possible due to the structural alterations we described. These findings reveal that physiological cholinergic activity is important to maintain the structure and function of the neuromuscular system and help to understand some of the neuromuscular adverse effects experienced by chronically increased NMJ neurotransmission, such as individuals treated with cholinesterase inhibitors.

Cholinergic Stimulation by Pyridostigmine Bromide Before Myocardial Infarction Prevent Cardiac and Autonomic Dysfunction

Inflammatory processes and cardiovascular autonomic imbalance are very relevant characteristic of the enormous dynamic process that is a myocardial infarction (MI). In this sense, some studies are investigating pharmacological therapies using acetylcholinesterase inhibitors, such as pyridostigmine bromide (PYR), aiming to increase parasympathetic tone after MI. Here we hypothesized that the use of PYR before the MI might bring an additional positive effect to the autonomic function, and consequently, in the inflammatory response and cardiac function. The present study aimed to evaluate left ventricular function, baroreflex sensitivity, autonomic modulation, and inflammatory profile in PYR-treated rats previously to MI. Methods: Male Wistar rats (250–300 g) were treated for 60 days with PYR. After treatment, they were submitted to the MI. After the MI, the autonomic and ventricular function were evaluated, as well as the systemic, left ventricle, and adipose tissue inflammatory profile. Results: PYR, performed before MI, prevented HR increase, systolic function impairment, baroreflex sensitivity drop, as well as pulse interval variance, RMSSD, blood pressure and parasympathetic modulation reduction in treated rats compared to untreated rats. Also, this positive functional changes may have been a result of the reduced inflammatory parameters in the left ventricle (IFN-γ, IL-6, and IL-1β), as well as increased IL-10 expression and IL-10/TNF-α ratio in treated animals before MI. Conclusion: Prior treatment with PYR prevents impairment of the autonomic nervous system after MI, which may be associated with the attenuated expression of inflammatory factors and heart dysfunction.

Effect of pyridostigmine on in vivo and in vitro respiratory muscle of mdx mice

The current work was conducted to verify the contribution of neuromuscular transmission defects at the neuromuscular junction to Duchenne Muscular Dystrophy disease progression and respiratory dysfunction. We tested pyridostigmine and pyridostigmine encapsulated in liposomes (liposomal PYR), an acetylcholinesterase inhibitor to improve muscular contraction on respiratory muscle function in mdx mice at different ages. We evaluated in vivo with the whole-body plethysmography, the ventilatory response to hypercapnia, and measured in vitro diaphragm strength in each group. Compared to C57BL10 mice, only 17 and 22 month-old mdx presented blunted ventilatory response, under normocapnia and hypercapnia. Free pyridostigmine (1mg/kg) was toxic to mdx mice, unlike liposomal PYR, which did not show any side effect, confirming that the encapsulation in liposomes is effective in reducing the toxic effects of this drug. Treatment with liposomal PYR, either acute or chronic, did not show any beneficial effect on respiratory function of this DMD experimental model. The encapsulation in liposomes is effective to abolish toxic effects of drugs.