Antiallodynic effects of alpha lipoic acid in an optimized RR‐EAE mouse model of MS‐neuropathic pain are accompanied by attenuation of upregulated BDNF‐TrkB‐ERK signaling in the dorsal horn of the spinal cord

Abstract

Neuropathic pain may affect patients with multiple sclerosis (MS) even in early disease. In an experimental autoimmune encephalomyelitis (EAE)-mouse model of MS, chronic alpha lipoic acid (ALA) treatment reduced clinical disease severity, but MS-neuropathic pain was not assessed. Hence, we investigated the pain-relieving efficacy and mode of action of ALA using our optimized relapsing-remitting (RR)-EAE mouse model of MS-associated neuropathic pain. C57BL/6 mice were immunized with MOG35-55 and adjuvants (Quil A and pertussis toxin) to induce RR-EAE; sham-mice received adjuvants only. RR-EAE mice received subcutaneous ALA (3 or 10 mg kg−1 day−1) or vehicle for 21 days (15–35 d.p.i.; [days postimmunization]); sham-mice received vehicle. Hindpaw hypersensitivity was assessed blinded using von Frey filaments. Following euthanasia (day 35 d.p.i.), lumbar spinal cords were removed for immunohistochemical and molecular biological assessments. Fully developed mechanical allodynia in the bilateral hindpaws of vehicle-treated RR-EAE mice was accompanied by marked CD3+ T-cell infiltration, microglia activation, and increased brain-derived neurotrophic factor (BDNF)-tyrosine kinase B (TrkB) signaling in the dorsal horn of the lumbar spinal cord. Consequently, phospho-ERK, a marker of central sensitization in neuropathic pain, was upregulated in the spinal dorsal horn. Importantly, hindpaw hypersensitivity was completely attenuated in RR-EAE mice administered ALA at 10 mg kg−1 day−1 but not 3 mg kg−1 day−1. The antiallodynic effect of ALA (10 mg kg−1 day−1) was associated with a marked reduction in the aforementioned spinal dorsal horn markers to match their respective levels in the vehicle-treated sham-mice. Our findings suggest that ALA at 10 mg kg−1 day−1 produced its antiallodynic effects in RR-EAE mice by reducing augmented CD3+ T-cell infiltration and BDNF-TrkB-ERK signaling in the spinal dorsal horn.

Attenuation of the Infiltration of Angiotensin II Expressing CD3+ T-Cells and the Modulation of Nerve Growth Factor in Lumbar Dorsal Root Ganglia – A Possible Mechanism Underpinning Analgesia Produced by EMA300, An Angiotensin II Type 2 (AT2) Receptor Antagonist

“…The lumbar DRG sections from all treatment groups were air-dried prior to immunostaining followed by washing with PBS containing 0.05% Tween 20 (Sigma-Aldrich, Sydney, NSW, Australia) (referred herein as PBST) for 2 × 10 min. Subsequently, the sections were incubated for 1–2 h in blocking buffer containing 10% normal goat serum (NGS) (Invitrogen, Mulgrave, VIC, Australia) or 5% Bovine Serum Albumin (BSA) (Sigma–Aldrich) as appropriate for each IHC antibody ( Muralidharan et al, 2014 ; Khan et al, 2015 ). Later, the sections were incubated with appropriate primary antibodies for at least 15–20 h at ∼4–8°C.…”

Comparative studies of glial fibrillary acidic protein and brain‐derived neurotrophic factor expression in two transgenic mouse models of Alzheimer’s disease

“…During all experiments, control slides using primary or secondary antibody alone were used to confirm the absence of autofluorescence or background noise. The primary antibodies selected herein have been extensively used and validated for their specificity 48–50 …”

Pain in autoimmune disorders

“…The role of microglia in autoimmune disease‐associated pain has also been explored. For example, several studies have shown that microglial activation contributes to neuropathic pain development in multiple sclerosis (Olechowski et al, ; Zhu et al, ; Khan et al, ). A reduction of microglial activation is associated with a reduction in pain in multiple sclerosis (Khan et al, ).…”

“…For example, several studies have shown that microglial activation contributes to neuropathic pain development in multiple sclerosis (Olechowski et al, ; Zhu et al, ; Khan et al, ). A reduction of microglial activation is associated with a reduction in pain in multiple sclerosis (Khan et al, ). The common pathways described above, such as the factalkine signalling pathway, have also been implicated in multiple sclerosis‐related pain (Schmitz et al, ; Zhu et al, ).…”