Of mice, microglia, and (wo)men: a case series and mechanistic investigation of hydroxychloroquine for complex regional pain syndrome

Inhibition of Pyroptosis by Hydroxychloroquine as a Neuroprotective Strategy in Ischemic Stroke

Hydroxychloroquine (HCQ), a well-known antimalarial and anti-inflammatory drug, has demonstrated potential neuroprotective effects in ischemic stroke by inhibiting pyroptosis, a programmed cell death associated with inflammation. This study investigates the impact of HCQ on ischemic stroke pathology using both in vivo and in vitro models. In vivo, C57BL/6 mice subjected to middle cerebral artery occlusion (MCAO) were treated with HCQ. Neurological deficits, infarct volume, and the expression of pyroptosis markers were evaluated. The results demonstrated that HCQ significantly improved motor function and reduced infarct volume in the MCAO mouse model. In vitro, BV2 microglial cells exposed to lipopolysaccharide (LPS) and oxygen-glucose deprivation (OGD) were treated with HCQ. Western blot and immunofluorescence analyses revealed that HCQ effectively suppressed the expression of pyroptosis markers GSDMD and NLRP3 in both in vivo and in vitro models. These findings suggest that HCQ mitigates ischemic stroke damage by inhibiting pyroptosis, highlighting its potential as a therapeutic agent for ischemic stroke. This study provides novel insights into the molecular mechanisms by which HCQ exerts its neuroprotective effects, offering a promising new avenue for developing safe, cost-effective, and widely applicable stroke treatments. The potential of HCQ to modulate neuroinflammatory pathways presents a significant advancement in ischemic stroke therapy, emphasizing the importance of targeting pyroptosis in stroke management and the broader implications for treating neuroinflammatory conditions.Significance Statement Ischemic stroke remains a leading cause of disability and death globally, with limited effective treatments. This study reveals that HCQ significantly mitigates ischemic stroke damage by inhibiting pyroptosis, a form of programmed cell death. Using in vivo and in vitro models, HCQ was shown to improve motor function and reduce infarct volume, highlighting its potential as a neuroprotective agent. These findings offer a promising new therapeutic approach for ischemic stroke, emphasizing the importance of targeting pyroptosis in stroke treatment.

Temporal changes of spinal microglia in murine models of neuropathic pain: a scoping review

Neuropathic pain (NP) is an ineffectively treated, debilitating chronic pain disorder that is associated with maladaptive changes in the central nervous system, particularly in the spinal cord. Murine models of NP looking at the mechanisms underlying these changes suggest an important role of microglia, the resident immune cells of the central nervous system, in various stages of disease progression. However, given the number of different NP models and the resource limitations that come with tracking longitudinal changes in NP animals, many studies fail to truly recapitulate the patterns that exist between pain conditions and temporal microglial changes. This review integrates how NP studies are being carried out in murine models and how microglia changes over time can affect pain behavior in order to inform better study design and highlight knowledge gaps in the field. 258 peer-reviewed, primary source articles looking at spinal microglia in murine models of NP were selected using Covidence. Trends in the type of mice, statistical tests, pain models, interventions, microglial markers and temporal pain behavior and microglia changes were recorded and analyzed. Studies were primarily conducted in inbred, young adult, male mice having peripheral nerve injury which highlights the lack of generalizability in the data currently being collected. Changes in microglia and pain behavior, which were both increased, were tested most commonly up to 2 weeks after pain initiation despite aberrant microglia activity also being recorded at later time points in NP conditions. Studies using treatments that decrease microglia show decreased pain behavior primarily at the 1- and 2-week time point with many studies not recording pain behavior despite the involvement of spinal microglia dysfunction in their development. These results show the need for not only studying spinal microglia dynamics in a variety of NP conditions at longer time points but also for better clinically relevant study design considerations.

Chronic pain and complex regional pain syndrome are associated with alterations to the intestinal microbiota in both humans and mice. An observational cross-sectional study

Objective

This study aimed to evaluate pain metrics and gut microbiota differences from human subjects with complex regional pain syndrome (CRPS) compared to cohabitants (HHC) and non-cohabitating (biobank) controls. In addition, we aimed evaluate longitudinal changes of gut microbiota using a mouse model of acute and chronic CRPS.

Methods

In an observational, cross-sectional study, 25 patients with CRPS and 24 household controls (HHC) were recruited, completed pain questionnaires, and submitted stool samples. 23 biobank stool samples were matched to the CRPS group. Additionally, longitudinal stool samples were collected from a mouse model of acute and chronic CRPS. 16S rRNA gene sequencing analysis was performed on all samples.

Results

A diagnosis of CRPS is associated with higher pain, increased pain interference, and decreased physical and social function when compared to HHC. Interestingly, 46% of HHC reported significant daily pain. In the households where HHC were also suffering from pain, there was decreased bacterial richness and diversity when compared to households wherein only the participant with CRPS suffered from pain. Furthermore, when comparing households where the HHC had significant pain, CRPS was clinically more severe. In the mouse model of CRPS, we observed decreased bacterial richness and diversity when compared to non-cohabitating littermate controls.

Conclusions

Both humans living in chronic pain households and mice shared distinct taxa over the time course of disease and pain chronicity. These findings suggest that microbiota changes seen in CRPS as well as in a mouse model of CRPS may reflect pain chronicity and may indicate that pain alone can contribute to microbiota dysbiosis. The trial was registered at ClinicalTrials.gov (NCT03612193).

Complex Regional Pain Syndrome: Evidence-Based Advances in Concepts and Treatments

PURPOSE OF REVIEW

This review presents the most current information about the epidemiology of complex regional pain syndrome (CRPS), classification and diagnostic criteria, childhood CRPS, subtypes, pathophysiology, conventional and less conventional treatments, and preventive strategies.

RECENT FINDINGS

CRPS is a painful disorder with multifactorial pathophysiology. The data describe sensitization of the central and peripheral nervous systems, inflammation, possible genetic factors, sympatho-afferent coupling, autoimmunity, and mental health factors as contributors to the syndrome. In addition to conventional subtypes (type I and type II), cluster analyses have uncovered other proposed subtypes. Prevalence of CRPS is approximately 1.2%, female gender is consistently associated with a higher risk of development, and substantial physical, emotional, and financial costs can result from the syndrome. Children with CRPS seem to benefit from multifaceted physical therapy leading to a high percentage of symptom-free patients. The best available evidence along with standard clinical practice supports pharmacological agents, physical and occupational therapy, sympathetic blocks for engaging physical restoration, steroids for acute CRPS, neuromodulation, ketamine, and intrathecal baclofen as therapeutic approaches. There are many emerging treatments that can be considered as a part of individualized, patient-centered care. Vitamin C may be preventive. CRPS can lead to progressively painful sensory and vascular changes, edema, limb weakness, and trophic disturbances, all of which substantially erode healthy living. Despite some progress in research, more comprehensive basic science investigation is needed to clarify the molecular mechanisms of the disease so that targeted treatments can be developed for better outcomes. Incorporating a variety of standard therapies with different modes of action may offer the most effective analgesia. Introducing less conventional approaches may also be helpful when traditional treatments fail to provide sufficient improvement.

Sex-distinct microglial activation and myeloid cell infiltration in the spinal cord after painful peripheral injury

Chronic pain is a common and often debilitating problem that affects 100 million Americans. A better understanding of pain's molecular mechanisms is necessary for developing safe and effective therapeutics. Microglial activation has been implicated as a mediator of chronic pain in numerous preclinical studies; unfortunately, translational efforts using known glial modulators have largely failed, perhaps at least in part due to poor specificity of the compounds pursued, or an incomplete understanding of microglial reactivity. In order to achieve a more granular understanding of the role of microglia in chronic pain as a means of optimizing translational efforts, we utilized a clinically-informed mouse model of complex regional pain syndrome (CRPS), and monitored microglial activation throughout pain progression. We discovered that while both males and females exhibit spinal cord microglial activation as evidenced by increases in Iba1, activation is attenuated and delayed in females. We further evaluated the expression of the newly identified microglia-specific marker, TMEM119, and identified two distinct populations in the spinal cord parenchyma after peripheral injury: TMEM119+ microglia and TMEM119- infiltrating myeloid lineage cells, which are comprised of Ly6G + neutrophils and Ly6G- macrophages/monocytes. Neurons are sensitized by inflammatory mediators released in the CNS after injury; however, the cellular source of these cytokines remains somewhat unclear. Using multiplex in situ hybridization in combination with immunohistochemistry, we demonstrate that spinal cord TMEM119+ microglia are the cellular source of cytokines IL6 and IL1β after peripheral injury. Taken together, these data have important implications for translational studies: 1) microglia remain a viable analgesic target for males and females, so long as duration after injury is considered; 2) the analgesic properties of microglial modulators are likely at least in part related to their suppression of microglial-released cytokines, and 3) a limited number of neutrophils and macrophages/monocytes infiltrate the spinal cord after peripheral injury but have unknown impact on pain persistence or resolution. Further studies to uncover glial-targeted therapeutic interventions will need to consider sex, timing after injury, and the exact target population of interest to have the specificity necessary for translation.