Blood-borne and brain-derived microparticles in morphine-induced anti-nociceptive tolerance

Persistent neuroinflammation and functional deficits in a murine model of decompression sickness

We hypothesized that early intra-central nervous system (CNS) responses in a murine model of decompression sickness (DCS) would be reflected by changes in the microparticles (MPs) that exit the brain via the glymphatic system, and due to systemic responses the MPs would cause inflammatory changes lasting for many days leading to functional neurological deficits. Elevations on the order of threefold of blood-borne inflammatory MPs, neutrophil activation, glymphatic flow, and neuroinflammation in cerebral cortex and hippocampus were found in mice at 12 days after exposure to 760 kPa of air for 2 h. Mice also exhibited a significant decline in memory and locomotor activity, as assessed by novel object recognition and rotarod testing. Similar inflammatory changes in blood, neuroinflammation, and functional impairments were initiated in naïve mice by injection of filamentous (F-) actin-positive MPs, but not F-actin-negative MPs, obtained from decompressed mice. We conclude that high pressure/decompression stress establishes a systemic inflammatory process that results in prolonged neuroinflammation and functional impairments in the mouse decompression model.NEW & NOTEWORTHY Elevated glymphatic flow due to astrocyte and microglial activation from high-pressure exposure triggers release of microparticles (MPs) to the circulation where neutrophil activation and production of filamentous (F)-actin expressing MPs result in a persistent feed-forward neuroinflammatory cycle and functional deficits lasting for at least 12 days.

Microparticles in Human Perspiration as an Inflammatory Response Index

A blood component analysis is an early step for evaluating inflammatory disorders, but it can be unfeasible in some settings. This pilot study assessed whether extracellular vesicle (EV) changes in perspiration are parallel to those occurring in blood as an alternative or complementary option to diagnose an inflammatory response. In parallel studies, EVs were analyzed in perspiration and blood obtained before and after five self-contained underwater breathing apparatus (SCUBA) divers at the National Aquarium in Baltimore performed a dive to 3.98 m of sea water for 40 min, and five non-divers performed an exercise routine at ambient atmospheric pressure. The results demonstrated that microparticles (MPs) are present in perspiration, their numbers increase in the blood in response to SCUBA diving, and the interleukin (IL)-1β content increases. In contrast, while blood-borne MPs became elevated in response to terrestrial exercise, no statistically significant increases occurred in perspiration, and there were no changes in IL-1β. There were no statistically significant elevations in the exosomes in perspiration or blood in response to SCUBA diving and few changes following terrestrial exercise. These findings suggest that an MP perspiration analysis could be a non-invasive method for detecting inflammatory responses that can occur due to the oxidative stress associated with SCUBA diving.

Inhibition of spinal BRD4 alleviates pyroptosis and M1 microglia polarization via STING-IRF3 pathway in morphine-tolerant rats

BACKGROUND

Morphine tolerance has been a challenging medical issue. Neuroinflammation is considered as a critical mechanism for the development of morphine tolerance. Bromodomain-containing protein 4 (BRD4), a key regulator in cell damage and inflammation, participates in the development of chronic pain. However, whether BRD4 is involved in morphine tolerance and the underlying mechanisms remain unknown.

METHODS

The morphine-tolerant rat model was established by intrathecal administration of morphine twice daily for 7 days. Behavior test was assessed by a tail-flick latency test. The roles of BRD4, pyroptosis, microglia polarization and related signaling pathways in morphine tolerance were elucidated by Western blot, real-time quantitative polymerase chain reaction, and immunofluorescence.

RESULTS

Repeated morphine administration upregulated BRD4 level, induced pyroptosis, and promoted microglia M1-polarization in spinal cord, accompanied by the release of proinflammatory cytokines, such as TNF-α and IL-1β. JQ-1, a BRD4 antagonist, alleviated the development of morphine tolerance, diminished pyroptosis and induced the switch of microglia from M1 to M2 phenotype. Mechanistically, stimulator of interferon gene (STING)- interferon regulatory factor 3 (IRF3) pathway was activated and the protective effect of JQ-1 against morphine tolerance was at least partially mediated by inhibition of STING-IRF3 pathway.

CONCLUSION

This study demonstrated for the first time that spinal BRD4 contributes to pyroptosis and switch of microglia polarization via STING-IRF3 signaling pathway during the development of morphine tolerance, which extend the understanding of the neuroinflammation mechanism of morphine tolerance and provide an alternative strategy for the precaution against of this medical condition.

Neuroinflammation with increased glymphatic flow in a murine model of decompression sickness

This project investigated glial-based lymphatic (glymphatic) function and its role in a murine model of decompression sickness (DCS). DCS pathophysiology is traditionally viewed as being related to gas bubble formation from insoluble gas on decompression. However, a body of work implicates a role for a subset of inflammatory extracellular vesicles, 0.1 to 1 µm microparticles (MPs) that are elevated in human and rodent models in response to high gas pressure and rise further after decompression. Herein, we describe immunohistochemical and Western blot evidence showing that following high air pressure exposure, there are elevations of astrocyte NF-κB and microglial-ionized calcium-binding adaptor protein-1 (IBA-1) along with fluorescence contrast and MRI findings of an increase in glymphatic flow. Concomitant elevations of central nervous system-derived MPs coexpressing thrombospondin-1 (TSP) drain to deep cervical nodes and then to blood where they cause neutrophil activation. A new set of blood-borne MPs are generated that express filamentous actin at the surface that exacerbate neutrophil activation. Blood-brain barrier integrity is disrupted due to activated neutrophil sequestration that causes further astrocyte and microglial perturbation. When postdecompression node or blood MPs are injected into naïve mice, the same spectrum of abnormalities occur and they are blocked with coadministration of antibody to TSP. We conclude that high pressure/decompression causes neuroinflammation with an increased glymphatic flow. The resulting systemic liberation of TSP-expressing MPs sustains the neuroinflammatory cycle lasting for days.NEW & NOTEWORTHY A murine model of central nervous system (CNS) decompression sickness demonstrates that high gas pressure activates astrocytes and microglia triggering inflammatory microparticle (MP) production. Thrombospondin-expressing MPs are released from the CNS via enhanced glymphatic flow to the systemic circulation where they activate neutrophils. Secondary production of neutrophil-derived MPs causes further cell activation and neutrophil adherence to the brain microvasculature establishing a feed-forward neuroinflammatory cycle.

Research progress of p38 as a new therapeutic target against morphine tolerance and the current status of therapy of morphine tolerance

With the development of the medical industry, new painkillers continue to appear in people's field of vision, but so far no painkiller can replace morphine. While morphine has a strong analgesic effect, it is also easy to produce pain sensitivity and tolerance. Due to the great inter-individual differences in patient responses, there are few clear instructions on how to optimise morphine administration regimens, which complicates clinicians' treatment strategies and limits the effectiveness of morphine in long-term pain therapy. P38MAPK is a key member of the MAPK family. Across recent years, it has been discovered that p38MAPK rises dramatically in a wide range of morphine tolerance animal models. Morphine tolerance can be reduced or reversed by inhibiting p38MAPK. However, the role and specific mechanism of p38MAPK are not clear. In this review, we synthesise the relevant findings, highlight the function and potential mechanism of p38MAPK in morphine tolerance, as well as the present status and efficacy of morphine tolerance therapy, and underline the future promise of p38MAPK targeted morphine tolerance treatment.

The YTHDF1-TRAF6 pathway regulates the neuroinflammatory response and contributes to morphine tolerance and hyperalgesia in the periaqueductal gray

Long-term use of opioids such as morphine has negative side effects, such as morphine analgesic tolerance and morphine-induced hyperalgesia (MIH). These side effects limit the clinical use and analgesic efficacy of morphine. Elucidation of the mechanisms and identification of feasible and effective methods or treatment targets to solve this clinical phenomenon are important. Here, we discovered that YTHDF1 and TNF receptor-associated factor 6 (TRAF6) are crucial for morphine analgesic tolerance and MIH. The m6A reader YTHDF1 positively regulated the translation of TRAF6 mRNA, and chronic morphine treatments enhanced the m6A modification of TRAF6 mRNA. TRAF6 protein expression was drastically reduced by YTHDF1 knockdown, although TRAF6 mRNA levels were unaffected. By reducing inflammatory markers such as IL-1β, IL-6, TNF-α and NF-κB, targeted reduction of YTHDF1 or suppression of TRAF6 activity in ventrolateral periaqueductal gray (vlPAG) slows the development of morphine analgesic tolerance and MIH. Our findings provide new insights into the mechanism of morphine analgesic tolerance and MIH indicating that YTHDF1 regulates inflammatory factors such as IL-1β, IL-6, TNF-α and NF-κB by enhancing TRAF6 protein expression.

Opioid tolerance and opioid-induced hyperalgesia: Is TrkB modulation a potential pharmacological solution?

Opioids are widely prescribed for moderate to severe pain in patients with acute illness, cancer pain, and chronic noncancer pain. However, long-term opioid use can cause opioid tolerance and opioid-induced hyperalgesia (OIH), contributing to the opioid misuse and addiction crisis. Strategies to mitigate opioid tolerance and OIH are needed to reduce opioid use and its sequelae. Currently, there are few effective pharmacological strategies that reduce opioid tolerance and OIH. The intrinsic tyrosine kinase receptor B (TrkB) ligand, brain-derived neurotrophic factor (BDNF), has been shown to modulate pain. The BDNF-TrkB signaling plays a role in initiating and sustaining elevated pain sensitivity; however, increasing evidence has shown that BDNF and 7,8-dihydroxyflavone (7,8-DHF), a potent blood-brain barrier-permeable ligand to TrkB, exert neuroprotective, anti-inflammatory, and antioxidant effects that may protect against opioid tolerance and OIH. As such, TrkB signaling may be an important therapeutic avenue in opioid tolerance and OIH. Here, we review 1) the mechanisms of pain, opioid analgesia, opioid tolerance, and OIH; 2) the role of BDNF-TrkB in pain modulation; and 3) the neuroprotective effects of 7,8-DHF and their implications for opioid tolerance and OIH.

Astrocyte-derived microparticles initiate a neuroinflammatory cycle due to carbon monoxide poisoning

We hypothesized that carbon monoxide (CO) establishes an inflammatory cycle mediated by microparticles (MPs). Mice exposed to a CO protocol (1000 ​ppm for 40 ​min and then 3000 ​ppm for 20 ​min) that causes neuroinflammation exhibit NF-κB activation in astrocytes leading to generation of MPs expressing thrombospondin-1(TSP-1) that collect in deep cervical lymph nodes draining the brain glymphatic system. TSP-1 bearing MPs gain access to the blood stream where they activate neutrophils to generate a new family of MPs, and also stimulate endothelial cells as documented by leakage of intravenous 2000 ​kDa dextran. At the brain microvasculature, neutrophil and MPs sequestration, and myeloperoxidase activity result in elevations of the p65 subunit of NF-κB, serine 536 phosphorylated p65, CD36, and loss of astrocyte aquaporin-4 that persist for at least 7 days. Knock-out mice lacking the CD36 membrane receptor are resistant to all CO inflammatory changes. Events triggered by CO are recapitulated in naïve wild type mice injected with cervical node MPs from CO-exposed mice, but not control mice. All MPs-mediated events are inhibited with a NF-κB inhibitor, a myeloperoxidase inhibitor, or anti-TSP-1 antibodies. We conclude that astrocyte-derived MPs expressing TSP-1 establish a feed-forward neuroinflammatory cycle involving endothelial CD36-to-astrocyte NF-κB crosstalk. As there is currently no treatment for CO-induced neurological sequelae, these findings pose several possible sites for therapeutic interventions.

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Carbon monoxide (CO) causes neurological injuries poorly correlated to hypoxic stress.

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Astrocyte NF-κB triggers thrombospondin-1(TSP-1) microparticle (MP) production.

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TSP-1 MPs enter the blood stream, stimulating neutrophils and endothelium.

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Circulating MPs linkage to endothelial cell CD36 causes vascular damage.

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Endothelial CD36-to-astrocyte NF-κB crosstalk establishes a neuroinflammatory cycle.

The Effects of Hyperbaric Oxygen on Rheumatoid Arthritis: A Pilot Study

BACKGROUND/OBJECTIVE

This case series pilot study assessed the effects of hyperbaric oxygen therapy (HBO2) for treating rheumatoid arthritis (RA).

METHODS

Ten RA subjects received 30 HBO2 treatments over 6 to 10 weeks. Serial rheumatologic evaluations (ie, the Disease Activity Scale [DAS28], the Routine Assessment of Patient Index Data 3, and the Pain and Sleep Quality Questionnaire) were completed at baseline, throughout the course of the study, and at the 6-month follow-up.

RESULTS

There was a statistically significant effect of HBO2 therapy over time on the DAS28-Global Health (p = 0.01), the DAS28-C-reactive protein (p = 0.002), and the DAS28-erythrocyte sedimentation rate (p = 0.008) measures; these analyses excluded 2 patients who were in clinical remission at baseline. Selected post hoc comparisons showed significantly lower DAS28-Global Health, DAS28-C-reactive protein, and DAS28-erythrocyte sedimentation rate scores at 3 and 6 months relative to baseline. In addition, statistically significant decreases in pain as measured by the Routine Assessment of Patient Index Data 3 and Pain and Sleep Quality Questionnaire were observed at the end of HBO2 relative to baseline.

CONCLUSIONS

Hyperbaric oxygen therapy is effective for joint pain in patients with RA based on data from multiple, validated clinical measures. Further research with more subjects and the use of a control group is necessary.

Brain-derived extracellular vesicles mediated coagulopathy, inflammation and apoptosis after sepsis

INTRODUCTION

The activation of coagulation, inflammation and other pathways is the basic response of the host to infection in sepsis, but this response also causes damage to the host. Brain-derived extracellular vesicles (BDEVs) have been reported to cause a hypercoagulable state that can rapidly develop into consumptive coagulopathy, which is consistent with the pathophysiological process of sepsis-induced coagulopathy. However, the role of BDEVs in sepsis-induced coagulopathy remains unclear.

MATERIALS AND METHODS

Male Sprague-Dawley (SD) rats were used for sepsis modeling using cecal ligation puncture (CLP). Flow cytometry was used to measure the levels of circulating BDEVs. Enzyme-linked immunosorbent assay (ELISA) was used to measure the serum levels of plasminogen activator inhibitor type 1 (PAI-1), thrombin-antithrombin (TAT), D-dimer, fibrinogen(Fib), tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and IL-6. Nanoparticle tracking analysis (NTA) and Transmission electron microscopy (TEM) were used to identify BDEVs. Western blot (WB) was used to determine the expression of glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), bax, bcl-2 and cleaved caspase-3. Hematoxylin-eosin (HE) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining were performed to detect tissue injury. Survival was monitored over the course of 168 h.

RESULTS

We found that a large number of BDEVs were released into the circulating blood in septic rats. Moreover, we observed that BDEVs injection activated the systemic coagulation reaction and induced lung, liver and kidney inflammation and apoptosis(P < .05). Compared with BDEVs from sham-operated rats, BDEVs from septic rats exacerbated this process(P < .05).

CONCLUSIONS

This finding suggests that inhibiting BDEVs may yield therapeutic benefits in the treatment of sepsis-induced coagulopathy.

Involvement of TCF7L2 in generation of morphine-induced antinociceptive tolerance and hyperalgesia by modulating TLR4/ NF-κB/NLRP3 in microglia

Morphine is an opioid agonist and a nonselective mu, kappa and delta receptor agonist. It is a commonly used analgesic drug for the treatment of acute and chronic pain as well as cancer pain. Morphine is particularly important to address the problem of morphine tolerance. Tcf7l2, known as a risk gene for schizophrenia and autism, encodes a member of the LEF1/TCF transcription factor family. TCF7L2 is an important transcription factor that is upregulated in neuropathic pain models. However, the relationship between TCF7L2 and morphine tolerance has not been reported. In this study, we found that morphine tolerance led to the upregulation of TCF7L2 in the spinal cord, and also led to the upregulation of TCF7L2 expression in glial cells, which promoted inflammation related signal, and activated TLR4 / NF-κB/NLRP3 pathway. In addition, TCF7L2 regulated microglial cell activation induced by chronic morphine treatment. Mechanically, we found that TCF7L2 transcriptionally regulated TLR4 expression, and the depletion of TCF7L2 alleviated morphine tolerance induced by chronic morphine treatment, and further alleviated pain hypersensitivity induced by chronic morphine treatment. We therefore suggested that TCF7L2 regulates the activation of TLR4/ NF-κB/NLRP3 pathway in microglia, and is involved in the formation of morphine tolerance. Our results provide a new idea for the regulation mechanism of morphine tolerance.

Methylnaltrexone crosses the blood-brain barrier and attenuates centrally-mediated behavioral effects of morphine and oxycodone in mice

BACKGROUND

Antagonism of peripheral opioid receptors by methylnaltrexone (MNTX) was recently proposed as a potential mechanism to attenuate the development of opioid analgesic tolerance based on experiments conducted in mice. However, reports indicate that MNTX is demethylated to naltrexone (NTX) in mice, and NTX may subsequently cross the blood-brain barrier to antagonize centrally-mediated opioid effects. The goal of this study was to determine whether MNTX alters centrally-mediated behaviors elicited by the opioid analgesics, morphine and oxycodone, and to quantify concentrations of MNTX and NTX in blood and brain following their administration in mice.

METHODS

Combinations of MNTX and morphine were tested under acute and chronic conditions in thermal nociceptive assays. Effects of MNTX and NTX pretreatment were assessed in an oxycodone discrimination operant procedure. Blood and brain concentrations of these antagonists were quantified after their administration using liquid chromatography-mass spectrometry.

RESULTS

MNTX dose-dependently attenuated acute and chronic morphine antinociception. MNTX and NTX dose-dependently antagonized the discriminative stimulus effects of oxycodone. MNTX and NTX were detected in both blood and brain after administration of MNTX, confirming its demethylation and demonstrating that MNTX itself can cross the blood-brain barrier.

CONCLUSIONS

These results provide converging behavioral and analytical evidence that MNTX administration in mice attenuates centrally-mediated effects produced by opioid analgesics and results in functional concentrations of MNTX and NTX in blood and brain. Collectively, these findings indicate that MNTX cannot be administered systemically in mice for making inferences that its effects are peripherally restricted.