Impaired chronic pain-like behaviour and altered opioidergic system in the TASTPM mouse model of Alzheimer's disease

Galectin-3 activates spinal microglia to induce inflammatory nociception in wild type but not in mice modelling Alzheimer's disease

Musculoskeletal chronic pain is prevalent in individuals with Alzheimer's disease (AD); however, it remains largely untreated in these patients, raising the possibility that pain mechanisms are perturbed. Here, we utilise the TASTPM transgenic mouse model of AD with the K/BxN serum transfer model of inflammatory arthritis. We show that in male and female WT mice, inflammatory allodynia is associated with a distinct spinal cord microglial response characterised by TLR4-driven transcriptional profile and upregulation of P2Y12. Dorsal horn nociceptive afferent terminals release the TLR4 ligand galectin-3 (Gal-3), and intrathecal injection of a Gal-3 inhibitor attenuates allodynia. In contrast, TASTPM mice show reduced inflammatory allodynia, which is not affected by the Gal-3 inhibitor and correlates with the emergence of a P2Y12- TLR4- microglia subset in the dorsal horn. We suggest that sensory neuron-derived Gal-3 promotes allodynia through the TLR4-regulated release of pro-nociceptive mediators by microglia, a process that is defective in TASTPM due to the absence of TLR4 in a microglia subset.

CD206+/MHCII- macrophage accumulation at nerve injury site correlates with attenuation of allodynia in TASTPM mouse model of Alzheimer's disease

Chronic pain is undertreated in people with Alzheimer's disease (AD) and better understanding of the underlying mechanisms of chronic pain in this neurodegenerative disease is essential. Neuropathic pain and AD share a significant involvement of the peripheral immune system. Therefore, we examined the development of nerve injury-induced allodynia in TASTPM (APPsweXPS1.M146V) mice and assessed monocytes/macrophages at injury site. TASTPM developed partial allodynia compared to WT at days 7, 14 and 21 days after injury, and showed complete allodynia only after treatment with naloxone methiodide, a peripheralized opioid receptor antagonist. Since macrophages are one of the sources of endogenous opioids in the periphery, we examined macrophage infiltration at injury site and observed that CD206+/MHCII- cells were more numerous in TASTPM than WT. Accordingly, circulating TASTPM Ly6Chigh (classical) monocytes, which are pro-inflammatory and infiltrate at the site of injury, were less abundant than in WT. In in vitro experiments, TASTPM bone marrow-derived macrophages showed efficient phagocytosis of myelin extracts containing amyloid precursor protein, acquired CD206+/MHCII- phenotype, upregulated mRNA expression of proenkephalin (PENK) and accumulated enkephalins in culture media. These data suggest that in TASTPM nerve-injured mice, infiltrating macrophages which derive from circulating monocytes and may contain amyloid fragments, acquire M2-like phenotype after myelin engulfment, and release enkephalins which are likely to inhibit nociceptive neuron activity via activation of opioid receptors.

Long-term follow-up of intracerebroventricular injection of streptozotocin-inducing pain sensitization

Age is known to be the major risk factor for both pain sensation and sporadic Alzheimer's disease (sAD). Pain management in AD is a critical health condition. However, assessing pain in sAD patients is challenging. The intracerebroventricularly injected streptozotocin (icv-STZ) rat model of sAD has been brought to the fore as a hopefully suitable model that could mimic some features of sAD. However, the exact mechanism by which this agent may induce AD-like pathology is largely unknown. In some studies, analgesic drugs have been suggested as possible prevention of AD and icv-STZ-induced AD-like pathology. Therefore, this study used formalin and tail-flick tests to investigate whether different doses of icv-STZ injections could affect acute and inflammatory pain sensation and edema volume over time. Behavioral responses were observed at four testing time points (1, 2.5, 3.5, and 6 months postinjection). The results indicate that icv-STZ was able to significantly decrease the animals' formalin pain threshold in both a time- and dose-dependent manner. Formalin-induced acute and chronic pain scores of animals treated with streptozotocin 3 mg/kg (STZ3) increased dramatically 2.5 months after injection and persisted thereafter. The augmentation in pain score induced by streptozotocin 1 mg/kg (STZ1) was observed from 3.5 months after STZ injection. However, the effect of streptozotocin 0.5 mg/kg (STZ0.5) was NS until 6 months after injection. However, formalin-induced paw edema occurred with a longer delay and was not detectable in STZ0.5-treated animals. In addition, only STZ3-treated animals significantly reduced the thermal pain threshold of animals 6 months after injection. These observations indicate that icv-STZ can sensitize central and/or peripheral receptors to pain. The effect of STZ is dose- and time-dependent. AD-like pathology induced by icv-STZ could be partially activated via pain processing pathways. Therefore, anti-inflammatory agents could alleviate AD-like symptoms via pain treatments.

Chronic Pain in the Elderly: Mechanisms and Perspectives

Chronic pain affects a large part of the population causing functional disability, being often associated with coexisting psychological disorders, such as depression and anxiety, besides cognitive deficits, and sleep disturbance. The world elderly population has been growing over the last decades and the negative consequences of chronic pain for these individuals represent a current clinical challenge. The main painful complaints in the elderly are related to neurodegenerative and musculoskeletal conditions, peripheral vascular diseases, arthritis, and osteoarthritis, contributing toward poorly life quality, social isolation, impaired physical activity, and dependence to carry out daily activities. Organ dysfunction and other existing diseases can significantly affect the perception and responses to chronic pain in this group. It has been proposed that elderly people have an altered pain experience, with changes in pain processing mechanisms, which might be associated with the degeneration of circuits that modulate the descending inhibitory pathways of pain. Aging has also been linked to an increase in the pain threshold, a decline of painful sensations, and a decrease in pain tolerance. Still, elderly patients with chronic pain show an increased risk for dementia and cognitive impairment. The present review article is aimed to provide the state-of-art of pre-clinical and clinical research about chronic pain in elderly, emphasizing the altered mechanisms, comorbidities, challenges, and potential therapeutic alternatives.

Anxiety enhances pain in a model of osteoarthritis and is associated with altered endogenous opioid function and reduced opioid analgesia

Introduction

Negative affect, including anxiety and depression, is prevalent in chronic pain states such as osteoarthritis (OA) and associated with greater use of opioid analgesics, potentially contributing to present and future opioid crises.

Objectives

We tested the hypothesis that the interaction between anxiety, chronic pain, and opioid use results from altered endogenous opioid function.

Methods

A genetic model of negative affect, the Wistar-Kyoto (WKY) rat, was combined with intra-articular injection of monosodium iodoacetate (MIA; 1 mg) to mimic clinical presentation. Effects of systemic morphine (0.5-3.5 mg·kg^-1) on pain behaviour and spinal nociceptive neuronal activity were compared in WKY and normo-anxiety Wistar rats 3 weeks after MIA injection. Endogenous opioid function was probed by the blockade of opioid receptors (0.1-1 mg·kg^-1 systemic naloxone), quantification of plasma β-endorphin, and expression and phosphorylation of spinal mu-opioid receptor (MOR).

Results

Monosodium iodoacetate-treated WKY rats had enhanced OA-like pain, blunted morphine-induced analgesia, and greater mechanical hypersensitivity following systemic naloxone, compared with Wistar rats, and elevated plasma β-endorphin levels compared with saline-treated WKY controls. Increased MOR phosphorylation at the master site (serine residue 375) in the spinal cord dorsal horn of WKY rats with OA-like pain (P = 0.0312) indicated greater MOR desensitization.

Conclusions

Reduced clinical analgesic efficacy of morphine was recapitulated in a model of high anxiety and OA-like pain, in which endogenous opioid tone was altered, and MOR function attenuated, in the absence of previous exogenous opioid ligand exposure. These findings shed new light on the mechanisms underlying the increased opioid analgesic use in high anxiety patients with chronic pain.

Patterns of cognitive decline and somatosensory processing in a mouse model of amyloid accumulation

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Despite copious amyloid plaques, 5XFAD mice show modest signs of cognitive decline.

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At ages 2 to 13 months old 5XFAD mice show no signs of sensory or pain dysfunctions.

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5XFAD mice may not be a valid model for pain abnormalities in the context of AD.

Pain and cognitive decline increase with age. In particular, there is a troubling relationship between dementia and pain, with some studies showing higher prevalence and inadequate treatment of pain in this population. Alzheimer’s disease (AD) is one of the most common causes of dementia in older adults. Amyloid plaques are a hallmark of AD. The downstream processes these plaques promote are believed to affect neuronal and glial health and activity. There is a need to better understand how the neuropathological changes of AD shape neural activity and pain sensitivity. Here, we use the 5XFAD mouse model, in which dense amyloid accumulations occur at early ages, and in which previous studies reported signs of cognitive decline. We hypothesized that 5XFAD mice develop sensory and pain processing dysfunctions. Although amyloid burden was high throughout the brain, including in regions involved with sensory processing, we identified no functionally significant differences in reflexive or spontaneous signs of pain. Furthermore, expected signs of cognitive decline were modest; a finding consistent with variable results in the literature. These data suggest that models recapitulating other pathological features of Alzheimer’s disease might be better suited to studying differences in pain perception in this disease.

Endogenous opiates and behavior: 2019

This paper is the forty-second consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2019 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

End-of-life care for people with advanced dementia and pain: a qualitative study in Swedish nursing homes

Background

Of the Swedish people with advanced dementia, the majority die in nursing homes. Unresolved pain can occur in people with a terminal illness such as dementia. However, pain management in people with advanced dementia is often suboptimal and inadequate, with fewer palliative care interventions than offered to cancer patients. Although they are largely responsible for the care of these people, few studies have addressed the experiences of registered nurses in this respect. Therefore, the aim of this study was to describe the experiences of nurses in caring for people with advanced dementia and pain at the end of life.

Methods

The study had a descriptive explorative design. Individual qualitative, semi-structured interviews were carried out with 13 nurses from 12 nursing homes in Sweden. The results were analysed using thematic content analysis.

Results

The nurses described communicative, relational and organisational challenges. One major issue involved difficulties communicating with the person with advanced dementia, resulting in uncertain pain assessment. Other difficulties involved the differentiation of pain from anxiety, the balance of benefits and risks with morphine administration, and the creation of good relationships with healthcare personnel and the persons’ relatives. Relatives can greatly affect the assessment and management of pain, both because of their ability to interpret pain behaviour and by questioning the care given. Good pain management was facilitated by good communication and relationships with healthcare staff and relatives, extensive professional nursing experience, and already knowing the person with advanced dementia.

Conclusions

This study highlights the need for nursing homes to employ specialist nurses who have been trained in the appropriate knowledge and skills to deal with the challenges of end-of-life care for people with advanced dementia and pain. Additionally, there should be resources and strategies available for providing information to family members and for involving them in the decision-making process, as they are often unfamiliar with the multitude of considerations involved in decisions such as whether to administer morphine or not.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12912-021-00566-7.

Intermittent fasting with a high-protein diet mitigated osteoarthritis symptoms by increasing lean body mass and reducing inflammation in osteoarthritic rats with Alzheimer's disease-like dementia

Menopausal women are susceptible to osteoarthritis(OA) and memory impairment. We hypothesised that Alzheimer's-like disease(AD) exacerbates OA and that intermittent fasting(IMF) with a high-protein(H-P) diet would enhance memory function and relieve OA symptoms in oestrogen-deficient animals induced AD and OA. The action mechanism was also explored. Ovariectomised Sprague-Dawley rats were fed high-fat(H-F) or H-P diets for 2 weeks, and then they had a hippocampal infusion of β-amyloid(25-35) for 4 weeks to induce AD and an injection of monoidoacetate(MIA) into the articular cartilage to induce OA. Non-AD groups had non-AD symptoms by hippocampal amyloid-β(35-25) infusion. IMF suppressed memory impairment in AD rats, especially those fed H-P diets. Compared with non-AD, AD exacerbated OA symptoms, including swelling, limping, slowed treadmill running speed, and uneven weight distribution in the left leg. The exacerbations were linked to increased inflammation and pain, but IMF and H-P lessened the exacerbation. Lean body mass(LBM) decreased with AD, but H-P protected against LBM loss. Histological examination of the knee joint revealed the degree of the cellular invasion into the middle zone, and the changes in the tidemark plateau were greatest in the AD-AL with H-F, while non-AD-IMF improved the cellular invasion to as much as non-AD-AL. H-P reduced the infiltration into the middle zone of the knee and promoted collagen production. In conclusion, AD exacerbated the articular cartilage deterioration and memory impairment, and IMF with H-P alleviated the memory impairment and osteoarthritic symptoms by decreasing hippocampal amyloid-β deposition and proinflammatory cytokine expressions and by increasing LBM.

Protagonist Role of Opioidergic System on Post-Traumatic Stress Disorder and Associated Pain

OBJECTIVE

Post-traumatic stress disorder (PTSD) and chronic pain often co-occur. Studies have shown an interaction between pain and PTSD. In this narrative review, we aim to support conducting comprehensive studies by describing PTSD, pain and determining whether opioidergic system, its agonist and antagonist manipulation could positively or negatively affect PTSD symptoms and concurrent pain.

METHODS

Term searches was done in Google Scholar, Scopus, ScienceDirect, Web of Science and PubMed databases as well as hand searching in key resource journals from 1979-2019.

RESULTS

There are a lot of contradictions and disputes when endogenous opioidergic system and opioidergic antagonist system are studied in PTSD patients. Exogenous morphine administration in PTSD patients can decrease the symptoms of PTSD but it doesn't have a pain reduction effect to an acceptable level. Beta-endorphin as an endogenous opioid is effective in pain reduction in the moment of events but after minutes to hours, the endorphins withdrawal syndrome leads to exaggerated intrusive thoughts and flashbacks of PTSD, which exacerbate the pain. It has also been shown that naloxone, as an opioidergic antagonist, can reduce or increase the PTSD symptoms and its associated pain.

CONCLUSION

Data suggest different roles of opioidergic system and their antagonist in pain control and mood in PTSD. However, further investigations need to be done in order to reveal the role of endogenous opioidergic system and opioidergic antagonist system as a mediator in PTSD patients suffering from acute or chronic pain.

Analgesic treatments in people with dementia - how safe are they? A systematic review

INTRODUCTION

People with dementia may be unable to verbally express pain and suffer from untreated pain. Use of analgesics in people with dementia has increased during the last decade, in particular opioid analgesics with high potential for adverse effects.

AREAS COVERED

This article presents a systematic review of the current evidence for safety and tolerability of analgesic drugs from randomized controlled trials in people with dementia. Relevant trials were identified by a literature search in the EMBASE, MEDLINE, and Cochrane databases from inception to November 2018. The search included the main terms 'dementia' and 'analgesic' or their subterms, and was filtered to limit results to clinical trials.

EXPERT OPINION

Although pain treatment is increasingly recognized as an important clinical issue in people with advanced dementia, there is currently a lack of evidence to support safety evaluations of commonly used analgesics in this group. To inform treatment decisions and enable care providers to appropriately monitor patients at risk of adverse effects, it is necessary to conduct well-designed clinical trials to investigate the relative efficacy and safety of analgesics in people with dementia, with particular emphasis on harmful effects of long-term opioid use as well as short-term use of nonsteroidal anti-inflammatory drugs.