Inhibition of Hsp90 in the spinal cord enhances the antinociceptive effects of morphine by activating an ERK-RSK pathway

Inhibiting spinal cord-specific hsp90 isoforms reveals a novel strategy to improve the therapeutic index of opioid treatment

Opioids are the gold standard for the treatment of chronic pain but are limited by adverse side effects. In our earlier work, we showed that Heat shock protein 90 (Hsp90) has a crucial role in regulating opioid signaling in spinal cord; Hsp90 inhibition in spinal cord enhances opioid anti-nociception. Building on these findings, we injected the non-selective Hsp90 inhibitor KU-32 by the intrathecal route into male and female CD-1 mice, showing that morphine anti-nociceptive potency was boosted by 1.9-3.5-fold in acute and chronic pain models. At the same time, tolerance was reduced from 21-fold to 2.9 fold and established tolerance was rescued, while the potency of constipation and reward was unchanged. These results demonstrate that spinal Hsp90 inhibition can improve the therapeutic index of morphine. However, we also found that systemic non-selective Hsp90 inhibition blocked opioid pain relief. To avoid this effect, we used selective small molecule inhibitors and CRISPR gene editing to identify 3 Hsp90 isoforms active in spinal cord (Hsp90α, Hsp90β, and Grp94) while only Hsp90α was active in brain. We thus hypothesized that a systemically delivered selective inhibitor to Hsp90β or Grp94 could selectively inhibit spinal cord Hsp90 activity, resulting in enhanced opioid therapy. We tested this hypothesis using intravenous delivery of KUNB106 (Hsp90β) and KUNG65 (Grp94), showing that both drugs enhanced morphine anti-nociceptive potency while rescuing tolerance. Together, these results suggest that selective inhibition of spinal cord Hsp90 isoforms is a novel, translationally feasible strategy to improve the therapeutic index of opioids.

Anti-inflammatory activities of novel heat shock protein 90 isoform selective inhibitors in BV-2 microglial cells

Heat shock protein 90 (Hsp90) is a family of chaperone proteins that consists of four isoforms: Hsp90α, Hsp90β, glucose-regulated protein 94 (Grp94), and tumor necrosis factor type 1 receptor-associated protein (TRAP1). They are involved in modulating the folding, maturation, and activation of their client proteins to regulate numerous intracellular signaling pathways. Previous studies demonstrated that pan-Hsp90 inhibitors reduce inflammatory signaling pathways resulting in a reduction of inflammation and pain but show toxicities in cancer-related clinical trials. Further, the role of Hsp90 isoforms in inflammation remains poorly understood. This study aimed to determine anti-inflammatory activities of Hsp90 isoforms selective inhibitors on the lipopolysaccharide (LPS)-induced inflammation in BV-2 cells, a murine microglial cell line. The production of inflammatory mediators such as nitric oxide (NO), interleukin 1 beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) was measured. We also investigated the impact of Hsp90 isoform inhibitors on the activation of nuclear factor kappa B (NF-κB), nuclear factor erythroid 2-related factor 2 (Nrf2), and mitogen-activated protein kinases (MAPKs). We found that selective inhibitors of Hsp90β reduced the LPS-induced production of NO, IL-1β, and TNF-α via diminishing the activation of NF-κB and Extracellular signal-regulated kinases (ERK) MAPK. The Hsp90α, Grp94, TRAP1 inhibitors had limited effect on the production of inflammatory mediators. These findings suggest that Hsp90β is the key player in LPS-induced neuroinflammation. Thereby providing a more selective drug target for development of medications involved in pain management that can potentially contribute to the reduction of adverse side effects associated with Hsp90 pan inhibitors.

Terpenes from Cannabis sativa induce antinociception in a mouse model of chronic neuropathic pain via activation of adenosine A2A receptors

ABSTRACT

Terpenes are small hydrocarbon compounds that impart aroma and taste to many plants, including Cannabis sativa. A number of studies have shown that terpenes can produce pain relief in various pain states in both humans and animals. However, these studies were methodologically limited and few established mechanisms of action. In our previous work, we showed that the terpenes geraniol, linalool, β-pinene, α-humulene, and β-caryophyllene produced cannabimimetic behavioral effects via multiple receptor targets. We thus expanded this work to explore the potential antinociception and mechanism of these Cannabis terpenes in a mouse model of chronic pain. We first tested for antinociception by injecting terpenes (200 mg/kg, IP) into male and female CD-1 mice with mouse models of chemotherapy-induced peripheral neuropathy (CIPN) or lipopolysaccharide-induced inflammatory pain, finding that the terpenes produced roughly equal antinociception to 10 mg/kg morphine or 3.2 mg/kg WIN55,212. We further found that none of the terpenes produced reward as measured by conditioned place preference, while low doses of terpene (100 mg/kg) combined with morphine (3.2 mg/kg) produced enhanced antinociception vs either alone. We then used the adenosine A2A receptor (A2AR) selective antagonist istradefylline (3.2 mg/kg, IP) and spinal cord-specific CRISPR knockdown of the A2AR to identify this receptor as the mechanism for terpene antinociception in CIPN. In vitro cAMP and binding studies and in silico modeling studies further suggested that the terpenes act as A2AR agonists. Together these studies identify Cannabis terpenes as potential therapeutics for chronic neuropathic pain and identify a receptor mechanism for this activity.

Discovery of a novel homoisoflavonoid derivative 5g for anti-osteoclastic bone loss via targeting FGFR1

Several flavonoids have been shown to exert anti-osteoporosis activity. However, the structure-activity relationship and the mechanism of anti-osteoporosis activity of flavonoids remain unknown. In this study, we prepared a series of novel homoisoflavonoid (HIF) derivatives to evaluate their inhibitory effects on osteoclastogenesis using TRAP-activity in vitro assay. Then, the preliminary structure-activity relationship was studied. Among the evaluated novel flavonoids, derivative 5g exerted the most inhibitory bioactivity on primary osteoclast differentiation without interfering with osteogenesis. It was hence selected for further in vitro, in vivo and mechanism of action investigation. Results show that 5g likely directly binds to the fibroblast growth factor receptor 1 (FGFR1), decreasing the activation of ERK1/2 and IκBα/NF-κB signaling pathways, which in turn blocks osteoclastogenesis in vitro and osteoclastic bone loss in vivo. Our study shows that homoisoflavonoid (HIF) derivatives 5g can serve as a potential novel candidate for treating osteoporosis via inhibition of FGFR1.

HSP90 inhibition in the mouse spinal cord enhances opioid signaling by suppressing an AMPK-mediated negative feedback loop

Opioids and other agonists of the μ-opioid receptor are effective at managing acute pain, but their chronic use can lead to tolerance that limits their efficacy. We previously reported that inhibiting the chaperone protein HSP90 in the spinal cords of mice promotes the antinociceptive effects of opioids in a manner that involved increased activation of the kinase ERK. Here, we found that the underlying mechanism involves the relief of a negative feedback loop mediated by the kinase AMPK. Intrathecal treatment of male and female mice with the HSP90 inhibitor 17-AAG decreased the abundance of the β1 subunit of AMPK in the spinal cord. The antinociceptive effects of 17-AAG with morphine were suppressed by intrathecal administration of AMPK activators and enhanced by an AMPK inhibitor. Opioid treatment increased the abundance of phosphorylated AMPK in the dorsal horn of the spinal cord, where it colocalized with a neuronal marker and the neuropeptide CGRP. Knocking down AMPK in CGRP-positive neurons enhanced the antinociceptive effects of morphine and demonstrated that AMPK mediated the signal transduction between HSP90 inhibition and ERK activation. These data suggest that AMPK mediates an opioid-induced negative feedback loop in CGRP neurons of the spinal cord and that this loop can be disabled by HSP90 inhibition to enhance the efficacy of opioids.

Strategies towards safer opioid analgesics-A review of old and upcoming targets

Opioids continue to be of use for the treatment of pain. Most clinically used analgesics target the μ opioid receptor whose activation results in adverse effects like respiratory depression, addiction and abuse liability. Various approaches have been used by the field to separate receptor-mediated analgesic actions from adverse effects. These include biased agonism, opioids targeting multiple receptors, allosteric modulators, heteromers and splice variants of the μ receptor. This review will focus on the current status of the field and some upcoming targets of interest that may lead to a safer next generation of analgesics. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Terpenes from Cannabis sativa Induce Antinociception in Mouse Chronic Neuropathic Pain via Activation of Spinal Cord Adenosine A2A Receptors

Terpenes are small hydrocarbon compounds that impart aroma and taste to many plants, including Cannabis sativa. A number of studies have shown that terpenes can produce pain relief in various pain states in both humans and animals. However, these studies were methodologically limited and few established mechanisms of action. In our previous work, we showed that the terpenes geraniol, linalool, β-pinene, α-humulene, and β-caryophyllene produced cannabimimetic behavioral effects via multiple receptor targets. We thus expanded this work to explore the efficacy and mechanism of these Cannabis terpenes in relieving chronic pain. We first tested for antinociceptive efficacy by injecting terpenes (200 mg/kg, IP) into male and female CD-1 mice with chemotherapy-induced peripheral neuropathy (CIPN) or lipopolysaccharide-induced inflammatory pain, finding that the terpenes produced roughly equal efficacy to 10 mg/kg morphine or 3.2 mg/kg WIN55,212. We further found that none of the terpenes produced reward as measured by conditioned place preference, while low doses of terpene (100 mg/kg) combined with morphine (3.2 mg/kg) produced enhanced antinociception vs. either alone. We then used the adenosine A2A receptor (A2AR) selective antagonist istradefylline (3.2 mg/kg, IP) and spinal cord-specific CRISPR knockdown of the A2AR to identify this receptor as the mechanism for terpene antinociception in CIPN. In vitro cAMP and binding studies and in silico modeling studies further suggested that the terpenes act as A2AR agonists. Together these studies identify Cannabis terpenes as potential therapeutics for chronic neuropathic pain, and identify a receptor mechanism in the spinal cord for this activity.

Glia turn opioids painful

Co-targeting glial cells may block the paradoxical increase in pain caused by repeated opioid use.

Inhibition of HSP90 Preserves Blood-Brain Barrier Integrity after Cortical Spreading Depression

Cortical spreading depression (CSD) is a pathophysiological mechanism underlying headache disorders, including migraine. Blood-brain barrier (BBB) permeability is increased during CSD. Recent papers have suggested that heat shock proteins (HSP) contribute to the integrity of the blood-brain barrier. In this study, the possible role of HSP90 in CSD-associated blood-brain barrier leak at the endothelial cell was investigated using an in vitro model, for the blood-endothelial barrier (BEB), and an in vivo model with an intact BBB. We measured barrier integrity using trans endothelial electric resistance (TEER) across a monolayer of rodent brain endothelial cells (bEnd.3), a sucrose uptake assay, and in situ brain perfusion using female Sprague Dawley rats. CSD was induced by application of 60 mM KCl for 5 min in in vitro experiments or cortical injection of KCl (1 M, 0.5 µL) through a dural cannula in vivo. HSP90 was selectively blocked by 17-AAG. Our data showed that preincubation with 17-AAG (1 µM) prevented the reduction of TEER values caused by the KCl pulse on the monolayer of bEnd.3 cells. The elevated uptake of 14C-sucrose across the same endothelial monolayer induced by the KCl pulse was significantly reduced after preincubation with HSP90 inhibitor. Pre-exposure to 17-AAG significantly mitigated the transient BBB leak after CSD induced by cortical KCl injection as determined by in situ brain perfusion in female rats. Our results demonstrated that inhibition of HSP90 with the selective agent 17-AAG reduced CSD-associated BEB/BBB paracellular leak. Overall, this novel observation supports HSP90 inhibition mitigates KCl-induced BBB permeability and suggests the development of new therapeutic approaches targeting HSP90 in headache disorders.

Antagonism of the mu-delta opioid receptor heterodimer enhances opioid antinociception by activating Src and calcium/calmodulin-dependent protein kinase II signaling

ABSTRACT

The opioid receptors are important regulators of pain, reward, and addiction. Limited evidence suggests the mu and delta opioid receptors form a heterodimer (MDOR), which may act as a negative feedback brake on opioid-induced analgesia. However, evidence for the MDOR in vivo is indirect and limited, and there are few selective tools available. We recently published the first MDOR-selective antagonist, D24M, allowing us to test the role of the MDOR in mice. We thus cotreated CD-1 mice with D24M and opioids in tail flick, paw incision, and chemotherapy-induced peripheral neuropathy pain models. D24M treatment enhanced oxymorphone antinociception in all models by 54.7% to 628%. This enhancement could not be replicated with the mu and delta selective antagonists CTAP, naltrindole, and naloxonazine, and D24M had a mild transient effect in the rotarod test, suggesting this increase is selective to the MDOR. However, D24M had no effect on morphine or buprenorphine, suggesting that only specific opioids interact with the MDOR. To find a mechanism, we performed phosphoproteomic analysis on brainstems of mice. We found that the kinases Src and CaMKII were repressed by oxymorphone, which was restored by D24M. We were able to confirm the role of Src and CaMKII in D24M-enhanced antinociception using small molecule inhibitors (KN93 and Src-I1). Together, these results provide direct in vivo evidence that the MDOR acts as an opioid negative feedback brake, which occurs through the repression of Src and CaMKII signal transduction. These results further suggest that MDOR antagonism could be a means to improve clinical opioid therapy.

Transcriptome Analysis Reveal Candidate Genes and Pathways Responses to Lactate Dehydrogenase Inhibition (Oxamate) in Hyperglycemic Human Renal Proximal Epithelial Tubular Cells

Diabetic kidney disease (DKD) is the leading cause of both chronic kidney disease (CKD) and end-stage renal disease (ESRD). Previous studies showed that oxamate could regulate glycemic homeostasis and impacted mitochondria respiration in a hyperglycemia-dependent manner in the rat proximal tubular cells. To explore the transcriptome gene expression profiling of kidney tissues in human renal proximal epithelial tubular cell line (HK-2), we treated HK-2 cells with high D-glucose (HG) for 7 days before the addition of 40 mM oxamate for a further 24 hours in the presence of HG in this study. Afterwards, we identified 3,884 differentially expressed (DE) genes based on adjusted P-value ≤ 0.05 and investigated gene relationships based on weighted gene co-expression network analysis (WGCNA). After qRT-PCR validations, MAP1LC3A, MAP1LC3B (P-value < 0.01) and BECN1 were found to show relatively higher expression levels in the treated groups than the control groups, while PGC1α (P-value < 0.05) showed the lower expressions. Accordingly, enrichment analyses of GO terms and KEGG pathways showed that several pathways [e.g., lysosome pathway (hsa04142) and p53 signaling pathway (hsa04115)] may be involved in the response of HK-2 cells to oxamate. Moreover, via WGCNA, we identified two modules: both the turquoise and blue modules were enriched in pathways associated with lysosome. However, the p53 signaling pathway was only found using all 3,884 DE genes. Furthermore, the key hub genes IGFBP3 (adjusted P-value = 1.34×10^-75 and log₂(FC) = 2.64) interacted with 6 up-regulated and 12 down-regulated DE genes in the network that were enriched in the p53 signaling pathway. This is the first study reporting co-expression patterns of a gene network after lactate dehydrogenase inhibition in HK-2 cells. Our results may contribute to our understanding of the underlying molecular mechanism of in vitro reprogramming under hyperglycemic stress that orchestrates the survival and functions of HK-2 cells.

CLec-TM1-ERK-GSK3β Pathway Regulates Vibrio splendidus-Induced IL-17 Production in Oyster

C-type lectins are a family of pattern recognition receptors that recognize microbial components and subsequently activate the signaling cascade to induce the production of proinflammatory cytokines. In the current study, the homologs of ERK (named as CgERK) and GSK3β (named as CgGSK3β) and a novel C-type lectin with a transmembrane domain (named as CgCLec-TM1) were identified from oyster Crassostrea gigas CgCLec-TM1 was able to bind Escherichia coli and Vibrio splendidus through its carbohydrate recognition domain and then activated CgERK by inducing its phosphorylation. The activated CgERK interacted with CgGSK3β to phosphorylate it at Ser⁹, which eventually induced the expressions of CgIL-17-1 and CgIL-17-5. The interaction between CgERK and CgGSK3β, as well as the phosphorylation of CgGSK3β, could be inhibited by ERK inhibitor (PD98059) to reduce the expressions of CgIL-17-1 and CgIL-17-5. CgGSK3β in oyster was proposed as a new substrate of CgERK. The results defined a CLec-TM1-ERK-GSK3β signaling pathway in oyster, which was activated by V. splendidus and then induced CgIL-17 productions.

Cannabis sativa terpenes are cannabimimetic and selectively enhance cannabinoid activity

Limited evidence has suggested that terpenes found in Cannabis sativa are analgesic, and could produce an "entourage effect" whereby they modulate cannabinoids to result in improved outcomes. However this hypothesis is controversial, with limited evidence. We thus investigated Cannabis sativa terpenes alone and with the cannabinoid agonist WIN55,212 using in vitro and in vivo approaches. We found that the terpenes α-humulene, geraniol, linalool, and β-pinene produced cannabinoid tetrad behaviors in mice, suggesting cannabimimetic activity. Some behaviors could be blocked by cannabinoid or adenosine receptor antagonists, suggesting a mixed mechanism of action. These behavioral effects were selectively additive with WIN55,212, suggesting terpenes can boost cannabinoid activity. In vitro experiments showed that all terpenes activated the CB1R, while some activated other targets. Our findings suggest that these Cannabis terpenes are multifunctional cannabimimetic ligands that provide conceptual support for the entourage effect hypothesis and could be used to enhance the therapeutic properties of cannabinoids.