HSP60 is involved in the neuroprotective effects of naloxone

Abstract

Heat shock protein (HSP)60 is primarily a mitochondrial protein. Previous experiments have found that changes in the location of intracellular HSP60 have been associated with apoptosis. Extracellular HSP60 mediates apoptosis via its ligand, Toll‑like receptor (TLR)-4. TLR-4 is an important factor expressed on microglia, with a central role in generating neuroimmune responses in the pathogenesis of neurodegenerative disorders. Naloxone is a highly effective nonselective opioid receptor antagonist, and has been reported to be pharmacologically beneficial for the treatment of brain diseases through inhibiting microglia activation. However, the mechanisms underlying these beneficial effects of naloxone remain poorly understood. The present study aimed to investigate the role of HSP60 in the neuroprotective effects of naloxone on the production of proinflammatory mediators in lipopolysaccharide (LPS)-stimulated BV2 murine microglial cells and the possible signaling pathways involved. The results demonstrated that naloxone significantly inhibited the expression and release of HSP60 in BV2 cells. The expression levels of heat shock factor (HSF)-1 were upregulated in LPS‑activated BV2 cells, which indicated that the increased expression of HSP60 was driven by HSF-1 activation. However, increased HSF‑1 levels may be downregulated by naloxone. The levels of TLR‑4 were elevated in activated BV2 cells, and then inhibited by naloxone. Activation of TLR‑4 is characterized by activation of nuclear factor-κB (NF-κB) followed by the production of various proinflammatory and neurotoxic factors. Data from the present study demonstrated that naloxone reduced the expression levels of NF-κB and its upstream protein caspase‑3, and reduced the LPS-induced production of nitric oxide, inducible nitric oxide synthase, tumor necrosis factor α, interleukin-1β and interleukin-6 in BV2 microglia. In light of this data, it was concluded that naloxone may exert its neuroprotective and anti‑inflammatory effects by inhibiting microglia activation through a HSP60‑TLR‑4‑NF‑κB signaling pathway.

Neuroprotective effect of heat shock protein 60 on matrine-suppressed microglial activation

“…2C). HSF-1 is a transcription factor that regulates HSP60 expression and release (9). Western blot analysis revealed that the expression of HSF-1 was significantly upregulated by LPS compared with the control group; however, subsequent MT treatment significantly reduced this increase (both P<0.05; Fig.…”

“…It has been demonstrated that HSP60 is highly expressed by activated microglia, and that the extracellular release of HSP60 increases the production of other proinflammatory factors through binding to toll-like receptor 4 (TLR-4) and stimulating neuronal cell death (8,9). Thus, the regulation of HSP60 production is a potential therapeutic option for the treatment of neurodegenerative disorders.…”

Novel Toll-like receptor-4 antagonist (+)-naloxone protects mice from inflammation-induced preterm birth

“…(+)-Naloxone and related drug compounds have potential benefits over neutralising antibodies and other TLR4 antagonists. (+)-Naloxone potently blocks LPS-induced TLR4-mediated signaling in a variety of non-pregnancy models, suppressing NFκB activation and inhibiting TNF and IL1B induction in immune cells3435. As well as capacity to access and cross the placental barrier37, the established safety profile of closely related (−)-naloxone in pregnancy and infants is encouraging.…”

“…(+)-Naloxone is a newly identified TLR4 antagonist that is the non-opioid isomer of the opioid receptor antagonist (−)-naloxone31, a well-described nonselective antagonist of the μ-opioid receptor commonly prescribed for opioid addiction, including in pregnant women and neonates32. (+)-Naloxone binds MD2 to prevent LPS engagement with TLR433 leading to diminished immune NFκB activation and IL1B, IL6 and TNF synthesis343536. In contrast to anti-TLR4 neutralizing antibodies24, (+)-naloxone is a small molecule which can penetrate across the placenta37, with a pharmacokinetic profile affording it short systemic exposure or longer term delivery if required.…”

Sildenafil Improves Brain Injury Recovery following Term Neonatal Hypoxia-Ischemia in Male Rat Pups

“…Flumazenil reduces the seizure threshold [70], and seizure activity is thought to be part of the injurious process after HI in neonates [71]. Midazolam and naloxone have also been shown to be neuroprotective in some rodent models of stroke [72,73]. Despite these potential effects, we chose to use the sedative drugs rather than the more commonly described halothane or isoflurane - which have also been described as potentially neuroprotective by providing a preconditioning effect [74] - as fentanyl and midazolam are also often used in human asphyxiated newborns and reproduce more accurately what the newborns are going through.…”