Biphalin, a Dimeric Enkephalin, Alleviates LPS-Induced Activation in Rat Primary Microglial Cultures in Opioid Receptor-Dependent and Receptor-Independent Manners

Abstract

Neuropathic pain is relatively less responsive to opioids than other types of pain, which is possibly due to a disrupted opioid system partially caused by the profound microglial cell activation that underlines neuroinflammation. We demonstrated that intrathecally injected biphalin, a dimeric enkephalin analog, diminished symptoms of neuropathy in a preclinical model of neuropathic pain in rats (CCI, chronic constriction injury of the sciatic nerve) at day 12 postinjury. Using primary microglial cell cultures, we revealed that biphalin did not influence cell viability but diminished NO production and expression of Iba1 in LPS-stimulated cells. Biphalin also diminished MOP receptor level, as well as pronociceptive mediators (iNOS, IL-1β, and IL-18) in an opioid receptor-dependent manner, and it was correlated with diminished p-NF-κB, p-IκB, p-p38MAPK, and TRIF levels. Biphalin reduced IL-6, IL-10, TNFα, p-STAT3, and p-ERK1/2 and upregulated SOCS3, TLR4, and MyD88; however, this effect was not reversed by naloxone pretreatment. Our study provides evidence that biphalin diminishes neuropathy symptoms, which might be partially related to reduced pronociceptive mediators released by activated microglia. Biphalin may be a putative drug for future pain therapy, especially for the treatment of neuropathic pain, when the lower analgesic effects of morphine are correlated with profound microglial cell activation.

Lipopolysaccharide from Rhodobacter sphaeroides (TLR4 antagonist) attenuates hypersensitivity and modulates nociceptive factors

“…Furthermore, in our primary microglial cell cultures, we observed an increase in IBA-1 protein level after LPS stimulation with a significant downregulation of TLR4 protein (Popiolek-Barczyk et al. 2017 ). Therefore, despite the undoubted microglia-TLR4 relationship, the tendency for changes in these two factors (IBA-1 and TLR4) is not necessarily parallel.…”

The opioid peptide biphalin modulates human corneal epithelial wound healing in vitro

“…[19; 25-27] The antinociceptive effect of biphalin has been suggested to have a potential role in the treatment of cancer pain, abdominal pain associated with in ammatory bowel disease, and in neuropathic pain via different routes of administration, such as subcutaneous, intravenous, intrathecal, intracerebroventricular, and intraperitoneal. [9,28,29] Furthermore, recent studies have revealed the bene cial role of biphalin on cell viability and neuroprotection against excitotoxic and ischemic damage by inhibiting protein kinase Cdependent sodium potassium-chloride cotransporter expression in focal brain ischemia by activating downstream survival mitogen-activated protein kinases, and by inhibiting reactive oxygen species production in an opioid receptor-dependent manner, which was challenged by naltrexone. [19,25,30] Biphalin also acts as an immunomodulatory agent by stimulating human T cell proliferation, natural killer cell cytotoxicity in vitro, and interleukin-2 production and diminishes pro-and anti-in ammatory factors in lipopolysaccharide-treated microglial cells.…”

Regulatory mechanisms and therapeutic potential of microglial inhibitors in neuropathic pain and morphine tolerance

“…NPP is relatively less responsive to opioids than other types of pain. This might be due to the microglial activation caused by severe neuroinflammation, leading to the destruction of the opioid system, which can inhibit the effect of morphine and other opioid drugs on pain control (Popiolek-Barczyk et al, 2017). Microglia communicate with neurons, astrocytes, and other cells, including cells of the immune system, through several receptors and signaling pathways.…”

“…Microglia communicate with neurons, astrocytes, and other cells, including cells of the immune system, through several receptors and signaling pathways. Activated glial cells synthesize and release large amounts of glial mediators such as cytokines, chemokines, growth factors, and proteases, promoting interactions between glial cells and glial cell-neurons (Popiolek-Barczyk and Mika, 2016;Popiolek-Barczyk et al, 2017). Many studies have attempted to determine the roles of these intracellular pathways, which might be involved in the development and maintenance of NPP and morphine tolerance.…”