Burn injury-induced pain (BIP) is a complex condition whose spinal mechanisms remain incompletely understood. Although spinal glucagon-like peptide-1 receptor (GLP-1R) signaling has been implicated in pain modulation, its contribution to BIP remains unclear. Using a mouse model of second-degree burn injury, we characterized nociceptive behaviors, spinal glial responses, and the temporal and cellular distribution of GLP-1R using immunoblotting, immunofluorescence, and RNAscope in situ hybridization. We then evaluated the antinociceptive effects of intrathecal semaglutide, their sensitivity to pharmacological GLP-1R antagonism, and the functional contribution of endogenous enkephalin/δ-opioid receptor (DOR) signaling. Burn injury increased spinal GLP-1R expression during the peak phase of pain hypersensitivity. GLP-1R immunoreactivity and Glp1r transcripts showed a substantial association with GFAP-positive astrocytic profiles, while detectable signals were also present in microglia and neurons. Intrathecal semaglutide attenuated mechanical allodynia and thermal hyperalgesia, and these effects were reduced by pharmacological GLP-1R antagonism. Acute semaglutide responsiveness was also observed in female mice. Semaglutide increased spinal Penk mRNA and enkephalin immunoreactivity in vivo and increased Penk expression and extracellular enkephalin levels in primary spinal astrocyte-enriched cultures. In spinal tissue, enkephalin immunoreactivity was more frequently associated with GFAP-positive profiles than with Iba1-or NeuN-positive profiles. Moreover, enkephalin neutralization and DOR antagonism attenuated semaglutide-induced antinociception. Together, these findings support a functional spinal enkephalin/DOR pathway linked to intrathecal semaglutide treatment and consistent with GLP-1R involvement in BIP.

Subtle structural modifications at the 3-position of opioid peptides have been reported to modulate their receptor binding affinity and functional activity. Our previous work identified a novel cyclic hexapeptide, Tyr-c[D-Lys-Gly-Phe-Asp]-D-Pro-NH2, as a multitarget full agonist at μ-, κ-, and δ-opioid receptors (MOR, KOR, and DOR). In the present study, 16 novel analogs of this hexapeptide were synthesized by replacing the Gly3 residue with phenylalanine and its derivatives to investigate their structure-activity relationships. Functional characterization demonstrated that these modifications generated analogs exhibiting varying selectivity and efficacy profiles at opioid receptors. Notably, analog 9 containing p-F-Phe3 exhibited MOR and KOR agonism/DOR antagonism and produced potent antinociception following peripheral administration, with reduced antinociceptive tolerance, physical dependence, and respiratory depression. Surprisingly, analog 11 containing p-Br-Phe3 acted as a potent and selective MOR antagonist. Pharmacological blockade of the peripheral MOR by analog 11 significantly attenuated fentanyl-induced antinociceptive tolerance, highlighting its therapeutic potential.

Depression entails a range of pathological processes in the brain, typically characterized by altered microglial state, neural dysfunction, and vascular dysregulation. While it is well established that activated microglia inflict damage to neurons through direct and indirect microglia-neuron interactions, their interaction with vasculature and the associated regulation of vascular structure and function in depression remain poorly understood. Here, using a mouse model of depression induced by chronic unpredictable stress (CUS), we find that in stressed mice, activated microglia present reduced motility and decreased contact area with vasculature, which is accompanied by pathological vascular structure and function, characterized by reduced vessel density, narrowed vascular diameters, and sluggish blood flow velocity. We observe that vascular structure in the stressed mice is rapidly modified by the vessel-associated microglia (VAM). These VAM show upregulated angiotensin II type 1 receptor (AT1R) expression, which is not present in the vascular-uncontacted microglia. Furthermore, we demonstrate that AT1R signaling together with altered microglial state under chronic stress are critical mediators for the altered microglia-vascular interactions, vascular dysregulation, as well as the depression-like behaviors. Together, our findings reveal that under CUS, the aberrant microglial-vascular interaction, including the dysregulated microglial vasoregulation arising from AT1R signaling and altered microglial state, leads to depression, forging a new link between chronic stress and depression.

Opioid receptors, as members of the G-protein-coupled receptor (GPCR) superfamily, represent promising therapeutic targets for managing nociception. Herein, we designed, synthesized, and pharmacologically characterized the novel bifunctional decapeptide, MKOP002. In vitro, MKOP002 activated both µ- and κ-opioid receptors (MOR and KOR), exhibiting G protein-biased agonism at MOR. Subcutaneous (s.c.) injection of MKOP002 produced significant antinociceptive effects through the peripheral MOR and KOR in the tail-flick test. Notably, MKOP002 demonstrated potent and dose-dependent antinociceptive efficacy across various models of acute, inflammatory, and neuropathic pain. Additionally, MKOP002 exhibited antipruritic effects comparable to CR845, mediated by both the peripheral and central KOR. Similar to CR845, at the high doses, MKOP002 induced sedation via central KOR at least partially, and also resulted in depressive-like behaviors. Importantly, MKOP002 did not elicit MOR-associated adverse effects such as tolerance, constipation, respiratory depression, or addiction. These findings underscore the therapeutic potential of MKOP002 as a lead compound for antinociceptive and antipruritic therapy, supporting the development of bifunctional MOR/KOR agonists as a safer opioid strategy.

Recently, κ-opioid receptor (KOR) agonists have been attractive therapeutic candidates for the treatment of pain and pruritus. To advance the development of effective and safer peripherally restricted KOR agonists, we designed, synthesized, and evaluated 21 novel chimeric peptides incorporating the N-terminal tetrapeptide sequence of CR845 and the C-terminal “address” domain derived from dynorphin A. In vitro calcium mobilization assays confirmed the selective and full KOR agonism for all the compounds. Among these, analogues 4, 9, and 17 emerged as optimized analogues, exhibiting potent analgesic and antipruritic effects comparable to those of CR845 after subcutaneous administration, through the activation of the peripheral KOR. Additionally, subcutaneous administration of these 3 optimized analogues induced sedation without eliciting aversion or depressive-like side effects. Notably, analogue 4 was selected as the final candidate due to its high potency in KOR agonism and minimal sedative effects, making it the most promising drug candidate for the development of efficient and safe antinociceptive and antipruritic therapies.

Opioid analgesics are critical for managing moderate-to-severe pain，yet are limited by adverse gastrointestinal (GI) effects, notably constipation. This necessitates developing novel opioid agonists with robust analgesia and reduced GI side effects. The cyclic hexapeptide Tyr-c[D-Lys-Gly-p-F-Phe-Asp]-D-Pro-NH2 (analog 15), a recently characterized multifunctional agonist of μ-opioid receptor (MOR), κ-opioid receptor (KOR), and δ-opioid receptor (DOR), exhibits potent antinociception following subcutaneous (s.c.) administration with constipation observed only at high doses. To further evaluate its GI impact, we assessed the effects of analog 15 on intestinal motility using in vivo upper GI transit and colonic bead expulsion assays. Our results indicated that fentanyl, analog 15, and its parent peptide analog 0 dose-dependently slowed upper GI transit and colonic expulsion after s.c. administration, with the upper GI tract exhibiting greater sensitivity. Mechanistically, fentanyl inhibited the GI motility via both central and peripheral opioid receptors, whereas analog 15 inhibited upper GI transit exclusively through the peripheral MOR, KOR, and DOR, and suppressed colonic transit via the peripheral MOR and KOR, both effects were independent of the central opioid receptor pathway. In conclusion, we demonstrated that the high doses of analog 15 inhibited GI motility through peripherally restricted activation of multiple opioid receptors. This finding aligns with analog 15's limited blood-brain barrier (BBB) permeability, which explains its reduced constipating effects while preserving potent analgesia, thereby supporting the therapeutic potential of multi-target peripheral opioid agonists.

BACKGROUND AND PURPOSE:The opioid crisis caused by the proliferation of fentanyl-related drugs has intensified concerns about the utilisation of opioid analgesics. Herein, a novel peptide-drug conjugate FENPFF01, incorporating the neuropeptide FF (NPFF) and fentanyl pharmacophores, was synthesised and pharmacologically characterised. EXPERIMENTAL APPROACH:The agonist activities of FENPFF01 at opioid and NPFF receptors were characterised in in vitro functional assays. Antinociceptive effects and underlying pharmacological mechanisms of FENPFF01 were assessed in multiple mouse pain models. The side effects of FENPFF01 were further investigated through antinociceptive tolerance, respiratory function, addiction potential and gastrointestinal transit tests. KEY RESULTS:FENPFF01 functioned as a mixed partial agonist at the μ-opioid and NPFF2 receptors, and a full agonist at NPFF1 receptor. Subcutaneous FENPFF01 produced potent antinociception in acute, inflammatory and post-operative pain, which was mediated by the μ receptor. The in vivo pharmacological and pharmacokinetic data demonstrated that FENPFF01 could penetrate the blood-brain barrier (BBB) and activate the μ receptor in the brain to elicit antinociception. Importantly, chronic administration of FENPFF01 did not induce antinociceptive tolerance or observable effects on spinal microglial activation, which may be partly attributable to the activation of the NPFF2 receptor. FENPFF01 also did not affect arterial gas parameters, respiratory rate, locomotor activity, conditioned place preference response, physical dependence and gastrointestinal transit. CONCLUSIONS AND IMPLICATIONS:The newly developed peptide-drug conjugate FENPFF01 exhibited strong antinociception with reduced opioid-like side effects. It represents an interesting candidate for developing novel analgesics with multi-targeted agonist properties, aiming to address the widespread issues associated with opioid misuse.

Depression entails a range of pathological processes in the brain, typically characterized by microglia activation, neural dysfunction, and vascular dysregulation. While it is well established that activated microglia inflict damage to neurons through direct and indirect microglia-neuron interactions, their interaction with vasculature and the associated regulation of vascular structure and function in depression remain poorly understood. Here, using a mouse model of depression induced by chronic unpredictable stress (CUS), we find that in stressed mice, activated microglia present reduced motility and decreased contact area with vasculature, which is accompanied by pathological vascular structure and function, marked by reduced vessel density, narrowed vascular diameters, and sluggish blood flow velocity. We observe that vascular structure in the stressed mice is rapidly modified by the vascular-contacted microglia. These vascular-contacted microglia show upregulated angiotensin II type 1 receptor (AT1R) expression, which is not present in the vascular-uncontacted microglia. Furthermore, we demonstrate that AT1R signaling together with microglia activation under chronic stress are critical mediators for the altered microglial-vascular contact situation, vascular dysregulation, as well as the depression-like behaviors. Together, our findings reveal that under CUS, the aberrant microglial-vascular interaction, including the dysregulated microglial vasoregulation arising from AT1R signaling and microglia activation, leads to depression, forging a new link between chronic stress and depression. ### Competing Interest Statement The authors have declared no competing interest. the “Double First-Class” Research Start-up Funds of Lanzhou University

It is widely recognized that developing bi- or multifunctional opioid compounds could offer a valuable approach to pain management with fewer side effects compared to single-target compounds. In this study, we designed and characterized two novel chimeric peptides, EM-1-DLS and EM-2-DLS, incorporating endomorphins (EMs) and the ghrelin receptor antagonist [D-Lys3]-GHRP-6 (DLS). Functional assays demonstrated that EM-1-DLS and EM-2-DLS acted as κ-opioid receptor (κ-OR)-preferring agonists, weak μ-opioid receptors (μ-OR) and ghrelin receptor (GHSR) agonists. Upon intracerebroventricular (i.c.v.) administration in mice, both EM-1-DLS and EM-2-DLS exhibited dose- and time-dependent antinociceptive effects in the tail withdrawal test. EM-1-DLS demonstrated the highest antinociceptive potency among the peptides, with an ED50 approximately 8-fold greater than EM-1, while EM-2-DLS showed comparable effects to EM-2. The antinociceptive actions of EM-1-DLS involved activation of GHS-R1α, μ-OR, and κ-OR, whereas EM-2-DLS acted via GHS-R1α, δ-OR, and κ-OR pathways. Additionally, acute antinociceptive tolerance was investigated, revealing that EM-1-DLS induced a tolerance ratio of 2.33-fold, significantly lower than the 5.19-fold ratio induced by EM-1. Cross-tolerance ratios between the chimeric peptides and EMs ranged from 0.92 to 1.76, indicating reduced tolerance compared to EMs alone. These findings highlight the potential of these chimeric peptides to mitigate pain with diminished tolerance development, suggesting a promising strategy for the development of new analgesic therapies with improved safety profiles.

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) show substantial efficacy in regulating blood glucose levels and lipid metabolism, initially as an effective treatment for diabetes mellitus. In recent years, GLP-1RAs have become a focal point in the medical community due to their innovative treatment mechanisms, robust therapeutic efficacy, and expansive development prospects. Notably, GLP-1RAs benefit pain management through their neuroprotective and metabolic regulatory properties, such as inhibiting inflammation responses and oxidative stress, promoting β-endorphin release and modulating several other crucial biological pathways. Hence GLP-1RAs hold promise for repurposing as treatments for pain disorders. In this narrative review, we thoroughly trace the current preclinical and clinical evidence of seven pain modalities, including inflammatory pain, osteoarthritis, visceral pain, neuropathic pain, diabetic neuropathy, cancer pain and headache, to support the efficacy and underlying biological mechanisms of GLP-1RAs as therapeutic agents for pain suffering. Despite these promising findings, further research is necessary to establish their long-term efficacy, optimal dosing strategies, and potential synergistic interactions of GLP-1RAs with existing pain management therapies. Future clinical trials should aim to distinguish the direct analgesic effects of GLP-1RAs from their metabolic benefits and explore their broader applications in pain conditions. The ongoing exploration of new indications for GLP-1RAs further highlights their transformative potential in advancing medical treatments across diverse clinical fields.

Pharmacological research has showed that multi-targeted drug therapies offer superior efficacy and reduced side effects compared to single-target drug therapies. In this study, we designed and characterized four novel chimeric peptides G(1-5)-EM2, EM2-G(1-5), G(1-9)-EM2 and EM2-G(1-9) which incorporate endomorphin-2 (EM-2) and the active fragments of ghrelin. Calcium mobilization assays revealed that these four chimeric peptides acted as weak mixed agonists for the μ-opioid receptor (MOR), κ-opioid receptor (KOR), and growth hormone secretagogue receptor 1α (GHS-R1α). The results of fluorescence imaging experiments indicated that G(1-5)-EM2 and G(1-9)-EM2 could penetrate the blood-brain barrier (BBB) following intravenous (i.v.) injection. All chimeric peptides induced almost equal antinociceptive effects compared with EM-2 or better antinociceptive effects than EM-2 after intracerebroventricular (i.c.v.) injection in the acute pain in mice. Among them, G(1-5)-EM2 could cross the BBB and enter the brain to induce antinociceptive effect through central opioid receptors after i.v. injection. Our findings demonstrated that the chimeric peptides produced significant antinociception mainly via MOR, DOR and GHS-R1α without inducing antinociceptive tolerance, or with a lower tendency for antinociceptive tolerance after i.c.v. injection in the acute pain in mice. Furthermore, the chimeric peptides mitigated or eliminated the digestive side effects associated with EM-2. The collective results highlight G(1-5)-EM2 as the most promising candidate among the chimeric peptides. The chimeric peptides represent a promising class of potential analgesics for clinical pain management. However, further optimization is necessary to maximize their therapeutic potential.

The Fe(III)-activated Potassium peroxymonosulfate (PMS) system is a green advanced oxidation technology extensively utilized for water treatment and pollutant removal. However, the removal efficiency of this system is limited by the pH range and the slow cycling rate of Fe(III)/Fe(II). In this paper, polydopamine (PDA) was prepared by oxidative polymerization and then introduced into the Fe(III)/PMS system. The experimental results showed that the removal rate of 50 mg/L Rhodamine B (RhB) (100 ml) reached 99.37 % within 12 min under the conditions of PDA (5 mg), Fe(III) (0.15 mmol), and PMS (0.03 mmol). Additionally, the system achieved effective removal of RhB over a wide pH range (2-11), with a removal rate exceeding 90 % at pH = 11. Interference experiments with common anions and organic humic acid matter in water revealed that, except for HCO3-, the influence of others was relatively small. By analyzing the chemical states of the PDA surface before and after the reaction, as well as the Fe(II) generation and PMS decomposition process, it was found that the phenolic quinone groups on the PDA surface played a key role in the conversion of Fe(III) to Fe(II), and this process accelerated the generation of active species. Quenching experiments and EPR tests indicated that sulfate radicals (SO4 center dot-), hydroxyl radicals (center dot OH), singlet oxygen (1O2), and superoxide radicals (center dot O2-) were involved in the removal of RhB.

BACKGROUND:Accumulating evidence suggests that glial mechanisms are pivotal in regulating chronic pain. Our previous findings revealed that the interactions between spinal microglia and astrocytes are crucial for burn-induced pain hypersensitivity. However, the mechanisms underlying burn-induced peripheral sensitisation remain incompletely understood. METHODS:Sensory neurone-satellite glial cell (SGC) interactions within peripheral dorsal root ganglia were investigated using in vitro and in vivo experiments. Behavioural tests were conducted to evaluate the therapeutic potential of targeting peripheral sensitisation mechanisms for burn pain management. RESULTS:Burn injury upregulated calcitonin gene-related peptide (CGRP) expression in sensory neurones (1.5-fold; P=0.013) through transient receptor potential vanilloid 1 (TRPV1) channels. Pharmacological blockade of the TRPV1/CGRP signalling pathway effectively attenuated burn-induced mechanical allodynia and thermal hyperalgesia. Additionally, neurone-derived CGRP triggered SGC activation (from 6.8% pre-injury to 41.6% at day 5 post-injury), concomitant with enhanced gap junction-mediated SGC coupling (from 16.7% pre-injury to 40.5% at day 5 post-injury). Furthermore, chemokine expression (particularly CXCL1) in SGCs was elevated after burn injury, which potentiated sensory neurone excitability and exacerbated pain hypersensitivity. Blocking SGC coupling exerted potent analgesic effects in this burn pain model. CONCLUSIONS:A novel neurone-SGC interaction mechanism drives burn-induced peripheral sensitisation, providing translational implications for burn pain therapeutics.

Burn induced-pain (BIP) is one of the most common pain symptoms, which seriously affects the quality of sufferer life. Researches show that multi-targeted drug therapies offer superior efficacy and fewer side effects compared to single-target drug therapies. Consequently, in this study, we developed G(1-5)-EM2, a multi-targeted peptide designed to target μ-opioid receptor and the growth hormone secretagogue receptor 1α (GHS-R1α), and explored its antinociceptive effects on burn injury pain. Calcium mobilization experiments revealed that G(1-5)-EM2 demonstrated weak multi-agonist activities to μ-opioid receptor and κ-opioid receptor as well as GHS-R1α in vitro. Near-infrared fluorescence imaging experiments demonstrated that G(1-5)-EM2 could penetrate the blood-brain barrier (BBB) and access the brain following intravenous injection. The enzymatic stability of G(1-5)-EM2 was significantly enhanced compared to EM2. Our results indicated that intrathecal administration of G(1-5)-EM2 mitigated mechanical allodynia and thermal hyperalgesia in BIP. These antinociceptive effects of G(1-5)-EM2 were partially mediated through μ-opioid receptor and GHS-R1α. Moreover, intrathecal administration of G(1-5)-EM2 significantly decreased burn-induced up-regulation of phosphorylated p38 MAPK, phosphorylated NF-κBp65 and TRPV1 in the ipsilateral spinal cord, reduced the levels of IL-1β, IL-6 and TNF-α in serum, and enhanced wound healing in burned skin. Repeated intrathecal administration of G(1-5)-EM2 produced a non-tolerance-forming antinociception in BIP. These results suggest that the multi-targeted peptide G(1-5)-EM2 exhibits a novel role in alleviating BIP with fewer side effects and may represent a promising strategy for developing new analgesic drugs.

Increasing evidence indicates that neuropeptide FF (NPFF) produces analgesic effects and augments opioid-induced analgesia at the spinal level. However, our recent research demonstrated that NPFF exerted complex opioid-modulating effects in an inflammatory pain model after intrathecal (i.t.) injection. Consistent with previous findings, we found that i.t. NPFF dose-dependently attenuated complete Freund's adjuvant-induced pain hypersensitivity. Interestingly, pharmacological results illustrated that NPFF exhibited opposite opioid-modulating effects at the spinal level depending on its administration dosage, wherein i.t. NPFF potentiated morphine-induced anti-allodynia at the dose of 10 nmol, while attenuated morphine analgesia at an ultra-low-dose of 10 pmol. Behavioral results obtained from neuropeptide FF receptor 2 (NPFFR2) knockout animals suggested that both pro- and anti-opioid effects of NPFF were mediated by NPFFR2. Moreover, these modulating effects of spinal NPFFR2 were selectively targeting mu-opioid receptor, had no effect on delta- and kappa-opioid receptor agonist-induced analgesia. Finally, the opioid-modulating effects of NPFF were further verified using in vitro calcium imaging assay, demonstrating that pretreated with NPFF in primary-cultured spinal neurons significantly attenuated the inhibitory effects of morphine on high-K+-induced neuronal excitability. Taken together, our results suggested that NPFF exhibited dual modulating effects on morphine-induced analgesia after i.t. administration, which provides a possible mechanism to explain the complex opioid-modulating effects of endogenous NPFF systems.

Neuropeptide FF (NPFF) plays a critical role in various physiological processes through the activation of neuropeptide FF receptor 1 and 2 (NPFFR1 and NPFFR2). Numerous evidence has indicated that NPFF exhibits opposite opioid-modulating effects on opioid-induced analgesia after supraspinal and spinal administrations, while the detailed role of NPFFR1 and NPFFR2 remains unclear. In this study, we employed pharmacological and genetic inhibition of NPFFR to investigate the modulating roles of central NPFFR1 and NPFFR2 in opioid-induced analgesia and hyperalgesia, using a male mouse model of acute fentanyl-induced analgesia and secondary hyperalgesia. Our findings revealed that intrathecal (i.t.) injection of the nonselective NPFFR antagonist RF9 significantly enhanced fentanyl-induced analgesia, whereas intracerebroventricular (i.c.v.) injection did not show the same effect. Moreover, NPFFR2 deficient (npffr2-/-) mice exhibited stronger analgesic responses to fentanyl compared to wild type (WT) or NPFFR1 knockout (npffr1-/-) mice. Intrathecal injection of RF9 in npffr1-/- mice also significantly enhanced fentanyl-induced analgesia. These results indicate a crucial role of spinal NPFFR2 in the enhancement of opioid analgesia. Contrastingly, hyperalgesia induced by fentanyl was markedly reversed in npffr1-/- mice but remained unaffected in npffr2-/- mice. Similarly, i.c.v. injection of the selective NPFFR1 antagonist RF3286 effectively prevented fentanyl-induced hyperalgesia in WT or npffr2-/- mice. Notably, co-administration of i.c.v. RF3286 and i.t. RF9 augmented fentanyl-induced analgesia while reducing hyperalgesia. Collectively, these findings highlight the modulating effects of blocking spinal NPFFR2 and supraspinal NPFFR1 on fentanyl-induced analgesia and hyperalgesia, respectively, which shed a light on understanding the pharmacological function of NPFF system in future studies.

The neuropeptide FF (NPFF) system regulates various physiological and pharmacological functions, particularly pain modulation. However, the modulatory effect of NPFF system on itch remains unclear. To investigate the modulatory effect and functional mechanism induced by NPFF system on acute itch, we examined the effects of supraspinal administration of NPFF and related peptides on acute itch induced by intradermal (i.d.) injection of histamine or chloroquine in male mice. Our results indicated that intracerebroventricular (i.c.v.) administration of NPFF dose-dependently prevented histamine- or chloroquine-induced acute itch behaviors. In addition, the modulatory effect of NPFF was not affected by the selective NPFF receptor antagonist RF9. Furthermore, we investigated the effects of NPVF and dNPA, the selective agonists of NPFF1 and NPFF2 receptors respectively, on the acute itch. The results demonstrated that both NPFF agonists effectively prevented acute itch induced by histamine or chloroquine in a manner similar to NPFF, and their effects were also not modified by RF9. To further investigate the possible mechanism of the NPFF receptors agonists, the NPFF-derived analogues [Phg8]-NPFF and NPFF(1-7)-NH2 that could not activate NPFF receptors in cAMP assays were subsequently tested in the acute itch model. Interestingly, [Phg8]-NPFF, but not NPFF(1-7)-NH2, prevented acute itch behavior after i.c.v. administration. In conclusion, our findings reveal that NPFF and related peptides prevent histamine- and chloroquine-induced acute itch through a NPFF receptor-independent mechanism. And it was revealed that the C-terminal phenyl structure of NPFF may play a crucial role in these modulatory effects on acute itch.

With the current unmet demand for effective pain relief, analgesics without major central adverse effects are highly appealing, such as peripherally restricted kappa-opioid receptor (KOR) agonists. In this study, Conorphin-66, an analog of the selective KOR peptide agonist Conorphin T, was pharmacologically characterized in a series of experiments, with CR845 serving as the reference compound. Firstly, in vitro functional assay indicated that Conorphin-66 selectively activates KOR and exhibits weak β-arrestin2 signaling bias (-1.54 versus -4.35 for CR845). Additionally, subcutaneous Conorphin-66 produced potent antinociception in mouse pain models with ED50 values ranged from 0.02 to 3.28 μmol/kg, including tail-flick test, post-operative pain, formalin pain, and acetic acid-induced visceral pain. Similarly, CR845 exert potent antinociception in mouse pain models ranged from 0.15 to 1.47 μmol/kg. Notably, antagonism studies revealed that the analgesic effects of Conorphin-66 were mainly mediated by the peripheral KOR. Furthermore, Conorphin-66 produced non-tolerance-forming antinociception over 8 days. Unlike CR845, subcutaneous Conorphin-66 did not promote the sedation, anxiogenic effects, depressive-like effects, but did exhibit diuretic activity. Further study showed that Conorphin-66 does not have apparent antipruritic effects in an acute itch model. Overall, Conorphin-66 emerges as a novel peripherally restricted KOR agonist that produced potent antinociception with reduced side effects.

The cyclic peptide c[d-Lys(2), Asp(5)]-DN-9 has recently been identified as a multifunctional opioid/neuropeptide FF receptor agonist, displaying potent analgesic activity with reduced side effects. This study utilized Tyr-c[d-Lys-Gly-Phe-Asp]-d-Pro-NH2 (0), a cyclic hexapeptide derived from the opioid pharmacophore of c[d-Lys(2), Asp(5)]-DN-9, as a chemical template. We designed, synthesized, and characterized 22 analogs of 0 with a single amino acid substitution to investigate its structure-activity relationship. Most of these cyclic hexapeptide analogs exhibited multifunctional activity at mu and delta opioid receptors (MOR and DOR, respectively) and produced antinociceptive effects following subcutaneous administration. The lead compound analog 15 showed potent agonistic activities at the MOR, kappa opioid receptor (KOR), and DOR in vitro and produced a strong and long-lasting analgesic effect through peripheral MOR and KOR in the tail-flick test. Further biological evaluation identified that analog 15 did not cause significant side effects such as tolerance, withdrawal, or reward liability.

在我国人民生活水平不断改善、物质条件不断提高的同时,糖尿病患者数量也呈现逐步增加的趋势,形成了糖尿病足溃疡(diabetic foot ulcer,DFU)庞大的患者群体储备.糖尿病足作为糖尿病致残、致死的严重并发症之一,溃疡创面经久不愈是其主要特点,这也导致了糖尿病足溃疡患者住院时间动辄数月,而患者每次治疗的费用则以万计 [1].因此,一些能够切实有效防治糖尿病足溃疡的临床策略也逐步成为目前中外医学领域的关注热点.糖尿病足溃疡可归属于中医学"脱疽"范畴,祖国医学对此病的认识由来已久.《外科理例》载:"足大指赤肿焮痛,此脾经积毒下注而然,名曰脱疽."中医外科医家认为,脱疽乃是饮食不节,嗜食膏粱厚味,日久蕴热生毒,下注血脉而致,病机无外乎本虚标实两端.