Dermorphin

Abstract

The opioid receptor family comprises classical; MOP (mu/µ), KOP (kappa/k), DOP(delta/δ) receptors along with non-classical Nociceptin/Orphanin FQ (N/OFQ) peptide receptor (NOP). Expression on glial cells is controversial where there is a role for glia and opioids in pain processing and immunomodulation. Here we detail expression and function of opioid receptors in a wide range of established and primary glia. Namely, 1321N1 human astrocytoma, C6 rat astrocytoma, mouse primary astrocytes, human MO3.13 oligodendrocyte like cells, human HOG oligodendrocytoma, mouse EOC-20 microglia and mouse primary microglia. We used (i)-PCR for mRNA, (ii)-radioligand binding and (iii)-fluorescent probe binding for expression, (iv)-MAPK for activation and (v)-scratch assay for migration. MOP mRNA was detected in C6 and mouse primary astrocytes only. NOP mRNA was found in 1321N1, C6 and mouse primary astrocytes along with MO3.13 and HOG cells. There was variable expression of DOP and KOP; this was not probed further. Surprisingly, microglia (EOC-20 or primary mouse) did not express mRNA for opioid receptors unless treated with media from astrocytes. mRNA expression profile was generally matched by [3H]-DPN binding to classical and [3H]-N/OFQ binding to non-classical opioid receptors. In addition, C6, mouse primary and 1321N1 astrocytes along with MO3.13 and HOG cells bound the fluorescent NOP probe N/OFQATTO594. C6 and primary mouse astrocytes also bound the MOP fluorescent probe DermorphinATTO488. Where expressed both MOP and NOP supported Endomorphin-1 and N/OFQ-induced phosphorylation of ERK1/2 and reduced scratch migration. In microglia, astrocyte modulated opioid receptor expression could influence central opioid-immunomodulation and pain processing; further studies are required.

Abstract

The neuropeptide's multifaceted involvement in various components of neural homeostasis impacts pain and behavioral regulation. One of the highly potent neuropeptides is dermorphin, extracted from the skin of the Amazon frog (Phyllomedusa sauvagei). The unique feature of dermorphin is the D-Ala residue in its sequence, which has inspired researchers to search for dermorphin analogs for use as pharmaceuticals. The primary objective of this study is to synthesize several new linear and cyclic dermorphin analogs and evaluate them as potential non-invasive analgesics. By exploring our method for converting linear peptides into 2,5-diketopiperazine(2,5-DKP) derivatives, which stabilize peptide structures, we synthesize several new dermorphin linear peptides and chimeric cyclopeptidomimetics. These compounds were tested in vitro and in vivo to determine their biological activities and potential applicability as pharmaceuticals. For the evaluation of in vitro opioid activity, the "Guinea Pig Ileum" (GPI) test was used. D2 showed the highest activity, and cyclopeptides D3 and D4 showed high activity. We can assume that dermorphin analogues D2, D3, and D4 are potent agonists of µ-type opioid receptors and have high opioid activity. However, this needs to be verified using molecular modeling methods in further research. The analgesic effects of dermorphins have been evaluated in the "Hot-Plate" and "Tail-Flick" tests. In rats, D2 dermorphin analogues demonstrated dose-dependent analgesic effect in the "Water Tail-Flick" test after intranasal administration. A smaller dose of 0.5 µg/kg resulted in 40% analgesia and a short-term state of stupor. The maximum long-lasting analgesia was observed at a dose of 1.0 µg/kg, which induced complete stupor. The analgesic effect of peptide D2 after intraperitoneal administration at a 5.0 mg/kg dose was over 50%. The "Open-Field" test demonstrated a dose-dependent (15, 50, 150 μg/kg) peptide D2 suppression effect on behavioural reactions in rats following intranasal administration. A new modification of linear peptides, combined with a 2,5-DKP scaffold (D3 and D4), proved promising for oral use based on the results of analgesic effect evaluation in mice following intragastric administration.

Abstract

Opioids are among the most effective drugs for treating moderate to severe pain. Unfortunately, opioid use, even short-term, can lead to addiction, tolerance, overdose, and respiratory depression. Therefore, efforts to design and develop novel compounds that would retain analgesic activity while reducing side effects continue unabated. The present study was designed to investigate the respiratory and cardiovascular effects of the hybrid peptide LENART01, which has evidenced potent antinociceptive and antimicrobial activity. This hybrid peptide, composed of N-terminally located dermorphin and C-terminal modified ranatensin pharmacophore, was tested in vivo in anesthetized rats. The main effect of LENART01 was apnea in 70% of examined animals, sighing, and a significant increase in blood pressure. Interestingly, the hybrid induced sighs less frequently than ranatensin, and apnea dependent on vagus nerve mu opioid receptor activation much less frequently and less intensely than dermorphin itself. This shows that LENART01 is a safer opioid system-related agent as compared to dermorphin for its prospective use in the treatment of pain.

Abstract

The South American shamanic Kambô ritual involves applying the skin secretions of Phyllomedusa bicolor (giant monkey frog) to superficial burns for purported spiritual and therapeutic benefits. These secretions contain a complex mix of bioactive peptides, such as phyllocaerulein, phyllomedusin, phyllokinin, sauvagine, dermorphins, and deltorphins, that interact with diverse neurotransmitter and hormone receptor systems. Specifically, these peptides engage cholecystokinin (CCK) receptors, neurokinin-1 (NK1) receptors, bradykinin B2 receptors, corticotropin-releasing factor (CRF) receptors, and opioid receptors (μ and δ subtypes), influencing gastrointestinal, cardiovascular, endocrine, and neurologic pathways. While often short-lived, these peptides provoke profound physiological disturbances, including violent emesis, vasodilation, fluid shifts, and antidiuretic hormone (ADH) dysregulation. The combination of these effects with ritualistic overhydration of water can trigger life-threatening hyponatremia, cerebral edema, and ultimately, brain death. We present the first documented case of brain death associated with Kambô toxicity. A 35-year-old female developed headache, emesis, and unilateral fixed and dilated pupil within hours of a Kambô ritual. Imaging demonstrated diffuse cerebral edema and loss of intracranial blood flow. Laboratory workup revealed severe hyponatremia, likely due to excessive water intake, peptide-induced emesis with sodium loss, and suspected SIADH. Despite aggressive medical management, the patient progressed to brain death. Kambô rituals are unregulated and increasingly practiced in Western countries despite a lack of medical oversight. The ritual's unique combination of cutaneous toxin delivery, extreme emesis, and excessive water hydration creates a perfect storm for acute symptomatic hyponatremia and cerebral herniation. Physicians should consider Kambô exposure in patients presenting with acute neurologic decline and dot-like burn patterns. Public awareness, clinician education, and the development of treatment algorithms are critical as the use of this neurotoxic ritual continues to expand.

Abstract

Burn injury-induced chronic pain is a highly debilitating condition that profoundly impacts the well-being of military veterans and the general population. Current pain management for burn injured patients mainly relies on central opioids, often causing sedation, addiction, and physical dependence. This study aims to investigate the effects of Dermorphin [D-Arg2, Lys4] (1-4) amide (DALDA), a peripherally acting μ-opioid receptor (MOR) agonist in an animal model of burn injury-induced chronic pain while unravelling the underlying mechanisms. Soldering apparatus was used to induce burn pain in Sprague Dawley rats followed by testing for both evoked and ongoing pain behaviours. Molecular investigations were performed for TRPV1, NR2B, neuro-inflammatory and glia cell markers (TNF-α, IL-6, Iba-1 & ICAM-1), and neuropeptides (CGRP), using western blotting and RT-PCR analysis. Burn-injured rats exhibited significant hypersensitivity to mechanical, thermal, and cold stimuli, along with severe ongoing pain. Systemic administration of DALDA significantly reduced evoked pain behaviour in a dose-dependent manner (1, 3, and 10 mg/kg), with the 10 mg/kg s.c. dose effectively alleviating spontaneous pain without causing drug addiction. DALDA also restored antioxidant enzyme levels in the sciatic nerve and downregulated burn injury-induced molecular changes, including TRPV1, NR2B, and CGRP, as well as neuroinflammatory markers such as TNF-α and IL-6 in the DRG and spinal cord of rats. Activation of peripheral μ-opioid receptors efficiently mitigates both evoked and spontaneous pain in burn-injured rats, without causing central nervous system (CNS)-related side effects. Findings from the present study demonstrate a promising approach to mitigate burn pain, overcoming the limitations associated with centrally acting opioids.