Dynorphin B

Mechanism of Action

• N-terminal Tyr-Gly-Gly-Phe-Leu (Leu-enkephalin) sequence engages the conserved opioid binding pocket; C-terminal sequence provides KOR selectivity
• KOR Gi/Go coupling: reduces cAMP, opens Kir channels, closes N-type calcium channels; net neuronal inhibition
• Produces dysphoria, sedation, and analgesia similar to dynorphin A; central KOR agonism modulates stress circuitry
• Less potent than dynorphin A at NMDA receptor (non-opioid effect); dynorphin B effects more predominantly opioid-receptor mediated
• Released from hypothalamic neurons during stress and high-fat feeding; contributes to negative reinforcement of appetitive behaviors

Research Findings

• Dynorphin B-13 and dynorphin A-17 co-released from prodynorphin neurons; ratio may shift in disease states
• Dynorphin B analgesia in tail-flick assay (IC50 ~1 nmol intrathecal) is comparable to dynorphin A and slightly less potent than U-50,488 (synthetic KOR agonist)
• Elevated dynorphin B levels in CSF of chronic pain patients, contributing to central sensitization
• KOR antagonists (JDTic, aticaprant) effectively block dynorphin B-mediated dysphoria in rodent models
• Dynorphin B co-localizes with cgrp/" class="wiki-internal-link">CGRP in primary afferent neurons; potential interaction in pain modulation

Research Protocols

• Antinociception assay: 1-10 nmol intrathecal in mice; tail-flick or hot-plate latency measurement
• KOR binding: Ki ~0.4-1 nM for dynorphin B at human KOR in radioligand displacement assays
• Conditioned place aversion (CPA): 1-3 mg/kg IP to establish KOR-mediated aversive state in rodents
• Prodynorphin fragment comparison: dynorphin B, A, and neo-endorphins tested in parallel for KOR/MOR/DOR selectivity

Interactions

• Dynorphin A: sibling peptide from same prodynorphin precursor; similar KOR potency but distinct NMDA receptor interaction
• KOR antagonists (JDTic, aticaprant, CERC-501): block dynorphin B analgesia and dysphoria; in clinical development for depression
• Naloxone/naltrexone: partially block dynorphin B at KOR; higher concentrations required than for MOR blockade

Safety Profile

Endogenous opioid. Not used clinically. KOR agonism produces sedation, dysphoria, diuresis, and psychotomimesis at supraphysiological doses; KOR antagonists targeting this pathway are in Phase II for depression and alcohol use disorder.

Legal & Regulatory

Research peptide; not approved as therapeutic