Mechanism of Action
Enkephalinase Inhibition
Spinorphin inhibits APN and NEP with IC50 values in the low micromolar range, extending the synaptic lifetime of enkephalin/" class="wiki-internal-link">met-enkephalin and leu-enkephalin. This indirect mechanism amplifies endogenous opioid signaling without direct receptor activation at physiological doses. At higher concentrations, spinorphin also shows weak delta-opioid receptor binding (Ki ~10 uM), contributing to direct analgesic activity.
Comparison to Opiorphin
Spinorphin (bovine, 10 aa) and opiorphin (human, 5 aa; QRFSR) share the enkephalinase inhibition mechanism but differ in sequence and potency. Spinorphin shares the C-terminal TQRF motif with NPFF-family peptides, giving it NPFF receptor activity that opiorphin lacks. This dual enkephalinase inhibition + NPFF receptor modulation gives spinorphin broader neuromodulatory activity.
Research Summary
Analgesia
PreclinicalIV spinorphin produces naloxone-reversible analgesia in hot plate and tail flick tests in rodents. At 10 mg/kg IV, it shows analgesic efficacy comparable to moderate doses of morphine. The effect duration is limited by rapid plasma degradation. Spinorphin also reduces allodynia in nerve injury pain models, suggesting utility beyond acute nociception.
Anti-Inflammatory Activity
PreclinicalSpinorphin inhibits neutrophil chemotaxis and superoxide production in vitro. In carrageenan-induced paw inflammation models, spinorphin reduces inflammatory edema and thermal hyperalgesia. This anti-inflammatory component may be mediated via NPFF receptor signaling and opioid receptor activation on immune cells.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Analgesia (rodent) | 5-20 mg/kg IV | Single injection | Intravenous |
| APN/NEP inhibition (in vitro) | 1-100 uM | Single assay | Enzyme inhibition assay |
| Anti-inflammatory (rodent) | 5-10 mg/kg SC | Single or twice daily | Subcutaneous |
Spinorphin is a research tool only. No human data. Rapid degradation and high doses needed limit therapeutic translation. It is studied as a structural lead for stable analog development.
Interactions
Safety Profile
No human safety data. In rodents, spinorphin at analgesic doses does not cause respiratory depression, sedation, or constipation seen with direct opioid receptor agonists. The NPFF receptor component may modulate opioid tolerance development. Rapid plasma degradation limits systemic exposure after peripheral administration. No commercial product exists.
References
- [1]Nishizawa N, et al. Spinorphin, a novel endogenous compound that inhibits aminopeptidase M and is derived from the hemoglobin beta chain. FEBS Lett. 2000;476(3):185-189.
- [2]Nishizawa N, et al. Analgesic activity of spinorphin, a novel endogenous compound derived from bovine hemoglobin. Life Sci. 2000;68(1):83-90.
- [3]Rougeot C, et al. Inhibitors of enkephalin catabolism: new therapeutic tool in inflammation and pain. Biochem Pharmacol. 2002;63(3):293-300.