Mechanism of Action
CB1 Inverse Agonism
Hemopressin (PVNFKLLSH) acts as an inverse agonist at CB1 cannabinoid receptors, reducing constitutive CB1 activity below baseline. Unlike CB1 neutral antagonists (like rimonabant) that simply block agonist binding, inverse agonists suppress the receptor's basal signaling activity. Through CB1 inverse agonism, hemopressin reduces appetite, produces hypotension, and may reduce synaptic endocannabinoid tone in pain circuits.
Extended Forms and CB2 Agonism
N-terminally extended hemopressin forms VD-hemopressin (Val-Asp-PVNFKLLSH) and RVD-hemopressin (Arg-Val-Asp-PVNFKLLSH) activate CB2 receptors, producing anti-nociceptive and anti-inflammatory effects distinct from CB1 signaling. CB2 is expressed on immune cells and in the CNS, where its activation reduces neuroinflammation and modulates pain without the psychoactive effects of CB1 agonism.
Research Summary
Pain Modulation
AnimalHemopressin produces anti-nociception in inflammatory and neuropathic pain models through a mechanism that is partly naloxone-insensitive, suggesting non-opioid components. CB1 inverse agonism in descending pain pathways and extended-form CB2 agonism in spinal microglia both contribute to analgesia. Hemopressin pain effects differ qualitatively from both exogenous cannabinoids and classical opioids.
Appetite and Food Intake
AnimalConsistent with CB1 inverse agonism, hemopressin injection reduces food intake in fasted and fed mice. CB1 blockade in the hypothalamus reduces feeding drive, and hemopressin effects on appetite mirror those of rimonabant (a CB1 neutral antagonist that was briefly approved for obesity). Unlike rimonabant, hemopressin's inverse agonist profile may differ in CNS effects.
Cardiovascular Effects
AnimalHemopressin was originally identified by its hypotensive effect in rats. The mechanism involves CB1 inverse agonism on vasomotor neurons and potentially direct vascular effects. Blood pressure reduction is dose-dependent and reversed by CB1 agonists, confirming the cannabinoid mechanism of the cardiovascular effect.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| Pain research | 1-10 mg/kg | Single or daily x 1 week | Subcutaneous |
| Appetite / CB1 research | 1-30 mg/kg | Single dose pre-feeding | IP or SC (animal) |
Hemopressin research is strictly animal-based. No human protocols exist. The discovery that hemoglobin-derived peptides modulate the endocannabinoid system is a recent finding with evolving research directions.
Interactions
Safety Profile
Hemopressin has been studied in animal models with no identification of significant toxicity at effective doses. CB1 inverse agonism raises theoretical concerns about mood effects, given that the CB1 neutral antagonist rimonabant was withdrawn from the market due to psychiatric side effects (depression, suicidal ideation). Whether inverse agonism shares these risks is unknown. CB2 agonism (extended forms) is generally considered to have a favorable safety profile. No human safety data exists.
References
- [1]Heimann AS, et al. Hemopressin is an inverse agonist of CB1 cannabinoid receptors. Proc Natl Acad Sci. 2007;104(51):20588-20593.
- [2]Dale CS, et al. Antinociceptive action of hemopressin in experimental hyperalgesia. Peptides. 2005.
- [3]Bauer M, et al. Identification of opioid and cannabinoid peptide precursors in hemoglobin fragments. Biochemistry. 2012.