BQ-788

Summary

BQ-788 is a synthetic peptide that selectively blocks endothelin‑B (ET_B) receptors. It is employed as a research tool to dissect the role of ET_B‑mediated signalling in vascular tone, bronchoconstriction, cell growth and inflammation. The compound is not approved for therapeutic use and is administered intravenously or by other experimental routes in animal and human studies.

Mechanism of Action

BQ‑788 binds competitively to the ligand‑binding site of ET_B receptors, preventing endothelin‑1 (ET‑1) and related peptides from activating the receptor. In vitro it inhibits 125I‑ET‑1 binding with an IC50 of ~1.2 nM, while showing >1000‑fold lower affinity for ET_A receptors. By blocking ET_B, it suppresses downstream pathways that mediate vasodilation, bronchial smooth‑muscle contraction, cellular proliferation and clearance of circulating ET‑1.

What the Research Shows

Early pharmacological work demonstrated that BQ‑788 potently and selectively blocks ET_B receptors in cultured human heart cells and rabbit pulmonary arteries, with no agonist activity up to 10 µM. In conscious rats, intravenous infusion (3 mg·kg⁻¹·h⁻¹) abolished ET_B‑mediated depressor responses to ET‑1 or sarafotoxin, raised plasma ET‑1 levels, and increased blood pressure in Dahl salt‑sensitive hypertensive rats. Human forearm studies used BQ‑788 together with the ET_A antagonist BQ‑123 to show that ET_B contributes to ET‑1‑induced vasoconstriction, and that nebivolol reduces this tone. A microdialysis study in young women found that ET_B blockade with 300 nM BQ‑788 altered estradiol‑dependent microvascular dilation. In pig models of hypoxic pulmonary vasoconstriction, BQ‑788 abolished the ET‑1‑driven pulmonary vasodilatory phase, confirming an ET_B‑mediated dilation mechanism. The peptide has also been used to explore bronchoconstriction, tumor growth and lipopolysaccharide‑induced organ failure in animal models.

Reported Benefits

BQ‑788 provides a highly selective pharmacological probe for ET_B receptors, enabling researchers to isolate ET_B‑specific effects on vascular tone, bronchial reactivity, cell proliferation and inflammatory responses. Its potency (nanomolar IC50) allows low‑concentration experiments, and its lack of agonist activity reduces confounding activation. The compound has clarified the contribution of ET_B to estrogen‑modulated vasodilation in women and to pulmonary vasodilation during hypoxia, supporting mechanistic insights that guide development of non‑peptide ET_B antagonists.

Limitations of the Evidence

As a peptide, BQ‑788 is rapidly degraded by gastric enzymes and has a short plasma half‑life, limiting systemic use outside controlled experimental settings. Selectivity diminishes at high concentrations, and in vivo data show paradoxical blood‑pressure elevation in hypertensive rats, indicating complex physiological effects. Human data are limited to acute forearm or microvascular studies; there are no chronic safety or efficacy trials, and the compound has never progressed to clinical approval. Consequently, its translational relevance remains uncertain.

Safety Considerations

Acute studies report no agonist activity of BQ‑788 up to 10 µM, and no overt toxicity in short‑term animal experiments. However, intravenous infusion in rats increased circulating ET‑1 and raised blood pressure in salt‑sensitive hypertensive models, suggesting potential hypertensive risk with systemic exposure. The peptide’s rapid degradation may produce metabolites of unknown activity. No formal human safety data are available, and caution is warranted when interpreting dose‑response results, especially in vulnerable cardiovascular or pulmonary models.

How It Is Administered

BQ‑788 is administered experimentally as a sterile peptide solution, typically via intravenous infusion in rodents (e.g., 3 mg·kg⁻¹·h⁻¹). It has also been delivered intracoronary, intrathecal and subcutaneous routes in preclinical studies. In human microdialysis experiments, a concentration of 300 nM was perfused locally. Formulations are limited to aqueous solutions; the peptide is not available in oral dosage forms due to enzymatic degradation.

Routes of Administration

Goals & Uses

• Pain and nociception researchNeuroscience ResearchLow
• Vascular tone researchCardiovascular ResearchModerate
• Pulmonary hypertension researchCardiovascular ResearchLow
• Fibrosis attenuationFibrotic DiseasesLow
• Renal protectionRenalModerate
• Pulmonary hypertensionCardiovascularModerate
• Endothelin system dissectionPharmacological ToolHigh
• Tumor vasculature modulationOncology ResearchLow

Contraindications

• Clinical therapeutic useRegulatoryHigh
• PregnancyPopulationHighPotential fetal risk or insufficient safety data

Adverse Effects

• Blood pressure elevationCardiovascularUnknown
• Injection site reactionsLocalUnknown
• HypotensionCardiovascularUncommonLow blood pressure
• TachycardiaCardiovascularUncommonAbnormally fast heart rate
• VasoconstrictionCardiovascularUnknown

Drug Interactions

• BQ-123 (ET-A antagonist)Moderate
• Endothelin-1Low

Population Constraints

• General human population (therapeutic)Regulatory ConstraintAbsolute
• Pregnant subjectsReproductiveRelative

Regulatory Status

• European UnionInvestigationalUsed in clinical trial settings.
• United StatesInvestigationalAvailable only for IND‑supported research.
• United KingdomInvestigationalResearch use only.

BQ-788 has no regulatory approval in any jurisdiction. It is used exclusively as a research compound in preclinical and some early clinical investigational studies.

Evidence & Sources

• Chronic Nebivolol Treatment Suppresses Endothelin-1-Mediated Vasoconstrictor Tone in Adults With Elevated Blood Pressure
  Journal ArticleModerateDiehl KJ, et al.2016-01-01T00:00:00.000000Z
• Peptide and non-peptide antagonists targeting endothelin receptors in physiology and pathology
  Journal ArticleModerateHoude M, Labonté J, D'Orléans-Juste P2011-01-01T00:00:00.000000Z
• Gateways to Clinical Trials
  Journal ArticleModerateBayés M, Rabasseda X, Prous JR2002-01-01T00:00:00.000000Z
• BQ-788, a selective endothelin ET(B) receptor antagonist
  Journal ArticleModerateOkada M, Nishikibe M2002-01-01T00:00:00.000000Z
• ET(B) receptor-mediated vasodilation is regulated by estradiol in young women
  Journal ArticleModerateShoemaker LN, et al.2021-01-01T00:00:00.000000Z
• Endothelin in the pulmonary circulation with special reference to hypoxic pulmonary vasoconstriction
  Journal ArticleModerateHolm P1997-01-01T00:00:00.000000Z

Frequently Asked Questions