Pentapeptide-18 (Leuphasyl) Peptide

Pentapeptide-18 mimics enkephalins, binding to opioid receptors on presynaptic neurons. This reduces calcium channel opening and catecholamine (acetylcholine, norepinephrine) vesicle release. The effect is similar to Argireline but through an opioid receptor-mediated pathway rather than SNARE interference.

Pentapeptide-18, marketed under the trade name Leuphasyl, is a synthetic enkephalin-mimetic pentapeptide with the sequence Tyr-D-Ala-Gly-Phe-Leu-NH2 (a stabilized analog of [Leu]-enkephalin). Its mechanism centers on modulating presynaptic acetylcholine release at cholinergic nerve terminals, particularly those innervating facial mimetic muscles. Unlike Argireline (Acetyl Hexapeptide-8), which acts postsynaptically by destabilizing the SNARE complex, Leuphasyl operates upstream at the level of neuronal excitability.

Enkephalin Receptor Engagement

Pentapeptide-18 is structurally derived from native opioid pentapeptides and exhibits binding affinity for delta- and mu-opioid receptor subtypes localized on presynaptic neuronal membranes. Activation of these G-protein coupled receptors (Gi/o coupled) inhibits adenylyl cyclase, reducing intracellular cAMP. The downstream consequence is closure of voltage-gated calcium channels (primarily N-type Cav2.2) and opening of inwardly rectifying potassium channels (GIRK), both of which hyperpolarize the presynaptic membrane.

Suppression of Catecholamine and Acetylcholine Release

By reducing calcium influx into the nerve terminal, Pentapeptide-18 attenuates the calcium-dependent fusion of synaptic vesicles with the presynaptic membrane. This decreases quantal release of acetylcholine into the neuromuscular junction. In research models of facial expression musculature, this presynaptic dampening has been associated with reduced amplitude of muscle contraction in response to repeated stimulation.

Synergy with Postsynaptic SNARE-Targeting Peptides

A key research interest in Pentapeptide-18 is its complementary mechanism to Argireline. Whereas Argireline mimics the N-terminus of SNAP-25 and competitively inhibits SNARE complex assembly postsynaptically, Leuphasyl reduces the upstream signal driving vesicle release. Combined studies have reported additive or synergistic reductions in muscle contraction biomarkers in cell-based assays.¹ This dual-targeting approach forms the rationale for many multi-peptide cosmetic research formulations.

Topical Bioavailability Considerations

The C-terminal amidation (-NH2) of Pentapeptide-18 enhances metabolic stability against carboxypeptidase degradation in skin extracellular matrix. The D-Ala substitution at position 2 further resists aminopeptidase cleavage, extending its half-life in topical research vehicles. Penetration into the epidermis is limited by molecular weight (~556 Da, near the 500 Da Lipinski threshold), and research vehicles often employ liposomal or microemulsion delivery to enhance stratum corneum permeation.

Downstream Cellular Effects

In preclinical chromaffin cell models—classic systems for studying catecholamine release—Pentapeptide-18 has been reported to reduce noradrenaline secretion in a dose-dependent manner. This finding extrapolates to the cosmetic research hypothesis that reducing neurotransmitter output at facial NMJs may diminish dynamic expression line formation over chronic exposure.

Pentapeptide-18 (Leuphasyl) supplied for research is a single synthetic pentapeptide active. Commercial Leuphasyl raw material from cosmetic ingredient suppliers (e.g., Lipotec) is typically delivered as a glycerin/water solution containing the active peptide at approximately 0.05% w/w along with carrier and preservative components. The table below documents the active and carrier components encountered in standard research-grade Leuphasyl preparations.

Lyophilized vs Solution Form

AminoCore Research may supply Pentapeptide-18 as either (a) lyophilized pure peptide powder (≥98% HPLC purity, no carriers) or (b) the commercial cosmetic raw material in solution form. Researchers should confirm the form of their specific lot via the certificate of analysis.

Active Peptide Characteristics

• Sequence: Tyr-D-Ala-Gly-Phe-Leu-NH2 (H-Tyr-D-Ala-Gly-Phe-Leu-NH2)
• Amino Acid Count: 5 (with D-Ala substitution at position 2)
• Modifications: C-terminal amidation; D-Ala at position 2 for protease resistance
• Class: Enkephalin analog / synthetic opioid pentapeptide
• INCI Name: Pentapeptide-18
• Trade Name: Leuphasyl (Lipotec S.A.)
• Appearance: White to off-white lyophilized powder (pure form) or clear viscous liquid (solution form)
• Solubility: Soluble in water, glycerin, propylene glycol; insoluble in non-polar organic solvents
• Purity (lyophilized): ≥98% by HPLC

The structural derivation from [Leu]-enkephalin (Tyr-Gly-Gly-Phe-Leu) with a single D-amino acid substitution makes Pentapeptide-18 chemically distinct from the native neuropeptide while retaining receptor affinity and gaining substantial metabolic stability in topical research vehicles.

Pentapeptide-18 (Leuphasyl) is typically supplied as a lyophilised powder or as a stabilised aqueous/glycerin solution depending on the supplier specification. For research use, the following handling protocol is recommended to preserve peptide integrity and ensure consistent results in topical formulation studies.

Reconstitution Protocol (Lyophilised Powder)

1. Equilibrate to room temperature before opening the vial. Cold vials exposed to ambient air can accumulate condensation, which introduces moisture into the lyophilised cake and accelerates hydrolytic degradation.
2. Select an appropriate solvent. Bacteriostatic water (0.9% benzyl alcohol) or sterile water for injection is suitable for short-term aqueous studies. For cosmetic formulation work, a propylene glycol/water (30:70) or glycerin/water (20:80) vehicle improves peptide stability and compatibility with downstream emulsion phases.
3. Calculate concentration. Example: 10 mg of peptide + 2 mL solvent = 5 mg/mL stock. Cosmetic working concentrations are typically 0.0005%–0.05% (5–500 ppm) of the final formulation.
4. Add solvent slowly down the side of the vial. Do not inject solvent directly onto the lyophilised cake at high velocity.
5. Swirl gently until fully dissolved. Do not vortex or shake aggressively — mechanical agitation can shear the peptide backbone and generate insoluble aggregates.
6. Filter sterilise through a 0.22 µm PES filter if the working solution is intended for cell culture or sensitive skin-model assays.

Formulation Compatibility Notes

• pH window: Optimal stability is observed in the range pH 4.5–6.5. Strongly alkaline phases (pH > 8) can promote racemisation at the D-Ala residue and degrade the enkephalin-like activity.
• Avoid strong oxidisers in the same phase: hydrogen peroxide, high-concentration retinaldehyde, and certain AHAs at low pH can degrade the tyrosine and phenylalanine residues.
• Compatibility with Argireline: Leuphasyl is frequently co-formulated with Acetyl Hexapeptide-8. Both peptides are stable in similar pH/temperature windows and can be added together to the cool-down phase (below 40°C) of an emulsion.
• Heat sensitivity: Add only during the cool-down phase. Prolonged exposure above 45°C accelerates degradation.

Handling Precautions

Wear nitrile gloves and work in a clean environment to avoid contamination. Document lot number, reconstitution date, and solvent system for every working solution. Discard any solution showing turbidity, discolouration, or precipitate formation, as these indicate aggregation or microbial contamination. For research use only — not intended for human or veterinary application.

Proper storage of Pentapeptide-18 (Leuphasyl) is critical for maintaining the structural integrity of the enkephalin-like sequence and ensuring reproducible activity in skin model and formulation research. The peptide is generally more stable than native Leu-enkephalin due to the D-alanine substitution at position 2, which confers resistance to aminopeptidase cleavage, but it remains sensitive to moisture, heat, oxidation, and prolonged light exposure.

Lyophilised Powder

• Long-term storage: −20°C or colder in a frost-free freezer, sealed under desiccant in the original vial. Under these conditions, the powder retains specification for 24 months or longer.
• Short-term storage: 2–8°C (refrigeration) is acceptable for up to 30 days if the vial remains unopened and sealed.
• Transit: Ambient temperature shipping for 5–10 days does not significantly impact stability provided the vial is sealed and protected from direct sunlight.
• Protect from light: Store in amber vials or in the original opaque packaging. The tyrosine residue is mildly photosensitive and can undergo oxidative degradation under prolonged UV exposure.

Reconstituted Solutions

• Aqueous stock (water or bacteriostatic water): Store at 2–8°C and use within 14–21 days. Avoid repeated freeze-thaw cycles, which can promote aggregation.
• Glycerin or propylene glycol vehicles: Improved stability — typically 30–60 days at 2–8°C when properly preserved.
• Finished cosmetic formulations: Stability depends on the broader matrix (preservative system, pH buffer, antioxidant load). Accelerated stability testing (40°C / 75% RH for 12 weeks) is recommended for any new formulation.

Stability Considerations

Pentapeptide-18 is susceptible to:

• Hydrolysis of the peptide bond under extreme pH (especially pH < 3 or > 9).
• Oxidation of the tyrosine and phenylalanine residues in the presence of free radicals or transition metals (Fe³⁺, Cu²⁺). Inclusion of chelators (EDTA, sodium phytate) in formulations is advisable.
• Microbial degradation — always use sterile technique and adequate preservation in any aqueous system.

For research-grade material, document storage conditions and reconstitution history on each vial. Discard solutions that show visible precipitation, discolouration, or off-odour. These quality controls are essential for reproducible results in topical efficacy and skin-equivalent studies.