Research Peptide Storage and Stability: What the Literature Reports

Introduction

A lyophilized peptide is a peptide that has been freeze-dried into a solid, and the stability literature reports that this solid degrades far more slowly than the same peptide dissolved in water. Peptides in storage undergo deamidation, oxidation, hydrolysis, aggregation and surface adsorption at rates governed by temperature, moisture and light, and manufacturers establish shelf life through stability studies under ICH guideline Q1A(R2).

Key facts

• Lyophilization removes water from a frozen solution by sublimation under reduced pressure in three stages: freezing, primary drying and secondary drying [1, 2].
• Manning, Patel and Borchardt (1989) classified peptide and protein degradation into chemical pathways (proteolysis, deamidation, oxidation, racemization, beta-elimination) and physical pathways (aggregation, precipitation, denaturation, adsorption to surfaces) [3].
• Robinson and Robinson (2001) measured deamidation rates for 306 asparaginyl sequences in model peptides at pH 7.4 and 37 degrees Celsius, showing the rate depends on neighboring residues [7].
• Pikal and colleagues (1991) reported methionine oxidation, asparagine deamidation and aggregation in freeze-dried human growth hormone during storage at 25 and 40 degrees Celsius [11].
• Costantino, Langer and Klibanov (1994) reported that aggregation of lyophilized insulin correlated directly with water uptake by the powder [12].
• ICH Q1A(R2) specifies long-term testing at 25 degrees Celsius and 60 percent relative humidity (or 5 degrees Celsius for refrigerated materials) and accelerated testing at 40 degrees Celsius and 75 percent relative humidity for six months [17].
• The 2010 Egrifta label required refrigerated storage at 2 to 8 degrees Celsius for the lyophilized vial; the 2019 Egrifta SV and 2025 Egrifta WR labels specify 20 to 25 degrees Celsius [20, 21, 22].

What does lyophilized mean for a peptide?

A lyophilized peptide is a peptide that has been freeze-dried: its aqueous solution was frozen and the ice removed by sublimation under vacuum, leaving a dry, porous solid. Wang (2000) described the process in three stages, freezing, primary drying in which ice sublimes, and secondary drying in which residual bound water is desorbed [1]. Tang and Pikal (2004) described the resulting cake as a porous matrix whose structure is the imprint of the ice crystals that sublimed away [2].

The purpose of the process, as the formulation literature reports it, is stabilization. Wang (2000) noted that the dried state restricts the molecular motions and water-dependent reactions responsible for degradation in solution [1]. The physical chemistry is covered in the library's article on why peptides are lyophilized.

Lyophilized is not a synonym for stable. It describes the physical form; the residual moisture, the excipients and the storage conditions determine how stable a particular lyophilized peptide actually is [1, 11].

Why are lyophilized peptides more stable than peptide solutions?

Lyophilized peptides are more stable than solutions because the dominant chemical degradation reactions require water, either as a reactant or as the medium that lets molecules move and collide. Wang (1999) reported that hydrolysis, deamidation and many oxidation reactions proceed continuously in aqueous solution at rates governed by pH, temperature and buffer composition [6].

Yoshioka and Aso (2007) reviewed the relationship between molecular mobility and chemical stability in amorphous pharmaceutical solids and reported that chemical reaction rates in dried solids correlate with the mobility of the molecules, which falls sharply as water content drops below the glass transition [13]. Manning and colleagues (2010) reported the same principle in their update on protein stability: solid-state degradation continues but at rates orders of magnitude below solution rates when moisture is low [4].

Cleland, Powell and Shire (1993) described aggregation, the most common physical degradation route, as strongly dependent on concentration, pH, ionic strength and temperature in solution [5]. Laboratory diluents are addressed in the article on bacteriostatic water.

What degradation pathways affect peptides in storage?

The stability literature groups peptide degradation into chemical pathways, which alter covalent bonds, and physical pathways, which alter conformation or state without changing the covalent structure [3, 4]. The table summarizes the pathways, the residues reported as susceptible and the drivers reported in the cited reviews.

Pathway	Type	Susceptible residues or sites	Reported drivers	Source
Deamidation	Chemical	Asparagine, glutamine (fastest at Asn-Gly)	pH, temperature, water, neighboring residues	Robinson 2001 [7]; Cleland 1993 [5]
Oxidation	Chemical	Methionine, cysteine, tryptophan, histidine, tyrosine	Oxygen, peroxides, metal ions, light	Li 1995 [8]; Hovorka 2001 [9]; Kerwin 2007 [10]
Hydrolysis	Chemical	Peptide bonds, especially at aspartate	Water, extreme pH, temperature	Manning 1989 [3]; Wang 1999 [6]
Racemization and beta-elimination	Chemical	Cystine, serine, aspartate	Alkaline pH, temperature	Manning 1989 [3]
Disulfide interchange	Chemical	Cysteine and cystine	Moisture, temperature, alkaline conditions	Costantino 1994 [12]
Aggregation	Physical	Hydrophobic and unfolded regions	Concentration, temperature, moisture, interfaces, freeze-thaw stress	Cleland 1993 [5]; Kueltzo 2008 [15]
Adsorption to surfaces	Physical	Whole peptide, charge and hydrophobicity dependent	Container material, dilution, absence of carrier protein	Goebel-Stengel 2011 [16]

Deamidation is the best-quantified pathway. Robinson and Robinson (2001) measured deamidation rates for 306 asparaginyl sequences in model peptides and reported that the rate is set primarily by the residue following the asparagine [7]. Li, Schöneich and Borchardt (1995) described methionine and cysteine as the most readily oxidized residues, with tryptophan, histidine and tyrosine also susceptible [8]; Hovorka and Schöneich (2001) covered metal-catalyzed and peroxide-driven mechanisms [9].

Goebel-Stengel and colleagues (2011) measured recovery of eight radiolabeled endocrine peptides from glass and plastic tubes and reported large, peptide-specific losses to container surfaces [16]. Adsorption is a physical loss of material, not a chemical change to it.

How do temperature, moisture and light affect lyophilized peptides?

Temperature, moisture and light each raise the rate of degradation of lyophilized peptides, and the published data show the effects compound. Pikal and colleagues (1991) stored freeze-dried human growth hormone at 25 and 40 degrees Celsius and reported methionine oxidation, asparagine deamidation and aggregation in the solid, with the amount depending on excipients and residual moisture [11].

Costantino, Langer and Klibanov (1994) exposed lyophilized insulin to elevated temperature and humidity and reported both covalent aggregation, through thiol-catalyzed disulfide interchange, and non-covalent aggregation, with the extent correlating directly with water uptake by the powder [12].

Moisture matters because water restores molecular mobility to the amorphous solid. Yoshioka and Aso (2007) reported that sorbed water lowers the glass transition temperature of amorphous pharmaceuticals and raises reaction rates [13], and Wang (2000) identified residual moisture as a primary determinant of solid-state shelf life [1].

Light drives photo-oxidation. Kerwin and Remmele (2007) reviewed photodegradation of protein biologics and reported that tryptophan, tyrosine, phenylalanine and cysteine undergo primary photo-oxidation, with downstream changes to secondary and tertiary structure [10]. ICH guideline Q1B sets the standard photostability test conditions used to assess this susceptibility [18].

Freezing and thawing a solution is a distinct stress. Cao and colleagues (2003) attributed freeze denaturation of model proteins to the ice-liquid interface [14], and Kueltzo and colleagues (2008) reported that aggregation of an antibody during freeze-thawing depended on pH, concentration and container material [15]. A lyophilized solid contains no bulk water to freeze.

Does lyophilized tesamorelin need to be refrigerated?

For the FDA-approved product, the answer depends on which formulation the label describes; for research-grade tesamorelin, the answer is whatever the supplier's certificate of analysis states. The original 2010 Egrifta label, for lyophilized vials formulated with mannitol, states that non-reconstituted vials "must be stored at refrigerated temperature, between 2°C and 8°C (36°F and 46°F)" and protected from light in the original box [20]. The label also directs that reconstituted solution not be refrigerated or frozen and be discarded if not used immediately, which reflects the solution instability described above [20].

The reformulated products carry different statements. The Egrifta SV label (approved 2019) states storage of the lyophilized SV vial "at room temperature at 20°C to 25°C (68°F to 77°F)" with excursions permitted to 15 to 30 degrees Celsius, protected from light [21]. The Egrifta WR label (2025) states storage of the WR vial at 20 to 25 degrees Celsius in the original box [22]. The same peptide therefore carries a refrigerated statement in one formulation and a room-temperature statement in two others, because each formulation had its own stability studies.

Research-grade tesamorelin is a separate research-use-only reference material, not the approved drug product, and its formulation differs from the Egrifta products. Its storage condition and retest date come from the supplier's certificate of analysis, not the FDA label. The same applies to every peptide in the catalog, including BPC-157; what a certificate contains is explained in understanding a peptide COA.

How do manufacturers determine and state a peptide's shelf life?

Manufacturers determine shelf life through formal stability studies standardized in ICH guideline Q1A(R2), adopted by the FDA, the European Medicines Agency and Japan's regulator [17]. The guideline defines the re-test period as the time a drug substance is expected to remain within specification under defined storage conditions, and shelf life as the equivalent period for a drug product under its labeled conditions [17].

Q1A(R2) sets three tiers of study. Stress testing exposes the material to heat, high humidity, oxidation, photolysis and a range of pH values in solution to identify degradation products and validate the analytical method [17]. Long-term testing runs at 25 degrees Celsius and 60 percent relative humidity (or 5 degrees Celsius for refrigerated materials) for at least 12 months on three batches [17].

The guideline's accelerated testing runs at 40 degrees Celsius and 75 percent relative humidity for six months, and a significant change there triggers intermediate testing at 30 degrees Celsius [17].

ICH Q5C adds guidance for biotechnological and biological products, noting that extrapolation from elevated-temperature data is less reliable for these molecules [19]. Cleland, Powell and Shire (1993) made the same point, reporting that shelf life for proteins must be established case by case [5].

The output of these studies is the storage statement and the expiry or retest date printed on the label and the certificate of analysis; for research reference materials, the certificate is the controlling document. Supplier documentation is covered in how to evaluate a research peptide supplier and what research peptides are.

Summary

A lyophilized peptide is a freeze-dried solid that the stability literature reports degrades far more slowly than the same peptide in solution, because the water needed for deamidation, hydrolysis, oxidation and molecular mobility has been removed. Degradation proceeds through chemical pathways (deamidation, oxidation, hydrolysis, racemization, disulfide interchange) and physical pathways (aggregation, adsorption), at rates set by temperature, moisture and light. The approved tesamorelin products carry formulation-specific storage statements: refrigerated for the 2010 vial, room temperature for the 2019 and 2025 vials. Research-grade material follows its supplier's certificate of analysis, set under ICH Q1A(R2).

References

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17. International Council for Harmonisation. Q1A(R2): Stability Testing of New Drug Substances and Products. Step 4, February 2003. Source: database.ich.org
18. International Council for Harmonisation. Q1B: Photostability Testing of New Drug Substances and Products. Step 4, November 1996. Source: database.ich.org
19. International Council for Harmonisation. Q5C: Stability Testing of Biotechnological/Biological Products. Step 4, November 1995. Source: database.ich.org
20. Theratechnologies Inc. EGRIFTA (tesamorelin for injection) prescribing information, NDA 022505, approved November 2010. U.S. Food and Drug Administration. Source: accessdata.fda.gov
21. Theratechnologies Inc. EGRIFTA SV (tesamorelin for injection) prescribing information. DailyMed, U.S. National Library of Medicine. DailyMed drug label
22. Theratechnologies Inc. EGRIFTA WR (tesamorelin for injection) prescribing information. DailyMed, U.S. National Library of Medicine. DailyMed drug label