Effect of radical scavengers on the inactivation of papain by ascorbic acid in the presence of cupric ions

Formulation Studies During Preclinical Development of Influenza Hemagglutinin and Virus-Like Particle Vaccine Candidates

A critical element of vaccine formulation studies is the identification of chemical and physical degradation pathways that compromise structural integrity, and which may in turn affect the clinical safety and efficacy, of macromolecular antigens. Formulation development helps optimize and maintain the long-term storage stability and viability of vaccine antigens in pharmaceutically relevant dosage forms. The protocols presented in this manuscript highlight the use of accelerated stability studies for the formulation of influenza vaccine candidates including virus-like particles (VLP) and particle forming hemagglutinin (HA) antigens. Three case studies, each targeting a different facet of preclinical vaccine formulation development, are reviewed: (1) excipient screening experiments to mitigate VLP physical degradation, (2) methods for monitoring a specific chemical perturbation of the recombinant HA antigen and elucidating its effect on in vitro potency, and (3) maintaining HA conformational stability in the presence of freeze-thaw and freeze-drying stresses.

The effect of neighboring amino acid residues and solution environment on the oxidative stability of tyrosine in small peptides

The effects of neighboring residues and formulation variables on tyrosine oxidation were investigated in model dipeptides (glysyl tyrosine, N-acetyl tyrosine, glutamyl tyrosine, and tyrosyl arginine) and tripeptide (lysyl tyrosyl lysine). The tyrosyl peptides were oxidized by light under alkaline conditions by a zero-order reaction. The rate of the photoreaction was dependent on tyrosyl pK(a), which was perturbed by the presence of neighboring charged amino acid residues. The strength of light exposure, oxygen headspace, and the presence of cationic surfactant, cetyltrimethylammonia chloride had a significant effect on the kinetics of tyrosyl photo-oxidation. Tyrosine and model tyrosyl peptides were also oxidized by hydrogen peroxide/metal ions at neutral pH. Metal-catalyzed oxidation followed first-order kinetics. Adjacent negatively charged amino acids accelerated tyrosine oxidation owing to affinity of the negative charges to metal-ions, whereas positively charged amino acid residues disfavored the reaction. The oxidation of tyrosine in peptides was greatly affected by the presence of adjacent charged residues, and the extent of the effect depended on the solution environment.

Biotechnology applications of amino acids in protein purification and formulations

Amino acids are widely used in biotechnology applications. Since amino acids are natural compounds, they can be safely used in pharmaceutical applications, e.g., as a solvent additive for protein purification and as an excipient for protein formulations. At high concentrations, certain amino acids are found to raise intra-cellular osmotic pressure and adjust to the high salt concentrations of the surrounding medium. They are called "compatible solutes", since they do not affect macromolecular function. Not only are they needed to increase the osmotic pressure, they are known to increase the stability of the proteins. Sucrose, glycerol and certain amino acids were used to enhance the stability of unstable proteins after isolation from natural environments. The mechanism of the action of these protein-stabilizing amino acids is relatively well understood. On the contrary, arginine was accidentally discovered as a useful reagent for assisting in the refolding of recombinant proteins. This effect of arginine was ascribed to its ability to suppress aggregation of the proteins during refolding, thereby increasing refolding efficiency. By the same mechanism, arginine now finds much wider applications than previously anticipated in the research and development of proteins, in particular in pharmaceutical applications. For example, arginine solubilizes proteins from loose inclusion bodies, resulting in efficient production of active proteins. Arginine suppresses protein-protein interactions in solution and also non-specific adsorption to gel permeation chromatography columns. Arginine facilitates elution of bound proteins from various column resins, including Protein-A or dye affinity columns and hydrophobic interaction columns. This review covers various biotechnology applications of amino acids, in particular arginine.

Chemical pathways of peptide degradation. X: effect of metal-catalyzed oxidation on the solution structure of a histidine-containing peptide fragment of human relaxin

PURPOSE

To elucidate the major degradation products of the metal-catalyzed oxidation of (cyclo S-S) AcCys-Ala-X-Val-Gly-CysNH2 (X = His, cyclic-His peptide), which is a fragment of the protein relaxin, and the effect of this oxidation on its solution structure.

METHODS

The cyclic-His peptide and its potential oxidative degradation products, cyclic-Asp peptide (X = Asp) and cyclic-Asn peptide (X = Asn), were prepared by using solid phase peptide synthesis and purified by preparative HPLC. The degradation of the cyclic-His peptide was investigated at pH 5.3 and 7.4 in an ascorbate/cupric chloride/oxygen [ascorbate/Cu(II)/O2] system in the absence or presence of catalase (CAT), superoxide dismutase (SOD), isopropanol, and thiourea. The oxidation of the cyclic-His peptide was also studied in the presence of hydrogen peroxide (H2O2). All reactions were monitored by reversed-phase HPLC. The main degradation product of the cyclic-His peptide formed at pH 7.4 in the presence of ascorbate/Cu(II)/O2 was isolated by preparative HPLC and identified by 1H NMR and electrospray mass spectrometry. The complexation of Cu(II) with the cyclic-His peptide was determined with 1H NMR. The solution structure of the cyclic-His peptide in the presence and absence of Cu(II) at pH 5.3 and 7.4 and the solution structure of the main degradation product were determined using circular dichroism (CD).

RESULTS

CAT and thiourea were effective in stabilizing the cyclic-His peptide to oxidation by ascorbate/Cu(II)/O2, while SOD and isopropanol were ineffective. Cyclic-Asp and cyclic-Asn peptides were not observed as degradation products of the cyclic-His peptide oxidized at pH 5.3 and 7.4 in an ascorbate/Cu(II)/O2 system. The main degradation product formed at pH 7.4 was the cyclic 2-oxo-His peptide (X = 2-oxo-His). At pH 5.3, numerous degradation products were formed in low yields, including the cyclic 2-oxo-His peptide. The cyclic 2-oxo-His peptide appeared to have a different secondary structure than did the cyclic-His peptide as determined by CD. 1H NMR results indicate complexation between the cyclic-His peptide and Cu(II). CD results indicated that the solution structure of the cyclic-His peptide in the presence of Cu(II) at pH 5.3 was different than the solution structure observed at pH 7.4.

CONCLUSIONS

H2O2 and superoxide anion radical (O(*-)2) were deduced to be the intermediates involved in the ascorbate/Cu(II)/O2-induced oxidation of cyclic-His peptide. H2O2 degradation by a Fenton-type reaction appears to form secondary reactive-oxygen species (i.e., hydroxyl radical generated within complex forms or metal-bound forms of hydroxyl radical) that react with the peptide before they diffuse into the bulk solution. CD results indicate that different complexes are formed between the cyclic-His peptide and Cu(II) at pH 5.3 and pH 7.4. These different complexes may favor the formation of different degradation products. The apparent structural differences between the cyclic-His peptide and the cyclic 2-oxo-His peptide indicate that conformation of the cyclic-His peptide was impacted by metal-catalyzed oxidation.

Instability, stabilization, and formulation of liquid protein pharmaceuticals

One of the most challenging tasks in the development of protein pharmaceuticals is to deal with physical and chemical instabilities of proteins. Protein instability is one of the major reasons why protein pharmaceuticals are administered traditionally through injection rather than taken orally like most small chemical drugs. Protein pharmaceuticals usually have to be stored under cold conditions or freeze-dried to achieve an acceptable shelf life. To understand and maximize the stability of protein pharmaceuticals or any other usable proteins such as catalytic enzymes, many studies have been conducted, especially in the past two decades. These studies have covered many areas such as protein folding and unfolding/denaturation, mechanisms of chemical and physical instabilities of proteins, and various means of stabilizing proteins in aqueous or solid state and under various processing conditions such as freeze-thawing and drying. This article reviews these investigations and achievements in recent years and discusses the basic behavior of proteins, their instabilities, and stabilization in aqueous state in relation to the development of liquid protein pharmaceuticals.

An SOD-mimicry mechanism underlies the role of nitroxides in protecting papain from oxidative inactivation

Nitroxide stable free radicals have previously been found to afford protection in various biological systems against diverse types of oxidative stress, including, ischemia/reperfusion, hyperoxia, mechanical trauma, toxic xenobiotics, ionizing radiation, gastric and colonic irritants or strong oxidants. Dismutation of superoxide has originally been suggested to be one of the mechanisms that underlie the anti-oxidant effect of nitroxides. However, no direct evidence has been found, so far, to support this assumption. In the present study, superoxide and H2O2, generated enzymatically, were used to directly inactivate papain, a sulfhydryl enzyme, in vitro. The rate of papain inactivation served to assess the damage. The reaction mixtures contained a chelate in order to prevent the effect of adventitious redox-active metal ions, pre-empt the Fenton reaction and avoid hydroxyl-induced damage. Catalase or SOD alone partially protected the papain from inactivation. The protective effect of nitroxides resembled that of SOD in several aspects: a) nitroxides provided partial protection; b) the protective effect of nitroxides did not increase with the elevation of their concentration (above 0.5 mM); c) the combined addition of SOD and the nitroxide did not provide greater protection than that demonstrated by nitroxides or SOD separately; d) the effects of catalase with the nitroxide were additive; e) the nitroxide, like SOD itself, did not protect papain from H2O2-induced inactivation; f) the nitroxide was found not to be consumed in the course of the reaction but rather to be recycled. The results indicate that: (a) the main species responsible for the papain inactivation in a system in which the effect of transition metals is pre-empted, are O2-. and H2O2; (b) nitroxides inhibit the oxidative damage by removing superoxide not stoichiometrically, but rather catalytically as SOD-mimics; (c) nitroxides do not afford protection when the oxidative damage is induced directly by H2O2 (and not mediated by redox-active metals).

Chemical pathways of peptide degradation: IX. Metal-catalyzed oxidation of histidine in model peptides

PURPOSE

To elucidate the nature of the reactive oxygen species (i.e., superoxide anion radical, hydroxyl radical, and hydrogen peroxide) involved in the metal-catalyzed oxidation of histidine (His) in two model peptides.

METHODS

The degradation of AcAla-His-ValNH2 (Ala-peptide) and AcCysNH2-S-S-AcCys-His-VaNH2 (Cys-peptide) was investigated at pH 5.3 and 7.4 in an ascorbate/cupric chloride/oxygen (ascorbate/ Cu(II)/O2) system, both in the absence and presence of selective scavengers (i.e., catalase, superoxide dismutase, mannitol, sodium formate, isopropanol, and thiourea) of the reactive oxygen species. All reactions were monitored by HPLC. The major degradation products were characterized by electrospray mass spectrometry.

RESULTS

The Cys-peptide was more stable than the Ala-peptide at pH 5.3 and 7.4. Both peptides displayed greater stability at pH 5.3 than at 7.4. At pH 5.3, 35 +/- 0.7% of the Cys-peptide and 18 +/- 1% of the Ala-peptide remained after 7 hours, whereas at pH 7.4, 16 +/- 3% of the Cys-peptide and 4 +/- 1% of the Ala-peptide remained. Catalase, thiourea, bicinchoninic acid, and ethylenediaminetetraacetate were effective at stabilizing both peptides toward oxidation, while superoxide dismutase, mannitol, isopropanol, and sodium formate were ineffective. The main degradation products of the Ala- and Cys-peptides at pH 7.4 appeared to be AcAla-2-oxo-His-ValNH2 and AcCysNH2-S-S-AcCys-2-oxo-His-ValNH2, respectively.

CONCLUSIONS

Hydrogen peroxide, Cu(I), and superoxide anion radical were deduced to be intermediates involved in the oxidation of the Ala- and Cys-peptides. Hydrogen peroxide degradation to secondary reactive oxygen species may have led to the oxidation of the peptides. The degradation of hydrogen peroxide by a Fenton-type reaction was speculated to form a complexed form of hydroxyl radical that reacts with the peptide before diffusion into the bulk solution.