Impurity profiling quality control testing of synthetic peptides using liquid chromatography-photodiode array-fluorescence and liquid chromatography-electrospray ionization-mass spectrometry: The obestatin case

Development of a sensitive and quantitative HPLC-FLD method for the determination of obestatin in human plasma

Obestatin is a gastrointestinal system peptide. The quantification of this peptide is conventionally performed using immunological techniques. In this study, a selective and sensitive HPLC method coupled with fluorescence detection for the quantitation of obestatin in human plasma was developed and validated. The separation was obtained on a C18 (4.6 × 100 mm, 3.5-μm particles) column using a mobile phase composed of acetonitrile and water, both including 0.1% trifluoroacetic acid. The developed method was found to be linear in the concentration range of 20 to 1000 ng/mL, with a coefficient of determination of 0.9982. The precision results were less than 10%, and the accuracy results were between 92% and 107%. The detection and quantification limit values were obtained as 2.8 and 9.4 ng/mL, respectively. Analyte solutions were found stable for 24 h at room temperature, three freeze-thaw cycles, and 2 weeks at -20°C. The developed method was successfully used for the quantification of obestatin in human plasma samples. In conclusion, the developed method is sensitive and specific for measuring the plasma concentrations of obestatin.

Synthesis and characterization of two potential impurities (des-ethyl-Ganirelix) generated in the Ganirelix manufacturing process

Controlling certain diseases using peptide drugs has remarkably increased in the past two decades. In this regard, a generic formulation is an upfront solution to fulfill market demands. Ganirelix, a leading peptide active pharmaceutical ingredient (API) primarily used as a gonadotropin-releasing hormone antagonist (GnRH), has established a potential market value worldwide. But its generic formulation mandates detailed impurity profiles from a synthetic source and contemplates the sameness of a reference-listed drug (RLD). Post-chemical synthesis and processing of Ganirelix, some commercial sources have revealed two new potential impurities among many known, which show the deletion of an ethyl group from the hArg(Et)2 residue at the sixth and eighth positions, named des-ethyl-Ganirelix. These impurities are unprecedented in traditional peptide chemistry, and such monoethylated-hArg building blocks are not easily accessible commercially to synthesize these two impurities. Here, we have outlined the synthesis, purification, and enantiomeric purity characterization of the amino acids and their incorporation in the Ganirelix peptide sequence to synthesize these potential peptide impurities. This methodology will enable the convenient synthesis of side-chain substituted Arg and hArg derivatives in peptide drug discovery platforms.

KLK3 in the Regulation of Angiogenesis-Tumorigenic or Not?

In this focused review, we address the role of the kallikrein-related peptidase 3 (KLK3), also known as prostate-specific antigen (PSA), in the regulation of angiogenesis. Early studies suggest that KLK3 is able to inhibit angiogenic processes, which is most likely dependent on its proteolytic activity. However, more recent evidence suggests that KLK3 may also have an opposite role, mediated by the ability of KLK3 to activate the (lymph)angiogenic vascular endothelial growth factors VEGF-C and VEGF-D, further discussed in the review.

Role of GPR39 in Neurovascular Homeostasis and Disease

GPR39, a member of the ghrelin family of G protein-coupled receptors, is zinc-responsive and contributes to the regulation of diverse neurovascular and neurologic functions. Accumulating evidence suggests a role as a homeostatic regulator of neuronal excitability, vascular tone, and the immune response. We review GPR39 structure, function, and signaling, including constitutive activity and biased signaling, and summarize its expression pattern in the central nervous system. We further discuss its recognized role in neurovascular, neurological, and neuropsychiatric disorders.

Determining the Sources of Variance in the Preparation of Analytical Standards for Chromatographic Analysis of a Lyophilized Peptide Drug Substance by Nested ANOVA Statistical Analysis

Synthetic peptides used as therapeutic medicines is continuing to grow as an area of focus within the pharmaceutical industry due to specificity and potency. As such, quality control areas need to continue to advance their capabilities to ensure that appropriate analyses are being performed, and that the data generated are both accurate and precise. One area which poses a significant challenge compared with traditional small molecule drug products is having a highly robust, low variability method of quantifying the assay of the active substance. As many peptide therapeutics are formulated as liquid drug products for injection and preparation procedures to make these samples amenable to traditional chromatographic analysis are inherently low variability (i.e., a simple dilution), potential sources of variance derived from the preparation of the analytical standards used to quantify the assay of the product must be investigated. Here, a fully nested ANOVA experimental design was utilized to examine this process. Such a design allowed for multiple variables to be interrogated as well as the potential interplay of such differences. It was determined that sonication of the standards contributed the most variance, while the balance used and scale on which the standard preparation procedure was performed also contributed significantly. Finally, different procedures for introducing the material into a coulometric Karl Fischer (KF) titration device to quantify the water content of the drug substance were compared and showed that indirect quantification by anhydrous methanol extraction is a significantly more variable method than using an Oven KF autosampler.

Obestatin controls skeletal muscle fiber-type determination

Obestatin/GPR39 signaling stimulates skeletal muscle growth and repair by inducing both G-protein-dependent and -independent mechanisms linking the activated GPR39 receptor with distinct sets of accessory and effector proteins. In this work, we describe a new level of activity where obestatin signaling plays a role in the formation, contractile properties and metabolic profile of skeletal muscle through determination of oxidative fiber type. Our data indicate that obestatin regulates Mef2 activity and PGC-1α expression. Both mechanisms result in a shift in muscle metabolism and function. The increase in Mef2 and PGC-1α signaling activates oxidative capacity, whereas Akt/mTOR signaling positively regulates myofiber growth. Taken together, these data indicate that the obestatin signaling acts on muscle fiber-type program in skeletal muscle.

Quality evaluation of synthetic quorum sensing peptides used in R&D

Peptides are becoming an important class of molecules in the pharmaceutical field. Closely related peptide-impurities in peptides are inherent to the synthesis approach and have demonstrated to potentially mask biomedical experimental results. Quorum sensing peptides are attracting high interest in R&D and therefore a representative set of quorum sensing peptides, with a requested purity of at least 95.0%, was evaluated for their purity and nature of related impurities. In-house quality control (QC) revealed a large discrepancy between the purity levels as stated on the supplier׳s certificate of analysis and our QC results. By using our QC analysis flowchart, we demonstrated that only 44.0% of the peptides met the required purity. The main compound of one sample was even found to have a different structure compared to the desired peptide. We also found that the majority of the related impurities were lacking amino acid(s) in the desired peptide sequence. Relying on the certificates of analysis as provided by the supplier might have serious consequences for peptide research, and peptide-researchers should implement and maintain a thorough in-house QC.

Blood-brain transfer and antinociception of linear and cyclic N-methyl-guanidine and thiourea-enkephalins

Enkephalins are active in regulation of nociception in the body and are key in development of new synthetic peptide analogs that target centrally located opioid receptors. In this study, we investigated the in vivo blood-brain barrier (BBB) penetration behavior and antinociceptive activity of two cyclic enkephalin analogs with a thiourea (CycS) or a N-methyl-guanidine bridge (CycNMe), and their linear counterparts (LinS and LinNMe) in mice, as well as their in vitro metabolic stability. (125)I-LinS had the highest blood-brain clearance (K1=3.46μL/gmin), followed by (125)I-LinNMe, (125)I-CycNMe, and (125)I-CycS (K1=1.64, 0.31, and 0.11μL/gmin, respectively). Also, these peptides had a high metabolic stability (t1/2>1h) in mouse serum and brain homogenate, and half-inhibition constant (Ki) values in the nanomolar range with predominantly μ-opioid receptor selectivity. The positively charged NMe-enkephalins showed a higher antinociceptive activity (LinNMe: 298% and CycNMe: 205%), expressed as molar-dose normalized area under the curve (AUC) relative to morphine, than the neutral S-enkephalins (CycS: 122% and LinS: 130%).

CD8+ T-cell recognition of a synthetic epitope formed by t-butyl modification

We set out to clone Bax-specific CD8+ T-cells from peripheral blood samples of primary chronic lymphocytic leukemia patients. A number of clones were generated using a Bax peptide pool and their T-cell epitope was mapped to two peptides sharing a common 9-aa sequence (LLSYFGTPT), restricted by HLA-A*0201. However, when these T-cell clones were tested against highly purified syntheses (>95%) of the same peptide sequence, there was no functional response. Subsequent mass spectrometric analysis and HPLC fractionation suggested that the active component in the original crude peptide preparations (77% pure) was a peptide with a tert-butyl (tBu) modification of the tyrosine residue. This was confirmed by modification of the inactive wild type (wt) sequence to generate functionally active peptides. Computer modeling of peptide:HLA-A*0201 structures predicted that the tBu modification would not affect interactions between peptide residues and the HLA binding site. However these models did predict that the tBu modification of tyrosine would result in an extension of the side chain out of the peptide-binding groove up towards the TCR. This modified product formed <1% of the original P603 crude peptide preparation and <0.05% of the original 23 peptide mixture used for T-cell stimulation. The data presented here, illustrates the potential for chemical modifications to change the immunogenicity of synthetic peptides, and highlights the exquisite capacity of TCR to discriminate between structurally similar peptide sequences. Furthermore this study highlights potential pitfalls associated with the use of synthetic peptides for the monitoring and modulating of human immune responses. This article is protected by copyright. All rights reserved.

Identification of site-specific heterogeneity in peptide drugs using intact mass spectrometry with electron transfer dissociation

RATIONALE

Protamine sulfate is a peptide drug product consisting of multiple basic peptides. As traditional high-performance liquid chromatography (HPLC) separation methods may not resolve these peptides, as well as any possible peptide-related impurities, a method utilizing top-down mass spectrometry was developed for the characterization of complex peptide drug products, including any low-level impurities, which is described in this study.

METHODS

Herring protamine sulfate was used as a model system to demonstrate the applicability of the method. Direct infusion mass spectrometry and tandem mass spectrometry (MS/MS) on a high-resolution, mass accurate instrument with electron transfer dissociation (ETD) were used to identify all the species present in the herring protamine sulfate sample. Identifications were made based on mass accuracy analysis as well as MS/MS fragmentation patterns.

RESULTS

Complete sequence coverage of the three abundant herring protamine peptides was obtained using the top-down ETD-MS/MS method, which also identified a discrepancy with the published herring protamine peptide sequences. Additionally, three low-abundance related peptide species were also identified and fully characterized. These three peptides had not previously been reported as herring protamine peptides, but could be related to the published sequences through amino acid additions and/or substitutions.

CONCLUSIONS

A method for the characterization of protamine, a complex peptide drug product, was developed that can be extended to other complex peptide or protein drug products. The selectivity and sensitivity of this method improves a regulator's ability to identify peptide impurities not previously observed using the established methods and presents an opportunity to better understand the composition of complex peptide drug products.

Pharmaceutical impurities and degradation products: uses and applications of NMR techniques

Current standards and regulations demand the pharmaceutical industry not only to produce highly pure drug substances, but to achieve a thorough understanding of the impurities accompanying their manufactured drug substances and products. These challenges have become important goals of process chemistry and have steadily stimulated the search of impurities after accelerated or forced degradation procedures. As a result, impurity profiling is one of the most attractive, active and relevant fields of modern pharmaceutical analysis. This activity includes the identification, structural elucidation and quantitative determination of impurities and degradation products in bulk drugs and their pharmaceutical formulations. Nuclear magnetic resonance (NMR) spectroscopy has evolved into an irreplaceable approach for pharmaceutical quality assessment, currently playing a critical role in unequivocal structure identification as well as structural confirmation (qualitative detection), enabling the understanding of the underlying mechanisms of the formation of process and/or degradation impurities. NMR is able to provide qualitative information without the need of standards of the unknown compounds and multiple components can be quantified in a complex sample without previous separation. When coupled to separative techniques, the resulting hyphenated methodologies enhance the analytical power of this spectroscopy to previously unknown levels. As a result, and by enabling the implementation of rational decisions regarding the identity and level of impurities, NMR contributes to the goal of making better and safer medicines. Herein are discussed the applications of NMR spectroscopy and its hyphenated derivate techniques to the study of a wide range pharmaceutical impurities. Details on the advantages and disadvantages of the methodology and well as specific challenges with regards to the different analytical problems are also presented.

Obestatin does not modify weight and nutritional behaviour but is associated with metabolic syndrome in old women

OBJECTIVE

Ghrelin and obestatin have apparent opposite orexigenic and anorexigenic effects, although the latter has not been firmly demonstrated in humans. So far, little data have been reported in relation to its potential association with metabolic syndrome (MS). The objective was to study obestatin concentrations in relation to nutritional parameters and eating behaviours in old women.

DESIGN, PATIENTS AND MEASUREMENTS

Prospective study; a total of 110 women (age: 76.93 ± 6.32) from the Mataró Ageing Study were included. Individuals were characterized by anthropometric variables, lipids, glucose, blood pressure, MS components (Adult Treatment Panel III criteria), anorexia and nutritional status by Mini Nutritional Assessment Short Form (MNA-SF) and re-evaluated at 2-year follow-up. Obestatin was measured by IRMA.

RESULTS

58.2% of the subjects had MS; at 2-year follow-up 24.1% had a weight loss >5%, 7.2% >10%, and 26.4% changed their MNA-SF score to risk of malnutrition category. Anorexia was present in 38.4%. Obestatin levels were not related to either change of weight, MNA-SF or anorexia, but a positive correlation was found with the absolute difference between basal and 2-year waist circumference (WC) (r = 0.429; P < 0.001) and relative difference between basal and 2-year WC (r = 0.420; P < 0.001); both remained significant after adjusting for age and body mass index. When obestatin was divided into quartiles, a significant lineal trend was observed in relation to WC (P = 0.049), absolute and relative difference between basal and 2-year WC (both P < 0.001). Obestatin was associated with glucose impairment (69.0% in 4th quartile vs 47.5% in 1st to 3rd, P = 0.047; after adjustment, P = 0.098) and MS (77.8% in 4th vs 51.3% in 1st to 3rd, P = 0.017; after adjustment, P = 0.046, OR 2.90 (1.02-8.25) 4th vs 1st to 3rd).

CONCLUSIONS

Obestatin is elevated in aged women bearing MS but is otherwise not associated with other nutritional parameters, weight loss or anorexia.

Chloroquine-N-oxide, a major oxidative degradation product of chloroquine: identification, synthesis and characterization

Chloroquine (CQ) (1) which has endured as one of the most powerful antimalarial drugs was subjected to oxidative stress conditions and the degradation profile was studied. The oxidative stress condition of CQ furnished one major degradation product along with other minor degradation products. The unknown major degradation product was identified in HPLC and pure impurity was isolated using column chromatography. The structure of this major product was elucidated using UV, FT-IR, (1)H NMR, (13)C NMR, 2D NMR (HSQC) and mass spectral data. Based on the results obtained from the different spectroscopic studies, it was confirmed that the N-oxide was formed at the tertiary amine nitrogen instead of the pyridine nitrogen. Subsequently, an efficient and simple synthetic approach was developed for the synthesis of chloroquine-N-oxide using a work-up procedure that does not require chromatography techniques for further purification. It was observed that the spectral data of the isolated degradation product coincided appropriately with the synthesized product spectral data.

Obestatin receptor in energy homeostasis and obesity pathogenesis

Based on the bioinformatic prediction, Zhang and colleagues discovered obestatin, a new 23-amino acid hormone from rat stomach extract encoded by the ghrelin gene. Obestatin is present not only in the gastrointestinal tract, but also in the spleen, mammary gland, breast milk, and plasma. Obestatin appears to function as part of a complex gut-brain network whereby hormones and substances from the stomach, intestine and the brain about satiety or hunger. Given the current research regarding the effects of obestatin and its possible cognate receptor(s), this chapter provides the latest review of the physiological and pathological characteristics of this hormone and its possible receptor(s) in energy homeostasis and obesity.

Reversed-phase fused-core HPLC modeling of peptides

Different fused-core stationary phase chemistries (C18, Amide, Phenyl-hexyl and Peptide ES-C18) were used for the analysis of 21 structurally representative model peptides. In addition, the effects of the mobile phase composition (ACN or MeOH as organic modifier; formic acid or acetic acid, as acidifying component) on the column selectivity, peak shape and overall chromatographic performance were evaluated. The RP-amide column, combined with a formic acid–acetonitrile based gradient system, performed as best. A peptide reversed-phase retention model is proposed, consisting of 5 variables: log SumAA, log Sv, clog P, log nHDon and log nHAcc. Quantitative structure-retention relationship (QSRR) models were constructed for 16 different chromatographic systems. The accuracy of this peptide retention model was demonstrated by the comparison between predicted and experimentally obtained retention times, explaining on average 86% of the variability. Moreover, using an external set of 5 validation peptides, the predictive power of the model was also demonstrated. This peptide retention model includes the novel in-silico calculated amino acid descriptor, AA, which was calculated from log P, 3D-MoRSE, RDF and WHIM descriptors.

In vitro metabolic stability of iodinated obestatin peptides

Different iodinated mouse obestatin peptides have been characterized toward their in vitro stability in the main metabolic compartments plasma, liver and kidney. Using HPLC-UV for quantification, significant differences in the degradation kinetics of the iodinated peptides, arising from both enzymatic proteolysis and dehalogenation, were found when compared to the native, unmodified peptide. HPLC-MS/MS analysis demonstrated that the cleavage sites were dependent upon the biological matrix and the location of the amino acid residue incorporating the iodine atom(s). The degrading proteases were found to target peptide bonds further away from the iodine incorporation, while proteolytic cleavages of nearby peptide bonds were more limited. Diiodinated amino acid residue containing peptides were found to be more susceptible to deiodination than the mono-iodinated derivative. In plasma, the percentage of peptide degradation solely attributed to deiodinase activity after 20 min incubation reached up to 25% for 2,5-diiodo-H(19)-obestatin compared to 20% and only 3% for (3,5-diiodo-Y(16))- and (3-iodo-Y(16)) obestatin, respectively. Hence, our results demonstrate that the different iodinated peptides pose significantly different metabolization properties and thus, also different biological activities are expected for peptides upon iodination.

T cells recognizing a peptide contaminant undetectable by mass spectrometry

Synthetic peptides are widely used in immunological research as epitopes to stimulate their cognate T cells. These preparations are never completely pure, but trace contaminants are commonly revealed by mass spectrometry quality controls. In an effort to characterize novel major histocompatibility complex (MHC) Class I-restricted β-cell epitopes in non-obese diabetic (NOD) mice, we identified islet-infiltrating CD8+ T cells recognizing a contaminating peptide. The amount of this contaminant was so small to be undetectable by direct mass spectrometry. Only after concentration by liquid chromatography, we observed a mass peak corresponding to an immunodominant islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)_206-214 epitope described in the literature. Generation of CD8+ T-cell clones recognizing IGRP_206-214 using a novel method confirmed the identity of the contaminant, further underlining the immunodominance of IGRP_206-214. If left undetected, minute impurities in synthetic peptide preparations may thus give spurious results.

The influence of peptide impurity profiles on functional tissue-organ bath response: the 11-mer peptide INSL6[151-161] case

Bioactive peptides have great pharmaceutical potential as nutraceuticals, diagnostics, and therapeutic drugs in several clinical areas. Thus, the search for novel lead peptides with a biological function has attracted renewed interest. Crude peptide material (i.e., ~70% purity) of INSL6[151-161] (NH₂-FRSLFWGNHSQ-COOH) was found to trigger a contractile response in guinea pig ileum longitudinal smooth muscle preparations using tissue-organ baths. However, the purified peptide (i.e., ≥ 95% purity) had no effect on this model. Further investigation with crude materials from other suppliers, with purities ranging between 50% and 80%, indicated that the crude products gave a false-positive functional tissue-organ bath conclusion. These observations question the functionality conclusions when using crude-purity peptide materials; during the initial research or discovery phase, peptide quality is generally neglected, possibly leading to misinterpretation of biological results due to by-products from peptide synthesis and, thus, wrong fail/pass decisions. Therefore, we strongly recommend appropriate quality control testing before using any peptides for initial biomedical research or discovery purposes.

Biological effects of obestatin

Obestatin, a 23-amino-acid peptide, is derived from the preproghrelin precursor. Obestatin was identified in 2005 as a hormone regulating food intake and energy, and having opposite effects to those of ghrelin. However, as studies have progressed, many disputes on the physiological function of obestatin have emerged. The food intake suppressive effects of obestatin have not been replicated in many studies. Nonetheless, many biological roles of obestatin have been revealed, and obestatin is thought to be associated with a variety of biological functions such as feeding, drinking, incretion, memory, and sleep, and with neuropsychiatric manifestations. The biological effects of obestatin will be reviewed in this article.

Stability-indicating HPLC-DAD/UV-ESI/MS impurity profiling of the anti-malarial drug lumefantrine

BACKGROUND

Lumefantrine (benflumetol) is a fluorene derivative belonging to the aryl amino alcohol class of anti-malarial drugs and is commercially available in fixed combination products with β-artemether. Impurity characterization of such drugs, which are widely consumed in tropical countries for malaria control programmes, is of paramount importance. However, until now, no exhaustive impurity profile of lumefantrine has been established, encompassing process-related and degradation impurities in active pharmaceutical ingredients (APIs) and finished pharmaceutical products (FPPs).

METHODS

Using HPLC-DAD/UV-ESI/ion trap/MS, a comprehensive impurity profile was established based upon analysis of market samples as well as stress, accelerated and long-term stability results. In-silico toxicological predictions for these lumefantrine related impurities were made using Toxtree® and Derek®.

RESULTS

Several new impurities are identified, of which the desbenzylketo derivative (DBK) is proposed as a new specified degradant. DBK and the remaining unspecified lumefantrine related impurities are predicted, using Toxtree® and Derek®, to have a toxicity risk comparable to the toxicity risk of the API lumefantrine itself.

CONCLUSIONS

From unstressed, stressed and accelerated stability samples of lumefantrine API and FPPs, nine compounds were detected and characterized to be lumefantrine related impurities. One new lumefantrine related compound, DBK, was identified and characterized as a specified degradation impurity of lumefantrine in real market samples (FPPs). The in-silico toxicological investigation (Toxtree® and Derek®) indicated overall a toxicity risk for lumefantrine related impurities comparable to that of the API lumefantrine itself.

Ghrelin gene products and the regulation of food intake and gut motility

A breakthrough using "reverse pharmacology" identified and characterized acyl ghrelin from the stomach as the endogenous cognate ligand for the growth hormone (GH) secretagogue receptor (GHS-R) 1a. The unique post-translational modification of O-n-octanoylation at serine 3 is the first in peptide discovery history and is essential for GH-releasing ability. Des-acyl ghrelin, lacking O-n-octanoylation at serine 3, is also produced in the stomach and remains the major molecular form secreted into the circulation. The third ghrelin gene product, obestatin, a novel 23-amino acid peptide identified from rat stomach, was found by comparative genomic analysis. Three ghrelin gene products actively participate in modulating appetite, adipogenesis, gut motility, glucose metabolism, cell proliferation, immune, sleep, memory, anxiety, cognition, and stress. Knockdown or knockout of acyl ghrelin and/or GHS-R1a, and overexpression of des-acyl ghrelin show benefits in the therapy of obesity and metabolic syndrome. By contrast, agonism of acyl ghrelin and/or GHS-R1a could combat human anorexia-cachexia, including anorexia nervosa, chronic heart failure, chronic obstructive pulmonary disease, liver cirrhosis, chronic kidney disease, burn, and postsurgery recovery, as well as restore gut dysmotility, such as diabetic or neurogenic gastroparesis, and postoperative ileus. The ghrelin acyl-modifying enzyme, ghrelin O-Acyltransferase (GOAT), which attaches octanoate to serine-3 of ghrelin, has been identified and characterized also from the stomach. To date, ghrelin is the only protein to be octanylated, and inhibition of GOAT may have effects only on the stomach and is unlikely to affect the synthesis of other proteins. GOAT may provide a critical molecular target in developing novel therapeutics for obesity and type 2 diabetes.

Obestatin, obesity and diabetes

The high prevalence of obesity and diabetes will lead to higher rates of morbidity and mortality. It is well known that ghrelin plays a potential role in obesity and diabetes. Obestatin, a novel 23 amino acid amidated peptide encoded by the same gene that encodes ghrelin, was initially reported to have opposite actions to ghrelin in the regulation of food intake, emptying of the stomach and body weight. Recent work suggests that obestatin also regulate beta-cell survival and insulin secretion. The ghrelin-obestatin system is, therefore, a promising target for the developing of new drugs for the treatment of obesity and diabetes. This review summarizes the interrelationship between obestatin, obesity and diabetes.

Contamination of synthetic HuD protein spanning peptide pools with a CMV-encoded peptide

To detect HuD-specific T cells in patients with Hu-antibody associated paraneoplastic neurological syndromes (Hu-PNS), we used short-term stimulation assays with HuD protein spanning peptide pools (PSPP) with purities of at least 70% and found reproducible false-positive CD8+ T-cell responses in three of 127 individuals (two healthy controls and one Hu-PNS patient), which all shared HLA-A*2402 and HLA-B*1801. After testing the 15-mer peptides of the HuD antigen separately, we discovered that the same three 15-mers yielded the CD8+ T cell response in those three individuals. This highly unusual result could not be reproduced when using new batches of peptides with a higher level of purity (>82% and >95%). Therefore, we assumed this response was not directed against the HuD peptides and analyzed the HuD 15-mers by Fourier transform ion cyclotron resonance (FT-ICR) tandem mass spectrometry (MS/MS), which showed the presence of a cytomegalovirus (CMV)-encoded peptide (AIAEESDEEEAIVAY) as a contaminant. The three responding individuals all were CMV-seropositive and the contaminating peptide appeared to fit in the binding groove of HLA-B*18. Our data reveal that synthetic PSPP may contain immunogenic contaminations which may cause false positive results in T-cell stimulation assays.

Analytical, biopharmaceutical and regulatory evaluation of topical testosterone preparations

Testosterone-containing pharmaceutical products for topical use were obtained from the pharmacist or through the internet. The legal status of the different products obtained is discussed: some products through the internet were clearly a medicinal product according to the current definitions, while they are not registered as such. Assay and impurity profiles of each of the marketed samples were obtained using HPLC-UV and ESI-iontrap MS. The analytical results were evaluated relative to the reporting, identification and qualification thresholds as defined by the the International Conference on Harmonisation (ICH) and the European Pharmacopoeia (Ph. Eur.). Preparations with impurities above the qualification threshold were observed. Moreover, in vitro release profiles over an artificial membrane were obtained using a standardised cell in a paddle dissolution bath as well as in a static Franz diffusion cell, using phosphate buffered saline (PBS; pH 7.0) containing 5% bovine serum albumin (BSA) as dissolution or receptor fluid. This biopharmaceutical quality attribute differs significantly between the preparations tested. In conclusion, the equivalency of topical testosterone preparations is not assured, nor on their legal status, nor on their impurity profiling nor on their biopharmaceutical behaviour. This calls for an urgent trans-national product-class harmonisation approach.

In vitro metabolic stability of obestatin: kinetics and identification of cleavage products

The in vitro metabolic stability testing on synthetic obestatin peptides from two different species (human hOb and mouse mOb) using HPLC analysis is described. A reversed-phase C(18) column of 300A pore size was used, with a gradient system based on aqueous formic acid and acetonitrile. Electrospray ionization (ESI) ion trap mass spectrometry was used for identification of the chromatographic eluting peptide metabolic products, while UV (DAD) and fluorescence served quantitative purposes. Differences in the metabolic degradation kinetics of hOb and mOb were found in plasma, liver and kidney homogenate, with half-lives ranging between 12.6 and 138.0min. Proteolytic hydrolysis at the N-terminal Phe residue and cleavage at Pro(4)-Phe(5) were found to be two major metabolic pathways, accounting for more than 50% of the metabolic degradation. Several other labile peptide bonds were located. The influence of a standard protease inhibitor cocktail was investigated, as well as the metabolism of iodinated human obestatin in liver homogenate. Our results indicate that the major instability of obestatin peptides, as currently used in biomedical investigations, should be taken into account in the interpretation of the obtained results.