Comparison of various in vitro model systems of the metabolism of synthetic doping peptides: Proteolytic enzymes, human blood serum, liver and kidney microsomes and liver S9 fraction

Therapeutic peptides in the treatment of digestive inflammation: Current advances and future prospects

Digestive inflammation is a widespread global issue that significantly impacts quality of life. Recent advances have highlighted the unique potential of therapeutic peptides for treating this condition, owing to their specific bioactivity and high specificity. By specifically targeting key proteins involved in the pathological process and modulating biomolecular functions, therapeutic peptides offer a novel and promising approach to managing digestive inflammation. This review explores the development history, pharmacological characteristics, clinical applications, and regulatory mechanisms of therapeutic peptides in treating digestive inflammation. Additionally, the review addresses pharmacokinetics and quality control methods of therapeutic peptides, focusing on challenges such as low bioavailability, poor stability, and difficulties in delivery. The role of modern biotechnologies and nanotechnologies in overcoming these challenges is also examined. Finally, future directions for therapeutic peptides and their potential impact on clinical applications are discussed, with emphasis placed on their significant role in advancing medical and therapeutic practices.

Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro

BACKGROUND

TB-500 (Ac-LKKTETQ), derived from the active site of thymosin β4 (Tβ4), has various biological functions in its unacetylated form, LKKTETQ. These functions include actin binding, dermal wound healing, angiogenesis, and skin repair. The biological effects of TB-500, however, have not been documented. And the analysis of TB-500 and its metabolites have been neither simultaneously quantified nor structurally identified using synthesized authentic standards.

METHODS

This study was aimed to investigating simultaneous analytical methods of TB-500 and its metabolites in in-vitro and urine samples by using UHPLC-Q-Exactive orbitrap MS, and to comparing the biological activity of its metabolites with the parent TB-500. The metabolism of TB-500 was investigated in human serum, various in-vitro enzyme systems, and urine samples from rats treated with TB-500, and their biological activities measured by cytotoxicity and wound healing experiments were also evaluated in fibroblasts.

RESULTS

The simultaneous analytical method for TB-500 and its metabolites was developed and validated. The study found that Ac-LK was the primary metabolite with the highest concentration in rats at 0-6 h intervals. Also, the metabolite Ac-LKK was a long-term metabolite of TB-500 detected up to 72 hr. No cytotoxicity of the parent and its metabolites was found. Ac-LKKTE only showed a significant wound healing activity compared to the control.

CONCLUSION

The study provides a valuable tool for quantifying TB-500 and its metabolites, contributing to the understanding of metabolism and potential therapeutic applications. Our results also suggest that the previously reported wound-healing activity of TB-500 in literature may be due to its metabolite Ac-LKKTE rather than the parent form.

In-house standards derived from doping peptides: Enzymatic and serum stability and degradation profile of GHRP and GHRH-related peptides

Matrix effect and sample pretreatment significantly affect the percentage recovery of peptides in biological matrices, affecting the method robustness and accuracy. To counteract this effect, an internal standard (IS) is used; however, in most cases this is not available, which limits the analytical method. It is important to identify short peptides that can be used as ISs in the quantification of peptides in biological matrices. In this study, doping peptides GHRP-4, GHRP-5, GHRP-6, Sermorelin (1-11), Sermorelin (13-20) and Sermorelin (22-29) were synthesized using solid-phase peptide synthesis. Treatment with human blood, trypsin and chymotrypsin was used to determine the stability of the peptides. Products were evaluated using the high-performance liquid chromatography-diode array detector (HPLC-DAD) method. The analytical methodology and sample pretreatment were effective for the analysis of these molecules. A unique profile related to protein binding and enzymatic stability of each peptide was established. GHRP-4, GHRP-6 and Sermorelin (22-29) can be considered as in-house ISs as they were stable to enzyme and blood treatment and can be used for the quantification of peptides in biological samples. Peptides GHRP-6 and Sermorelin (22-29) were used to analyse a dimeric peptide (26 [F] LfcinB (20-30)2 ) in four different matrices to test these peptides as in-house IS.

Detection and quantification of the metabolite Ac-Tβ1-14 in in vitro experiments and urine of rats treated with Ac-Tβ4: A potential biomarker of Ac-Tβ4 for doping tests

Thymosin β4 (Tβ4) was reported to exert various beneficial bioactivities such as tissue repair, anti-inflammation, and reduced scar formation, and it is listed on the prohibited substances in sports by the World Anti-Doping Agency. However, no metabolism studies of Tβ4 were reported yet. Previously, our lab reported in in vitro experiment that a total of 13 metabolites were found by using multiple enzymes, and six metabolites (Ac-Tβ31-43 , Ac-Tβ17-43 , Ac-Tβ1-11 , Ac-Tβ1-14 , Ac-Tβ1-15 , and Ac-Tβ1-17 ) were confirmed by comparing with the synthetic standards. This study was aimed at identifying new metabolites of Tβ4 leucine aminopeptidase (LAP), human kidney microsomes (HKM), cultured huvec cells, and rats after administration of Tβ4 protein to develop biomarkers for detecting doping drugs in sports. A method for detecting and quantifying Ac-Tβ1-14 was developed and validated using Q-Exactive orbitrap mass spectrometry. The limit of detection (LOD) and limit of quantification (LOQ) of the Ac-Tβ1-14 were 0.19 and 0.58 ng/mL, respectively, and showed a good linearity (r2  = 0.9998). As a result, among the six metabolites above, Ac-Tβ1-14 , as a common metabolite, was found in LAP, HKM, huvec cells exposed to Tβ4, and the urine of rats intraperitoneally treated with 20-mg/kg Tβ4. And the metabolite Ac-Tβ1-14 was quantitatively determined by 48 h in rats, with the highest concentration occurring between 0 and 6 h. Ac-Tβ1-14 was not detected in non-treated control groups, including human blank urine. These results suggest that Ac-Tβ1-14 in urine is a potential biomarker for screening the parent Tβ4 in doping tests.

Metabolism Characterization and Chemical and Plasma Stability of Casearin B and Caseargrewiin F

Oral preparations of Casearia sylvestris (guacatonga) are used as antacid, analgesic, anti-inflammatory, and antiulcerogenic medicines. The clerodane diterpenes casearin B and caseargrewiin F are major active compounds in vitro and in vivo. The oral bioavailability and metabolism of casearin B and caseargrewiin F were not previously investigated. We aimed to assess the stability of casearin B and caseargrewiin F in physiological conditions and their metabolism in human liver microsomes. The compounds were identified by UHPLC-QTOF-MS/MS and quantified by validated LC-MS methods. The stability of casearin B and caseargrewiin F in physiological conditions was assessed in vitro. Both diterpenes showed a fast degradation (p < 0.05) in simulated gastric fluid. Their metabolism was not mediated by cytochrome P-450 enzymes, but the depletion was inhibited by the esterase inhibitor NaF. Both diterpenes and their dialdehydes showed a octanol/water partition coefficient in the range of 3.6 to 4.0, suggesting high permeability. Metabolism kinetic data were fitted to the Michaelis-Menten profile with KM values of 61.4 and 66.4 µM and Vmax values of 327 and 648 nmol/min/mg of protein for casearin B and caseargrewiin F, respectively. Metabolism parameters in human liver microsomes were extrapolated to predict human hepatic clearance, and suggest that caseargrewiin F and casearin B have a high hepatic extraction ratio. In conclusion, our data suggest that caseargrewiin F and casearin B present low oral bioavailability due to extensive gastric degradation and high hepatic extraction.

Synthetic Peptides in Doping Control: A Powerful Tool for an Analytical Challenge

Peptides are very diverse molecules that can participate in a wide variety of biological processes. In this way, peptides are attractive for doping, since these molecules can activate or trigger biological processes that can improve the sports performance of athletes. Peptide molecules are found in the official World Anti-Doping Agency lists, mainly in sections S2, S4, and S5. In most cases, these molecules have a very short half-life in the body and/or are identical to natural molecules in the body, making it difficult to analyze them as performance-enhancing drugs. This article reviews the role of peptides in doping, with special emphasis on the peptides used as reference materials, the pretreatment of samples in biological matrices, the instrumentation, and the validation of analytical methodologies for the analysis of peptides used in doping. The growing need to characterize and quantify these molecules, especially in complex biological matrices, has generated the need to search for robust strategies that allow for obtaining sensitive and conclusive results. In this sense, strategies such as solid phase peptide synthesis (SPPS), seeking to obtain specific peptides, metabolites, or isotopically labeled analogs, is a key tool for adequate quantification of different peptide molecules in biological matrices. This, together with the use of optimal methodologies for sample pretreatment (e.g., SPE or protein precipitation), and for subsequent analysis by high-resolution techniques (mainly hyphenated LC-HRMS techniques), have become the preferred instrumentation to meet the analytical challenge involved in the analysis of peptides in complex matrices.

Genotoxicity of 12 Mycotoxins by the SOS/umu Test: Comparison of Liver and Kidney S9 Fraction

Liver S9 fraction is usually employed in mutagenicity/genotoxicity in vitro assays, but some genotoxic compounds may need another type of bioactivation. In the present work, an alternative S9 fraction from the kidneys was used for the genotoxicity assessment of 12 mycotoxins with the SOS/umu test. The results were compared with liver S9 fraction, and 2-4 independent experiments were performed with each mycotoxin. The expected results were obtained with positive controls (4-nitroquinoline-N-oxide and 2-aminoanthracene) without metabolic activation or with liver S9, but a potent dose-dependent effect with 4-nitroquinoline-N-oxide and no activity of 2-aminoanthracene with kidney S9 were noticed. Aflatoxin B1 was genotoxic with metabolic activation, the effect being greater with liver S9. Sterigmatocystin was clearly genotoxic with liver S9 but equivocal with kidney S9. Ochratoxin A, zearalenone and fumonisin B1 were negative in all conditions. Trichothecenes were negative, except for nivalenol, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, T-2 and HT-2 toxins, which showed equivocal results with kidney S9 because a clear dose-response effect was not observed. Most of the mycotoxins have been assessed with kidney S9 and the SOS/umu test for the first time here. The results with the positive controls and the mycotoxins confirm that the organ used for the S9 fraction preparation has an influence on the genotoxic activity of some compounds.

Investigations into the In Vitro Metabolism of hGH and IGF-I Employing Stable-Isotope-Labelled Drugs and Monitoring Diagnostic Immonium Ions by High-Resolution/High-Accuracy Mass Spectrometry

Studying the metabolism of prohibited substances is an essential element in anti-doping research in order to facilitate and improve detectability. Whilst pharmacokinetic studies on healthy volunteers are valuable, they are often difficult, not least due to safety reasons and ethical constraints, especially concerning peptidic substances, which must be administered parenterally. Hence, there is a growing need for suitable in vitro models and sophisticated analytical strategies to investigate the metabolism of protein- and peptide-derived drugs. These include human growth hormone (hGH) and its main mediator insulin-like growth factor-I (IGF-I), both prohibited in professional sports for their anabolic and lipolytic effects, while challenging in their detection, as they occur naturally in the human body.Within this study, the in vitro metabolism of hGH and IGF-I was investigated using a stable-isotope-labelled reporter ion screening strategy (IRIS). A combination of liquid chromatography, high-resolution mass spectrometry, and characteristic immonium ions generated by internal dissociation of the stable-isotope-labelled peptidic metabolites enabled the detection of specific fragments. Several degradation products for hGH and IGF-I were identified within this study. These metabolites, potentially even indicative for subcutaneous administration of the drugs, could serve as promising targets for the detection of hGH and IGF-I misuse in future anti-doping applications.

Recent advances in identifying and utilizing metabolites of selected doping agents in human sports drug testing

Probing for evidence of the administration of prohibited therapeutics, drugs and/or drug candidates as well as the use of methods of doping in doping control samples is a central assignment of anti-doping laboratories. In order to accomplish the desired analytical sensitivity, retrospectivity, and comprehensiveness, a considerable portion of anti-doping research has been invested into studying metabolic biotransformation and elimination profiles of doping agents. As these doping agents include lower molecular mass drugs such as e.g. stimulants and anabolic androgenic steroids, some of which further necessitate the differentiation of their natural/endogenous or xenobiotic origin, but also higher molecular mass substances such as e.g. insulins, growth hormone, or siRNA/anti-sense oligonucleotides, a variety of different strategies towards the identification of employable and informative metabolites have been developed. In this review, approaches supporting the identification, characterization, and implementation of metabolites exemplified by means of selected doping agents into routine doping controls are presented, and challenges as well as solutions reported and published between 2010 and 2020 are discussed.

Modulation of co-stimulatory signal from CD2-CD58 proteins by a grafted peptide

Peptides were designed to inhibit the protein-protein interaction of CD2 and CD58 to modulate the immune response. This work involved the design and synthesis of eight different peptides by replacing each amino acid residue in peptide 6 with alanine as well as grafting the peptide to the sunflower trypsin-inhibitor framework. From the alanine scanning studies, mutation at position 2 of the peptide was shown to result in increased potency to inhibit cell adhesion interactions. The most potent peptide from the alanine scanning was further studied for its detailed three-dimensional structure and binding to CD58 protein using surface plasmon resonance and flow cytometry. This peptide was used to graft to the sunflower trypsin inhibitor to improve the stability of the peptide. The grafted peptide, SFTI-a1, was further studied for its potency as well as its thermal, chemical, and enzymatic stability. The grafted peptide exhibited improved activity compared to our previously grafted peptide and was stable against thermal and enzymatic degradation.

Detection of LongR3 -IGF-I, Des(1-3)-IGF-I, and R3 -IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposes

Insulin-like growth factor-I (IGF-I) and its analogs LongR³ -IGF-I, Des(1-3)-IGF-I, and R³ -IGF-I are prohibited substances in sport. Although they were never approved for use in humans, they are readily available as black market products for bodybuilding and can be used to enhance physical performance. This study's aims were to validate a fast and sensitive detection method for IGF-I analogs and to evaluate their detectability after intramuscular administration in rats. The sample preparation consisted of an immunopurification on MSIA™ microcolumns using a polyclonal anti-human-IGF-I antibody. The target substances were then directly analyzed by nano-liquid chromatography coupled with high-resolution mass spectrometry. Abundant signs of lower quality, oxidized peptide forms were found in black market products, justifying the need to monitor at least both the native and mono-oxidized forms. The analytical performance of this method (linearity, carry over, detection limits, precision, specificity, recovery, and matrix effect) was studied by spiking the analogs into human serum. Following a single intramuscular administration (100 μg/kg) in rats, detection was evaluated up to 36 h after injection. While unchanged Des(1-3)-IGF-I and R³ -IGF-I were detected until 24 h after administration, LongR³ -IGF-I disappeared rapidly after 4 h. Des(1)-LongR³ -IGF-I, a new N-terminal Long-R³ -IGF-I degradation product, was detected in addition to Des(1-10)-LongR³ -IGF-I and Des(1-11)-LongR^3- IGF-I: the latter was detected up to 16 h. The same products were found after in vitro incubation of the analogs in human whole blood, suggesting that observations in rats may be extrapolated to humans and that the validated method may be applicable to antidoping testing.

Comprehensive insights into the formation of metabolites of the ghrelin mimetics capromorelin, macimorelin and tabimorelin as potential markers for doping control purposes

Analytical methods to determine the potential misuse of the ghrelin mimetics capromorelin (CP-424,391), macimorelin (macrilen, EP-01572) and tabimorelin (NN703) in sports were developed. Therefore, different extraction strategies, i.e. solid-phase extraction, protein precipitation, as well as a "dilute-and-inject" approach, from urine and EDTA-plasma were assessed and comprehensive in vitro/in vivo experiments were conducted, enabling the identification of reliable target analytes by means of high resolution mass spectrometry. The drugs' biotransformation led to the preliminary identification of 51 metabolites of capromorelin, 12 metabolites of macimorelin and 13 metabolites of tabimorelin. Seven major metabolites detected in rat urine samples collected post-administration of 0.5-1.0 mg of a single oral dose underwent in-depth characterization, facilitating their implementation into future confirmatory test methods. In particular, two macimorelin metabolites exhibiting considerable abundances in post-administration rat urine samples were detected, which might contribute to an improved sensitivity, specificity, and detection window in case of human sports drug testing programs. Further, the intact drugs were implemented into World Anti-Doping Agency-compliant initial testing (limits of detection 0.02-0.60 ng/ml) and confirmation procedures (limits of identification 0.18-0.89 ng/ml) for human urine and blood matrices. The obtained results allow extension of the test spectrum of doping agents in multitarget screening assays for growth hormone-releasing factors from human urine.

Hepatic in vitro metabolism of peptides; Comparison of human liver S9, hepatocytes and Upcyte hepatocytes with cyclosporine A, leuprorelin, desmopressin and cetrorelix as model compounds

The number of approved peptide therapeutics has increased significantly in recent years. Peptide therapeutics have many advances over small molecule drugs, such as higher affinity to target and lower toxicity profiles. Although peptide-like drugs are mainly metabolized/catabolized in the body for smaller peptides and amino acids, metabolite identification still has an essential part of in their development, especially if their structure contains modified amino acids, and also to identify the metabolic soft spots enabling modification to more stable sequence. The use of human derived in vitro systems is an important tool when investigating metabolism of peptide drugs, and comparison of results by various hepatic systems was investigated here. Peptides were incubated in several different in vitro human liver-derived subcellular and cellular incubation systems, i.e. liver S9 fraction, suspended cryo-preserved human primary hepatocytes and plated Upcyte hepatocytes. Samples were collected at different time points and analysed by UPLC/HR-MS-method developed for the purpose. Both substrate disappearance and metabolite formation were monitored, and the systems were compared. S9 fraction formed the highest number of metabolites for leuprorelin and cetrorelix, while for desmopressin and cyclosporin, primary hepatocytes and liver S9 produced similar metabolite profiles. Interestingly, not only cyclosporin, but also leuprorelin and cetrorelix showed metabolites whose formation was CYP (NADPH) dependent in liver S9. For leuprorelin and cetrorelix, the metabolites that showed NADPH dependency with liver S9, were not detected with hepatocytes, even though for leuprorelin these reactions played a major role in liver S9. The hydrolytic metabolic reactions were very similar between liver S9 and hepatocytes, i.e. the metabolite profiles in hepatocytes matched better with liver S9 profiles without NADPH, which may be caused by cell uptake rate limitation with hepatocytes, or then hydrolytic processes are more stressed in peptide metabolism with hepatocytes, in comparison to CYP-mediated processes.

Doping control analysis of small peptides: A decade of progress

Small peptides are handled in the field of sports drug testing analysis as a separate group doping substances. It is a diverse group, which includes but is not limited to growth hormone releasing-factors and gonadotropin-releasing hormone analogues. Significant progress has been achieved during the past decade in the doping control analysis of these peptides. In this article, achievements in the application of liquid chromatography-mass spectrometry-based methodologies are reviewed. To meet the augmenting demands for analyzing an increasing number of samples for the presence of an increasing number of prohibited small peptides, testing methods have been drastically simplified, whilst their performance level remained constant. High-resolution mass spectrometers have been installed in routine laboratories and became the preferred detection technique. The discovery and implementation of metabolites/catabolites in testing methods led to extended detection windows of some peptides, thus, contributed to more efficient testing in the anti-doping community.

In vivo studies of a peptidomimetic that targets EGFR dimerization in NSCLC

Studies related to lung cancer have shown a link between human epidermal growth factor receptor-2 (HER2) expression and poor prognosis in patients with non-small cell lung cancer (NSCLC). HER2 overexpression has been observed in 3-38% of NSCLC, while strong HER2 protein overexpression is found in 2.5% of NSCLC. However, HER2 dimerization is important in lung cancer, including EGFR mutated NSCLC. Since HER2 dimerization leads to cell proliferation, targeting the dimerization of HER2 will have a significant impact on cancer therapies. A peptidomimetic has been designed that can be used as a therapeutic agent for a subset of NSCLC patients overexpressing HER2 or possessing HER2 as well as EGFR mutation. A cyclic peptidomimetic (18) has been designed to inhibit protein-protein interactions of HER2 with its dimerization partners EGFR and HER3. Compound 18 exhibited antiproliferative activity in HER2-positive NSCLC cell lines at nanomolar concentrations. Western blot analysis showed that 18 inhibited phosphorylation of HER2 and Akt in vitro and in vivo. Stability studies of 18 at various temperature and pH (pH 1 and pH 7.6), and in the presence of liver microsomes indicated that 18 was stable against thermal and chemical degradation. Pharmacokinetic parameters were evaluated in nude mice by administrating single doses of 4 mg/kg and 6 mg/kg of 18 via IV. The anticancer activity of 18 was evaluated using an experimental metastasis lung cancer model in mice. Compound 18 suppressed the tumor growth in mice when compared to control. A proximity ligation assay further proved that 18 inhibits HER2:HER3 and EGFR: HER2 dimerization. Overall, these results suggest that 18 can be a potential treatment for HER2-dimerization related NSCLC.

Metabolite Identification of Therapeutic Peptides and Proteins by Top-down Differential Mass Spectrometry and Metabolite Database Matching

As metabolism impacts the efficacy and safety of therapeutic peptides and proteins (TPPs), understanding of the metabolic fate of TPPs is critical for their preclinical and clinical development. Despite the continued increase of new TPPs entering clinical trials, the metabolite identification (MetID) of these emerging modalities remains challenging. In the present study, we report an analytical workflow for MetID of TPPs. Using insulin detemir as an example, we demonstrated that top-down differential mass spectrometry (dMS) was able to distinguish and discover metabolites from complex biological matrices. For structural interpretation, we developed an algorithm to generate a complete and nonredundant theoretical metabolite database for a TPP of any topology (e.g., branched, multicyclic, etc.). Candidate structures of a metabolite were obtained by matching the monoisotopic mass of a dMS feature to the theoretical metabolite database. Finally, the MS/MS sequence tags enabled unambiguous characterization of metabolite structures when isobaric/isomeric candidates were present. This platform is widely applicable to TPPs with complex structures and will ultimately guide the structural optimization of TPPs in pharmaceutical development.

Fully automated dried blood spot sample preparation enables the detection of lower molecular mass peptide and non-peptide doping agents by means of LC-HRMS

The added value of dried blood spot (DBS) samples complementing the information obtained from commonly routine doping control matrices is continuously increasing in sports drug testing. In this project, a robotic-assisted non-destructive hematocrit measurement from dried blood spots by near-infrared spectroscopy followed by a fully automated sample preparation including strong cation exchange solid-phase extraction and evaporation enabled the detection of 46 lower molecular mass (< 2 kDa) peptide and non-peptide drugs and drug candidates by means of LC-HRMS. The target analytes included, amongst others, agonists of the gonadotropin-releasing hormone receptor, the ghrelin receptor, the human growth hormone receptor, and the antidiuretic hormone receptor. Furthermore, several glycine derivatives of growth hormone–releasing peptides (GHRPs), arguably designed to undermine current anti-doping testing approaches, were implemented to the presented detection method. The initial testing assay was validated according to the World Anti-Doping Agency guidelines with estimated LODs between 0.5 and 20 ng/mL. As a proof of concept, authentic post-administration specimens containing GHRP-2 and GHRP-6 were successfully analyzed. Furthermore, DBS obtained from a sampling device operating with microneedles for blood collection from the upper arm were analyzed and the matrix was cross-validated for selected parameters. The introduction of the hematocrit measurement method can be of great value for doping analysis as it allows for quantitative DBS applications by managing the well-recognized “hematocrit effect.”

A comprehensive review of bioactive peptides obtained from animal byproducts and their applications

Livestock generates high quantities of residues, which has become a major socioeconomic issue for the meat industry. This review focuses on the identification of bioactive peptides (BPs) in animal byproducts and meat wastes. Firstly, the main bioactivities that peptides can have will be described and the methods for their evaluation will be discussed. Secondly, the various origins of these BPs will be studied. Then, the techniques and tools for the generation of BPs will be detailed in order to discuss, in the final part, how peptides could be used and assimilated. BPs possess diverse biological activities and can be strategic candidates for substituting synthetic molecules. In silico potentiality studies are a helpful tool to understand and predict BPs released from proteins and their potential activities. However, in vitro validation is often required. Although BP use is compelled by strict regulations in relation to the field of application, they are also limited by their low bioavailability and bioaccessibility. Therefore, it is important to test peptide stability during gastrointestinal digestion. Protective strategies have been discussed since their use could improve the stability and effectiveness of BPs.

GC-MS and LC-MS/MS pilot studies on the guanidine (NG)-dimethylation in native, asymmetrically and symmetrically NG-dimethylated arginine-vasopressin peptides and proteins in human red blood cells

Protein-arginine methyltransferases catalyze the methylation of the guanidine (N^G) group of proteinic L-arginine (Arg) to produce monomethyl and dimethylarginine proteins. Their proteolysis releases the free amino acids monomethylarginine (MMA), symmetric dimethylarginine (SDMA) and asymmetric dimethylarginine (ADMA), respectively. MMA, SDMA and ADMA are inhibitors of the nitric oxide synthase (NOS) activity. High circulating and low urinary concentrations of ADMA and SDMA are considered risk factors in the cardiovascular and renal systems, mainly due to their inhibitory action on NOS activity. Identity, biological activity and concentration of N^G-methylated proteins are largely unknown. The present study addressed these issues by using GC-MS and LC-MS/MS approaches. GC-MS was used to quantify free ADMA released by classical HCl-catalyzed hydrolysis of three synthetic Arg-vasopressin (V) peptides and of unknown endogenous N^G-dimethylated proteins. The cyclic (c) disulfide forms of Arg-vasopressin analogs, i.e., Arg-vasopressin (cV-Arg-Gly-NH₂), asymmetrically N^G-dimethylated vasopressin (cV-ADMA-Gly-NH₂) and symmetrically N^G-dimethylated vasopressin (cV-SDMA-Gly-NH₂) were used as model peptides in quantitative GC-MS analyses of ADMA, SDMA and other expected amino acids from the hydrolyzed Arg-vasopressin analogs. cV-ADMA-Gly-NH₂ and cV-SDMA-Gly-NH₂ were discriminated from cV-Arg-Gly-NH₂ by LC-MS and LC-MS/MS, yet they were indistinguishable from each other. The same applies to the respective open (o) reduced and di-S-acetamide forms of oV-ADMA-Gly-NH₂, oV-SDMA-Gly-NH₂ and oV-Arg-Gly-NH₂. Our LC-MS and LC-MS/MS studies suggest that the Arg-vasopressin analogs form [(M-H)]⁺ and [(M-H)+H]⁺ in the positive ESI mode and undergo in part conversion of their terminal Gly-NH₂ (NH₂, 16 Da) group to Gly-OH (OH, 17 Da). The product ion mass spectra of the di-S-acetamide forms are complex and contain several intense mass fragments differing by 1 Da. cV-ADMA-Gly-NH₂ and cV-SDMA-Gly-NH₂ induced platelet aggregation in platelet-rich human plasma with moderately different initial velocity and maximal aggregation rates compared to cV-Arg-Gly-NH₂. Previous studies showed that human red blood cells are rich in large (>50 kDa) ADMA-containing proteins of unknown identity. Our LC-MS/MS proteomic study identified several membrane and cytosolic erythrocytic N^G-dimethylated proteins, including spectrin-α (280 kDa), spectrin-β (247 kDa) and protein 4.1 (80 kDa). Being responsible for the stability of the erythrocyte membrane, the newly identified main targets for N^G-dimethylation in human erythrocytes should be given a closer look in erythrocytic diseases like hereditary spherocytosis.

The In Vitro Biotransformation of the Fusion Protein Tetranectin-Apolipoprotein A1

As more and more protein biotherapeutics enter the drug discovery pipelines, there is an increasing interest in tools for mechanistic drug metabolism investigations of biologics in order to identify and prioritize the most promising candidates. Understanding or even predicting the in vivo clearance of biologics and to support translational pharmacokinetic modeling activities is essential, however there is a lack of effective and validated in vitro cellular tools. Although different mechanisms have to be adressed in the context of biologics disposition, the scope is not comparable to the nowadays widely established tools for early characterization of small molecule disposition. Here, we describe a biotransformation study of the fusion protein tetranectin apolipoprotein A1 by cellular systems. The in vivo biotransformation of tetranectin apolipoprotein A1 has been described previously, and the same major biotransformation product could also be detected in vitro, by a targeted and highly sensitive detection method based on chymotrypsin digest. In addition, the protease responsible for the formation of this biotransformation product could be elucidated to be DPP4. To our knowledge, this is one of the first reports of an in vitro biotransformation study by cells of a therapeutic protein.

Effects of recombinant human growth hormone on protein malnutrition and IGF-1 and IL-2 gene expression levels in chronic nephrotic syndrome

The aim of the study was to investigate the effects of recombinant human growth hormone on protein malnutrition and insulin-like growth factor-1 (IGF-1) and interleukin-2 (IL-2) gene expressions in chronic nephrotic syndrome. Eighty patients with chronic nephrotic syndrome were admitted to our hospital. The patients were included in the study period from January 2015 to December 2016 and were divided into two groups (40 cases in each group) according to the random number method. All the patients enrolled received symptomatic and supportive treatment. The observation group was injected subcutaneously with recombinant human growth hormone, while the control group was treated with Shenyankangfu tablets. The recovery time of the clinical symptoms, change in serum protein, caloric intake and protein metabolism after intervention were compared between the two groups. Changes in serum cystatin C, IGF-1 and IL-2 before intervention, and at 1 week, 1 month and 3 months after intervention were detected, and the adverse reactions in the two groups were observed during the treatment. After intervention, the improvement time of proteinuria, hypoproteinemia, edema and hyperlipidemia in the observation group was significantly shorter than that in the control group (P<0.05). The expression of transferrin, pre-albumin, albumin and total protein in the observation group was significantly superior increased compared to those in the observation group prior to intervention and the control group after intervention (P<0.05). In addition the caloric intake, protein intake and urea nitrogen survival rate in the observation group were significantly superior to those in the observation group prior to intervention and the control group after intervention (P<0.05). At 1 week, 1 month and 3 months after intervention, the levels of serum cystatin C, IGF-1 and IL-2 in the observation group were markedly obviously lower than those in the control group during the same period (P<0.05). The total proportion of allergy, systemic pruritus, nausea and vomiting, abdominal distension and abdominal pain in the observation group was obviously lower than that in the control group (P<0.05). Compared with the traditional Chinese medicine Shenyankangfu tablets applied in the control group, the recombinant human growth hormone used for patients with chronic nephrotic syndrome can improve the clinical symptoms more quickly, regulate the protein metabolism and reduce the inflammatory response in the body, which also has fewer adverse reactions and higher safety.