NIST Interlaboratory Study on Glycosylation Analysis of Monoclonal Antibodies: Comparison of Results from Diverse Analytical Methods

Glycosylation is a topic of intense current interest in the development of biopharmaceuticals because it is related to drug safety and efficacy. This work describes results of an interlaboratory study on the glycosylation of the Primary Sample (PS) of NISTmAb, a monoclonal antibody reference material. Seventy-six laboratories from industry, university, research, government, and hospital sectors in Europe, North America, Asia, and Australia submitted a total of 103 reports on glycan distributions. The principal objective of this study was to report and compare results for the full range of analytical methods presently used in the glycosylation analysis of mAbs. Therefore, participation was unrestricted, with laboratories choosing their own measurement techniques. Protein glycosylation was determined in various ways, including at the level of intact mAb, protein fragments, glycopeptides, or released glycans, using a wide variety of methods for derivatization, separation, identification, and quantification. Consequently, the diversity of results was enormous, with the number of glycan compositions identified by each laboratory ranging from 4 to 48. In total, one hundred sixteen glycan compositions were reported, of which 57 compositions could be assigned consensus abundance values. These consensus medians provide community-derived values for NISTmAb PS. Agreement with the consensus medians did not depend on the specific method or laboratory type. The study provides a view of the current state-of-the-art for biologic glycosylation measurement and suggests a clear need for harmonization of glycosylation analysis methods.

A simple method to systematically study oxidatively modified proteins in biological samples and its applications

Increased oxidative stress with elevated levels of reactive oxygen/nitrogen species (ROS/RNS) plays an important role in the pathophysiology of many disease states. Increased ROS/RNS can modulate the cellular macromolecules of DNA, lipids, and proteins, negatively affecting their normal functions. Numerous reports have described the properties and implications of oxidized DNA and lipids. However, oxidative modifications of proteins were not fully studied partially due to the requirement for specific reagents, the lack of methods to detect, purify, and identify oxidatively modified proteins, and the relatively late development of highly sensitive analytical instruments. This chapter describes the detailed procedure for systematically identifying oxidative-modified proteins in biological samples. Applications and other suggestions to this method are also described to understand the functional roles of oxidatively modified proteins in promoting endoplasmic reticulum (ER) stress and mitochondrial dysfunction, which ultimately contribute to organ damage.

Validation of a HeLa Mx2/Luc reporter cell line for the quantification of human type I interferons

Although antiviral assays have been the most widely available biological assays for interferons (IFNs), they are less sensitive and provide considerable interassay variation. In this study, we demonstrate a new reporter cell line, which is based on HeLa cells transfected with a plasmid containing a human Mx2 promoter driving a luciferase (Luc) cDNA. To characterize the specific gene expression profiles induced by interferon alpha, we analyzed the microarray results of interferon response gene expression induced by IFN-alpha2a or IFN-alpha2b treatment with HeLa cells. We found that the Mx2 gene increased the most by treatment with both IFN-alpha2a and IFN-alpha2b. Based on this result, we designed a reporter cell line, HeLa-Mx2, suitable for determination of IFN-alpha. HeLa cells were stably transfected with the luciferase gene under the control of Mx2 promoter. The expression of luciferase can be easily measured for luminescence using a 96-well luminometer and has been correlated with the concentration of added IFN and cell density. In the validation results, our reporter cell line had specificity for type I IFN, but the significant effects of a number of other cytokines such as tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-2, IL-5, IL-6 and GM-CSF, or type II interferon (IFN-gamma) were not observed. Moreover, the robustness of our cell line is demonstrated by the lack of an effect of the HeLa-Mx2 cell culture's age on the performance of the reporter gene assay. The reporter gene assay demonstrated reproducible dose-response curves for IFN-alpha2a in the range of 1-10,000 IU/ml. The 95% confidential limit and total coefficient of variation estimates ranged between 96 and 116 and 10.51% in the reducible range mentioned above, respectively. In conclusion, we established a stable IFN-responsible HeLa-Mx2 cell line, which has advantages with regard to simplicity, selectivity, and reliability over conventional cytopathic effect reduction assays used to quantify IFN-alpha activity.

Ascorbate attenuates trimethyltin-induced oxidative burden and neuronal degeneration in the rat hippocampus by maintaining glutathione homeostasis

The specific role of endogenous glutathione in response to neuronal degeneration induced by trimethyltin (TMT) in the hippocampus was examined in rats. A single injection of TMT (8 mg/kg, i.p.) produced a rapid increase in the formation of hydroxyl radical and in the levels of malondialdehyde (MDA) and protein carbonyl. TMT-induced seizure activity significantly increased after this initial oxidative stress, and remained elevated for up to 2 weeks post-TMT. Although a significant loss of hippocampal Cornus Ammonis CA1, CA3 and CA4 neurons was observed at 3 weeks post-TMT, the elevation in the level of hydroxyl radicals, MDA, and protein carbonyl had returned to near-control levels at that time. In contrast, the ratio of reduced to oxidized glutathione remained significantly decreased at 3 weeks post-TMT, and the glutathione-like immunoreactivity of the pyramidal neurons was decreased. However glutathione-positive glia-like cells proliferated mainly in the CA1, CA3, and CA4 sectors and were intensely immunoreactive. Double labeling demonstrated the co-localization of glutathione-immunoreactive glia-like cells and reactive astrocytes, as indicated by immunostaining for glial fibrillary acidic protein. This suggests that astroglial cells were mobilized to synthesize glutathione in response to the TMT insult. The TMT-induced changes in glutathione-like immunoreactivity appear to be concurrent with changes in the expression levels of glutathione peroxidase and glutathione reductase. Ascorbate treatment significantly attenuated TMT-induced seizures, as well as the initial oxidative stress, impaired glutathione homeostasis, and neuronal degeneration in a dose-dependent manner. These results suggest that ascorbate is an effective neuroprotectant against TMT. The initial oxidative burden induced by TMT may be a causal factor in the generation of seizures, prolonged disturbance of endogenous glutathione homeostasis, and consequent neuronal degeneration.

Identification of oxidized mitochondrial proteins in alcohol-exposed human hepatoma cells and mouse liver

Heavy alcohol consumption can damage various cells and organs partly through production of reactive oxygen species (ROS) and mitochondrial dysfunction. Treatment with antioxidants can significantly reduce the degree of damage. Despite well established roles of ROS in alcohol-induced cell injury, the proteins that are selectively oxidized by ROS are poorly characterized. We hypothesized that certain cysteinyl residues of target proteins are oxidized by ROS upon alcohol exposure, and these modified proteins may play roles in mitochondrial dysfunction. A targeted proteomics approach utilizing biotin-N-maleimide (biotin-NM) as a specific probe to label oxidized cysteinyl residues was employed to investigate which mitochondrial proteins are modified during and after alcohol exposure. Human hepatoma HepG2 cells with transduced CYP2E1 (E47 cells) were used as a model to generate ROS through CYP2E1-mediated ethanol metabolism. Following exposure to 100 mM ethanol for 4 and 8 h, the biotin-NM-labeled oxidized proteins were purified with agarose coupled to either streptavidin or monoclonal antibody against biotin. The purified proteins were resolved by two-dimensional gel electrophoresis and protein spots that displayed differential abundances were excised from the gel, in-gel digested with trypsin and analyzed for identity utilizing either matrix-assisted laser desorption-time of flight mass spectrometry or microcapillary reversed-phase liquid chromatography-tandem mass spectrometry. The results demonstrate that heat shock protein 60, protein disulfide isomerase, mitochondrial aldehyde dehydrogenases, prohibitin, and other proteins were oxidized after alcohol exposure. The identity of some of the proteins purified with streptavidin-agarose was also confirmed by immunoblot analyses using the specific antibody to each target protein. This method was also used to identify oxidized mitochondrial proteins in the alcohol-fed mouse liver. These results suggest that exposure to ethanol causes oxidation of various mitochondrial proteins that may negatively affect their function and contribute to alcohol-induced mitochondrial dysfunction and cellular injury.

Cloning and sequencing of a 2,5-dichlorohydroquinone reductive dehalogenase gene whose product is involved in degradation of gamma-hexachlorocyclohexane by Sphingomonas paucimobilis

Sphingomonas (formerly Pseudomonas) paucimobilis UT26 utilizes gamma-hexachlorocyclohexane (gamma-HCH), a halogenated organic insecticide, as a sole carbon and energy source. In a previous study, we showed that gamma-HCH is degraded to 2,5-dichlorohydroquinone (2,5-DCHQ) (Y. Nagata, R. Ohtomo, K. Miyauchi, M. Fukuda, K. Yano, and M. Takagi, J. Bacteriol. 176:3117-3125, 1994). In the present study, we cloned and characterized a gene, designated linD, directly involved in the degradation of 2,5-DCHQ. The linD gene encodes a peptide of 343 amino acids and has a low level of similarity to proteins which belong to the glutathione S-transferase family. When LinD was overproduced in Escherichia coli, a 40-kDa protein was found after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Northern blot analysis revealed that expression of the linD gene was induced by 2,5-DCHQ in S. paucimobilis UT26. Thin-layer chromatography and gas chromatography-mass spectrometry analyses with the LinD-overexpressing E. coli cells revealed that LinD converts 2,5-DCHQ rapidly to chlorohydroquinone (CHQ) and also converts CHQ slowly to hydroquinone. LinD activity in crude cell extracts was increased 3.7-fold by the addition of glutathione. All three of the Tn5-induced mutants of UT26, which lack 2,5-DCHQ dehalogenase activity, had rearrangements or a deletion in the linD region. These results indicate that LinD is a glutathione-dependent reductive dehalogenase involved in the degradation of gamma-HCH by S. paucimobilis UT26.

The stress exercise test and oxygen uptake in normal Korean men

In order to observe physiologic responses to exercise and measure the normal value of maximal oxygen uptake, an exercise stress test, using a bicycle ergometer, was carried out on 82 normal males, 20 to 60 years of age. The exercise test consisted of 1 minute of unloaded cycling with an increment of 25 watts each minute to the point of exhaustion. Oxygen uptake, anaerobic threshold(AT), minute ventilation, and CO₂ output were measured with an automatic gas analyzer and a pneumotachograph during the exercise. The results are summarized as follows: 1. The maximal oxygen uptake in the 20–29 year-old group of subjects was 39.6ml/min/kg, and it decreased with advancing age. 2. The anaerobic threshold was 1.22–1.5 L/min in all age groups. No significant differences by age were observed. The mean ratio of the anaerobic threshold to the maximal oxygen uptake was 57%. 3. The minute ventilation at maximal exercise was 65% of the maximal voluntary ventilation. This means that the subject cannot perform exercise at all, because of shortness of breath, that some potentially useful ventilation is left.

A large pedunculated left ventricular thrombus with recurrent systemic thromboembolism in a young man

We present the case of a young man who has suffered from recurrent systemic thromboembolism since he developed an acute interior wall myocardial infarction at the age of 27. A large elongated, pendunculated left ventricular thrombus was found by two dimensional echocardiography and was successfully removed by open heart surgery.