Glycation of human tissue and serum creatine kinase

Aggregation of protein therapeutics enhances their immunogenicity: causes and mitigation strategies

Protein aggregation in biotherapeutics has been identified to increase immunogenicity, leading to immune-mediated adverse effects, such as severe allergic responses including anaphylaxis. The induction of anti-drug antibodies (ADAs) moreover enhances drug clearance rates, and can directly block therapeutic function. In this review, identified immune activation mechanisms triggered by protein aggregates are discussed, as well as physicochemical properties of aggregates, such as size and shape, which contribute to immunogenicity. Furthermore, factors which contribute to protein stability and aggregation are considered. Lastly, with these factors in mind, we encourage an innovative and multidisciplinary approach with regard to further research in the field, with the overall aim to avoid immunogenic aggregation in future drug development.

Glycated proteome: from reaction to intervention

Glycation, a nonenzymatic reaction between reducing sugars and proteins, is a proteome wide phenomenon, predominantly observed in diabetes due to hyperglycemia. Glycated proteome of plasma, kidney, lens, and brain are implicated in the pathogenesis of various diseases, including diabetic complications, neurodegenerative diseases, cancer, and aging. This review discusses the strategies to characterize protein glycation, its functional implications in different diseases, and intervention strategies to protect the deleterious effects of protein glycation.

pH dependent effect of glycosylation on protein stability

The effect of glycosylation state on the thermal and storage stability of interleukin-2 mutein (IL-2 mutein) was investigated. The thermal stability of IL-2 mutein was studied by DSC and UV. An accelerated storage stability study was conducted at 40 degrees C in the dark and analyzed by UV, SDS-PAGE, and RP-HPLC. The unfolding temperatures (Tu) of both glycosylated and unglycosylated forms of IL-2 mutein are similar (within +/-1 degrees C) at pH 5.5 and 7.5. At pH 4.0, the Tu of glycosylated IL-2 mutein was 4 degrees C lower than that of the unglycosylated form. The precipitation temperature of glycosylated IL-2 mutein is similar to that of the unglycosylated form at pH 5.5 but 4 degrees C higher at pH 7.5. The precipitation temperature is not detectable for both forms at pH 4.0. During storage, both glycosylated and unglycosylated IL-2 mutein form aggregates (soluble and insoluble) and other degradation products. The aggregates are formed by both physical and chemical mechanisms. The major pathway of chemical aggregation appears to be disulfide bond formation/exchange. The glycosylated form is much less stable than the unglycosylated form at pH 4.0 and both forms are most stable at pH 5.5 in terms of thermal stability, precipitation rate and total degradation rate. This study clearly demonstrates that the effect of glycosylation on the stability of a protein is pH-dependent.

Serum total and lipid-bound sialic acid levels following acute myocardial infarction

Although serum total sialic acid has been shown to be a cardiovascular risk factor, with elevated levels associated with increased cardiovascular mortality and also with cerebrovascular disease, the reason for the elevation in serum sialic acid content remains obscure. It has been shown that an increased output of serum proteins by the liver due to some type of acute phase reaction may be one of the possible sources of an increased serum sialic acid concentration in patients with myocardial infarction. An increase in the activity of sialidase, which cleaves the terminal sialic acid residues from oligosaccharides, glycoproteins and gangliosides, may also play an important role in the elevation of serum total sialic acid in myocardial infarction. Elevated serum total sialic acid in the blood might result either from the shedding or secreting of sialic acid from the cell membrane surface, or releasing of cellular sialic acid from the cell into the bloodstream due to cell damage after myocardial infarction. The purpose of the present study is to investigate serum total and lipid-bound sialic acid and the enzymes serum lactate dehydrogenase, creatine kinase and aspartate aminotransferase in patients with acute myocardial infarction, at 24 h post-infarction (day 1), 48 h post-infarction (day 2) and 72 h post-infarction (day 3). A possible role of cell damage in the elevation of serum total and lipid-bound sialic acid levels in these patients was also evaluated. In this study, 40 patients with myocardial infarction ranging in age from 42 to 68 years, and 26 healthy volunteers ranging in age from 45 to 71 years were included. Serum total sialic acid determination was carried out by the thiobarbituric acid method of Warren and lipid-bound sialic acfd by the method of Katopodis. Our data shows that a) there is a gradual increase in the levels of serum total sialic acid and lipid-bound sialic acid during the first three days after the acute myocardial infarction and b) the elevation in serum total sialic acid levels correlates with the elevation in lactate dehydrogenase activity only on day 1 following infarction. Therefore, either the shedding or secreting of sialic acid from the cell or cell membrane surface may be partly responsible for an increased serum sialic acid concentration especially on day 1 following myocardial infarction.

Prolonged Hyperlipasemia Attributable to a Novel Type of Macrolipase

Background: We present the case of an 80-year-old woman who was admitted to hospital with an intermittent volvulus of the right colon. A total colectomy was performed. Initially, serum amylase and lipase increased concordantly, but after a few weeks amylase normalized (85 U/L), whereas lipase increased to 3764 U/L. This discrepancy and persistence of hyperlipasemia suggested a macromolecular form of lipase.

Methods: The nature of the macromolecular complex was studied using high-pressure liquid gel-permeation chromatography, affinity chromatography, (immuno)electrophoresis, and immunodiffusion.

Results: Gel-permeation chromatography revealed a macrolipase, with a molecular mass >900 kDa, that contributed up to 56% of total serum lipase activity. Butanol extraction of the specimen did not alter the elution profile. The thermostabilities of pancreatic lipase and the macroform were similar, whereas activation energy (Ea) was lower in the macromolecular lipase (28 ± 4 kJ · mol−1 · K−1 vs 48 ± 7 kJ · mol−1 · K−1 (P = 0.02). Agarose electrophoresis showed a broad band of lipase activity at the application site. Protein A-Sepharose affinity gel chromatography excluded IgG-linked lipase. Agarose electrophoresis and immunofixation excluded linkage to other immunoglobulins. Radial immunodiffusion did not show lipase activity in the immunoglobulin precipitation bands. Radial immunodiffusion with α2-macroglobulin (α2-MG) antibodies showed a diffuse spot of lipase activity within the precipitation band, suggesting a macromolecular association between lipase and α2-MG. Affinity gel chromatography against α2-MG showed lipase activity in the α2-MG-bound fractions.

Conclusion: This is the first report of a macrolipase in which an association between α2-MG and lipase is described.

Massive glycation of protein HC, a low molecular weight lipocalin, in non-diabetic individuals

Human protein HC is a member of the lipocalin superfamily with unique properties since it carries a covalently bound fluorescent chromophore mediating the linkage of the major part of protein HC to several plasma proteins, with IgA as the dominating complex partner. Native protein HC displays characteristic absorption and fluorescence spectra similar to those of glycated proteins with advanced glycosylation end products (AGEs). In vitro glycation of protein HC induces the formation of fibril aggregates with a corresponding increase of absorption in the visible region of the spectrum. Boronate-affinity chromatography and a novel galactosyltransferase assay indicate that protein HC is modified with residues of glucose exposed in a terminal non-reducing position which is typical of glycated proteins. The glycation level of several isolated batches of protein HC as measured by both assays was around 35%, which represents the highest level described for human plasma-derived proteins from healthy individuals.

Post-translational non-enzymatic modification of proteins. II. Separation of selected protein species after glycation and other carbonyl-mediated modifications

There are two strategies applicable to revealing non-enzymatic post-translational modifications of proteins; while assaying of the hydrolytically stable adducts was the subject of our previous communication [1], here we attempted to review separation technologies for the unfragmented modified proteins. There are a few standard procedures used for this purpose, namely Laemmli gel electrophoresis, different modes of gel permeation chromatography and boronate affinity chromatography. The latter approach makes use of the vicinal hydroxy groups present in glycated proteins. Some (but not all) arising adducts exhibit typical fluorescence which can be exploited for detection. In most cases fluorescence is measured at 370/440 nm for the so-called advanced glycation products or at 335/385 nm for the only so far well characterized glycation marker (pentosidine). Some indication exists that, e.g., synchronous fluorescence detection will probably in the future add to the selectivity and allow the distinction of the different adducts arising during non-enzymatic post-translational modifications (glycation). The proteins reviewed are serum albumin, collagen and lens proteins while glycation of hemoglobin is the subject of another review within the present volume.

Posttranslational heterogeneity of bone alkaline phosphatase in metabolic bone disease

Bone alkaline phosphatase is a marker of osteoblast activity. In order to study the posttranscriptional modification (glycosylation) of bone alkaline phosphatase in bone disease, we investigated the relationship between mass and catalytic activity of bone alkaline phosphatase in patients with osteoporosis and hyperthyroidism. Serum bone alkaline phosphatase activity was measured after lectin precipitation using the Iso-ALP test kit. Mass concentration of bone alkaline phosphatase was determined with an immunoradiometric assay (Tandem-R Ostase). In general, serum bone alkaline phosphatase mass and activity concentration correlated well. The activity : mass ratio of bone alkaline phosphatase was low in hyperthyroidism. Activation energy of the reaction catalysed by bone alkaline phosphatase was high in osteoporosis and in hyperthyroidism. Experiments with neuraminidase digestion further demonstrated that the thermodynamic heterogeneity of bone alkaline phosphatase can be explained by a different glycosylation of the enzyme.