Identification of [6-Hydroxy-2-(hydroxymethyl)-5-oxo-5,6-dihydro-2H-pyran-3-yl]-cysteine (HHPC) as a Cysteine-specific Modification Formed from 3,4-Dideoxyglucosone-3-ene (3,4-DGE)

Abstract

Glucose degradation products (GDPs) are formed from glucose and other reducing sugars during heat treatment, for example, in heat-sterilized peritoneal dialysis fluids or foods. Because of their reactive mono-and dicarbonyl structure, they react readily with proteins, resulting in the formation of advanced glycation end products (AGEs), loss of protein functionality, and cytotoxicity. Among the GDPs, 3,4-dideoxyglucosone-3-ene (3,4-DGE) exerts the strongest effects despite its relatively low concentration levels. The goal of the present study was therefore to identify the structure of specific protein modifications deriving from 3,4-DGE. A nonapeptide containing the reactive amino acids lysine, arginine, and cysteine was incubated with 3,4-DGE and the dominant GDPs 3-deoxyglucosone (3-DG) and 3deoxygalactosone (3-DGal) in concentrations as present in peritoneal dialysis fluids (235 μM 3-DG, 100 μM 3-Gal, and 11 μM 3,4-DGE). Glycation rate and product formation were determined by ultra-HPLC−MS/MS (UHPLC−MS/MS). 3,4-DGE showed the strongest glycation activity. After 2 h of incubation, 3,4-DGE had modified 57% of the nonapeptide, whereas 3-DG had modified only 2% and 3-DGal had modified 29% of the peptide. A stable 3,4-DGE-derived cysteine modification was isolated. Its structure was determined by comprehensive NMR and MS experiments to be [6-hydroxy-2-(hydroxymethyl)-5oxo-5,6-dihydro-2H-pyran-3-yl]-cysteine (HHPC), which represents a novel cysteine−AGE derived from 3,4-DGE. The results indicate that 3,4-DGE might contribute to a severe loss of protein functionality by forming cysteine-specific AGEs, such as HHPC.

The Chemistry of Protein Oxidation in Food

“…Low‐molecular thiols such as glutathione are depleted by oxidation during dough processing . In this context, however, it is necessary to mention that the disappearance of thiol groups does not necessarily imply oxidation because thiols can also participate in Maillard reactions . The sulfenic acid ( 55 ) as a further cysteine oxidation product was identified after oxidation of β‐lactoglobulin with hydrogen peroxide in a model system …”

“…[199] In this context, however,itisnecessary to mention that the disappearance of thiol groups does not necessarily imply oxidation because thiols can also participate in Maillard reactions. [161,200] Thes ulfenic acid (55)a safurther cysteine oxidation product was identified after oxidation of b-lactoglobulin with hydrogen peroxide in amodel system. [151] Theq uantification of oxidation products of methionine (30), especially methionine sulfoxide (31), is as erious problem in food analysis.During protein hydrolysis by hydrochloric acid, 31 may be reduced to 30,b ut 30 may just as well be oxidized to 31.…”

Die Chemie der Proteinoxidation in Lebensmitteln

“…Niedermolekulare Thiole wie Glutathion werden durch Oxidationsreaktionen bei der Teigbereitung verbraucht . Allerdings bedeutet der Abbau von Thiolgruppen nicht zwingend eine Oxidation, da Thiolgruppen auch an der Maillard‐Reaktion beteiligt sein können . Die Sulfensäure 55 (Schema ) als weiteres Cysteinoxidationsprodukt wurde nach Oxidation von β‐Lactoglobulin mit Wasserstoffperoxid in einem Modellsystem nachgewiesen …”

“…[199] Allerdings bedeutet der Abbau von Thiolgruppen nicht zwingend eine Oxidation, da Thiolgruppen auch an der Maillard-Reaktion beteiligt sein kçnnen. [161,200] Die Sulfensäure 55 (Schema 7) als weiteres Cysteinoxidationsprodukt wurde nach Oxidation von b-Lactoglobulin mit Wasserstoffperoxid in einem Modellsystem nachgewiesen. [151] Die Quantifizierung der Oxidationsprodukte von Methionin (30), vor allem Methioninsulfoxid (31), stellt in der Lebensmittelanalytik eine anspruchsvolle Aufgabe dar.B ei der salzsauren Hydrolyse kann 31 zu 30 reduziert, 30 kann jedoch auch zu 31 oxidiert werden.…”

Metal cations promote α-dicarbonyl formation in glucose-containing peritoneal dialysis fluids

“…As a consequence, however, a variety of reactive GDPs are formed [1]. Most GDPs contain an αdicarbonyl moiety that reacts readily with nucleophilic side chains of amino acids such as lysine, arginine, or cysteine to form advanced glycation products (AGEs) [2][3][4]. AGEs are responsible for a critical loss of protein function, such as the impairment of enzymatic activity or receptor binding [5][6][7][8].…”