Glucosepane is a new biomarker for the severity of osteoarthritis

Levels of amino acids and glycated, oxidised, or nitrated proteins in culture media of chondrocytes cultivated in multi-layers and in the blood of guinea pigs or osteoarthritis patients were studied by mass spectrometry.

This study analysed 60 male, 3-week-old guinea pigs. At 4-weeks and subsequently 8-week intervals until week 36, 12 animals were sacrificed and evaluated for histological severity of knee osteoarthritis and cartilage vascularisation. Patients with early and advanced osteoarthritis and healthy subjects were recruited. Human chondrocytes cultured in multilayers were treated for 10 days with IL-1β. Amino acids and glycated, oxidised, and nitrated proteins were analysed in the serum of guinea pigs, osteoarthritis patients and in the culture medium conditioned by chondrocytes by stable isotopic dilution analysis liquid chromatography-tandem mass spectrometry.

The results showed that the severity of osteoarthritis increased progressively in guinea pigs with age. Glycated, oxidised, and nitrated amino acids were increased markedly at week 36. Glucosepane and dityrosine increased progressively from weeks 20 and 28, respectively. Glucosepane was correlated with the osteoarthritis histological severity (r=0.58, p<0.0001) and the Young’s modulus (r=0.52-0.56, p<0.0001). Oxidation of free adducts was correlated with osteoarthritis severity (p<0.0009-0.0029) and hydroxyproline with cartilage thickness (p<0.0003-0.003). In the clinical study, plasma glucosepane was increased 38% in patients with early osteoarthritis (p<0.05) and 6-fold in patients with advanced osteoarthritis (p<0.001) compared to healthy subjects. IL-1β increased the release of glycated, oxidised, and nitrated products from chondrocytes in vitro.

It was concluded that glycation, oxidation, and nitration of proteins are reactions related to the severity of osteoarthritis. The products of these reactions can be detected in blood by mass spectrometry and candidate as biomarkers of osteoarthritis. More specifically, glucosepane is an advanced glycation product strongly increased in the severe form of the disease and therefore considered as a potential biomarker for diagnosis and progression of osteoarthritis.[2]