The proinflammatory cytokines interleukin-1α and tumor necrosis factor α promote the expression and secretion of proteolytically active cathepsin S from human chondrocytes.

Osteoarthritis and rheumatoid arthritis are destructive joint diseases that involve the loss of articular cartilage. Degradation of cartilage extracellular matrix is believed to occur due to imbalance between the catabolic and anabolic processes of resident chondrocytes. Previous work has suggested that various lysosomal cysteine cathepsins participate in cartilage degeneration; however, their exact roles in disease development and progression have not been elucidated. In order to study degradation processes under conditions resembling the in vivo milieu of the cartilage, we cultivated chondrocytes on a type II collagen-containing matrix. Stimulation of the cultivated chondrocytes with interleukin-1α and/or tumor necrosis factor α resulted in a time-dependent increase in cathepsin S expression and induced its secretion into the conditioned media. Using a novel bioluminescent activity-based probe, we were able to demonstrate a significant increase in proteolytic activity of cathepsin S in the conditioned media of proinflammatory cytokine-stimulated chondrocytes. For the first time, cathepsin S was demonstrated to be secreted from chondrocytes upon stimulation with the proinflammatory cytokines, and displayed proteolytic activity in culture supernatants. Its stability at neutral pH and potent proteolytic activity on extracellular matrix components mean that cathepsin S may contribute significantly to cartilage degradation and may thus be considered a potential drug target in joint diseases.

Selective and sensitive monitoring of caspase-1 activity by a novel bioluminescent activity-based probe.

The role of caspase-1 in inflammation has been studied intensely over recent years. However, the research of caspase-1 has remained difficult mainly due to the lack of sensitive and selective tools to monitor not only its abundance but also its activity. Here we present a bioluminescent activity-based probe (ABP) for caspase-1, developed by the Reverse Design concept, where chemically optimized protease inhibitors are turned into selective substrate ABPs. The probe exhibits excellent selectivity for caspase-1 and ∼1000-fold increase in sensitivity compared to available fluorogenic peptidic caspase-1 substrates. Moreover, we have been able to monitor and quantify specific caspase-1 activity directly in cell lysates. The activity correlated well with processing of prointerleukin-1ß and prointerleukin-18 in phorbol 12-myristate 13-acetate (PMA)-stimulated cells. A detectable caspase-1 activity was present also in nonstimulated cells, consistent with processing of constitutively expressed prointerleukin-18.

New phenylselanyl group activation: synthesis of aziridines and oxazolidin-2-ones.

After the study of different phenylselanyl group activators, halogenation by N-bromosuccinimide (NBS) has been shown to be the most suitable manner for cyclizing beta-phenylselanyl amines into aziridines and also enabled production of oxazolidin-2-ones from N-Boc beta-phenylselanyl amines in excellent yield.