hymecromone and Osteoarthritis

Using in vitro models, we previously reported that 4-methylumbelliferone (4-MU) blocked many of the pro-catabolic features of activated chondrocytes. 4-MU also blocked safranin O loss from human cartilage explants exposed to interleukin 1β (IL1β) in vitro. However, the mechanism for this chondroprotective effect was independent of the action of 4-MU as a hyaluronan (HA) inhibitor. Interestingly, overexpression of HA synthase 2 (HAS2) also blocked the same pro-catabolic features of activated chondrocytes as 4-MU via a mechanism independent of extracellular HA accumulation. Data suggest that altering UDP-sugars may be behind these changes in chondrocyte metabolism. However, all of our previous experiments with 4-MU or HAS2 overexpression were performed in vitro. The purpose of this study was to confirm whether 4-MU was effective at limiting the effects of osteoarthritis (OA) on articular cartilage in vivo. The progression of OA was evaluated after destabilization of the medial meniscus (DMM) surgery on C57BL/6 mice in the presence or absence of 4-MU-containing chow. Mice fed 4-MU after DMM surgery exhibited significant suppression of OA starting from an early stage in vivo. Mice fed 4-MU exhibited lower OARSI scores after DMM; reduced osteophyte formation and reduced MMP3 and MMP13 immunostaining. 4-MU also exerted pronounced chondroprotective effects on murine joint cartilage exposed to IL1β in vitro and, blocked IL1β-enhanced lactate production in cartilage explants. Therefore, 4-MU is effective at significantly reducing the loss of proteoglycan and reducing MMP production both in vitro and in vivo as well as cartilage damage and osteophyte formation in vivo after DMM. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res. 38:1122-1131, 2020.

Topics: Animals; Arthritis, Experimental; Drug Evaluation, Preclinical; Female; Hymecromone; Male; Mice, Inbred C57BL; Osteoarthritis

Depletion of the cartilage proteoglycan aggrecan is one of the earliest events that occurs in association with osteoarthritis. This loss is often accompanied by a coordinate loss in another glycosaminoglycan, hyaluronan. Chondrocytes experimentally depleted of cell-associated hyaluronan respond by switching to a pro-catabolic metabolism that includes enhanced production of endogenous inflammatory mediators and increased synthesis of matrix metalloproteinases. Hyaluronan turnover is also increased. Together, such a response provides for possible establishment of a self-perpetuating spiral of events that maintains or prolongs the pro-catabolic state. Chondrocytes or cartilage can also be activated by treatment with pro-inflammatory cytokines and mediators such as IL-1β, TNFα, LPS, fibronectin fragments, and hyaluronan oligosaccharides. To determine the mechanism of chondrocyte activation due to hyaluronan loss, a depletion method was required that did not include degrading the hyaluronan. In recent years, several laboratories have used the coumarin derivative, 4-methylumbelliferone, as a potent inhibitor of hyaluronan biosynthesis, due in part to its ability to sequester intracellular UDP-glucuronic acid and inhibition of hyaluronan synthase transcription. However, contrary to our expectation, although 4-methylumbelliferone was indeed an inhibitor of hyaluronan biosynthesis, this depletion did not give rise to an activation of chondrocytes or cartilage. Rather, 4-methylumbelliferone directly and selectively blocked gene products associated with the pro-catabolic metabolic state of chondrocytes and did so through a mechanism preceding and independent of hyaluronan inhibition. These data suggest that 4-methylumbelliferone has additional useful applications to block pro-inflammatory cell activation events but complicates how it is used for defining functions related to hyaluronan.

Topics: Cartilage, Articular; Cells, Cultured; Chondrocytes; Humans; Hyaluronic Acid; Hymecromone; Osteoarthritis