Measurement of lactic acid in cultured chondrocytes
To examine the role of HIF-1α in the glycosis in human OA chondrocytes, the level of lactic acid was measured in culture chondrocytes by the method reported by Pfander et al. [21]. Supernatants from chondrocyte cultures were collected after 24 hours under normoxic or hypoxic conditions. Lactic acid was determined by a colorimetric assay (Sigma) at 540 nm in accordance with the manufacturer's instructions. Lactic acid levels were normalized to total protein content as measured by the Bradford assay (Bio-Rad, Hercules, CA, USA)