SOD activity in the end stage knee and hip osteoarthritic cartilage significantly lower than non osteoarthritic cartilage independent of age-related change

Abstract

Purpose: Recent study has shown that SOD gene expression level or protein level does not necessarily reflect SOD activity since SOD is post-translationally modified after protein synthesis. The trend of SOD activity in end-stage osteoarthritic (OA) tissues remains unknown. The purpose of this study was to examine the possibility of using SOD as an OA biomarker by examining the SOD activity in OA-affected knee cartilage and synovium from patients with end-stage knee OA and in OA-affected femoral head cartilage from patients with end-stage hip OA. Methods: To evaluate the SOD activity in end-stage knee OA cartilage and synovium, samples of cartilage and synovium were taken from the outside of the patellofemoral joint with biopsy forceps. Cartilage and synovium obtained from the knee joint of patients who underwent total knee arthroplasty for end-stage knee OA were defined as end-stage knee OA cartilage and synovium. Cartilage and synovium obtained from the knee joint of patients who underwent knee arthroscopy for meniscal tears or anterior cruciate ligament reconstruction were defined as control specimens. The degree of OA was evaluated using the Kellgren-Lawrence classification. The SOD activity in the samples was analyzed using SOD activity assay based on the auto-oxidation rate of hematoxylin (NWLSS SOD assay). Next, to evaluate the SOD activity in end-stage hip OA cartilage, OA cartilage samples were obtained from the femoral head of patients who underwent total hip arthroplasty for hip OA. Non-OA cartilage samples were obtained from the femoral head of patients who underwent bipolar hip arthroplasty for femoral head neck fractures. The SOD activity in the samples was evaluated using SOD assay based on inhibition of nitroblue tetrazolium reduction (Cayman’s SOD assay). The results of SOD assays are expressed in units per mg protein. This study protocol was approved by the ethics committee of Juntendo Tokyo Koto Geriatric Medical Center. Informed consent was obtained from all patients prior to the study. Results: The SOD activity in end-stage knee OA cartilage was significantly lower than non-OA cartilage (Fig 1A). Furthermore, the SOD activity in end-stage knee OA synovium was significantly lower than that non-OA synovium (Fig 1B). The mean age of the knee OA patients was significantly higher than that of the non-OA patients (Table 1). There was no significant correlation between the SOD activity in the synovium and age (Fig 1D). However, the SOD activity in the cartilage showed a weak negative correlation with age (Fig 1C). Therefore, we cannot deny the possibility that aging induced a decrease in the SOD activity level in the cartilage and synovium of patients with end-stage OA. To investigate the correlation between SOD activity and aging, we focused on the femoral head cartilage, for which it is easy to eliminate the effects of aging. We aimed to prove the causal relationship of SOD activity with aging by comparing the SOD activity in the femoral head cartilage of patients without OA who had a femoral neck fracture and the SOD activity in the femoral head cartilage of patients with hip OA. The average age of non-OA patients with femoral neck fractures was significantly higher than that of patients with end-stage hip OA (Table 2). However, the SOD activity in the femoral head cartilage of patients with hip OA was significantly lower than that of non-OA patients (Fig 2A).There was no significant correlation between the SOD activity in the cartilage and age (Fig 2B). Finally, we evaluated the correlation between NWLSS SOD assay and Cayman’s SOD assay using femoral head cartilage. We found a strong positive correlation between NWLSS SOD assay and Cayman’s SOD assay (Fig 3). Conclusions: It is known that SOD decreases with age. Since SOD activity decreased in knee OA and hip OA cartilage regardless of the age of the control group, it was revealed that the decrease in SOD activity is more related to OA than to age. These data suggested that SOD activity plays an important role in human OA.Table 1Baseline characteristics of patients from Fig 1CharacteristicsControls (N= 10)Knee OA (N =18)P valueAge (years)30.4±14.176.8±9.1< 0.001Gender (Male/female)Male 5, Female 5Male 0, Female 18- Open table in a new tab Table 2Baseline characteristics of patients from Fig 2Characteristicsnon OA (N = 14)hip OA (N = 10)P valueAge (years)82.64±6.4270.0±8.17< 0.001Gender (Male/female)Male 3, Female 11Male 0, Female 11- Open table in a new tab View Large Image Figure ViewerDownload Hi-res image Download (PPT)