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High-intensive therapeutic lowering of systemic cholesterol does not ameliorate osteoarthritis development in knee joints of humanized dyslipidemic mice

      Purpose: High systemic cholesterol levels are associated with osteoarthritis (OA) development. Novel therapeutic high-intensive cholesterol-lowering therapies have recently been shown to diminish western type diet (WTD) induced atherosclerosis. Here, we investigated the potency of these therapeutic cholesterol-lowering strategies to attenuate OA development in dyslipidemic APOE*3Leiden.CETP mice.
      Methods: Female APOE*3Leiden.CETP mice (n=13-16 per group) were fed a chow or WTD with 0.30% cholesterol and 15% saturated fat for 38 weeks. After 13 weeks, mice were matched into a baseline group (sacrificed at t=13w) and 5 groups that received WTD alone or with treatment for 25 weeks: atorvastatin alone (A), in combination with PCSK9 inhibitor alirocumab (AA) or ANGPTL3 inhibitor evinacumab (AE), or triple treatment (AAE). Metabolic dysfunction was monitored throughout the study and knee joints were analysed for cartilage degradation, synovial inflammation and osteophyte formation using histology and immunohistochemistry.
      Results: Systemic administration of cholesterol-lowering interventions resulted in a significant reduction of body weight (A: -16%; AA: -8%; AE: -12%; AAE: -18% at end point) without changes in food intake. WTD-feeding manifested itself in dyslipidemia, with high cholesterol levels that were significantly reduced after administration of therapeutic cholesterol-lowering interventions (A: -46%; AA: -74%; AE: -74%; -AAE: 86% at end point). Using detailed OARSI scoring, dyslipidemic mice showed a mild but significant increase in cartilage degeneration at end point (7.8 ± 1.9) compared to baseline controls (3.8 ± 1.8, 2.1-fold increase, p=0.001). A strong increase in NITEGE staining, representing proteolytic activity by aggrecanases was observed at end point. However, therapeutic cholesterol lowering did not ameliorate further progression of cartilage destruction. Dyslipidemic APOE*3Leiden.CETP mice developed minor synovial inflammation which was not affected by cholesterol-lowering interventions. Alarmin S100A8, a marker for macrophage activation, showed minor expression in the synovial lining of all treatment groups, supporting the absence of joint inflammation in this model. Finally, we determined whether high plasma cholesterol levels promoted osteophyte formation. The total number of osteophytes and osteophyte maturation stage was comparable between all groups despite reduction of systemic cholesterol levels.
      Conclusions: Therapeutic cholesterol-lowering interventions did not slow the progression of cartilage degradation and osteophyte formation in dyslipidemic APOE*3Leiden.CETP mice with minor joint inflammation. These findings suggest that therapeutic cholesterol-lowering interventions in the absence of local inflammation within the knee joint cannot prevent progression of OA.