LAUSR

Objectives: Application of growth factors for cartilage injury has been considered in recent studies; however, the effect of blocking detrimental growth factors for cartilage injury has not been well described. It is known that transforming growth factor beta 1 (TGF-β1) is overproduced in osteoarthritic joints. It has been reported that angiotensin II-induced activation of TGF-β1-pSmad2/3 signaling, which can result in fibrosis, can be inhibited by losartan (an FDA-approved hypertension drug). Although bone marrow stimulation (BMS) is often the first choice for clinical treatment of cartilage injuries, fibrocartilage, not pure hyaline cartilage, has been reported after BMS surgery. Our lab has shown that blocking TGF-β1 with losartan can decrease fibrosis in muscle injury models. We hypothesized that blocking TGF-β1 would improve cartilage healing in a rabbit osteochondral defect injury model via decreasing the amount of fibrocartilage formation, and increase hyaline-like cartilage formation, thus enhancing BMS-mediated cartilage repair. Methods: An osteochondral defect (diameter: 5 mm, depth: 2 mm) was made in the patellar groove of 48 New Zealand White rabbits. The rabbits were divided into 3 groups (N=8/group/time point) randomly: a control group (defect only), a BMS group (osteochondral defect + BMS), and a losartan-treated group (osteochondral defect + BMS + losartan). For the rabbits in the losartan-treated group, 10mg/kg/day dose of losartan was administrated orally from the day after surgery through the day of euthanasia. Rabbits were sacrificed 6 weeks and 12 weeks post-operatively, respectively. Macroscopic appearance, microcomputed tomography (microCT), histological assessment, and gene expression were evaluated. Results: The losartan-treated group scored highest in the International Cartilage Repair Society (ICRS) macroscopic assessment. MicroCT showed healing of the bony defect in the losartan-treated group, in comparison to no healing in the control group and partial healing in the BMS group. Histologically, results obtained using the Modified O’Driscoll ICRS grading system yielded significantly superior scores in the losartan-treated group compared to both the control group and the BMS group (12 weeks, mean [SD], control: 30.1 [3.6], BMS: 35.0 [3.7], losartan-treated: 41.4 [4.7]; p< 0.001 compared to control group, p= 0.012 compared to BMS group, respectively). TGF-β1 signaling and TGF-β activated kinase-1 were suppressed in the fat pad tissues. Conclusion: Biologically regulated BMS by blocking TGF-β1 (oral intake of losartan) provided superior cartilage repair via decreasing fibrocartilage formation and resulting in hyaline-like cartilage, compared to outcomes from BMS only. FDA-approved blocking growth factor drugs will be a new frontier of biologically regulated BMS, which will be easily translatable into clinical settings as an off-label use. Figure: Macroscopy, microCT, and Histological finding at 12 weeks after surgery. A: Macroscopic findings. B: MicroCT. C: Histological findings. D: ICRS macroscopic score. E: Modified O’Driscoll score. BMS + Iosartan group showed significantly higher ICRS macroscopic score and better healing of subchondral bone in microCT. Histologically, columnar organization of chondrocytes with plenty of Safranin O positive, Col II positive matrix was seen in BMS + Iosartan group. Modified O’Driscoll score of BMS + Iosartan group was significantly higher than that of Defect group and BMS group. *: P < 0.05, **: P < 0.01. Bar = 1mm (× 20) / 200 µm (× 200). BMS: bone marrow stimulation, HE: hematoxylin and eosin.