Effect of Oral Losartan on Orthobiologics: Implications for Platelet-Rich Plasma and Bone Marrow Concentrate-A Rabbit Study.

Gilberto Y Nakama,Polina Matre,Johnny Huard,Marc J Philippon,Xiaodong Mu,Sabrina Gonzalez,Kaitlyn E Whitney,Hajime Utsunomiya,Justin W Arner,Sudheer Ravuri

doi:10.3390/ijms21197374

Abstract

Recent efforts have focused on customizing orthobiologics, such as platelet-rich plasma (PRP) and bone marrow concentrate (BMC), to improve tissue repair. We hypothesized that oral losartan (a TGF-β1 blocker with anti-fibrotic properties) could decrease TGF-β1 levels in leukocyte-poor PRP (LP-PRP) and fibrocytes in BMC. Ten rabbits were randomized into two groups (N = 5/group): osteochondral defect + microfracture (control, group 1) and osteochondral defect + microfracture + losartan (losartan, group 2). For group 2, a dose of 10mg/kg/day of losartan was administrated orally for 12 weeks post-operatively. After 12 weeks, whole blood (WB) and bone marrow aspirate (BMA) samples were collected to process LP-PRP and BMC. TGF-β1 concentrations were measured in WB and LP-PRP with multiplex immunoassay. BMC cell populations were analyzed by flow cytometry with CD31, CD44, CD45, CD34, CD146 and CD90 antibodies. There was no significant difference in TGF-β1 levels between the losartan and control group in WB or LP-PRP. In BMC, the percentage of CD31+ cells (endothelial cells) in the losartan group was significantly higher than the control group (p = 0.008), while the percentage of CD45+ cells (hematopoietic cells-fibrocytes) in the losartan group was significantly lower than the control group (p = 0.03).

Highlights

Fibrosis is the excessive formation of connective tissue as a result of exaggerated deposition of extracellular matrix (ECM) factors during tissue healing [1,2,3]
Bone Marrow Concentrate Flow Cytometry Results In bone marrow concentrate (BMC), the percentage of CD31+ cells in the losartan group was significantly higher than the control group (52.4 ± 10.8% vs. 28.4 ± 6.6%, p = 0.008), while the percentage of CD45+ cells in the losartan group was significantly lower than the control group (2.9 ± 2.5% vs. 15.0 ± 9.7%, p = 0.03) (Figure 2)
We found no significant difference between the losartan group versus the control group in mesenchymal stem cells (MSCs) (6.45 ± 0.7% vs. 6.56 ± 2.0%, p = 0.31), CD146+ cells (25.5 ± 11.1% vs. 12.3 ± 4.9%, p = 0.15) and CD45+ CD34+ cells (2.66 ± 2.34% vs. 8.00 ± 5.71%, p = 0.056) (Figure 3)

Summary

Introduction

Fibrosis is the excessive formation of connective tissue as a result of exaggerated deposition of extracellular matrix (ECM) factors (i.e., collagen) during tissue healing [1,2,3]. As an example of fibrotic impairment of cardiac muscle, the lack of hypertension control causes myocardial injury, and the perpetuation of injury leads to pathological myocardial repair that results in the recruitment of fibroblasts [7,8]. The EndMT pathway plays a key role in cytoskeleton remodeling and scar tissue formation through the activation of endothelial cells (CD31+ cells) that undergo phenotypical changes, leading to the breakdown of basement membranes and reaching interstitial tissues [9,10,11]. Transforming growth factor-beta 1 (TGF-β1) plays a key role in EndMT activation and proliferation through the TGF-β1/Smad-dependent pathway that regulates TGF-β1 transcription, collagen expression [7,8]. Inhibition of the TGF-β1/Smad-dependent pathway using targeted agents may be a promising strategy to downregulate EndMT and, fibrosis formation in musculoskeletal tissue

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Conclusion