Identifying synovial fluid microenvironment phenotypes in patients presenting with knee osteoarthritis

Abstract

Purpose: Osteoarthritis (OA) is the most common form of arthritis, and an estimated 9 million Americans suffer from symptomatic knee OA. These patients often have widely varying symptomology. Typically, these patients are initially treated with noninvasive treatments such as exercise, physical therapy, and/or a knee brace. Often, these treatments only temporarily delay the onset of more severe OA, and surgery is frequently required to best restore joint function. However, such surgeries, including total knee replacement (TKR), are sporadically effective in improving joint function and/or alleviating joint pain. Alternatively, minimally invasive procedures, such as needle based procedures, are a promising treatment option. The knee synovial fluid (SF) microenvironment (ME) contains many markers, including pro-inflammatory cytokines, anti-inflammatory cytokines, and matrix metalloproteinases (MMPs) that can be analyzed and used to characterize the status of a patient’s OA joint ME. Patients receiving minimally invasive, needle based procedures to treat OA present clinically with different subsets of symptoms such as varying levels of pain, varying ranges of activity levels, and wide ranging levels of joint swelling and inflammation. It stands to reason that there may be subsets, or phenotypes, within the SF ME of this broad OA population. The objective of this study is to determine whether the broad population of patients presenting with knee OA can be categorized into phenotypes based on the levels of several markers in the ME of the knee joint SF. Methods: This clinical research study was approved for n = 200 patients by the International Cellular Medicine Society’s Institutional Review Board on August 31, 2015. Patients presenting with knee OA based on MRI imaging or Kellgren–Lawrence Grade 2 scores were approached to participate in the study. Prior to receiving a patented Regenexx® SD bone marrow aspirate (BMA) treatment, approximately 0.5 cc of knee SF was aspirated and analyzed for various ME markers. The knee SF was analyzed for pro-inflammatory cytokines, anti-inflammatory cytokines, anabolic growth factors, anti-catabolic factors, and MMP products (Fig 1). The markers were analyzed using a Quansys multiplex ELISA platform. Upon complete enrollment of the study, cluster analysis will be utilized to determine if distinct phenotypes exist within the more broad OA disease profile. Results: Synovial fluid was analyzed for a small investigatory subset (n = 16) of the total approved study patients (n = 200). Several anabolic growth factors, anti-inflammatory cytokines, and anti-catabolic factors were present at measureable levels in the SF: Ang-2, bFGF, HGF, PDGF, VEGF, TGF, TIMP-1, TIMP-2, and IL-10. Additionally, there were measureable levels of several catabolic factors and pro-inflammatory cytokines: MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, IL-1, IL-2, IL-6, IL-8, IL12p70, IL-15, IL-23, IFNγ, and TNFα. Of most notable interest are the varying levels of MMPs. With this small, investigatory pilot study, it does appear that there is SF ME phenotypes present within the greater OA patient population (Fig. 2). Conclusions: Patients who present with knee OA have different clinical presentation phenotypes, i.e., severe swelling after the Regenexx® SD procedure v. minimal swelling that resolves quickly after treatment (<1 week). It stands to reason that the anabolic and catabolic knee ME markers could be used to characterize these phenotypes on a molecular level. This could provide valuable a priori information for predicting the likelihood of success for a minimally invasive, regenerative medicine treatment regime and/or for affecting the OA ME towards a phenotype that more positively correlates with successful clinical outcomes for patients receiving regenerative medicine treatments.View Large Image Figure ViewerDownload Hi-res image Download (PPT)