Introduction

The terms regenerative medicine and biologic therapy refer to treatments that allow the body to restore form and function by relying on biological mechanisms that exist in the body. These mechanisms include growth factors and cells that can differentiate to repair and restore injured tissue. Since this concept has been introduced there has been great pressure to initiate treatment with these therapies as they hold such great promise. As such, the commercial opportunities to develop these therapies led to techniques and product being introduced in advance of the availability of meaningful scientific evidence supporting these treatments. In order to show that use of regenerative therapies should gain widespread use in our veterinary patients a number of challenges must be addressed.

There must be evidence that these treatments are safe and efficacious. Standardized protocols and standardization of the terms describing both scientific methods and products are essential.

Challenges in the current literature related to treatment protocols include questions such as:

• What cells are being injected?
• How many cells should be administered?
• What growth factors are known to be present?
• Have cells been activated?
• The list of questions goes on…

Outcome measures are also extremely variable in studies related to these therapies. Owner evaluation, veterinary assessment, questionnaires and objective data such as use of force plates. Many factors will make evidence-based practice related to use of biologic and regenerative therapies in veterinary practice challenging. The effort and expense in designing proper research trials to evaluate these emerging therapies is required to determine if the perceived benefits of this approach are worth the effort and provide a benefit to our patient’s health. This discussion will look at the most commonly available biologic therapies. The term ‘stem cells’ will include stromal vascular fraction (SVF) and cultured stem (stromal) cell therapy. ‘Blood-derived’ products include platelet-rich plasma (PRP), autologous conditioned serum (ACS)/interleukin-receptor antagonist protein (IRAP) and autologous conditioned protein (APS).

‘Stem Cell’ Products

Stromal Vascular Fraction

Stromal vascular fraction (SVF) is usually a point-of-care therapy that is typically prepared by the harvest of autologous adipose tissue followed by mechanical and chemical digestion followed by centrifugation allowing isolation of the cellular SVF pellet from the remaining lipid and extracellular components. No further processing such as culture expansion or homogenization of the cells takes place. Much less than 5% of the cells remaining in the SVF could even loosely be classified as true stem cells with pluripotent capacity. Cultured stem cell therapy involves the harvest of fat or bone followed by culture expansion over a period of weeks, resulting in homogenization of a stem cell population and greatly increased the number of available cells. In spite of these differences, SVF therapy is often incorrectly called ‘stem cell therapy.’ Advantages of SVF therapy include the ability to use this product patient side as well as SVF administration does not require the laboratory, expertise and time required for cell culture.

There are a number of published reports describing intra-articular SVF injection for treatment of treating intra-articular cartilage damage and OA in dogs for over a decade.^1,2 Two recent prospective, randomized, controlled trials with objective functional outcome measures failed to provide consistent evidence of the benefit of SVF injection based upon those objective kinetic data.^3,4 A more recent study looked at SVF treatment in canine stifle joints with OA and found no statistically significant improvements in function, cartilage biochemical composition, or histology for SVF-treated knees.⁵ As a result, there remains uncertainty as to whether the use of SVF is truly beneficial in terms of symptom relief, functional improvements, disease modifying effects or cartilage regenerative capacity. In turn, there remains a need to evaluate the efficacy of SVF more thoroughly and augment its potential regenerative benefits.

Stem (Stromal) Cells

Stem cells derived from harvesting of fat are known as adipose derived stromal cells (ASC). These cells have gained interest as an osteoarthritis treatment and several recent studies have examined their efficacy in clinical cases. Patient improvement of lameness when compared to placebo control groups have been reported in a number of these studies using both visually assessed lameness scores and owner evaluation of lameness and quality of life.^6,7 Some reports of improvement following administration of ASCs have been based on objective force plate data.^8,9 ASC therapy in OA is reported to be based on the immunomodulatory capacity and trophic effects that mesenchymal stem cells (MSC) provide. ASCs are thought to have immunomodulatory effects that make them an ideal therapy for active inflammatory conditions. ASCs are also thought to have ability to recruit local host cells that can induce a response that is deemed beneficial to reducing inflammation. These immunomodulatory properties mean that ASCs are well-tolerated and incorporated into the local environment. The potential for use of cultured stromal cells requires a more thorough investigation to determine potential for treatment of inflammatory diseases and to determine the potential regenerative capacity.

Platelet-Rich Plasma (PRP)

There is no fixed definition of platelet-rich plasma but the most commonly used is a plasma preparation that contains a higher concentration of platelets than that found in the whole blood from which the PRP was prepared. The proposed mechanism by which PRP may be beneficial is the provision of growth factors, stored within the platelet alpha granules. These factors are thought to reduce inflammation and initiate anabolic processes and tissue healing. The growth factors stored in the alpha granules include that are most commonly associated with facilitation of tissue healing include vascular endothelial growth factor (VEGF), platelet-derived growth factors (PDGF) AA, AB, and BB, and transforming growth factor (TGF). The applications for which PRP has been used in human and veterinary medicine include injection into injured tendons/muscles/ligaments, use in fractures to facilitate bone healing, and intra-articular injection for symptomatic management of osteoarthritis. Several studies have been published supporting the use of PRP as a treatment for OA. A prospective, randomized, controlled study compared the efficacy of PRP to saline injection for treatment of OA in 20 dogs. The study included objective force plate data for half the dogs in addition to using validated subjective outcome measures for all dogs. Significant improvements in objective and subjective outcomes over a 12-week follow up period with intra-articular use of the PRP was found when compared to the control saline group.¹⁰ Franklin et al. assessed a number of intra-articular treatments including PRP for treatment of OA created using an osteochondral defect model. Changes in blinded subjective lameness scores and objective kinetic weight bearing were both significantly improved with use of PRP in comparison to the sham (saline) treatment group.⁵ There is growing evidence in support of intra-articular use of PRP in dogs for the management of OA.

References

1.  Black LL, Gaynor J, Adams C, et al. Effect of intra-articular injection of autologous adipose-derived mesenchymal stem and regenerative cells on clinical signs of chronic osteoarthritis of the elbow joint in dogs. Vet Ther. 2008;9(03):192–200.

2.  Black LL, Gaynor J, Gahring D, et al. Effect of adipose-derived mesenchymal stem and regenerative cells on lameness in dogs with chronic osteoarthritis of the coxofemoral joints: a randomized, double-blinded, multicenter, controlled trial. Vet Ther. 2007;8(04):272–284.

3.  Upchurch DA, Renberg WC, Roush JK, et al. Effects of administration of adipose-derived stromal vascular fraction and platelet-rich plasma to dogs with osteoarthritis of the hip joints. Am J Vet Res. 2016;77(09):940–951.

4.  Kiefer K, Lin K, Fitzpatrick N, et al. Does adipose-derived stromal cell adjuvant therapy for fragmented medial coronoid process in dogs influence outcome? A pilot project. Veterinary Evidence. 2016;1(04):1–17

5.  Franklin SP, Stoker AM, Bozynski CC, et al. Comparison of platelet-rich plasma, stromal vascular fraction (SVF), or SVF with an injectable PLGA nanofiber scaffold for the treatment of osteochondral injury in dogs. J Knee Surg. 2018;31:686–697.

6.  Guercio A, DiMarco P, Casella S, et al. Production of canine mesenchymal stem cells from adipose tissue and their application in dogs with chronic osteoarthritis of the humeroradial joints. Cell Biol Intl. 2012;36(2):189–194.

7.  Vilar JM, Morales M, Santana A, et al. Controlled, blinded force platform analysis of the effect of intraarticular injection of autologous adipose-derived mesenchymal stem cells associated to PRGF-Endoret in osteoarthritic dogs. BMC Vet Res. 2013;9(1):131.

8.  Vilar JM, Batista M, Morales M, et al. Assessment of the effect of intraarticular injection of autologous adipose-derived mesenchymal stem cells in osteoarthritic dogs using a double blinded force platform analysis. BMC Vet Res. 2014;10(1):143.

9.  Cuervo B, et al. Hip osteoarthritis in dogs: a randomized study using mesenchymal stem cells from adipose tissue and plasma rich in growth factors. Int J Mol Sci. 2014;15(8):13437–13460.

10.  Fahie MA, Ortolano GA, Guercio V, et al. A randomized controlled trial of the efficacy of autologous platelet therapy for the treatment of osteoarthritis in dogs. J Am Vet Med Assoc. 2013;243(9):1291–1297.