Treatment of Osteochondral Defects in the Rabbit's Knee Joint by Implantation of Allogeneic Mesenchymal Stem Cells in Fibrin Clots

Summary

An experimental technique for the treatment of osteochondral defects in the rabbit's knee joint is described. The implantation of allogeneic mesenchymal stem cells into osteochondral defects provides a promising development in the field of tissue engineering. The preparation of fibrin-cell-clots in vitro offers a standardized method for implantation.

Abstract

The treatment of osteochondral articular defects has been challenging physicians for many years. The better understanding of interactions of articular cartilage and subchondral bone in recent years led to increased attention to restoration of the entire osteochondral unit. In comparison to chondral lesions the regeneration of osteochondral defects is much more complex and a far greater surgical and therapeutic challenge. The damaged tissue does not only include the superficial cartilage layer but also the subchondral bone. For deep, osteochondral damage, as it occurs for example with osteochondrosis dissecans, the full thickness of the defect needs to be replaced to restore the joint surface ¹. Eligible therapeutic procedures have to consider these two different tissues with their different intrinsic healing potential ². In the last decades, several surgical treatment options have emerged and have already been clinically established ^3-6.

Autologous or allogeneic osteochondral transplants consist of articular cartilage and subchondral bone and allow the replacement of the entire osteochondral unit. The defects are filled with cylindrical osteochondral grafts that aim to provide a congruent hyaline cartilage covered surface ^3,7,8. Disadvantages are the limited amount of available grafts, donor site morbidity (for autologous transplants) and the incongruence of the surface; thereby the application of this method is especially limited for large defects.

New approaches in the field of tissue engineering opened up promising possibilities for regenerative osteochondral therapy. The implantation of autologous chondrocytes marked the first cell based biological approach for the treatment of full-thickness cartilage lesions and is now worldwide established with good clinical results even 10 to 20 years after implantation ^9,10. However, to date, this technique is not suitable for the treatment of all types of lesions such as deep defects involving the subchondral bone ¹¹.

The sandwich-technique combines bone grafting with current approaches in Tissue Engineering ^5,6. This combination seems to be able to overcome the limitations seen in osteochondral grafts alone. After autologous bone grafting to the subchondral defect area, a membrane seeded with autologous chondrocytes is sutured above and facilitates to match the topology of the graft with the injured site. Of course, the previous bone reconstruction needs additional surgical time and often even an additional surgery. Moreover, to date, long-term data is missing ¹².

Tissue Engineering without additional bone grafting aims to restore the complex structure and properties of native articular cartilage by chondrogenic and osteogenic potential of the transplanted cells. However, again, it is usually only the cartilage tissue that is more or less regenerated. Additional osteochondral damage needs a specific further treatment. In order to achieve a regeneration of the multilayered structure of osteochondral defects, three-dimensional tissue engineered products seeded with autologous/allogeneic cells might provide a good regeneration capacity ¹¹.

Beside autologous chondrocytes, mesenchymal stem cells (MSC) seem to be an attractive alternative for the development of a full-thickness cartilage tissue. In numerous preclinical in vitro and in vivo studies, mesenchymal stem cells have displayed excellent tissue regeneration potential ^13,14. The important advantage of mesenchymal stem cells especially for the treatment of osteochondral defects is that they have the capacity to differentiate in osteocytes as well as chondrocytes. Therefore, they potentially allow a multilayered regeneration of the defect.

In recent years, several scaffolds with osteochondral regenerative potential have therefore been developed and evaluated with promising preliminary results ^1,15-18. Furthermore, fibrin glue as a cell carrier became one of the preferred techniques in experimental cartilage repair and has already successfully been used in several animal studies ^19-21 and even first human trials ²².

The following protocol will demonstrate an experimental technique for isolating mesenchymal stem cells from a rabbit's bone marrow, for subsequent proliferation in cell culture and for preparing a standardized in vitro-model for fibrin-cell-clots. Finally, a technique for the implantation of pre-established fibrin-cell-clots into artificial osteochondral defects of the rabbit's knee joint will be described.

Protocol

A. Preparation of a Donor Rabbit for the Isolation of Mesenchymal Stem Cells (Surgery Room)

1. Cells are isolated from male New Zealand White (NZW) rabbits at age of 4 months and approximately 3 kg body weight.
2. Induce anesthesia by propofol (10 mg/kg body weight i.v.) and sacrifice with sodium pentobarbital (100 mg/kg body weight i.v.).
3. Shave fur from hind limbs, back and belly with an electric clipper and vacuum the fur.
4. Disinfect the shaved area thoroughly with 70% ethanol.
5. Use blunt forceps, sharp scissors (or scalpel) and bone cutters for tissue and ligaments.
6. Make an incision along the cranial surface of ....

Results

The described surgical technique permits a successful isolation and implantation of allogeneic mesenchymal stem cells into an artificial osteochondral defect. The experimental setup resulted in a successful integration of the implant into the surrounding cartilage.

The defect was filled by repair tissue with similar biomechanical properties and similar durability compared to the surrounding cartilage. The fibrin-cell-clot was prepared in vitro on a sterile plate with pre-drilled holes.......

Discussion

In recent years, the possibility of treating complex articular osteochondral defects - such as those resulting from osteochondritis dissecans, osteonecrosis and trauma - with Tissue Engineering approaches became more and more attractive. In the previously mentioned pathologic entities, tissue damage extends to the subchondral bone and involves two tissues characterized by different intrinsic healing capacities ¹. There is an increasing interest in the role of subchondral bone for the pathogenic processes of os.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
DMEM	Biochrom AG	F 0415
FCS	PAN Biotech GmbH	0401
Propofol	Fresenius Kabi
Penicillin/Streptomycin	Biochrom AG	A 2210	1,000 units/10 μg/μl in 0.9% NaCl
PBS Dulbecco (1X)	Biochrom AG	L1815
Ethanol (70%)	Merck KGaA	410230
Trypan Blue Solution (0.4%)	Sigma-Aldrich	T8154
Biocoll Separation Sol.	Biochrom AG	L6115	Isotonic solution Density: 1,077 g/ml
Trypsin-EDTA 0.05%	Invitrogen GmbH	25300-054
Fentanyl	DeltaSelectGmBH	1819340
NaCl solution (0.9%)	BBraun	8333A193
Syringes (Injekt)	BBraun	4606108V
Needles (Sterican)	BBraun	4657519
Forceps (blunt/sharp)	Aesculap
Scissors	Aesculap
Scalpels	Feather Safety Razor Co	02.001.30.022
Pipettes research	Eppendorf
Bone Cutter	Aesculap
Tissue culture dishes 100 mm/150 mm	TPP AG	93100/93150	Growth area 60.1 mm2/147.8 mm2
Tissue culture flasks 25/75 mm2	TPP AG	90025/90075	25 mm2, 75 mm2
Centrifuge Tubes (50 ml)	TPP AG	91050	Gamma-sterilized
CO2 Incubator	Forma Scientific Inc.
Cell culture laminar flow hood Hera Safe	Heraeus Instruments
Sterile saw	Aesculap
Centrifuge Megafuge 2.0 R	Heraeus Instruments
Hemocytometer	Brand GmbH+Co KG	717810	Neubauer
Air operated power drill	Aesculap
TISSUCOL-Kit 1.0 ml Immuno	Baxter	2546648
Fibers (4-0 Monocryl, 4-0 Vicryl)	Ethicon
Spray dressing (OpSite)	Smith&Nephew	66004978	Permeable for water vapor