Regenerative medicine is a branch of medicine that develops methods to grow, repair, or replace damaged or diseased cells, organs or tissues. It has gained significant momentum in recent years. Stem cells are undifferentiated cells with the capability to self-renew and differentiate into tissue cells with specialized functions. Stem cell therapies are therefore used to overcome the body's inability to regenerate damaged tissues and metabolic processes after acute or chronic insult. The concept of stem cell therapy was first introduced in 1991 by Caplan, who proposed that massive differentiation of cells into the desired tissue could be achieved by isolation, cultivation, and expansion of stem cells in in vitro conditions. Among different stem cell types, mesenchymal stem cells (MSC) currently seem to be the most suitable for therapeutic purposes, based on their simple isolation and culturing techniques, and lack of ethical issues regarding their usage. Because of their remarkable immunomodulatory abilities, MSCs are increasingly gaining recognition in veterinary medicine. Developments are primarily driven by the limitations of current treatment options for various medical problems in different animal species. MSCs represent a possible therapeutic option for many animal diseases, such as orthopedic, orodental and digestive tract diseases, liver, renal, cardiac, respiratory, neuromuscular, dermal, olfactory, and reproductive system diseases. Although we are progressively gaining an understanding of MSC behavior and their mechanisms of action, some of the issues considering their use for therapy are yet to be resolved. The aim of this review is first to summarize the current knowledge and stress out major issues in stem cell based therapies in veterinary medicine and, secondly, to present results of clinical usage of stem cells in veterinary patients.

Remarkable immunomodulatory abilities of mesenchymal stem cells, also called multipotent mesenchymal stromal cells or medicinal signaling cells (MSCs), have entailed significant advances in veterinary regenerative medicine in recent years. Despite positive outcomes from MSC therapies in various diseases in dogs and cats, differences in MSC characteristics between small animal veterinary patients are not well-known. We performed a comparative study of cells' surface marker expression, viability, proliferation, and differentiation capacity of adipose-derived MSCs (ADMSCs) from dogs and domestic cats. The same growth media and methods were used to isolate, characterize, and culture canine and feline ADMSCs. Adipose tissue was collected from 11 dogs and 8 cats of both sexes. The expression of surface markers CD44, CD90, and CD34 was detected by flow cytometry. Viability at passage 3 was measured with the hemocytometer and compared to the viability measured by flow cytometry after 1 day of handling. The proliferation potential of MSCs was measured by calculating cell doubling and cell doubling time from second to eighth passage. Differentiation potential was determined at early and late passages by inducing cells toward adipogenic, osteogenic, and chondrogenic differentiation using commercial media. Our study shows that the percentage of CD44+CD90+ and CD34−/− cells is higher in cells from dogs than in cells from cats. The viability of cells measured by two different methods at passage 3 differed between the species, and finally, canine ADMSCs possess greater proliferation and differentiation potential in comparison to the feline ADMSCs.

Under appropriate culture conditions, mesenchymal stem cells (MSC), also called more properly multipotent mesenchymal stromal cells (MMSC), can be induced toward differentiation into different cell lineages. In order to guide stem cell fate within an environment resembling the stem cell niche, different biomaterials are being developed. In the present study, we used silk fibroin (SF) as a biomaterial supporting the growth of MMSC and studied its effect on chondrogenesis of canine adipose–derived MMSC (cADMMSC). Adipose tissue was collected from nine privately owned dogs. MMSC were cultured on SF films and SF scaffolds in a standard cell culture medium. Cell morphology was evaluated by scanning electron microscopy (SEM). Chondrogenic differentiation was evaluated by alcian blue staining and mRNA expression of collagen type 1, collagen type 2, Sox9, and Aggrecan genes. cADMMSC cultured on SF films and SF scaffolds stained positive using alcian blue. SEM images revealed nodule-like structures with matrix vesicles and fibers resembling chondrogenic nodules. Gene expression of chondrogenic markers Sox9 and Aggrecan were statistically significantly upregulated in cADMMSC cultured on SF films in comparison to negative control cADMMSC. This result suggests that chondrogenesis of cADMMSC could occur when cells were grown on SF films in a standard cell culture medium without specific culture conditions, which were previously considered necessary for induction of chondrogenic differentiation.

In the present pilot study, we evaluated different supplemental therapies using autologous multipotent mesenchymal stromal cells (MMSCs) for the treatment of cranial cruciate ligament defects in dogs. We used tibial tuberosity advancement (TTA) and augmented it by supportive therapy with MMSCs in three patient groups. In the first patient group, the dogs were injected with MMSCs directly into the treated stifle one month after surgery. In the second group, MMSCs were delivered in a silk fibroin scaffold which was placed in the osteotomy gap during surgery. In the third group, MMSCs were first mixed with bone tissue and blood from the patient and delivered into the osteotomy gap during surgery. In the control group, patients underwent the TTA procedure but did not receive MMSC treatment. In the group of patients who received cells in the silk fibroin scaffold during surgery, the osteotomy gap did not heal, presumably due to the low absorption of silk fibroin. Patients who received MMSCs mixed with bone tissue and blood during surgery into the osteotomy gap recovered clinically faster and had better healing of the osteotomy gap than dogs from the other two treated groups and from the control group, as assessed by clinical examination and quantification of radiographs. In conclusion, dogs that received stem cells directly into the osteotomy gap (Group 3) recovered faster compared to dogs from Groups 1 (MMSCs injected into the joint one month after surgery), 2 (cells implanted into the osteotomy gap in a silk fibroin scaffold), and the control group that did not receive additional MMSCs treatment.

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Some limited reports suggest that cells can survive in the cadavers for much longer than it was previously thought.  In our study we explored how time after death, tissue type (muscle, brain and adipose tissue), storage temperature of cadavers (4 °C or at room temperature) and form of tissue storage (stored as cadavers or tissue pieces in phosphate buffered saline) affect the success of harvesting live cells from mice after death. Cells were isolated from dead tissues and grown in standard conditions. Some cells were used for RNA extraction and RT² Profiler™ PCR Array for cell lineage identification was performed to establish which lineages the cells obtained from post mortem tissues belong to. Results of our study showed that viable cells can be regularly isolated from muscle and brain tissue 3 days post mortem and with difficulty up to 6 days post mortem. Viable cells from brain tissue can be isolated up to 9 days post mortem. No cells were isolated from adipose tissue except immediately after death. In all instances viable cells were isolated only when tissues were stored at 4 °C. Tissue storage did not affect cell isolation. Isolated cells were progenitors from different germ layers. Our results show that live cells could be obtained from mouse cadavers several days after death.Key words: mouse; cadaver; stem cells; brain; muscle; adipose tissue IZOLACIJA ŽIVIH CELIC IZ RAZLIČNIH TKIV MIŠI DO DEVET DNI PO SMRTI Izvleček: Nekatere raziskave kažejo, da je preživetje celic v truplih precej daljše, kot je bilo znano do sedaj. V naši raziskavi smo proučevali, kako na uspešnost izolacije živih celic po smrti miši vplivajo različen čas izolacije po smrti, vrsta tkiva (mišično, možgansko in maščobno), temperatura shranjevanja trupel ter oblika shranjenega tkiva (kot koščki tkiv ali kot celi kadavri). Izolacija in gojenje celic iz tkiv mrtvih miši sta potekali pod standardnimi pogoji. Da bi ugotovili, katerim celičnim linijam pripadajo izolirane celice, je bil del celic uporabljen za izolacijo RNK in nadaljno uporabo v sistemu identifikacije izvornih celičnih linij z verižno reakcijo s polimerazo v realnem času. Rezultati naše raziskave so pokazali, da je žive celice mogoče izolirati iz mišičnega in možganskega tkiva 3 dni po smrti, pogojno tudi do 6 dni po smrti. Iz možganskega tkiva je bilo žive celice mogoče izolirati tudi do 9 dni po smrti. Iz maščobnega tkiva je bilo celice mogoče izolirati zgolj takoj po smrti, ne pa tudi v kasnejših časovnih intervalih. V vseh primerih so bile celice izolirane samo v primeru shranjevanja tkiv pri 4°C. Oblika shranjenega tkiva na izolacijo celic ni vplivala. Izolirane celice so pripadale različnim zarodnim plastem. Rezultati raziskave so pokazali, da je žive celice iz mišjih trupel mogoče izolirati tudi več dni po smrti.Ključne besede: miš; truplo; matične celice; možgansko tkivo; mišično tkivo; maščobno tkivo