Stem cell therapy: A novel treatment approach for oral mucosal lesions.

Stem cells have enormous potential to alleviate sufferings of many diseases that currently have no effective therapy. The research in this field is growing at an exponential rate. Stem cells are master cells that have specialized capability for self-renewal, potency and capability to differentiate to many cell types. At present, the adult mesenchymal stem cells are being used in the head and neck region for orofacial regeneration (including enamel, dentin, pulp and alveolar bone) in lieu of their proliferative and regenerative properties, their use in the treatment of oral mucosal lesions is still in budding stages. Moreover, there is scanty literature available regarding role of stem cell therapy in the treatment of commonly seen oral mucosal lesions like oral submucous fibrosis, oral lichen planus, oral ulcers and oral mucositis. The present review will focus on the current knowledge about the role of stem cell therapies in oral mucosal lesions and could facilitate new advancements in this area (articles were obtained from electronic media like PubMed, EBSCO, Cochrane and Medline etc., from year 2000 to 2014 to review the role of stem cell therapy in oral mucosal lesions).

In the modern era, where biology and biotechnology have replaced the chemistry, we are exploring “biological solutions to biological problems.” Stem cell therapy is a part of regenerative medicine that involves the use of undifferentiated cells in order to cure the disease. It is believed that stem cell treatments have the potential to change the face of human disease and reduce the suffering.[1]

Stem cell-based therapies are being investigated for the treatment of many conditions, including neurodegenerative conditions such as Parkinson's disease, cardiovascular disease, liver disease, diabetes, autoimmune diseases and for nerve regeneration.[2] In orofacial region these therapies are being used for tooth and periodontal regeneration, temporomandibular joint reconstruction, alveolar bone regeneration. Craniofacial stem cells including dental pulp derived stem cells have the potential to cure a number of diseases.

Present day treatment modalities for oral mucosal lesions like ulcerative lesions, premalignancies and malignancies mainly consist of steroids and antioxidants (which provide only a short term and symptomatic relief) and surgery with or without chemo/radiotherapy (which leave the patient with certain amount of morbidity). Advances in stem cell technology have opened new vistas for treatment of these lesions. Various studies have shown the successful role of stem cell therapies in the treatment of precancerous conditions, oral ulcers, wounds and mucositis.[3] The recent concept of cancer stem cells (CSCs) has directed scientific communities toward a new area of research and possible potential treatment modalities for oral cancer.[4] The present article will discuss the role of stem cell applications in oral mucosal lesions.

Basic Concepts of Stem Cells

Stem cells and it's types

Stem cells are the precursors of the body tissue. They are defined as immature or undifferentiated cells that are capable of generating daughter cells identical to themselves or of differentiating into diverse cellular phenotypes.[5] There are various types of stem cells. Embryonic stem cells, harvested from fertilized egg or blastocyst, have an extraordinary ability to form many cell types. Adult stem cell, found deep within organs and tissues, spread diffusely throughout and have restricted ability to proliferate. Induced pluripotent stem cells (iPSCs) are adult cells that have been genetically reprogrammed to an embryonic stem cell-like state by being forced to express genes and factors important for maintaining the defining properties of embryonic stem cells. They express stem cell markers also and are capable of generating cells characteristic of all three germ layers. iPSCs may prove to be useful tools for drug development and modeling of diseases and in transplantation medicine.[67]

The stem cells are also divided into totipotent stem cells (e.g., fertilized egg cell or zygote), that can generate all cell and tissue types present in an organism; Pluripotent stem cells (like embryonic stem cells) can generate the majority of cell and tissue types present in an organism; multipotent stem cells (like mesenchymal stem cells [MSC]) can generate a limited number of cell and tissue types, usually dependent on their germ layer of origin.[7]

Properties of stem cells

The main properties of stem cell, which make it different from any other specialized cells in the body are: Self-renewal, that is the ability to go through numerous cycles of cell division while maintaining their undifferentiated state; differentiation, that is the ability to differentiate into a specialized cell type and the ability to grow in vitro, in a laboratory, under a given environment.[7]

Extraction of stem cells

Stem cells can be derived from the following sources like embryonic stem cells sources and adult stem cells sources[78] [Figure 1]. The tissue samples containing stem cells are placed under specific conditions in laboratories/stem cell banks. The extraction of these stem cells is possible due to unique receptors like Oct4, TRA-1-60 (called as stem cell markers) present on the stem cell surface.[9] The extracted stem cells are grown on an appropriate scaffold made of biomaterials (like polyglycolic acid, polytetrafluoroethylene), fibrin sealant and certain growth factors, which act as temporary matrix during the regeneration of tissue.[1011]

Figure 1

Sources of stem cells

Applications of Stem Cell in Orofacial Region

Mesenchymal stem cells derived from dental and nondental sources have been effectively used for regeneration in maxillofacial region like regeneration of tooth, pulp, periodontal ligament, production of enamel and dentin, regeneration of salivary gland, repair of cleft lip and palate and craniofacial regeneration.[121314] However, the use of stem cell treatment for oral mucosal lesions is a new concept, which needs to be reviewed to promote the research further in the area.

Stem Cell Therapy in Oral Mucosal Lesions

Among oral mucosal lesions, stem cell research is presently focused on the treatment of certain lesions only. These oral mucosal lesions are:

Ulcerative lesions: Like oral ulcers and wounds, oral mucositis, pemphigus vulgaris

Premalignant disorders: Oral submucous fibrosis (OSMF), oral lichen planus (OLP)

Malignant lesions: Like oral carcinomas.

The main mechanism behind the use of stem cells in these lesions is discussed underneath.

Ulcerative lesions

Oral ulcers and wound healing

Optimum healing of a cutaneous wound requires a good integration of the complex biological and molecular events of cell migration and proliferation and extracellular matrix deposition, angiogenesis and remodeling. Large wounds take a long time to heal, and defective healing leaves behind unacceptable scars and strictures.

Bone marrow-derived MSCs (BM-MSCs) are self-renewing, expandable stem cells and are able to differentiate into adipocytes, osteoblasts, and chondrocytes. These cells possess the ability to engraft at the site of injury and promote tissue regeneration and wound healing through synergistic downregulation of proinflammatory cytokines and increased production of soluble factors with antioxidant, antiapoptotic, and proangiogenic properties.[15] In oral wounds, they exhibit increased re-epithelialization, cellularity, intracellular matrix formation and neoangiogenesis, thereby accelerate wound healing.[16] Hence, MSC therapy can be a promising therapeutic modality for oral ulcers and wounds [Figure 2].

Figure 2

Role of mesenchymal stem cells in wound healing

El-Menoufy et al. submucosally injected autologous BM-MSCs suspended in phosphate buffered saline around formocresol induced oral ulcers in dogs. There was increased expression of both collagen and VEGF (vascular endothelial growth factor) genes in MSCs-treated ulcers compared with controls.[17] Similar results were seen by Aziz Aly et al. in a study on formocresol induced oral ulcers in dogs using BM and adipose-derived stem cells. Hence concluded MSCs transplantation may help accelerate the healing of oral ulcers.[18]

Oral mucositis

Oral mucositis is one of the most debilitating side effects which occur with chemo or radiotherapy. Management of mucositis is fairly symptomatic as yet. Presently MSCs have been explored in its management by virtue of their immunomodulatory, antiinflammatory functions as well as regenerative properties. Their therapeutic efficacy can further be increased by transgenic approach or preconditioning them with certain factors like pro-inflammatory cytokines.[15]

Zhang et al. injected spheroid gingiva-derived mesenchymal stem cells (GMSCs) in mice with chemotherapy-induced oral mucositis and found that treatment with GMSCs decreased the severity and incidence of ulceration and restored the papillae structure, the lining, and thickness of the epithelial layer as compared with those of untreated disease group. The improved therapeutic benefits of spheroid-derived GMSCs may be attributed to their increased capabilities for engraftment and survival at the injury sites, trans-differentiation into epithelial cells, and preconditioning to hypoxic and oxidative challenges. Hence, GMSCs could prove a sure shot therapy in oral mucositis following the cancer therapies.[15]

Pemphigus vulgaris

Pemphigus vulgaris is a potentially life-threatening disease, primarily affects the mucous membranes of patients over the age of 50 years characterised by formation of autoantibodies, directed against desmosomal glycoproteins (dsg1, dsg3) present on the cell surface of the keratinocyte, resulting in the formation of intraepithelial bullae and mucosal ulceration.

The effective treatment of pemphigus vulgaris is long-term use of corticosteroids that itself has detrimental systemic complications.[19] The immunomodulatory and antiinflammatory properties of stem cells can be utilized in the treatment of the condition. In a research Vanikar et al.(2007) performed allogenic hematopoietic stem cell transplant (HSCT) with nonmyeloablative low-intensity conditioning in nine patients of Pemphigus vulgaris and found that the existing skin lesions started to regress within 24 h of stem cell treatment.[20]

In a similar study consisted of clinical trial on patients with pemphigus vulgaris to evaluate the effects of allogenic HSCT into thymus, BM and peripheral circulation on central and peripheral arms of self-tolerance; it was found that the recovery began within 24 h of HSCT and new lesions stopped after 6 months.[21] Stem cell therapy in pemphigus not only has shown promises in treatment but also brings about a shift towards nonsteroidal approach in autoimmune diseases. However, the use of stem cell therapy for oral pemphigus is yet to be ascertained and needs clinical trials [Figure 3].

Figure 3

Role of stem cells in pemphigus vulgaris by virtue of immunosuppressive properties

Premalignant disorders

Oral submucous fibrosis

Oral submucous fibrosis is a chronic, insidious disease associated with both significant morbidity (including pain, reduced oral opening) and an increased risk of malignancy. Various agents like Areca nut, gutkha, spices etc., are known to cause insult to oral mucosa by increasing cytokine production and release of reactive oxygen species; which in turn results in increased synthesis of collagen, decreased collagen breakdown, compromised vascularity and increased tissue oxidative stress, ultimately resulting in clinical OSMF.[22]

Various medicinal, as well as surgical treatment modalities, have been tried to intervene the disease process at different levels, but with limited success. Stem cell-based therapy is evolving as a promising new approach in this direction.

Stem cell therapy is primarily aimed at neoangiogenesis by releasing cytokines and growth factors (paracrine effect).

This may result in increased free radical scavenging by antioxidants (either naturally occurring or extraneous)

Neoangiogenesis may also facilitate the removal of senescent cells from the lesions by supplying more number of scavenging defense cells and reversal of hypoxia in the diseased tissue.

Stem cell therapy may help to stimulate resident tissue stem cells to transform into new fibroblasts, which may help in the removal of disintegrated biochemically and morphologically altered collagen fibers[2324] [Figure 4].

Figure 4

Role of stem cell therapy in oral submucous fibrosis at various levels. (a) Removal of pathologically altered collagen and stimulation of healthy collagen. (b) Promoting neoangiogenesis. (c) Promoting antioxidant action

Sankaranarayanan et al. have demonstrated the effectiveness of stem cell treatment in OSMF patients by injecting 0.5–1 ml of marrow-derived stem cell concentrate into labial and buccal mucosa and tongue under local anesthesia. They found reduction in blanching, improved suppleness of the mucosa, decrease in the burning sensation while consuming spicy food, significant increase in the mouth opening and the results were found to be sustained in the follow-up period from 6 months to 5 years.[24]

Oral lichen planus

Oral lichen planus is a chronic mucocutaneous disease with uncertain etiopathogenesis. Various factors like stress, genetics, systemic diseases, drugs, dental restorative materials and viruses are known to cause the disease either by an antigen-specific mechanisms like activating cytotoxic T-cells and nonspecific mechanisms like mast cell degranulation and matrix metalloproteinase activation. Both of these cause the disruption of the basement membrane, which in turn triggers apoptosis of basal epithelial cells.[2526]

Satisfactory therapy results are not, usually, achieved with conventional treatment (mainly consists of topical or systemic steroids). A new therapy employing T-cell immune modulation using MSCs have been proposed to treat OLP. MSCs can be easily isolated and expanded in vitro and in vivo and can be utilized via systemic infusion or local application to the lesion site. In addition to their regenerative capacities, culture-expanded MSCs possess the unique ability to modulate immune responses (both in vitro and in vivo) and may function as immunomodulators in the maintenance of peripheral tolerance, transplantation tolerance and autoimmunity. Making use of multiple pathways, MSCs suppress the function of a broad range of immune cells, including T-cells and B-cells[27] [Figure 5].

Figure 5

Action of stem cells in modulation of immune response in oral lichen planus (shown at points A and B)

Malignant lesions

Oral carcinomas

Surgery and external beam radiation has been the mainstay of treatment for head and neck squamous cell carcinomas. Despite the recent improvement in treatment modalities, the cancer recurrence and treatment failures continue to occur in a significant percentage of patients. Studies in a wide variety of malignancies have demonstrated that a distinct subpopulation of tumor cells, termed CSCs, contain the ability to undergo self-renewal and differentiation and hence have the ability to initiate tumorigenesis and support ongoing tumor growth.[2829]

Stem cells here play a dual role-in carcinogenesis and in the development of possible new cancer treatment options in future. For past so many years stem cells have been used in the replenishment of blood and immune system damage during treatment of cancer by chemotherapy or radiotherapy.[30]

Apart from their use in the immuno-reconstitution, the stem cells have been reported to contribute in the tissue regeneration as they have extraordinary capacity to regenerate and differentiate. The MSCs have been used in the cell-based bone reconstruction following chemotherapy and surgery in malignancies like osteosarcoma and Ewing sarcoma.[31]

Another important aspect of their use in cancer therapy is the use as delivery vehicles.[32] Systematic delivery of drug or gene therapy has promising future but is currently limited by various factors such as immune detection, nonspecific accumulation in normal tissues and poor permeation. Stem cells can act as cell-based carriers that may target the desired site. The recent concept of use of stem cells as delivery vehicles came from the fact that the tumors send out chemo-attractants such as VEGF to recruit MSC to form the supporting stroma of the tumor.[33] However, further work is required to understand the role of stem cells in cancer therapies, with the eventual goal of eliminating the residual disease and recurrence [Figure 6].

Figure 6

Role of stem cells in cancer therapy

To summarize, the pivotal role of stem cell therapy in oral mucosal lesions is primarily aimed at neoangiogenesis, tissue regeneration, increased cellularity, modulation of collagen gene expression and immunomodulation, thereby making it noninterventional and innovative treatment modality [Figure 7].

Figure 7

Summarization of biology of stem cells in oral mucosal lesions

Conclusion

Remedies in the medical field have always resulted from human inquisitiveness to know the nature and duplicate it. The conservative treatment of life-threatening and disfiguring defects and diseases is becoming the treatment of choice. The ability to treat currently incurable diseases has become a reality with the evolution of stem cell therapy. Though certain studies have confirmed the effectiveness of stem cell therapy in oral mucosal disorders like OSMF, for diseases like oral ulcers and mucositis, the research is mainly confined to animal models and more human research trials are needed to ascertain the role of stem cells in their management. There lies the need of extensive research by team of professionals including stem cell biologists, molecular biologists, geneticists, biomaterial scientists, mechanical engineers and clinicians with knowledge of oral and maxillofacial disorders to make stem cell therapy a promising tool in such conditions. The evolution of more methods of stem cell therapy in the future will give more simple, definitive and effective treatment of most of the oral mucosal diseases.