TRANSPLANTATION OF GOLD NANOPARTICLES WITH OR WITHOUT BONE MARROW STEM CELLS FOR REGENERATION OF SURGICALLY INDUCED TONGUE DEFECT IN RATS

The ultimate goal of tongue reconstruction is restoring the tongue integrity while preserve its critical functions(i.e., articulation, mastication, and deglutition) and minimize the morbidity profile of a selected reconstructive technique. Mesenchymal stem cells (MSCs) used in tissue engineering became a therapeutic selectiondue to numerous advantagesas regeneration of damaged tissues withhigh quality without the formation of fibrous tissue, minimal donor site morbidity in comparison withautografts and a low risk ofdisease transmition and autoimmune rejection. Bone marrow stem cells (BMSCs) areexpandable stem, self-renewing,embedded at the site of injury and motivate tissue regeneration and wound healing. In oral wounds, they revealgreater re-epithelialization, intracellular matrix formation,cellularity, and neoangiogenesis, thusspeed up wound healing.Gold nanoparticles (GNPs) application in medical fields is growingdue to the chemical and physical properties like biocompatibility, optical properties,facile surface modification and stability.GNP usage in regenerative medicine is safe if the implanted tissue is replacing a tissue/organresectedbecause of tumor.

The ultimate goal of tongue reconstruction is restoring the tongue integrity while preserve its critical functions(i.e., articulation, mastication, and deglutition) and minimize the morbidity profile of a selected reconstructive technique. Mesenchymal stem cells (MSCs) used in tissue engineering became a therapeutic selectiondue to numerous advantagesas regeneration of damaged tissues withhigh quality without the formation of fibrous tissue, minimal donor site morbidity in comparison withautografts and a low risk ofdisease transmition and autoimmune rejection. Bone marrow stem cells (BMSCs) areexpandable stem, self-renewing,embedded at the site of injury and motivate tissue regeneration and wound healing. In oral wounds, they revealgreater re-epithelialization, intracellular matrix formation,cellularity, and neoangiogenesis, thusspeed up wound healing.Gold nanoparticles (GNPs) application in medical fields is growingdue to the chemical and physical properties like biocompatibility, optical properties,facile surface modification and stability.GNP usage in regenerative medicine is safe if the implanted tissue is replacing a tissue/organresectedbecause of tumor.

…………………………………………………………………………………………………….... Introduction:-Tongue
Tongue is a movable organ inside the oral cavity with severalutilities, and it guides for underlying systemic diseases. It is a movable muscular structure contributes in the functions of speech and swallowing. It is responsible for mastication and turning over the food in the mouth propelling it inward (1) . The morphological structure of tongue and its papillae varyextensively in dissimilartypes of mammals due to the functional actions, surrounding environment effect, manipulation of food manner, swallowing, theanimal care, and animals'vocal modulations (2) .

Histology of tongue
The tonguesuperior surface is rough and irregular. A V-shaped line sulcus terminalis divides it into anterior part (body), and posterior part (base).The tongue is roofedwith a keratinized stratified squamous epithelium which is dense on the upper surface, while over the inferior surface issmooth and thin. The epithelium on lateral sides and upper surfaces of tongue display a largeamount of projecting papillae that covers epithelium and a centralcore of connective tissue. Papillae are lesssettled or absent on inferior surface (3) .

Tongue disorders
Tongue disorders are mostly seen in individuals wearing dentures and usetobacco. The greatestpublic tongue complaints are geographic tongue, thenhairy tongue and fissured tongue. Tongue overgrowths usually necessitatetissue removal and biopsied to differentiate benign tumorssuch as granular cell tumors, fibromas, lymphoepithelial cysts from premalignant leukoplakia or malignant tumors as squamous cell carcinoma (4) . Tongue may be injured by mechanical, thermal, electrical or chemical means (5) .Tongue is susceptible to numerous diseases such as glossitis and inflamatory diseases like geographic tongue, oral thrushand median rhomboid glossitis,black hairy tongue, oral hairy leukoplakia, fissured tongueand burning mouth syndrome. Numerous types of oral cancer mainly disturb the tongue. The most common is squamous cell carcinoma (6) .

Tongue regeneration
Defects in any living tissues are regained by a natural sequence of activities for healing done for repair or regeneration. Though, natural repair and regeneration can lose tolerability and regulation in case of large trauma or surgery, causing undesirable outcomes as fibrosis and aging. Restoringthe living tissueusingrenewable cells is named tissue regeneration technology (7) .
Several studies have been made in animals for tissue regenerationfor example;stem cellsand extracellular matrix scaffolds to improve the theory of oral tissue regeneration to applyclinically in dentistry, (8) .

Stem cells
Stem cells are undifferentiated cells that have the character of self-renewal. They have the possibility to progress into numerous cell linesvia differentiation.Different categories of stem cells are known, dependent on type of cells that it can generate and the position in body. Oral tissues are presented to be a source of stem cells (9) .
Tissue engineering using MSCs became a good selection for regeneration with numerousbenefits aselevated regeneration quality forimpaired tissues devoid of fibrous tissue formation, minimal donor site morbidity in comparison withautograftsthat demonstrate autoimmune rejection and disease transmition (10) .

Bone Marrow Stem Cells
Bone marrow stem cellshave the ability to self-renew, differentiate into adipocytes, osteoblasts, and chondrocytes in expandable stem cells. They are able tobe embedded at the injury site and enhance tissue regeneration and healing of woundsdue to synergistic downregulation of proinflammatory cytokines and improved production of soluble factors with antiapoptotic, proangiogenic, and antioxidant properties. In oral wounds, they displaygreater reepithelialization, cellularity, intracellular matrix formation and neoangiogenesis, sospeed up wound healing (11) . Nanotechnology A nanoparticle or ultrafine particle is known as a particle of matter that is between 1 to 100 nanometres diameter. In nanotechnology, a particle is known as a minorbodywhich acts as anentireelementtaking in consideration its transport and properties (12) . Nanotechnology is used recently in different fields as electrical, optical, and magnetic fields as well as structural performance at the molecular and sub molecular level. Their features of being safe, cheap, easily carried and administrated, give them the capabilityofremodeling a range of medical and biotechnology applications (13) . Restoration of tissue function and defect site by tissue engineering include implantation of biomaterial scaffolds that are porous, biodegradable and implanted with adequate amount of normal cells (14) .

Gold nanoparticles (GNPs)
Gold nanoparticles are studied nowadays for applicationclinically innanomedicine. In spite ofgreat number ofresearches done in cancer therapyapplyingGNP; their application in regenerative medicine and tissue engineering is stillprogressing.When comparing GNP with other nanoparticles, GNPs' properties ascolloidal stability, little toxicity, and physicochemical propertiesleaded to making them appropriate multifunctional forphototherapy,drug delivery, cell imaging and diagnosis purposes. Moreoverresearchesstudying GNPs capability to enhance stem cell differentiation for bone tissue engineering, to increase the mechanical and adhesive characters of scaffolds and surface topography guiding cell behaviors are required (15) .  (17) in vivo Animal rat model To study the therapeutic benefits of GMSCs on chemotherapy-induced oral mucositistobe embeddedat site of injuryand survival.
Seedingof GMSCs reduced the aggressiveness and prevalence of ulceration and repaired papillae configuration, and epithelial layerthickness. Qilin et al 2017 (18) In vivo Animal rat model Fakhr et al 2017 (19) In vivo Animal rat model to evaluate the effect of SC versus simvastatin on the mucous membrane and salivary glands of the tongue of rats with streptozotocininduced DM Tongue of rats treated with SC showed almost normal histology This indicates that bone marrow-derived SC are responsible for repairing the tissues and replacing them when injured or exposed to tear, wear or diseases. Zhang et al 2019 (20) In vivo Animal rat model To evaluate the effect of combined seeding of small intestinal submucosaextracellular matrix (SIS-ECM) with gingival mesenchymal stem cells (GMSCs) in a critically dimensioned tongue defect model.
Tongue lingual papillae treated with SIS-ECM \GMSCs retrieval and taste bud restoration by increasing release of CK14, CK8, and markers for taste bud cells. This also raises BDNF expression; a growth factor with asignificanteffecton the proliferation and differentiation of basal progenitor cells into taste bud cells.

Study design Aim Result
Heo et al 2014 (21) in vitro and in vivo  (23) In vivo Animal rat model To estimate the power of using bioactive glass (BG) and BG-GNPs composites on skin wound regeneration in investigational rats for 14 days.

18%
BG-GNPs-Vaseline ointment is a favorableapplicant for wound healing submissions with strong vascular proliferation and complete wound regeneration El-Halwagy et al 2020 (24) In vivo Animal rat model To evaluate the potential impacts of gold nanoparticles on the mucous membrane of the albino rats' tongues Exposure to gold nanoparticles solution caused atrophic and degenerative changes of both the dorsal and ventral surfaces of the tongue. A recovery period of one-month can lead to regeneration and improvement in the histological picture.

Study design Aim Result
Changqing et al 2010 (25) In vitro To investigate the cellular effects of GNPson the mesenchymal stem cells differentiation(MSCs) and the relatedcellular mechanisms.
GNPs are adopted by MSCs causing increase in their migration rateto osteoblast cells over adipocyte cells throughencouragingosteogenic transcriptional outline. Volkova N et al 2017 (26) In vivo Animal rat model To study the effect of different concentrations of 15nm gold nanoparticles on features of mesenchymal stem cells.
It was established that GNPs with concentrations of 1.5-6 g/ml are nontoxic for MSCs, whereasincreasingto 9 g/ml is toxic, demonstrated by the decreased synthesis of collagen 1135 type I and adipogenic differentiation.

Conclusions:-
GNP is a promising candidate for tongue defect regeneration. BMSCs therapy is considered as a promising choice for regeneration of tongue defect. We suggest that GNPs enhance stem cell therapy therefore; combinationof BMSc andGNP is of great interest and importance for tongue repair.