Sibel Yildirim

Isolation Methods of Dental Pulp Stem Cells

Easy and quick isolation of the most primitive stem cell populations from available tissues is warranted for tissue engineering. The most reliable cell source for dental tissue engineering is that of autologous pulp stem/progenitor cells isolated from deciduous or primary teeth. The ease of isolation and high expansion potential in vitro has made them very attractive as a model system for many researchers.

Characterization of DPSC

Both SHED and DPSC have characteristic indistinguishable fibroblastic characteristics (Fig 6.1). They preserve plasticity during at least 25 passages, while maintaining the normal karyotype and the rate of expansion characteristic of stem cells (Kerkis et al. 2006).

Dental Pulp Is a Connective Tissue

Although dental pulp has been classified as a loose connective tissue, several unique properties such as the presence of odontoblasts, absence of histamine-releasing mast cells, tissue confinement in a hard cavity with little collateral circulation, and vascular access limited to the root apex are the features that distinguish pulp tissue from other connective tissues (Dummett and Kopel 2002).

Dental Pulp Is a Complex Adaptive System

The damaged or lost structure of teeth caused by caries or trauma can be treated clinically by replacement with an artificial material (fillings) and the outcome is usually satisfactory. Yet, tooth loss is the most common organ failure. The complex biological structure of the tooth organ including the enamel, dentin, cementum, and pulp create obstacles for any ambitious dream of the substitution of artificial material with a bio-tooth. Although the focus of the most regenerative studies is toward achieving a means to repeat evolutionary signals secondarily and initiate development secondarily, lack of understanding of the nature and interactions of tooth creating cells blocks this goal. Efforts to discover possible lineage-specific propensities within one group of cells are progressing more favourably. Although stem cells have been taken out of the body and manipulated ex vivo, there are many steps for successful cell-based therapies due to committed cells being unable to orchestrate the regeneration of complex tooth structures (Yildirim et al. 2011a).

Dental Pulp Stem Cells (DPSC)

Stem cell technology is developing at a rapid pace. Every piece of seemingly unrelated, floating data is being conglomerated to broaden current knowledge and move closer to the inevitable shift in paradigms of current fundamental cell biology systems. The question of what a stem cell actually is may no longer require further discussion; however, there are still some differences in opinion between groups in terms of their functional roles.

Immunomodulatory Effects of DPSC

In addition to regenerative properties, the immunoregulatory properties of MSC have been demonstrated both in vivo and in vitro. Because of the low expression of MHC class II and co-stimulatory molecules, they are immunoprivileged cells. MSC can modulate the function of immune cells with different pathways of the immune response by means of direct cell-to-cell interactions and soluble factor secretions. They display immunosuppressive effects in a number of situations. In vitro, MSC inhibit cell proliferation of T cells, B-cells, natural killer cells, and dendritic cells. The immunomodulatory effect of MSC is mediated by a nonspecific anti-proliferative action of these cells, and it is dependent on cell-to-cell contact or secreted soluble factors such as indoleamine 2,3-dioxygenase (IDO), prostaglandin E2, nitric oxide (NO), HLA-G, transforming growth factor (TGF)-β, interferon (IFN)-γ, and interleukin (IL)-1β (Nasef et al. 2008; Shi et al. 2011; De Miguel et al. 2012).

Reprogramming of DPSC to Induced Pluripotent Stem Cells

Generating a pluripotent cell in vitro by rewinding the internal clock of any somatic cell to an embryonic state and then forwarding its conversion into the desired differentiated cell fate represents a rational and ongoing approach in regenerative medicine (Yildirim 2012). There are available human tissues with no ethical or surgical concern, such as fat, blood, biopsy specimens, skin, plugged hair, and extracted teeth (Aasen et al. 2008; Sun et al. 2009; Ye et al. 2009; Yan et al. 2010).

Determination of fluoride levels after brewing in three Turkish black tea products

The aim of this study was to determine the fluoride levels at two different brewing times of 15 samples with different production dates belonging to each of the three different tea products, which were grown and served as commercial products in Turkey. In this study, 15 samples of each tea products (Filiz Çay, Rize Turist Çayı, Doğuş Karadeniz Lüks Rize Çayı) with different production dates were steeped with double-distilled de-ionized water (1% m/V) at two different brewing times (5-10 min). The fluoride levels of all samples were measured with combined fluoride electrode. The average fluoride value after five minutes of brewing was found as 1.66 ppm in the Rize Turist Çayı group, 1.69 ppm in the Doğuş Karadeniz Lüks Rize Çayı group, and 1.38 ppm in the Filiz Çay group. The average fluoride value after ten minutes of brewing of the Rize Turist Çayı group was 1.87 ppm. Doğuş Karadeniz Lüks Rize Çayı group was 1.88 ppm, and the Filiz Çay group was 1.53 ppm. While there were no statistical differences between Rize Turist Çayı and Doğuş Karadeniz Lüks Rize Çayı, the fluoride level of Filiz Çayı was found lower than the other products. Fluoride levels of tea samples suggested that tea consumption is an important source on daily fluoride intake.

New Treatment Modalities by Disease-Specific and Patient-Specific Induced Pluripotent Stem Cells

The broadly accepted and deeply rooted belief in developmental biology was that terminally differentiated cells had lost the potential to produce other cell types. In 2006, however, mouse somatic cells were reprogrammed as induced pluripotent stem (iPS) cells that resembled embryonic stem cells. This therapeutic promise is being challenged by thousand of researchers worldwide to understand the ability of these cells to reverse biological clocks. Utilizing both “forward” and “reverse” genetic approaches with the aid of iPS cells offers exciting prospects for dissecting molecular mechanisms of commitment and differentiation in a cell lineage. This discovery will help clarify our understanding of the rewired regulatory networks active in somatic and pluripotent cells.

Induced Pluripotent Stem Cells (iPSCs)

Takahashi and Yamanaka showed that overexpression of defined transcription factors can also convert cells (or nuclei) to pluripotent state. The idea was the factors that maintain pluripotency in ESCs might induce pluripotency in somatic cells. They tested 24 transcription factors on the basis of their important roles in mESCs. They introduced combinations of those genes into mouse fibroblasts through retroviral transduction. The cells were carrying an antibiotic-resistance gene that would only be expressed when F-box protein 15 gene (Fboxo15) was turned on. They designed this experiment so that this antibiotic-resistance gene could also be turned on if pluripotency was induced by the combination of 24 candidate genes. Surprisingly they found that only four of these factors were sufficient to generate ESC-like colonies. The combination of genes was octamer 3/4 (Oct4, also known as Pou5f1), SRY box–containing gene 2 (Sox2), Kruppel-like factor 4 (Klf4) and c-Myc (later called OKSM). These reprogrammed cells were called as induced pluripotent stem cells (iPSCs).