Stem cells are special cells in the body that provide a continuous source of new cells. Stem cells have two unique features: they are unspecialized which retains the ability of self-renewal by cell division, almost without limit. They also have the ability to become specific cells of a particular tissue or organ. For example, in the intestine, they constantly replace worn out cells that line the intestinal surface.
There are many types of stem cells but the two basic kinds of stem cells are called embryonic stem cells and somatic stem cells.
The embryonic stem cells are more primitive, in that they have a greater capability of dividing into many different kinds of cells. At a certain stage the embryo will undergo a change in which three fundamental tissues are formed. These tissues are known as ectoderm, endoderm and mesoderm. It is by selective and specific differentiation that these three tissues will form all the organs and tissues of the body. The ectoderm for example will form the hair, the skin, the teeth, and the nervous system, including the brain. Let us follow one of these cells as it selects a career pathway and goes through the various stages. For example, an ectodermal stem cell decides that he wants to be a skin cell. First, he will divide into two separate cells; let us call them A and B. Cell A will remain an active ectodermal stem cell with full capabilities to become any number of other types of cells, while Cell B is now irreversibly programmed to become a skin cell. At first it starts out as a keratinocytoblast in the skin and resides forever in the bottom layer, also called the basal layer; for short we call the keratinocytoblast a basal cell.
Cell B will now continue to differentiate, that is, make the necessary internal changes physically and chemically to eventually become a stratum corneum cell. Once the cell starts to differentiate, it can no longer stop the process until it has finally achieved the end stage, that is, a cornified cell.
Endodermal cells can select from a variety of pathways but they are limited to the gastrointestinal tract and all its associated organs. The mesodermal cells are the lucky guys. They can choose to become a variety of cells ranging from bone to blood, they can stay put in one place or they can choose to wander about the body forever. For instance, a mesodermal cell that chooses the pathway to be a blood cell has six different roadways to follow. First it must decide to be a red cell, or a white blood cell. Now there is just one roadway for becoming a red cell but five roadways for becoming a white cell. It can become a neutrophile, a basophile, an eosinophile, a monocyte or a lymphocyte. Whatever road, or pathway, it chooses it must first irreversibly become a limited stem cell and is forever destined to travel that road. One of the characteristics of stem cells is that the original stem cell stays the same after the first division on the pathway to differentiate, while the daughter cell will lose this ability and continue to progress to an end cell, that is, a fully differential adult cell.
These early embryonic stem cell are called totipotential cells, that is, they can become any type of cell, but after they change into mesoderm, ectoderm or endoderm they are called pluripotential cells since they have partially differentiated. Certain adult cells, known as somatic cells, retain the ability to be altered and reprogrammed to become stem cells. Scientists are just beginning to work with these cells and they are proving to be a source of possible use in medical therapeutics. One application of stem cells is to replace worn out, damaged or nonviable body cells.
Embryonic and Adult Stem Cells
Human embryonic and adult stem cells share certain characteristics that allow them to be used in cell therapy, but there are certain distinct differences between the two groups of cells. One major difference between adult and embryonic stem cells is that the adult stem cells are limited both in the type of cell they can produce as well as the number of cells they can produce; generally they are limited to replacing cells of their tissue of origin. Embryonic stem cells, on the other hand, can differentiate into all cell types of the body because they are totipotent. While embryonic stem cells can be grown relatively easily in large numbers, adult stem cells are not plentiful, are often difficult to separate from normal tissue and generally cannot be produced in large numbers. Review work is being done in this area but scientists have many problems remaining to be solved. Scientists believe that tissues derived from embryonic and adult stem cells may differ in the likelihood of being rejected after transplantation. We do not yet know whether tissues derived from embryonic stem cells would cause transplant rejection, since the first phase 1 clinical trials testing the safety of cells derived from human embryos have only recently been approved by the United States Food and Drug Administration (FDA).
One major advantage of adult stem cells is their ability to resist tissue rejection. It appears that adult stem cells are less likely to be rejected when implanted in a person, since in most cases the adult stem cells will be derived from the patient who is to receive them. This represents a big deal, since immune rejection has to be overcome in cases of tissue transplant by the continuous administration of immunosuppressive drugs. These are nasty types of drugs that have some extremely unpleasant side effects. Any system that could get around immune rejection would be a tremendous boost to therapeutic medicine.
Some Uses of Human Stem Cells
Human stem cell research is opening many avenues of investigation. One area upon which they are shedding light is how undifferentiated stem cells become the differentiated cells and thus able to form tissues and organs. We know that much of cellular control depends on turning on specific genes, then turning them off after they do their job. Unfortunately, in the case of cancer, the normal mechanism has gotten out of control. A better understanding of the genetic and molecular controls of these processes would help us to understand the disease process as well as help us to develop the necessary therapeutic measures to control the disease. Just being able to control cell proliferation and differentiation requires a tremendous amount of biological know-how; complete knowledge in this area would be an enormous advance to science.
Cancer remains one of the largest areas of interest to scientists because it is not only a terrible disease, in many cases it is also baffling for the major defect strikes at the very heart of biological control of growth and differentiation. Tissue and organ replacement is also a major goal of stem cell research. Imagine how wonderful it would be able to grow a human heart from the patient’s own cells with no fear of organ rejection! Donated organs and tissues are the only sources today to be able to replace damaged tissue or organs.
Within his book, Advanced Professional Skin Care, Medical Edition, Peter T. Pugliese, M.D., provides aestheticians with a complete diagrammatic explanation of the structures, processes and terms of cell biology. Regarding stem cell therapy, Dr. Pugliese says, “So far our ability to build artificial organs has been pretty puny, perhaps a better word is crude. We must give credit to the scientists working in this field but we have a long way to go. If ever there was a field ripe for harvest, tissue replacement is one of them. The neurological diseases alone such as Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), and stroke claim a suitable number of tragic cases every year. Add to this heart disease, the inflammatory tissue diseases such as rheumatoid and osteoarthritis, the many tragic burn victims, and those unfortunate trauma victims who lose organs and limbs. We pray that God may inspire scientists working in this area to enable them to find the keys that will unlock this awesome mystery.”
Stem Cells and Skin Care
So what does all this mean for the aesthetician faced with a plethora of new products claiming to improve the skin? How to differentiate between the hype and what can really help? Begin by understanding that the focus for topical use is far away from the media controversy over using human stem cells to treat debilitating degenerative disease. That is not our expertise, nor is it our fight. The emerging cosmetic use focuses on plant stem cells. So let us explore the differences between these sources.
Plant stem cells are unlike many adult animal stem cells in that they are totipotent, meaning they can give rise to any plant tissue. They are also plentiful, located in apical meristems of roots and shoots (buds for example). In further contrast to animal cells, any somatic plant cell can revert from its differentiated state to become a totipotent stem cell. Thus, in order to harvest stem cells, companies that produce stem cells will often wound a plant so that some of its cells around the wound will revert to stem cells. Once harvested, plant stem cell tissue is grown in culture to produce large quantities for industrial demand, a process which proves to be both a renewable and eco-friendly resource. To prepare stem cell cultures for use in a product, the cultures are either dried down to a powder or extracted. In either case, the live stem cell itself is destroyed. When cultures are dried to a powder, stem cells break apart in the process. Instead of drying, stem cells may also be extracted for their important components (much like making a juice or pressing olives for their oil) and in this case extracts are also usually dried a little and then resuspended in solvents such as glycerin. Any claim or implication that a product contains live stem cells is utterly false.
Perhaps as protection during or as a result of their rapid division, stem cells are rich in potent antioxidants providing great advantages to human skin. Each species of stem cell will also produce its own special profile of secondary metabolites, meaning molecules that are not needed for the cell’s growth and reproduction. Secondary metabolites often coevolved with a plant’s environment to deter predators or attract other organisms for mutual benefit. Regardless, it is the secondary metabolites that are often of benefit to human skin, activating protective pathways in human cells or stimulating growth and division. Grape stem cells provide an excellent example of these actions; they produce a profile of metabolites that are photo-protective for the human skin and delay cellular senescence. Many secondary metabolites also act as anti-fungal or anti-bacterial compounds that provide further protection for the skin. For example, lilac and Marrubium vulgare contain verbascoside, a compound known for its antimicrobial activity and anti-inflammatory activity.
The most well know stem cells are currently derived from the Swiss apple and edelweiss, with information readily available. Some of the lesser known stem cells with interesting secondary metabolite profiles are derived from Marrubium vulgare, gardenia and Centella asiatica. For example, Marrubium vulgare is not only rich in antioxidants and verbascoside, it also contains Forsythoside B, which among its other metabolites, activates protective and detoxification processes in human cells, thus preparing the skin for future attacks from environmental aggressors. Gardenia stem cells produce effective antioxidants, including feruloyl-6-glucoside. Finally, Centella asiatica extracts contain caffeoylquinic acid derivatives and other metabolites that provide firming and restructuring actions as well as antioxidant activity. To decide on the right stem cell for a product, the formulator should do their own research into each stem cell’s secondary metabolite profiles and choose the best for the intended effect. Stem cells can be incorporated into serums, creams or lotions and are best added at cold stages to ensure the stability of all secondary metabolites.
As with any exciting new ingredient category, myth and misinformation from marketers surrounds the use of stem cells in skin care. The goal of this profession is to utilize scientific validity in the selection and use of stem cells in functional, elegant skin care formulation, and to educate clients with realistic expectations in using stem cell-containing products.
Michael Q. Pugliese, BS, L.E. became the third-generation CEO of Circadia by Dr. Pugliese, Inc. in 2006. Under Michael’s leadership, the Circadia brand has grown to achieve international recognition and distribution. He is a licensed aesthetician, a member of the Society of Cosmetic Chemists, and regularly attends their education events to stay on the cutting edge of new product development. Michael’s compelling original lectures honor the tenets of modern skin science discovered by his grandfather, and add today’s application of that information in an ever-changing business and scientific environment.