In recent years, suppliers have introduced plant cell ingredients to the skin and hair care markets, termed plant stem cells, extracts or derivatives. This is, in part, due to the popularity of stem cells in the medical field, which have been used to regenerate tissues including the skin. Therefore, to contribute to skin healing, a wave of excitement and expectation has motivated marketing and R&D departments to look back at plant cell technology as a way to bring stem cell-associated claims to personal care. While plant stem cells initially were marketed for their technological potential, they recently have been identified as an alternative, sustainable mean to produce nature-derived extracts and molecules.
While this technology was initially marketed as “plant stem cell technology,” some scientists consider this terminology confusing and not appropriate since cells derived from callus are not all stem cells but rather a mixture of stem, de-differentiated and partially differentiated cells. It is also clear that differences exist between human and plant stem cells themselves, as well as their final application and scope in dermatology.
Plant cell cultures have mostly been investigated for the commercial synthesis of high-value, secondary low molecular weight metabolites. Such molecules are synthesized by plants in response to environmental pressure and are essential for survival and adaptation. Attempts to cultivate plant cells began in the early 20th century, but it was not until between the 1940s and 1960s that the technology was optimized, including its industrial scale-up.
Plant cells derived from plant tissues are cultivated under defined physical and chemical conditions in vitro. These conditions are different for each type of plant and tissue, and must be optimized on a case-by-case basis. Explants from leaves, meristems, roots and stems are sterilized and plated in solid growth media with the growth factors and nutrients needed by that species. Explants then proliferate into a callus of non-differentiated cells that also contains stem cells. During this step, the most proliferative explants, i.e., the less differentiated explants, are selected.
Once callus is formed, it can be initially evaluated and screened for specific product/s of interest. Callus can then be transferred in liquid medium to grow a suspension culture. This culture can be collected, filtered, extracted and finally lyophilized in a powder rich in metabolites that will go to further analysis and validation for quality and quantity.
Produced from primary metabolites such as amino acids, lipids and carbohydrates, secondary metabolites are involved in the plant’s defense mechanisms against herbivores and pathogens. These metabolites often contribute to the plant color, taste and odor, but they do not directly affect the plant’s growth and development. Chemically, they are active molecules such as alkaloids, sterols, phenolic compounds, etc., with essential physiological roles that often enter signaling pathways.