Platelets, also called thrombocytes, are cell fragments made in the bone marrow and found in circulating blood. They play a key role in blood clotting and wound healing. Recently, researchers have discovered that the contents of platelets released when they are broken down, known as human platelet lysate (HPL), support stem cell growth similar to fetal bovine serum (FBS). This has potential applications in cell therapy and regenerative medicine.
What is in Platelets?
Platelets contain over 300 proteins that are released when the platelets break open, or lyse. Some of the most important growth factors in platelets that support cell growth include platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-β), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), fibroblast growth factor (FGF), and insulin-like growth factor (IGF). These growth factors mimic the environment around injuries and promote processes like cell migration, proliferation, and differentiation that are important for wound healing.
Comparison to FBS
FBS has traditionally been used to supplement cell culture media. However, it carries some disadvantages like risk of contamination with pathogens, unwanted immune responses, and ethical concerns due to animal welfare issues involved in harvesting fetal calf serum. In contrast, Human Platelet Lysate is derived from blood already collected from consenting adult donors for transfusion purposes. It is therefore safer, more consistent in composition and abundance, and eliminates the controversy around use of fetal bovine serum.
Human Platelet Lysate Composition
The profile of growth factors and other proteins in HPL depends on how it is prepared from platelets. Typically platelets obtained from donated whole blood are activated to induce degranulation and release of contents. They are then lysed to break open the platelet membranes. The supernatant containing the released growth factors and proteins can then be collected after centrifugation. HPL preparations contain varying concentrations of growth factors depending on the exact protocol used for generating the platelet lysate. A standardized HPL concentration with optimal growth factor levels benefits cell culture and therapeutic applications.
Support of Stem Cell Growth and Differentiation
Several studies have shown that HPL effectively supports expansion and maintenance of adult stem cells from different sources like bone marrow, adipose tissue, dental pulp and umbilical cord without losing their stemness. HPL promotes proliferation of mesenchymal stem cells (MSCs) in a comparable or better manner than FBS. It also preserves their multilineage potential, allowing differentiation of MSCs into bones, cartilage, fat, and other connective tissues. This makes HPL a good xeno-free alternative to FBS for stem cell-based therapies.
Clinical Applications of Human Platelet Lysate
Given its ability to expand stem cells, HPL has potential applications in cell-based therapies and regenerative medicine. Some areas where HPL may be useful include:
- Bone regeneration: HPL expanded MSCs are being evaluated in clinical trials for applications like bone defects from trauma, surgery or osteonecrosis. Initial results indicate bone formation.
- Wound healing: Topical application of HPL or transplantation of HPL-cultured stem cells shows promise for hard-to-heal wounds, burns and ulcers.
- Cardiac repair: Preclinical studies reveal MSCs grown in HPL reduce scar size after myocardial infarction and improve heart function. Cardiac cell therapy trials are ongoing.
- Liver disease: Human platelet lysate supports growth of hepatic stem cells and bile duct stem cells, opening possibilities for cell therapy in conditions like liver failure.
- Neural regeneration: HPL may aid growth of neural stem/progenitor cells and Schwann cells for spinal cord injury, stroke and neurodegenerative disorders.
Challenges and Future Perspectives
While HPL appears safer than FBS, further standardization of production methods is needed to ensure consistency in growth factor levels. Large-scale production and validation for commercial and clinical use needs to be addressed. Long-term effects and immune responses after cellular implantation also require evaluation. With ongoing research, HPL shows promise as an xeno-free, clinically-compliant alternative to FBS for stem cell culture and applications in regenerative medicine. Its availability from routine blood donation could make cell-based therapies more cost-effective and scalable globally in future.
As an extract of human platelets, human platelet lysate mimics the natural environment for wound healing and stem cell regulation in the body. Preliminary research demonstrates HPL supports stem cell expansion comparable or superior to FBS without the risks of contamination or immunogenicity. With refinements in production and standardization, HPL holds potential as a safer replacement for FBS in cell culture and therapeutic applications like tissue engineering and regenerative medicine. It could unlock new possibilities for commercialization and greater access to stem cell therapies worldwide.
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