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Platelets and Exosomes

By June 21, 2024October 23rd, 2024No Comments

Platelets, also called thrombocytes, are disc-shaped components of blood and, moreover, play an essential role in many physiological processes. They do not have a nucleus and therefore cannot reproduce themselves, yet they exhibit active RNA metabolism during their 7-day life span.

Platelets, in fact, are derived from megakaryocytes in the bone marrow. The primary function of platelets is hemostasis; however, they also contain and transport molecules involved in numerous regenerative processes. These processes include wound healing, cell activation and proliferation, angiogenesis, immune cell recruitment and inflammation, bone regeneration and cartilage repair.

Once activated, platelets secrete large amounts of growth factors, cytokines, and bioactive proteins that contribute to and support the tissue repair process.

The highest amount of growth factors is the following:

  • Platelet derived growth factor
  • Transforming growth factor
  • Epidermal growth factor
  • Insulin like growth factor
  • Fibroblast growth factor
  • Vascular endothelial growth factor

The alpha granules of platelets contain these growth factors, which are released upon activation and, consequently, stimulate cell proliferation, migration, chemotaxis, differentiation, and angiogenesis. They also promote the formation of the extracellular matrix.

Introduction to Extracellular Vesicles (EVs) in Platelet-Rich Plasma (PRP)

Besides the growth factors, these blood products contain a heterogenous group of cell membrane derived vesicles. We call these extracellular vesicles, and they may be the main contributors to PRP’s effects .These blood derived extracellular vesicles in the plasma may originate from different cell types such as leukocytes, erythrocytes, dendritic cells, platelets, mast cells, epithelial cells and endothelial cells. Most originate from the megakaryocytes in the bone marrow and thought to originate from platelet precursor cells. The extracellular vesicles are classified as to their size. The larger are the extracellular vesicles and the smaller are the exosomes. However, both classes are called EV’s.

Biological Function of EVs: A Molecular Cargo

EV’s, including exosomes and micro-vesicles, sometimes called microparticles or ectosomes exist in almost all biological fluids carrying molecules such as proteins, lipids, and RNA either on their surface or within the lumen. They are generated and released from nearly all cell types into the extracellular space. The biomolecules carried by EV’s are reflective of the cell of origin.

Historical Discovery of Platelet-Derived EVs

These EVs were observed in 1967 for the first time by Wolf et al and he named them “platelet dust”. Recent studies shows that platelet derived-EVs act as a cargo of several molecules including signaling molecules, growth factors, lipids, proteins., nucleic acids (mRNA) which mediate cell to cell communication, immune reaction, inflammatory response, and reparation.

PRP: A Powerful Therapeutic Tool

Platelet-Rich Plasma (PRP) refers to a concentrated solution of autologous human platelets that exceeds normal physiological levels in a small volume of plasma. Numerous studies demonstrate the effectiveness of PRP in treating conditions such as musculoskeletal injuries and degenerative joint disorders, without significant side effects.

The Role of Extracellular Vesicles in PRP’s Mechanism of Action

Although PRP has been extensively studied, the precise mechanism behind its therapeutic action remains under debate. It is possible that EVs play a pivotal role in directing the effects of PRP.

Activation of PRP: A Critical Step

Activation is a critical step in the action of PRP. This can be accomplished by tissue damage at the site or by extraneous means, but inactivated PRP does not achieve the same regeneration as activated PRP.

After activation, the outer membrane of macrovesicles is penetrated, and platelets release bioproteins, cytokines, and growth factors through extracellular secretion. The dynamic content of platelet-EVs including proteins from the platelet membrane, cytosol, organelles, adhesion receptors, coagulation factors, transcription factors, growth factors, active enzymes, cytokines, chemokines and their receptors is mainly dependent on the mechanism of platelet activation, the agonist used and the time of stimulation.

Different modes of platelet activation may lead to the heterogeneous PL-EV populations with different surface marker expression and protein profiles. This can affect their role in intercellular communication. Studies have proven that EVs from activated platelets by ADP contain different protein cargo in comparison to those activated by collagen or thrombin. This certainly implies that EVs can have different functions based on the mode of activation.

Isolation of Platelet Derived Exosomes

There is no standard method to isolate PRP-EVs and there is no single detection technique with high sensitivity to detect EVs from platelets. It is often impossible to compare results of studies as various isolation methods produce EVs with different yields and purities. The isolation process of EVs from plasma is complicated because the plasma contains other non EVs with similar size and densities and can contaminate the sample.

The typical protocol to obtain EVs from platelets involved centrifugation, separation of the PRP, activation and a second centrifugation. These steps are unwieldy, and the platelets can be prematurely activated to release the exosomes. The blood collection process, the handling, timing, choice of anti-coagulant, storage are all variables causing inaccurate results in treatment and outcomes.

It is well known that EV’s are present in a wide range of body fluids including blood, urine, saliva, CSF, amniotic fluid, breast milk and ascites.

Do Platelet Derived Exosomes Regenerate?

PL-EVs may play a duel role in inflammation stimulating either pro or anti- inflammatory effects depending on the expression of surface markers or microenvironment. Data has shown that

EV’s exert strong immunomodulatory activity on smooth muscle cells and stimulates vascular remodeling.

Platelet-EV’s induce angiogenesis both in vitro and in vivo. This is important to revascularization of the ischemic myocardium.

Platelet -EV’s may be utilized for treatment following brain injury according to results describing their positive role In neuronal cell proliferation, survival and differentiation to form glia cells and neurons.

In a diabetic rat model, encapsulated PL-EV’s increased re-epithelialization and collagen synthesis which led to faster wound healing and closure compared to untreated wounds.

In an osteoarthritic model, it was demonstrated that PL-EVs had a better effect in promoting chondrocyte proliferation and migration and attenuating apoptosis than PRP alone in vivo and in vitro rat model.

PL-EV’s positively modulate the growth, migration and differentiation potential of stem cells from different sources. This enhanced potency of stem cell populations resident in tissues is important in treating and preventing degenerative diseases.

PRP is known to accelerate tissue repair and regeneration, but its underlying mechanism remains unclear. Clinical research is encouraging, suggesting that PL-EVs may be key to the mechanism behind PRP-induced tissue regeneration.

Platelet Rich Plasma and Exosomes

To date, studies have shown the great potential of PRP-EV’s in the field of tissue repair and regeneration. Recent findings suggest that PRP-EV’s may be a superior alternative in regenerative medicine when compared to PRP alone. PRP-EV’s may have more significant advantages over PRP in regenerative medicine for the following reasons:

  • Some studies have demonstrated a higher concentration of growth factors.
  • The smaller size is beneficial for the transfer across biological barriers.
  • Lower immunogenicity
  • Provide a more sufficient protection from loaded cargo due to the phospholipid layer.
  • Contain abundant information molecules such as proteins, lipids and RNA for intercellular communication.

Many barriers exist in the manufacturing process, along with technical challenges in forming and harvesting platelet-rich plasma extracellular vesicles. Nonetheless, the therapeutic applications and clinical outcomes to date, exemplifies that PRP-EV’s may be the regenerative treatment of the future.

What is the Best Regenerative Product Currently?

The literature clearly documents the advantage of Platelet Rich Plasma. There are currently 20,000 articles or studies on the PubMed website concerning the applications and merits of

PRP. However, this article has outlined the advantages of extracellular vesicles in regenerative medicine.

Exosomes sourced from mesenchymal stem cells offers a superior regenerative product. Exosomes from this natural source contain proteins, messenger RNA, and other bioactive molecules that enhance regenerative capabilities when combined with PRP.

Increasing studies reveal that platelets and exosomes activate intracellular signaling pathways, alter vascular reactivity, and induce angiogenesis. This can restore endothelial integrity after vascular injury and trigger neurogenesis in a stroke model.

Torreggiani et al demonstrated that bone marrow stromal cells treated with the PRP-exosome combination showed a significant increase in cell proliferation, migration and osteogenesis. Torreggiani implied that the combination might be one of the effectors of the actions of PRP.

Although exosomes derived from platelets are difficult and costly to extract and concentrate, the exosomes from mesenchymal stem cells are just the opposite. Manufacturers readily obtain them, and they have virtually perfected the process of production and concentration. These products have shown superior regenerative capabilities.

Exosomes from PRP may offer a superior product for regenerative medicine, but until they are reliably sourced in guaranteed concentrations at a reasonable cost, mesenchymal stem cells remain the best source for exosomes.

Consider the combination of PRP and Exosomes extracted from mesenchymal stem cells as the ultimate treatment in regenerative therapy today.

Studies

Why Juventix?

Juventix Regenerative Medical is an industry leader in the regenerative medical field. Our Platelet Rich Plasma Kits are FDA cleared and designed for safety, sterility and effectiveness. Our kits are scientifically manufactured to provide a platelet concentrate, devoid of red blood cells with a minimum number of leukocytes that are critical to the regenerative process.

Juventix Regenerative Medical offers a LED Activator to activate the platelets and begin the regenerative process. The activation is a critical step in the release of cytokines, growth factors and bioactive proteins from the alpha granules on the platelets and is accomplished with LED light. This negates the use of chemical additives such as Calcium Chloride, Thrombin or Collagen. This mode of activation by LED light provides sustained growth factor release versus older methods of activation while adhering to the minimal manipulation guidelines of the FDA.

Juventix Regenerative Medical supplies a bio-incubator to transform the Platelet Rich Plasma into an Injectable Platelet Rich Fibrin. The Platelet Rich Fibrin, commonly called the “second generation of platelet products” has different cytokines and growth factors than the original PRP. These different cytokines provide an anti-inflammatory microenvironment and can be used confidently in inflammatory conditions.

Juventix Regenerative Medical is proud to collaborate with Evolutionary Biologics to offer exosomes and other related biologics. This collaboration together provides the ultimate regenerative treatments for the regenerative professional today.

RESTORE, REVIVE, REGENERATE- JUVENTIX REGENERATIVE MEDICAL

 

Regenerative Regards,

Dr. Robert McGrath

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