Hadi Alphonse Goubran

Blood-derived biomaterials and platelet growth factors in regenerative medicine

Several biomaterials can be obtained from human blood. Some are used for clinical indications requiring a high content in fibrinogen, while others are used because they contain multiple platelet growth factors. Mimicking thrombin-induced physiological events of coagulation leading to fibrino-formation and platelet activation, blood biomaterials have critical advantages of being devoid of tissue necrotic effects and of being biodegradable by body enzymes. Fibrin-based biomaterials, known as fibrin glues or fibrin sealants, have been used for more than 30 years as surgical hemostatic and sealing agents, demonstrating benefits in essentially all surgical fields, including reconstructive plastic surgery and wound treatment. Clinical interest in platelet growth factor-rich biomaterials (often known as platelet gels or platelet-rich-plasma) has emerged more recently. Platelet gels are used in clinical situations to achieve wound healing and repair soft and hard tissues. Applications include the healing of recalcitrant ulcers and burns, and stimulation of osseous tissue regeneration in dentistry, implantology, and maxillofacial and plastic surgery. They were evaluated recently in knee osteoarthritis and for the repair of musculoskeletal tissue lesions in sports medicine. Platelet lysates are now used as a substitute for fetal bovine serum and for ex vivo clinical-scale expansion of stem cells, opening new perspectives in regenerative medicine. We present the scientific rationale that prevailed in the development of blood biomaterials, describe their modes of production and biochemical and functional characteristics, and present clinical applications in regenerative medicine.

Platelet microparticles: detection and assessment of their paradoxical functional roles in disease and regenerative medicine.

There is increasing research on and clinical interest in the physiological role played by platelet microparticles (PMPs). PMPs are 0.1-1-μm fragments shed from plasma membranes of platelets that are undergoing activation, stress, or apoptosis. They have a phospholipid-based structure and express functional receptors from platelet membranes. As they are the most abundant microparticles in the blood and they express the procoagulant phosphatidylserine, PMPs likely complement, if not amplify, the functions of platelets in hemostasis, thrombosis, cancer, and inflammation, but also act as promoters of tissue regeneration. Their size and structure make them instrumental in platelet-cell communications as a delivery tool of platelet-borne bioactive molecules including growth factors, other signaling molecules and micro (mi)RNA. PMPs can therefore be a pathophysiological threat or benefit to the cellular environment when interacting with the blood vasculature. There is also increasing evidence that PMP generation is triggered during blood collection, separation into components, and storage, a phenomenon potentially leading to thrombotic and inflammatory side effects in transfused patients. Evaluating PMPs requires strict pre-analytical and analytical procedures to avoid artifactual generation and ensure accurate assessment of the number, size repartitioning, and functional properties. This review describes the physical and functional methods developed for analyzing and quantifying PMPs. It then presents the functional roles of PMPs as markers or triggers of diseases like thrombosis, atherosclerosis, and cancer, and discusses the possible detrimental immunological impact of their generation in blood components. Finally we review the potential function of PMPs in tissue regeneration and the prospects for their use in therapeutic strategies for human health.

Regulation of Tumor Growth and Metastasis: The Role of Tumor Microenvironment

The presence of abnormal cells with malignant potential or neoplastic characteristics is a relatively common phenomenon. The interaction of these abnormal cells with their microenvironment is essential for tumor development, protection from the body’s immune or defence mechanisms, later progression and the development of life-threatening or metastatic disease. The tumor microenvironment is a collective term that includes the tumor’s surrounding and supportive stroma, the different effectors of the immune system, blood platelets, hormones and other humoral factors. A better understanding of the interplay between the tumor cells and its microenvironment can provide efficient tools for cancer management, as well as better prevention, screening and risk assessment protocols.

The platelet-cancer loop

The relationship between cancer and thrombosis has been established since 1865 when Armand Trousseau described superficial thrombophlebitis as forewarning sign of occult visceral malignancy. Platelets are the primary hemostatic tool and play a primordial role in cancer-induced thrombosis. Tumor-induced numerical and functional platelet abnormalities have been described in conjunction to changes in coagulation. Such changes are reported even in the absence of clinically detectable thrombosis and correlate with tumor progression and metastasis. Reciprocally, platelets seem to interplay with the tumors and the immune system, both directly and indirectly favoring tumor progressions, tethering and distant spread. A number of growth factors supporting tumor growth, angiogenesis and metastasis are released from the platelets. A reciprocating loop of tumor-induced platelet activation/platelet-induced tumor growth and dissemination is initiated, acting as a thrombosis trigger/tumor amplifier. Recent studies have demonstrated that the use of anti-platelet agents can break this loop resulting in a reduction of short-term risk for incident cancer, cancer mortality and metastasis. The beneficial effect in reduction in cancer-induced thrombosis remains to be established. The current review aims at shedding the light on the intimate reciprocal cross-talk between platelets and cancer and on exploring the potential beneficial effect of anti-platelet agents in breaking the deadly loop of tumor amplification.

Platelets Effects on Tumor Growth

Unlike other blood cells, platelets are small anucleate structures derived from marrow megakaryocytes. Thought for almost a century to possess solely hemostatic potentials, platelets, however, play a much wider role in tissue regeneration and repair and interact intimately with tumor cells. On one hand, tumor cells induce platelet aggregation (TCIPA), known to act as the trigger of cancer-associated thrombosis. On the other hand, platelets recruited to the tumor microenvironment interact, directly, with tumor cells, favoring their proliferation, and, indirectly, through the release of a wide palette of growth factors, including angiogenic and mitogenic proteins. In addition, the role of platelets is not solely confined to the primary tumor site. Indeed, they escort tumor cells, helping their intravasation, vascular migration, arrest, and extravasation to the tissues to form distant metastasis. As expected, nonspecific or specific inhibition of platelets and their content represents an attractive novel approach in the fight against cancer. This review illustrates the role played by platelets at primary tumor sites and in the various stages of the metastatic process.

Platelet-cancer interactions.

Platelets play a crucial role in the pathophysiological processes of hemostasis and thrombosis. Increasing evidence indicates that they fulfill much broader roles in balancing health and disease. The presence of tumor cells affects platelets both numerically, through a wide variety of mediators and cytokines, or functionally through tumor cell-induced platelet activation, the first step toward cancer-induced thrombosis. This induction results from signaling events through the different platelet receptors, or may be cytokine-mediated. Reciprocally, upon activation, the platelets will release a myriad of growth factors from their dense and α-granules and peroxisomes; these will directly impact tumor growth, tethering, and spread. A similar cross-talk is initiated between tumor microvesicles stimulating the platelets and platelet microparticles, promoting both thrombosis and tumor growth. A vicious loop of activation thereafter takes place. Platelets directly and indirectly promote tumor growth, and enable a molecular mimicry coating the malignant growth and allowing metastasizing cells to escape T-cell-mediated immunity and natural killer cell surveillance. Breaking this vicious activation loop with nonspecific platelet inhibitors, such as aspirin, or by targeting specific sites on the activation cascade may offer a mean to reduce both the risks of development and progression of cancer and the risk of thrombosis.

A process for solvent/detergent treatment of plasma for transfusion at blood centers that use a disposable-bag system

BACKGROUND: Solvent/detergent (S/D) inactivates enveloped viruses in plasma. The current technology requires a plasma fractionation facility and is applied to large plasma pools, which increases the cost and risks of exposure to S/D‐resistant pathogens and lowers the content of protein S and α2‐antiplasmin. Two S/D treatment procedures for single donations or minipools of plasma have been developed with a single‐use bag system.

Platelet microparticles and cancer: An intimate cross-talk

Blood cell-derived microparticles (MP), in general, and platelet MPs (PMPs), in particular, have emerged as important contributors, as well as markers, of the delicate balance between health and disease. They may, on one hand, have beneficial effects by supporting tissue repair and regeneration, as well as hemostasis, but may, on the other hand, be a pro-coagulant promoter leading to the thrombotic events seen in the context of cancer. PMPs can act as a direct tumor growth enhancer through the release of potent growth factors in the tumor micro-environment. Tumor engraftment can also be stimulated by the pro-angiogenic potentials of platelet growth factors released by PMPs. PMPs, by their pro-inflammatory and immunomodulatory functions, can also exert an indirect role in the metastatic multistep process by helping malignant cells to escape from immunological surveillance. The possible detrimental effect of transfusions in cancer patients has been debated for several years and the role played by PMPs present in blood products is receiving specific attention, considering their propensity to trigger thrombosis and support tumors. The intimate PMP-tumors crosstalk may therefore result in pro-thrombotic states and a physiological state favorable to tumor growth, tethering and dissemination. Laboratory and experimental studies are needed to better unveil the contribution of PMPs as coagulation promoters, as well as potential markers and targets to treat cancer.

Minipool Caprylic Acid Fractionation of Plasma Using Disposable Equipment: A Practical Method to Enhance Immunoglobulin Supply in Developing Countries

Background Immunoglobulin G (IgG) is an essential plasma-derived medicine that is lacking in developing countries. IgG shortages leave immunodeficient patients without treatment, exposing them to devastating recurrent infections from local pathogens. A simple and practical method for producing IgG from normal or convalescent plasma collected in developing countries is needed to provide better, faster access to IgG for patients in need. Methodology/Principal Findings IgG was purified from 10 consecutive minipools of 20 plasma donations collected in Egypt using single-use equipment. Plasma donations in their collection bags were subjected to 5%-pH5.5 caprylic acid treatment for 90 min at 31°C, and centrifuged to remove the precipitate. Supernatants were pooled, then dialyzed and concentrated using a commercial disposable hemodialyzer. The final preparation was filtered online by gravity, aseptically dispensed into storage transfusion bags, and frozen at <-20°C. The resulting preparation had a mean protein content of 60.5 g/L, 90.2% immunoglobulins, including 83.2% IgG, 12.4% IgA, and 4.4% IgM, and residual albumin. There was fourfold to sixfold enrichment of anti-hepatitis B and anti-rubella antibodies. Analyses of aggregates (<3%), prekallicrein (5-7 IU/mL), plasmin (26.3 mU/mL), thrombin (2.5 mU/mL), thrombin-like activity (0.011 U/g), thrombin generation capacity (< 223 nM), and Factor XI (<0.01 U/mL) activity, Factor XI/XIa antigen (2.4 ng/g) endotoxin (<0.5 EU/mL), and general safety test in rats showed the in vitro safety profile. Viral validation revealed >5 logs reduction of HIV, BVDV, and PRV infectivity in less than 15 min of caprylic acid treatment. Conclusions/Significance 90% pure, virally-inactivated immunoglobulins can be prepared from plasma minipools using simple disposable equipment and bag systems. This easy-to-implement process could be used to produce immunoglobulins from local plasma in developing countries to treat immunodeficient patients. It is also relevant for preparing hyperimmune IgG from convalescent plasma during infectious outbreaks such as the current Ebola virus episode.

Impact of Transfusion on Cancer Growth and Outcome

For many years, transfusion of allogeneic red blood cells, platelet concentrates, and plasma units has been part of the standard therapeutic arsenal used along the surgical and nonsurgical treatment of patients with malignancies. Although the benefits of these blood products are not a matter of debate in specific pathological conditions associated with life-threatening low blood cell counts or bleeding, increasing clinical evidence is nevertheless suggesting that deliberate transfusion of these blood components may actually lead to negative clinical outcomes by affecting patient’s immune defense, stimulating tumor growth, tethering, and dissemination. Rigorous preclinical and clinical studies are needed to dimension the clinical relevance, benefits, and risks of transfusion of blood components in cancer patients and understand the amplitude of problems. There is also a need to consider validating preparation methods of blood components for so far ignored biological markers, such as microparticles and biological response modifiers. Meanwhile, blood component transfusions should be regarded as a personalized medicine, taking into careful consideration the status and specificities of the patient, rather than as a routine hospital procedure.