Recombinant Thrombin: Safety and Immunogenicity in Burn Wound Excision and Grafting:

Thrombin and Thrombin-Incorporated Biomaterials for Disease Treatments

Thrombin, a coagulation-inducing protease, has long been used in the hemostatic field. During the past decades, many other therapeutic uses of thrombin have been developed. For instance, burn treatment, pseudoaneurysm therapy, wound management, and tumor vascular infarction (or tumor vasculature blockade therapy) can all utilize the unique and powerful function of thrombin. Based on their therapeutic effects, many thrombin-associated products have been certificated by the Food and Drug Administration, including bovine thrombin, human thrombin, recombinant thrombin, fibrin glue, etc. Besides, several thrombin-based drugs are currently undergoing clinical trials. In this article, the therapeutic uses of thrombin (from the initial hemostasis to the latest cancer therapy), the commercially available drugs associated with thrombin, and the pros and cons of thrombin-based therapeutics (e.g., adverse immune responses related to bovine thrombin, thromboinflammation, and vasculogenic "rebounds") are summarized. Further, the current challenges and possible future research directions of thrombin-incorporated biomaterials and therapies are discussed. It is hoped that this review may provide a valuable reference for researchers in this field and help them to design safer and more effective thrombin-based drugs for fighting against various intractable diseases.

Topical Hemostatic Agents in Burn Surgery: A Systematic Review

Acute burn surgery has long been associated with significant intra-operative bleeding. Several techniques were introduced to limit hemorrhage, including tourniquets, tumescent infiltration, and topical agents. To date, no study has comprehensively investigated the available data regarding topical hemostatic agents in burn surgery. A systematic review was performed by two independent reviewers using electronic databases (PubMed, Scopus, Web of Science) from first available to September 10, 2021. Articles were included if they were published in English and described or evaluated topical hemostatic agents used in burn excision and/or grafting. Data were extracted on the agent(s) used, their dosage, mode of delivery, hemostasis outcomes, and complications. The search identified 1982 nonduplicate citations, of which 134 underwent full-text review, and 49 met inclusion criteria. In total, 32 studies incorporated a vasoconstrictor agent, and 28 studies incorporated a procoagulant agent. Four studies incorporated other agents (hydrogen peroxide, tranexamic acid, collagen sheets, and TT-173). The most common vasoconstrictor used was epinephrine, with doses ranging from 1:1000 to 1:1,000,000. The most common procoagulant used was thrombin, with doses ranging from 10 to 1000 IU/ml. Among the comparative studies, outcomes of blood loss were not reported in a consistent manner, therefore meta-analysis could not be performed. The majority of studies (94%) were level of evidence III-V. Determining the optimal topical hemostatic agent is limited by low-quality data and challenges with consistent reporting of intra-operative blood loss. Given the routine use of topical hemostatic agents in burn surgery, high-quality research is essential to determine the optimal agent, dosage, and mode of delivery.

Advancements in Regenerative Strategies Through the Continuum of Burn Care

Burns are caused by several mechanisms including flame, scald, chemical, electrical, and ionizing and non-ionizing radiation. Approximately half a million burn cases are registered annually, of which 40 thousand patients are hospitalized and receive definitive treatment. Burn care is very resource intensive as the treatment regimens and length of hospitalization are substantial. Burn wounds are classified based on depth as superficial (first degree), partial-thickness (second degree), or full-thickness (third degree), which determines the treatment necessary for successful healing. The goal of burn wound care is to fully restore the barrier function of the tissue as quickly as possible while minimizing infection, scarring, and contracture. The aim of this review is to highlight how tissue engineering and regenerative medicine strategies are being used to address the unique challenges of burn wound healing and define the current gaps in care for both partial- and full-thickness burn injuries. This review will present the current standard of care (SOC) and provide information on various treatment options that have been tested pre-clinically or are currently in clinical trials. Due to the complexity of burn wound healing compared to other skin injuries, burn specific treatment regimens must be developed. Recently, tissue engineering and regenerative medicine strategies have been developed to improve skin regeneration that can restore normal skin physiology and limit adverse outcomes, such as infection, delayed re-epithelialization, and scarring. Our emphasis will be centered on how current clinical and pre-clinical research of pharmacological agents, biomaterials, and cellular-based therapies can be applied throughout the continuum of burn care by targeting the stages of wound healing: hemostasis, inflammation, cell proliferation, and matrix remodeling.

The modulation of coagulation by aptamers: an up-to-date review

Coagulation and anticoagulation system is kept in balance by the orchestrated action of a variety of biological factors, and the disruption of this balance leads to the risk of hemorrhage or thrombosis. Oligonucleotide aptamers are single-stranded DNA (ssDNA) or RNA ligands that are synthesized in vitro and bind to target molecules through dimensional structure with high specificity and affinity, and thus represent attractive candidates for the development of agents to maintain the balance of coagulation and anticoagulation. In this review, we summarize recent progress in aptamer-based application in the modulation of coagulation. The aptamers with specific chemical and biological characteristics have great potential to be explored as agents for the treatment of blood coagulation abnormalities.

Medical management of paediatric burn injuries: best practice part 2

Burns remain a leading cause of injury in the paediatric population in Australia despite efforts in prevention. Advances in surgical management include novel debridement methods and blood conserving techniques. Patients with severe burns (>20%) remain significantly more complex to manage as a result of extensive alterations in metabolic processes. There appears increasing evidence to support the use of pharmacological modulators of the hyper-metabolic state in these patients. The management of a child with burns involves acute, subacute and long-term planning. This holistic approach seems optimally co-ordinated by a Burns Unit in which each discipline required to provide care to these children in order to achieve optimal outcomes is represented.

Blood utilization: fostering an effective hospital transfusion culture

An effective hospital transfusion culture should encourage clinicians to consider the possibility of transfusion in their patients well before the need actually arises, and to plan ahead in an attempt to use blood products most efficiently. Strategies for improved blood utilization include timely and adequate preoperative assessment of risk, optimization of baseline hemoglobin, anticipation of potential transfusion problems, intraoperative techniques to minimize blood loss, blood conservation technologies, transfusion guidelines and targeted therapy, point of care testing, and massive transfusion protocols. Attention to these elements promotes a safe and cost-effective transfusion culture.

Recombinant human thrombin: safety and immunogenicity in pediatric burn wound excision

BACKGROUND

Previous studies of recombinant human thrombin (rThrombin) enrolled adult and adolescent patients. This phase 4, open-label, single-group study was conducted in pediatric patients undergoing synchronous burn wound excision and skin grafting to provide information regarding the safety and immunogenicity of rThrombin (primary and secondary endpoints) in this population.

METHODS

Topical rThrombin was applied as a hemostatic aid during a surgical procedure (day 1). Adverse events and clinical laboratory abnormalities were recorded during the study. Immunogenicity samples were collected on days 1 and 29 (study end). Study results were summarized with descriptive statistics.

RESULTS

Thirty patients enrolled and 28 completed the study. Mean age was 6.9 years (range, 0.9-17.8 years); 40.0% of patients were girls. Flame and scald were the most common burn types (33.3% each, n = 10/30). Mean graft size was 3.6% total body surface area. Procedural pain (50.0% patients), pruritus (43.3%), and anemia (30.0%) were the most commonly reported adverse events. All adverse events and clinical laboratory abnormalities were considered unrelated to treatment. No patients developed anti-rThrombin product antibodies at day 29.

CONCLUSIONS

In pediatric patients undergoing burn wound excision and skin grafting, rThrombin was well tolerated and did not lead to the formation of anti-rThrombin product antibodies.

Red blood cell transfusion following burn

A severe burn will significantly alter haematologic parameters, and manifest as anaemia, which is commonly found in patients with greater than 10% total body surface area (TBSA) involvement. Maintaining haemoglobin and haematocrit levels with blood transfusion has been the gold standard for the treatment of anaemia for many years. While there is no consensus on when to transfuse, an increasing number of authors have expressed that less blood products should be transfused. Current transfusion protocols use a specific level of haemoglobin or haematocrit, which dictates when to transfuse packed red blood cells (PRBCs). This level is known as the trigger. There is no one 'common trigger' as values range from 6 g dl(-1) to 8 g dl(-1) of haemoglobin. The aim of this study was to analyse the current status of red blood cell (RBC) transfusions in the treatment of burn patients, and address new information regarding burn and blood transfusion management. Analysis of existing transfusion literature confirms that individual burn centres transfuse at a lower trigger than in previous years. The quest for a universal transfusion trigger should be abandoned. All RBC transfusions should be tailored to the patient's blood volume status, acuity of blood loss and ongoing perfusion requirements. We also focus on the prevention of unnecessary transfusion as well as techniques to minimise blood loss, optimise red cell production and determine when transfusion is appropriate.

Hemostasis in burn surgery--a review

Over the past 30 years, techniques of early excision and grafting along with enhancement of critical care have significantly improved survival following burn injury. Despite these advancements, large volume blood loss associated with surgical intervention continues to be a challenging aspect of burn surgery. This review article will examine the methods of limiting blood loss during surgical procedures.

State-of-the-Art Review: Hemostats, Sealants, and Adhesives II: Update As Well As How and When to Use the Components of the Surgical Toolbox

The goal of this submission is to describe how and when to best use hemostats, sealants, and adhesives as well as to compare their characteristics and to update the surgical toolbox with respect to any new products approved by the Food and Drug Administration (FDA) as of this date (November 2009). The materials will be presented in 3 major groups each containing specific categories: (1) hemostats; mechanical, active, flowable, and fibrin sealant, (2) sealants; fibrin sealant, polyethylene glycol polymer, and albumin and glutaraldehyde, (3) adhesives; cyanoacrylate, albumin and glutaraldehyde, and fibrin sealant. The categories will be used for comparisons based on safety, efficacy, usability, and cost. Recommendations with respect to how and when to best use these materials will be presented. A review of the recent literature is also provided with respect to the most recent uses of these materials in specific surgical specialties.

Thrombin use in surgery: an evidence-based review of its clinical use

When surgical ligation of bleeding fails, or is not possible, surgeons rely on a number of hemostatic aids, including thrombin. This review discusses the history, pharmacology and clinical application of thrombin as a surgical hemostat. The initial thrombin was bovine in origin, but its use has been complicated by the formation of antibodies that cross-react with human coagulation factors. This has been associated with life-threatening bleeding and in some circumstances anaphylaxis and death. Human thrombin, isolated from pooled plasma of donors, was developed in an effort to minimize these risks, but its downsides are its limited availability and the potential for transmitting blood-borne pathogens. Recently a recombinant thrombin has been developed, and approved for use by the FDA. It has the advantage of being minimally antigenic and devoid of the risk of viral transmission. Thrombin is often used in conjunction with other hemostatic aids, including absorbable agents such as Gelfoam, and with fibrinogen in fibrin glues. The last part of this review will discuss these agents in detail, and review their clinical applications.

Cross-reactivity of rabbit anti-bovine thrombin IgGs with human alpha-thrombin and a recombinant version of human thrombin (Recothrom)

It has been reported that patients exposed to topical bovine thrombin preparations may develop antibodies against bovine thrombin, factr V or various other proteins found in these preparations. Such antibodies can cross-react with human endogenous coagulation proteins and may lead to alterations in the coagulation laboratory parameters, hypersensitivity reactions, and severe bleeding or thrombosis. The underlying mechanisms for the coagulopathy are not fully understood yet. To better understand the cross-reactivity of anti-bovine thrombin antibodies with human corresponding coagulation proteins, bovine crude thrombin, and its purified versions, thrombin 4A (the old version of Thrombin-JMI before year 2008) and thrombin 4B (the current version of Thrombin-JMI on market), were used to generate relevant anti-bovine thrombin immunoglobulin G (IgGs) in rabbits. Using Western blotting, the cross-reactivity of each IgG with human alpha-thrombin and a recombinant version of human thrombin (Recothrom) was investigated. The results indicated that no cross-reactivity with either human alpha-thrombin or Recothrom was observed with both anti-bovine crude thrombin IgGs and thrombin 4B IgGs. However, anti-bovine thrombin 4A IgGs showed apparent cross-reactivity with human alpha-thrombin and Recothrom in a protein amount-dependent manner. Furthermore, the results revealed that the cross-reactivity of anti-bovine thrombin 4A IgGs with human alpha-thrombin and Recothrom was immunization time-dependent. The minimum concentration of 4A IgG required to exhibit cross-reactivity with human alpha-thrombin and Recothrom varied considerably among individual rabbits. These results indicate that rabbit anti-bovine thrombin IgGs can cross-react with human alpha-thrombin and Recothrom, suggesting that human antibodies against bovine thrombin may also cross-react with human recombinant thrombin. Thus, the patients who were previously exposed to bovine thrombin may also develop antibodies which can cross-react with human recombinant thrombin.