Introduction: Many cardiac arrest survivors die later due to hemorrhage or thromboembolism, thought to be caused by acquired coagulopathy in post-cardiac arrest syndrome (PCAS) from shock and reperfusion injury. Understanding PCAS is a priority identified by the AHA for the prevention of complications in cardiac arrest survivors. Shock dysregulates both coagulation and fibrinolysis. The key effector enzyme thrombin (Th), is responsible for both up- and down-regulating coagulation and fibrinolysis. Measuring early Th activity may allow for predicting PCAS coagulopathy, and early medical intervention in the ED. Therefore, we aimed to characterize the time-course profile of early coagulation using an established pig model of cardiac arrest. Methods: Yorkshire pigs were anaesthetised and intubated, had VF-arrest induced by pacing, and were resuscitated per ACLS. Rotational thromboelastometry (ROTEM) was performed on whole blood at four times: baseline, intra-arrest, post-arrest, and death, using the fibrin-based test with tissue factor to initiate clotting in the presence of a platelet inhibitor cytochalasin D (FIBTEM). Clot time (CT), clot formation time (CFT), alpha-angle during clot formation (Alpha), clot amplitude at 10 min (A10), maximum clot firmness (MCF), and maximum lysis as total percentage (ML%) were quantified. The primary outcome is the overall coagulation initiation measured by CFT, while secondary outcomes include ROTEM parameters reflecting Th activity. Parameters are compared over time in SPSS using repeated measures ANOVA and Bonferroni correction. Results: Pilot data from one experiment show that cardiac arrest causes immediate early changes to coagulation that subsequently normalized with ROSC (Figure 1). CFT was impaired immediately upon cardiac arrest (2.3-fold increase), normalized with ROSC, and impaired again at death when compared with baseline. Consistent with clotting impairment, A10, Alpha, and MCF were all reduced with cardiac arrest, normalized with ROSC, and impaired again at death. Conclusion: Higher initial indices of coagulopathy in patients with cardiac arrest appear to correlate with death and thromboembolism. In this pilot, CFT is acutely modified by cardiac arrest. Since CFT is affected by overall Th activity, early Th dysregulation may be a critical driver of coagulopathy. Th may therefore be a lead target that is modifiable in the emergency post-arrest setting to decrease morbidity and mortality from PCAS in cardiac arrest survivors.

Platelet ultrastructural alterations representing spurious activation have been identified in pathological conditions. A limitation of platelet studies is that sample preparation may lead to artifactual activation processes which may confound results, impacting the use of scanning electron microscopy as a supplemental diagnostic tool. We used scanning electron microscopy and flow cytometry to analyze platelet activation in platelet-rich plasma (PRP) and whole blood (WB) samples. PRP generated using a single high g force centrifugation, and WB samples treated with a red blood cell lysis buffer, were exposed to increasing concentrations of the agonist thrombin. Platelets in lysed WB samples responded to thrombin by elevating the activation marker CD62p definitively, with corresponding ultrastructural changes indicating activation. Conversely, CD62p expression in PRP preparations remained static. Ultrastructural analysis revealed fully activated platelets even under low concentration thrombin stimulation, with considerable fibrin deposition. It is proposed that the method for PRP production induced premature platelet activation, preventable by using an inhibitor of platelet aggregation and fibrin polymerization. Nevertheless, our results show a definitive correspondence between flow cytometry and scanning electron microscopy in platelet activation studies, highlighting the potential of the latter technique as a supplemental diagnostic tool.

Background: Brain injury after intracerebral hemorrhage (ICH) arises from numerous contributors, of which some also play essential roles. Notably, thrombin production, needed to stop bleeding, also causes acute cell death and edema. In some rodent models of ICH, peri-hematoma neurons die over weeks. Hence we evaluated whether thrombin is responsible for this chronic degeneration. Functional impairments after ICH also result from sub-lethal damage to neurons, especially the loss of dendrites. Thus, we evaluated whether thrombin infusion alone, a reductionist model of ICH, causes similar injury. Methods: Adult rats had a modest intra-striatal infusion of thrombin (1 U) or saline followed by a behavioral test, to verify impairment, 7 days later. After this they were euthanized and tissue stained with Golgi-Cox solution to allow the assessment of dendritic morphology in striatal neurons. In a second experiment, rats survived 7 or 60 days after thrombin infusion in order to histologically determine lesion volume. Results: Thrombin caused early cell death and considerable atrophy in surviving peri-lesion neurons, which had less than half of their usual numbers of branches. However, total tissue loss was comparable at 7 (24.1 mm3) and 60 days (25.6 mm3). Conclusion: Thrombin infusion causes early cell death and neuronal atrophy in nearby surviving striatal neurons but thrombin does not cause chronic tissue loss. Thus, the chronic degeneration found after ICH in rats is not simply and solely due to acute thrombin production. Nonetheless, thrombin is an important contributor to behavioral dysfunction because it causes cell death and substantial dendritic injury.

Rhinophyma is considered to be the final stage of rosacea and has an unknown aetiology. We present two new surgical adjuncts for the treatment of this condition. The microdebrider is easy to use and allows precise contouring of the nose. It shares the same underlying principle as free-hand scalpel shaving but outperforms this method in key areas. We also describe a novel use for FloSeal®, a gelatin-thrombin co-mixture, utilizing its haemostatic properties to address bleeding from the re-shaped denuded nose.

Calmodulin (CaM), the ubiquitous, eukaryotic, bilobal calcium-binding regulatory protein, has been cleaved by thrombin to create two fragments, TM1 (1–106) and TM2 (107–148). NMR and CD results indicate that TM1 and TM2 can associate in the presence of Ca2+ to form a complex similar to native CaM, even though the cleavage site is not in the linker region between two helix-loop-helix domains, but rather within an α-helix. Cadmium-113 NMR results show that this complex has enhanced metal-ion binding properties when compared to either TM1 or TM2 alone. This complex can bind several CaM-binding target peptides, as shown by gel bandshift assays, circular dichroism spectra, and 13C NMR spectra of biosynthetically methyl-13C-Met-labeled TM1 and TM2; moreover, gel bandshift assays show that the addition of a target peptide strengthens the interactions between TM1 and TM2 and increases the stability of the complex. Cadmium-113 NMR spectra indicate that the TM1:TM2 complex can also bind the antipsychotic drug trifluoperazine. However, in contrast to CaM:peptide complexes, the TM1:TM2:peptide complexes are disrupted by 4 M urea; moreover, TM1 and TM2 in combination are unable to activate CaM-dependent enzymes. This suggests that TM1:TM2 mixtures cannot bind target molecules as tightly as intact CaM, or perhaps that binding occurs but additional interactions with the target enzymes that are necessary for proper activation are perturbed by the proteolytic cleavage. The results presented here reflect the importance of the existence of helix-loop-helix Ca2+-binding domains in pairs in proteins such as CaM, and extend the understanding of the association of such domains in this class of proteins in general.

Hirudin is an anticoagulant polypeptide isolated from a medicinal leech that inhibits thrombin with extraordinary potency (Kd = 0.2–1.0 pM) and selectivity. Hirudin is composed of a compact N-terminal region (residues 1–47, cross-linked by three disulfide bridges) that binds to the active site of thrombin, and a flexible C-terminal tail (residues 48–64) that interacts with the exosite I of the enzyme. To minimize the sequence of hirudin able to bind thrombin and also to improve its therapeutic profile, several N-terminal fragments have been prepared as potential anticoagulants. However, the practical use of these fragments has been impaired by their relatively poor affinity for the enzyme, as given by the increased value of the dissociation constant (Kd) of the corresponding thrombin complexes (Kd = 30–400 nM). The aim of the present study is to obtain a derivative of the N-terminal domain 1–47 of hirudin displaying enhanced inhibitory potency for thrombin compared to the natural product. In this view, we have synthesized an analogue of fragment 1–47 of hirudin HM2 in which Val1 has been replaced by tert-butylglycine, Ser2 by Arg, and Tyr3 by β-naphthylalanine, to give the BugArgNal analogue. The results of chemical and conformational characterization indicate that the synthetic peptide is able to fold efficiently with the correct disulfide topology (Cys6–Cys14, Cys16–Cys28, Cys22–Cys37), while retaining the conformational properties of the natural fragment. Thrombin inhibition data indicate that the effects of amino acid replacements are perfectly additive if compared to the singly substituted analogues (De Filippis V, Quarzago D, Vindigni A, Di Cera E, Fontana A, 1998, Biochemistry 37:13507–13515), yielding a molecule that inhibits the fast or slow form of thrombin by 2,670- and 6,818-fold more effectively than the natural fragment, and that binds exclusively at the active site of the enzyme with an affinity (Kd,fast = 15.4 pM, Kd,slow = 220 pM) comparable to that of full-length hirudin (Kd,fast = 0.2 pM, Kd,slow = 5.5 pM). Moreover, BugArgNal displays absolute selectivity for thrombin over the other physiologically important serine proteases trypsin, plasmin, factor Xa, and tissue plasminogen activator, up to the highest concentration of inhibitor tested (10 μM).