Saratin (an inhibitor of platelet-collagen interaction) decreases platelet aggregation and homocysteine-mediated postcarotid endarterectomy intimal hyperplasia in a dose-dependent manner

Molecular cloning and functional analysis of HnSaratin from Hirudo nipponia

In order to finish a bloodmeal successfully, hematophagous organisms often stored a variety of anticoagulant proteins in their salivary glands, such as proteins that inhibit platelet aggregation. When they ingest a bloodmeal, these proteins are injected into the host to prevent the blood from clotting. As one of the origins of leeches used in traditional Chinese medicine, H. nipponia was proved to be clinically effective in treatment of cardiovascular and cerebrovascular diseases. This study cloned the sequence of HnSaratin cDNA derived from salivary glands of H. nipponia. The sequence contains an open reading frame of 387 bp, encoding a protein of 128 amino acids containing a signal peptide of 21 amino acids. After removal of the signal peptide, the molecular mass of mature HnSaratin was 12.37 kDa, with a theoretical isoelectric point (pI) of 3.89. The N-terminal of mature HnSaratin was folded into a globular structure, in which 3 disulfide bonds, a ββαβββ topology and 2 Glu residues that binds collagenous Lys2 were located, and the C-terminal formed a flexible region. The fusion HnSaratin protein was obtained by a prokaryotic expression system. The protein showed anti-platelet aggregation activity, and was observed to prevent blood clotting in rats. The significant high expression of HnSaratin mRNA in salivary glands was induced by bloodmeal ingestion of H. nipponia. Briefly, our work provides theoretical basis for further development and utilization of H. nipponia.

Aspirin use and platelet aggregation in ischemic onset-type pediatric moyamoya patients with intractable headaches (moya-ache)

BACKGROUND

NSAIDs (nonsteroidal anti-inflammatory drugs) were administered to patients with ischemic onset-type moyamoya disease who experience headaches, but their therapeutic effect was very poor and resulted in a drop in quality of life (QOL). On the other hand, patients who were administered aspirin initially to prevent transient ischemic attacks (TIA) were observed to have a better QOL with the absence of headaches. Here, we report on patients with ischemic onset-type moyamoya disease experiencing headaches who received aspirin in order to verify its safety and effectiveness.

METHODS

From October 2012 to July 2014, 35 patients (male: 19, female: 16 average age: 10.5 ± 3.9) with ischemic onset-type pediatric moyamoya disease and who were admitted or commuted to hospital and had surgical treatment were evaluated for background, moyamoya staging (Suzuki), presence/absence of TIA, and platelet aggregation activity by adenosine diphosphate (ADP)/collagen turbidity test. The patients were divided into four groups depending on the intensity of headache prior to being administered aspirin, and the Kruskal-Wallis test was carried out for platelet aggregation activity and moyamoya staging. Also, the 4 × 2 χ² test was carried out for the presence/absence of TIA. Next, the items which were significant in these tests were used as independent variables to analyze the risk of headache onset, using logistic regression analysis.

RESULTS

One item with statistical significance was the platelet aggregation test(PAT) value (on collagen) (P < 0.0001). A logistic regression analysis was carried out, using this value as an independent variable and headache intensity-as a dependent variable. As a result, an increase in PAT value by 1 translated into 4.43 times higher risk of the onset of intractable headache, and the onset of intractable headaches was predicted at 58.8% with collagen. The risk of developing a headache decreased as a result of aspirin administration, and the decrease was dependent on the collagen-induced aggregation suppression effect of aspirin. Aspirin was administered in the range of 1.6~9.5 mg/kg/day, and the PAT value decreasing rate was 42.9% on average. One case alone experienced nasal bleeding, and all cases showed an improvement in the intractable headaches.

CONCLUSIONS

In patients with ischemic onset-type pediatric moyamoya disease who experience headaches, the platelet aggregation activity is accelerated, and aspirin administration is effective in alleviating headaches by inhibiting platelet activation, detected by the collagen PAT.

Platelet Aggregability as a Predictor of Restenosis Following Carotid Endarterectomy

BACKGROUND

Antiplatelet drugs are administered before and after carotid endarterectomies (CEAs), but their efficacy for preventing restenosis remains unclear. Hence, this study aimed to identify associations between postoperative restenosis and platelet aggregability in CEA patients.

METHODS

Thirty-six consecutive CEA patients treated at Tokyo Women's Medical University from May 2013 to March 2015 were included in this retrospective study. Restenosis was defined as a stenosis ratio greater than or equal to 50% per the European Carotid Surgery Trial criteria or peak systolic velocity of 150 cm/s on carotid ultrasound. Platelet aggregability was measured turbidimetrically using a light-transmission platelet aggregometer and analyzed in terms of aggregation profiles for 2 concentrations of collagen used to induce aggregation (.25 and 2.0 μg/mL). Patients were automatically divided into 9 classes (Class 1-9, from the lowest to the highest aggregability) using a software program according to area under their platelet aggregation curves. Each class was subdivided into 10 further gradations for a total of 90 possible scores (10-99) using a software program. Patients were divided into high- and low-platelet aggregability score groups (cut-off = 49).

RESULTS

Data were analyzed for 36 of the 99 patients. Restenosis was observed in 10 (28%) patients. Restenosis incidence was significantly higher in patients with high-platelet aggregability score than in those with low-platelet aggregability score (50.0% [7/14] versus 13.6% [3 of 22]: P = .0176, odds ratio = 6.34, 95% CI: 1.27-31.57).

CONCLUSIONS

Platelet aggregability is a useful metric for predicting and preventing restenosis after CEA. It has potential as an indicator for determining the optimal dose of antiplatelet drugs.

Targeting von Willebrand Factor in Ischaemic Stroke: Focus on Clinical Evidence

Despite great efforts in stroke research, disability and recurrence rates in ischaemic stroke remain unacceptably high. To address this issue, one potential target for novel therapeutics is the glycoprotein von Willebrand factor (vWF), which increases in thrombogenicity especially under high shear rates as it bridges between vascular sub-endothelial collagen and platelets. The rationale for vWF as a potential target in stroke comes from four bodies of evidence. (1) Animal models which recapitulate the pathogenesis of stroke and validate the concept of targeting vWF for stroke prevention and the use of the vWF cleavage enzyme ADAMTS13 in acute stroke treatment. (2) Extensive epidemiologic data establishing the prognostic role of vWF in the clinical setting showing that high vWF levels are associated with an increased risk of first stroke, stroke recurrence or stroke-associated mortality. As such, vWF levels may be a suitable marker for further risk stratification to potentially fine-tune current risk prediction models which are mainly based on clinical and imaging data. (3) Genetic studies showing an association between vWF levels and stroke risk on genomic levels. Finally, (4) studies of patients with primary disorders of excess or deficiency of function in the vWF axis (e.g. thrombotic thrombocytopenic purpura and von Willebrand disease, respectively) which demonstrate the crucial role of vWF in atherothrombosis. Therapeutic inhibition of VWF by novel agents appears particularly promising for secondary prevention of stroke recurrence in specific sub-groups of patients such as those suffering from large artery atherosclerosis, as designated according to the TOAST classification.

Current and Future Techniques in Wound Healing Modulation after Glaucoma Filtering Surgeries

Filtering surgeries are frequently used for controlling intraocular pressure in glaucoma patients. The long-term success of operation is intimately influenced by the process of wound healing at the site of surgery. Indeed, if has not been anticipated and managed accordingly, filtering surgery in high-risk patients could end up in bleb failure. Several strategies have been developed so far to overcome excessive scarring after filtering surgery. The principal step involves meticulous tissue handling and modification of surgical technique, which can minimize the severity of wound healing response at the first place. However, this is usually insufficient, especially in those with high-risk criteria. Thus, several adjuvants have been tried to stifle the exuberant scarring after filtration surgery. Conventionally, corticosteroids and anti-fibrotic agents (including 5-fluorouracil and Mitomycin-C) have been used for over three decades with semi-acceptable outcomes. Blebs and bleb associated complications are catastrophic side effects of anti-fibrotic agents, which occasionally are encountered in a subset of patients. Therefore, research continues to find a safer, yet effective adjuvant for filtering surgery. Recent efforts have primarily focused on selective inhibition of growth factors that promote scarring during wound healing process. Currently, only anti-VEGF agents have gained widespread acceptance to be translated into routine clinical practice. Robust evidence for other agents is still lacking and future confirmative studies are warranted. In this review, we explain the importance of wound healing process during filtering surgery, and describe the conventional as well as potential future adjuvants for filtration surgeries.

Wound modulation after filtration surgery

Filtration surgery is the standard invasive procedure for the management of intraocular pressure in advanced glaucoma. The key to a successful outcome is to modulate the normal wound healing cascade that leads to closure of the newly created aqueous outflow pathway. Antifibrotic agents such as mitomycin C and 5-fluorouracil have been increasingly used to modulate the wound healing process and increase surgical success. Although these agents have proven efficacy, they also increase the risk of complications. Efforts have centered on the identification of novel agents and techniques that can influence wound modulation without these complications. We detail new agents and methods under investigation to control wound healing after filtration surgery.

Prevention of ocular scarring post glaucoma filtration surgery using the inflammatory cell and platelet binding modulator saratin in a rabbit model

Clinical Relevance

Late complications can occur with use of current antimetabolites to prevent scarring following glaucoma filtration surgery (GFS). Safer, more targeted, anti-fibrosis agents are sought.

Objectives

The protein saratin has been shown to exhibit anti-fibrotic and anti-thrombotic properties in response to injury, but had not been used for glaucoma surgery. The goal of this study was to compare the efficacy of saratin with that of the widely accepted mitomycin-C (MMC) in prolonging bleb survival following GFS in the rabbit model. Two saratin delivery routes were compared; a single intraoperative topical application versus a combination of intraoperative topical application with two additional postoperative injections.

Methods

Twenty-four New Zealand White rabbits underwent GFS and received either intraoperative topical saratin, intraoperative topical saratin plus two injections on post-operative days 4 and 8, balanced saline solution (BSS), or MMC. The bleb tissues and their elevation durations were compared based on clinical and histological findings.

Results

Rabbits receiving topical+injections of saratin had a mean bleb survival of 33.6±8.5 days, significantly higher than the negative BSS controls, which averaged 17.4±6.0 days (p = 0.018). No improvement over BSS was seen for rabbits receiving topical saratin only (15.5±4.8 days, p = 0.749). Rabbits receiving saratin did not develop bleb avascularity and thinning associated with MMC treatment and there were no apparent clinical signs of toxicity.

Conclusions

Treatment with a single intraoperative topical application plus two additional postoperative injections significantly prolonged bleb elevation comparable to MMC, but without toxicity; however, topical application alone was ineffective.

Aegyptin, a novel mosquito salivary gland protein, specifically binds to collagen and prevents its interaction with platelet glycoprotein VI, integrin alpha2beta1, and von Willebrand factor

Blood-sucking arthropods have evolved a number of inhibitors of platelet aggregation and blood coagulation. In this study we have molecularly and functionally characterized aegyptin, a member of the family of 30-kDa salivary allergens from Aedes aegypti, whose function remained elusive thus far. Aegyptin displays a unique sequence characterized by glycine, glutamic acid, and aspartic acid repeats and was shown to specifically block collagen-induced human platelet aggregation and granule secretion. Plasmon resonance experiments demonstrate that aegyptin binds to collagen types I-V (K(d) approximately 1 nm) but does not interact with vitronectin, fibronectin, laminin, fibrinogen, and von Willebrand factor (vWf). In addition, aegyptin attenuates platelet adhesion to soluble or fibrillar collagen. Furthermore, aegyptin inhibits vWf interaction with collagen type III under static conditions and completely blocks platelet adhesion to collagen under flow conditions at high shear rates. Notably, aegyptin prevents collagen but not convulxin binding to recombinant glycoprotein VI. These findings suggest that aegyptin recognizes specific binding sites for glycoprotein VI, integrin alpha2beta1, and vWf, thereby preventing collagen interaction with its three major ligands. Aegyptin is a novel tool to study collagen-platelet interaction and a prototype for development of molecules with antithrombotic properties.

The leech product saratin is a potent inhibitor of platelet integrin α2β1 and von Willebrand factor binding to collagen

Subendothelial collagen plays an important role, via both direct and indirect mechanisms, in the initiation of thrombus formation at sites of vascular injury. Collagen binds plasma von Willebrand factor, which mediates platelet recruitment to collagen under high shear. Subsequently, the direct binding of the platelet receptors glycoprotein VI and alpha2beta1 to collagen is critical for platelet activation and stable adhesion. Leeches, have evolved a number of inhibitors directed towards platelet-collagen interactions so as to prevent hemostasis in the host during hematophagy. In this article, we describe the molecular mechanisms underlying the ability of the leech product saratin to inhibit platelet binding to collagen. In the presence of inhibitors of ADP and thromboxane A2, both saratin and 6F1, a blocking alpha2beta1 mAb, abrogated platelet adhesion to fibrillar and soluble collagen. Additionally, saratin eliminated alpha2beta1-dependent platelet adhesion to soluble collagen in the presence of an Src kinase inhibitor. Moreover, saratin prevented platelet-rich plasma adhesion to fibrillar collagen, a process dependent upon both alpha2beta1 and von Willebrand factor binding to collagen. Furthermore, saratin specifically inhibited the binding of the alpha2 integrin subunit I domain to collagen, and prevented platelet adhesion to collagen under flow to the same extent as observed in the presence of a combination of mAbs to glycoprotein Ib and alpha2beta1. These results demonstrate that saratin interferes with integrin alpha2beta1 binding to collagen in addition to inhibiting von Willebrand factor-collagen binding, presumably by binding to an overlapping epitope on collagen. This has significant implications for the use of saratin as a tool to inhibit platelet-collagen interactions.