In Vitro Evaluation of Focused Ultrasound-Enhanced TNK-Tissue Plasminogen Activator-Mediated Thrombolysis

Fibrinogen binding to activated platelets and its biomimetic thrombus-targeted thrombolytic strategies

Thrombosis is associated with various fatal arteriovenous syndromes including ischemic stroke, myocardial infarction, and pulmonary embolism. However, current clinical thrombolytic treatment strategies still have many problems in targeting and safety to meet the thrombolytic therapy needs. Understanding the molecular mechanism that underlies thrombosis is critical in developing effective thrombolytic strategies. It is well known that platelets play a central role in thrombosis and the binding of fibrinogen to activated platelets is a common pathway in the process of clot formation. Based on this, a concept of biomimetic thrombus-targeted thrombolytic strategy inspired from fibrinogen binding to activated platelets in thrombosis was proposed, which could selectively bind to activated platelets at a thrombus site, thus enabling targeted delivery and local release of thrombolytic agents for effective thrombolysis. In this review, we first summarized the main characteristics of platelets and fibrinogen, and then introduced the classical molecular mechanisms of thrombosis, including platelet adhesion, platelet activation and platelet aggregation through the interactions of activated platelets with fibrinogen. In addition, we highlighted the recent advances in biomimetic thrombus-targeted thrombolytic strategies which inspired from fibrinogen binding to activated platelets in thrombosis. The possible future directions and perspectives in this emerging area are briefly discussed.

An in vitro Model for Experimental Evaluation of Sonothrombolysis under Tissue-mimicking Material Conditions

Background

The mechanical properties of therapeutic ultrasound (US) have attracted scientific interest for thrombolysis enhancement in combination with thrombolytic agents and microbubbles (MBs). The aim of the study was to develop an in vitro model to observe how the effects of sonothrombolysis change in the case where a tissue-mimicking material (TMM) is placed in the path of the US beam before the clot.

Methods

Fully retracted blood clots were prepared and pulse sonicated for 1 h under various conditions. The system was in a state of real circulating flow with a branch of an open bypass and an occluded tube containing a blood clot, thus mimicking the case of ischemic stroke. The effectiveness of thrombolysis was quantified in milligrams of clots removed. An agar-based TMM was developed around the occluded tube.

Results

The clot breakdown in a TMM was found to be more pronounced than in water, presumably due to the retention of the acoustic field. A higher level of acoustic power was required to initiate clot lysis (>76 W acoustic power) using only focused US (FUS). The greatest thrombolysis enhancement was observed with the largest chosen pulse duration (PD) and the use of MBs (150 mg clot mass lysis). The synergistic effect of FUS in combination with MBs on the enzymatic fibrinolysis enhanced thrombolysis efficacy by 260% compared to thrombolysis induced using only FUS. A reduction in the degree of clot lysis was detected due to the attenuation factor of the intervening material (30 mg at 1 and 4 ms PD).

Conclusion

In vitro thrombolytic models including a TMM can provide a more realistic evaluation of new thrombolytic protocols. However, higher acoustic power should be considered to compensate for the attenuation factor. The rate of clot lysis is slow and the clinical use of this method will be challenging.

Advances in Biological Application of and Research on Low-Frequency Ultrasound

In recent years, the in-depth study of low-frequency sonophoresis (LFS) has greatly elucidated its biological effects in various therapeutic applications, including drug delivery, enhanced healing, thrombolytic technology, anti-inflammatory effects and tumor treatment. Specifically, numerous studies have reported its use in drug delivery and synergistic antitumor activity, indicating a new treatment direction for cancer. However, there are significant gaps in the understanding of LFS in terms of frequency and sound intensity safety; these issues are becoming increasingly important in understanding the biological effects of LFS ultrasound. This article reviews the treatment mechanism and current applications of LFS technology and discusses and summarizes its safety and application prospects.

The promising shadow of microbubble over medical sciences: from fighting wide scope of prevalence disease to cancer eradication

Microbubbles are typically 0.5-10 μm in size. Their size tends to make it easier for medication delivery mechanisms to navigate the body by allowing them to be swallowed more easily. The gas included in the microbubble is surrounded by a membrane that may consist of biocompatible biopolymers, polymers, surfactants, proteins, lipids, or a combination thereof. One of the most effective implementation techniques for tiny bubbles is to apply them as a drug carrier that has the potential to activate ultrasound (US); this allows the drug to be released by US. Microbubbles are often designed to preserve and secure medicines or substances before they have reached a certain area of concern and, finally, US is used to disintegrate microbubbles, triggering site-specific leakage/release of biologically active drugs. They have excellent therapeutic potential in a wide range of common diseases. In this article, we discussed microbubbles and their advantageous medicinal uses in the treatment of certain prevalent disorders, including Parkinson's disease, Alzheimer's disease, cardiovascular disease, diabetic condition, renal defects, and finally, their use in the treatment of various forms of cancer as well as their incorporation with nanoparticles. Using microbubble technology as a novel carrier, the ability to prevent and eradicate prevalent diseases has strengthened the promise of effective care to improve patient well-being and life expectancy.

Overexpression of circRNA circUCK2 Attenuates Cell Apoptosis in Cerebral Ischemia-Reperfusion Injury via miR-125b-5p/GDF11 Signaling

Circular RNAs (circRNAs) are expressed at high levels in the brain and are involved in various central nervous system diseases. However, the potential role of circRNAs in ischemic stroke-associated neuronal injury remains largely unknown. Herein, we uncovered the function and underlying mechanism of the circRNA UCK2 (circUCK2) in ischemia stroke. The oxygen-glucose deprivation model in HT-22 cells was used to mimic ischemia stroke in vitro. Neuronal viability and apoptosis were determined by Cell Counting Kit-8 (CCK-8) assays and TUNEL (terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick end labeling) staining, respectively. Middle cerebral artery occlusion was conducted to evaluate the function of circUCK2 in mice. The levels of circUCK2 were significantly decreased in brain tissues from a mouse model of focal cerebral ischemia and reperfusion. Upregulated circUCK2 levels significantly decreased infarct volumes, attenuated neuronal injury, and improved neurological deficits. circUCK2 reduced oxygen glucose deprivation (OGD)-induced cell apoptosis by regulating transforming growth factor β (TGF-β)/mothers against decapentaplegic homolog 3 (Smad3) signaling. Furthermore, circUCK2 functioned as an endogenous miR-125b-5p sponge to inhibit miR-125b-5p activity, resulting in an increase in growth differentiation factor 11 (GDF11) expression and a subsequent amelioration of neuronal injury. Consequently, these findings showed that the circUCK2/miR-125b-5p/GDF11 axis is an essential signaling pathway during ischemia stroke. Thus, the circRNA circUCK2 may serve as a potential target for novel treatment in patients with ischemic stroke.

Therapeutic Potentials of Localized Blood-Brain Barrier Disruption by Noninvasive Transcranial Focused Ultrasound: A Technical Review

The demands for region-specific, noninvasive therapies for neurologic/psychiatric conditions are growing. The rise of transcranial focused ultrasound technology has witnessed temporary and reversible disruptions of the blood-brain barrier in the brain with exceptional control over the spatial precisions and depth, all in a noninvasive manner. Starting with small animal studies about a decade ago, the technique is now being explored in nonhuman primates and humans for the assessment of its efficacy and safety. The ability to transfer exogenous/endogenous therapeutic agents, cells, and biomolecules across the blood-brain barrier opens up new therapeutic avenues for various neurologic conditions, with a possibility to modulate the excitability of regional brain function. This review addresses the technical fundamentals, sonication parameters, experimental protocols, and monitoring techniques to examine the efficacy/safety in focused ultrasound-mediated blood-brain barrier disruption and discuss its potential translations to clinical use.

Advances in Sonothrombolysis Techniques Using Piezoelectric Transducers

One of the great advancements in the applications of piezoelectric materials is the application for therapeutic medical ultrasound for sonothrombolysis. Sonothrombolysis is a promising ultrasound based technique to treat blood clots compared to conventional thrombolytic treatments or mechanical thrombectomy. Recent clinical trials using transcranial Doppler ultrasound, microbubble mediated sonothrombolysis, and catheter directed sonothrombolysis have shown promise. However, these conventional sonothrombolysis techniques still pose clinical safety limitations, preventing their application for standard of care. Recent advances in sonothrombolysis techniques including targeted and drug loaded microbubbles, phase change nanodroplets, high intensity focused ultrasound, histotripsy, and improved intravascular transducers, address some of the limitations of conventional sonothrombolysis treatments. Here, we review the strengths and limitations of these latest pre-clincial advancements for sonothrombolysis and their potential to improve clinical blood clot treatments.

In vitro examination of the thrombolytic efficacy of tenecteplase and therapeutic ultrasound compared to rt-PA

BACKGROUND

Optimizing thrombolytic therapy is vital for improving stroke outcomes. We aimed to develop standardized thrombolysis conditions to evaluate the efficacy of tenecteplase (TNK) compared to the current gold standard rt-PA (alteplase), with and without additional ultrasound treatment. We also wanted to introduce a new analytical approach to quantify fibrin fiber density in transmission electron microscopy (TEM).

METHODS

In vitro clots that are similar to ex vivo clots concerning their histological condition and their durability were generated from whole blood. For five treatment groups we compared relative clot weight loss (each n = 60) and fibrin fiber density in TEM (each n = 5). The control group (A) was treated only with plasma. Two groups were designated for each rt-PA (B + C) and TNK (D + E). Groups C and E were additionally treated with ultrasound. Dosages were 50 μg/ml for rt-PA and 30 μg/ml for TNK. Results were evaluated by using analyses of variance (ANOVA) and post-hoc t-tests.

RESULTS

Weight loss was increased significantly for all groups compared to the control group. Both TNK groups showed significantly increased weight loss compared to their counterpart rt-PA group (p ≤ 0.001). For TEM only group D showed significantly decreased fibrin fiber density (p < 0.05) compared to both rt-PA groups. Ultrasound did not significantly increase dissolution of clots with either method (best p = 0.16).

CONCLUSIONS

Tenecteplase dissolved clots more effectively than rt-PA with and without ultrasound. A higher sample size could provide more convincing results for TEM.

In-vitro assessment of the thrombolytic efficacy of therapeutic ultrasound

BACKGROUND

Ultrasound is mainly used as a diagnostic tool. Several studies demonstrated that therapeutic ultrasound (TUS) can enhance thrombolysis, but the optimal mechanical parameters to achieve this biological effect are still unknown.

METHODS

We assembled 46 blood clots in a closed in-vitro circulatory model. Clots were randomly divided into 7 groups, control group and six TUS groups of three frequencies (0.3, 0.5, 0.7 MHz) and six intensities (0.75, 1.5, 3, 237.7, 475, 950 W/cm²). Treatment was composed of 12 repetitions, 5 min US application and 3 min pause, lasting 93 min in total. Clots' weight and flow rate were measured before and after the treatment.

RESULTS

Mean initial clot weight (0.318 ± 0.129 g) and flow (0.53 ± 0.31 ml/min) were comparable among the experimental groups. We found a final clot weights reduction (0.15 ± 0.05, 0.16 ± 0.06, 0.09 ± 0.07, 0.21 ± 0.09, 0.17 ± 0.09, 0.17 ± 0.07 and 0.18 ± 0.02 g in groups 1 through 6, respectively) and a flow increase (30.61 ± 19.76, 52.1 ± 25.44, 28.78 ± 8.15, 43.93 ± 20.03, 40.86 ± 18.25 and 45.10 ± 22.20 ml/min in groups 1-6, respectively) in all TUS groups. Clot weight change (%) and flow increase reveals that the TUS profile f = 0.5 MHz I = 1.5 W/cm² was most efficacious. In the control group, clot weight change was +6.3% of baseline and flow increase of 4.4% of baseline, whereas -75.4% of baseline and 209.3% of baseline in the f = 0.5 MHz I = 1.5 W/cm² profile were noted, respectively.

CONCLUSIONS

Our study proved that TUS at low frequency (0.5 MHz) is most effective, whereas changing the intensity of TUS has only a minor effect on clot lysis magnitude.

Evaluation of a small flat rectangular therapeutic ultrasonic transducer intended for intravascular use

BACKGROUND

The aim of the proposed study was to evaluate the performance of a flat rectangular (2×10mm²) transducer operating at 4MHz. The intended application of this transducer is intravascular treatment of thrombosis and atherosclerosis.

METHODS

The transducer's thermal capabilities were tested in two different gel phantoms. MR thermometry was used to demonstrate the thermal capabilities of this type of transducer.

RESULTS

Temperature measurements demonstrated that this simple and small transducer adequately produced high temperatures, which can be utilized for therapeutic purposes. These high temperatures were confirmed using thermocouple and MR measurements. Pulsed ultrasound in combination with thrombolytic drugs and microbubbles was utilized to eliminate porcine thrombi.

CONCLUSIONS

The proposed transducer has the potentials to treat atherosclerotic lesions using the thermal properties of ultrasound, since high temperatures can be achieved in less than 5s. The results revealed that the destruction of thrombi using pulsed ultrasound requires long exposure time and high microbubble dosage.