Nicolas Geis

Ultrasound targeted microbubble destruction for drug and gene delivery.

Background: Gas-filled microbubbles have been used as ultrasound contrast agents for some decades. More recently, such microbubbles have evolved as experimental tools for organ- and tissue-specific drug and gene delivery. When sonified with ultrasound near their resonance frequency, microbubbles oscillate. With higher ultrasound energies, oscillation amplitudes increase, leading to microbubble destruction. This phenomenon can be used to deliver a substance into a target organ, if microbubbles are co-administered loaded with drugs or gene therapy vectors before i.v. injection. Objective: This review focuses on different experimental applications of microbubbles as tools for drug and gene delivery. Different organ systems and different classes of bioactive substances that have been used in previous studies will be discussed. Methods: All the available literature was reviewed to highlight the potential of this non-invasive, organ-specific delivery system. Conclusion: Ultrasound targeted microbubble destruction has been used in various organ systems and in tumours to successfully deliver drugs, proteins, gene therapy vectors and gene silencing constructs. Many proof of principle studies have demonstrated its potential as a non-invasive delivery tool. However, too few large animal studies and studies with therapeutic aims have been performed to see a clinical application of this technique in the near future. Nevertheless, there is great hope that preclinical large animal studies will confirm the successful results already obtained in small animals.

New doxorubicin-loaded phospholipid microbubbles for targeted tumor therapy: in-vivo characterization.

Doxorubicin(DOX) is a potent chemotherapy drug that is often limited by severe adverse effects such as cardiac toxicity and myelosupression. Drug targeting with non invasive techniques would be desirable, aiming at increased local drug concentration and reduced systemic side effects. Ultrasound(US) targeted destruction of drug loaded microbubbles(MBs) has evolved as a promising strategy for non invasive local gene and drug delivery. A recently developed novel DOX-loaded microbubble (DOX-MB) formulation was previously tested in-vitro, with optimal DOX loading capacity, ideal physical characteristics and preserved antiproliferative efficacy. The aim of this study was to evaluate applicability and efficacy of DOX-loaded MBs in a pancreas carcinoma model of the rat. First, immediate toxicity was tested in rats ruling out in-vivo MB agglomeration/capillary adhesion with subsequent embolisation/occlusion of the pulmonary vasculature. In a second set of experiments, tumors derived from pancreas carcinomas were implanted in both flanks of Lewis rats. After establishing the tumors, DOX-MBs were administered intravenously while one of the two tumors was exposed to US (1.3 MHz; mechanical index 1.6). DOX tissue concentration was measured in tumors and control organs after the experiment. Finally, efficacy of US targeted destruction of DOX-MBs in tumors was studied, looking at tumor growth after two therapeutic applications. All rats survived the DOX-MB administration without any sign of embolisation/occlusion of the pulmonary vasculature. US targeted destruction of DOX-MBs leads to a 12-fold higher tissue concentration of DOX and a significantly lower tumor growth in the target tumor compared to the contralateral control tumor. In conclusion, novel DOX-loaded MBs can be safely administered to rats, leading to a relevant increase in local drug concentration and reduction in tumor growth.

Microbubbles as a Vehicle for Gene and Drug Delivery: Current Clinical Implications and Future Perspectives

Ultrasound targeted microbubble destruction (UTMD) has evolved as a novel system for non-invasive, organ- and tissue-specific drug and gene delivery. Initially developed as ultrasound contrast agents, microbubbles (MBs) have increasingly gained attention for their ability to directly deliver different classes of bioactive substances (e.g. genes, drugs, proteins, gene silencing constructs) to various organ systems and tumors. Bioactive substances can be attached to or incorporated in the microbubble shells. Applying ultrasound at their resonance frequency, microbubbles oscillate. When using higher ultrasound energies, oscillation amplitudes increase, finally resulting in microbubble destruction. This leads to increased capillary and cell membrane permeability in the immediate vicinity of the ruptured MBs, thus facilitating tissue and cell penetration of co-administered or loaded bioactive substances. Numerous proof of principle studies have been performed, demonstrating the broad potential of UTMD as a site-specific, non-invasive therapeutic tool, delivering microbubble payload to various target tissues and organ systems or facilitating uptake of bioactive substances into tissues or cells. This review focuses on current in vivo studies and therapeutic approaches of UTMD. Promising results give hope for future clinical applications of this novel non-viral vector system. Nevertheless, several limitations remain, which will also be discussed in this review article.

One year clinical efficacy and reverse cardiac remodelling in patients with severe mitral regurgitation and reduced ejection fraction after MitraClip implantation.

The aim of the present study was to investigate 1 year clinical and functional efficacy of percutaneous mitral valve (MV) repair using MitraClip™ in high‐risk surgical patients with symptomatic severe MV regurgitation (MR) and reduced LVEF.

Left atrial appendage occlusion in atrial fibrillation after intracranial hemorrhage

Objective: To evaluate the safety and feasibility of percutaneous left atrial appendage occlusion (LAAO) in patients with atrial fibrillation (AF) and previous intracranial hemorrhage (ICH). Methods: In an explorative, prospective, single-center, observational study, LAAO was performed in patients with previous ICH and AF using the Amplatzer Cardiac Plug device. Risks of ischemic strokes and hemorrhagic complications were estimated using the CHA2DS2Vasc score and the HAS-BLED score. Before and 1, 6, 12, and 24 months after the procedure, clinical status and complications were recorded. Major complications were predefined as periprocedural stroke, death, pericardial effusion, and device embolism. Results: LAAO was performed in 20 patients. Based on CHA2DS2Vasc score (mean 4.5 ± 1.4) and HAS-BLED score (mean 4.7 ± 1.0), annual risks of stroke and hemorrhagic complications were 4.0%–6.7% and 8.7%–12.5%, respectively. No patient had a procedure-related complication. Minor postprocedural complications were observed in 4/20 patients (2 inguinal hematoma, 1 self-limiting asystole, and 1 thrombus formation on device). No ischemic or hemorrhagic stroke occurred during a mean follow-up of 13.6 ± 8.2 months. Conclusions: In this first study of LAAO in patients with previous ICH, LAAO appears feasible and safe. A larger, controlled trial is needed to assess the efficacy and safety of the procedure compared to other preventive measures. Classification of evidence: This study provides Class III evidence that in patients with a history of previous ICH and AF, percutaneous LAAO is safe and feasible.

Spatial distribution of ultrasound targeted microbubble destruction increases cardiac transgene expression but not capillary permeability.

Ultrasound targeted microbubble destruction (UTMD) has evolved as a promising tool for organ specific gene and drug delivery. Using DNA-loaded microbubbles, cardiac transfection has been shown to be feasible. However, two-dimensional properties of the ultrasound beam limit cardiac transgene expression to the focal zone, thus, reducing its potential therapeutic effect. The aim of this study was to test if spatial distribution of ultrasound targeted microbubble destruction in the heart could lead to augmented transgene expression or increased capillary permeability. Lipid microbubbles containing plasmids with a luciferase transgene were used to target rat hearts. The diagnostic ultrasound probe was fixed in a mid-short axis view with a gel stand-off between the chest and probe. Ultrasound (1.3 MHz) with a mechanical index of 1.6 was intermittently applied to rats during microbubble infusion. Rats were randomized to either stay in that position or move horizontally in a cranio-caudal direction (3 mm sweep) relative to the ultrasound probe during UTMD. After 4 days, organs were harvested and analyzed for reporter gene expression. Another group of rats received Evans Blue, followed by UTMD with unloaded microbubbles. Again, rats were randomized into a static or moving group. Hearts were harvested to evaluate extravasation of Evans Blue. Moving rats in a cranio-caudal direction significantly increased transgene expression by 19-fold in the anterior heart, by sixfold in the posterior heart and by 32-fold in the apex. Interestingly, Evans Blue extravasation was not augmented in the moving group. Spatial distribution of UTMD may increase transgene expression due to sonication of larger areas in the heart. In contrast, capillary permeability does not increase, indicating less capillary damage.

Safety and efficacy of MitraClip™ therapy in patients with severely impaired left ventricular ejection fraction: results from the German transcatheter mitral valve interventions (TRAMI) registry

The aim of the present study was to assess the safety and efficacy of percutaneous mitral valve repair using the MitraClip™ device in patients with severely reduced systolic left ventricular (LV) function.

Percutaneous repair of mitral valve regurgitation in patients with severe heart failure: comparison with optimal medical treatment

Abstract Background: Occurrence of severe mitral valve (MV) regurgitation (MR) is an independent negative predictor of mortality in patients with severe systolic heart failure (HF). This study examines clinical effects and cardiac reverse remodelling in patients with severe systolic HF receiving percutaneous mitral valve repair (PMVR) using MitraClip in comparison to patients receiving optimal medical therapy only. Methods: Between 2010 and 2014, 86 patients (Society of Thoracic Surgeons score: 10.5% ± 1.2%) with severe HF (left ventricular [LV] ejection fraction; LVEF: 25% ± 2%; LV endsystolic diameter [LVESD]: 55 ± 3 mm) and severe MR received PMVR using MitraClip. Cardiac reverse remodelling and clinical parameters were compared to HF patients with severe MR (from our HF outpatient clinic; n = 69; LVEF: 26% ± 1.4%; LVESD: 53 ± 2 mm) receiving optimal medical therapy (OMT) only. All patients received stable OMT and were characterised by echocardiography, 6-minwalk-distance test and cardiac biomarkers within a 24 months observation period. Results: PMVR in patients with end-stage HF and severe MR resulted in reduction of MR and significant additional cardiac reverse remodelling (LVEF: 26 ± 1.4 vs. 33% ± 2%, p < .05; LVESD: 53 ± 2 vs. 47 ± 2 mm, p < .05) over the 24 months observation period as compared to pharmacologically-only managed comparators. Conclusions: Both OMT and PMVR cause cardiac reverse remodelling and relief of symptoms in patients with HF and severe MR. PMVR results in significant additional cardiac reverse remodelling compared to pharmacologically-only managed patients.

The Effects of Mitral Valve Repair on Memory Performance, Executive Function, and Psychological Measures in Patients With Heart Failure.

Objectives Heart failure (HF) is a prevalent disease that remains costly and associated with a high mortality rate. HF is also associated with poor neurocognitive functioning. For the treatment for HF patients with severe mitral regurgitation, the MitraClip device has emerged as a promising interventional tool that reduces the mitral valve leakage and thus increases cardiac output. Currently, there is only limited knowledge on changes in cognitive and psychosocial functioning before and after the MitraClip intervention. Methods Cognitive function (memory and executive function) and psychosocial measures (depression, anxiety, and quality of life) were assessed before and after the MitraClip intervention in 24 HF patients and 23 healthy participants (comparison group). Results MitraClip intervention in HF patients was followed by improvements in figural long-term memory (p = .003) and executive function (planning ability, p < .001) relative to the comparison group. In addition, the intervention resulted in a significant improvement in depression (p = .002), anxiety (p = .003) and quality of life scores (physical p = .017, mental p = .013) as well as improved 6-minute walk test results over time (p = .002). Conclusions The presented data provide evidence of a significant improvement in memory and executive function as well as in depression, anxiety, and quality of life scores in patients with chronic HF after MitraClip intervention. Further research is needed to shed light on the long-term development of cognitive function, psychosocial well-being, and clinical parameters after MitraClip intervention and how these factors depend on one another.

High Throughput Echocardiography in Conscious Mice: Training and Primary Screens

PURPOSE Genetic engineering techniques led to an exponential increase in the number of transgenic and knock-out mouse models. For many genetically modified mice, high throughput echocardiography is an essential part of a systematic screening workflow. Many researchers perform mouse echocardiography in conscious animals to avoid anesthesia-induced impairment of cardiac function. However, it has been controversially discussed whether mice need to be habituated to handling before their cardiac function can be assessed. The aim of this study was to test the influence of training on parameters assessed during conscious mouse echocardiography. In addition, we tested whether a simple and fast echocardiography protocol has sufficient sensitivity and specificity for primary screening. MATERIALS AND METHODS Examined parameters include fractional shortening, heart rate and respiratory rate. A total of 139 mice were examined in this study with a total of 587 echocardiograms. 103 mice were examined on five consecutive days (with examinations on day 1 - 4 regarded as training), 36 mice were only examined on day 1 and 5. RESULTS Fractional shortening, heart rate and respiratory rate did not show any statistically significant difference between day 1 and day 5 in both groups. The sensitivity and specificity of fractional shortening assessment for predicting a homozygote knock out genotype were 86 % and 97 %, respectively. CONCLUSION We conclude that conscious mouse echocardiography can be performed in untrained mice. Fractional shortening measurements may suffice for correct phenotyping in a high throughput setting.