Effects of Optison on pulmonary gas exchange and hemodynamics

Microbubble Size and Dose Effects on Pharmacokinetics

Optimization of contrast-enhanced imaging and focused ultrasound therapy requires a comprehensive understanding of in vivo microbubble (MB) pharmacokinetics. Prior studies have focused pharmacokinetic analysis on indirect techniques, such as ultrasound imaging of the blood pool and gas chromatography of exhaled gases. The goal of this work was to measure the MB concentration directly in blood and correlate the pharmacokinetic parameters with the MB size and dose. MB volume dose (MVD) was chosen to combine the size distribution and number into a single-dose parameter. Different MB sizes (2, 3, and 5 μm diameter) at 5-40 μL/kg MVD were intravenously injected. Blood samples were withdrawn at different times (1-10 min) and analyzed by image processing. We found that for an MVD threshold < 40 μL/kg for 2 and 3 μm and <10 μL/kg for 5 μm, MB clearance followed first-order kinetics. When matching MVD, MBs of different sizes had comparable half-lives, indicating that gas dissolution and elimination by the lungs are the primary mechanisms for elimination. Above the MVD threshold, MB clearance followed biexponential kinetics, suggesting a second elimination mechanism mediated by organ retention, possibly in the lung, liver, and spleen. In conclusion, we present the first direct MB pharmacokinetic study, demonstrate the utility of MVD as a unified dose metric, and provide insights into the mechanisms of MB clearance from circulation.

Therapeutic silence of pleiotrophin by targeted delivery of siRNA and its effect on the inhibition of tumor growth and metastasis

Pleiotrophin (PTN) is a secreted cytokine that is expressed in various cancer cell lines and human tumor such as colon cancer, lung cancer, gastric cancer and melanoma. It plays significant roles in angiogenesis, metastasis, differentiation and cell growth. The expression of PTN in the adult is limited to the hippocampus in an activity-dependent manner, making it a very attractive target for cancer therapy. RNA interference (RNAi) offers great potential as a new powerful therapeutic strategy based on its highly specific and efficient silencing of a target gene. However, efficient delivery of small interfering RNA (siRNA) in vivo remains a significant hurdle for its successful therapeutic application. In this study, we first identified, on a cell-based experiment, applying a 1:1 mixture of two PTN specific siRNA engenders a higher silencing efficiency on both mRNA and protein level than using any of them discretely at the same dose. As a consequence, slower melanoma cells growth was also observed for using two specific siRNA combinatorially. To establish a robust way for siRNA delivery in vivo and further investigate how silence of PTN affects tumor growth, we tested three different methods to deliver siRNA in vivo: first non-targeted in-vivo delivery of siRNA via jetPEI; second lung targeted delivery of siRNA via microbubble coated jetPEI; third tumor cell targeted delivery of siRNA via transferrin-polyethylenimine (Tf-PEI). As a result, we found that all three in-vivo siRNAs delivery methods led to an evident inhibition of melanoma growth in non-immune deficiency C57BL/6 mice without a measureable change of ALT and AST activities. Both targeted delivery methods showed more significant curative effect than jetPEI. The lung targeted delivery by microbubble coated jetPEI revealed a comparable therapeutic effect with Tf-PEI, indicating its potential application for target delivery of siRNA in vivo.

Safety of echocardiographic contrast in hospitalized patients with pulmonary hypertension: a multi-center study

AIMS

Echocardiographic contrast (EC) improves the diagnostic accuracy of suboptimal echocardiograms. In October 2007, the Food and Drug Administration (FDA) placed a black box warning on the label of the perflutren-based agents Definity and Optison, contraindicating their use in patients with pulmonary hypertension (PHT) and unstable cardiopulmonary status, after serious cardiopulmonary reactions occurred in temporal relation to EC administration. In 2008 and 2011, the FDA revised the black box warning allowing their use in this same population. However, limited data exist regarding the safety profile of these agents in patients with PHT.

METHODS AND RESULTS

Consecutive hospitalized patients with PHT who were referred for echocardiographic evaluation, but required the use of EC, were included. All our patients received the EC agent Definity. We evaluated these patients for serious adverse events (respiratory decompensation, hypotension, syncope, convulsions, arrhythmias, anaphylactic reactions, or death) occurring within 24 h of EC administration. The study group included 1513 patients (age 69 ± 14 years, 55% males, BMI 33 ± 9 kg/m(2)), of which 911 (60%) had mild PHT, 515 (34%) had moderate PHT, and 87 (6%) had severe PHT. The mean pulmonary artery systolic pressures (PASP) in the groups with mild, moderate, and severe PHT were 41 ± 4 (range 35-49) mmHg, 55 ± 5 (range 50-69) mmHg, and 78 ± 9 (range 70-122) mmHg, respectively. The incidence of adverse events in all subgroups was rare (0.002%) and they were not attributed to EC because of temporal and clinical considerations.

CONCLUSION

The use of the EC agent Definity is safe in hospitalized patients with PHT.

Microbubbles as ultrasound triggered drug carriers

Originally developed as contrast agents for ultrasound imaging and diagnostics, in the past years, microbubbles have made their way back from the patients' bedside to the researcher's laboratory. Microbubbles are currently believed to have great potential as carriers for drugs, small molecules, nucleic acids, and proteins. This review provides insight into this intriguing new frontier from the perspective of the pharmaceutical scientist. First, basic aspects on the application of ultrasound-targeted microbubble destruction for drug delivery will be presented. Next, we will review the recently applied approaches for manufacturing and drug-loading microbubbles. Important quality issues and characterization techniques for advanced microbubble formulation will be discussed. Finally, we will provide an assessment of the prospects for microbubbles in drug and gene therapy, illustrating the problems and requirements for their future development.

Contrast ultrasound: general principles and veterinary clinical applications

The concept of contrast enhancement has significantly extended the usefulness of ultrasound imaging in human medicine and medical research over the past decade. The persistence and efficacy of ultrasound contrast agents has been improved and specific imaging sequences have been developed. Contrast ultrasound provides Doppler and grey-scale enhancement. Doppler examinations are improved when studying deep or small vessels and vessels with low flow velocities. Specific contrast imaging sequences allow detection of tissue enhancement with grey-scale ultrasound which enables assessment of tissue perfusion. Major clinical applications of contrast ultrasound in the human medicine field are the heart, the parenchymal organs such as the liver, spleen and kidneys, and vascular applications. Many other interesting applications have been identified and beside their diagnostic value, intensive research is currently investigating the use of ultrasound contrast agents for therapeutic applications such as targeted delivery of drug- or gene-loaded microbubbles. In the last few years, contrast ultrasound has also been introduced in veterinary medicine. Its usefulness has been shown in diseases of the liver, spleen, kidney, pancreas, lymph nodes and superficial tumours. In the present article, an overview of the physical principles, imaging techniques and image analyses is presented. In addition, a literature review details the current use in veterinary medicine and areas of potential utilization are discussed.

Effects of IMAGENT on pulmonary hemodynamics and gas exchange in dogs

Imagent is an IV injected contrast echocardiography agent designed to image the left ventricle after traversing the pulmonary circulation. We examined the effect of Imagent on pulmonary function by injecting either Imagent (n = 8) or equivalent volume of saline (n = 7) IV in randomly ordered 1, 8 and 16 mg/kg doses in dogs with preexisting pulmonary hypertension. We found that Imagent had no effects on cardiac output, pulmonary gas exchange, lung wet:dry ratio or static compliance. However, the 16 mg/kg dose of Imagent increased both pulmonary artery pressure (PAP) transiently by an average of 5.7 mmHg (p < 0.05) 2 to 3 min after injection and pulmonary vascular resistance (PVR) by 5.9 mmHg per l/min (p < 0.05) 4 min after injection before returning to preinjection levels. The lower doses of Imagent did not affect PAP or PVR. These results imply that the approved clinical dose of Imagent (0.125 mg/kg) will not affect pulmonary hemodynamics, gas exchange or mechanical properties in dogs with preexisting pulmonary hypertension.

Absence of clinically significant increase in pulmonary artery pressure after intravenous perflutren injection for myocardial perfusion imaging in pigs

OBJECTIVE

We sought to evaluate the impact of a continuous intravenous infusion of perflutren on systemic pulmonary artery pressures at clinically relevant doses for myocardial perfusion imaging in pigs.

METHODS

Five anesthetized, ventilated, open-chest pigs were administered perflutren intravenously at a rate of 0.0364 mL/kg/min over approximately 5 minutes.

RESULTS

Optimal, sustained myocardial opacification was achieved in all animals. Perflutren produced transient, reversible increases in pulmonary artery pressures versus baseline: 10.6% (3.0 +/- 1.4 mm Hg; 95% confidence interval 1.7-4.2; P < .01) for systolic, 15.2% (2.5 +/- 1.4 mm Hg; 95% confidence interval 1.3-3.7; P < .05) for diastolic, and 11.6% (2.6 +/- 1.1 mm Hg; 95% confidence interval 1.68-3.65; P < .01) for mean pressures. Heart rate and systemic arterial pressures displayed nonsignificant increases during perflutren infusion compared with baseline.

CONCLUSION

A continuous intravenous infusion of perflutren at a rate achieving optimal, sustained myocardial perfusion imaging in pigs induces a mild, transient, not clinically significant increase in pulmonary artery pressures without affecting heart rate or systemic arterial pressures.

Adenosine triphosphate stress myocardial contrast echocardiography detects coronary artery stenosis with greater sensitivity than wall-motion abnormality measurements

BACKGROUND

Although stress myocardial contrast echocardiography (MCE) can be used to detect coronary stenosis, its efficacy relative to other methods, such as detection of wall-motion abnormalities, remains unknown. Thus, the goal of this study was to compare the sensitivity of MCE versus wall-motion abnormality detection in the assessment of coronary artery stenosis.

METHOD

Nine dogs with severe but nonflow limiting stenosis in the circumflex coronary artery underwent evaluation with real-time MCE along the short-axis view during infusion of Optison. The equation of y = a (1 - e -betat ) + c, which fits the replenishment curve of MCE, was calculated in the midseptum (normal region) and in the lateral wall (ischemic region) before and during adenosine triphosphate infusion. Wall-motion abnormalities were also evaluated by visual assessment and by measurement of wall thickening.

RESULTS

Area under the receiver operating characteristic curve in beta- and A x beta-value, and percent wall thickening, was 0.963, 0.963, and 0.889, respectively, indicating that the diagnostic accuracy for detecting the coronary artery stenosis by real-time MCE was higher than that by the wall-motion assessment.

CONCLUSION

Real-time MCE has higher sensitivity in detecting coronary stenosis during adenosine triphosphate stress test when compared with wall-motion assessment.

Anaphylactoid response to Optison(R) and its effects on pulmonary function in two dogs

Two of 26 anesthetized dogs given the cardiac echo-enhancing agent Optison showed anaphylactoid responses (AR) related to the human albumin component of this agent. The episodes of AR were self-limited, and could be reproduced by human albumin injection alone. Gas exchange was maintained by mechanical ventilation and 5 cm H(2)O PEEP, and dispersion of ventilation remained normal during AR despite severe hypotension. We suggest that: (1) pre-screening by measuring blood pressure response to intravenous injection of small doses of Optison, and (2) availability of access to the airway in addition to emergency agents may be prudent preventive measures when Optison is used in animals to enhance echocardiographic imaging.

Safety of ultrasound contrast agents

The use of ultrasound contrast agents has increased over recent years. The Contrast Media Safety Committee (CMSC) of the European Society of Urogenital Radiology (ESUR) decided to review the safety of ultrasound contrast agents in humans and to draw up guidelines. A comprehensive literature search and review was carried out. The resulting report was discussed by the CMSC of ESUR and at the 11th European Symposium on Urogenital Radiology in Santiago de Compostela, Spain, in 2004. Ultrasound contrast agents approved for clinical use are well tolerated, and serious adverse reactions are rarely observed. Adverse events are usually minor (e.g. headache, nausea, altered taste, sensation of heat) and self-resolving. These symptoms may not be related to the ultrasound contrast materials as they have also been observed in placebo-control groups. Intolerance to some components may occur. Generalized allergy-like reactions occur rarely. Ultrasound contrast agents are generally safe. The ultrasound scanning time and the acoustic output should be kept to the lowest level consistent with obtaining diagnostic information. Adverse reactions should be treated symptomatically.

Grey scale enhancement of rabbit liver and kidney by intravenous injection of a new lipid-coated ultrasound contrast agent

AIM: To assess the grey scale enhancement of a new lipid-coated ultrasound contrast agent in solid abdominal organs as liver and kidney.

METHODS: Size distribution and concentration of the lipid-coated contrast microbubbles were analyzed by a Coulter counter. Two-dimensional (2D) second harmonic imaging of the hepatic parenchyma, the inferior vena cava and the right kidney of the rabbits were acquired before and after contrast agent injection. Images were further quantified by histogram in Adobe Photoshop 6.0. Time-intensity curves of hepatic parenchyma, inferior vena cava and renal cortex were generated from the original grey scale.

RESULTS: The 2D images of hepatic parenchyma and cortex of the kidney were greatly enhanced after injection and the peak time could last more than 50 min.

CONCLUSION: This new lipid ultrasound contrast agent could significantly enhance the grey scale imaging of the hepatic parenchyma and the renal cortex for more than 50 min.

In vivo study of microbubbles as an MR susceptibility contrast agent

The potential application of gas microbubbles as a unique intravascular susceptibility contrast agent for MRI has not been fully explored. In this study, the MR susceptibility effect of an ultrasound microbubble contrast agent, Optison, was studied with rat liver imaging at 7 T. Optison suspension in two different doses (0.15 mL/kg and 0.4 mL/kg) was injected into rats, and induced transverse relaxation rate increases (deltaR2*) of 29.1 +/- 1.6 s(-1) (N = 2) and 61.5 +/- 12.9 s(-1) (N = 6), respectively, in liver tissue. Liver uptake of intact albumin microbubbles was observed 10 min after injection. Eight of the 16 rats studied showed no susceptibility enhancement. This is probably attributable to the intravascular microbubble growth due to transmural CO2 supersaturation in the cecum and colon in small animals that causes microbubble aggregation and trapping in the inferior vena cava (IVC). In vitro deltaR2* measurements of Optison suspension at different concentrations are also reported.