Real-Time Microfluidic Blood-Counting System for PET and SPECT Preclinical Pharmacokinetic Studies.

UNLABELLED: Small-animal nuclear imaging modalities have become essential tools in the development process of new drugs, diagnostic procedures, and therapies. Quantification of metabolic or physiologic parameters is based on pharmacokinetic modeling of radiotracer biodistribution, which requires the blood input function in addition to tissue images. Such measurements are challenging in small animals because of their small blood volume. In this work, we propose a microfluidic counting system to monitor rodent blood radioactivity in real time, with high efficiency and small detection volume (∼1 µL). METHODS: A microfluidic channel is built directly above unpackaged p-i-n photodiodes to detect ß-particles with maximum efficiency. The device is embedded in a compact system comprising dedicated electronics, shielding, and pumping unit controlled by custom firmware to enable measurements next to small-animal scanners. Data corrections required to use the input function in pharmacokinetic models were established using calibrated solutions of the most common PET and SPECT radiotracers. Sensitivity, dead time, propagation delay, dispersion, background sensitivity, and the effect of sample temperature were characterized. The system was tested for pharmacokinetic studies in mice by quantifying myocardial perfusion and oxygen consumption with (11)C-acetate (PET) and by measuring the arterial input function using (99m)TcO4 (-) (SPECT). RESULTS: Sensitivity for PET isotopes reached 20%-47%, a 2- to 10-fold improvement relative to conventional catheter-based geometries. Furthermore, the system detected (99m)Tc-based SPECT tracers with an efficiency of 4%, an outcome not possible through a catheter. Correction for dead time was found to be unnecessary for small-animal experiments, whereas propagation delay and dispersion within the microfluidic channel were accurately corrected. Background activity and sample temperature were shown to have no influence on measurements. Finally, the system was successfully used in animal studies. CONCLUSION: A fully operational microfluidic blood-counting system for preclinical pharmacokinetic studies was developed. Microfluidics enabled reliable and high-efficiency measurement of the blood concentration of most common PET and SPECT radiotracers with high temporal resolution in small blood volume.

EP 80317, a selective CD36 ligand, shows cardioprotective effects against post-ischaemic myocardial damage in mice.

AIMS: The CD36 receptor plays an important role in facilitating fatty acid transport to the heart. The present study aimed to assess whether EP 80317, a selective synthetic peptide ligand of CD36, is cardioprotective in a murine model of myocardial ischaemia and reperfusion (MI/R) injury. METHODS AND RESULTS: Mice were pretreated with daily subcutaneous injections of EP 80317 for 14 days before being subjected to a 30 min ligation of the left anterior descending coronary artery. The treatment reduced the infarct area and improved myocardial haemodynamics and function, as shown by an increase in cardiac output, ejection fraction and stroke work, and a reduced total peripheral resistance. In contrast, administration of EP 51389, a tripeptide analogue devoid of binding affinity to CD36, did not protect against myocardial injury. Six hours after myocardial reperfusion, EP 80317-treated mice showed reduced myocardial fatty acid uptake, as assessed by micro-positron emission tomography, in agreement with reduced levels of circulating non-esterified fatty acids. Studies using [(14)C]-palmitate infusion revealed reduced lipolysis, although no significant change in insulin or catecholamine plasma levels were observed. Increased expression levels of adipogenic and anti-lipolytic genes further supported an effect of EP 80317 in preventing fatty acid mobilization from adipose tissue. No effect of the treatment was observed in CD36(-/-) mice. CONCLUSION: Our results show that pretreatment with EP 80317 protected the heart against damage and dysfunction elicited by MI/R, along with a transient reduction in peripheral lipolysis. Our findings support CD36 as a novel target for the treatment of ischaemic cardiopathy.