An anesthetic method compatible with (18)F-FDG-PET studies in mice

Abstract

The purpose of this study was to establish an experimental setting and an anesthetic method compatible with future sequential studies using (18)F-FDG-PET single scans, i.e. autoradiographic measurements, for the estimation of metabolic rate of glucose (MRglc) in mice. In this study we had no access to a small animal PET scanner and therefore focus was on the anesthetic setting and optimization of the input function as a preparation for the future tumor metabolic studies. Initially, four combinations of intraperitoneal (ip) anesthesia were tested on tumor bearing mice. Fentanyl-fluanisone plus diazepam yielded low and stable blood glucose levels and kept the animals sedated for approximately 2 h. The anesthesia was also tested in a longitudinal (18)F-FDG study, where tumor bearing mice were anesthetized, injected with (18)F-FDG, and sampled for blood, before, one day after, and 8 days after treatment with cisplatin. The animals were in good condition during the entire study period. To validate the method, average MRglc of whole brain and cerebellum in mice were calculated and compared with the literature. The average MRglc in the whole brain and cerebellum were 46.2±4.4 and 39.0±3.1 µmol 100g(-1) min(-1). In the present study, we have shown that an ip anesthesia with a combination of fentanyl-fluanisone and diazepam is feasible and provides stable and low blood glucose levels after a fasting period of 4 h in experiments in nude mice with xenografted human tumors. We have also verified that (18)F-FDG, intraperitoneally administrated, results in an expected plasma activity uptake and clearance. The method doesn't alter the uptake in brain which is an indirect indication that the anesthesia doesn't alter the uptake in other organs. In combination with meticulous animal handling this set-up is reliable and future sequential tumor studies of early metabolic effects with calculation of MRglc following cytotoxic therapy are made possible.

Keywords: 18F-FDG; anesthesia; metabolic rate of glucose (MRglc); mice.

Figure 1

The protocol including time points for start of fasting, injection of anesthetics, and injection of ¹⁸F-FDG. Blood glucose and blood activity sampling time points during the experiments are also shown, Glc=glucose.

Figure 2

Typical representative time-activity curve from an ip injection of ¹⁸F-FDG. Errors from gamma counting statistics (< 3%) were taken as reported by the software. Error in the blood volumes in the capillary tubes was conservatively estimated at 10%. The total uncertainty in the data points in Figure 2 was calculated by combining these contributing errors in quadrature. The last data point, at 55 min post injection, was extrapolated linearly from the two previous.