Positron Emission Tomography with [(18)F]FLT Revealed Sevoflurane-Induced Inhibition of Neural Progenitor Cell Expansion in vivo

Abstract

Neural progenitor cell expansion is critical for normal brain development and an appropriate response to injury. During the brain growth spurt, exposures to general anesthetics, which either block the N-methyl-d-aspartate receptor or enhance the γ-aminobutyric acid receptor type A can disturb neuronal transduction. This effect can be detrimental to brain development. Until now, the effects of anesthetic exposure on neural progenitor cell expansion in vivo had seldom been reported. Here, minimally invasive micro positron emission tomography (microPET) coupled with 3'-deoxy-3' [(18)F] fluoro-l-thymidine ([(18)F]FLT) was utilized to assess the effects of sevoflurane exposure on neural progenitor cell proliferation. FLT, a thymidine analog, is taken up by proliferating cells and phosphorylated in the cytoplasm, leading to its intracellular trapping. Intracellular retention of [(18)F]FLT, thus, represents an observable in vivo marker of cell proliferation. Here, postnatal day 7 rats (n = 11/group) were exposed to 2.5% sevoflurane or room air for 9 h. For up to 2 weeks following the exposure, standard uptake values (SUVs) for [(18)F]-FLT in the hippocampal formation were significantly attenuated in the sevoflurane-exposed rats (p < 0.0001), suggesting decreased uptake and retention of [(18)F]FLT (decreased proliferation) in these regions. Four weeks following exposure, SUVs for [(18)F]FLT were comparable in the sevoflurane-exposed rats and in controls. Co-administration of 7-nitroindazole (30 mg/kg, n = 5), a selective inhibitor of neuronal nitric oxide synthase, significantly attenuated the SUVs for [(18)F]FLT in both the air-exposed (p = 0.00006) and sevoflurane-exposed rats (p = 0.0427) in the first week following the exposure. These findings suggested that microPET in couple with [(18)F]FLT as cell proliferation marker could be used as a non-invasive modality to monitor the sevoflurane-induced inhibition of neural progenitor cell proliferation in vivo.

Keywords: [18F]FLT; neural progenitor cell; positron emission tomography; proliferation; sevoflurane.

Figure 1

The structure of [¹⁸F]FLT and its phosphorylation by thymidine kinase 1 (TK₁).

Figure 2

Attenuated [¹⁸F]FLT uptake in the hippocampal region was revealed by serial microPET scans for the first 2 weeks following sevoflurane exposure on PND 7. On PND 7, the treated rats were exposed to sevoflurane (2.5%) mixed with oxygen for 9 h (n = 11); the control rats (n = 11) were exposed to room air. One (A), 2 (B), and 4 (C) weeks following the exposure, the animals were examined using microPET (scan time = 90 min) following the administration of [¹⁸F]FLT (18.5 MBq/dose) by i.p. injection. Standard uptake values (SUVs) are presented as means ± SEM. The [¹⁸F]FLT uptake in the hippocampus of sevoflurane-exposed rats was significantly attenuated compared with air-exposed rats in weeks 1 (p < 0.0001) and 2 (p = 0.0108) following the anesthetic exposure. (*p < 0.05, repeated measures linear mixed effect model). By week 4, the SUVs in the sevoflurane-exposed rats and the air-exposed rats were no longer significantly different (p = 0.9047, repeated measures linear mixed effect model).

Figure 3

Co-administration of 7-NI induced inhibition upon [¹⁸F]FLT uptake in the hippocampal regions in either air- or sevoflurane- exposed rats. On PND 7, the rats (n = 5) were treated with 7-NI i.p. (30 mg/kg body weight, dissolved in corn oil) 18 and 1 h prior to and 4 h following the beginning of 9 h-exposure to either sevoflurane or air. One, 2, and 4 weeks after exposure the animals were assessed via microPET 30 min after the injection of [¹⁸F]FLT i.p. (18.5 MBq/dose). In week 1, the [¹⁸F]FLT uptake of the hippocampus region in rats co-administrated with 7-NI was significantly lower than those in rats exposed to either air (p = 0.00006) or sevoflurane (p = 0.0427) only. In week 4 after exposure, the SUV in sevoflurane-exposed plus 7-NI group remained significantly lower than that of group exposed to sevoflurane only (p = 0.0077, Dunnett’s test). SUVs are presented as means ± SEM, asterisks denote significant differences in [¹⁸F]FLT uptake between the rats co-administrated 7-NI and those exposed to air or sevoflurane alone in weeks 1, 2 or 4 after exposure (*p < 0.05, repeated measures linear mixed effect model, Dunnett’s test for multiple comparisons).