Online ¹H‐MRS measurements of time‐varying lactate production in an animal model of glioma during administration of an anti‐tumoral drug

Abstract

The aims of this study were to implement a magnetic resonance spectroscopy (MRS) protocol for the online profiling of subnanomolar quantities of metabolites sampled from the extracellular fluid using implanted microdialysis and to apply this protocol in glioma-bearing rats for the quantification of lactate concentration and the measurement of time-varying lactate concentration during drug administration. MRS acquisitions on the brain microdialysate were performed using a home-built, proton-tuned, microsolenoid with an active volume of 2 μL. The microcoil was placed at the outlet of the microdialysis probe inside a preclinical magnetic resonance imaging (MRI) scanner. C6-bearing rats were implanted with microdialysis probes perfused with artificial cerebrospinal fluid solution and the lactate dehydrogenase (LDH) inhibitor oxamate. Microcoil magnetic resonance spectra were continuously updated using a single-pulse sequence. Localized in vivo spectra and high-resolution spectra on the dialysate were also acquired. The limit of detection and limit of quantification per unit time of the lactate methyl peak were determined as 0.37 nmol/√min and 1.23 nmol/√min, respectively. Signal-to-noise ratios (SNRs) of the lactate methyl peak above 120 were obtained from brain tumor microdialysate in an acquisition time of 4 min. On average, the lactate methyl peak amplitude measured in vivo using the nuclear magnetic resonance (NMR) microcoil was 193 ± 46% higher in tumor dialysate relative to healthy brain dialysate. A similar ratio was obtained from high-resolution NMR spectra performed on the collected dialysate. Following oxamate addition in the perfusate, a monotonic decrease in the lactate peaks was observed in all animals with an average time constant of 4.6 min. In the absence of overlapping NMR peaks, robust profiling of extracellular lactate can be obtained online using a dedicated sensitive NMR microcoil. MRS measurements of the dynamic changes in lactate production induced by anti-tumoral drugs can be assessed accurately with temporal resolutions on the order of minutes. The MRS protocol can be readily transferred to the clinical environment with the use of suitable clinical microdialysis probes.

Neuroprotective role of lactate in rat neonatal hypoxia-ischemia

“…The enzyme lactate dehydrogenase (LDH) was also blocked with oxamate to assess the implication of lactate metabolism in the neuroprotection. 42 , 43 Motor and behavioral studies were also carried out to evaluate the long-term effect of lactate injection on cognitive functions. Our results demonstrate that both exogenous and endogenous lactate exert a neuroprotective effect on neonatal HI insult and open the way to clinical trials in the future, as already ongoing in human adult TBI.…”

Online Quantification of Lactate Concentration in Microdialysate During Cerebral Activation Using 1H-MRS and Sensitive NMR Microcoil

“…This time lag corresponds to the time required for the dialysate to travel the distance from the microdialysis membrane to the NMR microsolenoid. Measurement of this transit time was reported in a previous study (Crémillieux et al, 2018). This increase in lactate was observed in five consecutive spectra, a time window that corresponds ~15 min whisker stimulation period.…”

“…In a recent study (Crémillieux et al, 2018), we showed that, in the absence of macromolecules and lipids in the microdialysate, an accurate determination of lactate levels both in a glioma and in the healthy brain could be obtained online using a sensitive NMR microcoil. In this previous study the detection and quantification of lactate was, however, performed under isoflurane anesthesia, which is known to highly increase brain lactate concentration (Horn and Klein, 2010).…”

“…On the other hand, NMR profiling can be performed using a sensitive NMR detection coil optimized for the collected dialysate. In recent studies (Glöggler et al, 2016; Crémillieux et al, 2018), we reported the feasibility of using NMR microsolenoids, with inner volumes ranging from 1 to 2 μL, for an online quantitative assay of extracellular brain metabolites in healthy and glioma-bearing rats. Thanks, among other things, to the optimization of the microcoil-filling factor and to the reduction of magnetic susceptibility effects, the limit of quantification (signal-to-noise ratio>10) for lactate was lowered to 1.2 nmol/qopnamemin, corresponding to a lactate concentration of 0.6 mmol.L −1 /qopnamemin in the dialysate.…”

Evaluation of Hypoxia in Hepatocellular Carcinoma Using QuantitativeMRI: Significances, Challenges, and Advances

“…During the long acquisition time, several metabolites (such as lactate) may be detected inappropriately due to the dynamic nature of metabolic processes in vivo since MRS detects steady-state metabolite levels instead of real-time production and excretion rate. 50,51 Therefore, methods such as two-dimensional wavelet encoding-spectroscopic imaging have been proposed to shorten the acquisition time and reduce voxel size. 52 MRS has considerable potential to evaluate metabolism in tumors, and efforts are underway to improve its quantitative accuracy and correct for other factors affecting assessment accuracy.…”