Quantitative Analysis of Apoptotic Cell Death Using Proton Nuclear Magnetic Resonance Spectroscopy

Nuclear magnetic resonance metabolic fingerprint of bevacizumab in mutant IDH1 glioma cells

Background

Malignant gliomas are rapidly growing tumours that extensively invade the brain and have bad prognosis. Our study was performed to assess the metabolic effects of bevacizumab on the glioma cells carrying the IDH1 mutation, a mutation, associated with better prognosis and treatment outcome. Bevacizumab is known to inhibit tumour growth by neutralizing the biological activity of vascular endothelial growth factor (VEGF). However, the direct effects of bevacizumab on tumour cells metabolism remain poorly known.

Materials and methods

The immunoassay and MTT assay were used to assess the concentration of secreted VEGF and cell viability after bevacizumab exposure. Metabolomic studies on cells were performed using high resolution magic angle spinning spectroscopy (HRMAS).

Results

mIDH1-U87 cells secreted VEGF (13 ng/mL). Regardless, bevacizumab had no cytotoxic effect, even after a 72h exposure and with doses as high as 1 mg/mL. Yet, HRMAS analysis showed a significant effect of bevacizumab (0.1 mg/mL) on the metabolic phenotype of mIDH1-U87 cells with elevation of 2-hydroxyglutarate and changes in glutamine group metabolites (alanine, glutamate, glycine) and lipids (polyunsaturated fatty acids [PUFA], glycerophosphocholine, and phosphocholine).

Conclusions

In mIDH1-U87 cells, changes in glutamine group metabolites and lipids were identified as metabolic markers of bevacizumab treatment. These data support the possibility of a functional tricarboxylic acid cycle that runs in reductive manner, as a probable mechanism of action of bevacizumab in IDH1 mutated gliomas and propose a new target pathway for effective treatment of malignant gliomas.

Clinical applications of metabolomics in oncology: a review

Metabolomics, an omic science in systems biology, is the global quantitative assessment of endogenous metabolites within a biological system. Either individually or grouped as a metabolomic profile, detection of metabolites is carried out in cells, tissues, or biofluids by either nuclear magnetic resonance spectroscopy or mass spectrometry. There is potential for the metabolome to have a multitude of uses in oncology, including the early detection and diagnosis of cancer and as both a predictive and pharmacodynamic marker of drug effect. Despite this, there is lack of knowledge in the oncology community regarding metabolomics and confusion about its methodologic processes, technical challenges, and clinical applications. Metabolomics, when used as a translational research tool, can provide a link between the laboratory and clinic, particularly because metabolic and molecular imaging technologies, such as positron emission tomography and magnetic resonance spectroscopic imaging, enable the discrimination of metabolic markers noninvasively in vivo. Here, we review the current and potential applications of metabolomics, focusing on its use as a biomarker for cancer diagnosis, prognosis, and therapeutic evaluation.

Metabolomics using 1H-NMR of apoptosis and Necrosis in HL60 leukemia cells: differences between the two types of cell death and independence from the stimulus of apoptosis used

High-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy was used to examine and compare the metabolic variations that occur in cells of the HL60 promyelocytic leukemia cell line after induction of apoptosis by ionizing radiation and the antineoplastic drug doxorubicin as well as after induction of necrosis by heating. Apoptosis and necrosis were confirmed by fluorescence microscopy using the chromatin stain Hoechst 33258, agarose gel electrophoresis of DNA, and determination of caspase 3 enzymatic activity. The 1H-NMR experiments revealed that the spectra of both samples containing apoptotic cells were characterized by the same trend of several important metabolites. Specifically, an increase in CH2 and CH3 mobile lipids, principally of CH2, decreases in glutamine and glutamate, choline-containing metabolites, taurine and reduced glutathione were observed. By contrast, the sample containing necrotic cells presented a completely different profile of 1H-NMR metabolites since it was characterized by a significant increase in all the metabolites examined, with the exception of CH2 mobile lipids, which remain unchanged, and reduced glutathione, which decreased. The results suggest that variations in 1H-NMR metabolites are specific to apoptosis independent of the physical or chemical nature of the stimulus used to induce this mode of cell death, while cells dying from necrosis are characterized by a completely different behavior of the same metabolites.

Temporal Dynamics of1H-NMR-Visible Metabolites during Radiation-Induced Apoptosis in MG-63 Human Osteosarcoma Spheroids

The metabolic changes that occur as a function of time in MG-63 osteosarcoma three-dimensional tumor spheroids undergoing radiation-induced apoptosis were studied using high-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. Specifically, the (1)H-NMR spectra of MG-63 spheroids collected at 24, 48 and 72 h after exposure to 5 Gy of ionizing radiation were compared to the spectra of their respective controls. Small spheroids (about 50-80 microm in diameter) with no hypoxic center were used. Apoptosis was verified by both staining of spheroid DNA with the Hoechst 33258 dye and determination of caspase 3 enzyme activity at the three times examined. The results demonstrate that, as the percentage of apoptosis rises with time after exposure to ionizing radiation, the metabolic changes that take place in MG-63 spheroids follow very precise temporal dynamics. In particular, significant time-related increases in both CH(2) and CH(3) mobile lipids, considered by many authors as markers of apoptosis, were observed. In addition, temporal variations were also observed in choline-containing metabolites, reduced glutathione (GSH), glutamine/glutamate, taurine, alanine, creatine/phosphocreatine and lactate. These data show that in addition to CH(2) and CH(3) lipids, other metabolites can also be extremely useful in a deeper understanding of the temporal dynamics of radiation-induced apoptosis. This comprehension is particularly important in spheroids, a cell model of great complexity that resembles in vivo tumors much more closely than monolayer cultures. Ultimately, it is hoped that such studies can help to evaluate the outcome of radiotherapy protocols more accurately.

Time dependency of metabolic changes in rat lens after in vivo UVB irradiation analysed by HR-MAS 1H NMR spectroscopy

The lens ability to protect against, and repair ultraviolet radiation (UVR) induced damages, is of crucial importance to avoid cataract development. The influence of UVR-induced damage and repair processes on the lens metabolites are not fully understood. Observation of short- and long-term changes in light scattering and the metabolic profile of pigmented rat lenses after threshold UVR exposure might serve to better understand the protective mechanisms in the lens. By using high resolution magic angle spinning (HR-MAS) 1H NMR spectroscopy it was possible to investigate the metabolites of intact rat lenses. Brown-Norway rats were exposed to 15 kJm(-2) UVB irradiation. One eye was exposed and the contralateral served as control. The rats were sacrificed 5, 25, 125, and 625 hr post-exposure and the lenses were removed. The degree of cataract was quantified by measurement of lens forward light scattering. Thereafter, proton NMR spectra from intact lenses were obtained and relative changes in metabolite concentrations were determined. The light scattering in the lens peaked at 25 hr post-exposure and decreased thereafter. The lowest level of light scattering was measured 625 hr after exposure. No significant changes in concentration were observed for the metabolites 5 and 25 hr post-exposure except the total amount of adenosine tri- and diphosphate (ATP/ADP) that showed a significant decrease already 5 hr after exposure. At 125 hr the lens concentrations of lactate, succinate, phospho-choline, taurine, betaine, myo-inositol, and ATP/ADP showed a significant decrease (p<0.05). Phenylalanine was the only metabolite that revealed a significant increase 125 hr post-exposure. At 625 hr most of the metabolic changes seemed to normalise back to control levels. However, the concentration of betaine and phospho-choline were still showing a significant decrease 625 hr after UVB irradiation. The impact of UVB irradiation on the metabolic profile did not follow the same time dependency as the development of cataract. While the light scattering peaked at 25 hr post-exposure, significant changes in the endogenous metabolites were observed after 125 hr. Both the metabolic changes and the light scattering seemed to average back to normal within a month after exposure. Significant decrease in osmolytes like taurine, myo-inositol and betaine indicated osmotic stress and loss of homeostasis. This study also demonstrated that HR-MAS 1H NMR spectroscopy provides high quality spectra of intact lenses. These spectra contain a variety of information that might contribute to a better understanding of the metabolic response to drugs or endogenous stimuli like UVB irradiation.

Noninvasive magnetic resonance spectroscopic imaging biomarkers to predict the clinical grade of pediatric brain tumors

The diagnosis and therapy of childhood brain tumors, most of which are low grade, can be complicated because of their frequent adjacent location to crucial structures, which limits diagnostic biopsy. Also, although new prognostic biomarkers identified by molecular analysis or DNA microarray gene profiling are promising, they too depend on invasive biopsy. Here, we test the hypothesis that combining information from biologically important intracellular molecules (biomarkers), noninvasively obtained by proton magnetic resonance spectroscopic imaging, will increase the diagnostic accuracy in determining the clinical grade of pediatric brain tumors. We evaluate the proton magnetic resonance spectroscopic imaging exams for 66 children with brain tumors. The intracellular biomarkers for choline-containing compounds (Cho), N-acetylaspartate, total creatine, and lipids and/or lactate were measured at the highest Cho region and normalized to the surrounding healthy tissue total creatine. Neuropathological grading was done with WHO criteria. Normalized Cho and lipids and/or lactate were elevated in high-grade (n = 23) versus low-grade (n = 43) tumors, which multiple logistic regression confirmed are independent predictors of tumor grade (for Cho, odds ratio 24.8, P < 0.001; and for lipids and/or lactate, odds ratio 4.4, P < 0.001). A linear combination of normalized Cho and lipids and/or lactate that maximizes diagnostic accuracy was calculated by maximizing the area under the receiver operating characteristic curve. Proton magnetic resonance spectroscopic imaging, although not a proxy for histology, provides noninvasive, in vivo biomarkers for predicting clinical grades of pediatric brain tumors.