A technique for monitoring mammalian cell growth and inhibition in situ via Fourier transform infrared spectroscopy

Towards identifying the mode of action of drugs using live-cell FTIR spectroscopy

Fourier transform infrared spectroscopy (FTIR) has been shown to be a promising tool for identifying the mode of action of drugs.

Attenuated total reflection Fourier-transform infrared (ATR-FTIR) imaging of tissues and live cells

FTIR spectroscopic imaging is a label-free, non-destructive and chemically specific technique that can be utilised to study a wide range of biomedical applications such as imaging of biopsy tissues, fixed cells and live cells, including cancer cells. In particular, the use of FTIR imaging in attenuated total reflection (ATR) mode has attracted much attention because of the small, but well controlled, depth of penetration and corresponding path length of infrared light into the sample. This has enabled the study of samples containing large amounts of water, as well as achieving an increased spatial resolution provided by the high refractive index of the micro-ATR element. This review is focused on discussing the recent developments in FTIR spectroscopic imaging, particularly in ATR sampling mode, and its applications in the biomedical science field as well as discussing the future opportunities possible as the imaging technology continues to advance.

In situ Fourier transform infrared analysis of live cells' response to doxorubicin

The study of the response of cancer cells to chemotherapy drugs is of high importance due to the specificity of some drugs to certain types of cancer and the resistance of some specific cancer types to chemotherapy drugs. Our aim was to develop and apply the label-free and non-destructive Fourier transform infrared (FTIR) method to determine the sensitivity of three different cancer cell-lines to a common anti-cancer drug doxorubicin at different concentrations and to demonstrate that information about the mechanism of resistance to the chemotherapy drug can be extracted from spectral data. HeLa, PC3, and Caco-2 cells were seeded and grown on an attenuated total reflection (ATR) crystal, doxorubicin was applied at the clinically significant concentration of 0.1-20 μM, and spectra of the cells were collected hourly over 20 h. Analysis of the amide bands was correlated with cell viability, which had been cross validated with MTT assays, allowing to determine that the three cell lines had significantly different resistance to doxorubicin. The difference spectra and principal component analysis (PCA) highlighted the subtle chemical changes in the living cells under treatment. Spectral regions assigned to nucleic acids (mainly 1085 cm(-1)) and carbohydrates (mainly 1024 cm(-1)) showed changes that could be related to the mode of action of the drug and the mechanism of resistance of the cell lines to doxorubicin. This is a cost-effective method that does not require bioassay reagents but allows label-free, non-destructive and in situ analysis of chemical changes in live cells, using standard FTIR equipment adapted to ATR measurements.

Synchrotron IR spectromicroscopy: chemistry of living cells

Advanced analytical capabilities of synchrotron IR spectromicroscopy meet the demands of modern biological research for studying molecular reactions in individual living cells. (To listen to a podcast about this article, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.).

In situ observation of a cell adhesion and metabolism using surface infrared spectroscopy

In this study, we report on an in situ monitoring system of living cultured cells using infrared absorption spectroscopy in the geometry of multiple internal reflections (MIR-IRAS). In order to observe living cultured cells, the temperature in the sample chamber of a FT-IR spectrometer was maintained at 37 degrees C and a humidified gas mixture containing 5% CO(2) was introduced into the sample chamber. Human breast cell line MCF-7 cultured on Si MIR prisms were placed in the sample chamber and infrared spectra of MCF-7 cells were collected for 5 h. It was found that the adhesion and metabolism of MCF-7 cells could be monitored by the absorption intensity of amide-II protein band (1,545 cm(-1)) and also by the absorption intensities of CH( x ) bands (2,700-3,100 cm(-1)). These results suggest that our system is useful for a nondestructive and non-label monitoring of cell viability. Our method based on infrared absorption spectroscopy has a potential for bioscreening application.

Effects of ELF magnetic field on membrane protein structure of living HeLa cells studied by Fourier transform infrared spectroscopy

The effects of exposure to a 50 Hz magnetic field (maximum of 41.7 to 43.6 mT) on the membrane protein structures of living HeLa cells were studied using attenuated total reflection infrared spectroscopy. One min of such exposure shifted peak absorbance of the amide I band to a smaller wave number, reduced peak absorbance of the amide II band, and increased absorbance at around 1600 cm(-1). These results suggest that exposure to the ELF magnetic field has reversible effects on the N-H inplane bending and C-N stretching vibrations of peptide linkages, and changes the secondary structures of alpha-helix and beta-sheet in cell membrane proteins.

Real-time in situ monitoring of freely suspended and immobilized cell cultures based on mid-infrared spectroscopic measurements

Glucose and lactate profiles in Chinese hamster ovary cell cultures were accurately monitored in real time and in situ during three bioreactor batch cultures lasting 11,15, and 15 days performed within a 60-day period. Monitoring was accomplished using in situ-collected mid-infrared spectra analyzed with a priori one-time established partial least-squares regression models. The robustness of the technique was demonstrated by application of these models without modification after 2.3 years. Neither recalibration nor instrument maintenance was required during the 2.3-year period, except for the daily filling of liquid nitrogen for detector cooling during operation. The lactate calibration model yielded accurate absolute concentration estimations during each of the batch cultures with standard errors of estimate from 1 to 3 mM. The a priori-established glucose calibration model yielded concentration estimations with an off-set, which was constant throughout a culture. Adjustment of the off-set before inoculation resulted in accurate concentration estimations with Standard errors of estimate of approximately 1 mM for each of the bioreactor cultures. Sensitivity in detecting differences of 0.5 mM and selectivity against variation of one metabolite while the other was kept constant was demonstrated during standard additions of either glucose or lactate. The sensor system proved to be reliable, simple, accurate, sterile, and capable of long-term automatic operation and is considered to be mature enough to be routinely applied for in situ (on-line) cell culture monitoring.

Discrimination among Bacillus cereus, B. mycoides and B. thuringiensis and some other species of the genus Bacillus by Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) in conjunction with canonical variate analysis was found to be effective in discriminating among spectra of 9 representative strains of Bacillus spp., including B. cereus, B. mycoides and B. thuringiensis. The method was also able to discriminate according to species among spectra of 14 other non-type strains of B. cereus, 12 of B. mycoides and 12 of B. thuringiensis with a success rate of > 95%, even without using a prior classification of the groups by species. FTIR spectroscopy can be used for the rapid and accurate differentiation of species in the genus Bacillus that are of importance to the food and dairy industry.

Chemostat flow cell system: an in vitro model for the evaluation of antiplaque agents

We developed an experimental in vitro model of dental plaque to assess the potential efficacy of antiplaque agents. The model used a chemostat, which provided a continuous source of 5 species of oral bacteria grown in an artificial "saliva-like" medium. This mixture was pumped through six flow cells, each containing two types of surfaces on which plaque formed and was subsequently measured. Formation of bacterial plaque on hydroxyapatite surfaces was assessed by measurement of the DNA and protein content of the plaque film. The amount of bacterial plaque formed on germanium surfaces was measured by attenuated total reflectance (ATR/FT-IR) spectroscopy. Plaque viability was also assessed by a fluorescent staining technique. The quantity of plaque formed on both types of surfaces gradually increased with the duration of flow (from 24 to 72 h) through the cells during a 72-hour experimental period. The flow cells were then pulsed with experimental treatment solutions for 30 s, twice daily. Parallel to results of human clinical studies, the model was capable of discriminating among water, a placebo mouthrinse, and an active antimicrobial mouthrinse formulation containing 0.03% triclosan. It therefore offers a valuable alternative to animal model testing and allows for more rapid evaluations under well-controlled experimental conditions.

Monitoring of bacterial growth and structural analysis as probed by FT-IR spectroscopy

Fourier-transform infrared spectroscopy was used to explore structural changes in bacteria under different incubation conditions. In particular, differences between Bradyrhizobium japonicum (BRJ) grown in liquid and on solid media were investigated, as well as the rearrangement of BRJ after transfer from one medium to the other. The FT-IR absorption bands located between 1200 and 900 cm-1 region, vary in spectral shape and intensity when BRJ were suspended in solution medium or plated on solid medium. In agreement with the electronic micrograph data, these spectroscopic changes are due to the changes involving the bacterial wall (peptidoglycan) when BRJ are plated in agar medium. By means of this FT-IR ultrastructural study of Bradyrhizobium japonicum bacteria, it has been possible to follow and to evaluate the rate of the molecular change in bacteria without any destructive interference. This indicates that FT-IR spectroscopy can prove to be a valuable technique in the monitoring of metabolic events in bacterial cells relevant to agriculture as well as environmental and health sciences.

Biochemical analysis and mapping of atherosclerotic human artery using FT-IR microspectroscopy

We report the application of FT-IR microspectroscopy for in situ spectroscopic characterization of molecular constituents of human atherosclerotic lesions. Since water content in tissue affects conformation-sensitive protein vibrational bands, tissue specimens were examined under moist conditions. In all measurements, vibrational bands from water were found to dominate the spectrum. By removing these water contributions, well resolved bands due to tissue components were readily observed. Utilizing the high sensitivity and good spatial resolution of IR microspectroscopy, spectra from a sample volume of 40 x 40 x 4 microns3 were collected using unstained cryostat sections mounted on a BaF2 flat in neutral isotonic saline. Microstructures were confirmed histologically by light microscopy in stained serial sections. In the spectrum of normal intima, major bands due to amide I (1656 cm-1), amide II (1556 cm-1), and CH bending (1457 cm-1) vibrations of the proteins collagen and elastin were observed. In the spectrum of the intima of noncalcified atherosclerotic plaque, major bands due to both proteins and lipids were observed. The lipid bands at 1734, 1468, 1171 and 1058 cm-1 were assigned to the C = O (ester) stretch, CH2 bend, C--O (ester) stretch and C--O stretch, respectively. At a more detailed level, bands specific to free cholesterol, and cholesterol esters were identified. A plot of the integrated intensity ratio of these bands to the protein amide II mode versus depth from the luminal surface confirmed a heterogeneous distribution of these constituents in the atheromatous core. In the spectra of calcified atherosclerotic plaque, bands were attributed to three types of biochemical microstructures: proteins (1657, 1555, 1243 cm-1), lipids (1735, 1466, 1170, 1085, 1055 cm-1) and calcium minerals such as hydroxyapatite (1094, 1040, 962 cm-1), and carbonated apatite (1463, 1412, 872 cm-1). The results demonstrate that IR microspectroscopy can be used for in situ characterization of molecular constituents in human unstained arterial sections. The molecular information obtained from these studies could be important in understanding the pathogenesis of atherosclerosis.