Spectroscopic Probing of Dynamic Changes during Stimulation and Cell Remodeling in the Single Cardiac Myocyte

Spectroscopic analysis of myoglobin and cytochrome c dynamics in isolated cardiomyocytes during hypoxia and reoxygenation

Raman microspectroscopy was applied to monitor the intracellular redox state of myoglobin and cytochrome c from isolated adult rat cardiomyocytes during hypoxia and reoxygenation. The nitrite reductase activity of myoglobin leads to the production of nitric oxide in cells under hypoxic conditions, which is linked to the inhibition of mitochondrial respiration. In this work, the subsequent reoxygenation of cells after hypoxia is shown to lead to increased levels of oxygen-bound myoglobin relative to the initial levels observed under normoxic conditions. Increased levels of reduced cytochrome c in ex vivo cells are also observed during hypoxia and reoxygenation by Raman microspectroscopy. The cellular response to reoxygenation differed dramatically depending on the method used in the preceding step to create hypoxic conditions in the cell suspension, where a chemical agent, sodium dithionite, leads to reduction of cytochromes in addition to removal of dissolved oxygen, and bubbling-N2 gas leads to displacement of dissolved oxygen only. These results have an impact on the assessment of experimental simulations of hypoxia in cells. The spectroscopic technique employed in this work will be used in the future as an analytical method to monitor the effects of varying levels of oxygen and nutrients supplied to cardiomyocytes during either the preconditioning of cells or the reperfusion of ischaemic tissue.

Monitoring Changes in the Redox State of Myoglobin in Cardiomyocytes by Raman Spectroscopy Enables the Protective Effect of NO Donors to Be Evaluated

Raman microspectroscopy has been used to monitor changes in the redox and ligand-coordination states of the heme complex in myoglobin during the preconditioning of ex vivo cardiomyocytes with pharmacological drugs that release nitric oxide (NO). These chemical agents are known to confer protection on heart tissue against ischemia-reperfusion injury. Subsequent changes in the redox and ligand-coordination states during experimental simulations of ischemia and reperfusion have also been monitored. We found that these measurements, in real time, could be used to evaluate the preconditioning treatment of cardiomyocytes and to predict the likelihood of cell survival following a potentially lethal period of ischemia. Evaluation of the preconditioning treatment was done at the single-cell level. The binding of NO to myoglobin, giving a 6-coordinate ferrous-heme complex, was inferred from the measured Raman bands of a cardiomyocyte by comparison to pure solution of the protein in the presence of NO. A key change in the Raman spectrum was observed after perfusion of the NO-donor was completed, where, if the preconditioning treatment was successful, the bands corresponding to the nitrosyl complex were replaced by bands corresponding to metmyoglobin, Mb(III). An observation of Mb(III) bands in the Raman spectrum was made for all of the cardiomyocytes that recovered contractile function, whereas the absence of Mb(III) bands always indicated that the cardiomyocyte would be unable to recover contractile function following the simulated conditions of ischemia and reperfusion in these experiments.

Label-free evaluation of myocardial infarction and its repair by spontaneous Raman spectroscopy

Raman spectroscopy, which provides information about molecular species and structures of biomolecules via intrinsic molecular vibrations, can analyze physiological and pathological states of tissues on the basis of molecular constituents without staining. In this study, we analyzed Raman spectra of myocardial infarction and its repair in rats using the hypothesis that the myocardium in the course of myocardial infarction and its repair could be recognized by spontaneous Raman spectroscopy on the basis of chemical changes in myocardial tissues. Raman spectra were acquired from unfixed frozen cross sections of normal and infarcted heart tissues upon excitation at 532 nm. Raman spectra of the infarcted tissues were successfully obtained at characteristic time points: days 2, 5, and 21 after coronary ligation, at which the main components of the infarcted region were coagulation necrosis, granulation tissue, and fibrotic tissue, respectively. The latent variable weights calculated by a multivariate classification method, partial least-squares-discriminant analysis (PLS-DA), revealed fundamental information about the spectral differences among the types of tissues on the basis of molecular constituents. A prediction model for the evaluation of these tissue types was established via PLS-DA. Cross-validated sensitivities of 99.3, 95.3, 96.4, and 91.3% and specificities of 99.4, 99.5, 96.5, and 98.3% were attained for the discrimination of normal, necrotic, granulation, and fibrotic tissue, respectively. A two-dimensional image of a marginal area of infarction was successfully visualized via PLS-DA. Our results demonstrated that spontaneous Raman spectroscopy combined with PLS-DA is a novel label-free method of evaluating myocardial infarction and its repair.

Three powerful research tools from single cells into single molecules: AFM, laser tweezers, and Raman spectroscopy

By using three physical techniques (atomic force microscopy (AFM), laser tweezers, and Raman spectroscopy), many excellent works in single-cell/molecule research have been accomplished. In this review, we present a brief introduction to the principles of these three techniques, and their capabilities toward single-cell/molecule research are highlighted. Afterward, the advances in single-cell/molecule research that have been facilitated by these three techniques are described. Following this, their complementary assets for single-cell/molecule research are analyzed, and the necessity of integrating the functions of these three techniques into one instrument is proposed.

Label-free separation of human embryonic stem cells and their cardiac derivatives using Raman spectroscopy

Self-renewable, pluripotent human embryonic stem cells (hESCs) can be differentiated into cardiomyocytes (CMs), providing an unlimited source of cells for transplantation therapies. However, unlike certain cell lineages such as hematopoietic cells, CMs lack specific surface markers for convenient identification, physical separation, and enrichment. Identification by immunostaining of cardiac-specific proteins such as troponin requires permeabilization, which renders the cells unviable and nonrecoverable. Ectopic expression of a reporter protein under the transcriptional control of a heart-specific promoter for identifying hESC-derived CMs (hESC-CMs) is useful for research but complicates potential clinical applications. The practical detection and removal of undifferentiated hESCs in a graft, which may lead to tumors, is also critical. Here, we demonstrate a nondestructive, label-free optical method based on Raman scattering to interrogate the intrinsic biochemical signatures of individual hESCs and their cardiac derivatives, allowing cells to be identified and classified. By combination of the Raman spectroscopic data with multivariate statistical analysis, our results indicate that hESCs, human fetal left ventricular CMs, and hESC-CMs can be identified by their intrinsic biochemical characteristics with an accuracy of 96%, 98%, and 66%, respectively. The present study lays the groundwork for developing a systematic and automated method for the noninvasive and label-free sorting of (i) high-quality hESCs for expansion and (ii) ex vivo CMs (derived from embryonic or adult stem cells) for cell-based heart therapies.

Spectroscopical and mechanical characterization of normal and thalassemic red blood cells by Raman Tweezers

In this work, the effects of thalassemia, a blood disease quite diffuse in the Mediterranean sea region, have been investigated at single cell level using a Raman Tweezers system. By resonant excitation of hemoglobin Raman bands, we have examined the oxygenation capability of beta-thalassemic erythrocytes. A reduction of this fundamental erythrocyte function has been found. The measurements have been performed on a significant number of red blood cells; the relative statistical analysis is presented. Moreover, the response to photo-induced oxidative stress of diseased cells with respect to the normal ones has been analyzed. Finally, the deformability of thalassemic erythrocytes has been quantified by measuring the membrane shear modulus by using a double-trap system: the measurements have revealed an increase in membrane rigidity of more than 40%, giving evidence that the genetic defect associated to thalassemia, which manly relies on hemoglobin structure, also strongly affects the erythrocyte mechanical properties. Our results demonstrate that the developed set-up may have potential for the monitoring of blood diseases and their response to drug therapies.