Sulfhemoglobin under the spotlight - Detection and characterization of SHb and HbFeIII-SH

Surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) in label-free characterization of erythrocyte membranes and extracellular vesicles at the nano-scale and molecular level

The manuscript presents the potential of surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) for label-free characterization of extracellular microvesicles (EVs) and their isolated membranes derived from red blood cells (RBCs) at the nanoscale and at the single-molecule level, providing detection of a few individual amino acids, protein and lipid membrane compartments. The study shows future directions for research, such as investigating the use of the mentioned techniques for the detection and diagnosis of diseases. We demonstrate that SERS and TERS are powerful techniques for identifying the biochemical composition of EVs and their membranes, allowing the detection of small molecules, lipids, and proteins. Furthermore, extracellular vesicles released from red blood cells (REVs) can be broadly classified into exosomes, microvesicles, and apoptotic bodies, based on their size and biogenesis pathways. Our study specifically focuses on microvesicles that range from 100 to 1000 nanometres in diameter, as presented in AFM images. Using SERS and TERS spectra obtained for REVs and their membranes, we were able to characterize the chemical and structural properties of microvesicle membranes with high sensitivity and specificity. This information may help better distinguish and categorize different types of EVs, leading to a better understanding of their functions and potential biomedical applications.

A Suggested Mechanism for Green Discoloration of the Postmortem Brain

ABSTRACT

In the putrefied brain, the cortex and basal ganglia show dark-grayish to green discoloration due to sulfhemoglobin formed from hydrogen sulfide (H 2 S) produced by endogenous bacteria and hemoglobin. In this study, we propose and demonstrate another mechanism of green discoloration in the brain. The formalin-fixed brain of a cadaver donated for medical education with no putrefaction was used. Half of the brain was immersed in sodium hydrosulfide solution, to imitate the H 2 S produced by bacteria. This half showed greenish discoloration, mainly in the basal ganglia and cortex. The other half showed positive Perls' Prussian blue staining, mainly in the basal ganglia and cortex. The area of greenish discoloration due to H 2 S and the region positive for Perls' Prussian blue staining coincided. Tissue treatment with strong oxidizing agents is required to liberate heme iron. The positive Perls' Prussian blue staining in this study thus does not reflect heme iron. In conclusion, we considered that non-heme iron compounds physiologically present in the brain and H 2 S represent sources of putrefactive greenish discoloration in the brain.