Reactive Halogen Species: Role in Living Systems and Current Research Approaches.

Reactive halogen species (RHS) are highly reactive compounds that are normally required for regulation of immune response, inflammatory reactions, enzyme function, etc. At the same time, hyperproduction of highly reactive compounds leads to the development of various socially significant diseases - asthma, pulmonary hypertension, oncological and neurodegenerative diseases, retinopathy, and many others. The main sources of (pseudo)hypohalous acids are enzymes from the family of heme peroxidases - myeloperoxidase, lactoperoxidase, eosinophil peroxidase, and thyroid peroxidase. Main targets of these compounds are proteins and peptides, primarily methionine and cysteine residues. Due to the short lifetime, detection of RHS can be difficult. The most common approach is detection of myeloperoxidase, which is thought to reflect the amount of RHS produced, but these methods are indirect, and the results are often contradictory. The most promising approaches seem to be those that provide direct registration of highly reactive compounds themselves or products of their interaction with components of living cells, such as fluorescent dyes. However, even such methods have a number of limitations and can often be applied mainly for in vitro studies with cell culture. Detection of reactive halogen species in living organisms in real time is a particularly acute issue. The present review is devoted to RHS, their characteristics, chemical properties, peculiarities of interaction with components of living cells, and methods of their detection in living systems. Special attention is paid to the genetically encoded tools, which have been introduced recently and allow avoiding a number of difficulties when working with living systems.

Imaging human keratinocytes grown on electrospun mats by scanning electron microscopy.

Drying is a critical step in preparing cell samples for examination with scanning electron microscopy (SEM). The two commonly used drying procedures are the critical point drying (CPD) and the chemical drying using hexamethyldisilazane (HMDS drying). Here we compared the application of these procedures for the drying of HaCaT human keratinocyte cells grown on electrospun nylon mats. Both drying procedures allowed us to obtain images of the cells and characterize the microvilli on the cell surface. After HMDS drying the membrane was less damaged than after CPD. Both drying procedures could be used to investigate contact guidance-the substrate-induced changes in cell shape. The aspect ratio of HaCaT cells grown on the aligned and random mats was 4.2 ± 2.8 and 1.5 ± 0.3, respectively.