Helicobacter pylori, a gram-negative bacteria usually found in stomach and first part of small intestine, is known to cause infections and ulcers and may have association with cancer. Normally, the treatment options include combinations of antibiotics with proton pump inhibitors and antiinflammatory drugs. However, all of them have high systemic exposure, and hence, unfavourable side effects, whereas their exposure in stomach mucus, the predominant location of the bacteria, is very limited. We have attempted to develop a predominantly gut-restricted formulations of antibiotic + adjuvant combinations as a basis for potentially more safe and efficacious treatment of gastrointestinal tract infections. We have considered E. coli (as a model of H. pylori) and Lactobacilli to study the antibacterial activity of nanogel with combined drugs (classical antibiotics and individual components of essential oils). It has been shown that levofloxacin (LF) in combination with zephirol demonstrates synergy effect against E. coli (cell viability has decreased by about 50%) and weakens the effect against Lactobacilli. A number of other combinations of antibiotic + adjuvant is also shown to be effective. Using FTIR and UV spectroscopy, it has been proved that chitosan nanogels with the drug are well adsorbed on the mucosal model, thereby increasing the bioavailability of drugs. Using ABTS assay, the antioxidant properties of flavonoids and other drugs are shown, which is potentially necessary to minimize the harmful effects of toxins and radicals produced by pathogens. Thus, chitosan nanogels loaded with a combination of drugs can be considered as a new strategy for the treatment of infectious diseases of the gastrointestinal tract, and applicable to difficult-to-treat bacteria.

Fluorescent labels, especially FRET probes, are promising tools for studying a number of bio-chemical processes. In this paper, we promoted 2 important applications of FRET probes (MUTMAC-R6G and FITC-R6G): i) the formation of micelles from surfactants of various natures and polymers (chitosan – fatty acid), as well as ii) monitoring of enzymatic activity with improved parameters (increased analytical signal and improved selectivity due to shift to the long-wavelength region). The formation of micelles is accompanied by the convergence of fluorophores in the hydrophobic micelle core by a distance closer than in the buffer solution, thus r/R0 (where R0 – Foerster radius) is chosen as an analytical signal of micelle formation, including critical micelle concentration (CMC) and critical pre-micelle concentration (CPMC). The CMC values calculated using FRET probes are in a good agreement with literature data. At the same time, the r/R0 function provides valuable information about the nature and mechanism of micelle formation. With the second analytical application of FRET probes, we considered the optimization of techniques for studying enzymatic activity. The enzyme catalyses the reaction with the release of a fluorescent product, the signal from which may not be enough for detection, or it may be quenched, for example, in the reverse micelles (AOT-octane). Here we have proposed a solution – a FRET probe containing a rhodamine 6G (R6G) acceptor, which allows us to monitor the enzymatic reaction selectively (in the red region, 550-600 nm), and obtain a significantly higher fluorescence yield (potentially from 10 to 250 times). Thus, we have demonstrated a high potential for the FRET probes application as indicators of micelle formation as well as for the study of the enzyme catalytic activity. In the future, the method developed has prospects for application in the visualization of the enzyme functioning in cells due to the shift of the fluorescence signal to the long-wavelength region with an increase in the signal selectivity to suppress autofluorescence.

There are several well-known methods for determining enzyme catalytic activity, including spectral techniques and electrochemical approaches. However, at present, there is no definitive solution to the challenges associated with the fluorescent approach in, for instance, systems of reverse micelles, non-aqueous media, and model biomembranes. We propose the use of the fluorescent resonant energy transfer (FRET) technique, which can enhance the selectivity of fluorescent detection of enzyme activity by shifting the maximum emission wavelength to the longer-wavelength range and reducion the influence of medium components. As fluorescence donors, we have used derivatives of 4-methylumbelliferone (MUmb) and 7-amino-4-methylcoumarin (AMC), which also serve as substrates for hydrolases such as chymotrypsin, phosphatase, and asparaginase. During the catalytic depletion of substrates, an accumulation of a highly fluorescent product is observed. This product can be specifically detected using the fluorescent marker rhodamine 6G (R6G), which emits light in the red region of the spectrum (550–600 nm) with high quantum yield. A significant FRET effect is observed when forming AOT reverse micelles. This is due to the proximity of fluorophores within the hydrophobic core of the micelle, which is shorter than in a buffer solution. This approach have practical implications for visualizing intracellular processes. The FRET technique can be used to determine intracellular enzymatic activity by detection with confocal laser scanning microcopy (CLSM), as demonstrated with L-asparaginase, a clinically important anti-leukemia medication. The approach suggested will allow researchers to study enzyme activity within cells. This has the potential to revolutionize medicine by improving drug development and shedding light on previously unknown aspects of cellular metabolism.