Stable multicomponent capsules for the delivery of remdesivir (Veklury^®) are produced through subsequent electrostatic adsorption of oppositely charged components on oil emulsion droplets. For the first time, the encapsulation and release of the medicine Veklury^® from polymer capsules was reported. In this study, the effect of the physicochemical properties of chitosan on the size and stability of the produced structures is investigated, on the loaded amount of drug and on the kinetics of drug release in conditions close to the physiological ones. Microbiological studies of the capsules and their constituents were performed via in vitro assays against HCT-8 cell lines and human coronavirus HCoV-OC43. A detailed analysis was performed on the influence of the properties of produced capsules on cytotoxicity against the chosen cell line, as well as their effect on the replication cycle of the virus, the virucidal activity of the samples against the viability of the extracellular virions, and their effect on viral adsorption on the cell membrane.

Disease’s severity, mortality rates, and common failures to achieve clinical improvement during the unprecedented COVID-19 pandemic exposed the emergency need for new antiviral therapeutics with higher efficacy and fewer adverse effects. This study explores the potential to encapsulate multi-component plant extracts in liposomes as optimized delivery systems and to verify if they exert inhibitory effects against human seasonal betacoronavirus OC43 (HCoV-OC43) in vitro. The selection of Sambucus nigra, Potentilla reptans, Allium sativum, Aesculus hippocastanum, and Glycyrrhiza glabra L. plant extracts was based on their established pharmacological and antiviral properties. The physicochemical characterization of extract-loaded liposomes was conducted by DLS and electrokinetics. Encapsulated amounts of the extract were evaluated based on the total flavonoid content (TFC) and total polyphenol content (TPC) by colorimetric methods. The BALB 3T3 neutral red uptake (NRU) phototoxicity/cytotoxicity assay was used to estimate compounds’ safety. Photo irritation factors (PIFs) of the liposomes containing extracts were <2 which assigned them as non-phototoxic substances. The antiviral capacities of liposomes containing medicinal plant extracts against HCoV-OC43 were measured by the cytopathic effect inhibition test in susceptible HCT-8 cells. The antiviral activity increased by several times compared to “naked” extracts’ activity reported previously. A. hippocastanum extract showed 16 times higher inhibitory properties reaching a selectivity index (SI) of 58.96. Virucidal and virus-adsorption effects were investigated using the endpoint dilution method and ∆lgs comparison with infected and untreated controls. The results confirmed that nanoparticles do not directly affect the viral surface or cell membrane, but only serve as carriers of the active substances and the observed protection is due solely to the intracellular action of the extracts.

The difficulties faced by the society in its goal of reducing mortality and improving the health status during the period of the COVID-19 pandemic showed that it is necessary to develop new approaches in the therapy of infectious diseases, leading to higher treatment efficiency and few side effects. The subject of the present study is the formation and characterization of the proper-ties of stable liposomes loaded with extracts from Bulgarian medicinal plants and monitoring their antiviral action against the human strain of coronavirus OC43 (HCoV-OC43) in vitro. The hydrodynamic diameter and -potential of the liposomes containing each type of payload were determined with DLS and electrokinetics. The encapsulated amount of extracts was evaluated against quercetin and gallic acid by using colourimetric methods. The BALB 3T3 Neutral Red Uptake (NRU) phototoxicity/cytotoxicity assay was used to estimate the safety of the compounds. For assessment of the antiviral activity against HCoV-OC43 of liposomes (Lip) containing medicinal plant extracts, the cytopathic effect inhibition test was used. Measurements of the virucidal activity and the effect on the virus adsorption stage was carried out using the endpoint dilution method, and ∆lgs were calculated by comparison with untreated controls. The estimated photo irritation factors (PIF) for the Lip containing extracts were < 2 which assigns them to the category of non-phototoxic substances. When the extracts were introduced into the liposomes as their carriers, the antiviral activity of the vesicles against the replication of HCoV-OC43 in vitro in-creased by several times compared to their individual activity described in our previous study. The determination of the effect of structures loaded with extracts on the extracellular virions and the stage of their adsorption to sensitive HCT-8 cells proved that the liposomes do not affect directly the viral surface or cell membrane, but only perform a function of carriers of the active substances and the observed result is due solely to the intracellular action of the extracts.

Plant extracts remain an important source of antiviral agents, while nanocarrier-based delivery systems have emerged as a promising strategy for improving their therapeutic safety and efficacy. Building on previous findings indicating that nanoliposomal encapsulation improved the anti-coronavirus activity of Aesculus hippocastanum seed extract against human coronavirus strain OC43 (HCoV-OC43), the present study evaluated whether encapsulation reduces the genotoxic effects of the extract and explored a potential molecular basis for the previously observed antiviral activity. Genotoxicity assessment using the alkaline comet assay in MRC-5 human lung fibroblasts demonstrated that at 1 mg/mL, liposomal encapsulation was associated with an approximately 86.0% reduction in %Tail DNA, from 21.301 ± 0.368% for the free extract to 2.984 ± 1.523% for the liposome-encapsulated extract. In parallel, chemical profiling by high-performance liquid chromatography coupled with high-resolution tandem mass spectrometry (HPLC–HRMS/MS) enabled the identification and tentative annotation of 46 metabolites, including triterpenoid saponins, flavonoids, indole-3-acetic acid glycosides, and organic acids. Based on this phytochemical profile, representative constituents were subjected to molecular docking against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nonstructural proteins Nsp5 and Nsp12 to investigate their potential contribution to the previously demonstrated antiviral activity of the extract. Among the evaluated compounds, hesperidin exhibited the most favorable predicted binding affinity toward both targets, while quercetin also showed favorable interactions, suggesting that flavonoid constituents may contribute to the antiviral activity of the extract. These findings indicate that liposomal encapsulation improves the biological safety profile of A. hippocastanum seed extract, while phytochemical characterization and molecular docking provide preliminary insights into the constituents that may contribute to its previously demonstrated anti-coronavirus activity.