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Background: Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has created enormous medical and economic burdens on human society. However, the co-existence of COVID-19 and diseases in tropical regions is not taken seriously. To improve the understanding of the current status and trends on crosstalk of COVID-19 and tropical diseases, this paper provided an analysis, from a bibliometric perspective, of the COVID-19-related publications in ″Tropical Medicine″-entitled journals. Methods: We used Clarivate Analytics and VOSviewer to analyze 783 publications in seven ″ Tropical Medicine″-entitled journals. Document overview, basic bibliometric characteristics, citation performance, co-authorship, co-citation, bibliographic coupling, and co-occurrence of keywords and terms were summarized in this article. Results: Document overview revealed that 76.12% of the related publications were published in open access mode, and basic bibliometric characteristics indicated that the year 2021 was the peak of the number of publications, the documents in the seven journals were unevenly distributed, and ″ article″ was the main publication type. The citation performance analysis elucidated that the documents of interest were frequently cited. The co-authorship analysis showed cooperation networks on the level of region, organization and author. General knowledge of COVID-19 was the overlap of co-citation and bibliographic coupling behavior. Finally, the co-occurrence of keywords and terms revealed the current and emerging hotspots. Conclusions: The main current research focuses in ″Tropical Medicine″-entitled journals are the clinical features of COVID-19 patients, and the emerging trends are the hesitancy in making vaccines against SARS-CoV-2 and the circumstance where COVID-19 coexisted with tropical diseases. In summary, this bibliometric analysis of COVID-19-related studies in seven ″Tropical Medicine″-entitled journals highlights the current research focuses of this field to inspire future studies.

As one of the most studied mesoporous silica nanoparticles (MSNs) in drug delivery systems, Mobil Composition of Matter No. 41 (MCM-41) possesses unique properties including perfect channel architecture, excellent load capacity, and good biocompatibility. However, the applications of MCM-41 nanoparticles in drug delivery have not yet been industrialized, due to the interaction between MCM-41 and biomolecules (especially proteins) that affect their in vivo behaviors after dosing. To investigate the interactions between MCM-41 and proteins, this study selected bovine serum albumin (BSA), lysozyme (Lyso), and bovine hemoglobin (BHb) as model proteins and characterized the ultraviolet-visible, fluorescence, circular dichroism spectra and the protein adsorption of MCM-41-protein complex. The UV-Vis spectra exhibited the different absorption increment degrees of three proteins. The fluorescence spectra showed that the fluorescence intensity of proteins changed by different trends. The CD spectra indicated that the secondary structure changes were ranked as BSA > Lyso > BHb, which is consistent with the protein’s adsorption capability on MCM-41. It was shown that there were three different patterns of MCM-41-proteins interactions. The hydrophilic and low-charged BSA followed the strong interaction pattern, the hydrophilic but heavily charged Lyso followed the moderate interaction pattern, and the hydrophobic BHb followed the weak interaction pattern. Different interaction patterns would lead to different effects on the structural properties of proteins, the surface chemistry of MCM-41, and the absorption capability of proteins on MCM-41. We believe our study will provide a better insight into the application of MCM-41 nanoparticles in drug delivery systems.

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The injective lyotropic liquid crystalline nanogels (LLCNs) were widely used in drug delivery systems. But when administered in vivo, LLCNs exposed to the biological environment interact with proteins. Recently, it has been shown that nanoparticles coated with zwitterions can inhibit their interaction with proteins. Thus, in this study, the interaction between proteins and LLCNs coated with the zwitterionic material sulfobetaine (GLLCNs@HDSB) was investigated using bovine serum albumin (BSA) as a model protein. Interestingly, it was found that GLLCNs@HDSB at higher concentrations (≥0.8 mg/mL) could block its interaction with BSA, but not at lower concentrations (<0.8 mg/mL), according to the results of ultraviolet, fluorescence, and circular dichroism spectra. In the ultraviolet spectra, the absorbance of GLLCNs@HDSB (0.8 mg/mL) was 1.9 times higher than that without the sulfobetaine coating (GLLCNs) after incubation with protein; the fluorescence quenching intensity of GLLCNs@HDSB was conversely larger than that of the GLLCNs; in circular dichroism spectra, the ellipticity value of GLLCNs@HDSB was significantly smaller than that of the GLLCNs, and the change in GLLCNs@HDSB was 10 times higher than that of the GLLCNs. Generally, nanoparticles coated with sulfobetaine can inhibit their interaction with proteins, but in this study, LLCNs showed a concentration-dependent inhibitory effect. It could be inferred that in contrast to the surface of nanoparticles covered with sulfobetaine in other cases, the sulfobetaine in this study interacted with the LLCNs and was partially inserted into the hydrophobic region of the LLCNs. In conclusion, this study suggests that coating-modified nanoparticles do not necessarily avoid interacting with proteins, and we should also study coating-modified nanoparticles interacting with proteins both in vitro and in vivo. In the future, finding a coating material to completely inhibit the interaction between LLCNs and proteins will generate a great impetus to promote the clinical transformation of LLCNs.