One of potential inhibitors which is widely used for the clinical treatment of COVID-19 in comorbid patients is Angiostensin Converting Enzyme-1 (ACE1) inhibitor. A safer peptide-based ACE1 inhibitor derived from salmon skin collagen, that is considered as the by-product of the fish processing industry have been investigated in this study. The inhibitory activity against ACE1 was examined using in vitro and in silico methods. In vitro analysis includes the extraction of acid-soluble collagen, characterization using FTIR, Raman, UV–Vis, XRD, cytotoxicity assay, and determination of inhibition against ACE1. In silico method visualizes binding affinity, molecular interaction, and inhibition type of intact collagen and active peptides derived from collagen against ACE1 using molecular docking. The results of FTIR spectra detected amide functional groups (A, B, I, II, III) and imine proline/hydroxyproline, while the results of Raman displayed peak absorption of amide I, amide III, proline/hydroxyproline ring, phenylalanine, and protein backbone. Furthermore, UV–Vis spectra showed typical collagen absorption at 230 nm and based on XRD data, the chain types in the samples were α-helix. ACE1 inhibition activity was obtained in a concentration-dependent manner where the highest was 82.83% and 85.84% at concentrations of 1000, and 2000 µg/mL, respectively, and showed very low cytotoxicity at the concentration less than 1000 µg/mL. In silico study showed an interaction between ACE1 and collagen outside the active site with the affinity of − 213.89 kcal/mol. Furthermore, the active peptides of collagen displayed greater affinity compared to lisinopril, namely HF (His-Phe), WYT (Trp-Tyr-Thr), and WF (Trp-Phe) of − 11.52; − 10.22; − 9.58 kcal/mol, respectively. The salmon skin-derived collagen demonstrated ACE1 inhibition activity with a non-competitive inhibition mechanism. In contrast, the active peptides were predicted as potent competitive inhibitors against ACE1. This study indicated that valorization of fish by-product can lead to the production of a promising bioactive compound to treat COVID-19 patient with diabetic comorbid. Graphical Abstract

The purpose of this study was to determine the effect of silver nanoparticles (AgNPs) from different green synthesis medium and their various particle sizes on antibacterial activity. The article review method compares the results of 11 studies obtained from the PubMed database, Web of Science, and ScienceDirect indexed by Scopus in the last five years. The search was conducted based on the phrases nanoparticles, antibacterial, Green synthesis, and AgNPs. Green synthesis of AgNPs with various plant extracts produces different sizes of nanoparticles. The smallest size AgNPs were obtained in the range of 5-15 nm and an average of 13 nm extracted using the leaves of the Pacific Yew tree (Taxus brevifolia). Meanwhile, AgNPs with the best antibacterial effectiveness were obtained from the Blume flower extract (Wedelia urticifolia) measuring less than 30 nm providing a zone of inhibition for S. aureus, K. pneumoniae, E. coli, and P. aeruginosa bacteria.