Metformin is among the most prescribed medications worldwide and the first-line therapy for type 2 diabetes. However, gastrointestinal side effects are common and can be dose limiting. The total daily metformin dose frequently reaches several grams, and poor absorption results in high intestinal drug concentrations. Here, we report that metformin inhibits the activity of enteropeptidase and other digestive enzymes at drug concentrations predicted to occur in the human duodenum. Treatment of mouse gastrointestinal tissue with metformin reduces enteropeptidase activity; further, metformin-treated mice exhibit reduced enteropeptidase activity, reduced trypsin activity, and impaired protein digestion within the intestinal lumen. These results indicate that metformin-induced protein maldigestion could contribute to the gastrointestinal side effects and other impacts of this widely used drug.
Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike glycoprotein (S) binds to angiotensin-converting enzyme 2 (ACE2) to mediate membrane fusion via two distinct pathways: 1) a surface, serine protease-dependent or 2) an endosomal, cysteine protease-dependent pathway. In this study, we found that SARS-CoV-2 S has a wider protease usage and can also be activated by TMPRSS13 and matrix metalloproteinases (MMPs). We found that MMP-2 and MMP-9 played roles in SARS-CoV-2 S cell-cell fusion and TMPRSS2- and cathepsin-independent viral entry in cells expressing high MMP levels. MMP-dependent viral entry required cleavage at the S1/S2 junction in viral producer cells, and differential processing of variants of concern S dictated its usage; the efficiently processed Delta S preferred metalloproteinase-dependent entry when available, and less processed Omicron S was unable to us metalloproteinases for entry. As MMP-2/9 are released during inflammation, they may play roles in S-mediated cytopathic effects, tropism, and disease outcome.
© 2022 The Author(s).

Coronavirus disease 2019 (COVID-19) can lead to multi-organ failure influenced by comorbidities and age. Binding of the severe acute respiratory syndrome coronavirus 2 spike protein (SARS-CoV-2 S protein) to angiotensin-converting enzyme 2 (ACE2), along with proteolytic digestion of the S protein by furin and transmembrane protease serine subtype 2 (TMPRSS2), provokes internalization of SARS-CoV-2 into the host cell. Productive infection occurs through viral replication in the cytosol and cell-to-cell transmission. The catalytic activity of TMPRSS2 can be blocked by the trypsin-like serine protease inhibitor camostat, which impairs infection by SARS-CoV-2. At the site of infection, immune cells, such as neutrophils, infiltrate and become activated, releasing neutrophil serine proteases (NSPs), including cathepsin G (CatG), neutrophil elastase (NE), and proteinase 3 (PR3), which promote the mounting of a robust immune response. However, NSPs might be involved in infection and the severe outcome of COVID-19 since the uncontrolled proteolytic activity is responsible for many complications, including autoimmunity, chronic inflammatory disorders, cardiovascular diseases, and thrombosis. Here, we demonstrate that camostat does not inhibit the catalytic activity of CatG, NE, and PR3, indicating the need for additional selective serine protease inhibitors to reduce the risk of developing severe COVID-19.

Renal tubular casts originating from detached epithelial cells after ischemia-reperfusion injury (IRI) can obstruct tubules and negatively impact glomerular filtration rate. Using multiphoton imaging of 400-μm-thick kidney sections, the distribution of casts and morphometric measurement of tubules was performed along the entire nephron for the first time. Tubular nuclei are shed before cell detachment, and visually occlusive casts (grade 3) appeared at 12 h after IRI at the S3/thin descending limb (tDL) junction. Grade 3 casts peaked at 24 h after injury [present in 99% of S3, 78% of tDL, 76% of thin ascending limb (tAL), 60% of medullary thick ascending limb (mTAL), and 10% of connecting tubule segments]. Cast formation in the S3 correlated with selective loss of cell numbers from this tubule segment. By day 3, most mTALs and connecting tubules were cast free, whereas 72% of S3 tubules and 58% of tDLs still contained grade 3 casts. Although bulk phagocytosis of cast material by surviving tubular cells was not observed, mass spectrometry identified large numbers of tryptic peptides in the outer medulla, and trypsin levels were significantly increased in the kidney and urine 24 h after IRI. Administration of either antipain or camostat to inhibit trypsin extended cast burden to the S2, led to sustained accumulation of S3 casts after IRI, but did not affect cast burden in the mTAL or renal function. Our data provide detailed and dynamic mapping of tubular cast formation and resolution after IRI that can inform future interventions to accelerate cast clearance and renal recovery.NEW & NOTEWORTHY This detailed characterization of the dynamic distribution of dead cell debris in ischemically injured kidney tubules reveals which cells in the kidney are most severely injured, when and where tubular casts form, and when (and to a lesser extent, how) they are cleared.

SARS-CoV-2 and its vaccine/immune-escaping variants continue to pose a serious threat to public health due to a paucity of effective, rapidly deployable, and widely available treatments. Here, we address these challenges by combining Pegasys (IFNα) and nafamostat to effectively suppress SARS-CoV-2 infection in cell culture and hamsters. Our results indicate that Serpin E1 is an important mediator of the antiviral activity of IFNα and that both Serpin E1 and nafamostat can target the same cellular factor TMPRSS2, which plays a critical role in viral replication. The low doses of the drugs in combination may have several clinical advantages, including fewer adverse events and improved patient outcome. Thus, our study may provide a proactive solution for the ongoing pandemic and potential future coronavirus outbreaks, which is still urgently required in many parts of the world.