Biology subjects

Gross, U.

Publications and source records attributed to Gross, U..

4 recordsLinked to original sources

bioRxiv2026

Decoupling of CO2 and O2 fluxes reveals oxygen-independent decarboxylation in anoxic mammalian cells

Canonical understanding of cellular respiration holds that CO2 production tracks oxygen consumption, and mammalian cells deprived of oxygen are thought to rely on lactate fermentation, which yields no net CO2. Because standard respirometry infers CO2 flux either from oxygen consumption or from extracellular acidification rather than measuring it directly, a CO2 flux decoupled from oxygen would go undetected or be misattributed to glycolysis. Using direct measurement of CO2 and O2 fluxes from the gas phase in anoxic mammalian cells, we show that a substantial CO2 efflux persists after oxygen is fully removed. This anoxic flux scales linearly with normoxic CO2 and with cell mass, and exhibits a lower activation energy than normoxic respiration, suggesting a distinct rate-limiting chemistry. Pyruvate and -ketobutyrate increased the anoxic CO2 flux while lactate dehydrogenase inhibition abolished the pyruvate-induced increase, supporting a role for cytosolic NAD+ regeneration in oxygen-independent decarboxylation. 13C tracing identified a substantial glutamine-derived component, consistent with mitochondrial decarboxylation, and a smaller glucose-derived component associated with the cytosolic pentose phosphate pathway. Direct CO2 measurement thus reframes lactate dehydrogenase as an enabler of oxygen-independent decarboxylation.

biochemistry↗

bioRxiv2021

N4-hydroxycytidine and inhibitors of dihydroorotate dehydrogenase synergistically suppress SARS-CoV-2 replication

Effective therapeutics to inhibit the replication of SARS-CoV-2 in infected individuals are still under development. The nucleoside analogue N4-hydroxycytidine (NHC), also known as EIDD-1931, interferes with SARS-CoV-2 replication in cell culture. It is the active metabolite of the prodrug Molnupiravir (MK-4482), which is currently being evaluated for the treatment of COVID-19 in advanced clinical studies. Meanwhile, inhibitors of dihydroorotate dehydrogenase (DHODH), by reducing the cellular synthesis of pyrimidines, counteract virus replication and are also being clinically evaluated for COVID-19 therapy. Here we show that the combination of NHC and DHODH inhibitors such as teriflunomide, IMU-838/vidofludimus, and BAY2402234, strongly synergizes to inhibit SARS-CoV-2 replication. While single drug treatment only mildly impaired virus replication, combination treatments reduced virus yields by at least two orders of magnitude. We determined this by RT-PCR, TCID50, immunoblot and immunofluorescence assays in Vero E6 and Calu-3 cells infected with wildtype and the Alpha and Beta variants of SARS-CoV-2. We propose that the lack of available pyrimidine nucleotides upon DHODH inhibition increases the incorporation of NHC in nascent viral RNA, thus precluding the correct synthesis of the viral genome in subsequent rounds of replication, thereby inhibiting the production of replication competent virus particles. This concept was further supported by the rescue of replicating virus after addition of pyrimidine nucleosides to the media. Based on our results, we suggest combining these drug candidates, which are currently both tested in clinical studies, to counteract the replication of SARS-CoV-2, the progression of COVID-19, and the transmission of the disease within the population. SIGNIFICANCEO_LIThe strong synergy displayed by DHODH inhibitors and the active compound of Molnupiravir might enable lower concentrations of each drug to antagonize virus replication, with less toxicity. C_LIO_LIBoth Molnupiravir and DHODH inhibitors are currently being tested in advanced clinical trials or are FDA-approved for different purposes, raising the perspective of rapidly testing their combinatory efficacy in clinical studies. C_LIO_LIMolnupiravir is currently a promising candidate for treating early stages of COVID-19, under phase II/III clinical evaluation. However, like Remdesivir, it appears only moderately useful in treating severe COVID-19. Since the combination inhibits virus replication far more strongly, and since DHODH inhibitors may also suppress excessive immune responses, the combined clinical application bears the potential of alleviating the disease burden even at later stages. C_LI

molecular biology↗

bioRxiv2020

The folate antagonist methotrexate diminishes replication of the coronavirus SARS-CoV-2 and enhances the antiviral efficacy of remdesivir in cell culture models

The search for successful therapies of infections with the coronavirus SARS-CoV-2 is ongoing. We tested inhibition of host cell nucleotide synthesis as a promising strategy to decrease the replication of SARS-CoV-2-RNA, thus diminishing the formation of virus progeny. Methotrexate (MTX) is an established drug for cancer therapy and to induce immunosuppression. The drug inhibits dihydrofolate reductase and other enzymes required for the synthesis of nucleotides. Strikingly, the replication of SARS-CoV-2 was inhibited by MTX in therapeutic concentrations around 1 M, leading to more than 1000-fold reductions in virus progeny in Vero C1008 (Vero E6) as well as Calu-3 cells. Virus replication was more sensitive to equivalent concentrations of MTX than of the established antiviral agent remdesivir. MTX strongly diminished the synthesis of viral structural proteins and the amount of released virus RNA. Virus replication and protein synthesis were rescued by folinic acid (leucovorin) and also by inosine, indicating that purine depletion is the principal mechanism that allows MTX to reduce virus RNA synthesis. The combination of MTX with remdesivir led to synergistic impairment of virus replication, even at 300 nM MTX. The use of MTX in treating SARS-CoV-2 infections still awaits further evaluation regarding toxicity and efficacy in infected organisms, rather than cultured cells. Within the frame of these caveats, however, our results raise the perspective of a two-fold benefit from repurposing MTX for treating COVID-19. Firstly, its previously known ability to reduce aberrant inflammatory responses might dampen respiratory distress. In addition, its direct antiviral activity described here would limit the dissemination of the virus. SIGNIFICANCEO_LIMTX is one of the earliest cancer drugs to be developed, giving rise to seven decades of clinical experience. It is on the World Health Organizations List of Essential Medicines, can be administered orally or parenterally, and its costs are at single digit {euro} or $ amounts/day for standard treatment. In case of its successful further preclinical evaluation for treating SARS-CoV-2 infections, its repurposing to treat COVID-19 would thus be feasible, especially under low-resource conditions. C_LIO_LIAdditional drugs exist to interfere with the synthesis of nucleotides, e.g. additional folate antagonists, inhibitors of GMP synthetase, or inhibitors of dihydroorotate dehydrogenase (DHODH). Such inhibitors have been approved as drugs for different purposes and might represent further therapeutic options against infections with SARS-CoV-2 C_LIO_LIRemdesivir is currently the most established drug for treating COVID-19. Our results argue that MTX and remdesivir, even at moderate concentrations, can act in a synergistic fashion to repress virus replication to a considerably greater extent than either drug alone. C_LIO_LICOVID-19, in its severe forms, is characterized by pneumonia and acute respiratory distress syndrome, and additional organ involvements. These manifestations are not necessarily a direct consequence of virus replication and cytopathic effects, but rather a result of an uncontrolled inflammatory and immune response. Anti-inflammatory drugs such as glucocorticoids are thus being evaluated for treating COVID-19. However, this bears the risk of re-activating virus spread by suppressing a sufficient and specific immune response. In this situation, it is tempting to speculate that MTX might suppress both excessive inflammation as well as virus replication at the same time, thus limiting both the pathogenesis of pneumonia and also the spread of virus within a patient. C_LI

molecular biology↗

bioRxiv2019

Global genomic population structure of Clostridioides difficile

Clostridioides difficile is the primary infectious cause of antibiotic-associated diarrhea. Local transmissions and international outbreaks of this pathogen have been previously elucidated by bacterial whole-genome sequencing, but comparative genomic analyses at the global scale were hampered by the lack of specific bioinformatic tools. Here we introduce EnteroBase, a publicly accessible database (http://enterobase.warwick.ac.uk) that automatically retrieves and assembles C. difficile short-reads from the public domain, and calls alleles for core-genome multilocus sequence typing (cgMLST). We demonstrate that the identification of highly related genomes is 89% consistent between cgMLST and single-nucleotide polymorphisms. EnteroBase currently contains 13,515 quality-controlled genomes which have been assigned to hierarchical sets of single-linkage clusters by cgMLST distances. Hierarchical clustering can be used to identify populations of C. difficile at all epidemiological levels, from recent transmission chains through to pandemic and endemic strains, and is largely compatible with prior ribotyping. Hierarchical clustering thus enables comparisons to earlier surveillance data and will facilitate communication among researchers, clinicians and public-health officials who are combatting disease caused by C. difficile.

microbiology↗