Amino acids requirements of measles virus in HeLa cells

Arginine depletion as a therapeutic approach for patients with COVID-19

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a source of significant morbidity and death worldwide, and effective treatments are urgently needed. Clinical trials have focused largely on direct antiviral therapies or on immunomodulation in patients with severe manifestations of COVID-19. One therapeutic approach that remains to be clinically investigated is disruption of the host-virus relationship through amino acid restriction, a strategy used successfully in the setting of cancer treatment. Arginine is an amino acid that has been shown in nonclinical studies to be essential in the life cycle of many viruses. Therefore, arginine depletion may be an effective therapeutic approach against SARS-CoV-2. Several arginine-metabolizing enzymes in clinical development may be a viable approach to induce a low arginine environment to treat COVID-19 and other viral diseases. Herein, we explore the rationale for arginine depletion as a therapeutic approach for COVID-19.

Pegylated arginine deiminase lowers hepatitis C viral titers and inhibits nitric oxide synthesis

BACKGROUND

The arginine-degrading enzyme, arginine deiminase conjugated to polyethylene glycol (ADI-SS PEG 20,000 mw), reduces extracellular arginine, has minimal toxicity, decreases tumor burden and improves liver function in patients with chronic hepatitis C virus infection (HCV) and inoperable hepatocellular carcinoma (HCC). Reduced extracellular arginine inhibits viral replication through unknown mechanisms. It is hypothesized that ADI-SS PEG 20,000 mw reduces HCV viral titers through nitric oxide (NO)-dependent effects.

METHODS

The effects of ADI-SS PEG 20,000 mw (dose, 160 IU/m2; three cycles of four once-weekly i.m. injections) on HCV titers, serum NO and plasma arginine, were evaluated using archived plasma from patients with HCC and HCV and in vitro cell model measurements of HCV replication.

RESULTS

ADI-SS PEG 20,000 mw selectively inhibited HCV replication in vitro (IC50 = 0.027 IU/mL). Fifteen HCC/HCV patients completed treatment. The HCV titers were reduced by up to 99% in five out of 10 (50%) HCV-serotype 1b patients (P = 0.0093). These patients also experienced significant improvements in liver function (P = 0.0091). There were concomitant reductions of plasma arginine and serum NO levels. The HCV titer was not reduced in HCV-type 2c patients.

CONCLUSION

Reduction of extracellular arginine by ADI-SS PEG 20,000 mw in HCC patients reduces HCV viral titers and improves liver function, possibly through suppression of NO.

Amino acid requirements for the growth of Aedes albopictus clone C6/36 cells and for the production of dengue and Chikungunya viruses in the infected cells

Amino acid requirements for the growth of Aedes albopictus, clone C6/36, cells and for the production of dengue (DEN) and Chikungunya (CHIK) viruses were examined by growing the cells or the viruses in media which were deprived of one of the 20 amino acids. Cell growth was markedly inhibited when cystine was omitted from the medium, and to a lesser extent by arginine deprivation. On the other hand, omission of alanine, asparagine, aspartic acid, and glutamic acid at the same time did not affect cell growth. Marked accumulation of alanine was observed in the medium when the cells were grown for 8 days in complete medium, with concomitant depletion of aspartic acid and glutamic acid. The production of CHIK virus was inhibited markedly by omission of cystine from the medium after virus infection, while the production of DEN viruses was more affected by glycine deprivation, although cystine deprivation also inhibited virus production to a lesser extent. On the other hand, production of CHIK and DEN viruses was not affected when alanine, asparagine, aspartic acid, and glutamic acid were omitted from the medium at the same time.

Characterization of a yeast phase specific protein from a fungus, Histoplasma capsulatum

We have characterized an unusual yeast phase specific protein from Histoplasma capsulatum. The protein, which we have called protein 6, is produced by the yeast cells which have been derepressed for sulfite reductase, and it can account for more than 40% of the total extract protein. Synthesis of both sulfite reductase and protein 6 is subject to cysteine repression. However, sulfite reductase activity is maximal in logarithmically growing cells whereas protein 6 is synthesized de novo and accumulated by stationary phase cells. The following are the major physicochemical properties of protein 6: (1) the native protein has a molecular weight of about 15 000; (2) electrophoresis on a sodium dodecyl sulfate polyacrylamide gel yielded a single band with a molecular weight 7600; (3) protein 6 is capable of reducing the dye, nitroblue tetrazolium, and cytochrome c, a property that has been found to be shared by a number of trypsin inhibitors, and (4) the molecule is negatively charge and is relatively resistant to proteolysis. The amino acid composition of protein 6 has been determined.