SARS-CoV-2 Seroprevalence among Healthcare Workers in General Hospitals and Clinics in Japan.

Coronavirus disease 2019 (COVID-19) has become a serious public health problem worldwide. In general, healthcare workers are considered to be at higher risk of COVID-19 infection. However, the prevalence of COVID-19 among healthcare workers in Japan is not well characterized. In this study, we aimed to examine the seroprevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antibodies among 2160 healthcare workers in hospitals and clinics that are not designated to treat COVID-19 patients in Japan. The prevalence of SARS-CoV-2 immunoglobulin G was 1.2% in August and October 2020 (during and after the second wave of the pandemic in Japan), which is relatively higher than that in the general population in Japan (0.03-0.91%). Because of the higher risk of COVID-19 infection, healthcare workers should be the top priority for further social support and vaccination against SARS-CoV-2.

Pepstatin A induces extracellular acidification distinct from aspartic protease inhibition in microglial cell lines.

The extrusion of protons is considered a very general parameter of the activation of many kinds of membrane or intracellular molecules, such as receptors, ion channels, and enzymes. We found that pepstatin A caused a reproducible, concentration-related increase in the extracellular acidification rate in two microglial cell lines, Ra2 and 6-3. Washing abolished pepstatin A-induced acidification immediately. However, pepstatin A did not cause the extracellular acidification in other cell types, such as CHO, C6 glioma, and NIH3T3 cells. These observations strongly suggest that pepstatin A interacts with certain membrane proteins specific to both Ra2 and 6-3 cells from outside. N-methylmaleimide and N,N'-dicyclohexylcarbodiimide, inhibitors of H(+)-ATPase, were found to reduce pepstatin A-induced response strongly, while bafilomycin A1, a vacuolar H(+)-ATPase inhibitor, vanadate, a P-type H(+)-ATPase inhibitor, and NaN3, an F1 ATPase inhibitor, virtually did not. 5-(N-ethyl-N-isopropyl) amiloride, an inhibitor of Na(+)/H(+) exchanger isoform 1, greatly enhanced pepstatin-induced response, while amiloride did not. Zn(2+), a voltage-dependent proton channel blocker, did not affect pepstatin-induced response neither. Staurosporine, a nonspecific inhibitor of protein kinase C, inhibited pepstatin A-induced response, while chelerythrine, more selective inhibitor of protein kinase C, greatly enhanced it. H-7 and H-8 did not affected the response. These findings suggest that pepstatin A induces extracellular acidification in microglia cell lines, Ra2 and 6-3, through an N-methylmaleimide- and N,N'-dicyclohexylcarbodiimide-sensitive, but bafilomycin A1-insensitive, ATPase, which seems to be distinct from protein kinase C-dependent process.

How does prolonged caloric restriction ameliorate age-related impairment of long-term potentiation in the hippocampus?

Prolonged dietary restriction has been reported to suppress age-induced phenomena. In order to investigate how prolonged caloric restriction reduces age-related deterioration of hippocampal synaptic transmission, we compared the levels of major hippocampal polyunsaturated fatty acids, arachidonic acid and docosahexaenoic acid between 4- and 26-month-old rats. The Ca(2+) responses upon perfusion of NMDA or 30 mM K(+) between 4- and 26-month-old rats with prolonged dietary restriction were also compared using the fluorescent probe Fura-2. A decrease in membrane arachidonic acid is thought to be a major causal factor in the age-related impairment of long-term potentiation. Long-term caloric restriction seems to increase arachidonic acid levels regardless of age. However, there is no significant difference of hippocampal arachidonic acid levels between in freely feeding 4- and 26-month-old rats. Similar results were obtained from the measurement of hippocampal docosahexaenoic acid levels. Under caloric restriction, the 500 microM N-methyl-D-aspartate-induced Ca(2+) response was greatly reduced by aging, while the 30 mM K(+)-induced Ca(2+) response was not affected. In our preliminary data, the amplitude of the population spike after tetanic stimulation did not differ between 4- and 26-month-old rats under caloric restriction, while 50 microM of 2-amino-5-phosphonovaleric acid, a N-methyl-D-aspartate antagonist, markedly inhibited a potentiation of the population spike in 4-month-old rats, but with negligible inhibition in 26-month-old rats. From these results, an age-related impairment of hippocampal excitatory synaptic transmission may not be solely due to the reduction of membrane arachidonic acid. Caloric restriction might prevent age-related reduction in hippocampal synaptic transmission by enhancing non-N-methyl-D-aspartate mechanisms.