Action spectrum for the in vitro induction of simian virus 40 by ultraviolet radiation

SARS-CoV-2 inactivation by ultraviolet radiation and visible light is dependent on wavelength and sample matrix

Numerous studies have demonstrated that SARS-CoV-2 can be inactivated by ultraviolet (UV) radiation. However, there are few data available on the relative efficacy of different wavelengths of UV radiation and visible light, which complicates assessments of UV decontamination interventions. The present study evaluated the effects of monochromatic radiation at 16 wavelengths from 222 nm through 488 nm on SARS-CoV-2 in liquid aliquots and dried droplets of water and simulated saliva. The data were used to generate a set of action spectra which quantify the susceptibility of SARS-CoV-2 to genome damage and inactivation across the tested wavelengths. UVC wavelengths (≤280 nm) were most effective for inactivating SARS-CoV-2, although inactivation rates were dependent on sample type. Results from this study suggest that UV radiation can effectively inactivate SARS-CoV-2 in liquids and dried droplets, and provide a foundation for understanding the factors which affect the efficacy of different wavelengths in real-world settings.

Action spectra again?

Action spectroscopy has a long history and is of central importance to photobiological studies. Action spectra were among the first assays to point to chlorophyll as the molecule most responsible for plant growth and to DNA as the genetic material. It is useful to construct action spectra early in the investigation of new areas of photobiological research in an attempt to determine the wavelength limits of the radiation region causing the studied response. But due to the severe absorption of ultraviolet (UV) radiation by biological samples, UV action spectra were first limited to small cells (bacteria and fungi). Advances in techniques (e.g. single cell culture) and analysis allowed accurate action spectra to be reported even for mammalian cells. But precise analytical action spectra are often difficult to obtain when large, pigmented, or groups of cells are investigated. Here some action spectra are limited in interpretation and merely supply a wavelength vs effect curve. When polychromatic sources are employed, the interpretation of action spectra is even more complex and formidable. But such polychromatic action spectra can be more directly related to ambient responses. Since precise action spectra usually require the completion of a relatively large number of careful experiments using somewhat sophisticated equipment over a range of at least six wavelengths, they are often not pursued. But they remain central to the elucidation of the effect being studied. The worldwide community has agreed that stratospheric ozone is depleting, with the possibility of a consequent rise in the amount of UV-B (290-320 nm) reaching the earth's surface. It is therefore essential that new action spectra be completed for UV-B effects on a large variety of responses of human, animal, and aquatic plant systems. Combining these action spectra with the known amounts of UV-B reaching the biosphere can give rise to solar UV effectiveness spectra that, in turn, can give rise to estimates of effect. Preliminary estimates suggest that ozone layer depletion may seriously impact such important biological end-points as skin cancer, cataracts, the immune system, crop yields, and oceanic phytoplankton. So action spectra continue to play a central role in important photobiological research.

Varying sensitivity of human skin fibroblasts to polychromatic ultraviolet light

The inactivation of normal and xeroderma pigmentosum cells has been compared following exposure to environmentally relevant wavelengths of ultraviolet light or to the more commonly investigated 254-nm ultraviolet light. The sensitivity of xeroderma pigmentosum cells to polychromatic long-wavelength ultraviolet light was greatly lower than that observed using 254-nm light. Such variations in the relative sensitivities of normal and xeroderma pigmentosum cells support the likelihood that the lesions which contribute to cellular alterations induced by solar wavelengths of ultraviolet light are different from those which predominate at 254 nm.

Enhanced induction of SV40 replication from transformed mammalian cells by fusion with UV-irradiated untransformed cells

DNA-damaging agents such as ultraviolet (UV) light are known to cause stimulation of virus replication in SV40-transformed hamster and human cells. The dose-response curves of UV-induced SV40 replication in transformed hamster cells resemble that obtained for UV-enhanced reactivation (ER) and UV-enhanced mutagenesis (EM) of SV40 or herpes viruses in mammalian cells. We have investigated whether UV-enhanced production of SV40 from transformed hamster (THK) and human (NB-E) cells belongs to the same category of conditional responses as ER and EM. To answer this question we have made use of the phenomenon that fusion of the SV40-transformed cells with monkey cells that are permissive to SV40 results in a considerable increase in the production of SV40 virus. When THK or NB-E cells were fused with UV-irradiated CV-1 cells at various times after irradiation, induction of SV40 was further increased and reached a maximum value of 2--3-fold when fusion was delayed for 24-48 h after irradiation. The kinetics of enhanced SV40 induction resembled that of ER and EM, suggesting that the UV-stimulated part of the induction represents one of the pleiotropic responses that are transiently induced in mammalian cells by DNA-damaging agents. Evidence is presented, showing that this transient effect can be induced only in cells that are permissive to SV40 replication. This suggests that the enhanced induction observed after fusion with irradiated monkey cells may be attributed to a transient increase in the activity of "permissiveness' factors. No enhanced induction was found when the THK or NB-E cells were fused with irradiated rodent cells, that are not or only slightly permissive to SV40 replication.

Differential effect of ultraviolet light on the induction of simian virus 40 and a cellular mutator phenotype in transformed mammalian cells

UV irradiation of simian virus 40 (SV40)-transformed human and hamster cells induced them both to express a mutator phenotype and to produce SV40. The mutator could also be activated indirectly by transfecting unirradiated cells with UV-damaged calf thymus DNA. In contrast, UV-damaged exogenous DNA failed to rescue SV40 from unirradiated transformed cells. These results suggest that the expression of transforming viruses and of cellular mutator functions is regulated by at least partially independent mechanisms. Unlike the activation of a cellular mutator phenotype, the rescue of SV40 from virus-transformed mammalian cells by UV light might require that the integrated viral DNA and/or specific cellular sequences are directly damaged.

An SV40 mammalian inductest for putative carcinogens

This paper describes an in vitro mammalian inductest for putative carcinogens. Several chemical agents were tested using this system which relies on the induction of Simian virus 40 from SV40-transformed hamster kidney cells as an indicator of potential carcinogenic hazard. Aflatoxin B1, sterigmatocystin and aflatoxin G1 were found to be the most efficient inducers in this system followed by the polycyclic hydrocarbons 9,12-dimethylbenzanthracene and benzo[a]pyrene. In principle, this test is similar to a bacterial inductest and the results obtained in the mammalian inductest are compared to those obtained for the same compounds in the bacterial inductest. In addition, SV40 induction is known to occur in response to ultraviolet radiation and ultraviolet radiation plus the photosensitizing drug, 8-methoxypsoralen.