Early life exposure to ultraviolet A light does not cause melanoma in a fish model that previously made that connection, scientists from The University of Texas MD Anderson Cancer Center reported today in the online Early Edition of the Proceedings of the National Academy of Sciences.
UVA exposure is unlikely to have contributed to the rise in the incidence of melanoma over the past 30 years, the researchers conclude, because the fish model had been the only animal model to indicate a connection between exposure to UVA at a young age and later development of melanoma.
"Our data refute the only direct evidence that UVA causes melanoma, which is not to say that UVA is harmless," said the study's lead author David Mitchell, Ph.D., professor in M. D. Anderson's Department of Carcinogenesis located at its Science Park – Research Division in Smithville, Texas. "UVA is just not as dangerous as we thought because it doesn't cause melanoma."
UVA is a carcinogen responsible for squamous cell carcinomas that also causes premature aging of the skin and suppresses the immune system. It's also possible, the authors note, that long-term chronic exposure to UVA can hasten the progression to malignancy of melanocytes in the skin that are already on the path to becoming melanoma.
Mitchell and colleagues tested the effects of UVA and ultraviolet B (UVB) light exposure in melanoma-prone fish hybrids that develop the disease spontaneously 15-20 percent of the time without exposure to UV light.
The scientists exposed a hybrid form of the genus Xiphophorus, more commonly known as platyfishes and swordtails, to either UVA or UVB daily between their fifth and 10th day of life. The fish were then scored for melanoma 14 months after exposure.
"We found that UVB exposure induced melanoma in 43 percent of the 194 treated fish, a much higher rate than the 18.5 percent incidence in the control group that received no UV exposure," Mitchell said. This was expected because UVB exposure at an early age is a well-established cause of melanoma.
Only 12.4 percent of 282 fish exposed to UVA developed the disease, which is not statistically different from the control group.
An influential 1993 study using the same hybrid fish connected UVA exposure to melanoma. Until that study, Mitchell said, sunscreens protected only against UVB exposure, which was of immediate public health concern because UVA makes up 90 percent of the ultraviolet light spectrum of sunlight.
"The thought was that people who used sunscreen stayed out in the sun longer, absorbing a higher dose of UVA, causing a higher risk for melanoma" Mitchell said. Most sunscreens now protect against UVA. However, the increase in the incidence of melanoma has been thought to be partly attributable to childhood exposure to UVA back when sunscreens blocked only UVB. That's unlikely, given the new results, Mitchell said.
The 1993 experiment could not be replicated in mammalian models of melanoma, Mitchell said, and a statistical retrospective of the 1993 paper indicated problems with sample sizes that were too small to yield a definitive answer on UVA exposure.
So, Mitchell and colleagues conducted the experiment again, with much larger sample sizes that provided the statistical power to reach stronger conclusions.
They also stratified the melanomas found in each group by severity, with the control and UVB-exposed fish having a higher incidence of severe, stage IV disease, while those exposed to UVA had significantly more early stage melanomas.
UVB exposure damages DNA directly, while UVA is thought to inflict its damage indirectly by inducing melanin free radicals that react with DNA to form oxidative damage that leads to melanoma. Previous studies had shown a correlation between melanin radical formation and melanoma in the UVA range of the solar spectrum. Since Mitchell and colleagues found no connection between UVA and melanoma, they note that the role of melanin free radicals in this disease is brought into question.
This research was funded by grants from the National Cancer Institute and the National Institute of Environmental Health Sciences.
Co-authors with Mitchell are André Fernandez, Ph.D., Rodney Nairn, Ph.D., Rachel Garcia, Lakshmi Paniker, David Trono and Irma Gimenez-Conti, Ph.D., D.D.S., all of the Department of Carcinogenesis; and Howard Thames, Ph.D., of MD Anderson's Department of Biostatistics. Mitchell, Thames, Conti and Nairn are also on the faculty of the University of Texas Graduate School of Biomedical Sciences, a joint program of MD Anderson and The University of Texas Health Science Center at Houston.
About M. D. Anderson
The University of Texas M. D. Anderson Cancer Center in Houston ranks as one of the world's most respected centers focused on cancer patient care, research, education and prevention. M. D. Anderson is one of only 40 comprehensive cancer centers designated by the National Cancer Institute. For six of the past eight years, including 2009, M. D. Anderson has ranked No. 1 in cancer care in "America's Best Hospitals," a survey published annually in U.S. News & World Report.
Scott Merville | EurekAlert!
Using fragment-based approaches to discover new antibiotics
21.06.2018 | SLAS (Society for Laboratory Automation and Screening)
Scientists learn more about how gene linked to autism affects brain
19.06.2018 | Cincinnati Children's Hospital Medical Center
In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.
Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...
Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...
Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.
Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...
The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.
Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.
An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.
Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...
13.06.2018 | Event News
08.06.2018 | Event News
05.06.2018 | Event News
22.06.2018 | Materials Sciences
22.06.2018 | Earth Sciences
22.06.2018 | Life Sciences