Exposure to non-ionizing radiation provokes changes in rat thyroid morphology and expression of HSP-90
Misa-Agustiño MJ, Jorge-Mora T, Jorge-Barreiro FJ, Suarez-Quintanilla J, Moreno-Piquero E, Ares-Pena FJ, López-Martín E.Exposure to non-ionizing radiation provokes changes in rat thyroid morphology and expression of HSP-90. Exp Biol Med (Maywood). 2015 Feb 2. pii: 1535370214567611. [Epub ahead of print]
Non-ionizing radiation at 2.45 GHz may modify the morphology and expression of genes that codify heat shock proteins (HSP) in the thyroid gland. Diathermy is the therapeutic application of non-ionizing radiation to humans for its beneficial effects in rheumatological and musculo-skeletal pain processes.
We used a diathermy model on laboratory rats subjected to maximum exposure in the left front leg, in order to study the effects of radiation on the nearby thyroid tissue. Fifty-six rats were individually exposed once or repeatedly (10 times in two weeks) for 30 min to 2.45 GHz radiation in a commercial chamber at different non-thermal specific absorption rates (SARs), which were calculated using the finite difference time domain technique. We used immunohistochemistry methods to study the expression of HSP-90 and morphological changes in thyroid gland tissues.
Ninety minutes after radiation with the highest SAR, the central and peripheral follicles presented increased size and the thickness of the peripheral septa had decreased. Twenty-four hours after radiation, only peripheral follicles radiated at 12 W were found to be smaller. Peripheral follicles increased in size with repeated exposure at 3 W power.
Morphological changes in the thyroid tissue may indicate a glandular response to acute or repeated stress from radiation in the hypothalamic-pituitary-thyroid axis. Further research is needed to determine if the effect of this physical agent over time may cause disease in the human thyroid gland.
The thyroid gland is one of the most superficial vital organs and possibly more vulnerable to EMFs.7 Chronic exposure to microwaves at a RF of 2.45 GHz has been shown to significantly affect the hypothalamus–pituitary–thyroid (HPT) axis, provoking changes in body temperature, behavior, and thyroid hormone concentrations.8 Alterations in human and animal levels of thyroid stimulating hormone and other thyroid hormones have also been reported with chronic exposure to frequencies used in mobile telephones, such as 900 MHz.
Heat shock protein (HSP) 90 is a chaperone protein regulating several client proteins involved in thyroid cancer development and the level of expression is higher than in normal tissues. This chaperone has emerged as an exciting target in the development of cancer chemotherapeutics.11,12 Recently, we discovered that repeated, acute subthermal radiation for 30 min at 2.45 GHz can alter cellular stress levels in rat hypothalamus13 and thyroid gland,14 without initially altering apoptotic capacity. Surprisingly, in spite of frequent direct and indirect exposure to non-ionizing radiation in human environments and indications that radiation provokes a degree of stress in thyroid cells, there is very little research describing morphological changes that point to precocious re-adjustments of the mammalian thyroid gland after close-range exposure to non-ionizing radiation at 2.45 GHz.
Group A: single exposure and studied after 90 min (n = 18): The rats were divided into three subgroups (n = 6); each rat was exposed to 30 mina of microwave radiation at three levels: 0 (control), 3, and 12 W.b The rats were kept alive for 90 minc and then euthanized and perfused with fixative.
Group B: single exposure and studied after 24 h (n = 18): The rats were divided into three subgroups (n = 6); each rat was exposed to 30 min of microwave radiation at three levels: 0 (control), 3, and 12 W.b The rats were kept alive for 24 hc and then euthanized and perfused with fixative.
Group C: repeated exposure and studied after 90 min (n = 20): Rats in this group were irradiated at 3 W for 30 min/day, for a total of 10 times in a two-week period. On the last day of exposure, the rats were irradiated and after 90 min were euthanized and perfused with fixative. They were then tested for HSP-90 expression. In the non-irradiated control group (n = 10), rats were immobilized for each of the 10 sessions and euthanized on the last day, following the same protocol as the irradiated animals.
... we found that the interaction of non-ionizing radiation at a frequency of 2.45 GHz caused modifications in the morphology of the thyroid gland tissue and in the distribution of the constituent cellular stress protein known as HSP-90. The morphology of the thyroid gland underwent the following changes due to radiation:
- The size of central and peripheral follicles increased and the thickness of the peripheral septa decreased 90 min after single exposure. After 24 h, central follicles had decreased in size, but hypertrophy was still present in the peripheral follicles of thyroid gland exposed to the higher SAR level.
- Repeated stimulus of the thyroid gland at the lower SAR level triggered adaptation and an increase in the size of peripheral follicles.
- The observed localization of the expression of this protein in the supportive tissue of the septa, specifically in the fibers and in the capsular and lobular membranes suggests that this stress protein constitutes an important component of glandular architecture and is probably dedicated to maintaining glandular structure and morphology. The distribution of HSP-90 in thyroid membranes and cells was diminished after single (if the SAR and time after radiation increased) and repeated exposure to radiation.
We chose to experimentally examine small animals at 2.45 GHz RF because of the wide range of potential applications, from therapeutics to tissue diathermy (this frequency resonates with H2O, facilitating greater penetration) to telecommunications involving WIFI, UMTS, or Bluetooth. We used subthermal SAR levels of 0.102 ± 12.10–3 and 0.429 ± 12.10–3 W/kg at 2.45 GHz in the right front leg, near the thyroid, to ensure that the non-ionizing radiation would not cause direct thermal effects to the gland. Research of this type requires immobilization of the animal, which itself has been found to generate a certain amount of stress. It must also be noted that radiation can catalyze single or repetitive activation of different neuron populations in rat hypothalamus, which intervene in the HPT axis. We cannot therefore assume that the effects of non-ionizing radiation to the thyroid are limited to its tissues; it must be treated as part of a system with multiple, interacting entry points. Other studies have described how microwave radiation at 2.45 GHz affects brain physiopathology and provokes changes in cerebral functioning and behavior. In the present study, the thyroid system is directly or indirectly affected by alterations in the HPT axis as well as by biochemical changes in the thyroid itself due to exposure to microwaves.
Recent research has described how EMFs can constitute external sources for the formation of free radicals in blood cells, the brain, spermatozoids,and myocardial tissue. The thyroid gland is by nature an oxidative organ, and when additional oxidative abuse is caused by exogenous pro-oxidants (ionizing radiation would be the most significant), damage to the macromolecules in the gland increases, possibly leading to thyroid pathology or cancer. In spite of this, a direct relation between thyroid cancer and exposure to EMFs has not yet been established. However, the search is ongoing for biomarkers in thyroid diseases that would make early detection, diagnosis, and intervention possible. HSP-90 is physiologically essential in cellular processes such as hormone signaling and control, proliferation, and differentiation of the cellular cycle. In prior studies, we described a decrease in HSP-90 and 70 due to acute radiation at 2.45 GHz in the thyroid gland, with no apparent effect in the apoptotic activity of thyroid cells. HSP-90 is known to play a modulatory role against thyroid cancer due to its primarily antiapoptotic function. In the present work, we have observed how, after 30 min exposure, the immunoreactivity of HSP-90 is histologically distributed throughout the thyroid gland in places where kinase proteins had previously been activated, between the capsular and lobular membranes and in the follicular and parafollicular cells.
... cellular damage in the thyroid gland was directly related to the SAR level and/or number of exposures applied to the tissue.
... In the present experiment, exposure of rat thyroid gland to RF at 2.45 GHz and 0.102 ± 12.10–3 SAR increased HSP-90 marking in the parafollicular cells. However, HSP-90 stress immunomarking decreased in the parafollicular cells at 0.429 ± 12.10–3 SAR or with repeated exposure (see Figure 7). HSP-90 in the parafollicular cell is sensitive to the nature and intensity of radiation stimulus, which can modify cellular function and serve as a biomarker for cellular damage.
Thyroid gland exposed to 2.45 GHz radiation in this experimental model of diathermy in rats presented the following visible morphological effects: (a) glandular hypertrophy in relation to the SAR and/or number of exposures; (b) modification of the distribution of HSP-90 associated with membranes and parafollicular cells. These effects might not be exclusively or directly produced by radiation and can be included with other indirect effects from the hypothalamus. However, further research is needed to ascertain whether the continued effect of this physical agent could provoke pathology in the thyroid gland.
Joel M. Moskowitz, Ph.D., Director
Center for Family and Community Health
School of Public Health
University of California, Berkeley
Electromagnetic Radiation Safety
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