Interactions of radiofrequency radiation-induced hyperthermia and 2-methoxyethanol teratogenicity in rats

Effects of Radiofrequency Electromagnetic Field (RF-EMF) exposure on pregnancy and birth outcomes: A systematic review of experimental studies on non-human mammals

BACKGROUND

The World Health Organization is coordinating an international project aimed at systematically reviewing the evidence regarding the association between radiofrequency electromagnetic field (RF-EMF) exposure and adverse health effects. Within the project, 6 topics have been prioritized by an expert group, which include reproductive health outcomes.

OBJECTIVES

According to the protocol published in 2021, a systematic review and meta-analyses on the adverse effects of RF-EMF exposure during pregnancy in offspring of experimental animals were conducted.

METHODS

Three electronic databases (PubMed, Scopus and EMF Portal) were last searched on September 8 or 17, 2022. Based on predefined selection criteria, the obtained references were screened by two independent reviewers. Studies were included if they met the following criteria: 1) original, sham controlled experimental study on non-human mammals exposed in utero, published in peer-reviewed journals, 2) the experimental RF-EMF exposure was within the frequency range 100 kHz-300 GHz, 3) the effects of RF-EMF exposure on fecundity (litter size, embryonic/fetal losses), on the offspring health at birth (decrease of weight or length, congenital malformations, changes of sex ratio) or on delayed effects (neurocognitive alterations, female infertility or early-onset cancer) were studied. Study characteristics and outcome data were extracted by two reviewers. Risk of bias (RoB) was assessed using the Office of Health Assessment and Translation (OHAT) guidelines. Study results were pooled in a random effects meta-analysis comparing average exposure to no-exposure and in a dose-response meta-analysis using all exposure doses, after exclusion of studies that were rated at "high concern" for RoB. Subgroup analyses were conducted for species, Specific Absorption Rate (SAR) and temperature increase. The certainty of the evidence was assessed using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach.

RESULTS

Eighty-eight papers could be included in this review. Effects on fecundity. The meta-analysis of studies on litter size, conducted at a whole-body average SAR of 4.92 W/kg, did not show an effect of RF-EMF exposure (MD 0.05; 95% CI -0.21 to 0.30). The meta-analysis of studies on resorbed and dead fetuses, conducted at a whole-body average SAR of 20.26 W/kg, showed a significant increase of the incidence in RF-EMF exposed animals (OR 1.84; 95% CI 1.27 to 2.66). The results were similar in the dose-response analysis. Effects on the offspring health at birth. The meta-analysis of studies on fetal weight, conducted at a whole-body average SAR of 9.83 W/kg, showed a small decrease in RF-EMF exposed animals (SMD 0.31; 95% CI 0.15 to 0.48). The meta-analysis of studies on fetal length, conducted at a whole-body average SAR of 4.55 W/kg, showed a moderate decrease in length at birth (SMD 0.45; 95% CI 0.07 to 0.83). The meta-analysis of studies on the percentage of fetuses with malformations, conducted at a whole-body average SAR of 6.75 W/kg, showed a moderate increase in RF-EMF exposed animals (SMD -0.45; 95% CI -0.68 to -0.23). The meta-analysis of studies on the incidence of litters with malformed fetuses, conducted at a whole-body average SAR of 16.63 W/kg, showed a statistically significant detrimental RF-EMF effect (OR 3.22; 95% CI 1.9 to 5.46). The results were similar in the dose-response analyses. Delayed effects on the offspring health. RF-EMF exposure was not associated with detrimental effects on brain weight (SMD 0.10; 95% CI -0.09 to 0.29) and on learning and memory functions (SMD -0.54; 95% CI -1.24 to 0.17). RF-EMF exposure was associated with a large detrimental effect on motor activity functions (SMD 0.79; 95% CI 0.21 to 1.38) and a moderate detrimental effect on motor and sensory functions (SMD -0.66; 95% CI -1.18 to -0.14). RF-EMF exposure was not associated with a decrease of the size of litters conceived by F2 female offspring (SMD 0.08; 95% CI -0.39 to 0.55). Notably, meta-analyses of neurobehavioural effects were based on few studies, which suffered of lack of independent replication deriving from only few laboratories.

DISCUSSION

There was high certainty in the evidence for a lack of association of RF-EMF exposure with litter size. We attributed a moderate certainty to the evidence of a small detrimental effect on fetal weight. We also attributed a moderate certainty to the evidence of a lack of delayed effects on the offspring brain weight. For most of the other endpoints assessed by the meta-analyses, detrimental RF-EMF effects were shown, however the evidence was attributed a low or very low certainty. The body of evidence had limitations that did not allow an assessment of whether RF-EMF may affect pregnancy outcomes at exposure levels below those eliciting a well-known adverse heating impact. In conclusion, in utero RF-EMF exposure does not have a detrimental effect on fecundity and likely affects offspring health at birth, based on the meta-analysis of studies in experimental mammals on litter size and fetal weight, respectively. Regarding possible delayed effects of in utero exposure, RF-EMF probably does not affect offspring brain weight and may not decrease female offspring fertility; on the other hand, RF-EMF may have a detrimental impact on neurobehavioural functions, varying in magnitude for different endpoints, but these last findings are very uncertain. Further research is needed on the effects at birth and delayed effects with sample sizes adequate for detecting a small effect. Future studies should use standardized endpoints for testing prenatal developmental toxicity and developmental neurotoxicity (OECD TG 414 and 426), improve the description of the exposure system design and exposure conditions, conduct appropriate dosimetry characterization, blind endpoint analysis and include several exposure levels to better enable the assessment of a dose-response relationship.

PROTOCOL REGISTRATION AND PUBLICATION

The protocol was published in Pacchierotti et al., 2021 and registered in PROSPERO CRD42021227746 (https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=227746).

The Contribution of In Vivo Mammalian Studies to the Knowledge of Adverse Effects of Radiofrequency Radiation on Human Health

The proliferation of cellular antennas and other radiofrequency radiation (RFR) generating devices of the last decades has led to more and more concerns about the potential health effects from RFR exposure. Since the 2011 classification as a possible carcinogen by the International Agency for Research on Cancer (IARC), more experimental studies have been published that support a causal association between RFR exposure and health hazards. As regard cancer risk, two long-term experimental studies have been recently published by the US National Toxicology Program (NTP) and the Italian Ramazzini Institute (RI). Despite important experimental differences, both studies found statistically significant increases in the development of the same type of very rare glial malignant tumors. In addition to carcinogenicity, reproductive organs might be particularly exposed, as well as sensitive to RFR. In this work, we reviewed the currently available evidence from in vivo studies on carcinogenicity and reproductive toxicity studies in order to summarize the contribution of experimental research to the prevention of the adverse effects of RFR on human health.

Polymeric-gold nanohybrids for combined imaging and cancer therapy

Here, the use of folic acid (FA)-functionalized, doxorubicin (DOXO)/superparamagnetic iron oxide nanoparticles (SPION)-loaded poly(lactic-co-glycolic acid) (PLGA)-Au porous shell nanoparticles (NPs) as potential nanoplatforms is reported for targeted multimodal chemo- and photothermal therapy combined with optical and magnetic resonance imaging in cancer. These polymeric-gold nanohybrids (PGNH) are produced by a seeded-growth method using chitosan as an electrostatic "glue" to attach Au seeds to DOXO/SPION-PLGA NPs. In order to determine their potential as theranostic nanoplatforms, their physicochemical properties, cellular uptake, and photothermal and chemotherapeutic efficiencies are tested in vitro using a human cervical cancer (HeLa) cell line. The present NPs show a near-infrared (NIR)-light-triggered release of cargo molecules under illumination and a great capacity to induce localized cell death in a well-focused region. The functionalization of the PGNH NPs with the targeting ligand FA improves their internalization efficiency and specificity. Furthermore, the possibility to guide the PGNH NPs to cancer cells by an external magnetic field is also proven in vitro, which additionally increases the cellular uptake and therapeutic efficiency.

Thermal thresholds for teratogenicity, reproduction, and development

The human embryo and foetus may be especially vulnerable to chemical and physical insults during defined stages of development. In particular, the scheduled processes of cell proliferation, cell migration, cell differentiation, and apoptosis that occur at different times for different organ structures can be susceptible to elevated temperatures. With limited ability to regulate temperature on its own, the developing embryo and foetus is entirely dependent upon the mother's thermoregulatory capacity. As a general rule, maternal core body temperature increases of ∼2°C above normal for extended periods of time, 2-2.5°C above normal for 0.5-1 h, or ≥4°C above normal for 15 min have resulted in developmental abnormalities in animal models. Significant differences in thermoregulation and thermoneutral ambient temperatures make direct extrapolation of animal data to humans challenging, and the above temperatures may or may not be reasonable threshold predictions for adverse developmental effects in humans. Corresponding specific absorption rate (SAR) values that would be necessary to cause such temperature elevations in a healthy adult female would be in the range of ≥15 W/kg (whole body average or WBA), with ∼4 W/kg required to increase core temperature 1°C. However, smaller levels of thermal stress in the mother that are asymptomatic might theoretically result in increased shunting of blood volume to the periphery as a heat dissipation mechanism. This could conceivably result in altered placental and umbilical blood perfusion and reduce heat exchange with the foetus. It is difficult to predict the magnitude and threshold for such an effect, as many factors are involved in the thermoregulatory response. However, a very conservative estimate of 1.5 W/kg WBA (1/10th the threshold to protect against measurable temperature increases) would seem sufficient to protect against any significant reduction in blood flow to the embryo or foetus in the pregnant mother. This is more than three times above the current WBA limit for occupational exposure (0.4 W/kg) as outlined in both IEEE C95.1-2005 and ICNIRP-1998 international safety standards for radiofrequency (RF) exposures. With regard to local RF exposure directly to the embryo or foetus, significant absorption by the mother as well as heat dissipation due to conductive and convective exchange would offer significant protection. However, a theoretical 1-W/kg exposure averaged over the entire 28-day embryo, or averaged over a 1-g volume in the foetus, should not elevate temperature more than 0.2°C. Because of safety standards, exposures to the foetus this great would not be attainable with the usual RF sources. Foetal exposures to ultrasound are limited by the US Food and Drug Administration (FDA) to a maximum spatial peak temporal average intensity of 720 mW/cm(2). Routine ultrasound scanning typically occurs at lower values and temperature elevations are negligible. However, some higher power Doppler ultrasound devices under some conditions are capable of raising foetal temperature several degrees and their use in examinations of the foetus should be minimised.

Multifunctional nanoparticles for combined doxorubicin and photothermal treatments

To facilitate combined doxorubicin and photothermal treatments, we developed doxorubicin-loaded poly(lactic-co-glycolic acid)-gold half-shell nanoparticles (DOX-loaded PLGA-Au H-S NPs) by depositing Au films on DOX-loaded PLGA NPs. As the PLGA NPs biodegraded, DOX was released, and heat was locally generated upon near-infrared (NIR) irradiation due to NIR resonance of DOX-loaded PLGA H-S NPs. Compared with chemotherapy or photothermal treatment alone, the combined treatment demonstrated a synergistic effect, resulting in higher therapeutic efficacy and shorter treatment times. Since our NPs selectively deliver both heat and drug to tumorigenic regions, they may improve the therapeutic effectiveness with minimal side effects.

Calculation of induced current densities and specific absorption rates (SAR) for pregnant women exposed to hand-held metal detectors

The finite difference time domain (FDTD) method in combination with a well established frequency scaling method was used to calculate the internal fields and current densities induced in a simple model of a pregnant woman and her foetus, when exposed to hand-held metal detectors. The pregnant woman and foetus were modelled using a simple semi-heterogeneous model in 10 mm resolution, consisting of three different types of tissue. The model is based on the scanned shape of a pregnant woman in the 34th gestational week. Nine different representative models of hand-held metal detectors operating in the frequency range from 8 kHz to 2 MHz were evaluated. The metal detectors were placed directly on the abdomen of the computational model with a spacing of 1 cm. Both the induced current density and the specific absorption rate (SAR) are well below the recommended limits for exposure of the general public published in the ICNIRP Guidelines and the IEEE C95.1 Standard. The highest current density is 8.3 mA m(-2) and the highest SAR is 26.5 microW kg(-1). Compared to the limits for the induced current density recommended in the ICNIRP Guidelines, a minimum safety factor of 3 exists. Compared to the IEEE C95. 1 Standard, a safety factor of 60 000 for the specific absorption rate was found. Based on the very low specific absorption rate and an induced current density below the recommended exposure limits, significant temperature rise or nerve stimulation in the pregnant woman or in the foetus can be excluded.

Developmental Toxicity Interactions of Methanol and Radiofrequency Radiation or 2-Methoxyethanol in Rats

This research was undertaken to determine potential interactions among chemical and physical agents. Radiofrequency (RF) radiation is used in numerous workplaces, and many workers are concurrently exposed to RF radiation and various chemicals. The developmental toxicity of RF radiation is associated with the degree and duration of hyperthermia induced by the exposure. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), enhanced teratogenicity in rats. Interactions were noted at even the lowest levels of 2ME tested, but only at hyperthermic levels of RF radiation. The purpose of the present research is to investigate if the interactive effects noted for RF radiation and 2ME are unique to these agents, or if similar interactions might be seen with other chemicals. Because methanol is widely used as a solvent as well as fuel additive, and, at high levels, is teratogenic in animals, we selected methanol as a chemical to address generalizability. Based on the literature and our pilot studies, 0, 2, or 3 g/kg methanol (twice, at 6-hour intervals) were administered on gestation day 9 or 13 to groups of 10 Sprague-Dawley rats. Dams treated on day 9 were given methanol and exposed to RF radiation sufficient to maintain colonic temperature at 41°C for 60 minutes (or sham). Those treated on day 13 were given methanol plus either 0 or 100 mg/kg 2ME. Because we observed that methanol produced hypothermia, some groups were given the initial dose of methanol concurrently with the RF or 2ME, and others were given the first dose of methanol 1.5 hours prior to RF or 2ME. Dams were sacrificed on gestation day 20, and the fetuses were examined for external malformations. The results indicate that RF radiation or methanol on day 9 increased the incidence of resorbed fetuses, but no interactive effects were observed. The resorptions were highest in groups given the experimental treatments 1.5 hours apart. The higher dose of methanol also reduced fetal weights. Administration of 2ME or methanol on day 13 increased the rate of malformations, and there was evidence of a positive interaction between 2ME and methanol. Fetal weights were reduced by 2ME and methanol alone, but no interaction was observed. Also, separation of the dosing with the teratogens did not affect the results. These results point out that interactions in developmental toxicology, such as those of RF radiation, 2ME, and methanol that we have studied, are complex, and such interactions cannot be fully understood or predicted without more research. It is important that combined exposure effects be considered when developing both physical agent and chemical agent exposure guidelines and intervention strategies.

Developmental toxicity interactions of salicylic acid and radiofrequency radiation or 2-methoxyethanol in rats

Radiofrequency (RF) radiation is used in a variety of workplaces where workers are concurrently exposed to chemicals. Combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The purpose of the present research was to determine if the synergistic effects noted for RF radiation and 2ME are generalizable to other chemicals. Since salicylic acid (SA) is widely used as an analgesic and is teratogenic in animals, SA was selected to address generalizability. Based on the literature and our pilot studies, 0, 250, or 350 mg/kg SA were administered by gavage on gestation Day 9 or 13 to rats. Concurrently rats given SA on Day 9 were exposed to RF radiation sufficient to maintain colonic temperature at 41 degrees C for 60 min (or sham). Those given SA on Day 13 were also given 0 or 100 mg/kg 2ME (gavage). Dams were sacrificed on gestation Day 20, and the fetuses were examined for external malformations. The data provide no evidence of synergistic interactions between RF radiation and salicylic acid (resorptions and malformations). Limited evidence of antagonism was observed between 2ME and salicylic acid (fetal weights). This investigation highlights the importance of additional research on interactions in developmental toxicology, and emphasizes the need to consider combined exposure effects when developing both physical agent and chemical agent exposure guidelines and intervention strategies.