Introduction
In recent times there has been some controversy over the impact of electromagnetic radiation on human health.
The significance of mobile phone radiation on male reproduction is a key element of this debate since several studies have suggested a relationship between mobile phone use and semen quality . The potential mechanisms involved have not been established, however, human spermatozoa are known to be particularly vulnerable to oxidative stress by virtue of the abundant availability of substrates for free radical attack and the lack of cytoplasmic space to accommodate antioxidant enzymes . Moreover, the induction of oxidative stress in these cells not only perturbs their capacity for fertilization but also contributes to sperm DNA damage . The latter has, in turn, been linked with poor fertility, an increased incidence of miscarriage and morbidity in the offspring, including childhood cancer.
More commonly used cellular phones operate at a frequency of 850 to 1800 MHz ; the radiant energy is absorbed by human body tissues and organs by aerial effect and/or coupling the RF signal and/or resonant absorption. The specific absorption rate defines the amount of RF energy absorbed into local tissues and represents a measure for evaluating the emission of transmitters located nearby the body. For cellular phones, SAR varies from 0.12 to 1.6 watts/kg of body weight .
Leydig cells, seminiferous tubules, and spermatozoa are the main targets of the damage caused by mobile phones on the male reproductive tract. In particular, cellular phone exposure reduces testosterone biosynthesis, impairs spermatogenesis, and damages sperm DNA. Scrotal hyperthermia and oxidative stress are the main mechanisms by which the damage is generated. It is well known that testicular temperature is 2°C to 3°C lower than rectal temperature, and the optimal temperature for spermatogenesis is considered to be 35°C . From this point of view, the habit of keeping a mobile phone in the trouser pocket or the duration of its use may have an impact on possible generation of hyperthermia and oxidative stress as well.
In this context, it is significant that human spermatozoa are uniquely sensitive to oxidative stress for a variety of reasons. Firstly, these cells are largely devoid of the cytoplasm that in somatic cells houses the antioxidant enzymes that offer a first line of defense against free radical attack. Secondly, these cells possess abundant targets for the induction of peroxidative damage including polyunsaturated fatty acids and DNA. Thirdly, these cells are professional generators of reactive oxygen species, that appear to emanate largely from the sperm mitochondria and, possibly, plasma membrane NADH oxidases. Thus if any cell type would be vulnerable to the oxidative stress reportedly generated on exposure to RF-EMR, it would be human spermatozoa.
Effects of the Exposure to Mobile Phones on Male Reproduction: A Review of the Literature, 2013
Mobile Phone Radiation Induces Reactive Oxygen Species Production and DNA Damage in Human Spermatozoa In Vitro, 2009
Reactive oxygen species or ROSs are species such as superoxide (O2-), hydrogen peroxide (H2O2), and hydroxyl radical (•OH) and are associated with cell damage. ROSs form as a natural by-product of the normal metabolism of oxygen and have important roles in cell signaling.
Free radicals tend to damage particularly three components of the cell: lipids, proteins and nucleic acids.
- Lipid peroxidation ; in particular of plasma membrane and membranes of intracellular organelles is a common cellular damage due to ROS and RNS (Reactive nitrogen species). Free radicals, in presence of oxygen, react with double bonds of membrane lipids generating lipid peroxides which, being reactive, propagate causing extensive damage to the membranes . ROS more formidable in this case is • OH.
- Oxidation of proteins ; in particular free radicals act by oxidizing the side groups of amino acids, damaging the function of the protein, promote the formation of crosslinks as the disulfide bond, altering the structure or folding . They can also give rise to modified amino acids .
- Damage to the DNA ; free radicals can cause mutations or damage macroscopically the DNA and alter the chemical structure of the nitrogenous bases such as by forming new 8-ossiguanina or 5-idrossimetiluracile . Through this type of damage are contributory cause of cellular aging and promote cancer .
Human Studies
RF-EMR (Radio Frequency-Electromagnetic Radiation) disrupts human sperm motility and vitality and induces intracellular reactive oxygen species (ROS)
In an initial experiment, functional human spermatozoa were exposed to RF-EMR at an SAR of 27.5 W/kg. This exposure induced a highly significant decline in both vitality ( Figure A ) and motility ( Figure B ) compared with the unexposed controls. Exposed spermatozoa also produced significantly higher amounts of ROS than background levels ( Figure C ) and MitoSOX red (MSR= red mitochondrial superoxide indicator) probes ( Figure D ) suggesting that free radical generation had been initiated as a consequence of RF-EMR and that the mitochondria were significantly involved in this response.
RF-EMR has a negative impact on human spermatozoa over a range of SAR values
Extending the range of SAR values to include the values covered by conventional mobile phones (0.5 W/kg–1.5 W/kg), it was observed that high quality spermatozoa displayed a decline in both vitality and motility after exposure to RF-EMR in a dose- dependent manner. The control populations maintained an average vitality of 89%; however, significant reductions in vitality were observed at exposure levels as low as 1.0 W/kg ( Figure A ). Similarly, the control populations maintained motilities at an average of 86% over the incubation period, however after exposure to RF-EMR at levels of 1.0 W/kg, motility was observed to significantly decrease to 68% and decreased still further at higher SAR exposures ( Figure B ).
Reactive Oxygen Species are central to the RF-EMR response
Exposure of human spermatozoa to RF-EMR over a range of SAR levels resulted in a dose-dependent activation of ROS generation ( Figure A ). In this analysis, a significant increase in ROS positive cells was observed after exposure at 1.0 W/kg; thereafter ROS production rose rapidly with SAR values up to 4.3 W/kg and then began to plateau reaching a peak of 30% at the highest exposure levels assessed ( Figure A ). Spermatozoa exposed to increasing levels of RF-EMR, generated a significant, dose-dependent increase in ROS generation by the mitochondria. At SAR values above 4.3 W/kg, RF-EMR induced mitochondrial ROS begun to plateau reaching 30% at the maximal SAR values assessed ( Figure B ). The ROS production elicited by RF-EMR involved electron leakage from the mitochondrial electron transport chain .
In order to control for bulk thermal effects of RF-EMR exposure, spermatozoa were also incubated at temperatures ranging from 21°C–50°C for 2 h ( Figure C ). This analysis did reveal an effect of heat on free radical generation by human spermatozoa possibly due to the activation of an apoptotic response, however these effects were only significant above 40°C. Thus at the temperature at which these experiments were performed (21°C) the highest observed RF-EMR-induced temperature rise (+0.4°C at 27.5 W/kg), could not of itself account for the increased ROS response observed across the range of SAR settings evaluated in this study.
RF-EMR induces oxidative DNA damage (8-OH-dG)
In order to determine whether the ROS generation induced on exposure of human spermatozoa to RF-EMR resulted in a state of oxidative stress, it was monitored the expression of 8-hydroxy-2′-deoxyguanosine (8-OH-dG), a marker for oxidative damage to sperm DNA. As the SAR level was increased, the amount of oxidative DNA damage expressed in the spermatozoa became elevated ( Figure A ). A significant increase in 8-OH-dG expression became apparent at low SAR values (<5.0 W/kg) rising to a maximum of around 20% at the highest levels of exposure (27.5 W/kg). By plotting the 8-OH-dG positive cells against the MSR signal ( Figure B ) it was apparent that a strong positive correlation existed between the two parameters; the higher the level of mitochondrial ROS generation , the greater the degree of oxidative DNA damage in the spermatozoa.
RF-EMR induces DNA fragmentation in human spermatozoa
As illustrated in Figure 5A , human spermatozoa responded to RF-EMR exposure with a significant increase in DNA strand breaks at an SAR of 2.8 W/kg that increased rapidly with rising SAR values and then reached a plateau so that at the highest SAR level assessed (27.5 W/kg), 29% of the cells expressed significant DNA fragmentation . This DNA damage was highly correlated with free radical generation by the sperm mitochondria giving a correlation coefficient of R2 = 0.861 ( Figure B ). Moreover, the level of DNA fragmentation was highly correlated with 8-OH-dG formation (R2=0.725; Figure C ) such that sperm cells exhibiting high levels of oxidative DNA damage, also possessed high levels of DNA fragmentation.
In vivo studies
In one experiment twenty healthy male volunteers aged 19 to 40 were studied.
Each subject was exposed to RF-EMR radiation through the use of a cellular phone 2 h/day, 5 days/week, for 1 month. They measured serum (for adrenocorticotropin, thyrotropin, growth hormone, PRL, LH, and FSH concentrations) in nine weekly blood samples obtained starting 3 weeks before the commencement of the exposure and ending 2 weeks after exposure.
Within each individual, the preexposure hormone concentration was used as a control. One month of intermittent exposure to cell phone RF-EMR did not induce a long-lasting or cumulative effect on the hormone secretion rate of the anterior pituitary gland in humans.
Nevertheless, in another experiment, were studied human males of reproductive age reporting the effect of mobile phone radiation on any or all measures of semen volume, total sperm count, sperm concentration, sperm motility or sperm morphology.
It was showed that there was significant heterogeneity among effect sizes, which suggest that some of the semen parameters may not be affected by mobile phone exposure.
Hence, combined effect-size for each of the semen parameters were calculated separately, and it was found that sperm concentration, sperm morphology, sperm motility, proportion of non-progressive motile sperm (%), proportion of slow progressive motile sperm (%), and sperm viability were deteriorated in individuals exposed to mobile phone radiation.
By contrast, semen volume, liquefaction time, semen pH, proportion of rapid progressive motile sperm (%), and semen viscosity were not affected by mobile phone usage.
Mobile phones affect multiple sperm quality traits: a meta-analysis, 2013
Challenging cell phone impact on reproduction: A Review, 2012
Mobile Phone Radiation Induces Reactive Oxygen Species Production and DNA Damage in Human Spermatozoa In Vitro, 2009
Conclusions
The particular significance of the present study is that it not only demonstrates a direct effect of RF-EMR on sperm motility, vitality and DNA integrity but also identifies a potential causative mechanism involving electron leakage from the mitochondrial electron transport chain and the induction of oxidative DNA damage .
In part, these mechanistic insights have been achieved because the cell type used, the human spermatozoon , has an extremely simple cellular architecture , lacking significant cytosol and possessing few cellular organelles other than the sperm nucleus, flagellum and mitochondria. One consequence of this structure is that these cells are uniquely vulnerable to oxidative stress. Moreover, such stress is already known to induce the functional and structural lesions observed in this study including both a loss of motility mediated by peroxidative damage to the sperm plasma membrane, as well as the formation of DNA base adducts in the sperm nucleus that ultimately lead to DNA fragmentation.
Notwithstanding the specialized nature of mammalian spermatozoa, the mechanisms suggested by this study may also apply to RF-EMR-mediated damage in other cell types . The RF-EMR used for communications, including mobile phone networks, is not of high enough power to be classed as ionizing radiation . The latter has sufficient energy to pull away electrons, dramatically altering the properties of affected molecules and typically creating extremely reactive radical species. RF-EMR does not contain sufficient energy for these processes. Nevertheless, this form of radiation may have other effects on larger scale systems such as cells and organelles, which stem from the perturbation of charged molecules and the disruption of electron flow . Mitochondria have one of the largest standing membrane potentials in the body and their energetic functions are entirely dependent on the regulated movement of electrons and protons within the inner mitochondrion membrane. Theoretically, such fluxes might be susceptible to disruptions in local electric fields induced by RF-EMR, offering a potential link between this form of radiation and the non-thermal biological effects observed in this study.
Data in humans have been criticized to be subject to recall bias ; nevertheless, cohort studies are scarce, as most of the published literature relied on case–control and time-trend studies. Additionally, the lack of control groups in human studies (men or women who do not use cell phones) is obvious. In vitro studies on human sperms or granulosa cells might not be a good representative of the effect of RF-EMR because in real life the device and the reproductive organs are separated by multiple tissue layers.
Therefore, designing experimental conditions to mimic real lifelike cell phone exposure might be the next step in answering unknown clinical questions. Additionally, isolating cell phone RF-EMR from other environmental factors (including the ones that emit radiations that might constitute potential confounders) might be a challenge for ideal study design.
