Effect of High Light Level on Sperm Parameters in Mice



Mohammadi H¹ ; Dehghan SF² ; Abdollahi MB³ ; Kalantar M⁴ ; Kaydany M⁴ Show Affiliations
Source: Iran Occupational Health Published:2019

Abstract

Background and aims: Eyesight is considered as one of the most important senses in the human being. In this regard, it is necessary to provide optimal lighting in the living environment and to show objects and enhance differential contrast, as well as preventing visual fatigue and glare. The advancement of technology and the increased need for shift work have made individuals, according to their type and nature of work, exposed to high-intensity light. Among such occupations, which are considered as very precise jobs, we can mention clockwork, mapping, electronic work, etc. High levels of natural or artificial lighting in some businesses can be considered as a harmful physical factor. In-vivo studies have shown that exposure to light can affect fertility and the quality of semen and sperm. Hereof, papers mostly focus on the effects of non-visible radiation or on the effect of radiation wavelengths, and less studies have been conducted to investigate the effect of visible light, in particular on the high intensity of lighting, on semen parameters. Since high light level of natural or artificial sources in some workplaces may be considered as a hazardous physical agent, the present study aimed to assess the effect of light level of 1000 lux on sperm parameters in mice. Methods: The study population included 12 healthy male adult mice of the same age (7 weeks) with approximately the same weights (30 ± 2.5 g). Six were considered as a control group and six were considered as case group. Animals were kept in polycarbonate Plexiglas containers during the test and after testing time kept in special cages. Food and water were freely access available to the animals. The average temperature of the room was 24-28°C, the relative humidity was 60-40%, and the air velocity was 0.14-0.16 m/s. Light intensity measured during 8 hours of daily exposure was 1000 lux and at animal room less than 100 lux were measured by a lux meter. The amount of light needed for testing was only provided through a projector equipped with 400-watt metallic halide bulbs with white light. Experiments were conducted under controlled conditions for a period of five consecutive days and eight hours of exposure daily. At the end of the exposure scenario, animals of each group were anesthetized with Ketamine-xylazine injections, the epidermis of the testicles was stretching out and put on in a culture medium for semen analysis. Paraffin molds and 5-micron slices were provided and all tests related to tissue index were performed on the samples. Also, by optical microscope with magnification of 400x, spermatogonium, spermatocyte, spermatid and sperm cells was counted. The internal and external diameter of the sperm tubes was calculated using the Image J software. The mean three-time intra-group replication of the data with a significant level of 0.05 was reported. Data were analyzed by one-way ANOVA and Tukey's post hoc tests. Results: in assessing the morphology of sperm in case group, the more abnormalities (with hairpin curved sperm) was found than the one of the control. There was a significant difference of the internal diameter of the spermatozoa tubes (case: 97.11 ± 1.79 μm; control: 66.82 ± 1.02 μm) between the case and control groups (P<0.01), while there was no significant difference between the two groups in case of the external diameter (case: 160.27 ± 1.95 μm; control: 161.98 ± 1.33 μm) (P>0.05). The percentage of total motile sperms (case: 60.7 ± 0.96; control: 72.4 ± 1.02), percentage of sperm with normal morphology (case: 45.50 ± 3.58; control: 73.35 ± 1.6) and the percentage of living sperm (case: 58.68 ± 1.44; control: 74.36 ± 1.65) were significantly different between the two groups (P<0.01). No significant difference in the number of sperm in millions (case: 4.11 ± 1.11; control: 4.51 ± 0.09) was observed between the two groups (P> 0.05). Microscopic images showed that the internal diameter of the spermatozoa tubes in the case group have been changed in comparison with the control group. Result show tissue degradation, disruption of spermatogenic cell and destruction of the medial part of the spermatozoa tubes in the case group as compared to the control group. The presence of irregularity, entanglement and abnormalities in the case group was clear compared to the control group. Conclusion: The aim of this study was to investigate the effect of exposure to light 1000 lux on sperm parameters in male mice. Previously, a similar study on the effect of high intensity lighting on reproductive ability and quality of semen was not reported. While today, exposure to high-intensity light in precise jobs and shift works is so common. According to the findings of this study, exposures to light 1000 lux reduced motility, percentage of natural morphology and rate of living sperm, which is expected to increase the possibility of different degrees of infertility in male. Also there was an increase in the internal diameter of the spermatozoa tubes due to exposure with 1000 lux, indicating cell differentiation and death in a large number of reproductive and germ cells of different classes. Cellular mechanisms regarding the interaction between visible light and sperm are still debatable. Most researchers believe that the first step in finding the interaction between light-cells is the formation of reactive oxygen species (ROS) by light-sensitive elements in endogenous cell. Although in male reproduction, ROS is known to be harmful to sperm function, it has now been shown that very low concentrations of ROS in signal transmission pathways lead to sperm acrosome responses, which seems essential for fertilization. The results of other studies show that visible light can change the redox state of sperm cells by inducing ROS production. Since one of the most important functions of the regulator cells is to maintain cell redox homeostasis, this change can modulate the intracellular movement of Ca2+. Changes in ROS and Ca2+ both play a vital role in controlling sperm motility and fertilization capacity of mammalian sperm. In addition, a study has shown that visible light increases the amount of ATP (Adenosine triphosphate) in sperm cells. However, more studies are needed to fully investigate the effects different intensities of visible light exposure on the sperm fertilizing ability. Since the precise determination of the cellular redox state depends on the cellular conditions and the parameters of the light used for radiation, the optimal light conditions for each animal's spermatozoa for therapeutic purposes should be determined. Considering that studies focus mainly on lower intensity of visible light, in order to conclude definitively, more comprehensive studies are required on different animal species or on human sperms. Due to the fact that today, in precise and high-precise jobs, exposures of people with high-intensity radiation occur, it is advisable to take appropriate control measures in the workplace in order to prevent the potential adverse effects of exposure to high intensity illumination. In conclusion, according to our findings, exposure to the light level of 1000 lux may reduce total motility, natural morphology percentage and survival rate of sperms, which is expected to increase with the possibility of different degrees of infertility with male factor over time. There was also an increase in the internal diameter of the sperm membranes due to the exposure to 1000 lux, indicating cell differentiation and death in a large number of different germ cells. © 2019 Iran University of Medical Sciences. All rights reserved.