Apoptotic cell death in erythrocytes of p53-deficient medaka (Oryzias latipes) after γ-irradiation

Responses of hematopoietic cells after ionizing-irradiation in anemic adult medaka (Oryzias latipes)

PURPOSE

Hematopoietic tissues of vertebrates are highly radiation sensitive and the effects of ionizing radiation on the hematopoiesis have been studied in mammals and teleosts for decades. In this study, radiation responses in the kidney, the main hematopoietic organ in teleosts, were investigated in Japanese medaka (Oryzias latipes), which has been a model animal and a large body of knowledge has been accumulated in radiation biology.

METHODS

Kidney, the main hematopoietic tissue of adult medaka fish, was locally irradiated using proton and carbon ion beams irradiation system of Takasaki Ion Accelerator for Advanced Radiation Application (TIARA), QST, and the effects on peripheral blood cells and histology of the kidney were investigated.

RESULTS

When only kidneys were locally irradiated with proton or carbon ion beam (15 Gy), the hematopoietic cells in the irradiated kidney and cell density in the peripheral blood decreased 7 days after the irradiation in the same manner as after the whole-body irradiation with γ-rays (15 Gy). These results demonstrate that direct irradiation of the hematopoietic cells in the kidney induced cell death and/or cell cycle arrest and stopped the supply of erythroid cells. Then, the cell density in the peripheral blood recovered to the control level within 4 days and 7 days after the γ-ray and proton beam irradiation (15 Gy), respectively, while the cell density in the peripheral blood did not recover after the carbon ion beam irradiation (15 Gy). The hematopoietic cells in the irradiated kidneys temporarily decreased and recovered to the control level within 21 days after the γ-ray or proton beam irradiation (15 Gy), while it did not recover after the carbon ion beam irradiation (15 Gy). In contrast, the recovery of the cell density in the peripheral blood delayed when anemic medaka were irradiated 1 day after the administration of phenylhydrazine. With and without γ-ray irradiation, a large number of hematopoietic cells was still proliferating in the kidney 7 days after the anemia induction.

CONCLUSIONS

The results obtained strongly suggest that the hematopoietic stem cells in medaka kidney prioritize to proliferate and increase peripheral blood cells to eliminate anemia, even when they are damaged by high-dose irradiation.

Phosphorylation of p53 by Cdk5 contributes to benzo[a]pyrene-induced neuronal apoptosis

Benzo[a]pyrene (B[a]P) is a ubiquitous carcinogenic pollutant in the environment, however, the potential neurotoxic effects of B[a]P has not been elucidated clearly. In the present study, we explored the potential involvement of p53 phosphorylation by Cdk5 in B[a]P-induced neuronal apoptosis at both in vitro and in vivo settings. For in vitro studies, primary cortical neurons isolated from the brains of Sprague Dawley (SD) rat pup were exposed to 0, 10, 20, and 40 μM of B[a]P for 12, 24, or 48 h. For in vivo studies, SD rats were injected intraperitoneally with 0, 1.0, 2.5, and 6.25 mg/kg of B[a]P every other day for 1, 2, or 3 months. Our results demonstrated that exposure to B[a]P caused a dose- and a time-dependent increase in neuronal apoptotic ratio in both in vitro and in vivo studies. There was also a dose- and a time-dependent upregulation of p35, p25, Cdk5, and phosphorylated p53 at Ser15 after B[a]P exposure. In order to explore whether B[a]P-induced increased neuronal apoptosis was through Cdk5/p53 pathway, roscovitine, a specific Cdk5 inhibitor, was applied to pretreat neurons prior to B[a]P exposure. The results showed that pretreatment of neurons with roscovitine partially rescued cells from B[a]P-induced apoptosis, and alleviated B[a]P-induced upregulation of phosphorylated p53 at Ser15. Our results suggest that Cdk5/p53 signaling pathway may be involved in B[a]P-induced neuronal apoptosis, which will provide information to further elucidate the molecular mechanisms of B[a]P-induced neurotoxicity.

Low Dose-Rate Irradiation of Gamma-Rays-Induced Cytotoxic and Genotoxic Alterations in Peripheral Erythrocytes of p53-Deficient Medaka (Oryzias latipes)

Morphological alterations and nuclear abnormalities in fish erythrocytes have been used in many studies as bioindicators of environmental mutagens including ionizing radiation. In this study, adult Japanese medaka (Oryzias latipes) were irradiated with gamma rays at a low dose rate (9.92 μGy/min) for 7 days, giving a total dose of 100 mGy; and morphological alterations, nuclear abnormalities, and apoptotic cell death induced in peripheral erythrocytes were investigated 8 h and 7 days after the end of the irradiation. A variety of abnormalities, such as tear-drop cell, crenated cell, acanthocyte, sickled cell, micronucleated cell, eccentric nucleus, notched nucleus, and schistocyte, were induced in the peripheral erythrocytes of the wild-type fish, and a less number of abnormalities and apoptotic cell death were induced in the p53-deficient fish. These results indicate that low dose-rate chronic irradiation of gamma rays can induce cytotoxic and genotoxic effects in the peripheral erythrocytes of medaka, and p53-deficient medaka are tolerant to the gamma-ray irradiation than the wild type on the surface.

γ-H2AX foci as indication for the DNA damage in erythrocytes of medaka (Oryzias latipes) intoxicated with 4-nonylphenol

The present study aimed to investigate the genotoxicity in erythrocytes induced after exposure of medaka (Oryzias latipes) to 4-nonylphenol (4-NP). Adult female medaka fish were exposed to 4-NP at three sublethal concentrations for 15 days to compare their sensitivity with that of catfish as an aquatic model. Comet assay and γ-H2AX were used as biomarkers to detect DNA damage in erythrocytes. Exposure to 4-NP resulted in an increase in the tail moment in a dose-dependent manner. The highest level of DNA damage was recorded after exposure to 100 μg/l 4-NP. The number of foci was increased after exposure to 4-NP, indicating damage to DNA. The present results confirmed the high level of morphological alterations and apoptosis of erythrocytes detected in the first part of this study. 4-NP induced genotoxic effects in medaka, which were found to be more sensitive than catfish after exposure to 4-nonylphenol. Graphical abstract.

Comparative histology of wild-type and p53-deficient medaka (Oryzias latipes): nephrotoxic effect of ultraviolet A radiation

Ultraviolet radiation is an ecological factor that directly affects terrestrial organisms through suppression of immunity or damage to internal organs. The present study assessed the effects of ultraviolet A (UVA) radiation on the kidneys of both wild-type (WT) and p53-deficient medaka (Oryzias latipes) and evaluated which strain was more resistant to the effects of UVA. Fish were divided into four groups: control group 1 (Cwt and Cp53), kept for 3 days without UVA exposure; group 2 (1wt and 1p53), fish exposed daily to UVA for 1 h day-1 for 3 days; group 3 (2wt and 2p53), fish exposed daily to UVA for 2 h day-1 for 3 days; and group 4 (3wt and 3p53), fish exposed daily to UVA for 3 h day-1 for 3 days. Samples of tissues were obtained 24 h after UVA exposure. The most obvious histopathological changes induced by UVA radiation in kidney tissues of both strains of medaka (WT and p53-deficient) were high levels of vacuolation of tubular cells followed by necrosis. The tubular segments lost their normal shape which appeared like a network structure and their cells with clear cytoplasm. Necrosis of lymphoid tissues and spots of brown pigmentation (possibly melanomacrophages) were sporadically seen in interstitial lymphoid tissues, while shrinkage of glomeruli, diminution of periodic acid-Schiff staining, and increased amount of collagenous fibers were observed. Our results confirmed the harmful effects of UVA radiation on kidney tissues of both WT and p53-deficient medaka. However, WT medaka was affected more than p53-deficient medaka.

Protective effect of p53 knockout on 4-nonylphenol-induced nephrotoxicity in medaka (Oryzias latipes)

In the past few decades, environmental pollutants have become common because of misused nonionic surfactants and detergents. Nonylphenol ethoxylates (NPs) are one of the most important contaminants of water. Therefore, the present study aimed to investigate the protective blocking effect of apoptosis (deficient P53 gene) on 4-nonylphenol (4-NP)-induced nephrotoxicity of medaka (Oryzias latipes). We divided 36 fish into six groups: two different control groups of wild type (Wt; Hd-rR) control and p53 (-/-) control, and four different treated with 4-nonylphenol (50 μg/L and 100 μg/L) for 15 days. Histology, immunochemistry, and TUNEL assays confirmed that 4-NP causes nephrotoxicity. Our results showed that 4-NP administration significantly disturbed the kidney structure and function and 4-NP-treated fish showed dilated glomerular vessels, had less glomerular cellular content, decreased expression of glomerular proteins, and an increased level of apoptosis compared with a Wt control group (P < 0.05). As p53 is an apoptotic inducer, some protection in p53-deficient medaka was found as nephrotoxic effects of 4-NP were minimized significantly. Our study demonstrated for the first time to our knowledge that 4-NP induces apoptosis, causing nephrotoxicity in medaka. We found that blocking apoptosis blocking was able to protect the kidney from the toxic effects of 4-NP.

Cytotoxic and hemotoxic effects of silver nanoparticles on the African Catfish, Clarias gariepinus (Burchell, 1822)

The present study investigates the hemotoxic and cytotoxic impacts of two acute doses of silver nanoparticles (AgNPs) on the African catfish, Clarias garepinus in comparison to the impact of AgNO₃ and the control fish. AgNPs-induced impacts were recorded on some biological and hematological indices of that species on the bases of their size (20 and 40 nm) and concentration (10 and 100 µg) but no significant interaction. AgNO₃ had very low impact on these indices in comparison to AgNPs. Recovery period for 15 days was found to be valid to remove AgNPs and AgNO₃ toxicity for most indices. The condition factor exhibited stability under stress whereas the hepatosomatic index was more sensitive to AgNPs. The AgNPs-induced hematological changes recorded were corresponding with different blood cell alterations which increased in frequency from the control and AgNO₃ to 40 nm/100 µg; such blood cell alterations disappeared to great extent after recovery period of 15-days in a reverse order.

SDS-PAGE technique as biomarker for fish toxicological studies

Although many studies on the hematological and biochemical parameters in fishes have been done, still there are some shortage in the estimation and evaluation of the baseline's values of marine and freshwater fishes. Recently, the use of hematology and biochemistry of fishes in toxicology, aquaculture, environmental pollution, feeding, and antioxidants studies has been increased. In this study we introduced the importance of those parameters and their importance as biomarkers in fish toxicology from previous literature and as new findings. Hemato-biochemical parameters were widely used in fish toxicological studies. Many researches have used the protein electrophoresis as a valid tool to determining intra and inter-specific variation among species. Protein profile was extensively used in determining the health of fish, as indicators of anemia or other diseases provide information about the existence of the disease, and in the diagnosis of disease. So, to carry out the aim of this study, we reported one of the more advanced techniques used SDS-PAGE as molecular biomarker for protein profile analysis in fish with shedding the light on the importance of hematological and biochemical parameters in fish toxicological studies.