In vivo genotoxicity of nitrates and nitrites in germ cells of male mice. I. Evidence for gonadal exposure and lack of heritable effects

Assessment of sodium nitrate (NaNO3) effects on the reproductive system, liver, pancreas and kidney of male rats

Nitrate (NO₃) toxicity is a serious global issue that results in impairment of physiological systems of our body. The present study aimed to investigate the effects of different concentration of NaNO₃ (10, 100, 500 and 1000 mg/kg bw) on the male reproductive system, liver, kidney and pancreas. Adult male Wistar rats were divided into five groups of five animals each (n = 5). The first group served as controls. The second, third, fourth and fifth groups of rat were orally intubated with 10, 100, 500 and 1000 mg/kg bw of NaNO₃ for 52 days. After the treatment period, the rats were sacrificed and NO₃ induced alterations on selected organs were assessed. There was a dose dependent decrease in sperm motility, serum concentration of testosterone, body weight and organ weight, and increase in abnormal sperm morphology in the NaNO₃ treated groups compared with the controls. Further, histological analysis confirmed that NO₃ induced toxicity. Shrunken seminiferous tubules and loss of spermatids in testes, shrinkage of acinar cells of the pancreas, sinusoidal congestion and necrosis in the liver, atrophy of glomeruli and congestion of renal tubules of the kidney were the histological alterations observed in rats treated with100 and 500 mg/kg NaNO₃. However, 100% mortality was observed in rats treated with 1000 mg/kg NaNO₃. The present study clearly demonstrated the toxic effects of NaNO₃ on both the reproductive system and other organs of the body. The study might inform human studies; where in the chances of male infertility may be more a problem for individuals in areas with NO₃-rich ground water.

The effect of prolonged dietary sodium nitrate treatment on the hypothalamus-pituitary-gonadal axis and testicular structure and function in streptozotocin-induced diabetic male rats

The aim of this study was to evaluate the effect of prolonged dietary nitrate supplementation on the gonadotropin level, testicular histology and morphometry, expression of miR-34b and p53 mRNA, and spermatogenesis in streptozotocin-induced diabetic male rats.

METHODS

Fifty male Wistar rats were divided into 5 groups: Control (C), control + nitrate (CN), diabetes (D), diabetes + insulin (DI), and diabetes + nitrate (DN). Diabetes was induced using 45 mg kg^-1 of streptozotocin intraperitoneally. Rats in the CN and DN groups were administered sodium nitrate in drinking water (100 mg L^-1). NPH insulin (2-4 U d^-1) was injected subcutaneously in the DI group for 2 months. Nitrate and insulin supplementation was started one month after confirmation of diabetes.

RESULTS

Nitrate supplementation in the DN group significantly increased the body weight (p < 0.05), sperm parameters (p < 0.001), indices of spermatogenesis (p < 0.001), and testis histopathology as well as decreased the blood glucose level (p < 0.001) compared to the untreated diabetic group, although it had no significant effect on testicular parameters, LH and FSH levels. Nitrate administration in the DN group also decreased miR-34b (p < 0.001) and p53 mRNA (p < 0.001) expression, and increased serum insulin and NOx levels compared to the untreated diabetic rats.

CONCLUSIONS

Chronic nitrate supplementation in streptozotocin-induced diabetic rats improved fertility parameters, which may be associated with increased miR-34b and decreased p53 mRNA.

Sodium nitrite negatively affects reproductive ability and offspring survival in female mice

Sodium nitrite (NaNO₂) is an industrial chemical that is frequently used as a food additive to prevent botulism and enhance glossiness, such as curing meat. In addition, in some regions, water source NaNO₂ concentrations exceed standard regulatory levels. Whether the excessive intake of NaNO₂ has toxic effects on female fertility and fetal development remain unknown. In this study, we administered ICR mice control saline, low-dose NaNO₂ (60 mg/kg/day), or high-dose NaNO₂ (120 mg/kg/day) by intragastric gavage for 21 days. We then assessed oocyte morphology, spindle-chromosome dynamics, mitochondrial distribution, ATP content, apoptotic cell numbers, DNA damage levels, histone modifications, reactive oxygen species (ROS) levels, and offspring survival. Results showed that NaNO₂ treatment decreased oocyte number, impaired polar body extrusion, and increased zona pellucida thickness in oocytes. Furthermore, NaNO₂ disrupted MII spindle integrity, caused abnormal mitochondrial distribution, decreased ATP content, and increased levels of ROS and H3K4me2. Moreover, the number of oocytes in early stages of apoptosis and with levels of DNA damage increased in NaNO₂-treated mice along with decreased offspring numbers and survival rates. We demonstrated the negative effects of NaNO₂ on female reproductive abilities in mice.

Re-evaluation of potassium nitrite (E 249) and sodium nitrite (E 250) as food additives

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re‐evaluating the safety of potassium nitrite (E 249) and sodium nitrite (E 250) when used as food additives. The ADIs established by the SCF (1997) and by JECFA (2002) for nitrite were 0–0.06 and 0–0.07 mg/kg bw per day, respectively. The available information did not indicate in vivo genotoxic potential for sodium and potassium nitrite. Overall, an ADI for nitrite per se could be derived from the available repeated dose toxicity studies in animals, also considering the negative carcinogenicity results. The Panel concluded that an increased methaemoglobin level, observed in human and animals, was a relevant effect for the derivation of the ADI. The Panel, using a BMD approach, derived an ADI of 0.07 mg nitrite ion/kg bw per day. The exposure to nitrite resulting from its use as food additive did not exceed this ADI for the general population, except for a slight exceedance in children at the highest percentile. The Panel assessed the endogenous formation of nitrosamines from nitrites based on the theoretical calculation of the NDMA produced upon ingestion of nitrites at the ADI and estimated a MoE > 10,000. The Panel estimated the MoE to exogenous nitrosamines in meat products to be < 10,000 in all age groups at high level exposure. Based on the results of a systematic review, it was not possible to clearly discern nitrosamines produced from the nitrite added at the authorised levels, from those found in the food matrix without addition of external nitrite. In epidemiological studies there was some evidence to link (i) dietary nitrite and gastric cancers and (ii) the combination of nitrite plus nitrate from processed meat and colorectal cancers. There was evidence to link preformed NDMA and colorectal cancers.

Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re-evaluating the safety of sodium nitrate (E 251) and potassium nitrate (E 252) when used as food additives. The current acceptable daily intakes (ADIs) for nitrate of 3.7 mg/kg body weight (bw) per day were established by the SCF (1997) and JECFA (2002). The available data did not indicate genotoxic potential for sodium and potassium nitrate. The carcinogenicity studies in mice and rats were negative. The Panel considered the derivation of an ADI for nitrate based on the formation of methaemoglobin, following the conversion of nitrate, excreted in the saliva, to nitrite. However, there were large variations in the data on the nitrate-to-nitrite conversion in the saliva in humans. Therefore, the Panel considered that it was not possible to derive a single value of the ADI from the available data. The Panel noticed that even using the highest nitrate-to-nitrite conversion factor the methaemoglobin levels produced due to nitrite obtained from this conversion would not be clinically significant and would result to a theoretically estimated endogenous N-nitroso compounds (ENOC) production at levels which would be of low concern. Hence, and despite the uncertainty associated with the ADI established by the SCF, the Panel concluded that currently there was insufficient evidence to withdraw this ADI. The exposure to nitrate solely from its use as a food additive was estimated to be less than 5% of the overall exposure to nitrate in food based on a refined estimated exposure scenario. This exposure did not exceed the current ADI (SCF, 1997). However, if all sources of exposure to dietary nitrate are considered (food additive, natural presence and contamination), the ADI would be exceeded for all age groups at the mean and the highest exposure.

Detection of Effects on Male Reproduction—A Literature Survey

The 1CH (International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use) Guideline for Detection of Toxicity to Reproduction for Medicinal Products, adopted at the Second ICH Conference in Orlando, FL, U.S.A., emphasized the need for research into the suitability of various methods for the detection of effects on fertility in males. The current project was undertaken to compare the efficiency of methods by evaluating reports in the open literature. The results of the examination of 117 substances or substance classes support the view that histopathology and organ weight analysis provide the best general-purpose means of detecting substances with the potential to affect male fertility. Examinations at up to 4 weeks of treatment appear to be as effective as examinations conducted at later times. Mating with females for detection of effects unrelated to interference with sperm production appears to provide an optimal combination because adding other methodologies does not materially improve the detection rate. As to the timing of the mating trial, a 2-week premating period is as efficient as mating at 4 weeks and apparently more efficient than mating after prolonged premating treatment.

Toxicogenomic evaluation of chemically induced chromosomal imbalance using DNA image analysis

The study of carcinogenic potential of a variety of chemical agents such as food additives and drugs of abuse via the application of various in vitro methodologies constitutes the first step for the evaluation of their toxicogenomic profile. Considering the chromosomal theories of carcinogenesis, where it is stated that aneuploidy and chromosomal imbalance (instability) are among the main causes of carcinogenesis, chemicals capable to induce such changes in the cells could be considered as potential carcinogens. Chromosomal imbalance and aneuploidy directly affect the overall DNA content of the exposed cell as well as other cellular morpho- and densitometric features. These features can be measured by means of computerized DNA image analysis technologies and include DNA content (DNA Index), Proliferation Index, Ploidy Balance, Degree of Aneuploidy, Skewness and Kurtosis. Considering the enormous number of untested chemicals and drugs of abuse that follow non-genotoxic mechanisms of carcinogenesis, the establishment of a reliable technology for the estimation of chemically induced chromosomal imbalance is of particular importance in toxicogenomic studies. In the present article and based on our previously published work, we highlight the advantages of the applications of DNA image analysis technology in an easy-to-use experimental model for the evaluation of the potential risk of various chemicals. The use of this technology for the detection of chemically induced chromosomal instability will contribute to the development of safer regulatory directives concerning the use of chemicals in food and pharmaceutical industry, as well as in the clarification of mechanisms of action of drugs of abuse.

Analysis of clastogenic effect of Porto Alegre drinking water supplies on mouse bone marrow cells

Studies were conducted to evaluate the clastogenic activity of drinking water from Porto Alegre and Guaíba (Rio Grande do Sul, Brazil) estuarine waters. Mouse bone marrow was the target organ. C57B1/6 male and female mice received the water samples as their only liquid supply. Bone marrow cells were collected on the 16th day after the beginning of treatment. The analysis of metaphases demonstrated that the water supplies did not increase the structural chromosome aberration frequencies compared to the control groups. Concerning numerical alterations, only one treated female group showed a significant difference (loss of one chromosome) when compared to the control group, but this result is not considered relevant.