Developmental toxicity study of sodium molybdate dihydrate administered in the diet to Sprague Dawley rats

Molybdenum - a scoping review for Nordic Nutrition Recommendations 2023

Molybdenum is an essential element in the form of the molybdenum cofactor (Moco). In humans, Moco is required for four enzymes: xanthine oxidase (XO), aldehyde oxidase, sulfite oxidase (SO), and mitochondrial amidoxime-reducing component (mARC). The enzymes are involved in the oxidation of purines to uric acid, metabolism of aromatic aldehydes and heterocyclic compounds, and in the catabolism of sulfur amino acids. Molybdenum cofactor deficiency is a rare autosomal recessive syndrome due to a defective synthesis of Moco, resulting in a deficiency of all the molybdoenzymes. There are no reports on clinical signs of dietary molybdenum deficiency in otherwise healthy humans. Water-soluble molybdate is efficiently absorbed from the digestive tract. The body retention is regulated by urinary excretion. Plasma molybdenum reflects long-term intake and 24-h urinary excretion is related to recent intake. There are no biochemical markers of molybdenum status. Cereal products are the main contributors to molybdenum dietary intake, estimated to 100-170 μg/day in Nordic studies. Little data are available on molybdenum toxicity in humans. A tolerable upper intake level of molybdenum has been based on reproductive toxicity in rats, but the effects have not been reproduced in more recent studies. The U.S. Institute of Medicine (IOM, present National Academy of Sciences, Engineering, and Medicine; NASEM) established a Recommended Dietary Allowance of 45 μg/day in adult men and women in 2001, based on a small study reporting urinary excretion in balance with intake at 22 μg/day. The European Food Safety Authority (EFSA) considered in 2013 the evidence to be insufficient to derive an Average Requirement and a Population Reference Intake, but proposed an Adequate Intake of 65 μg/day for adults.

OECD 414 supplementary prenatal developmental toxicity study of sodium molybdate dihydrate in the rat and benchmark dose evaluation

In a continuing investigation of the potential for reproductive and developmental toxicity of molybdenum (Mo), consequent to the previous published OECD studies [1,2] and as directed by the European Chemicals Agency [3], a supplemental rat GLP-compliant Prenatal Developmental Toxicity (PNDT) study was conducted to investigate higher dose levels of sodium molybdate dihydrate (SMD) in an identical study design (OECD 414)[4] to Murray et al. 2014a [1], at dietary concentrations calculated to provide target Mo levels of 80 and 120 mg/kg bw/day (the maximum-tolerated dose). There was no effect on post-implantation loss, litter size, sex ratio or the incidence of external, visceral or skeletal fetal malformations or variations. Fetal weight was reduced proportionate to maternal dose. Minimal differences observed in the ossification status of some extremities of fetuses from females receiving 120 mg Mo/kg bw/day were confirmed as transient by skeletal examination of PND 21 pups from a further group of females receiving the same dose regime. There was no evidence of copper depletion in serum, placenta or liver. A benchmark dose evaluation using continuous and dichotomous approaches by combining the fetal body weight data from this study and the previous study determined that the BMD05 ranged from 47 to 57 mg Mo/kg bw/day, depending on the modelling approach and the BMDL05 estimates ranged from 37 to 47 mg Mo/kg bw/day. These levels are considered a more statistically robust point of departure for risk assessment for reproductive effects than the established NOAEL of 40 mg Mo/kg bw/day.

Sodium molybdate dihydrate does not exhibit developmental or reproductive toxicity in Sprague-Dawley rats maintained on a marginal copper diet

Groups of 24 weanling female Sprague-Dawley rats were administered molybdenum (Mo) as sodium molybdate dihydrate (SMD) in drinking water at target dose levels of 0, 20, or 40 mg Mo/kg bw/day and fed a semi-purified marginal copper (6.2 ppm Cu) AIN-93 G diet for 8 weeks prior to mating, through cohabitation and pregnancy until Gestation Day 21. The objective was to confirm the reproductive and developmental effects of SMD reported by Fungwe et al. (1990) at estimated doses as low as 1.5 mg Mo/kg bw/day in a similarly designed study with marginal Cu diet (6.3 ppm). There were no test material-related effects at 20 or 40 mg Mo/kg bw/day on mortality, clinical observations, body weight, body weight gain, food consumption, estrous cycling, reproductive performance, maternal macroscopic pathology, ovarian or uterine parameters, litter size, resorptions, fetal sex ratio, fetal weight, or external fetal malformations or variations. Water consumption was increased compared to controls at both dose levels during the pre-mating and gestation periods, with no apparent adverse impact. There was no evidence of copper depletion in serum at any dose level. In conclusion, the no-observed-adverse-effect levels (NOAELs) for systemic, maternal reproductive, and developmental toxicity in this marginal Cu diet study are 40 mg Mo/kg bw/day, consistent with the results of guideline developmental and reproductive toxicity studies of SMD. The results of Fungwe et al. were not replicated, even at higher dose levels of Mo, and their inconsistencies with guideline toxicity studies of Mo are not explained by the marginal dietary Cu level.

Crosstalk between Mfn2-mediated mitochondria associated membranes disorder and autophagy induced by molybdenum and cadmium in sheep heart

To investigate the crosstalk of mitochondria associated membranes (MAMs) disorder and autophagy co-induced by molybdenum (Mo) and cadmium (Cd) in sheep hearts. A total of 48 sheep were randomly divided into 4 groups: control group, Mo group, Cd group and Mo + Cd group. The intragastric administration lasted for 50 days. The results showed that Mo or/and Cd exposure could cause morphological damage, imbalance of trace elements and antioxidant function, Ca²⁺ concentration decreased markedly, and significantly increase the contents of Mo or/and Cd in myocardium. Additionally, the mRNA and protein levels of endoplasmic reticulum stress (ERS) related factors and mitochondrial biogenesis related factors were altered by Mo or/and Cd, as well as the content of ATP, inducing ERS and mitochondrial dysfunction. Meanwhile, Mo or/and Cd could lead to the alteration of expression level of MAMs-related genes and proteins, and the distance between mitochondria and endoplasmic reticulum (ER), resulting in MAMs disorder. Moreover, Mo or/and Cd exposure upregulated the mRNA and protein levels of autophagy related factors. In conclusion, our results revealed that Mo or/and Cd exposure caused ERS, mitochondrial dysfunction and structural MAMs disruption, ultimately leading to autophagy in sheep hearts, and the effects of Mo and Cd co-exposure were more obvious.

Terrestrial ecological risk analysis via dietary exposure at uranium mine sites in the Grand Canyon watershed (Arizona, USA)

The U.S. Department of the Interior recently included uranium (U) on a list of mineral commodities that are considered critical to economic and national security. The uses of U for commercial and residential energy production, defense applications, medical device technologies, and energy generation for space vehicles and satellites are known, but the environmental impacts of uranium extraction are not always well quantified. We conducted a screening-level ecological risk analysis based on exposure to mining-related elements via diets and incidental soil ingestion for terrestrial biota to provide context to chemical characterization and exposures at breccia pipe U mines in northern Arizona. Relative risks, calculated as hazard quotients (HQs), were generally low for all biological receptor models. Our models screened for risk to omnivores and insectivores (HQs>1) but not herbivores and carnivores. Uranium was not the driver of ecological risk; arsenic, cadmium, copper, and zinc were of concern for biota consuming ground-dwelling invertebrates. Invertebrate species composition should be considered when applying these models to other mining locations or future sampling at the breccia pipe mine sites. Dietary concentration thresholds (DCTs) were also calculated to understand food concentrations that may lead to ecological risk. The DCTs indicated that critical concentrations were not approached in our model scenarios, as evident in the very low HQs for most models. The DCTs may be used by natural resource and land managers as well as mine operators to screen or monitor for potential risk to terrestrial receptors as mine sites are developed and remediated in the future.

Molybdenum Induces Mitochondrial Oxidative Damage in Kidney of Goats

The purpose of this study was to evaluate the effects of excessive molybdenum (Mo) on renal function and oxidative stress in goats. Twenty-seven healthy goats were randomly allotted in three groups and were fed deionized water to which sodium molybdate [(NH₄)₆Mo₇O₂₄·4H₂O] was added at different doses of 0, 15, and 45 mg Mo/(kg·BW) for 50 days, respectively. The results indicated that white blood cell (WBC) counts were significantly increased (P < 0.05), while red blood cell (RBC) counts, hemoglobin (HGB), and mean corpuscular hemoglobin concentration (MCH) were tended to decrease with the increasing of the experimental period in high-Mo group compared with the control group. Besides, blood urea nitrogen (BUN) and creatinine (CREA) contents in serum were increased (P < 0.05) in both groups supplemented with molybdenum. Meanwhile, contents of copper (Cu) from the both experimental groups were significantly decreased (P < 0.05), while contents of zinc (Zn) and iron (Fe) were increased (P < 0.05) in serum. The contents of Cu were significantly increased (P < 0.05), while the contents of zinc (Zn) and iron (Fe) did not obviously change (P > 0.05) in the kidney. In addition, the activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT) significantly decreased (P < 0.05) in the mitochondria, whereas malondialdehyde (MDA) and nitric oxide synthase (NOS) expression significantly increased (P < 0.05). Collectively, these results indicated that excess Mo exposure could induce secondary Cu deficiency and oxidative stress in the kidney, which finally undermine the renal function of goats.

Biomonitoring Equivalents for molybdenum

Molybdenum is an essential trace element for mammalian, plant, and other animal systems. The Institute of Medicine (IOM) has established an Estimated Average Requirement (EAR) to assure sufficient molybdenum intakes for human populations; however excessive exposures can cause toxicity. As a result, several agencies have established exposure guidance values to protect against molybdenum toxicity, including a Reference Dose (RfD), Tolerable Daily Intake (TDI) and a Tolerable Upper Intake Level (UL). Biomonitoring for molybdenum in blood or urine in the general population is being conducted by the Canadian Health Measures Survey (CHMS) and the U.S. National Health and Nutrition Examination Survey (NHANES). Using pharmacokinetic data from controlled human dosing studies, Biomonitoring Equivalents (BEs) were calculated for molybdenum in plasma, whole blood, and urine associated with exposure guidance values set to protect against both nutritional deficits and toxicity. The BEEAR values in plasma, whole blood and urine are 0.5, 0.45 and 22 μg/L, respectively. The BEs associated with toxicity range from 0.9 to 31 μg/L in plasma, 0.8-28 μg/L in whole blood and 200-7500 μg/L in urine. These values can be used to interpret molybdenum biomonitoring data from a nutritional and toxicity perspective.