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Diet is an important variable in toxicology. There are mixed reports on the impact of soy components on energy utilization, fat deposition, and reproductive parameters. Three generations of CD-1 mice were fed irradiated natural ingredient diets with varying levels of soy (NIH-41, 5K96, or 5008/5001), purified irradiated AIN-93 diet, or the AIN-93 formulation modified with ethanol-washed soy protein concentrate (SPC) or SPC with isoflavones (SPC-IF). NIH-41 was the control for pairwise comparisons. Minimal differences were observed among natural ingredient diet groups. F0 males fed AIN-93, SPC, and SPC-IF diets had elevated glucose levels and lower insulin levels compared with the NIH-41 group. In both sexes of the F1 and F2 generations, the SPC and SPC-IF groups had lower body weight gains than the NIH-41 controls and the AIN-93 group had an increased percent body fat at postnatal day 21. AIN-93 F1 pups had higher baseline glucose than NIH-41 controls, but diet did not significantly affect breeding performance or responses to glucose or uterotrophic challenges. Reduced testes weight and sperm in the AIN-93 group may be related to low thiamine levels. Our observations underline the importance of careful selection, manufacturing procedures, and nutritional characterization of diets used in toxicological studies., (Published by Elsevier Ltd.)

Consumption of soy infant formula represents a unique exposure scenario in which developing children ingest a mixture of endocrine-active isoflavones along with a substantial portion of daily nutrition. Genistein and daidzein were administered as glucoside conjugates to neonatal rhesus monkeys in a fortified commercial soy formula at 5, 35, and 70 days after birth. A single gavage dosing with 10 mg/kg bw genistein and 6 mg/kg bw daidzein was chosen to represent the upper range of typical daily consumption and to facilitate complete pharmacokinetic measurements for aglycone and total isoflavones and equol. Adult monkeys were also gavaged with the same formula solution at 2.8 and 1.6 mg/kg bw genistein and daidzein, respectively, and by IV injection with isoflavone aglycones (5.2 and 3.2 mg/kg bw, respectively) to determine absolute bioavailability. Significant differences in internal exposure were observed between neonatal and adult monkeys, with higher values for dose-adjusted AUC and Cmax of the active aglycone isoflavones in neonates. The magnitude and frequency of equol production by the gut microbiome were also significantly greater in adults. These findings are consistent with immaturity of metabolic and/or physiological systems in developing non-human primates that reduces total clearance of soy isoflavones from the body., (Published by Elsevier Ltd.)

Effects of the dosing matrix and timing on the onset of renal crystal formation were evaluated in male and non-pregnant female rats (Fisher 344) exposed to both melamine (MEL) and cyanuric acid (CYA) for 28 days. Rats were fed ground feed containing 60 ppm MEL and 60 ppm CYA, (5 mg/kg bw/day equivalent), or exposed via oral gavage to carboxymethylcellulose containing 5 mg/kg bw MEL followed by 5 mg/kg bw CYA either consecutively (<1 min apart) or delayed 45 min after MEL. Staggered gavage exposure to MEL/CYA caused extensive renal crystal formation as compared to when the two compounds were administered consecutively or in feed. Treatment related effects included reduced weight gain, feed consumption, and testicular weight and increased kidney weight, water consumption and urine output. Animals from the staggered MEL/CYA gavage exposure group became ill and were removed after 9 days of exposure. Approximately 1 week after the initiation of exposure microscopic urinalysis revealed MEL/CYA crystals in both groups of gavaged animals but not in the MEL/CYA feed treatment groups. Urinary crystals were smaller (10 μm) in animals consecutively gavaged. In contrast the urinary crystals were larger (20-40 μm) and frequently clumped in the animals in the staggered gavage group., (Published by Elsevier Ltd.)

Tricaine methanesulfonate, a sedative for temporarily immobilizing fish, has a 21-day withdrawal time. Benzocaine has been proposed as an alternative sedative because a withdrawal period may not be required. Since benzocaine is known to induce methemoglobinemia, the potential for orally administered benzocaine to induce methemoglobin was assessed in rats. Sprague-Dawley rats were given a single gavage administration of 64mg benzocaine hydrochloride per kg bw and then euthanized at intervals up to 120min. Plasma levels of benzocaine were relatively low at all times, whereas methemoglobin peaked at 24min. Additional rats were orally gavaged with 0-1024mg benzocaine hydrochloride per kg bw and euthanized after 24min. Plasma levels of benzocaine increased from 0.01μM at 2mg per kg bw to 2.9μM at 1024mg per kg bw. Methemoglobin levels did not differ from controls at doses up to 32mg per kg bw in females and 64mg per kg bw in males, whereupon the value increased to ∼80% at 1024mg per kg bw. These data were used to estimate the potential impact of benzocaine residues in fish and suggest that the consumption of fish treated with benzocaine hydrochloride will not cause methemoglobinemia in humans., (Published by Elsevier Ltd.)