Comparative metabolism and pharmacokinetics of diisobutyl ketone and diisobutyl carbinol in male SD rats.

Diisobutyl ketone (DIBK) and diisobutyl carbinol (DIBC) are important organic solvents widely used as industrial intermediates. It was hypothesized that DIBC and DIBK have common metabolic pathways and metabolites, and as such, toxicological data on DIBK could be used to characterize the hazards of DIBC. To confirm or refute this hypothesis a comparative metabolism and pharmacokinetics assessment of DIBK and DIBC was conducted. Dosing was via single oral gavage dosing in male SD rats, followed by blood collection, metabolite identification, major biomarker quantitation, and pharmacokinetics analysis. Overall, the major metabolites of both DIBC and DIBK in blood were their corresponding monohydroxylated metabolites (DIBC alcohol and DIBK alcohol) with the site of hydroxylation at the σ and σ-1 positions, respectively. Quantitative analysis of DIBC, DIBK, DIBC-alcohol, and DIBK-alcohol in blood samples collected from 5min to 120h after single dosing indicated the following: (1) DIBC and DIBK are both well absorbed following oral gavage with substantial evidence of enterohepatic recirculation of DIBK, DIBC, DIBK-alcohol, and DIBC-alcohol; (2) DIBK and DIBC are interconverted metabolically in rats; (3) DIBC and DIBK have similar bioavailability after oral administration; (4) higher systemic exposure was found for DIBK-alcohol than DIBC-alcohol, implying that DIBC-alcohol may be more easily conjugated and eliminated in bile. In summary, the metabolic similarities and the difference in systemic exposure to metabolites between these substances observed in the current study support the hypothesis that DIBC might have a lower potential toxicity than that of DIBK. The current study results support that toxicological data on DIBK could be used to characterize the hazards of DIBC.

Toxicokinetic profile of N-(2-aminoethyl)ethanolamine in the female Wistar rat and distribution into the late gestation fetus and milk.

N-(2-aminoethyl)ethanolamine (AEEA) caused aneurysms of the great vessels in rats exposed in utero and during the first days post partum, exacerbated by postnatal treatment of the lactating dams (Moore et al., 2012). The purpose of this work was to examine the systemic availability of AEEA during gestation and early lactation. The absorption of AEEA was determined following oral administration to nonpregnant and pregnant female Wistar rats. A single dose administered by gavage (0.5 or 50 mg/kg) on gestation day 18 was rapidly and extensively (>90%) absorbed from the gastrointestinal tract (absorption t(1/2) = 0.1-0.2 hr). Elimination from the plasma followed a biphasic pattern, with a rapid elimination phase (t(1/2 α) = 1.6-1.8 hr) followed by a slower phase (t(1/2 ß) = 16.7-17.3 hr). Following repeated gavage administration during gestation day 17 to 19, (14) C-AEEA-derived radioactivity readily partitioned into the fetus and was evenly distributed therein, but cleared approximately twofold slower from the fetal blood and tissues than the maternal blood and chorioallantoic placenta. When administered to lactating dams during lactation days 1 to 12, (14) C-AEEA-derived radioactivity preferentially partitioned into the milk reaching levels that were between 1.6- and 2.5-fold higher than the maternal blood. Although the concentration of AEEA equivalents in the maternal blood remained quite consistent, the concentration in the milk fell by almost 40% between lactation days 4 and 12, probably reflecting an increase in milk production over this same period. We confirm exposure of the offspring to AEEA both in utero and during lactation, but that AEEA does not appear to specifically concentrate in the great vessels.

Role of iodine in the toxicity of diiodomethyl-p-tolylsulfone (DIMPTS) in rats: ADME.

Metabolism of diiodomethyl-p-tolylsulfone (DIMPTS) was investigated in rats to determine the role of iodide in its toxicity. Fischer 344 (F-344) (5 or 50mg/kg) or Sprague Dawley (SD) (5mg/kg) rats were gavaged with (14)C-DIMPTS or dermally applied with 5mg/kg (F-344 only) and absorption, distribution, metabolism and excretion (ADME) determined. Additional experiments were conducted with its deiodinated analog (methyl-p-tolylsulfone, MPTS) in female F-344 rats (20mg/kg) for comparison. Orally administered (14)C-DIMPTS was rapidly absorbed and eliminated in urine (92%). The elimination t(½) was 1-4h. Dermally applied (14)C-DIMPTS remained undetectable in plasma with bioavailability ≈ 7%, only 5-7% of the dose was recovered in urine. DIMPTS liberated one or both of its iodine atoms upon absorption. The rate of elimination of the liberated iodide from the systemic circulation was 2- to 3-fold slower in SD than F-344 rats, which resulted in higher bioavailability of iodide to SD rats. DIMPTS was primarily oxidized at the benzylic methyl moiety forming the corresponding benzoic acid. Glutathione conjugation on the sulfonyl methyl group, via displacement of I(-) was also observed. Overall 67-80% of the total iodine atoms were metabolically released from DIMPTS. The MPTS was rapidly absorbed from the GI tract, metabolized and eliminated in urine similar to that of DIMPTS. These data were compared to iodide toxicokinetic results of a reproductive toxicity study for DIMPTS (80 mg/kg/day) and MPTS (32 mg/kg/day), where DIMPTS was toxic to dams and pups, while MPTS caused no toxicity. These data show that the liberated iodide is the ultimate toxicant of DIMPTS, which is readily transported to pups through milk, while the methyltolylsulfone backbone structure (MPTS) of DIMPTS is relatively nontoxic.

Development of a Web-based program to improve communication about sex.

Adolescent sexual risk behavior is a serious and prevalent problem among American youth. Mothers may play a key role in discussing sex and sexual risk behavior with their adolescent children. However, mothers may lack the knowledge and skills to successfully communicate. The purpose of this study was to develop a Web site to teach mothers how to communicate with their children about sex and to demonstrate the efficacy of this Web-based program. This pilot study included 35 rural, low-income mothers of middle-school adolescents. Mothers were randomly assigned to either the Web-based experimental group or written information-only control group. Mothers in the experimental group received computers and Internet access to the Web-based program, peer support, and expert advice from a pediatric nurse practitioner. Major findings of the study were that the Web-based intervention was equally effective at improving mothers' knowledge, communication skills, and self-efficacy as the written material control and that low-income rural women who have had little to no prior experience with computers can effectively learn Web-based health-related information. Future implications for nursing are discussed.

Mechanism of trifluralin-induced thyroid tumors in rats.

Trifluralin, an herbicide, has been reported to cause a significant increase in thyroid follicular cell tumors in male Fischer 344 rats. This study was designed to determine the mechanism of thyroid hyperactivity after trifluralin exposure. A group of 15 male Fischer 344 rats were exposed to trifluralin-fortified (6500 ppm) diet for 2 weeks. The time weighted average daily intake of trifluralin was 441+/-77 mg/kg/day. Ten rats of the group were sacrificed and the sera analyzed for T3, T4, and TSH levels. The livers were also analyzed for selected T4-specific UGT gene expression and total UGT enzyme activity. In the trifluralin treated rats, the serum T3 and T4 levels decreased by 17% and 90%, respectively and TSH increased by 37% more than the control rats. Trifluralin-induced total hepatic UGT enzymes (2.4-fold) and mRNA expression of selected hepatic UGT isozymes (UGT1A1, 1.4-fold; UGT1A6, 6.4-fold; UGT2B1, 3.7-fold). For the remaining 5 rats in the group, bile was collected for 2 h and analyzed for free and conjugated T3 and T4. The total amount of T4 in bile more than doubled in trifluralin treated rats. Trifluralin treatment increased bile flow, caused a 3.2-fold increase in biliary elimination of conjugated T4 and 63% increase in conjugated T3. Based on these data, the decrease in total serum T3 and T4 levels in the trifluralin treated rats was due to enhanced peripheral metabolism and an increase in bile flow that results in a compensatory increase in TSH synthesis and secretion. The increased levels of TSH with chronic exposure to trifluralin would exert a continuous stimulation of the thyroid gland leading to cellular hypertrophy and proliferation predisposing to the development of follicular cell tumors in rats.

Pharmacokinetics of aminomethylpropanol in rats following oral and a novel dermal study design.

This study determined the oral and dermal ADME of 2-amino-2-methyl-1-propanol (AMP), a substituted aliphatic alcohol used in a number of industrial and consumer products. Groups of 4 male Fischer 344 rats received either a single bolus oral or dermal dose of 18 mg/kg (14)C-AMP in water. The dermal dose was applied to an area of 12 cm(2) on the back of the rats for 6h under semi-occluded conditions and fitted with rodent jackets to prevent grooming. Time-course blood and excreta were collected, radioactivity determined and blood and urine analyzed for AMP and metabolites. The orally administered (14)C-AMP was rapidly absorbed and eliminated in urine. Elimination of radioactivity from blood was biphasic with a rapid alpha phase (t(1/2 alpha) approximately 1h) followed by a slower beta phase (t(1/2 beta)=41+/-4h plasma and 69+/-34 h RBC). Total urinary elimination accounted for 87-93% of the dose, most (72-77%) within the first 48 h. Fecal elimination accounted for only 3-10%. Only 3-4% of the dose was found in tissues 168h post-dosing. The total dermal absorption of (14)C-AMP was 42% that included approximately 8% of the dose remaining at the application site 162 h after washing. Less than 1% of the applied dose remained in the stratum corneum and approximately 6% of the dose was found in tissues. Urinary elimination was 43% of the administered dose, most ( approximately 17%) within 48 h, and approximately 2% was eliminated in feces. It took much longer to reach plasma C(max) after dermal application (8.5+/-4.7 h in plasma and 4.0+/-2.8h in RBC) than the oral dose (0.3h) and the AUC(0-->alpha) for dermal dose was approximately 8-fold lower than with the oral dose. Again, elimination of the radioactivity from blood was biphasic with apparent t(1/2 alpha) of 9+/-6 and 2+/-1h for plasma and RBC, respectively. However, the alpha phase was "flipped-flopped" due to relatively slow dermal penetration and rapid elimination of the systemically absorbed dose, which was corrected to approximately 0.3 h after separating alpha elimination phase from the absorption. The slope of the beta phase became parallel to the oral route upon cessation of the absorption from the dose site skin, between 18 and 42 h post-washing. No metabolite of AMP was detected either in blood or excreta of any rat. Results of this study suggests that toxicologically significant concentrations of AMP are unlikely to be achieved in the systemic circulation and/or target tissues in humans as a result of dermal application of products containing AMP. Additionally, systemically absorbed dose will be rapidly eliminated from the body with little remaining at the application site.

Quantitation of 8-hydroxydeoxyguanosine in DNA by liquid chromatography/positive atmospheric pressure photoionization tandem mass spectrometry.

A methodology has been developed and validated for quantifying 8-hydroxydeoxyguanosine (8-OHdG) in both commercial DNA and DNA isolated from livers of male Sprague-Dawley rats by liquid chromatography/positive atmospheric pressure photoionization tandem mass spectrometry. The analytical method conditions, including conditions for stabilizing 8-OHdG during complex nuclease P1 enzymatic digestion, were also evaluated. The limit of detection for 8-OHdG was 1.0 ng/mL (17.6 fmol on-column), and the linearity of the calibration curve was greater than 0.998 from 1.0 to 500 ng/mL. The intraday assay precision relative standard deviation (RSD) value for quality control (QC) samples was < or =5.59% with accuracies ranging from 91.84 to 117.61%. The interday assay precision (RSD) value was < or =1.76% with accuracies ranging from 91.84 to 116.67%. This method, combined with the LC/UV analysis of deoxyguanosine (dG), was used for determination of the levels of 8-OHdG/10(6) dG in DNA nuclease P1 enzymatic hydrolysates from both commercial DNA and rat liver DNA.

Effect of organic carbon content, clay type, and aging on the oral bioavailability of hexachlorobenzene in rats.

Bioavailability of lipophilic chemicals is influenced by the physicochemical properties of soils/sediment such as particle size, pH, clay, and organic carbon content. The present study investigated the effects of sediment composition and aging on the oral bioavailability of hexachlorobenzene (HCB) in rats. Formulated sediments were prepared using various ratios of kaolinite and montmorillonite clay, sand, peat moss, and black carbon, spiked with (14)C-HCB, and orally administered to rats prior to and after one year of aging in dark at 10 degrees C. In the nonaged sediments there was a 21 to 45% reduction in the oral bioavailability of HCB when compared to the corn oil standard without any clear pattern of the impact of the sediment clay and/or organic carbon content. One year of aging resulted in statistically significant (p = 0.049) reduction in the oral bioavailability of HCB from the sediments compared to the corn oil standard and nonaged sediment indicating stronger interactions between HCB and sediment contents with aging. The mean reduction in oral bioavailability after one year of aging ranged from approximately 5 to 14% greater than that observed for nonaged sediments. The fecal elimination of the HCB-derived radioactivity from the one-year-aged sediments was much higher than the nonaged sediments, consistent with the lower absorption from the gastrointestinal tract due to lower desorption of HCB from the aged sediments. Increase in the fecal elimination and decrease in oral bioavailability of (14)C-HCB was related to the increase in clay and black carbon.

X-linked creatine transporter (SLC6A8) mutations in about 1% of males with mental retardation of unknown etiology.

Mutations in the creatine transporter gene, SLC6A8 (MIM 30036), located in Xq28, have been found in families with X-linked mental retardation (XLMR) as well as in males with idiopathic mental retardation (MR). In order to estimate the frequency of such mutations in the MR population, a screening of 478 males with MR of unknown cause was undertaken. All 13 exons of SLC6A8 were sequenced using genomic DNA. Six novel potentially pathogenic mutations were identified that were not encountered in at least 588 male control chromosomes: two deletions (p.Asn336del, p.Ile347del) and a splice site alteration (c.1016+2C>T) are considered pathogenic based on the nature of the variant. A mutation (p.Arg391Trp) should be considered pathogenic owing to its localization in a highly conserved region. Two other missense variants (p.Lys4Arg, p.Gly26Arg) are not conserved but were not observed in over 300 male control chromosomes. Their pathogenicity is uncertain. A missense variant (p.Val182Met), was classified as a polymorphism based on a normal creatine/creatinine (Cr:Crn) ratio and cerebral creatine signal in proton magnetic resonance spectroscopy (H-MRS) in the patient. Furthermore, we found 14 novel intronic and neutral variants that were not encountered in at least 280 male control chromosomes and should be considered as unclassified variants. Our findings of a minimum of four pathogenic mutations and two potentially pathogenic mutations indicate that about 1% of males with MR of unknown etiology might have a SLC6A8 mutation. Thus, DNA sequence analysis and/or a Cr:Crn urine screen is warranted in any male with MR of unknown cause.