Metabolism and disposition of a beta 3-adrenergic receptor agonist LY 368842 in male Fisher 344 rats.

The metabolism and disposition of LY 368842, a beta 3-adrenergic receptor agonist, were characterized in F344 rats following oral or intravenous administration of [(14)C]LY 368842. These studies were conducted as part of the investigation of the mechanism of dark liver pigmentation in LY 368842-treated F344 rats. The maximum plasma concentration of LY 368842 was reached at 3 h after an oral dose, with an elimination half-life of 4 h. The oral bioavailability of LY 368842 was determined as 8%. A tissue distribution study by quantitative whole-body autoradiography indicated high concentrations of radiocarbon in gastrointestinal contents and moderate concentrations in liver. The radiocarbon was rapidly eliminated in rats, with approximately 3% of the dose recovered in urine and 90% in faeces over 168 h. In bile duct-cannulated rats, about 42% of the dose was recovered in bile and 41% remained in the faeces. Metabolites of LY 368842 were identified in rat urine, faeces, bile and plasma samples. Oxidative metabolism of LY 368842 led to the formation of a hydroxy metabolite, an indole-2,3-dione metabolite and oxidative cleavage products such as amine and diol metabolites. Several glucuronide conjugates were also identified in rat bile. These data suggest that LY 368842 is not completely absorbed but is widely distributed, extensively metabolized and rapidly eliminated in rats after oral administration.

Clinical applications of composite intramembranous bone grafts.

The aim of this article is to introduce the composite intramembranous bone graft mixed with demineralized bone matrix to the clinician and to demonstrate its various clinical applications in the field of clinical orthodontics in the form of case reports. Understanding the mechanism of healing of this composite bone graft provides sound experimental precedent that allows this graft material to become a predictable part of our future orthodontic management. The cases highlighted here took advantage of the several properties of the composite intramembranous demineralized bone matrix graft. An accidental loss of the buccal plate of bone occurred during extraction of a buccally placed premolar for orthodontic purposes. The defect was repaired using chin bone mixed with demineralized bone matrix, and the teeth were successfully moved into the grafted area. A 5-year follow-up showed a stable gingival condition at the grafted area. In this report, ridge augmentation with intramembranous demineralized bone matrix as an adjunct to orthodontic treatment allowed successful placement of endosseous implants. In conclusion, the same graft material was successfully used in the repair of a massive alveolar cleft. Long-term follow-up of these cases showed that this graft is a promising graft material that could be integrated into our orthodontic practice.

Metabolism and disposition of moxonidine in Fischer 344 rats.

The metabolism and disposition of moxonidine (4-chloro-5-(imidazolidin-2-ylidenimino)-6-methoxy-2-methylp yrimidine ), a potent central-acting antihypertensive agent, were investigated in F344 rats. After an i.v. or oral administration of 0.3 mg/kg of [(14)C]moxonidine, the maximum plasma concentrations of moxonidine were determined to be 146.0 and 4.0 ng/ml, respectively, and the elimination half-lives were 0.9 and 1.1 h, respectively. The oral bioavailability of moxonidine was determined to be 5.1%. The metabolic and elimination profiles of moxonidine were determined after an oral administration of 5 mg/kg of [(14)C]moxonidine. More than fifteen phase I and phase II metabolites of moxonidine were identified in the different biological matrices (urine, plasma, and bile). Oxidative metabolism of moxonidine leads to the formation of hydroxymethyl moxonidine and a carboxylic acid metabolite as the major metabolites. Several GSH conjugates, cysteinylglycine conjugates, cysteine conjugates, and a glucuronide conjugate were also identified in rat bile samples. The radiocarbon was eliminated primarily by urinary excretion in rats, with 59.5% of total radioactivity recovered in the urine and 38.4% recovered in the feces within 120 h. In bile duct-cannulated rats, about 39.7% of the radiolabeled dose was excreted in the urine, 32.6% excreted in the bile, and approximately 2% remained in the feces. The results from a quantitative whole body autoradiography study indicate that radiocarbon associated with [(14)C]moxonidine and/or its metabolites was widely distributed to tissues, with the highest levels of radioactivity observed in the kidney and liver. In summary, moxonidine is well absorbed, extensively metabolized, widely distributed into tissues, and rapidly eliminated in rats after oral administration.

Healing of autogenous intramembranous bone in the presence and absence of homologous demineralized intramembranous bone.

This study was designed to examine the osteogenecity of demineralized bone matrix (DBM) prepared from intramembranous (IM) bone and to quantitatively assess the amount of new bone formed by IM autogenous bone grafts with or without DBM(IM). Forty-two defects were created in 42 New Zealand White rabbits. Twenty-one defects were grafted with IM bone alone, and the other 21 defects were grafted with composite IM-DBM(IM). Eleven rabbits, 22 defects were used as controls, where 11 defects were left empty (passive control) and the other 11 defects were filled with rabbit skin collagen (active control). Tissues were retrieved on days 1, 2, 3, 4, 5, 6, 7, and 14 for qualitative and quantitative analysis. Cells involved in the healing of composite IM and IM-DBM(IM) bone grafts were identified. No cartilage cells were detected during the healing of either grafts. Appearance of small blood vessels into the newly formed matrix was seen on day 5 in IM bone grafts and on day 4 in composite IM-DBM(IM) bone graft. Quantitative analysis was performed by means of image analysis on 100 sections of tissues retrieved after 14 days. Approximately 204% more new bone was formed in defects grafted with composite IM-DBM(IM) than in those grafted with IM bone alone (P <.0001). No bone was formed across the defects in either active or passive controls. In conclusion, DBM(IM) significantly increases the osteogenicity of IM bone grafts.

Spaced dentition--open, close or redistribute?

A spaced dentition can be due to various reasons such as hypodontia, tooth size discrepancy and impeded eruption. The dilemma for clinicians is whether to close, open or redistribute space. Closing space by orthodontics eliminates the need for prosthetic rehabilitation but it might compromise aesthetics and function. On the other hand, opening space is more complex and requires long-term maintenance. Based on these drawbacks, a careful occlusal analysis and an individualized treatment plan are mandatory for achieving the best result. The prognosis for closing space and substituting congenitally missing maxillary laterals with canines depends on factors such as overjet, lip support, crown colour, shape and root position. If these are unfavourable, opening space for prosthetic replacement is then preferred. Discrepancy between tooth and jaw size results either in spacing or crowding. The location of the spacing and the amount of overjet are important factors guiding the direction of treatment.

Ultrastructural identification of cells involved in the healing of intramembranous bone grafts in both the presence and absence of demineralised intramembranous bone matrix.

Alveolar bone defects are conditions that impede the progress of orthodontic treatment. This study compared the mechanics of the healing of autogenous intramembranous (IM) bone grafts and grafts comprising a mixture of IM and demineralised bone matrix of autogenous intramembranous origin (DBMIM), in an attempt to determine the reliability of each material. Thirty-two New Zealand white rabbits had a single defect created in their skull. Sixteen were grafted with IM bone alone (Group I: autogenous IM), and the other 16 had a combined graft of composite IM sandwiched between two layers of DBMIM (Group II: composite IM-DBMIM). A third group (Group III) of eight rabbits each had two defects created in their skull; one defect was left empty (A: passive control) and the other filled with rabbit-skin collagen (B: active control). In Groups I and II, inflammatory cells were found to be present on Days 1 and 2 of tissue retrieval. The appearance of the mesenchymal cells and preosteoblasts, osteoblasts and osteocytes was earlier (Day 3) in Group II than in Group I (Day 5). In both groups, preosteoblasts, osteoblasts and osteocytes were observed with no cartilage at the intermediate stage. In conclusion, autogenous IM bone grafts and IM bone grafts in the presence of DBMIM healed through an osteogenic ossification route.

Disposition of the novel anti-schizophrenic drug [14C]olanzapine in male Fischer 344 and female CD rats following single oral dose administration.

These studies comprehensively evaluate the distribution of [14C]olanzapine (2-methyl-4-(4-methyl-1-piperazinyl)-10H-thieno(2,3-b)-1,5)benzodiazepin e, CAS 132539-06-1, LY170053) a novel anti-schizophrenic compound, following single oral dose administration in male Fischer 344 rats, and pregnant and non-pregnant lactating female CD rats. The disposition of radiocarbon was determined and tissue pharmacokinetics evaluated in male Fischer 344 rats following a single oral 8 mg/kg dose at 2, 6, 24, 48, 72, and 96 h postdose using quantitative whole-body autoradiographic (QWBA) techniques in conjunction with image analysis. This study demonstrated that [14C]olanzapine and/or metabolites were rapidly absorbed and widely distributed with a tmax of 2 h postdose in most tissues. Persistent but declining concentrations of radiocarbon were detected in feces, kidney, liver, and Harderian, preputial, and thyroid glands at 96 h postdose. Placental transfer of [14C]olanzapine was evaluated at 0.5, 1, 3, 6, and 24 h postdose on gestation day 12, the mid-point of organogenesis, by tissue dissection and liquid scintillation spectroscopy (LSC) and on gestation day 18, a time which enabled visualization of fetal tissues by whole-body autoradiography (WBA). The placental transfer studies indicated that all tissues analyzed had a tmax of 1 or 3 h postdose with maternal liver consistently containing high concentrations of radiocarbon. Embryos contained measurable concentrations of radiocarbon throughout the time course of these studies confirming that [14C]olanzapine and/or its metabolites crossed the placenta. Additionally, the disposition of [14C]olanzapine in milk and plasma of lactating female CD rats confirmed pup exposure through milk ingestion.

Quantitative whole-body autoradiography in pregnant rabbits to determine fetal exposure of potential teratogenic compounds.

Whole-body autoradiography (WBA) allows the determination of sites of accumulation and differential distribution of radiolabeled compounds within organs. WBA is routinely conducted in pregnant rats to evaluate placental transfer and fetal distribution of potential developmental toxins. This technique has recently been adapted to evaluate tissue distribution in the pregnant rabbit, which may be a more appropriate model for some pharmaceutical candidates. A preliminary WBA study was conducted on New Zealand white (NZW) rabbits at gestation day 18, 1 h following a single oral dose of 14C-glucose. The purpose of this study was to validate the use of WBA techniques in assessing the placental transfer of compounds in pregnant rabbits. Antiviral compound LY217896 sodium demonstrated developmental toxicity in the pregnant NZW rabbit following multiple oral doses of 10 mg/kg on gestation days 6 through 18. WBA techniques were used to determine the distribution of radiocarbon 30 minutes following a single oral 10-mg/kg dose of 14C-LY217896 sodium in pregnant NZW rabbits on gestation day 18.

Whole-body disposition and polyglutamate distribution of the GAR formyltransferase inhibitors LY309887 and lometrexol in mice: effect of low-folate diet.

PURPOSE: The whole-body autoradiographic distribution of two radiolabeled antifolate inhibitors of GAR formyltransferase, lometrexol and LY309887, were compared in tumor-bearing mice maintained on standard diet (SD) and a low-folate diet (LFD) in order to determine the total amounts of drug that accumulated in blood, tumor, liver and kidney. The time-dependent changes in tissue distribution were evaluated over a 7-day period in order to compare the pharmacokinetic properties of both inhibitors and to assess the influence of dietary folate on this distribution. In addition, the effect of dietary folate on polyglutamation of compound accumulating in the liver was measured. The results have bearing on the potential of these two clinical agents to produce delayed toxicity in cancer patients and the use of dietary folate to modulate or prevent the development of this toxicity. METHODS: Single equimolar i.v. doses of [14C]LY309887 and [14C]lometrexol were administered to C3H mammary tumor bearing mice on SD or LFD, and the disposition of these compounds was quantitated using whole-body autoradiography. Livers were also harvested and extracted for determination of polyglutamate distribution. Animals were sacrificed both early and late (7 days) after dosing to determine the long-term retention of these compounds. RESULTS: Whole-body autoradiography revealed that the highest concentrations of both compounds were in liver and kidney. Concentrations of both compounds were two-fold higher in livers from LFD mice than in livers from SD mice. Lometrexol concentrations in liver averaged 2.8- and 2.2-fold higher than LY309887 in SD and LFD livers, respectively. In SD livers, the polyglutamate profiles of both compounds were similar, with hexaglutamates being the longest chain species detected. In LFD livers, hexaglutamates of LY309887 were observed, while hepta- and octaglutamates of lometrexol were detected after 168 h. CONCLUSIONS: The reduced hepatic retention and biochemical profile of LY309887 compared to lometrexol suggest that it may be less likely to produce delayed cumulative toxicity while still retaining antitumor activity. However, the increased hepatic accumulation observed in LFD mice emphasizes the importance of assessing and supplementing folate in cancer patients treated with this class of compounds.

Disposition of the opioid antagonist, LY255582, in rats and dogs.

LY255582 is a phenylpiperidine opioid antagonist under development as an appetite suppressant and for the treatment of obesity. Female beagles were administered [14C]LY255582 at dosages of 0.72 mg/kg intravenously or 7.2 mg/kg orally. The majority (54-58%) of the radioactivity was eliminated in the urine over 8 days after both oral and intravenous drug administration, primarily as polar metabolites. Peak plasma levels of parent drug in the dog were 11.5 and 311 ng/ml after oral and intravenous administration, respectively, and declined with a half-life of 3.2 hr. Peak plasma levels of LY255582 in the rat were 7.9 and 160 ng/ml after administration of [14C]LY255582 at dosages of 35 mg/kg orally and 1 mg/kg intravenously, respectively. The half-life of parent drug in rats was 1.5 hr; however, the terminal half-lives of radioactivity equivalents were 7.9 and 31.7 hr after intravenous and oral administration, respectively. The bioavailability of parent LY255582 was < 1% in both the rat and the dog, primarily because of extensive first-pass metabolism. Whole-body autoradiographic studies in rats after administration of a single oral 35 mg/kg dose of [14C]LY255582 indicated that radioactivity was rapidly absorbed and distributed throughout the body. Radioactivity concentrated in the liver and was eliminated slowly. Little or no parent drug was eliminated in the urine of either species. As in the urine, the major residues present in the liver and bile of rats orally administered [14C]LY255582 were uncharacterized polar metabolites with little parent drug present.

Comparison of quantitative whole-body autoradiographic and tissue dissection techniques in the evaluation of the tissue distribution of [14C]daptomycin in rats.

Quantitative whole-body autoradiography (QWBA) was evaluated and compared to tissue dissection/liquid scintillation counting (TD/LSC) techniques by determining the tissue distribution of radiocarbon in rats following iv administration of the antibiotic [14C]daptomycin (LY146032). QWBA, using computer-assisted video-image analysis, was initially evaluated by characterizing and calibrating commercial standards to blood and brain, kidney, liver, and lung homogenates. Frozen (carboxymethyl)cellulose blocks containing tissue homogenates spiked with [14C]glucose (370-37,000 Bq/g or 10-1000 nCi/g) were sectioned and optical densities (OD) measured. Characterization of QWBA included repeated measures data analysis to determine the significance of tissue type and intra- and inter-section and block variability. Regression models relating OD to radiocarbon concentration were also used to calibrate commercial standards for use in QWBA analyses. Results indicated that there were no substantial differences between OD readings from different tissues; however, the greatest source of variation in OD reading was section thickness. Because quantitative variations were largely attributed to section thickness, an internal standard (IS), consisting of liver homogenates spiked with [14C]glucose, was evaluated as a correction factor. Tissue concentrations of radiocarbon in male Fischer 344 rats were evaluated by QWBA and TD/LSC techniques 0.25 h following a single iv 10 mg/kg dose of [14C]daptomycin. Results indicated that tissue concentrations of radiocarbon obtained by QWBA, normalized using an IS, were comparable to those obtained by TD/LSC.

Biotransformation of the antiviral agent 1,3,4-thiadiazol-2-ylcyanamide (LY217896) and characteristics of a mesoionic ribose metabolite.

The biotransformation of the antiinfluenza agent 1,3,4-thiadiazol-2-ylcyanamide (LY217896, I) was studied. In addition to a urea metabolite (II) formed by transformation of the cyanamide functionality, another highly polar metabolite was found in mouse urine and in BSC-1, MDCK, and other cell culture incubations of [14C]LY217896. Using 13C-labeled LY217896 together with NMR and MS techniques, this highly polar metabolite was identified as a ribose derivative (III), which apparently exists in a mesoionic form (i.e. positive and negative charges within the same ring system). It was also found that this ribose is formed from LY217896 and ribose-1-phosphate in a reaction catalyzed by the enzyme purine nucleoside phosphorylase, but that the reverse reaction (cleavage of the ribose) is not observed under the conditions used. When tested in vitro using the same assay as that used to measure the antiviral activity of LY217896, this ribose and the urea metabolite exhibit essentially no activity. The presence of a ribose has been implicated in the activity of antiviral compounds such as ribavirin and anticancer agents like 2-aminothiadiazole and tiazofurin, which are structurally similar to LY217896. These activities have been postulated to involve either mono- or triphosphorylated forms, or NAD-type analogs. Possible implications of the formation of this mesoionic ribose metabolite for the mechanism of antiviral activity of LY217896 are discussed.