Synthesis and characterization of pH-sensitive poly(organophosphazene) hydrogels

A new class of pH-sensitive hydrogels has been designed and synthesized. These are novel polyphosphazenes that bear various ratios of sodium oxybenzoate and methoxyethoxyethoxy side groups. These water-soluble macromolecules were cross-linked by 60Co gamma irradiation and the products were allowed to absorb water to form hydrogels. The hydrogels had higher equilibrium degrees of swelling in basic than in acidic buffer solutions, and polymers with a higher loading of the ionic side group showed higher swellability than those with a lower loading of this side group. The effects of ionic strength, cation charge and radiation dose on the degree of swelling were also studied. A study of the diffusion of the dye Biebrich Scarlet from the hydrogels showed complete release of the dye in 4-12 h in pH 7.4 buffer solution but significantly lower release at pH 2 even after 48 h. The release rate also varied as the side-group ratios were changed. The prehydrogel polymers were synthesized via the macromolecular substitution reactions of poly(dichlorophosphazene) with sodium methoxyethoxyethoxide and the sodium salt of propyl 4-hydroxybenzoate, followed by ester hydrolysis to yield the sodium carboxylate. The hydrogels are of interest for possible use as pH-sensitive membranes and for a number of potential biomedical applications.

Absorption and disposition kinetics of 3,3',4,4'-tetrachloroazoxybenzene in the male Fischer 344 rat

3,3',4,4'-Tetrachloroazoxybenzene (TCAOB) is a structural analog of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). It is formed as a byproduct during the synthesis of industrial products such as herbicides. TCAOB is a ligand for the Ah receptor and, at much higher doses, exhibits toxicities similar to TCDD. Although the reduced in vivo toxicity of TCAOB probably reflects differences in disposition, this study characterized its absorption and disposition kinetics. Male Fischer 344 rats were administered [14C]TCAOB (3.4 or 34 mg/kg p.o., 3.4 mg/kg i.v.), and the excretion of the radiolabel was monitored over 96 hr. After the low and high dose, 35% and 30% of the [14C]TCAOB were eliminated in the urine, with 55% and 54% eliminated in the feces. At 96 hr, the adipose tissue:blood ratios of [14C]TCAOB equivalents were 8 and 26 for the low and high doses, respectively. After the intravenous dose of TCAOB, the adipose tissue:blood ratio was 21 at 96 hr. Other tissue:blood ratios were of little significance (0.06-3.2). Pharmacokinetic parameters indicate that the parent molecule is cleared from blood with an average half-life of 7 hr and an average clearance of 11 ml/min.kg. Absolute bioavailability was calculated to be approximately 9%. Urine contained a variety of dichlorolaniline conjugates, which support the importance of azo reduction in the disposition of TCAOB. When compared with TCDD, the absorption of TCAOB is greatly reduced and the elimination of metabolites greatly enhanced. Therefore, at equal molar oral doses, TCAOB would express lower levels of Ah receptor-mediated toxicity than those defined for TCDD.

Lack of bioavailability of dichlorobenzidine form diarylide azo pigments: molecular dosimetry for hemoglobin and DNA adducts

The hypothetical release of 3,3'-dichlorobenzidine (DCB) from two insoluble azo pigments and from a soluble azo dye was investigated in female Wistar rats for a 4 week treatment with 0.2% (w/w) Colour Index Pigment 13 (PY13) or 0.2% (w/w) Colour Index Pigment Yellow 17 (PY17) in the diet or 0.06% (w/v) Colour Index Direct Red 46 (DR46) in the drinking water. Steady-state DCB-hemoglobin adduct levels were determined by GC/MS with negative chemical ionization as well as DCB-DNA adduct levels in the liver by (32)P-postlabelling and compared with the respective adduct levels obtained in animals after treatment for 4 weeks with 0.00024, 0.0012 or 0.006% (w/v) DCB in the drinking water. A dose-proportional increase in adduct levels from 8.1 ng/g hemoglobin and 2.6 ng/g DNA (relative adduct level, RAL, 3.3x10(-9)) to 160 ng/g hemoglobin and 45.4 ng/g DNA (RAL 56.1x10(-9)) was observed in the DCB-treated rats. In rats treated with DR46 total adduct levels of 17.7 ng/g hemoglobin and 5.2 ng/g DNA (RAL 6.4x10(-9))were determined. No hemoglobin of DNA adducts were found in rats treated with PY17 in the diet, at a limit of detection of 0.1 ng/g hemoglobin and 0.08 ng/g DNA (RAL 0.1x10(-9)). In animals treated with PY13 in the diet no adducts or only minimal amounts slightly above the limit of detection could be identified. Taking into consideration that PY13 was contaminated with 0.02% of the respective soluble monoazo compound, it is concluded that the small amounts of DCB detected have been released from the contaminating soluble monoazo compound and not from insoluble PY13. The results of the present study demonstrate the lack of bioavailability of DCB from the diarylide azo pigments PY17 and PY13.

3,3',4,4'-tetrachloroazobenzene absorption, disposition, and metabolism in male Fischer 344 rats

3,3',4,4'-Tetrachloroazobenzene (TCAB) is a contaminant generated during the synthesis of 3,4-dichloroaniline and 3,4-dichloroaniline-derived pesticides. TCAB is isosteric to 2,3,7,8-tetrachlorodibenzo-p-dioxin and has been shown to bind to the Ah receptor. Following oral administration of [14C]TCAB (3.2 and 32 mg/kg), 39-45% of the dosed radioactivity was excreted into the urine and 53-56% was recovered in the feces within 48 hr. Less than 6% of the dosed radioactivity remained in the tissues examined at 96 hr. After intravenous administration (3.2 mg/kg), 33% of the dose was excreted in the bile during 6 hr. TCAB metabolites in urine were identified using LC/MS. The major metabolites were sulfate ester conjugates of hydroxylated mono- or dichloroaniline derivatives. Some of these metabolites were also acetylated. After intravenous administration, the disappearance of [14C]TCAB from blood was monitored, and the pharmacokinetic profile was consistent with a two-compartment model. Pharmacokinetic parameters reveal that the compound is readily cleared from the blood with a t1/2 of 4.0 hr, clearance of 12.3 ml/min.kg, and an apparent volume of distribution of 4.3 liters/kg. The absolute oral bioavailability was determined to be 30%. The extensive azo reduction of TCAB decreases its systemic absorption after oral administration and thereby limits the amount of parent compound available to interact with the Ah receptor and decreases the Ah receptor-mediated toxicity.

Synthesis and applicability of a photolabile 7,7-azi analogue of 3-sulfated taurine-conjugated bile salts

For the identification of proteins involved in hepatobiliary transport, the photolabile derivative 7,7-ASLCT ((7,7-azi-3 alpha-sulfato-5 beta-cholan-24-oyl)-2'-aminoethanesulfonate) was synthesized. 7,7-ASLCT is taken up into liver and excreted into bile completely unmetabolized at a rate between the excretion rate of SLCT ((3 alpha-sulfato-5 beta-cholan-24-oyl)-2'- aminoethanesulfonate) and SCCT ((7 alpha-hydroxy-3 alpha-sulfato-5 beta- cholan-24-oyl)-2'-aminoethanesulfonate). The dependency of flux rate of uptake into freshly isolated hepatocytes on the concentration of 7,7-ASLCT in presence of Na+ (143 mM) and with Na+ depletion (1 mM) is best described by the assumption of two simple transport systems, the kinetic parameters of which are similar to those of SLCT. As studied in the presence of Na+, 7,7-ASLCT and SLCT exhibit a clearly competitive cross-inhibition of uptake with inhibition constants that are similar to the corresponding half-saturation constants. Photoaffinity labeling of isolated hepatocytes using 7,7-ASLCT (400 microM) resulted in the irreversible inhibition of the uptake of 7,7-ASLCT and SLCT to similar extents, confirming the kinetic data that 7,7-ASLCT is a true competing substrate for the uptake of SLCT. Because in intact rat liver 7,7-ASLCT and SLCT mutually inhibit their biliary excretion, the photolabile derivative shares with SLCT the same pathways in uptake and in excretion. Thus, 7,7-ASLCT should be appropriate for the study of hepatobiliary transport of sulfated and taurine-conjugated bile salts by photoaffinity labeling.

Bio-metabolic disposition of metanil yellow, orange II and their blend by caecal microflora of rats

Caecal microflora were employed to study the degradation pattern, with time course of Metanil yellow and Orange II-two extensively used non-permitted food colours. Metanil yellow and Orange II showed the respective Degradation Index 50 (DI 50) values of 369 and 288 min. However, the blend of Metanil yellow and Orange II (1:1) resulted in the D1 50.value of 288 min. Metanil yellow, Orange II and their blend were resolved into respective metabolites in different solvent systems.

Age-dependent uptake and retrograde axonal transport of exogenous albumin and transferrin in rat motor neurons

This study presents evidence for retrograde axonal transport of exogenous albumin and transferrin in adult brainstem motor neurons, whereas plasma proteins are not transported in neonatal motor neurons. The plasma protein uptake in motor neurons was dose-dependent, suggesting a nonspecific (fluid-phase) uptake mechanism. Further evidence for nonspecific uptake of exogenous transferrin in the motor neuron was found in the presence of transferrin receptor only on the soma and not on the axon terminal. The immunoreaction product of the exogenous plasma proteins was localized as perinuclear granules in association with the lysosomal system, as verified by staining for the lysosomal marker cathepsin D and by ultrastructural examinations. The results suggest that albumin and transferrin derived from hepatic synthesis gain access to motor neurons nonspecifically by retrograde axonal transport, whereas transferrin derived from intracerebral synthesis specifically gains access to motor neurons due to receptor-mediated uptake at the soma of the neuron. The lack of plasma proteins in developing motor neurons suggests that retrograde axonal transport of plasma proteins has no significance for developing axons. Plasma proteins have a potential for transporting toxic metals to motor neurons. Intraneuronal uptake of aluminum-transferrin either by nonspecific uptake in axon terminals or by receptor-mediated uptake at the soma may have a role in the pathogenesis of the motor neuron disease amyotrophic lateral sclerosis.

O/W lipid emulsions for parenteral drug delivery. II. Effect of composition on pharmacokinetics of incorporated drug

The potential usefulness of O/W lipid emulsions as injectable drug delivery systems for lipophilic drugs was examined using a model lipophilic drug, sudan II (clogP = 5.4) in the normal rats. The standard lipid emulsion composed of soybean oil and egg yolk phosphatides increased the blood concentration of sudan II after i.v. injection when compared with its solubilized solution by plasma. However, it was still lower than that of the oil particles, and the distribution of sudan II to liver, lungs, adipose tissue, heart, and muscle was not altered, and only that to brain and kidneys was decreased. Herein, the effect of extensive alterations in the lipid emulsion composition on the blood concentration and organ distribution of sudan II was examined in comparison with the standard formulation. Addition of cholesterol, use of pure egg yolk phosphatidylcholine, use of phospholipids with saturated alkyl chain, use of saturated long chain triglycerides, and use of saturated medium chain triglycerides were tested. The oil particles of all tested lipid emulsions were still located in plasma space, and use of saturated medium chain triglycerides was the most effective way to increase blood concentration of sudan II, resulting in higher distribution to liver, lungs, spleen, and brain. This was caused by the increase of the steady-state partition of sudan II to the oil particles, and not by alteration of their organ distribution clearance.

Bioaccumulation and toxic effects of elevated levels of 3,3',4,4'-tetrachloroazobenzene (33'44'-TCAB) towards aquatic organisms. I: A simple method for the rapid extraction, detection and determination of 33'44'-TCAB in multiple biological samples

The polychlorinated aromatic compound 3,3',4,4'-tetrachloroazobenzene (33'44'-TCAB) is a contaminant of 3,4-dichloroaniline based herbicides, but there have been no reports of methods for the quantitative determination of 33'44'-TCAB in biological organisms. In this communication we address this knowledge gap by presenting a method for the rapid extraction, detection and determination of 33'44'-TCAB in multiple biological samples based on the alkaline decomposition of the sample followed by alumina cartridge column chromatography and GC-HRMS analysis.

Bioaccumulation and toxic effects of elevated levels of 3,3',4,4'-tetrachloroazobenzene (33'44'-TCAB) towards aquatic organisms. II: Bioaccumulation and toxic effects of dietary 33'44'-TCAB on the Japanese Medaka (Oryzias latipes)

The polychlorinated aromatic compound 3,3',4,4'-tetrachloroazobenzene (33'44'-TCAB) is a contaminant of 3,4-dichloroaniline (3,4-DCA) based herbicides, and of agricultural soils. In this study, the Japanese Medaka (Oryzias latipes) was exposed to 0.5-2500 ppm 33'44'-TCAB through its diet. There was a distinct trend towards increased mortality and increased body burdens of 33'44'-TCAB with increasing 33'44'-TCAB charge in the food. At the highest levels of exposure, there was a significant number of excess deaths compared to control groups.

Bioaccumulation and toxic effects of elevated levels of 3,3',4,4'-tetrachloroazobenzene (33'44'-TCAB) towards aquatic organisms. III: Bioaccumulation and toxic effects of detrital 33'44'-TCAB on the aquatic snail, Indohiramakigai (Indoplanorbis exustus)

The polychlorinated aromatic compound 3,3',4,4'-tetrachloroazobenzene (33'44'-TCAB) is a contaminant of many 3,4-dichloroaniline (3,4-DCA) based herbicides, and of agricultural soils. In this study, the aquatic snail Indohiramakigai (Indoplanorbis exustus) was exposed to detrital 33'44'-TCAB. The snails absorbed 33'44'-TCAB from their environment, but only to a maximum level of approximately 287 ppb (whole body basis). This level of 33'44'-TCAB did not appear to cause any harmful effects.

O/W lipid emulsions for parenteral drug delivery. I. Pharmacokinetics of the oil particles and incorporated sudan II

The potential usefulness of oil in water (O/W) lipid emulsions as parenteral drug delivery system for lipophilic drugs was examined in tumor-bearing rats. A model lipophilic drug, sudan II (PCoct = 226000), was formulated in five lipid emulsions consisting of soybean oil and various surfactants. Compared with HCO-60 micellar and plasma solutions of sudan II, the blood concentration of sudan II was markedly elevated by administration as a lipid emulsion. However, the distribution of sudan II to the liver, lungs, spleen, and adipose tissue was not altered, and that to the brain, heart, kidneys, muscle, and tumor was slightly decreased. To understand these results, pharmacokinetic analysis was performed using a newly derived compartmental model, and moreover, the organ distribution clearance was analyzed. It was suggested that the oil particles deliver the incorporated drug selectively to the liver, lungs, and spleen, and the speed of delivery could be surpressed by using HCO-60. However, in the case of sudan II, its rapid release from the oil particles after i.v. injection prevented a drastic alteration in the distribution of sudan II. The simulation studies suggested that a considerable decrease in the release rate or an increase in partition coefficient (experimentally more than 10(8) would be required for delivery.

Activation by caecal reduction of the azo dye D & C red no. 9 to a bacterial mutagen

D & C Red No. 9 is a monoazo dye used for manufacturing printing inks, rubber and plastics, and as an additive in cosmetics and drugs. In an NTP carcinogenicity study in rats and mice it induced splenic sarcomas and liver nodules in male rats; no chemical-related tumours were induced in mice. On the basis of its contradictory responses in a range of in vitro tests and its inactivity in several in vivo genotoxicity assays, it has been suggested that the dye may act as a non-genotoxic carcinogen. We tested the dye in the Salmonella mutagenicity assay using several different protocols. The dye was not mutagenic when tested using the standard (aerobic) preincubation protocol. Variable responses were seen when the flavin mononucleotide (FMN) reduction protocol was used. A third protocol was provided by incubating the test compound overnight with a rat caecal preparation under anoxic conditions to reduce the azo bond. Ethyl acetate extracts of this incubation mixture, when tested in the standard preincubation protocol using induced rat liver S9, yielded dose-related mutagenic responses in TA100, and a weak response in TA98. The presuemed major reduction product, 1-amino-2-naphthol (1-A-2-N) was mutagenic to TA100, but not TA98, in standard protocols with S9. The results show that it is necessary to use a protocol in which D & C Red No. 9 is reduced in order to demonstrate the mutagenicity of this dye. The non-genotoxicity previously reported for D & C Red No. 9, may have been due to insufficient reductive cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of barrier creams: an in vitro technique on human skin

A method was developed to measure in vitro on human skin the effectiveness of barrier creams against three dyes (eosin, methyl-violet and oil red O) with different n-octanol/water partition coefficients (0.19, 29.8 and 165, respectively). Some galenic properties (water washability, water content and viscosity) of the products were also evaluated to try to understand the mechanisms of such a protection. The barrier creams were assayed by measurements of the dyes in the epidermis of protected skin samples after an application time of 30 min. Whereas some products showed some degree of protection, as claimed on the packaging, we demonstrated in several cases disagreement with the manufacturer's information. Surprisingly, petrolatum was found to provide the best protection of all tested products in our in vitro model. There was no correlation between the galenic parameters of the assayed products and the level of protections, indicating that neither the water content nor the consistence of the formulations influenced the protection effectiveness. In conclusion, regarding the possible skin effects of some irritants, our results stress that barrier creams should be used with caution, knowing the protection limits of some of the formulations marketed.

Biomonitoring of aromatic amines. IV: Use of hemoglobin adducts to demonstrate the bioavailability of cleavage products from diarylide azo pigments in vivo

The release and availability of the carcinogenic component of the soluble azo dye Direct Red 46 and the insoluble azo pigment Pigment Yellow 17 were analyzed in Wistar rats using hemoglobin adducts as a dosimeter. The levels of hemoglobin adducts were found to be very low. Intestinal cleavage and release of 3,3'-dichlorobenzidine (3,3'-DCB) from Direct Red 46 and Pigment Yellow 17 was calculated to be 3% and 0.6% of the dose, respectively, in a 4-week feeding study. It is proposed to measure blood samples from exposed humans in order to test the applicability of the method and eventually to use it for controlling human exposure to the carcinogenic colorant components.

[The virulence and cytochemical properties of Leishmania major during long-term cultivation]

It has been shown that morphogenesis of Leishmania major in each culture passage is characterised by the depletion of RNA and increase in its dispersion degree, by the change of the NADP-H-diaphorese, peroxidase and Janus green-B-oxidative activity in the promastigotes. Cytochemical peculiarities of invasive metacyclic promastigotes are an extreme depletion of RNA, its disperse form, a low activity of oxidative enzymes. This properties may manifest the pre-adaptation of Leishmania promastigotes to the development in vertebrate host. In the process of long-term cultivation of L. major the virulence, the metacyclogenesis, and the level of NADF-H-diaphorase and peroxidase activity decrease from passage to passage, but the ability to oxidate the Janus green-B increases.

Reduction of azo dyes during in vitro percutaneous absorption

The azoreduction of phenylazo-2-naphthol (Sudan I), 5-(phenylazo)-6-hydroxynaphthalene-2-sulfonic acid [aniline subsidiary color of FD&C Yellow No. 6 (ANSC)], and phenylazophenol [Solvent Yellow 7 (SY7)] in skin during percutaneous absorption was measured and the contributions of cytosolic and microsomal reductions were characterized. By using a series of azo dyes with a common U-14C-labeled phenylazo moiety, percutaneous absorption and metabolism were measured in vitro in flow-through diffusion cells with Sencar mouse, hairless guinea pig, and human skin. Azoreductase assays using subcellular fractions from skin of all species were used to examine intracellular rates and distribution for the series of dyes. The absorption of the lipophilic dyes Sudan I and SY7 from a finite surface dose of 5 micrograms/cm2 was extensive in all species. In mouse, 32.8 +/- 2.8% of the applied Sudan I dose and 64.1 +/- 3.3% of the applied SY7 dose were absorbed in 24 hr. In the hairless guinea pig, 57.6 +/- 5.9% of the applied Sudan I dose and 67.8 +/- 4.6% of the applied SY7 dose were absorbed in 24 hr. Human skin was least permeable, with 26.4 +/- 6.7% of the applied Sudan I dose and 36.1 +/- 4.5% of the applied SY7 dose absorbed in 24 hr. Sudan I and SY7 were extensively reduced in skin of all species during percutaneous absorption (29.5 and 26.5%, respectively, of the absorbed dose in human skin and greater than 50% of the applied dose in other species). ANSC was the least absorbed, with 5% or less penetrating. SY7 was preferentially reduced in the skin cytosol of all species, whereas Sudan I was equally reduced in the skin cytosol and microsomal fractions. The site of azoreduction in the cell may affect the metabolic fate of the liberated arylamine. The extensive azoreduction observed during percutaneous absorption may modulate the toxicities of these compounds and must be considered when effective doses are determined for quantitative risk assessments from dermal exposures.

Comparison of cytochrome P-450- and peroxidase-mediated activations of carcinogenic azo dyes and N-nitrosamines

Carcinogenic azo dyes (dimethylaminoazobenzene, Sudan I) and N-nitrosamines (N-nitrosomethylaniline, N-nitrosomethylbenzylamine) are oxidized by cytochrome P-450 isoenzymes and peroxidase yielding metabolites which in vitro bind to DNA and transfer RNA (tRNA). The parallelism and differences in oxidative reactions are described. Peroxidase is more effective than P-450 in activating reactions of some carcinogens studied. The presence of either of these enzymes is supposed to be responsible for the organ and/or cell type specific effects of the carcinogens studied.

Hepatic uptake of lipid-soluble drugs from fat emulsion

Oil violet in a fat emulsion was taken up into the parenchymal cells of rat liver in vitro. The uptake was greater at 37 degrees C than 25 degrees C or 4 degrees C, and it was increased by addition of postheparin plasma including lipoprotein lipase activity into the reaction medium. The uptake from the emulsion with smaller particles was greater than that from the emulsion with larger particles. The hepatic uptake of 14C-cholesteryl oleate in the emulsion by recirculating perfusion of the liver in situ was also increased by postheparin plasma in the perfusion medium. Its enhancing effect was found for distribution in the parenchymal cells but not in the Kupffer cells. The previous perfusion of Intralipos of the commercial fat emulsion reduced the hepatic uptake of 14C-cholesteryl oleate in the emulsion. The emulsion particle sizes were reduced by postheparin plasma both in vitro and in situ. Consequently, it was suggested that a lipid-soluble compound entrapped in the fat emulsion is taken up into the parenchymal cells by receptor-mediated process via the reduced particle sizes emulsion (remnant), which is a mechanism similar to the dietary fat metabolism.

Long-term low-dose mutation studies in human cells: metanil yellow and orange II

We tested the mutagenic effects of two commonly used fold colors, metanil yellow and orange II, in AHH-1 human lymphoblast cells. The cell line, which is competent for oxidative metabolism of various chemicals, was exposed to both compounds in high-dose x short-term (3 day) or high-dose x long-term (10-day) and low-dose x long-term (20-day) treatments. Concentrations of metanil yellow and orange II as low as 22 nM and 12 nM, respectively, were sufficient to induce mutation rates which were equal to twice the spontaneous mutation rate at the HPRT locus in AHH-1 cells.

Metabolic disposition of 14C-metanil yellow in guinea pigs

The absorption, metabolism and excretion of 14C-metanil yellow was studied in guinea pigs. Following administration of a single po dose of 5 mg dye (7.6 mu Ci)/kg body weight, 83.4% was excreted through urine and feces within 96 h with the majority accounted for in feces. Liver, kidney and spleen did not have marked accumulation of counts, whereas testes and gastrointestinal tract retained 1.9 and 9.7% of the radioactivity, respectively. Analysis of urine and feces detected 2 azo-reduction metabolites of metanil yellow which were characterized by TLC and IR, NMR and mass spectroscopic studies as metanilic acid and p-aminodiphenylamine.

Photo-modulated ion channels based on covalently linked gramicidins

The covalent coupling of two gramicidin A monomers proved to be a useful tool for the rational design of ion channels with predictable electrophysiological properties (Stankovic, C.J., Heinemann, S.H., Delfino, J.M., Sigworth, F.J. and Schreiber, S.L. (1989) Science 244, 813-817; Stankovic, C.J., Heinemann, S.H. and Schreiber, S.L. (1990) J. Am. Chem. Soc. 112, 3702-3704). Herein we report on our first efforts to equip such channels with an artificial gating mechanism. Gramicidin monomers were covalently linked with 3,3'-azobis(benzeneacetic acid). Based on computer modeling of the beta-helix channel motif, this linker in its dark-adapted (trans) form does not allow for the formation of unimolecular ion channels, while the photo-activated (cis) form was expected to provide this possibility. The electrophysiological assays showed that (A) the trans-isomer does form characteristic ion channels, and (B) irradiation transforms these channels into a new distinct, flickering channel type in a reversible manner. The results are discussed in the framework of intermolecular gramicidin aggregates.

Age-related changes in biotransformation of azoxymethane and methylazoxymethanol in vitro

1. Age-related changes in hepatic hydroxylation of azoxymethane (AZO) to methylazoxymethanol (MAM), as well as colonic phase I metabolism of MAM by alcohol dehydrogenase (ADH) were examined in young (2-4 months), middle-aged (12-14 months), and old (22-24 months) male Fischer 344 rats. In addition, the possibility that colonic glucuronyltransferase might be involved in the biotransformation of MAM was also investigated. 2. A significant decrease in hepatic conversion of AZO to MAM was found in old vs young rats, concomitant with a decrease in hepatic cytochrome P-450 content, while no age-related difference was found in the colonic metabolism of MAM by ADH. MAM inhibition of colonic 4-methylumbelliferone glucuronyltransferase was non-competitive, suggesting indirectly that colonic glucuronyltransferase is not involved in conjugation of MAM. 3. It is concluded that ageing in the male Fischer 344 rat results in alternations of AZO and MAM biotransformation which indicate that AZO may be less carcinogenic in older rats.

Enhancing effect of pyrrolidone derivatives on the transdermal penetration of sulfaguanidine, aminopyrine and Sudan III

The enhancing effect of pyrrolidone derivatives on the percutaneous penetration of sulfaguanidine, aminopyrine and sudan III was investigated using in vitro technique and excised rat skin. 1-Methyl (MP), 1-hexyl (HP) and 1-lauryl-2-pyrrolidone (LP) were used as penetration enhancers. Aminopyrine showed high penetration through skin although sulfaguanidine and sudan III showed little penetration. Pyrrolidone derivatives enhanced their penetrations. Especially HP and LP enhanced the penetration of sulfaguanidine to a high extent. Sudan III was not detected in the receptor phase regardless of the presence of enhancer. Pyrrolidone derivatives significantly increased the skin accumulation of sulfaguanidine, aminopyrine and sudan III. Penetration of pyrrolidone derivatives was also determined. MP and HP showed high penetrations. LP was not detectable in the receptor phase. MP, HP and LP showed high skin accumulations. These results suggested the usefulness of pyrrolidone derivatives as percutaneous penetration enhancers.

Evaluation of arterialized vein graft permeability with Evans blue dye and iodine 125-labeled albumin

This study measured endothelial permeability, quantitatively (with iodine 125-labeled albumin) and qualitatively (with Evans blue dye) in arterialized vein grafts in 9 adult dogs. In each dog, the right common carotid artery was ligated and arterial flow was reconstituted with a 5-cm bypass graft of right external jugular vein. Twenty-four hours before the dogs were killed, each dog received both 125I-labeled albumin (8 microCi/kg) and Evans blue dye (15 mg/kg) intravenously. After the dogs' death, each arterialized vein graft and each left external jugular vein (as control) was harvested and studied. Arterialized vein graft permeability was significantly increased over control at 1, 3, and 6 months (3 dogs at each interval). Scanning electron microscopy revealed confluent endothelium in all specimens. This increased permeability may play a role in vein graft atherosclerosis.

The role of topical agents in the healing of full-thickness wounds

Eight topical agents in current use were studied for their effects on wound contraction and rate of reepithelialization of full-thickness excisions using a porcine animal model. The following agents were applied daily for a period of 27 days: scarlet red ointment, benzoyl peroxide lotion, bacitracin ointment, silver sulfadiazine cream, aloe vera gel, tretinoin cream, capsaicin cream, and mupirocin ointment. The rate of reepithelialization was significantly enhanced by treatment with capsaicin, bacitracin, silver sulfadiazine, and scarlet red, and was markedly retarded by treatment with tretinoin. Wound contraction was significantly retarded by mupirocin, bacitracin, and silver sulfadizine. Knowledge of the effects of topical agents on various aspects of healing allows the clinician to choose the most appropriate material to use in a given clinical situation to optimize the healing process and produce the best final result.

Azodicarbonamide: methods for the analysis in tissues of rats and inhalation disposition

1. A method has been developed for measuring azodicarbonamide (ADA) and its metabolite biurea in tissues of rat. The method is based on the reaction of ADA with triphenylphosphine; the derivative so formed was isolated and quantified using reversed-phase h.p.l.c. Quantification was by u.v. detection with 14C-ADA as internal standard. Biurea was measured by oxidation to ADA, followed by treatment as described above. 2. When biurea was added to tissues at 100-400 micrograms, recoveries of 92-125% were observed. In contrast, recoveries of ADA added to tissues were generally much less than 100% and could not be reliably determined. The inability to quantify ADA added to tissues was ascribed to its rapid and facile reduction by tissue sulphydryl groups. 3. When rats were exposed to ADA aerosol concentrations of 200, 100, 50 and 0 mg/m3 for 13 weeks by inhalation, a non-linear dose-dependent accumulation of biurea was observed in lungs. No ADA was detected in lungs. Neither biurea nor ADA could be detected in kidneys.

Effects of the pH dependence of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide-formazan absorption on chemosensitivity determined by a novel tetrazolium-based assay

The tetrazolium dye, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), is reduced by live but not dead cells, and this reaction is used as the end point in a rapid drug-screening assay. It can also be used for accurate determinations of drug sensitivity but only if a quantitative relationship is established between cell number and MTT-formazan production. We have shown that reduction of MTT to MTT-formazan by cells is dependent on the amount of MTT in the incubation medium. The concentration required to give maximal MTT-formazan production differs widely between cell lines. The absorption spectrum of MTT-formazan varies with cell number and with pH. At a low cell density or a high pH, the absorption maximum is at a wavelength of 560 to 570 nm. However, at a high cell density or a low pH, there are two absorption maxima; one at 510 nm and a second at about 570 nm. Measurements of absorbance at 570 nm underestimate MTT-formazan production and, hence, cell number at high cell densities. This error can result in a 10-fold underestimation of chemosensitivity. Addition of a buffer at pH 10.5 to the solubilized MTT-formazan product can overcome the effects of both cell density and culture medium on the absorption spectrum. Provided that sufficient MTT is used and the pH of the MTT-formazan product is controlled, dye reduction can be used to estimate cell numbers in a simple chemosensitivity assay the results of which agree well with a commonly used clonogenic assay.

[Distribution and metabolism of azoxybenzene in the rat]

No sex differences could been shown after absorption and distribution of azoxybenzen in the rat. The highest level occur in the thyroid gland, the adrenals and in the fat tissues. The maximum level was reached 30 min. after application.

[Absorption of C14-labeled dye "active red 5CX"++ immobilized on polysaccharides in the rat gastrointestinal tract]

Rats were maintained on a diet containing 14C-aniline procion dye "active red 5CX" either in a hydrolyzed or chemically immobilized form on starch and cellulose. Absorption of the label, distribution in tissues and excretion were studied within 6-48 hrs. Independently on the forms of the preparation used more than 80% of the label occurred in blood and were then excreted with urine. Molecule of the azo-dye appears to degrade in large intestine by means of microflora with splitting of the azo-bond and the potentially toxic metabolites developed penetrated into a body media. Immobilization of the dye on polymers, including cellulose was not an effective approach to prevent these reactions.

[Comparative study on the mutagenic activity of rat liver and bladder S9 by fluctuation test]

Mutagenicity of seven aromatic amines, two heterocyclic amines, two azo compounds and one polycyclic aromatic hydrocarbon was examined with a fluctuation test modified by Gatehouse. The test was performed by using Salmonella typhimurium TA98 in the presence of liver and bladder S9 from PCB pretreated rats. Seven out of 12 compounds showed mutagenic activities with liver S9 and seven with bladder S9. Benzidine, 3-methylcholanthrene and 2-acetylaminofluorene showed a negative response with bladder S9 but a positive response with liver S9. The mutagenicity of the seven compounds observed with bladder S9 had a lower sensitivity than with liver S9. 3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole and 3-amino-1-methyl-5H-pyrido[4,3-b]indole showed mutagenic activity at lower concentrations than the other compounds which showed mutagenic activity either with bladder S9 or liver S9. Mutagenicity of 3-methylcholanthrene was observed at high concentration only in the presence of liver S9. The findings from the present study suggested that aromatic amines, heterocyclic amines and polycyclic aromatic hydrocarbons were more likely to be activated to strong mutagens with liver S9 than with bladder S9.

Pharmacokinetic and phase I study of intravenous DON (6-diazo-5-oxo-L-norleucine) in children

DON (6-diazo-5-oxo-L-norleucine), a glutamine antagonist, has been subjected to limited clinical trials since 1957. Use of the drug in adults has been curtailed due to sparse reports of effectiveness as well as its dose-limiting toxicities, i.e., severe nausea, vomiting and mucositis. In earlier studies, children given DON orally in combination with 6-mercaptopurine had significant prolongation of remission of acute leukemias during maintenance therapy. As DON is acid-labile and relatively unstable in solution, oral administration does not appear to be ideal for DON. In the trial described in this report, i.v. DON therapy was studied, using i.v. chlorpromazine to control vomiting, in 20 children, 17 of whom were evaluable following treatment at DON dose levels ranging from 150 mg/m2 to 520 mg/m2. Nausea and vomiting, the dose-limiting toxicity for adults, was controlled with chlorpromazine. Mucositis, which has also been observed in adults, did not occur in the children given DON i.v. A maximum tolerated dose was not defined; however, the projected maximum tolerated dose appears to be in excess of 450 mg/m2. DON was measured in plasma using a rapid-sampling HPLC procedure. The total body clearance, plasma t1/2, and area under the plasma concentration curve (AUC) were calculated using a noncompartmental method. The drug is rapidly cleared from plasma (t 1/2 = 3 h), and its volume of distribution is approximately twice that of total body water in children. These pharmacokinetic data, differ from that of adults reported by others. Specifically, the plasma t 1/2 for children is longer: total body clearance (Cl), and volume of distribution at steady state (Vss) are greater. In addition, no dose dependency of t 1/2, Cl or Vss was observed in this study, and the DON pharmacokinetics were linear and predictable. Five of nine children with acute leukemia showed improvement, though insufficient for classification as partial response, and five of eight children with solid tumors also showed improvement. Further trials using DON in combination with thiopurines or other agents appear indicated.

Transvascular flux and tissue accrual of Evans blue: effects of endotoxin and histamine

We investigated the relationship between the pharmacokinetics of exogenous molecules and transcapillary flux by studying the intravascular and tissue content and the histologic distribution of Evans blue in guinea pigs. Pharmacokinetic analysis demonstrated that 87% of the decline in intravascular Evans blue during the first 3 hours after administration was a result of transvascular flux to tissue compartments. Rapidly and slowly equilibrating compartments were identified. Greater than 90% of the clearances in lung and heart were rapid compartment clearances. Histologically, the distribution of Evans blue in these tissues was predominantly extracellular and similar to the distribution of fluorescein-labeled dextran. By contrast, the accumulation in kidney and liver was kinetically similar to characteristics of the slowly equilibrating compartment. This corresponded histologically to the predominant intracellular uptake of Evans blue in these tissues. Generalized increases in capillary permeability were produced by endotoxin or histamine infusion. Both treatments were associated with a more rapid initial decline in intravascular content of Evans blue than was found in control animals. Although the histologic distribution of Evans blue in tissues was not altered, endotoxin was associated with a more rapid appearance of Evans blue in the lung and heart than was seen in controls. We conclude that the initial decline in intravascular content of Evans blue corresponds to the intercompartmental clearance and to transcapillary macromolecular flux. The initial decline in serum concentrations may therefore be useful in studying disorders of generalized capillary permeability. Furthermore, the initial accrual of Evans blue in the lung and heart may be used as a marker of transcapillary macromolecular flux in those tissues.

Metabolic disposition of 14C-labelled amaranth in the rat, mouse and guinea-pig

The absorption, metabolism and excretion of orally administered 14C-labelled amaranth has been studied in the rat, mouse and guinea-pig. Following administration of a single oral dose of either 2 or 200 mg/kg, most of the radioactivity was excreted in the urine and faeces in the first 24 hr, and substantially all of the dose was recovered in the excreta within 72 hr. In the rat and mouse, the principal route of excretion was the faeces, whereas in the guinea-pig, urinary excretion accounted for up to 50% of the dose. In the rat and guinea-pig the proportion of the dose excreted in the urine was significantly greater at the lower dose level. No marked accumulation of radioactivity was found in any tissues 72 hr after the administration of the labelled colouring. For all three species most of the radioactivity was shown to be associated with naphthionic acid, with traces of unchanged amaranth and a number of other unidentified metabolites also being detected. In the rat and mouse substantially all of the remaining radioactivity was associated with a single unidentified component. Naphthionic acid was found in the faeces of all three species along with a substantial, but variable, amount of unchanged dye. At least six other radioactive peaks were seen in the chromatograms of faecal extracts; two of these peaks had similar chromatographic properties to the unknown metabolites in the urine, but there was no peak corresponding to 1-amino-2-naphthol-3,6-disulphonic acid (1-ANDSA), previously reported as a urinary metabolite of amaranth. In studies of absorption from isolated loops of small intestine of the rat, mouse and guinea-pig, no significant absorption of amaranth was detected over a 100-fold concentration range (20-2000 ppm).

Metabolic disposition of 14C-labelled Brown HT in the rat, mouse and guinea-pig

The absorption, metabolism, tissue distribution and excretion of 14C-labelled Brown HT has been studied in the rat, mouse and guinea-pig. Following administration of a single oral dose of either 50 or 250 mg Brown HT/kg, substantially all of the dose was excreted in the urine and faeces within 72 hr, with the majority (more than 80%) being accounted for in the faeces. A significant difference in urinary excretion of radioactivity was seen between male and female rats, as well as clear species differences at the two dose levels used. In all species studied, naphthionic acid was the major urinary metabolite, whereas in the faeces naphthionic acid, trace quantities of unchanged dye and at least two unidentified metabolites were found. Pregnant rats eliminated a single oral dose of 14C-labelled colouring at a rate similar to that in non-pregnant females, but some retention of radioactivity was found in the foetuses. Radioactivity was present in all tissues of male rats 24 hr after an oral dose of 250 mg 14C-labelled Brown HT/kg, with the highest concentrations in the gastro-intestinal tract, kidney and lymph nodes. Clearance from the gastro-intestinal tract was more rapid than from other tissues, but by day 7, the concentration of radioactivity (less than 0.001% of the dose/g) was similar in all tissues except the kidney and mesenteric lymph nodes. Similar results were obtained with animals pretreated for 21 days with either unlabelled or 14C-labelled Brown HT (250 mg/kg/day) prior to a radioactive dose. For most tissues examined, the concentration of radioactivity was greater with pretreatment than without. These results suggest that despite the rapid reduction and elimination of the major part of an oral dose of Brown HT, some colouring and/or metabolites accumulate in most tissues of male rats during repeated daily administration, but that only in the kidney and mesenteric lymph nodes is the accumulation tissue-specific. The accumulated radioactivity is cleared rapidly from most tissues on cessation of treatment. No significant absorption of either Brown HT, metabolites or subsidiary dyes was detected using isolated loops of small intestine.

Effects of chronic dietary ethanol on in vivo and in vitro metabolism of methylazoxymethanol and on methylazoxymethanol-induced DNA methylation in rat colon and liver

We examined the metabolism of 14C-labeled methylazoxymethanol (MAM) in male F344 rats pair-fed for 21.0 days either a liquid control diet, an isocaloric liquid diet containing 6.6% ethanol by volume (continuous ethanol diet), or the ethanol diet for 20.5 days followed by the control diet for 0.5 day (interrupted ethanol diet). Compared to rats fed the control liquid diet, metabolism of [1,2-14C]MAM acetate to exhaled 14CO2 was inhibited by 25 to 42% in rats fed the continuous ethanol diet, but was initially stimulated by 90% in rats given the interrupted ethanol diet. MAM-induced DNA methylation, as reflected in 7-methylguanine and O6-methylguanine content 24 h after carcinogen administration, was inhibited in the colon mucosae of rats fed the interrupted ethanol diet by 52 to 54%, and an even greater inhibition (71 to 86%) of DNA methylation occurred in the colon mucosae of rats fed the continuous ethanol diet. Liver DNA methylation was significantly inhibited (by 32 to 42%) only in those rats fed the continuous ethanol diet. Liver microsomes isolated from rats fed the 3 diets metabolized MAM to formic acid and methanol in vitro, but liver microsomes from rats fed the continuous ethanol diet were 12 to 15 times more active than liver microsomes from rats fed the control diet. Liver microsomes isolated from rats fed the interrupted ethanol diet were only 3 to 5 times more active in MAM metabolism than liver microsomes from rats fed the control diet, indicating very rapid turnover of the ethanol-induced enzyme(s) catalyzing the oxidation of MAM. Although chronic ethanol feeding enhanced the activity of liver microsomes for MAM metabolism, ethanol was found to inhibit the reaction competitively. Hepatocytes isolated from rats fed the continuous ethanol diet were considerably more sensitive to MAM-induced unscheduled DNA synthesis than hepatocytes isolated from rats given the control liquid diet, indicating that the stimulation of MAM metabolism by dietary ethanol results in increased DNA damage, observable in an in vitro system. Thus, the increased metabolic activation of MAM, due to enzyme induction by ethanol which is observed in vitro, is not reflected in increased liver DNA methylation in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)