Biomedical subjects

R J Mountfield

Publications and source records attributed to R J Mountfield.

8 recordsLinked to original sources

PubMed2001

The use of election paramagnetic resonance spectroscopy in early preformulation experiments: the impact of different experimental formulations on the release of a lipophilic spin probe into gastric juice.

The lipophilic spin probe TEMPOL-benzoate was dissolved in different experimental formulations, including polyethylene glycol 400 (PEG 400), Miglyol, glycerol monooleate (GMO), and Cremophor RH-40. Samples were measured by electron paramagnetic resonance (EPR) spectroscopy before and after addition to human gastric juice. The distance between the first and the third peak in the EPR spectrum (2a(N)) was measured to monitor the polarity of the spin probe's microenvironment. Moreover, the ratio between the signal amplitudes of the second and the third peak (a/b ratio) was used to monitor the mobility of the spin probe in a certain formulation. Thus, by calculating 2a(N) and the a/b ratio of the EPR spectra it was possible to determine a potential release of the spin probe from different formulations into gastric juice. It was found that oily and surface-active vehicles (Miglyol, Cremophor RH-40, and GMO) were more suitable to protect a lipophilic compound from being released within a gastric environment than PEG 400. Our results demonstrate that EPR spectroscopy seems to be a promising tool in early preformulation experiments to monitor the release of spin probes from formulations of different nature. This kind of experiment can be of value for the optimization of exploratory formulations.

Chemistry, Pharmaceutical↗

PubMed2000

Potential inhibitory effects of formulation ingredients on intestinal cytochrome P450.

The use of common formulation ingredients (categorized into six groups) for preclinical animal studies has been assessed with respect to cytochrome P450 (CYP) inhibition, specifically CYP3A inhibition, in expressed human CYP3A4, human liver microsomes, dog- and cynomolgus monkey intestinal microsomes. Results indicated a wide range of inhibition potentials and there appeared to be species differences with inhibition of CYP3A activity. Generally, greater inhibition of CYP3A activity was observed with amphiphilic ingredients (for example mixed micellar solutions, Tween 80, and oleic acid). From the data presented, it can be predicted that the majority of the ingredients tested would not have a significant impact on the potential inhibition, by the formulation, on any apparent first pass metabolism in the intestinal tract for new drug entities being tested in the preclinical environment. However a number of common ingredients will require further investigation based on the estimated concentration within the gastrointestinal tract.

Animals↗

PubMed2000

The impact of co-solvents and the composition of experimental formulations on the pump rate of the ALZET osmotic pump.

The water-miscible co-solvents polyethylene glycol 400 (PEG400), N-methyl-2-pyrrolidone (NMP), and N, N-dimethylacetamide (DMA) exhibit the potential to increase the solubility of poorly water-soluble compounds and therefore they represent promising vehicles for compound delivery using osmotic pumps in early discovery experiments. Thus, the selected co-solvents were investigated for their compatibility with the interior of ALZET osmotic pumps. Moreover, 1-week pumps were filled with mixtures of either the co-solvents with water (60:40, v/v), with neat PEG400, or with PEG400/water mixtures of different concentrations. It was determined whether the composition of an experimental formulation could have an impact on the overall pump rate with 14C-mannitol being used as the model compound. It was found that neat PEG400 was compatible with the reservoir material, whereas NMP and DMA were tolerable only in aqueous solutions up to 60%. PEG400, NMP, and DMA mixtures with water (60:40) resulted in release rates comparable to those of water and PEG400/water mixtures of lower co-solvent concentration. Moreover, as demonstrated using the various PEG400/water mixtures, the amount of co-solvent in the formulation had no significant impact on the overall release profile. By contrast, the use of neat PEG400 resulted in a significant decrease in the pump rate.

Drug Delivery Systems↗

PubMed2000

Metabolism of levormeloxifene, a selective oestrogen receptor modulator, in the Sprague-Dawley rat, Cynomolgus monkey and postmenopausal woman.

1. The metabolic fate of levormeloxifene in the Sprague-Dawley rat, Cynomolgus monkey and postmenopausal volunteer has been investigated. 2. Two doses of [14C]levormeloxifene, 0.7 and 50 mg/kg, were given to the male and female rat and monkey, and a single 20-mg dose to the postmenopausal volunteer. 3. The primary route of excretion in all three species was the faeces. Metabolism was similar in all three species, with demethylation forming the major metabolite in the rat and postmenopausal volunteer. One of the major metabolites in the monkey involved an oxidative ring opening of a pyrrole ring. 4. The main site of metabolism of levormeloxifene is the liver and the majority of the drug and its metabolites is excreted via the faecal route. Metabolic pathways appear to be similar in the three species studied.

Administration, Oral↗

PubMed2000

Metabolism, disposition, excretion, and pharmacokinetics of levormeloxifene, a selective estrogen receptor modulator, in the rat.

The tissue distribution, pharmacokinetics, metabolism, and excretion of the selective estrogen receptor modulator levormeloxifene have been investigated after oral administration of [(14)C]-levormeloxifene to male and female Sprague-Dawley rats. The quantitative distribution of radiolabeled levormeloxifene and/or metabolites was confirmed by whole body autoradiography. Levormeloxifene was absorbed from the gastrointestinal tract and was widely distributed into tissues, with peak radioactive concentrations generally being observed 4 h after administration in the intestine, liver, lung, kidney, spleen, pancreas, adrenals, and ovary (females). Fecal elimination was the major excretion route of radioactivity. In a separate pharmacokinetic study, plasma C(max) was generally observed 6 h after dose administration and the half-life of elimination was long (24 h) and a doubling in dose resulted in an approximate doubling in exposure. The majority of the drug was excreted as norlevormeloxifene; the 7-desmethyl metabolite of levormeloxifene, via the formation of phase II metabolites (glucuronides) and excretion into the bile. Unchanged drug was also excreted, mainly from 0 to 24 h, and accounted for about 6 to 12% of the dose. Together these two components accounted for approximately 50% of the radioactivity excreted. Additional metabolites isolated and identified by liquid chromatography-tandem mass spectrometry, and accounting for 1 to 5% of the excreted radioactivity in rat feces during the first 24 h, included two monohydroxylevormeloxifene species, a pyrrolidinone ring-opened metabolite of levormeloxifene, and desmethylnorlevormeloxifene.

Animals↗

PubMed2000

Selective and potent inhibition of human CYP2C19 activity by a conformationally targeted antipeptide antibody.

A conformationally targeted anti-peptide antibody was produced by immunizing a rabbit with a cyclized peptide corresponding to a loop region of human CYP2C19 (residues 250-261). In an enzyme-linked immunosorbent assay, the antibody bound strongly to recombinant CYP2C19 and poorly to recombinant CYP2C8, CYP2C9, and CYP2C18. In immunoblotting studies, the antibody bound strongly to recombinant CYP2C19 and weakly to recombinant CYP2C8. No binding to recombinant CYP1A2, CYP2C9, CYP2C18, CYP2D6, CYP2E1, and CYP3A4 was detected. In immunoinhibition experiments, the anti-peptide antibody targeted against CYP2C19 potently inhibited (S)-mephenytoin 4'-hydroxylase activity of human hepatic microsomal fraction (>90%). It had no appreciable effect on ethoxyresorufin O-deethylase (CYP1A2), tolbutamide methyl-hydroxylase (CYP2C9), dextromethorphan O-demethylase (CYP2D6), 4-nitrophenol hydroxylase (CYP2E1), or testosterone 6beta-hydroxylase (CYP3A4) activity of human hepatic microsomal fraction. However, large amounts of purified IgG fractions were able to inhibit up to 35% of paclitaxel 6alpha-hydroxylase (CYP2C8) activity. In conclusion, we have demonstrated that an anti-peptide antibody targeted against residues 250 to 261 of human CYP2C19 selectively and potently inhibited CYP2C19 activity of human hepatic microsomal fraction.

Amino Acid Sequence↗

PubMed2000

Structure-function analysis of human CYP3A4 using a specific proinhibitory antipeptide antibody.

An anti-peptide antibody targeted against residues 253 to 269 of human CYP3A4 was produced that specifically and potently inhibited its activity in human hepatic microsomal fraction (>90%). The function of this region in P450 catalysis was investigated. Antibody binding to CYP3A4 was unable to affect the magnitude of the Type I spectrum on addition of testosterone. It also had no effect on the K(m) of the enzyme for testosterone, but it did cause a marked decrease in V(max) (>90%) of testosterone 6 beta-hydroxylation. There was no change in the ability of the antibody-bound CYP3A4 to form the steady-state level of the enzymatically or chemically reduced P450-CO complex or even the steady-state level of the dioxy-ferrous complex during testosterone metabolism, but the oxidation of NADPH by CYP3A4 in the presence of antibody was 60% that of CYP3A4 in the absence of antibody. The binding of the antibody also resulted in potent inhibition of cumene hydroperoxide-supported testosterone 6 beta-hydroxylase activity of human liver microsomal fraction (>90%). Our conclusion is that the loop region targeted in CYP3A4 is not involved in substrate binding, in reductase binding, in the transfer of the first or second electron from the reductase to CYP3A4, or in the binding of molecular oxygen. We speculate that antibody binding to CYP3A4 inhibits enzyme activity by destabilizing the ternary hydroperoxo complex, by interfering with the second proton transfer, and/or by interfering with the conformational changes that are suggested to be induced by substrate binding.

Amino Acid Sequence↗

PubMed1998

The formation of 1-hydroxymethylnaphthalene and 6-hydroxymethylquinoline by both oxidative and reductive routes in Cunninghamella elegans.

Extraction of medium after incubation of the fungus, Cunninghamella elegans, with 0.03% (w/v) 1-methylnaphthalene produced mainly 1-hydroxymethylnaphthalene together with some 1-naphthoic acid and hydroxynaphthoic acid. Higher concentrations of substrate were inhibitory to biotransformation. Similar incubations with 1-naphtoic acid as substrate resulted in reduction of the carboxyl group to give 1-hydroxymethylnaphthalene. When 6-methylquinoline was used, the main product was 6-hydroxymethylquinoline but also some quinoline-6-carboxylic acid and some 6-methylquinoline-N-oxide were identified. In a 2-l fermenter 2.5 g substrate was transformed in 324 h. The 6-hydroxymethylquinoline was also produced by reduction of quinoline-6-carboxylic acid by the organism.

Biodegradation, Environmental↗