Relationship between difference spectra and metabolism. Barbiturates, drug interaction and species difference

"Diabetic striatopathy": clinical presentations, controversy, pathogenesis, treatments, and outcomes

Diabetic striatopathy (DS) is a rare medical condition with ambiguous nomenclature. We searched PubMed database from 1992 to 2018 for articles describing hyperglycemia associated with chorea/ballism and/or neuroimages of striatal abnormalities. Descriptive analysis was performed on demographic/clinical characteristics, locations of striatal abnormalities on neuroimages, pathology findings, treatment strategies, and outcomes. In total, 176 patients (male:female = 1:1.7) were identified from 72 articles with mean age 67.6 ± 15.9 (range, 8-92). Among them, 96.6% had type 2 DM with 17% being newly diagnosed. Average blood glucose and glycated hemoglobin concentrations were 414 mg/dL and 13.1%, respectively. Most patients (88.1%) presented with hemichorea/hemiballism. Isolated putamen and combined putamen-caudate nucleus involvements were most common on neuroimaging studies with discrepancies between CT and MRI findings in about one-sixth of patients. Unilateral arm-leg combination was the most frequent with bilateral chorea in 9.7% of patients. Chorea and imaging anomalies did not appear concomitantly in one-tenth of patients. Successful treatment rates of chorea with glucose-control-only and additional anti-chorea medications were 25.7% and 76.2%, respectively, with an overall recurrence rate being 18.2%. The most commonly used anti-chorea drug was haloperidol. To date, four out of six pathological studies revealed evidence of hemorrhage as a probable pathogenesis.

Essential role of singlet oxygen species in cytochrome P450-dependent substrate oxygenation by rat liver microsomes

Previously, we reported that singlet oxygen (1O2) was involved in rat liver microsomal P450-dependent substrate oxygenations in such reactions as p-hydroxylation of aniline, O-deethylation of 7-ethoxycoumarin, omega- and (omega-1)-hydroxylations of lauric acid, O-demethylation of p-nitroanisole, and N-demethylation of aminopyrine. In order to confirm the generality of 1O2 involvement, we have further investigated which kinds of reactive oxygen species (ROS) are formed during P450-dependent substrate oxygenation in microsomes. We examined CYP2E1-dependent hydroxylation of p-nitrophenol in rat liver microsomes in the presence of some ROS scavengers, because CYP2E1 has been reported to predominantly generate ROS in the hepatic microsomes and to relate with the oxidative stress in the body. The addition of 1O2 quenchers, beta-carotene, suppressed the hydroxylation of p-nitrophenol. Furthermore, a nonspecific P450 inhibitor, SKF525A, and a ferric chelator, deferoxamine, both suppressed the hydroxylation. No other ROS scavengers such as superoxide dismutase (SOD), catalase, or mannitol altered the reaction. 1O2 was detectable during the reaction in the microsomes as measured by an electron spin resonance (ESR) spin-trapping method when 2,2,6,6-tetramethyl-4-piperidone (TMPD) was used as a spin-trapping reagent. The 1O2 was quenched by additions of beta-carotene, p-nitrophenol, and SKF525A. The reactivity of p-nitrophenol and 1O2 correlated linearly with its hydroxylation rate in the microsomes. On the basis of these results, we conclude that 1O2 contributes to the p-nitrophenol hydroxylation in rat liver microsomes, by adding a new example of 1O2 involvement in the CYP2E1-dependent substrate oxygenations.

Inhibition of lignocaine metabolism by beta-adrenoceptor antagonists in rat and human liver microsomes

1. The inhibition of lignocaine metabolism by beta-adrenoceptor antagonists (beta-blockers) was investigated in rat and human liver microsomes. 2. Thirteen beta-blockers (concn. 50 microM) incubated with substrate (4.27 microM) and rat liver microsomes, showed a strong linear correlation between percentage inhibition of lignocaine metabolism and the distribution coefficients of the beta-blockers (r2 = 0.842, P less than 0.001). Similar results for four beta-blockers were obtained using human liver microsomes. 3. In rat liver, which metabolizes lignocaine by aromatic hydroxylation and N-dealkylation, inhibition was selective for the former route. Human liver microsomes metabolize the drug mainly by N-dealkylation and inhibition of this pathway was observed. 4. Liver microsomes from rats treated orally with beta-blockers (0.34 nmol kg per day for 5 days) showed impaired metabolism of lignocaine and impaired formation of 3-hydroxy-lignocaine, despite the absence of significant residues of beta-blocker. 5. 14C-Propanolol was bound irreversibly to rat liver microsomal protein; binding accounted for 4.1 +/- 0.3% (n = 4) dose after 30 min incubation. Exclusion of co-factors and addition of glutathione (GSH, 1 mM) lowered binding by 96% and 70%, respectively. Propanolol inhibited lignocaine metabolism to the same extent in the presence or absence of GSH. The 14C-propanolol bound to liver microsomes from propranolol-treated rats decreased in parallel with inhibition of lignocaine metabolism at 18 to 48 h after pretreatment. 6. These studies indicate at least two mechanisms for the inhibition of lignocaine metabolism by beta-blockers, namely, a 'lipid solubility hypothesis', where the effects may be related to the unchanged drug and a 'metabolite hypothesis', with the possible involvement of an irreversibly bound species.

Prediction of hepatic first-pass metabolism and plasma levels following intravenous and oral administration of barbiturates in the rabbit based on quantitative structure-pharmacokinetic relationships

Based on the concept of physiological pharmacokinetics, the hepatic first-pass metabolism and plasma levels following intravenous and oral administration of barbiturates in the rabbit was predicted based on the relationships between principle kinetic parameters and lipophilicity (chloroform-water partition coefficient). Good log-log linear relationships between kinetic parameters and lipophilicity were obtained for the seven barbiturates examined. The values of correlation coefficient were improved slightly by using the corrected values for partition coefficients of nonionic molecules in the cases of principle parameters such as drug-protein and drug-blood cell affinity, intrinsic hepatic clearance, and unbound volume of distribution. There was also a good linear relationship between absorption rate constant (mean absorption time) and lipophilicity. The mean hepatic transit time was negligible for the most lipophilic drug (hexobarbital) examined; this suggests that the mean absorption time for these barbiturates does reflect the absorption process. The available fraction in relation to hepatic first-pass metabolism was well predicted from the lipophilicity by both well-stirred and parallel-tube models, and the difference in the values predicted by both models was minimal. There were good relationships between predicted and observed values for plasma levels after intravenous and oral administration, except for two (cyclobarbital and phenobarbital) of the seven drugs used. The great difference between predicted and observed values for these two drugs was considered due to substituent effects in liver metabolism.

Biotransformation of terodiline. III. Opposed stereoselectivity in the benzylic and aromatic hydroxylations in rat liver microsomes

1. Terodiline (N-tert-butyl-4,4-diphenyl-2-butylamine) is a racemic drug with anticholinergic and/or calcium antagonistic activity, which is subject to renewed interest as a potential remedy for urinary incontinence. As part of the current investigations on terodiline, the metabolism of its enantiomers is being investigated. 2. The metabolism of the enantiomers of terodiline in rat liver microsomes is slow, as for the racemate, though the S-enantiomer is metabolized more rapidly than its optical antipode. Phenobarbitone pretreatment of the rats enhances the metabolism with a marked increase in the conversion of the S-enantiomer. 3. While aromatic p-hydroxylation greatly exceeds benzylic oxidation in the metabolism of R-terodiline, this situation is reversed in the metabolism of S-terodiline. Moreover, the rate of aromatic p-hydroxylation of racemic terodiline follows that of R-terodiline, while the rate of benzylic hydroxylation of racemic terodiline follows that of S-terodiline. Phenobarbital pretreatment of the rats had little or no effect on aromatic p-hydroxylation but markedly increased benzylic oxidation. 4. Separation of the mixture of p-hydroxylated metabolites into diastereomeric pairs showed that their composition is highly dependent on which form of terodiline is used as substrate. 5. The results from the study are compatible with the participation of multiple forms of cytochrome P-450 enzymes.

Stereoselective high-affinity binding of 3H-alaproclate to membranes from rat cerebral cortex

The binding of 3H-alaproclate, a selective 5-hydroxytryptamine uptake inhibitor, to membranes prepared from the rat cerebral cortex was investigated by a filtration technique. It was found that 3H-alaproclate bound with high affinity to three or four different sites and to one low affinity site. The binding to two of these sites was displaceable by 1 microM proadifen (SKF 525A), an inhibitor of drug metabolism. From iterative nonlinear regression analysis the KD-values of these sites were calculated to about 1 and 28 nM and the Bmax values 1.5 and 19 pmol/g wet tissue, respectively. The high affinity binding that was not displaceable by proadifen but by 10 microM alaproclate had KD-values of 1 nM and 6 nM and Bmax-values of 0.4 and 2 pmol/g wet tissue. The low affinity binding that was not displaceable by proadifen had a KD-value of about 200 nM and a Bmax-value of about 90 pmol/g tissue. The possible relationship between the proadifen sensitive high affinity binding of 3H-alaproclate and the brain cytochrome P-450 is discussed.

Substrate-induced spectral changes in human normal and chronic myeloid leukemic granulocytes

Several drugs/chemicals were allowed to interact with the cytochrome P-450 dependent mixed function oxidase system in the postmitochrondrial supernatant fractions of Ficoll-Hypaque-separated granulocytes from human normal subjects and patients with chronic myeloid leukemia. The substrate-induced spectral changes were followed by recording the difference spectra. Compounds conventionally classified as type I and type II substrates, on addition to S1 fractions of both normal and leukemic granulocytes, caused spectral changes that were reverse to those reported for the rat liver microsomes. Aminopyrine, phenobarbital, and Tween 80 evoked a reverse type I spectral change with a peak at 420-430 nm and a trough at 380-400 nm, whereas aniline and pyridine induced a modified type I (a reverse type II) spectral change characterized by a peak at 408 nm and a trough at 421 nm. These changes were found to be quantitatively proportional to the amounts of substrate added. However, the magnitude of the peaks and troughs was considerably less in the S1 fraction of the leukemic granulocytes. Correspondingly, total heme content was significantly decreased in S1 fractions of CML granulocytes as compared to similar fractions of normal granulocytes.

Spectral changes resulting from the interaction of some N-alkyl nitrosamines and rat liver microsomes

Dimethyl (DMN) and diethyl nitrosamine (DEN) do not give characteristic spectral changes upon interaction with rat liver microsomes, while dipropyl (DPN) and dibutyl (DBN) nitrosamine cause type I spectral changes. The spectral binding constant is 100 mM for DPN and 1.17 mM for DBN. The maximal spectral change is 3.2 X 10(6) and 1.0 X 10(6) absorbance units per milligram protein for DPN and DBN respectively.

Metabolism of metoprolol in the rat in vitro and in vivo

1. Metoprolol was metabolized in rat liver microsomes in vitro by O-demethylation with subsequent oxidation and by aliphatic hydroxylation of the methoxy-ethyl substituent and by oxidative deamination of the propanolisopropylamine side-chain. The same routes of metabolism in the rat in vivo were revealed from urinary metabolites. Eight metabolites were identified by g.l.c.-mass spectrometry by comparison with synthetized reference compounds. 2. Metoprolol binds to cytochrome-P-450 eliciting a type I difference spectrum with KS = 23 +/- 2-0 muM. The apparent Michaelis-Menten constant Km = 39 +/- 4-0 muM and Vmax = 1-28 +/- 0-22 nmol/mg protein X min were not significantly affected by pre-treatment of the rats with metoprolol or phenobarbital. Metoprolol pre-treatment had no effect on the cytochrome-P-450 level in the microsomes nor on the rate of metabolism of four standard substrates. Phenobarbital increased the cytochrome P-450 as expected. 3. Four metabolites representing the three main routes of metabolism were quantitatively determined after metabolism with rat liver microsomes and compared with the urinary levels of the same compounds. The same major metabolites were found in vitro and in vivo. The total amount of metabolites was not influenced by pre-treatment with metoprolol or phenobarbital. The relative amounts of the three main metabolites were slightly affected by pre-treatment.