Significant Metabolic Interactions Research Articles

Influence of a Nigerian honey on CYP3A4 biotransformation of quinine in healthy volunteers.

Some studies, howbeit with conflicting reports, have suggested that consumption of honey has a potential to modulate drug metabolizing enzymes which may result in a honey-drug interaction. Numerous studies have established that honey varies in composition, influenced by the dominant floral, processing and environmental factors. Thus, variation in honey composition may be a contributing factor to the controversial results obtained. No previous drug interaction study has been carried out with any honey from Africa. CYP 3A4 is an important enzyme in drug metabolism studies as it is involved in the metabolism of over 50% of drugs in clinical use and quinine remains very relevant in malaria treatment in the tropics, and we therefore determined whether there is potential drug interaction between a Nigerian honey and quinine, a drug whose metabolism to 3-hydroxyquinine is mediated majorly by CYP3A4. In a three-phase randomized crossover study with a washout period of 2weeks between each treatment phase, ten (10) healthy volunteers received quinine sulphate tablet (600mg single dose) alone (phase 1) or after administration of 10ml of honey (Phase 2) and 20mL of honey (Phase 3) twice daily for seven (7) days. Blood samples were collected at the 16th hour post-quinine administration in each phase, and quinine and its major metabolite, 3-hydroxyquinine, were analysed using a validated HPLC method. After scheduled doses of honey, the mean metabolic ratios of quinine (3-hydroxyquinine/quinine) increased by 24·4% (with 10mL of honey) and reduced by 23·9% (with 20mL of honey) when compared to baseline. These magnitudes of alteration in the mean metabolic ratios were not significant (P>0·05; Friedman test). The geometric mean (95% CI) for the metabolic ratio of quinine before and after honey intake at the two dose levels studied was 0·82 (0·54, 1·23) and 1·29 (0·96, 1·72), respectively, and were also not significant (P=0·296 and 0·081 respectively; Student's t-test). This is a pioneer study on the effect of Nigerian/African honey on quinine metabolism. Thefindings indicated that low and high doses of honey did not significantly affect metabolism of quinine to 3-hydroxyquinine. This suggests that CYP3A4 activity is not significantly altered following low or high dose of honey, as CYP3A4 has been reported to be responsible for the conversion of quinine to 3-hydroxyquinine. In conclusion, the outcome of this study suggests that there may be no potential significant metabolic interaction between Nigerian honey and quinine administration.

Inhibition of Magnolol and Honokiol on Cytochrome P450 Enzymes in Rat and Human Liver Microsomes

ObjectiveThe purpose of this work is to evaluate the in vitro inhibitory effect of magnolol (MN) and honokiol (HN) on rat/human cytochrome P450 (CYP) enzymes (1A2/1A2, 2D/2D6, 3A/3A4, 2E1/2E1, and 2C/2C9). MethodsRat liver microsomes (RLM) and human liver microsomes (HLM) were used as the enzyme sources. After the probe substrate of each CYP isoforms was co-incubated individually with MN or HN in RLM or HLM, the metabolite production of each probe substrate in RLM and HLM incubation medium was determined and used to evaluate the activity of corresponding CYP isoforms. ResultsMN inhibited rat CYP1A2 and human CYP3A4 with the IC50 values of 10.0 and 56.2 μmol/L, respectively. HN inhibited rat CYP1A2 and CYP2E1, human CYP1A2 and CYP3A4 with the IC50 values of 12.1, 12.6, 17.8, and 43.9 μmol/L, respectively. ConclusionHN is a moderate or weak inhibitor of human CYP1A2. Both MN and HN are weak or non inhibitors of the other tested human CYP isoforms. The results suggest that no significant metabolic interaction seems likely to occur when the substrate drugs of CYP isoforms tested in the present work are co-administered with MN and HN.

The metabolic and ecological interactions of oxalate-degrading bacteria in the Mammalian gut.

Oxalate-degrading bacteria comprise a functional group of microorganisms, commonly found in the gastrointestinal tract of mammals. Oxalate is a plant secondary compound (PSC) widely produced by all major taxa of plants and as a terminal metabolite by the mammalian liver. As a toxin, oxalate can have a significant impact on the health of mammals, including humans. Mammals do not have the enzymes required to metabolize oxalate and rely on their gut microbiota for this function. Thus, significant metabolic interactions between the mammalian host and a complex gut microbiota maintain the balance of oxalate in the body. Over a dozen species of gut bacteria are now known to degrade oxalate. This review focuses on the host-microbe and microbe-microbe interactions that regulate the degradation of oxalate by the gut microbiota. We discuss the pathways of oxalate throughout the body and the mammalian gut as a series of differentiated ecosystems that facilitate oxalate degradation. We also explore the mechanisms and functions of microbial oxalate degradation along with the implications for the ecological and evolutionary interactions within the microbiota and for mammalian hosts. Throughout, we consider questions that remain, as well as recent technological advances that can be employed to answer them.

Respiratory effects of diazepam/methadone combination in rats: A study based on concentration/effect relationships

BackgroundMethadone may cause respiratory depression and fatalities. Concomitant use of benzodiazepines in methadone-treated patients for chronic pain or as maintenance therapy for opiate abuse is common. However, the exact contribution of benzodiazepines to methadone-induced respiratory toxicity remains debatable. MethodsWe investigated the respiratory effects of the combination diazepam (20mg/kg)/methadone (5mg/kg) in the rat, focusing on methadone concentration/effect relationships. Respiratory effects were studied using arterial blood gases and whole-body plethysmography. Plasma concentrations of both R- and S-methadone enantiomers were measured using high-performance liquid chiral chromatography coupled to mass spectrometry. To clarify mechanisms of diazepam/methadone interaction, methadone metabolism was investigated in vitro using rat liver microsomes. ResultsDiazepam/methadone co-administration significantly increased methadone-related effects on inspiratory time (p<0.001) but did not significantly alter the other respiratory parameters when compared with methadone alone, despite significant increase in the area under the curve of plasma R-methadone concentrations measured during 240min (p<0.05). Diazepam/methadone co-incubation with microsomes in vitro resulted in a significant inhibition of methadone metabolism (p<0.01), with 50%-inhibitory diazepam concentrations of 25.02±0.18μmol/L and 25.18±0.23μmol/L for R- and S-methadone, respectively. ConclusionWe concluded that co-administration of high-doses of diazepam and methadone in rats is not responsible for additional respiratory depression in comparison to methadone alone, despite significant metabolic interaction between the drugs. In humans, although our experimental data may suggest the relative safety of benzodiazepine/methadone co-prescription, physicians should remain cautious as other underlying conditions may enhance this drug–drug interaction.

The In Vitro Inhibition of Human CYP1A2, CYP2D6 and CYP3A4 by Tetrahydropalmatine, Neferine and Berberine

The purpose of this study was to investigate the in vitro inhibition potential of the three purified herbal constituents tetrahydropalmatine (Tet), neferine (Nef) and berberine (Ber) towards recombinant human CYP1A2, CYP2D6 and CYP3A4 metabolic activities. In vitro incubations were performed with phenacetin, dextromethorphan and testosterone, respectively, as CYP substrates and their metabolites were determined by validated HPLC methods. Positive control inhibitors were run for each CYP in all incubation series. Inhibition was expressed by IC₅₀ values. All herbal constituents demonstrated some, but variable, inhibition potencies towards the investigated CYP enzymes. CYP2D6 was the most sensitive for inhibition and then mainly by Tet and Ber with IC₅₀ values of 3.04 ± 0.26 µM and 7.40 ± 0.36 µM, respectively. CYP3A4 and especially CYP1A2 were inhibited to a much smaller extent by all constituents. Neferine showed the lowest overall interaction potential towards the CYP enzymes investigated. The CYP inhibition potential for the purified constituents could be related to their chemical structures. No clinical significant metabolic interaction seems likely to occur between the CYP enzymes and herbal constituents tested, with a possible exception for the CYP2D6 inhibition by Tet and Ber.

A five-probe drug cocktail for phenotyping of CYP isozymes with ?high-throughput? LC-MS method

Background This study was performed to validate a five-probe drug cocktail, caffeine, tolbutamide, omeprazole, debrisoquine and midazolam, for simultaneous phenotyping of CYP1A2, 2C9, 2C19, 2D6 and 3A activities. Methods Sixteen healthy male Chinese subjects underwent four study sessions in a cross-over manner, during which they received single oral doses of 500mg tolbutamide (regimen I), 20mg debrisoquine (regimen II), and 10mg caffeine+40mg omeprazole+3.75mg midazolam (regimen III, negative interaction among these three drugs documented in the literature) alone, or a combination of the five drugs (regimen IV). Two blood samples at 2 and 3h and urine at 0–6 and 6–12 h post-dosing were collected. The concentrations of each probe drug and its metabolite were determined by a LC-MS method with one extraction procedure and rapid turn-around time. Results The phenotypic measurements for each enzyme after separate or combined administration are shown below: (see Table) Conclusion The administration of the five-drug cocktail did not result in any significant metabolic interactions. Therefore we conclude that this cocktail can be utilized for simultaneous determination of CYP1A2, 2C9, 2C19, 2D6 and 3A activities in human subjects. In view of the easy availability of these probe drugs in many countries and the relatively “high-throughput” assay, this method may offer a useful approach for pharmacogenetic and drug interaction studies. Clinical Pharmacology & Therapeutics (2005) 77, P35–P35; doi: 10.1016/j.clpt.2004.12.027 CYP Phenotypic index Regimen I/II/III Regimen IV (cocktail) P (t-test) 1A2 paraxathine/caffeine 0.60 ± 0.42 0.69 ± 0.35 0.96 2C9 (hydroxytolbutamide + carboxytolbutamide)/tolbutamide 1084 ± 620 1176 ± 669 0.12 2C19 5-hydroxyomeprazole/omeprazole 0.81 ± 0.43 0.88 ± 0.43 0.42 2D6 4-hydroxydebrisoquine/debrisoquine 0.62 ± 0.56 0.54 ± 0.51 0.11 3A 1′-hydroxymidazolam/midazolam 0.55 ± 0.19 0.53 ± 0.27 0.83

Olanzapine

Multicentre trials in patients with schizophrenia confirm that olanzapine is a novel antipsychotic agent with broad efficacy, eliciting a response in both the positive and negative symptoms of schizophrenia. Compared with traditional antipsychotic agents, olanzapine causes a lower incidence of extrapyramidal symptoms and minimal perturbation of prolactin levels. Generally, olanzapine is well tolerated. The pharmacokinetics of olanzapine are linear and dose-proportional within the approved dosage range. Its mean half-life in healthy individuals was 33 hours, ranging from 21 to 54 hours. The mean apparent plasma clearance was 26 L/h, ranging from 12 to 47 L/h. Smokers and men have a higher clearance of olanzapine than women and nonsmokers. After administering [14C]olanzapine, approximately 60% of the radioactivity was excreted in urine and 30% in faeces. Olanzapine is predominantly bound to albumin (90%) and alpha 1-acid glycoprotein (77%). Olanzapine is metabolised to its 10- and 4'-N-glucuronides, 4'-N-desmethylolanzapine [cytochrome P450 (CYP) 1A2] and olanzapine N-oxide (flavin mono-oxygenase 3). Metabolism to 2-hydroxymethylolanzapine via CYP2D6 is a minor pathway. The 10-N-glucuronide is the most abundant metabolite, but formation of 4'-N-desmethylolanzapine is correlated with the clearance of olanzapine. Olanzapine does not inhibit CYP isozymes. No clinically significant metabolic interactions were found between olanzapine and diazepam, alcohol (ethanol), imipramine, R/S-warfarin, aminophylline, biperiden, lithium or fluoxetine. Fluvoxamine, an inhibitor of CYP1A2, increases plasma concentrations of olanzapine; inducers of CYP1A2, including tobacco smoke and carbamazepine, decrease olanzapine concentrations. Orthostatic changes were observed when olanzapine and diazepam or alcohol were coadministered. Pharmacodynamic interactions occurred between olanzapine and alcohol, and olanzapine and imipramine, implying that patients should avoid operating hazardous equipment or driving an automobile while experiencing the short term effects of the combinations. Individual factors with the largest impact on olanzapine pharmacokinetics are gender and smoking status. The plasma clearance of olanzapine generally varies over a 4-fold range, but the variability in the clearance and concentration of olanzapine does not appear to be associated with the severity or duration of adverse effects or the degree of efficacy. Thus, dosage adjustments appear unnecessary for these individual factors. However, dosage modification should be considered for patients characterised by a combination of factors associated with decreased oxidative metabolism, for example, debilitated or elderly women who are nonsmokers.

The role of triphasic levonorgestrel in oral contraception: a review of metabolic and hemostatic effects.

Epidemiological studies suggesting a possible association between the use of combined oral contraceptives and an increased risk of cardiovascular disease have led to extensive investigations into the effect of oral contraceptives on lipid and carbohydrate metabolism, and on hemostasis. Since this association was originally suggested, the steroid dose in oral contraceptives has been significantly reduced and new progestogens have been developed. Also, triphasic formulations have been introduced which offer a well-balanced estrogen/progestogen ratio, allowing a further reduction in the progestogen dose per cycle, and thus helping to minimize unwanted metabolic and hemostatic effects. The metabolic interactions of triphasic levonorgestrel, the first triphasic formulation to be introduced, have received particular attention. Lipid metabolism appears to be largely unaffected by triphasic levonorgestrel, most studies reporting no significant change in high- (HDL-C) or low-density lipoprotein-cholesterol (LDL-C) levels. Several studies have reported a decrease in the lipoprotein subfraction HDL2-C levels, but in most cases measurements of the LDL-C/HDL-C and apolipoprotein A-1/B ratios reveal no clinically significant effects. Concerning lipids, most studies suggest that triphasic levonorgestrel has less metabolic impact than the monophasic formulation. In common with all currently available oral contraceptives, triphasic levonorgestrel appears to have some effect on carbohydrate metabolism. The study results vary, however; some investigators have found an impairment of glucose tolerance, whereas others have not detected any significant effect. Compared with lipid and carbohydrate metabolism, fewer studies have investigated the effect of triphasic levonorgestrel on hemostasis. In common with all estrogen-containing oral contraceptives, levonorgestrel appears to stimulate some procoagulant activity, elevating the levels of factors VII and X, and fibrinogen. However, the effect of triphasic levonorgestrel appears to be balanced, with most studies reporting a corresponding increase in anti-coagulant-fibrinolytic activity. Although most of the studies reviewed here reported some statistically significant metabolic interactions, many authors comment that the changes are probably not clinically relevant in terms of an altered risk of cardiovascular disease. The true risk of vascular disease associated with modern low-dose oral contraceptives remains to be confirmed when sufficient epidemiological data eventually become available.

Calorimetric analysis of the oxidative influence of granulocytes on erythrocytes

The heat production of human granulocytes activated with phorbol-12-myristate-13-acetate was determined in the absence and presence of erythrocytes. The heat produced by the erythrocytes agreed with the enthalpy change calculated, assuming that glucose oxidation had occurred. Reaction of the heme with CO almost completely prevented the metabolic response of the erythrocytes. The primary site of the metabolic activation for the erythrocytes in response to oxidant stress, exerted by the toxic granulocyte metabolites, is presumed to be the heme group. The data obtained demonstrate that significant metabolic interactions occur between activated granulocytes and erythrocytes. The power evolution observed is explained in terms of glucose combustion.

Altered induction response of hepatic cytochrome P-450 to phenobarbital, 3-methylcholanthrene, and β-naphthoflavone in organotin-treated animals

The effects of tricyclohexyltin hydroxide on the induction of cytochrome P-450 in liver by phenobarbital, 3-methylcholanthrene and β-naphthoflavone were studied. A single dose of the organotin (15 mg/kg body wt) prevented the full extent of phenobarbital induction of cytochrome P-450 from occurring; this was the case whether tricyclohexyltin was given 48 hr preceding a single injection of phenobarbital, or administered simultaneously with the first of three daily doses of the drug. Elevation of hepatic heme oxygenase (EC 1.14.99.3) activity accompanied these changes in cytochrome P-450, but the induction of this enzyme was not affected by phenobarbital treatment. The induction of cytochrome P-448 by 3-methylcholanthrene and β-naphthoflavone was not affected to the same extent by a single injection of tricyclohexyltin, while heme oxygenase induction was less pronounced when these cytochrome P-448 inducers were given together with the organotin. The changes in cytochrome P-450 content and in its functional activity resulting from the various treatments were further examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of the microsomal fractions. The electrophoretic profiles illustrate clearly that the apoprotein moieties of the various cytochrome P-450 subspecies are affected to a considerable extent by treatment with tricyclohexyltin hydroxide alone, and staining in these bands was noticeably reduced even when phenobarbital was administered together with the organotin. In contrast, tricyclohexyltin failed to decreased the 3-methylcholanthrene- or β-naphthoflavone-induced cytochrome P-450 subspecies. These data suggest that significant metabolic interactions can occur from exposure to a combination of environmental chemicals and drugs resulting in an altered metabolism of heme and cytochrome P-450.

An evaluation of the metabolic interaction with myogenic vascular reactivity during blood flow autoregulation.

An attempt was made to evaluate the possible metabolic interaction with myogenic vascular reactivity during autoregulation of blood flow in sympathectomized cat skeletal muscle. This was done by studying the extent to which a purely myogenic response, elicited by a standardized 2 s vascular transmural pressure impulse stimulus was altered when mean arterial inflow pressure was varied in the range from 160 down to 40 mmHg. The observations were made during the steady state blood flows encountered at the different pressure levels. The data were corrected for the effects of physical factors inherent in altered basal vascular tone and intravascular pressure with the aid of a mathematical model for purely myogenic responses. The results demonstrated a flow dependent decline in myogenic vascular reactivity during reduction of arterial pressure, even in the range where blood flow was autoregulated quite effectively. This suggested a significant metabolic interaction with myogenic reactivity, an interpretation corroborated by a similar decline in myogenic reactivity found during more defined activation of the vascular metabolic control system by graded light muscle exercise. The fact that a significant metabolic interaction was revealed even at such minute flow changes that occur in the autoregulatory range indicates a high 'gain' in the metabolic feedback interacting, directly or indirectly, with myogenic mechanisms in local vascular regulation.