Selective inhibitory effects of suberosin on CYP1A2 in human liver microsomes.

Suberosin is a natural phytoconstituent isolated from Citropsis articulata, especially employed for its anticoagulant properties. Although metabolic studies assessing suberosin have been conducted, it is possible interactions with drugs and food have not yet been investigated. In the present study, we analyzed the selective inhibitory effects of suberosin on cytochrome P450 (CYP) enzymes using a cocktail probe assay. Various concentrations of suberosin (0-50 µM) were incubated with isoform-specific CYP probes in human liver microsomes (HLMs). We found that suberosin significantly inhibited CYP1A2-catalyzed phenacetin O-deethylation, exhibiting IC50 values of 9.39 ± 2.05 and 3.07 ± 0.45 µM with and without preincubation in the presence of ß-NADPH, respectively. Moreover, suberosin showed concentration-dependent, but not time-dependent, CYP1A2 inhibition in HLMs, indicating that suberosin acts as a substrate and reversible CYP1A2 inhibitor. Using a Lineweaver-Burk plot, we found that suberosin competitively inhibited CYP1A2-catalyzed phenacetin O-deethylation. Furthermore, suberosin showed similar inhibitory effects on recombinant human CYP1A1 and 1A2. In conclusion, suberosin may elicit herb-drug interactions by selectively inhibiting CYP1A2 during the concurrent administration of drugs that act as CYP1A2 substrates.

Gut microbiota and host Cyp450s co-contribute to pharmacokinetic variability in mice with non-alcoholic steatohepatitis: Effects vary from drug to drug.

INTRODUCTION: Pharmacokinetic variability in disease state is common in clinical practice, but its underlying mechanism remains unclear. Recently, gut microbiota has been considered to be pharmacokinetically equivalent to the host liver. Although some studies have explored the roles of gut microbiota and host Cyp450s in drug pharmacokinetics, few have explored their effects on pharmacokinetic variability, especially in disease states. OBJECTIVES: In this study, we aim to investigate the effects of gut microbiota and host Cyp450s on pharmacokinetic variability in mice with non-alcoholic steatohepatitis (NASH), and to elucidate the contribution of gut microbiota and host Cyp450s to pharmacokinetic variability in this setting. METHODS: The pharmacokinetic variability of mice with NASH was explored under intragastric and intravenous administrations of a cocktail mixture of omeprazole, phenacetin, midazolam, tolbutamide, chlorzoxazone, and metoprolol, after which the results were compared with those obtained from the control group. Thereafter, the pharmacokinetic variabilities of all drugs and their relations to the changes in gut microbiota and host Cyp450s were compared and analyzed. RESULTS: The exposures of all drugs, except metoprolol, significantly increased in the NASH group under intragastric administration. However, no significant increase in the exposure of all drugs, except tolbutamide, was observed in the NASH group under intravenous administration. The pharmacokinetic variabilities of phenacetin, midazolam, omeprazole, and chlorzoxazone were mainly associated with decreased elimination activity in the gut microbiota. By contrast, the pharmacokinetic variability of tolbutamide was mainly related to the change in the host Cyp2c65. Notably, gut microbiota and host Cyp450s exerted minimal effects on the pharmacokinetic variability of metoprolol. CONCLUSION: Gut microbiota and host Cyp450s co-contribute to the pharmacokinetic variability in mice with NASH, and the degree of contribution varies from drug to drug. The present findings provide new insights into the explanation of pharmacokinetic variability in disease states.

Acetaminophen Has Lipid Composition-Dependent Membrane Interactivity That Could Be Related to Nephrotoxicity but Not to Analgesic Activity and Hepatotoxicity.

OBJECTIVE: Although acetaminophen is one of the most widely used over-the-counter drugs, the mechanisms by which this classical drug exerts analgesic, hepatotoxic, and nephrotoxic effects remain unclear. We hypothesized that acetaminophen might act on cellular membranes of nerves, liver, and kidneys. In order to verify this hypothesis, we studied the interactivity of acetaminophen with biomimetic lipid bilayer membranes by comparing with structurally related phenacetin. METHODS: Liposomal membranes (unilamellar vesicles suspended in the buffer of pH 7.4) were prepared with phospholipids and cholesterol to mimic the membrane lipid composition of neuronal cells, hepatocytes, and nephrocytes. They were subjected to reactions with acetaminophen and phenacetin at clinically relevant concentrations, followed by measuring fluorescence polarization to determine their membrane interactivity to modify membrane fluidity. RESULTS: Acetaminophen and phenacetin interacted with neuro-mimetic and hepato-mimetic membranes to increase membrane fluidity at 10-100 µM. Both drugs were more effective in fluidizing hepato-mimetic membranes than neuro-mimetic membranes. Although the relative membrane-interacting potency was phenacetin >> acetaminophen in neuro-mimetic and hepato-mimetic membranes, such membrane effects conflicted with their relative analgesic and hepatotoxic effects. Acetaminophen and phenacetin strongly interacted with nephro-mimetic membranes to increase membrane fluidity at 2-100 µM and 0.1-100 µM, respectively. Phenacetin interacted significantly with nephro-mimetic membranes at lower concentrations (<2 µM) than acetaminophen, which was consistent with their relative nephrotoxic effects. CONCLUSION: In comparison with phenacetin, lipid composition-dependent membrane interactivity of acetaminophen could be related to nephrotoxicity but not to analgesic activity and hepatotoxicity.

Construction of DOX/APC co-loaded BiOI@CuS NPs for safe and highly effective CT imaging and chemo-photothermal therapy of lung cancer.

Recently, a variety of nanoparticles have been widely used as imaging agents or carriers for the diagnosis and therapy of lung cancer. However, their poor imaging effect, high toxicity, pro-inflammatory effect and ineffective treatment are still a great challenge. In this work, we reported a novel kind of BiOI@CuS nanoparticle to achieve safe and effective therapy of lung cancer by co-loading hydrochloric acid doxorubicin (DOX) and aspirin phenacetin and caffeine (APC). The nanoparticles can effectively relieve inflammatory reactions induced by photo-thermal therapy (PTT). In vitro and in vivo assays showed that DOX/APC co-loaded BiOI@CuS exhibited an effective chemo-photothermal comprehensive therapy effect and good CT imaging capability. Consequently, this multifunctional nanosystem provides a versatile and promising platform in the imaging and treatment of lung cancer in further applications.

Low-diluted Phenacetinum disrupted the melanoma cancer cell migration.

Dynamic and reciprocal interactions generated by the communication between tumor cells and their matrix microenvironment, play a major role in the progression of a tumor. Indeed, the adhesion of specific sites to matrix components, associated with the repeated and coordinated formation of membrane protrusions, allow tumor cells to move along a determined pathway. Our study analyzed the mechanism of action of low-diluted Phenacetinum on murine cutaneous melanoma process in a fibronectin matrix environment. We demonstrated a reduction of dispersed cell migration, early and for as long as 24 h, by altering the formation of cell protrusions. Moreover, low-diluted Phenacetinum decreased cell stiffness highly on peripheral areas, due to a disruption of actin filaments located just under the plasma membrane. Finally, it modified the structure of the plasma membrane by accumulating large ordered lipid domains and disrupted B16 cell migration by a likely shift in the balance between ordered and disordered lipid phases. Whereas the correlation between the excess of lipid raft and cytoskeleton disrupting is not as yet established, it is clear that low-diluted Phenacetinum acts on the actin cytoskeleton organization, as confirmed by a decrease of cell stiffness affecting ultimately the establishment of an effective migration process.

Bio-isosteric replacement of amide group with 1,2,3-triazole in phenacetin improves the toxicology and efficacy of phenacetin-triazole conjugates (PhTCs).

AIM: Inflammatory algesia and pyresia are common pathological consequences of physiological defense. Phenacetin introduced as effective analgesic anti-pyretic agent, was proscribed from therapeutic use because of associated systemic toxicity. The aim of the study was to evaluate the potency of 1,2,3-triazole conjugation in reducing toxicity and increasing efficacy of the phenacetin nucleus. MAIN METHODS: The amide bond implicated as the cause of phenacetin toxicity was bioisosterically replaced with 1,2,3-triazoles to yield a series of PhTCs(PhTC1, PhTC2 and PhTC3). The toxicology of the synthesized conjugates in reference to phenacetin was evaluated in accordance with OECD test guidelines 420, 425 and 407. For the purpose of evaluating anti-inflammatory potency carrageenan induced paw edema and croton oil induced ear edema models were evaluated. Anti-nociceptive efficacy was assessed using Eddy's hot plate and acetic acid induced writhing experimental models. For anti-pyretic efficacy, the conjugates were submitted to Brewer's yeast antipyretic assay. KEY FINDINGS: Toxicological examination of PhTCs in comparison to phenacetin revealed that, phenacetin treatment caused considerable nephrotoxicity and hepatotoxicity in experimental models PhTCs were devoid of such toxic manifestations. Results of pharmacological assays showed that the entire series of PhTCs possessed better anti-inflammatory, anti-nociceptive and anti-pyretic potential than phenacetin. Furthermore it was revealed that the pharmacological profile of PhTC1 with triazole substitution at para position of the phenol ring exhibited potency even better than that exhibited by the reference standards. CONCLUSION: Bioisosteric replacement of amide bond by 1,2,3-triazole in the phenacetin moiety yields conjugates with superior efficacy and diminished toxicity, thus opening neo avenues in treatment of inflammatory syndromes.

Influences of Corydalis decumbens on the Activities of CYP450 Enzymes in Rats with a Cocktail Approach.

Corydalis decumbens, a Traditional Chinese Medicine, has been widely used for the alternative and/or complementary therapy of hypertension, arrhythmias rheumatoid arthritis, sciatica, stroke, hemiplegia, paraplegia, and vascular embolism. The aim of this study was to determinate the potential effects of Corydalis decumbens on the five cytochrome P450 (CYP) enzyme activities (CYP1A2, CYP3A4, CYP2C9, CYP2C19, and CYP2D6) by cocktail approach. To evaluate whether concurrent use of Corydalis decumbens interferes with the effect of several prescription drugs, saline (control group) or Corydalis decumbens (XTW group) were administrated via gavage for 7 successive days. A probe cocktail solution (phenacetin, omeprazole, metoprolol, tolbutamide, and midazolam) was given 24 h after the last dose of saline or Corydalis decumbens. A specific and sensitive UHPLC-MS/MS method was validated for the determination of five substrates and their metabolites in control group and XTW group. Our results indicated that Corydalis decumbens could have inductive effects of CYP2C19 and inhibit the activities of CYP1A2 and CYP3A4. However, Corydalis decumbens had no significant influence on CYP2C9 and CYP2D6. The herb-drug interaction should require more attention by careful monitoring and appropriate drug dosing adjustments to the concurrent use of western medications which were metabolized by CYP1A2, CYP2C19, and CYP3A4 in human-Corydalis decumbens, Cytochrome P450, Cocktail, Pharmacokinetics, herb-drug interactions.

A UHPLC-MS/MS method coupled with liquid-liquid extraction for the quantitation of phenacetin, omeprazole, metoprolol, midazolam and their metabolites in rat plasma and its application to the study of four CYP450 activities.

Drug-drug interactions (DDIs) are thought to be associated with the inhibition of cytochrome P450 activities. The cocktail method with analysis of the metabolism of two or more probe drugs is used to determine CYP450 activities. In this study, we established a UHPLC-MS/MS method for simultaneous quantitation of four CYP450 probe drugs (phenacetin, omeprazole, metoprolol and midazolam) and their metabolites (acetaminophen, 5'-hydroxy omeprazole, α-hydroxy metoprolol and 1'-hydroxy midazolam) in rat plasma. Sample preparation by plasma protein precipitation was combined with a liquid-liquid extraction method. The separation was carried out on a ZORBAX Eclipse Plus C18 Rapid Resolution High Definition column with a gradient elution, using water containing 0.1% formic acid (A) and acetonitrile (B) in a run time of only 3.0 min. Detection was conducted with a 6420 series triple-quadrupole tandem mass spectrometer, using ESI in positive ion mode with multiple reaction monitoring (MRM). The calibration curves were linear over the concentration range 10-5000 ng/mL for phenacetin, omeprazole, metoprolol and midazolam, and 1-500 ng/mL for their metabolites. Intra- and inter-day precisions were within 15%, and the accuracies were in the range of 87-112%. The method was successfully applied to the pharmacokinetic study of probe drugs/metabolites and DDIs with 3-n-butylphthalide (NBP) after administration of a single oral dose of phenacetin, omeprazole, metoprolol and midazolam in rats.

3D engineered In vitro hepatospheroids for studying drug toxicity and metabolism.

Drug toxicity is one of the reasons for late stage drug attrition, because of hepatotoxicity. Various in vitro liver models like primary human hepatocytes, immortalized human hepatic cell lines, liver slices and microsomes have been used; but limited by viability, hepatic gene expression and function. The 3D-engineered construct of hepatocyte-like-cells (HLCs) differentiated from stem cells, may provide a limitless source of hepatocytes with improved reproducibility. Towards this end, we used hepatospheroids (diameter=50-80µm) differentiated from human-umbilical-cord-mesenchymal stem cells (hUC-MSCs) on 3D scaffold GEVAC (Gelatin-vinyl-acetate-copolymer) as in vitro model for studying drug metabolism/toxicity. Our data demonstrated that hUC-MSCs-derived-hepatospheroids cultured on GEVAC expressed significantly higher drug-metabolizing enzymes (CYPs) both at mRNA and activity level compared to 2D culture, using HR-LC/MS. We further showed that hepatospheroids convert phenacetin (by CYP1A2) and testosterone (by CYP3A4) to their human-specific metabolites acetaminophen and 6ß-hydroxytestosterone with a predictive clearance rate of 0.011ml/h/106 cells and 0.021ml/h/106 cells respectively, according to first-order kinetics. Hepatotoxicity was confirmed by exposing hepatospheroids to ethanol and acetaminophen; ROS generation, cell viability, cytoskeleton structure, elevation of liver function enzymes, i.e. AST and ALT, was analyzed. To the best of our knowledge, this is the first report to use hUC-MSCs-derived-hepatospheroids on GEVAC as in vitro model for drug metabolism/toxicity study; which can replace the conventional 2D-models used in drug development.

Long-term human primary hepatocyte cultures in a microfluidic liver biochip show maintenance of mRNA levels and higher drug metabolism compared with Petri cultures.

Human primary hepatocytes were cultivated in a microfluidic bioreactor and in Petri dishes for 13 days. mRNA kinetics in biochips showed an increase in the levels of CYP2B6, CYP2C19, CYP2C8, CYP3A4, CYP1A2, CYP2D6, HNF4a, SULT1A1, UGT1A1 mRNA related genes when compared with post extraction levels. In addition, comparison with Petri dishes showed higher levels of CYP2B6, CYP2C19, CYP2C8, CYP3A4, CYP1A2, CYP2D6 related genes at the end of culture. Functional assays illustrated a higher urea and albumin production over the period of culture in biochips. Bioreactor drug metabolism (midazolam and phenacetin) was not superior to the Petri dish after 2 days of culture. The CYP3A4 midazolam metabolism was maintained in biochips after 13 days of culture, whereas it was almost undetectable in Petri dishes. This led to a 5000-fold higher value of the metabolic ratio in the biochips. CYP1A2 phenacetin metabolism was found to be higher in biochips after 5, 9 and 13 days of culture. Thus, a 100-fold higher metabolic ratio of APAP in biochips was measured after 13 days of perfusion. These results demonstrated functional primary human hepatocyte culture in the bioreactor in a long-term culture. Copyright © 2016 John Wiley & Sons, Ltd.

Long-term culture and cryopreservation does not affect the stability and functionality of human embryonic stem cell-derived hepatocyte-like cells.

Human embryonic stem cells (hESCs) are predicted to be an unlimited source of hepatocytes which can pave the way for applications such as cell replacement therapies or as a model of human development or even to predict the hepatotoxicity of drug compounds. We have optimized a 23-d differentiation protocol to generate hepatocyte-like cells (HLCs) from hESCs, obtaining a relatively pure population which expresses the major hepatic markers and is functional and mature. The stability of the HLCs in terms of hepato-specific marker expression and functionality was found to be intact even after an extended period of in vitro culture and cryopreservation. The hESC-derived HLCs have shown the capability to display sensitivity and an alteration in the level of CYP enzyme upon drug induction. This illustrates the potential of such assays in predicting the hepatotoxicity of a drug compound leading to advancement of pharmacology.

A sensitive and high-throughput LC-MS/MS method for inhibition assay of seven major cytochrome P450s in human liver microsomes using an in vitro cocktail of probe substrates.

A sensitive and high-throughput LC-MS/MS method was established and validated for the simultaneous quantification of seven probe substrate-derived metabolites (cocktail assay) for assessing the in vitro inhibition of cytochrome P450 (CYP) enzymes in pooled human liver microsomes. The metabolites acetaminophen (CYP1A2), hydroxy-bupropion (CYP2B6), n-desethyl-amodiaquine (CYP2C8), 4'-hydroxy-diclofenac (CYP2C9), 4'-hydroxy-mephenytoin (CYP2C19), dextrorphan (CYP2D6) and 1'-hydroxy-midazolam (CYP3A4/5), together with the internal standard verapamil, were eluted on an Agilent 1200 series liquid chromatograph in <7 min. All metabolites were detected by an Agilent 6410B tandem mass spectrometer. The concentration of each probe substrate was selected by substrate inhibition assay that reduced potential substrate interactions. CYP inhibition of seven well-known inhibitors was confirmed by comparing a single probe substrate assay with cocktail assay. The IC50 values of these inhibitors determined on this cocktail assay were highly correlated (R(2) > 0.99 for each individual probe substrate) with those on single assay. The method was selective and showed good accuracy (85.89-113.35%) and between-day (RSD <13.95%) and within-day (RSD <9.90%) precision. The sample incubation extracts were stable at 25 °C for 48 h and after three freeze-thaw cycles. This seven-CYP inhibition cocktail assay significantly increased the efficiency of accurately assessing compounds' potential inhibition of the seven major CYPs in drug development settings.

Functional characterization of eight human CYP1A2 variants: the role of cytochrome b5.

BACKGROUND: Interindividual variability in cytochrome P450 (CYP)-mediated xenobiotic metabolism is extensive. CYP metabolism requires two electrons, which can be donated by NADPH cytochrome P450 oxidoreductase (CYPOR) and/or cytochrome b5 (b5). Although substantial number of studies have reported on the function and effect of b5 in CYP-mediated catalysis, its mode of action is still not fully understood. OBJECTIVE: The aim of this work was to examine the effect of b5 on the activities of eight natural-occurring variants of human CYP1A2, namely, T83M, S212C, S298R, G299S, I314V, I386F, C406Y, and R456H. MATERIALS AND METHODS: An approach, as used in our former study was applied, coexpressing these polymorphic CYP1A2 variants separately with CYPOR and b5 in the bacterial cell model BTC-CYP. For each variant, 16 different activity parameters were measured, using eight different substrates. This heterogeneous data set was merged with the one of our former study (i.e. without b5) and a multivariate analysis was carried out. RESULTS: This analysis indicated that b5 seems to have the ability to affect CYP1A2 variants to behave more like the wild-type variant. This was especially the case for variant I386F, for which the presence of b5 was crucial to show activity. Variants T83M and C406Y showed considerably different activity-profiles when in the presence of b5. Furthermore, our data seem to implicate CYP1A2 residue G299 in its interaction with CYPOR and/or b5. CONCLUSION: Results indicate the ability of b5 to affect CYP1A2 variants to behave more like the wild-type variant, attenuating detrimental effects of structural mutations of these variants, seemingly through extensive allosteric effects.

Combined use of filtered and edited 1 H NMR spectroscopy to detect 13 C-enriched compounds in complex mixtures.

In conventional metabolism and pharmacokinetic studies, radioactive isotopes are used to identify and quantify the breakdown products of xenobiotics. However, the stable isotope (13) C provides a cheaper and less hazardous alternative. Metabolites of (13) C-enriched xenobiotics can be detected, quantified and identified by (13) C-filtered NMR spectroscopy. However, one obstacle to using (13) C is its 1.1% natural abundance that produces a background signal in (13) C-filtered NMR spectra of crude biological extracts. The signal makes it difficult to distinguish between (13) C-enriched xenobiotics resonances from endogenous metabolites unrelated to the xenobiotic. This study proposes that the (13) C background signal can be distinguished from resonances of (13) C-enriched xenobiotics by the absence of a (12) C component in the xenobiotic. This is detected by combined analysis of (13) C-filtered and -edited NMR spectra. The theory underlying the approach is described and the method is demonstrated by the detection of sub-microgram amounts of (13) C-enriched phenacetin in crude extracts of hepatocyte microsomes.

Investigation of cytochrome P450 1A2 and 3A inhibitory properties of Danshen tincture.

Danshen (Salvia miltiorrhiza Bunge) as a famous Traditional Chinese medicine is widely used in the treatment of cardiovascular and cerebrovascular diseases in the world. Danshen tincture (DT), extracted from Danshen root with a mixture of water and alcohol, is a commonly used preparation method for human consumption. The aim of this study was to investigate the effects of DT on the cytochrome P450 (CYP) 1A2 and 3A activities by human and rat liver microsomes. Effects of DT were assessed with use of Danshen ethanolic extract (DEE) and selective substrates, markers of CYP activities. DEE (0.5-10 µg/ml) competitively inhibited human and rat liver microsomal CYP1A2 activity with inhibition constant (K(i)) values at 3.40 and 5.16 µg/ml, respectively. At the same time, DEE (2.5-20 µg/ml) not only noncompetitively inhibited human liver microsomal CYP3A4/5 activity with a K(i) of 11.9 µg/ml, but also competitively inhibited rat liver microsomal CYP3A1/2 activity with a K(i) of 52.1 µg/ml. The data indicate that DEE inhibited the metabolism of CYP1A2 and 3A substrates in human and rat liver in vitro with different mode of inhibition. This study may be helpful for clinical application of Danshen tincture.

Differential role of cyclooxygenase isozymes on neuronal density in hippocampus CA1 region of intracerebroventricular streptozotocin treated rat brain.

Intracerebroventricular (ICV) administration of streptozotocin (STZ) causes degeneration of hippocampal neurons through unknown mechanisms that further lead to dementia. On assumption that enzyme cyclooxygenase (COX), which catalyzes the production of pro-inflammatory prostaglandins, may be involved in ICV-STZ induced neurodegeneration, the present study was designed to investigate the effects of chronic treatment with selective inhibitor of COX-1, COX-2 or COX-3 on hippocampal neuronal density in ICV-STZ treated rats. Drugs were administered daily for 21 days, intraperitoneally, in sham control as well as ICV-STZ treated rats. After 21 days of treatment, rats were sacrificed and histological changes were observed in Cornus Ammonis (CA)-1 region of hippocampus at light microscopic level. Histopathological evaluation showed that valeryl salicylate (selective COX-1 inhibitor; 5 and 10 mg/kg; i.p.) and etoricoxib (selective COX-2 inhibitor; 5 and 10 mg/kg; i.p.) significantly increased the survival of hippocampus CA1 neurons in a dose dependent manner. On the contrary, phenacetin (selective COX-3 inhibitor; 20 and 40 mg/kg; i.p.) treatment had no effect on reduced neuronal density in ICV-STZ treated rats. In summary, these findings provide the first comprehensive description about the differential role of COX isozymes in ICV-STZ induced neuronal death in hippocampal CA1 regions of the rat brain.

Arylacetamide deacetylase is a determinant enzyme for the difference in hydrolase activities of phenacetin and acetaminophen.

Phenacetin was withdrawn from the market because it caused renal failure in some patients. Many reports indicated that the nephrotoxicity of phenacetin is associated with the hydrolyzed metabolite, p-phenetidine. Acetaminophen (APAP), the major metabolite of phenacetin, is also hydrolyzed to p-aminophenol, which is a nephrotoxicant. However, APAP is safely prescribed if used in normal therapeutic doses. This background prompted us to investigate the difference between phenacetin and APAP hydrolase activities in human liver. In this study, we found that phenacetin is efficiently hydrolyzed in human liver microsomes (HLM) [CL(int) 1.08 +/- 0.02 microl/(min . mg)], whereas APAP is hardly hydrolyzed [0.02 +/- 0.00 microl/(min . mg)]. To identify the esterase involved in their hydrolysis, the activities were measured using recombinant human carboxylesterase (CES) 1A1, CES2, and arylacetamide deacetylase (AADAC). Among these, AADAC showed a K(m) value (1.82 +/- 0.02 mM) similar to that of HLM (3.30 +/- 0.16 mM) and the highest activity [V(max) 6.03 +/- 0.14 nmol/(min . mg)]. In contrast, APAP was poorly hydrolyzed by the three esterases. The large contribution of AADAC to phenacetin hydrolysis was demonstrated by the prediction with a relative activity factor. In addition, the phenacetin hydrolase activity by AADAC was activated by flutamide (5-fold) as well as that in HLM (4-fold), and the activity in HLM was potently inhibited by eserine, a strong inhibitor of AADAC. In conclusion, we found that AADAC is the principal enzyme responsible for the phenacetin hydrolysis, and the difference of hydrolase activity between phenacetin and APAP is largely due to the substrate specificity of AADAC.

Evaluation of the activity of P450 enzymes in rats: use of the single marker or combined drug administration.

OBJECTIVES: A "cocktail" of several substrates is frequently used to assess metabolic activity of multiple cytochrome P450 enzymes in one session. Some interactions among substrates can appear and may influence the rate of biotransformation of other ones. Our current work was aimed on the influence of tolbutamide on cytochrome P450-mediated metabolism of phenacetin and vice versa. DESIGN: In the presented work, the biotransformation rates of phenacetin and tolbutamide (markers of rat CYP1A2 and CYP2C6/11 metabolic activities, respectively) administered either separately or both simultaneously were compared. The model of isolated perfused rat liver was used. RESULTS: Phenacetin had no significant effect on tolbutamide hydroxylation. Tolbutamide addition to the perfusion medium significantly increased the rate of O-deethylation of phenacetin. CONCLUSION: Some differences in the rate of P450-mediated metabolism can be observed when comparing assessment using combination of two model substrates with the common way (single marker administration). Due to these differences, results obtained by the mentioned methodologies might not be fully comparable.

Acetaminophen, phenacetin and dipyrone do not modulate pressor responses to arachidonic Acid or to pressor agents.

In contrast to nonsteroidal anti-inflammatory drugs (NSAIDs), the nonopioid analgesics phenacetin, acetaminophen and dipyrone exhibit weak anti-inflammatory properties. An explanation for this difference in pharmacologic activity was provided by the recent discovery of a new cyclooxygenase isoform, cyclooxygenase (COX)-3, that is reported to be inhibited by phenacetin, acetaminophen and dipyrone. However, COX-3 was found to be a spliced variant of COX-1 and renamed COX-1b. Although recent studies provide evidence for the existence of this new COX isoform, it is uncertain whether this COX-3 (COX-1b) isoform, or putative acetaminophen-sensitive pathway, plays a role in the generation of vasoactive prostaglandins. NSAIDs increase systemic blood pressure by inhibiting the formation of vasodilator prostanoids. Angiotensin II, norepinephrine and other vasoconstrictor agents have been reported to release prostaglandins. It is possible that this acetaminophen-sensitive pathway also modulates pressor responses to these vasoconstrictor agents. Therefore, the purpose of the present study was to determine whether this acetaminophen-sensitive pathway plays a role in the generation of vasoactive products of arachidonic acid or in the modulation of vasoconstrictor responses in the pulmonary and systemic vascular bed of the intact-chest rat. In the present study, the nonopioid analgesics did not attenuate changes in pulmonary or systemic arterial pressure in response to injections of the prostanoid precursor, arachidonic acid, to the thromboxane A(2) mimic, U46619, or to angiotensin II or norepinephrine. The results of the present study do not provide evidence in support of a role of a functional COX-3 (COX-1b) isoform, or an acetaminophen-sensitive pathway, in the generation of vasoactive prostanoids or in the modulation of responses to vasoconstrictor hormones in the intact-chest rat.

Effect of sodium ozagrel on the activity of rat CYP2D6.

The aim of the study was to investigate the influence of sodium ozagrel on CYP2D6 (cytochromeP450 2D6) activity. The studies were performed with rat urine and liver microsomes and chemical inhibitors. The metabolism of dextromethorphan (dextrophan/dextromethorphan, dextrophan is a metabolite of dextromethorphan) and phenacetin (paracetamol/phenacetin, paracetamol is a metabolites of phenacetin) was used as probe to measure CYP2D6 and CYP1A2 (cytochromeP450 1A2) activity, respectively, determined by high-performance liquid chromatography (HPLC). The results showed that the metabolism of dextrophan/dextromethorphan in the sodium ozagrel-treated group (37 mg/kg) was higher than that of the control (P<0.05/6) in both in vivo and in vitro studies (r=0.9811). The rate of dextromethorphan metabolism was inhibited by sodium ozagrel and cimetidine in rat liver microsomes prepared from sodium ozagrel-treated rats and control rats group (sodium ozagrel IC(50)=26.5 microM, cimetidine IC(50)=86.3 microM in sodium ozagrel-treated group; sodium ozagrel IC(50)=13.9 microM, cimetidine IC(50)=24.8 microM in control group). The inhibitory effect of sodium ozagrel on CYP2D6 activity was noncompetitive with dextromethorphan with a K(i) of 324.94 microM. Kinetic parameters of the reactions were established by using Lineweaver-Burk with K(m)=0.67 mM and V(max)=2.13 pm/min/mg protein for the sodium ozagrel-treated group and K(m)=0.29 mM, and V(max)=0.91 pm/min/mg protein for the control group, respectively. The expression of CYP2D6 protein in the treated group was higher than that of the control group, as determined by Western blotting. The activity and expression of CYP1A2 did not show obvious differences in the control group and sodium ozagrel treated group. In conclusion, sodium ozagrel metabolism in rats is mediated primarily through CYP2D6, and sodium ozagrel can induce CYP2D6 activity.