Sara De Martin

Cytochrome P450 1A2 is a major determinant of lidocaine metabolism in vivo: Effects of liver function

This study was designed (1) to evaluate the effect of a cytochrome P450 (CYP) 1A2 inhibitor, fluvoxamine, on the pharmacokinetics of intravenous lidocaine and its 2 pharmacologically active metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), to confirm recent in vitro results indicating that CYP1A2 is the main isoform responsible for lidocaine biotransformation and (2) to assess whether liver function has any influence on the fluvoxamine‐lidocaine interaction.

Differential effect of chronic renal failure on the pharmacokinetics of lidocaine in patients receiving and not receiving hemodialysis

The effect of chronic renal failure (CRF) on the pharmacokinetics of lidocaine, a drug cleared almost exclusively by hepatic metabolism, has thus far only been evaluated in patients undergoing regular hemodialysis. This study had 2 objectives: (1) to investigate the effect of CRF on the pharmacokinetics of lidocaine in both patients undergoing hemodialysis and patients not undergoing hemodialysis and (2) to test the effects of plasma from the patients examined and of lidocaine metabolites possibly accumulated in vivo on lidocaine biotransformation in vitro.

NAD+-dependent SIRT1 deactivation has a key role on ischemia–reperfusion-induced apoptosis

Ischemia-reperfusion (IR) leads to severe organ injury and dysfunction. Sirtuins (SIRTs) are a family of histone deacetylases (HDACs) that require nicotinamide adenine dinucleotide (NAD(+)) for the deacetylation reaction. SIRTs play a major role in counteracting cellular stress and apoptosis. This study aimed to investigate the mechanisms of heart protection against apoptosis by SIRTs and the molecular pathways involved in SIRTs regulation and function in a rat model of IR injury. Hearts of male Wistar-Kyoto rats were subjected to 30-min ischemia followed by reperfusion up to 6h. IR increased cardiomyocyte apoptosis; the cleavage of caspase 3, induced a transient upregulation of SIRT1 and downregulation of SIRT6 expression, but decreased SIRT1 activity and reduced NAD(+) content. IR also increased forkhead box protein O1 (FoxO1) expression and FoxO1 binding to SIRT1 promoter region. Resveratrol restored SIRT1 activity and NAD(+) level by an AMPK-dependent mechanism, reduced cardiomyocyte apoptosis, and attenuated caspase 3 cleavage via heat shock factor-1 deacetylation and heat shock protein (HSP) expression upregulation. Our data show new potential molecular mechanisms of up and downstream regulation of SIRT1 in IR. The interplay among FoxO1, SIRT1, NAD(+), AMPK, HSP, and SIRT6 depicts a complex molecular network that protects the heart from apoptosis during IR and may be susceptible to therapeutic interventions.

Liver dysfunction markedly decreases the inhibition of cytochrome P450 1A2-mediated theophylline metabolism by fluvoxamine.

In vivo inhibition of cytochrome P450 (CYP) 1A2 by fluvoxamine causes a reduction in the clearance of the high‐extraction drug lidocaine, which decreases in proportion to the degree of liver dysfunction. The objectives of this study were (1) to evaluate the effect of liver cirrhosis on the inhibition by fluvoxamine of the metabolic disposition of theophylline, a CYP1A2 substrate with a low‐extraction ratio, to assess whether decreased sensitivity to CYP1A2 inhibition in liver disease is a general characteristic of CYP1A2 substrates, regardless of their pharmacokinetic properties, and (2) to investigate the mechanism(s) underlying the effect of liver dysfunction on CYP1A2 inhibition.

In vitro hepatic conversion of the anticancer agent nemorubicin to its active metabolite PNU-159682 in mice, rats and dogs: A comparison with human liver microsomes

We recently demonstrated that nemorubicin (MMDX), an investigational antitumor drug, is converted to an active metabolite, PNU-159682, by human liver cytochrome P450 (CYP) 3A4. The objectives of this study were: (1) to investigate MMDX metabolism by liver microsomes from laboratory animals (mice, rats, and dogs of both sexes) to ascertain whether PNU-159682 is also produced in these species, and to identify the CYP form(s) responsible for its formation; (2) to compare the animal metabolism of MMDX with that by human liver microsomes (HLMs), in order to determine which animal species is closest to human beings; (3) to explore whether differences in PNU-159682 formation are responsible for previously reported species- and sex-related differences in MMDX host toxicity. The animal metabolism of MMDX proved to be qualitatively similar to that observed with HLMs since, in all tested species, MMDX was mainly converted to PNU-159682 by a single CYP3A form. However, there were marked quantitative inter- and intra-species differences in kinetic parameters. The mouse and the male rat exhibited V(max) and intrinsic metabolic clearance (CL(int)) values closest to those of human beings, suggesting that these species are the most suitable animal models to investigate MMDX biotransformation. A close inverse correlation was found between MMDX CL(int) and previously reported values of MMDX LD(50) for animals of the species, sex and strain tested here, indicating that differences in the in vivo toxicity of MMDX are most probably due to sex- and species-related differences in the extent of PNU-159682 formation.

Enzyme Inhibition and Induction in Liver Disease

This article reviews the influence of liver functional status on pharmacokinetic interactions due to inhibition and induction of drug-metabolizing enzymes. Recent human studies have shown that the magnitude of inhibitory interactions caused by the reversible CYP1A2 inhibitor fluvoxamine decreases as liver function worsens, and virtually vanishes in patients with more advanced hepatocellular insufficiency. This effect of liver dysfunction is independent of the pharmacokinetic characteristics of the CYP1A2 substrate, since it has been observed with both high- and low-clearance drugs. It is most probably due to reduced uptake of the inhibitory drug by the cirrhotic liver. In order to ascertain whether this is a general phenomenon, the following questions remain to be addressed: 1) whether the inhibition of any CYP isoform is reduced in liver disease; 2) whether the effect of liver dysfunction depends on the chemical nature of the inhibitory drug, since both reduced in vivo inhibition and in vitro uptake by the cirrhotic liver have so far been shown only for basic drugs; 3) lastly, if similar effects can also be observed with irreversible and quasi-irreversible inhibitors, as their accumulation kinetics in the hepatocyte may differ from those of a reversible inhibitor. Although many in vivo and in vitro studies have examined the inducibility of drug-metabolizing enzymes in liver disease, available data are incomplete and conflicting, since both well-preserved and severely curtailed responses to inducing agents have been reported. The reasons for these variable responses are most probably methodological, i.e., differences in the type and degree of liver dysfunction of the animals and patients examined, and in the type and dosage of the inducing agent used. Nonetheless, the results of those few studies which used pathologically homogeneous animal or patient groups suggest that, like basal enzyme expression, drug-inducible expression is also substantially preserved in mild to moderate liver disease, whereas it is lost in severe hepatic dysfunction. For a definitive conclusion, further studies are necessary which examine etiologically homogeneous patient groups and stratify patients rigorously according to their functional hepatic reserve. Such studies should also examine inducers with different physicochemical properties and acting by different mechanisms, since the expression of both hepatic transporters and nuclear receptors may be differentially affected by liver function impairment.

Pharmacokinetic drug interactions in liver disease: An update

Inhibition and induction of drug-metabolizing enzymes are the most frequent and dangerous drug-drug interactions. They are an important cause of serious adverse events that have often resulted in early termination of drug development or withdrawal of drugs from the market. Management of such interactions by dose adjustment in clinical practice is extremely difficult because of the wide interindividual variability in their magnitude. This review examines the genetic, physiological, and environmental factors responsible for this variability, focusing on an important but so far neglected cause of variability, liver functional status. Clinical studies have shown that liver disease causes a reduction in the magnitude of interactions due to enzyme inhibition, which is proportional to the degree of liver function impairment. The effect of liver dysfunction varies quantitatively according to the nature, reversible or irreversible, of the inhibitory interaction. The magnitude of reversible inhibition is more drastically reduced and virtually vanishes in patients with advanced hepatocellular insufficiency. Two mechanisms, in order of importance, are responsible for this reduction: decreased hepatic uptake of the inhibitory drug and reduced enzyme expression. The extent of irreversible inhibitory interactions is only partially reduced, as it is only influenced by the decreased expression of the inhibited enzyme. Thus, for appropriate clinical management of inhibitory drug interactions, both the liver functional status and the mechanism of inhibition must be taken into consideration. Although the inducibility of drug-metabolizing enzymes in liver disease has long been studied, very conflicting results have been obtained, mainly because of methodological differences. Taken together, the results of early animal and human studies indicated that enzyme induction is substantially preserved in compensated liver cirrhosis, whereas no definitive conclusion as to whether it is significantly reduced in the decompensated state of cirrhosis was provided. Since ethical constraints virtually preclude the possibility of performing methodologically rigorous investigations in patients with severe liver dysfunction, studies have recently been performed in animals rigorously stratified according to the severity of liver insufficiency. The results of these studies confirmed that enzyme induction is virtually unaffected in compensated cirrhosis and indicated that the susceptibility of enzyme induction to severe liver dysfunction depends on the type of nuclear receptor involved and also varies among enzyme isoforms under the transcriptional control of the same nuclear receptor. These findings make it clear that no general conclusion can be reached from the study of any particular enzyme and partly explain the conflicting results obtained by previous studies. Since no general guidelines can be provided for the management of drug interactions resulting from enzyme induction, both the effects and the plasma concentration of the induced drug should be strictly monitored. The findings discussed in this review have important methodological implications as they indicate that, contrary to current guidelines, the magnitude of metabolic drug-drug interactions in patients with liver disease cannot be inferred from studies in healthy subjects.

Severe liver cirrhosis markedly reduces AhR-mediated induction of cytochrome P450 in rats by decreasing the transcription of target genes.

Although the induction of cytochrome P450 (CYP) has long been investigated in patients with cirrhosis, the question whether liver dysfunction impairs the response to CYP inducers still remains unresolved. Moreover, the mechanism underlying the possible effect of cirrhosis on induction has not been investigated. Since ethical constraints do not permit methodologically rigorous studies in humans, this question was addressed by investigating the effect of the prototypical inducer benzo[a]pyrene (BP) on CYP1A1 and CYP1A2 in cirrhotic rats stratified according to the severity of liver dysfunction. We simultaneously assessed mRNA level, protein expression and enzymatic activity of the CYP1A enzymes, as well as mRNA and protein expressions of the aryl hydrocarbon receptor (AhR), which mediates the BP effect. Basal mRNA and protein expressions of CYP1A1 were virtually absent in both healthy and cirrhotic rats. On the contrary, CYP1A2 mRNA, protein and enzyme activity were constitutively present in healthy rats and decreased significantly as liver function worsened. BP treatment markedly increased the concentrations of mRNA and immunodetectable protein, and the enzymatic activities of both CYP1A enzymes to similar levels in healthy and non-ascitic cirrhotic rats. Induced mRNA levels, protein expressions and enzymatic activities of both CYPs were much lower in ascitic rats and were proportionally reduced. Both constitutive and induced protein expressions of AhR were significantly lower in ascitic than in healthy rats. These results indicate that the inducibility of CYP1A enzymes is well preserved in compensated cirrhosis, whereas it is markedly reduced when liver dysfunction becomes severe. Induction appears to be impaired at the transcriptional level, due to the reduced expression of AhR, which controls the transcription of CYP1A genes.

Fluvoxamine pharmacokinetics in healthy elderly subjects and elderly patients with chronic heart failure

AIMS To investigate the effects of age and chronic heart failure (CHF) on the oral disposition kinetics of fluvoxamine. METHODS A single fluvoxamine dose (50 mg) was administered orally to 10 healthy young adults, 10 healthy elderly subjects and 10 elderly patients with CHF. Fluvoxamine concentration in plasma was measured for up to 96 h. RESULTS With the exception of apparent distribution volume, ageing modified all main pharmacokinetic parameters of fluvoxamine. Thus, peak concentration was about doubled {31 +/- 19 vs. 15 +/- 9 ng ml(-1); difference [95% confidence interval (CI)] 16 (3, 29), P < 0.05}, and area under the concentration-time curve was almost three times higher [885 +/- 560 vs. 304 +/- 84 ng h ml(-1); difference (95% CI) 581 (205, 957), P < 0.05]; half-life was prolonged by 63% [21.1 +/- 6.2 vs. 12.9 +/- 6.4 h; difference (95% CI) 8.2 (2.3, 14.1), P < 0.01], and oral clearance was halved (1.12 +/- 0.77 vs. 2.25 +/- 0.66 l h(-1) kg(-1); difference (95% CI) -1.13 (-1.80, -0.46), P < 0.001]. A significant inverse correlation was consistently observed between age and oral clearance (r=-0.67; P < 0.001). The coexistence of CHF had no significant effect on any pharmacokinetic parameters in elderly subjects. CONCLUSIONS Ageing results in considerable impairment of fluvoxamine disposition, whereas CHF causes no significant modifications. Therefore, adjustment of initial dose and subsequent dose titrations may be required in elderly subjects, whereas no further dose reduction is necessary in elderly patients with CHF.

The Phytocomplex from Fucus vesiculosus and Ascophyllum nodosum Controls Postprandial Plasma Glucose Levels: An In Vitro and In Vivo Study in a Mouse Model of NASH

Edible seaweeds have been consumed by Asian coastal communities since ancient times. Fucus vesiculosus and Ascophyllum nodosum extracts have been traditionally used for the treatment of obesity and several gastrointestinal diseases. We evaluated the ability of extracts obtained from these algae to inhibit the digestive enzymes α-amylase and α-glucosidase in vitro, and control postprandial plasma glucose levels in a mouse model of non-alcoholic steatohepatitis (NASH); a liver disease often preceding the development of Type 2 diabetes (T2DM). This model was obtained by the administration of a high-fat diet. Our results demonstrate that these algae only delayed and reduced the peak of blood glucose (p < 0.05) in mice fed with normal diet, without changing the area under the blood glucose curve (AUC). In the model of NASH, the phytocomplex was able to reduce both the postprandial glycaemic peak, and the AUC. The administration of the extract in a diet particularly rich in fat is associated with a delay in carbohydrate digestion, but also with a decrease in its assimilation. In conclusion, our results indicate that this algal extract may be useful in the control of carbohydrate digestion and absorption. This effect may be therapeutically exploited to prevent the transition of NASH to T2DM.