Genome-wide association study identifies loci influencing concentrations of liver enzymes in plasma.

Concentrations of liver enzymes in plasma are widely used as indicators of liver disease. We carried out a genome-wide association study in 61,089 individuals, identifying 42 loci associated with concentrations of liver enzymes in plasma, of which 32 are new associations (P = 10(-8) to P = 10(-190)). We used functional genomic approaches including metabonomic profiling and gene expression analyses to identify probable candidate genes at these regions. We identified 69 candidate genes, including genes involved in biliary transport (ATP8B1 and ABCB11), glucose, carbohydrate and lipid metabolism (FADS1, FADS2, GCKR, JMJD1C, HNF1A, MLXIPL, PNPLA3, PPP1R3B, SLC2A2 and TRIB1), glycoprotein biosynthesis and cell surface glycobiology (ABO, ASGR1, FUT2, GPLD1 and ST3GAL4), inflammation and immunity (CD276, CDH6, GCKR, HNF1A, HPR, ITGA1, RORA and STAT4) and glutathione metabolism (GSTT1, GSTT2 and GGT), as well as several genes of uncertain or unknown function (including ABHD12, EFHD1, EFNA1, EPHA2, MICAL3 and ZNF827). Our results provide new insight into genetic mechanisms and pathways influencing markers of liver function.

Antibacterial burst-release from minimal Ag-containing plasma polymer coatings.

Biomaterials releasing silver (Ag) are of interest because of their ability to inhibit pathogenic bacteria including antibiotic-resistant strains. In order to investigate the potential of nanometre-thick Ag polymer (Ag/amino-hydrocarbon) nanocomposite plasma coatings, we studied a comprehensive range of factors such as the plasma deposition process and Ag cation release as well as the antibacterial and cytocompatible properties. The nanocomposite coatings released most bound Ag within the first day of immersion in water yielding an antibacterial burst. The release kinetics correlated with the inhibitory effects on the pathogens Pseudomonas aeruginosa or Staphylococcus aureus and on animal cells that were in contact with these coatings. We identified a unique range of Ag content that provided an effective antibacterial peak release, followed by cytocompatible conditions soon thereafter. The control of the in situ growth conditions for Ag nanoparticles in the polymer matrix offers the possibility to produce customized coatings that initially release sufficient quantities of Ag ions to produce a strong adjacent antibacterial effect, and at the same time exhibit a rapidly decaying Ag content to provide surface cytocompatibility within hours/days. This approach seems to be favourable with respect to implant surfaces and possible Ag-resistance/tolerance built-up.

Clinical pharmacokinetics of mycophenolic acid and its metabolites in solid organ transplant recipient

Mycophenolate mofetil (MMF), an ester prodrug of the immunosuppressant mycophenolic acid (MPA), is widely used for maintenance immunosuppressive therapy and prevention of renal allograft rejection in renal transplant recipients.MPA inhibits inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in the “de novo” synthesis of purine nucleotides, thus suppressing both T-cell and B-cell proliferation. MPA shows a complex pharmacokinetics with considerable interand intra- patient by between- and within patient variabilities associated to MPA exposure. Several factors may contribute to it. The pharmacokinetic modeling according to the population pharmacokinetic approach with the non-linear mixed effects models has shown to be a powerful tool to describe the relationships between MMF doses and the MPA exposures and also to identify potential predictive patients’ demographic and clinical characteristics for dose tailoring during the post-transplant immunosuppresive treatment.

Valganciclovir in adult solid organ transplant recipients: pharmacokinetic and pharmacodynamic characteristics and clinical interpretation of plasma concentration measurements.

Valganciclovir and ganciclovir are widely used for the prevention of cytomegalovirus (CMV) infection in solid organ transplant recipients, with a major impact on patients' morbidity and mortality. Oral valganciclovir, the ester prodrug of ganciclovir, has been developed to enhance the oral bioavailability of ganciclovir. It crosses the gastrointestinal barrier through peptide transporters and is then hydrolysed into ganciclovir. This review aims to describe the current knowledge of the pharmacokinetic and pharmacodynamic characteristics of this agent, and to address the issue of therapeutic drug monitoring. Based on currently available literature, ganciclovir pharmacokinetics in adult solid organ transplant recipients receiving oral valganciclovir are characterized by bioavailability of 66 +/- 10% (mean +/- SD), a maximum plasma concentration of 3.1 +/- 0.8 mg/L after a dose of 450 mg and of 6.6 +/- 1.9 mg/L after a dose of 900 mg, a time to reach the maximum plasma concentration of 3.0 +/- 1.0 hours, area under the plasma concentration-time curve values of 29.1 +/- 5.3 mg.h/L and 51.9 +/- 18.3 mg.h/L (after 450 mg and 900 mg, respectively), apparent clearance of 12.4 +/- 3.8 L/h, an elimination half-life of 5.3 +/- 1.5 hours and an apparent terminal volume of distribution of 101 +/- 36 L. The apparent clearance is highly correlated with renal function, hence the dosage needs to be adjusted in proportion to the glomerular filtration rate. Unexplained interpatient variability is limited (18% in apparent clearance and 28% in the apparent central volume of distribution). There is no indication of erratic or limited absorption in given subgroups of patients; however, this may be of concern in patients with severe malabsorption. The in vitro pharmacodynamics of ganciclovir reveal a mean concentration producing 50% inhibition (IC(50)) among CMV clinical strains of 0.7 mg/L (range 0.2-1.9 mg/L). Systemic exposure of ganciclovir appears to be moderately correlated with clinical antiviral activity and haematotoxicity during CMV prophylaxis in high-risk transplant recipients. Low ganciclovir plasma concentrations have been associated with treatment failure and high concentrations with haematotoxicity and neurotoxicity, but no formal therapeutic or toxic ranges have been validated. The pharmacokinetic parameters of ganciclovir after valganciclovir administration (bioavailability, apparent clearance and volume of distribution) are fairly predictable in adult transplant patients, with little interpatient variability beyond the effect of renal function and bodyweight. Thus ganciclovir exposure can probably be controlled with sufficient accuracy by thorough valganciclovir dosage adjustment according to patient characteristics. In addition, the therapeutic margin of ganciclovir is loosely defined. The usefulness of systematic therapeutic drug monitoring in adult transplant patients therefore appears questionable; however, studies are still needed to extend knowledge to particular subgroups of patients or dosage regimens.

Clinical pharmacokinetics of mycophenolic acid and its metabolites in solid organ transplant recipient

Mycophenolate mofetil (MMF), an ester prodrug of the immunosuppressant mycophenolic acid (MPA), is widely used for maintenance immunosuppressive therapy and prevention of renal allograft rejection in renal transplant recipients.MPA inhibits inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in the “de novo” synthesis of purine nucleotides, thus suppressing both T-cell and B-cell proliferation. MPA shows a complex pharmacokinetics with considerable interand intra- patient by between- and within patient variabilities associated to MPA exposure. Several factors may contribute to it. The pharmacokinetic modeling according to the population pharmacokinetic approach with the non-linear mixed effects models has shown to be a powerful tool to describe the relationships between MMF doses and the MPA exposures and also to identify potential predictive patients’ demographic and clinical characteristics for dose tailoring during the post-transplant immunosuppresive treatment.

Single spin-echo T 2 relaxation times of cerebral metabolites at 14.1 T in the in vivo rat brain.

OBJECT: To determine the single spin-echo T 2 relaxation times of uncoupled and J-coupled metabolites in rat brain in vivo at 14.1 T and to compare these results with those previously obtained at 9.4 T. MATERIALS AND METHODS: Measurements were performed on five rats at 14.1 T using the SPECIAL sequence and TE-specific basis-sets for LCModel analysis. RESULTS AND CONCLUSION: The T 2 of singlets ranged from 98 to 148 ms and T 2 of J-coupled metabolites ranged from 72 ms (glutamate) to 97 ms (myo-inositol). When comparing the T 2s of the metabolites measured at 14.1 T with those previously measured at 9.4 T, a decreasing trend was found (p < 0.0001). We conclude that the modest shortening of T 2 at 14.1 T has a negligible impact on the sensitivity of the (1)H MRS when performed at TE shorter than 10 ms.

The glucose transporter 4 FQQI motif is necessary for Akt Substrate of 160-Kilodalton-dependent plasma membrane translocation but not Golgi-localized g-ear-containing Arf-binding protein-dependent entry into the insulin-responsive storage compartment.

Newly synthesized glucose transporter 4 (GLUT4) enters into the insulin-responsive storage compartment in a process that is Golgi-localized γ-ear-containing Arf-binding protein (GGA) dependent, whereas insulin-stimulated translocation is regulated by Akt substrate of 160 kDa (AS160). In the present study, using a variety of GLUT4/GLUT1 chimeras, we have analyzed the specific motifs of GLUT4 that are important for GGA and AS160 regulation of GLUT4 trafficking. Substitution of the amino terminus and the large intracellular loop of GLUT4 into GLUT1 (chimera 1-441) fully recapitulated the basal state retention, insulin-stimulated translocation, and GGA and AS160 sensitivity of wild-type GLUT4 (GLUT4-WT). GLUT4 point mutation (GLUT4-F5A) resulted in loss of GLUT4 intracellular retention in the basal state when coexpressed with both wild-type GGA and AS160. Nevertheless, similar to GLUT4-WT, the insulin-stimulated plasma membrane localization of GLUT4-F5A was significantly inhibited by coexpression of dominant-interfering GGA. In addition, coexpression with a dominant-interfering AS160 (AS160-4P) abolished insulin-stimulated GLUT4-WT but not GLUT4-F5A translocation. GLUT4 endocytosis and intracellular sequestration also required both the amino terminus and large cytoplasmic loop of GLUT4. Furthermore, both the FQQI and the SLL motifs participate in the initial endocytosis from the plasma membrane; however, once internalized, unlike the FQQI motif, the SLL motif is not responsible for intracellular recycling of GLUT4 back to the specialized compartment. Together, we have demonstrated that the FQQI motif within the amino terminus of GLUT4 is essential for GLUT4 endocytosis and AS160-dependent intracellular retention but not for the GGA-dependent sorting of GLUT4 into the insulin-responsive storage compartment.

Effect of dark chocolate on renal tissue oxygenation as measured by BOLD-MRI in healthy volunteers.

Background: Cocoa is rich in flavonoids, has anti-oxidative properties and increases the bioavailability of nitric oxide (NO). Adequate renal tissue oxygenation is crucial for the maintenance of renal function. The goal of this study was to investigate the effect of cocoa-rich dark chocolate (DC) on renal tissue oxygenation in humans, as compared to flavonoid-poor white chocolate (WC). Methods: Ten healthy volunteers with preserved kidney function (mean age ± SD 35 ± 12 years, 70% women, BMI 21 ± 3 kg/m2) underwent blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) before and 2 hours after the ingestion of 1 g/kg of DC (70% cocoa). Renal tissue oxygenation was determined by the measurement of R2* maps on 4 coronal slices covering both kidneys. The mean R2* (= 1/T2*) values in the medulla and cortex were calculated, a low R2* indicating high tissue oxygenation. Eight participants also underwent BOLD-MRI at least 1 week later, before and 2 hours after the intake of 1 g/kg WC. Results: The mean medullary R2* was lower after DC intake compared to baseline (28.2 ± 1.3 s-1 vs. 29.6 ± 1.3 s-1, p = 0.04), whereas cortical and medullary R2* values did not change after WC intake. The change in medullary R2* correlated with the level of circulating (epi)catechines, metabolites of flavonoids (r = 0.74, p = 0.037), and was independent of plasma renin activity. Conclusion: This study suggests for the first time an increase of renal medullary oxygenation after intake of dark chocolate. Whether this is linked to flavonoid-induced changes in renal perfusion or oxygen consumption, and whether cocoa has potentially renoprotective properties, merits further study.

Clinical pharmacokinetics of mycophenolic acid and its metabolites in solid organ transplant recipient

Mycophenolate mofetil (MMF), an ester prodrug of the immunosuppressant mycophenolic acid (MPA), is widely used for maintenance immunosuppressive therapy and prevention of renal allograft rejection in renal transplant recipients.MPA inhibits inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in the “de novo” synthesis of purine nucleotides, thus suppressing both T-cell and B-cell proliferation. MPA shows a complex pharmacokinetics with considerable interand intra- patient by between- and within patient variabilities associated to MPA exposure. Several factors may contribute to it. The pharmacokinetic modeling according to the population pharmacokinetic approach with the non-linear mixed effects models has shown to be a powerful tool to describe the relationships between MMF doses and the MPA exposures and also to identify potential predictive patients’ demographic and clinical characteristics for dose tailoring during the post-transplant immunosuppresive treatment.

Clinical pharmacokinetics of mycophenolic acid and its metabolites in solid organ transplant recipient

Mycophenolate mofetil (MMF), an ester prodrug of the immunosuppressant mycophenolic acid (MPA), is widely used for maintenance immunosuppressive therapy and prevention of renal allograft rejection in renal transplant recipients.MPA inhibits inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in the “de novo” synthesis of purine nucleotides, thus suppressing both T-cell and B-cell proliferation. MPA shows a complex pharmacokinetics with considerable interand intra- patient by between- and within patient variabilities associated to MPA exposure. Several factors may contribute to it. The pharmacokinetic modeling according to the population pharmacokinetic approach with the non-linear mixed effects models has shown to be a powerful tool to describe the relationships between MMF doses and the MPA exposures and also to identify potential predictive patients’ demographic and clinical characteristics for dose tailoring during the post-transplant immunosuppresive treatment.

Clinical pharmacokinetics of mycophenolic acid and its metabolites in solid organ transplant recipient

Mycophenolate mofetil (MMF), an ester prodrug of the immunosuppressant mycophenolic acid (MPA), is widely used for maintenance immunosuppressive therapy and prevention of renal allograft rejection in renal transplant recipients.MPA inhibits inosine monophosphate dehydrogenase (IMPDH), an enzyme involved in the “de novo” synthesis of purine nucleotides, thus suppressing both T-cell and B-cell proliferation. MPA shows a complex pharmacokinetics with considerable interand intra- patient by between- and within patient variabilities associated to MPA exposure. Several factors may contribute to it. The pharmacokinetic modeling according to the population pharmacokinetic approach with the non-linear mixed effects models has shown to be a powerful tool to describe the relationships between MMF doses and the MPA exposures and also to identify potential predictive patients’ demographic and clinical characteristics for dose tailoring during the post-transplant immunosuppresive treatment.

Pharmacogenetics-based population pharmacokinetic analysis of etravirine in HIV-1 infected individuals.

OBJECTIVES: Etravirine (ETV) is metabolized by cytochrome P450 (CYP) 3A, 2C9, and 2C19. Metabolites are glucuronidated by uridine diphosphate glucuronosyltransferases (UGT). To identify the potential impact of genetic and non-genetic factors involved in ETV metabolism, we carried out a two-step pharmacogenetics-based population pharmacokinetic study in HIV-1 infected individuals. MATERIALS AND METHODS: The study population included 144 individuals contributing 289 ETV plasma concentrations and four individuals contributing 23 ETV plasma concentrations collected in a rich sampling design. Genetic variants [n=125 single-nucleotide polymorphisms (SNPs)] in 34 genes with a predicted role in ETV metabolism were selected. A first step population pharmacokinetic model included non-genetic and known genetic factors (seven SNPs in CYP2C, one SNP in CYP3A5) as covariates. Post-hoc individual ETV clearance (CL) was used in a second (discovery) step, in which the effect of the remaining 98 SNPs in CYP3A, P450 cytochrome oxidoreductase (POR), nuclear receptor genes, and UGTs was investigated. RESULTS: A one-compartment model with zero-order absorption best characterized ETV pharmacokinetics. The average ETV CL was 41 (l/h) (CV 51.1%), the volume of distribution was 1325 l, and the mean absorption time was 1.2 h. The administration of darunavir/ritonavir or tenofovir was the only non-genetic covariate influencing ETV CL significantly, resulting in a 40% [95% confidence interval (CI): 13-69%] and a 42% (95% CI: 17-68%) increase in ETV CL, respectively. Carriers of rs4244285 (CYP2C19*2) had 23% (8-38%) lower ETV CL. Co-administered antiretroviral agents and genetic factors explained 16% of the variance in ETV concentrations. None of the SNPs in the discovery step influenced ETV CL. CONCLUSION: ETV concentrations are highly variable, and co-administered antiretroviral agents and genetic factors explained only a modest part of the interindividual variability in ETV elimination. Opposing effects of interacting drugs effectively abrogate genetic influences on ETV CL, and vice-versa.

Prediction of free imatinib concentrations based on total plasma concentrations in patients with gastrointestinal stromal tumours.

AIM: Total imatinib concentrations are currently measured for the therapeutic drug monitoring of imatinib, whereas only free drug equilibrates with cells for pharmacological action. Due to technical and cost limitations, routine measurement of free concentrations is generally not performed. In this study, free and total imatinib concentrations were measured to establish a model allowing the confident prediction of imatinib free concentrations based on total concentrations and plasma proteins measurements. METHODS: One hundred and fifty total and free plasma concentrations of imatinib were measured in 49 patients with gastrointestinal stromal tumours. A population pharmacokinetic model was built up to characterize mean total and free concentrations with inter-patient and intrapatient variability, while taking into account α1 -acid glycoprotein (AGP) and human serum albumin (HSA) concentrations, in addition to other demographic and environmental covariates. RESULTS: A one compartment model with first order absorption was used to characterize total and free imatinib concentrations. Only AGP influenced imatinib total clearance. Imatinib free concentrations were best predicted using a non-linear binding model to AGP, with a dissociation constant Kd of 319 ng ml(-1) , assuming a 1:1 molar binding ratio. The addition of HSA in the equation did not improve the prediction of imatinib unbound concentrations. CONCLUSION: Although free concentration monitoring is probably more appropriate than total concentrations, it requires an additional ultrafiltration step and sensitive analytical technology, not always available in clinical laboratories. The model proposed might represent a convenient approach to estimate imatinib free concentrations. However, therapeutic ranges for free imatinib concentrations remain to be established before it enters into routine practice.

Increased plasma levels of N-terminal brain natriuretic peptide (NT-proBNP) in type 2 diabetic patients with vascular complications.

AIMS: The plasma levels of either brain natriuretic peptide (BNP) or the N-terminal fragment of the prohormone (NT-proBNP) have recently gained extreme importance as markers of myocardial dysfunction. Patients with type 2 diabetes are at high risk of developing cardiovascular complications. This study was aimed to assess whether plasma NT-proBNP levels are at similar levels in type 2 diabetics with or without overt cardiovascular diseases. METHODS: We assayed plasma NT-proBNP in 54 type 2 diabetics, 27 of whom had no overt macro- and/or microvascular complications, while the remaining ones had either or both. The same assay was carried out in 38 healthy control subjects age and sex matched as a group with the diabetics. RESULTS: Plasma NT-proBNP was higher in diabetics (median 121 pg/ml, interquartile range 50-240 pg/ml, ) than in those without complications (37 pg/ml, 21-54 pg/ml, P<0.01). Compared with the controls (55 pg/ml, 40-79 pg/ml), only diabetics with vascular complications had significantly increased plasma NT-proBNP levels (P<0.001). In the diabetics, coronary heart disease and nephropathy (defined according to urinary excretion of albumin) were each independently associated with elevated values of plasma NT-proBNP. CONCLUSIONS: In type 2 diabetes mellitus, patients with macro- and/or micro-vascular complications exhibit an elevation of plasma NT-proBNP levels compared to corresponding patients with no evidence of vascular disease. The excessive secretion of this peptide is independently associated with coronary artery disease and overt nephropathy. The measurement of circulating NT-proBNP concentration may therefore be useful to screen for the presence of macro- and/or microvascular disease.