Midazolam oxidation in cattle liver microsomes: The role of cytochrome P450 3A.

In humans, the cytochrome P450 3A (CYP3A) subfamily is involved in midazolam (MDZ) biotransformation into 1'- and 4-hydroxy metabolites, and the former serves as a probe for CYP3A catalytic activity. In veterinary species is still crucial to identify enzyme- and species-specific CYP substrates; thus, the aim of this study was to characterize MDZ oxidation in cattle liver. A HPLC-UV method was used to measure 1'- and 4-hydroxy MDZ (1'- and 4-OHMDZ, respectively) formation in cattle liver microsomes and assess the role of CYP3A by an immunoinhibition study. Moreover, MDZ hydroxylation was evaluated in 300 cattle liver samples and results were correlated with testosterone hydroxylation. Formation of both metabolites conformed to a single-enzyme Michaelis-Menten kinetics. Values of Vmax and Km were 0.67 nmol/min/mg protein and 6.16 µM for 4-OHMDZ, and 0.06 nmol/min/mg protein and 10.08 µM for 1'-OHMDZ. An anti-rat CYP3A1 polyclonal antibody inhibited up to 50% and 94% 1'- and 4-OHMDZ formation, respectively. MDZ oxidation in liver microsomes was poorly correlated with testosterone hydroxylation. In conclusion, cattle metabolized MDZ to 1'-OHMDZ and 4-OHMDZ. The immunoinhibition results indicated a major contribution of CYP3As to 4-OHMDZ formation and the involvement of other CYPs in 1'-OHMDZ production, paving the way for further investigations.

Upregulation of inducible NO synthase by exogenous adenosine in vascular smooth muscle cells activated by inflammatory stimuli in experimental diabetes.

BACKGROUND: Adenosine has been shown to induce nitric oxide (NO) production via inducible NO synthase (iNOS) activation in vascular smooth muscle cells (VSMCs). Although this is interpreted as a beneficial vasodilating pathway in vaso-occlusive disorders, iNOS is also involved in diabetic vascular dysfunction. Because the turnover of and the potential to modulate iNOS by adenosine in experimental diabetes have not been explored, we hypothesized that both the adenosine system and control of iNOS function are impaired in VSMCs from streptozotocin-diabetic rats. METHODS: Male Sprague-Dawley rats were injected with streptozotocin once to induce diabetes. Aortic VSMCs from diabetic and nondiabetic rats were isolated, cultured and exposed to lipopolysaccharide (LPS) plus a cytokine mix for 24 h in the presence or absence of (1) exogenous adenosine and related compounds, and/or (2) pharmacological agents affecting adenosine turnover. iNOS functional expression was determined by immunoblotting and NO metabolite assays. Concentrations of adenosine, related compounds and metabolites thereof were assayed by HPLC. Vasomotor responses to adenosine were determined in endothelium-deprived aortic rings. RESULTS: Treatment with adenosine-degrading enzymes or receptor antagonists increased iNOS formation in activated VSMCs from nondiabetic and diabetic rats. Following treatment with the adenosine transport inhibitor NBTI, iNOS levels increased in nondiabetic but decreased in diabetic VSMCs. The amount of secreted NO metabolites was uncoupled from iNOS levels in diabetic VSMCs. Addition of high concentrations of adenosine and its precursors or analogues enhanced iNOS formation solely in diabetic VSMCs. Exogenous adenosine and AMP were completely removed from the culture medium and converted into metabolites. A tendency towards elevated inosine generation was observed in diabetic VSMCs, which were also less sensitive to CD73 inhibition, but inosine supplementation did not affect iNOS levels. Pharmacological inhibition of NOS abolished adenosine-induced vasorelaxation in aortic tissues from diabetic but not nondiabetic animals. CONCLUSIONS: Endogenous adenosine prevented cytokine- and LPS-induced iNOS activation in VSMCs. By contrast, supplementation with adenosine and its precursors or analogues enhanced iNOS levels in diabetic VSMCs. This effect was associated with alterations in exogenous adenosine turnover. Thus, overactivation of the adenosine system may foster iNOS-mediated diabetic vascular dysfunction.

The role of antibody responses against glycans in bioprosthetic heart valve calcification and deterioration.

Bioprosthetic heart valves (BHVs) are commonly used to replace severely diseased heart valves but their susceptibility to structural valve degeneration (SVD) limits their use in young patients. We hypothesized that antibodies against immunogenic glycans present on BHVs, particularly antibodies against the xenoantigens galactose-α1,3-galactose (αGal) and N-glycolylneuraminic acid (Neu5Gc), could mediate their deterioration through calcification. We established a large longitudinal prospective international cohort of patients (n = 1668, 34 ± 43 months of follow-up (0.1-182); 4,998 blood samples) to investigate the hemodynamics and immune responses associated with BHVs up to 15 years after aortic valve replacement. Early signs of SVD appeared in <5% of BHV recipients within 2 years. The levels of both anti-αGal and anti-Neu5Gc IgGs significantly increased one month after BHV implantation. The levels of these IgGs declined thereafter but anti-αGal IgG levels declined significantly faster in control patients compared to BHV recipients. Neu5Gc, anti-Neu5Gc IgG and complement deposition were found in calcified BHVs at much higher levels than in calcified native aortic valves. Moreover, in mice, anti-Neu5Gc antibodies were unable to promote calcium deposition on subcutaneously implanted BHV tissue engineered to lack αGal and Neu5Gc antigens. These results indicate that BHVs manufactured using donor tissues deficient in αGal and Neu5Gc could be less prone to immune-mediated deterioration and have improved durability.

MHC matching fails to prevent long-term rejection of iPSC-derived neurons in non-human primates.

Cell therapy products (CTP) derived from pluripotent stem cells (iPSCs) may constitute a renewable, specifically differentiated source of cells to potentially cure patients with neurodegenerative disorders. However, the immunogenicity of CTP remains a major issue for therapeutic approaches based on transplantation of non-autologous stem cell-derived neural grafts. Despite its considerable side-effects, long-term immunosuppression, appears indispensable to mitigate neuro-inflammation and prevent rejection of allogeneic CTP. Matching iPSC donors' and patients' HLA haplotypes has been proposed as a way to access CTP with enhanced immunological compatibility, ultimately reducing the need for immunosuppression. In the present work, we challenge this paradigm by grafting autologous, MHC-matched and mis-matched neuronal grafts in a primate model of Huntington's disease. Unlike previous reports in unlesioned hosts, we show that in the absence of immunosuppression MHC matching alone is insufficient to grant long-term survival of neuronal grafts in the lesioned brain.

Phenotypic activation and pharmacological outcomes of spontaneously differentiated human monocyte-derived macrophages.

Macrophage activation has been observed in vivo under physiological and pathological conditions, and may represent an attractive target for pharmacological modulation. This study tested the hypothesis that human blood-derived macrophages generated in vitro in the absence of specific macrophage growth factors respond flexibly to activation stimuli and pharmacological treatment. Monocytes were differentiated to macrophages for 7 days in culture in RPMI 1640 with 10% FCS. The resulting population showed predominance of the M2 over M1 phenotype as measured by flow cytometry and the expression of M1 vs. M2 markers was not mutually exclusive. Activation with LPS/IFN-γ for 48 h significantly increased the fraction of surface CD68-expressing cells, the CD14(+)/CD16(-)/CD68(+) subset and cell-bound TNF-α levels, whereas expression of the CC chemokine receptor (CCR)-2 was unchanged. Expression of the M2 markers CD206, CD163 and CX3CR1 was down-regulated following M1 activation compared with resting and after pre-exposure to M2-triggers. By contrast, alternative activation with IL-4/IL-13 for 48 h did not increase M2 markers, while CD206 up-regulation was observed after 7 days. Both activation signals induced changes in gene expression profiles as shown by Q-PCR. Treatment with 100 nM dexamethasone enhanced the M2 morphotype and CD163 expression while preventing LPS/IFN-γ-induced CD163 down-regulation. After 1-week dexamethasone treatment, virtually all cells acquired a CD163(+)/CD206(+)/CX3CR1(+) M2 phenotype. Therefore, these protocols appear to be useful to perform screens of pharmacological agents targeting human macrophage activation.

Regulation of SIRT1 in vascular smooth muscle cells from streptozotocin-diabetic rats.

Sirtuins enzymes are a conserved family of nicotinamide adenine dinucleotide (NAD)-dependent deacetylases and ADP-ribosyltransferases that mediate responses to oxidative stress, fasting and dietary restriction in mammals. Vascular smooth muscle cells (VSMCs) are involved in many mechanisms that regulate vascular biology in vivo but the role of SIRT1 has not been explored in much detail. Therefore, we investigated the regulation of SIRT1 in cultured VSMCs under various stress conditions including diabetes. Sprague-Dawley rats were made diabetic by injecting a single dose of streptozotocin (65 mg/Kg), and aortic VSMCs were isolated after 4 weeks. Immunocytochemistry showed that SIRT1 was localized predominantly in the nucleus, with lower staining in VSMCs from STZ-diabetic as compared with normoglycemic rats. Previous diabetes induction in vivo and high glucose concentrations in vitro significantly downregulated SIRT1 amounts as detected in Western blot assays, whereas TNF-α (30 ng/ml) stimulation failed to induce significant changes. Because estrogen signaling affects several pathways of oxidative stress control, we also investigated SIRT1 modulation by 17ß-estradiol. Treatment with the hormone (10 nM) or a selective estrogen receptor-α agonist decreased SIRT1 levels in VSMCs from normoglycemic but not in those from STZ-diabetic animals. 17ß-estradiol treatment also enhanced activation of AMP-dependent kinase, which partners with SIRT1 in a signaling axis. SIRT1 downregulation by 17ß-estradiol could be observed as well in human peripheral blood mononuclear cells, a cell type in which SIRT1 downregulation is associated with insulin resistance and subclinical atherosclerosis. These data suggest that SIRT1 protein levels are regulated by diverse cellular stressors to a variable extent in VSMCs from diabetic and normoglycemic rats, warranting further investigation on SIRT1 as a modulator of VSMC activity in settings of vascular inflammation.

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.

Flavonoids diosmetin and hesperetin are potent inhibitors of cytochrome P450 2C9-mediated drug metabolism in vitro.

The aim of this study was to examine in vitro, by means of kinetic analysis and molecular docking simulations, the effects of the flavone diosmetin and its flavanone analog hesperetin on CYP (cytochrome P450) 2C9-mediated drug metabolism. To this purpose, the conversion of diclofenac to 4'-hydroxydiclofenac by human liver microsomes was used as a model assay for assessing the CYP2C9 inhibitory activity of these two flavonoids. Kinetic analyses showed that diosmetin and hesperetin were reversible, dead-end inhibitors of 4'-hydroxydiclofenac formation; their mean K(i) (inhibitor dissociation constant) values were 1.71 ± 0.58 and 21.50 ± 3.62 µM, respectively. Diosmetin behaved as a competitive inhibitor, since it increased markedly the K(m) (substrate concentration yielding 50% of V(max)) of the reaction without affecting the V(max) (maximum velocity of reaction). Hesperetin modified markedly K(m) and to a lesser extent also modified V(max), thus acting as a mixed competitive-noncompetitive inhibitor. The results of molecular docking simulations were consistent with those of kinetic analysis, since they showed that the putative binding sites of both diosmetin and hesperetin coincided with the CYP2C9 substrate binding site. The demonstration that diosmetin and hesperetin inhibit CYP2C9-mediated diclofenac metabolism at low micromolar concentrations is of potential clinical relevance because CYP2C9 is responsible for the biotransformation of various therapeutically important drugs that have narrow therapeutic indexes.

Synthesis and preliminary in vitro biological evaluation of 4-[(4-hydroxyphenyl)sulfanyl]but-3-en-2-one, a 4-mercaptophenol derivative designed as a novel bifunctional antimelanoma agent.

We report the synthesis and preliminary in vitro biological evaluations of 4-[(4-hydroxyphenyl)sulfanyl]but-3-en-2-one, a compound designed as a potential bifunctional antimelanoma agent, bearing both a tyrosinase-activatable phenolic moiety and a GSH-reactive alpha,beta-unsaturated carbonyl group. Both the E (1) and Z (2) isomers of the synthesized compound proved to be very good substrates of mushroom tyrosinase, reacted quickly with GSH at physiological pH, and showed a significant cytotoxic activity against B16F1 murine melanoma cells.

Flavonoids diosmetin and luteolin inhibit midazolam metabolism by human liver microsomes and recombinant CYP 3A4 and CYP3A5 enzymes.

We evaluated the effects of increasing concentrations of the flavonoids salvigenin, diosmetin and luteolin on the in vitro metabolism of midazolam (MDZ), a probe substrate for cytochrome P450 (CYP) 3A enzymes, which is converted into 1'-hydroxy-midazolam (1'-OH-MDZ) and 4-hydroxy-midazolam (4-OH-MDZ) by human liver microsomes. Salvigenin had only a modest effect on MDZ metabolism, whereas diosmetin and luteolin inhibited in a concentration-dependent manner the formation of both 1'-OH-MDZ and 4-OH-MDZ, with apparent K(i) values in the 30-50mumol range. Both diosmetin and luteolin decreased 1'-OH-MDZ formation by human recombinant CYP3A4, but not CYP3A5, whereas they decreased 4-OH-MDZ formation by both recombinant enzymes. To assess whether any relationship exists between the physico-chemical characteristics of flavones and their effects on MDZ metabolism, we tested the effects of three other flavones (flavone, tangeretin, chrysin) on MDZ metabolism by human liver microsomes. Whereas flavones possessing more than two hydroxyl groups (luteolin, diosmetin) inhibited MDZ biotransformation, flavones lacking hydroxyl groups in their A and B rings (flavone, tangeretin) stimulated MDZ metabolism. We also found close relationships between the maximum stimulatory or inhibitory effects of flavones on 1'-OH-MDZ and 4-OH-MDZ formation rates and their log of octanol/water partition coefficients (logP) or their total number of hydroxyl groups. The results of the study may be of clinical relevance since they suggest that luteolin and diosmetin may cause pharmacokinetic interactions with co-administered drugs metabolized via CYP3A.