Suppression of superoxide/hydrogen peroxide production at mitochondrial site IQ decreases fat accumulation, improves glucose tolerance and normalizes fasting insulin concentration in mice fed a high-fat diet.

We developed S1QEL1.719, a novel bioavailable S1QEL (suppressor of site IQ electron leak). S1QEL1.719 prevented superoxide/hydrogen peroxide production at site IQ of mitochondrial complex I in vitro. The free concentration giving half-maximal suppression (IC50) was 52 nM. Even at 50-fold higher concentrations S1QEL1.719 did not inhibit superoxide/hydrogen peroxide production from other sites. The IC50 for inhibition of complex I electron flow was 500-fold higher than the IC50 for suppression of superoxide/hydrogen peroxide production from site IQ. S1QEL1.719 was used to test the metabolic effects of suppressing superoxide/hydrogen peroxide production from site IQin vivo. C57BL/6J male mice fed a high-fat chow for one, two or eight weeks had increased body fat, decreased glucose tolerance, and increased fasting insulin concentrations, classic symptoms of metabolic syndrome. Daily prophylactic or therapeutic oral treatment of high-fat-fed animals with S1QEL1.719 decreased fat accumulation, strongly protected against decreased glucose tolerance and prevented or reversed the increase in fasting insulin level. Free exposures in plasma and liver at Cmax were 1-4 fold the IC50 for suppression of superoxide/hydrogen peroxide production at site IQ and substantially below levels that inhibit electron flow through complex I. These results show that the production of superoxide/hydrogen peroxide from mitochondrial site IQin vivo is necessary for the induction and maintenance of glucose intolerance caused by a high-fat diet in mice. They raise the possibility that oral administration of S1QELs may be beneficial in metabolic syndrome.

Superoxide produced by mitochondrial site IQ inactivates cardiac succinate dehydrogenase and induces hepatic steatosis in Sod2 knockout mice.

Superoxide produced by mitochondria has been implicated in numerous physiologies and pathologies. Eleven different mitochondrial sites that can produce superoxide and/or hydrogen peroxide (O2.-/H2O2) have been identified in vitro, but little is known about their contributions in vivo. We introduce novel variants of S1QELs and S3QELs (small molecules that suppress O2.-/H2O2 production specifically from mitochondrial sites IQ and IIIQo, respectively, without compromising bioenergetics), that are suitable for use in vivo. When administered by intraperitoneal injection, they achieve total tissue concentrations exceeding those that are effective in vitro. We use them to study the engagement of sites IQ and IIIQo in mice lacking functional manganese-superoxide dismutase (SOD2). Lack of SOD2 is expected to elevate superoxide levels in the mitochondrial matrix, and leads to severe pathologies and death about 8 days after birth. Compared to littermate wild-type mice, 6-day-old Sod2-/- mice had significantly lower body weight, lower heart succinate dehydrogenase activity, and greater hepatic lipid accumulation. These pathologies were ameliorated by treatment with a SOD/catalase mimetic, EUK189, confirming previous observations. A 3-day treatment with S1QEL352 decreased the inactivation of cardiac succinate dehydrogenase and hepatic steatosis in Sod2-/- mice. S1QEL712, which has a distinct chemical structure, also decreased hepatic steatosis, confirming that O2.- derived specifically from mitochondrial site IQ is a significant driver of hepatic steatosis in Sod2-/- mice. These findings also demonstrate the ability of these new S1QELs to suppress O2.- production in the mitochondrial matrix in vivo. In contrast, suppressing site IIIQo using S3QEL941 did not protect, suggesting that site IIIQo does not contribute significantly to mitochondrial O2.- production in the hearts or livers of Sod2-/- mice. We conclude that the novel S1QELs are effective in vivo, and that site IQ runs in vivo and is a significant driver of pathology in Sod2-/- mice.

Profiling induction of cytochrome p450 enzyme activity by statins using a new liquid chromatography-tandem mass spectrometry cocktail assay in human hepatocytes.

Human hepatocytes in primary culture are a very useful model to directly assess induction of gene expression by xenobiotics. We developed a cytochrome P450 (P450) activity cocktail assay using model substrates for the seven important P450s 1A2 (phenacetin), 2B6 (bupropion), 2C8 (amodiaquine), 2C9 (tolbutamide), 2C19 (S-mephenytoin), 2D6 (propafenone), and 3A4 (atorvastatin). Metabolite formation was determined by liquid chromatography-tandem mass spectrometry in hepatocyte culture supernatants. Atorvastatin has not been previously assessed as a CYP3A probe drug. We demonstrate highly selective atorvastatin ortho-hydroxylation by CYP3A4 by recombinant P450s. In human liver microsomes ortho-hydroxyatorvastatin formation was highly correlated with CYP3A4 protein content (r(s) = 0.78, p < 0.0001, n = 150). We profiled induction of these P450 activities in primary human hepatocytes after treatment with 30 microM atorvastatin, lovastatin, pravastatin, rosuvastatin, and simvastatin for 24 to 72 h. Except for pravastatin, all statins induced P450 activities to various degrees, approximately in the order atorvastatin > simvastatin > lovastatin > rosuvastatin. Inducibility of P450s followed the order CYP2C8 > CYP3A4 > CYP2C9 > CYP2B6 > CYP2C19 approximately CYP2D6 > CYP1A2. The strongest induction was observed for amodiaquine N-desalkylation, which was induced approximately 20-fold. Quantitative reverse transcription-polymerase chain reaction confirmed corresponding changes on the mRNA level with even more dramatic induction up to almost 100-fold. These data suggest a broader inducing effect of statins on cytochrome P450s and possibly other absorption, distribution, metabolism, and excretion genes than previously known, thus further emphasizing their drug-drug interaction potential. Our cocktail assay should be helpful for economical use of human hepatocytes in the assessment of P450 induction by drugs and drug candidates.

eIF2B activator prevents neurological defects caused by a chronic integrated stress response.

The integrated stress response (ISR) attenuates the rate of protein synthesis while inducing expression of stress proteins in cells. Various insults activate kinases that phosphorylate the GTPase eIF2 leading to inhibition of its exchange factor eIF2B. Vanishing White Matter (VWM) is a neurological disease caused by eIF2B mutations that, like phosphorylated eIF2, reduce its activity. We show that introduction of a human VWM mutation into mice leads to persistent ISR induction in the central nervous system. ISR activation precedes myelin loss and development of motor deficits. Remarkably, long-term treatment with a small molecule eIF2B activator, 2BAct, prevents all measures of pathology and normalizes the transcriptome and proteome of VWM mice. 2BAct stimulates the remaining activity of mutant eIF2B complex in vivo, abrogating the maladaptive stress response. Thus, 2BAct-like molecules may provide a promising therapeutic approach for VWM and provide relief from chronic ISR induction in a variety of disease contexts.

Effect of gemfibrozil, rifampicin, or probenecid on the pharmacokinetics of the SGLT2 inhibitor empagliflozin in healthy volunteers.

BACKGROUND: Empagliflozin is a potent, oral, selective inhibitor of sodium glucose cotransporter 2 in development for the treatment of type 2 diabetes mellitus. OBJECTIVE: The goal of these studies was to investigate potential drug-drug interactions between empagliflozin and gemfibrozil (an organic anion-transporting polypeptide 1B1 [OATP1B1]/1B3 and organic anion transporter 3 [OAT3] inhibitor), rifampicin (an OATP1B1/1B3 inhibitor), or probenecid (an OAT3 and uridine diphosphate glucuronosyltransferase inhibitor). METHODS: Two open-label, randomized, crossover studies were undertaken in healthy subjects. In the first study, 18 subjects received the following in 1 of 2 randomized treatment sequences: a single dose of empagliflozin 25 mg alone and gemfibrozil 600 mg BID for 5 days with a single dose of empagliflozin 25 mg on the third day. In the second study, 18 subjects received a single dose of empagliflozin 10 mg, a single dose of empagliflozin 10 mg coadministered with a single dose of rifampicin 600 mg, and probenecid 500 mg BID for 4 days with a single dose of empagliflozin 10 mg on the second day in 1 of 6 randomized treatment sequences. RESULTS: In the gemfibrozil study, 11 subjects were male, mean age was 35.1 years and mean body mass index (BMI) was 23.47 kg/m(2). In the rifampicin/probenecid study, 10 subjects were male, mean age was 32.7 years and mean BMI was 23.03 kg/m(2). Exposure to empagliflozin was increased by coadministration with gemfibrozil (AUC0-∞: geometric mean ratio [GMR], 158.50% [90% CI, 151.77-165.53]; Cmax: GMR, 115.00% [90% CI, 106.15-124.59]), rifampicin (AUC0-∞: GMR, 135.20% [90% CI, 129.58-141.06]; Cmax: GMR, 175.14% [90% CI, 160.14-191.56]), and probenecid (AUC0-∞: GMR, 153.47% [90% CI, 146.41-160.88]; Cmax: GMR, 125.60% [90% CI, 113.67-138.78]). All treatments were well tolerated. CONCLUSIONS: Increases in empagliflozin exposure were <2-fold, indicating that the inhibition of the OATP1B1/1B3, OAT3 transporter, and uridine diphosphate glucuronosyltransferases did not have a clinically relevant effect on empagliflozin exposure. No dose adjustments of empagliflozin were necessary when it was coadministered with gemfibrozil, rifampicin, or probenecid. ClinicalTrials.gov identifiers: NCT01301742 and NCT01634100.

Paraoxonase (PON1 and PON3) Polymorphisms: Impact on Liver Expression and Atorvastatin-Lactone Hydrolysis.

Atorvastatin δ-lactone, a major, pharmacologically inactive metabolite, has been associated with toxicity. In a previous study we showed that polymorphisms of UGT1A3 influence atorvastatin δ-lactone formation. Here we investigated the reverse reaction, atorvastatin δ-lactone hydrolysis, in a human liver bank. Screening of microarray data revealed paraoxonases PON1 and PON3 among 17 candidate esterases. Microsomal δ-lactone hydrolysis was significantly correlated to PON1 and PON3 protein (r(s) = 0.60; r(s) = 0.62, respectively; P < 0.0001). PON1 and PON3 were strongly correlated to each other (r(s) = 0.60) but PON1 was shown to be more extensively glycosylated than PON3. In addition a novel splice-variant of PON3 was identified. Genotyping of 40 polymorphisms within the PON-locus identified PON1 promoter polymorphisms (-108T > C, -832G > A, -1741G > A) and a tightly linked group of PON3 polymorphisms (-4984A > G, -4105G > A, -1091A > G, -746C > T, and F21F) to be associated with changes in atorvastatin δ-lactone hydrolysis and expression of PON1 but not PON3. However, carriers of the common PON1 polymorphisms L55M or Q192R showed no difference in δ-lactone hydrolysis or PON expression. Haplotype analysis revealed decreased δ-lactone hydrolysis in carriers of the most common haplotype *1 compared to carriers of haplotypes *2, *3, *4, and *7. Analysis of non-genetic factors showed association of hepatocellular and cholangiocellular carcinoma with decreased PON1 and PON3 expression, respectively. Increased C-reactive protein and γ-glutamyl transferase levels were associated with decreased protein expression of both enzymes, and increased bilirubin levels, cholestasis, and presurgical exposure to omeprazole or pantoprazole were related to decreased PON3 protein. In conclusion, PON-locus polymorphisms affect PON1 expression whereas non-genetic factors have an effect on PON1 and PON3 expression. This may influence response to therapy or adverse events in statin treatment.

A systems biology approach to dynamic modeling and inter-subject variability of statin pharmacokinetics in human hepatocytes.

BACKGROUND: The individual character of pharmacokinetics is of great importance in the risk assessment of new drug leads in pharmacological research. Amongst others, it is severely influenced by the properties and inter-individual variability of the enzymes and transporters of the drug detoxification system of the liver. Predicting individual drug biotransformation capacity requires quantitative and detailed models. RESULTS: In this contribution we present the de novo deterministic modeling of atorvastatin biotransformation based on comprehensive published knowledge on involved metabolic and transport pathways as well as physicochemical properties. The model was evaluated on primary human hepatocytes and parameter identifiability analysis was performed under multiple experimental constraints. Dynamic simulations of atorvastatin biotransformation considering the inter-individual variability of the two major involved enzymes CYP3A4 and UGT1A3 based on quantitative protein expression data in a large human liver bank (n = 150) highlighted the variability in the individual biotransformation profiles and therefore also points to the individuality of pharmacokinetics. CONCLUSIONS: A dynamic model for the biotransformation of atorvastatin has been developed using quantitative metabolite measurements in primary human hepatocytes. The model comprises kinetics for transport processes and metabolic enzymes as well as population liver expression data allowing us to assess the impact of inter-individual variability of concentrations of key proteins. Application of computational tools for parameter sensitivity analysis enabled us to considerably improve the validity of the model and to create a consistent framework for precise computer-aided simulations in toxicology.

Distinction between human cytochrome P450 (CYP) isoforms and identification of new phosphorylation sites by mass spectrometry.

In mammals, Cytochrome P450 (CYP) enzymes are bound to membranes of the endoplasmic reticulum and mitochondria, where they are responsible for the oxidative metabolism of many xenobiotics as well as organic endogenous compounds. In humans, 57 isoforms were identified which are classified based on sequence homology. In the present work, we demonstrate the performance of a mass spectrometry-based strategy to simultaneously detect and differentiate distinct human Cytochrome P450 (CYP) isoforms including the highly similar CYP3A4, CYP3A5, CYP3A7, as well as CYP2C8, CYP2C9, CYP2C18, CYP2C19, and CYP4F2, CYP4F3, CYP4F11, CYP4F12. Compared to commonly used immunodetection methods, mass spectrometry overcomes limitations such as low antibody specificity and offers high multiplexing possibilities. Furthermore, CYP phosphorylation, which may affect various biochemical and enzymatic properties of these enzymes, is still poorly analyzed, especially in human tissues. Using titanium dioxide resin combined with tandem mass spectrometry for phosphopeptide enrichment and sequencing, we discovered eight human P450 phosphorylation sites, seven of which were novel. The data from surgical human liver samples establish that the isoforms CYP1A2, CYP2A6, CYP2B6, CYP2E1, CYP2C8, CYP2D6, CYP3A4, CYP3A7, and CYP8B1 are phosphorylated in vivo. These results will aid in further investigation of the functional significance of protein phosphorylation for this important group of enzymes.