The synthesis of [ C]4-acetylphenylalanine, effect on cell viability, and assessment of protein incorporation in male rat hepatocytes.

PEGylation is a proven approach to prolonging the duration of action and enhancing biophysical solubility and stability of peptides. 4-Acetylphenylalanine is a novel amino acid with a ketone side chain that is uniquely reactive in proteins. The ketone functionality can react with an aminooxy functionalized polyethyleneglycol polymer to form a stable oxime adduct of the protein.

Evaluation of microRNAs-208 and 133a/b as differential biomarkers of acute cardiac and skeletal muscle toxicity in rats.

Conventional circulating biomarkers of cardiac and skeletal muscle (SKM) toxicity lack specificity and/or have a short half-life. MicroRNAs (miRNAs) are currently being assessed as biomarkers of tissue injury based on their long half-life in blood and selective expression in certain tissues. To assess the utility of miRNAs as biomarkers of cardiac and SKM injury, male Sprague-Dawley rats received a single dose of isoproterenol (ISO); metaproterenol (MET); allylamine (AAM); mitoxantrone (MIT); acetaminophen (APAP) or vehicle.

Utilization of the Zucker Diabetic Fatty (ZDF) Rat Model for Investigating Hypoglycemia-related Toxicities.

Glucokinase (GK) catalyzes the initial step in glycolysis and is a key regulator of glucose homeostasis. Therefore, glucokinase activators (GKa) have potential benefit in treating type 2 diabetes. Administration of a Bristol-Myers Squibb GKa (BMS-820132) to healthy euglycemic Sprague-Dawley (SD) rats and beagle dogs in 1 mo toxicology studies resulted in marked and extended hypoglycemia with associated clinical signs of toxicity and degenerative histopathological changes in the stomach, sciatic nerve, myocardium, and skeletal muscles at exposures comparable to those expected at therapeutic clinical exposures.

Carcinogenicity risk assessment supports the chronic safety of dapagliflozin, an inhibitor of sodium-glucose co-transporter 2, in the treatment of type 2 diabetes mellitus.

Introduction: Dapagliflozin is a selective inhibitor of the sodium-glucose co-transporter 2 (SGLT2) that increases urinary glucose excretion to reduce hyperglycemia in the treatment of type 2 diabetes mellitus. A robust carcinogenicity risk assessment was undertaken to assess the chronic safety of dapagliflozin and SGLT2 inhibition.

Methods: Genotoxicity potential of dapagliflozin and its metabolites was assessed in silico, in vitro, and in vivo.

Nonclinical toxicology assessments support the chronic safety of dapagliflozin, a first-in-class sodium-glucose cotransporter 2 inhibitor.

Dapagliflozin, a first-in-class, selective inhibitor of sodium-glucose cotransporter 2 (SGLT2), promotes urinary glucose excretion to reduce hyperglycemia for the treatment of type 2 diabetes. A series of nonclinical studies were undertaken to evaluate dapagliflozin in species where it was shown to have pharmacologic activity comparable with that in humans at doses that resulted in supratherapeutic exposures. In vitro screening (>300 targets; 10 μmol/L) indicated no significant off-target activities for dapagliflozin or its primary human metabolite.

Targeting the kidney and glucose excretion with dapagliflozin: preclinical and clinical evidence for SGLT2 inhibition as a new option for treatment of type 2 diabetes mellitus.

Sodium-glucose cotransporter-2 (SGLT2) inhibitors are a novel class of glucuretic, antihyperglycemic drugs that target the process of renal glucose reabsorption and induce glucuresis independently of insulin secretion or action. In patients with type 2 diabetes mellitus, SGLT2 inhibitors have been found to consistently reduce measures of hyperglycemia, including hemoglobin A1c, fasting plasma glucose, and postprandial glucose, throughout the continuum of disease. By inducing the renal excretion of glucose and its associated calories, SGLT2 inhibitors reduce weight and have the potential to be disease modifying by addressing the caloric excess that is believed to be one of the root causes of type 2 diabetes mellitus.

Targeting renal glucose reabsorption for the treatment of type 2 diabetes mellitus using the SGLT2 inhibitor dapagliflozin.

Sodium-glucose co-transporter 2 (SGLT2) plays a key role in glucose homeostasis as the key transporter responsible for most renal glucose reabsorption in the proximal tubules of the kidney. Dapagliflozin is a potent, selective, and reversible inhibitor of SGLT2 that lowers blood glucose levels in an insulin-independent fashion. This novel agent has been studied extensively in patients with type 2 diabetes mellitus (T2DM).

Cannabinoid receptor antagonist-induced striated muscle toxicity and ethylmalonic-adipic aciduria in beagle dogs.

Ibipinabant (IBI), a potent cannabinoid-1 receptor (CB1R) antagonist, previously in development for the treatment of obesity, causes skeletal and cardiac myopathy in beagle dogs. This toxicity was characterized by increases in muscle-derived enzyme activity in serum and microscopic striated muscle degeneration and accumulation of lipid droplets in myofibers. Additional changes in serum chemistry included decreases in glucose and increases in non-esterified fatty acids and cholesterol, and metabolic acidosis, consistent with disturbances in lipid and carbohydrate metabolism.

Validated LC-MS/MS methods for the determination of dapagliflozin, a sodium-glucose co-transporter 2 inhibitor in normal and ZDF rat plasma.

Background: Dapagliflozin is an inhibitor of sodium-glucose co-transporter 2 (SGLT-2) in development for the treatment of Type 2 diabetes. To support toxicology studies, LC-MS/MS methods were developed and validated for the quantitation of dapagliflozin in rat plasma.

Results: The assay uses solid phase extraction and LC-MS/MS analysis in negative ion electrospray ionization mode.

Effects of 6-hydroxydopamine on mitochondrial function and glutathione status in SH-SY5Y human neuroblastoma cells.

SH-SY5Y human neuroblastoma cells were incubated with 6-hydroxydopamine (6-OHDA) for 4 and 24 h to examine the mechanism of cell death and to determine the time-dependent effects of 6-OHDA on cellular glutathione status. After 4 h, 6-OHDA significantly depleted cellular ATP and GSH concentrations with only slight increases in cell death. GSH:GSSG ratios and mitochondrial membrane potential (Deltapsim) were significantly decreased during 4 h incubations with 6-OHDA.

Effects of troglitazone on HepG2 viability and mitochondrial function.

Troglitazone (TRO), a member of the thiazolidinedione class of drugs, has been associated with hepatotoxicity in patients. The following in vitro study was conducted to investigate the effects of TRO on mitochondrial function and viability in a human hepatoma cell line, HepG2. TRO induced a concentration- and time-dependent increase in cell death, as measured by lactate dehydrogenase release.

Etomoxir-induced oxidative stress in HepG2 cells detected by differential gene expression is confirmed biochemically.

Although they are known to be effective antidiabetic agents, little is published about the toxic effects of carnitine palmitoyltransferase-1 (CPT-1) inhibitors, such as etomoxir (ET). These compounds inhibit mitochondrial fatty acid beta-oxidation by irreversibly binding to CPT-1 and preventing entry of long chain fatty acids into the mitochondrial matrix. Treatment of HepG2 cells with 1 mM etomoxir for 6 h caused significant modulations in the expression of several redox-related and cell cycle mRNAs as measured by microarray analysis.

Vitamin E succinate protects hepatocytes against the toxic effect of reactive oxygen species generated at mitochondrial complexes I and III by alkylating agents.

The mechanism of alpha-tocopheryl succinate (TS) cytoprotection against mitochondria-derived oxidative stress was investigated. Incubation of isolated rat hepatocytes with ethyl methanesulfonate (EMS), a mitochondrial alkylating toxicant caused mitochondrial dysfunction and necrotic cell death that was dependent on the production of reactive oxygen species (ROS) and lipid peroxidation. Mitochondria isolated from these cells showed a 3-fold increase in lipid hydroperoxides and a selective depletion of alpha-tocopherol (T), which preceded cell death.

Mitochondrial electron transport inhibitors cause lipid peroxidation-dependent and -independent cell death: protective role of antioxidants.

Mitochondrial electron transport inhibitors induced two distinct pathways for acute cell death: lipid peroxidation-dependent and -independent in isolated rat hepatocytes. The toxic effects of mitochondrial complex I and II inhibitors, rotenone (ROT) and thenoyltrifluoroacetone (TTFA), respectively, were dependent on oxidative stress and lipid peroxidation, while cell death induced by inhibitors of complexes III and IV, antimycin A (AA) and cyanide (CN), respectively, was caused by MMP collapse and loss of cellular ATP. Accordingly, cellular and mitochondrial antioxidant depletion or supplementation, in general, resulted in a dramatic potentiation or prevention, respectively, of toxic injury induced by complex I and II inhibitors, with little or no effect on complex III and IV inhibitor-induced toxicity.

Enhanced antioxidant and cytoprotective abilities of vitamin E succinate is associated with a rapid uptake advantage in rat hepatocytes and mitochondria.

Numerous in vitro studies attest to the enhanced ability of vitamin E succinate (TS), as compared with conventional vitamin E compounds such as unesterified d-alpha-tocopherol (T) and d-alpha-tocopheryl acetate (TA), to protect hepatocytes from toxic oxidative stress. In the present study we tested the hypothesis that this unique protective ability is related to an enhanced cellular accumulation of TS. The results of this study indicate, using both in vitro and in vivo model systems, that acute TS administration results in a rapid increase in T and TS content and antioxidant protection of hepatocytes and mitochondria.

Glutathione-dependent regulation of nitric oxide production in isolated rat hepatocyte suspensions.

Freshly isolated suspensions of rat parenchymal liver cells (hepatocytes) spontaneously produce large amounts of nitrite following collagenase isolation. Our previous studies indicate that nitrite production is associated with the expression of inducible nitric oxide synthase (iNOS) and reflects NO production. Depletion of glutathione (GSH) with diethylmaleate (DEM) inhibited nitrite production, and this inhibition was time-dependent.

Glutathione depletion and the production of reactive oxygen species in isolated hepatocyte suspensions.

Diethyl maleate (DEM) (5 mM) and ethyl methanesulfonate (EMS) (35 mM) treatments rapidly depleted cellular reduced glutathione (GSH) below detectable levels (1 nmol/10(6) cells), and induced lipid peroxidation and necrotic cell death in freshly isolated rat hepatocytes. In hepatocytes incubated with 2.5 mM DEM and 10 mM EMS, however, the complete depletion of cellular GSH observed was not sufficient to induce lipid peroxidation or cell death.

Antiproliferative and apoptotic effects of tocopherols and tocotrienols on normal mouse mammary epithelial cells.

Studies were conducted to determine the comparative effects of tocopherols and tocotrienols on normal mammary epithelial cell growth and viability. Cells isolated from midpregnant BALB/c mice were grown within collagen gels and maintained on serum-free media. Treatment with 0-120 microM alpha- and gamma-tocopherol had no effect, whereas 12.

Characterization of nitric oxide production following isolation of rat hepatocytes.

Freshly isolated suspensions of rat parenchymal liver cells (hepatocytes) produce large amounts of nitrite following isolation. Nitrite production was inhibited by the inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine, as well as the transcription inhibitor actinomycin D. Increases in iNOS mRNA, protein, and activity levels correlated with the formation of nitrite.

Induction of stress proteins in rat cardiac myocytes by antimony.

The effects of nonlethal concentrations of potassium antimonyl tartrate (PAT) were examined in cultured neonatal rat cardiac myocytes. PAT (5, 10 microM) significantly increased cellular reduced glutathione (GSH) and heme oxygenase activity after 18 h. GSH levels and heme oxygenase activity were increased 2.

Administration of the tris salt of alpha-tocopheryl hemisuccinate inactivates CYP2E1, enhances microsomal alpha-tocopherol levels and protects against carbon tetrachloride-induced hepatotoxicity.

A series of tocopherol compounds were examined for their capacity to protect against carbon tetrachloride (CCl4)-induced hepatotoxicity in rats. Of the tocopherol compounds tested in our study, only the tris salt of d-alpha-tocopheryl hemisuccinate (TS-tris) protected against CCl4-induced hepatotoxicity. The administration of d-alpha-tocopherol (alpha-T) and the nonhydrolyzable tocopherol ether, d-alpha-tocopheryloxybutyrate tris salt (TSE-tris), failed to protect against CCl4-induced hepatotoxicity.

Time-dependent production of nitric oxide by rat hepatocyte suspensions.

Isolated hepatocyte suspensions prepared by collagenase perfusion released high levels of nitrite into the extracellular medium during an 8-hr incubation. The release was time dependent, with increases first occurring by 4 hr and continuing throughout the remainder of the incubation period. Nitrite production was inhibited by the nitric oxide synthase (NOS) inhibitors aminoguanidine and N(G)-nitro-L-arginine methyl ester (L-NAME), indicating that the nitrite is derived from nitric oxide (NO) production from NOS activity.

A fluorescence plate reader assay for monitoring the susceptibility of biological samples to lipid peroxidation.

The susceptibility of biological samples to lipid peroxidation can be determined by exposing samples to a lipid peroxidation initiator and measuring the length of time prior to the onset of lipid peroxidation. Previous studies have shown that aldehydes generated by lipid peroxidation can react with amines to produce fluorescent products. We have utilized this principle to develop a fluorescence plate reader assay for measuring susceptibility to lipid peroxidation.