Simultaneous quantification of trimethoprim metabolites in pediatric plasma.

The dual agent antibiotic, trimethoprim/sulfamethoxazole (TMP-SMX), has been prescribed to treat or prevent infections for over 50 years. However, there are no published validated analytical methods for the measurement of TMP metabolites in humans. We developed methodology enabling reliable quantification of TMP and 5 metabolites in human plasma. Chromatographic separation was achieved in less than 8 min using a biphenyl column. Analytes were detected in positive electrospray mode using a tandem Waters Xevo-TQ-XS mass spectrometer. Precision and accuracy values for all analytes were within 15% of nominal values during assay validation.

Screening Trimethoprim Primary Metabolites for Covalent Binding to Albumin.

Modification of endogenous proteins by drugs and drug metabolites are thought to be a cause of idiosyncratic adverse drug reactions (IADRs). Trimethoprim (TMP) is a commonly prescribed antibiotic that has been implicated in IADRs; however, there is no known mechanism by which this drug or its metabolites modify proteins. This study describes the results of screening trimethoprim and its primary metabolites for the ability to covalently modify human serum albumin (HSA). The first step of the screen was in vitro reactions of the compounds with HSA followed by western blotting with antisera specific to drug-modified proteins. Compounds with positive signal in the western blot were then screened using an untargeted peptide profiling method to discover modified peptides. This strategy identified two sites in HSA that are modified by incubation with a TMP metabolite, α-hydroxy trimethoprim (Cα-OH-TMP).

Preliminary observations of mitochondrial dysfunction in Prader-Willi syndrome.

Prader-Willi syndrome (PWS) is a complex multisystem disorder because of errors in genomic imprinting with severe hypotonia, decreased muscle mass, poor suckling, feeding problems and failure to thrive during infancy, growth and other hormone deficiency, childhood-onset hyperphagia, and subsequent obesity. Decreased energy expenditure in PWS is thought to contribute to reduced muscle mass and physical activity but may also relate to cellular metabolism and disturbances in mitochondrial function. We established fibroblast cell lines from six children and adults with PWS and six healthy controls for mitochondrial assays. We used Agilent Seahorse XF extracellular flux technology to determine real-time measurements of several metabolic parameters including cellular substrate utilization, Adenosine Triphosphate (ATP)-linked respiration, and mitochondrial capacity in living cells. Decreased mitochondrial function was observed in the PWS patients compared to the healthy controls with significant differences in basal respiration, maximal respiratory capacity, and ATP-linked respiration. These results suggest disturbed mitochondrial bioenergetics in PWS although the low number of studied subjects will require a larger subject population before a general consensus can be reached to identify if mitochondrial dysfunction is a contributing factor in PWS.

Sustained O-GlcNAcylation reprograms mitochondrial function to regulate energy metabolism.

Dysfunctional mitochondria and generation of reactive oxygen species (ROS) promote chronic diseases, which have spurred interest in the molecular mechanisms underlying these conditions. Previously, we have demonstrated that disruption of post-translational modification of proteins with ß-linked N-acetylglucosamine (O-GlcNAcylation) via overexpression of the O-GlcNAc-regulating enzymes O-GlcNAc transferase (OGT) or O-GlcNAcase (OGA) impairs mitochondrial function. Here, we report that sustained alterations in O-GlcNAcylation either by pharmacological or genetic manipulation also alter metabolic function. Sustained O-GlcNAc elevation in SH-SY5Y neuroblastoma cells increased OGA expression and reduced cellular respiration and ROS generation. Cells with elevated O-GlcNAc levels had elongated mitochondria and increased mitochondrial membrane potential, and RNA-sequencing analysis indicated transcriptome reprogramming and down-regulation of the NRF2-mediated antioxidant response. Sustained O-GlcNAcylation in mouse brain and liver validated the metabolic phenotypes observed in the cells, and OGT knockdown in the liver elevated ROS levels, impaired respiration, and increased the NRF2 antioxidant response. Moreover, elevated O-GlcNAc levels promoted weight loss and lowered respiration in mice and skewed the mice toward carbohydrate-dependent metabolism as determined by indirect calorimetry. In summary, sustained elevation in O-GlcNAcylation coupled with increased OGA expression reprograms energy metabolism, a finding that has potential implications for the etiology, development, and management of metabolic diseases.

Arsenite Effects on Mitochondrial Bioenergetics in Human and Mouse Primary Hepatocytes Follow a Nonlinear Dose Response.

Arsenite is a known carcinogen and its exposure has been implicated in a variety of noncarcinogenic health concerns. Increased oxidative stress is thought to be the primary cause of arsenite toxicity and the toxic effect is thought to be linear with detrimental effects reported at all concentrations of arsenite. But the paradigm of linear dose response in arsenite toxicity is shifting. In the present study we demonstrate that arsenite effects on mitochondrial respiration in primary hepatocytes follow a nonlinear dose response. In vitro exposure of primary hepatocytes to an environmentally relevant, moderate level of arsenite results in increased oxidant production that appears to arise from changes in the expression and activity of respiratory Complex I of the mitochondrial proton circuit. In primary hepatocytes the excess oxidant production appears to elicit adaptive responses that promote resistance to oxidative stress and a propensity to increased proliferation. Taken together, these results suggest a nonlinear dose-response characteristic of arsenite with low-dose arsenite promoting adaptive responses in a process known as mitohormesis, with transient increase in ROS levels acting as transducers of arsenite-induced mitohormesis.

Functional coupling of ATP-binding cassette transporter Abcb6 to cytochrome P450 expression and activity in liver.

Although endogenous mechanisms that negatively regulate cytochrome P450 (P450) monooxygenases in response to physiological and pathophysiological signals are not well understood, they are thought to result from alterations in the level of endogenous metabolites, involved in maintaining homeostasis. Here we show that homeostatic changes in hepatic metabolite profile in Abcb6 (mitochondrial ATP-binding cassette transporter B6) deficiency results in suppression of a specific subset of hepatic P450 activity. Abcb6 null mice are more susceptible to pentobarbital-induced sleep and zoxazolamine-induced paralysis, secondary to decreased expression and activity of Cyp3a11 and Cyp2b10. The knock-out mice also show decrease in both basal and xeno-inducible expression and activity of a subset of hepatic P450s that appear to be related to changes in hepatic metabolite profile. These data, together with the observation that liver extracts from Abcb6-deficient mice suppress P450 expression in human primary hepatocytes, suggest that this mouse model may provide an opportunity to understand the physiological signals and the mechanisms involved in negative regulation of P450s.