Abstract only
Modification of the enzymatic activity of cytochrome P450 (CYP450) enzymes can alter the metabolism of the drug substrate for that enzyme, and thereby alter the biological activity of ...the drug leading to potentially harmful drug‐drug interactions. The activity and in some cases the induction of these CYP450 family members is mediated by haem, an essential prosthetic group of these detoxifying enzymes. In the present study we investigated whether the mitochondrial half transporter Abcb6, which regulates cellular haem biosynthesis and cellular haemoprotein pool, plays a role in the expression and/or function of CYP450s. We found that over‐expression of Abcb6 in HepG2 cells lead to an increase in CYP3A4 mRNA expression. In contrast over‐expression of Abcb6 in K562 cells resulted in decreased expression of CYP3A4, CYP2E1 and CYP2D6 mRNA. We tested whether prototypical inducers of CYP450 expression regulated Abcb6 expression and found that both pregnenolone‐16α carbonitrile (PCN) and 1,4‐bis2‐(3,5‐dichloropyridyloxy) benzene (TCPOBOP), two well known inducers of CYP450, also induced Abcb6 expression both
in vitro
and
in vivo
. Cumulatively these findings suggest that Abcb6 might play a role in the metabolism and disposition of drugs and environmental chemicals, and may affect drug clearance and drug toxicity.
Objective
This study examines discontinuation of psychotherapy from a consumer decision‐making perspective. Two plausible predictors, the level of illness and rate of progress from where the patient ...started, were examined as predictors of treatment discontinuation.
Method
Using data from 139 patients (45.5% women; mean age = 32.18 years) participating in a 12‐week transdiagnostic cognitive‐behavioral therapy program for anxiety, weekly assessments of anxiety severity were examined to investigate the extent to which level of anxiety and rate of improvement predicted treatment discontinuation.
Results
Support was found for a significant interaction effect wherein at higher anxiety levels, rate of progress was less associated with discontinuation than at lower anxiety levels.
Conclusion
Faster rates of anxiety reduction are associated with greater likelihood of discontinuation when the client is at a lower level of anxiety, whereas rate of improvement is less associated with discontinuation if there remains continued impairment and room for improvement. As such, clinicians should monitor rates of improvement throughout treatment to help identify and evaluate patients at increased risk of premature discontinuation.
Abstract only
Hypoxia plays critical roles in the pathobiology of heart disease, cancer, stroke, and chronic lung disease, which are responsible for 60% of deaths in the United States. Evidence ...suggests that hypoxic survival often requires reprogramming of mitochondrial basal metabolism. However, our understanding of the fundamental mechanisms that regulate mitochondrial metabolism are still incomplete. During our studies evaluating the physiological significance of the mitochondrial transporter ABCB6, we uncovered a novel pathway in which loss of ABCB6 expression shifts the balance between mitochondrial respiration and glycolysis because ABCB6 expression decreased mitochondrial respiratory rate and increased glycolysis rate. More importantly, we found that the major transcriptional sensor of oxygen hypoxia‐inducible factor (HIF) was involved in the activation of Abcb6 expression under hypoxic conditions. Further, ABCB6 promoter contains hypoxia response (HRE) elements. These HREs are functional because the promoter is activated by the hypoxia mimetic, desferoxamine as well as directly by co‐transfected HIF1‐alpha. Moreover, in cells with a defective HIF, ABCB6 expression is not upregulated by hypoxia. Finally, ectopic overexpression of ABCB6 reveals that ABCB6 protects cells from the cytotoxicity induced by hypoxia. These studies reveal that ABCB6, a mitochondrial ABC transporter, is regulated by hypoxia and the major hypoxia transcription factor HIF1‐alpha. This upregulation by hypoxia is compatible with ABCB6 overexpression providing a survival advantage under hypoxic conditions.
Support or Funding Information
P20RR021940‐7
T32ES007079
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.
Background: Physiological signals that negatively regulate CYP450s are not well understood.
Results: Loss of Abcb6 in mice results in suppression of CYP450 activity.
Conclusion: Suppression of P450 activity in Abcb6 deficiency may result from altered endogenous metabolites involved in maintaining homeostasis.
Significance: Understanding metabolite alterations in Abcb6 deficiency should help understand the physiological signals and the mechanisms involved in negative regulation of P450s.
Heme is an important regulator of biological processes, but an unresolved question remains, can heme regulate the switch between glycolysis and mitochondrial oxidation in mammalian cells? Here we ...show that ABCB6, a member of the ATP‐binding cassette (ABC) family and an activator of heme synthesis facilitates a heme dependent metabolic transition between mitochondrial oxidative phosphorylation and glycolytic metabolism. ABCB6 is upregulated by the Hif‐1α pathway and mimicking this, overexpression of ABCB6 primarily increased mitochondrial heme, reduced pyruvate‐fueled mitochondrial oxygen consumption and increased hypoxic survival. Suppression of heme synthesis abolished this hypoxic survival advantage. Deletion of ABCB6 increased mitochondrial oxygen consumption in the inherently hypoxic double‐negative thymocytes. We hypothesized that pyruvate dehydrogenase (PDH) activity was suppressed by heme and directly demonstrated that heme potently inhibited PDH activity. Hemin‐agarose affinity chromatography revealed that only one subunit of the multimeric PDH complex, PDHA1, is bound to heme. Mutagenesis of PDHA1 suggested that the heme binding site was distinct from the substrate binding site, a finding consistent with heme inhibiting PDH non‐competitively. Heme binding to PDHA1 resulted in its dissociation from the PDH complex. PDHA1 dissociation was reversible, as dilution of heme containing PDH promoted reformation of the complex, which paralleled restoration of PDH activity. These findings reveal a new relationship between heme production and the ability to metabolically switch from pyruvate oxidation in the mitochondria to its glycolytic conversion to lactate.
Support or Funding Information
This work was supported by NIH and by the ALSAC.
This is from the Experimental Biology 2019 Meeting. There is no full text article associated with this published in The FASEB Journal.
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.
Abstract only
Non‐alcoholic steatohepatitis is associated with hepatic free cholesterol accumulation and defective autophagy activity, which sensitize hepatocytes to injury and inflammation. Bile ...acid synthesis is the only quantitatively significant mechanism for hepatic cholesterol catabolism. Stimulating bile acid synthesis prevented hypercholesterolemia and hepatic steatosis in mice. Autophagy delivers intracellularly stored cholesterol to the lysosome where cholesterol ester is hydrolyzed for subsequent cellular distribution, efflux and bile acid synthesis. The objective of this study is to investigate the molecular link between cholesterol and bile acid metabolism and autophagic activity in hepatocytes and in mouse models of fatty liver disease. Confocal microscopy, immunoblot and cathespin B activity assay showed that excessive intracellular free cholesterol accumulation caused by free cholesterol loading and inhibition of cholesterol esterification in the endoplasmic reticulum (ER) with an ACAT inhibitor blocked autophagosome/lysosome fusion and impaired lysosome function in cholesterol‐laden HepG2 cells. In contrast, cholesterol ester accumulation induced by purified human low‐density lipoprotein treatment increased lysosome function without inhibiting autophagy activity. In addition, bile acid treatment blocked autophagosome/lysosome fusion without affecting key autophagy gene expression in HepG2 cells. Interestingly, over‐expression of CYP7A1 by adenoviral gene delivery, which induced ER cholesterol catabolism and caused relative ER cholesterol depletion, strongly induced autophagy flux in both human hepatocytes and HepG2 cells. Based on this novel regulatory relationship between ER cholesterol sensing and autophagy activity, confocal microscopy, electron microscopy and immunoblot further revealed that cholestyramine administration strongly induced hepatic autophagy in lean mice, and restored hepatic autophagy activity and improved hepatic steatosis in obese mice. The cholestyramine‐mediated hepatic autophagy induction can be attributed to CYP7A1‐mediated ER cholesterol catabolism and decreased hepatic bile acid signaling. In conclusion, these results suggest that hepatic autophagy is regulated by an intracellular cholesterol sensing mechanism, and is an integral part of the complex regulatory network that maintains cholesterol homeostasis in hepatocytes. This study supports a new concept of targeting the enterohepatic bile acid‐CYP7A1‐cholesterol‐autophagy axis to selectively modulate hepatic autophagy activity in fatty liver disease.
Support or Funding Information
NIDDK and NIAAA
Cytarabine (Ara-C) and Daunorubicin (Dnr) forms the backbone of acute myeloid leukemia (AML) therapy. Drug resistance and toxic side effects pose a major threat to treatment success and hence ...alternate less toxic therapies are warranted. NF-E2 related factor-2 (Nrf2), a master regulator of antioxidant response is implicated in chemoresistance in solid tumors. However, little is known about the role of Nrf2 in AML chemoresistance and the effect of pharmacological inhibitor brusatol in modulating this resistance. Primary AML samples with high ex-vivo IC50 to Ara-C, ATO, Dnr had significantly high NRF2 RNA expression. Gene-specific knockdown of NRF2 improved sensitivity to these drugs in resistant AML cell lines by decreasing the expression of downstream antioxidant targets of Nrf2 by compromising the cell's ability to scavenge the ROS. Treatment with brusatol, a pharmacological inhibitor of Nrf2, improved sensitivity to Ara-C, ATO, and Dnr and reduced colony formation capacity. AML cell lines stably overexpressing NRF2 showed increased resistance to ATO, Dnr and Ara-C and increased expression of downstream targets. This study demonstrates that Nrf2 could be an ideal druggable target in AML, more so to the drugs that function through ROS, suggesting the possibility of using Nrf2 inhibitors in combination with chemotherapeutic agents to modulate drug resistance in AML.
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