Fatty Acid‐Induced Hepatocellular Carcinoma Growth is Mediated by Decreasing Mitochondrial H2O2 Emission Coupled to Increased Glutathione Levels

Abstract

Rationale and HypothesisHigh fat diets are associated with increased hepatocellular carcinoma (HCC) risk, as well as increased HCC growth rates. Accelerated HCC growth in response to fatty acid challenges has been attributed to a variety of signalling pathways, but the role of metabolic and redox flexibility in mediating a pro‐growth environment in this context has not been examined. Here we examined the direct effect of fatty acid challenges on HCC growth in relation to altered metabolic and redox homeostasis.Experimental approachThe HCC cell line HepG2 was incubated with 0μM, 50μM and 100μM palmitoylcarnitine (PCarn) for up to 48 hrs. We measured clonogenic survival, mitochondrial H2O2 emission and glutathione following PCarn incubations with and without the glutathione depleting agent buthionine sulfoximine (BSO) and inhibition of uncoupling protein‐2 (UCP2) activity by genipin.Results100μM PCarn increased clonogenic survival in HepG2 by 8% more than control (p<0.05) at 48 hrs which represents a marked early effect considering the population doubling time of HepG2 cells is ~48 hrs. This was associated with an increase in both reduced and oxidized glutathione at both 24 and 48 hrs (p<0.05). Depleting glutathione with BSO prevented PCarn‐stimulated growth (p<0.05). In a separate experiment, acute incubations of 100μM PCarn increased H2O2 emission within the first 10 minutes (p<0.05) followed by a decrease in H2O2 at 1 hr that remained lower at 24 hrs (p<0.05). The acute increase in H2O2 followed by a more chronic depression in H2O2 suggested PCarn might have triggered a compensatory mechanism. In support of this notion, inhibition of UCP2 with genipin sensitized HepG2 cells to PCarn‐induced decreases in clonogenic survival (p<0.05) without a change in UCP2 protein content.ConclusionCollectively, this data suggests that PCarn‐induced HCC growth is in part attributed to elevated glutathione. Increases in glutathione may be a result of UCP2 rapidly attenuating PCarn‐induced H2O2 emission which may permit greater glutathione synthetic rates and creation of a pro‐growth redox environment.Support or Funding InformationFunding was provided to C.G.R.P. by National Science and Engineering Research Council (#436138‐2013) with infrastructure supported by Canada Foundation for Innovation, Ontario Research Fund and the James H. Cummings Foundation. P. C. T. was supported by an NSERC CGS‐D scholarship.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.