Cardiolipin and electron transport chain abnormalities in mouse brain tumor mitochondria: lipidomic evidence supporting the Warburg theory of cancer

Abstract

Otto Warburg first proposed that cancer originated from irreversible injury to mitochondrial respiration, but the structural basis for this injury has remained elusive. Cardiolipin (CL) is a complex phospholipid found almost exclusively in the inner mitochondrial membrane and is intimately involved in maintaining mitochondrial functionality and membrane integrity. Abnormalities in CL can impair mitochondrial function and bioenergetics. We used shotgun lipidomics to analyze CL content and composition in highly purified brain mitochondria from the C57BL/6J (B6) and VM/Dk (VM) inbred strains and from subcutaneously grown brain tumors derived from these strains to include an astrocytoma and ependymoblastoma (B6 tumors), a stem cell tumor, and two microgliomas (VM tumors). Major abnormalities in CL content or composition were found in all tumors. The compositional abnormalities involved an abundance of immature molecular species and deficiencies of mature molecular species, suggesting major defects in CL synthesis and remodeling. The tumor CL abnormalities were also associated with significant reductions in both individual and linked electron transport chain activities. A mathematical model was developed to facilitate data interpretation. Otto Warburg first proposed that the prime cause of cancer was impaired energy metabolism (1, 2). This impairment involved irreversible injury to cellular respiration that was followed in time by a gradual dependence on fermentation (glycolytic) energy to compensate for the energy lost from respiration. Cell viability requires a constant delta G′ of ATP hydrolysis of approximately 257 kJ/mol (3, 4). Most normal mammalian cells achieve this level of useable energy through respiration, whereas tumor cells achieve this level through a combination of respiration and glycolysis (2, 5). Indeed, elevated glycolysis is the metabolic hallmark of nearly all tumors, including brain tumors, and is the basis for tumor imaging using labeled glucose analogs (5-8). Much controversy has surrounded the Warburg theory, however, largely over issues regarding the Pasture effect and aerobic glycolysis (9-14). Numerous structural and biochemical abnormalities occur in tumor cell mitochondria that could compromise function, thus forcing a reliance on glycolysis for cell survival (5,6,9,(15)(16)(17). Although several prior studies have evaluated the lipid composition of tumor mitochondria (18)(19)(20)(21)(22)(23)(24)(25), no prior studies have evaluated both the content and the composition of cardiolipin (CL) in highly purified mitochondria isolated from brain tumors and from their orthotopic host tissue.CL (1,3-diphosphatidyl-sn -glycerol) is a complex mitochondrial-specific phospholipid that regulates numerous enzyme activities, especially those related to oxidative phosphorylation and coupled respiration (26-31). CL binds complexes I, III, IV, and V and stabilizes the super complexes (I/III/IV and II/III/IV), demonstrating an absolute requirement of CL for catalytic activity of these enzyme comp...

Antioxidant capacity and toxicological evaluation ofPterospartum tridentatumflower extracts

“…This decline in respiratory activities is not consistent, and therefore, we hypothesized that instead of respiratory complexes' specific inhibition, this lower respiratory activity could be due to unspecific interactions of hydrophobic compounds with the mitochondrial inner membrane that could interfere with membrane fluidity (Kiebish, Han, Cheng, Chuang, & Seyfried, 2008). Indeed, swelling assay performed with Kacetate showed a slight increase in membrane permeability in the presence of P. tridentatum concentrations (250 or 500 mg.L 71 ) commonly used in traditional medicine (or to flavor rice), however these declines are not reflected in phosphorylative efficiency.…”

Metabolic reprogramming of the tumor

“…Warburg averred that an irreversible injury to respiration had to occur in order to trigger the progressive striving of cells that had succeeded to engage in lactic fermentation to fulfill their energy needs, leading ultimately to the formation of a tumor (Warburg, 1956a). Mutations in mitochondrial DNA (Bonora et al, 2006), and defective mitochondrial lipid content and structure (Kiebish et al, 2008), were found to squelch respiration in some tumors, while malfunction of some Krebs cycle enzymes also contributes to apoptosis resistance and aerobic glycolysis (King et al, 2006). This suggests that mitochondrial defects may have a role in certain cancers.…”

Dynamic simulation of cardiolipin remodeling: greasing the wheels for an interpretative approach to lipidomics

“…The pellet was resuspended in HM buffer without BSA, and the protein concentration of the resuspended mitochondrial fractions was determined using the BCA protein assay (Thermo Scientifi c, Rockford, IL). disease states ( 12,13,(15)(16)(17)(18)(19). This diversity is regulated by differences in cardiolipin biosynthesis and catabolism, remodeling acyl selectivities, and transacylase as well as acyltransferase activities ( 20,21 ).…”