Effect of glucose administered in vivo or in vitro on the respiratory quotient of rat liver tissue after partial hepatectomy

Can the Mitochondrial Metabolic Theory Explain Better the Origin and Management of Cancer than Can the Somatic Mutation Theory?

A theory that can best explain the facts of a phenomenon is more likely to advance knowledge than a theory that is less able to explain the facts. Cancer is generally considered a genetic disease based on the somatic mutation theory (SMT) where mutations in proto-oncogenes and tumor suppressor genes cause dysregulated cell growth. Evidence is reviewed showing that the mitochondrial metabolic theory (MMT) can better account for the hallmarks of cancer than can the SMT. Proliferating cancer cells cannot survive or grow without carbons and nitrogen for the synthesis of metabolites and ATP (Adenosine Triphosphate). Glucose carbons are essential for metabolite synthesis through the glycolysis and pentose phosphate pathways while glutamine nitrogen and carbons are essential for the synthesis of nitrogen-containing metabolites and ATP through the glutaminolysis pathway. Glutamine-dependent mitochondrial substrate level phosphorylation becomes essential for ATP synthesis in cancer cells that over-express the glycolytic pyruvate kinase M2 isoform (PKM2), that have deficient OxPhos, and that can grow in either hypoxia (0.1% oxygen) or in cyanide. The simultaneous targeting of glucose and glutamine, while elevating levels of non-fermentable ketone bodies, offers a simple and parsimonious therapeutic strategy for managing most cancers.

A method for measuring the molecular ratio of inhalation to exhalation and effect of inspired oxygen levels on oxygen consumption

Using a new method for measuring the molecular ratio (R) of inhalation to exhalation, we investigated the effect of high fraction of inspired oxygen (FIO2) on oxygen consumption (VO2), carbon dioxide generation (VCO2), and respiratory quotient (RQ) in mechanically ventilated rats. Twelve rats were equally assigned into two groups by anesthetics: intravenous midazolam/fentanyl vs. inhaled isoflurane. R, VO2, VCO2, and RQ were measured at FIO2 0.3 or 1.0. R error was ± 0.003. R was 1.0099 ± 0.0023 with isoflurane and 1.0074 ± 0.0018 with midazolam/fentanyl. R was 1.0081 ± 0.0017 at an FIO2 of 0.3 and 1.0092 ± 0.0029 at an FIO2 of 1.0. There were no differences in VCO2 among the groups. VO2 increased at FIO2 1.0, which was more notable when midazolam/fentanyl was used (isoflurane-FIO2 0.3: 15.4 ± 1.1; isoflurane-FIO2 1.0: 17.2 ± 1.8; midazolam/fentanyl-FIO2 0.3: 15.4 ± 1.1; midazolam/fentanyl-FIO2 1.0: 21.0 ± 2.2 mL/kg/min at STP). The RQ was lower at FIO2 1.0 than FIO2 0.3 (isoflurane-FIO2 0.3: 0.80 ± 0.07; isoflurane-FIO2 1.0: 0.71 ± 0.05; midazolam/fentanyl-FIO2 0.3: 0.79 ± 0.03; midazolam/fentanyl-FIO2 1.0: 0.59 ± 0.04). R was not affected by either anesthetics or FIO2. Inspired 100% O2 increased VO2 and decreased RQ, which might be more remarkable when midazolam/fentanyl was used.

On the Origin of ATP Synthesis in Cancer

ATP is required for mammalian cells to remain viable and to perform genetically programmed functions. Maintenance of the ΔG′_ATP hydrolysis of −56 kJ/mole is the endpoint of both genetic and metabolic processes required for life. Various anomalies in mitochondrial structure and function prevent maximal ATP synthesis through OxPhos in cancer cells. Little ATP synthesis would occur through glycolysis in cancer cells that express the dimeric form of pyruvate kinase M2. Mitochondrial substrate level phosphorylation (mSLP) in the glutamine-driven glutaminolysis pathway, substantiated by the succinate-CoA ligase reaction in the TCA cycle, can partially compensate for reduced ATP synthesis through both OxPhos and glycolysis. A protracted insufficiency of OxPhos coupled with elevated glycolysis and an auxiliary, fully operational mSLP, would cause a cell to enter its default state of unbridled proliferation with consequent dedifferentiation and apoptotic resistance, i.e., cancer. The simultaneous restriction of glucose and glutamine offers a therapeutic strategy for managing cancer.

Mitochondrial Substrate-Level Phosphorylation as Energy Source for Glioblastoma: Review and Hypothesis

Glioblastoma multiforme (GBM) is the most common and malignant of the primary adult brain cancers. Ultrastructural and biochemical evidence shows that GBM cells exhibit mitochondrial abnormalities incompatible with energy production through oxidative phosphorylation (OxPhos). Under such conditions, the mitochondrial F0-F1 ATP synthase operates in reverse at the expense of ATP hydrolysis to maintain a moderate membrane potential. Moreover, expression of the dimeric M2 isoform of pyruvate kinase in GBM results in diminished ATP output, precluding a significant ATP production from glycolysis. If ATP synthesis through both glycolysis and OxPhos was impeded, then where would GBM cells obtain high-energy phosphates for growth and invasion? Literature is reviewed suggesting that the succinate-CoA ligase reaction in the tricarboxylic acid cycle can substantiate sufficient ATP through mitochondrial substrate-level phosphorylation (mSLP) to maintain GBM growth when OxPhos is impaired. Production of high-energy phosphates would be supported by glutaminolysis—a hallmark of GBM metabolism—through the sequential conversion of glutamine → glutamate → alpha-ketoglutarate → succinyl CoA → succinate. Equally important, provision of ATP through mSLP would maintain the adenine nucleotide translocase in forward mode, thus preventing the reverse-operating F0-F1 ATP synthase from depleting cytosolic ATP reserves. Because glucose and glutamine are the primary fuels driving the rapid growth of GBM and most tumors for that matter, simultaneous restriction of these two substrates or inhibition of mSLP should diminish cancer viability, growth, and invasion.

Glucagon-like peptide-1 analogues exenatide and liraglutide exert inhibitory effect on the early phase of liver regeneration after partial hepatectomy in rats

Glucagon-like peptide-1 (GLP-1) is an incretin known for proliferative and antiapoptotic effects on various tissues. Exenatide and Liraglutide are GLP-1 analogues used in clinical practice as antidiabetic drugs. Since GLP-1 and its analogues exert significant effect on liver metabolism and since changes in intermediary metabolism play an important role in the process of liver regeneration, we decided to determine the effect of Exenatide and Liraglutide on the early phase of liver regeneration and selected metabolic parameters in a model of 2/3 partial hepatectomy (PHx) in rats. Animals were submitted either to PHx or laparotomy and received 3 doses of either GLP-1 analogues (Exenatide - 42 microg/kg b.w., Liraglutide - 0.75 mg/kg b.w.) or saline intraperitoneally. We analyzed body and liver weight, liver bromodeoxyuridine incorporation, liver content of DNA, triacylglycerols and cholesterol and biochemical serum parameters. Bromodeoxyuridine labeling was significantly lower in hepatectomized rats receiving either type of GLP-1 analogues when compared to hepatectomized controls. This effect was more pronounced in the Liraglutide group compared to Exenatide (p<0.001). In addition, liver DNA content was lower in hepatectomized rats receiving Liraglutide than in hepatectomized control rats (p<0.001). In conclusion, GLP-1 analogues Exenatide and Liraglutide significantly inhibited an early phase of liver regeneration after PHx in rats. This inhibitory effect was more pronounced in rats receiving Liraglutide.

Cancer as a metabolic disease: implications for novel therapeutics

Emerging evidence indicates that cancer is primarily a metabolic disease involving disturbances in energy production through respiration and fermentation. The genomic instability observed in tumor cells and all other recognized hallmarks of cancer are considered downstream epiphenomena of the initial disturbance of cellular energy metabolism. The disturbances in tumor cell energy metabolism can be linked to abnormalities in the structure and function of the mitochondria. When viewed as a mitochondrial metabolic disease, the evolutionary theory of Lamarck can better explain cancer progression than can the evolutionary theory of Darwin. Cancer growth and progression can be managed following a whole body transition from fermentable metabolites, primarily glucose and glutamine, to respiratory metabolites, primarily ketone bodies. As each individual is a unique metabolic entity, personalization of metabolic therapy as a broad-based cancer treatment strategy will require fine-tuning to match the therapy to an individual’s unique physiology.

Plasma carnitine kinetics during orthotopic liver transplantation

BACKGROUND

Carnitine is synthesized mainly in the liver and plays an essential role in the transport of fatty acids in liver mitochondria for subsequent oxidation and energy production.

METHODS

The plasma concentrations of free carnitine, acylcarnitine, total ketone bodies, lactate, pyruvate, and hepatocyte growth factor (HGF) were measured during liver transplantation.

RESULTS

The plasma free carnitine and acylcarnitine concentrations and the lactate to pyruvate ratio in patients with compromised grafts (group A) were significantly higher than those in patients with well-functioning grafts (group B) after reperfusion. The acylcarnitine concentration in group B decreased after incision, but it remained at a high level in group A. Significant correlations were found between the concentrations of HGF and free and acylcarnitine after reperfusion.

CONCLUSION

The accelerated flux of carnitine in the graft may be associated with deterioration of energy metabolism in the graft. An increased acylcarnitine concentration may reflect impaired liver regeneration.

Hypercaloric lipid and glucose infusion reduces the mitochondrial respiratory activity in the regenerating rat liver

In order to evaluate the liver mitochondrial response to an increased energy load, eight groups of rats were studied: a control group (no surgery), a sham-operated group, and 6 groups that had undergone partial hepatectomy (PH). The PH rats either had no infusion following surgery, saline, isocaloric lipid, hypercaloric lipid, isocaloric glucose or hypercaloric glucose infusion. After isolation of liver mitochondria 6, 12, 18 and 24 h after surgery states 3 and 4 of respiration were measured in vitro in the presence of succinate. State 3 and 4 mitochondrial respiration was higher in the sham-operated rats 6 h after surgery than in the control animals, and a gradual decrease towards control values occurred in the 12-24 h period following surgery. Results in mitochondria from PH rats showed variable results, in most cases both State 3 and 4 respiration was higher after PH, while the respiratory control index in general was lower. State 3 respiration was significantly increased in the PH isocaloric lipid and glucose infused groups 6, 12 and 18 h, but not 24 h after partial hepatectomy. The PH hypercaloric glucose and hypercaloric lipid infused rats showed decreases in the liver mitochondrial oxygen consumption after 6, 12 and 18 h of liver regeneration, this was more pronounced after hypercaloric lipid infusion. These results suggest that, in vitro, the surgery tends to increase Status 3 and Status 4 mitochondrial respiration. The hypercaloric parenteral nutrition, both lipid and glucose based, significantly decreased liver mitochondrial oxygen consumption in partially hepatectomized rats, particularly in the first hours of liver regeneration, with restoration 24 h after surgery.

Liver regeneration in partially hepatectomized rats infused with carnitine and lipids

Male Wistar rats were subjected to 65-70% hepatectomy. Immediately after surgery a 6-hour infusion was given containing 115 kJ/kg b.w. of long-chain fatty acids (Nutralipid Spofa) (N) or N combined with L-carnitine (Carnitene Sigma Tau) in doses 8 mg (12.4 mumol), 40 mg (62 mumol) and 200 mg (310 mumol)/kg b.w. The rats were killed 6, 18, 21, 24 and 30 h after surgery. The results of our study demonstrate that infusion of lipids combined with carnitine, has a stimulating dose-dependent effect on liver regeneration in partially hepatectomized rats, excluding the low dose of carnitine--8 mg/kg. The dose of carnitine of 40 mg/kg had the highest stimulating effect on the course of the liver DNA synthesis, culminating 21 h after partial hepatectomy. Later, 24 and 30 h after hepatectomy, the mitotic activity of hepatocytes was highest in rats infused with carnitine in doses of 200 mg/kg b.w.