Changes in liver gluconeogenesis during the development of Walker-256 tumour in rats

Peripheral insulin resistance is early, progressive, and correlated with cachexia in Walker-256 tumor-bearing rats

Insulin (INS) resistance is often found in cancer-bearing, but its correlation with cachexia development is not completely established. This study investigated the temporal sequence of the development of INS resistance and cachexia to establish the relationship between these factors in Walker-256 tumor-bearing rats (TB rats). INS hepatic sensitivity and INS resistance-inducing factors, such as free fatty acids (FFA) and tumor necrosis factor-α (TNF-α), were also evaluated. Studies were carried out on Days 2, 5, 8, and/or 12 after inoculation of tumor cells in rats. The peripheral INS sensitivity was assessed by the INS tolerance test and the INS hepatic sensitivity in in situ liver perfusion. TB rats with 5, 8, and 12 days of tumor, but not 2 days, showed decreased peripheral INS sensitivity (INS resistance), retroperitoneal fat, and body weight, compared to healthy rats, which were more pronounced on Day 12. Gastrocnemius muscle wasting was observed only on Day 12 of tumor. The peripheral INS resistance was significantly correlated (r = -.81) with weight loss. Liver INS sensitivity of TB rats with 2 and 5 days of tumor was unchanged, compared to healthy rats. TB rats with 12 days of tumor showed increased plasma FFA and increased TNF-α in retroperitoneal fat and liver, but not in the gastrocnemius, compared to healthy rats. In conclusion, peripheral INS resistance is early, starts along with fat and weight loss and before muscle wasting, progressive, and correlated with cachexia, suggesting that it may play an important role in the pathogenesis of the cachectic process in TB rats. Therefore, early correction of INS resistance may be a therapeutic approach to prevent and treat cancer cachexia.

[13C]bicarbonate labelled from hyperpolarized [1-13C]pyruvate is an in vivo marker of hepatic gluconeogenesis in fasted state

Hyperpolarized [1-¹³C]pyruvate enables direct in vivo assessment of real-time liver enzymatic activities by ¹³C magnetic resonance. However, the technique usually requires the injection of a highly supraphysiological dose of pyruvate. We herein demonstrate that liver metabolism can be measured in vivo with hyperpolarized [1-¹³C]pyruvate administered at two- to three-fold the basal plasma concentration. The flux through pyruvate dehydrogenase, assessed by ¹³C-labeling of bicarbonate in the fed condition, was found to be saturated or partially inhibited by supraphysiological doses of hyperpolarized [1-¹³C]pyruvate. The [¹³C]bicarbonate signal detected in the liver of fasted rats nearly vanished after treatment with a phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, indicating that the signal originates from the flux through PEPCK. In addition, the normalized [¹³C]bicarbonate signal in fasted untreated animals is dose independent across a 10-fold range, highlighting that PEPCK and pyruvate carboxylase are not saturated and that hepatic gluconeogenesis can be directly probed in vivo with hyperpolarized [1-¹³C]pyruvate.

Can et al. demonstrate the ability to use hyperpolarized [1-13C]pyruvate at nearphysiological concentrations to directly assess liver enzymatic activities by 13C magnetic resonance. While in the fed state, the normalized [13C]bicarbonate signal produced from hyperpolarized [1-13C]pyruvate derives from PDH activity, which is saturated at supraphysiological doses, it results from PEPCK in the fasted state and is dose-independent, allowing non-invasive in vivo detection of hepatic gluconeogenesis.”

Use of plasma-free amino acids as biomarkers for detecting and predicting disease risk

This paper reviews developments regarding the use of plasma-free amino acid (PFAA) profiles as biomarkers for detecting and predicting disease risk. This work was initiated and first published in 2006 and was subsequently developed by Ajinomoto Co., Inc. After commercialization in 2011, PFAA-based tests were adopted in over 1500 clinics and hospitals in Japan, and numerous clinician-led studies have been performed to validate these tests. Evidence is accumulating that PFAA profiles can be used for diabetes prediction and evaluation of frailty; in particular, decreased plasma essential amino acids could contribute to the pathophysiology of severe frailty. Integration of PFAA evaluation as a biomarker and effective essential amino acid supplementation, which improves physical and mental functions in the elderly, could facilitate the development of precision nutrition, including personalized solutions. This present review provides the background for the technology as well as more recent clinical findings, and offers future possibilities regarding the implementation of precision nutrition.

Active pyruvate dehydrogenase and impaired gluconeogenesis in orthotopic hepatomas of rats

BACKGROUND

Therapies targeting altered activity of pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) have been proposed for hepatomas. However, the activities of these pathways in hepatomas in vivo have not been distinguished. Here we examined pyruvate entry into the tricarboxylic acid (TCA) cycle through PDH versus PC in vivo using hepatoma-bearing rats.

METHODS

Hepatoma-bearing rats were generated by intrahepatic injection of H4IIE cells. Metabolism of ¹³C-labeled glycerol, a physiological substrate for both gluconeogenesis and energy production, was measured with ¹³C NMR analysis. The concentration of key metabolites and the expression of relevant enzymes were measured in hepatoma, surrounding liver, and normal liver.

RESULTS

In orthotopic hepatomas, pyruvate entry into the TCA cycle occurred exclusively through PDH and the excess PDH activity compared to normal liver was attributed to downregulated pyruvate dehydrogenase kinase (PDK) 2/4. However, pyruvate carboxylation via PC and gluconeogenesis were minimal, which was linked to downregulated forkhead box O1 (FoxO1) by Akt activity. In contrast to many studies of cancer metabolism, lactate production in hepatomas was not increased which corresponded to reduced expression of lactate dehydrogenase. The production of serine and glycine in hepatomas was enhanced, but glycine decarboxylase was downregulated.

CONCLUSIONS

The combination of [U-¹³C₃]glycerol and NMR analysis enabled investigation of multiple biochemical processes in hepatomas and surrounding liver. We demonstrated active PDH and other related metabolic alterations in orthotopic hepatomas that differed substantially not only from the host organ but also from many earlier studies with cancer cells.

Infusion of high concentration of lactate in perfused liver, simulating in vivo hyperlactatemia, prevents the reduction of gluconeogenesis in Walker-256 tumor-bearing rats

Gluconeogenesis (GN) is increased in patients with cancer cachexia, but is reduced in liver perfusion of Walker-256 tumor-bearing cachectic rats (TB rats). The causes of these differences are unknown. We investigated the influence of circulating concentrations of lactate (NADH generator) and NADH on GN in perfused livers of TB rats. Lactate, at concentrations similar to those found on days 5 (3.0 mM), 8 (5.5 mM), and 12 (8.0 mM) of the tumor, prevented the reduction of GN from 2.0 mM lactate (lactatemia of healthy rat) in TB rats. NADH, 50 or 75 μM, but not 25 μM, increased GN from 2.0 mM lactate in TB rats to higher values than healthy rats. High concentrations of pyruvate (no NADH generator, 5.0 and 8.0 mM) did not prevent the reduction of GN from 2.0 mM pyruvate in TB rats. However, 50 or 75 μM NADH, but not 25 μM, increased GN from 2.0 mM pyruvate in TB rats to similar or higher values than healthy rats. High concentration of glutamine (NADH generator, 2.5 mM) or 50 μM NADH prevented the reduction of GN from 1 mM glutamine in TB rats. Intraperitoneal administration of pyruvate (1.0 mg/kg) or glutamine (0.5 mg/kg) similarly increased the glycemia of healthy and TB rats. In conclusion, high lactate concentration, similar to hyperlactatemia, prevented the reduction of GN in perfused livers of TB rats, an effect probably caused by the increased redox potential (NADH/NAD⁺ ). Thus, the decreased GN in livers from TB rats is due, at least in part, to the absence of simulation of in vivo hyperlactatemia in liver perfusion studies.

Decreased hepatic response to glucagon, adrenergic agonists, and cAMP in glycogenolysis, gluconeogenesis, and glycolysis in tumor-bearing rats

The response to glucagon and adrenaline in cancer cachexia is poorly known. The aim of this study was to investigate the response to glucagon, adrenergic agonists (α and β) and cyclic adenosine monophosphate (cAMP) on glycogenolysis, gluconeogenesis, and glycolysis in liver perfusion of Walker-256 tumor-bearing rats with advanced cachexia. Liver ATP content was also investigated. Rats without tumor (healthy) were used as controls. Agonists α (phenylephrine) and β (isoproterenol) adrenergic, instead of adrenaline, and cAMP, the second messenger of glucagon and isoproterenol, were used in an attempt to identify mechanisms involved in the responses. Glucagon (1 nM) stimulated glycogenolysis and gluconeogenesis and inhibited glycolysis in the liver of healthy and tumor-bearing rats, but their effects were lower in tumor-bearing rats. Isoproterenol (20 µM) stimulated glycogenolysis, gluconeogenesis, and glycolysis in healthy rats and had virtually no effect in tumor-bearing rats. cAMP (9 µM) also stimulated glycogenolysis and gluconeogenesis and inhibited glycolysis in healthy rats but had practically no effect in tumor-bearing rats. Phenylephrine (2 µM) stimulated glycogenolysis and gluconeogenesis and inhibited glycolysis and these effects were also lower in tumor-bearing rats than in healthy. Liver ATP content was lower in tumor-bearing rats. In conclusion, tumor-bearing rats with advanced cachexia showed a decreased hepatic response to glucagon, adrenergic agonists (α and β), and cAMP in glycogenolysis, gluconeogenesis, and glycolysis, which may be due to a reduced rate of regulatory enzyme phosphorylation caused by the low ATP levels in the liver.

Effects of metformin on insulin resistance and metabolic disorders in tumor-bearing rats with advanced cachexia

Metformin (MET) is widely used in the correction of insulin (INS) resistance and metabolic abnormalities in type 2 diabetes. However, its effect on INS resistance and metabolic disorders associated with cancer cachexia is not established. We investigated the MET effects, isolated or associated with INS, on INS resistance and metabolic changes induced by Walker-256 tumor in rats with advanced cachexia. MET (500 mg·kg−1, oral) and MET + INS (1.0 IU·kg−1, s.c.) were administered for 12 days, starting on the day of tumor cell inoculation. Tumor-bearing rats showed adipose and muscle mass wasting, body mass loss, anorexia, decreased Akt phosphorylation in retroperitoneal and mesenteric adipose tissue, peripheral INS resistance, hypoinsulinemia, reduced INS content and secretion from pancreatic islets, and also inhibition of glycolysis, gluconeogenesis, and glycogenolysis in liver. MET and MET + INS treatments did not prevent these changes. It can be concluded that treatments with MET and MET + INS did not prevent the adipose and muscle mass wasting and body mass loss of tumor-bearing rats possibly by not improving INS resistance. Therefore, MET, used for the treatment of INS resistance in type 2 diabetes, is not effective in improving INS resistance in the advanced stage of cancer cachexia, evidencing that the drug does not have the same beneficial effect in these 2 diseases.

Hepatic Activation of the FAM3C-HSF1-CaM Pathway Attenuates Hyperglycemia of Obese Diabetic Mice

FAM3C is a member of the family with sequence similarity 3 (FAM3) gene family, and this study determined its role and mechanism in regulation of hepatic glucose/lipid metabolism. In obese diabetic mice, FAM3C expression was reduced in the liver, and hepatic FAM3C restoration improved insulin resistance, hyperglycemia, and fatty liver. FAM3C overexpression increased the expression of heat shock factor 1 (HSF1), calmodulin (CaM), and phosphorylated protein kinase B (Akt) and reduced that of gluconeogenic and lipogenic genes in diabetic mouse livers with the suppression of gluconeogenesis and lipid deposition. In cultured hepatocytes, FAM3C overexpression upregulated HSF1 expression, which elevated CaM protein level by inducing CALM1 transcription to activate Akt in a Ca²⁺- and insulin-independent manner. Furthermore, FAM3C overexpression promoted nuclear exclusion of FOXO1 and repressed gluconeogenic gene expression and gluconeogenesis in a CaM-dependent manner in hepatocytes. Hepatic HSF1 overexpression activated the CaM-Akt pathway to repress gluconeogenic and lipogenic gene expression and improve hyperglycemia and fatty liver in obese diabetic mice. In conclusion, the FAM3C-HSF1-CaM-Akt pathway plays important roles in regulating glucose and lipid metabolism in hepatocytes independent of insulin and calcium. Restoring hepatic FAM3C expression is beneficial for the management of type 2 diabetes and fatty liver.