Adenylate energy charge of rat and human cultured hepatocytes

Quantification of all 12 canonical ribonucleotides by real-time fluorogenic in vitro transcription

Enzymatic methods to quantify deoxyribonucleoside triphosphates have existed for decades. In contrast, no general enzymatic method to quantify ribonucleoside triphosphates (rNTPs), which drive almost all cellular processes and serve as precursors of RNA, exists to date. ATP can be measured with an enzymatic luminometric method employing firefly luciferase, but the quantification of other ribonucleoside mono-, di-, and triphosphates is still a challenge for a non-specialized laboratory and practically impossible without chromatography equipment. To allow feasible quantification of ribonucleoside phosphates in any laboratory with typical molecular biology and biochemistry tools, we developed a robust microplate assay based on real-time detection of the Broccoli RNA aptamer during in vitro transcription. The assay employs the bacteriophage T7 and SP6 RNA polymerases, two oligonucleotide templates encoding the 49-nucleotide Broccoli aptamer, and a high-affinity fluorogenic aptamer-binding dye to quantify each of the four canonical rNTPs. The inclusion of nucleoside mono- and diphosphate kinases in the assay reactions enabled the quantification of the mono- and diphosphate counterparts. The assay is inherently specific and tolerates concentrated tissue and cell extracts. In summary, we describe the first chromatography-free method to quantify ATP, ADP, AMP, GTP, GDP, GMP, UTP, UDP, UMP, CTP, CDP and CMP in biological samples.

Coenzyme Q Depletion Reshapes MCF-7 Cells Metabolism

Mitochondrial dysfunction plays a significant role in the metabolic flexibility of cancer cells. This study aimed to investigate the metabolic alterations due to Coenzyme Q depletion in MCF-7 cells. Method: The Coenzyme Q depletion was induced by competitively inhibiting with 4-nitrobenzoate the coq2 enzyme, which catalyzes one of the final reactions in the biosynthetic pathway of CoQ. The bioenergetic and metabolic characteristics of control and coenzyme Q depleted cells were investigated using polarographic and spectroscopic assays. The effect of CoQ depletion on cell growth was analyzed in different metabolic conditions. Results: we showed that cancer cells could cope from energetic and oxidative stress due to mitochondrial dysfunction by reshaping their metabolism. In CoQ depleted cells, the glycolysis was upregulated together with increased glucose consumption, overexpression of GLUT1 and GLUT3, as well as activation of pyruvate kinase (PK). Moreover, the lactate secretion rate was reduced, suggesting that the pyruvate flux was redirected, toward anabolic pathways. Finally, we found a different expression pattern in enzymes involved in glutamine metabolism, and TCA cycle in CoQ depleted cells in comparison to controls. Conclusion: This work elucidated the metabolic alterations in CoQ-depleted cells and provided an insightful understanding of cancer metabolism targeting.

Coenzyme Q biosynthesis inhibition induces HIF-1α stabilization and metabolic switch toward glycolysis

Coenzyme Q₁₀ (CoQ, ubiquinone) is a redox-active lipid endogenously synthesized by the cells. The final stage of CoQ biosynthesis is performed at the mitochondrial level by the 'complex Q', where coq2 is responsible for the prenylation of the benzoquinone ring of the molecule. We report that the competitive coq2 inhibitor 4-nitrobenzoate (4-NB) decreased the cellular CoQ content and caused severe impairment of mitochondrial function in the T67 human glioma cell line. In parallel with the reduction in CoQ biosynthesis, the cholesterol level increased, leading to significant perturbation of the plasma membrane physicochemical properties. We show that 4-NB treatment did not significantly affect the cell viability, because of an adaptive metabolic rewiring toward glycolysis. Hypoxia-inducible factor 1α (HIF-1α) stabilization was detected in 4-NB-treated cells, possibly due to the contribution of both reduction in intracellular oxygen tension and ROS overproduction. Exogenous CoQ supplementation partially recovered cholesterol content, HIF-1α degradation, and ROS production, whereas only weakly improved the bioenergetic impairment induced by the CoQ depletion. Our data provide new insights on the effect of CoQ depletion and contribute to shed light on the pathogenic mechanisms of ubiquinone deficiency syndrome.

Hepatoprotective effect of Caesalpinia gilliesii and Cajanus cajan proteins against acetoaminophen overdose-induced hepatic damage

This study aims to evaluate two proteins derived from the seeds of the plants Cajanus cajan (Leguminosae) and Caesalpinia gilliesii (Leguminosae) for their abilities to ameliorate the toxic effects of chronic doses of acetoaminphen (APAP) through the determination of certain biochemical parameters including liver marker enzymes: alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and total bilirubin. Also, total protein content and hepatic marker enzyme, lactate dehydrogenase were studied. Moreover, liver antioxidants, glutathione (GSH), nitric oxide, and lipid peroxides were determined in this study. Hepatic adenosine triphosphatase (ATPase), adenylate energy charge (ATP, adenosine diphosphate, adenosine monophosphate, and inorganic phosphate), and phosphate potential, serum interleukin-6, tumor necrosis factor-α, and myeloperoxidase were also examined in the present study. On the other hand, histopathological examination of intoxicated and liver treated with both proteins was taken into consideration. The present results show disturbances in all biochemical parameters and hepatic toxicity signs including mild vascular congestion, moderate inflammatory changes with moderate congested sinusoids, moderate nuclear changes (pyknosis), moderate centrilobular necrosis, fatty changes, nuclear pyknosis vascular congestion, and change in fatty centrilobular necrosis liver. Improvement in all biochemical parameters studied was noticed as a result of treatment intoxicated liver with C. gilliesii and C. cajan proteins either paracetamol with or post paracetamol treatment. These results were documented by the amelioration signs in rat's hepatic architecture. Thus, both plant protein extracts can upregulate and counteract the inflammatory process, minimize damage of the liver, delay disease progression, and reduce its complications.

A simplified approach to human islet quality assessment

BACKGROUND

The successful treatment of patients with type 1 diabetes by islet transplantation is affected by a multitude of factors of which infusion of the highest quality tissue is essential. The current standard pretransplant quality assessments lack sensitivity, accuracy, and objectivity in the determination of islet viability and potency. We hypothesized that a multiparametric approach focused on islet cell metabolic state, mitochondrial integrity, and in vitro glucose-stimulated insulin secretion (GSIS) could provide data predictive of in vivo function. The objective of this study was to validate a novel set of islet quality assays and develop a simplified islet quality scoring system for both basic research and clinical applications.

METHODS

A series of 42 human islet preparations were screened using standard and novel methods, which included determination of yield, viability by fluorescent microscopy, GSIS, percentage of islet loss in culture, quantification of adenine nucleotides, flow cytometric measurement of viability, apoptosis, and mitochondrial membrane potential (MMP). In vivo functional potency was tested by minimal model transplant in streptozotocin-induced diabetic NOD.scid mice.

RESULTS

Functionally potent islet preparations showed significantly greater numbers of cells with polarized MMP, higher ATP-to-ADP ratios, and increased glucose-induced insulin secretion. The MMP, ATP-to-ADP ratio, and GSIS data were combined into a single islet scoring formula that showed more than 86% accuracy in predicting in vivo functional potency.

CONCLUSIONS

Our study demonstrates that a multiparametric approach using objective assessments focused on islet cell mitochondrial integrity and in vitro function can provide data predictive of in vivo function.

Functional and energetic characterization of P-gp-mediated doxorubicin transport in rainbow trout (Oncorhynchus mykiss) hepatocytes

An assessment of energetic costs associated with P-glycoprotein (P-gp)-mediated xenobiotic efflux is important in understanding the energy budgets, tradeoffs, and fitness of organisms inhabiting contaminated environments. Here, a functional characterization and determination of the energetic costs associated with doxorubicin (DOX) efflux was examined in isolated hepatocytes of rainbow trout. The accumulation and efflux of DOX were both concentration dependent. The efflux of DOX over a 3 h incubation period resulted in a significant decrease in intracellular ATP concentrations (maximum decrease 25%) compared to control baseline levels, while significant increases in concentrations of ADP (max. 26%), AMP (max. 36%) and inorganic phosphate (max. 11%). were observed. In addition, significant reductions in the adenylate energy charge ([AEC]: max 11%), and phosphorylation potential ([PP]: max. 53%) were shown in cells incubated with DOX compared to control cells. Inhibition of DOX efflux (max. 61%) by the non-competitive P-gp inhibitor tariquidar (XR9576), demonstrated that changes in ATP, ADP, AMP, inorganic phosphate concentrations, AEC and PP in DOX-exposed hepatocytes were mainly due to P-gp activity. Overall, these results indicate that the exposure of trout hepatocytes to DOX increases energetic and metabolic costs that are associated specifically with P-gp efflux activity.

Adenine nucleotides in snail muscles as one of biomarkers of fluoride toxicity

The aim of this work was to determine the extent of bioaccumulation of fluorides in tissues of Helix aspersa maxima. The toxicity of fluorides administered orally on the energy balance of the snail's foot was investigated based on measurements of concentrations of adenine nucleotides and their metabolism degradation products. Quantitation of fluoride levels was done in soft tissues (foot, hepatopancreas) and shells of mature snails. Qualitative and quantitative analysis of purine compounds was performed in slices of foot from mature snails. Fluoride concentrations in pulverized shells were measured using an ion-selective electrode. Gas chromatography was used to determine fluoride concentrations in soft tissues (hepatopancreas and foot). Purines were measured in foot muscle slices with high-performance liquid chromatography (HPLC). Fluoride levels in soft tissues of the snail cannot serve as an indicator for biomonitoring purposes as no significant accumulation was observed during exposure to maximum allowable concentrations of fluoride in drinking water. Contrary to this, levels of fluoride in the shell rose significantly with this concentration of fluoride in drinking water. The effect of fluorides on energy metabolism of foot muscle was evidenced by elevated AMP levels, increased adenine nucleotide pool and reduced conversion of ADP to ATP. Exposure to rising F(-) concentrations was accompanied by decreasing values of the adenylate energy charge AEC. Determination of AMP or AEC in foot muscle of exposed snails seems to be a useful indicator of fluoride effects on metabolic activity.

Effect of nitric oxide on hepatic dysfuction in rat obstructive jaundice

AIM: To examine whether obstructive jaundice influences the production of nitric oxide and alters hepatic functions including energy metabolism.

METHODS: Hepatocytes were isolated by perfusing the liver with collagenase and cultured from a rat model of obstructive jaundice or sham-control. Rat cultured hepatocytes were incubated with cytokines including IL-1. The production of nitric oxide was measured with Griess reagent method and Western blot analysis. Adenine nucleotides (ATP, ADP and AMP) were measured by a high performance liqiud chromatography. Ketone bodies in the medium were measured enzymatically.

RESULTS: Obstructive jaundice increased the production of nitric oxide by IL-1 time-and dose- dependently. Western blot analysis revealed that protein levels of iNOS were unchanged between two groups. IL-1 decreased the ATP content and KBR in obstructive jaundice but not that in sham-control. Addition of L-NMMA blocked the decreases of ATP content and KBR as well as nitric oxide production.

CONCLUSION: Enhancement of nitric oxide production following obstructive jaundice is associated with the alteration of hepatic energy metabolism through mitochondrial dysfuntion, resulting in liver failure. Regulation of nitric oxide may be a useful therapy for preventing liver damage in obstructive jaundice.

CHARACTERIZATION OF THE HUMAN HEPATOCELLULAR CARCINOMA (HEPG2) CELL LINE AS AN IN VITRO MODEL FOR CADMIUM TOXICITY STUDIES

Biochemical indicators and in vitro models, if they mimic in vivo responses, offer potentially sensitive tools for inclusion in toxicity assessment programs. The purpose of this study was to determine whether the HepG2 cell line would mimic known in vivo or in vitro (or both) responses of mammalian systems when confronted with cadmium (Cd2+). Uptake and compartmentalization of Cd2+, metallothionein (MT) compartmentalization, and glutathione (GSH) depletion were examined. In addition, several cytotoxic and stress effects, e.g., viability (neutral red [NR] uptake, 3-[4,5-dimethylthiozole-2-yl]-2,5,-biphenyl tetrazolium bromide [MTT] dye conversion, and live/dead [L/D]), membrane damage (lactate dehydrogenase leakage), metabolic activity (adenosine triphosphate levels), and detoxification capabilities (GSH content, cytochrome P4501A1/2 [EROD (ethoxyresorufin-o-deethylase)] activity, and MT induction), were measured in both naive (no previous exposure) and Cd2+ preexposed cells. Cadmium uptake increased during a 24-h period. Metallothionein induction occurred in response to both Cd2+ and ZnCl2; however, Cd2+ was the more potent inducer. Both Cd2+ and MT were localized primarily in the cytoplasmic compartment. All biochemical responses, except EROD, showed concentration- response relationships, after 24-h exposure to Cd2+ (ranges 0-3 ppm [26.7 microM]). Cadmium effects were reduced in preexposed cells, indicating adaptive tolerance or increased resistance had occurred. Twenty-four-hour LC50, dose causing death of 50% of the test subjects, values were 0.97, 0.69, and 0.80 ppm (8.7, 6.2, and 7.2 microM) for naive cells and 1.45, 1.21, and 1.39 ppm (12.9, 10.7, and 12.3 microM) for preexposed cells based on the NR, MTT, and L/D assays, respectively. These data indicate that this carcinoma cell line is a useful in vitro model for cadmium toxicity studies.

Hepatocellular dysfunction induced by nitric oxide production in hepatocytes isolated from rats with sepsis

In the process of sepsis, the failing organ is not necessarily directly injured or involved in the primary disease process, and the development of distant organ failure may be induced by the host's primed response on an initial insult followed by subsequent insult. We hypothesized that enhancement of nitric oxide (NO) production in the presence of interleukin (IL)-1beta in hepatocytes, isolated under septic conditions, could be implicated in the change in liver energy metabolism, thus resulting in hepatocellular dysfunction. We performed cecal ligation and puncture (CLP group) or a sham operation (sham group) in rats and then isolated hepatocytes from the liver at 6 h postoperatively. The cultured hepatocytes were treated with IL-1beta in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) or L-arginine. Effects on nitric oxide production, ATP content, and ketone body ratio (KBR) were then compared between the CLP and sham groups. IL-1beta augmented the induction of NO production in hepatocytes from the CLP group compared with the sham group. IL-1beta markedly decreased cellular ATP content and KBR in the CLP group. The addition of L-arginine further enhanced the decreases of ATP content and KBR concomitantly with the increase of NO production in the CLP group. In contrast, L-NMMA, an inhibitor of nitric oxide synthase, abolished the effects of IL-1beta on ATP content and KBR, as well as on NO production. These results demonstrate that enhancement of NO production by IL-1beta stimulation is involved in cellular failure through mitochondrial dysfunction in the liver of septic rats. This experimental finding may explain clinical phenomenon that an initial insult primes the host so that the host's response is greatly amplified on a second or subsequent insult, resulting in the development of distant organ failure.

Myoglobin gene expression attenuates hepatic ischemia reperfusion injury

BACKGROUND

Cellular functions are maintained by a continuous supply of ATP, which is supplied efficiently by mitochondrial oxidative phosphorylation. Since myoglobin, found in cardiac myocytes and red skeletal muscle, but not in the liver, facilitates oxygen diffusion under low oxygen conditions and enhances oxidative phosphorylation, this study seeks to enhance hepatic ATP levels and attenuate ischemia-reperfusion injury in rodent livers by adenovirus-mediated myoglobin expression.

MATERIAL AND METHODS

After infecting Hep3B and rodent livers with adenovirus carrying CMV promoter sequences linked to the human myoglobin gene (AdCMVMyo), reverse transcriptase-PCR and immunodetection for myoglobin, and cellular and hepatic ATP levels were examined. The effect of myoglobin was evaluated in a hepatic ischemia-reperfusion model in the rat.

RESULTS

Myoglobin expression was confirmed in Hep3B and rat livers after AdCMVMyo infection. The ATP levels in Hep3B cells and C57BL/6 mice livers 72 h after AdCMVMyo transfection were significantly higher than control levels and those after adenovirus-mediated beta-galactosidase transfection. Finally, expression of myoglobin attenuated ischemia-reperfusion injury in the rat liver.

CONCLUSION

These results indicate that myoglobin gene transfer to the liver enhanced ATP levels both in vitro and in vivo and might be a novel strategy to reduce ischemia-reperfusion injury.

Increased nitric oxide production in hepatocytes is involved in liver dysfunction following obstructive jaundice

BACKGROUND

Obstructive jaundice damages critical functions in the liver. However, the mechanisms involved in hepatic dysfunction are obscure. Nitric oxide is implicated in liver injury under various pathological conditions. We previously reported that proinflammatory cytokine interleukin-1beta (IL-1beta) stimulated the production of nitric oxide in hepatocytes, which was associated with mitochondrial dysfunction. Studies were performed to examine whether obstructive jaundice influences the production of nitric oxide in hepatocytes and alters hepatic energy metabolism.

MATERIAL AND METHODS

Hepatocytes were isolated and cultured from a rat model of obstructive jaundice or sham control. Nitric oxide production, ATP content, and ketone body ratio (acetoacetate/beta-hydroxybutyrate; KBR) were compared between the two groups in the presence of IL-1beta.

RESULTS

Hepatocytes obtained from obstructive jaundice rats markedly increased the levels of nitric oxide production stimulated by IL-1beta compared with those from sham control. Western blot analysis revealed that the enhancement of nitric oxide production was a posttranslational event, since protein levels of inducible nitric oxide synthase (NOS) were unchanged between the two groups. IL-1beta decreased cellular ATP content in obstructive jaundice but not in sham control. Further, the KBR, which is a marker of mitochondrial redox state, was lower in obstructive jaundice than in sham control. Addition of N(G)-monomethyl-L-arginine, an inhibitor of NOS, abolished the decreases in ATP content and KBR as well as the nitric oxide production.

CONCLUSIONS

These results indicate that a priming of nitric oxide production following obstructive jaundice is associated with the alteration of hepatic energy metabolism in part through mitochondrial dysfunction. Regulation of nitric oxide production may be a useful therapy for preventing liver dysfunction in obstructive jaundice.

An enhancement of nitric oxide production regulates energy metabolism in rat hepatocytes after a partial hepatectomy

BACKGROUND/AIMS

Infection after a liver resection often results in hepatic failure. Nitric oxide is one of the candidates which has been suspected to cause cellular dysfunction during infection in the liver. We have previously reported that the inflammatory cytokine interleukin-1beta (IL-1beta) induced the expression of the inducible nitric oxide synthase gene in primary cultured rat hepatocytes. We hypothesized that an enhancement of nitric oxide production after the resection was implicated in a change in liver energy metabolism, thus resulting in liver dysfunction.

METHODS

In this study, we performed a 70% hepatectomy or a sham operation in rats, and then isolated hepatocytes from the remnant liver by collagenase perfusion. The cultured hepatocytes were treated with cytokines including IL-1beta. The effects on nitric oxide induction, the ATP content and ketone body ratio (acetoacetate/beta-hydroxybutyrate) were then compared between the partial hepatectomized (PH) and sham-operated (control) rats.

RESULTS

IL-1beta augmented the induction of nitric oxide production two-fold in hepatocytes from the PH rats as compared to the control rats. IL-1beta markedly decreased the ATP content in the PH rats, although IL-1beta also decreased the ATP content in the control rats, but to a lesser extent. IL-1beta also decreased the ketone body ratio in both groups. The addition of L-arginine further stimulated the inhibition of the ATP levels and the ketone body ratio concomitantly with increased nitric oxide production in the PH rats. N(G)-monomethyl-L-arginine, an inhibitor of nitric oxide synthase, abolished the effects of IL-1beta on the ATP levels and ketone body ratio, as well as on the nitric oxide production.

CONCLUSIONS

These results demonstrate that the decreased ATP content observed in PH rats resulted from an increase in nitric oxide production. The decrease in ketone body ratio indicates that nitric oxide-induced mitochondrial dysfunction contributes significantly to ATP attenuation in hepatocytes. Therefore, the regulation of nitric oxide induction may be crucial for preventing liver failure after a hepatic resection.

A simplified model of hypoxic injury in primary cultured rat hepatocytes

The Anaeropack system for cell culture, which was originally designed for the growth of anaerobic bacteria, was used to produce a hypoxic atmosphere for cultured hepatocytes. We measured changes in the oxygen and carbon dioxide concentrations and the atmospheric temperature in an airtight jar. We also measured changes in the pH of the medium during hypoxia to assess the accuracy of this system. Moreover, we used three durations (2, 3, and 4 h) of hypoxia and 8 h of reoxygenation in cultured rat hepatocytes, and then measured the lactate dehydrogenase (LDH), ketone body concentration (acetoacetate + beta-hydroxybutyrate), and the ketone body ratio (KBR: acetoacetate/beta-hydroxybutyrate) in the medium in order to assess the suitability of this system as a model for reperfusion following liver ischemia. The oxygen concentration dropped to 1% or less within 1 h. The concentration of carbon dioxide rose to about 5% at 30 min after the induction of the hypoxic conditions, and was maintained at this level for 5 h. No effect of the reaction heat produced by the oxygen absorbent in the jar was recognized. The extent of cell injury produced by changing the hypoxic parameters was satisfactorily reflected by the KBR, the ketone body concentration, and the LDH activity released into the medium. Because this model can duplicate the conditions of the hepatocytes during revascularization following ischemic liver, and the Anaeropack system for cell culture is easy to manipulate, it seems suitable for the experimental study of hypoxic injury and revascularization in vitro.

Regulation of energy metabolism by interleukin-1beta, but not by interleukin-6, is mediated by nitric oxide in primary cultured rat hepatocytes

The effects of inflammatory cytokines (interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha) on energy metabolism were studied in primary cultured rat hepatocytes. Adenine nucleotide (ATP, ADP, and AMP) content, lactate production, the ketone body ratio (acetoacetate/beta-hydroxybutyrate) reflecting the liver mitochondrial redox state (NAD+/NADH), and nitric oxide formation were measured. Insulin increased ATP content in hepatocytes and had a maximal effect after 8-12 h of culture. Both interleukin-1beta and interleukin-6, but not tumor necrosis factor-alpha, significantly inhibited the ATP increase time- and dose-dependently. Interleukin-1beta and interleukin-6 also stimulated lactate production. During the same period, interleukin-1beta but not interleukin-6 decreased the ketone body ratio. Furthermore, interleukin-1beta markedly stimulated nitric oxide formation in hepatocytes, and this increase was blocked by NG-monomethyl-L-arginine (a nitric oxide synthase inhibitor) and by interleukin-1 receptor antagonist. NG-monomethyl-L-arginine reversed inhibition of the ATP increase, decrease in the ketone body ratio, and increase in lactate production, which were induced by interleukin-1beta. Interleukin-1 receptor antagonist completely abolished all of the effects induced by interleukin-1beta. These results demonstrated that interleukin-1beta and interleukin-6 affect the insulin-induced energy metabolism in rat hepatocytes by different mechanisms. Specifically, interleukin-1beta inhibits ATP synthesis by causing the mitochondrial dysfunction, a process which may be mediated by nitric oxide.

The accumulation and energy load of exogenous lipids in cirrhotic rat liver after partial hepatectomy

BACKGROUND

The suitability of three energy substrates, glucose, medium-chain triglycerides (MCT) and long-chain triglycerides (LCT), was studied in cirrhotic rats after a partial hepatectomy.

METHODS

Rats with thioacetamide-induced cirrhosis underwent a 70% hepatectomy, and were divided into three groups. Each group was then injected with 14C-labeled glucose, 14C-labeled MCT or 14C-labeled LCT, respectively. The subsequent tissue distribution of 14C and the cumulative amount of expired 14CO2 were determined. In a second experiment, the 70%-hepatectomized cirrhotic rats received total parenteral nutrition (TPN). The source of the nonprotein calories was 100% glucose (glucose group), 60% MCT + 40% glucose (MCT group), and 60% LCT + 40% glucose (LCT group). The adenylate energy charge and the glycogen content in the liver remnant were determined.

RESULTS

The tissue distribution of 14C revealed that the fat emulsions accumulated preferentially in the liver. One hour after the partial hepatectomy, the concentration of 14C-labeled MCT in the liver remnants was threefold higher than in sham-operated controls. Similarly, the concentration of 14C-labeled LCT was twofold higher. The adenylate energy charge in the glucose group with TPN recovered to preoperative levels within 1-hour after the partial hepatectomy, whereas the LCT group with TPN showed a 24-hour delay in their recovery. The MCT group with TPN exhibited an intermediate time course.

CONCLUSIONS

It is suggested that the specific accumulation of MCT and especially LCT emulsions in the cirrhotic liver remnant acts as an energy load rather than an energy substrate.