Characteristics of glutamine metabolism in human precision-cut kidney slices: a 13C-NMR study

Exploring porcine kidney explants as a model for the study of nephrotoxins and the therapeutic potential of phytic acid

The use of in vivo models to assess nephrotoxicity has faced ethical limitations. A viable alternative is the ex vivo model that combines the 3 R principles with the preservation of tissue histology. Here, we established a gentamicin nephrotoxicity model using pigs` kidney explants and investigated the effect of phytic acid (IP6) against gentamicin- induced nephrotoxicity. A total of 360 kidney explants were divided into control, gentamicin (10 mM), IP6 (5 mM), and gentamicin+IP6 groups. The activity of gammaglutamyltransferase (GGT), creatinine levels, histological assessment, oxidative stress, and inflammatory cytokine expression were analyzed. Exposure to gentamicin induced an increase in GGT activity, creatinine levels, lesion score, lipoperoxidation and IL-8 expression. Explants exposed to IP6 remained like the control. The addition of IP6 to gentamicin prevented tissue damage, increasing the antioxidant status and gene expression of IL-10. This model proved to be an adequate experimental approach for identifying nephrotoxins and potential products to modulate the toxicity.

Functional Metabolomics Analysis Elucidating the Metabolic Biomarker and Key Pathway Change Associated With the Chronic Glomerulonephritis and Revealing Action Mechanism of Rhein

Chronic glomerulonephritis (CGN) as the culprit of kidney failure can increase the mortality of critically ill patients and seriously threatens people’s health all over the world. This study using metabolomics strategy is to reveal the potential therapeutic mechanism-related targets to evaluate the effects of rhein (RH) on CGN rats. Changes of serum metabolites and pathways were analyzed by non-targeted metabolomic method based on liquid chromatography-mass spectrometry (LC-MS) combined with ingenuity pathway analysis. In addition, the levels of biochemical indicators were also detected. A total of 25 potential biomarkers were identified to express serum metabolic turbulence in CGN animal model, and then 16 biomarkers were regulated by RH trending to the normal states. From metabolite enrichment and pathway analysis, pharmacological activity of RH on CGN were mainly involved in six vital metabolic pathways including phenylalanine, tyrosine and tryptophan biosynthesis, phenylalanine metabolism, arachidonic acid metabolism, tricarboxylic acid cycle (TCA cycle), alanine, aspartate, and glutamate metabolism, arginine and proline metabolism. It suggested CGN treatment with RH, which may be mediated via interference with metabolic pathway such as amino acid metabolism, arachidonic acid metabolism, and TCA cycle to regulating inflammation, oxidation response and immune regulation against CGN. It showed that metabolomics method offer deeply insight into the therapeutic mechanisms of natural product.

Effect of Yeast Fermentate Supplementation on Intestinal Health and Plasma Biochemistry in Heat-Stressed Pekin Ducks

One experiment was conducted to determine the effects of supplementing Saccharomyces cerevisiae-derived yeast fermentate (Diamond V Mills, Cedar Rapids, IA, USA) in the feed (XPC; 1.25 kg/metric ton feed, days 0-35) or drinking water (AviCare; 160 mL/100 L, days 0-35) on plasma biochemical and immune parameters, as well as ileal histomorphology of mixed-sex Pekin ducks grown to 35 d and exposed to cyclic heat stress (8 h/d) or thermoneutral environment (days 21-35). On the day of hatching, 144 straight run White Pekin ducks were randomly assigned to one of six treatments: stressed control (CS), stressed + XPC (XS), stressed + AviCare (AS), non-stressed control (CN), non-stressed + XPC (XN), and non-stressed + AviCare (AN). On day 33, blood samples were collected from 12 birds/treatment to assess plasma chemistry, packed cell volume, and plasma levels of interleukin (IL)-1α, IL-8, and α1-acid glycoprotein (α1-AGP). On day 34, ileum sections were collected from 12 birds/treatment to assess goblet cell density, villus length, crypt depth, and villus/crypt ratio from 6 villi per sample. Plasma phosphorus was influenced by diet (p < 0.001) and heat-diet interaction (p = 0.003), and was higher in XS than XN, and higher in AS than AN. Heat stress increased plasma glutamate dehydrogenase (GLDH) (p = 0.008). Uric acid was increased by adding yeast fermentate to the feed or drinking water (p = 0.002), but was not influenced by heat (p > 0.05). The heat-diet interaction affected plasma IL-1α (p = 0.021) and sodium (p = 0.046). Heat stress reduced villus length (p < 0.001), villus/crypt ratio (p < 0.001), and goblet cell density (p < 0.001), but did not affect crypt depth (p > 0.05). Both XPC and AviCare increased villus length (p < 0.001) and villus/crypt ratio (p < 0.001), and decreased crypt depth (p < 0.001), but did not affect goblet cell density (p > 0.05). Although adding yeast fermentate to the feed or drinking water does not appear to alleviate the effects of heat stress on goblet cell density, both routes of administration improved other measures of villus morphology and affected amino acid metabolism.

Protocols and Applications of Cellular Metabolomics in Safety Studies Using Precision-Cut Tissue Slices and Carbon 13 NMR

Numerous xenobiotics are toxic to human and animal cells by interacting with their metabolism, but the precise metabolic step affected and the biochemical mechanism behind such a toxicity remain often unknown. In an attempt to reduce the ignorance in this field, we have developed a new approach called cellular metabolomics. This approach, developed in vitro, provides a panoramic view not only of the pathways involved in the metabolism of physiological substrates of any normal or pathological human or animal cell but also of the beneficial and adverse effects of xenobiotics on these metabolic pathways. Unlike many cell lines, precision-cut tissue slices, for which there is a renewed interest, remain metabolically differentiated for at least 24-48 h and allow to study the effect of xenobiotics during short-term and long-term incubations. Cellular metabolomics (or metabolic flux analysis), which combines enzymatic and carbon 13 NMR measurements with mathematical modeling of metabolic pathways, is illustrated in this brief chapter for studying the effect of insulin on glucose metabolism in rat liver precision-cut slices and of valproate on glutamine metabolism in human renal cortical precision-cut slices. The use of very small amounts of test compounds allows to predict their toxic effect and eventually their beneficial effects very early in the research and development processes. Cellular metabolomics is complementary to other omics approaches, but, unlike them, provides functional, mechanistic, and dynamic pieces of information by measuring enzymatic fluxes.

Use of precision-cut renal cortical slices in nephrotoxicity studies

1.Unlike cell lines and primary cells in culture, precision-cut tissue slices remain metabolically differentiated for at least 24-48 h and allow to study the effect of xenobiotics during short-term and long-term incubations. 2.In this article, we illustrate the use of such an experimental model to study the nephrotoxic effects of (i) chloroacetaldehyde, a metabolite of the anticancer drug ifosfamide, (ii) of cobalt chloride, a potential leakage product of the cobalt-containing nanoparticles, and (iii) of valproate, a widely used antiepileptic drug. 3.Since all the latter test compounds, like many toxic compounds, negatively interact with cellular metabolic pathways, we also illustrate our biochemical toxicology approach in which we used not only enzymatic but also carbon 13 NMR measurements and mathematical modelling of metabolic pathways. 4.This original approach, which can be applied to any tissue, allows to predict the nephrotoxic effects of milligram amounts of test compounds very early during the research and development processes of drugs and chemicals. This approach, combined with the use of cells that retain their in vivo metabolic properties and, therefore, are predictive, reduces the risk, the time and cost of such processes.

Brain slices from glutaminase-deficient mice metabolize less glutamine: a cellular metabolomic study with carbon 13 NMR

In the brain, glutaminase is considered to have a key role in the provision of glutamate, a major excitatory neurotransmitter. Brain slices obtained from wild-type (control) and glutaminase-deficient (GLS1+/-) mice were incubated without glucose and with 5 or 1 mmol/L [3-(13)C]glutamine as substrate. At the end of the incubation, substrate removal and product formation were measured by both enzymatic and carbon 13 nuclear magnetic resonance ((13)C-NMR) techniques. Slices from GLS1+/- mice consumed less [3-(13)C]glutamine and accumulated less [3-(13)C]glutamate. They also produced less (13)CO(2) but accumulated amounts of (13)C-aspartate and (13)C-gamma-aminobutyric acid (GABA) that were similar to those found with brain slices from control mice. The newly formed glutamine observed in slices from control mice remained unchanged in slices from GLS1+/- mice. As expected, flux through glutaminase in slices from GLS1+/- mice was found diminished. Fluxes through all enzymes of the tricarboxylic acid cycle were also reduced in brain slices from GLS1+/- mice except through malate dehydrogenase with 5 mmol/L [3-(13)C]glutamine. The latter diminutions are consistent with the decreases in the production of (13)CO(2) also observed in the slices from these mice. It is concluded that the genetic approach used in this study confirms the key role of glutaminase for the provision of glutamate.

Rat brain slices oxidize glucose at high rates: a (13)C NMR study

Since glucose is the main cerebral substrate, we have characterized the metabolism of various (13)C glucose isotopomers in rat brain slices. For this, we have used our cellular metabolomic approach that combines enzymatic and carbon 13 NMR techniques with mathematical models of metabolic pathways. We identified the fate and the pathways of the conversion of glucose carbons into various products (pyruvate, lactate, alanine, aspartate, glutamate, GABA, glutamine and CO(2)) and determined absolute fluxes through pathways of glucose metabolism. After 60 min of incubation, lactate and CO(2) were the main end-products of the metabolism of glucose which was avidly metabolized by the slices. Lactate was also used at high rates by the slices and mainly converted into CO(2). High values of flux through pyruvate carboxylase, which were similar with glucose and lactate as substrate, were observed. The addition of glutamine, but not of acetate, stimulated pyruvate carboxylation, the conversion of glutamate into succinate and fluxes through succinate dehydrogenase, malic enzyme, glutamine synthetase and aspartate aminotransferase. It is concluded that, unlike brain cells in culture, and consistent with high fluxes through PDH and enzymes of the tricarboxylic acid cycle, rat brain slices oxidized both glucose and lactate at high rates.

Protocols and applications of cellular metabolomics in safety studies using precision-cut tissue slices and carbon 13 NMR

Numerous xenobiotics are toxic to human and animal cells by interacting with their metabolism, but the precise metabolic step affected and the biochemical mechanism behind such a toxicity often remain unknown. In an attempt to reduce the ignorance in this field, we have developed a new approach called cellular metabolomics. This approach, developed in vitro, provides a panoramic view not only of the pathways involved in the metabolism of physiologic substrates of any normal or pathologic human or animal cell but also of the beneficial and adverse effects of xenobiotics on these metabolic pathways. Unlike many cell lines, precision-cut tissue slices, for which there is a renewed interest, remain metabolically differentiated for at least 24-48 h and allow to study the effect of xenobiotics during short-term and long-term incubations. Cellular metabolomics (or cellular metabonomics), which combines enzymatic and carbon 13 NMR measurements with mathematical modeling of metabolic pathways, is illustrated in this brief chapter for studying the effect of insulin on glucose metabolism in rat liver precision-cut slices, and of valproate on glutamine metabolism in human renal cortical precision-cut slices. The use of very small amounts of test compounds allows to predict their toxic effect and eventually their beneficial effects very early in the research and development processes. Cellular metabolomics is complementary to other omics approaches, but, unlike them, provides functional and dynamic pieces of information by measuring enzymatic fluxes.

Systemic activation of glutamate dehydrogenase increases renal ammoniagenesis: implications for the hyperinsulinism/hyperammonemia syndrome

The hyperinsulism/hyperammonemia (HI/HA) syndrome is caused by glutamate dehydrogenase (GDH) gain-of-function mutations that reduce the inhibition by GTP, consequently increasing the activity of GDH in vivo. The source of the hyperammonemia in the HI/HA syndrome remains unclear. We examined the effect of systemic activation of GDH on ammonia metabolism in the rat. 2-Aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) is a nonmetabolizable analog of the natural GDH allosteric activator leucine. A dose of 100 mumol BCH/100 g rat resulted in a mild systemic hyperammonemia. Using arterial-venous (A-V) differences, we exclude the liver, intestine, and skeletal muscle as major contributors to this BCH-induced hyperammonemia. However, renal ammonia output increased, as demonstrated by an increase in A-V difference for ammonia across the kidney in BCH-treated animals. Isolated renal cortical tubules incubated with BCH increased the rate of ammoniagenesis from glutamine by 40%. The flux through GDH increased more than twofold when BCH was added to renal mitochondria respiring on glutamine. The flux through glutaminase was not affected by BCH, whereas glutamate-oxaloacetate transaminase flux decreased when normalized to glutaminase flux. These data show that increased renal ammoniagenesis due to activation of GDH can explain the BCH-induced hyperammonemia. These results are discussed in relation to the organ source of the ammonia in the HI/HA syndrome as well as the role of GDH in regulating renal ammoniagenesis.

Targets of chloroacetaldehyde-induced nephrotoxicity

Chloroacetaldehyde, one of the main products of hepatic ifosfamide metabolism, contributes to its nephrotoxicity. However, the pathophysiology of this toxicity is not fully understood. The present work examined the time and dose effects of clinically relevant concentrations of chloroacetaldehyde (25-75microM) on precision-cut rat renal cortical slices metabolizing a physiological concentration of lactate. Chloroacetaldehyde toxicity was demonstrated by the decrease in total glutathione and cellular ATP levels. The drop of cellular ATP was linked to the inhibition of oxidative phosphorylation at the level of complex I of the mitochondrial respiratory chain. The large decrease in glucose synthesis from lactate was explained by the inhibition of some gluconeogenic enzymes, mainly glyceraldehyde 3-phosphate dehydrogenase. The decrease in lactate utilization was demonstrated not only by a defect of gluconeogenesis but also by the decrease in [(14)CO(2)] formation from [U-(14)C]-lactate. All the effects of chloroacetaldehyde were concentration and time-dependent. Finally, the chloroacetaldehyde-induced inhibition of glyceraldehyde 3-phosphate dehydrogenase, which is also a glycolytic enzyme, suggests that, under conditions close to those found during ifosfamide therapy, the inhibition of glycolytic pathway by chloroacetaldehyde might be responsible, at least in part, for the therapeutic efficacy of ifosfamide.

In vivo mesna and amifostine do not prevent chloroacetaldehyde nephrotoxicity in vitro

Chloroacetaldehyde (CAA) is the putative metabolite responsible for ifosfamide-induced nephrotoxicity. Whereas evidence suggests that sodium 2-mercaptoethanesulfonate (mesna) and amifostine protect renal cells against CAA toxicity in vitro, their efficacy in clinical studies is controversial. To better understand the discrepancy between in vivo and in vitro results, we combined the in vivo intraperitoneal administration of either saline or mesna (100 mg/kg) or amifostine (200 mg/kg) in rats and the in vitro study of CAA toxicity to both proximal tubules and precision-cut renal cortical slices. The measured renal cortical concentrations of mesna and amifostine were 0.6+/-0.1 micromol/g and 1.2+/-0.2 micromol/g, respectively; these drugs did not cause renal toxicity. Despite this, none of the adverse effects of 0.5 mM CAA was prevented by the previous in vivo administration of mesna or amifostine. Toxicity of 0.5 mM CAA to rat proximal tubules was shown by the fall of cellular adenosine triphosphate (ATP), total glutathione and coenzyme A + acetyl-coenzyme A levels and by the altered metabolic viability of renal cells. Long-term exposure of cortical slices to CAA concentrations > or =30 microM caused severe cell toxicity (i.e. decrease in cellular ATP, total glutathione, and coenzyme A + acetyl-coenzyme A levels), which was not prevented by the in vivo administration of mesna or amifostine.

Mechanisms of the ifosfamide-induced inhibition of endocytosis in the rat proximal kidney tubule

The Fanconi syndrome is a common side effect of the chemotherapeutic agent ifosfamide. Current evidences suggest that chloroacetaldehyde (CAA), one of the main metabolites of ifosfamide activation, contributes to its nephrotoxicity. However, the pathophysiology of CAA-induced Fanconi syndrome is not fully understood. The present work examined the adverse effects of CAA on precision-cut rat renal cortical slices, which allowed studying the toxic effect of CAA on proximal endocytosis. We demonstrated that clinically relevant concentrations of CAA (< or =200 microM) are able to inhibit the uptake of horseradish peroxidase, a marker of proximal tubular cell endocytosis in renal tubular proximal cells. CAA > or =75 microM has adverse effects, both on viability parameters and on energy metabolism, as shown by the great decrease in total glutathione and ATP levels. In addition, the V-ATPase, which plays a crucial role in intracellular vesicle trafficking, was inhibited by 100 microM of CAA. By contrast, the slight decrease in Na-K-ATPase activity observed for CAA> or = 125 microM (maximum inhibition: 33%) could not totally explain the inhibition of the reabsorption processes. In conclusion, the addition of the two main adverse effects of CAA (decrease in ATP levels and inhibition of the V-ATPase) could explain the inhibition of endocytosis and the Fanconi syndrome observed during ifosfamide treatments.

Validation of Renal Oxidative Metabolism Measurement by Positron-Emission Tomography

Either in research or in clinical practice, the exploration of renal oxidative metabolism is limited by the lack of noninvasive measurement. Positron-emission tomography using carbon-11 acetate may estimate tissue oxidative metabolism by measuring acetate turnover in the Krebs cycle. Although extensively studied in cardiology, this method has never been validated for renal oxidative metabolism measurement. The aim of this study is the validation of acetate turnover compared with the invasive renal oxygen consumption measurement. Renal oxygen consumption and tubular sodium reabsorption were measured invasively in 10 anesthetized pigs. Simultaneously, acetate turnover was estimated by the clearance of carbon-11 acetate in the renal cortex, after a 166-MBq injection of carbon-11 acetate. Renal oxidative metabolism was measured under various conditions induced by mechanical and pharmacological interventions. Renal oxygen consumption and acetate turnover varied on a wide range from 0.05 to 0.29 mmol min −1 (>5-fold) and from 0.025 to 0.188 minutes −1 (>7-fold), respectively. Acetate turnover was very significantly correlated with renal oxygen consumption ( P <0.0001; R =0.82) and tubular sodium reabsorption ( P =0.001; R =0.67). This study demonstrates that acetate turnover measures renal oxidative metabolism noninvasively and quantitatively, consistent with changes in tubular sodium reabsorption. This method may be applied to assess oxidative metabolism in animal models and in humans.

Glutamine gluconeogenesis in the small intestine of 72 h-fasted adult rats is undetectable

Recent reports have indicated that 48-72 h of fasting, Type 1 diabetes and high-protein feeding induce gluconeogenesis in the small intestine of adult rats in vivo. Since this would (i) represent a dramatic revision of the prevailing view that only the liver and the kidneys are gluconeogenic and (ii) have major consequences in the metabolism, nutrition and diabetes fields, we have thoroughly re-examined this question in the situation reported to induce the highest rate of gluconeogenesis. For this, metabolically viable small intestinal segments from 72 h-fasted adult rats were incubated with [3-13C]glutamine as substrate. After incubation, substrate utilization and product accumulation were measured by enzymatic and NMR spectroscopic methods. Although the segments utilized [13C]glutamine at high rates and accumulated 13C-labelled products linearly for 30 min in vitro, no substantial glucose synthesis could be detected. This was not due to the re-utilization of [13C]glucose initially synthesized from [13C]glutamine. Arteriovenous metabolite concentration difference measurements across the portal vein-drained viscera of 72 h-fasted Wistar and Sprague-Dawley rats clearly indicated that glutamine, the main if not the only gluconeogenic precursor taken up, could not give rise to detectable glucose production in vivo. Therefore we challenge the view that the small intestine of the adult rat is a gluconeogenic organ.

Precision-cut organ slices to investigate target organ injury

Drug-induced organ injury is a multifaceted process, involving numerous cell types and mediators, and remains a significant safety issue in pharmaceutical development and clinical therapy. Organ slices, an in vitro model representing the multicellular, structural and functional features of in vivo tissue, is a promising model for elucidating mechanisms of drug-induced organ injury and for characterising species susceptibilities. Time- and concentration-dependent drug-induced effects on organ slice gene expression, function and morphology are providing insight into the molecular and biochemical pathways leading to organ dysfunction, an altered morphology and the induction of repair pathways. Human organ slice studies are valuable for bridging the extrapolation of animal-derived data and for identifying mechanisms relevant for humans. The liver is the major organ used in organ slice studies; however, the utility of extrahepatic-derived slices, as well as cocultures for investigating multiple organ involvement in tissue injury is increasing. Organ slice investigations can further our understanding of the cell types and cell interactions involved in drug-induced injury and the consequences of drug-induced off-target effects for identifying compound liabilities that will impact safety.