Effects of preoperative oral carbohydrate supplementation on postoperative metabolic stress response of patients undergoing elective abdominal surgery

BACKGROUND

The goal of the present study was to evaluate the effects of preoperative oral carbohydrate supplementation (OCH) on the postoperative metabolic stress response of patients undergoing elective abdominal surgery.

METHODS

The study was designed as a controlled, prospective, cohort study including 38 patients treated with OCH (800 mL the day before surgery and 400 mL within 3 h before the induction of anesthesia) and 38 controls matched for surgical procedure. Fasting glucose, insulin, insulin resistance (HOMA-IR index), cortisol, and interleukin 6 (IL-6) were assessed before and after surgery (postoperative day (POD) 1, 2, and 3).

RESULTS

The administration of OCH resulted in lower fasting glucose, HOMA-IR index, cortisol, and IL-6 on both POD 1 and POD 2. At multivariable regression analyses, the reduction of these parameters was independent of sex, age, body mass index, and major abdominal surgery. Particularly, models including OCH treatment explained 70, 63, and 66 % of the variance of the increase in IL-6 levels at POD 1, POD 2, and POD 3, respectively. The effect of OCH on changes in glucose, insulin resistance, and cortisol on POD 1 and POD 2 disappeared after the inclusion of IL-6 in the models.

CONCLUSIONS

Treatment with OCH was associated with attenuation of the postoperative metabolic stress response. We hypothesize that modulation of the inflammatory response is one of the mechanisms involved.

Age-related changes in intracellular TH1/TH2 cytokine production, immunoproliferative T lymphocyte response and natural killer cell activity in newborns, children and adults

To evaluate the development of the neonatal immune system, we measured T lymphocyte response to Con A, intracellular IL-2, IL-4, IFN-gamma and IL-10 production, and natural killer cell (NKC) activity in 12 very preterm, 12 preterm and 20 term neonates, 10 children and 10 adults. Immunoproliferation to Con A was significantly lower in cord blood than in children or adults. The percentage of CD4+ lymphocytes was significantly higher in newborns while CD8+ cells were higher at older ages, with a resulting gradual decline of the CD4+/CD8+ ratio. The percentage of IL-2-producing CD4+ and CD8+ cells was higher in all newborn groups than in children and adults, while the percentage of IL-4-producing cells was higher for CD8+ and lower for CD4+ cells in cord blood than in children and adults. Neonates had substantially lower percentages of CD4+ and CD8+ IFN-gamma-producing cells. A significant negative correlation was observed between gestational age and IFN-gamma-CD4+-, IL-2-CD8+-, and IL-10- CD4+-producing cells. In addition, a positive correlation was found between gestational age and IL-10-CD8+-producing cells. Percentages of CD4+/CD45RA+ cells were higher and CD4+/CD45RO+ percentages were lower in newborns than in children and adults. NKC activity in infants was significantly correlated with gestational age and significantly impaired compared to children and adults. On the whole, these results suggest a gradual development of immunity during gestation and show significant immaturity of cellular immune response at birth. The reduction of NKC activity, the lower proliferative response of T cells, the reduced cytotoxic response and a dysregulated cytokine production may contribute to the neonatal increased risk of infection and to the low incidence of graft-versus-host disease after cord blood transplantation.

Stimulation of p38 MAP kinase reduces acidosis and Na(+) overload in preconditioned hepatocytes

Ischemic preconditioning has been shown to improve liver resistance to hypoxia/reperfusion damage. A signal pathway involving A(2A)-adenosine receptor, G(i)-proteins, protein kinase C and p38 MAP kinase is responsible for the development of hypoxic preconditioning in hepatocytes. However, the coupling of this signal pathway with the mechanisms responsible for cytoprotection is still unknown. We have observed that stimulation of A(2A)-adenosine receptors or of p38 MAPK by CGS21680 or anisomycin, respectively, appreciably reduced intracellular acidosis and Na(+) accumulation developing during hypoxia. These effects were reverted by p38 MAPK inhibitor SB203580 as well as by blocking vacuolar proton ATPase with bafilomycin A(1). SB203580 and bafilomycin A(1) also abolished the cytoprotective action exerted by both CGS21680 and anisomycin. We propose that the stimulation of p38 MAPK by preconditioning might increase hepatocyte resistance to hypoxia by activating proton extrusion through vacuolar proton ATPase, thus limiting Na(+) overload promoted by Na(+)-dependent acid buffering systems.

Signal pathway involved in the development of hypoxic preconditioning in rat hepatocytes

Ischemic preconditioning improves liver resistance to hypoxia and reduces reperfusion injury following transplantation. However, the intracellular signals that mediate the development of liver hypoxic preconditioning are largely unknown. We have investigated the signal pathway leading to preconditioning in freshly isolated rat hepatocytes. Hepatocytes were preconditioned by 10-minute incubation under hypoxic conditions followed by 10 minutes of reoxygenation and subsequently exposed to 90 minutes of hypoxia. Preconditioning reduced hepatocyte killing by hypoxia by about 35%. A similar protection was also obtained by preincubation with chloro-adenosine or with A(2A)-adenosine receptor agonist CGS21680, whereas A(1)-adenosine receptor agonist N-phenyl-isopropyladenosine (R-PIA) was inactive. Conversely, the development of preconditioning was blocked by A(2)-receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX), but not by A(1)-receptor antagonist 8-cyclopenthyl-1, 3-dipropylxanthine (DPCPX). In either preconditioned or CGS21680-treated hepatocytes a selective activation of delta and epsilon protein kinase C (PKC) isoforms was also evident. Inhibition of heterotrimeric G(i) protein or of phospholypase C by, respectively, pertussis toxin or U73122, prevented PKC activation as well as the development of preconditioning. MEK inhibitor PD98509 did not interfere with preconditioning that was instead blocked by p38 MAP kinase inhibitor SB203580. The direct activation of p38 MAPK by anisomycin A mimicked the protection against hypoxic injury given by preconditioning. Consistently, an increased phosphorylation of p38 MAPK was observed in preconditioned or CGS21680-treated hepatocytes, and this effect was abolished by PKC-blocker, chelerythrine. We propose that a signal pathway involving A(2A)-adenosine receptors, G(i)-proteins, phospholypase C, delta- and epsilon-PKCs, and p38 MAPK, is responsible for the development of liver ischemic preconditioning.

Ethanol potentiates hypoxic liver injury: role of hepatocyte Na(+) overload

Centrilobular hypoxia has been suggested to contribute to hepatic damage caused by alcohol intoxication. However, the mechanisms involved are still poorly understood. We have investigated whether alterations of Na(+) homeostasis might account for ethanol-mediated increase in hepatocyte sensitivity to hypoxia. Addition of ethanol (100 mmol/l) to isolated rat hepatocytes incubated under nitrogen atmosphere greatly stimulated cell death. An increase in intracellular Na(+) levels preceded cell killing and Na(+) levels in hepatocytes exposed to the combination of ethanol and hypoxia were almost twice those in hypoxic cells without ethanol. Na(+) increase was also observed in hepatocytes incubated with ethanol in oxygenated buffer. Ethanol addition significantly lowered hepatocyte pH. Inhibiting ethanol and acetaldehyde oxidation with, respectively, 4-methylpyrazole and cyanamide prevented this effect. 4-methylpyrazole, cyanamide as well as hepatocyte incubation in a HCO(3)(-)-free buffer or in the presence of Na(+)/H(+) exchanger blocker 5-(N,N-dimethyl)-amiloride also reduced Na(+) influx in ethanol-treated hepatocytes. 4-methylpyrazole and cyanamide similarly prevented ethanol-stimulated Na(+) accumulation and hepatocyte killing during hypoxia. Moreover, ethanol-induced Na(+) influx caused cytotoxicity in hepatocytes pre-treated with Na(+), K(+)-ATPase inhibitor ouabain. Also in this condition 4-methylpyrazole and 5-(N,N-dimethyl)-amiloride decreased cell killing. These results indicate that ethanol can promotes cytotoxicity in hypoxic hepatocytes by enhancing Na(+) accumulation.

Liver/kidney microsomal antibody type 1 targets CYP2D6 on hepatocyte plasma membrane

BACKGROUND

Liver/kidney microsomal antibody type 1 (LKM1) is the marker of type 2 autoimmune hepatitis (AIH) and is detected in up to 6% of patients with hepatitis C virus (HCV) infection. It recognises linear and conformational epitopes of cytochrome P450IID6 (CYP2D6) and may have liver damaging activity, provided that CYP2D6 is accessible to effector mechanisms of autoimmune attack.

METHODS

The presence of LKM1 in the plasma membrane was investigated by indirect immunofluorescence and confocal laser microscopy of isolated rat hepatocytes probed with 10 LKM1 positive sera (five from patients with AIH and five from patients with chronic HCV infection) and a rabbit polyclonal anti-CYP2D6 serum.

RESULTS

Serum from both types of patient stained the plasma membrane of non-permeabilised cells, where the fluorescent signal could be visualised as discrete clumps. Conversely, permeabilised hepatocytes showed diffuse submembranous/cytoplasmic staining. Adsorption with recombinant CYP2D6 substantially reduced plasma membrane staining and LKM1 immunoblot reactivity. Plasma membrane staining of LKM1 colocalised with that of anti-CYP2D6. Immunoprecipitation experiments showed that a single 50 kDa protein recognised by anti-CYP2D6 can be isolated from the plasma membrane of intact hepatocytes.

CONCLUSIONS

AIH and HCV related LKM1 recognise CYP2D6 exposed on the plasma membrane of isolated hepatocytes. This observation supports the notion that anti-CYP2D6 autoreactivity may be involved in the pathogenesis of liver damage.

Alterations of Na(+) homeostasis in hepatocyte reoxygenation injury

Reperfusion injury represents an important cause of primary graft non-function during liver transplantation. However, the mechanism responsible for cellular damage during reoxygenation has not yet been completely understood. We have investigated whether changes in intracellular Na(+) distribution might contribute to cause hepatocyte damage during reoxygenation buffer after 24 h of cold storage. Hepatocyte reoxygenation resulted in a rapid increase in cellular Na(+) content that was associated with cytotoxicity. Na(+) accumulation and hepatocyte death were prevented by the omission of Na(+) from the incubation medium, but not by the addition of antioxidants. Blocking Na(+)/H(+) exchanger and Na(+)/HCO(3)(-) co-transporter by, respectively, 5-(N,N-dimethyl)-amiloride or omitting HCO(3)(-) from the reoxygenation medium significantly decreased Na(+) overload and cytotoxicity. Stimulation of ATP re-synthesis by the addition of fructose also lowered Na(+) accumulation and cell death during reoxygenation. A significant protection against Na(+)-mediated reoxygenation injury was evident in hepatocytes maintained in an acidic buffer (pH 6.5) or in the presence of glycine. The cytoprotective action of glycine or of the acidic buffer was reverted by promoting Na(+) influx with the Na(+)/H(+) ionophore monensin. Altogether, these results suggest that Na(+) accumulation during the early phases of reoxygenation might contribute to liver graft reperfusion injury.

Ischemic preconditioning reduces Na(+) accumulation and cell killing in isolated rat hepatocytes exposed to hypoxia

Short periods of ischemia followed up by reperfusion are known to protect the heart against injury caused by a subsequent sustained ischemia. This phenomenon, known as ischemic preconditioning, has also been recently shown to reduce ischemic liver damage, but the mechanisms involved are still unknown. By using isolated hepatocytes as an in vitro model of liver preconditioning, we have investigated the possible effect of preconditioning on intracellular pH and Na(+) homeostasis. Freshly isolated rat hepatocytes were preconditioned by 10 minutes of incubation under hypoxic conditions followed up by 10 minutes of reoxygenation and subsequently exposed to 90 minutes of hypoxia. Although preconditioning did not ameliorate adenosine triphosphate (ATP) depletion, preconditioned hepatocytes exhibited an increased resistance to cell killing during hypoxic incubation. Intracellular acidosis and Na(+) accumulation developing during hypoxia were appreciably reduced in preconditioned cells. The effects of preconditioning on intracellular pH, Na(+) homeostasis, and cytotoxicity were mimicked by stimulating protein kinase C (PKC) with 4beta-phorbol-12-myristate-13-acetate (PMA) or 1,2 dioctanoyl-glycerol (1,2 DOG). Conversely, inhibiting PKC with chelerythrine or blocking vacuolar proton ATPase (V-ATPase) with bafilomycin A(1) abolished the protection given by preconditioning or by PMA treatment on hypoxic acidosis, Na(+) overload, and hepatocyte killing. Similarly, the addition of Na(+) ionophore monensin also reverted the cytoprotection exerted by preconditioning. This indicated that ischemic preconditioning of isolated hepatocytes decreased cell killing during hypoxia by preventing intracellular Na(+) accumulation. We propose that, after preconditioning, the stimulation of PKC might activate proton extrusion through V-ATPase, thus, limiting intracellular acidosis and Na(+) overload promoted by Na(+)-dependent acid buffering systems.

Intracellular Na+ accumulation and hepatocyte injury during cold storage

BACKGROUND

The mechanisms responsible for liver damage during cold storage are still not completely understood. We have investigated the role played by alterations of Na+ homeostasis in cell injury during cold hypoxia.

METHODS

The changes in Na+ distribution were investigated in isolated rat hepatocytes stored at 4 degrees C under hypoxic conditions.

RESULTS

Hepatocyte cold stored up to 72 hr in Krebs-Henseleit-Hepes buffer showed a progressive increase in intracellular Na+ content that preceded the loss of cell viability. Na+ accumulation and cell death were prevented using Na+-free, acidic (pH 6.5) or glycine-supplemented storage media. The Na+ ionophore monensin reverted the cytoprotection exerted by glycine and by the acidic medium, but not that given by Na+-free Krebs-Henseleit-Hepes. A low Na+ content was also important for the cytoprotection observed using University of Wisconsin solution.

CONCLUSIONS

Na+ overload might contribute to liver graft injury occurring during cold storage.

Alterations of cell volume regulation in the development of hepatocyte necrosis

Intracellular Na+ accumulation has been shown to contribute to hepatocyte death caused by anoxia or oxidative stress. In this study we have investigated the mechanism by which Na+ overload can contribute to the development of cytotoxicity. ATP depletion in isolated hepatocytes exposed to menadione-induced oxidative stress or to KCN was followed by Na+ accumulation, loss of intracellular K+, and cell swelling. Hepatocyte swelling occurred in two phases: a small amplitude swelling (about 15% of the initial size) with preservation of plasma membrane integrity and a terminal large amplitude swelling associated with cell death. Inhibition of Na+ accumulation by the use of a Na+-free medium prevented K+ loss, cell swelling, and cytotoxicity. Conversely, blocking K+ efflux by the addition of BaCl2 did not influence Na+ increase and small amplitude swelling, but greatly stimulated large amplitude swelling and cytotoxicity. Menadione or KCN killing of hepatocytes was also enhanced by inducing cell swelling in an hypotonic medium. However, increasing the osmolarity of the incubation medium did not protect against large amplitude swelling and cytotoxicity, since stimulated Na+ accumulation and K+ efflux. Altogether these results indicate that the impairment of volume regulation in response to the osmotic load caused by Na+ accumulation is critical for the development of cell necrosis induced by mitochondrial inhibition or oxidative stress.

Glycine protects against hepatocyte killing by KCN or hypoxia by preventing intracellular Na+ overload in the rat

Glycine has been shown to prevent hepatocyte death induced by anoxia and by several toxic agents. However, the mechanisms responsible for such a cytoprotective effect have not yet been entirely clarified. We have previously shown that an uncontrolled increase in intracellular Na+ is critical for hepatocyte killing induced by adenosine triphosphate (ATP) depletion. We herein report that protection by glycine (2 mmol/L) against cytotoxicity induced in isolated rat hepatocyte by potassium cyanide (KCN) or hypoxia was associated with the prevention of cytosolic Na+ accumulation. The addition of the Na+ ionophore, monensin, abolished the effects of glycine on both Na+ increase and cytotoxicity. Pretreating hepatocytes with the glycine-receptor antagonist, strychnine (1 mmol/L), similarly prevented Na+ overload and cell killing. Glycine at high concentrations and strychnine are known to block Cl- channels in many cell types. Consistently, we have observed that glycine and strychnine prevented the increase of intracellular Cl- levels caused by hypoxia or KCN. Incubation of hepatocytes in a Cl(-)-free medium, obtained by substituting chloride with membrane-impermeable gluconate, significantly reduced Na+ accumulation and cell killing triggered by hypoxia or KCN. Both these effects were abolished by the addition of monensin. The cytoprotective action exerted by hepatocyte incubation in the Cl(-)-free medium was, however, lost when membrane-permeable nitrate, which allowed Na+ accumulation, was used instead to replace chloride. Altogether, these results indicate that glycine inhibition of Cl- conductance protects against hepatocyte killing induced by KCN and hypoxia by interfering with intracellular Na+ accumulation triggered by ATP depletion.

Plasma membrane hydroxyethyl radical adducts cause antibody-dependent cytotoxicity in rat hepatocytes exposed to alcohol

BACKGROUND & AIMS

We reported previously that patients with alcoholic liver disease (ALD) have circulating immunoglobulins reacting with cytochrome P4502E1 (CYP2E1) complexed with hydroxyethyl free radicals. The aim of this study was to investigate whether hydroxyethyl radical adducts are present on the plasma membranes of ethanol-treated hepatocytes and their role in antibody-dependent cytotoxicity.

METHODS

Immunofluorescence confocal laser microscopy, Western blotting, and antibody-dependent cell-mediated cytotoxicity assay were used.

RESULTS

Isolated rat hepatocytes incubated in vitro with ethanol or obtained from ethanol-treated animals showed strong surface fluorescence when exposed to rabbit anti-hydroxyethyl radical serum or sera from patients with ALD. No surface fluorescence was evident on control hepatocytes or after scavenging hydroxyethyl radicals with 4-pyridyl-1-oxide-t-butyl nitrone. The presence of CYP2E1-hydroxyethyl radical adducts on hepatocyte plasma membranes was shown by Western blot and by immunofluorescence using double staining for human and rabbit anti-CYP2E1 immunoglobulin G. Cytotoxicity was observed in ethanol-treated hepatocytes incubated with immunoglobulin G from patients with ALD and normal human blood mononuclear cells. This effect was blocked by preabsorbing the sera with human albumin complexed with hydroxyethyl radicals, which also eliminated the antibody reaction with the plasma membranes.

CONCLUSIONS

Hydroxyethyl radicals bound to CYP2E1 on hepatocyte plasma membranes can target immune reactions triggered by alcohol abuse.

Role of Na+/Ca2+ exchanger in preventing Na+ overload and hepatocyte injury: opposite effects of extracellular and intracellular Ca2+ chelation

We have previously shown that an increase of intracellular Na+ occurs in isolated rat hepatocytes undergoing ATP depletion and that Na+ accumulation is associated with an uncontrolled influx of Ca2+ through the activation in reverse mode of the Na+/Ca2+ exchanger. In the present study we have investigated the relationship between alterations of Na+ and Ca2+ homeostasis and hepatocyte killing using treatments which differentially chelate extracellular or intracellular Ca2+. Chelation of extracellular Ca2+ by ethylene glycol bis-(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) potentiated Na+ overload and cell killing induced in isolated rat hepatocytes by hypoxia or menadione. Similar effects were also observed when Na+ accumulation was induced by the combined addition of Na+ ionophore monensin and the inhibition of plasma membrane Na+/K+ ATPase by ouabain. Conversely, the use of the intracellular Ca2+ chelator EGTA acetoxymethyl ester (EGTA/AM) reduced Na+ overload and hepatocyte death induced by hypoxia or cell treatment with menadione or monensin plus ouabain. The effects of EGTA/AM were reverted in the presence of bepridil, an inhibitor of Na+/Ca2+ exchanger. Altogether these results indicated that differential chelation of intracellular or extracellular Ca2+ influences in opposite ways hepatocyte killing due to ATP depletion by modulating intracellular Na+ levels through the reversed activity of the Na+/Ca2+ exchanger.

Activation of human immunodeficiency virus long terminal repeat by arachidonic acid

Arachidonic acid is the precursor of highly reactive mediators, including prostaglandins and leukotrienes, and the most abundant n-6 polyunsaturated fatty acid in mammalian cell membranes. It is released from phospholipids upon many inflammatory stimuli. In this study, a chloramphenicol acyltransferase reporter gene, under control of the human immunodeficiency virus-1 long terminal repeat, was strongly induced upon treating human promonocytes with arachidonic acid. The n-3 fatty acid eicosapentenoic, found in abundance in fish oil, had no effect. HIV-1 long terminal repeat activation by arachidonic acid was suppressed by inhibitors of both lipoxygenase and cyclooxygenase pathways, suggesting that metabolites, rather than arachidonic acid itself, mediated the stimulatory effect. This is the first report linking HIV-1 expression to the metabolism of arachidonic acid.

Nuclear factor kB is activated by arachidonic acid but not by eicosapentaenoic acid

The omega-6 arachidonic acid supplementation of the human promonocytic cell line U937 strongly stimulates the nuclear translocation of the transcription factor NF-kB. Inhibitors of arachidonate oxidative metabolism prevent NF-kB activation, indirectly indicating a role for prostaglandin and leukotriene metabolites in the genesis of this phenomenon. Of note, omega-3 eicosapentaenoic acid does not exert any effect on NF-kB DNA binding. In subsequent experiments, prostaglandin E2 consistently showed the ability to activate NF-kB in U937 promonocytic cells, as well as in J774 macrophages. NF-kB activation by arachidonate, together with the lack of effect by eicosapentaenoic acid, suggests a way to modulate the expression of certain genes by means of a suitable dietary n-6/n-3 fatty acid ratio.

4-Hydroxynonenal triggers Ca2+ influx in isolated rat hepatocytes

Addition of micromolar concentrations of 4-hydroxynonenal (4-HNE), a reactive end-product of lipid peroxidation, to isolated rat hepatocytes was found to cause an early and transient increase in cytosolic Ca2+ concentration followed by a more pronounced and progressive elevation. Such a late effect of 4-HNE was prevented by chelation of extracellular Ca2+ with EGTA or by the addition of GdCl3, which is known to block the activity of store operated Ca2+ channels in the hepatocyte plasma membrane. Moreover, the preincubation of isolated hepatocytes with the phospholipase C inhibitor U73122 resulted in a complete inhibition of both the early increase of cytosolic Ca2+ and the subsequent Ca2+ inflow. When 4-HNE was added to the hepatocytes 5 min after the emptying of intracellular Ca2+ pools by thapsigargin, the aldehyde caused a further increase in the accumulation of Ca2+ which was prevented in the presence of GdCl3. Taken together these results indicate that in hepatocytes 4-HNE causes Ca2+ inflow across GdCl3-sensitive Ca2+ channels. The mechanism responsible for such an effect is triggered by the emptying of intracellular Ca2+ pools likely resulting from 4-HNE mediated stimulation of phospholypase C, but 4-HNE also appears to interfere with the channel protein(s) or with the mechanism(s) regulating capacitative Ca2+ inflow.

Alteration of Na+ homeostasis as a critical step in the development of irreversible hepatocyte injury after adenosine triphosphate depletion

The exposure of isolated hepatocytes to the redox-cycling quinone menadione caused an early loss of mitochondrial membrane potential, adenosine triphosphate (ATP) depletion, and decreased intracellular pH. These alterations were followed by an increase in intracellular Na+ and, ultimately, cell death. If HCO3- was omitted from the incubation buffer, or the hepatocytes were incubated in an acidic medium (pH 6.5) the accumulation of Na+ was markedly reduced. Inhibition of the Na+/H+ exchanger and of the Na+/HCO3- cotransporter by, respectively, amiloride and 4,4'-di-isothiocyano-2,2'-disulfonic acid stilbene (DIDS) suppressed the initial Na+ influx but did not prevent subsequent Na+ accumulation, because amiloride and DIDS inhibited the Na+/K+ pump. The omission of HCO3- from the extracellular medium or the incubation in acidic conditions also prevented menadione toxicity, without interfering with the loss of mitochondrial membrane potential and with ATP depletion. A similar protection was evident when hepatocytes were incubated with menadione in a medium without Na+. The preservation of adequate levels of ATP by supplementing hepatocytes with fructose allowed the initial Na+ load to be recovered and provided partial protection against menadione toxicity. These effects were suppressed if Na+/K(+)-ATPase was inhibited with ouabain. Taken together, these results indicated that the activation of the Na+/HCO3- cotransporter and of the Na+/H+ exchanger in response to the decrease of intracellular pH stimulated an enhanced influx of Na+. When the activity of the Na+/K+ pump was not able to control Na+ levels because of ATP depletion, such an uncontrolled Na+ influx precipitated irreversible injury and caused hepatocyte death.

The operation of Na+/Ca2+ exchanger prevents intracellular Ca2+ overload and hepatocyte killing following iron-induced lipid peroxidation

Stimulation of lipid peroxidation by incubating isolated rat hepatocytes with ADP/FeCl3 caused a time dependent increase in cytosolic free Ca2+ levels, without influencing cellular Na+ content. Omission of Na+ from the incubation medium greatly increased the accumulation of Ca2+, which was partially reverted upon transferring the cells in a Na+ containing medium. This suggested that a Na(+)-dependent Ca2+ transporter was activated upon the elevation of cytosolic Ca2+ and partially counteracted the influx of Ca2+ promoted by lipid peroxidation. In the presence of Na+ cell death was not associated with the increase of Ca2+ induced by peroxidative injury; however, decrease of mitochondrial membrane potential and loss of cell viability followed by massive accumulation of Ca2+ occurring in hepatocytes incubated with ADP/FeCl3 in a Na(+)-free medium. Both these effects were completely prevented by chelation of extracellular Ca2+ with EGTA. Thus, we conclude that Na(+)-dependent Ca2+ transporter is involved in controlling excessive accumulation of Ca2+ induced by stimulation of lipid peroxidation and can prevent hepatocyte death caused by Ca(2+)-dependent alterations of mitochondrial activity.

Sodium-mediated cell swelling is associated with irreversible damage in isolated hepatocytes exposed to hypoxia or mitochondrial toxins

Incubation of isolated rat hepatocytes under hypoxic conditions or in the presence of inhibitors of mitochondrial functions such as KCN or carbonylcyanide m-chlorophenylhydrazone (CCCP) causes an increase of intracellular Na+ content and cell swelling. Both these effects precede the appearance of irreversible damage as measured by trypan blue staining of non-vital hepatocytes. When the increase of cellular Na+ is prevented by substitution of NaCl in the incubation medium with equimolar amount of choline chloride both cell swelling and loss of viability are greatly reduced. Thus, we propose that osmotic stress induced by an uncontrolled accumulation of Na+ might be associated with the ultimate events precipitating irreversible membrane lesions in hepatocyte undergoing metabolic inhibition.

Evidence for a sodium-dependent calcium influx in isolated rat hepatocytes undergoing ATP depletion

ATP depletion caused by menadione and triethyllead in isolated hepatocytes is associated with intracellular acidosis and a sustained increase in intracellular Na+ and Ca2+ concentrations. Removal of Na+ from the incubation medium as well as the inclusion of EGTA largely prevented the increase in cytosolic Ca2+, thus indicating that Ca2+ was mobilized from the extracellular medium in response to Na+ load. To further validate these findings, hepatocytes were incubated with a combination of sodium propionate and ouabain in order to induce intracellular acidosis and inhibit Na+ extrusion. This treatment promoted a marked increase in intracellular Na+ and Ca2+ concentrations that was prevented by omission of Na+ from the incubation medium as well as by agents that inhibited cellular Na+ influx. These data indicate that following Na+ load, Ca2+ can be accumulated in hepatocytes via a Na+/Ca2+ antiporter operating on a reverse mode.

Alterations of hepatocyte Ca2+ homeostasis by triethylated lead (Et3Pb+): are they correlated with cytotoxicity?

Isolated rat hepatocytes were used to investigate the biochemical mechanisms of toxicity of triethyllead (Et3Pb+), a highly neurotoxic degradation product of the antiknocking petrol additive tetraethyllead. As early as 5 min from the addition of 50 microM Et3Pb+ to hepatocyte suspensions a decrease of mitochondrial membrane potential and of the capacity of mitochondria and microsomes to retain Ca2+ occurred. A dose-dependent release of mitochondrial Ca2+ as well as an inhibition of microsomal Ca(2+)-ATPase activity were also evident when Et3Pb+ (from 2.5 microM up to 50 microM) was added to, respectively, isolated liver mitochondria and microsomes. Further experiments using hepatocytes loaded with the Ca2+ indicator Fura-2AM demonstrate that 1 min from addition of Et3Pb+ the cytosolic free Ca2+ levels increased by about 3-fold. High affinity plasma membrane Ca(2+)-ATPase activity was also significantly inhibited in hepatocytes treated with Et3Pb+, suggesting that an impairement of the mechanisms controlling the efflux of extracellular Ca2+ was concomitantly involved in the rise in cytosolic Ca2+ concentration. The increase in the cytosolic Ca2+ levels caused by Et3Pb+ was followed by a rapid decline of cell viability. However, the addition of EGTA or of the intracellular Ca2+ chelator BAPTA/AM did not affect either the time-course or the extent of cytotoxicity. Conversely, fructose, a glycolytic substrate that was able to support ATP production, prevented hepatocyte death. Thus, the depletion of cellular energy stores rather than the increase in cytosolic Ca2+ appears to be the mechanism by which Et3Pb+ causes irreversible injury in isolated hepatocytes.

Mitochondrial damage and its role in causing hepatocyte injury during stimulation of lipid peroxidation by iron nitriloacetate

Incubation of isolated rat hepatocytes with 0.1 mM iron nitrilotriacetic acid (FeNTA) caused a rapid rise in lipid peroxidation followed by a substantial increase in trypan blue staining and lactate dehydrogenase release, but did not affect the protein and non-protein thiol content of the cells. Hepatocyte death was preceded by the decline of mitochondrial membrane potential, as assayed by rhodamine 123 uptake, and by the depletion of cellular ATP. Chelation of extracellular Ca2+ by ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid or inhibition of Ca2+ cycling within the mitochondria by LaCl3 or cyclosporin A did not prevent the decline of rhodamine 123 uptake. On the other hand, a dramatic increase in the conjugated diene content was observed in mitochondria isolated from FeNTA-treated hepatocytes. Oxidative damage of mitochondria was accompanied by the leakage of matrix enzymes glutamic oxalacetic aminotransferase (GOT) and glutamate dehydrogenase (GLDH). The addition of the antioxidant N,N'-diphenylphenylene diamine (DPPD) completely prevented GOT and GLDH leakage, inhibition of rhodamine 123 uptake, and ATP depletion induced by FeNTA, indicating that Ca(2+)-independent alterations of mitochondrial membrane permeability consequent to lipid peroxidation were responsible for the loss of mitochondrial membrane potential. DPPD addition also protected against hepatocyte death. Similarly hepatocytes prepared from fed rats were found to be more resistant than those obtained from starved rats toward ATP depletion and cell death caused by FeNTA, in spite of undergoing a comparable mitochondrial injury. A similar protection was also observed following fructose supplementation of hepatocytes isolated from starved rats, indicating that the decline of ATP was critical for the development of FeNTA toxicity. From these results it was concluded that FeNTA-induced peroxidation of mitochondrial membranes impaired the electrochemical potential of these organelles and led to ATP depletion which was critical for the development of irreversible cell injury.

Lipid peroxidation and irreversible damage in the rat hepatocyte model. Protection by the silybin-phospholipid complex IdB 1016

IdB 1016 is a new silybin-phospholipid complex which is more bioavailable than the flavonoid silybin itself and displays free radical scavenging and antioxidant properties in liver microsomes. We report here that the addition of increasing concentrations of IdB 1016 to isolated rat hepatocytes caused a dose-dependent inhibition of lipid peroxidation induced by ADP-Fe3+ or cumene hydroperoxide. Moreover, IdB 1016 at the concentration which completely prevented MDA formation also protected isolated hepatocytes against the toxicity of pro-oxidant agents such as allyl alcohol, cumene hydroperoxide and bromotrichloromethane, without interfering with the activation mechanism of these xenobiotics. Similar protection was also obtained in hepatocytes prepared from animals pretreated in vivo with IdB 1016 while rat supplementation with pure silybin was totally inefficient. These results indicate IdB 1016 as being a potentially useful protective agent against free radical-mediated toxic liver injury.

Comparative evaluation of the antioxidant activity of alpha-tocopherol, alpha-tocopherol polyethylene glycol 1000 succinate and alpha-tocopherol succinate in isolated hepatocytes and liver microsomal suspensions

The antioxidant activity of alpha-tocopherol polyethylene glycol 1000 succinate (TPGS) and of alpha-tocopherol succinate (TS) has been examined in isolated hepatocytes and microsomal fractions from rat liver. Both TPGS and TS require esterase activity to yield free alpha-tocopherol and, hence, antioxidant activity. TPGS and TS consistently exerted a more effective antioxidant protection than an equivalent amount of directly-added free alpha-tocopherol. The low antioxidant efficiency of directly added free alpha-tocopherol in such water-based experimental systems as used here seems to be due to its extreme hydrophobicity. TPGS, on the other hand, is an extremely hydrophilic compound that is being examined as a useful source of alpha-tocopherol in certain clinical situations and is here shown to be a convenient and effective source for experimental studies into lipid peroxidation and antioxidant mechanisms.

Studies on the antioxidant and free radical scavenging properties of IdB 1016 a new flavanolignan complex

Silybin has been complexed in 1:1 ratio with phosphatidyl choline to give IdB 1016 in order to increase its bioavailability. The antioxidant and free radical scavenger action of this new form of silybin has been evaluated. One hour after the intragastric administration to rats of IdB 1016 (1.5 g/kg b.wt.) the concentration of silybin in the liver microsomes was estimated to be around 2.5 micrograms/mg protein corresponding to a final concentration in the microsomal suspension used of about 10 microM. At these levels IdB decreased by about 40% the lipid peroxidation induced in microsomes by NADPH, CCl4 and cumene hydroperoxide, probably by acting on lipid derived radicals. Spin trapping experiments showed, in fact, that the complexed form of silybin was able to scavenge lipid dienyl radicals generated in the microsomal membranes. In addition, IdB 1016 was also found to interact with free radical intermediates produced during the metabolic activation of carbon tetrachloride and methylhydrazine. These effects indicate IdB 1016 as a potentially protective agent against free radical-mediated toxic damage.

Effects of carbon tetrachloride on calcium homeostasis. A critical reconsideration

The incubation of isolated rat hepatocytes with 0.172 mM carbon tetrachloride caused a rapid decrease in the calcium content of both mitochondrial and extramitochondrial compartments. However, the release of Ca2+ from the intracellular stores was not associated with an increase in the cytosolic Ca2+ levels as measured by activation of phosphorylase alpha or by Quin-2 fluorescence. A rapid rise in hepatocyte free calcium was only observed with concentrations of CCl4 higher than 0.172 mM. The lack of activation of phosphorylase alpha was not due to the inhibition of the enzyme by CCl4, since in CCl4-treated hepatocytes the phosphorylase activity could be stimulated by glucagon, butyryl--cAMP or by the increase of cell calcium induced by the addition of A23187. Ca2+-dependent ATPase of plasma membranes was only slightly affected in the early phases of poisoning with CCl4 when both mitochondrial and extramitochondrial calcium pools were already lowered. This led to the conclusion that calcium released from intracellular organelles could be extruded from the cells in sufficient amounts to prevent the increase of the cytosolic levels. A rise in hepatocyte free calcium was observed during the second hour of incubation with CCl4, concomitantly with the appearance of both LDH leakage and plasma membrane blebbing. The addition of EGTA to the medium prevented both the increase in cytosolic Ca2+ and the blebbing suggesting that they were a consequence of an influx of calcium into the cells. However, neither EGTA nor the addition of inhibitors of calcium-dependent phospholipase A2 or non-lysosomal proteases were able to protect against cell death. These latter results suggested that the alterations of calcium distribution induced by CCl4 in isolated hepatocytes were not a primary cause of the toxic effects, although they did not exclude that a sustained rise in cytosolic Ca2+ could contribute in the progression of cell injury.

Pro-hemolytic effect of aldehydic products of lipid peroxidation

In order to evaluate the pro-hemolytic action exerted by different classes of biogenic aldehydes, normal red cells obtained from human beings of both sexes were incubated at 37 degrees C under iso or hypo-osmotic conditions in the presence of hydroxyalkenals or alkanals, in a concentration compatible with those actually recovered during red cell lipid peroxidation. None of the tested aldehydes showed a direct hemolytic effect, i.e. red cell lysis in iso-osmotic conditions. Conversely, almost all assayed alkanals and hydroxyalkenals exhibited a pre-lytic damage of human erythrocytes, as detected in the red cells suspended in hypo-osmotic medium. The highest pro-hemolytic effect was displayed by hexanal, nonanal, 2-nonenal and 4-hydroxynonenal.

Effect of spin traps in isolated rat hepatocytes and liver microsomes

Spin traps are increasingly employed in the detection of free radicals in biological systems, including liver microsomes and isolated hepatocytes. Two spin traps phenyl-t-butyl nitrone (PBN) and 4-pyridyl-l-oxide-t-butyl nitrone (4-POBN) have been tested for their effects on hepatocyte viability and mixed-function oxidase activity. High concentration of PBN but not of 4-POBN proved to moderately affect liver cell integrity, without interfering with intracellular ATP or cytochrome P-450 content. PBN also decreased hepatocyte GSH content, probably as the result of its metabolism to benzaldehyde. The two spin traps were found to inhibit aminopyrine demethylase and ethoxycoumarin deethylase activity in hepatocytes and microsomes. At low concentrations (1-5 mM) PBN enhanced aniline hydroxylase while high concentrations of the spin trap inhibited this activity. The inhibition of the monooxygenase system was not caused by damage of microsomal enzymes, but rather by competition with other substrates for the binding to the haemoprotein. The effects of spin traps on mixed function oxidase systems should be taken into account when evaluating the results of spin trapping experiments.

Mechanisms responsible for carbon tetrachloride-induced perturbation of mitochondrial calcium homeostasis

Incubation of isolated hepatocytes with CCl4 results in early reduction of the intracellular calcium content, mostly due to loss from the mitochondrial compartment. CCl4 treatment directly affects mitochondrial functions as indicated by the inhibition of Ca2+ uptake in cells permeabilized to the ion by digitonin exposure and by the reduction of intracellular ATP content in hepatocytes incubated in a glucose-free medium. Such mitochondrial damage is not caused by CCl4-induced stimulation of lipid peroxidation since it is not prevented by alpha-tocopherol, used at a concentration able to inhibit completely peroxidative reactions without interfering with CCl4 activation. All data together are in favour of a direct action of CCl4-reactive metabolites on liver cell calcium homeostasis.