Current status of calcium in hepatocellular injury

Preservation on calcium homeostasis is involved in mitochondrial protection of Limonium sinense against liver damage in mice

Mechanisms underlying the mitochondrial protection of Limonium sinense extracts (LSE) was studied in lipopolysaccharide and D-galactosamine (LPS/D-GalN) intoxicated mice. It was found that increased activities of serum aspartate aminotransferase and alanine aminotransferase induced by LPS/D-GalN were significantly inhibited by pretreatment with LSE. The obvious disruption of membrane potential, intramitochondrial Ca ²⁺ overload and suppression in mitochondrial Ca ²⁺ -ATPase activity induced by LPS/D-GalN were significantly blocked by pretreatment with LSE. It was concluded that mechanisms underlying protection of LSE against liver mitochondria damage might be related to the preservation on mitochondrial Ca ²⁺ homeostasis through the preservation on mitochondrial Ca ²⁺ -ATPase activity.

Efficacy of Sargassum polycystum (Phaeophyceae) sulphated polysaccharide against paracetamol-induced DNA fragmentation and modulation of membrane-bound phosphatases during toxic hepatitis

1. The aim of the present study was to assess the protective effect of Sargassum polycystum (sulphated polysaccharide) extract against paracetamol-induced DNA strand breaks and modulation of membrane-bound phosphatases, protein thiols and inorganic cations during toxic hepatitis. 2. Seaweed extract (200 mg/kg per day for 21 days) was administered to male Wistar rats against paracetamol challenge. Serum and liver tissues were used to assess levels of ATPase, protein thiols and inorganic cations using atomic absorption spectroscopy. The fragmentation of DNA was assessed by agarose gel electrophoresis. 3. Paracetamol induced intracellular stress, accompanied by changes in the structural and functional characteristics of liver cell membranes, which affected DNA integrity, membrane-bound ATPase and inorganic cations homeostasis. Rats intoxicated with paracetamol (800 mg/kg, i.p.) showed significant impairment in activities of total ATPase, Mg2+-ATPase, Ca+-ATPase and Na+/K+-ATPase, with concomitant changes in the levels of tissue protein thiols and inorganic cations, such as Na+, K+ and Ca2+. These changes were prevented in animals pretreated with S. polycystum extract, which indicates that S. polycystum supplementation could exert some protective effect against paracetamol-induced toxic hepatitis in rats. 4. The protective effect of the seaweed extract may be due to the presence of sulphated compounds that have free radical-scavenging activity.

Treatment of alcoholic hepatitis

Cirrhosis and its sequelae are responsible for close to 2% of all causes of death in the United States. Some studies have suggested that the costs of liver disease may account for as much as 1% of all health care spending, with alcohol-related liver disease (ALD) representing a major portion. It accounts for between 40% to 50% of all deaths due to cirrhosis, with an accompanying rate of progression of up to 60% in patients with pure alcoholic fatty liver over 10 years, and a 5-year survival rate as low as 35% if patients continue to drink. A subset of patients with ALD will develop an acute, virulent form of injury, acute alcoholic hepatitis, which has a substantially worse prognosis. Despite enormous progress in understanding the physiology of this disease, much remains unknown, and therefore, a consensus regarding effective therapy for ALD is lacking. Conventional therapy is still based largely on abstinence from alcohol, as well as general supportive and symptomatic care. Unfortunately, hepatocellular damage may progress despite these measures. Multiple treatment interventions for both the short- and long-term morbidity and mortality of this disease have been proposed, but strong disagreement exists among experts regarding the value of any of the proposed specific therapeutic interventions.

D-galactosamine induced hepatocyte apoptosis is inhibited in vivo and in cell culture by a calcium calmodulin antagonist, chlorpromazine, and a calcium channel blocker, verapamil

Studies were conducted in C57BL/6N Crj male mice and in cultured hepatocytes to clarify the relationship between galactosamine (GaIN) induced apoptosis and [Ca2+]i kinetics. Chlorpromazine (CPZ), a Ca(2+)-calmodulin antagonist, and verapamil (VR), a Ca(2+)-channel blocker each inhibited GaIN-induced DNA fragmentation and the appearance of apoptotic bodies. The kinetics of calcium uptake were evaluated using a calcium analyzer with the acetoxymethyl ester of fura-PE3 (fura-PE3/AM, 2.5 microM) as the calcium reporter. An increase in [Ca2+]i was detected in the cultured hepatocytes within 3 hours after treatment with 20 mM GaIN; this increase was inhibited by pretreatment with either 20 microM CPZ or 30 microM VR. Ca2+ imaging by confocal laser scanning microscopy showed that increase in [Ca2+]i after treatment with GaIN was initially localized around nuclei, while [Ca2+]i signals were later diffuse and observed throughout the cytoplasm. The activities of lactate dehydrogenase (LDH) and serum glutamate-pyruvate transaminase (sGPT), used as indicators of plasma membrane damage and leakage, however, were not reduced by pretreatment with CPZ or VR. From these findings, we infer that the DNA fragmentation in GaIN-induced hepatocyte apoptosis is associated with an elevation in the perinuclear concentration of Ca2+, but GaIN-induced necrotic cell death is triggered through pathway(s) that are insensitive to blockage of Ca2+ influx and therefore appear to occur independently of elevation in [Ca2+]i. These results help to clarify the role of calcium flux in hepatocyte apoptosis and necrosis induced by exposure to hepatotoxins in vivo and in vitro.

Bile salt tauroursodeoxycholic acid modulation of Bax translocation to mitochondria protects the liver from warm ischemia-reperfusion injury in the rat

BACKGROUND

Tauroursodeoxycholic acid (TUDC) is a hydrophilic bile acid that has a cytoprotective effect in primary biliary cirrhosis and primary sclerosing cholangitis. TUDC also protects hepatocytes from hydrophobic bile acid-induced apoptosis. The aim of this study was to determine whether TUDC ameliorates hepatocyte apoptosis during ischemia-reperfusion injury.

METHODS

We used a rat model of hepatic warm ischemia-reperfusion injury to assess the effects of TUDC. Male Sprague-Dawley rats were subjected to 1 or 2 hr of normothermic ischemia followed by 3 or 6 hr of reperfusion. The treatment group received TUDC (50 mg/kg) by bolus intravenous injection 30 min before initiation of ischemia, whereas the control group received saline only. Blood samples for biochemical analysis were obtained after 6 hr of reperfusion. Liver biopsies for histological assessment were obtained 3 and 6 hr after reperfusion. Hepatocyte apoptosis was determined by terminal dUTP nick-end labeling. The pro-apoptotic protein Bax was quantified at the mRNA and protein level.

RESULTS

Treatment with TUDC significantly reduced serum transaminase levels. This was associated with a significant amelioration in the levels of hepatocyte apoptosis in the TUDC-treated group compared with control. Furthermore, Western blot analysis of Bax expression in liver tissue indicated that TUDC inhibited the translocation of Bax from the cytosol to the mitochondria.

CONCLUSIONS

TUDC significantly reduced hepatic injury in this model. The beneficial effects of TUDC upon hepatocyte apoptosis were related to the modulation of Bax protein translocation.

Metabolic effects of intraportal nutrition in humans

OBJECTIVE

We investigated the metabolic effects of intravenous nutrition through a portal (PN) or systemic (SN) peripheral vein.

METHODS

Twenty patients were randomized to receive PN or SN nutrition after colorectal surgery. The daily regimen included 900 kcal and 100 g of amino acid (AA). Visceral proteins and hepatic enzymes were measured on days 0, 1, 3, 5, and 7, and plasma arterovenous differences and limb flux of AA were measured on days 0, 3, and 7; urinary nitrogen and 3-CH3-histidine were analyzed daily.

RESULTS

Serum albumin on day 7 was still depressed (P = 0.01) in SN and fully restored in PN patients. Prealbumin levels increased significantly (P = 0.05) in the PN group only. Plasma levels of glutamine and asparagine were higher in PN than in SN patients, and this difference was statistically significant (P = 0.05). SN patients had significantly more negative limb-muscle balance of valine and tyrosine, whereas PN patients had a higher muscle release of citrulline and taurine.

CONCLUSIONS

In conclusion, short-term PN is safe and has some metabolic benefits: it accelerates recovery from postoperative hypoalbuminemia and hypopnealbuminemia and is associated with a higher plasma level of glutamine and an AA plasma pattern that is closer to normal. PN blunts the catabolic response of the muscle, decreasing loss of proteins and release of some AA involved in hepatic gluconeogenesis.

Glycochenodeoxycholic acid (GCDC) induced hepatocyte apoptosis is associated with early modulation of intracellular PKC activity

The effect of GCDC-induced apoptosis on PKC activity and PKC's role in GCDC-induced hepatocyte apoptosis is unclear. The specific aims of this study were to determine if GCDC-induced apoptosis changed intracellular PKC activity and if modulation of PKC activity affected GCDC-induced hepatocyte apoptosis. Apoptosis was induced in isolated hepatocytes using GCDC. PKC activity was measured and specific PKC and calpain inhibitors were used to study the effects of PKC and calpain modulation on GCDC-induced apoptosis. After 4 h exposure, 50 microM GCDC induced apoptosis in 42% of hepatocytes. Intracellular PKC activity decreased to 44% of controls 2 h after exposure of hepatocytes to GCDC (p < 0.001). Pre-incubation of hepatocytes with the calpain protease inhibitor restored PKC activity in GCDC exposed hepatocytes to 91 +/- 5% of control cells. Pre-incubation of hepatocytes with a calpain inhibitor decreased GCDC-induced apoptosis as did pre-incubation with the PKC activating phorbol ester, PMA. The combination of calpain inhibition and PMA further reduced GCDC-induced apoptosis but caused low level hepatic apoptosis. Inhibition of PKC with chelerythrine also substantially reduced GCDC-induced hepatocyte apoptosis. GCDC-induced apoptosis is associated with decreases in total cellular PKC activity, which appear to be dependent on intracellular calpain-like protease activity. The combination of protease inhibition and phorbol ester pretreatment preserved total cellular PKC activity and decreased GCDC-induced apoptosis but induced low level apoptosis in the absence of GCDC exposure. PKC inhibition also decreased GCDC-induced hepatocyte apoptosis highlighting the complex interactions of PKC and proteases during GCDC-induced apoptosis.

The protein kinase inhibitor 1-(5-isoquinolinylsulfonyl)-2-methyl-piperzine (H-7) prevents and reverses Ca(2+)-mediated injury in isolated rat hepatocyte couplets

We have recently shown that protein kinase C (PKC) activation induces similar morphological and functional alterations in couplets to that caused by increments of intracellular Ca(2+). Since certain PKC isoforms are activated by Ca(2+), we tested whether the PKC inhibitor H-7 can counteract the alterations induced by this ion in couplets. The Ca(2+) ionophore A23187, which can mobilize Ca(2+) from extracellular and intracellular sources, decreased, in a dose-dependent manner, the percentage of couplets accumulating the fluorescent bile acid analogue cholyl-lysyl-fluorescein (CLF) in their canalicular vacuoles, i.e., in the canalicular vacuolar accumulation test (cVA of CLF), a measure of the overall capability of the couplets to secrete and retain CLF. To a similar extent, A23187 also decreased the percentage of couplets retaining CLF once secreted, i.e., in the canalicular vacuole retention test (cVR of CLF), a measure of tight junctional integrity. ATP (50 microM), another Ca(2+)-elevating compound, altered canalicular function in a similar extent to A23187. All these functional changes were prevented by H-7 in a dose-dependent manner. Canalicular dysfunction was accompanied by bleb formation and extensive redistribution of F-actin from the pericanalicular area to the cell body, which was also fully prevented by H-7; the intracellular Ca(2+) chelator, 1, 2-bis(o-aminophenoxy)-ethene-N,N,N',N'-tetraacetate tetrakis-(acetomethylester), (BAPTA/AM) (20 microM) had virtually the same preventive effects as H-7. Both H-7 and BAPTA/AM not only prevented but also reversed the decrease in cVA of CLF and blebbing induced by A23187. Thus, H-7 can both prevent and reverse Ca(2+)-mediated hepatocellular injury.

Membrane stabilizing effects of calcium and taxol during the cold storage of isolated rat hepatocytes

BACKGROUND

Calcium plays an important role in liver preservation and preservation induces depletion of cellular Ca. This may affect hepatocyte cytoskeleton integrity necessary for maintaining cell shape and organ viability. We tested the effects of a microtubular stabilizer (Taxol) in liver cell preservation.

METHODS

Isolated rat hepatocytes were preincubated with or without a microtubule stabilizing agent, 100 microM Taxol, at 37 degrees C for 20 min, then stored in the University of Wisconsin (UW) solution +/-1.5 mM CaC12 at 4 degrees C for up to 48 hr. After storage, the cells were rewarmed in Krebs-Henseleit buffer with air at 37 degrees C for 1 hr. Morphological changes in the plasma membrane (scanning electron microscopy) and cell viability (percentage of lactate dehydrogenase [LDH] release) before and after rewarming were studied.

RESULTS

Hepatocytes showed time-dependent increase in bleb formation (cytoskeleton disruption) during cold storage. Rewarming the cells caused even greater bleb formation and increased LDH release (cell death). Pretreatment of cells with Taxol and cold storage in the UW solution with 1.5 mM Ca suppressed both bleb formation and LDH release in 48-hr coldstored cells.

CONCLUSIONS

Cold storage of hepatocytes leads to reperfusion injury and cell death. This can be suppressed with Taxol and Ca. This suggests that hypothermia induces changes in cellular Ca and a disruption of the microtubules, leading to loss of cell viability. Improved liver preservation may require suppression of Ca-dependent disruption of the cytoskeleton system of liver cells.

Reduction of ischemia-reperfusion injury of the liver by in vivo adenovirus-mediated gene transfer of the antiapoptotic Bcl-2 gene

OBJECTIVE

To examine the possibility of reducing ischemia-reperfusion injury (I/R injury) to the mouse liver by in vivo adenovirus-mediated gene transfer of the antiapoptotic human Bcl-2 gene.

SUMMARY BACKGROUND DATA

Ischemia-reperfusion injury has been demonstrated in a number of clinically relevant diseases such as myocardial infarction, cerebrovascular disease, sepsis, peripheral vascular disease, and organ transplantation. In this regard, apoptosis plays a central role.

METHODS

Normal C57BL/6 mice were used. An adenovirus (deltaE1) vector containing the human Bcl-2 gene was developed in the authors' laboratory. An adenovirus vector encoding an irrelevant gene (beta-galactosidase, AdCMVLacZ) was used as a control. Taking advantage of the hepatotropic properties of adenovirus vectors, gene transfer was performed with 1 x 10(9) plaque-forming units by intravenous tail injection, 48 hours before the ischemic injury. Ischemic-reperfusion injury was induced by temporal and segmental occlusion of hepatic blood flow. Aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase activity was measured using standard assays. Liver biopsies were obtained before and 6 hours after I/R injury for morphologic assessment, and apoptosis was determined in situ with a histochemical assay.

RESULTS

The expression of AdCMVhBcl-2 vector was confirmed by reverse transcription-polymerase chain reaction and functionally validated in apoptotic studies in endothelial cells. Expression of the Bcl-2 gene protects against I/R injury, as shown by a significant decrease in transaminases (p < 0.05) and necrosis and apoptosis (p < 0.001), and permanent survival (p < 0.0001), compared with sham-operated animals and animals treated with AdCMVLacZ.

CONCLUSIONS

Genetic modification of the liver to induce cytoprotection has potential applications to prevent I/R injury to the liver in surgical interventions, including liver transplantation.

3,4-Methylenedioxymethamphetamine (ecstasy)-induced hepatotoxicity: effect on cytosolic calcium signals in isolated hepatocytes

AIMS/BACKGROUND

Hepatocellular damage has been reported as a consequence of 3,4-methylenedioxymethamphetamine (MDMA) intake. However, little is known about the cellular mechanisms involved. The present study was undertaken to evaluate the effects of MDMA on cell viability as well as free calcium levels ([Ca2+]i) in short-term cultured hepatocytes. Reduced glutathione (GSH), adenosine-5'-triphosphate (ATP) and lipid peroxidation were investigated to evaluate the toxic effect of MDMA, in vitro, using freshly isolated rat hepatocytes.

METHODS

In order to measure cytosolic free Ca2+ concentrations ([Ca2+]i), rat hepatocytes were loaded with the Ca2+ indicator fura-2-acetoxymethylester (fura-2-AM).

RESULTS

A sustained rise of ([Ca2+]i) after incubation with MDMA was the most noteworthy finding. In Ca2+-free medium, MDMA caused a reduced increase of ([Ca2+]i). On the other hand, MDMA (0.1-5 mM) induced a concentration-dependent and time exposure-dependent GSH and ATP depletion. Although it did not reach statistical significance, GSH deficits were accompanied by a tendency to increase lipid peroxidation 3 h after MDMA incubation.

CONCLUSIONS

The above data suggest that the marked rise of ([Ca2+]i) and subsequent ATP and GSH depletion can lead to a rapid decrease in cell viability.

A synergistic effect of extracellular hypocalcemic condition for hyperoxic reoxygenation injury in rat hepatocytes

BACKGROUND

Calcium accumulation of cells and mitochondria during reperfusion or reoxygenation has been implicated as a potential factor in cell injury as the result of mitochondrial damage. The objective of this study was to disclose whether or not low extracellular calcium ion concentration ([Ca2+]ex) in the medium at the time of reoxygenation might prevent calcium accumulation and attenuate hepatocytes injury after severe hypoxia.

METHODS

Isolated rat hepatocytes were incubated under a hyperoxic or hypoxic atmosphere for 60 min. During the ensuing 60-min hyperoxic reoxygenation, medium [Ca2+]ex was varied from 0.6 microM to 2.0 mM by altering total calcium and addition of chelators.

RESULTS

Incubation in low [Ca2+]ex reduced total cellular calcium and mitochondrial calcium in both the hyperoxic and hypoxic group. Under hyperoxic/hyperoxic incubation (control), hepatocytes were able to maintain potassium balance when [Ca2+]ex was >3.0 microM (pCa=5.5) and cellular viability (% lactate dehydrogenase release) at all levels of extracellular calcium. Under hypoxic/hyperoxic incubation (reoxygenation), however, loss of the ability to restore potassium balance as well as apparent increase in lactate dehydrogenase release were observed at severely low [Ca2+]ex (<30 microM; pCa=4.5). This low [Ca2+]ex-induced exacerbation of hepatocytes viability could not be generated under mild reoxygenation such as normoxia.

CONCLUSIONS

In normal isolated hepatocytes, very low [Ca2+]ex levels produce only very subtle changes in membrane permeability of isolated hepatocytes. After hypoxia, however, hypocalcemia acts synergistically with hyperoxic reoxygenation to produce more severe damage. These results suggested that [Ca2+]ex should be maintained on the physiological level to attenuate hepatocytes injury after severe hypoxia.

Alteration in cellular calcium and mitochondrial functions in the rat liver during cold preservation

BACKGROUND

Preservation injury is multifactorial and its mechanism is still incompletely defined. Calcium may play an important role in preservation injury.

METHODS

The effects of hypothermia on cytosolic free calcium concentration ([Ca2+]I) and total cellular calcium content in isolated rat hepatocytes were investigated by using fura-2 fluorescence and atomic absorption spectroscopy. Fura-2 loaded cells were placed into a prechilled (7 degrees C) cuvette equipped with a stirrer or preserved in the University of Wisconsin (UW) solution for up to 48 hr. In some experiments, cells were pretreated with inhibitors of Ca2+ release from mitochondria (m-iodobenzylguanidine [MIBG]) and from endoplasmic reticulum (ryanodine [RYA]) for 20 min at 37 degrees C. Mitochondrial functions after preservation were evaluated by measuring ATP and respiratory rates.

RESULTS

Cooling to 7 degrees C caused a rapid increase in [Ca2+]I that was substantially blocked by MIBG and RYA pretreatment. The elevated calcium gradually leaked out of the cells into the Ca2+-free medium. In long-term storage of the cells in the UW solution, there was a marked decrease in both cytosolic free calcium and total cellular calcium. Pretreatment of the livers with MIBG before cold preservation in the UW solution resulted in a stimulation of ATP regeneration in tissue slices. MIBG pretreatment also improved mitochondrial respiratory functions after cold preservation.

CONCLUSIONS

Thus, the loss of mitochondrial function after liver preservation in the UW solution may be related to the effects of hypothermia on calcium metabolism. Approaches to help maintain calcium homeostasis during storage may improve organ preservation.

Randomised controlled double-blind trial of the calcium channel antagonist amlodipine in the treatment of acute alcoholic hepatitis

BACKGROUND/AIMS

Calcium channel blockers have a hepatoprotective action in animal models of alcohol-induced liver injury but their effect in alcoholic liver disease in humans has not been previously investigated. We have conducted a randomised, placebo-controlled trial to investigate the possible benefit of the calcium channel blocker amlodipine in terms of 4-week survival in hospitalised patients with severe acute alcoholic hepatitis.

METHODS

Sixty-two patients with acute alcoholic hepatitis were randomised to receive 5-10 mg amlodipine each day for 1 year or an identical capsule containing placebo. In 36 (58%), acute alcoholic hepatitis was confirmed on biopsy and in the remainder on clinical and laboratory criteria. There were no statistically significant differences in clinical characteristics and disease severity in the treated and placebo groups.

RESULTS

Of the 32 patients receiving amlodipine, there were six deaths (19%) in the first 4 weeks compared with seven (23%) of the placebo patients (p=0.329). Causes of death were similar in the amlodipine and control groups, with liver failure predominant. Analysis by the Cox proportional hazards model after adjustment for other prognostic factors showed survival was not significantly influenced by active treatment (p=0.07). One patient in each group was withdrawn because of the development of hypotension, but this did not recur on reintroduction of the capsules.

CONCLUSIONS

This study shows that calcium channel blockers are well tolerated with few side effects in advanced alcoholic liver disease, but there is no conclusive evidence from this study that calcium channel blockers are helpful in the treatment of alcoholic hepatitis.

Calpain is a mediator of preservation-reperfusion injury in rat liver transplantation

Proteases as well as alterations in intracellular calcium have important roles in hepatic preservation-reperfusion injury, and increased calpain activity recently has been demonstrated in liver allografts. Experiments were designed to evaluate (i) hepatic cytosolic calpain activity during different periods of cold ischemia (CI), rewarming, or reperfusion, and (ii) effects of inhibition of calpain on liver graft function using the isolated perfused rat liver and arterialized orthotopic liver transplantation models. Calpain activity was assayed using the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-7-amino-4-methyl coumarin (AMC) and expressed as mean +/- SD pmol AMC released/min per mg of cytosolic protein. Calpain activity rose significantly after 24 hr of CI in University of Wisconsin solution and further increased with longer preservation. Activity also increased within 30 min of rewarming, peaking at 120 min. Increased durations of CI preceding rewarming resulted in significantly higher activity (P < 0.01). Calpain activity increased rapidly upon reperfusion and was significantly enhanced by previous CI (P < 0.01). Calpain inhibition with Cbz-Val-Phe methyl ester significantly decreased aspartate aminotransferase released in the isolated perfused rat liver perfusate (P < 0.05). Duration of survival after orthotopic liver transplantation using livers cold-preserved for 40 hr was also significantly increased (P < 0.05) with calpain inhibitor. In conclusion, calpain proteases are activated during each phase of transplantation and are likely to play an important role in the mechanisms of preservation-reperfusion injury.

Cytosolic-free calcium increases to greater than 100 micromolar in ATP-depleted proximal tubules

Previous studies have shown that cytosolic-free Ca2+ (Caf) increases to at least low micromolar concentrations during ATP depletion of isolated kidney proximal tubules. However, peak levels could not be determined precisely with the Ca2+-sensitive fluorophore, fura-2, because of its high affinity for Ca2+. Now, we have used two low affinity Ca2+ fluorophores, mag-fura-2 (furaptra) and fura-2FF, to quantitate the full magnitude of Caf increase. Between 30 and 60 min after treatment with antimycin to deplete ATP in the presence of glycine to prevent lytic plasma membrane damage, Caf measured with mag-fura-2 exceeded 10 microM in 91% of tubules studied and 68% had increases to greater than 100 microM. Caf increases of similar magnitude that were dependent on influx of medium Ca2+ were also seen using the new low Ca2+ affinity, Mg2+-insensitive, fluorophore fura-2FF in tubules depleted of ATP by hypoxia, and these increases were reversed by reoxygenation. Total cell Ca2+ levels in antimycin-treated or hypoxic tubules did not change, suggesting that mitochondria were not buffering the increased Caf during ATP depletion. Considered in the context of the high degree of structural preservation of glycine-treated tubule cells during ATP depletion and the commonly assumed Ca2+ requirements for phospholipid hydrolysis, actin disassembly, and Ca2+-mediated structural damage, the remarkable elevations of Caf demonstrated here suggest an unexpected resistance to the deleterious effects of increased Caf during energy deprivation in the presence of glycine.

Hepatotoxicity of ethanol: protective effect of calcium channel blockers in isolated hepatocytes

This study examines the effects of three calcium channel blockers (verapamil, nifedipine and diltiazem) on isolated rat hepatocytes exposed to ethanol. In the first part of our study, hepatocytes were incubated with increasing concentrations of ethanol (100, 300, 500, 1000 mM) for varying times. Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) release were measured to evaluate the cytotoxic effects of ethanol. The concentration of 300 mM and time of incubation of 45 min were chosen for cytoprotection experiments in which calcium channel blockers, at two different concentrations, were added to the medium 30 min prior to the addition of ethanol. ALT, AST and LDH release as well as lipid peroxidation and cellular reduced glutathione (GSH) were measured. Nifedipine and verapamil (25 microM) reduced ALT, AST and LDH activities. The highest dose of diltiazem (50 microM) was more effective than the lowest one (25 microM). Ethanol caused a significant depletion of cellular GSH content as well as a moderate enhancement of lipid peroxidation. While none of the three calcium channel blockers was able to restore the decrease in GSH levels, diltiazem (25 microM) and nifedipine (50 microM) showed the greatest effect, significantly reducing lipid peroxidation.

Effects of volatile anesthetics on the calcium ionophore A23187-mediated alterations in hepatic flow and metabolism in the perfused liver in fasted rats

Alterations in intracellular calcium homeostasis have been implicated in heptic injury. Volatile anesthetics modulate the homeostasis of intracellular calcium. The effects of volatile anesthetics on the hemodynamic and metabolic alterations induced by the calcium ionophore A23187 were studied using isolated liver perfusion in fasted rats. The liver was isolated from 24 hr-fasted male Sprague-Dawley rats, and perfused through the portal vein at a constant pressure of 1.2 kPa in a recirculating perfusion-aeration system. Halothane, isoflurane and sevoflurane were administered at 2%, 3% and 4.4%, respectively. All volatile anesthetics maintained basal hepatic flow, reduced oxygen consumption, and transiently enhanced net lactate production. A23187 at initial concentrations of 0.8 to 3.2 microM decreased hepatic flow and oxygen consumption in a dose-dependent manner, and enhanced lactate production. All anesthetics significantly attenuated the decreases in hepatic flow and oxygen consumption after administration of A23187 at 1.6 microM. None of the anesthetics significantly influenced the A23187-induced enhancement of net lactate production. Volatile anesthetics may attenuate the hepatic vasoconstriction and oxygen debt induced by intracellular calcium overload.

Mitigation of nitrofurantoin-induced toxicity in the perfused rat liver

1. Nitrofurantoin is an antimicrobial agent which produces hepatotoxicity caused by the redox cycling of the nitro group and its radical anion. This futile cycling triggers a complex series of events known collectively as oxidative stress. 2. Our goal was to determine treatment strategies which could mitigate nitrofurantoin-induced toxicity in the isolated perfused rat liver. We co-infused various agents which blocked early or late events in the progression to toxicity. Tissue levels of glutathione and protein thiols were measured as indicators of the progression to toxicity and lactate dehydrogenase leakage into the perfusate was used as a marker of irreversible cell death. 3. Five treatments significantly (P < 0.05) decreased LDH leakage (reported as thousands of units accumulated in perfusate at 300 min, mean+/-standard error, n = 3-4) when compared to nitrofurantoin alone (274 +/- 37). These treatments were adenosine-2'-monophosphate (120 +/- 53), penicillamine (90 +/- 29), N-(2-mercaptopropionyl)-glycine (120 +/- 49) and bromosulfophthalein with (80 +/- 29) or without 5,5'-difluro-1,2-bis(O-aminophenoxy)ethane-N,N,N'N'-tetraace tic acid (101 +/- 46). Two other treatments, N-acetylcysteine (183 +/- 7) and dithiothreitol (166 +/- 59) delayed the onset of toxicity. Finally, calpeptin (319 +/- 34) which blocks activation of nonlysosomal proteases was ineffective. 4. We concluded that early intervention on the pathway to toxicity was most effective. The strategies detailed here may prove beneficial in treating hepatotoxicity seen following nitrofurantoin therapy.

Effect of verapamil on allyl alcohol hepatotoxicity

The effects of verapamil, a calcium channel blocker, on allyl alcohol (AA) hepatotoxicity were studied in vivo. AA administration induced an increase of serum alanine aminotransferase (ALT) concentration and liver necrosis by means of glutathione (GSH) depletion. Pretreatment with verapamil reduced the increase of ALT in plasma and the morphological signs of necrosis induced by AA administration. Verapamil did not affect GSH levels by itself but prevented the decrease of the tripeptide by AA. In vitro, but not in vivo, verapamil inhibited the activity of alcohol dehydrogenase (ADH), the key enzyme in the conversion of AA into the toxic metabolite acrolein. These data indicate that verapamil protects against AA toxicity, probably by preventing the production of acrolein, its reactive metabolite.

Enzymic lipid peroxidation--a consequence of cell injury?

It is postulated that cell injury activates "dormant" enzymes to produce lipid hydroperoxides. In a first step, membrane lipids are cleaved by esterases. The unsaturated fatty acids thus produced are converted in a second step by lipoxygenases to lipid hydroperoxides (LOOHs). In a third, nonenzymic step, these LOOHs, together with dienoic hydroxy fatty acids produced by enzymic reduction of LOOHs, react with a second oxygen molecule to generate dihydroperoxy-fatty acids and hydroxy-hydroperoxy-fatty acids, which are degraded to alpha-hydroxyladehydic compounds. This last reaction requires production of LO'-radicals by iron ions that also are generated as a result of cell damage. In addition, alpha-hydroxyaldehydes are produced by hydrolysis of plasmalogen epoxides, which are generated by oxidation of plasmalogens with LOO' or by action of epoxidases. We hypothize that alpha-hydroxyaldehydes act as second messengers. The release of lipoxygenase and the consequent lipid hydroperoxidation is postulated to occur in massive cell damage (e.g., myocardial infarction), in chronic diseases such as rheumatism, diabetes and atherosclerosis, in aging, and in control of cell proliferation.

Effect of tauroursodeoxycholic acid on bile flow and calcium excretion in ischemia-reperfusion injury of rat livers

BACKGROUND/AIMS

Tauroursodeoxycholic acid is known to have a hepatoprotective action in cholestatic disorders. We evaluated whether oral pretreatment with tauroursodeoxycholic acid could protect the liver from ischemia-reperfusion injury, with particular regard to its effect on bile flow and biliary calcium excretion.

METHODS

A 1-hour in vivo ischemia-reperfusion model of 70% of the lobes of rat liver was used. Animals were divided into six groups (each group; n = 8); a non-ischemia sham group (CS), a control group without bile acids (CON), and 4 bile acid groups; 10 mg/kg and 50 mg/kg (U10, U50), taurocholic acid 10 mg/kg (CA10) and tauroursodeoxycholic acid 10 mg/kg (CD10). Bile acids were given orally for 7 days before operation.

RESULTS

Three hours after reperfusion, oral bile acid pretreatment failed to reduce the hepatic ischemia-reperfusion injury biochemically, but histological improvement was observed in the tauroursodeoxycholic acid groups. After reperfusion, tauroursodeoxycholic acid significantly increased bile flow from the ischemic liver, and also significantly increased serum calcium concentration. Although tauroursodeoxycholic acid did not change biliary calcium concentration, it significantly enhanced total biliary calcium output during reperfusion.

CONCLUSION

Thus, tauroursodeoxycholic acid inhibited tissue calcium accumulation and enhanced sinusoidal and biliary calcium output during hepatic ischemia-reperfusion. However, it is still unclear if calcium mobilization is part of the protective mechanisms of tauroursodeoxycholic acid in ischemia-reperfusion injury of the liver.

Role of mitochondria in the etiology and pathogenesis of Parkinson's disease

We discuss the etiology and pathogenesis of Parkinson's disease (PD). Our group and others have found a decrease in complex I of the mitochondrial electron transfer complex in the substantia nigra of patients with PD; in addition, we reported loss of the alpha-ketoglutarate dehydrogenase complex (KGDHC) in the substantia nigra. Dual loss of complex I and the KGDHC will deleteriously affect the electron transport and ATP synthesis; we believe that energy crisis is the most important mechanism of nigral cell death in PD. Oxidative stress has also been implicated as an important contributor to nigral cell death in PD, but we believe that oxidative stress is a secondary phenomenon to respiratory failure, because respiratory failure will increase oxygen free-radical formation and consume glutathione. The primary cause of mitochondrial respiratory failure has not been elucidated yet, but additive effect of environmental neurotoxins in genetically predisposed persons appears to be the most likely possibility.

Calcium and phospholipase A2 appear to be involved in the pathogenesis of hemorrhagic shock-induced mucosal injury and bacterial translocation

OBJECTIVE

The mechanism by which hemorrhagic shock injures the gut and leads to the translocation of bacteria remains incompletely determined. Since increased free cellular calcium levels and phospholipase A2 activity can lead to cellular injury and both have been documented in certain shock states, the hypothesis that calcium or phospholipase A2 may play a role in hemorrhagic shock-induced gut mucosal injury and bacterial translocation was tested.

DESIGN

Prospective animal study with concurrent controls.

SETTING

Small animal laboratory.

SUBJECTS

Fifty-seven male Sprague-Dawley rats weighing 250 to 350 g.

INTERVENTIONS

Five groups of rats were tested utilizing a nonlethal hemorrhagic shock model (mean arterial pressure of 30 mm Hg for 30 mins). These groups included: a) sham-shock, b) shock, c) shock plus quinacrine (inhibitor of phospholipase A2), d) shock plus diltiazem (calcium-channel blocker) administered 5 mins before hemorrhage, and e) shock plus diltiazem administered at the end of shock period and before resuscitation. At 24 hrs postshock or sham-shock, the animals were killed, the mesenteric lymph node and cecum were cultured and the gut was examined histologically.

MEASUREMENTS AND MAIN RESULTS

The occurrence rate of shock-induced bacterial translocation (90%) was significantly reduced in rats receiving quinacrine (27%) or preshock diltiazem (21%) (p < .05), but not postshock diltiazem (63%). Bacterial translocation did not occur in sham-shocked rats. The same amount of blood withdrawal was needed between all groups of rats to induce and maintain shock. Quinacrine and diltiazem administration largely prevented shock-induced ileal and cecal mucosal injury.

CONCLUSIONS

The observation that quinacrine and preshock diltiazem limited the extent of shock-induced mucosal injury and bacterial translocation indicate that calcium and phospholipase A2 are involved in the pathogenesis of shock-induced mucosal injury and bacterial translocation. The fact that preshock but not postshock diltiazem was protective indicates that the process leading to shock-induced calcium-mediated tissue injury and bacterial translocation was initiated during the ischemic rather than the reperfusion period. However, since neither quinacrine nor diltiazem was fully protective, other factors, such as oxidants, are also likely to be involved in the pathogenesis of shock-induced mucosal injury and bacterial translocation.

Liver cell necrosis: cellular mechanisms and clinical implications

Based on our current understanding, we have developed a provisional model for hepatocyte necrosis that may be applicable to cell necrosis in general (Figure 6). Damage to mitochondria appears to be a key early event in the progression to necrosis. At least two pathways may be involved. In the first, inhibition of oxidative phosphorylation in the absence of the MMPT leads to ATP depletion, ion dysregulation, and enhanced degradative hydrolase activity. If oxygen is present, toxic oxygen species may be generated and lipid peroxidation can occur. Subsequent cytoskeleton and plasma membrane damage result in plasma membrane bleb formation. These steps are reversible if the insult to the cell is removed. However, if injury continues, bleb rupture and cell lysis occur. In the second pathway, mitochondrial damage results in an MMPT. This step is irreversible and leads to cell death by as yet uncertain mechanisms. It is important to note that MMPT may occur secondary to changes in the first pathway (e.g. oxidative stress, increased Cai2+, and ATP depletion) and that all the "downstream events" occurring in the first pathway may result from MMPT (e.g., ATP depletion, ion dysregulation, or hydrolase activation). Proof of this model's applicability to cell necrosis in general awaits further validation. In this review, we have attempted to highlight the advances in our understanding of the cellular mechanisms of necrotic injury. Recent advances in this understanding have allowed scientists and clinicians a better comprehension of liver pathophysiology. This knowledge has provided new avenues of therapy and played a key role in the practice of hepatology as evidenced by advances in organ preservation. Understanding the early reversible events leading to cellular and subcellular damage will be key to prevention and treatment of liver disease. Hopefully, disease and injury specific preventive or pharmacological strategies can be developed based on this expanding data base.

Oxidant injury to hepatic mitochondria in patients with Wilson's disease and Bedlington terriers with copper toxicosis

BACKGROUND/AIMS

Copper overload leads to liver injury in humans with Wilson's disease and in Bedlington terriers with copper toxicosis; however, the mechanisms of liver injury are poorly understood. This study was undertaken to determine if oxidant (free radical) damage to hepatic mitochondria is involved in naturally occurring copper toxicosis.

METHODS

Fresh liver samples were obtained at the time of liver transplantation from 3 patients with Wilson's disease, 8 with cholestatic liver disease, and 5 with noncholestatic liver disease and from 8 control livers. Fresh liver was also obtained by open liver biopsy from 4 copper-overloaded and 4 normal Bedlington terriers and from 8 control dogs. Hepatic mitochondria and microsomes (humans only) were isolated, and lipid peroxidation was measured by lipid-conjugated dienes and thiobarbituric acid-reacting substances. In humans, liver alpha-tocopherol content was measured.

RESULTS

Lipid peroxidation and copper content were significantly increased (P < 0.05) in mitochondria from patients with Wilson's disease and copper-overloaded Bedlington terriers. More modest increases in lipid peroxidation were present in microsomes from patients with Wilson's disease. Mitochondrial copper concentrations correlated strongly with the severity of mitochondrial lipid peroxidation. Hepatic alpha-tocopherol content was decreased significantly in Wilson's disease liver.

CONCLUSIONS

These data suggest that the hepatic mitochondrion is an important target in hepatic copper toxicity and that oxidant damage to the liver may be involved in the pathogenesis of copper-induced injury.

Early cellular events couple covalent binding of reactive metabolites to cell killing by nephrotoxic cysteine conjugates

Addition of the nephrotoxic cysteine conjugate, S-(1,2-dichlorovinyl)-L-cysteine (DCVC), to the LLC-PK1 line of renal epithelial cells leads to covalent binding of reactive intermediates followed by thiol depletion, lipid peroxidation, and cell death (Chen et al., 1990, J. Biol. Chem., 265:21603-21611). The present study was designed to determine if increased intracellular free calcium might play a role in this pathway of DCVC-induced toxicity by comparing the temporal relationships among increased intracellular free calcium, lipid peroxidation, and cytotoxicity. Intracellular free calcium increased 1 hr after DCVC treatment, long before LDH release occurred. The elevation of intracellular free calcium and cytotoxicity was prevented by inhibiting DCVC metabolism with AOA. The cell-permeable chelators, Quin-2AM and EGTA-AM, prevented the toxicity. Pretreatment of cells with a nontoxic concentration of ionomycin increased intracellular free calcium and potentiated DCVC-induced LDH release. However, the antioxidant, DPPD, which blocks lipid peroxidation and toxicity, did not affect the increase in intracellular free calcium, whereas buffering intracellular calcium with Quin-2AM or EGTA-AM blocked both lipid peroxidation and toxicity without preventing the depletion of nonprotein sulfhydryls by DCVC. Ruthenium red, an inhibitor of mitochondrial calcium uptake, also blocked cell death. We hypothesize that covalent binding of the reactive fragment from DCVC metabolism leads to deregulation of intracellular calcium homeostasis and elevation of intracellular free calcium. Increased intracellular free calcium may in turn be coupled to mitochondrial damage and the accumulation of endogenous oxidants which cause lipid peroxidation and cell death.

Ca2+ influx initiates death of hepatocytes injured by activation of complement

To clarify the role of cytosolic Ca2+ in hepatocellular death, we exposed cultured hepatocytes to human serum and a monoclonal antibody directed against rat liver plasma membranes to produce complement-mediated cell injury. The change in cytosolic Ca2+ concentration was measured by fura2 and fluo3 fluorescence. With the addition of monoclonal antibody, an increase in cytosolic Ca2+ was observed, followed by cell death. Both the increase in intracellular Ca2+ and cell death were prevented by intracellular Ca2+ chelation or removal of extracellular Ca2+. We conclude that an increase in cytosolic Ca2+ plays a major role in hepatocellular injury induced by exposure of the cell membrane to monoclonal antibody.

Calcium in pig livers following ischemia and reperfusion

Calcium concentrations in pig livers were serially estimated following ischemia-reperfusion. Ischemia was produced by clamping the hepatic artery and the portal vein for 90 min (Group 1, n = 6) or for 180 min (Group 2, n = 6) during temporary side-to-side portacaval shunt performed before the induction of ischemia. Although there were no significant changes in hepatic calcium concentrations during ischemia, an immediate accumulation of calcium occurred 30 min after reperfusion in both groups. After these increases, the hepatic calcium concentration decreased to near the pre-ischemic level within 20 min in all animals in Group 1. The recovery of calcium was incomplete in Group 2. When the peak was defined as the highest level of calcium and the bottom as the lowest point after peak 60 min after reperfusion, the mean-peak was 11.0 +/- 1.3 (mean +/- SEM) nmol/mg dry weight liver in Group 1 and 12.8 +/- 1.4 nmol/mg dry weight liver in Group 2 (not significant). However, the mean-bottom in Group 1 was lower than that in Group 2 (5.5 +/- 0.3 and 8.1 +/- 0.8 nmol/mg dry weight liver, respectively, p < 0.05). These results indicate that hepatic calcium increases immediately after reperfusion and that recovery from this calcium accumulation seems to be a crucial factor for minimizing cellular injury.

Effects of Ca2+ deregulation on mitochondrial membrane potential and cell viability in nucleated cells following lytic complement attack

We have previously shown [Papadimitriou JC. Ramm LE. Drachenberg CB. Trump BF. Shin ML. (1991) J. Immunol., 147, 212-217] that formation of lytic C5b-9 channels on Ehrlich ascites tumor cells induced rapid depletion of adenine nucleotides associated with prelytic leakage preceding cell death. Extracellular Ca2+ concentration ([Ca2+]e) reduction by chelation markedly delayed the onset of cell death, although the adenine nucleotide leakage was enhanced. In the present study, we examined the temporal relationships between ionized cytosolic Ca2+ ([Ca2+]i), mitochondrial membrane potential (delta psi m) and cell death in individual cells by digital imaging fluorescence microscopy (DIFM), during the earliest phase of C5b-9 attack. The results showed an immediate, > 20-fold rise in [Ca2+]i, rapidly followed by dissipation of delta psi m and subsequent acute cell death. These events were markedly delayed by chelation of Ca2+e, but not by nominally Ca2+ free medium. Differing from previous reports indicating propidium iodide labeling of viable cells bearing C5b-9 channels, with DIFM we observed nuclear fluorescence with that marker only in association with cell death. These findings indicate that Ca2+ influx through lytic C5b-9 channels is responsible for the massive increase in [Ca2+]i, as well as for the rapid loss of delta psi m, followed by acute cell death. When this [Ca2+]i increase is prevented, the cell death is probably related to metabolic depletion.

Effect of oxidative stress and disruption of Ca2+ homeostasis on hepatocyte canalicular function in vitro

Isolated rat hepatocyte couplets were used to study the effects of menadione and a rise in the intracellular concentration of calcium on biliary canalicular function. Canalicular function was assessed by counting the percentage of couplets which were able to accumulate the fluorescent cholephile, cholyl lysyl fluorescein (CLF) into the canalicular vacuole between the two cells. Menadione induced a concentration-dependent inhibition of the canalicular vacuole accumulation (CVA) of CLF reaching 7.6 +/- 1.8% of control at 100 microM menadione. This disruption was not prevented by blocking receptor-operated calcium channels with Ni2+ (300 microM). The concentration range of menadione used did not deplete cellular ATP content. In contrast glutathione content was reduced to 52% of its control value by 100 microM menadione. A rise in cytosolic calcium induced by the calcium ionophore, A23187 (up to 30 microM) also disrupted CVA in a concentration-dependent manner. Release of endoplasmic reticulum calcium stores by thapsigargin (50 nM) affected the retention of canalicular contents to a much lesser extent, although it was able to stimulate a reduction in canalicular area to 40% of its original value, assumed to be due to canalicular contraction. Menadione (30 and 100 microM) reduced the fluorescence of phalloidin-FITC-labelled F-actin in both the total and pericanalicular cytoskeleton. Canalicular function was therefore disrupted by non-lethal concentrations of menadione via a mechanism which does not appear to involve ATP depletion or the entry of extracellular calcium, but is associated with a depletion of both cellular glutathione and F-actin. An increase in the concentration of intracellular calcium can stimulate canalicular contraction, and at relatively high concentrations calcium can also disrupt canalicular function.

Inhibition of mitochondrial respiration in vivo is an early event in acetaminophen-induced hepatotoxicity

Morphological changes in mitochondria are observed early in the course of acetaminophen (AA)-induced hepatotoxicity, and mitochondrial dysfunction has been observed both in vivo and in vitro following exposure to AA. This study examined the early effects of AA exposure in vivo on mitochondrial respiration and evaluated the effectiveness of N-acetyl-L-cysteine (NAC) in protecting against respiratory dysfunction. Mitochondria were isolated from the livers of fasted, male CD-1 mice 0, 0.5, 1, 1.5 or 2 h after administration of a hepatotoxic dose of AA (750 mg/kg). Glutamate- and succinate-supported mitochondrial respiration were subsequently assessed by polarographic measurement of state 3 (ADP-stimulated) and state 4 (resting) rates of oxygen consumption and determination of the corresponding respiratory control ratios (RCR: state 3/state 4) and ADP:O ratios. Hepatotoxicity was assessed histologically and by measuring plasma alanine aminotransferase (ALT) activity. The earliest sign of mitochondrial dysfunction observed in this study was a significant decrease in the ADP:O ratio for the oxidation of glutamate 1 h post-dosing. At 1.5 and 2 h post-dosing the RCRs for both glutamate- and succinate-supported respiration were significantly decreased. All of the respiratory parameters measured in this study were significantly decreased, with the exception of succinate-supported state 4 respiration which was significantly increased, 2 h after AA administration. Thus, inhibition of mitochondrial respiration preceded overt hepatic necrosis, indicated by an elevation of ALT activity, which was not observed until 3 and 4 h post-dosing. In addition, mitochondrial respiratory dysfunction correlated with morphological alterations.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporin A blocks 6-hydroxydopamine-induced efflux of Ca2+ from mitochondria without inactivating the mitochondrial inner-membrane pore

Oxidative stress causes Ca(2+)-loaded mitochondria to release Ca2+. The mechanism of this efflux is unclear, but it appears to be associated with the opening of a pore in the mitochondrial inner membrane. Pore opening depolarizes the mitochondria, letting solutes enter the mitochondrial matrix, causing swelling. Cyclosporin A (CsA) prevents opening of this pore. The neurotoxin 6-hydroxydopamine (6HD) autoxidizes, producing free radicals, which cause oxidative stress. In this paper it is shown that 6HD-induced efflux from Ca(2+)-loaded mitochondria was prevented by CsA. The 6HD-induced Ca2+ efflux was not accompanied by mitochondrial swelling, depolarization of the mitochondrial inner membrane or movement of radiolabelled sucrose into the mitochondrial matrix. In agreement with others [Schlegel, Schweizer and Richter (1992) Biochem. J. 285, 65-69], these findings suggest that the mitochondrial pore remained closed during pro-oxidant-induced Ca2+ efflux. However, the implication that CsA blocks pro-oxidant-induced Ca2+ efflux by some mechanism other than inactivating the mitochondrial pore, suggests that the interaction of CsA with mitochondria may be more complex than is currently supposed.

Protective effect of various calcium antagonists against an experimentally induced calcium overload in isolated hepatocytes

The effect of the hepatotoxic substance diamidinothionaphthene (98/202) on cytosolic, mitochondrial and extra-mitochondrial calcium distribution was measured in isolated rat hepatocytes. The drastic disturbance of the intracellular calcium homeostasis caused by this substance (increase of the cytosolic and mitochondrial calcium contents and depletion of extra-mitochondrial calcium stores, which at last lead to cell death) gave rise to an investigation of the possible cytoprotective effect of calcium antagonists of various chemical classes: verapamil, diltiazem, and nifedipine on isolated hepatocytes. Our results show that all three calcium antagonists prevented cell death caused by 98/202. The 98/202-induced increase of cytosolic and mitochondrial calcium content was inhibited by all three calcium antagonists. However, only verapamil was able to inhibit the depletion of extra-mitochondrial calcium stores. Since 98/202-induced cell death occurs only in the presence of extracellular calcium, it is concluded that calcium antagonists are also able to inhibit the influx of extracellular calcium in liver cells, which leads to a calcium overload of the cytosol and mitochondria. The various ways of interfering with the calcium homeostasis of liver cells qualifies the hepatotoxic substance 98/202 as a suitable in vitro hepatotoxicity model for testing the hepatoprotective effect of different calcium antagonists.

Effect of flushing of the liver graft upon plasma calcium and magnesium concentrations

Previous studies of total and ionized calcium in the plasma of liver transplant recipients have been conducted in patients with preexisting liver disease or who received blood transfusion. The intraoperative decline in plasma total and ionized calcium has been attributed to the effects of liver disease and/or the citrate in transfused blood. The present study was conducted in normal porcine recipients of liver stored either with EuroCollins or University of Wisconsin (UW) solution for 6 hr, compared with livers flushed with Ringer's lactate without storage. No blood transfusion was given. Mean total plasma calcium levels declined significantly after storage with UW solution to a nadir approximately 65-70% of preoperative levels. This decline persisted for two to five days. Mean levels of plasma ionized calcium declined lowest after flushing with UW solution but only to 82% of preoperative (NS). There was an increase in plasma total magnesium in the recipients of livers flushed with EuroCollins or UW solutions, which resolved within 30 min and which was probably related to magnesium content of the flushing solution. It is concluded that while the changes in plasma total and ionized calcium are moderate and of little clinical significance, they could be aggravated under clinical conditions by massive blood transfusion. Changes in plasma magnesium seemed to be directly attributable to the magnesium content of flushing solutions but the same relationship did not exist for changes in plasma calcium.

Prostacyclin elevation following glutathione depletion in vivo. Possible threshold dependency in liver and lung

The major objective of this study was to determine if a threshold level of glutathione (GSH) depletion is required to elevate plasma prostacyclin (6-ketoPGF1 alpha) in male Sprague-Dawley rats. Rats were treated i.p. with various doses of phorone, diethyl maleate (DEM), or GSH with and without DEM. Similar maximal depletions of hepatic GSH (to 10% of control) and renal GSH (to 50% of control) were observed with DEM and phorone, but lung GSH was depleted maximally by only 30% with phorone compared with a 70% depletion by DEM. Changes in lung GSH, but not kidney GSH, were closely correlated with changes in hepatic GSH 6-KetoPGF1 alpha levels in the lung were 10- to 30-fold higher than in kidney or liver, and there was a stronger correlation between lung and plasma 6-ketoPGF1 alpha than with the other two tissues. The increase in lung 6-ketoPGF1 alpha following GSH depletion did not appear to be due to a shift in prostaglandin metabolite synthesis since reciprocal changes in PGE2 were not observed; lung PGE2 levels were largely unaffected by DEM or phorone. Both DEM and phorone elevated plasma 6-ketoPGF1 alpha but the magnitude of increase for DEM (5- to 6-fold) was much greater than the 2-fold increase for phorone. The increase in plasma 6-ketoPGF1 alpha by 1.0 mL DEM/kg was attenuated by simultaneous administration of 2 mmol GSH/kg. The results indicate that the lung may be responsible for increases in plasma 6-ketoPGF1 alpha following GSH depletion and that a critical level of GSH depletion in the liver and/or lung may be necessary to elevate plasma 6-ketoPGF1 alpha levels.

Effects of tauroursodeoxycholic acid on cytosolic Ca2+ signals in isolated rat hepatocytes

BACKGROUND

Tauroursodeoxycholic acid (TUDCA) is of potential benefit in cholestatic disorders. However, the effects of TUDCA on cytosolic free calcium [(Ca2+)i], which regulates hepatocyte secretion, are unknown.

METHODS

The effect of TUDCA on (Ca2+)i was investigated in groups of isolated rat hepatocytes by microspectrofluorometry and in single cells by confocal line scanning microscopy.

RESULTS

Administration of TUDCA (5-50 mumol/L) induced a nearly fourfold increase of basal levels of (Ca2+)i. After a 15 minute treatment period, the TUDCA (10 mumol/L)-induced change in (Ca2+)i was higher than that of other mono-, di-, and trihydroxy bile acids at equimolar concentrations. Pretreatment with TUDCA (10 mumol/L) markedly reduced or abolished increases in (Ca2+)i induced by phenylephrine (1 mumol/L), the microsomal Ca(2+)-translocase inhibitor 2,5-di-(tert-butyl)-1,4-benzohydroquinone (25 mumol/L), or taurolithocholic acid (10-25 mumol/L). In Ca(2+)-free medium, TUDCA caused only a reduced and transient increase in (Ca2+)i. TUDCA (10 mumol/L) induced Ca2+ oscillations in all single cells that responded. However, levels of inositol-1,4,5-trisphosphate (IP3) in hepatocytes were not increased by treatment with TUDCA (10 mumol/L).

CONCLUSIONS

TUDCA at physiological concentrations potently modulates (Ca2+)i signals in hepatocytes by (1) mobilizing microsomal IP3-sensitive Ca2+ stores by an IP3-independent mechanism, (2) initiating Ca2+ oscillations, and (3) inducing influx of extracellular Ca2+.

Lipid peroxidation--a common pathogenetic mechanism?

Lipid peroxidation is considered at present as one of the basic mechanisms involved in reversible and irreversible cell and tissue damage. The current knowledge about the role of peroxidative breakdown of polyunsaturated fatty acids in the pathogenesis of various diseases has been reviewed. Lipid peroxidation leads to degradation of the lipid membrane, interaction of degradation products with intra- and extracellular targets and to the production of new reactive oxygen species during the course of the chain reaction thus leading to damage of cells and tissues. According to our current view lipid peroxidation is implicated in the pathogenesis of cancer, inflammatory processes, atherosclerosis, toxic injury by xenobiotics and ischemic-reperfusion damage.

Lung mitochondrial function following oxygen exposure and diethyl maleate-induced depletion of glutathione

Diethyl maleate (DEM) pretreatment has previously been shown to result in a transient depletion of lung glutathione and an associated decrease of the time to the onset of rat mortality resulting from exposures to 100% oxygen in vivo. The effects of oxygen exposure on mitochondrial energy metabolism were assessed by measurements of ADP-stimulated rates of O2 utilization by lung homogenates prepared from untreated and DEM-treated rats following 4 and 24 hr of exposure to either air or 100% oxygen. Twenty-four hours of oxygen exposure of untreated rats resulted in significant decreases in lung homogenate ADP-stimulated rates of respiration supported by the substrates, pyruvate, isocitrate, and alpha-ketoglutarate. No changes were observed in succinate-supported respiration, indicating that oxygen exposure appears to adversely affect NAD-linked rather than FAD-linked pathways of mitochondrial energy metabolism. The decreased lung mitochondrial glutathione, observed 4 hr following DEM treatment, returned to normal levels following 24 hr of air and oxygen exposure. No effects of glutathione depletion were observed on ADP-stimulated rates of respiratory activity 4 hr following DEM treatment. The DEM-induced transient depletion of glutathione also did not result in any additional detrimental effects on mitochondrial respiratory activity following 24 hr of oxygen exposure in vivo. These results suggested that transient mitochondrial depletion of glutathione does not accelerate the oxygen-induced impairment of mitochondrial energy metabolism. The onset of mortality associated with DEM-pretreatment might therefore result from a failure of glutathione-dependent cytosolic protective mechanisms, rather than from an increased rate of oxygen-induced mitochondrial damage.

Cyclosporin A protects hepatocytes subjected to high Ca2+ and oxidative stress

Hepatocytes incubated with 0.8 mM t-butylhydroperoxide are protected by cyclosporin A when the medium Ca2+ concentration is 10 mM, but not when it is 2.5 mM. The highest Ca2+ level is associated with an inhibition of t-butylhydroperoxide-dependent malondialdehyde accumulation and with mitochondrial Ca2+ loading within the cells. These findings are new evidence that t-butylhydroperoxide can kill cells by peroxidation-dependent and -independent mechanisms, and suggest that the mitochondrial permeability transition and the resultant de-energization are components of the peroxidation-independent mechanism. Cyclosporin A may have considerable utility for the protection of cells subjected to oxidative stress.

Ruthenium red delays the onset of cell death during oxidative stress of rat hepatocytes

Our objective was to determine if ruthenium red protects against lethal oxidative injury of rat hepatocytes. tert-Butyl hydroperoxide, 100 mumol/L, was used to produce oxidative stress. After 2 hours of oxidative stress, cell viability was greater with than without 25 mumol/L ruthenium red (37% vs. 4.6%; P less than 0.01). Despite this cytoprotection, ruthenium red did not alter the rate or extent of glutathione depletion, malondialdehyde generation, or adenosine triphosphate depletion. In contrast, ruthenium red did retard loss of the mitochondrial membrane potential (78% vs. 42% within 30 minutes; P less than 0.01). However, the protective effect of ruthenium red could not solely be explained by preserving the mitochondrial membrane potential. Indeed, ruthenium red still improved cell survival after 2 hours of exposure to 10 mumol/L carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler (39% vs. 13%; P less than 0.01). Cytosolic free calcium values did not change during the uncoupling of mitochondria, suggesting that the cytoprotective properties of ruthenium red cannot be explained by blocking mitochondrial calcium transport. Ruthenium red did inhibit proteolysis after 2 hours of exposure to tert-butyl hydroperoxide (434 +/- 62 vs. 242 +/- 20 nmol/10(6) cells; P = 0.016) or CCCP (236 +/- 50 vs. 99 +/- 38 nmol/10(6) cells; P = 0.04). The results indicate that ruthenium red appears to protect against hepatocellular injury by inhibiting degradative proteolytic activity. It is concluded that proteolysis may be an important mechanism contributing to lethal oxidative injury of hepatocytes.

Techniques for pharmacological and toxicological studies with isolated hepatocyte suspensions

Since its introduction in 1969, the high-yield preparation of isolated hepatocytes has become a frequently used tool for the study of hepatic uptake, excretion, metabolism and toxicity of drugs and other xenobiotics. Basic preparative methods are now firmly established involving perfusion of the liver with a balanced-saline solution containing collagenase. Satisfactory procedures are available for determining cell yields, for expressing cellular activities and for establishing optimal incubation conditions. Gross cellular damage can be detected by means of trypan blue or by measuring enzyme leakage, and damaged cells can be removed from the preparation. Specialized techniques are available for preparing hepatocyte couplets and suspensions enriched with periportal or perivenous hepatocytes. The isolated hepatocyte preparation is particularly convenient for the study of the kinetics of hepatic drug uptake and excretion because the cells can be rapidly separated from the incubation medium. Isolated liver cells have also proved valuable for investigating drug metabolism since they show many of the features of the intact liver. However, they also show important differences such as losses of membrane specialization, some degree of cell polarity and the capacity to form bile. The many consequences of the hepatic toxicity of xenobiotics including lipid peroxidation, free radical formation, glutathione depletion, and covalent binding to macromolecules are also readily studied with the isolated liver cell preparation. A particular advantage is the ease with which morphological changes as a result of drug exposure can be observed in isolated hepatocytes. However, it must be remembered that the isolation procedure inevitably introduces changes that may make the cells more susceptible than the normal liver to damage by xenobiotic agents. Despite its limitations, the isolated hepatocyte preparation is now firmly established in the armamentarium of the investigator examining the interaction of the liver with xenobiotics.

Transient induction of the mitochondrial permeability transition by uncoupler plus a Ca(2+)-specific chelator

Determinations of aqueous space volumes, swelling and Mg2+ release experiments demonstrate that EGTA plus uncoupler causes the permeability transition in Ca(2+)-loaded mitochondria. Extramitochondrial Mg2+ is required to obtain this effect. Changes in transition-dependent parameters are smaller and more varied when induced by EGTA plus uncoupler than when induced by Ruthenium red plus uncoupler, although inhibitor-sensitive experiments show that the same basic mechanism is involved in both cases. Measurements of sucrose trapping and sucrose or inulin accessible space, after changes in transition-dependent parameters are complete, indicate that rapid reversal occurs when the transition is induced by EGTA plus uncoupler, explaining why limited responses are obtained. Data support the hypothesis that an external divalent cation binding site regulates activity of the mitochondrial Ca2+ uniporter.

Cytosolic Ca2+ deregulation and blebbing after HgCl2 injury to cultured rabbit proximal tubule cells as determined by digital imaging microscopy

Acute injury to renal proximal tubule cells has previously been shown to result in elevated cytosolic Ca2+ ([Ca2+]i), blebbing, and eventual cell death. In this study, digital imaging fluorescence microscopy was used to evaluate these changes in response to HgCl2 treatment of cultured rabbit proximal tubular cells. Monolayer cells loaded with fura-2 were treated with 10, 50, or 100 microM HgCl2 in both 1.37 mM CaCl2-containing and nominally Ca(2+)-free (less than 5 microM) Hanks' balanced salt solution. [Ca2+]i was estimated by measuring the ratio of fluorescent image pairs (collected at 340- and 380-nm excitation), morphological changes were observed by phase-contrast microscopy, and viability was assessed by trypan blue exclusion. After exposure of cells to 10 microM HgCl2, [Ca2+]i initially increased about 2-fold by 5 min; after 50 or 100 microM HgCl2, [Ca2+]i rapidly rose 2- to 3-fold, peaked at 1-3 min, and then generally decreased slightly. In nominally Ca(2+)-free (less than 5 microM) medium, [Ca2+]i stabilized, but in 1.37 mM Ca(2+)-containing medium, [Ca2+]i continued to slowly rise, often reaching levels of fura-2 saturation. The rate and extent of blebbing and the rate of cell death were increased in the presence of 1.37 mM Ca2+. These results show that sustained elevations of [Ca2+]i precede both cell blebbing and cell death and that when these elevations are limited by removing extracellular Ca2+ the amount of blebbing is reduced and cell viability is prolonged.