An electron microscopic study of apoptosis induced by cycloheximide in rat liver

Protective Effect of Curcumin against Doxazosin- and Carvedilol-Induced Oxidative Stress in HepG2 Cells

Doxazosin and carvedilol have been evaluated as an alternative treatment against chronic liver lesions and for their possible role during the regeneration of damage caused by liver fibrosis in a hamster model. However, these drugs have been reported to induce morphological changes in hepatocytes, affecting the recovery of liver parenchyma. The effects of these α/𝛽 adrenoblockers on the viability of hepatocytes are unknown. Herein, we demonstrate the protective effect of curcumin against the possible side effects of doxazosin and carvedilol, drugs with proven antifibrotic activity. After pretreatment with 1 μM curcumin for 1 h, HepG2 cells were exposed to 0.1–25 μM doxazosin or carvedilol for 24, 48, and 72 h. Cell viability was assessed using the MTT assay and SYTOX green staining. Morphological changes were detected using the hematoxylin and eosin (H&E) staining and scanning electron microscopy (SEM). An expression of apoptotic and oxidative stress markers was analyzed using reverse transcription-quantitative PCR (RT-qPCR). The results indicate that doxazosin decreases cell viability in a time- and dose-dependent manner, whereas carvedilol increases cell proliferation; however, curcumin increases or maintains cell viability. SEM and H&E staining provided evidence that doxazosin and carvedilol induced morphological changes in HepG2 cells, and curcumin protected against these effects, maintaining the morphology in 90% of treated cells. Furthermore, curcumin positively regulated the expression of Nrf2, HO-1, and SOD1 mRNAs in cells treated with 0.1 and 0.5 μM doxazosin. Moreover, the Bcl-2/Bax ratio was higher in cells that were treated with curcumin before doxazosin or carvedilol. The present study demonstrates that curcumin controls doxazosin- and carvedilol-induced cytotoxicity and morphological changes in HepG2 cells possibly by overexpression of Nrf2.

Visualization of acute liver damage induced by cycloheximide in rats using PET with [(18)F]FEDAC, a radiotracer for translocator protein (18 kDa)

Liver damage induced by drug toxicity is an important concern for both medical doctors and patients. The aim of this study was to noninvasively visualize acute liver damage using positron emission tomography (PET) with N-benzyl-N-methyl-2-[7,8-dihydro-7-(2-[¹⁸F]fluoroethyl)-8-oxo-2-phenyl-9H-purin-9-yl]acetamide ([¹⁸F]FEDAC), a radiotracer specific for translocator protein (18 kDa, TSPO) as a biomarker for inflammation, and to determine cellular sources enriching TSPO expression in the liver. A mild acute liver damage model was prepared by a single intraperitoneal injection of cycloheximide (CHX) into rats. Treatment with CHX induced apoptosis and necrotic changes in hepatocytes with slight neutrophil infiltration. The uptake of radioactivity in the rat livers was measured with PET after injection of [¹⁸F]FEDAC. The uptake of [¹⁸F]FEDAC increased in livers damaged from treatment with CHX compared to the controls. Presence of TSPO was examined in the liver tissue using quantitative reverse transcriptase-polymerase chain reaction and immunohistochemical assays. mRNA expression of TSPO was elevated in the damaged livers compared to the controls, and the level was correlated with the [¹⁸F]FEDAC uptake and severity of damage. TSPO expression in the damaged liver sections was mainly found in macrophages (Kupffer cells) and neutrophils, but not in hepatocytes. The elevation of TSPO mRNA expression was derived from the increase of the number of macrophages with TSPO and neutrophils with TSPO in damaged livers. From this study we considered that PET imaging with [¹⁸F]FEDAC represented the mild liver damage through the enhanced TSPO signal in inflammatory cells. We conclude that this method may be a useful tool for diagnosis in early stage of acute liver damage.

Comparison of radiolabeled isatin analogs for imaging apoptosis with positron emission tomography

INTRODUCTION

Caspase-3 is one of the executioner caspases activated as a result of apoptosis. Radiolabeled isatins bind to caspase-3 with high affinity and are potential tracers for use with positron emission tomography to image apoptosis. We compared the ability of two novel radiolabeled isatins, [18F]WC-IV-3 and [11C]WC-98, to detect caspase-3 activation in a rat model of cycloheximide-induced liver injury.

METHODS

Male Sprague-Dawley rats were treated with cycloheximide and then imaged with microPET 3 h later with [18F]WC-IV-3 and [11C]WC-98. Biodistribution studies were also performed simultaneously, with caspase-3 activation verified by fluorometric enzyme assay and Western blots.

RESULTS

MicroPET imaging studies demonstrated similar behavior of both tracers but with a lower maximum peak with [11C]WC-98 than with [18F]WC-IV-3. Biodistribution studies demonstrated increased uptake of both tracers in the liver and spleen, but this was statistically significant only in the liver with both compounds. The level of [18F]WC-IV-3 uptake appeared to correlate roughly with rates of caspase-3 activation by the enzyme assay, but the magnitude of difference between treated and control groups was lower than that observed in previously published data with [18F]WC-II-89, another radiolabeled isatin analog. Activation was also confirmed in the liver and spleen but not in fat by Western blot.

CONCLUSION

[18F]WC-IV-3 uptake appears to correlate with increased caspase-3 enzyme activity, but the dynamic range of uptake of these two tracers appears to be less than that seen with [18F]WC-II-89. Studies are ongoing to verify these results in other animal models of apoptosis.

Synthesis, radiolabeling, and in vivo evaluation of an 18F-labeled isatin analog for imaging caspase-3 activation in apoptosis

A non-peptide-based isatin sulfonamide analog, WC-II-89, was synthesized and its inhibition toward recombinant human caspase-3 and other caspases was determined. This compound showed high potency for inhibiting caspase-3 and -7, and high selectivity against caspases-1, -6, and -8. [(18)F]WC-II-89 was synthesized via a nucleophilic substitution of the corresponding mesylate precursor in high yield and radiochemical purity. Biodistribution studies using [(18)F]WC-II-89 revealed higher uptake in liver and spleen of cycloheximide-treated rats, an animal model of apoptosis, relative to control animals. Western blot analysis confirmed the presence of activated caspase-3 in the liver and spleen of cycloheximide-treated animals. MicroPET imaging studies revealed a high uptake of the radiotracer in the liver of a cycloheximide-treated rat relative to the untreated control. These data suggest that [(18)F]WC-II-89 is a potential radiotracer for imaging caspase-3 activation in tissues undergoing apoptosis.

Tangutorine induces p21 expression and abnormal mitosis in human colon cancer HT-29 cells

A novel beta-carboline alkaloid, tangutorine (benz[f]indolo[2,3-a]quinolizidine) was isolated from the leaves of Nitraria tangutorum L. [Duan JA, Williams ID, Che CT, Zhou RH, Zhao RH, Tangutorine: a novel beta-carboline alkaloid from Nitraria tangutorum. Tetrahedron Lett 1999;40:2593-6], and its unique structural characters led us to initiate a study of its potential anti-proliferation activity. The in vitro treatment with low doses of tangutorine slightly stimulated the proliferation of human colon cancer HT29 cells until at concentrations higher than 6.25 microg/ml when the cell numbers, cellular MTT reduction, and cell proliferation by 3H-thymidine incorporation decreased in a dose-dependent manner (IC50=15 microg/ml=48 microM). Morphological studies of cells by fluorescence and electron microscopy did not show features for apoptosis but only large vacuoles, swollen mitochondria and dense cytoskeletal filaments bunching in the cytoplasm. Immunoblotting analysis revealed a dramatic induction of cyclin kinase inhibitor p21 as well as an inhibition of topoisomerase II expression at 25 microg/ml tangutorine, thereby impeding cell progression from S to G2/M phase. Cells accumulated at G1 phase of the cell cycle at concentrations > or =50 microg/ml tangutorine. Interestingly, some cells escaped from prolonged growth arrest without cell division and resulted in binucleated and polyploid G1 cells. Taken all results together, tangutorine induced a p21 suppression of all cyclins and their associated kinases, such as the topoisomerase II, and thus inhibited normal DNA replication and mitosis.

Kupffer cell-derived interleukin 10 is responsible for impaired bacterial clearance in bile duct-ligated mice

Extrahepatic cholestasis often evokes liver injury with hepatocyte apoptosis, aberrant cytokine production, and-most importantly-postoperative septic complications. To clarify the involvement of aberrant cytokine production and hepatocyte apoptosis in impaired resistance to bacterial infection in obstructive cholestasis, C57BL/6 mice or Fas-mutated lpr mice were inoculated intraperitoneally with 10(7) colony-forming units of Escherichia coli 5 days after bile duct ligation (BDL) or sham celiotomy. Cytokine levels in sera, liver, and immune cells were assessed via enzyme-linked immunosorbent assay or real-time reverse-transcriptase polymerase chain reaction. BDL mice showed delayed clearance of E. coli in peritoneal cavity, liver, and spleen. Significantly higher levels of serum interleukin (IL) 10 with lower levels of IL-12p40 were observed in BDL mice following E. coli infection. Interferon gamma production from liver lymphocytes in BDL mice was not increased after E. coli infection either at the transcriptional or protein level. Kupffer cells from BDL mice produced low levels of IL-12p40 and high levels of IL-10 in vitro in response to lipopolysaccharide derived from E. coli. In vivo administration of anti-IL-10 monoclonal antibody ameliorated the course of E. coli infection in BDL mice. Furthermore, BDL-lpr mice did not exhibit impairment in E. coli killing in association with little hepatic injury and a small amount of IL-10 production. In conclusion, increased IL-10 and reciprocally suppressed IL-12 production by Kupffer cells are responsible for deteriorated resistance to bacterial infection in BDL mice. Fas-mediated hepatocyte apoptosis in cholestasis may be involved in the predominant IL-10 production by Kupffer cells.

Caspase activity in newt spermatogonial apoptosis induced by prolactin and cycloheximide

We previously showed in vivo and in vitro, that among the spermatogenic stages of the newt, prolactin (PRL) induces apoptosis specifically in the penultimate stage of secondary spermatogonia. In the current report, we demonstrate in vitro that cycloheximide (CHX), an inhibitor of protein synthesis, induces morphological apoptotic changes similar to those caused by PRL, such as chromatin condensation and apoptotic body formation. Next, we found that Z-VAD-fmk, an inhibitor of various caspases, suppressed the apoptosis induced by PRL and CHX, but ICE inhibitor Ac-YVAD-CHO or caspase-3 inhibitor Ac-DEVD-CHO did not. As high caspase activity was present in extracts of testes treated with CHX, we suggest that an unidentified caspase induces the morphological changes of apoptosis in newt spermatogonia.

Complement binding is an early feature of necrotic and a rather late event during apoptotic cell death

The phagocytosis of dying cells is an integral feature of apoptosis and necrosis. There are many receptors involved in recognition of dying cells, however, the molecular mechanisms of the scavenging process remain elusive. The activation by necrotic cells of complement is well established, however, the importance of complement in the scavenging process of apoptotic cells was just recently described. Here we report that the complement components C3 and C4 immediately bound to necrotic cells. The binding of complement was much higher for lymphocytes compared to granulocytes. In case of apoptotic cell death complement binding was a rather late event, which in lymphocytes was preceded by secondary necrosis. Taken together complement binding is an immediate early feature of necrosis and a rather late event during apoptotic cell death. We conclude that complement may serve as an opsonin for fragments of apoptotic cells that have escaped regular scavenging mechanisms.

Intravenous injection of cycloheximide induces apoptosis and up-regulates p53 and Fas receptor expression in the rat liver in vivo

A single administration of protein synthesis inhibitor, cycloheximide (CHX) induces apoptosis of hepatocytes in vivo. We investigated the underlying mechanisms of this phenomenon and the role of p53 and Fas receptor using terminal dUTP nick end labeling (TUNEL), quantitative reverse transcription polymerase chain reaction and immunohistochemistry. Rat liver tissue specimens were obtained at different time intervals after injection of CHX. The proportion of TUNEL-positive apoptotic hepatocytes increased with time and reached a plateau at 2.5h after the injection. The p53 and Fas receptor mRNAs and the proportion of immunoreactive p53-positive and Fas receptor-positive hepatocytes increased markedly with time from 1h after the administration. Since the time course of increased proportion of apoptotic hepatocytes does not parallel that of p53- or Fas receptor-positive hepatocytes and apoptotic hepatocytes appeared prior to up-regulation of p53 and Fas receptor expression, it is likely that the enhanced expression of p53 and Fas receptor is not involved directly in CHX-induced apoptosis of hepatocytes in vivo. Rats injected with a single intravenous dose of CHX, however, provide a simple and useful model for investigating the apoptotic machinery and the molecular mechanism of transcriptional up-regulation of p53 and Fas receptor in hepatocytes.

Prevention of cycloheximide-induced apoptosis in hepatocytes by adenosine and by caspase inhibitors

The mechanism by which cycloheximide induces apoptosis in isolated rat hepatocytes was studied. Cycloheximide (1-300 microM) induced apoptosis within 3-4 hr in the hepatocytes. Specific apoptotic characteristics such as blebbing, phosphatidyl serine (PS) exposure, chromatin condensation, and nuclear fragmentation were induced. Cycloheximide (CHX) dose dependently activated the caspase-3-like proteases, but not the caspase-1-like proteases. Pretreatment of the hepatocytes with 100 microM of the caspase inhibitors z-Val-Ala-DL-Asp-fluoromethylketone or Ac-Asp-Glu-Val-Asp-aldehyde completely abrogated the caspase activation and the apoptosis. Addition of adenosine (100 microM) reduced phosphatidyl serine exposure and other morphological characteristics of apoptosis by 50%; however, it did not prevent the activation of the caspases, suggesting that adenosine inhibited downstream of caspase activation. The adenosine receptor antagonist 8-[4-[[[[(2-aminoethyl)amino]-carbonyl]methyl]oxy]phenyl]-1,3-dipropylxa nthine abolished the capacity of adenosine to prevent apoptosis, indicating that prevention was receptor-mediated. During apoptosis, the mitochondrial membrane potential in apoptotic cells (cells with PS exposition) was decreased to 50-60% of the control value; in the population viable cells, however, the mitochondrial membrane potential remained stable. Prevention of apoptosis by the caspase inhibitor z-Val-Ala-DL-Asp-fluoromethylketone or adenosine prevented the decrease in mitochondrial membrane potential. In conclusion, CHX rapidly induces apoptosis in isolated rat hepatocytes, which is inhibited by adenosine at a relatively late step.

Fasting-induced apoptosis in rat liver is blocked by cycloheximide

The effect of cycloheximide (CH) on the fasting-induced changes of rat liver cell and protein turnover has been investigated. Late starvation phase (3-4-day-fasting period) was characterised by a decrease in liver weight and protein and DNA content. The loss of DNA was not related to liver cell necrosis but due not only to depression of cell proliferation as shown by the drop in the labelling index but also induction of apoptosis. This type of apoptosis was documented by the increase in the apoptotic index (cells labelled by TUNEL) and transglutaminase activity as well as by DNA fragmentation. The liver cells of fasted rats appeared smaller as shown by the higher cell density and DNA/protein ratio than in controls. Females were more resistant to fasting-induced apoptosis than males. A single dose of CH, a drug primary known as inhibitor of protein synthesis, induced or enhanced apoptosis in fed and 2-days fasted male rats, respectively, without any sign of cell necrosis. On the contrary, the administration of repeated doses of CH blocked apoptosis induced by fasting. CH "froze" protein and DNA content as well as apoptotic process at the level of 2 days-fasted rats. While fasting-induced liver protein loss resulted from a marked reduction in protein synthesis with a slight decrease in degradation, repeated treatment with CH virtually blocked protein loss by abolishing protein catabolism. These data suggest a direct relationship between the catabolic side of protein turnover and the apoptotic process.

Cyclosporin A protects Balb/c mice from liver damage induced by superan tigen SEB and D-GalN

AIM: To investigate the pathogenic effect of SEB and D-GalN on liver and the protection of cyclosporin A, the relationship between hepatic apoptosis and necrosis and the possible mechanism of acute hepatic necrosis.

METHODS: After staphylococcal enterotoxin B (SEB) mixed with D-galactosamine (D-GalN) were injected intraperitoneally into Balb/c mice and those previously treated with cyclosporin A, blood samples were collected and livers were isolated at 2, 6, 12, 24h. Patterns of hepatocellular death were studied morphologically and biochemically, circulating cytokines (TNF-α, IFN-γ) and mice mortality within 24h was assessed.

RESULTS: The SEB could induce the typical apoptotic changes of hepatocytes, the D-GalN could induce hepatocytes apoptosis and degeneration at the same time, and the mice having received the SEB + D-GalN injections developed apoptosis at 2 and 6h, but after 12h hepatocytes were characterized by severe injury, whereas all the examinations in the cyclosporin A treated mice were normal.

CONCLUSION: Hepatic cell apoptosis might be related to necrosis, and massive hepatocyte apoptosis is likely the initiating step of acute hepatic necrosis in mice. The effects induced by SEB and D-GalN on hepatocytes might be mediated by T cells, and could be prevented by cyclosporin A.

Novel formula for cell kinetics in xenograft model of hepatocellular carcinoma using histologically calculable parameters

The growth rate of tumors should be assessed in terms of both tumor cell proliferation and death. The former is considered to be determined by growth fraction and cell-cycle time, whereas the latter is mainly determined by apoptosis, especially in tumors with a low level of necrosis. While most hepatocellular carcinomas (HCCs) in a relatively early stage contain only a small amount of necrosis, the growth rate supposedly depends mainly on growth fraction, cell-cycle time, and apoptosis. However, their quantitative relationship remains unknown. We have derived a novel theoretical formula for determining this relationship in nonnecrotic HCC, using Ki-67-positive index, apoptotic score, and a correction factor, all calculable by histological assessment without injecting labeling agents. Furthermore, we confirmed the reliability of this formula, using a xenograft model of human HCC with less than 15% necrosis. In this model the values of cell-cycle time calculated from the formula were very close to those estimated by a conventional double-labeling method and showed high correlations. Since our novel formula can clarify the cell kinetics without cumbersome labeling procedures, it is expected to be clinically applicable to HCC with a small portion of necrosis, using the radiographically measured growth rate and the histologically assessed cell kinetic parameters.

The mechanism of thioacetamide-induced apoptosis in the L37 albumin-SV40 T-antigen transgenic rat hepatocyte-derived cell line occurs without DNA fragmentation

The hepatotoxicant thioacetamide (TH) has classically been used as a model to study hepatic necrosis; however, recent studies have shown that TH can also induce apoptosis. In this report we demonstrate that 2.68+/-0.54% of the albumin-SV40 T-antigen transgenic rat hepatocytes undergo TH-induced apoptosis, a level comparable to other in vivo models of liver apoptosis. In addition, TH could induce apoptosis and necrosis in the L37 albumin-SV40 T-antigen transgenic rat liver-derived cell line. Examination of dying L37 cells treated with 100 mM TH by electron microscopy revealed distinct morphological characteristics that could be attributed to apoptosis. Quantitation of apoptosis by FACS analysis 24 h after treatment with 100 mM TH revealed that 81.3+/-1.6% of the cells were undergoing apoptosis. In contrast, when L37 cells were treated with 250 mM TH, cells exhibited characteristics consistent with necrotic cell death. DNA fragmentation ladders were produced by growth factor withdrawal-induced apoptosis; however, in 100 mM TH-induced apoptosis, DNA fragmentation ladders were not observed. Analysis of endonuclease activity in L37 cells revealed that the enzymes were not inactivated in the presence of 100 mM TH. The data presented in this report indicate that the L37 cell line could be used to study the mechanism of TH-induced apoptosis that was not mediated through a mechanism requiring DNA fragmentation.

Hepatic sinusoidal endothelium heterogeneity with respect to the recognition of apoptotic cells

The recognition and removal of human apoptotic peripheral lymphocytes in selected populations of periportal and perivenous endothelial cells was studied in in situ and in vitro experiments. Apoptotic peripheral blood lymphocytes once injected into the liver circulation were retained by the sinusoids showing a large heterogeneity of distribution: apoptotic cells are found in the periportal tract double the amount found in the perivenous region. Apoptotic PBL adhesion was lowered to a sixth of the control after preinjection with a sugar mixture (Mannose, N-acetylgalactosamine, N-acetylglucosamine, D-galactose), as suggested by the expression of modified surface glycoconjugates on the plasma membrane of apoptotic cells. A bimodal profile of the distribution of the hepatic sinusoidal cell population, regarding the number of galactose and mannose receptors and the porosity index, was found. Two endothelial cell subsets were present: low porosity cells (average index 14 +/- 6%; periportal tract) with a high number of carbohydrate binding sites, and high porosity cells (average index 26 +/- 7%; perivenous tract), with a low number of carbohydrate binding sites.

Liver apoptosis

Apoptosis, also called programmed cell death, is a peculiar form of cell death different from cell necrosis in many morphological and biochemical aspects. Like mitosis or differentiation, apoptosis is a normal cell phenomenon which depends on the expression of genes capable of inducing or inhibiting this type of cell destruction. But apoptosis can also be triggered by many external factors and has been described in many diseases. The very different conditions where programmed cell death occurs suggest that the mechanisms leading to the activation of apoptosis-controlling genes are variable. As in other cells, apoptosis occurs in the liver cells, first in the normal state during liver development and then in the adult liver, respectively for liver organogenesis and the renewal of hepatocytes. But apoptosis is also present in various viral, immunological, malignant or drug-induced human liver diseases. In addition, in the animal, hepatocyte apoptosis can be triggered either in vivo or in vitro by many toxic agents. In contrast to other cells, the mechanisms leading to liver cell apoptosis remain poorly investigated. However, two proteins could play an important role in this field, the fas/apo-1 protein present at the surface of hepatocytes and the bcl-2 protein localized in biliary cells. Analysis of the genes controlling the expression of these two proteins could provide essential information on the mechanisms of liver apoptosis.