Repair of radiation damage in noncycling parenchymal hepatocytes

Reevaluation of CBE value of BPA for hepatocytes

The compound biological effectiveness (CBE) value of boronophenylalanine (BPA) for hepatocytes was experimentally determined for the purpose of boron neutron capture therapy (BNCT) for liver tumors. In this study, the critical reevaluation of previous value was performed. In previous experimental studies, the contribution of β component of dose was ignored in the response curve to X-ray. X-ray dose cell survival curves were estimated by combining the α/β values obtained in the ordinary micronucleus (MN) assay with the curve of MN-negative cell fraction (MN(-)F) to dose. This curve was compared to the boron neutron capture reaction (BNCR) dose curve. As a result, the CBE value was 4 at doses close to 0 Gy, decreasing to about 1.0 at doses close to 4.5 Gy. The new value is smaller than the previous value 4.2. This indicates that the bioequivalent dose to normal liver is lower than previously expected. Therefore, higher doses can be given to the tumor.

Irradiation leads to sensitization of hepatocytes to TNF-alpha-mediated apoptosis by upregulation of IkappaB expression

This study aimed to reveal the pathophysiological signalling responsible for radiation-induced sensitization of hepatocytes to TNF-alpha-mediated apoptosis. IkappaB was upregulated in irradiated hepatocytes. Administration of IkappaB antisense oligonucleotides prior to irradiation inhibited occurrence of apoptosis after TNF-alpha administration. Caspases-8, -9 and -3 activities were increased in irradiated hepatocytes and downregulation of apoptosis by IkappaB antisense oligonucleotides was mediated by suppression of caspases-9 and -3 activation but not of caspase-8 activation, suggesting that radiation-induced sensitization of hepatocytes to TNF-alpha-mediated apoptosis additionally requires changes upstream of caspase-8 activation. Herein, upregulation of FLIP may play a crucial role. Cleavage of bid, upregulation of bax, downregulation of bcl-2 and release of cytochrome c after TNF-alpha-administration depend on radiation-induced upregulation of IkappaB, thus demonstrating an apoptosis permitting effect of IkappaB.

Irradiation leads to apoptosis of Kupffer cells by a Hsp27-dependant pathway followed by release of TNF-alpha

In a previous publication, we were able to show that irradiation of Kupffer cells, the liver resident macrophages, leads to an increased TNF-alpha concentration in the culture medium. The pathomechanisms underlying this phenomenon, however, remained to be elucidated. Here, we show that following irradiation of Kupffer cells, the apoptosis rate increased drastically within 48 h. At the same time, the total TNF-alpha concentration in cell lysates of Kupffer cells attached to the culture plate decreased. However, normalization of the TNF-alpha concentration with respect to cell number revealed that TNF-alpha concentration per attached cell remained constant during the observation period. Western blot analysis showed that heat shock protein 27 (Hsp27) is strongly downregulated and bax is upregulated in irradiated Kupffer cells as compared to sham-irradiated cells. Overexpression of Hsp27 in Kupffer cells was shown to prevent the effect of irradiation on bax expression, apoptosis and, at the same time, on increase of TNF-alpha concentration in the Kupffer cell medium. We conclude that irradiation of Kupffer cells leads to apoptosis because of downregulation of Hsp27 and consecutive upregulation of bax expression. Furthermore, we suggest that apoptosis of Kupffer cells leads to an increase of TNF-alpha concentration in the culture medium which may be due to cell death rather than active release or synthesis.

Effect of radiation on gene expression of rat liver chemokines: in vivo and in vitro studies

The aim of the study was to analyze the effect of a single irradiation on chemokine gene expression in the rat liver and in isolated rat hepatocytes. RNA extracted from livers and from hepatocytes within the first 48 h after irradiation was analyzed by real-time PCR and the Northern blot assay. The chemokine concentrations in the serum of irradiated rats were measured quantitatively by ELISA. A significant radiation-induced increase of CINC1, IP10, MCP1, MIP3alpha, MIP3beta, MIG and ITAC gene expression could be detected at the RNA level in the liver. CINC1, MCP1 and IP10 serum levels were significantly increased. In rat hepatocytes in vitro, only MIP3alpha showed a radiation-induced increase in expression, while CINC1, IP10, MIP3beta, MIG, MIP1alpha, ITAC and SDF1 RNA levels were significantly down-regulated. However, incubation of irradiated hepatocytes in vitro with either TNF-alpha, IL1beta, or IL6 plus TNF-alpha led to up-regulation of MCP1, IP10 and MCP1 or CINC1 and MIP3beta, respectively. Irradiation of the liver induces up-regulation of the genes of the main proinflammatory chemokines, probably through the action of locally synthesized proinflammatory cytokines. The reason for the lack of liver inflammation in this model has still to be clarified.

x-Irradiation in Rat Liver: Consequent Upregulation of Hepcidin and Downregulation of Hemojuvelin and Ferroportin-1 Gene Expression

PURPOSE

To prospectively analyze hepcidin, hemojuvelin, and ferroportin-1 expression after x-irradiation of rat liver and isolated rat hepatocytes.

MATERIALS AND METHODS

The treatment of the rats and this study were approved by the local committee and the public authority on animal welfare. Rat livers in vivo and isolated rat hepatocytes in vitro were irradiated. The total number of rats in this study was 43. RNA extracted from livers (1, 3, 6, 12, 24, and 48 hours after irradiation) and from hepatocytes (1, 3, 6, 12, and 24 hours after irradiation) was analyzed with real-time polymerase chain reaction and Northern blot. Cytokines and prohepcidin in serum of irradiated rats were quantitatively detected with enzyme-linked immunosorbent assay. Sham-irradiated animals served as controls in all experiments. Differences between sham-irradiated and irradiated data groups were tested with analysis of variance and Dunnett post hoc test.

RESULTS

In vivo, a significant radiation-induced increase of hepcidin (P=.034), interleukin (IL) 1beta (P=.008), IL-6 (P<.011), and tumor necrosis factor alpha (TNF-alpha) (P=.047) expression could be detected within the first 48 hours after irradiation. Expression of hemojuvelin (P=.008) and ferroportin-1 (P=.002) was significantly decreased. Serum iron levels were decreased because of irradiation (P<.058); prohepcidin serum levels were increased (P=.05). In rat hepatocytes in vitro, hepcidin RNA levels were significantly downregulated after irradiation (P<.001). Incubation of irradiated hepatocytes with IL-1beta, IL-6, or TNF-alpha led to upregulation of hepcidin expression in vitro up to 6 hours after irradiation, with subsequent significant downregulation for incubation with IL-1beta (P<.001). Hemojuvelin expression behaved in a way opposite to that of hepcidin.

CONCLUSION

x-Irradiation of the liver induced changes of hepcidin gene expression that are probably induced by acute phase mediators produced within the liver itself.

Identification of genes responsive to gamma radiation in rat hepatocytes and rat liver by cDNA array gene expression analysis

The mechanisms underlying hepatocellular damage after irradiation are obscure. We identified genes induced by radiation in isolated rat hepatocytes in vitro by cDNA array gene expression analysis and then screened in vivo experiments with those same genes using real-time PCR and Western blotting. Hepatocytes were irradiated and cDNA array analyses were performed 6 h after irradiation. The mRNA of differentially expressed genes was quantitatively analyzed by real-time PCR. cDNA array analyses showed an up-regulation of 10 genes in hepatocytes 6 h after irradiation; this was confirmed by real-time PCR. In vivo, rat livers were irradiated selectively. Treated and sham-irradiated controls were killed humanely 1, 3, 6, 12, 24 and 48 h after irradiation. Liver RNA was analyzed by real-time PCR; expression of in vivo altered genes was also analyzed at the protein level by Western blotting. Up-regulation was confirmed for three of the in vitro altered genes (multidrug resistance protein, proteasome component C3, eukaryotic translation initiation factor 2). Histologically, livers from irradiated animals were characterized by steatosis of hepatocytes. Thus we identified genes that may be involved in liver steatosis after irradiation. The methods shown in this work should help to further clarify the consequences of radiation exposure in the liver.

Irradiation leads to susceptibility of hepatocytes to TNF-alpha mediated apoptosis

BACKGROUND AND PURPOSE

The pathogenesis of radiation-induced-liver-disease (RILD) is still unknown. We tested the hypothesis that irradiated liver macrophages influence the viability of radiation stressed hepatocytes.

PATIENTS AND METHODS

Hepatocytes and liver macrophages were isolated from rat liver, cultured and irradiated with doses of 2, 8, and 25 Gy. Cell viability was measured by trypan blue exclusion, and by annexin V/propidium iodide staining. TNF-alpha in the supernatants from liver macrophage cell culture was quantitatively detected by ELISA. TNF-alpha mRNA from liver macrophages was measured by real time PCR.

RESULTS

Irradiation had no influence on cell viability. Apoptosis of irradiated hepatocytes was detected 24h after replacing 50% of medium with supernatants of irradiated liver macrophages 6 h after irradiation (32.0+/-5.8% compared to solely irradiated cells (12+/-2.9%, P=0.02)). In supernatants of hepatocytes, no TNF-alpha secretion could be measured. A radiation dependent increase was found in supernatants of liver macrophages. Addition of anti-TNF-alpha-antibodies to the supernatants of irradiated liver macrophages reduced apoptosis (20+/-0.9%). Incubation of irradiated hepatocytes with purified recombinant TNF-alpha increased apoptosis in irradiated hepatocytes. This effect could be abrogated by additional administration of TNF-alpha-antibodies.

CONCLUSIONS

Irradiation leads to susceptibility of hepatocytes to TNF-alpha mediated apoptosis. Liver macrophages may be one of the sources of TNF-alpha in case of liver-irradiation. This cell-cell-interaction may be an important initial step towards RILD and liver fibrosis.

Cyclophosphamide metabolism, liver toxicity, and mortality following hematopoietic stem cell transplantation

Liver toxicity caused by high-dose myeloablative therapy leads to significant morbidity after hematopoietic cell transplantation. We examined the hypothesis that liver toxicity after cyclophosphamide and total body irradiation is related to cyclophosphamide through its metabolism to toxins. Cyclophosphamide was infused at 60 mg/kg over 1 to 2 hours on each of 2 consecutive days, followed by total body irradiation. Plasma was analyzed for cyclophosphamide and its major metabolites. Liver toxicity was scored by the development of sinusoidal obstruction syndrome (veno-occlusive disease) and by total serum bilirubin levels. The hazards of liver toxicity, nonrelapse mortality, tumor relapse, and survival were calculated using regression analysis that included exposure to cyclophosphamide metabolites (as the area under the curve). Of 147 patients, 23 (16%) developed moderate or severe sinusoidal obstruction syndrome. The median peak serum bilirubin level through day 20 was 2.6 mg/dL (range, 0.5-41.1 mg/dL). Metabolism of cyclophosphamide was highly variable, particularly for the metabolite o-carboxyethyl-phosphoramide mustard, whose area under the curve varied 16-fold. Exposure to this metabolite was statistically significantly related to sinusoidal obstruction syndrome, bilirubin elevation, nonrelapse mortality, and survival, after adjusting for age and irradiation dose. Patients in the highest quartile of o-carboxyethyl-phosphoramide mustard exposure had a 5.9-fold higher risk for nonrelapse mortality than did patients in the lowest quartile. Engraftment and tumor relapse were not statistically significantly related to cyclophosphamide metabolite exposure. Increased exposure to toxic metabolites of cyclophosphamide leads to increased liver toxicity and nonrelapse mortality and lower overall survival after hematopoietic cell transplantation.

Drug and radiation resistance in spheroids: cell contact and kinetics

Cells from multicellular spheroids are often more resistant than monolayers to drugs and radiation. While explanations for resistance can be based on differences in cell cycle distribution, inability of the drug to penetrate the spheroid, or the presence of hypoxic cells, these mechanisms do not adequately explain resistance to all agents. Small spheroids (containing about 25-50 cells) exposed to ionizing radiation, hyperthermia, photodynamic therapy, or topoisomerase II inhibitors, are more resistant to killing than monolayers; the close three-dimensional contact in spheroids has been implicated in this resistance. Proposed mechanisms for the 'contact effect' include gap junctional 'reciprocity', cell shape mediated changes in (repair-related) gene expression, and alterations in chromatin packaging which influence DNA repair. The consequences of the contact effect are especially important for multifraction exposures. Another form of resistance can be demonstrated during repetitive treatments; 'regrowth resistance' reflects the capacity of spheroid cells to proliferate more efficiently to compensate for cell killing.

The lower radiosensitivity of mouse kidney cells irradiated in vivo than in vitro: a cell contact effect phenomenon

For mouse kidney cells assayed in primary culture, the Do and n values were 1.1 +/- 0.06 Gy and 7 +/- 2 for single cells irradiated in vitro, and 1.3 +/- 0.08 Gy and 25 +/- 11 for in vivo irradiation. The lower radiosensitivity in vivo was shown not to be caused by natural hypoxia, as the average oxygen enhancement ratios were 2.6 +/- 0.3 for in vitro and 2.8 +/- 0.4 for in vivo irradiation. Irradiations of fragments of kidney tubules produced similar survivals as irradiations of kidneys in situ, even for irradiation immediately before the fragments were disaggregated into single cells. The critical point of change in radiosensitivity from in vivo to in vitro values due to this contact effect was the time that the kidney cells were monodispersed.

Acute response of mouse kidney clonogens to fractionated irradiation in situ and then assayed in primary culture

Although the difference in sensitivity to the changes in dose fraction size between early-responding and late-responding tissues is well established, the underlying mechanisms in terms of target-cell responses are not yet clearly identified for any tissue. The radiosensitivity of mouse kidney cells after in situ single-dose, 2, 8, and 16 fraction X-irradiations was measured in primary culture using a clonogenic assay. The assay was made 12 h after single doses or 12 h after the last dose of the multifraction regimens. When analysed using the linear-quadratic model, as predicted the individual alpha components for all the different fractionation schedules were not significantly different, and the changes in the beta values were consistent with those expected on the basis of the reciprocal fraction numbers. When all four data sets were integrated to derive a common alpha/beta ratio, the result was 4.4 +/- 1.3 (1SE) Gy, or 2.8 +/- 0.9 Gy (a better fit) if the single-dose data set was excluded. These values fall into the range reported for kidney using assays of tissue function at long times after irradiation. Hence, it has been shown for the first time that the fractionation sensitivity of a late-responding organ is mimicked by that of a clonogenic cell population in that organ. The evidence also suggests that the time available prior to fixation of potentially lethal damage does not influence the low alpha/beta ratio observed for the kidney.

Radiation protection of rat parenchymal hepatocytes with S-2-(3-aminopropylamino)ethylphosphorothioic acid

The ability to protect parenchymal hepatocytes from ionizing radiation damage with S-2-(3-aminopropylamino)-ethylphosphorothioic acid (WR-2721) was investigated. The clonogenic survival of irradiated hepatocytes was determined with an in vivo transplantation assay system. Injection of WR-2721 (400 mg/kg) immediately after irradiation was without protective effect. In contrast, an intraperitoneal (IP) injection of WR-2721 30 min prior to 60Co irradiation resulted in a significant protection of parenchymal hepatocytes. The mean lethal dose (Do) and extrapolation number (n) of the survival curve for unprotected hepatocytes as 2.9 Gy and 1.8, respectively. The Do and n values for hepatocytes protected with WR-2721 were 5.7 Gy and 1.8, respectively. Thus, WR-2721 at a concentration of 400 mg/kg acted as a dose modifying agent with a dose modifying factor of approximately 2.0. Decreasing the concentration of WR-2721 to 200 mg/kg did not significantly reduce the radioprotective effectiveness of the drug. However, at concentrations less than 200 mg/kg, the radioprotective effect decreased in a dose-response manner with a concentration of 150 mg/kg providing 50% of the maximum effect observed.

Survival curves for normal-tissue clonogens: a comparison of assessments using in vitro, transplantation, or in situ techniques

A survey of survival curves in the literature, for clonogenic cells (clonogens) in normal tissues, highlights the following features: the sensitivity of some human and dog clonogens apparently is greater than that of their counterparts in mice and sheep, assessed in vitro. However, this should be interpreted with caution because of the possibility of cell selection and the ability to modify sensitivity markedly in some systems by variations in growth conditions; extrapolation numbers are in general higher when assessed in vivo than in vitro. This is due partly to the lack of measurements of repair of potentially-lethal damage using many assays in vitro. This feature increases the extrapolation number when measured using transplantation assays in vivo; epithelial clonogens in vivo demonstrate a remarkable similarity in sensitivity between tissues. The range is similar for clonogens assayed in situ or by transplantation, and this argues against the possibility that a resistant subpopulation may be selected in most assays in situ. It is emphasized from the comparisons that caution must be exercised in extrapolating results, obtained for clonogens assayed in vitro or by transplantation in vivo, to the situation in situ.

Survival of parenchymal hepatocytes irradiated with 14.3 MeV neutrons

The purpose of these experiments was to estimate the RBE of neutrons for parenchymal hepatocytes as a function of neutron dose and to determine the ability of liver cells to repair potentially lethal damage (PLD) after neutron exposure. Hepatocyte reproductive survival was used as the biological end point in these studies and hepatocyte survival was determined with an in vivo transplantation clonogenic assay system. The 14.3 MeV neutrons were generated by a D-T reaction at the University of Wisconsin's gas target neutron source. The average neutron dose rate was 20 cGy/min. The estimated survival data for neutron exposed hepatocytes were best described by a single hit-single target model (i.e., n = 1.0) with a D0 = 170 cGy. In contrast to the results obtained with 60Co, hepatocytes exposed to neutrons are unable to repair PLD. The RBE value, when the reproductive survival was estimated 30 min after radiation exposure, is independent of neutron dose and equal to 1.6 +/- 0.1. In contrast, when the reproductive survival was estimated 24 hrs after radiation exposure, the RBE was found to increase with decreasing neutron dose and equal 4.2 +/- 0.5 at 50 cGy.

The kinetics of in situ repair in rat mammary cells

The kinetics of in situ repair (ISR) was investigated in normal rat mammary epithelial cells exposed in vivo to 8 Gy 137 Cs gamma rays. ISR as measured by transplantation assay was completed by 4 hours after exposure. Although ISR in the three normal epithelial cell types thus far tested differs from repair of potentially lethal damage in tumour cells and cultured fibroblasts in that it affects the shoulder and not the slope of the survival curve, the current study shows that the time course of ISR resembles that for repair of potentially lethal damage in both tumours and fibroblasts.