gamma-Linolenic acid and eicosapentaenoic acid induce modifications in mitochondrial metabolism, reactive oxygen species generation, lipid peroxidation and apoptosis in Walker 256 rat carcinosarcoma cells.
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The polyunsaturated fatty acids gamma-linolenic acid (GLA) and eicosapentaenoic acid (EPA) are cytotoxic to tumour cells. GLA inhibits Walker 256 tumour growth in vivo, causing alterations in mitochondrial ultrastructure and cellular metabolism. The objective of the present study was to investigate the mechanisms behind fatty acid inhibition of Walker 256 tumour growth under controlled in vitro conditions. At a concentration of 150 microM, both GLA and EPA caused a decrease in cell proliferation and an increase in apoptotic index. Increases in reactive oxygen species (ROS) and lipid peroxide production were identified, as well as alterations in energy metabolism and the deposition of large amounts of triacylglycerol in the form of lipid droplets. Mitochondrial respiratory chain complexes I+III and IV had significantly decreased activity and mitochondrial membrane potential was greatly diminished. Intracellular ATP concentrations were maintained at 70-80% of control values despite the decreased mitochondrial function, which may be in part due to increased utilisation of glucose for ATP generation. Cytochrome c release from mitochondria was found, as was caspase-3-like activation. DNA fragmentation in situ revealed many apoptotic events within the cell population. The mechanism(s) by which ROS and lipid peroxides induce apoptosis remains unclear, but the effects of GLA and EPA appear to involve the mitochondrial pathway of apoptosis induction leading to cytochrome c release, caspase activation, loss of mitochondrial membrane potential and DNA fragmentation. (+info)
Effects of leucine supplemented diet on intestinal absorption in tumor bearing pregnant rats.
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BACKGROUND: It is known that amino acid oxidation is increased in tumor-bearing rat muscles and that leucine is an important ketogenic amino acid that provides energy to the skeletal muscle. METHODS: To evaluate the effects of a leucine supplemented diet on the intestinal absorption alterations produced by Walker 256, growing pregnant rats were distributed into six groups. Three pregnant groups received a normal protein diet (18% protein): pregnant (N), tumor-bearing (WN), pair-fed rats (Np). Three other pregnant groups were fed a diet supplemented with 3% leucine (15% protein plus 3% leucine): leucine (L), tumor-bearing (WL) and pair-fed with leucine (Lp). Non pregnant rats (C), which received a normal protein diet, were used as a control group. After 20 days, the animals were submitted to intestinal perfusion to measure leucine, methionine and glucose absorption. RESULTS: Tumor-bearing pregnant rats showed impairment in food intake, body weight gain and muscle protein content, which were less accentuated in WL than in WN rats. These metabolic changes led to reduction in both fetal and tumor development. Leucine absorption slightly increased in WN group. In spite of having a significant decrease in leucine and methionine absorption compared to L, the WL group has shown a higher absorption rate of methionine than WN group, probably due to the ingestion of the leucine supplemented diet inducing this amino acid uptake. Glucose absorption was reduced in both tumor-bearing groups. CONCLUSIONS: Leucine supplementation during pregnancy in tumor-bearing rats promoted high leucine absorption, increasing the availability of the amino acid for neoplasic cells and, mainly, for fetus and host utilization. This may have contributed to the better preservation of body weight gain, food intake and muscle protein observed in the supplemented rats in relation to the non-supplemented ones. (+info)
Influence of hepatic arterial blockage on blood perfusion and VEGF, MMP-1 expression of implanted liver cancer in rats.
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AIM: To investigate the influence of hepatic arterial blockage on blood perfusion of transplanted cancer in rat liver and the expression of vascular endothelial growth factor (VEGF) and matrix metalloproteinase-1 (MMP-1), and to explore the mechanisms involved in transarterial embolization (TAE)-induced metastasis of liver cancer preliminarily. METHODS: Walker 256 carcinosarcoma was transplanted into rat liver to establish the liver cancer model. Hepatic arterial ligation (HAL) was used to block the hepatic arterial blood supply and simulate TAE. Blood perfusion of tumor in control, laparotomy control, and HAL group was analyzed by Hoechst 33342 labeling assay, the serum VEGF level was assayed by ELISA, the expression of VEGF and MMP-1 mRNA was detected by in situ hybridization. RESULTS: Two days after HAL, the number of Hoechst 33342 labeled cells which represent the blood perfusion of tumor directly and hypoxia of tumor indirectly in HAL group decreased significantly compared with that in control group (329+/-29 vs 384+/-19, P<0.01). The serum VEGF level in the HAL group increased significantly as against that of the control group (93 ng.L(-1)+/-44 ng.L(-1) vs 55 ng.L(-1)+/-19 ng.L(-1), P<0.05). The expression of VEGF and MMP-1 mRNA in the tumor tissue of the HAL group increased significantly compared with that of the control and the laparotomy control groups (P<0.05). The blood perfusion data of the tumor, represented by the number of Hoechst 33342 labeled cells, showed a good linear inverse correlation with the serum VEGF level (r=-0.606, P<0.05) and the expression of VEGF mRNA in the tumor tissue ( r =-0.338, P<0.01). CONCLUSION: Blockage of hepatic arterial blood supply results in decreased blood perfusion and increased expression of metastasis-associated genes VEGF and MMP-1 of transplanted liver cancer in rats. Decreased blood perfusion and hypoxia may be the major cause of up-regulated expression of VEGF. (+info)
Gamma-linolenic acid alters the composition of mitochondrial membrane subfractions, decreases outer mitochondrial membrane binding of hexokinase and alters carnitine palmitoyltransferase I properties in the Walker 256 rat tumour.
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Gamma-linolenic acid (GLA) is known to be an inhibitor of Walker 256 tumour growth in vivo and causes changes in both mitochondrial structure and cellular metabolism. The aim of the present study was to investigate in greater detail the changes in energy metabolism and ultrastructure induced by GLA in this tumour model. A diet containing 5.5% GLA, which is sufficient to cause a 45% decrease in tumour growth, was found to almost double the triacylglycerol (TAG) content of the tumour and to increase the quantity of 20:3 n-6, 20:4 n-6, 22:4 n-6 and 22:5 n-6 in the TAG fraction as determined by gas chromatography-mass spectrometry (GCMS) analysis. Morphometric analysis of the tumour by electron microscopy confirmed this increase in TAG content, identifying a doubling of lipid droplet content in the GLA dietary group. The surface density of mitochondrial cristae was reduced, along with a reduction in the number of contact sites (CS) and matrix granules. These three parameters are likely indicators of a reduction in mitochondrial metabolic activity. Measurement of hexokinase activity identified that much of the total hexokinase activity was in the mitochondrially bound form (66.5%) in the control tumour and that GLA caused a decrease in the amount of enzyme in the bound form (39.3%). The fatty acyl chain composition of the tumour mitochondrial subfractions, outer membranes (OM), CSs and inner membranes (IM) was determined by GCMS. All subfractions showed considerable increases in 20:3 n-6 and decreases in 18:1 n-9, 18:2 n-6 and 22:6 n-3, when exposed to GLA diet. These changes were reflected in a large increase in the n-6/n-3 ratio in the GLA OM vs. the control OM, 21.299 vs. 6.747, respectively. The maximal activity of OM carnitine palmitoyltransferase I (CPT I) was found to be decreased by 61.6% in the GLA diet group. This was accompanied by a decrease in malonyl CoA sensitivity and a decrease in affinity for 16:0 CoA substrate. Such changes in CPT I may be the cause of cytoplasmic acyl CoA accumulation seen in this tumour model. These effects, together with previously reported increases in lipid peroxidation, lead to the conclusion that GLA may cause inhibition of tumour cell growth through separate but interlinked pathways, all of which eventually lead to apoptosis and a decrease in tumour development. The influence of mitochondrial OM fatty acyl chain composition upon two important enzymes of energy metabolism, hexokinase and CPT I, both of which have been linked to apoptosis, is of considerable importance for future studies on fatty acid-induced cell death. (+info)
Humoral mediated macrophage response during tumour growth.
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Reticuloendothelial (RE) phagocytic and circulating plasma opsonic activity was evaluated in rats transplanted with the Walker 256 carcinoma tumour in an attempt to evaluate the role of opsonic protein in governing the functional state of the macrophage system. Animals transplanted intramuscularly with 2 X 10(4) viable tumour cells manifested 2 peaks of RE stimulation at 6 and 14 days post-transplantation with a subsequent decline in the phagocytic activity over the 14-30 day period. Increased phagocytic activity as determined by colloid clearance was primarily a reflection of hepatic Kupffer cell hyperphagocytosis while the decline in phagocytic activity was related to a decrease in Kupffer cell function. The initial peak of RE stimulation was associated with an elevation in the blood opsonin level and no significant enlargement of the liver and spleen. In contrast, the second peak of RE stimulation at 14 days was associated with both an elevation in opsonin levels and an associated hepatic and splenic enlargement. The decline in phagocytic activity over the 14-30 day interval was associated with a progressive decline in the plasma opsonic activity, a return of the spleen to its normal size in relationship to the body weight, and a persistent hepatomegaly. These findings suggest that the alterations in macrophage function during tumour growth may be mediated in part by changes in the opsonic or phagocytosis promoting capacity of plasma. Since opsonic protein contributes to the discriminatory capacity of macrophages, it is suggested that changes in the blood opsonin level may condition the anti-tumour capacity of the macrophage system with respect to host defence aginst malignant disease. (+info)
An implantable rat liver tumor model for experimental transarterial chemoembolization therapy and its imaging features.
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AIM: To establish an ideal implantable rat liver tumor model for interventional therapy study and examine its angiographic signs and MRI, CT features before and after embolization. METHODS: Forty male Wistar rats were implanted with Walker-256 tumor in the left lateral lobe of liver. Digital subtraction angiography (DSA) and transarterial chemoembolization were performed on day 14 after implantation. Native computer tomography (CT, n=8) and native magnetic resonance (MR, n=40) were performed between the day 8 and day 21 after implantation. The radiological morphological characteristics were correlated with histological findings. RESULTS: Successful implantation was achieved in all forty rats, which was confirmed by CT and MRI. MR allowed tumor visualization from day 8 while CT from day 11 after implantation. The tumors were hypodensity on CT, hypointense on MR T1-weighted and hyperintense on T2-weighted. The model closely resembled human hepatocarcinoma in growth pattern and the lesions were rich in vasculature on angiography and got its filling mainly from the hepatic artery. Before therapy, tumor size was 211.9+/-48.7 mm(3). No ascites, satellite liver nodules or lung metastasis were found. One week after therapy, tumor size was 963.6+/-214.8 mm(3) in the control group and 356.5+/-78.4mm(3) in TACE group. Ascites (4/40), satellite liver nodules (7/40) or lung metastasis (3/40) could be seen on day 21. CONCLUSION: Walker-256 tumor rat model is suitable for the interventional experiment. CT and MRI are helpful in animal optioning and evaluating experimental results. (+info)
Influence of methionine/valine-depleted enteral nutrition on nucleic acid and protein metabolism in tumor-bearing rats.
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AIM: To investigate the effects of methionine/valine-depleted enteral nutrition (EN) on RNA, DNA and protein metabolism in tumor-bearing (TB) rats. METHODS: Sprague-Dawlley (SD) rats underwent jejunostomy for nutritional support. A suspension of Walker-256 carcinosarcoma cells was subcutaneously inoculated. 48 TB rats were randomly divided in 4 groups: A, B, C and D. The TB rats had respectively received jejunal feedings supplemented with balanced amino acids, methionine-depleted, balanced amino acids and valine-depleted for 6 days before injection of 740 KBq (3)H- methionine/valine via jejunum. The (3)H incorporation rate of the radioactivity into RNA, DNA and proteins in tumor tissues at 0.5, 1, 2, 4 h postinjection of tracers was assessed with liquid scintillation counter. RESULTS: Incorporation of (3)H into proteins in groups B and D was (0.500+/-0.020) % to (3.670+/-0.110) % and (0.708+/-0.019) % to (3.813+/-0.076) % respectively, lower than in groups A ((0.659+/-0.055) % to (4.492+/-0.108) %) and C ((0.805+/-0.098) % to (4.180+/-0.018) %). Incorporation of (3)H into RNA, DNA in group B was (0.237+/-0.075) % and (0.231+/-0.052) % respectively, lower than in group A (P<0.01). There was no significant difference in uptake of (3)H by RNA and DNA between group C and D (P>0.05). CONCLUSION: Protein synthesis was inhibited by methionine/valine starvation in TB rats and nucleic acid synthesis was reduced after methionine depletion, thus resulting in suppression of tumor growth. (+info)
Identification of the products of mitochondrial transcription in the walker corcinosarcoma by the use of actinomycin D and ethidium bromide.
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The major RNA species present in the purified mitochondrial fraction of the Walker carcinoma were investigated in order to determine which of them are located in the mitochondria and coded by the organelle DNA. The subcellular distribution of these RNA's and the in vivo sensitivity of the transcription process to selective inhibitors were examined. Among the different species separated by polyacrylamide gel electrophoresis, only the 21 and 16 Se RNA's were found exclusively in the purified mitochondria, approximately Se being the S value estimated from the relative electrophoretic mobility of the RNA. A bifid peak observed in the 16-15 Se region was shown to be an artifact caused by the ribonuclease inhibitor, naphthalene disulfonate. Ethidium bromide at high doses inhibited the incorporation in vivo of 32P into 21, 16, and 4 Se RNA, but the nuclear transcription of cytoplasmic RNA was also inhibited to the same extent. No significant effect was observed at lower doses. In contrast, actinomycin D exerted a differential inhibition of the synthesis of 28 and 18 Se RNA from both the cytoplasmic and the mitochondrial fractions, practically without affecting the transcription of the 21 and 16 Se species. The incorporation of 32P into mitochondrial 4 Se RNA was also considerably more resistant to the drug than the synthesis of the cytoplasmic tRNA. It is concluded that the 21, 16, and Se RNA's are the only major discrete species transcribed from mitochondrial DNA present in the Walker carcinoma. (+info)