Low expression of ecto-5'-nucleotidase in the pig heart - a potential barrier to xenotransplantation.
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Journal Article↗
Biomedical subjects
Z Kochan
Publications and source records attributed to Z Kochan.
Increase of lipogenic enzyme mRNA levels in rat white adipose tissue after multiple cycles of starvation-refeeding.
Recently, we have found that despite the significant reduction of body weight after multiple starvation-refeeding cycles, white adipose tissue (WAT) exhibits surprisingly high rates of lipogenesis and lipogenic enzyme activities. The purpose of this study was to determine the response of WAT lipogenic enzyme mRNAs of rats subjected to multiple cycles of 3 days fasting and 3 days of refeeding. Despite the body weight reduction, significant increase of lipogenic enzymes (ie, fatty acid synthase [FAS], acetyl-coenzyme A [CoA] carboxylase [ACC], adenosine triphosphate (ATP)-citrate lyase [ACL], NADP-linked malic enzyme [ME], and glucose 6-phosphate dehydrogenase [G6PDH]) mRNAs in WAT was found after multiple cycles of starvation-refeeding of rats on standard laboratory diet. These findings, together with the results published recently, indicate that multiple cycles of starvation-refeeding cause the increased lipogenesis in WAT by upregulation of the lipogenic enzymes gene expression.
Adipose Tissue↗
The decrease of rat postprandial plasma triacylglycerol concentration after multiple cycles of starvation-refeeding.
The effect of multiple cycles of starvation-refeeding on rat body weight and on plasma lipid concentration was studied. After 1 cycle of starvation-refeeding, the rat body weight did not change significantly; however the postprandial plasma triacylglycerol concentration decreased approximately 2-fold as compared to rats fed ad libitum. After 8 cycles of starvation-refeeding, both rat body weight and plasma triacylglycerols concentration decreased. In contrast, the plasma cholesterol (both total and HDL cholesterol) concentration did not change appreciably either after 1 or 8 cycles of starvation-refeeding as compared to control. Although the postprandial plasma triacylglycerol concentration decreased in both groups (i.e. after 1 and 8 cycles of starvation-refeeding), this phenomenon appears to last longer after 8 cycles of starvation-refeeding. The epididymal white adipose tissue weight decreased after both 1 and 8 cycles of starvation-refeeding. After 1 cycle of starvation-refeeding followed by 3, 6 and 9 days of ad libitum feeding, the epididymal white adipose tissue weight increased progressively, reaching the control value at day 9. In contrast, after 8 cycles of starvation-refeeding followed by 9 days of ad libitum feeding, the epididymal white adipose tissue weight did not reach the control value. These results suggest that dieting is associated with body and adipose tissue weight loss as well as with the decrease of plasma triacylglycerol concentration. Furthermore, our results suggest that better maintenance of low adipose tissue weight and low plasma triacylglycerol concentration may be achieved after multiple cycles of starvation-refeeding.
Adipose Tissue↗
Lipogenesis in experimental chronic renal failure in rats.
Hyperlipidemia is a common occurance in patients with chronic renal failure (CRF) and has been the subject of many clinical and experimental studies. Despite this, the role of lipogenesis in the development of hyperlipidemia is still obscure. The present study is based on a rat model of CRF involving a two-stage subtotal nephrectomy. In this study, we measured the activity of fatty acid synthase (FAS). This is the rate-limiting enzyme of lipogenesis and is present in liver and white adipose tissue (WAT). Using isotopic methods, we also determined the rate of lipogenesis in vivo in liver and WAT. In both liver and WAT, the results of the analyses were similar. In the uremic rats, there was a tendency for the FAS activity to rise. However, the difference was not statistically significant. Furthermore, there was no increase in the rate of lipogenesis in vivo in either tissue. In summary, the results of our study confirm the thesis that lipogenesis does not play a role in the development of hypertriglyceridemia seen in an experimental CRF in rats.
Adipose Tissue↗
Low leptin mRNA level in adipose tissue and normoleptinemia in experimental chronic renal failure.
BACKGROUND: Anorexia and weight loss frequently accompany chronic renal failure (CRF). Although multiple metabolic changes occur during CRF, a bulk of evidence indicates that the decrease in caloric intake plays a major role in CRF-induced weight loss. Recently, it has been suggested that elevated plasma leptin concentrations could contribute to anorexia and to downregulation of leptin gene expression in CRF patients. However, in some CRF patients, plasma leptin concentrations have been found to be lower than one could expect. Thus we assumed that inhibition of leptin synthesis plays an important role in the regulation of plasma leptin concentrations in CRF patients. METHODS: To test this assumption, the leptin mRNA level in rat white adipose tissue from ad-libitum-fed control (sham operated), pair-fed control (sham operated) and rats with experimentally induced CRF has been measured by Northern blotting analysis. In addition, serum leptin concentration (by radioimmunoassay) was determined in all three groups of animals. RESULTS: The results of the present study indicate that in experimental CRF the leptin mRNA level is decreased by about 50% as compared to the sham-operated animals (ad-libitum-fed and pair-fed controls). The mean serum leptin concentration in CRF rats was essentially similar to the leptin concentration in sham-operated ones. CONCLUSION: The data obtained suggest that in CRF animals the serum leptin concentration might be affected not only by the decrease in leptin removal in the kidney, but also by the decrease in leptin secretion from adipose tissue. Furthermore, the results of the study suggest that leptin may be only one of many factors involved in the pathogenesis of malnutrition associated with CRF.
Adipose Tissue↗
Adenine incorporation in endothelial cells.
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Adenine↗
TNF-alpha reduces the activity of ecto-5'-nucleotidase in human endothelial cells.
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5'-Nucleotidase↗
The effect of adenosine metabolism inhibition and nucleotide precursor supply on adenosine production in human heart endothelial cells.
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Adenine↗
Differential effect of clofibrate on acetyl-CoA carboxylase mRNA level in rat white and brown adipose tissue.
Regulation of some lipogenic enzyme gene expression by clofibrate was studied in rat white and brown adipose tissue. In white adipose tissue the drug administration for 14 days to rats resulted in the increase in acetyl-CoA carboxylase, ATP-citrate lyase, and glucose 6-phosphate dehydrogenase mRNA levels. Opposing effect of clofibrate on the acetyl-CoA carboxylase, ATP-citrate lyase, and glucose 6-phosphate dehydrogenase mRNA levels was found in brown adipose tissue. These data indicate a tissue specificity of clofibrate action on lipogenic enzyme gene expression. The results presented in this paper provide further evidence that hypolipidaemia caused by the treatment with clofibrate cannot be related to the inhibition of fatty acid synthesis in white adipose tissue in rat.
Acetyl-CoA Carboxylase↗
Comparative study of the lipogenic potential of human and rat adipose tissue.
The reported low activity of lipogenic enzymes (especially adenosine triphosphate [ATP]-citrate lyase) in human adipose tissue led to the general conclusion that in humans lipogenesis occurs primarily in the liver. However, recent studies indicate that the liver plays a minor role in de novo lipogenesis and suggest that adipose tissue may be the principal lipogenic human tissue. In an attempt to resolve these contradictions we reinvestigated the lipogenic potential of human adipose tissue and compared with adipose tissue of rats fed a high-fat diet for 2 weeks and fasted overnight before death. These conditions mimic the nutritional state of patients at the moment of tissue sampling. We found that overnight fasting of the rats maintained previously for 12 days on a high-fat diet caused a decrease of ATP-citrate lyase of about 7-fold. Thus, in human adipose tissue, the mean activity of ATP-citrate lyase was approximately 8 times lower than in rats fed a high-fat diet and fasted overnight, and about 50 times lower than in rats maintained on normal laboratory diet. Unlike ATP-citrate lyase, fatty acid synthase (FAS) activity was only slightly lower in human adipose tissue than in rats maintained on a normal laboratory diet. Comparable FAS activity was found when rats were fed a high-fat diet and fasted overnight. The average activities of human adipose tissue acetyl-coenzyme A carboxylase, malic enzyme, and glucose-6-phosphate dehydrogenase were approximately 3-, 4-, and 6-fold lower than in adipose tissue from rats fed a high-fat diet and fasted overnight before tissue sampling, while the activity of 6-phosphogluconate dehydrogenase in humans was higher than in rat adipose tissue. No significant differences in lipogenic enzyme activities were found between male and female and between lean and obese patients. The rate of fatty acid synthesis in intact pieces of human adipose tissue was approximately 5 times lower than in adipose tissue pieces of rats fed a high-fat diet and fasted overnight before tissue samples were taken. The comparison of the lipogenic potential of humans and rats (maintained on the diet to mimic the nutritional state of patients at the time of tissue sampling) suggests that human adipose tissue is an important site of fatty acid synthesis.
ATP Citrate (pro-S)-Lyase↗
Adenine incorporation in human and rat endothelium.
Adenine (ADE) reutilisation is an important pathway of adenylate pool regeneration. Data on the rate of this process in different types of cells, its regulation and the importance of species differences is limited. In this study we evaluated adenine incorporation rate and the effect of metabolic factors on this process in human and rat endothelium and compared it to adenine phosphoribosyltransferase (APRT) activity. Microvascular endothelial cells from human (HE) and rat (RE) hearts and a transformed human microvascular endothelial cell line (HMEC-1) were investigated. The rate of adenine incorporation into the adenine nucleotide pool under control conditions was 3.1+/-0.3, 82.8+/-11.1 and 115.1+/-11.2 pmol/min per mg protein for HE, RE and HMEC-1, respectively. In the presence of 2.5 mM ribose or elevated inorganic phosphate concentration in the medium (4.8 mM), few changes were observed in all types of cells. In the presence of both ribose and high inorganic phosphate, the rate of adenine incorporation for RE and HMEC-1 was not significantly different from control, while in HE the rate of adenine incorporation into adenine nucleotides was increased by 75%. Activities of APRT in RE and HMEC-1 were 237.7+/-23.2 and 262.0+/-30.6 pmol/min per mg protein respectively while the activity in HE was markedly lower 48.7+/-3.0 pmol/min per mg protein. In conclusion, nucleotide synthesis from adenine seems to be a slow process in human cardiac microvascular endothelium but it is fast and efficient in rat heart microvascular endothelial cells. Low APRT activity in normal human endothelial cells seems to be the most likely mechanism for this. However, adenine incorporation rate and APRT activity could be greatly enhanced in human endothelium, as demonstrated in transformed cells.
Adenine↗
Tissue-specific effect of clofibrate on rat lipogenic enzyme gene expression.
Fibrate derivatives are commonly used to treat hyperlipidaemia; however, the mechanism of the antilipidaemic action of these drugs is still unknown. The effect of clofibrate (fibrate derivative) administration for 14 days on lipogenesis and on malic enzyme (EC 1.1.1.40) and fatty acid synthase (EC 2.3.1.85) gene expression in brown and white adipose tissues and in the liver was examined in rats. The rate of brown adipose tissue lipogenesis in the clofibrate-treated animals was significantly lower than that of the control rats. The rate of liver and white adipose tissue lipogenesis was not affected significantly by clofibrate. In brown adipose tissue, the drug treatment resulted in a depression of fatty acid synthase and malic enzyme mRNA levels. The fatty acid synthase mRNA level did not change significantly in the liver, whereas the malic enzyme mRNA level increased approximately 6-fold in this organ after clofibrate treatment. The malic enzyme mRNA level in white adipose tissue increased about 2-fold, while the fatty acid synthase mRNA level was unchanged after clofibrate feeding. The results presented in this paper provide further evidence that the hypolipidaemia caused by treatment of rats with clofibrate cannot be related to the inhibition of fatty acid synthesis in the liver and white adipose tissue. These data also indicate that clofibrate exhibits tissue specificity.
Adipose Tissue↗
Effect of clofibrate on malic enzyme and leptin mRNAs level in rat brown and white adipose tissue.
Two previous studies have reported contradictory results regarding the effect of fibrates treatment on obese (ob) gene expression in rodents. The purpose of the present study was to reinvestigate this issue. We examined the effect of clofibrate (fibrate derivative) administration for 14 days to rats on malic enzyme (as an adequate control of fibrates action) and leptin mRNAs level in the white and brown adipose tissues (WAT and BAT, respectively). The malic enzyme activity and malic enzyme mRNA level in white adipose tissue increased significantly after clofibrate feeding. In brown adipose tissue, the drug treatment resulted in depression of malic enzyme activity and malic enzyme mRNA level. Under the same conditions, leptin mRNA level did not change in these tissues. The results presented in this paper provide further evidence that the clofibrate (activator of peroxisome proliferator activated receptor alpha), feeding is without effect on ob gene expression in rat white and brown adipose tissue. Furthermore, the present study demonstrates that clofibrate causes opposite effects on malic enzyme gene expression in WAT (up-regulation) and BAT (down-regulation).
Adipose Tissue↗
Adenine/ribose supply increases adenosine production and protects ATP pool in adenosine kinase-inhibited cardiac cells.
The objective of the present study was to establish the optimal combination of inhibitors of adenosine metabolism and nucleotide precursors resulting in long-term increase in endogenous adenosine concentration without adverse metabolic consequences in non-ischemic cardiomyocytes and endothelial cells. Cardiomyocytes and endothelial cells were isolated after collagenase digestion of the rat heart. Freshly isolated cardiac myocytes or cultured endothelial cells were incubated for up to 8 h with no inhibitors or substrates or with various combinations of adenosine deaminase inhibitor: 5 micron M erythro-9(2-hydroxy-3-nonyl)adenine (EHNA), adenosine kinase inhibitors: 10 micro M 5'-iodotubercidin (ITu) or 10 micro M 5'-aminoadenosine (AA) and nucleotide precursors: 100 micro M adenine, 2.5 mm ribose and 5 mm inorganic phosphate. Nucleotide, nucleoside and base concentrations were evaluated at the end of the incubation by HPLC in cardiomyocyte or endothelial cells extracts and in incubation media. Adenosine content in cardiomyocyte suspension was enhanced after 3 h incubation in the presence of ITu+EHNA as compared to EHNA alone (2.8+/-0.2 v 0.9+/-0.2 nmol/mg protein, respectively). ATP decreased from an initial value of 22.7+/-0.7 nmol/mg protein to 18.9+/-0.7 in the presence of ITu+EHNA, while ATP was maintained at 21.8+/-0.7 nmol/mg protein with EHNA. With adenine+ITu+EHNA, the changes were similar to those observed with ITu+EHNA. However, with ribose+adenine+ITu+EHNA, ATP increased to 25. 8+/-1.2 nmol/mg protein and adenosine concentration was elevated to 3.9+/-0.3 nmol/mg protein. Similar results were observed if AA was used instead of ITu to inhibit adenosine kinase. All the changes were maintained after 8 h of incubation. Adenosine content was increased in endothelial cells incubated with ITu+EHNA to 3.1+/-0.4 nmol/mg protein as compared to 1.1+/-0.2 nmol/mg protein with EHNA alone after 3 h, while ATP decreased (18.1+/-1.1 v 22.0+/-1.4 nmol/mg protein with EHNA+ITu or EHNA, respectively). In the presence of adenine+ITu+EHNA, adenosine content increased after 3 h to 6.5+/-0.9 nmol/mg protein while ATP was elevated to 26.1+/-0.8 nmol/mg protein. Additional presence of ribose was without effect. No changes in adenylate energy charge were observed in cardiomyocytes or endothelium under any conditions studied. Inhibition of adenosine kinase and adenosine deaminase caused a decrease in ATP together with increased adenosine content both in endothelial cells and cardiomyocytes. However, the addition of adenine (endothelial cells) or adenine with ribose (cardiomyocytes) together with inhibitors of adenosine metabolism protected cells from ATP depletion and further increased adenosine concentration.
Adenine↗
Effects of adenine/ribose supply on adenosine production and ATP concentration in adenosine kinase inhibited cardiac cells.
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Adenine↗
Dietary alpha-tocopherol prevents dehydroepiandrosterone-induced lipid peroxidation in rat liver microsomes and mitochondria.
Dehydroepiandrosterone (DHEA), an adrenal steroid, causes lipid peroxidation in rat liver microsomes and mitochondria and induces hepatocarcinogenesis. It was investigated whether alpha-tocopherol, a naturally occurring free radical chain terminator, could decrease lipid peroxidation. When DHEA-free diet supplemented with increasing concentrations of alpha-tocopherol (25, 50, 100, 200, 400 and 1000 mg/kg diet) was fed to rats for 7 days, a marked lipid peroxidation (measured as thiobarbituric acid reactive substances formation) was observed at concentrations 25 and 50 mg/kg in liver microsomes and mitochondria isolated from these animals. Lipid peroxidation was significantly reduced at concentrations > or = 100 mg/kg. When DHEA (500 mg/kg diet) was fed to rats simultaneously with increasing concentrations of alpha-tocopherol, strong lipid peroxidation was observed at alpha-tocopherol concentrations < or = 200 mg/kg diet. However, microsomes and mitochondria isolated from livers of rats fed alpha-tocopherol at doses of 400 and 1000 mg/kg diet produced only negligible amounts of thiobarbituric acid reactive substances. The data show that high concentrations of alpha-tocopherol in the diet decrease DHEA-induced microsomal and mitochondrial lipid peroxidation. Our results support the concept that alpha-tocopherol can protect against DHEA-induced lipid peroxidation and consequently against steroid-induced liver cell damage and, perhaps, also tumour development.
Animals↗
Unususal increase of lipogenesis in rat white adipose tissue after multiple cycles of starvation-refeeding.
The purpose of the study was to determine the response of liver and brown (BAT) and white (WAT) adipose tissue lipogenesis and total body weight in rats subjected to multiple cycles of 3 days of fasting and 3 days of refeeding. Rats fasted for 3 days showed significant reduction in body weight. These changes were reversed on 3 days' refeeding. Body weight was much higher in rats fed ad libitum than in animals experiencing more than one cycle of 3 days of fasting followed by 3 days of refeeding. Despite the significant body weight reduction, an unusual increase of lipogenesis in WAT was found after multiple cycles of starvation-refeeding of rats on standard laboratory diet. The rate of lipogenesis in the liver and BAT was also elevated but to a much smaller extent. A parallel increase in enzymatic activities related to fatty acid synthesis, ie, fatty acid synthase, acetyl-coenzyme A carboxylase, adenosine triphosphate (ATP)-citrate lyase, NADP-linked malic enzyme, and hexose monophosphate shunt dehydrogenases, suggests that the increased rate of lipogenesis in WAT is a consequence of increased lipogenic enzyme activities. These data suggest that upregulation of WAT lipogenesis occurs after the multiple cycles of the starvation-refeeding protocol. An unusual increase of lipogenesis in rat WAT may have a survival advantage, because starved-refed rats must develop the ability to ingest large amounts of food during a refeeding period to store it in a convenient form than can be used as an oxidizable substrate during a period of starvation. Moreover, these results suggest that it is possible to develop appropriate starvation-refeeding conditions that may inhibit body weight gain.
Adipose Tissue↗