Increased rate of cholesterologenesis--a possible cause of hypercholesterolemia in experimental chronic renal failure in rats.

Hypercholesterolemia plays an important role in the lipid abnormalities in chronic renal failure (CRF). It is thought to contribute to both a progression of renal failure and atherosclerosis. Despite intensive research, the etiopathogenesis of hypercholesterolemia in CRF patients is still obscure. The present study was designed to evaluate the possible role of cholesterol overproduction in the development of hypercholesterolemia associated with experimental CRF. We found that plasma total cholesterol and cholesterol distributed in VLDL, LDL and HDL concentrations were significantly enhanced in CRF rats. Simultaneously, the rate of liver cholesterol biosynthesis in vivo (measured by determining the incorporation of tritium from tritiated water intraperitoneally injected into cholesterol ), liver microsomal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and liver HMG-CoA reductase mRNA presence were elevated. Significant increases in activity of liver malic enzyme, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, NADPH-producing enzyme (required for cholesterol synthesis) have also been observed in CRF rats. In conclusion, the increased rate of liver cholesterol biosynthesis due to increase of HMG-CoA reductase and NADPH-producing enzyme gene expression could be one of the possible causes of hypercholesterolemia in CRF animals.

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.

[Adenine reutilization as a cause of increased ATP concentration in erythrocytes of patients with chronic renal failure]. / Reutylizacja adeniny jedna z przyczyn wzrostu stezenia ATP w erytrocytach pacjentów z przewlekla niewydolnoscia nerek.

Abnormalities of adenine nucleotide metabolism are observed in erythrocytes of patients with chronic renal failure (CRF) and the elevated ATP concentration is the most impressive one. In humans, adenine and/or adenosine reutilization is the only source of purine moiety used to erythrocyte adenine nucleotide synthesis. In the present study we have focused on the role of adenine as a substrate for the intraerythrocyte ATP production. 10 patients with CRF and 10 healthy volunteers (control group) were included into the study. Using HPLC, the measurements were performed in plasma and erythrocyte extracts. We observed a few fold higher adenine concentration in both plasma and erythrocytes of patients with CRF when compared with control group. There was also elevated an intraerythrocyte ATP concentration in the studied group of patients. Moreover, we have found a positive correlations between a) plasma creatinine concentration and plasma adenine concentration, b) plasma creatinine concentration and erythrocyte adenine concentration, c) plasma adenine concentration and intraerythrocyte ATP concentration. It appears that increased adenine reutilization could be a principle reason of the increased ATP synthesis in erythrocytes of patients with CRF.

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.

[Renal replacement therapy results in correction of plasma and erythrocyte adenine nucleotide abnormalities in patients with chronic renal failure]. / Leczenie nerkozastepcze koryguje stezenie adeniny w osoczu i metabolizm adenylanów w erytrocytach pacjentów z przewlekla niewydolnoscia nerek.

High concentration of intraerythrocyte ATP is a common phenomenon in patients with chronic renal failure (CRF). It is likely that this is a result of increased plasma concentration of adenine--one of purine moiety donors which is necessary for ATP synthesis. In the present study we monitored changes of both adenine and intraerythrocyte ATP concentration during renal replacement therapy. We have also estimated the influence of erythropoietin treatment. 4 groups of patients were included into the study: 22 patients with CRF, 22 patients on maintenance hemodialysis treatment (11 patients with EPO therapy), 19 patients after kidney transplantation (7 patients with insufficiency of transplanted kidney) and 26 healthy volunteers served as a control group. The measurements were performed in plasma and erythrocyte extracts using HPLC. Significant decrease of high plasma adenine concentration was observed after both HD session and successful kidney transplantation, however the achieved values were still higher than in healthy volunteers. Kidney transplantation resulted in a permanent decrease of plasma adenine concentration, but along with the deterioration of transplanted kidney function, the plasma adenine concentration reincreased. Also, it started to increase right after HD session had ended. On the other hand, the intraerythrocyte concentration of adenine and ATP after successful kidney transplantation and single HD session came back to normal values. Also in this case, along with the deterioration of transplanted kidney function, both studied parameters reincreased. We have not observed any significant influence of erythropoietin treatment on studied adenine nucleotide concentration in hemodialysis patients. The present study confirms the strong interrelationship between the adenine nucleotide metabolism abnormalities and the advancement of renal failure. The abnormalities intensify along with the disease progression and the renal replacement therapy results in partial their correction.

Accelerated degradation of adenine nucleotide in erythrocytes of patients with chronic renal failure.

Recently, we have shown that erythrocytes obtained from patients with chronic renal failure (CRF) exhibited an increased rate of ATP formation from adenine as a substrate. Thus, we concluded that this process was in part responsible for the increase of adenine nucleotide concentration in uremic erythrocytes. There cannot be excluded however, that a decreased rate of adenylate degradation is an additional mechanism responsible for the elevated ATP concentration. To test this hypothesis, in this paper we compared the rate of adenine nucleotide breakdown in the erythrocytes obtained from patients with CRF and from healthy subjects. Using HPLC technique, we evaluated: (1) hypoxanthine production by uremic RBC incubated in incubation medium: (a) pH 7.4 containing 1.2 mM phosphate (which mimics physiological conditions) and (b) pH 7.1 containing 2.4 mM phosphate (which mimics uremic conditions); (2) adenine nucleotide degradation (IMP, inosine, adenosine, hypoxanthine production) by uremic RBC incubated in the presence of iodoacetate (glycolysis inhibitor) and EHNA (adenosine deaminase inhibitor). The erythrocytes of healthy volunteers served as control. The obtained results indicate that adenine nucleotide catabolism measured as a hypoxanthine formation was much faster in erythrocytes of patients with CRF than in the cells of healthy subjects. This phenomenon was observed both in the erythrocytes incubated at pH 7.4 in the medium containing 1.2 mM inorganic phosphate and in the medium which mimics hyperphosphatemia (2.4 mM) and metabolic acidosis (pH 7.1). The experiments with EHNA indicated that adenine nucleotide degradation proceeded via AMP-IMP-Inosine-Hypoxanthine pathway in erythrocytes of both patients with CRF and healthy subjects. Iodoacetate caused a several fold stimulation of adenylate breakdown. Under these conditions: (a) the rate of AMP catabolites (IMP + inosine + adenosine + hypoxanthine) formation was substantially higher in the erythrocytes from patients with CRF; (b) in erythrocytes of healthy subjects degradation of AMP proceeded via IMP and via adenosine essentially at the same rate; (c) in erythrocytes of patients with CRF the rate of AMP degradation via IMP was about 2 fold greater than via adenosine. The results presented in this paper suggest that adenine nucleotide degradation is markedly accelerated in erythrocytes of patients with CRF.

Increased rate of adenine incorporation into adenine nucleotide pool in erythrocytes of patients with chronic renal failure.

BACKGROUND: Elevated purine nucleotide pool (mainly ATP) in erythrocytes of patients with chronic renal failure (CRF) is a known phenomenon, however the mechanism responsible for this abnormality is far from being clear. We hypothesize that the increased rate of adenine incorporation into adenine nucleotide pool is responsible for the elevated level of ATP in uremic erythrocytes. METHODS: In chronically uremic patients we evaluated using HPLC technique: (a) plasma adenine concentration; (b) the rate of adenine incorporation into adenine nucleotide pool in uremic erythrocytes. Additionally, the effect of higher than physiological phosphate concentration (2.4 mM) and lower than physiological pH (7.1) on adenine incorporation into erythrocytes adenine nucleotide pool was investigated. Healthy volunteers with normal renal function served as control. RESULTS: The concentration of adenine in plasma of CRF patients was found to be significantly higher than in plasma of healthy subjects. In contrast, adenosine concentration was similar both in healthy humans and in CRF patients. In isolated erythrocytes of uremic patients (incubated in the medium pH 7.4, containing 1.2 mM inorganic phosphate) adenine was incorporated into adenine nucleotide pool at a rate approximately 2-fold higher than in erythrocytes from healthy subjects. The rate of adenosine incorporation into adenine nucleotide pool was similar in erythrocytes of both studied groups. Incubation of erythrocytes obtained from healthy subjects in the medium pH 7.4, containing 2.4 mM inorganic phosphate, caused the increase of adenine incorporation into adenine nucleotide pool by about 60%. Incubation of the cells in the pH 7.1 buffer containing 2. 4 mM inorganic phosphate increased the rate of adenine incorporation into adenylate approximately 2-fold as compared to erythrocytes incubated in the medium pH 7.4 containing 1.2 mM inorganic phosphate. Erythrocytes obtained from uremic patients and incubated in the pH 7.1 medium containing 2.4 mM phosphate incorporated adenine into adenine nucleotide pool at a rate similar to erythrocytes incubated in the medium pH 7.4 containing 1.2 mM phosphate. Erythrocytes obtained from either healthy subjects or from patients with CRF and incubated in the presence of higher than physiological concentration of inorganic phosphate (2.4 mM) and lower than physiological pH (7. 1) did not exhibit any increase in the rate of adenisine incorporation into adenine nucleotide pool. CONCLUSION: These results suggest that the increased rate of adenine incorporation into adenine nucleotide pool could be partially responsible for the increased concentration of ATP in uremic erythrocytes.

Effect of clofibrate on plasma lipid concentration and liver malic enzyme gene expression in rats with experimental chronic renal failure.

Fibrates have been used clinically to treat dyslipidemias, including chronic renal failure (CRF)-related hypertriacylgliceridemia. In addition to their effects on plasma triacylglycerol concentration, fibrates also induce hepatomegaly (due to peroxisome proliferation) and increase liver malic enzyme activity. Since most experiments regarding fibrates action have been performed on healthy animals, in this paper we compare the effect of clofibrate on: a) plasma lipid concentration; b) liver weight; c) liver malic enzyme gene expression (malic enzyme activity, malic enzyme protein level and malic enzyme mRNA abundance) in control (sham-operated) animals and rats with CRF. The data presented in this paper indicate that: a) the clofibrate treatment causes a decrease in triacylglycerol concentration both in the control and rats with CRF, however the effect of the drug was more pronounced in the latter; b) administration of clofibrate induces hepatomegaly both in the control and rats with CRF; c) the liver malic enzyme gene expression is similarly affected by clofibrate in the control and rats with CRF. It is concluded that the beneficial, therapeutic effect of clofibrate on plasma lipid concentration is more pronounced in rats with CRF, but the side effects (hepatomegaly and the increase in malic enzyme gene expression) of fibrates are essentially similar in the control and rats with CRF.

[Oral calcitriol pulse therapy in treatment of secondary hyperparathyroidism in patients with long term hemodialysis]. / Dawki uderzeniowe calcitriolu stosowane doustnie w leczeniu wtórnej nadczynnosci przytarczyc u pacjentów przewlekle dializowanych.

Oral calcitriol pulse therapy slowly becomes a method of choice in the treatment of secondary hyperparathyroidism in hemodialysis patients. It appears to be equally effective and simultaneously significantly cheaper than an intravenous therapy. In last year we have applied such a treatment to 12 hemodialysis patients with severe secondary hyperparathyroidism (iPTH range: 447-1228 pg/ml). All of them were hemodialysed 3 times a week with dialysate Ca+2 level 1.25-1.75 mM/l. Calcium carbonate was administered to maintain serum Ca level between 9.0-11.0 mg/dl and phosphate below 6.0 mg/dl. The patients were given calcitriol at dose 0.1 microgram/kg once a week, but it was obligatory to take a drug at bedtime, at least two hours after the last meal, a day before hemodialysis. During the treatment we divided the patients into two groups: I-patients who responded to our treatment (7/12); II-treatment was unsuccessful (5/12). In this group we decided to increase the dose of calcitriol to 0.075 micrograms/kg twice a week after 6 months use of a previous one. We have achieved statistically significant decrease of parathormone (p < 0.001) and alkaline phosphatase (p < 0.02) in group I and after the increase the dose of calcitriol there occurred the decrease of parathormone (p < 0.05) and alkaline phosphatase (p < 0.002) in group II. Simultaneously we have observed a great clinical improvement. Our results confirm the fact that even severe secondary hyperparathyroidism can be successfully treated with oral calcitriol pulse therapy. Administering of high doses of calcitriol at bedtime increases safety of this procedure-we have not observed any case of hypercalcemia.

[Some clinical aspects of erythropoietin action used at doses not affecting erythropoiesis in hemodialysed patients]. / Niektóre kliniczne aspekty dzialania erytropoetyny stosowanej w dawkach nie pobudzajacych erytropoezy u pacjentów przewlekle dializowanych.

Erythropoietin has become a crucial point in treatment of anaemia in patients with chronic renal failure. Recently a very important point of concern are the non hematological aspects of its action. The aim of presented study was to evaluate the biochemical and clinical effects of using erythropoietin at doses not influence hemopoiesis. 10 hemodialysis patients with stable hemoglobin and hematocrit levels, were given erythropoietin at dose of 7-10U/kg.b.w./d--the dose not affecting erythropoiesis. Erythropoietin was administered subcutaneously, 3 times a week, for 12 weeks. In this way, we tried to evaluate the direct effects of erythropoietin action, not associated with a correction of anemia. After the therapy a statistically significant decrease was seen of total cholesterol (p < 0.01), LDL-cholesterol (p < 0.01) in serum of these patients. The concentration of triglycerides, HDL-cholesterol, glucose and insulin changed in a variable mode. We did not find any significant changes in hemoglobin and hematocrit levels, but despite of that we observed a significant decrease of lactate (p < 0.01). It seems that the global result of all mentioned changes was a great improvement in the "quality of life" of this group of patients.