Dialyzable Substance Research Articles

Sclerostin levels in uremic patients: a link between bone and vascular disease

Sclerostin is a marker of low-turnover bone disease in end stage renal disease patients. The aim of this study was to evaluate serum sclerostin in uremic patients, analyzing its behavior during a single hemodialysis session. Twenty-one adult patients on intermittent hemodialysis treatment were enrolled. Acetate Free Bio-filtration (AFB) was the technique employed. Uremic patients were characterized by higher levels of serum sclerostin when compared with values observed in healthy subjects. Sclerostin assessed in pre-dialysis samples was 1.4 ± 1.02 ng/mL, whereas, in post dialysis samples, a reduction of sclerostin values was observed (0.8 ± 0.6 ng/mL; p: 0.008). Sclerostin correlated with parameters of dialysis adequacy, such as creatinine levels and Kt/V values, and it was significantly associated with atherosclerotic disease. Receiver operating characteristics analysis revealed a good diagnostic profile in identifying atherosclerotic disease. Sclerostin, a full dialyzable substance during AFB dialysis, is closely associated with atherosclerotic disease. Its reduction obtained through AFB could represent a defensive mechanism, improving vascular disease and renal osteodystrophy.

Propofol in paediatric anaesthesia

In this review we intend to ascertain trends in propofol administration for paediatric anaesthesia and sedation. Propofol is being 'discovered' by non-anaesthesiologist practitioners of paediatric sedation. However it appears that the drug is not infrequently administered alone for painful procedures, necessitating large doses that result in uncontrolled general anaesthesia with a high potential for adverse events. An elegant technique comprises small doses of short-acting opioid (e.g. fentanyl 1 mug/kg) with low-dose propofol infusion. This does not result in worsening of pre-existing right-to-left intracardiac shunts. The dilemma is to educate non-anaesthesiologists about propofol pharmacokinetics and pharmacodynamics and in particular about the advantages of combined drug therapy. A paediatric target-controlled system for propofol has undergone preliminary clinical evaluation and it is hoped that administration according to pharmacokinetic principles will refine administration to infants and children. Sporadic cases of the propofol infusion syndrome in patients receiving prolonged sedation in intensive care units continue to be reported (characterized by metabolic acidosis, rhabdomyolysis and myocardial failure). It appears that one mechanism may be a deficiency of mitochondrial oxidative processes possibly induced by a dialyzable substance, perhaps a propofol metabolite. Propofol has been used with some success in treating postoperative laryngospasm and for tracheal intubation without muscle relaxants. Propofol should be used with extreme caution for prolonged sedation in intensive care unit patients, at dose rates of below 5 mg/kg per h, while maintaining extreme vigilance for signs of developing propofol infusion syndrome. If used correctly propofol is a suitable drug for sedation outside the operating room.

The Postdialytic Rise in the Plasma Total Homocysteine Concentration Is Delayed

Background/Aims: The mechanism behind the uremic hyperhomocysteinemia has not been elucidated. Possibly, dialyzable uremic toxins play a role, e.g. as enzyme inhibitors. If so, the conditions for enzymatic removal would be expected to improve after dialysis. Therefore, we studied the postdialytic pattern of the plasma total homocysteine (tHcy) concentration. Methods: We collected blood samples from 19 stable, vitamin-supplemented hemodialysis patients before and at 5, 60, as well as at 480 min after a dialysis session. The patients were studied after dialysis with a low-flux dialyzer (Polyflux 6L) and a high-flux dialyzer (Polyflux 14S). Results: The mean predialytic plasma tHcy concentration was 13.3 µmol/l which is considerably lower than the concentrations observed in our previous studies. In all patients, the plasma tHcy concentration fell during treatment with both types of dialyzers (average decrease 28 ± 7%, p < 0.0001, and 31 ± 8%, p < 0.0001, respectively). No postdialytic change in the plasma tHcy concentration was observed at 60 min after low-flux dialysis, however, after high-flux dialysis, the plasma tHcy concentration was significantly lower at 60 min postdialysis than at 5 min (3 ± 8%, p < 0.05). At 480 min after dialysis, a significant postdialytic increase in the plasma tHcy concentration was found (6 ± 9%, p < 0.01, and 11 ± 5%, p < 0.0001, respectively) both in the case of low-flux and high-flux treatment. Conclusions: In the postdialytic phase, we observed a short-lived stability in the plasma tHcy concentration, and in the case of high-flux dialysis, even a slight decrease in the plasma tHcy concentration. The results support the hypothesis that dialyzable substances interfere with homocysteine removal.

Monitoring cardiovascular changes during hemodialysis in children.

Hemodialysis (HD) causes rapid volume shifts and circulatory changes. In chronic renal failure (CRF) Na+/K+ATP-ase is depressed, whereas endogenous digoxin-like factor (EDLF) is elevated. Our aim was to characterize HD-induced cardiovascular adaptation and its possible links to Na+/K+ATP-ase and EDLF. Eleven children with CRF on HD (aged 14.7 +/- 3.7 years) and 11 healthy children were investigated for basic circulatory parameters. Thoracic impedance (Zo) and circulatory parameters were monitored by impedance cardiography (ICG) during HD. Erythrocyte Na+/K+ATP-ase and EDLF were measured before and after HD. Up to the loss of 6% of total body weight, Zo rose linearly with fluid removal, above this no further increase occurred. Heart rate and mean arterial pressure (MAP) were inversely related (r = -0.97); MAP rose in the first and decreased in the second part of HD. Systemic vascular resistance paralleled MAP, whereas stroke volume rapidly decreased, but stabilized in the second part of HD. The ratio of preejection period/ventricular ejection time (PEP/VET) correlated positively with HD duration (r = 0.92), suggesting diminished cardiac filling. Cardiac index (CI) remained stable. EDLF was high in uremia accompanied by depressed Na+/K+ATP-ase (P < 0.05 and P < 0.01, respectively). Following HD Na+/K+ATP-ase normalized. Correlation between Na+/K+ATP-ase activity and MAP was linear (r = 0.85). In conclusion, ICG during HD provides detailed information concerning circulatory adaptation resulting in stable CI, suggesting that the dialysis-induced hypovolemia is compensated by the centralization of the blood volume. Changes of Na+/K+ATP-ase indicate that dialyzable blood pressure-regulating substance(s) inhibit(s) the pump. However, lack of further correlation between Na+/K+ATP-ase, EDLF, and cardiovascular parameters indicates the complexity of the regulatory processes.

Cardiac Troponin T Is Elevated in Asymptomatic Patients With Chronic Renal Failure

Patients with chronic renal failure (CRF) are at increased risk for myocardial events that are difficult to evaluate due to atypical symptoms and chronically elevated protein markers of cardiac damage. This study evaluated cardiac troponin T (cTnT), a sensitive marker of cardiac injury, in patients with CRF without myocardial infarction symptoms, and assessed potential causes for elevated cTnT. Blood was obtained from 38 patients with CRF immediately before hemodialysis and from 16 of them post-dialysis, from 21 peritoneal dialysis patients, 10 patients with CRF not on dialysis, 11 patients with cardiomyopathy, and 10 adolescent patients with CRF undergoing hemodialysis. Samples were analyzed for myoglobin, creatine kinase, creatine kinase isoenzyme-MB (CK-MB), lactate dehydrogenase, lactate dehydrogenase isoenzyme-1 (LD-1), and cTnT. Cardiac TnT was elevated in: 71% of patient with CRF undergoing hemodialysis with no significant differences between pre- and post-dialysis values, 57% of patients with CRF on peritoneal dialysis, 30% of patients with CRF without dialysis, 18% of patients with cardiomyopathy, and 20% of adolescent patients with CRF undergoing hemodialysis. Myoglobin was elevated in almost all patients with CRF undergoing hemodialysis and without dialysis, whereas CK-MB and LD-1 were rarely elevated. Cross-reacting dialyzable substances and myocardial stretch were not major causes for elevated cTnT. Until future studies clarify the etiology of elevated cTnT in patients with CRF, results should be interpreted cautiously.

Glutamate release from the ovine fetal brain during maternal hemorrhage. A study using chronic in utero cerebral microdialysis.

Glutamate has been implicated in the pathophysiology of neuronal injury associated with cerebral hypoxia-ischemia. A model using chronic in utero microdialysis was developed to sample the extracellular space of the fetal brain. Using this model, we tested the hypothesis that glutamate efflux from the parasagittal parietal cortex of near-term fetuses would increase during maternal hemorrhage. Twelve near-term fetal sheep were instrumented with vascular catheters, and a microdialysis probe(s) was implanted into the parasagittal parietal cortex. After a 3-day recovery period, the animals were subjected to maternal hemorrhage until either the fetal pH was < 7.00 or the fetus died. The extracellular glutamate concentration in the collected dialysate was determined by high pressure liquid chromatography (HPLC). Maternal hemorrhage resulted in an 80-90% decrease in uterine blood flow, a decrease fetal po2, and a mixed metabolic and respiratory fetal acidosis. There were two groups of fetuses, survivors (n = 5) and nonsurvivors (n = 7). The nonsurvivor group showed a large increase (10-30-fold) in peak glutamate release (P = 0.0015). Survivors demonstrated a small (threefold) increase that was not statistically significant (P = 0.065), unless one animal with very low probe recovery was excluded (P = 0.0048). Extracellular glutamate release from the fetal brain can occur during maternal hemorrhage with fetal acidemia. The pathophysiologic role (if any) of glutamate release in the survivors remains to be elucidated. Our results are consistent with the hypothesis that in utero release of glutamate occurs during periods of fetal asphyxia. This experimental preparation of chronic fetal brain microdialysis can be used to monitor the brain extracellular concentration of any dialyzable substance in response to stress, including maternal hemorrhage.

Factors affecting the ethanol productivity of yeast in molasses

The ethanol production by a laboratory yeast strain, X2180-1B, was less than half that by an alcohol yeast, YOY655, in a molasses medium containing 30% sugars, although X2180-1B produced approximately the same amount of ethanol as YOY655 in a nutrition medium with the same sugar content. The weak productivity of X2180-1B in the molasses was ascribed to the limitation of sucrose hydrolysis in the molasses. The invertase activity of X2180-1B was 0.019 (mmol sucrose/min/mg protein) in the nutrition medium, but substantially zero in the molasses, while that of YOY655 was 1.75 in the nutrition medium and 1.15 even under the inhibitory conditions in molasses. External addition of invertase greatly enhanced the ethanol productivity of only X2180-1B. The inhibitory factors of invertase in molasses were heat-stable and dialyzable substances.

Antipyrine as a dialyzable reference to correct differences in efficiency among and within sampling devices during in vivo microdialysis

Antipyrine was investigated as a dialyzable substance that could be used to quantitate relative differences in the efficiency of dialysis among multiple microdialysis probes and by a single probe over time. The contribution of effective membrane surface area to recovery variability was tested by the introduction of air into microdialysis probes. Reduction of effective membrane surface area reduced antipyrine recovery. Dialysates from probes implanted in the jugular vein, brain, and liver of rats receiving antipyrine demonstrated differences in antipyrine concentration among probes within the same rat. These results suggest dissimilar efficiencies of the probes to recover antipyrine, which should be uniformly distributed throughout body water. Dialysates from blood, brain, and liver probes in rats that received both antipyrine and tritiated water ( 3H 2O) showed differences in antipyrine and 3H 2O concentrations among probes. Variability of antipyrine and 3H 2O concentrations over time within a probe were positively correlated, suggesting that the cause(s) of temporal variability affected both of these markers of body water. Correction of antipyrine tissue/ blood ratios, using 3H 2O blood/tissue ratios from the same sampling period, reduced the variability in antipyrine tissue/blood ratios, producing ratios closer to the expected value of 1. Differences in probe efficiency contributing to the variability of antipyrine and 3H 2O recovery would also be expected to influence the recovery of other substances during microdialysis. The administration of antipyrine during microdialysis experiments is suggested to enable reduction of temporal and site-related differences in substance recovery that are due to differences in probe efficiency. Other methods are necessary to determine the actual extracellular concentration of dialyzed substances and the integrity of the blood-brain barrier.

An activity which restores theta toxin activity in some theta toxin-deficient mutants of Clostridium perfringens.

Group a mutants of Clostridium perfringens are deficient in theta toxin but release a dialyzable substance ("substance A"), which restores theta toxin activity to group b mutants, into a culture supernatant; group b mutants are defective in "substance A" release. "Substance A" activity appeared in the exponentially growing phase of group a mutants and disappeared in the stationary phase. "Substance A" activity was most stable at pH 5.0 and 0 C and even increased threefold in the first 5 hr, but gradually decreased during the following 15 hr. It was quickly inactivated at neutral and higher pHs at 0 C.

Polyamines in the anemia of end-stage renal disease

The improvement in the anemia in patients with end-stage renal disease (ESRD) on continuous ambulatory peritoneal dialysis (CAPD) suggests that dialyzable substances present in the sera of uremic patients either inhibit erythropoiesis directly or inactivate erythropoietin (EPO). In the present study predialysis sera from patients with ESRD inhibited erythroid colony (CFU-E) (N = 10) formation to a significantly (P less than 0.01) greater degree than granulocyte-macrophage (CFU-GM) (N = 7) colony formation in mouse bone marrow (MBM) cultures. The polyamines spermine (SP) (18 to 560 nm/ml) and spermidine (SD) (4 to 648 nm/ml) exerted a more significant (P less than 0.05) inhibition of CFU-E (N greater than or equal to 5) than that of CFU-GM (N greater than or equal to 5) growth. Concentrations of 0.80, 1.0, and 1.5 nm/ml of putrescine (PU) were 92%, 85%, and 77% of erythroid colony (CFU-E) controls (N = 4) and 104%, 130%, and 127% of CFU-GM controls (N = 4). Putrescine (PU) at 1.5 nm/ml also produced a significant (P less than 0.05) inhibition of CFU-E, whereas CFU-GM were stimulated by PU. These data suggest that predialysis sera from uremic patients, as well as SP, SD, and PU, are selectively more inhibitory to CFU-E than CFU-GM growth. The immunoreactivity of EPO was not significantly changed when it was coincubated with SP, SD and PU and measured by radioimmunoassay. PU was found to inhibit noncompetitively the bioactivity of EPO in a CFU-E assay. These data support the hypothesis that polyamines may be important uremic toxins in the anemia of ESRD.

Microbial manganese reduction mediated by bacterial strains isolated from aquifer sediments

One hundred and five strains isolated from aquifer sediments andEscherichia coli ML30S were tested for their ability to reduce manganese oxides. Eighty-two strains, includingE. coli, reduced manganese. In most cases the bacterial activity decreased the pH and Eh below 6.75 and 350 mV, respectively, enhancing a spontaneous and nonspecific reduction of manganese. However, for 12 strains the reduction was specifically catalyzed by bacteria; the high pH and Eh values would not permit a spontaneous reduction of manganese. Some of the most active strains were identified as genera common in soils and waters, i.e.,Pseudomonas, Bacillus, Corynebacterium, andAcinetobacter. Two strains were studied in detail. One of the strains, identified asPseudomonas fluorescens, required contact between the cells and the manganese oxides for reduction to occur. The reduction was inhibited by 15 mM of sodium azide. The other strain, identified asAcinetobacter johnsonii, catalyzed manganese reduction by an inductive and dialyzable substance which was excreted by the bacteria. The mechanism involved has not been previously demonstrated.

Studies on the growth of Eikenella corrodens strain 23834.

The growth characteristics and nutritional requirements of Eikenella corrodens strain 23834 were studied. Generation times, growth rates, and cell yields were determined employing a basal medium supplemented with yeast extract (YE), vitamins, amino acids, phosphate, nitrogen, and sulfate. Incubation was in a variety of air, CO2, and N2 atmospheres. Incubation statically in air or in 10% CO2+ 90% air did not affect the growth rate, while Na2CO3, bubbling with various atmospheres, shaking, or anaerobic incubation all decreased the growth rate. Atmospheric CO2 was found not to be a requirement for growth. The addition of 1‐2.5% YE decreased the generation time and increased the cell yield. The growth‐promoting factor(s) of YE was a low molecular weight, water‐soluble, dialyzable substance which is stable to and not extractable by chloroform‐methanol. Vitamins and amino acids singly or in combination were slightly growth‐promoting and purines, pyrimidines, and acetate had no effect on Eikenella growth. Increasing concentrations of phosphate inhibited growth, while nitrate but not sulfate proved essential for growth.

Hemoglobin Production in Human Bone Marrow Cultures Is Inhibited by Lyophilized Coagulation Factor Concentrates

Transfusion of blood products may be followed by viral hepatitis and aplastic anemia despite improved techniques for prevention. In view of the need for intensive therapy of hemophilia with blood products, the authors investigated the capacity of these concentrates to influence cultures of human bone marrow cells. Factor VIII concentrates contained a heat-stable dialyzable substance(s) that drastically impaired 59Fe incorporation in normal human bone marrow. Factor IX concentrates had less and cryoprecipitate had no such inhibitory activity. These studies may offer information regarding the effects of various blood products on bone marrow function.

A tetrodotoxin-like substance found in the Brazilian frog Brachycephalus ephippium

A tetrodotoxin-like substance, denoted ephippiotoxin, was obtained from the tissues of Brachycephalus ephippium, a small pumpkin-coloured frog collected in the Atlantic Forest of the southeast region of Brazil. Ephippiotoxin is a dialyzable substance soluble in water, methanol and ethanol, but insoluble in organic solvents such as chloroform and other apolar solvents. After treatment with active charcoal (Norit-A) and purification with ion-exchange Amberlite IRC-50 resin (NH 4 + form), a freeze-dried residue was obtained, with a toxicity of c. 117 μg/kg (mice, i.p.). Ephippiotoxin showed the same mobility as crystalline tetrodotoxin (Sankyo) when submitted to thin-layer chromatography (silica gel G) using seven different solvent systems. White mice (20 ± 1 g) injected i.p. with either B. ephippium tissue extracts or semi-purified toxin showed partial paralysis of the hind limbs, lethargy, altered breathing rhythm and clonic convulsions. Death occurred within 1.5 – 30 min after injection, depending on the dose. Ephippiotoxin induced atrioventricular diastolic blockade in the toad heart. It also inhibited the response of toad striated muscle to direct and indirect electric stimulation and blocked the compound action potential of isolated frog sciatic nerve.

Impaired metabolism of guanidinoacetic acid in uremia.

In order to investigate the guanidinoacetic acid (GAA) metabolism in uremia, we have measured serum guanidino compounds in patients with chronic renal failure (CRF) in comparison with normal subjects, and the renal content of GAA and glycine amidinotransferase (GAT) activity in the kidney of experimental CRF rabbits. Serum concentrations of guanidinosuccinic acid (GSA) and methylguanidine (MG) in the patients with CRF were higher than those in the normal subjects, as well as serum urea nitrogen (BUN) and creatinine (Cr) levels. The serum GAA levels were however, significantly lower and showed a tendency to decrease inversely with the elevation of BUN in the patients with CRF under conservative therapy. On the contrary, in the patients under maintenance hemodialysis (MHD) therapy, the serum GAA level did not decrease in spite of the elevation of BUN. Four anephric patients under MHD therapy showed a level of serum GAA similar to the other MHD patients. In the CRF rabbits, the renal GAA content was significantly lower than in the sham-operated rabbits and showed an inverse correlation with BUN. Renal GAT activity was also significantly lower in the CRF rabbits, showing a positive correlation with serum GAA concentration and an inverse correlation with BUN. These results indicate that renal GAT activity decreases as the BUN level rises in the course of renal damage, resulting in lower concentration of serum GAA in the uremic state; in a more advanced stage of renal failure, the inability of the kidney to synthesize GAA may be compensated by other organ(s). Some dialyzable substances which might inhibit renal GAT activity may also be present.

Changes in insulin binding during hemodialysis in uremic patients.

To investigate factors responsible for altered insulin sensitivity in uremia, we studied 125I-insulin binding to erythrocytes in 20 uremic patients before and after dialysis. In uremic patients, predialysis binding was 50% lower in comparison with healthy controls (4.35 +/- 1.79 vs. 9.37 +/- 1.30%; p less than 0.01). Five-hour dialysis treatment resulted in a rapid increase in binding (on average to 55%; p less than 0.01). During the course of dialysis, binding to erythrocytes from 2 selected patients steadily increased in a time-dependent manner (on average 24%/h). The dialysis-induced increase in binding did not correlate with the changes in plasma insulin levels, but depended on the efficiency of dialysis as assessed by a relative decrease in plasma urea and creatinine. After an intravenous glucose load, the insulin-to-glucose ratio decreased in parallel with the increase in binding after dialysis. The results indicate that uremic plasma contains dialyzable substances which reversibly inhibit insulin binding, leading to altered insulin sensitivity.

A new sea urchin toxin and its effect on spontaneous transmitter release at frog neuromuscular junctions.

The authors extracted a dialyzable substance from sea urchin (Diadematidae) collected in Fiji, and investigated its effect on the frequency of miniature endplate potentials (MEPPs) in the sartorius muscle of the frog. This substance was shown to be different from previously known biologically active substances in many respects. The increase of MEPP frequency by the application of toxin was significant and dose-dependent. The frequency began increasing immediately after application and returned to normal after washing. This increasing action of toxin on MEPP frequency was strengthened by increased calcium concentration, but even in Ca-depleted solution toxin action was significant. Toxin action in Ca-free Mg2+ solution was found to be just as remarkable as in Ca2+ solution, and was dependent on magnesium concentration. Toxin action was also found to depend significantly on sodium concentration. The toxin did not change membrane potential of the muscle appreciably. From these results, the depolarization of the nerve terminal was not considered to be the main effect of toxin on MEPP frequency. The increasing action of toxin on MEPP frequency was interpreted as being the result of increased permeability of the nerve terminal to both divalent cations and Na+.

Effect of hemodialysis on somatosensory evoked potentials in uremia patients

Spinal and cortical potentials in response to unilateral stimulation of the median nerve of the wrist were recorded in 13 uremic patients, 1 h prior to and 1 h after dialysis. A comparison of the data from these patients with those of a control group revealed a slowing of impulse conduction in the peripheral nerve only, whereas the central part of the somatosensory system was not affected. Amplitudes of the evoked potentials tended to increase after dialysis. This could be due to a decrease of descending inhibition or a transitory change of the resting membrane potential caused by the elimination of dialyzable substances.

Endogenous cryogen excreted by the kidneys.

Injection (iv) of human urine into rabbits results in a fall in body temperature accompanied by peripheral vasodilation in a thermoneutral ambient temperature and suppression of shivering metabolism in the cold. There were no consistent changes in mean arterial pressure in response to the injection of urine. If the production of urine is prevented by occlusion of the ureters of rabbits, body temperature falls. Injection of endogenous pyrogen (iv) into rabbits, which have had their ureters occluded, results in a significant attenuation in the magnitude of the fever as compared to controls. These observations suggest that there is an endogenously produced cryogenic substance ("endogenous cryogen") normally excreted in an active form by the kidneys and which when either injected, or prevented from being excreted (by clamping the ureters), results in a regulated fall in body temperature. In addition, in human patients on regular dialysis treatment who still had residual renal function, the oral temperature was slightly below normal before hemodialysis and slightly above normal after hemodialysis, a difference averaging 0.39 degrees C (P less than 0.001). These data are in agreement with the hypothesis that endogenous cryogen is a dialyzable substance, and that its concentration is reduced (and therefore the patient's body temperature rises) during hemodialysis.

Two factors affecting on iron-oxidizing activities of Thiobacillus ferrooxidans.

The solubilization method of the iron-oxidizing system of T. ferrooxidans was investigated. Two factors affected the iron-oxidizing and cytochrome-oxidizing activities of the bacterium, and they were separated by sonication in different ionic strengths of potassium phosphate buffer (pH 7.5). One of them stimulated both activities and was tentatively called the stimulating factor. The other inhibited both activities and was tentatively called the inhibiting factor. The stimulating factor was a light yellowish-green and heat labile substance. The inhibiting factor was a fairly heat stable and not dialyzable substance and masked the stimulating factor activity.