Urinary Excretion of Creatol, an In Vivo Biomarker of Hydroxyl Radical, in Patients with Chronic Renal Failure

Creatol (CTL) is a hydroxyl radical adduct of creatinine (Cr). The serum methylguanidine (MG) level and the MG/Cr molar ratio are reported to be biomarkers for oxidative stress. The aim of this study was to examine whether urinary excretion of CTL, another oxidative stress-related marker, is increased in patients with chronic renal failure (CRF). One hundred twenty-four non-dialyzed patients with chronic renal failure (serum Cr level, 1.3-10.0 mg/dL) were recruited from our hospitals. Urine and serum levels of CTL and MG were determined by high-performance liquid chromatography with the use of 9, 10- phenanthrenequinone as a fluorogenic reagent. The CTL/Cr and (CTL+MG)/Cr molar ratios in spot urine samples were also compared with those in 24-h urine samples. The urinary CTL/Cr and (CTL+MG)/Cr molar ratios increased with decreases in Cr clearance in patients with CRF. Correlations between serum and spot urine (CTL+MG)/Cr and between serum and spot urine CTL/Cr were quite similar to those in 24-h urine samples. CTL/Cr and (CTL+MG)/Cr molar ratios in both 24-h urine and spot urine samples appear to be useful indices of the severity of CRF.

Oxidative and nitrosative mediators in hepatic injury caused by whole body hyperthermia in rats

The involvement of oxidative and nitrosative mediators in liver injury caused by heat stress remains unclear. This study aimed to elucidate the role of endothelial nitric oxide synthase (eNOS), and inducible NOS (iNOS)-derived NO and nitrotyrosine in the whole-body hyperthermia (WBH)-induced liver injury. Rats were anesthetized with intraperitoneal pentobarbital, and were exposed to a heating lamp for 60 min to raise the core temperature to 42.5 degrees C. The rats were maintained at the hyperthermic state for an additional 50 min. Blood urea nitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, lactic dehydrogenase, creatine phosphokinase, amylase, lipase, nitrate/nitrite, methyl guanidine, and proinflammatory cytokines (tumor necrosis factoralpha, interleukin-1beta and interleukin-10) were measured before and 14 h after hyperthermia. Immunohistochemical staining was employed to detect the eNOS, iNOS and nitrotyrosine levels. Western blotting was used to examine the expression of heatshock protein 70 (HSP 70). Histopathological examination of the liver tissue was performed. WBH caused liver injury accompanied with significant increases in biochemical factors, nitrate/nitrite, methyl guanidine, and proinflammatory cytokines. In addition, WBH enhanced the eNOS, iNOS, nitrotyrosine and HSP 70 levels. WBH caused hepatic injury. The pathogenetic mechanism is likely mediated through the NOS-derived NO, free radical, proinflammatory cytokines and nitrotyrosine. The enhanced expression of HSP 70 may play a protective role.

The detrimental role of inducible nitric oxide synthase in the pulmonary edema caused by hypercalcemia in conscious rats and isolated lungs

We aim to test the hypothesis that hypercalcemia produces pulmonary edema (PE) and to elucidate the mechanism. Experimentations were carried out in conscious rats and isolated perfused rat lungs. We evaluated PE by lung weight changes, protein concentration in bronchoalveolar lavage, dye leakage, and microvascular permeability. Plasma nitrate/nitrite, methyl guanidine (MG), proinflammatory cytokines, procalcitonin levels, and histopathological examinations were evaluated. Immunochemical staining and reverse-transcriptase polymerase chain reaction (RT-PCR) were used to detect inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) in the lungs. Hypercalcemia was produced in the conscious rat and isolated perfused lungs. Calcitonin and L-N(6) (1-iminoethyl)-lysine (L-Nil) were administered before hypercalcemia to observe their effects. Hypercalcemia caused severe PE in rats. Pathological and immunochemical examinations revealed hemorrhagic edema with iNOS activity in the alveolar macrophages and epithelial cells. RT-PCR showed an increase in iNOS mRNA expression. Hypercalcemia increased nitrate/nitrite, MG, proinflammatory cytokines and procalcitonin levels. Pretreatment with calcitonin or L-Nil prevented these changes. In conclusion, hypercalcemia caused PE in conscious rats and isolated perfused rat lungs. The increases in nitrate/nitrite, free radicals, proinflammatory cytokines, procalcitonin and iNOS activity suggest that hypercalcemia induces a sepsis-like syndrome. The effect of hypercalcemia on the lung may involve iNOS and NO.

Clinical and pathological features of fat embolism with acute respiratory distress syndrome

FES (fat embolism syndrome) is a clinical problem, and, although ARDS (acute respiratory distress syndrome) has been considered as a serious complication of FES, the pathogenesis of ARDS associated with FES remains unclear. In the present study, we investigated the clinical manifestations, and biochemical and pathophysiological changes, in subjects associated with FES and ARDS, to elucidate the possible mechanisms involved in this disorder. A total of eight patients with FES were studied, and arterial blood pH, PaO(2) (arterial partial pressure of O(2)), PaCO(2) (arterial partial pressure of CO(2)), biochemical and pathophysiological data were obtained. These subjects suffered from crash injuries and developed FES associated with ARDS, and each died within 2 h after admission. In the subjects, chest radiography revealed that the lungs were clear on admission, and pulmonary infiltration was observed within 2 h of admission. Arterial blood pH and PaO(2) declined, whereas PaCO(2) increased. Plasma PLA(2) (phospholipase A(2)), nitrate/nitrite, methylguanidine, TNF-alpha (tumour necrosis factor-alpha), IL-1beta (interleukin-1beta) and IL-10 (interleukin-10) were significantly elevated. Pathological examinations revealed alveolar oedema and haemorrhage with multiple fat droplet depositions and fibrin thrombi. Fat droplets were also found in the arterioles and/or capillaries in the lung, kidney and brain. Immunohistochemical staining identified iNOS (inducible nitric oxide synthase) in alveolar macrophages. In conclusion, our clinical analysis suggests that PLA(2), NO, free radicals and pro-inflammatory cytokines are involved in the pathogenesis of ARDS associated with FES. The major source of NO is the alveolar macrophages.

Inhibition of inducible nitric oxide synthase attenuates acute endotoxin-induced lung injury in rats

1. In the present study, we investigated the effects of the inducible nitric oxide (iNOS) inhibitors S-methylisothiourea (SMT) and l-N(6)-(1-iminoethyl)-lysine (l-Nil) on endotoxin-induced acute lung injury (ALI), as well as the associated physiological, biomedical and pathological changes, in anaesthetized Sprague-Dawley rats and in rat isolated perfused lungs. 2. Endotoxaemia was induced by an intravenous (i.v.) infusion of lipopolysaccharide (LPS; Escherichia coli 10 mg/kg). Lipopolysaccharide produced systemic hypotension and tachycardia. It also increased the lung weight/bodyweight ratio, lung weight gain, exhaled nitric oxide (NO), the protein concentration in bronchoalveolar lavage and microvascular permeability. 3. Following infusion of LPS, plasma nitrate/nitrite, methyl guanidine, pro-inflammatory cytokines (tumour necrosis factor-alpha and interleukin-1beta) were markedly elevated. Pathological examination revealed severe pulmonary oedema and inflammatory cell infiltration. Pretreatment with SMT (3 mg/kg, i.v.) or l-Nil (3 mg/kg, i.v.) significantly attenuated the LPS-induced changes and ALI. 4. The results suggest that the inflammatory responses and ALI following infusion of LPS are due to the production of NO, free radicals and pro-inflammatory cytokines through the iNOS system. Inhibition of iNOS is effective in mitigating the endotoxaemic changes and lung pathology. Inhibitors of iNOS may be potential therapeutic agents for clinical application in patients with acute respiratory distress syndrome.

Ischemia/Reperfusion of the Liver Induces Heart Injury in Rats

OBJECTIVE

We evaluated the cardiovascular injury induced by ischemia and reperfusion (I/R) of the liver by measuring changes in blood levels of cardiac troponin I (cTNI), an index of cardiovascular injury, as well as levels of selected indicators of an inflammatory response.

MATERIALS AND METHODS

Ischemia was induced in the rat liver by clamping the common hepatic artery and portal vein for 40 minutes, after which flow was restored, and the liver reperfused for 90 minutes. Blood samples were collected prior to ischemia and after reperfusion. cTNI as well as levels of tumor necrosis factor alpha (TNFalpha), hydroxyl radical (.OH), nitric oxide (NO), and alanine transferase (ALT) were measured.

RESULTS

I/R of the liver induced a significant increase in ALT (P<.001). Increased cTNI levels (P<.05) were associated with inflammatory responses, such as elevated levels of TNFalpha (P<.001), . OH (P<.001), and NO (P<.001). After administration of 3-aminobenzamide, a poly(ADP-ribose) polymerase (PARP) inhibitor, liver and heart injuries were significantly attenuated (P<.05).

CONCLUSIONS

I/R-induced liver injury was associated with cardiovascular injury, perhaps resulting from inflammatory responses triggered by elevated levels of reactive radical species of nitric oxide, superoxide, and peroxynitrite, by which PARP was activated. 3-Aminobenzamide, significantly attenuated I/R-induced liver and heart injuries.

Endotoxin-induced acute lung injury is enhanced in rats with spontaneous hypertension

1. Acute lung injury (ALI), or acute respiratory distress syndrome, is a major cause of mortality in endotoxaemia. The present study tested whether the endotoxaemia-induced changes and associated ALI were enhanced in rats with established hypertension and to examine the possible mechanisms involved. 2. Fifty spontaneously hypertensive rats (SHR) and the same number of normotensive Wistar Kyoto (WKY) rats, aged 12-15 weeks, were used. The experiments were performed in conscious, unanaesthetized rats. Endotoxaemia was produced by intravenous lipopolysaccharide (LPS; 10 mg/kg). N(G)-Nitro-L-arginine methyl ester (L-NAME; 10 mg/kg, i.v.), L-N(6)-(1-iminoethyl)-lysine (L-Nil; 5 mg/kg, i.v.) and 3-morpholinosydnonimine (SIN-1; 5 mg/kg, i.v.) were given 5 min before LPS to observe the effects of nitric oxide synthase (NOS) inhibition and nitric oxide (NO) donation. 3. We monitored arterial pressure and heart rate and evaluated ALI by determining the lung weight/bodyweight ratio, lung weight gain, leakage of Evans blue dye, the protein concentration in bronchoalveolar lavage and histopathological examination. Plasma nitrate/nitrite, methyl guanidine, pro-inflammatory cytokines, including tumour necrosis factor-alpha and interleukin-1beta, and lung tissue cGMP were determined. Expression of mRNA for inducible and endothelial NOS was examined using reverse transcription-polymerase chain reaction. 4. Lipopolysaccharide caused systemic hypotension, ALI and increases in plasma nitrate/nitrite, methyl guanidine, pro-inflammatory cytokines and lung cGMP content. The LPS-induced changes were greater in SHR than in WKY rats. Pretreatment with L-NAME or L-Nil attenuated, whereas the NO donor SIN-1 aggravated, the endotoxin-induced changes. 5. In conclusion, rats with genetic hypertension are more susceptible to endotoxaemia and this results in a greater extent of ALI compared with normotensive WKY rats.

Propofol exerts protective effects on the acute lung injury induced by endotoxin in rats

Acute lung injury (ALI) is a major culprit of mortality in endotoxemia. Propofol has been commonly used in critical ill patients for sedation. This experiment attempted to elucidate the effects and possible mechanisms of propofol on the ALI induced by endotoxin. Experimentations were carried out using anesthetized, ventilated rats and isolated perfused rat lungs. Endotoxemia was induced by intravenous lipopolysaccharide (LPS, 10 mg kg(-1)). Various groups of rats received infusion of physiological saline solution (PSS) and LPS. Five min after LPS, propofol at low dose (5 mg kg(-1)h(-1)) or high dose (10 mg kg(-1)h(-1)) was infused for 6h. In isolated perfused rat lungs, PSS, LPS, and propofol (30 or 60 mg kg(-1)) were added into the perfusion circuit. During or after 6h observation, we determined the lung weight (LW)/body weight ratio, LW gain, exhaled nitric oxide (NO) and protein concentration in broncheoalveolar lavage. Lung pathology was evaluated to quantify the lung injury score. Plasma nitrate/nitrite, methyl guanidine (MG), tumor necrosis factor(alpha), and interleukin-1(beta) were examined. Blood leukocytes were counted. Capillary filtration coefficient (K(fc)) was obtained in isolated perfused lungs. Posttreatment of propofol at low or high dose attenuated or prevented the extent of ALI. It also reduced the plasma nitrate/nitrite, MG, and pro-inflammatory cytokines including tumor necrosis factor(alpha) (TNF(alpha)) and interleukin-1(beta) (IL-1(beta)). In the isolated perfused rat lungs, propofol significantly reduced the LPS-induced increase in K(fc). This agent did not affect the leukocytopenia caused by LPS. Accordingly, the effects of propofol on the ALI were not related to leukocyte activation or sequestration. Our results suggest that propofol exerts protective effect on the endotoxin-induced ALI. The mechanisms of actions may be mediated through inhibition on the release of pro-inflammatory cytokines, free radicals and NO. In addition, propofol abrogates the microvascular leakage of water and protein in the lungs. The results imply that the use of propofol in critically ill is not only for sedation, but also useful for the prevention of inflammatory progression and lung damage.

N-acetylcysteine abrogates acute lung injury induced by endotoxin

1. Acute lung injury (ALI) or acute respiratory distress syndrome is a serious clinical problem with high mortality. N-Acetylcysteine (NAC) is an anti-oxidant and a free radical scavenger. It has been reported recently that NAC ameliorates organ damage induced by endotoxin (lipopolysaccharide; LPS) in conscious rats. The present study was designed to evaluate the effects of NAC on LPS-induced ALI and other changes in anaesthetized rats. 2. Sprague-Dawley rats were anaesthetized with pentobarbital (40 mg/kg, i.p.). Endotracheal intubation was performed to provide artificial ventilation. Arterial pressure and heart rate were monitored. The extent of ALI was evaluated with the lung weight (LW)/bodyweight ratio, LW gain, exhaled nitric oxide (NO) and protein concentration in bronchoalveolar lavage (PCBAL). Haematocrit, white blood cells, plasma nitrate/nitrite, methyl guanidine (MG), tumour necrosis factor (TNF)-alpha and interleukin (IL)-1b were measured. Pathological changes in the lung were examined and evaluated. 3. Endotoxaemia was produced by injection of 10 mg/kg, i.v., LPS (Escherichia coli). Animals were randomly divided into three groups. In the vehicle group, rats received an i.v. drip of physiological saline solution (PSS) at a rate of 0.3 mL/h. The LPS group received an i.v. drip of PSS for 1 h, followed by LPS (10 mg/kg by slow blous injection, i.v., over 1-2 min). Rats in the LPS + NAC group received NAC by i.v. drip at a rate of 150 mg/kg per h (0.3 mL/h) for 60 min starting 10 min before LPS administration (10 mg/kg by slow blous injection, i.v., over 1-2 min). Each group was observed for a period of 6 h. 4. N-Acetylcysteine treatment improved the LPS-induced hypotension and leukocytopenia. It also reduced the extent of ALI, as evidenced by reductions in LW changes, exhaled NO, PCBAL and lung pathology. In addition, NAC diminished the LPS-induced increases in nitrate/nitrite, MG, TNF-a and IL-1b. 5. In another series of experiments, LPS increased the mortality rate compared with the vehicle group (i.v. drip of PSS at a rate of 0.3 mL/h) during a 6 h observation period. N-Acetylcysteine, given 10 min prior to LPS, significantly increased the survival rate. 6. The results of the present study suggest that NAC exerts a protective effect on the LPS-induced ALI. The mechanisms of action may be mediated through the reduction of the production of NO, free radicals and pro-inflammatory cytokines.

Ascorbate Supplement Reduces Oxidative Stress in Dyslipidemic Patients Undergoing Apheresis

OBJECTIVE

The effect of ascorbate treatment on apheresis-induced oxidative stress in uremic and dyslipidemic patients was evaluated.

METHODS AND RESULTS

We developed a chemiluminescence-emission spectrum and high-performance liquid chromatography analysis to assess the effect of ascorbate supplement on plasma reactive oxygen species (ROS) scavenging activity and oxidized lipid/protein production in hyperlipidemic and uremic patients undergoing apheresis. Apheresis was efficient in reduction of atherogenic lipoproteins, complement, fibrinogen, soluble intercellular adhesion molecule-1, and oxidative parameters including phosphatidylcholine hydroperoxide (PCOOH), malonaldehyde, methylguanidine, and diotyrosine. Apheresis itself, however, activated leukocytes to increase ROS activity and reduced the plasma ROS scavenging activity. Ascorbate administration selectively diminished apheresis-enhanced H2O2 and inflammatory mediators such as tumor necrosis factor alpha (TNF-alpha) and monocyte chemoattractant protein-1. Chronically dyslipidemic and uremic patients undergoing biweekly apheresis plus ascorbate treatment had lower levels of C-reactive protein and PCOOH than did those without ascorbate treatment during a 6-month follow-up study period.

CONCLUSIONS

We demonstrate that apheresis with ascorbate treatment provides a therapeutic potential in reducing atherosclerotic risk via inhibition of H2O2-induced oxidative stress in patients with uremia or dyslipidemia.

N-Acetylcysteine ameliorates lipopolysaccharide-induced organ damage in conscious rats

Lipopolysaccharide is strongly associated with septic shock, leading to multiple organ failure. It can activate monocytes and macrophages to release proinflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and nitric oxide (NO). The present experiments were designed to induce endotoxin shock by an intravenous injection of Klebsiella pneumoniae lipopolysaccharide (LPS, 10 mg/kg) in conscious rats. Arterial pressure and heart rate (HR) were continuously monitored for 48 h after LPS administration. N-Acetylcysteine was used to study its effects on organ damage. Biochemical substances were measured to reflect organ functions. Biochemical factors included blood urea nitrogen (BUN), creatinine (Cre), lactic dehydrogenase (LDH), creatine phosphokinase (CPK), aspartate transferase (GOT), alanine transferase (GPT), TNF-alpha, IL-1 beta, methyl guanidine (MG), and nitrites/nitrates. LPS caused significant increases in blood BUN, Cre, LDH, CPK, GOT, GPT, TNF-alpha, IL-1 beta, MG levels, and HR, as well as a decrease in mean arterial pressure and an elevation of nitrites/nitrates. N-Acetylcysteine suppressed the release of TNF-alpha, IL-1 beta, and MG, but enhanced NO production. These actions ameliorate LPS-induced organ damage in conscious rats. The beneficial effects may suggest a potential chemopreventive effect of this compound in sepsis prevention and treatment.

The protective effect of niacinamide on ischemia-reperfusion-induced liver injury

Reperfusion of ischemic liver results in the generation of oxygen radicals, nitric oxide (NO) and their reaction product peroxynitrite, all of which may cause strand breaks in DNA, which activate the nuclear enzyme poly(ADP ribose)synthase (PARS). This results in rapid depletion of intracellular nicotinamide adenine dinucleotide and adenosine 5'-triphosphate (ATP) and eventually induces irreversible cytotoxicity. In this study, we demonstrated that niacinamide, a PARS inhibitor, attenuated ischemia/reperfusion (I/R)-induced liver injury. Ischemia was induced by clamping the common hepatic artery and portal vein of rats for 40 min. Thereafter, flow was restored and the liver was reperfused for 90 min. Blood samples collected prior to I and after R were analyzed for methyl guanidine (MG), NO, tumor necrosis factor (TNF-alpha) and ATP. Blood levels of aspartate transferase (AST), alanine transferase (ALT) and lactate dehydrogenase (LDH) which served as indexes of liver injury were measured. This protocol resulted in elevation of the blood NO level (p < 0.01). Inflammation was apparent, as TNF-alpha and MG levels were significantly increased (p < 0.05 and p < 0.001). AST, ALT and LDH were elevated 4- to 5-fold (p < 0.001), while ATP was significantly diminished (p < 0.01). After administration of niacinamide (10 mM), liver injury was significantly attenuated, while blood ATP content was reversed. In addition, MG, TNF-alpha and NO release was attenuated. These results indicate that niacinamide, presumably by acting with multiple functions, exerts potent anti-inflammatory effects in I/R-induced liver injury.

Influence of 72% injury in one kidney on several organs involved in guanidino compound metabolism: a time course study

Arginine (Arg) produced from citrulline originates mostly from kidneys. Arg is involved in guanidino compound biosynthesis, which requires interorgan co-operation. In renal insufficiency, citrulline accumulates in the plasma in proportion to renal damage. Thus, disturbances in Arg and guanidino compound metabolism are expected in several tissues. An original use of the model of nephrectomy based on ligating branches of the renal artery allowed us to investigate Arg and guanidino compound metabolism simultaneously in injured (left) and healthy (right) kidneys. The left kidney of adult rats was subjected to 72% nephrectomy. Non-operated, sham-operated and nephrectomized rats were studied for a period of 21 days. Constant renal growth was observed only in the healthy kidneys. Guanidino compound levels were modified transiently during the first 48 h. The metabolism and/or tissue content of several guanidino compounds were disturbed throughout the experimental period. Arg synthesis was greatly reduced in the injured kidney, while it increased in the healthy kidney. The renal production of guanidinoacetic acid decreased in the injured kidney and its urinary excretion was reduced. The experimentally proven toxins alpha-keto-delta-guanidinovaleric acid and guanidinosuccinic acid (GSA) accumulated only in the injured kidney. The urinary excretion of GSA and methylguanidine increased in nephrectomized rats. When the injured kidney grew again, the level of some guanidino compounds tended to normalize. Nephrectomy affected the guanidino compound levels and metabolism in muscles and liver. In conclusion, the specific accumulation of toxic guanidino compounds in the injured kidney reflects disturbances in renal metabolism and function. The healthy kidney compensates for the injured kidney's loss of metabolic functions (e.g. Arg: production). This model is excellent for investigating renal metabolism when a disease destroys a limited area in one kidney, as is observed in patients.

Creatol, an oxidative product of creatinine in hemodialysis patients

Creatol (CTL) is a product resulting from the reaction of creatinine (Cr) with the hydroxyl radical and is identified as a precursor of methylguanidine (MG), a uremic toxin. In this study, we investigated serum CTL levels together with those of Cr and MG in 66 patients who were on maintenance hemodialysis (HD). Prior to dialysis, the mean serum levels of Cr, CTL and MG were 967 (= 11.1 mg/dl)+/-267 microM, 11.1+/-4.8 microM and 5.8+/-2.9 microM, respectively. The mean CTL level was about 1.1% that of Cr, and the CTL plus MG level was about 1.4% that of the Cr level. The reduction rates of Cr, CTL and MG by a single HD were 62.6 6.1%, 71.0+/-10.3% and 51.9+/-11.6%, respectively. The CTL level at 0.5, 1 and 6 h after HD increased rapidly by 20.7+/-8.7%, 31.7+/-14.7% and 80.1+/-27.3%, respectively. There was a significant correlation between CTL or CTL/Cr and parathyroid hormone in patients who had just undergone parathyroidectomy. No significant correlation was found between CTL or CTL/Cr and those factors which seems to be related to the predialysis levels of reactive oxygen. Therefore, because of the good clearance of CTL and its rapid conversion to MG, its usefulness for the estimation of hydroxyl radical generation in HD patients is limited.

Automatic system for the assay of guanidino compounds to assess uremic status and effect of hemodialysis

An automated HPLC system coupled with fluorometry was established for the sensitive, rapid, and accurate assay of serum guanidines. Naturally fluorescent materials characteristic of the sera of uremic patients (uremic fluorescences) which interfere with the assay were removed simultaneously with deproteinization. Application of this method revealed that the uremic patients who are capable of excreting urine under hemodialysis therapy show low serum guanidinosuccinic acid levels. The interval between hemodialysis sessions in one of these patients was prolonged while monitoring guanidinosuccinic acid level using the present method without any hazardous effect.

N epsilon-(carboxymethyl)lysine in blood from maintenance hemodialysis patients may contribute to dialysis-related amyloidosis

BACKGROUND

Recent studies demonstrated not only that advanced glycation end product could be found in amyloid tissue from patient with dialysis related amyloidosis, but also that amyloid beta2-microglobulin was modified with N(epsilon)-(carboxymethyl)lysine (CML). We wanted to determine if CML could be a biomarker in these patients.

METHODS

To raise polyclonal anti-carboxymethyllysine antibody, human serum albumin was carboxymethylated by glyoxylic acid and was immunized to rabbits as antigen. Carboxymethyllysine-hemoglobin (CML-Hb) levels were measured by the dot blotting method using this antibody.

RESULTS

The levels of CML-Hb were 6.68 +/- 3.10 nmol CML/mg Hb in nondiabetic hemodialysis patients (N = 70), 6.39 +/- 3.43 nmol CML/mg Hb in diabetic hemodialysis patient (N = 21), and 3.13 +/- 0.88 nmol CML/mg Hb in 47 healthy volunteers. For clinical signs of dialysis-related amyloidosis, 70 nondiabetic hemodialysis patients were scored according Gejyo's criteria. The CML-Hb levels in patients with a high amyloid score as well as a low amyloid score were significantly higher than in patients with negative amyloid score (8.89 +/- 3.53 nmol CMLmg Hb, 7.28 +/- 2.32 nmol CML/mg Hb vs. 5.11 +/- 2.09 nmol CML/mg Hb, P < 0.001, P < 0.05). Furthermore, the CML-Hb levels correlated significantly with serum values of the methylguanidine over creatinine ratio and hyaluronate.

CONCLUSIONS

We suggest that CML-Hb is increased in blood from patients on maintenance hemodialysis and is thus a potential biomarker of oxidative damage in these patients. Moreover, CML-modification of protein may play a pathogenic role in the development of dialysis related amyloidosis.

[Chronic renal failure and guanidino compounds]

Guanidino compounds are known as uremic toxins which increase in the blood of patients with renal failure. Guanidino succinic acid (GSA) and methyl guanidine (MG) have been intensively studied since they are toxic and are candidate markers which reflect the pathological stage of nephritis. GSA correlates well with blood urea nitrogen and therefore indicates the reduction of renal function. MG does not appear in the early stage of renal failure and abruptly increases at the stage of serious uremia. MG is produced by the oxidation of creatinine (CTN) with active oxygen. The MG/CTN ratio in the serum therefore reflects the degree of the generation of active oxygen. Accordingly, active oxygen scavengers may be useful for the treatment of uremia.

Convulsions in hemodialysis (HD) patients with elevated polymorphonuclear leukocyte elastase (PMNE) levels

Eight hemodialysis (HD) patients with convulsions of unknown cause were monitored for serum levels of uremic toxins such as methylguanidine(MG), and polymorphonuclear leukocyte elastase (PMNE). Twenty HD patients without convulsions served as controls. In the convulsion group, MG and PMNE were high. In 2 patients, convulsions subsided after daily hemodiafiltration (HDF). Although PMNE was thought to be a mediator of injury in the present series, no significant correlation was found between PMNE and either neutrophil numbers or endotoxin levels. PMNE may indicate the over production of cytokines not associated with serious infection or septicemia. In patients with renal failure and complications of unknown cause, intensified dialysis therapy such as frequent HDF may be useful when combined with treatment of the underlying disease producing the toxins. PMNE measurement is useful in assessing the uremia caused by high cytokine levels and, together with methylguanidin (MG) serum levels, can indicate the severity of the convulsion.

Proof that green tea tannin suppresses the increase in the blood methylguanidine level associated with renal failure

The effects of a green tea tannin mixture and its individual tannin components on methylguanidine were examined in rats with renal failure. The green tea tannin mixture caused a dose-dependent decrease in methylguanidine, a substance which accumulates in the blood with the progression of renal failure. Among individual tannin components, the effect was most conspicuous with (-)-epigallocatechin 3-O-gallate and (-)-epicatechin 3-O-gallate, while other components not linked to gallic acid showed only weak effects. Thus, the effect on methylguanidine was found to vary among different types of tannin.

Changes in serum levels of creatol and methylguanidine in renal injury induced by lipid peroxide produced by vitamin E deficiency and GSH depletion in rats

A novel creatinine metabolite, creatol (5-hydroxycreatinine), is a key precursor in the synthesis of the uremic toxin methylguanidine (MG). Creatinine is converted to creatol within the mammalian body and this conversion is mediated specifically by hydroxyl radicals. We investigated the production of creatol and MG from creatinine in rats with renal failure induced by the lipid peroxide produced as a consequence of vitamin E deficiency and depletion of the reduced form of glutathione (GSH). In addition, we examined serum levels of other guanidino compounds, namely guanidinoacetic acid (GAA) and guanidinosuccinic acid (GSA). The injury to kidneys induced by the depletion of GSH in combination with vitamin E deficiency caused markedly elevated serum levels of creatol, MG and GSA and decreased serum GAA. The molar ratio of creatol to creatinine in the serum, which should be an index of the oxygen stress mediated by hydroxyl radicals, increased with time. Therefore, the enhanced production of creatol in vitamin-E-deficient rats that have been depleted of GSH might be due to the enhanced production of oxygen radicals in this system.

[Study on the clinical effect of rhubarb on nitrogen-metabolism abnormality due to chronic renal failure and its mechanism]

It is well known that diet therapy is effective for inhibition of the advancement of chronic renal failure. Rhubarb, which can improve nitrogen metabolism, may allow delay in the introduction of the hemodialysis. After performing diet therapy with an energy intake of 35 Kcal/kg and a salt volume of less than 7g in 38 cases with chronic renal failure (CRF), 5 healthy volunteers (N) and 5 cases with liver cirrhosis (LC), 1.0g of rhubarb was administered orally. The blood urea nitrogen (BUN) did not vary in N, decreased in cases with LC and CRF (rhubarb-administered group), but increased in cases with CRF (non-rhubarb-administered group). The serum creatinine (s-Cr) did not vary in N and cases with LC and CRF (rhubarb-administered group), but was elevated in cases with CRF (non-rhubarb-administered group). Serum methylguanidine did not vary in N and cases with LC, decreased in cases with CRF (rhubarb-administered group), and increased in cases with CRF (non-rhubarb-administered group). The chronological level of 1/Cr in cases with CRF (rhubarb-administered group) was improved. In addition to the diet therapy, administration of rhubarb inhibited increase of BUN and serum creatinine in cases with chronic renal failure and was effective for the reduction of uremic substances. Therefore, it was concluded that rhubarb can retard the introduction-period of hemodialysis and can also inhibit deterioration of the disease.

Diabetic renal failure and serum accumulation of the creatinine oxidative metabolites creatol and methylguanidine

Diabetic patients (n = 23) with chronic renal failure (CRF) accumulate the creatinine (Cr) oxidative metabolites creatol (CTL) and methylguanidine (MG; a uremic toxin) in their sera. Analysis of serum CTL, a key intermediate in mammalian Cr catabolism into MG, is shown to offer some useful diagnostic information on CRF, especially in the determination of an initial stage of pathological renal failure. The sera of all diabetic (n = 23) and nondiabetic (n = 20) patients with CRF (s-Cr > 1.25 mg/dl) contained s-CTL (> 2 micrograms/dl), whereas those from normal subjects (n = 18) and diabetic patients (n = 18) without CRF contained no detectable s-CTL. A similar accumulation of s-MG was observed, but only when s-Cr was higher than 2.0 mg/dl. Although each s-CTL (Y: microgram/dl, Y': mol/l) and s-MG level (Z: microgram/dl, Z': mol/l) is highly correlated with s-Cr (X: mg/dl, X': mol/l) in a normal equation, Y or Z = AX + B, an alternative correlation in a second-order equation, Y or Z = alpha X2 + beta X, could also fit well. Since the quadratic equation can be convertible to Y/X or Z/X = alpha X + beta [Y'/X' or Z'/X' = alpha' X+ beta'] and active oxygen species, especially hydroxyl radicals, convert Cr into CTL, Y/X, Y'/X', Z/X and Z'/X' values which might be a kind of indices for oxygen stress (oxidative stress) increased in proportion to the increased severity of CRF in such patients. Although its meaning and interpretation are still debatable, diabetic CRF patients had a significantly higher alpha' value (2.2) than that (0.89) of nondiabetic CRF patients. All serum values for Cr, CTL and MG were measured with HPLC.

Plasma methylguanidine and creatinine concentrations in cats with experimentally induced acute renal failure

Plasma methylguanidine (MG) and creatinine (CRN) concentrations were measured in 11 cats with experimentally induced acute renal failure by a two-stage surgical procedure. According to the progression of renal failure, both plasma MG and CRN levels increased. A significant positive correlation (y = 0.187X - 0.379, lambda = 0.9176, P < 0.001) was found between plasma MG and CRN levels. These results suggested that the increase in plasma MG level was an available indicator for uremic status in cats.

Serum guanidino compound levels in uremic pediatric patients treated with hemodialysis or continuous cycle peritoneal dialysis. Correlations between nerve conduction velocities and altered guanidino compound concentrations

Serum levels of twelve guanidino compounds (GCs) and nerve conduction velocities were determined in a dialyzed renal insufficient pediatric population. Two dialytic groups were considered: one subjected to hemodialysis (HD, 11 patients) and one subjected to continuous cycle peritoneal dialysis (CCPD, 13 patients). Before HD, marked increases were found for guanidino-succinic acid (207 times), methylguanidine (> or = 67 times), argininic acid (24 times), creatinine and alpha-N-acetylarginine (18 times) and guanidine (> or = 14 times) when compared to controls. Important significant increases were still present after an HD session for guanidinosuccinic acid (49 times), methylguanidine (34 times), creatinine (7 times) and alpha-N-acetylarginine and guanidine (6 times). After HD, creatine, arginine and homoarginine were lower than in controls. All GCs, with the exception of creatine, decreased significantly after a single HD session with percentage decrease ranging between 40% (for arginine) and 77% (for guanidinosuccinic acid). Creatine decreased in a statistically nonsignificant manner by 48%. Marked increases were found in the CCPD group for guanidinosuccinic acid (114 times), alpha-N-acetylarginine (12 times), argininic acid (15 times), creatinine (22 times), guanidine (> or = 11 times) and methylguanidine (> or = 48 times). Concentrations of guanidinosuccinic acid before and after HD and in CCPD were comparable to those reported to be toxic in vitro and in vivo. No clinical or electrophysiological indications of polyneuropathy were observed in our population. Sensory and motor nerve conduction studies showed few abnormalities apart from a significant correlation between argininic acid concentration or guanidine levels and the peroneal nerve conduction velocity in the CCPD-treated group.

Effects of ginseng in nephrectomized rats

Ginseng extract and its active component, saponin, were administered orally to nephrectomized rats for 90 d, and changes in blood and urine parameters and renal tissue lesions were assessed. Rats given saponin showed a significant decrease in the concentrations of blood urea nitrogen, creatinine and methylguanidine and a significant increase in total protein and albumin in the blood, with reduce urinary excretion of protein. There was also slight amelioration of the degree of mesangial proliferation, the severity of extratubular lesions and glomerular sclerotic lesions, and the extent of tubular interstitial lesions. However, these histological changes were inconspicuous in nephrectomized rats given ginseng extract.

Effect of recombinant human erythropoietin on synthesis of methylguanidine in uraemic patients on haemodialysis or continuous ambulatory peritoneal dialysis

The effect of recombinant human erythropoietin (rHuEPO) on synthesis of methylguanidine was studied in 6 uraemic patients on haemodialysis and 5 uraemic patients on continuous ambulatory peritoneal dialysis (CAPD). The two groups of patients were started on a 24-week course of thrice weekly 1500 IU of rHuEPO by the intravenous route. Serum methylguanidine level and methylguanidine/creatinine ratio were comparable in these groups. In the two groups no significant differences were observed in these measurements comparing the pretreatment values with those 4, 8, 12 or 24 weeks after starting rHuEPO administration. During rHuEPO therapy, serum methylguanidine levels and methylguanidine/creatinine ratio showed no considerable difference between the two groups. These findings suggest that administration of rHuEPO does not alter methylguanidine synthesis in uraemic patients on haemodialysis and CAPD.

Ontogenetic differences in convulsive action and cerebral uptake of uremic guanidino compounds in juvenile mice

Guanidinosuccinate (GSA) and methylguanidine (MG) are endogenous, convulsant guanidino compounds which have been shown to be greatly increased in uremic patients. In the present study, we have investigated the age-related differences in convulsive action and cerebral uptake of these compounds in juvenile mice of 7, 14 and 21 days old. An age-dependent decrease was apparent in the severity of the GSA- and MG-induced convulsions and toxicity. Mean latency for the appearance of clonic convulsions increased with increasing age. Two hours following the i.p. injection of GSA or MG in a dose of 250 mg/kg, the resulting brain concentration decreased with increasing age of the animals. This effect was more pronounced in the case of MG. Neither for GSA, nor for MG was this age-dependent effect apparent after 30 min. GSA and MG serum as well as brain concentrations were lower in 21-day-old mice than in 7-day-old ones. However, the brain/serum concentration ratios of GSA and of MG were significantly lower in 21-day-old mice than in 7-day-old ones, indicating that at least part of the difference in brain level can be explained by higher permeability of the immature blood-brain barrier to these uremic guanidino compounds. In addition, brain/serum ratios of GSA in mice of 7 days old and in mice of 21 days old were significantly lower than the ratios of MG in these age groups, indicative of lower overall blood-brain barrier permeability to GSA than to MG.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between serum levels of methylguanidine and glycemic control in IDDM children

OBJECTIVE

To examine the serum levels of methylguanidine in IDDM children and compare them with markers for glycemic control. Reports have indicated that active oxygen, which damages various tissues, increases in diabetes mellitus. The increase of active oxygen is one of the risk factors for diabetic complications. The synthesis of methylguanidine, a metabolic product of guanidine, is mainly regulated by active oxygen.

RESEARCH DESIGN AND METHODS

Forty-eight children with IDDM (mean age 13.3 yr) and 17 age-matched nondiabetic control subjects were studied. Diabetic children were divided into a well-controlled group (HbA1c < 8%, n = 24) and a poorly controlled group (HbA1c > 8%, n = 24). Serum concentrations of methylguanidine were measured by enzymatic assay.

RESULTS

Levels of methylguanidine in the poorly controlled group (1.31 +/- 0.08 microM) were significantly higher than those in both the well-controlled group (0.85 +/- 0.08 microM) and the control group (0.59 +/- 0.11 microM), respectively (P < 0.01). Methylguanidine levels showed a positive correlation with the levels of HbA1c (P < 0.01) or fructosamine (P < 0.01). No significant correlations were noted between methylguanidine levels and age, sex, duration of diabetes, or insulin dose.

CONCLUSIONS

Our data indicate that the levels of methylguanidine in IDDM children might be affected by glycemic control and that the determination of serum methylguanidine levels could be a useful test for evaluating the state of diabetic control.

[A study on plasma allantoin in patients undergoing maintenance hemodialysis]

Current studies have reported that free radical molecules had anticipated intimately with the pathogenesis of some complications specific for a long term hemodialysis. Among substances generated by free radical reaction, methylguanidine (MG) had been well known as most popular parameter in hemodialyzed patient, but allantoin (Alt) had been reported to be generated from uric acid by hydroxyradical, too. In this study, we measured serum level of Alt in long term hemodialyzed patient and analysed in the comparison with serum level of sialic acid, MG, and MG/Cr value. Serum level of Alt in patients group varied from 2.6 to 105.9 nmol/ml, which was significantly higher as compared with exclusively undetectable level in normal volunteers (n = 15). Serum level of Alt in each patient showed a significant correlation with serum level of a sialic acid (r = 0.400 p < 0.02). Furthermore, although serum level of Alt failed to show a significant correlation with serum level of MG, but showed a significant correlation with MG/Cr value. (r = 0.485 p < 0.01). In addition, higher level could be found in patient group having higher serum level of MG or MG/Cr value. Based upon those results, we proposed that a measurement of serum level of Alt could be of value in detection of free radical reaction in long term hemodialyzed patient.

[Guanidino compounds and aliphatic monoamines in acute and chronic renal failure]

Small molecular weight uremic toxins, guanidino compounds and aliphatic monoamines, were measured in the serum of chronic and acute renal failure (CRF and ARF) patients. A close correlation was noticed between guanidinosuccinic acid (GSA) and serum urea nitrogen (BUN) and also between methylguanidine and serum creatinine (Cr) in nondialyzed and dialyzed CRF patients. The same relation was seen in ARF patients showing rapid change of metabolic conditions, which suggested the tight linkage between guanidino compounds and protein metabolites. On the other hand, dimethylamine (DMA) was related with Cr in CRF patients, however, not in ARF patients. Since the production of DMA from Cr is carried out mainly, but relatively slowly, by bacterias in the intestine, the rapid metabolic change of ARF may not affect DMA synthesis. Furthermore, the DMA synthesis from trimethylamine-N-oxide (TMA-N-O) was studied using liver homogenate. The liver homogenate produced DMA by adding TMA-N-O as substrate. However, the kidney homogenate could synthesize it even without substrate. Therefore, the kidney seems to be a major site of DMA production as well as the intestine.

Effects of creatinine, creatol and methylguanidine on renal function

Creatinine (Cr), creatol or methylguanidine (MG) was administered intraperitoneally to normal rats, and several renal function parameters were examined in an attempt to clarify the pathology under the various conditions. The glomerular filtration rate, renal plasma flow and renal blood flow after administration of Cr remained virtually unchanged when compared to those in the control group. In contrast, administration of creatol induced a significant decrease in these renal functions. Further decreases in the renal functions were observed in the rats given MG. However, the level of serum MG was extraordinarily high in the rats given creatol or MG. The toxic effects are discussed on the basis of the above results.

[Methylguanidine kinetics during oral active vitamin D pulse therapy for secondary hyperparathyroidism]

Active vitamin D (VD) metabolite preparations have been used in the management of secondary hyperparathyroidism (2 degrees HPT) due to impaired calcium and phosphorus metabolism and can allegedly be expected to prevent, to some extent, the progression of this pathological condition. Unfortunately, however, it is not uncommon for us in routine clinical practice to find 2 degrees HPT of moderate or greater severity embarrassingly unamenable to treatment with these VD preparations in ordinary oral therapeutic doses. Recent studies have gradually reported that intravenous administration of 1,25-(OH)2D3 and oral active VD pulse therapy has been therapeutic approach to 2 degrees HPT. Methylguanidine (MG) among other GCs, its precursor is already identified as creatinine and activated oxygen as well PTH and VD are known to participate in the process leading to its formation. In the present study, we administered oral 1,25-(OH)2D3 pulse therapy to patients with chronic renal failure for the treatment of 2 degrees HPT in an attempt to assess the effectiveness of this therapeutic regimen and to explore the clinical effect of MG on responsiveness to the therapy. The purpose of this paper is to present the results thus obtained. Oral 1,25-(OH)2D3 pulse therapy (6 micrograms once a week) was administered to 21 hemodialysis patients with for 12 weeks. Of these 21, 10 patients responded to the therapy with a more than 20% reduction in serum (PTH): (responsive group), whereas the remaining 11 did not (resistant group). Pretreatment serum PTH levels were significantly higher in the latter group than the former.(ABSTRACT TRUNCATED AT 250 WORDS)

[Studies of the effects of low-molecular uremic toxins on anaerobic metabolism of human erythrocytes]

The effect of methylguanidine (MG) and guanidinosuccinic++ acid (GSA) on the anaerobic glycolysis of normal human red blood cells was studied in vitro after three-hours incubation at temperature 37 degrees C. The changes of glucose and lactic acid levels as well as intermediate metabolites and adenine nucleotides of carbohydrate metabolism were determined. Glucose and lactic acid were measured with enzymatic methods, however main phosphate compounds and nucleotide coenzymes were determined by a method of column chromatography. The studies have shown, that GSA in concentrations approximate to those appearing in the plasma patients with chronic renal failure, insignificant enhanced glucose utilization in normal erythrocytes with simultaneous significant decrease produce of lactic acid. Methylguanidine have weakly effected on this process. Subsequent studies have demonstrated that mixture MG (5.4 x 10(-5) mol/dm3) and GSA (2.8 x 10(-5) mol/dm3) induced characteristic changes in composition of main phosphate compounds of carbohydrate metabolism in human red blood cells. The statistically significant decrease of ATP in blood cells with simultaneous increase ADP and AMP were observed. The concentrations of hexose monophosphate, fructose-1,6-diphosphate, triosephosphate, and 2,3-diphosphoglycerinic acid were also higher. The inorganic phosphate concentration was over 80% higher than in control cells. The results of our studies have revealed that energetic metabolism was inhibited in red blood cells which were incubated with MG and GSA.

[Platelet aggregation in chronic renal failure--whole blood aggregation and effect of guanidino compounds]

Studies were performed on the platelet aggregation (PA) in patients with chronic renal failure (CRF) and normal subjects (NS). The PA was investigated in the whole blood by the electrical impedance method. The concentrations of plasma (P-) and erythrocyte (E-) guanidinosuccinic acid (GSA) and methylguanidine (MG) in uremic patients with CRF were determined by high performance liquid chromatography. GSA and MG are guanidino compounds (GC) and have been widely shown to act as uremic toxins. The effects of GSA and/or MG on the PA of NS were also investigated. The results showed that the PA of conservative therapy patients with CRF was significantly lower than that of NS, while the PA of hemodialysis (HD) patients was improved. The PA of continuous ambulatory peritoneal dialysis (CAPD) patients was rather high and the possibility of sugar and lipid metabolic disorders was suggested as the cause. The concentrations of P- and E-GSA and MG in uremic patients with CRF were increased. But there were no significant correlations between the PA and the concentrations of GSA and MG. In vitro, GSA and/or MG at a high concentration exerted a significant inhibitory effect, while at a low concentration they showed a lesser inhibitory effect on the PA. In conclusion, based on their inhibition of the PA in patients with CRF, the dialyzable materials, GSA and MG, are considered to represent active uremic toxins.

Effects of rhubarb tannins on uremic toxins

The effects of each of several tannins purified from Rhei Rhizoma on serum constituents were investigated in rats with adenine-induced renal failure. Blood levels of urea nitrogen, methylguanidine (MG), and guanidinosuccinic acid (GSA) were significantly decreased in rats given (-)-epicatechin 3-O-gallate at a dose of 2.5, 5 or 10 mg/kg body weight/day for 24 days. The creatinine (Cr) level was also significantly decreased in rats given 5 and 10 mg of this compound. A significant decrease in urea nitrogen, MG, and GSA was found in rats given 6.25 mg of procyanidin B-2 3,3'-di-O-gallate. However, unlike the former two components the administration of 12.5 mg of procyanidin C-1 3,3',3''-tri-O-gallate produced a considerable or significant increase in bLood levels of urea nitrogen, Cr, MG, and GSA. RG-tannin had a weaker overall effect on serum constituents except for GSA in comparison with the corresponding effect of (-)-epicatechin 3-O-gallate and 6.25 mg of procyanidin B-2 3,3'-di-O-gallate. Rhatannin tended to increase the serum nitrogen constituents.

Guanidino compounds in uraemic dialysed patients

The concentrations of guanidino compounds in blood are raised in uraemic patients and may have toxic effects. The concentrations of 13 guanidino compounds in serum were measured in 29 patients with chronic renal failure treated by chronic intermittent haemodialysis using liquid cation exchange chromatography with a highly sensitive fluorescence detection method. For taurocyamine we used another column system. Substantial increases in guanidinosuccinic acid, creatine, N-alpha-acetylarginine, creatinine, guanidine and methylguanidine were found. The values obtained for taurocyamine and beta-guanidinoproprionic acid were much lower than those reported by others: a much smaller increase was observed for beta-guanidinoproprionic acid and taurocyamine was only doubled in 4 of 29 uraemic patients. The concentrations of other guanidino compounds such as arginine and guanidinoacetic acid were normal. No differences were found between the polycystic renal disease, the chronic glomerulonephritis and the interstitial nephritis subgroups.

Simultaneous determination of serum cations, anions and uremic toxins by ion chromatography using an immobilized enzyme

A procedure is described for the analysis of serum cations and uremic toxins by simultaneous conductivity (CD) and ultraviolet (UV) photometric detection and using phosphoric acid as the eluent. In addition, studies were made on the determination of urea in serum using immobilized urease, and on the simultaneous determination of cationic and anionic compounds. The ammonium ion produced from urea by immobilized urease was determined by CD. No significant differences in amounts were found between the present method and conventional colorimetric methods. There was no significant reduction in immobilized urease activity after two months of continuous use. Simultaneous analysis of cationic and anionic compounds in serum was performed by switching valves in order to change the eluents and to change the channel to the analytical column. No marked base-line variation was observed and satisfactory recovery of anions was achieved.

Plasma levels of a novel antidysrhythmic agent, meobentine sulfate, in humans as determined by radioimmunoassay

A radioimmunoassay for the quantitation of meobentine sulfate, a novel antidysrhythmic and antifibrillatory agent in biological fluids, is described. Antisera were raised in rabbits in response to immunization with a conjugate of bovine serum albumin and a meobentine analog with a propionic acid sidechain ortho to the methoxyl group. These antisera have low affinities for N- and O-desmethylmeobentine metabolites, which show less than 5% cross-reaction in radioimmunoassay procedures employing either tritiated or radioiodinated radioligands. The radioimmunoassay using[125I]meobentine was capable of detecting less than 0.4 ng/ml (40-pg mass) of meobentine. This assay was used to demonstrate the absorption of meobentine in humans after oral administration and also permitted studies of meobentine sulfate disposition in human plasma following two (2.5 and 5 mg/kg) oral doses. Mean peak meobentine concentrations in plasma occurred 3 hr postdose in both cases and were 230 and 451 ng/ml following the 2.5- and 5-mg/kg doses, respectively. The approximate mean terminal half-life after all treatments was 12 hr.

A selective method for determination of methylguanidine in biological fluids. Its application in normal subjects and uremic patients

A selective analytical method for the determination of methylguanidine in plasma in biological fluids has been developed. Methylguanidine is extracted in a column to dichloromethane as an ion pair with hexanitrodiphenylamine (dipicrylamine). It is isolated from coextracted compounds by partition chromatography as the picrate ion-pair. The methylguanidine fraction is collected and after reextraction to a buffer solution the methylguanidine content is quantitatively determined photometrically as picrate. An absolute recovery of 95 +/- 5% was obtained in the concentration range 1.5-10 microgram/ml plasma. The concentration of methylguanidine in plasma was higher in uremic patients, (44.4 +/- 5.71 mumol/l in conservatively-treated and 42.4 +/- 7.87 mumol/l in dialysis-treated patients) than in normal subjects, (4.0 mumol/l), but still lower than reported by other investigators using non-specific methods and also lower than the concentrations found to be toxic in experimental animals. There was a significant correlation between methylguanidine and creatinine concentration but no correlation between methylguanidine and urea concentration in plasma. No obvious relation was found between plasma methylguanidine concentration and various uremic symptoms, mode of treatment or protein intake.