Fluorometrical analysis of guanidino compounds in human cerebrospinal fluid

Stable isotope dilution method for the determination of guanidinoacetic acid by gas chromatography/mass spectrometry

For more than 30 years, guanidinoacetic acid (GAA), together with other guanidino compounds, has been proposed as an important marker for renal failure, in kidney transplantation, and for renal metabolism, especially for the metabolic activity of the renal proximal tubules. Since the discovery of the first patient with guanidinoacetic acid methyltransferase deficiency in 1994 by Stöckler et al. (Pediatr. Res. 1994; 36: 409), GAA has become of great interest for all laboratories involved in the diagnosis of metabolic diseases. In the literature there are several methods described for the determination of GAA, ranging from ion-exchange chromatography with post-column derivatisation, enzymatic methods, gas chromatography/mass spectrometry (GC/MS), to liquid chromatography/atmospheric pressure chemical ionisation mass spectrometry (LC/APCI-MS). Here a stable isotope dilution method for quantitative and accurate determination of GAA in urine, plasma, and cerebrospinal fluid is described. GAA is converted to the bis(trifluoromethyl)pyrimidine di(tert-butyldimethylsilyl) derivative by stepwise derivatisation with hexafluoroacetylacetone and N-(tert-butyldimethylsilyl)-N-methyltrifluoroacetamide (MTBSTFA). Analysis can be performed using a standard benchtop GC/MS system. For quantitative GAA determination with 1,2-(13)C-GAA as internal standard, selected ion monitoring is performed using m/z 460/462, with m/z 432/433 and 375/376 as qualifiers.

Increase of methylguanidine and guanidinoacetic acid in the brain of amygdala-kindled rats

Guanidino compounds are intrinsic chemoconvulsants. We investigated the regional and time-dependent changes of these compounds in the amygdala (AM) of kindled rats versus electroconvulsive shock (ECS) seizures using high-performance liquid chromatography (HPLC). Twenty-eight days after the last AM-kindled seizure, guanidinoacetic acid (GAA) and methylguanidine (MG) levels were significantly increased in the bilateral AM as compared with those of control rats, which had been implanted with electrodes but were not stimulated. Both compounds, however, tended to decrease in the bilateral AM after ECS seizure. In addition, we measured these compounds after induction of one afterdischarge (AD) in the AM. These compounds increased significantly 7 days after AD was induced in the ipsilateral AM. We suggest that the increase of these compounds is coincident with AD generation and specific to AM kindling and the kindled state.

Chromatography and electrophoresis of creatinine and other guanidino compounds

Chromatographic methods, in general, are considered as the definitive and reference procedure. The HPLC procedures reviewed all seem to provide improved and adequate specificity and sensitivity for CRN assay. The HPLC methods are relatively easy to use, have nearly complete recoveries (greater than or equal to 95%) and have good precision. The within- and between-day variations are often less than 4% [85,87,90,94-97,99]. Most of the methods developed [84,85,90,91,94,97,99] were tested for potential interference and the specificity for CRN was demonstrated. One important advantage of the HPLC method [85] is that the presence of an interfering substance in the biological sample can most likely be detected by its influence on the sharpness and resolution of the CRN peak. It is understandable that there are possibilities that other constituents in the biological sample may also be co-eluting with CRN and the investigator should carefully examine the chromatogram obtained for any sign of interference. Ginman and Colliss [107] reported that azathioprine, cyclosporin A, cefotaxime and prednisolone used in patients after renal transplant interfered with the HPLC assay: the results are 40% higher than those by Jaffe method. These interferences, however, were corrected with a slight modification of the HPLC conditions [107]. Because of the non-specificity associated with the Jaffe reaction, the results obtained from Jaffe-based assays often exceed those from HPLC methods [95,108,109]. Such overestimation would be especially significant when the serum CRN is in the normal range where small changes may be indicative of a significant change in a patient's renal function [95,111]. It appears that HPLC methods are the methods of choice for simultaneous analysis of endogenous guanidino compounds. Depending on the purpose of analysis, one would choose a particular type of method, e.g., one among those representative methods listed in Table 1. If one is interested in measuring MG and GSA levels in serum or plasma, then depending on the sensitivity requirement and available instrumentations, one could choose many method listed in Table 1. However, if one needs to measure AARG, ARG and ARA, in addition to MG and GSA, then method 4 in Table 1 would be more appropriate. If TAU is the compound of interest, then one of the methods 2,3,4,5, and 7 with an appropriate deproteinization procedure would be desirable.

Measurement during convulsions of guanidino compound levels in cerebrospinal fluid collected with a catheter inserted into the cisterna magna of rabbits

An easy method for collecting cerebrospinal fluid (CSF) was developed using a catheter inserted into the cisterna magna of rabbits. Levels of guanidino compounds in CSF collected by this method were measured. Levels of guanidinoacetic acid and creatinine increased at the onset of a pentylenetetrazol (PTZ)-induced convulsion. These levels normalized 2 h after the convulsion. The arginine level started to decrease 2 h after the convulsion, continued to decrease gradually and normalized 4 days after the convulsion. These results suggest that guanidinoacetic acid and creatinine are related to the initiation of PTZ-induced convulsions, and that 4 days are required for the metabolism of guanidino compounds to return to normal after a convulsion in rabbits.

CSF creatinine in schizophrenia

Concentrations of creatinine in cerebrospinal fluid (CSF) from schizophrenic patients and healthy control subjects were determined by a liquid chromatographic method. The concentration of creatinine in CSF from schizophrenic patients was lower (42.8 nmol/ml) than that of the controls (54.4 nmol/ml). The concentration of creatinine was correlated to the levels of homovanillic acid and 5-hydroxyindoleacetic acid. Treatment of the schizophrenic patients with sulpiride (800 mg daily), but not with chlorpromazine, elevated the concentration of creatinine in the CSF.

Biochemistry and neurotoxicology of guanidino compounds. History and recent advances

Guanidino compounds are known to have important biological roles, such as the participation of arginine in ureagenesis, and of creatine in muscular contraction. On the other hand, the high toxicity of guanidino compounds, such as methylguanidine and guanidine, has been under study for quite a long time in the biochemical as well as clinical fields. In this review, the author summarizes the experimental results of neurophysiological and neurochemical studies on guanidino compound-induced seizures, conducted by his colleagues since 1966, and introduces several topics arising from their recent investigations on guanidino compounds and seizure mechanism, i.e., (1) alpha-guanidino-glutaric acid in the cobalt epileptic focus and its convulsive activity; (2) guanidino-ethanesulfonic acid and epilepsy; (3) delta-guanidinovaleric acid, and endogenous and specific GABA receptor antagonist; and (4) guanidino compounds as radical generators.

The biosynthesis of 2-guanidinoethanol in intact mice and isolated perfused rabbit kidneys

The metabolic pathway for the synthesis of 2-guanidinoethanol (GEt) was studied in intact mice and isolated perfused rabbit kidneys. GEt excretions in 24-hr urine increased after the intraperitoneal injection of ethanolamine (EA) into mice. Perfusion of isolated rabbit kidneys with EA and L-arginine (Arg) enhanced the GEt excretion from the ureter. This enhancement was observed in an EA concentration-dependent manner under the presence of Arg. When glycine (Gly) was added to the perfusion medium together with EA and Arg, the enhancement of GEt excretion was inhibited, whereas, guanidinoacetic acid excretion was increased to the same extent as during the perfusion with Gly and Arg. These results indicate that GEt is synthesized from Arg and EA in the kidney and that this synthesis is catalyzed by Arg:Gly amidinotransferase (EC 2.1.4.1.). We also described the guanidino compound excretion levels, including levels of GEt, in the rabbit, mouse, rat, and cat. The levels varied considerably with mammalian species.

High-performance liquid chromatographic analysis of guanidino compounds using ninhydrin reagent. II. Guanidino compounds in blood of patients on haemodialysis therapy

An automated high-performance liquid chromatographic method using alkali-ninhydrin reagent for the post-column derivatization of guanidines has been developed. This procedure was applied to measurements made before and after haemodialysis. Among the guanidino compounds found in human blood, methylguanidine showed the lowest removal rate. The removal rate of guanidinosuccinic acid correlated with the plasma alpha 1-globulin fraction. The removal rate of each guanidino compound decreased with the period of dialysis.

Identification of 2-guanidinoethanol in human urine

Guanidino compounds in normal human urine were analyzed by high-performance liquid chromatography; an unknown peak was observed in the chromatogram that was identical to the peak of synthetic 2-guanidinoethanol. In another experiment, the substance was purified from human urine by successive use of strongly acidic ion-exchanger, thin-layer chromatography and then weakly acidic ion-exchanger. After this it was reacted with acetylacetone to form dimethylpyrimidyl derivative. After further reaction of this derivative with trifluoroacetic anhydrate, it was analyzed by gas chromatography/mass spectrometry. The mass chromatogram and mass spectrum were identical to those of the trifluoroacetylated dimethylpyrimidyl derivative of synthetic 2-guanidinoethanol. This is the first report on the identification of 2-guanidinoethanol in human urine. The concentration of 2-guanidinoethanol in the urine of healthy humans was 5.7 +/- 1.8 (mean +/- SD) mumol/g creatinine.