Bart Marescau

Guanidino compounds in serum and urine of nondialyzed patients with chronic renal insufficiency

Levels of 15 guanidino compounds and urea were determined in serum and urine of nondialyzed patients with chronic renal insufficiency subdivided according to etiology and creatinine clearances. No significantly different guanidino compound levels in serum and urine were found for the interstitial nephritis, glomerulonephritis, nephrangiosclerosis, and diabetic nephropathy subgroups. Subdividing the patients according to creatinine clearance yields the following results: (1) Serum guanidinosuccinic acid (GSA) and methylguanidine levels of patients with end-stage renal failure (creatinine clearance < 10 mL/min) are up to 100 and 35 times higher than control levels, while guanidine, creatinine, and symmetrical dimethylarginine (SDMA) are increased about 10 times. Serum levels of asymmetrical dimethylarginine (ADMA) are only doubled in end-stage renal failure. Serum levels of guanidinoacetic acid (GAA) and homoarginine are significantly decreased. (2) Urinary excretion levels of most guanidino compounds decrease with decreasing creatinine clearance except for GSA and methylguanidine. (3) Greater than 90% of patients with creatinine clearance ranging from subnormal to 40 mL/min have serum SDMA levels higher than the upper-normal limit; up to 80% have increased GSA levels. (4) The clearance rates of some of the guanidino compounds could be calculated: with the exception of arginine, they decrease with decreasing creatinine clearance. This study shows specific abnormal guanidino compound levels in serum and urine of nondialyzed patients with chronic renal insufficiency that can be used as complementary diagnostic parameters. The best correlation between serum guanidino compound levels and the degree of renal insufficiency is found for GSA, SDMA, methylguanidine, and guanidine. Urinary excretion levels of ADMA correlate best with decreasing creatinine clearance. Serum levels of GSA and especially SDMA are candidate indicators for the onset of renal failure.

Chemical models of epilepsy with some reference to their applicability in the development of anticonvulsants

This paper reviews chemical models of epilepsy and their relevance in the identification and characterization of anticonvulsants. For each convulsant we discuss possible modes of administration, clinical type(s) of seizures induced, proposed mechanism(s) of epileptogenesis and, where available, responsiveness of the induced seizures to anticonvulsants. The following compounds are reviewed: pentylenetetrazol, bicuculline, penicillin, picrotoxin, beta-carbolines, 3-mercaptopropionic acid, hydrazides, allylglycine; the glycine antagonist strychnine; gamma-hydroxybutyrate; excitatory amino acids (glutamate, aspartate, N-methyl-D-aspartate, quisqualate, kainate, quinolinic acid); monosubstituted guanidino compounds, metals (alumina, cobalt, zinc, iron); neuropeptides (opioid peptides, corticotropin releasing factor, somatostatin, vasopressin); cholinergic agents (acetylcholine, acetylcholinesterase inhibitors, pilocarpine); tetanus toxin; flurothyl; folates; homocysteine and colchicine. Although there are a multitude of chemical models of epilepsy, only a limited number are applied in the routine screening of potential anticonvulsants. Some chemical models have a predictive value with regard to the clinical profile of efficacy of the tested anticonvulsants. Some chemical models may contribute to a better understanding of possible mechanisms of epileptogenesis.

Guanidino compounds in serum, urine, liver, kidney, and brain of man and some ureotelic animals

Guanidino compound levels were quantitatively determined in serum, urine, liver, kidney, and brain of man and of some ureotelic animals. The guanidino compounds were separated over a cation exchange resin, using sodium citrate buffers, and detected with the fluorescence ninhydrin method. Species-specific differences in the levels of some guanidino compounds in the studied ureotelic animals are shown. alpha-Keto-delta-guanidinovaleric acid is a naturally occurring guanidino compound in ureotelic animals, and is not restricted to the pathobiochemistry of hyperargininemic patients. The fasting serum levels observed in beagles are the same as those found in hyperargininemic patients. In serum, liver, and kidney, the homoarginine, beta-guanidinopropionic acid, and gamma-guanidinobutyric acid levels are the highest in rats. The last two compounds have the highest levels of the studied guanidino compounds, with the exception of creatinine, in kidney. Specific high levels of gamma-guanidinobutyric acid and argininic acid are found in brain of rabbits.

Guanidino compounds in serum and cerebrospinal fluid of non-dialyzed patients with renal insufficiency

Twelve guanidino compounds were determined in simultaneously sampled serum and cerebrospinal fluid of eight non-dialyzed patients with renal insufficiency. Liquid cation exchange chromatography with a highly sensitive fluorescence detection method was used. In patients with serum urea levels about 10 times higher than in controls, the levels of guanidinosuccinic acid, creatinine, guanidine and methylguanidine, in serum as well as in cerebrospinal fluid, are at least 10 times higher than in control subjects. The levels of argininic acid and N-alpha-acetylarginine (in serum) and gamma-guanidinobutyric acid (in cerebrospinal fluid) are slightly increased (less than 10 X). The levels of the other guanidino compounds are close to normal values. A significant positive correlation exists between the guanidinosuccinic acid, creatinine and guanidine levels in serum and cerebrospinal fluid. The accumulation of several experimentally proven toxic guanidino compounds could contribute to the complex nervous system symptomatology and the hematological complications seen in renal insufficiency.

Homoarginine Levels Are Regulated by l-Arginine:Glycine Amidinotransferase and Affect Stroke Outcome Results From Human and Murine Studies

Background— Endogenous arginine homologues, including homoarginine, have been identified as novel biomarkers for cardiovascular disease and outcomes. Our studies of human cohorts and a confirmatory murine model associated the arginine homologue homoarginine and its metabolism with stroke pathology and outcome. Methods and Results— Increasing homoarginine levels were independently associated with a reduction in all-cause mortality in patients with ischemic stroke (7.4 years of follow-up; hazard ratio for 1-SD homoarginine, 0.79 [95% confidence interval, 0.64–0.96]; P=0.019; n=389). Homoarginine was also independently associated with the National Institutes of Health Stroke Scale+age score and 30-day mortality after ischemic stroke (P<0.05; n=137). A genome-wide association study revealed that plasma homoarginine was strongly associated with single nucleotide polymorphisms in the L-arginine:glycine amidinotransferase (AGAT) gene (P<2.1×10−8; n=2806), and increased AGAT expression in a cell model was associated with increased homoarginine. Next, we used 2 genetic murine models to investigate the link between plasma homoarginine and outcome after experimental ischemic stroke: (1) an AGAT deletion (AGAT−/−) and (2) a guanidinoacetate N-methyltransferase deletion (GAMT−/−) causing AGAT upregulation. As suggested by the genome-wide association study, homoarginine was absent in AGAT−/− mice and increased in GAMT−/− mice. Cerebral damage and neurological deficits in experimental stroke were increased in AGAT−/− mice and attenuated by homoarginine supplementation, whereas infarct size in GAMT−/− mice was decreased compared with controls. Conclusions— Low homoarginine appears to be related to poor outcome after ischemic stroke. Further validation in future trials may lead to therapeutic adjustments of homoarginine metabolism that alleviate stroke and other vascular disorders.

L-arginine:glycine amidinotransferase deficiency protects from metabolic syndrome

Phosphorylated creatine (Cr) serves as an energy buffer for ATP replenishment in organs with highly fluctuating energy demand. The central role of Cr in the brain and muscle is emphasized by severe neurometabolic disorders caused by Cr deficiency. Common symptoms of inborn errors of creatine synthesis or distribution include mental retardation and muscular weakness. Human mutations in l-arginine:glycine amidinotransferase (AGAT), the first enzyme of Cr synthesis, lead to severely reduced Cr and guanidinoacetate (GuA) levels. Here, we report the generation and metabolic characterization of AGAT-deficient mice that are devoid of Cr and its precursor GuA. AGAT-deficient mice exhibited decreased fat deposition, attenuated gluconeogenesis, reduced cholesterol levels and enhanced glucose tolerance. Furthermore, Cr deficiency completely protected from the development of metabolic syndrome caused by diet-induced obesity. Biochemical analyses revealed the chronic Cr-dependent activation of AMP-activated protein kinase (AMPK), which stimulates catabolic pathways in metabolically relevant tissues such as the brain, skeletal muscle, adipose tissue and liver, suggesting a mechanism underlying the metabolic phenotype. In summary, our results show marked metabolic effects of Cr deficiency via the chronic activation of AMPK in a first animal model of AGAT deficiency. In addition to insights into metabolic changes in Cr deficiency syndromes, our genetic model reveals a novel mechanism as a potential treatment option for obesity and type 2 diabetes mellitus.

Serum creatine, creatinine, and other guanidino compounds in patients with thyroid dysfunction

Serum levels of creatine (CT), creatinine (CTN), urea, guanidinosuccinic acid (GSA), guanidinoacetic acid (GAA), guanidine (G), arginine (Arg), homoarginine (Harg), argininic acid (ArgA), and alpha-keto-delta-guanidinovaleric acid (alpha-K-delta-GVA) were measured in 54 patients with hyperthyroidism, 56 with subclinical hyperthyroidism, 28 with subclinical hypothyroidism, and 51 with hypothyroidism compared with 62 euthyroid controls. In agreement with previous reports, serum CT increased (+35%) and CTN decreased (-17.6%) in hyperthyroidism as compared with normal thyroid function, whereas the opposite was seen in hypothyroidism (-17.7% and +11%, P < .0001). Original findings from this study are a highly significant decrease in GSA (-41.7%) and GAA (-36.8%) in hyperthyroidism and an increase in GSA (+36%) in hypothyroidism (P < .0001). In addition, a slight decrease in hyperthyroidism and hypothyroidism was noted for Arg (-6.2% and -13.2%, P = .001) and Harg (-14.8% and -18.1%, P = .05). By contrast, no significant change was seen in levels of urea, G, ArgA, and alpha-K-delta-GVA. No major differences were found for any of the compounds between subclinical hypothyroidism, euthyroidism, and subclinical hyperthyroidism. There was a highly significant positive linear correlation between urea and GSA levels in hyperthyroidism, euthyroidism, and hypothyroidism (r = .68, r = .77, and r = .75, P < .0001), taking into account that for the same increase in urea, GSA increased threefold more in hypothyroid versus hyperthyroid patients. In conclusion, apart from CT and CTN, significant changes can be found in serum levels of GSA, GAA, Arg, and Harg in patients with thyroid dysfunction. Subclinical thyroid dysfunction does not seem to induce changes in serum levels of guanidino compounds. Decreased serum GSA and GAA levels might be an additional indicator of hyperthyroidism.

Homeostatic Plasticity of Striatal Neurons Intrinsic Excitability following Dopamine Depletion

The striatum is the major input structure of basal ganglia and is involved in adaptive control of behaviour through the selection of relevant informations. Dopaminergic neurons that innervate striatum die in Parkinson disease, leading to inefficient adaptive behaviour. Neuronal activity of striatal medium spiny neurons (MSN) is modulated by dopamine receptors. Although dopamine signalling had received substantial attention, consequences of dopamine depletion on MSN intrinsic excitability remain unclear. Here we show, by performing perforated patch clamp recordings on brain slices, that dopamine depletion leads to an increase in MSN intrinsic excitability through the decrease of an inactivating A-type potassium current, I A. Despite the large decrease in their excitatory synaptic inputs determined by the decreased dendritic spines density and the increase in minimal current to evoke the first EPSP, this increase in intrinsic excitability resulted in an enhanced responsiveness to their remaining synapses, allowing them to fire similarly or more efficiently following input stimulation than in control condition. Therefore, this increase in intrinsic excitability through the regulation of I A represents a form of homeostatic plasticity allowing neurons to compensate for perturbations in synaptic transmission and to promote stability in firing. The present observations show that this homeostatic ability to maintain firing rates within functional range also occurs in pathological conditions, allowing stabilizing neural computation within affected neuronal networks.

Serum guanidino compound levels and the influence of a single hemodialysis in uremic patients undergoing maintenance hemodialysis.

Guanidino compounds are increased in uremia and are highly suspected to be uremic toxins. The serum levels of 11 guanidino compounds and the influence of a single hemodialysis were evaluated in 30 steady-state uremic patients undergoing maintenance hemodialysis. Guanidino compound levels were detected using liquid cation exchange chromatography with a highly sensitive fluorescence detection method. Highly standardized dialysis procedures were performed. Before hemodialysis, high levels were found for guanidinosuccinic acid, N-alpha-acetylarginine, argininic acid, creatinine, gamma-guanidinobutyric acid, guanidine and methylguanidine. Guanidinosuccinic acid reached levels associated with toxic effects in vitro. After hemodialysis, although lowered, guanidinosuccinic acid, creatinine, guanidine and methylguanidine were still markedly increased. No differences in the percent decrease, during a single hemodialysis, of the studied compounds were found using different membranes such as cellulose acetate, cuprophane and polyacrylonitrile membranes. Substantial differences, however, in the percent decrease of the different guanidino compounds were found, ranging from 25 +/- 13% for arginine to 74 +/- 7.5% for guanidinosuccinic acid. Data reported here show that guanidino compounds are raised in serum of uremic patients undergoing maintenance hemodialysis, before as well as after a single hemodialysis, while substantial differences in the percent decrease of the different guanidino compounds are found.

Amino acids and biogenic amines in cerebrospinal fluid of patients with Parkinson's disease.

To study changes in amino acid metabolism and biogenic amines in Parkinsons disease, we set up a prospective study and measured biogenic amines, their main metabolites, and 22 different amino acids, in cerebrospinal fluid of Parkinsons disease patients (n = 24) and age-matched controls (n = 30). A trend toward higher dopamine levels in Parkinsons disease patients was interpreted as an effect of treatment with levodopa and/or selegiline. Significantly lower concentrations of the dopamine metabolite 3,4-dihydroxyphenylacetic acid in the Parkinsons disease group might reflect dopaminergic cell loss. Our results revealed decreased serotonin catabolism that was interpreted as an effect of treatment with selegiline. Whereas all amino acid levels were unchanged, taurine was significantly lower in Parkinsons disease patients. Studies showed that taurine exerts a trophic action on the central nervous system. In this view, decreased taurine in a neurodegenerative disorder as Parkinsons disease deserves attention.