Serum Carnosinase Deficiency Research Articles

Dual Effect of Carnosine on ROS Formation in Rat Cultured Cortical Astrocytes.

Carnosine is composed of β-alanine and L-histidine and is considered to be an important neuroprotective agent with antioxidant, metal chelating, and antisenescence properties. However, children with serum carnosinase deficiency present increased circulating carnosine and severe neurological symptoms. We here investigated the in vitro effects of carnosine on redox and mitochondrial parameters in cultured cortical astrocytes from neonatal rats. Carnosine did not alter mitochondrial content or mitochondrial membrane potential. On the other hand, carnosine increased mitochondrial superoxide anion formation, levels of thiobarbituric acid reactive substances and oxidation of 2',7'-dichlorofluorescin diacetate (DCF-DA), indicating that carnosine per se acts as a pro-oxidant agent. Nonetheless, carnosine prevented DCF-DA oxidation induced by H2O2 in cultured cortical astrocytes. Since alterations on mitochondrial membrane potential are not likely to be involved in these effects of carnosine, the involvement of N-Methyl-D-aspartate (NMDA) receptors in the pro-oxidant actions of carnosine was investigated. MK-801, an antagonist of NMDA receptors, prevented DCF-DA oxidation induced by carnosine in cultured cortical astrocytes. Astrocyte reactivity induced by carnosine was also prevented by the coincubation with MK-801. The present study shows for the very first time the pro-oxidant effects of carnosine per se in astrocytes. The data raise awareness on the importance of a better understanding of the biological actions of carnosine, a nutraceutical otherwise widely reported as devoid of side effects.

Impairment of electron transfer chain induced by acute carnosine administration in skeletal muscle of young rats.

Serum carnosinase deficiency is an inherited disorder that leads to an accumulation of carnosine in the brain tissue, cerebrospinal fluid, skeletal muscle, and other tissues of affected patients. Considering that high levels of carnosine are associated with neurological dysfunction and that the pathophysiological mechanisms involved in serum carnosinase deficiency remain poorly understood, we investigated the in vivo effects of carnosine on bioenergetics parameters, namely, respiratory chain complexes (I–III, II, and II-III), malate dehydrogenase, succinate dehydrogenase, and creatine kinase activities and the expression of mitochondrial-specific transcription factors (NRF-1, PGC-1α, and TFAM) in skeletal muscle of young Wistar rats. We observed a significant decrease of complexes I–III and II activities in animals receiving carnosine acutely, as compared to control group. However, no significant alterations in respiratory chain complexes, citric acid cycle enzymes, and creatine kinase activities were found between rats receiving carnosine chronically and control group animals. As compared to control group, mRNA levels of NRF-1, PGC-1α, and TFAM were unchanged. The present findings indicate that electron transfer through the respiratory chain is impaired in skeletal muscle of rats receiving carnosine acutely. In case these findings are confirmed by further studies and ATP depletion is also observed, impairment of bioenergetics could be considered a putative mechanism responsible for the muscle damage observed in serum carnosinase-deficient patients.

A novel, quantitative assay for homocarnosine in cerebrospinal fluid using stable-isotope dilution liquid chromatography–tandem mass spectrometry

We describe a rapid and sensitive method for the quantification of homocarnosine in physiological fluids, with particular emphasis on cerebrospinal fluid (CSF). Homocarnosine was quantified as the butyl derivative, with (2)H(2)-l-homocarnosine as internal standard. Following deproteinization of CSF samples, supernatants were evaporated to dryness and derivatized with 10% 6M HCl in butanol. Samples were chromatographed on a C(18) column and detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS) operating in the multiple reaction monitoring mode. The intra- and inter-assay variations were 4.6 and 10.9%, respectively. Mean recovery of homocarnosine at two concentrations was 105%. The limit of detection in CSF approximated 20 nmol/L. CSF homocarnosine is age dependent and ranges from <0.02 to 10 micromol/L. Our method is applicable to the analysis of CSF derived from patients with heritable defects in the GABA pathway, patients with homocarnosinosis or serum carnosinase deficiency, and should be applicable to other model systems in order to further explore the biological role and significance of homocarnosine in mammalian systems.

Inherited disorders of GABA metabolism.

Gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter in the mammalian central nervous system, is produced from glutamic acid in a reaction catalysed by glutamic acid decarboxylase. The sequential actions of GABA-transaminase (converting GABA to succinic semialdehyde) and succinic semialdehyde dehydrogenase (oxidizing succinic semialdehyde to succinic acid) allow oxidative metabolism of GABA through the tricarboxylic acid cycle. The inherited disorders of GABA metabolism include: (1) pyridoxine-dependent seizures (?glutamic acid decarboxylase deficiency) (> 50 patients); (2) GABA-transaminase deficiency (2 patients/1 family); (3) succinic semialdehyde dehydrogenase deficiency (32 patients/21 families); and (4) homocarnosinosis associated with serum carnosinase deficiency (3 patients/1 family). Homocarnosine is a brain-specific dipeptide of GABA and L-histidine. Of these four defects, definitive enzymatic diagnoses have been made only for GABA-transaminase and succinic semialdehyde dehydrogenase deficiencies. The presumptive mode of inheritance for all disorders is autosomal recessive, and all are associated with central nervous system dysfunction. Only succinic semialdehyde dehydrogenase deficiency manifests organic aciduria, which may account for the higher number of patients identified with this disorder; identification of additional patients with some of the other disorders will require increased request for analysis of cerebrospinal fluid metabolites by paediatricians and neurometabolic specialists.

Serum carnosinase deficiency: a non-disabling phenotype?

Serum carnosinase deficiency (McKusick 21220) is a rare condition, described in 13 cases. Ten additional individuals with serum carnosinase deficiency have been identified. All continued to excrete increased amounts of carnosine in their urine despite a meat-free diet for 3 days. Serum carnosinase activity ranged from 0-30% of normal. In four individuals a normal Km for carnosine of 0.12 mM was observed, while in five individuals an increased Km was found. Homocarnosine levels in CSF in three individuals ranged from 3.4 to 15 mM. Clinical symptoms in these individuals were as follows: attention deficit disorder: 4; non progressive developmental delay: 1; neurofibromatosis: 1; absences seizures: 1; severe, but non-progressive mental retardation, seizures and neurosensory hearing loss: 1; progressive childhood dementia; 1; clinically normal: 1. There was no correlation between severity and type of the neurological symptoms and residual serum carnosinase activity. Although a definite conclusion can only be made after a considerably higher number of individuals has been analyzed, the suspicion that serum carnosinase deficiency is unrelated to the neurological symptoms is strengthened by these observations. There may, however, be an association with a predisposition for mental deficiency.

Homocamosinosis: lack of serum carnosinase is the defect probably responsible for elevated brain and CSF homocarnosine

Patients afflicted with homocarnosinosis have elevated concentrations of homocarnosine in brain and CSF. It has been reported that they lack brain homocarnosinase. However, we have found that these patients are deficient in serum carnosinase, a dipeptidase which hydrolyzes homocarnosine about 5% as rapidly as it splits carnosine. Homocamosinase could not be detected in normal human brain extracts after isoelectric focusing or DEAE-cellulose column chromatography. The ability of brain extracts to hydrolyze homocarnosine thus appears to be attributable solely to the serum carnosinase which is present because of serum trapped in the brain sample. Preliminary data indicate that homocarnosinase is probably not present in 13 other human tissues. Normal CSF contained serum carnosinase, whereas the CSF of a homocarnosinosis patient was lacking this enzyme. Thus it appears that the elevated concentrations of homocarnosine in the CSF of homocarnosinosis patients are attributable to serum carnosinase deficiency.

Serum carnosinase deficiency: Decreased affinity of the enzyme for the substrate

Serum carnosinase deficiency: Decreased affinity of the enzyme for the substrate

Homocarnosinosis: hypercarnosinuria.

Abstract: Homocarnosine (γ‐aminobutyrylhistidine) is a brain‐specific dipeptide. Homocarnosinosis is a familial metabolic disorder in which spastic paraplegia, progressive mental deficiency, and retinal pigmentation coexist with increased CSF homocarnosine levels, i.e. approximately 20 times higher than the mean control level. In the present study, the urinary excretion of carnosine (β‐alanylhistidine) and anserine (β‐alanyl‐1‐methylhistidine) was determined in patients with homocarnosinosis and in their close relatives. Both the patients and their relatives were also loaded with chicken meat, which is rich in anserine and carnosine. The results were compared with those obtained in childhood hypercarnosinuria with serum carnosinase deficiency. Somewhat surprisingly, patients with homocarnosinosis were also shown to have hypercarnosinuria. Chicken meat loading in healthy individuals results in increased excretion of carnosine and anserine and, in addition, 1‐methylhistidine in the urine. Homocarnosinosis patients and patients with serum carnosinase deficiency also showed an increased excretion of carnosine and anserine, but 1‐methylhistidine was not detected in serum carnosinase deficiency, and it was present only in very small amounts in homocarnosinosis. This defect seems to be due to lack of the hydrolyzing enzyme activity. The biochemical and clinical similarities between adult homocarnosinosis and infantile serum carnosinase deficiency are intriguing. A complete insight into the relationship between them must await further investigation.

Serum carnosinase deficiency concomitant with mental retardation.

Extract: A family was studied in which two boys with progressive neurologic disease exhibited carnosinemia (20–30 μUmol/ml serum), carnosinuria (60–200 μUmol/24 hr), and a deficiency in serum carnosinase activity (<0.03 μUmol/hr/ml). Their sister, who is apparently both physically and mentally normal, also exhibits carnosinuria and is deficient in serum carnosinase activity. Tissue extracts of liver, kidney, and spleen obtained at autopsy of one of the male patients were assayed for carnosinase and other enzyme activities and were subjected to starch block electrophoresis at pH 7.0 for 4 hr at 4°. The starch block electrophoreses, under conditions which readily demonstrate two electrophoretic forms of the enzyme in normal tissue extracts, revealed that only one of the two forms was present. This activity corresponded to the slower form in normal tissues and appeared to be present in normal concentrations. Speculation: The excretion of abnormal quantities of carnosine and/or anserine in the urine appears to be related to inherited serum carnosinase deficiency, but further studies are required to determine the association of the deficiency of the enzyme with progressive neurologic disease as well as the nature and role of the two electrophoretic forms of tissue carnosinase activity.

A new sensitive method for the determination of serum carnosinase activity using l-carnosine-[ i- 14C]β-alanyl as substrate

A new method has been developed for the determination of serum carnosinase activity using l-carnosine-[1- 14C]β-alanyl as substrate. The serum carnosinase activity was calculated from the ratio decomp./min β-alanine: total decomp./min at the end of the incubation. The K m -value of the serum carnosinase-catalysed hydrolysis of l-carnosine was found to be 7.1 · 10 −5 M. In adults the mean value for serum carnosinase activity amounted to 44.2 ± 14 (S.D.) units/1. In serum of newborns only very low carnosinase activities were found. This sensitive method may be applied to detect patients with serum carnosinase deficiency.