Neurotoxic effects of endogenous materials: quinolinic acid, L-pyroglutamic acid, and thyroid releasing hormone (TRH)

Jejunal Transcriptomic Profiling for Differences in Feed Conversion Ratio in Slow-Growing Chickens

Simple Summary

The slow-growing Korat chicken (KR) is economically attractive, as KR meat has a high selling price and has thus been used in Thailand to support smallholder farmers. However, low feed efficiency in KR stockbreeding makes the product less competitive and improving KR feed efficiency is central to increasing KR profitability. Using RNA sequencing, we compared the jejunal transcriptomic profiles of low- and high-feed conversion ratio (FCR) KR chickens, to identify FCR-related transcriptional variation and biological pathways. Gene Ontology and Kyoto Encyclopedia of Gene and Genome analysis revealed that the main pathways involved in KR FCR variation are related to immune response, glutathione metabolism, vitamin transport and metabolism, lipid metabolism, and neuronal and cardiac maturation, development, and growth. This is the first study to investigate, in the jejunum, the molecular genetic mechanisms affecting the FCR of slow-growing chickens. These findings will be useful in line-breeding programs to improve feed efficiency and profitability in slow-growing chicken stockbreeding.

Abstract

Improving feed efficiency is an important breeding target for the poultry industry; to achieve this, it is necessary to understand the molecular basis of feed efficiency. We compared the jejunal transcriptomes of low- and high-feed conversion ratio (FCR) slow-growing Korat chickens (KRs). Using an original sample of 75 isolated 10-week-old KR males, we took jejunal samples from six individuals in two groups: those with extremely low FCR (n = 3; FCR = 1.93 ± 0.05) and those with extremely high FCR (n = 3; FCR = 3.29 ± 0.06). Jejunal transcriptome profiling via RNA sequencing revealed 56 genes that were differentially expressed (p < 0.01, FC > 2): 31 were upregulated, and 25 were downregulated, in the low-FCR group relative to the high-FCR group. Functional annotation revealed that these differentially expressed genes were enriched in biological processes related to immune response, glutathione metabolism, vitamin transport and metabolism, lipid metabolism, and neuronal and cardiac maturation, development, and growth, suggesting that these are important mechanisms governing jejunal feed conversion. These findings provide an important molecular basis for future breeding strategies to improve slow-growing chicken feed efficiency.

The Footprint of Kynurenine Pathway in Neurodegeneration: Janus-Faced Role in Parkinson's Disorder and Therapeutic Implications

Progressive degeneration of neurons and aggravation of dopaminergic neurons in the substantia nigra pars compacta results in the loss of dopamine in the brain of Parkinson's disease (PD) patients. Numerous therapies, exhibiting transient efficacy have been developed; however, they are mostly accompanied by side effects and limited reliability, therefore instigating the need to develop novel optimistic treatment targets. Significant therapeutic targets have been identified, namely: chaperones, protein Abelson, glucocerebrosidase-1, calcium, neuromelanin, ubiquitin-proteasome system, neuroinflammation, mitochondrial dysfunction, and the kynurenine pathway (KP). The role of KP and its metabolites and enzymes in PD, namely quinolinic acid (QUIN), kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), 3-hydroxyanthranillic acid (3-HAA), kunurenine-3-monooxygenase (KMO), etc. has been reported. The neurotoxic QUIN, N-methyl-D-aspartate (NMDA) receptor agonist, and neuroprotective KYNA-which antagonizes QUIN actions-primarily justify the Janus-faced role of KP in PD. Moreover, KP has been reported to play a biomarker role in PD detection. Therefore, the authors detail the neurotoxic, neuroprotective, and immunomodulatory neuroactive components, alongside the upstream and downstream metabolic pathways of KP, forming a basis for a therapeutic paradigm of the disease while recognizing KP as a potential biomarker in PD, thus facilitating the development of a suitable target in PD management.

Final Safety Assessment for PCA and Sodium PCA

PCA is the cosmetic ingredient term used for the cyclic organic compound known commonly as pyroglutamic acid. Sodium PCA is the sodium salt of PCA. Both are used as hair and skin conditioning agents. These ingredients are recommended to be used in a concentration range of 0.2-4%. One optical isomer of PCA (the L form) is a naturally occurring component of mammalian tissue. PCA applied to the skin is absorbed to a limited extent. Absorption is in addition to PCA already present in the skin. In short-term and subchronic studies in several animal species, findings were unremarkable except for neurotoxicity in mice when injected interstriatally. No such findings were seen in similar studies using rats or with oral administration using mice. In animal studies, Sodium PCA was nonirritating to the eye and skin at concentrations up to 50%. No evidence of phototoxicity, sensitization, or comedogenicity was found. These ingredients were not genotoxic. In a range of clinical tests, PCA and Sodium PCA were found to be nonirritating and nonsensitizing (with and without UV exposure). Based on the low actual skin penetration of dermally applied PCA and in recognition of the endogenous levels found in the skin, it was considered that reproductive and developmental toxicity data were not critical to completion of the safety assessment. Based on the available data, it was concluded that PCA and Sodium PCA are safe as presently used in cosmetic formulations. These ingredients, however, should not be used in cosmetic products containing nitrosating agents.

Quinolinic acid: an endogenous neurotoxin with multiple targets

Quinolinic acid (QUIN), a neuroactive metabolite of the kynurenine pathway, is normally presented in nanomolar concentrations in human brain and cerebrospinal fluid (CSF) and is often implicated in the pathogenesis of a variety of human neurological diseases. QUIN is an agonist of N-methyl-D-aspartate (NMDA) receptor, and it has a high in vivo potency as an excitotoxin. In fact, although QUIN has an uptake system, its neuronal degradation enzyme is rapidly saturated, and the rest of extracellular QUIN can continue stimulating the NMDA receptor. However, its toxicity cannot be fully explained by its activation of NMDA receptors it is likely that additional mechanisms may also be involved. In this review we describe some of the most relevant targets of QUIN neurotoxicity which involves presynaptic receptors, energetic dysfunction, oxidative stress, transcription factors, cytoskeletal disruption, behavior alterations, and cell death.

Substrate channeling in proline metabolism

Proline metabolism is an important pathway that has relevance in several cellular functions such as redox balance, apoptosis, and cell survival. Results from different groups have indicated that substrate channeling of proline metabolic intermediates may be a critical mechanism. One intermediate is pyrroline-5-carboxylate (P5C), which upon hydrolysis opens to glutamic semialdehyde (GSA). Recent structural and kinetic evidence indicate substrate channeling of P5C/GSA occurs in the proline catabolic pathway between the proline dehydrogenase and P5C dehydrogenase active sites of bifunctional proline utilization A (PutA). Substrate channeling in PutA is proposed to facilitate the hydrolysis of P5C to GSA which is unfavorable at physiological pH. The second intermediate, gamma-glutamyl phosphate, is part of the proline biosynthetic pathway and is extremely labile. Substrate channeling of gamma-glutamyl phosphate is thought to be necessary to protect it from bulk solvent. Because of the unfavorable equilibrium of P5C/GSA and the reactivity of gamma-glutamyl phosphate, substrate channeling likely improves the efficiency of proline metabolism. Here, we outline general strategies for testing substrate channeling and review the evidence for channeling in proline metabolism.

L-pyroglutamic acid inhibits energy production and lipid synthesis in cerebral cortex of young rats in vitro

In the present study we investigated the effects of L-pyroglutamic acid (PGA), which predominantly accumulates in the inherited metabolic diseases glutathione synthetase deficiency (GSD) and gamma-glutamylcysteine synthetase deficiency (GCSD), on some in vitro parameters of energy metabolism and lipid biosynthesis. We evaluated the rates of CO2 production and lipid synthesis from [U-14C]acetate, as well as ATP levels and the activities of creatine kinase and of the respiratory chain complexes I-IV in cerebral cortex of young rats in the presence of PGA at final concentrations ranging from 0.5 to 3 mM. PGA significantly reduced brain CO2 production by 50% at the concentrations of 0.5 to 3 mM, lipid biosynthesis by 20% at concentrations of 0.5 to 3 mM and ATP levels by 52% at the concentration of 3 mM. Regarding the enzyme activities, PGA significantly decreased NADH:cytochrome c oxireductase (complex I plus CoQ plus complex III) by 40% at concentrations of 0.5-3.0 mM and cytochrome c oxidase activity by 22-30% at the concentration of 3.0 mM, without affecting the activities of succinate dehydrogenase, succinate:DCPIP oxireductase (complex II), succinate:cytochrome c oxireductase (complex II plus CoQ plus complex III) or creatine kinase. The results strongly indicate that PGA impairs brain energy production. If these effects also occur in humans, it is possible that they may contribute to the neuropathology of patients affected by these diseases.

Immunohistochemical localization of 5-oxo-L-prolinase, an enzyme of the gamma-glutamyl cycle, in porcine brain microvessels

The immunohistochemical analysis of the distribution of 5-oxo-L-prolinase in porcine brain at the light microscopic level was performed with an antibody raised against the enzyme purified from pig kidney. The present study reveals the specific expression of 5-oxo-L-prolinase in brain capillaries with an average diameter of 4.1+/-0.9 microm, while larger blood vessels remain unstained. Porcine kidney and skeletal muscle show no endothelial-specific staining with the antibody. In some cases, the asymmetrical staining pattern in cross and longitudinal sections of brain microvessels indicate endothelial- but also pericyte-specific expression.

Kinetic parameters and tissue distribution of 5-oxo-L-prolinase determined by a fluorimetric assay

5-Oxo-L-prolinase (5-OPase) catalyses the hydrolysis of 5-oxo-L-proline to glutamate with concomitant stoichiometric cleavage of ATP to ADP, a reaction which is known to be part of the gamma-glutamyl cycle-an interrelated series of reactions involved in the synthesis and metabolism of glutathione. As recent studies indicate, this cyclic pathway plays a crucial role in the regulation of amino acid transport. Apparently, the intermediate product 5-oxo-L-proline functions as a second messenger molecule that upregulates the activity of certain amino acid transport systems. Thus, the degradation of 5-oxo-L-proline by 5-OPase leads to the downregulation of this stimulus. In this study, a new sensitive fluorimetric assay for 5-OPase activity was established which is based on the derivatization of glutamate with o-phthaldialdehyde in the presence of thiols and subsequent separation of the products by HPLC. The method is suitable for the screening of chromatography fractions as well as for the determination of the kinetic parameters Km and Vmax of purified 5-OPase. Additionally, it can be used for the measurement of enzyme activity in crude cell extracts and evaluation of tissue distribution.

Neurochemical effects of L-pyroglutamic acid

The effect of L-pyroglutamic acid, a metabolite that accumulates in pyroglutamic aciduria, on different neurochemical parameters was investigated in adult male Wistar rats. Glutamate binding, adenylate cyclase activity and G protein coupling to adenylate cyclase were assayed in the presence of the acid. L-pyroglutamic acid decreased Na(+)-dependent and Na(+)-independent glutamate binding. Basal and GMP-PNP stimulated adenylate cyclase activity were not affected by the acid. Furthermore, rats received unilateral intrastriatal injections of 10-300 nmol of buffered L-pyroglutamic acid. Vehicle (0.25 M Tris-Cl, pH 7.35-7.4) was injected into the contralateral striatum. Neurotoxic damage was assessed seven days after the injection by histological examination and by weighing both cerebral hemispheres. No difference in histology or weight could be identified between hemispheres. These results suggest that, although capable of interfering with glutamate binding, pyroglutamate did not cause a major lesion in the present model of neurotoxicity.

Picolinic acid protects against quinolinic acid-induced depletion of NADPH diaphorase containing neurons in the rat striatum

Previous studies in our laboratory have demonstrated that focal injections of picolinic acid (PIC) protect the cholinergic neurons of the nucleus basalis magnocellularis (nbm) against quinolinic acid (QUIN)-induced neurotoxicity. The present study was designed to examine the effects of chronic infusions of QUIN and PIC on nicotinamide adenine dinucleotide (NADPH) diaphorase containing neurons of the rat striatum. Using osmotic minipumps, QUIN (6 nmol/h) and PIC (18 nmol/h) were infused alone or in combination to examine the neurotoxic effects of QUIN and the potential anti-neurotoxic action of PIC. Exposure to QUIN for 7 days severely depleted NADPH diaphorase-positive neurons. When co-infused with this neurotoxic dose of QUIN, PIC attenuated the depletion of NADPH diaphorase neurons induced by QUIN. The infusion of PIC alone did not affect the number of these neurons. These results indicate that PIC itself is not neurotoxic and effectively prevents chronic QUIN-induced neurotoxicity in the rat striatum. Since PIC and QUIN are derived from the same metabolic pathway, a balance between endogenous compounds that produce neurotoxicity and those antagonizing these effects may be important in normal neuronal function.

Neurotoxicity of quinolinic acid and its derivatives in hypoxic rat hippocampal slices

The excitotoxicity of quinolinic acid (2,3-pyridinedicarboxylic acid), a potent endogenous N-methyl-D-aspartate (NMDA)-type agonist, was characterized in the hypoxic hippocampal slice preparation. A series of other pyridinedicarboxylic acids was also tested in this preparation in order to obtain information about the structural requirements for the interaction between the NMDA receptor and its agonists. Of the 7 pyridinedicarboxylic acids tested, only quinolinic acid and its anhydride exerted their excitotoxicity by enhancing hypoxic neuronal damage in rat hippocampal slices at a relatively low concentration (100 microM). Much higher concentration (1 mM) of 3,4-pyridinedicarboxylic acid was required to exhibit any enhancement of hypoxic neuronal damage. The rest of the derivatives were innocuous. The effect of quinolinic acid was blocked by DL-2-amino-5-phosphonovaleric acid, by elevated magnesium levels in the incubation medium or by perfusion with a medium depleted of calcium. Aglycemic damage was also enhanced by quinolinic acid. It appears from the present study that two adjacent carboxylic groups on the pyridine ring, preferably at positions 2 and 3, are a prerequisite for an interaction between the NMDA receptor and its agonist. However, other factors may have great influence on that interaction as was evident from the total impotency of 6-methyl-quinolinic acid. The hypoxic hippocampal slice preparation and its neuronal function is an inexpensive model system, sensitized to the neurotoxins, and thus, allows the easy screening and evaluation of potential ligands of the glutamate receptor and its subtypes.

Hypodense eosinophils and interleukin 5 activity in the blood of patients with the eosinophilia-myalgia syndrome

The recent recognition of the eosinophilia-myalgia syndrome (EMS) associated with the ingestion of L-tryptophan prompted an analysis of the peripheral blood eosinophil phenotypes and of the serum eosinophil hematopoietins in this disorder. Five patients with an illness characterized by the abrupt onset of aching skeletal muscles, edema, thickening and induration of the skin, and marked blood eosinophilia associated with L-tryptophan ingestion provided eosinophils, serum, or both, for evaluation. Gradient sedimentation density analysis of the peripheral blood eosinophils from four of these patients revealed that 43 +/- 13% (mean +/- SEM) of the cells had converted to the abnormal (hypodense) sedimenting phenotype. When normodense eosinophils from the reference donors were cultured for 3 days in medium supplemented with increasing concentrations of serum from the patients with EMS, their viability increased in a dose-dependent manner to 45%, which was significantly augmented over the effect of normal serum. This eosinophil viability-sustaining activity was inhibited by 76 +/- 7% (mean +/- SEM; n = 3) by the addition of anti-interleukin 5 (IL-5) but not by neutralizing antibodies monospecific for either granulocyte/macrophage colony-stimulating factor (GM-CSF) or IL-3. IL-5, an eosinophilopoietic factor, converts normodense peripheral blood eosinophils in vitro to a hypodense sedimenting form with extended viability and augmented biologic responses to activating stimuli. Thus, the presence of IL-5 in the sera of patients with EMS may contribute to the development and maintenance of the eosinophilia and may regulate the conversion of the peripheral blood eosinophils to the hypodense phenotype with augmented pathobiologic potential.

Lamotrigine protects against kainate but not ibotenate lesions in rat striatum

Pretreatment of rats with 8-16 mg/kg of lamotrigine 1 h before intrastriatal injections of 2 nm of kainic acid significantly attenuated the neurotoxicity as evidenced by measurements of striatal choline acetyltransferase and glutamate decarboxylase activities. No significant effect was seen on the toxicity of intrastriatal injections of quinolinic acid or ibotenic acid. These differential effects are further evidence that these neurotoxins act at different excitatory amino acid receptors and that the neurotoxicity of kainate is uniquely dependent on neuronally released glutamate.

gamma-Glutamyltransferase activity is unchanged in acutely quinolinate-lesioned rat neostriatum but is elevated in Huntington's disease caudate

gamma-Glutamyltransferase (GGT; gamma-glutamyl transpeptidase) was measured in the neostriata of rats 5-7 days after local injections of 0-150 nmol of quinolinic acid. In contrast to the high levels seen in studies on the caudate in a few Huntington's disease cases, GGT activity showed no significant relation to the amount of quinolinic acid injected or to the extent of neuronal loss, as indicated by assays of choline acetyltransferase and glutamate decarboxylase on the same striatal homogenates. The chronicity of the degenerative disease, contrasted with the acuteness of the lesion, may explain the difference.

Effect of MK-801, kynurenate, glycine, dextrorphan and 4-acetylpyridine on striatal toxicity of quinolinate

Measurements of striatal choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities indicated that systemic administration of 4-8 mg/kg of MK-801 to rats completely blocked neuronal damage due to intrastriatal injections of 75-150 nmol of quinolinic acid. Similar experiments with 0-2 mg/kg MK-801 suggested the ED50 might be between 1 and 1.5 mg/kg for protection against 50 nmol of intrastriatal quinolinic acid, and between 2 and 3 mg/kg for 75 nmol. Repeated pretreatment with kynurenate (3 x 300 mg/kg) gave significant but not complete protection against similar doses of quinolinic acid, with the protective effect being greater for GAD than for ChAT. Glycine appeared to potentiate the effect of high doses of quinolinic acid on ChAT and the other pretreatments tested (dextrorphan, dextromethorphan, 4-acetylpyridine) had no significant effect.

Tetrahydroaminoacridine potentiates neurotoxicity of quinolinic acid in rat striatum

Intraperitoneal injection of 5 mg/kg of tetrahydro-9-amino-acridine (THA) in rats 1 h before intrastriatal injection of 50-150 nmol of quinolinic acid potentiated the local neurotoxicity as indicated by measurements of striatal levels of glutamate decarboxylase and choline acetyltransferase. A larger dose (10 mg/kg) THA had no significant effect. The results are discussed in terms of THA's binding to various elements of the NMDA/sigma receptor complex and reported data on such binding are confirmed.

Striatal deficiency of L-pyroglutamic acid in Huntington's disease is accompanied by increased plasma levels

L-Pyroglutamic acid (L-PGA), a cyclized glutamate analogue, was measured in plasma, cerebrospinal fluid and brain tissue of patients with Huntington's disease (HD) and controls. In HD, plasma L-PGA was elevated and possibly reflects an increased requirement of cell membranes to be protected against peroxidative damage. L-PGA was decreased in caudate and putamen of HD patients. We suggest that striatal deficiency of L-PGA in HD is a consequence of neuronal loss which characteristically occurs in HD striatum.

Hypothesis: a role for quinolinic acid in the neuropathology of glutaric aciduria type I

Glutaric aciduria type I is an autosomal recessive metabolic disorder of children associated with severe dystonic motor disturbances and degeneration in the cerebral cortex, striatum and cerebellum. Biochemical studies demonstrate a deficiency in the enzyme glutaryl-CoA dehydrogenase. This enzyme metabolizes substrate derived from dietary tryptophan that could otherwise be converted to quinolinic acid within the brain. The law of mass action predicts that the production of quinolinic acid should be increased in glutaric aciduria type I. Quinolinic acid is a potent neurotoxin and convulsant when it is injected into the central nervous system of experimental animals. This paper argues that quinolinic acid may accumulate within the brain and cause the neuropathology of glutaric aciduria type I.