Decrease In Aspartate Levels Research Articles

Metabolic Alterations Caused by KRAS Mutations in Colorectal Cancer Contribute to Cell Adaptation to Glutamine Depletion by Upregulation of Asparagine Synthetase

A number of clinical trials have shown that KRAS mutations of colorectal cancer (CRC) can predict a lack of responses to anti-epidermal growth factor receptor–based therapy. Recently, there have been several studies to elucidate metabolism reprogramming in cancer. However, it remains to be investigated how mutated KRAS can coordinate the metabolic shift to sustain CRC tumor growth. In this study, we found that KRAS mutation in CRC caused alteration in amino acid metabolism. KRAS mutation causes a marked decrease in aspartate level and an increase in asparagine level in CRC. Using several human CRC cell lines and clinical specimens of primary CRC, we demonstrated that the expression of asparagine synthetase (ASNS), an enzyme that synthesizes asparagine from aspartate, was upregulated by mutated KRAS and that ASNS expression was induced by KRAS-activated signaling pathway, in particular PI3K-AKT-mTOR pathway. Importantly, we demonstrated that KRAS-mutant CRC cells could become adaptive to glutamine depletion through asparagine biosynthesis by ASNS and that asparagine addition could rescue the inhibited growth and viability of cells grown under the glutamine-free condition in vitro. Notably, a pronounced growth suppression of KRAS-mutant CRC was observed upon ASNS knockdown in vivo. Furthermore, combination of L-asparaginase plus rapamycin markedly suppressed the growth of KRAS-mutant CRC xenografts in vivo, whereas either L-asparaginase or rapamycin alone was not effective. These results indicate ASNS might be a novel therapeutic target against CRCs with mutated KRAS.

158 POSTER Targeting bladder tumor cells in vivo and in the urine by a peptide identified using phage display

A number of clinical trials have shown that KRAS mutations of colorectal cancer (CRC) can predict a lack of responses to anti-epidermal growth factor receptor–based therapy. Recently, there have been several studies to elucidate metabolism reprogramming in cancer. However, it remains to be investigated how mutated KRAS can coordinate the metabolic shift to sustain CRC tumor growth. In this study, we found that KRAS mutation in CRC caused alteration in amino acid metabolism. KRAS mutation causes a marked decrease in aspartate level and an increase in asparagine level in CRC. Using several human CRC cell lines and clinical specimens of primary CRC, we demonstrated that the expression of asparagine synthetase (ASNS), an enzyme that synthesizes asparagine from aspartate, was upregulated by mutated KRAS and that ASNS expression was induced by KRAS-activated signaling pathway, in particular PI3K-AKT-mTOR pathway. Importantly, we demonstrated that KRAS-mutant CRC cells could become adaptive to glutamine depletion through asparagine biosynthesis by ASNS and that asparagine addition could rescue the inhibited growth and viability of cells grown under the glutamine-free condition in vitro. Notably, a pronounced growth suppression of KRAS-mutant CRC was observed upon ASNS knockdown in vivo. Furthermore, combination of L-asparaginase plus rapamycin markedly suppressed the growth of KRAS-mutant CRC xenografts in vivo, whereas either L-asparaginase or rapamycin alone was not effective. These results indicate ASNS might be a novel therapeutic target against CRCs with mutated KRAS.

Effects of pharmacological manipulation on neurotransmitter and other amino acid levels in the CSF of the Senegalese baboon Papio papio

The concentrations of GABA, glutamate, aspartate, glycine, taurine, glutamine, asparagine and alanine were determined in the CSF of 10 Senegalese baboons (Papio papio) following initial ketamine anaesthesia and subsequent administration (4 h later) of different compounds known to alter either inhibitory or excitatory neurotransmission. Ketamine itself was apparently without effect as the administration of a second dose of ketamine did not significantly alter the levels of any of the amino acids studied, although GABA levels tended to decrease. The presence of haemolysed material in occasional samples was associated with high GABA, glutamate, aspartate, taurine and asparagine levels. Therefore only haemolysate-free samples were included for analysis. Of the compounds administered, γ-vinyl GABA had the most evident effect on CSF amino acid levels, increasing GABA (>5-fold) and decreasing glutamate (>50%), aspartate (40–50%), asparagine (20%) and alanine (30–35%) levels. The changes in GABA, glutamate and aspartate were still apparent 24 h post-γ-vinyl GABA administration. In contrast, sodium valproate did not significantly alter the CSF levels of any of the amino acids studied. Upon acute administration allylglycine decreased the CSF concentrations of GABA and alanine, but not glutamate. These alterations are unlikely related to the occurrence of allylglycine-induced convulsions (in 2 of 4 experiments) as electroconvulsive shock did not alter CSF amino acid levels. During the experimental period encompassing the allylglycine injection (8 weeks), basal (initial post-ketamine, pre-drug sample) amino acid levels were abnormal with large increases in glutamate, GABA, aspartate and taurine whereas asparagine levels were below the limit of detection. Diazepam administration was followed by a significant increase in taurine and a decrease in aspartate levels. Administration of MK-801 was associated with an increase in taurine levels, whereas GABA levels were low immediately after PCP. No other changes in CSF amino acids were observed after the NMDA-channel blockers. The present results suggest that the Papio papio is a useful model for studying the alterations in CSF amino acids following pharmacological manipulation of central neurotransmitter systems. GABA and glutamate levels appear to be the most sensitive to change. For compounds with a long onset and/or duration of action the amino acid levels should be measured over several hours post-drug administration.

Regulation of transmitter gamma-aminobutyric acid (GABA) synthesis and metabolism illustrated by the effect of gamma-vinyl GABA and hypoglycemia.

The effect of different treatments on amino acid levels in neostriatum was studied to throw some light on the synthesis and metabolism of gamma-aminobutyric acid (GABA). Irreversible inhibition of GABA transaminase by microinjection of gamma-vinyl GABA (GVG) led to a decrease in aspartate, glutamate, and glutamine levels and an increase in the GABA level, such that the nitrogen pool remained constant. The results indicate that a large part of brain glutamine is derived from GABA. Hypoglycemia led to an increase in the aspartate level and a decrease in glutamate, glutamine, and GABA levels. The total amino acid pool was decreased compared with amino acid levels in normoglycemic rats. GVG treatment of hypoglycemic rats led to a decrease in the aspartate level and a further reduction in glutamate and glutamine levels. In this case, GABA accumulation continued, although the glutamine pool was almost depleted. The GABA level increased postmortem, but there were no detectable changes in levels of the other amino acids. Pretreatment of the rats with hypoglycemia reduced both glutamate and glutamine levels with a subsequent decreased postmortem GABA accumulation. The half-maximal GABA synthesis rate was obtained when the glutamate level was reduced by 50% and the glutamine level was reduced by 80%.

Anticonvulsant activity of intracerebroventricularly administered valproate and valproate analogues. a dosedependent correlation with changes in brain aspartate and GABA levels in DBA/2 mice

Valproate and the branch-chain valproate analogues, 2-propyl-hexanoate and 2-ethyl-hexanoate, block sound-induced seizures in DBA/2 mice following their intracerebroventricular administration, the ED 50 values for the suppression the the clonic phase of the seizures being 6.0, 5.0, and 10.2 μmoles respectively. The straight-chain analogues, butyrate and pentanoate, have no anticonvulsant activity. Systemic administration of branched-chain valproate analogues has previously shown a progressive increase in the anticonvulsant activity of the analogues with an increase in the chain-length of the molecules. This relationship is abolished when the same analogues are injected directly into the ventricles. The icv administration of the 2 straight-chain, inactive analogues produces no effect on brain aspartate and GABA levels (with the exception of a butyrate-induced 34% rise in forebrain GABA level). There is a dose-dependent decrease in aspartate levels in cerebellum and forebrain (up to 45–55% reduction), and a dose-dependent increase in GABA levels in forebrain (up to 30–75% rise) 30 min after the icv administration of the 3 anticonvulsant branched-chain fatty acids. 2-Propyl-hexanoate does not affect the cerebellar GABA level significantly, while valproate and 2-ethyl-hexanoate administration produce 20–40% increases in cerebellar GABA levels.