Luisa Mattoli

Inhibitors of kynurenine hydroxylase and kynureninase increase cerebral formation of kynurenate and have sedative and anticonvulsant activities

Kynurenate is an endogenous antagonist of the ionotropic glutamate receptors. It is synthesized from kynurenine, a tryptophan metabolite, and a significant increase in its brain concentration could be useful in pathological situations. We attempted to increase its neosynthesis by modifying kynurenine catabolism. Several kynurenine analogues were synthesized and tested as inhibitors of kynurenine hydroxylase (E.C.1.14.13.9) and of kynureninase (E.C.3.7.1.3), the two enzymes which catalyse the conversion of kynurenine to excitotoxin quinolinate. Among these analogues we observed that nicotinylalanine, a compound whose pharmacological properties have previously been reported, had an IC50 of 900 +/- 180 microM as inhibitor of kynurenine hydroxylase and of 800 +/- 120 microM as inhibitor of kynureninase. In the search for more potent molecules we noticed that meta-nitrobenzoylalanine had an IC50 of 0.9 +/- 0.1 microM as inhibitor of kynurenine hydroxylase and of 100 +/- 12 microM as inhibitor of kynureninase. When administered to rats meta-nitrobenzoylalanine (400 mg/kg) significantly increased the concentration of kynurenine (up to 10 times) and kynurenate (up to five times) in the brain. Similar results were obtained in the blood and in the liver. Furthermore meta-nitrobenzoylalanine increased in a dose dependent, long lasting (up to 13 times and up to 4 h) manner the concentration of kynurenate in the hippocampal extracellular fluid, as evaluated with a microdialysis technique. This increase was associated with a decrease in the locomotor activity and with protection from maximal electroshock-induced seizures in rats or from audiogenic seizures in DBA/2 mice. The conclusions drawn from the present study are: (i) meta-nitrobenzoylalanine is a potent inhibitor of kynurenine hydroxylase also affecting kynureninase; (ii) the inhibition of these enzymes causes a significant increase in the brain extracellular concentration of kynurenate; (iii) this increase is associated with sedative and anticonvulsant actions, suggesting a functional antagonism of the excitatory amino acid receptors.

Comparison of the Neurochemical and Behavioral Effects Resulting from the Inhibition of Kynurenine Hydroxylase and/or Kynureninase

Abstract: Several kynurenine analogues were synthesized and tested as inhibitors of the enzymes kynurenine hydroxylase and/or kynureninase with the aim of identifying new compounds able to inhibit the synthesis of quinolinic acid (an endogenous excitotoxin) and to increase that of kynurenic acid, an endogenous antagonist of ionotropic glutamate receptors. Among these analogues, we selected m‐nitrobenzoylalanine (mNBA) as an inhibitor of kynurenine hydroxylase and o‐methoxybenzoylalanine (oMBA) as an inhibitor of kynureninase. When administered to rats, mNBA was more potent than oMBA in increasing the content of kynurenine and of kynurenic acid in the brain, blood, liver, and kidney. This confirms that hydroxylation is the main pathway of kynurenine metabolism. Both mNBA and oMBA (50–400 mg/kg i.p.) increased the concentration of kynurenate in hippocampal extracellular spaces (as measured with a microdialysis technique) and, when simultaneously injected, their effects were additive. This biochemical effect was associated with a decrease in locomotor activity in rats and with a protection of audiogenic convulsions in DBA/2 mice. In conclusion, the results of the present experiments indicate the possibility of increasing the neosynthesis of kynurenic acid by inhibiting the enzymes that metabolize kynurenine to 3‐hydroxykynurenine or to anthranilic acid. The increased synthesis of kynurenate is associated with behavioral effects such as sedation and protection from seizures, which suggests a functional antagonism of the excitatory amino acid receptors.

Synthesis and activity of enantiopure (S) (m-nitrobenzoyl) alanine, potent kynurenine-3-hydroxylase inhibitor

Abstract The enantioselective synthesis of S (+) ( m -nitrobenzoyl)alanine along with the inhibition of kynurenine-3-hydroxylase and kynureninase activity are reported.

Modulation of the Kynurine Pathway of Tryptophan Metabolism in Search for Neuroprotective Agents. Focus on Kynurenine-3-Hydroxylase

A novel potent and selective kynurenine-3-hydroxylase inhibitor is descibed along a preliminary evaluation in a in vivo gerbil model of its ability to increase the kynurenine and kynurenic acid concentration in both plasma and brain. These data support the notion that kynurenine-3-hydroxylase inhibitors may have a sustained therapeutic potential in those diseases characterized by unbalance in the QUIN/KYNA branches of the kynurenine pathway.

Chromatographic separation and evaluation of the lipophilicity by reversed-phase high-performance liquid chromatography of fullerene-C60 derivatives

Abstract Two water-soluble regioisomers of tris -dicarboxymethanofullerene-C 60 with D 3 ( 3 ) or C 3 ( 4 ) symmetry have been shown to possess interesting neuroprotective properties, among which the free radical scavenging activity is particularly relevant. Here we report a faster preparative scale separation of the two trisadducts along with analytical RP-HPLC data of 3 and 4 in order to provide additional information for the evaluation of their membrane permeability.

Kynurenine-3-Hydroxylase and its Selective Inhibitors

The modulation of the kynurenine (KYN) catabolic pathway of L-Tryptophan (L-Trp) is gaining a considerable interest since the discovery that two metabolites along the route, kynurenic acid (KYNA) and quinolinic acid (QUIN), act in an opposite manner at excitatory amino acid (EAA) receptors (Schwarcz, 1993). KYNA is a non selective antagonist at the strychnine-insensitive glycine site of the NMDA receptor complex and is endowed with neuroprotective properties (Foster et al., 1984). QUIN, on the other hand, is a selective agonist at the NMDA site of the NMDA receptor complex and is a relatively potent neurotoxin implicated in the pathogenesis of a number of neurodegenerative diseases.