Volume 28, Issue 2

The kynurenine pathway (KP) is the metabolic pathway via which L-tryptophan is converted to nicotinamide. It serves important immune-regulatory roles. This article will review the evidence for involvement of the KP in scleroderma and present a possible model of kynurenine regulation of the cytokine cascade.

Conjugated and unconjugated pteridines and their derivatives are important cofactors in cellular metabolism. Hence, the amount of unconjugated pteridines in biological fluids has been found to be modified as a result of several disorders. It is necessary to note that while for the control of pteridines in urine samples there are numerous reference data, the literature referred to for the analysis of these analytes in serum/plasma is scarce. In biological fluids, pteridines can exist in different oxidation states, and these compounds can be classified into two groups according to: (a) oxidized or aromatic pteridines and (b) reduced pteridines. Oxidized pteridines yield a strong fluorescence signal, whereas reduced pteridines present a low quantum yield of fluorescence. In order to enable the analysis of the reduced forms, several preoxidation procedures to generate aromatic rings have been established. Also, stabilization of the reduced forms by the addition of reducing agents has been widely reported. The objective of this paper is to show possibilities and different approaches in the analysis of pteridines in serum samples. We have mainly focused on the description of the current situation in the application of high-performance chromatography methods with fluorimetric detection.

The analysis of pterins in the cerebrospinal fluid (CSF) is mandatory for the etiologic diagnosis of inborn errors of dopamine and serotonin metabolism. The success of the available therapeutic strategies for preventing the ongoing brain dysfunction is tightly dependent of the early diagnosis of these neurotransmitter disorders. Previous methods of pterins determination in the CSF have in common at least one reversed phase HPLC step coupled to electrochemical or fluorescence detection (FD). They differ in the oxidation procedure of the reduced forms of pterins into their oxidized fluorescent counterparts. Most of the methods using the FD include at least one offline chemical oxidation procedure and cannot allow the direct quantification of tetrahydrobiopterin (BH4). A recent method proposed a single step simultaneous quantification of all forms of pterins including BH4 by HPLC coupled to FD after post-column coulometric oxidation. Nowadays, recent advances in mass spectrometry (MS), notably in term of sensitivity, allow the direct unambiguous determination of all forms of pterins in the CSF by LC-MS/MS.

As the disease-free 5-year-survival of late stage laryngeal carcinoma patients is extremely low, indoleamine-2,3-dioxygenase-1 (IDO)-induced tryptophan degradation may represent an immune escape mechanism which plays an important role in cancer spreading in advanced stage laryngeal cancers. We examined whether the late stage laryngeal cancer enhances tumor immune evasion by the expression of systemic IDO activities and chronic cellular immune activation. Twenty-two of 42 male laryngeal cancer patients were classified as late stage cancer according to American Joint Committee on Cancer (AJCC) criteria. Their serum neopterin, tryptophan and kynurenine concentrations were compared with 30 cancer-free individuals. IDO activity was approved by correlation between serum neopterin and kynurenine/tryptophan. Late stage cancer patients preoperatively showed a significantly higher IDO activity compared to controls and early stage cancer cases. Six months after tumor removal, late stage cancer patients although having higher serum neopterin concentration compared to early stage patients or controls, they showed a significant decrease in IDO activity and tryptophan consumption. Increased systemic IDO activity may provoke the escape of tumor cells from the immune surveillance of the host. High IDO activity is due to the presence of tumor mass. Persistence of high serum neopterin levels despite tumor removal may indicate poor prognosis.

Dictyostelium discoideum Ax2 is well-known for the synthesis of d -threo-tetrahydrobiopterin (DH4) with a smaller amount of l -erythro-tetrahydrobiopterin (BH4). DH4 synthesis from 6-pyruvoyltetrahydropterin (PPH4) is catalyzed by aldose reductase (AR)-like protein and sepiapterin reductase (SR) via an intermediate 1′-oxo-2′- d -hydroxypropyl tetrahydropterin, which is non-enzymatically oxidized to d -sepiapterin in the absence of SR. However, l -sepiapterin was a dominant product in the reaction of a cellular extract of spr − disrupted in the SR gene. In order to investigate its potential role in tetrahydropteridine synthesis, the enzyme catalyzing l -sepiapterin synthesis from PPH4 was purified from spr − . Via mass spectrometry, the protein was identified to be encoded by alrA . AlrA consists of 297 amino acid residues sharing a high sequence identity with human AR. However, in the co-incubation assay, DH4 synthesis was not detected and, furthermore, the recombinant AlrA was observed to suppress BH4 synthesis by SR, which was known to prefer 1′-oxo-2′- d -hydroxypropyl tetrahydropterin to PPH4. Although intracellular DH4 level in alrA − was decreased to 60% of the wild type, it is presumed to result from the antioxidant function of DH4. Therefore, despite the structural and catalytic identities with human AR, AlrA seems to be involved in neither BH4, nor DH4 synthesis under normal physiological conditions.