Reduced pteridine derivatives induce apoptosis in human neuronal NT2/HNT cells

Neopterin, Inflammation, and Oxidative Stress: What Could We Be Missing?

Neopterin has been extensively used as a clinical marker of immune activation during inflammation in a wide range of conditions and stresses. However, the analysis of neopterin alone neglects the cellular reactions that generate it in response to interferon-γ. Neopterin is the oxidation product of 7,8-dihydroneopterin, which is a potent antioxidant generated by interferon-γ-activated macrophages. 7,8-Dihydroneopterin can protect macrophage cells from a range of oxidants through a scavenging reaction that generates either neopterin or dihydroxanthopterin, depending on the oxidant. Therefore, plasma and urinary neopterin levels are dependent on both macrophage activation to generate 7,8-dihydroneopterin and subsequent oxidation to neopterin. This relationship is clearly shown in studies of exercise and impact-induced injury during intense contact sport. Here, we argue that neopterin and total neopterin, which is the combined value of 7,8-dihydroneopterin and neopterin, could provide a more comprehensive analysis of clinical inflammation than neopterin alone.

Genetic association study of putative functional single nucleotide polymorphisms of genes in folate metabolism and spina bifida

OBJECTIVE

We tested putative functional single nucleotide polymorphisms (SNPs) in genes that regulate the folate/homocysteine metabolism pathway for their contribution to spina bifida (SB) susceptibility.

STUDY DESIGN

The study consisted of 610 unrelated simplex SB patient families. Genotypes of 46 SNPs located in the coding sequence or promoter region of 11 genes were investigated. Associations between transmission of alleles and SB in the offspring were examined using the reconstruction combined transmission disequilibrium test.

RESULTS

Significant association of SNP rs5742905 in cystathionine-beta-synthase, rs1643649 in dihydrofolate reductase, rs2853533 in thymidylate synthetase, and rs3737965 in methylenetetrahydrofolate reductase was found (P = .015, .041, .021, and .007 respectively).

CONCLUSION

Transmission disequilibrium of SNP alleles in cystathionine-beta-synthase, dihydrofolate reductase, methylenetetrahydrofolate reductase, and thymidylate synthetase confers an increased susceptibility to SB.

Potential to inhibit growth of atherosclerotic plaque development through modulation of macrophage neopterin/7,8-dihydroneopterin synthesis

The rise in plasma neopterin observed with increasing severity of vascular disease is a strong indicator of the inflammatory nature of atherosclerosis. Plasma neopterin originates as the oxidation product of 7,8-dihydroneopterin secreted by gamma-interferon stimulated macrophages within atherosclerotic plaques. Neopterin is increasingly being used as a marker of inflammation during clinical management of patients with a range of disorders including atherosclerosis. Yet the role of 7,8-dihydroneopterin/neopterin synthesis during the inflammatory process and plaque formation remains poorly understood and controversial. This is partially due to the unresolved role oxidants play in atherosclerosis and the opposing roles of 7,8-dihydroneopterin/neopterin. Neopterin can act as pro-oxidant, enhancing oxidant damage and triggering apoptosis in a number of different cell types. Neopterin appears to have some cellular signalling properties as well as being able to chelate and enhance the reactivity of transition metal ions during Fenton reactions. In contrast, 7,8-dihydroneopterin is also a radical scavenger, reacting with and neutralizing a range of reactive oxygen species including hypochlorite, nitric oxide and peroxyl radicals, thus protecting lipoproteins and various cell types including macrophages. This has led to the suggestion that 7,8-dihydroneopterin is synthesized to protect macrophages from the oxidants released during inflammation. The oxidant/antioxidant activity observed in vitro appears to be determined both by the relative concentration of these compounds and the specific chemistry of the in vitro system under study. How these activities might influence or modulate the development of atherosclerotic plaque in vivo will be explored in this review.

Neopterin in HIV-1 infection

Neopterin is well established as a reliable marker in HIV-1 infection. Neopterin concentrations measured in urine or serum indicate sensitively the course and progression of the disease as well as efficacy of anti-retroviral therapy. The main trigger for neopterin production is Th1-type cytokine interferon-gamma. During acute HIV-1 infection, enhanced formation of neopterin occurs already at a very early time point, before antibody seroconversion takes place. After this stage, neopterin concentrations in serum and urine closely correlate with virus load in the circulation of HIV-1-infected patients. Data provide evidence for an important role of immune activation and Th1-type cytokine interferon-gamma in the pathogenesis of HIV-1 infection. This review subsumes the importance of neopterin as a marker in HIV-1 infection. Further evidence is increasing, that neopterin derivatives might modulate immune response by interfering with the cellular redox balance, activating redox-sensitive transcription factors, or inducing apoptosis in specific cell types. The possible impact of neopterin derivatives and of other biochemical pathways induced by interferon-gamma such as indoleamine 2,3-dioxygenase in chronic diseases like HIV-1 infection is discussed.

Interference of 7,8-dihydroneopterin with peroxynitrite-mediated reactions

By in vitro studies 7,8-dihydroneopterin, which is secreted by macrophages stimulated by interferon-gamma, was reported to be a radical scavenger as well as a prooxidative agent depending on the experimental settings. In this study, we investigated the interference of 7,8-dihydroneopterin with peroxynitrite mediated reactions by different analytical procedures. Luminol chemiluminescence and oxidation of the spin probe 1-hydroxy-2,2,6,6-tetramethyl-4-oxo-piperidine induced by peroxynitrite were inhibited by 7,8-dihydroneopterin. On the other hand, we found that 7,8-dihydroneopterin very efficiently inhibits nitration of tyrosine by peroxynitrite. Hydroxylation, however, was rather enhanced than inhibited, suggesting that 7,8-dihydroneopterin reacts in quite different manner with the intermediates generated from peroxynitrite. We provide the first evidence that a pterin radical is formed from a dihydropterin using EPR spectroscopy and 2,2,4-trimethyl-2H-imidazole-1-oxide as a spin trap. We conclude that 7,8-dihydroneopterin while being a weak scavenger of superoxide acts as a very efficient inhibitor of tyrosine nitration induced by peroxynitrite.

Tetrahydropteridines suppress gene expression and induce apoptosis of activated RAW264.7 cells via formation of hydrogen peroxide

Tetrahydrobiopterin, a redox-active cofactor, is essential for nitric oxide (NO) biosynthesis. Previous work showed that intracellular tetrahydrobiopterin levels modulate activity of nitric oxide synthases (NOSs). The 4-amino analog of tetrahydrobiopterin is an effective inhibitor of all three purified NOS isoforms that, in intact cells, preferentially targets the inducible isoenzyme. In vivo, 4-amino-tetrahydrobiopterin prolonged allograft survival and rescued rats from septic shock. Here we investigated the effects of tetrahydrobiopterin and its 4-amino analog on RAW264.7 murine macrophages activated with lipopolysaccharide. Surprisingly, both tetrahydropteridines inhibited NO formation. This was caused by downregulation of inducible NOS expression rather than by affecting enzyme activity. In addition, expression of tumor necrosis factor-alpha was impaired, and apoptosis, as characterized by quantifying DNA content and caspase-3 activation and being associated with the formation of a 33 kDa fragment of nuclear factor-kappaB p65, was induced. The effects of tetrahydropteridines were scavenged by catalase or glutathione but not by superoxide dismutase. Like tetrahydropteridines, hydrogen peroxide at concentrations comparable to those found in tetrahydropteridine-treated cultures affected gene expression and cell survival, whereas increasing intracellular tetrahydrobiopterin levels by sepiapterin did not. Thus, extracellular tetrahydropteridines suppress gene expression and induce apoptosis in RAW264.7 cells via hydrogen peroxide formed in the culture medium during autoxidation.

Induction of apoptosis in human blood T cells by 7,8-dihydroneopterin: the difference between healthy controls and patients with systemic lupus erythematosus

Neopterin (Neo) and 7,8-dihydroneopterin (H(2)Neo) are produced by human monocyte-derived macrophages upon stimulation with IFN-gamma. Increased amounts of Neo and H(2)Neo in human body fluids are found in many disorders, including viral infections and autoimmune diseases. Recent data suggest that neopterin derivatives may exhibit distinct biochemical functions activating redox-sensitive transcription factors and inducing apoptosis in various cell lines. In this study we investigated the effect of H(2)Neo on human peripheral blood T cells (PBT) from healthy blood donors in comparison with PBT isolated from patients with systemic lupus erythematosus (SLE). H(2)Neo induced apoptosis in healthy PBT in a concentration-dependent manner. In short time culture, a significantly lower ability of PBT isolated from patients with SLE to undergo apoptosis in response to H(2)Neo compared to healthy controls was detected. Our results suggest a possible role of the neopterin derivative H(2)Neo in T cell apoptosis mediated by stimulated monocytes/macrophages.

Reduced pteridine derivatives induce apoptosis in PC12 cells

In cerebrospinal fluid of patients with cerebral infections, elevated concentrations of the pteridine compounds neopterin and 7,8-dihydroneopterin were detected. Here, the potential of pteridines to induce apoptosis of the rat pheochromocytoma cells (PC12) was investigated. In contrast to aromatic pteridines like neopterin, the reduced forms 7,8-dihydroneopterin, 5,6,7,8-tetrahydrobiopterin and 7,8-dihydrobiopterin led to a significant increase of apoptotic cells. After terminal differentiation, cells were less sensitive to incubation with pteridines. A noticeable augmentation of apoptosis was observed upon incubation with 7,8-dihydroneopterin and 7,8-dihydrofolic acid. Antioxidants partly protected PC12 cells from pteridine-induced apoptosis, suggesting the involvement of reactive oxygen intermediates. Exposure of cells to 7,8-dihydroneopterin led to activation of the mitogen-activated protein (MAP) kinase and to a lesser degree also of JUN/SAP kinase. Results implicate that high concentrations of reduced pteridines, might contribute to the pathogenesis involved in neurodegeneration.

7,8-Dihydroneopterin induces apoptosis of Jurkat T-lymphocytes via a Bcl-2-sensitive pathway

Activated cell-mediated immunity is known to be accompanied by elevated concentrations of 7,8-dihydroneopterin which in high concentrations was found to interfere with the oxidant-antioxidant balance. In this study we investigated whether 7,8-dihydroneopterin mediates apoptosis of Jurkat T-lymphocytes via a CrmA- or Bcl-2-sensitive pathway. Transient transfection assays with CrmA and Bcl-2 expression constructs showed that apoptosis was not affected by CrmA whereas it was significantly decreased upon cotransfection with Bcl-2 constructs. Results suggest that 7,8-dihydroneopterin-induced apoptosis of T-lymphocytes is mediated by a Bcl-2-sensitive pathway.

Influence of cytokines tumor necrosis factor-alpha and interferon-gamma on signaling cascades associated with apoptosis in rat PC12 cells

During cell-mediated immune response, increased amounts of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) are released. In the present study, we investigated the potential of these two cytokines to mediate apoptosis and to alter signal transduction pathways involved in undifferentiated PC12 cells. To induce apoptosis, the pteridine 7,8-dihydroneopterin (NH2) was used. TNF-alpha alone and TNF-alpha in combination with IFN-gamma led to no alteration in cell viability during 48 h of incubation. TNF-alpha was able to slightly elevate apoptosis compared with cells stimulated with NH2 alone. The combination of TNF-alpha and IFN-gamma almost completely abrogated the rate of apoptosis induced by NH2. Similar degrees of activation of extracellular protein kinase were found after the addition of cytokines or cytokines in combination with NH2. Stress-activated protein kinase (SAPK) was not activated by the cytokines alone, whereas adding the cytokine TNF-alpha to NH2-stimulated cells resulted in activation of SAPK after 15 min.