6-formylpterin, a xanthine oxidase inhibitor, intracellularly generates reactive oxygen species involved in apoptosis and cell proliferation

Dual-channel nanoelectrochemical sensor for monitoring intracellular ROS and NADH kinetic variations of their concentrations

Reactive oxygen species (ROS) and nicotinamide adenine dinucleotide (NADH) are important intracellular redox-active molecules involved in various pathological processes including inflammation, neurodegenerative diseases, and cancer. However, the fast dynamic changes and mutual regulatory kinetic relationship between intracellular ROS and NADH in these biological processes are still hard to simultaneously investigate. A dual-channel nanowire electrode (DC-NWE) integrating two conductive nanowires, one functionalized with platinum nanoparticles and the other with conductive polymer, was nanofabricated for the selective and simultaneous real-time monitoring of intracellular ROS and NADH release by mitochondria in single living MCF-7 tumoral cells stimulated by resveratrol. The production of ROS was observed to occur tenths of a second before the release of NADH, a significant new piece of information suggesting a mechanism of action of resveratrol. Beyond the importance of the specific data gathered in this study, this work established the feasibility of simultaneously monitoring multiple species and analyzing their kinetics relationships over sub-second time scales thanks to dual-channel nanowire electrodes. It is believed that this concept and its associated nanoelectrochemical tools might benefit to a deeper understanding of mutual regulatory relationship between intracellular crucial molecular markers during physiological and pathological processes as well as for evaluating medical treatments.

Properties and reactivity of the folic acid and folate photoproduct 6-formylpterin

Folates (vitamin B9) are essential components of our diet and our gut microbiota. They are omnipresent in our cells and blood. Folates are necessary for DNA synthesis, methylation, and other vital bioprocesses. Folic acid (FA), as the synthetic form of folates, is largely found in supplements and fortified foods. FA and folate drugs are also extensively used as therapeutics. Therefore, we are continuously exposed to the pterin derivatives, and their photo-degradation products, such as 6-formylpterin (6-FPT) and pterin-6-carboxylic acid. During ultraviolet radiation, these two photolytic products generate reactive oxygen species (ROS) responsible for the cellular oxidative stress. 6-FPT can exhibit variable pro/anti-oxidative roles depending on the cell type and its environment (acting as a cell protector in normal cells, or as an enhancer of drug-induced cell death in cancer cells). The ROS-modulating capacity of 6-FPT is well-known, whereas its intrinsic reactivity has been much less investigated. Here, we have reviewed the properties of 6-FPT and highlighted its capacity to form covalent adducts with the ROS-scavenging drug edaravone (used to treat stroke and amyotrophic lateral sclerosis) as well as its implication in immune surveillance. 6-FPT and its analogue acetyl-6-FPT function as small molecule antigens, recognized by the major histocompatibility complex-related class I-like molecule, MR1, for presentation to mucosal-associated invariant T (MAIT) cells. As modulators of the MR1/MAIT machinery, 6-FPT derivatives could play a significant immuno-regulatory role in different diseases. This brief review shed light on the multiple properties and cellular activities of 6-FPT, well beyond its primary ROS-generating activity.

Securinine Induces Differentiation of Human Promyelocytic Leukemic HL-60 Cells through JNK-Mediated Signaling Pathway

Acute myeloid leukemia is characterized by abnormal differentiation of hematopoietic stem cells, leading to the accumulation of immature myeloid cells. Differentiation therapy has been a successful treatment option for acute promyelocytic leukemia but suffers from adverse effects. Therefore, search for novel differentiation-inducing agents with minimal side effects is desirable. Securinine, a naturally-occurring alkaloid, induces differentiation in various leukemic cells and apoptosis in other types of cancers. However, the underlying molecular mechanism(s) remain elusive. Our study aimed to elucidate the possible molecular mechanism(s) and signaling events involved in securinine-induced differentiation of HL-60 cells. Securinine inhibited proliferation in a time- and dose-dependent manner and triggered differentiation. A higher CD14+ population indicated maturation toward monocytic lineage. Securinine caused cell cycle arrest at the G0/G1 phase and enhanced ROS generation. Quantitative gene expression analysis showed significant down-regulation of C/EBP-α, C/EBP-ε, GAΤΑ, and c-myc and up-regulation of the PU.1 gene. The expression of distinct protein kinases Lyn, Chk-2, Yes, FAK, c-Jun, and JNK were enhanced. Use of specific inhibitors of crucial intracellular signaling proteins indicated that JNK and ERK blockade resulted in a significant decline in differentiation. These data thus confirm that securinine induces differentiation through the activation of the JNK-ERK signaling pathway in HL-60 cells.

The role of urinary pteridines as disease biomarkers

Pteridines and their derivatives function as intermediates in the metabolism of several vitamins and cofactors, and their relevance to disease has inspired new efforts to study their roles as disease biomarkers. Recent analytical advances, such as the emergence of sensitive mass spectrometry techniques, new workflows for measuring pteridine derivatives in their native oxidation states and increased multiplexing capacities for the simultaneous determination of many pteridine derivatives, have enabled researchers to explore the roles of urinary pteridines as disease biomarkers at much lower levels with greater accuracy than with previous technologies or methods. As a result, urinary pteridines are being increasingly studied as putative cancer biomarkers with promising results being reported from exploratory studies. In addition, the role of urinary neopterin as a universal biomarker for immune system activation is being investigated in new diseases where it is anticipated to become a useful supplementary marker in clinical diagnostic settings. In summary, this review provides an overview of recent developments in the clinical study of urinary pteridines as disease biomarkers, covers the most promising aspects of advanced analytical techniques being developed for the determination of urinary pteridines and discusses the major challenges associated with implementing pteridine biomarkers in clinical laboratory settings.

Contemporary issues surrounding folic Acid fortification initiatives

The impact of folate on health and disease, particularly pregnancy complications and congenital malformations, has been extensively studied. Mandatory folic acid fortification therefore has been implemented in multiple countries, resulting in a reduction in the occurrence of neural tube defects. However, emerging evidence suggests increased folate intake may also be associated with unexpected adverse effects. This literature review focuses on contemporary issues of concern, and possible underlying mechanisms as well as giving consideration the future direction of mandatory folic acid fortification. Folate fortification has been associated with the presence of unmetabolized folic acid (PteGlu) in blood, masking of vitamin B12 deficiency, increased dosage for anti-cancer medication, photo-catalysis of PteGlu leading to potential genotoxicity, and a role in the pathoaetiology of colorectal cancer. Increased folate intake has also been associated with twin birth and insulin resistance in offspring, and altered epigenetic mechanisms of inheritance. Although limited data exists to elucidate potential mechanisms underlying these issues, elevated blood folate level due to the excess use of PteGlu without consideration of an individual's specific phenotypic traits (e.g. genetic background and undiagnosed disease) may be relevant. Additionally, the accumulation of unmetabolized PteGlu may lead to inhibition of dihydrofolate reductase and other enzymes. Concerns notwithstanding, folic acid fortification has achieved enormous advances in public health. It therefore seems prudent to target and carefully monitor high risk groups, and to conduct well focused further research to better understand and to minimize any risk of mandatory folic acid fortification.

Enhancement of Radiation-induced Apoptosis by 6-Formylpterin

Radiation-induced apoptosis and its possible enhancement in the presence of 6-formylpterin (6-FP), a metabolite of folic acid, were examined in human myelomonocytic lymphoma U937 cells. When cells were treated with 6-FP at a nontoxic concentration of 300 microM, and then exposed to X-rays at a dose of 10 Gy, significant enhancement of radiation-induced apoptosis as determined by nuclear morphological change, phosphatidylserine (PS) externalization and DNA fragmentation were observed. Flow cytometry for the detection of intracellular hydrogen peroxide (H2O2) revealed that 6-FP increased the formation of intracellular H2O2, which further increased when the cells were irradiated. Decrease of mitochondria trans-membrane potential (MMP), release of cytochrome c from mitochondria, and activation of caspase-3 were enhanced after the combined treatment. Remarkable activation of protein kinase C delta (PKC delta) and its translocation from cytosol to mitochondria were detected in combined treatment. Increase of intracellular Ca2+ concentrations ([Ca2+]i) was also observed, however, neither calpain I nor calpain II could inhibit the apoptosis. In addition, c-Jun NH2-terminal kinase (JNK) activation was not enhanced in the combined treatment. A protein involved in a caspase-independent apoptosis pathway, apoptosis inducing factor (AIF), remained unchanged even 3 h after treatment. These results indicate that intracellular H2O2 generated by 6-FP enhances radiation-induced apoptosis via the mitochondria-mediated caspase-dependent pathway, with the active involvement of PKC delta.

Anticancer photodynamic and non-photodynamic effects of pterin derivatives on a pancreatic cancer cell line

To evaluate the feasibility of two kinds of pterin derivatives, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-pivaloylpteridin-4-one (DFP) and 2-(N,N-dimethylaminomethyleneamino)-3-pivaloylpteridin-4-one (DP), as anticancer drugs, their photodynamic and non-photodynamic effects on pancreatic cancer cell line Panc-1 cells were examined. For photodynamic effects, cell death 48 h after UV-A irradiation was more prominent in cells preloaded with DP than DFP. When cells were simply incubated for 96 h without irradiation, DFP induced cell death, while DP suppressed cell proliferation. Furthermore, DP was much more soluble in water than DFP. These findings collectively indicated that DP is more feasible as an anticancer drug than DFP.

Synthesis of 6-formylpterin nucleoside analogs and their ROS generation activities in the presence of NADH in the dark

We demonstrated previously that 3-position-modified 6-formylpterin (6FP) derivatives produce reactive oxygen species (ROS) such as hydrogen peroxide (H(2)O(2)) from oxygen in the presence of NADH in the dark. It has been shown that 6FP derivatives markedly generate ROS, which gives rise to their particular physiological activities, such as induction of apoptosis in cellular and living systems, suggesting that such compounds provide a hint for the design of a ROS controlling agent in vivo. However, it is not well understood why such unique activities appear on chemical modification. In the present study, in order to see the effect on ROS generation activity in the dark by the modification of the 1-position in 6FP, we have developed a new synthetic procedure for nucleoside analogs of 6FP and prepared 1-(beta-d-ribofuranosyl)-2-(N,N-diethylaminomethyleneamino)-6-formylpteridin-4-one (RDEF) and 1-(beta-d-ribofuranosyl)-2-(piperidine-1-ylmethyleneamino)-6-formylpteridin-4-one (RPIF) in which the 1-position of 6FP is glycosylated. At pH 7.4, NADH was spontaneously oxidized to NAD(+) in the presence of RDEF in the dark. Using electron paramagnetic resonance analysis coupled with the spin trapping technique, we show that O(2) was converted to H(2)O(2)via superoxide anion radical ( O(2)(-)) during this reaction. The modification of the 1-position of 6FP did not cancel ROS generation activities, which were demonstrated in 3-position-modified 6FPs. Since the 6FP derivatives developed in the present study have a ribose moiety, these compounds can be subjected to further derivatization, such as incorporation into oligonucleotides, oligosaccharides, proteins, or any other compounds that recognize and interact with specific biomolecules, and therefore would be useful in pharmaceutical investigations that need generation of appropriate and controllable amounts of ROS in vivo.

Reactive oxygen species generation through NADH oxidation by 6-formylpterin derivatives in the dark

6-formylpterin (6FP) has been reported to produce reactive oxygen species (ROS) such as *O2- and H2O2 from O2 in the presence of NADH under light condition. In the present study, we prepared a variety of 6FP derivatives and found that 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-pivaloylpteridin-4-one and 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-methylpteridin-4-one, in which the 2-amino groups are modified by a dimethylaminomethylene group and the 3-positions by pivaloyl and methyl groups and 2-amino-6-formyl-3-methylpteridin-4-one in which the amino group at the 2-position is free and the 3-position is modified by a methyl group generated H2O2 from O2 on oxidation of NADH to NAD+ in the dark. However, 6FP and 2-(N,N-dimethylaminomethyleneamino)-6-formylpteridin-4-one, in which the 3-position is free did not yield H2O2. These results indicate that modification of the 3-position is essential to make the activities of 6FP available in the dark and would be suggestive for designing pharmaceutical compounds that generate appropriate and controllable amounts of ROS in vivo.

Novel 6-formylpterin derivatives: chemical synthesis and O2 to ROS conversion activities

6-Formylpterin (6FP) has been demonstrated to have strong neuroprotective effects against transient ischemia-reperfusion injury in gerbils. Also it has been shown that in rats, 6FP protected retinal neurons even when it was administered after the ischemic insult. Since there is a significant need for such a compound that effectively suppresses the events caused by the lack of oxygen supply, 6FP has attracted further investigation. Unfortunately, however, 6FP is hardly soluble in water at neutral pH and in organic solvents because of its self-assembling ability. Although a several mM solution of 6FP is available in alkaline water, it is unstable. In the present study, a novel chemical derivatization of 6FP has been developed which maintains the formyl group on the 6-position of 6FP, which is essential for the physiological activities of 6FP, and increases solubility in water and organic solvents. In the method, the 2- and 3-positions of 6FP were modified by a three component coupling reaction: 6FP was subjected to the reaction with acid chloride and N,N-dimethylformamide. The derivatives synthesized here, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-pivaloylpteridine-4-one 1, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-isobutyrylpteridine-4-one 2, and 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-o-toluoylpteridine-4-one 3, showed high solubility in water (1.0-5.6 mM) and organic solvents. The O(2) conversion property has also been determined for the derivative 1. Using an oxygen electrode, it has been found that O(2) is consumed in the presence of 1 and NADH at around pH 7.4 and that the rate of O(2) consumption is enhanced by UV-A irradiation. Electron paramagnetic resonance (EPR) analysis coupled with DMPO spin trapping has also revealed that in the presence of NADH, 1 converts O(2) to O(2)(-), which is further reduced to OH. By UV-A illumination in the analogous systems, (1)O(2) formation was observed. These results are similar to those reported previously for 6FP.

Mechanism and characteristics of stimuli-dependent ROS generation in undifferentiated HL-60 cells

It has been widely believed that undifferentiated human promyelocytic leukemia cells (HL-60) have no ability to generate reactive oxygen species (ROS) responding to stimuli. We report here that undifferentiated HL-60 cells possess NADPH oxidase and that generation of superoxide can be measured using a highly sensitive chemiluminescence dye, L-012. Five subunits of NADPH oxidase, namely, gp91(phox), p22(phox), p67(phox), p47(phox), and Rac 2, were detected in undifferentiated HL-60 cells by immunoblotting analysis. The contents of these NADPH oxidase components in the cells were increased with the differentiation induced by phorbol myristate acetate (PMA), except for p22(phox). Messenger RNAs of these subunits were also detected by the RT-PCR method, and their expressions increased except that of p22(phox) with the differentiation induced by PMA. Kinetic analysis using L-012 revealed that HL-60 cells generated substantial amounts of ROS by various stimulants, including formylmethionyl-leucyl-phenylalanine, PMA, myristic acid, and a Ca2+ ionophore, A23187. Both diphenyleneiodonium (an inhibitor of FAD-dependent oxidase) and apocynin (a specific inhibitor of NADPH oxidase) suppressed this stimuli-dependent ROS generation. Genistein, staurosporine, uric acid, and sodium azide inhibited the ROS generation in undifferentiated HL-60 cells in a similar way to that in undifferentiated neutrophils. These results suggested that the mechanism of ROS generation in undifferentiated HL-60 cells is the same as that in primed neutrophils.

Photodynamic effects of a novel pterin derivative on a pancreatic cancer cell line

6-Formylpterin (6FP) has the potential to produce singlet oxygen (1O2) under UV-A radiation. In order to apply this potential to anti-cancer photodynamic therapy (PDT), we prepared a novel variant of 6FP, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-pivaloylpteridine-4-one (6FP-tBu-DMF), and examined its photodynamic effects on a pancreatic cancer cell line, Panc-1 cells. The study using laser scanning confocal microscopy showed that the drug uptake, the 1O2 generation, and cell death were observed in the 6FP-tBu-DMF-treated cells, while these phenomena were not observed in the 6FP-treated cells. The MTT assay also showed the decrease in cell viability only in the 6FP-tBu-DMF-treated cells. Since 6FP and 6FP-tBu-DMF generate 1O2 to the same extent under UV-A radiation in aqueous solutions, these results indicated that the differences in the photodynamic effects between 6FP and 6FP-tBu-DMF were entirely attributed to the differences in the cell permeability between them. The development of cell permeable pterin derivatives has the potential for application in PDT.

Protective effects of intracellular reactive oxygen species generated by 6-formylpterin on tumor necrosis factor-alpha-induced apoptotic cell injury in cultured rat hepatocytes

The effects of 6-formylpterin on tumor necrosis factor (TNF)-alpha-induced apoptotic cell injury were studied in cultured rat hepatocytes. The incubation of the hepatocytes with TNF-alpha and actinomycin D (ActD) induced the apoptotic cell injury. The level of aspartate transaminase (AST) in the culture supernatant increased, and the cell viability, estimated by mitochondrial respiration (MTT assay), decreased. The DNA fragmentation and the caspase 3-like activity, which are characterized to apoptosis, increased. When the hepatocytes were incubated with 100-500 microM 6-formylpterin, the intracellular formation of reactive oxygen species (ROS) was observed, and the ratio of reduced and oxidized glutathione (GSH/GSSG) of whole cell lysate decreased. The co-incubation of the TNF-alpha/ActD-treated hepatocytes with 100-500 microM 6-formylpterin attenuated the TNF-alpha/ActD-induced apoptotic cell injury. The level of AST decreased and the cell viability increased. Both the DNA fragmentation and the caspase 3-like activity decreased. The caspases, executors of apoptosis, are known to require a reduced cystein in their active site to function, and the intact intracellular GSH/GSSG is essential for the caspase activation. Therefore, our findings suggest that intracellular ROS generated by 6-formylpterin decline the intracellular redox state to an oxidant state, which suppresses the caspase activity and prevents the apoptotic cell injury of hepatocytes.

Effects of intracellular reactive oxygen species generated by 6-formylpterin on T cell functions

The intracellular generation of reactive oxygen species (ROS) by 6-formylpterin and its effects on the human T cell functions were examined in vitro. When T cells isolated from fresh blood were incubated with 6-formylpterin for 1hr, the oxygen consumption and concomitant ROS generation were observed. The incubation of T cells with 50-500microM 6-formylpterin for 24hr brought about the elevation of intracellular ROS without inducing cell death. In contrast, the incubation of T cells with exogenously administered hydrogen peroxide (H(2)O(2)) or other pterin derivatives (6-hydroxymethylpterin, pterin-6-carboxylic acid, pterin, neopterin, biopterin and folic acid) for 24hr did not cause the intracellular ROS elevation. In the T cells stimulated with mitogenic lectin phytohemagglutinin (PHA) in conjunction with phorbol myristate acetate (PMA), 6-formylpterin suppressed the NF-kappaB-dependent transcription, the production of cytokines (IFN-gamma and IL-2) and the cell proliferation. These suppressive effects of 6-formylpterin were all reversed by N-acetyl-l-cystein (NAC). However, 6-formylpterin did not inhibit the NF-kappaB-DNA binding of the nuclear extracts obtained from the PHA/PMA-stimulated T cells. Since the NF-kappaB-DNA binding assay performed in vitro merely shows the presence or absence of NF-kappaB subunit in the nuclear extracts but not guarantees the actual binding of NF-kappaB with DNA in the nucleus, these findings suggest that intracellular ROS generated by 6-formylpterin does not affect the translocation of NF-kappaB to the nucleus but that it inhibits the NF-kappaB-dependent transcription in the nucleus, resulting in the suppression of cytokine production and cell proliferation in the activated T cells.

6-Formylpterin protects retinal neurons from transient ischemia-reperfusion injury in rats: a morphological and immunohistochemical study

Neuroprotective effects of 6-formylpterin (6FP) on transient retinal ischemia-reperfusion injury were evaluated in rats by means of counting the number of retinal ganglion cells, measuring the thicknesses of the inner plexiform and inner nuclear layers, and by immunohistochemical detection of apoptotic cells in the retina. Sixty-one Sprague-Dawley rats (12 weeks, male, 295-330 g) were subjected to transient retinal ischemia-reperfusion by elevated intra-ocular pressure (80 mmHg for 60 min). Intraperitoneal injection of 6FP (3.8 mg/kg) was performed before or after ischemia. The retina was histologically better preserved in rats with 6FP treatment than without 6FP treatment. 6FP showed more strong neuroprotective effects when it was administered before ischemia. The number of single-stranded DNA-positive cells in the retina also decreased remarkably in rats with 6FP treatment, especially when administered before ischemia. These results suggest that 6FP protects retinal neurons from transient ischemia-reperfusion injury, at least in part by inhibiting apoptotic cell death.

Effects of 6-formylpterin as an internal source of hydrogen peroxide on cell death of human peripheral blood leukocytes

The intracellular generation of hydrogen peroxide (H(2)O(2)) by 6-formylpterin and its effects on the cell surface exposure of phosphatidylserine (PS) as a marker of cell death were examined in human peripheral blood leukocytes, and the effects were compared with those of exogenously administered H(2)O(2). Neutrophils, monocytes and lymphocytes were isolated from fresh blood, and cultured for 24 h in vitro. In neutrophils, the intracellular H(2)O(2) generation was observed when the cells were incubated with 100-500 microM 6-formylpterin, and the PS exposure due to spontaneous apoptosis was inhibited. The underlying mechanism of the inhibition was attributed to the suppression of both activation and activity of caspase-3. On the other hand, exogenously administered 100 microM H(2)O(2) did not affect the PS exposure. The intracellular H(2)O(2) generation was also observed in monocytes and lymphocytes. In monocytes, 500 microM 6-formylpterin induced more PS exposure than 100 microM H(2)O(2) did. In lymphocytes, up to 500 microM 6-formylpterin did not induce conspicuous PS exposure, while 100 microM H(2)O(2) induced severe PS exposure. These findings indicated that the resistance against an internal and external source of H(2)O(2) are different among leukocytes, for example, lymphocytes are poorly resistant against external H(2)O(2) but highly resistant against internal one.

The sensitivity of digestive tract tumor cells to As2O3 is associated with the inherent cellular level of reactive oxygen species

AIM: To explore the correlation of the inherent cellular ROS level with the susceptibility of the digestive tract tumor cells to apoptosis inducted by As₂O₃.

METHODS: Two gastric carcinoma cell lines, SGC7901 and MKN45, and two esophageal carcinoma cell lines, EC/CUHK1(alternatively named EC1.71) and EC1867 with low concentration(2 μmol·L^-1)of As₂O₃ were cultured respectly, which confirmed the difference in apoptosis susceptibility between SGC7901 and MKN45, and between EC/CUHK1 and EC1867. The cells were incubated with dihydrogenrhodamine123 (DHR123), used as a ROS capture in absence of As₂O₃. The fluorescent intensity of rhodamine123, which was the product of cellular oxidation of DHR123, was detected by flow cytometry, and ROS was measured.

RESULTS: Apoptosis induced by a low concentration of As₂O₃ was more readily to occur in SGC7901 (22.4% ± 2.4%) and EC/CUHK1(27.0% ± 2.9%) than in MKN45(2.1% ± 0.5%) and EC1867(0.8% ± 0.5%). In other words, SGC7901 was more sensitive than MKN45 to As₂O₃, meanwhile EC/CUHK1 was more sensitive than EC1867 to As₂O₃. The level of inherent cellular ROS in SGC7901(650 ± 37) was higher than that in MKN45(507 ± 22)(P < 0.01), and the level of inherent cellular ROS in EC/CUHK1(462 ± 17) was higher than that in EC1867(187 ± 12) (P < 0.01).

CONCLUSIONS: The cellular sensitivity to apoptosis induced by As₂O₃ is associated with the difference in cellular ROS level. The inherent ROS level might determinate the apoptotic sensitivity of tumor cells to As₂O₃.

6-formylpterin intracellularly generates hydrogen peroxide and restores the impaired bactericidal activity of human neutrophils

The effects of 6-formylpterin on the impaired bactericidal activity of human neutrophils were examined ex vivo. When neutrophils isolated from fresh blood were incubated with 6-formylpterin, the intracellular production of hydrogen peroxide (H(2)O(2)) occurred. The H(2)O(2) generation by 6-formylpterin in neutrophils occurred in the presence of diphenyleneiodonium (DPI), an inhibitor of NADPH-oxidase. When neutrophils were incubated with DPI, the killing rate of catalase-positive bacteria, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), significantly decreased. This impaired bactericidal activity of the DPI-treated neutrophils was a mimic for chronic granulomatous disease (CGD). However, the killing rate of the DPI-treated neutrophils against E. coli and S. aureus significantly increased when 6-formylpterin was administered. Since 6-formylpterin intracellularly generates H(2)O(2) independent from the NADPH-oxidase, it was considered to improve the impaired bactericidal activity of the DPI-treated neutrophils. The use of 6-formylpterin may serve as an option of therapy for CGD.