Neopterin derivatives together with cyclic guanosine monophosphate induce c-fos gene expression

Neopterin as a potential cytoprotective brain molecule

Neopterin, a byproduct of the tetrahydrobiopterin de novo pathway, is found in increased levels in cerebrospinal fluid and plasma and significantly increases upon damage, infection or during immune system activation. The production of this compound seems almost restricted to the monocyte/macrophage linage cells, in response to interferon-γ stimulation. However, it is unclear whether and which nervous cells are able to synthesize neopterin, respond to any stressor applied extracellularly, or even the role of the compound in the central nervous system. Here we propose a potential cytoprotective role of neopterin in the brain, and show evidence that cultured rat astrocytes are responsive to the molecule; the pterin elicited increased hemeoxygenase-1 cellular content and decreased oxidative stress induced by mitochondrial dysfunction. Further studies are needed to clarify neopterin's cytoprotective effects in the central nervous system, and its potential role in different neuroinflammatory diseases.

Levels in neurotransmitter precursor amino acids correlate with mental health in patients with breast cancer

Breast cancer is the most common cancer among females. Approximately 30% of cancer patients develop depression or depressive adaptation disorder within 5 years post diagnosis. Low grade inflammation and subsequent changes in neurotransmitter levels could be the pathophysiological link. In the current study we investigated the association of neurotransmitter precursor amino acids with a diagnosis of depression or state anxiety in 154 subjects suffering from breast cancer (BCA(+)), depression (DPR(+)), both or neither. Sociodemographic parameters, severity of depressive symptoms, and state anxiety (ANX) were recorded. Neopterin, kynurenine/tryptophan and phenylalanine/tyrosine were analysed by HPLC or ELISA. Significantly higher serum neopterin values were found in DPR(+) patients (p = 0.034) and in ANX(+) subjects (p = 0.008), as a marker of Th1-related inflammation. The phenylalanine/tyrosine ratio (index of the catecholamine pathway) was associated with the factors "breast cancer" and "depression" and their interaction (all p < 0.001); it was highest in the DPR(+)BCA(+) group. The kynurenine/tryptophan ratio (index of the serotonin pathway) was significantly associated with the factors "breast cancer" and "state anxiety" and their interaction (p < 0.001, p = 0.026, p = 0.02, respectively); it was highest in the ANX(+)BCA(+) group. In BCA(+) patients kynurenine/tryptophan ratios correlated with severity of state anxiety (r = 0.226, p = 0.048, uncorrected) and phenylalanine/tyrosine ratios with severity of depressive symptoms (r = 0.376, p < 0.05, corrected). In conclusion, levels of neurotransmitter precursor amino acids correlate with mental health, an effect which was much more pronounced in BCA(+) patients than in BCA(-) subjects. Aside from identifying underlying pathophysiological mechanisms, these results could be the basis for future treatment studies: in BCA(+) patients with depression the use of serotonin-noradrenaline reuptake inhibitors might be recommended while in those with predominant anxiety selective serotonin reuptake inhibitors might be the treatment of choice.

A non-specific biomarker of disease activity in HIV/AIDS patients from resource-limited environments

BACKGROUND

A general non-specific marker of disease activity that could alert the clinician and prompt further investigation would be of value in patients with HIV/AIDS, especially in resource limited environments.

OBJECTIVE

To investigate the potential of neopterin as non-specific biomarker in patients with advanced HIV/AIDS.

METHODS

Cross-sectional study in 105 HIV positive patients (75 on highly active antiretroviral treatment (HAART). Neopterin was assessed by enzyme linked immune-absorbent assay and cytokines by flow cytometry.

RESULTS

Neopterin levels were significantly higher (p<0.001) for the total patient than for the control group. Significant correlations between neopterin and plasma indicators of inflammation showed neopterin to be a good indicator of active inflammatory status and of the effect of HAART on the immune system. Neopterin was superior to C-reactive protein and to individual cytokines as indicator of immune deficiency. Increased neopterin levels were associated with a decline in albumin, haemoglobin and the albumin/globulin ratio, and with increases in red cell distribution width.

CONCLUSIONS

Plasma neopterin is a good non-specific biomarker of disease activity in HIV/AIDS patients. It is a good indicator of inflammatory activity, perpetuation of inflammation-associated co-morbidities, degree of immune deficiency and has predictive value for underlying disease, and for monitoring the HAART response.

Serum neopterin levels in female dogs with malignant mammary tumours

In this study, we have determined serum neopterin levels in female dogs with primary malignant mammary tumours. The study involved 50 female dogs which had a malignant mammary tumours removed surgically (32 animals with carcinoma, 12 animals with sarcoma and 6 animals with carcinosarcoma) and 10 clinically healthy female dogs. Serum neopterin levels were determined using a commercial ELISA kit. The mean neopterin levels were lower in the malignant tumour groups than in healthy animals but differences were statistically significant only in carcinoma and sarcoma groups. The decrease of neopterin levels in animals with malignant mammary tumours may suggest their decreased cellular immunity. Moreover, it might indicate that decreased activity of cellular mechanisms of the anti-neoplastic response is one of the factors associated with the development and course of malignant mammary tumours in female dogs; however, further studies are necessary.

Inflammatory biomarker, neopterin, predominantly enhances myelopoiesis, which suppresses erythropoiesis via activated stromal cells

Neopterin is produced by monocytes and is a useful biomarker for inflammation. We found previously that neopterin enhanced myelopoiesis but suppressed B-lymphopoiesis triggered by the positive and negative regulations of cytokines produced by stromal cells in mice. The effects of neopterin on erythropoiesis during the enhancement of myelopoiesis were determined in the present study using C57BL/6J mice. The intravenous injection of neopterin into mice resulted in a prolonged decrease in the number of femoral erythroid progenitor cells (BFU-Es and CFU-Es), whereas the number of femoral myeloid progenitor cells (CFU-GMs) was increased. Interestingly, the oscillatory changes in the number of erythroid progenitor cells were reciprocal to those of myeloid progenitor cells. The expression of Cdc42, a regulator of the balance between erythropoiesis and myelopoiesis, was down-regulated, implying that the suppression of erythropoiesis is due to myelopoietic predominance. Furthermore, the expression of SDF-1 in stromal cells, a negative regulator of erythropoiesis, was up-regulated. These results suggest that neopterin facilitates myelopoiesis in the bone marrow by suppressing erythropoiesis, thereby contributing to the potential up-regulation of inflammatory process.

Neopterin, a prognostic marker in human malignancies

Increased neopterin concentrations are established in patients with an activated cellular (= Th1-type) immune response which includes allograft rejection, viral infection and autoimmune disorders as well as various malignant tumors. In patients with several types of cancer, neopterin concentrations in body fluids like urine, serum/plasma or ascites parallel the course of the disease, and a higher neopterin concentration in patients is an independent predictor of a shorter survival period. Neopterin is released in large amounts from human monocyte-derived macrophages and dendritic cells preferentially following stimulation with the pro-inflammatory cytokine interferon-gamma, thus reflecting the immune activation status. Therefore, not only as a laboratory diagnostic tool, the measurement of neopterin concentrations allows studying the immunological network and its interaction with the pathogenesis of tumor development. It contributes to a better understanding how immune activation is involved in the development of tumor-induced immune escape and tumor antigen specific tolerance.

Inflammatory biomarker, neopterin, enlarges splenic mast-cell-progenitor pool: Prominent impairment of responses in age-related stromal cell-impairment mouse SCI/SAM

Neopterin is produced by monocytes and is a useful biomarker of inflammatory responses. We found that neopterin enhances granulopoiesis, but suppresses B-lymphopoiesis triggered by the positive and negative regulations of cytokines produced by stromal cells in mice. In this study, neopterin was found to regulate mast cell development, which was confirmed in the mouse model of senescent stromal-cell impairment (SCI). In non-SCI mice (=less senescent stage of SCI mice), neopterin decreased the number of colonies of IL-3-dependent mast-cell progenitor cells (CFU-mast) from unfractionated bone-marrow cells, but not that from the lineage-negative bone-marrow cell population without stromal cells in a semisolid in vitro system. Neopterin increased the gene expression and protein production of TGF-beta, a negative regulator of CFU-mast, in cultured stromal cells, indicating that neopterin suppressed CFU-mast colony formation by inducing TGF-beta in stromal cells. In contrast to this in vitro study, in vivo treatment with neopterin did not significantly up-regulate TGF-beta. The intravenous injection of neopterin into mice decreased the number of femoral CFU-mast and the expression level of the gene for stem cell factor (SCF), a positive regulator of CFU-mast, whereas the number of splenic CFU-mast and SCF gene expression level increased. In SCI mice, the in vivo and in vitro responses of mast cell development and cytokine gene expression level to neopterin treatment were less marked than those in non-SCI mice. These results suggest that, firstly, neopterin augments the splenic pool of CFU-mast by the production of SCF, and secondly, such neopterin function becomes impaired during senescence because of an impaired stromal-cell function, resulting in the down-modulation of host-defense mechanisms.

Neopterin as an indicator of immune activation and prognosis in patients with gynecological malignancies

Malignant tumors may contribute to host response that involves both the adaptive and innate immune systems. Among other biochemical indicators of systemic immune and inflammatory activity, activation of macrophages by interferon-gamma induces a marked increase in the production of neopterin. Neopterin production by activated macrophages is also associated with tryptophan degradation. In addition to tumors of other primary locations, increased urinary and serum neopterin concentrations have been reported in patients with gynecological cancers, including epithelial ovarian carcinoma, cervical carcinoma, endometrial carcinoma, uterine sarcomas, and vulvar carcinoma, but not in women with benign neoplasms or precancerous disorders. Increased neopterin concentrations have been associated with poor prognosis. Elevated levels of neopterin have also been observed in the tumor microenvironment. Systemic (urinary or serum) or local (ascitic fluid) neopterin concentrations increased after therapeutic administration of cytokines. Elevated neopterin concentrations have been associated with anemia of chronic disease and increased urinary zinc loss in patients with gynecological malignancy. Elevated neopterin has also been connected with depressed function of peripheral blood lymphocytes and a decrease in CD4+ T-cell numbers.

Effects of Neopterin on the Hematopoietic Microenvironment of Senescence-Accelerated Mice (SAM)

The pteridine neopterin (NP) is produced by monocytes and is known to be a useful marker of immunological activation, although, it remains elusive whether neopterin itself exhibits biological functions. Recently, we found that NP stimulates hematopoietic cell proliferation and differentiation by activating bone marrow stromal cell function. In order to elucidate the biological effect of NP on stromal cells, its effects on hematopoiesis was determined in the mouse model of age-related stromal impairment, senescence-accelerated mice (SAMs). An intraperitoneal administration of NP increased the number of peripheral leukocytes and CFU-GM in the bone marrow and spleen of young SAMs, however, no increase of CFU-GM in old SAMs (stromal impairment) was observed when compared with young SAMs. NP also increased the CFU-GM colony formation of bone marrow and spleen cells from young SAMs in a soft agar culture system, but it did not enhance CFU-GM colony formation of cells from old SAMs cultured in this system. Treatment with NP induced the production of hematopoietic stimulating factors, including IL-6 and GM-CSF, by bone marrow stromal cells from young SAMs but stromal cells from old SAMs did not respond to NP stimulation. Further studies will be required to clarify the mechanism by which NP stimulates the production of hematopoietic growth factors from stromal cells, the results of this study indicate that NP is a potent hematopoietic regulatory factor by activating stromal cell function(s).

The role of prostaglandins in triggering the liver regeneration cascade

Following injury or surgical resection, the liver has the remarkable ability to regenerate. Despite over 100 years of research, the trigger of the liver regeneration cascade has only recently been identified. Shear stress-induced nitric oxide (NO), released secondary to a hemodynamic event following partial hepatectomy (PHX), has been implicated as the trigger of the liver regeneration cascade. However, it is also known that prostaglandins (PGs) are released following PHX, and in response to shear stress. Therefore, it is hypothesized that PGs, released secondary to an increase in the blood flow-to-liver mass ratio following PHX, trigger the liver regeneration cascade, and that NO and PGs interact during the triggering event. An index of initiation of the liver regeneration cascade, c-fos mRNA expression 15 min after PHX, has been employed. As expected, c-fos mRNA expression increased 15 min after PHX and this increase was inhibited by the NO synthase antagonist, l-NAME. This inhibition was reversed by the NO donors, SIN-1 and SNAP, and by the PGs, PGE2 and PGI2. Also, the increase in c-fos mRNA expression was inhibited by indomethacin, a cyclooxygenase antagonist. This inhibition was also reversed by the NO donors, SIN-1 and SNAP, and by the PGs, PGE2 and PGI2. These results suggest that there is interaction between NO and PGs in triggering the liver regeneration cascade, and that in a situation where either NO or COX is inhibited, provision of excess exogenous NO or PGs can reverse the inhibition. This suggests that exogenous NO and/or PGs may play a role in potentiation of the liver regeneration cascade.

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.

Neopterin: a prognostic variable in operations for lung cancer

BACKGROUND

We studied the prognostic value of preoperatively measured neopterin to predict survival of lung cancer patients. Neopterin is produced and secreted by interferon-gamma-stimulated monocytic cells. High urinary neopterin concentrations are found in patients with viral infections, allograft rejection episodes, and some malignant diseases. In various tumor types high urinary neopterin concentrations are associated with a worse prognosis.

METHODS

Preoperative neopterin levels of 110 patients (29 women, 81 men) with lung cancer including 7 patients with small cell lung cancer were measured and related to the time of survival after operation. Patients with clinically suspected stage IIIB lung cancer were not operated and therefore not enrolled in this study. Infectious diseases were not apparent at the time of preoperative urine sampling. Median postoperative follow-up period was 17.4 months.

RESULTS

In a univariate analysis, patients with a preoperative neopterin concentration of more than 212 micromol/mol creatinine (4th quartile) were determined to have a significantly lower survival probability. In a multivariate analysis, a neopterin concentration of more than 212 micromol/mol creatinine (p < 0.01) and T-stage status (p < 0.005) were determined to be significantly predictive variables for worse survival prognosis.

CONCLUSIONS

Preoperative neopterin proved to be a reliable prognostic factor for survival. Immunology may provide an accurate assessment of tumor aggression and its clinical behavior. In this sense, neopterin can serve as an immunologically based estimation of malignant outgrowth. In patients who are operable by clinical tumor stage but have a high risk for operation, elevated preoperative neopterin may help in the decision for a nonoperative treatment.

Inflammation marker 7,8-dihydroneopterin induces apoptosis of neurons and glial cells: a potential contribution to neurodegenerative processes

Since neopterin is elevated in the cerebrospinal fluid of patients with inflammatory neurological disorders we investigated the source of neopterin in the brain and a possible contribution of biological active pteridines to the development of brain lesions. Astrocytic, neuronal and microglial cell lines were shown to be negative for neopterin production even after stimulation with interferon-gamma (IFN-gamma) indicating that infiltrating monocytes/macrophages might be responsible for neopterin level in CNS. Whereas neopterin did not affect viability of brain cells, its derivative 7,8-dihydroneopterin (7,8-DHN) induced dose-dependently cellular apoptosis in astrocytes and neurons probably via enhancement of nitric oxide synthase (iNOS) expression. This mechanism might represent a possible link between inflammation in the brain and neurodegeneration.

Neopterin derivatives modulate toxicity of reactive species on Escherichia coli

Neopterin and 7,8-dihydroneopterin are released by human monocytes/macrophages upon stimulation with interferon-gamma. In parallel, a panel of highly reactive species is produced by macrophages as part of their cytotoxic armature, which is directed against microbial and viral challenge and against malignant growth. Recently, neopterin and 7,8-dihydroneopterin were shown to modulate the action of reactive species in vitro. In this study we investigated the impact of neopterin and 7,8-dihydroneopterin on the toxicity of reactive species, namely chloramine-T, H2O2, hypochlorite, nitrite, and formaldehyde, respectively. We studied the growth inhibition of Escherichia Coli (E. coli) by these toxic agents and its modulation by neopterin and 7,8-dihydroneopterin. Bacterial growth was monitored by optical density of suspension cultures at 600 nm. Compared to control experiments, neopterin enhanced toxicity of all reactive species tested except formaldehyde, while 7,8-dihydroneopterin reduced activity of hypochlorite and chloramine-T. No significant impact of the pteridines could be established for H2O2-mediated and formaldehyde-mediated growth inhibition. The data support the concept that neopterin and 7,8-dihydroneopterin produced during immune response in humans could be important to modulate the action of reactive species released in parallel.

Neopterin Is an Independent Prognostic Variable in Females with Breast Cancer

Background: Neopterin, produced by human monocytes/macrophages upon stimulation by interferon-γ, is a sensitive marker for monitoring Th1-cell immune response in humans. In malignant diseases, the frequency of increases in neopterin in the serum and urine of patients depends on tumor stage and type.

Methods: In a retrospective study comprising 129 females with breast cancer, urinary neopterin/creatinine ratios were measured at the time of diagnosis. Tumor characteristics were determined concomitantly.

Results: Urinary neopterin was increased in 18% of the patients. It did not correlate with tumor size or lymph node status, but it was influenced by the presence of distant metastases (P &lt;0.05) and by tumor differentiation (P = 0.01). When product-limit estimates were calculated after follow-up for up to 13 years (median follow-up, 56 months), the presence of distant metastases (P &lt;0.001), neopterin (P &lt;0.001), tumor size (P = 0.001), and lymph node status (P &lt;0.01) were significant predictors of survival. By multivariate analysis, a combination of the variables presence of distant metastases (P &lt;0.001), neopterin (P &lt;0.01), and lymph node status (P &lt;0.05) was found to jointly predict survival. In lymph node-negative patients without distant metastases, the relative risk of death associated with increased neopterin concentrations was 2.5 compared with patients with neopterin concentrations within the reference interval.

Conclusion: Urinary neopterin provides additional prognostic information in patients with breast cancer.

Effects of neopterin and 7,8-dihydroneopterin on hypoxia-induced renal erythropoietin production

Activation of the human cellular immune system is associated with greatly increased formation of the pteridines neopterin and 7,8-dihydroneopterin. It has been postulated that pteridines play a role in the pathogenesis of the anaemia of inflammation. Herein, we studied effects of pteridines on renal function, primarily on the synthesis of erythropoietin (Epo). The experiments were performed with isolated rat kidneys which were perfused hypoxically (pO2 26 mmHg) at constant pressure (100 mmHg) in a serum-free recirculation system for 3 h. The results show that the rate of the production of Epo was significantly lowered when neopterin or 7,8-dihydroneopterin were added to the perfusate. Neopterin (200 microM) also reduced the renal Epo mRNA level. Both pteridines increased renal vascular resistance. 7,8-Dihydroneopterin lowered urine flow and glomerular filtration rate more potently than neopterin. Renal O2 consumption and parameters of exocrine renal function (fractional reabsorption rates of sodium, glucose and water) were not altered by the pteridines, while the glomerular permeability was greatly increased. These results suggest that activated macrophages may not only inhibit the synthesis of Epo by generating cytokines and reactive O2 species but also by the release of pteridines. In vivo, high concentrations of pteridines in renal tissue may aggravate the anaemia of inflammation.

Neopterin as a prognostic parameter in patients with squamous-cell carcinomas of the oral cavity

Concentrations of neopterin, which is produced by human monocytes/macrophages upon stimulation by interferon-gamma, were measured in urine specimens in 23 patients with squamous-cell carcinoma of the oral cavity at diagnosis and in 12 treated patients with the same disease when recurrence of the tumor was recognized. Tumor histology and routine laboratory parameters were concomitantly determined. Urinary neopterin values showed no statistically significant correlation with tumor differentiation, tumor size or patient age, but they were significantly higher in patients with a recurrent tumor. Patients were followed for up to 4 years, and the ability of all variables to predict fatal outcome was assessed. In univariate analysis, only neopterin (p = 0.01) and the variable recurrent vs. first-diagnosed tumor were significant predictors of survival. In multivariate analysis, a combination of neopterin (p < 0.01) and the variable recurrent vs. first-diagnosed tumor (p = 0.06) was found to jointly predict survival. Thus, urinary neopterin concentrations provide valuable prognostic information in patients with squamous-cell carcinoma of the oral cavity.

Stimulatory effects of neopterin on hematopoiesis in vitro are mediated by activation of stromal cell function

The pteridine neopterin (NP) was shown to be produced by monocytes and is known to be a useful marker of immunological activation, although, its biological activity is still unclear. Recently, we found that intravenous administration of NP increased the numbers of blood leukocytes, and granulocyte-macrophage progenitor cells (CFU-GM) in the bone marrow and spleens of mice. In order to elucidate the mechanism whereby NP stimulates hematopoiesis, the effects of NP on hematopoietic stem cell proliferation and differentiation in vitro were studied using a long-term bone marrow culture (LTMC) system with cloned stromal cell line, MS-5. Adding NP to the LTMC increased the numbers of cells in total, CFU-GM and colony-forming unit in spleen (CFU-S). NP also increased the number of CFU-GM in a soft agar culture system, but it did not enhance CFU-GM colony formation when target bone marrow cells were semi-purified (T, B and adherent cell-depleted bone marrow cells) and cultured in this system, suggesting that NP did not directly affect the proliferation of hematopoietic progenitors. Conditioned medium obtained from NP-treated stromal cells had much greater colony-stimulating activity than that obtained from untreated stromal cells. Furthermore, NP treatment stimulated the production of IL-6 and GM-CSF by stromal cells. All these findings suggest that NP stimulates hematopoietic cell proliferation and differentiation in vitro by activating stromal cell function.

Calcium-dependence of hydrogen peroxide-induced c-fos expression and growth stimulation of multicellular prostate tumor spheroids

Hydrogen peroxide (H2O2) in nanomolar concentrations (20-100 nM) stimulated the growth of small (diameter 100 +/- 30 microm) multicellular prostate cancer spheroids and increased c-fos expression. H2O2 transiently raised [Ca2+]i by Ca2+ release from intracellular stores as the transient persisted in low (10 nM) Ca2+ solution but was abolished when intracellular Ca2+ stores were depleted by thapsigargin or chelation of [Ca2+]i with BAPTA. The H2O2-induced [Ca2+]i transient was furthermore inhibited by the P2-purinoreceptor antagonists suramin and basilen blue, indicating that H2O2 may act via purinergic receptor stimulation. Treatment of spheroids with either suramin, basilen blue or BAPTA inhibited the H2O2-induced growth stimulation and c-fos expression, indicating that the H2O2-mediated growth stimulation of multicellular spheroids is mediated via a Ca2+-dependent pathway.

Chronic immune stimulation, oxidative stress, and apoptosis in HIV infection

Infection with the human immunodeficiency virus (HIV) is accompanied by a decrease in CD4+ T cell numbers and the ultimate disruption of immunological functions. In sera of infected patients, elevated levels of interferon-gamma are detected, which is indicative of an activated TH1-type immune response. T-cell-derived interferon-gamma leads to the expression of various proinflammatory cytokines and enhanced macrophage capacity to secrete reactive oxygen intermediates. In addition, interferon-gamma is the major stimulator for the biosynthesis of neopterin and its reduced form, 7,8-dihydroneopterin. Neopterin is known as a sensitive immune activation marker in clinical laboratory diagnosis. Recent data implied a potential role of neopterin derivatives in oxygen free-radical-mediated processes, e.g. high concentrations of 7,8-dihydroneopterin were found to interfere with the oxidant-antioxidant balance, and may lead to apoptosis of human cells. In addition, 7,8-dihydroneopterin was found to be effective in the activation of redox-sensitive transcription factors and in the induction of HIV-1 gene expression. In this commentary, we describe our current view as to how neopterin derivatives, in concert with cytokines and reactive oxygen intermediates, may lead the way to the final destruction of the cellular immune system.

trans-Activation of the HIV type 1 promoter by 7,8-dihydroneopterin in vitro

Infection with human immunodeficiency virus type 1 and 2 is associated with elevated concentrations of neopterin, released in large quantities by human macrophages on stimulation with interferon gamma. Evidence has suggested a potential role of neopterin derivatives in oxygen radical-mediated processes. Here we show that the redox-sensitive transcription factors AP-1 and NF-kappaB are activated by 7,8-dihydroneopterin, either directly (AP-1), or by the synergistic action with tumor necrosis factor alpha (NF-kappaB). We could further demonstrate that 7,8-dihydroneopterin enhances HIV-1 expression as shown in transient transfection assays using HIV-1 CAT promoter-reporter gene constructs. In sera of HIV+ patients 7,8-dihydroneopterin significantly correlated with neopterin and HIV-1 p24 antigen. On the basis of our data we therefore assume that 7,8-dihydroneopterin might augment progression to higher stages of HIV-associated disease.

Neopterin and 7,8-dihydroneopterin induce apoptosis in the rat alveolar epithelial cell line L2

The neopterin derivatives, neopterin and 7,8-dihydroneopterin, modulate the cellular oxidant-antioxidant balance as well as the expression of the inducible nitric oxide synthase (iNOS) gene. Since apoptosis can be induced by reactive oxygen intermediates and nitric oxide (NO) we investigated whether these neopterin derivatives induce apoptotic cell death. As model we selected the rat alveolar epithelial cell line L2. 24 h incubation of neopterin (1-1000 microM) as well as 7,8-dihydroneopterin (1-1000 microM) resulted in a significant increase of percent apoptotic cells (measured by FACS analysis). Coincubation of both pteridines with the cytomix (interferon-gamma plus tumor necrosis factor-alpha) led to a significantly higher apoptosis than the cytomix alone. In contrast to the cytomix, no iNOS gene expression and no NO release could be detected after incubation with neopterin or 7,8-dihydroneopterin. We conclude that neopterin and 7,8-dihydroneopterin are per se inducers of apoptosis which is not mediated by nitric oxide. This may be of importance in inflammatory pulmonary diseases associated with an activation of the cellular immune system.

Role of neopterin and 7,8-dihydroneopterin in human immunodeficiency virus infection: marker for disease progression and pathogenic link

Human immunodeficiency virus (HIV) infection is associated with increased concentrations of neopterin derivatives, released in large quantities by human macrophages on stimulation with interferon-gamma (INF-gamma). Neopterin concentrations thus inversely correlate with absolute CD4+ T-cell numbers and strongly predict progression of disease from latency to AIDS. Investigations of hydrogen peroxide-induced chemiluminescence indicated a potential role of neopterin and 7,8-dihydroneopterin in oxygen free radical-mediated processes. Indeed, 7,8-dihydroneopterin is able to enhance tumor necrosis factor alpha (TNF-alpha)-induced apoptosis, accompanied by an increased production of reactive oxygen intermediates (ROIs). In line with this finding, the same combination appears to contribute to the upregulation of HIV replication due to activation of nuclear factor-kappa B (NF-kappa B), a central enhancer element of the HIV LTR promoter. Thus, besides the role of neopterin as sensitive indicator of disease activity in HIV infection, neopterin derivatives apparently are associated with the cascade of events that regulate the HIV production in infected individuals.

Effects of the selective bisindolylmaleimide protein kinase C inhibitor GF 109203X on P-glycoprotein-mediated multidrug resistance

Inhibition of protein kinase C (PKC) is discussed as a new approach for overcoming multidrug resistance (MDR) in cancer chemotherapy. For evaluation of this concept we applied the bisindolylmaleimide GF 109203X, which shows a highly selective inhibition of PKC isozymes alpha, beta 1, beta 2, gamma, delta and epsilon in vitro. The efficacy of this compound in modulation of MDR was examined using several P-glycoprotein (P-gp)-overexpressing cell lines including a MDR1-transfected HeLa clone, and was compared with the activities of dexniguldipine-HCI (DNIG) and dexverapamil-HC1 (DVER), both of which essentially act via binding to P-gp. As PKC alpha has been suggested to play a major role in P-gp-mediated MDR, cell lines exhibiting different expression levels of this PKC isozyme were chosen. On crude PKC preparations or in a cellular assay using a cfos(-711)CAT-transfected NIH 3T3 clone, the inhibitory qualities of the bisindolylmaleimide at submicromolar concentrations were demonstrated. At up 1 microM final concentrations of the PKC inhibitor GF 109203X, a concentration at which many PKC isozymes should be blocked substantially, no cytotoxic or MDR-reversing effects whatsoever were seen, as monitored by 72 h tetrazolium-based colorimetric MTT assays or a 90 min rhodamine 123 accumulation assay. Moreover, depletion of PKC alpha by phorbol ester in HeLa-MDR1 transfectants had no influence on rhodamine 123 accumulation after 24 or 48 h. MDR reversal activity of GF 109203X was seen at higher final drug concentrations, however. Remarkably, [3H]vinblastine-sulphate binding competition experiments using P-gp-containing crude membrane preparations demonstrated similar dose dependencies as found for MDR reversion by the three modulators, i.e. decreasing efficacy in the series dexniguldipine-HCl > dexverapamil-HCl > GF 109203X. Similar interaction with the P-gp in the micromolar concentration range was revealed by competition of GF 109203X with photoincorporation of [3H]azidopine into P-gp-containing crude membrane preparations. No significant effect of the PKC inhibitor on MDR1 expression was seen, which was examined by cDNA-PCR. Thus, the bisindolylmaleimide GF 109203X probably influences MDR mostly via direct binding to P-gp. Our work identifies the bisindolylmaleimide GF 109203X as a new type of drug interacting with P-gp directly, but does not support the concept of a major contribution of PKC to a P-gp-associated MDR, at least using the particular cellular model systems and the selective, albeit general, PKC inhibitor GF 109203X.

Regulation of gene expression by cGMP-dependent protein kinase. Transactivation of the c-fos promoter

The cAMP/cAMP-dependent protein kinase (A-kinase) and Ca2+/calmodulin-dependent protein kinase (Cam-kinase) signal transduction pathways are well known to regulate gene transcription, but this has not been demonstrated directly for the cGMP/cGMP-dependent protein kinase (G-kinase) signal transduction pathway. Here we report that transfection of G-kinase into G-kinase-deficient cells causes activation of the human c-fos promoter in a strictly cGMP-dependent manner. The effect of G-kinase appeared to be mediated by several sequence elements, most notably the serum response element (SRE), the AP-1 binding site (FAP), and the cAMP response element (CRE). The magnitude of G-kinase transactivation of the fos promoter was similar to that of A-kinase, but there were significant differences between G-kinase and A-kinase activation of single enhancer elements and of a chimeric Gal4-CREB transcription factor. Our results indicate that G-kinase transduces signals to the nucleus independently of A-kinase or Ca2+, although it may target some of the same transcription factors as A-kinase and Cam-kinase.

Effects of neopterin-derivatives on H2O2-induced luminol chemiluminescence: mechanistic aspects

Neopterin, 6-D-erythro-1',2',3'-trihydroxypropyl-pterin, and its dihydroform, 7,8-dihydro-neopterin, are synthesized by human monocytes/macrophages upon stimulation by interferon-gamma. In the presence of iron chelator complexes neopterin enhances hydrogen peroxide-induced luminol chemiluminescence at neutral or slightly alkaline pH (7.5). In contrast, 7,8-dihydroneopterin scavenges chemiluminescence independently from the pH value and iron. In this study, we explored in more detail the mechanism possibly involved: analysis of the reaction products shows that 7,8-dihydroneopterin is oxidized and degraded to 7,8-dihydroxanthopterin and xanthopterin, whereas the neopterin molecule is not chemically altered during the chemiluminescence reaction. Investigations of the neopterin-induced effect show that mannitol, a scavenger of hydroxyl radicals, does not alter the enhancing effect of neopterin. L-histidine, which scavenges singlet oxygen almost as effective as hydroxyl radicals, reduces the enhancing effect of neopterin. However, singlet oxygen was not detectable during the reaction by measuring monomol light emission (1270 nm). When replacing hydrogen peroxide by 3-morpholinosydnonimine, a generator of hydroxyl radicals, or naphthalene-endoperoxide, a generator of singlet oxygen, in the luminol chemiluminescence assay, neopterin shows no enhancing effect irrespective of the presence of iron-(III)-EDTA. The data suggest that neopterin enhances hydrogen peroxide-induced luminol chemiluminescence in the presence of iron-(III)-EDTA by formation of a catalytic complex that seems to favor the formation of oxygen intermediates which derive from hydrogen peroxide and react with luminol.

Urinary neopterin excretion in patients with squamous carcinoma of the oral cavity

Urinary neopterin concentrations were studied in 30 patients with squamous carcinoma or adenoid cystic carcinoma of the oral cavity. Compared to healthy controls 19 patients (63%) had increased neopterin concentrations. There was a statistically significant correlation between neopterin levels and tumor differentiation but no correlation of neopterin values with tumor size. Longitudinal studies will be necessary to evaluate a potential usefulness of neopterin concentrations to predict prognosis in squamous carcinomas of the oral cavity.