Evaluation of a new simple and rapid enzyme-linked immunosorbent assay kit for neopterin determination

A systematic review and meta-analysis of neopterin in rheumatic diseases

Introduction

Novel biomarkers of inflammation and oxidative stress might enhance the early recognition, management, and clinical outcomes of patients with rheumatic diseases (RDs). We assessed the available evidence regarding the pathophysiological role of neopterin, the oxidation product of 7,8-dihydroneopterin, a pteridine generated in macrophages activated by interferon-γ, by conducting a systematic review and meta-analysis of studies reporting its concentrations in biological fluids in RD patients and healthy controls.

Methods

We searched electronic databases for relevant articles published between inception and 31 August 2023. The risk of bias and the certainty of evidence were assessed using the Joanna Briggs Institute Critical Appraisal Checklist and the Grades of Recommendation, Assessment, Development and Evaluation Working Group system, respectively.

Results

In 37 studies, when compared to healthy controls, RD patients had significantly higher concentrations of neopterin both in plasma or serum (standard mean difference, SMD=1.31, 95% CI 1.01 to 1.61; p<0.001; moderate certainty of evidence) and in the urine (SMD=1.65, 95% CI 0.86 to 2.43, p<0.001; I2 = 94.2%, p<0.001; low certainty of evidence). The results were stable in sensitivity analysis. There were non-significant associations in meta-regression and subgroup analysis between the effect size and age, male to female ratio, year of publication, sample size, RD duration, C-reactive protein, erythrocyte sedimentation rate, specific type of RD, presence of connective tissue disease, analytical method used, or biological matrix investigated (plasma vs. serum). By contrast, the effect size was significantly associated with the geographical area in studies assessing serum or plasma and with the type of RD in studies assessing urine.

Discussion

Pending additional studies that also focus on early forms of disease, our systematic review and meta-analysis supports the proposition that neopterin, a biomarker of inflammation and oxidative stress, can be useful for the identification of RDs. (PROSPERO registration number: CRD42023450209).

Systematic review registration

PROSPERO, identifier CRD42023450209.

Determination of neopterin in urine of industrial workers by HPLC

This study aimed to determine neopterin levels in the urine of industrial workers by the high-performance liquid chromatography method. Intra- and inter-day precision values for neopterin in urine were less than 3.14, and accuracy (relative error) was better than 3.00%. The limits of detection and quantification of neopterin were 0.3 and 1.0 ng/mL, respectively. Also, the developed method was applied to real samples to determine the neopterin levels in the urines of industrial workers, who have been exposed to various chemicals such as formaldehyde, heavy metals and thinners. Urine neopterin levels of industrial workers including auto painters, bodywork and furniture workers were statistically compared with healthy volunteers. The highest and lowest values of urinary neopterin for industrial workers were obtained 908.96 and 119.86 μmol/mol, respectively. Our investigation demonstrates that there is a meaningful difference in urinary neopterin levels between the workers and the control groups (P<0.05). Workers in the auto paint, body and furniture business may have been exposed to a toxic environmental exposure in their occupation. As a result, an increase in the concentration of neopterin in the urine may be important in the diagnosis and treatment of various diseases.

Urinary neopterin: a novel biomarker of disease progression in amyotrophic lateral sclerosis

BACKGROUND

To evaluate urinary neopterin, a marker of pro-inflammatory state, as a potential biomarker of disease prognosis and progression in amyotrophic lateral sclerosis (ALS); and to compare its utility to urinary neurotrophin receptor p75 extracellular domain (p75^ECD ).

METHODS

Observational study including 21 healthy controls and 46 people with ALS, 29 of whom were sampled longitudinally. Neopterin and p75^ECD were measured using enzyme-linked immunoassays. Baseline and longitudinal changes in clinical measures, neopterin and urinary p75^ECD were examined, and prognostic utility explored by survival analysis.

RESULTS

At baseline, urinary neopterin was higher in ALS compared to controls (181.7 ± 78.9 μmol/mol creatinine vs 120.4 ± 60.8 μmol/mol creatinine, p= 0.002, Welch's t-test) and correlated with ALSFRS-R (r= -0.36, p= 0.01). Combining previously published urinary p75^ECD results from 22 ALS patients with a further 24 ALS patients, baseline urinary p75^ECD was also higher compared to healthy controls (6.0 ± 2.7 vs 3.2 ± 1.0 ng/mg creatinine p<0.0001) and correlated with ALSFRS-R (r= -0.36, p= 0.01). Urinary neopterin and p75^ECD correlated with each other at baseline (r= 0.38, p= 0.009). In longitudinal analysis, urinary neopterin increased on average (±SE) by 6.8 ± 1.1 μmol/mol creatinine per month (p<0.0001) and p75^ECD by 0.19 ± 0.02 ng/mg creatinine per month (p<0.0001) from diagnosis in 29 ALS patients.

CONCLUSION

Urinary neopterin holds promise as marker of disease progression in ALS and is worthy of future evaluation for its potential to predict response to anti-inflammatory therapies.

Effect of dietary supplementation of phytogenic feed additive on performance traits, serum neopterin, and cutaneous basophil hypersensitivity response in heat-induced stress model of broiler chickens

Objective

The trial was aimed at assessing the effect of phytogenic feed additive (PFA), a natural adaptogen, on growth performance, serum neopterin level, and cutaneous basophil hypersensitivity (CBH) response in heat-induced stress model of broilers.

Materials and Methods

One-day-old Ross 308 chicks (N = 360) were randomly distributed among normal control (NOR), heat-stress control (HSC), and PFA treatment (HSC plus PFA at 200 gm/ton of feed) group. HSC and PFA groups were subjected to heat stress (HS) (32°C-36°C) from 9:00 a.m. to 5:00 p.m. for 35 days. The impact of HS on growth performance, serum neopterin level, and CBH response was assessed.

Results

High ambient temperature worsened the performance traits [bodyweight (p < 0.05) and feed conversion ratio] and significantly lowered the serum neopterin level and CBH response in the HSC group when compared to the NOR group. However, supplementation of PFA at 200 gm/ton of feed to birds mitigated the detrimental effects of HS.

Conclusion

PFA at 200 gm/ton demonstrated the immunomodulatory effect through the restoration of serum neopterin level, CBH response, and growth performance traits in heat-stressed broiler chickens. Thus, PFA can be used as a natural adaptogen to increase the stress resistance and mitigate the negative consequences of various stressors in broiler chickens.

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.

A New Diagnostic and Prognostic Marker in Endometrial Cancer: Neopterin

OBJECTIVE

In this study, we investigated the correlation between serum and urinary neopterin levels as well as the stage of the disease in women with endometrial cancer.Increased neopterin concentrations are reported in patients with activation of macrophages by interferon-γ, which includes the following: viral infections, autoimmune disorders, allograft rejection, and various malignant tumors. In patients with several types of cancer, high-neopterin concentrations in body fluids like serum/plasma, urine, ascites, and cerebrospinal fluid indicate the course of the disease, and it is associated with poor prognosis. In the light of foregoing, we aimed to investigate the role of neopterin as a prognostic biomarker in endometrial cancer.

MATERIALS AND METHODS

Serum neopterin concentrations were determined by enzyme-linked immunosorbent assay and urinary neopterin by high-performance liquid chromatography in 41 patients with endometrial cancer (group 2) and 41 healthy women (group 1).

RESULTS

Increased urinary neopterin levels were observed in patients with endometrial cancer (P < 0.001), and the difference in the urinary neopterin levels between low and high stages of endometrial cancer was significant (P < 0.01; stage I-II vs stage III-IV, respectively). Serum neopterin levels did not show a significant difference in each group.

CONCLUSIONS

This study suggests that urinary neopterin levels are relevant in evaluating the endometrial cancer stage and follow-up of the disease. As a result, using neopterin and cancer antigen 125 together would be useful in determining the prognosis of endometrial cancer and its posttreatment progression.

Determination of Urinary Neopterin/Creatinine Ratio to Distinguish Active Tuberculosis from Latent Mycobacterium tuberculosis Infection

Background. Biomarkers to distinguish latent from active Mycobacterium (M.) tuberculosis infection in clinical practice are lacking. The urinary neopterin/creatinine ratio can quantify the systemic interferon-gamma effect in patients with M. tuberculosis infection. Methods. In a prospective observational study, urinary neopterin levels were measured by enzyme linked immunosorbent assay in patients with active tuberculosis, in people with latent M. tuberculosis infection, and in healthy controls and the urinary neopterin/creatinine ratio was calculated. Results. We included a total of 44 patients with M. tuberculosis infection and nine controls. 12 patients had active tuberculosis (8 of them culture-confirmed). The median age was 15 years (range 4.5 to 49). Median urinary neopterin/creatinine ratio in patients with active tuberculosis was 374.1 micromol/mol (129.0 to 1072.3), in patients with latent M. tuberculosis infection it was 142.1 (28.0 to 384.1), and in controls it was 146.0 (40.3 to 200.0), with significantly higher levels in patients with active tuberculosis (p < 0.01). The receiver operating characteristics curve had an area under the curve of 0.84 (95% CI 0.70 to 0.97) (p < 0.01). Conclusions. Urinary neopterin/creatinine ratios are significantly higher in patients with active tuberculosis compared to patients with latent infection and may be a significant predictor of active tuberculosis in patients with M. tuberculosis infection.

Neopterin: a potential marker in chronic peripheral arterial disease

Neopterin is a marker of macrophage activation that has exhibited high plasma levels in atherosclerotic diseases including coronary heart disease and critical limb ischemia. The role of neopterin in chronic peripheral arterial disease (PAD) has yet to be elucidated. In the present study, neopterin (Ν) serum concentrations were analyzed in asymptomatic (AsP) and symptomatic (SyP) patients with PAD as well as controls (C). In total 120 subjects, 40 AsP [ankle brachial index (ABI) ≤0.90], 40 SyP (ABI ≤0.90 plus pain in legs) and 40 controls (ABI >0.9) were enrolled. The results of the present study showed that neopterin plasma levels were statistically different among the groups. These findings demonstrated that activation of N‑mediated monocyte‑macrophage, was also observed in chronic PAD.

Protein chip for the parallel quantification of high and low abundant biomarkers for sepsis

We present herein a protein chip for diagnosis of sepsis that combines both a sandwich and a binding inhibition format in order to quantify high (CRP) and low abundant proteins (cytokines, PCT, neopterin) in parallel. Using the combined assay format the lowest detectable concentrations for CRP, IL-6, IL-8, IL-10, TNFα, PCT, and neopterin are 3 mg/L, 15 ng/L, 26 ng/L, 65 ng/L, 40 ng/L, 78 ng/L, and 0.46 μg/L. Four different combined assay formats are tested, using separate or joint incubation steps of analytes and detection antibodies. Yet, low limit of detection (LOD) and short processing time are contradictory: while the combined assay performed in a multistep protocol is extremely sensitive (e.g., the LOD for IL-6 is 15 ng/L), but more time-consuming (4 h), the all-in-one protocol takes only 2.5 h, but suffers from lower sensitivity compared with the multistep protocol (e.g., the LOD for IL-6 is up to 40 times enhanced). Reproducibility is good in both cases (CV 5-20%).

The value of increased neopterin levels in reducing transfusion-transmitted virus infections: detection of a donation from a HBsAg positive chronic carrier by screening of neopterin in Turkish blood donors

Neopterin is an early, sensitive and non-specific marker of cellular immunity. In the present study, serum levels of neopterin were measured by ELISA in 2760 volunteer blood donors, all negative by routine screening tests. Neopterin concentrations ranged from 0.001 to 62.1 nmol/l. 141 donors (5.1%) were found to have high (> or =11 nmol/l) neopterin levels, and 57 of them accepted further investigations within about 3 weeks after their donation. Six had clinical symptoms, and 7 were positive for viral markers. Retesting of neopterin revealed that 2 of 57 donors still showed elevated results, who were adenovirus IgM and HBsAg positive donors, respectively. The present detection of a HBsAg positive donor who yielded negative result initially and a patient with adenovirus infection indicates that routine screening of neopterin levels in blood banks may reduce the risk for viral transmission.

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 levels during the early phase of human immunodeficiency virus, hepatitis C virus, or hepatitis B virus infection

BACKGROUND

A study was conducted to assess the diagnostic sensitivity of neopterin screening of blood donors with regard to the detection of window-phase specimens of human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis B virus (HBV) infection.

STUDY DESIGN AND METHODS

In total, 1002 diagnostic window-phase specimens from 98 seroconversion panels (29 HIV-1, 52 HCV, and 17 HBV) were analyzed with viral antigen detection, viral nucleic acid amplification testing (NAT), and neopterin quantitation assays. The study was completed by the analysis of 92 anti-hepatitis B core antigen (HBc)-reactive and 103 alanine aminotransferase (ALT)-elevated blood donor specimens.

RESULTS

A significant association between elevated neopterin concentrations and the very early phase of HIV-1 infection was found. No significant correlation could be observed between neopterin levels and the early phase of HCV or HBV infection. Neopterin concentration was not increased in specimens from blood donors with anti-HBc reactivity or ALT elevation.

CONCLUSIONS

Neopterin screening of blood donors may identify window-phase cases of HIV, but not of HCV or HBV infection. The diagnostic sensitivity of neopterin screening during the HIV window phase is similar to that of the p24 antigen test. With the introduction of viral NATs in blood screening, there is no additional benefit of neopterin screening with regard to the three blood-borne viruses HIV, HCV, and HBV. Acute phases of other infectious agents, however, have been reported to be detected by neopterin enzyme-linked immunosorbent assays.

Serum neopterin, tumor necrosis factor-α and soluble tumor necrosis factor receptor II (p75) levels and disease activity in Egyptian female patients with systemic lupus erythematosus

OBJECTIVE

To determine the clinical value of assaying serum levels of neopterin, tumor necrosis factor-alpha (TNF-alpha) and soluble tumor necrosis factor receptor II (p75) (sTNFRII) in patients with systemic lupus erythematosus (SLE), manifested clinically with lupus nephritis (LN), neuropsychiatric lupus erythematosus (NPLE), and/or vasculitis compared with established parameters (complements C3 and C4).

PATIENTS AND METHODS

Serum concentrations of neopterin, TNF-alpha and sTNFRII were studied in 40 female patients with SLE at various degrees of disease activity and in 10 healthy controls, matched for age and sex, using an ELISA kit. Disease activity was assessed by the SLE disease activity index (SLEDAI) score. Thirty-five, 30 and 28 of our patients presented with LN, NPLE and/or vasculitis, respectively, as the main clinical manifestation.

RESULTS

Serum levels of neopterin, TNF-alpha and sTNFRII were significantly increased, while the TNF-alpha/sTNFRII ratio, C3 and C4 levels of SLE patients were significantly lower than those of healthy controls. Neopterin and sTNFRII were the only parameters that showed significantly higher levels in SLE patients with mild activity compared to normal subjects and were the only parameters that showed a significant elevation in membranous nephritis and in mild NPLE compared to patients without nephritis and NPLE. Patients with vasculitis had significant elevation of serum neopterin, TNF-alpha and sTNFRII levels compared to patients without vasculitis. We found significant correlations between all measured variables and the SLEDAI score. Also, serum neopterin levels showed significant positive correlation with serum TNF-alpha, sTNFRII and TNF-alpha/sTNFRII levels. Serum neopterin and sTNFRII could be used to identify SLE patients from normals with a sensitivity and specificity of 100%. Multivariate linear regression analysis showed that serum sTNFRII was the only significant independent variable among parameters for prediction of SLE disease activity.

CONCLUSION

We suggest that serum sTNFRII and neopterin are more sensitive markers of disease activity than TNF-alpha, C3 or C4. However, sTNFRII may be a clinically useful independent marker for prediction of SLE disease activity and to differentiate normal subjects from those having mild SLE.

Association between homocysteine and neopterin in healthy subjects measured by a simple HPLC-fluorometric method

OBJECTIVES

Neopterin and homocysteine promote vascular smooth muscle cell proliferation through the activation of nuclear factor(kappa) B. The aim of this study was to investigate the relation between these two compounds in healthy subjects by a rapid HPLC-fluorometric method which simplifies sample pretreatment for the measurement of neopterin in serum.

DESIGN AND METHODS

In 40 healthy subjects (45.9 +/- 2.1 yr, mean +/- SEM, 10 males, 30 females) serum neopterin concentrations were measured by HPLC-fluorometry and enzyme-linked immunusorbant assay-ELISA and the results were compared. Urinary neopterin and plasma total homocysteine concentrations were assayed by HPLC-fluorometry.

RESULTS

Serum neopterin concentrations measured by HPLC and ELISA were 7.5 +/- 0.4 and 7.4 +/- 0.3 nmol/L, respectively, r = 0.92, p < 0.01. Urinary neopterin level was 163.9 +/- 11.0 nmol/mmol creatinine and plasma total homocysteine 7.6 +/- 0.4 micromol/L. A significant positive correlation was observed between serum neopterin and plasma total homocysteine (r = 0.59, p < 0.01).

CONCLUSIONS

A simple and rapid sample pretreatment for the measurement of neopterin in serum has been introduced. The significant positive correlation between neopterin and homocysteine implies that, interference with leukocyte function might be a new possible mechanism for the deleterious effects of homocysteine on vascular function.