Urinary Biopyrrins: A New Marker of Oxidative Stress in Psoriasis

Abstract

Background:

Psoriasis is a common chronic, relapsing, immune-mediated disease involving skin and joints of genetically predisposed individuals. Oxidative stress has been found to play many important roles in cellular damage and loss of function in a number of tissues and organs and is believed to contribute to the pathogenesis of a variety of diseases. Urinary biopyrrin levels have gained attention as an indicator of oxidative stress.

Aim and Objective:

To measure urinary biopyrrins excretion as a marker of oxidative stress in psoriasis.

Patients and Methods:

This case–control study was carried out on 85 subjects; 55 cases with chronic plaque psoriasis and 30 age, gender and body mass index-matched normal subjects as a control group. Urinary biopyrrin levels were measured using enzyme immunoassay.

Results:

There was a highly significant difference between cases and controls regarding urinary biopyrrins level (P < 0.001). There was significant positive correlation between biopyrrins level and both the age of cases (r = 0.28, P = 0.01) and psoriasis area and severity index score (r = 0.99, P < 0.001).

Conclusion:

Urinary biopyrrins are increased in patients with psoriasis, and the level is correlated with disease severity. Further large-scale studies involving different ages and different clinical varieties of the disease are needed to expand and validate current findings. The clinical usefulness of antioxidants in psoriasis treatment needs to be evaluated in future research. Furthermore, the value of biopyrrins as biomarkers for monitoring response to therapy needs to be evaluated.

What was known?

• Psoriasis is a cutaneous disease associated with oxidative stress

• Urinary biopyrrins can be used to assess the presence of oxidative stress.

Introduction

Psoriasis is a chronic inflammatory skin disease affecting about 3% of the population worldwide.[1] It is characterized by erythematous scaly papules and plaques.[2]

The etiology is not known, but genetic and immunological factors, trauma, emotional stress, alcohol, smoking, and infections were taken into account.[3] In the past few years, researchers focused their attention on oxidative stress, considering it an important player in psoriasis pathogenesis.[4,5]

Bilirubin is known to be an intrinsic antioxidant that reacts with reactive oxygen species (ROS) and generates several hydrophilic metabolites called biopyrrins.[6] Biopyrrins are excreted in urine because of their hydrophilic properties. Therefore, urinary biopyrrins excretion can reflect the severity of oxidative stress.

This work is aimed to measure urinary biopyrrins excretion as a marker of oxidative stress in psoriasis.

Patients and Methods

This case–control study was carried out on 85 subjects. These included 55 cases with chronic plaque psoriasis and 30 age-, gender and body mass index-matched normal subjects as a control group.

A written consent form approved by The Local Ethical Research Committee was obtained from every participant before the study initiation. This was in accordance with the Helsinki Declaration of 1975 (revised in 2000).

All studied patients were subjected to comp’lete history taking and general and dermatological examination. Clinical data describing the patients’ demographics (age and gender) as well as clinical variables (disease duration, age of onset, affected sites, itching, koebnerization, joint or mucosal affection, and family history of psoriasis) were all documented. Disease duration was calculated from disease onset to time of the first visit.

The severity of the disease was assessed by the psoriasis area and severity index (PASI) score.[7]

Exclusion criteria

Exclusion criteria included the presence of concomitant inflammatory disease, such as infections and autoimmune disorders, immune-compromised patients, diabetes mellitus, familial hypercholesterolemia, neoplastic diseases, obesity, liver and kidney diseases, and recent major surgical procedures. Patients who were on diuretics, hormone replacement therapy, those who use alcohol and those who smoke were also excluded. Patients practicing excessive exercise apart from daily life activities and those taking any treatment including vitamins and anti-inflammatory drugs in the last 3 months were excluded.

Sample collection

Fifty milliliters of fresh voided, early morning urine samples were collected in sterilized container, and transported on ice to the research laboratory, where they were processed immediately.

Measurement of urinary biopyrrins

Urinary biopyrrins were measured using an enzyme-linked immunosorbent assay (ELISA) kit (GSCIENCE, USA) according to the manufacturer's recommendation. The concentration of urinary biopyrrins was adjusted by the urinary creatinine concentration.[8]

Statistical analysis

Results were collected, tabulated and statistically analyzed by IBM personal computer and statistical package SPSS version 11 (SPSS Inc, Chicago, Illinois, USA). Results were expressed as mean ± standard deviation (SD). Student's t-test was used for comparison between two groups having quantitative variables. Mann–Whitney U-test was used for comparison between two groups not normally distributed having quantitative variables. Pearson's coefficient test (r) was used to study the correlation between two quantitative parameters. P value of < 0.05 was considered statistically significant.

Results

Clinical data of studied cases were shown in Table 1.

Table 1.

Clinical data of selected cases

Urinary biopyrrins in the studied groups

Regarding biopyrrins level among cases, it ranged from 2 to 9.7 nmol/mg creatinine with mean ± SD of 5.71 ± 2.06 nmol/mg creatinine and median value of 5.40 nmol/mg creatinine [Figure 1a]. In controls, it ranged from 1.5 to 5.2 nmol/mg creatinine with mean ± SD of 3.16 ± 1.05 nmol/mg creatinine [Figure 1a]. There was highly significant difference between cases and controls regarding urinary biopyrrins level (P < 0.001) [Figure 1a].

Figure 1.

(a) Biopyrrins levels in studied groups. (b) Significant positive correlation between urinary biopyrrins and age of studied cases. (c) Significant positive correlation between urinary biopyrrins and psoriasis area and severity index score of studied cases

Correlation between urinary biopyrrins level and clinical parameters of studied cases

There was significant positive correlation between biopyrrins level and both age of cases (r = 0.28, P = 0.01) [Figure 1b] and PASI score (r = 0.99, P < 0.001) [Figure 1c]. No significant association was detected between high (>5.40 nmol/mg creatinine) or low (<5.40 nmol /mg creatinine) biopyrrins and other clinical parameters (gender, age of onset, disease duration, affected sites, itching, koebnerization, joint or mucosal affection, and family history of psoriasis).

Discussion

Among a number of biological defense systems in the human body, bilirubin represents one of the most potent antioxidant substances. It has been reported to act as a strong antioxidant in vitro[9] and to have powerful protective functions in vivo when the mechanisms of antioxidant defence are challenged.[10,11] ROS oxidize bilirubin to produce biopyrrins, which have been used as oxidative stress markers.[12]

Chronic inflammation is capable of inducing oxidative stress as inflammatory cells produce free radicals and soluble mediators such as metabolites of arachidonic acid, cytokines, and chemokines, which act by further producing reactive species.[13]

Plasma membrane of keratinocytes in psoriatic lesions have a significant increase in arachidonic acid which is the natural substance for the synthesis of malondialdehyde, an end product of lipid peroxidation.[14] In addition, increased ROS production from neutrophils,[15] keratinocytes and fibroblasts[16] have been reported in psoriasis. ROS can act as second messengers in the induction of several biological responses such as the activation of nuclear factor kappa-light-chain-enhancer of activated B cells or activator protein 1, the generation of cytokines and the modulation of signaling pathways.[17,18] Psychological stress was claimed to play a role in psoriasis pathogenesis.[19] Psychological stress is associated with increased levels of free radicals[20] and altered antioxidant enzyme activities.[21]

Furthermore, oxidative stress leads to cell damage by continuous chain reactions and may be responsible for activation of phospholipase A2, production of many mediators by arachidonate, deactivation of adenylate cyclase and activation of guanylate cyclase leading to decrease in the cyclic adenosine monophosphate/cyclic guanosine monophosphate ratio responsible for epidermal proliferation in psoriasis.[5]

In the last years, increases in plasma biochemical markers of oxidative stress, malondialdehyde, glutathione peroxidase and superoxide dismutase, have been reported in patients with psoriasis.[5,22]

Therefore, the question of whether oxidative stress is a primary or secondary event in psoriasis pathogenesis remained unanswered.

This work aimed to measure urinary biopyrrins excretion as a marker of oxidative stress in psoriasis.

The current study showed a significant difference between psoriatic cases and healthy controls regarding urinary biopyrrins level. This may underscore previous reports of oxidative stress in psoriasis. To the best of our knowledge, this is the first clinical report to analyze the urinary levels of biopyrrins in psoriasis. Increased urinary biopyrrins was reported in atopic dermatitis,[23] heart failure,[24] acute myocardial infarction,[25] asthma[26] unconjugated hyperbilirubinemia[27] perinatal stress[28] and in workers with asbestos exposure.[29]

In the current work, there was a significant correlation between urinary biopyrrins levels and PASI score. Therefore, the extent of oxidative stress is associated with disease severity. A similar finding was detected in atopic dermatitis.[23]

The significant positive correlation between urinary biopyrrins and age of studied cases, detected in the present work, can be explained by the known observation of increased oxidative stress with aging.[30] However, Ito et al. reported that there was no significant correlation between age and urinary biopyrrins levels in patients with asthma.[26] Further studies are needed for firmer conclusion.

It is noteworthy that the attenuation of oxidative stress might be a relevant therapeutic approach, and it would be useful to recommend additional drugs with antioxidant effects in psoriasis treatment. Activators of peroxisome proliferator-activated receptors were shown to induce antioxidant enzymes, allowing a reduction in oxidative stress and inflammation.[31] Moreover, the possibility of their use as novel anti-inflammatory drugs in the treatment of inflammatory skin diseases has been suggested.[32] It was suggested that antioxidant treatments in patients with psoriasis may be valuable in two respects: (1) To decrease the inflammation in skin tissues by virtue of the inactivating effect of free radicals; and (2) to confer stability on cell membranes by a positive effect on membrane stabilization and repair.[33] Further clinical trials are therefore recommended to clarify the clinical usefulness of such agents in psoriasis treatment.

Novío et al. reported the efficacy of urinary biopyrrins as a potential biomarker for monitoring of the response to treatment with anxiolytics.[34] Whether biopyrrins can be used to monitor the response to systemic or biological treatment in psoriasis or not, needs further research and if applicable, it will have several advantages (i) the determination of biopyrrins is a simple screening method[35] that can be assessed by a well-established ELISA system,[36] making the test a noninvasive option in comparison with other methods that are invasive (e.g., blood sampling);[37](ii) because of the hydrophilic properties of the biopyrrins, they are immediately excreted in urine after their production,[12] so their continuous monitoring can indicate the intensity of oxidation in vivo[38,39] and detect early changes (but not lasting ones) in a patient's condition;[40] (iii) biopyrrins in urine more sensitively reflect oxidative stress than those in blood[36] or than other systemic oxidative stress indicators (malondialdehyde and lipid peroxide), which react readily with substances in the body.[41]

In addition, urinary biopyrrins were found to correlate well with oxidative stress accompanying psychological stress.[38] The role of psychological stress in psoriasis pathogenesis was suggested.[19] However, to the best of our knowledge, no studies have investigated the association between psychological stress and oxidative stress in this disease entity; this is an area that requires future investigation.

From the aforementioned results we can come to conclude that urinary biopyrrins are increased in patients with psoriasis and the level is correlated with the disease severity. Further large-scaled studies involving different ages and different clinical varities of the disease are needed to expand and validate current findings. The clinical usefulness of antioxidants in psoriasis treatment needs to be evaluated in future research. Furthermore, the value of biopyrrins as biomarkers for monitoring response to therapy needs to be evaluated.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

What is new?

• To the best of our knowledge, urinary biopyrrins were not investigated before in psoriasis

• Urinary biopyrrins level is correlated with the disease severity

• The clinical usefulness of antioxidants in psoriasis treatment needs to be evaluated.