Myéloperoxidase et volume prostatique : étude préliminaire

25 septembre 2018

Auteurs : T. Roumeguère, P. Van Antwerpen, L. Vanhamme, C. Delporte, A. Rousseau, E. Wespes, M. Vanhaeverbeek, K. Zouaoui Boudjeltia
Référence : Prog Urol, 2018, 10, 28, 482-487




 




Introduction


Benign prostatic hyperplasia (BPH) is a very common age-related disease [1].


Several parameters including androgens, dietary factors, inflammatory mediators and oxidative stress have been considered to play a role for the development of BPH, but there is no consensus as to which is the primary one [2].


Oxidative stress is associated with aging and age-related degenerative diseases such as BPH. Chronic inflammation is well documented in the development of BPH but the significance of inflammation on the development and severity of lower urinary tract syndrome (LUTS) due to BPH has not been established yet [3].


In vivo, oxidative stress might be modulated by several enzymes or proteins such as myeloperoxidase (MPO) and angiotensin II (Ang II). In response to a high level of pro-inflammatory cytokines, MPO can promote oxidative damages to host tissues [4]. MPO has recently been observed in prostate tissue and this intriguing location might be linked to prostate diseases [5]. Causes of intraprostatic inflammation remain unclear and it has been suggested that systemic inflammation could contribute to the progression of inflammation within the prostate. Ang II exerts a variety of biological actions, including (i) NADPH oxidase (NOX) activation, (ii) stimulation of cell growth, migration, and inflammation of smooth muscle cells and fibroblasts, (iii) facilitation of sympathetic activity [6, 7, 8, 9]. In this context, a higher Ang II specific activity was reported in patients suffering of BPH compared to healthy patients. However, Ang II functional significance for the pathophysiology of BPH is poorly understood [11].


Zouaoui Boudjeltia et al. showed that activation of NADP (H) oxidase by Ang II increased oxidation of low-density lipoproteins (LDL) by MPO (leading to the so called Mox-LDL) at the surface of endothelial cells, a mechanism underlying the correlation between these factors in endothelial dysfunction [4]. Moreover, MPO and Ang II interplay in the bloodstream to produce Mox-LDLs which have a proinflammatory action as they promote the release of cytokines such as IL-8 and TNF α by endothelial cells and monocytes, respectively [12, 13].


The link between prostate volume and systemic factors involved in the activation (Ang II and MPO) of oxidative stress is thus not clearly established in vivo. The present study aims at investigating the clinical association between Myeloperoxidase and the volume of the prostate to better understand mechanisms underlying benign prostatic hyperplasia.


Material and methods


Selection of the patients and clinical characterization


After approval by the Ethics Committee of Erasme University hospital (ULB), 121 patients aged over 45 years (48-70 years) seen in outpatient clinics of our institution with or without any complaints of LUTS were prospectively included in the study. The reasons for visits were urinary disorders or erectile dysfunction. All subjects signed an informed consent form specifying the purpose of the study and methods of blood sampling and transrectal ultrasound of the prostate. Patients under α -blockers or 5-α-reductase inhibitors were not included in the study (in order to avoid potential confounders factors on prostate volume or severity of lower urinary tract symptoms) as well as patients with diabetes or high-blood pressure treatment (Angiotensin II receptor blockers, angiotensin converting enzyme inhibitors...). Statins drugs were also considered as an exclusion factor. Body mass index (BMI) was calculated. Each patient filled the International Prostate Symptoms Score (IPSS) questionnaire in order to assess his own evaluation of lower urinary tract symptoms. A single operator performed all prostate evaluations with a BK leopard 7Hz probe. Total volume (TV) and transitional zone volume (TZ) of the prostate were systematically measured.


At the time of prostate ultrasound measurement, a venous blood sample (10mL) was collected and then centrifuged for 10minutes at 4000rpm. The supernatant was collected and frozen. Blood tests were performed at the Laboratory of Experimental Medicine of the University Hospital of Charleroi, site A, Vésale, Unit 222-ULB. All measured parameters are shown in Table 1.


Mox-LDL and Angiotensin II assays


Mox-LDL were measured with a specific antibody, which has previously been fully characterized [14].


Ang II was assayed in blood plasma using a radioimmunoassay kit (The BioSource angiotensin II kit, BioSource Europe SA, rue de l'Industrie 8, B-1400 Nivelles, Belgium).


Activity of MPO and total MPO assay


The activity of MPO was measured using the Specific Immunological Extraction Followed by Enzymatic Detection (SIEFED) method as described by Franck et al. for human fluids [15]. Total MPO content in plasma was measured using a sandwich human MPO ELISA kit (ELIZEN MPO, Zentech SE, Belgium). These analyses allow to calculate the active MPO fraction from the total MPO and the specific activity of MPO (activity/antigen ratio).


Statistics


SigmaStat® software package (Jandle Scientific) was used. Univariate analyses were depicted by Pearson's coefficient. Multilinear regression analysis was tested using a stepwise backward selection of the explicative variables that are known to be involved in reactive oxygen species (ROS) production. The standardized regression coefficients (Std Coeff) are given and a probability level of P <0.05 was considered as statistically significant.


Results


Clinical characteristics and biological parameters of subjects are shown in Table 1. A positive correlation was observed between BMI and total volume (TV) of the prostate (P =0.02) but not with the transitional zone volume (TZ) (P =0.23). There was a positive correlation between TV, TZ and PSA level (P <10−6). No correlation has been demonstrated between IPSS and TV or TZ. A weak correlation between Testosterone and IPSS was highlighted (Pearson's coefficient R=−0.17; P =0.05).


In multivariate analysis (Table 2), a first model was run with TV as dependent variable while Mox-LDLs, Ang II, Age, BMI, testosterone and MPO activity/antigen ratio were introduced as independent variables. TV was related to the combination of age, Ang II and MPO specific activity (Figure 1). Furthermore, a negative correlation between TV and MPO specific activity was observed (Std Coef=−0.272, P =0.004). Twenty-seven percent of the variability of TV could be explained by these variables.


Figure 1
Figure 1. 

3D representation of correlations between total prostate volume (TV), MPO specific activity (MPO act/ant) and angiotensin II (Ang II).




A second model was run with TZ as dependent variable. In this model, significant correlations were confirmed between TZ and age and MPO specific activity but Ang II was no longer retained with a R2 of 0.26. A negative correlation between TZ and MPO specific activity was also observed (Std Coef=−0.21, P =0.016). No correlation was found between Mox-LDL and prostate volume.


No correlation was observed between MPO and IPSS (IPSS-MPO antigen: R=0.16; P =0.08; IPSS-MPO activity: R=0.19; P =0.19; IPSS-MPO specific activity: R: −0.11; P =0.23, respectively).


No correlation was observed between Ang II and IPSS (R=−0.07; P =0.38).


Discussion


Benign prostatic hyperplasia (BPH) is a highly prevalent chronic disease in elderly patients with a long period of development and progression. Chronic inflammation has been documented for years in BPH, being associated to either disease initiation or progression [16]. A number of cytokines and growth factors are associated to immune dysregulation and chronic inflammation in BPH, including those responsible for the permanent attraction of leukocytes and those that promote the growth of prostate cells [17]. Inflammation influences the tissue microenvironment through the production of ROS, cyclooxygenase activity, and nitric oxide synthesis that are all linked to the deleterious effects of inflammation on prostate tissue [3]. However, the significance of inflammation on the development and progression of BPH is not well established.


Our focus on MPO presence and a potential activity in prostate tissue is consistent with its putative mutagen activity. MPO can indeed induce alterations of gene expression. They can all result in cell proliferation and death. Moreover, we recently demonstrated the presence of MPO in prostate epithelial cells [5]. Is MPO active in prostate tissue with a local effect of MPO in prostate diseases? MPO could be synthetized by prostatic epithelial cells and not only as commonly accepted by the myeloid lineage but its origin remains unknown.


The negative correlation observed in the present study between MPO specific activity and prostate volumes (TV and TZ) does not answer these questions and rather brings additional interrogations. Indeed, these results indicate an inverse correlation between prostate volume and plasma MPO specific activity whereas neither MPO quantity nor MPO activity are correlated. It is of interest to remind that MPO is also able, in some conditions, to have a catalase like activity meaning a potential protective role against inflammation and oxidative damage due to ROS by reduction of H2 O2 . This illustrates the complexity of the potential role of MPO and the careful interpretations that may be endorsed [5]. The latter phenomenon could be due to a higher increase of MPO quantity than MPO activity. While it is difficult to draw final conclusions, these data emphasized the importance of measuring both MPO concentration and activity [18]. Furthermore, Van Antwerpen et al. showed that glycosylation pattern of MPO has an impact on its enzymatic activity [19]. Therefore, posttranslational modifications could influence MPO specific activity in the prostate.


We report in the present study that plasma level of Ang II is correlated with the total prostate volume (TV) but not with the transitional zone volume (TZ). This could be explained by the design of this cross sectional study that did not involve backtracking of the natural history of BPH. Indeed, It is also consistent with a higher impact of Ang II on epithelial tissue rather than stromal tissue, the latter is predominant in TZ and TZ is slightly increased in the population of the study. Ang II is secreted in part by the prostate basal epithelial cells in vitro and angiotensin receptors are expressed in the prostate glandular epithelium [20]. Ang II receptors were also detected in the periurethral stromal and vascular smooth muscle of the prostate and increased expression of angiotensin-converting enzyme in BPH supports the hypothesis that renin-angiotensin system could be implicated in the pathogenesis of BPH [10]. Moreover, prostate and systemic renin-angiotensin system regulations are suggested to be independent and Ang II plasma level and Ang II prostatic level could be independent as previously observed [20]. The causal link in BPH between increased of plasma and tissue levels of Ang II and cell growth within the prostate remain to be established.


Another intriguing observation is the absence of correlation between Mox-LDL and prostate volume. Indeed, we have recently emphasized the predominant contribution of both MPO and Ang II for production of Mox-LDL in bloodstream [13] and Mox-LDL is one of the major factors that induces ROS production in prostatic epithelial cells.


Clinical comments and limitations must be drawn including the analysis of a specific small sample number of men at the time of the study. Enrolled patients were thus presented with or without LUTS due to BPH but with a low mean IPSS of 9.8 having failed to highlight any correlation. TV and TZ were not very large in our population. Testosterone blood levels were low to normal, not suggesting an influence on prostate volume. Finally, to demonstrate that oxidative stress will induce prostatic enlargement, longitudinal study is necessary.


Conclusion


If the interplay between Angiotensin II and Myeloperoxidase seems physio-pathologically possible, the contribution of both factors in BPH remains unclear. If any conclusion cannot be drawn, clarification requires future measurements focusing on MPO potential contribution on the severity of prostatic disease as this enzyme can locally promote pro-oxidant effects.


Disclosure of interest


The authors declare that they have no competing interest, including specific financial interests or relationships and affiliations relevant to the subject matter or materials discussed in the manuscript.




Table 1 - Mean and standard deviation (SD) values of the various parameters studied on 121 patients.
Parameters  Mean  SD 
Age (years)  58.8  10.8 
BMI (kg/m2 26.1  3.8 
TV (mL)  40  19 
TZ (mL)  16.5  13 
PSA (ng/mL)  3.56  5.06 
IPSS  9.76  7.22 
Testosterone (ng/dL)  3.18  1.73 
Angiotensin II (pmol/L)  13.5  10.8 
Mox-LDL (μg/mL)  9.46  8.67 
MPO Activity (MPOA) (mU/mL)  27.4  17.8 
MPO Antigen (MPOAg) (ng/mL)  49.8  35.7 
MPO specific activity (mU/ng)  0.601  0.241 



Légende :
BMI: Body mass index; TV: total prostate volume; TZ: transitional zone prostate volume; PSA: Prostate Specific Antigen; IPSS: International Prostate Symptoms Score.



Table 2 - Multivariate analysis of backward regression in the total population.
N=121  Standardised regression coefficient  P -value 
Model 1     
TV R2=0.27; F=11.09; P <0.001     
Age  0.44  <0.001 
MPO specific activity  −0.27  0.004 
ANG II  0.19  0.039 
Model 2     
TZ R2=0.26; F=14.94; P <0.001     
Age  0.48  <0.001 
MPO specific activity  −0.21  0.016 



Légende :
Parameters introduced in the stepwise multiple regression analysis: Mox-LDL; Ang II; Age; BMI; Testosterone; MPO antigen; MPO activity; MPO specific activity; TV: Total volume; TZ: Transitional zone volume. (Homoscedasticity passed, for TV: P =0.66; for TZ: P =0.56).


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© 2018 
Publié par Elsevier Masson SAS.