The profile of oxidative stress markers (arachidonic and linoleic acid derivatives) in patients with benign prostatic hyperplasia in relation to metabolic syndrome

Introduction

Benign prostatic hyperplasia (BPH) is a prevalent disease among the aging male population worldwide. Clinical symptoms of BPH include lower urinary tract symptoms (LUTS), as well as prostate volume enlargement (BPE) and bladder outlet obstruction (BOO) [1–3]. The precise mechanism of BPH pathophysiology and development remains incompletely understood. Nevertheless, there are several risk factors that have been shown to increase the likelihood of developing BPH in men. Such factors include age, hyperinsulinemia and insulin resistance, obesity, steroid hormone disorders, and the influence of genetic factors. In recent years, there has been a notable increase in research on metabolic syndrome (MetS) - a factor increasing the risk of BPH and involved in its development. Abundant scientific evidence points to the role of metabolic disorders [4]. Furthermore, there is mounting evidence that links the onset of inflammation with the development of prostate diseases, including benign prostatic hyperplasia and prostate cancer [5]. BPH and MetS are important factors influencing the health quality of life (HRQoL) index in aging men [6, 7]. Metabolic syndrome (MetS) abnormalities lead to systemic inflammation and oxidative stress [8]. Typical features of MetS include disturbed lipid parameters: increased levels of low-density lipoproteins (LDL) and triglycerides (TG), as well as decreased levels of high-density lipoproteins (HDL). This dyslipidemia results in the production of interleukin-8 (IL-8) [9, 10]. Genetic and environmental factors that influence the pathogenesis of metabolic syndrome are also regarded as risk factors for chronic disease. Dietary fatty acids may be an important contributor to the evolution or prevention of MetS [11]. Previous studies of MetS patients have shown a link between serum fatty acids level and a variety of diseases, including nonalcoholic fatty liver disease (NAFLD) [12], chronic kidney disease [13], systemic lupus erythematosus (SLE) [14], and arteriosclerosis [15]. There are studies indicating the effect of fatty acid on hormonal and biochemical parameters in patients diagnosed with BPH. Preliminary evaluation and analysis of patients with BPH showed that metabolic syndrome may contribute to changes in the concentrations of polyunsaturated fatty acids (PUFA) [9].

Polyunsaturated fatty acids (PUFAs) can be classified according to the number of carbon atoms that follow the final double bond in the fatty acid chain. Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) (omega-3 (ω-3)) contain n-3 carbon atoms. Arachidonic acid (AA) and linoleic acid (LA) (omega-6 (ω-6)) contain n-6 carbon atoms [16].

PUFA, AA, LA and its metabolites are important in regulating the course of inflammatory processes and diseases resulting from them. Three distinct enzyme systems may be involved in AA metabolism, namely cyclooxygenases (COX), lipoxygenases (LOX) and cytochrome (CYP) P450 enzymes, generating a broad spectrum of biologically active mediators derived from fatty acids. The oxidation products of arachidonic acid include: eicosanoids: prostanoides – prostaglandins (PGs), prostacyclin (PGI), thromboxane (TX); leukotrienes (LTs); lipoxines (LX) and hydroxyeicosatetraenoic acids (HETEs) [17]. Whereas, the products of LA oxidation are stable hydroxyoctadecadienoic acids (HODEs) [18] as shown in Figure 1.

Prostaglandin E2 (PGE2) is a member of the prostanoid lipid class, a subcategory of eicosanoids that are formed through the oxidation of essential fatty acids (EFA) with a 20-carbon chain. Prostaglandin E2 (PGE2) is a lipid that plays a pivotal role in the inflammatory response, including the progression of neoplastic processes. PGE2 exerts effects on cell proliferation and the process of apoptosis, in addition to influencing angiogenesis and immune responses. Additionally, PGE2 has been demonstrated to promote pyrogenic effects and has strong immunosuppressive properties, which contribute to the resolution phase of acute inflammation. This, in turn, facilitates tissue healing and the establishment of homeostasis [19].

Leukotrienes, 5-HETE and 5-oxo-ETE are regarded as potent mediators of inflammation. They are pivotal intermediates in the 5-LOX pathway, which induces macrophage infiltration, thereby instigating an inflammatory response [20]. The activating effect of 5-HETE on human neutrophils is approximately 100 times weaker than that of 5-oxo-ETE. Furthermore, 5-oxo-ETE has been demonstrated to facilitate neutrophil aggregation and act as a chemoattractant for human eosinophils and basophils. Additionally, 5-oxo-ETE has been shown to play a role in the induction of monocyte migration. It has also been confirmed that 5-oxo-ETE is involved in the pathogenesis of various diseases, including asthma, allergy, and cancer development [20].

Lipoxins (LX) are lipid-derived anti-inflammatory mediators. LX exert anti-inflammatory effects, including the inhibition of pro-inflammatory factor expression while simultaneously promoting the expression of anti-inflammatory factors. Additionally, LX has been demonstrated to inhibit the inflammatory action of neutrophils and promote their phagocytosis by macrophages [21]. LXs help to dampen inflammation and promote tissue repair. Their role is confirmed in chronic inflammation, cancer, respiratory tract, neurodegenerative and liver diseases, endometriosis, and retinal degeneration [22].

The metabolite 15-HETE of arachidonic acid (AA) is frequently elevated during inflammatory conditions. 12-HETE is an arachidonic acid metabolite of 12-LOX, and one of its biological functions is to act as a chemoattractant for neutrophils. [23]. This acid also affects the stimulation and inhibition of platelets [24]. 12(S)-HETE is also involved in the motor phase of metastasis, acting via the GPR31 receptor. This phase consists of cell adhesion, spreading, secretion of proteases and regression of endothelial cells. Moreover, it also has a protective function against apoptosis and can stimulate angiogenesis. [25]. It has been demonstrated that 15S-HETE plays a role in regulating the function of vascular smooth muscle and endothelial cells. Furthermore, it may also be involved in cellular proliferation and the course of inflammation. In contrast to 12S-HETE, 15S-HETE may participate in protective and immune responses against cancer cells. In the context of prostate cancer, 15S-HETE may play a role in the inhibition of cell cycle progression in prostate cancer cells [24]. 16-R/S HETE is cytochrome P450-derived metabolite of AA metabolism. It is isolated from human PMNs (polymorphonuclear cells) and act as endogenous regulator for these cells [26]. Moreover, 16-HETE functions as neutrophil suppressor [27]. Given its vasodilatory properties, 16-HETE can be regarded as a potential therapeutic target in the management of cardiovascular disorders [26]. Vascular endothelial cells that are hypoxic are capable of producing 18R/S-HEPE. Moreover, it has been demonstrated that 18-HEPE possesses anti-inflammatory and anti-apoptotic properties [28]. 18-HEPE is cardioprotective by inhibition of macrophage-mediated proinflammatory activation of cardiac fibroblasts [29, 30]. Moreover, there is a report that 18-HEPE is a potential anticancer metabolite [31]. Another property of 18-HEPE is the increase in BDNF mRNA expression in Müller glia cells, which affects the ameliorate retinal neuronal cell dysfunction [32].

Hydroxyoctadecadienoic acids (9-HODE and 13-HODE) play a pivotal role in cell signaling and the regulation of inflammatory processes, which occurs through the involvement of adhesion molecules. Additionally, these acids are associated with the degranulation and chemotaxis of neutrophils. Moreover, during the course of processes involving HODE acids, superoxide is produced by macrophages and receptor PPAR-γ (gamma) is activated. Moreover they are involved in inhibition of protein kinase C. The role of these acids has been confirmed in the regulation of inflammation occurring in the course of metabolic syndrome, atherosclerosis, but also in the neoplastic process [33].

Maresins are effective anti-inflammatory mediators, which have a strong protective effect in inflammation, oxidative stress and immune diseases. They act as inhibitors of neutrophil infiltration and naive T cell differentiation. Furthermore, they inhibit the expression of proinflammatory cytokines, including interleukins 1β and 6, as well as TNF-α. Maresin 1 is derived from DHA20, and it is produced in macrophages, platelets and neutrophils [34].

Resolvins are synthesised from DHA, n-3DPA (docosapentaenoic acid), and EPA. They possess immunomodulatory functions, including the inhibition of leukocyte infiltration and the capacity to enhance phagocytosis by macrophages. Moreover, they are involved in the regulation of cytokine secretion, which mediates the reduction of inflammatory pain. Resolvins play a pivotal role in modulating the progression of inflammatory processes within the nervous system, joints, and blood vessels [35]. Resolvin E1 (RvE1) has been demonstrated to be involved in the mitigation of intestinal inflammation through the enhanced production of the anti-inflammatory cytokine IL-10 by macrophages [36].

Among the functions of RvE1, its action on reducing the level of leukocyte adhesion proteins (CD11 and CD18) and the activation of platelets are particularly noteworthy. Additionally, RvE1 induces the apoptosis of PMN cells, thereby limiting the extent of inflammation [29].

Resolvin D1 (RvD1), synthesised from docosahexaenoic acid (DHA), has been demonstrated to prevent organ damage occurring during inflammation of the lungs, kidneys, pancreas, liver and peritoneum (confirmed in an animal model). The anti-inflammatory effect of RvD1 may be mediated by inhibiting neutrophil recruitment and inflammatory cytokine production [37].

Proteins constitute a family of pro-resolving mediators. They are involved in combating bacterial and viral infections by increasing the efficacy of the killing process and, as a result, microbial clearance. Additionally, PD1 limits leukocyte infiltration, but also reduces NF-KB signaling, pro-inflammatory chemokines and cytokines, inflammasome formation and COX-2 activation. Furthermore, PD1 has been demonstrated to exert a robust neuroprotective effect. PD1 has been shown to facilitate the enhanced expression of antiviral interferon (lambda) in bronchial epithelial cells, which in humans may exert a considerable impact on the attenuation of inflammatory processes within lung tissue. [38].

This study represents one of the first to examine the levels of linoleic acid derivatives and anti- and pro-inflammatory mediators in patients with BPH and aging men without BPH.

The primary objective was to examine the profile of lipid markers of oxidative stress (arachidonic and linoleic acid derivatives) in the serum of patients with BPH and concomitant metabolic syndrome.

Results

Anthropometric measurements were performed in patients from both groups. No statistically significant differences were observed in body weight, BMI and waist circumference between patients from the control and BPH group (Table 1). Analysis of variance (ANOVA) was conducted on the control and study groups with respect to MetS, the results of which are presented in Table 2.

Lipid parameters in serum were measured in the control and study group (Table 1). Statistical analysis revealed that total cholesterol (p = 0.059), LDL cholesterol (p < 0.001) and glucose (p < 0.001) levels were statistically significantly higher in the healthy patients group. Conversely, the patients with BPH exhibited statistically higher TG (p < 0.05) and HDL cholesterol (p < 0.001) levels.

Discussion

The state of knowledge of BPH and its pathophysiology is improving. This topic is still subject to research and numerous discussions. In our investigation, we analyze as many lipid-derived inflammatory markers in men with BPH. The coexistence of MetS in these patients was also taken into account in order to find out whether the examined parameters can be involved in the pathophysiology of BPH and MetS.

The primary risk factors for the development of BPH are hormonal disorders [39, 40], MetS, obesity, and other metabolic disorders, as well as chronic inflammation [41]. Inflammation is an orderly, physiological process resulting from the immune system, i.e. the type of defense of the body in response to a damaging factor and the subsequent healing of tissues [42]. Chronic inflammation can lead to tissue damage, pathology, and disease. Changes in the blood vessels are the underlying cause of the inflammatory reaction (when vasodilation occurs, and tissue blood supply and vascular permeability increase, leukocytes or plasma proteins can enter the inflamed area). Chemical mediators are then released in the region of the inflammatory reaction. Many types of inflammatory cells and mediators are involved in this process [43]. Depending on the nature of the inflammatory stimulus, the anatomical site, and the type of inflammatory response, these mediators can include lipids, peptides, or amino acid derivatives.

As essential nutrients, fatty acids are involved in metabolism and cellular biochemical transformations. PUFAs are important components of the phospholipids of all cells. Improper regulation of fatty acids can cause inflammation and carcinogenesis [44]. PUFAs regulate inflammatory processes through various mechanisms, which include participating as mediators or altering the composition of cell membranes. The primary mediators of inflammation are PUFA derivatives specifically arachidonic acid (AA) and linoleic acid (LA) [45, 46], as well as their oxidation products including prostaglandin (PG), thromboxane (TX), 5-oxo-eicosatetraenoic acid (5-oxo-ETE), 12- and 15-hydroxyeicosatetraenoic acid (HETE), and 9- and 13-hydroxyoctadecadienoic acids (HODEs) [45, 46]. PUFAs are found in frequently eaten foods, and their overconsumption can lead to higher levels of prostaglandins in the body [46]. The content of AA and n-3 fatty acids―eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)―can be changed by their exogenous administration [46]. Fatty acids, activated by acyl-CoA synthetase, can then undergo beta oxidation to acetyl-COA in the mitochondrion or be attached to triglycerides or phospholipids [44, 47]. The metabolism of AA depends, among other things, on acyl-CoA synthetase long-chain family member 9. In addition, higher concentrations of AA contribute to a decrease in the activity of cyclo-oxygenase-2 (COX-2), but stimulate the processes in which lipoxygenase (LOX) is involved. This, in turn, reduces the concentration and activity of prostaglandin E2, and stimulates the production of lipoxin A4 (LXA₄).

Our research showed that men with BPH had lower prostaglandin E2 levels than healthy controls. Similarly, Fowke et al. (2016) [48] did not confirm the relationship between prostate hyperplasia and increased prostaglandin E2 levels. Some authors have confirmed the involvement of prostaglandin E2 in the process of prostate cancer formation and its metastasis to other organs [49, 50]. Nevertheless, the role of prostaglandin E2 seems to be still unclear, as Kiely et al. (2021) [51] do not confirm the relationship between higher prostaglandin E2 levels and prostate cancer progression.

LA is the main component of LDLs. Elevated LDL levels combined with oxidative stress and antioxidant deficiency stimulate oxidative processes, playing an important role in the regulation of inflammatory processes. LA also affects the processes within respiratory tract smooth muscles and the vascular wall, thereby regulating pain sensitivity and endogenous steroid hormones associated with the etiopathogenesis of metabolic syndrome disorders. The metabolic effects of LA derivatives, which include HODEs, oxo-octadecadienoic acids (oxo-ODE), epoxy-octadecadienoic acid, and epoxy-keto-octadecenoic acids, remain unexplained.

They have a pleiotropic effect (beneficial or deleterious), and so it is impossible to identify a clear answer. As mentioned earlier, prostaglandin and thromboxane are produced from AA (omega-6 (ω-6) polyunsaturated fatty acid), which may suggest that eating foods high in ω-6 fatty acids may induce or inhibit inflammatory processes [52].

HETEs and HODEs are involved in the inhibition of granulocyte aggregation, and dilate blood vessels, thereby affecting inflammatory responses in the pathogenesis of atherosclerosis and MetS [24, 46].

This, in turn, may be related to urological diseases (including BPH), which are known to be associated with inflammation [53]. It is believed that dietary fatty acids and their derivatives, by modulating inflammatory reactions, may affect the remodeling of the prostate epithelium, and consequently the functioning of the gland, thus increasing susceptibility to its disorders [54].

Our study of lipid markers of inflammation revealed statistically significant differences in 5-oxo-ETE levels between the male groups. 5-Oxo-ETE is one of the more potent ‘agents’ for cell signaling, involved in autocrine and paracrine regulation. It has also been postulated that 5-oxo-ETE contributes to the local inflammatory response and stimulates cancer cell proliferation. It may also play a role as a pro-inflammatory mediator in diabetes [24].

Men with BPH exhibited statistically significantly higher concentrations of 12-HETE. It had previously been reported that 12-HETE levels were higher in the urine of BPH patients than of men without prostate disease [55, 56]. Moreover, Dilly et al. (2013) [57] demonstrated that in prostate tumor cells, 12-HETE stimulates the release of matrix metalloproteinase 9 (MMP-9), which plays a significant role in the process of tumor angiogenesis. There is also a link between the development of prostate adenocarcinoma and 12-HETE. This may indicate that this marker is involved in the formation of benign and malignant lesions in the prostate. This marker may also inhibit platelet aggregation induced by thromboxanes A2 (TXA2), leading to platelet destruction mediated by reactive oxygen species (ROS) [58]. Furthermore, it may serve as a mediator for some of the pro-inflammatory and pro-apoptotic effects of specific cytokines involved in the pathogenesis of diabetes [59], which is a component of MetS. However, we were unable to show statistically significant differences in the concentrations of this marker depending on MetS.

Our study also demonstrated statistically significant higher levels of 15-HETE in patients with BPH. To date, evidence has emerged to suggest that 15-HETE may be involved in the regulation of vascular smooth muscle and endothelial cell function, cell proliferation, and the development of inflammation [24, 60]. There is also evidence for the involvement of this marker in the neoplastic process in the prostate [61].

We showed that serum 9-HODE concentrations were statistically significantly higher in men with BPH compared to controls. According to Spiteller et al. (1998) [62], this marker is associated with oxidative stress, inflammation, and numerous pathological conditions. Studies show links to atherosclerosis, diabetes, Alzheimer’s disease, NAFLD, psoriasis, chronic inflammation, obesity, and cancer. To date, no studies have been conducted in patients with BPH.

In our study, we also presented scientific evidence for the involvement of the following markers in BPH: 5(S),6(R),15(R)-LTXA4 and 5-HETE, whose serum concentrations in men with BPH were statistically significantly higher than in those without BPH. Moreover, the co-existence MetS was proven to affect the concentrations of 5(S), 6(R)-LTXA4 in the study group. Due to the lack of scientific evidence in the literature, the role of these markers in the pathogenesis of BPH remains unclear.

A breakthrough in understanding the pathophysiology of inflammation was made with the discovery of special lipid mediators associated with endogenous alleviation of inflammation. This is an active process involving endogenous anti-inflammatory and proresolving lipid mediators [63]. They include several groups of mediators known as lipoxin (LX), resolvin (Rv), protectin (PD), and maresin (MaR). Lipoxins are derived from ω-6 acids, and resolvins, protectins, and maresins from ω-3 acids [64].

The findings of our study indicated the existence of statistically significant discrepancies in the concentrations of resolvin E1, protectins D1, and maresins 1. Patients with BPH exhibited elevated serum concentrations of the aforementioned biomarkers. Studies suggest that lipid mediators are involved in alleviating inflammatory and allergic reactions, wound healing, and relieving neuropathic pain. So far, a protective effect of resolvin E1 against bronchial asthma and complications in the form of respiratory tract infections has been described [65]. Based on a mouse model study, resolvins E1 exhibit anti-inflammatory and analgesic effects, by inhibiting the expression of pro-inflammatory cytokines, neutrophil infiltration, and TNF-α activity [66]. Maresin 1 increases the uptake of apoptotic neutrophils by macrophages, stimulates macrophage phagocytosis, and reduces neutrophil penetration into inflammatory foci. It also inhibits the production of leukotriene B4―an AA metabolite―by direct inactivation of the enzyme, leukotriene A4 hydrolase (LTA4H). The effect may be suppression of the inflammatory response by reducing the production of the pro-inflammatory mediator, leukotriene B4 [67].

Conclusions

Despite new information and evidence on specialized lipid mediators, the existing literature remains deficient in its analysis of mediators in diverse models of inflammation, and their potential contribution to the pathophysiology of chronic diseases. BPH is the result of many factors that reinforce each other’s adverse effects on the prostate gland. Endocrine disorders cannot be considered as the only factors determining the development of BPH [68]. It is evident that androgens exert a pivotal influence on the formation of the male genitourinary tract, facilitating the differentiation and proliferation of stromal and prostatic epithelial cells. The findings of the present study indicate that pro-inflammatory mediators and suppressors of inflammation may play a role in the in the development of BPH, but their exact contribution has yet to be investigated.

Materials and Methods