Article
Effects of lisinopril treatment on the pathophysiology of PCOS and plasminogen activator inhibitor-1 concentrations in rats

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Abstract

Research question

Angiotensin-converting enzyme inhibition results in a significant reduction in plasma concentrations of plasminogen activator inhibitor-1 (PAI-1). What are the effects of lisinopril treatment on PAI-1 concentrations and the morphology and function of the ovaries in the letrozole-induced polycystic ovary syndrome (PCOS) rat model?

Design

This prospective randomized controlled animal study involved female Wistar albino rats. Twelve rats were assigned as controls (group I). In the study group (n = 48), letrozole (an aromatase inhibitor) was administered for PCOS modelling for 9 weeks. After confirming disrupted oestrous cycles, the study group was randomized into two groups: group II (n = 24; letrozole only) and group III (n = 24; letrozole + lisinopril 15 mg/kg per day). After 12 weeks, each group was divided randomly into two. Biochemical, histopathological and immunohistochemical analyses was performed in subgroups designated A, and fertilization rates were studied in subgroups designated B.

Results

Lisinopril treatment reduced the weight and area of the ovaries, the number and wall thickness of cystic follicles, and serum concentrations of LH and testosterone, relative to group II (P < 0.001). Circulating PAI-1 concentrations were significantly different among three groups (7.7 ± 0.9 ng/ml, 9.8 ± 0.7 ng/ml and 8.6 ± 0.7 ng/ml for groups IA, IIA and IIIA; P < 0.001). Pregnancy rates were 100%, 0% and 16.7% in groups IB, IIB and IIIB.

Conclusions

In the letrozole-induced rodent PCOS model, lisinopril modifies the action of letrozole, possibly by inhibition of systemic and ovarian production of PAI-1. The use of PAI-1 inhibitors deserves further investigation in understanding the pathogenesis of PCOS.

Introduction

Polycystic ovary syndrome (PCOS) is an endocrinological disorder characterized by anovulatory menstrual cycles in women of reproductive age. Although the prevalence varies depending on the diagnostic criteria used, the average incidence of PCOS in reproductive-age women is 6.5–8% (Norman et al., 2007). This group of patients usually presents with infertility, obesity, amenorrhoeic cycles due to oligo/anovulation, and recurrent pregnancy losses during their reproductive period. Women with PCOS may also face increased risks of metabolic syndrome, glucose intolerance, dyslipidaemia, type 2 diabetes mellitus, cerebrovascular events, obstructive sleep apnoea and unopposed oestrogen-induced endometrial cancer at later ages (Chang and Katz, 1999; Fauser and Bouchard, 2011).

Although the aetiopathogenesis of PCOS is not well understood, endocrine and coagulation system abnormalities are suspected in its development. Four studies stand out in support of this argument. First, Dahlgrenet and colleagues proposed a model of myocardial infarction progression risk in patients with PCOS and predicted that the risk of myocardial infarction would be seven times higher in the PCOS group (Dahlgren et al., 1992). Second, vascular endothelial dysfunction, an important marker of cardiovascular disease, has been identified in patients with PCOS (Kravariti et al., 2005). Third, in some women with PCOS the presence of insulin resistance has been reported to be independent of body mass index (Dunaif et al., 1989). Fourth, approximately 40% of women have PCOS that is complicated by obesity-induced insulin resistance (Legro et al., 2004). Furthermore, there is a striking similarity with the long-term complications of PCOS, related to the increased metabolic risks seen in both conditions, including insulin resistance, diabetes and cardiovascular events; there are also elevated plasma concentrations of plasminogen activator inhibitor-1 (PAI-1), a key regulator of fibrinolysis and extracellular proteolysis, (Avellone et al., 1994; Juhan-Vague et al., 1989). Additionally, elevated concentrations of PAI-1 are associated with increased risk of thrombosis and atherosclerosis (Vaughan, 2005). An aberrant tissue expression of components of the PAI-1 system has also been associated with tissue invasion by TGF-β1-induced PAI-1 transcription that involves Reactive Oxygen Species (ROS) generation and fibrosis (Samarakoon et al., 2013).

PAI-1 is a member of the serine protease inhibitor (SERPIN) superfamily and inhibits the plasminogen activators tissue plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA); both of these proteolytically convert plasminogen into plasmin, the critical enzyme for clot lysis, ovulation and implantation (Piquette et al., 1993; Politis et al., 1990; Puistola et al., 1995; Sappino et al., 1989). Plasmin also converts procollagenase to collagenase, which degrades type IV collagen in the basement membrane of the dominant follicle during ovulation. Components of the plasminogen activation system can be demonstrated in the follicular fluid of the human ovary, in the granulosa cells and on the wall of the dominant follicle in vitro (Piquette et al., 1993, Puistola et al., 1995). Additionally, Ambekar and colleagues have reported that plasminogen was degraded in the follicular fluid of the ovaries of women with PCOS (Ambekar et al., 2015).

Although a significant correlation between PCOS and elevated PAI-1 concentrations has been reported (Andersen et al., 1995; Atiomo et al., 1998), the effects of reducing or correcting PAI-1 concentrations on the reproductive function of women with PCOS have not been studied. Previously, lisinopril (an angiotensin-converting enzyme [ACE] inhibitor) treatment was shown to decrease androgen concentrations via the ovarian renin–angiotensin system (OVRAS) (Hacıhanefioglu et al., 2002). Furthermore, Vaughan and co-workers have reported that ACE inhibition resulted in a significant reduction in plasma concentrations of PAI-1 (Vaughan et al., 1997). These findings suggest that the effects of lisinopril treatment on ovarian function deserve further examination (Liu et al., 1986; Yoshimura et al., 1996b). This study therefore investigated the effects of lisinopril on plasma concentrations of PAI-1 and sex-steroid hormones, ovarian histopathology and spontaneous clinical pregnancy rates in rats with letrozole-induced PCOS.

Section snippets

Materials and methods

This prospective randomized controlled animal study was approved by Health Research and Application Center, Animal Experiments Local Ethical Committee (4 March 2019, Meeting number 0053, Decision number 580), Health Sciences University, Ankara. The study by Kauffmann and colleagues was referenced to calculate the sample size for letrozole-induced PCOS modelling (Kauffman et al., 2015). Each study group was determined to include at least six rats so that 90% power with 1% alpha error would be

Oestrus cycle patterns of rats determined by consecutive smear tests

Four out of the 64 rats were excluded from the study due to initial acyclic or irregular oestrus cycle patterns, determined by consecutive smear tests carried out at the beginning of the study. Sixty rats with regular cycles were therefore included.

Smear tests performed during the 9th week of the study showed that group I animals (control; n = 12) had regular oestrus cycle patterns, whereas rats in group II (letrozole only; n = 24) and group III (letrozole + lisinopril; n = 24) displayed an

Discussion

In this study, PAI-1 concentration was higher in the letrozole-induced PCOS rats than the control group; the decrease in PAI-1 concentration following the use of lisinopril, an ACE inhibitor, may lead to an improvement in ovulatory function with better clinical pregnancy rates. The results support the hypothesis that letrozole induces PCOS in rats and that lisinopril modifies the action of letrozole, possibly by inhibition of the systemic and ovarian production of PAI-1.

A variety of hormonal

Bugra Coskun is currently an Assistant Professor at Yuksek Ihtisas University Medical School, Ankara, Turkey. He obtained his MD at EGE University, İzmir, and completed his residency and ART certification programme at the University of Health Sciences, Ankara. His research interests are reproductive endocrinology and fertility preservation in women.

Key Message

In the letrozole-induced PCOS rodent model, lisinopril, an angiotensin-converting enzyme inhibitor, modifies the effects of

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    Bugra Coskun is currently an Assistant Professor at Yuksek Ihtisas University Medical School, Ankara, Turkey. He obtained his MD at EGE University, İzmir, and completed his residency and ART certification programme at the University of Health Sciences, Ankara. His research interests are reproductive endocrinology and fertility preservation in women.

    Key Message

    In the letrozole-induced PCOS rodent model, lisinopril, an angiotensin-converting enzyme inhibitor, modifies the effects of letrozole treatment, possibly by inhibiting systemic and ovarian production of PAI-1. Thus, inhibition of the PAI-1 pathway, which participates in the pathogenesis of PCOS, deserves further investigation, particularly with selective PAI-1 inhibitors.

    These authors contributed equally to this work.

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