BPH was a ubiquitous chronic progressive disease[7]. Aging and the presence of androgen are considered as essential links for the development of BPH, but the exact pathogenesis of BPH was still unclear[8, 9]. In recent years, the role of sex hormone level has been paid more and more attention to scholars. In particular, the synergy between estrogen and androgen played a prominent role in the pathogenesis of BPH. In vitro studies, King et al.[10] found that increasing the ratio of estrogen to androgen could promote the proliferation of prostate stromal cells and epithelial cells. Current research found that there was a balance mechanism between estrogen and androgen in the body. Maintaining a dynamic balance between estrogen and androgen levels contributes to the normal growth and development of the prostate and the maintenance of physiological functions, while breaking the original balance may be the cause of changes in prostate proliferation and apoptosis, leading to BPH[11].
Inflammation was an important defense response for the body to resist pathogen invasion and repair tissue damage. However, excessive or uncontrolled inflammatory response could also cause tissue damage, becoming the basic pathological mechanism for the occurrence and development of diseases. Inflammation also played a very central role in the development of various prostate diseases including BPH[12]. Compared with normal prostate, almost all prostate biopsy and surgical tissues had a large number of inflammatory factors infiltrated[13]. The IPSS, the prostate volume and the serum PSA were relatively higher in patients with more severe inflammation[14], and the degree of chronic inflammation was also inseparable from the clinical progress of BPH[15]. It has been suggested that elevated levels of lymphocyte-derived cytokines, such as IL-2, IL-4, and IFN-γ, could be found in the resected BPH tissues. These inflammatory factors seem to be involved in the stimulation of prostate fibromuscular growth[16]. In addition, BPH and chronic prostatitis could mutually induce, promote, and aggravate disease progression, and formed a vicious circle[17].
The interaction between androgens and inflammation played an important role in the pathogenesis of many tumors. In animal models, androgens could decrease the concentration of circulating pro-inflammatory factors and increase the levels of cytokines with anti-inflammatory effects[18]. Preclinical studies have shown that the inflammation and tissue structure reconstruction in the prostate of males with hypogonadism were more serious, but this phenomenon disappeard with the addition of androgen[19]. In addition, compared with people with normal gonadal function, patients with hypogonadism were five times more likely to have inflammation in the prostate gland, and the degree of inflammation was often more severe. Naslund et al.[20]found that oral estrogen significantly increased the degree of non-bacterial inflammation of the prostate in rats. Therefore, the academic community gradually realized that some inflammatory response genes in the body were regulated by sex hormones, but how the level of sex hormones in the body affects the expression of these inflammatory response genes was still poorly understood.
In this study, we used castration combined with different ratios of estrogen/ androgen to successfully induce the inflammatory response in SD rats. At the same time, the inflammatory response in the prostate tissue of each group of SD rats were systematically evaluated according to the international prostatitis histological diagnosis and grading standards. We found that only part of the glands showed a little inflammatory cell infiltration in the blank group. By contrast, the number of inflammatory cells in the glands of the castrated group relatively increased. However, according to the international prostatitis histological diagnosis and grading standards, the blank group and the castration group were scored 1 point in three aspects: the anatomical location of inflammatory cell infiltration, the tissue area of inflammatory cell infiltration and the density of typical inflammatory cells. After the rats were castrated, when the concentration of exogenous E was constant (E0.05 mg/kg), increased the concentration of exogenous DHT (0-0.15 mg/kg) of SD rats in each group. From the perspective of the anatomical location involved in inflammatory cells infiltration, the inflammation scores of rats in each group increased gradually as well. However, when the exogenous DHT concentration reached at 0.5 mg/kg, even if the DHT concentration increased again, the inflammation score did not increase further but decreased. In addition, judging from the tissue area affected by inflammatory cells infiltration and the density of typical inflammatory cells, After the rats were castrated, the source of androgen was blocked. When a constant dose of exogenous E was given to stimulate, and the exogenous DHT concentration increased gradually, we found that the inflammation score in each group of rats increased gradually with the increase of DHT concentration. Therefore, we believed that when SD rats were given a certain dose of exogenous E concentration stimulation after castration, and increased gradually the exogenous DHT concentration. When DHT was within a certain concentration range, whether it was viewed from the anatomical location of inflammatory cells infiltration, tissue areas affected by inflammatory cells infiltration and typical inflammatory cells density, which could induce the inflammation response in SD rats. However, judging from the performance of the E0.05 + DHT0.5 group and the E0.05 + DHT1.5 group in the anatomical locations involved in inflammatory cell infiltration, there may be an inflection point between the ratio of estrogen/ androgen and the inflammation of the prostate. After crossing this inflection point, the inflammation of the prostate did not deepen even if the concentration of exogenous androgen increased again. Of course, it needs to be confirmed by more systematic and comprehensive experiments in vivo and vitro.
In our clinical work, we have found that BPH usually occured in middle-aged and elderly patients whose androgen levels have been reduced and estrogen levels were relatively high, while rarely occured in young patients with high androgen levels and relatively low estrogen levels. In addition, according to the epidemiological survey data, the incidence of chronic prostatitis was higher in people aged 40–49 and over 60 years old[21, 22, 23, 24]. Therefore, we found that both BPH and chronic prostatitis were prone to occur in middle-aged and elderly patients whose androgen levels have decreased and estrogen levels were relatively increased. Seethalakshmi et al.[25] induced chronic non-bacterial prostatitis in rats by using 17- -estradiol and found that the pathological manifestations of estradiol-induced non-bacterial prostatitis in rats were similar to those of clinical chronic non-bacterial prostatitis. In addition, Kwon et al.[26]successfully induced chronic non-bacterial prostatitis by giving oral soy isoflavones to SD rats, which confirmed that oral estrogen could also cause prostatitis, and further proved that the significance of hormone level changes in the occurrence of prostatitis. However, for middle-aged and elderly patients with low androgen levels, the effects of changes in different levels of estrogen/ androgen on BPH and prostate inflammation were still unclear. In this study, we supplemented the castrated rats with a constant concentration of exogenous DHT(0.15 mg/kg) lower than the physiological dose, and used the different concentrations of exogenous E to stimulate SD rats. Establishing a rat model in which androgen levels were relatively low and estrogen was sequentially increased (that was also in line with the performance of hormone levels in middle-aged and elderly men). We found that when the concentration of exogenous DHT was constant and the concentration of exogenous E increased gradually. SD rats in each groups either from the perspective of the anatomical location of inflammatory cells infiltration involvement ratings, or from the perspective of the regional scale of inflammatory cells infiltration involvement. With the increase of exogenous E concentration, and the inflammatory score in each group showed a gradual increase trend. To a certain extent, the results of this study also reflected from the perspective of animal experiments why BPH and chronic prostatitis rarely occured in young patients with high androgen levels and relatively low estrogen levels. However, it usually occured in middle-aged and elderly patients with relatively low androgen levels and relatively high estrogen levels.
In addition, we used immunohistochemistry to detect the expression of TGF-β1, IL-6, and IL-8 in the prostate tissue of SD rats in each group. After quantitative analysis, we found that: Compared with the blank group, the positive rate of TGF-β1, IL-6, and IL-8 in the prostate tissue of SD rats increased after castration, which indicated that castration or decreased androgen levels could induce the inflammation response of the prostate tissue in SD rats and the expression of TGF-β1, IL-6 and IL-8 could increase to a certain extent. In addition, after the rats are castrated, when the exogenous E concentration was constant, the positive rates of TGF-β1 and IL-8 in the E0.05 + DHT0.015 group, the E0.05 + DHT0.05 group, the E0.05 + DHT0.15 group and the E0.05 + DHT0.5 group all increased with the increase of exogenous DHT concentration to a certain extent. However, when the concentration of exogenous DHT exceeded 0.5 mg/kg, even if the concentration of exogenous DHT increased again, the positive rates of TGF-β1 and IL-8 in the E0.05 + DHT1.5 group did not increase again with the increase of exogenous DHT. While the positive rates of TGF-β1 and IL-8 in the E0.05 + DHT1.5 group decreased to a certain extent compared with the E0.05 + DHT0.5 group. In addition, when the concentration of exogenous DHT was constant, the concentration of exogenous E increased gradually. The positive rates of TGF-β1, IL-6, and IL-8 in each group of SD rats increased to a certain extent with the concentration of exogenous E. Therefore, we believed that TGF-β1, IL-6, and IL-8 were involved in the regulation of prostate inflammation in SD rats, and their positive rate expression varied with the change in the levels of estrogen and androgen in SD rats, and the positive rates expression of TGF-β1, IL-6 and IL-8 could reflect the inflammation in the prostate tissues of SD rats to a certain extent.