We have reported that the complement system activation, a major component of the innate immune system, including classical complement pathway was involved in the growth of benign prostatic hyperplasia (BPH) by using model rats and human BPH tissues. However, the mechanism from complement system activation to the growth process of BPH remained unclear. On the other hand, it has recently been noted that inflammasome, the protein complex which works as an inflammation amplification system, was associated with complement activation thorough C5a activation. Furthermore, resveratrol, a natural polyphenolic agent, was reported to exert a protective effect in acute lung injury by suppressing the NLR family pyrin domain containing 3 (NLRP3) inflammasome signaling. Therefore, we analyzed the expression and function of NLRP3 inflammasome including related molecules for inflammasome using BPH model rats and the antiproliferative effect by resveratrol to elucidate the mechanism of BPH growth.

BPH model rats, which resembles human BPH tissues pathologically, were used in this study. The urogenital sinus (UGS) isolated from the 20-day-old male rat embryos was implanted under the right ventral prostate of 7-week-old male rats. After the host rats had been sacrificed at 2, 3, or 8 weeks after UGS implantation, the right ventral prostate was used as BPH tissue, and the left ventral prostate tissue was used as a control. Expression and function analysis of C5a, NLRP3, Caspase-1, IL-1β, IL-18 by qRT-PCR, western blotting analysis, and immunohistochemical (IHC) analysis using pathological BPH model rat tissues at 2, 3, and 8 weeks (n=6, respectively) after fetal UGS implantation was performed. Serum IL-1β levels were also measured by ELISA to evaluate inflammasome activation. Furthermore, the NLRP3 pathway inhibitor, resveratrol (50 mg/kg), was administered to BPH model rats to evaluate the antiproliferative effect. The expression and function analysis of C5a, NLRP3, Caspase-1, IL-1β, IL-18 was performed by using BPH model rat with or without resveratrol. Proliferative effect of BPH tissues was evaluated by the expression of Ki-67 proteins.

Gene and protein expression levels of C5a, NLRP3, Caspase-1, IL-1β, and IL-18 was significantly up-regulated in BPH tissues compared to normal prostate tissues respectively, and showed an increase time-dependently (p<0.05). BPH model rats had significantly increased serum IL-1β levels compared to intact rats (987.6 pg/mL vs. 1501.1 pg/mL; p<0.05), and showed an increase time-dependently. In IHC analysis, significant deposition of NLRP3 was observed abundantly in stromal area. Resveratrol administration significantly decreased the prostate weight of BPH tissues and the expression of NLRP3, Caspase-1, IL-1β, and IL-18 (p <0.05). The expression of Ki-67 in BPH tissues with resveratrol showed a significant decrease compared to the BPH tissues without resveratrol (p <0.05).

In this study, the association between NLRP3 inflammasome system and the growth process of BPH was analyzed by using stromal-dominant BPH model rat. The expression and function analysis of C5a, NLRP3, Caspase-1, IL-1β, and IL-18 indicated that the pathway of NLRP3 inflammasome by C5a was activated in the growth process of BPH. In addition, this activation of inflammasome was located in the stromal area of BPH, describing that NLRP3 inflammasome system had an important role for the proliferation of BPH stromal area. The expression and function analysis by resveratrol administration showed that the expression of the molecules at downstream from NLRP3 inflammasome was significantly decreased in BPH tissues with resveratrol compared to without resveratrol. These results suggested that resveratrol effectively suppressed the NLRP3 inflammasome activation during the BPH growth process in model rats. Furthermore, resveratrol significantly suppressed the BPH proliferation and reduced prostate weight.

The activation of NLRP3 inflammasome by complement component C5a promotes IL-1β and IL-18 production via Caspase-1 and amplifies inflammation during the growth process of BPH. In addition, the inhibition of NLRP3 inflammasome decreased inflammasome activation, and induced reduction of prostate volume. Our results suggested that inflammasome might be a therapeutic target during the growth process of BPH.

Hata J, Matsuoka K, Kojima Y, et al. Complement activation by autoantigen recognition in the growth process of benign prostatic hyperplasia. Sci Rep. 2019; 9: 20357.