植化素調節類固醇生成機制之探討

Abstract

動物透過內分泌系統以調控許多生理機制，睪丸內的萊吉氏細胞（Leydig cells）、卵巢內的粒性細胞（granulosa cell）、黃體細胞（luteal cell）以及腎上腺皮質細胞（adrenal cortical cell）透過類固醇生成（steroidogenesis）合成許多類固醇內泌素以調控生理功能。這些細胞主要受到內泌素分子調控其功能，然而處理特定蛋白質、藥物或是來自植物中的植化素（phytochemicals）亦可以調控類固醇生成細胞，因此本研究的目的在探討特定情況下類固醇生成會如何受到調控。 雄性素為前列腺癌細胞生長所必需，因此抑制體內雄性素濃度為治療前列腺癌的第一要務。文獻指出薑黃所萃取的薑黃素（curcumin）具有抑制腫瘤細胞生長並促進凋亡的功效，本研究則發現薑黃素亦有抑制萊吉氏細胞合成睪固酮的功效。此現象與細胞內促進Star表現的轉錄因子之mRNA表現量受到薑黃素抑制有關，證實了薑黃素可抑制睪固酮合成，因此在治療前列腺癌更有優勢。 代謝症候群（metabolic syndrome）已成為廣受討論的健康議題並且與代謝性症狀包括高血壓、高血脂以及糖尿病息息相關。糖尿病在男性糖尿病患者中造成的併發症包括勃起障礙（erectile dysfunction, ED），其成因除了神經與心血管性之外，亦有研究認為高血糖會對睪丸產生氧化壓力（oxidative stress）而使其所合成的睪固酮濃度低下而使得血管內皮細胞無法合成足夠的一氧化氮（nitric oxide）以維持血管舒張以及勃起反應。本研究以模擬糖尿病的動物模式，證實高血糖或胰島素阻抗的情況下，確實會透過增加睪丸內氧化壓力，並抑制類固醇生成基因表現以及睪固酮合成，給予槲黃素（quercetin）處理可以有效改善因胰島素阻抗所造成的睪固酮濃度低下；肥胖亦為代謝症候群中常見的症狀之一，肥胖時體內上升的瘦體素（leptin）已被證實能抑制腎上腺對ACTH刺激的反應而抑制其醣類皮質素的分泌。在高脂飼糧誘發肥胖小鼠模式中，我們證實了體內瘦體素濃度較高的小鼠對於ACTH的反應較差，處理槲黃素後則可改善。根據相關文獻我們推論，槲黃素可以影響瘦體素下游訊息傳遞路徑，並增加腎上腺細胞內cAMP濃度，以維持其類固醇生成功能，然確切的證據仍需細胞學的研究加以證實。 類固醇內泌素中多數為性內泌素，因此類固醇生成的調控在生殖生理中至為重要。有文獻指出懷孕母畜攝食松葉會造成流產，肇因於松葉中的異柏油酸（isocupressic acid）具有抑制孕酮分泌的功能。小鼠萊吉氏細胞株MA-10的研究成果顯示，處理異柏油酸會抑制蛋白激酶A的磷酸化，並抑制Star與Cyp11a1的表現最後抑制類固醇生成。最後，近年來對於kisspeptin在生殖生理方面的研究都集中在其對於腦部的功能，本研究的最後一部分則探討其是否具有直接調控睪丸類固醇生成的功能。結果發現kisspeptin並不會直接調控初代萊吉氏細胞的睪固酮分泌能力，但後續實驗則暗示了kisspeptin可能參與調控睪丸的發育過程。 綜上所述，除了現今已知的內泌素分子之外，植化素亦有調控類固醇生成的能力。這些研究的成果提供了新藥開發可參考的未來方向可透過影響類固醇內泌素的合成以調控正常生理。

Animals use endocrine system to regulate physiological mechanisms. Leydig cell, granulosa cell, luteum cell and adrenal cortical cell producing steroid hormones controlled by endrocrine system through steroidogenesis. However, specific peptides, chemicals and phytochemicals extract from plants are found can regulate steroidogenesis. The purpose of this study is to clearify the mechanism of how steroidogenesis be effected under specific condition. Androgen is necessary for prostate cancer growth so decreasing androgen level is important in prostate cancer treatment. Curcumin was found inhibiting proliferation and metastasis of prostate cancer cell lines. Here we found that curcumin inhibits testosterone production in Leydig cell via suppressing expression of sterodiogenic genes. These results provide more evidences on curcumin as an effective drug for the treatment of prostate cancer. Metabolic syndrome is closely links to many symptoms including hypertension, hypercholesterolemia and diabetes. Erectile dysfunction is one symptoms of diabetes. With diabetic mice models, we comfirmed that hyperglycemia induced oxidative stress decrease testosterone level through suppressing steroidogenic genes expressionn in testis. Support quercetin as antioxidant restores testosterone production under insulin resistance. The other hand, leptin elevated in obese individual suppresses adrenal response to ACTH stimulation also glucocorticoid secretion. In this study, we confirm high leptin level in high-fat diet-induced obese mice cause poor adrenal response to ACTH while quercetin restores adrenal response. We hypothesize that quercetin interfere JAK2-PI3K pathway to restore adrenal steroidogenesis suppressed by leptin, more evidences are need to prove this hypothesis. Consumption of ponderosa pine needles causes late-term abortions in cattle and isocupressic acid (IA) responsible for the effect. With murine Leydig cell MA-10, we found that IA does not affect enzyme activities of steroidogenic genes but inhibits their expression through attenuating cAMP-PKA signaling. Thus, steroid production was suppressed. Since testes are essential for male reproduction and recent studies show that Kiss1 and Kiss1r are expressed in testes. To investigate their function in testes, primary mice Leydig cell was used in this study. Our results showed that Kiss1 did not affect testosterone production in primary Leydig cells, but suggest that expression pattern of KISS1 follows the stages of testicular development. Future studies are need to determine if kisspeptin regulates testicular development during puberty. In general, steroidogenesis is important to physiological regulation, this report demonstrate that some phytochemicals can effect steroids production directly, these results provide new direction on new food additives development and new drog discovery.