Radiation-induced erectile dysfunction: Recent advances and future directions

Abstract

Prostate cancer is one of the most prevalent cancers and the second leading cause of cancer-related deaths in men in the United States. A large number of patients undergo radiation therapy (RT) as a standard care of treatment; however, RT causes erectile dysfunction (radiation-induced erectile dysfunction; RiED) because of late side effects after RT that significantly affects quality of life of prostate cancer patients. Within 5 years of RT, approximately 50% of patients could develop RiED. Based on the past and current research findings and number of publications from our group, the precise mechanism of RiED is under exploration in detail. Recent investigations have shown prostate RT induces significant morphologic arterial damage with aberrant alterations in internal pudendal arterial tone. Prostatic RT also reduces motor function in the cavernous nerve which may attribute to axonal degeneration may contributing to RiED. Furthermore, the advances in radiogenomics such as radiation induced somatic mutation identification, copy number variation and genome-wide association studies has significantly facilitated identification of biomarkers that could be used to monitoring radiation-induced late toxicity and damage to the nerves; thus, genomic- and proteomic-based biomarkers could greatly improve treatment and minimize arterial tissue and nerve damage. Further, advanced technologies such as proton beam therapy that precisely target tumor and significantly reduce off-target damage to vital organs and healthy tissues. In this review, we summarize recent advances in RiED research and novel treatment modalities for RiED. We also discuss the possible molecular mechanism involved in the development of RiED in prostate cancer patients. Further, we discuss various readily available methods as well as novel strategies such as stem cell therapies, shockwave therapy, nerve grafting with tissue engineering, and nutritional supplementations might be used to mitigate or cure sexual dysfunction following radiation treatment.

Figure 1

Probable mechanisms of radiation-induced erectile dysfunction. (A) Neuronal damage: there is inflammation and neuronal nitric oxid synthase (nNOS) reduction resulting from radiation therapy (RT) in cavernous nerve. Late RT-mediated effects on cavernous nerve can lead to erectile dysfunction after 3-5 years. (B) Vascular damage: fibrotic changes in blood vessels resulting from RT resulting in less blood flow in the erection chamber. (C) Smooth muscle atrophy: the corpus cavernosa undergoes atrophy similar to other muscles when they go unused.

Figure 2

Probable molecular mechanisms of radiation-induced erectile dysfunction. Radiation therapy causes increase in reactive oxygen species, leading to inflammation leading to tissue toxicities. CN, cavernous nerve; mTOR, mechanistic target of rapamycin; NFK, nuclear factor kappa; ROS, reactive oxygen; TGF, transforming growth factor.