Androgens Explained: Biosynthesis, Metabolism, and Disease Relevance

Introduction

Figure 1. Overview of androgen biosynthesis, metabolism, and disease relevance.

What Are Androgens? Biological Functions Beyond Reproduction

Major Types of Androgen Hormones

Androgens are C19 steroid hormones synthesized from cholesterol through a series of enzymatic reactions occurring primarily in steroidogenic tissues, including the testes, adrenal glands, and ovaries. The major androgen-related molecules include testosterone, dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), and androstenedione.

Testosterone

Testosterone is the primary circulating androgen in humans and plays essential roles in:

• development of male reproductive tissues;
• maintenance of skeletal muscle and bone;
• regulation of metabolic processes;
• modulation of reproductive function.

In males, testosterone is primarily produced by Leydig cells in the testes under regulation from the hypothalamic-pituitary-gonadal (HPG) axis. In females, lower levels of testosterone are produced by ovarian and adrenal pathways and serve as precursors for estrogen biosynthesis and contributors to physiological androgen signaling. (Elzenaty et al., 2022)

Dihydrotestosterone (DHT)

DHT is generated from testosterone through the activity of steroid 5alpha-reductase enzymes, particularly SRD5A1 and SRD5A2. Compared with testosterone, DHT exhibits stronger affinity and transcriptional activity toward the androgen receptor (AR). DHT is particularly important in tissues such as the prostate, external genitalia, and hair follicles.

The conversion between testosterone and DHT represents a critical regulatory step controlling local androgen activity. Therefore, androgen action is strongly influenced by tissue-specific enzyme expression rather than systemic hormone levels alone.

DHEA and Androstenedione

Dehydroepiandrosterone (DHEA) and androstenedione are steroid precursors produced mainly in adrenal and gonadal tissues. Although DHEA itself has relatively weak androgenic activity, it serves as an important substrate for downstream androgen synthesis.

Recent studies have expanded the understanding of androgen biology by identifying adrenal-derived 11-oxygenated androgen pathways. These metabolites, including 11-ketotestosterone, exhibit biological activity comparable to classical androgens and contribute to androgen-related disorders such as PCOS and castration-resistant prostate cancer. (Storbeck & O'Reilly, 2023)

Androgen Receptor Signaling and Cellular Regulation

The primary mechanism of androgen action occurs through the androgen receptor (AR), a member of the nuclear receptor superfamily. After binding to androgen ligands, AR undergoes conformational changes, translocates into the nucleus, and regulates transcription of androgen-responsive genes.

AR signaling controls multiple biological processes, including:

• reproductive tissue development;
• muscle protein synthesis;
• bone remodeling;
• mitochondrial function;
• metabolic regulation.

Although classical androgen signaling involves genomic regulation through transcriptional control, increasing evidence indicates that AR can also participate in rapid non-genomic signaling pathways involving intracellular signaling molecules and membrane-associated processes. (Elzenaty et al., 2022; Ahmad & Newell-Fugate, 2022)

Figure 2. Androgen receptor signaling pathway.

Androgen Biosynthesis: From Cholesterol to Active Hormones

Androgen biosynthesis is a tightly regulated steroidogenic process that converts cholesterol into biologically active androgen hormones through a series of enzymatic reactions. This pathway occurs mainly in steroidogenic tissues, including testicular Leydig cells, adrenal cortical cells, and ovarian theca cells.

Although testosterone is often considered the major androgen hormone, androgen production involves a complex network of precursor molecules and metabolic intermediates. The balance between synthesis, conversion, and degradation determines androgen availability in different tissues. Recent advances in steroid metabolomics have further revealed that previously underappreciated androgen metabolites, including 11-oxygenated androgens, contribute significantly to human endocrine physiology. (Elzenaty et al., 2022; Storbeck & O'Reilly, 2023)

Figure 3. Steroidogenic pathway from cholesterol to active androgens.

The Classical Steroidogenic Pathway

The classical androgen biosynthesis pathway begins with cholesterol, which serves as the universal precursor for all steroid hormones. Cholesterol is transported into mitochondria by the steroidogenic acute regulatory protein (StAR), where the first and rate-limiting step of steroidogenesis occurs.

The major pathway can be summarized as:

Cholesterol → Pregnenolone → 17alpha-Hydroxypregnenolone → DHEA → Androstenedione → Testosterone → Dihydrotestosterone (DHT)

Each conversion step is controlled by specific steroidogenic enzymes.

CYP11A1: Initiation of Steroidogenesis

The first step of androgen synthesis is mediated by cytochrome P450 cholesterol side-chain cleavage enzyme (CYP11A1, also known as P450scc). CYP11A1 converts cholesterol into pregnenolone, initiating the production of steroid hormones.

Because CYP11A1 controls entry into the steroidogenic pathway, alterations in CYP11A1 activity can affect multiple hormone classes, including glucocorticoids, mineralocorticoids, and sex steroids.

CYP17A1: A Central Enzyme for Androgen Production

CYP17A1 performs two critical enzymatic activities:

17alpha-hydroxylase activity

converts pregnenolone and progesterone derivatives into hydroxylated intermediates.

17,20-lyase activity

generates androgen precursors including DHEA.

Through these activities, CYP17A1 represents a key regulatory point controlling androgen production.

The importance of CYP17A1 is particularly evident in prostate cancer, where increased intratumoral androgen synthesis can contribute to resistance against androgen deprivation therapy. Targeting CYP17A1 with inhibitors such as abiraterone has therefore become an important therapeutic strategy for advanced prostate cancer. (Zhang et al., 2022)

HSD3B and HSD17B: Testosterone Formation

Following DHEA production, additional enzymatic reactions generate androstenedione and testosterone.

3beta-Hydroxysteroid dehydrogenase (HSD3B) converts DHEA into androstenedione.

17beta-Hydroxysteroid dehydrogenases (HSD17B) regulate the reversible conversion between androstenedione and testosterone.

Different HSD17B isoforms show distinct tissue distributions and catalytic properties, allowing local regulation of androgen availability.

For example:

• HSD17B3: highly expressed in testicular Leydig cells, promotes testosterone synthesis
• HSD17B5: contributes to androgen production in peripheral tissues

This tissue-specific enzyme expression explains why androgen activity cannot always be predicted from circulating testosterone levels alone.

SRD5A: Conversion of Testosterone into DHT

Testosterone is converted into dihydrotestosterone (DHT) by steroid 5alpha-reductase enzymes:

• SRD5A1
• SRD5A2

DHT has a higher affinity for the androgen receptor compared with testosterone and produces stronger transcriptional activation.

SRD5A2-mediated DHT production is particularly important in:

• prostate development
• benign prostatic hyperplasia
• androgenetic alopecia

Pharmacological inhibition of 5alpha-reductase using finasteride or dutasteride reduces DHT production and is clinically used for prostate enlargement and hair loss treatment.

Alternative "Backdoor" Pathway of Androgen Biosynthesis

In addition to the classical pathway, androgen synthesis can occur through an alternative route known as the backdoor pathway.

Unlike the classical pathway, which produces testosterone as an intermediate, the backdoor pathway converts steroid precursors into DHT-related metabolites without requiring testosterone formation.

The pathway involves:

• 17alpha-hydroxyprogesterone
• 5alpha-reduced intermediates
• androstanediol
• DHT

This pathway was initially characterized in fetal development but is now recognized as relevant in several human diseases.

Emerging evidence suggests that alternative androgen pathways may contribute to:

• congenital adrenal hyperplasia
• PCOS
• castration-resistant prostate cancer

The discovery of these alternative pathways has expanded the understanding of androgen biology, demonstrating that androgen activity depends on a complex metabolic network rather than a single linear pathway. (Storbeck & O'Reilly, 2023)

Androgen Metabolism and Tissue-Specific Regulation

Androgen metabolism determines hormone availability, biological activity, and tissue-specific responses. After synthesis, androgens undergo enzymatic conversion, activation, and clearance processes that regulate their local and systemic effects.

Testosterone can be converted into the more potent androgen dihydrotestosterone (DHT) by steroid 5alpha-reductases (SRD5A1 and SRD5A2). This conversion is particularly important in tissues such as the prostate, skin, and reproductive organs, where local DHT production contributes to androgen receptor (AR)-mediated signaling. In addition, testosterone can be converted into estradiol through aromatase (CYP19A1), highlighting the interconnected regulation between androgen and estrogen pathways.

Androgen activity is also controlled through metabolic inactivation pathways, including sulfation and glucuronidation mediated by enzymes such as sulfotransferases (SULTs) and UDP-glucuronosyltransferases (UGTs). These reactions reduce steroid activity and facilitate hormone clearance.

Importantly, circulating androgen concentrations do not always reflect tissue-specific androgen activity. Local enzyme expression, sex hormone-binding globulin (SHBG) levels, androgen receptor abundance, and downstream signaling pathways collectively determine biological responses.

Recent studies have further expanded the understanding of androgen metabolism by identifying 11-oxygenated androgens, including 11-ketotestosterone, as biologically active metabolites involved in endocrine disorders such as polycystic ovary syndrome (PCOS) and adrenal-related androgen excess. (Storbeck & O'Reilly, 2023)

Comprehensive steroid metabolomics using LC-MS/MS provides a powerful approach to characterize diverse androgen metabolites and investigate complex hormone regulation networks.

Figure 4. Overview of androgen metabolic pathways showing activation, conversion, and inactivation routes.

Disease Relevance of Androgen Dysregulation

Disrupted androgen homeostasis contributes to multiple human diseases by affecting hormone signaling, metabolism, and tissue function.

Androgens in Prostate Cancer

Androgen receptor (AR) signaling plays a central role in prostate cancer development and progression. Many prostate tumors remain dependent on androgen signaling, making androgen deprivation therapy (ADT) a major treatment strategy. However, resistance can develop through mechanisms including increased AR expression, receptor alterations, and local androgen synthesis within tumor tissues. (Zhang et al., 2022)

Understanding changes in androgen metabolism is therefore important for identifying therapeutic resistance mechanisms and potential biomarkers.

Androgen Excess in Polycystic Ovary Syndrome

PCOS is one of the most common endocrine disorders affecting reproductive-age women and is characterized by hyperandrogenism, ovarian dysfunction, and metabolic abnormalities.

Elevated androgen production can contribute to impaired follicular development, insulin resistance, and altered metabolic profiles. Recent studies have highlighted the importance of both classical and adrenal-derived androgen pathways in PCOS pathophysiology. (Wang et al., 2023)

Aging, Metabolism, and Chronic Disease

Androgen levels gradually decline with aging and are associated with changes in muscle mass, bone health, and metabolic function. Reduced androgen signaling has been linked with sarcopenia, altered body composition, and increased risk of metabolic disorders.

Because androgen-related diseases involve complex interactions between hormones, metabolism, and gene regulation, integrated molecular approaches are increasingly valuable for understanding disease mechanisms.

Analytical Strategies for Studying Androgen Metabolism

Accurate characterization of androgen metabolism requires analytical approaches capable of detecting structurally similar steroid molecules at low concentrations. Traditional immunoassays have been widely used for hormone measurement; however, their accuracy can be affected by antibody cross-reactivity and limited metabolite coverage.

Mass spectrometry-based steroid hormone profiling has become an important analytical strategy for investigating androgen pathways due to its high sensitivity, specificity, and ability to simultaneously quantify multiple steroid metabolites.

LC-MS/MS-Based Steroid Hormone Profiling

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) combines chromatographic separation with highly selective mass detection, enabling accurate identification and quantification of steroid hormones.

Compared with conventional methods, LC-MS/MS provides several advantages:

• improved discrimination between structurally similar steroids;
• detection of low-abundance androgen metabolites;
• simultaneous analysis of multiple steroid pathways;
• reliable quantitative measurement.

Targeted steroid metabolomics using LC-MS/MS is particularly valuable for studying androgen-related disorders because it enables measurement of testosterone, DHT, DHEA, androstenedione, and emerging metabolites such as 11-oxygenated androgens.

Recent clinical studies have emphasized the importance of comprehensive steroid profiling because single hormone measurements may not fully capture alterations in androgen metabolism. (Heijboer & Hannema, 2023)

Multi-Omics Integration in Androgen Research

Androgen regulation involves interactions between steroid metabolism, gene expression, protein activity, and cellular signaling. Therefore, single-layer analysis may provide limited insight into the mechanisms underlying androgen-related diseases.

Multi-omics integration combines complementary molecular information from different biological levels:

For example, combining steroid metabolomics with transcriptomic analysis can reveal whether altered androgen levels result from changes in hormone synthesis enzymes, metabolic conversion pathways, or receptor-mediated responses.

In cancer research, multi-omics approaches can help characterize androgen receptor signaling networks and identify molecular mechanisms associated with treatment resistance. In endocrine disorders such as PCOS, integrated profiling can provide insights into the relationship between androgen excess, metabolic dysfunction, and inflammatory pathways.