Inhibition of the androgen-activating enzyme AKR1C3 selectively decreases systemic and intra-adipose 11-oxygenated androgens in women

This study demonstrates that inhibiting the enzyme AKR1C3 selectively reduces the activation of 11-oxygenated androgens, but not classic androgens, in both systemic circulation and adipose tissue of women, offering a targeted therapeutic strategy for androgen excess conditions like PCOS.

The Gist

The Big Picture: A New Kind of "Androgen" Problem

Imagine your body is a bustling city. In this city, there are "messengers" called androgens (hormones like testosterone) that tell your body how to function. For a long time, doctors thought there was only one main type of messenger: the "Classic" androgen (Testosterone).

However, scientists recently discovered a second, hidden group of messengers called 11-oxygenated androgens. These are just as powerful as the classic ones, but they have been hiding in plain sight.

This paper focuses on a condition called PCOS (Polycystic Ovary Syndrome), which affects about 1 in 7 women. In PCOS, the city gets flooded with too many of these messengers, causing problems like weight gain, trouble with blood sugar, and reproductive issues.

The Culprit: The "Factory Worker" (AKR1C3)

The paper identifies a specific enzyme (a biological machine) called AKR1C3 as the main culprit.

• The Analogy: Think of AKR1C3 as a factory worker in a warehouse called Adipose Tissue (your body fat).
• The Job: This worker takes raw materials (inactive hormone precursors) and assembles them into finished, active products (the messengers).
• The Twist: This worker has two assembly lines:
  1. Line A (Classic): Makes the "Classic" messengers (Testosterone).
  2. Line B (11-Oxygenated): Makes the "New" messengers (11-Ketotestosterone).

The Discovery: The Worker Loves Line B

The researchers found something surprising about this factory worker:

1. Location: The worker is most active in fat cells, especially in women and in people with obesity.
2. Preference: While the worker can do both jobs, they strongly prefer Line B. In fact, in women's fat tissue, this worker produces 10 times more of the "New" messengers than the "Classic" ones.

Why does this matter?
Because for years, doctors have been trying to fix PCOS by trying to stop the production of the "Classic" messengers. But this paper says, "Wait a minute! You're ignoring the main problem!" The real flood of messengers in women's fat tissue is coming from Line B, not Line A.

The Solution: A "Selective Brake"

The researchers tested a new drug (an inhibitor) designed to put a brake on this factory worker (AKR1C3).

• The Experiment: They took human fat tissue and added the brake.
• The Result: The brake worked perfectly, but with a special twist. It slowed down Line B (the New messengers) almost completely, but it barely touched Line A (the Classic messengers).
• The Real-World Test: They gave this drug to women in a clinical trial. The results matched the lab: their levels of the "New" messengers dropped significantly, while their "Classic" testosterone levels stayed mostly the same.

The "Vicious Circle" of Fat and Hormones

The paper explains a nasty cycle that happens in women with PCOS and obesity:

1. High insulin (from eating or insulin resistance) tells the fat cells to build more of this factory worker (AKR1C3).
2. More workers mean more active messengers are made in the fat.
3. These messengers make the fat cells store even more fat and become resistant to insulin.
4. This leads to even higher insulin, which creates even more workers.

The Breakthrough: By using this new drug to stop the factory worker, you break the cycle. You stop the fat from making the messengers that are causing the metabolic trouble.

The Takeaway

This paper is like finding a leak in a boat. For years, everyone was trying to bail water out of the front of the boat (blocking Testosterone), but the real hole was in the back (blocking the 11-oxygenated androgens).

By using a targeted tool to plug the back hole, the researchers found a way to:

1. Drastically reduce the specific hormones causing trouble in women's fat tissue.
2. Avoid messing up the body's natural testosterone levels (which are needed for bone health and muscle).
3. Offer a new, more precise treatment for PCOS and the metabolic problems that come with it.

In short: We found the specific machine making the wrong hormones in women's fat, and we found a way to turn that machine off without turning off the whole factory.

Technical Summary

1. Problem Statement

• Clinical Context: Polycystic Ovary Syndrome (PCOS) affects 10–15% of women globally and is characterized by androgen excess, which drives metabolic complications such as insulin resistance, dysglycemia, and metabolic dysfunction-associated steatotic liver disease (MASLD).
• Therapeutic Gap: There are currently no pharmacological therapies specifically approved to treat androgen excess-induced metabolic dysfunction in women with PCOS.
• Scientific Knowledge Gap: While the "classic" androgen pathway (converting androstenedione to testosterone) is well-studied, a recently identified "11-oxygenated" androgen pathway (converting 11β-hydroxyandrostenedione to 11-ketotestosterone) has been shown to be elevated in PCOS and post-menopausal women. Both pathways are activated by the enzyme Aldo-keto reductase 1C3 (AKR1C3). It was unclear whether inhibiting AKR1C3 would selectively target the 11-oxygenated pathway or broadly suppress all androgens, and whether adipose tissue acts as a primary site for this activation in women.

2. Methodology

The study employed a comprehensive translational approach combining in silico, in vitro, ex vivo, and in vivo models:

• Gene Expression Analysis:
  • Analyzed bulk RNA-Seq data from the GTEx Project to assess AKR1C3 and HSD11B1 expression across tissues, sexes, and BMI.
  • Utilized single-nucleus RNA-Seq (snRNA-Seq) from adipose tissue biopsies (obese vs. lean, male vs. female) to identify specific cell types expressing these enzymes.
• Ex Vivo Tissue Incubations:
  • Used human subcutaneous and visceral adipose tissue explants from women undergoing elective surgery (bariatric and gynecological).
  • Incubated tissues with precursors: Androstenedione (A4) (classic pathway) and 11-ketoandrostenedione (11KA4) (11-oxygenated pathway).
  • Tested the effect of the selective AKR1C3 inhibitor BAY2299242 (BAY2) on androgen conversion.
  • Control: Compared results with SGBS adipocytes (a common in vitro model) to validate the model's relevance.
• In Vitro Assays:
  • HEK293T cells transfected with AKR1C3 to determine IC50 values for BAY2.
  • Luciferase reporter assays to measure Androgen Receptor (AR) transactivation.
• In Vivo Clinical Trial (Phase 2a):
  • Analyzed serum samples from a randomized, placebo-controlled trial (AKRENDO) involving 21 premenopausal women.
  • Participants received either BAY1128688 (BAY1) (60 mg twice daily) or placebo for 12 weeks.
  • Comprehensive serum androgen profiling was performed using LC-MS/MS at baseline, during treatment, and post-treatment.
• Computational Modeling:
  • Fitted a validated kinetic model of peripheral steroid metabolism to ex vivo and clinical data to predict enzyme activity levels and simulate the effects of varying degrees of AKR1C3 inhibition in women with PCOS.

3. Key Contributions & Results

A. Adipose Tissue as a Major Site of Androgen Activation

• Expression: Adipocytes are the primary cell type expressing AKR1C3 and the Androgen Receptor (AR) in adipose tissue.
• Sex and Obesity Differences: AKR1C3 expression is significantly higher in women than men (specifically in subcutaneous fat) and is positively correlated with BMI in women. Expression is also higher in individuals with obesity compared to lean individuals.
• Enzyme Co-expression: The enzyme HSD11B1 (which inactivates 11-oxygenated androgens but activates classic androgens) is also expressed in adipocytes but at lower levels than AKR1C3.

B. Preferential Activation of 11-Oxygenated Androgens

• Ex Vivo Findings: In human female adipose tissue explants, the conversion of 11KA4 to active 11-ketotestosterone (11KT) and 11β-hydroxytestosterone (11OHT) was >10-fold higher than the conversion of A4 to Testosterone (T).
• Model Limitation: SGBS adipocytes showed the opposite pattern (preferring classic androgen activation), indicating they are not a suitable model for studying human female adipose androgen metabolism.

C. Selective Inhibition by AKR1C3 Blockers

• Ex Vivo: Treatment with BAY2 caused a major decrease in the generation of 11-oxygenated androgens (11KT, 11OHT) but only a minor reduction in Testosterone generation.
• In Vivo (Clinical Trial): In premenopausal women treated with BAY1 for 12 weeks:
  • 11-oxygenated androgens (11KT, 11OHT): Showed a significant and sustained decrease.
  • Testosterone (T): Showed only a very minor decrease.
  • Precursors: Levels of 11OHA4 and 11KA4 remained unchanged, confirming the blockage occurs at the activation step (AKR1C3), not production.
  • Compensatory Mechanism: A progressive increase in 5α-reduced steroids (including DHT) was observed over 12 weeks, suggesting a counter-regulatory upregulation of 5α-reductase activity in response to androgen suppression, which returned to baseline after treatment cessation.

D. Computational Modeling in PCOS

• Increased Activity: The model predicted that systemic AKR1C3 activity is 2.6-fold higher in women with PCOS compared to healthy controls.
• Therapeutic Prediction: Simulations indicated that inhibiting AKR1C3 could reduce 11KT levels in PCOS patients to the median of healthy women with only ~24% residual enzyme activity. Conversely, even full inhibition would not reduce Testosterone levels in PCOS to the median of healthy controls, highlighting the pathway's specificity.

4. Significance and Implications

• Novel Therapeutic Strategy: The study identifies AKR1C3 inhibition as a precision medicine approach to treat androgen excess in women. Unlike current therapies (e.g., anti-androgens) that broadly block receptors, AKR1C3 inhibitors selectively target the 11-oxygenated androgen pathway, which is the dominant androgen source in adipose tissue and is disproportionately elevated in PCOS and post-menopause.
• Metabolic Relevance: Since adipose tissue is a key driver of the "vicious circle" linking androgen activation to insulin resistance and lipotoxicity, selectively reducing intra-adipose 11-oxygenated androgens offers a potential mechanism to ameliorate the metabolic dysfunction associated with PCOS, not just the reproductive symptoms.
• Biomarker Shift: The findings suggest that clinical assessment of androgen excess in women should move beyond measuring Testosterone alone to include 11-oxygenated androgens, as a significant subset of women may have "normal" testosterone but elevated 11KT driving their pathology.
• Safety Profile: The selective nature of the inhibition (sparing classic testosterone significantly) may offer a better safety profile regarding bone health and other testosterone-dependent functions compared to broad androgen suppression.

Conclusion: This paper provides robust evidence that adipose tissue is a major site of 11-oxygenated androgen activation in women, driven by AKR1C3. Pharmacological inhibition of AKR1C3 selectively disrupts this pathway, offering a promising new therapeutic avenue for managing the metabolic and reproductive complications of PCOS.