Emerging Neuroendocrine Involvement Driving Research in PCOS

Tara Haelle

September 06, 2022

Polycystic ovary syndrome (PCOS) affects an estimated 8%-13% of women, and yet "it has been quite a black box for many years," as Margo Hudson, MD, an assistant professor of endocrinology, diabetes, and hypertension at Harvard Medical School, Boston, puts it. That black box encompasses not only uncertainty about the etiology and pathophysiology of the condition but even what constitutes a diagnosis.

Even the international guidelines on PCOS management endorsed by the American Society for Reproductive Medicine – a document developed over 15 months with the input of 37 medical organizations covering 71 countries – notes that PCOS diagnosis is "controversial and assessment and management are inconsistent." The result, the guidelines note, is that "the needs of women with PCOS are not being adequately met."

One of the earliest diagnostic criteria, defined in 1990 by the National Institutes of Health, required only hyperandrogenism and irregular menstruation. Then the 2003 Rotterdam Criteria added presence of polycystic ovaries on ultrasound as a third criterion. Then the Androgen Excess Society determined that PCOS required presence of hyperandrogenism with either polycystic ovaries or oligo/amenorrhea anovulation. Yet the Endocrine Society notes that excess androgen levels are seen in 60%-80% of those with PCOS, suggesting it's not an essential requirement for diagnosis, leaving most to diagnose it in people who have two of the three key criteria. The only real agreement on diagnosis is the need to eliminate other potential diagnoses first, making PCOS always a diagnosis of exclusion.

Further, though PCOS is known as the leading cause of infertility in women, it is more than a reproductive condition, with metabolic and psychological features as well. Then there is the range of comorbidities, none of which occur in all patients with PCOS but all of which occur in a majority and which are themselves interrelated. Insulin resistance is a common feature, occurring in 50%-70% of people with PCOS. Accordingly, metabolic syndrome occurs in at least a third of people with PCOS and type 2 diabetes prevalence is higher in those with PCOS as well.

Obesity occurs in an estimated 80% of women with PCOS in the United States, though it affects only about 50% of women with PCOS outside the United States, and those with PCOS have an increased risk of hypertension. Mood disorders, particularly anxiety and depression but also, to a lesser extent, bipolar disorder and obsessive-compulsive disorder, are more likely in people with PCOS. And given that these comorbidities are all cardiovascular risk factors, it's unsurprising that recent studies are finding those with PCOS to be at greater risk for cardiometabolic disease and major cardiovascular events.

"The reality is that PCOS is a heterogenous entity. It's not one thing – it's a syndrome," Lubna Pal, MBBS, a professor of ob.gyn. and director of the PCOS Program at Yale University, New Haven, Conn., said in an interview. A whole host of factors are likely playing a role in the causes of PCOS, and those factors interact differently within different people. "We're looking at things like lipid metabolism, fetal origins, the gut microbiome, genetics, epigenetics, and then dietary and environmental factors," Nichole Tyson, MD, division chief of pediatric and adolescent gynecology and a clinical associate professor at Stanford (Calif.) Medicine Children's Health, said in an interview. And most studies have identified associations that may or may not be causal. Take, for example, endocrine disruptors. BPA levels have been shown to be higher in women with PCOS than women without, but that correlation may or may not be related to the etiology of the condition.

The Hypothalamic-Pituitary-Adrenal Axis

In trying to understand the pathophysiology of the condition, much of the latest research has zeroed in on potential mechanisms in the hypothalamic-pituitary-adrenal axis. "A consistent feature of PCOS is disordered gonadotropin secretion with elevated mean LH [luteinizing hormone], low or low normal FSH [follicle-stimulating hormone], and a persistently rapid frequency of GnRH [gonadotropin-releasing hormone] pulse secretion," wrote authors of a scientific statement on aspects of PCOS.

"I think the balance is heading more to central neurologic control of the reproductive system and that disturbances there impact the GnRH cells in the hypothalamus, which then go on to give us the findings that we can measure peripherally with the LH-FSH ratio," Hudson said in an interview.

The increased LH levels are thought to be a major driver of increased androgen levels. Current thinking suggests that the primary driver of increased LH is GnRH pulsatility, supported not only by human studies but by animal models as well. This leads to the question of what drives GnRH dysregulation. One hypothesis posits that GABA neurons play a role here, given findings that GABA levels in cerebrospinal fluid were higher in women with PCOS than those with normal ovulation.

But the culprit garnering the most attention is kisspeptin, a protein encoded by the KISS1 gene that stimulates GnRH neurons and has been linked to regulation of LH and FSH secretion. Kisspeptin, along with neurokinin B and dynorphin, is part of the triumvirate that comprises KNDy neurons, also recently implicated in menopausal vasomotor symptoms. Multiple systematic reviewsand meta-analyses have found a correlation between higher kisspeptin levels in the blood and higher circulating LH levels, regardless of body mass index. While kisspeptin is expressed in several tissues, including liver, pancreas, gonad, and adipose, it's neural kisspeptin signaling that appears most likely to play a role in activating GnRH hormones and disrupting normal function of the hypothalamic-pituitary-adrenal axis.

But as noted, in at least one systematic review of kisspeptin and PCOS, "findings from animal studies suggest that kisspeptin levels are not increased in all subtypes of PCOS." And another review found "altered" levels of kisspeptin levels in non-PCOS patients who had obesity, potentially raising questions about any associations between kisspeptin and obesity or insulin resistance.

Remaining Chicken-and-Egg Questions

A hallmark of PCOS has long been, and continues to be, the string of chicken-or-egg questions that plague understanding of it. One of these is how depression and anxiety fit into the etiology of PCOS. Exploring the role of specific neurons that may overstimulate GnRH pulsatility may hold clues to a common underlying mechanism for the involvement of depression and anxiety in patients with PCOS, Hudson speculated. While previous assumptions often attributed depression and anxiety in PCOS to the symptoms – such as thin scalp hair and increased facial hair, excess weight, acne, and irregular periods – Hudson pointed out that women can address many of these symptoms with laser hair removal, weight loss, acne treatment, and similar interventions, yet they still have a lot of underlying mental health issues.

It's also unclear whether metabolic factors so common with PCOS, particularly insulin resistance and obesity, are a result of the condition or are contributors to it. Is insulin resistance contributing to dysregulation in the neurons that interferes with normal functioning of the hypothalamic-pituitary-adrenal axis? Is abnormal functioning along this axis contributing to insulin resistance? Or neither? Or both? Or does it depend? The authors of one paper wrote that "insulin may play both direct and indirect roles in the pathogenesis of androgen excess in PCOS," since insulin can "stimulate ovarian androgen production" and "enhance ovarian growth and follicular cyst formation in rats."

Pal noted that "obesity itself can evolve into a PCOS-like picture," raising questions about whether obesity or insulin resistance might be part of the causal pathway to PCOS, or whether either can trigger its development in those genetically predisposed.

"Obesity does appear to exacerbate many aspects of the PCOS phenotype, particularly those risk factors related to metabolic syndrome," wrote the authors of a scientific statement on aspects of PCOS, but they add that "it is currently debated whether obesity per se can cause PCOS." While massive weight loss in those with PCOS and obesity has improved multiple reproductive and metabolic issues, it hasn't resolved all of them, they write.

Hudson said she expects there's "some degree of appetite dysregulation and metabolic dysregulation" that contributes, but then there are other women who don't have much of an appetite or overeat and still struggle with their weight. Evidence has also found insulin resistance in women of normal weight with PCOS. "There may be some kind of metabolic dysregulation that they have at some level, and others are clearly bothered by overeating," Hudson said.

Similarly, it's not clear whether the recent discovery of increased cardiovascular risks in people with PCOS is a result of the comorbidities so common with PCOS, such as obesity, or whether an underlying mechanism links the cardiovascular risk and the dysregulation of hormones. Pal would argue that, again, it's probably both, depending on the patient.

Then there is the key feature of hyperandrogenemia. "An outstanding debate is whether the elevated androgens in PCOS women are merely a downstream endocrine response to hyperactive GnRH and LH secretion driving the ovary, or do the elevated androgens themselves act in the brain (or pituitary) during development and/or adulthood to sculpt and maintain the hypersecretion of GnRH and LH?" wrote Eulalia A. Coutinho, PhD, and Alexander S. Kauffman, PhD, in a 2019 review of the brain's role in PCOS.

These problems may be bidirectional or part of various feedback loops. Sleep apnea is more common in people with PCOS, Tyson noted, but sleep apnea is also linked to cardiovascular, metabolic, and depression risks, and depression can play a role in obesity, which increases the risk of obstructive sleep apnea. "So you're in this vicious cycle," Tyson said. That's why she also believes it's important to change the dialogue and perspective on PCOS, to reduce the stigma attached to it, and work with patients to empower them in treating its symptoms and reducing their risk of comorbidities.

Recent and Upcoming Changes in Treatment

Current treatment of PCOS already changes according to the symptoms posing the greatest problems at each stage of a person's life, Hudson said. Younger women tend to be more bothered about the cosmetic effects of PCOS, including hair growth patterns and acne, but as they grow out of adolescence and into their 20s and 30s, infertility becomes a bigger concern for many. Then, as they start approaching menopause, metabolic and cardiovascular issues take the lead, with more of a focus on lipids, diabetes risk, and heart health.

In some ways, management of PCOS hasn't changed much in the past several decades, except in an increased awareness of the metabolic and cardiovascular risks, which has led to more frequent screening to catch potential conditions earlier in life. What has changed, however, is improvements in the treatments used for symptoms, such as expanded bariatric surgery options and GLP-1 agonists for treating obesity. Other examples include better options for menstrual management, such as new progesterone IUDs, and optimized fertility treatments, Tyson said.

"I think with more of these large-scale studies about the pathophysiology of PCOS and how it may look in different people and the different outcomes, we may be able to tailor our treatments even further," Tyson said. She emphasized the importance of identifying the condition early, particularly in adolescents, even if it's identifying young people at risk for the condition rather than actually having it yet.

Early identification "gives us this chance to do a lot of preventative care and motivate older teens to have a great lifestyle, work on their diet and exercise, and manage cardiovascular" risk factors, Tyson said.

"What we do know and recognize is that there's so many spokes to this PCOS wheel that there really should be a multidisciplinary approach to care," Tyson said. "When I think about who would be the real doctors for patients with PCOS, these would be gynecologists, endocrinologists, dermatologists, nutritionists, psychologists, sleep specialists, and primary care at a minimum."

Pal worries that the label of PCOS leaves it in the laps of ob.gyns. whereas, "if it was called something else, everybody would be involved in being vigilant and managing those patients." She frequently reiterated that the label of PCOS is less important than ensuring clinicians treat the symptoms that most bother the patient.

And even if kisspeptin does play a causal role in PCOS for some patients, it's only a subset of individuals with PCOS who would benefit from therapies developed to target it. Given the complexity of the syndrome and its many manifestations, a "galaxy of pathways" are involved in different potential subtypes of the condition. "You can't treat PCOS as one entity," Pal said.

Still, Hudson is optimistic that the research into potential neuroendocrine contributions to PCOS will yield therapies that go beyond just managing symptoms.

"There aren't a lot of treatments available yet, but there may be some on the horizon," Hudson said. "We're still in this very primitive stage in terms of therapeutics, where we're only addressing specific symptoms, and we haven't been able to really address the underlying cause because we haven't understood it as well and because we don't have therapies that can target it," Hudson said. "But once there are therapies developed that will target some of these central mechanisms, I think it will change completely the approach to treating PCOS for patients."

This article originally appeared on MDedge.com, part of the Medscape Professional Network.


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