The allopregnanolone to progesterone ratio across the menstrual cycle and in menopause
Introduction
Neuroactive steroids are metabolites of sex steroids that modulate neurotransmission. The best studied neuroactive steroid is the progesterone metabolite 3α-5α-tetrahydroprogesterone, also known as allopregnanolone, which is made both in the brain and peripherally by the adrenal glands, ovaries, and testes. Progesterone is converted to allopregnanolone in a two-step process by the enzymes 5α-reductase, which converts progesterone to 5α-dihydroprogesterone (5α-DHP), and 3α-hydroxysteroid-dehydrogenase (3α-HSD), which converts 5α-DHP to allopregnanolone (King, 2013). In the brain, allopregnanolone acts as a positive allosteric modulator at GABAA receptors with 10 times the potency of benzodiazepines (King, 2013; Majewska et al., 1986; Morrow et al., 1987). Moreover, there are limited clinical data linking relative allopregnanolone deficiency with mood disorders. Low serum and cerebrospinal fluid (CSF) levels of allopregnanolone have been observed in patients with mood disorders such as depression, anxiety, and post-traumatic stress disorder (Eser et al., 2006; Rasmusson et al., 2006; Uzunova et al., 1998), and several studies have demonstrated an inverse relationship between allopregnanolone levels and severity of depressive symptoms (Dichtel et al., 2018; Girdler et al., 2001; Wang et al., 1996). In addition, a recently published placebo-controlled trial demonstrating efficacy of an oral positive allosteric modulator of GABAA receptors (SAGE-217) administered for 14 days to patients with major depressive disorder supports a potential link (Gunduz-Bruce et al., 2019).
While cyclical variations of estrogen and progesterone are implicated in the etiology of luteal phase disorders such as premenstrual syndrome (PMS), premenstrual dysphoric disorder (PMDD), and catamenial epilepsy, it has been postulated that allopregnanolone may also play a role. Most studies measuring allopregnanolone in premenopausal women across the menstrual cycle and all studies of postmenopausal women have been subject to limitations of immunoassay cross-reactivity (Bixo et al., 1997; Genazzani et al., 1998; Girdler et al., 2001; Monteleone et al., 2000; Nyberg et al., 2005; Wang et al., 1996). Furthermore, whether conversion of progesterone to allopregnanolone decreases across the menstrual cycle or after menopause is unknown. It is now possible to measure neuroactive steroid levels by gas chromatography-mass spectrometry (GC/MS) after separation by high pressure liquid chromatography (HPLC), which can accurately distinguish allopregnanolone from precursor steroids, including progesterone, as well as structurally similar isomers with markedly different neuroactive effects, thus overcoming limitations of immunoassays (Cheney et al., 1995a). Two recent studies using GC/MS demonstrated a rise in allopregnanolone across the menstrual cycle (Martinez et al., 2016; Pineles et al., 2018). However, progesterone was not simultaneously measured at all menstrual cycle phases, so it is unknown whether the ratio of allopregnanolone to progesterone varies during the menstrual cycle. Given the potential protective function of allopregnanolone in depression as well as the deleterious mood effects demonstrated in some studies of exogenous progesterone administration (Andreen et al., 2003; Klatzkin et al., 2006; Natale et al., 2001), an understanding of the relationship between progesterone and allopregnanolone across the cycle may provide insight into the pathogenesis of mood symptoms associated with the luteal phase.
No published studies using GC/MS have investigated changes in allopregnanolone levels with menopausal status. Studies using immunoassays have demonstrated no difference in serum allopregnanolone levels between postmenopausal women and premenopausal women in the follicular phase (Genazzani et al., 1998), and higher postmortem brain concentrations of allopregnanolone in premenopausal women in the luteal phase compared to postmenopausal women (Bixo et al., 1997).
In the current study, we measured serum levels of allopregnanolone and progesterone by GC/MS at each phase of the menstrual cycle in 10 premenopausal women and at one time point in 24 postmenopausal women, all of whom were non-depressed. Given the high prevalence of luteal phase mood disorders and premenstrual symptoms among reproductive-age women (Direkvand-Moghadam A et al., 2014), we hypothesized that in the setting of a considerable increase in progesterone levels from the follicular to luteal phase, conversion to allopregnanolone would not parallel the increase in its precursor; therefore the ratio of allopregnanolone to progesterone would decrease from the follicular to the luteal phase. Additionally, we hypothesized that postmenopausal women would have similar allopregnanolone to progesterone ratios as premenopausal women in the follicular phase in the context of low progesterone levels. A better understanding of the changes in neuroactive steroid levels and their precursors across the menstrual cycle and in menopause may identify therapeutic targets for luteal phase disorders and mood disorders.
Section snippets
Subjects
This study was approved by the Partners Healthcare Institutional Review Board and complied with Health Insurance Portability and Accountability Act guidelines. Written consent was obtained from all participants prior to study procedures. For all subjects, serum allopregnanolone and progesterone were measured at 0800 h after an overnight fast. To assess the variability of allopregnanolone across the menstrual cycle, we studied 10 healthy premenopausal women [PRE], each at three times points in a
Clinical characteristics
By design, the mean age of postmenopausal women was higher than that of premenopausal women [61 ± 7 (SD) (range 52–73) vs 34 ± 7 (SD) (range 23–44) years, p < 0.0001]. There was no difference in mean BMI between the groups [27.3 ± 4.9 (SD) (range 20.4–36.6) (POST) vs 25.8 ± 3.9 (SD) (range 19.9–31.4) kg/m2 (PRE), p = 0.44]. Average time since onset of menopause for the postmenopausal women was 8.5 ± 5.4 (SD) years. All subjects were non-smokers.
Allopregnanolone and progesterone across the menstrual cycle
Allopregnanolone levels increased from the
Discussion
This preliminary study is the first to characterize the allopregnanolone to progesterone ratio, as a proxy for metabolism of progesterone to allopregnanolone, across the menstrual cycle and in non-depressed post-menopausal women using serum GC/MS measurements for both allopregnanolone and progesterone. As we hypothesized and now show, the ratio of allopregnanolone to progesterone decreases across the menstrual cycle; our data show that this decrease is 8-fold from the follicular to the luteal
Funding
This work was supported by the National Institutes of Health (Grant Numbers T32 DK007028, K24 HL092902, K23 DK113220, K23 AT0080434, R34 MH099315, and R34 MH099310) and the Harvard Catalyst/The Harvard Clinical and Translational Science Center (Grant Number 1UL1TR001102 and Grant Number M01-RR-01066, from the National Center for Research Resources).
Declaration of Competing Interest
Dr. Mischoulon has received research support from Nordic Naturals. He has provided unpaid consulting for Pharmavite LLC and Gnosis USA, Inc. He has received honoraria for speaking from the Massachusetts General Hospital Psychiatry Academy, Blackmores, and PeerPoint Medical Education Institute, LLC. He has received royalties from Lippincott Williams & Wilkins for published book “Natural Medications for Psychiatric Disorders: Considering the Alternatives.” Within the past three years, Dr.
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2022, PsychoneuroendocrinologyCitation Excerpt :GABAA receptors have been previously implicated in state-dependent fear memory (Bouton et al., 1990) and GABA modulators have been reported to confer state-dependent contextual fear memories in mice (Jovasevic et al., 2015). The estrous and menstrual cycles of female rats and humans, respectively, yield natural fluctuations in PROG and ALLO levels that can influence GABAA receptor function (Corpéchot et al., 1993; Kimball et al., 2020). This suggests that estrous cycle-related fluctuations in PROG might confer state-dependent fear memory in naturally cycling female rats.
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These authors contributed equally.