A specific immunoassay for proAMH, the uncleaved proprotein precursor of anti-Müllerian hormone

Proteolytic activation of anti-Müllerian hormone is suppressed in adolescent girls

PURPOSE

The ratio of the anti-Müllerian hormone (AMH) precursor (proAMH) to active AMH (AMH_N,C) is higher in childhood than in adulthood but has never been quantified during adolescence. The ratio of proAMH to total AMH (AMH prohormone index, API) was examined during the puberty in healthy girls. The API was also compared between girls with and without polycystic ovary syndrome (PCOS) to determine if there were differences that could assist in PCOS diagnosis during adolescence.

METHODS

Total AMH and proAMH were measured by immunoassay in a single-centre, cross-sectional observational study; 61 controls and 29 girls with PCOS were included in the study (age range 8-21 years). The API was calculated as proAMH as a percentage of total AMH. Differences in API between control and PCOS subjects and across age-groups were examined by Welch's ANOVA. The relationship between API and a range of metabolic parameters was examined by Pearson correlation.

RESULTS

The API in healthy females increased between the ages of 10~15 years and declined from 15~20 years (p < 0.001). The API was negatively correlated with body mass index in the control (p = 0.04) and PCOS groups (p = 0.007). The API was associated with factors related to adiposity and lipid metabolism. The API was not significantly different in control girls and girls with PCOS.

CONCLUSIONS

Higher API during adolescence suggests that proteolytic activation of proAMH is suppressed during this life stage. API was not different between control girls and girls with PCOS indicating that it is not useful in diagnosis of PCOS during adolescence.

Anti-Müllerian Hormone in Female Reproduction

Anti-Müllerian hormone (AMH), also called Müllerian inhibiting substance, was shown to be synthesized by the ovary in the 1980s. This article reviews the main findings of the past 20 years on the regulation of the expression of AMH and its specific receptor AMHR2 by granulosa cells, the mechanism of action of AMH, the different roles it plays in the reproductive organs, its clinical utility, and its involvement in the principal pathological conditions affecting women. The findings in respect of regulation tell us that AMH and AMHR2 expression is mainly regulated by bone morphogenetic proteins, gonadotropins, and estrogens. It has now been established that AMH regulates the different steps of folliculogenesis and that it has neuroendocrine effects. On the other hand, the importance of serum AMH as a reliable marker of ovarian reserve and as a useful tool in the prediction of the polycystic ovary syndrome (PCOS) and primary ovarian failure has also been acknowledged. Last but not least, a large body of evidence points to the involvement of AMH in the pathogenesis of PCOS.

Challenges in Measuring AMH in the Clinical Setting

Serum anti-Mullerian hormone (AMH) is a widely used marker of functional ovarian reserve in the assessment and treatment of infertility. It is used to determine dosing of gonadotropins used for superovulation prior to in vitro fertilization, as well as to determine the degree of damage to ovarian reserve by cytotoxic treatments such as chemotherapy. AMH is also now used to predict proximity to menopause and potentially provides a sensitive and specific test for polycystic ovarian syndrome. Twenty one different AMH immunoassay platforms/methods are now commercially available. Of those compared, the random-access platforms are the most reliable. However, to date there has not been an agreed common international AMH reference preparation to standardize calibration between the various immunoassays. Recently, a purified human AMH preparation (code 16/190) has been investigated by the World Health Organization as a potential international reference preparation. However, this was only partially successful as commutability between it and serum samples was observed only in some but not all immunoassay methods. Development of a second generation reference preparation with wider commutability is proposed.

Establishment of a homogeneous immunoassay-light-initiated chemiluminescence assay for detecting anti-Müllerian hormone in human serum

Anti-Müllerian hormone (AMH) is known as a reliable marker of ovarian reserve (OR). The determination of AMH is of great importance and most existed AMH detection methods are heterogeneous immunoassay. In this study, a novel homogeneous sandwich immunoassay-light-initiated chemiluminescence assay (LICA) for detecting AMH serum level was developed. This AMH-LICA was performed by incubating serum samples with AMH mouse monoclonal antibody coated with chemibeads, streptavidin-coated sensibeads, and biotinylated AMH mouse monoclonal antibody. Sensitivity, precision, accuracy and cross-reactivity of this assay were evaluated. Besides, a regression analysis showed a high correlation between AMH-LICA and Roche Elecsys® AMH assay (y = 0.9851x + 0.07147, R² = 0.9569). As a homogeneous immunoassay, this AMH-LICA could accurately and rapidly determine the serum level of AMH with high-throughput. Thus, this new developed assay may be a new useful analytical tool for the determination of AMH.

High Variability of Molecular Isoforms of AMH in Follicular Fluid and Granulosa Cells From Human Small Antral Follicles

Anti-Müllerian hormone (AMH) is a member of the TGF-β superfamily produced by follicular granulosa cells (GCs) in women from late gestation to the end of reproductive life. AMH is thought to inhibit aromatase (i.e., CYP19) expression and decrease the conversion of androgens to oestrogens, especially in small antral follicles before dominance is achieved. Thus, AMH acts as a gatekeeper of ovarian steroidogenesis. However, the exact function and processing of AMH has not been fully elucidated. The present study measured and determined AMH isoforms in human follicular fluid (FF) from small antral follicles and in human GCs using four ELISAs, western blot, and immunofluorescence analysis. We evaluated the presence of the following isoforms: full-length AMH precursor (proAMH), cleaved associated AMH (AMH_N,C), N-terminal pro-region (AMH_N), and active C-terminal (AMH_C) AMH. A negative correlation between follicle diameter and the AMH forms was detected. Moreover, western blot analysis detected various AMH forms in both FFs and GCs, which did not match our consensus forms, suggesting an unknown proteolytic processing of AMH. The presence of these new molecular weight isoforms of AMH differs between individual follicles of identical size in the same woman. This study detected several AMH forms in FF and GCs obtained from human small antral follicles, which suggests that intrafollicular processing of AMH is complex and variable. Thus, it may be difficult to develop an antibody-based AMH assay that detects all AMH isoforms. Furthermore, the variability between follicles suggests that designing a recombinant AMH standard will be difficult.

Persistent Müllerian duct syndrome: an update

Male sex differentiation is driven by two hormones, testosterone and anti-Müllerian hormone (AMH), responsible for regression of Müllerian ducts in male fetuses. Mutations inactivating AMH or AMH receptor type 2 (AMHR2) are responsible for persistent Müllerian duct syndrome (PMDS) in otherwise normally virilised 46,XY males. This review is based on published cases, including 157 personal ones. PMDS can present in one of three ways: bilateral cryptorchidism, unilateral cryptorchidism with contralateral hernia and transverse testicular ectopia. Abnormalities of male excretory ducts are frequent. Testicular malignant degeneration occurs in 33% of adults with PMDS. Cancer of Müllerian derivatives is less frequent. Fertility is rare but possible if at least one testis is scrotal and its excretory ducts are intact. Up to January 2019, 81 families with 65 different mutations of the AMH gene, mostly in exons 1, 2 and 5, have been identified. AMHR2 gene mutations comprising 64 different alleles have been discovered in 79 families. The most common mutation, a 27-bp deletion in the kinase domain, was found in 30 patients of mostly Northern European origin. In 12% of cases, no mutation of AMH or AMHR2 has been detected, suggesting a disruption of other pathways involved in Müllerian regression.

The proportion of cleaved anti-Müllerian hormone is higher in serum but not follicular fluid of obese women independently of polycystic ovary syndrome

RESEARCH QUESTION

Does the relative distribution of anti-Müllerian hormone (AMH) isoforms differ between patients depending on their body mass index (BMI) and polycystic ovary syndrome (PCOS) status in serum and follicular fluid?

DESIGN

Obese and normal weight patients (PCOS [n = 70]; non-PCOS [n = 37]) were selected for this case-control study in the serum. Between 2018 and 2019, obese (n = 19) and normal weight (n = 20) women with or without PCOS who were receiving IVF treatment were included in the follicular fluid study. The bio-banked serums and follicular fluid were tested for total AMH (proAMH and AMH_N,C combined) and proAMH using an automatic analyzer. The AMH prohormone index (API = [proAMH]/[total AMH]x 100) was calculated as an inverse marker of conversion of proAMH to AMH_N,C, with only the latter isoform that could bind to the AMH receptor complex.

RESULTS

The API was not significantly different between controls and women with PCOS, whereas obese women had a lower API compared with their normal weight counterparts. Grouping PCOS and controls, a lower API was found in obese versus normal weight women, suggesting a greater conversion of proAMH to AMH_N,C. The API in the serum was significantly correlated with metabolic parameters. In the follicular fluid, API is not different between obese and normal weight women independently of PCOS and is higher than in the concomitant serum.

CONCLUSIONS

The proportion of inactive form of AMH in the serum is higher in normal weight versus obese women but not in the follicular fluid, independently of PCOS. The conversion of proAMH into the cleaved isoform is likely to occur in extra-ovarian tissues and to exacerbate in obese individuals.

Relative levels of the proprotein and cleavage-activated form of circulating human anti-Müllerian hormone are sexually dimorphic and variable during the life cycle

Anti‐Müllerian hormone (AMH) is a gonadal hormone, which induces aspects of the male phenotype, and influences ovarian follicular recruitment. AMH is synthesized as a proprotein (proAMH), which is incompletely cleaved to the receptor‐competent AMH_N,C. AMH ELISAs have not distinguished between proAMH and AMH_N,C; consequently, the physiological ranges of circulating proAMH and AMH_N,C are unknown. A novel proAMH ELISA has been used to assay serum proAMH in humans. Total AMH was also measured, enabling the AMH_N,C concentration to be calculated. Stored serum from 131 boys, 80 younger, and 106 older men were examined, with serum from 14 girls and 18 women included for comparison. The mean levels of proAMH and AMH_N,C in pM were respectively: boys (253, 526), men (7.7, 36), elderly men (5.7, 19), girls (3.3, 15), and women (5.2, 27) (boys vs. men, P < 0.001; girls vs. women, P = 0.032). The proportion of proAMH as a percentage of total AMH (API) was approximately twofold higher in boys than men (P < 0.001) with little overlap between the ranges, with girls also exhibiting lesser cleavage of their AMH than women (P < 0.001). The API varied within each population group. In young men, the API did not correlate with circulating levels of the other testicular hormones (testosterone, InhB, and INSL3). In conclusion, the cleavage of circulating AMH varies extensively within the human population, with most individuals having significant levels of proAMH. The physiological and clinical relevance of circulating proAMH needs to be established.

Changes in Circulating ProAMH and Total AMH during Healthy Pregnancy and Post-Partum: A Longitudinal Study

Circulating Anti-Müllerian hormone (AMH) is derived from the gonads, and is a mixture of the prohormone (proAMH), which does not bind to AMH receptors, and receptor-competent AMH. The functions of a hormone are partially defined by the factors that control its levels. Ovarian reserve accounts for 55~75% of the woman-to-woman variation in AMH level, leaving over 25% of the biological variation to be explained. Pregnancy has been reported to decrease circulating AMH levels, but the observations are inconsistent, with the effect of pregnancy on the bioactivity of AMH being unknown. We have therefore undertaken a longitudinal study of circulating proAMH and total AMH during pregnancy. Serum samples were drawn at 6–8 gestational time-points (first trimester to post-partum) from 25 healthy women with prior uneventful pregnancies. The total AMH and proAMH levels were measured at each time-point using ELISA. The level of circulating total AMH progressively decreased during pregnancy, in all women (p<0.001). On average, the percentage decline between the first trimester and 36–39 weeks’ gestation was 61.5%, with a standard deviation of 13.0% (range 30.4–81.2%). The percentage decline in total AMH levels associated with maternal age (R = -0.53, p = 0.024), but not with the women’s first trimester AMH level. The postpartum total AMH levels showed no consistent relationship to the woman’s first trimester values (range 31–273%). This raises the possibility that a fundamental determinant of circulating AMH levels is reset during pregnancy. The ratio of proAMH to total AMH levels exhibited little or no variation during pregnancy, indicating that the control of the cleavage/activation of AMH is distinct from the mechanisms that control the total level of AMH.

Variation in circulating antimüllerian hormone precursor during the periovulatory and acute postovulatory phases of the human ovarian cycle

OBJECTIVE

To determine whether the relative quantity of circulating AMH precursor (proAMH) declines relative to levels of the active form (AMH_N,C) in the periovulatory phase of the ovarian cycle.

DESIGN

Longitudinal study.

SETTING

Local community.

PATIENT(S)

Sixteen women aged between 18 to 30 years with regular menstrual cycles between 25 to 35 days long.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Serum concentrations of proAMH and total AMH (proAMH and AMH_N,C combined) measured by immunoassay, with relative levels of proAMH expressed as the AMH prohormone index (API = [ProAMH]/[Total AMH] × 100).

RESULT(S)

The mean API in the 11 eligible women fell from 20.7 during the luteinizing hormone (LH) surge period to 18.7 during the acute postsurge period. No statistically significant differences in the API were observed among samples taken at single time points in the early follicular, midfollicular, midluteal, and late luteal phases.

CONCLUSION(S)

This study suggests that activation of AMH by proteolytic enzymes is largely stable throughout the ovarian cycle. However, there is a subtle but robust decrease in the level of proAMH relative to AMH_N,C in the acute postovulatory period. This may indicate that periovulatory increases in prohormone convertases cause increases in proAMH cleavage rates. Alternatively, rapid changes in the hierarchy of follicle developmental stages during ovulation may result in changes in the relative ratios of proAMH and AMH_N,C.

The Anti-Müllerian Hormone Precursor (proAMH) Is Not Converted to the Receptor-Competent Form (AMHN,C) in the Circulating Blood of Mice

Anti-Müllerian hormone (AMH) is a gonadal hormone that regulates aspects of male sexual differentiation and ovarian function. AMH is synthesized as the AMH proprotein precursor (proAMH), which is converted to a receptor-binding form (AMHN,C) by proteolytic cleavage. ProAMH appears to be the predominant species in the ovary, whereas AMHN,C is the prevalent form in circulation. The aim of this study was to determine whether cleavage of proAMH occurs before it is released from the gonad or while in circulation. The individual half-lives of the proAMH and AMHN,C were also determined, as this has important implications for understanding the mechanisms of AMH signaling. Recombinant human (rh)-proAMH or rh-AMHN,C was injected iv into mice. AMH levels were analyzed in a series of repeated blood samples using an assay that detects human, but not murine, AMH. The degree of cleavage of injected proAMH was assessed by immunoprecipitation and Western blotting. The elimination half-life curves were biphasic. The fast-phase elimination was estimated at 6 and 11 minutes for rh-proAMH and rh-AMHN,C, respectively. The slow-phase half-life estimates were 2.4 and 3.8 hours for rh-proAMH and rh-AMHN,C, respectively. Immunoprecipitation of rh-proAMH 1 hour after injection determined that no detectable conversion of proAMH to AMHN,C was occurring in circulation. The data suggest that the ratio of proAMH to AMHN,C in the circulation is not altered after it is released from the gonads and that the levels of these 2 circulating forms are likely to reflect AMH activity in the gonad.