Enzyme immunoassays for inhibins, activins and follistatins

Follistatin and the Breast Implant Capsule

Supplemental Digital Content is available in the text.

Background:

Breast capsular contracture remains an elusive problem faced by plastic surgeons and is the leading long-term complication after breast implantation. Follistatin (Fst) is a protein with known anti-inflammatory and antifibrotic properties and has the potential to limit the severity of diseases associated with inflammation and fibrosis such as capsular contracture. The aim of this study was to examine the effect of Fst288 on capsular fibrosis around silicone implants in a mouse model.

Methods:

BALB/c mice were implanted subcutaneously with untreated silicone implants (baseline control). In the experimental group, immediately after silicone implant insertion, the implant pocket received either a single injection of 1 µg Fst288 or normal saline (internal control). The animals were killed at 3, 5, 7, 14, 28, and 90 days after surgery, and serum, implants, and the surrounding tissue were removed for histological and immunohistochemical analyses.

Results:

Fst288 treatment resulted in significant decreases in capsule thickness at 28 days (P < 0.05) and 3 months (P < 0.001), decreased collagen production at 14 days (P < 0.05) and 3 months (P < 0.01), decreased angiogenesis at 3 months (P < 0.001), decreased α-smooth muscle actin levels at 3 months (P < 0.05), and a decrease in the number of CD45+ cells at days 5 (P < 0.05) and 7 (P < 0.01), respectively, when compared with control implants.

Conclusions:

A single injection of Fst288 at the time of silicone implant insertion into the mice results in a significant reduction in pericapsular inflammation and capsular fibrosis.

Inhibin B and luteinizing hormone levels in girls aged 6-11 years from NHANES III, 1988-1994

OBJECTIVE

To evaluate inhibin B and luteinizing hormone (LH) levels in a large, representative cross-sectional sample of US girls and characterize the relationships of these laboratory values with age, clinical signs of puberty and other correlates.

DESIGN

Cross-sectional analysis of LH and inhibin B in banked serum from 720 girls aged 6-11 years who participated in the Third National Health and Nutrition Examination Survey (NHANES III).

MEASUREMENTS

Levels of inhibin B and LH, race, ethnicity and anthropometric measurements were compared for all girls. Visual assessment of pubertal stage was performed on girls aged 8 years and older. A two-part model was used to establish normative data and Tobit regression models were used to evaluate associations with participant characteristics. Receiver operating characteristic (ROC) analysis was performed to identify optimum cut points predictive of puberty onset.

RESULTS

Mean hormone levels progressively increased with age. LH levels progressively increased with pubertal stage. Inhibin B levels increased gradually from breast stage I to II, then more sharply to peak at stage III, followed by a plateau at stages IV and V. ROC curves indicated that both hormones were consistent with pubertal onset as indicated by breast stage II.

CONCLUSIONS

This study characterizes inhibin B and LH values in a large, representative cross-sectional sample of US girls. Inhibin B can be a useful tool in combination with other clinical and biochemical parameters to evaluate gonadal function as a reflection of pubertal progression in girls.

The regulation and functions of activin and follistatin in inflammation and immunity

The activins are members of the transforming growth factor β superfamily with broad and complex effects on cell growth and differentiation. Activin A has long been known to be a critical regulator of inflammation and immunity, and similar roles are now emerging for activin B, with which it shares 65% sequence homology. These molecules and their binding protein, follistatin, are widely expressed, and their production is increased in many acute and chronic inflammatory conditions. Synthesis and release of the activins are stimulated by inflammatory cytokines, Toll-like receptor ligands, and oxidative stress. The activins interact with heterodimeric serine/threonine kinase receptor complexes to activate SMAD transcription factors and the MAP kinase signaling pathways, which mediate inflammation, stress, and immunity. Follistatin binds to the activins with high affinity, thereby obstructing the activin receptor binding site, and targets them to cell surface proteoglycans and lysosomal degradation. Studies on transgenic mice and those with gene knockouts, together with blocking studies using exogenous follistatin, have established that activin A plays critical roles in the onset of cachexia, acute and chronic inflammatory responses such as septicemia, colitis and asthma, and fibrosis. However, activin A also directs the development of monocyte/macrophages, myeloid dendritic cells, and T cell subsets to promote type 2 and regulatory immune responses. The ability of both endogenous and exogenous follistatin to block the proinflammatory and profibrotic actions of activin A has led to interest in this binding protein as a potential therapeutic for limiting the severity of disease and to improve subsequent damage associated with inflammation and fibrosis. However, the ability of activin A to sculpt the subsequent immune response as well means that the full range of effects that might arise from blocking activin bioactivity will need to be considered in any therapeutic applications.

Inherent capacity of the pituitary gland to produce gonadotropins is not influenced by the number of ovarian follicles > or = 3 mm in diameter in cattle

We hypothesised that higher serum FSH concentrations in cattle with low v. high follicle numbers during follicular waves are caused by a different capacity of the pituitary gland to produce gonadotropins. Dairy cows with high (> or = 30; n = 5) and low (< or = 15; n = 5) follicle numbers were selected and serum concentrations of oestradiol and FSH during an oestrous cycle were measured. Cows were ovariectomised at oestrus and bled frequently up to 8 days after ovariectomy. After 33 days, cows were injected with gonadotropin-releasing hormone (GnRH) and bled intensively up to 8 h after GnRH injection. One day later, animals were injected with follicular fluid (FF) from bovine follicles and were bled intensively up to 2 days after the first injection. Serum concentrations of FSH and LH were measured. After 2 days, cows were killed and their pituitary glands collected. Prior to ovariectomy, serum oestradiol concentrations were similar between groups, whereas FSH concentrations were higher in cattle with low v. high numbers of follicles. No differences were detected in serum gonadotropin concentrations after ovariectomy, GnRH injection or FF challenge between groups. The results indicate that the inherent capacity of the pituitary gland to secrete gonadotropins does not differ between cattle with high v. low numbers of follicles during follicular waves.

Beyond CA125: the coming of age of ovarian cancer biomarkers. Are we there yet?

Ovarian cancer (OC) is the fourth leading cause of cancer deaths among women in the United States, despite its relatively low incidence of 50 per 100,000. Even though advances in therapy have been made, the OC fatality-to-case ratio remains exceedingly high, due to the lack of accurate tools to diagnose early-stage disease when cure is still possible. The most studied marker for OC, CA125, is only expressed by 50-60% of patients with early stage disease. Large efforts have been deployed to identify novel serum markers, yet no single marker has emerged as a serious competitor for CA125. Various groups are investing in combination approaches to increase the diagnostic value of existing markers, but many markers may still lie in under-explored areas of ovarian cancer biology, such as tumor vasculature environment and post-translational modifications (glycomics).

Inflammatory networks in the control of spermatogenesis : chronic inflammation in an immunologically privileged tissue?

Spermatogenesis is a complex, organized process involving intimate interactions between the developing germ cells and supporting Sertoli cells. The process is also highly regulated. Studies suggest that regulation in the seminiferous epithelium involves molecules normally associated with either immune or inflammatory processes; in particular, interleukin 1a (IL1a), IL6, tumor necrosis factor (TNFa), activin A and nitric oxide (NO). While there is considerable evidence that these inflammatory mediators have effects on spermatogonial and spermatocyte development as well as critical supportive functions of the Sertoli cells, which are undoubtedly of considerable importance during testicular inflammation, there remains some skepticism regarding the significance of these molecules with respect to normal testicular function. Nonetheless, it is evident that expression of these regulators varies across the cycle of the seminiferous epithelium in a consistent manner, with major changes in production coinciding with key events within the cycle. This review summarizes the evidence supporting the hypothesis that inflammatory cytokines play a role in normal testicular spermatogenesis, as well as in the etiology of inflammation induced sub-fertility. The balance of data leads to the striking conclusion that the cycle of the seminiferous epithelium resembles a chronic inflammatory event. This appears to be a somewhat paradoxical assertion, since the testis is an immunologically privileged tissue based on its well-established ability to support grafts with minimal rejection responses. However, it may be argued that local immunoregulatory mechanisms, which confer protection from immunity on both transplanted tissues and the developing spermatogenic cells, are equally necessary to prevent local inflammation responses associated with the spermatogenic process from activating the adaptive immune response.

Inhibin as a diagnostic marker for ovarian cancer

The inhibins are a family of growth factors comprised of several different species that are secreted in the female principally from the ovarian follicle. The inhibins perform best as markers of ovarian cancer when measured collectively (total inhibin) by immunoassays targeted to common epitopes. After menopause with the depletion of ovarian follicles, the circulating level of total inhibin becomes undetectable. In contrast, serum total inhibin levels are elevated in women with ovarian cancer, in particular those with granulosa cell tumours and those with the mucinous subtype of epithelial carcinoma. Investigations into the clinical utility of inhibin to detect ovarian cancer have shown that it complements CA125, an established marker of epithelial ovarian cancer, in that each performs best in detecting different subtypes of ovarian cancer. In some published studies, the two markers together have detected up to 95% of ovarian cancers with 95% specificity.

Changes in Circulating and Testicular Levels of Inhibin A and B During Postnatal Development in Bulls

We investigated testicular and circulating levels of dimeric inhibins in Holstein bulls from the infantile to postpubertal periods (5 to 50 weeks of age) and examined the relationship between the profiles of circulating dimeric inhibins and FSH. Concentrations of total inhibin and inhibin B in the testis were highest at 4 to 5 weeks of age but decreased gradually as the bulls aged. Testicular inhibin A levels showed a gradual decline to a nadir at 15 to 26 weeks of age, but by 39 weeks, they were high again. The contents of total inhibin, inhibin A, and inhibin B per testis generally increased with age. Fractionation of testicular homogenates obtained from 15-week-old bulls by a combination of immunoaffinity chromatography and SDS-PAGE confirmed the presence of two major molecular weight forms (32 and 45 kDa) of dimeric inhibins in the testes. Circulating levels of total inhibin and inhibin A showed a significant increase in bulls at around 10 to 14 weeks of age compared to the levels between 5 and 7 weeks of age but decreased thereafter. However, immunoreactivity for inhibin B was not detected in the peripheral circulation, probably because of low sensitivity of the inhibin B assays. The concentrations of plasma FSH were high at 5 weeks of age but declined to lower levels between 11 and 40 weeks, and then increased from 41 weeks onward. There was no significant correlation between the plasma levels of FSH and inhibin A or total inhibin. The results clearly indicate that the bull testis produces inhibin A and B and secretes at least inhibin A into the circulation during postnatal development. However, the profile of circulating FSH in bulls shows no reciprocal relationship with the inhibin A or total inhibin profile during the postnatal period.

Cytokine profiles in the testes of rats treated with lipopolysaccharide reveal localized suppression of inflammatory responses

Evidence indicates that the testis possesses a reduced capacity to mount inflammatory and rejection responses, which undoubtedly contributes to the ongoing survival of the highly immunogenic germ cells. The contribution of local cytokine expression to this condition was investigated in adult male rats treated with lipopolysaccharide to induce inflammation. Cytokine mRNA and protein expression were determined in tissue extracts and fluids by Northern blot analysis, quantitative PCR, or RNAse protection assay and specific ELISAs. Testicular expression of the proinflammatory cytokines, interleukin (IL)-1β and tumor necrosis factor-α was considerably attenuated compared with the liver (control tissue); in contrast, the testicular IL-6 response was enhanced. Expression of IL-10, a type 2 immunoregulatory cytokine, was similar in both testis and liver, whereas the immunoregulatory/anti-inflammatory cytokines transforming growth factor-β1and activin A were constitutively elevated in both normal and inflamed testes. The IL-1β and transforming growth factor-β1proteins were present principally in their latent (inactive) forms, indicating that enzymic processing is an important control mechanism for these two cytokines within the testis. These data indicate that inflammatory and regulatory cytokine activity is regulated at both transcriptional and posttranslational levels in a testis-specific manner. It is concluded that a novel pattern of suppression of proinflammatory cytokine responses and normal or elevated expression of immunoregulatory cytokines may be responsible for reduced inflammatory responses and enhanced graft survival in the testis. These data have important implications for the understanding and treatment of male autoimmune infertility, testicular inflammation. and carcinogenesis.

The role of activin, follistatin and inhibin in testicular physiology

The role of the inhibins, activins and follistatins in testicular function are being more clearly defined following studies describing the cellular localisation of these proteins to the testis and the availability of specific assay systems enabling measurement of these proteins. Taken together with the results of targetted gene inactivation experiments, several concepts emerge. Inhibin B is predominantly produced by the Sertoli cell in many adult male mammals whereas there is a perinatal peak of inhibin A in the rat. In contrast, activin A has its highest concentrations in the immediate post-natal period during which it is involved in the developmental regulation of both germ cells and Sertoli cells being modulated by follistatin. Activin A levels are considerably lower in the adult testis but Sertoli cell production is stimulated by interleukin-1 and inhibited by FSH. Little is known about the production of activin B due to the absence of a suitable assay but the beta(B) subunit mRNA is expressed in germ cells and Sertoli cells and is stage-dependent. This pattern of expression suggest that it may be involved in autocrine or paracrine actions within the seminiferous epithelium.

Changes in circulating and testicular levels of inhibin A and B and activin A during postnatal development in the rat

This study describes the testicular levels of inhibin/activin subunits by Northern analysis and in situ hybridization and serum and testicular levels of inhibins A and B and activin A by enzyme linked immunosorbent assays (ELISA) during postnatal development in the rat. We show that serum inhibin A levels are less than 4 pg/ml throughout postnatal life. Serum inhibin B levels peak at 572 +/- 119 pg/ml (mean +/- se) at d 40 post partum (pp) before falling to 182 +/- 35 pg/ml in mature males. Serum activin A decreases from 294 +/- 29 pg/ml at d 6 to 132 +/- 27 pg/ml at maturity. Within the testis, inhibin A levels fall from 0.330 +/- 0.108 ng/g at d 15 to less than 0.004 ng/g at maturity. Inhibin B levels peak at 43.9 +/- 4.2 ng/g at d 6 before falling to 1.6 +/- 0.13 ng/g at maturity. Testicular activin A levels fall from 18.6 +/- 2.2 ng/g at d 6 to 0.094 +/- 0.013 ng/g at maturity. Northern profiles of testicular inhibin/activin subunits correlate with immunoreactive levels demonstrated by ELISA. In situ hybridization suggests that beta(A) and beta(B) subunit expression is largely restricted to the seminiferous tubule, particularly Sertoli cells, spermatogonia, and primary spermatocytes. These data support the view that inhibin B is the major inhibin in the male rat and that levels relate to Sertoli cell number and activity. Furthermore, the demonstration of high local concentrations of activin A during the period of Sertoli cell proliferation and the onset of spermatogenesis support its proposed role because a modulator of testicular development and function.

Establishment and Characterization of a Human Ovarian Granulosa Tumor Cell line (HSOGT)

We successfully established a novel ovarian granulosa tumor cell line (HSOGT). The tumor tissue of the ovary was derived from a 25 year-old Japanese woman under her consent. The cell line was maintained for over 14 months, subcultured more than 73 times, and had a population doubling time of 18.9 hours. Phase contrast microscopy displayed a pavement-like arrangement without contact inhibition. The chromosome number showed a wide distribution of aneuploidy and the mode was 83; many marker chromosomes were observed. The HSOGT was also successfully xenotransplanted into nude mice. The cell line produced estradiol and has preserved some characters of granulosa cells with stable growth in vitro. We firmly believe that this cell line will be a most useful tool for endocrinological investigation of human granulosa cells.

Inhibin B is the major form of inhibin secreted from testes in male Japanese macaques ( Macaca fuscata)

In order to clarify the cellular source and forms of bioactive inhibin in male Japanese macaques ( Macaca fuscata), circulating concentrations of inhibin A and B, and immunohistochemical localization of inhibin subunits in testis were studied. Plasma concentrations of testosterone were also measured. The present study showed that inhibin B was clearly detected in the plasma of male Japanese macaques. Moreover, concentrations of both inhibin B and testosterone during the breeding (mating) season were significantly higher than those of the non-breeding season. On the other hand, plasma inhibin A was detected neither during the breeding seasons nor during the non-breeding seasons. Positive stainings with alpha and betaB subunit antibodies were observed in the Sertoli cells, however staining with betaA subunit antibody was not observed in the testicular samples. These results indicate that inhibin B is the major circulating inhibin and probably secreting from Sertoli cells in male Japanese macaques.

Plasma concentrations of inhibin a and follicle-stimulating hormone differ between cows with two or three waves of ovarian follicular development in a single estrous cycle

Patterns of ovarian follicle development were monitored daily in Holstein-Friesian cows that had two (n = 4) or three (n = 4) waves of ovarian follicle development during a single estrous cycle. The plasma from daily blood samples was used in assays for inhibin A, FSH, progesterone, and estradiol-17beta. Mean cycle lengths for cows with two and three waves were 21.8 and 25.3 days, respectively (P < 0.02). Although the average number of follicles >3-mm diameter on each pair of ovaries was similar for two- and three-wave cows on Days 2, 3, and 4 (Day 0 = day of ovulation; 8.6 vs. 9.6 follicles), there were more follicles >6-mm diameter on the ovaries of cows with two waves on Days 3 and 4. This difference was associated with a shorter interval from wave emergence to peak concentrations of inhibin A during the first wave in two-wave cows (2.0 vs. 3.8 days; P = 0.03) and with higher peak concentrations (474 vs. 332 pg/ml; P = 0.03). Differences in peak FSH concentrations were not significant (1.7 vs. 1.3 ng/ml; P = 0.10) and were inversely related to inhibin A concentrations. The peak concentrations of inhibin A and FSH in the second nonovulatory wave in the three-wave cows were similar to the low concentrations measured in the first wave (292 vs. 332 pg/ml of inhibin A, 1.3 vs. 1.3 ng/ml of FSH; P > 0.20). Average peak concentrations of inhibin A and FSH were similar during the ovulatory wave for cows with either two or three waves in a cycle (432 vs. 464 pg/ml of inhibin A, 2.3 vs. 2.1 ng/ml of FSH; P > 0.3). The lower concentrations of FSH during the emergence of the first follicular wave in cows with three-wave cycles may have reduced the rate of development of some of the follicles and reduced the concentrations of inhibin A. This pattern of lower concentrations of FSH and inhibin A was repeated in the second nonovulatory wave but not in the ovulatory wave. Subtle differences in the concentrations of these two hormones may underlie the mechanism that influences the number of waves of ovarian follicle development that occur during the bovine estrous cycle.

Alterations in peripheral concentrations of inhibin A in cattle studied using a time-resolved immunofluorometric assay: relationship with estradiol and follicle-stimulating hormone in various reproductive conditions

The aims of this study were to develop a sensitive and specific assay for bovine inhibin A using europium and to investigate the endocrine role of inhibin A in various reproductive conditions by characterizing the relationship between profiles of inhibin A, FSH, and estradiol and follicle growth during the postpartum period, during the intact estrous cycle, and in cows with follicular cysts. The time-resolved immunofluorometric assay (Tr-IFMA) for bovine inhibin A, using purified polyclonal antibodies to alpha and beta(A) subunits, was specific for bovine inhibin A and did not cross-react with bovine activin A, activin AB, activin B, pro-alphaC or human recombinant inhibin B. The detection limit of the IFMA was 3.3 pg/ml expressed in terms of bovine 32-kDa inhibin A. Dose-response curves of plasma samples obtained from intact and FSH-stimulated cows and cystic cows were parallel to the standard without any preassay processing of samples. Plasma inhibin A levels increased (P < 0.01) concomitant with emergence of nonovulatory or ovulatory follicular waves during the postpartum period. In cystic cows, plasma inhibin A was sustained at high levels for a longer period, associated with growth of persistent dominant follicles. The highest levels of inhibin A were noted during the growth phase of normal and persistent dominant follicles; however, inhibin A levels declined (P < 0.01) as these dominant follicles ceased to grow or ovulated. An inverse relationship between patterns of plasma inhibin A and FSH existed during each follicular wave in the three physiologic conditions. Increases in plasma inhibin A levels were associated with increases in plasma estradiol levels during most follicular waves; however, there was no increase in plasma estradiol level and no relationship between patterns of estradiol and FSH during follicular waves observed during the early postpartum period or midluteal phase of the estrous cycle. In conclusion, the Tr-IFMA does not require pretreatment of samples and can be used for precise measurement of bovine inhibin A without interference with free inhibin alpha subunits. Inhibin A, produced primarily during growth of the dominant follicle, functions as a negative feedback regulator for FSH secretion throughout the postpartum period and the estrous cycle, whereas estradiol appears to have a minor role in regulation of FSH compared with inhibin A, especially during the early postpartum period and midluteal phase of the estrous cycle. The results also indicate that a persistent dominant follicle sustains inhibin A production for a longer period than the dominant follicle emerging in the estrous cycle and establishes long-term dominance by suppressing emergence of a new follicular wave.

Enzyme immunoassays for inhibins, activins and follistatins

In this short review, the authors summarise the inhibin, activin and follistatin assays developed by the Oxford group and collaborators, and some of the main purposes for which they have been applied. Over 500 research publications have used these assays. We also discuss new assays recently developed at the request of our collaborators for particular applications, and comment on outstanding assay problems.