Adrenomedullin in mammalian and human skin glands including the mammary gland

Adrenomedullin as a potential biomarker involved in patients with hereditary hemorrhagic telangiectasia

BACKGROUND

Adrenomedullin (AM) is a vasoactive peptide mostly secreted by endothelial cells with an important role in preserving endothelial integrity.  The relationship between AM and hereditary hemorrhagic telangiectasia (HHT) is unknown. We aimed to compare the serum levels and tissue expression of AM between HHT patients and controls.

METHODS

Serum AM levels were measured by radioimmunoassay and compared between control and HHT groups. AM levels were also compared among HHT subgroups according to clinical characteristics. The single nucleotide polymorphism (SNP) rs4910118 was assessed by restriction analysis and sequencing. AM immunohistochemistry was performed on biopsies of cutaneous telangiectasia from eight HHT patients and on the healthy skin from five patients in the control group.

RESULTS

Forty-five HHT patients and 50 healthy controls were included, mean age (SD) was 50.7 (14.9) years and 46.4 (9.9) years (p = 0.102), respectively. HHT patients were mostly female (60% vs 38%, p = 0.032). Median [Q1-Q3] serum AM levels were 68.3 [58.1-80.6] pg/mL in the HHT group and 47.7 [43.2-53.8] pg/mL in controls (p<0.001), with an optimal AM cut-off according to Youden's J statistic of 55.32 pg/mL (J:0.729). Serum AM levels were similar in the HHT subgroups. No patient with HHT had the SNP rs4910118. AM immunoreactivity was found with high intensity in the abnormal blood vessels of HHT biopsies.

CONCLUSIONS

We detected higher AM serum levels and tissue expression in patients with HHT than in healthy controls. The role of AM in HHT, and whether AM may constitute a novel biomarker and therapeutic target, needs further investigation.

Expression and distribution of the adrenomedullin system in newborn human thymus

Adrenomedullin (AM) is a multifunctional peptide endowed with various biological actions mediated by the interaction with the calcitonin receptor-like receptor (CLR), which couples to the receptor activity-modifying proteins 2 or 3 (RAMP2 or RAMP3) to form the functional plasma membrane receptors AM1 and AM2, respectively. In this study, we investigated for the first time the expression and localization of AM, CLR, RAMP2 and RAMP3 in human thymic tissue from newborns and in primary cultures of thymic epithelial cells (TECs) and thymocytes. Immunohistochemical analysis of thymic tissue showed that both AM and RAMP2 are abundantly expressed in the epithelial cells of medulla and cortex, blood vessels and mastocytes. In contrast, RAMP3 could not be detected. In cultured TECs, double immunofluorescence coupled to confocal microscopy revealed that AM is present in the cytoplasmic compartment, whereas RAMP2 could be detected in the cytoplasm and nucleus, but not in the cell membrane. At variance with RAMP2, CLR was not only present in the nucleus and cytoplasm of TECs, but could also be detected in the cell membrane. The nuclear and cytoplasmic localizations of RAMP2 and CLR and the absence of RAMP2 in the cell membrane were confirmed by western-blot analysis performed on cell fractions. AM, RAMP2 and CLR could also be detected in thymocytes by means of double immunofluorescence coupled to confocal microscopy, although these proteins were not present in the whole thymocyte population. In these cells, AM and RAMP2 were detected in the cytoplasm, whereas CLR could be observed in the cytoplasm and the plasma membrane. In conclusion, our results show that the AM system is widely expressed in human thymus from newborns and suggest that both AM1 receptor components CLR and RAMP2 are not associated with the plasma membrane of TECs and thymocytes but are located intracellularly, notably in the nucleus.

Neuroendocrine markers are expressed in human mammary glands

BACKGROUND

Regulatory peptides have previously been detected in epithelial cells of human mammary glands. As these peptides are produced by scattered neuroendocrine cells in the epithelium of other tissues the aim of this study was to investigate whether the mammary glands express molecular markers for neuroendocrine cells.

MATERIAL AND METHODS

Specimens from 28 human mammary glands were retrieved. The distribution of immunoreactive cells was determined using immunohistochemistry with antibodies versus a set of endocrine markers including peptide hormones, chromogranins/secretogranins, vesicular monoamine transporters, synaptophysin, serotonin and synaptic vesicle protein 2.

RESULTS

Cells of the luminal epithelium of ducts and lobules of human mammary glands expressed vesicular monoamine transporter 2 and chromogranin B, as well as the previously reported regulatory peptides obestatin, ghrelin, adrenomedullin and apelin. Using consecutive sections, it was revealed that the immunoreactivity patterns of the regulatory peptides and vesicular monoamine transporter 2 were similar. Interestingly, immunoreactivity for secretogranin II, secretogranin III and chromogranin B was identified in myoepithelial cells. No immunoreactivity was detected for chromogranin A or synaptophysin.

CONCLUSION

Specific cells in the epithelium and myoepithelium of mammary glands express neuroendocrine markers suggesting that mammary glands may have neuroendocrine functions.

Secretory phenomena in the non-lactating human mammary gland

The normal non-lactating premenopausal human mammary gland has been shown by immunohistochemistry and transmission electron microscopy to secrete a number of antimicrobial peptides such as beta-defensins, the cathelicidin LL37, lactoferrin and adrenomedullin. In addition, the non-lactating gland elaborates a prominent glycocalyx at the apical membrane of the glandular epithelial cells, parts of which are shed into the lumen of endpieces and ducts. This glycocalyx includes the mucins MUC 1 and MUC 4, a strongly Alcian Blue positive palyanionic component and sulfated material stained with Aldehyde Fuchsin. MUC 1 and the Alcian Blue positive material are considered to play an antimicrobial role, too. Lactalbumin and lipid droplets also occur in the non-lactating gland. At the EM-level secretory phenomena operating by exocytosis and by means of the apocrine mechanism have been observed. Cytoskeletal components presumably play a role in apocrine secretion. Apart from secretion at the cellular apex, secretion at the cellular basis also occurs regularly, which may represent the production of para- or endocrine factors.

Adrenomedullin (AM) and adrenomedullin binding protein (AM-BP) in the bovine mammary gland and milk: Effects of stage of lactation and experimental intramammary E. coli infection

Adrenomedullin (AM) has been characterized as an endogenous tissue survival factor and modulator of many inflammatory processes. Because of the increased susceptibility of the mammary gland to infection during the time surrounding parturition in the cow, we investigated how milk and tissue content of AM and its binding protein (AM-BP) might be affected by the stage of lactation and the udder health status. Milk and mammary biopsy samples were obtained from Holstein cows 21 days prior to and at various times after calving to represent the dry period and early and mid-stages of lactation. Additional cows received an intramammary challenge with Escherichia coli for immunohistochemical characterization of AM and AM-BP. Milk AM concentrations were relatively constant across the stages of lactation while AM-BP increased two-fold (P<0.04) between early and mid-lactation. Milk AM (P<0.04) and AM-BP (P<0.03) increased as somatic cell counts (SCCs) increased within a given stage of lactation. Tissue content of both (AM and AM-BP) were significantly affected by stage of lactation, lowest in the dry period and progressively increasing to peak at mid-lactation as well as increasing in association with higher levels of SCCs. Following E. coli challenge, AM increased in epithelial cells surrounding mammary alveoli presenting high levels of SCCs. The data suggest that AM and AM-BP are cooperatively regulated in the mammary gland during lactation; changes in localized tissue AM and AM-BP content reflect a dynamic regulation of these tissue factors in the bovine mammary gland consistent with their protective effects within inflamed tissue.

Differentiation of the HaCaT keratinocyte cell line: modulation by adrenomedullin

BACKGROUND

Adrenomedullin (AM) is a multifunctional peptide produced by a wide variety of cells, including keratinocytes. We, and others, have demonstrated that AM has a role as a growth regulatory factor of the skin and contributes as an antimicrobial agent in the integument's protective barrier. It is not known whether AM has a role in differentiating keratinocytes.

OBJECTIVES

To study the role of AM in keratinocyte differentiation, modulating the effects of calcium and in addition, to assess whether differentiated keratinocytes are still capable of initiating an inflammatory response.

METHODS

HaCaT cells were differentiated using CaCl2. Expression of transglutaminase type 1 (TG1) and E2F1 genes was used to monitor differentiation. AM secretion was measured by enzyme-linked immunosorbent assay (ELISA). NF-kappaB activity and interleukin (IL)-6 secretion in the cells were assessed after exposure to calcium and AM by electrophoretic mobility shift assay and ELISA, respectively.

RESULTS

Secretion of AM by the keratinocyte cell line HaCaT was found to be increased during 1 mmol L(-1) CaCl2-induced cell differentiation but not 0.1 mmol L(-1) CaCl2. All treatments showed low levels of the cell proliferation marker, E2F1. Over time, cells incubated in the presence of 0.1 mmol L(-1) or 1 mmol L(-1) of CaCl2 showed an increase in TG1 expression, a marker of early differentiation. The addition of AM showed a decrease in TG1 expression when combined with 0.1 mmol L(-1) CaCl2, but not with 1 mmol L(-1) CaCl2. In addition, cells kept in 0.1 mmol L(-1) CaCl2 showed translocation of NF-kappaB after 48 h and 72 h of incubation, which was abolished when AM was added to the cells. Treatment with 1 mmol L(-1) CaCl2 led to earlier translocation of NF-kappaB at 24 h after treatment and addition of AM did not abolish the effect of 1 mmol L(-1) CaCl2 on NF-kappaB activation. Cells incubated in 0.1 mmol L(-1) CaCl2 showed increased secretion of IL-6 over time, consistent with NF-kappaB activation. The addition of AM to cells incubated with 0.1 mmol L(-1) CaCl2 showed a rapid decrease in IL-6 secretion after only 6 h. However, 1 mmol L(-1) CaCl2 did not induce secretion of IL-6 and the addition of AM did not affect the result.

CONCLUSIONS

Our data indicate that AM can reverse calcium-induced differentiation when 0.1 mmol L(-1) CaCl2 is used but not 1 mmol L(-1) CaCl2. Cells differentiated with 0.1 mmol L(-1) CaCl2 are still capable of generating an inflammatory response, showing signs of late NF-kappaB activation and IL-6 secretion that can be inhibited by AM. However, cells differentiated with 1 mmol L(-1) CaCl2 lose their ability to secrete IL-6 but not AM, which could be acting as an antimicrobial peptide.

Adrenomedullin: a new target for the design of small molecule modulators with promising pharmacological activities

Adrenomedullin (AM) is a 52-amino acid peptide with a pluripotential activity. AM is expressed in many tissues throughout the body, and plays a critical role in several diseases such as cancer, diabetes, cardiovascular and renal disorders, among others. While AM is a protective agent against cardiovascular disorders, it behaves as a stimulating factor in other pathologies such as cancer and diabetes. Therefore, AM is a new and promising target for the development of molecules which, through their ability to regulate AM levels, could be used in the treatment of these pathologies.

Adrenomedullin signals through NF-kappaB in epithelial cells

Adrenomedullin is a peptide found in a variety of cells and tissues and involved in a multitude of biological processes. Recently, adrenomedullin has been identified as a host defense peptide and as such it plays a role in the inflammatory response. The transcription factor NF-kappaB is a major regulator of genes involved in the inflammatory response and the aim of this study was to determine whether NF-kappaB played a role in the inflammatory process triggered by adrenomedullin. Skin epithelial cells (HaCaTs) were used as our model in vitro. Western blot analysis from adrenomedullin-stimulated HaCaT cells revealed a rapid degradation of NF-kappaB inhibitor alpha and beta followed by the translocation of free NF-kappaB to the nucleus, where it was detected by Texas Red immunostaining after incubation with adrenomedullin for 15 min. Electromobility shift assay showed that NF-kappaB present in the nucleus was active, since it bound to a probe containing an NF-kappaB binding site. Supershift assays indicated that p50 and p65, members of the NF-kappaB family, were both part of the NF-kappaB dimmers involved in adrenomedullin cell signaling. HaCaTs secreted interleukin-6 in response to AM, which was significantly attenuated by the NF-kappaB inhibitor SN-50. Taken together, the data lend support for an immunoregulatory role for AM.

The clinical relevance of adrenomedullin: a promising profile?

Adrenomedullin (AM) is a peptide that possesses potentially beneficial properties. Since the initial discovery of the peptide by Kitamura et al. in 1993, the literature has been awash with reports describing its novel mechanisms of action and huge potential as a therapeutic target. Strong evidence now exists that AM is able to act as an autocrine, paracrine, or endocrine mediator in a number of biologically significant functions, including the endothelial regulation of blood pressure, protection against organ damage in sepsis or hypoxia, and the control of blood volume through the regulation of thirst. Its early promise as a potential mediator/modulator of disease was not, however, entirely as a result of the discovery of physiological functions but due more to the observation of increasing levels measured in plasma in direct correlation with disease progression. In health, AM circulates at low picomolar concentrations in plasma in 2 forms, a mature 52-amino acid peptide and an immature 53-amino acid peptide. Plasma levels of AM have now been shown to be increased in a number of pathological states, including congestive heart failure, sepsis, essential hypertension, acute myocardial infarction, and renal impairment. These earliest associations have been further supplemented with evidence of a role for AM in other pathologies including, most intriguingly, cancer. In this review, we offer a timely review of our current knowledge on AM and give a detailed account of the putative role of AM in those clinical areas in which the best therapeutic opportunities might exist.

Nitric oxide metabolites and adrenomedullin in human breast milk

We found high concentrations of nitrite/nitrate (166-1460 micromol/l) in 43 milk samples obtained from 32 women during postpartum days 1-8, which indicates enhanced mammary nitric oxide (NO) secretion. We detected adrenomedullin (AM) (2.7-20.7 pmol/l) only in 9 of the 43 samples using highly specific immunoradiometric assay. It is uncertain whether the entire adrenomedullin is actively secreted in human milk.

Expression of adrenomedullin and its receptors in human salivary tissue

Adrenomedullin is a multifunctional peptide produced by a wide range of different cells and tissues. This study was designed to investigate whether adrenomedullin is present in human saliva and in salivary glands. It was expected that saliva may contain high concentrations of adrenomedullin, which has antimicrobial activity in vitro, which may have functional implications in the oral cavity. Saliva from the submandibular and parotid glands contained higher concentrations of adrenomedullin than did the circulation, but lower concentrations than in whole saliva. This suggests that oral epithelium may contribute the majority of the adrenomedullin peptide found in saliva. Specific adrenomedullin receptors were found in cell lines from the submandibular (HSG) and parotid (HSY) salivary glands. These findings suggest a paracrine/autocrine role for adrenomedullin in these tissues; however, the concentration of adrenomedullin in saliva was insufficient to suggest a significant antimicrobial action in the healthy oral cavity.

Apocrine Glands in the Eyelid of Primates Contribute to the Ocular Host Defense

Apocrine glands of Moll are regular components of primate eyelids. We studied the distribution and localization of these glands in three different primate species, the common marmoset, the rhesus monkey, and the hamadryas baboon. In addition, we tested the primate glands of Moll with antibodies against antimicrobial proteins, cytoskeletal proteins and the androgen receptor. The glands of Moll differ in abundance and distribution in different monkeys. In the common marmoset, a representative of the New World monkeys, Platyrrhini, the apocrine glands are frequently found at the lid margin and in the overlying epidermis of the lid. In the rhesus monkey and the hamadryas baboon, representatives of Old World monkeys, Catarrhini, apocrine glands are rarer and located predominantly at the margin of the lid. The immunohistochemical analysis indicates the presence of a variety of antimicrobial proteins, e.g. lysozyme, beta-defensin-2, adrenomedullin, lactoferrin, and IgA, in these glands. Interestingly, there are basically no androgen receptors in the nuclei of apocrine glands at the lid margin in all three monkey species. In the common marmoset, however, androgen receptors are found in apocrine glands of the overlying epidermis of the lid. We speculate that the glands of Moll are derived from apocrine glands as found in the skin of the entire body in New World monkeys which developed at the lid margins of higher primates and humans into specialized glands secreting agents of host defense in the eye.

Tissue and plasma expression of the angiogenic peptide adrenomedullin in breast cancer

Adrenomedullin (ADM) is an angiogenic factor that has also been shown to be a mitogen and a hypoxia survival factor for tumour cells. These properties point to ADM as a potential promoter of human malignancies, but little data are available concerning the expression of ADM in human breast cancer. In the present work, we have examined ADM peptide expression in a series of malignant breast tumours by immunohistochemistry using a newly developed anti-ADM monoclonal antibody. In addition, ADM plasma concentrations in breast cancer patients and healthy controls were determined by radioimmunoassay. Of the examined breast cancer samples, 27/33 (82%) showed a moderate to strong staining intensity. ADM-peptide expression in breast tumours was significantly correlated with axillary lymph node metastasis (P=0.030). Analysis of ADM plasma concentrations showed no significant difference between the circulating ADM levels of breast cancer patients and healthy controls. However, a significant positive correlation was found between tumour size and plasma ADM levels (r=0.641, P=0.017). Moreover, ADM levels in breast cancer patients correlated with the presence of lymph node metastasis (P=0.002). In conclusion, we have shown for the first time that ADM peptide is widely expressed in breast cancer and that the degree of expression is associated with lymph node metastasis. ADM peptide in plasma of breast cancer patients reflects the size of the primary tumour, but is unlikely to be a useful tumour marker for the detection of breast cancer. Plasma ADM might represent an independent predictor of lymph node metastasis. The clinical implications of these findings remain to be evaluated.

Adrenomedullin expression by gastric epithelial cells in response to infection

Many surface epithelial cells express adrenomedullin, a multifunctional peptide found in a wide number of body and cell systems. Recently, we and others have proposed that adrenomedullin has an important novel role in host defense. This peptide has many properties in common with other cationic antimicrobial peptides, including the human beta-defensins. Upon exposure of human gastric epithelial cells to viable cells of invasive or noninvasive strains of Helicobacter pylori, Escherichia coli, Salmonella enterica, or Streptococcus bovis, a significant increase in adrenomedullin secretion from these cells was demonstrated. Adrenomedullin gene expression was also increased in response to these microorganisms. Similar observations were noted when these cells were incubated with proinflammatory cytokines such as interleukin 1 alpha (IL-1 alpha), IL-6, tumor necrosis factor alpha and lipopolysaccharide. In cultured cells and an animal infection model, increased adrenomedullin peptide and gene expression was demonstrated when exposed to E. coli or Mycobacterium paratuberculosis, respectively. The data suggest there is a strong association between epithelial infection, inflammation, and adrenomedullin expression, which may have clinical relevance. The regulation of adrenomedullin expression may have therapeutic applications, such as improving or enhancing mucosal immunity.

Cell and molecular biology of the multifunctional peptide, adrenomedullin

Adrenomedullin (AM) is a recently discovered regulatory peptide involved in many functions including vasodilatation, electrolyte balance, neurotransmission, growth, and hormone secretion regulation, among others. This 52-amino acid peptide is expressed by specific cell types in many organs throughout the body. A complex receptor system has been described for AM; it requires at least the presence of a seven-transmembrane-domain G-protein-coupled receptor, a single-transmembrane-domain receptor activity modifying protein, and a receptor component protein needed to establish the connection with the downstream signal transduction pathway, which usually involves cyclicAMP. In addition, a serum-binding protein regulates the biological actions of AM, frequently by increasing AM functional attributes. Changes in levels of circulating AM correlate with several critical diseases, including cardiovascular and renal disorders, sepsis, cancer, and diabetes. Whether AM is a causal agent, a protective reaction, or just a marker for these diseases is currently under investigation. New technologies seeking to elevate and/or reduce AM levels are being investigated as potential therapeutic avenues.