Nitric oxide synthase activity in human pituitary adenomas

Targeting Nrf2-Mediated Oxidative Stress Response Signaling Pathways as New Therapeutic Strategy for Pituitary Adenomas

Oxidative stress and oxidative damage are the common pathophysiological characteristics in pituitary adenomas (PAs), which have been confirmed with many omics studies in PA tissues and cell/animal experimental studies. Nuclear factor erythroid 2 p45-related factor 2 (Nrf2), the core of oxidative stress response, is an oxidative stress sensor. Nrf2 is synthesized and regulated by multiple factors, including Keap1, ERK1/2, ERK5, JNK1/2, p38 MAPK, PKC, PI3K/AKT, and ER stress, in the cytoplasm. Under the oxidative stress status, Nrf2 quickly translocates from cytoplasm into the nucleus and binds to antioxidant response element /electrophile responsive element to initiate the expressions of antioxidant genes, phases I and II metabolizing enzymes, phase III detoxifying genes, chaperone/stress response genes, and ubiquitination/proteasomal degradation proteins. Many Nrf2 or Keap1 inhibitors have been reported as potential anticancer agents for different cancers. However, Nrf2 inhibitors have not been studied as potential anticancer agents for PAs. We recommend the emphasis on in-depth studies of Nrf2 signaling and potential therapeutic agents targeting Nrf2 signaling pathways as new therapeutic strategies for PAs. Also, the use of Nrf2 inhibitors targeting Nrf2 signaling in combination with ERK inhibitors plus p38 activators or JNK activators targeting MAPK signaling pathways, or drugs targeting mitochondrial dysfunction pathway might produce better anti-tumor effects on PAs. This perspective article reviews the advances in oxidative stress and Nrf2-mediated oxidative stress response signaling pathways in pituitary tumorigenesis, and the potential of targeting Nrf2 signaling pathways as a new therapeutic strategy for PAs.

Decreased nitric oxide serum level after pituitary adenoma resection

BACKGROUND

Nitric oxide (NO) is synthesized by the conversion of Arginine (Arg) into the NO and Citrulline (Cit). Although the NO is involved into the pathogenesis of several physiological and pathological processes, the role of NO in pituitary adenomas (PA) progression is not determined. Our purpose was to evaluate the relationship between NO and PA as well as the effect of tumor resection on NO metabolites level in serum.

METHODS

The study group consisted of 21 patients with PA, 18 patients with macroadenomas and 3 with microadenomas. Venous blood samples were collected at two time-points; 1) before the surgery and 2) 3-5 days after PA resection. Arg and Cit levels were determined by the automated ion-exchange chromatography with usage of Amino Acids Analyser (AAA 400). Commercially available kit for the evaluation of nitrate/nitrite serum levels was applied for indirect assessment of serum NO level.

RESULTS

Significant decrease in NO concentration after the surgery was observed in comparison with the time-point 1. Arg level did not significantly change during the study period. Cit level was ranged below the detection limit of applied method.

CONCLUSIONS

The decrease of NO level after the pituitary adenoma resection indicates the relationship between NO synthesis and PA occurrence.

Heterogeneity analysis of the proteomes in clinically nonfunctional pituitary adenomas

Background

Clinically nonfunctional pituitary adenomas (NFPAs) without any clinical elevation of hormone and with a difficulty in its early-stage diagnosis are highly heterogeneous with different hormone expressions in NFPA tissues, including luteinizing hormone (LH)-positive, follicle-stimulating hormone (FSH)-positive, LH/FSH-positive, and negative (NF). Elucidation of molecular mechanisms and discovery of biomarkers common and specific to those different subtypes of NFPAs will benefit NFPA patients in early-stage diagnosis and individualized treatment.

Methods

Two-dimensional gel electrophoresis (2DGE) and PDQuest image analyses were used to compare proteomes of different NFPA subtypes (NF-, LH-, FSH-, and LH/FSH-positive) relative to control pituitaries (Con). Differentially expressed proteins (DEPs) were characterized with mass spectrometry (MS). Each set of DEPs in four NFPA subtypes was evaluated with overlap analysis and signaling pathway network analysis with comparison to determine any DEP and pathway network that are common and specific to each NFPA subtype.

Results

A total of 93 differential protein-spots were determined with comparison of each NFPA type (NF-, LH-, FSH-, and LH/FSH-positive) versus control pituitaries. A total of 76 protein-spots were MS-identified (59 DEPs in NF vs. Con; 65 DEPs in LH vs. Con; 63 DEPs in FSH vs. Con; and 55 DEPs in LH/FSH vs. Con). A set of DEPs and pathway network data were common and specific to each NFPA subtype. Four important common pathway systems included MAPK-signaling abnormality, oxidative stress, mitochondrial dysfunction, and cell-cycle dysregulation. However, these pathway systems were, in fact, different among four NFPA subtypes with different protein-expression levels of most of nodes, different protein profiles, and different pathway network profiles.

Conclusions

These result data demonstrate that common and specific DEPs and pathway networks exist in four NFPA subtypes, and clarify proteome heterogeneity of four NFPA subtypes. Those findings will help to elucidate molecular mechanisms of NFPAs, and discover protein biomarkers to effectively manage NFPA patients towards personalized medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-014-0069-6) contains supplementary material, which is available to authorized users.

The clinical and pathological significance of nitric oxide synthase in human pituitary adenomas: a comparison with MIB-1

The purpose of the present study was to define the clinical and pathological significance of nitric oxide synthase (NOS) in human pituitary adenomas, and to compare these values with those of the MIB-1 labeling index (LI) using an immunohistochemical method. Tissue specimens from 82 cases of surgically-treated pituitary adenomas were immunostained for hormone production for the MIB-1 LI and for the three NOS isoenzymes and five normal pituitary glands were immunostained for the three NOS isoenzymes as a control. The correlation between the clinical variables (age, functional status, tumor size, Hardy's grading, cavernous and/or sphenoid invasiveness, and progression) and mean MIB-1 LI, or between the same clinical variables and NOS immunoreactivity (IR) were analyzed. There was a statistically significant difference in the MIB-1 LI between macroadenomas and microadenomas, and between invasive adenomas and noninvasive adenomas. On the other hand, there was a statistically significant difference in the inducible NOS (iNOS) IR between invasive adenomas and noninvasive adenomas. Furthermore, the iNOS IR had a significant correlation with the MIB-1 LI. Invasive adenomas have a higher iNOS IR, and this correlated with the MIB-1 LI. These findings may be due to the function of iNOS, which plays an important role in tissue injury and repair.

Pituitary adenoma nitroproteomics: current status and perspectives

Oxidative stress is extensively associated with tumorigenesis. A series of studies on stable tyrosine nitration as a marker of oxidative damage were performed in human pituitary and adenoma. This paper reviews published research on the mass spectrometry characteristics of nitropeptides and nitroproteomics of pituitary controls and adenomas. The methodology used for nitroproteomics, the current status of human pituitary nitroproteomics studies, and the future perspectives are reviewed. Enrichment of those low-abundance endogenous nitroproteins from human tissues or body fluid samples is the first important step for nitroproteomics studies. Mass spectrometry is the essential approach to determine the amino acid sequence and locate the nitrotyrosine sites. Bioinformatics analyses, including protein domain and motif analyses, are needed to locate the nitrotyrosine site within the corresponding protein domains/motifs. Systems biology techniques, including pathway analysis, are necessary to discover signaling pathway networks involving nitroproteins from the systematically global point of view. Future quantitative nitroproteomics will discover pituitary adenoma-specific nitroprotein(s). Structural biology techniques such as X-ray crystallography analysis will solidly clarify the effects of tyrosine nitration on structure and functions of a protein. Those studies will eventually address the mechanisms and biological functions of tyrosine nitration in pituitary tumorigenesis and will discover nitroprotein biomarkers for pituitary adenomas and targets for drug design for pituitary adenoma therapy.

Endocrine cells and blood vessels work in tandem to generate hormone pulses

Hormones are dynamically collected by fenestrated capillaries to generate pulses, which are then decoded by target tissues to mount a biological response. To generate hormone pulses, endocrine systems have evolved mechanisms to tightly regulate blood perfusion and oxygenation, coordinate endocrine cell responses to secretory stimuli, and regulate hormone uptake from the perivascular space into the bloodstream. Based on recent findings, we review here the mechanisms that exist in endocrine systems to regulate blood flow, and facilitate coordinated cell activity and output under both normal physiological and pathological conditions in the pituitary gland and pancreas.

Functional importance of blood flow dynamics and partial oxygen pressure in the anterior pituitary

The pulsatile release of hormone is obligatory for the control of a range of important body homeostatic functions. To generate these pulses, endocrine organs have developed finely regulated mechanisms to modulate blood flow both to meet the metabolic demand associated with intense endocrine cell activity and to ensure the temporally precise uptake of secreted hormone into the bloodstream. With a particular focus on the pituitary gland as a model system, we review here the importance of the interplay between blood flow regulation and oxygen tensions in the functioning of endocrine systems, and the known regulatory signals involved in the modification of flow patterns under both normal physiological and pathological conditions.

Signaling pathway networks mined from human pituitary adenoma proteomics data

Background

We obtained a series of pituitary adenoma proteomic expression data, including protein-mapping data (111 proteins), comparative proteomic data (56 differentially expressed proteins), and nitroproteomic data (17 nitroproteins). There is a pressing need to clarify the significant signaling pathway networks that derive from those proteins in order to clarify and to better understand the molecular basis of pituitary adenoma pathogenesis and to discover biomarkers. Here, we describe the significant signaling pathway networks that were mined from human pituitary adenoma proteomic data with the Ingenuity pathway analysis system.

Methods

The Ingenuity pathway analysis system was used to analyze signal pathway networks and canonical pathways from protein-mapping data, comparative proteomic data, adenoma nitroproteomic data, and control nitroproteomic data. A Fisher's exact test was used to test the statistical significance with a significance level of 0.05. Statistical significant results were rationalized within the pituitary adenoma biological system with literature-based bioinformatics analyses.

Results

For the protein-mapping data, the top pathway networks were related to cancer, cell death, and lipid metabolism; the top canonical toxicity pathways included acute-phase response, oxidative-stress response, oxidative stress, and cell-cycle G2/M transition regulation. For the comparative proteomic data, top pathway networks were related to cancer, endocrine system development and function, and lipid metabolism; the top canonical toxicity pathways included mitochondrial dysfunction, oxidative phosphorylation, oxidative-stress response, and ERK/MAPK signaling. The nitroproteomic data from a pituitary adenoma were related to cancer, cell death, lipid metabolism, and reproductive system disease, and the top canonical toxicity pathways mainly related to p38 MAPK signaling and cell-cycle G2/M transition regulation. Nitroproteins from a pituitary control related to gene expression and cellular development, and no canonical toxicity pathways were identified.

Conclusions

This pathway network analysis demonstrated that mitochondrial dysfunction, oxidative stress, cell-cycle dysregulation, and the MAPK-signaling abnormality are significantly associated with a pituitary adenoma. These pathway-network data provide new insights into the molecular mechanisms of human pituitary adenoma pathogenesis, and new clues for an in-depth investigation of pituitary adenoma and biomarker discovery.

Mass spectrometric identification of in vivo nitrotyrosine sites in the human pituitary tumor proteome

The chemically stable tyrosine nitration of a protein involves the addition of a nitro group (-NO(2)) to the phenolic ring of a tyrosine residue, which may be associated with nervous system physiological and pathological processes. Identification of nitrotyrosine sites on a protein could clarify the functional significance of the modification. Due to the rarity of nitrotyrosine sites in a proteome, tandem mass spectrometry, coupled with different techniques that isolate and enrich nitrotyrosine-containing proteins from a pituitary proteome, is currently the most effective method for site identification. Commercially available nitrotyrosine polyclonal/monoclonal antibodies enable one to detect nitrotyrosine-containing proteins in a two-dimensional gel electrophoresis (2DGE) map, and to preferentially enrich nitrotyrosine-containing proteins with immunoprecipitation. Our present protocols have integrated different isolation/enrichment techniques (2DGE; Western blots; nitrotyrosine immunoaffinity precipitation) and two different tandem mass spectrometry methods (MALDI-MS/MS; ESI-MS/MS) to determine the amino acid sequence of nitrotyrosine-containing peptides that derive from nitrated proteins. Bioinformatics tools are then used to correlate nitrotyrosine sites with a functional domain/motif in order to understand the relationship between tyrosine nitration and the structural/functions of proteins.

The human pituitary nitroproteome: detection of nitrotyrosyl-proteins with two-dimensional Western blotting, and amino acid sequence determination with mass spectrometry

Nitric oxide is an important mediator that participates in reduction-oxidation (redox) mechanisms and in cellular signal transduction pathways. Two types of post-translational modifications are induced by nitric oxide: S-nitrosylation of cysteine residues and nitration of tyrosine residues. Two-dimensional gel electrophoresis-based Western blotting was used to detect, and liquid chromatography (LC)-tandem mass spectrometry (MS/MS) to determine the amino acid sequence of, several different nitrated proteins in the human pituitary. Proteins from several 2D gel spots, which corresponded to the strongly positive anti-nitrotyrosine Western blot spots, were subjected to in-gel trypsin-digestion and LC-MS/MS analysis. MS/MS, SEQUEST analysis, and de novo sequencing were used to determine the nitration site of each nitrated peptide. A total of four different nitrated peptides were characterized and were matched to four different proteins: synaptosomal-associated protein, actin, immunoglobulin alpha Fc receptor, and cGMP-dependent protein kinase 2. Those nitrotyrosyl-proteins participate in neurotransmission, cellular immunity, and cellular structure and mobility.