Ultrastructural features of apoptosis in human pituitary adenomas

Expression of BCL-2, BAX and P53 Proteins in Pituitary Adenomas an Immunohistochemical Study

Aims and Background

Although pituitary adenomas are usually benign lesions, their growth rate is highly variable and unpredictable. Apoptosis appears to be an important process in neoplastic lesions. The purpose of this study was to investigate the expression of apoptosis-related proteins including Bcl-2, bax and p53 in pituitary adenomas and its correlation with hormone function, tumor size, local control, and proliferative activity.

Study Design

The expression of Bcl-2, Bax and p53 proteins and hormonal function were determined in formalin-fixed, paraffin-embedded tissue from 41 untreated pituitary adenomas using immunohistochemistry. The patients were followed for a median of 60 months (range, 12 to 95). Patient charts were reviewed to record tumor recurrence and size. Tumor proliferative activity was assessed by immunohistochemistry using Ki-67 antibody.

Results

Of 41 pituitary adenomas, 26 (63%) were hormone-secreting and 15 (37%) non-functioning, 34 (83%) were macroadenoma and 7 (17%) microadenoma, and 15 (37%) showed local relapse. Six (14%) adenomas were of low proliferative activity, whereas the others (86%) were non-proliferative. Immunohistochemically, 31 adenomas (75%) showed bcl-2 positivity, 37 (90%) bax positivity, and 7 (17%) p53 positivity. Statistical analysis revealed that Bcl-2 protein expression significantly diminished in prolactin-secreting and non-functioning adenomas (P = 0.005 and P = 0.006, respectively), and increased in growth hormone-secreting adenomas (P = 0.003). In addition, expression of bax protein significantly decreased in recurrent tumors, in contrast to p53 protein, which showed a significant increase (P = 0.03 and P = 0.002, respectively).

Conclusions

We think that apoptosis-related proteins such as Bcl-2, Bax and p53 may be significantly related to hormone function and local control in pituitary adenomas.

Biomarkers of pituitary carcinomas

Pituitary carcinoma is a rare tumor originating from adenohypophyseal cells. Currently, diverse pathogenetic mechanisms, i.e. de novo versus malignant transformation from pituitary adenoma, remain obscure and require further investigation. During the last two decades, scientific research added new horizons not only in regards to general tumor concepts but also in next generation biomarker armamentarium that sheds light on alternate pathways in carcinogenesis. Areas covered: In this review, the impact of apoptotic and proliferative markers, angiogenesis, telomerase activity, H-ras, HIF-1, HER-2/neu, Rb gene, and microRNAs in pathogenetic mechanisms of pituitary carcinomas were revised. Expert commentary: It is becoming increasingly important for the need of standardization of new biomarkers but also for better comprehension of the diverse pathways in tumorigenesis. This can only be accomplished by tapping into the continuously expanding spectrum of new biomarkers.

Pituitary Cell Turnover: From Adult Stem Cell Recruitment through Differentiation to Death

The recent demonstration using genetic tracing that in the adult pituitary stem cells are normally recruited from the niche in the marginal zone and differentiate into secretory cells in the adenopituitary has elegantly confirmed the proposal made when the pituitary stem cell niche was first discovered 5 years ago. Some of the early controversies have also been resolved. However, many questions remain, such as which are the markers that make a pituitary stem cell truly unique and the exact mechanisms that trigger recruitment from the niche. Little is known about the processes of commitment and differentiation once a stem cell has left the niche. Moreover, the acceptance that pituitary cells are renewed by stem cells implies the existence of regulated mechanisms of cell death in differentiated cells which must themselves be explained. The demonstration of an apoptotic pathway mediated by RET/caspase 3/Pit-1/Arf/p53 in normal somatotrophs is therefore an important step towards understanding how pituitary cell number is regulated. Further work will elucidate how the rates of the three processes of cell renewal, differentiation and apoptosis are balanced in tissue homeostasis after birth, but altered in pituitary hyperplasia in response to physiological stimuli such as puberty and lactation. Thus, we can aim to understand the mechanisms underlying human disease due to insufficient (hypopituitarism) or excess (pituitary tumor) cell numbers.

The effects of X-ray irradiation on the proliferation and apoptosis of MCF-7 breast cancer cells

To investigate the effects of X-ray irradiation on the proliferation and apoptosis of MCF-7 breast cancer cells; MCF-7 breast cancer cells were irradiated with X-ray. After irradiation, morphological changes and growth inhibition rate of the irradiated cells were observed under an inverted microscope. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to assess the proliferation of the irradiated MCF-7 cells. Transmission electron microscope was used to observe the morphology and ultrastructure of the irradiated MCF-7 cells. Western blotting was used to analyze the expression level of apoptosis-related protein caspase-3. Our results showed, at 48 h after the irradiation (0 Gy and 8 Gy), cells oval in shape, cell shrinkage or swelling and partial formation of debris under inverted microscope; as well as cytoplasmic vacuolization or inspissation, increased electron density of cytoplasm, structural damage of organelles, blurred mitochondrial cristae and chromatin margination under transmission electron microscopy; the survival rate of MCF-7 cells in X-ray group was 17.3% lower than that in control group (0 Gy) (p < 0.001); while caspase-3 expression increased evidently in X-ray group compared with control group (0 Gy) (p < 0.05). In conclusion, X-ray irradiation can inhibit the proliferation of MCF-7 cells and induce apoptosis through increasing caspase-3 expression.

Biomarkers of pituitary neoplasms: a review (Part II)

Several new markers have shown a capacity to predict the clinicopathological behavior of pituitary neoplasms; these markers have shown potential to correlate with tumor subtype and size and patient age and sex. These various markers are involved in a host of cellular functions, including cell-cycle progression, cell proliferation, apoptosis, cell adhesion, and tumor vascularity. In this companion article to our first review of Ki-67 as a marker of pituitary adenomas, we present and analyze the literature regarding matrix metalloproteinases and their inhibitors (tissue inhibitor metalloproteinases), vascular endothelial growth factor, fibroblast growth factor and its receptor, apoptotic markers and p53, as well as cyclooxygenase-2, galectin-3, and pituitary tumor transforming gene. Some of these markers, such as fibroblast growth factor and fibroblast growth factor receptor and matrix metalloproteinases, show particular promise in their ability to identify pituitary tumors that behave in an aggressive manner. We suggest the need for uniform design and application of methods and standardized criteria for the interpretation of results. A uniform approach will establish clinicopathological utility of emerging markers.

Morphologic changes of prolactin-producing pituitary adenomas after short treatment with dopamine agonists

Treatment of patients with prolactin (PRL)-producing pituitary adenomas with dopamine agonists has proved successful for most cases. Dopamine agonists inhibit PRL secretion, suppress cell proliferation, and may induce apoptosis to adenoma cells. Dopamine agonists induce striking morphologic changes in the majority of treated PRL-producing adenomas. To date, these morphologic effects have been primarily described only after long-term treatment. To the best of our knowledge, no similar studies have investigated apoptotic alterations induced after short-term therapy. The purpose of this report is to describe the morphologic changes seen in PRL-producing adenomas after short-term dopamine agonist treatment. We present two cases of PRL-producing macroadenomas, both from male patients who received treatment with dopamine agonists, the first for 5 and the second for 8 days. In contrast to long-term treatment, no striking reduction of PRL immunoreactivity was noted. Slight stromal fibrosis was noted in case 1, which contained several cells all in late phase of apoptosis. In addition to typical apoptotic cells, numerous "dark" cells representing another common form of cell death were also noted. These novel findings represent characteristic features of short-term dopamine agonist treatment, which are not seen in long-term treatment.

Predictive markers of pituitary adenoma behavior

The optimal goal for pathologists is to provide important information to clinicians in order to predict tumor biology. Specific morphologic features may serve as predictive markers of tumor behavior. Macroscopic invasion of the perisellar tissues, defined as radiographic or gross operative finding, is considered a more consistent prognostic indicator. Regarding morphology, cytologic atypia is not a reliable feature. In contrast, the number of mitoses is very important for prognosis. Given that only scarce mitoses can be identified in some aggressive cases, Ki-67 represents an alternative key feature to assess tumor proliferation. In the recent World Health Organization classification, the Ki-67 labeling index (LI) represents a major prognostic indicator for pituitary adenomas. Expression of the p53 gene product is very important for tumor biology. Adenomas with more than 3% Ki-67 LI and extensive p53 immunoreactivity are classified as 'atypical adenomas'. Apoptosis and mitoses represent two adverse and asynchronous events, maintaining the optimal cell numbers. Using DNA labeling techniques, we can identify apoptotic cells. A higher apoptotic LI was found in functioning compared with nonfunctioning adenomas, in microadenomas, particularly in corticotrope adenomas, and in untreated adenomas, particularly prolactinomas. Cytogenetic analysis of chromosomes may provide important information regarding tumor development and progression. Increased chromosome 11 copies are more frequent in functioning, aneuploid pituitary adenomas. Monosomy or partial loss of chromosome 11 in adenomas with a normal or increased DNA LI indicates complex genomic abnormalities of chromosomes, other than chromosome 11. Immunohistochemical detection of somatostatin receptors is important, as their density in the cytoplasmic membrane is directly related to the effectiveness of somatostatin analogues. Therefore, morphologic assessment of the somatostatin receptor profile can predict the responsiveness and validate the effectiveness of treatment with somatostatin analogues. We can conclude that among the currently available predictive factors, tumor invasiveness is important, whereas the presence of mitoses, the Ki-67 LI, p53 expression and apoptosis are very important; DNA ploidy and fluorescent in situ hybridization analysis, although important, are difficult to apply. Finally, in the near future, immunohistochemistry for somatostatin receptors will be a very important application.

Microvascular structural entropy: a novel approach to assess angiogenesis in pituitary tumors

Entropy, a measure of the degree of disorder in a system, has recently been used in different morphologic studies to quantify regularity. Our aims were (a) to study the structural organization of the microvascular bed in prolactin (PRL)-producing adenomas and carcinomas, the most vascularized of pituitary tumors, by assessing microvascular structural entropy (MSE), and (b) to determine whether the degree of disorder of the capillary bed correlates with tumor cell proliferation as estimated by MIB-1 labeling, microvessel density (MVD), the most widely used method of quantifying blood vessel formation, and various clinicopathologic parameters (gender, age, tumor size and invasiveness). The morphometric study demonstrated statistically significant differences in MIB-1 labeling, MVD, and MSE between PRL-producing adenomas and carcinomas. Unlike MIB-1 labeling index (PRL-producing adenomas 1.5 +/- 0.27; carcinomas 15.0 +/- 4.04) and MVD (PRL-producing adenomas 2.7 +/- 0.34; carcinomas 4.2 +/- 0.72), the MSE values were significantly higher in adenomas (171.5 +/- 25.37) than in carcinomas (67.9 +/- 17.45). These results indicate that PRL-producing carcinomas have a less chaotic distribution of vessels than benign adenomas. In contrast to a lack of correlation between microvessel density and other morphometric parameters, a strong negative correlation was found between MSE and MIB-1 labeling index (r = 0.511, p = 0.003). It thus appears that regular, less chaotic microvascular geometry contributes to increased proliferative activity in PRL cell tumors. Analysis of MSE may provide an independent parameter of tumor behavior, and contributes to a better understanding of the role of microvasculature in pituitary tumor progression.

Correlation of bcl-2 and bax with apoptosis in human pituitary adenomas

Bcl-2 oncogene and Bax gene play an important role in regulating apoptosis. In the present study, the expression of bcl-2 and bax was investigated and correlated with apoptosis in a series of 81 pituitary adenomas. Bcl-2 and bax proteins were localized by immunohistochemistry and the histoscore (HSC) was assessed by multiplying the immunohistostaining grade (1 to 4) by the staining intensity grade (1 to 3). According to bcl-2/bax HSC the tumors were separated in group A when > or = 1 and group B when < 1. The apoptotic labeling index (ALI) was accessed by the in situ end-labeling (ISEL) technique. Bcl-2 protein was equally detected in functioning and nonfunctioning adenomas with statistically significant higher HSC in nonfunctioning tumors (P < 0.03). Bax protein was immunopositive in the substantial majority of adenomas with significantly higher HSC in functioning as compared to nonfunctioning adenomas (P < 0.0009). The ALI was significantly higher in functioning adenomas as compared to nonfunctioning adenomas (P < 0.04). In addition, ALI was significantly higher in group B than in group A (P < 0.004) and it was correlated with bax HSC (P < 0.004). Finally, the group B of bcl-2/bax significantly predominated in nonfunctioning tumors (P < 0.0009) and in microadenomas (P = 0.05), as compared with functioning adenomas and macroadenomas respectively. In conclusion, our findings suggest that bcl-2 and bax molecules play a role in the regulation of apoptotic mechanisms in pituitary adenomas.