Hypothalamic mediation of reduced GH secretion in diabetic rats: evidence for reduced cholinergic inhibition of somatostatin release

Translation Animal Models of Diabetic Kidney Disease: Biochemical and Histological Phenotypes, Advantages and Limitations

Animal models play a crucial role in studying the pathogenesis of diseases, developing new drugs, identifying disease risk markers, and improving means of prevention and treatment. However, modeling diabetic kidney disease (DKD) has posed a challenge for scientists. Although numerous models have been successfully developed, none of them can encompass all the key characteristics of human DKD. It is essential to choose the appropriate model according to the research needs, as different models develop different phenotypes and have their limitations. This paper provides a comprehensive overview of biochemical and histological phenotypes, modeling mechanisms, advantages and limitations of DKD animal models, in order to update relevant model information and provide insights and references for generating or selecting the appropriate animal models to fit different experimental needs.

Ghrelin improves growth hormone responses to growth hormone-releasing hormone in a streptozotocin-diabetic model of delayed onset

GH secretion is markedly altered in diabetes mellitus (DM) in both rats and humans, albeit in opposite directions. In the rat, diabetes suppresses pulsatile GH secretion, especially high amplitude pulses, and decreases GH responses to secretagogue, depending inversely on severity of metabolic alteration. In the present study, we wanted to address the GH responses to GHRH and low doses of ghrelin in a streptozotocin (STZ) model of diabetes characterized by the delayed onset of the metabolic alterations. We have shown that the administration of high doses of STZ (90 mg/kg in 0.01 M solution of chloride-sodium, ip) to five-day-old pups (n5-STZ) can induce the appearance of a characteristic diabetic syndrome in adult age, the diabetic triad, with elevated plasma glucose levels: polyuria, polydipsia, hyperphagia, and reduced body weight gain. At the age of 3 months, in these n5-STZ male and female rats the GH responses to GHRH (1 microg/kg) and GHRH combined with ghrelin (1+3 microg/kg) had diminished both in punctual times and in the area under the curve (AUC). However, the combined administration of GHRH and ghrelin, being the more potent stimulus, elicited a synergistic GH response. Thus, male and female rats with delayed onset diabetes displayed an altered GH response to GHRH, although the combined administration of GHRH and ghrelin was able to restore the GH secretion with a synergistic effect.

Regulation of neoplastic angiogenesis

The progressive growth of neoplasms and the production of metastasis depend on the development of adequate vasculature, i.e., angiogenesis. The extent of angiogenesis is determined by the balance between positive- and negative-regulating molecules that are released by tumor and host cells in the microenvironment. The growth of many neoplasms is associated with the absence of the endogenous inhibitor of angiogenesis, interferon beta (IFN beta). A survey of multiple mouse and human tumors shows a lack of IFN beta associated with extensive angiogenesis. Therapy with IFN alpha or beta either by subcutaneous injection of the protein or by introduction of viral vectors that contain the IFN beta gene inhibit angiogenesis and, hence, progressive tumor growth.

Mitogen-activated protein kinase mediates epidermal growth factor-induced morphogenesis in pituitary GH3 cells

Epidermal growth factor (EGF) causes pituitary GH3 cells to change from their normal predominantly rounded morphology to much more elongated cells with extensive filopodia, and this effect is accompanied by a parallel increase in cell volume. In view of this, and because EGF receptor expression is increased in some pituitary tumours, we examined the mechanism of this EGF-induced morphological effect as it may play a role in tumour invasiveness. The effect of treatment of the cells with EGF (1 nm, 4 days) was determined visually (expressed as percent non round cells) and by measuring the cell volume by Coulter Counter analysis. EGF treatment caused the cells to change their morphology with percent non round cells increasing from 37% in control cells to 74% in EGF-treated cultures; this was accompanied by a parallel increase in cell volume. Treatment of the cells with EGF in the presence of the MEK1 inhibitor (PD98059) completely blocked the EGF-induced morphological changes, showing that activation of the mitogen-activated protein kinase (MAPK) pathway is necessary to mediate this effect. Transfection of the cells with a constitutively activated mutant of MEK1 produced a similar morphological change to that produced by EGF treatment, with the proportion of non round cells increasing to 62% with a parallel increase in cell volume compared to cells transfected with the empty vector, demonstrating that direct activation of MAPK pathway is sufficient to mediate the observed morphological effects. The effects produced by activated MEK1 transfection could be blocked by PD98059. EGF had opposing effects on prolactin and growth hormone (GH) secretion by the cells, increasing prolactin release and inhibiting GH release. Transfection of the cells with activated MEK1 produced similar effects on hormone release as EGF treatment. In conclusion, the morphological effects of EGF on GH3 cells are mediated by activation of the MAPK pathway as blockade of this pathway abolished the observed effect, and direct activation of this pathway by transfection with an activated mutant of MEK1 was able to duplicate these effects. This mechanism may contribute to the growth and possibly local invasiveness of some pituitary tumours that express the EGF receptor.

Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human

During the last decade, the GH axis has become the compelling focus of remarkably active and broad-ranging basic and clinical research. Molecular and genetic models, the discovery of human GHRH and its receptor, the cloning of the GHRP receptor, and the clinical availability of recombinant GH and IGF-I have allowed surprisingly rapid advances in our knowledge of the neuroregulation of the GH-IGF-I axis in many pathophysiological contexts. The complexity of the GHRH/somatostatin-GH-IGF-I axis thus commends itself to more formalized modeling (154, 155), since the multivalent feedback-control activities are difficult to assimilate fully on an intuitive scale. Understanding the dynamic neuroendocrine mechanisms that direct the pulsatile secretion of this fundamental growth-promoting and metabolic hormone remains a critical goal, the realization of which is challenged by the exponentially accumulating matrix of experimental and clinical data in this arena. To the above end, we review here the pathophysiology of the GHRH somatostatin-GH-IGF-I feedback axis consisting of corresponding key neurotransmitters, neuromodulators, and metabolic effectors, and their cloned receptors and signaling pathways. We propose that this system is best viewed as a multivalent feedback network that is exquisitely sensitive to an array of neuroregulators and environmental stressors and genetic restraints. Feedback and feedforward mechanisms acting within the intact somatotropic axis mediate homeostatic control throughout the human lifetime and are disrupted in disease. Novel effectors of the GH axis, such as GHRPs, also offer promise as investigative probes and possible therapeutic agents. Further understanding of the mechanisms of GH neuroregulation will likely allow development of progressively more specific molecular and clinical tools for the diagnosis and treatment of various conditions in which GH secretion is regulated abnormally. Thus, we predict that unexpected and enriching insights in the domain of the neuroendocrine pathophysiology of the GH axis are likely be achieved in the succeeding decades of basic and clinical research.

Association of tumor angiogenesis with bone marrow micrometastases in breast cancer patients

BACKGROUND AND PURPOSE

The microscopic detection of tumor cells (micrometastases) in bone marrow and the extent of blood vessel formation (angiogenesis) in primary tumor specimens are recognized as independent prognostic markers in patients with breast cancer. Since micrometastases occur as a consequence of interaction between the neoplastic cells and the tumor neovasculature, we have examined the relationship between these markers to determine whether the degree of angiogenesis is related to the presence of micrometastases.

METHODS

Micrometastases were identified in bone marrow aspirates collected from multiple sites in 214 breast cancer patients prior to surgery (mastectomy or lumpectomy). Tumor cells were detected through an examination of epithelial membrane antigen expression and an analysis of cell morphology. Tumor vascularity was graded semiquantitatively or quantitatively (Chalkley point count) after immunohistochemical staining of the CD31 antigen expressed by the endothelial cells. The reproducibility and accuracy of the vascular grading were validated by use of kappa statistics. Associations between micrometastases and clinicopathologic characteristics, including angiogenesis, were examined using chi-squared and logistic regression techniques. All tests of statistical significance were two-sided.

RESULTS

Of the 214 patients, 42 (20%) were positive for bone marrow micrometastases and 75 (35%) had tumors of high vascular grade. There was 86% agreement between vascular grades assessed twice for 35 tumors (kappa statistic = 0.66); for 22 evaluated tumors, there was absolute concordance between vascular grade and Chalkley point count. There were significant positive associations between tumor angiogenesis and micrometastasis (P = .01), tumor grade (P = .003), and estrogen receptor expression (P = .007); however, no significant associations were observed with tumor size (P = .9), lymph node status (P = .33), vascular invasion (peritumoral blood or lymph vessels) (P = .9), menopausal status (P = .17), or age (P = .12). Adjusting for confounding factors, multivariate analysis showed that only tumor angiogenesis (odds ratio = 2.7; P = .016) and vascular invasion (odds ratio = 2.7; P = .012) were significant determinants for the presence of micrometastases.

CONCLUSIONS

This study suggests that an assessment of tumor angiogenesis and vascular invasion gives a reliable indication of the likelihood of the presence of bone marrow micrometastases in patients with breast cancer and that both processes contribute to metastases.

Somatostatin: the neuroendocrine story

Since its original discovery as the neuroendocrine hormone responsible for inhibiting growth hormone (GH) secretion, our understanding of the functions of somatostatin [or somatotrophin release inhibitory hormone (SRIH)], both in the periphery and the CNS, has grown enormously. With the cloning of five SRIH receptors, much interest has centred recently on the potential use of SRIH analogues in the treatment of clinical conditions ranging from human cancers to Alzheimer's and Parkinson's diseases. There is a growing recognition that the physiological functions of GH also need to be extended beyond its role in growth control, e.g. to a role in the maintenance of normal immune, cardiovascular and reproductive functions. Here, Glenda Gillies addresses the importance of somatostatinergic systems in regulating the sexually dimorphic patterns of GH secretion as well as their influence on other endocrine hormones. She also considers the neurotransmitter/neuromodulator actions of SRIH within the hypothalamus, where it is involved in the neural control and integration of many aspects of endocrine function, as well as its potential role in the maturation of the hypothalamus during the critical perinatal period.