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Biomedical subjects

L J Hofland

Publications and source records attributed to L J Hofland.

At least 19 recordsLinked to original sources
PubMed2002

Tissue distribution of octreotide binding receptors in normal mice and strains prone to autoimmunity.

Somatostatin has diverse functions, including immunomodulatory functions. In humans, sites of active inflammation can be visualized by the administration of 111In-DTPA(0)-octreotide, a radiolabelled somatostatin analogue. We wished to establish an animal model for preclinical evaluation of the effects of somatostatin analogues on the immune system. However, most animal models for immunological diseases are murine. This report is a preliminary study of the distribution of somatostatin receptors in mouse tissues, with emphasis on the immune system. Tissue distribution of octreotide binding receptors in normal (BALB/c) mice was determined in vivo by receptor binding of 111In-DTPA(0)-octreotide and in vitro and ex vivo by receptor autoradiography. Additionally, we investigated the tissue distribution of octreotide binding receptors in inflammatory lesions in a murine model of immune mediated disease, i.e. pre-diabetic pancreatic infiltration in the non-obese diabetic mouse strain. High specific uptake of radioactivity was seen in the thymus (range 1-1.7% ID/g) and the pituitary (1-1.6% ID/g) in all mouse strains. Specific uptake was also found in the stomach (0.1-0.7% ID/g), in the adrenal glands (0.1-0.3% ID/g) and in the pancreas (0.1-0.3% ID/g). However, we did not detect increased uptake of radiolabelled octreotide in the pancreas of pre-diabetic NOD mice. Autoradiography on tissue sections confirmed the presence of octreotide binding sites in the tissues that showed specific uptake. Moreover, by using autoradiography we could localize the cortex of the thymus and the anterior part of the pituitary as the localization of specific and high affinity, octreotide binding sites. A high, but not a receptor mediated, uptake of radioactivity was seen in the kidneys and was significantly higher in females than in males (12-19% vs 4% ID/g, respectively). Our results point to profound species differences in the tissue distribution of octreotide binding receptors. Of particular interest is the high uptake of 111In-DTPA(0)-octreotide in the cortex of the mouse thymus. This offers perspectives for the use of this animal in studies concerning the effect of somatostatin analogues on the immune system. To our knowledge, this is the first report on the tissue distribution of octreotide binding receptors in mice.

Animals↗
PubMed2001

Internalization-defective mutants of somatostatin receptor subtype 2 exert normal signaling functions in hematopoietic cells.

The regulatory peptide somatostatin (SST) acts via a family of G-protein-coupled receptors comprising five subtypes (SSTR1-5). G-protein-coupled receptors activate multiple signaling mechanisms, which variably depend on internalization and intracellular routing of activated receptors. We have recently demonstrated that hematopoietic precursors express SSTR2 and that SST is a chemoattractant for these cells. Herein, we characterize critical regions in SSTR2 involved in endocytosis and describe how ligand-induced internalization impacts on two major signaling functions of SSTR2 in hematopoietic cells, the activation of the Erk pathway and the induction of promigratory responses.

Amino Acid Sequence↗
PubMed2001

Effect of inflammatory cytokines and growth factors on tumour cell adhesion to the peritoneum.

In this experimental study, the effect of inflammatory cytokines and growth factors on tumour cell adhesion to the peritoneum was investigated. A reproducible in vitro assay was developed to study the adhesion of CC531 colon carcinoma cells to an autologous monolayer of rat mesothelial cells. Tumour cell adhesion to mesothelium pre-incubated with interleukin-1beta (IL-1beta) and epidermal growth factor (EGF) resulted in at least 60% more tumour cell adhesion at maximal stimulation (p</=0.001). Transforming growth factor-beta (TGF-beta) pre-incubation resulted in minor, though significant stimulation of cell adhesion (maximal 16%, p<0.05). The effect of IL-1beta was time- and dose-dependent. No mesothelial cell proliferation took place after pretreatment with IL-1beta, indicating that enhanced adhesion was not based on an increase in the number of mesothelial cells. Pretreatment with EGF stimulated mesothelial cell growth as measured by DNA analysis. This effect on cell growth and adhesion was dose-dependent. Additional blocking experiments with anti-IL-1beta resulted in statistically significant inhibition of IL-1beta-stimulated tumour cell adhesion (p</=0.01), demonstrating the specificity of this effect. Interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), IL-6, and insulin-like growth factor (IGF-I) pre-incubation had no effect on tumour cell adhesion. These results prove that IL-1beta and EGF are significant promoting factors in tumour cell adhesion to mesothelium in vitro and may therefore account for tumour recurrence in the peritoneum in vivo.

Animals↗
PubMed2001

Neuroendocrine tumor markers.

Tumor markers used in the diagnosis and follow-up of patients with neuroendocrine tumors are in most instances not specific for a given tumor and circulate under normal conditions in the serum, making their use as an early diagnostic tool difficult (low sensitivity). By combining hormone measurements with tissue responsiveness, demonstrations of inappropriate secretions of PTH, insulin, and gastrin during hypercalcemia, hypoglycemia, and hyperacidity, respectively, become highly sensitive and specific diagnostic tests. The application of polyclonal antibodies in RIAs of hormones, such as ACTH, insulin, and gastrin, increase the diagnostic level of hormone measurements in patients with neuroendocrine tumors. Other markers, such as chromogranin A, neuron-specific enolase, and alpha-subunit, as well as peptide receptor visualization, are of increasing importance in the diagnosis and follow-up of neuroendocrine and non-neuroendocrine tumors.

Biomarkers, Tumor↗
PubMed2001

Somatostatin modulates G-CSF-induced but not interleukin-3-induced proliferative responses in myeloid 32D cells via activation of somatostatin receptor subtype 2.

INTRODUCTION: Somatostatin, originally identified as a peptide involved in neurotransmission, functions as an inhibitor of multiple cellular responses, including hormonal secretion and proliferation. Somatostatin acts through activation of G-protein-coupled receptors of which five subtypes have been identified. We have recently established that human CD34/c-kit expressing hematopoietic progenitors and acute myeloid leukemia (AML) cells exclusively express SSTR2. A major mechanism implicated in the antiproliferative action of somatostatin involves activation of the SH2 domain-containing protein tyrosine phosphatase SHP-1. While 0.1-1 x 10(-9) M of somatostatin, or its synthetic stable analog octreotide, can inhibit G-CSF-induced proliferation of AML cells, little or no effects are seen on GM-CSF- or IL-3-induced responses. MATERIALS AND METHODS: To study the mechanisms underlying the antiproliferative responses of myeloblasts to somatostatin, clones of the IL-3-dependent murine cell line 32D that stably express SSTR2 and G-CSF receptors were generated. RESULTS: Similar to AML cells, octreotide inhibited G-CSF-induced but not IL-3-induced proliferative responses of 32D[G-CSF-R/SSTR2] cells. Somatostatin induced SHP-1 activity and inhibited G-CSF-induced, but not IL-3-induced, activation of the signal transducer and activator of transcription proteins STAT3 and STAT5. CONCLUSION: Based on these data and previous results, we propose a model in which recruitment and activation of the tyrosine phosphatase SHP-1 by SSTR2 is involved in the selective negative action of somatostatin on G-CSF-R signaling.

Animals↗
PubMed2001

In vitro secretion of FSH by cultured clinically nonfunctioning and gonadotroph pituitary adenomas is directly correlated with locally produced levels of activin A.

OBJECTIVE: Expression of mRNAs encoding activin and its antagonists inhibin and follistatin has been described in human pituitary adenomas, including clinically nonfunctioning adenomas (NFAs) and gonadotroph adenomas (Gn-omas). Since many of the NFAs and Gn-omas secrete FSH in vitro, we hypothesized that locally produced activin may stimulate secretion of FSH in these pituitary adenomas. PATIENTS AND METHODS: Pituitary adenoma tissue was obtained from 38 patients diagnosed preoperatively as having NFAs (n = 17), Gn-omas (n = 5), prolactinomas (n = 6) or growth hormone (GH)-producing adenomas (n = 10). Actual protein levels of activin, inhibin, follistatin, FSH and LH were measured in media of these 38 cultured pituitary adenomas. In addition, we investigated correlations between concentrations of these growth factors and hormones in NFAs and Gn-omas. RESULTS: Gn-omas were found to secrete significantly more activin A in their culture medium than PRL- and GH-producing adenomas (P < 0.05). Inhibin A and inhibin B protein levels in culture media were very low. A positive correlation between levels of activin A and FSH (r = 0.56, P < 0.005) was found, while no correlation between activin A and LH could be detected. Furthermore, levels of follistatin were positively correlated with activin A levels (r = 0.73, P < 0.0005). Comparison of the activin A:follistatin ratio with the measured FSH protein levels showed an even stronger relationship (r = 0.79, P < 0.0005). CONCLUSIONS: It is concluded that levels of activin A, follistatin and FSH in media of cultured nonfunctioning adenomas and gonadotroph adenomas are positively correlated. This suggests that these adenomas secrete FSH in response to the relatively high locally produced levels of activin A.

Activins↗
PubMed2001

Neuroendocrine aspects of immunolymphoproliferative diseases.

Exchange of information occurs between cells of neuroendocrine and immune systems. Neuroendocrine hormones may modulate lymphoid cell activities, including proliferation and mitogenesis, and immune cells may produce neuropeptides as well. Neuropetide Y is synthesized in B-cell leukaemia lymphoblasts, while substance P immunoreactivity has been detected in neoplastic haematological samples of different types of leukaemias. The presence of receptors for neuropeptides on different animal and human lymphoid cell lines, as well as in several types of animal and human lymphoproliferative diseases has been demonstrated. Species variability in receptor distribution has been shown as well. Receptor expression in immune cells may be regulated by changes in microenvironmental conditions, it may also be related to the activation and/ or proliferation state of cells. Vasoactive intestinal peptides receptors have been detected in myeloma cells, while somatostatin receptors have been first detected in vitro on resting lymphocytes and cells of the monocyte/macrophage lineage, and later on human activated lymphocytes and on lymphoblastic leukaemia cells. Somatostatin receptors have been found in biopsies from patients with malignant lymphomas. Tumor localization in non-Hodgkin lymphomas and Hodgkin's disease can be visualized by in vivo somatostatin receptor scintigraphy, contributing to establish the diagnosis and the stage of the disease. Recently. somatostatin receptors have been in vivo and in vitro detected in human thymic tumors. Although treatment of lymphoproliferative diseases with somatostatin analogs is a little explored field, partial remission was found in patients with low-grade non-Hodgkin lymphoma and cutaneous T-cell lymphoma, and a successful treatment with octreotide has been reported in patients with thymoma. Specific somatostatin receptors present in progenitors of immune cells are not expressed in the mature phenotype, while they can be detected in transformed cell lines. The possibility that this phenomenon is caused by oncogene expression cannot be ruled out. Moreover, preliminary data showed a developmental expression of somatostatin receptors in lymphoid cells, suggesting a potential role for neuropeptide receptors as differentiation markers. Although controlled studies are warranted to investigate the efficacy of the currently available analogs, somatostatinergic compounds may be of interest in the treatment of lymphoproliferative malignancies. A promising approach in refractory patients with somatostatin receptor positive malignant lymphomas may be radionuclide-targeted and cytotoxic analog therapy. These concepts increase the possibility of a wider antitumor treatment with ligands for neuroepeptide receptors than in established 'classic' neuroendocrine tumors.

Cell Differentiation↗
PubMed2001

Somatostatin receptor subtype expression in human tumors.

The presence of functional SSR in tumors has several clinical implications which include the possibility a) to control hormonal hypersecretion and related symptomatology by treatment with SS-analogs, b) to detect SSR positive tumors and their metastases by in vivo SSR scintigraphy, and c) to carry out SSR-targeted radiotherapy using radiolabeled SS-analogs. The majority of SSR positive tumors show a differential expression of somatostatin receptor subtypes, sst2 receptors being the most frequently expressed SSR subtype. The predominant expression of sst2 receptors forms the basis for the successful application of sst2 preferring agonists in the treatment of patients with GH-secreting pituitary adenomas, as well as in patients with carcinoid or islet cell tumors. Sst2 and sst5 receptors appear to be differentially involved in the regulation of normal and tumoral pituitary hormone secretion. Additionally, sst2 receptors are involved in the receptor-mediated internalisation of sst2 preferring radiolabeled SS-analogs. The predominant expression of sst2 receptors in neuroendocrine tumors probably determines the successful application of radio-labeled SS-analogs for the detection of primary tumors and their metastases by SSR scintigraphy. In conclusion, the efficacy of treatment with SS-analogs, the visualisation of SSR-positive tumors, as well as the possibility to carry out SSR-targeted radiotherapy, may very well depend upon the density and subtype of SSR that is expressed by the tumors. Therefore, the characterisation of SSR subtypes in human tumors may have important clinical consequences.

Adenoma↗
PubMed2001

Blockade of the growth hormone (GH) receptor unmasks rapid GH-releasing peptide-6-mediated tissue-specific insulin resistance.

The roles of GH and its receptor (GHR) in metabolic control are not yet fully understood. We studied the roles of GH and the GHR using the GHR antagonist pegvisomant for metabolic control of healthy nonobese men in fasting and nonfasting conditions. Ten healthy subjects were enrolled in a double blind, placebo-controlled study on the effects of pegvisomant on GHRH and GH-releasing peptide-6 (GHRP-6)-induced GH secretion before and after 3 days of fasting and under nonfasting conditions (n = 5). Under the condition of GHR blockade by pegvisomant in the nonfasting state, GHRP-6 (1 microg/kg) caused a increase in serum insulin (10.3 +/- 2.1 vs. 81.3 +/- 25.4 mU/L; P < 0.001) and glucose (4.2 +/- 0.3 vs. 6.0 +/- 0.6 mmol/L; P < 0.05) concentrations. In this group, a rapid decrease in serum free fatty acids levels was also observed. These changes were not observed under GHR blockade during fasting or in the absence of pegvisomant. We conclude that although these results were obtained from an acute study, and long-term administration of pegvisomant could render different results, blockade of the GHR in the nonfasting state induces tissue-specific changes in insulin sensitivity, resulting in an increase in glucose and insulin levels (indicating insulin resistance of liver/muscle), but probably also in an increase in lipogenesis (indicating normal insulin sensitivity of adipose tissue). These GHRP-6-mediated changes indicate that low GH bioactivity on the tissue level can induce changes in metabolic control, which are characterized by an increase in fat mass and a decrease in lean body mass. As a mechanism of these GHRP-6-mediated metabolic changes in the nonfasting state, direct nonpituitary-mediated GHRP-6 effects on the gastroentero-hepatic axis seem probable.

Adult↗
PubMed2001

Systemic ghrelin levels in subjects with growth hormone deficiency are not modified by one year of growth hormone replacement therapy.

OBJECTIVE: Ghrelin stimulates growth hormone (GH) secretion both in vivo and in vitro. Ghrelin is mainly produced in and released from the stomach but it is probably also produced in the hypothalamic arcuate nucleus. Whether pituitary GH release is under the control of ghrelin from the stomach and/or from the arcuate nucleus is not known. Moreover, no data on the feedback of GH on systemic ghrelin concentrations are available. It has recently been suggested that ghrelin may induce obesity. DESIGN: In this study, we addressed the following two questions: a) are circulating ghrelin levels increased in human GH deficiency (GHD), and b) does GH treatment modify ghrelin levels in human GHD? METHODS: The study group consisted of 23 patients with GHD. Eighteen had developed adult-onset GHD and five had developed GHD in their childhood (childhood-onset GHD). Ghrelin was measured with a commercially available radioimmunoassay. All measurements were performed twice, first at baseline, before the start of GH replacement therapy, and then again after one year of therapy. GH doses were adjusted every 3 months, targeting serum total IGF-I levels within the normal gender- and age-related reference values for the healthy population. Maintenance doses were continued once the target serum total IGF-I levels were reached. RESULTS: The sum of skinfolds and body water increased significantly, body fat mass and percentage body fat decreased significantly and body mass index and waist-hip ratio were not significantly changed by one year of GH replacement therapy. Before the start of GH replacement therapy, mean value and range for fasting ghrelin in the studied GHD subjects tended to be lower in comparison with healthy subjects in the control group although the difference did not reach significance (GHD ghrelin mean 67.8 pmol/l, range 37.6-116.3 pmol/l; control mean 83.8 pmol/l, range 35.4-132 pmol/l; P=0.11). One year of GH replacement therapy did not modify circulating ghrelin levels (ghrelin before GH therapy: 67.8 pmol/l, range 37.6-116.3 pmol/l; after GH therapy: 65.3 pmol/l, range 35.8-112.6; P=0.56). CONCLUSIONS: We did not observe elevated ghrelin levels in adult GHD subjects and GH replacement therapy did not modify circulating ghrelin levels, despite significant decreases in body fat mass and percentage body fat. It is conceivable that the lack of ghrelin modifications after long-term GH therapy was due to the reduction of adiposity and insulin on one hand, and increased GH secretion on the other. However, it is still possible that systemic ghrelin is involved in the development of obesity, both in normal and GHD subjects.

Adipose Tissue↗
PubMed2000

GIP-dependent adrenal Cushing's syndrome with incomplete suppression of ACTH.

ACTH-independent Cushing's syndrome may be due to the development of ectopic hormone receptors in adrenal tissue. Thus, in food-dependent Cushing's syndrome the adrenals aberrantly express receptors for gastric inhibitory polypeptide (GIP). We present the case of a 60-year-old woman with food-dependent Cushing's syndrome whose cortisol levels increased after stimulation with CRH. In this patient with Cushing's syndrome the finding of low basal plasma cortisol levels in the late night and early morning as well as a paradoxical rise of plasma cortisol during a 7-h infusion with dexamethasone (carried out without any restriction in food intake), suggested that cortisol production was stimulated at times of food intake. Hourly measurements of plasma cortisol for 48 h revealed prominent meal-related peaks. A plasma cortisol response, elicited by oral glucose administration, could be prevented by octreotide. Plasma ACTH was low or undetectable. CRH administration was followed by a ACTH response from 3 to 16 ng/l and a plasma cortisol response from 230 to 680 nmol/l. Octreotide treatment for nearly five months induced a partial clinical and biochemical remission. Total bilateral adrenalectomy was performed. The left adrenal was grossly enlarged (7 x 5.5 x 4 cm) and the right adrenal was slightly enlarged (6 x 4 x 1.8 cm). Microscopy revealed bilateral nodular hyperplasia. Cell suspensions of adrenal tissue from the patient did respond in a dose-dependent fashion to stimulation with GIP and were very sensitive to stimulation with synthetic ACTH1-24. However, CRH had no significant effect on cortisol production in vitro. Using RT-PCR amplification and cDNA hybridization, GIP receptor was found to be overexpressed in the left and right adrenal tissues from this patient as compared to adrenal tissues from a normal individual or from non GIP-dependent adrenal Cushing's syndrome. There was no evidence of presence of adrenal CRH receptors. Thus, in this patient with food-dependent Cushing's syndrome, the CRH-induced plasma ACTH and cortisol response is probably mediated by an incomplete suppression of the HPA axis as a result of the intermittent food-dependent nature of Cushing's syndrome.

Adrenal Cortex↗
PubMed2000

Age-related decrease of somatostatin receptor number in the normal human thymus.

The thymus exhibits a pattern of aging oriented toward a physiological involution. The structural changes start with a steady decrease of thymocytes, whereas no major variations occur in the number of thymic epithelial cells (TEC). The data concerning the role of hormones and neuropeptides in thymic involution are equivocal. We recently demonstrated the presence of somatostatin (SS) and three different SS receptor (SSR) subtypes in the human thymus. TEC selectively expressed SSR subtype 1 (sst(1)) and sst(2A). In the present study we investigated whether SSR number is age related in the thymus. Binding of the sst(2)-preferring ligand (125)I-Tyr(3)-octreotide was evaluated in a large series of normal human thymuses of different age by SSR autoradiography and ligand binding on tissue homogenates. The score at autoradiography and the number of SSR at membrane homogenate binding (B(max)) were inversely correlated with the thymus age (r = -0.84, P < 0.001; r = -0.82, P < 0.001, respectively). The autoradiographic score was positively correlated with the B(max) values (r = 0.74, P < 0.001). Because the TEC number in the age range considered remains unchanged, the decrease of octreotide binding sites might be due to a reduction of sst(2A) receptor number on TEC. The age-related expression of a receptor involved mainly in controlling secretive processes is in line with the evidence that the major changes occurring in TEC with aging are related to their capabilities in producing thymic hormones. In conclusion, SS and SSR might play a role in the involution of the human thymus. These findings underline the links between the neuroendocrine and immune systems and support the concept that neuropeptides participate in development of cellular immunity in humans.

Adolescent↗
PubMed2000

Somatostatin receptor subtypes in human thymoma and inhibition of cell proliferation by octreotide in vitro.

Somatostatin (SS) and SS receptor (SSR) subtypes, code-named sst1-5, are heterogeneously expressed in the normal human thymus. This suggests their involvement in controlling the immune and/or neuroendocrine functions in this organ. Moreover, recently a high in vivo uptake of [111In-DTPA-D-Phe1]octreotide has been reported in patients bearing thymoma. The present study characterizes in vivo and in vitro, functional SS-binding sites in a human thymoma. A high uptake of [111In-DTPA-D-Phe1]octreotide was observed in the chest of a patient with myasthenia gravis due to a cortical thymoma. Specific binding of [125I-Tyr11] SS-14 was found on a membrane preparation of the surgically removed thymoma. Scatchard analysis showed high affinity binding sites (Kd, 47.5 +/- 2.5 pmol/L) with low maximum binding capacity (23.5 +/- 2.5 fmol/mg membrane protein). RT-PCR analysis showed the presence of sst1, sst2A, and a predominant sst3 messenger RNA (mRNA) expression in the tumor tissue. Primary cultured tumor cells expressed sst3 mRNA only. In contrast to the normal thymus, SS mRNA was not expressed. By immunohistochemistry, the tumor cells highly expressed sst3 receptors, weakly expressed sst1 receptors, and showed no immunostaining for sst2A receptors. sst2A immunoreactivity was found in the stromal compartment of the tumor, particularly on the endothelium of small intratumoral blood vessels. In primary cultured tumor cells, both SS and octreotide (10 nmol/L) significantly inhibited [3H]thymidine incorporation by 40.6% and 43.2%, respectively. The following conclusions were reached. 1) As this tumor displayed a high immunoreactivity for sst3 and the cultured tumor cells expressed the sst3 mRNA only, this SSR may be the subtype involved in the inhibition of epithelial tumor cell proliferation by octreotide in vitro. 2) A loss of endogenous SS production in this thymoma might be implicated in the uncontrolled cell growth. 3) In this case, the sst3 may play a role in determining the uptake of [111In-DTPA-D-Phe1]octreotide by in vivo SS receptor scintigraphy.

Antineoplastic Agents, Hormonal↗
PubMed2000

Long-term treatment with the dopamine agonist quinagolide of patients with clinically non-functioning pituitary adenoma.

OBJECTIVE: This study was performed to evaluate the effect of prolonged treatment with the dopamine agonist quinagolide on serum gonadotropin and alpha-subunit concentrations and tumor volume in patients with clinically non-functioning pituitary adenomas (CNPA). DESIGN: Ten patients with CNPA were treated with quinagolide (0.3 mg daily). The median duration of treatment was 57 months (range 36-93 months). Blood samples for measurement of serum gonadotropin and alpha-subunit concentrations were drawn before treatment, after 5 days, and at each outpatient visit. Computerized tomography or magnetic resonance imaging of the pituitary region and Goldmann perimetry were done before and at regular intervals during treatment. RESULTS: A significant decrease of serum FSH, LH or alpha-subunit concentrations was found in nine patients. The levels remained low during the entire treatment period. In two out of three patients with pre-existing visual field defects a slight improvement was shown during the first months of treatment, but eventually deterioration occurred in all three patients. A fourth patient developed unilateral ophthalmoplegia during treatment. During the first year tumor volume decreased in three patients, but in two of them regrowth occurred after a few months. In six patients progressive tumor growth occurred despite sustained suppression of gonadotropin or alpha-subunit levels. CONCLUSIONS: Long-term treatment of patients with CNPA with high doses of the dopamine agonist quinagolide could not prevent progressive increase in tumor size in most patients. It remains unproven whether quinagolide retards CNPA growth. Additional studies are needed to investigate whether subgroups of patients, e.g. those with positive dopamine receptor scintigraphy or those with marked hypersecretion of intact gonadotropins or subunits, will respond more favorably to treatment with dopamine agonists.

Adenoma↗