Effects of octreotide exposure during pregnancy in acromegaly.

BACKGROUND: Only six women who were treated with somatostatin analogues (SSAs) throughout their pregnancies have been described so far. The influence of SSAs on the course of pregnancy and newborn outcomes remains largely unknown. Many aspects of SSAs pharmacokinetics in mother and foetus have not yet been defined. METHODS AND FINDINGS: We report a case study on the effects of octreotide on uterine artery blood flow, octreotide concentrations in biological fluids of mother and newborn, and somatostatin (SST) receptor expression and binding at the level of the maternal-foetal barrier tissues in an acromegalic woman treated with short-acting octreotide throughout her pregnancy. An acute decrease in uterine artery blood flow was observed after octreotide injections, without affecting the pregnancy course, delivery, or foetal development. Octreotide concentrations were high in maternal serum and colostrum and lower in umbilical cord serum, amniotic fluid, and newborn serum. All SST receptor subtypes can be expressed in placental tissue but their binding profile was weak both in the placenta and umbilical cord. The child was healthy and developed normally up to age 6 from an anthropometric, metabolic, and endocrine point of view. We reviewed all published reports on pregnancy SSA exposure and outcomes were compared to a time-matched group of acromegalic women not exposed to SSA. No significant effect on the mother or foetus was observed. CONCLUSIONS: Short-acting octreotide appears not to affect the function of the maternal-foetal barrier or foetal development, except for the occurrence of acute, reversible, and clinically irrelevant haemodynamic changes. These data support the feasibility and safety of treatment with short-acting octreotide in acromegalic women during pregnancy and excludes major matters of concern about the effects of this medication on pregnancy itself and its outcome.

Moderate decline in select synaptic markers in the prefrontal cortex (BA9) of patients with Alzheimer's disease at various cognitive stages.

Synaptic loss, plaques and neurofibrillary tangles are viewed as hallmarks of Alzheimer's disease (AD). This study investigated synaptic markers in neocortical Brodmann area 9 (BA9) samples from 171 subjects with and without AD at different levels of cognitive impairment. The expression levels of vesicular glutamate transporters (VGLUT1&2), glutamate uptake site (EAAT2), post-synaptic density protein of 95 kD (PSD95), vesicular GABA/glycine transporter (VIAAT), somatostatin (som), synaptophysin and choline acetyl transferase (ChAT) were evaluated. VGLUT2 and EAAT2 were unaffected by dementia. The VGLUT1, PSD95, VIAAT, som, ChAT and synaptophysin expression levels significantly decreased as dementia progressed. The maximal decrease varied between 12% (synaptophysin) and 42% (som). VGLUT1 was more strongly correlated with dementia than all of the other markers (polyserial correlation = -0.41). Principal component analysis using these markers was unable to differentiate the CDR groups from one another. Therefore, the status of the major synaptic markers in BA9 does not seem to be linked to the cognitive status of AD patients. The findings of this study suggest that the loss of synaptic markers in BA9 is a late event that is only weakly related to AD dementia.

Somatostatin receptor type 2 undergoes plastic changes in the human epileptic dentate gyrus.

Temporal lobe epilepsy (TLE) is characterized by hippocampal sclerosis together with profound losses and phenotypic changes of different classes of interneurons, including those expressing somatostatin (SRIF). To understand the functional significance of the plasticity of SRIF transmission in TLE, unraveling the status of SRIF receptors is, however, a prerequisite. To address this issue, we characterized expression and distribution of the major SRIF receptor, the sst2 subtype, in hippocampal tissue resected in patients with TLE using complementary neuroanatomic approaches. In patients with hippocampal sclerosis, the number of cells expressing sst2 receptor mRNA as well as sst2 receptor-binding sites and immunoreactivity decreased significantly in the CA1-3, reflecting neuronal loss. By contrast, in the dentate gyrus, sst2 receptor mRNA expression was strongly increased in the granule cell layer, and sst2 receptor-binding sites and immunoreactivity was preserved in the inner but decreased significantly in the outer molecular layer. In this latter region, pronounced changes in SRIF terminal fields were observed. Decreased receptor density in the distal dendrites of granule cells is likely to reflect downregulation of sst2 receptors in response to physiopathologic release of SRIF. Because sst2 receptors have anticonvulsant and antiepileptogenic properties, this phenomenon may contribute to the etiology of TLE seizures.

Aging, but not tau pathology, impacts olfactory performances and somatostatin systems in THY-Tau22 mice.

Somatostatin (SOM) cortical levels decline in Alzheimer's disease (AD) in correlation with cognitive impairment severity, the latter being closely related to the presence of neurofibrillary tangles. Impaired olfaction is another hallmark of AD tightly related to tau pathology in the olfactory pathways. Recent studies showed that SOM modulates olfactory processing, suggesting that alterations in SOM levels participate to olfactory deficits in AD. Herein, we first observed that human olfactory peduncle and cortex are enriched in SOM cells and fibers, in aged postmortem brains. Then, the possible link between SOM alterations and olfactory deficits was evaluated by exploring the impact of age and tau hyperphosphorylation on olfactory SOM networks and behavioral performances in THY-Tau22 mice, a tauopathy transgenic model. Distinct molecular repertoires of SOM peptide and receptors were associated to sensory or cortical olfactory processing structures. Aging mainly affected SOM neurotransmission in piriform and entorhinal cortex in wild-type mice, although olfactory performances decreased. However, no further olfactory impairment was evidenced in THY-Tau22 mice until 12 months although tau pathology early affected olfactory cortical structures. Thus, tau hyperphosphorylation per se has a limited impact on olfactory performances in THY-Tau22 mice.

Somatostatin binds to murine macrophages through two distinct subsets of receptors.

Somatostatin (SRIF) exerts anti-inflammatory effects, in part by deactivating monocytes/macrophages. Thus, the objective of this study was to characterize specific receptors for SRIF on these cells. Macrophages isolated from mouse peritoneal cells bound [125I]Tyr(0), D-Trp(8) SRIF(14) specifically. Scatchard analysis of saturation binding data revealed two classes of binding sites with an affinity of 0.44+/-0.13 and 2.58+/-0.56 nM, respectively. By sensitive and specific RT-PCR, the mRNAs for the five SRIF receptors (SSTR1 to SSTR5) could be detected. Evidence for the involvement of SSTR1 and SSTR2 in the binding of SRIF to the high and low affinity sites, respectively, was obtained by the demonstration that (1) only SSTR1 and SSTR2 subtype-specific agonists were active in competing for [125I]Tyr(0), D-Trp(8) SRIF(14) binding to high and low affinity sites, respectively, and (2) [125I]Tyr(0), D-Trp(8) SRIF(14) bound to high but not low affinity sites on macrophages isolated from SSTR2 knock-out mice. In conclusion, we have identified and characterized two different SRIF receptor subtypes in murine macrophages.

Characterisation of [125I]-Tyr0DTrp8-somatostatin binding in sst1- to sst4- and SRIF-gene-invalidated mouse brain.

Five somatostatin receptors (sst) have been cloned and mRNAs for the first four (sst1-4) are expressed in many brain regions. In the present work, we compared the distribution of the non-selective ligand [125I]-Tyr0-DTrp8-SRIF14 by autoradiography in 24 brain regions and pituitary in wild type, sst1- to sst4- or SRIF-gene invalidated (KO) mice. [125I]-Tyr0-DTrp8-SRIF14 binding was not significantly modified in sst1 KO mouse brain with the noticeable exception of the substantia nigra and only moderately decreased in pituitary. For sst2 KO mice, a general decrease (>75%) was observed in most regions, with the noticeable exception of the olfactory bulb and CA1 field of the hippocampus. SST3 KO brain displayed a decrease in binding in the external plexiform layer of the olfactory bulb only (-54%). For sst4 KO mice, [125I]-Tyr0-DTrp8-SRIF14 binding levels in the external plexiform (-35%) and glomerular (-39%) layers of the olfactory bulb as well as the hippocampus CA1 field (-68%) were significantly decreased. In SRIF KO mice, a significant increase in binding levels was observed in olfactory bulb, anterior olfactory nucleus, frontal cortex upper layers, lateral septum, CA1 field, zona incerta and lateral hypothalamus, substantia nigra, periaqueductal grey and parabrachial nucleus. Competition with selective ligands (CH275, octreotide or L-779,976, L-796,778, L-803,087, and octreotide or L-817,778, for sst1-5 receptors, respectively) was in accordance with these findings. Moreover, octreotide was still able to compete on residual [125I]-Tyr0-DTrp8-SRIF14 binding sites in sst2 KO pituitary. It is concluded that most [125I]-Tyr0-DTrp8-SRIF14 binding sites in mouse brain and pituitary belong to the sst2 subtype but for the olfactory bulb (sst3 and sst4 receptors), the CA1 of the hippocampus (sst4 receptors) and the pituitary (sst5 and sst1 receptors) in which other subtypes are also expressed. The overall increase in [125I]-Tyr0-DTrp8-SRIF14 binding in SRIF KO mice indicates that SRIF receptors, mostly from the sst2 subtype, are regulated by the endogenous ligand(s).

Actions of Agonists and Antagonists of the ghrelin/GHS-R Pathway on GH Secretion, Appetite, and cFos Activity.

The stimulatory effects of ghrelin, a 28-AA acylated peptide originally isolated from stomach, on growth hormone (GH) secretion and feeding are exclusively mediated through the growth hormone secretagogue 1a receptor (GHS-R1a), the only ghrelin receptor described so far. Several GHS-R1a agonists and antagonists have been developed to treat metabolic or nutritional disorders but their mechanisms of action in the central nervous system remain poorly understood. In the present study, we compared the activity of BIM-28163, a GHS-R1a antagonist, and of several agonists, including native ghrelin and the potent synthetic agonist, BIM-28131, to modulate food intake, GH secretion, and cFos activity in arcuate nucleus (ArcN), nucleus tractus solitarius (NTS), and area postrema (AP) in wild-type and NPY-GFP mice. BIM-28131 was as effective as ghrelin in stimulating GH secretion, but more active than ghrelin in inducing feeding. It stimulated cFos activity similarly to ghrelin in the NTS and AP but was more powerful in the ArcN, suggesting that the super-agonist activity of BIM-28131 is mostly mediated in the ArcN. BIM-28163 antagonized ghrelin-induced GH secretion but not ghrelin-induced food consumption and cFos activation, rather it stimulated food intake and cFos activity without affecting GH secretion. The level of cFos activation was dependent on the region considered: BIM-28163 was as active as ghrelin in the NTS, but less active in the ArcN and AP. All compounds also induced cFos immunoreactivity in ArcN NPY neurons but BIM-28131 was the most active. In conclusion, these data demonstrate that two peptide analogs of ghrelin, BIM-28163, and BIM-28131, are powerful stimulators of appetite in mice, acting through pathways and key brain regions involved in the control of appetite that are only partially superimposable from those activated by ghrelin. A better understanding of the molecular pathways activated by these compounds could be useful in devising future therapeutic applications, such as for cachexia and anorexia.

A natural variant of obestatin, Q90L, inhibits ghrelin's action on food intake and GH secretion and targets NPY and GHRH neurons in mice.

BACKGROUND: Ghrelin and obestatin are two gut-derived peptides originating from the same ghrelin/obestatin prepropeptide gene (GHRL). While ghrelin stimulates growth hormone (GH) secretion and food intake and inhibits γ-aminobutyric-acid synaptic transmission onto GHRH (Growth Hormone Releasing Hormone) neurons, obestatin blocks these effects. In Humans, GHRL gene polymorphisms have been associated with pathologies linked to an unbalanced energy homeostasis. We hypothesized that one polymorphism located in the obestatin sequence (Q to L substitution in position 90 of the ghrelin/obestatin prepropeptide, rs4684677) may impact on the function of obestatin. In the present study, we tested the activity of native and Q90L obestatin to modulate ghrelin-induced food intake, GH secretion, cFos activity in GHRH and Neuropeptide Y (NPY) neurons and γ-aminobutyric-acid activity onto GHRH neurons. METHODOLOGY/PRINCIPAL FINDINGS: Food intake, GH secretion and electrophysiological recordings were assessed in C57BL/6 mice. cFos activity was measured in NPY-Renilla-GFP and GHRH-eGFP mice. Mice received saline, ghrelin or ghrelin combined to native or Q90L obestatin (30 nmol each) in the early light phase. Ghrelin stimulation of food intake and GH secretion varied considerably among individual mice with 59-77% eliciting a robust response. In these high-responders, ghrelin-induced food intake and GH secretion were reduced equally by native and Q90L obestatin. In contrast to in vivo observations, Q90L was slightly more efficient than native obestatin in inhibiting ghrelin-induced cFos activation within the hypothalamic arcuate nucleus and the nucleus tractus solitarius of the brainstem. After ghrelin injection, 26% of NPY neurons in the arcuate nucleus expressed cFos protein and this number was significantly reduced by co-administration of Q90L obestatin. Q90L was also more potent that native obestatin in reducing ghrelin-induced inhibition of γ-aminobutyric-acid synaptic transmission onto GHRH neurons. CONCLUSIONS/SIGNIFICANCE: These data support the hypothesis that Q90L obestatin partially blocks ghrelin-induced food intake and GH secretion by acting through NPY and GHRH neurons.

Expression, localization, and functional coupling of the somatostatin receptor subtype 2 in a mouse model of oxygen-induced retinopathy.

Purpose. In the mouse model of oxygen-induced retinopathy (OIR), somatostatin-14 (SRIF) acting at the SRIF receptor subtype 2 (sst(2)) inhibits angiogenic responses to hypoxia through a downregulation of vascular endothelial growth factor. Information about where SRIF-sst(2) interactions take place is lacking, and downstream effectors mediating SRIF-sst(2) antiangiogenic actions are unknown. Methods. In the OIR model, retinal expression of SRIF was evaluated with RT-PCR and radioimmunoassay. The bindings of [(125)I]LTT-SRIF-28 and [(125)I]Tyr(3)-octreotide were measured in coronal sections of the eye. With Western blot analysis, the authors evaluated the levels of sst(2A) and the expression and activity of the signal transducer and activator of transcription (STAT)3. The analysis of STAT3 was performed in hypoxic mice treated with the sst(2) agonist octreotide or with the sst(2) antagonist D-Tyr(8) cyanamid 154806 (CYN). Retinal localization of sst(2A) was assessed by single and double immunohistochemistry with an endothelial cell marker. Results. In the hypoxic retina, both SRIF and sst(2) levels as well as [(125)I]Tyr(3)-octreotide binding were downregulated. In addition, sst(2A) immunostaining was decreased in the neuroretina but was increased in capillaries. Hypoxia increased both the expression and the activity of STAT3. This increase was inhibited by octreotide but was strengthened by CYN. Conclusions. These data suggest that sst(2) expressed by capillaries may be responsible for the antiangiogenic effects of SRIF and that downstream effectors in this action include the transcription factor STAT3. These results support the possibility of using sst(2)-selective ligands in the treatment of proliferative retinopathies and indicate STAT3 as an additional target for a novel therapeutic approach.

Somatostatin interneurons delineate the inner part of the external plexiform layer in the mouse main olfactory bulb.

Neuropeptides play a major role in the modulation of information processing in neural networks. Somatostatin, one of the most concentrated neuropeptides in the brain, is found in many sensory systems including the olfactory pathway. However, its cellular distribution in the mouse main olfactory bulb (MOB) is yet to be characterized. Here we show that approximately 95% of mouse bulbar somatostatin-immunoreactive (SRIF-ir) cells describe a homogeneous population of interneurons. These are restricted to the inner lamina of the external plexiform layer (iEPL) with dendritic field strictly confined to the region. iEPL SRIF-ir neurons share some morphological features of Van Gehuchten short-axon cells, and always express glutamic acid decarboxylase, calretinin, and vasoactive intestinal peptide. One-half of SRIF-ir neurons are parvalbumin-ir, revealing an atypical neurochemical profile when compared to SRIF-ir interneurons of other forebrain regions such as cortex or hippocampus. Somatostatin is also present in fibers and in a few sparse presumptive deep short-axon cells in the granule cell layer (GCL), which were previously reported in other mammalian species. The spatial distribution of somatostatin interneurons in the MOB iEPL clearly outlines the region where lateral dendrites of mitral cells interact with GCL inhibitory interneurons through dendrodendritic reciprocal synapses. Symmetrical and asymmetrical synaptic contacts occur between SRIF-ir dendrites and mitral cell dendrites. Such restricted localization of somatostatin interneurons and connectivity in the bulbar synaptic network strongly suggest that the peptide plays a functional role in the modulation of olfactory processing.

Somatostatinergic systems in brain: networks and functions.

Somatostatin is abundantly expressed in mammalian brain. The peptide binds with high affinity to six somatostatin receptors, sst1, sst2A and B, sst3 to 5, all belonging to the G-protein-coupled receptor family. Recent advances in the neuroanatomy of somatostatin neurons and cellular distribution of sst receptors shed light on their functional roles in the neuronal network. Beside their initially described neuroendocrine role, somatostatin systems subserve neuromodulatory roles in the brain, influencing motor activity, sleep, sensory processes and cognitive functions, and are altered in brain diseases like affective disorders, epilepsia and Alzheimer's disease.

Loss of VGLUT1 and VGLUT2 in the prefrontal cortex is correlated with cognitive decline in Alzheimer disease.

Several lines of evidence suggest that the glutamatergic system is severely impaired in Alzheimer disease (AD). Here, we assessed the status of glutamatergic terminals in AD using the first available specific markers, the vesicular glutamate transporters VGLUT1 and VGLUT2. We quantified VGLUT1 and VGLUT2 in the prefrontal dorsolateral cortex (Brodmann area 9) of controls and AD patients using specific antiserums. A dramatic decrease in VGLUT1 and VGLUT2 was observed in AD using Western blot. Similar decreases were observed in an independent group of subjects using immunoautoradiography. The VGLUT1 reduction was highly correlated with the degree of cognitive impairment, assessed with the clinical dementia rating (CDR) score. A significant albeit weaker correlation was also observed with VGLUT2. These findings provide evidence indicating that glutamatergic systems are severely impaired in the A9 region of AD patients and that this impairment is strongly correlated with the progression of cognitive decline. Our results suggest that VGLUT1 expression in the prefrontal cortex could be used as a valuable neurochemical marker of dementia in AD.

Activated somatostatin type 2 receptors traffic in vivo in central neurons from dendrites to the trans Golgi before recycling.

Understanding the trafficking of G-protein-coupled receptors (GPCRs) is of particular importance, especially when modifications of the neurochemic environment occur as in pathological or therapeutic circumstances. In the central nervous system, although some GPCRs were reported to internalize in vivo, little is known about their trafficking downstream of the endocytic event. To address this issue, distribution and expression pattern of the major somatostatin receptor subtype, the somatostatin type 2 (sst2), was monitored in the hippocampus using immunofluorescence, autoradiographic and immunogold experiments from 10 minutes to 7 days after in vivo injection of the receptor agonist octreotide. We then analyzed whether postendocytic trafficking of the receptor was dependent upon integrity of the microtubule network using colchicine-injected animals. Together, our results suggest that upon agonist stimulation, dendritic receptors are retrogradely transported through a microtubule-dependent mechanism to a trans Golgi domain enriched in the t-SNARE syntaxin 6 and trans Golgi network 38 proteins, before recycling. Because we show that the exit rate from the trans Golgi apparatus back to the plasma membrane (hours) is slower than the entry rate (minutes), the neuronal postendocytic trafficking of sst2 receptor is likely to have functional consequences in several neurological diseases in which an increase in somatostatin release occurs.