7 research outputs found
Somatostatin receptor 2A expression in choroidal neovascularization secondary to age-related macular degeneration
PURPOSE: The growth of ocular neovascularization is regulated by a balance
between stimulating and inhibiting growth factors. Somatostatin affects
angiogenesis by inhibiting the growth hormone-insulin-like growth factor
axis and also has a direct antiproliferative effect on human retinal
endothelial cells. The purpose of our study is to investigate the
expression of somatostatin receptor (sst) subtypes and particularly sst
subtype 2A (sst2A) in normal human macula, and to study sst2A in different
stages of age-related maculopathy (ARM), because of the potential
anti-angiogenic effect of somatostatin analogues. METHODS: Sixteen eyes
(10 enucleated eyes, 4 donor eyes, and 2 surgically removed choroidal
neovascular [CNV] membranes) of 15 patients with eyes at different stages
of ARM were used for immunohistochemistry. Formaldehyde-fixed
paraffin-embedded slides were incubated with a polyclonal anti-human sst2A
antibody. mRNA expression of five ssts and somatostatin was determined in
the posterior pole of three normal human eyes by reverse
transcriptase-polymerase chain reaction. RESULTS: The immunohistochemical
expression of sstA in newly formed endothelial cells and fibroblast-like
cells was strong in fibrovascular CNV membranes. mRNA of sst subtypes 1,
2A, and 3, as well as somatostatin, was present in the normal posterior
pole; sst subtypes 4 and 5 were not detectable. CONCLUSIONS: Most
early-formed CNV in ARM express sst2A. The presence of mRNA of sst subtype
2A was observed in normal human macula, and subtypes 1 and 3 and
somatostatin are also present. sst2A receptors bind potential
anti-angiogenic somatostatin analogues such as octreotide. Therefore,
somatostatin analogues may be an effective therapy in early stages of CNV
in ARM
Somatostatin receptor 2A expression in choroidal neovascularization secondary to age-related macular degeneration
PURPOSE: The growth of ocular neovascularization is regulated by a balance
between stimulating and inhibiting growth factors. Somatostatin affects
angiogenesis by inhibiting the growth hormone-insulin-like growth factor
axis and also has a direct antiproliferative effect on human retinal
endothelial cells. The purpose of our study is to investigate the
expression of somatostatin receptor (sst) subtypes and particularly sst
subtype 2A (sst2A) in normal human macula, and to study sst2A in different
stages of age-related maculopathy (ARM), because of the potential
anti-angiogenic effect of somatostatin analogues. METHODS: Sixteen eyes
(10 enucleated eyes, 4 donor eyes, and 2 surgically removed choroidal
neovascular [CNV] membranes) of 15 patients with eyes at different stages
of ARM were used for immunohistochemistry. Formaldehyde-fixed
paraffin-embedded slides were incubated with a polyclonal anti-human sst2A
antibody. mRNA expression of five ssts and somatostatin was determined in
the posterior pole of three normal human eyes by reverse
transcriptase-polymerase chain reaction. RESULTS: The immunohistochemical
expression of sstA in newly formed endothelial cells and fibroblast-like
cells was strong in fibrovascular CNV membranes. mRNA of sst subtypes 1,
2A, and 3, as well as somatostatin, was present in the normal posterior
pole; sst subtypes 4 and 5 were not detectable. CONCLUSIONS: Most
early-formed CNV in ARM express sst2A. The presence of mRNA of sst subtype
2A was observed in normal human macula, and subtypes 1 and 3 and
somatostatin are also present. sst2A receptors bind potential
anti-angiogenic somatostatin analogues such as octreotide. Therefore,
somatostatin analogues may be an effective therapy in early stages of CNV
in ARM
Differential expression of somatostatin receptor subtypes in human peripheral blood mononuclear cell subsets
BACKGROUND: Somatostatin (SS)-binding sites have been demonstrated in
human lymphoid tissues and peripheral blood cells. However, not much is
known with respect to the SS receptor subtype (sst) expression pattern and
the expression of SS itself in the immune system. OBJECTIVE: The aim of
this study was to evaluate the mRNA expression of the five known sst
(sst(1-5)) in peripheral blood mononuclear cell (sub)populations.
Moreover, the expression of the mRNAs encoding SS and the SS-like peptide
cortistatin (CST) in immune cell subsets was studied. METHODS: RT-PCR and
quantitative PCR were performed to evaluate sst, SS and CST mRNA
expression in cells in the basal or activated state.
Fluorescence-activated cell sorter (FACS) analysis using fluorescent SS
was performed to visualize sst protein on cell membranes. RESULTS: B- and
T-lymphocytes selectively expressed sst(3) mRNA. sst(3) expression in
B-lymphocytes was significantly lower compared with T-lymphocytes.
Unstimulated, freshly isolated monocytes did not express any sst mRNA.
Upon activation, monocytes selectively expressed sst(2) mRNA, whereas
T-lymphocyte activation upregulated sst(3) expression. sst(2) mRNA
expression on monocytes was confirmed by FACS analysis. B- and
T-lymphocytes did not express SS mRNA, while both cell types expressed CST
mRNA. CST mRNA expression was downregulated following T-lymphocyte
activation. CONCLUSION: We demonstrate for the first time unequivocally
that human peripheral blood B- and T-lymphocytes selectively express
sst(3), whereas monocytes do not express sst. However, upon activation,
monocytes are induced to express sst(2A). No expression of SS mRNA was
detected in any cell type, whereas all cell types expressed CST mRNA. The
differential expression of sst and CST mRNA in lymphocytes and monocytes
s
Somatostatin receptor subtype expression in cells of the rat immune system during adjuvant arthritis
Somatostatin is a neuropeptide that is widely distributed throughout the
body. It acts as a neurohormone and a neurotransmitter an
In vitro characterization of somatostatin receptors in the human thymus and effects of somatostatin and octreotide on cultured thymic epithelial cells
Somatostatin (SS) and its analogs exert inhibitory effects on secretive
and proliferative processes of various cells via high affinity SS
receptors (SS-R). SS analogs bind with different affinity to the five
cloned SS-R subtypes. Octreotide, an octapeptide SS analog, binds with
high affinity to the SS-R subtype 2 (sst2). SS-R have been demonstrated in
vivo and in vitro on cells from endocrine and immune systems. Among the
lymphatic tissues, the thymus has been shown to contain the highest amount
of SS, suggesting a local functional role of the peptide. We investigated
the SS distribution and SS-R expression pattern in the normal human thymus
using autoradiography, membrane homogenate binding studies, and RT-PCR. In
addition, the effect of SS and octreotide on growth of cultured thymic
epithelial cells (TEC) was studied. By autoradiography, binding of
[125I-Tyr0]-SS-28 and [125I-Tyr3]-octreotide was detected in all seven
thymuses studied. Specific [125I-Tyr3]-octreotide binding was shown on
membrane preparations from thymuses, while not from cultured thymocytes.
RT-PCR showed the expression of sst1, sst2A and sst3 messenger RNA (mRNA)
in the thymic tissue, whereas sst1 and sst2A mRNAs were found in isolated
TEC. SS mRNA was present in thymic tissue and in isolated TEC. SS and
octreotide significantly inhibited 3H-thymidine incorporation in 3 of 3
and 6 of 6 TEC cultures, respectively. The percent inhibition ranged from
38.8 to 66.8% for SS and from 19.1 to 59.5% for octreotide. In conclusion,
SS mRNA and sst1, sst2A, and sst3 mRNAs are expressed in the normal human
thymus. Cultured TEC selectively express sst1 and sst2A mRNA and respond
in vitro to SS and octreotide administration with an inhibition of cell
proliferation. These data suggest a paracrine/autocrine role of SS and its
receptors in the regulation of cell growth in thymic microenviron
17-beta-estradiol-dependent regulation of somatostatin receptor subtype expression in the 7315b prolactin secreting rat pituitary tumor in vitro and in vivo
In the present study, we have investigated the role of estrogens in the
regulation of somatostatin receptor subtype (sst) expression in 7315b
PRL-secreting rat pituitary tumor cells in vitro and in vivo. sst were
undetectable in freshly dispersed cells of the transplantable 7315b tumor.
When 7315b cells were cultured in medium containing 10% FCS, the number of
high affinity sst increased with prolonged culture time. However, when the
medium was supplemented with 10% horse serum (HS) instead of FCS, no sst
were detectable on 7315b cells even after three weeks of culturing. In
contrast to HS, FCS contains high E2-levels (HS, 8 pM; FCS, 134 pM). The
antiestrogen tamoxifen (0.5 microM) significantly inhibited the sst number
to 50.5% of the value of untreated FCS-grown cells, suggesting that E2
stimulates sst expression in 7315b rat pituitary tumor cells. E2 (10 nM)
induced a rapid increase in sst number in HS-grown 7315b cells. Octreotide
(1 microM) significantly inhibited PRL release and the intracellular PRL
concentration of 7315b cells that were cultured in medium supplemented
with FCS or with HS + 10 nM E2 but not in HS alone. This indicates that
the sst present on these cells are biologically active. RT-PCR analysis
revealed that none of the five currently known sst subtypes were present
in freshly dispersed 7315b pituitary tumor cells. The expression of sst2-
and sst3-messenger RNA (mRNA) was unequivocally correlated to the presence
of E2 because these sst subtypes were detected only in cells that were
cultured for 7 and 14 days in medium supplemented with FCS or with HS + 10
nM E2. sst1, sst4 and sst5 messenger RNA could not be detected. The 7315b
tumor itself synthesizes and secretes huge amounts of PRL. The high PRL
levels in tumor-bearing rats inhibit the ovarian E2-production. No
detectable E2 levels could be measured in the serum of 7315b tumor-bearing
rats. The sc administration of 20 micrograms/day E2-benzoate normalized
the circulating E2 levels in 7315b tumor-bearing rats. Moreover,
E2-treatment indeed induced sst expression in vivo as shown by ligand
binding studies using membrane homogenates and [125I-Tyr3]-octreotide as
radioligand and by autoradiography on tissue sections. In agreement with
the in vitro studies, the expression of the sst2 subtype was established
by RT-PCR analysis in 7315b tumors of E2-treated rats. However, in
contrast to the in vitro studies, E2-treatment did not effectuate the
expression of the sst3 subtype, suggesting that the in vitro stimulus of
E2 is stronger. In conclusion: 1) sst2 and sst3 expression in the 7315b
rat prolactinoma model is primarily dependent upon the presence of
estrogens; 2) the antihormonal action of octreotide in 7315b tumor cells
in vitro is mediated via the sst2 and/or sst3 subtypes; 3) the absence of
sst expression in vivo can be explained by the hormonal environment of the
7315b tumor cells. The 7315b tumor cells in vivo may down regulate their
own receptor status via their host, because of the ensuring
hyperprolactinemia results in a hypo-estrogenic state