Somatostatin analog lanreotide inhibits myocyte replication and several growth factors in allograft arteriosclerosis

Somatostatin-Dopamine Chimeric Molecules in Neuroendocrine Neoplasms

Neuroendocrine neoplasms (NENs) are a widely heterogeneous family of neoplasms arising from neuroendocrine cells, which are interspersed throughout the body. Despite NENs are relatively rare, their incidence and prevalence are constantly increasing probably due to the improvement in earlier diagnosis and patients’ management. When surgery is not curative, particularly for patients with metastatic disease, several medical options are available. Somatostatin analogues (SSA) are the first-line medical therapy for well-differentiated NENs. Interestingly, the heterodimerization of somatostatin receptors (SSTs) with dopamine receptors (DRs) has been discovered in NENs. This phenomenon results in hybrid receptors with enhanced functional activity. On these bases, chimeric molecules embracing somatostatin and dopamine features have been recently developed. The aim of this review is to provide a comprehensive overview of the available preclinical and clinical data regarding chimeric somatostatin-dopamine agonists as a new class of “magic bullet” in the therapy of NENs.

Lanreotide Induces Cytokine Modulation in Intestinal Neuroendocrine Tumors and Overcomes Resistance to Everolimus

Somatostatin analogs mantain their major role in the treatment of patients with advanced neuroendocrine tumors (NETs) and have multiple modulatory effects on the immune system. Here, we evaluated the effects of lanreotide treatment on expression of Th1, Th2 cytokine patterns in serum of patients with NETs and in bronchial and pancreatic NET cell lines. Our results showed that lanreotide treatment promoted a Th1 cytotoxic immune-phenotype in patients with NETs originated by intestinal sites. Similar results were obtained also in vitro where lanreotide induced expression of Th1 cytokines only in pancreatic and not in bronchial-derived NET cell lines. It seems, therefore, that cytokinomics can represent a useful tool for the identification of tumor biomarkers for the early diagnosis and evaluation of the response to therapy in NET patients. To avoid the drug-resistance induced by everolimus (mTOR inhibitor), we made the pancreatic NET cell line resistant to this drug. After treatment with lanreotide we found that the drug reduced its viability compared to that of sensitive cells. These data may have direct implications in design of future translation combination trial on NET patients.

Antibody array strategy for human growth factor secretome profiling of GH-secreting adenomas

PURPOSES

To test if the antibody array strategy could be utilized to simultaneously detect the secretion of multiple growth factors by human pituitary GH-adenomas and to measure octreotide-induced alterations.

METHODS

Specimens of human pituitary adenomas were cultured and incubated with or without octreotide for 24 h. Conditional media were analyzed by human growth factor antibody array and VEGF concentrations were measured by ELISA. Media were also analyzed for GH concentrations. p21 expression levels were examined by Western blot of the specimens lysates.

RESULTS

The antibody arrays successfully identified growth factors secreted by GH-adenomas in vitro. Octreotide treatment induced both elevations and reductions in growth factors secretion. GH response to octreotide was measured, and in this small-sized study resistant and sensitive GH-adenomas presented with no unique secretome pattern of each of the groups. Octreotide-induced VEGF alterations analyzed by the antibody array and by ELISA were not fully matched.

CONCLUSIONS

This study suggests that the broad proteomic strategy of antibody arrays may be utilized to study the growth factors secretion pattern of GH-adenomas and its regulation by somatostatin analogs or other compounds.

Somatostatin preserved blood brain barrier against cytokine induced alterations: possible role in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory neurological disorder associated with demyelination, impaired blood brain barrier (BBB), axonal damage and neuronal loss. In the present study, we measured somatostatin (SST) and tumor necrosis factor-α (TNF-α) like immunoreactivity in CSF samples from MS and non-MS patients. We also examined the role of SST in cytokines and lipopolysaccharide (LPS)-induced damage to the BBB using human brain endothelial cells in culture. Most of the cerebrospinal fluid (CSF) samples studied from definite MS patients exhibited lower somatostatin (SST)-like immunoreactivity and higher expression of TNF-α in comparison to non-MS patients. Treatment of cells with cytokines and LPS blocked SST secretion and decreased SST expression. Human brain endothelial cells expressed all five somatostatin receptors (SSTRs) with increased expression of SSTR2 and 4 upon treatment with cytokines and LPS. Cytokines and LPS-induced disruption of the tight junction proteins Zonula occludens (ZO-1) organization was restored in presence of SST, SSTR2 or SSTR4 selective agonists. Furthermore, inflammation induced changes in extracellular signal-regulated kinases (ERK1/2 and ERK5) signaling and altered expression of endothelial and inducible nitric oxide synthase are modulated in presence of SST. These data indicate that decreased levels of SST contribute to failure of the BBB in MS.

Isoproterenol induced hypertrophy and associated signaling pathways are modulated by somatostatin in H9c2 cells

BACKGROUND

Somatostatin (SST), a growth hormone inhibitory peptide plays key role in regulation of cell proliferation via modulation of mitogen activated protein kinases (MAPKs) and cell survival pathway. In cardiac physiology, β-Adrenergic receptors (β-ARs) play crucial role in regulation of downstream signaling pathways in receptor specific manner. The aim of the current study was to delineate the mechanistic insight for the role of SST on β-AR mediated signaling which promotes hypertrophy and apoptosis in rat fetal cardiomyocytes (H9c2 cells). Accordingly, SST dependent changes in signaling molecules including second messenger cAMP, PKA/CREB as well as MAPKs including ERK and p38 which are key mediators of hypertrophy and apoptosis were analyzed.

METHODS AND RESULTS

In the present study, we determined receptor specific effects on intracellular cAMP levels, signaling by western blot analysis and apoptosis by using JC-1 and Hoechst-33258 staining. Here, we present the data which indicates that SST inhibits isoproterenol induced hypertrophy and apoptosis in H9c2 cells. Importantly, SST inhibits β-ARs agonist induced cAMP activation and SST mediated inhibition of cAMP was enhanced in presence of β-ARs antagonist. SST enhances β2AR agonist formoterol mediated effects on PKA, CREB and ERK1/2 phosphorylations whereas it inhibits isoproterenol mediated ERK1/2 and p38 signaling in concentration dependent manner.

CONCLUSIONS

Taken together, these results presented here provide a novel insight for the potential role of SST in regulation of β-AR mediated effects on hypertrophy and modulation of hypertrophy promoting signaling in H9c2 cells.

Intimal Hyperplasia in Rats after Subcutaneous Injection of a Somatostatin Analog

The somatostatin analog octreotide was administered to male and female Sprague-Dawley rats by subcutaneous injection for thirteen weeks at 0 (saline control), 0 (placebo control [mannitol and lactic acid; pH 4.2]), 1.25 mg/kg/day and 2.5 mg/kg/day to explore its potential effect on cutaneous vascular morphology. The placebo caused an increase in the incidence of intimal hyperplasia compared to saline controls in female rats; octreotide increased the incidence and severity of intimal hyperplasia in males and females. Intimal hyperplasia consisted of increased numbers of cells located between the endothelial cell layer and the internal elastic lamina. Severity was based on the degree of compromise of the vascular lumen (regardless of vessel size and number), with severely affected vessels having no visible lumen. Intimal hyperplasia in rats treated with octreotide was considered to be an unexpected and adverse finding, given that this compound and other somatostatin analogs have been investigated as reducers of intimal proliferation or restenosis after angioplasty in humans and that no such lesion has been reported in the literature for this class of compound to date. The induction of intimal hyperplasia by the placebo is also a notable finding; this may be because of the low pH of the formulation.

Oestradiol inhibition of vascular myointimal proliferation following immune, chemical and mechanical injury

The lower incidence of coronary artery disease in premenopausal women and in postmenopausal women treated with oestrogen supports the hypothesis that oestrogen protects the vasculature from injuries or from responding to injuries with arteriosclerosis. The mechanism remains unknown, although currently the most frequent suggestion is that oestrogen induces beneficial quantitative and qualitative changes in serum lipoprotein concentrations. We studied other mechanisms and in particular the direct effects of 17 beta-oestradiol on vascular smooth muscle and the endothelium. Our focus has been on the vascular response to injury by myointimal and medial thickening, leading to narrowing or occlusion of the vessel. This is frequently seen in coronary arteries within months following angioplasty and a few years following cardiac transplantation. We find that oestradiol treatment protects and reduces the vascular response to injury in three in vivo and one in vitro models: (1) in the rabbit cardiac allograft where oestrogen inhibits accelerated graft atherosclerosis; (2) in monocrotaline- or hypoxia-induced pulmonary hypotension in the rat, where oestrogen attenuates pulmonary artery pressure, right ventricular hypertrophy and medial thickening of the pulmonary artery; (3) oestrogen protects against balloon injury in rabbit aorta; and (4) it inhibits smooth muscle cell proliferation in the porcine left anterior descending coronary artery.

Expression pattern of somatostatin receptor subtypes 1-5 in human skin: an immunohistochemical study of healthy subjects and patients with psoriasis or atopic dermatitis

In psoriasis and atopic dermatitis, the inflammatory events have neurogenic components and the neuropeptides modify the functions of immuno-active cells in the skin. Somatostatin is a neuropeptide with several neuroendocrine and immunomodulating properties and mediates its actions by five distinct subtypes of G-protein-coupled receptors (SSTR1-5). This study describes the distribution of SSTR1-5, analysed with immunohistochemistry, in psoriasis, atopic dermatitis and controls. Normal human skin and lesional skin from patients with psoriasis or atopic dermatitis showed many similarities, but also some differences, as regards SSTR expression. SSTR1-3 were strongly expressed in the epidermis of healthy skin, and in the skin of patients with psoriasis or atopic dermatitis. It is noteworthy that SSTR4 and 5 were strongly expressed in the epidermis of psoriasis patients, but weakly expressed in the epidermis of those with atopic dermatitis and normal skin. The intensity of the staining also varied considerably between the different layers of the epidermis, especially in psoriasis patients. In all cases, the dendritic cells, found mostly in the papillary and upper reticular dermis, showed a strong expression of SSTR1-4, but a weak expression of SSTR5. SSTR1-5 were strongly expressed in the sweat glands in all skin biopsies. Hair follicles and sebaceous glands expressed all five subtypes. Striated muscle fibres showed an intense positive expression of SSTR1-4, but a weak or negative expression of SSTR5. The wide distribution and expression pattern of all five SSTRs in human skin suggest that somatostatin is involved in the interactions between the nervous system and the skin.

Rationale for the use of somatostatin analogs as antitumor agents

BACKGROUND

There is a need for novel antitumor agents that demonstrate efficacy in currently refractory tumors without adding to the toxicity of therapy. The somatostatin analogs, which have demonstrated antineoplastic activities in experimental tumor models, and good tolerability and safety profiles are attractive candidates.

MATERIALS AND METHODS

Data from preclinical studies provide evidence for direct and indirect mechanisms by which somatostatin analogs exert antitumor effects.

RESULTS

Direct antitumor activities, mediated through somatostatin receptors (sst(1)-sst(5)) expressed in tumor cells, include blockade of autocrine/paracrine growth-promoting hormone and growth factor production, inhibition of growth factor-mediated mitogenic signals and induction of apoptosis. Indirect antitumor effects include inhibition of growth-promoting hormone and growth factor secretion, and antiangiogenic actions. Many human tumors express more than one somatostatin receptor subtype, with sst(2) being predominant. Somatostatin analogs such as octreotide and lanreotide, which present a high affinity for sst(2), are in current clinical use to alleviate symptoms in patients with endocrine tumors, and radiolabeled somatostatin analogs have been developed for diagnosis and radiotherapy.

CONCLUSIONS

While the rationale exists for the use of somatostatin analogs as antitumor agents, studies are ongoing to identify analogs with activity across the range of receptor subtypes to maximize the potential of such treatment.

Elimination of vascular fibrointimal hyperplasia by somatostatin receptor 1,4-selective agonist

The somatostatin analogs octreotide and lanreotide, selective to receptor subtypes 2 and 5, failed clinical efficacy for the prevention of restenosis after percutaneous transluminal angioplasty. These findings might have been the result of targeting a wrong subset of receptors. In rat arteries, subtypes 1 and 4 are expressed 3-4 times more prominently than 2 and 5, and subtype 1 is the nearly exclusive subtype in atherosclerotic human vessels. Here, we demonstrate that daily s.c. injections (50-500 microg/kg/d) of CH275 (DesAA1,2,5(D-W8,IAmp9)Somatostatine-14), selective to subtypes 1 and 4, dose-dependently inhibited intimal hyperplasia 14 days after rat carotid denudation injury (for intimal area P=0.0002 across the dose range). CH275 was more effective than somatostatin-14 (equal affinity to all five subtypes, P=0.03), or octreotide (selective to subtypes 2 and 5, P=0.098). When rats were given the peptides for 14 days with end-point at 28 days, CH275 still significantly inhibited intimal area expansion. Both CH275 and octreotide inhibited the outgrowth of cells from postinjury aortic tissue punch-explants and the distance migrated in vitro, but not cell replication, which indicated that the effects of somatostatin analogs were directed on the migration of intimal cell progenitors rather than on their proliferation.

Chronic allograft nephropathy: An update

Chronic allograft nephropathy is the most prevalent cause of renal transplant failure in the first post-transplant decade, but its pathogenesis has remained elusive. Clinically, it is characterized by a slow but variable loss of function, often in combination with proteinuria and hypertension. The histopathology is also not specific, but transplant glomerulopathy and multilayering of the peritubular capillaries are highly characteristic. Several risk factors have been identified, such as advanced donor age, delayed graft function, repeated acute rejection episodes, vascular rejection episodes, and rejections that occur late after transplantation. A common feature of chronic allograft nephropathy is that it develops in grafts that have undergone previous damage, although the mechanism(s) responsible for the progressive fibrosis and tissue remodeling has not yet been defined. Hypotheses to explain chronic allograft nephropathy include the immunolymphatic theory, the cytokine excess theory, the loss of supporting architecture theory, and the premature senescence theory. The most effective option to prevent chronic allograft nephropathy is to avoid graft injury from both immune and nonimmune mechanisms.

Somatostatin and its receptor family

Somatostatin (SST), a regulatory peptide, is produced by neuroendocrine, inflammatory, and immune cells in response to ions, nutrients, neuropeptides, neurotransmitters, thyroid and steroid hormones, growth factors, and cytokines. The peptide is released in large amounts from storage pools of secretory cells, or in small amounts from activated immune and inflammatory cells, and acts as an endogenous inhibitory regulator of the secretory and proliferative responses of target cells that are widely distributed in the brain and periphery. These actions are mediated by a family of seven transmembrane (TM) domain G-protein-coupled receptors that comprise five distinct subtypes (termed SSTR1-5) that are endoded by separate genes segregated on different chromosomes. The five receptor subtypes bind the natural SST peptides, SST-14 and SST-28, with low nanomolar affinity. Short synthetic octapeptide and hexapeptide analogs bind well to only three of the subtypes, 2, 3, and 5. Selective nonpeptide agonists with nanomolar affinity have been developed for four of the subtypes (SSTR1, 2, 3, and 4) and putative peptide antagonists for SSTR2 and SSTR5 have been identified. The ligand binding domain for SST ligands is made up of residues in TMs III-VII with a potential contribution by the second extracellular loop. SSTRs are widely expressed in many tissues, frequently as multiple subtypes that coexist in the same cell. The five receptors share common signaling pathways such as the inhibition of adenylyl cyclase, activation of phosphotyrosine phosphatase (PTP), and modulation of mitogen-activated protein kinase (MAPK) through G-protein-dependent mechanisms. Some of the subtypes are also coupled to inward rectifying K(+) channels (SSTR2, 3, 4, 5), to voltage-dependent Ca(2+) channels (SSTR1, 2), a Na(+)/H(+) exchanger (SSTR1), AMPA/kainate glutamate channels (SSTR1, 2), phospholipase C (SSTR2, 5), and phospholipase A(2) (SSTR4). SSTRs block cell secretion by inhibiting intracellular cAMP and Ca(2+) and by a receptor-linked distal effect on exocytosis. Four of the receptors (SSTR1, 2, 4, and 5) induce cell cycle arrest via PTP-dependent modulation of MAPK, associated with induction of the retinoblastoma tumor suppressor protein and p21. In contrast, SSTR3 uniquely triggers PTP-dependent apoptosis accompanied by activation of p53 and the pro-apoptotic protein Bax. SSTR1, 2, 3, and 5 display acute desensitization of adenylyl cyclase coupling. Four of the subtypes (SSTR2, 3, 4, and 5) undergo rapid agonist-dependent endocytosis. SSTR1 fails to be internalized but is instead upregulated at the membrane in response to continued agonist exposure. Among the wide spectrum of SST effects, several biological responses have been identified that display absolute or relative subtype selectivity. These include GH secretion (SSTR2 and 5), insulin secretion (SSTR5), glucagon secretion (SSTR2), and immune responses (SSTR2).

Differential regulation of somatostatin receptor types 1-5 in rat aorta after angioplasty

Treatment of restenosis after angioplasty with octapeptide somatostatin (SST) analogs has met with variable success. These analogs bind with high affinity to only two SST receptor (SSTR) subtypes (2 and 5), display moderate affinity for SSTR3, and low affinity for SSTR1 and 4. To optimize the vasculoprotective effect of SST, we have investigated the pattern of expression of all five SSTRs in rat thoracic aorta in the resting state and at 15 min, 3, 7, and 14 days after balloon endothelial denudation. SSTR1-5 were analyzed as mRNA by semiquantitative reverse transcriptase-polymerase chain reaction and as protein by immunocytochemistry. All five SSTRs were expressed in rat aorta both as mRNA and protein and displayed a time-dependent, subtype-selective response to endothelial denudation. mRNA for SSTR1 and 2 increased acutely (SSTR1 > SSTR2) on days 3 and 7, coincident with smooth muscle cell (SMC) proliferation, and declined to basal levels by day 14. SSTR3 and 4 displayed a different pattern with a delayed, more gradual increase in mRNA beginning at days 3-7 and continued to increase thereafter. SSTR5 mRNA was constitutively expressed at a low level and showed no change during the 2 wk postinjury period. By immunohistochemistry, SSTR1-5 antigens were localized predominantly in SMC that were present in the media or had migrated into the intima; antigen expression correlated with receptor mRNA expression. Notably, only SSTR1,3,4 were expressed in the intima: SSTR1 and 4 during the proliferative burst and SSTR3 and 4 after proliferation, when SMC migration into the intima continues. These results demonstrate dynamic changes in SSTR1-5 expression after vascular trauma localized to areas of vascular SMC migration and replication. In view of their early and prominent induction, SSTR1 may be the optimal subtype to target for inhibition of myointimal proliferation, and SSTR3 and 4 for migration and remodeling.

Region-specific antiproliferative effect of VIP and PACAP-(1-38) on rabbit enteric smooth muscle

The ability of neuropeptides to modulate enteric smooth muscle proliferation was examined in primary explant cultures of rabbit gastric antrum and colon smooth muscle. Cell proliferation was determined by [3H]thymidine incorporation measurements and cell counting. Subcultured rabbit antrum and colon myocytes (passages 2-6) preserved a smooth muscle phenotype, as verified by immunohistochemistry for alpha-smooth muscle actin and electron microscopy. Both vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating peptide-(1-38) [PACAP-(1-38)] concentration dependently (10(-10) to 10(-6) M) inhibited the serum-induced [3H]thymidine incorporation [in colon, 48.2 +/- 5.8 and 55.6 +/- 9.3% of control with 10(-6) M VIP and 10(-7) M PACAP-(1-38)] and inhibited increase in cell numbers in cultures derived from the colon but not in those from the antrum. Effects of VIP and PACAP-(1-38) were mimicked by forskolin (10(-7) to 10(-6) M) but not by 8-bromo-cGMP, whereas theophylline enhanced the effects of VIP. Inhibition of nitric oxide synthase with NG-nitro-L-arginine methyl ester (10(-3.5) M) did not alter the effects of VIP. Substance P, motilin, calcitonin gene-related peptide, and somatostatin had no effect. A single class of 125I-labeled VIP binding sites was found in antrum and colon myocyte cultures with an equal affinity for VIP and PACAP-(1-38) [dissociation constant (Kd) in antrum = 3.4 +/- 0.8 nM for VIP and 2.0 +/- 1.0 nM for PACAP-(1-38); Kd in colon = 2.0 +/- 1.0 nM for VIP and 2.8 +/- 1.6 nM for PACAP-(1-38)]. Density of binding sites in the antrum was higher than in the colon. In disease states such as inflammatory bowel disease, inhibition of myocyte proliferation by VIP and PACAP may serve to control smooth muscle hyperplasia in the colon but not in the antrum.

Chronic allograft vasculopathy: new strategies for drug development

Chronic rejection reflects cumulative trauma to the allograft regardless of its origin. The main histologic feature in chronic rejection in all allografts is proliferative allograft vasculopathy. According to the current paradigm, chronic rejection can be prevented by more intensive and selective immunosuppression. Experimental retransplantation to donor strain suggests that elimination of histoincompatibility does not prevent progression of the disorder after the initial stimulus has been sufficiently strong or long-lasting. In order to design additional sites for intervention after this point of no return, attention has focused on the regulation of the synthesis and/or action of smooth muscle cell growth factors. In several preclinical models, the blocking of growth factor synthesis, blocking of the binding of the growth factors to their receptors, and/or growth factor signaling downstream of the receptor, have successfully been used in the inhibition of the intimal response and allograft vasculopathy. Inhibition of proteolytic enzymes, necessary for smooth muscle cell locomotion, may provide additional sites of intervention. However, on most occasions, the inhibitory effect is incomplete only 30% to 50% of maximal. The future will demonstrate whether several approaches must be applied concomitantly, or whether genes regulating several of these ligands and their receptors simultaneously can be identified and exploited.

Chronic rejection: risk factors, regulation, and possible sites of therapeutic intervention

Clinical chronic rejection corresponds histologically to proliferative allograft vasculopathy. This disorder reflects the cumulative trauma to the allograft regardless of its origin. As a consequence of trauma, inflammation is generated, leading to endothelial and smooth muscle cell activation, smooth muscle replication and migration, and graft arterial intimal thickening. According to the current paradigm, chronic rejection can be avoided by more intensive and selective immunosuppression and by avoiding the known predisposing factors. Retransplantation experiments in experimental animals to donor or F1-strain suggest, however, that elimination of histoincompatibility does not prevent the progression of the disorder once it has been initiated. To design additional sites of intervention after the "point-of-no-return," attention has been focused on the regulation of the synthesis of growth factors, binding of the growth factors to the receptors, and to signalling downstream of the receptor. Also, inhibition of proteolytic enzymes, necessary for the locomotion of the smooth muscle cells, is a possible target. On most occasions, however, the inhibitory effect is at the most 30 to 50% of the maximal, and only the future will show whether several of these approaches must be applied concomitantly or whether genes regulating several of these processes simultaneously can be identified and exploited.

Human proximal tubular epithelial cells express somatostatin: regulation by growth factors and cAMP

Somatostatin modulates several renal tubular cell functions, including gluconeogenesis and proliferation. In this study, we demonstrate that cultured human proximal tubular epithelial cells (PTEC) express somatostatin. We also demonstrate positive and negative regulation of PTEC somatostatin production. We found that PTEC derived from 14 different human donors consistently expressed somatostatin mRNA and/or peptide as detected by RT-PCR and enzyme-linked immunoassay. Furthermore, Northern blot analysis revealed that PTEC express the same size mRNA transcript (750 nucleotides) as human thyroid carcinoma (TT) cells. The PTEC mitogens, epidermal growth factor(EGF) and hydrocortisone, inhibit PTEC somatostatin secretion, whereas forskolin (a direct stimulator of adenylate cyclase) and fetal bovine serum stimulate secretion. These findings raise the possibility that renal-derived somatostatin modulates tubular cell function in an autocrine/paracrine manner. Manipulation of this pathway may lead to novel methods with which to alter tubular cell proliferation and function in vivo.

Differential effects of somatostatin and angiopeptin on cell proliferation

1. Somatostatin (SRIF) exerts antiproliferative effects, and angiopeptin (an sst2/sst5 receptor-selective analogue) has recently been evaluated in clinical trials for the prophylaxis of restenosis following coronary angioplasty. Using an in vitro model of cell growth we have examined the effects of SRIF and angiopeptin on cell proliferation in CHO-K1 cells stably transfected with the human or rat recombinant sst2 or sst5 receptor and compared these with their effects on rat aortic vascular smooth muscle cells (VSMC) expressing endogenous somatostatin receptors. 2. In CHO-KI cells, expressing either human or rat recombinant sst2 or sst5 receptors, or in rat aortic VSMC, SRIF and angiopeptin (0.1-1000 nM) had no effect on basal re-growth of cells into a denuded area of a previously confluent monolayer. In contrast, basic fibroblast growth factor (bFGF, 10 ng ml(-1)) stimulated re-growth of these cells. 3. SRIF (0.1-1000 nM) caused a concentration-dependent inhibition of the bFGF-stimulated re-growth in CHO-K1 cells expressing human sst2 (h sst2) or sst5 (h sst5) receptors (pIC50=8.05+/-0.03 and 8.56+/-0.12, respectively). In contrast, angiopeptin (0.1-1000 nM) acted as a partial agonist at the h sst2 receptor (44.6+/-2.7% inhibition of the bFGF-stimulated re-growth at 100 nM; pIC50=8.69+/-0.25) but was devoid of any agonist activity at the h sst5 receptor. 4. In CHO-K1 cells stably expressing rat recombinant sst2 (r sst2) or sst5 (r sst5) receptors, SRIF (0.1-1000 nM) was able to inhibit the bFGF-stimulated re-growth (pIC50=7.98+/-24 and 8.50+/-0.12, respectively). Angiopeptin (0.1-1000 nM) caused a concentration-dependent inhibition of bFGF-stimulated re-growth at the r sst2 receptor (pIC50=8.08+/-0.24) but acted as a partial agonist at the r sst5 receptor (maximum response= 57.7+/-3.6% inhibition of bFGF-stimulated re-growth at 100 nM; pIC50=8.60+/-0.16). 5. Although angiopeptin was inactive as an agonist at the h sst5 receptor, 100 nM angiopeptin potently antagonized the SRIF-induced inhibition of proliferation in CHO h sst5 (estimated pKB= 10.4+/-0.3). 5-Hydroxytryptamine (0.1 nM-10 microM) also inhibited bFGF-stimulated re-growth (pIC50=8.36+/-0.11) and angiopeptin had no effect on this response (pKB<7). 6. SRIF (0.1-1000 nM) caused a concentration-dependent (pIC50=8.04+/-0.08) inhibition of bFGF-stimulated re-growth in VSMC, whereas angiopeptin displayed weak agonist activity, only inhibiting bFGF-stimulated re-growth at concentrations greater than 100 nM. Angiopeptin (100 nM) caused a rightward displacement of the concentration-effect curve to SRIF with an estimated pKB value of 7.70+/-0.12. 7. These findings suggest that the low intrinsic activity of angiopeptin at the h sst2 receptor, combined with its lack of agonist activity at the h sst5 receptor, may explain the poor clinical efficacy of angiopeptin in trials for coronary artery restenosis, which contrasts with encouraging data found in equivalent in vivo animal studies.

Exposure of vascular allografts to insulin-like growth factor-I (IGF-I) increases vascular expression of IGF-I ligand and receptor protein and accelerates arteriosclerosis in rats

BACKGROUND

Accelerated arteriosclerosis limits the survival of transplanted hearts. We hypothesized that insulin-like growth factor-I (IGF-I) is crucial in accelerating transplant arteriosclerosis. Recently, we reported that exposure to IGF-I prior to transplantation accelerates transplant arteriosclerosis in the rat aorta allograft model. Here, we studied the mechanism whereby IGF-I exposure accelerates transplant arteriosclerosis.

METHODS

The abdominal aorta was harvested from male Brown Norway rats and exposed to 0, 200, or 500 ng/ml of IGF-I at 37 degrees C for 30 min prior to transplantation to the abdominal position of male Lewis rats. The allografts were harvested 14 days later and processed for immunohistochemical staining for alpha-actin, growth factors (IGF-I, IGF-I receptor, platelet-derived growth factor-BB, and basic fibroblast growth factor), and immunological markers (major histocompatibility complex class II antigen, macrophage, and CD4- and CD8-positive T cells).

RESULTS

By 14 days, the ex vivo IGF-I donor aorta treatment with IGF-I increased in a concentration-dependent manner the expression of IGF-I and IGF-I receptor in both the intima and the adventitia. In contrast, the expression of platelet-derived growth factor-BB was decreased in a concentration-dependent manner in the intima while basic fibroblast growth factor remained unchanged. The cell-mediated immune response was not affected by IGF-I at 14 days after transplantation, which suggests that the immune events associated with acceleration of transplant arteriosclerosis may occur at an earlier time.

CONCLUSION

Acceleration of transplant arteriosclerosis by exposure to IGF-I is associated with increased IGF-I ligand and receptor expression in the allograft vascular wall. These data further suggest that IGF-I may be a major factor in mediating graft arteriosclerosis.

Sustained anti-CD4/CD8 treatment blocks inflammatory activation and intimal thickening in mouse heart allografts

We evaluated inflammatory activation and vascular thickening in a heterotopic murine heart transplant model. C57BL/6J recipient mice received anti-CD4 therapy (days 1 to 4 after transplantation) or sustained, combined anti-CD4/CD8 therapy (days 1 to 4, weekly thereafter). Morphometric analysis of grafts (> 95 days) found the mean percentage of vessel occlusion to be 51.7% in allografts treated with anti-CD4, 8.3% in allografts treated with sustained anti-CD4/CD8, and 6.7% in isografts. Mean transcript levels of the adhesion molecules P-selectin, intercellular adhesion molecule 1 (ICAM-1), and leukocyte function-associated antigen 1 (LFA-1) and the cytokines interleukin 4 (IL-4), interferon-gamma (IFN-gamma), inducible nitric oxide synthase (iNOS), allograft inflammatory factor 1 (AIF-1), and monocyte chemoattractant protein 1 (MCP-1) were measured with reverse transcription-polymerase chain reaction [RT-PCR] assays using deoxycytidine triphosphate radiolabeled with phosphorus 32 [32P-dCTP]. The assays were normalized against glyceraldehyde-3-phosphate dehydrogenase [G3PDH] Levels were found to be significantly higher in the anti-CD4 group than in the anti-CD4/CD8 group. A strong correlation was also found between the percentage of luminal occlusion and the expression of these markers of inflammation (r = .92-.99, P < .0001). Sustained therapy involving proximal blockade of CD4 and CD8 interrupts pathways leading to inflammation and vascular thickening. However, long-term heart allografts in mice treated with a short course of anti-CD4 display an ongoing inflammatory cell activation that culminates in arteriosclerosis. This model may help examine the role of targeted immune factors using knockout mice to identify those causally involved in vessel thickening.

Acceleration of arteriosclerosis of the rat aorta allograft by insulin growth factor-I

We demonstrate here, for the first time, the mitogenic effect of insulin-like growth factor-I (IGF-I) on the development of transplant arteriosclerosis in a rat orthotopic aorta allotransplantation model (Brown Norway to Lewis). 125I-IGF-I uptake by the abdominal aorta of male Brown Norway rats occurred within 30 min. Consequently, we exposed the donor abdominal aorta to 0, 200, or 500 ng/ml IGF-I at 37 degrees C for 30 min ex vivo (n=7 per group), before transplantation. Fourteen days after transplantation, intimal thickening of the allografts in each of the three groups was 0.18+/-0.02 (IGF-I at 0 ng/ml), 0.23+/-0.03 (IGF-I at 200 ng/ml), and 0.30+/-0.03 (IGF-I at 500 ng/ml), respectively (mean+/-SEM, P<0.005 for 500 ng/ml vs. 0 ng/ml). [3H]thymidine incorporation (cpm/microg protein) in the transplanted grafts at 7 days after transplantation (n=4 per group) was 40.6+/-7.6, 78.5+/-12.3, and 66.9+/-10.1, respectively (P<0.01 for 200 ng/ml vs. 0 ng/ml). [3H]thymidine incorporation in the native thoracic aorta of the recipient was 23.4+/-4.4. We conclude that acceleration of allograft myointimal proliferation and intimal thickening was induced directly by IGF-I.

Angiopeptin inhibits thymidine incorporation by explants of porcine coronary arteries

Angiopeptin, a stable octapeptide analog of somatostatin, inhibits proliferation in a variety of cancer cell lines. We studied the effect of angiopeptin on 3H-thymidine uptake into ring segments from the porcine coronary tree. The incorporation of 3H-thymidine into segments of porcine left anterior descending (LAD) coronary artery was time dependent and reached a plateau after 48 h. The addition of angiopeptin (48.1 and 96.2 nM) to the culture medium significantly inhibited 3H-thymidine incorporation into the segments by 36.7 +/- 10.1% and 48.3 +/- 2.3% of the control, respectively. Forskolin (100 microM), inhibited 3H-thymidine incorporation (52.7 +/- 10.1%) to the same degree as did angiopeptin (96.2 nM). Incubation of the segments with 125I-labeled angiopeptin, for 2 h at 37 degrees C, showed angiopeptin uptake to be time dependent and exhibited a first-order kinetics, reaching equilibrium after 30 min. Autoradiographic studies showed a uniform distribution of angiopeptin within the endothelium, media, and adventitia. Most of the labeling was associated with the nuclei of the cells. Angiopeptin, after 30-min incubation, did not significantly modify the basal levels of cyclic adenosine monophosphate (cAMP). In contrast, forskolin (100 microM) elicited a 50-fold increase of the basal levels of cAMP. These results indicate that in addition to its endocrine effects, angiopeptin reduces the rate of proliferation by acting directly on the vessel wall.

Altered expression of transforming growth factor-beta S in chronic renal rejection

We examined the altered expression of transforming growth factor-beta s in chronic renal rejection in humans, including transforming growth factor beta-1 (TGF-beta 1), TGF-beta 2, TGF-beta 3 and their receptors, transforming growth factor beta receptor type I (T beta R-I) and T beta R-II. Using Northern blot analysis and immunohistochemistry, 10 specimens of chronically rejected and 8 normal kidney samples were analyzed. By Northern blot analysis the expression of mRNA encoding TGF-beta 1, TGF-beta 2, TGF-beta 3 (P < 0.02), T beta R-I and T beta R-II (P < 0.02) was decreased in chronically rejected renal cortex samples, compared to normal controls. Immunohistochemical analysis of the normal renal cortex showed strong immunostaining for TGF-beta 1 and TGF-beta 3, and mild immunostaining for TGF-beta 2 in the proximal and distal tubulointerstitium, but no signal for any of the TGF-beta isoforms in the glomeruli or in the cortical vessels. In sharp contrast, the glomeruli and the cortical vessels of the rejected kidney specimens exhibited strong immunostaining for TGF-beta 1 and TGF-beta 3, whereas the tubules revealed a decrease in immunoreactivity. T beta RI and T beta RII immunostaining showed similar changes as observed with TGF-beta 1 and TGF-beta 3 antibodies. There was a concomitant increase in B-cell accumulation in the glomeruli, while T-cells and macrophages were diffusely abundant in the rejected samples. Since TGF-beta S are potent inducers of extracellular matrix proteins and have been shown to be involved in fibrotic disease, the increase in TGF-beta 1 and TGF-beta 3 immunoreactivity in the glomeruli suggests that there is a redistribution in TGF-beta expression in chronic renal allograft rejection. Together with changes affected by B-cell mediated immunity, the above alterations might contribute to the histopathological changes that occur in this disorder, such as intimal fibrosis, arteriosclerosis and glomerular and tubular sclerosis.

Blockade of growth factor synthesis and growth factor action: two possible sites of interference in allograft vessel disease and coronary bypass or balloon injury

When injured, vascular endothelial cells produce growth factors that cause smooth muscle cells (SMC) to migrate from the media to the intima of the vessel wall, replicate in the intima, and stimulate arteriosclerotic changes. Interference with the actions of growth factors in allograft arteriosclerosis was explored. The somatostatin analog angiopeptin was administered to allograft-recipient rats after transplantation of aortic allografts between major and minor histoincompatible rat strains. Levels of epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), and platelet-derived growth factor (PDGF) in grafts from angiopeptin-treated recipients were 35% to 75% of levels in grafts from nontreated recipients. Replication of SMC in the media and intima was reduced by 30% to 90% and intimal thickening by approximately 50%. The effect of blockade of IGF-1 receptors (IGF-1R) on the intimal response was also investigated. SMC cultures were serum-deprived of growth factors, then stimulated to replicate by addition of PDGF-B and EGF. Anti-IGF-1 and anti-IGF-1R antibodies reduced SMC replication by 50% and 90%, respectively. A D-amino acid analog of IGF-1, JB3, inhibited SMC replication and dose-dependently inhibited insulin receptor substrate 1 (IRS-1) and IGF-1R phosphorylation in vitro. Infusion of JB3 into rats undergoing balloon dilatation injury inhibited SMC replication in the injured vascular area by nearly 70%, but inhibited intimal thickening by only 30%. In conclusion, interference in the growth factor response may be one way of reducing/preventing vascular injury. However, blockade of more than one growth factor may be needed to achieve an optimal effect.

Chronic rejection and late renal allograft dysfunction

Renal transplantation is currently standard therapy for end-stage kidney disease for children. Despite the considerable improvement in short-term results, the expected allograft half-life has remained the same. This is due to chronic rejection/late graft dysfunction which has proved resistant to therapeutic attempts. During the last few years the multifactorial pathogenesis of chronic renal allograft rejection has been clarified to some extent. Early injury by immunological and non-immunological mechanisms is followed by vascular remodelling due to repetitive cycles of cytokine release, upregulation of growth factors, and vascular smooth muscle cell proliferation. This leads to typical concentric arteriosclerosis and ischemia. Secondary kidney-specific mechanisms are initiated by the reduction in functioning renal mass and lead to gradual progression of chronic rejection. There is no single optimal therapy. Several attempts to influence the pathophysiological cascade have been promising. Attention should be focused on minimizing early immunological/non-immunological injury in order to attenuate future progression of chronic rejection. A significant prolongation of allograft half-life may be achieved during the next decade with the introduction of new therapeutic agents and comprehensive approach to treatment. This would be especially beneficial for pediatric recipients, reducing the need for retransplantation in adulthood.

Mycophenolate mofetil (MMF, RS-61443) inhibits inflammation and smooth muscle cell proliferation in rat aortic allografts

To investigate the impact of mycophenolate mofetil (MMF) on allograft arteriosclerosis (chronic rejection) in rat aortic allograft model, we administrated MMF 20 mg/kg/day from the day of transplantation and sacrificed the rats at 1-12 months afterwards. MMF significantly suppressed all major histological manifestations of allograft arteriosclerosis, i.e. adventitial inflammation, media necrosis and intimal thickening and cellularity. There was a significant decrease in the replication rate (3H-thymidine incorporation) of inflammatory cells in the adventitia and of smooth muscle cells (SMC) in the media. MMF did not have any major effect on mRNA expression of several growth factors, (determined by polymerase chain reaction with inbuilt glyceraldehyde-3-phosphate dehydrogenase control), which have previously been demonstrated to be elevated in nonimmunosuppressed allografts. Immunoperoxidase staining showed a 40% reduction in the number of adventitial interleukin-2 receptors expressing lymphoid cells in MMF-treated allografts. The intensity of SMC alpha-actin staining was also significantly reduced. As the results suggested that MMF may have a direct antiproliferative effect on SMC, this possibility was investigated in primary SMC cultures in vitro and using the carotid denudation model in vivo. Both approaches showed inhibition of SMC proliferation by MMF. Our results indicate that MMF inhibits histopathological changes of chronic rejection by reducing the immune response and possible replication of SMC.

Role of vascular endothelial cells in the allograft response

Following transplantation endothelial cells lining an allograft come into contact with immune cells of the recipient. Activation of an immune response, by graft endothelial or other cells, will lead to local increases in cytokine production and cell-mediated lysis. Inflammatory cytokines have been shown, mainly in vitro, to have marked effects on endothelial function and act to produce a pro-thrombotic, pro-adhesive and promitogenic phenotype. These data are reviewed and ways in which these changes could lead to rejection due to graft lysis or vascular occlusion are discussed.

Experimental therapeutics and clinical studies in (re)stenosis

Restenosis is defined functionally as loss of luminal vessel patency following various methods of interventional cardiology, but ultrastructurally, it represents a wound healing response that involves smooth muscle migration, proliferation and matrix deposition at the site of injury. Currently, despite intensive experimental and clinical studies, there are no therapeutic agents that are able to suppress pharmacologically the clinical restenosis. Ultrastructural pathology and animal modeling have played a pivotal role in defining new experimental therapies and rationales for clinical trials. However, concerns regarding the lack of suitable animal models persist and of the many compounds reported efficacious preclinically, none have demonstrated clinical benefit in preventing restenosis. Animal modeling studies now include the use of true restenosis studies, which may be more clinically relevant and pharmacologically predictive of clinical performance.

Hyperlipidemia accelerates allograft arteriosclerosis (chronic rejection) in the rat

The relevance of hyperlipidemia in allograft arteriosclerosis (chronic rejection) is controversial. Isolated hypercholesterolemia induced with cholesterol-cholic acid-diet (CC-diet) or hypertriglyceridemia induced with glycerol-diet (G-diet) had no or only a protective effect on aortic allograft arteriosclerosis in the rat. Combined hyperlipidemia with both diets (CC+G-diet) enhanced allograft arteriosclerosis by doubling intimal thickness and cellularity (P < .05) but had no effect on host arteries. Compared with normolipidemic controls, the CC+G-diet increased the total serum cholesterol concentration 4.8-fold (P < .05). Levels of VLDL2 and IDL increased 4.8- and 18.1-fold (P < .05), and their composition changed from triglyceride-rich to cholesterol-rich lipoproteins in an atherogenic direction. The CC+G-diet had no effect on the structure of inflammation in the vascular wall. Instead, significant lipid deposits were observed, and the expression of epidermal growth factor and insulin-like growth factor-1 was significantly elevated in the vascular wall. Thus, elevations in VLDL and IDL lipoprotein levels and their cholesterol content associate with the generation of allograft arteriosclerosis in rats. Deposition of lipids in the vascular wall seems to induce local synthesis of certain growth factors, which ultimately leads to the induction of smooth muscle cell replication.

Cytomegalovirus infection enhances mRNA expression of platelet-derived growth factor-BB and transforming growth factor-beta 1 in rat aortic allografts. Possible mechanism for cytomegalovirus-enhanced graft arteriosclerosis

We have recently demonstrated that rat cytomegalovirus (RCMV) infection induces an early inflammatory response in the adventitia (perivasculitis) and in the subendothelial space (endothelialitis) as well as doubles smooth muscle cell (SMC) proliferation and intimal thickening of rat aortic allografts performed from the DA (AG-B4, RT1a) to the WF (AG-B2, RT1v) strain. In this study, the impact of RCMV infection on the structure of inflammation in the allograft adventitia and on the expression of SMC growth factors in the allograft vascular wall was investigated. The recipient rats were inoculated with 10(5) plaque-forming U of RCMV Maastricht strain or left noninfected and used as controls. The allografts were removed at 7 days and 1 and 3 months after transplantation and processed for morphometry and immunohistochemistry. RNA was isolated for reverse transcriptase polymerase chain reaction (RT-PCR). RCMV infection was associated with significantly upregulated presence (P < .05) of T helper (W3/25), T cytotoxic (OX8), and natural killer (3.2.3) cells in the allograft adventitia 7 days after transplantation but not thereafter. More monocyte/macrophages (OX42) were also present in RCMV-infected allografts, but the difference was not significant. Concomitantly, RCMV infection significantly enhanced (P < .05) the expression of major histocompatibility complex class II (OX6) and almost doubled (P = NS) the expression of interleukin-2R (CD25), intercellular adhesion molecule-1 (CD54;1A29), and lymphocyte function-associated antigen-1 alpha-chain (CD11a; WT.1) in the adventitial inflammatory infiltrate. RCMV infection was linked with an early, prominent expression of both PDGF-BB mRNA at 7 days (P < .05) and at 1 month (P < .025) and of transforming growth factor-beta 1 mRNA at 7 days (P < .025) and at 1 month (P < .025) after transplantation. A less-prominent mRNA upregulation of acidic fibroblast growth factor (P < .05) was associated with RCMV infection at 7 days and at 1 month, as well as of epidermal growth factor at 1 month after transplantation, when compared with noninfected allografts, although the mRNA expression in both groups was below the levels of nontransplanted DA aortas. RCMV infection almost doubled basic fibroblast growth factor mRNA expression (P = NS) in the allograft vascular wall at 7 days and at 1 month. RCMV infection had no additional impact on insulin-like growth factor-1 mRNA expression when compared with noninfected allografts.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytomegalovirus infection-enhanced allograft arteriosclerosis is prevented by DHPG prophylaxis in the rat

BACKGROUND

Major risk factors for accelerated allograft arteriosclerosis include humoral and cellular immune response, hyperlipidemia, and viral infections. We demonstrated earlier that rat cytomegalovirus (RCMV) infection doubles smooth muscle cell proliferation and intimal thickening of rat aortic allografts. In this study, the effects of 9-(1,3-dihydroxy-2-propoxymethyl)guanine (DHPG) on RCMV-enhanced rat allograft arteriosclerosis are investigated.

METHODS AND RESULTS

Aortic allografts from the DA to the WF rat strain were used. The recipients were inoculated with 10(5) plaque-forming units of RCMV 1 day after transplantation. Two groups of RCMV-infected rats were treated with DHPG with an initial dose of 20 mg/kg IP and a maintenance dose of 10 mg/kg IP twice a day for a period of 14 days. In the DHPG prophylaxis group (n = 22), the drug administration started 1 day before infection, and in the DHPG treatment group (n = 17), 7 days after infection. One group of infected rats was left untreated (n = 21). The grafts were removed 7 and 14 days and 1, 3, and 6 months after transplantation. In the DHPG prophylaxis group, no virus could be recovered by plaque assays. In the treatment group, 50% of rats were virus-positive at 1 month and 40% at 3 months. DHPG prophylaxis prevented the infiltration of inflammatory cells and their proliferation in the adventitia of RCMV-infected recipients (P < .01), with a 60% reduction in the interleukin-2 receptor expression (P < .05) and a 30% decrease in major histocompatibility complex class II expression (P = NS). DHPG prophylaxis did not significantly alter the levels of insulin-like growth factor-1, epidermal growth factor, platelet-derived growth factor-BB, transforming growth factor-beta 1, acidic fibroblast growth factor, and basic fibroblast growth factor messages in the allograft vascular wall. Early media necrosis was reduced. Arteriosclerotic alterations and proliferation of smooth muscle cells were both reduced 50% to 70% by DHPG prophylaxis (P < .05 at 3 months). The responses in the DHPG treatment group were quite similar but less impressive and statistically nonsignificant.

CONCLUSIONS

We consider it likely that DHPG inhibits arteriosclerotic alterations primarily by reducing the infectious virus and thereby the inflammatory response in the allograft vascular wall; another possibility is a direct antiproliferative effect on smooth muscle cell replication. A dose-dependent inhibitory effect of DHPG on smooth muscle cell replication was recorded in an in vitro study.

Murine model of accelerated transplant arteriosclerosis

To define the role of specific gene deletions and mutations in the development of transplant arteriosclerosis, we generated an accelerated model of the disease in mice. Carotid arteries were transplanted between B.10A(2R) (H-2h2) donor mice and C57BL/6J (H-2b) recipients and compared with arteries isografted between H-2b mice. Immunosuppressive drugs were not used. Within 7 days, the allografted carotid artery formed a neointima composed of mononuclear leukocytes (CD45+) that were predominantly monocytes or macrophages (ie, CD11b+ cells with single-lobed nuclei). CD4+ and CD8+ cells were present as well. By 30 days, the neointima became exuberant, and mononuclear leukocytes were largely replaced by smooth muscle cells. Cells staining for proliferating-cell nuclear antigen were abundantly present in the intima at both early and late time points, indicating the proliferation of mononuclear leukocytes and smooth muscle cells. The area of the intima increased from day 7 to day 30 (P < .0005), as did the number of nuclei (P = .0005), but the density of the nuclei decreased (P = .02), suggesting the formation of extracellular matrix. Six of the eight isografts formed no neointima, and in samples from the remaining two, a single layer of smooth muscle neointimal cells covered just a portion of the vessel circumference. This model, which reproduces many of the features of human transplant arteriosclerosis but at an accelerated pace, should prove useful for determining the roles in transplant arteriosclerosis of genes that code for components of immunologic and inflammatory responses.