Insulin, insulin-like growth factors, and vascular endothelium

Cardiac hypertrophy and insulin therapy in a pre-term newborn: is there a relationship?

Background

Hypertrophic cardiomyopathy (HCM) in newborns is a rare condition with heterogeneous etiologies. While the relationship between hyperinsulinism and cardiac hypertrophy (CH) is known, hyperinsulinism has not been reported as cause of HCM.

Case presentation

We report the case of cardiac hypertrophy (CH) in an Extremely Low Birth Weight (ELBW) infant; this patient underwent insulin therapy after the onset of persistent hyperglycemia due to parenteral nutrition (PN), supporting the hypothesis of a role of iatrogenic hyperinsulinemia in the development of HCM.

Conclusions

The present case underlines the importance of a close cardiological follow-up in infants undergoing insulin infusion for an alteration in the glucose metabolism.

Why Should Growth Hormone (GH) Be Considered a Promising Therapeutic Agent for Arteriogenesis? Insights from the GHAS Trial

Despite the important role that the growth hormone (GH)/IGF-I axis plays in vascular homeostasis, these kind of growth factors barely appear in articles addressing the neovascularization process. Currently, the vascular endothelium is considered as an authentic gland of internal secretion due to the wide variety of released factors and functions with local effects, including the paracrine/autocrine production of GH or IGF-I, for which the endothelium has specific receptors. In this comprehensive review, the evidence involving these proangiogenic hormones in arteriogenesis dealing with the arterial occlusion and making of them a potential therapy is described. All the elements that trigger the local and systemic production of GH/IGF-I, as well as their possible roles both in physiological and pathological conditions are analyzed. All of the evidence is combined with important data from the GHAS trial, in which GH or a placebo were administrated to patients suffering from critical limb ischemia with no option for revascularization. We postulate that GH, alone or in combination, should be considered as a promising therapeutic agent for helping in the approach of ischemic disease.

Neonatal cardiac hypertrophy: the role of hyperinsulinism-a review of literature

Hypertrophic cardiomyopathy (HCM) in neonates is a rare and heterogeneous disorder which is characterized by hypertrophy of heart with histological and functional disruption of the myocardial structure/composition. The prognosis of HCM depends on the underlying diagnosis. In this review, we emphasize the importance to consider hyperinsulinism in the differential diagnosis of HCM, as hyperinsulinism is widely associated with cardiac hypertrophy (CH) which cannot be distinguished from HCM on echocardiographic examination. We supply an overview of the incidence and treatment strategies of neonatal CH in a broad spectrum of hyperinsulinemic diseases. Reviewing the literature, we found that CH is reported in 13 to 44% of infants of diabetic mothers, in approximately 40% of infants with congenital hyperinsulinism, in 61% of infants with leprechaunism and in 48 to 61% of the patients with congenital generalized lipodystrophy. The correct diagnosis is of importance since there is a large variation in prognoses and there are various strategies to treat CH in hyperinsulinemic diseases.Conclusion: The relationship between CH and hyperinsulism has implications for clinical practice as it might help to establish the correct diagnosis in neonates with cardiac hypertrophy which has both prognostic and therapeutic consequences. In addition, CH should be recognized as a potential comorbidity which might necessitate treatment in all neonates with known hyperinsulinism.What is Known:• Hyperinsulinism is currently not acknowledged as a cause of hypertrophic cardiomyopathy (HCM) in textbooks and recent Pediatric Cardiomyopathy Registry publications.What is New:• This article presents an overview of the literature of hyperinsulinism in neonates and infants showing that hyperinsulinism is associated with cardiac hypertrophy (CH) in a broad range of hyperinsulinemic diseases.• As CH cannot be distinguished from HCM on echocardiographic examination, we emphasize the importance to consider hyperinsulinism in the differential diagnosis of HCM/CH as establishing the correct diagnosis has both prognostic and therapeutic consequences.

Caveolin-1 phosphorylation regulates vascular endothelial insulin uptake and is impaired by insulin resistance in rats

AIMS/HYPOTHESIS

As insulin entry into muscle interstitium is rate-limiting for its overall peripheral action, defining the route and regulation of its entry is critical. Caveolin-1 is required for caveola formation in vascular endothelial cells (ECs) and for EC insulin uptake. Whether this requirement reflects simply the need for caveola availability or involves a more active role for caveolae/caveolin-1 is not known. Here, we examined the role of insulin-stimulated tyrosine 14 (Tyr(14))-caveolin-1 phosphorylation in mediating EC insulin uptake and the role of cellular Src-kinase (cSrc), TNF-α/IL-6 and high fat diet (HFD) in regulating this process.

METHODS

Freshly isolated ECs from normal or HFD-fed rats and/or cultured ECs were treated with FITC-labelled or regular insulin with or without a Src or phosphotidylinositol-3-kinase inhibitor, TNF-α or IL-6, or transfecting FLAG-tagged wild-type (WT) or mutant (Y14F) caveolin-1. Tyr(14)-caveolin-1/Tyr(416) cSrc phosphorylation and FITC-insulin uptake were quantified by immunostaining and/or western blots.

RESULTS

Insulin stimulated Tyr(14)-caveolin-1 phosphorylation during EC insulin uptake. Inhibiting cSrc, but not phosphotidylinositol-3-kinase, reduced insulin-stimulated caveolin-1 phosphorylation. Furthermore, inhibiting cSrc reduced FITC-insulin uptake by ∼50%. Overexpression of caveolin-1Y14F inhibited, while overexpression of WT caveolin-1 increased, FITC-insulin uptake. Exposure of ECs to TNF-α or IL-6, or to 1-week HFD feeding eliminated insulin-stimulated caveolin-1 phosphorylation and inhibited FITC-insulin uptake to a similar extent.

CONCLUSIONS/INTERPRETATION

Insulin stimulation of its own uptake requires caveolin-1 phosphorylation and Src-kinase activity. HFD in vivo and proinflammatory cytokines in vitro both inhibit this process.

Estrogen-IGF-1 interactions in neuroprotection: ischemic stroke as a case study

The steroid hormone 17b-estradiol and the peptide hormone insulin-like growth factor (IGF)-1 independently exert neuroprotective actions in neurologic diseases such as stroke. Only a few studies have directly addressed the interaction between the two hormone systems, however, there is a large literature that indicates potentially greater interactions between the 17b-estradiol and IGF-1 systems. The present review focuses on key issues related to this interaction including IGF-1 and sex differences and common activation of second messenger systems. Using ischemic stroke as a case study, this review also focuses on independent and cooperative actions of estrogen and IGF-1 on neuroprotection, blood brain barrier integrity, angiogenesis, inflammation and post-stroke epilepsy. Finally, the review also focuses on the astrocyte, a key mediator of post stroke repair, as a local source of 17b-estradiol and IGF-1. This review thus highlights areas where significant new research is needed to clarify the interactions between these two neuroprotectants.

Endothelial Insulin Resistance Protects the Heart Against Prolonged Ischemia–Reperfusion Injury But Does Not Prevent Insulin Transport Across the Endothelium in a Mouse Langendorff Model

Aim:

The endothelium plays an important role in the maintenance of cardiovascular homeostasis in healthy individuals. Insulin resistance can lead to the development of endothelial dysfunction, which is an important step in the pathogenesis of atherosclerosis. We investigated specifically whether the presence of vascular insulin resistance and endothelial dysfunction has any influence on the myocardial tolerance to ischemia–reperfusion (IR) injury, using Endothelial Specific Mutant Insulin Receptor Over-expressing (ESMIRO) mice, which exhibit vascular insulin resistance and vascular dysfunction.

Methods:

ESMIRO or wild-type (WT) littermate mouse hearts were isolated and perfused on a Langendorff apparatus. These were subjected to either 35-minute or 45-minute ischemia followed by reperfusion, after which infarct size was determined. The ability of insulin to activate its target kinase pathway, that is, phosphoinositide 3 (PI3) kinase/protein kinase B (AKT) in ESMIRO hearts was also assessed by Western blot analysis.

Results:

Compared to 35-minute ischemia, the extended 45-minute ischemic protocol significantly exacerbated myocardial infarction in WT mice, (56% ± 4%, n = 6 vs 32% ± 4%, n = 9; P < .01) but not in ESMIRO littermates (34% ± 7%, n = 6 vs 32% ± 3%, n = 9; not significant), suggesting some form of protective phenotype. Insulin treatment was associated with a significant increase in AKT phosphorylation in the myocardium in both the ESMIRO mice and WT littermates, and this was attenuated in both by inhibition of PI3 kinase using LY294002. Thus, insulin was able to directly activate PI3 kinase/AKT in the myocardium despite the absence of functional endothelial insulin receptors in the ESMIRO mice.

Conclusion:

(1) Insulin at pharmacologic concentrations can be transported across the endothelium independent of vascular insulin receptors and (2) vascular insulin resistance and/or endothelial dysfunction are protective against prolonged IR injury in the Langendorff model.

Age-related macular degeneration-associated silent polymorphisms in HtrA1 impair its ability to antagonize insulin-like growth factor 1

Synonymous single nucleotide polymorphisms (SNPs) within a transcript's coding region produce no change in the amino acid sequence of the protein product and are therefore intuitively assumed to have a neutral effect on protein function. We report that two common variants of high-temperature requirement A1 (HTRA1) that increase the inherited risk of neovascular age-related macular degeneration (NvAMD) harbor synonymous SNPs within exon 1 of HTRA1 that convert common codons for Ala34 and Gly36 to less frequently used codons. The frequent-to-rare codon conversion reduced the mRNA translation rate and appeared to compromise HtrA1's conformation and function. The protein product generated from the SNP-containing cDNA displayed enhanced susceptibility to proteolysis and a reduced affinity for an anti-HtrA1 antibody. The NvAMD-associated synonymous polymorphisms lie within HtrA1's putative insulin-like growth factor 1 (IGF-1) binding domain. They reduced HtrA1's abilities to associate with IGF-1 and to ameliorate IGF-1-stimulated signaling events and cellular responses. These observations highlight the relevance of synonymous codon usage to protein function and implicate homeostatic protein quality control mechanisms that may go awry in NvAMD.

Caveolin-1 is required for vascular endothelial insulin uptake

As insulin's movement from plasma to muscle interstitium is rate limiting for its metabolic action, defining the regulation of this movement is critical. Here, we address whether caveolin-1 is required for the first step of insulin's transendothelial transport, its uptake by vascular endothelial cells (ECs), and whether IL-6 and TNFα affect insulin uptake or caveolin-1 expression. Uptake of FITC-labeled insulin was measured using confocal microscopy in control bovine aortic ECs (bAECs), in bAECs in which caveolin-1 was either knocked down or overexpressed, in murine ECs from caveolin-1(-/-) mice and in bAECs exposed to inflammatory cytokines. Knockdown of caveolin-1 expression in bAECs using specific caveolin-1 siRNA reduced caveolin-1 mRNA and protein expression by ∼ 70%, and reduced FITC-insulin uptake by 67% (P < 0.05 for each). Over-expression of caveolin-1 increased insulin uptake (P < 0.05). Caveolin-1-null mouse aortic ECs did not take up insulin and re-expression of caveolin-1 by transfecting these cells with FLAG-tagged caveolin-1 DNA rescued FITC-insulin uptake. Knockdown of caveolin-1 significantly reduced both insulin receptor protein level and insulin-stimulated Akt1 phosphorylation. Knockdown of caveolin-1 also inhibited insulin-induced caveolin-1 and IGF-1 receptor translocation to the plasma membrane. Compared with controls, IL-6 or TNFα (20 ng/ml for 24 h) inhibited FITC-insulin uptake as well as the expression of caveolin-1 mRNA and protein (P < 0.05 for each). IL-6 or TNFα also significantly reduced plasma membrane-associated caveolin-1. Thus, we conclude that insulin uptake by ECs requires expression of caveolin-1 supporting a role for caveolae mediating insulin uptake. Proinflammatory cytokines may inhibit insulin uptake, at least in part, by inhibiting caveolin-1 expression.

Pituitary macroadenoma co-existent with supraclinoid internal carotid artery cerebral aneurysm: a case report and review of the literature

With improved angiographic techniques and magnetic resonance angiography available today, an increasing number of incidental aneurysms are being detected. Occurrence of an intracranial aneurysm together with a pituitary adenoma presents tremendous risk to the patient, particularly when the aneurysm lies near the operative field.

A 61-year-old woman presented with a progressive visual field defect. Neurological examination revealed bi-temporal haemianopia. Cerebral magnetic resonance imaging and angiography revealed a pituitary macroadenoma co-existent with a cerebral aneurysm near the sellar region. The patient underwent an endovascular procedure for aneurysm embolisation and then underwent surgery for removal of the pituitary adenoma via a trans-sphenoidal approach.

We report our experience and emphasize the need for critical evaluation of neuroradiological examinations for precise diagnosis for avoiding a possible life-threatening situation.

Transcriptome and proteome expressions involved in insulin resistance in muscle and activated T-lymphocytes of patients with type 2 diabetes

We analyzed the genes expressed (transcriptomes) and the proteins translated (pro- teomes) in muscle tissues and activated CD4(+) and CD8(+) T-lymphocytes (T-cells) of five Type 2 diabetes (T2DM) subjects using Affymetrix microarrays and mass spectrometry, and compared them with matched non-diabetic controls. Gene expressions of insulin receptor (INSR), vitamin D receptor, insulin degrading enzyme, Akt, insulin receptor substrate-1 (IRS-1), IRS-2, glucose transporter 4 (GLUT4), and enzymes of the glycolytic pathway were decreased at least 50% in T2DM than in controls. However, there was greater than two-fold gene upregulation of plasma cell glycoprotein-1, tumor necrosis factor alpha (TNFalpha, and gluconeogenic enzymes in T2DM than in controls. The gene silencing for INSR or TNFalpha resulted in the inhibition or stimulation of GLUT4, respectively. Proteome profiles corresponding to molecular weights of the above translated transcriptomes showed different patterns of changes between T2DM and controls. Meanwhile, changes in transcriptomes and proteomes between muscle and activated T-cells of T2DM were comparable. Activated T-cells, analogous to muscle cells, expressed insulin signaling and glucose metabolism genes and gene products. In conclusion, T-cells and muscle in T2DM exhibited differences in expression of certain genes and gene products relative to non-diabetic controls. These alterations in transcriptomes and proteomes in T2DM may be involved in insulin resistance.

Differential regulation of pregnancy associated plasma protein-A in human coronary artery endothelial cells and smooth muscle cells

BACKGROUND

Pregnancy-associated plasma protein-A (PAPP-A), a metalloproteinase that serves to modulate local insulin-like growth factor (IGF) action, is upregulated in atherosclerotic plaque. However, little is known about the cellular mechanisms underlying this elevated PAPP-A.

OBJECTIVE

To continue study of PAPP-A expression and its regulation in human vascular cells, with a focus on endothelial cells.

DESIGN

Primary cultures of human coronary artery endothelial cells (ECs) were treated without and with cytokines, growth factors, or low density lipoprotein (LDL). PAPP-A mRNA, protein, and protease activity were assessed using real-time PCR, ultra-sensitive PAPP-A ELISA and cell-free proteolysis of IGF binding protein (IGFBP-4), respectively. In addition, vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), monocyte chemotactic protein (MCP-1), IGF-I, IGF-I receptor, and IGFBP-4 and -5 mRNA expression levels were determined.

RESULTS

ECs in culture show little basal PAPP-A expression. The pro-inflammatory cytokines, tumor necrosis factor (TNF)-alpha and interleukin (IL)-beta, stimulated PAPP-A expression (TNF-alpha>>IL-1beta), whereas there was no effect of IL-6, transforming growth factor-beta, IGF-I, insulin, fibroblast growth factor or epidermal growth factor in these cells. Stimulation of PAPP-A expression by TNF-alpha was associated with significantly increased VCAM, ICAM, and MCP-1 expression but without major changes in other IGF system components. TNF-alpha-induced VCAM, ICAM, and MCP-1 expression (4h) preceded PAPP-A expression (24h). The anti-oxidant, N-acetyl cysteine, inhibited TNF-alpha-induced PAPP-A expression without altering the induction in VCAM, ICAM, and MCP-1. Treatment with native or oxidized LDL had no effect on PAPP-A expression in ECs. Comparative results in human coronary smooth muscle cells indicated qualitative and quantitative differences in PAPP-A expression and regulation between the two vascular cell types.

CONCLUSIONS

Human coronary artery ECs express PAPP-A mRNA and functional protein when activated by the pro-inflammatory cytokine, TNF-alpha. This study complements work on PAPP-A expression in human coronary artery SMCs and human monocyte-derived macrophages and suggests an interactive model of PAPP-A regulation and action in human atherosclerotic plaque.

Expression of insulin-like growth factor system genes during the early postnatal neurogenesis in the mouse hippocampus

Insulin-like growth factor-1 (IGF-1) is essential to hippocampal neurogenesis and the neuronal response to hypoxia/ischemia injury. IGF (IGF-1 and -2) signaling is mediated primarily by the type 1 IGF receptor (IGF-1R) and modulated by six high-affinity binding proteins (IGFBP) and the type 2 IGF receptor (IGF-2R), collectively termed IGF system proteins. Defining the precise cells that express each is essential to understanding their roles. With the exception of IGFBP-1, we found that mouse hippocampus expresses mRNA for each of these proteins during the first 2 weeks of postnatal life. Compared to postnatal day 14 (P14), mRNA abundance at P5 was higher for IGF-1, IGFBP-2, -3, and -5 (by 71%, 108%, 100%, and 98%, respectively), lower for IGF-2, IGF-2R, and IGFBP-6 (by 65%, 78%, and 44%, respectively), and unchanged for IGF-1R and IGFBP-4. Using laser capture microdissection (LCM), we found that granule neurons and pyramidal neurons exhibited identical patterns of expression of IGF-1, IGF-1R, IGF-2R, IGFBP-2, and -4, but did not express other IGF system genes. We then compared IGF system expression in mature granule neurons and their progenitors. Progenitors exhibited higher mRNA levels of IGF-1 and IGF-1R (by 130% and 86%, respectively), lower levels of IGF-2R (by 72%), and similar levels of IGFBP-4. Our data support a role for IGF in hippocampal neurogenesis and provide evidence that IGF actions are regulated within a defined in vivo milieu.

In Human Endothelial Cells Amino Acids Inhibit Insulin-induced Akt and ERK1/2 Phosphorylation by an mTOR-dependent Mechanism

In several cellular systems, amino acids synergize with insulin in promoting protein synthesis through the activation of the protein kinases p70/S6-K and PHAS-1. Such activations are mediated by the upstream kinase: mammalian target of rapamycin (mTor). In this work we have investigated the intracellular pathways involved in insulin-induced and amino acid-induced p70/S6-K activations in human endothelial cells. In human umbilical vein endothelial cells, insulin induces the phosphorylation of p70/S6-K at 5 minutes decreasing thereafter, whereas amino acids alone or associated with insulin phosphorylate p70/S6-K at all the time points analyzed (60 minutes). Insulin and amino acids phosphorylate p70/S6-K by mTor-dependent and phosphotidylinositol 3-kinase-dependent mechanisms, whereas the mitogen-activated protein kinase pathway is involved only when p70/S6-K is activated by insulin. Insulin induces the phosphorylation of Akt and extracellular signal-regulated protein kinase (ERK) 1/2, whereas amino acids did not. Moreover, amino acids suppress the phosphorylations induced by insulin. The inhibitory effects of amino acids are reverted by the mTor inhibitor rapamycin. Insulin-induced phosphorylation of Akt (at 15 and 30 minutes) is not accompanied by the phosphorylation of the downstream kinase p70/S6-K, indicating the existence of a negative feedback at this level. Our data demonstrate that at the level of human endothelial cells, amino acids synergize with insulin in the phosphorylation of the kinase that lies downstream mTor, as p70/S6-K, whereas they inhibit the upstream kinases Akt and extracellular signal-regulated protein kinase 1/2 when activated by insulin, by an mTor-dependent mechanism.

De novo emergence of insulin-stimulated glucose uptake in human aortic endothelial cells incubated with high glucose

Elevated glucose concentrations have profound effects on cell function. We hypothesized that incubation of human aortic endothelial cells (HAEC) with high glucose increases insulin signaling and develops the appearance of insulin-stimulated glucose uptake by the cells. Compared with 5 mM glucose, incubation of HAEC with 30 mM glucose for up to 48 h increased in a time-dependent manner expression of insulin receptor, insulin receptor substrate (IRS)-1, IRS-2, and GLUT1 proteins. High glucose also increased the specific binding of (125)I-labeled insulin in HAEC accompanied by accelerated production of interleukin (IL)-6 and IL-8. Short-term stimulation by 50 microU/ml insulin did not activate [(14)C]glucose uptake by HAEC incubated in 5 mM glucose. However, an addition of insulin to high glucose-exposed endothelial cells led to a significant increase in [(14)C]glucose uptake in a glucose concentration- and time-dependent fashion, reaching a plateau at 48 h of incubation. Furthermore, incubation of HAEC with 30 mM glucose resulted in a new insulin-stimulated extracellular signal-regulated kinase-1/2 mitogen-activated protein kinase phosphorylation and increased lipid peroxidation and production of reactive oxygen species. These studies show for the first time that high glucose increases expression of insulin receptors and downstream elements of the insulin-signaling pathway and transforms "insulin-resistant" aortic endothelial cells into "insulin-sensitive" tissue regarding glucose uptake.

Insulin at physiological concentrations selectively activates insulin but not insulin-like growth factor I (IGF-I) or insulin/IGF-I hybrid receptors in endothelial cells

In muscle, physiologic hyperinsulinemia, presumably acting on endothelial cells (ECs), dilates arterioles and regulates both total blood flow and capillary recruitment, which in turn influences glucose disposal. In cultured ECs, however, supraphysiological (e.g. >or=10 nM) insulin concentrations are typically used to study insulin receptor (IR) signaling pathways and nitric oxide generation. IGF-I receptors (IGF-IRs) are more abundant than IR in ECs, and they also respond to high concentrations of insulin. To address whether IR mediates responses to physiologic insulin stimuli, we examined the insulin concentration dependence of IR and IGF-IR-mediated insulin signaling in bovine aortic ECs (bAECs). We also assessed whether insulin/IGF-I hybrid receptors were present in bAECs. Insulin, at 100-500 pM, significantly stimulated the phosphorylation of IRbeta, Akt1, endothelial isoform of nitric oxide synthase, and ERK 1/2 but not the IGF-IRbeta subunit. At concentrations 1-5 nm or greater, insulin dose-dependently enhanced the tyrosine phosphorylation of IGF-IRbeta, and this was inhibited by IGF-IR neutralizing antibody. In addition, immunoprecipitation of IRbeta pulled down the IGF-IRbeta, and the IRbeta immunocytochemically colocalized with IGF-IRbeta, suggesting that ECs have insulin/IGF-I hybrid receptors. We conclude that: 1) insulin at physiological concentrations selectively activates IR signaling in bAECs; 2) bAECs express IGF-IR and insulin/IGF-I hybrid receptors in addition to IR; 3) high concentrations of insulin (>or=1-5 nM) activate IGF-IR and hybrid receptors as well as IR; and 4) this crossover activation can confound interpretation of studies of insulin action in ECs when high insulin concentrations are used.

Redox modulation of insulin signaling and endothelial function

Reactive oxygen and nitrogen species (ROS and RNS) recently emerged as critical signaling molecules in cardiovascular research. Several studies over the past decade have shown that physiological effects of vasoactive factors are mediated by these reactive species and, conversely, that altered redox mechanisms are implicated in the occurrence of metabolic and cardiovascular diseases. Oxidant stress occurs when ROS and/or RNS production exceeds the cell natural antioxidant systems, and pathological events ensue. Cardiovascular risk factors are associated with an imbalance of the redox equilibrium toward oxidative stress, leading to endothelial activation and proinflammatory processes implicated in atherogenesis and metabolic disorders. Recent studies indicate that insulin and insulin-sensitizing drugs activate antiinflammatory pathways that may limit oxidant stress in insulin target tissues. The main goal of this brief review is to discuss recent progress in the field of cellular redox signaling as it pertains to insulin modulation of vascular endothelial function in cardiovascular diseases.

Role of serum insulin-like growth factor I in mammalian brain aging

Modern societies face new public health challenges associated with an increasingly aging population. Among these, pathological conditions linked to brain aging are paramount. Old age is a risk factor for important neurological impairments such as Alzheimer's disease or stroke. Even healthy elderly people usually present with milder forms of cognitive decline. This is possibly related to less-pronounced brain deficits seen in normal aging, including the shrinkage of neurons and the dense network of neurons and glia in the central nervous system known as the neuropil, a lower neurogenetic rate, impaired angiogenesis or brain accumulation of deleterious compounds. At least in mammals, age is also associated with a decline in insulin-like growth factor-I (IGF-I) levels, a well-known neuroprotective agent. Recently, a relationship between serum IGF-I and "house-keeping" mechanisms in the brain has been evidenced in laboratory rodents. Serum IGF-I increases adult neurogenesis, sustains neuronal health through a variety of fundamental homeostatic mechanisms, participates in brain angiogenesis, contributes to brain beta-amyloid clearance and affects learning and memory. Overall, diminished trophic input resulting from decreasing serum IGF-I levels during aging likely contributes to brain senescence in mammals.

Preoperative serum levels of follicle stimulating hormone (FSH) and prognosis in invasive breast cancer

AIMS

We investigated the association between preoperative serum levels of follicle stimulating hormone (FSH) and the prognosis in women with invasive breast cancer.

METHODS

Serum levels of FSH were measured in 182 premenopausal and 581 peri- or postmenopausal women with invasive breast cancer. They were followed for a mean time of 84 months. The study endpoint was death from breast cancer (182 events). Analyses were stratified on menopausal status.

RESULTS

None of the estimates showed a statistically significant result. In both pre- and postmenopausal women there was a nominally higher probability of survival with a higher FSH level. Point estimates in multivariate analysis incorporating age, tumour diameter, axillary lymph status, estrogen and progesterone receptor content and year of treatment indicated a stronger association with FSH levels in premenopausal than postmenopausal women (relative hazard 0.63 or 0.85, respectively in the highest compared with the lowest quartile).

CONCLUSION

We did not find any statistically significant association between preoperative serum level of FSH and prognosis. Today, FSH is not a clinical target for intervention or a clinically useful prognostic factor and the results of clinical studies up to date can only be used for motivation of further experimental laboratory research.

Growth hormone induces eNOS expression and nitric oxide release in a cultured human endothelial cell line

Growth hormone deficiency is linked to cardiovascular disease and particularly increased peripheral vascular resistance. Surprisingly, its role in endothelial nitric oxide (NO) synthetase (eNOS) regulation and NO release is basically unknown. We therefore studied the effects of different doses of somatotropin in cultures of a human endothelial cell line (EAhy926). We investigated expression and activity of eNOS, as well as other target genes known to be deregulated in cardiovascular disease including E-selectin and the lectin-like oxidized low density lipoprotein receptor. Treatment of cultured human endothelial cells with somatotropin resulted in significant (P<0.05) increases of eNOS gene and protein expression, as well as NO release, whereas production of intracellular reactive oxygen species was significantly reduced, at the highest somatotropin dose level. The enhanced eNOS gene/protein expression and enzyme activity correlate well. Our findings are suggestive for a novel role of growth hormone in endothelial biology, and particularly NO production.

Insulin and lysophosphatidylcholine synergistically stimulate NO-dependent cGMP production in human endothelial cells

AIMS

Nitric oxide (NO) is an important regulator of cardiovascular homeostasis. Lysophosphatidylcholine (lyso-PC), a major constituent of oxidized low density lipoproteins (oxLDL), has been reported to impair nitric oxide-dependent vasodilatation. This study investigated the possible mechanism of the lyso-PC effect on insulin-stimulated NO-dependent of cyclic guanosine 3',5'-monophosphate (cGMP) generation in human endothelial cells.

METHODS

The intracellular concentration of cGMP in cultured human umbilical vein endothelial cells (HUVECs) was used to estimate NO production. The levels of endothelial nitric oxide synthase (eNOS) protein expression were assessed by Western blotting analyses.

RESULTS

Both insulin, at physiological concentration, and lyso-PC stimulated rapid and prolonged intracellular of cGMP production, and together induced a marked synergistic response (for short-term stimulation: 1185 +/- 285.9% over control level (100%) compared with insulin and lyso-PC alone (384.8 +/- 67.4% and 357 +/- 205%, respectively; P < 0.001), for long-term stimulation: 3495 +/- 1377%, compared with insulin and lyso-PC alone (663 +/- 131% and 487 +/- 250%, P = 0.002)). Stimulated levels of cGMP accumulation were completely abrogated by NOS inhibitor, indicating NO involvement in the effects of insulin and lyso-PC. Stimulated NO synthesis was not associated with altered eNOS protein expression. Cell subfractionation studies demonstrate that insulin and lyso-PC each alone induced translocation of eNOS from the membrane to the cytosolic compartment and together caused a synergistic translocation.

CONCLUSIONS

The presented data suggest that insulin and lyso-PC synergistically upregulate endothelial NO production via eNOS translocation from the membrane fraction to the cytosol. This study raises the possibility that an interplay between various factors accompanying diabetes can lead to endothelial NO overproduction or desensitization of NO-dependent responses. Appropriate rather than necessarily high levels of nitric oxide is the determinant of vascular health.

Acute effects of growth hormone on vascular function in human subjects

GH is involved in the long-term regulation of peripheral vascular resistance and vascular reactivity. We determined whether GH plays a role in the acute regulation of vascular function in humans. The acute vascular effects of GH were studied in eight healthy subjects according to a double-blind, placebo-controlled design. Forearm blood flow (FBF), vascular resistance, and nitric oxide (NO) production were monitored during a 4-h infusion of GH into the brachial artery at a rate chosen to raise local GH to stress levels (approximately 40 ng/ml). During GH infusion, FBF rose 75% (P < 0.05), whereas forearm vascular resistance decreased comparably (P < 0.05). These changes were paralleled by augmented forearm release of NO (P < 0.02). GH heightened the response of FBF to the endothelium-dependent vasodilator acetylcholine (Ach; P < 0.02). With the highest Ach dose, FBF reached 30.4 +/- 4.2 and 16.9 +/- 3.1 ml/dl x min in the GH and placebo studies, respectively (P < 0.005). The slopes of the dose-response curves also differed markedly (0.45 +/- 0.07 and 0.25 +/- 0.05 ml/dl x min/ microg in the GH and placebo studies, respectively; P < 0.01). GH caused an upward shift of the FBF response to the endothelium-independent vasodilator sodium nitroprusside (P < 0.01), but did not affect the slope of the dose-response curve. GH infusion did not cause any appreciable increment in the venous IGF-I concentration in the test arm. In conclusion, GH acutely lowers peripheral vascular resistance and stimulates endothelial function. These effects are mediated by activation of the NO pathway and appear to be independent of IGF-I.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.

Extracellular angio-associated migratory cell protein plays a positive role in angiogenesis and is regulated by astrocytes in coculture

The extracellular form of angio-associated migratory cell protein (AAMP), a recently discovered protein, plays a positive role in angiogenesis and can be regulated by astrocytes. Angiogenic activities are inhibited by an affinity-purified, polyclonal antibody generated to recombinant AAMP. Inhibition of endothelial cell tube formation was previously shown and now endothelial cell migration assays using this antibody show dose-dependent inhibition (75%) of endothelial cell migration. Also, antisense inhibition has been used to determine the effects of reducing total AAMP (extracellular and intracellular forms). An AAMP-specific antisense oligonucleotide that targets a region near its amino terminus, anti-MES, inhibits (45%) total AAMP production by bovine aortic endothelial cells (BAECs), compared to a negative control oligonucleotide. Paradoxically, comparable use of antisense-MES results in a 27% increase in BAEC motility. Decreased cellular production of total AAMP (via antisense) that results in an increase of endothelial migration contrasts with antibody inhibition of extracellular AAMP that decreases migration. This indicates compartment-specific roles for AAMP in angiogenesis. Transwell cocultures of human astrocytes and BAECs increase (53%) the amount of extracellular AAMP found associated with endothelial cells. Therefore, regulation of extracellular AAMP by astrocytes is hypothesized to aid in angiogenesis of the nervous system. Extracellular AAMP's positive role may be either as a promoter or as a permissive protein in this process.

Insulin inhibits coronary endothelial cell calcium entry and coronary artery relaxation

Hyperinsulinemia is closely related to coronary artery disease. Endothelial cells are important for the control of vascular tone, and dysfunction of endothelial cells has been implicated in coronary artery disease. The direct effects of insulin on coronary endothelial cells are nonetheless unknown. In this study, the acute effects of high-dose insulin were investigated on agonist-induced intracellular Ca(2+) concentration ([Ca(2+)](i)) in porcine coronary endothelial cells and coronary relaxation. Bradykinin (10 n M ) and cyclopiazonic acid (100 microM), an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, provoked large increases in [Ca(2+)](i) in coronary endothelial cells. This increase was dose-dependently inhibited by a 10-min preincubation with high doses of insulin (10, 30, 100 mU/ml). Under Ca(2+)-free conditions, bradykinin and cyclopiazonic acid provoked transient, small increases in [Ca(2+)](i). These increases were not affected by pretreatment with insulin (100 mU/ml). Bradykinin (1, 10, 100, 1,000 n M ) and cyclopiazonic acid (10 microM) significantly relaxed porcine coronary artery rings precontracted with histamine (1 microM). The vasodilator effects of bradykinin and cyclopiazonic acid were dose-dependently inhibited by insulin. These acute effects were not observed at physiologic concentrations. Our data indicate that high-dose insulin inhibits agonist-induced Ca(2+) response in coronary endothelial cells and attenuates agonist-induced coronary vasodilatation. The study suggests that hyperinsulinemia might be associated with coronary artery disease via derangement of endothelial Ca(2+)-dependent functions.

Hypopituitarism and atherosclerosis

In the last decade, retrospective cohort data has provided evidence of premature atherosclerosis in patients with hypopituitarism which may account for the recently observed increased death rate from vascular events in these patients. The exact mechanism(s) for such propensity to atherosclerotic vascular disease is not yet completely clear. It is possible that hormonal factors may be the initiating mechanisms with subsequent secondary metabolic abnormalities acting as risk factors for development of atherosclerosis. This seems to be more evident in female hypopituitary patients compared with their male counterparts. Female patients have higher frequency and more pronounced abnormalities of various risk factors as well as surrogate markers of early vascular disease. This may explain why morbidity and mortality in women is in excess of men in retrospective epidemiological studies. Addressing abnormal hormonal factors, especially in females, is a primary objective in managing these patients both in the clinical arena as well as in trials designed to reduce the risk of atherosclerotic vascular disease in these patients. While short-term growth hormone treatment may ameliorate some of the vascular risk factors and improve endothelial function, it remains to be shown whether this translates into long-term reduction in morbidity and mortality from vascular, especially cerebrovascular, disease.

Effects of insulin-like growth factor-1 on retinal endothelial cell glucose transport and proliferation

Insulin-like growth factor-1 (IGF-1) plays important roles in the developing and mature retina and in pathological states characterized by retinal neovascularization, such as diabetic retinopathy. The effects of IGF-1 on glucose transport and proliferation and the signal transduction pathways underlying these effects were studied in a primary bovine retinal endothelial cell (BREC) culture model. IGF-1 stimulated uptake of the glucose analog 2-deoxyglucose in a dose-dependent manner, with a maximal uptake at 25 ng/mL (3.3 nM) after 24 h. Increased transport occurred in the absence of an increase in total cellular GLUT1 transcript or protein. IGF-1 stimulated activity of both protein kinase C (PKC) and phosphatidylinositol-3 kinase (PI3 kinase), and both pathways were required for IGF-1-mediated BREC glucose transport and thymidine incorporation. Use of a selective inhibitor of the beta isoform of PKC, LY379196, revealed that IGF-1 stimulation of glucose transport was mediated by PKC-beta; however, inhibition of PKC-beta had no effect on BREC proliferation. Taken together, these data suggest that the actions of IGF-1 in retinal endothelial cells couple proliferation with delivery of glucose, an essential metabolic substrate. The present studies extend our general understanding of the effects of IGF-1 on vital cellular activities within the retina in normal physiology and in pathological states such as diabetic retinopathy.

The role of phosphatidylinositol 3-kinase and the mitogen-activated protein kinases in insulin-like growth factor-I-mediated effects in vascular endothelial cells

Despite an improved understanding of the molecular mechanisms of insulin-like growth factor-I (IGF-I) signaling and the recognition that IGF-I mediates many effects in endothelial cells, some of which may be important for atherosclerosis, little is known about the signal transduction pathways that mediate the effects of IGF-I in endothelial cells. To that end, we examined the signaling pathways activated by IGF-I in endothelial cells and their contribution to IGF-I-stimulated endothelial cell migration and nuclear factor (NF)-kappaB-dependent transcription. Treatment of bovine pulmonary artery endothelial cells (PAEC) with IGF-I activated the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)1/2 and ERK5. In contrast, IGF-I had no effect on either c-Jun amino-terminal kinase or p38 kinase activity. IGF-I also activated phosphatidylinositol (PI) 3-kinase, as reflected by increased phosphorylation of AKT: There was no evidence of cross-talk between the ERK and PI 3-kinase pathways in PAEC. In PAEC transiently transfected with pTK81-NFkappaB-Luc, which contained four copies of the NF-kappaB DNA binding site 5' to a minimal promoter and the luciferase gene, treatment with 50 ng/ml IGF-I increased luciferase activity 1.8-fold. Inhibition of ERK activity using PD98059 and PI 3-kinase activity with LY 294002 abrogated the induction of NF-kappaB-dependent transcription by IGF-I, suggesting that both pathways contribute to the effect of IGF-I on NF-kappaBdependent transcription. In contrast to the effect of tumor necrosis factor-alpha on NF-kappaB activation, Western blot analyses demonstrated that IGF-I had no effect on IkappaB phosphorylation and degradation or nuclear translocation and DNA binding of NF-kappaB. These data suggest a direct of effect of IGF-I on nuclear NF-kappaB. IGF-I also increased endothelial cell migration approximately 2-fold, as demonstrated using a Boyden chamber apparatus. IGF-I-induced endothelial cell migration was inhibited, in part, by LY 294002 but not PD98059. Together, these studies demonstrate that IGF-I activates multiple signaling pathways in endothelial cells with little evidence for cross-talk between the pathways. Moreover, these pathways appear to mediate both overlapping and distinct effects in that activation of both PI 3-kinase and the ERKs contributed to the stimulation of NF-kappaB-dependent transcription by IGF-I, whereas only PI 3-kinase mediated IGF-I-stimulated endothelial cell migration.

Angiogenesis: regulators and clinical applications

Angiogenesis is a fundamental process in reproduction and wound healing. Under these conditions, neovascularization is tightly regulated. Unregulated angiogenesis may lead to several angiogenic diseases and is thought to be indispensable for solid tumor growth and metastasis. The construction of a vascular network requires different sequential steps including the release of proteases from "activated" endothelial cells with subsequent degradation of the basement membrane surrounding the existing vessel, migration of endothelial cells into the interstitial space, endothelial cell proliferation, and differentiation into mature blood vessels. These processes are mediated by a wide range of angiogenic inducers, including growth factors, chemokines, angiogenic enzymes, endothelial specific receptors, and adhesion molecules. Finally, when sufficient neovascularization has occurred, angiogenic factors are down-regulated or the local concentration of inhibitors increases. As a result, the endothelial cells become quiescent, and the vessels remain or regress if no longer needed. Thus, angiogenesis requires many interactions that must be tightly regulated in a spatial and temporal manner. Each of these processes presents possible targets for therapeutic intervention. Synthetic inhibitors of cell invasion (marimastat, Neovastat, AG-3340), adhesion (Vitaxin), or proliferation (TNP-470, thalidomide, Combretastatin A-4), or compounds that interfere with angiogenic growth factors (interferon-alpha, suramin, and analogues) or their receptors (SU6668, SU5416), as well as endogenous inhibitors of angiogenesis (endostatin, interleukin-12) are being evaluated in clinical trials against a variety of solid tumors. As basic knowledge about the control of angiogenesis and its role in tumor growth and metastasis increases, it may be possible in the future to develop specific anti-angiogenic agents that offer a potential therapy for cancer and angiogenic diseases.

Endothelium-derived factors as paracrine mediators of prostate cancer progression

BACKGROUND

Vascular endothelium represents a complex network of cells producing a large number of active substrates affecting physiologic, metabolic, and immunologic properties of the whole organism, as well as particular organs or tissues. The potential influence of endothelium-derived paracrine factors on prostate cancer progression has only begun to be examined.

METHODS

This review summarizes recent literature on endothelium-derived factors, including vasoactive agents, peptide growth factors, cytokines, and colony-stimulating factors, involved in the development and progression of prostate cancer.

RESULTS

Endothelial cells produce an array of active substrates, many of which have been shown to influence prostate cancer growth. Available data demonstrate the positive impact of such molecules as endothelin-1, basic FGF, TGF-beta, IL-6, and IL-8 on prostate cancer progression. Many other endothelium-derived factors NO, IGF, PDGF, IL-1, G-CSF, and GM-CSF (Nitric Oxide, Insulin-Like Growth Factor, Platelet-Derived Growth Factor, Interleukin-1, Granulocyte Colony Stimulating Factor, and Granulocyte-Macrophage Colony Stimulating Factor) are, at best, implicated in prostate cancer growth, and in most cases support cancer progression.

CONCLUSIONS

A better understanding of endothelium-derived factors, as paracrine mediators of prostate carcinogenesis and progression, should aid in the development of novel therapeutic strategies.

Growth hormone and hexarelin prevent endothelial vasodilator dysfunction in aortic rings of the hypophysectomized rat

The endothelial vasodilation mechanism(s) has been investigated in aortic rings of hypophysectomized male rats as well as hypophysectomized rats treated for 7 days with growth hormone (GH, 400 microg/kg, s.c.) or hexarelin (80 microg/kg, s.c.). Tissue preparations from intact animals were taken as controls. The results obtained indicate that the release of 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) from aortic rings of hypophysectomized rats was markedly reduced (51%; p<0.01) as compared with that of control preparations; the peak response to cumulative concentration of endothelin-1 (ET-1, from 10(-11) to 10(-5) M) was increased 2.4-fold (p<0.01) versus controls; the relaxant activity of acetylcholine (ACh, from 10(-10) to 10(-4) M) in norepinephrine-precontracted aortic rings was reduced by 39.5+/-4.4%. Pretreatment of hypophysectomized rats with GH or hexarelin markedly antagonized the hyperresponsiveness of the aortic tissue to ET-1 and allowed a consistent recovery of both the relaxant activity of ACh and the generation of 6-keto-PGF1alpha. Collectively these findings support the concept that dysfunction of vascular endothelial cells may be induced by a defective GH function. Because a replacement regimen of GH restored the somatotropic function and increased plasma insulin-like growth factor-I (IGF-I) concentrations in the hypophysectomized rats, it is suggested that IGF-I may have protected the vascular endothelium acting as a biologic mediator of GH action. In contrast to GH, hexarelin replacement neither increased body weight nor affected the plasma concentrations of IGF-I, indicating that its beneficial action on vascular endothelium was divorced from that on somatotropic function and was likely due to activation of specific endothelial receptors.

Growth hormone (GH) replacement therapy reduces serum sialic acid concentrations in adults with GH-deficiency: a double-blind placebo-controlled study

OBJECTIVES

Patients with adult GH-deficiency are thought to have an increased risk of cardiovascular disease. Sialic acid (SA) concentrations have been proposed as a marker of atherosclerotic disease probably related to an inflammatory response of the arterial wall. SA as a marker of cardiovascular disease in adult GH-deficiency and its relation to changes in fasting lipid profile and hormone concentrations have not yet been investigated.

PATIENTS

We performed a randomised, double-blind placebo-controlled study in 18 patients with adult GH-deficiency before and after 3 months GH replacement therapy (0.036 U/kg/d; GH-treated group: 6 females, 3 males; age: 47.3 +/- 5.4 years., mean +/- SEM; placebo-group: 5 females, 4 males; mean age 50.2 +/- 4.7). In addition, SA concentrations were measured in 18 sex and age matched healthy control subjects.

METHODS

Blood samples were obtained after an overnight fast. Serum SA, triglycerides and cholesterol were measured using enzymatic methods. Lipoprotein classes were separated by ultracentrifugation. Insulin and IGF-I were determined by radioimmunoassay, HbA1C was measured by anion exchange liquid chromatography.

RESULTS

SA concentrations of the patients with adult GH-deficiency were not significantly different compared to the control group (GH-deficient group: 2.29 +/- 0.02 mmol/l, mean +/- SEM vs. control group: 2.09 +/- 0.13 mmol/l, P = 0.25). Before GH replacement therapy SA concentrations correlated positively with the patients age (r = 0.45; P < 0.04) and fasting insulin concentrations (r = 0.5; P < 0.03) but not with fasting lipid profile. GH replacement therapy significantly increased IGF-I (GH: + 27 +/- 2.6 vs. placebo: + 1.0 +/- 0.8 nmol/l, P < 0.001) and fasting insulin concentrations (GH: + 71.9 +/- 8.0 vs. placebo: + 19.6 +/- 22.6 pmol/l, P < 0.04) compared to placebo therapy. SA concentrations (GH: - 0.41 +/- 0.15 vs. placebo: - 0.01 +/- 0.12 mmol/l, P < 0.05), total cholesterol (GH: - 0.71 +/- 0.16 vs. placebo: 0.23 +/- 0.21 mmol/l, P < 0.003) and LDL-cholesterol (- 0.71 +/- 0.14 vs. placebo: - 0.12 +/- 0.21 mmol/l P < 0.04) significantly decreased after GH replacement therapy compared to placebo therapy. No significant correlation between changes in SA concentrations and changes in lipid profile were observed following GH replacement therapy.

CONCLUSION

These results suggest that, firstly, GH replacement therapy may have a beneficial effect on the pathogenesis of atherosclerosis despite the increase in insulin concentrations, a surrogate marker of insulin resistance, secondly, the proposed beneficial effect of GH on the atherosclerotic process is likely to be multifactorial and cannot only be explained by changes in lipid profile and finally, SA might be a useful marker for the process of atherosclerotic disease in interventional studies.

Growth hormone replacement therapy in adults with growth hormone deficiency improves vascular reactivity

OBJECTIVE

Patients with adult growth hormone (GH) deficiency are thought to be of increased risk of cardiovascular disease. Impaired vascular reactivity to endothelium derived nitric oxid (NO) is an early event in the development of atherosclerosis. In order to detect a possible effect of GH on vascular endothelium we examined forearm vasodilator responses in 8 patients with adult GH-deficiency before and after 3 months GH replacement therapy.

METHODS

Forearm blood flow studies were performed using venous occlusion plethysmography. Blood flow was measured at baseline and during intra-arterial infusions of 3 cumulative doses (7.5, 15 and 30 microg/minutes) of acetylcholine chloride and of sodium nitroprusside (1, 3 and 10 microg/minutes). Fasting blood samples were collected for measurement of lipid profile, Haemoglobin A1C (HbA1C), glucose, IGF-I and insulin.

RESULTS

GH replacement therapy significantly increased IGF-I concentrations and tended to increase fasting insulin concentrations (IGF-I: 72.7 +/- 12.4 vs. 130.8 +/- 18.5 microg/l, P < 0.001; fasting insulin: 14.3 +/- 3.4 vs. 32.9 +/- 18.6, mU/l, P = 0.06). Fasting lipid profile, glucose and HbA1C did not significantly change. Blood flow responses to acetylcholine were significantly greater after GH replacement therapy (10.3 +/- 1.0 vs. 17.6 +/- 2.5 ml/minutes/100 ml for the highest dose, P < 0.03). There was a strong tendency to increased blood flow response to nitroprusside after GH therapy (10.7 +/- 1.2 vs. 17.5 +/- 1.7 ml/minutes/100 ml for the highest dose, P = 0.06).

CONCLUSION

These findings suggest that GH replacement therapy may have a beneficial effect on endothelium function which is independent of quantitative changes in fasting lipid profile.

Growth hormone (GH) and atherosclerosis: changes in morphology and function of major arteries during GH treatment

Patients with hypopituitarism have increased carotid artery intima-media thickness and reduced arterial distensibility. The effect of 2 years of growth hormone (GH) replacement therapy on these parameters was studied in 11 GH-deficient men (age range, 24-49 years) with hypopituitarism and compared with 12 healthy, age-matched men with no evidence of pituitary or vascular disease. Before treatment the intima-media of the common carotid arteries and the carotid bifurcations were significantly thicker in patients (P < 0.001) than in the control group. Treatment with GH normalized the intima-media thickness of the common carotid artery within 6 months and of the carotid bifurcation within 3 months. The changes in intima-media thickness of the carotid artery were negatively correlated with changes in serum levels of insulin-like growth factor I during treatment. There was a significant improvement in flow-mediated, endothelium-dependent dilation of the brachial artery at 3 months, which was sustained at 6, 18 and 24 months of GH treatment (P < 0.05). Thus, GH replacement therapy in GH-deficient men reverses early morphological and functional atherosclerotic changes in major arteries, and may reduce rates of vascular morbidity and mortality.

Pharmacological modulation of endothelial function by insulin in the rat aorta

Nitric oxide (NO)-mediated vasodilation induced by hyperinsulinaemia might involve an indirect action which promotes agonist-stimulated endothelial function. Our aim was to attempt to demonstrate such modulation of endothelium-dependent vasodilation by insulin in the rat isolated aorta. We found that vasodilation in response to acetylcholine, but not to adenosine diphosphate (ADP), histamine or the calcium ionophore A23187, was modestly enhanced after 20-min pretreatment with human insulin (100 nM) whereas endothelium-independent responses to the NO donor sodium nitroprusside were not significantly affected. Human insulin thus has the acute pharmacological action of selectively enhancing muscarinic receptor-mediated endothelial function in rat aortic vascular smooth muscle in-vitro.

Insulin-like growth factors in plasma and afferent mammary lymph of lactating cows deprived of feed or treated with bovine somatotropin

The galactopoietic actions of bovine somatotropin are both direct and indirect. Indirect actions are apparently mediated by the insulin-like growth factor (IGF) system. The objective of this study was to compare systemic (plasma) versus local (lymph) concentrations of IGF. Afferent mammary lymph most nearly represents the extracellular fluid that is bathing mammary tissue. Catheters were surgically implanted in the jugular vein and the superficial afferent mammary lymph vessels of four lactating cows. A crossover design was utilized to evaluate the effects of bovine somatotropin (bST). After 2 d of basal sampling, either bST (40 mg/d) or excipient was administered daily for 5 d. After the conclusion of the bST study, a second study was conducted in which cows were deprived of feed for 36 h. Blood and lymph were simultaneously sampled at least every 6 h throughout both studies. Milk yield was increased by bST, and concentrations of IGF-I were increased in plasma and lymph. The relationship between plasma and lymph concentrations for IGF-II, bST, insulin, glucose, urea nitrogen, and nonesterified fatty acids were similar during bST treatment. Milk yield was reduced 76% by 36 h of feed deprivation. Feed deprivation also caused a reduction of IGF-I in plasma, but concentrations of IGF-I in lymph were not altered. In contrast, changes in IGF-II, bST, insulin, glucose, urea nitrogen, and nonesterified fatty acids that were caused by feed deprivation followed similar patterns in plasma and lymph. Clearly, if IGF-I mediates the mammary actions of bST, then concentrations of IGF-I in plasma correlate with milk yield responses as well as, if not better than, concentrations in lymph.

Serum total IGF-I, free IGF-I, and IGFB-1 levels in an elderly population: relation to cardiovascular risk factors and disease

Recently, a method to measure free insulin-like growth factor-I (IGF-I) levels has been developed. Free IGF-I levels may have greater physiological and clinical relevance than total (bound and free) IGF-I. The associations between the circulating IGF-I/IGF binding protein (IGFBP) system and cardiovascular disorders was studied. In a cross-sectional study of 218 healthy persons (103 men, 115 women) aged 55 to 80 years, fasting serum (total and free) IGF-I and IGFBP-1 levels, lipid profile, insulin, and glucose were measured. In addition, blood pressure, body mass index (BMI), and waist-hip ratio (WHR) were measured. Ultrasonography of both carotid arteries was performed to investigate the presence of atherosclerotic lesions. A history of angina pectoris, the presence of a possible or definite myocardial infarction on the ECG, and plaques in the carotid arteries were used as indicators of presence of cardiovascular signs and symptoms. Free IGF-I was inversely related to serum triglycerides (P=.04, adjusted for age and sex). Mean free IGF-I levels in subjects without signs or symptoms of cardiovascular diseases were significantly higher than in those with at least one cardiovascular symptom or sign (P=.002, adjusted for age and sex). Free IGF-I levels were also higher in subjects who had no atherosclerotic plaques in the carotid arteries (P=.02, adjusted for age and sex) and who had never smoked (P=.02, adjusted for age and sex). IGFBP-1 showed an inverse relation with insulin, BMI, and WHR and a positive relation with HDL cholesterol. The associations between IGFBP-1 levels and HDL cholesterol, WHR, and BMI remained significant after adjustment for fasting insulin levels. High fasting serum free IGF-I levels are associated with a decreased presence of atherosclerotic plaques and coronary artery disease and lower serum triglycerides, whereas high fasting IGFBP-1 levels are associated with a more favorable cardiovascular risk profile. The findings suggest that the IGF-I/IGFBP system is related to cardiovascular risk factors and atherosclerosis.

Effects of insulin-like growth factor I on the renal juxtamedullary microvasculature

To characterize the effects on the rat renal preglomerular microvasculature of insulin-like growth factor I (IGF-I), experiments were performed using the in vitro blood-perfused juxtamedullary nephron preparation. IGF-I induced a reversible vasodilation of pre- but not postglomerular microvessels in a dose-dependent manner (10(-9)-10(-7) M). The IGF-I-induced vasodilation was similar in all preglomerular vascular segments: interlobular artery, 11.5 +/- 1.2% of control (n = 16); mid-afferent arterioles, 11.6 +/- 1.7% (n = 24); and juxtaglomerular afferent segments, 16.1 +/- 2.8% (n = 19). Renal autoregulatory capacity was not reduced by IGF-I. Pretreatment with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (10(-4) M) completely inhibited the vasodilatory response to IGF-I. IGF-I induced a rapid increase of NO concentration in intact renal microvessels, monitored by a NO-selective voltametric microelectrode. Pretreatment with the cyclooxygenase inhibitor indomethacin (10(-5) M) not only abrogated the IGF-I-induced dilation, but, moreover, IGF-I elicited a small but significant (approximately 10%) vasoconstriction in all preglomerular vessels. These results indicate that the renal vascular effects of IGF-I involve activation of two endogenous vasodilators (NO and vasodilatory prostaglandins). In addition, IGF-I may also release an undefined vasoconstrictor.

Cell adhesion molecules and insulin-like growth factor-1 in vascular disease

PURPOSE

Recent advances in the understanding of the biologic mechanisms of vascular diseases suggest that multifactorial stimulation of the endothelial cell and its subsequent adhesion to leukocytes is a prerequisite to the formation of atherosclerotic and restenotic lesions. As leukocyte-endothelial cell interaction is coordinated by a variety of cell adhesion molecules (CAMs), we hypothesized that the expression of certain CAMs is up-regulated in the vasculature of patients who have peripheral vascular disease. In addition, we proposed that insulin-like growth factor-1 (IGF-1) increases monocyte-endothelial adhesion by means of upregulation of these CAMs.

METHODS

Using immunohistochemical techniques, the expression of intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), E-selectin, and P-selectin was examined in human vascular disease specimens. Normal aortas obtained from the organ retrieval system were studied as control specimens. Adhesion studies between human umbilical vein endothelial cells (HUVECs) incubated with IGF-1 and purified human blood monocytes labeled with 51chromium were completed. Western blotting and flow cytometry were performed to show CAM expression on IGF-1-treated HUVECs.

RESULTS

Of the CAMs, ICAM-1, P-selectin, and E-selectin were distinctly increased in diseased specimens when compared with control specimens (p < 0.05). Adhesion studies showed an increase in monocyte-endothelial cell adhesion of as much as 40% to 45% (p < 0.01) over baseline, with peak adherence occurring 4 hours after treatment with IGF-1. IGF-1 increased adherence in a dose- and time-dependent manner. The threshold concentration of IGF-1 that induced increased adhesion was 20 ng/ml, with a maximum effect occurring at 150 ng/ml. This increased adhesion was attenuated by pretreatment with IGF-I receptor antibody, as well as with genistein and herbimycin-A, which are potent and selective tyrosine kinase inhibitors. Increased adhesion correlated with an increase in the expression of CAMs on the surface of the HUVECs. An additive effect on adhesion was observed between IGF-1 and tumor necrosis factor-alpha (TNF-alpha) and endothelin-1 (ET-1). Finally, immunohistochemical analysis of human vascular disease specimens revealed an increased expression of IGF-1 receptors as compared with control specimens (p < 0.05).

CONCLUSIONS

These results suggest that IGF-1 may be important in the pathogenesis of peripheral vascular disease by increasing endothelial cell-monocyte adhesion by means of an increase in the expression of ICAM-1 and VCAM-1.

Experimentally induced acute hyperinsulinemia stimulates endogenous nitric oxide production in humans: detection using urinary NO2-/NO3-excretion

Insulin-mediated glucose metabolism in skeletal muscle is associated with a proportional increase in muscle perfusion. The vasodilatory effect of insulin is thought to be mediated in part by endothelium-derived nitric oxide (NO). The present study was performed to determine whether acute hyperinsulinemia has any stimulatory effect on endogenous NO production in humans. Bolus intravenous injection of insulin (0.1 IU/kg body weight) caused a significant increase in urinary excretion of NO2-/NO3- together with a significant decrease in blood pressure, whereas saline infusion alone had no effect on these parameters. The increased NO response to insulin was almost comparable to that obtained with infusion of 30 g L-arginine. The acute effect of hyperinsulinemia on endogenous NO formation supports the concept that NO may mediate the vasodilatory action of insulin in humans.

Nitric oxide may mediate the hemodynamic effects of recombinant growth hormone in patients with acquired growth hormone deficiency. A double-blind, placebo-controlled study

We studied the effects of recombinant growth hormone on systemic nitric oxide (NO) formation and hemodynamics in a double-blind, placebo-controlled trial in adult patients with acquired growth hormone deficiency. 30 patients were randomly allocated to either recombinant human growth hormone (r-hGH; 2.0 IU/d) or placebo for 12 mo. In the subsequent 12 mo, the study was continued with both groups of patients receiving r-hGH. In months 1, 3, 6, 9, and 12 of each year, urine and plasma samples were collected for the determination of urinary nitrate and cyclic GMP as indices of systemic NO production, and of plasma IGF-1 levels. Cardiac output was measured in months 1, 12, and 24 by echocardiography. r-hGH induced a fourfold increase in plasma IGF-1 concentrations within the first month of treatment. Urinary nitrate and cyclic GMP excretion rates were low at baseline in growth hormone-deficient patients (nitrate, 96.8+/-7.4 micromol/mmol creatinine; cyclic GMP, 63.6+/-7.1 nmol/mmol creatinine) as compared with healthy controls (nitrate, 167.3+/-7.5 micromol/mmol creatinine; cyclic GMP, 155.2+/-6.9 nmol/mmol creatinine). These indices of NO production were significantly increased by r-hGH, within the first 12 mo in the GH group, and within the second 12 mo in the placebo group. While systolic and diastolic blood pressure were not significantly altered by r-hGH, cardiac output significantly increased by 30-40%, and total peripheral resistance decreased by approximately 30% in both groups when they were assigned to r-hGH treatment. In the second study year, when both groups were given r-hGH, there were no significant differences in plasma IGF-1, urinary nitrate, or cyclic GMP excretion, or hemodynamic parameters between both groups. In conclusion, systemic NO formation is decreased in untreated growth hormone-deficient patients. Treatment with recombinant human growth hormone normalizes urinary nitrate and cyclic GMP excretion, possibly via IGF-1 stimulation of endothelial NO formation, and concomitantly decreases peripheral arterial resistance. Increased NO formation may be one reason for improved cardiovascular performance of patients with acquired hypopituitarism during growth hormone therapy.

Insulin-stimulated production of nitric oxide is inhibited by wortmannin. Direct measurement in vascular endothelial cells

Hypertension is associated with insulin-resistant states such as diabetes and obesity. Nitric oxide (NO) contributes to regulation of blood pressure. To gain insight into potential mechanisms linking hypertension with insulin resistance we directly measured and characterized NO production from human umbilical vein endothelial cells (HUVEC) in response to insulin using an amperometric NO-selective electrode. Insulin stimulation of HUVEC resulted in rapid, dose-dependent production of NO with a maximal response of approximately 100 nM NO (200,000 cells in 2 ml media; ED50 approximately 500 nM insulin). Although HUVEC have many more IGF-1 receptors than insulin receptors (approximately 400,000, and approximately 40,000 per cell respectively), a maximally stimulating dose of IGF-1 generated a smaller response than insulin (40 nM NO; ED50 approximately 100 nM IGF-1). Stimulation of HUVEC with PDGF did not result in measurable NO production. The effects of insulin and IGF-1 were completely blocked by inhibitors of either tyrosine kinase (genestein) or nitric oxide synthase (L-NAME). Wortmannin (an inhibitor of phosphatidylinositol 3-kinase [PI 3-kinase]) inhibited insulin-stimulated production of NO by approximately 50%. Since PI 3-kinase activity is required for insulin-stimulated glucose transport, our data suggest that NO is a novel effector of insulin signaling pathways that are also involved with glucose metabolism.