The role of growth factors in the development of diabetic retinopathy

The estimation of metaloproteinases and their inhibitors blood levels in patients with pancreatic tumors

Background

The aim of the study was to evaluate the concentration of proteolytic enzymes, MMP-2 and MMP-9, and their tissue inhibitors, TIMP-1 and TIMP-2, in the blood of patients with benign and malignant pancreatic tumors.

Methods

MMP-2, MMP-9, TIMP-1, and TIMP-2 were evaluated in the patients with benign and malignant pancreatic tumors before surgery and in the 30-day follow-up. The study covered 134 patients aged 54 to 76 years, who were divided into groups by TNM staging.

Results

Before the operation, the highest mean concentration of MMP-2 was found in patients with unresectable cancer, whereas the highest level of MMP-9 was in patients with resectable cancer. The highest level of TIMP-1 was noted in patients with inflammatory tumors. In 1 month following the operation, the highest level of MMP-2 was also in patients with unresectable cancer and the highest level of TIMP-2 in patients with inflammatory tumors.

Conclusions

The evaluation of the level of the studied cytokines in the pancreatic tumor patients can be diagnostically significant in the differentiation of benign and malignant changes. The changes in the levels of the studied enzymes and their inhibitors can have a prognostic value in the clinical severity of pancreatic cancer.

Hyaluronan production regulation from porcine hyalocyte cell line by cytokines

The objective of this study were to establish a cell line derived from porcine hyalocytes and to investigate the regulation of hyaluronan (HA) synthesis in response to cytokines. After 50 passages of the cells derived from porcine vitreous tissue, a cell line was generated. The immortalized cells showed fibroblastic morphology. The cell doubling time was 56.9h. In the mRNA level, the cells expressed plate-derived growth factor (PDGF) alpha receptor, PDGF beta receptor, transforming growth factor-beta (TGF-beta) type I receptor, TGF-beta type II receptor, CD44, collagen type I, collagen type II, glial fibrillary acidic protein (GFAP), hyaluronan synthase (HAS) 2, HAS 3 and beta-actin. In the protein level, GFAP was expressed in this cell line. S-100 protein and cytokeratin were not detected. Stimulation with TGF-beta1 and/or PDGF-BB induced a marked increase in the expression level of HAS2 mRNA, and induced HA production. TGF-beta1 stimulated HAS2 expression through the signal transduction pathway including Smad 2,3,4. In summary, this report constitutes the first successful immortalization of porcine hyalocyte cells. The production of HA was induced from the generated porcine hyalocyte cell line under the stimulation of TGF-beta1 and/or PDGF-BB, which may be related to the pathogenesis of proliferative membrane formation in proliferative vitreo-retinal diseases.

Systemic IGF-I treatment inhibits cell death in diabetic rat retina

Diabetic retinopathy can result in apoptotic cell death of retinal neurons, as well as significant visual loss. It is further known that insulin-like growth factor (IGF) levels are reduced in diabetes and that IGF-I can prevent cell death in many cell types. In this study, we tested the hypothesis that systemic treatment with IGF-I could inhibit death of neuroretinal cells in diabetic rats by examining the expression of proapoptotic markers. In diabetic rat retina, the number of TUNEL-immunoreactive cells increased approximately sixfold in the photoreceptor layer (P<.001) and eightfold in the inner nuclear layer (INL; P<.001); phospho-Akt (p-Akt; Thr 308) immunoreactivity increased eightfold in the ganglion cell layer (GCL; P<.001) and threefold in the INL (P<.01). Subcutaneous IGF-I treatment significantly reduced the number of TUNEL (P<.001) and p-Akt immunoreactive retinal cells (P<.05) in diabetic rats approximately to the level of the nondiabetic group. Qualitative results showed that caspase-3 and BAD immunoreactivities were also elevated in diabetes and reduced in IGF-I-treated animals. Elevated TUNEL and p-Akt immunoreactivities were localized to distinct cell layers in the retina of diabetic rats. Early intervention with systemic IGF-I reduced the presence of proapoptotic markers indicative of neuroretinal cell death, despite ongoing hyperglycemia and weight loss. The eye is a special sensory organ, and these data show that cell loss in the nervous system, even in uncontrolled diabetes, can be prevented by IGF-I administration.

Angiogenesis in prolactinomas: regulation and relationship with tumour behaviour

Tumours are dependent on angiogenesis for growth and inhibition of angiogenesis has become a target for antineoplastic therapy. In the pituitary, unlike other tissues, vascularization is lower in adenomas compared to the normal gland. Despite this finding, a relationship between increased vascularity and several aspects of prolactinoma behaviour such as size, invasiveness, surgical outcome and malignancy, has been demonstrated. The process of angiogenesis is the result of a balance of stimulating and inhibiting factors. It is likely that an interaction between gene expression (such as pituitary tumour transforming gene (PTTG) and a novel gene located within the Edpm5 quantitative trait locus), hormonal stimuli including oestrogens, dopamine, 16 kDa fragments of prolactin and proangiogenic and antiangiogenic growth factors (for example, vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF-2), determine the final angiogenic phenotype of prolactinomas, and thus subsequent tumour behaviour. The elucidation of all the factors involved in the regulation of angiogenesis and their interactions might open new possibilities in the treatment of prolactinomas, especially in those cases with resistance or intolerance to dopamine agonists.

Effect of acute reduction of free fatty acids by acipimox on growth hormone-releasing hormone-induced GH secretion in type 1 diabetic patients

BACKGROUND

In type 1 diabetes mellitus (DM1), high GH basal levels and exaggerated responses to several stimuli have been described. Acipimox is an antilipolytic drug that produces an acute reduction of free fatty acids (FFA). The aim of this study was to evaluate the effect of the reduction of plasma FFA with acipimox, alone or in combination with GHRH, on GH secretion in DM1.

METHODS

Six type 1 diabetic patients were studied (three women, three men), mean age of 30 +/- 2.1 years, body mass index (BMI) 23.1 +/- 1.5 kg/m2. As a control group, six normal healthy subjects of similar age, sex and weight were studied. Each patient and control received GHRH [1 microg/kg intravenously (i.v.) at min 180], acipimox (250 mg orally at min 0 and 120) and GHRH plus acipimox on three separated days. Subjects served as their own control. Blood samples were taken at appropriate intervals for determination of GH, FFA and glucose.

RESULT

In control subjects, the GH area under the curve (AUC; microg/l x 120 min) was for acipimox-treated 1339 +/- 292 and 1528 +/- 330 for GHRH-induced secretion. The GH AUC after the administration of GHRH plus acipimox was 3031 +/- 669, significantly greater than the response after acipimox alone (P<0.05) or GHRH alone (P<0.05). In diabetic patients, the GH AUC was for acipimox-treated 2516 +/- 606 and 1821 +/- 311 for GHRH-induced secretion. The GH AUC after the administration of GHRH plus acipimox was 7311 +/- 1154, significantly greater than the response after acipimox alone (P<0.05) or GHRH alone (P<0.05). The GH response after acipimox was increased in diabetic when compared with normal (P<0.05), with a GH AUC of 1339 +/- 292 and 2515 +/- 606 for normal subjects and diabetic patients, respectively. The GH response after acipimox plus GHRH was increased in diabetic when compared with normal (P<0.05), with a GH AUC of 3031 +/- 669 and 7311 +/- 1154 for normal subjects and diabetic patients, respectively. The administration of acipimox induced a FFA reduction during the entire test.

CONCLUSIONS

Reduction of free fatty acids with acipimox is a stimulus for GH secretion in DM1. The combined administration of GHRH plus acipimox induces a markedly increased GH secretion in type 1 diabetic patients when compared with normal subjects. These data suggest that patients with DM1 exhibit a greater GH secretory capacity than control subjects, despite the fact that endogenous FFA levels seems to exert a greater inhibitory effect on GH secretion in these patients.

Angiogenesis in endocrine tumors

Angiogenesis is the process of new blood vessel development from preexisting vasculature. Although vascular endothelium is usually quiescent in the adult, active angiogenesis has been shown to be an important process for new vessel formation, tumor growth, progression, and spread. The angiogenic phenotype depends on the balance of proangiogenic growth factors such as vascular endothelial growth factor (VEGF) and inhibitors, as well as interactions with the extracellular matrix, allowing for endothelial migration. Endocrine glands are typically vascular organs, and their blood supply is essential for normal function and tight control of hormone feedback loops. In addition to metabolic factors such as hypoxia, the process of angiogenesis is also regulated by hormonal changes such as increased estrogen, IGF-I, and TSH levels. By measuring microvascular density, differences in angiogenesis have been related to differences in tumor behavior, and similar techniques have been applied to both benign and malignant endocrine tumors with the aim of identification of tumors that subsequently behave in an aggressive fashion. In contrast to other tumor types, pituitary tumors are less vascular than normal pituitary tissue, although the mechanism for this observation is not known. A relationship between angiogenesis and tumor size, tumor invasiveness, and aggressiveness has been shown in some pituitary tumor types, but not in others. There are few reports on the role of microvascular density or angiogenic factors in adrenal tumors. The mechanism of the vascular tumors, which include adrenomedullary tumors, found in patients with Von Hippel Lindau disease has been well characterized, and clinical trials of antiangiogenic therapy are currently being performed in patients with Von Hippel Lindau disease. Thyroid tumors are more vascular than normal thyroid tissue, and there is a clear correlation between increased VEGF expression and more aggressive thyroid tumor behavior and metastasis. Although parathyroid tissue induces angiogenesis when autotransplanted and PTH regulates both VEGF and MMP expression, there are few studies of angiogenesis and angiogenic factors in parathyroid tumors. An understanding of the balance of angiogenesis in these vascular tumors and mechanisms of vascular control may assist in therapeutic decisions and allow appropriately targeted treatment.

Tumour-Induced Angiogenesis: A Review

Angiogenesis, the formation of new blood vessels, has become a broad subject and is a very active area for current research. This paper describes the main biological events involved in angiogenesis and their importance in cancer progression. In the first section, a fundamental overview of tumour biology is presented. In the second section, the biology of healthy blood vessels is described and, in the third section, the mechanisms of cell migration and proliferation, which are crucial to angiogenesis, are discussed. In the fourth section, a detailed account of tumour-induced angiogenesis is given, whilst the pro- and anti-angiogenic factors involved are reviewed in the fifth section. Finally, the processes of tumour invasion and metastasis are examined in the sixth section.

Antiangiogenic effects of somatostatin analogues

Inhibition of angiogenesis has become a target for antineoplastic therapy and for treatment of retinal neovascularization. The presence of somatostatin receptors on tumour cells and on the proliferating vascular endothelium has led to several in vitro and in vivo studies to investigate the antiproliferative and antiangiogenic effects of somatostatin analogues. Currently available data suggest that somatostatin analogues might inhibit angiogenesis directly through somatostatin receptors present on endothelial cells and also indirectly through the inhibition of growth factor secretion such as IGF-I and vascular endothelial growth factor (VEGF) and reducing monocyte chemotaxis. However, beneficial effects on inhibition of neovascularization have been questioned by some studies. More work is therefore required to firmly establish the role of somatostatin analogues as potential antiangiogenic therapy. The currently available somatostatin analogues have high affinity for somatostatin receptor subtype 2 (sst2) and, to a lesser extent, sst5 and sst3. However, because vascular endothelial cells express several types of somatostatin receptors, it will be important to investigate somatostatin analogues with different receptor subtype affinities, which might increase the spectrum of available therapy for tumours.

Haemodynamics in microvascular complications in type 1 diabetes

Type 1 diabetes is commonly associated with microvascular complications. Most of the microvascular blood vessels are involved but those in the kidney, retina and large nerves exhibit the more significant pathology. Haemodynamic and metabolic factors both alone and through the activation of a common pathway contribute to the characteristic dysfunction observed in diabetic vasculopathy. The haemodynamic abnormalities in type 1 diabetes are characterized by increased systemic blood pressure and altered blood flow with subsequent activation of various vasoactive factors, which can contribute to the maintenance of the haemodynamic alterations and to the development and progression of the microvascular complications. These vasoactive factors include vasoconstrictors such as angiotensin II, and endothelin, as well as vasodilators such as nitric oxide (NO). Systemic hypertension and vasoactive factors independently and in interaction with the metabolic pathway activate intracellular second messengers, nuclear transcription factors and various growth factors which lead to the typical functional and structural alterations of diabetic microvascular complications. Therapeutic strategies involved in the management and prevention of diabetic complications currently include antihypertensive agents, particularly those that interrupt the renin-angiotensin system. Further understanding of the interactions among the vasoactive factors, the intracellular second messengers and the growth factors may help to identify novel strategies to influence the action of the vasoactive factors. These novel therapies, together with specific inhibitors of the metabolic pathway or the common pathway, may provide the possibility of preventing or even reversing the progression of diabetic microvascular complications.

Role of vasoactive factors in the pathogenesis of early changes in diabetic retinopathy

Several interactive and mutually perpetuating abnormal biochemical pathways, such as protein kinase C (PKC) activation, augmented polyol pathway, and non-enzymatic glycation, may be activated as a result of sustained hyperglycemia in diabetes. These abnormal pathways may in turn influence several vasoactive factors, which are probably instrumental in the production of functional and morphological changes in the retina in diabetes. The vasoactive factors such as endothelins, nitric oxide, vascular endothelial growth factors, etc., are of importance in mediating functional and structural alterations in early diabetic retinopathy. Intricate and interactive regulatory mechanism(s) among these factors may control ultimate availability of these molecules to produce biologically significant effects. A better understanding of these factors and their interactions would aid the development of adjuvant therapies for the treatment of diabetic retinopathy.

Basic fibroblast growth factor in patients with intermittent claudication: results of a phase I trial

OBJECTIVES

This phase I study was designed to evaluate the safety, tolerability and pharmacokinetics of intra-arterial basic fibroblast growth factor (bFGF) in patients with atherosclerotic peripheral arterial disease (PVD) and intermittent claudication. We also assessed the effects of basic fibroblast growth factor (bFGF) on calf blood flow as a measure of biologic activity.

BACKGROUND

Preclinical studies have shown that bFGF, an angiogenic peptide, promotes collateral development in animal models of myocardial and hind limb ischemia. The safety and efficacy of bFGF in patients is unknown, and early clinical trials are underway in coronary and peripheral arterial disease.

METHODS

A double-blind, placebo-controlled, dose-escalation trial was conducted in patients with claudication demonstrating ankle/brachial index <0.8. Patients were randomly assigned to placebo (n = 6), 10 microg/kg of bFGF (n = 4), 30 microg/kg of bFGF once (n = 5) and 30 microg/kg of bFGF on two consecutive days (n = 4). Study drug was infused into the femoral artery of the ischemic leg. Detailed safety information including retinal photography for neovascularization were obtained through one year. Calf blood flow was measured with strain gauge plethysmography in the two higher dose treatment groups and in four placebo patients at baseline, one month and three to seven months after treatment.

RESULTS

Intra-arterial bFGF was safe and well-tolerated. The half-life was 46 +/- 21 min. Calf blood flow increased at one month by 66 +/- 26% (mean +/- SEM) and at six months by 153 +/- 51% in bFGF-treated patients (n = 9, p = 0.002). Flow did not change significantly in the placebo group.

CONCLUSIONS

In this initial randomized, double-blind, placebo-controlled trial in patients with atherosclerotic PVD and claudication, bFGF was well-tolerated. The data suggest a salutary biologic effect, and initiation of phase 2 trials is warranted.

Reduced retinal vascularization in children with growth hormone deficiency

The neovascularization in diabetic retinopathy is believed to involve locally produced angiogenic factors. In addition, there are indications that GH may influence retinal vascularization. To investigate the role of GH in retinal vascularization, we examined the retinal vascular pattern in children with congenital GH deficiency. Retinal vessel morphology was evaluated by digital image analysis of ocular fundus photographs in 39 children (5 girls and 34 boys, aged 3.6-18.7 yr) with congenital GH deficiency, and it was compared to that of 100 healthy controls. Twenty children had received GH treatment (0.1 IU/kg daily). All children were born at term, and none of the children had any clinical signs of ocular disease or reduced vision. Children with GH insufficiencies, regardless of whether they were treated with GH, had a significantly lower number of vascular branching points than the reference group (P < 0.0001). Thirty-three percent of the GH-insufficient individuals had a number of vascular branching points less than or equal to the fifth percentile of the reference group. The reduced retinal vascularization observed in children with congenital GH deficiency suggests that GH may be of importance for angiogenesis.

Elevated serum levels of soluble vascular cell adhesion molecule-1 in NIDDM patients with proliferative diabetic retinopathy

We studied 68 Japanese NIDDM patients (38 men and 30 women), aged 56.9+/-1.2 years (range 33-75 years), with a BMI of 23.1+/-0.5 kg/m2 without hypertension, dyslipidemia, and diabetic macroangiopathy for evaluating the relationship between serum soluble vascular cell adhesion molecule-1 (sVCAM-1) levels and the severity of diabetic retinopathy. Fundus examination was performed by an ophthalmologist using an ophthalmoscope, and the findings were graded as: (1) no signs of diabetic retinopathy (NDR), (2) background diabetic retinopathy (BDR), or (3) proliferative diabetic retinopathy (PDR). Serum sVCAM-1 levels were measured in duplicate by enzyme-linked immunosorbent assay using the soluble VCAM-1 KIT (R&D Systems Ltd., Ablingdon, Oxfordshire, UK). There was no difference in serum sVCAM-1 levels between patients with BDR (n = 17) and patients with NDR (n = 40) (1035.3+/-104.4 and 978.8+/-48.9 ng/ml, respectively, P = 0.8), but patients with PDR (n = 11) showed a significant increase of serum sVCAM-1 levels compared with patients with NDR (1281.8+/-166.3 and 978.8+/-48.9 ng/ml, respectively, P = 0.02). Although serum sVCAM-1 levels were correlated, not only with age but also with the known diabetic duration (r = 0.39, P = 0.001, and r = 0.40, P = 0.0007, respectively), age-adjusted sVCAM-1 levels were still significantly higher in the PDR group than in the NDR group. In contrast. serum sVCAM-1 levels were not related to the presence of diabetic nephropathy or HbA1c levels. Our results suggest that sVCAM-1 might be implicated in the development of the diabetic retinopathy, and measurement of serum sVCAM-1 levels in NIDDM patients maybe clinically useful for assessing the severity and possibly the activity of diabetic retinopathy.

Intravitreal growth factors in proliferative diabetic retinopathy: correlation with neovascular activity and glycaemic management

AIM

Many growth factors are implicated in proliferative diabetic retinopathy (PDR). It was decided to test the hypothesis that no one factor is predominant but that a regular profile of levels of different growth factors might be operating, and that the profile might differ according to whether or not insulin therapy was part of the patient's glycaemic management. The levels of several growth factors in vitrectomy samples were therefore determined from diabetic patients with tractional, non-haemorrhagic sequelae of PDR and these levels were correlated with (a) each other (growth factor profile), (b) neovascular activity, and (c) the method of glycaemic management (insulin treated (IT) or non-insulin treated (NIT)).

METHODS

72 samples of vitreous were obtained from either diabetic patients with PDR (n = 51) or non-diabetic (control) patients (n = 21). Levels of bFGF, IGF-I, EGF, and insulin were determined by radioimmunoassay; levels of TGF-beta 2 by ELISA; and levels of IGF-I binding protein by western ligand blotting. The data were analysed using appropriate statistics.

RESULTS

There was no regular growth factor profile. bFGF levels were significantly greater in vitreous from NIT patients compared with IT patients and controls. The highest levels of bFGF were found in NIT patients with actively vascularised membranes. TGF-beta 2 levels were significantly greater in vitreous from IT patients compared with NIT patients and controls The highest levels of TGF-beta 2 were found in IT patients with actively vascularised membranes. IGF-I levels were significantly greater in diabetics (irrespective of insulin treatment) than non-diabetics and the highest levels of IGF-I were found in IT patients with actively vascularised membranes. A 34 kDa IGFBP was the predominant IGFBP identified in vitreous and was found to be elevated in diabetics patients.

CONCLUSION

In PDR there is a correlation between intravitreal growth factor levels and both disease state (whether active or fibrotic) and method of glycaemic management.