Effect of glycation on basic fibroblast growth factor induced angiogenesis and activation of associated signal transduction pathways in vascular endothelial cells: possible relevance to wound healing in diabetes

Xylosyltransferase I acceptor properties of fibroblast growth factor and its fragment bFGF (1-24)

Human basic fibroblast growth factor (bFGF) is a heparin-binding growth factor containing a G-S-G-motif which is a potential recognition sequence of xylosyltransferase I (XT-I). Here, we show that the recombinant human bFGF was xylosylated in vitro by human XT-I and that the fragment bFGF (1-24) is a good XT-I acceptor (K(m) = 20.8 microM for native XT-I and K(m) = 22.3 microM for recombinant XT-I). MALDI and MALDI-PSD time-of-flight mass spectrometric analyses of the xylosylated bFGF protein demonstrate the transfer of xylose to the serine residue of the G-S-G-motif in the amino terminal end of bFGF. The peptide bFGF (1-24) is well suitable as an acceptor substrate for XT-I and can be used in a radiochemical assay to measure the XT-I activity in cell culture supernatant and human body fluids, respectively. Furthermore, we could demonstrate that the XT-I interacts strongly with heparin and that this glycosaminoglycan is a predominantly non-competitive inhibitor of the enzyme using the fragment bFGF (1-24) as xylose acceptor.

Impaired retinal angiogenesis in diabetes: role of advanced glycation end products and galectin-3

Suppression of angiogenesis during diabetes is a recognized phenomenon but is less appreciated within the context of diabetic retinopathy. The current study has investigated regulation of retinal angiogenesis by diabetic serum and determined if advanced glycation end products (AGEs) could modulate this response, possibly via AGE-receptor interactions. A novel in vitro model of retinal angiogenesis was developed and the ability of diabetic sera to regulate this process was quantified. AGE-modified serum albumin was prepared according to a range of protocols, and these were also analyzed along with neutralization of the AGE receptors galectin-3 and RAGE. Retinal ischemia and neovascularization were also studied in a murine model of oxygen-induced proliferative retinopathy (OIR) in wild-type and galectin-3 knockout mice (gal3(-/-)) after perfusion of preformed AGEs. Serum from nondiabetic patients showed significantly more angiogenic potential than diabetic serum (P < 0.0001) and within the diabetic group, poor glycemic control resulted in more AGEs but less angiogenic potential than tight control (P < 0.01). AGE-modified albumin caused a dose-dependent inhibition of angiogenesis (P < 0.001), and AGE receptor neutralization significantly reversed the AGE-mediated suppression of angiogenesis (P < 0.01). AGE-treated wild-type mice showed a significant increase in inner retinal ischemia and a reduction in neovascularization compared with non-AGE controls (P < 0.001). However, ablation of galectin-3 abolished the AGE-mediated increase in retinal ischemia and restored the neovascular response to that seen in controls. The data suggest a significant suppression of angiogenesis by the retinal microvasculature during diabetes and implicate AGEs and AGE-receptor interactions in its causation.

Advanced glycation endproducts--role in pathology of diabetic complications

Diabetes mellitus is a common endocrine disorder characterised by hyperglycaemia and predisposes to chronic complications affecting the eyes, blood vessels, nerves and kidneys. Hyperglycaemia has an important role in the pathogenesis of diabetic complications by increasing protein glycation and the gradual build-up of advanced glycation endproducts (AGEs) in body tissues. These AGE form on intra- and extracellular proteins, lipids, nucleic acids and possess complex structures that generate protein fluorescence and cross-linking. Protein glycation and AGE are accompanied by increased free radical activity that contributes towards the biomolecular damage in diabetes. There is considerable interest in receptors for AGEs (RAGE) found on many cell types, particularly those affected in diabetes. Recent studies suggest that interaction of AGEs with RAGE alter intracellular signalling, gene expression, release of pro-inflammatory molecules and free radicals that contribute towards the pathology of diabetic complications. This review introduces the chemistry of glycation and AGEs and examines the mechanisms by which they mediate their toxicity. The role of AGEs in the pathogenesis of retinopathy, cataract, atherosclerosis, neuropathy, nephropathy, diabetic embryopathy and impaired wound healing are considered. There is considerable interest in anti-glycation compounds because of their therapeutic potential. The mechanisms and sites of action of selected inhibitors, together with their potential in preventing diabetic complications are discussed.

Therapeutic Angiogenesis in Peripheral Arterial Disease: Can Biotechnology Produce an Effective Collateral Circulation?

The physiological processes of angiogenesis, vasculogenesis and arteriogenesis contribute to the growth of collateral vessels in response to obstructive arterial disease causing lower limb or myocardial ischaemia, but in clinical practice the endogenous angiogenic response is often suboptimal or impaired, e.g. by factors such as ageing, diabetes or drug therapies. Therapeutic angiogenesis is an application of biotechnology to stimulate new vessel formation via local administration of pro-angiogenic growth factors in the form of recombinant protein or gene therapy, or by implantation of endothelial progenitor cells that will synthesize multiple angiogenic cytokines. Numerous experimental and clinical studies have sought to establish 'proof of concept' for therapeutic angiogenesis in PAD and myocardial ischaemia using different treatment modalities, but the results have been inconsistent. This review summarises the mechanisms of angiogenesis and the results of recent trials evaluating the efficacy and safety of different gene therapy, recombinant protein and cellular-based treatment approaches to enhance collateral vessel formation.

Divergent pathways of gene expression are activated by the RAGE ligands S100b and AGE-BSA

Activation of the receptor for advanced glycation end products (RAGE) reportedly triggers a variety of proinflammatory responses. However, our previous work revealed that RAGE-binding AGEs free of endotoxin were incapable of inducing vascular cell adhesion molecule-1 (VCAM-1) or tumor necrosis factor-alpha (TNF-alpha) expression. Thus, the objective of this study was to clarify the role of AGEs in cell activation through gene expression profiling using both in vitro and in vivo model systems. Endothelial cells treated with AGE-BSA, previously shown to bind RAGE with high affinity, did not show gene expression changes indicative of an inflammatory response. In contrast, the alternate RAGE ligand, S100b, triggered an increase in endothelial mRNA expression of a variety of immune-related genes. The effects of AGEs were studied in vivo using healthy mice exposed to two different treatment conditions: 1) intravenous injection of a single dose of model AGEs or 2) four intraperitoneal injections of model AGEs (once per day). In both cases, the liver was extracted for gene expression profiling. Both of the short-term AGE treatments resulted in a moderate increase in liver mRNA levels for genes involved in macrophage-based clearance/detoxification of foreign agents. Our findings using AGEs with strong RAGE-binding properties indicate that AGEs may not uniformly play a role in cellular activation.

Adverse effects of dietary glycotoxins on wound healing in genetically diabetic mice

Advanced glycoxidation end products (AGEs) are implicated in delayed diabetic wound healing. To test the role of diet-derived AGE on the rate of wound healing, we placed female db/db (+/+) (n = 55, 12 weeks old) and age-matched control db/db (+/-) mice (n = 45) on two diets that differed only in AGE content (high [H-AGE] versus low [L-AGE] ratio, 5:1) for 3 months. Full-thickness skin wounds (1 cm) were examined histologically and for wound closure. Serum 24-h urine and skin samples were monitored for N(epsilon)-carboxymethyl-lysine and methylglyoxal derivatives by enzyme-linked immunosorbent assays. L-AGE-fed mice displayed more rapid wound closure at days 7 and 14 (P < 0.005) and were closed completely by day 21 compared with H-AGE nonhealed wounds. Serum AGE levels increased by 53% in H-AGE mice and decreased by 7.8% in L-AGE mice (P < 0.04) from baseline. L-AGE mice wounds exhibited lower skin AGE deposits, increased epithelialization, angiogenesis, inflammation, granulation tissue deposition, and enhanced collagen organization up to day 21, compared with H-AGE mice. Reepithelialization was the dominant mode of wound closure in H-AGE mice compared with wound contraction that prevailed in L-AGE mice. Thus, increased diet-derived AGE intake may be a significant retardant of wound closure in diabetic mice; dietary AGE restriction may improve impaired diabetic wound healing.

Heart disease in diabetic patients

Both type 1 and type 2 diabetic patients have an increased incidence of ischemic heart disease and congestive heart failure. Cardiovascular disease accounts for up to 80% of the excess mortality in patients with type 2 diabetes. The burden of cardiovascular disease is especially pronounced in diabetic women. Factors that underlie diabetic heart disease include multiple vessel coronary artery disease, long-standing hypertension, metabolic derangements such as hyperglycemia and dyslipidemia, microvascular disease, and autonomic neuropathy. There is also increased sudden death associated with diabetes, which is due, in part, to the underlying autonomic neuropathy. This article reviews diabetic cardiac disease, with an emphasis on type 2 diabetes.