Effect of an aldose reductase inhibitor on type IV collagen production by human endothelial cells cultured in high glucose

Basement membrane proteins in various arterial beds from individuals with and without type 2 diabetes mellitus: a proteome study

BACKGROUND

Basement membrane (BM) accumulation is a hallmark of micro-vessel disease in diabetes mellitus (DM). We previously reported marked upregulation of BM components in internal thoracic arteries (ITAs) from type 2 DM (T2DM) patients by mass spectrometry. Here, we first sought to determine if BM accumulation is a common feature of different arteries in T2DM, and second, to identify other effects of T2DM on the arterial proteome.

METHODS

Human arterial samples collected during heart and vascular surgery from well-characterized patients and stored in the Odense Artery Biobank were analysed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). We included ascending thoracic aortas (ATA) (n = 10 (type 2 DM, T2DM) and n = 10 (non-DM)); laser capture micro-dissected plaque- and media compartments from carotid plaques (n = 10 (T2DM) and n = 9 (non-DM)); and media- and adventitia compartments from ITAs (n = 9 (T2DM) and n = 7 (non-DM)).

RESULTS

We first extended our previous finding of BM accumulation in arteries from T2DM patients, as 7 of 12 pre-defined BM proteins were significantly upregulated in bulk ATAs consisting of > 90% media. Although less pronounced, BM components tended to be upregulated in the media of ITAs from T2DM patients, but not in the neighbouring adventitia. Overall, we did not detect effects on BM proteins in carotid plaques or in the plaque-associated media. Instead, complement factors, an RNA-binding protein and fibrinogens appeared to be regulated in these tissues from T2DM patients.

CONCLUSION

Our results suggest that accumulation of BM proteins is a general phenomenon in the medial layer of non-atherosclerotic arteries in patients with T2DM. Moreover, we identify additional T2DM-associated effects on the arterial proteome, which requires validation in future studies.

A role for collagen type IV in cardiovascular disease?

Over the past decade, studies have repeatedly found single-nucleotide polymorphisms located in the collagen ( COL) 4A1 and COL4A2 genes to be associated with cardiovascular disease (CVD), and the 13q34 locus harboring these genes is one of ~160 genome-wide significant risk loci for coronary artery disease. COL4A1 and COL4A2 encode the α₁- and α₂-chains of collagen type IV, a major component of basement membranes in various tissues including arteries. Despite the growing body of evidence indicating a role for collagen type IV in CVD, remarkably few studies have aimed to directly investigate such a role. The purpose of this review is to summarize the clinical reports linking 13q34 to coronary artery disease, atherosclerosis, and artery stiffening and to assemble the scattered pieces of evidence from experimental studies based on vascular cells and tissue collectively supporting a role for collagen type IV in atherosclerosis and other macrovascular disease conditions.

Stimulating effect of growth hormone on type IV collagen production by endothelial cells cultured in normal and high glucose

Collagen IV accumulation is characteristic of diabetic angiopathy. To test the possible contribution of GH, we studied its effects on collagen IV production by human umbilical vein endothelial cells at 5.5 and 16.7 mmol/l glucose. GH (100 ng/ml) markedly increased collagen IV level in the culture supernatant and in the insoluble extracellular matrix and cell fraction at both glucose concentrations. This stimulating effect of GH was additional to that of high glucose. It was more pronounced on collagen IV than on total protein synthesis. GH increased free latent gelatinase activity slightly at normal and markedly at high glucose. Using GF109203X, a PKC inhibitor, we observed that high glucose, but not GH, activated PKC. These two factors stimulating collagen IV production appear to work through different pathways, favoring an additivity of their effects. This supports the contribution of high plasma GH in diabetic vascular basement membrane thickening.

Aldose reductase inhibitors: therapeutic implications for diabetic complications

The 'late complications' of diabetes mellitus, i.e., nephropathy, neuropathy and retinopathy are firmly rooted in inadequate control of blood glucose: hyperglycaemia. Hyperglycaemia causes elevated cytosolic glucose and/or rates of glucose metabolism, i.e., 'hyperglysolia,' within cells of vulnerable tissues. Although the molecular basis for the pathogenic effects of hyperglysolia remains to be proven, substantial evidence points to a key role for increased glucose metabolism through a cytosolic enzyme, aldose reductase (AR). Recent human genetic and biochemical data link polymorphisms of the AR gene (technically called the AR2 gene) and elevated tissue levels of AR with strongly altered risks for diabetic complications. Despite several genetic reports failing to confirm such an association, there are now ten concordant reports from five continents that certain polymorphisms of the AR gene are associated with an ~ 3- to 20-fold higher risk for diabetic complications. Moreover, in US and European diabetic study populations the principle allele of the AR gene associated with elevated disease risk, the Z-2 allele, correlates with an ~ 2- to 3-fold increase in AR expression. These results, together with recent clinical, experimental and pharmacological data, provide powerful new support for the rationale for research and development of aldose reductase inhibitors (ARIs) targeted at slowing the progression of diabetic complications. Although past clinical trials of ARIs have been disappointing, this has stemmed from overly optimistic expectations, inadequate trial designs and lack of pharmacological robustness and/or acceptable systemic toleration of the agents tested. However, a more realistic and encouraging perspective for therapeutic expectations for ARIs has arisen from recent data revealing that the seemingly modest short-term effects of intensified glycaemic control and of pancreatic transplantation are followed by substantial long-term benefits on diabetic complications. In addition, robust inhibition of AR in human nerve has recently yielded dose-dependent efficacy on nerve structure and function. Thus, the quest for well-tolerated, potent ARIs continues to be a worthy and more urgent objective than ever before.

The effect of elevated extracellular glucose on migration, adhesion and proliferation of SV40 transformed human corneal epithelial cells

PURPOSE

To examine the effect of elevated extracellular glucose, thus simulating diabetes, on migration, adhesion and proliferation of SV40 transformed human corneal epithelial (HCE) cells.

METHODS

HCE cells were maintained in serum supplemented media containing 5 mM, 17.5 mM or 38 mM D-glucose. Cell migration was determined using Blind well chambers fitted with fibronectin/collagen I coated filters. In adhesion experiments, cells were allowed to adhere to extracellular matrix protein-coated wells for 90 min at 37 degrees C. Non-adherent cells were removed by washing, then the fluorochrome calcein-AM was added to quantitate the number of attached cells. Proliferation was determined by plating the cells at low density, then quantitating viable cells with calcein-AM 5 to 7 days later.

RESULTS

Raising extracellular glucose from 5 mM to 17.5 mM significantly increased cell migration by 42%. When glucose was further raised to 38 mM, migration was not significantly different from that in 5 mM glucose. Adhesion to fibronectin and collagen I (but not IV) was significantly increased (62% and 32% respectively) when cells were cultured in 17.5 mM glucose. Similarly, proliferation was increased by 44%. Adhesion and proliferation tended to be decreased at 38 mM compared to 17.5 mM glucose, but not significantly so. In the presence of 5 mM glucose and mannitol (12.5 mM or 33 mM), neither migration, adhesion nor proliferation were significantly different from that in 5 mM glucose alone.

CONCLUSION

Elevated extracellular glucose modulates migration, adhesion and proliferation of HCE cells. The effects are dependent on the concentration of glucose and are not due to changes in osmolality since mannitol failed to produce similar results. Our in vitro findings suggest that high-glucose effects may directly contribute to the etiology of impaired corneal wound healing in diabetes.

Aldose reductase: a window to the treatment of diabetic complications?

Kinetic studies on the aldose reductase protein (AR2) have shown that it does not behave as a classical enzyme in relation to ring aldose sugars. These results have been confirmed by X-ray crystallography studies, which have pinpointed binding sites for pharmacological "aklose reductase inhibitors" (ARIs). As with non-enzymic glycation reactions, there is probably a free-radical element involved derived from monosaccharide autoxidation. In the case of AR2, there is free radical oxidation of NADPH by autoxidising monosaccharides, enhanced in the presence of the NADPH-binding protein. Whatever the behaviour of AR2, many studies have showed that sorbitol production is not an initiating aetiological factor in the development of diabetic complications in humans. Vitamin E (alpha-tocopherol), other antioxidants and high fat diets can delay or prevent cataract in diabetic animals even though sorbitol and fructose levels are not modified; vitamin C acts as an AR1 in humans. Protein post-translational modification by glyc-oxidation or other events is probably the key factor in the aetiology of diabetic complications. There is now no need to invoke AR2 in xylitol biosynthesis. Xylitol can be produced in the lens from glucose, via a pathway involving the enzymes myo-inositol-oxygen oxidoreductase, D-glucuronate reductase. L-gulonate NAD(+)-3-oxidoreductase and L-iditol-NAD(+)-5-oxidoreductase, all of which have recently been found in bovine and rat lens. This chapter investigates the molecular events underlying AR2 and its binding and kinetics. Induction of the protein by osmotic response elements is discussed, with detailed analysis of recent in vitro and in vivo experiments on numerous ARIs. These have a number of actions in the cell which are not specific, and which do not involve them binding to AR2. These include peroxy-radical scavenging and recently discovered effects of metal ion chelation. In controlled experiments, it has been found that incubation of rat lens homogenate with glucose and the copper chelator o-phenanthroline abolishes production of sorbitol. Taken together, these results suggest AR2 is a vestigial NADPH-binding protein, perhaps similar in function to a number of non-mammalian crystallins which have been recruited into the lens. There is mounting evidence for the binding of reactive aldehyde moieties to the protein, and the involvement of AR2 either as a 'housekeeping' protein, or in a free-radial-mediated 'catalytic' role. Interfering with the NADPH binding and flux levels--possibly involving free radicals and metal ions--has a deleterious effect. We have yet to determine whether aldose reductase is the black sheep of the aldehyde reductase family, or whether it is a skeleton in the cupboard, waiting to be clothed in the flesh of new revelations in the interactions between proteins, metal ions and redox metabolites.