Selective pericyte degeneration in the retinal capillaries of galactose-fed dogs results from apoptosis linked to aldose reductase-catalyzed galactitol accumulation

Whole-body galactose oxidation as a robust functional assay to assess the efficacy of gene-based therapies in a mouse model of Galactosemia

Despite the implementation of lifesaving newborn screening programs and a galactose-restricted diet, many patients with classic galactosemia develop long-term debilitating neurological deficits and primary ovarian insufficiency. Previously, we showed that the administration of human GALT mRNA predominantly expressed in the GalT gene-trapped mouse liver augmented the expression of hepatic GALT activity, which decreased not only galactose-1 phosphate (gal-1P) in the liver but also peripheral tissues. Since each peripheral tissue requires distinct methods to examine the biomarker and/or GALT effect, this highlights the necessity for alternative strategies to evaluate the overall impact of therapies. In this study, we established that whole-body galactose oxidation (WBGO) as a robust, noninvasive, and specific method to assess the in vivo pharmacokinetic and pharmacodynamic parameters of two experimental gene-based therapies that aimed to restore GALT activity in a mouse model of galactosemia. Although our results illustrated the long-lasting efficacy of AAVrh10-mediated GALT gene transfer, we found that GALT mRNA therapy that targets the liver predominantly is sufficient to sustain WBGO. The latter could have important implications in the design of novel targeted therapy to ensure optimal efficacy and safety.

Galactose-Induced Skin Aging: The Role of Oxidative Stress

Skin aging has been associated with a higher dietary intake of carbohydrates, particularly glucose and galactose. In fact, the carbohydrates are capable of damaging the skin's vital components through nonenzymatic glycation, the covalent attachment of sugar to a protein, and subsequent production of advanced glycation end products (AGEs). This review is focused on the role of D-galactose in the development of skin aging and its relation to oxidative stress. The interest in this problem was dictated by recent findings that used in vitro and in vivo models. The review highlights the recent advances in the underlying molecular mechanisms of D-galactose-mediated cell senescence and cytotoxicity. We have also proposed the possible impact of galactosemia on skin aging and its clinical relevance. The understanding of molecular mechanisms of skin aging mediated by D-galactose can help dermatologists optimize methods for prevention and treatment of skin senescence and aging-related skin diseases.

Application of a Flow-Based Hollow-Fiber Co-Culture System to Study Cellular Influences under Hyperglycemic Conditions

Elucidation of the basic mechanisms underlying human disease pathogenesis depends on the findings afforded to us through in vivo and in vitro approaches. While there are inherent limitations in any model system, 2D in vitro culture systems tend to be particularly restricted due to their static nature. Here, we adapted a flow-based hollow-fiber cartridge system to better understand the cellular influences of human retinal microvascular endothelial cells and mouse-derived neutrophils under high glucose conditions similar to those observed in diabetes. Analyses by western blot and flow cytometry indicate that pro-inflammatory molecules known to be associated with the pathogenesis of diabetic retinopathy were significantly elevated following high glucose exposure, including VEGF, ICAM-1, and ROS. Changes in mitochondrial potential were also observed. Further, we demonstrate that this innovative system allows for cross-species co-culture as well as long-term culturing conditions. This in vitro modeling system not only mimics the retinal microvasculature, it also allows for the examination of cellular interactions and mechanisms that contribute to diabetic retinopathy, a visually debilitating complication of diabetes.

Comparison of naturally aging and D-galactose induced aging model in beagle dogs

Animal models have been used to study aging for decades. In numerous aging studies, beagles are the most commonly used breed of dog. However, few studies have compared between naturally aging models and experimentally induced aging models in beagle dogs. In the present study, a D-galactose induced aging model was compared with a naturally aging model, and young adult dogs were considered as the young control group. The level of malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in serum, and brain tissue were measured. Histopathological comparisons of the liver, kidneys, heart, lungs and spleen were evaluated using hematoxylin and eosin (H&E) staining, in addition, the brain was evaluated by H&E staining, and Nissl staining. The expression levels of aging-associated factors in the hippocampus, including proliferating cell nuclear antigen (PCNA), P16 and P21 were also determined through reverse transcription quantitative-polymerase chain reaction, and western blot analysis. The results indicated that D-galactose induced aging significantly increased the MDA level, while the levels of SOD and GSH-Px were diminished when compared with the young control group, which was similar to the naturally aging group. Parallel histopathological features were observed in the D-galactose induced aging and naturally aging groups compared with the young control group. However, a reduced expression level of PCNA, and increased expression levels of P16 and P21 were observed in the naturally ageing and induced aging groups compared with the young control group. The results of the current study demonstrated that the beagle dogs in D-galactose induced aging model exhibited significant similarities with the naturally aging model, providing evidence to support that the D-galactose induced aging model may be applied to aging studies.

Protective effect of a phenolic extract containing indoline amides from Portulaca oleracea against cognitive impairment in senescent mice induced by large dose of D-galactose /NaNO2

ETHNOPHARMACOLOGICAL RELEVANCE

Portulaca oleracea L. is a potherb and also a widely used traditional Chinese medicine. In accordance with its nickname "longevity vegetable", pharmacological study demonstrated that this plant possessed antioxidant, anti-aging, and cognition-improvement function. Active principles pertaining to these functions of P. oleracea need to be elucidated.

AIM OF THE STUDY

The present study evaluated the effect of a phenolic extract (PAAs) from P. oleracea which contained specific antioxidant indoline amides on cognitive impairment in senescent mice.

MATERIALS AND METHODS

PAAs was prepared through AB-8 macroporous resin column chromatography. Total phenol content was determined using colorimetric method, and contents of indoline amides were determined using HPLC-UV method. Senescent Kunming mice with cognitive dysfunction were established by intraperitoneal injection of D-galactose (D-gal, 1250mg/kg/day) and NaNO₂ (90mg/kg/day) for 8 weeks, L-PAAs (360mg/kg/day), H-PAAs (720mg/kg/day), and nootropic drug piracetam (PA, 400mg/kg/day) as the positive control were orally administered. Spatial learning and memory abilities were evaluated by Morris water maze experiment. Activities of AChE, SOD, CAT, and levels of GSH and MDA in the brain or plasma were measured. Hippocampal morphology was observed by HE staining.

RESULTS

Chronic treatment of large dose of D-gal/NaNO₂ significantly reduced lifespan, elevated AChE activity, decreased CAT activity, compensatorily up-regulated SOD activity and GSH level, increased MDA level, induced neuronal damage in hippocampal CA1, CA3 and CA4 regions, and impaired cognitive function. Similar to PA, PAAs prolonged the lifespan and improved spatial memory ability. Moreover, PAAs improved learning ability. H-PAAs significantly reversed compensatory increase in SOD activity to the normal level, elevated serum CAT activity, and reduced MDA levels in brain and plasma, more potent than L-PAAs. Besides these, PAAs evidently inhibited hippocampal neuronal damage. However, it had no effect on brain AChE activity.

CONCLUSION

PAAs as the bioactive principles of P. oleracea attenuated oxidative stress, improved survival rate, and enhanced cognitive function in D-gal/NaNO₂-induced senile mice, similar to piracetam. This phenolic extract provides a promising candidate for prevention of aging and aging-related cognitive dysfunction in clinic.

Racemic oleracein E increases the survival rate and attenuates memory impairment in D-galactose/NaNO₂-induced senescent mice

BACKGROUND

Compounds that possess a pyrrolidone skeleton are a rich resource for the discovery of nootropic drugs. Oleracein E (OE), which possesses both tetrahydroisoquinoline and pyrrolidone skeletons, was first isolated from the medicinal plant Portulaca oleracea L. and was thought to be an active component in the cognition-improvement effect induced by this herb. The aim of this study was to investigate the effect of OE on cognitive impairment in senescent mice and its underlying mechanism of action.

METHOD

Senescent Kunming mice were established by the intraperitoneal injection of D-galactose (D-gal, 1250 mg/kg/d) and NaNO2 (90 mg/kg/d) for 8 weeks. OE (3 mg/kg/d, 15 mg/kg/d) was orally administered for 8 weeks, and the nootropic drug piracetam (PA, 400 mg/kg/d) was used as a positive control. A Morris water maze was used to assess cognitive ability. GSH and MDA levels and T-AOC, SOD, and CAT activities in the brain or plasma were determined. Hippocampal morphology was observed by HE staining, and expression of the anti-apoptotic protein Bcl-2 and the pro-apoptotic proteins Bax and Caspase-3 was observed by immunohistochemical staining.

RESULTS

Large-dosage treatments with D-gal/NaNO2 for 8 weeks significantly reduced survival, impaired spatial memory capacity, compensatorily up-regulated GSH level and T-AOC and SOD activities, decreased CAT activity, and induced hippocampal neuronal damage and apoptosis as reflected by the apparent low expression of Bcl-2 and high expression of Bax and Caspase-3. OE significantly prolonged lifespan and was more potent than PA. Similar to PA, OE at 15 mg/kg/d improved memory capacity. The underlying mechanism of action was related to the reversal of abnormal brain antioxidant biomarkers (GSH, T-AOC, and SOD) to normal levels and the inhibition of hippocampal neuronal apoptosis.

CONCLUSION

OE from P. oleracea is an active compound for improving cognitive function and is also a candidate nootropic drug for the treatment of age-related dementia.

Novel transgenic mouse models develop retinal changes associated with early diabetic retinopathy similar to those observed in rats with diabetes mellitus

Retinal capillary pericyte degeneration has been linked to aldose reductase (AR) activity in diabetic retinopathy (DR). Since the development of DR in mice and rats has been reported to differ and that this may be linked to differences in retinal sorbitol levels, we have established new murine models of early onset diabetes mellitus as tools for investigating the role of AR in DR. Transgenic diabetic mouse models were developed by crossbreeding diabetic C57BL/6-Ins2(Akita)/J (AK) with transgenic C57BL mice expressing green fluorescent protein (GFP), human aldose reductase (hAR) or both in vascular tissues containing smooth muscle actin-α (SMAA). Changes in retinal sorbitol levels were determined by HPLC while changes of growth factors and signaling were investigated by Western Blots. Retinal vascular changes were quantitatively analyzed on elastase-digestion flat mounts. Results show that sorbitol levels were higher in neural retinas of diabetic AK-SMAA-GFP-hAR compared to AK-SMAA-GFP mice. AK-SMAA-GFP-hAR mice showed induction of the retinal growth factors VEGF, IGF-1, bFGF and TGFβ, as well as signaling changes in P-Akt, P-SAPK/JNK, and P-44/42 MAPK. Increased loss of nuclei per capillary length and a significant increase in the percentage of acellular capillaries presented in 18 week old AK-SMAA-GFP-hAR mice. These changes are similar to those observed in streptozotocin-induced diabetic rats. Retinal changes in both mice and rats were prevented by inhibition of AR. These studies confirm that the increased expression of AR in mice results in the development of retinal changes associated with the early stages of DR that are similar to those observed in rats.

Novel diabetic mouse models as tools for investigating diabetic retinopathy

OBJECTIVE

Mouse models possessing green fluorescent protein (GFP) and/or human aldose reductase (hAR) in vascular tissues have been established and crossed with naturally diabetic Akita mice to produce new diabetic mouse models.

RESEARCH DESIGN AND METHODS

Colonies of transgenic C57BL mice expressing GFP (SMAA-GFP), hAR (SMAA-hAR) or both (SMAA-GFP-hAR) in vascular tissues expressing smooth muscle actin were established and crossbred with C57BL/6-Ins2(Akita)/J (AK) mice to produce naturally diabetic offspring AK-SMAA-GFP and AK-SMAA-GFP-hAR. Aldose reductase inhibitor AL1576 (ARI) was administered in chow. Retinal and lenticular sorbitol levels were determined by HPLC. Retinal functions were evaluated by electroretinography (ERGs). Growth factor and signaling changes were determined by Western Blots using commercially available antibodies. Retinal vasculatures were isolated from the neural retina by enzymatic digestion. Flat mounts were stained with PAS-hematoxylin and analyzed.

RESULTS

Akita transgenics developed DM by 8 weeks of age with blood glucose levels higher in males than females. Sorbitol levels were higher in neural retinas of AK-SMAA-GFP-hAR compared to AK-SMAA-GFP mice. AK-SMAA-GFP-hAR mice also had higher VEGF levels and reduced ERG scotopic b-wave function, both of which were normalized by AL1576. AK-SMAA-GFP-hAR mice showed induction of the retinal growth factors bFGF, IGF-1, and TGFβ, as well as signaling changes in P-Akt, P-SAPK/JNK and P-44/42 MAPK that were also reduced by ARI treatment. Quantitative analysis of flat mounts in 18 week AK-SMAA-GFP-hAR mice revealed increased loss of nuclei/capillary length and a significant increase in the percentage of acellular capillaries present which was not seen in AK-SMAA-GFP-hAR treated with ARI.

CONCLUSIONS/SIGNIFICANCE

These new mouse models of early onset diabetes may be valuable tools for assessing both the role of hyperglycemia and AR in the development of retinal lesions associated with diabetic retinopathy.

Enhanced cerebral but not peripheral angiogenesis in the Goto-Kakizaki model of type 2 diabetes involves VEGF and peroxynitrite signaling

We previously reported enhanced cerebrovascular remodeling and arteriogenesis in experimental type 2 diabetes. This study tested the hypotheses that 1) cerebral but not peripheral angiogenesis is increased in a spatial manner and 2) peroxynitrite orchestrates vascular endothelial growth factor (VEGF)-mediated brain angiogenesis in diabetes. Stereology of brain, eye, and skeletal muscle microvasculature was evaluated in control and diabetic rats using three-dimensional images. Migration and tube formation properties of brain microvascular endothelial cells (BMECs) were analyzed as markers of angiogenesis. Vascular density, volume, and surface area were progressively increased from rostral to caudal sections in both the cerebral cortex and striatum in diabetic rats. Unperfused new vessels were more prominent and the pericyte-to-endothelial cell ratio was decreased in diabetes. Vascularization was greater in the retina but lower in the peripheral circulation. VEGF and nitrotyrosine levels were higher in cerebral microvessels of diabetic animals. Migratory and tube formation properties were enhanced in BMECs from diabetic rats, which also expressed high levels of basal VEGF, nitrotyrosine, and membrane-type (MT1) matrix metalloprotease (MMP). VEGF-neutralizing antibody and inhibitors of peroxynitrite, src kinase, or MMP blocked the migration. Diabetes increases and spatially regulates cerebral neovascularization. Increased VEGF-dependent angiogenic function in BMECs is mediated by peroxynitrite and involves c-src and MT1-MMP activation.

The isolation and characterization of β-glucogallin as a novel aldose reductase inhibitor from Emblica officinalis

Diabetes mellitus is recognized as a leading cause of new cases of blindness. The prevalence of diabetic eye disease is expected to continue to increase worldwide as a result of the dramatic increase in the number of people with diabetes. At present, there is no medical treatment to delay or prevent the onset and progression of cataract or retinopathy, the most common causes of vision loss in diabetics. The plant Emblica officinalis (gooseberry) has been used for thousands of years as a traditional Indian Ayurvedic preparation for the treatment of diabetes in humans. Extracts from this plant have been shown to be efficacious against the progression of cataract in a diabetic rat model. Aldose reductase (ALR2) is implicated in the development of secondary complications of diabetes including cataract and, therefore, has been a major drug target for the development of therapies to treat diabetic disease. Herein, we present the bioassay-guided isolation and structure elucidation of 1-O-galloyl-β-D-glucose (β-glucogallin), a major component from the fruit of the gooseberry that displays selective as well as relatively potent inhibition (IC₅₀ = 17 µM) of AKR1B1 in vitro. Molecular modeling demonstrates that this inhibitor is able to favorably bind in the active site. Further, we show that β-glucogallin effectively inhibits sorbitol accumulation by 73% at 30 µM under hyperglycemic conditions in an ex-vivo organ culture model of lenses excised from transgenic mice overexpressing human ALR2 in the lens. This study supports the continued development of natural products such as β-glucogallin as therapeutic leads in the development of novel therapies to treat diabetic complications such as cataract.

High glucose induces mitochondrial morphology and metabolic changes in retinal pericytes

PURPOSE

Mitochondrial dysfunction is known to play a role in retinal vascular cell loss, a prominent lesion of diabetic retinopathy. High glucose (HG) has been reported to induce mitochondrial fragmentation and dysfunction in retinal endothelial cells, contributing to apoptosis. In this study, the effects of HG on mitochondrial morphology, membrane potential, and metabolic changes and whether they could contribute to HG-induced apoptosis in retinal pericytes were investigated.

METHODS

Bovine retinal pericytes (BRPs) were grown in normal or HG medium for 7 days. Both sets of cells were double stained with mitochondrial membrane potential-independent dye and tetramethylrhodamine-ethyl-ester-perchlorate (TMRE) and imaged by confocal microscopy. The images were analyzed for average mitochondria shape, by using form factor and aspect ratio values, and membrane potential changes, by using the ratio between the red and green dye. BRPs grown in normal or HG medium were analyzed for transient changes in oxygen consumption and extracellular acidification with a flux analyzer and apoptosis by TUNEL assay.

RESULTS

BRPs grown in HG media exhibited significant fragmentation of mitochondria and increased membrane potential heterogeneity compared with the BRPs grown in normal medium. Concomitantly, BRPs grown in HG showed reduced steady state and maximum oxygen consumption and reduced extracellular acidification. Number of TUNEL-positive pericytes was increased in HG condition as well.

CONCLUSIONS

In HG condition, mitochondria of retinal pericytes display significant fragmentation, metabolic dysfunction, and reduced extracellular acidification. The detrimental effects of HG on mitochondrial function and cellular metabolism could play a role in the accelerated apoptosis associated with the retinal pericytes in diabetic retinopathy.

Response of rat retinal capillary pericytes and endothelial cells to glucose

AIM

The purpose of this study was to investigate the effects of hyperglycemia, its fluctuations, and glucose starvation on the expression of glucose-regulated protein 78/binding immunoglobulin protein (GRP78/BiP), one of the most commonly used markers of endoplasmic reticulum stress, in rat capillary pericytes and endothelial cells cultured separately and together.

METHODS

Conditionally immortalized rat retinal pericyte and endothelial cell lines were cultured in dishes coated with collagen type I in Dulbecco's modified Eagle's medium containing 5.5  mM glucose. For cocultures, pericytes and endothelial cells were seeded together on rat tail collagen type I-coated cell culture plates. After 24  h of initial culture, the medium was replaced with serum-free medium containing 0-100  mM glucose for periods of up to 72  h. GRP78/BiP, caspase-3, and nuclear factor-κB expression were investigated using western blots.

RESULTS

No significant increase in GRP78/BiP expression was observed when pericytes, endothelial cells, or cocultures were exposed to either 25, 50, or 100  mM glucose for 48  h compared with the control level of 5.5  mM glucose. Similarly, no change in expression of GRP78/BiP was observed when media glucose levels were reduced from either 5.5 or 25 to 1  mM. GRP78/BiP expression significantly increased when cells were cultured for 24  h in glucose-deprived medium. This was accompanied by a time-dependent increase in the expression of caspase-3 and nuclear factor-κB.

CONCLUSION

In diabetic retinopathy, hyperglycemia has been reported to induce apoptosis in retinal capillary vascular cells, but these studies suggest that the apoptosis is not linked to the expression of GRP78/BiP, one of the most commonly used markers of endoplasmic reticulum stress. However, GRP78/BiP-linked apoptosis may play a role in vascular changes associated with retinal ischemia/reperfusion.

Retinal redox stress and remodeling in cardiometabolic syndrome and diabetes

Diabetic retinopathy (DR) is a significant cause of global blindness; a major cause of blindness in the United States in people aged between 20–74. There is emerging evidence that retinopathy is initiated and propagated by multiple metabolic toxicities associated with excess production of reactive oxygen species (ROS). The four traditional metabolic pathways involved in the development of DR include: increased polyol pathway flux, advanced glycation end-product formation, activation of protein kinase Cisoforms and hexosamine pathway flux. These pathways individually and synergisticallycontribute to redox stress with excess ROS resulting in retinal tissue injury resulting in significant microvascular blood retinal barrier remodeling. The toxicity of hyperinsulinemia, hyperglycemia, hypertension, dyslipidemia, increased cytokines and growth factors, in conjunction with redox stress, contribute to the development and progression of DR. Redox stress contributes to the development and progression of abnormalities of endothelial cells and pericytes in DR. This review focuses on the ultrastructural observations of the blood retinal barrier including the relationship between the endothelial cell and pericyte remodeling in young nine week old Zucker obese (fa/ fa) rat model of obesity; cardiometabolic syndrome, and the 20 week old alloxan induced diabetic porcine model. Preventing or delaying the blindness associated with these intersecting abnormal metabolic pathways may be approached through strategies targeted to reduction of tissue inflammation and oxidative—redox stress. Understanding these abnormal metabolic pathways and the accompanying redox stress and remodeling mayprovide both the clinician and researcher a new concept of approaching this complicated disease process

Polyol formation in cell lines of rat retinal capillary pericytes and endothelial cells (TR-rPCT and TR-iBRB)

PURPOSE

The two most widely investigated animal models for diabetic retinopathy (DR) are the rat and dog. In dogs, aldose reductase (AR) is present only in retinal capillary pericytes and their destruction has been linked to polyol accumulation and resulting apoptosis. Since both rat capillary pericytes and endothelial cells have been reported to contain AR, the role of polyol pathway activity in capillary cell destruction has been investigated in rat retinal capillary pericyte (TR-rPCT) and endothelial (TR-iBRB) cells.

METHODS

TR-rPCT and TR-iBRB cell lines were recloned and their identities were reconfirmed by characteristic immunostaining. Cells were cultured up to 72 h in media containing 50 mM glucose or galactose with/without the AR inhibitors or a sorbitol dehydrogenase inhibitor (SDI) or with 30 mM 3-fluoro-3-deoxyglucose. Polyol levels were determined by HPLC or (19)F-NMR. Apoptosis was detected with TUNEL/DAPI staining.

RESULTS

Smooth muscle actin is present only in pericytes while only endothelial cells stain for von Willebrand factor and accumulate acetylated low-density lipoprotein. AR is present in both cells but AR levels are lower in endothelial cells. Aldehyde reductase is also present in both cells. Cells cultured in 50 mM glucose or galactose show significant polyol accumulation in pericytes but endothelial cells show little accumulation of galactitol and no accumulation of sorbitol. Sorbitol accumulation in pericytes resulted in increased cellular permeability and increased TUNEL staining, which was reduced by AR inhibition.

CONCLUSIONS

Although both rat retinal pericytes and endothelial cells contain AR, sorbitol accumulation and TUNEL staining primarily occur in pericytes and are inhibited by AR inhibitors.

The roles of galactitol, galactose-1-phosphate, and phosphoglucomutase in galactose-induced toxicity in Saccharomyces cerevisiae

The uptake and catabolism of galactose by the yeast Saccharomyces cerevisiae is much lower than for glucose and fructose, and in applications of this yeast for utilization of complex substrates that contain galactose, for example, lignocellulose and raffinose, this causes prolonged fermentations. Galactose is metabolized via the Leloir pathway, and besides the industrial interest in improving the flux through this pathway it is also of medical relevance to study the Leloir pathway. Thus, genetic disorders in the genes encoding galactose-1-phosphate uridylyltransferase or galactokinase result in galactose toxicity both in patients with galactosemia and in yeast. In order to elucidate galactose related toxicity, which may explain the low uptake and catabolic rates of S. cerevisiae, we have studied the physiological characteristics and intracellular metabolite profiles of recombinant S. cerevisiae strains with improved or impaired growth on galactose. Aerobic batch cultivations on galactose of strains with different combinations of overexpression of the genes GAL1, GAL2, GAL7, and GAL10, which encode proteins that together convert extracellular galactose into glucose-1-phosphate, revealed a decrease in the maximum specific growth rate when compared to the reference strain. The hypothesized toxic intermediate galactose-1-phosphate cannot be the sole cause of galactose related toxicity, but indications were found that galactose-1-phosphate might cause a negative effect through inhibition of phosphoglucomutase. Furthermore, we show that galactitol is formed in S. cerevisiae, and that the combination of elevated intracellular galactitol concentration, and the ratio between galactose-1-phosphate concentration and phosphoglucomutase activity seems to be important for galactose related toxicity causing decreased growth rates.

Cellular signaling and potential new treatment targets in diabetic retinopathy

Dysfunction and death of microvascular cells and imbalance between the production and the degradation of extracellular matrix (ECM) proteins are a characteristic feature of diabetic retinopathy (DR). Glucose-induced biochemical alterations in the vascular endothelial cells may activate a cascade of signaling pathways leading to increased production of ECM proteins and cellular dysfunction/death. Chronic diabetes leads to the activation of a number of signaling proteins including protein kinase C, protein kinase B, and mitogen-activated protein kinases. These signaling cascades are activated in response to hyperglycemia-induced oxidative stress, polyol pathway, and advanced glycation end product formation among others. The aberrant signaling pathways ultimately lead to activation of transcription factors such as nuclear factor-κB and activating protein-1. The activity of these transcription factors is also regulated by epigenetic mechanisms through transcriptional coactivator p300. These complex signaling pathways may be involved in glucose-induced alterations of endothelial cell phenotype leading to the production of increased ECM proteins and vasoactive effector molecules causing functional and structural changes in the microvasculature. Understanding of such mechanistic pathways will help to develop future adjuvant therapies for diabetic retinopathy.

Pathophysiology of impaired ovarian function in galactosaemia

Classical galactosaemia is an inherited inborn error of the major galactose assimilation pathway, caused by galactose-1-phosphate uridyltransferase (GALT) deficiency. Many GALT mutations have been described, with different clinical consequences. In severe forms, newborns present with a life-threatening, acute toxic syndrome that rapidly regresses under a galactose-restricted diet. However, long-term complications, particularly cognitive and motor abnormalities, as well as hypergonadotrophic hypogonadism in female patients are still unavoidable. The pathogenesis of galactose-induced ovarian toxicity remains unclear but probably involves galactose itself and its metabolites such as galactitol and UDP-galactose. Possible mechanisms of ovarian damage include direct toxicity of galactose and metabolites, deficient galactosylation of glycoproteins and glycolipids, oxidative stress and activation of apoptosis. As there is no aetiological treatment, clinical management of ovarian failure in galactosaemic patients principally relies on hormonal replacement therapy to induce pubertal development and to prevent bone loss and other consequences of estrogen deprivation. Further investigations will be necessary to better understand the metabolic flux of galactose through its biochemical pathways and the mechanisms of these secondary complications. The aim of this article is to present an extensive review on the pathogenesis and clinical management of galactose-induced premature ovarian failure.

Substrates modified by advanced glycation end-products cause dysfunction and death in retinal pericytes by reducing survival signals mediated by platelet-derived growth factor

AIMS/HYPOTHESIS

Premature death of retinal pericytes is a pathophysiological hallmark of diabetic retinopathy. Among the mechanisms proposed for pericyte death is exposure to AGE, which accumulate during diabetes. The current study used an in vitro model, whereby retinal pericytes were exposed to AGE-modified substrate and the mechanisms underlying pericyte death explored.

METHODS

Pericytes were isolated from bovine retinal capillaries and propagated on AGE-modified basement membrane (BM) extract or non-modified native BM. The extent of AGE modification was analysed. Proliferative responses of retinal pericytes propagated on AGE-modified BM were investigated using a 5-bromo-2-deoxy-uridine-based assay. The effect of extrinsically added platelet-derived growth factor (PDGF) isoforms on these proliferative responses was also analysed alongside mRNA expression of the PDGF receptors. Apoptotic death of retinal pericytes grown on AGE-modified BM was investigated using terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling labelling, mitochondrial membrane depolarisation and by morphological assessment. We also measured both the ability of PDGF to reverse Akt dephosphorylation that was mediated by AGE-modified BM, and increased pericyte apoptosis.

RESULTS

Retinal pericytes exposed to AGE-modified BM showed reduced proliferative responses in comparison to controls (p<0.05-0.01), although this effect was reversed at low-AGE modifications. PDGF mRNA levels were differentially altered by exposure to low and high AGE levels, and AGE-modified BM caused significantly increased apoptosis in retinal pericytes. Pre-treatment of AGE-modified BM with PDGF-AA and -BB reversed the apoptosis (p<0.05-0.001) and restored Akt phosphorylation in retinal pericytes.

CONCLUSIONS/INTERPRETATION

Evidence suggests that substrate-derived AGE such as those that occur during diabetes could have a major influence on retinal pericyte survival. During diabetic retinopathy, AGE modification of vascular BM may reduce bioavailability of pro-survival factors for retinal pericytes.