Diabetic-like retinopathy: early and late intervention therapies in galactose-fed rats

PURPOSE: To determine whether the diabetic-like thickening of retinal capillary basement membrane (RCBM) that develops in the galactose-fed rat model of diabetic ocular complications could be halted or ameliorated after 4 or 8 months of galactosemia by treatment with ARI-509, a potent new aldose reductase inhibitor (ARI), or by withdrawal of the galactose diet. METHODS: Weanling female Sprague-Dawley rats were randomized into eight groups and fed laboratory chow plus 50% starch, control group (CON); 50% D-galactose, galactose-fed group (GAL); 50% D-galactose with ARI-509 at 25 mg/kg or 10 mg/kg body wt per day, high-dose prevention group (HDP) and low-dose prevention group (LDP), respectively; 50% D-galactose for 4 or 8 months and then intervention by addition of ARI-509 (25 mg/kg body wt per day), 4-month intervention group (4IN) and 8-month intervention group (8IN), respectively; or 50% D-galactose for 4 or 8 months and then intervention by withdrawing galactose and replacing it with the 50% starch diet, 4-month galactose withdrawal group (4GW) and 8-month galactose withdrawal group (8GW), respectively. After 4, 8, 16, and 24 months of the experimental diets, the levels of carbohydrates in tissues and the extent of RCBM thickening in capillaries of the outer plexiform layer were determined in all groups. RESULTS: Retinal polyol was reduced by 95% in all ARI-treated groups and by 100% in the 4GW and 8GW groups after withdrawal of the galactose. The mean RCBM thickness increased rapidly in GAL rats, becoming almost two times greater (189 +/- 9.4 nm) than in CON rats (103 +/- 3.4 nm) by 24 months. Treatment with ARI-509 in high and low doses (HDP, LDP) initiated with the introduction of the galactose diet significantly prevented RCBM thickening at all time points (P < 0.05). In contrast, intervention by withdrawing galactose from the diet or by adding the high dose of ARI-509 had no significant effect (P < 0.05) on RCBM thickening until the 24-month time point (4IN, 166 +/- 10.3 nm; 8IN, 161 +/- 8.2 nm; 4GW, 136 +/- 5.1 nm; 8GW, 163 +/- 9.6 nm). CONCLUSIONS: Both early and late interventions decreased RCBM thickening compared with that in untreated GAL rats. The decreased thickening, however, was not evident until 16 to 20 months after the intervention. Because RCBM thickening is one of the earliest changes in diabetic and galactosemic retinopathy, the findings suggest that RCBM thickening and possibly subsequent retinal lesions are caused by early biochemical alterations induced by the galactose diet that are not readily reversed. The delayed response to therapy is consistent with that observed in the Diabetes Control and Complications Trial. The cumulative evidence indicates that intervention should begin as early after onset of diabetes as possible, and long follow-up periods should be used to evaluate efficacy.     

Intravitreous injections of vascular endothelial growth factor produce retinal ischemia and microangiopathy in an adult primate

PURPOSE: The purpose of the study is to determine the effect of exogenous vascular endothelial growth factor (VEGF) on the primate retina and its vasculature. METHODS: Ten eyes of five animals were studied. Physiologically relevant amounts of the 165 amino acid isoform of human recombinant VEGF were injected into the vitreous of six healthy cynomolgus monkey eyes. Inactivated human recombinant VEGF or vehicle was injected into four contralateral control subject eyes. Eyes were assessed by slit-lamp biomicroscopy, tonometry, fundus color photography, fundus fluorescein angiography, light microscopy, and immunostaining with antibodies against proliferating cell nuclear antigen and factor VIII antigen. RESULTS: All six bioactive VEGF-injected eyes developed dilated, tortuous retinal vessels that leaked fluorescein. Eyes receiving multiple injections of VEGF developed progressively dilated and tortuous vessels, venous beading, edema, microaneurysms, intraretinal hemorrhages and capillary closure with ischemia. The severity of the retinopathy correlated with the number of VEGF injections. None of the four control eyes exhibited any abnormal retinal vascular changes. The endothelial cells of retinal blood vessels were proliferating cell nuclear antigen positive only in the bioactive VEGF-injected eyes. CONCLUSION: Vascular endothelial growth factor is sufficient to produce many of the vascular abnormalities common to diabetic retinopathy and other ischemic retinopathies, such as hemorrhage, edema, venous beading, capillary occlusion with ischemia, microaneurysm formation, and intraretinal vascular proliferation.     

Anxiety and cognitive performance in adolescent women with disruptive behavior disorders

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific angiogenic and permeability-inducing factor that has been implicated in the pathogenesis of diabetic retinopathy. In the present study, the localization and magnitude of VEGF, VEGF receptor-1 (VEGFR-1), and VEGF receptor-2 (VEGFR-2) gene expression were examined in the eye of streptozotocin-induced diabetic rats using quantitative in situ hybridization. VEGF protein was also examined by immunohistochemistry. Abundant VEGF mRNA and protein were present in the retinae of control rats. In the retinae of diabetic rats, VEGF gene expression was increased compared with control animals (p = 0.001). The increase in VEGF mRNA was noted in the ganglion cell layer and inner nuclear layer but not in the pigment epithelium of the retina. VEGF was also detected in blood vessels, ciliary body, and lens epithelium in both control and diabetic rats. The distributions of VEGFR-1 and VEGFR-2 were similar in both control and diabetic rats. VEGFR-1 mRNA was present beneath the inner limiting membrane and in the ganglion cell layer, inner nuclear layer, outer plexiform layer, and outer limiting membrane of the retina; it was also detected in blood vessels, the ciliary body, and the cornea. The magnitude and distribution of ocular VEGFR-1 mRNA were not affected by experimental diabetes. Expression of VEGFR-2 mRNA was noted in the inner nuclear layer and pigment epithelium of the retina and in blood vessels. An increase in VEGFR-2 mRNA in the diabetic retina was restricted to the inner nuclear layer. The presence of VEGF and its receptors in the control retina suggests a physiologic role for VEGF within the eye. The changes in retinal expression of VEGF and VEGFR-2 in association with diabetes suggest a role for this pathway in diabetic retinopathy.     

Regenerating sciatic nerve does not utilize circulating cholesterol

Vascular endothelial growth factor (VEGF) is a major contributor to retinal neovascularization. The possible participation of VEGF and its high-affinity tyrosine kinase receptors, flk-1 and flt-1, in early background diabetic retinopathy was studied in the streptozotocin-induced diabetic rat model of experimental retinopathy using in situ hybridization, blotting techniques, and immunohistochemistry. Diabetic retinopathy was assessed by quantitative morphometry of retinal digest preparations. The number of acellular capillaries increased 2.7-fold in diabetic animals with diabetes' duration of 6 months compared with nondiabetic controls. VEGF expression was not detectable by in situ hybridization in nondiabetic rats but was highly increased in the ganglion cell layer and in the inner and outer nuclear layers of retinas from diabetic animals. VEGF protein was extractable only from diabetic retinas, and a strong immunolabeling was detected in vascular and perivascular structures. Increased flk-1 and flt-1 mRNA levels were also found in the ganglion cell and both nuclear layers of diabetic samples only. Dot blot and Western blot analyses confirmed the increase in flk-1 mRNA and protein in diabetic retinas. Also, flk-1 immunoreactivity was associated with vascular and nonvascular structures of the inner retinas from diabetic animals. These data obtained from a rodent model in which retinal neovascularization does not occur support the concept that the VEGF/VEGF receptor system is upregulated in early diabetic retinopathy.     

High glucose-induced mesangial cell altered contractility: role of the polyol pathway

Glomerular mesangial cells cultured in high glucose conditions display impaired contractile responsiveness. It was postulated that glucose metabolism through the polyol pathway leads to altered mesangial cell contractility involving protein kinase C. Rat mesangial cells were growth-arrested for 24 h with 0.5% fetal bovine serum in either normal (5.6 mmol/l) or high (30 mmol/l) glucose concentrations or high glucose plus the aldose reductase inhibitor, ARI-509 (100 micromol/l). The reduction of cell planar surface area (contraction) in response to endothelin-1 (0.1 micromol/l), or to phorbol 12-myristate 13-acetate (50 pmol/l), was studied by videomicroscopy. In response to endothelin-1, mesangial cells in normal glucose contracted to 52+/-3% of initial planar area. In high glucose, the significantly (p < 0.05) smaller cell size and no contractile responsiveness to endothelin-1 were normalized with ARI-509. Membrane-associated diacylglycerol, measured by a kinase specific 32P-phosphorylation assay, in high glucose was unchanged after 3 h, but significantly increased (p < 0.05) after 24 h which was normalized with ARI-509. Protein kinase C activity, measured by in situ 32P-phosphorylation of the epidermal growth factor receptor substrate was: increased by 32% at 3 h of high glucose, unchanged by ARI-509; and decreased significantly (p < 0.05) at 24 h compared to cells in normal glucose, normalized by ARI-509. Total cellular protein kinase C-alpha, -delta and -epsilon, analysed by immunoblotting, were unchanged in high glucose at 24 h. Only protein kinase C-epsilon content was reduced by ARI-509 in both normal and high glucose. Therefore, high glucose-induced loss of mesangial cell contractility, diacylglycerol accumulation and altered protein kinase C activity are mediated through activation of the polyol-pathway, although no specific relationship between elevated diacylglycerol and protein kinase C activity was observed. In high glucose, altered protein kinase C function, or another mechanism related to the polyol pathway, contribute to loss of mesangial cell contractile responsiveness.     

Localization of vascular endothelial growth factor in human retina and choroid

OBJECTIVE: To examine the distribution and relative levels of vascular endothelial growth factor (VEGF) in the nondiabetic and preproliferative diabetic human retina and choroid. METHODS: Immunohistochemical localization was performed on frozen sections from cryopreserved postmortem human tissue using a polyclonal antibody against VEGF and a streptavidin peroxidase system. Eyes from 5 subjects without diabetes and 8 subjects with diabetes were examined and analyzed using a 7-point immunohistochemical grading system. RESULTS: In subjects without diabetes, weak or no VEGF immunoreactivity was associated with retinal blood vessels. In subjects with diabetes, we found significantly increased immunoreactivity in the retinal vascular endothelium and blood vessel walls. Vascular endothelial growth factor immunoreactivity was also associated with intravascular leukocytes in subjects with and without diabetes. In the choroid of subjects without diabetes, immunoreactivity was almost exclusively associated with intravascular leukocytes, whereas in diabetic subjects, immunoreactivity was localized within choriocapillaris endothelium, choroidal neovascular endothelium, and migrating retinal pigment epithelium cells. CONCLUSIONS: The observed increase in VEGF immunoreactivity in the diabetic retina and choroid suggests that VEGF may contribute to 2 well-documented events during retinopathy: increased vascular permeability and angiogenesis.     

Preventive action of vitamin E-containing liposomes on cataractogenesis in young adult rats fed a 25% galactose diet

The preventive action of vitamin E (Vit. E)-containing liposomes on cataractogenesis was examined in male Wistar rats (five weeks old) fed a 25% galactose diet. Vit. E-containing liposomes prepared with dipalmitoylphosphatidylcholine were instilled into both eyes three times a day over a 45-day period. Cataract appeared at 18-day galactose feeding and developed gradually thereafter. Simultaneous Vit. E-containing liposome instillation delayed this cataractogenesis. Lenses of 18-day galactose-fed rats showed decreases in Vit. E and reduced glutathione (GSH) contents and Na+, K(+)-ATPase activity and increases in lipid peroxide (LPO), galactitol, and water contents. Lenses of 45-day galactose fed rats showed decreases in GSH content and Na+,K(+)-ATPase activity and increases in Vit. E, LPO, galactitol, and water contents. Serum Vit. E and cholesterol levels decreased in 18-day galactose-fed rats, while both levels increased in 45-day galactose-fed rats. Simultaneous Vit. E-containing liposome instillation prevented these changes except for the changes of lenticular galactitol and water contents and serum Vit. E and cholesterol levels. These results indicate that simultaneously instilled Vit. E-containing liposomes can delay cataractogenesis in young adult rats fed a 25% galactose diet mainly by the antioxidative action of Vit. E contained in the instilled liposomes.     

Promotion of healthy lifestyle: knowledge and attitudes of primary care physicians

Preretinal neovascularization and chronic retinal oedema are the two major sight-threatening complications that can occur during diabetic retinopathy. Ocular neovascularization is strongly associated with retinal ischaemia, and growth factors have been implicated in its pathogenesis. The ischaemic retina is assumed to secrete growth factors that stimulate residual vessels to proliferate. Interest has focused on basic fibroblast growth factor (bFGF), insulin-like growth factor-1 (IGF-1), platelet-derived growth factor (PDGF), transforming growth factor beta (TGF beta) and more recently vascular endothelial cell growth factor (VEGF). Histologic studies have demonstrated the presence of growth factor proteins and receptors and/or their mRNA, mainly VEGF, PDGF, and bFGF, in preretinal membranes of patients with proliferative diabetic retinopathy. Elevated intravitreal levels of IGF-1 and VEGF correlating with neovascular activity have been found in some patients. However, a direct causal relationship between ischaemia, growth factors and neovascularization has not been clearly demonstrated despite considerable research work. To date, the growth factor correlating most closely with neovascularization is VEGF. As many growth factors seem to be produced during the neovascular process, their specific inhibition probably will have limited effects. Laser photocoagulation of the retina has proved beneficial for regression of new vessels, probably through destruction of the ischaemic retina producing neovascular growth factors, and is currently the only treatment for proliferative diabetic retinopathy. Inhibition of IGF-1 by somatostatin analogs has produced unsatisfactory results. Other vascular inhibitors are currently being studied.     

Roles of vascular endothelial growth factor and astrocyte degeneration in the genesis of retinopathy of prematurity

PURPOSE: To assess the role of vascular endothelial growth factor (VEGF) in the feline model of retinopathy of prematurity (ROP). METHODS: Retinopathy of prematurity was induced in neonatal cats by raising them in an oxygen-enriched (70% to 80%) atmosphere for 4 days to suppress vessel formation and then returning them to room air for 3 to 27 days. In situ hybridization was used to detect the expression of VEGF and its high-affinity receptor, flk-1, in the retina of neonatal cats, and glial fibrillary acidic protein immunocytochemistry was used to assess astrocyte status. RESULTS: The expression of VEGF in the innermost layers of retina fell in hyperoxia and increased on return to room air. Vascular endothelial growth factor expression was transient; it was maximal where vessels were about to form, and it rapidly downregulated after vessels had formed. During the proliferative vasculopathy of ROP, VEGF expression was stronger than in the normally developing retina, and the astrocytes that normally express VEGF degenerated. After the degeneration of astrocytes, VEGF was expressed by neurones of the ganglion cell layer. flk-1 was expressed by intraretinal and preretinal vessels. Supplemental oxygen therapy reduced or eliminated the overexpression of VEGF expression, astrocyte degeneration, and formation of preretinal vessels. CONCLUSIONS: Regulation of VEGF by tissue oxygen mediates the inhibition of vessel growth during hyperoxia and the subsequent proliferative vasculopathy. Degeneration of retinal astrocytes creates conditions for the growth of preretinal vessels.     

BDNF attenuates functional and structural disorders in nerves of galactose-fed rats

Galactose intoxication of rats was used to disrupt metabolism of Schwann cells and skeletal muscle, two sites that contain the polyol-forming enzyme aldose reductase (AR). Galactose-fed rats develop a neuropathy characterized by nerve conduction deficits and axonal atrophy. To investigate the possibility that galactose metabolism by AR influences axonal function and structure by altering production of neurotrophic factors, the impact of galactose intoxication on nerve and muscle BDNF levels and the effects of exogenous BDNF treatment on galactose neuropathy were examined using biochemical, electrophysiologic and morphometric techniques. Galactose feeding increased BDNF protein in peripheral nerve and muscle. Exogenous BDNF treatment attenuated motor nerve conduction velocity deficits in the sciatic nerve of galactose-fed animals and myelin splitting of motor axons in the ventral root. In contrast, sensory nerve conduction velocity (SNCV) deficits in the sciatic nerve and myelin splitting in the central projections of sensory neurons were not prevented by BDNF treatment. BDNF treatment did not attenuate reduced axonal caliber in the sciatic nerve, but did ameliorate the diminution of the caliber of central sensory projections in the dorsal root. These findings point to the potential use of BDNF in the treatment of peripheral neuropathies.     

Time-dependent aspects of osmolyte changes in rat kidney, urine, blood and lens with sorbinil and galactose feeding

Sorbitol plus myo-inositol, betaine and glycerophosphorylcholine (GPC) are cellular osmolytes in the mammalian renal medulla. Galactosemia and hyperglycemia can cause excessive levels of galactitol or sorbitol in several organs via aldose reductase (AR) catalysis. AR inhibitors can reduce these polyols. To examine osmolyte responses to polyol perturbations, male Wistar rats were fed normal diet, the AR inhibitor sorbinil (at 40 mg/kg/d), 25% galactose, or a combination, for 10, 21 and 42 days. All animals at 21 days had higher apparent renal AR activity than at 10 or 42 days, possibly providing resistance to sorbinil. Sorbinil feeding alone tended to increase urinary, plasma and renal urea levels. It reduced AR activity and sorbitol contents in renal inner medulla, though less so at 21 days; other renal osmolytes, especially betaine, were elevated. Galactose feeding caused little change in renal AR activity, and resulted in high galactose and galactitol contents in renal medulla, urine, blood and lens (and higher renal Na+ contents at 10 days). Renal sorbitol, inositol and GPC decreased, while betaine contents trended higher at all times. Sorbinilgalactose feeding reduced renal AR activities and galactitol contents (again less so at 21 days), urine, blood and lens galactitol, and further reduced renal sorbitol contents. At 10 and 21 days it tended to raise renal betaine more, and restore inositol (but not GPC) contents to control levels. At 42 days it reduced renal and urinary Na+ and galactose, and decreased renal betaine to control levels. Under most conditions, total renal (non-urea) organic osmolyte contents (presumed to be mostly intracellular) and Na+ plus galactose contents (presumed mostly extracellular) changed together such that cell volumes may have been maintained. The exception was 10 days on galactose, where total osmolytes appeared too low. In galactose-fed animals, urine/plasma ratios suggest some renal galactitol efflux, and cellular galactitol probably helps maintain osmotic balance rather than cause swelling.     

Subclinical thyroid disease in the elderly

The present study investigated the effect of NT-3, a neurotrophin expressed in nerve and skeletal muscle, on myelinated fiber disorders of galactose-fed rats. Adult, female Sprague-Dawley rats were fed diets containing complete micronutrient supplements and either 0% D-galactose (control) or 40% D-galactose. Treated controls received 20 mg/kg NT-3 and treated galactose-fed rats received 1, 5, or 20 mg/kg NT-3 three times per week by subcutaneous injections. After 2 months, sciatic and saphenous sensory nerve conduction velocity (SNCV) and sciatic motor nerve conduction velocity (MNCV) were measured and the sciatic, sural, peroneal and saphenous nerves and dorsal and ventral roots processed for light microscopy. Treatment of control animals with NT-3 had no effect on any functional or structural parameter. Compared to control values, galactose feeding induced a sensory and motor nerve conduction deficit and a reduction in axonal caliber. Treatment with 5 and 20 mg/kg NT-3 ameliorated deficits in sciatic and saphenous SNCV in galactose-fed rats but had no effect on the MNCV deficit. NT-3 treatment also attenuated the decrease in mean axonal caliber in the dorsal root and sural nerve but not in the saphenous nerve, ventral root and peroneal nerve. These observations show that NT-3 can selectively attenuate the sensory conduction deficit of galactose neuropathy in a dose-dependent manner that depends only in part on restoration of axonal caliber of large-fiber sensory neurons.     

Ocular vascular endothelial growth factor levels in diabetic rats are elevated before observable retinal proliferative changes

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor. VEGF levels in ocular tissue of 6-, 12-, 18- and 28-week-old Goto-Kakizaki (GK) rats, a well-known model of non-insulin-dependent diabetes, were evaluated by highly sensitive ELISA. VEGF concentrations in the GK rat as well as in non-diabetic Wistar rat significantly decreased from the age of 6 weeks to 18 weeks. However, although VEGF concentrations in the Wistar rat continued to fall significantly from 18 to 28 weeks of age, the levels were maintained between 18 and 28 weeks of age in GK rats. Levels were significantly different between the GK and Wistar rats at 28 weeks of age. Results of immunohistochemical studies of the eyes of Wistar and GK rats at 28 weeks of age suggest diffuse distribution of this cytokine in cells of neural origin. Weak to moderate VEGF immunoreactivity was exhibited mainly in the ganglion cell layer, inner plexiform layer and inner/outer nuclear layers in rats with and without diabetes. However, in the retinal optic nerve fiber layer, retinal pigment epithelium and choroid, strong VEGF immunoreactivity was noted only in the GK rat. In conclusion, increased VEGF production in certain ocular tissue, similar to that in humans, is observed quite early, at least before the appearance of observable retinal changes in the diabetic GK rat. This also suggests that the GK rat can be used as a model of initial or latent phase diabetic retinopathy.     

Basic fibroblast growth factor is neither necessary nor sufficient for the development of retinal neovascularization

Basic fibroblast growth factor (FGF2) is constitutively expressed in the retina and its expression is increased by a number of insults, but its role in the retina is still uncertain. This study was designed to test the hypothesis that altered expression of FGF2 in the retina affects the development of retinal neovascularization. Mice with targeted disruption of the Fgf2 gene had no detectable expression of FGF2 in the retina by Western blot, but retinal vessels were not different in appearance or total area from wild-type mice. When FGF2-deficient mice were compared with wild-type mice in a murine model of oxygen-induced ischemic retinopathy, they developed the same amount of retinal neovascularization. Transgenic mice with a rhodopsin promoter/Fgf2 gene fusion expressed high levels of FGF2 in retinal photoreceptors but developed no retinal neovascularization or other abnormalities of retinal vessels; in the ischemic retinopathy model, they showed no significant difference in the amount of retinal neovascularization compared with wild-type mice. These data indicate that FGF2 expression is not necessary nor sufficient for the development of retinal neovascularization. This suggests that agents that specifically antagonize FGF2 are not likely to be useful adjuncts in the treatment of retinal neovascularization and therapies designed to increase FGF2 expression are not likely to be complicated by retinal neovascularization.     

Retinal hypoxia in long-term diabetic cats

PURPOSE: To determine whether the retina is hypoxic in early stages of diabetic retinopathy in cats and to correlate intraretinal PO2 with fluorescein angiographic and histologic alterations. METHODS: Intraretinal PO2 was measured with microelectrodes in three cats with long-standing diabetes (>6 years) that had been followed with fluorescein angiographs every 6 months. Average PO2 in the inner vascularized half of the retina was compared with similar measurements in 21 control animals. Photoreceptor oxygen consumption was also compared. The retinal vascular endothelium of the diabetic animals was stained for ADPase activity in flatmounts, and transverse sections were used to visualize microscopic alterations in vascular structure. RESULTS: PO2 in the inner half of the retina was abnormally low in the diabetic cats, 7.7+/-5.2 mm Hg (35 penetrations in 3 cats) versus 16.4+/-9.3 mm Hg in normal cats (85 penetrations in 21 cats) (P < 0.001). Oxygenation was almost normal in some regions of the diabetic retinas, but little evidence of oxygen supply from the retinal circulation was observed in other regions. Inner retinal hypoxia was present in areas with no detectable capillary dropout in fluorescein angiograms or flatmounts. The worst changes histologically were microaneurysms, leukocyte and platelet plugging of aneurysms and venules, and degenerating endothelial cells in capillary walls. These histologic abnormalities were confined to small regions, some of which could be positively correlated with markedly abnormal PO2 profiles. Photoreceptor oxygen utilization was not affected in two diabetic cats, but was below normal in one animal in which choroidal PO2 was low. CONCLUSIONS: This is the first direct demonstration of retinal hypoxia in early diabetic retinopathy, before capillary dropout was evident clinically. Hypoxia was correlated with endothelial cell death, leukocyte plugging of vessels, and microaneurysms.     

Bacterial and human cell mutagenicity study of some C18H10 cyclopenta-fused polycyclic aromatic hydrocarbons associated with fossil fuels combustion

Maximal activity of NADP.H-cytochrome c reductase was found in the liver, the lowest one--in the retina. On the contrary, the highest activity of aldose reductase was observed in the retina, the lowest one--in the liver. The activity of NADP.H-cytochrome c reductase in the retina of rats with hereditary degeneration of the retina increased to the 60th day of postnatal life by 33%, the increase reaching 273% to the 90th day. In the brain cortex, the increase in the activity to the 45-60th days amounted to 22-34%, whereas at the age of 90 days the difference between healthy and patient rats, as well as the difference between males and females became less significant. The activity of aldose reductase in the cortex and retina in patient rats at the 20th day was 35% lower than in healthy animals. In the liver of patient rats, to the age of 45 days, the activity of aldose reductase decreased by 38%. At other periods, no significant differences were observed between healthy and patient animals with respect to the activity of this enzyme.     

Redescription of Babesia equi Laveran, 1901 as Theileria equi Mehlhorn, Schein 1998

Prolonged hyperglycemia results in a number of diabetic complications, including retinopathy. Pericyte degeneration is one of the earliest histological changes observed in the development of diabetic retinopathy. Increased free radicals generated under hyperglycemia could damage the retina, which abounds in polyunsaturated fatty acids. In the current study, a severalfold increase in thiobarbituric acid-reactive substances was found in rat retina cultured in hyperglycemic medium, which decreased significantly when trolox, an amphipathic antioxidant, was included in the medium. To examine the contribution of oxidative stress in vivo, diabetic rats were fed trolox (0.4% in the diet) during the course of the experiments. After 5 mo of hyperglycemia, whole mounts of retinal vessels were prepared and endothelial cells (E) and pericytes (P) were counted. The ratio of E/P in the retinas obtained from normal rats, diabetic rats, and diabetic rats fed trolox were 1.74 +/- 0.186, 3.78 +/- 0.47, and 2.32 +/- 0.24, respectively. A significant restoration of pericytes by trolox suggests the involvement of oxidative injury during pericyte loss in diabetic retinopathy.     

Regulation of glucose transporter (GLUT 3) and aldose reductase mRNA inbovine retinal endothelial cells and retinal pericytes in high glucose and high galactose culture

The regulation of GLUT-3 and aldose reductase mRNA in retinal endothelial cells and retinal pericytes was studied in response to variations in the extracellular concentration of hexoses. In physiological concentrations of glucose (5 mmol/l), an increase in the level of GLUT-3 mRNA was observed in cultured cells compared to the level of mRNA found in the absence of glucose. In contrast, there was little change in the level of GLUT-3 mRNA when the cells were cultured in the presence of 5 mmol/l galactose. In high concentrations of glucose, there was a decline in GLUT-3 mRNA indicating that the GLUT-3 mRNA is regulated by the extracellular concentration of glucose. In contrast, at both 5 mmol/l and 25 mmol/l glucose, the level of aldose reductase mRNA was increased. Furthermore, there were differences in the magnitude of the increase of aldose reductase mRNA between bovine retinal pericytes and bovine retinal endothelial cells with a greater increase being observed in the pericytes. We propose that this demonstration of a facilitative glucose transporter system within retinal cells, and in particular the specific response to different hexoses and the known distinct kinetic parameters of the transporter system in specific cell types, highlights the heterogeneity of hexose transport mechanisms in retinal cells. Thus, hypergalactosaemia as a model system for the study of diabetic retinopathy should be used with caution.