Augmented polyol pathway activity and retinal pigment epithelial permeability in the diabetic BB rat

SPARC: a key player in the pathologies associated with obesity and diabetes

SPARC (secreted protein acidic and rich in cysteine, also known as osteonectin or BM-40) is a widely expressed profibrotic protein with pleiotropic roles, which have been studied in a variety of conditions. Notably, SPARC is linked to human obesity; SPARC derived from adipose tissue is associated with insulin resistance and secretion of SPARC by adipose tissue is increased by insulin and the adipokine leptin. Furthermore, SPARC is associated with diabetes complications such as diabetic retinopathy and nephropathy, conditions that are ameliorated in the Sparc-knockout mouse model. As a regulator of the extracellular matrix, SPARC also contributes to adipose-tissue fibrosis. Evidence suggests that adipose tissue becomes increasingly fibrotic in obesity. Fibrosis of subcutaneous adipose tissue may restrict accumulation of triglycerides in this type of tissue. These triglycerides are, therefore, diverted and deposited as ectopic lipids in other tissues such as the liver or as intramyocellular lipids in skeletal muscle, which predisposes to insulin resistance. Hence, SPARC may represent a novel and important link between obesity and diabetes mellitus. This Review is focused on whether SPARC could be a key player in the pathology of obesity and its related metabolic complications.

The fast oscillation of the EOG in diabetes with and without mild retinopathy

There is ample evidence that the retinal pigment epithelium (RPE) is affected in diabetes, and that epitheliopathy may be among the early changes. The fast oscillation (FO) of the electro-oculogram (EOG) reflects the activity of the RPE, most notably the mechanisms responsible for pumping fluid and ions in the retina-to-choroid direction. The FO was measured in three groups of subjects: normal controls, eyes of diabetic individuals with no evidence of retinopathy, and eyes of diabetics with mild background retinopathy. FO amplitude, light trough voltage and dark peak voltage in both diabetic groups were all significantly reduced, independent of retinopathy status. The peak to trough ratio was unaffected. These changes, reduced voltages and smaller light-evoked voltage changes, are consistent with a decrease in the resistance of the RPE and may relate to accumulation of fluid in the sub-retinal space.

Alterations in basal glucose metabolism during late pregnancy in the conscious dog

We assessed basal glucose metabolism in 16 female nonpregnant (NP) and 16 late-pregnant (P) conscious, 18-h-fasted dogs that had catheters inserted into the hepatic and portal veins and femoral artery approximately 17 days before the experiment. Pregnancy resulted in lower arterial plasma insulin (11 +/- 1 and 4 +/- 1 microU/ml in NP and P, respectively, P < 0.05), but plasma glucose (5.9 +/- 0.1 and 5.6 +/- 0.1 mg/dl in NP and P, respectively) and glucagon (39 +/- 3 and 36 +/- 2 pg/ml in NP and P, respectively) were not different. Net hepatic glucose output was greater in pregnancy (42.1 +/- 3.1 and 56.7 +/- 4.0 micromol. 100 g liver(-1).min(-1) in NP and P, respectively, P < 0.05). Total net hepatic gluconeogenic substrate uptake (lactate, alanine, glycerol, and amino acids), a close estimate of the gluconeogenic rate, was not different between the groups (20.6 +/- 2.8 and 21.2 +/- 1.8 micromol. 100 g liver(-1). min(-1) in NP and P, respectively), indicating that the increment in net hepatic glucose output resulted from an increase in the contribution of glycogenolytically derived glucose. However, total glycogenolysis was not altered in pregnancy. Ketogenesis was enhanced nearly threefold by pregnancy (6.9 +/- 1.2 and 18.2 +/- 3.4 micromol. 100 g liver(-1).min(-1) in NP and P, respectively), despite equivalent net hepatic nonesterified fatty acid uptake. Thus late pregnancy in the dog is not accompanied by changes in the absolute rates of gluconeogenesis or glycogenolysis. Rather, repartitioning of the glucose released from glycogen is responsible for the increase in hepatic glucose production.

Diabetes, hyperglycemia, and age-related maculopathy. The Beaver Dam Eye Study

PURPOSE

The purpose of this study is to examine the association among hyperglycemia, diabetes status, and age-related maculopathy in a population-based study of people between the ages of 43 and 86 years who lived in Beaver Dam, Wisconsin between 1988 and 1990.

METHODS

Age-related maculopathy was determined from stereoscopic fundus photographs.

RESULTS

In the nondiabetic group (n = 4291), no relationship was found between glycosylated hemoglobin and any signs of age-related maculopathy. Diabetes status was not associated with early age-related maculopathy. People 75 years of age or older with diabetes (n = 85) had a higher frequency of exudative macular degeneration (9.4%) than those without (4.7%) but had similar frequencies of pure geographic atrophy (3.8% for those with diabetes and 3.4% for those without diabetes). The relative risk of exudative macular degeneration in men with diabetes who were 75 years of age or older compared with those who did not have diabetes was 10.2 (95% confidence interval [CI]: 2.4, 43.7); for females it was 1.1 (95% CI: 0.4, 3.0).

CONCLUSION

These data suggest that diabetes is not related to early age-related maculopathy or geographic atrophy. The relationship of exudative macular degeneration to diabetes in older men, but not women, may be a result of chance. Further longitudinal study of this observation is needed.

Anionic sites in diabetic basement membranes and their possible role in diffusion barrier abnormalities in the BB-rat

Basement membrane anionic sites, thought to be responsible for charge selective permeability barriers, were investigated in retinal, endoneurial, and muscle capillary basement membranes and in Bruch's membrane of diabetic, and age- and sex-matched non-diabetic BB-rats using an ultrastructural quantitative histochemical technique. Six months of diabetes was associated with significant basement membrane thickening which was linearly related to a decrease in anionic site density suggesting a relative loss of proteoglycans. Calculation of anionic sites per unit length of basement membrane, reflecting their absolute number, revealed a significant loss in basement membrane, constituting part of normal blood-tissue barrier systems such as retinal and endoneurial capillary basement membranes, and the basement membrane of the retinal pigment epithelium. The absolute number of anionic sites in normally permeable microvessels, such as those of muscle and choriocapillaries, was unaltered by diabetes. We conclude that this specific loss of anionic sites in basement membranes of tissues affected by chronic diabetic complications may in part be responsible for permeability abnormalities seen in these tissues.