Synergism of mechanisms underlying early-stage changes in retina function in male hyperglycemic db/db mice in the absence and presence of chemically-induced dyslipidemia

Abstract

Abstract The study was designed to quantify retina function in a spontaneous mutation mouse model of diabetes, in which sustained dyslipidemia was induced chemically. The goal of the study was to identify if dyslipidemia in the presence of hyperglycemia resulted in either a synergistic, or a merely additive, exacerbation of retinal and visual dysfunctions in diabetes. Two cohorts of mice, male C57BL/6 and C57BL/KsJ-db/db mice were divided into two groups each. One group of each strain received the triblock copolymer, poloxamer 407 (P-407), administered by intraperitoneal injection (“WT P-407” and “db/db P-407” groups) with saline as a control in the remaining two groups (“WT” and “db/db” groups). Blood glucose, total cholesterol (TC) and total triglyceride (TG) levels were quantified using enzyme-based colorimetric assays. Retina function was measured using electroretinography (ERG) and visual acuity was determined by behaviorally assessing parameters of the optomotor reflex. TC and TG levels were normal in both saline controls (WT) and db/db mice but were significantly elevated in the WT P-407 group (p < 0.01 for TC; p < 0.001 for TG), while levels of the same lipids were further elevated in the db/db P-407 group when compared to the WT P-407 group levels (p < 0.001 for both TC and TG). Behavioral assessment of the optomotor reflex indicated reduced visual acuity for the db/db P-407 group when compared to either the WT P-407 or the db/db groups (p < 0.001, p < 0.0001). ERG measurements of scotopic retina function showed a significant decline in the scotopic b-wave amplitude of the WT P-407 animals (p < 0.01) and a further reduction for the db/db P-407 group when compared to controls (p < 0.0001). Very significant, strong correlations between scotopic b-wave amplitude and implicit time to TC (r = − 0.8376, p = < 0.0001 and r = 0.7069, p = 0.0022, respectively) and TG levels (r = − 0.8554, p = < 0.0001 and r = 0.7150, p = 0.0019, respectively) were found. Dyslipidemia in the presence of hyperglycemia synergistically exacerbated the severity of retinal dysfunction in diabetes. P-407 administration significantly elevated plasma TC and TG levels in male wild-type (WT) and diabetic mice (db/db), but the resulting hyperlipidemia was more significantly pronounced in the diabetic mice. While elevated plasma lipid and blood glucose levels were individually correlated with a decline in retinal function, the combination of both exacerbated retinal dysfunction. This model of combined hyperglycemia and dyslipidemia can be used to dissect individual contributions of features of the metabolic syndrome to the pathogenesis of retinal dysfunction in diabetes.