Abstract
Purpose:
Lipoprotein-associated phospholipase A2 (Lp-PLA2) has been shown to modulate vascular inflammatory responses in atherosclerosis. In diabetic retinopathy and diabetic macular edema (DME) there is increasing recognition of a pro-inflammatory etiology and we hypothesized that Lp-PLA2 inhibition may prove protective. The impact of systemic Lp-PLA2 inhibition is currently under investigation in DME patients.
Methods:
Brown Norwegian (BN) rats were rendered diabetic with a single streptozotocin injection. Once hyperglycemia was established, rats were dosed daily via intraperitoneal injection of either vehicle or the Lp-PLA2 inhibitor SB435495 (0.25mg/kg - 10mg/kg) for 28 days. Blood samples were collected immediately prior to initial dosing, and 24h post the final drug dosing to determine pharmacokinetics and enzyme inhibition levels. Breakdown of the blood retinal barrier (BRB) was assessed by Evans Blue leakage assay and extravasation of immuno-reactive rat albumin. Retinal expression of growth factors and pro-inflammatory cytokines were quantified by real-time PCR and microglial and macrophage cell activation was assessed by isolectin and CD68 immunocytochemistry.
Results:
Enzymatic activity of Lp-PLA2 was suppressed by 72.8, 57.5, 33.5, and 19.1 % in hyperglycemic BN rats dosed with 10, 5, 1, and 0.25 mg/kg SB435495 respectively. Lp-PLA2 inhibition reduced BRB breakdown in a dose-dependent manner (p =0.0233 for dose-response relationship), whereas in a pair-wise comparison only the 10mg/kg dose was significantly different from hyperglycemic control (p=0.0397). Numbers of CD68 immuno-reactive macrophages were unaltered in diabetic rats when compared to non-diabetic controls and SB435495 treated diabetic animals. Microglia showed an activated phenotype in diabetic animals compared to non-diabetic animals and the activated phenotype was not impacted by SB435495 treatment.
Conclusions:
Inhibition of Lp-PLA2 reduces BRB compromise in diabetes without impact on diabetes-induced microglial activation, therefore this enzyme may be a viable therapeutic target in DME.
Keywords: 499 diabetic retinopathy •
562 inner retina dysfunction: biochemistry and cell biology •
533 gene/expression