Abstract
Proliferative retinopathy is a complication of sickle cell disease (SCD). Promotion of angiogenesis by opioids (
Cancer Res 62: 4491, 2002
) suggests that opioid analgesics used to treat pain may exaggerate retinopathy in patients with SCD. To examine the hypothesis that morphine augments retinopathy, we used sickle mice with transgenes for human α and βS globin (NY1DD model) and their wild type (WT) C57/BL6 controls. Simulating the analgesic doses used in humans, we injected morphine subcutaneously (50 mg / day / 70 Kg with 10 mg increments every 2 weeks and / or equimolar amount of naloxone) for 6 to 15 months into 9 – 11 months old mice. Retinal vasculature was visualized with darkfield illumination using adenosine diphosphatese reaction. Morphine induced neovascularization, corkscrew formation resembling microangiopathy in human, arterio-venous anastomoses and several vascular tufts in the inner 1/3 and whole retina after 10 and 15 months of treatment, respectively in all NY1DD but not in WT mice. Only 1/5 or 2/7 PBS-treated NY1DD mice showed early neovascular changes at 20 (treated for 10 mo) or 26 (treated for 15 mo) months of age, respectively. Retinopathy scores by ICROP system used in neonatal intensive care units for abnormal vessels, blood vessel tortuosity and tufts in NY1DD mice were: 10 mo treatment, PBS, 1.5±0.5; morphine, 10±0.7 (p<0.0001 vs PBS); morphine + naloxone, 4±1; naloxone, 3.8±1.2 and 15 mo treatment, PBS, 5.9±2 and morphine, 13±0.5 (p<0.003 vs PBS). Naloxone significantly inhibited (p<0.005, morphine vs morphine +naloxone) morphine-induced retinopathy, suggesting an opioid receptor-mediated mechanism. To elucidate the mechanism of morphine-induced retinopathy we isolated retinal endothelial cells (REC) by panning with anti-CD31 from WT and NY1DD mice. Similar to VEGF induced proliferation and survival, morphine stimulated 5–6 fold proliferation and increased survival by about 75% in both WT and NY1DD REC, in a dose dependent manner. Both VEGF164 and morphine stimulated time-dependent MAPK/ERK and STAT3 phosphorylation in WT REC. VEGF and morphine stimulate nitric oxide synthase pathway and stimulate angiogenesis. This raised the possibility of a cross-talk between VEGF receptor(s) and opioid receptor(s). We found that morphine stimulates the phosphorylation of VEGFR2/Flk1 in WT REC which co-immunoprecipitated with mu opioid receptor (MOR) using anti-MOR antibodies. Both, morphine- or VEGF-induced phospho STAT3 also co-immunoprecipitated with MOR, suggesting that activation of either MOR or Flk1 transactivates the other. Thus, addition of morphine to the VEGF replete microenvironment in SCD can have an exaggerating effect on the progression of retinopathy. Since patients with SCD receive opioids for long periods of time, we speculate that retinopathy in these patients may in part be due to opioid use.Author notes
Corresponding author
2005, The American Society of Hematology
2005
