Real-time quantitative PCR measurement of circulatory rhodopsin mRNA in healthy subjects and patients with diabetic retinopathy.

Diabetic retinopathy is the commonest complication of diabetes and is the biggest single cause of registered blindness in the UK. No biochemical tests exist to determine the precise state and rate of change of the eyes in the diabetic patient. In the present study, using real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR), we measured mRNA encoding the retina-specific pigment protein rhodopsin (RHO) in the peripheral blood of healthy individuals (n = 20) and diabetic patients (n = 46) with and without retinopathy. Beta-actin mRNA was also assayed and results are expressed as a ratio of RHO to beta-actin mRNA. Peripheral blood was taken by venipucture directly into PAXgene Blood RNA collection tubes and RNA extracted by use of the PAXgene Blood RNA extraction kit, as per the manufacturer's (Qiagen) instructions. Diabetic patients were divided into three groups defined by the severity of retinopathy as assessed by fundoscopy: A, diabetic without retinopathy; B, background retinopathy; and C, preproliferative retinopathy. Medians of the ratios between groups were compared. RHO mRNA was successfully detected and quantified in peripheral blood in all healthy and diabetic groups, with levels shown to be significantly higher in diabetic patients than in healthy controls (2.54 x 10(-5) vs. 1.29 x 10(-5); P = 0.002). Significant differences in RHO mRNA levels were also seen between healthy control subjects and diabetic groups A (2.52 x 10(-5); P = 0.022), B (1.98 x 10(-5); P = 0.028), and C (5.08 x 10(-5); P = 0.002). The results suggest that there is an increase in circulatory RHO mRNA with the severity of diabetic retinopathy.