Although, increased oxidative stress and hypomethylation of long interspersed 
nuclear element-1 (LINE-1) associate with bladder cancer (BCa) development, the 
relationship between these alterations is unknown. We evaluated the oxidative 
stress and hypomethylation of the LINE-1 in 61 BCa patients and 45 normal 
individuals. To measure the methylation levels and to differentiate the LINE-1 
loci into hypermethylated, partially methylated and hypomethylated, peripheral 
blood cells, urinary exfoliated cells and cancerous tissues were evaluated by 
combined bisulfite restriction analysis PCR. The urinary total antioxidant 
status (TAS) and plasma protein carbonyl content were determined. The LINE-1 
methylation levels and patterns, especially hypomethylated loci, in the blood 
and urine cells of the BCa patients were different from the levels and patterns 
in the healthy controls. The urinary TAS was decreased, whereas the plasma 
protein carbonyl content was increased in the BCa patients relative to the 
controls. A positive correlation between the methylation of LINE-1 in the 
blood-derived DNA and urinary TAS was found in both the BCa and control groups. 
The urinary hypomethylated LINE-1 loci and the plasma protein carbonyl content 
provided the best diagnostic potential for BCa prediction. Based on 
post-diagnostic samples, the combination test improved the diagnostic power to a 
sensitivity of 96% and a specificity of 96%. In conclusion, decreased LINE-1 
methylation is associated with increased oxidative stress both in healthy and 
BCa subjects across the various tissue types, implying a dose-response 
association. Increases in the LINE-1 hypomethylation levels and the number of 
hypomethylated loci in both the blood- and urine-derived cells and increase in 
the oxidative stress were found in the BCa patients. The combination test of the 
urinary hypomethylated LINE-1 loci and the plasma protein carbonyl content may 
be useful for BCa screening and monitoring of treatment.