Beschreibung:
<jats:p>Highly methylated Long Interspersed Nucleotide Elements 1 (<jats:italic>LINE-1</jats:italic>) constitute approximately 20% of the human genome, thus serving as a surrogate marker of global genomic DNA methylation. To date, there is still lacking a consensus about the precise location in <jats:italic>LINE-1</jats:italic> promoter and its methylation threshold value, making challenging the use of <jats:italic>LINE-1</jats:italic> methylation as a diagnostic, prognostic markers in cancer. This study reports on a technical standardization of bisulfite-based DNA methylation analysis, which ensures the complete bisulfite conversion of repeated <jats:italic>LINE-1</jats:italic> sequences, thus allowing accurate <jats:italic>LINE-1</jats:italic> methylation value. In addition, the study also indicated the precise location in <jats:italic>LINE-1</jats:italic> promoter of which significant variance in methylation level makes <jats:italic>LINE-1</jats:italic> methylation as a potential diagnostic biomarker for lung cancer. A serial concentration of 5-50-500 ng of DNA from 275 formalin-fixed paraffin-embedded lung tissues were converted by bisulfite; methylation level of two local regions (at nucleotide position 300–368 as <jats:italic>LINE-1</jats:italic>.<jats:italic>1</jats:italic> and 368–460 as <jats:italic>LINE-1</jats:italic>.<jats:italic>2</jats:italic>) in <jats:italic>LINE-1</jats:italic> promoter was measured by real time PCR. The use of 5 ng of genomic DNA but no more allowed to detect <jats:italic>LINE-1</jats:italic> hypomethylation in lung cancer tissue (14.34% versus 16.69% in non-cancerous lung diseases for <jats:italic>LINE-1</jats:italic>.<jats:italic>1</jats:italic>, p < 0.0001, and 30.28% versus 32.35% for <jats:italic>LINE-1</jats:italic>.<jats:italic>2</jats:italic>, p < 0.05). Our study thus highlighted the optimal and primordial concentration less than 5 ng of genomic DNA guarantees the complete <jats:italic>LINE-1</jats:italic> bisulfite conversion, and significant variance in methylation level of the <jats:italic>LINE-1</jats:italic> sequence position from 300 to 368 allowed to discriminate lung cancer from non-cancer samples.</jats:p>