Colorectal cancer (CRC) is a common cause of death worldwide, and represents the third most common
form of cancer and the second leading cause of cancer-related death in the world. Human paraoxanase (PON1) is a
Ca-dependent esterase synthesized in liver and related to high density lipoprotein (HDL) and protecting low density
lipoprotein (LDL) by hydrolysis of lipid peroxides. This study aimed to evaluate the relation between CRC and
PON1 enzyme activity and polymorphism. Fifty patients of both sexes diagnosed as CRC patients along with eighty
healthy persons of matchable age and sex were enrolled in the study. The circulating levels of serum level of lipid
profile, PON1 and Aryl esterase (ARE) enzymes were determined by spectrophotometer assays. PON1 gene
polymorphism was done using polymerase chain reaction (PCR) technique. The present work showed significant
reduction of the serum levels of HDL and triglycerides (TG) concomitant with significant elevation of the serum
level of LDL in patients compared to controls. Plasma total cholesterol (TC) shows no significance difference
between patients and controls. As regard PON1 gene polymorphism, the present study demonstrated that, the QQ
genotype was the most frequent among the CRC patients and the controls (60%), followed by QR genotype (32%).
The RR was the least frequent genotype in the two populations (8%). These finding indicated that the serum PON1
and ARE activities were significantly lower in CRC patients compared to healthy subjects concomitant with
significant increase in the serum level of LDL and significant reduction of HDL and TG. Also there were significant
difference of genotype distribution of PON1 between patients and control groups. These observations suggested the
hypothesis that defects in the antioxidant system capacity and altered PON 1 activity may be involved in the
pathogenesis of CRC.