Experimental Study on the Molecular Mechanism of Anthraquinone Cathartics in Inducing Melanosis Coli

Objective：To explore the significance of colonic epithelial cell apoptosis and tumor necrosis factorα（TNF-α）changing in pathogenesis of melanosis coli（MC）in guinea pig and the molecular mechanism of rhubarb（Rhu）in inducing the disease,by means of using different dosages of Rhu to induce the disease. Methods：One hundred and forty-four male guinea pigs,clean grade,were randomized according to their body weight into 5 groups,the untreated normal group and the 4 Rhu groups treated,respectively,with different doses of Rhu,3 g/kg·d for low dose（Rhu-I）group,6 g/kg·d for moderate dose（Rhu-m）group,12 g/kg·d for high dose（Rhu-h）group and 24 g/kg·d for super-high dose（Rhu-s）group via gastric infusion.All animals were sacrificed 60 days later,their viscera were taken for observing the pathologic and morphologic changes with HE, melanin and melatonin staining,and the apoptosis of colonic epithelial cells was detected with TUNEL stain and transmission electric microscopy.In addition,the levels of TNF-αin serum and colonic tissue were measured using ELISA and RT-PCR.Results：The pathological changes of MC could be found by naked eye in all Rhu groups,especially apparent at caecum and proximal end of colon,but did not found in gallbladder,jejunum and ileum.In normal guinea pigs,the colonic membrane was pink in color with no apparent pigment deposition. Membranous color deepened in the Rhu groups depending on the dosage of Rhu used.MC scoring showed the highest scores revealed in the Rhu-s group（6.00±0.00）,which was significantly different to those in the Rhu-I （3.86±0.69）,Rhu-m（4.43±0.79）and Rhu-h groups（4.88±0.35,all P0.05）.Levels of cell apoptosis in colon and TNF-αin serum in all Rhu groups were higher than those in the normal group（P0.01）,but showed no significant difference among the Rhu groups（P0.05）.Moreover,a positive correlation was found in the degree of induced MC with apoptosis rate and TNF-αlevel.Conclusions：Rhu（anthraquinone purgatives）had apparent effect on inducing MC;its molecular mechanism is maybe to destroy intestinal mucosal barrier and advance proinflammatory factor TNF-αreleasing,which leads to colonic epithelial cells apoptosis,and finally induce the change of MC due to the deposition of brown pigments,i.e.the macrophage phagocytized apoptotic body,on the colonic membrane.

Expression of aquaporin 8 and its relationship with melanosis coli

Background The relationship between melanosis coli （MC） and aquaporin 8 （AQP8） has not yet been elucidated. The aim of this research was to investigate the relationship between the expression of AQP8 and the pathological mechanism of MC.Methods Expression of AQP8 was detected by immunohistochemistry and reverse transcription-polymerase chain reaction （RT-PCR） in 37 MC colon tissues and 13 control colon tissues. Global gene expression analysis was also used to identify differently expressed genes. Its relationship with MC was analyzed by SPSS 11.5 statistical software.Results The positive rate of AQP8 expression detected by immunohistochemistry in the MC group was 24.3% （9/37）,significantly lower than the 69.2% （9/13） in the control group （P 〈0.05）. The relative expression level of AQP8 in MC group was 0.639±0.160, lower than 0.921±0.148 of controls （P 〈0.05）. Global gene expression analysis showed that AQP8 mRNA expression was downregulated in MC patients.Conclusions The decreased AQP8 expression in MC patients indicates that chronic use of laxatives containing anthraquinone may cause reduced water absorption. The expression of AQP8 may be related to MC.

“Melanosis” in the small and large intestine

Deposition of pigment in the intestinal mucosa is commonly observed by the endoscopist, especially within the colon, and particularly during investigations for constipation. Pigment may also be detected in the small intestine. Although labeled as melanosis, electron microscopy and X-ray analytical methods have provided evidence that this pigment is not melanin at all, but lipofuscin. Often, herbal remedies or anthracene containing laxatives are often historically implicated, and experimental studies in both humans and animal models have also confirmed the intimate relationship with these pharmacological or pseudo-pharmacological remedies. The appearance of melanosis coli during colonoscopy is largely due to pigment granule deposition in macrophages located in the colonic mucosa. The pigment intensity is not uniform, being more intense in the cecum and proximal colon compared to the distal colon. Possibly, this reflects higher luminal concentrations of an offending agent in the proximal compared to distal colon, differential absorption along the length of the colon, or finally, differences in macrophage distribution within the colon. Mucosal lymphoid aggregates normally display a distinct absence of pigment producing a "starry sky" appearance, especially in the rectosigmoid region. Interestingly, some focal, usually sessile, colonic mucosal neoplastic lesions, rather than submucosal lesions, may be better appreciated as pigment deposition may be absent or limited. If detected, removal and further histopathologic analysis of the polyp may be facilitated.