Chemopreventive effect of myrtenal on bacterial enzyme activity and the development of 1,2-dimethyl hydrazine-induced aberrant crypt foci in Wistar Rats

摘要

Abstract Colon cancer remains as a serious health problem around the world despite advances in diagnosis and treatment. Dietary fibers are considered to reduce the risk of colon cancer as they are converted to short chain fatty acids by the presence of anaerobic bacteria in the intestine, but imbalanced diet and high fat consumption may promote tumor formation at different sites, including the large bowel via increased bacterial enzymes activity. The present study was conducted to characterize the inhibitory action of myrtenal on bacterial enzymes and aberrant crypt foci (ACF). Experimental colon carcinogenesis induced by 1,2-dimethylhydrazine is histologically, morphologically, and anatomically similar to human colonic epithelial neoplasm. Discrete microscopic mucosal lesions such as ACF and malignant tumors function as important biomarkers in the diagnosis of colon cancer. Methylene blue staining was carried out to visualize the impact of 1,2-dimethylhydrazine and myrtenal. Myrtenal-treated animals showed decreased levels of bacterial enzymes such as β-glucuronidase, β-glucosidase, and mucinase. Characteristic changes in the colon were noticed by inhibiting ACF formation in the colon. In conclusion, treatment with myrtenal provided altered pathophysiological condition in colon cancer-bearing animals with evidence of decreased crypt multiplicity and tumor progression. Keywords aberrant crypt foci ; colon cancer ; monoterpenes ; myrtenal prs.rt("abs_end"); 1. Introduction Colorectal cancer is a major cause of death in developed countries with an increased rate of morbidity and mortality [1] . The incidence rate continues to rise as people change their lifestyles and food habits [2] . In this regard, substance-use disorders are associated with numerous medical, psychiatric, psychological, spiritual, economic, social, family, and legal problems, creating a significant burden for affected individuals, their families, and society [3] . Insidious factors such as alcohol, smoking, sedentary lifestyle, aging, and diet are the most important exogenous promoters of colon cancer [4] . Supporting this, Chang [5] investigated the mechanisms by which alcohol damages immune defense function to identify therapeutic targets for effective treatment of alcoholic patients with severe bacterial infection. Davie [6] stated that dietary fibers are considered to reduce the risk of colon cancer as they are converted to short chain fatty acids by the presence of anaerobic bacteria in the intestine, which prevents the invasion of pathogenic bacteria [7] . However, imbalanced diet and high fat consumption is known to alter this protective metabolism of the intestinal microflora, and reduce the host immune response by increased bacterial enzyme activity [8] . Thereby β-glucuronidase activity in the intestine plays a major role in the generation of toxic and carcinogenic metabolites that may promote tumor formation at different sites, including the large bowel [9] . In that way, 1,2-dimethylhydrazine (DMH), a procarcinogen, is metabolized by β-glucuronidase enzymes along with its metabolic pathway in the liver and released as a carcinogen in the colon epithelium to induce colon cancer in experimental animals [10] . A variety of fungi and bacteria synthesize the major component enzyme, β-glucosidase, which can synergistically convert cellulose into glucose for the enzymatic depolymerization of cellulosic material [11] . Enzymatic hydrolysis of cellulose is a major limitation in lignocellulose's conversion to glucose, as β-glucosidase activity causes accumulation of aglycones [12] . Robertson et?al [13] proved that hydrolytic activity of the bacterial enzyme mucinase acts on the destruction of mucins or their prosthetic polysaccharides by the bacteria. The intestinal mucinous layer also experiences an autolytic enzyme hydrolysis, leading to altered permeability of the mucosal membrane. Nitroreductase is involved in the reduction of nitrogen-containing compounds including nitro functional group members such as dinitrotoluene, nitrobenzenes, and nitropyrenes to amines. A number of these proteins are described as oxidoreductases and are primarily found in bacterial lineages that exhibit toxic, mutagenic or carcinogenic activities [14] and [15] . Colon cancer has been postulated as a complex and multistage process that includes a series of pathological alterations ranging from discrete microscopic mucosal lesions, such as aberrant crypt foci (ACF), to malignant tumors [16] . ACF are generally considered the earliest identifiable macroscopic lesion within the colonic mucosa that may be associated with risk of future neoplastic development [17] . Due to morphological and genetic similarities in ACF development between rodents and humans, this preneoplastic lesion may be used in cancer screening and prevention studies for the detection of risk factors and protective factors associated with colon cancer progression [18] . Among various biomarke