Colon melanosis - otherwise known as pseudomelanosis of the colon - is a benign condition, characterized by the appearance of more or less intense brownish nuances on the colic mucosa. The term melanosis is in any case improper, given that the brownish color - or even black in the most serious cases - is not linked to the increased synthesis of melanin, but to the permanence of protein and lipid substances (lipofuscin) within the macrophages that populate the walls of this intestinal tract.
Colonic melanosis is diagnosed by colonoscopy or sigmoidoscopy; more rarely, the diagnosis is made following the microscopic examination of biopsy specimens of moss colic.
In the figure above, taken from the textbook "General and applied pharmacognosy of Alessandro Bruni, Ed. Piccin" we find a list of the main natural anthraquinone laxatives, sorted according to the power of their laxative effect and according to the importance of the relative contraindications. Not surprisingly, the two characteristics go hand in hand and as the one increases, the other increases as well. Still considering this widespread category of natural laxatives, the purgative effect also varies according to the conditions in which the plant has grown and the methods of processing used to produce the drug. In synthetic laxatives, on the contrary, the active ingredient is purified and precisely dosed.
Melanosis of the colon is a benign condition and is no longer considered to be precancerous, although - especially in the past - it has been repeatedly associated with an increased risk of developing colorectal cancer.
In most cases, colon melanosis appears due to chronic use of anthraquinone laxatives (see figure). In particular, the typical brownish nuances of the colonic mucosa begin to form after about four months of continued assumption of these principals.
In addition to being substantially harmless, the melanosis of the colon is also reversible, provided that the use of anthraquinone laxatives is suspended and a different approach is taken to the problem of constipation.
Among the other possible causes of pseudomelanosis of the colon are all the conditions characterized by an accelerated cell turnover. The presence of lipofuscins is in fact related to aging and to apoptotic phenomena.
Anthraquinones can be considered prodrugs; once they are in fact, they cross the gastrointestinal tract without being absorbed; after which, at the level of the large intestine - thanks to the intervention of the local bacterial flora - the anthraquinones are converted into their active form, strongly irritating to the colic mucosa. The cell damage induced by anthraquinones, besides producing a laxative effect (increased secretion and intestinal motility), creates damage of apoptotic origin, with macrophage intervention and accumulation of lipofuscin within these cells of the immune system. Precisely this accumulation, as mentioned, lies at the origin of colon melanosis.
