Background: The compositional nature of the pigment of melanosis coli
is essentially unknown. Previous histochemical studies suggested that
this pigment has certain similarities with lipofuscin (i.e., age-depen
dent pigment) and ceroids (i.e., pathologically derived pigments) and
that it may contain, therefore, polymerized glycolipids and glycoprote
ins. However, the saccharide composition of this pigment was never exp
lored by lectin histochemical procedures, which was the main object of
this study. Methods: Colonoscopic biopsy specimens from eight patient
s with melanosis coli and from three normal control subjects were stud
ied by fluorescent microscopy and by standard and lectin histochemistr
y. The number of apoptoses in the lining colonic epithelium was also e
valuated histologically. Results: Apoptotic bodies were significantly
more numerous in patients with melanosis coli than in control subjects
. The pigment that accumulates in macrophages of the lamina propia sho
wed autofluorescence, sudanophilia, acid-fastness, and positiveness to
PAS and Schmorl's reactions, all of which are common to lipofuscin an
d ceroids, plus an intense argentaffin reaction abolished by bleaching
, indicative of a melanic substance. Lectin histochemistry showed, in
decreasing order of frequency, the presence of alpha-D-mannose, sialic
acid, beta-D-galactose (lactose), gal-beta-(1-3)acetyl-galactosamine,
alpha-D-galactose, and alpha-L-fucose, but no terminal alpha-D-acetyl
-galactosaminyl residues. Conclusions: The significant increase of apo
ptotic bodies in the lining colonic epithelium indicated that this typ
e of cell death is not due to the natural programmed cell renewal, but
to the action of laxatives. Because the autofluorescent pigment of me
lanosis coli contains melanin (as well as glycoconjugates) and is not
dependent on age but on the use of anthranoid laxatives, it should be
categorized as a ''melanized ceroid.'' The lectin affinities of this p
igment indicated that it contains a substantial number of saccharide r
esidues almost similar to those found in the ceroid pigment of human a
ortic atheromas. These findings and considerations on the metabolism a
nd pharmacokinetics of anthranoids suggested that the apoptotic epithe
lial cells, rather than the laxatives, may be the source of the pigmen
t saccharides, whereas the precursors of the melanic substance may be
derived from the anthranoids.