Lectin from Elder (Sambucus nigra) as a marker of apoptotic and necrotic death

Apoptosis is a tightly regulated process of cell death which results in cell fragmentation and removal of demised cells by phagocytosis. The several glycosylation changes described in apoptotic cells, usually by means of fluorescent lectins, are often cell specific and the identification of apoptosis-associated carbohydrate changes of general significance is still lacking. Sambucus nigra agglutinin (SNA) is a widely used tool for the detection of 2,6-sialylated lactosamine, a carbohydrate epitope often associated with cancer, which is the product of sialyltransferase ST6Gal.1. In this study, we show that cell lines of different histological origin, such as colon, breast, pancreas and bladder cancer undergoing apoptosis display a strong increase of SNA reactivity, through a ST6Gal.1-independent mechanism. This change is specific, in that the reactivity with other lectins, such as Maakia amurensis lectin, peanut agglutinin and leukoagglutinin does not show any consistent change. Surprisingly, also a heat treatment which induces primary necrosis causes a specific increase of SNA reactivity. In the colon cancer cell lines SW48 and SW948 which are basically devoid of measurable ST6Gal.1 activity and which express very low levels of SNA reactivity, apoptosis- or necrosis-inducing treatments induce increased SNA reactivity but do not activate the dormant ST6Gal.1 activity. The spontaneous apoptosis occurring in human neutrophiles at the end of their brief life, also causes a strong increase of SNA reactivity. Together, these data indicate that SNA detects specifically a change occurring in apoptotic and necrotic cells, regardless their histological origin and the nature of the apoptotic stimulus.