Effect of an intraluminal food-bulk on low calorie induced hyperbilirubinaemia

Unconjugated bilirubin induces apoptosis in colon cancer cells by triggering mitochondrial depolarization

Bilirubin is the principal end product of heme degradation. Prompted by epidemiologic analyses demonstrating an inverse correlation between serum bilirubin levels and cancer mortality, we examined the effect(s) of bilirubin on the growth and survival of colon adenocarcinoma cells. Adenocarcinoma cell monolayers were treated with bilirubin over a range of bilirubin:BSA molar ratios (0-0.6), and viability was assessed colorimetrically. Apoptosis was characterized by TUNEL assay, annexin V staining and caspase-3 activation. The mechanism(s) by which bilirubin induces apoptosis was investigated by Western blotting for cytochrome c release, assaying for caspase-8 and caspase-9 activation and for mitochondrial depolarization by JC-1 staining. The direct effect of bilirubin on the membrane potential of isolated mitochondria was evaluated using light-scattering and fluorescence techniques. Bilirubin decreased the viability of all colon cancer cell lines tested in a dose-dependent manner. Cells exhibited substantial apoptosis when exposed to bilirubin concentrations ranging 0-50 microM, as demonstrated by an 8- to 10-fold increase in TUNEL and annexin V staining and in caspase-3 activity. Bilirubin treatment evokes specific activation of caspase-9, enhances cytochrome c release into the cytoplasm and triggers the mitochondrial permeability transition in colon cancer monolayers. Additionally, bilirubin directly induces the depolarization of isolated rat liver mitochondria, an effect that is not inhibited by cyclosporin A. Bilirubin stimulates apoptosis of colon adenocarcinoma cells in vitro through activation of the mitochondrial pathway, apparently by directly dissipating mitochondrial membrane potential. As this effect is triggered at concentrations normally present in the intestinal lumen, we postulate a physiologic role for bilirubin in modulating colon tumorigenesis.

Gilbert's syndrome

While Gilbert's syndrome is extremely common and benign, its pathogenesis may not be as straightforward as once believed. It has been used as a model to examine aberrations of virtually every step in bilirubin metabolism. The clinical hallmarks are of a hereditary, chronic, mild unconjugated hyperbilirubinaemia. Not infrequently subclinical haemolysis may coexist. Liver histology is normal although some minor ultrastructural abnormalities may be evident. The universal defect appears to be a reduction in hepatic bilirubin-GT activity. However, other associated abnormalities in bilirubin metabolism, which occur less consistently, suggest that this may not be the sole defect in all patients. The syndrome is almost certainly part of a spectrum which includes the Crigler-Najjar syndromes; molecular biology data suggests that there is an absence of one (or even more) GT isoenzymes in these disorders. Whether one or more genes is consistently culpable remains open to speculation. Despite the complicated pathogenesis of Gilbert's syndrome, management remains simply reassurance alone.