In vitro DNA-damaging effects of intestinal and related tetrapyrroles in human cancer cells

Abstract

Epidemiological studies report a negative association between circulating bilirubin concentrations and the risk for cancer and cardiovascular disease. Structurally related tetrapyrroles also possess in vitro anti-genotoxic activity and may prevent mutation prior to malignancy. Furthermore, few data suggest that tetrapyrroles exert anti-carcinogenic effects via induction of cell cycle arrest and apoptosis. To further investigate whether tetrapyrroles provoke DNA-damage in human cancer cells, they were tested in the single cell gel electrophoresis assay (SCGE). Eight tetrapyrroles (unconjugated bilirubin, bilirubin ditaurate, biliverdin, biliverdin-/bilirubin dimethyl ester, urobilin, stercobilin and protoporphyrin) were added to cultured Caco2 and HepG2 cells and their effects on comet formation (% tail DNA) were assessed. Flow cytometric assessment (apoptosis/necrosis, cell cycle, intracellular radical species generation) assisted in revealing underlying mechanisms of intracellular action. Cells were incubated with tetrapyrroles at concentrations of 0.5, 5 and 17 μM for 24 h. Addition of 300 μM tertiary-butyl hydroperoxide to cells served as a positive control. Tetrapyrrole incubation mostly resulted in increased DNA-damage (comet formation) in Caco2 and HepG2 cells. Tetrapyrroles that are concentrated within the intestine, including protoporphyrin, urobilin and stercobilin, led to significant comet formation in both cell lines, implicating the compounds in inducing DNA-damage and apoptosis in cancer cells found within organs of the digestive system.

Looking to the horizon: the role of bilirubin in the development and prevention of age-related chronic diseases

“…Interactions with the synthetic mutagen 2,4,7-trinitro-9-fluorenone, as has been confirmed for a series of porphyrins and tetrapyrrole compounds, may account for the important anti-mutagenic effects of bile pigments [213,214]. Furthermore, bilirubin and its derivatives induce cell cycle arrest [215], apoptosis and cytostasis in multiple cancer cell lines [216,217], which indicates a possible anti-carcinogenic effect of bilirubin. Bilirubin may also protect against cancer by interfering with pro-carcinogenic signalling pathways [via activation of extracellular-signal-regulated kinase (ERK)], and inhibit tumour cell proliferation [216].…”

“…Furthermore, bilirubin induces mitochondrial depolarization in colon cancer cells, and provokes apoptosis in human gastric cancer cells [215]. Anti-genotoxic activity (DNA damage) seems to be present in malignant cells only [4,217]. In a recent study, investigating the anti-genotoxic effects of intestinally abundant tetrapyrroles (urobilin, stercobilin, protoporphyrin), DNA-damaging effects were reported in HepG2 and Caco2 cells.…”

Anti-Genotoxic Potential of Bilirubin In Vivo: Damage to DNA in Hyperbilirubinemic Human and Animal Models

“…Importantly, a recent Japanese (13) and an Austrian (14) in vitro study with human carcinoma cell lines indicate anti-genotoxic effects of bilirubin, by induction of typical comet tails. Moreover, bilirubin leads to cell-cycle arrest and subsequent apoptosis in various cancer cell lines (13,14).…”

“…Recently, a possible protective role of the UGT1A1 Ã 28 allele on colorectal cancer (CRC) was detected and patients with CRCs had lower serum bilirubin levels than controls (10). In vitro anti-oxidative and antigenotoxic properties of bilirubin were shown in recent reports (12)(13)(14). Therefore, it is hypothesized that subjects with elevated bilirubin levels are more resistant to oxidative stress-related diseases because Gilbert syndrome individuals possess reduced levels of oxidative stress (15,16).…”

How to Increase Brightness of Near-Infrared Fluorescent Proteins in Mammalian Cells

“…Similarly, an intravenous injection of BV did not increase fluorescence of HT1080 tumor xenografts expressing smURFP(Rodriguez et al, 2016). Importantly, BV has a broad range of biological activities and besides of protecting from cellular oxidative stress (Satoh et al, 2003) it also affects cell proliferation (Nuhn et al, 2009), cell survival, and activation of several signaling pathways (Gibbs and Maines, 2007; Miralem et al, 2012; Mölzer et al, 2013). Therefore, an exogenous supply of tetrapyrroles, such as BV and BVMe 2 , to cultured cells and in vivo should be performed with caution to avoid affecting metabolism.…”