Biliverdin protects against the deterioration of glucose tolerance in db/db mice

Abstract

Aims/hypothesis We have previously shown a negative correlation between serum bilirubin levels and prevalence of type 2 diabetes, suggesting that bilirubin inhibits development of this disease. To confirm this hypothesis, we investigated whether administration of biliverdin, the precursor of bilirubin, protects against the deterioration of glucose tolerance in db/db mice, a rodent model of type 2 diabetes. Methods Biliverdin (20 mg/kg daily) was orally administered to 5-week-old db/db mice for 4 weeks. After 4 weeks of treatment, i.p. glucose tolerance and insulin tolerance tests were performed. Insulin content was evaluated by immunostaining and ELISA. Oxidative stress markers (8-hydroxy-2′-deoxyguansosine and dihydroethidium staining) and expression of NADPH oxidase components Pdx1 and Bax were also evaluated in isolated islets. Results Treatment with biliverdin partially prevented worsening of hyperglycaemia and glucose intolerance in db/db mice. This effect was accompanied by a significant increase in insulin content and Pdx1 expression, and a significant decrease of apoptosis and Bax expression in pancreatic islets from db/db mice. At the same time, levels of oxidative stress markers and NADPH oxidase component production in islets were normalised. Biliverdin had little effect on HOMA of insulin resistance or insulin resistance evaluated by insulin tolerance tests. Conclusions/interpretation Biliverdin may protect against progressive worsening of glucose tolerance in db/db mice, mainly via inhibition of oxidative stress-induced beta cell damage.

Maternal high-fat diet induces insulin resistance and deterioration of pancreatic β-cell function in adult offspring with sex differences in mice

“…Average area of Ͼ200 islets/mouse was evaluated. Immunostaining for 8-hydroxy-2=-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, was carried out as described previously (24).…”

“…Pancreatic islets were isolated at 20 wk by intraductal collagenase perfusion, as described previously (24,33,54). Islet insulin content was measured by ELISA and adjusted for DNA content.…”

“…Extracted RNA (4 g) was converted to single-strand cDNA using a QuantiTect Reverse Transcription Kit (Qiagen). The mRNA levels were determined by real-time quantitative RT-PCR using an iQ SYBR Green Supermix (Bio-Rad) with the Bio-Rad Chromo 4/Opticon system, as described previously (24,25), and normalized to ␤-actin levels. The following (sense and antisense) primer pairs were used: pancreatic and duodenal homeobox factor-1 (PDX-1), 5=-ACTTGAGCGTTCCAATACGG-3= and 5=-AGGGG-GAACGACTCTAGGAA-3=; Gp91phox, 5=-ACTGCGGAGAGTTTG-GAAGA-3= and 5=-GGTGATGACCACCTTTTGCT-3=; NAD(P)H oxidase 4 (NOX4),5=-ATTTGGATAGGCTCCAGGCAAAC-3= and 5=-CACATGGGTATAAGCTTTGTGAGCA-3=; glutathione peroxidase-1 (Gpx), 5=-ACAGTCCACCGTGTATGCCTTC-3= and 5=-CTCT-TCATTCTTGCCATTCTCCTG-3=; TNF␣, 5=-AGCCCCCAGTCTG-TATCCTT-3= and 5=-CTCCCTTTGCAGAACTCAGG-3=; IL-6, 5=-CCAGAGATACAAAGAAATGATGG-3= and 5=-ACTCCAGAA-GACCAGAGGAAAT-3=; MCP-1, 5=-AGGTCCCTGTCATGC-TTCTG-3= and 5=-TCTGGACCCATTCCTTCTTG-3=; F4/80, 5=-CC-TGGACGAATCCTGTGAAG-3= and 5=-GGTGGGACCACAGA-GAGTTG-3=; CD11c, 5=-GAGCCAGAACTTCCCAACTG-3= and 5=-TCAGGAACACGATGTCTTGG-3=; and ␤-actin, 5=-TGACAGGATG-CAGAAGGAGA-3= and 5=-GCTGGAAGGTGGACAGTGAG-3=.…”

“…First, we measured expression of NAD(P)H oxidase gp91phox, a major source of superoxide production in isolated islets (24).…”

Bilirubin as an important physiological modulator of oxidative stress and chronic inflammation in metabolic syndrome and diabetes: a new aspect on old molecule

“…In addition, we also reported that biliverdin treatment partially prevented a worsening of glucose tolerance in db/db mice via inhibition of oxidative stress-induced pancreatic b cell damage, accompanied by normalization of the expression of NAD(P)H oxidase subunits in b cells [11]. Notably, more recent studies have shown that bilirubin has anti-inflammatory properties, and also has the potential properties in activation of Akt and eNOS and synthesis of NO [12], which improves endothelial cell function and insulin resistance as well. In recent years, chronic inflammation is considered to play an important role in multiple organ damage in obesity, metabolic syndrome, and …”