Developmental exposure to a very low dose of bisphenol A induces persistent islet insulin hypersecretion in Fischer 344 rat offspring

BACKGROUND

In children with obesity, accentuated insulin secretion has been coupled with development of type 2 diabetes mellitus (T2DM). Bisphenol A (BPA) is a chemical with endocrine- and metabolism-disrupting properties which can be measured in a majority of the population. Exposure to BPA has been associated with the development of metabolic diseases including T2DM.

OBJECTIVE

The aim of this study was to investigate if exposure early in life to an environmentally relevant low dose of BPA causes insulin hypersecretion in rat offspring.

METHODS

Pregnant Fischer 344 rats were exposed to 0.5 (BPA0.5) or 50 (BPA50) µg BPA/kg BW/day via drinking water from gestational day 3.5 until postnatal day 22. Pancreata from dams and 5- and 52-week-old offspring were procured and islets were isolated by collagenase digestion. Glucose-stimulated insulin secretion and insulin content in the islets were determined by ELISA.

RESULTS

Basal (5.5 mM glucose) islet insulin secretion was not affected by BPA exposure. However, stimulated (11 mM glucose) insulin secretion was enhanced by about 50% in islets isolated from BPA0.5-exposed 5- and 52-week-old female and male offspring and by 80% in islets from dams, compared with control. In contrast, the higher dose, BPA50, reduced stimulated insulin secretion by 40% in both 5- and 52-week-old female and male offspring and dams, compared with control.

CONCLUSION

A BPA intake 8 times lower than the European Food Safety Authority's (EFSA's) current tolerable daily intake (TDI) of 4 µg/kg BW/day of BPA delivered via drinking water during gestation and early development causes islet insulin hypersecretion in rat offspring up to one year after exposure. The effects of BPA exposure on the endocrine pancreas may promote the development of metabolic disease including T2DM.

Role of fatty liver in the association between obesity and reduced hepatic insulin clearance

AIM

Hepatic insulin clearance (HIC) is important in regulating plasma insulin levels. Diminished HIC causes inappropriate hyperinsulinaemia, and both obesity and fatty liver (FL), which are known to decrease HIC, can be found either together in the same patient or on their own. The mechanism by which obesity reduces HIC is presumed to be mediated by FL. However, few reports have examined the role of FL in the relationship between obesity and HIC in type 2 diabetes (T2D) patients. Therefore, our study investigated the association of HIC with clinical factors, including insulin sensitivity indices, focusing on the presence or absence of FL and obesity in T2D patients.

METHOD

Baseline data from 419 patients with T2D (279 men, 140 women; mean age: 57.6 years; body mass index: 25.5kg/m²) controlled by diet and exercise were analyzed. HIC was calculated from the ratio of fasting c-peptide to fasting insulin levels (HIC_CIR). Correlation analyses between HIC_CIR and clinical variables were performed using Pearson's product-moment correlation coefficients and single regression analysis in all participants and in those with obesity and FL either alone or in combination.

RESULTS

HIC_CIR was significantly correlated with whole-body insulin sensitivity indices and influenced by FL, but only in the FL group was obesity independently influenced HIC level. HIC_CIR decreased in those with both FL and obesity compared with those with only one such complication.

CONCLUSION

HIC_CIR may be used to evaluate whole-body insulin sensitivity in T2D. Also, compared with obesity, the influence of FL strongly contributed to a reduced HIC.

TRIAL REGISTRATION NUMBER

These trials were registered by the Japan Pharmaceutical Information Centre clinical trials information (JapicCTI) as 101349 and 101351.