Effects of a high-fat diet and global aryl hydrocarbon receptor deficiency on energy balance and liver retinoid status in male Sprague-Dawley rats.

The physiological functions of the aryl hydrocarbon receptor (AHR) are only beginning to unfold. Studies in wildtype and AHR knockout (AHRKO) mice have recently disclosed that AHR activity is required for obesity and steatohepatitis to develop when mice are fed with a high-fat diet (HFD). In addition, a line of AHRKO mouse has been reported to accumulate retinoids in the liver. Whether these are universal manifestations across species related to AHR activity level is not known yet. Therefore, we here subjected wildtype and AHRKO male rats (on Sprague-Dawley background) to HFD feeding coupled with free access to 10% sucrose solution and water; controls received a standard diet and water. Although the HFD-fed rats consumed more energy throughout the 24-week feeding regimen, they did not get overweight. However, relative weights of the brown and epididymal adipose tissues were elevated in HFD-fed rats, while that of the liver was lower in AHRKO than wildtype rats. Moreover, the four groups exhibited diet- or genotype-dependent differences in biochemical variables, some of which suggested marked dissimilarities from AHRKO mice. Expression of pro- and anti-inflammatory genes was induced in livers of HFD-fed AHRKO rats, but histologically they did not differ from others. HFD reduced the hepatic concentrations of retinyl palmitate, 9-cis-4-oxo-13,14-dihydroretinoic acid and (suggestively) retinol, whereas AHR status had no effect. Hence, the background strain/line of AHRKO rat is resistant to diet-induced obesity, and AHR does not modulate this or liver retinoid concentrations. Yet, subtle AHR-dependent differences in energy balance-related factors exist despite similar weight development.

Associations of persistent organic pollutants in human adipose tissue with retinoid levels and their relevance to the redox microenvironment.

Humans are exposed to a myriad of chemical substances in both occupational and environmental settings. Persistent organic pollutants (POPs) have drawn attention for their adverse effects including cancer and endocrine disruption. Herein, the objectives were 1) to describe serum and adipose tissue retinol levels, along with serum retinol binding protein 4 (RBP4) concentrations, and 2) to assess the associations of adipose tissue POP levels with these retinoid parameters, as well as their potential interaction with the previously-observed POP-related disruption of redox microenvironment. Retinol was measured in both serum and adipose tissue along with RBP4 levels in serum samples of 236 participants of the GraMo adult cohort. Associations were explored by multivariable linear regression analyses and Weighted Quantile Sum regression. Polychlorinated biphenyls (PCBs) 180, 153 and 138 were related to decreased adipose tissue retinol levels and increased serum RBP4/retinol ratio. Dicofol concentrations > limit of detection were associated with decreased retinol levels in serum and adipose tissue. Additionally, increased adipose tissue retinol levels were linked to an attenuation in previously-reported associations of adipose tissue PCB-153 with in situ superoxide dismutase activity. Our results revealed a suggestive link between retinoids, PCBs and redox microenvironment, potentially relevant for both mechanistic and public health purposes.