Molecular imaging shows that high fat diet decreases both glucose and lipid metabolism in brown adipose tissue in rodents

Objectives Brown adipose tissue (BAT) is a mitochondrial rich fat that aids in body temperature regulation and burns energy as opposed to storing it. The effects and mechanism of dietary fat on the metabolic processes in brown adipose tissue (BAT) are still unclear. Herein, we designed a set of experiments to investigate glucose and lipid metabolism changes in BAT when mice are on high fat diets.

Methods A group of C57BL/6 mice received high fat diet for 4 weeks while a 2nd group of C57BL/6 mice were maintained on the normal chow as control. Prior to PET imaging, the mice were fasted for about 12 hours. Mice received 0.15 mCi of 18F-FDG via tail vein injection and were scanned on a Siemens Inveon small animal PET/CT scanner at 1 hour post-injection (n = 3 per group). On a different day, the same two groups of mice were administered a fatty acid SPECT tracer, 125I-BMIPP. The mice were scanned on a NanoSPECT/CT small animal scanner at 1 hour post-injection (n = 4 per group). The target activity in BAT was calculated as percentage injected dose per gram (%ID/g). Differences in the uptake values between groups was tested for significance using the Students' t-test. p<0.05 was considered significant.

Results From the quantitative data analysis of FDG-PET, the mice on high fat diet (3.7 ± 1.0 %ID/g) showed significantly lower FDG uptake in BAT than those on normal diet (8.0 ± 0.9 %ID/g) with p < 0.01. Similarly, the 125I-BMIPP uptake in mice on high fat diet (3.7 ± 0.9 %ID/g) was significantly lower in BAT than those on normal diet (7.2 ± 1.3 %ID/g) with p < 0.01.

Conclusions This study demonstrates that high fat diet does reduce both glucose and lipid metabolism in BAT. While FDG has been used to study metabolism in BAT to our knowledge this is the first study to use BMIPP to alterations in fatty acid metabolism in BAT. The molecular mechanism for this alternation is under investigation.