Obesity-induced changes in lipid mediators persist after weight loss.

BACKGROUND: Obesity induces significant changes in lipid mediators, however, the extent to which these changes persist after weight loss has not been investigated. SUBJECTS/METHODS: We fed C57BL6 mice a high-fat diet to generate obesity and then switched the diet to a lower-fat diet to induce weight loss. We performed a comprehensive metabolic profiling of lipid mediators including oxylipins, endocannabinoids, sphingosines and ceramides in key metabolic tissues (including adipose, liver, muscle and hypothalamus) and plasma. RESULTS: We found that changes induced by obesity were largely reversible in most metabolic tissues but the adipose tissue retained a persistent obese metabolic signature. Prostaglandin signaling was perturbed in the obese state and lasting increases in PGD2, and downstream metabolites 15-deoxy PGJ2 and delta-12-PGJ2 were observed after weight loss. Furthermore expression of the enzyme responsible for PGD2 synthesis (hematopoietic prostaglandin D synthase, HPGDS) was increased in obese adipose tissues and remained high after weight loss. We found that inhibition of HPGDS over the course of 5 days resulted in decreased food intake in mice. Increased HPGDS expression was also observed in human adipose tissues obtained from obese compared with lean individuals. We then measured circulating levels of PGD2 in obese patients before and after weight loss and found that while elevated relative to lean subjects, levels of this metabolite did not decrease after significant weight loss. CONCLUSIONS: These results suggest that lasting changes in lipid mediators induced by obesity, still present after weight loss, may play a role in the biological drive to regain weight.

Comparison of breast milk vitamin A concentration measured in fresh milk by a rapid field assay (the iCheck FLUORO) with standard measurement of stored milk by HPLC.

Availability of rapid, point-of-contact analytical methods would facilitate the use of breast milk vitamin A concentration (BMVA) to assess vitamin A (VA) status. We compared BMVA concentrations measured by high-performance liquid chromatography (HPLC) (the standard technique) with those by iCheck FLUORO, a new portable fluorometer that can rapidly quantify BMVA. Casual breast milk samples (n=154) were collected during a representative survey in Yaoundé and Douala, Cameroon. Milk fat and BMVA concentrations (by iCheck) were measured in fresh milk in the field. After storage at <-20 °C, BMVA concentrations were also measured by HPLC. BMVA values from the two methods were highly correlated (R(2)=0.72 for BMVA/l; R(2)=0.62 for BMVA/g fat, both P<0.0001). HPLC values were greater than iCheck values on average, and the difference increased with increasing BMVA. The iCheck FLUORO could be useful for monitoring fortification programs, but before-after surveys to assess change in BMVA concentrations should use one method consistently.