Acute and Repeated Treatment with 5-PAHSA or 9-PAHSA Isomers Does Not Improve Glucose Control in Mice

Abstract

Fatty acid esters of hydroxylated fatty acids (FAHFAs) were discovered as a novel class of endogenous mammalian lipids whose profound effects on metabolism have been shown. In the current study, in vitro and in vivo the metabolic effects of two of these FAHFAs, namely palmitic acid-5- (or -9) -hydroxy-stearic acid (5- or 9-PAHSA, respectively) were profiled. In DIO mice fed with differentially composed low- or high-fat diets, acute and subchronic treatment with 5-PAHSA and 9-PAHSA alone, or in combination, did not significantly improve the deranged metabolic status. Neither racemic 5- or 9-PAHSA, nor the enantiomers were able to: (1) increase basal or insulin-stimulated glucose uptake in vitro, (2) stimulate GLP-1 release from GLUTag cells, or (3) induce GSIS in rat, mouse, or human islets or in a human pancreatic β cell line. Therefore, our data do not support the further development of PAHSAs or their derivatives for the control of insulin resistance and hyperglycemia.

Methodological Issues in Studying PAHSA Biology: Masking PAHSA Effects

“…However, it was used with the lard diet on which the mice had not developed glucose intolerance. There is no LFD control for the lard diet, but the glucose values in HFD vehicle mice in Figures 3A and 3D in Pflimlin et al (2018) appear similar to the values for LFD vehicle in their Figure 2A. Hence, it is difficult to interpret these data.…”

“…Although we showed beneficial effects of constant PAHSA infusion by subcutaneous minipump for 9–13 days (Syed et al, 2018) or daily gavage for 12 days (unpublished data) in chow-fed mice, we have not published effects of a single dose of PAHSAs in young, lean chow-fed mice with normal glucose tolerance and insulin sensitivity. To that point, in the study by Pflimlin et al, there is no evidence of glucose intolerance in their vehicle-treated HFD mice, and data indicating insulin resistance are insufficient, consisting only of elevated insulin levels 4.5 hr after food removal with no statistical difference reported for insulin tolerance test (ITT) (Figure 3B in Pflimlin et al, 2018). In fact, Figure 2B in Pflimlin et al indicates that glucose tolerance is not different between vehicle-treated LFD and HFD mice using the hydrogenated vegetable diet, in contrast to the glucose intolerance and insulin resistance seen with this same HFD in Yore et al (2014) and Syed et al (2018).…”

“…For one OGTT, Pflimlin et al used the PEG400/Tween80 vehicle (Figure 3D in Pflimlin et al, 2018). However, it was used with the lard diet on which the mice had not developed glucose intolerance.…”

“…We appreciate the attempt to corroborate our findings as reproducibility of results by different laboratories is critical. While these different results may be perceived as a reproducibility issue, numerous methodological differences, some of which were mentioned by Pflimlin et al (2018) in their “limitations” section, can explain why Pflimlin et al’s experiments did not detect anti-diabetic effects (Tables S1 and S2). None of the experiments in Pflimlin et al repeated the protocols used in any previous PAHSA/FAHFA papers.…”

“…Pflimlin et al (2018) recently challenged the finding that PAHSAs have beneficial metabolic effects. We appreciate the attempt to corroborate our findings as reproducibility of results by different laboratories is critical.…”