Metabolic Profiling Reveals an Abnormal Pattern of Serum Fatty Acids in MRL/lpr Mice Under Treatment With Prednisone

Abstract

Glucocorticoids (GCs) are commonly used to treat systemic lupus erythematosus (SLE). Unfortunately, excessive GCs can induce many side effects associated with disordered fatty acid (FA) metabolism. Although an increased level of total FA has been found after GCs treatment, it is not clear whether all FA species increased or only certain FA species were altered. A gas chromatography-mass spectrometry-based FA profiling approach was performed to reveal the alterations of FA species in SLE model mice (MRL/lpr) after treatment with 5 mg/kg of prednisone. The study showed a distinct FA profile in MRL/lpr mice compared to the controls, mainly manifested by elevated polyunsaturated FAs (arachidonate, docosahexaenoate, etc.), which are related to the inflammatory state; and altered (product FA/precursor FA) ratios representing the estimated activities of FA desaturase and elongase (higher activities of multiple elongases, △4 desaturase, △5 desaturase, △6 desaturase, and lower activity of △8 desaturase). Treatment with 5 mg/kg of prednisone decreased the total level of n-6 polyunsaturated FA in MRL/lpr mice; in particular, the level of arachidonate and estimated activity of △5 desaturase were reduced to the control level. Moreover, prednisone induced additional perturbations in FAs, including not only saturated FAs, but also monounsaturated FAs and n-3 polyunsaturated FAs, indicating that there was a strong effect of prednisone on FA metabolism. These results may be valuable for further studies of the side effects of GCs treatment.

Keywords: fatty acid; metabolic profiling; prednisone; side effects; systemic lupus erythematosus.

Figure 1

Schematic diagram of the study design (n = 5 for each group).

Figure 2

Analytical characteristics of the GC-MS-based FA profiling approach. (A) A representative total ion chromatogram of serum FAs. (B) RSD distribution plot of 30 species of FAs in five QCs; the columns indicate the number of FAs in the specified RSD range, and the line indicates the percentage of summed FA response in the specified RSD range. (C) PCA score plot of all samples based on FA profiles.

Figure 3

PCA score plots of different pairwise groups. (A) C57/BL6 and MRL/lpr groups, (B) C57/BL6 and GC groups, and (C) MRL/lpr and GC groups (n = 5 for each group).

Figure 4

Changes in the total levels of various FAs. (A) TFA, SFA, MUFA and PUFA, and (B) n-3 PUFA and n-6 PUFA. Results are expressed as mean ± SEM (n = 5 for each group). The P values were obtained from ANOVA followed by Tukey’s post hoc test. *P < 0.05.

Figure 5

Alteration of serum FA species and product/precursor ratios in MRL/lpr mice compared to those in C57/BL6 mice. (A) Bar plots of changed FA species. Results are expressed as mean ± SEM (n = 5 for each group). (B) Box plots of changed product/precursor FA ratios (n = 5 for each group). The P values were obtained from ANOVA followed by Tukey’s post hoc test. *P < 0.05, ^#P < 0.1.

Figure 6

FA species with significant alterations under treatment with prednisone (n = 5 for each group). The FAs were clustered based on their Pearson correlation coefficients. Red represents higher concentrations, while blue represents lower concentrations.

Figure 7

FA biosynthesis pathway changes in the MRL/lpr group (A) and the GC group (B) compared to the C57/BL6 group (n = 5 for each group). Dotted arrow: estimated desaturase activity; solid arrow: estimated elongase activity; red: significantly increased (P < 0.05); blue: significantly decreased (P < 0.05); #: slightly changed (P < 0.1).