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Characterization of secretory sphingomyelinase activity, lipoprotein sphingolipid content and LDL aggregation in ldlr-/- mice fed on a high-fat diet.

Deevska GM, Sunkara M, Morris AJ, Nikolova-Karakashian MN - Biosci. Rep. (2012)

Bottom Line: An increased macrophage secretion seemed to be responsible for the elevated S-SMase activity.S-SMase mediates diet-induced changes in LDL ceramide content and aggregation.S-SMase effectiveness in inducing aggregation is dependent on diet-induced enrichment of LDL with SM, possibly through increased hepatic synthesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Division of Cardiovascular Medicine, University of Kentucky, A. B. Chandler Medical Center, Lexington, KY 40536, U.S.A.

ABSTRACT
The propensity of LDLs (low-density lipoproteins) for aggregation and/or oxidation has been linked to their sphingolipid content, specifically the levels of SM (sphingomyelin) and ceramide. To investigate this association in vivo, ldlr (LDL receptor)- mice (ldlr-/-) were fed on a modified (atherogenic) diet containing saturated fats and cholesterol. The diet led to significantly elevated SM content in all serum lipoproteins. In contrast, ceramide increased only in the LDL particles. MS-based analyses of the lipid acyl chain composition revealed a marked elevation in C16:0 fatty acid in SM and ceramide, consistent with the prevalence of palmitic acid in the modified diet. The diet also led to increased activity of the S-SMase [secretory SMase (sphingomyelinase)], a protein that is generated by ASMase (acid SMase) and acts on serum LDL. An increased macrophage secretion seemed to be responsible for the elevated S-SMase activity. ASMase-deficient mice (asm-/-/ldlr-/-) lacked S-SMase activity and were protected from diet-induced elevation in LDL ceramide. LDL from asm-/-/ldlr-/- mice fed on the modified diet were less aggregated and oxidized than LDL from asm+/+/ldlr-/- mice. When tested in vitro, the propensity for aggregation was dependent on the SM level: only LDL from animals on modified diet that have high SM content aggregated when treated with recombinant S-SMase. In conclusion, LDL-SM content and S-SMase activity are up-regulated in mice fed on an atherogenic diet. S-SMase mediates diet-induced changes in LDL ceramide content and aggregation. S-SMase effectiveness in inducing aggregation is dependent on diet-induced enrichment of LDL with SM, possibly through increased hepatic synthesis.

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Ceramide and SM species in the serum of mice on atherogenic or control dietTotal serum lipid extracts were prepared from asm−/−/ldlr−/− and asm+/+/ldlr−/− mice placed on either standard (Std) or modified (Md) diet for 10 weeks. Ceramide (A) and SM (B) species were quantified by monitoring precursor product ion pairs using HPLC–ESI/tandem MS. The ceramide/SM molar ratio was calculated in each sample (C). Means±S.D. are shown (n=3 animals per group). Bonferonni post-hoc test analyses comparing the effect of the diet for mice from the same genotype are shown (*P<0.05 and #P<0.001). Std, standard diet; Md, modified diet.
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Figure 6: Ceramide and SM species in the serum of mice on atherogenic or control dietTotal serum lipid extracts were prepared from asm−/−/ldlr−/− and asm+/+/ldlr−/− mice placed on either standard (Std) or modified (Md) diet for 10 weeks. Ceramide (A) and SM (B) species were quantified by monitoring precursor product ion pairs using HPLC–ESI/tandem MS. The ceramide/SM molar ratio was calculated in each sample (C). Means±S.D. are shown (n=3 animals per group). Bonferonni post-hoc test analyses comparing the effect of the diet for mice from the same genotype are shown (*P<0.05 and #P<0.001). Std, standard diet; Md, modified diet.

Mentions: Lastly, we addressed the question whether S-SMase has any preference towards SM with a specific fatty acid length and/or saturation (Figure 6). The major ceramide species found in the serum of asm−/−/ldlr−/− and asm+/+/ldlr−/− mice on both diets were C24:1 ceramide, followed by C24:0 and C16:0 ceramides (Figure 6A), which is similar to what is seen in the serum of healthy humans [23]. The most prominent SM species were C24:0 and C16:0 (Figure 6B). The ceramide/SM ratios for all species were uniformly affected by the diet for both mouse genotypes. This indicates that S-SMase has no apparent specificity for a substrate with a particular fatty acid. Some preference, however, may exist for the very long fatty-acid chains, since the genotype-related changes in C24:0 species appeared to be somewhat larger than those for the C16:0 species.


Characterization of secretory sphingomyelinase activity, lipoprotein sphingolipid content and LDL aggregation in ldlr-/- mice fed on a high-fat diet.

Deevska GM, Sunkara M, Morris AJ, Nikolova-Karakashian MN - Biosci. Rep. (2012)

Ceramide and SM species in the serum of mice on atherogenic or control dietTotal serum lipid extracts were prepared from asm−/−/ldlr−/− and asm+/+/ldlr−/− mice placed on either standard (Std) or modified (Md) diet for 10 weeks. Ceramide (A) and SM (B) species were quantified by monitoring precursor product ion pairs using HPLC–ESI/tandem MS. The ceramide/SM molar ratio was calculated in each sample (C). Means±S.D. are shown (n=3 animals per group). Bonferonni post-hoc test analyses comparing the effect of the diet for mice from the same genotype are shown (*P<0.05 and #P<0.001). Std, standard diet; Md, modified diet.
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Related In: Results  -  Collection

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Figure 6: Ceramide and SM species in the serum of mice on atherogenic or control dietTotal serum lipid extracts were prepared from asm−/−/ldlr−/− and asm+/+/ldlr−/− mice placed on either standard (Std) or modified (Md) diet for 10 weeks. Ceramide (A) and SM (B) species were quantified by monitoring precursor product ion pairs using HPLC–ESI/tandem MS. The ceramide/SM molar ratio was calculated in each sample (C). Means±S.D. are shown (n=3 animals per group). Bonferonni post-hoc test analyses comparing the effect of the diet for mice from the same genotype are shown (*P<0.05 and #P<0.001). Std, standard diet; Md, modified diet.
Mentions: Lastly, we addressed the question whether S-SMase has any preference towards SM with a specific fatty acid length and/or saturation (Figure 6). The major ceramide species found in the serum of asm−/−/ldlr−/− and asm+/+/ldlr−/− mice on both diets were C24:1 ceramide, followed by C24:0 and C16:0 ceramides (Figure 6A), which is similar to what is seen in the serum of healthy humans [23]. The most prominent SM species were C24:0 and C16:0 (Figure 6B). The ceramide/SM ratios for all species were uniformly affected by the diet for both mouse genotypes. This indicates that S-SMase has no apparent specificity for a substrate with a particular fatty acid. Some preference, however, may exist for the very long fatty-acid chains, since the genotype-related changes in C24:0 species appeared to be somewhat larger than those for the C16:0 species.

Bottom Line: An increased macrophage secretion seemed to be responsible for the elevated S-SMase activity.S-SMase mediates diet-induced changes in LDL ceramide content and aggregation.S-SMase effectiveness in inducing aggregation is dependent on diet-induced enrichment of LDL with SM, possibly through increased hepatic synthesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Division of Cardiovascular Medicine, University of Kentucky, A. B. Chandler Medical Center, Lexington, KY 40536, U.S.A.

ABSTRACT
The propensity of LDLs (low-density lipoproteins) for aggregation and/or oxidation has been linked to their sphingolipid content, specifically the levels of SM (sphingomyelin) and ceramide. To investigate this association in vivo, ldlr (LDL receptor)- mice (ldlr-/-) were fed on a modified (atherogenic) diet containing saturated fats and cholesterol. The diet led to significantly elevated SM content in all serum lipoproteins. In contrast, ceramide increased only in the LDL particles. MS-based analyses of the lipid acyl chain composition revealed a marked elevation in C16:0 fatty acid in SM and ceramide, consistent with the prevalence of palmitic acid in the modified diet. The diet also led to increased activity of the S-SMase [secretory SMase (sphingomyelinase)], a protein that is generated by ASMase (acid SMase) and acts on serum LDL. An increased macrophage secretion seemed to be responsible for the elevated S-SMase activity. ASMase-deficient mice (asm-/-/ldlr-/-) lacked S-SMase activity and were protected from diet-induced elevation in LDL ceramide. LDL from asm-/-/ldlr-/- mice fed on the modified diet were less aggregated and oxidized than LDL from asm+/+/ldlr-/- mice. When tested in vitro, the propensity for aggregation was dependent on the SM level: only LDL from animals on modified diet that have high SM content aggregated when treated with recombinant S-SMase. In conclusion, LDL-SM content and S-SMase activity are up-regulated in mice fed on an atherogenic diet. S-SMase mediates diet-induced changes in LDL ceramide content and aggregation. S-SMase effectiveness in inducing aggregation is dependent on diet-induced enrichment of LDL with SM, possibly through increased hepatic synthesis.

Show MeSH
Related in: MedlinePlus