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The regulation of ceramide content by 5‐aminoimidazole‐4‐carboxamide ribonucleoside (AICAR) in rat skeletal muscle

The purpose of this study was to determine if AICAR regulates ceramide content under oversupply of palmitate in rat skeletal muscle. To examine if AICAR controls ceramide metabolism, soleus muscles from rats were isolated and incubated for 5 hr in KHB supplemented with 5 mM glucose and with or without 2 mM palmitate, 2 mM AICAR, and 2 mM L‐cycloserine (L‐CS). Total ceramide mass in the soleus was significantly increased by ~35% in palmitate treated group over the control group (122.02 ± 2.07 pmol/mg vs. 90.79 ± 1.24 pmol/mg, respectively) (P<0.05). Both L‐CS and AICAR decreased palmitate‐induced ceramide synthesis by ~20% and ~14%, respectively (97.15 ± 2.5 pmol/mg and 105.79 ± 1.94 pmol/mg) (P<0.05) over the palmitate group. We also measured serine palmitoyltransferase (SPT) to determine if AICAR regulates ceramide synthesis by inhibiting SPT. Total SPT protein level increased by ~27% (P<0.05) and SPT activity increased by ~44% (P<0.05) over the control group. By contrast, when L‐CS was added to the incubation media, both SPT protein level and enzyme activity were notably decreased by ~17% and ~23%, respectively (P<0.05). Also, AICAR treatment blunted palimitate‐induced SPT protein level and enzyme activity by 11% (P<0.05) and 20% (P<0.05), respectively, compared with the palmitate group. These data suggest that fatty acid oversupply causes ceramide accumulation and AICAR is partly associated with ceramide metabolism by inhibiting SPT in rat soleus muscle.