Muscle adaptation to short-term fasting in healthy lean humans.
BACKGROUND
It has been demonstrated repeatedly that short-term fasting induces insulin resistance, although the exact mechanism in humans is unknown to date. Intramyocellular sphingolipids (i.e. ceramide) have been suggested to induce insulin resistance by interfering with the insulin signaling cascade in obesity.


OBJECTIVE
Our objective was to study peripheral insulin sensitivity together with muscle ceramide concentrations and protein kinase B/AKT phosphorylation after short-term fasting. MAIN OUTCOME MEASURES AND DESIGN: After 14- and 62-h fasting, glucose fluxes were measured before and after a hyperinsulinemic euglycemic clamp. Muscle biopsies were performed in the basal state and during the clamp to assess muscle ceramide and protein kinase B/AKT.


RESULTS
Insulin-mediated peripheral glucose uptake was significantly lower after 62-h fasting compared with 14-h fasting. Intramuscular ceramide concentrations tended to increase during fasting. During the clamp the phosphorylation of protein kinase B/AKT at serine(473) in proportion to the total amount of protein kinase B/AKT was significantly lower. Muscle ceramide did not correlate with plasma free fatty acids.


CONCLUSIONS
Fasting for 62 h decreases insulin-mediated peripheral glucose uptake with lower phosphorylation of AKT at serine(473). AKT may play a regulatory role in fasting-induced insulin resistance. Whether the decrease in AKT can be attributed to the trend to higher muscle ceramide remains unanswered.
Soeters
Maarten R
MR
Department of Endocrinology and Metabolism, Academic Medical Center, Amsterdam, The Netherlands. m.r.soeters@amc.uva.nl
Sauerwein
Hans P
HP
Dubbelhuis
Peter F
PF
Groener
Johanna E
JE
Ackermans
Mariëtte T
MT
Fliers
Eric
E
Aerts
Johannes M
JM
Serlie
Mireille J
MJ
D000222:Adaptation, Physiological; D000328:Adult; D002518:Ceramides / Q000032:analysis; D005215:Fasting / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D013851:Thinness / Q000378:metabolism*
D002518:Ceramides; D005230:Fatty Acids, Nonesterified; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose