FFA-induced hepatic insulin resistance in vivo is mediated by PKCδ, NADPH oxidase, and oxidative stress.
Fat-induced hepatic insulin resistance plays a key role in the pathogenesis of type 2 diabetes in obese individuals. Although PKC and inflammatory pathways have been implicated in fat-induced hepatic insulin resistance, the sequence of events leading to impaired insulin signaling is unknown. We used Wistar rats to investigate whether PKCδ and oxidative stress play causal roles in this process and whether this occurs via IKKβ- and JNK-dependent pathways. Rats received a 7-h infusion of Intralipid plus heparin (IH) to elevate circulating free fatty acids (FFA). During the last 2 h of the infusion, a hyperinsulinemic-euglycemic clamp with tracer was performed to assess hepatic and peripheral insulin sensitivity. An antioxidant, N-acetyl-L-cysteine (NAC), prevented IH-induced hepatic insulin resistance in parallel with prevention of decreased IκBα content, increased JNK phosphorylation (markers of IKKβ and JNK activation, respectively), increased serine phosphorylation of IRS-1 and IRS-2, and impaired insulin signaling in the liver without affecting IH-induced hepatic PKCδ activation. Furthermore, an antisense oligonucleotide against PKCδ prevented IH-induced phosphorylation of p47(phox) (marker of NADPH oxidase activation) and hepatic insulin resistance. Apocynin, an NADPH oxidase inhibitor, prevented IH-induced hepatic and peripheral insulin resistance similarly to NAC. These results demonstrate that PKCδ, NADPH oxidase, and oxidative stress play a causal role in FFA-induced hepatic insulin resistance in vivo and suggest that the pathway of FFA-induced hepatic insulin resistance is FFA → PKCδ → NADPH oxidase and oxidative stress → IKKβ/JNK → impaired hepatic insulin signaling.
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Sandra
S
Pereira
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Edward
E
Park
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Yusaku
Y
Mori
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
C Andrew
CA
Haber
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Ping
P
Han
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Toyoyoshi
T
Uchida
Department of Physiology, University of Toronto, Toronto, Ontario, Canada; Department of Medicine, University of Toronto, Toronto, Ontario, Canada; and.
Laura
L
Stavar
Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada;
Andrei I
AI
Oprescu
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Khajag
K
Koulajian
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Alexander
A
Ivovic
Department of Physiology, University of Toronto, Toronto, Ontario, Canada; Department of Medicine, University of Toronto, Toronto, Ontario, Canada; and.
Zhiwen
Z
Yu
Department of Physiology, University of Toronto, Toronto, Ontario, Canada; Department of Medicine, University of Toronto, Toronto, Ontario, Canada; and.
Deling
D
Li
Center for Diabetes and Endocrine Research and the Department of Physiology and Pharmacology, University of Toledo College of Medicine, Toledo, Ohio; and.
Thomas A
TA
Bowman
Metabolic and Cardiovascular Diseases Laboratory, Alberta Institute for Human Nutrition, University of Alberta, Edmonton, Alberta, Canada;
Jay
J
Dewald
Inserm, U1149, CNRS-ERL8252, Centre de Recherche sur l'Inflammation, Paris, France; Laboratoire d'Excellence Inflamex, Faculté de Médecine, Université Paris Diderot, Sorbonne Paris Cité, Site Xavier Bichat, Paris, France;
Jamel
J
El-Benna
Metabolic and Cardiovascular Diseases Laboratory, Alberta Institute for Human Nutrition, University of Alberta, Edmonton, Alberta, Canada;
David N
DN
Brindley
Department of Medicine, Diabetes Research Center, Albert Einstein College of Medicine, Bronx, New York;
Roger
R
Gutierrez-Juarez
Department of Physiology, University of Toronto, Toronto, Ontario, Canada;
Tony K T
TK
Lam
Center for Diabetes and Endocrine Research and the Department of Physiology and Pharmacology, University of Toledo College of Medicine, Toledo, Ohio; and.
Sonia M
SM
Najjar
ISIS Pharmaceuticals Inc., Carlsbad, California.
Robert A
RA
McKay
ISIS Pharmaceuticals Inc., Carlsbad, California.
Sanjay
S
Bhanot
Department of Physiology, University of Toronto, Toronto, Ontario, Canada; Department of Medicine, University of Toronto, Toronto, Ontario, Canada; and.
I George
IG
Fantus
Department of Physiology, University of Toronto, Toronto, Ontario, Canada; Department of Medicine, University of Toronto, Toronto, Ontario, Canada; and Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada; adria.giacca@utoronto.ca.
Adria
A
Giacca
D000818:Animals; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007333:Insulin Resistance / Q000502:physiology*; D008099:Liver / Q000378:metabolism*; D019255:NADPH Oxidases / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D005230:Fatty Acids, Nonesterified; D019255:NADPH Oxidases; C087857:protein kinase C gamma; D011493:Protein Kinase C; D005947:Glucose
antioxidant; antisense oligonucleotides; free fatty acids; hyperinsulinemic-euglycemic clamp; insulin resistance