Prevention of fat-induced insulin resistance by salicylate

Abstract

Insulin resistance is a major factor in the pathogenesis of type 2 diabetes and may involve fat-induced activation of a serine kinase cascade involving IKK-beta. To test this hypothesis, we first examined insulin action and signaling in awake rats during hyperinsulinemic-euglycemic clamps after a lipid infusion with or without pretreatment with salicylate, a known inhibitor of IKK-beta. Whole-body glucose uptake and metabolism were estimated using [3-(3)H]glucose infusion, and glucose uptake in individual tissues was estimated using [1-(14)C]2-deoxyglucose injection during the clamp. Here we show that lipid infusion decreased insulin-stimulated glucose uptake and activation of IRS-1-associated PI 3-kinase in skeletal muscle but that salicylate pretreatment prevented these lipid-induced effects. To examine the mechanism of salicylate action, we studied the effects of lipid infusion on insulin action and signaling during the clamp in awake mice lacking IKK-beta. Unlike the response in wild-type mice, IKK-beta knockout mice did not exhibit altered skeletal muscle insulin signaling and action following lipid infusion. In summary, high-dose salicylate and inactivation of IKK-beta prevent fat-induced insulin resistance in skeletal muscle by blocking fat-induced defects in insulin signaling and action and represent a potentially novel class of therapeutic agents for type 2 diabetes.

Figure 1

Metabolic parameters and insulin-stimulated whole-body and skeletal muscle (soleus) glucose uptake in awake control (black bars), salicylate (light gray bars), lipid (open bars), and lipid-salicylate (dark gray bars) rats. (a) Plasma salicylate concentrations during basal and hyperinsulinemic-euglycemic clamp. (b) Plasma FFA concentrations during basal and hyperinsulinemic-euglycemic clamp. (c) Insulin-stimulated whole-body glucose uptake in vivo. (d) Insulin-stimulated skeletal muscle glucose uptake in vivo. Values are means ± SE for six to seven experiments. *P < 0.05 versus control group.

Figure 2

Insulin-stimulated whole-body and skeletal muscle (soleus) glucose metabolic flux in awake control (black bars), salicylate (light gray bars), lipid (open bars), and lipid-salicylate (dark gray bars) rats. (a) Insulin-stimulated whole-body glycolysis in vivo. (b) Insulin-stimulated whole-body glycogen/lipid synthesis in vivo. (c) Insulin-stimulated skeletal muscle glycolysis in vivo. (d) Insulin-stimulated skeletal muscle glycogen synthesis in vivo. Values are means ± SE for six to seven experiments. *P < 0.05 versus control group.

Figure 3

Insulin signaling in skeletal muscle (gastrocnemius) of the control (black bars), salicylate (light gray bars), lipid (open bars), and lipid-salicylate (dark gray bars) rats. (a) Insulin-stimulated tyrosine phosphorylation of insulin receptor. (b) Insulin-stimulated tyrosine phosphorylation of IRS-1. (c) Insulin-stimulated IRS-1–associated PI 3-kinase activity. Values are means ± SE for six to seven experiments. *P < 0.05 versus control group.

Figure 4

Insulin action in liver and epididymal white adipose tissue in the control (black bars), salicylate (light gray bars), lipid (open bars), and lipid-salicylate rats (dark gray bars). (a) Basal rates of endogenous glucose production. (b) Percent suppression of basal endogenous glucose production during insulin-stimulated state. (c) Insulin-stimulated glucose uptake in epididymal white adipose tissue. Values are means ± SE for six to seven experiments.

Figure 5

Metabolic parameters and insulin-stimulated whole-body and skeletal muscle (gastrocnemius) glucose uptake in awake control (black bars), IKK-β KO (light gray bars), control-lipid (open bars), and IKK-β KO-lipid (dark gray bars) mice. (a) Plasma FFA concentrations during basal and hyperinsulinemic-euglycemic clamp. (b) Insulin-stimulated percent suppression of basal EGP. (c) Insulin-stimulated whole-body glucose uptake in vivo. (d) Insulin-stimulated skeletal muscle glucose uptake in vivo. Values are means ± SE for three to five experiments. *P < 0.05 versus control group; ^†P < 0.05 versus IKK-β KO-lipid group.

Figure 6

Insulin-stimulated whole-body and skeletal muscle (gastrocnemius) glucose metabolic flux in awake control (black bars), IKK-β KO (light gray bars), control-lipid (open bars), and IKK-β KO-lipid (dark gray bars) mice. (a) Insulin-stimulated whole-body glycolysis in vivo. (b) Insulin-stimulated whole-body glycogen/lipid synthesis in vivo. (c) Insulin-stimulated skeletal muscle glycolysis in vivo. (d) Insulin-stimulated skeletal muscle glycogen synthesis in vivo. Values are means ± SE for three to five experiments. *P < 0.05 versus control group; ^†P < 0.05 versus IKK-β KO-lipid group.

Figure 7

Insulin signaling in skeletal muscle (gastrocnemius) and insulin action in fat of the control (black bars), IKK-β KO (light gray bars), control-lipid (open bars), and IKK-β KO-lipid (dark gray bars) mice. (a) Insulin-stimulated tyrosine phosphorylation of IRS-1 in skeletal muscle. (b) Insulin-stimulated IRS-1–associated PI 3-kinase activity in skeletal muscle. (c) Insulin-stimulated glucose uptake in intrascapular brown adipose tissue. (d) Insulin-stimulated glucose uptake in epididymal white adipose tissue. Values are means ± SE for three to five experiments. *P < 0.05 versus control group; ^†P < 0.05 versus IKK-β KO-lipid group.