Glucagon-like peptide 1 decreases lipotoxicity in non-alcoholic steatohepatitis

Abstract

Background & aims: Insulin resistance and lipotoxicity are pathognomonic in non-alcoholic steatohepatitis (NASH). Glucagon-like peptide-1 (GLP-1) analogues are licensed for type 2 diabetes, but no prospective experimental data exists in NASH. This study determined the effect of a long-acting GLP-1 analogue, liraglutide, on organ-specific insulin sensitivity, hepatic lipid handling and adipose dysfunction in biopsy-proven NASH.

Methods: Fourteen patients were randomised to 1.8mg liraglutide or placebo for 12-weeks of the mechanistic component of a double-blind, randomised, placebo-controlled trial (ClinicalTrials.gov-NCT01237119). Patients underwent paired hyperinsulinaemic euglycaemic clamps, stable isotope tracers, adipose microdialysis and serum adipocytokine/metabolic profiling. In vitro isotope experiments on lipid flux were performed on primary human hepatocytes.

Results: Liraglutide reduced BMI (-1.9 vs. +0.04kg/m(2); p<0.001), HbA1c (-0.3 vs. +0.3%; p<0.01), cholesterol-LDL (-0.7 vs. +0.05mmol/L; p<0.01), ALT (-54 vs. -4.0IU/L; p<0.01) and serum leptin, adiponectin, and CCL-2 (all p<0.05). Liraglutide increased hepatic insulin sensitivity (-9.36 vs. -2.54% suppression of hepatic endogenous glucose production with low-dose insulin; p<0.05). Liraglutide increased adipose tissue insulin sensitivity enhancing the ability of insulin to suppress lipolysis both globally (-24.9 vs. +54.8pmol/L insulin required to ½ maximally suppress serum non-esterified fatty acids; p<0.05), and specifically within subcutaneous adipose tissue (p<0.05). In addition, liraglutide decreased hepatic de novo lipogenesis in vivo (-1.26 vs. +1.30%; p<0.05); a finding endorsed by the effect of GLP-1 receptor agonist on primary human hepatocytes (24.6% decrease in lipogenesis vs. untreated controls; p<0.01).

Conclusions: Liraglutide reduces metabolic dysfunction, insulin resistance and lipotoxicity in the key metabolic organs in the pathogenesis of NASH. Liraglutide may offer the potential for a disease-modifying intervention in NASH.

Keywords: Adipose tissue; Glucagon-like peptide 1; Insulin sensitivity; Lipolysis; Non-alcoholic fatty liver.

Copyright © 2015 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.

Figures

Graphical abstract

Fig. 1

Liraglutide significantly reduces hepatic insulin resistance, but has no effect on muscle insulin sensitivity. (A) Tukey box-and-whisker plots highlight that liraglutide significantly increased the suppression of hepatic EGP with low-dose insulin compared to placebo. (B) Weight-adjusted Gd rates at low- and high-dose insulin phases of the euglycaemic clamp highlight that liraglutide did not change muscle insulin sensitivity (Gd) compared to placebo. ∗p <0.05 treatment vs. baseline (using paired Wilcoxon signed-rank tests). Unpaired Mann-Whitney tests were used to compare liraglutide vs. placebo.

Fig. 2

Liraglutide significant reduces whole body lipolysis and adipose insulin resistance. (A) Tukey box-and-whisker plots representing NEFA concentrations at the basal and hyperinsulinaemic phases of euglycaemic clamp. Liraglutide reduced NEFA at every phase of the clamp compared to placebo. (B) Tukey box-and-whisker plots representing the effect of liraglutide vs. placebo on insulin concentration required to achieve ½ maximal suppression of circulating NEFA (INS-½-max NEFA). ∗p <0.05 treatment vs. baseline (using paired Wilcoxon signed-rank tests). Unpaired Mann-Whitney tests were used to compare liraglutide vs. placebo.

Fig. 3

Liraglutide reduces abdominal SAT lipolysis and insulin resistance (IR). Line graphs (A, B) represent the mean ± SE concentrations of glycerol in the interstitial fluid measured from the SAT of each participant using in situ microdialysis throughout the 6 hour euglycaemic clamp. Liraglutide (A) decreased glycerol release throughout the clamp, whereas there were no clear differences after placebo treatment (B). (C) Tukey box-and-whisker plots (area under the curve analysis) highlight that liraglutide significantly reduced glycerol release from SAT in response to both low-dose and high-dose insulin compared to placebo, representing decreased abdominal SAT IR. ∗p <0.05 treatment vs. baseline (using paired Wilcoxon signed-rank tests). Unpaired Mann-Whitney tests were used to compare liraglutide vs. placebo.

Fig. 4

GLP-1R analogues significantly reduce hepatic DNL in vivo and in vitro, respectively. (A) Tukey box-and-whisker plots demonstrate that 12 weeks treatment with liraglutide significantly reduces hepatic DNL compared to placebo in patients with NASH (data ∗p <0.05 vs. placebo). (B) Exendin-4 significantly reduces DNL in primary human hepatocytes in culture. DNL was defined by the amount of 14C acetate incorporated into intracellular lipid in primary human hepatocytes. Exendin-4 has no effect on NEFA uptake (3H-palmitate taken up by the cells) (C) and β-oxidation (amount of 3H water released from the cells) (D) in hepatoma cell lines (HuH7). In vitro data in (B, C, D) are presented as mean ± SE percentages of the untreated controls. Untreated control was DMEM with 0.5% BSA. Insulin 5 nM served as a positive control. In vitro experiments were performed four times with each treatment in quadruplicate. ∗p <0.05 vs. untreated control.

Fig. 5

GLP-1R analogue, exendin-4, has direct anti-steatotic effects on hepatocytes in vitro. Exendin-4 (100 nM) reduces triglyceride content of NEFA-loaded HuH7 cells, as represented by (A) Oil Red O Staining (original magnification 10×, 40×) and (B) colorimetric triglyceride quantification assay. ∗p <0.05, ∗∗p <0.01 vs. untreated cells. (This figure appears in colour on the web.)