Incretin based therapies: A novel treatment approach for non-alcoholic fatty liver disease

The regulatory effects of second-generation antipsychotics on lipid metabolism: Potential mechanisms mediated by the gut microbiota and therapeutic implications

Second-generation antipsychotics (SGAs) are the mainstay of treatment for schizophrenia and other neuropsychiatric diseases but cause a high risk of disruption to lipid metabolism, which is an intractable therapeutic challenge worldwide. Although the exact mechanisms underlying this lipid disturbance are complex, an increasing body of evidence has suggested the involvement of the gut microbiota in SGA-induced lipid dysregulation since SGA treatment may alter the abundance and composition of the intestinal microflora. The subsequent effects involve the generation of different categories of signaling molecules by gut microbes such as endogenous cannabinoids, cholesterol, short-chain fatty acids (SCFAs), bile acids (BAs), and gut hormones that regulate lipid metabolism. On the one hand, these signaling molecules can directly activate the vagus nerve or be transported into the brain to influence appetite via the gut-brain axis. On the other hand, these molecules can also regulate related lipid metabolism via peripheral signaling pathways. Interestingly, therapeutic strategies directly targeting the gut microbiota and related metabolites seem to have promising efficacy in the treatment of SGA-induced lipid disturbances. Thus, this review provides a comprehensive understanding of how SGAs can induce disturbances in lipid metabolism by altering the gut microbiota.

Effect of novel glucose lowering agents on non-alcoholic fatty liver disease: A systematic review and meta-analysis

BACKGROUND

The efficacy of novel glucose-lowering drugs in treating non-alcoholic fatty liver disease (NAFLD) in patients with and without type-2 diabetic patients (T2DM) remains unclear.

AIM

To conduct a meta-analysis to evaluate the efficacy of 3 novel glucose-lowering drug classes, namely glucagon-like peptide-1 receptor agonists (GLP-1RA), sodium-glucose co-transporter 2 (SGLT2) inhibitors, and dipeptidyl-peptidase-4 (DPP4) inhibitors on hepatic parameters: Aspartate Aminotransferase (AST), Alanine Aminotransferase (ALT), Gamma-Glutamyl Transferase (GGT), Bilirubin, and FIB-4 (Fibrosis).

METHODS

MEDLINE was searched from inception through October 2021 for randomized placebo or active glucose-lowering drug-controlled trials. A random-effects model was used to pool the results. A p-value of less than or equal to 0.05 was considered significant. Results were presented as weighted mean differences (WMD) and corresponding 95% confidence intervals (CIs).

RESULTS

Our pooled analysis consisted of 40 studies. A significant reduction was seen in AST with SGLT2 inhibitors (WMD = -2.31 IU/L, 95%CI: -3.16 to -1.47 IU/L, P < 0.00001) and GLP-1RA (WMD = -3.29 IU/L, 95%CI: -5.98 to -0.61 IU/L, P = 0.02). Similarly, significant reduction was seen in ALT with SGLT2 inhibitors (WMD = -5.93 IU/L, 95%CI: -7.70 to -4.16 IU/L, P < 0.00001) and GLP-1RAs (WMD = -9.92 IU/L, 95%CI: -19.89 to 0.05 IU/L, P = 0.05). In contrast, DPP-4 inhibitors showed no significant reduction in AST (WMD = -3.20 IU/L, 95%CI: -11.13 to 4.73 IU/L, P = 0.43) or ALT (WMD = -4.81 IU/L, 95%CI: -15.83 to 6.21 IU/L, P = 0.39). A significant reduction in GGT was seen with SGLT2 inhibitors (WMD = -6.49 IU/L, 95%CI: -11.09 to -1.89 IU/L, P = 0.006) and GLP-1RAs (WMD = -12.38 IU/L, 95%CI: -15.69 to -9.07 IU/L, P < 0.00001). However, significant results were not observed with DPP-4 inhibitors (WMD = -0.92 IU/L, 95%CI: -5.80 to 3.96 IU/L, P = 0.71). There was a statistically significant reduction in FIB-4 index with SGLT2 inhibitors (WMD = -0.21, 95%CI: -0.40 to -0.03, P = 0.02) and GLP-1 RA (WMD = -0.15, 95%CI: -0.29 to 0.00, P = 0.05). Lastly, SGLT2 inhibitors led to a significant change in bilirubin levels (WMD = 2.03, 95%CI: 0.76 to 3.30, P = 0.002) while the change in bilirubin was not significant with GLP-1 agonists (WMD = -0.21, 95%CI: -1.09 to 0.66, P = 0.63) and DPP-4 inhibitors (WMD = 0.14, 95%CI: -1.55 to 1.83, P = 0.87).

CONCLUSION

SGLT2 inhibitors and GLP-1 agonists have a beneficial effect on hepatic parameters in patients with NAFLD. However, further research is needed to evaluate the effect of DPP-4 inhibitors on hepatic function properly.

Novel glucose-lowering drugs for non-alcoholic fatty liver disease

BACKGROUND

The efficacy of novel glucose-lowering drugs in treating non-alcoholic fatty liver disease (NAFLD) is unknown.

AIM

To evaluate the efficacy of glucose-lowering drugs dipeptidyl peptidase-4 (DPP-4) inhibitors, glucagon-like peptide-1 receptor agonists (GLP-1 RAs), and sodium-glucose cotransporter 2 (SGLT2) inhibitors in treating NAFLD and to perform a comparison between these treatments.

METHODS

Electronic databases were systematically searched. The inclusion criteria were: Randomized controlled trials comparing DPP-4 inhibitors, GLP-1 RAs, or SGLT2 inhibitors against placebo or other active glucose-lowering drugs in NAFLD patients, with outcomes of changes in liver enzyme [alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST)] from baseline.

RESULTS

Nineteen studies were finally included in this meta-analysis. Compared with placebo or other active glucose-lowering drug treatment, treatment with DPP-4 inhibitors, GLP-1 RAs, and SGLT2 inhibitors all led to a significant decrease in ALT change and AST change from baseline. The difference between the DPP-4 inhibitor and SGLT2 inhibitor groups in ALT change was significant in favor of DPP-4 inhibitor treatment (P < 0.05). The trends of reduction in magnetic resonance imaging proton density fat fraction and visceral fat area changes were also observed in all the novel glucose-lowering agent treatment groups.

CONCLUSION

Treatment with DPP-4 inhibitors, GLP-1 RAs, and SGLT2 inhibitors resulted in improvements in serum ALT and AST levels and body fat composition, indicating a beneficial effect in improving liver injury and reducing liver fat in NAFLD patients.

Determining whether the effect of liraglutide on non-alcoholic fatty liver disease depends on reductions in the body mass index

Background and Aim

Non‐alcoholic fatty liver disease (NAFLD) initially presents as steatosis, which can progress to non‐alcoholic steatohepatitis (NASH), and often presents clinically alongside metabolic syndromes. Glucagon‐like peptide‐1 receptor agonists (GLP‐1 RAs) are regularly utilized to treat type 2 diabetes mellitus. The GLP‐1 RA—liraglutide—ameliorates liver enzymes, histological features, and liver fat content of patients with NASH. However, few studies have examined whether the effect of GLP‐1 RAs depends on changes in the patient's body mass index (BMI). Therefore, this retrospective study aimed to investigate whether the efficacy of liraglutide depended on the baseline BMI or a reduction in BMI.

Methods

Fifty‐five Japanese patients with type 2 diabetes mellitus and NAFLD who received liraglutide treatment for 24 weeks were assessed. The association between BMI and liver function or fibrosis was evaluated based on the aspartate aminotransferase, alanine aminotransferase, and fibrosis‐4 indices.

Results

We found that 24 weeks of liraglutide treatment improved liver function and fibrosis in patients with type 2 diabetes mellitus and NAFLD, regardless of BMI changes or obesity status.

Conclusions

Our findings provide important insight into the impact of BMI on liver function and fibrosis in patients with type 2 diabetes mellitus and NAFLD who are treated with liraglutide.

Effects of liraglutide on metabolic syndrome in WBN/Kob diabetic fatty rats supplemented with a high-fat diet

BACKGROUND

Liraglutide, a GLP-1 receptor agonist, has recently been used to treat metabolic syndrome (MS) because of its anti-diabetic and anti-obesity effects. We have previously shown that Wistar Bonn Kobori diabetic and fatty (WBN/Kob-Lepr fa , WBKDF) rats fed a high-fat diet (HFD) developed MS including marked obesity, hyperglycemia, and dyslipidemia. To obtain further information on WBKDF-HFD rats as a severe MS model, we performed a pharmacological investigation into the anti-MS effects of liraglutide in this model.

METHODS

Seven-week-old male WBKDF-HFD rats were allocated to three groups (N = 8 in each group): a vehicle group, a low-dose liraglutide group, and a high-dose liraglutide group. They received subcutaneous injections of either saline or liraglutide at doses of 75 or 300 μg/kg body weight once daily for 4 weeks.

RESULTS

Results showed that liraglutide treatment reduced body weight gain and food intake in a dose-dependent manner. The marked hyperglycemia and the glucose tolerance were also significantly ameliorated in the liraglutide-treated groups. Moreover, liraglutide also reduced the plasma triglyceride concentration and liver fat accumulation.

CONCLUSIONS

The present study demonstrated that liraglutide could significantly alleviate MS in WBKDF-HFD rats, and the reaction to liraglutide is similar to human patients with MS. WBKDF-HFD rats are therefore considered to be a useful model for research on severe human MS.

Development and Progression of Non-Alcoholic Fatty Liver Disease: The Role of Advanced Glycation End Products

Non-alcoholic fatty liver disease (NAFLD) affects up to 30% of the adult population and is now a major cause of liver disease-related premature illness and deaths in the world. Treatment is largely based on lifestyle modification, which is difficult to achieve in most patients. Progression of simple fatty liver or steatosis to its severe form non-alcoholic steatohepatitis (NASH) and liver fibrosis has been explained by a 'two-hit hypothesis'. Whilst simple steatosis is considered the first hit, its transformation to NASH may be driven by a second hit. Of several factors that constitute the second hit, advanced glycation end products (AGEs), which are formed when reducing-sugars react with proteins or lipids, have been implicated as major candidates that drive steatosis to NASH via the receptor for AGEs (RAGE). Both endogenous and processed food-derived (exogenous) AGEs can activate RAGE, mainly present on Kupffer cells and hepatic stellate cells, thus propagating NAFLD progression. This review focuses on the pathophysiology of NAFLD with special emphasis on the role of food-derived AGEs in NAFLD progression to NASH and liver fibrosis. Moreover, the effect of dietary manipulation to reduce AGE content in food or the therapies targeting AGE/RAGE pathway on disease progression is also discussed.

Obesity Paradox in Chronic Liver Diseases: Product of Bias or a Real Thing?

In recent years, evidence supporting the theory of obesity paradox has increased, showing that obese/overweight people with prevalent chronic diseases experience lower mortality compared with patients of normal weight. So far, evidence is most comprehensive in cardiovascular and chronic renal diseases; however, published studies are prone to many biases, enabling us to reach a definite conclusion. Available data in chronic liver disease is scarce and ambiguous. Obesity is traditionally associated with nonalcoholic fatty liver disease and steatosis in viral hepatitis and as such one would not expect the obesity paradox to be a real possibility in liver disease. Yet, there seem to be new data indicating the opposite - the obesity paradox exists in severe and end-stage liver cirrhosis, which could be attributed to a better lean mass in patients with higher body mass index, meaning that sarcopenia, as one of the most important prognostic factors of survival, is less likely to be present. Nonetheless, the problem of various methodological problems addressing the association between body weight and mortality, which is present both in liver disease and other chronic diseases, are preventing us from attaining an unanimous conclusion. Still, we should be aware that the obesity paradox might be true, especially in severe and end-stage illness. This suggests focusing our efforts toward preserving or building up fat-free mass and decreasing inflammatory activity responsible for catabolism and sarcopenia, and implying that the underlaying cause should be treated.

Liraglutide Inhibits Hepatitis C Virus Replication Through an AMP Activated Protein Kinase Dependent Mechanism

Insulin resistance and diabetes are both associated with chronic hepatitis C virus (HCV) infection, and the glucagon-like peptide-1(GLP-1) receptor agonist, liraglutide, is a common therapy for diabetes. Our aim was to investigate whether liraglutide treatment can inhibit HCV replication. A cell culture-produced HCV infectious system was generated by transfection of in vitro-transcribed genomic JFH-1 ribonucleic acid (RNA) into Huh-7.5 cells. Total RNA samples were extracted to determine the efficiency of HCV replication. The Ava5 cells were treated with liraglutide and cell viability was calculated. A Western blot analysis of the protein expression was performed. The immunoreactive blot signals were also detected. Liraglutide activated GLP-1 receptors in the HCV infectious system, and inhibited subgenomic HCV RNA replication in the HuH-7.5 cells. The Western blot analysis revealed both HCV protein and replicon RNA were reduced after treatment with liraglutide in a dose-dependent manner. Liraglutide decreased the cell viability of HCV RNA at an optimum concentration of 120 μg/mL, activated the 5′ adenosine monophosphate-activated protein kinase (AMPK) and the phosphorylated- transducer of regulated cyclic adenosine monophosphate (CAMP) response element-binding protein 2 (TORC2), thereby decreasing the cell viability of phosphoenolpyruvate carboxykinase (PEPCK) and G6pase RNA Therefore, we conclude that liraglutide can inhibit HCV replication via an AMPK/TORC2-dependent pathway.

Treating nonalcoholic steatohepatitis with antidiabetic drugs: Will GLP-1 agonists end the struggle?

Nonalcoholic fatty liver disease (NAFLD) is highly associated with insulin resistance (IR), type 2 diabetes mellitus and metabolic syndrome, being characterized as the hepatic component of metabolic syndrome. Despite its high prevalence, no pharmacological treatment has been established, as of yet. A growing body of evidence, however, shows that reducing IR can result in improvement of the biochemical and histological features of nonalcoholic steatohepatitis (NASH)-the aggressive form of NAFLD that can lead to cirrhosis and hepatocellular carcinoma. Unfortunately, the several trials that have assessed the effect of various antidiabetic agents to date have failed to establish an effective and safe treatment regimen for patients with NAFLD. Glucagon-like peptide-1 (commonly known as GLP-1) agonists are a novel class of antidiabetic drugs that improve insulin sensitivity and promote weight loss. They also appear to have a direct effect on the lipid metabolism of hepatocytes, reducing hepatic steatosis. Several trials have demonstrated that GLP-1 agonists can reduce aminotransferase levels and improve liver histology in patients with NAFLD, suggesting that these agents could serve as an alternative treatment option for these patients. This manuscript discusses the role and potential mechanisms of GLP-1 agonists in the treatment of NASH.

The GLP-1 Analogs Liraglutide and Semaglutide Reduce Atherosclerosis in ApoE-/- and LDLr-/- Mice by a Mechanism That Includes Inflammatory Pathways

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The GLP-1RAs liraglutide and semaglutide reduce cardiovascular risk in type 2 diabetes patients.

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In ApoE^−/− mice and LDLr^−/− mice, liraglutide and semaglutide treatment significantly attenuated plaque lesion development, in part independently of body weight and cholesterol lowering.

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Semaglutide decreased levels of plasma markers of systemic inflammation in an acute inflammation model (lipopolysaccharide), and transcriptomic analysis of aortic atherosclerotic tissue revealed that multiple inflammatory pathways were down-regulated by semaglutide.

The glucagon-like peptide-1 receptor agonists (GLP-1RAs) liraglutide and semaglutide reduce cardiovascular risk in type 2 diabetes patients. The mode of action is suggested to occur through modified atherosclerotic progression. In this study, both of the compounds significantly attenuated plaque lesion development in apolipoprotein E-deficient (ApoE^−/−) mice and low-density lipoprotein receptor-deficient (LDLr^−/−) mice. This attenuation was partly independent of weight and cholesterol lowering. In aortic tissue, exposure to a Western diet alters expression of genes in pathways relevant to the pathogenesis of atherosclerosis, including leukocyte recruitment, leukocyte rolling, adhesion/extravasation, cholesterol metabolism, lipid-mediated signaling, extracellular matrix protein turnover, and plaque hemorrhage. Treatment with semaglutide significantly reversed these changes. These data suggest GLP-1RAs affect atherosclerosis through an anti-inflammatory mechanism.

Sitagliptin reduces insulin resistance and improves rat liver steatosis via the SIRT1/AMPKα pathway

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease. It is asymptomatic at presentation and is frequently identified among individuals with metabolic dysfunction, including obesity and diabetes. NAFLD is primarily characterized by the accumulation of triacylglycerol in the liver. Since insulin resistance and fat metabolism dysregulation are major causes of type 2 diabetes and NAFLD, anti-diabetes agents are widely considered as potential therapy strategies for NAFLD. Sitagliptin, an inhibitor of dipeptidyl peptidase-4, has been developed as an oral anti-hyperglycemic agent. In the present study, the effect of sitagliptin on the progression of NAFLD was evaluated in a rat model fed with a high fat diet (HFD). It was identified that sitagliptin significantly suppressed lipid accumulation in rat blood and liver and improved insulin resistance. Furthermore, it was revealed that sitagliptin reactivated the HFD-suppressed SIRT1/AMPK axis pathway and upregulated its downstream target genes, modulating fatty acid metabolism. These findings demonstrate a preventive effect of sitagliptin on hepatic lipid dysregulation and suggest that sitagliptin has potential as a clinical therapeutic strategy for NAFLD.

Protective Effects of Gemigliptin, a Dipeptidyl Peptidase-4 Inhibitor, against Cisplatin-Induced Nephrotoxicity in Mice

Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used antihyperglycemic agents for the treatment of type 2 diabetes mellitus. Recently, the pleiotropic actions of DPP-4 inhibitors have drawn much attention. In the present study, we aimed to examine whether gemigliptin, a recently developed DPP-4 inhibitor, could protect against cisplatin-induced nephrotoxicity. We showed that pretreatment with gemigliptin attenuated cisplatin-induced renal dysfunction, as shown by analysis of plasma creatinine levels and blood urea nitrogen and histological damage. Elevated plasma levels of active glucagon-like peptide-1 were observed in gemigliptin-pretreated mice after cisplatin treatment, compared to that in cisplatin alone-treated mice. Gemigliptin attenuated cisplatin-induced apoptotic cell death, as assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and Western blot analysis in the kidneys. Gemigliptin also decreased the plasma levels of tumor necrosis factor-α and monocyte chemoattractant protein-1 and attenuated nuclear staining of nuclear factor kappa-B p65 in the kidneys. In addition, gemigliptin increased the protein expression of heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) in the kidneys of cisplatin-treated mice. Taken together, these results suggest that pretreatment with gemigliptin protects against cisplatin-induced nephrotoxicity in mice, possibly via inhibition of apoptotic cell death and inflammatory responses through induction of HO-1 and NQO1 expression.

Extrapancreatic effects of incretin hormones: evidence for weight-independent changes in morphological aspects and oxidative status in insulin-sensitive organs of the obese nondiabetic Zucker rat (ZFR)

Incretin‐based therapies are widely used to treat type 2 diabetes. Although hypoglycemic actions of incretins are mostly due to their insulinotropic/glucagonostatic effects, they may also influence extrapancreatic metabolism. We administered exendin‐4 (Ex‐4), a long‐acting glucagon‐like peptide receptor agonist, at low dose (0.1 nmol/kg/day) for a short period (10 days), in obese nondiabetic fa/fa Zucker rats (ZFRs). Ex‐4‐treated ZFRs were compared to vehicle (saline)‐treated ZFRs and vehicle‐ and Ex‐4‐treated lean rats (LRs). Blood glucose levels were measured at days 0, 9, and 10. Ingested food and animal weight were recorded daily. On the day of sacrifice (d10), blood was sampled along with liver, epididymal, subcutaneous, brown adipose, and skeletal muscle tissues from animals fasted for 24 h. Plasma insulin and blood glucose levels, food intake, and body and epididymal fat weight were unchanged, but gross morphological changes were observed in insulin‐sensitive tissues. The average size of hepatocytes was significantly lower in Ex‐4‐treated ZFRs, associated with decreased number and size of lipid droplets and 4‐hydroxy‐2‐nonenal (HNE) staining, a marker of oxidative stress (OS). Myocytes, which were smaller in ZFRs than in LRs, were significantly enlarged and depleted of lipid droplets in Ex‐4‐treated ZFRs. Weak HNE staining was increased by Ex‐4. A similar observation was made in brown adipose tissue, whereas the elevated HNE staining observed in epididymal adipocytes of ZFRs, suggestive of strong OS, was decreased by Ex‐4. These results suggest that incretins by acting on OS in insulin‐sensitive tissues may contribute to weight‐independent improvement in insulin sensitivity.

Hepatic DPP4 DNA Methylation Associates With Fatty Liver

Hepatic DPP4 expression is elevated in subjects with ectopic fat accumulation in the liver. However, whether increased dipeptidyl peptidase 4 (DPP4) is involved in the pathogenesis or is rather a consequence of metabolic disease is not known. We therefore studied the transcriptional regulation of hepatic Dpp4 in young mice prone to diet-induced obesity. Already at 6 weeks of age, expression of hepatic Dpp4 was increased in mice with high weight gain, independent of liver fat content. In the same animals, methylation of four intronic CpG sites was decreased, amplifying glucose-induced transcription of hepatic Dpp4 In older mice, hepatic triglyceride content was increased only in animals with elevated Dpp4 expression. Expression and release of DPP4 were markedly higher in the liver compared with adipose depots. Analysis of human liver biopsy specimens revealed a correlation of DPP4 expression and DNA methylation to stages of hepatosteatosis and nonalcoholic steatohepatitis. In summary, our results indicate a crucial role of the liver in participation to systemic DPP4 levels. Furthermore, the data show that glucose-induced expression of Dpp4 in the liver is facilitated by demethylation of the Dpp4 gene early in life. This might contribute to early deteriorations in hepatic function, which in turn result in metabolic disease such as hepatosteatosis later in life.

Linagliptin alleviates fatty liver disease in diabetic db/db mice

AIM

To study the effects of linagliptin on the structural signs of non-alcoholic fatty liver disease (NAFLD) in db/db mice.

METHODS

Male diabetic db/db mice (BKS.Cg-Dock7^m+/⁺Lepr^db/J) aged 10 wk received the dipeptidyl peptidase 4 (DPP4) inhibitor linagliptin (10 mg/kg) or saline as a placebo once per day by gavage for 8 wk. Intact db/db mice served as controls. Structural changes in the liver were analyzed from light and electron microscopic images of sections from intact, placebo-treated and linagliptin-treated animals. We estimated the changes in hepatocytes, sinusoidal cells, liver microvasculature and lymphatic roots. Hepatic staining for lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) was assessed by immunohistochemistry.

RESULTS

In 18-wk-old diabetic mice, liver steatosis (predominantly microvesicular and mediovesicular steatosis) was accompanied by dilation of the roots of the lymphatic system, interlobular blood vessels and bile canaliculi. Compared to saline-treated mice, linagliptin-treated mice exhibited a reduction in the mean numeral densities of hepatocytes with lipid droplets (92.4% ± 1.7% vs 64.9% ± 5.8% per field of view, P = 0.0002) and a lower proportion of hepatocytes with a high density of lipid droplets (20.7% ± 3.6% vs 50.4% ± 3.1%, P = 0.0007). We observed heterogeneous hepatocytes and relatively preserved cell structures in the linagliptin group. Dilation of blood and lymphatic vessels, as well as ultrastructural changes in the hepatocyte endoplasmic reticulum and mitochondria, were alleviated by linagliptin treatment. In intact and placebo-treated mice, immunohistochemical staining for LYVE-1 was observed in the endothelial cells of interlobular lymphatic vessels and on the membranes of some endothelial sinusoidal cells. We observed an enlarged LYVE-1 reaction area in linagliptin-treated mice compared to intact and placebo-treated mice. The improvement in the structural parameters of the liver in linagliptin-treated mice was independent to changes in the plasma glucose levels.

CONCLUSION

The DPP4 inhibitor linagliptin alleviates liver steatosis and structural changes in the hepatic microvasculature and lymphatic roots in a model of NAFLD in diabetic db/db mice.

Non-alcoholic fatty liver disease and dyslipidemia: An update

Non-alcoholic fatty liver (NAFLD) is the most common liver disease worldwide, progressing from simple steatosis to necroinflammation and fibrosis (leading to non-alcoholic steatohepatitis, NASH), and in some cases to cirrhosis and hepatocellular carcinoma. Inflammation, oxidative stress and insulin resistance are involved in NAFLD development and progression. NAFLD has been associated with several cardiovascular (CV) risk factors including obesity, dyslipidemia, hyperglycemia, hypertension and smoking. NAFLD is also characterized by atherogenic dyslipidemia, postprandial lipemia and high-density lipoprotein (HDL) dysfunction. Most importantly, NAFLD patients have an increased risk for both liver and CV disease (CVD) morbidity and mortality. In this narrative review, the associations between NAFLD, dyslipidemia and vascular disease in NAFLD patients are discussed. NAFLD treatment is also reviewed with a focus on lipid-lowering drugs. Finally, future perspectives in terms of both NAFLD diagnostic biomarkers and therapeutic targets are considered.

The glucagon-like peptide-1 analogue exendin-4 reverses impaired intracellular Ca(2+) signalling in steatotic hepatocytes

The release of Ca(2+) from the endoplasmic reticulum (ER) and subsequent replenishment of ER Ca(2+) by Ca(2+) entry through store-operated Ca(2+) channels (SOCE) play critical roles in the regulation of liver metabolism by adrenaline, glucagon and other hormones. Both ER Ca(2+) release and Ca(2+) entry are severely inhibited in steatotic hepatocytes. Exendin-4, a slowly-metabolised glucagon-like peptide-1 (GLP-1) analogue, is known to reduce liver glucose output and liver lipid, but the mechanisms involved are not well understood. The aim of this study was to determine whether exendin-4 alters intracellular Ca(2+) homeostasis in steatotic hepatocytes, and to evaluate the mechanisms involved. Exendin-4 completely reversed lipid-induced inhibition of SOCE in steatotic liver cells, but did not reverse lipid-induced inhibition of ER Ca(2+) release. The action of exendin-4 on Ca(2+) entry was rapid in onset and was mimicked by GLP-1 or dibutyryl cyclic AMP. In steatotic liver cells, exendin-4 caused a rapid decrease in lipid (half time 6.5min), inhibited the accumulation of lipid in liver cells incubated in the presence of palmitate plus the SOCE inhibitor BTP-2, and enhanced the formation of cyclic AMP. Hormone-stimulated accumulation of extracellular glucose in glycogen replete steatotic liver cells was inhibited compared to that in non-steatotic cells, and this effect of lipid was reversed by exendin-4. It is concluded that, in steatotic hepatocytes, exendin-4 reverses the lipid-induced inhibition of SOCE leading to restoration of hormone-regulated cytoplasmic Ca(2+) signalling. The mechanism may involve GLP-1 receptors, cyclic AMP, lipolysis, decreased diacylglycerol and decreased activity of protein kinase C.

Effect of incretin therapies compared to pioglitazone and gliclazide in non-alcoholic fatty liver disease in diabetic patients not controlled on metformin alone: An observational, pilot study

AIM

To compare the effect of different hypoglycemic drugs on laboratory and ultrasonographic markers of non-alcoholic fatty liver disease (NAFLD) in patients with type 2 diabetes not controlled on metformin alone.

METHODS

Prospective study of diabetic patients treated with metformin in combination with gliclazide, pioglitazone, sitagliptin, exenatide, or liraglutide. NAFLD was assessed by abdominal ultrasound and NAFLD fibrosis score was calculated at baseline and 6 months.

RESULTS

Fifty-eight patients completed 6 months of follow-up: 15 received gliclazide, 13 pioglitazone, 15 sitagliptin, 7 exenatide, and 8 liraglutide. NAFLD affected 57.8% of patients at baseline, and its ultrasonographic course varied depending on changes in weight (P=.009) and waist circumference (P=.012). The proportions of patients who experienced ultrasonographic improvement in the different treatment groups were: 33.3% with gliclazide, 37.5% with pioglitazone, 45.5% with sitagliptin, 80% with exenatide, and 33% with liraglutide (P=.28).

CONCLUSIONS

Qualitative ultrasonographic NAFLD improvement in diabetic patients treated with metformin in combination with other hypoglycemic drugs is associated to change over time in weight and waist circumference. Long-term clinical trials are needed to assess whether incretin therapies result in better liver outcomes than other hypoglycemic therapies.

Gastrointestinal actions of glucagon-like peptide-1-based therapies: glycaemic control beyond the pancreas

The gastrointestinal hormone glucagon-like peptide-1 (GLP-1) lowers postprandial glucose concentrations by regulating pancreatic islet-cell function, with stimulation of glucose-dependent insulin and suppression of glucagon secretion. In addition to endocrine pancreatic effects, mounting evidence suggests that several gastrointestinal actions of GLP-1 are at least as important for glucose-lowering. GLP-1 reduces gastric emptying rate and small bowel motility, thereby delaying glucose absorption and decreasing postprandial glucose excursions. Furthermore, it has been suggested that GLP-1 directly stimulates hepatic glucose uptake, and suppresses hepatic glucose production, thereby adding to reduction of fasting and postprandial glucose levels. GLP-1 receptor agonists, which mimic the effects of GLP-1, have been developed for the treatment of type 2 diabetes. Based on their pharmacokinetic profile, GLP-1 receptor agonists can be broadly categorized as short- or long-acting, with each having unique islet-cell and gastrointestinal effects that lower glucose levels. Short-acting agonists predominantly lower postprandial glucose excursions, by inhibiting gastric emptying and intestinal glucose uptake, with little effect on insulin secretion. By contrast, long-acting agonists mainly reduce fasting glucose levels, predominantly by increased insulin and reduced glucagon secretion, with potential additional direct inhibitory effects on hepatic glucose production. Understanding these pharmacokinetic and pharmacodynamic differences may allow personalized antihyperglycaemic therapy in type 2 diabetes. In addition, it may provide the rationale to explore treatment in patients with no or little residual β-cell function.

Baseline ALT levels as a marker of glycemic response to treatment with GLP-1 receptor agonists

BACKGROUND AND OBJECTIVES

This study aimed to assess if ALT levels, as a marker of non-alcoholic fatty liver disease, may predict HbA1c response to treatment with GLP-1 receptor agonists (GLP-1 RAs).

PATIENTS AND METHODS

A retrospective, longitudinal, analytical study was conducted including patients with type 2 diabetes mellitus continuously treated with GLP-1 agonists (85% with liraglutide) for one year. Patients were divided into two groups according to baseline ALT levels, with 24 U/L (the median of the distribution) as the cut-off point. The dependent variable was HbA1c change (one-year follow-up minus baseline). The predictive value of ALT levels above 24 U/L and ALT change was analyzed using multivariate linear regression adjusted to age, gender, diabetes duration, type and dose of GLP-1 RA, baseline HbA1c, baseline body mass index (BMI), and change in BMI.

RESULTS

A total of 117 patients (48% females) aged 58.6 (SD 9.6) years were enrolled into the study. Treatment was associated with a change in ALT of -4.3 U/L (p=0.041) and a change in HbA1c of -1.1% (p<0.0001). Decreases in HbA1c (-1.41% vs -0.76%; p=0.045) and ALT (-9.25 vs 0.46 U/L; p=0.002) were significantly higher in patients with ALT levels above the median. In the multivariate analysis, both ALT>24 U/L (b=-0.74; 95%CI: -1.31 to -0.18; p=0.011) and ALT change (b=0.028; 95%CI: 0.010 to 0.046; p=0.003), were significant response predictors.

CONCLUSIONS

Elevated baseline transaminase values and decreased transaminase levels during follow-up are associated to a favorable glycemic response to GLP-1 RAs.

Incretin-based therapies for the treatment of non-alcoholic fatty liver disease: A systematic review and meta-analysis

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver disease in Western societies. Despite its significance, there are no well-proven pharmacological treatments. Two novel classes of potential pharmacotherapies are the glucagon-like peptide-1 receptor agonists (GLP-1 RA) and dipeptidyl peptidase-4 inhibitors (DPP-4I), collectively known as incretin-based therapies. These have several metabolic and anti-inflammatory actions that may be of benefit in NAFLD. The aim of this meta-analysis was to evaluate their efficacy via a structured retrieval and pooled analysis of relevant studies.

METHODS

Studies were sourced from electronic databases and meeting abstracts. Main inclusion criteria were original studies investigating treatment of adults with NAFLD using GLP-1 RA/DPP-4I. Key outcomes were a change in serum alanine transaminase (ALT), as a marker of liver inflammation, and improvement in disease status measured by imaging or histology.

RESULTS

Initial searching retrieved 1357 peer-reviewed articles and abstracts. Four studies met all inclusion and exclusion criteria. There were a total of 136 participants with NAFLD and concomitant type 2 diabetes mellitus (T2DM). Meta-analysis (random-effects model) revealed a significant decrease in serum ALT following treatment (mean reduction 14.1 IU/L, 95% confidence intervals [CI] 8.3-19.8, P < 0.0001). In two studies with imaging and tissue data, treatment was found to significantly reduce steatosis, inflammation, and fibrosis.

CONCLUSION

The significant decrease in a key biochemical marker of hepatic inflammation following treatment with incretin-based therapies, as well as improvements in imaging and histology, suggests these agents may be effective options for managing NAFLD with comorbid T2DM.

Treatment of nonalcoholic fatty liver disease: Where do we stand? an overview

Nonalcoholic fatty liver disease (NAFLD) is currently the most common liver disease worldwide, the prevalence of which had progressively increased over the past 10 years where other liver diseases remained at the same prevalence rates or are expected to decrease as in the case of hepatitis C virus (HCV). The treatment of NAFLD is of prime concern to health care professionals and patients due to the significant mortality and morbidity it implies; the problem is further escalated by the fact that standard of care medications targeting NAFLD remain experimental and without evidence base. Treatment nowadays is focused on lifestyle modification and managing the comorbid associated diseases, with a possible role for some hepatic protective agents. This review presents all the medications that had been proposed and used for the treatment of NAFLD with or without scientific rationale and includes agents for weight loss, insulin sensitizers, drugs that reduce blood lipids, glucagon-mimetics, drugs that may reduce fibrosis, angiotensin receptor blockers, and medicines believed to reduce endoplasmic reticular stress such as vitamin E, ursodeoxycholic acid, and S-adenosyl methionine. A quick review of the newer agents that proved to be promising such as obeticholic acid and GFT505 and the medicines that are still in the pipeline is also presented.

The Dipeptidyl Peptidase-4 Inhibitor Teneligliptin Attenuates Hepatic Lipogenesis via AMPK Activation in Non-Alcoholic Fatty Liver Disease Model Mice

Non-alcoholic fatty liver disease (NAFLD), which is strongly associated with metabolic syndrome, is increasingly a major cause of hepatic disorder. Dipeptidyl peptidase (DPP)-4 inhibitors, anti-diabetic agents, are expected to be effective for the treatment of NAFLD. In the present study, we established a novel NAFLD model mouse using monosodium glutamate (MSG) and a high-fat diet (HFD) and investigated the effects of a DPP-4 inhibitor, teneligliptin, on the progression of NAFLD. Male MSG/HFD-treated mice were divided into two groups, one of which received teneligliptin in drinking water. Administration of MSG and HFD caused mice to develop severe fatty changes in the liver, but teneligliptin treatment improved hepatic steatosis and inflammation, as evaluated by the NAFLD activity score. Serum alanine aminotransferase and intrahepatic triglyceride levels were significantly decreased in teneligliptin-treated mice (p < 0.05). Hepatic mRNA levels of the genes involved in de novo lipogenesis were significantly downregulated by teneligliptin (p < 0.05). Moreover, teneligliptin increased hepatic expression levels of phosphorylated AMP-activated protein kinase (AMPK) protein. These findings suggest that teneligliptin attenuates lipogenesis in the liver by activating AMPK and downregulating the expression of genes involved in lipogenesis. DPP-4 inhibitors may be effective for the treatment of NAFLD and may be able to prevent its progression to non-alcoholic steatohepatitis.

Nonalcoholic fatty liver disease: Pathogenesis and incretin based therapies

Nonalcoholic fatty liver disease is considered a hepatic manifestation of metabolic syndrome (MS). The current treatment of non-alcoholic fatty liver disease (NAFLD) principally involves amelioration of MS components by lifestyle modification. Effective pharmacological agents for fatty liver treatment are lacking. Incretins are gut derived hormones secreted into the circulation in response to nutrient ingestion that can enhance glucose-stimulated insulin secretion, and represent a new class of drugs for treatment of type 2 diabetes, including glucagon-like peptide 1 analogues and dipeptidyl aminopeptidase 4 inhibitors. There are several experimental and clinical trials exploring the efficacy of incretin based therapies in NAFLD treatment, however, further studies are needed to assess the long-term effect of incretin based therapies on NAFLD.

Pharmacokinetics in patients with chronic liver disease and hepatic safety of incretin-based therapies for the management of type 2 diabetes mellitus

Patients with type 2 diabetes mellitus have an increased risk of chronic liver disease (CLD) such as non-alcoholic fatty liver disease and steatohepatitis, and about one-third of cirrhotic patients have diabetes. However, the use of several antidiabetic agents, such as metformin and sulphonylureas, may be a concern in case of hepatic impairment (HI). New glucose-lowering agents targeting the incretin system are increasingly used for the management of type 2 diabetes. Incretin-based therapies comprise oral inhibitors of dipeptidyl peptidase-4 (DPP-4) (gliptins) or injectable glucagon-like peptide-1 (GLP-1) receptor agonists. This narrative review summarises the available data regarding the use of both incretin-based therapies in patients with HI. In contrast to old glucose-lowering agents, they were evaluated in specifically designed acute pharmacokinetic studies in patients with various degrees of HI and their hepatic safety was carefully analysed in large clinical trials. Only mild changes in pharmacokinetic characteristics of DPP-4 inhibitors were observed in patients with different degrees of HI, presumably without major clinical relevance. GLP-1 receptor agonists have a renal excretion rather than liver metabolism. Specific pharmacokinetic data in patients with HI are only available for liraglutide. No significant changes in liver enzymes were reported with DPP-4 inhibitors or GLP-1 receptor agonists, alone or in combination with various other glucose-lowering agents, in clinical trials up to 2 years in length. On the contrary, preliminary data suggested that incretin-based therapies may be beneficial in patients with CLD, more particularly in the presence of non-alcoholic fatty liver disease. Nevertheless, caution should be recommended, especially in patients with advanced cirrhosis, because of a lack of clinical experience with incretin-based therapies in these vulnerable patients.

A concise review of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome and the incidence of which is rising rapidly due to the increasing epidemic of obesity in both adults and children. The initial accumulation of fat followed by subsequent inflammation is central to the development of liver damage, and is critically influenced by host factors including age, gender, presence of diabetes, genetic polymorphisms and more recently by the gut microbiome. An increasing body of data suggest that NAFLD is also an independent risk factor of cardiovascular disease, which remains the commonest cause of mortality in such patients. This review focusses on the pathogenesis of NAFLD, and the evolution of new approaches to the management and treatment of NAFLD.

Diabetes and Hepatitis C: A Two-Way Association

Diabetes and hepatitis C infection are both prevalent diseases worldwide, and are associated with increased morbidity and mortality. Most studies, but not all, have shown that patients with chronic hepatitis C are more prone to develop type 2 diabetes (T2D) compared to healthy controls, as well as when compared to patients with other liver diseases, including hepatitis B. Furthermore, epidemiological studies have revealed that patients with T2D may also be at higher risk for worse outcomes of their hepatitis C infection, including reduced rate of sustained virological response, progression to fibrosis and cirrhosis, and higher risk for development of hepatocellular carcinoma. Moreover, hepatitis C infection and mainly its treatment, interferon α, can trigger the development of type 1 diabetes. In this review, we discuss the existing data on this two-way association between diabetes and hepatitis C infection with emphasis on possible mechanisms. It remains to be determined whether the new curative therapies for chronic hepatitis C will improve outcomes in diabetic hepatitis C patients, and conversely whether treatment with Metformin will reduce complications from hepatitis C virus infection. We propose an algorithm for diabetes screening and follow-up in hepatitis C patients.