Journal Logo

Diabetes and the endocrine pancreas I: Edited by Allison B. Goldfine

Nonalcoholic fatty liver disease in type 2 diabetes mellitus

Cusi, Kenneth

Author Information
Current Opinion in Endocrinology, Diabetes and Obesity: April 2009 - Volume 16 - Issue 2 - p 141-149
doi: 10.1097/MED.0b013e3283293015
  • Free

Abstract

Introduction

Nonalcoholic fatty liver disease is a chronic liver condition characterized by insulin resistance and hepatic fat accumulation, in the absence of other identifiable causes of fat accumulation, such as alcohol abuse, viral hepatitis, autoimmune hepatitis, alpha-1 antitrypsin deficiency, medications like corticosteroids and estrogens, and other conditions [1••]. Hepatic steatosis may range from a ‘benign’ indolent deposition of fat to severe lipotoxicity-induced steatohepatitis with necroinflammation [known as nonalcoholic steatohepatitis (NASH)] (Table 1). NASH is an overlooked complication of type 2 diabetes mellitus (T2DM) that if missed may carry serious long-term consequences. NASH is frequently associated with fibrosis and approximately 10% of patients develop cirrhosis. The risk of hepatocellular carcinoma is also increased in patients with T2DM and NASH [2•]. Diabetes, dyslipidemia, hypertension, and cardiovascular disease (CVD) occur more frequently in individuals with NAFLD [3••]. NAFLD may also be associated with a greater risk of renal disease in patients with T2DM [4]. Health care costs have been long suspected to be higher in NASH patients, a finding recently confirmed in a large cohort of 4224 from Western Germany [5].

Table 1
Table 1:
Clinical features of NAFLD and NASH

Unfortunately, clinicians are frequently unaware that patients with T2DM are uniquely prone to NASH because the disease is associated with few symptoms, there is a lack of sensitive noninvasive diagnostic tests, and physicians usually just rely on liver transaminases to diagnose liver disease. However, alanine aminotransferase (ALT) or aspartate aminotransferase (AST) are normal in most patients with NASH. Another limiting diagnostic factor is that the distinction between benign steatosis or active NASH can only be done by performing a liver biopsy, a procedure that both patients and doctors are reluctant to pursue. However, recent work has broadened our understanding of the disease and offered new treatments, suggesting that it will not be long before screening for fatty liver disease, either noninvasively or in selected cases with a liver biopsy, will be incorporated into our routine evaluation of patients in the same way that we currently do for other chronic complications of diabetes.

Type 2 diabetes: a major risk factor for NASH

Using the gold-standard magnetic resonance and spectroscopy (MRS) technique for the noninvasive assessment of hepatic steatosis, the prevalence of NAFLD (defined as liver fat >5%) has been estimated to be 34% in the USA or approximately 70–80 million people [6]. This prevalence is, however, believed to be much higher in T2DM. In our laboratory, the prevalence of NAFLD by MRS in 107 unselected patients with T2DM was 76% [7], which is similar to recent studies from Italy [8] and Brazil [9]. Of note, most diabetic patients had normal liver transaminases [7]. A normal AST and ALT is consistent with earlier studies suggesting that liver transaminases are frequently not increased even in the presence of advanced fibrosis and cirrhosis [10–12]. This has been confirmed recently in a large cohort of 458 Italian patients with biopsy-proven NASH [13•]. In this study, NASH was diagnosed in 59 and 74% of the patients with normal and increased ALT, respectively. Diabetes was the single most important predictor of NASH and fibrosis. In only those with normal ALT, NASH was strongly predicted by insulin resistance [odds ratio (OR) = 1.97; 95% confidence interval (CI) 1.2–3.7]. Therefore, normal ALT levels should not preclude the clinician from pursuing an histological diagnosis if the disease is suspected. Considering that up to 40% of adults with NAFLD have progressive liver damage [1••] and that the majority of patients with cryptogenic cirrhosis are diabetic [14,15•], it follows that NASH in T2DM must be frequently missed until it is too late and end-stage liver disease develops.

In the largest (n = 129) and longest follow-up (13.7 ± 1.3 years) study of patients with NASH, Ekstedt et al.[16] reported that survival was significantly reduced. Decreased survival was due to cardiovascular and liver-related causes, including end-stage liver disease (5.4%) and hepatocellular carcinoma (2.3%). In a recent study in children with NAFLD (mean age = 13.4 years) 40% had progression of fibrosis in a follow-up liver biopsy at 28 months [17]. This is of concern as the prevalence of NAFLD is rapidly increasing in children and adolescents, particularly in Hispanics [18]. Once again, it is likely that NASH may develop early in life in an increasing number of children and that the window of opportunity for intervention is overlooked by many physicians.

As with adults, metabolic syndrome (MetS) is common in children with NAFLD [19•,20] and is a strong predictor of future NASH and fibrosis [1••]. In a recent large analysis in 827 patients, advanced fibrosis was closely related to obesity, insulin resistance, and diabetes [21•]. Obesity and T2DM share a ‘metabolic soil’ that promotes hepatocyte lipotoxicity: adipose tissue insulin resistance, subclinical inflammation, hyperinsulinemia, and abnormal glucose metabolism [22]. Perseghin et al.[23] recently reported an association between hepatic and cardiac triglyceride accumulation, with a close correlation between the development of NAFLD and abnormalities in left ventricular energy metabolism. Of interest, treatment with pioglitazone reduces both hepatic and myocardial steatosis [24], suggesting that lipotoxicity is a common metabolic abnormality to both tissues.

Recent developments in the diagnosis of NASH

Nonalcoholic fatty liver disease is most commonly diagnosed by a combination of clinical, laboratory, and imaging studies (Table 1). Ultrasound is the most widely used imaging tool, but its sensitivity is poor at low to moderate degrees of steatosis and it decreases further with increasing central adiposity [1••,25]. At present, MRS is the most reliable imaging technique for hepatic fat steatosis [6,26,27], having found in our hands a close correlation with fat estimated from liver biopsies in patients with NASH (K. Cusi, et al., unpublished). Unfortunately, no imaging technique can replace a liver biopsy to confirm the diagnosis of NASH. A liver biopsy may be a reasonable approach to diagnose NASH and stage the disease in individuals who are at the highest risk of disease progression such as in obesity, metabolic syndrome, and/or T2DM, if the information obtained will prompt a more aggressive treatment approach.

There is an active search for more practical ways to study the large numbers of patients with NAFLD and T2DM. Efforts include the use of plasma biomarkers [28–30,31••] and imaging by transient elastography [32•,33]. A promising biomarker is the measurement of plasma cytokeratin-18 fragments (marker of hepatocyte apoptosis), which has been reported to be increased in patients with NASH compared to those with simple steatosis or normal livers [34] and reduced with pioglitazone treatment in association with histological improvement. The use of transient elastography has recently shown a good correlation between liver ‘stiffness’ by this imaging technique and fibrosis stage [35], including in pediatric populations [36••]. These approaches are promising but await more definitive validation in larger and more diverse populations.

NAFLD: role of adipose tissue insulin resistance, fatty acids, and lipotoxicity

Defects at multiple levels may tip the metabolic balance towards hepatic fat accumulation: excessive substrate supply to the liver (i.e. fatty acids, glucose); intrahepatic mismatch between lipid synthesis and oxidation; inadequate export to peripheral tissues; and a combination of the above. Many molecular defects at these different steps have been described in NAFLD but exceed the scope of this brief review [37–42]. Among the metabolic defects, chronic hyperinsulinemia and hyperglycemia as observed in T2DM are of paramount importance as they promote lipogenesis by upregulating hepatic sterol regulatory element binding protein 1c (SREBP1c) and carbohydrate regulatory element binding protein (ChREBP) activity, respectively. High carbohydrate/fructose-based diets promote de novo lipogenesis and activate harmful inflammatory pathways [i.e. c-jun N-terminal kinase (JUN)-signaling pathway] with hepatocyte apoptosis [43]. Increased consumption of dietary carbohydrates is common in patients with NAFLD and has been recently associated with increased hepatic mRNA expression of fructokinase, a key enzyme for fructose metabolism, and in fatty acid synthase, an important lipogenic enzyme [44]. Restriction of dietary carbohydrates reduces hepatic fat [45] and elevated ALT [46] in obese patients with NAFLD.

In T2DM excessive rates of lipolysis from insulin-resistant adipose tissue is also a driving force for the development of steatosis [22,47•,48]. Adipocytes account for approximately 60–70% of the free fatty acid (FFA) used for hepatic triglyceride synthesis and very low-density lipoprotein (VLDL) secretion [49]. Many factors that regulate VLDL metabolism may promote steatosis. For example, the activity of stearoyl-CoA desaturase 1 (SCD1), a rate-limiting enzyme in monounsaturated fatty acid synthesis essential for the assembly of VLDL particles, has been reported to be low in obese patients with NAFLD [50]. Down-regulation of hepatic tumor suppressor phosphatase and tensin homolog (PTEN) by unsaturated fatty acids induces steatosis by impairing insulin signaling and affecting incorporation, esterification, and extracellular release of fatty acids, including the alteration of hepatic apoB-lipoprotein production and microsomal triglyceride transfer protein (MTP) stability [51,52]. These effects are mediated by a cross-talk between the mammalian target of rapamycin (mTOR) and NF-κB [51]. In contrast to these studies, blocking VLDL secretion alone in a mouse model of hepatic steatosis lacking MTP caused hepatic steatosis, but not hepatic necroinflammation, NF-κB activation, or insulin resistance [53]. Taken together, these studies highlight the complex interplay between steatosis, hepatic insulin resistance, and tissue damage in NASH.

Liver steatosis may also be due to an altered composition of hepatic fat. Recently, Puri et al.[54•] reported an increased content of triacylglycerol (TAG), diacylglycerol (DAG), and of free cholesterol in NASH patients. A cholesterol-rich diet promotes steatohepatitis with activation of NF-κB signaling in hyperlipidemic mouse models [55], and mitochondrial toxicity with outer mitochondrial membrane permeabilization, cytochrome c release, caspase-3 activation, and hepatocellular death from mitochondrial glutathione depletion induced by free cholesterol [56]. However, more attention has been recently placed on the toxic role of saturated FFA in the development of NASH. Human hepatocytes incubated with unsaturated fatty acids accumulate large amounts of triglyceride without harm, but saturated fatty acids (i.e. palmitate) readily cause endoplasmic reticulum stress and apoptosis, as they are poorly incorporated into triglyceride [57]. Fatty acids impair insulin signaling and activate proinflammatory serine/threonine kinases and the Iκβ/NF-κB pathway, promote the accumulation of DAG, and enhance the expression of cytokines such as TNF-α and IL-1β [22]. Unsaturated fatty acids prevent palmitate-induced apoptosis by channeling palmitate into less harmful triglyceride pools and away from apoptotic pathways [58]. Inhibition of acyl-coenzyme A:diacylglycerol acyltransferase (DGAT) 2 (the enzyme that catalyzes the final step in triglyceride synthesis) in obese, diabetic db/db mice fed a methionine-choline-deficient (MCD) diet reduces steatosis at the expense of exacerbating oxidative stress, liver injury, and fibrosis [40]. Therefore, it appears that the target of treatment may not be steatosis per se but the prevention of saturated fatty acid formation and lipotoxicity-induced mitochondrial damage. Saturated fatty acids induce mitochondrial dysfunction and oxidative stress by mechanisms dependent on lysosomal disruption and activation of cathepsin B [41]. As proof-of-concept it has been recently shown that fatty acid-induced mitochondrial oxidative stress and hepatocyte apoptosis could be prevented by glycyrrhizin, the major bioactive component of licorice root extract, by stabilizing lysosomal membranes and inhibiting cathepsin B activity [59]. We have found that it is the combination of elevated plasma FFA and insulin levels, as compared to either factor alone or hyperglycemia, that causes the greatest degree of hepatic steatosis and mitochondrial dysfunction in rodents [60•], pointing to the value of therapies that can reverse lipotoxicity for the prevention of NASH.

From adipose tissue insulin resistance to NASH: the failure to adapt to a lipotoxic environment

From the above, one may conceptually delineate several steps in the development of NASH. Still, our data are fragmented and arise largely from rodents given the natural difficulties of accessing human liver tissue. One must keep in mind that there are significant metabolic/molecular differences between livers from humans and rodents, and even between rodent species. With these limitations in mind, Fig. 1 is an effort to organize our current understanding of NAFLD and NASH in a schematic framework for hypothesis generation and future testing. This is obviously subject to rapid change as new information emerges. A prerequisite or ‘first step’ for NASH appears to be adipose tissue insulin resistance, providing the necessary ‘lipotoxic environment’ that ensures ample substrate supply to the liver (i.e. high FFA flux) and compensatory hyperinsulinemia that stimulates lipogenesis. The ‘second step’ towards NASH is the development of hepatic steatosis and of a lipid pool from where lipid-derived toxic metabolites may activate inflammatory pathways. Dietary and genetic factors [61,62•] may condition the metabolic adaptation of the liver to this harmful environment, particularly of several mitochondrial-related energy regulators, such as 5′ AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α, peroxisome proliferator-activated receptor- (PPAR)- γ, PPAR-α, and others, such as adiponectin [63,64]. Plasma adiponectin levels are low in patients with T2DM with NASH [26]. Administration of adiponectin to steatotic mice dramatically alleviates hepatomegaly, fat accumulation, and inflammation by increasing carnitine palmitoyltransferase (CPT)-I activity and enhancing hepatic fatty acid oxidation while inhibiting fatty acid synthesis [65]. Zhou et al.[66] recently reported that in adiponectin knockout mice impaired mitochondrial respiratory chain (MRC) activity can be completely overturned by adiponectin replenishment, with reversal of steatosis, accumulation of lipid peroxidation products, and down-regulation of uncoupling protein 2 (UCP2). The ‘third step’ for the progression from simple ‘bland’ steatosis to active necroinflammation depends on the ability of the liver to adapt to longstanding triglyceride accumulation. Failure would lead to FFA-induced lipotoxicity with mitochondrial dysfunction, endoplasmic reticulum stress, reactive oxygen species (ROS) formation, and chronic necroinflammation. Fibrosis is the final or ‘fourth step’, involving chronic activation of hepatic stellate cells in a yet poorly understood cross-talk of Kupffer cells with hepatocytes [38]. Of note, recent evidence indicates that adiponectin inhibits effect hepatic stellate cell activation [67], highlighting a potential therapeutic target and the multiple roles of this hormone in NASH.

Figure 1
Figure 1:
Proposed framework on the progression from adipose tissue insulin resistance to NAFLD and NASH

Treatment of NAFLD

The current view of NAFLD as a serious condition with potential for considerable morbidity and mortality has stimulated the search for strategies ranging from lifestyle changes to a variety of pharmacological interventions.

Weight loss and lifestyle intervention

Most weight-loss studies in NAFLD/NASH are pilot studies of short duration (2–12 months) and limited success, reporting a decrease in hepatic steatosis and liver transaminases, but with modest improvement in necroinflammation or fibrosis [26,68,69•]. Reduction of visceral fat may be a particularly important target, as recent studies suggest a close relationship between visceral fat and hepatic steatosis [26,27], as well as with inflammation, and even fibrosis [26,27,70].

Bariatric surgery is gaining momentum for the treatment of obesity associated with comorbidities such as T2DM and NASH, with long-term reports of reduction in overall mortality [71]. In NASH, results have been encouraging in terms of histological improvement [72] and are not associated with a paradoxical exacerbation of liver inflammation and fibrosis as reported in earlier series [73].

Pharmacological interventions in NAFLD and NASH

As listed in Table 2, a number of pharmacological interventions have been tried in NAFLD/NASH but with overall limited benefit [1••]. Antioxidant agents may arrest lipid peroxidation and cytoprotective agents stabilize phospholipid membranes, but agents tried unsuccessfully or with modest benefit so far include: ursodeoxycholic acid [74,75], vitamin E (α tocopherol) and C [76–78], and pentoxifilline [79], among others. Weight-loss agents such as orlistat have had no significant benefit compared to weight loss alone [80,81]. Recent interest in angiotensin receptor blockers (ARBs) arises from their potential to modulate activated hepatic stellate cells responsible for collagen synthesis and hepatic fibrosis. Kurita et al.[82] recently reported that in obese, diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats, olmesartan reversed steatohepatitis and fibrosis induced by a MCD diet. A modest effect on ALT and/or fibrosis has been reported in recent small studies with losartan [83], olmesartan [84,85], and telmisartan [84,86], although no randomized controlled trials are yet available. Inhibition of transforming growth factor (TGF)-beta (which activates hepatic stellate cells) appears as another interesting target. In obese diabetic OLETF rats the anti-TGF-beta agent Tranilast or N-(3′,4′-dimethoxycinnamoyl)-anthranilic acid successfully prevented activation of hepatic stellate cells, down-regulated the expression of TGF-beta and TNF-α-dependent genes, and attenuated hepatic steatosis, inflammation, and fibrosis [87].

Table 2
Table 2:
Clinical trials with pharmacological agents in NAFLD/NASH

Statins have not been examined in large controlled prospective trials, but their use appears to be overall safe if patients with NASH are closely followed [88–90]. In small uncontrolled trials modest or no benefit has been reported with the use of other lipid-lowering agents such as fibrates [91], omega-3 fatty acids [92], or probucol, a lipid-lowering drug with antioxidant effects [93].

The shared metabolic abnormalities of T2DM and NAFLD help explain the greater success in NASH of agents used to treat diabetes. Metformin [94] improves elevated AST/ALT and steatosis [95–100] and to a lesser extent inflammation [97,100]. However, not all studies have seen a reduction in steatosis with metformin [101]. We have recently found that intensive insulin therapy (basal and premeal rapid-acting insulin) in patients with T2DM and NAFLD significantly reduces hepatic steatosis as assessed by MRS [102], and that the substitution of premeal insulin for exenatide twice daily for 6 months can further lower hepatic fat content [103].

However, thiazolidinediones (TZDs) have attracted the most attention for the treatment of NASH [104•]. Early small pilot studies with TZDs met variable success [78,105,106]. In the first randomized, double-blind, placebo-controlled trial (RCT), we were able to show that 6 months of pioglitazone treatment improved glycemic control, insulin sensitivity, systemic inflammation [plasma C-reactive protein (hsCRP), TNF-α, and TGF-β, among others], and liver histology in patients with NASH and impaired glucose tolerance (IGT) or T2DM [26]. Treatment ameliorated adipose, hepatic, and muscle insulin resistance and was associated with a significant approximately 50% decrease in necroinflammation (P < 0.002) and a 37% reduction of fibrosis within the pioglitazone-treated group, although this did not reach statistical significance when compared with placebo (P = 0.08) (Fig. 2). These results generated considerable interest on the role of TZDs in NASH [107,108]. Improvement in hepatocellular injury and fibrosis has been recently reported in another controlled trial with pioglitazone [109•]. Importantly, there was no alteration in total body water volume or water retention in our clinical trial when measured by three different state-of-the-art techniques, suggesting that its use is overall safe in this population in the absence of preexisting heart failure [110].

Figure 2
Figure 2:
Mean scores for inflammation, ballooning necrosis, steatosis, and fibrosis in liver biopsies before and after a hypocaloric diet (−500 kcal/day) and pioglitazone or a hypocaloric diet and placebo in 55 patients with IGT or T2DM and NASH

In the first RCT with rosiglitazone in NASH, this TZD also reduced plasma ALT levels and steatosis, but had no significant effect on necrosis, inflammation, or fibrosis [111•]. A preliminary report of the 2-year, open-label follow-up of this trial has also been disappointing with no significant benefit from rosiglitazone treatment [112]. The reasons for these discrepant results compared to pioglitazone remain unclear, but may include intrinsic pharmacological differences (i.e. as shown for their cardiovascular profile) or in the populations studied [104•]. Ongoing longer-term clinical trials with pioglitazone in predominantly nondiabetic (PIVENS trial) or diabetic (K. Cusi, et al., unpublished) patients will teach us more about the long-term safety and efficacy of TZDs in NASH.

Conclusion

Nonalcoholic fatty liver disease is no longer considered a benign condition in patients with T2DM. The possibility of fatty liver disease should be entertained as a part of the routine evaluation of patients with T2DM, in the same way we search for microvascular complications and CVD. Awareness by healthcare providers is essential for an early diagnosis and timely implementation of lifestyle and pharmacological interventions. A normal plasma ALT or AST level should not mislead clinicians into dismissing the possibility of fatty liver disease as transaminases in most patients are not elevated. New laboratory and imaging tests promise to make the diagnosis easier than at the present time and minimize the need for a liver biopsy. Thiazolidinediones are emerging as promising agents for the treatment of NASH. However, more information is needed about their long-term safety and efficacy before the use of TZDs can be routinely recommended.

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

• of special interest

•• of outstanding interest

Additional references related to this topic can also be found in the Current World Literature section in this issue (pp. 194–195).

1•• Ali R, Cusi K. New diagnostic and treatment approaches in nonalcoholic fatty liver disease (NAFLD). Ann Med 2009. [Epub ahead of print]. http://dx.doi.org/10.1080/07853890802552437 Comprehensive overview of the risk factors for the development of NASH with emphasis on future diagnostic and treatment approaches.
2• Bugianesi E, Vanni E, Marchesini G. NASH and the risk of cirrhosis and hepatocellular carcinoma in type 2 diabetes. Curr Diab Rep 2007; 7:175–180. Detailed review about the close relationship in patients with diabetes between NASH, cirrhosis and hepatocellular carcinoma.
3•• Targher G, Marra F, Marchesini G. Increased risk of cardiovascular disease in nonalcoholic fatty liver disease: causal effect or epiphenomenon? Diabetologia 2008; 51:1947–1953. Review assessing the cluster of cardiovascular risk factors associated with NAFLD and the specific risk associated with the presence of fatty liver.
4 Targher G, Chonchol M, Bertolini L, et al. Increased risk of CKD among type 2 diabetics with nonalcoholic fatty liver disease. J Am Soc Nephrol 2008; 19:1564–1570.
5 Baumeister SE, Völzke H, Marschall P, et al. Impact of fatty liver disease on healthcare utilization and costs in a general population: a 5-year observation. Gastroenterology 2008; 134:85–94.
6 Browning JD, Szczepaniak LS, Dobbins R, et al. Prevalence of hepatic steatosis in an urban population in the United States: impact of ethnicity. Hepatology 2004; 40:1387–1395.
7 Chen J, Mathew M, Finch J, Cusi K. The prevalence of NAFLD in T2DM is highest among Hispanics and is closely related to hepatic and adipose tissue insulin resistance [abstract]. Diabetes 2009; 58 (Suppl 1).
8 Targher G, Lorenzo B, Roberto P, et al. Prevalence of nonalcoholic fatty liver disease and its association with cardiovascular disease among type 2 diabetic patients. Diabetes Care 2007; 30:1212–1218.
9 Leite N, Salles G, Araujo A, Villela-Nogueira C, Cardoso C. Prevalence and associated factors of nonalcoholic fatty liver disease in patients with type-2 diabetes mellitus. Liver Int 2009; 29:113–119.
10 Mofrad P. Clinical and histologic spectrum of nonalcoholic fatty liver disease associated with normal ALT values. Hepatology 2003; 37:1286–1292.
11 Sorrentino P. Silent nonalcoholic fatty liver disease-a clinical-histological study. J Hepatol 2004; 41:751–757.
12 Amarapurkar D, Patel N. Clinical spectrum and natural history of nonalcoholic steatohepatitis with normal alanine aminotransferase values. Trop Gastroenterol 2004; 25:130–134.
13• Fracanzani A, Valenti L, Bugianesi E, et al. Risk of severe liver disease in nonalcoholic fatty liver disease with normal aminotransferase levels: a role for insulin resistance and diabetes. Hepatology 2008; 48:792–798. Valuable study in a large cohort of patients with NASH about the possibility of significant liver disease in NASH even in the presence of normal liver transaminases.
14 Maheshwari A, Paul JT. Cryptogenic cirrhosis and NAFLD: are they related? Am J Gastroenterol 2006; 101:664–668.
15• Caldwell S, Lee V. Cryptogenic cirrhosis. AASLD Postgraduate Course 2008; 2008:48–57. State-of-the-art review on cryptogenic cirrhosis and its frequent association with obesity and T2DM.
16 Ekstedt M, Franzén L, Mathiesen U, et al. Long-term follow-up of patients with NAFLD and elevated liver enzymes. Hepatology 2006; 44:865–873.
17 A-Kader H, Henderson J, Vanhoesen K, et al. Nonalcoholic fatty liver disease in children: a single center experience. Clin Gastroenterol Hepatol 2008; 6:799–802.
18 Schwimmer J. Definitive diagnosis and assessment of risk for nonalcoholic fatty liver disease in children and adolescents. Semin Liver Dis 2007; 27:312–318.
19• Schwimmer J, Pardee P, Lavine J, et al. Cardiovascular risk factors and the metabolic syndrome in pediatric nonalcoholic fatty liver disease. Circulation 2008; 118:277–283. Highlights the early development of cardiovascular risk factors in children with NAFLD.
20 Demircioglu F, Kocyigit A, Arslan N, et al. Intima-media thickness of carotid artery and susceptibility to atherosclerosis in obese children with nonalcoholic fatty liver disease. J Pediatric Gastroenterol Nutr 2008; 47:68–75.
21• Harrison S, Oliver D, Arnold H, et al. Development and validation of a simple NAFLD clinical scoring system for identifying patients without advanced disease. Gut 2008; 57:1441–1447. Valuable examination of risk factors in a large population of patients with NAFLD.
22 Cusi K. Evolving concepts in lipotoxicity. AASLD Postgraduate Course 2008; 2008:72–84.
23 Perseghin G, Lattuada G, De Cobelli F, et al. Increased mediastinal fat and impaired left ventricular energy metabolism in young men with newly found fatty liver. Hepatology 2008; 47:51–58.
24 Zib I, Jacob A, Lingvay I, et al. Effect of pioglitazone therapy on myocardial and hepatic steatosis in insulin-treated patients with type 2 diabetes. J Investig Med 55:ePub (electronic version); 2007.
25 Mehta SR, Thomas EL, Bell JD, et al. Noninvasive means of measuring hepatic fat content. World J Gastroenterol 2008; 14:3476–3483.
26 Belfort R, Harrison SA, Brown K, et al. A placebo-controlled trial of pioglitazone in subjects with nonalcoholic steatohepatitis. N Engl J Med 2006; 355:2297–2307.
27 Gastaldelli A, Cusi K, Pettiti M, et al. Relationship between hepatic/visceral fat and hepatic insulin resistance in nondiabetic and type 2 diabetic subjects. Gastroenterology 2007; 133:496–506.
28 Poynard T, Ratziu V, Charlotte F, et al, and the LIDO study group, and the CYTOL study group. Diagnostic value of biochemical markers (NashTest) for the prediction of non alcoholic steatohepatitis in patients with nonalcoholic fatty liver disease. BMC Gastroenterol 2006; 6:34.
29 Ratziu V, Massard J, Charlotte F, et al, and the LIDO study group, and the CYTOL study group. Diagnostic value of biochemical markers (FibroTest-FibroSURE) for the prediction of liver fibrosis in patients with nonalcoholic fatty liver disease. BMC Gastroenterol 2006; 6:6.
30 Angulo P, Hui J, Marchesini G, et al. The NAFLD fibrosis score: a noninvasive system that identifies liver fibrosis in patients with NAFLD. Hepatology 2007; 45:846–854.
31•• Wieckowska A, McCullough A, Feldstein A. Noninvasive diagnosis and monitoring of nonalcoholic steatohepatitis: present and future. Hepatology 2007; 46:582–589. Excellent review on the current role and future potential of plasma biomarkers for the management of NAFLD and NASH.
32• Friedrich-Rust M, Ong MF, Martens S, et al. Performance of transient elastography for the staging of liver fibrosis: a meta-analysis. Gastroenterology 2008; 134:960–974. Comprehensive review on the role of this imaging technique from the available literature.
33 Castera L, Forns X, Alberti A. Noninvasive evaluation of liver fibrosis using transient elastography. J Hepatol 2008; 48:835–847.
34 Wieckowska A, McCullough A, Feldstein A, et al. In vivo assessment of liver cell apoptosis as a novel biomarker of disease severity in nonalcoholic fatty liver disease. Hepatology 2006; 44:27–33.
35 Yoneda M, Mawatari H, Fujita K, et al. Noninvasive assessment of liver fibrosis by measurement of stiffness in patients with nonalcoholic fatty liver disease (NAFLD). Digest Liver Dis 2008; 40:371–378.
36•• Nobili V, Vizzutti F, Arena U, et al. Accuracy and reproducibility of transient elastography for the diagnosis of fibrosis in pediatric nonalcoholic steatohepatitis. Hepatology 2008; 48:442–448. The following (ref.
36•• [37–42] The following (ref.
37 Pessayre D. Role of mitochondria in nonalcoholic fatty liver disease. J Gastroenterol Hepatol 2007; 22:S20–S27.
38 Elsharkawy A, Mann D. Nuclear factor-kappaB and the hepatic inflammation-fibrosis-cancer axis. Hepatology 2007; 46:590–597.
39 Greenfield V, Cheung O, Sanyal A. Recent advances in nonalcholic fatty liver disease. Curr Opin Gastroenterol 2008; 24:320–327.
40 Choi SS, Diehl AM. Hepatic triglyceride synthesis and nonalcoholic fatty liver disease. Curr Opin Lipidol 2008; 19:295–300.
41 Li Z, Berk M, McIntyre TM, et al. The lysosomal-mitochondrial axis in free fatty acid-induced hepatic lipotoxicity. Hepatology 2008; 47:1495–1503.
42 Marra F, Gastaldelli A, Svegliati Baroni G, et al. Molecular basis and mechanisms of progression of nonalcoholic steatohepatitis. Trends Mol Med 2008; 14:72–81.
43 Wei Y, Wang D, Topczewski F, Pagliassotti M. Fructose-mediated stress signaling in the liver: implications for hepatic insulin resistance. J Nutr Biochem 2007; 18:1–9.
44 Ouyang X, Cirillo P, Sautin Y, et al. Fructose consumption as a risk factor for nonalcoholic fatty liver disease. J Hepatol 2008; 48:993–999.
45 Tendler D, Lin S, Yancy WS Jr, et al. The effect of a low-carbohydrate, ketogenic diet on nonalcoholic fatty liver disease: a pilot study. Digest Dis Sci 2007; 52:589–593.
46 Ryan MC, Abbasi F, Lamendola C, et al. Serum alanine aminotransferase levels decrease further with carbohydrate than fat restriction in insulin-resistant adults. Diabetes Care 2007; 30:1075–1080.
47• Adiels M, Taskinen M-R, Boren J. Fatty liver, insulin resistance, and dyslipidemia. Curr Diabetes Rep 2008; 8:60–64. Excellent review on the topic.
48 Korenblat KM, Fabbrini E, Mohammed BS, Klein S. Liver, muscle, and adipose tissue insulin action is directly related to intrahepatic triglyceride content in obese subjects. Gastroenterology 2008; 134:1369–1375.
49 Donnelly KL, Smith CI, Schwarzenberg SJ, et al. Sources of fatty acids stored in liver and secreted via lipoproteins in patients with nonalcoholic fatty liver disease. J Clin Invest 2005; 115:1343–1351.
50 Stefan N, Peter A, Cegan A, et al. Low hepatic stearoyl-CoA desaturase 1 activity is associated with fatty liver and insulin resistance in obese humans. Diabetologia 2008; 51:648–656.
51 Vinciguerra M, Veyrat-Durebex C, Moukil MA, et al. PTEN down-regulation by unsaturated fatty acids triggers hepatic steatosis via an NF-kappaBp65/mTOR-dependent mechanism. Gastroenterology 2008; 134:268–280.
52 Qiu W, Federico L, Naples M, et al. Phosphatase and tensin homolog (PTEN) regulates hepatic lipogenesis, microsomal triglyceride transfer protein, and the secretion of apolipoprotein B-containing lipoproteins. Hepatology 2008; 48:1799–1809.
53 Minehira K, Young SG, Villanueva CJ, et al. Blocking VLDL secretion causes hepatic steatosis but does not affect peripheral lipid stores or insulin sensitivity in mice. J Lipid Res 2008; 49:2038–2044.
54• Puri P, Baillie RA, Wiest MM, et al. A lipidomic analysis of nonalcoholic fatty liver disease. Hepatology 2007; 46:1081–1090. Provocative study on the role of different types of lipids in the development of NASH using novel techniques in the field.
55 Wouters K, van Gorp PJ, Bieghs V, et al. Dietary cholesterol, rather than liver steatosis, leads to hepatic inflammation in hyperlipidemic mouse models of nonalcoholic steatohepatitis. Hepatology 2008; 48:474–486.
56 Mari M, Colell A, Morales A, et al. Mechanism of mitochondrial glutathione-dependent hepatocellular susceptibility to TNF despite NF-kappaB activation. Gastroenterology 2008; 134:1507–1520.
57 Gentile C, Pagliassotti M. The endoplasmic reticulum as a potential therapeutic target in nonalcoholic fatty liver disease. Curr Opin Investig Drugs 2008; 9:1084–1088.
58 Listenberger L, Han X, Lewis S, et al. Triglyceride accumulation protects against fatty acid-induced lipotoxicity. Proc Natl Acad Sci U S A 2003; 100:3077–3082.
59 Wu X, Zhang L, Gurley E, et al. Prevention of free fatty acid-induced hepatic lipotoxicity by 18 beta-glycyrrhetinic acid through lysosomal and mitochondrial pathways. Hepatology 2008; 47:1905–1915.
60• Wang S, Kamat A, Swamy A, et al. Hepatic steatosis is associated with mitochondrial dysfunction in obese and diabetic rats [abstract]. Diabetes 2008; 55 (Suppl 1). Study dissecting the role of FFA, glucose, and insulin in the induction of mitochondrial dysfunction in rodent models of NAFLD.
61 Greco D, Kotronen A, Westerbacka J, et al. Gene expression in human NAFLD. Am J Physiol Gastrointest Liver Physiol 2008; 294:G1281–G1287.
62• Mark N, deAlwis W, Day C. Genes and nonalcoholic fatty liver disease. Curr Diabetes Rep 2008; 8:156–163. Comprehensive review on the different genes reported to be involved in the development of NAFLD.
63 Musso G, Gambino R, De Michieli F, et al. Adiponectin gene polymorphisms modulate acute adiponectin response to dietary fat: possible pathogenetic role in NASH. Hepatology 2008; 47:1167–1177.
64 Tomita K, Oike Y, Teratani T, et al. Hepatic AdipoR2 signaling plays a protective role against progression of nonalcoholic steatohepatitis in mice. Hepatology 2008; 48:458–473.
65 Xu A, Wang Y, Keshaw H, et al. The fat-derived hormone adiponectin alleviates alcoholic and nonalcoholic fatty liver diseases in mice. J Clin Invest 2003; 112:91–100.
66 Zhou M, Xu A, Tam PK, et al. Mitochondrial dysfunction contributes to the increased vulnerabilities of adiponectin knockout mice to liver injury. Hepatology 2008; 48:1087–1096.
67 Ding X, Saxena NK, Lin S, et al. The roles of leptin and adiponectin: a novel paradigm in adipocytokine regulation of liver fibrosis and stellate cell biology. Am J Pathol 2005; 166:1655–1669.
68 Wang R, Koretz R, Yee H. Is weight reduction an effective therapy for nonalcoholic fatty liver? A systematic review. Am J Med 2003; 115:554–559.
69• Harrison S, Day C. Benefits of lifestyle modification in NAFLD. Gut 2007; 56:1760–1769. Excellent review on the topic.
70 van der Poorten D, Milner KL, Hui J, et al. Visceral fat: a key mediator of steatohepatitis in metabolic liver disease. Hepatology 2008; 48:449–457.
71 Sjostrom L, Narbro K, Sjostrom CD, et al, the Swedish Obese Subjects S. Effects of bariatric surgery on mortality in Swedish obese subjects. N Engl J Med 2007; 357:741–752.
72 de Freitas AC, Campos AC, Coelho JC. The impact of bariatric surgery on nonalcoholic fatty liver disease. Curr Opin Clin Nutr Metab Care 2008; 11:267–274.
73 Luyckx FH, Desaive C, Thiry A, et al. Liver abnormalities in severely obese subjects: effects of drastic weight loss after gastroplasty. Int J Obes Relat Metab Disord 1998; 22:222–226.
74 Lindor KD, Kowdley KV, Heathcote EJ, et al. Ursodeoxycholic acid for treatment of nonalcoholic steatohepatitis: results of a randomized trial. Hepatology 2004; 39:770–778.
75 Dufour JF, Oneta CM, Gonvers JJ, et al, and the Swiss Association for the Study of the Liver. Randomized placebo-controlled trial of ursodeoxycholic acid with vitamin E in nonalcoholic steatohepatitis. Clin Gastroenterol Hepatol 2006; 4:1537–1543.
76 Harrison SA, Torgerson S, Hayashi P, et al. Vitamin E and vitamin C treatment improves fibrosis in patients with nonalcoholic steatohepatitis [see comment]. Am J Gastroenterol 2003; 98:2485–2490.
77 Sanyal AJ, Mofrad PS, Contos MJ, et al. A pilot study of vitamin E versus vitamin E and pioglitazone for the treatment of nonalcoholic steatohepatitis. Clin Gastroenterol Hepatol 2004; 2:1107–1115.
78 Nobili V, Manco M, Devito R, et al. Lifestyle intervention and antioxidant therapy in children with nonalcoholic fatty liver disease: a randomized, controlled trial. Hepatology 2008; 48:119–128.
79 Adams LA, Zein CO, Angulo P, Lindor KD. A pilot trial of pentoxifylline in nonalcoholic steatohepatitis. Am J Gastroenterol 2004; 99:2365–2368.
80 Zelber-Sagi S, Kessler A, Brazowsky E, et al. A double-blind randomized placebo-controlled trial of orlistat for the treatment of nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol 2006; 4:639–644.
81 Harrison S, Fecht W, Brunt E, Neuschwander-Tetri B. Orlistat for overweight subjects with nonalcoholic steatohepatitis: a randomized, prospective trial. Hepatology 2009; 49:80–86.
82 Kurita S, Takamura T, Ota T, et al. Olmesartan ameliorates a dietary rat model of nonalcoholic steatohepatitis through its pleiotropic effects. Eur J Pharmacol 2008; 588:316–324.
83 Yokohama S, Tokusashi Y, Nakamura K, et al.: . Inhibitory effect of angiotensin II receptor antagonist on hepatic stellate activation in nonalcoholic steatohepatitis. World J Gastroenterol 2006; 12:322–326.
84 Enjoji M, Kotoh K, Kato M, et al. Therapeutic effect of ARBs on insulin resistance and liver injury in patients with NAFLD and chronic hepatitis C: a pilot study. Int J Mol Med 2008; 22:521–527.
85 Hirose A, Ono M, Saibara T, et al. Angiotensin II type 1 receptor blocker inhibits fibrosis in rat nonalcoholic steatohepatitis. Hepatology 2007; 45:1375–1381.
86 Jin H, Yamamoto N, Uchida K, et al. Telmisartan prevents hepatic fibrosis and enzyme-altered lesions in liver cirrhosis rat induced by a choline-deficient L-amino acid-defined diet. Biochem Biophys Res Commun 2007; 364:801–807.
87 Uno M, Kurita S, Misu H, et al. Tranilast, an antifibrogenic agent, ameliorates a dietary rat model of nonalcoholic steatohepatitis. Hepatology 2008; 48:109–118.
88 Liberopoulos EN, Athyros VG, Elisaf MS, Mikhailidis DP. Statins for nonalcoholic fatty liver disease: a new indication? Aliment Pharmacol Ther 2006; 24:698–699.
89 Argo K, Loria P, Caldwell S, Lonardo A. Statins in liver disease: a molehill, an iceberg, or neither? Hepatology 2008; 48:662–669.
90 Riley P, Sudarshi D, Johal M, et al. Weight loss, dietary advice and statin therapy in nonalcoholic fatty liver disease: a retrospective study. Int J Clin Pract 2008; 62:374–381.
91 Basaranoglu M, Acbay O, Sonsuz A. A controlled trial of gemfibrozil in the treatment of patients with nonalcoholic steatohepatitis. J Hepatol 1999; 31:384–1384.
92 Vega G, Chandalia M, Szczepaniak L, Grundy S. Effects of N-3 fatty acids on hepatic triglyceride content in humans. J Investig Med 2008; 56:780–785.
93 Merat S, Aduli M, Kazemi R, et al. Liver histology changes in nonalcoholic steatohepatitis after one year of treatment with probucol. Digest Dis Sci 2008; 53:2246–2250.
94 Cusi K, DeFronzo R. Metformin: a review of its metabolic effects. Diabetes Rev 1998; 6:89–131.
95 Marchensini G, Bianchi G, Tomassetti S, et al. Metformin in nonalcoholic steatohepatitis. Lancet 2001; 348:893–894.
96 Uygun A, Kadayifci A, Isik A, et al. Metformin in the treatment of patients with nonalcoholic steatohepatitis. Aliment Pharmacol Ther 2004; 19:537–544.
97 Bugianesi E, Gentilcore E, Manini R, et al. A randomized controlled trial of metformin versus vitamin E or prescriptive diet in nonalcoholic fatty liver disease. Am J Gastroenterol 2005; 100:1082–1090.
98 Lingvay I, Raskin P, Szczepaniak L. Effect of insulin-metformin combination on hepatic steatosis in patients with type 2 diabetes. J Diabetes Complications 2007; 21:137–142.
99 de Oliveira C, Stefano J, de Siqueira E, et al. Combination of N-acetylcysteine and metformin improves histological steatosis and fibrosis in patients with nonalcoholic steatohepatitis. Hepatol Res 2008; 38:159–165.
100 Nobili V, Manco M, Ciampalini P, Alisi A, Devito R, Bugianesi E, Marcellini M, Marchesini G. Metformin use in children with nonalcoholic fatty liver disease: an open-label, 24-month, observational pilot study. Clin Therap 2008; 30:1168–1176.
101 Tiikkainen M, Hakkinen A-M, Korsheninnikova E, et al. Effects of rosiglitazone and metformin on liver fat content, hepatic insulin resistance, insulin clearance, and gene expression in adipose tissue in patients with type 2 diabetes. Diabetes 2004; 53:2169–2176.
102 Mathew M, Ali R, Kumar P, et al. Intensive insulin therapy reduces hepatic steatosis and improves insulin secretion in T2DM [abstract]. Diabetes 2009; 58 (Suppl 1).
103 Mendoza C, Ali R, Mathew M, et al. Replacement of premeal insulin for exenatide reduces hepatic steatosis and improves insulin secretion in patients with T2DM [abstract]. Diabetes 2009; 58 (Suppl 1).
104• Cusi K. Thiazolidinediones for the treatment of nonalcoholic steatohepatitis (NASH). Exp Rev Gastroenterol Hepatol 2009; (in press). Comprehensive review on the mechanisms and potential role of TZDs for the management of NASH.
105 Caldwell SH, Hespenheide EE, Redick JA, et al. A pilot study of a thiazolidinedione, troglitazone, in nonalcoholic steatohepatitis. Am JGastroenterol 2001; 96:519–525.
106 Neuschwander-Tetri BA, Brunt EM, Kent R, et al. Improved nonalcoholic steatohepatitis after 48 weeks of treatment with the PPAR-γ ligand rosiglitazone. Hepatology 2003; 38:1008–1017.
107 Serfaty L. Pioglitazone: the beginning of a new era for NASH? J Hepatol 2007; 47:160–162.
108 Lang L. Pioglitazone trial for NASH: results show promise. Gastroenterology 2007; 132:836–838.
109• Aithal GP, Thomas JA, Kaye PV, et al. Randomized, placebo-controlled trial of pioglitazone in nondiabetic subjects with nonalcoholic steatohepatitis. Gastroenterology 2008; 135:1176–1184. A 12-month RCT of pioglitazone in NASH showing a significant effect on metabolic parameters, insulin sensitivity, and histological variables such as liver injury and fibrosis.
110 Balas B, Belfort R, Harrison S, et al. Pioglitazone treatment increases whole body fat but not total body water in patients with nonalcoholic steatohepatitis. J Hepatol 2007; 47:565–570.
111• Ratziu V, Giral P, Jacqueminet S, et al, Group TLS. Rosiglitazone for NASH: one year results of the randomized placebo-controlled fatty liver improvement with rosiglitazone therapy (FLIRT) trial. Gastroenterology 2008; 135:100–110. A 12-month RCT of rosiglitazone in NASH showing a significant effect on liver transaminases, insulin resistance, and steatosis.
112 Ratziu V, Charlotte F, Bernhard C, et al. Long-term efficacy of rosiglitazone in NASH: results of the extension phase of the FLIRT-2 trial. Hepatology 2008; 48:803A.
Keywords:

insulin resistance; nonalcoholic fatty liver disease; nonalcoholic steatohepatitis; pioglitazone; rosiglitazone; steatosis; thiazolidiendiones; type 2 diabetes

© 2009 Lippincott Williams & Wilkins, Inc.