Insulin resistance exhibits varied metabolic abnormalities in nonalcoholic fatty liver disease, chronic hepatitis B and the combination of the two: a cross-sectional study

Nonalcoholic fatty liver disease (NAFLD) and chronic hepatitis B (CHB) are the two most common types of liver diseases worldwide. The growing epidemic of NAFLD has reached over 26% of the world’s population [1], and chronic hepatitis B virus (HBV) infection affects over 300 million patients [2]. Notably, their overlap is also common, with a prevalence of up to 25–30% in CHB [3].

Metabolic risk factor burden, including abdominal obesity, hypertension, dyslipidemia, diabetes mellitus and hyperuricemia, has been verified to strongly affect the progression and even all-cause mortality of CHB and NAFLD [4, 5]. The constellation of metabolic disturbances may be more crucial than single components of metabolic syndrome in determining the long-term prognoses of both diseases. Therefore, the focus on the relationship among metabolic disturbance, HBV infection and NAFLD is growing. NAFLD predisposes individuals to the development of all metabolic comorbidities, whereas meta-analysis shows that patients with CHB have reduced risks of metabolic syndrome or some of its components compared to the general population [6]. However, in the context of complex interactions where hepatic steatosis and virologic backgrounds play opposite roles, the metabolic derangement effect of NAFLD on CHB remains unclear.

Insulin resistance (IR) is acknowledged as the physiological basis of metabolic syndrome and NAFLD and is characterized by an impairment of insulin-mediated glucose utilization in target tissues [7]. In insulin-resistant states, disrupted glucose homeostasis induces excess lipid substrate deposition in the liver, which is involved in the liver fibrosis progression and development of hepatocellular carcinoma of CHB [5, 7]. Moreover, increasing evidence indicates that IR and associated diabetes are overrepresented in CHB [8‐11]. For example, an increased association was observed between maternal HBsAg carrier status and risk development of gestational diabetes in a retrospective cohort [9]. Lu et al. also showed an increased frequency of HBV infection in type 2 diabetic patients but not in patients with adult-onset autoimmune diabetes [10]. Another cross-sectional study with a large sample size demonstrated that CHB status was independently associated with IR defined by homeostasis model assessment (HOMA) criteria or a quantitative insulin check index [12]. As noted, superimposed IR does not increase in parallel with metabolic syndrome in CHB patients, unlike NAFLD with IR, which increases the risk of metabolic abnormalities. This evidence suggests that IR may mediate distinct metabolic profiles in CHB with or without NAFLD. However, whether different types of liver diseases have the same metabolic consequences as the degree of IR increases or whether all of these metabolic components should be monitored aggressively for those patients with IR remains unclear.

Given the high prevalence of IR, metabolic syndrome, NAFLD and CHB, clarifying their associations plays an important role in developing screening strategies, especially for identifying patients with higher risks of specific combinations of metabolic complications at various levels of IR severity. The aims of the study were to assess the influence of IR severity measured by the HOMA on the risks of metabolic factors in subjects with NAFLD, CHB and CHB with NAFLD.

In this cross-sectional study conducted in China, we identified different dose–response patterns between insulin resistance and metabolic comorbidities among CHB, NAFLD and CHB combined with NAFLD in 2782 age-matched and gender-matched cases and controls via risk factor analysis. Almost half of the patients with CHB combined with NAFLD had IR, a proportion that was significantly higher than that in other groups with chronic HBV infection or NAFLD alone. We found that increased HOMA-IR was linearly associated with the prevalence of metabolic syndromes in the CHB with NAFLD group. We also found a graded association between the HOMA-IR and uric acid. These associations persisted after multivariable adjustment, including baseline FBG and CHOL concentrations, SBP and BMI. The diverse abovementioned associations remained significant after adjusting for confounders, including family history, age and sex.

Insulin resistance was overrepresented in patients with CHB and NAFLD and to a somewhat greater degree in those who had CHB combined with NAFLD than in the control subjects. Given that insulin resistance contributes to the development of type 2 diabetes, the high prevalence of IR in the CHB group was in line with the previous finding that diabetes is more likely to appear in CHB infection [8‐12]. In light of the positive correlation between obesity and insulin resistance, a subgroup analysis stratified by BMI was performed to observe these independent trends. Intriguingly, the proportion of IR and its severity remained elevated in patients with CHB combined with NAFLD compared to those affected by either disease alone. Therefore, a greater risk of IR implies the importance of detecting glucose metabolism at preliminary stages in patients simultaneously affected by CHB and NAFLD.

Insulin resistance has been recognized as a key mechanism of liver steatosis and metabolic morbidity and mortality [7, 24]. When systemic IR exists, the accompanied compensatory hyperinsulinemia over activates insulin receptor-PI3K–Akt signaling in two different organs: liver and adipose tissue [7, 25]. In the former, excess insulin acts as a potent regulator for driving lipogenic genes expression, which leads to over de novo lipogenesis, impaired mitochondrial fatty acid oxidation and subsequent liver inflammation, whereas the latter promotes lipolysis and secret increased levels of adipokines, free fatty lipids and inflammatory cytokines [25]. Therefore, much more toxic lipids were entered, produced, accumulated in liver and released to circulation, causing endothelial dysfunction, hyperlipidemia and related metabolic disorders [7]. The progressively dysregulated metabolism in the liver exacerbate IR in turn, forming positive feedback of worsening metabolism [25]. Although a stepwise increase in IR with the risk of metabolic syndrome was initially reported in NAFLD subjects, the association between IR and CHB with NAFLD was not as well-known as that between IR and NAFLD. Our current results reported that hypertension and increased uric acid show similar trends in CHB with and without NAFLD and first found that IR indicated different clusters of metabolic complications, especially in CHB with NAFLD. No clear trend was found in the association between the fourth quartile of HOMA-IR and hypertriglyceridemia level risk in CHB with NAFLD, while a stepwise increase in IR was associated with an increased risk of hypertriglyceridemia in both CHB and NAFLD. Our findings reinforce those of previous studies demonstrating that HBV infection is negatively associated with hypertriglyceridemia [26] and provide evidence that HBV infection negates the promoting effect of IR on TG levels. One possible mechanism explaining this phenomenon is that HBV products, including HBV protein X, interrupt de-novo lipid synthesis and secretion under insulin-resistant conditions, which are characterized by inhibition of Apo-C3 expression [27] and Apo-B secretion [28]. As the major protein component of triglyceride (TG)-rich lipoproteins, decreased Apo-B and Apo-C3 concentrations therefore lower serum very-low-density lipoprotein (VLDL) and TG levels.

Several studies reported the inverse association of HBsAg positivity with total cholesterol and LDL-C. In a large cross-sectional study conducted in a Taiwanese cohort with 56,336 participants [29], patients with positive HBsAg had a significantly lower frequency of hypercholesterolemia. Additionally, a longitudinal study further demonstrated an inverse association between HBV infection and dyslipidemia occurrence over time [30]. Notably, IR exhibited a positive association with higher LDL-C levels in CHB with NAFLD than in CHB or NAFLD alone in our study. Our findings suggested that concomitant steatosis during HBV infection modifies the association between IR and LDL-C. A higher HOMA-IR index might serve as a predictive factor for the prevalence of hypercholesterolemia. Although the underlying mechanism needs further exploration, the combination of HBV infection and NAFLD appears to have an opposite effect on liver cholesterol metabolism from that on TG metabolism.

Insulin resistance was identified as a driver of hepatic steatosis progression [31]. IR severity has been proven to be significantly associated with the degree of steatosis in NAFLD. The present study observed similar associations with increased HOMA-IR and intrahepatic triglyceride (IHTG) content in both NAFLD and CHB with NAFLD. Moreover, we also observed a greatly increased prevalence of elevated ALT levels in CHB with NAFLD compared with those in NAFLD after adjusting for compounding factors. This finding suggests that HBV infection may have a synergic effect with IR on liver damage. In addition to chronic HBV-infection-induced inflammatory response and lipotoxicity caused by steatosis in hepatocytes, IR predisposes cells to reactive oxygen species generation and lipid peroxidation [7], and thus, these factors contribute to liver injury aggravation. Liver damage is accompanied by increased production of proinflammatory cytokines, which are, in turn, involved in IR.

Our findings strongly highlight the high risk of IR occur in both NAFLD, CHB and their combination, and the necessity for initiating screening and intervention. Without cure for IR by drugs, combination of dietary modification and intensified exercise training remained the cornerstone in the management of IR and its comorbidities [32]. Adjusting the calories, ratio of carbohydrate, fatty acid and proteins in the diet have both been advocated as dietary strategies to improve insulin sensitivity. There is emerging evidence that Mediterranean-style diet, hypocaloric low-carbohydrate or low-fat diet (by energy deficit of 500–750 kcal/day), and low-glycaemic index (GI) diet confer improved weight control and metabolic profiles among insulin resistance, metabolic syndrome and NAFLD patients [32, 33]. An individualized exercise intervention, such as high-intensity interval training, moderate-intensity for 150 min/weeks or 75 min/weeks of vigorous-intensity exercise, may also provide an additional therapeutic effect on insulin resistance [34]. Therefore, our results evaluating the effect of IR on varied metabolic disorders provided the evidence base for individualized dietary and exercise recommendations on modifying insulin sensitivity to reduce progression to related metabolic diseases.

Our study had some limitations. First, we did not apply the euglycemic clamp technique, the gold standard of IR measurement, for analysis. The euglycemic clamp technique is limited in our large population study because of its cost and complexity. Thus, the conclusion that the relationships among insulin resistance and metabolic alteration across different liver diseases needs further study. Second, we conducted a cross-sectional study based on the Chinese population, and we need a larger sample of long-term follow-up data in the future to support our conclusions. Furthermore, assessing the impact of viral factors on IR severity and their interactions with metabolic profiles would be interesting. Third, other confounders related to metabolic parameters, such as dietary habits, were not available, and we could not adjust for such confounders and further explored the potential benefit of modulating insulin resistance through individualized nutritional intervention.

Chronic hepatitis B with NAFLD patients have a higher prevalence of insulin resistance, and a high burden of insulin resistance is associated with an increased risk of related metabolic disorders (total cholesterol, LDL-cholesterol, hypertension and high uric acid but not triglycerides) and liver fat content. Although our study was a cross-sectional analysis, this is the first time we used a dose–response trend analysis method to estimate the relationships between IR severity at diagnosis and related metabolic disorders among subjects with CHB, NAFLD and CHB with NAFLD. These findings in our study add to existing evidence that IR meditates different extents of metabolic abnormalities in different liver diseases, suggesting that in patients with CHB combined with NAFLD, insulin resistance and related metabolic disorders need intensive management.