Tohoku J. Exp. Med., 2011, 223, 227-233 Monocytes and Nonalcoholic Fatty Liver
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Elevated Peripheral Blood Monocyte Fraction in Nonalcoholic Fatty Liver Disease Hack-Lyoung Kim,1,2 Goh Eun Chung,3 In Young Park,1 Jin Man Choi,1 Se-Min Hwang,4 Jeong-Hoon Lee2 and Donghee Kim3 1
Armed Forces Seoul Hospital, Seoul, Korea Department of Internal Medicine, Seoul National University Hospital, Seoul, Korea 3 Department of Internal Medicine, Healthcare Research Institute, Seoul National University Hospital Healthcare System Gangnam Center, Seoul, Korea 4 Department of Preventive Medicine, The Armed Forces Medical Commands, Gyeonggi-do, Korea 2
An elevated white blood cell (WBC) count is associated with nonalcoholic fatty liver disease (NAFLD); however, a leukocyte subtype that is involved in the pathogenesis of NAFLD is not known. This study was conducted to investigate the association between NAFLD and WBC subtype fractions (%) among healthy elderly Koreans. A total of 794 subjects who underwent a health check-up were investigated. After excluding excessive alcohol intake and other liver diseases, NAFLD was diagnosed based on sonographic findings: hyperechogenecity of liver tissue, difference of echogenicity between liver and kidney, and visibility of vascular structures. The prevalence of NAFLD among entire cohort was 39.0% (310/794). The presence of NAFLD was significantly associated with higher blood WBC counts (5,485 ± 1073 vs. 5,230 ± 995 per mm3, p = 0.001) and monocyte fraction (6.08 ± 2.40% vs. 5.12 ± 1.31%, p < 0.001). The multiple logistic regression analysis, after controlling confounders, including age, gender, body mass index, systolic and diastolic blood pressure, fasting blood glucose, alanine aminotransferase, triglyceride, and high-density lipoprotein cholesterol, showed that the prevalence risk of NAFLD was increased significantly according to the monocyte fraction quartiles: odds ratios (ORs) and 95% confidence intervals (CIs) for NAFLD were 1.00, 2.75 (1.63-4.62), 2.84 (1.67-4.84) and 5.17 (3.03-8.83), respectively. There were no significant associations between NAFLD and the total WBC count quartiles in this model. These results indicate that the elevated peripheral blood monocyte fraction is associated with NAFLD. The monocyte fraction might be a useful marker for NAFLD. Keywords: association; fatty liver; inflammation; monocyte; pathophysiology Tohoku J. Exp. Med., 2011, 223 (3), 227-233. © 2011 Tohoku University Medical Press eases such as infection, cardiovascular disease, cancers and metabolic syndrome, and increased WBC count is associated with a high risk of morbidity and mortality (Kannel et al. 1992; Brown et al. 2004; Jee et al. 2005; Shankar et al. 2006, 2007; Ruggiero et al. 2007). A recent study showed that the peripheral blood WBC count was elevated in patients with NAFLD compared to patients without NAFLD (Lee et al. 2010); this finding suggests the role of inflammatory processes in the development of NAFLD. The peripheral blood WBC is comprised of neutrophils, lymphocytes, monocytes, eosinophils and basophils. Each subtype involved in the inflammatory process in a different way. A number of observational studies have shown a positive correlation between the counts of certain types of leukocytes and the metabolic syndrome or cardiovascular disease (Tsai et al. 2007; Kim et al. 2008). However, the relationship between specific subtypes of leukocyte and
Nonalcoholic fatty liver disease (NAFLD) is a major cause of chronic liver disease worldwide. It is characterized by a wide spectrum of liver damage ranging from simple steatosis to steatohepatitis, liver cirrhosis and hepatocellular carcinoma (Angulo 2002; Adams et al. 2005). Insulin resistance has been identified as an essential factor in the pathophysiology of the development of NAFLD. Several components of metabolic syndrome such as obesity, hypertension, diabetes and dyslipidemia are known risk factors for NAFLD (Angulo 2002; Adams et al. 2005). Thus, NAFLD is considered an indicator of cardiovascular disease due to the shared risk factors (Choi et al. 2009; Lizardi-Cervera and Aguilar-Zapata 2009; Treeprasertsuk et al. 2010). The white blood cell (WBC) count is routinely measured as a marker for systemic inflammation. The WBC count has been reported to be elevated in a variety of dis-
Received December 13, 2010; revision accepted for publication February 16, 2011. doi: 10.1620/tjem.223.227 Correspondence: Goh Eun Chung, M.D., Department of Internal Medicine, Healthcare Research Institute, Seoul National University Hospital Healthcare System Gangnam Center, 39FL., Gangnam Finance Center 737, Yeoksam-Dong, Gangnam-Gu, Seoul 135-984, Korea. e-mail:
[email protected]
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NAFLD has not been studied. The WBC subtype is inexpensive, and can be obtained easily in the clinical setting. The information on which subtypes of WBCs are more important in patient with NAFLD may provide greater insight into the pathophysiology of NAFLD. Therefore, this study was performed to investigate the association between NAFLD and WBC subtypes, independent of standard risk factors for NAFLD; the WBC subtypes associated with the pathogenesis of NAFLD were studied in healthy elderly Koreans.
Methods Study population The study subjects were recruited from participants undergoing routine health exams at the Armed Forces Seoul Hospital (Seoul, Korea) from January 1, 2005 to December 31, 2009. According to the following exclusion criteria, 563 subjects were excluded: subjects with 1) WBC counts of less than 4,000 or more than 10,000 cells/ mm3 to rule out a possible bone marrow disorder, active infection or inflammation (n = 182); 2) chronic viral hepatitis or other chronic liver diseases (n = 44); 3) a history of excessive alcohol consumption (140 g/week or more for men and 70 g/week or more for women) (n = 58); 4) any condition that may affect the blood cell counts including chronic kidney disease (estimated glomerular filtration rate by Cockroft-Gault method < 60 mL/min/1.73m2) (n = 250), rheumatologic diseases or cancers (n = 15); and 5) incomplete laboratory data (n = 18). After these exclusions, a total of 794 subjects (age range: 34-86 years, 69.4% are male) were included in the final investigation. Approval for the study protocol was obtained from the Institutional Review Boards of the Armed Forces Medical Command (Gyeonggi-do, Korea). Informed consent was not obtained owing to routine nature of information collected. Data collection Information regarding the underlying diseases, medication history, and alcohol drinking habits was recorded by trained personnel, a family medicine doctor using standardized questionnaire. Systolic and diastolic blood pressure, body weight, and height were measured by a trained nurse. The body mass index (BMI) was calculated as the ratio of weight (kg)/height 2 (m 2). Hypertension was physician reported for systolic blood pressure (SBP) ≥ 140 mmHg, diastolic blood pressure (DBP) ≥ 90 mmHg, or a history of use of anti-hypertensive medications. Diabetes was determined by physician report and was based on a fasting blood glucose (FBG) level ≥ 126 mg/dL or use of medications for diabetes. Hypercholesterolemia was physician reported for a low density lipoprotein level ≥ 160 mg/dL, or use of cholesterol lowering medications. After an overnight fast (≥ 12 hours), 10 mL of venous blood was obtained from the antecubital vein of each subject in the morning. The total WBC count and the subtype fractions (%) were analyzed by an automated blood cell counter (ADVIA 120, Bayer, NY, USA). Alanine aminotransferase (ALT), γ-glutamyl transferase (GGT), triglyceride (TG), high-density lipoprotein (HDL) cholesterol, and FBG were measured by enzymatic methods using an automated chemistry analyzer (Toshiba TBA-120 FR, Toshiba Medical Systems, Tokyo, Japan). A diagnosis of fatty liver was based on liver ultrasonography with a 3.5-MHz transducer (Acuson Sequoia 512, Siemens, Mountain View, CA, USA). Ultrasonographic examination was carried out by
two experienced radiologists who were blinded to the laboratory data. The inter- and intra-operator reliabilities obtained by Spearman’s correlation analyses were 0.802 and 0.870, respectively. Fatty liver was diagnosed in the presence of two of the three following criteria: increased hepatic echogenicity compared to the spleen or the kidney, blurring of the liver vasculature and deep attenuation of the ultrasonographic signal (Erdogmus et al. 2008; Schwenzer et al. 2009). Hepatic steatosis was graded according to criteria described previously (Lee et al. 2010): control (grade 0), normal echogenicity; mild (grade 1), slight diffuse increase in bright homogenous echoes of the liver parenchyma, with normal visualization of intrahepatic vessels and diaphragm; moderate (grade 2), diffuse increase in bright echoes in liver parenchyma, with slightly impaired visualization of intrahepatic vessels and diaphragm; and severe (grade 3), marked increase in echogenicity with poor penetration of the posterior portion of right lobe of liver, and with poor visualization of intrahepatic vessels and diaphragm. A liver with any degree of hepatic steatosis was considered to have NAFLD in the present study. Statistical analysis Data are presented as mean values with standard deviation or percentage. Because the WBC subtype counts are obtained by multiplying the total WBC count and its subtype fraction (%), multicollinearity can be a problem. Therefore, the subtype fraction was considered a variable rather than the count. For the univariate analysis, continuous variables were compared using the Student’s t-test and categorical variables were compared using the χ2 test. Variables that were statistically significant by the univariate analysis were added to the multiple logistic regression analysis. For the logistic regression analysis, laboratory parameters were categorized based on the data from the National Health Insurance Corporation of Korea (Jun et al. 2008), and the total WBC count and monocyte fraction were divided into quartiles. The odds ratios (ORs) and 95% confidence intervals (CIs) for the prevalence risk of NAFLD were obtained after controlling for standard risk factors using binary logistic regression analysis. Comparison of the monocyte fraction according to the severity of NAFLD was estimated using one-way analysis of variances (ANOVA). The prevalence of NAFLD according to the monocyte fraction quartile was estimated by the χ2 test of linear by linear association. Receiver operating characteristic (ROC) curve analysis was used to evaluate the optimal cut-off points of the monocyte fraction for detecting NAFLD. A two-tailed p value of < 0.05 was considered statistically significant. All data were analyzed using SPSS for Windows 13.0 (Chicago, IL, USA).
Results Baseline characteristics of subjects The prevalence of NAFLD among the entire cohort was 39.0% (310 of 794). The baseline characteristics of 484 subjects without NAFLD and 310 with NAFLD are shown in Table 1. Subjects with NAFLD were older (age: 66.4 ± 7.4 vs. 64.7 ± 8.4 years, p = 0.004) and predominantly male (78.7 vs. 63.4%, p < 0.001). Most of the metabolic parameters including BMI (25.3 ± 2.2 vs. 23.4 ± 2.2 kg/m2, p < 0.001), SBP (130.4 ± 13.8 vs. 124.2 ± 14.1 mmHg, p < 0.001), DBP (80.7 ± 7.9 vs. 76.9 ± 8.3 mmHg, p < 0.001), FBG (102.1 ± 17.0 vs. 97.1 ± 16.6 mg/dL, p < 0.001), HDL cholesterol (47.6 ± 10.2 vs. 55.9 ± 12.7 mg/
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Monocytes and Nonalcoholic Fatty Liver Table 1. Baseline characteristics of study population. Characteristics
Normal (n = 484)
NAFLD (n = 310)
p
Age, years
64.7 ± 8.4
66.4 ± 7.4
0.004
Male sex, n (%) Body mass index, kg/m2
307 (63.4)
244 (78.7)
< 0.001
23.4 ± 2.2
25.3 ± 2.2
< 0.001
79 (16.5) 30 (6.3) 19 (4.0)
65 (21.1) 28 (9.1) 17 (5.5)
0.102 0.135 0.312
124.2 ± 14.1 76.9 ± 8.3
130.4 ± 13.8 80.7 ± 7.9
< 0.001 < 0.001
20.0 ± 9.9 28.2 ± 22.4 97.1 ± 16.6 55.9 ± 12.7 91.6 ± 50.3
26.9 ± 13.1 34.1 ± 20.2 102.1 ± 17.0 47.6 ± 10.2 134.7 ± 75.4
< 0.001 < 0.001 < 0.001 < 0.001 < 0.001
5,230 ± 995
5,485 ± 1,073
57.4 ± 8.6 33.5 ± 8.1 5.12 ± 1.31 2.92 ± 2.30 0.57 ± 0.31
56.0 ± 8.4 34.1 ± 8.2 6.08 ± 2.40 2.91 ± 2.03 0.59 ± 0.41
Underlying diseases, n (%) Hypertension Diabetes Hypercholesterolemia Blood pressure, mmHg Systolic Diastolic Laboratory parameters Alanine aminotransferase, U/L γ-glutamyl transferase, U/L Fasting blood glucose, mg/dL HDL cholesterol, mg/dL Triglyceride, mg/dL Total WBC count (per mm3) WBC subtype fraction, % Neutrophil Lymphocyte Monocyte Eosinophil Basophil
0.001 0.127 0.350 < 0.001 0.955 0.438
Values are expressed as mean ± standard deviation or number. NAFLD, nonalcoholic fatty liver disease; HDL, high density lipoprotein; WBC, white blood cell.
dL, p < 0.001) and TG (134.7 ± 75.4 vs. 91.6 ± 50.3 mg/dL, p < 0.001) were more unfavorable in subjects with NAFLD compared to subjects without NAFLD. As expected, the ALT (26.9 ± 13.1 vs. 20.0 ± 9.9 U/L, p < 0.001) and GGT (34.1 ± 20.2 vs. 28.2 ± 22.4 U/L, p < 0.001) were significantly higher in subjects with NAFLD when compared to subjects without NAFLD. Underlying disease including hypertension, diabetes and hypercholesterolemia did not differ between the two groups (p > 0.05). The presence of NAFLD was significantly associated with a higher blood WBC count (5,485 ± 1,073 vs. 5,230 ± 995 per mm3, p = 0.001) and monocyte fraction (6.08 ± 2.40 vs. 5.12 ± 1.31%, p < 0.001). There was no significant association between the presence of NAFLD and the other fractions of neutrophils, lymphocytes, eosinophils and basophils (p > 0.05 for each). Association between NAFLD and peripheral blood monocyte fraction To investigate the independent relationship between each variable and NAFLD, a multiple logistic regression analysis was performed (Table 2). The variables that were significant ( p < 0.05) in the univariate analyses were added to the logistic regression analysis as factors should be controlled. Male gender (OR = 2.388; 95% CI = 1.300-4.386;
p = 0.005), high BMI (OR = 3.125; 95% CI = 2.201-4.437; p < 0.001), high ALT (OR = 2.672; 95% CI = 1.514-4.430; p = 0.001), low HDL (OR = 2.589; 95% CI = 1.514-4.430; p = 0.001) and high TG (OR = 2.803; 95% CI = 1.7604.464; p < 0.001) had significant positive associations with the presence of NAFLD. In addition, a high monocyte fraction was significantly associated with the presence of NAFLD. The prevalence risk of NAFLD for the highest versus the lowest quartile of the monocyte fraction was 5.175 (95% CI = 3.030-8.837; p < 0.001) after adjustment for confounders. There was no significant association between the presence of NAFLD and the total WBC count in this model ( p > 0.05). Since WBC count is significantly different by gender (Allan and Alexander 1968), we additionally analyzed the data according to gender stratification. As a result, the association between monocyte fraction and NAFLD remains significant in both gender, however, the significance is stronger in men than in women (Table 3). Fig. 1 shows the prevalence of NAFLD in relationship to the blood monocyte fraction quartiles. The percentage of NAFLD gradually increased in accordance with monocyte fraction quartiles: 12.2, 24.3, 27.6 and 35.9%, respectively ( p < 0.001), clearly suggesting that the prevalence of NAFLD was positively associated with the peripheral blood
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H.L. Kim et al. Table 2. Logistic regression analysis of factors associated with NAFLD. β
SE
OR
95% CI
Age ≥ 65 years
0.057
0.187
1.058
0.734 - 1.527
Male sex BMI ≥ 25 kg/m2
0.871
0.310
2.388
1.300 - 4.386
0.005
1.139 0.410 0.084 0.983
0.179 0.224 0.266 3.000
3.125 1.507 1.088 2.672
2.201 - 4.437 0.972 - 2.336 0.647 - 1.831 1.514 - 4.430
< 0.001 0.067 0.751 0.001
−0.341
0.317
0.711
0.382 - 1.323
0.282
0.230
0.179
1.259
0.886 - 1.790
0.199
0.951
0.274
2.589
1.514 - 4.430
0.001
1.031
0.237
2.803
1.760 - 4.464
< 0.001
0.245 0.243 0.251
1 1.491 1.509 1.391
0.923 - 2.408 0.938 - 2.430 0.851 - 2.273
0.102 0.090 0.188
0.265 0.271 0.273
1 2.753 2.849 5.175
1.639 - 4.626 1.676 - 4.845 3.030 - 8.837
< 0.001 < 0.001 < 0.001
Variable
SBP ≥ 140 mmHg DBP ≥ 90 mmHg ALT ≥ 35 U/L GGT ≥ 65 U/L in men, ≥ 35 U/L in women FBG ≥ 100 mg/dL HDL ≤ 40 mg/dL in men ≤ 50 mg/dL in women TG ≥ 150 mg/dL WBC count 1st quartile 2nd quartile 3rd quartile 4th quartile Monocyte fraction 1st quartile 2nd quartile 3rd quartile 4th quartile
0.399 0.412 0.330
1.013 1.047 1.644
p 0.761
Β, standardized regression coefficient; SE, standard error; OR, odds ratio; CI, confidence interval. NAFLD, nonalcoholic fatty liver disease; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; ALT, alanine aminotransferase; GGT, γ-glutamyl transferase; FBG, fasting blood glucose; HDL, high-density lipoprotein; TG, triglyceride; WBC, white blood cell.
monocyte fraction. Fig. 2 shows the mean values of the peripheral blood monocyte fraction according to the NAFLD severity. The monocyte fraction increased according to the NAFLD severity; 5.12, 6.03 and 6.22%, respectively, however, the difference was not significant between mild and moderate or severe NAFLD ( p = 0.671). The area under the ROC curve of the monocyte fraction was 0.670 (95% CI = 0.632-0.708), shown in Fig. 3. A cut-off value of 5.0% of the monocyte fraction resulted in a sensitivity and specificity were 73.4% and 51.0% for estimating the presence of NAFLD, respectively. When the univariate comparative analyses were performed using the WBC subtype counts instead of the fractions, similar results demonstrating a strong positive relationship between the monocyte count and NAFLD were obtained (data not shown).
Discussion The results of this study showed that the peripheral blood monocyte fraction was independently associated with NAFLD in healthy elderly Koreans with a normal range of total WBC count, after controlling of age, gender, BMI, ALT, GGT, FBG, HDL and TG. The prevalence of NAFLD was higher in the patients with a high monocyte fraction: the prevalence of NAFLD for the highest monocyte fraction was 5.175. These findings suggest that the monocyte frac-
tion might be a useful marker for assessing NAFLD. This is the novel finding showing a strong positive relationship between the monocyte fraction and NAFLD. The exact mechanism linking elevated monocytes and NAFLD remains unclear. Nevertheless, several possible explanations can be considered for this association between an increase in the monocyte fraction and NAFLD. Cardiovascular risk factors including components of the metabolic syndrome are closely related to NAFLD. Many different studies have demonstrated that patients with NAFLD present with increased subclinical atherosclerosis compared to individuals without NAFLD; cardiovascular disease is the second most common cause of death in patients with NAFLD (Choi et al. 2009; Lizardi-Cervera and Aguilar-Zapata 2009; Treeprasertsuk et al. 2010). Increased inflammation, endothelial dysfunction and thrombosis have been suggested as causes of cardiovascular diseases in patients with NAFLD (Targher 2007; LizardiCervera and Aguilar-Zapata 2009; Treeprasertsuk et al. 2010). The monocytes are central to this pathophysiology and play an important role. Circulating monocytes attach to the artery wall of atherosclerotic foci, where they differentiate into lipid-laden macrophages and recruit other inflammatory cells leading to the development of an atherosclerotic plaque (Weijenberg et al. 1996; Chapman et al. 2004). This close connection of pathogenesis between car-
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Monocytes and Nonalcoholic Fatty Liver Table 3. Logistic regression analysis* of factors associated with NAFLD according to gender stratification. Variable Age ≥ 65 years BMI ≥ 25 kg/m2 Diabetes SBP ≥ 140 mmHg DBP ≥ 90 mmHg ALT ≥ 35 U/L GGT ≥ 35 U/L in women FBG ≥ 100 mg/dL HDL ≤ 40 mg/dL in men ≤ 50 mg/dL in women TG ≥ 150 mg/dL WBC count 1st quartile 2nd quartile 3rd quartile 4th quartile Neutrophil fraction 1st quartile 2nd quartile 3rd quartile 4th quartile Lymphocyte fraction 1st quartile 2nd quartile 3rd quartile 4th quartile Monocyte fraction 1st quartile 2nd quartile 3rd quartile 4th quartile Basophil fraction 1st quartile 2nd quartile 3rd quartile 4th quartile
Men
Women
β
OR
95% CI
p
β
OR
95% CI
p
0.57
1.059
0.68 - 1.65
0.800
0.376
1.456
0.66 - 3.02
0.351
1.080 – 0.166 −0.194 0.049 – 0.261
2.944 – 1.181 0.824 1.050 – 1.298
1.91 - 4.52 – 0.69 - 2.00 0.43 - 1.54 1.02 - 1.07 – 0.85 - 1.97
< 0.001 – 0.540 0.547 < 0.001 – 0.222
1.001 0.457 0.921 0.855 0.684 0.161 0.086
2.21 1.579 2.512 2.352 1.982 1.175 1.090
1.25 - 5.90 0.36 - 6.86 1.02 - 6.13 0.78 - 7.09 0.50 - 7.86 0.36 - 3.76 0.45 - 2.61
0.011 0.542 0.043 0.129 0.331 0.787 0.846
1.062
2.893
1.63 - 5.11
< 0.001
†
†
†
†
0.982
2.669
1.49 - 4.76
0.001
1.039
2.825
1.09 - 7.31
0.032
0.310 0.658 0.344
1 1.364 1.931 1.274
0.74 - 2.49 1.09 - 3.41 0.77 - 2.56
0.313 0.024 0.259
0.500 -0.472 0.486
1 1.648 0.624 1.626
0.66 - 0.40 0.19 - 2.01 0.57 - 4.16
0.279 0.429 0.361
0.771 1.356 1.557
1 2.163 3.881 4.744
0.92 - 5.50 1.32 - 11.35 1.30 - 17.28
2.163 0.013 0.018
– – –
– – –
– – –
– – –
0.585 0.776 1.931
1 1.794 2.172 6.896
0.79 - 4.06 0.79 - 5.94 1.96 - 24.2
0.162 0.131 0.003
– – –
– – –
– – –
– – –
1.216 1.297 2.157
1 3.374 3.658 8.645
1.62 - 7.02 1.78 - 7.52 4.11 - 18.18
0.001 < 0.001 < 0.001
1.271 0.858 0.805
1 2.564 2.358 2.237
1.49 - 8.48 0.84 - 6.57 0.68 - 7.34
0.004 0.101 0.184
0.308 0.318 0.262
1 1.360 1.374 1.300
0.78 - 2.35 0.78 - 2.40 0.68 - 2.47
0.270 0.268 0.425
– – –
– – –
– – –
– – –
*Variables that showed significant association with NAFLD in univariate analyses were included in this multiple logistic regression analsysis. †all women have HDL ≤ 50 mg/dL. Β, standardized regression coefficient; OR, odds ratio; CI, confidence interval. NAFLD, nonalcoholic fatty liver disease; BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; ALT, alanine aminotransferase; GGT, γ-glutamyl transferase; FBG, fasting blood glucose; HDL, high density lipoprotein; TG, triglyceride; WBC, white blood cell.
diovascular disease and NAFLD suggests that the elevated monocyte fraction in patients with NAFLD was not an incidental finding in this study. Furthermore, it can be suggested that the monocytes may be an important mediator of both the development of cardiovascular disease and NAFLD. Additional evidence is derived from the fact that
inflammation is actively involved in the pathogenesis of NAFLD, and monocytes are one of the markers of inflammation. Insulin resistance results in hepatic lipid accumulation, which is the first and crucial step in the development of NAFLD and provides a source of oxidative stress triggering the inflammatory process (Tilg and Moschen 2008; Dowman et al. 2010). Hepatic inflammation is considered
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H.L. Kim et al.
Fig. 1. The prevalence of NAFLD according to monocyte fraction quartiles. p value of each comparison was estimated by χ2 test and *p value was estimated by χ2 test of linear by linear association. NAFLD, nonalcoholic fatty liver disease; Q, quartile.
Fig. 3. Receiver operating characteristic (ROC) curve of monocyte fraction for detecting NAFLD. NAFLD, nonalcoholic fatty liver disease.
Fig. 2. Monocyte fraction according to the severity of NAFLD. p value of each comparison was estimated by Scheffe post-hoc analysis of ANOVA (analysis of variance). NAFLD, nonalcoholic fatty liver disease.
the underlying cause of cell death and disease progression, especially, from steatosis to nonalcoholic steatohepatitis (NASH) (Arrese and Karpen 2010; Byrne 2010). Many circulating inflammatory cells such as neutrophils, lymphocytes and monocytes were observed in the liver (Tiniakos et al. 2010), and various systemic inflammatory markers such as the tumor necrosis factor (TNF)-α, interleukin (IL)-6 and C-reactive protein (CRP) have been reported to be elevated in the blood of patients with NAFLD (Byrne 2010). Although the exact mechanism associated on why only monocyte fraction was increased in patients with NAFLD is not known exactly, these findings are in agreement with accumulating evidence showing that the inflammatory process is deeply involved in the development of NAFLD (Arrese and Karpen 2010; Byrne 2010; Dowman et al. 2010; Tiniakos et al. 2010). The total WBC count, an indolent chronic inflammatory marker, is an established risk factor for the development of cardiovascular disease and associated with morbid-
ity and mortality (Kannel et al. 1992; Brown et al. 2004; Jee et al. 2005; Shankar et al. 2006, 2007; Ruggiero et al. 2007). A recent large population study among Koreans showed that the total WBC count is also an independent risk factor for NAFLD (Jun et al. 2008). In the present study, however, the total WBC count was not a predictor of NAFLD. Although the WBC count was significantly higher in the patients with NAFLD compared to those without NAFLD by the univariate analysis, this association was no longer present after controlling for confounders in the logistic regression analysis. The potential limitations of this study include the followings. This study was conducted with cross-sectional design, and there is a possibility of temporal relationship between high monocyte fraction and NAFLD. A longitudinal study including serial measurements of the monocyte fraction is needed to confirm the results of this study. Inflammatory markers such as IL-6, CRP and fibrinogen, were not included in the evaluation, and important information about systemic inflammation was not obtained. In addition, because NAFLD was diagnosed based on ultrasonographic findings in this study, other pathology such as NASH could not be differentiated. Although ultrasonography can help to determine the presence and degree of fatty infiltration of the liver, it cannot be used to accurately determine the severity of liver damage, which can only be confirmed by a liver biopsy (Angulo 2002; Schwenzer et al. 2009).
Conclusion The results of this study showed that the peripheral
Monocytes and Nonalcoholic Fatty Liver
blood monocyte fraction was associated with NAFLD and may contribute to the pathogenesis of NAFLD. This result suggests that the monocyte fraction, an inexpensive and universally obtained test result, might be a useful marker for NAFLD. Further longitudinal studies and/or laboratory experiments are needed to clarify the underlying mechanisms of this association.
Conflict of Interest The authors report no conflict of interest associated with this manuscript.
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