| |
Carotid Artery Intima-media Thickness in Nonalcoholic Fatty Liver Disease
|
| |
| |
The American Journal of Medicine
8 January 2008.
Anna Ludovica Fracanzani MDa, Larry Burdick MDa, Sara Raselli PhDb, Paola Pedotti MDc, Liliana Grigore MDb, Gennaro Santorelli MDa, Luca Valenti MDa, Alessandra Maraschi MDa, Alberico Catapano MDb and Silvia Fargion MDa, ,
aCentro Malattie Metaboliche del Fegato, Dipartimento Medicina Interna, Universita di Milano, Milano, Italy
bCentro Studi Aterosclerosi SISA, Dipartimento di Scienze Farmacologiche, Universita di Milano, Milano, Italy
cUnita di Genetica ed Epidemiologia Molecolare, Ospedale Maggiore Policlinico, Fondazione IRCCS, Milano, Italy.
Clinical implication of the results of our study is that patients with nonalcoholic fatty liver disease, independently of severity of liver disease, should be considered at high risk for cardiovascular complications and screened for carotid artery disease.
In our paired-sample case-control study performed in a large series of subjects, we demonstrated that patients with nonalcoholic fatty liver disease, independently of the severity of liver damage, had higher intima-media thickness values and prevalence of carotid plaques than matched controls.....The strongest independent risk predictors of intima-media thickness >0.64 mm, considering the overall series (375 subjects), was the presence of steatosis..... Liver biopsy performed in 54 patients who did not differ from nonbiopsied patients for cardiovascular risk factors showed the presence of macrovesicular steatosis in all of them (grade 1 in 32 [60%], grade 2 in 10 [19%], grade 3 in 12 [22%]), with a mean percentage of cells with fatty droplets of 23%, 42%, and 68%, respectively.
Abstract
Purpose
To evaluate, in patients with nonalcoholic fatty liver disease with no or mild alterations of liver function tests, carotid artery intima-media thickness and the presence of plaques and to define determinants of vascular damage.
Methods
A paired-sample case-control study: 125 patients with nonalcoholic fatty liver disease and 250 controls, without a prior diagnosis of diabetes, hypertension, and cardiovascular disease, matched for sex, age, and body mass index. B-mode ultrasound was used for evaluation of carotid intima-media thickness and presence of small plaques.
Liver biopsy performed in 54 patients who did not differ from nonbiopsied patients for cardiovascular risk factors showed the presence of macrovesicular steatosis in all of them (grade 1 in 32 [60%], grade 2 in 10 [19%], grade 3 in 12 [22%]), with a mean percentage of cells with fatty droplets of 23%, 42%, and 68%, respectively. Twenty-five (46%) patients had nonalcoholic steatohepatitis, none had cirrhosis, there was advanced fibrosis (stage >3) in 5 (9%), stage 2 in 4 (8%), stage 1 in 17 (31%), and absence of fibrosis in 28 (52%). No significant difference in intima-media thickness values was observed between patients with pure fatty liver and nonalcoholic steatohepatitis, as well as biopsied and nonbiopsied.
Ox-LDL values were measured in available sera of 32 patients. Those with higher intima-media thickness (1.05 ± 0.26 mm) had higher ox-LDL values compared with those with lower intima-media thickness (0.7 ± 0.1 mm) (17 cases, 65.26 ± 45 EU/mL, and 15 cases 29.5 ± 17 EU/mL, P = .01).
Results
A significant difference in mean values of intima-media thickness (0.89 ± 0.26 and 0.64 ± 0.14 mm, P = .0001) and prevalence of plaques (26 [21%] and 15 [6%], P <.001) was observed in nonalcoholic fatty liver disease patients and controls. Variables significantly associated with intima-media thickness higher than 0.64 mm (median value in controls), in both patients and controls were: age (P = .0001), systolic blood pressure (P = .004), total and low-density lipoprotein cholesterol (P ≦.02 and P = .01, respectively), fasting glucose (P = .0001), and cardiovascular risk (P = .0001) and, only in controls, metabolic syndrome (P = .0001), HOMA-insulin resistance (P = .01), and body mass index (P = .0003). At multivariate logistic regression performed in the overall series of subjects, independent risk predictors of intima-media thickness higher than 0.64 mm were presence of steatosis (odds ratio [OR] = 6.9), age (OR 6.0), and systolic blood pressure (OR 2.3).
Conclusion
Patients with nonalcoholic fatty liver disease, even with no or mild alterations of liver tests, should be considered at high risk for cardiovascular complications.
Nonalcoholic fatty liver disease includes a wide spectrum of liver diseases ranging from fatty liver alone, usually a benign and nonprogressive condition, to nonalcoholic steatohepatitis, which may progress to liver cirrhosis.[1] and [2] Insulin resistance is the underlying condition that facilitates nonalcoholic fatty liver disease occurrence3 and is the key pathogenetic event of obesity, type II diabetes, and dyslipidemia. Recently, nonalcoholic fatty liver disease has been included among the components of the metabolic syndrome,[1], [4] and [5] at high risk of coronary heart disease and cardiovascular complications.[6], [7], [8] and [9] A high prevalence of fatty liver, evaluated by ultrasound, associated with hyperinsulinemia or insulin resistance and cardiovascular disease, also has been reported in the general population[10], [11], [12], [13] and [14] and in patients with documented coronary artery disease or stroke.15
· Nonalcoholic fatty liver disease is strongly associated with atherosclerotic damage to the carotid artery, even in patients without significantly impaired liver function, hypertension, or diabetes.
· Nonalcoholic fatty liver disease might be inherently atherogenic.
· Patients with this disease are at high risk for cardiovascular complications and should be screened for carotid artery disease, regardless of liver function test results.
Carotid B mode ultrasound imaging has been used for evaluation of carotid atherosclerosis.[16] and [17] Intima-media thickness of carotid artery, a validated parameter for detecting subclinical atherosclerosis,[18] and [19] has been shown to predict myocardial infarction and stroke.[20] and [21] Recently, a relationship between nonalcoholic fatty liver disease and atherosclerosis has been reported in healthy men, and it has been suggested to reflect the overall adverse impact of the metabolic syndrome, in particular of insulin resistance and increased visceral fat.22 In addition, endothelial dysfunction has been reported23 in nonalcoholic fatty liver disease and related to the metabolic syndrome.
Carotid atherosclerosis has been detected in patients with nonalcoholic fatty liver disease in cross-sectional studies[22], [24] and [25], and more recently, carotid intima-media thickness has been related to the severity of liver damage.26
Our aim was to evaluate intima-media thickness and carotid plaques in a case-control study including a large series of patients with nonalcoholic fatty liver disease with no or mild liver test alterations and matched controls, and to define the determinants of vascular damage.
Results
The baseline demographic, clinical, and biochemical characteristics of patients with nonalcoholic fatty liver disease and controls are shown in Table 1. HDL cholesterol (40.2 ± 11 vs 50.2 ± 12 mg/100 mL, P ≦.0001), triglycerides (158 ± 96 vs 122 ± 27 mg/100 mL, P ≦.0001), fasting glucose (96.6 ± 19 vs 92.5 ± 13 mg/100 mL, P ≦.01), HOMA-IR (3.8 ± 2.7 vs 2.9 ± 1.7), alanine-aminotransferase (46.6 ± 35 vs 11.6 ± 5.2 UI/L), gamma-glutamyltransferase (58.8 ± 78 vs 25.2 ± 16 UI/L, and cardiovascular risk (FRS, 10 years %) (14.5 ± 10 vs 9.5 ± 7.6 years, P ≦.0001) were significantly different in the 2 groups. Metabolic syndrome was present in 51 (41%) patients and in 26 (10%) controls (P ≦.0001).
In patients with nonalcoholic fatty liver disease, abnormal glucose metabolism was present in 49 (38%), fasting glucose between 110 and 126 mg/100 mL in 21 (17%), impaired glucose tolerance after OGTT in 26 (21%), 6 of whom also had increased fasting glucose, and diabetes in 10 (8%), 3 diagnosed after OGTT.
Because we had no information on steatosis of our control group, we divided subjects according to alanine-aminotransferase quartiles and analyzed the characteristics of controls in the different alanine-aminotransferase quartiles. Subjects in the higher quartile (alanine-aminotransferase 14-39 UI/L, median alanine-aminotransferase 21 ± 4.1, 56 cases) were significantly younger (49 ± 11 years and 53 ± 11 years, P = .04), had higher total cholesterol (238 ± 43 and 217 ± 38 UI/L, P ≦.0001), LDL cholesterol (162 ± 38 and 143 ± 35 mg/100 mL, P ≦.001), lower HDL cholesterol (47 ± 12 and 51 ± 13 mg/100 mL, P ≦.02), higher triglycerides (142 ± 68 and 112 ± 73 mg/100 mL, P ≦.004), HOMA-IR (3.3 ± 2.3 and 2.8 ± 1.5, P ≦.03), and prevalence of metabolic syndrome (17% and 8%, P ≦.03).
Vascular Damage
The mean value of carotid intima-media thickness was 0.89 ± 0.26 mm in patients and 0.64 ± 0.14 mm in controls (P ≦.0001). No difference in intima-media thickness was observed in controls in different alanine-aminotransferase quartiles. Carotid plaques were detected in 26 (21%) patients and in 15 (6%) controls (P ≦.0001). None had clinically relevant carotid stenosis (ie, ≥60%).
Variables significantly associated with intima-media thickness higher than 0.64 mm (median value observed in controls) are shown in Table 2. Age, total and LDL cholesterol, fasting glucose, systolic blood pressure, and FRS were significantly associated with intima-media thickness higher than 0.64 mm in the overall series of subjects, as well as in patients with nonalcoholic fatty liver disease and in controls evaluated separately, whereas metabolic syndrome, BMI, diastolic pressure, and HOMA-IR were significantly associated with intima-media thickness higher than 0.64 mm in the overall series but, when groups were considered separately, only in controls.
Table 2. Variables Significantly Associated with Carotid Intima-media Thickness (IMT) > OR ≦0.64 mm in the Overall Series of Subjects and in Nonalcoholic Fatty Liver Disease and Controls Evaluated Separately
Mean ± SD (%).
Metabolic syndrome defined by positivity for 3 or more of the following criteria: 1) fasting glucose >110 mg/dL; 2) central obesity (waist circumference >102 cm [men] and >88 cm [women]); 3) arterial pressure >130/85 mm Hg; 4) triglyceride levels >150 mg/dL or current use of fibrates; 5) HDL cholesterol <40 mg/dL (men) and <50 mg/dL (women).
A significant correlation between alanine-aminotransferase, gamma-glutamyltransferase, and intima-media thickness as continuous variables (Spearman coefficient for alanine-aminotransferase 0.33 [P = .0001] and gamma-glutamyltransferase 0.19 [P = .0002]) was found in the overall series, but not when patients with nonalcoholic fatty liver disease and controls were analyzed separately.
Multivariate logistic regression analysis was performed to evaluate independent factors associated with intima-media thickness >0.64 mm in the overall series of subjects. The model included intima-media thickness >0.64 mm as dependent variable and several risk factors (age, sex, BMI, cholesterol, triglycerides, fasting glucose, HOMA-IR, FRS, smoke, diabetes, blood pressure, metabolic syndrome, steatosis) as fully adjusted multiple logistic regression model variables (Table 3). The strongest independent risk predictors of intima-media thickness >0.64 mm, considering the overall series (375 subjects), was the presence of steatosis. This also, was confirmed excluding control subjects in the upper alanine-aminotransferase quartile (14-39 UI/L, median 21 ± 4.1 [56 cases]) who could possibly have steatosis. Analyzing separately patients and controls, the strongest variables associated with intima-media thickness higher than >0.64 mm in both groups were age and blood pressure.
Discussion
In the present study, we evaluated intima-media thickness and looked for carotid plaques in patients with nonalcoholic fatty liver disease with no or only mild liver function test alterations, and investigated the relationship between vascular damage and metabolic alterations. In our paired-sample case-control study performed in a large series of subjects, we demonstrated that patients with nonalcoholic fatty liver disease, independently of the severity of liver damage, had higher intima-media thickness values and prevalence of carotid plaques than matched controls.
A first problem we faced was that in different studies,[7], [8], [18] and [34] values of carotid intima-media thickness in normal populations markedly differed, with increasing evidence that even low intima-media thickness values were associated with carotid atherosclerosis and increased risk of cardiovascular events. According to this we arbitrarily used the median value of intima-media thickness of our large series of asymptomatic subjects included in a health surveillance program for cardiovascular events as cutoff value. Steatosis was the strongest variable independently associated with intima-media thickness. Our findings confirm previous results in patients with nonalcoholic fatty liver disease in cross-sectional studies,[22], [24] and [25] and in a case-control study in which patients with nonalcoholic fatty liver disease were enrolled only if they had increased alanine-aminotransferase.26 Given that nonalcoholic fatty liver disease is the hepatic manifestation of the metabolic syndrome, our results are in line with the increased risk of atherosclerosis in subjects with metabolic syndrome[7], [8] and [35] and with the relation between early atherosclerosis and insulin resistance, present in almost all patients with nonalcoholic fatty liver disease.[12], [13], [14] and [36] At logistic regression analysis performed in the overall series of subjects, the strongest independent risk predictors of vascular damage was steatosis followed by age and systolic blood pressure. We found a significant association between intima-media thickness higher than 0.64 mm and HOMA-IR in the overall series and in controls, but only a trend in patients, possibly for the evenly increased HOMA-IR. Consistent with the role of glucose metabolism abnormalities is the significant relation between increased carotid intima-media thickness and increased fasting glucose and impaired glucose tolerance, as previously reported.[37] and [38] Interestingly, a moderately increased risk for cardiovascular events in patients with type 2 diabetes and associated nonalcoholic fatty liver disease compared with those without nonalcoholic fatty liver disease was reported in a large prospective study.39 The same authors found a higher intima-media thickness in patients with nonalcoholic fatty liver disease and increased alanine-aminotransferase than in controls and reported the highest values in nonalcoholic steatohepatitis.26 Differently from this study, we did not observe higher intima-media thickness in nonalcoholic steatohepatitis than in pure fatty liver. The different characteristics of the patients included in our study, no or mild alterations of liver tests versus chronically elevated alanine-aminotransferase and prevalence of nonalcoholic steatohepatitis (46 % vs 81%), may account for these apparent discrepancies.26 A possible limitation of our study is the small number of patients with liver biopsy due to the normality of biochemical tests in the majority of our cases.
Epidemiological data suggest that cardiovascular mortality is increased in patients with nonalcoholic fatty liver disease.[40] and [41] Our results indirectly support this hypothesis, because the presence of nonalcoholic fatty liver disease was the strongest variable independently associated with intima-media thickness higher than 0.64 mm and possibly widespread atherosclerosis. This suggests that nonalcoholic fatty liver disease could be atherogenetic by itself, as hypothesized by Brea et al25 analyzing a small series of subjects. In favor of the proatherogenetic role of nonalcoholic fatty liver disease is the finding that despite similar BMI, prevalence of diabetes, and hypertension, patients with nonalcoholic fatty liver disease had higher intima-media thickness and prevalence of plaques than controls. Interestingly, we found a significant association between intima-media thickness and metabolic syndrome only in controls (data not shown), suggesting that in patients with nonalcoholic fatty liver disease, steatosis itself has a prevalent role in inducing vascular damage. The earlier age of intima-media thickness >0.64 mm in patients than in controls further supports the proatherogenetic role of nonalcoholic fatty liver disease, not only in middle age but also in young adults. Recently, on the basis of a 2-fold increased atherosclerosis in autopsies of children with fatty liver, it was hypothesized that atherosclerosis begins in childhood and progresses through adulthood, leading to lesions responsible for later cardiovascular disease.42
It was recently shown that patients with nonalcoholic fatty liver disease have endothelial dysfunction potentially responsible for cardiovascular disease in the long term.23 Enhanced oxidative stress, inflammation with release of inflammatory cytokines, and abnormal lipoprotein metabolism could account for the proatherogenic effect of nonalcoholic fatty liver disease.[23], [24], [43] and [44] In keeping with this are the increased levels of ox-LDL in patients with higher intima-media thickness, as previously reported.[45] and [46] Visceral fat, even in normal weight or slightly overweight subjects with steatosis, could play a direct role in the development of atherosclerosis through its multiple secreted factors.[22] and [47]
In the present study, a moderate alcohol intake was more prevalent in controls than in patients. Although controversial data suggest that alcohol reduces the risk of coronary heart disease, we did not find a significant correlation between alcohol intake and intima-media thickness.[48] and [49]
A further limitation of this study is the lack of information on the presence of steatosis in controls. We assumed that subjects in the high alanine-aminotransferase quartile, in which alanine-aminotransferase values were between 14 and 39 UI/L (median 21 ± 4.1), might have steatosis.50 Intima-media thickness of this subgroup was similar to that of subjects in the other alanine-aminotransferase quartiles, although metabolic parameters differed. Results of multivariate analyses in which subjects in the upper alanine-aminotransferase quartile were included or not included, were similar. In controls, we also evaluated the fatty liver index, recently proposed as a simple and accurate predictor of hepatic steatosis in the general population,51 and only 10 (4%) subjects fulfilled the criteria for the diagnosis of steatosis. Finally, the possible inclusion of controls with nonalcoholic fatty liver disease may have led to underestimation of the differences in the intima-media thickness between the 2 groups rather than the opposite.
In conclusion, our study suggests that a careful evaluation not only of the liver but also of the cardiovascular system should be performed in nonalcoholic fatty liver disease to prevent later morbidity related to atherosclerosis. Clinical implication of the results of our study is that patients with nonalcoholic fatty liver disease, independently of severity of liver disease, should be considered at high risk for cardiovascular complications and screened for carotid artery disease.
Methods
Patients
We studied 125 consecutive patients with nonalcoholic fatty liver disease (109 males, 16 females, mean age 49 ± 13 years) who presented to our liver unit between June 2002 and December 2004. The diagnosis of nonalcoholic fatty liver disease was based on ultrasonography and confirmed by biopsy in 54 patients. Thirty-four (27%) patients were referred because of abnormalities in liver tests, 16 (13%) for dyslipidemia, 45 (36%) for hyperferritinemia, and 30 (24%) for liver steatosis detected by ultrasonography performed for abdominal pain or liver-unrelated causes. In all patients, daily alcohol intake was lower than 20 g (confirmed by at least one family member). Patients with chronic viral hepatitis, autoimmune hepatitis, hereditary hemochromatosis, Wilson's disease, and drug-induced liver disease were excluded.
Controls
Two hundred fifty subjects from the same geographic area of patients, included in a health surveillance program previously submitted to screening for cardiovascular risk in the Progression Lesions Intima Carotid study,27 matched 1:2 (the best possible match) with patients by paired-sample techniques for sex, age (± 5 years), and body mass index (BMI) (± 1.5) were enrolled. All controls had alanine-aminotransferase within normal range (5-39 UI/L), were negative for hepatitis C virus, hepatitis B virus, and human immunodeficiency virus infections or history of liver disease.
No patient or control was previously diagnosed with diabetes, hypertension, or cardiovascular disease. All patients gave informed, written consent to participate in the study according to a protocol approved by the Senior Staff Committee of our institutions, a board comparable to an Institutional Review Board. Clinical, alcohol, and pharmacologic history, smoking habits, BMI, waist circumference (measured in a standing position at the level of the umbilicus) and arterial blood pressure (defined as the mean of the second and third reading of 3 consecutive blood pressure measurements), complete blood count, liver tests alanine-aminotransferase and gamma-glutamyltransferase, fasting glucose, total and high-density lipoprotein (HDL) cholesterol, triglyceride, uric acid, and hepatitis B and C serological analysis were available in all subjects. All tests were determined by standard laboratory procedures, insulin by a commercially purchased radioimmunoassay (RIA, Biochem Immunosystems, Bologna, Italy).
In all subjects, the cardiovascular risk (Framingham risk score [FRS]) was calculated according to the third report of the National Cholesterol Education Program's Adult Treatment Panel III (ATP III).28 The diagnosis of metabolic syndrome was based on the ATP III criteria.28
Insulin Resistance Assessment
Insulin resistance was evaluated according to the homeostatic metabolic assessment (HOMA) insulin resistance index (fasting serum insulin μIU/mL X fasting serum glucose mMol/L/22.5) and the insulin level at 120 minutes following oral glucose tolerance test (OGTT) performed with 75 g of glucose, according to World Health Organization criteria.[29], [30] and [31]
Liver biopsies, performed for persistently abnormal liver biochemical tests or increased ferritin in 54 patients, were processed routinely. The diagnosis of nonalcoholic steatohepatitis was based on Brunt criteria.32 The severity of steatosis was graded 1 to 3 according to the percentage of cells with fatty droplets (1: 10%-33%, 2: 33%-66%, and 3: >66%).
Assessment of Carotid Atherosclerosis
Early vascular atherosclerosis evaluated by the measurement of maximum intima-media thickness was determined by high-resolution B-mode ultrasound with a 7.5-MHz transducer, as described previously.[16], [17], [18] and [33] Results of intima-media thickness represent the mean intima-media thickness on the right and left sides. For the common carotid artery, bilateral images were obtained 2 cm proximal to the dilatation of the carotid bulb; for each subject, 3 measurements on both sides were performed. Two experienced sonographers unaware of the individuals' disease status performed intima-media thickness. The inter-rater correlation between repeated intima-media thickness measurements was 0.96 mm (P <.001), with similar averages of the 2 sets of readings. The scanning protocol included imaging of the common and internal carotid arteries of both sides in multiple longitudinal and transverse planes. In all regions of interest the presence of the plaques also was recorded.
A carotid plaque was defined as a focal thickening ≥1.2 mm at the level of carotid artery.
Serum Oxidized Low-density Lipoprotein
Serum anti oxidized low-density lipoprotein (Ox-LDL) antibodies concentration was measured by ELISA (ImmunoLisa, IMMCO Diagnostic, Buffalo, NY) and expressed as enzyme units (EU/mL).
Statistical Analysis
Results are expressed as means ± standard deviation for continuous variables and as frequencies for categorical variables. Mean values were compared by t test for unequal variances. Frequencies were compared by chi-squared test. Continuous variables were correlated by Spearman test. Multivariate analyses (using a conditional logistic regression model) were performed to assess the association between carotid and metabolic variables. Values of P ≦.05 were considered statistically significant. All the statistical analyses were performed with SAS 8.2 software system (SAS Institute Inc., Cary, NC).
|
|
| |
| |
|
|
|
