Impact of obesity on liver function tests: is nonalcoholic fatty liver disease the only player? A review article

Objectives

Obesity and nonalcoholic fatty liver disease (NAFLD) are common worldwide health problems with a strong relationship in between. NAFLD is currently the most common cause of abnormal liver function tests (LFT) because of obesity pandemic. The question is NAFLD the only player of abnormal LFT in obesity?

Methodology

This article reviews the most important topics regarding the derangements of LFT in obesity through a PubMed search strategy for all English-language literature.

Results

The reported abnormal LFT in obesity were increased serum levels of transaminases (alanine aminotransaminase, aspartate aminotransaminase), gamma glutamyl transferase, and alkaline phosphatase and decreased serum levels of bilirubin and albumin. Besides novel potential hepatic markers of NAFLD/NASH such as triglycerides/high-density lipoprotein cholesterol ratio, sex hormone-binding globulin, fibroblast growth factor 21, and markers of hepatocyte apoptosis i.e. cytokeratin 18 and microribonucleic acids (miRNAs). Beyond NAFLD, there are other underlying players for the abnormal LFT in obesity such as oxidative stress, inflammation, and insulin resistance.

Conclusion

Derangements of LFT in obesity are attributed to NAFLD but also to obesity itself and its related oxidative stress, insulin resistance, and chronic inflammatory state. Abnormal LFT predict more than just liver disease.

Updated reference ranges for aminotransferase levels of Korean children and young adolescents based on the risk factors for metabolic syndrome

We investigated the reference values of liver enzymes based on cardiometabolic risks among children and adolescents using the Korea National Health and Nutrition Examination Survey. A total of 8091 subjects aged 10-18 years were included from the data from 2007-2017. Overall, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and the AST/ALT ratio varied with sex and age. AST levels tended to decrease with age, but ALT levels had a U-shaped curve, which resulted in a gradual increase in the AST/ALT ratio after age 13. The prevalence of MetS was strongly associated with elevated AST or ALT and a decreased AST/ALT ratio. The prevalence ratios of the development of MetS were also elevated in groups with high levels of AST and ALT and a low AST/ALT ratio. Particularly in the combined ALT and AST/ALT analyses, borderline-high levels also showed a high prevalence ratio of MetS. Liver enzymes were also involved in the increase in the adjusted mean values for each risk factor for MetS. Here, we provided updated reference values for liver enzymes based on the analysis between population-based data and cardiometabolic risk factors; AST, ALT and the AST/ALT ratio might be useful in the early diagnosis and treatment of MetS.

Association between FTO (rs17817449) genetic variant, gamma-glutamyl transferase, and hypertension in Slovak midlife women

OBJECTIVES

This cross-sectional study investigates associations between the FTO rs 17817449 genetic variant, liver enzymes, and hypertension in Slovak midlife women.

METHODS

We assessed 576 Slovak women aged 39 to 65 years. The women were interviewed and examined during their medical examination at local Health Centers and then divided into subgroups according to their blood pressure status; 255 women with hypertension and 321 normotensive. The FTO genetic variant was detected by polymerase chain reaction-restriction fragment length polymorphism. Resultant data was analyzed by linear regression analysis and general linear models to adjust for risk factors associated with gamma-glutamyl transferase levels (GGT), including waist to hip ratio (WHR) and uric acid (UA).

RESULTS

A significant association between the FTO variant and GGT levels was observed in the hypertensive group after control for confounding covariates, including WHR and UA (p = .004). The predicted GGT level for GT/TT hypertensive carriers is 0.158 μkat/L higher than for GG carriers. Moreover, the two-way analysis of covariance revealed significant interaction between FTO effects and hypertension on logGGT levels (p = .042). Finally, hypertensive women with the T-allele had the highest estimated marginal mean value of logGGT at -0.39 μkat/L while the GG-genotype in both hypertensive and normotensive women had the lowest value at -0.54 μkat/L.

CONCLUSIONS

This study suggests that the FTO (rs17817449) variant is associated with higher serum GGT levels in hypertensive midlife women.

Gamma-glutamyltransferase activity as a surrogate biomarker of metabolic health status in young nondiabetic obese women

Aim: We investigated the association of gamma-glutamyltransferase (GGT) activity with atherogenic risk factors and metabolic health status in young nondiabetic obese women. Methods & results: In 140 obese women GGT activity was independently associated with BMI, triglyceride to high-density cholesterol ratio and homeostasis model assessment. Metabolically healthy but obese women had significantly lower GGT activity, associated with a normal insulin sensitivity, favorable lipid profile and apolipoprotein B to apolipoprotein AI ratio. GGT activity showed good diagnostic accuracy to distinguish between metabolically healthy but obese and obese women at risk (77.8% sensitivity and 60% specificity). GGT activity >17 U/l can predict atherogenic risk and insulin resistance. Conclusion: GGT activity may serve as a potential surrogate biomarker of atherogenic risk and metabolic health status.

Cardiorespiratory fitness, waist circumference and liver enzyme levels in European adolescents: The HELENA cross-sectional study

OBJECTIVES

(1) To examine whether cardiorespiratory fitness (CRF) is related to liver enzyme levels independent of waist circumference (WC), and (2) To test whether having a high CRF is associated with an improved liver enzyme profile with a high WC.

DESIGN

Cross-sectional.

METHODS

CRF (20m-shuttle-run test) and WC were assessed in 811 European adolescents (48.5% males) aged 12.5-17.5 years. Fatty liver biomarkers included fasting serum alanine-aminotransferase (ALT), gamma-glutamyl-transpeptidase (GGT) and the aspartate-aminotransferase to ALT (AST/ALT) ratio. Participants were categorized as fit or unfit (CRF below or above 43.8mL/kg/min and 34.6mL/kg/min, for boys and girls, respectively) and as high or non-high WC (sex and age-specific cut-offs).

RESULTS

CRF was associated with ALT (β=-0.106; p=0.049) and GGT levels (β=-0.225; p<0.001) and AST/ALT ratio (β=0.234; p<0.001), yet these relationships were attenuated after further controlling for WC (all p>0.1). High WC and fit adolescents had lower ALT levels (28±1U/L vs. 23±2U/L, unfit and fit respectively, p=0.018) and higher AST/ALT ratio (0.94±0.04 vs. 1.10±0.06, unfit and fit respectively, p=0.010) than those who were high WC but unfit.

CONCLUSIONS

The results showed that CRF is not independently associated with liver enzymes, and that WC is a stronger predictor in adolescents. These findings also suggest that high CRF may have specific protective effects on liver enzyme levels in adolescents with high WC. Exercise programs focused on increasing CRF and decreasing abdominal adiposity could be a good alternative in the treatment and prevention of obesity related fatty liver disease in adolescents.

Liver enzymes and clustering cardiometabolic risk factors in European adolescents: the HELENA study

OBJECTIVES

This study aimed to explore the associations of liver biomarkers with cardiometabolic risk factors and their clustering, and to provide reference values (percentiles) and cut-off points for liver biomarkers associated with high cardiometabolic risk in European adolescents.

METHODS

Alanine aminotransferase (ALT), gamma-glutamyltransferase (GGT), aspartate aminotransferase to ALT ratio (AST/ALT), waist circumference, blood pressure, triglycerides, high-density lipoprotein cholesterol and insulin were measured in 1084 adolescents. We computed a continuous cardiometabolic risk score and defined the high cardiometabolic risk.

RESULTS

Higher ALT and GGT and lower AST/ALT were associated with adiposity and with the number of adverse cardiometabolic risk factors (Ps < 0.05). Higher GGT and lower AST/ALT were associated with higher cardiometabolic risk score (Ps < 0.001) in males and females, and ALT only in males (Ps < 0.001). Gender- and age-specific percentiles for liver biomarkers were provided. Receiver operating characteristic analyses showed a significant discriminatory accuracy of AST/ALT in identifying the low/high cardiometabolic risk (Ps < 0.01) and thresholds were provided.

CONCLUSIONS

Higher GGT and lower AST/ALT are associated with higher cardiometabolic risk factors and their clustering in male and female European adolescents, whereas the associations of ALT were gender dependent. Our results suggest the usefulness of AST/ALT as a screening test in the assessment of adolescents with high cardiometabolic risk and provide gender- and age-specific thresholds that might be of clinical interest.

'Aussie normals': an a priori study to develop clinical chemistry reference intervals in a healthy Australian population

Development of reference intervals is difficult, time consuming, expensive and beyond the scope of most laboratories. The Aussie Normals study is a direct a priori study to determine reference intervals in healthy Australian adults. All volunteers completed a health and lifestyle questionnaire and exclusion was based on conditions such as pregnancy, diabetes, renal or cardiovascular disease. Up to 91 biochemical analyses were undertaken on a variety of analytical platforms using serum samples collected from 1856 volunteers. We report on our findings for 40 of these analytes and two calculated parameters performed on the Abbott ARCHITECTci8200/ci16200 analysers. Not all samples were analysed for all assays due to volume requirements or assay/instrument availability. Results with elevated interference indices and those deemed unsuitable after clinical evaluation were removed from the database. Reference intervals were partitioned based on the method of Harris and Boyd into three scenarios, combined gender, males and females and age and gender. We have performed a detailed reference interval study on a healthy Australian population considering the effects of sex, age and body mass. These reference intervals may be adapted to other manufacturer's analytical methods using method transference.