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The associations of thyroid function parameters with non-alcoholic fatty liver disease (NAFLD) and hepatic iron overload are not entirely clear. We have cross-sectionally investigated these associations among 2734 participants of two population-based cross-sectional studies of the Study of Health in Pomerania. Serum levels of thyroid-stimulating hormone (TSH), free tri-iodothyronine (fT3), and free thyroxine (fT4) levels were measured. Liver fat content (by proton-density fat fraction) as well as hepatic iron content (by transverse relaxation rate; R2*) were assessed by quantitative MRI. Thyroid function parameters were associated with hepatic fat and iron contents by median and logistic regression models adjusted for confounding. There were no associations between serum TSH levels and liver fat content, NAFLD, or hepatic iron overload. Serum fT4 levels were inversely associated with liver fat content, NAFLD, hepatic iron contents, and hepatic iron overload. Serum fT3 levels as well as the fT3 to fT4 ratio were positively associated with hepatic fat, NAFLD, hepatic iron contents, but not with hepatic iron overload. Associations between fT3 levels and liver fat content were strongest in obese individuals, in which we also observed an inverse association between TSH levels and NAFLD. These findings might be the result of a higher conversion of fT4 to the biologically active form fT3. Our results suggest that a subclinical hyperthyroid state may be associated with NAFLD, particularly in obese individuals. Furthermore, thyroid hormone levels seem to be more strongly associated with increased liver fat content compared to hepatic iron content.
Non-alcoholic fatty liver disease (NAFLD) is gaining in importance and is linked to obesity.
Especially, the development of fibrosis and portal hypertension in NAFLD patients requires treatment.
Transgenic TGR(mREN2)27 rats overexpressing mouse renin spontaneously develop NAFLD with
portal hypertension but without obesity. This study investigated the additional role of obesity in this
model on the development of portal hypertension and fibrosis. Obesity was induced in twelve-week
old TGR(mREN2)27 rats after receiving Western diet (WD) for two or four weeks. Liver fibrosis
was assessed using standard techniques. Hepatic expression of transforming growth factor-β1
(TGF-β1), collagen type Iα1, α-smooth muscle actin, and the macrophage markers Emr1, as well as
the chemoattractant Ccl2, interleukin-1β (IL1β) and tumor necrosis factor-α (TNFα) were analyzed.
Assessment of portal and systemic hemodynamics was performed using the colored microsphere
technique. As expected, WD induced obesity and liver fibrosis as confirmed by Sirius Red and Oil Red
O staining. The expression of the monocyte-macrophage markers, Emr1, Ccl2, IL1β and TNFα were
increased during feeding of WD, indicating infiltration of macrophages into the liver, even though this
increase was statistically not significant for the EGF module-containing mucin-like receptor (Emr1)
mRNA expression levels. Of note, portal pressure increased with the duration of WD compared
to animals that received a normal chow. Besides obesity, WD feeding increased systemic vascular
resistance reflecting systemic endothelial and splanchnic vascular dysfunction. We conclude that
transgenic TGR(mREN2)27 rats are a suitable model to investigate NAFLD development with liver
fibrosis and portal hypertension. Tendency towards elevated expression of Emr1 is associated with
macrophage activity point to a significant role of macrophages in NAFLD pathogenesis, probably
due to a shift of the renin–angiotensin system towards a higher activation of the classical pathway.The hepatic injury induced by WD in TGR(mREN2)27 rats is suitable to evaluate different stages of
fibrosis and portal hypertension in NAFLD with obesity