The key findings we provide are briefly i) subjects with FL and NASH exhibit quite the same elevated values of serum TGF-β1, both greater than those present in CHC patients; ii) there is a fair correlation between levels of this cytokine and ferritin in FL patients.
Our data somehow disagree with the body of present knowledge. In fact, they provide evidence for the idea that, being fibrosis the key process that distinguishes the non-progressive from the progressive form of NAFLD and having found a marker of fibrosis well represented in FL patients, FL should not be considered a benign disease yet. Further, we failed to confirm the crucial role of CRP in differentiating FL from NASH even though NASH patients revealed the highest concentrations .
Discussing possible mechanisms and explanations for our findings, we emphasize that TGF-β1-induced fibrosis in organ pathology and dysfunction appears to be increasingly relevant to a variety of distinct diseases .
Enhanced serum TGF-β1 concentrations could represent a marker of early activation of mesenchymal HSCs. This interpretation is strengthened by the findings of a negative correlation of serum TGF-β1 with fibrosis score, feature of stable collagen deposition, and by a good correlation between the same cytokine and serum ferritin. In fact, liver iron deposits in CHC are common and associated with activation of HSCs, ultimately contributing to liver damage [10, 17].
Increasing evidence suggests hepatocyte apoptosis, due to increased oxidative stress, is a key mediator of liver injury in NAFLD . But, is apoptosis restricted to hepatocytes alone? It is likely that, in an initial phase, apoptosis also acts on activated HSCs decreasing the collagen fibres . This could happen in FL. Successively, this mechanism does not prevent the waterfall effect of hepatic fibrosis, characteristic feature of NASH. Alternatively, being the deposition and degradation of hepatic fibrous tissue a dynamic equilibrium course, increased expression patterns of matrix-metalloproteinases -1, -2, -3, and tissue inhibitors of metalloproteinases -1 and -2 genes could promotes the degradation of extra-cellular matrix in an early step, such as in FL. Anyway, the mechanisms remain to be further studied.
Although our results are referred to a larger population, we are not able to confirm that high levels of plasma TGF-β1 represent a possible method of diagnosing NASH in NAFLD patients .
We found that the criterion of liver enzymes increase, widely used to separate NASH from FL, is vanishing according to a recent study in which 25 out of 64 (39%) patients with biopsy-proven FL was found to have ALT levels superior to 30 U/L . In addition, having found no or negative correlation between ALT activity and TGF-β1 levels in NASH and CHC patients, respectively, suggests that TGF-β1 is related to apoptosis rather than to inflammation.
Still, discussing other limitations, we should ask some questions.
Firstly, does a randomized determination mirror the "at steady state" serum concentration of this cytokine?
TGF-β1 differs from the majority of growth regulatory factors since it is generally synthesized and secreted in a biologically latent form, and this must be activated before TGF-β1 can exert its biological effects on target cells. TGF-β1 in this latent complex had a long plasma half-life (more than 100 min). Having found elevated values of serum TGF-β1 in FL, it is likely that a hepatic over-expression of the same cytokine is present. The only one serum determination for each patient is a "snapshot in time" methodology, but this is understandable; this alone with small numbers of patients in the 3 subgroups limits any definitive conclusion that can be drawn from this study.
Secondly, why are not evident histological features of fibrosis in FL patients undergone liver biopsy?
Our findings do not represent an isolate case. In fact, HSC activation was not correlated to HAI and fibrosis score, valued by Knodell and Batts separate systems, in a subset of patients who developed severe hepatitis C recurrence on 4-month after liver transplantation . The interpretation could be that we similarly faced an early fibrogenesis that would have been apparent across a long period of time, making the TGF-β1, indirect marker of HSC activation, better useful in predicting the subsequent hepatic fibrosis.
We could have carried out other markers of fibrosis for the noninvasively staging of NAFLD patients . However, to date, none of these markers have been independently validated in different populations in a prospective way. Moreover, all of these studies have been tested in a cross-sectional fashion, and then the role of these biomarkers for monitoring disease progression remains completely unknown.
To let us get down to the grassroots of the FL benignity from the beginning we should relay on longitudinal observations lasting several years, but this approach is difficult to plan. Crucial future research directions could be assessing liver fibrosis in FL patients during a long period of time by using non invasive tools such as fibrosis markers or elastograghy.