Structural Entropy of Liver Histological Sections as an Integrative Index of Tissue Disorganization in Constant-Light-Induced Hepatic Remodeling with Aging-Associated Features.

Objective: To evaluate whether structural entropy of liver histological sections reflects tissue disorganization in a rat model of constant light exposure (dark deprivation) and to explore its associations with morphofunctional parameters of hepatic remodeling. Methods: Male Wistar rats (n = 120) were divided into a control group (12:12 h light/dark) and a constant light group (24 h/day, 3 months). Biochemical, histological, immunohistochemical (p16, p21, p53, BMAL1, CLOCK, PER2, Ki-67) and ultrastructural parameters were assessed. Shannon entropy was calculated on hematoxylin and eosin-stained sections using a graph-based approach based on nuclear spatial distribution and size heterogeneity. Results: Constant light exposure caused a >2-fold decrease in serum melatonin, suppression of BMAL1 and CLOCK expression (3.7- and 3.5-fold, respectively), a rise in PER2 (+29.8%), and marked increases in p16 (23.8-fold), p21 (6.7-fold), p53 (+80.9%), steatosis, hyperglycemia, and mitochondrial dysfunction (decreased cristae count, reduced circularity index). Entropy increased by 21.4% and showed strong correlations with steatosis score (r = 0.93), p53-positive cells (r = 0.88), PER2-positive cells (r = 0.86), and an inverse correlation with melatonin (r = -0.81). Partial correlations adjusted for treatment revealed that entropy remained associated with local morphological and ultrastructural parameters but not with systemic biochemical markers, suggesting that entropy primarily reflects tissue-level remodeling. An exploratory regression model, albeit with substantial multicollinearity, explained 87.5% of entropy variance, with steatosis and circadian markers as major contributors. Conclusion: Constant light exposure induces hepatic alterations that share multiple features with aging-associated phenotypes, including steatosis, cellular senescence, mitochondrial dysfunction, and circadian disruption. Structural entropy is an exploratory quantitative index of tissue disorganization that correlates with key morphofunctional parameters of hepatic remodeling. However, because the study lacked aged comparator groups, melatonin replacement, recovery models, and independent validation, entropy should not be considered a validated biomarker of biological liver age. Its potential applicability in digital pathology and geroprotective research requires confirmation in future studies with appropriate experimental designs.