The effect of dark deprivation on the morphofunctional state and rhythmostasis of the liver under CCl₄ toxic exposure has been studied. The relevance of this study is due to the fact that the hepatotoxic effect of carbon tetrachloride on the liver is well studied, but there are very few data on the relationship between CCl₄ intoxication and circadian biorhythms, and most of the studies consider the susceptibility of the organism in general and of the liver in particular to the influence of CCl₄ in some separate periods of the rhythm, but not the influence of this chemical agent on the structure of the whole rhythm. In addition, earlier studies indicate that light disturbance causes certain changes in the morphofunctional state of the liver and the structure of the circadian rhythm of a number of parameters. As a result of this study, we found that the effect of CCl₄ in conditions of prolonged dark deprivation causes more significant structural and functional changes in hepatocytes, as well as leading to significant changes in the circadian rhythms of a number of parameters, which was not observed in the action of CCl₄ as a monofactor. We assume that the severity of structural and functional changes is due to the light-induced deficiency of melatonin, which has hepatoprotective properties. Thus, the mechanisms of CCl₄ action on CRs under conditions of light regime violations leave a large number of questions requiring further study, including the role of melatonin in these processes.

Circadian rhythm disruption induced by exposure to light—excessive in duration and intensity (dark deprivation)—and the impact of hepatotoxins are both significant risk factors for liver pathology. The purpose of this research was to evaluate the potentially synergistic effects of continuous lighting and carbon tetrachloride (CCl₄) toxicity on the structural and functional organization and daily (circadian) rhythmicity of the liver in rats, as well as to look at the corrective capability of exogenous melatonin under such influences. The experiment was conducted on 200 outbred 6-month-old Wistar rat males, which were distributed into five groups, including a control (normal light/dark cycle), dark deprivation (constant light), CCl₄ intoxication, and combined exposure to CCl₄ and dark deprivation with or without melatonin administration (0.3 mg/kg). Histological, immunohistochemical (Ki-67, Per2, and Bmal1), biochemical, and ELISA methods were used. Circadian rhythms were analyzed using cosinor. It was shown that dark deprivation and CCl₄ intoxication act synergistically, potentiating liver damage. The most severe necrosis (54.17 ± 9.13%), steatosis (57.85 ± 12.14%), and suppression of regenerative potential (decreased proportion of binucleated hepatocytes to 2.17 ± 0.21%) were observed in the group with combined exposure. This correlated with a substantial decline in melatonin content in blood plasma (7.85 ± 2.1 pg/mL) and a profound disruption in circadian rhythms. Administration of exogenous melatonin exerted pronounced hepatoprotective and chronotropic effects: it significantly reduced pathological changes (necrosis reduced to 16.35 ± 6.17%), stimulated regeneration (binucleated hepatocytes increased to 13.57 ± 0.81%), and restored the circadian rhythms of the studied parameters to levels close to those of the control. The key pathogenetic link in the potentiation of CCl₄ hepatotoxicity under dark deprivation is light-induced deficiency of endogenous melatonin. Exogenous melatonin demonstrated high efficacy in correcting both structural and functional damage and liver desynchronosis, confirming its therapeutic potential under conditions of combined exposure to chronodisruptors and toxins.

Disruption of circadian rhythms caused by constant artificial lighting (“light pollution”) is a significant risk factor for the development of metabolic and age-associated pathologies. The liver, as a central metabolic organ with pronounced circadian regulation of its functions, is particularly vulnerable to desynchronosis. The aim of this study was to evaluate the effect of three-month dark deprivation (constant lighting) and the corrective action of exogenous melatonin on the morphofunctional state of the liver in young mature rats. The experiment used 3-month-old male Wistar rats, divided into groups: control (standard light:dark cycle 10:14 h), dark deprivation group (DD, constant lighting 24 h/day), and DD + Melatonin group (DD + Mel, dark deprivation with melatonin administered in drinking water at a dose of 12 mg/L). After 3 months (animal age 6 months), a comprehensive analysis was performed. It was shown that dark deprivation causes a profound (more than five-fold) suppression of plasma melatonin levels, which is accompanied by the formation of a pro-senescent and metabolically dysfunctional phenotype of the liver. This was manifested by the development of steatosis, an 18% increase in hepatocyte area, a 30% decrease in the proportion of binucleated hepatocytes, activation of cellular senescence markers (p16, p21) and stress markers (p53), and suppression of the expression of circadian transcription factors BMAL1 and CLOCK. At the ultrastructural level, lipofuscin accumulation, damage to mitochondria and the Golgi apparatus were noted. Biochemically, hyperglycemia, increased AST activity, hypoproteinemia, hypoalbuminemia, hypercholesterolemia, and hypertriglyceridemia were revealed. Administration of exogenous melatonin completely prevented the development of these disorders, normalizing hormone levels, morphology, ultrastructure, biochemical parameters, and the expression of key molecular markers. Thus, three-month dark deprivation induces complex pro-senescent remodeling and metabolic dysfunction of the liver, mediated by melatonin deficiency, while exogenous melatonin demonstrates a pronounced hepatoprotective and chronoprotective effect.

Disruption of the natural light regimen is considered a key pathogenetic factor in the development of desynchronosis and associated diseases. The pineal gland, as a neuroendocrine organ, is a central component of the circadian system and the primary target of the pathogenic effects of disrupted lighting. However, it remains unclear whether the mechanisms of pineal damage differ between different types of light stress. In this study, 120 male Wistar rats underwent a comprehensive analysis of the morphofunctional state of the pineal gland under two lighting regimens: constant lighting and intermittent constant light. Using light and electron microscopy, immunohistochemistry, ELISA, and cosinor analysis, it was established that the two regimens induce qualitatively different types of light stress. The obtained data indicate that constant lighting induces a degenerative phenotype with loss of rhythmic organization, whereas the shift regimen produces a phenotype of chronic re-adaptation with hyperactivation of the lysosomal system, paradoxical overexpression of clock genes, and pronounced metabolic disturbances. The identified differential markers may serve as a basis for preclinical evaluation of the efficacy of chronobiotic therapy and for the development of prevention strategies for disorders associated with shift work and light pollution.

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.