SUMMARYResearch backgroundDespite clearly recognized links between increased body mass and increased risk for various pathological conditions, therapeutic options to treat obesity are still very limited. The aim of the present study is to explore the effect of low-molecular-mass collagen fragments obtained from the scales of Antarctic wild marine fish on rats' visceral and subcutaneous white adipose tissue in a high-calorie diet-induced obesity model.Experimental approachThe study was conducted on outbred rats, which were divided into 3 experimental groups: (i) control, consuming standard food (3.81 kcal/g), (ii) obese group, consuming a high-calorie diet (5.35 kcal/g), and (iii) obese group, consuming a high-calorie diet (5.35 kcal/g) with intragastric administration of low-molecular-mass collagen fragments (at a dose 1 g/kg of body mass during 6 weeks). Low-molecular-mass collagen fragments were obtained by a procedure that included collagen extraction from fish scales and enzymatic hydrolysis with pepsin. Apart from hematoxylin and eosin staining, fibrosis level was assessed by histochemical Van Gieson’s trichrome picrofuchsin staining, and mast cells were analysed by toluidine blue O staining.Results and conclusionsGroup treated with low-molecular-mass fragments of collagen exhibited decreased rate of mass gain, relative mass, area occupied by collagen fibre of both visceral and subcutaneous adipose tissue, and cross-sectional area of both visceral and subcutaneous adipocytes. Treatment with low-molecular-mass fragments of collagen reduced the infiltration of immune cells, number of mast cells and their redistribution back to the septa. This was also accompanied by a decreased number of the crown-like structures formed by the immune cells, which are markers of chronic inflammation that accompanies obesity.Novelty and scientific contributionThis is the first study that reports the anti-obesity effect of low-molecular-mass fragments produced as a result of controlled hydrolysis of collagen from the scales of Antarctic wild marine fish in thein vivomodel. Another novelty of this work is the observation that the tested collagen fragments not only reduce the body mass, but also improve the morphological and inflammatory parameters (decrease in the number of crown-like structures, immune cell infiltration, fibrosis and mast cells). Altogether, our work suggests that low-molecular-mass collagen fragments are a promising candidate for amelioration of some comorbidities linked to obesity.