# Comparative Analysis of Fatty Acids Concentration in Liver and Muscle Tissues of Rats and Mice
## 1 Introduction  
Among the myriad of fatty acids (FA), saturated (SFA) and unsaturated (UFA), they exhibit distinct biochemical properties that can profoundly influence cellular functions and contribute to the development of metabolic disorders [1]. Despite the vast body of literature exploring lipid metabolism, there is a notable gap in the understanding of species-specific variations, particularly in the context of rodents. This paper aims to address this gap by undertaking a comprehensive analysis of the FAs concentrations derived from polar (PL) and non-polar (NPL) lipids in the liver and muscle tissues of two commonly studied rodent models, rats (_Rattus norregicus_) and mice (_Mus musculus_). While these two species share a substantial genetic homology, emerging evidence suggests existing differences in their metabolism [2]. Understanding the distinct FAs profiles in rats and mice may offervaluable insights into the evolutionarily conserved and species-specific aspects of lipid metabolism, thereby informing future research endeavors and pointing out the potential implications for human health. The intricate relationship between diet, metabolism, and health has been a focal point in biomedical research, with lipids playing a pivotal role in these interconnections [3]. FAs are essential components of our diet and play an important role in maintaining human health. These organic molecules are not only crucial for energy storage but also serve as structural elements in cell membranes (polar lipids) and as precursors for various bioactive lipid mediators [4; 5; 6]. In recent years, there has been growing interest in the composition, and distribution of different fatty acid classes, particularly SFAs, MUFAs, and PUFAs, due to their profound impact on human health [7]. SFAs are characterized by the presence of single bonds only in their hydrocarbon chains, making them relatively stable and solid at room temperature. While SFAs are necessary for certain physiological functions, excessive consumption has been linked to adverse health outcomes, including cardiovascular diseases [8]. In contrast, UFAs such as MUFAs and PUFAs, primarily found in olive oil, avocados, and nuts, are valued for their potential health benefits, such as improved lipid profiles, anti-inflammatory properties, and reduced risk of heart disease [9]. The presence of different lipid species within the pool of fatty acids eligible for integration has been proposed to impact the diversity of membrane phospholipids. As the ratio of lipids containing MUFAs chains rises compared to SFAs, more MUFAs are likely assimilated into membrane phospholipids, consequently altering membrane properties. The presence of a single double bond introduces a degree of polarity to MUFAs, which can affect their interactions with cellular membranes and various enzymes [10]. PUFAs are characterized by multiple double bonds in their hydrocarbon chains and can be further classified into omega-3 (n-3) and omega-6 (n-6) fatty acids. These essential fatty acids are not synthesized by the human body and must be delivered into the human body with diet. PUFAs play a critical role in inflammation regulation, brain development, and cardiovascular health [11]. The optimal balance between n-3 and n-6 PUFAs is essential for organism inflammation status, and their imbalance is associated with various chronic diseases. The presence of multiple double bonds in PUFAs increases their polarity, thereby affecting membrane fluidity, cell signaling, and eicosanoid production [11]. Recent findings suggest that while diet, sex, and genotype each contribute to overall variance in lipidomic profiles, organ identity remains the most defining factor for lipid composition. This comprehensive lipidomic characterization serves as a valuable reference for future biomedical research using mouse models [12]. Similarly, lipidomic profiles across different tissues in rats, underscoring the tissue-specific nature of lipid composition.