Hepatic lipid quantity and quality in type 2 diabetes mellitus

The incidence of type 2 diabetes mellitus (T2DM) has been increasing worldwide. In the pathophysiology of metabolic diseases, including T2DM, both the quantity and quality of lipids that accumulate in the body have attracted significant research attention. Excess lipids accumulate in non-adipose tissues, such as the liver and skeletal muscles, leading to insulin resistance and an increased risk of developing T2DM. The liver is the central organ for glucose and lipid metabolism, and impaired hepatic regulatory mechanisms lead to hyperglycemia, insulin resistance, and hepatic lipid accumulation. Hepatic triglyceride (TG) accumulation contributes to the development of hepatic insulin resistance; however, the quantity of TGs alone is insufficient to explain the development of glucose and lipid metabolic dysfunctions. Thus, we focus on lipid quality, particularly fatty acids. In addition to TGs, phospholipids store fatty acids, which vary in carbon chain length, number of double bonds, and position of double bonds (such as ω3 and ω6), resulting in lipid diversity. Changes in the fatty acid chains of phospholipids are also strongly associated with glucose and lipid metabolism. In this mini review, we discuss the involvement of hepatic lipid quantity and quality in T2DM, with the aim of contributing to the development of novel T2DM therapies.