Direct free fatty acid storage in different sized adipocytes from the same depot

Abstract

ObjectiveHuman adipocytes take up free fatty acids (FFA) directly from the circulation, even at times of high lipolytic activity. Whether these processes occurs simultaneously within the same cells or are partitioned between different cells, for example large and small cells, is unknown.Design and MethodsWe measured direct FFA storage in subcutaneous fat in 13 adults using a continuous infusion of [U-13C]palmitate and a bolus of [1-14C]palmitate followed 30 min later by abdominal and femoral adipose biopsies. The adipocytes were isolated by digestion procedures and separated into small, medium and large populations by differential floatation.ResultsWe were able to isolate populations of adipocytes that were statistically and clinically (~3 fold different) in size. Adipocyte lipid SA was not different between small, medium and large cells, therefore, FFA storage per unit lipid was not different. However, FFA storage rates were significantly (2-4 times) greater per cell in large than small cells (P < 0.005). In summary, relative to lipid content, FFA storage rates are not different in large and small adipocytes, however, large cells have greater storage rates per cell.ConclusionsThis suggests that the processes of FFA release and storage are taking place simultaneously in adipocytes.

Adipose Tissue Meal‐Derived Fatty Acid Uptake Before and After Diet‐Induced Weight Loss in Adults with Overweight and Obesity

“…Fatty acid synthase and LPL activity were increased in smaller adipocytes when expressed per number of cells (32). In contrast, fatty acid uptake was higher in larger compared to smaller adipocytes when expressed per cell, whereas there were no differences when fatty acid uptake was expressed per AT mass (33). Our results are in line with the latter study.…”

Inverse relationship between body mass index and mitochondrial oxidative phosphorylation capacity in human subcutaneous adipocytes

“…One interpretation might be that there is a compromise in the respiratory capacity of not only enlarged fat cells but all adipocytes from obese individuals. Comparable inverse associations were also found for other essential biochemical functions of adipocytes, like lipolysis and FFA storage (20,28).…”

Adipocyte size as a determinant of metabolic disease and adipose tissue dysfunction

“…Interestingly, when expressed per lipid weight, no difference in lipid uptake was found among small (83 mm), medium (103 mm) or large (117 mm) diameter adipocytes. On the other hand, when expressed per cell number, larger adipocytes had higher rates of lipid uptake 95 . These experiments did not include insulinstimulated conditions.…”

“…Interestingly, rates of exchange were lower in cells with larger lipid droplets compared to those with smaller lipid droplets, suggesting that cells with large lipid droplets are less efficient in transporting and possibly metabolizing fatty acids than those with small lipid droplets 94 . An in vivo study was performed by the group of Jensen and collaborators to assess rates of lipid uptake in small, medium or large adipocytes with radioactive and stable-isotope-labeled fatty acids 95 . Interestingly, when expressed per lipid weight, no difference in lipid uptake was found among small (83 mm), medium (103 mm) or large (117 mm) diameter adipocytes.…”