The concentration of β-carotene in human adipocytes, but not the whole-body adipocyte stores, is reduced in obesity

Abstract

We have examined the concentration of β-carotene in the fat of isolated abdominal subcutaneous adipocytes obtained from lean (BMI<23 kg/m²), non-obese with higher BMI (23≤BMI<28 kg/m²), obese (BMI≥28 kg/m²), and from a group of obese subjects with type 2 diabetes. The concentration of β-carotene was 50% lower in the adipocytes from the obese and obese/diabetic groups compared with the lean and non-obese groups. Interestingly, the total amount of β-carotene in the adipocyte stores of each subject was constant among all groups. Triacylglycerol constituted 92±1% (by weight) of the adipocyte lipids in the lean group and this was increased to 99±2% in the obese group with diabetes (p<0.05). The concentration of cholesteryl esters was in all cases <0.1 g per 100 g of total lipids, demonstrating that mature human adipocytes have negligible stores of cholesteryl ester. Our findings demonstrate that adipocyte concentrations of β-carotene are reduced in obese subjects. The lower concentrations in adipocytes from subjects with type 2 diabetes apparently reflect subjects obesity. Our finding that whole-body stores of β-carotene in adipocytes are constant raises new questions regarding what function it serves, as well as the mechanisms for maintaining constant levels in the face of varied adipose tissue mass among individuals over a period of time.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Concentration of TAG and β-carotene in lipid extracts of adipocytes.

The concentrations of TAG (A) and of β-carotene (B) were determined in lipid extracts of isolated adipocytes from subjects that were divided into groups of lean (BMI2), non-obese (23≤BMI<28 kg/m2), obese (BMI≥28 kg/m2), or obese subjects with type 2 diabetes (as indicated). Lines indicate significant differences between indicated groups (p<0.05).

Figure 2. Correlation of BMI and insulin-resistance index (HOMA) with adipocyte concentration of β-carotene.

(A) All subjects were included. There is a significant correlation between adipocyte content of β-carotene and BMI of donor subjects: Y = 7.14–0.10X; r2 = 0.10; p = 0.02. (B) All non-diabetic subjects were included. There is no significant correlation between adipocyte content of β-carotene and HOMA of non-diabetic donor subjects.

Figure 3. Total adipocyte stores of β-carotene in subjects.

Whole body content of β-carotene stored in adipocytes was determined for each subject as the adipocyte concentration of β-carotene adjusted for total body fat. No statistically significant difference was found between the mean values in the groups using one-way analysis of variance (ANOVA), p>0.5.