Independent positive association of plasma ß-carotene concentrations with adiponectin among non-diabetic obese subjects.

PURPOSE: Many epidemiological studies find an inverse correlation between carotenoids intake or carotenoids plasma concentrations and body mass index (BMI), insulin resistance or metabolic syndrome in the general population. However, it is not clear whether these relationships occur in obese population. METHODS: We conducted a cross-sectional study in 108 obese non-diabetic patients. RESULTS: There was an inverse correlation between plasma levels of pro-vitamin A carotenoids (α-carotene, ß-carotene and ß-cryptoxanthin) and both BMI and insulin resistance (estimated by the HOMA-IR). No correlation between plasma concentrations of lycopene or lutein/zeaxanthin and BMI or insulin resistance was found. The inverse association between the three pro-vitamin A carotenoids and HOMA-IR disappeared after adjustment for BMI and waist circumference. Interestingly, we identified a positive association between concentrations of ß-carotene and adiponectin in plasma that was independent of sex, age, smoking status, BMI and waist circumference. To our knowledge, such association has never been described in obese patients. CONCLUSION: These results suggest the existence of a favourable effect of ß-carotene on insulin sensitivity in obese individuals that could involve a positive regulation of adiponectin, either directly or via its pro-vitamin A activity. The demonstration of the potential benefits of ß-carotene towards insulin sensitivity would open the way to dietary strategies to prevent metabolic syndrome.

Two common single nucleotide polymorphisms in the gene encoding beta-carotene 15,15'-monoxygenase alter beta-carotene metabolism in female volunteers.

The key enzyme responsible for beta-carotene conversion into retinal is beta-carotene 15,15'-monoxygenase (BCMO1). Since it has been reported that the conversion of beta-carotene into vitamin A is highly variable in up to 45% of healthy individuals, we hypothesized that genetic polymorphisms in the BCMO1 gene could contribute to the occurrence of the poor converter phenotype. Here we describe the screening of the total open reading frame of the BCMO1 coding region that led to the identification of two common nonsynonymous single nucleotide polymorphisms (R267S: rs12934922; A379V: rs7501331) with variant allele frequencies of 42 and 24%, respectively. In vitro biochemical characterization of the recombinant 267S + 379V double mutant revealed a reduced catalytic activity of BCMO1 by 57% (P<0.001). Assessment of the responsiveness to a pharmacological dose of beta-carotene in female volunteers confirmed that carriers of both the 379V and 267S + 379V variant alleles had a reduced ability to convert beta-carotene, as indicated through reduced retinyl palmitate:beta-carotene ratios in the triglyceride-rich lipoprotein fraction [-32% (P=0.005) and -69% (P=0.001), respectively] and increased fasting beta-carotene concentrations [+160% (P=0.025) and +240% (P=0.041), respectively]. Our data show that there is genetic variability in beta-carotene metabolism and may provide an explanation for the molecular basis of the poor converter phenotype within the population.