All-trans beta-carotene is absorbed preferentially to 9-cis beta-carotene, but the latter accumulates in the tissues of domestic ferrets (Mustela putorius puro).

The algae Dunaliella bardawil and Dunaliella salina naturally contain large concentrations of all-trans and 9-cis beta-carotene (betaC). The purpose of this study was to compare the relative serum and tissue accumulation of all-trans and 9-cis betaC in ferrets fed different ratios of all-trans/9-cis betaC derived from two commercial sources, D. bardawil or D. salina (Betatene). Male ferrets (7 wk old) were fed carotene-free, pelleted diets for 27 d. Beginning on d 18, groups of ferrets (n = 6 or 7) received daily, one of six oral supplements varying in ratios of 9-cis and all-trans betaC mixed with approximately 1.0mL of Ensure. Four supplements containing 5.2-8.3 micromol total betaC were prepared from a 20% Betatene preparation, D. bardawil, a high-cis Betatene preparation, and Betatene further enriched in 9-cis betaC with all-trans betaC/9-cis betaC ratios of 2.2, 1.5, 0.6 and 0.4, respectively. Two control supplements, high and low betaC, were prepared from commercial betaC beadlets. The high control supplement had an all-trans/9-cis ratio of 19.0, whereas 9-cis betaC was not detected in the low supplement. On d 27, serum and tissues were obtained for HPLC analysis of betaC and its isomers. Analysis of livers showed that all-trans betaC was the primary isomer present, but 9-cis and other isomers were also detected in all groups. The hepatic all-trans/9-cis ratios were 5.9, 4.9, 2.5, 1.4, 52.2 and47.5, respectively, for the groups listed above. Lower amounts of all-trans and 9-cis betaC were found in kidneys compared with the liver, but ratios of all-trans/9-cis were not different among groups. Only trace amounts of 9-cis betaC were found in serum. These results demonstrate that the algae D. bardawil and D. salina provide a bioavailable source of betaC isomers, but, as in humans, absorption of 9-cis betaC is poor and any 9-cis betaC absorbed is apparently cleared by the liver.

Ferrets (Mustela putoius furo) inefficiently convert beta-carotene to vitamin A.

The ferret has recently been used as a model to evaluate the absorption and metabolism of several carotenoids; however, little is known about the vitamin A (VA) requirements of this species or the ability of ferrets to convert dietary beta-carotene (betaC) to VA. Three studies were conducted to estimate the daily utilization of VA in ferrets and to determine the effect of prior VA status on the ability of ferrets to utilize betaC as a source of VA. Weanling male ferrets were fed a pelleted, low carotenoid, semipurified diet either with (+VA) or without VA (-VA) for 21- to 35-d prefeeding periods. Upon initiation of the experiments, several ferrets were killed to determine base-line VA status. The remaining ferrets were fed VA, betaC, or VA and betaC in pelleted feed (Studies 1-3) or liquid carrier (Study 3) for 16-21 additional days. Hepatic VA and betaC concentrations were used as the primary indicators of VA status, although serum and adrenal VA and betaC also were measured. The results showed the following: 1) provision of betaC at up to a 15:1 weight ratio of betaC to VA in pelleted feed or liquid carrier was not sufficient to maintain hepatic VA stores after a -VA prefeeding period; 2) the daily utilization rate of VA by ferrets ranged from 80 to 171 microg in the three studies; 3) the ferret was confirmed to be a species that has the majority of its serum VA in ester form; and 4) feeding -VA diets significantly reduced serum retinyl esters but had less effect on serum retinol. We conclude that although ferrets can convert betaC to VA, the process is inefficient. The ferret model can be most appropriately used when studying the biological effect of tissue betaC stores on VA status and is less appropriate for the evaluation of dietary betaC conversion to VA.

The mongolian gerbil (Meriones unguiculatus) is an appropriate animal model for evaluation of the conversion of beta-carotene to vitamin A.

Vitamin A (VA) deficiency is the leading cause of blindness in children in developing countries. Dietary intervention with foods rich in provitamin A carotenoids, such as beta-carotene (betaC), has been suggested as one solution to this problem. The objective of the two studies described in this paper was to examine the utilization of betaC as a source of VA at different stages of VA depletion using the Mongolian gerbil as a model. Male 4- to 5-wk-old Mongolian gerbils were fed powdered betaC-free semipurified diets either with or without VA for 26 d (Study 1), or without VA for 8-10 wk (Study 2). Gerbils were then fed diets with or without VA (20.9 nmol/g diet) and/or betaC [(67.0 micromol/g diet (Study 1) and 145.9 micromol/g diet (Study 2)] for variable periods. Two (Study 1) or three (Study 2) days before termination of the study, 3-4 gerbils per group were dosed orally with 14C-betaC. Tissues were evaluated for VA and betaC content by HPLC. Liver was extracted with and without saponification to evaluate 14C-betaC and 14C-VA content. The results demonstrate the following: 1) the gerbil is an appropriate animal model to study betaC utilization; 2) 20.9 nmol VA/g diet is more than sufficient for this species; 3) the daily VA utilization rate for this species is calculated to be 3.1 microg/100 g body weight; 4) a highly bioavailable source of betaC at a 6:1 weight ratio of betaC:VA is sufficient to reverse marginal VA status in this model; and 5) a highly bioavailable source of betaC fed between a 6:1 and 13:1 weight ratio to VA provides equivalent VA status as preformed VA in Mongolian gerbils.