Tissue Stores of β-Carotene Are Not Conserved for Later Use as a Source of Vitamin A during Compromised Vitamin A Status in Mongolian Gerbils (Meriones unguiculatus)

Abstract

Vitamin A (VA) deficiency remains a serious problem in the world today. Current approaches to preventing or treating VA deficiency, including dietary intervention with provitamin A compounds, rely on the body converting ingested beta-carotene (betaC) to VA. However, it is not known whether betaC that is already in the tissues can be used as a source of VA to prevent deficiency. The objectives of these studies were to determine whether tissue betaC stores are converted to VA when the Mongolian gerbils have low VA status and whether previously fed betaC is retained in the tissues for later conversion to VA. In the first study, gerbils were prefed diets with betaC (20.3 +/- 6.2 nmol/g diet) (+betaC) or without betaC (-betaC), and with VA [2.4 +/- 1.5 nmol/g diet (+betaC diet) or 12.0 +/- 4.2 nmol/g diet (-betaC diet)] for 7 d, and then depleted of both betaC and VA for up to 84 d. On d 0 after the prefeeding period, hepatic betaC stores were 13.3 +/- 9.1 nmol. These stores were significantly lower after 28d of consuming the -VA/-betaC diet (2.16 +/- 1.7 nmol), even though the hepatic VA concentrations did not change. In the second study, the gerbils were prefed a -VA/+betaC diet (74.3 +/- 19. 7 nmol betaC/g diet) for 7 d, and then fed a betaC-free diet either with (7.1 +/- 1.4 nmol/g) or without VA for up to 34 d. Hepatic betaC stores after the 7-d prefeeding period were 38.1 +/- 20.6 nmol, and were significantly higher than after 7d of consuming either a +VA/-betaC (12.4 +/- 10.8 mmol) or -VA/-betaC diet (11.4 +/- 8.0 nmol). The results from both studies suggest that a substantial amount of hepatic betaC is rapidly lost when betaC is eliminated from the diet and therefore is not conserved to meet later VA needs. The presence of VA in the diet (Study 2) did not affect the rate of betaC loss from the serum and tissues. Moreover, no evidence was found that the stored betaC was utilized for VA. The data suggest that there may be two pools of hepatic betaC, one that is lost rapidly and another that is lost more slowly over time, but losses are not affected by VA status.

Biosynthesis, Absorption, Metabolism and Transport of Retinoids

“…Recently this intriguing possibility has been explored experimentally. THATCHER et al (1998) investigated whether ~carotene present (stored) within tissues of the Mongolian gerbil was used as a source for retinoid synthesis when the gerbils were placed on a retinoid-deficient diet. Specifically, THATCHER et al (1998), using different nutritional protocols, observed that loss of fj-carotene from serum and tissues was not influenced by the presence of retinoid in the diet.…”

Bioavailability of β-carotene (βC) from purple carrots is the same as typical orange carrots while high-βC carrots increase βC stores in Mongolian gerbils(Meriones unguiculatus)

“…Mongolian gerbils absorb bC intact at physiological doses and accumulate bC in liver, spleen, kidney, adrenal, adipose, and lung (Pollack et al 1994). Mongolian gerbils convert bC to VA with similar efficiency to that of man (Lee et al 1998) and bC consumption results in accumulation of hepatic and extrahepatic VA stores (House et al 1997;Lee et al 1998;Thatcher et al 1998). Furthermore, once bC is removed from the diet, liver bC stores are rapidly depleted and not utilised for VA (Thatcher et al 1998).…”

“…Mongolian gerbils convert bC to VA with similar efficiency to that of man (Lee et al 1998) and bC consumption results in accumulation of hepatic and extrahepatic VA stores (House et al 1997;Lee et al 1998;Thatcher et al 1998). Furthermore, once bC is removed from the diet, liver bC stores are rapidly depleted and not utilised for VA (Thatcher et al 1998). No study to date has tested the effect of purple carrot phenolic compounds on bC absorption.…”

Methods for Assessing Aspects of Carotenoid Bioavailability

“…A major disadvantage can be their small size and weight, impeding the sampling of large volumes of tissues, or to conduct any operations. In addition, in contrast to other animal species, including rats, Mongolian gerbils seem to be relatively resistant to vitamin A deficiency, taking months to develop symptoms, regardless of the original liver and nutritional vitamin A status [30,193,194]. Humans have shown symptoms of vitamin A deficiency such as impaired dark adaptation after several months [195] -being in contrast to gerbils if one considers the short live time of the animals.…”