Use of Compartmental Modeling and Retinol Isotope Dilution to Determine Vitamin A Stores in Young People with Sickle Cell Disease Before and After Vitamin A Supplementation.

BACKGROUND: Suboptimal plasma retinol concentrations have been documented in US children with sickle cell disease (SCD) hemoglobin SS type (SCD-HbSS), but little is known about vitamin A kinetics and stores in SCD. OBJECTIVES: The objectives were to quantify vitamin A total body stores (TBS) and whole-body retinol kinetics in young people with SCD-HbSS and use retinol isotope dilution (RID) to predict TBS in SCD-HbSS and healthy peers as well as after vitamin A supplementation in SCD-HbSS subjects. METHODS: Composite plasma [13C10]retinol response data collected from 22 subjects with SCD-HbSS for 28 d after isotope ingestion were analyzed using population-based compartmental modeling ("super-subject" approach); TBS and retinol kinetics were quantified for the group. TBS was also calculated for the same individuals using RID, as well as for healthy peers (n = 20) and for the subjects with SCD-HbSS after 8 wk of daily vitamin A supplements (3.15 or 6.29 µmol retinol/d [900 or 1800 µg retinol activity equivalents/d]). RESULTS: Model-predicted group mean TBS for subjects with SCD-HbSS was 428 µmol, equivalent to ∼11 mo of stored vitamin A; vitamin A disposal rate was 1.3 µmol/d. Model-predicted TBS was similar to that predicted by RID at 3 d postdosing (mean, 389 µmol; ∼0.3 µmol/g liver); TBS predictions at 3 compared with 28 d were not significantly different. Mean TBS in healthy peers was similar (406 µmol). RID-predicted TBS for subjects with SCD-HbSS was not significantly affected by vitamin A supplementation at either dose. CONCLUSIONS: Despite differences in plasma retinol concentrations, TBS was the same in subjects with SCD-HbSS compared with healthy peers. Because 56 d of vitamin A supplementation at levels 1.2 to 2.6 times the Recommended Dietary Allowance did not increase TBS in these subjects with SCD-HbSS, further work will be needed to understand the effects of SCD on retinol metabolism. This trial was registered as NCT03632876 at clinicaltrials.gov.

Use of Theoretical Subjects to Develop a Method for Assessing Equivalence of Dietary Vitamin A in a Mixed Diet.

BACKGROUND: Although the vitamin A (VA) equivalency of provitamin A carotenoids from single foods or capsules has been studied using several approaches, there is currently no reliable method to determine VA equivalency for mixed diets. OBJECTIVES: To reach the objective of identifying a method to determine the VA equivalency of provitamin A carotenoids in mixed diets, we tested a new approach using preformed VA as proxy for provitamin A. METHODS: We studied 6 theoretical subjects who were assigned physiologically plausible values for dietary VA intake, retinol kinetic parameters, plasma retinol pool size, and VA total body stores. Using features in the Simulation, Analysis and Modeling software, we specified that subjects ingested a tracer dose of stable isotope-labeled VA on day 0 followed by 0-µg supplemental VA or 200, 400, 800, 1200, 1600, and 2000 µg VA daily from day 14 to day 28; we assigned VA absorption to be 75%. For each supplement level, we simulated plasma retinol specific activity (SAp) over time and calculated the mean decrease in SAp relative to 0 µg. Group mean data were fitted to a regression equation to calculate predicted VA equivalency at each supplement level on day 28. RESULTS: For each subject, higher VA supplement loads resulted in lower SAp, with the magnitude of the decrease differing among subjects. The mean predicted amount of absorbed VA was within 25% of individual subjects' assigned amount for 4 of the 6 subjects, and the mean ratio of predicted to assigned amount of absorbed VA over all supplement loads ranged from 0.60 to 1.50, with an overall mean ratio of 1.0. CONCLUSIONS: Results for preformed VA suggest that this protocol may be useful for determining VA equivalency of provitamin A carotenoids in free-living subjects if mixed diets with known provitamin A content were substituted for the VA supplements.

Kinetics of omega-3 fatty acid transfer to milk differs between fatty acids and stage of lactation in dairy cows.

Fatty acids (FA) differ in their transfer efficiencies and metabolic partitioning and lactating cows provide a robust model to investigate kinetics of FA transport. The objective was to compare kinetics of n-3 polyunsaturated FA (PUFA) trafficking through plasma and into milk. In the first experiment, ten ruminally cannulated multiparous Holstein cows were used in a crossover design with 7 d periods. Cows were milked at 6 h intervals and abomasal treatments provided a single dose of 80.1 g of α-linolenic acid as free FA (ALA-FFA) or 45.5 g EPA and 32.9 g DHA (LCn3-FFA). Transfer of n-3 PUFA to milk was nearly 50% higher for ALA-FFA than LCn3-FFA (48.2 and 32.7% of the bolus) and fit a bi-exponential model. Rapid transport of n-3 PUFA, assumed to be directly through chylomicrons, was nearly twice as high in ALA-FFA than LCn3-FFA and the subsequent slow transport, assumed to be indirect transfer through tissue recycling, was over 2.5-fold higher in LCn3-FFA than in ALA-FFA. Plasma analysis revealed LCn3-FFA enriched phospholipids and cholesterol esters, which had a slow clearance. In the second experiment, 4 cows received a bolus of a mixture of ALA, EPA, and DHA prepartum while not lactating and around d 10, 55, and 225 of lactation. Transfer of ALA to milk did not differ between stages of lactation, but DHA was lower in early compared to mid and late lactation. In conclusion, dietary ALA is rapidly and efficiently transferred to milk in cows while EPA and DHA are rapidly incorporated into plasma or tissue fractions not available to the mammary gland. This demonstrates clear differences in trafficking and partitioning of n-3 PUFA that ultimately impact tissue and organelle enrichment with implications for effective doses.

Priming with Retinoic Acid, an Active Metabolite of Vitamin A, Increases Vitamin A Uptake in the Small Intestine of Neonatal Rats.

Given that combined vitamin A (VA) and retinoic acid (RA) supplementation stimulated the intestinal uptake of plasma retinyl esters in neonatal rats, we administrated an RA dose as a pretreatment before VA supplementation to investigate the distinct effect of RA on intestinal VA kinetics. On postnatal days (P) 2 and 3, half of the pups received an oral dose of RA (RA group), while the remaining received canola oil as the control (CN). On P4, after receiving an oral dose of 3H-labeled VA, pups were euthanized at selected times (n = 4-6/treatment/time) and intestine was collected. In both CN and RA groups, intestinal VA mass increased dramatically after VA supplementation; however, RA-pretreated pups had relatively higher VA levels from 10 h and accumulated 30% more VA over the 30-h study. Labeled VA rapidly peaked in the intestine of CN pups and then declined from 13 h, while a continuous increase was observed in the RA group, with a second peak at 10 h and nearly twice the accumulation of 3H-labeled VA compared to CN. Our findings indicate that RA pretreatment may stimulate the influx of supplemental VA into the intestine, and the increased VA accumulation suggests a potential VA storage capacity in neonatal intestine.

The "Super-Child" Approach Is Applied To Estimate Retinol Kinetics and Vitamin A Total Body Stores in Mexican Preschoolers.

BACKGROUND: Retinol isotope dilution (RID) and model-based compartmental analysis are recognized techniques for assessing vitamin A (VA) status. Recent studies have shown that RID predictions of VA total body stores (TBS) can be improved by using modeling and that VA kinetics and TBS in children can be effectively studied by applying population modeling ("super-child" approach) to a composite data set. OBJECTIVES: The objectives were to model whole-body retinol kinetics and predict VA TBS in a group of Mexican preschoolers using the super-child approach and to use model predictions of RID coefficients to estimate TBS by RID in individuals. METHODS: Twenty-four healthy Mexican children (aged 3-6 y) received an oral dose (2.96 µmol) of [13C10]retinyl acetate in corn oil. Blood samples were collected from 8 h to 21 d after dosing, with each child sampled at 4 d and at 1 other time. Composite data for plasma labeled retinol compared with time were analyzed using a 6-component model to obtain group retinol kinetic parameters and pool sizes. Model-predicted TBS was compared with mean RID predictions at 4 d; RID estimates at 4 d were compared with those calculated at 7-21 d. RESULTS: Model-predicted TBS was 1097 µmol, equivalent to ∼2.4 y-worth of VA; using model-derived coefficients, group mean RID-predicted TBS was 1096 µmol (IQR: 836-1492 µmol). TBS at 4 d compared with a later time was similar (P = 0.33). The model predicted that retinol spent 1.5 h in plasma during each transit and recycled to plasma 13 times before utilization. CONCLUSIONS: The super-child modeling approach provides information on whole-body VA kinetics and can be used with RID to estimate TBS at any time between 4 and 21 d postdose. The high TBS predicted for these children suggests positive VA balance, likely due to large-dose VA supplements, and warrants further investigation.

Vitamin A supplementation redirects the flow of retinyl esters from peripheral to central organs of neonatal rats raised under vitamin A-marginal conditions.

Background: Vitamin A (VA; retinol) supplementation is used to reduce child mortality in countries with high rates of malnutrition. Existing research suggests that neonates (<1 mo old) may have a limited capacity to store VA in organs other than the liver; however, knowledge about VA distribution and kinetics in individual, nonhepatic organs is limited.Objective: We examined retinol uptake and turnover in nonhepatic organs, including skin, brain, and adipose tissue, in neonatal rats without and after VA supplementation.Design: Sprague-Dawley neonatal rats (n = 104) were nursed by mothers fed a VA-marginal diet (0.35 mg retinol/kg diet) and treated on postnatal day 4 with an oral dose of either VA (6 µg retinyl palmitate/g body weight) or canola oil (control), both containing 1.8 µCi of [3H]retinol. Subsequently, pups (n = 4 · group-1 · time-1) were killed at 13 different times from 30 min to 24 d after dosing. The fractional and absolute transfer of chylomicron retinyl esters (CM-REs), retinol bound to retinol-binding protein (RBP-ROH), and total retinol were estimated in WinSAAM software.Results: VA supplementation redirected the flow of CM-REs from peripheral to central organs and accumulated mainly in the liver. The RBP-ROH released from the liver was acquired mainly by the peripheral tissues but not retained efficiently, causing repeated recycling of retinol between plasma and tissues (541 compared with 5 times in the supplemented group and control group, respectively) and its rapid turnover in all organs, except the brain and white adipose tissue. Retinol stores in the liver lasted for ∼2 wk before being gradually transferred to other organs.Conclusions: VA supplementation administered in a single high dose during the first month after birth is readily acquired but not retained efficiently in peripheral tissues of neonatal rats, suggesting that a more frequent, lower-dose supplementation may be necessary to maintain steady VA concentrations in rapidly developing neonatal tissues.

Vitamin A and retinoic acid combined have a more potent effect compared to vitamin A alone on the uptake of retinol into extrahepatic tissues of neonatal rats raised under vitamin A-marginal conditions.

BACKGROUND: Vitamin A (VA, retinol) supplementation is widely used to reduce child mortality in low-income countries. However, existing research suggests that supplementation with VA alone may not be optimal for infants. OBJECTIVE: We compared the effect of VA vs. VA combined with retinoic acid (VARA) on retinol uptake and turnover in organs of neonatal rats raised under VA-marginal conditions. METHODS: Secondary analysis was conducted on data obtained from two prior kinetic studies of Sprague-Dawley neonatal rats nursed by mothers fed a VA-marginal diet (0.35 mg retinol equivalents/kg diet). On postnatal d 4, pups had been treated with a single dose of VA (6 µg/g; n = 52; VA study), VA + 10% retinoic acid (6 µg/g; n = 42; VARA study) or placebo (canola oil; n = 94; both studies), all containing ~2 µCi of [3H]retinol as the tracer for VA. Total retinol concentrations and tracer levels had been measured in plasma and tissues from 1 h to 14 d after dosing. Control group data from both studies were merged prior to analysis. Kinetic parameters were re-estimated and compared statistically. RESULTS: VARA supplementation administered to neonatal rats within a few days after birth resulted in a lower turnover of retinol in the lungs, kidneys, and carcass and less frequent recycling of retinol between plasma and organs (100 vs. 288 times in VARA- vs. VA-treated group). Although the VA supplementation resulted in a higher concentration of retinol in the liver, VARA supplementation led to a higher uptake of postprandial retinyl esters into the lungs, intestines, and carcass. CONCLUSIONS: Given the relatively higher retinol uptake into several extrahepatic organs of neonates dosed orally with VARA, this form of supplementation may serve as a targeted treatment of low VA levels in the extrahepatic organs that continue to develop postnatally.

Vitamin A Supplementation Increases the Uptake of Chylomicron Retinyl Esters into the Brain of Neonatal Rats Raised under Vitamin A-Marginal Conditions.

BACKGROUND: The most rapid phase of brain development occurs during the neonatal period. Vitamin A (VA; retinol) is critical for many aspects of this process, including neurogenesis, synaptic plasticity, learning, and memory formation. However, the metabolism of retinol in the neonatal brain has not been extensively explored. OBJECTIVE: We examined the uptake of VA into the brain in neonatal rats raised under VA-marginal conditions (control group) and assessed the effect of VA supplementation on the uptake of VA into the brain. METHODS: Sprague-Dawley neonatal rats (n = 104) nursed by mothers fed a VA-marginal diet were randomly assigned and treated on postnatal day 4 with an oral dose of either VA (6 µg retinyl palmitate/g body weight) or canola oil as the control, both of which contained 1.8 µCi [(3)H]retinol. Pups (n = 4/group at a time) were killed at 13 sampling times from 30 min to 24 d after dosing. The uptake of total retinol, chylomicron-associated retinyl esters (REs), and retinol bound to retinol-binding protein (RBP) was estimated with the use of WinSAAM version 3.0.8. RESULTS: Total retinol mass in the brain was closely dependent on its mass in plasma over time (r = 0.91; P < 0.001). The uptake of retinol into the brain involved both postprandial chylomicrons and RBP, with RBP delivering most of the retinol in the control group [0.27 nmol/d (RBP) compared with 0.01 nmol/d (chylomicrons)]. VA supplementation increased the fractional uptake of chylomicron REs from 0.3% to 1.2% of plasma pool/d, decreased that of RBP retinol from 0.5% to 0.2% of plasma pool/d, and increased the transfer rate of chylomicron REs from nearly zero to 0.7 nmol/d, causing a day-long elevation in the brain mass of total retinol. CONCLUSION: Postprandial chylomicrons may be a primary mechanism for delivering a recently ingested large dose of VA to the brain of neonatal rats raised under VA-marginal conditions.

Vitamin A Supplementation Transiently Increases Retinol Concentrations in Extrahepatic Organs of Neonatal Rats Raised under Vitamin A-Marginal Conditions.

BACKGROUND: Vitamin A (VA; retinol) supplementation is recommended for children aged >6 mo in countries with high rates of malnutrition, but the distribution and retention of VA in body tissues have not been extensively explored. OBJECTIVE: We sought to determine the distribution and retention of VA in tissues of neonatal rats raised under VA-marginal conditions. METHODS: Sprague-Dawley neonatal rats (n = 104; 63 males) nursed by mothers fed a VA-marginal diet (0.35 mg retinol equivalents/kg diet) were randomized and treated on postnatal day 4 with an oral dose of either VA (6 µg retinyl palmitate/g body weight) or canola oil as control. Pups (n = 4/group) were killed at 13 time points from 30 min to 24 d after dose administration. The total retinol concentration and mass were determined in all collected organs. RESULTS: In the control group, plasma VA was marginal (0.8 µmol/L), whereas liver VA was deficient (<70 nmol/g). Nonetheless, the liver contained most (∼76%) of the total VA mass in the body, whereas extrahepatic nondigestive organs together contained ∼13%. White adipose tissue (WAT), which was nearly absent before postnatal day 12, contained only ∼1%. In VA-supplemented neonates, the mean total retinol concentrations in all organs were significantly greater than in control pups. However, this increase lasted for only ∼1 d in most extrahepatic tissues, with the exception of WAT, in which it lasted 18 d. CONCLUSIONS: Extrahepatic organs in neonatal rats raised under VA-marginal conditions store relatively little VA, and the scarcity of adipose tissue may predispose neonates to a low-VA status. The effect of VA supplementation on VA content in most extrahepatic organs is transient. A more frequent supplementation along with other nutritional interventions may be necessary for maintaining a steady supply of retinol to the rapidly developing extrahepatic organs.

Direct and indirect vitamin A supplementation strategies result in different plasma and tissue retinol kinetics in neonatal rats.

Many questions remain regarding vitamin A (VA) supplementation of infants. Herein we compared direct oral VA supplementation of the neonate and indirect treatment through maternal dietary VA (M-VA) treatment on VA status and kinetics in neonatal rats. Treatments included direct VA combined with retinoic acid (RA) [D-VARA; VA (6 mg/kg) + 10% RA, given orally to neonates on postnatal day (P)2 and P3] and indirect VA supplementation through increased M-VA, compared with each other and oil-treated neonates. [(3)H]retinol was administered orally to all neonates on P4. Plasma and tissue [(3)H]retinol kinetics were determined from 1 h to 14 days post-dosing. D-VARA versus placebo dramatically increased liver and lung retinol, but only in the first 8-10 days. In M-VA neonates, liver and lung VA increased progressively throughout the study. Compartmental modeling of plasma [(3)H]retinol showed that both D-VARA and indirect M-VA reduced retinol recycling between plasma and tissues. Compartmental models of individual tissues predicted that D-VARA stimulated the uptake of VA in chylomicrons to extrahepatic tissues, especially intestine, while the uptake was not observed in M-VA neonates. In conclusion, indirect maternal supplementation had a greater sustained effect than D-VARA on neonatal VA status, while also differentially affecting plasma and tissue retinol kinetics.

Vitamin A kinetics in neonatal rats vs. adult rats: comparisons from model-based compartmental analysis.

A critical role for vitamin A (VA) in development is well established, but still relatively little is known about whole-body VA metabolism in early postnatal life. Recently, methods of mathematical modeling have begun to shed light on retinol kinetics in the postnatal growth period and on the effect of retinoid supplementation on retinol kinetics. Comparison of kinetic parameters from tracer studies in neonatal rats with those previously determined in models of VA metabolism in the adult suggests both similarities and differences in the relative transfer rates of plasma retinol to extrahepatic tissues, resulting in similarities and differences in kinetic parameters and inferences about physiologic processes. Similarities between neonatal and adult models include the capacity for efficient digestion and absorption of VA; characteristics of a high-response system; extensive retinol recycling among liver, plasma, and extrahepatic tissues; and comparable VA disposal rates. Differences between neonatal and adult models include that, in neonates, retinol turnover is faster and retinol recycling is much more extensive; there is a greater role for extrahepatic tissues in the uptake of chylomicron VA; and the intestine plays an important role in chylomicron VA uptake, especially in neonatal rats treated with a supplement containing VA. In summary, retinol kinetic modeling in the neonatal rat has provided a first view of whole-body VA metabolism in this age group and suggests that VA kinetics in neonatal rats differs in many ways from that in adults, perhaps reflecting an adaption to the lower VA concentration found in neonates compared with adults.

Compartmental modeling of whole-body vitamin A kinetics in unsupplemented and vitamin A-retinoic acid-supplemented neonatal rats.

Little is known about the contribution of different tissues to whole-body vitamin A (VA) kinetics in neonates. Here, we have used model-based compartmental analysis of tissue tracer kinetic data from unsupplemented (control) and VA-retinoic acid (VARA)-supplemented neonatal rats to determine VA kinetics in specific tissues under control and supplemented conditions. First, compartmental models for retinol kinetics were developed for individual tissues, and then an integrated compartmental model incorporating all tissues was developed for both groups. The models predicted that 52% of chylomicron (CM) retinyl ester was cleared by liver in control pups versus 22% in VARA-treated pups, whereas about 51% of VA was predicted to be extrahepatic in 4- to 6-day-old unsupplemented neonatal rats. VARA increased CM retinyl ester uptake by lung, carcass, and intestine; decreased the release into plasma of retinol that had been cleared by liver and lung as CM retinyl esters; stimulated the uptake of retinol from plasma holo-retinol binding protein into carcass; and decreased the retinol turnover out of the liver. Overall, neonatal VA trafficking differed from that previously described for adult animals, with a larger contribution of extrahepatic tissues to CM clearance, especially after VA supplementation, and a significant amount of VA distributed in extrahepatic tissues.

Retinol kinetics in unsupplemented and vitamin A-retinoic acid supplemented neonatal rats: a preliminary model.

Vitamin A (VA) metabolism in neonates is virtually uncharacterized. Our objective was to develop a compartmental model of VA metabolism in unsupplemented and VA-supplemented neonatal rats. On postnatal day 4, pups (n = 3/time) received 11,12-[(3)H]retinol orally, in either oil (control) or VA combined with retinoic acid (VARA) [VA (∼6 mg/kg body weight) + 10% retinoic acid]. Plasma and tissues were collected at 14 time points up to 14 days after dose administration. VARA supplementation rapidly, but transiently, increased total retinol mass in plasma, liver, and lung. It decreased the peak fraction of the dose in plasma. A multi-compartmental model developed to fit plasma [(3)H]retinol data predicted more extensive recycling of retinol between plasma and tissues in neonates compared with that reported in adults (144 vs. 12-13 times). In VARA pups, the recycling number for retinol between plasma and tissues (100 times) and the time that retinol spent in plasma were both lower compared with controls; VARA also stimulated the uptake of plasma VA into extravascular tissues. A VARA perturbation model indicated that the effect of VARA in stimulating VA uptake into tissues in neonates is both dramatic and transient.

Vitamin A-fortified milk increases total body vitamin A stores in Mexican preschoolers.

Vitamin A (VA) deficiency (VAD) continues to be a major nutritional problem in developing countries, including Central America. In Mexico, milk is a well-accepted vehicle for the administration of micronutrients, including VA, to preschoolers. Thus, we conducted a randomized, controlled, clinical trial to investigate the efficacy of daily consumption of 250 mL of VA-fortified milk (which provided 196 retinol equivalents/d) for 3 mo on VA stores in mildly to moderately VAD (serum retinol concentration 0.35-0.7 µmol/L) preschoolers who were not enrolled in a food assistance program. Twenty-seven mildly to moderately VAD children were randomly assigned based on screening measurements to either the intervention (n = 14) or control group (n = 13) (children in the control group did not receive placebo). All children in the control group and 79% (n = 11) of the children in the intervention group completed the study. The total body VA (TBVA) pool size was estimated using the deuterated retinol dilution technique before and after the intervention. After 3 mo, median changes in the serum retinol concentration for the intervention and control groups were 0.13 and -0.21 µmol/L, respectively (P = 0.009). Median changes in the TBVA stores were 0.06 and 0.01 mmol, respectively (P = 0.006) and estimated median changes in the liver VA concentration were 0.09 and 0.01 µmol/g, respectively (P = 0.002). The VA-fortified milk was well accepted among preschoolers and significantly increased TBVA stores, liver VA stores, and serum retinol concentration, indicating that it may be an effective means to ameliorate VAD in young Mexican children.

No improvement in suboptimal vitamin A status with a randomized, double-blind, placebo-controlled trial of vitamin A supplementation in children with sickle cell disease.

BACKGROUND: Suboptimal vitamin A status is prevalent in children with type SS sickle cell disease (SCD-SS) and is associated with hospitalizations and poor growth and hematologic status. The supplemental vitamin A dose that optimizes suboptimal vitamin A status in this population is unknown. OBJECTIVE: The efficacy of Recommended Dietary Allowance (RDA) doses (based on age and sex) of vitamin A (300, 400, or 600 µg retinyl palmitate/d) or vitamin A + zinc (10 or 20 mg zinc sulfate/d) compared with placebo to optimize vitamin A status was assessed in children aged 2.0-12.9 y with SCD-SS and a suboptimal baseline serum retinol concentration (<30 µg/dL). DESIGN: In this randomized, double-blind, placebo-controlled trial, vitamin A status (serum retinol, prealbumin, retinol-binding protein, and relative-dose-response test) and disease-related illness events were assessed. RESULTS: Twelve months of vitamin A supplementation at the doses recommended for healthy US children (based on age and sex) failed to improve serum retinol values in either group (vitamin A: n = 23; vitamin A + zinc: n = 18) compared with placebo (n = 21). By 12 mo, the increase (±SD) in serum retinol (3.6 ± 2.8 µg/dL) in those taking 600 µg vitamin A/d was significantly different from the decrease (±SD; -2.8 ± 2.4 µg/dL) in those taking 300 µg/d, which possibly suggests a dose-response relation (P < 0.05) with RDA doses. CONCLUSIONS: Compared with placebo, 12 mo of vitamin A supplementation at the RDA for healthy children did not improve serum retinol values in children with SCD-SS, which possibly suggests that higher doses are needed. However, the existence of alternative conclusions emphasizes the need for future research.

Plasma turnover of 3,4-didehydroretinol (vitamin A2) increases in vitamin A-deficient rats fed low versus high dietary fat.

Relationships between increased adiposity and fat-soluble vitamin storage and metabolism are poorly understood. To examine these associations, 6% or 21% dietary fat was fed to rats for 11 weeks and tissue vitamin A storage determined. Two levels of supplemental vitamin A were administered. At the end of the tenth week, 3,4-didehydroretinol (DR) was administered orally, and its kinetics were followed for 1 week in serum and tissues. Model-based compartmental analysis was applied to these data. Kidney total retinol (R) concentrations were elevated in rats fed 6% compared with 21% dietary fat (n = 24/group). The fractional transfer coefficient (FTC) describing the movement of tracer from plasma to extravascular stores was two times higher in the 6% compared with the 21% fat group. Consistent with the elevated renal R in 6% fat fed rats, there was a 2-fold increase in the FTC representing tracer distribution from plasma to kidney in the 6% compared with 21% fat group. Taken together with a fat main effect on renal vitamin A, our data support the evidence that faster turnover of kidney R may help set the mechanism governing vitamin A tissue distribution during deficiency. Rats fed 21% versus 6% dietary fat conserved hepatic R more efficiently.

alpha-Lipoic acid and glutathione protect against the prooxidant activity of SOD/catalase mimetic manganese salen derivatives.

Manganese(III) N,N'-ethylenebis(salicylideneiminato) chloride (Mn-salen chloride) and manganese(III) N,N'-ethylenebis(3-methoxysalicylideneiminato) chloride (Mn-(3,3'-MeO)salen chloride) are in vitro superoxide dismutase and catalase mimetics. They protect against free radical-related disease in animals, but Mn-salen can also be a potent prooxidant, damaging free DNA. Mn-salen protects human fibroblast DNA against hydrogen peroxide damage, however, damage to free DNA was confirmed by the comet assay. The DNA-damaging activity was dramatically reduced by co-administration with glutathione with the combination being less damaging to free DNA than either molecule alone. alpha-Lipoic acid, an antioxidant disulfide commonly used as a dietary supplement, also prevented Mn-salen prooxidant activity. Mn-(3,3'-MeO)salen protected fibroblasts against hydrogen peroxide as efficiently as Mn-salen and showed little damaging activity against free DNA. Protection was invested by both complexes in the presence and in the absence of EDTA, a potential competing chelator. Stabilities of the complexes with respect to decomposition and inactivation were studied by spectroscopic and electrochemical techniques. The complexes' binding to, and cleavage of, DNA was measured using a quartz crystal resonant sensor. Mn-salen was shown to bind strongly to DNA, prior to cleaving it; Mn-(3,3'-MeO)salen bound weakly and left DNA intact. Co-administration of either glutathione or alpha-lipoic acid appears to inhibit binding by Mn-salen thus preventing DNA-cleavage.

Dietary retinoic acid alters vitamin A kinetics in both the whole body and in specific organs of rats with low vitamin A status.

To study the effects of exogenous retinoic acid on vitamin A (VA) metabolism, we analyzed previously collected tracer kinetic data on VA dynamics in rats with low vitamin A (LA) status either with (LA+RA) or without (LA) retinoic acid supplementation. In spite of low VA intake ( approximately 7 nmol/d), the LA+RA rats were in a slight positive VA balance (0.325 nmol/d vs. -0.168 for LA) for 35 d after administration of [(3)H]retinol-labeled plasma. Using the Windows version of the Simulation, Analysis and Modeling software, we determined that the VA disposal rate was lower in LA+RA than in LA rats (3.98 vs. 5.00 nmol/d) as was the system fractional catabolic rate (0.0548 vs. 0.110 d(-1)). Model-predicted traced mass and residence times (the average time that a molecule of retinol spends in an organ before irreversible loss) were higher for liver (19.4 vs. 1.8 nmol; 5.0 vs. 0.36 d), kidneys (7.0 vs. 2.1 nmol; 1.4 vs. 0.42 d), small intestine (2.1 vs. 0.42 nmol; 0.43 vs. 0.084 d), and lungs (3.2 vs. 0.10 nmol; 1.6 vs. 0.021 d) in the LA+RA compared with the LA rats; there were no major differences for eyes, testes, adrenal glands, or remaining carcass. We conclude that RA supplementation of rats with low VA status affects VA metabolism at both the whole-body level and in specific organs. These organs (liver, kidneys, small intestine, and lungs) have the enzymatic capability and an appropriate cell type to store retinyl esters.