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Articles

All-rac--Tocopherol Acetate Is a Better Vitamin E Source than all-rac--Tocopherol Succinate for Broilers¹

Department of Animal Nutrition and Physiology, Danish Institute of Agricultural Sciences, Research Centre Foulum, DK-8830 Tjele, Denmark

²To whom correspondence should be addressed.

	ABSTRACT

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The difference in bioavailabilities of the acetate and succinate esters of all-rac--tocopherol was investigated in a feeding experiment with broilers. The experiment was initiated with 96 12-d-old male Cobb broilers and lasted for 4 wk. The two sources of vitamin E were fed to eight groups of broilers at four different dietary levels (50, 100, 150 and 200 mg/kg feed, including the naturally occurring -tocopherol). A total collection of droppings for determination of apparent tocopherol absorption were performed at two separate time periods (d 28–34 and d 35–41). There were no differences among the eight experimental groups with respect to animal performance or feed intake. At all dietary levels, the apparent absorption coefficient for all-rac--tocopherol succinate was significantly lower than that of the acetate ester. The mean (± SD) apparent absorption coefficient for all-rac--tocopherol succinate was 58.0 ± 5.4 compared with 70.8 ± 5.6 for all-rac--tocopherol acetate. Furthermore, the apparent absorption coefficients for both esters was significantly lower in the first collection period (d 28–34) than in the second collection period (d 35–41). This difference in the apparent absorption coefficient between the succinate and the acetate ester was accompanied by significant differences in -tocopherol concentrations in plasma, breast muscle, liver and adipose tissue of the broilers, which were lower in those fed the succinate ester. Based on a comparison of plasma and tissue responses, the succinate ester was utilized only 69–76% as efficiently as the acetate ester. In vitro studies showed a significantly higher capacity of pancreatic carboxyl ester hydrolase to hydrolyze -tocopherol acetate compared to -tocopherol succinate. This difference in intestinal hydrolysis of the two vitamin E sources may explain the observed differences in biopotency.

KEY WORDS: • bioavailability • antioxidant • apparent absorption • pancreatic carboxyl ester hydrolase • broilers

	INTRODUCTION

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In recent years, the level of dietary fat in broiler feeds has increased to raise the energy content of the feed. Rapeseed and soybean oil are some of the most common fat sources and inclusion of 75–100 g oil per kg feed is common practice in Denmark (Jensen et al. 1998 ). This high level of unsaturated fatty acids in the diet is believed to facilitate the absorption of the fat-soluble vitamins (Ullrey 1972 ), but high levels of unsaturated fatty acids in the feed also increases the broilers' demand for antioxidants (Harwitt 1986 ).

Because of the role of tocopherols in the protection of biological membranes against oxidative damage, supplementation of broiler diets with commercially available vitamin E (-tocopherol) is obligatory in most feed formulations (Jakobsen et al. 1995 ). The major source of commercially available vitamin E is synthetic all-rac--tocopherol esterified to acetate or to sodium succinate to protect the phenolic group against oxidation. The acetate ester is an oil at room temperature, whereas the succinate ester is a solid powder; the latter is the most stable at room temperature.

The biological activities of all-rac--tocopherol, all-rac--tocopherol acetate and all-rac--tocopherol succinate, determined by the rat fetal resorption assay, are considered equal on a molar basis (Pryor 1997 ). However, Hidiroglou et al. (1992) demonstrated in an experiment with sheep a significantly lower concentration of -tocopherol in plasma after an oral dose of D--tocopherol succinate compared to an oral dose of D--tocopherol acetate. In a single oral dose experiment with humans, Cheeseman et al. (1995) demonstrated a significantly higher initial concentration 6 and 7 h after administration of -tocopherol originating from the acetate ester compared to the succinate ester.

Prior to absorption in the small intestine both esters require hydrolysis to the free alcohol in the intestinal lumen by pancreatic carboxyl ester hydrolase (CEL)³ (Muller et al. 1976 ) at the concurrent presence of bile salts (Gallo-Torres, 1970 ).

In a feeding experiment with broilers, Combs (1978) compared the utilization of all-rac--tocopherol, the acetate ester thereof and the water-soluble ester D--tocopherol polyethylene glycol 1000 succinate (TPGS). He found an equal utilization of all-rac--tocopherol and all-rac--tocopherol acetate at dietary levels ~40 mg equivalents of all-rac--tocopherol/kg feed . Above that level, the acetate ester was less efficiently utilized than the free alcohol. TPGS was very poorly utilized at all experimental levels. Therefore, Combs (1978) concluded that the affinity of CEL in the intestine of broilers is very low for TPGS relative to all-rac--tocopherol acetate. Furthermore, the activity of this esterase may approach saturation at dietary levels >35–40 mg all-rac--tocopherol equivalents/kg feed.

Because of the uncertainty regarding the utilization of different -tocopherol esters, we compared the applicability of all-rac--tocopherol acetate and all-rac--tocopherol succinate as vitamin E sources in fat-rich broiler feed fed to fast-growing broilers.

	MATERIALS AND METHODS

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Animals and diets.

A total of 96 1-day-old male broiler chickens (Cobb) were obtained from the production plant of The Danish Institute of Agricultural Sciences (Tjele, Denmark) and kept in a floor pen, where they received a starter diet until 12 d of age. The starter diet included a vitamin mixture providing 42 mg vitamin E as all-rac--tocopherol acetate.

On d 12 the birds were weighed and housed two and two in separate metabolism cages. Each pair of birds was randomly assigned to one of eight experimental groups, which were repeated in six blocks. The experiment was conducted over a period of 4 wk, and the chickens had free access to feed and water. Body weight and feed intake were registered weekly. The type of -tocopherol provided was either all-rac--tocopherol succinate or all-rac--tocopherol acetate. The -tocopherol esters were supplied in a silica based matrix by Leo Pharmaceutical Products, DK-2750 Ballerup, Denmark.

The composition of the starter diet as well as of the experimental diets is shown in Table 1. Diets contained, in addition to their natural content, increasing amounts of -tocopherol (20, 60, 100 and 140 mg/kg feed) added either as -tocopherol succinate (group S50, S100, S150 and S200) or as -tocopherol acetate (group A50, A100, A150 and A200).

Determination of tocopherols.

The concentrations of tocopherols were analyzed by HPLC after saponification and extraction into heptane as previously described (Jensen et al. 1998 ). Briefly, 1 g of a finely ground feed sample or 2 g of homogenized droppings were suspended in a mixture of 24.0 mL ethanol (960 mL/L), 9.0 mL methanol, 10.0 mL ascorbic acid in water (200 g/L) and 7.0 mL KOH-water (500 g/L). The mixture was saponified for 30 min at 80°C (boiling) in the dark and cooled in cold water. Exactly 2 mL of the saponified mixture were diluted with 0.50 mL water, after which tocopherols were quantitatively extracted with two portions of 5.0 mL heptane. Determination of tocopherols in blood plasma and tissues was performed by mixing 0.500 mL plasma, 150 mg liver or 400 mg muscle with 2.00 mL ethanol, 0.50 mL methanol, 1.00 mL ascorbic acid solution, 0.30 mL KOH-water (500 g/L) and water to a final volume of 5.50 mL. After saponification (20 min at 70°C) and cooling, tocopherols were quantitatively extracted with two portions of 5 mL heptane. Adipose tissue (100 mg) was dissolved in 10 mL heptane and heated for 2 h in the dark at 70°C before injection into the HPLC.

The HPLC column used for the determination of tocopherols was a 4.0 x 125 mm Perkin Elmer HS-5-Silica column (Perkin-Elmer, Gmbh, D-7770 Überlingen, Germany), and heptane modified with 2-propanol (3.0 mL/L) and degassed with helium constituted the mobile phase. Fluorescence detection was performed with an excitation wavelength of 290 nm and an emission wavelength of 327 nm. Identification and quantification of the tocopherols were obtained by comparison of retention time as well as peak areas with external standards. The following extinction coefficients in ethanol were used: -tocopherol, E_1cm^1% = 71.0 at 294 nm and -tocopherol, E_1cm^1% = 92.8 at 298 nm (Merck D-6100 Darmstadt, Germany).

Apparent absorption experiment.

At two separate time periods (d 28–34 and d 35–41), a total collection of droppings was conducted from three of the blocks. The coefficient for the apparent absorption of -tocopherol was calculated as

Retention of -tocopherol in blood plasma and tissues.

At the end of experiment all birds were slaughtered. Blood plasma and samples of liver, breast muscle (Musculus pectoralis superficialis) and abdominal fat were collected and stored at -80°C until analysis. The intestines of six broilers from groups S150 and A150 were removed. The small intestine was divided into jejunum and ileum, corresponding to segments cranial and caudal to the Meckels diverticulum. The content was emptied and frozen at -20°C for later analysis of digestive enzymes and tocopherol content.

Enzyme activities.

Digesta were diluted in three volumes of an isotonic saline (9 g/L) and homogenized (20,000 rpm, 2 min, 0°C; Ultra Turrax, IKA-Labortechnik, Staufen, Germany). The samples were centrifuged (12,800 x g, 4°C, 20 min), the supernatant was collected for analysis and the pellet was dissolved in the same volume of an isotonic saline solution and centrifugation was repeated. The activities of trypsin, chymotrypsin, amylase, lipase and carboxylester hydrolase were determined in both supernatants, according to procedures described previously (Jensen et al. 1997 ). Benzoyl DL arginine p-nitroanilide (Sigma B 4875, Sigma, St. Louis, MS) and succinyl ala-ala-pro-phe p-nitroanilide (Sigma, S 7388) were used as substrates for the determination of trypsin and chymotrypsin activity, respectively. Amylase activity was measured using the Phadebas^® amylase reagent (Pharmacia Diagnostics, Uppsala, Sweden). The activity of lipase was determined by a titremetric method, in which the hydrolysis of tributyrin by lipase in the presence of bile salts was followed. Carboxylester hydrolase activity was determined using p-nitrophenylacetate (Sigma N 8130) as a substrate.

One unit of enzyme activity was defined as the hydrolysis of 1 µmol of substrate in 1 min. The results of enzyme activities per gram digesta are given as the sum of the mean values from both supernatants.

In vitro hydrolysis of -tocopherol esters by pancreatic CEL.

Pancreatic juice was obtained from pigs that were surgically fitted with a catheter in the pancreatic duct for continuous collection of pure pancreatic juice (Jensen et al. 1997 ). The pancreatic juice was diluted to an CEL activity of 100 U/L with isotonic saline. The in vitro hydrolysis of -tocopherol succinate and -tocopherol acetate was performed in a reagent solution containing 5 mmol/L sodium acetate, 6 mmol/L sodium cholate and 0.3 mol/L Tris/HCl buffer, pH 7.4. The amounts of -tocopherol succinate and -tocopherol acetate varied in the range of 0.5–26 µmol/L. To this solution 0.2 mL diluted pancreatic juice was added, and the final volume was adjusted to 2.0 mL. The enzymatic hydrolysis was allowed to take place for 20 min at 37°C, while the samples were frequently shaken. The reaction was stopped by adding 1.5 mL ethanol and -tocopherol was extracted with 5 mL heptane before analysis by HPLC.

Statistical analysis.

Values in the text are means ± SD; n = 6, for apparent absorption and enzyme activities experiment; n = 12, for plasma and tissue samples. Statistical analysis of the observed results was performed by a three-way ANOVA using the General Linear Models procedure of SAS^® (SAS institute 1988 ):

Where Y_ijk is the dependent variable, µ is the overall mean, _i is the systemic effect of treatment (-tocopherol acetate or succinate), ß is the effect of -tocopherol concentration in the feed, (ß)_ij is the interaction between type and concentration of tocopherols, _k is the effect of block, and _ijk is the random error. In cases in which the overall effect was significant (P < 0.05), means were compared pair-wise by Fisher's least significant difference procedure.

The results obtained from the two intestinal segments were analyzed by a paired t-test. The results determined in the in vitro hydrolysis experiment with pancreatic CEL was analyzed by linear regression of the substrate concentration ([s], µmol/L -tocopherol ester) against the substrate concentration divided with the amount of -tocopherol liberated (nmol/h) (Hanes plot). According to the Michaelis-Menten equation [V = V_max x [s]/(K_M + [s])] a Hanes plot is a straight line. K_M (µmol/L substrate) was calculated as the intercept divided with the slope, and V_max (nmol/h of reaction product liberated) was calculated as the reciprocal slope.

	RESULTS

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Diets.

Because of the presence of natural RRR--tocopherol in the feed, all experimental diets had a higher -tocopherol concentration than expected, but the four corresponding succinate and acetate diets had the same analyzed -tocopherol concentrations (Table 1) . In addition, each diet contained 66 mg -tocopherol/kg and 19 mg -tocopherol/kg of natural origin.

Animal performance.

The chickens performed well throughout the experiment. However, one chicken from group A200 died 2 d before slaughter (40 d old). The post mortem findings were ascites, enlargement of the heart and accumulation of fluid in the pericardium.

No significant difference in growth performance and feed conversion efficiency were found among the experimental groups. The mean body weight at 42 d of age was 2452 ± 67g. The feed conversion during the 4 wk experiment was 0.62 ± 0.02 g gain/g feed consumed.

Apparent absorption of tocopherols.

-Tocopherol originating from all-rac--tocopherol succinate had, at all inclusion levels, a significantly lower apparent absorption coefficient than -tocopherol from all-rac--tocopherol acetate (Table 2 ) (P < 0.001). Thus the overall mean apparent absorption coefficient for -tocopherol from the succinate groups was 58.0 compared to 70.8 for the groups fed the acetate ester of all-rac--tocopherol. The apparent absorption coefficients were not influenced by the diet -tocopherol concentration (P > 0.8).

View this table: [in this window] [in a new window]   Table 2. Apparent absorption coefficients of tocopherols from the -tocopherol succinate and -tocopherol acetate diets measured in broilers at 34 and 41 d1

Digestive enzymes and tocopherols in the small intestine.

None of the digestive enzyme activities were affected by the dietary treatment; therefore, the results from the broilers analyzed were pooled. However, the enzyme activities in jejunum contents were significantly lower than in ileal contents. (Table 3). The activities of the proteolytic enzymes in the ileum contents were only 50% of the activities in the jejunum contents, and the activity of pancreatic CEL and lipase was only 10% of the activities in the jejunum contents. The activity of amylase in the ileum contents was only 27% of the activity in the jejunum content.

View this table: [in this window] [in a new window]   Table 3. Trypsin, chymotrypsin, amylase, pancreatic carboxylester hydrolase (CEL) and lipase activities and -tocopherol concentration in jejunum and ileum digesta in individual broilers fed (S150) or (A150)1

In vitro hydrolysis of -tocopherol esters by pancreatic CEL.

The in vitro hydrolysis experiment with -tocopherol succinate and -tocopherol acetate was performed with -tocopherol ester concentrations comparable to the expected digesta concentrations. The capacity of porcine pancreatic CEL to hydrolyze -tocopherol succinate was only 1.5% of the corresponding capacity to hydrolyze -tocopherol acetate (Fig. 1 ).

View larger version (16K): [in this window] [in a new window]   Figure 1. Hydrolysis of -tocopherol from -tocopherol succinate and -tocopherol acetate by porcine pancreatic carboxyl ester hydrolase (CEL). Based on the Michaelis-Menten equation; Succinate: Y(nmol/h) = 1.7 (nmol/h) x X(µmol/L)/(1.0 + X)(µmol/L); R2 = 0.993, n = 9. Acetate: Y = 110(nmol/h) x X(µmol/L)/(20.6 + X)(µmol/L); R2 = 0.88, n = 14.

Retention of -tocopherol in plasma and tissue.

At all supplementation levels the concentration of -tocopherol was lower in plasma and tissues from chickens supplemented with all-rac--tocopherol succinate (P = 0.001, Table 4). These differences were small at the low supplementation level (S50 and A50), but were more pronounced at higher dietary concentrations of all-rac--tocopherol, as indicated by significant dose effects (P < 0.001).

View this table: [in this window] [in a new window]   Table 4. Concentrations of -tocopherol in blood plasma and tissue samples from broilers fed increasing amounts of -tocopherol succinate and -tocopherol acetate in the diets1

	DISCUSSION

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The apparent absorption data showed a good agreement with blood plasma and tissue data with respect to the observed differences between the two -tocopherol esters. The observed ratio between the utilization of the acetate and succinate ester of all-rac--tocopherol was comparable with that in humans (Cheeseman et al. (1995 ) and lambs (Hidiroglou et al. 1992 ).

The lower apparent absorption coefficient and the lower plasma and tissue -tocopherol response of broilers to the succinate ester, compared to the acetate ester observed in vivo, is likely caused by a lower affinity of the less hydrophobic all-rac--tocopherol succinate to intestinal hydrolysis by pancreatic CEL as shown in the in vitro experiment. The inhibiting effect of the succinate ester on the apparent absorption of -tocopherol could be due to a disturbance of the surfaces of the emulsified lipid particles or the mixed bile salt, phospholipid, cholesterol, free fatty acid and monoglyceride-containing micelles by the greater hydrophility of all-rac--tocopherol succinate. The tocopherols, and perhaps also other fat-soluble compounds, may be less available for absorption because of the physical and chemical conditions of these emulsified lipid particles and mixed micelles are of great importance both for enzymatic hydrolysis of lipid molecules and their subsequent absorption (Ullrey 1972 ).

Pancreatic CEL and lipase showed the most pronounced decrease from jejunum to ileum in activity of the analyzed digestive enzymes. Thus, it is evident that the time available for enzymatic hydrolysis by this esterase may be limiting because the transit time of digesta in the small intestine is very short (van der Klis and Van Voorst, 1993 ).

The concentration of -tocopherol in blood plasma, liver and abdominal fat indicated that, as a vitamin E source, the succinate ester was 69–71% as available as the acetate ester. In the breast muscle this relative efficiency was 76%, whereas the apparent absorption experiment showed a relative efficiency of 82%. The fact that the apparent absorption experiment showed a higher utilization of the succinate ester relative to the acetate ester than did the plasma and tissue responses may be due to a higher intestinal degradation of the succinate ester than of the acetate ester, whereby the apparent absorption coefficients are overestimated.

At the lowest dietary inclusion level, the difference in utilization was more or less masked by the concurrent occurrence of natural RRR--tocopherol from the basal feed.

The observed increase in apparent absorption of tocopherols from the first to the second period is most likely an age effect, as shown in earlier experiments (Engberg et al. 1996 , Liu et al. 1995 ). These experiments also revealed that oxidized lipids in the diet (Engberg et al. 1996 ) as well as dietary fibers (Liu et al. 1995 ) had negative influences on the apparent absorption of tocopherols.

In conclusion, the present experiment showed significantly higher utilization of all-rac--tocopherol acetate than all-rac--tocopherol succinate in broilers because of a low affinity of pancreatic CEL towards hydrolysis of the succinate ester in combination with a low activity of pancreatic CEL and a short transit time of digesta in the small intestine.

	ACKNOWLEDGMENTS

 
The authors thank Elsebeth Lyng Pedersen, Marie Lilleris and Helle Krogh Rygaard for excellent technical assistance.

	FOOTNOTES

 
¹ This work was supported by Leo Pharmaceutical Products, DK-2750 Ballerup, Denmark.

³ Abbreviations used: A50, 50 mg -tocopherol acetate; A100, 100 mg -tocopherol acetate; A150, 150 mg -tocopherol acetate; A200, 200 mg -tocopherol acetate; CEL, pancreatic carboxyl ester hydrolase (EC 3.1.1.1); S50, 50 mg -tocopherol succinate; S100, 100 mg -tocopherol succinate; S150, 150 mg -tocopherol succinate; S200, 200 mg -tocopherol succinate; TPGS, D--tocopherol polyethylene glycol 1000 succinate.

Manuscript received December 2, 1998. Initial review completed December 30, 1998. Revision accepted March 25, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

1. Cheeseman K. H., Holley A. E., Kelly F. J., Wasil M., Hughes L., Burton G. Biokinetics in humans of RRR--tocopherol: The free phenol, acetate ester and succinate ester forms of vitamin E. Free Rad. Biol. Med. 1995;19:591-598[Medline]

2. Combs G. F. Jr Studies on the utilization of vitamin E alcohol and esters by the chick. Poult. Sci. 1978;57:223-229[Medline]

3. Engberg R. M., Lauridsen C., Jensen S. K., Jakobsen K. Inclusion of oxidized vegetable oil in broiler diets. 1. The influence on nutrient digestibility and on the antioxidative status of broilers in vivo. Poult. Sci. 1996;75:1003-1011[Medline]

4. Gallo-Torres H. E. Obligatory role of bile for the intestinal absorption of vitamin E. Lipids 1970;5:379-384[Medline]

5. Harwitt M. K. The promotion of vitamin E. J. Nutr. 1986;116:1371-1377

6. Hidiroglou N., McDowell L. R., Papas A. M., Antapli M., Wilkinson N. S. Bioavailability of vitamin E compounds in Lambs. J. Anim. Sci. 1992;70:2556-2561[Abstract]

7. Jakobsen K., Engberg R. M., Andersen J. O., Jensen S. K., Sørensen P., Henckel P., Bertelsen G., Skibsted L. H., Jensen C. Supplementation of Broiler diets all-race-- or a mixture of natural source RRR--,-,- Tocopheryl Acetate: 1. Effect on Vitamin E Status of Broilers in vivo and at Slaughter. Poult. Sci. 1995;74:1984-1994[Medline]

8. Jensen M. S., Gabert V. M., Jørgensen H., Engberg R. M. Collection of pancreatic juice from growing pigs. A comparative study of the pouch and the catheter method. Int. J. Pancreatol. 1997;21:173-184[Medline]

9. Jensen S. K., Jensen C., Jakobsen K., Engberg R. M., Andersen J. O., Lauridsen C., Sørensen P., Henckel P., Skibsted L. H., Bertelsen G. Supplementation of broiler diets with retinol acetate, ß-carotene or canthaxanthin: Effect on vitamin and oxidative status of broilers in vivo and meat stability. Acta Agric. Scand. Sect. A Anim. Sci. 1998;48:28-37

10. Liu Y. G., Jensen S. K., Eggum B. O. The influence of seed size on digestibility and growth performance of broiler chickens fed full-fat rapeseed. J. Sci. Food Agric. 1995;67:135-140

11. Muller D.P.R., Manning J. A., Mathias P. M., Harries J. T. Int. J. Vit. Nutr. Res. 1976;46:207-210

12. Pryor, W. A. (1997) Vitamin E and carotenoid Abstracts 1996. VERIS. La Granye, IL.

13. SAS Institute SAS User's Guide: Statistics 1988 SAS Institute Inc Cary, NC.

14. Ullrey D. E. Biological availability of fat-soluble vitamins: Vitamin A and carotene. J. Anim. Sci. 1972;35:648-657

15. Van der Klis J. D., Van Voorst A. The effect of carboxy methyl cellulose (a soluble polysaccharide) on the rate of marker excretion from the gastrointestinal tract of broilers. Poult. Sci. 1993;72:503-512

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This Article Abstract Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Jensen, S. K. Articles by Hedemann, M. S. Search for Related Content PubMed PubMed Citation Articles by Jensen, S. K. Articles by Hedemann, M. S.