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© 2002 The American Society for Nutritional Sciences J. Nutr. 132:1610S-1612S, June 2002

Supplement: Waltham International Symposium

Cats Absorb ß-Carotene, but It Is Not Converted to Vitamin A

Florian J. Schweigert3, Jens Raila, Brigitta Wichert* and Ellen Kienzle*

Institute of Nutritional Science, University Potsdam, Potsdam-Rehbrücke, Germany and * Institute of Physiology, Physiological Chemistry and Animal Nutrition, Ludwig-Maximilians-University Munich, Munich, Germany

3To whom correspondence should be addressed. E-mail: fjschwei{at}rz.uni-potsdam.de.

KEY WORDS: • cat • beta-carotene • vitamin A • carotene cleavage • plasma

EXPANDED ABSTRACT

In many mammals ß-carotene can be converted to retinol in the intestinal mucosa as well as in tissues such as the liver (1). Early investigations, however, indicated that the domestic cat lacks the ability to convert ß-carotene to vitamin A (2,3). Because neither dietary nor parenterally administered ß-carotene can prevent the development of vitamin A deficiency, it had been concluded that the cat is strictly dependent on preformed vitamin A in the diet. Renewed interest in carotenoids in pet nutrition has emerged because of their potentially beneficial antioxidative and immunological effects (4,5). These findings highlight the need for additional studies to clarify the assumptions that dietary ß-carotene can not be used as a source for vitamin A in domestic cats. The aim of the present study was to determine the bioavailability of ß-carotene and its provitamin A activity by measuring the appearance of ß-carotene and retinyl esters (retinyl palmitate and retinyl stearate) in the chylomicron fraction, in blood plasma and in urine of domestic cats after a single oral dose of ß-carotene.


   MATERIALS AND METHODS
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 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 LITERATURE CITED
 
Six adult domestic cats (3 male, 3 female; 2–5 y; 3.8–6.0 kg body weight) were fed a vitamin A–deficient diet. The diet had the following calculated approximate composition (g/kg): crude protein, 570; crude fiber, 60; crude fat, 190; N-free extracts, 120; crude ash, 60; and consisted of cooked greaves meal, 740; rice, 130; and sunflower oil, 130. The greaves meal was UV-irradiated for 48 h (Sterisolstrahler Typ NN 30-89, length 1 m with a distance of 20 cm; Original Hanau, Germany). After this treatment the vitamin A concentration in the greaves meal was below the HPLC detection limit of 2 µg/kg dry matter (6). The vitamin A–deficient UV-irradiated diet was given individually to each cat in restricted amounts for a period of 28 d. The cats were kept in groups. For sampling of urine, cats were kept individually in metabolism cages according to the regulatory rules for animal welfare of the German Society of Experimental Animal Science. The research protocol was approved by the Animal Welfare Committee Munich, Germany. At d 23 of feeding the depleted diet, the cats were given a single ß-carotene bolus (100 mg/kg body weight; Sigma, Deisenhofen, Germany) dissolved in 2 mL sunflower oil or sunflower oil alone through a syringe directly to the back of the mouth. Blood samples were taken from the cephalic or saphenous veins into EDTA evacuated tubes before the bolus was given and after 2 and 12 h. Urine was collected for 24 h daily into individual bottles beneath metabolic cages until 96 h after dosing.

The plasma was separated by centrifugation at 1500 x g at 4°C. The chylomicrons were isolated from 1 mL fresh plasma by preparative ultracentrifugation (30 min, 100.000 x g at 10°C) at density < 1.006 g/mL (7). Plasma and chylomicron ß-carotene and vitamin A (retinol and retinyl esters) concentrations were measured using a gradient-HPLC system as described (6). Triacylglycererol concentrations were determined enzymatically (Sigma).

Statistical analysis

The data were expressed as means ± SD. A one-way analysis of variance (ANOVA) and Tukey‘s test was performed to test the differences among variables with SAS software (SAS Institute, Cary, NC). The level of statistical significance was taken as P < 0.05.


   RESULTS
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 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 LITERATURE CITED
 
Plasma ß-carotene concentrations increased for 12 h after the administration of a single oral bolus of ß-carotene in sunflower oil. The administration of ß-carotene had no effects on plasma levels of retinyl ester (palmitate, stearate) but a significant decrease in plasma retinol (Table 1).


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  		TABLE 1 Plasma ß-carotene, retinol and retinyl ester concentrations in healthy cats in the control and ß-carotene (100 mg/kg BW) group, at baseline and at 2 and 12 h after dosing1

 
Table 2 shows the postprandial chylomicron response at 2 and 12 h after the dosage. In control animals a slight increase in the concentration of retinyl stearate in chylomicrons between these two time points was observed. No differences between treated and untreated cats were observed. Traces of ß-carotene were detected 2 h after the dosage of ß-carotene.


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  		TABLE 2 Chylomicron ß-carotene, retinol and retinyl ester concentrations in healthy cats in the control and ß-carotene (100 mg/kg BW) group, at baseline and at 2 and 12 h after dosing1

 
ß-Carotene, retinol and retinyl ester were not detected in any of the control urine samples. In the urine of ß-carotene fed cats, ß-carotene was excreted, but neither retinol nor retinyl esters were excreted. ß-Carotene was first detected after 24 h (68 ± 35 nmol/L). Concentrations peaked at 48 h (137 ± 65 nmol/L) and decreased to 15 ± 13 and 11 ± 7 nmol/L at 72 and 96 h, respectively.


   DISCUSSION
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 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
LITERATURE CITED
 
The results of this study are in agreement with previous reports (4) that cats are able to absorb ß-carotene when administered at a pharmacological dose. The postadministration pattern of ß-carotene in plasma appeared to be different from that reported for humans (8) in that the rise in plasma concentrations was slower and elevated levels persisted for a longer period of time. Cats were similar to dogs in that the plasma contained retinyl ester, of which the main component was retinyl stearate (9,10). They are also similar in that vitamin A deficiency occurs only after several months of consuming a diet without vitamin A (3,6).

The appearance of ß-carotene and retinyl esters in the chylomicron fraction has been used as a noninvasive method to assess the bioavailability and provitamin A activity of ß-carotene. In most animals following absorption, ß-carotene is oxidized in the enterocyte to retinol, which is esterified to retinyl esters, packaged in chylomicrons and secreted into the lymph (11). Thus, in the case of an intestinal conversion of ß-carotene to vitamin A, an increase in postprandial chylomicron retinyl ester concentrations would be expected. In cats, however, ß-carotene in the chylomicron fraction was detected only at low levels from 2 h postdosage onward and no differences in the amount of retinyl esters were observed between animals with or without ß-carotene. This would suggest that, despite the ability of cats to absorb ß-carotene, none or only trace amounts, which would not be detectable with this method, were converted to vitamin A in cats that were not vitamin A deficient. In addition to this conclusion, the occurrence of retinyl esters in chylomicrons of control cats fed a vitamin A–depleted diet for 4-wk support observations made on cell cultures that the retinyl ester secretion is not dependent on the availability of retinol for the enterocyte (12). Chylomicron retinyl ester in cats is composed of not only retinyl palmitate but also stearate. This is different from humans and experimental animals in which primarily retinyl palmitate is present (11). In addition, the results suggest that in cats as in dogs (6) the occurrence of substantial amounts of retinyl esters in plasma despite the cat being on a vitamin A deficient diet for over 4 wk is not dependent on diet as in other species (11). Both aspects, the delayed increase in plasma ß-carotene levels and the lack of conversion to vitamin A, might suggest that cats differ from other mammals in the absorption and metabolism of ß-carotene investigated so far.

Despite cats and dogs being similar in having retinyl esters in plasma, cats excrete ß-carotene, not esters, in the urine, a peculiarity also observed in ferrets (Raila and Schweigert, 1999, unpublished). Because the concentration of ß-carotene in urine peaked at 48 h and was detectable at 96 h, this indicates that the ß-carotene was not a result from fecal contamination. The mechanism by which ß-carotene is excreted in urine is not known.

In conclusion, the study has demonstrated that cats are able to absorb ß-carotene from the diet. Cats provide a potential model for the study of the role of ß-carotene as an antioxidant and as an immune modulator independent of its provitamin A activity. In most other animal models the effect of ß-carotene can equally be attributed to vitamin A formed from ß-carotene in the gut or in other tissues of the body. Additionally, the results of this study support the concept that cats rely solely on preformed vitamin A in their diet.


   FOOTNOTES
 
1 Presented as part of the Waltham International Symposium: Pet Nutrition Coming of Age held in Vancouver, Canada, August 6–7, 2001. This symposium and the publication of symposium proceedings were sponsored by the Waltham Centre for Pet Nutrition. Guest editors for this supplement were James G. Morris, University of California, Davis, Ivan H. Burger, consultant to Mars UK Limited, Carl L. Keen, University of California, Davis, and D’Ann Finley, University of California, Davis. Back

2 Supported by grant INK 26-TP 12 from Deutsche Forschungsgemeinschaft. Back


   LITERATURE CITED
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 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 

1. Schweigert, F. J. (1998) Metabolism of carotenoids in mammals. Britton, G. Liaaen-Jensen, S. Pfander, H. eds. Carotenoids 1998:249-284 Birkhäuser Verlag Basel/Boston/Berlin. .

2. Ahmad, B. (1931) The fate of carotene after absorption in the animal organism. Biochem. J. 25:1195-1204.

3. Gershoff, S., Andrus, S., Hegsted, D. & Lentini, E. (1957) Vitamin A deficiency in cats. Lab. Invest. 6:227-240.[Medline]

4. Chew, B. P., Park, J. S., Weng, B. C., Wong, T. S., Hayek, M. G. & Reinhart, G. A. (2000) Dietary beta-carotene absorption by blood plasma and leukocytes in domestic cats. J. Nutr. 130:2322-2325.[Abstract/Free Full Text]

5. Kim, H. W., Chew, B. P., Wong, T. S., Park, J. S., Weng, B. B., Byrne, K. M., Hayek, M. G. & Reinhart, G. A. (2000) Modulation of humoral and cell-mediated immune responses by dietary lutein in cats. Vet. Immunol. Immunopathol. 73:331-341.[Medline]

6. Schweigert, F. J. & Bok, V. (2000) Vitamin A in blood plasma and urine of dogs is affected by the dietary level of vitamin A. Int. J. Vitam. Nutr. Res. 70:84-91.[Medline]

7. Terpstra, A. H. (1985) Isolation of serum chylomicrons prior to density gradient ultracentrifugation of other serum lipoprotein classes. Anal. Biochem. 150:221-227.[Medline]

8. van den Berg, H. & van Vliet, T. (1998) Effect of simultaneous, single oral doses of beta-carotene with lutein or lycopene on the beta-carotene and retinyl ester responses in the triacylglycerol-rich lipoprotein fraction of men. Am. J. Clin. Nutr. 68:82-89.[Abstract]

9. Schweigert, F. J., Ryder, O. A., Rambeck, W. A. & Zucker, H. (1990) The majority of vitamin A is transported as retinyl esters in the blood of most carnivores. Comp. Biochem. Physiol. A 95:573-578.[Medline]

10. Raila, J., Buchholz, I., Aupperle, H., Raila, G., Schoon, H. A. & Schweigert, F. J. (2000) The distribution of vitamin A and retinol-binding protein in the blood plasma, urine, liver and kidneys of carnivores. Vet. Res. 31:541-551.[Medline]

11. Harrison, E. H. & Hussain, M. M. (2001) Mechanisms involved in the intestinal digestion and absorption of dietary vitamin A. J. Nutr. 131:1405-1408.[Abstract/Free Full Text]

12. Nayak, N., Harrison, E. H. & Hussain, M. M. (2001) Retinyl ester secretion by the intestinal cells is a specific and regulated process that is dependent on the assembly and secretion of chylomicrons. J. Lipid Res. 42:272-280.[Abstract/Free Full Text]





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