Vitamin E Biochemistry and Function: A Case Study in Male Rabbit C Castellini 1 , E Mourvaki 1 , A Dal Bosco 1 and F Galli 2 1 Department of Biologia Vegetale, Biotecnologie Agroambientali e Zootecniche, Borgo XX Giugno 74-06100 Perugia, Italy; 2 Department of Scienze Biochimiche e Biotecnologiche Molecolari, Sez. Biochimica cellulare, University of Perugia, Perugia, Italy Contents Vitamin E supplementation has become a common procedure to promote growth and health and improve the qualitative characteristics of farm animals. It has been demonstrated to be an efficient strategy for improving their reproductive function. Germ cells are particularly vulnerable to oxidative damage and may thus require additional antioxidant protection. The aim of this review is to give a comprehensive overview of the current knowledge of the biochemistry and physiology of vitamin E; successively, the effect of this compound on the reproductive activity of rabbit buck is accurately described. In particular, this review examines studies on the effects of animal age, dose and duration of vitamin E supplementation, as well as the co- supplementation with selenium, vitamin C and polyunsatu- rated fatty acids. Several investigations have shown beneficial effects in bucks supplemented with vitamin E levels higher than the standard dietary requirement (50 mg/kg) particularly when the semen isstored.However,the exactdietary intake of vitamin E should be decided according to specific tissue needs for the individual vitamin E forms and the specific saturation markers. Introduction Vitamin E, like other lipophilic vitamins, plays a key role in animal nutrition and health. For a long time, it has been regarded as the mostpotent,lipid-soluble, chain-breaking antioxidant in nature and itsuse has been widely promoted to help protect cell components from oxidative damage (Burton et al. 1982;Brigelius- Flohe and Traber 1999). Recently,several other biolo- gical activitiesof vitamin E have been reported including the regulation of cellular signalling and gene activity, modulation of immune function and induction of apoptosis(Azzi et al. 2002;Brigelius-Floheet al. 2002). Dietary vitamin E is essentialduring the growth period in domestic animals and therefore, a nutritional deficiency of vitamin E may occur more frequently in youngerdomesticanimalsthan in older ones. The consequences of such a deficiency includemuscular dystrophy in weanling rabbits (Chan et al. 1979)and chickens (Shih et al. 1977),and neurological lesions in rats (Southam et al. 1991). The clinical effects of vitamin E deficiency may become even more severe if combined with an absence of selenium or vitamin C. This implies a synergic action between vitamin E and these compounds in vivo (Hill et al. 2001, 2003).In current animal breeding practices, however, nutrient requirements are not determined in terms of avoiding a deficiency but ratherin terms of determining the dose required to improve certain characteristics. Thus, the levels of these compounds to enhance some specific functions should be higher than those required to prevent a deficiency. Impairmentof mammalian fertility hasalso been attributed to vitamin E deficiency. The crucialrole of vitamin E in animal reproduction has been recognized since 1922 (Evans and Bishop 1922). To date, there are approximately 100 publications on this topic, which highlightthe beneficial effectsof thisantioxidanton viability, membrane integrity and motility of spermato- zoa of different species. The protective effects of vitamin E against oxidative damage of sperm cells become even more significant when hygienic conditions are poorly controlled,as they frequentlyoccur in field. Such conditionsare associated with increased incidence of infections/inflammations of reproductiveapparatus. During inflammation, the antioxidant defence of repro- ductive system downplays and generates an oxidative stress (Potts and Pasqualotto 2003), which may impair testis function and affect negatively semen characteris- tics (O’Bryan et al. 2000). Although there is an abundance of scientific data on the beneficialeffectsof vitamin E, references to its dietary intake in domestic animals are still limited and under consideration because there is a lack of informa- tion regarding the metabolic fate and the mechanism of action of this compound at the tissue level. Absorption of vitamin E occurs through non-specific processes, while its transportinto very-low-density lipoprotein (VLDL) and ensuing lipoproteins is highly regulated. Among the naturally occurring forms of vitamin E (a-, b-, c- and d-tocopherols and tocotrienols), a-T contri- butes mainly to maintaining vitamin E homeostasis in the body,while the other forms are extensively degra- ded. However, the role of tocopherol-oxidized products in cell biology is yet to be clearly explained. The aim of this review is to give a comprehensive overview of the current knowledge on the metabolism of vitamin E and its role in male fertility, mainly in rabbit. For this purpose, the mechanisms of absorption, trans- port and tissue distribution, as wellas the degradation of the differentforms of vitamin E are discussed. Finally, the effect of supplementation with supranutri- tionaldoses of vitamin E on semen characteristics and fertility in rabbit bucks is discussed. Vitamin E Metabolism Eight distinct molecules are included in the definition of vitamin E, a-, b-, c- and d-tocopherol (tocotrienol), each consisting of a chromanol ring with a saturated (unsat- urated) side-chain of 16 carbon atoms (Schneider 2005). Considering that cellular enzymes and receptors usually existin a given structural conformation and react in a highly stereospecific manner,the aforementioned Reprod Dom Anim 42, 248–256 (2007); doi: 10.1111/j.1439-0531.2006.00760.x ISSN 0936-6768 2007 The Authors. Journal compilation 2007 Blackwell Verlag