Rat brain iron concentration is lower following perinatal copper deficiency

Proper brain development requires a balance of essential nutrients to ensure that hyperplasia and hypertrophy produce the correct number of optimally differentiated cells in a timely manner. Even micronutrient imbalance, such as iron and zinc (Zn) deficiency, can impact on behavioral development (Wauben and Wainwright 1999). Another essential metal, copper (Cu), is also necessary for proper brain development. Ewes grazing on pastures low in Cu content produce ataxic lambs with brain deformities (Bennetts and Chapman 1937). Laboratory rodents (guinea pigs, rats and mice) fed Cu-deficient diets during gestation produce offspring exhibiting hypomyelination, and focal and widespread necrosis (Everson et al. 1967; Carlton and Kelly 1969; Prohaska and Smith 1982). Recent studies in rats have indicated that recovery from perinatal Cu deficiency may be impossible, as persistent sensory motor dysfunction has been observed in rats repleted with a generous supply of Cu for over 6 months (Prohaska and Hoffman 1996; Penland and Prohaska 2004). Biochemical mechanisms for the altered brain neurochemistry and behavior associated with Cu deficiency have not been elucidated. Mammals express about a dozen Cu-dependent enzymes. Changes in these cuproenzymes due to Cu restriction may be connected to neuropathology (O'Dell and Prohaska 1983). Cu deficiency is associated with lower brain cytochrome c oxidase activity (Gallagher et al. 1956). This could alter mitochondrial function and brain energy metabolism. Lower brain Cu, Zn-superoxide dismutase activity may render the brain susceptible to reactive oxygen toxicity (Prohaska and Wells 1974). Reduction in brain norepinephrine due to lower dopamine-β-monooxygenase activity in Cu deficiency could impact on brain development (Prohaska and Wells 1974). Lower activity of peptidyl α-amidating monooxygenase in Cu-deficient brain might limit neuropeptide activation (Prohaska et al. 1995). However, none of these hypotheses have been thoroughly tested. Other factors may be responsible for the neuropathology and behavioral changes of copper deficiency. One such possibility is iron (Fe) limitation. It is well established that Fe deficiency in perinatal development has long-lasting behavioral effects even after dietary Fe supplementation (Beard and Connor 2003). Iron deficiency results in hypomyelination (Beard et al. 2003), alters monoamine metabolism (Youdim and Green 1976), and is associated with lower cytochrome oxidase activity (de Deungria et al. 2000). Thus, there are many similarities between perinatal Cu and Fe deficiencies. Previous observations showed that brains of Cu-deficient rat pups had significantly lower concentrations of Fe, but not zinc, compared with Cu-adequate pups (Prohaska and Wells 1975). Since Cu-deficient rat pups are anemic and the previous brain Fe data were on tissue that contained blood, it was believed that most, if not all, of the apparent difference in brain Fe content could be explained by hemoglobin differences between controls and Cu-deficient rat pups. Anemia is a hallmark feature of both dietary Cu and Fe deficiency (Fox 2003). A recent study confirmed the reduction in rat pup brain Fe following perinatal Cu deficiency and also reported that this deficit persisted following 6 months of recovery (Penland and Prohaska 2004). Furthermore, the lower brain Fe levels of Cu-repleted rats occurred in animals with normal hemoglobin content, ruling out the possibility of blood contamination. Perinatal Fe deficiency also results in a persistent reduction in Fe content upon repletion (Dallman et al. 1975). The purpose of the current studies was to evaluate brain Fe accumulation during perinatal Cu deficiency, to analyze the contribution of blood Fe in non-perfused rat brain, and to determine whether the cell perceived the putative changes in the brain by measuring transferrin receptor expression, a protein whose expression is influenced by brain Fe status (Siddappa et al. 2003).