| BackgroundAs an important brain region related to learning and memory,hippocampus is sensitive to iron deficiency or overload.During the study of effects of exercises on iron status in each brain region,our group found that long-term aerobic exercise would result in enhanced storage iron levels in hippocampus of female rats.However,we still do not know how exercises cause elevated iron storage in hippocampus and whether the elevated iron level affects oxidative stress or apoptosis in hippocampus.Moreover,whether dietary iron contents affect iron status in hippocampus in exercised animal is still not clear.ObjectivesBased on the effects of dietary iron contents and exercises on systemic iron status,we focused on the independent and interaction effects of both factors on iron metabolism,oxidative stress and cell apoptosis in hippocampus and learning ability as well.We also performed a preliminary study to explore the mechanism of exercise-induced iron regulation.Findings can provide a theoretical basis for adjusting dietary iron intake for exercised population.MethodsPart ?Ninety female SD rats aged 21 days were randomly divided into 3 groups fed with low dietary iron content(12 mg/kg),sufficient dietary iron content(45 mg/kg),and high dietary iron content(1000 mg/kg)respectively.One month later,each group was subdivided into swimming and resting groups.Therefore,90 rats eventually were divided into 6 groups:exercise rats with low iron diet(EL,n=19),sedentary rats with low iron diet(SL,n=12),exercise rats with sufficient iron diet(ES,n=16),sedentary rats with sufficient iron diet(SS,n=12),exercise rats with high iron diet(EH,n=19)and sedentary rats with high iron diet(SH,n=12).Rats in exercise groups swam in a glass basin(80 cm×50 cm ×80 cm)filled with tap water to a depth of 50-52 cm and the water temperature was 34-36?.The rats swam 30 min/d in the first week and 60 min/d in the second week.From the third week,the rats swam 120 min/d,5 days/week.The exercise period lasted for 3 months.Rats in sedentary groups did not swim.After 3 months,Morris water maze was utilized to examine the spatial learning capability of each group.Then all the rats were fasted overnight.In the next day,after anesthesia blood was collected from heart to determine the hematological indices.The livers were isolated to determine the non-heme iron level(NHI).Hippocampus of each rat was dissected to determine the NHI level,other metal element levels,iron regulation protein levels,oxidative stress level and apoptosis in it.Whole brains were fixed to perform immunohistochemical staining for Bcl-2 and Bax.TUNEL assay was also used to evaluate cell apoptosis.Part ?Forty female SD rats weighing 180±10 g were randomly and equally divided into 4 groups:sedentary group(S1),exercise group(E1),sedentary+L-NAME group(S2),exercise+L-NAME group(E2).The dietary iron content was 80 mg/kg.The rat in S2 and E2 was supplied with water containing 1 mg/mL L-NAME.Both exercise groups performed the swimming protocol as part I.At the end of experiment,the hippocampus was harvested from each anesthetized rat to determine NHI,bleomycin detectable iron(BDI)and NOx levels in it.The expression levels of iron regulatory proteins,iron transport proteins and nitric oxide synthases in hippocampus were also examined.Results1.Low iron diet resulted in hypochromic microcytic anemia concomitant with decreased liver storage iron levels;while high iron diet had no effect on hematological indices except for liver iron overload.Long-term aerobic exercise significantly decreased hematological indices of rats with sufficient dietary iron and had no effect on those of rats with low or high dietary iron.Exercises had no effect on liver storage iron in rats with sufficient or low dietary iron,but increased that in rats with high dietary iron.2.Low iron diet increased IRP1 expression level in hippocampus significantly while raised iron storage insignificantly.High iron diet had no effect on iron storage and iron related protein levels in hippocampus.Long-term aerobic exercise had significant impact on iron related proteins in hippocampus in rats with sufficient dietary iron which resulted in increased iron storage in hippocampus.Long-term aerobic exercise only increased the expression of ferritin in hippocampus in rats with low or high dietary iron without impact on the levels of NHI and other iron related proteins.3.Neither dietary iron content nor exercise had effect on the levels of sodium,potassium,magnesium,copper and manganese in hippocampus.Long-term aerobic exercise increased calcium levels significantly and zinc levels insignificantly in hippocampus in rats with sufficient dietary iron.4.Long-term exercise increased the levels of SOD,TAOC in hippocampus in rats with sufficient dietary iron,decreased those in hippocampus in rats with low dietary iron,and had no impact on those in hippocampus in rats with high dietary iron.Both low and high dietary iron contents increased the level of oxidative stress in hippocampus in sedentary or exercised rats,and low dietary iron affected the oxidative stress in hippocampus more profoundly.5.The Bax/Bcl-2 ratio,escape latency of rats with low iron diets increased significantly when compared with those of rats with sufficient iron diets;while Bax/Bcl-2 ratio,escape latency of rats with high iron diets only increased a little.Although long-term aerobic exercise had no effect on Bax/Bcl-2 ratio and escape latency of rats with 3 levels of dietary iron,the escape latency in exercised rats with sufficient dietary iron was slightly shorter than that in sedentary rats with sufficient iron.6.Long-term aerobic exercise increased the level of nitric oxide in hippocampus in rats with sufficient dietary iron,which in turn increased the levels of NHI and BDI in hippocampus by affecting the expression of iron regulatory and export proteins in it.Conclusions1.Exercise-induced low iron status was distinct from nutritional iron deficiency.Although enhancing the level of dietary iron could improve low iron status concomitant with exercise,it also caused iron overload.2.Iron status in hippocampus was not parallel to systemic iron status.Effects of exercise on iron metabolism in hippocampus are closely related to dietary iron.Long-term aerobic exercise changed the expression of iron regulatory proteins and increased iron storage in hippocampus in rats with sufficient dietary iron,but had no significant impact on iron storage in hippocampus in rats either with high or low dietary iron.Low iron diet decreased NHI level in hippocampus in exercised rats while high iron diet had no impact.3.Dietary iron and exercise had interactional effects on oxidative stress in hippocampus.Exercise increased antioxidant capacity of hippocampus in rats with sufficient dietary iron,decreased that of hippocampus in rats with low iron diet,and had no impact on that of hippocampus in rats with high iron diet.Both of low and high dietary iron could increase oxidative stress in hippocampus.4.Both of low and high dietary iron increased apoptosis in hippocampus and decreased the ability of learning and memory of rats.Although long-term aerobic exercise had no significant effects on apoptosis or learning ability and memory in rats,it still enhanced the learning ability of rats with sufficient dietary iron insignificantly.5.Elevated synthesis of nitric oxide was one of the mechanisms through which exercise regulated the iron metabolism in hippocampus.6.In summary,dietary iron and long-term exercises had interactional effects on systemic iron status,iron metabolism,oxidative stress,apoptosis in hippocampus and learning abilities of rats as well.Both low and high dietary iron had deleterious effects,and low dietary iron affected more profoundly.Supplement with large doses of iron to exercised population not only led to iron overload but also increased oxidative stress in hippocampus and even reduced learning ability and memory.Hence,subtle consideration should be taken before iron supplementation was prescribed for exercise populations. |
PDF Full Text Request