学 术 报 告 厅
译者:郑薇薇(哈尔滨医科大学公共卫生学院,哈尔滨 150001)
早期膳食长期程序性效应的实验数据
Experimental evidence for longterm programming effects of early diet
摘 要:在胚胎或胎盘发育的特殊时期进行营养控制,尽管不会对胚胎的重量产生影响,但可以导致胚胎器官发育过程中的实质性改变。尤其是使营养素受限制幼仔的肾脏和脂肪量发生了较大的定向改变,同时瘦素,胰岛素样生长因I/II和糖皮质激素受体的mRNA水平增高。对幼仔时期的营养素限制,会使刚成年大鼠出现心血管的压力反射变迟钝。交感神经刺激血清瘦素水平增加,这在对照组是不会出现的,这说明了脂肪细胞应激对敏感性的恢复。总之,对早期发育时期的营养素整体限制,一定形式上改变了成年鼠的生理状况,说明了如果再给予相应的环境刺激则会对后期疾病产生诱导作用。
关键词:胚胎发育;mRNA;瘦素;胚胎;应激;肾脏;脂肪
1 成人疾病的程序化发展
高血压和肥胖是冠心病的主要威胁因素,是超过50岁的人群的一种常见致死原因1。由全世界不同群体得到的广域的流行病学证据显示胎儿接触到的营养及激素环境的定向改变对后期的心血管疾病具有决定性的影响2,3。流行病学及动物实验也都说明了适时的母体营养是后期结果的关键决定因素4-6。确切的说,这种影响也可发生在出生时体重无差异的情况下。事实上,虽然能量摄入相差的范围较大,但是体重的差异却并不很大,这一点很令人吃惊7。子宫内的母体营养素限制的长期后果呈现出相关性,或者这种相关性会通过营养素恢复的时间、强度、持续时间而被放大8, 9。而后,营养素的摄入变得越来越重要,特别是在出生后,此时营养素摄取以及身体生长发育已不再受限制,个体可以实现全部生长潜势。在本综述中,我们重点收集肾脏和脂肪发育的宫内程序性影响,其前提是肾脏免疫功能低下,脂肪储存过多与成人高血压具有强相关性10。
2 胎儿程序影响的动物模型
小型及大型动物模型的研究都发现,无论是在妊娠期还是在确定怀孕的一段时期实施母体膳食控制,都会对健康产生长期后果6, 11。但是不同动物模型产生的反映差异很大,这反映了不同种属动物存在生长发育时强加给母亲的代谢改变有很大差异。大鼠在妊娠期对营养失调呈现出独特的易损性,这可能是由于它们窝生的特点、妊娠期短和妊娠后期几天胎盘及胎儿的迅速生长的原因。大鼠的妊娠产物在胚胎发育过程中显示了罕见的蛋白质添加比率(估计是羊和人类胎儿的23倍12)相对于母体体重在足月时总体重量相对较高(胎儿的总体体重是母体体重的25%-35%羊是7%-10%,人是3%-5%)。另外,羊的胎儿在胎盘生长中的快相过程与人类胎儿相似13。通过羊的繁殖发现:它们如同人和一些单幼仔动物,经过一个长期的妊娠过程在出生时有相似的体重和一个发育成熟的下丘脑-脑垂体轴。
3 营养干预和胎儿的程序影响宏
量或者微量营养素整体缺乏或者失调是否直接对胚胎发育造成负面影响,仍是一个存有争议的问题。迄今为止,从已有的流行病学和动物实验得到的比较公认的看法是宏量营养素对程序性影响的作用较大[4, 14]。一个最有特性的胎儿程序设计的动物模型是大鼠,它对高低蛋白质膳食的特性都已经进行了检测11, 15。这些试验重复显示了,在妊娠全过程11或者特殊时期,母体消耗低蛋白膳食将导致后代的血压升高16。影响的大小部分是由于暴露的时间决定的,并且部分研究还显示了起影响有性别差异。值得注意的是,低蛋白饮食对脂肪沉积无任何促进作用,这与高蛋白的饮食恰好相反15。然而,在子宫内暴露于高或低蛋白的任何程序性效应在晚期的脂肪沉积方面都显示对出生后膳食的依赖型。大鼠的幼仔在胎儿发育时期的高蛋白膳食,只有其在出生后喂食标准饲料时才会变得肥胖15。同时,报告说对于小鼠,出生后过度的营养消耗伴随低蛋白膳食几乎会使1318出现肥胖症和寿命缩短的现象。这种反映的程度不是很清楚,可能是由于脂肪细胞内部的特殊改变造成的,或者与食欲调节的中心介导效应有关。
4 妊娠营养干预的组织特异性
对妊娠大鼠在整体上的营养素限制将导致全部后代出现子宫内发育迟缓,但只会使其在青春期后才出现肥胖。这种模型的后代显示了成年合并症,这些合并症包括坐式/静态行为(sedentary behaviour)19、高胰岛素血症和高瘦素水平20, 21。肥胖与食欲过盛相关联,无论是标准膳食还是高碳水化合物膳食均可观察到。这些大鼠也会出现高血压,这种效应可以通过生长激素治疗纠正22。迄今为止,这个模型没有肾脏的负面影响的报道。
与人类流行病学和大型动物试验相比该大鼠动物模型高血压的程序影响具有更高的放大性。收缩压增高20-40mmHg既发生在孕期的低蛋白饮食11的情况,也发生在孕期铁摄入不足23及脂肪过量摄入24的情况。受损肾脏发育伴随低蛋白饮食或者铁缺乏可能导致较高的血压23, 25。对母体高脂肪饮食的肾功能的后期结果没有报道,尽管雄性及雌性个体血清肾上腺皮质素都会增加,但是只有雌性后代的血压增高24。这个模型有趣的是,血管的内皮功能异常,例如内皮组织依赖性扩张(endothelium dependent dilation)不具有性别差异,同时这个模型也不能说明这种机制与高血压的进展有关。
长期的食用低蛋白饮食的不良后果不仅仅局限血压的改变,还包括异常的胰腺发育情况,例如,β-细胞的量、小岛血管化作用都降低26。这种缺陷可以通过牛磺酸补充克服,牛磺酸具有恢复胎儿小岛血管内正常体积和细胞密度的有益效应27。牛磺酸也可预防血管内皮生长因子和胎儿肝激酶-1受体的低表达。还不知道牛磺酸是否也同样可以调整有害的心血管后果。此外,另一方面,尽管胰腺功能受损,其后代出生存在牛磺酸不足损害也不会引起肥胖症。
5 胎儿时期程序性影响成年后
疾病的机制
肾脏—一个涉及胎儿程序性影响的基础器官。大型动物,例如羊,早期的肾脏发育对于过度的肾上腺皮质类固醇高度敏感28。一个胎儿肾脏成熟的关键时期是原肾的发育时期及随后的退化时期29,与着床时期一致。在这个时期暴露高水平的糖皮质激素对糖皮质激素受体的数量没有影响,但是,可出现很多肾功能的直接后果,尿囊液中重量克分子渗透压浓度、钠及氯化物含量降低和钾浓度增高30。这些特殊的适应已经被解释为早产儿中肾内Na 、K、ATPase活性的增量调节。母体低蛋白膳食生育的幼仔的增量调节也相似的提高31。妊娠早期受到地塞米松作用的胎儿,同时会在妊娠晚期注射3d的血管紧张素II的侵润32,显示出了尿流量率的增加,这证实了存在肾功能的改变。后代持续出现较高静息血压而不是不受应激的血压28。
大鼠后代,在子宫内暴露于低蛋白饮食产生的较高的血压很可能是由于肾单位数量的减少33,也可能是由于在子宫内暴露于过高的糖皮质激素34,抑制了肾素血管紧张素系统35。下面的研究支持这种观点,羊早期到中期妊娠过程限制能量,其后代肾脏糖皮质激素受体和糖皮质激素反映应答基因,如血管紧张素原2-受体ImRNA增加36。后代肾单位数量以及11β羟化类固醇脱氢酶2型的活性减少37, 38,因此导致了继发应激敏感性的增加。有趣的是,作为机体的一个功能器官,肾脏在营养素限制组和对照组后代的重量随年龄增长而减少。同时,营养限制组后代的血压由低于对照组转变成高于对照组。这种血压升高的转变是伴随着子宫内营养素限制的,因此显示出了一种年龄相关过程。心血管压力反射的复位是维持血压的一个重要因素,这种压力反射是血压移动改变中维护中央压力的要点:如果不能完全复位则后期高血压出现的危险性就会增加39。母体营养素限制的绵羊的后代显示出了在注射血管紧张素II后对压力反射敏感性的迟缓,因此,相对于对照组,心动过速伴随中央血压的降低是可能的39, 40。在生命早期的关键时期,局部血管紧张素II活性增强如孤束核和窦房节是可能的机制之一。
胎儿脂肪的增长是受营养的严格调控的,并对母亲妊娠期间营养状况的变换高度敏感。妊娠早期开始的营养素限制可增强胎儿脂肪沉积,但母体在妊娠后期营养不足却减少胎儿脂肪沉积41。限制母体营养素的后代出现脂肪含量增高,并且保持这种高的状态。足月时,脂肪过多伴随有瘦素、增加的胰岛素-生长因子I/II和糖皮质激素受体的mRNA的量增高36, 37。这些特殊效应在营养素限制时期伴有母体血浆皮质醇(maternal plasma cortisol)、甲状腺激素、瘦素浓度的降低36, 42。而后,刚成年的个体,营养素限制的幼仔显示出交感神经刺激后血浆瘦素增加,这种刺激在对照组没有被观察到,说明了脂肪细胞对应激的敏感性恢复40。在生命晚期的特殊时期增加营养是否会使这种症状恶化有待进一步证实,举个例子,在哺乳期,脂肪是身体最快的增长部位。
总之,胚胎及胎盘发育时期的营养素限制程序化影响成人的生理机能39。这提示成年后再经历某些环境刺激时发生某些疾病的易感性。
参考文献:
1. Law CM, Shiell AW. Is blood pressure inversely related to birth weight﹖ The strength of evidence from a systematic review of the literature. J Hypertens, 1996, 148 935-941.
2. Barker DJ. In utero programming of chronic disease. Clin SciLond, 1998, 952 115-128.
3. Curhan GC, Willett WC, Rimm EB, et al. Birth weight and adult hypertension, diabetes mellitus, and obesity in US men. Circulation, 1996,15 9412 3246-3250.
4. Roseboom TJ, van der Meulen JHP, Osmond C, Barker DJP, Ravelli ACJ and Blecker OP. Plasma lipid profile in adults after perinatal exposure to famine. Am J Clin Nutr, 2000, 72 1101-1106.
5. Roseboom TJ, van der Meulen JHP, Osmond C, Barker DJP, Ravelli ACJ. S.-T. von Montfrans GA, Michels RPJ and Blecker OP. Coronary heart disease in adults after perinatal exposure to famine. Heart, 2000, 84 595-598.
6. Symonds ME, Pearce S, Bispham J, Gardner DS and Stephenson T. Timing of nutrient restriction and programming of fetal adipose tissue development. Proc Nutr Soc, 2004, 63 (In press).
7. Symonds ME, Gardner DS, Pearce S and Stephenson T. in Fetal Nutrition and Adult Disease-Programming of chronic disease through fetal exposure to undernutrition ed. S. C. Langley-Evans 353-380 CAB International, Oxford, 2004.
8. Dandrea J, Wilson V, Gopalakrishnan G, Heasman L, Budge H, Stephenson T and Symonds ME. Maternal nutritional manipulation of placental growth and glucose transporter-1 abundance in sheep. Reprod, 2001, 122 793-800.
9. Symonds ME, Budge H, Stephenson T and McMillen IC. Fetal endocrinology and development-manipulation and adaptation to long term nutritional and environmental challenges. Reprod, 2001, 121 853-862.
10. Hall JE. The kidney, hypertension, and obesity. Hypertension, 2003, 413 Pt 2 625-633.
11. Langley-Evans SC. Fetal programming of cardiovascular function through exposure to maternal undernutrition. Proc Nutr Soc, 2001, 60 505-513.
13. Heasman L, Clarke L, Dandrea J, Stephenson T and Symonds ME. Correlation of fetal number with placental mass in sheep. Cont Rev Obs Gynecol,1998, 10 275-280 .
14. Godfrey K, Robinson S, Barker DJP, Osmond C and Cox V. Maternal nutrition in early and late pregnancy in relation to placental and fetal growth. BMJ, 1996, 312 410-414.
15. Daenzer M, Ortmann S, Klaus S, et al. Prenatal high protein exposure decreases energy expenditure and increases adiposity in young rats. J Nutr, 2002, 1322 142-144.
16. Kwong WY, Wild AE, Roberts P, Willis AC, and Fleming TP. Maternal undernutrition during the preimplantation period of rat development causes blastocyst abnormalities and programming of postnatal hypertension. Development, 2000, 127 4195-4202.
17. Ozanne SE, Nave BT, Wang CL, Shepherd PR, Prins J, and Smith GD. Poor fetal growth causes long-term changes in expression of insulin signalling components in adipocytes. Am J Physiol, 1997, 273 E46-E51.
18. Ozanne SE, Hales CN. Lifespan Catch-up growth and obesity in male mice. Nature, 2004, 4276973 411-412.
19. Vickers MH, Breier BH, McCarthy D, et al. Sedentary behavior during postnatal life is determined by the prenatal environment and exacerbated by postnatal hypercaloric nutrition.Am J Physiol Regul Integr Comp Physiol, 2003, 2851 R271-3.
20. Vickers MH, Breier BH, Cutfield WS, et al. Fetal origins of hyperphagia, obesity, and hypertension and postnatal amplification by hypercaloric nutrition. Am J Physiol Endocrinol Metab, 2000, 2791 E83-7.
21. Vickers MH, Reddy SIBA, and Breier BH. Dysregulation of the adipoinsular axis-a mechanism for the pathogenesis of hyperleptinemia and adipogenic diabetes induced by fetal programming. J. Endocrinol, 2001, 170 323-332.
22. Vickers MH, Ikenasio BA, Breier BH, et al. Adult growth hormone treatment reduces hypertension and obesity induced by an adverse prenatal environment. J Endocrinol, 2002, 1753 615-23.
23. Gambling L, Dunford S, Wallace DI, et al. Iron deficiency during pregnancy affects postnatal blood pressure in the rat. J Physiol, 2003, 552Pt 2 603-610.
24. Khan IY, Taylor PD, Dekou V, et al. Gender-linked hypertension in offspring of lardfed pregnant rats. Hypertension, 2003, 411 168-75.
25. Nwagwu MO, Cook A, and Langley-Evans SC. Evidence of progressive deterioration of renal function in rats exposed to a maternal low-protein diet in utero. Brit J Nutr, 2000, 83 79-85.
26. Snoeck A, Remacle C, Reusens B, et al. Effect of low protein diet during pregnancy on the fetal rat endocrine pancreas. Biol Neonate, 1990, 572 107-118.
27. Boujendar S, Arany E, Hill D, et al. Taurine supplementation of a low protein diet fed to rat dams normalizes the vascularization of the fetal endocrine pancreas. J Nutr, 2003, 1339 2820-2825.
28. Dodic M, Hantzis V, Duncan J, Rees S, Koukoulas I, Johnson K, Wintour EM, and Moritz K. Programming effects of short prenatal exposure to cortisol. FASEB J, 2002, 16 1017-1026.
29. Wintour EM, Alcorn D, Butkus A, Congiu M, Earnest L, Pompolo S, and Potocnik SJ. Ontogeny of hormonal and excretory function of the meso-and metanephros in the ovine fetus. Kidney Int, 1996, 50 1624-1633.
30. Peers A, Hantzis V, Dodic M, Koukoulas I, Gibson A, Baird R, Salemi R, and Wintour EM. Functional glucocorticoid recetpors in the mesonephros of the ovine fetus. Kidney Int, 2001, 59 425-433.
31. Bertram CE, Trowern AR, Copin N, Jackson AA, and Whorwood CB. The maternal diet during pregnancy programs altered expression of the glucocorticoid receptor and type 2 11-hydroxysteroid dehydrogenase Potential molecular mechanisms underlying the programming of hypertension in utero. Endocrinology, 2001, 142 2841-2853 .
32. Moritz K, Johnson K, Douglas-Denton, Wintour REM, and Dodic M. Maternal glucocorticoid treatment programs alterations in the renin-angiotensin system ovine fetal kidney. Endocrinology,2002, 143 4455-4463 .
33. McMullen S, Gardner DS, Langley-Evans SC. Prenatal programming of angiotensin II type 2 receptor expression in the rat. Br J Nutr, 2004, 911 133-140.
34. Langley-Evans SC, Phillips GJ, Benediktsson R, Gardner DS, Edwards CRW, Jackson AA, and Seckl JR. Protein intake in pregnancy, placental glucocorticoid metabolism and the programming of hypertension. Placenta, 1996, 17 169-172.
35. Woods LL, Ingelfinger JR, Nyengaard JR, and Rasch R. Maternal protein restriction suppresses the newborn reninangiotensin system and programs adult hypertension in rats, 2001, 49 460-467.
36. Bispham J, Gopalakrishnan GS, Dandrea J, Wilson V, Budge H, Keisler DH, Broughton Pipkin F, Stephenson T, and Symonds ME. Maternal endocrine adaptation throughout pregnancy to nutritional manipulation consequences for maternal plasma leptin and cortisol and the programming of fetal adipose tissue development. Endocrinology, 2003, 144 3575-3585.
37. CB Whorwood, KM Firth, H Budge and ME Symonds, Maternal undernutrition during earlyto midgestation programmes tissuespecific alterations in the expression of the glucocorticoid receptor, 11-hydroxysteroid dehydrogenase isoforms and type 1 angiotensin Ⅱ receptor in neonatal sheep. Endocrinology, 2001, 142 1778-1785.
38. Passingham L, Kurlak LO, Gopalakrishnan G, Budge H, Rhind SM, Rae MT, Kyle CE, Stephenson T, and Symonds ME. The effect of maternal nutrient restriction during early to mid-gestation on the enzyme activity of 11 beta hydroxysteroid dehydrogenase type 2 in sheep kidneys of 3 year old offspring. Early Hum Dev, 2004, (In press).
39. Gardner DS, Pearce S, Dandrea J, et al. Peri-implantation undernutrition programs blunted angiotensin II evoked baroreflex responses in young adult sheep. Hypertension, 2004, 436 1290-6.
40. Gopalakrishnan GS, Gardner DS, Rhind SM, et al. Programming of adult cardiovascular function after early maternal undernutrition in sheep. Am J Physiol Regul Integr Comp Physiol, 2004, 2871 R12-20.
41. Budge H, Edwards LJ, McMillen IC, et al. Nutritional manipulation of fetal adipose tissue deposition and uncoupling protein 1 messenger RNA abundance in the sheep differential effects of timing and duration. Biol Reprod, 2004, 711 359-65.
42. Clarke L, Heasman L, Juniper DT, and Symonds ME. Maternal nutrition in early-mid gestation and placental size in sheep. Br J Nutr, 1998, 79359-364.
43. Clarke L, Buss DS, Juniper DT, et al. Adipose tissue development during early postnatal life in ewe-reared lambs. Exp Physiol, 1997, 826 1015-1027.
注:文章中的参考文献缺12