Simon J. M. Welham

FETAL EXPOSURE TO A MATERNAL LOW PROTEIN DIET IMPAIRS NEPHROGENESIS AND PROMOTES HYPERTENSION IN THE RAT

Epidemiological evidence suggests that hypertension and coronary heart disease are programmed by exposure to a poor diet during intrauterine life. It has been proposed that the prenatal environment may exert an adverse effect on the development of the kidney and hence later control of blood pressure. These assertions are supported by animal experiments. In the rat, fetal exposure to a maternal low protein diet is associated with disproportionate patterns of fetal growth and later elevation of blood pressure. Pregnant female rats were fed control (18% casein) or low protein diets throughout pregnancy, or during specific periods. Nephron number was determined at day 20 gestation, full term and 4 weeks of age. Exposure to low protein throughout gestation, or in mid-late gestation increased total nephron number at day 20. By term nephron number was reduced, relative to controls, in rats that were undernourished between days 8-14 or 15-22 gestation. At 4 weeks postnatally rats exposed to low protein throughout fetal life had a reduced (13%) nephron complement and blood pressures 13 mmHg above control animals. Lower renal size and elevated blood pressure persisted to 19 weeks of age, at which time glomerular filtration rate was normal. The data are consistent with the hypothesis that maternal undernutrition may programme the renal nephron number and hence impact upon adult blood pressure and the development of renal disease.

Epigenetic Modification of the Renin-Angiotensin System in the Fetal Programming of Hypertension

Hypertension is a major risk factor for cardiovascular and cerebrovascular disease. Lifelong environmental factors (eg, salt intake, obesity, alcohol) and genetic factors clearly contribute to the development of hypertension, but it has also been established that stress in utero may program the later development of the disease. This phenomenon, known as fetal programming can be modeled in a range of experimental animal models. In maternal low protein diet rat models of programming, administration of angiotensin converting enzyme inhibitors or angiotensin receptor antagonists in early life can prevent development of hypertension, thus implicating the renin-angiotensin system in this process. Here we show that in this model, expression of the AT1b angiotensin receptor gene in the adrenal gland is upregulated by the first week of life resulting in increased receptor protein expression consistent with the increased adrenal angiotensin responsiveness observed by others. Furthermore, we show that the proximal promoter of the AT1b gene in the adrenal is significantly undermethylated, and that in vitro, AT1b gene expression is highly dependent on promoter methylation. These data suggest a link between fetal insults to epigenetic modification of genes and the resultant alteration of gene expression in adult life leading ultimately to the development of hypertension. It seems highly probable that similar influences may be involved in the development of human hypertension.

Intrauterine Programming of Cardiovascular Disease by Maternal Nutritional Status

The origins of cardiovascular disease are related to genetic factors, postnatal environmental and behavioral influences, and also the environment experienced in utero. Patterns of disproportionate fetal growth consistent with maternal undernutrition appear to be predictive of later hypertension and coronary heart disease. These findings from epidemiologic studies are strongly supported by animal studies. Experimental models are suggestive of a role for glucocorticoid hormones in the intrauterine programming of cardiovascular function. New understanding of the relationships between maternal diet and the development and maturation of fetal tissues may enable prevention of cardiovascular disease by intervention in early life.

Maldevelopment of the Human Kidney and Lower Urinary Tract. An Overview.

© 2003 Elsevier Inc. All rights reserved..This chapter focuses on the maldevelopment of human kidney and lower urinary tract, which include the ureter and urinary bladder. Renal malformations are the major cause of chronic renal failure in children. With advances in technology, babies with minimal renal function can be dialyzed from birth and toddlers can receive kidney transplants from the age of one year. The chapter describes the possible causes of human kidney and lower urinary tract malformations, which can be classified into two categories: (1) mutations, and possibly polymorphisms, of genes expressed during development, and (2) environmental influences on development, which can be further subdivided into changes that originate outside the fetus, such as alterations of maternal diet, and changes within the fetus that disrupt normal development, such as impairment of normal fetal urinary flow due to physical obstruction of the urinary tract. Human kidney or lower urinary tract malformation are reported in association with teratogens-angiotensin converting enzyme inhibitors, drugs used to treat high blood pressure cocaine, corticosteroids, ethanol, gentamycin, glucose, nonsteroidal anti-inflammatory drugs, and vitamin A and its derivatives.

Corticosteroid-induced kidney dysmorphogenesis is associated with deregulated expression of known cystogenic molecules, as well as indian hedgehog

An intact genome is essential for kidney growth and differentiation, but less is known about whether, and how, an altered fetal milieu modifies these processes. Maternal low-protein diets perturb growth of the metanephros, the precursor of the mature kidney. Fetal corticosteroid overexposure may, in part, mediate this, because such diets downregulate placental 11beta-hydroxysteroid dehydrogenase-2, which degrades maternal corticosteroids. We report that glucocorticoid and mineralocorticoid receptors are expressed in mouse metanephric epithelia. Metanephroi maintained in organ culture with hydrocortisone (1.4 or 14 microM) underwent a dose-dependant deceleration of overall growth accompanied by cyst formation. Dexamethasone, a glucocorticoid, reproduced these outcomes, but aldosterone, a mineralocorticoid, did not. Hydrocortisone upregulated transcripts levels of cadherin-11 and downregulated prospero-related homeobox-1, hence mimicking reported effects of maternal low-protein diet. Hydrocortisone also upregulated transcripts encoding Na(+)-K(+)-ATPase subunits and ligands for the epidermal growth factor receptor, all previously implicated in renal cyst growth. The most upregulated transcript, however, was indian hedgehog, and the encoded protein was immunodetected in metanephric cysts. Furthermore, in the presence of hydrocortisone, cystogenesis, but not whole organ growth, was significantly reduced by cyclopamine, a drug downregulating hedgehog signaling. Finally, both glucocorticoid receptor and indian hedgehog proteins were detected by immunohistochemistry in cystic tubules within human dysplastic kidneys, consistent with the hypothesis that these molecules modify the severity of this congenital malformation. Collectively, our observations raise the possibility that enhanced hedgehog signaling is an important stimulus for renal cyst formation. Furthermore, pharmacological inhibition of this pathway should be explored as a potential therapy for renal cystic diseases, starting with relevant animal models.

Excess maternal salt intake produces sex-specific hypertension in offspring: putative roles for kidney and gastrointestinal sodium handling.

Hypertension is common and contributes, via cardiovascular disease, towards a large proportion of adult deaths in the Western World. High salt intake leads to high blood pressure, even when occurring prior to birth – a mechanism purported to reside in altered kidney development and later function. Using a combination of in vitro and in vivo approaches we tested whether increased maternal salt intake influences fetal kidney development to render the adult individual more susceptible to salt retention and hypertension. We found that salt-loaded pregnant rat dams were hypernatraemic at day 20 gestation (147±5 vs. 128±5 mmoles/L). Increased extracellular salt impeded murine kidney development in vitro, but had little effect in vivo. Kidneys of the adult offspring had few structural or functional abnormalities, but male and female offspring were hypernatraemic (166±4 vs. 149±2 mmoles/L), with a marked increase in plasma corticosterone (e.g. male offspring; 11.9 [9.3–14.8] vs. 2.8 [2.0–8.3] nmol/L median [IQR]). Furthermore, adult male, but not female, offspring had higher mean arterial blood pressure (effect size, +16 [9–21] mm Hg; mean [95% C.I.]. With no clear indication that the kidneys of salt-exposed offspring retained more sodium per se, we conducted a preliminary investigation of their gastrointestinal electrolyte handling and found increased expression of proximal colon solute carrier family 9 (sodium/hydrogen exchanger), member 3 (SLC9A3) together with altered faecal characteristics and electrolyte handling, relative to control offspring. On the basis of these data we suggest that excess salt exposure, via maternal diet, at a vulnerable period of brain and gut development in the rat neonate lays the foundation for sustained increases in blood pressure later in life. Hence, our evidence further supports the argument that excess dietary salt should be avoided per se, particularly in the range of foods consumed by physiologically immature young.

Remote conditioning or erythropoietin before surgery primes kidneys to clear ischemia-reperfusion-damaged cells: a renoprotective mechanism?

Acute kidney injury is common, serious with no specific treatment. Ischemia-reperfusion is a common cause of acute kidney injury (AKI). Clinical trials suggest that preoperative erythropoietin (EPO) or remote ischemic preconditioning may have a renoprotective effect. Using a porcine model of warm ischemia-reperfusion-induced AKI (40-min bilateral cross-clamping of renal arteries, 48-h reperfusion), we examined the renoprotective efficacy of EPO (1,000 iu/kg iv.) or remote ischemic preconditioning (3 cycles, 5-min inflation/deflation to 200 mmHg of a hindlimb sphygmomanometer cuff). Ischemia-reperfusion induced significant kidney injury at 24 and 48 h (χ(2), 1 degree of freedom, >10 for 6/7 histopathological features). At 2 h, a panel of biomarkers including plasma creatinine, neutrophil gelatinase-associated lipocalin, and IL-1β, and urinary albumin:creatinine could be used to predict histopathological injury. Ischemia-reperfusion increased cell proliferation and apoptosis in the renal cortex but, for pretreated groups, the apoptotic cells were predominantly intratubular rather than interstitial. At 48-h reperfusion, plasma IL-1β and the number of subcapsular cells in G2-M arrest were reduced after preoperative EPO, but not after remote ischemic preconditioning. These data suggest an intrarenal mechanism acting within cortical cells that may underpin a renoprotective function for preoperative EPO and, to a limited extent, remote ischemic preconditioning. Despite equivocal longer-term outcomes in clinical studies investigating EPO as a renoprotective agent in AKI, optimal clinical dosing and administration have not been established. Our data suggest further clinical studies on the potential renoprotective effect of EPO and remote ischemic preconditioning are justified.

Protein restriction in the pregnant mouse modifies fetal growth and pulmonary development: role of fetal exposure to β‐hydroxybutyrate

Maternal undernutrition during sensitive periods of pregnancy results in offspring predisposed towards the development of a number of diseases of adulthood, including hypertension and diabetes. In order to determine the nature of any gross alterations in fetal growth during early organogenesis, we supplied timed‐mated pregnant mice with diets containing 6% protein (6%P), 9% protein (9%P) or 18% protein (18%P; control) from day 0 of pregnancy. At embryonic days 11 (E11), 12 (E12) and 13 (E13), females were killed and fetuses removed. Gross morphological analysis revealed that fetal limb growth was impaired between E11 and E12 in 6%P animals, but this recovered by E13. Likewise, fetal liver growth and lung branching morphogenesis were seen to exhibit an initial growth impairment at E12 followed by a rapid recovery by E13. Coincident with the observed changes in fetal growth, we noted an elevation in maternal hepatic triglyceride content, expression of the ketogenic 3‐hydroxy‐3‐methylglutaryl‐CoA synthase 2 (Hmgcs2) and circulating plasma β‐hydroxybutyrate (BOHB). In addition, fetal liver Hmgcs2 expression was switched on by E13 in both 6%P‐ and 9%P‐exposed animals. Exogenous BOHB did not influence branching morphogenesis in fetal lung explant cultures; however, we cannot rule out the possibility that this may occur in vivo. In conclusion, we find that disturbance of fetal growth by maternal dietary protein restriction is associated and therefore potentially indicated by changes in maternal and fetal ketone body metabolism.

Maldevelopment of the Human Kidney and Lower Urinary Tract

© 2003 Elsevier Inc. All rights reserved..This chapter focuses on the maldevelopment of human kidney and lower urinary tract, which include the ureter and urinary bladder. Renal malformations are the major cause of chronic renal failure in children. With advances in technology, babies with minimal renal function can be dialyzed from birth and toddlers can receive kidney transplants from the age of one year. The chapter describes the possible causes of human kidney and lower urinary tract malformations, which can be classified into two categories: (1) mutations, and possibly polymorphisms, of genes expressed during development, and (2) environmental influences on development, which can be further subdivided into changes that originate outside the fetus, such as alterations of maternal diet, and changes within the fetus that disrupt normal development, such as impairment of normal fetal urinary flow due to physical obstruction of the urinary tract. Human kidney or lower urinary tract malformation are reported in association with teratogens-angiotensin converting enzyme inhibitors, drugs used to treat high blood pressure cocaine, corticosteroids, ethanol, gentamycin, glucose, nonsteroidal anti-inflammatory drugs, and vitamin A and its derivatives.

Remote effects of acute kidney injury in a porcine model

Acute kidney injury (AKI) is a common and serious condition with no specific treatment. An episode of AKI may affect organs distant from the kidney, further increasing the morbidity associated with AKI. The mechanism of organ cross talk after AKI is unclear. The renal and immune systems of pigs and humans are alike. Using a preclinical animal (porcine) model, we tested the hypothesis that early effects of AKI on distant organs is by immune cell infiltration, leading to inflammatory cytokine production, extravasation, and edema. In 29 pigs exposed to either sham surgery or renal ischemia-reperfusion (control, n = 12; AKI, n = 17), we assessed remote organ (liver, lung, brain) effects in the short (from 2- to 48-h reperfusion) and longer term (5 wk later) using immunofluorescence (for leukocyte infiltration, apoptosis), a cytokine array, tissue elemental analysis (e.g., electrolytes), blood hematology and chemistry (e.g., liver enzymes), and PCR (for inflammatory markers). AKI elicited significant, short-term (∼24 h) increments in enzymes indicative of acute liver damage (e.g. , AST: ALT ratio; P = 0.02) and influenced tissue biochemistry in some remote organs (e.g., lung tissue [Ca(2+)] increased; P = 0.04). These effects largely resolved after 48 h, and no further histopathology, edema, apoptosis, or immune cell infiltration was noted in the liver, lung, or hippocampus in the short and longer term. AKI has subtle biochemical effects on remote organs in the short term, including a transient increment in markers of acute liver damage. These effects resolved by 48 h, and no further remote organ histopathology, apoptosis, edema, or immune cell infiltration was noted.