Simon C. Langley-Evans

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.

Protein intake in pregnancy, placental glucocorticoid metabolism and the programming of hypertension in the rat

Hypertension is strongly predicted by a low birthweight:placental weight ratio. Two independent models have been described to explain this association; less than optimal maternal protein nutrition leading to fetal undernutrition, or glucocorticoid excess. Pregnant rats were fed diets containing 18 per cent casein (control) or 9 per cent casein, balanced for energy. On day 20 of gestation the pregnancies were terminated and placentae collected for determination of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) activity. Placental 11 beta HSD normally protects the fetus from the effects of maternal glucocorticoids. Activity was specifically attenuated by mild protein restriction (33 per cent in activity), whilst activities of glucocorticoid-insensitive control enzymes were unchanged and glucocorticoid-inducible glutamine synthetase activity was increased (27 per cent), relative to activity in placentae from control animals. The nutritional manipulation during pregnancy significantly increased systolic blood pressure (17 mmHg) in the resulting offspring in early adulthood. A possible common pathway whereby maternal environmental factors may influence fetal and placental growth and programme disease is inferred.

Developmental programming of health and disease.

The environment encountered in fetal and neonatal life exerts a profound influence on physiological function and risk of disease in adult life. Epidemiological evidence suggests that impaired fetal growth followed by rapid catch-up in infancy is a strong predictor of obesity, hypertension, non-insulin-dependent diabetes and CHD. Whilst these associations have been widely accepted to be the product of nutritional factors operating in pregnancy, evidence from human populations to support this assertion is scarce. Animal studies clearly demonstrate that there is a direct association between nutrient imbalance in fetal life and later disease states, including hypertension, diabetes, obesity and renal disease. These associations are independent of changes in fetal growth rates. Experimental studies examining the impact of micro- or macronutrient restriction and excess in rodent pregnancy provide clues to the mechanisms that link fetal nutrition to permanent physiological changes that promote disease. Exposure to glucocorticoids in early life appears to be an important consequence of nutrient imbalance and may lead to alterations in gene expression that have major effects on tissue development and function. Epigenetic mechanisms, including DNA methylation, may also be important processes in early-life programming.

Prenatal exposure to a maternal low-protein diet programmes a preference for high-fat foods in the young adult rat

Nutrient restriction in pregnancy has been shown to programme adult obesity. Modulation of feeding behaviour may provide a mechanism through which obesity may be programmed. Pregnant Wistar rats were fed either a control diet or a low-protein (LP) diet throughout gestation. Their offspring were allocated to a self-selected-diet protocol to assess appetite and food preferences at 12 and at 30 weeks of age. Self-selection of high-fat, high-protein or high-carbohydrate foods by 12-week-old rats indicated that the prenatal environment influenced feeding behaviour. Both male and female offspring of LP-fed mothers consumed significantly more of the high-fat (P<0.001) and significantly less (P<0.02) of the high-carbohydrate food than the control animals. Female, but not male, offspring of LP-fed rats failed to adjust food intake to maintain a constant energy intake and had higher fat (P<0.005) and energy intakes (P<0.05) than control female rats. At 30 weeks of age there were no differences in the pattern of food selection between the two groups of animals. Male offspring of LP-fed rats had significantly more gonadal fat than control animals (P<0.05), but analysis of total body fat content indicated that there was no significant difference in overall adiposity. The present study suggests that in young adults at least, early life exposure to undernutrition determines a preference for fatty foods. Maternal nutrition may thus promote changes in systems that are involved in control of appetite or the perception of palatability.

Hypertension induced by foetal exposure to a maternal low-protein diet, in the rat, is prevented by pharmacological blockade of maternal glucocorticoid synthesis

Background Hypertension and coronary heart disease are programmed by maternal undernutrition in utero. The feeding of low-protein diets to rats during their pregnancy results in higher blood pressure in the offspring from the age of weaning. Objective To determine whether a low-protein diet increases foetal exposure to glucocorticoids of maternal origin, resulting in altered hypothalamic–pituitary–adrenal axis function and hypertension. Design Rats were fed an 18% casein diet (control) or a 9% casein diet (low protein) during pregnancy. Low-protein-fed dams were injected with metyrapone to inhibit corticosterone synthesis or with metyrapone plus a replacement dose of corticosterone. The offspring of these pregnancies had their blood pressure determined when they were aged 7 weeks. Methods The systolic blood pressure was determined using an indirect tail-cuff method. Glucocorticoid action in the hypothalamus was measured using glycerol-3 phosphate dehydrogenase as a reference enzyme. Results Blood pressures of rats exposed to maternal low-protein diets in utero were elevated significantly relative to those of control rats. The animals that had been exposed to a maternal low-protein diet also exhibited increased glycerol-3 phosphate dehydrogenase (GPDH) activity in the hypothalamus, whereas their pyruvate kinase activity was not changed. The offspring of rats injected with metyrapone did not have raised blood pressure or GPDH activities. Replacement of corticosterone during pregnancy had no effect upon the blood pressures and GPDH activities of male offspring, but it reversed the effects of metyrapone in female offspring. Conclusions Exposure to a maternal low-protein diet in utero programmes hypertension in the rat. The data are consistent with the hypothesis that corticosteroids of maternal origin play a role in this programming effect.

Fetal programming of cardiovascular function through exposure to maternal undernutrition.

A substantial and robust body of epidemiological evidence indicates that prenatal dietary experience may be a factor determining cardiovascular disease risk. Retrospective cohort studies indicate that low birth weight and disproportion at birth are powerful predictors of later disease risk. This prenatal influence on non-communicable disease in later life has been termed programming. Maternal nutritional status has been proposed to be the major programming influence on the developing fetus. The evidence from epidemiological studies of nutrition, fetal development and birth outcome is, however, often weak and inconclusive. The validity of the nutritional programming concept is highly dependent on experimental studies in animals. The feeding of low-protein diets in rat pregnancy results in perturbations in fetal growth and dimensions at birth. The offspring of rats fed low-protein diets exhibit a number of metabolic and physiological disturbances, and are consistently found to have high blood pressure from early postnatal life. This experimental model has been used to explore potential mechanisms of programming through which maternal diet may programme the cardiovascular function of the fetus. Indications from this work are that fetal exposure to maternally-derived glucocorticoids plays a key role in the programming mechanism. Secondary to this activity, the fetal hypothalamic-pituitary-adrenal axis may stimulate renin-angiotensin system activity, resulting in increased vascular resistance and hypertension.

Childhood obesity and risk of the adult metabolic syndrome: a systematic review

Background:While many studies have demonstrated positive associations between childhood obesity and adult metabolic risk, important questions remain as to the nature of the relationship. In particular, it is unclear whether the associations reflect the tracking of body mass index (BMI) from childhood to adulthood or an independent level of risk. This systematic review aimed to investigate the relationship between childhood obesity and a range of metabolic risk factors during adult life.Objective:To perform an unbiased systematic review to investigate the association between childhood BMI and risk of developing components of metabolic disease in adulthood, and whether the associations observed are independent of adult BMI.Design:Electronic databases were searched from inception until July 2010 for studies investigating the association between childhood BMI and adult metabolic risk. Two investigators independently reviewed studies for eligibility according to the inclusion/exclusion criteria, extracted the data and assessed study quality using the Newcastle–Ottawa Scale.Results:The search process identified 11 articles that fulfilled the inclusion and exclusion criteria. Although several identified weak positive associations between childhood BMI and adult total cholesterol, low-density lipo protein-cholesterol, triglyceride and insulin concentrations, these associations were ameliorated or inversed when adjusted for adult BMI or body fatness. Of the four papers that considered metabolic syndrome as an end point, none showed evidence of an independent association with childhood obesity.Conclusions:Little evidence was found to support the view that childhood obesity is an independent risk factor for adult blood lipid status, insulin levels, metabolic syndrome or type 2 diabetes. The majority of studies failed to adjust for adult BMI and therefore the associations observed may reflect the tracking of BMI across the lifespan. Interestingly, where adult BMI was adjusted for, the data showed a weak negative association between childhood BMI and metabolic variables, with those at the lower end of the BMI range in childhood, but obese during adulthood at particular risk.

Periodontal disease is associated with lower antioxidant capacity in whole saliva and evidence of increased protein oxidation.

The aim of this cohort study was to determine whether periodontitis and gingivitis are associated with impaired salivary antioxidant status and increased oxidative injury. One hundred and twenty-nine patients attending a routine dental check-up were recruited for the study. Periodontal disease status was characterized using the Community Periodontal Index of Treatment Needs (CPITN) system. Total salivary antioxidant capacity and salivary ascorbate, urate and albumin were determined in a sample of whole unstimulated saliva. Protein carbonyl concentrations were determined as an index of oxidative injury. Patients in the lowest tertile of CPITN score exhibited decreased salivary delivery of antioxidants and specifically urate than patients in the upper tertile. Poor periodontal health was associated with increased concentrations of protein carbonyls in saliva. Women had significantly lower total antioxidant status than men, regardless of periodontal health. Periodontal disease is associated with reduced salivary antioxidant status and increased oxidative damage within the oral cavity.

In utero exposure to maternal low protein diets induces hypertension in weanling rats, independently of maternal blood pressure changes

The association between maternal nutrition, fetal growth and the later development of hypertension was investigated in the rat. Animals were habituated to diets containing 18% (control) or 9% (low) protein by weight. The rats were mated and maintained on the diets until the end of pregnancy. Lactating dams were transferred onto standard chow diet. Systolic blood pressure was determined in male and female weanling offspring, using an indirect tail-cuff method. To assess the direct effects of low protein diets upon blood pressure of adult animals, a group of male and female rats were fed 18% or 9% protein for 14 days. Blood pressure was determined at the beginning and end of the feeding period. Blood pressure was additionally assessed over 14 days in pregnant rats fed control or low protein diets. Low protein diets did not alter systolic blood pressure in adult male or female rats. The blood pressures of pregnant females fed 18% or 9% protein diets did not significantly differ at any stage of pregnancy. Rats fed 9% protein diets gave birth to significantly smaller pups. Litter sizes were unaltered, and no differences in perinatal mortality were observed. Pups exposed to maternal low protein in utero had higher systolic blood pressure at the age of 4 weeks, when compared to control pups. The phenomenon was observed in both male and female offspring. Blood pressures at 4 weeks of age were strongly associated with maternal protein intake (r = -0.55). Associations were also noted between blood pressure and maternal weight at mating (r = 0.48), and weight gain in pregnancy (r = -0.30). Fetal exposure to maternal low protein diets induces hypertension in rats. The phenomenon is observed early in life and is independent of sex and the influence of maternal blood pressure. The low protein diet itself did not produce an increase in the blood pressure of adult rats.

Exposure to undernutrition in fetal life determines fat distribution, locomotor activity and food intake in ageing rats

Objective:To assess the long-term impact of undernutrition during specific periods of fetal life, upon central adiposity, control of feeding behaviour and locomotor activity.Design:Pregnant rats were fed a control or low-protein (LP) diet, targeted to early (LPE), mid (LPM) or late (LPL) pregnancy or throughout gestation (LPA). The offspring were studied at 9 and 18 months of age.Measurements:Adiposity was assessed by measuring weight of abdominal fat depots relative to body weight. Locomotor activity was assessed using an infrared sensor array system in both light and dark conditions. Hypothalamic expression of mRNA for galanin and the galanin 2 receptor (Gal2R) was determined using real-time PCR.Results:At 9 months, male rats exposed to LP in utero had less fat in the gonadal depot, but were of similar body weight to controls. By 18 months, the males of groups LPA and LPM had more abdominal and less subcutaneous fat. Females deposited more fat centrally than males between 9 and 18 months of age, and this was more marked in groups LPA and LPL. Food intake was greater in LPM males. Among females hypophagia was noted in groups LPA and LPL. Expression of galanin and Gal2R were unaffected by maternal diet. Total locomotor activity was reduced in LPE males and all LP females in the light but not in the dark.Conclusion:Locomotor activity and feeding behaviour in aged rats are subject to prenatal programming influences. Fetal undernutrition does not programme obesity in rats without postnatal dietary challenge.