Reply to: Schreuder

The role of the kidney in the pathogenesis of hypertension has long been established, although recent studies challenge renal hegemony and suggest an important role for vascular cells as well (1,2). In recent years, the formulation has expanded and now includes the concept that chronic hypertension and kidney disease are also related to events that occur during the prenatal period and usually result in low birth weight (LBW). A recent overview considered the role of fetal programming in the development of adult kidney disease and hypertension (3). The aim of this review is to present further evidence to support an association between LBW and the increased prevalence of hypertension as well as progression toward chronic kidney disease (CKD) in adult life. Various potential mechanisms for this association are discussed, specifically the low nephron number (LNN) hypothesis and related cellular and molecular mechanisms that have been proposed. LBW infants are defined as infants who weigh ≤2500 g at birth. Infants who are delivered before 37 wk from the first day of the last menstrual period are termed preterm. The LBW infant population can be divided into preterm, appropriate for gestational age (AGA), or small for gestational age (SGA). The predominant cause of LBW infants in the United States is preterm birth, whereas in developing countries, the cause is often intrauterine growth restriction (IUGR). During the year 2004, 8.1% of births in the United States were LBW, and more than half of these were preterm. During the past two decades, there has been an increase in the prevalence of LBW as higher risk pregnancies progress to term and postnatal survival improves (4) (Figure 1). Figure 1. Percentage of infants who were born preterm and percentage who were born with low birth weight (LBW; defined in text): United States, 1990, 1995, 2000, …

Diabetic renal disease (diabetic nephropathy) is a leading cause of end-stage renal failure. Once the process has started, it cannot be reversed by glycaemic control, but progression might be slowed by control of blood pressure and protein restriction. To assess the effects of dietary protein restriction on the progression of diabetic nephropathy in patients with diabetes. We searched The Cochrane Library, MEDLINE, EMBASE, ISI Proceedings, Science Citation Index Expanded and bibliographies of included studies. Randomised controlled trials (RCTs) and before and after studies of the effects of a modified or restricted protein diet on diabetic renal function in people with type 1 or type 2 diabetes following diet for at least four months were considered. Two reviewers performed data extraction and evaluation of quality independently. Pooling of results was done by means of random-effects model. Twelve studies were included, nine RCTs and three before and after studies. Only one study explored all-cause mortality and end-stage renal disease (ESRD) as endpoints. The relative risk (RR) of ESRD or death was 0.23 (95% confidence interval (CI) 0.07 to 0.72) for patients assigned to a low protein diet (LPD). Pooling of the seven RCTs in patients with type 1 diabetes resulted in a non-significant reduction in the decline of glomerular filtration rate (GFR) of 0.1 ml/min/month (95% CI -0.1 to 0.3) in the LPD group. For type 2 diabetes, one trial showed a small insignificant improvement in the rate of decline of GFR in the protein-restricted group and a second found a similar decline in both the intervention and control groups. Actual protein intake in the intervention groups ranged from 0.7 to 1.1 g/kg/day. One study noted malnutrition in the LPD group. We found no data on the effects of LPDs on health-related quality of life and costs. The results show that reducing protein intake appears to slightly slow progression to renal failure but not statistically significantly so. However, questions concerning the level of protein intake and compliance remain. Further longer-term research on large representative groups of patients with both type 1 and type 2 diabetes mellitus is necessary. Because of the variability amongst patients, there might perhaps be a six month therapeutic trial of protein restriction in all individuals, with continuation only in those who responded best. Trials are required of different types of protein.

Low-protein (LP) diets extend lifespan through a comprehensive improvement in metabolic health across multiple tissues and organs. Many of these metabolic responses to protein restriction are secondary to transcriptional activation and release of FGF21 from the liver. However, the effects of an LP diet on the kidney in the context of aging has not been examined. Therefore, the goal of the current study was to investigate the impact of chronic consumption of an LP diet on the kidney in aging mice lacking FGF21. Wild-type (WT; C57BL/6J) and FGF21 knockout (KO) mice were fed a normal protein diet (20% casein) or an LP (5% casein) diet ad libitum from 3 to 22 mo of age. The LP diet led to a decrease in kidney weight and urinary albumin-to-creatinine ratio in both WT and FGF21 KO mice. Although the LP diet produced only mild fibrosis and infiltration of leukocytes in WT kidneys, the effects were significantly exacerbated by the absence of FGF21. Accordingly, transcriptomic analysis showed that inflammation-related pathways were significantly enriched and upregulated in response to LP diet in FGF21 KO mice but not WT mice. Collectively, these data demonstrate that the LP diet negatively affected the kidney during aging, but in the absence of FGF21, the LP diet-induced renal damage and inflammation were significantly worse, indicating a protective role of FGF21 in the kidney.NEW & NOTEWORTHY Long-term protein restriction is not advantageous for an otherwise healthy, aging kidney, as it facilitates the development of renal tubular injury and inflammatory cell infiltration. We provide evidence using FGF21 knockout animals that FGF21 is essential to counteract the renal injury and inflammation during aging on a low-protein diet.

Several studies have shown that total nephron (glomerular) number varies widely in normal human kidneys. Whereas the studies agree that average nephron number is approximately 900,000 to 1 million per kidney, numbers for individual kidneys range from approximately 200,000 to >2.5 million. Several studies have shown loss of glomeruli due to age-related glomerulosclerosis. The rates of loss vary among individuals depending upon blood pressure, diseases affecting the kidney, and other attributes of health, but most of the variation in nephron number is present at birth and is therefore developmentally determined. For example, in a relatively small study of nephron number in 15 children <3 months of age, we found that nephron number ranged from approximately 250,000 to 1.1 million. Given that no new nephrons are formed in human kidneys after approximately 36 weeks' gestation, much interest has focused on renal function and health in individuals born with relatively low nephron endowment. Several studies have reported a direct correlation between birth weight and nephron number and an indirect association between nephron number and blood pressure. Associations between low birth weight and cardiovascular disease, including hypertension, have also been widely reported. This report provides an update on our current knowledge of human nephron number and the associations with adult health and disease.

Nitrosamines are well-known carcinogenic agents. Humans are exposed to nitrosamines in various ways, the most important of which is the diet. Pentoxifylline is a xanthine derivative, which is used as a drug that inhibits inflammatory factors, reduces blood viscosity, improves peripheral blood flow, and increases oxygenation of tissue. This study was designed to evaluate the effects of pentoxifylline against damage induced by nitrosamine to the kidneys of rats. In this study, 48 male rats were randomly assigned to 8 groups: control normal group and nitrosamine control treated group (40 mg/kg); pentoxifylline groups (25, 50, 100 mg/kg) and nitrosamine + pentoxifylline treated groups (25, 50, 100 mg/kg). Treatments were administered either intraperitoneally (nitrosamine) or orally (pentoxifylline) on a daily basis for 28 days. The normalized kidney weight, glomeruli characteristics, thiobarbituric acid reactive species, antioxidant capacity, kidney function indicators, and serum nitrite oxide levels were investigated. Nitrosamine administration increased kidney malondialdehyde (MDA) level, kidney weight, blood urea nitrogen (BUN), creatinine, and nitrite oxide levels and decreased significantly glomeruli number and tissue ferric reducing/antioxidant power (FRAP) level compared to the control normal group (P < 0.05). The pentoxifylline and pentoxifylline + nitrosamine treatments reduced BUN, kidney MDA level, creatinine, glomerular diameter, and nitrite oxide levels significantly at all doses and increased the glomeruli number, kidney weight, and tissue FRAP level compared to the nitrosamine control group (P < 0.05). It seems that pentoxifylline administration improved kidney injury induced by nitrosamine in rats.

This study examined the effect of açaí (Euterpe oleracea Mart.) seed extract (ASE) on cardiovascular and renal alterations in adult offspring, whose mothers were fed a low-protein (LP) diet during pregnancy. Four groups of rats were fed: control diet (20% protein); ASE (200 mg/kg per day); and LP (6% protein); LP + ASE (6% protein + ASE) during pregnancy. After weaning, all male offspring were fed a control diet and sacrificed at 4 months old. We evaluated the blood pressure, vascular function, serum and urinary parameters, plasma and kidney oxidative damage, and antioxidant activity and renal structural changes. Hypertension and the reduced acetylcholine-induced vasodilation in the LP group were prevented by ASE. Serum levels of urea, creatinine and fractional excretion of sodium were increased in LP and reduced in LP + ASE. ASE improved nitrite levels and the superoxide dismutase and glutathione peroxidase activity in LP, with a corresponding decrease of malondialdehyde and protein carbonyl levels. Kidney volume and glomeruli number were reduced and glomerular volume was increased in LP. These renal alterations were prevented by ASE. Treatment of protein-restricted dams with ASE provides protection from later-life hypertension, oxidative stress, renal functional and structural changes, probably through a vasodilator and antioxidant activity.

The nutritional status, prenatally and early postnatally, plays a critical role in postnatal growth and development. Early malnutrition may change the original programming of organs, especially those in developmental phases, which can result in long-term changes in metabolism. The association between a low birth weight and the increased risk on type 2 diabetes, hypertension and cardiovascular disease is well known. In the present study we investigated whether intrauterine malnutrition or direct postnatal food restriction affects the onset of puberty in male and female rats. Intrauterine growth retardation (IUGR) was induced by uterine artery ligation on day 17 of gestation and postnatal food restriction (FR) by litter-enlargement to 20 pups per mother from day 2 after birth until weaning (24 d). Both models of malnutrition resulted in a persistent growth failure postnatally. The parameter of the onset of puberty was balano-preputial-separation (BPS) in the male rat and vaginal opening (VO) in the female rat. In both male IUGR (n = 26) and FR (n = 20) rats, the age at BPS was significantly delayed, with 48.1 +/- 1.9 d (p < 0.0001) and 50.4 +/- 2.9 d (p < 0. 0001), respectively, compared with controls (n = 30) with 45.8 +/- 1.4 d. In female IUGR rats (n = 37) the age at VO was significantly delayed, with 37.4 +/- 2.7 d (p < 0.04) compared with 36.1 +/- 1.5 d in controls (n = 23), but not in female FR rats (n = 18) with 36.5 +/- 2.2 d. Weight at onset of puberty did not differ between male IUGR and control rats, 194.5 +/- 20.0 g and 201.7 +/- 16.8 g, respectively, but was significantly lower in male FR rats with a weight of 175.6 +/- 17.5 g (p < 0.0001). In female IUGR as well as in female FR rats, weight at onset of puberty was significantly lower compared with controls: weight in IUGR 106.1 +/- 13.1 g (p < 0.001), weight in FR 85.3 +/- 7.6 g (p < 0.0001) and weight in controls 116.9 +/- 9.3 g. We conclude that early malnutrition, during late gestation or direct postnatally, results in a delayed onset of puberty in IUGR and FR male rats and in IUGR female rats, but not in FR female rats. The onset of puberty in these growth retarded rats as well as in controls does not depend on the achievement of a certain, crucial weight. The perinatal period appears to be a "critical time period" for the maturational process of pubertal development.

BackgroundThe total number of nephrons has been measured mainly from post-mortem studies and only in selected populations. Data from living subjects are scanty, and direct comparisons among different glomerular diseases are lacking. The present work exploits modern methodology to estimate the total nephron number in glomerulopathies with prevalent proteinuria/nephrotic syndrome versus glomerulopathies with nephritic syndrome (IgA nephropathy (IgAN), lupus nephritis), thus extending previous observations about the number and function of glomeruli in different physiological and pathological states.MethodsThis is a retrospective study based on one hundred and seven patients who have undergone renal biopsy. The glomerular density has been estimated from the biopsy specimens and the total cortical volume has been obtained from ultrasound recordings. Stereological methods have been applied to calculate the total number of nephrons and their volume. The correlation between clinical parameters and quantitative morphological data have studied using the Pearson correlation coefficient (r).ResultsThe total number of nephrons inversely correlated with the systolic blood pressure (r = −0.4, p < 0.05). In proteinuric diseases, such as focal segmental glomerulo-sclerosis (FSGS), membranous nephropathy (MN) and diabetes, the change in estimated GFR (eGFR) directly correlated with the total number of non-sclerotic glomeruli (NSG) (r = 0.62, p < 0.01), whereas in nephritic syndrome no significant correlation was observed. The alterations in eGFR occurring in nephritic syndromes such as IgAN cannot be explained on the basis of the number of NSG.DiscussionThe fusion of the podocyte foot-processes that typically occurs in purely proteinuric diseases does not modify the glomerular filtration rate: therefore in these situations, the change in eGFR depends mainly on the number of available glomeruli. On the other side, the eGFR decrease occurring in nephritic syndromes, such as IgAN, cannot be explained simply on the basis of the number of NSG and likely depends on the substantial involvement of the mesangial axis. Future studies should verify whether these changes are reversible with appropriate therapy, thus reversing eGFR decrease.

Fetal Compensatory Renal Growth Due to Unilateral Ureteral Obstruction

Age and Protein Restriction Followed by Balanced Refeeding Affect Pancreatic Digestive Enzyme Outputs and Turnover Times in Rats

Drug metabolism can be affected by chronic renal failure (CRF). Although it is known that several drugs that are known to be acetylated accumulate in CRF, the effect of CRF on N-acetyltransferase (NAT), the enzyme responsible for this acetylation, is unknown. Herein is reported that protein and gene expression of both Nat isoforms in the liver was reduced by >30% and Nat2 activity was reduced by 50% in rats with CRF compared with control rats. Incubation of hepatocytes with serum from rats with CRF suggested that a circulating factor is responsible for the decrease in protein and gene expression. For testing the hypothesis that parathyroid hormone may be this factor, CRF was induced in parathyroidectomized rats; downregulation of Nat expression and activity was not observed in these rats. Furthermore, addition of parathyroid hormone to cultured hepatocytes induced a decrease in Nat2 protein and gene expression. In conclusion, liver acetylation of drugs in a rat model of CRF is reduced by a downregulation of Nat1 and Nat2 isoforms, secondary to decreased gene expression. Parathyroid hormone seems to be an important mediator of this phenomenon.

Normal and abnormal kidneys collected from broiler chickens at slaughter (6 to 7 weeks of age and of mixed sex) were evaluated to establish histopathologic and morphometric parameters for broilers. Normal kidneys (group D) had an overall mean glomerular diameter of 67.4 +/- 27.8 microns. Abnormal groups (Groups A, B, and C) had an average glomerular diameter of 75.2 +/- 32.1 microns, which was significantly different (P < 0.01) from that of Group D. All glomerular diameters in Group A (otherwise normal birds with swollen kidneys) were significantly different (P < 0.01) from corresponding diameters in Group D. In Group B (birds condemned for Marek's disease virus), only the mammalian glomeruli were significantly different from Group D mammalian glomeruli (P < 0.01). A significant increase in glomerular density was observed for all abnormal groups and glomerular types. The data indicate that glomerular diameter and cellularity might be practical and sensitive indicators of early glomerular changes that can occur in grossly swollen kidneys. Increased glomerular density indicates tubular loss or increase in glomerular numbers.

IntroductionThe number of nephrons is a critical determinant of renal health, because chronic kidney disease often results from a reduction in functional nephrons. Variability in the number of nephrons is influenced by genetic, racial, prenatal, and postnatal factors. Estimating the number of nephrons is crucial for establishing a baseline, before the onset of age-related nephron loss. This study aimed to estimate number of nephrons in pediatric patients by using imaging and histological techniques.MethodsThis retrospective study included pediatric patients with renal tumors, who are undergoing nephrectomy and contrast-enhanced computed tomography (CT) between January 2010 and January 2021. Postsurgical renal tissue specimens were fixed, stained, and scanned into high-resolution digital images. Nonsclerotic glomerular density was calculated using stereological methods, whereas renal cortical volume was measured using ITK-SNAP software on CT images. The total number of nephrons was estimated based on cortical volume and glomerular density. Statistical analyses were conducted to identify the correlations between the number of nephrons and clinical factors.ResultsTwenty-one children met the inclusion criteria. The cohort comprised 13 boys (61.9%) and 8 girls (38.1%) with a median age at nephrectomy of 2.5 years. The median number of nephrons per kidney was 925,000 (interquartile range [IQR]: 845,000–1,020,000). Higher number of nephrons was significantly correlated with older age at nephrectomy (ρ = 0.47, P = 0.036) and larger body surface area (BSA; ρ = 0.45, P = 0.034).ConclusionThis study offers new insights into pediatric nephron endowment, emphasizing the importance of early nephron assessment for predicting long-term renal outcomes.

Nephron endowment refers to the total number of nephrons an individual is born with, as nephrogenesis in humans is completed by 36 weeks of gestation and no new nephrons are formed post-birth. Nephron number refers to the total number of nephrons measured at any point in time post-birth. Both genetic and environmental factors influence both nephron endowment and number. Understanding how specific genes or factors influence the process of nephrogenesis and nephron loss or demise is important as individuals with lower nephron endowment or number are thought to be at a higher risk of developing renal or cardiovascular disease. Understanding how environmental exposures over the course of a person's lifetime affects nephron number will also be vital in determining future disease risk. Thus, the ability to assess whole kidney nephron number quickly and reliably is a basic experimental requirement to better understand mechanisms that contribute to or promote nephrogenesis or nephron loss. Here, we describe the acid maceration method for the estimation of whole kidney nephron number based on the procedure described by Damadian, Shawayri, and Bricker, with slight modifications. The acid maceration method provides fast and reliable estimates of nephron number (as assessed by counting glomeruli) that are within 5% of those determined using more advanced, albeit expensive, methods such as magnetic resonance imaging. Moreover, the acid maceration method is an excellent high-throughput method to assess nephron number in large numbers of samples or experimental conditions.

Studies were carried out to explore the influence of soy protein and food restriction on age-related changes in serum PTH and bone. Three groups of male Fischer 344 rats were studied from 6 weeks of age. Group A rats were fed ad libitum diet A, which has casein as the protein source. Group B rats were fed diet B (with casein as protein source) at 60% of the mean ad libitum food intake. Group C rats were fed ad libitum diet C, which has soy protein as the protein source. The animals were killed at periodic intervals beginning at 6 months of age after an overnight fast. Serum PTH, measured with an intact N-terminal-specific RIA, and immunoreactive calcitonin increased progressively with aging. The increase was markedly suppressed by food restriction, and in the case of PTH by the soy protein diet as well. Serum creatinine started to increase after 18 months of age, and both dietary regimens of groups 2 and 3 retarded the increase. Aging was associated with a fall in serum 25-hydroxyvitamin D, and loss of bone occurred during the terminal part of life in the ad libitum-fed animals. These were prevented by food restriction, while the soy protein diet delayed the onset of bone loss. We conclude from these findings and other data from this study that in the male F344 rats 1) an age-related increase in serum PTH precedes an age-related increase in serum creatinine concentration; 2) an age-related decline in renal function probably contributes to age-related hyperparathyroidism, which, in turn, contributes to senile bone loss; 3) food restriction inhibits age-related hyperparathyroidism and senile bone loss; 4) on the basis of the data from rats fed a soy protein-containing diet, a decline in renal function and progressive hyperparathyroidism are not inevitable consequences of aging in the ad libitum fed rats.