Urinary prostaglandins, vasopressin, and kallikrein excretion in healthy children from birth to adolescence

Pravastatin Therapy and Biomarker Changes in Children and Young Adults with Autosomal Dominant Polycystic Kidney Disease

BACKGROUND AND OBJECTIVES

Disease-specific treatment options for autosomal dominant polycystic kidney disease are limited. Clinical intervention early in life is likely to have the greatest effect. In a 3-year randomized double-blind placebo-controlled phase 3 clinical trial, the authors recently showed that pravastatin decreased height-corrected total kidney volume (HtTKV) progression of structural kidney disease over a 3-year period. However, the underlying mechanisms have not been elucidated.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Participants were recruited nationally from July 2007 through October 2009. Plasma and urine samples collected at baseline, 18 months, and 36 months from 91 pediatric patients enrolled in the above-mentioned clinical trial were subjected to mass spectrometry-based biomarker analysis. Changes in biomarkers over 3 years were compared between placebo and pravastatin-treated groups. Linear regression was used to evaluate the changes in biomarkers with the percent change in HtTKV over 3 years.

RESULTS

Changes in plasma concentrations of proinflammatory and oxidative stress markers (9- hydroxyoctadecadienoic acid, 13-hydroxyoctadecadienoic acid, and 15-hydroxyeicosatetraenoic acid [HETE]) over 3 years were significantly different between the placebo and pravastatin-treated groups, with the pravastatin group showing a lower rate of biomarker increase. Urinary 8-HETE, 9-HETE, and 11-HETE were positively associated with the changes in HtTKV in the pravastatin group.

CONCLUSIONS

Pravastatin therapy diminished the increase of cyclooxygenase- and lipoxygenase-derived plasma lipid mediators. The identified biomarkers and related molecular pathways of inflammation and endothelial dysfunction may present potential targets for monitoring of disease severity and therapeutic intervention of autosomal dominant polycystic kidney disease.

Urinary prostaglandin E2 in the newborn and infant

Prostaglandin E(2) (PGE(2)) belongs to a family of biologically active lipids derived from the 20-carbon essential fatty acids. Renal PGE(2) is involved in the development of the kidney; it also contributes to regulate renal perfusion and glomerular filtration rate, and controls water and electrolyte balance. Furthermore, this mediator protects the kidney against excessive functional changes during the transition from fetal to extrauterine life, when it counteracts the vasoconstrictive effects of high levels of angiotensin II and other mediators. There is evidence that PGE(2) plays an important pathophysiological role in neonatal conditions of renal stress, and in congenital or acquired nephropaties. Thus, measurement of urinary PGE(2) as an index of renal synthesis of this primary prostaglandin may represent a non-invasive and sensitive method of investigating the homeostatic function of the kidney in early life. The aim of this literature review is to examine urinary PGE(2) as a non-invasive marker of renal homeostasis in the newborn and infant under both physiological and pathological conditions, or during treatments with widely used, potentially toxic drugs.

Development of water transport in the collecting duct

The ability of the immature kidney to concentrate urine is lower than in adults. This can lead to severe water and electrolyte disorders, especially in premature babies. Resistance to AVP and lower tonicity of the medullary interstitium seem to be the major factors limiting urine concentration in newborns. AVP-stimulated cAMP generation is impaired. This is the result of inhibition of the production by PGE(2) acting through EP3 receptors and increased degradation by phosphodiesterase IV. The expression of aquaporin-2 (AQP2) in the immature kidney is low; however, under conditions of water deprivation and after stimulation with DDAVP, it rises to adult levels. The expression of AQP3 and AQP4 is intact at birth and does not seem to contribute to the hyporesponsiveness to AVP. Low sodium transport by thick ascending loops of Henle, immaturity of the medullary architecture, and adaptations in the transport of urea contribute to the lower tonicity of the medullary interstitium. This paper reviews the alterations in the AVP signal transduction pathway in the immature kidney.

Postnatal maturation of tissue kallikrein-producing cells (connecting tubule cells) in the rat kidney: a morphometric and immunohistochemical study

The mature, fully differentiated connecting tubule (CNT) cell plays an important role in the regulation of serum potassium levels and synthesizes the enzyme tissue kallikrein, a main component of a renal vasoactive system, the kallikrein-kinin system. To characterize the growth of CNT cells (tissue kallikrein-producing cells), we studied the rat kidney at three different time points of postnatal development: at day 5, day 15, and day 30. The CNT cells were identified on tissue sections by a standardized immunohistochemical procedure. The tissue kallikrein content was determined by radioimmunoassay and the activity of the enzyme in kidney homogenates was measured using a selective synthetic substrate. The number of immunolabeled CNT and CNT cells per cortex area gradually increased from day 5 to day 30. A similar rise in the content and activity of tissue kallikrein was observed when the enzyme levels were determined by radioimmunoassay or by the enzymatic method. In addition, the morphometric analysis showed that the distal end of CNT had larger cells that displayed a more intense tissue kallikrein staining than those present in the proximal end, suggesting that the postnatal development of CNT is induced from its juxtamedullary portion. Our results show that tissue kallikrein expression is very low in the newborn rat, increasing gradually with age to reach adult levels at day 30. This finding, together with the morphometric data, suggests immaturity of CNT cells in newborn rats, a fact that could contribute to explaining the high serum potassium levels reported at this stage. In addition, the contrasting behavior of kallikrein and renin in the postnatal development (kallikrein increasing and renin decreasing) could explain the gradual decrease in renal vascular resistance and increase in renal blood flow observed after birth.

Normal prostaglandinuria E2 in Gitelman's syndrome, the hypocalciuric variant of Bartter's syndrome

In familial Bartter's syndrome, hyperprostaglandinuria is considered a constant feature and prostanoid synthetase inhibition often positively influences the disease course. The urinary calcium excretion distinguishes two clinically and biochemically different variants, namely, classic Bartter's syndrome (normocalciuric or hypercalciuric variant; urinary calcium to creatinine > or = 35.3 mg/mg 10(-3)) and Gitelman's syndrome (hypocalciuric variant; urinary calcium to creatinine < 35.3 mg/mg 10(-3)). In the hypocalciuric variant of Bartter's syndrome prostanoid synthetase inhibition is of little benefit. Since the production of prostanoids has not been extensively studied in Gitelman's syndrome, the urinary excretion of prostaglandin E2 was assessed by radioimmunoassay in 11 untreated patients with Gitelman's syndrome (aged 10 to 21 years; five females and six males) and in 11 healthy controls (aged 11 to 20 years; five females and six males). The urinary excretion of prostaglandin E2 was similar in both study groups. The study provides the rationale for the poor effect of prostanoid synthetase inhibition in the hypocalciuric variant of Bartter's syndrome. The assessment of urinary excretion of prostaglandin E2 does not represent a diagnostic sine qua non in the context of familial Bartter's syndrome.

Molecular aspects of kallikrein and kininogen in the maturing kidney

Kinins are vasoactive paracrine peptides which participate in a wide range of functions, including the regulation of local organ blood flow, systemic blood pressure, transepithelial water and electrolyte transport, cellular growth, capillary permeability and inflammatory response, and pain. The recent introduction of specific bradykinin receptor subtype antagonists has greatly advanced our understanding of the role of the kallikrein-kinin system (KKS) in various physiological and disease states. However, a major gap remains in our knowledge of the role of kinins in early development. In this review, evidence is presented that the developing nephron expresses both tissue kallikrein and kininogen, and that the genes encoding the components of the KKS are subject to considerable developmental regulation. The activity of the intrarenal kinin-generating system is lowest in the developing kidney and increases with age. Completion of nephrogenesis is characterized by a marked surge in intrarenal kallikrein synthesis and gene transcription. Maturation is associated with redistribution of intrarenal kallikrein and its messenger RNA from the inner to outer cortical nephrons following the centrifugal pattern of nephron development. Challenges for the future include delineation of the direct role of kinins in the maturation of renal functions and elucidation of the molecular mechanisms underlying the developmental expression of the KKS.

Regulation of extracellular fluid volume in neonates

This review summarises mechanisms of control of extracellular fluid volume in the neonatal period. 'Normal' body fluid distribution and methods of its measurement are discussed as well as regulatory mechanisms with particular emphasis on hormonal and renal aspects.

The syndrome of hypertension and hyperkalaemia with normal glomerular filtration rate: is there a deficiency in vasodilator prostaglandins?

1. In Gordon's syndrome (GS; a syndrome of hypertension and hyperkalaemia with normal glomerular filtration rate), excessive proximal sodium reabsorption leads to suppression of renin and aldosterone, hyperkalaemia and hyperchloraemic acidosis. 2. Low urinary levels of vasodilator prostaglandins (PG) have been reported in GS, suggesting renal hypoprostaglandinism as a pathophysiological mechanism. 3. In four cases of GS, levels of vasodilator prostaglandins PGE2 and 6-keto-PGF1 alpha were low. 4. In one case of GS, low PGE2 levels were normalized by dietary salt restriction or diuretic therapy.

Urinary excretion of prostaglandins during infancy and childhood: influence of age, sodium restriction and posture

The influences of age, sodium restriction and posture on 24-hour urinary excretion of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF 2 alpha), 6-keto-prostaglandin F1 alpha (6-keto-PGF 1 alpha) and thromboxane B2 (TXB2) were investigated in 111 healthy children and youngsters in the age between 1 day and 16 years. A considerable degree of variation was found in normal 24-hour urinary prostaglandin excretion in all age groups. There was no significant effect of age on the urinary excretion of prostaglandins when data were corrected for body surface area. In addition, sodium restriction and posture had no influence on the excretion of PGE2, PGF 2 alpha, 6-keto-PGF 1 alpha and TXB2. Our results indicate that in the first days of life the kidney already has the capacity to synthesize prostaglandins in amounts comparable to older children.

Endocrine control of electrolyte balance during development

The endocrine control of electrolyte balance during development is reviewed. It is suggested that the high urinary sodium excretion observed in premature infants may be secondary to the immaturity of the adrenal gland to adequately increase the secretion of aldosterone (Sulyok et al, 1979b), and to the inability of the distal tubule to respond appropriately to a rise in circulating aldosterone levels (Sulyok et al, 1979a). On the other hand, the elevated plasma aldosterone levels observed in term newborn infants may play an important role in the blunted response of the newborn kidney to saline loading (Sulyok et al, 1979a; Spitzer, 1982). The ability of ANP to induce a natriuresis and to contribute to fluid and electrolyte homeostasis during development has been investigated. It has been found that the immature kidney is less responsive to ANP than later in life (Chevalier et al, 1988; Robillard et al, 1988). On the other hand, it has been suggested that a rise in plasma ANP during the first five days of life may contribute to the physiological weight loss associated with the extracellular volume contraction occurring shortly after birth (Tulassay et al, 1987). The role of glucocorticoids, prostaglandins and the kallikrein-kinin system in regulating electrolyte balance during development is also reviewed.

Direct radioimmunoassay of active and inactive human glandular kallikrein: some physiological and pathological variabilities

We have developed a sensitive and specific radioimmunoassay which allows the detection of human glandular kallikrein in biologic fluids at a level of 40 pg/ml. The antisera did not recognize human plasma kallikrein and glandular kallikrein from other species including marmoset. Furthermore the antibody did not bind pro-kallikrein but was specific for the trypsin activated kallikrein. The antibody inhibited the kininogenase activity of standard kallikrein incubated with human kininogen. However active kallikrein inhibited by inhibitors bound at the active site is still detectable, indicating that the antibody is specific for the structure of the active form but not for the active site. In normotensive subjects, daily urinary kallikrein excretion increased with age until 30, then a decrease was observed. In renal transplanted recipients a progressive increase of the active form was found. A low concentration of immunoreactive active kallikrein was detected in lymphatic fluids of patients suffering from acute pancreatitis treated by lymphatic drainage; although this kallikrein is the active immunoreactive form, a very weak kininogenase activity was measured, suggesting a partial inhibition by anti-proteases. These data provide complementary evidence for the physiological and pathological role of glandular kallikrein.

Eicosanoids in renal function

The major role of renal eicosanoid synthesis appears to be a protective one. In the cortex, prostaglandin synthesis minimises potential anoxic and ischaemic damage by vasodilatation. In the medulla, prostaglandin synthesis appears to stabilise the corticomedullary solute gradient and may play a role in cell volume regulation. Mono-oxygenase production at this site, by modifying blood flow and cellular active transport processes could again serve a protective function against anoxia and ischaemia. The release of erythropoietin also appears to be prostaglandin dependent. It is likely that leukotrienes released from inflammatory cells within the kidney will affect renal haemodynamics and capillary permeability as in other tissues.

Plasma phospholipid fatty acids and urinary excretion of prostaglandins PGE1 and PGE2 in infants during total parenteral nutrition, with continuous or sequential administration of fat emulsion

During total parenteral nutrition, using an identical supply of fat emulsion (350 mg/kg/24 hr) to correct essential fatty acid deficiency in children, the efficacy of two methods of administration was studied: continuous over 24 hr, or discontinuous 3 hr/day. At the beginning of the study, all the infants (1-4 months old) had proven essential fatty acid deficiency. After at least 1 month of one of the two nutritional protocols (continuous or discontinuous), plasma phospholipid fatty acid composition and PGE1 and PGE2 urinary excretion were measured. The results obtained indicate better utilization of the fat emulsion when it is administered almost every day, in continuous infusion over 24 hr (1 g/kg/24 hr of Intralipid 20%).

Urinary kallikrein: assay validation and physiological variability

Decreased urinary kallikrein (UK) output has been suggested as a preclinical indicator of essential hypertension. In preparation for UK studies in hypertension prone Utah kindreds, we assessed selected UK assay parameters and physiological variability. Precision for the colorimetric kallikrein assay was quite acceptable, coefficient of variation (CV) less than 5% within run and 14% day-to-day at a concentration of 9.5 TU/l. The mean recovery was 105% and assay results were correlated with results from the 3H-TAME esterase method, r = 0.990. Urine specimens were stable at room temperature for up to 4 days, frozen at -20 degrees C for 6 weeks, or frozen at -80 degrees C after Sephadex treatment for a year. UK output varied significantly throughout the day with excretion highest in the morning. Urine collections at 10.00, 12.00 and 14.00 had significantly (p less than 0.05) more UK than the overnight collection. Intra- and inter-individual variations were of the same magnitude, mean 20%. In children UK output increased with age until the adult levels were reached at age 15. Male and female values were similar. Smoking; consumption of alcohol, coffee, tea, cola of chocolate; and female hormone medications did not significantly influence the 12-hour UK output in the 1110 caucasian subjects.

Urinary excretion of renal prostaglandins, kallikrein, vasopressin and aldosterone in essential hypertension

To assess the relationship between pressor and depressor factors in essential hypertension, the urinary excretion rates of prostaglandins E2 and F2 alpha, kallikrein, vasopressin and aldosterone were compared between 53 untreated hypertensive patients and 53 age- and sex-matched normotensive controls. Mean basal levels of plasma renin activity and of urinary prostaglandins, vasopressin and aldosterone were similar in both groups, but urinary kallikrein was significantly lower in the hypertensive patients. A weak relationship was found in the hypertensives between diastolic blood pressure, and vasopressin or aldosterone, and between vasopressin and prostaglandin E2, and in the normotensives between vasopressin and prostaglandin F2 alpha. In conclusion, these results do not provide evidence for an important imbalance between pressor and depressor factors in essential hypertension, as reflected by the urinary excretion of the major humoral factors and hormones involved in the regulation of blood pressure.

Effects of maternal ritodrine administration on neonatal renal function

Because of its effects on the cardiovascular and renin-angiotensin systems and on fluid and electrolyte homeostasis, maternal administration of ritodrine to inhibit preterm labor may cause significant alterations in renal function in the newborn infant. We determined inulin clearance, plasma renin activity, urinary arginine vasopressin excretion, and serum and urine electrolyte concentrations and osmolalities at 12 to 36 hours of life and at 6 days of life in 15 infants whose mothers had received ritodrine and in 15 infants whose mothers did not (control infants). At the time of each study, plasma ritodrine concentrations were obtained in the infants whose mothers received ritodrine. The infants whose mothers had received ritodrine had significantly lower inulin clearances and higher plasma renin activity and urinary arginine vasopressin excretion on day 1 but not on day 6. Gestational age was inversely correlated with plasma ritodrine concentration, plasma renin activity, and urinary arginine vasopressin excretion. There were no overt clinical signs of renal failure in any of the infants, and no differences in serum and urine electrolyte values, osmolality, fractional sodium excretion, or urine flow rate were observed between the groups.