Fetal urinary insulin-like growth factor I and binding protein 3 in bilateral obstructive uropathies

Congenital urinary tract obstruction

Congenital urinary tract obstruction is a heterogenous condition with a varying natural history. Accurate diagnosis within the late-first and second trimesters allows for counselling of the parents and planning of multi-disciplinary care for the pregnancy and newborn. Antenatal investigations to predict postnatal renal function are of varying accuracy. However, some factors have been shown to be predictive of poor outcome in terms of renal function at birth and infancy. There is the possibility of in-utero intervention in these fetuses.

Fetal lower urinary tract obstruction

Fetal lower urinary tract obstruction affects 2.2 per 10,000 births. It is a consequence of a range of pathological processes, most commonly posterior urethral valves (64%) or urethral atresia (39%). It is a condition of high mortality and morbidity associated with progressive renal dysfunction and oligohydramnios, and hence fetal pulmonary hypoplasia. Accurate detection is possible via ultrasound, but the underlying pathology is often unknown. In future, magnetic resonance imaging (MRI) may be increasingly used alongside ultrasound in the diagnosis and assessment of fetuses with lower urinary tract obstruction. Fetal urine analysis may provide improvements in prenatal determination of renal prognosis, but the optimum criteria to be used remain unclear. It is now possible to decompress the obstruction in utero via percutaneous vesico-amniotic shunting or cystoscopic techniques. In appropriately selected fetuses intervention may improve perinatal survival, but long-term renal morbidity amongst survivors remains problematic.

Systematic review of accuracy of fetal urine analysis to predict poor postnatal renal function in cases of congenital urinary tract obstruction

OBJECTIVE

To evaluate the clinical usefulness of analysis of fetal urine in the prediction of poor postnatal renal function in cases of congenital urinary tract obstruction.

METHODS

A systematic review was performed. We conducted extensive electronic searches (database inception-2006). The reference lists of articles obtained were searched for any further articles. Two reviewers independently selected the articles in which the accuracy of fetal urinalysis was evaluated to predict poor postnatal renal function. There were no language restrictions. Data were extracted on study characteristics, quality and results, to construct 2 x 2 tables. Likelihood ratios for positive (LR+) and negative (LR-) test results were generated for the different fetal urinary analytes at various thresholds.

RESULTS

There were 23 articles that met the selection criteria, including a total of 572 women and 63 2 x 2 tables. The two most accurate tests were calcium > 95th centile for gestation (LR + 6.65, 0.23-190.96; LR - 0.19, 0.05-0.74) and sodium > 95th centile for gestation (LR + 4.46, 1.71-11.6; LR - 0.39, 0.17-0.88). beta(2)-microglobulin was found to be less accurate (LR + 2.92, 1.28-6.69; LR - 0.53, 0.24-1.17).

CONCLUSION

The current evidence demonstrates that none of the analytes of fetal urine investigated so far can be shown to yield clinically significant accuracy to predict poor postnatal renal function.

Animal models of fetal renal disease

Fetal models of urinary tract disease have been used for many years and have provided unique and important insights into the pathophysiology of these conditions. This review will summarize the principal model systems used and the current directions of investigation. These models (including rabbit, opossum, sheep and recently swine) have demonstrated that in utero obstruction of the urinary tract alters renal growth, differentiation and produces stereotypical patterns of tissue response, particularly fibrosis. New molecular understanding of these processes has identified specific mechanisms that may be key elements in the development of renal dysfunction due to obstruction. These factors include the renin-angiotensin system (RAS) and its interaction with TGF-beta in altering growth regulation and tissue fibrosis. These factors offer the prospect of clinical utility as markers of disease progression as well as pharmacologic therapy. Gene knockout systems have opened a new horizon of molecular models of congenital obstructive uropathy with insights into the role of the RAS in particular. It remains to be defined how closely these knockouts represent the human conditions they resemble. Continued application of fetal models of urinary obstruction, integrating large animal and knockout systems offers promise for improved diagnosis and treatment in these challenging conditions.

Invasive assessment of fetal renal abnormalities: urinalysis, fetal blood sampling and biopsy

There are a number of potential biochemical markers that may have some role in predicting renal function postnatally. These include urinary sodium, calcium and beta2-microglobulin. The latter may also be measured in fetal serum. However, the accuracy of these parameters at a point in time is far from perfect as urinary tract obstruction is a progressive disease which may be best defined by repeated observations throughout pregnancy.

Congenital obstructive uropathy: its origin and contribution to end-stage renal disease in children

Most children with end-stage renal failure are born with abnormal kidneys, with fetal obstructive uropathy accounting for about half these cases. Posterior urethral valves (PUV) is overwhelmingly the most common, specific diagnosis, and is confined to boys. In general, the condition is sporadic, although familial cases have been reported, perhaps suggesting that genetic factors play a role in pathogenesis. PUV can present antenatally, detected on routine fetal ultrasonography, or postnatally, when it is associated with renal failure and bladder dysfunction. Advances in postnatal surgery and medical management have reduced the mortality in PUV, but it is uncertain whether antenatal diagnosis or treatment (eg, with vesicoamniotic shunts) improves long-term renal outcome. Other disorders associated with human fetal obstructive uropathy are urethral atresia, the prune belly syndrome, and multicystic dysplastic kidney. The nephropathy associated with fetal obstructive uropathy is renal dysplasia and comprises undifferentiated and metaplastic tissues. Several studies in animals and in humans suggest that fetal urine flow impairment causes deregulation of renal precursor cell turnover and expression of growth factor/survival and transcription factor genes. Furthermore, some of these morphologic and molecular changes can be ameliorated experimentally by fetal surgical decompression or administration of specific growth factors.

Free insulin-like growth factor-1 and unilateral complete ureteral obstruction in the rat

OBJECTIVES

To determine the effect of unilateral ureteral obstruction on renal free insulin-like growth factor-1 (IGF-1) content in the kidneys and the possible role of free IGF-1 in compensatory growth in the nonobstructed kidney in an experimental model.

METHODS

The content of free IGF-1 and total protein in the obstructed and nonobstructed kidneys were measured 7 days after unilateral ureteral obstruction. The weights of the kidneys were also determined. The results were compared with those of the sham-operated animals.

RESULTS

The mean renal free IGF-1 level of the obstructed kidneys was significantly lower than the mean renal free IGF-1 level of the sham-operated kidneys (P = 0.03), and the mean renal free IGF-1 level of the nonobstructed kidneys was significantly higher than the mean renal free IGF-1 level of the sham-operated kidneys (P <0.0001). The serum free IGF-1 levels in the two groups were not different. The mean weight of the obstructed and nonobstructed kidneys was significantly higher than those of the sham-operated kidneys (1.49 +/- 0.09 and 1.03 +/- 0.03 versus 0.88 +/- 0.02 g, P <0.0001 and P = 0.006, respectively). The obstructed kidneys had significantly lower mean protein content than the nonobstructed kidneys and had significantly higher mean protein content than the sham-operated kidneys (P <0.0001 and P = 0.0004, respectively).

CONCLUSIONS

Our results reveal that compensatory renal growth is driven by a rise in the free IGF-1 concentration after unilateral ureteral obstruction.

Fetal interventions for obstructive uropathy

Obstructive uropathy is a significant source of morbidity and mortality in the neonate and infant, despite advances in postnatal management. Diagnosis is typically made early in the second trimester on the basis of sonographic measurements. In utero therapy holds promise for improved outcomes by preventing progressive urinary tract damage and permitting drainage of urine into the amniotic space to minimize the pulmonary sequelae of oligohydramnios. Multiple studies with animal models have showed the benefits of midgestational intervention, but large prospective, randomized studies have not yet been performed to confirm these findings in humans. Standardization of the diagnostic evaluation allows for refined patient selection, resulting in improved postnatal outcomes after fetal vesicoamniotic shunting. Research into the role of specific growth factors and immunoproteins in renal development and function may further improve patient selection and outcome. This article reviews diagnosis, technique, and outcomes for fetal treatment of obstructive uropathy.

Fetal uropathy

Our understanding of the causes, mechanisms, and prenatal management of fetal obstructive uropathy has increased significantly. Improved methods of prenatal evaluation have allowed the better selection of fetuses for invasive therapy, and studies indicate better survival and renal outcomes in carefully selected cases. New biological markers in fetal urine may provide a better understanding of the pathological processes of renal damage, additional prognostic markers, and lead to non-surgical approaches to preventing renal damage.

Diagnosis of fetal renal anomalies

Urinary tract abnormalities are fairly common in the perinatal period. Ultrasonography is an effective diagnostic tool for identifying fetal urinary tract anomalies and can be helpful in establishing prognosis and guiding treatment decisions. The sonographer is encouraged to characterize and localize the fetal urinary tract abnormality when identified. In doing so, the correct diagnosis can be selected from the differential possibilities, providing vital clinical information needed to develop a care plan for both the pregnant woman and her fetus.