Amniotic fluid levels of phospholipase A2 in fetal rats with retinoic acid induced myelomeningocele: the potential "second hit" in neurologic damage

State of the art in translating experimental myelomeningocele research to the bedside

Myelomeningocele (MMC), the commonest type of spina bifida (SB), occurs due to abnormal development of the neural tube and manifest as failure of the complete fusion of posterior arches of the spinal column, leading to dysplastic growth of the spinal cord and meninges. It is associated with several degrees of motor and sensory deficits below the level of the lesion, as well as skeletal deformities, bladder and bowel incontinence, and sexual dysfunction. These children might develop varying degrees of neuropsychomotor delay, partly due to the severity of the injuries that affect the nervous system before birth, partly due to the related cerebral malformations (notably hydrocephalus-which may also lead to an increase in intracranial pressure-and Chiari II deformity). Traditionally, MMC was repaired surgically just after birth; however, intrauterine correction of MMC has been shown to have several potential benefits, including better sensorimotor outcomes (since exposure to amniotic fluid and its consequent deleterious effects is shortened) and reduced rates of hydrocephalus, among others. Fetal surgery for myelomeningocele, nevertheless, would not have been made possible without the development of experimental models of this pathological condition. Hence, the aim of the current article is to provide an overview of the animal models of MMC that were used over the years and describe how this knowledge has been translated into the fetal treatment of MMC in humans.

Diffusion weighted imaging as a biomarker of retinoic acid induced myelomeningocele

Neural tube defects are a common congenital anomaly involving incomplete closure of the spinal cord. Myelomeningocele (MMC) is a severe form in which there is complete exposure of neural tissue with a lack of skin, soft tissue, or bony covering to protect the spinal cord. The all-trans retinoic acid (ATRA) induced rat model of (MMC) is a reproducible, cost-effective means of studying this disease; however, there are limited modalities to objectively quantify disease severity, or potential benefits from experimental therapies. We sought to determine the feasibility of detecting differences between MMC and wild type (WT) rat fetuses using diffusion magnetic resonance imaging techniques (MRI). Rat dams were gavage-fed ATRA to produce MMC defects in fetuses, which were surgically delivered prior to term. Average diffusion coefficient (ADC) and fractional anisotropy (FA) maps were obtained for each fetus. Brain volumes and two anatomically defined brain length measurements (D1 and D2) were significantly decreased in MMC compared to WT. Mean ADC signal was significantly increased in MMC compared to WT, but no difference was found for FA signal. In summary, ADC and brain measurements were significantly different between WT and MMC rat fetuses. ADC could be a useful complementary imaging biomarker to current histopathologic analysis of MMC models, and potentially expedite therapeutic research for this disease.

Amylase concentration and activity in the amniotic fluid of fetal rats with retinoic acid induced myelomeningocele. J Matern Fetal Neonatal Med 2020;35:147-154. [PMID: 31910702 DOI: 10.1080/14767058.2020.1713082]

Background: In utero neurologic injury in myelomeningocele (MMC) occurs via a two-hit process: failed neural tube closure followed by neurodegeneration in utero. Meconium in the amniotic fluid contains pancreatic digestive enzymes and is neurotoxic in rat models of MMC.Objectives: The objectives of this study were to demonstrate the neurotoxicity of α-amylase and to compare the enzyme concentration and activity in the amniotic fluid of rats with retinoic acid induced MMC to a healthy control population.Study design: Timed pregnant Sprague Dawley rats were gavage fed all-trans retinoic acid (60 mg/kg) in olive oil on gestational day E10 to induce a MMC defect. Control rats received olive oil. Amniotic fluid was collected on embryonic days E15, E17, E19, and E21. The amniotic fluid amylase concentration and relative activity were measured at each gestational age, and levels were compared between the MMC and control groups using Wilcoxon Rank Sum and Kruskal-Wallis tests. In a subset of dams sacrificed on E10.5, neuroepithelial cells were isolated from control embryos and exposed to α-amylase in increasing concentrations. Percentage of cell survival was assessed with CellProfiler software.Results: Amniotic fluid amylase activity for embryonic days E15, E17, E19, and E21 was determined for MMC and control pups. Amylase activity increased significantly from E15 to E21 in both control (p = 3.0 × 10^-5) and MMC (p = 1.5 × 10^-5) groups. Relative amylase activity was significantly increased in MMC pups compared to controls on E19 (247,792.8 versus 106,263.6; p = .0019) and E21 (772,645.8 versus 481,975.3; p = .021); no difference was detected on E15 (36,646.8 versus 40,179.3; p = .645) or E17 (121,617.5 versus 71,750; p = 1.000). In vitro, amylase demonstrated dose-dependent toxicity to fetal rat neuroepithelial cells.Conclusion: Amylase concentration and activity level were higher in the amniotic fluid of rats with retinoic acid induced MMC compared to controls with advancing gestational age. As amylase is toxic to neural epithelial cells, the higher activity of this digestive enzyme in fetuses with MMC may be a contributor to neural tube damage in utero. Future research should focus on amylase and other digestive enzymes in human MMC, as they may serve as potential targets of in utero therapy.

In utero repair of fetal rat myelomeningocele affects neuromuscular development in the bladder

Fetal repair of myelomeningocele (MMC) has been proven to be beneficial for the central nervous system development; however, the effect of fetal MMC repair on bladder function remains controversial. The objective of the present study was to establish an early timepoint for in utero MMC repair using a rat model, and to investigate the changes in bladder development subsequent to that intervention. Sprague Dawley rats were divided into the MMC, MMC repair and control groups. MMC rat fetus models were created by treating pregnant rats with all-trans retinoic acid. The MMC defect was then repaired in utero at embryonic day 17 (E17) using a chitosan-gelatin membrane patch. Fetal rat bladders were removed at E19 and E21 in each group, as well as at stage E17 in the MMC and control groups. Differential expression of β-III-tubulin, α-smooth muscle actin (α-SMA), nerve growth factor (NGF) and acetylcholinesterase (AChE) mRNA, and β-III-tubulin and α-SMA protein in the bladder following fetal repair was measured and compared among the three groups. In addition, the expression of NGF mRNA was significantly elevated at E21 in the MMC group compared with that of the control group, however, the level decreased in the repair group at stage E21. The expression of α-SMA mRNA significantly increased at E19 and then decreased at E21 in the repair group compared with that of the MMC group; however, there were no significant changes in α-SMA protein following the repair. Furthermore, the repair enhanced β-III-tubulin mRNA expression at E19, but ameliorated the decrease of β-III-tubulin protein at E21. The expression of AChE mRNA increased in the MMC group at E19 and E21 compared with that of the control group, although it was not significantly altered following repair as compared with that of the MMC group. In conclusion, in the current study, abnormal neuromuscular development was observed in the MMC bladder, which enabled a certain degree of improvement in the in utero MMC repair.