Regulation of Placental Amino Acid Transport and Fetal Growth.

The fetus requires amino acids for the processes of protein synthesis, carbon accretion, oxidative metabolism, and biosynthesis, which ultimately determine growth rate in utero. The fetal supply of amino acids is critically dependent on the transport capacity of the placenta. System A amino acid transporters in the syncytiotrophoblast microvillous plasma membrane, directed toward maternal blood, actively accumulate amino acids, while system L exchangers mediate uptake of essential amino acids from the maternal circulation. The functional capacity and protein abundance of these transporters in the placenta are related to fetal growth in both humans and experimental animals. Maternal nutritional and endocrine signals including insulin, insulin-like growth factors, adipokines, and steroid hormones regulate placental amino acid transport, against the background of growth signals originating from the fetus. Anabolic signals of abundant maternal resource availability stimulate placental amino acid transport to optimize offspring fitness, whereas catabolic signals reduce placental amino acid transport in an attempt to ensure survival and long-term reproductive capacity of the mother when resources are scarce. These signals regulate placental amino acid transport by controlling transcription, translation, plasma membrane trafficking, and degradation of transporters. Adaptations in placental amino acid transport capacity may underlie either under- or overgrowth of the fetus when maternal nutrient and hormone levels are altered as a result of altered maternal nutrition or metabolic disease. Strategies to modulate placental amino acid transport may prove effective to normalize fetal growth in intrauterine growth restriction and fetal overgrowth.

Gene targeting in primary human trophoblasts.

Studies in primary human trophoblasts provide critical insights into placental function in normal and complicated pregnancies. Mechanistic studies in these cells require experimental tools to modulate gene expression. Lipid-based methods to transfect primary trophoblasts are fairly simple to use and allow for the efficient delivery of nucleic acids, but potential toxic effects limit these methods. Viral vectors are versatile transfection tools of native trophoblastic or foreign cDNAs, providing high transfection efficiency, low toxicity and stable DNA integration into the trophoblast genome. RNA interference (RNAi), using small interfering RNA (siRNA) or microRNA, constitutes a powerful approach to silence trophoblast genes. However, off-target effects, such as regulation of unintended complementary transcripts, inflammatory responses and saturation of the endogenous RNAi machinery, are significant concerns. Strategies to minimize off-target effects include using multiple individual siRNAs, elimination of pro-inflammatory sequences in the siRNA construct and chemical modification of a nucleotide in the guide strand or of the ribose moiety. Tools for efficient gene targeting in primary human trophoblasts are currently available, albeit not yet extensively validated. These methods are critical for exploring the function of human trophoblast genes and may provide a foundation for the future application of gene therapy that targets placental trophoblasts.

Pediatric inflammatory bowel disease: assessment with scintigraphy with 99mTc white blood cells.

PURPOSE: To evaluate the sensitivity and specificity of scintigraphy with technetium 99m white blood cells (WBC) for detection of colonic inflammation in children with and children without inflammatory bowel disease (IBD). MATERIALS AND METHODS: In 215 patients, uptake of 99mTc WBC in 3,440 bowel segments was graded. In 137 of the 215 patients, the 99mTc WBC scans were interpreted blindly and findings compared with results at colonoscopy and endoscopic biopsy. Planar, single photon emission computed tomographic, and maximum-activity-projection images were reviewed together. In 78 children without recent endoscopic biopsy results, 99mTc WBC scan findings were compared with laboratory values, the gastroenterologist's initial clinical assessment, and findings at long-term clinical follow-up. RESULTS: In 128 of 137 children with recent biopsies, findings at histologic examination and on 99mTc WBC scans were correlated. There were seven false-negative and two false-positive studies. Sensitivity was 90%, specificity 97%, positive predictive value 97%, negative predictive value 93%, prevalence of disease 53%, and overall accuracy 93%. In 75 of 78 (96%) children without recent biopsies, 99mTc WBC scan findings were consistent with the laboratory values, gastroenterologist's clinical assessment, and long-term clinical follow-up findings. CONCLUSION: Scintigraphy with 99mTc WBC is a useful noninvasive diagnostic test to determine the extent and distribution of inflammation in children with IBD.