Taurine deficiency and neuronal migration

Amniotic fluid amino acid concentrations are modified by maternal dietary glucose, gestational age, and fetal growth in rats

Amniotic fluid (AF) contains free amino acids that enter via transplacental and transmembranous routes from maternal sources; subsequently, the developing fetus "ingests" these amino acids early in gestation through unkeratinized skin and later through continuous AF swallowing. Our objectives were as follows: 1) to determine whether a restriction of maternal dietary glucose modulates the free AF amino acid pool, and 2) to establish whether any diet-induced changes were predictive of fetal weight near term (d 21.5). To produce varying in utero growth rates, pregnant rat dams were fed varying levels of glucose (0, 12, 24, 60%) throughout pregnancy. AF samples, collected on gestational days 18-21, were precolumn derivatized by 9-fluorenylmethyloxychloroformate to produce stable primary and secondary amino acid derivatives required for HPLC detection at low amino acid concentrations. Eighteen amino acids were identified. A 2-way ANOVA with main effects of diet (< or =12% and > or =24% glucose) and gestational age (d 18/19 and 20/21) showed that 2 AF amino acids, methionine and phenylalanine, and 12 AF amino acids were independently modified by diet and gestational age, respectively. Of note were the 364% increase in AF methionine and the constant decline in AF taurine as both gestational age lengthened and fetal weight increased. Multiple regression demonstrated that in addition to methionine, 3 specific AF amino acids, cysteine, lysine, and tyrosine, predicted fetal weight. These results demonstrate that the AF amino acid pool can be modified by the glucose content of the maternal diet and that specific AF amino acids are associated with gestational age and fetal growth.

L-serine in disease and development

The amino acid L-serine, one of the so-called non-essential amino acids, plays a central role in cellular proliferation. L-Serine is the predominant source of one-carbon groups for the de novo synthesis of purine nucleotides and deoxythymidine monophosphate. It has long been recognized that, in cell cultures, L-serine is a conditional essential amino acid, because it cannot be synthesized in sufficient quantities to meet the cellular demands for its utilization. In recent years, L-serine and the products of its metabolism have been recognized not only to be essential for cell proliferation, but also to be necessary for specific functions in the central nervous system. The findings of altered levels of serine and glycine in patients with psychiatric disorders and the severe neurological abnormalities in patients with defects of L-serine synthesis underscore the importance of L-serine in brain development and function. This paper reviews these recent insights into the role of L-serine and the pathways of L-serine utilization in disease and during development, in particular of the central nervous system.

The effects of taurine on hNT neurons transplanted in adult rat striatum

Taurine acts as an antioxidant able to protect neurons from free radical-mediated cellular damage. Moreover, it modulates the immune response of astrocytes that participate in neurodegenerative processes. The objective of this study was to examine whether taurine can prevent or attenuate the host inflammatory response induced by the xenotransplantation of neurons derived from the human teratocarcinoma cell line (hNT neurons). Male Sprague-Dawley rats were treated IP with either saline or taurine. Animals from both groups were perfused on the 4th or 11th day and the saline or taurine was administered from the start of the study until the day prior to sacrifice. The brains were processed immunohistochemically using antibodies against glial fibrillary acidic protein (GFAP), microglia (OX42), and human nuclear matrix antigen (NuMA). In the saline group, NuMA labeling revealed small grafts on the 4th day and no surviving cells on the 11th day. However, in the group that received taurine there were surviving grafts at both time points. Strong immunoreactivity for GFAP and OX42 was detected in the saline group surrounding the transplant. These effects were reduced in animals receiving taurine. Taken together, these results demonstrated that taurine was able to facilitate graft survival and attenuate the immune response generated by the xenograft.

A spatiotemporal wave of turnover and functional maturation of olfactory receptor neurons in the spiny lobster Panulirus argus

Olfactory receptor neurons (ORNs) of crustaceans are housed in aesthetasc sensilla that are located on the lateral flagellum of the antennule. We used young adult spiny lobsters to examine turnover of aesthetascs and functional maturation of their ORNs after molting. The proliferation zone for new aesthetascs is located in the proximal part of the aesthetasc-bearing region and progressively moves along a distoproximal axis. Older aesthetascs are lost in the distal part of the aesthetasc-bearing region. As a result, an aesthetasc may be shed three to six molts after it differentiates. Taurine-like immunoreactivity is elevated in ORNs of aesthetascs that have yet to emerge on the cuticular surface and thereafter decreases gradually and asynchronously. ORNs from the distalmost-developing aesthetascs lose taurine-like immunoreactivity immediately before sensillar emergence, whereas ORNs from the most proximal and lateral new aesthetascs retain taurine-like immunoreactivity throughout the intermolt stage after sensillar emergence. Furthermore, taurine-like immunoreactivity is inversely correlated with odor responsiveness. These results suggest that taurine-like immunoreactivity reveals immature ORNs and that their functional maturation is not synchronized with molting and may not be completed until many weeks after sensillar emergence. Our data suggest successive spatiotemporal waves of birth, differentiation and functional maturation, and death of ORNs.

Effects of taurine depletion on cell migration and NCAM expression in cultures of dissociated mouse cerebellum and N2A cells

Cultures of dissociated cerebellum from 5- to 6-day-old mice as well as of the N2A neuronal cell line were exposed to guanidino ethane sulfonate (GES, 2-5 mM) to reduce the cellular taurine content. Control cultures were kept in culture medium or medium containing 2-5 mM GES plus 2-5 mM taurine to restore the intracellular taurine content. Taurine depletion led to changes in the expression of certain splice variants of NCAM mRNA such as the AAG and the VASE containing forms, while no differences were seen in the expression of the three forms of NCAM protein. In the N2A cells taurine depletion led to a decreased migration rate of the cells. The results suggest that the reduced migration rate of neurons caused by taurine depletion may be correlated to changes in expression of certain adhesion molecules such as NCAM. Moreover, taurine appears to be involved in regulation of transcription processes.

Plasma concentration of taurine is higher in malnourished than control children: differences between kwashiorkor and marasmus

Plasma free amino acids were determined in the plasma of severely malnourished children under two years of age. A total of thirty-one patients and eleven controls were evaluated: seventeen cases of kwashiorkor, eight cases of marasmus, and six cases of marasmic-kwashiorkor. Fasting plasma samples were taken in the morning on the day of admission. Fasting plasma samples were also taken from nine patients at discharge after two months in the hospital where they received a balanced diet as treatment. A partial reversal of the signs of malnutrition was observed at discharge. In the whole group of patients ad admission, lower concentrations of tyrosine, methionine, tryptophan, and leucine and higher concentrations of aspartate, glutamate, and taurine were observed compared to controls. Taurine continued to be elevated in the malnourished group at the time of discharge. Marasmic children, as compared to controls, had high aspartate and low tryptophan levels, but taurine levels were not significantly different from controls. Kwashiorkor patients had low tyrosine, methionine, tryptophan, and lysine, and significantly higher taurine plasma levels. The elevated concentration of taurine might be the result of a redistribution of this amino acid to provide specific tissues with the required amount for development.