Branched Chain Amino Acids Improve Complex Maze Learning in Rat Offspring Prenatally Exposed to Hyperphenylalaninemia: Implications for Maternal Phenylketonuria

Abstract

ABSTRACT. Maternal phenylketonuria results in a high incidence of children born who are mentally retarded. It has been suggested that blood-brain-barrier transport of phenylalanine may be reduced by competitive inhibition of transporter uptake by supplemental administration of other large neutral amino acids. We hypothesized that large neutral amino acids might also be effective at improving the outcome of fetuses exposed to hyperphenylalaninemia in utero. If correct, sparing of embryonic CNS development might be possible. Pregnant rats were given a hyperphenylalaninemic diet alone or the same diet supplemented with a combination of valine, isoleucine, and leucine. As adults, the progeny exposed in utero to hyperphenylalaninemia showed characteristic learning deficits in a complex maze, while those exposed in utero to hyperphenylalaninemia combined with valine, isoleucine, and leucine showed no deficits in maze acquisition. The valine, isoleucine, and leucine supplement may show promise as a treatment for intrauterinely acquired mental deficiency associated with maternal phenylketonuria. (2) found that 95% of pregnant PKU women with serum phenylalanine levels 220 mg/dL delivered at least one child who was mentally deficient. Other findings were microcephaly (90%), growth retardation (56%), and congenital heart defects (40%). Reinstatement of a phenylalaninerestricted diet before or after recognition of pregnancy has produced mixed, but generally unsatisfactory, results (2-7).This has led to the search for new approaches. Phenylalanine and other LNAA share a common transport carrier for selective CNS uptake (8-12). It has been established that increasing the concentration of one or more LNAA competitively inhibits the transport into brain of other amino acids in this group. This approach has been suggested as a means of reducing the influx of phenylalanine in PKU (13)(14)(15)(16)(17)(18). Early experiments to assess this have shown promise (13-1 5, 17-22), but in no case was evidence provided that such approaches could produce lasting cognitive improvement. Given that mental retardation is the most prevalent untoward effect of maternal PKU, we sought to test the efficacy of the branched-chain LNAA to improve embryo-fetal development in pregnant hyperphenylalaninemic rats to determine if sparing of CNS development in the progeny was possible. MATERIALS AND METHODS PCPA, ~,~~~-c h l o r o~h e n~l a l a n i n eNulliparous female Sprague-Dawley CD (VAF/Plus) rats PFC, pair-fed control (Charles River Breeding Laboratories, Portage, MI) were bred VIL, valine, isoleucine, and leucine and on d 4 (sperm plug = d 0) were randomly assigned to one of three treatment groups on a wt matched basis. Experimental diets were provided on gestation d 5-15. The PKU group received diet containing 2.5% added L-phenylalanine (phe) and PKU, an inherited disorder of phenylalanine metabolism, has 0.12% PCPA by wt (23-25) ad libitum. PCPA is a ~h e n~l a l a n i n e been treated during the last 30 through a of hydroxylase inhibitor (26-27)...

Cincinnati water maze: A review of the development, methods, and evidence as a test of egocentric learning and memory

“…The only variation was that most experiments gave 2 trials/day, in two experiments only, though, 1 trial/day was given, but the same total number of trials was used, i.e., 12. For the 2 trial/day experiments, significant CWM effects were found in hyperphenylalaninemic rats, and these deficits were mitigated by treatment with branched chain amino acids as an hypothesized therapeutic treatment (Vorhees and Berry, 1989). Other experiments showed large effects of prenatal sodium phenytoin on path-A and path-B errors (Weisenburger et al, 1990) and significant but not as large increases in errors after prenatal ethanol (Vorhees, 1988).…”

Large neutral amino acids block phenylalanine transport into brain tissue in patients with phenylketonuria

“…In addition, improvements on a neuropsychologic task were shown for VIL treatment (5,39). The VIL approach was also used in an animal model of maternal PKU (40). Rats exposed to high phenylalanine levels in utero showed characteristic learning deficits, which could be prevented by VIL treatment.…”

Phenylketonuria (PKU) – A Success Story

“…Pratt (Pratt, 1982) reviewed the evidence to date and predicted that adding tyrosine or leucine, valine and isoleucine only, would be ineffective. Despite this, several studies in rats and humans claimed neurological/psychometric improvement with the administration of the branch chain amino acids -valine, leucine and isoleucine (Jordan, 1985;Vorhees, 1989). Experiments with 4 adult volunteers with PKU and 4 normal controls (Knudsen et al, 1995) revealed, in PKU, brain permeability to large neutral amino acids is reduced by about 50%.…”

“…Both groups had similar serum levels of phenylalanine but the experimental group had lower brain levels. Further rat experiments were carried out (Vorhees & Berry, 1989), where pregnant hyperphenylalaninemic rats were given supplements valine, isoleucine and leucine. This improved performance of their offspring in a complex maze test.…”