Meta-analysis of data from animal studies: a practical guide

Meta-analyses of data from human studies are invaluable resources in the life sciences and the methods to conduct these are well documented. Similarly there are a number of benefits in conducting meta-analyses on data from animal studies; they can be used to inform clinical trial design, or to try and explain discrepancies between preclinical and clinical trial results. However there are inherit differences between animal and human studies and so applying the same techniques for the meta-analysis of preclinical data is not straightforward. For example preclinical studies are frequently small and there is often substantial heterogeneity between studies. This may have an impact on both the method of calculating an effect size and the method of pooling data. Here we describe a practical guide for the meta-analysis of data from animal studies including methods used to explore sources of heterogeneity.

Inhibiting BDNF expression by antisense oligonucleotide infusion causes loss of nigral dopaminergic neurons

Brain derived neurotrophic factor (BDNF) expression is significantly reduced in the Parkinson's disease substantia nigra. This neurotrophin has potent affects on dopaminergic neuron survival protecting them from the neurotoxins MPTP and 6-hydroxydopamine (6-OHDA) commonly used to create animal models of Parkinson's disease and also promoting dopaminergic axonal sprouting. In this study, we demonstrate that an antisense oligonucleotide infusion (200 nM for 28 days) to prevent BDNF production in the substantia nigra of rats mimics many features of the classical animal models of Parkinson's disease. 62% of antisense treated rats rotate (P < or = 0.05) in response to dopaminergic receptor stimulation by apomorphine. 40% of substantia nigra pars compacta tyrosine hydroxylase immunoreactive neurons are lost (P < or = 0.00001) and dopamine uptake site density measured by (3)H-mazindol autoradiography is reduced by 34% (P < or = 0.005). Loss of haematoxylin and eosin stained nigral neurons is significant (P < or = 0.0001) but less extensive (34%). These observations indicate that loss of BDNF expression leads both to down regulation of the dopaminergic phenotype and to dopaminergic neuronal death. Therefore, reduced BDNF mRNA expression in Parkinson's disease substantia nigra may contribute directly to the death of nigral dopaminergic neurons and the development of Parkinson's disease.

Macrophages and Microglia Produce Local Trophic Gradients That Stimulate Axonal Sprouting Toward but Not beyond the Wound Edge

Following injury to the mammalian CNS, axons sprout in the vicinity of the wound margin. Growth then ceases and axons fail to cross the lesion site. In this study, using dopaminergic sprouting in the injured striatum as a model system, we have examined the relationship of periwound sprouting fibers to reactive glia and macrophages. In the first week after injury we find that sprouting fibers form intimate relationships with activated microglia as they traverse toward the wound edge. Once at the wound edge, complicated plexuses of fibers form around individual macrophages. Axons, however, fail to grow further into the interior of the wound despite the presence of many macrophages in this location. We find that the expression of BDNF by activated microglia progressively increases as the wound edge is approached, while GDNF expression by macrophages is highest at the immediate wound margin. In contrast, the expression of both factors is substantially reduced within the macrophage-filled interior of the wound. Our data suggest that periwound sprouting fibers grow toward the wound margin along an increasing trophic gradient generated by progressively microglial and macrophage activation. Once at the wound edge, sprouting ceases over macrophages at the point of maximal neurotrophic factor expression and further axonal growth into the relatively poor trophic environment of the wound core fails to occur.

Periwound dopaminergic sprouting is dependent on numbers of wound macrophages

Injury to many regions of the central nervous system, including the striatum, results in a periwound or 'abortive' sprouting response. In order to directly evaluate whether macrophages play an important role in stimulating periwound sprouting, osteopetrotic (op/op) mice, which when young are deficient in a variety of macrophage subtypes, were given striatal wounds and the degree of dopaminergic sprouting subsequently assessed. Two weeks postinjury, significantly fewer wound macrophages were present in the striata of op/op mice compared with controls (144 +/- 30.1 in op/op mice vs. 416.6 +/- 82.3 in controls, P < 0.005, analysis performed on a section transecting the middle of the wound). Dopamine transporter immunohistochemistry revealed a marked decrease in the intensity of periwound sprouting in the op/op group of animals. Quantification of this effect using [H3]-mazindol autoradiography confirmed that periwound sprouting was reduced significantly in the op/op mice compared with controls (71.4 +/- 21.7 fmol/mg protein in op/op mice vs. 210.7 +/- 27.1 fmol/mg protein in controls, P < 0.0005). In the two groups of animals the magnitude of the sprouting response in individuals was closely correlated with the number of wound macrophages (R = 0.83, R2 = 0.69). Our findings provide strong support for the crucial involvement of macrophages in inducing dopaminergic sprouting after striatal injury.

Reduced BDNF mRNA expression in the Parkinson's disease substantia nigra

Brain-derived neurotrophic factor (BDNF) has potent effects on survival and morphology of dopaminergic neurons and thus its loss could contribute to death of these cells in Parkinson's disease (PD). In situ hybridization revealed that BDNF mRNA is strongly expressed by dopaminergic neurons in control substantia nigra pars compacta (SNpc). In clinically and neuropathologically typical PD, SNpc BDNF mRNA expression is reduced by 70% (P = 0.001). This reduction is due, in part, to loss of dopaminergic neurons which express BDNF. However, surviving dopaminergic neurons in the PD SNpc also expressed less BDNF mRNA (20%, P = 0.02) than their normal counterparts. Moreover, while 15% of control neurons had BDNF mRNA expression >1 SD below the control mean, twice as many (28%) of the surviving PD SNpc dopaminergic neurons had BDNF mRNA expression below this value. This 13% difference in proportions (95% CI 8-17%, P < or = 0.000001) indicates the presence of a subset of neurons in PD with particularly low BDNF mRNA expression. Moreover, both control and PD neurons displayed a direct relationship between the density of BDNF mRNA expression per square micrometer of cell surface and neuronal size (r(2) = 0.93, P </= 0.00001) which was lost only in PD neurons expressing the lowest levels of BDNF mRNA. If BDNF is an autocrine/paracrine factor for SNpc dopaminergic neurons, loss of BDNF-expressing neurons may compromise the well-being of their surviving neighbors. Moreover, neurons expressing particularly low levels of BDNF mRNA may be those at greatest risk of injury in PD and possibly the trigger for the degeneration itself.

Inhibition of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor expression reduces dopaminergic sprouting in the injured striatum

After striatal injury, sprouting dopaminergic fibres grow towards and intimately surround wound macrophages which, together with microglia, express the dopaminergic neurotrophic factors glial cell line-derived neurotrophic factor (GDNF) and brain derived neurotrophic factor (BDNF). To evaluate the importance of these endogenously secreted neurotrophic factors in generating striatal peri-wound dopaminergic sprouting, the peri-wound expression of BDNF or GDNF was inhibited by intrastriatal infusion of antisense oligonucleotides for 2 weeks in mice. Knock-down of both BDNF and GDNF mRNA and protein levels in the wounded striatum were confirmed by in situ hybridization and enzyme-linked immunosorbent assay, respectively. Dopamine transporter immunohisto-chemistry revealed that inhibition of either BDNF or GDNF expression resulted in a marked decrease in the intensity of peri-wound sprouting. Quantification of this effect using [H3]-mazindol autoradiography confirmed that peri-wound sprouting was significantly reduced in mice receiving BDNF or GDNF antisense infusions whilst control infusions of buffered saline or sense oligonucleotides resulted in the pronounced peri-wound sprouting response normally associated with striatal injury. BDNF and GDNF thus appear to be important neurotrophic factors inducing dopaminergic sprouting after striatal injury.

New dopaminergic neurons in Parkinson's disease striatum

A new population of dopaminergic neurons has been identified in Parkinson's disease striatum. These neurons are sufficiently numerous to have an important effect on dopaminergic function in the striatum.

Sprouting of dopaminergic axons after striatal injury: confirmation by markers not dependent on dopamine metabolism

Striatal injury increases dopamine metabolism in the nigrostriatal system but it is unclear whether this response is due to increased synthesis and activation of tyrosine hydroxylase within existing dopamine terminals and/or branching and sprouting of new terminals. While monitoring the density of tyrosine hydroxylase immunoreactive fibers suggests that sprouting occurs, this technique alone cannot adequately answer this question since the intensity of staining and thus the visibility of individual fibers are intimately linked to dopaminergic activity. However, by examining axons and their branches using markers that are independent of dopamine metabolism it is possible to determine whether dopaminergic sprouting does in fact take place. One month after using a Scouten wire knife to create a small lesion in the left striatum of normal C57/bl-6 mice, silver staining revealed an increase in the total number of neuronal fibers throughout the injured striatum. This was accompanied by intense staining of tyrosine hydroxylase-positive fibers around the wound and an increased density of striatal fibers labeled with dextran-biotin after injection of this neuronal tracer into the substantia nigra 1 month after striatal surgery and 5 days prior to sacrifice. The increase in tyrosine hydroxylase immunoreactivity confirms previous observations of increased dopaminergic activity after striatal injury. The increases in silver staining and dextran-biotin transport provide independent evidence that this increase in dopaminergic activity occurs because of sprouting of new fibers originating in the substantia nigra.

Effect of chronic angiotensin-converting enzyme inhibition on striatal dopamine content in the MPTP-treated mouse

We have previously shown that chronic treatment with the angiotensin-converting enzyme inhibitor perindopril increased striatal dopamine levels by 2.5-fold in normal Sprague-Dawley rats, possibly via modulation of the striatal opioid or tachykinin levels. In the present study, we investigated if this effect of perindopril persists in an animal model of Parkinson's disease, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse. C57BL/6 mice were treated with the neurotoxin (30 mg/kg/day intraperitoneally) for 4 days and then left for 3 weeks to allow the degeneration of striatal dopaminergic terminals. At this time, the mice exhibited a 40% decrease in striatal dopamine content and an accompanying 46% increase in dopamine D2 receptor levels compared with control untreated mice. The dopamine content returned to control levels, and the increase in dopamine D2 receptor levels was attenuated in mice treated with perindopril (5 mg/kg/day orally for 7 days) 2 weeks after the last dose of MPTP. When the angiotensin-converting enzyme inhibitor was administered (5 mg/kg/day for 7 days) immediately after the cessation of the MPTP treatment, there was no reversal of the effect of the neurotoxin in decreasing striatal dopamine content. Our results demonstrate that perindopril is an effective agent in increasing striatal dopamine content in an animal model of Parkinson's disease.

Activated macrophages and microglia induce dopaminergic sprouting in the injured striatum and express brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor

Nigrostriatal dopaminergic neurons undergo sprouting around the margins of a striatal wound. The mechanism of this periwound sprouting has been unclear. In this study, we have examined the role played by the macrophage and microglial response that follows striatal injury. Macrophages and activated microglia quickly accumulate after injury and reach their greatest numbers in the first week. Subsequently, the number of both cell types declines rapidly in the first month and thereafter more slowly. Macrophage numbers eventually cease to decline, and a sizable group of these cells remains at the wound site and forms a long-term, highly activated resident population. This population of macrophages expresses increasing amounts of glial cell line-derived neurotrophic factor mRNA with time. Brain-derived neurotrophic factor mRNA is also expressed in and around the wound site. Production of this factor is by both activated microglia and, to a lesser extent, macrophages. The production of these potent dopaminergic neurotrophic factors occurs in a similar spatial distribution to sprouting dopaminergic fibers. Moreover, dopamine transporter-positive dopaminergic neurites can be seen growing toward and embracing hemosiderin-filled wound macrophages. The dopaminergic sprouting that accompanies striatal injury thus appears to result from neurotrophic factor secretion by activated macrophages and microglia at the wound site.

Expression of brain-derived neurotrophic factor and TrkB neurotrophin receptors after striatal injury in the mouse

Brain-derived neurotrophic factor (BDNF) promotes the survival and differentiation of nigral dopaminergic neurons and supports the activity of dopaminergic cells grafted into the striatum. However, little attention has been given to the physiological role of endogenous BDNF and its receptor TrkB within the nigrostriatal dopamine system. We know that striatal injury is followed by long-term stimulation of dopaminergic activity in the striatum, could BDNF play a role in this phenomenon? One week after physical injury to the striatum of C57/Black mice, just before dopaminergic activation becomes obvious, in situ hybridization on coronal sections through mouse striatum reveals that BDNF mRNA expression increases significantly before returning to basal levels within 1 month. Expression of mRNA for TrkB follows a very different pattern. No change of expression of the full-length and catalytically competent TrkBTK+ receptor is seen. However, expression of the truncated form of the receptor TrkTK-, which lacks the catalytic tyrosine kinase domain, does increase and stays elevated for at least 2 months after injury. When combined with observations of dopaminergic activation after striatal injury and the neuroprotective effects of BDNF introduced into the striatum, our findings suggest that BDNF and TrkBTK- do indeed play a role in dopaminergic regeneration and repair.

Expression of glial cell line-derived neurotrophic factor (GDNF) mRNA following mechanical injury to mouse striatum

Although glial cell line-derived neurotrophic factor (GDNF) expression is low in the adult brain, its administration protects dopaminergic neurons against a range of insults, leading to the suggestion of a role in dopaminergic regeneration. If locally produced GDNF is to fulfil a role in dopaminergic regeneration after injury, it seems reasonable to hypothesize that its expression will increase after mechanical trauma. We have demonstrated that GDNF mRNA expression increases within 6 h of using a wire knife to injure adult mouse striatum. Expression doubles after 1 week and remains elevated for at least 1 month. Most GDNF expression is associated with haemosiderin-containing cells, indicating production by brain macrophages. GDNF production by macrophages may be essential for neural regeneration following CNS trauma.

Dopaminergic responses to striatal damage

The improvements obtained by grafting dopamine-rich tissues into the striatum of patients with Parkinson's disease are generally attributed to production and release of dopamine by the graft. However, it is becoming increasingly clear that grafting also stimulates the host dopaminergic system. We provide evidence in a mouse model of striatal damage that surgical cavitation induces a concerted response from the dopaminergic system with proliferation of striatal presynaptic dopamine uptake sites, increased tyrosine hydroxylase activity, increased concentrations of dopamine, dihydroxyphenylacetic acid and homovanillic acid. The response increases with time and ultimately includes contralateral stimulation of striatal tyrosine hydroxylase activity and elevation of dihydroxyphenylacetic acid and homovanillic acid concentrations. The time course and extent of the host dopaminergic response suggests that it may make a significant contribution to observed clinical improvements after intrastriatal transplantation in human parkinsonism.

Leukaemia inhibitory factor prevents injury induced proliferation of striatal dopamine uptake sites

The injury associated with implantation of an inert gelatin matrix (gel foam) into normal mouse striatum induces a long-lived increase in binding of [3H]mazindol to presynaptic dopamine uptake sites, probably due to proliferation of striatal dopaminergic terminals. Because of the known effects of leukaemia inhibitory factor (LIF) on catecholaminergic cells, we tested the hypothesis that LIF may alter the striatal dopaminergic response to injury in vivo. Application of LIF to mouse striatum in a gel foam implant abolished the usual injury induced proliferation of dopamine uptake sites. The ability of LIF to prevent proliferation of dopamine terminals may have important implications for our understanding of neural regeneration, the aetiology of Parkinson's disease and its treatment by intrastriatal grafting.

Intrastriatal angiotensin II induces turning behaviour in 6-hydroxydopamine lesioned rats

In rats with unilateral 6-hydroxydopamine lesions in the nigrostriatal pathway, injection of angiotensin II (2 nmol) into the unlesioned striatum elicited dose-related tight rotations ipsilateral to the lesion. This rotation was suppressed by coadministration of the angiotensin AT1 receptor antagonist, losartan (2 nmol), which had no significant effect when injected alone. Preadministration of the dopamine antagonist, haloperidol (2 mg/kg i.p.) completely blocked angiotensin II-induced turning at doses of 0.3-3 nmol, and partially at 10 nmol. These results further confirm the hypothesis that Ang II is intrinsically involved in modulating dopamine release in the striatum, an effect which is mediated predominantly by AT1 receptors.

Analysis of sequence contexts flanking T.G mismatches leads to predictions about reactivity of the mismatched T to osmium tetroxide

Osmium tetroxide and hydroxylamine are used to detect mutations in DNA and RNA after hybridization of mutant and wild-type DNA. Mismatched T and C bases, respectively, are modified by these reagents and the DNA strand cleaved at the mismatched bases by subsequent treatment with piperidine. This allows detection and location of the mutation. Although most T.G mismatches have been reported to be reactive to osmium tetroxide, some have been reported to be unreactive. The aim of this study was to collect and analyze the reactive and unreactive T.G mismatches. We have collected sequence contexts of all reactive and unreactive T.G mismatches for analysis. This involves 10 unreactive T.G mismatches (plus one T.C) and 19 reactive T.G mismatches. Sequence effects of bases surrounding these mismatches must influence this reactivity. There must be many types of such sequence effects. We postulate that because of the dominance of 5' G bases near the T of unreactive T.G mismatches and the absence of 5' G bases in reactive T.G mismatches that the stacking of the 5' G on the mismatched T is the reason for this lack of reactivity in the majority of the cases studied here.

Malonyl coenzyme A decarboxylase deficiency

Two new cases of malonyl coenzyme A (CoA) decarboxylase deficiency are described. Hitherto, the worldwide experience of the disorder has been confined to reports on two affected Australian children. The new cases are Scots born and are the offspring of consanguinous parents of Scots/Irish origin. They were investigated during episodes of vomiting and febrile convulsions associated with concomitant developmental delay. Malonic aciduria and grossly reduced malonyl CoA decarboxylase activity were demonstrated and the total ion current chromatograms of urinary organic acid profiles obtained by gas chromatography-mass spectrometry are presented. The clinical and biochemical features of the Scots and Australian patients are compared.

Surgical damage stimulates proliferation of dopamine uptake sites in normal mouse brain

To test the hypothesis that proliferation of host dopaminergic tissue in response to injury plays an important role in the response to intrastriatal grafting, we transplanted autologous adrenal medullary to striatum in normal C57-black mice and compared this procedure with transplantation of non-dopaminergic tissue (frontal cortex) or a non-cellular matrix (Gelfoam). [3H]Mazindol autoradiography revealed that all three protocols resulted in a marked proliferation of dopamine uptake sites 10 months after transplantation.

Dopa resistance in multiple-system atrophy: loss of postsynaptic D2 receptors

Postmortem autoradiography was used to explore the mechanisms underlying L-dopa resistance in 2 patients with multiple-system atrophy. Indices of striatal presynaptic dopamine terminal loss and dopamine (D1 and D2) receptors were provided by 3H-mazindol, 3H-SCH 23390, and 125I-sulpiride binding. Neuronal loss, gliosis, and loss of postsynaptic D2 receptors preferentially involved the middle and posterior of the putamen, that region of the striatum most intimately involved in motor function. Loss of D1 receptors in the same area occurred in only 1 patient. These findings suggest that in multiple-system atrophy, resistance to L-dopa is due to a loss of putamental D2 receptors. The differential effects on D1 and D2 receptors in 1 patient implies that different subpopulations of striatal neurons were selectively involved.

Cerebrospinal fluid concentrations of pterins and metabolites of serotonin and dopamine in a pediatric reference population

Accurate diagnosis and management of inborn errors of monoamine neurotransmitter and tetrahydrobiopterin metabolism depend on reliable reference ranges of key metabolites. Cerebrospinal fluid (CSF) was collected in a standardized way from 73 children and young adults with neurologic disease, with strict exclusions. In each specimen, concentrations of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (HIAA), total neopterin, 7,8-dihydrobiopterin, and tetrahydrobiopterin (BH4) were measured using HPLC. There was a continuous decrement in CSF HVA, HIAA, and BH4 during the first few years of life; this was independent of height (or length). Age-related reference ranges for each metabolite are given. Extensive correlations between HVA, HIAA, 7,8-dihydrobiopterin, and BH4 were further analyzed by multiple regression. Age and CSF BH4 were significant explanatory variables for CSF HIAA, but CSF HVA had only HIAA as a significant explanatory variable.

Identification and in vitro expression of mutations causing dihydropteridine reductase deficiency

Six mutations resulting in the recessive inherited disorder dihydropteridine reductase deficiency are reported, five of which are previously unknown. Two are nonsense mutations, resulting in premature termination of the protein, with the remaining four being missense mutations. The mutations found lie in the middle to 3' end of the dihydropteridine reductase reading frame, with the exception of one mutation which lies at codon 23, which is the only mutation found in more than one patient. The mutation pattern can be described as heterogeneous. The wild type and several of the mutant DHPR cDNA's were expressed in E. coli and the proteins purified and examined by a variety of techniques, including calculation of kinetic constants. One mutation (Gly23-->Asp) results in completely inactive protein, while a second (Trp108-->Gly) has substantial activity but does not completely dimerize. Both this mutant and a third, His158-->Tyr, are extremely susceptible to in vitro protease digestion, indicating that their three-dimensional structure has been altered. The protein studies underline the heterogeneous nature of DHPR mutations, in that the effects of different amino acid substitutions on the DHPR enzyme are varied.

Two new mutations in the dihydropteridine reductase gene in patients with tetrahydrobiopterin deficiency

Two new mutations have been identified within the dihydropteridine reductase (DHPR) gene in two patients with DHPR deficiency. The total coding sequence of the cDNA has been screened by chemical cleavage of mismatch in both patients and selected portions of the cDNA have been sequenced. The first mutation identified causes a glycine to aspartic acid substitution at codon 23 and seems particularly frequent in Mediterranean patients. Its occurrence within a glycine string common to the amino-terminal region in NADH dependent enzymes suggests a possible causal mechanism for the defect. The second change involves a tryptophan to glycine substitution at codon 108 and is carried by both alleles in the second patient. It occurs in a motif which shows similarities with a region of dihydrofolate reductase (DHFR) and is highly conserved within different animal species.

A fluorimetric assay for succinic semialdehyde dehydrogenase activity suitable for prenatal diagnosis of the enzyme deficiency

Succinic semialdehyde dehydrogenase (SSAD) is an enzyme involved in the turnover of the neurotransmitter 4-aminobutyrate (GABA). Deficiency of SSAD results in developmental delay, ataxia, seizures and 4-hydroxybutyric aciduria. We have developed a simple fluorimetric assay for the enzyme and applied it to measurement of SSAD activity in a range of cell types often used for prenatal and postnatal diagnosis of enzyme defects. Lymphocytes from children with SSAD deficiency were found to have < 5% of the activity found in lymphocytes from normal children. Heterozygotes are asymptomatic and have intermediate enzyme activities. Although SSAD activity has been detected previously in uncultured chorionic villi, we found that SSAD was not expressed in cultured chorionic villus cells nor in some fibroblast-like amniocytes from control fetuses. Lymphocytes from fetal blood and non-fibroblastic amniocytes have high SSAD activities, and should be suitable for prenatal diagnosis of SSAD deficiency.

Tryptophan and serotonin metabolism in familial erythrophagocytic lymphohistiocytosis

Reduced concentrations of tryptophan and 5-hydroxyindoleacetic acid (the major CSF metabolite of serotonin) were found in the cerebrospinal fluid of two children with familial erythrophagocytic lymphohistiocytosis. This was associated with elevated cerebrospinal fluid neopterin concentrations indicating increased macrophage activity within the central nervous system. In one child, cytotoxic therapy induced a complete clinical remission and an increase of tryptophan and 5-hydroxyindoleacetic acid concentrations to normal; during a subsequent relapse, concentrations of these analytes again fell below normal. In the other child, in whom therapy produced only a transient improvement, tryptophan and 5-hydroxyindoleacetic acid concentrations remained low and the child died. It is likely that increased activity of indoleamine 2,3-dioxygenase induced by the activation of macrophages was responsible for the disturbance in serotonin and tryptophan homeostasis within the brain. Excessive tryptophan catabolism and the disturbance of serotonin turnover may play a role in the aetiology of the neurological symptoms seen in familial erythrophagocytic lymphohistiocytosis.

Mutation detection in phenylketonuria by using chemical cleavage of mismatch: importance of using probes from both normal and patient samples

mRNA from a postmortem liver sample of a patient with classical phenylketonuria was examined using the chemical cleavage of mismatch (CCM) method to search for mutations in phenylalanine hydroxylase. Initial screening identified a heterozygous alteration in exon 2 which changed the encoded amino acid from phenylalanine (TTC) to leucine (TTG) at codon 39 and a polymorphism at codon 430 where the change from CTG to CTC did not alter the encoded leucine. Use of the CCM technique also revealed that the control reference clone differed from the published sequence by having a substitution of isoleucine (ATT) for methionine (ATG) at codon 276 and CAA rather than CAG as the codon for glutamine 232. By using the mRNA from the patient instead of the control as the source for the radiolabeled probe for the CCM technique, a second previously undetected alteration was identified in exon 10 where the change from TCA to CCA at codon 349 altered the amino acid from serine to arginine. Judicious choice of probes gives the CCM method the potential to detect close to 100% of single base mutations.

Continuous venovenous hemofiltration in the management of acute decompensation in inborn errors of metabolism

Continuous venovenous hemofiltration was used to treat two neonates, one with maple syrup urine disease and the other with an inborn error of long-chain fatty acid oxidation. The latter infant had hypoglycemia, hyperammonemia and lactic acidosis. In both cases, acceptable biochemical control was achieved within 8 hours. This therapy offers the potential to overcome acute crises rapidly in a wide range of inborn errors of intermediary metabolism.

Insertion of an extra codon for threonine is a cause of dihydropteridine reductase deficiency

The mutation in a patient with dihydropteridine reductase deficiency has been located and characterized. Polymerase chain reaction (PCR) was used to amplify the coding sequence of human dihydropteridine reductase from the messenger RNA of skin fibroblasts. Chemical cleavage of mismatches indicated a mismatched thymine and cytosine at approximately 117 and 147 bases, respectively, from the end of the probe. Cloning and sequencing of the mutant PCR products revealed the insertion of the triplet ACT (threonine), after alanine 122 (base 390). Amplification of a small region around this mutation by using genomic DNA as the PCR target indicates that the mutation is completely within an exon. Unequal crossing-over at the second base in the preceding alanine codon and duplication of the bases CTA may be the mechanism of mutagenesis. The cleavage site 147 bases from the end of the probe corresponded to the conversion of guanine to adenine at base 420 (CTG to CTA) and does not alter the code for leucine. This change, which was also seen in another dihydropteridine reductase-deficient child and in a control subject probably represents a common neutral polymorphism.

Central nervous system involvement in the erythrophagocytic disorders of infancy: the role of cerebrospinal fluid neopterins in their differential diagnosis and clinical management

In two children with familial erythrophagocytic lymphohistiocytosis accompanied by neurologic symptoms, total neopterin concentrations in cerebrospinal fluid were 200 times higher than in controls and 10 to 20 times higher than in five children with presumed neurologic disease due to primary viral infections (human immunodeficiency virus, herpes simplex, measles) of the CNS. In one child with familial erythrophagocytic lymphohistiocytosis, clinical remission was accompanied by a fall in neopterin concentrations to normal; in a second child, who died, total neopterin concentrations remained high. In two other children with a diagnosis of infection-associated hemophagocytic syndrome without any neurologic disturbance, neopterin concentrations were also elevated but only to 10 times the concentrations in controls. Total neopterin concentrations in cerebrospinal fluid provide a measure of the severity of macrophage infiltration and activation within the CNS, and are useful in assessing the need for intensive chemotherapy and monitoring the response to treatment.

Neurodevelopmental delay and focal seizures as presenting symptoms of human immunodeficiency virus I infection

Three children presenting with neurological symptoms were subsequently diagnosed as being infected with the human immunodeficiency virus I (HIV). All children showed normal development for about 12-18 months of age but later developed psychomotor and developmental regression. One child presented with generalised hypotonia, another with focal seizures, and the third with spastic quadriplegia. Two of the children showed areas of abnormal brain density on computed tomography and in one case there was calcification of the basal ganglia. In two of the children cerebrospinal fluid contained reduced amounts of total folate and elevated concentrations of neopterin. The possibility of a link between the deranged folate metabolism and the neurological symptoms in HIV infection is discussed.

Analysis and clinical significance of pterins

This review briefly describes the biochemistry of pterins, their involvement in pathological processes and the use of pterin measurement in diagnosis and monitoring of disease. Chromatographic and other methods of pterin analysis are detailed with particular emphasis being placed on the need for correct sample collection and handling.

Direct analysis of tetrahydrobiopterin in cerebrospinal fluid by high-performance liquid chromatography with redox electrochemistry: prevention of autoxidation during storage and analysis

Measurement of tetrahydrobiopterin in cerebrospinal fluid requires careful handling of samples during storage and analysis. Addition of dithioerythritol and deoxygenation of the mobile phase with helium prevents breakdown of tetrahydrobiopterin during chromatography. Tetrahydrobiopterin in cerebrospinal fluid is unstable at room temperature, 100% being lost within 3.5 h, this breakdown does not generate equivalent quantities of dihydrobiopterin and biopterin. Addition of dithioerythritol and diethylenetriaminepenta-acetic acid to cerebrospinal fluid prevents breakdown of tetrahydrobiopterin for 6 mth at -70 degrees C and for up to 5 h at 4 degrees C. At room temperature less than 5% of tetrahydrobiopterin was lost after 2 h.

Estimation of tetrahydrobiopterin and other pterins in cerebrospinal fluid using reversed-phase high-performance liquid chromatography with electrochemical and fluorescence detection

We describe an isocratic, reversed-phase high-performance liquid chromatographic method for the simultaneous measurement of fully oxidised, dihydro- and tetrahydropterins in cerebrospinal fluid. Tetrahydrobiopterin is detected electrochemically using an ESA Coulochem detector in the redox mode. Dihydropterins are detected by fluorescence following post-column electrochemical oxidation, and fully oxidised pterins by their natural fluorescence. Apart from addition of antioxidants, no sample preparation is required. Comparison is made with methods requiring chemical oxidation for detection of tetrahydrobiopterin. Some results on children with neurological disease are presented.

Pteridines and mono-amines: relevance to neurological damage

Patients with phenylalanine hydroxylase deficiency show increased concentrations of biopterins and neopterins, and reduced concentrations of serotonin and catecholamines, when phenylalanine concentrations are raised. The pterin rise reflects increased synthesis of dihydroneopterin and tetrahydrobiopterin, and the amine fall a reduction in amine synthesis due to inhibition by phenylalanine of tyrosine and tryptophan transport into neurones. The pterin and amine changes appear to be independent of each other and are present in the central nervous system as well as the periphery; they disappear when phenylalanine concentrations are reduced to normal. Patients with arginase deficiency show a similar amine disturbance but have normal pterin levels. The amine changes probably contribute neurological symptoms but pterin disturbance is not known to affect brain function. Patients with defective biopterin metabolism exhibit severely impaired amine synthesis due to tetrahydrobiopterin deficiency. Pterin concentrations vary with the site of the defect. Symptoms include profound hypokinesis and other features of basal ganglia disease. Neither symptoms nor amine changes are relieved by controlling phenylalanine concentrations. Patients with dihydropteridine reductase (DHPR) deficiency accumulate dihydrobiopterins and develop secondary folate deficiency which resembles that occurring in patients with defective 5,10-methylene tetrahydrofolate reductase activity. The latter disorder is also associated with Parkinsonism and defective amine and pterin turnover in the central nervous system, and a demyelinating illness occurs in both disorders. In DHPR deficiency cerebral calcification may develop in a similar distribution to that seen in congenital folate malabsorption and methotrexate toxicity. Symptoms are ameliorated by therapy with 5-formyltetrahydrofolate but exacerbated by folic acid.

Investigation of vitamin A nutrition in pregnant British Asians and their infants

Plasma retinol and retinol-binding protein (RBP) concentrations were lower in 23 South London Asian women of Indo-Pakistani origin than in 21 non-Asian controls during pregnancy (P less than 0.01 and P less than 0.05 respectively). Cord blood concentrations of retinol and RBP were the same in Asians and non-Asians. Plasma retinol concentration decreased with increasing gestation (P less than 0.01), but RBP concentration did not alter. Retinyl palmitate, 8000 i.u. daily from 30 weeks gestation to term, was given to a group of 14 Asian mothers with low plasma retinol concentrations. This caused a significant increase in maternal plasma retinol concentration at delivery compared with 15 controls, indicating possible deficiency, but did not affect cord blood concentrations. There was no difference in anthropometric measurements of the infants of control or supplemented mothers, nor was there a correlation between the anthropometric measurements and the plasma retinol or RBP concentrations.

Plasma retinol and retinol-binding protein in pre-term infants born small for gestational age or of appropriate weight for age

Plasma retinol and retinol-binding protein (RBP) were measured in 39 pre-term infants, 15 of whom were small-for-gestational age (SGA), within 48 h of birth. Retinol concentrations were inversely correlated with gestational age and birth weight, but there was no significant difference between the well grown pre-term infants and the SGA infants. RBP concentrations were not correlated with gestation or birth weight, but the values in SGA infants were significantly lower than in well grown infants (P less than 0.01). Although RBP was highly correlated with retinol in well grown infants (P less than 0.001), no such correlation was observed in SGA infants. The significance of this is discussed.

Relationship between vitamin A and bone disease in chronic renal failure

A study has been made of possible interrelationships between circulating vitamin A concentration and indicators of altered calcium homeostasis in 31 patients with stable chronic renal failure. Plasma retinol concentrations were high, possibly as a result of increased retinol-binding-protein concentrations secondary to renal failure. There was no correlation between retinol concentration and any other measurement, including vitamin A intake. However, there were significant correlations between plasma parathyroid hormone and calcium, phosphate, alkaline phosphatase, urea, and creatinine concentrations; and those patients with radiological sub-periosteal erosions tended to have the highest concentrations of circulating parathyroid hormone. Our data give no support to the contention that vitamin A status has any bearing on the progression and severity of the hyperparathyroid bone disease of renal failure.

A simple automated injection technique for the high-pressure liquid chromatographic determination of plasma retinol

We describe a rapid automated method for determination of retinol in 100 microliters plasma. A lipid extract of plasma is analysed by reverse phase high pressure liquid chromatography using methanol-water as eluent. Automation of injection is achieved by adaptation of a Technicon AutoAnalyzer Sampler 2 coupled with a Micromedic dilution system and a pneumatically actuated loop injector. Twenty patients' specimens can be analysed in 4 hours, including extraction time, standards, and quality controls, with one extract injected every 4 minutes.