High activities of erythrocyte glutathione peroxidase in patients with the Lesch-Nyhan syndrome

Oxygenation of the newborn. The impact of one molecule on newborn lives

Hypoxanthine is a purine metabolite which increases during hypoxia and therefore is an indicator of this condition. Further, when hypoxanthine is oxidized to uric acid in the presence of xanthine oxidase, oxygen radicals are generated. This was the theoretical basis for suggesting and studying, beginning in the 1990s, resuscitation of newborn infants with air instead of the traditional 100% O2. These studies demonstrated a 30% reduction in mortality when resuscitation of term and near term infants was carried out with air compared to pure oxygen. The mechanism for this is not fully understood, however the hypoxanthine -xanthine oxidase system increases oxidative stress and plays a role in regulation of the perinatal circulation. Further, hyperoxic resuscitation inhibits mitochondrial function, and one reason may be that genes involved in ATP production are down-regulated. Thus, the study of one single molecule, hypoxanthine, has contributed to the global prevention of an estimated 2-500,000 annual infant deaths.

Altered gastrointestinal motility in an animal model of Lesch-Nyhan disease

Mutations in the HGPRT1 gene, which encodes hypoxanthine-guanine phosphoribosyltransferase (HGprt), housekeeping enzyme responsible for recycling purines, lead to Lesch-Nyhan disease (LND). Clinical expression of LND indicates that HGprt deficiency has adverse effects on gastrointestinal motility. Therefore, we aimed to evaluate intestinal motility in HGprt knockout mice (HGprt¯). Spontaneous and neurally evoked mechanical activity was recorded in vitro as changes in isometric tension in circular muscle strips of distal colon. HGprt¯ tissues showed a lower in amplitude spontaneous activity and atropine-sensitivity neural contraction compared to control mice. The responses to carbachol and to high KCl were reduced, demonstrating a widespread impairment of contractility. L-NAME was not able in the HGprt¯ tissues to restore the large amplitude contractile activity typical of control. In HGprt¯ colon, a reduced expression of dopaminergic D1 receptor was observed together with the loss of its tonic inhibitory activity present in control-mice. The analysis of inflammatory and oxidative stress in colonic tissue of HGprt¯ mice revealed a significant increase of lipid peroxidation associated with over production of oxygen free radicals. In conclusion, HGprt deficiency in mice is associated with a decrease in colon contractility, not dependent upon reduction of acetylcholine release from the myenteric plexus or hyperactivity of inhibitory signalling. By contrast the increased levels of oxidative stress could partially explain the reduced colon motility in HGprt¯ mice. Colonic dysmotility observed in HGprt¯ mice may mimic the gastrointestinal dysfunctions symptoms of human syndrome, providing a useful animal model to elucidate the pathophysiology of this problem in the LND.

Multifocal atrophy of cerebellar internal granular neurons in lesch-nyhan disease: case reports and review

The neuropathologic findings in 31 cases (aged 6 months to 33 years) of Lesch-Nyhan disease (hypoxanthine-guanine phosphoribosyltransferase deficiency) have been previously reported. Herein 2 additional cases, a 10-year-old boy and a 21-year-old man, are described. Both cases had unusual cerebellar abnormalities comprising multifocal internal granular layer atrophy with sparing of the Purkinje layer, one had a slightly small brain, and neither had striatal abnormalities. Careful review of the literature indicates that the most prevalent neuropathologic abnormalities are small cerebrum (13 of 33 cases) and multifocal cerebellar lesions (9 of 33 cases), although these could be underreported. Other authors have disregarded these abnormalities, focusing on the apparently normal basal nuclei, and they have suggested that the clinical neurologic abnormalities are based solely on changes in neurotransmitters. We discuss potential mechanisms of cerebellar damage, suggest that the cerebellar abnormality could in part explain the clinical syndrome, and recommend that cerebellar structure and function should be more carefully studied in Lesch-Nyhan disease.

Oxidative stress and dopamine deficiency in a genetic mouse model of Lesch-Nyhan disease

Lesch-Nyhan disease, a neurogenetic disorder caused by congenital deficiency of the purine salvage enzyme hypoxanthine guanine phosphoribosyl transferase, is associated with a prominent loss of striatal dopamine. The current studies address the hypothesis that oxidant stress causes damage or dysfunction of nigrostriatal dopamine neurons in a knockout mouse model of the disease, by assessing several markers of oxidative damage and free radical scavenging systems. Some of these measures provided evidence for an increase in oxidative stress in the mutant mice (aconitase activity, oxidized glutathione, and lipid peroxides), but others did not (superoxide dismutase, protein thiol content, carbonyl protein content, total glutathione, glutathione peroxidase, catalase, and thiobarbituric reducing substances). Immunolocalization of heme-oxygenase 1 provided no evidence for oxidative stress restricted to specific elements of the striatum or midbrain in the mutants. Striatal dopamine systems of the mutant mice were more vulnerable to a challenge with the neurotoxin 6-hydroxydopamine, but they were not protected by cross-breeding the mutants with transgenic mice over-expressing superoxide dismutase. Overall, these data provide evidence for increased oxidative stress, but the failure to protect the knockout mice by over-expressing SOD1 argues that oxidative stress is not the sole process responsible for the loss of striatal dopamine.

Hypoxanthine impairs morphogenesis and enhances proliferation of a neuroblastoma model of Lesch Nyhan syndrome

Extracellular purines have essential roles in neuronal development; hence, disruptions in their metabolism as reported in Lesch Nyhan syndrome (LNS) could result in developmental abnormalities. The deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGPRT) in LNS leads to increased hypoxanthine and uric acid production. We have reported that HGPRT-deficient B103-4C neuroblastoma, a neuronal model of LNS, proliferated less and differentiated more than their HGPRT-positive B103 counterparts. Here, we sought to determine whether differences in proliferation and differentiation would occur when these cells were cultured in the presence of hypoxanthine or in a hypoxanthine-/serum-free chemically defined media (NBMN2). In media with 1% serum, hypoxanthine (50 microM) significantly increased the proliferation of both cell lines with a greater effect on B103-4C cells. In 1% serum media, hypoxanthine increased differentiation of B103 but decreased B103-4C differentiation. In NBMN2, B103 proliferated far more than B103-4C, but both cell types differentiated to the same extent. These results are interpreted to suggest that elevated levels of central nervous system (CNS) hypoxanthine as reported in LNS may affect neuronal development, and to implicate hypoxanthine and abnormal neuronal development as causative factors in the etiology of LNS.

Phenotype determination of a common Pro-Leu polymorphism in human glutathione peroxidase 1

Oxidative stress has been implicated in human illness such as cardiovascular and neurodegenerative disease. The genetic mechanisms involved are only poorly understood. Here we describe the determination of the allelic frequency and phenotype of a common polymorphism in Se-dependent glutathione peroxidase 1 (GPX1) in Finnish/Swedish populations. A proline/leucine variant occurs at position 197 close to the C-terminus of the protein. The more common allele encoding the Pro variant is present at 59% in a Finnish/Swedish population (n = 66) and at 73% in a Swedish population (n = 315). The genotypes encoding Pro/Pro, Pro/Leu, and Leu/Leu are distributed according to the Hardy-Weinberg relationship. The Swedish population consisted of 101 stroke cases and 214 controls. No significant association between allele frequency and risk to suffer from stroke was evident. Erythrocyte GPX activity was determined in the Finnish/Swedish population and no significant differences were obtained between the genotypes. It can be concluded that the Pro/Leu genetic variation does not appear to compromise the defense against oxidative stress in red blood cells nor to be associated with stroke.

Oxygen toxicity in the neonatal period

Oxygen is toxic because it produces oxygen radicals. One important oxygen radical generating system is hypoxanthine-xanthine oxidase. Hypoxic newborn babies who have elevated concentrations of hypoxanthine in tissues and body fluids and simultaneously are treated with supplementary oxygen, may therefore produce oxygen radicals in excess overwhelming the body's natural defence systems against free radicals. Further, the capacity of many of these defence systems are probably reduced in the preterm baby. A series of conditions in neonates may, at least partly, be caused by oxygen radicals, e.g. bronchopulmonary dysplasia, retinopathy of prematurity, necrotising enterocolitis and patent ductus arteriosus. These conditions may be different facets of one disease; the "Oxygen radical disease in neonatology". It is speculated that oxygen radicals play a role in regulating the perinatal circulation. This new insight concerning the role of oxygen radicals may have fundamental consequences for treatment and handling of sick newborn babies.