Glucosylsphingosine accumulation in mice and patients with type 2 Gaucher disease begins early in gestation.

Gaucher disease, the most common of the sphingolipidoses, results from the inherited deficiency of the enzyme glucocerebrosidase (EC 3.2.1.45). Although type 2 (acute neuronopathic) Gaucher disease is associated with rapidly progressive and fatal neurologic deterioration, the pathophysiologic mechanisms leading to the neurologic symptoms and early demise remain uncharacterized. While the pathology encountered in Gaucher disease has been attributed to glucocerebroside storage, glucosylsphingosine (Glc-sph), a cytotoxic compound, also accumulates in the tissues. Elevations of brain Glc-sph have been reported in patients with types 2 and 3 Gaucher disease. In this study, Glc-sph levels were measured using HPLC in tissues from mice with type 2 Gaucher disease created with a null glucocerebrosidase allele. Compared with unaffected littermates, homozygous mice with type 2 Gaucher disease had approximately a 100-fold elevation of Glc-sph in brain, as well as elevated levels in other tissues. This accumulation was detected in utero by E 13 and increased progressively throughout gestation. Similarly, elevated Glc-sph levels were seen in human fetuses with type 2 Gaucher disease, indicating that therapy initiated after birth may be too late to prevent the sequelae of progressive neurologic damage that begins early in gestation. These findings suggest that the accumulation of Glc-sph may be responsible for the rapid demise of mice with type 2 Gaucher disease and the devastating clinical course seen in patients with type 2 Gaucher disease.

Mice with an aspartylglucosaminuria mutation similar to humans replicate the pathophysiology in patients.

Aspartyglucosaminuria (AGU) is a lysosomal storage disease with autosomal recessive inheritance that is caused by deficient activity of aspartylglucosaminidase (AGA), a lysosomal enzyme belonging to the newly described enzyme family of N-terminal hydrolases. An AGU mouse model was generated by targeted disruption of the AGA gene designed to mimic closely one human disease mutation. These homozygous mutant mice have no detectable AGA activity and excrete aspartylglucosamine in their urine. Analogously to the human disease, the affected homozygous animals showed storage in lysosomes in all analyzed tissues, including the brain, liver, kidney and skin, and lysosomal storage was already detected in fetuses at 19 days gestation. Electron microscopic studies of brain tissue samples demonstrated lysosomal storage vacuoles in the neurons and glia of the neocortical and cortical regions. Magnetic resonance images (MRI) facilitating monitoring of the brains of living animals indicated cerebral atrophy and hypointensity of the deep gray matter structures of brain-findings similar to those observed in human patients. AGU mice are fertile, and up to 11 months of age their movement and behavior do not differ from their age-matched littermates. However, in the Morris water maze test, a slow worsening of performance could be seen with age. The phenotype mimics well AGU in humans, the patients characteristically showing only slowly progressive mental retardation and relatively mild skeletal abnormalities.

Mice that lack thrombospondin 2 display connective tissue abnormalities that are associated with disordered collagen fibrillogenesis, an increased vascular density, and a bleeding diathesis.

Thrombospondin (TSP) 2, and its close relative TSP1, are extracellular proteins whose functions are complex, poorly understood, and controversial. In an attempt to determine the function of TSP2, we disrupted the Thbs2 gene by homologous recombination in embryonic stem cells, and generated TSP2-null mice by blastocyst injection and appropriate breeding of mutant animals. Thbs2-/- mice were produced with the expected Mendelian frequency, appeared overtly normal, and were fertile. However, on closer examination, these mice displayed a wide variety of abnormalities. Collagen fiber patterns in skin were disordered, and abnormally large fibrils with irregular contours were observed by electron microscopy in both skin and tendon. As a functional correlate of these findings, the skin was fragile and had reduced tensile strength, and the tail was unusually flexible. Mutant skin fibroblasts were defective in attachment to a substratum. An increase in total density and in cortical thickness of long bones was documented by histology and quantitative computer tomography. Mutant mice also manifested an abnormal bleeding time, and histologic surveys of mouse tissues, stained with an antibody to von Willebrand factor, showed a significant increase in blood vessels. The basis for the unusual phenotype of the TSP2-null mouse could derive from the structural role that TSP2 might play in collagen fibrillogenesis in skin and tendon. However, it seems likely that some of the diverse manifestations of this genetic disorder result from the ability of TSP2 to modulate the cell surface properties of mesenchymal cells, and thus, to affect cell functions such as adhesion and migration.

Metaxin, a gene contiguous to both thrombospondin 3 and glucocerebrosidase, is required for embryonic development in the mouse: implications for Gaucher disease.

We have identified a murine gene, metaxin, that spans the 6-kb interval separating the glucocerebrosidase gene (GC) from the thrombospondin 3 gene on chromosome 3E3-F1. Metaxin and GC are transcribed convergently; their major polyadenylylation sites are only 431 bp apart. On the other hand, metaxin and the thrombospondin 3 gene are transcribed divergently and share a common promoter sequence. The cDNA for metaxin encodes a 317-aa protein, without either a signal sequence or consensus for N-linked glycosylation. Metaxin protein is expressed ubiquitously in tissues of the young adult mouse, but no close homologues have been found in the DNA or protein data bases. A targeted mutation (A-->G in exon 9) was introduced into GC by homologous recombination in embryonic stem cells to establish a mouse model for a mild form of Gaucher disease. A phosphoglycerate kinase-neomycin gene cassette was also inserted into the 3'-flanking region of GC as a selectable marker, at a site later identified as the terminal exon of metaxin. Mice homozygous for the combined mutations die early in gestation. Since the same amino acid mutation in humans is associated with mild type 1 Gaucher disease, we suggest that metaxin protein is likely to be essential for embryonic development in mice. Clearly, the contiguous gene organization at this locus limits targeting strategies for the production of murine models of Gaucher disease.

Consequences of beta-glucocerebrosidase deficiency in epidermis. Ultrastructure and permeability barrier alterations in Gaucher disease.

Hydrolysis of glucosylceramide by beta-glucocerebrosidase results in ceramide, a critical component of the intercellular lamellae that mediate the epidermal permeability barrier. A subset of type 2 Gaucher patients displays ichthyosiform skin abnormalities, as do transgenic Gaucher mice homozygous for a null allele. To investigate the relationship between glucocerebrosidase deficiency and epidermal permeability barrier function, we compared the stratum corneum (SC) ultrastructure, lipid content, and barrier function of Gaucher mice to carrier and normal mice, and to hairless mice treated topically with bromoconduritol B epoxide (BrCBE), an irreversible inhibitor of glucocerebrosidase. Both Gaucher mice and BrCBE-treated mice revealed abnormal, incompletely processed, lamellar body-derived sheets throughout the SC interstices, while transgenic carrier mice displayed normal bilayers. The SC of a severely affected type 2 Gaucher's disease infant revealed similarly abnormal ultrastructure. Furthermore, the Gaucher mice demonstrated markedly elevated transepidermal water loss (4.2 +/- 0.6 vs < 0.10 g/m2 per h). The electron-dense tracer, colloidal lanthanum, percolated between the incompletely processed lamellar body-derived sheets in the SC interstices of Gaucher mice only, demonstrating altered permeability barrier function. Gaucher and BrCBE-treated mice showed < 1% and < 5% of normal epidermal glucocerebrosidase activity, respectively, and the epidermis/SC of Gaucher mice demonstrated elevated glucosylceramide (5- to 10-fold), with diminished ceramide content. Thus, the skin changes observed in Gaucher mice and infants may result from the formation of incompetent intercellular lamellar bilayers due to a decreased hydrolysis of glucosylceramide to ceramide. Glucocerebrosidase therefore appears necessary for the generation of membranes of sufficient functional competence for epidermal barrier function.

Human CYP1A1 gene: cosegregation of the enzyme inducibility phenotype and an RFLP.

The human CYP1A1 (cytochrome P1450) gene encodes an enzyme involved in the activation of procarcinogens, such as benzo[a]pyrene, to the ultimate reactive intermediate. Approximately 10% of the human population exhibit high CYP1A1 inducibility, and Kouri et al. reported that the high-inducibility phenotype might be at greater risk than low-inducibility individuals for cigarette smoke-induced bronchogenic carcinoma. In one 3-generation family of 15 individuals, we show here that the high-CYP1A1-inducibility phenotype segregates concordantly with an infrequent polymorphic site located 450 bases downstream from the CYP1A1 gene. Our findings are consistent with the study of Kawajiri et al., who demonstrated an association between this polymorphism and an increased incidence of squamous-cell lung cancer. Our data suggest that the CYP1A1 structural gene, or a region near this gene, might be correlated with the inducibility phenotype.

Production of delta-aminolevulinic acid: characterization of murine liver 4,5-dioxovaleric acid: L-alanine aminotransferase.

1. We report on the kinetic properties of murine liver 4,5-dioxovaleric acid:L-alanine aminotransferase (DOVA transaminase). 2. The transamination of 4,5-dioxovaleric acid (DOVA) led to the production of delta-aminolevulinic acid. 3. L-Alanine was the preferred amino group donor among the common 20 amino acids. 4. The optimum pH of the reaction was 7-8. 5. A Km of 220 microM for DOVA and a Km of 970 microM for L-alanine were obtained. 6. The reaction was inhibited by each of the following: glyoxylate, beta-chloroalanine, methylglyoxal, delta-aminolevulinate, pyruvate, heme, and gabaculine. 7. None of several xenobiotic inducers of microsomal mixed function oxidases tested had a significant effect on DOVA transaminase activity in studies performed with murine primary hepatocyte cultures.

Production of delta-aminolevulinate: subcellular localization and purification of murine hepatic L-alanine: 4,5-dioxovaleric acid aminotransferase.

1. L-Alanine: 4,5-dioxovaleric acid aminotransferase (DOVA transaminase) activity was measured in murine liver, kidney and spleen homogenates. 2. Among the organs examined, the specific activity of the enzyme was highest in kidney, followed by liver then spleen. 3. No differences in DOVA transaminase activity in kidney, liver and spleen homogenates were detected between mouse strains C57BL/6J and DBA/2J. 4. Based on enzyme activity, the capacity of DOVA transaminase to catalyze the formation of delta-aminolevulinic acid (ALA) in liver appeared much greater than the capacity of ALA synthase. 5. In DBA/2J animals, DOVA transaminase activity in liver mitochondrial fractions prepared by differential centrifugation was 24 nmol ALA formed/hr/mg protein compared with 0.63 nmol ALA formed/hr/mg protein for ALA synthase. 6. Cell fractionation analyses indicated that liver DOVA transaminase is located in the mitochondrial matrix. 7. The liver enzyme was purified from mitoplasts by chromatography on DEAE-Sephacel followed by affinity chromatography on L-alanine-AH-Sepharose. 8. The specific activity of the purified DOVA transaminase was 1600 nmol ALA formed/hr/mg protein. 9. The yield of the purification was ca 90 micrograms of protein per gram liver wet weight. 10. The purified enzyme had a subunit mol. wt of 146,000 +/- 5000 as determined by electrophoresis under denaturing conditions.

Preferential activation of 6-aminochrysene and 2-aminoanthracene to mutagenic moieties by different forms of cytochrome P450 in hepatic 9000 X g supernatants from the rat.

6-Aminochrysene and 2-aminoanthracene were activated to metabolites which were mutagenic to Salmonella typhimurium TA98 by hepatocytes or hepatic 9000 X g supernatants (S9s) from control or xenobiotic-treated rats. Hepatocytes from Aroclor-1254-treated rats were more efficient than hepatocytes from untreated rats at activating these aromatic amines. When plate-incorporation and liquid-incubation bacterial mutagenesis assays were performed in the presence of limiting amounts of rat hepatic S9, 2-aminoanthracene was activated to a greater extent in both cases, as judged by his+ revertant formation, by 3-methylcholanthrene-induced hepatic S9 than by phenobarbital-induced or control S9s. In contrast, 6-aminochrysene was activated more efficiently by phenobarbital-induced S9 than by 3-methylcholanthrene-induced or control S9s. This unexpected finding was confirmed employing polyclonal antibodies directed against specific forms of rat cytochrome P450. Thus, when employing Aroclor-1254-induced S9 as a source of metabolic activation, antibody directed against cytochrome P450IA1 inhibited the activation of 2-aminoanthracene but not of 6-aminochrysene. In contrast, antibody directed against cytochrome P450IIB1 inhibited the activation of 6-aminochrysene but not of 2-aminoanthracene. These results suggest that under conditions in which the amounts of S9 added are rate-limiting, the two aromatic amines are preferentially activated by different induced forms of cytochrome P-450.

Variations in aryl hydrocarbon hydroxylase activities in mitogen-activated human and nonhuman primate lymphocytes.

A fluorometric assay for the cytochrome P-450-dependent enzyme system, aryl hydrocarbon hydroxylase (AHH), was performed in mitogen-activated human lymphocytes from over 300 different humans and from 64 baboons. Results reveal: a) an average interindividual variation in AHH activity of approximately 0.25 (coefficient of variation); range of activities among humans and baboon subjects of approximately 40-fold; c) both genetic and environmental determinants of interindividual variation, and d) high AHH activity in humans associated with primary lung cancer. Confirmation of these results awaits the development of improved methods for phenotyping humans and for prospective cancer patient studies. DNA probes might be employed in future studies to determine specific mRNA content, and to search for DNA polymorphisms in and near the human cytochrome P-450 gene.

Aryl hydrocarbon hydroxylase inducibility among primary relatives of children with leukemia or solid tumors.

In mice, there is a correlation between genetically regulated levels of inducible aryl hydrocarbon hydroxylase (AHH) activity and the risk of polycyclic hydrocarbon-induced leukemia or solid tumors. Recent clinical studies suggest a relationship between high AHH activity and lung cancer associated with cigarette smoking (Kouri, R.E., McKinney, C.E., Slomiany, D.J., Snodgrass, D.R., Wray, N.P., and McLemore, T.L. Cancer Res. 42: 5030-5037, 1982). To determine whether there is a similar genetic relationship in humans between inducible AHH and the occurrence of pediatric cancers, we examined AHH activity in mitogen-stimulated benzo(a)anthracene-treated lymphocyte cultures from primary relatives of children with leukemia or solid tumors. Control families (parents and siblings with no history of cancer) comprised friends or neighbors of the proband families. By comparing variance among family members with variance among nonrelated individuals, we conclude that a small, but real, genetic component is detectable. Adjusting for age, smoking history, and the length of time during which the lymphocytes had been cryopreserved, however, we find no difference among 77 leukemia, 71 solid tumor, and 100 control family members with regard to median units (+/- median S.E.) of maximally induced AHH activity per unit of reduced nicotinamide adenine dinucleotide-cytochrome c reductase activity: 0.31 +/- 0.03; 0.28 +/- 0.03; and 0.28 +/- 0.03, respectively. Thus, benzo(a)anthracene-induced AHH activity in cultured mitogen-activated lymphocytes in our study population does not appear to be associated with the risk of occurrence of childhood leukemia or solid tumors.

Positive correlation between high aryl hydrocarbon hydroxylase activity and primary lung cancer as analyzed in cryopreserved lymphocytes.

Blood samples from closely monitored patients at the Veterans Administration Hospital in Houston, Texas, were collected, coded, and sent to Microbiological Associates over an 8-month period. Lymphocytes were isolated and cryopreserved at -190 degrees. Lymphocyte samples were simultaneously thawed, phytohemagglutinin activated, and analyzed for benz(a)anthracene-induced aryl hydrocarbon hydroxylase (AHH) levels, [3H]thymidine incorporation, and reduced nicotinamide adenine dinucleotide-dependent cytochrome b5 (cytochrome c) reductase activity. Determinations were made at both 96 and 120 hr in culture, and peak activities were compared among a total of 51 individuals who expressed such lesions as squamous cell carcinomas (22%), adenocarcinomas (14%), oat cell carcinomas (6%), chronic obstructive pulmonary disease (22%), and other nonmalignant diseases. Of the 14 highest AHH/cytochrome c activities observed, all were found in patients with primary lung cancer. Mean AHH/cytochrome c activities were 0.89 for lung cancer patients (a total of 21) and 0.47 for noncancer patients (a total of 30) (p less than 0.001). No relationship was observed between AHH/cytochrome c activity and age of patient, numbers of cigarettes smoked, family history of cancer, location or histological type of tumor, or level of phytohemagglutinin blastogenesis ([3H]thymidine cpm/cytochrome c). Whether the higher AHH levels are the cause or the result of the primary lung cancer remains to be determined.

A method for detecting aryl hydrocarbon hydroxylase activities in cryopreserved human lymphocytes.

Aryl hydrocarbon hydroxylase (AHH) activity, NADH-dependent cytochrome c reductase (cyt c) activity, and [3H]thymidine (3H-TdR) incorporation were monitored in human lymphocytes cryopreserved for periods up to 1 year. A standard procedure for freezing, thawing and culturing of these lymphocytes was developed. Kinetics for expression of benz[a]anthracene-(BA)-induced AHH activity, cyt c activity, and 3H-TdR incorporation were similar in both freshly cultured and cryopreserved cells. Lymphocyte samples from 10 individuals were collected once per month over a 3-month period and cells were either cultured at the time of donation or cryopreserved for later assay. Results indicated that the cryopreserved lymphocytes efficiently responded to mitogen activation. The intra-individual variation in AHH activities was reduced in the cryopreserved lymphocytes compared to the freshly cultured cells, and the relative ranking of these individuals in terms of their AHH activities remained constant for both fresh and cryopreserved samples. Cryopreservation seems to offer significant advantages over the freshly cultured lymphocytes because it allows for lymphocyte samples to be collected in diverse geological locations and over extended periods of time and yet permits for the culture and assay of all the cell samples at exactly the same time.