Automated assessment of functional lung imaging with 68Ga-ventilation/perfusion PET/CT using iterative histogram analysis

PURPOSE

Functional lung mapping from Ga⁶⁸-ventilation/perfusion (V/Q) PET/CT, which has been shown to correlate with pulmonary function tests (PFTs), may be beneficial in a number of clinical applications where sparing regions of high lung function is of interest. Regions of clumping in the proximal airways in patients with airways disease can result in areas of focal intense activity and artefact in ventilation imaging. These artefacts may even shine through to subsequent perfusion images and create a challenge for quantitative analysis of PET imaging. We aimed to develop an automated algorithm that interprets the uptake histogram of PET images to calculate a peak uptake value more representative of the global lung volume.

METHODS

Sixty-six patients recruited from a prospective clinical trial underwent both V/Q PET/CT imaging and PFT analysis before treatment. PET images were normalised using an iterative histogram analysis technique to account for tracer hotspots prior to the threshold-based delineation of varying values. Pearson's correlation between fractional lung function and PFT score was calculated for ventilation, perfusion, and matched imaging volumes at varying threshold values.

RESULTS

For all functional imaging thresholds, only FEV1/FVC PFT yielded reasonable correlations to image-based functional volume. For ventilation, a range of 10-30% of adapted peak uptake value provided a reasonable threshold to define a volume that correlated with FEV1/FVC (r = 0.54-0.61). For perfusion imaging, a similar correlation was observed (r = 0.51-0.56) in the range of 20-60% adapted peak threshold. Matched volumes were closely linked to ventilation with a threshold range of 15-35% yielding a similar correlation (r = 0.55-0.58).

CONCLUSIONS

Histogram normalisation may be implemented to determine the presence of tracer clumping hotspots in Ga-68 V/Q PET imaging allowing for automated delineation of functional lung and standardisation of functional volume reporting.

PET-detected pneumonitis following curative-intent chemoradiation in non-small cell lung cancer (NSCLC): recognizing patterns and assessing the impact on the predictive ability of FDG-PET/CT response assessment

PURPOSE

Inflammatory FDG uptake in the lung (PET-pneumonitis) following curative-intent radiotherapy (RT)/chemo-RT (CRT) in non-small cell lung cancer (NSCLC) can pose a challenge in FDG-PET/CT response assessment. The aim of this study is to describe different patterns of PET-pneumonitis to guide the interpretation of FDG-PET/CT and investigate its association with tumor response and overall survival (OS).

METHODS

Retrospective analysis was performed on 87 NSCLC patients in three prospective trials who were treated with radical RT (n = 7) or CRT (n = 80), with baseline and post-treatment FDG-PET/CT. Visual criteria were performed for post-treatment FDG-PET/CT response assessment. The grading of PET-pneumonitis was based on relative lung uptake intensity compared to organs of reference and classified as per Deauville score from grade 1-5. Distribution patterns of PET-pneumonitis were defined as follows: A) patchy/sub-pleural; B) diffuse (involving more than a segment); and C) peripheral (diffusely surrounding a photopenic region).

RESULTS

Follow-up FDG-PET/CT scans were performed approximately 3 months (median, 89 days; interquartile range, 79-93) after RT. Overall, PET-pneumonitis was present in 62/87 (71%) of patients, with Deauville 2 or 3 in 12/62 (19%) and 4 or 5 in 50/62 (81%) of patients. The frequency of patterns A, B and C of PET-pneumonitis was 19/62 (31%), 20/62 (32%) and 23/62 (37%), respectively. No association was found between grade or pattern of PET-pneumonitis and overall response at follow-up PET/CT (p = 0.27 and p = 0.56, respectively). There was also no significant association between PET-pneumonitis and OS (hazard ratio [HR], 1.3; 95% confidence interval [CI], 0.6-2.5; p = 0.45). Early FDG-PET/CT response assessment, however, was prognostic for OS (HR, 1.7; 95% CI, 1.2-2.2; p < 0.001).

CONCLUSION

PET-pneumonitis is common in early post-CRT/RT, but pattern recognition may assist in response assessment by FDG-PET/CT. While FDG-PET/CT is a powerful tool for response assessment and prognostication, PET-pneumonitis does not appear to confound early response assessment or to independently predict OS.

What 18F-FDG PET Response-Assessment Method Best Predicts Survival After Curative-Intent Chemoradiation in Non-Small Cell Lung Cancer: EORTC, PERCIST, Peter Mac Criteria, or Deauville Criteria?

The optimal methodology for defining response with ¹⁸F-FDG PET after curative-intent chemoradiation for non-small cell lung cancer (NSCLC) is unknown. We compared survival outcomes according to the criteria of the European Organization for Research and Treatment of Cancer (EORTC), PERCIST 1.0, the Peter Mac metabolic visual criteria, and the Deauville criteria, respectively. Methods: Three prospective trials of chemoradiation for NSCLC, involving baseline and posttreatment ¹⁸F-FDG PET/CT imaging, were conducted between 2004 and 2016. Responses were categorized as complete metabolic response (CMR), partial metabolic response, stable metabolic disease, or progressive metabolic disease. Cox proportional-hazards models and log-rank tests assessed the impact of each response on overall survival (OS). Results: Eighty-seven patients underwent ¹⁸F-FDG PET/CT before and after radical chemoradiation for NSCLC. Follow-up ¹⁸F-FDG PET/CT scans were performed at a median of 89 d (interquartile range, 79-93 d) after radiotherapy. Median follow-up and OS after PET response imaging were 49 and 28 mo, respectively. Interobserver agreements for EORTC, PERCIST, Peter Mac, and Deauville had κ values of 0.76, 0.76, 0.87, and 0.84, respectively. All 4 response criteria were significantly associated with OS. Peter Mac and Deauville showed better fit than EORTC and PERCIST and distinguished better between CMR and non-CMR. Conclusion: All 4 response criteria were highly predictive of OS, but visual criteria showed greater interobserver agreement and stronger discrimination between CMR and non-CMR, highlighting the importance of visual assessment to recognize radiation pneumonitis, changes in lung configuration, and patterns of response.

Respiratory-gated (4D) FDG-PET detects tumour and normal lung response after stereotactic radiotherapy for pulmonary metastases

BACKGROUND

Response assessment after stereotactic ablative body radiotherapy (SABR) in lung can be confounded by radiation-induced inflammation, fibrosis and subsequent alteration of tumour motion. The purpose of this prospective pilot study was to evaluate the utility of four-dimensional (4D) FDG-PET/CT for post-SABR tumour and normal lung response assessment in pulmonary oligometastases.

MATERIAL AND METHODS

Patients enrolled from February 2010 to December 2011 in this prospective ethics approved study had 1-2 pulmonary metastases on staging FDG-PET. Serial contemporaneous 3D and 4D FDG-PET/CT scans were performed at baseline, 14 days and 70 days after a single fraction of 26 Gy SABR. Tumour response was evaluated in 3D and 4D using SUVmax, RECIST and PERCIST criteria. Normal lung radiotoxicity was evaluated using SUVmean within 0-2 Gy, 2-5 Gy, 5-10 Gy, 10-20 Gy and 20 + Gy isodose volumes.

RESULTS

In total, 17 patients were enrolled of which seven were ineligible due to interval progression from staging PET to baseline 4D-PET. The mean time between scans was 62 days. At a median follow-up of 16 months, 10 patients with 13 metastases received SABR, with no patient having local progression. The vector of tumour motion was larger in patients with discordant 3D and 4D PET PERCIST response (p < 0.01), with a mean (± SEM) motion of 10.5 mm (± 0.96 mm) versus 6.14 mm (± 0.81 mm) in those patients with concordant 3D and 4D response. Surrounding normal lung FDG uptake at 70 days was strongly correlated to delivered radiation dose (r(2) = 0.99, p < 0.01), with significant elevations across all dose levels (p ≤ 0.05), except the < 2 Gy volume (p = 0.30).

CONCLUSIONS

We demonstrate high rates of interval progression between staging PET scans in patients with oligometastases. We found that tumour response on conventional 3D PET is not concordant with 4D PET for tumours with large motion. Normal lung metabolic uptake is strongly dose dependent after SABR, a novel finding that should be further validated.

Development of a clinical assay for detection of GAA mutations and characterization of the GAA mutation spectrum in a Canadian cohort of individuals with glycogen storage disease, type II

Glycogen storage disease, type II (GSDII; Pompe disease; acid maltase deficiency) is an autosomal recessive disease caused by mutations of the GAA gene that lead to deficient acid alpha-glucosidase enzyme activity and accumulation of lysosomal glycogen. Although measurement of acid alpha-glucosidase enzyme activity in fibroblasts remains the gold standard for the diagnosis of GSDII, analysis of the GAA gene allows confirmation of clinical or biochemical diagnoses and permits predictive and prenatal testing of individuals at risk of developing GSDII. We have developed a clinical molecular test for the detection of GAA mutations based on cycle sequencing of the complete coding region. GAA exons 2-20 are amplified in six independent PCR using intronic primers. The resulting products were purified and sequenced. Preliminary studies using this protocol were conducted with DNA from 21 GSDII-affected individuals from five centers across Canada. In total, 41 of 42 mutations were detected (96.7% detection rate). Mutations spanned intron 1 through exon 19 and included nine novel mutations. Haplotype analysis of recurrent mutations further suggested that three of these mutations are likely to have occurred independently at least twice. Additionally, we report the identification of the c.-32-13T>G GAA mutation in an individual with infantile variant GSDII, despite reports of this mutation being associated almost exclusively with late-onset forms of the disease. The development of a clinical molecular test provides an important tool for the management and counseling of families and individuals with GSDII, and has provided useful information about the GAA mutation spectrum in Canada.

A comparative study of cytoplasmic granules imaged by the real-time microscope, Nile Red and Filipin in fibroblasts from patients with lipid storage diseases

Cytoplasmic granules in fibroblasts, visualized without stains, or labelled with Nile red, Filipin, or anti-LAMP-1 (lysosome-associated membrane protein 1), were imaged using the real-time microscope (RTM). New advances in light microscope technology were applied to detect cytoplasmic granules (RTM-visible granules) and characterize them by imaging contrast, size, shape, cellular distribution, composition, motion dynamics and quantity. Appearing as solid spheroids or ring structures, the majority of the RTM-visible granules contained Nile-red labelled neutral lipids. A smaller subpopulation, appearing dimmer, with less imaging contrast, contained Filipin-labelled free cholesterol. Most lipid storage granules have a diameter ranging from 0.3 mum to 0.6 mum, with a small population measuring up to 1 mum. They typically clustered in the perinuclear region and displayed relatively small oscillatory motion. Immunofluorescence based on LAMP-1 labelling highlighted granular structures that were distinct and separate from RTM-visible granules and other structures in the light modality of the microscope. RTM-visible granules were associated with disease phenotypes that have increased cellular neutral lipid stores corresponding to the Nile red-labelled droplets (e.g. triacylglycerides, cholesterol esters). As predicted, the fibroblast strains with a defect resulting in Wolman disease, when compared to control samples, consistently had RTM-visible granules, higher in imaging contrast and with larger diameters, that were labelled with Nile red, and also an increased frequency of Filipin-cholesterol complexes. By comparison, in fibroblasts where the lipid storage is less evident (Gaucher and Farber diseases) or from GM(1) gangliosidosis, where the primary storage substances are oligosaccharides, fewer and smaller RTM-visible granules were observed. In some cases, changes in contrast and morphology in the unstained cytoplasmic compartments were more evident than in the labelled structures. In summary, applying the RTM imaging system to fibroblasts enables differences between the various disease types to be seen and, in specific examples, a unique phenotype can be readily discerned.

Sulfatide and Na+-K+-ATPase: A Salinity-sensitive Relationship in the Gill Basolateral Membrane of Rainbow Trout

We investigated the effect of salinity on the relationship between Na(+)-K(+)-ATPase and sulfogalactosyl ceramide (SGC) in the basolateral membrane of rainbow trout (Oncorhynchus mykiss) gill epithelium. SGC has been implicated as a cofactor in Na(+)-K(+)-ATPase activity, especially in Na(+)-K(+)-ATPase rich tissues. However, whole-tissue studies have questioned this role in the fish gill. We re-examined SGC cofactor function from a gill basolateral membrane perspective. Nine SGC fatty acid species were quantified by tandem mass spectrometry (MS/MS) and related to Na(+)-K(+)-ATPase activity in trout acclimated to freshwater or brackish water (20 ppt). While Na(+)-K(+)-ATPase activity increased, the total concentration and relative proportion of SGC isoforms remained constant between salinities. However, we noted a negative correlation between SGC concentration and Na(+)-K(+)-ATPase activity in fish exposed to brackish water, whereas no correlation existed in fish acclimated to freshwater. Differential Na(+)-K(+)-ATPase/SGC sensitivity is discussed in relation to enzyme isoform switching, the SGC cofactor site model and saltwater adaptation.

Impaired elastic-fiber assembly by fibroblasts from patients with either Morquio B disease or infantile GM1-gangliosidosis is linked to deficiency in the 67-kD spliced variant of beta-galactosidase

We have previously shown that intracellular trafficking and extracellular assembly of tropoelastin into elastic fibers is facilitated by the 67-kD elastin-binding protein identical to an enzymatically inactive, alternatively spliced variant of beta-galactosidase (S-Gal). In the present study, we investigated elastic-fiber assembly in cultures of dermal fibroblasts from patients with either Morquio B disease or GM1-gangliosidosis who bore different mutations of the beta-galactosidase gene. We found that fibroblasts taken from patients with an adult form of GM1-gangliosidosis and from patients with an infantile form, carrying a missense mutations in the beta-galactosidase gene-mutations that caused deficiency in lysosomal beta-galactosidase but not in S-Gal-assembled normal elastic fibers. In contrast, fibroblasts from two cases of infantile GM1-gangliosidosis that bear nonsense mutations of the beta-galactosidase gene, as well as fibroblasts from four patients with Morquio B who had mutations causing deficiency in both forms of beta-galactosidase, did not assemble elastic fibers. We also demonstrated that S-Gal-deficient fibroblasts from patients with either GM1-gangliosidosis or Morquio B can acquire the S-Gal protein, produced by coculturing of Chinese hamster ovary cells permanently transected with S-Gal cDNA, resulting in improved deposition of elastic fibers. The present study provides a novel and natural model validating functional roles of S-Gal in elastogenesis and elucidates an association between impaired elastogenesis and the development of connective-tissue disorders in patients with Morquio B disease and in patients with an infantile form of GM1-gangliosidosis.

Characterization of beta-galactosidase mutations Asp332-->Asn and Arg148-->Ser, and a polymorphism, Ser532-->Gly, in a case of GM1 gangliosidosis

We have identified and characterized three missense mutations in a patient with type 1 G(M1) gangliosidosis, namely a substitution of G for A at nucleotide position 1044 (G1044-->A; in exon 10) on one allele, which converts Asp(332) into asparagine, and both a mutation (C492-->A in exon 4, leading to the amino acid change of Arg(148)-->Ser) and a polymorphism (A1644-->G in exon 15, leading to a change of Ser(532)-->Gly) on the other allele. This patient had less than 1% residual beta-galactosidase activity and minimally detectable levels of immunoreactive beta-galactosidase protein in fibroblasts. To account for the above findings, a series of expression and immunolocalization studies were undertaken to assess the impact of each mutation. Transient overexpression in COS-1 cells of cDNAs encoding Asp(332)Asn, Arg(148)Ser and Ser(532)Gly mutant beta-galactosidases produced abundant amounts of precursor beta-galactosidase, with activities of 0, 84 and 81% compared with the cDNA clone for wild-type beta-galactosidase (GP8). Since the level of vector-driven expression is much less in Chinese hamster ovary (CHO) cells than in COS-1 cells, and we knew that exogenous beta-galactosidase undergoes lysosomal processing when expressed in these cells, transient expression studies were performed of Arg(148)Ser and Ser(532)Gly, which yielded active forms of the enzyme. In this case, the Arg(148)Ser and Ser(532)Gly products gave rise to 11% and 86% of the control activity respectively. These results were not unexpected, since the Arg(148)Ser mutation introduced a major conformational change into the protein, and we anticipated that it would be degraded in the endoplasmic reticulum (ER), whereas the polymorphism was expected to produce near-normal activity. To examine the effect of the Asp(332)Asn mutation on the catalytic activity, we isolated CHO clones permanently transfected with the Asp(332)Asn and Asp(332)Glu constructs, purified the enzymes by substrate-analogue-affinity chromatography, and determined their kinetic parameters. The V(max) values of both mutant recombinant enzymes were markedly reduced (less than 0.9% of the control), and the K(m) values were unchanged compared with the corresponding wild-type enzyme isolated at the same time. Both the Arg(148)Ser beta-galactosidase in CHO cells and Asp(332)Asn beta-galactosidases (in COS-1 and CHO cells) produced abundant immunoreaction in the perinuclear area, consistent with localization in the ER. A low amount was detected in lysosomes. Incubation of patient fibroblasts in the presence of leupeptin, which reduces the rate of degradation of lysosomal beta-galactosidase by thiol proteases, had no effect on residual enzyme activity, and immunostaining was again detected largely in the perinuclear area (localized to the ER) with much lower amounts in the lysosomes. In summary, the Arg(148)Ser mutation has no effect on catalytic activity, whereas the Asp(332)Asn mutation seriously reduces catalytic activity, suggesting that Asp(332) might play a role in the active site. Immunofluorescence studies indicate the expressed mutant proteins with Arg(148)Ser and Asp(332)Asn mutations are held up in the ER, where they are probably degraded, resulting in only minimum amounts of the enzyme becoming localized in the lysosomes. These results are completely consistent with findings in the cultured fibroblasts. Our results imply that most of the missense mutations described in G(M1) gangliosidosis to date have little effect on catalytic activity, but do affect protein conformation such that the resulting protein cannot be transported out of the ER and fails to arrive in the lysosome. This accounts for the minimal amounts of enzyme protein and activity seen in most G(M1) gangliosidosis patient fibroblasts.

Decreased elastin deposition and high proliferation of fibroblasts from Costello syndrome are related to functional deficiency in the 67-kD elastin-binding protein

Costello syndrome is characterized by mental retardation, loose skin, coarse face, skeletal deformations, cardiomyopathy, and predisposition to numerous malignancies. The genetic origin of Costello syndrome has not yet been defined. Using immunohistochemistry and metabolic labeling with [3H]-valine, we have established that cultured skin fibroblasts obtained from patients with Costello syndrome did not assemble elastic fibers, despite an adequate synthesis of tropoelastin and normal deposition of the microfibrillar scaffold. We found that impaired production of elastic fibers by these fibroblasts is associated with a functional deficiency of the 67-kD elastin-binding protein (EBP), which is normally required to chaperone tropoelastin through the secretory pathways and to its extracellular assembly. Metabolic pulse labeling of the 67-kD EBP with radioactive serine and further chase of this tracer indicated that both normal fibroblasts and fibroblasts from patients with Costello syndrome initially synthesized comparable amounts of this protein; however, the fibroblasts from Costello syndrome patients quickly lost it into the conditioned media. Because the normal association between EBP and tropoelastin can be disrupted on contact with galactosugar-bearing moieties, and the fibroblasts from patients with Costello syndrome revealed an unusual accumulation of chondroitin sulfate-bearing proteoglycans (CD44 and biglycan), we postulate that a chondroitin sulfate may be responsible for shedding EBP from Costello cells and in turn for their impaired elastogenesis. This was further supported by the fact that exposure to chondroitinase ABC, an enzyme capable of chondroitin sulfate degradation, restored normal production of elastic fibers by fibroblasts from patients with Costello syndrome. We also present evidence that loss of EBP from fibroblasts of Costello syndrome patients is associated with an unusually high rate of cellular proliferation.

Molecular basis of GM1 gangliosidosis and Morquio disease, type B. Structure-function studies of lysosomal beta-galactosidase and the non-lysosomal beta-galactosidase-like protein

GM1 gangliosidosis and Morquio B disease are distinct disorders both clinically and biochemically yet they arise from the same beta-galactosidase enzyme deficiency. On the other hand, galactosialidosis and sialidosis share common clinical and biochemical features, yet they arise from two separate enzyme deficiencies, namely, protective protein/cathepsin A and neuraminidase, respectively. However distinct, in practice these disorders overlap both clinically and biochemically so that easy discrimination between them is sometimes difficult. The principle reason for this may be found in the fact that these three enzymes form a unique complex in lysosomes that is required for their stability and posttranslational processing. In this review, I focus mainly on the primary and secondary beta-galactosidase deficiency states and offer some hypotheses to account for differences between GM1 gangliosidosis and Morquio B disease.

Early-infantile galactosialidosis: prenatal presentation and postnatal follow-up

Galactosialidosis (GS) is an autosomal recessive condition caused by combined deficiency of the lysosomal enzymes beta-galactosidase and alpha-neuraminidase. The combined deficiency has been found to result from a defect in protective protein/cathepsin A (PPCA), an intralysosomal protein which protects these enzymes from premature proteolytic processing. The most severe form of GS, the early-infantile form, results in early onset of edema, ascites, visceromegaly, and skeletal dysplasia. We report a case of early-infantile GS in a male infant who presented with nonimmune fetal hydrops (NIH), "coarse" facial appearance, massive fluid-filled inguinal hernias, multiple telangiectasia, and diffuse hypopigmentation; he subsequently developed visceromegaly. The diagnosis of GS was confirmed biochemically and the defect in PPCA characterized at the protein level. Examination of fetal peripheral blood smears sampled at 30 weeks gestation demonstrated vacuolation of lymphocytes, suggesting blood film examination may be a useful screening tool for cases of NIH where a metabolic disorder is suspected. Skeletal radiography at birth demonstrated punctate epiphyses of the femora, calcanei, and sacrum. We present a discussion of and differential diagnosis for this radiographic finding. To the best of our knowledge, this is the first case of early-infantile GS presenting with stippled epiphyses.

The 67-kDa enzymatically inactive alternatively spliced variant of beta-galactosidase is identical to the elastin/laminin-binding protein

Our previous studies showed immunological and functional similarities, as well as partial sequence homology, between the enzymatically inactive alternatively spliced variant of human beta-galactosidase (S-gal) and the 67-kDa elastin/laminin-binding protein (EBP) from sheep. To define the genetic origin of the EBP further, a full-length human S-gal cDNA clone was constructed and subjected to in vitro transcription/translation. The cDNA was also transfected into COS-1 cells and into the EBP-deficient smooth muscle cells (SMC) from sheep ductus arteriosus (DA). In vitro translation yielded an unglycosylated form of the S-gal protein, which immunoreacted with anti-beta-galactosidase antibodies and bound to elastin and laminin affinity columns. S-gal cDNA transfections into COS-1 and DA SMC increased expression of a 67-kDa protein that immunolocalized intracellularly and to the cell surface and, when extracted from the cells, bound to elastin. The S-gal-transfected cells displayed increased adherence to elastin-covered dishes, consistent with the cell surface distribution of the newly produced S-gal-encoded protein. Transfection of DA SMC additionally corrected their impaired elastic fiber assembly. These results conclusively identify the 67-kDa splice variant of beta-galactosidase as EBP.

Macrophage phagocytosis of polyethylene particulate in vitro

In this study, an in vitro model has been developed to examine the interactions of macrophages with ultrahigh molecular-weight polyethylene (UHMWPE) and high-density polyethylene (HDPE) particles. Polyethylene particles are the major constituent of the material debris formed as a result of orthopedic implant wear. However, the study of polyethylene particle interactions with cells has been limited. UHMWPE (18-20 microns) and HDPE (4-10 microns) were suspended in soluble collagen type I and subsequently solidified on glass coverslips. The particle chemistry was characterized by Fourier transform infra-red spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Mouse cell line macrophages (IC-21) were established on the collagen-particle substrata and maintained for up to 24 h. The response of the cells to the particles was examined by light and transmission electron microscopy (LM and TEM), as well as by scanning electron microscopy (SEM), and compared to cells on control collagen surfaces without particles. Histological analysis of the samples revealed that the macrophages surrounded larger particles (18-20 microns) and the cells appeared to be attached to the surface of the particles, and the smaller particles (4-10 microns) had been phagocytosed within 2 h. Inflammatory cytokines (TNF-alpha, IL-1 alpha, IL-1 beta, and IL-6), lysosomal enzymes (beta-galactosidase and hexosaminidase), and prostaglandin E2 were released into the medium, and IL-1 alpha, IL-1 beta, PGE2, beta-galactosidase, and hexosaminidase levels were significantly increased over collagen control values. The results demonstrate active phagochemotaxis by macrophages for wear particulates and validate this model as a means of studying the specific in vitro interactions of polyethylene with cells.

Maturation and degradation of beta-galactosidase in the post-Golgi compartment are regulated by cathepsin B and a non-cysteine protease

Lysosomal beta-galactosidase precursor is processed to a mature form and associated with protective protein in lysosomes. In this study we used two cysteine protease proinhibitors, E64-d for cathepsins B, S, H, and L, and CA074Me for cathepsin B. They are converted intracellularly to active forms, E-64c and CA074, respectively. Both active compounds inhibited maturation of the exogenous beta-galactosidase precursor, but E-64c did not inhibit further degradation to an inactive 50-kDa product. We concluded that cathepsin B participated exclusively in maturation of beta-galactosidase, and a non-cysteine protease was involved in further degradation and inactivation of the enzyme molecule.

Identification of Glu-268 as the catalytic nucleophile of human lysosomal beta-galactosidase precursor by mass spectrometry

Human lysosomal beta-galactosidase catalyzes the hydrolysis of beta-galactosides via a double displacement mechanism involving a covalent glycosyl enzyme intermediate. By use of the slow substrate 2,4-dinitrophenyl-2-deoxy-2-fluoro-beta-D-galactopyranoside, a glycosyl enzyme intermediate has been trapped on the enzyme. This has allowed the catalytic nucleophile to be identified as Glu-268 by peptic and tryptic digestion of the inactivated enzyme followed by high performance liquid chromatography-electrospray ionization tandem mass spectrometry of the peptide mixture. This glutamic acid is fully conserved in a sequence-related family of enzymes (Family 35), consistent with its essential role.

Early proteolytic cleavage with loss of a C-terminal fragment underlies altered processing of the beta-galactosidase precursor in galactosialidosis

Processing of human beta-galactosidase (beta-GAL) was studied in permanently transfected Chinese hamster ovary (CHO) cells and compared with that in normal cells and in cells from subjects with GM1-gangliosidosis, galactosialidosis and I-cell disease. Biosynthesis of beta-GAL in CHO cells results in the synthesis of an 88 kDa glycosylated and phosphorylated monomer precursor which is enzymically active and is secreted into the medium. Post-translational processing begins at the C-terminal end of the protein and gives rise to structurally related 67 and 64 kDa mature forms. These are subsequently degraded to give several inactive products of which a 50 kDa and a 18 kDa species are prominent. In normal fibroblasts only the 84 kDa precursor is readily detected inside cells, while the 88 kDa precursor is the only form secreted from cells in the presence of ammonium chloride. Processing of the precursor in normal fibroblasts results in the appearance of both the 67 and 64 kDa mature forms, which are also degraded to give 50 and 18 kDa products, as in transfected CHO cells. As affected controls, GM1-gangliosidosis cells showed a general loss of all forms of the enzyme, while in I-cell fibroblasts only the 84 kDa precursor and an 18 kDa degradation form were prominent. In galactosialidosis fibroblasts, taken from two different subjects, processing of beta-GAL was characterized by the respective appearance of intermediate 80 and 72 kDa enzymically inactive polypeptides, at levels lower than the normal amounts of the 67 and 64 kDa mature forms and higher than the normal amounts of degradation products, one of which is of 45 kDa and arises by endoproteolytic cleavage of the 80 kDa polypeptide. Incubation for up to 72 h in medium containing leupeptin, a potent inhibitor of thiol-dependent proteases, resulted in a significantly increased level of beta-GAL activity to near normal levels in fibroblasts from one galactosialidosis subject. Concordant with this, the abundance of the 84 kDa precursor was increased and the levels of the 80 kDa, 45 kDa and 18 kDa digestion products were diminished. However, in fibroblasts from the second galactosialidosis subject, the amount of the abnormal 72 kDa polypeptide was not influenced by leupeptin treatment. Leupeptin treatment did not increase enzymic activity levels in normal, GM1-gangliosidosis or I-cell disease fibroblasts, despite the fact that the production of the 50 kDa and 18 kDa degradation products was blocked in the presence of leupeptin. We concluded that in galactosialidosis the leupeptin-inhibitable proteolytic cleavage of a small fragment causes a conformational change of the precursor that precludes its further normal processing and results in its enzymic deficiency. This early abnormal trimming of beta-GAL is ascribable to a deficiency in the functional protective protein, the function of which is absolutely essential to render beta-GAL cryptic from at least two distinct and separate proteolytic attacks that together remove at least 12 kDa from the C-terminal end of the enzyme.

Late-onset Tay-Sachs disease presenting as catatonic schizophrenia: diagnostic and treatment issues

BACKGROUND

It is not commonly appreciated that patients with hexosaminidase A deficiency (Tay-Sachs disease) can first present in adulthood with psychiatric illness.

METHOD

A 17-year-old non-Jewish male patient was referred with a history of treatment-resistant catatonic schizophrenia. We uncovered coexistent neurologic abnormalities and evidence of cognitive decline. Metabolic screening revealed a severe deficiency of beta-hexosaminidase A. We reviewed the literature on late-onset gangliosidosis with attention to (1) the nature of the associated psychiatric and neurologic abnormalities and (2) the treatment of psychosis in these patients.

RESULTS

The patient's catatonia responded promptly to benzodiazepine therapy. Treatment with neuroleptic medication resulted in the rapid development of neuroleptic malignant syndrome. The patient was thereafter maintained on lorazepam with resolution of his acute psychiatric disturbances and unexpected improvement in his neurologic status.

CONCLUSION

Patients with hexosaminidase deficiency may first present in adolescence or adulthood with psychiatric illness, particularly schizophrenic-like psychosis. The presence of speech disturbance, gait abnormalities, movement disorders, and cognitive decline may indicate an underlying metabolic disorder. The use of traditional neuroleptics to treat the psychosis in such individuals may produce an unacceptably high risk/benefit ratio. Benzodiazepines may ameliorate the psychiatric and neurologic abnormalities in these patients.

Kinetic mechanism and characterization of human beta-galactosidase precursor secreted by permanently transfected Chinese hamster ovary cells

Chinese hamster ovary cell clones permanently transfected with the cDNA for human lysosomal beta-galactosidase secrete the enzyme precursor into the cell medium, from which it is purified to apparent homogeneity in a single step by affinity chromatography. The purified precursor is fully active, displays the same pH optimum and Km values as the mature placental enzyme, and has an intact C-terminus. The intact enzyme when chromatographed on a Sephacryl S-200 molecular-sieve column elutes as a 105,500 Da monomer, whereas on SDS/PAGE gels the polypeptide migrates as an 88 kDa polypeptide. A time course of digestion with glycopeptide-N-glycanase shows the gradual conversion of the precursor from an 88 to a 72 kDa protein, suggesting the presence of five N-linked oligosaccharides in the protein. The precursor is readily taken up in a mannose-6-phosphate-dependent manner into beta-galactosidase-deficient, GM1-gangliosidosis fibroblasts, and the enzyme activity is returned to normal levels. We show that the stereochemical course of enzymic hydrolysis involves the retention of the beta-configuration at the anomeric centre, suggesting a double-displacement mechanism. Furthermore, the enzyme is rapidly and irreversibly inactivated in the presence of the mechanism-based inactivator 2,4-dinitrophenyl-2-deoxy-2-fluoro-beta-D-galactopyranoside, which implicates a covalent intermediate. The enzyme is also inactivated by 1-ethyl-3(3-dimethylamino-propyl)carbodi-imide and by phenylglyoxal, which implicates carboxylate and arginine residues respectively in the active site. We conclude that the beta-galactosidase precursor is functionally identical to the mature lysosomal form of the enzyme and serves as an excellent enzyme source for investigation of structure-function relationships in the protein.

Homozygous presence of the crossover (fusion gene) mutation identified in a type II Gaucher disease fetus: is this analogous to the Gaucher knock-out mouse model?

Gaucher disease (GD) is an inherited deficiency of beta-glucocerebrosidase (EC 3.1.2.45, gene symbol GBA). In type I GD, the CNS is not involved (nonneuronopathic), whereas in type II GD (acute neuronopathic) CNS involvement is early and rapidly progressive, while in type III GD (subacute neuronopathic) CNS involvement occurs later and is slowly progressive. The T6433C (L444P) substitution is prevalent in type GD II. It may occur alone as a single base-pair mutation but often is found as part of a complex allele containing additional GBA nucleotide substitutions, G6468C (A456P) and G6482C (V460V), without (recNciI) or with (recTL) G5957C (D409H). This complex allele is presumed to have formed by recombination (crossover, fusion) of the structural gene with the pseudogene, which contains the mutated sequences. Two complex alleles have never been demonstrated to coexist in any individual. We devised a selective PCR method for the specific amplification of the normal and/or fusion gene. Using this procedure we demonstrated the fusion gene in homozygous form for the first time, in a Macedonian/Ashkenazi Jewish GD type II fetus. Both parents were carriers of the recombination. This was confirmed by direct sequence analysis. A previous conceptus in this family was stillborn at 36 weeks, with features of severe type II GD. Neonates showing a severe clinical phenotype, analogous to the early neonatal lethal disease occurring in mice homozygous for a null allele produced by targeted disruption of GBA, have been described elsewhere, but the specific mutations in these cases have not yet been characterized.(ABSTRACT TRUNCATED AT 250 WORDS)

Classification of disorders of GM2 ganglioside hydrolysis using 3H-GM2 as substrate

Rates of GM2 ganglioside hydrolysis by fibroblasts from normal controls and patients with GM2 gangliosidosis were measured in situ, with cells growing in tissue culture by assaying the decrease in cell-incorporated 3H-GM2 over time, and in vitro by assaying the rate of 3H-GM2 hydrolysis using fibroblast extracts in the presence of no additives, sodium taurocholate, and GM2 activator protein. In tissue culture, normal cells hydrolyzed cell-incorporated GM2 while fibroblasts from patients with GM2 gangliosidosis did not. The half life of GM2 in normal fibroblasts was 78 hours. In vitro, only normal fibroblast extracts hydrolyzed GM2 in the absence of additives. In the presence of 10 mM sodium taurocholate, rates of GM2 hydrolysis by normal fibroblast extracts were increased 5-16-fold, fibroblast extracts from AB and B1 variant patients hydrolyzed GM2 at normal rates, cell extracts from patients with Tay-Sachs disease hydrolyzed GM2 at nearly normal rates, and cell extracts from Sandhoff disease patients hydrolyzed GM2 at about 10% of normal rates. In the presence of 1 microgram of GM2 activator, rates of GM2 hydrolysis by normal fibroblast extracts were increased 8-25-fold, fibroblast extracts from a patient with the AB variant hydrolyzed GM2 at normal rates, and cell extracts from other variants of GM2 gangliosidosis did not hydrolyze GM2. The results suggest that measuring the persistence of 3H-GM2 in tissue culture over time will detect any variant of GM2 gangliosidosis and may be the ideal way to test for the presence of this disease. Variants can be distinguished by assaying the hydrolysis of 3H-GM2 using cell extracts in the absence of additives, with sodium taurocholate, and with activator.

The biochemistry and clinical features of galactosialidosis

Galactosialidosis is a heterogeneous disorder that is manifested in infantile, late infantile, juvenile/adult, and atypical forms. In every instance the primary defect is in the ability of protective protein to associate with beta-galactosidase and neuraminidase to protect them from intralysosomal proteolysis. The protective protein is in reality a serine protease that displays both cathepsin A and C-terminal deamidase activity. We summarize the major clinical features of each form, and the range of storage products accumulated. The concept of an intralysosomal complex containing beta-galactosidase and neuraminidase in addition to protective protein seems irrefutable but major gaps exist in our understanding of how the complex is formed and in what subcellular organelles, how it is sustained, and the protein domains contributed by the constituent enzymes that play a pivotal role in this process.

Nerve biopsy findings in Niemann-Pick type II (NPC)

The severe infantile form of Niemann-Pick disease type II was diagnosed in a 4-year-old girl and confirmed by demonstrating in cultured skin fibroblasts a deficiency of low-density lipoprotein-stimulated cholesterol ester synthesis of < 5% of normal. Electrodiagnostic studies revealed changes of a predominantly demyelinating motor and sensory polyneuropathy. Light microscope and ultrastructural examination of a peroneal nerve biopsy showed unique changes. Compacted myelin sheaths were disproportionately thin with marked globular irregularities in single teased nerve fibres and evidence of chronic demyelination. The majority of axons were preserved but axonal spheroids and cytoskeletal abnormalities akin to neuroaxonal dystrophy were noted. Membrane-bound multi-lobulated lysosomal inclusions of floccular and electron-dense material were present in Schwann cells (SC), endoneurial fibroblasts, macrophages, pericytes and endothelial cells. SC of myelinated fibres were stuffed with whorls of concentric osmiophilic membraneous profiles and electron-lucent material. The findings are diagnostic and differ from those of classical Niemann-Pick disease.

Genotype-phenotype pitfalls in Gaucher disease

Gaucher disease (GD), caused by inherited deficiency of beta-glucocerebrosidase (beta-Glc, EC 3.1.2.45), is classified type I if the CNS is not involved (non-neuronopathic), type II if CNS involvement is early and rapidly progressive (acute neuronopathic), and type III if CNS involvement occurs later and is slowly progressive (subacute neuronopathic). The clinical course is not predictable by measurement of residual beta-Glc activity. Patient classification by identification of specific mutations is more promising: homozygosity for the common A5841->G (N370S) mutation invariably predicts type I; homozygosity for the T6433->C (L444P) mutation usually indicates type III (Norbottnian). Type II disease patients often carry the T6433->C allele together with a complex allele derived in part from the downstream pseudogene by crossover or gene conversion, producing a T6433->C substitution, plus 2 or 3 additional single base substitutions (fusion gene). Employing selective PCR amplification of the structural gene, we detected homozygous T6433C (L444P) point mutations in a Caucasian boy, initially classified as having GD type I, who succumbed to severe visceral GD before age 3 years. A second novel PCR procedure for discriminating between the normal gene and the fusion gene confirmed the homozygous point mutation results. Post mortem neuropathological findings showed neuronal complex lipid accumulation consistent with late-onset type III disease. Although in Norbottnian patients it is generally accepted that onset of neurological findings is delayed, patients with the L444P/L444P genotype can only be initially classified as type III with this ancestry. Other patients described sporadically elsewhere are invariably considered type I until neurological findings arise.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of saposins on acid sphingomyelinase

The effect of saposins (A, B, C and D) on acid sphingomyelinase activity was determined using a crude human kidney sphingomyelinase preparation and a purified sphingomyelinase preparation from human placenta. Saposin D stimulated the activity of the crude enzyme by increasing its apparent Km and Vmax. values for sphingomyelin hydrolysis. Unlike the crude enzyme, the activity of the purified enzyme was strongly inhibited by saposin D as well as other saposins. Saposin D decreased the apparent Km and Vmax values of purified sphingomyelinase activity. The effects of saposin D on the activity of different sphingomyelinase preparations appear to depend on Triton X-100, which is present in the crude enzyme but not in the purified enzyme. When the detergent was removed from the crude preparation, the effect of saposin D changed from being stimulatory to inhibitory. Conversely, when the detergent is added to the purified enzyme, the effect of saposin D on sphingomyelinase activity changed from being inhibitory to stimulatory. While other saposins were inhibitory or had no effect on sphingomyelinase activity in the above assay system, not only saposin D but also saposins A and C exhibited a stimulatory effect upon purified sphingomyelinase activity when the substrate, sphingomyelin, was added in the form of liposomes without detergent. Saposin B was not only inhibitory in the liposome system, but also reduced the stimulatory effect of saposins A, C and D. These observations indicate that the stimulatory effect of saposins A, C and D on acid sphingomyelinase activity is greatly influenced by the physical environment of the enzyme and suggest that similar effects by saposins may be exerted in lysosomal membranes.

Human placental beta-galactosidase. Characterization of the dimer and complex forms of the enzyme

GM1 ganglioside beta-galactosidase (beta-Gal) is deficient in the autosomal recessive disorder GM1 gangliosidosis. A portion of the enzyme occurs in a complex with neuraminidase and an additional glycoprotein, protective protein, but the nature of the interactions conferring the stability of the complex is unknown. Affinity chromatography of beta-Gal on p-aminophenylthiogalactose-Sepharose (PATG-Sepharose) at pH 4.3, the pH optimum of beta-Gal, resulted in a 260-fold enrichment of beta-Gal, but the major protein in the fraction had an M(r) value of 74,000. Affinity chromatography on PATG-Sepharose at pH 5.2 showed substantial enrichment (4000-fold) of beta-Gal, and the mature form of the enzyme (M(r) 64,000) was the major protein in the preparation. Using h.p.l.c. molecular-sieve chromatography, we found that about 15% of the total beta-Gal occurred in a high-M(r) form (greater than 600,000), the presumptive complex, with 85% eluting at M(r) 150,000, suggestive of a dimer. This distribution was independent of both high (60 mg/ml) and low (5 mg/ml) protein concentration and the pH (pH 4.3 or 5.2) of the sample applied to the column. Furthermore, incubation for 90 min at 37 degrees C, conditions which had previously been suggested as optimal for formation of the complex, had no effect on this distribution. Further fractionation by anion-exchange chromatography and a second affinity column step yielded a beta-Gal preparation that contained a single polypeptide chain (M(r) 64,000), was devoid of neuraminidase and protective protein (absent carboxypeptidase activity), and when injected into rabbits gave rise to monospecific rabbit antisera. We conclude that the protein composition of the complex is variable (i.e. it is different when isolated at pH 4.3 and 5.2) and that the amount of beta-Gal tightly associated with the complex constitutes a small fraction of the total beta-Gal activity. The more prevalent form of the enzyme is a beta-Gal homodimer that is stable and devoid of either neuraminidase activity or protective protein.

Characteristics of the beta-galactosidase-carboxypeptidase complex in GM1-gangliosidosis and beta-galactosialidosis fibroblasts

Lysosomal beta-galactosidase (beta-Gal) occurs either alone in monomeric and dimeric forms, or in a high-M(r) complex with at least two additional proteins. One is neuraminidase and the second is the protective protein, which has also been shown to possess carboxypeptidase activity. beta-Gal activity is deficient in GM1-gangliosidosis as a primary defect, and is secondarily affected in galactosialidosis (GS), where the primary defect is the absence of protective protein activity. Fibroblasts from three patients with GM1-gangliosidosis, type 1, showed markedly reduced amounts of beta-Gal cross-reacting material (CRM), and a fourth appeared to have normal levels. A patient with type 2 GM1-gangliosidosis was also found to be CRM-normal. These findings demonstrate that patients with GM1-gangliosidosis type 1 are heterogeneous with respect to the level of residual beta-Gal protein. Fibroblasts from four patients with GS were strongly CRM-positive with an anti-beta-Gal antibody, as was a sample of brain from one of these patients, suggesting that the loss of beta-Gal activity is linked to a subtler change in the primary structure of the enzyme than has been previously thought. While three GS cell lines displayed reduced carboxypeptidase activity (to 32-42% of the control), one cell line was completely devoid of activity, demonstrating that while carboxypeptidase activity is a property of the protective protein this action is distinct and separate from its protective role. On direct immunoprecipitation with anti-beta-Gal antibody, a portion of the total carboxypeptidase activity co-precipitated with beta-Gal from extracts of normal and GM1-gangliosidosis cells, consistent with the presence of the complex in these cells. However, no carboxypeptidase activity was precipitable with this antibody from GS fibroblasts, suggesting the absence of complex from these cells. To examine this further, the various forms of beta-Gal were resolved by h.p.l.c. molecular-sieve chromatography. Three forms of beta-Gal activity were resolved in normal cells: a complex, a dimer and a monomer. Residual beta-Gal activity of GS cells resolved into two of these forms, the complex and the monomer. In normal and GM1-gangliosidosis cells a portion of the total carboxypeptidase activity co-chromatographed with the complex while the bulk of the activity occurred in a single 36,000-M(r) peak. Only the low-M(r) carboxypeptidase activity was detected in GS cells. This confirms our results on immunoprecipitation indicating that portions of the beta-Gal and the carboxypeptidase activities exist outside the complex in normal, GM1-gangliosidosis and GS cells. In summary, the loss of protective protein function from GS cells results in disproportionate loss of the dimeric and monomeric forms of beta-Gal activity, but does not result in the complete degradation of the protein.

Cholesterol esterification and Niemann-Pick disease: an approach to identifying the defect in fibroblasts

Fibroblasts from 13 patients with the clinical phenotype of type IIS, Niemann-Pick disease were evaluated for their ability to incorporate oleic acid into cholesterol esters via an LDL responsive mechanism. Eight patients displayed a severe deficiency (less than 8% of normal) of cholesterol ester (CE) synthesis while a clinically less affected group displayed intermediate levels (36% of normal) of synthetic capacity with no detectable overlap between these groups and the control range. There was no deficiency in cholesterol ester production in fibroblasts from a patient with Zellweger's disease, a disorder characterized by altered peroxisomes and abnormal peroxisomal cholesterol metabolism, while in I-cell disease, characterized by a primary deficiency of a phosphotransferase which results in altered targeting of lysosomal hydrolases, it was reduced to 25% of the control level. To further implicate lysosomal proteins in the etiology of type IIS, Niemann-Pick disease we measured the effect of correction (conditioned) medium, and the lysosomotropic agent, NH4Cl on cholesterol ester synthesis in fibroblasts. NH4Cl completely inhibited incorporation into CE by normal cells, thus mimicking the CE defect in type IIS, Niemann-Pick cells. Conditioned medium had no effect on incorporation into CE synthesis but medium conditioned in the presence of 10 mM NH4Cl stimulated incorporation into CE in the control but not in Niemann-Pick cells. When Niemann-Pick cells cultured in the presence of NH4Cl were challenged to synthesize CE in the absence of NH4Cl, a significant enhancement of CE synthesis was noted in representative cell lines from both groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

First trimester prenatal diagnosis of Tay-Sachs disease using the sulfated synthetic substrate for hexosaminidase A

Uncultured and cultured embryonic trophoblastic tissue obtained by chorionic villus sampling (CVS) displays enzyme activity towards 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranosyl-6-sulfate (MUGS), a specific substrate for Hexosaminidase A (Hex A), the enzyme deficient in Tay-Sachs disease (TSD). Specific activity is comparable to that found in cultured amniocytes and fibroblasts. The enzyme activity has a pH optimum of 4.1 and an apparent Km of 6 x 10(-4) mol/L. Thirteen pregnancies in eight families at risk for TSD were monitored by CVS using MUGS as the Hex A substrate. Four fetuses were proven affected by enzyme analysis of fetal tissues and cultured fetal fibroblasts obtained at the time of termination of the pregnancies. Nine fetuses were judged to be unaffected. Eight babies were clinically normal while the other pregnancy is continuing. The use of MUGS as substrate for Hex A makes prenatal diagnosis by CVS of families at risk for TSD simple, direct and accurate.

Properties of partially purified goat kidney beta-D-mannosidase

Lysosomal beta-D-mannosidase (EC 3.2.1.25) was purified 6900-fold from normal goat kidney by serial Concanavalin A-Sepharose 4B and Red A dye ligand affinity chromatography, followed by anion exchange and molecular sieve high performance liquid chromatography. The relative molecular mass of the enzyme was estimated by molecular sieving to be 79,000 +/- 3000. The apparent Km for the synthetic substrate, 4-methylumbelliferyl-beta-D-mannopyranoside, was 2.3-2.8 mM and the sharp, unimodal pH optimum was 5.5. Enzyme activity was inhibited by Hg2+, Zn2+, Ag+, Co2+ and the thiol reactive agent N-ethylmaleimide. The mannose derivatives p-nitrophenyl-beta-D- thiomannopyranoside and p-aminophenyl-beta-D-thiomannopyranoside inhibited enzyme activity and may be of use as immobilized ligands in future attempts to purify beta-D-mannosidase by specific affinity chromatography.

Caprine beta-D-mannosidosis: characterization of a model lysosomal storage disorder

Interest in using caprine beta-D-mannosidosis as a model to evaluate bone marrow transplantation in the treatment of human lysosomal storage disorders provided the stimulus for characterization of beta-D-mannosidase in selected goat tissues and induction of hemopoietic chimerism in the goat. Total beta-D-mannosidase activity was measured with the use of 4-methylumbelliferyl beta-D-mannopyranoside as substrate. Residual activity in mutant liver was 52% of control but no activity was detectable in mutant kidney or brain tissue. Normal adult goat liver contained two forms of beta-D-mannosidase, a nonlysosomal form (52%) with a broad pH range for optimum activity (4.5-8.0) and a lysosomal form (48%) with a pH optimum of 5.5. Residual enzyme in mutant liver consisted entirely of the nonlysosomal form. Normal adult thyroid, kidney and brain contained two major lysosomal isoenzymes with pIs 5.5 and 5.9 and traces of a minor isoenzyme with pI 5.0. Normal liver contained three isoenzymes with similar pIs; however, an isoenzyme with pI 5.0 predominated. In 60-day fetal liver lysosomal isoenzymes predominated and only trace amounts of nonlysosomal isoenzyme were detectable. Total hepatic beta-D-mannosidase activity increased towards adult levels during the last 90 days of gestation as a result of increasing nonlysosomal isoenzyme activity. Intraperitoneal injection of fetal liver cells into 60-day goat fetuses resulted in sustained hemopoietic chimerism in surviving kids without evidence of graft-versus-host-disease. These results suggest that transplantation of normal fetal liver cells into preimmunocompetent goat fetuses affected with beta-D-mannosidosis is feasible and may provide an alternative strategy for evaluation of postnatal bone marrow transplantation in the treatment of human lysosomal storage disorders.

Biosynthesis of sphingomyelinase in normal and Niemann-Pick fibroblasts

Deficient sphingomyelinase activity and massive storage of sphingomyelin are common to two clinically different forms of Niemann-Pick disease, called types A and B. Polyclonal antisera to human sphingomyelinase precipitated both enzyme activity and the polypeptide chain of purified placental sphingomyelinase. In normal fibroblasts, following a 19-h labelling period with [35S]methionine and immunoprecipitation of the labelled proteins, sphingomyelinase occurred as a single polypeptide with a mean molecular mass of 110 kilodaltons (kDa). Niemann-Pick disease type A and B fibroblasts also synthesized a sphingomyelinase polypeptide having the same molecular mass as that found in normal fibroblasts. In I-cell disease fibroblasts, a reduced amount of cross-reacting material was detected, suggesting that sphingomyelinase may be targeted to the lysosome via the phosphomannosyl receptor. Pulse-chase experiments demonstrated sphingomyelinase processing, as judged by a substantial loss of radiolabel and the appearance of an 84-kDa intermediate form of the enzyme. These results confirm and extend previous work based on autopsy specimens and urine, and show that Niemann-Pick disease fibroblasts synthesize a sphingomyelinase polypeptide. We show for the first time that an 84-kDa processed form of the enzyme is biosynthetically related to the 110-kDa polypeptide.

Selective damage to cochlear efferents by the choline neurotoxin ethylcholine mustard aziridinium ion (AF64A) in the chinchilla

The cholinotoxin ethylcholine mustard aziridinium ion (AF64A) was diluted in artificial perilymph to concentrations ranging from 10-100 microM, injected unilaterally into the bulla of chinchillas, and allowed to passively diffuse across the round window membrane. Following 21-day survival, the animals were sacrificed and ears removed and embedded in epoxy for histological evaluation under both light and transmission electron microscopy. At 10 microM concentration, selective degeneration of efferent fibers was observed in the efferent terminals on outer hair cells (OHC), tunnel radial fibers, tunnel spiral bundle, and the inner spiral bundle. Serial sections of the middle turn of an animal at 10 microM concentrations showed normal efferent terminals on approximately 50% of OHCs. At the higher concentrations non-specific damage was seen in OHCs, afferents, and some supporting cells. These data suggest that low doses AF64A produces selective damage to cochlear efferent terminals and fibers in the chinchilla.

Induction of hemopoietic chimerism in the caprine fetus by intraperitoneal injection of fetal liver cells

Intraperitoneal injection of allogeneic liver cells from 43-day-old male fetuses into normal 60-day female goat fetuses resulted in persistent hemopoietic chimerism in surviving recipients without clinical evidence of graft-versus-host disease. Transplantation of normal fetal liver cells into preimmunocompetent goat fetuses affected with beta-D-mannosidosis may provide an alternative strategy for evaluating hemopoietic stem cell transplantation in the treatment of human lysosomal storage diseases.

In vitro activation of neuraminidase in the beta-galactosidase-neuraminidase-protective protein complex by cathepsin C

Neuraminidase can be activated by incubation of crude glycoprotein fractions at acidic pH for 90 minutes at physiological temperature. This activation is inhibited by leupeptin. Incubation of the purified neuraminidase-beta-galactosidase-protective protein complex under the same conditions used for crude glycoprotein fractions did not lead to enhanced neuraminidase activity, but incubation in the presence of exogenous Cathepsin C at 4 degrees C resulted in marked enhancement of neuraminidase activity. This activation was again inhibited by leupeptin. Cathepsin D treatment resulted in destruction of neuraminidase under the same conditions and this effect was again inhibited by leupeptin. beta-galactosidase in crude glycoprotein fractions and in the complex was resistant to both Cathepsin C and D, while homogeneous beta-galactosidase was inactivated by these enzymes. We suggest that in vitro activation of neuraminidase may mimic the in vivo intralysosomal conversion of the neuraminidase precursor into the mature form of the enzyme.

Lysosphingolipids and mitochondrial function. II. Deleterious effects of sphingosylphosphorylcholine

Psychosine, sphingosylphosphorylcholine (52-104 microM), and other glycosphingolipids stimulate mitochondrial respiration (up to 500%) and inhibit oxidative phosphorylation to varying degrees. Above 104 microM these functions as well as uptake of Ca2+ are prevented. At 104 microM sphingosylphosphorylcholine inhibits the mitochondrial ATPase reaction in submitochondrial particles by 48%. Both sphingosylphosphorylcholine and psychosine enhance the active phosphate-dependent swelling of mitochondria. Passive swelling occurs in the presence of rotenone (when swelling does not normally occur) and under hypotonic conditions. A direct interaction of sphingosylphosphorylcholine with membranes is demonstrated by a discharge of the proton gradient across mitochondrial membranes, hemolysis of red blood cells, and binding to inner and outer mitochondrial membranes. Thus lysosphingolipids bind strongly to mitochondrial membranes and markedly alter mitochondrial function. This alteration would affect the ATP levels, thereby altering a wide range of ATP-dependent cellular functions. These results offer a partial explanation for the pathogenesis of representative lysosomal storage diseases.

Properties and prenatal ontogeny of beta-D-mannosidase in selected goat tissues

beta-D-Mannosidase activity in selected normal adult, neonatal and foetal goat tissues and in tissues from animals affected with caprine beta-mannosidosis was examined with the use of 4-methylumbelliferyl beta-D-mannopyranoside as substrate. The enzyme in normal adult thyroid, kidney and brain exhibited a sharp unimodal pH optimum at pH 5.0, whereas the enzyme in both normal adult and mutant liver exhibited broad pH ranges of activity (pH 4.5-8.0). No residual enzyme was detectable in mutant kidney or brain; in contrast, residual activity in mutant liver was 52% of that in a neonatal control. Concanavalin A-Sepharose 4B (Con A-Sepharose) fractionation of normal adult liver beta-D-mannosidase resolved the enzyme into an unbound (non-lysosomal) from (52%) with a broad pH range of activity (pH 4.5-8.0) and a bound (lysosomal) form (48%) with a sharp pH optimum of 5.5. The enzyme in mutant liver consisted entirely of the unbound (non-lysosomal) form. Beta-D-Mannosidase activity in normal adult thyroid, kidney and brain was resolved by chromatofocusing into two major isoenzymes, with pI 5.5 and 5.9, and traces of a minor isoenzyme, with pI 5.0. In normal adult liver the enzyme was also resolved into three isoenzymes with similar pI values; however, that with pI 5.0 predominated. The predominant form of the enzyme in 60-day-foetal liver was bound by Con A, exhibited a unimodal pH optimum (5.0) and was resolved into two isoenzymes, with pI 5.4 and 5.8; only traces of an isoenzyme with pI 5.0 were detectable. Total hepatic beta-D-mannosidase activity increased progressively towards adult values during the last 90 days of gestation as a result of increasing non-lysosomal isoenzyme activity (pI 5.0). Lysosomal beta-D-mannosidase was shown to occur in all normal goat tissues studied as multiple isoenzymes, which are genetically and developmentally distinct from the non-lysosomal isoenzyme occurring predominantly, if not exclusively, in liver.

Aggregation of plasma Z type alpha 1-antitrypsin suggests basic defect for the deficiency

The abnormal type of alpha 1-antitrypsin, PI (protease inhibitor) type Z, is associated with inclusion bodies in the liver, which contain non-secreted alpha 1-antitrypsin. Our studies show that Z protein has an inherent tendency to aggregate, even in plasma. Depending upon conditions, from 15 to 70% of the Z protein in plasma was in a high-Mr form, compared with 1.5% of M type alpha 1-antitrypsin. The high-Mr complex in plasma cannot be disaggregated using Triton X detergent or reducing conditions. This increased tendency to aggregate can be explained by the mutation affecting, tertiary structure and salt bridge formation in Z protein. We have observed this same tendency to aggregate for Mmalton alpha 1-antitrypsin, a rarer variant also associated with a plasma deficiency.

Phosphatidylcholine and 4-methylumbelliferyl phosphorylcholine hydrolysis by purified placental sphingomyelinase

We present evidence which indicates that highly purified placental acid sphingomyelinase hydrolyses [14C]phosphatidylcholine [( 14C]PC) and the synthetic phosphodiester 4-methylumbelliferyl phosphorylcholine (4-MUPC). Hydrolysis was achieved by phospholipase C phosphodiesterase action. Of the several detergents tested, sodium taurocholate alone was necessary for PC hydrolysis, while 4-MUPC was hydrolysed independent of any detergent requirement. The pH optima for the reactions were 4.6-4.8 for PC hydrolysis and 4.8-5.0 for 4-MUPC hydrolysis. As with sphingomyelin hydrolysis, degradation of both PC and 4-MUPC was inhibited by 5'-, 3'-, and 2'-AMP, 5'-AMP being the most effective of the three. Furthermore, the phosphodiesterase activity against PC and 4-MUPC copurified with sphingomyelinase from human placenta and cross-reacted with a specific anti-sphingomyelinase monoclonal antibody, strongly indicating identity of the phosphodiesterases. This explains phospholipase C deficiency in sphingomyelinase-deficient Niemann-Pick disease cells.

Regulation of mRNAs for three enzymes in the glial cell model C6 cell line

In the glial cell line C6, regulation of actinomycin D (Act-D)-sensitive translatable polysomal mRNAs of three key enzymes--glycerol phosphate dehydrogenase (GPDH; EC 1.1.1.8) and glutamine synthetase (GS) by glucocorticoids and lactate dehydrogenase (LDH; EC 1.1.1.27) by catecholamines--is described. Though the first two enzymes are hydrocortisone (HC)-inducible, the nature of their response to the hyperacetylating agent sodium butyrate is dramatically different. Furthermore the appearance of GPDH translatable poly(A)+ RNA in HC-induced cells is inhibited by the presence of cycloheximide (CHX), whereas the induction of GS is unaffected by CHX. These observations necessitate further probing into an existing model system to explain the varied mechanisms of induction of these two enzymes by a single inducer. In combination with the third enzyme whose induction by catecholamines is glial specific, we believe that the C6 cell represents the most appropriate cell line for molecular neurobiologists to study the mechanisms of hormone action in glia.

Studies on the activation of sphingomyelinase activity in Niemann-Pick type A, B, and C fibroblasts: enzymological differentiation of types A and B

Cultured skin fibroblast homogenates from patients with Niemann-Pick disease Type C, were able to degrade sphingomyelin liposomes at a normal rate. Fibroblasts from patients with Niemann-Pick disease Types A and B were less active (0.08-0.55 versus 0.96-2.93 nmol/h/mg). When fibroblasts were maintained in synthetic media (MCDB-104) devoid of fetal calf serum for a period of 21 days, sphingomyelinase activity measured at pH 3.8 increased in control and Niemann-Pick Type C (up to 15-fold) and in Niemann-Pick Type B (up to 3-fold) while Niemann-Pick Type A showed no significant increase in sphingomyelinase activity. Addition of a protein activator isolated from the spleen of a Type I Gaucher's disease patient stimulated a 2-7.5-fold increase in sphingomyelinase activity in normal, Niemann-Pick Type B and C fibroblasts, while under the same conditions the Niemann-Pick Type A fibroblast enzyme responded poorly. Our data show that the residual sphingomyelinase activity in Niemann-Pick Type A can be differentiated from that present in other phenotypic forms by its lack of response to the Gaucher activator. Furthermore, we can find no evidence to support the view that Niemann-Pick Type C sphingomyelinase differs from the normal enzyme in its response to Gaucher activator.

Solid-phase assay for the detection of low-abundance enzymes, and antibodies to enzymes in immune reactions, using acid sphingomyelinase as a model

The development of a solid-phase immunosorbent assay, suitable for use with enzyme antigens, is described. Acid sphingomyelinase and a mouse monoclonal anti-sphingomyelinase antibody have been used to determine optimal conditions for the assay. The assay involves immobilization of a second antibody (anti-mouse IgG) in the wells of a polyvinyl microtiter plate. Soluble immune complexes of first antibody (monoclonal anti-sphingomyelinase) and antigen (sphingomyelinase), incubated in separate vials, are then reacted in the anti-mouse IgG-coated assay wells, and the extent of the cross-reaction between antibody and antigen is measured by direct assay of enzyme retained in the well. A necessary condition of the assay is that antibody must not inhibit enzyme activity, which makes it especially suitable for monoclonal antibodies. The assay finds useful application in hybridoma fluid screening, equivalence point determination, and demonstration of cross-reacting enzyme from various tissue sources.

Human placental beta-galactosidase: structural and immunological observations

beta-Galactosidase purified to apparent homogeneity from human placenta occurred in two separable fractions. A low molecular mass form (relative mass (Mr) 170 000) is composed of a single polypeptide chain (Mr 70 000). This was derived from a larger form by molecular sieve chromatography at both low (10 mM) and high (500 mM) NaCl concentration. The larger form of beta-galactosidase also contains small amounts of two polypeptides with apparent Mr values of 23 000 and 35 000 daltons. Both forms of the enzyme hydrolyze synthetic aryl galactosides and natural glycolipid substrates at comparable rates. Antibodies raised in rabbits against the low Mr beta-galactosidase also cross-reacts with the high Mr enzyme. The antibody preparation also cross-reacted with beta-hexosaminidase even though the latter was found at very low levels in the antigen, as judged by lack of detection of representative protein bands on sodium dodecyl sulfate - polyacrylamide gel electrophoresis and enzyme activity measurements. A portion of this cross-reactivity (35%) against beta-hexosaminidase could not be absorbed from the preparation without the simultaneous loss of beta-galactosidase activity, suggesting that the two enzymes show a degree of antigenic identity.

Studies on the activation of the enzymatic hydrolysis of sphingomyelin liposomes

Two pH optima were observed for the hydrolysis of sphingomyelin liposomes by brain and fibroblast extracts; one at pH 4.2-4.5, the other at pH 7-8. The proportion of the acidic activity in fibroblasts was affected greatly by the culturing conditions. Both the acidic and neutral enzyme activities were deficient in Niemann-Pick Type A fibroblasts, suggesting that both were genetically related. Partially purified activators from normal as well as Gaucher disease spleen stimulated the hydrolysis of sphingomyelin, at both pH values, by fibroblast and brain extracts. After further purification by DE-52 and Sephacryl 200 column chromatography the Gaucher activator retained its ability to stimulate sphingomyelinase and was active as well towards beta-glucocerebrosidase and beta-galactocerebrosidase.

Monoclonal antibodies against human placental sphingomyelinase

Monoclonal antibodies against human placental acid sphingomyelinase have been raised. The antibodies are all of the IgG1 type, and are quite specific for the enzyme. One of the antibodies has been used to demonstrate a common antigenic identity of three polypeptides (mol.wts. 90,000, 72,000, and 48,000) of a purified sphingomyelinase preparation.

Enzymatic hydrolysis of sphingomyelin liposomes by normal tissues and tissues from patients with Niemann-Pick disease

Liposomes of [3H]sphingomyelin are readily hydrolyzed by extracts of human spleen, liver, cultured skin fibroblasts and purified placental sphingomyelinase in the absence of detergents. The pH optimum for hydrolysis by liver and spleen extracts was 6.5-7.0 while the fibroblast activity showed an optimum at pH 4.0-4.3. However, the pH optimum for purified placental sphingomyelinase in the presence of Triton X-100 (pH 5.0) is only slightly different from that displayed with liposomes (pH 5.3). The data clearly show that hydrolysis of liposomal sphingomyelin by sphingomyelinase is affected by the composition and purity of the enzyme source.

Improved purification of beta-galactosidase from rabbit brain: two separable fractions share kinetic and structural properties

beta-Galactosidase has been purified from rabbit brain by a procedure which gives substantially greater purification and yield than the previously reported method. The enzyme was solubilized in 4% aqueous butanol and purified by a procedure which included affinity chromatography on columns of concanavalin A - Sepharose (ConA-Sepharose) and aminophenylthiogalactoside Sepharose (APT galactoside-Sepharose). The activity was resolved by DEAE-Sepharose chromatography into two fractions; the first did not bind to the column and was eluted in the unbound fraction, while the second bound to the column and could be eluted with a salt gradient. The unbound and bound fractions were purified 7600-fold and 4900-fold, respectively, by the newly developed procedure. Both gave two closely migrating protein bands on polyacrylamide gel electrophoresis and the major contaminating protein was beta-hexosaminidase in each case. The enzyme in the unbound fraction had an isoelectric point (pI) of 6.7 and an apparent molecular weight by gel filtration of 114 000 +/- 10 000. The enzyme that bound to DEAE-Sepharose at pH 8.0 and comprised about 60% of the total acid beta-galactosidase activity of rabbit brain eluted from Sephacryl S-200 as a single peak with apparent molecular weight 140 000 +/- 10 000. The two fractions displayed similar relative specific activities towards the synthetic substrates and ganglioside GM1 and lactosyl ceramide. Neither enzyme hydrolyzed galactosyl ceramide. We have immunological evidence which suggests that the two fractions of beta-galactosidase are also structurally related.