Secondary deficiency of neuraminidase 1 contributes to CNS pathology in neurological mucopolysaccharidoses via hypersialylation of brain glycoproteins

Mucopolysaccharidoses (MPS) are lysosomal storage diseases caused by defects in catabolism of glycosaminoglycans. MPS I, II, III and VII are associated with lysosomal accumulation of heparan sulphate and manifest with neurological deterioration. Most of these neurological MPS currently lack effective treatments. Here, we report that, compared to controls, neuraminidase 1 (NEU1) activity is drastically reduced in brain tissues of neurological MPS patients and in mouse models of MPS I, II, IIIA, IIIB and IIIC, but not of other neurological lysosomal disorders not presenting with heparan sulphate storage. We further show that accumulated heparan sulphate disrupts the lysosomal multienzyme complex of NEU1 with cathepsin A (CTSA), β-galactosidase (GLB1) and glucosamine-6-sulfate sulfatase (GALNS) necessary to maintain enzyme activity, and that NEU1 deficiency is linked to partial deficiencies of GLB1 and GALNS in cortical tissues and iPSC-derived cortical neurons of neurological MPS patients. Increased sialylation of N-linked glycans in brain samples of human MPS III patients and MPS IIIC mice implicated insufficient processing of brain N-linked sialylated glycans, except for polysialic acid, which was reduced in the brains of MPS IIIC mice. Correction of NEU1 activity in MPS IIIC mice by lentiviral gene transfer ameliorated previously identified hallmarks of the disease, including memory impairment, behavioural traits, and reduced levels of the excitatory synapse markers VGLUT1 and PSD95. Overexpression of NEU1 also restored levels of VGLUT1-/PSD95-positive puncta in cortical neurons derived from iPSC of an MPS IIIA patient. Together, our data demonstrate that heparan sulphate-induced secondary NEU1 deficiency and aberrant sialylation of glycoproteins implicated in synaptogenesis, memory, and behaviour constitute a novel pathological pathway in neurological MPS spectrum crucially contributing to CNS pathology.

Graphical abstract

Structure of the immunoregulatory sialidase NEU1

Sialic acids linked to glycoproteins and glycolipids are important mediators of cell and protein recognition events. These sugar residues are removed by neuraminidases (sialidases). Neuraminidase-1 (sialidase-1 or NEU1) is a ubiquitously expressed mammalian sialidase located in lysosomes and on the cell membrane. Because of its modulation of multiple signaling processes, it is a potential therapeutic target for cancers and immune disorders. Genetic defects in NEU1 or in its protective protein cathepsin A (PPCA, CTSA) cause the lysosomal storage diseases sialidosis and galactosialidosis. To further our understanding of this enzyme's function at the molecular level, we determined the three-dimensional structure of murine NEU1. The enzyme oligomerizes through two self-association interfaces and displays a wide substrate-binding cavity. A catalytic loop adopts an inactive conformation. We propose a mechanism of activation involving a conformational change in this loop upon binding to its protective protein. These findings may facilitate the development of selective inhibitor and agonist therapies.

Structures of the mannose-6-phosphate pathway enzyme, GlcNAc-1-phosphotransferase

The mannose-6-phosphate (M6P) pathway is responsible for the transport of hydrolytic enzymes to lysosomes. N-acetylglucosamine-1-phosphotransferase (GNPT) catalyzes the first step of tagging these hydrolases with M6P, which when recognized by receptors in the Golgi diverts them to lysosomes. Genetic defects in the GNPT subunits, GNPTAB and GNPTG, cause the lysosomal storage diseases mucolipidosis types II and III. To better understand its function, we determined partial three-dimensional structures of the GNPT complex. The catalytic domain contains a deep cavity for binding of uridine diphosphate-N-acetylglucosamine, and the surrounding residues point to a one-step transfer mechanism. An isolated structure of the gamma subunit of GNPT reveals that it can bind to mannose-containing glycans in different configurations, suggesting that it may play a role in directing glycans into the active site. These findings may facilitate the development of therapies for lysosomal storage diseases.

Structure of the murine lysosomal multienzyme complex core

The enzymes β-galactosidase (GLB1) and neuraminidase 1 (NEU1; sialidase 1) participate in the degradation of glycoproteins and glycolipids in the lysosome. To remain active and stable, they associate with PPCA [protective protein cathepsin A (CTSA)] into a high-molecular weight lysosomal multienzyme complex (LMC), of which several forms exist. Genetic defects in these three proteins cause the lysosomal storage diseases GM1-gangliosidosis/mucopolysaccharidosis IV type B, sialidosis, and galactosialidosis, respectively. To better understand the interactions between these enzymes, we determined the three-dimensional structure of the murine LMC core. This 0.8-MDa complex is composed of three GLB1 dimers and three CTSA dimers, adopting a triangular architecture maintained through six copies of a unique GLB1-CTSA polar interface. Mutations in this contact surface that occur in GM1-gangliosidosis prevent formation of the LMC in vitro. These findings may facilitate development of therapies for lysosomal storage disorders.

Crystal structure of the nucleotide-metabolizing enzyme NTPDase4

The ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) are a family of enzymes found on the cell surface and in the lumen of certain organelles, that are major regulators of purinergic signaling. Their intracellular roles, however, have not been clearly defined. NTPDase4 (UDPase, ENTPD4) is a Golgi protein potentially involved in nucleotide recycling as part of protein glycosylation, and is also found in lysosomes, where its purpose is unknown. To further our understanding of NTPDase4 function, we determined its crystal structure. The enzyme adopts a wide open, inactive conformation. Differences in the nucleotide-binding site relative to its homologs could account for its substrate selectivity. The putative membrane-interacting loop of cell-surface NTPDases is drastically altered in NTPDase4, potentially affecting its interdomain dynamics at the Golgi membrane.

Identification of Allosteric Inhibitors against Active Caspase-6

Caspase-6 is a cysteine protease that plays essential roles in programmed cell death, axonal degeneration, and development. The excess neuronal activity of Caspase-6 is associated with Alzheimer disease neuropathology and age-dependent cognitive impairment. Caspase-6 inhibition is a promising strategy to stop early stage neurodegenerative events, yet finding potent and selective Caspase-6 inhibitors has been a challenging task due to the overlapping structural and functional similarities between caspase family members. Here, we investigated how four rare non-synonymous missense single-nucleotide polymorphisms (SNPs), resulting in amino acid substitutions outside human Caspase-6 active site, affect enzyme structure and catalytic efficiency. Three investigated SNPs were found to align with a putative allosteric pocket with low sequence conservation among human caspases. Virtual screening of 57,700 compounds against the putative Caspase-6 allosteric pocket, followed by in vitro testing of the best virtual hits in recombinant human Caspase-6 activity assays identified novel allosteric Caspase-6 inhibitors with IC50 and Ki values ranging from ~2 to 13 µM. This report may pave the way towards the development and optimisation of novel small molecule allosteric Caspase-6 inhibitors and illustrates that functional characterisation of rare natural variants holds promise for the identification of allosteric sites on other therapeutic targets in drug discovery.

Molecular Mechanism of Inhibition of Acid Ceramidase by Carmofur

Human acid ceramidase (AC) is a lysosomal cysteine amidase, which has received a great deal of interest in recent years as a potential target for the development of new therapeutics against melanoma and glioblastoma tumors. Despite the strong interest in obtaining structural information, only the structures of the apo-AC enzyme in its zymogen and activated conformations are available. In this work, the crystal structure of AC in complex with the covalent carmofur inhibitor is presented. Carmofur is an antineoplastic drug containing an electrophilic carbonyl reactive group that targets the catalytic cysteine. This novel structural data explains the basis of the AC inhibition, provides insights into the enzymatic properties of the protein, and is a great aid toward the structure-based drug design of potent inhibitors for AC, providing the detailed mechanism, which has eluded the scientific community for more than 30 years, of carmofur's mysterious 5-fluorouracil-independent antitumor activity.

The impact and indications for Oncotype DX on adjuvant treatment recommendations when third-party funding is unavailable

OBJECTIVES

Industry-supported decision impact studies demonstrate that Oncotype Dx (ODX) changes treatment recommendations (TR) in 24-40% of hormone receptor+/HER2- patients. ODX is not reimbursed by third-party payers in Australia, potentially resulting in more selective use. We sought to evaluate the impact of self-funded ODX on TRs.

METHODS

Data collected included demographics, tumor characteristics, indication for ODX and pre- and post-recurrence score (RS) TR. Primary endpoint was frequency of TR change and associations with TR change were sought.

RESULTS

Eighteen physicians contributed 382 patients (median age 54). A total of 232 (61%) of tumors were T1 and were grade 1, 2 and 3 in 49 (13%), 252 (66%) and 79 (21%). A total of 257 (67%) were node negative. Assay indications were: confirm need for chemotherapy (CT) (36%), confirm omission of CT (40%) and genuine equipoise (24%). RS was low (≤17) in 55%, intermediate (18-31) in 36% and high (≥32) in 9%. Thirty-eight percent of patients had TR change post-ODX. Sixty-five percent of patients recommended CT pre-ODX changed to hormone therapy alone (HT)-more likely if lower grade and if ER and/or PR > 10%. Fourteen percent of patients with pre-ODX TR for HT added CT-more likely if ER and/or PR ≤10% and if Ki67 > 15% Overall, TR for CT decreased from 47% to 24%.

CONCLUSION

Patient-funded ODX changed TRs in 38% of patients, de-escalating 65% from CT to HT and adding CT to 14% of those recommended HT. These changes were greater than an industry-funded study suggesting that physicians can identify situations where the assay may influence decisions.

Crystal structure of saposin D in an open conformation

Saposins are accessory proteins that aid in the degradation of sphingolipids by hydrolytic enzymes. Their structure usually comprises four α-helices arranged in various conformations including an open, V-shaped form that is generally associated with the ability to interact with membranes and/or enzymes to accentuate activity. Saposin D is required by the lysosomal hydrolase, acid ceramidase, which breaks down ceramide into sphingosine and free fatty acid, to display optimal activity. The structure of saposin D was previously determined in an inactive conformation, revealing a monomeric, closed and compact form. Here, we present the crystal structure of the open, V-shaped form of saposin D. The overall shape is similar to the open conformation found in other saposins with slight differences in the angles between the α-helices. The structure forms a dimer that serves to stabilize the hydrophobic surface exposed in the open form, which results in an internal, hydrophobic cavity that could be used to carry extracted membrane lipids.

Structural basis for nucleotide recognition by the ectoenzyme CD203c

The ecto-nucleotide pyrophosphatase/phosphodiesterase (NPP) enzyme family modulates purinergic signaling by degrading extracellular nucleotides. CD203c (NPP3, ENPP3) regulates the inflammatory response of basophils via ATP hydrolysis and is a marker for allergen sensitivity on the surface of these cells. Multiple other roles and substrates have also been proposed for this protein. In order to gain insight into its molecular functions, we determined the crystal structure of human NPP3 as well as its complex with an ATP analog. The enzyme exhibits little preference for nucleobase type, and forms specific contacts with the alpha and beta phosphate groups of its ligands. Dimerization of the protein does not affect its catalytic activity. These findings expand our understanding of substrate recognition within the NPP family.

DATABASE

Structural data are available in the Protein Data Bank under the accession numbers 6C01 (human NPP3) and 6C02 (human NPP3 T205A N594S with AMPCPP).

Structural basis for the activation of acid ceramidase

Acid ceramidase (aCDase, ASAH1) hydrolyzes lysosomal membrane ceramide into sphingosine, the backbone of all sphingolipids, to regulate many cellular processes. Abnormal function of aCDase leads to Farber disease, spinal muscular atrophy with progressive myoclonic epilepsy, and is associated with Alzheimer’s, diabetes, and cancer. Here, we present crystal structures of mammalian aCDases in both proenzyme and autocleaved forms. In the proenzyme, the catalytic center is buried and protected from solvent. Autocleavage triggers a conformational change exposing a hydrophobic channel leading to the active site. Substrate modeling suggests distinct catalytic mechanisms for substrate hydrolysis versus autocleavage. A hydrophobic surface surrounding the substrate binding channel appears to be a site of membrane attachment where the enzyme accepts substrates facilitated by the accessory protein, saposin-D. Structural mapping of disease mutations reveals that most would destabilize the protein fold. These results will inform the rational design of aCDase inhibitors and recombinant aCDase for disease therapeutics.

Acid ceramidase (aCDase) hydrolyzes lysosomal membrane ceramide into sphingosine and its dysfunction leads to a variety of disease phenotypes. Here, the authors present structures of aCDase in its proenzyme and autocleaved forms, which provides insight into its mechanism of action.

MRI Features Can Predict 1p/19q Status in Intracranial Gliomas

BACKGROUND AND PURPOSE

The 2016 revision of the World Health Organization Classification of Tumors of the Central Nervous System mandates codeletion of chromosomes 1p and 19q for the diagnosis of oligodendroglioma. We studied whether conventional MR imaging features could predict 1p/19q status.

MATERIALS AND METHODS

Patients with previous 1p/19q testing were identified through pathology department records, typically performed on the basis of an oligodendroglial component on routine histology; 69 patients met the inclusion criteria. Preoperative imaging of patients with grade II or III gliomas was retrospectively assessed by 2 neuroradiologists, blinded to the 1p/19q status. Thirteen MR imaging features were first assessed in a small initial cohort (n = 10), after which the criteria were narrowed for the remaining patients as a validation cohort.

RESULTS

There was 85% agreement between radiologists for the overall prediction of 1p/19q status in the validation cohort, with an accuracy of 84%. The presence of >50% T2-FLAIR mismatch and calcification was found to be the most useful for predicting 1p/19q status. The >50% T2-FLAIR mismatch variable was demonstrated in 14 tumors and had 100% specificity for identifying a noncodeleted tumor (P = .001), with 97% interobserver correlation. Calcification was visualized in 7 tumors, 6 of which were 1p/19q codeleted (specificity, 97%; P = .006), with 100% interobserver correlation.

CONCLUSIONS

The presence of >50% T2-FLAIR mismatch is highly predictive of a noncodeleted tumor, while calcifications suggest a 1p/19q codeleted tumor. If formal 1p/19q testing is not possible, a combined MR imaging-histologic assessment may improve the diagnostic accuracy over histology alone.

Mechanism of Injury and Clinical Variables in Thoracic Spine Fracture: A Case Control Study

Objective

To determine the mechanisms of injury and clinical findings significantly associated with traumatic thoracic spine (T-spine) fractures.

Methods

This was a case-control study in a tertiary adult trauma centre. Cases were patients admitted with traumatic T-spine fractures between January 1999 and August 2007, inclusive. Each case had two controls matched for gender, age and injury severity. Data were collected from patient medical records and the trauma service database. Factors potentially associated with T-spine fracture were derived from the literature, expert consensus and univariate analysis. Multivariate logistic regression was employed to determine factors significantly associated with T-spine fracture.

Results

Two hundred and sixty one cases and 512 controls were enrolled. Univariate analysis showed the mechanisms of fall from a height ≥2 meters (m) and motorbike accident ≥60 kilometers per hour were significantly associated with T-spine fracture (p<0.001). The clinical findings of thoracic back pain, tenderness, intoxication, step deformity and abnormal neurological symptoms were also significantly associated with T-spine fracture (p<0.05). Multivariate analysis indicated that falls from a height of ≥2 m and thoracic back pain were significantly and positively associated with T-spine fracture (p<0.001). However, intoxication was negatively associated with T-spine fracture.

Conclusions

Patients with T-spine injury are significantly more likely to have fallen from a height ≥2 m or to have had thoracic back pain but less likely to be intoxicated. These findings should be validated prospectively prior to development of clinical guidelines for the identification of patients who may benefit from CT screening of the thoracic spine.

A key tyrosine substitution restricts nucleotide hydrolysis by the ectoenzyme NPP5

The ecto-nucleotide pyrophosphatase/phosphodiesterase (NPP) family of proteins mediates purinergic signaling by degrading extracellular nucleotides and also participates in phospholipid metabolism. NPP5 (ENPP5) is the least characterized member of this group and its specific role is unknown. This enzyme does not display activity on certain nucleotides and on other typical NPP substrates. In order to gain insights into its function, we determined the crystal structure of human and murine NPP5. Structural comparison with close homologs revealed a key phenylalanine to tyrosine substitution that prevents efficient hydrolysis of nucleotide diphosphates and triphosphates; reversal of this mutation enabled degradation of these molecules. Interestingly, NPP5 is able to cleave nicotinamide adenine dinucleotide (NAD), suggesting a potential role of this enzyme in NAD-based neurotransmission. An NPP5-specific metal binding motif is found adjacent to the active site, although its significance is unclear. These findings expand our understanding of substrate specificity within the NPP family.

DATABASE

Structural data are available in the Protein Data Bank under the accession numbers 5VEM, 5VEN, and 5VEO.

Determinants of bone mineral density in young Australian women; results from the Safe-D study

The study aimed to explore determinants of bone parameters in young women. Most bone parameters were associated with height and lean mass. Bone parameters were not associated with vitamin D status. Future research should address whether interventions aimed at improving lean mass are beneficial to bone health in young women.

INTRODUCTION

The implementation of prevention strategies during young adulthood may be crucial for osteoporosis prevention in later life, yet literature examining the determinants of bone health in premenopausal women is limited. We aimed to assess determinants of bone health, including serum 25-hydroxyvitamin D (25OHD), in females aged 16-25 years, living in Victoria, Australia, recruited through Facebook advertising.

METHODS

Serum 25OHD was measured by liquid chromatography-tandem mass spectrometry and bone health was measured using dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) in 326 participants.

RESULTS

Mean (± standard deviation) serum 25OHD was 69 ± 28 nmol/L and the prevalence of vitamin D deficiency (serum 25OHD <50 nmol/L) was 26%. Seven percent of participants (n = 23) reported taking a vitamin D supplement. Two percent of participants had low lumbar spine bone mineral density (Z-score <-2.0), 5% at the hip and 7% at the femoral neck. Serum 25OHD levels were not associated with DXA bone parameters, nor with pQCT bone parameters. Most bone parameters were positively associated with height and lean mass.

CONCLUSION

Vitamin D status was not associated with bone health in young women in the current study. Our findings suggest that targeting other modifiable factors, such as lean body mass, is likely to be beneficial to bone health in young women. Longitudinal studies examining the association between vitamin D status and bone health in young women are necessary to confirm our findings. In addition, whether raising 25OHD levels is advantageous for young women's bone health is yet to be determined.

Bone loss with antiepileptic drug therapy: a twin and sibling study

Changes in areal bone mineral density (aBMD) and other predictors of bone loss were evaluated in 48 same-sex twin/age-matched sibling pairs discordant for antiepileptic drug (AED) use. AED users had reduced BMD at the hip regions. Prolonged AED users had greater aBMD loss, predicting a higher risk of bone fragility.

INTRODUCTION

To investigate the longitudinal associations of bone mineral measures with antiepileptic drug (AED) use, including enzyme-inducing (EIAED) and non-enzyme-inducing (NEIAED) types, and other predictors of bone loss in a study of 48 same-sex twin/age-matched sibling pairs (40 female, 8 male) discordant for AED use.

METHODS

Using dual-energy X-ray absorptiometry (DXA), areal bone mineral density (aBMD) and content (BMC) at the hip regions, forearm, lumbar spine, and whole body were measured twice, at least 2 years apart. The mean within-pair difference (MWPD), MWPD%, and mean annual rate of aBMD change were adjusted for age, weight, and height. Predictors of bone loss were evaluated.

RESULTS

AED users, compared to non-users, at baseline and follow-up, respectively, had reduced aBMD at the total hip (MWPD% 3.8, 4.4%), femoral neck (4.7, 4.5%), and trochanter regions (4.1, 4.6%) (p < 0.05). For the whole cohort, the annual rate of change in all aBMD/BMC (p > 0.05) regions did not differ within pairs. Nevertheless, EIAED users had greater aBMD loss than non-users (n = 20 pairs) at the total hip (1.7 vs. 0.3%, p = 0.013) and whole body regions (0.7% loss vs. 0.1% BMD gain, p = 0.019), which was not found in NEIAED-discordant pairs (n = 16). AED use >20 years predicted higher aBMD loss at the forearm (p = 0.028), whole body (p = 0.010), and whole body BMC (p = 0.031).

CONCLUSIONS

AED users had reduced aBMD at the hip regions. Prolonged users and EIAED users had greater aBMD loss, predicting a higher risk of bone fragility. Further prospective studies of AED effects on bone microarchitecture are needed.

The association between inflammation, obesity and elevated blood pressure in 16-25-year-old females

There is evidence to show an association between inflammation, obesity and elevated blood pressure. However, there is limited data for this relationship in adolescent females. We aimed to investigate the association between high sensitivity C-reactive protein (hs-CRP) and elevated blood pressure in young Australian females. Women aged 16-25 years living in Victoria were randomly recruited via targeted Facebook advertising. Socio-demographic information was collected via a web-based questionnaire. Anthropometric and blood pressure measurements were conducted by trained staff. Hs-CRP was assessed using the Abbott Architect assay. The demographic data were collected from 639 females (mean ±s.d. age: 22±3). The blood pressure data were available for 502 participants. Approximately 28% had elevated blood pressure (defined by a blood pressure reading ⩾120-139/80-89 mm Hg for adults and >90th and <95th percentiles for age, sex and height for adolescents). Approximately 24% had hs-CRP >3.0 mg l^-1 and 30% were overweight or obese. In multivariable logistic regression analyses, obese females (OR: 5.5, 95% CI: 2.4-12.5, P<0.001) were more likely to have elevated blood pressure compared with those with a body mass index (BMI) in the normal range. Elevated hs-CRP levels were associated with an increased odds of elevated blood pressure (OR: 3.4, 95% CI: 1.8-6.3, P<0.001). However, this association was no longer significant after adjustment for BMI. Findings from this study demonstrate that hs-CRP and obesity are associated with elevated blood pressure in young females. Thus, our findings may promote further research into the underlying mechanisms of these associations and related long-term health risks.

Crystal structure of the human alkaline sphingomyelinase provides insights into substrate recognition

Absorption of dietary sphingomyelin (SM) requires its initial degradation into ceramide, a process catalyzed by the intestinal enzyme alkaline sphingomyelinase (alk-SMase, NPP7, ENPP7). alk-SMase belongs to the nucleotide pyrophosphatase/phosphodiesterase (NPP) family, the members of which hydrolyze nucleoside phosphates, phospholipids, and other related molecules. NPP7 is the only paralog that can cleave SM, and its activity requires the presence of bile salts, a class of physiological anionic detergents. To elucidate the mechanism of substrate recognition, we determined the crystal structure of human alk-SMase in complex with phosphocholine, a reaction product. Although the overall fold and catalytic center are conserved relative to other NPPs, alk-SMase recognizes the choline moiety of its substrates via an NPP7-specific aromatic box composed of tyrosine residues. Mutational analysis and enzymatic activity assays identified features on the surface of the protein-a cationic patch and a unique hydrophobic loop-that are essential for accessing SM in bile salt micelles. These results shed new light on substrate specificity determinants within the NPP enzyme family.

Crystal Structure of the Acid Sphingomyelinase-like Phosphodiesterase SMPDL3B Provides Insights into Determinants of Substrate Specificity

The enzyme acid sphingomyelinase-like phosphodiesterase 3B (SMPDL3B) was shown to act as a negative regulator of innate immune signaling, affecting cellular lipid composition and membrane fluidity. Furthermore, several reports identified this enzyme as an off target of the therapeutic antibody rituximab, with implications in kidney disorders. However, structural information for this protein is lacking. Here we present the high resolution crystal structure of murine SMPDL3B, which reveals a substrate binding site strikingly different from its paralogs. The active site is located in a narrow boot-shaped cavity. We identify a unique loop near the active site that appears to impose size constraints on incoming substrates. A structure in complex with phosphocholine indicates that the protein recognizes this head group via an aromatic box, a typical choline-binding motif. Although a potential substrate for SMPDL3B is sphingomyelin, we identify other possible substrates such as CDP-choline, ATP, and ADP. Functional experiments employing structure-guided mutagenesis in macrophages highlight amino acid residues potentially involved in recognition of endogenous substrates. Our study is an important step toward elucidating the specific function of this poorly characterized enzyme.

Crystal structure of mammalian acid sphingomyelinase

Acid sphingomyelinase (ASMase, ASM, SMPD1) converts sphingomyelin into ceramide, modulating membrane properties and signal transduction. Inactivating mutations in ASMase cause Niemann-Pick disease, and its inhibition is also beneficial in models of depression and cancer. To gain a better understanding of this critical therapeutic target, we determined crystal structures of mammalian ASMase in various conformations. The catalytic domain adopts a calcineurin-like fold with two zinc ions and a hydrophobic track leading to the active site. Strikingly, the membrane interacting saposin domain assumes either a closed globular conformation independent from the catalytic domain, or an open conformation, which establishes an interface with the catalytic domain essential for activity. Structural mapping of Niemann-Pick mutations reveals that most of them likely destabilize the protein's fold. This study sheds light on the molecular mechanism of ASMase function, and provides a platform for the rational development of ASMase inhibitors and therapeutic use of recombinant ASMase.

Impact of insulin initiation on glycaemic variability and glucose profiles in a primary healthcare Type 2 diabetes cohort: analysis of continuous glucose monitoring data from the INITIATION study

AIM

To use continuous glucose monitoring to examine the effects of insulin initiation with glargine, with or without glulisine, on glycaemic variability and glycaemia in a cohort of people with Type 2 diabetes receiving maximum oral hypoglycaemic agents in primary healthcare.

METHODS

We conducted a post hoc analysis of continuous glucose monitoring data from 89 participants at baseline and at 24 weeks after insulin commencement. Indicators of glycaemic variability (standard deviation, J-index and mean amplitude of glycaemic excursion) and glycaemia (HbA1c , mean glucose, area under the glucose-time curve) were assessed. Multi-level regression analysis was used to identify the predictors of change.

RESULTS

Complete glycaemic variability data were available for 78 participants. Of these participants, 41% were women, their mean (sd) age was 59.2 (10.4) years, the median (interquartile range) diabetes duration was 10.4 (6.5, 13.3) years and the median (interquartile range) baseline HbA1c was 82.5 (71.6, 96.7) mmol/mol [9.7 (8.7, 11.0)%]. At baseline, BMI correlated negatively with standard deviation (r = -0.30) and mean amplitude of glycaemic excursion (r = -0.26), but not with J-index; HbA1c correlated with J-index (r = 0.61) but not with mean amplitude of glycaemic excursion and standard deviation. After insulin initiation the mean (sd) glucose level decreased [from 12.0 (3.0) to 8.5 (1.6) mmol/l; P < 0.001], as did the median (interquartile range) J-index [from 66.9 (47.7, 95.1) to 36.9 (27.6, 49.8) mmol/l; P < 0.001]. Baseline HbA1c correlated with a greater J-index reduction (r = -0.45; P < 0.001). The mean amplitude of glycaemic excursion and standard deviation values were unchanged. The baseline temporal profile, showing elevated postprandial morning glucose levels, was unchanged after insulin initiation, despite an overall reduction in glycaemia.

CONCLUSION

Insulin initiation reduced hyperglycaemia but did not alter glycaemic variability in adults with Type 2 diabetes receiving maximum oral hypoglycaemic agents. The most significant postprandial excursions were seen in the morning, which identifies prebreakfast as the most effective target for short-acting insulin therapy.

Structural Basis for Nucleotide Hydrolysis by the Acid Sphingomyelinase-like Phosphodiesterase SMPDL3A

Sphingomyelin phosphodiesterase, acid-like 3A (SMPDL3A) is a member of a small family of proteins founded by the well characterized lysosomal enzyme, acid sphingomyelinase (ASMase). ASMase converts sphingomyelin into the signaling lipid, ceramide. It was recently discovered that, in contrast to ASMase, SMPDL3A is inactive against sphingomyelin and, surprisingly, can instead hydrolyze nucleoside diphosphates and triphosphates, which may play a role in purinergic signaling. As none of the ASMase-like proteins has been structurally characterized to date, the molecular basis for their substrate preferences is unknown. Here we report crystal structures of murine SMPDL3A, which represent the first structures of an ASMase-like protein. The catalytic domain consists of a central mixed β-sandwich surrounded by α-helices. Additionally, SMPDL3A possesses a unique C-terminal domain formed from a cluster of four α-helices that appears to distinguish this protein family from other phosphoesterases. We show that SMDPL3A is a di-zinc-dependent enzyme with an active site configuration that suggests a mechanism of phosphodiester hydrolysis by a metal-activated water molecule and protonation of the leaving group by a histidine residue. Co-crystal structures of SMPDL3A with AMP and α,β-methylene ADP (AMPCP) reveal that the substrate binding site accommodates nucleotides by establishing interactions with their base, sugar, and phosphate moieties, with the latter the major contributor to binding affinity. Our study provides the structural basis for SMPDL3A substrate specificity and sheds new light on the function of ASMase-like proteins.

Outcomes in emergency general surgery following the introduction of a consultant-led unit

BACKGROUND

Patients presenting with emergency surgical conditions place significant demands on healthcare services globally. The need to improve emergency surgical care has led to establishment of consultant-led emergency surgery units. The aim of this study was to determine the effect of a changed model of service on outcomes.

METHODS

A retrospective observational study of all consecutive emergency general surgical admissions in 2009-2012 was performed. A 2-year time frame before and after the establishment of the emergency general surgery (EGS) service was used to determine the number of admissions and operations, emergency department and hospital length of stay, as well as complication rates.

RESULTS

The study included 7233 acute admissions. The EGS service managed 4468 patients (61·6 per cent increase) and performed 1804 operations (41·0 per cent increase). The most common diagnoses during the EGS period included acute appendicitis (532, 11·9 per cent), biliary disease (361, 8·1 per cent) and abdominal pain (561, 12·6 per cent). Appendicectomy (536, 29·7 per cent), cholecystectomy (239, 13·2 per cent) and laparotomy (226, 12·5 per cent) were the most commonly performed procedures. In the EGS period, time in the emergency department was reduced (from 8·0 to 6·0 h; P < 0·001), as was length of hospital stay (from 3·0 to 2·0 days; P < 0·001). The number of complications was reduced by 46·8 per cent, from 172 (6·2 per cent) to 147 (3·3 per cent) (P < 0·001), with a 53 per cent reduction in the number of deaths in the EGS period, from 29 (16·9 per cent) to seven (8 per cent) (P = 0·039).

CONCLUSION

The establishment of a consultant-led emergency surgical service has been associated with improved provision of care, resulting in timely management and improved clinical outcomes.

Efficacy of thiopurines and adalimumab in preventing Crohn's disease recurrence in high-risk patients - a POCER study analysis

BACKGROUND

Crohn's disease recurs in the majority of patients after intestinal resection.

AIM

To compare the relative efficacy of thiopurines and anti-TNF therapy in patients at high risk of disease recurrence.

METHODS

As part of a larger study comparing post-operative management strategies, patients at high risk of recurrence (smoker, perforating disease, ≥2nd operation) were treated after resection of all macroscopic disease with 3 months metronidazole together with either azathioprine 2 mg/kg/day or mercaptopurine 1.5 mg/kg/day. Thiopurine-intolerant patients received adalimumab induction then 40 mg fortnightly. Patients underwent colonoscopy at 6 months with endoscopic recurrence assessed blind to treatment.

RESULTS

A total of 101 patients [50% male; median (IQR) age 36 (25-46) years] were included. There were no differences in disease history between thiopurine- and adalimumab-treated patients. Fifteen patients withdrew prior to 6 months, five due to symptom recurrence (of whom four were colonoscoped). Endoscopic recurrence (Rutgeerts score i2-i4) occurred in 33 of 73 (45%) thiopurine vs. 6 of 28 (21%) adalimumab-treated patients [intention-to-treat (ITT); P = 0.028] or 24 of 62 (39%) vs. 3 of 24 (13%) respectively [per-protocol analysis (PPA); P = 0.020]. Complete mucosal endoscopic normality (Rutgeerts i0) occurred in 17/73 (23%) vs. 15/28 (54%) (ITT; P = 0.003) and in 27% vs. 63% (PPA; P = 0.002). The most advanced disease (Rutgeerts i3 and i4) occurred in 8% vs. 4% (thiopurine vs. adalimumab).

CONCLUSIONS

In Crohn's disease patients at high risk of post-operative recurrence adalimumab is superior to thiopurines in preventing early disease recurrence.

Geographical variation in incidence of knee arthroscopy for patients with osteoarthritis: a population-based analysis of Victorian hospital separations data

BACKGROUND/AIM

To evaluate the frequency and geographical variation in knee arthroscopy for adults (>25 years) with a concomitant diagnosis of osteoarthritis.

METHODS

This was a retrospective cohort study of hospital separations involving an elective knee arthroscopy in public and private hospitals in Victoria, Australia. Participants included patients receiving knee arthroscopies with a diagnosis code indicating osteoarthritis (OA) from 1 July 2008 to 30 June 2009. Records were excluded if the patient was under 25 years or their arthroscopy involved a ligament reconstruction. Crude rates per 100 000 population and negative binomial regression offset by total knee arthroscopy volume were used to analyse differences by region.

RESULTS

There were 9620 arthroscopic procedures meeting the inclusion criteria. There were 5500 (57.2%) admissions where the principal diagnosis was knee OA (gonarthrosis) and 3510 (36.5%) where the principal diagnosis indicated a mechanical derangement and there was a primary or associated diagnosis of OA. When we examined the incidence rate ratios (IRR) by region, after adjustment for relevant factors and accounting for the total knee arthroscopy volume within each region, we identified significant variation in knee arthroscopy rates for patients with OA. The region with the highest adjusted IRR was Barwon South Western (IRR: 1.26, 95% confidence interval (CI): 1.16-1.36) and the region with lowest adjusted incidence rate ratio was the Gippsland region (IRR: 0.89, 95% CI: 0.80-0.98).

CONCLUSIONS

We identified considerable geographical variation in arthroscopies for people with OA across Victoria. Further investigation is needed to understand whether this variation is a reflection of differences in OA prevalence, clinical decision-making or access.

Type 2 diabetes does not worsen prognosis in hepatocellular carcinoma

INTRODUCTION

Type 2 diabetes (T2DM) is associated with liver inflammation and carcinogenesis. The prevalence of T2DM among patients with liver cirrhosis and hepatocellular carcinoma is increasing. However, the effect of T2DM on the natural history of hepatocellular carcinoma is not known.

AIM

To examine the effect of T2DM on hepatocellular carcinoma (HCC) survival in treated and untreated disease.

METHODS

Retrospective analysis was performed on HCC cases diagnosed during 2000-2005, and prospectively during 2006-August 2007. Demographics, HCC staging, response to treatment, and survival were collected. A comparison was made between patients with T2DM and without T2DM.

RESULTS

One hundred and thirty-five patients were recruited in total; 58 (43%) had T2DM. Seventy (37 diabetic) patients were treated with percutaneous radiological therapies, with 168 treatments given. Treatment was determined by AASLD guidelines and patient tolerance, there was no randomisation. There was no significant difference in survival between diabetic and nondiabetic patients. There was a nonsignificant trend towards greater survival in diabetic patients (overall median survival diabetics 21 mths vs nondiabetics 5 mths, P=0.355).

CONCLUSIONS

T2DM does not negatively impact on the natural history of treated or untreated HCC.

Structural basis of carbohydrate recognition by calreticulin

The calnexin cycle is a process by which glycosylated proteins are subjected to folding cycles in the endoplasmic reticulum lumen via binding to the membrane protein calnexin (CNX) or to its soluble homolog calreticulin (CRT). CNX and CRT specifically recognize monoglucosylated Glc(1)Man(9)GlcNAc(2) glycans, but the structural determinants underlying this specificity are unknown. Here, we report a 1.95-Å crystal structure of the CRT lectin domain in complex with the tetrasaccharide α-Glc-(1→3)-α-Man-(1→2)-α-Man-(1→2)-Man. The tetrasaccharide binds to a long channel on CRT formed by a concave β-sheet. All four sugar moieties are engaged in the protein binding via an extensive network of hydrogen bonds and hydrophobic contacts. The structure explains the requirement for glucose at the nonreducing end of the carbohydrate; the oxygen O(2) of glucose perfectly fits to a pocket formed by CRT side chains while forming direct hydrogen bonds with the carbonyl of Gly(124) and the side chain of Lys(111). The structure also explains a requirement for the Cys(105)-Cys(137) disulfide bond in CRT/CNX for efficient carbohydrate binding. The Cys(105)-Cys(137) disulfide bond is involved in intimate contacts with the third and fourth sugar moieties of the Glc(1)Man(3) tetrasaccharide. Finally, the structure rationalizes previous mutagenesis of CRT and lays a structural groundwork for future studies of the role of CNX/CRT in diverse biological pathways.

A prospective randomized trial of itraconazole vs fluconazole for the prevention of fungal infections in patients with acute leukemia and hematopoietic stem cell transplant recipients

Fluconazole antifungal prophylaxis is standard care in allogeneic hematopoietic stem cell transplant (HSCT) recipients, but this drug lacks anti-Aspergillus activity, the primary cause of invasive fungal infection (IFI) in many transplantation centers. We performed a randomized trial to compare itraconazole vs fluconazole, for prevention of IFIs in patients with acute leukemia (AL) and HSCT recipients. One hundred and ninety-five patients were randomly assigned to either fluconazole or itraconazole antifungal prophylaxis, after stratification into high-risk and low-risk groups. Antifungal prophylaxis was started at the beginning of chemotherapy and continued until resolution of neutropenia, or until amphotericin B treatment was started. IFI occurred in 11 (11%) of itraconazole, and in 12 (12%) fluconazole recipients. Invasive candidiasis (IC) developed in two (2%) itraconazole and one (1%) fluconazole recipients, while invasive aspergillosis (IA) developed in nine (9%) itraconazole and 11(11%) fluconazole recipients. There was no difference in the incidence of total IFI, IC and IA between the two study arms. However, there was a nonsignificant trend towards reduced mortality among patients who developed IA while receiving itraconazole prophylaxis (3/9=33% vs 8/11=73%, P=0.095).

Preferential ATP-binding cassette transporter A1-mediated cholesterol efflux from late endosomes/lysosomes

Recently, ATP-binding cassette transporter A1 (ABCA1), the defective molecule in Tangier disease, has been shown to stimulate phospholipid and cholesterol efflux to apolipoprotein A-I (apoA-I); however, little is known concerning the cellular cholesterol pools that act as the source of cholesterol for ABCA1-mediated efflux. We observed a higher level of isotopic and mass cholesterol efflux from mouse peritoneal macrophages labeled with [(3)H]cholesterol/acetyl low density lipoprotein (where cholesterol accumulates in late endosomes and lysosomes) compared with cells labeled with [(3)H]cholesterol with 10% fetal bovine serum, suggesting that late endosomes/lysosomes act as a preferential source of cholesterol for ABCA1-mediated efflux. Consistent with this idea, macrophages from Niemann-Pick C1 mice that have an inability to exit cholesterol from late endosomes/lysosomes showed a profound defect in cholesterol efflux to apoA-I. In contrast, phospholipid efflux to apoA-I was normal in Niemann-Pick C1 macrophages, as was cholesterol efflux following plasma membrane cholesterol labeling. These results suggest that cholesterol deposited in late endosomes/lysosomes preferentially acts as a source of cholesterol for ABCA1-mediated cholesterol efflux.