Alessandra Barca

Effect of Saposins A and C on the Enzymatic Hydrolysis of Liposomal Glucosylceramide

The degradation of glucosylceramide in lysosomes is accomplished by glucosylceramidase with the assistance of, at least, another protein, saposin C (Sap C), which is generated from a large precursor together with three other similar proteins, saposins A, B, and D. In the present study, we have examined the effects of saposins on the enzymatic hydrolysis of glucosylceramide inserted in large and small phospholipid liposomes. The glucosylceramide contained in large unilamellar vesicles (LUV) was degraded by glucosylceramidase at a rate 7–8-fold lower than glucosylceramide inserted in small unilamellar vesicles (SUV). The separate addition of either Sap A or Sap C to the LUV system partially stimulated the sphingolipid degradation while saposins B and D had no effect. In the presence of both Sap A and Sap C, the rate of sphingolipid degradation was higher than the sum of the rates with the two saposins individually, indicating synergism in their actions. The stimulatory effect of the two saposins depended on the incorporation of an acidic phospholipid such as phosphatidylserine (PS) into LUV. The characteristics of glucosylceramidase activation by Sap C were different from those of Sap A. Sap C increased the rate of hydrolysis of both the artificial water soluble substrate, 4-methylumbelliferyl-β-d-glucopyranoside, and the lipid substrate, glucosylceramide, while Sap A only stimulated degradation of the sphingolipid. Also the binding properties of Saps A and C were markedly different. At acidic pH values, Sap C bound to PS-containing LUV and promoted the association of glucosylceramidase with the membrane. In contrast, Sap A had poor affinity for the membrane even in the presence of glucosylceramide; moreover, Sap A did not potentiate the capacity of Sap C to mediate glucosylceramidase binding. In conclusion, our results show that both Sap A and Sap C are required for maximal hydrolysis of glucosylceramide inserted in PS-containing LUV, that their effects are synergistic, and that their mode of action is different. Sap C is responsible for the membrane binding of glucosylceramidase, while Sap A stimulation is possibly related to its effect on the conformation of the enzyme. It can be envisaged that Sap A in conjunction with Sap C might have a physiological role in glucosylceramide degradation.

Saposin C induces pH-dependent destabilization and fusion of phosphatidylserine-containing vesicles

We have previously shown that saposin C (Sap C), a glucosylceramidase activator protein, interacts with phosphatidylserine (PS) large unilamellar vesicles (LUV), promoting the glucosylceramidase binding to the bilayer [(1993) FEBS Lett. 336, 159–162]. In the present paper the consequences of the Sap C interaction on the lipid organization of the vesicles are reported. It was found that Sap C perturbs the PS bilayer as shown by the release of an encapsulated fluorescent dye. Three different procedures, resonance energy transfer, gel filtration and electron microscopy, indicated that the activator protein is also able to make PS liposomes fuse. The effects of Sap C on PS vesicles were observed at low but not at neutral pH. The lipid composition of the bilayer also affected the Sap C‐induced destabilization; in fact, the presence of PS in mixed LUV was essential for significant leakage to occur. These results demonstrate for the first time that Sap C is a protein capable of destabilizing and fusing acidic phospholipid‐containing membranes in a pH‐dependent fashion.

Function of saposin C in the reconstitution of glucosylceramidase by phosphatidylserine liposomes

The function of saposin C (Sap C), a glucosylceramidase activator protein, in the enzyme stimulation by phosphatidylserine (PS) liposomes has been investigated. Using gel filtration experiments evidence was obtained for Sap C binding to PS large unilamellar vesicles (LUV) but not to glucosylceramidase. PS LUV, which by themselves are unable to tightly bind and stimulate the enzyme, acquire the capacity to also bind the enzyme after interaction with Sap C, making it express its full activity. Our results indicate that the primary step in the Sap C mode of action resides in its association with PS membranes; in turn, this association promotes the interaction between the membranes and glucosylceramidase.

Quality of colonoscopy in an organised colorectal cancer screening programme with immunochemical faecal occult blood test: the EQuIPE study (Evaluating Quality Indicators of the Performance of Endoscopy)

Objectives To assess variation in the main colonoscopy quality indicators in organised colorectal cancer (CRC) screening programmes based on faecal immunochemical test (FIT). Design Data from a case-series of colonoscopies of FIT-positive subjects were provided by 44 Italian CRC screening programmes. Data on screening history, endoscopic procedure and histology results, and additional information on the endoscopy centre and the endoscopists were collected. The adenoma detection rate (ADR) and caecal intubation rate (CIR) were assessed for the whole population and the individual endoscopists. To explore variation in the quality indicators, multilevel analyses were performed according to patient/centre/endoscopist characteristics. Results We analysed 75 569 (mean age: 61.3 years; men: 57%) colonoscopies for positive FIT performed by 479 endoscopists in 79 centres. ADR ranged from 13.5% to 75% among endoscopists (mean: 44.8%). ADR was associated with gastroenterology specialty (OR: 0.87 for others, 95% CI 0.76 to 0.96) and, at the endoscopy centre level, with the routine use of sedation (OR: 0.80 if occasional (<33%); 95% CI 0.64 to 1.00) and availability of screening-dedicated sessions (OR: 1.35; 95% CI 1.11 to 1.66). CIR ranged between 58.8% and 100% (mean: 93.1%). Independent predictors of CIR at the endoscopist level were the yearly number of screening colonoscopies performed (OR: 1.51 for endoscopists with >600 colonoscopies; 95% CI 1.11 to 2.04) and, at the endoscopy centre level, screening-dedicated sessions (OR: 2.18; 95% CI 1.24 to 3.83) and higher rates of sedation (OR: 0.47 if occasional; 95% CI 0.24 to 0.92). Conclusions The quality of colonoscopy was affected by patient-related, endoscopist-related and centre-related characteristics. Policies addressing organisational issues should improve the quality of colonoscopy in our programme and similar programmes.

Factor-V expression in platelets from human megakaryocytic culture.

The origin of platelet‐factor‐V has long been discussed. To elucidate whether and when human platelet‐factor‐V is synthesized by megakaryocytes, we utilized in vitro‐generated megakaryocytes capable of producing platelets. Factor‐V gene was silent in purified progenitors and megakaryocytic precursors but was expressed in late culture phase and maintained also in platelets. Similarly, factor‐V protein was expressed in mature proplatelet‐bearing megakaryocytes (immunofluorescence analysis); it was also detectable in cultured megakaryocytes and platelets (Western blotting) and within permeabilized cultured platelets (flow cytometry). The absence of other cells in our culture system indicates conclusively that human megakaryocytes synthesize factor‐V.

Studies on glucosylceramidase binding to phosphatidylserine liposomes: the role of bilayer curvature

The influence of phosphatidylserine (PS) liposome size on their capacity to activate and bind purified glucosylceramidase was investigated. Gel filtration and flotation experiments showed that large unilamellar vesicles (LUV) of either pure PS or PS in admixture with phosphatidylcholine (PC) are unable to tightly bind purified glucosylceramidase, and thus, to fully stimulate its activity. By contrast, small unilamellar vesicles (SUV) of PS adsorb glucosylceramidase can either be favoured or inhibited by factors affecting the bilayer curvature of PS liposomes. An increase of PS vesicle size induced by a fusogenic agent such as poly(ethylene glycol) (PEG), decreased enzyme binding and activity. On the contrary, the reduction of PS LUV size by sonication increased their stimulating ability. Enzyme association with PS SUV is reversible. In fact, glucosylceramidase bound to PS SUV was released from the lipid surface when the SUV were transformed into larger vesicles by PEG; dissociation from the vesicles resulted in a dramatic decrease of enzyme activity. Although PS LUV are unable to reconstitute glucosylceramidase, their association with oleic acid (OA) promotes the interaction with glucosylceramidase. This phenomenon is best explained in terms of OA-induced surface defects of PS LUV, with consequent exposure of the more hydrophobic part of the membrane and hence the improved binding of hydrophobic region/s of glucosylceramidase. Our data indicate that the physical organization of the PS-containing liposomes is of critical importance of glucosylceramidase reconstitution. The observation that physical changes of the lipid surface can markedly affect the enzyme activity offers a new approach to the study of glucosylceramidase regulation.

Direct mailing of faecal occult blood tests for colorectal cancer screening: a randomized population study from Central Italy

Background Sending faecal occult blood tests (FOBT) by mail has been proposed both as a method to increase participation and a way to reduce staff costs in colorectal cancer screening. Methods Two multicentre randomized controlled trials (ISRCTN10351276) were performed: one randomly assigned 3196 individuals who had previously participated in colorectal screening to receive a FOBT kit at home or a standard invitation; in the second, 4219 people aged 50–69 years who did not respond to a screening invitation were either sent a FOBT or a standard recall letter. The cost per returned kit was calculated in each arm. Results Participation was higher with direct FOBT mailing in both trials: relative risk 1.11 (95% CI 1.06–1.17) and 1.36 (95% CI 1.16–1.60) for previous responders and non-responders, respectively. The cost per returned kit for previous responders ranged from 4.24€ to 16.10€, and from 3.29€ to 7.36€ with FOBT mailing and standard invitation, respectively, not including staff costs; for non-responders it ranged from 17.13€ to 46.80€, and from 7.36€ to 18.30€ with FOBT mailing and standard recall, respectively. Conclusions The FOBT mailing strategy modestly increased participation. This method can be used on a population of previous responders to reduce personnel costs and workload. When used as a reminder to non-responders, this method increases costs.

Detection rate and predictive factors of sessile serrated polyps in an organised colorectal cancer screening programme with immunochemical faecal occult blood test: the EQuIPE study (Evaluating Quality Indicators of the Performance of Endoscopy).

Objectives To assess detection rate and predictive factors of sessile serrated polyps (SSPs) in organised colorectal cancer (CRC) screening programmes based on the faecal immunochemical test (FIT). Design Data from a case series of colonoscopies of FIT-positive subjects were provided by 44 Italian CRC screening programmes. Data on screening history, endoscopic procedure and histology results, and additional information on the endoscopy centre and the endoscopists were collected, including the age-standardised and sex-standardised adenoma detection rate (ADR) of the individual endoscopists. The SSP detection rate (SSP-DR) was assessed for the study population. To identify SSP-predictive factors, multilevel analyses were performed according to patient/centre/endoscopist characteristics. Results We analysed 72 021 colonoscopies, of which 1295 presented with at least one SSP (SSP-DR 1.8%; 95% CI 1.7% to 1.9%). At the per-patient level, SSP-DR was associated with males (OR 1.35; 95% CI 1.17 to 1.54) and caecal intubation (OR 3.75; 95% CI 2.22 to 6.34), but not with the FIT round. The presence of at least one advanced adenoma was more frequent among subjects with SSPs than those without (OR 2.08; 95% CI 1.86 to 2.33). At the per-endoscopist level, SSP-DR was associated with ADR (third vs first ADR quartile: OR 1.55; 95% CI 1.03 to 2.35; fourth vs first quartile: OR 1.89; 95% CI 1.24 to 2.90). Conclusion The low prevalence of SSPs and the lack of association with the FIT round argue against SSP as a suitable target for FIT-based organised programmes. Strict association of SSP-DR with the key colonoscopy quality indicators, namely caecal intubation rate and high ADR further marginalises the need for SSP-specific quality indicators in FIT-based programmes.

Appropriateness of the indication for colonoscopy: Is the endoscopist the 'gold standard'?

Background: The appropriate selection of patients for colonoscopy is crucial for an efficient use of endoscopy. The role of endoscopist in filtering out inappropriate referrals is largely unknown. Methods: A multicentre, prospective study was performed in which consecutive patients referred for colonoscopy during a 1-month period were enrolled. Before colonoscopy, the endoscopist assessed appropriateness of the endoscopic referral without directly consulting official guidelines, also collecting clinical and demographic variables. Appropriateness of the indication was eventually assessed by a group of experts based on the American Society for Gastrointestinal Endoscopy guidelines, representing the gold standard. Outcomes of the study were the inappropriateness rate and the main related causes, as well as the concordance rate between the endoscopists and the experts. A multivariate analysis was performed to identify predictors of inappropriateness. Results: One thousand seven hundred ninety-nine patients were enrolled in 20 centres, of which 1489 outpatients were included in the final analysis. According to the American Society for Gastrointestinal Endoscopy guidelines, 432 referrals were inappropriate, corresponding to an inappropriateness rate of 29%. At multivariate analysis, prescription of a repeated colonoscopy (≥2 colonoscopies in the same patient) was strongly associated with the inappropriateness of the indication (odds ratio: 8.8; 95% confidence interval: 6.2, 12.7). Postpolypectomy or post-colorectal cancer surveillance accounted for 77% of the inappropriate control procedures. A 79% concordance rate between endoscopist and expert assessment was found. Among the 317 discordant cases, postpolypectomy or post-colorectal cancer surveillance accounted for 51% of the cases, the endoscopists mistakenly classifying it as appropriate in 55% to 61% of the inappropriate cases. Conclusions: Inappropriateness in outpatient colonoscopy referrals remains high, surveillance procedures representing the most frequent source of inappropriateness.

Invitation strategies for colorectal cancer screening programmes: The impact of an advance notification letter

AIM To estimate the impact of an advance notification letter on participation in sigmoidoscopy (FS) and fecal immunochemical test (FIT) screening. METHODS Eligible subjects, invited in 3 Italian population based programmes using FS and in 5 using FIT, were randomised (1:1:1), within GP, to: A) standard invitation letter; B) advance notification followed after 1month by the standard invitation; and C) B+indication to contact the general practitioner (GP) to get advice about the decision to be screened. We calculated the 9-month attendance and the incremental cost of each strategy. We conducted a phone survey to assess GPs utilization and predictors of participation. RESULTS The advance notification was associated with a 20% increase in the attendance among 15,655 people invited for FS (B vs A - RR: 1.17, 95% CI: 1.10-1.25; C vs A - RR: 1.19, 95% CI: 1.12-1.27); the incremental cost ranged between 10 and 9 Euros. Participation in FIT screening (N=23,543) was increased only with simple pre-notification (B vs A - RR: 1.06, 95% CI: 1.02-1.10); the incremental cost was 22.5 Euros. GP consultation rate was not increased in group C. CONCLUSIONS An advance notification represents a cost-effective strategy to increase participation in FS screening; its impact on the response to FIT screening was limited.