Sphingomyelin/phosphatidylcholine/cholesterol phase diagram: boundaries and composition of lipid rafts

The ternary system palmitoylsphingomyelin (PSM)/palmitoyloleoylphosphatidylcholine (POPC)/cholesterol is used to model lipid rafts. The phase behavior of the three binary systems PSM/POPC, PSM/cholesterol, and POPC/cholesterol is first experimentally determined. Phase coexistence boundaries are then determined for ternary mixtures at room temperature (23 degrees C) and the ternary phase diagram at that temperature is obtained. From the diagram at 23 degrees C and the binary phase diagrams, a reasonable expectation is drawn for the ternary phase diagram at 37 degrees C. Several photophysical methodologies are employed that do not involve detergent extraction, in addition to literature data (e.g., differential scanning calorimetry) and thermodynamic rules. For the ternary phase diagrams, some tie-lines are calculated, including the one that contains the PSM/POPC/ cholesterol 1:1:1 mixture, which is often used in model raft studies. The diagrams here described are used to rationalize literature results, some of them apparently discrepant, and to discuss lipid rafts within the framework of liquid-ordered/liquid-disordered phase coexistence.

HCV-related fibrosis progression following liver transplantation: increase in recent years

BACKGROUND/AIMS

The natural history and predictors of HCV-related disease severity post-transplantation are uncertain. The aims of this study were to define the natural history of post-transplantation HCV infection by assessing the rate of fibrosis progression, to determine if the post-transplantation natural history differs from that observed pre-transplantation, and to identify predictors of post-transplantation disease progression.

METHODS

Post-transplantation biopsies (mean: 3+/-1.6/patient) from 284 patients were scored according to histologic stage, using the method of Desmet et al. Change in fibrosis score (fibrosis progression/year) post-transplantation was used as the primary outcome. Predictors analyzed included viral factors (genotype and viral load at transplantation), patient demographics, year of transplantation, country of transplantation, pre-transplantation fibrosis progression, immunosuppression and laboratory data.

RESULTS

There was a linear association between change in fibrosis score and time from transplantation, with a median rate of fibrosis progression per year of 0.3 (0.004-2.19/year). Using parametric time-to-event analysis, the expected median duration to cirrhosis was 10 years. The rate of post-transplantation fibrosis progression was significantly higher than pre-transplantation (0.2/year (0.09-0.8) p<0.0001), and higher in Spanish than US centers (0.48 (0.01-2.19) vs 0.28 (0.004-2.08); p=0.09) despite similar progression rates prior to transplantation. Variables independently associated with post-transplantation progression included year of transplantation (p=0.0001), race (p=0.02), number of methyl-prednisolone boluses (p=0.03), and HCV RNA levels at transplantation (p=0.01).

CONCLUSIONS

HCV-related disease progression is accelerated in immunocompromised compared to immunocompetent patients, with a progressive increase in patients who have recently undergone liver transplantation. Changes in patient management post-transplantation over time and between transplant centers may account for the increase in fibrosis progression observed in recent years.

Natural history of clinically compensated hepatitis C virus-related graft cirrhosis after liver transplantation

The natural history of clinically compensated hepatitis C virus (HCV) cirrhosis after liver transplantation is unknown. This information is relevant to transplant centers to improve the management of these patients and decide the optimal timing for retransplantation. The aims of the study were (1) to describe the natural history of patients with HCV-cirrhosis transplants in a center with annual liver biopsies, and (2) to determine predictors for clinical decompensation, retransplantation, and mortality rates. A total of 49 patients with HCV-graft cirrhosis, 39 clinically compensated at histologic diagnosis of cirrhosis (post-liver transplantation cirrhosis) were included and followed up for 1 year (15 days-3.5 years). All patients tested were infected with genotype 1b. Predictive variables included histologic activity index (HAI) at post-liver transplantation cirrhosis, liver function tests, age, sex, and maintenance immunosuppression. Eighteen of 39 patients developed at least 1 episode of decompensation after a median of 7.8 months (4 days-2.6 years; 93% ascites). The cumulative probability of decompensation was 8%, 17%, and 42% at 1, 6, and 12 months, respectively. Graft and patient survival rates were 100%, 85%, and 71% and 100%, 92%, and 74% at 1, 6, and 12 months, respectively. Patient survival rates dropped significantly once decompensation developed (93%, 61%, and 41% at 1, 6, and 12 months, respectively). Variables associated with decompensation, retransplantation, and mortality rate included a high Child-Pugh score (>A), low levels of albumin at post-liver transplantation cirrhosis, and a short interval between liver transplantation and post-liver transplantation cirrhosis. The natural history of clinically compensated HCV-graft cirrhosis is shortened when compared with immunocompetent patients. If retransplantation is considered, it should be performed promptly once decompensation develops.

High incidence of allograft cirrhosis in hepatitis C virus genotype 1b infection following transplantation: relationship with rejection episodes

The natural history of hepatitis C virus (HCV) infection following liver transplantation and predictors of disease severity remain controversial. The aims of the study were to assess in a homogeneous population of 81 cyclosporine-based HCV-infected liver transplant recipients mostly infected with genotype 1b and undergoing strict protocol annual biopsies: 1) the histological progression of posttransplantation HCV disease and, in particular, the incidence of HCV-related graft cirrhosis within the first 5 years after surgery; and 2) the relationship between progression to cirrhosis and i) rejection episodes and ii) first-year liver biopsy findings. We studied 81 consecutive HCV-RNA-positive patients (96% genotype 1b) undergoing liver transplantation between 1991 and 1996 with a minimum histological follow-up of 1 year. All patients received cyclosporine-based immunosuppression and underwent protocol yearly liver biopsies for the first 5 years. The mean histological follow-up was 32 months (range, 12-60 months). Biopsies were scored according to the histological activity index (HAI), with separate evaluation of grade (activity) and stage (fibrosis). Histological hepatitis, present in 97% of patients in the most recent biopsy, was moderate or severe in 64%. Twelve patients developed HCV-related cirrhosis at a median time of 24 months (range, 12-48 months), with an actuarial rate of HCV-cirrhosis of 3.7%, 8.5%, 16%, 28%, and 28% at 1, 2, 3, 4, and 5 years, respectively. Rejection was significantly more common among patients with cirrhosis versus those without (83% vs. 48%; P =.02), with an association between the incidence of cirrhosis and the number of rejection episodes: 5%, 15%, and 50% in patients without rejection, one and two episodes, respectively (P =.001). The degree of activity and fibrosis score in the first-year biopsy were higher in patients who developed cirrhosis than in those who did not (P =.008 and.18, respectively). In conclusion, HCV genotype 1b-infected liver recipients are at a high risk of developing graft cirrhosis in the first 4 to 5 years following transplantation, especially those with previous rejection episodes. First-year liver biopsies may help to sooner identify patients at the highest risk, improving further patient management.

Ceramide: a simple sphingolipid with unique biophysical properties

Ceramides are involved in a variety of cellular processes and in disease. Their biological functions are thought to depend on ceramides' unique biophysical properties, which promote strong alterations of cell membrane properties and consequent triggering of signaling events. Over the last decades, efforts were made to understand the impact of ceramide on membrane biophysical features. Several studies, performed in a multitude of membrane models, address ceramides' specific interactions, the effect of their acyl chain structure and the influence of membrane lipid composition and properties on ceramide biophysical outcome. In this review, a rationale for the multiple and complex changes promoted by ceramide is provided, highlighting, on a comprehensive and critical manner, the interactions between ceramides and specific lipids and/or lipid phases. Focus is also given to the interplay between ceramide and cholesterol, particularly in lipid raft-mimicking mixtures, an issue of intense debate due to the urgent need to understand the biophysical impact of ceramide formation in models resembling the cell membrane. The implications of ceramide-induced biophysical changes on lipid-protein interactions and cell signaling are also discussed, together with the emerging evidence for the existence of ceramide-gel like domains in cellular membranes.

Axonal plasticity and functional recovery after spinal cord injury in mice deficient in both glial fibrillary acidic protein and vimentin genes

The lack of axonal regeneration in the injured adult mammalian spinal cord leads to permanent functional disabilities. The inability of neurons to regenerate their axon is appreciably due to an inhospitable environment made of an astrocytic scar. We generated mice knock-out for glial fibrillary acidic protein and vimentin, the major proteins of the astrocyte cytoskeleton, which are upregulated in reactive astrocytes. These animals, after a hemisection of the spinal cord, presented reduced astroglial reactivity associated with increased plastic sprouting of supraspinal axons, including the reconstruction of circuits leading to functional restoration. Therefore, improved anatomical and functional recovery in the absence of both proteins highlights the pivotal role of reactive astrocytes in axonal regenerative failure in adult CNS and could lead to new therapies of spinal cord lesions.

Lipid Rafts have Different Sizes Depending on Membrane Composition: A Time-resolved Fluorescence Resonance Energy Transfer Study

The ternary lipid system palmitoylsphingomyelin (PSM)/palmitoyloleoylphosphatidylcholine (POPC)/cholesterol is a model for lipid rafts. Previously the phase diagram for that mixture was obtained, establishing the composition and boundaries for lipid rafts. In the present work, this system is further studied in order to characterize the size of the rafts. For this purpose, a time-resolved fluorescence resonance energy transfer (FRET) methodology, previously applied with success to a well-characterized phosphatidylcholine/cholesterol binary system, is used. It is concluded that: (1) the rafts on the low raft fraction of the raft region are small (below 20 nm), whereas on the other side the domains are larger; (2) on the large domain region, the domains reach larger sizes in the ternary system (> approximately 75-100 nm) than in binary systems phosphatidylcholine/cholesterol (between approximately 20 and approximately 75-100 nm); (3) the raft marker ganglioside G(M1) in small amounts (and excess cholera toxin subunit B) does not affect the general phase behaviour of the lipid system, but can increase the size of the rafts on the small to intermediate domain region. In summary, lipid-lipid interactions alone can originate lipid rafts on very different length scales. The conclusions presented here are consistent with the literature concerning both model systems and cell membrane studies.

Complete avoidance of calcineurin inhibitors in renal transplantation: a randomized trial comparing sirolimus and tacrolimus

Calcineurin inhibitors have decreased acute rejection and improved early renal allograft survival, but their use has been implicated in the development of chronic nephrotoxicity. We performed a prospective, randomized trial in kidney transplantation comparing sirolimus-MMF-prednisone to tacrolimus-MMF-prednisone. Eighty-one patients in the sirolimus group and 84 patients in the tacrolimus group were enrolled (mean follow-up = 33 months; range 13-47 months). At 1 year, patient survival was similar in the groups (98% with sirolimus, 96% with tacrolimus; p = 0.42) as was graft survival (94% sirolimus vs. 92% tacrolimus, p = 0.95). The incidence of clinical acute rejection was 10% in the tacrolimus group and 13% in the sirolimus group (p = 0.58). There was no difference in mean GFR measured by iothalamate clearance between the tacrolimus and sirolimus groups at 1 year (61 +/- 19 mL/min vs. 63 +/- 18 mL/min, p = 0.57) or 2 years (61 +/- 17 mL/min vs. 61 +/- 19 mL/min, p = 0.84). At 1 year, chronicity using the Banff schema showed no difference in interstitial, tubular or glomerular changes, but fewer chronic vascular changes in the sirolimus group. This study shows that a CNI-free regimen using sirolimus-MMF-prednisone produces similar acute rejection rates, graft survival and renal function 1-2 years after transplantation compared to tacrolimus-MMF-prednisone.

Clinical benefits of antiviral therapy in patients with recurrent hepatitis C following liver transplantation

Pegylated interferon (pegIFN) and ribavirin eradicates hepatitis C virus (HCV) in one third of liver recipients with recurrent disease. Side effects are frequent and potentially life threatening. Our aim was to define the long-term benefits of antiviral therapy in recurrent HCV. Eighty-nine (89) recipients (genotype 1: 86.5%) were treated with IFN (n = 31) or pegIFN (n = 58) plus ribavirin and 75 untreated contemporaneous disease-matched controls. The major end point was survival from transplantation. Survival, progression to cirrhosis and clinical decompensation since start of therapy were compared between sustained virologic responders (SVRs) and nonresponders (NRs). Results revealed 44 patients died during the follow-up (20% treated vs. 35% controls; p = 0.05). Patient survival was higher in treated compared to controls (7 years: 74% vs. 62%; p = 0.04). Among treated patients, an SVR was achieved in 37% (IFN 16% vs. peg-IFN 48%; p = 0.03). About 2/33 SVRs and 16/56 NRs died (p = 0.01) due to HCV-disease (56%), IFN-induced rejection (11%), both causes (11%) or others (22%). Five-year survival was greater in SVRs than in NRs (93% vs. 69%, p = 0.032). In patients without baseline cirrhosis, progression to cirrhosis occurred more frequently in NRs (27/42 vs. 6/16; p = 0.06). The 5-year risk of graft decompensation was higher in NRs (33% vs. 16%; p = 0.04). Antiviral therapy is associated with improved long-term outcome in recurrent HCV.

Quantifying molecular partition into model systems of biomembranes: an emphasis on optical spectroscopic methods

Optical spectroscopies have been intensively used to determine partition coefficients by a plethora of methodologies. The present review is intended to give detailed and useful information for the determination of partition coefficients and addresses several relevant aspects, namely: (i) definition and calculation of the partition coefficient between aqueous and lipidic phases; (ii) partition coefficients vs. "binding" formalisms; (iii) advantages of spectroscopic methodologies over separation techniques; (iv) formalisms for various experimental approaches based on UV-Vis absorption or fluorescence parameters (fluorescence intensity, lifetime, anisotropy and quenching); (v) experimental hints, artifacts and model limitations; and (vi) a brief survey of nonoptical techniques.

A critical role for ceramide synthase 2 in liver homeostasis: I. alterations in lipid metabolic pathways

Ceramide is an important lipid signaling molecule that plays critical roles in regulating cell behavior. Ceramide synthesis is surprisingly complex and is orchestrated by six mammalian ceramide synthases, each of which produces ceramides with restricted acyl chain lengths. We have generated a CerS2 null mouse and characterized the changes in the long chain base and sphingolipid composition of livers from these mice. Ceramide and downstream sphingolipids were devoid of very long (C22-C24) acyl chains, consistent with the substrate specificity of CerS2 toward acyl-CoAs. Unexpectedly, C16-ceramide levels were elevated, and as a result, total ceramide levels were unaltered; however, C16-ceramide synthesis in vitro was not increased. Levels of sphinganine were also significantly elevated, by up to 50-fold, reminiscent of the effect of the ceramide synthase inhibitor, fumonisin B1. With the exceptions of glucosylceramide synthase and neutral sphingomyelinase 2, none of the other enzymes tested in either the sphingolipid biosynthetic or degradative pathways were significantly changed. Total glycerophospholipid and cholesterol levels were unaltered, although there was a marked elevation in C18:1 and C18:2 fatty acids in phosphatidylethanolamine, concomitant with a reduction in C18:0 and C20:4 fatty acids. Finally, differences were observed in the biophysical properties of lipid extracts isolated from liver microsomes, with membranes from CerS2 null mice displaying higher membrane fluidity and showing morphological changes. Together, these results demonstrate novel modes of cross-talk and regulation between the various branches of lipid metabolic pathways upon inhibition of very long acyl chain ceramide synthesis.

De novo hepatitis B after liver transplantation from hepatitis B core antibody-positive donors in an area with high prevalence of anti-HBc positivity in the donor population

Transmission of hepatitis B virus (HBV) infection from donors who are negative for hepatitis B surface antigen (HBsAg-) but positive for antibody to hepatitis B core antigen (anti-HBc+) has been reported. However, previous studies were generally performed in geographic regions with a low prevalence of anti-HBc positivity in the liver donor population. The aims of this study are (1) to assess the risk for de novo hepatitis B in recipients of livers from anti-HBc+ donors in an area of high prevalence of anti-HBc positivity in the donor population, and (2) to analyze the risk factors for acquisition of HBV infection from anti-HBc+ donors. The transplantation experience of a single center between 1995 and 1998 was reviewed. Thirty-three of 268 liver donors (12%) were HBsAg- and anti-HBc+ during the study period. The proportion of anti-HBc+ donors increased with age; it was lowest (3.6%) in donors aged 1 to 20 years and highest (27.1%) in donors aged older than 60 years. Of the 211 HBsAg- recipients with 3 months or more of HBV serological follow-up, 30 received a liver from an anti-HBc+ donor and 181 received a liver from an anti-HBc- donor. Hepatitis B developed in 15 of 30 recipients (50%) of livers from anti-HBc+ donors but in only 3 of 181 recipients (1.7%) of livers from anti-HBc- donors (P < .0001). None of the 4 recipients who were antibody to HBsAg (anti-HBs)+ at the time of transplantation developed HBV infection after receiving a liver from an anti-HBc+ donor compared with 15 of 26 recipients (58%) who were anti-HBs- (P =.10). None of the 5 anti-HBc+ recipients developed hepatitis B compared with 15 of 25 anti-HBc- recipients (60%; P = 0.04). Child-Pugh score was significantly higher in recipients of livers from anti-HBc+ donors who developed HBV infection than in those who did not (9 +/- 2 v 7 +/- 1; P =.03). In our area, testing liver donors for anti-HBc is mandatory, particularly in older donors. With such information available, anti-HBc+ donors can be safely directed to appropriate recipients, mainly those with anti-HBs and/or anti-HBc at the time of transplantation. In the current era of donor shortage, this policy would allow adequate use of such donors.

Effect of ceramide structure on membrane biophysical properties: the role of acyl chain length and unsaturation

Ceramide is an important bioactive sphingolipid involved in a variety of biological processes. The mechanisms by which ceramide regulates biological events are not fully understood, but may involve alterations in the biophysical properties of membranes. We now examine the properties of ceramide with different acyl chains including long chain (C16- and C18-), very long chain (C24-) and unsaturated (C18:1- and C24:1-) ceramides, in phosphatidylcholine model membranes. Our results show that i) saturated ceramides have a stronger impact on the fluid membrane, increasing its order and promoting gel/fluid phase separation, while their unsaturated counterparts have a lower (C24:1-) or no (C18:1-) ability to form gel domains at 37°C; ii) differences between saturated species are smaller and are mainly related to the morphology and size of the gel domains, and iii) very long chain ceramides form tubular structures likely due to their ability to form interdigitated phases. These results suggest that generation of different ceramide species in cell membranes has a distinct biophysical impact with acyl chain saturation dictating membrane lateral organization, and chain asymmetry governing interdigitation and membrane morphology.

Ceramide-domain formation and collapse in lipid rafts: membrane reorganization by an apoptotic lipid

The effect of physiologically relevant ceramide concentrations (< or = 4 mol %) in raft model membranes with a lipid composition resembling that of cell membranes, i.e., composed of different molar ratios of an unsaturated glycerophospholipid, sphingomyelin, and cholesterol (Chol) along a liquid-disordered-liquid-ordered tie line was explored. The application of a fluorescence multiprobe and multiparameter approach, together with multiple fluorescence resonance energy transfer (FRET) pairs, in the well-characterized palmitoyl-oleoyl-phosphocholine (POPC)/palmitoyl-sphingomyelin (PSM)/Chol ternary mixture, revealed that low palmitoyl-ceramide (PCer) concentrations strongly changed both the biophysical properties and lipid lateral organization of the ternary mixtures in the low-to-intermediate Chol/PSM-, small raft size range (<25 mol % Chol). For these mixtures, PCer recruited up to three PSM molecules for the formation of very small ( approximately 4 nm) and highly ordered gel domains, which became surrounded by rafts (liquid-ordered phase) when Chol/PSM content increased. However, the size of these rafts did not change, showing that PCer did not induce the formation of large platforms or the coalescence of small rafts. In the high Chol/PSM-, large raft domains range (>33 mol % Chol), Chol completely abolished the effect of PCer by competing for PSM association. Lipid rafts govern the biophysical properties and lateral organization in these last mixtures.

Purification and characterization of a calicivirus as the causative agent of a lethal hemorrhagic disease in rabbits

The causative viral agent of a lethal rabbit hemorrhagic disease has been purified and characterized. In negative-stained preparations, the virions were icosahedral, measured 27 to 35 nm in diameter, were without an envelope, and showed 10 peripheral cup-shaped depressions. The major structural protein was 60 kilodaltons, which constitutes a unique characteristic of the Caliciviridae.

Early development of chronic active hepatitis in recurrent hepatitis C virus infection after liver transplantation: association with treatment of rejection

BACKGROUND/AIMS

We retrospectively studied 63 consecutive patients (mean age 54+/-8) with hepatitis C virus genotype 1b recurrence after liver transplantation and with a minimum histological follow-up of 1 year, in order to determine whether an early severe recurrence, defined as the development of chronic active hepatitis within the first 2 years post-liver transplantation, was associated with increased immunosuppression.

METHODS

The 1st year immunosuppression data (rejection episodes, boluses of methyl-prednisolone, cumulative doses of prednisone and azathioprine, OKT3 use) were recorded, and evaluated as predictive of severe recurrence at 1 and 2 years post-liver transplantation. Chronic active hepatitis and rejection were defined by histological criteria. Immunosuppression consisted of cyclosporine, azathioprine and prednisone. The treatment of rejection was based on a "bolus" of 1 g methyl-prednisolone/3 days.

RESULTS

At 1 year, 64% (40/63) of the patients had chronic active hepatitis, whereas of the 40 patients who had a 2nd year biopsy available, 75% had chronic active hepatitis at 2 years. At 1 year post-liver transplantation, no significant association was observed between immunosuppression and the development of chronic active hepatitis. In contrast, at 2 years, rejection (p=0.006), treatment of rejection (p=0.05), methyl-prednisolone boluses (p=0.013) and the number of rejection episodes (p=0.0034) occurring during the 1st year post-liver transplantation were significantly more common in patients with chronic active hepatitis. There was also a trend towards higher cumulative steroids (9447+/-3176.5 vs 7891.5+/-2111 mg) and higher cumulative azathioprine doses (13472+/-11154 vs 6233.5+/-5937 mg) in patients with chronic active hepatitis as compared to those who did not develop chronic active hepatitis.

CONCLUSIONS

Rejection and/or its treatment may accelerate the natural history of hepatitis C virus genotype 1b infection post-liver transplantation.

Liver transplantation in patients with portal vein thrombosis

The aim of this study is to analyze the incidence, risk factors, management, and follow-up of patients with portal vein thrombosis (PVT) undergoing primary orthotopic liver transplantation (OLT). Four hundred fifteen OLTs were performed in 391 patients. In 62 patients, partial (group 1; n = 48) or complete (group 2; n = 14) PVT was found at the time of surgery. Portal flow was reestablished by venous thrombectomy. In this study, we compare 62 primary OLTs performed in patients with PVT at the time of OLT with a group of 329 primary OLTs performed in patients without PVT (group 3) and analyze the incidence of PVT, use of diagnostic methods, surgical management, and outcome. We found no significant differences among the 3 groups for length of surgery, cold and warm ischemic times, and postoperative stay in the intensive care unit. With the piggyback technique, groups 1 and 2 had greater blood losses and required more blood transfusions than group 3. The early reoperation rate was greater in group 2. The incidence of rethrombosis was 4.8% (group 1, 2%; group 2, 14.3%). Reexploration and thrombectomy (2 patients) and retransplantation (1 patient) had a 100% mortality rate. In particular, the mortality rate of patients with complete PVT with extension into the splanchnic veins is high (33%). Three-month and 4-year patient survival rates were statistically similar in the 3 groups. The presence of PVT at the time of OLT is not a contraindication for OLT. However, if PVT extends into the splanchnic veins, the outcome is guarded.

Statistical evaluation of mathematical models for microbial growth

The aim of this study was to evaluate the suitability of several mathematical functions for describing microbial growth curves. The nonlinear functions used were: three-phase linear, logistic, Gompertz, Von Bertalanffy, Richards, Morgan, Weibull, France and Baranyi. Two data sets were used, one comprising 21 growth curves of different bacterial and fungal species in which growth was expressed as optical density units, and one comprising 34 curves of colony forming units counted on plates of Yersinia enterocolitica grown under different conditions of pH, temperature and CO(2) (time-constant conditions for each culture). For both sets, curves were selected to provide a wide variety of shapes with different growth rates and lag times. Statistical criteria used to evaluate model performance were analysis of residuals (residual distribution, bias factor and serial correlation) and goodness-of-fit (residual mean square, accuracy factor, extra residual variance F-test, and Akaike's information criterion). The models showing the best overall performance were the Baranyi, three-phase linear, Richards and Weibull models. The goodness-of-fit attained with other models can be considered acceptable, but not as good as that reached with the best four models. Overall, the Baranyi model showed the best behaviour for the growth curves studied according to a variety of criteria. The Richards model was the best-fitting optical density data, whereas the three-phase linear showed some limitations when fitting these curves, despite its consistent performance when fitting plate counts. Our results indicate that the common use of the Gompertz model to describe microbial growth should be reconsidered critically, as the Baranyi, three-phase linear, Richards and Weibull models showed a significantly superior ability to fit experimental data than the extensively used Gompertz.

Outcome of autoimmune hepatitis after liver transplantation

BACKGROUND

Recurrence of autoimmune hepatitis after liver transplantation is not rare, but there is little information about its time of onset, risk factors, response to treatment and prognosis. The aim of this study was to evaluate the rate of recurrence and outcome of autoimmune hepatitis after transplantation.

METHODS

The records of patients transplanted in eight centers in our country between 1984 and 1996 were retrospectively analyzed.

RESULTS

Forty-three of the 2331 (1.8%) recipients fulfilled diagnostic criteria of autoimmune hepatitis at the time of transplantation. Sixteen patients were excluded from evaluation. Nine (33%) of the 27 patients evaluated fulfilled criteria for recurrence of autoimmune hepatitis, with a mean time of recurrence after orthotopic liver transplantation of 2.6+/-1.5 years. Patients with recurrence had a longer follow-up time after transplantation (5.1 vs. 2.5 years, P=0.0012) and were receiving less immunosuppressive treatment. The estimated risk of recurrence of autoimmune hepatitis in the graft increased over time: 8% over the first year and 68% 5 years after transplantation. None of the seven patients with liver-kidney microsomal-positive antibodies recurred (P=0.059). Fifty percent of the patients failed to respond or responded only partially to therapy, although none of the patients have deteriorated clinically after 2.4+/-1.06 years of follow-up after recurrence.

CONCLUSIONS

Recurrence of autoimmune hepatitis in the graft is a common event with an incidence that increases over time as immunosuppression is reduced. Although response to treatment is poor, patient and graft survival do not appear to be decreased.

Cholesterol-rich fluid membranes solubilize ceramide domains: implications for the structure and dynamics of mammalian intracellular and plasma membranes

A uniquely sensitive method for ceramide domain detection allowed us to study in detail cholesterol-ceramide interactions in lipid bilayers with low (physiological) ceramide concentrations, ranging from low or no cholesterol (a situation similar to intracellular membranes, such as endoplasmic reticulum) to high cholesterol (similar to mammalian plasma membrane). Diverse fluorescence spectroscopy and microscopy experiments were conducted showing that for low cholesterol amounts ceramide segregates into gel domains that disappear upon increasing cholesterol levels. This was observed in different raft (sphingomyelin/cholesterol-containing) and non-raft (sphingomyelin-absent) membranes, i.e. mimicking different types of cell membranes. Cholesterol-ceramide interactions have been described mainly as raft sphingomyelin-dependent. Here sphingomyelin independence is demonstrated. In addition, ceramide-rich domains re-appear when either cholesterol is converted by cholesterol oxidase to cholestenone or the temperature is decreased. Ceramide is more soluble in cholesterol-rich fluid membranes than in cholesterol-poor ones, thereby increasing the chemical potential of cholesterol. Ceramide solubility depends on the average gel-fluid transition temperature of the remaining membrane lipids. The inability of cholestenone-rich membranes to dissolve ceramide gel domains shows that the cholesterol ordering and packing properties are fundamental to the mixing process. We also show that the solubility of cholesterol in ceramide domains is low. The results are rationalized by a ternary phospholipid/ceramide/cholesterol phase diagram, providing the framework for the better understanding of biochemical phenomena modulated by cholesterol-ceramide interactions such as cholesterol oxidase activity, lipoprotein metabolism, and lipid targeting in cancer therapy. It also suggests that the lipid compositions of different organelles are such that ceramide gel domains are not formed unless a stress or pathological situation occurs.

Experimental and clinical experience with urine amylase monitoring for early diagnosis of rejection in pancreas transplantation

Pancreas allograft rejection in dogs with pancreaticocystostomy can be predicted in advance of hyperglycemia by monitoring the urinary amylase (UA) concentration (U/L): In initial experiments, UA values declined to less than 1000 1.3 +/- 0.2 days before hyperglycemia in nonimmunosuppressed dogs, 3.3 +/- 1.0 days in dogs treated with cyclosporine (CsA), and 9.3 +/- 0.7 days in dogs treated with CsA, azathioprine (Aza), and prednisone (triple therapy). Autotransplanted control dogs maintained high urine amylase concentrations indefinitely (mean 125,544 +/- 36,931). In a subsequent experiment, in 19 dogs with bladder-drained pancreas allografts on CsA only for prophylactic immunosuppression, a five-day course of antirejection treatment with Aza (5.0 mg/kg) and antilymphocyte globulin ALG (1 mg/kg) was started in group A (n = 10) when a raise in serum glucose was detected, and in group B (n = 9) when a drop of UA below 1000 was observed. The functional allograft survival rate was 9.2 +/- 0.5 days in group A (treatment started after hyperglycemia) and 29.0 +/- 5.7 days in group B (treatment started after drop in UA) (P = .002). The UA dropped in all dogs before hyperglycemia, at a mean of 2.7 days in group A and 20.8 days in group B. Clinically, 8 patients received a whole cadaver pancreas transplant with urinary drainage of the exocrine secretions. All were followed with UA monitoring. Three recipients lost the grafts for technical reasons. Three recipients lost the grafts for technical reasons. One had a primary non-function and UA was below 1000 U/24 hr; two developed abscesses and the grafts were removed while functioning with high UA values. Five grafts are currently functioning; 3 recipients had no rejection episodes and their UA values ranged from 30,000 to 100,000 U/24 hr during their entire postoperative course. The other two had rejection episodes. In both cases UA decreased to baseline levels 1 and 4 days in advance of the hyperglycemia. After antirejection treatment UA rose again to high values and plasma glucose levels declined. Both patients are currently insulin-independent, with UA values ranging from 10,000 to 200,000 U/24 hr. Both experimentally and clinically UA is an early predictor of pancreas allograft rejection. The institution of early treatment of rejection episodes in dogs, based on UA, significantly improved allograft survival. Urine amylase monitoring in pancreas transplant recipients could lead to an early treatment of rejection and improve graft survival.

Are posttransplantation protocol liver biopsies useful in the long term?

Controversy exists about the usefulness of yearly protocol liver biopsies after liver transplantation, mainly among patients with normal transaminase levels. The aim of this study is to determine (1) the prevalence and cause of histological liver injury in transplant recipients with a minimum histological follow-up of 1 year (n = 254), and (2) the correlation between histological findings and transaminase values. The main indication for liver transplantation was viral-related cirrhosis (61%; 86% caused by hepatitis C virus [HCV]). Protocol liver biopsies were performed yearly for the first 5 years in HCV-infected transplant recipients and at 1 and 5 years in the remaining patients. Histological liver injury included several categories of liver damage (hepatitis, rejection, steatohepatitis, cholangitis, and Budd-Chiari-like lesions). Among biopsy specimens categorized as hepatitis, severe hepatitis was defined as the presence of stage 3 or greater fibrosis. The prevalence of liver injury increased significantly with time (42% v 56% at 1 and 5 years, respectively; P =.09) and was significantly greater in patients who underwent transplantation for HCV-related cirrhosis than in those who underwent transplantation for other reasons (P =.0001). The most frequent category of liver injury was hepatitis (97% and 96% at 1 and 5 years, respectively). Although a proportion of patients with liver injury (12% to 29%) had normal transaminase values, this percentage was almost null in patients with severe hepatitis. Normal histological characteristics were found in the vast majority of non-HCV-infected transplant recipients with normal transaminase values. Given the high prevalence of abnormal histological findings, particularly the increase over time of those defined as severe, protocol liver biopsies are clearly justified in HCV-infected transplant recipients. Conversely, given the rarity of abnormal histological findings, protocol liver biopsies should be questioned in non-HCV-infected transplant recipients with normal transaminase values.

Formation of ceramide/sphingomyelin gel domains in the presence of an unsaturated phospholipid: a quantitative multiprobe approach

To better understand how ceramide modulates the biophysical properties of the membrane, the interactions between palmitoyl-ceramide (PCer) and palmitoyl-sphingomyelin (PSM) were studied in the presence of the fluid phospholipid palmitoyl-oleoyl-phosphatidylcholine (POPC) in membrane model systems. The use of two fluorescent membrane probes distinctly sensitive to lipid phases allowed a thorough biophysical characterization of the ternary system. In these mixtures, PCer recruits POPC and PSM in the fluid phase to form extremely ordered and compact gel domains. Gel domain formation by low PCer mol fraction (up to 12 mol %) is enhanced by physiological PSM levels (approximately 20-30 mol % total lipid). For higher PSM content, a three-phase situation, consisting of fluid (POPC-rich)/gel (PSM-rich)/gel (PCer-rich) coexistence, is clearly shown. To determine the fraction of each phase a quantitative method was developed. This allowed establishing the complete ternary phase diagram, which helps to predict PCer-rich gel domain formation and explains its enhancement through PSM/PCer interactions.

The histology of solitary renal allografts at 1 and 5 years after transplantation

Previous studies suggest that the majority of renal allografts are affected by progressive, severe chronic histologic injury, yet studies using current protocols are lacking. The goal of this study was to examine the prevalence and progression of histologic changes using protocol allograft biopsies at 1 and 5 years after solitary kidney transplantation in patients transplanted between 1998 and 2004. Chronic histologic changes generally were mild at both 1 and 5 years and were similar in deceased and living donor kidneys. The overall prevalence of moderate or severe fibrosis was 13% (60/447) at 1 year and 17% (60/343) at 5 years. In a subgroup of 296 patients who underwent both 1- and 5-year biopsies, mild fibrosis present at 1 year progressed to more severe forms at 5 years in 23% of allografts. The prevalence of moderate or severe arteriolar hyalinosis was similar in tacrolimus and calcineurin inhibitor-free immunosuppression. These results in the recent era of transplantation demonstrate fewer, less severe and less progressive chronic histologic changes in the first 5 years after transplantation than previously reported.

Complexity of lipid domains and rafts in giant unilamellar vesicles revealed by combining imaging and microscopic and macroscopic time-resolved fluorescence

The application of fluorescence lifetime imaging microscopy to study gel/fluid and raftlike lipid domains in giant unilamellar vesicles (GUVs) is demonstrated here. Different regions of the ternary dipalmitoylphosphatidylcholine/dioleoylphosphatidylcholine/cholesterol phase diagram were studied. The head-labeled phospholipid Rhodamine-dioleoylphosphatidylethanolamine (Rhod-DOPE) was used as a fluorescent probe. Gel/fluid and liquid-ordered (l(o))/liquid-disordered (l(d)) phase separation were clearly visualized upon two-photon excitation. Fluorescence intensity decays in different regions of a GUV were also obtained with the microscope in fixed laser-beam configuration. The ensemble behavior of the system was studied by obtaining fluorescence intensity decays of Rhod-DOPE in nongiant vesicle suspensions. The fingerprints for gel/fluid coexistence and for the presence of l(o) raftlike phase, based on fluorescence lifetime imaging microscopy histograms and images, and on the fluorescence intensity decay parameters of Rhod-DOPE, are presented. The presence of three lipid phases in one single GUV is detected unequivocally. From the comparison of lifetime parameters, it can be concluded that the l(o) phase is formed in the binary dipalmitoylphosphatidylcholine/cholesterol but not in the dioleoylphosphatidylcholine/cholesterol mixture. The domains apparent in fluorescence intensity images have a more complex substructure revealed by analysis of the lifetime data. The potential applications of this combined imaging/microscopic/macroscopic methodology are discussed.