Viologen-Calix[6]arene Pseudorotaxanes. Ion-Pair Recognition and Threading/Dethreading Molecular Motions

A calix[6]arene wheel, whose cavity has been extended and rigidified by N-phenylureido groups on the upper rim, forms pseudorotaxane species with molecular axles containing the viologen (4,4'-bipyridinium) unit in CH(2)Cl(2) solution. In these conditions, the self-assembly process is very efficient, with associated DeltaG degrees values of around -8 kcal mol(-1). The counteranions of the bipyridinium-based threads play indeed an important role in the formation of the complex. The use of either tosylate or hexafluorophosphate salts of the guests affects both the stability of the complexes and the rate of the threading process. Such effects have been interpreted in terms of ion-pair recognition, suggesting that coordination of the counteranions of the viologen thread by the ureido groups of the calixarene wheel is crucial for the breaking of tight ion pairs prior to threading. The rate constants of the threading/dethreading reactions coupled with the redox processes of the viologen unit of the axle have been obtained by means of cyclic voltammetry. The pseudorotaxane species undergo fast dethreading (submicrosecond time scale) on electrochemical reduction of the guest. The heterogeneous electron-transfer kinetics for the reduction of the viologen unit is slowed upon encapsulation into the calixarene cavity.

Outcome of simultaneous kidney pancreas transplantation: a single center analysis

The aim of this study was to evaluate the outcome of simultaneous kidney pancreas transplantation (SKPT) by various surgical techniques. The 161 patients submitted to SKPT underwent the following: 36 pancreas with duct occlusion (from 1985 to 1989), 75 with whole pancreas with bladder diversion (from 1990 to 1998), and 50 whole pancreas with enteric diversion (40 with systemic and 10 with portal drainage) (from 1999 to September 2002). A positive effect on patient survival was evident using enteric diversion versus the duct occlusion group (P = .005), and versus the bladder diversion group (.035), and on pancreas graft survival in the enteric diversion versus the duct occlusion group (P < .028). These improvements may be due to refined donor and patient selection criteria, surgical technique, and immunosuppression.

Simultaneous pancreas-kidney transplantation: short- and long-term results

Simultaneous kidney and pancreas transplantation (SKPT) is the treatment of choice for a majority of type I diabetic patients with end-stage renal disease. With continual refinements in surgical technique and an evolving immunosuppressive arsenal, graft and patient survival have continually improved. The purpose of this study was to evaluate the short- and long-term results of SKPTs performed in 174 recipients from June 1985 to March 2003 including 37 segmental grafts with duct occlusion, 73 whole pancreas transplants with bladder diversion, and 64 whole pancreas grafts with enteric diversion. The series includes 160 cases with systemic drainage and 14 with portal drainage. In the segmental pancreas group, patient survival was 85%, 76%, and 53% with pancreas survival of 67%, 36%, and 15%, and kidney survival of 82%, 63%, and 15%, respectively, at 1, 5, and 10 years. Among the bladder diversion group, patient survival was 94%, 83%, and 73% pancreas survival 72%, 67%, and 65%, and kidney survival 89%, 78%, and 58%, respectively, 1, 5, and 10 years. Among the enter diversion group patient survival was 90% and 90% at 12 and 108 months, pancreas survival 80% and 65%, and kidney survival 85% and 85%, respectively. There were significant differences between curves of survival distribution according to the surgical technique applied for patients (P =.04), pancreas (P =.007), and kidney (P =.005). Based on the results from our study, the short- and long-term prognosis after SKPT is satisfactory, especially compared to the outcomes of long-term dialysis among patients with end-stage renal disease caused by type I diabetes.

Molecular landers as probes for molecular device-metal surface interactions

Specifically designed series of molecules (landers), comprising a central rigid polyaromatic core and several spacers that decouple the board from the metallic surface, have been synthesized. UHV-STM studies, on one hand, have shown important distortions of the molecule by interaction with the substrate. On the other hand, surface restructuring results from the presence of the molecules.

Synthesis of Cavity Extended Cyclotriveratrylenes

Aromatic nucleophilic substitution reaction of cyclotriguaiacylene 1 with fluorobenzene derivatives bearing electron-withdrawing groups X (CHO, COCH(3), CN, NO(2)) in the para position gives a series of cyclotriveratrylene derivatives (3a-d), where the X substituents can be transformed to hydrogen-bond donor groups to afford new CTV-based heteroditopic receptors. The substituents of compounds 3a-d favor the facile demethylation reaction of the CTV derivatives. Attempts to perform alkylation reactions on derivatives (8c,d) evidenced the formation of a stereoisomeric mixture of symmetrical and unsymmetrical compounds.

[The incidence, clinical implications, and risk factors of diabetes mellitus]

The incidence of diabetes in kidney transplant recipients is between 4 and 20% in patients previously not affected by this pathology. This difference is partially due to the immunosuppressive therapy administered. The incidence of diabetes is very high during the first quarter after the transplant, and it becomes stable during the following quarters. The presence of diabetes - evaluated by postprandial glycemia and glycated hemoglobin - should be checked quarterly during the first year after the transplant, every six months during the second year, and yearly starting from the third year. The immunosuppressive therapy (calcineurin inhibitors and steroids), familial history, age, race, and weight (BMI) are among the risk factors of diabetes post-transplant. An increased risk of rejection seems to be among the principal consequences of diabetes in transplant recipients. Moreover, these patients are more prone to infections, cardiovascular disease, and the degenerative complications of diabetes. These facts increase the risk of organ insufficiency, morbidity, and mortality. To manage diabetes in transplant recipients it is necessary to identify at-risk patients before the transplantation, thus avoiding complicated and hazardous examinations after the transplant. After the transplantation, the modifiable risk factors, such as the immunosuppressant drugs used and the control of body weight, must be checked. The control of hypertension is important as well.

Islet allotransplantation in type 1 diabetic patients

Islet transplantation was proposed more than 10 years ago as treatment for normalising glucose homeostasis in type 1 diabetic patients. Since the beginning it has aroused great interest among diabetic patients being an easy procedure, burdened by minor complications: islet transplantation in fact consists on a transhepatic percutaneous injection under local anaesthesia. The initial clinical outcomes not came up to expectations, being low the insulin independence rate and the long term graft function in recipients. Recently, thanks to the introduction of new immunosuppression strategies, clinical data greatly improved: insulin independence was reached in all recipients and maintained in more than 70% of them 2 years from the transplant. The need of an immunosuppression therapy limits the indication of islet transplantation to diabetic patients already immunosuppressed for a previous organ transplant or to patients with brittle diabetes, that is not controlled also with the new strategies of insulin treatment, with a poor quality of life and an increased rate of diabetic complications. Other problems are represented by the progressive decrease of graft function during long term follow up, and by the low number of organ donors that limits the number of transplantation feasible per year.

Enoximone maintains intestinal villus blood flow during endotoxemia

BACKGROUND

The objective of this study was to determine the effects of a continuous infusion of the phosphodiesterase inhibitor enoximone on mucosal villus blood flow in a normotensive model of endotoxemia.

METHODS

Twenty-four anesthetized and ventilated rats underwent laparotomy and a ileal portion was exteriorized and opened by an antimesenteric incision. The ileal segment was fixed on a plexiglass stage with the mucosal surface upward. Microcirculatory parameters were assessed by intravital videomicroscopy. The animals were randomly assigned to receive one of three treatments: infusion of Escherichia coli lipopolysaccharides (LPS, 2 mg/kg/h) without phosphodiesterase inhibitor pretreatment (LPS group); or infusion of LPS with enoximone pretreatment (10 microg x kg(-1) x min(-1), start 30 min before LPS infusion, enoximone group), or infusion of an eqivalent volume of NaCl 0.9% (control group). Macrohemodynamic parameters (MAP, HR) and microhemodynamic parameters of ileal mucosa (mean diameter of central arterioles = DA, and mean erythrocyte velocity within the arterioles = VE) were measured 30 min before and at 0, 60, and 120 min after induction of endotoxemia. Mucosal villus blood flow was calculated from DA and VE.

RESULTS

In this normotensive endotoxemia model MAP remained stable in the control and the LPS group but significantly decreased in the enoximone group. The endotoxin-induced decrease of VE and DE of central arterioles of mucosal villi could be prevented. Thus, mucosal villus blood flow did not decrease compared to the LPS group.

CONCLUSIONS

Our results indicate that enoximone during an early stage of sepsis contributes to systemic hypotension but prevents mucosal hypoperfusion.

Unidirectional threading of triphenylureidocalix[6]arene-based wheels: oriented pseudorotaxane synthesis

Triphenylureidocalix[6]arenes 5 a,b are heteroditopic receptors having a pinched cone structure able to interact with both the cation and the anion of ion pairs. They are able to act as wheels and form complexes of the pseudorotaxane type with axles derived from dialkylviologen salts. An investigation into the possibility of exploiting the different structural and chemical information present on the two distinct rims of the calixarene wheel as control elements to pivot the direction of the axle threading processes and give access to oriented pseudorotaxanes is reported. It was verified that, in C(6)D(6), an asymmetric dicationic axle derived from 4,4'-bipyridil bearing two alkyl chains, one of which has a stopper, and triphenylureidocalix[6]arenes 5 a or 5 b form 1:1 supramolecular complexes belonging to the class of pseudorotaxanes. The structure of these complexes has been inferred through (1)H NMR techniques. The data show that the axle accesses the calixarene cavity only through the wider rim. To further verify this issue, the new rotaxane 8, obtained by stoppering the pseudorotaxane derived from 5 b and the symmetrical axle 7 with diphenylacetyl chloride, was synthesised. In the (1)H NMR spectrum of 8, the aliphatic protons of the axle portion that resides at the wide rim of the wheel show chemical shifts that are almost identical to those observed in pseudorotaxanes 6. On the other hand, those that stick out of the narrow rim of 8 experience chemical shifts that could not be found in the oriented pseudorotaxanes 6.

Secretory defects induced by immunosuppressive agents on human pancreatic beta-cells

Despite the considerable interest for islet and pancreas transplantation, remarkably little is known about the direct effects of immunosuppressive drugs on human beta-cell function. We measured different insulin secretory parameters and insulin gene expression of human islets cultured for 5 days in the presence of mycophenolate mofetil (MMF), cyclosporin A (CsA), tacrolimus (FK506) or a mixture of 3 cytokines. Basal insulin release after exposure to cytokines and FK506 was significantly higher than in control islets. Responsiveness to an acute glucose stimulus did not differ significantly between control and treated islets. However, absolute incremental insulin responses (delta-AUCs) of islets exposed to cytokines or FK506 were significantly higher compared to islets exposed to CsA or MMF, mainly because of the higher basal release. Indeed, maximal over basal release (stimulation index, SI) tended to be lower in islets exposed to FK506 than in control islets. Insulin gene expression was significantly reduced only in islets exposed to CsA. FK506 was, among those tested, the immunosuppressive drug that most profoundly altered the normal insulin secretory pattern of human beta-cells, whereas CsA was the only inhibiting insulin gene expression. Although the abnormalities induced by the immunosoppressive drugs utilized in this study were modest, these in vitro data are consistent with the reported in vivo diabetogenicity of CsA and FK506 and point to MMF as the ideal immunosuppressive agent from a pancreatic beta-cell point of view.

Anion effects on the recognition of ion pairs by calix[4]arene-based heteroditopic receptors

A novel heteroditopic receptor (5) based on a rigid calix[4]arene cavity bearing at the upper rim four arylsulfonamido binding sites has been synthesized. The binding abilities of this new host have been investigated in apolar solvents toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) and compared with those of monotopic and heteroditopic calix[4]arene-bis(crown-3)-based receptors 1 and 2 in order to evaluate the role of the anion on ion-pair recognition. While monotopic host 1 shows an efficiency order toward the different salts that increases when the anion is less interactive (Hofmeister trend), an opposite role of the counteranion on the recognition process was observed with host 5 (anti-Hofmeister trend). A more complex behavior is experienced by host 2, which shows a high and leveled efficiency for all the anions tested. The results obtained were explained on the basis of the different types of ion pairs present in the recognition process. Further information on the role of the anion were obtained by the "dual host" strategy utilizing the tri-n-butylthioureido derivative of tren 7, which forms a stable complex with chloride anion. The very high efficiency shown by these heteroditopic hosts opens new routes in supramolecular projects and is a very interesting tool in the molecular recognition of ion-pairs and its applications.

Successful [correction of Succesful] transplantation of human islets in recipients bearing a kidney graft

AIMS/HYPOTHESIS

Islet transplantation is a minimally invasive approach to curing Type I (insulin-dependent) diabetes mellitus. Success has recently been reported in patients receiving solitary islet transplants but the outcome in patients receiving islets together with, or after, kidney transplants has been limited and unpredictable.

METHODS

Here we report successful islet transplantation in a cohort of 15 patients with Type I diabetes who were followed for at least 1 year after islet transplantation, after having already received kidney allografts because of end-stage nephropathy.

RESULTS

C-peptide after transplantation was higher than 0.17 nmol/l in all 15 recipients, reflecting the absence of primary non-function. Insulin requirement was reduced by over 50 % in all but one patient, and insulin independence was achieved in 10 (66 %) recipients, five of whom now have stable, prolonged insulin independence, well controlled fasting glycaemia, a substantial first-phase and normal second-phase response to glucose, normal insulin sensitivity (HOMA analyses) and HbA1 c of under 6.2 % (33, 26, 18, 13 and 12 months after transplantation respectively). Of importance for patient management, an assessment of fasting blood glucose and proinsulin values following overnight withdrawal of insulin administration one month after transplantation was a potent predictor of insulin independence, and could be used to decide patients who should have further islet preparations.

CONCLUSION/INTERPRETATION

These findings support the use of islet transplantation as a cure for Type I diabetes in patients with severe complications.

Anion allosteric effect in the recognition of tetramethylammonium salts by calix[4]arene cone conformers

Rigid calix[4]arene cone conformers, which are efficient receptors for quaternary ammonium salts, are usually obtained through the functionalization of their lower rim with suitable groups. Using flexible cone conformer of calix[4]arene, bearing four 4-hydroxybenzyl groups as cooperative and rigidifying structural elements at the upper rim of the calix, which act as anion binding groups, a new heteroditopic cavitand, 7, was synthesized. Whereas the tetramethoxy derivative 8 does not show any complexing ability, its tetrahydroxy analogue 7 recognizes tetramethylammonium salts with high efficiency. The binding abilities of this new receptor toward a series of tetramethylammonium salts (tosylate, chloride, acetate, trifluoroacetate, and picrate) have been investigated in CDCl(3) solution and compared to the monotopic and rigidified, through the lower rim, cone biscrown-3-calix[4]arene 9. The results obtained confirmed that in CDCl(3) ion pairing strongly affects binding. In particular, the rigid monotopic receptor 9 experiences good efficiency toward tetramethylammonium salts having anions with low ion-pairing ability such as trifluoroacetate or picrate. On the contrary, for the new heteroditopic cavitand 7, a reverse order of efficiency was found. In the latter case a different complexation mode was hypothesized in which the tetramethylammonium cation is deeply entrapped into the host cavity and its counteranion participates to the recognition process by coordination via hydrogen bonding by the four OH groups. To further support the role of the anion in the recognition process, a "dual host" approach, employing 7 or 9 in the presence of a specific receptor for chloride anion (10), was utilized. Molecular modeling studies confirmed that in the complexes formed by 7 and TMA salts the counteranion is involved in hydrogen bonding with the host OH groups and that the guests are bound as ligand-separated ion pairs.

Autoantibody response to islet transplantation in type 1 diabetes

Islet allotransplantation into patients with autoimmune type 1 diabetes represents a reexposure to autoantigen. Here, measurement of antibodies to GAD and IA-2 autoantigens before and after islet transplantation in 36 patients (33 receiving islet plus kidney grafts with cyclosporin and steroid-based immunosuppression, and 3 receiving solitary islet transplants with mycophenolate but cyclosporin-free immunosuppression) demonstrated marked rises in GAD antibodies within 7 days posttransplantation in 5 patients (3 receiving islet after kidney transplants, and 2 receiving solitary islet transplants) and within 30 days in the third patient receiving solitary islet transplantation. GAD antibodies were of the IgG1 subclass, against major autoantigenic epitopes, and in cases of islet after kidney transplants, the responses were short-lived and not accompanied by HLA antibodies. Two of these patients had subsequent marked rises of IA-2 antibodies, and an additional patient had a marked rise in IgM-GAD antibodies 3 years after transplantation. Insulin independence was not achieved in patients with autoantibody elevations and was significantly less frequent in these patients. These data are consistent with a reactivation of autoimmunity that may be dependent on immunosuppression therapy and is associated with impaired graft function.

Cardiovascular outcomes after kidney-pancreas and kidney-alone transplantation

BACKGROUND

This study retrospectively assessed, with an intention-to-treat analysis, the effect of kidney-pancreas transplantation (KP) on survival and cardiovascular outcome in type 1 diabetic uremic patients.

METHODS

A total of 351 uremic type 1 diabetic patients were enrolled on a waiting list for KP: 130 underwent KP transplantation, 25 underwent kidney transplantation alone (KA), whereas 196 patients remained on dialysis (WL). The three populations had similar cardiovascular conditions. Actuarial survival rates and causes of death were recorded over a period of seven years. Finally, 23 KP and 13 KA patients underwent left radionuclide ventriculography, during a follow-up of four years.

RESULTS

In the entire group of 351 patients the seven-year survival rate was 77.4% for KP, 56.0% for KA and 39.6% for WL (KP vs. WL, P = 0.01). Cardiovascular death rate was 7.6% in KP, 20.0% in KA and 16.1% in WL (KP versus WL, P = 0.03; KP vs. KA, P = 0.16). In the subsample studied with radionuclide ventriculography, left ventricular ejection fraction improved in KP, but did not in KA, with significant differences between groups at two and four years. At four years only the KP patients presented normal values of diastolic parameters, including the peak filling rate, time-to-peak filling rate, and peak filling rate/peak ejection rate ratio. Glycated hemoglobin was negatively associated with the ejection fraction, peak filling rate and peak filling rate/peak ejection rate ratio, and positively associated with the time-to-peak filling rate.

CONCLUSIONS

Normalization of blood glucose metabolism and improvement of blood pressure control obtained with KP transplant is associated with positive effects on survival, cardiovascular death rate, and left ventricular function.