The effect of cyclosporine on the use of hospital resources for kidney transplantation

Cyclosporine A and adverse effects on organs: histochemical studies

The discovery that cyclosporine A (CsA) was a powerful immunosuppressant had a significant impact on transplant medicine. Its molecular mechanism of action has been well defined in T cells and involved inhibition of critical signalling pathways that regulated T-cell activation. In fact, CsA inhibited calcineurin phosphatase activity and thereby activation of the transcription factor nuclear factor of activated T cells. Over 10 years, its use is limited by side effects, determining nephro- and hepatotoxicity, gingival hypertrophy, tremor and increased blood pressure. These negative effects have been identified through morphological alterations and/or clinical parameters, i.e. variation in glomerular filtration rate for nephrotoxicity. Nevertheless, CsA remains a therapeutic valuable agent and it is normally utilized into clinical practice even if different dose adjustments or discontinuations in a significant percentage of patients must be used. This review focuses on the following topics: mechanisms of action and drug metabolism, interactions with other drugs, clinical and morphological evaluation of toxic effects on target organs. In particular, the morphological evaluation of negative effects has been considered reporting light and ultrastructural studies on target organs both in normal and immunosuppressive conditions. Moreover, the histochemical and immunohistochemical variations in cellular metabolism and antigenic properties of cells present in the parenchyma of these organs are discussed.

Effects of tacrolimus on ischemia-reperfusion injury

In addition to efficacious immunosuppression for the benefit of organ transplantation, tacrolimus has diverse actions that result in amelioration of ischemia-reperfusion injury. Knowledge is accumulating rapidly on the mechanisms through which tacrolimus exerts these cytoprotective effects, including alterations in microcirculation, free radical metabolism, calcium-activated pathways, inflammatory cascades, mitochondrial stability, apoptosis, stress-response proteins, and tissue recovery. Within the nucleus, actions mediating the effects of tacrolimus appear to be dominantly influenced by interactions with the transcription factor, nuclear factor-kappaB. Because tacrolimus is a cornerstone agent in immunosuppression regimens throughout the world and knowledge of its cellular mechanisms is evolving, it is important to update the clinical literature with this information. We reviewed the published literature with intent to portray the interactions of tacrolimus in the intricate cellular mechanisms initiated by ischemia and reperfusion.

Biochemical analysis of mouse FKBP60, a novel member of the FKPB family

We have identified mouse and human FKBP60, a new member of the FKBP gene family. FKBP60 shares strongest homology with FKBP65 and SMAP. FKBP60 contains a hydrophobic signal peptide at the N-terminus, 4 peptidyl-prolyl cis/trans isomerase (PPIase) domains and an endoplasmic reticulum retention motif (HDEL) at the C-terminus. Immunodetection of HA-tagged FKBP60 in NIH-3T3 cells suggests that FKBP60 is segregated to the endoplasmic reticulum. Northern blot analysis shows that FKBP60 is predominantly expressed in heart, skeletal muscle, lung, liver and kidney. With N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as a substrate, recombinant GST-FKBP60 is shown to accelerate effectively the isomerization of the peptidyl-prolyl bond. This isomerization activity is inhibited by FK506. mFKBP60 binds Ca2+ in vitro, presumably by its C-terminal EF-hand Ca2+ binding motif, and is phosphorylated in vivo. hFKBP60 has been mapped to 7p12 and/or 7p14 by fluorescence in situ hybridization (FISH).

The effects of FK506 on dorsal column axons following spinal cord injury in adult rats: neuroprotection and local regeneration

There is considerable evidence that immunophilin ligands can promote the regeneration of axons in peripheral nerves and act as neuroprotective agents in the CNS. We have examined the effects of FK506 and GPI 1046 on the responses to partial transection of ascending spinal dorsal column axons at T9, in some cases combined with crush of one sciatic nerve. FK506 (0.5 or 2.0 mg/kg) and GPI 1046 (10 or 40 mg/kg) was administered subcutaneously immediately after surgery and five times a week thereafter. Some animals received methylprednisolone (MP) (two subcutaneous doses of 30 mg/kg) in addition to, or instead of, FK506. After survival times of 1-12 weeks, dorsal column axons were labeled transganglionically with cholera toxin B-HRP. There was massive axonal sprouting at the lesion sites in animals with sciatic nerve injury and immunophilin ligand treatment. In FK506-treated animals a few severed sensory axons regenerated for up to 10 mm rostral to the lesion. Of greater significance, 30% of 71 FK506-treated animals had spared axons in the dorsal column, extending to the nucleus gracilis, versus 8% of 50 control animals (P < 0.05), showing that FK506 reduces the likelihood of axonal destruction due to secondary injury. A combination of FK506 and MP afforded greater protection than MP alone (P < 0.05), but axonal survival was not affected by sciatic nerve crush, dose of FK506, or survival time after injury. GPI 1046 (n = 11) did not promote axonal survival. Thus FK506 protects axons from secondary injury following spinal cord trauma, and in this experimental model, its neuroprotective effect is greater than that of MP.

Predictors of the cost of liver transplantation

BACKGROUND

Orthotopic liver transplantation (OLT) is a highly effective but costly therapy for end-stage liver disease. However, there are limited data on the demographic and clinical variables that affect cost. We undertook a preliminary study using multiple regression techniques to analyze factors that influence the cost of OLT.

METHODS

Patient and demographic data, including laboratory values and charges for all liver transplantations performed between June 1992 and June 1993 were analyzed (n = 111). Linear regression with standard and log-transformed values was performed by using STATA software (Stata Corporation College Station, TX). Independent variables included in the analyses were age, sex, United Network for Organ Sharing (UNOS) status, primary versus retransplantation, liver-kidney transplantation, and laboratory parameters of both liver (aspartate aminotransferase, AST; alkaline phosphatase; bilirubin; albumin; and prothrombin time) and kidney (blood urea nitrogen, BUN; creatinine) function. An F-to-remove strategy was employed with a significance level set at P = .05.

RESULTS

The full model with 12 variables explained 37% of the total variation in charges. When one excludes variables that did not have a significant impact on cost, the remaining significant variables were BUN and UNOS status 1. The final model was Charges (US$) = 3,407 x BUN + 74,474 x status 1 + 102,662. This model accounted for 29% of the total variability with BUN accounting for the vast majority (26%).

CONCLUSIONS

Renal function is the most important predictor of cost of OLT (P < .001). UNOS status 1 further increases cost, but other hospitalized patients have similar costs when one controls for other clinical variables. The degree of liver impairment is less important in predicting cost.

Neural roles of immunophilins and their ligands

The immunophilins are a family of proteins that are receptors for immunosuppressant drugs, such as cyclosporin A, FK506, and rapamycin. They occur in two classes, the FK506-binding proteins (FKBPs), which bind FK506 and rapamycin, and the cyclophilins, which bind cyclosporin A. Immunosuppressant actions of cyclosporin A and FK506 derive from the drug-immunophilin complex binding to and inhibiting the phosphatase calcineurin. Rapamycin binds to FKBP and the complex binds to Rapamycin And FKBP-12 Target (RAFT). RAFT affects protein translation by phosphorylating p70-S6 kinase, which phosphorylates the ribosomal S6 protein, and 4E-BP1, a repressor of protein translation initiation. Immunophilin levels are much higher in the brain than in immune tissues, and levels of FKBP12 increase in regenerating neurons in parallel with GAP-43. Immunophilin ligands, including nonimmunosuppressants that do not inhibit calcineurin, stimulate regrowth of damaged peripheral and central neurons, including dopamine, serotonin, and cholinergic neurons in intact animals. FKPB12 is physiologically associated with the ryanodine and inositol 1,4,5-trisphosphate (IP3) receptors and regulates their calcium flux. By influencing phosphorylation of neuronal nitric oxide synthase, FKBP12 regulates nitric oxide formation, which is reduced by FK506.

Optimizing the use of cyclosporine in renal transplantation

OBJECTIVE

To review the existing data on the use of cyclosporine (CsA) in kidney transplantation, particularly with respect to therapeutic drug monitoring.

DATA SOURCES

A literature search was conducted of applicable articles related to therapeutic drug monitoring of cyclosporine in renal transplantation. Previous consensus guidelines were examined. Discussions on issues related to this topic convened in Toronto, ON, on June 15-16, 1994.

DATA SYNTHESIS

The literature was analyzed to examine patient factors and drug interactions affecting CsA concentrations, the effect of CsA concentrations on patient outcome, current methods of analysis, pharmacodynamic monitoring, and new immunosuppressants.

CONCLUSIONS

CsA has improved the success of kidney transplantation, reducing the incidence and severity of acute rejection and improving short-term patient and graft survival. The rate of graft loss after the first year (primarily due to chronic rejection) has remained largely unchanged. Sandimmune Neoral offers promise due to its better bioavailability and limited dependence on bile flow for absorption. Long-term studies are underway to determine its effectiveness and safety. Indications for therapeutic drug monitoring for CsA are provided.

Detection of noncovalent FKBP-FK506 and FKBP-Rapamycin complexes by capillary electrophoresis-mass spectrometry and capillary electrophoresis-tandem mass spectrometry

The well known biospecific noncovalent receptor-ligand association complexes between the immunophilin FKBP and the immunosuppressive drugs FK506 and Rapamycin (RM) were investigated by on-line capillary electrophoresis-mass spectrometry (CE-MS) under selected ion monitoring (SIM) conditions and by CE-MS with tandem mass spectrometry (CE-MS/MS) under selected reaction monitoring (SRM) conditions. Solutions of hFKBP (33.3 µM) were dissolved in 50 mM ammonium acetate at pH 7.5. Samples that contained 100 µM of FK506 or RM also were prepared under the same solution conditions. By using these aqueous pH neutral conditions, samples were analyzed by SIM CE-MS and SRM CE-MS and the target complexes were separated by CE with mass spectrometer detection of the individual complexes between FKBP and FK506 [hFKBP + FK506 + 7HJ(7+) as well as FKBP and RM [hFKBP + RM + 7HJ(7+). In an experiment where a mixture of FK506 and RM was analyzed in the presence of FKBP, a nine-to-one ratio of ion current abundances between the RM and FK506 complexes was observed as reported in the literature from other studies. These results suggest that CE-MS and CE-MS/MS may be yet another analytical method for studying noncovalent interactions of biologically important macromolecules under physiological conditions.

Dysplastic haemopoiesis following orthotopic liver transplantation: comparison with similar changes in HIV infection and primary myelodysplasia

To validate scientifically our prior empiric observations that patients develop significant haemopoietic dysplasia following solid organ transplantation, we developed a quantitative lineage-specific scoring system to evaluate dysplastic features of bone marrow aspirates and core biopsies. We used this scoring system to compare retrospectively randomly selected bone marrow aspirates and core biopsies from 19 patients undergoing orthotopic liver transplantation (OLT), 21 with a known history of human immunodeficiency virus (HIV) infection, and 18 with primary or chemotherapy-related myelodysplastic syndromes (MDS). Our results show that the OLT patient group developed significant but milder haemopoietic dysplastic changes than the HIV or MDS groups, and that the MDS group developed more severe dysplasia of the myeloid lineage than the other groups. The possible roles for drugs and infectious agents in the pathophysiology of dysplastic changes are discussed.

Hair growth-stimulating effects of cyclosporin A and FK506, potent immunosuppressants

Cyclosporin A (CsA), a cyclic endecapeptide, is a T cell-specific immunosuppressant and is successfully used in the field of organ transplantation. Another T cell-specific immunosuppressant, FK506, a more recently discovered macrolide antibiotic, is effective against graft rejection at much lower doses than CsA. Although totally different in structure, both compounds inhibit T cell activation by interfering with the production of interleukin-2 (IL-2) by inhibiting IL-2 gene expression, probably through the inhibition of calcineurin, a Ca2+/calmodulin-dependent phosphatase. Clinical studies have revealed that FK506 induces a variety of side effects in common with CsA. One of the most common side effects of CsA is hypertrichosis. The hair growth stimulating effect of CsA is observed not only in normal but also in pathological conditions of hair growth, i.e. in patients with alopecia areata and also in some patients with male-pattern alopecia. Although hypertrichosis is induced by both topical and oral administration of CsA, there has been no report showing that FK506 induces hypertrichosis. Recently we have found that topical application of FK506 to skins of mice, rats and hamsters markedly stimulates hair growth. This hair growth stimulating effect of FK506 is observed when applied topically but not by oral administration, even with a dose which causes marked immunosuppression. The hair growth stimulating effect of FK506 in normal animals may apparently be unrelated to its immunosuppressive effect. In vitro studies revealed that FK506 directly stimulates hair follicles. Mechanisms of hair growth stimulating effects of FK506 and CsA remain to be elucidated.(ABSTRACT TRUNCATED AT 250 WORDS)

Early adoption of cyclosporine and recombinant human erythropoietin: clinical, economic, and policy issues with emergence of high-cost drugs

The discovery of new drugs and their introduction into US markets will become an intense area of focus should health care reform result in Medicare insurance coverage for prescription drugs. Particular attention will be focused on high-cost drugs. Two high-cost drugs, cyclosporine and recombinant human erythropoietin (rHuEPO), introduced into the clinical management of patients with kidney disease during the past decade, provide some experience concerning the forces affecting the use of expensive drugs in a cost-conscious health care system. The decision to prescribe a drug will depend on provider's judgements of the drug's clinical benefits and costs compared with those of other possible therapies. It may also depend on payment policy. Both cyclosporine and rHuEPO were adopted rapidly and extensively by providers of end-stage renal disease care following US Food and Drug Administration approval, despite their high costs. Both drugs were remarkably effective, relatively safe, and able to be administered without great difficulty compared with the therapies they have replaced. There was no additional payment to hospitals for the initial use of cyclosporine, which was introduced in 1983 at the time when Medicare's prospective payment was established, since choice of immunosuppressive agent did not affect the fixed, per-admission payment determined by the diagnosis-related group for kidney transplantation. Medicare coverage for continuing outpatient use of cyclosporine was not initially provided, in contrast to rHuEPO, which was introduced in 1989 with Medicare outpatient coverage and payment of 80% of the allowed charge. Despite their high costs and different methods of insurance payment both drugs achieved a rather quick and high penetration rate into their respective populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and partial amino acid sequence of a 28 kDa cyclophilin-like component of the rat liver sigma receptor

The sigma (sigma) receptor, a putative non-opioid receptor site which has been suggested to function as a neuromodulator of dopaminergic and NMDA systems, and is found in brain, liver and many other tissues, has been purified > 560-fold from a detergent-solubilized rat liver membrane preparation by affinity chromatography, using an affinity matrix prepared from an oximino derivative of haloperidol. The affinity column selectively retained principal components of M(r) 28 kDa, 40 kDa and 65 kDa that could be eluted from the column with sigma-selective ligands, specifically dextrallorphan and haloperidol. After dialysis and concentration by ultrafiltration, a loss in density of the 65 kDa component and an increase in the 28 kDa and 40 kDa components was observed. A 15 amino acid N-terminal sequence was obtained for the 28 kDa protein which is identical to the N-terminal sequence of the 17 kDa rat cyclophilin A, a cytosolic protein, suggesting that a critical component of the rat liver sigma receptor may be a cyclophilin. These results support the suggestion that sigma receptors are a key link between the central nervous system and the immune system.

An intelligent and cost-effective computer dosing system for individualizing FK506 therapy in transplantation and autoimmune disorders

The accuracy and precision of an intelligent dosing system (IDS) for FK506 in predicting doses to achieve target drug levels has been prospectively evaluated in transplant and autoimmune patients. For dose individualization, the knowledge base is updated with patient-specific feedback including the current dose, drug level, and the new target level. The study population of 147 patients consisted of 97 transplant patients (liver and kidney) and 50 patients with autoimmune disorders. Patients in the transplant study group were entered sequentially and followed as a cohort. Patients in the autoimmune study group were randomly assigned to one of three predefined FK506 concentration windows (low, 0.1-.3; medium, 0.4-.7; and high, 0.8-1.3 ng/mL) as part of a concentration controlled clinical trial. Predictions of steady-state plasma drug levels were made throughout the clinical course of autoimmune patients and during the first 6 weeks post-transplant in liver and kidney recipients. FK506 concentration in plasma was measured by a monoclonal antibody based ELISA assay. Accuracy was computed as the mean prediction error (mpe). Precision was computed as the root mean squared prediction error (rmspe). The accuracy of the IDS in each study group was as follows: 0.016 ng/mL (liver), -0.034 ng/mL (kidney), and -0.022 ng/mL (autoimmune). Because the 95% confidence interval included zero in each case, the IDS showed no bias. The precision of the IDS in each study group was as follows: 0.133 ng mL (liver), 0.1903 ng/mL (kidney), and 0.1188 ng/mL (autoimmune). These results indicate that the FK506 IDS is both accurate and very precise (reproducible) in transplant and autoimmune patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative clinical, microbiologic, and economic audit of the use of oral ciprofloxacin and parenteral antimicrobials

OBJECTIVE

To examine the use of oral ciprofloxacin and parenteral antimicrobials in the treatment of acute infection (respiratory tract, urinary tract, blood) in hospitalized patients, with particular reference to severity of infection, outcome, and associated economic implications of each treatment.

DESIGN

A prospective, multicenter comparative audit was conducted in the UK over an 18-month period. The audit was undertaken by clinical pharmacists who reviewed the antimicrobial treatment of patients with infective episodes, who were receiving or could have received oral therapy.

PARTICIPANTS

Clinical pharmacists who collated the data all are employed in teaching hospitals.

MAIN OUTCOME MEASURES

Patients were identified for analysis by their type of infection, severity of illness, antimicrobial prescribed, route of administration, and response to therapy. Additionally, data on costs of the antimicrobials prescribed and the supplementary costs of drug administration were calculated.

RESULTS

Four hundred eighty-five patients were enrolled for analysis; 208 of the patients had respiratory tract infection, 112 had urinary tract infection, 138 had septicemia, and 27 had mixed infections. Sepsis scores were applied to 152 patients receiving oral ciprofloxacin and 333 patients receiving parenteral antimicrobials and yielded mean scores of 5.9 (SD 3.1, range 1-13) and 8.7 (SD 4.2, range 1-22), respectively. Of 485 patients, 188 were paired according to sepsis score results and route of administration. Resolution occurred in 133 patients (79 receiving oral and 54 receiving parenteral therapy), further therapy was required in 49 (11 oral and 38 parenteral), and treatment was withdrawn in 6 (4 oral and 2 parenteral). Microbiologic assessment yielded positive results in 227 patients (47 percent). Drug acquisition costs (based on 1 UK pound = 1.80 US $) per course of treatment were $47.23 (SD $38.32, range 5.40-218.70) for the oral group and $173.70 (SD 209.77, range 2.11-1021.40) for the parenteral group. Overall costs for treatment courses were $74.00 (SD $52.81, range 8.10-309.17) and $305.59 (SD $304.70, range 14.69-1345.00) for the two groups, respectively (p < 0.001).

CONCLUSIONS

This study suggest that, in patients with moderate infective episodes, oral ciprofloxacin may reduce overall treatment costs compared with the use of parenteral antimicrobial agents.

Inhibition of T cell signaling by immunophilin-ligand complexes correlates with loss of calcineurin phosphatase activity

Calcineurin, a Ca2+, calmodulin-dependent protein phosphatase, was recently found to bind with high affinity to two different immunosuppressant binding proteins (immunophilins) with absolute dependence on the presence of the immunosuppressants FK506 or cyclosporin A (CsA) [Liu et al. (1991) Cell 66, 807-815]. The binding affinities of the immunophilin-drug complexes toward calcineurin and the stoichiometry of the resultant multimeric complexes have now been determined, and structural elements of FK506, CsA, and calcineurin that are critical for mediating their interactions have been identified. Analogues of FK506 (FK520, FK523, 15-O-demethyl-FK520) and CsA (MeBm2t1-CsA and MeAla6-CsA) whose affinities for their cognate immunophilins do not correlate with their immunosuppressive activities have been prepared and evaluated in biochemical and cellular assays. We demonstrate a strong correlation between the ability of these analogues, when bound to their immunophilins, to inhibit the phosphatase activity of calcineurin and their ability to inhibit transcriptional activation by NF-AT, a T cell specific transcription factor that regulates IL-2 gene synthesis in human T cells. In addition, FKBP-FK506 and CyP-CsA do not inhibit members of the PP1, PP2A, and PP2C classes of serine/threonine phosphatases. These data suggest that calcineurin is the relevant cellular target of these immunosuppressive agents and is involved in Ca(2+)-dependent signal transduction pathways in, among others, T cells and mast cells.

Mechanisms and amelioration of acute renal allograft failure in the cyclosporine era

The fairly wide-ranging spectrum of tactics under investigation for ameliorating acute renal allograft dysfunction caused by harvest/preservation-related ischemia, acute CsA nephrotoxicity, and acute immunologic crises reflect the fact that no single approach has emerged as universally useful for mitigating the vasomotor nephropathy produced by the combined effects of each of these vectors of vasomotor renal allograft injury. Given the clinical heterogeneity of patients and allografts, it is the author's bias that, in addition to careful donor and recipient hemodynamic management, induction immunosuppressive regimens should be individualized on the basis of allograft function in the immediate postreperfusion period (judged by rate of diuresis, intraoperative parenchymal tone, renal scan profiles, and rate of decline of serum creatinine concentration) as well as patient-specific immunologic and general medical risk factors. Promising laboratory and clinical investigations of such agents as calcium channel blockers, substances promoting intrarenal vasodilator vs. vasoconstrictor prostaglandin formation, and atriopeptins have the potential to provide clinically helpful options with regard to adjunctive therapy for ameliorating acute renal allograft dysfunction associated with INF and ACR.

Human and Escherichia coli cyclophilins: sensitivity to inhibition by the immunosuppressant cyclosporin A correlates with a specific tryptophan residue

The human T-cell protein cyclophilin shows high affinity for and is the proposed target of the major immunosuppressant drug cyclosporin A (CsA). Cyclophilin also has peptidyl prolyl cis-trans isomerase activity that is inhibited by CsA with an IC50 of 6 nM, while by contrast a homologous PPIase from Escherichia coli has been found to be much less sensitive to CsA, shown here to be 500-fold less potent at an IC50 of 3000 nM. This E. coli rotamase lacks the single highly conserved tryptophan residue of eukaryotic cyclophilins, and we show here that mutation of the natural F112 to W112 enhances E. coli rotamase susceptibility to CsA inhibition by 23-fold. Correspondingly, the human W121 mutations to F121 or A121 yield cyclophilins with 75- and 200-fold decreased sensitivity to CsA, while kcat/Km values of rotamase activity in a tetrapeptide assay drop only 2- and 13-fold, respectively. This complementary gain and loss of CsA sensitivity to mutation to or from tryptophan validate the indole side chain as a major determinant in immunosuppressant drug recognition and the separation of PPIase catalytic efficiency from CsA affinity.

Purification and characterization of cyclosporine and FK-506 binding proteins from a human T-helper cell line

Cytosolic proteins that specifically bind cyclosporine A and FK-506 were isolated and purified from the JURKAT human T-helper cell line. These binding proteins were purified by affinity, molecular weight exclusion and weak cation exchange column chromatography. Radiolabeled cyclosporine A specifically bound to a approximately 17 kDa molecule which is cyclophilin and also bound to a approximately 50 kDa protein(s). Radiolabeled FK-506 did not bind to the approximately 17 kDa molecular weight protein, but specifically bound to soluble approximately 10 kDa and approximately 50 kDa proteins.

Chemistry and biology of the immunophilins and their immunosuppressive ligands

Cyclosporin A, FK506, and rapamycin are inhibitors of specific signal transduction pathways that lead to T lymphocyte activation. These immunosuppressive agents bind with high affinity to cytoplasmic receptors termed immunophilins (immunosuppressant binding proteins). Studies in this area have focused on the structural basis for the molecular recognition of immunosuppressants by immunophilins and the biological consequences of their interactions. Defining the biological roles of this emerging family of receptors and their ligands may illuminate the process of protein trafficking in cells and the mechanisms of signal transmission through the cytoplasm.

Cloning, expression, and purification of human cyclophilin in Escherichia coli and assessment of the catalytic role of cysteines by site-directed mutagenesis

The cDNA encoding human cyclophilin from the Jurkat T-cell lymphoma line has been cloned by the expression cassette polymerase chain reaction and sequenced, and an expression vector has been constructed under control of the tac promoter for efficient expression in Escherichia coli. Active cyclophilin is produced at up to 40% of soluble cell protein, facilitating a one-column purification to homogeneity. Wild-type cyclophilin was characterized for binding of the potent immunosuppressant agent cyclosporin A (Kd = 46 nM) by tryptophan fluorescence enhancement and for inhibition (IC50 = 19 nM) of cyclophilin's peptidyl-prolyl cis-trans isomerase (rotamase) activity. With N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide as the substrate, recombinant human cyclophilin has a high catalytic efficiency; kcat/Km is 1.4 X 10(7) M-1.S-1 at 10 degrees C. To test the prior suggestion that a cysteine residue may be essential for catalysis and immunosuppressant binding, the four cysteines at positions 52, 62, 115, and 161 were mutated individually to alanine and the purified mutant proteins were shown to retain full affinity for cyclosporin A and equivalent catalytic efficiency as a rotamase. Clearly the cysteines play no essential role in catalysis or cyclosporin A binding. These results rule out the recently proposed mechanism [Fischer, G., Wittmann-Liebold, B., Lang, K., Kiefhaber, T. & Schmid, F. X. (1989) Nature (London) 337, 476-478)] involving the formation of tetrahedral hemithioorthoamide. Whereas mechanisms that embody other tetrahedral intermediates may be operative, an alternative mechanism is considered that involves distortion of bound substrate with a twisted (90 degrees) peptidyl-prolyl amide bond.

The changing pattern of medical activity in a major Belgian university hospital

To evaluate the changes in the pattern of clinical activity in a 1900-bed Belgian teaching hospital in the period 1979-1987, we extracted data from the historical files of the hospital's central invoicing system. The total charge for a day of hospitalization, care and treatment increased by 83%. In this total per diem charge the share of hospital charges in the strict sense declined from 60 to 53%; the shares of charges for services and for pharmaceuticals rose, respectively, from 29 to 32, and from 10 to 15%. Within charges for services the share for diagnostic services declined by 22%; the share for surgery rose by 16%, and that for miscellaneous other services by 89%. For diagnostic services the decline was particularly clear for laboratory medicine (-32%) and for conventional imaging services (-22%), while cardiac and endoscopic investigations show a prominent expansion (+78 and +83%, respectively). In surgery the growth is quite homogeneous with the charges for urology, ophthalmology and orthopedics as the most important growers. In a group of miscellaneous, not diagnostic nor surgical services, which grows faster than all other groups, there is a marked shift from rather simple to technologically more advanced services. The increase in the pharmacy's bill results from increases in charge for both drugs (+49%) and materials (+95%). We conclude that the observed changes in charges reflect an intensification of care and an impact of technological innovation on clinical practice, including a phenomenon of substitution of old technologies for newer ones.