Regulation of pancreatic beta-cell growth and survival by the serine/threonine protein kinase Akt1/PKBalpha.

The physiological performance of an organ depends on an interplay between changes in cellular function and organ size, determined by cell growth, proliferation and death. Nowhere is this more evident than in the endocrine pancreas, where disturbances in function or mass result in severe disease. Recently, the insulin signal-transduction pathway has been implicated in both the regulation of hormone secretion from beta cells in mammals as well as the determination of cell and organ size in Drosophila melanogaster. A prominent mediator of the actions of insulin and insulin-like growth factor 1 (IGF-1) is the 3'-phosphoinositide-dependent protein kinase Akt, also known as protein kinase B (PKB). Here we report that overexpression of active Akt1 in the mouse beta cell substantially affects compartment size and function. There was a significant increase in both beta-cell size and total islet mass, accompanied by improved glucose tolerance and complete resistance to experimental diabetes.

Formulation and characterization of a captopril ethyl ester drug-in-adhesive-type patch for percutaneous absorption.

BACKGROUND: The ethyl ester of captopril has been shown to exhibit enhanced permeation across human skin compared to the parent drug. A drug-in-adhesive patch formulation of a captopril ethyl ester was therefore developed for optimum drug release. METHOD: A wide range of transdermal patches were prepared using two commercially available bioadhesive polymers. Investigational screening was conducted on the patches using microscopy, texture profile analysis, and infrared spectroscopy. Drug release profiles of suitable patches were obtained using both polydimethylsiloxane (Silastic) and porcine skin in vitro. RESULTS: Diffusion results across Silastic showed a gradual plateau in flux with increased drug loading that may be attributable to intramolecular interactions while flux across porcine skin was seen to increase with increasing patch thickness and attained a therapeutic level. CONCLUSIONS: This study demonstrated that adhesion and drug loading are significant factors in optimizing a topical patch formulation for the delivery of a captopril prodrug.

Metabolism of captopril carboxyl ester derivatives for percutaneous absorption.

OBJECTIVES: To determine the metabolism of captopril n-carboxyl derivatives and how this may impact on their use as transdermal prodrugs. The pharmacological activity of the ester derivatives was also characterised in order to compare the angiotensin converting enzyme inhibitory potency of the derivatives compared with the parent drug, captopril. METHODS: The metabolism rates of the ester derivatives were determined in vitro (using porcine liver esterase and porcine ear skin) and in silico (using molecular modelling to investigate the potential to predict metabolism). KEY FINDINGS: Relatively slow pseudo first-order metabolism of the prodrugs was observed, with the ethyl ester displaying the highest rate of metabolism. A strong relationship was established between in-vitro methods, while in-silico methods support the use of in-vitro methods and highlight the potential of in-silico techniques to predict metabolism. All the prodrugs behaved as angiotensin converting enzyme inhibitors, with the methyl ester displaying optimum inhibition. CONCLUSIONS: In-vitro porcine liver esterase metabolism rates inform in-vitro skin rates well, and in-silico interaction energies relate well to both. Thus, in-silico methods may be developed that include interaction energies to predict metabolism rates.

The application of Gaussian processes in the prediction of percutaneous absorption.

OBJECTIVES: The aim was to assess mathematically the nature of a skin permeability dataset and to determine the utility of Gaussian processes in developing a predictive model for skin permeability, comparing it with existing methods for deriving predictive models. METHODS: Principal component analysis was carried out in order to determine the nature of the dataset. MatLab software was used to assess the performance of Gaussian process, single linear networks (SLN) and quantitative structure-permeability relationships (QSPRs) using a range of statistical measures. KEY FINDINGS: Principal component analysis showed that the dataset is inherently non-linear. The Gaussian process model yielded a predictive model that provides a significantly more accurate estimate of skin absorption than previous models, particularly QSPRs (which were consistently worse than Gaussian process or SLN models), and does so across a wider range of molecular properties. Gaussian process models appear particularly capable of providing excellent predictions where previous studies have shown QSPRs to fail, such as where penetrants have high log P and high molecular weight. CONCLUSIONS: A non-linear approach was more appropriate than QSPRs or SLNs for the analysis of the dataset employed herein, as the prediction and confidence values in the prediction given by the Gaussian process are better than with other methods examined. Gaussian process provides a novel way of analysing skin absorption data that is substantially more accurate, statistically robust and reflective of our empirical understanding of skin absorption than the QSPR methods so far applied to skin absorption.

Transdermal delivery enhancement of haloperidol from gel formulations by 1,8-cineole.

The feasibility of using 10% 1,8-cineole as an enhancer for transdermal delivery of haloperidol has been examined. In-vitro transdermal delivery across full-thickness human, rabbit and hairless mouse skins was measured from three polymer gel systems, hypromellose (hydroxypropylmethylcellulose), Carbomer (Carbopol) 940 and macrogol (polyethylene glycol) using Franz cells. Values for the permeability coefficient kp, calculated as the product (Kh)x(D/h2) where these two factors were obtained from curve fitting of the non-steady-state equation over 24 h, were similar from the three formulations. The value of kp from hypromellose was significantly enhanced by cineole by factors of 6.2 (4.6-8.1), 5.6 (5.0-6.2) and 3.0 (2.6-3.4) for human, rabbit and mouse, respectively (mean and 95% confidence intervals). Enhancement ratios for K: 13.3 (8.3-20), 3.1 (2.5-3.9) and 2.0 (1.5-2.6), were higher than those for D: 0.47 (0.41-0.55), 1.8 (1.6-2.1) and 1.5 (1.3-1.8). This suggested that the barrier function of the skin lipids was marginally affected and the main effect was to increase the thermodynamic activity of the drug in the barrier. The enhancement achieved in human skin suggested that delivery could be safely enhanced by terpenoids.

Lack of direct inhibition of insulin secretion by exogenous insulin in the canine pancreas.

To test whether insulin secretion is self-regulatory, canine pancreata were isolated and perfused in vitro and were infused with 0.3, 0.6, or 1.2 mU/ml exogenous insulin. Basal and arginine-stimulated concentrations of C-peptide, glucagon, and somatostatin were measured. There were no significant differences between basal secretion nor the increment of arginine-stimulated secretion for each respective hormone at each exogenous insulin concentration. The second preparation studied was a vascularly isolated, yet innervated, in situ perfused pancreas. Exogenous insulin (1 mU/kg per min) was infused "systemically"; the pancreas received no insulin. Endogenous pancreatic insulin and C-peptide secretion was suppressed, while pancreatic glucagon secretion increased during systemic insulin infusion. No changes in pancreatic hormone secretion occurred after the sympathetic nerves were sectioned. These results suggest that exogenous insulin does not directly suppress the B cell, but can suppress insulin secretion through an indirect neurally mediated, insulin-dependent nerve mechanism.

Use of biosynthetic human C-peptide in the measurement of insulin secretion rates in normal volunteers and type I diabetic patients.

We undertook this study to examine the accuracy of plasma C-peptide as a marker of insulin secretion. The peripheral kinetics of biosynthetic human C-peptide (BHCP) were studied in 10 normal volunteers and 7 insulin-dependent diabetic patients. Each subject received intravenous bolus injections of BHCP as well as constant and variable rate infusions. After intravenous bolus injections the metabolic clearance rate of BHCP (3.8 +/- 0.1 ml/kg per min, mean +/- SEM) was not significantly different from the value obtained during its constant intravenous infusion (3.9 +/- 0.1 ml/kg per min). The metabolic clearance rate of C-peptide measured during steady state intravenous infusions was constant over a wide concentration range. During experiments in which BHCP was infused at a variable rate, the peripheral concentration of C-peptide did not change in proportion to the infusion rate. Thus, the infusion rate of BHCP could not be calculated accurately as the product of the C-peptide concentration and metabolic clearance rate. However, the non-steady infusion rate of BHCP could be accurately calculated from peripheral C-peptide concentrations using a two-compartment mathematical model when model parameters were derived from the C-peptide decay curve in each subject. Application of this model to predict constant infusions of C-peptide from peripheral C-peptide concentrations resulted in model generated estimates of the C-peptide infusion rate that were 101.5 +/- 3.4% and 100.4 +/- 2.8% of low and high dose rates, respectively. Estimates of the total quantity of C-peptide infused at a variable rate over 240 min based on the two-compartment model represented 104.6 +/- 2.4% of the amount actually infused. Application of this approach to clinical studies will allow the secretion rate of insulin to be estimated with considerable accuracy. The insulin secretion rate in normal subjects after an overnight fast was 89.1 pmol/min, which corresponds with a basal 24-h secretion of 18.6 U.

C-peptide and insulin secretion. Relationship between peripheral concentrations of C-peptide and insulin and their secretion rates in the dog.

Estimation of the insulin secretory rate from peripheral C-peptide concentrations depends upon the following characteristics of C-peptide kinetics: (a) equimolar secretion of insulin and C-peptide by pancreatic beta cells; (b) negligible hepatic extraction of C-peptide; (c) constant metabolic clearance rate (MCR) of C-peptide over a physiological and pathophysiological range of plasma levels; and (d) proportional changes in the secretion rate of C-peptide and its peripheral concentrations under varying physiological conditions. In the present experiments, the relationship between a variable intraportal infusion of C-peptide and its concentration in the femoral artery was explored in 12 pancreatectomized dogs. As the infusion of C-peptide was rapidly increased, the magnitude of its peripheral concentration initially increased less than the infusion rate by 20-30%. After an equilibration period of approximately 30 min, however, further increases and decreases in the intraportal infusion were accompanied by nearly proportional changes in its peripheral concentration. Estimates of the amount of C-peptide infused during the experiment based on the steady state C-peptide MCR and its peripheral concentration were within 20% of the amount of C-peptide actually infused. These experiments demonstrate that the portal delivery rate of C-peptide can be calculated from its MCR and peripheral concentration in the dog. They also provide a basis for testing the validity of more complicated models of insulin secretion based on peripheral C-peptide concentrations in the dog as well as other species, including man. Finally, we have shown that the hepatic extraction of endogenously secreted C-peptide is negligible in the basal state (3.1 +/- 6.1%), and does not change after oral glucose ingestion. The MCR of exogenous dog C-peptide was similar whether measured by constant peripheral intravenous infusion (12.3 +/- 0.7 ml/kg per min), constant intraportal infusion (13.4 +/- 0.6 ml/kg per min), or analysis of the decay curve after a bolus injection (13.5 +/- 0.7 ml/kg per min).

Metabolism of C-peptide in the dog. In vivo demonstration of the absence of hepatic extraction.

The in vivo hepatic metabolism of connecting peptide (C-peptide) in relation to that of insulin has not been adequately characterized. A radioimmunoassay for dog C-peptide was therefore developed and its metabolism studied in conscious mongrel dogs, with sampling catheters chronically implanted in their portal and hepatic veins and femoral artery. The hepatic extraction of endogenous C-peptide under basal conditions was negligible (4.3 +/- 4.5%) and was similar to the hepatic extraction of C-peptide measured during the constant exogenous infusion of C-peptide isolated from dog pancreas. Simultaneously measured hepatic extraction of endogenous and exogenously infused insulin were 43.8 +/- 7.6 and 47.5 +/- 4.4%, respectively. The metabolic clearance rate of infused C-peptide was 11.5 +/- 0.8 ml/kg per min and was constant over the concentration range usually encountered under physiological conditions. In additional experiments, the effect of parenteral glucose administration on the hepatic extraction of C-peptide and insulin was investigated. The hepatic extraction of C-peptide (6.2 +/- 4.0%) was again negligible in comparison with that of insulin (46.7 +/- 3.4%). Parenteral glucose administration did not affect the hepatic extraction of either peptide irrespective of whether it was infused peripherally, intraportally, or together with an intraportal infusion of gastrointestinal inhibitory polypeptide. The fasting C-peptide insulin molar ratio in both the portal vein (1.2 +/- 0.1) and femoral artery (2.1 +/- 0.3) was also unaffected by the glucose stimulus. These results therefore indicate that, since the hepatic extraction of C-peptide is negligible and its clearance kinetics linear, the peripheral C-peptide concentration should accurately reflect the rate of insulin secretion. New approaches to the quantitation of hepatic extraction and secretion of insulin by noninvasive techniques are now feasible.

Defective insulin secretion in hepatocyte nuclear factor 1alpha-deficient mice.

Mutations in the gene for the transcription factor hepatocyte nuclear factor (HNF) 1alpha cause maturity-onset diabetes of the young (MODY) 3, a form of diabetes that results from defects in insulin secretion. Since the nature of these defects has not been defined, we compared insulin secretory function in heterozygous [HNF-1alpha (+/-)] or homozygous [HNF-1alpha (-/-)] mice with null mutations in the HNF-1alpha gene with their wild-type littermates [HNF-1alpha (+/+)]. Blood glucose concentrations were similar in HNF-1alpha (+/+) and (+/-) mice (7.8+/-0.2 and 7.9+/-0.3 mM), but were significantly higher in the HNF-1alpha (-/-) mice (13.1+/-0.7 mM, P < 0.001). Insulin secretory responses to glucose and arginine in the perfused pancreas and perifused islets from HNF-1alpha (-/-) mice were < 15% of the values in the other two groups and were associated with similar reductions in intracellular Ca2+ responses. These defects were not due to a decrease in glucokinase or insulin gene transcription. beta cell mass adjusted for body weight was not reduced in the (-/-) animals, although pancreatic insulin content adjusted for pancreas weight was slightly lower (0.06+/-0.01 vs. 0.10+/-0.01 microg/mg, P < 0.01) than in the (+/+) animals. In summary, a null mutation in the HNF-1alpha gene in homozygous mice leads to diabetes due to alterations in the pathways that regulate beta cell responses to secretagogues including glucose and arginine. These results provide further evidence in support of a key role for HNF-1alpha in the maintenance of normal beta cell function.

Sustained expression of hepatocyte nuclear factor-6 leads to loss of pancreatic beta-cells by apoptosis.

Hepatocyte nuclear factor-6 (HNF-6) is the ONECUT-homeodomain transcription factor that is enriched in liver and also present in pancreas and central nervous system. It is expressed in the pancreatic bud at E10.5. In adult pancreas, its expression is restricted to the exocrine pancreas and duct cells. Since duct cells are thought to be precursors of endocrine cells and HNF-6 is involved in the regulation of the expression of HNF-4alpha and -1beta, genes that cause maturity onset diabetes of the young (MODY), we hypothesized that the sustained expression of HNF-6 would affect beta-cell function. We generated transgenic mice over-expressing human HNF-6 using the mouse insulin I promoter (MIP). We obtained one female founder in which the transgene had been incorporated into two sites; the chromosome (Ch) 14 and the X chromosome. The integration site of the latter was within centromeric heterochromatin and the transgene was inactivated. Studies on mice in which the transgene was integrated into Ch14 showed beta-cell specific defects functionally and pathologically. The insulin secretory response to glucose and arginine in the in situ-perfused pancreas was also significantly impaired in these mice. Immunohistochemical analysis revealed that the islets were smaller and had an abnormal architecture with an inverted ratio of alpha- and beta-cells resulting from beta-cell loss to 30% by 6-wk of age. The decreased number of beta-cells was quantified first time by fluorescent activated cell sorting using entire pancreata from the transgenic mice crossed with MIP-green fluorescent protein (GFP) mice. This severe loss of beta-cells involved programmed cell death.

Gastroretentive dosage forms: overview and special case of Helicobacter pylori.

The challenge to develop efficient gastroretentive dosage forms began about 20 years ago, following the discovery of Helicobacter pylori by Warren and Marshall. In order to understand the real difficulty of increasing the gastric residence time of a dosage form, we have first summarized the important physiologic parameters, which act upon the gastric residence time. Afterwards, we have reviewed the different drug delivery systems designed until now, i.e. high-density, intragastric floating, expandable, superporous hydrogel, mucoadhesive and magnetic systems. Finally, we have focused on gastroretentive dosage forms especially designed against H. pylori, including specific targeting systems against this bacterium.

Design, synthesis and characterization of captopril prodrugs for enhanced percutaneous absorption.

Most drugs are designed primarily for oral administration, but the activity and stability profiles desirable for this route often make them unsuitable for transdermal delivery. We were therefore interested in designing analogues of captopril, a model drug with poor percutaneous penetration, for which the sustained steady-state blood plasma level associated with transdermal delivery (and which is unattainable orally) would be particularly beneficial. Quantitative structure-permeability relationships (QSPRs) predicted that ester and thiol prodrug derivatives of captopril would have lower maximal transdermal flux (J(m)) than the parent drug, since the increases in permeability coefficient (k(p)) of prodrugs would be outweighed by the reductions in aqueous solubility. Therefore, the aim of this study was to synthesize a series of prodrugs of captopril and to determine if a QSPR model could be used to design therapeutically viable prodrugs. Molecules with the highest predicted k(p) values were synthesized and characterized, and J(m) measured in Franz diffusion cells from saturated aqueous donor across porcine skin (fresh and frozen). In-vitro metabolism was also measured. Captopril and the prodrugs crossed the skin relatively freely, with J(m) being highest for ethyl to butyl esters. Substantial first-order metabolism of the prodrugs was observed, suggesting that their enhanced percutaneous absorption was complemented by their metabolic performance. The results suggested that QSPR models provided excellent enhancements in drug delivery. This was not seen at higher lipophilicities, suggesting that issues of solubility need to be considered in conjunction with any such use of a QSPR model.

Mantle cell lymphoma: correlation of clinical outcome and biologic features with three histologic variants.

PURPOSE: Clinical data and histologic material were retrospectively analyzed in 46 cases of previously untreated mantle cell lymphoma (MCL) to more fully characterize the clinical response pattern of these lymphomas and to determine whether growth pattern significantly affected clinical outcome. MATERIALS AND METHODS: The histologic pattern was classified as diffuse (61%), nodular (13%), and mantle zone (26%) in accordance with stated criteria. RESULTS: Bone marrow infiltration was detected in 69% of cases; the frequency of involvement correlated with histologic pattern, being most common in diffuse variants and least common in mantle zone variants. Other sites of extranodal involvement were observed in 50% of cases. Cyclin-D1 staining revealed nuclear positivity in 23 of 25 patients (92%) and no difference was observed between the various histologic patterns. Rearrangement at the bcl-1 major translocation cluster (MTC) was detected in seven of 21 cases, without regard for histologic pattern. Complete response rates to doxorubicin-based regimens showed a striking correlation with histologic pattern. Seventy-three percent of patients with a mantle zone pattern attained a complete response compared with only 25% of patients with a nodular pattern and 19% with a diffuse pattern. Three-year survival rates were 100%, 50%, and 55% for patients with mantle zone, nodular, and diffuse histologic patterns, respectively. CONCLUSION: We conclude that (1) diffuse and nodular MCL are associated with a poor treatment response and a poor overall survival rate; (2) the mantle zone variant exhibits the clinical attributes of a low-grade lymphoma; and (3) the poor survival rates of patients with nodular and diffuse MCL suggest that these variants be classified as intermediate-grade lymphomas. However, the trend of the time to treatment failure curve does not indicate that current regimens can cure MCL.

Testicular lymphoma: late relapses and poor outcome despite doxorubicin-based therapy.

PURPOSE: To determine the significance of the International Prognostic Index (IPI) score in adults with testicular lymphoma treated with doxorubicin-based regimens. PATIENTS AND METHODS: Untreated adults with testicular lymphoma who presented between 1969 and 1993 were studied. Those with Ann Arbor stages III and IV were included if they had a testicular mass at presentation. RESULTS: We identified 22 patients, 21 with intermediate-grade and one with high-grade lymphoma. All 10 patients with an IPI score < or = 1 had Ann Arbor stage I disease, whereas the 12 with an IPI score more than 1 had Ann Arbor stage II to IV disease. Complete remission (CR) was achieved in 73% of patients. At 153 months, 22% of all complete responders and 40% and 0% of those with IPI scores < or = 1 and more than 1, respectively, remained in CR (P = .01). With a median follow-up time of 113 months for survivors, the failure-free survival (FFS) rate at 153 months was 16% for all patients or 32% and 0% for those with IPI scores < or = 1 and more than 1, respectively (P = .02). The CNS or contralateral testis were involved in all patients who failed to respond to primary therapy and in 50% of those who relapsed from CR. CONCLUSION: The prognosis of patients with testicular lymphoma appears poor despite doxorubicin-based chemotherapy. On the basis of failures in the CNS and contralateral testis, we recommend prophylactic intrathecal chemotherapy and scrotal radiotherapy for all patients. Those with an IPI score < or = 1 can be treated with conventional doxorubicin-based regimens, but those with an IPI score more than 1 should be considered for investigational systemic therapy.

Richter's syndrome: a report on 39 patients.

PURPOSE: The incidence, clinical features, laboratory findings, and treatment results of 39 patients with Richter's syndrome (RS) are reported. PATIENTS AND METHODS: Thirty-nine of 1,374 patients with chronic lymphocytic leukemia (CLL) developed RS. RESULTS: Features associated with RS included systemic symptoms (59%), progressive lymphadenopathy (64%), extranodal involvement (41%), elevation of lactate dehydrogenase (LDH; 82%), and a monoclonal gammopathy (44%). Analysis of the CLL karyotype showed no specific chromosomal abnormality that conferred increased risk; however, multiple abnormalities were common. Patients at all Rai stages and in complete response (CR) were at risk, including three CR patients with no residual disease at the level of detection by dual-parameter flow cytometry or restriction analysis for immunoglobulin (Ig) gene rearrangements. The incidence was not higher in patients who had received prior fludarabine or chlorodeoxyadenosine. The median survival duration was only 5 months, despite multiagent therapy. Patients who responded had prolonged survival durations (P < .001). Three of eight patients who survived more than 1 year had a de novo presentation of both CLL and large-cell lymphoma (LCL). Comparison of surface light-chain analysis from both low- and high-grade components demonstrated isotypic light-chain expression in 12 of 15 patients. Ig heavy- and light-chain gene rearrangement analysis showed identical rearrangement patterns in five of five patients. CONCLUSION: The clinical, laboratory, and survival characteristics of our RS patients were similar to those reported in earlier studies. Ig gene rearrangement and light-chain isotype analysis support a common origin for CLL and LCL. Despite progress in the treatment of CLL, the development of LCL remains a serious complication and continued surveillance in all CLL patients is warranted.

Hyper-CVAD and high-dose methotrexate/cytarabine followed by stem-cell transplantation: an active regimen for aggressive mantle-cell lymphoma.

PURPOSE: Diffuse and nodular forms of mantle-cell lymphoma (MCL) are consistently associated with poor prognosis. In an effort to improve the outcome, we adopted a treatment plan that consisted of four courses of fractionated cyclophosphamide (CY) 1,800 mg/m2 administered with doxorubicin (DOX), vincristine (VCR), and dexamethasone (Hyper-CVAD) that alternated with high-dose methotrexate (MTX) and cytarabine (Ara-C). After four courses, patients were consolidated with high-dose CY, total-body irradiation, and autologous or allogeneic blood or marrow stem-cell transplantation. PATIENTS AND METHODS: Forty-five patients were enrolled; 25 patients were previously untreated, 43 patients had Ann Arbor stage IV disease, and 42 patients had marrow involvement. Forty-one patients had diffuse histology, two patients had nodular, and two patients had blastic variants. RESULTS: Hyper-CVAD/MTX-Ara-C induced a response rate of 93.5% (complete response [CR], 38%; partial response [PR], 55.5%) after four cycles of pretransplantation induction chemotherapy. All patients who went on to undergo transplantation achieved CRs. For the 25 previously untreated patients, the overall survival (OS) and event-free survival (EFS) rates at 3 years were 92% (95% confidence interval [CI], 80 to 100) and 72% (95% CI, 45 to 98) compared with 25% (95% CI, 12 to 62; P = .005) and 17% (95% CI, 10 to 43; P = .007), respectively, for the previously treated patients. When compared with a historic control group who received a CY, DOX, VCR, and prednisone (CHOP)-like regimen, untreated patients in the study had a 3-year EFS rate of 72% versus 28% (P = .0001) and a better OS rate (92% v 56%; P = .05). Treatment-related death occurred in five patients: all were previously treated and two received allogeneic transplants. CONCLUSION: The Hyper-CVAD/MTX-Ara-C program followed by stem-cell transplantation is a promising new therapy for previously untreated patients with MCL.

High-dose chemotherapy for relapsed and refractory diffuse large B-cell lymphoma: mediastinal localization predicts for a favorable outcome.

PURPOSE: This study was performed to evaluate the outcome of high-dose chemotherapy and autologous transplantation in patients with diffuse B-cell large-cell lymphoma, and, specifically, to evaluate the impact of primary mediastinal localization on the outcome of high-dose chemotherapy. PATIENTS AND METHODS: A retrospective review was performed of all patients with diffuse large B-cell lymphoma who underwent autologous marrow or peripheral-blood stem-cell transplantation at our institution between January 1 986 and December 1995. RESULTS: Ninety patients were identified, of whom 31 (34%) had a primary mediastinal B-cell large-cell lymphoma (PML). Cumulative probabilities of disease-free survival, overall survival, and disease progression are 40% (95% confidence interval [CI], 29 to 51), 42% (95% CI, 31 to 53), and 52% (95% CI, 40 to 64), respectively. By univariate analysis, low lactate dehydrogenase (LDH) level and low Ann Arbor stage at transplant were associated with improved survival and disease-free survival. There was a trend for improved disease-free survival and survival for patients with PML. Multivariate stepwise Cox regression analysis showed that LDH level, Ann Arbor stage, and primary mediastinal localization were independent favorable prognostic factors for disease-free survival and survival. LDH level and Ann Arbor stage were also predictive for the risk of disease progression. CONCLUSION: Our results indicate that patients with PML may display an increased susceptibility to high-dose chemotherapy compared with other types of B-cell large-cell lymphoma. These findings, if confirmed, may have implications for the initial management of patients with PML.

The limitations to and valid use of C-peptide as a marker of the secretion of insulin.

The accuracy with which the secretion rate of insulin can be calculated from peripheral concentrations of C-peptide was investigated in conscious mongrel dogs. Biosynthetic human C-peptide and insulin were infused intraportally and their concentrations measured in the femoral artery. During steady-state infusions of C-peptide, the peripheral concentration changed in proportion to the infusion rate and the metabolic clearance rate (5.2 +/- 0.3 ml/kg/min) remained constant over a wide range of plasma concentrations. Application of a two-compartment mathematical model, in which the model parameters were estimated from analysis of C-peptide decay curves after intravenous bolus injections, allowed the intraportal infusion rate of C-peptide to be derived from peripheral C-peptide concentrations, even under non-steady-state conditions. Estimates of the intraportal infusion rate based on this model were 102.4 +/- 2.6% of the actual infusion rate as it was increasing and 102.3 +/- 5.5% of this rate as it was falling. The peripheral C-peptide: insulin molar ratio was influenced by the rate at which equimolar intraportal infusions of C-peptide and insulin were changed. The baseline C-peptide: insulin molar ratio (4.1 +/- 0.9) increased to peak values of 8.2 +/- 0.6, 10.3 +/- 2.0, and 14.9 +/- 1.3 when the infusion rate was increased and then decreased rapidly. Peak values of only 5.7 +/- 1.2 were found if the intraportal infusion rate was changed slowly.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of calcium channel mRNAs in rat pancreatic islets and downregulation after glucose infusion.

Recent studies have shown that two different voltage-dependent Ca2+ channels are expressed in pancreatic islets, the beta-cell/neuroendocrine-brain and the cardiac subtypes. The effects of chronic hyperglycemia on the levels in pancreatic islets of the mRNAs encoding the alpha 1-subunits of the beta-cell and cardiac subtype Ca2+ channels were studied in rats made hyperglycemic by infusion of glucose for 48 h. A competitive reverse transcriptase-polymerase chain reaction procedure was used to obtain quantitative data on the levels of these two transcripts in islets obtained from individual rats. The quantitative polymerase chain reaction data indicate that the levels of mRNA encoding the alpha 1-subunit of the beta-cell Ca2+ channel are 2.5-fold greater than those for the cardiac subtype. The levels of beta-cell Ca2+ channel mRNA were 72.9% lower in the glucose-infused animals when compared with the saline-infused animals (P < 0.005) and those of the cardiac channel were 72.1% lower in the animals infused with glucose (P < 0.02). In contrast, glucose infusion resulted in a twofold increase in insulin mRNA levels and did not significantly alter levels of beta-actin mRNA. In situ hybridization studies revealed that the mRNAs for these two Ca2+ channels are expressed at higher levels in normal rat islets than in the surrounding acinar tissue, which suggests that the observed changes in mRNA levels occur within cells of the pancreatic islet. To assess the possible functional consequences of this reduction in expression of mRNA for the Ca2+ channels, the insulin secretory responses of perfused pancreases to the Ca2+ channel agonist Bay K8644 were studied.(ABSTRACT TRUNCATED AT 250 WORDS)