Cryosurgery versus curettage for intraepidermal carcinoma: A randomized controlled trial

BACKGROUND

Cryosurgery is a common destructive treatment method for intraepidermal carcinoma (IEC) above the knee. Curettage alone is a simple, non-aggressive and inexpensive treatment method commonly used on benign skin lesions. However, only one study has assessed curettage for treatment of IEC.

OBJECTIVE

We aimed to (1) compare the effectiveness of cryosurgery (standard method) to curettage (experimental method) for treatment of IEC in regard to overall clearance rates at 1-year follow-up, and (2) investigate whether wound healing times differed between the treatment groups.

METHODS

In this randomized and controlled, non-inferiority trial, adult patients with one or more IEC with a diameter of 5-20 mm, located above the knee and suitable for destructive treatment were recruited from Sahlgrenska University Hospital (Gothenburg, Sweden). Lesions were randomized to treatment with either cryosurgery or curettage. Wound healing was assessed by a nurse after 4-6 weeks and through self-report forms. Overall clearance was assessed by a dermatologist after 1 year.

RESULTS

In total, 183 lesions in 147 patients were included, with 93 lesions randomized to cryosurgery and 90 to curettage. Eighty-eight (94.6%) of the lesions in the cryosurgery group and 71 (78.9%) in the curettage group showed an overall clearance at the 1-year follow-up visit (p = 0.002). The non-inferiority analysis was inconclusive. Curettage resulted in both shorter self-reported wound healing times (mean time 3.1 vs. 4.8 weeks, p < 0.001) and a larger proportion of healed wounds after 4-6 weeks (p < 0.001).

CONCLUSIONS

Cryosurgery and curettage both result in high clearance rates for treatment of IEC, but cryosurgery is significantly more effective. On the other hand, curettage may result in shorter wound healing times.

Curettage versus cryosurgery for superficial basal cell carcinoma: a prospective, randomised and controlled trial

Background

Basal cell carcinoma (BCC) is the most common cancer in the world and has a rising incidence. Current guidelines for low‐risk BCC including superficial BCC (sBCC) recommend several treatment options including destructive treatment methods, such as cryosurgery with or without prior curettage or curettage and electrodesiccation. Curettage only (i.e. without subsequent cryosurgery or electrodesiccation) is a simple and quick destructive treatment method used for many benign skin lesions but has not been sufficiently evaluated for the treatment of sBCCs.

Objectives

The objective was to compare the effectiveness of curettage vs. cryosurgery for sBCCs in terms of overall clinical clearance rates after 1 year as well as wound healing times.

Methods

A single‐centre non‐inferiority clinical trial was conducted. Non‐facial sBCCs with a diameter of 5–20 mm were randomised to either cryosurgery using one freeze–thaw cycle or curettage. At follow‐up visits, treatment areas were evaluated regarding the presence of residual tumour after 3–6 months and recurrence after 1 year. Further, wound healing times were assessed.

Results

In total, 228 sBCCs in 97 patients were included in the analysis. At 3–6 months, no residual tumours were seen in any of the treated areas. After 1 year, the clinical clearance rates for curettage and cryosurgery were 95.7% and 100%, respectively (P = 0.060). However, the non‐inferiority analysis was inconclusive. Wound healing times were shorter for curettage (4 weeks) compared to cryosurgery (5 weeks; P < 0.0001). Overall, patient satisfaction at 1 year was high.

Conclusions

Both treatment methods showed high clinical clearance rates after 1 year, whilst curettage reduced the wound healing time.

Serine/threonine protein phosphatase 5 regulates glucose homeostasis in vivo and apoptosis signalling in mouse pancreatic islets and clonal MIN6 cells

AIMS/HYPOTHESIS

During the development of type 2 diabetes mellitus, beta cells are often exposed to a high glucose/hyperlipidaemic environment, in which the levels of reactive oxygen species (ROS) are elevated. In turn, ROS can trigger an apoptotic response leading to beta cell death, by activating mitogen-activated protein kinase (MAPK) signalling cascades. Here we test the hypothesis that serine/threonine protein phosphatase 5 (PP5) acts to suppress proapoptotic c-Jun N-terminal kinase (JNK) signalling in beta cells.

METHODS

Ppp5c(-/-) and Ppp5c(+/+) mice were subjected to intraperitoneal glucose (IPGTT) or insulin tolerance tests. Pancreatic islets from Ppp5c(-/-) and Ppp5c(+/+) mice or MIN6 cells treated with short-interfering RNA targeting PP5 were exposed to palmitate or H(2)O(2) to activate MAPK signalling. Changes in protein phosphorylation, mRNA expression, apoptosis and insulin secretion were detected by western blot analysis, quantitative RT-PCR or ELISA.

RESULTS

Ppp5c(-/-) mice weighed less and exhibited reduced fasting glycaemia and improved glucose tolerance during IPGTT, but retained normal insulin sensitivity and islet volume. Comparison of MAPK signalling in islets from Ppp5c(-/-) mice and MIN6 cells revealed that the lack of PP5 was associated with enhanced H(2)O(2)-induced phosphorylation of JNK and c-Jun. Cells with reduced PP5 also showed enhanced JNK phosphorylation and apoptosis after palmitate treatment. PP5 suppression in MIN6 cells correlated with hypersecretion of insulin in response to glucose.

CONCLUSIONS/INTERPRETATION

PP5 deficiency in mice is associated with reduced weight gain, lower fasting glycaemia, and improved glucose tolerance during IPGTT. At a molecular level, PP5 helps suppress apoptosis in beta cells by a mechanism that involves regulation of JNK phosphorylation.

Effects of intravenous exenatide in type 2 diabetic patients with congestive heart failure: a double-blind, randomised controlled clinical trial of efficacy and safety

AIMS/HYPOTHESIS

The aim of this study was to determine whether exenatide improves haemodynamic function in patients with type 2 diabetes with congestive heart failure (CHF).

METHODS

The main eligibility criteria for inclusion were: male/female (18-80 years) with type 2 diabetes and CHF (ejection fraction ≤ 35%, and New York Heart Association functional class III or IV). Out of 237 patients screened, 20 male type 2 diabetic patients participated in this crossover trial design and were allocated (sequentially numbered) to i.v. infusions during two consecutive days with (1) exenatide (0.12 pmol/kg/min); and (2) placebo for 6 h followed by a washout period for 18 h, at Stockholm South Hospital, Sweden. Patients and researchers were blinded to the assignment. Cardiac haemodynamic variables were determined by right heart catheterisation. The primary endpoint was defined as an increase in cardiac index (CI) or a decrease in pulmonary capillary wedge pressure (PCWP) of ≥ 20%. Secondary endpoints were tolerability and safety of exenatide infusion.

RESULTS

CI increased at 3 and 6 h by 0.4 ± 0.1 (23%) and 0.33 ± 0.1 (17%) l min(-1) m(-2), during exenatide infusion vs -0.02 ± 0.1 (-1%) and -0.08 ± 0.1 (-5%) l min(-1) m(-2) during placebo (p = 0.003); and heart rate (HR) increased at 1, 3 and 6 h by 8 ± 3 (11%), 15 ± 4 (21%) and 21 ± 5 (29%) beats per min (bpm), during exenatide infusion vs -1 ± 2 (-2%), 1 ± 1 (2%) and 6 ± 2 (8%) bpm, during placebo (p = 0.006); and PCWP decreased at 1, 3 and 6 h by -1.3 ± 0.8 (-8%), -1.2 ± 1 (-8%) and -2.2 ± 0.9 (-15%) mmHg, during exenatide infusion vs 0.3 ± 0.5 (2%), 1 ± 0.6 (6%) and 1.4 ± 0.7 (8%) mmHg, during placebo (p = 0.001). No serious adverse event was observed. Adverse events were reported in nine patients (six, nausea; two, increased HR; one, increased systolic blood pressure).

CONCLUSIONS/INTERPRETATION

Infusion of exenatide in male type 2 diabetic patients with CHF increased the CI as a result of chronotropy, with concomitant favourable effects on PCWP and reasonable tolerability of the drug. The clinical implications of using exenatide in patients with CHF are still not clear and further studies are warranted.

TRIAL REGISTRATION

www.isrctn.org/ISRCTN47533126

Exendin-4 stimulates proliferation of human coronary artery endothelial cells through eNOS-, PKA- and PI3K/Akt-dependent pathways and requires GLP-1 receptor

Endothelial cells have a robust capacity to proliferate and participate in angiogenesis, which underlies the maintenance of intimal layer integrity. We previously showed the presence of the GLP-1 receptor in human coronary artery endothelial cells (HCAECs) and the ameliorative actions of GLP-1 on endothelial dysfunction in type 2 diabetic patients. Here, we have studied the effect of exendin-4 on cell proliferation and its underlying mechanisms in HCAECs. Incubation of HCAECs with exendin-4 resulted in a dose-dependent increase in DNA synthesis and an increased cell number, associated with an enhanced eNOS and Akt activation, which were inhibited by PKA, PI3K, Akt or eNOS inhibitors and abolished by a GLP-1 receptor antagonist. Similar effects were obtained by applying GLP-1 (7-36) or GLP-1 (9-36). Co-incubation of exendin-4 and GLP-1 did not show additive effects. Our results suggest that exendin-4 stimulates proliferation of HCAECs through PKA-PI3K/Akt-eNOS activation pathways via a GLP-1 receptor-dependent mechanism.

Reduced plasma levels of glucagon-like peptide-1 in elderly men are associated with impaired glucose tolerance but not with coronary heart disease

AIMS/HYPOTHESIS

Besides the insulinotropic effects of glucagon-like peptide-1 (GLP-1) mimetics, their effects on endothelial dysfunction and myocardial ischaemia are of interest. No previous study has investigated associations between plasma levels of GLP-1 and CHD.

METHODS

We investigated longitudinal relationships of fasting GLP-1 with the dynamic GLP-1 response after OGTT (difference between 60 min OGTT-stimulated and fasting GLP-1 levels [DeltaGLP-1]) and CHD in a population-based cohort of 71-year-old men. In the same cohort, we also cross-sectionally investigated the association between stimulated GLP-1 levels and: (1) cardiovascular risk factors (blood pressure, lipids, urinary albumin, waist circumference and insulin sensitivity index [M/I] assessed by euglycaemic-hyperinsulinaemic clamp); and (2) impaired glucose tolerance (IGT) and type 2 diabetes mellitus.

RESULTS

During the follow-up period (maximum 13.8 years), of 294 participants with normal glucose tolerance (NGT), 69 experienced a CHD event (13.8 years), as did 42 of 141 with IGT and 32 of 74 with type 2 diabetes mellitus. DeltaGLP-1 did not predict CHD (HR 1.0, 95% CI 0.52-2.28). The prevalence of IGT was associated with DeltaGLP-1, lowest vs highest quartile (OR 0.3, 95% CI 0.12-0.58), with no such association for type 2 diabetes mellitus (OR 1.0, 95% CI 0.38-2.86). M/I was significantly associated with DeltaGLP-1 in the type 2 diabetes mellitus group (r = 0.38, p < 0.01), but not in the IGT (r = 0.11, p = 0.28) or NGT (r = 0.10, p = 0.16) groups.

CONCLUSIONS/INTERPRETATION

Impaired GLP-1 secretion is associated with IGT, but not with type 2 diabetes mellitus. This finding in the latter group might be confounded by oral glucose-lowering treatment. GLP-1 does not predict CHD. Although DeltaGLP-1 was associated with insulin sensitivity in the type 2 diabetes mellitus group, GLP-1 does not seem to be a predictor of CHD in insulin-resistant patients.

Impact of glucagon-like peptide-1 on endothelial function

Cardiovascular (CV) disease is the major cause of mortality and morbidity in individuals with diabetes. Individuals with diabetes often have a variety of factors such as hyperglycaemia, dyslipidaemia, hypertension, insulin resistance and obesity, which increase their risks of endothelial dysfunction and CV disease. The incretin hormones, such as glucagon-like peptide-1 (GLP-1), induce the glucose-dependent secretion of insulin, improve beta-cell function and induce slowing of gastric emptying and feelings of satiety - which result in reduced food intake and weight loss. Therapeutic treatments targeting the incretin system, such as GLP-1 receptor agonists, offer the potential to address beta-cell dysfunction (one the underlying pathogenic mechanisms of type 2 diabetes), as well as the resulting hyperglycaemia. Initial evidence now suggests that incretins could have beneficial effects on endothelial function and the CV system through both indirect effects on the reduction of hyperglycaemia and direct effects mediated through GLP-1 receptor-dependent and -independent mechanisms. If these initial findings are confirmed in larger clinical trials, GLP-1 receptor antagonists could help to address the major CV risks faced by patients with diabetes.

Immunosuppression and the additive effect of plasma exchange in treatment of rapidly progressive glomerulonephritis

Attempts were made to evaluate the separate effect on kidney function of immunosuppressive treatment (IS) and plasma exchange (PE) in 27 patients with rapidly progressive glomerulonephritis (RPGN). Twenty-four of the patients were treated with PE. Initial IS was supplemented with PE within 6-12 days in 5 patients, and after at least 14 days in 13. Because of suspected septicemia, 2 patients were first treated with PE, and IS was not initiated until the possibility of septicemia had been excluded. In 4 severely ill patients wih rapid clinical deterioration, both treatments were started simultaneously. Twenty patients improved during one or both treatments, 4 with IS alone, 2 with IS and doubtfully with PE, 3 with IS and probably also with PE, 5 both with IS and PE and one with PE alone. In 5 patients the individual effects of IS and PE could not be evaluated. In another 2 patients the combined treatment seemed to influence the course favourably. In the remaining 7 patients the effect of the treatment was doubtful or nil. Two further patients with Goodpasture's syndrome were treated. They were admitted late, and both kinds of treatment were instituted simultaneously. One of them died in respiratory insufficiency, the other remained oliguric while the pulmonary changes faded. Thus, PE added a positive effect to IS in several patients with RPGN. The treatment had few and mostly mild side-effects.

Prenatal viral exposure followed by adult stress produces glucose intolerance in a mouse model

AIMS/HYPOTHESIS

It has been suggested that the uterine environment may influence metabolic disease occurring later in adult life, and that adult stress may promote disease outcome. Using a mouse model, we tested whether in utero exposure to Ljungan virus (LV) followed by adult exposure to stress produces diabetes. The influence of the timing of viral exposure over the course of pregnancy was also tested.

MATERIALS AND METHODS

Pregnant CD-1 mice were exposed i.p. to LV on pregnancy days 4, 8, 12 or 17. Adult male mice from these pregnancies were stressed by being kept in shared cages. Stress only, LV exposure in utero only, and no-stress/no virus exposure groups were also followed. Outcome variables included bodyweight, epididymal fat weight, baseline glucose, glucose tolerance tests (60 and 120 min) and serum insulin.

RESULTS

We demonstrated that male mice developed a type 2-like diabetes, including obesity, as adults if infected during pregnancy with LV. Diabetes at the age of 11 weeks was more severe in mice whose mothers were infected earlier than in those whose mothers were infected later in pregnancy. Only animals infected in utero and kept under stress developed diabetes; infection or stress alone did not cause disease.

CONCLUSIONS/INTERPRETATION

This work demonstrates that a type 2 diabetes-like disease can be virus-induced in a mouse model. Early in utero viral insults can set the stage for disease occurring during adult life, but the final manifestation of diabetes is dependent on the combination of early viral exposure and stress in adult life.

Influence of methotrexate, TNF blockers and prednisolone on antibody responses to pneumococcal polysaccharide vaccine in patients with rheumatoid arthritis

OBJECTIVE

To compare antibody responses to 23-valent pneumococcal vaccine (Pneumovax) in controls and patients with established rheumatoid arthritis (RA) treated with TNF blockers, methotrexate (MTX) or a combination of both.

METHODS

Patients with RA (n = 149) and healthy controls (n = 47) were vaccinated. Treatment with TNF blockers (etanercept or infliximab) and MTX was given to 50 patients, and 62 patients were treated with TNF blockers alone or with other DMARDs. MTX alone was given to 37 patients. Concentrations of immunoglobulin G (IgG) antibodies against pneumococcal capsular polysaccharides 23F and 6B were measured by enzyme-linked immunoassay before and 4-6 weeks after vaccination. An immune response was defined as a twofold or higher increase in antibody concentration following vaccination.

RESULTS

Prevaccination antibody levels for both 23F and 6B were similar in the patient groups. Antibody concentrations after vaccination increased significantly in all groups. Patients treated with TNF blockers without MTX showed better immune responses than those treated with TNF blockers in combination with MTX (P = 0.037 for 23F and P = 0.004 for 6B) or MTX alone (P<0.001 for both 23F and 6B). RA patients given MTX alone had the lowest immune responses. Prednisolone treatment did not influence the responses.

CONCLUSIONS

Patients treated with TNF blockers and controls showed similar responses to vaccination. In contrast, patients treated with MTX had reduced responses regardless of anti-TNF treatment. The findings do not argue against the use of pneumococcal vaccination in RA patients undergoing treatment with TNF blockers.

Bezafibrate-induced improvement in glucose uptake and endothelial function in protease inhibitor-associated insulin resistance

Protease inhibitors used as therapy for HIV-1 infection have been associated with metabolic side-effects such as peripheral fat wasting, central adiposity, hyperlipidaemia and insulin resistance. This metabolic disorder is known as the lipodystrophy syndrome. This syndrome can be recognized by the early appearance of an increase in serum triglyceride, cholesterol and plasma-free fatty acid levels. Here, we describe an HIV-1 positive patient with the lipodystrophy syndrome in whom a decline in serum triglycerides was seen along with a significant improvement in glucose uptake following treatment with bezafibrate for 3 months. This improvement may be a consequence of the Randle effect, i.e. increased availability of plasma-free fatty acids is negatively correlated to glucose uptake. We also noted a significant improvement in endothelial-dependent flow-mediated dilatation after treatment with bezafibrate. This effect could result from the increased glucose uptake observed and a decrease in insulin resistance secondary to the lowered triglyceride levels by bezafibrate. We conclude that bezafibrate may be of clinical utility in the lipodystrophy syndrome, through its beneficial effects on insulin resistance, glucose uptake and endothelial dysfunction.

Neurohormonal regulation of the insulin stimulus-secretion coupling in pancreatic islets

Type 2 diabetes mellitus, a major health care problem in the Western world, is a disease typified by a relative deficiency of insulin, leading to vast derangements in glucose and lipid homeostasis with disastrous vascular complications. Despite immense research efforts aiming at a clear understanding of the etiology of this complex disease, the molecular mechanisms causing the disorder still remain elusive. Here we review extant data from recent publications implicating novel signal transduction pathways and neurohormonal agonists as important regulators of the insulin stimulus-secretion coupling in the pancreatic beta-cell. Specifically, attention is paid to incretins such as glucagon-like peptide 1 (GLP-1), galanin, and other peptides produced in the gastrointestinal tract and by neuronal cells with the potential of governing beta-cell function in physiological and diabetic states.

Cellular pharmacodynamics of the cytotoxic guanidino-containing drug CHS 828. Comparison with methylglyoxal-bis(guanylhydrazone)

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine (CHS 828) is a new guanidino-containing compound with antitumoral activity both in vitro and in vivo. Its activity profile differs from those of standard cytotoxic drugs but the mechanism of action is not yet fully understood. CHS 828 is presently in early phase I and II clinical trials. In the present study, the pharmacodynamic effects at the cellular level of CHS 828 was compared to another compound containing two guanidino groups, methylglyoxal-bis(guanylhydrazone) (MGBG). MGBG is known to inhibit the synthesis of polyamines, which are important in, e.g., proliferation and macromolecular synthesis. The concentration-response relationship of CHS 828 closely resembled that of MGBG and the drugs were similar with respect to inhibition of DNA and protein synthesis. On the other hand, CHS 828 induced a significant increase in cellular metabolism while MGBG did not. The cytotoxic effect of MGBG was reversed by the addition of exogenous polyamines, while that of CHS 828 was unaffected. Unlike MGBG, there was also no effect of CHS 828 on the levels of decarboxylating enzymes in the polyamine biosynthesis. In conclusion, CHS 828 does not appear to share any major mechanisms of action with the polyamine synthesis inhibitor MGBG. Further studies will be required to define the exact mechanism of action of CHS 828.

[Postprandial hyperglycemia. Cardiovascular risks and new therapeutic strategies]

In contrast to fasting glucose, postprandial hyperglycemia in type 2-diabetes has been a relatively neglected area. However, postprandial glucose spikes contribute significantly to overall glycemic control and are strongly correlated with cardiovascular morbidity and mortality (as opposed to fasting glucose). Here we review extant data implicating postprandial hyperglycemia as a tangible target for novel antidiabetic drugs with improved potential to curb not only deleterious glucose excursions, but also the macrovascular complications associated with them.

gamma-tocopherol partially protects insulin-secreting cells against functional inhibition by nitric oxide

Preceding the onset of type 1 diabetes mellitus, pancreatic islets are infiltrated by macrophages secreting interleukin-1beta (IL-1beta) which induces beta-cell apoptosis and exerts inhibitory actions on islet beta-cell insulin secretion. IL-1beta seems to act chiefly through induction of nitric oxide (NO) synthesis. Hence, IL-1beta and NO have been implicated as key effector molecules in type 1 diabetes mellitus. In this paper, the influence of endogenously produced and exogenously delivered NO on the regulation of cell proliferation, cell viability and discrete parts of the stimulus-secretion coupling in insulin-secreting RINm5F cells was investigated. Because vitamin E may delay diabetes onset in animal models, we also investigated whether tocopherols may protect beta-cells from the suppressive actions of IL-1 and NO in vitro. To this end, the impact of NO on insulin secretory responses to activation of phospholipase C (by carbamylcholine), protein kinase C (by phorbol ester), adenylyl cyclase (by forskolin), and Ca(2+) influx through voltage-activated Ca(2+) channels (by K(+)-induced depolarization) was monitored in culture after treatment with IL-1beta or by co-incubation with the NO donor spermine-NONOate. It was found that cell proliferation, viability, insulin production and the stimulation of insulin release evoked by carbamylcholine and phorbol ester were impeded by IL-1beta or spermine-NONOate, whereas the hormone output by the other secretagogues was not altered by NO. Pretreatment with gamma-tocopherol (but not alpha-tocopherol) afforded a partial protection against the inhibitory effects of NO, whereas specifically inhibiting inducible NO synthase with N-nitro-L-arginine completely reversed the IL-1beta effects. In contrast, inhibiting guanylyl cyclase with ODQ (1H-[1,2, 4]oxadiazolo[4,3-alpha]-quinoxaline-1-one) or blocking low voltage-activated Ca(2+) channels with NiCl(2) failed to influence the actions of NO. In conclusion, our data show that NO inhibits growth and insulin secretion in RINm5F cells, and that gamma-tocopherol may partially prevent this. The results suggest that phospholipase C or protein kinase C may be targeted by NO. In contrast, cGMP or low voltage-activated Ca(2+) channels appear not to mediate the toxicity of NO in these cells. These adverse effects of NO on the beta-cell, and the protection by gamma-tocopherol, may be of importance for the development of the impaired insulin secretion characterizing type 1 diabetes mellitus, and offer possibilities for intervention in this process.

Fetal pancreatic islets express functional leptin receptors and leptin stimulates proliferation of fetal islet cells

OBJECTIVE

Previous studies have demonstrated that leptin can stimulate proliferation of insulin-secreting tumor cell lines. The objective of this study was to characterize whether leptin could stimulate proliferation of primary beta-cells too. Since adult beta-cells have very limited capacity for replication, we examined the effect of leptin on islets of Langerhans obtained from fetal rats, in a tissue culture system.

METHODS

Leptin receptor mRNA and c-fos mRNA were measured by RT-PCR. Proliferation of fetal rat islet cells was measured by a WST-1 colorimetric assay and [3H]-thymidine incorporation assay.

RESULTS

Leptin stimulated proliferation of serum-deprived fetal rat islet cells, as indicated by increased formation of formazan dye from a tetrazolium salt WST-1. Leptin stimulated DNA synthesis in islet cells, as indicated by increased [3H]-thymidine incorporation into DNA. The effect of leptin on islet cell proliferation was on average 39-50% of the effect obtained with 10% fetal bovine serum. Leptin increased c-fos mRNA expression by 2.8-fold in isolated fetal islets after 30 min treatment. In fetal pancreatic islets, both the common extracellular portion (OB-R) and the intact long form (OB-Rb) of the leptin receptor were readily detected by reverse transcriptase polymerase chain reaction.

CONCLUSION

Functional leptin receptors are expressed in pancreatic islet cells, as early as during the fetal stage of development of these microorgans. Leptin stimulates proliferation of fetal islet cells and might play a role in determining islet cell mass at birth.

Rapid Ca2+ influx and diacylglycerol synthesis in growth hormone-mediated islet beta -cell mitogenesis

Growth hormone (GH) is an important mitogenic stimulus for the insulin-producing beta-cell. We investigated the effects of GH on Ca(2+) handling and diacylglycerol (DAG) and cAMP formation in the beta-cell. GH elicited a rapid increase in the cytoplasmic free [Ca(2+)], which required extracellular Ca(2+) and was also blocked by pertussis toxin or protein kinase C (PKC) inhibition. GH also elevated islet DAG content, which should lead to PKC activation. Pertussis toxin and PKC inhibitors obliterated the mitogenicity of GH, suggesting involvement of GTP-binding proteins. PKC activation stimulated beta-cell proliferation, and it also activated phospholipase D. Islet cAMP content was not elevated by GH. Addition of a specific protein kinase A antagonist failed to influence the mitogenicity of GH, whereas a stimulatory cAMP agonist stimulated beta-cell replication. We conclude that GH rapidly increases the beta-cell cytoplasmic free [Ca(2+)] and also evokes a similar increase in DAG content via a phosphatidylcholine-specific phospholipase C, but does not affect mitogen-activated protein kinases, phospholipase D, or the cAMP signaling pathway. This rise in DAG may be of importance in translation of the stimulatory signal of GH into a proliferative response by the beta-cell, which seems to occur through GTP-binding proteins and PKC-dependent mechanisms.

Regulation of in vitro maturation of stimulus-secretion coupling in fetal rat islet beta-cells

We have studied the maturation of a glucose-responsive insulin release from fetal rat islets, and specifically investigated the impact of nutrients, alpha-adrenoceptors, imidazoline receptors, and cyclic adenosine monophosphate (cAMP). Islets were isolated from 21 -d-old fetal rats and maintained for 7 d in tissue culture at 3.3 or 11.1 mM glucose and various supplements. Culture in the presence of the nonglucidic nutrient alpha-ketoisocaproic acid (KIC), markedly enhanced both basal and stimulated insulin release from islets cultured at either low or high glucose. Additionally, KIC significantly elevated the insulin content of islets maintained in low glucose, whereas it slightly lowered it in islets cultured at high glucose. Culture with phentolamine, an antagonist of alpha-adrenergic and imidazoline receptors, markedly amplified both basal and glucose-stimulated insulin secretion when added with islets cultured in either low or high glucose. By contrast, the pure alpha2-adrenoceptor antagonist benextramine had no such effects. Addition to culture media of a membrane-permeant agonist (Sp-cAMP[S]) or antagonist (Rp-cAMP[S]) of cAMP-dependent protein kinases types I and II failed to influence basal or glucose-responsive insulin secretory rates at either glucose concentration during culture as well as islet insulin content. In conclusion, islet beta-cell differentiation and functional maturation of the stimulus-secretion coupling can be accelerated in vitro in fetal rat pancreatic tissue by nutrient stimulation, and by interference with imidazoline receptors, whereas cAMP seems virtually ineffective in this respect. These effectors may be of regulatory significance in the in vivo development of glucose-sensitive beta-cells.

Peptidergic regulation of maturation of the stimulus-secretion coupling in fetal islet beta cells

The stimulus-secretion coupling of the insulin-producing pancreatic islet beta cell is subject to functional maturation during fetal life. We studied the maturation of a glucose-responsive insulin release from fetal rat islets and specifically investigated the impact of peptidergic regulation. To this end, islets were isolated from 21-day-old fetal rats and maintained for 7 days in tissue culture at 3.3 or 11.1 mM glucose and various supplements. In islets cultured in low glucose, acutely raising the ambient glucose concentration to 16.7 mM evoked a modest stimulation of short-term insulin release that was more pronounced in islets maintained in high glucose. Moreover, the insulin content was much higher in islets cultured in high than in low glucose. Culture with growth hormone (GH) markedly amplified both basal and stimulated short-term insulin secretion from islets maintained in either low or high glucose. Additionally, GH significantly elevated the insulin content in islets maintained in low glucose. Transforming growth factor alpha (TGF-alpha) increased basal, but not glucose-stimulated, insulin release and insulin content in islets cultured in low glucose. Gastrin, expressed in islets during fetal life, did not affect basal or glucose-stimulated insulin release, or insulin content, in islets maintained in either low or high glucose. The addition of gastrin to TGF-alpha did not affect the results obtained with the latter peptide. Gastrin-releasing peptide failed to influence basal or glucose-responsive insulin secretory rates, and insulin content, at either glucose concentration during culture. The somatostatin analog Sandostatin (octreotide acetate) neither influenced basal nor stimulated short-term insulin release at any glucose concentration present during culture, whereas the hormone significantly decreased the insulin content of islets cultured in high glucose. Pancreastatin, produced by porcine islet beta and delta cells, failed to influence basal or glucose-responsive insulin secretory rates, and islet insulin content, at either glucose concentration during culture. Culture with gastric inhibitory peptide (GIP) or glucagon-like peptide I (GLP-1), two proposed incretins, did not affect short-term insulin secretion in response to 3.3 or 16.7 mM glucose irrespective of the ambient glucose concentration during culture. To the contrary, GLP-1, but not GIP, increased the content of insulin in islets cultured in low glucose. We conclude that islet beta-cell differentiation and functional maturation of the stimulus-secretion coupling can be modulated in vitro in fetal rat pancreatic tissue by peptidergic regulation and glycemic stimulation. We suggest that GH and TGF-alpha stimulate, while somatostatin, through paracrine interaction, may inhibit, these processes. These effectors may be of regulatory significance in the in vivo development of glucose-sensitive beta cells, and defects in these mechanisms may result in glucose intolerance in adult subjects.

Novel roles of complement in systemic lupus erythematosus--hypothesis for a pathogenetic vicious circle

We propose that impaired complement function enhances a pathogenetic vicious circle in SLE. In this process, induction and clearance of apoptotic cells is central. Apoptosis could be triggered by various etiological factors, such as infection, UV light, and drug reactions. Clearance of apoptotic material is reduced when complement function is impaired. Apoptosis leads to increased exposure of nuclear antigens to the immune system, to which estrogenic hormones could contribute. This could in turn lead to activation of autoreactive B cells, autoantibody production, and immune complex formation, all of which is accelerated by hypocomplementemia. Immune complexes may, at least partly via complement dependent mechanisms, accelerate apoptosis.

Polyamines regulate serine/threonine protein phosphatases in insulin-secreting cells

Reversible protein phosphorylation is an important mechanism by which cells transduce external signals into biologic responses. Levels of protein phosphorylation are determined by the balanced actions of both protein kinases and protein phosphatases (PPases). However, compared with protein kinases, regulation of PPases has been relatively neglected. The insulin secretagogue L-arginine, an immediate metabolic precursor to polyamines, causes a rapid and transient decrease in PPase-1 activity in insulin-secreting RINm5F cells. We here show that polyamines dose-dependently suppress PPase-1-like activity when added to RINm5F cell homogenates at physiologic concentrations (spermine > spermidine > putrescine), while having minor and inconsistent effects on PPase-2A-like activity. The IC50 value for spermine on PPase-1-like activity was approximately 4 mM. The inhibitory effect was reproduced and of comparable magnitude on purified PPases types 1 and 2A. On the other hand, when endogenous polyamine pools were exhausted by 4 days of exposure to the specific L-ornithine decarboxylase inhibitor DL-alpha-difluoromethylornithine, there was an increase in PPase-2A-like activity. Quantitative Western analysis revealed that the amount of PPase-2A protein did not change after this treatment. It is concluded that polyamines cause time-and concentration-dependent inhibitory effects on RINm5F cell PPase activities, which may contribute to the increase in phosphorylation state that occurs after secretory stimulation.

Short- and long-term effects of beta-cellulin and transforming growth factor-alpha on beta-cell function in cultured fetal rat pancreatic islets

The polypeptide beta-cellulin, identified in conditioned media from insulinoma cell cultures and produced by pancreatic islet cells, was recently identified as a possible autocrine growth factor for the pancreatic islet beta-cell. In this study, we investigated the short- and long-term actions of beta-cellulin, and the structurally related transforming growth factor-alpha (TGF-alpha), on beta-cell function in fetal rat pancreatic islets in vitro. We found that neither beta-cellulin nor TGF-alpha (10 nM each), in contrast to glucose (20 mM), acutely influenced beta-cell levels of cytosolic-free Ca2+. Additionally, whereas glucose markedly increased short-term (60-min) insulin release, neither beta-cellulin nor TGF-alpha (10 nM each) influenced the rate of hormone secretion at basal (3 mM) or stimulatory (20 mM) concentrations of glucose. Likewise, long-term (24-h) exposure of islets to a high glucose concentration significantly augmented the secretion of insulin. This effect was slightly potentiated by TGF-alpha (10 nM), but not beta-cellulin (10 nM), at high (but not low) glucose concentrations. Conversely, the islet insulin content was not significantly affected by beta-cellulin or TGF-alpha at any glucose concentration tested. We conclude that, although beta-cellulin is produced by islet cells, the peptide does not seem to be of importance for the regulation of insulin production by isolated pancreatic beta-cells.

Complement activation in patients with systemic lupus erythematosus without nephritis

OBJECTIVE

To study the association between disease activity and complement activation prospectively in patients with systemic lupus erythematosus (SLE).

PATIENTS AND METHODS

Twenty-one SLE patients were examined monthly for 1 yr. Disease activity, autoantibodies, conventional complement tests and the following complement activation products were investigated: C1rs-C1inh complexes, C4bc, Bb, C3a, C3bc, C5a and the terminal SC5b-9 complement complex (TCC).

RESULTS

Modest variation in disease activity was noted. None of the patients had nephritis. Flare was observed at 27 visits. Four patients had anti-C1q antibodies in conjunction with modestly low C1q concentrations. The complement parameters were rather constant during the observation period. Slightly to moderately decreased C4 (0.05-0.10 g/l) was found in 10 patients and severely decreased C4 (<0.05 g/l) in seven patients. Decreased C4 was not associated with increased complement activation. Complement activation products were either normal or slightly elevated. TCC was the only activation product correlating significantly with score for disease activity at flare. None of the variables tested predicted flares.

CONCLUSION

Complement tests are of limited importance in routine examination of SLE without nephritis, although TCC is suggested to be one of the most sensitive markers for disease activity.

[Interleukin-1 and nitric oxide involved in the pathogenesis of diabetes)]

Insulin-dependent diabetes mellitus (IDDM) is not only a common metabolic disorder in industrialised countries, but its incidence is still increasing, especially in Scandinavia. The article consists in a review of evidence implicating nitric oxide (NO) and the cytokine, interleukin-1 (IL-1), in the pathogenesis of IDDM. Cytotoxic effects of IL-1 and NO, generated through autoimmune reactions associated with insulitis and impairing the function of insulin-producing pancreatic beta-cells in IDDM, are discussed, as are possible pharmacological strategies for blocking this toxicity. Compounds capable of blocking IL-1 cell surface receptors and NO synthesis may prove beneficial in protecting beta-cells from autoimmune assault in IDDM. If IL-1 causes beta-cell dysfunction and destruction through NO synthesis in IDDM, several pathways in the IL-1-NO system are attractive potential targets for drugs protecting beta-cells against these effects, thus providing a means of intervening in the pathogenesis of IDDM.

[Time for more active lipid-lowering treatment of patients with diabetes. Negative effect of hyperlipidemia on beta-cells is a neglected field]

Type 2 diabetes mellitus is a common metabolic disorder whose prevalence is increasing in the western world. The ravaging complications of the disease constitute a major cause of hospitalisation and cardiovascular morbidity, and despite intensive research the pathogenic mechanism remain unknown. The article summarises some recent advances in the field of islet beta-cell dysfunction caused by hyperlipidaemia in the diabetic state, which results in perturbed insulin secretory capacity and overt glucose intolerance. In contrast to hyperglycaemia, the detrimental effects of hyperlipidaemia have been a relatively neglected area of diabetes research. However, the direct inhibitory effects of long-term hyperlipidaemia on beta-cell function, 'lipotoxicity,' should form the basis of a more active approach to lipid screening and pharmacological treatment of hyperlipidaemia in diabetes patients. Intervention in the leptin pathway may prove beneficial in future treatment strategies.

Aspects of novel sites of regulation of the insulin stimulus-secretion coupling in normal and diabetic pancreatic islets

Noninsulin-dependent diabetes mellitus (NIDDM), a major health care problem in the Western world, is a disease typified by a relative deficiency of insulin, leading to vast derangements in glucose and lipid homeostasis with disastrous vascular complications. Despite immense research efforts aimed at a clear understanding of the etiology of this complex disease, the molecular mechanisms causing the disorder still remain elusive. This article reviews extant data from recent publications implicating novel signal transduction pathways as important regulators of the insulin stimulus-secretion coupling in the pancreatic beta-cell. The significance of nitric oxide and serine/threonine protein phosphatases, and their inactivation by insulin secretagogues, glucose metabolites, ATP, GTP, glutamate, and inositol hexaphosphate in this arena is scrutinized. Additionally, also presented is the growing concept that an important signal for insulin secretion may reside in the inextricable interplay between glucose and lipid metabolism, specifically the generation of malonyl-CoA, which inhibits carnitine palmitoyltransferase 1 with the attendant accumulation of long-chain acyl CoA esters. Moreover, attention is directed towards novel intracellular actions of hypoglycemic sulfonylureas in the beta-cell. Finally, the importance of "lipotoxicity" and aberrations in glucose uptake and metabolism in beta-cell dysfunction is given consideration. Future research efforts should aim at further characterization of effects of second messengers on protein phosphorylation elements in beta-cells. Additionally, long-term regulation by glucose and the diabetic state (e.g., fatty acids and ketones) on beta-cell protein phosphatases, pyruvate dehydrogenase, and carnitine palmitoyltransferase 1 needs to be explored in greater depth. Clearly, the detrimental impact of diabetic hyperlipidemia on beta-cell function has been a relatively neglected area, but futu re pharmacological approaches directed at preventing lipotoxicity may prove beneficial in the treatment of diabetes.

Aspects of the involvement of interleukin-1 and nitric oxide in the pathogenesis of insulin-dependent diabetes mellitus

The possible involvement of the cytokine interleukin-1 (IL-1) and nitric oxide (NO) in the pathogenesis of insulin-dependent diabetes mellitus (IDDM) is reviewed and current and potential therapies are discussed. IDDM is a common disorder in the Western world and it is rising in incidence. In IDDM, islet-infiltrating macrophages produce IL-1 which is cytotoxic specifically to beta-cells in vitro. IL-1 increases beta-cell formation of NO, ceramide, prostaglandins, heat-shock proteins, and activates a protease. Additionally, IL-1 depresses beta-cell energy production, insulin gene expression and cyclic AMP synthesis, and impacts negatively on different parts of the insulin stimulus-secretion coupling, actions mimicked by NO. Conversely, blocking NO formation prevented many of these effects in most reports published. Also, changes in cyclic AMP and prostaglandins seem unlikely events in mediating the cytotoxicity of IL-1, while the role of ceramide remains less clear. Peptides capable of blocking beta-cell IL-1 receptors, and agents blocking NO synthesis may prove valuable in preserving beta-cell function in IDDM. Although IDDM causes immense morbidity and expense, uniformly effective preventive or beta-cell protective therapy is not currently available. If IL-1 is causing beta-cell dysfunction in human IDDM through NO production, several processes in the IL-1-NO connection are appropriate targets for agents protecting beta-cells from destruction and functional inhibition in IDDM.

Inhibition of phosphatases and increased Ca2+ channel activity by inositol hexakisphosphate

Inositol hexakisphosphate (InsP6), the dominant inositol phosphate in insulin-secreting pancreatic beta cells, inhibited the serine-threonine protein phosphatases type 1, type 2A, and type 3 in a concentration-dependent manner. The activity of voltage-gated L-type calcium channels is increased in cells treated with inhibitors of serine-threonine protein phosphatases. Thus, the increased calcium channel activity obtained in the presence of InsP6 might result from the inhibition of phosphatase activity. Glucose elicited a transient increase in InsP6 concentration, which indicates that this inositol polyphosphate may modulate calcium influx over the plasma membrane and serve as a signal in the pancreatic beta cell stimulus-secretion coupling.

Glucose stimulates islet beta-cell mitogenesis through GTP-binding proteins and by protein kinase C-dependent mechanisms

Glucose is a cardinal secretory and mitogenic stimulus for the insulin-producing pancreatic beta-cell both in vitro and in vivo, but the mechanisms by which the sugar acts mitogenically remain largely elusive. In this study, the intracellular pathways that convey glucose-induced mitogenic and secretory signaling in beta-cells were investigated. For this purpose, fetal rat pancreatic islets enriched in beta-cells were cultured in 3.3 or 16.7 mmol/l glucose for 3 days. It was found that glucose stimulated beta-cell replication, insulin secretion, and cAMP content. These effects were mimicked by agonists of cAMP-dependent protein kinases but not by guanosine-3',5'-cyclic monophosphate (cGMP). Antagonists of cAMP-dependent protein kinases failed to block the glucose-induced increments in beta-cell replication and insulin secretion. Glucose is known to activate protein kinase C, and a protein kinase C-activating phorbol ester was found to promote beta-cell mitogenesis and insulin secretion. Conversely, when protein kinase C was inhibited, the mitogenic (but not secretory) response to glucose was attenuated. There were no additive or synergistic effects on beta-cell replication when cAMP and phorbol ester were combined, whereas insulin secretion was potentiated by this combination. Artificially causing Ca2+ inlet by glibenclamide or ionomycin did not result in a stimulated mitogenic response, and preventing Ca2+ influx by blocking plasma membrane Ca2+ channels did not abolish the mitogenicity of glucose, although it reduced insulin secretion. Pretreatment of islets with pertussis toxin, known to regulate transduction of signals through heterotrimeric GTP-binding proteins, completely prevented the stimulatory effect of glucose on beta-cell mitogenesis but not on insulin secretion. We conclude that specific activation of protein kinase C or cAMP synthesis is sufficient to increase beta-cell mitogenesis and insulin secretion, whereas cGMP appears not to affect these processes. However, cAMP does not seem to mediate the mitogenicity or secretory action of glucose. The results instead suggest that signaling through GTP-binding proteins and protein kinase C activation is required for transduction of the mitogenic, but not secretory, message of the sugar in the beta-cell.

Nitric oxide donor SIN-1 inhibits insulin release

Preceding the onset of insulin-dependent diabetes mellitus, pancreatic islets are infiltrated by macrophages secreting interleukin-1 beta, which exerts cytotoxic and inhibitory actions on islet beta-cell insulin secretion through induction of nitric oxide (NO) synthesis. The influence of the NO donor 3-morpholinosydnonimine (SIN-1) on insulin secretion from isolated pancreatic islets in response to various secretagogues was investigated. Stimulation of insulin release evoked by glucose, phospholipase C activation with carbachol, and protein kinase C activation with phorbol ester were obtained by SIN-1, whereas the response to adenylyl cyclase activation or K(+)-induced depolarization was not affected. It is concluded that enzymes involved in glucose catabolism, phospholipase C or protein kinase C, may be targeted by NO. Reversal of SIN-1 inhibition of glucose-stimulated insulin release by dithiothreitol suggests that NO may inhibit insulin secretion partly by S-nitrosylation of thiol residues in key proteins in the stimulus-secretion coupling. These adverse effects of NO on the beta-cell stimulus-secretion coupling may be of importance for the development of the impaired insulin secretion characterizing diabetes mellitus.

Effects of transforming growth factor beta, tumor necrosis factor alpha and interferon gamma on pancreatic islet beta-cell responsiveness to transforming growth factor alpha

The insulin-producing pancreatic islet beta-cell, characterized by low proliferative potential, is normally not responsive to the polypeptide epidermal growth factor (EGF) or its homolog transforming growth factor alpha (TGF-alpha). Since EGF receptors in other tissues can be up-regulated by other growth factors and by cytokines, we have in this paper investigated whether such a beta-cell responsiveness to TGF-alpha, or EGF, can be conferred by co-culture with interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha) or transforming growth factor beta (TGF-beta) in various combinations. To this end, fetal rat pancreatic islets enriched in beta-cells were isolated and cultured for 3 days with or without 200 pM or 20 nM TGF-alpha. It was found that neither of these TGF-alpha concentrations affected beta-cell mitogenesis, insulin content or insulin secretion. However, IFN-gamma (1000 U/ml) evoked a modest stimulation of beta-cell replication, while suppressing insulin secretion and leaving the islet insulin content unaltered. TNF-alpha (1000 U/ml), on the other hand, affected none of these parameters either alone or in any combination with TGF-alpha or IFN-gamma. However, when TNF-alpha or IFN-gamma, either alone or in combination, were combined with the cytokine interleukin-1 beta, this resulted in islet disintegration, whereas the latter cytokine alone did not exert any gross necrotic changes evident by light microscopy. TGF-beta (500 pM) stimulated insulin secretion but did not influence islet insulin content or beta-cell mitogenesis either alone or in combination with TGF-alpha (200 pM or 20 nM). In no instance could any mitogenic or secretory response to low or high concentrations of TGF-alpha be conferred by IFN-gamma. TNF-alpha or TGF-beta whether used alone or in combinations. Hence, responsiveness to TGF-alpha or EGF in the beta-cell obviously cannot be achieved by any of these peptides.

Prostaglandins inhibit pancreatic beta-cell replication and long-term insulin secretion by pertussis toxin-insensitive mechanisms but do not mediate the actions of interleukin-1 beta

The effects of exogenous prostaglandins, inflammatory mediators known to be increased in pancreatic beta-cells by IL-1 beta, on the replication and long-term insulin secretion by beta-cells were investigated. Prostaglandins E1, E2, and F2 alpha suppressed beta-cell proliferation and long-term insulin secretion, thus mimicking the effects of IL-1 beta. The actions of prostaglandins were not prevented by pertussis toxin pretreatment. Additionally, the cyclooxygenase inhibitor indomethacin could not prevent the effects of IL-1 beta. It is concluded that prostaglandins suppress beta-cell growth and long-term insulin secretion without participation of pertussis-toxin sensitive GTP-binding proteins. In addition, although their synthesis is increased by IL-1 beta, prostaglandins seemingly do not convey the inhibitory actions of this cytokine in the beta-cell.

Aortobifemoral surgery induces complement activation and release of interleukin-6 but not tumour necrosis factor-alpha

The aim of the present study was to determine the inflammatory response by an extended analysis of complement in 16 patients undergoing aortobifemoral bypass surgery. The patients were randomized to receive either a bifurcated expanded polytetrafluoroethylene graft (n = 8; group I) or a collagen-impregnated knitted Dacron graft (n = 8; group II) to determine whether differences in graft surface properties might influence the inflammatory response during and after the procedure. The following components of complement: C1q, C4, C3, C3d, C5a and terminal complement complexes were all analysed. C-reactive protein and interleukin-6 were also determined to assess the acute phase response. The complement data were corrected for haemodilution, which was assessed from alpha 2-macroglobulin concentrations. A significant decrease of C1q (P < 0.0001) and an increase in C5a (P < 0.0005) was observed in both groups. C4 and C3 levels showed slight fluctuations in group I, whereas in group II these proteins increased significantly (P < 0.05, P < 0.005, respectively) between 2 and 7 days after surgery. Terminal complement complexes remained unchanged in both groups. Interleukin-6 levels peaked at 12-24 h and the C-reactive protein at 24-72 h. Higher interleukin-6 levels (P < 0.05) were found in group II 6 h after surgery compared with group I; no release of tumour necrosis factor-alpha was identified. An early inflammatory response was found in all patients. The patterns of the complement proteins varied with a C1q depletion and a C5a increase, interpreted as complement activation. Whether the variations between the two graft groups represent any differences in graft surface properties has to be further elucidated.

Lithium stimulation of rat pancreatic beta-cell replication is mediated through pertussis toxin-sensitive GTP-binding proteins and occurs independently of Ca2+ influx, cAMP, or protein kinase C activation

We recently demonstrated the mitogenic and secretagogic actions of lithium in the insulin-producing pancreatic beta-cell (Sjöholm A, Welsh N, Hellerström C: Lithium increases DNA replication, polyamine content and insulin secretion by rat pancreatic beta-cells in vitro. Am J Physiol 262:C391-C395, 1992). In this study, the influence of lithium on beta-cell signal transduction pathways was monitored and their importance for the stimulated cell replication and hormone secretion was elucidated by selective pharmacological probes. To this end, fetal rat pancreatic islets enriched in beta-cells were isolated and cultured for 3 days with or without 10 mmol/l LiCl. This resulted in a marked mitogenic response by the beta-cells, of similar magnitude to that obtained by pharmacological activation of cAMP-dependent protein kinases by forskolin or the Sp-diastereomer of cAMP or protein kinase C stimulation by phorbol ester. However, neither did lithium affect the islet content of cAMP (whereas forskolin did), nor was the mitogenic response to the ion impeded when islets were pretreated with the Rp-diastereomer of cAMP, a specific antagonist of cAMP-dependent protein kinases, or by the Ca2+ channel blocker D-600. The protein kinase C inhibitor 1-(5'-isoquinolinesulfonyl)-2-methylpiperazine prevented the mitogenicity of phorbol ester, but not that of lithium. Conversely, addition of increasing concentrations of inositol along with lithium also did not affect the mitogenicity of the ion, providing indirect evidence against the involvement of protein kinase C in mediating the growth-promoting effect of lithium in this system. It was found that pretreatment of islets with pertussis toxin, which inactivates GTP-binding proteins by ADP-ribosylation, prevented the mitogenicity and part of the secretagogic action of lithium. It is concluded that although specific activation of the cAMP and protein kinase C signaling systems appears sufficient to trigger a mitogenic response of the beta-cell, lithium seemingly does not work through any of these systems nor via Ca2+ influx in promoting beta-cell mitogenesis. Our results, moreover, suggest that the actions of lithium are conveyed by pertussis toxin-sensitive GTP-binding proteins.

Nitrogen dioxide pneumonitis in ice hockey players

Exposure to the toxic gases carbon monoxide and nitrogen dioxide (NO2) in indoor ice arenas occasionally occurs and may result in severe symptoms. The gases are produced by ice resurfacing machines operating on hydrocarbons, and in certain conditions toxic levels accumulate. The damage to lung tissues caused by NO2 may not be evident until after a latency time of 1/2-2 days. The role of corticosteroids in the treatment is controversial, but there are clinical experiences as well as experimental data supporting their use. We report two cases of toxic pneumonitis, with delayed onset, due to NO2 exposure during an ice hockey game in an indoor arena. Signs and symptoms were cough, dyspnoea, haemoptysis, hypoxaemia and reduced peak expiratory flow. Chest radiographs showed parenchymatous infiltrative lesions and alveolar consolidation. Both patients were treated with high doses of corticosteroids by inhalation and orally or intravenously. Their condition rapidly improved and pulmonary function was restored.

Effects of secretagogues on insulin biosynthesis and secretion in polyamine-depleted pancreatic beta-cells

To extend previous observations on the importance of polyamines for glucose-stimulated insulinogenesis (N. Welsh and A Sjöholm. Polyamines and insulin production in isolated mouse pancreatic islets. Biochem. J. 252: 701-707, 1988), the impact of other secretagogues on insulin secretion of islets partially depleted in polyamines by selective inhibitors of L-ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase was monitored. Glucose-sensitive, but not basal, insulin release was partially abolished in polyamine-deficient islets. Qualitatively similar impairments in insulin secretion were recorded when such islets were stimulated with nonglucidic nutrients (alpha-ketoisocaproic acid + L-glutamine), a cationic amino acid (L-arginine), activators of phospholipase C (carbachol) or protein kinase C (12-O-tetradecanoylphorbol 13-acetate), an adenosine 1', 5'-cyclic monophosphate-raising agent (forskolin), or a hypoglycemic sulfonylurea (glibenclamide). Additionally, glucose-responsive (pro)insulin biosynthesis was preferentially impeded in polyamine-deficient islets. It is concluded that polyamines act as permissive or stimulatory factors in insulin production and release. In addition, they seemingly do not act in an inhibitory manner on phospholipase C, protein kinase C, or Ca2+ flux into these islets, in contrast to reports in which insulinoma and other cells were used.

Diabetes mellitus and impaired pancreatic beta-cell proliferation

The factors that normally regulate the proliferation of the insulin-producing pancreatic beta-cell largely remain elusive although several factors have been identified that influence beta-cell growth in vitro. The adult beta-cell is normally virtually quiescent, but its replicatory activity can be enhanced in vitro by certain nutrients and growth factors, and long-term alterations in beta-cell mass constitute an important means to accommodate an increased demand for insulin. Likewise, expansion of the beta-cell mass by recruitment of beta-cells to proliferate may constitute a means by which the organism can compensate for the loss or dysfunction of beta-cells occurring in diabetes. However, neither in human or animal models for type-1 diabetes, nor in type-2 diabetes, is beta-cell regeneration a noteworthy feature. Thus, if beta-cells could be induced to replicate at a higher rate, this may prove beneficial in maintaining normoglycaemia, since the beta-cell mass is a major determinant of the total amount of insulin that can be secreted by the pancreas. The present review will focus on the normal regulation of beta-cell mitogenesis and hormones production in vitro and in vivo, and furthermore, will present evidence for an insufficient extent of beta-cell regeneration in different forms of diabetes mellitus. Additionally, the possibility of manipulating beta-cell proliferation by peptides and genetic engineering, and the significance of beta-cell mitogenesis in islet transplantation will be discussed in relation to treatments of diabetes mellitus.

Histaminergic regulation of pancreatic beta-cell replication and insulin secretion

Evidence suggest that histamine is required for the diabetogenic agent streptozotocin to exert its toxicity on islet beta-cells. The effects of histamine and L-histidine on the replication and long-term insulin secretion by pancreatic beta-cells were investigated. L-histidine dose-dependently increased insulin secretion and suppressed DNA synthesis without affecting the islet insulin content. Histamine suppressed beta-cell replication but failed to affect the islet content or secretion of insulin. Depletion of islet histamine contents by the specific and irreversible inhibitor of L-histidine decarboxylase, alpha-fluoromethyl-[S] histidine increased islet insulin content but failed to influence the rate of insulin secretion. The present results suggest that exogenously added L-histidine, but not histamine, stimulates insulin secretion whereas both substances suppress beta-cell growth. Endogenously formed histamine may have different roles in beta-cell function than exogenously delivered histamine, the latter likely acting through specific cell surface receptors.

Inhibition of serine/threonine protein phosphatases by secretagogues in insulin-secreting cells

Reversible protein phosphorylation is considered to be an important and versatile mechanism by which cells transduce external signals into biological responses. Cellular levels of protein phosphorylation are determined by the balanced actions of both protein kinases and protein phosphatases (PPases). Compared with protein kinases, however, serine/threonine PPases have received less attention. In the present study, the effects of known insulin secretagogues and some intracellular second messengers on the activities of serine/threonine PPases in insulin-secreting RINm5F insulinoma cells were investigated. The stimulation of intact RINm5F cells with the insulin secretagogues L-arginine, L-glutamine, KCl, or ATP elicited time-dependent changes in PPase activities with an early (1 min) decrease in type 1-like and/or type 2A-like PPase activity that gradually returned to normal levels. Addition of cAMP, cGMP, or prostaglandins E2 and F1 alpha at widely different concentrations to RINm5F cell homogenates failed to affect PPase activities. In contrast, addition of physiological concentrations of adenine nucleotides, which are known to increase upon secretory stimulation, to cell homogenates inhibited type 2A-like and, to a lesser extent, type 1-like, PPase activity (ATP > ADP > AMP > adenosine). ATP and ADP IC50 values for type 2A-like PPase were approximately 75 and 250 microM, respectively. The inhibitory effect of ATP was reproduced and of comparable magnitude when purified PPases (types 1 and 2A) were used instead of RINm5F cell homogenates. It is concluded that insulin secretagogues cause time- and concentration-dependent inhibitory effects on RINm5F cell PPase activities, which may contribute to the increase in the phosphorylation state that occurs after stimulation of insulin release. Thus, inhibition of protein dephosphorylation may be a novel regulatory mechanism controlling the stimulus-secretion coupling in insulin-producing cells.

Ceramide inhibits pancreatic beta-cell insulin production and mitogenesis and mimics the actions of interleukin-1 beta

Ceramide, generated during sphingomyelinase-induced sphingolipid cleavage, is considered an important mediator in cytokine signaling. The effects of endogenously generated and exogenously delivered ceramide on long-term insulin secretion and replication by pancreatic beta-cells were investigated, and compared to the effects of interleukin 1 beta (IL-1 beta). Generation of beta-cell ceramide by exogenous sphingomyelinase, or addition of cell-permeant ceramide analogs C2-ceramide and C6-ceramide, caused inhibitor effects on beta-cell insulin production and mitogenesis mimicing those evoked by IL-1 beta. Hence, ceramide may be involved in transducing the cytostatic and cytotoxic actions of IL-1 beta in the beta-cell.

Regulation of insulinoma cell proliferation and insulin accumulation by peptides and second messengers

The regulation of clonal rat insulinoma (RINm5F) cell proliferation and hormone accumulation was investigated with the aim of identifying putative compounds capable of inducing differentiation, i.e. decreased growth and increased insulin accumulation, by the tumor cells. In particular, interest was focused on the role of a number of peptides as well as pharmacological probes modulating various signal transduction systems and which have been shown to regulate normal beta-cell proliferation and insulin accumulation. Growth hormone stimulated insulin accumulation and inhibited DNA synthesis, whereas galanin and insulin-like growth factor I caused a moderate suppression of insulin accumulation but did not affect proliferation, while epidermal growth factor, transforming growth factor beta, platelet-derived growth factor, acidic and basic fibroblast growth factor, bradykinin and somatostatin were virtually inactive on all parameters tested. Exogenous prostaglandins E2 and F1 alpha were inactive, while the cycloxygenase inhibitor indomethacin slightly suppressed insulin accumulation. The cytokine IL-1 beta caused a significant decrease in both beta-cell mitogenesis and insulin accumulation, effects that were mediated through nitric oxide generation. The vitamin A derivative retinyl acetate slightly inhibited serum-stimulated DNA synthesis, but did not affect insulin accumulation. The vitamin E alpha-tocopherol significantly enhanced insulin release but did not affect mitogenesis. By contrast, gamma-tocopherol was inactive on both these parameters. The alpha-adrenergic agonist clonidine evoked a slight inhibition of serum-stimulated DNA synthesis, without influencing insulin accumulation, whereas phenylephrine did not affect any of these parameters. Carbamylcholine increased insulin accumulation, but not cell proliferation, whereas the adenylyl cyclase activator forskolin suppressed mitogenesis but did not affect insulin accumulation. Inhibition of protein kinase C with staurosporine or prolonged treatment with phorbol ester suppressed DNA synthesis, as did the tyrosine kinase inhibitor genistein. Stimulating Ca2+ influx by closing ATP-dependent K+ channels with glibenclamide enhanced DNA synthesis, while opening of these channels with diazoxide suppressed cell growth. Conversely, preventing Ca2+ influx by the Ca2+ channel antagonist D-600, chelating intracellular Ca2+ by fura-2 AM or inhibiting the Ca2+/calmodulin-dependent protein kinase by calmidazol resulted in a decreased DNA synthesis. On the other hand, uncontrolled influx or mobilization of Ca2+ by ionomycin or thapsigargin resulted in an arrested DNA synthesis. The present paper shows that RINm5F insulinoma cell proliferation and insulin accumulation can be modulated by various peptidergic and pharmacological agents regulating certain signal transduction pathways. However, mitogenesis in the insulinoma cells seemingly is controlled in a vastly different manner in comparison to that in normal beta-cells. The most spectacular finding in this screening study, i.e. that growth hormone, contrarily to its effect on normal beta-cells, suppresses insulinoma cell growth, merits further elucidation of the underlying mechanisms. Possibly the hormone might become of utility in a clinical setting in the treatment of patients with insulin-producing tumors.

Different prooxidant levels stimulate growth, trigger apoptosis, or produce necrosis of insulin-secreting RINm5F cells. The role of intracellular polyamines

Increasing concentrations (1-100 microM) of the redox cycling quinone, 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), stimulated growth, triggered apoptosis, or caused necrosis of pancreatic RINm5F cells, depending on the dose and duration of the exposure. Following the exposure of RINm5F cells to 10 microM DMNQ, ornithine decarboxylase activity and polyamine biosynthesis increased. This was accompanied by enhanced cell proliferation. Conversely, exposure to 30 microM DMNQ for 3 h resulted in the inhibition of ornithine decarboxylase, intracellular polyamine depletion, and apoptotic cell killing. Pretreatment of the cultures with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, restored polyamine levels and prevented apoptosis. Exposure to the same DMNQ concentration for only 1 h, with subsequent re-incubation in growth medium, neither caused polyamine depletion nor resulted in apoptosis. Finally, exposure to an even higher DMNQ concentration (100 microM) for either 1 or 3 h caused rapid intracellular Ca2+ overload, ATP, NAD+, and glutathione depletion, and extensive DNA single strand breakage, which resulted in necrotic cell death. Our results show that a disturbance of polyamine biosynthesis occurred prior to cell growth or apoptosis elicited by oxidative stress. In addition, we show that effects as opposite as cell proliferation and deletion, by either apoptosis or necrosis, can be induced, in the same system, by varying the exposure to a prooxidant.