R Giannarelli

Reducing insulin resistance with metformin: the evidence today

Insulin resistance, defined as the inability of insulin to exert a normal biological action at the level of its target tissues, is one of the principal pathogenetic defects of type 2 diabetes. Metformin, the most widely-prescribed insulin-sensitizing agent in current clinical use, improves blood glucose control mainly by improving insulin-mediated suppression of hepatic glucose production, and by enhancing insulin-stimulated glucose disposal in skeletal muscle. Experimental studies show that metformin-mediated improvements in insulin sensitivity may be associated with several mechanisms, including increased insulin receptor tyrosine kinase activity, enhanced glycogen synthesis, and an increase in the recruitment and activity of GLUT4 glucose transporters. In adipose tissue, metformin promotes the re-esterification of free fatty acids and inhibits lipolysis, which may indirectly improve insulin sensitivity through reduced lipotoxicity. The improved glycaemia with metformin is not associated with increased circulating levels of insulin, and the risk of hypoglycaemia with metformin is minimal. The therapeutic profile of metformin supports its use for the control of blood glucose, in diabetic patients and for the prevention of diabetes in subjects with impaired glucose tolerance. Moreover, the improvement by metformin of cardiovascular risk factors associated with the dysmetabolic syndrome may account for the significant improvements in macrovascular outcomes observed in the UK Prospective Diabetes Study.

Effects of pancreas-kidney transplantation on diabetic retinopathy

The effects of pancreas transplantation (PTx) on diabetic retinopathy (DR) are still debated. We studied the course of DR in 48 patients (age: 40 ± 7 years; males/females 26/22, body mass index (BMI): 23.0 ± 2.4 kg/m2, duration of diabetes: 24 ± 8 years) bearing a successful PTx (combined with a kidney). Follow‐up ranged 6–60 months (median: 17 months). Before transplantation, according to the Eurodiab Study classification, 12 patients (25%) had nonproliferative retinopathy (NPDR; mild, moderate or severe), and 36 patients (75%) had laser‐treated and/or proliferative retinopathy (LT/PDR). During the follow‐up, in the NPDR group improvement/deterioration was defined as regression/progression to a lower/higher retinopathy grade; in the LT/PTD group, stabilization was defined as no new neo‐vessel formation or development of new lesions requiring laser‐treatment. In the NPDR group, five (41.7%) patients improved of one or more lesion grading, three (25%) patients showed no change, and four (33.3%) patients progressed of one grade. In the LT/PDR group, the post‐transplant data were: stabilization in 35 (97%) patients, and worsening in one (3%) patient. The number of improved/stabilized patients was significantly higher in the transplanted than in a control group of nontransplanted type 1 diabetic patients. In conclusion, despite a relatively short follow‐up period, successful PTx in our cohort of patients was associated with improvement and/or stabilization of DR in the majority of recipients.

MASSIVE ISOLATION, MORPHOLOGICAL AND FUNCTIONAL-CHARACTERIZATION, AND XENOTRANSPLANTATION OF BOVINE PANCREATIC-ISLETS

The limited availability of human donors makes the search for alternative islet sources mandatory for future developments in pancreatic islet transplantation. In this study, we report on the massive isolation of bovine islets of proven in vitro and in vivo viability. The islets were prepared by collagenase digestion, sequential filtrations, and density-gradient purification by modifying a technique previously developed in our laboratory for the porcine pancreas. The prepurification yield was 2,743 +/- 78 islet equivalents (IE)/g pancreas (mean +/- SE), with a postpurification recovery of 78.7 +/- 2.2%. Purity ranged from 80 to 90%. The histological and immunocytochemical studies demonstrated the identity and integrity of the islets with well-preserved insulin-, glucagon-, and somatostatin-containing cells. The morphological integrity of cultured bovine islets was demonstrated for up to 4 weeks from isolation. Insulin secretion from freshly isolated islets was similar at 3.3 mmol/l glucose (0.36 +/- 0.06 pmol.IE-1.min-1) and at 14 mmol/l glucose (0.42 +/- 0.00 pmol.IE-1.min-1), and it increased significantly (P < 0.01) at 25 mmol/l glucose (1.44 +/- 0.12 pmol.IE-1.min-1). Arginine, theophylline, and propionic acid increased insulin secretion from freshly isolated islets at 3.3 and 14 mmol/l glucose, but not at 25 mmol/l glucose. Islets cultured at 37 degrees C in CMRL 1066 culture medium for at least 10 days were shown to become responsive to a lower glucose concentration, as demonstrated by the significant increase of insulin release in response to 14 mmol/l glucose, when compared with basal secretion. This recovered responsivity to glucose was maintained after 4 weeks of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

The biguanide compound metformin prevents desensitization of human pancreatic islets induced by high glucose

Pancreatic islet desensitization by high glucose concentrations is a temporary and reversible state of beta-cell refractoriness to glucose (and possibly other secretagogues), due to repeated or prolonged pre-exposure to increased glucose concentrations. We evaluated whether the oral antidiabetic agent metformin affects this phenomenon in isolated, human pancreatic islets, and whether the possible effects of the biguanide are influenced by the presence of a sulphonylurea, glyburide. Islets prepared from five human pancreases were incubated for 24 h in M199 culture medium containing either 5.5 or 22.2 mmol/l glucose, with or without a therapeutic concentration (2.4 microg/ml) of metformin. Then, the islets were challenged with either 3.3 mmol/l glucose, 16.7 mmol/l glucose, or 3.3 mmol/l glucose + 10 mmol/l arginine, and insulin release was measured. After incubation in the absence of metformin, the human islets exposed to 22.2 mmol/l glucose showed no significant increase in insulin release when challenged with 16.7 mmol/l glucose (confirming that hyperglycemia desensitizes pancreatic beta-cells). In the presence of metformin, the islets fully maintained the ability to significantly increase their insulin release in response to glucose, even when previously exposed to 22.2 mmol/l glucose. No major effect on arginine-induced insulin release was observed, whatever the culture conditions. The protective action of metformin was observed also when glyburide was present in the incubation medium, whereas the sulphonylurea alone did not affect insulin release from the islets previously exposed to high glucose concentrations. These in vitro results suggest that metformin can prevent the desensitization of human pancreatic islets induced by prolonged exposure to increased glucose concentrations.

Pancreas transplant alone determines early improvement of cardiovascular risk factors and cardiac function in type 1 diabetic patients

Background. The effects of pancreas transplant alone (PTA) on cardiovascular risk factors (CRF) and cardiac function in type 1 diabetes mellitus (T1DM) patients are still unsettled. Methods. We studied 13 T1DM patients who received PTA with portal drainage and 11 matched control patients. Parameters of glucose and lipid metabolism and several additional classic CRF were assessed before and up to 6 months posttransplant. Cardiac morphology and function were assessed by Doppler echocardiographic examination. Results. Insulin independence was promptly achieved and then maintained after PTA. Total and low-density lipoprotein cholesterol levels were significantly lower after transplantation, whereas high-density lipoprotein cholesterol and triglyceride concentrations did not change. Both systolic and diastolic blood pressure values and fibrinogen levels improved significantly. In addition, PTA determined a significant amelioration of several morphologic and functional cardiac indices. None of the measured parameters changed in the control patients. Conclusions. PTA with portal drainage induces an early improvement of CRF and ameliorates cardiac function in patients with T1DM.

Prolonged survival of discordant porcine islet xenografts

Purified porcine islets were prepared by collagenase digestion and density gradient purification, and transplanted under the kidney capsule of C57B/B6 mice with streptozotocin-induced diabetes which were receiving varying temporary immunosuppressive therapies. Islets that had been cultured for 1 day at 37 degree C were rejected after : 9+/-0.1 (mean+/-SE) days in control mice: 14+/-3 days in mice receiving mouse antilymphocyte serum (MLS) plus porcine antilymphocyte serum (PLS) on day of transplant (day 0); 43+/-6 days in mice treated for 1 week with anti-CD4 antibody (aCD4); 36+/-4 days in mice given aCD4 for 1 week plus PLS on days 0 and 7; 47+/-3 days in mice treated with aCD4 for 1 week plus MLS and PLS on day 21. Porcine islet survival in these latter three groups was significantly (P<0.01) and similarly longer than in the control and MLS plus PLS groups. Then, we transplanted islets that had been either cultured at 24 degrees C for 7 days or cryopreserved into 7-day aCD4-treated mice, to evaluate whether low temperature culture or the freezing-thawing procedure could affect survival. Neither 7-day, low temperature culture (mean survival time: 37+/-2 days) nor cryopreservation (mean survival time: 39+/-2 days) prolonged islets function further. Thus, the present study demonstrates that prolonged survival can be achieved with discordant porcine islet xenografts, and shows the greater efficacy of aCD4 treatment, which was not improved by additional immunosuppressive therapies we tested, nor by culture or cryopreservation of the islets.

Pharmacokinetic optimisation of oral hypoglycaemic therapy

SummaryTwo main classes of oral hypoglycaemic drugs, the sulphonylureas and the biguanides, are currently used in the therapy of type II, non-insulin-dependent diabetes mellitus (NIDDM). The basic pharmacokinetic properties of these agents are discussed with a view to efficient and safe treatment.Both first- and second-generation sulphonylureas are rapidly absorbed from the gastrointestinal tract. In the plasma compartment, these drugs are strongly bound to serum proteins. All sulphonylureas are metabolised in the liver, and the metabolites and the parent drugs are eliminated mainly in the urine, but also (second-generation derivatives) in the faeces. Rapid- and short-acting sulphonylureas may improve early insulin release and promote better postprandial glucose control. Long-acting derivatives may ensure better control of overnight glycaemia. The elderly are at risk of developing severe sulphonylurea-induced hypoglycaemia, and in this population the agent chosen should have a short or intermediate duration of action and no active metabolites. Caution is needed when prescribing any sulphonylurea in patients receiving drugs known to affect sulphonylurea action, and in those with impaired liver and/or kidney function.The bioavailability of the biguanides ranges from 40 to 60%. Binding to plasma proteins is absent or very low. Metformin and buformin are not metabolised and are excreted in the urine; phenformin undergoes hepatic hydroxylation and is excreted in both urine and faeces. Metformin is the only agent of this class currently recommended for clinical use. The main indications of metformin treatment are NIDDM associated with obesity and/or hyperlipidaemia, and in combination with sulphonylurea both as primary treatment and when secondary failure occurs with sulphonylurea alone. Lactic acidosis may develop in patients receiving therapy with biguanides, especially in the presence of a preexisting contraindication to their use.

Salivary insulin concentrations in type 2 (non-insulin-dependent) diabetic patients and obese non-diabetic subjects: relationship to changes in plasma insulin levels after an oral glucose load

SummaryThe presence of immunoreactive insulin in saliva and its relationship to plasma immunoreactive insulin was investigated in healthy subjects, newly diagnosed non-obese Type 2 (non-insulin-dependent) diabetic patients and obese non-diabetic subjects, basally and after an oral glucose tolerance test. The mean ± SEM fasting values of plasma and salivary immunoreactive insulin were significantly higher in diabetic patients and obese non-diabetic subjects than in normal volunteers (p<0.05). During the glucose challenge, the increase of salivary insulin was related with that of plasma in the three groups of subjects, with a time lag in normal and obese subjects. In normal volunteers, plasma and salivary peak values were respectively 49.5 ± 13.4 μU/ml (p<0.05 vs obese subjects) at 60 min and 12.0±3.3μU/min (p<0.05 vs obese subjects) at 120 min; in diabetic patients, the values were 51.7 ± 5.6 μU/ml (p<0.05 vs obese subjects) and 14.6±4.1 μU/min at 120 min; in obese subjects, the peak value for plasma insulin was 111.5±40.1 μU/ml at 90 min and for salivary insulin 15.6 ± 5.1 μU/min at 120 min. A positive linear relationship was shown between plasma and salivary insulin during the oral glucose tolerance test. The identity of salivary insulin was assessed by reversed-phase HPLC. We conclude that salivary immunoreactive insulin can be found in Type 2 diabetic patients and in obese non-diabetic subjects, as well as normal volunteers, that plasma and salivary insulin are related after a glucose load, and that differences exist in salivary insulin secretion patterns among the three groups of subjects.

Plasma biguanide levels are correlated with metabolic effects in diabetic patients.

Metabolic abnormalities occur in biguanide‐treated diabetic patients. We investigated the relationship between plasma metformin and phenformin concentrations and metabolic effects. Drug levels were measured in 37 type II diabetic patients by HPLC. The method was sensitive, specific, and linear over a wide range of drug concentrations. Metformin and phenformin values ranged from 236 to 718 ng/ml and from 28 to 114 ng/ml, respectively. The plasma metformin level was correlated with triglycerides (r = −0.55; P < 0.05) but not with drug dosage, plasma glucose, HbA1, creatinine, creatinine clearance, lactate, pyruvate, lipid, and clinical parameters. Plasma phenformin concentrations correlated with lactate (r = 0.49; P < 0.05) and HbA1 (r = 0.50; P < 0.05) but not with drug dosage, parameters of diabetes control, creatinine, creatinine clearance, pyruvate, and clinical parameters. The clinical usefulness of this HPLC method, the evidence that the increase of lactate is related to the circulating phenformin levels, and the demonstration that the metformin effect on triglyceride metabolism is correlated to plasma drug levels are the positive findings of this work.

Decreased salivary glucose secretory rate: usefulness for detection of diabetic patients with autonomic neuropathy

In this study we investigated whether the presence of diabetic autonomic neuropathy (DAN) leads to an altered composition of saliva. DAN was evaluated in 33 normal subjects and 31 diabetic patients by means of the Valsalva manoeuvre, R-R variation during deep breathing, heart rate response to standing and lying down and blood pressure response to standing. Salivary flow (ml/h), salivary glucose levels (mumol/l) and salivary glucose secretory rate (mumol/h) were measured in each subject. Twelve diabetic patients were positive for DAN. Salivary flow (13 +/- 2 ml/h) and glucose concentration (330 +/- 50 mumol/l) were not significantly lower in patients with DAN than in normal subjects (18 +/- 2 ml/h, 500 +/- 50 mumol/l) and diabetic patients without DAN (16 +/- 1.9 ml/h, 500 +/- 40 mumol/l). The salivary glucose secretion rate was significantly lower (P less than 0.02) in diabetic patients with DAN (4.2 +/- 1.0 mumol/h) than in normal subjects and diabetic patients without DAN (9.0 +/- 1.0 mumol/h and 8.0 +/- 0.9 mumol/h respectively). The test had a good sensitivity and specificity, and appeared to be particularly indicated in discriminating patients without DAN. It is suggested that the measurement of salivary glucose may represent a simple, quick and inexpensive method for the screening of diabetic autonomic neuropathy.