Paolo Fumelli

Osteopenia associated with non-insulin-dependent diabetes mellitus: what are the causes?

This study investigated whether alterations in bone mineral content (BMC) and/or in the phosphate-calcium metabolism exist in non-insulin-dependent diabetes mellitus (NIDDM); whether they are linked to glycaemic control and whether antidiabetic therapy--oral agents or insulin--influences BMC and mineral metabolism. A cross-section assessment compared BMC and mineral metabolism in 60 well-controlled and 50 poorly controlled diabetic patients under oral hypoglycaemic therapy with 50 healthy controls. A longitudinal assessment improved the high glucose levels of the poorly controlled diabetic group either by increasing oral treatment or by adding a bedtime NPH insulin. Glycaemic control, BMC and mineral metabolism were followed-up for 1 year. In NIDDM patients BMC is reduced. This reduction is more marked in poorly controlled diabetic patients. In well-controlled diabetes osteocalcin levels are low. In poorly controlled patients glycosuria, hypercalcuria and parathyroid hyperactivity are present. In both groups vitamins 25(OH)-D, 1,25(OH)2-D and calcitonin levels are normal. Improving metabolic control increased BMC, normalized urinary calcium excretion and parathyroid activity and reduced osteocalcin levels. The type of anti-diabetic therapy does not have any significant effect upon BMC or upon phosphate-calcium metabolism. In conclusion, in NIDDM a hard-to-define osteoblast deficit appears to exist. In poorly controlled diabetes the loss of BMC is aggravated by the negative calcium balance caused by the renal calcium leak. This is due to glucosuric-induced osmotic diuresis and is maintained by parathyroid activation.

Increased susceptibility to lipid oxidation of low-density lipoproteins and erythrocyte membranes from diabetic patients

The aim of the present study was to determine if low-density lipoproteins (LDLs) and red blood cell (RBC) membranes from diabetic patients present an increased susceptibility to lipoperoxidation, which might be related to the increased incidence of atherosclerosis in diabetes. LDLs and RBC membranes were isolated from 11 insulin-dependent (IDDM) and 18 non-insulin-dependent diabetic (NIDDM) patients and exposed to a peroxidative stress by incubation with phenylhydrazine. The susceptibility to peroxidation was determined by measuring the production of thiobarbituric acid-reactive substances (TBARS) after the incubation. The following parameters were also evaluated: plasma glucose, triglycerides (TG), phospholipids (PL), total and high-density lipoprotein (HDL) cholesterol, apolipoprotein (apo) A-I, apo B, hemoglobin A1c (HbA1c), LDL PL and cholesterol, LDL fatty acid composition, and RBC membrane PL and cholesterol. Although they were apparently normolipidemic, diabetic patients showed an increased susceptibility to peroxidation in LDLs and erythrocyte membranes as compared with control subjects. The amount of arachidonic acid in LDLs and the PL concentration of RBC membranes from diabetic patients were significantly higher than in normal subjects. The increased lipoperoxidability of both RBC membranes and LDLs might play a central role in the pathogenesis of the vascular complications of diabetes mellitus.

Reduced Na + -K + -ATPase Activity and Plasma Lysophosphatidylcholine Concentrations in Diabetic Patients

A fraction from normal human plasma inhibiting Na+ -K+ ATPase has been recently identified as lysophosphatidylcholine (LPC). The aim of this study was to investigate the existence of a relationship between the activity of the cellular membrane Na+ -K− -ATPase and plasma LPC in human diabetes. We studied 10 patients with insulin-dependent-diabetes mellitus (IDDM), 14 patients with non-insulin-dependent diabetes mellitus (NIDDM), and 10 sex- and age-matched control subjects. Plasma LPC concentrations were increased in both IDDM and NIDDM patients compared with control subjects. Na+ -K+ -ATPase activity was reduced in both groups of patients in erythrocyte and platelet membranes. There was a significant correlation between the concentrations of plasma LPC and Na+ -K+ -ATPase activity in both erythrocyte and platelet membranes (P < 0.01). To investigate the effect of LPC on the enzyme, Na+ -K+ -ATPase activity was determined in erythrocyte membranes obtained from six healthy subjects after in vitro incubation with increasing concentrations of LPC (1–10 microM). Enzymatic activity was significantly reduced by in vitro LPC at a concentration of 2.5 microM, with a further decrease at 5 microM. These data suggest that the decrease in Na+ -K+ -ATPase activity in diabetes might be due to increased LPC concentrations.

Zinc-Dependent Low Thymic Hormone Level in Type I Diabetes

Zinc is required for optimal functioning of the immune system. It was recently reported that one of the best-known thymic hormones responsible for the maturation and differentiation of the thymus-derived T-lymphocyte line, i.e., serum thymic factor (STF), is biologically active only when bound to zinc ions; in this form it has been called thymulin (Zn-STF). Because low serum and tissue zinc values have been reported to occur in diabetic conditions, and because defects of T-lymphocyte–dependent functions are also present in diabetic patients, even metabolically well-controlled diabetic patients, we investigated the serum level of zinc and the plasma level of both active Zn-STF and inactive STF thymic hormones in 15 young patients suffering from type I (insulin-dependent) diabetes. Serum zinc levels were significantly reduced in diabetic conditions and did not correlate with the degree of metabolic compensation measured by glycosylated hemoglobin. In diabetes, the active form of thymulin is strongly reduced, whereas the inactive form is abnormally elevated. In vitro zinc addition to diabetic plasma samples also induces zinc saturation of inactive thymic hormone molecules: the total thymic hormone measured in these experimental conditions shows values in diabetic patients comparable with those observed in healthy age-matched individuals, suggesting that low thymulin levels recorded in diabetic conditions are due not to a thymic failure in synthesizing and secreting thymic hormone but to a peripheral defect in zinc saturation of the hormone molecules. The zinc-dependent failure of thymic hormone, present even in fairly compensated diabetic conditions, might account for the apparent insulin-independent immunological abnormalities associated with type I diabetes.

Altered platelet membrane dynamic properties in type 1 diabetes

A modified platelet response to aggregating stimuli is supposed to play a role in the pathogenesis of diabetic macroangiopathy. We studied the fluidity and microheterogeneity of the external surface of the platelet membrane and the activities of the plasma membrane Na+-K+-ATPase and Ca2+-ATPase in 21 men with type 1 diabetes and in 20 control subjects before and after in vitro thrombin addition. In the resting state, platelets from type 1 diabetic patients showed an increased fluidity and microheterogeneity of the platelet membrane, a higher Ca2+-ATPase activity, and a reduced Na+-K+-ATPase activity in comparison with platelets from healthy subjects. The fatty acid composition was also modified, with increased C 16:1 and decreased C 18:0 content. Control cells incubated with thrombin showed a modification of the membrane parameters opposite to the response observed in type 1 cells after the stimulation. The incubation of control platelets in the resting state with high concentrations of glucose modified the fluidity of the plasma membrane Na+-K+-ATPase and Ca2+-ATPase activities in an opposite way in comparison with the alterations observed in type 1 platelets. This study suggests that in type 1 diabetic patients, the platelet membrane responds to activation with a molecular remodeling different from the response of healthy subjects. The abnormal organization of the membrane might contribute to the altered platelet functions in type 1 diabetic patients, but acute exposure to high glucose levels does not seem able to modify the platelet membrane in the way observed in type 1 diabetes.

Diabetes mellitus and chronic heart failure.

Cardiovascular disease has a high prevalence in diabetic patients. Diabetes mellitus is an important risk factor for atherosclerosis and coronary disease mainly through obesity, hyperlipidemia, insulin-resistance, hyperinsulinemia, hyperglycemia and altered homeostasis. The correlation between diabetes and chronic heart failure is not widely documented in the literature. According to the Framingham study, the incidence of cardiovascular morbidity per year is 39.1% in diabetic males and 17.2% in diabetic females; chronic heart failure afflicts 7.6% of diabetic males and 11.4% of diabetic females. Actual knowledge about pathophysiology suggests that cardiac involvement in diabetes is not only related to macrovascular injury but also to other factors, such as alterations of autonomic nervous system, that can contribute to diabetic cardiopathy. The present study evaluated the prevalence of chronic heart failure in an Italian diabetic population in order to discuss the rationale of the therapeutic strategies.

Coronary heart disease, type 2 diabetes mellitus and cardiovascular disease risk factors: a study on a middle-aged and elderly population.

The risk for all the manifestations of atherosclerotic disease is increased in patients affected by type 2 diabetes mellitus. The aim of the present work was to evaluate the prevalence of coronary heart disease (CHD) in a well-characterized middle-aged and elderly Italian diabetic population. The population studied included 3862 subjects, i.e. all the patients affected by type 2 diabetes of age >or=50 years attending the outpatient diabetes care unit of INRCA in Ancona (Italy) from 1 August 1997 to 31 July 1998. We collected and analysed both clinical and laboratory data by means of a computerized data base for the outpatient clinic management. The prevalence rate of CHD was 20.25% in this population. The groups with CHD and without CHD did not differ significantly with respect to age at onset of diabetes, body mass index and HbA1c levels, while patients with CHD were significantly older than patients without CHD and had a longer duration of diabetes. The prevalence of patients with hypertension (52.9 vs 63.0%, P<0.001), hypercholesterolemia (11.6 vs 14.1%, P<0.05) and hyperlipidemia (17.8 vs 23.3%, P<0.001) was significantly higher in the group of diabetic subjects affected by CHD than in patients not affected by heart ischemic disease. It might be hypothesized that the improvement of metabolic profile and the currently feasible control of non-diabetic risk factors could reduce cardiovascular disease rates in type 2 diabetic patients.

Apolipoprotein E Polymorphism as a Risk Factor for Vascular Disease in Diabetic Patients

OBJECTIVE To examine the prevalence of cardiovascular disease in diabetic patients as a function of apolipoprotein (apo) E polymorphism. RESEARCH DESIGN AND METHODS The apo E phenotypes and plasma lipid, lipoprotein, and apo levels were determined for 517 Italian diabetic patients. The prevalence of cardiovascular disease (defined as ischemic heart disease [IHD] and/or peripheral vascular disease and/or cerebrovascular disease) was assessed as a function of apo E polymorphism at entry and after 4 years. RESULTS The occurrence of vascular disease did not differ significantly between diabetic patients in the various categories of apo E phenotype either at entry into the study or after 4 years. When expressed as a percentage of patients with disease, we observed—for E2, E3, and E4 carriers, respectively—at entry: IHD, 20.0% (n = 14), 21.0% (n = 79), and 21.5% (n = 14); and macroangiopathy, 24.3% (n = 17), 29.3% (n = 110), and 24.6% (n = 16). Apo E polymorphism did not make a significant contribution to multiple logistic regression models designed to identify the factors associated with the occurrence of vascular disease in diabetic patients. CONCLUSION Apo E polymorphism and, notably, the apo E4 allele cannot be universally considered as a particular risk factor for cardiovascular disease in diabetic patients.

Nifedipine treatment in preeclampsia reverts the increased erythrocyte aggregation to normal

OBJECTIVES Our objectives were to assess erythrocyte aggregation in hypertensive pregnancy and to evaluate the effect of the antihypertensive treatment on it. STUDY DESIGN The mean entity of erythrocyte aggregation was determined by an automatic aggregometer in 57 pregnant women: 20 normotensive, seven chronically hypertensive, 10 chronically hypertensive with superimposed preeclampsia, and 20 with preeclampsia. Ten of the latter were subsequently treated by 40 mg/day oral nifedipine; the other 10 by 400 mg/day oral labetalol, to keep diastolic blood pressure < 90 mm Hg. Also, patients with superimposed preeclampsia were treated with 40 mg/day oral nifedipine. RESULTS Erythrocyte aggregation was increased in all the hypertensive pregnant patients compared with the normotensive pregnant controls, regardless of both the onset (chronic or pregnancy-induced) of hypertension and the status of plasma macromolecules. Antihypertensive treatment with labetalol significantly reduced the aggregability of erythrocytes, whereas treatment with nifedipine reverted it to normal. CONCLUSIONS Increased erythrocyte aggregation may be due to either conformational changes of the membrane occurring during hypertension or a redistribution of the ionic charges on the two surfaces of the membrane. The effect of nifedipine by restoring the ionic charges may be due to this latter event.

Modifications induced by insulin-dependent diabetes mellitus on human placental Na+/K+-adenosine triphosphatase

The causes of the reduced activity of Na+/K+-adenosine triphosphatase (ATPase) in human diabetes are still the object of controversy. The aim of this work was to investigate the mechanisms of inhibition by means of the study of the Na+/K+-ATPase purified from human placenta. We purified Na+/K+-ATPase from term placentas of six healthy women and six age-matched women with insulin-dependent diabetes mellitus (IDDM) in good metabolic control. The enzymatic activity was reduced in both the microsomal fraction and the purified Na+/K+-ATPase obtained from diabetic women, whereas no difference was found in the number of active molecules determined by anthroyl ouabain binding. The Na+/K+-ATPase purified from women with IDDM did not show any modification in the ouabain affinity or changes in the physicochemical structure of the ouabain binding site investigated by dynamic fluorescence or alterations in lateral diffusion. The activation energy of the enzyme was increased, whereas the tryptophan accessibility of the enzyme was lower in women with IDDM. The fluidity of the lipid anulus of the enzyme was higher in women with IDDM than in control women, as suggested by fluorescence polarization of 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene. The adenosine triphosphate-binding site, investigated by anisotropy decay studies of the fluorescent probe pyrene isothiocyanate, was modified in women with IDDM. It appears that the Na+/K+-ATPase of human placenta is altered in its disposition in IDDM.