Insulin resistance in obese subjects and newly diagnosed NIDDM patients and derangements of pyruvate dehydrogenase in their circulating lymphocytes

Abstract

BACKGROUND: In circulating lymphocytes of individuals with insulin resistance and overt hyperglycaemia (NIDDM patients), alterations, affecting pyruvate dehydrogenase (PDH), the key enzyme in glucose oxidative breakdown, have been observed. They include below normal enzyme activity and, in vitro, no enzyme response to insulin at low physiological levels (5 m mUaml) as well as activation up to the basal values of controls with insulin at high physiological levels (50 m mUaml), instead of activation and inhibition respectively, as in controls. OBJECTIVE: To investigate whether these alterations characterize circulating lymphocytes of individuals with insulin resistance in whom derangements of glucose homeostasis are absent (obese subjects with normal glucose tolerance), or present but still controllable (nonobese and obese newly diagnosed NIDDM patients on an appropriate diet). SUBJECTS: Thirty obese subjects (BMI 36 AE 3) responding normally to an oral glucose tolerance (OGT) test; 60 newly diagnosed NIDDM patients (30 nonobese, BMI 22 AE 4 and 30 obese, BMI 38 AE 2); 30 nonobese (BMI 21 AE 5) and nondiabetic subjects, with no family history for NIDDM, served as controls. METHODS: Evaluation of PDH activity in circulating lymphocytes before and after exposure to insulin at 5 and 50 m mUaml, and of clinical parameters before and during an OGT test. RESULTS: 1) In circulating lymphocytes of obese nondiabetic subjects as well as obese and nonobese newly diagnosed NIDDM patients, PDH activity was signi®cantly below normal. In vitro, enzyme response to insulin at 5 m mUaml was reduced in nonobese NIDDM patients with respect to controls, and absent in obese nondiabetic subjects and obese NIDDM patients. Enzyme response to insulin at 50 m mUaml was reversed in all individuals, which allowed enzyme activity to recover up to the basal level of controls. 2) In NIDDM patients and obese nondiabetic subjects, undergoing an OGT test, the area under the glycaemic curve (g-AUC) was as expected; the area under the insulinaemic curve (i-AUC) was increased in both groups with respect to controls, but signi®cantly only in the latter. CONCLUSION: In individuals with insulin resistance PDH activity in their circulating lymphocytes rises up to basal levels of controls, only if these cells are exposed to insulin at high physiological concentrations, and g-AUC is normal only in those subjects who have signi®cantly increased i-AUC. This suggests that with insulin at suf®ciently high concentrations both parameters can be corrected. We conclude that the derangements responsible for the alterations of the two parameters share common features and thus the described PDH alterations in circulating lymphocytes re¯ect systemic insulin resistance whether accompanied by hyperglycaemia or not.

In obese individuals dexfenfluramine corrects molecular derangements reflecting insulin resistance

“…Basal PDH activity in circulating lymphocytes of all participants recovered signi®cantly (P`0.0001), thereby approaching that of age-matched controls, 1 ( Figure 1 ± 3); further, in vitro, insulin at 33 pmolal, now determined sharp enzyme activation and at 330 pmolal clear inhibition (P`0.0001 and P`0.001 respectively, vs unstimulated cells; Figure 1); these responses were similar to those in controls. 1 At D 2 , when clinical and haematological parameters were still constant, basal PDH activity had already recovered signi®cantly with respect to D 0 (P`0.0001). However, with respect to D 21 , the difference was still signi®cant in the diabetic (P`0.001), but not in the non-diabetic group (P 0.06, Figures 2 and 3) 21 , and D 0 , respectively) and comparable to that in controls.…”

“…However, with respect to D 21 , the difference was still signi®cant in the diabetic (P`0.001), but not in the non-diabetic group (P 0.06, Figures 2 and 3) 21 , and D 0 , respectively) and comparable to that in controls. 1 …”

“…Circulating lymphocyte preparation was performed according to Boyu Èm as previously reported. 1,3 At the end of preparation, cells were suspended in 110 mm NaCl buffered in 40 mm Na 2 HPO 4 ± KH 2 PO 4 pH 7.4 (PBS-A). One part of the preparation was used immediately for insulin contact procedures, another part for cell counts, performed manually with a haemocytometer, and the remainder was pelleted, suspended in PBS-A enriched with 2 mgaml leupeptin and 20 mM EDTA (PBS-B), stored at 770 C and eventually used to evaluate PDH activity.…”

“…1 That is, in vivo PDH activity is below normal and, in vitro, it is unaffected by insulin at relatively low (33 pmolal) and enhanced at relatively high (330 pmolal) physiological concentrations. In controls, however, insulin succeeds in stimulating PDH at just 16 pmolal; peak enzyme activation is reached with insulin at 33 pmolal, but for insulin at 66 pmolal enzyme activity is again at basal values and signi®cantly below for insulin at 330 pmolal.…”

“…1 ± 4 In the above obese subjects PDH protein content is not defective. 1 PDH is the major determinant of glucose breakdown for energy purposes as well as of glucose utilization for fatty acid synthesis and it is well documented as a sensitive insulin target. 5 ± 10 Dexfenuramine is known to have bene®cial effects on poor insulin sensitivity concerning de®ned metabolic pathways.…”