John D. Bagdade

The Significance of Basal Insulin Levels in the Evaluation of the Insulin Response to Glucose in Diabetic and Nondiabetic Subjects

The level of insulin after an overnight fast (basal) in 37 obese and nonobese male subjects with normal and abnormal carbohydrate tolerance was directly related to the increase in insulin concentration during a 3 hr 100 g oral glucose tolerance test. Obesity, but not diabetes, was associated with an elevation of this basal insulin level. Thus obesity predicted with the magnitude of the insulin response to glucose ingestion. When the individual insulin values were expressed as per cent change from the basal level, this effect of obesity was excluded. The insulin levels of all subjects with normal carbohydrate tolerance promptly rose 5-7-fold, and reached peak values 1 hr after oral glucose. In contrast, the diabetic response (as per cent increase) was markedly reduced during the 1st hr, and maximal (but still subnormal) insulin levels were not attained until 2 hr. In all subjects the insulin response (quantitated by calculation of the area circumscribed by a plot of the per cent change in insulin with time) showed a significant inverse correlation with the glucose response. Thus increasing degrees of carbohydrate intolerance were associated with decreasing insulin responses. Elevated levels of insulin, in both the basal state and in response to glucose, were related to obesity.

Impaired Leukocyte Function in Patients with Poorly Controlled Diabetes

In order to assess the influence of poor diabetes control on function of leukocytes, polymorphonuclear leukocytes (PMNs) from patients with poorly controlled but nonketotic disease were studied before and after therapy. Before treatment, phagocytosis was significantly reduced (p < .001) and, consequently, the rate of killing the test organism (type 25 pneumococcus) was decreased (p < .01). Following antidiabetes therapy phagocytosis improved significantly; while microbicidal rates also improved, they remained less than control values (p < .01). Serum from the untreated diabetics uniformly reduced phagocytosis and microbicidal rates of control granulocytes; serum from controls improved phagocytosis by the diabetic PMNs, but restored normal microbicidal rates in only half of the patients. This transferable inhibitory effect of hyperglycemic diabetic serum on control granulocytes was abolished by dilution, and was reproduced in normal serum by the isosmotic addition of glucose. These studies suggest that (1) PMN function may be impaired during periods of poor diabetes control, as has been shown previously in ketoacidosis, and (2) hyperglycemia or a closely related factor may contribute to the defect.

Studies on the Mechanism of Increased Plasma Triglyceride Levels Induced by Oral Contraceptives

Abstract Increases in plasma triglyceride levels were observed in normal young women treated for two weeks with an oral contraceptive containing ethinyl estradiol and medroxyprogesterone. The mechanism of this phenomenon may be related to an observed decrease in postheparin lipolytic activity and impaired plasma triglyceride removal. At the same time serum insulin levels increased, perhaps stimulating endogenous hepatic triglyceride synthesis and secretion into plasma.

Accelerated cholesteryl ester transfer in plasma of patients with hypercholesterolemia.

To discern the mechanism(s) that underlie abnormal cholesteryl ester transfer (CET) in patients with hypercholesterolemia, we have studied this dysfunctional step in reverse cholesterol transport in 13 subjects with genetically heterogeneous forms of hypercholesterolemia (HC). In all HC patients, the mass of CE transferred in whole plasma from HDL to VLDL and LDL increased rapidly initially and was significantly greater than in controls at 1, 2, and 4 h (P less than 0.005). To further characterize this disturbance, we performed a series of recombination experiments. Combining HC d less than 1.063 containing acceptor VLDL + LDL with the d greater than 1.063 fraction from controls containing donor HDL + CE-transfer protein (CETP) and not the converse combination showed the same characteristics of accelerated CET noted with intact HC plasma, indicating that abnormal transfer was associated with the HC acceptor lipoproteins. When HC VLDL and its subfractions and LDL were isolated separately and then combined with control d greater than 1.063 fractions, accelerated CET was only associated with VLDL1. Consistent with an acceleration of the neutral lipid transfer reaction occurring between HDL and VLDL1 in HC in vivo, we found that the triglyceride/CE ratio was decreased in HC VLDL1 (P less than 0.001), and increased in HDL (P less than 0.25). CETP mass was significantly increased in HC plasma (HC 2.3 +/- 4 micrograms/ml vs. control 1.3 +/- 0.3 micrograms/ml; mean +/- SD; P less than 0.025). This series of observations demonstrate that CET is accelerated in the plasma of HC patients, and this disturbance results from dysfunction of the VLDL1 subfraction rather than an elevation of CETP levels. Since an abnormality of this type in vivo can lead to the accumulation of potentially atherogenic CE-enriched apoB-containing lipoproteins in plasma, it may be an additional previously unrecognized factor that increases cardiovascular risk in HC patients.

Accelerated cholesteryl ester transfer in patients with insulin-dependent diabetes mellitus.

Abstract. Abnormalities in cholesteryl ester transfer (CET) may play a role in the development of diabetic arterial vascular complications. To assess this important step systematically in reverse cholesterol transport, we have studied 20 treated, clinically stable, normolipidaemic patients. Contrary to the impairment in CET described previously in NIDDM, the mass of CE transferred from HDL to VLDL+LDL was significantly greater in IDDM patients than in controls at 1,2, and 4 h (P<0.001). When the d<1.063 plasma fractions from IDDM subjects were combined with controls d<1.063 fractions, an accelerated CET response was observed which was identical to that found in intact IDDM plasma. This finding, which indicates that this disturbance in CET was associated with the acceptor lipoproteins, was confirmed when we found that it was reproduced by the addition of IDDM VLDL and not LDL to control d>1.063 fractions.

Acute Insulin Withdrawal and the Regulation of Plasma Triglyceride Removal in Diabetic Subjects

The effects of acute insulin deprivation on the enzyme lipoprotein lipase (LPL) and on triglyceride (TG) removal from plasma in man are unknown. To assess the role of insulin availability on TG removal, plasma TG concentration and postheparin lipolytic activity (PHLA)—an indirect means of quantitating LPL—were measured in seven insulin-dependent diabetics before and forty-eight hours after insulin withdrawal. The TG elevation (p < .01) and diminished PHLA levels (p < .01) observed in all subjects were consistent with impaired TG removal. The delayed disappearance of C-14-labeled TG after insulin deprivation (p < .01) demonstrated in two subjects further suggests that insulin is required for maintaining normal LPL and TG removal.

Accelerated cholesteryl ester transfer in noninsulin-dependent diabetes mellitus

Alterations in core lipid composition of lipoproteins in noninsulin-dependent diabetes mellitus (NIDDM) patients have suggested that the heteroexchange of neutral lipids between HDL and the apo B-containing lipoproteins may be enhanced. For this reason, we studied cholesteryl ester transfer (CET) in ten sulfonylurea-treated patients with stable NIDDM. CET measured in all NIDDM subjects with an assay of mass transfer was significantly greater than that of controls at 1 and 2 h (P < 0.001); the transfer of radiolabeled CE also was increased in a subset of four of the NIDDM group (NIDDM k = 0.21 +/- 0.04 vs. control k = 0.10 +/- 0.05; P < 0.05). A weak correlation was demonstrable between the mass of CE transferred at 1 h and diabetic control expressed as plasma fructosamine (r = 0.58, P < 0.09). To characterize this disturbance in CET further, the donor (HDL + VHDL) and acceptor (VLDL + LDL) lipoprotein fractions were isolated by ultracentrifugation at d 1.063 g/ml from NIDDM and control plasma and a series of recombination experiments were performed. Combining NIDDM acceptor with control donor fractions that contained HDL and CETP and not the combination of NIDDM donor and control acceptor lipoproteins resulted in an accelerated CET response identical to that observed in NIDDM whole plasma. This observation indicated that the abnormality in CET in NIDDM was associated with the VLDL + LDL fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistent abnormalities in lipoprotein composition in noninsulin-dependent diabetes after intensive insulin therapy.

To determine whether rigorous insulin therapy, which normalized the routinely measured plasma lipids, also reversed qualitative abnormalities in the composition of lipoproteins in noninsulin-dependent diabetes mellitus (NIDDM), we studied 18 NIDDM patients (eight men and 10 women) before and 2 months after intensive insulin therapy. Glycosylated hemoglobin levels (11.7% vs. 8.7%), plasma triglyceride (TG) (250 +/- 91 vs. 164 +/- 56 mg/dl, p less than 0.001), and cholesterol (214 +/- 43 vs. 198 +/- 31 mg/dl, p less than 0.025) all fell, and both HDL2 cholesterol and HDL3 cholesterol increased (59.1% and 10.9%, respectively, p less than 0.001). However, abnormalities in two indices of lipoprotein surface constituents, which were present before insulin therapy, remained so thereafter. The first of these, the new cardiovascular risk factor, the plasma free cholesterol/lecithin ratio, which was increased before treatment, fell only slightly after therapy (pre-therapy 1.02 +/- 0.29 vs. post-therapy 0.90 +/- 0.17, p less than 0.4; reference group, 0.83 +/- 0.14), and remained elevated in very low density lipoprotein (VLDL) and low density lipoprotein (LDL). Secondly, the sphingomyelin/lecithin ratio, an index of the surface rigidity of lipoproteins, was abnormal before treatment in VLDL, HDL2, and HDL3, and this alteration persisted after insulin therapy in HDL3 (p less than 0.001). Lipoprotein core lipid abnormalities were also present before treatment: the TG/cholesteryl ester ratio was reduced in VLDL and increased in LDL, HDL2, and HDL3. Rigorous insulin therapy improved, but failed to fully correct, this disturbance.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the chylomicron origin of lipids accumulating in diabetic eruptive xanthomas: a correlative lipid biochemical, histochemical, and electron microscopic study.

Plasma lipoprotein alterations in nine insulin-dependent diabetics with hyperlipemia have been related to the lipid accumulating in eruptive xanthomas evolving in these patients. Histochemical and electron microscopic examination of xanthomas have been correlated with the lipid analyses in order to obtain additional evidence regarding the lipoprotein origin of lipids accumulating in the lesions. Both analytical and morphologic evidence suggested that circulating chylomicrons significantly contribute to the xanthoma lipids. All the patients had large quantities of circulating triglyceriderich chylomicrons which carried approximately 70% of the triglyceride found in the plasma. The fatty acid pattern of chylomicron and xanthoma triglycerides were similar. Triglyceride constituted the major lipid found in the xanthomas when they were sampled during their eruption. These findings, take in conjunction with histochemical and electron microscopic evidence of chylomicron particles in the dermal capillary walls, support the theory that blood lipoproteins, and particularly chylomicrons, permeated the vascular walls and the triglycerides carried by these lipoproteins apparently accumulated in tissue macrophages and perithelial cells which evolved into foam cells. Initiation of appropriate therapy resulted in clearance of the chylomicronemia and a concomitant resolution of the xanthomas as reflected by a decrease in total xanthoma lipid. Sequential studies of resolving xanthomas in five patients revealed that xanthoma triglyceride was mobilized more rapidly than cholesterol, resulting in a redistribution of the xanthoma lipids, so that the resolving lesions were cholesterol rich. Consistent with this change in lipid composition, correlative electron microscopy revealed loss of amorphous material from many of the foam cell vacuoles.

Influence of Obesity on the Relationship Between Insulin and Triglyceride Levels in Endogenous Hypertriglyceridemia

In order to assess the influence of obesity on the relationship between insulin and triglyceride levels, basal plasma triglyceride (TG) and immunoreactive insulin (IRI) levels prior to and during oral glucose (100 gm.) tolerance tests were compared in nonlipemic control subjects and patients with endogenous hypertriglyceridemia with comparable glucose tolerance. Basal IRI and body weight correlated closely in both lipemic (r = +.75, p < .001) and nonlipemic groups (r = +.72, p < .001), and no significant increase in basal IRI was observed in the lipemic subjects when matched for weight. In both lipemic and control groups basal IRI and TG levels were related to a comparable degree (r = +.44, p < .01); however, for any given basal IRI, TG levels in the lipemic group were dramatically increased. No relationship was demonstrable between TG and stimulated IRI levels expressed either as absolute increments or when the effects of obesity on insulin secretion were excluded by expression of each insulin response to glucose as a percentage of the basal level. In both groups, glucose intolerance and the per cent increment in IRI at both sixty and 180 min. were inversely related, and when matched for glucose tolerance, no quantitative difference in stimulated IRI levels was demonstrable in patients with endogenous hypertriglyceridemia and the control group. When factors such as glucose intolerance have been controlled, variations in IRI are best explained by variations in body weight. These findings indicate that the high IRI levels often observed in patients with endogenous hypertriglyceridemia result from coexisting obesity.