Quantitative relationship between plasma lipids and glycohemoglobin in type I patients. Longitudinal study of 212 patients

Outstanding improvement of the advanced lipoprotein profile in subjects with new-onset type 1 diabetes mellitus after achieving optimal glycemic control

AIMS

The impact of glycemic optimization on lipoprotein subfraction parameters in apparently normolipidemic subjects with new-onset type 1 diabetes mellitus (T1D) was examined.

METHODS

We evaluated the serum lipid and advanced lipoprotein profiles in twenty subjects at onset of T1D and twenty non-diabetic controls by laboratory methods and 1H NMR spectroscopy shortly after diabetes diagnosis (baseline), and after achieving optimal glycemic control (HbA1c ≤ 7.0%).

RESULTS

Advanced lipoprotein analysis revealed a significant reduction from baseline in serum concentrations of triglycerides (TG), cholesterol (C), and apolipoprotein (Apo)B-containing lipoproteins of treated subjects (VLDL-TG: -21%, IDL-TG: -30%, LDL-TG: -34%, LDL-TG: -36%, P < 0.05; VLDL-C: -23%, IDL-C: -44%, LDL-C: -16%; p < 0.05). Decreased VLDL and LDL lipids were mainly attributed to concomitant reductions in the concentration of medium-sized VLDL (-36%) and medium-sized LDL (-31%) and, to a lesser extent, to large-sized LDL (-14%). Notably, proatherogenic IDL characteristics and related surrogates of atherogenicity were resolved upon achievement of optimal glycemic status. Moreover, the concentration of HDL-TG was also reduced (-18%) at follow-up.

CONCLUSIONS

Our data showed that the achievement of optimal glycemic control after T1D onset corrected hidden derangements in ApoB-containing lipoproteins (particularly IDL) and HDL-TG that are related to higher cardiovascular risk in poorly controlled T1D.

Glucose control predicts 2-year change in lipid profile in youth with type 1 diabetes

OBJECTIVE

To test the hypothesis that a change in glycated hemoglobin (A1c) over a follow-up interval of approximately 2 years would be associated with concomitant changes in fasting lipids in individuals with type 1 diabetes (T1D).

STUDY DESIGN

All subjects with T1D diagnosed in 2002-2005 in the SEARCH for Diabetes in Youth study with at least 2 study visits ∼12 and ∼24 months after an initial visit were included (age at initial visit, 10.6 ± 4.1 years; 48% female; diabetes duration, 10 ± 7 months; 76% non-Hispanic white; A1c = 7.7% ± 1.4%). Longitudinal mixed models were fit to examine the relationship between change in A1c and change in lipid levels (total cholesterol [TC], high-density lipoprotein-cholesterol [HDL-c], low-density lipoprotein-cholesterol [LDL-c], log triglycerides [TG], and non-HDL-c) with adjustment for possible confounders.

RESULTS

Change in A1c over time was significantly associated with changes in TC, HDL-c, LDL-c, TG, and non-HDL-c over the range of A1c values. For example, for a person with an A1c of 10% and then a 2% decrease in A1c 2 years later (to 8%), the model predicted concomitant changes in TC (-0.29 mmol/L, -11.4 mg/dL), HDL-c (0.03 mmol/L, 1.3 mg/dL), LDL-c (-0.23 mmol/L, -9.0 mg/dL), and non-HDL-c (-0.32 mmol/L, -12.4 mg/dL) and an 8.5% decrease in TG (mmol/L).

CONCLUSIONS

Improved glucose control over a 2-year follow-up was associated with a more favorable lipid profile but may be insufficient to normalize lipids in dyslipidemic T1D youth needing to decrease lipids to goal.

Genetic variation in thioredoxin interacting protein (TXNIP) is associated with hypertriglyceridaemia and blood pressure in diabetes mellitus

AIMS

Thioredoxin interacting protein (TXNIP) is an attractive candidate gene for diabetes or diabetic dyslipidaemia, since TXNIP is the strongest glucose-responsive gene in pancreatic B-cells, TXNIP deficiency in a mouse model is associated with hyperlipidaemia and TXNIP is located in the 1q21-1q23 chromosomal Type 2 diabetes mellitus (DM) locus. We set out to investigate whether metabolic effects of TXNIP that were previously reported in a murine model are also relevant in human Type 2 DM.

METHODS

The frequency distribution of a 3' UTR single nucleotide polymorphism (SNP) in TXNIP was investigated in subjects with normal glucose tolerance (NGT; n = 379), impaired glucose tolerance (IGT; n = 228) and Type 2 DM (n = 230). Metabolic data were used to determine the effect of this SNP on parameters associated with lipid and glucose metabolism.

RESULTS

The frequency of the TXNIP variation did not differ between groups, but within the group of diabetic subjects, carriers of the TXNIP-T variant had 1.6-fold higher triglyceride concentrations (P = 0.015; n = 136) and a 5.5-mmHg higher diastolic blood pressure (P = 0.02; n = 212) than homozygous carriers of the common C-allele, whereas in non-diabetic subjects fasting glucose was 0.26 mmol/l lower (P = 0.002; n = 478) in carriers of the T-allele. Moreover, a significant interaction between plasma glucose concentrations and TXNIP polymorphism on plasma triglycerides was observed (P = 0.012; n = 544).

CONCLUSION

This is the first report to implicate TXNIP in a human disorder of energy metabolism, Type 2 diabetes. The effect of TXNIP on triglycerides is influenced by plasma glucose concentrations, suggesting that the biological relevance of TXNIP variations may be particularly relevant in recurrent episodes of hyperglycaemia.

Vitamin A, retinol binding protein and lipids in type 1 diabetes mellitus

OBJECTIVE

A case-control study was conducted to evaluate the effects of type 1 diabetes mellitus (IDDM) on plasma levels of vitamin A (retinol) and serum levels of retinol-binding protein (RBP) and their relationship with the atherogenic indicators.

SUBJECTS

A total of 47 randomised IDDM children were recruited from those treated at the Endocrinology Unit of the University Hospital of Granada (Spain). They were matched for age and sex with 16 healthy children.

METHODS

The following parameters were measured in all patients: serum concentrations of total cholesterol, triglycerides, high (HDL, spectrophotometry), very low (VLDL) and low (LDL) density lipoprotein cholesterol (Friedewald's formula); serum levels of RBP (kinetic nephelometry); plasma vitamin A and glycosilated haemoglobin (HbA1c; high performance chromatography).

RESULTS

Higher RBP concentrations in IDDM children (P=0.05), lower retinol levels (P=0.05) and lower vitamin A/cholesterol ratio (P=0.02) than in the control group were found; no differences in the atherogenic indicators were observed. There was a correlation between RBP and vitamin A (P=0.0001). Relationships between retinol, RBP and atherogenic indicators were demonstrated in the IDDM group (A-LDLc/HDLc (P=0.01); A-(VLDL+LDL)c/HDLc (P=0.007); RBP-LDLc/HDLc (P=0.05); RBP-(VLDL+LDL)c/HDLc (P=0.02)), and an inverse relationship was found between the vitamin A/TG ratio and HbA1c (P=0.004). The children with HbA1c>8% showed increased atherogenic indicators and lower vitamin A/CHOL and vitamin A/TG ratios than those with good control of the illness.

CONCLUSIONS

The IDDM children with poor metabolic control face a higher atherogenic risk and vitamin A 'relative deficiency' risk than those with good metabolic control of their illness. Relationships between retinol and RBP with atherogenic indicators were found. The results suggest that vitamin A therapeutic supplements in IDDM children may reduce or prevent atherogenic risk.

Lipid profiles and blood pressure: are they risk factors for the development of early background retinopathy and incipient nephropathy in children with insulin-dependent diabetes mellitus?

The objective of this study is to examine the influence of lipid profiles and blood pressure on the development of microvascular complications in adolescents with insulin-dependent diabetes mellitus (IDDM) in a matched pairs study. Patients with early background retinopathy (n = 21) or microalbuminuria (n = 15) and their respective statistical twins participated in the study. Serum total cholesterol, high-density lipoprotein (HDL) cholesterol, fasting triglycerides, glycosylated haemoglobin A1c (HbA1c), and systolic and diastolic blood pressure during 3 years prior to the development of early background retinopathy or incipient nephropathy were examined. The multivariate discriminant analysis demonstrated glycaemic control and HDL cholesterol to be the most important variables related to the development of retinal lesions (84% correctness), and diastolic blood pressure to be associated with microalbuminuria (57% correctness). In addition to poor glycaemic control, different factors seem to be important for the early retinal or renal lesions of juvenile IDDM.

Major decrements in glycated hemoglobin levels between 1978 and 1989 in patients with insulin-dependent diabetes mellitus

The Diabetes Control and Complications Trial has shown that intensive treatment can deter the development and progression of diabetic complications. Integral to intensive treatment is improved glycemic control. To describe the trend in glycemic control for subjects with insulin-dependent diabetes mellitus, we examined the medical records of 662 subjects seen between 1978 and 1989 at the Model Demonstration Unit of the Diabetes Research and Training Center (Washington University School of Medicine). Mean value of glycated hemoglobin showed steady decline from a peak of 11.5% in 1979 to 9.0% in 1989. This decline was observed both in subjects evaluated only once (annual rate of decline estimated from linear regression, -0.17 +/1 0.03; p = 0.0001) and in subjects evaluated more than once (annual rate of decline estimated from growth curves, -0.18 +/- 0.06; p = 0.0001). These results suggest that substantial lowering of glycated hemoglobin has occurred during the last decade. This reduction should result in a lowered risk of diabetic complications.

Very low density lipoprotein subfraction abnormalities in IDDM patients: any effect of blood glucose control?

Normolipidaemic insulin-dependent diabetic (IDDM) patients are characterized by an increase in the smaller VLDL particles, considered to be the most atherogenic. Since blood glucose control is one of the main regulators of lipid metabolism in diabetic patients, it could influence the shift in the distribution of VLDL subfractions towards smaller particles. To evaluate this possibility, VLDL subfractions, post-heparin lipoprotein lipase and hepatic lipase activities have been evaluated in male IDDM patients with either unsatisfactory blood glucose control (group 1, HbA1c > 8%, n = 18) or good blood glucose control (group 2, HbA1c < 8%, n = 16) and in 16 normoglycaemic individuals. The three groups were comparable for sex, age, body mass index, and plasma lipid levels. Three VLDL subfractions (large, Svedberg flotation unit (Sf) 175-400; intermediate, Sf 100-175; small, Sf 20-100) were separated by density gradient ultracentrifugation and analysed for cholesterol, triglyceride, and phospholipid levels. When compared to control subjects both groups of IDDM patients showed a clear shift in VLDL subfraction distribution with a significant increase in the proportion of small VLDL (group 1; 49 +/- 2%; p < 0.005; group 2: 51 +/- 3%, p < 0.01; control subjects 40 +/- 2%) (mean +/- SEM) in relation to total VLDL. By contrast, the absolute lipid concentration of small VLDL was higher only in group 1, compared to control subjects (35 +/- 4 vs 27 +/- 3 mg/dl, p = 0.05). Post-heparin hepatic lipase activity was significantly reduced in both IDDM groups (group 1: 254 +/- 19 mU/ml, p < 0.05; group 2: 202 +/- 19 mU/ml, p < 0.005; control subjects 317 +/- 31 mU/ml). In conclusion, normolipidaemic IDDM patients show an increase in the smallest VLDL, whatever their degree of blood glucose control. However, this abnormality may be clinically relevant only in patients with unsatisfactory blood glucose control, since absolute lipid concentration of these potentially atherogenic particles is only increased in this group.

LDL subclass phenotypes and triglyceride metabolism in non-insulin-dependent diabetes

Plasma low density lipoprotein (LDL) comprises multiple discrete subclasses differing in size, density, and chemical composition. A common, heritable phenotype characterized by the predominance of small, dense LDL particles (LDL subclass phenotype B) is associated with relatively increased concentrations of plasma triglycerides, reduced levels of high density lipoprotein, and increased risk of coronary artery disease in comparison with subjects with larger LDL (LDL subclass phenotype A). Population studies have indicated that approximately 20-30% of adult men have phenotype B, and another 15-20% have LDL of intermediate size. The lipid changes in phenotype B are similar to those that have been observed in patients with non-insulin-dependent diabetes mellitus (NIDDM). In the present study, we have assessed LDL subclass phenotypes in normolipidemic men with NIDDM and in age-matched control subjects who had similar lipid levels. There was a greater than twofold increase in the percentage of individuals with the LDL B phenotype in the NIDDM subjects. The LDL B phenotype was associated with higher plasma triglyceride levels and a trend toward lower high density lipoprotein cholesterol levels compared with the LDL A phenotype in the NIDDM subjects, as has been previously observed in control groups. Indices of diabetic control, such as fasting and hemoglobin A1 levels, were similar regardless of LDL phenotype pattern, suggesting that glycemic control was not likely to account for the increase in the LDL B phenotype. In both control and NIDDM subjects, the clearance of triglyceride-rich lipoproteins was slowed in the subjects with the LDL phenotype B compared with those with the A phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Atherogenic profiles in insulin-dependent diabetic patients and their treatment

Longitudinal studies have shown a large excess of cardiovascular mortality in insulin-dependent diabetic patients (IDDM) as compared to non-diabetic controls. Although diabetes appears to be an independent cardiovascular risk factor, increases in total and LDL-cholesterol together with a decrease of HDL-cholesterol are more pronounced in diabetics with cardiovascular disease. The general opinion, however, derived from a large number of cross-sectional studies, is that in well-controlled IDDM lipoprotein abnormalities are modest and only slightly different from matched non-diabetic controls. Most of the studies, however, used absolute criteria based on consensus statements and do not take the internal relations of the lipoproteins into account. When atherogenic indices (such as the relationship between total cholesterol and HDL-cholesterol or the Apo A1/apo B quotient) are used, 20 to 30% of an IDDM population considered to be in clinically acceptable control have to be considered pathological. This observation is even more important since the recent Diabetes Control and Complications Trial has shown that, especially in the younger group of patients, significantly higher total cholesterol and triglycerides and lower HDL-cholesterol were observed. Especially in these patients can diet and drug intervention be the most useful in the prevention of cardiovascular disease. These data are consistent with the fact that more sophisticated techniques have previously shown atherogenic changes in the composition of the VLDL-particles and lipoprotein enrichment in apo B. Since these techniques are not easily available in the clinic one has to refer to more classical techniques and the use of above mentioned atherogenic profiles to decide treatment.

Screening for hyperlipidaemia in diabetes mellitus. Relationship to glycaemic control

Diabetic patients have an increased risk of developing cardiovascular disease which, in part, may be due to lipid abnormalities. Our aim was to establish from an initial screening programme what proportion of diabetic patients attending a routine diabetic outpatient clinic had hyperlipidaemia despite having good or acceptable glycaemic control. We screened 299 randomly selected diabetic patients to assess the prevalence of hyperlipidaemia and its relationship to glycaemic control. Twenty-eight per cent had hyperlipidaemia (defined as cholesterol greater than 6.5 mmol/L and/or non-fasting triglycerides greater than 3 mmol/L). Of these hyperlipidaemic patients, 71% had good or acceptable glycaemic control as defined by a glycated haemoglobin value of less than 10%. Approximately 40% of type 2 diabetic patients had body mass index values outside recommended targets indicating the potential of weight reduction in this group as a treatment modality. Our results indicate that the majority of hyperlipidaemic diabetic patients had good or acceptable glycaemic control, and as such these patients are potential candidates for specific lipid lowering therapy.

Hyperlipidaemia in diabetes

Currently our knowledge of the role of lipid abnormalities as risk factors for CHD in diabetes is insufficient. We need to define exact risk parameters to target correctly the therapy of lipid disorders and to outline optimum therapeutic strategies. Therefore it is necessary to identify quantitative and qualitative abnormalities of lipoproteins and apoproteins which signify the risk of CHD and to define their predictive power in prospective trials. Obviously we need to know more about the pathophysiology of lipid abnormalities and the action of insulin. Because diabetic patients carry a high inherent risk of CHD, target values recommended for non-diabetic populations may not be optimal for diabetic populations, but should be lower. To date no primary or secondary intervention trials in diabetic populations have been carried out to show that the lowering of lipid values (serum and LDL cholesterol) will reduce the risk of CHD morbidity or mortality or will prevent the progression of CHD in diabetes. Since hypertriglyceridaemia and low HDL levels are typical abnormalities in NIDDM it is a unique target group to test whether lowering of triglycerides and raising of HDL cholesterol levels will reduce the risk of CHD. Therefore there is a pressing need for clinical trials in both IDDM and NIDDM to provide adequate information on the benefits of lipid-lowering therapy and to confirm treatment strategies.