Friedewald equation underestimates low-density lipoprotein cholesterol at low concentrations in young people with and without Type 1 diabetes

AIMS

Although the limitations of the Friedewald-calculated serum low-density lipoprotein cholesterol (LDL-C) are well recognized, many diabetes and lipid guidelines propose LDL-C as a therapeutic target. The validity of calculated LDL-C in people with Type 1 diabetes (T1DM) is uncertain and the use of alternatives such as non-high-density lipoprotein cholesterol (non-HDL-C) or apolipoprotein measurement unexplored. We have therefore measured LDL-C with the designated reference method and examined some of the potential sources of such bias, including plasma concentrations of other lipids and apolipoproteins.

METHODS

Seventy-four people with T1DM and 80 healthy control subjects were recruited. Fasting samples were collected for analysis of lipid profiles by a beta-quantification (BQ) reference method and by routine laboratory methods including direct HDL-C and calculation of LDL-C using the Friedewald formula.

RESULTS

Overall, Friedewald LDL-C was 0.29 +/- 0.02 (mean +/- SE) mmol/l (P < 0.001) lower in the two groups than by the BQ method. This resulted in misclassification of approximately 50% of people with a calculated LDL-C < 2.0 mmol/l. Overestimation of HDL-C by the routine assay [0.08 +/- 0.01 mmol/l (P < 0.001)] accounted for approximately 28% of the error in calculation of LDL-C and the remainder appeared to be as a result of triglyceride in lipoprotein particles other than very-low-density lipoprotein (VLDL). Correlation of non-HDL-C with apolipoprotein B was better than LDL-C with apolipoprotein B for both assays in both diabetic and non-diabetic populations.

CONCLUSIONS

Calculated LDL-C is unsuitable as a therapeutic target in T1DM. Consideration should be give to the greater use of apolipoprotein B or non-HDL-C in clinical practice.

Circulating endothelial progenitor cells, endothelial function, carotid intima-media thickness and circulating markers of endothelial dysfunction in people with type 1 diabetes without macrovascular disease or microalbuminuria

AIMS/HYPOTHESIS

Type 1 diabetes is associated with premature arterial disease. Bone-marrow derived, circulating endothelial progenitor cells (EPCs) are believed to contribute to endothelial repair. The hypothesis tested was that circulating EPCs are reduced in young people with type 1 diabetes without vascular injury and that this is associated with impaired endothelial function and increased carotid intima-media thickness (CIMT).

METHODS

We compared 74 people with type 1 diabetes with 80 healthy controls. CD34, CD133, vascular endothelial (VE) growth factor receptor-2 (VEGFR-2) and VE-cadherin antibodies were used to quantify EPCs and progenitor cell subtypes using flow-cytometry. Ultrasound assessment of endothelial function by brachial artery flow-mediated dilatation (FMD) and CIMT was made. Circulating endothelial markers, inflammatory markers and plasma plasminogen activator inhibitor-1 (PAI-1) levels were measured.

RESULTS

CD34+VE-cadherin+, CD133+VE-cadherin+ and CD133+VEGFR-2+ EPC counts were significantly lower in people with diabetes (46-69%; p = 0.004-0.043). In people with type 1 diabetes, FMD was reduced by 45% (p < 0.001) and CIMT increased by 25% (p < 0.001), these being correlated (r = -0.25, p = 0.033). There was a significant relationship between FMD and CD34+VE-cadherin+ (r = 0.39, p = 0.001), CD133+VEGFR-2+ (r = 0.25, p = 0.037) and CD34+ (r = 0.34, p = 0.003) counts. Circulating high-sensitivity C-reactive protein, PAI-1, interleukin-6 and E-selectin were significantly higher in the diabetes group (p < 0.001 to p = 0.049), the last two of these correlating with FMD (r = -0.27, p = 0.028 and r = -0.24, p = 0.048, respectively).

CONCLUSIONS/INTERPRETATION

These findings suggest that abnormalities of endothelial function in addition to pro-inflammatory and pro-thrombotic states are already common in people with type 1 diabetes before development of clinically evident arterial damage. Low EPC counts confirm risk of macrovascular complications and may account for impaired endothelial function and predict future cardiovascular events.

Insulin glargine in combination with nateglinide in people with Type 2 diabetes: a randomized placebo-controlled trial

OBJECTIVE

To determine the effect of adding nateglinide to therapy with insulin glargine in adults with Type 2 diabetes previously treated with insulin and with poor blood glucose control.

RESEARCH DESIGN AND METHODS

In this 16-week, double-blind, placebo-controlled study, people with Type 2 diabetes [n = 55, HbA(1c) 8.2 +/- 1.0 (+/- sd)%, duration of diabetes 12.8 +/- 6.0 years, duration of insulin treatment 6.0 +/- 4.0 years] were transferred to single bedtime injection of insulin glargine for a titration period of 4 weeks, and then randomized to nateglinide or matching placebo before meals in addition to insulin glargine. Metformin was continued if taken. Doses of insulin and oral medication were titrated to protocol for the treatment period of 12 weeks.

RESULTS

Baseline-adjusted self-monitored capillary blood glucose concentration at 12 weeks was significantly lower with nateglinide + insulin glargine compared with placebo + insulin glargine after breakfast [difference -2.3 (95% confidence interval -4.4, -0.2) mmol/l, P = 0.030], before lunch [-2.5 (-4.6, -0.3) mmol/l, P = 0.029], and after lunch [-2.3 (-4.3, -0.4) mmol/l, P = 0.021], but not at other times. Baseline-adjusted HbA(1c) was not lower with nateglinide + insulin glargine as compared with placebo + insulin glargine [7.8 +/- 1.4 vs. 8.3 +/- 1.0%, difference -0.43 (-0.98, 0.12)%].

CONCLUSIONS

Addition of nateglinide before meals to once-daily insulin glargine in people with long-standing diabetes already requiring insulin therapy improves blood glucose control in the early part of the day after breakfast and lunch, but does not provide good control of blood glucose levels overall.

Phaeochromocytomas presenting as acute crises after beta blockade therapy

OBJECTIVE

Phaeochromocytoma crisis is a life-threatening emergency that may be undiagnosed because of its numerous, nonspecific manifestations. We analysed, retrospectively, the presentation, management and outcome of patients who were admitted to our institution with phaeochromocytoma crises over a 5-year period.

RESULTS

Five patients (two males, three females; mean age 34.6 years, range 19-51 years) who presented as emergencies requiring intensive care, with multiple non-specific manifestations and previously undiagnosed pheochromocytoma, were identified. The initial presentation included features of cardiomyopathy (n = 3), atypical pneumonia with myocarditis (n = 1) and acute abdomen (n = 1). Only one of the five cases had a raised blood pressure at the time of the acute presentation. Initiation of beta blockers in four patients was associated with further deterioration in haemodynamic status, labile blood pressure and cardiac arrhythmias, which led to the diagnosis of the underlying phaeochromocytoma. Following intensive supportive therapy and alpha blockade, all five patients recovered and underwent elective surgical removal of phaeochromocytoma, uneventfully.

CONCLUSION

Unexplained cardiopulmonary dysfunction, particularly after the institution of beta blockers, should alert clinicians to the possibility of phaeochromocytoma. A high index of suspicion is essential to reduce morbidity and mortality in these patients through early diagnosis and aggressive management.

Sleep apnea syndrome among patients with hypothyroidism

OBJECTIVE

There is an association of sleep apnea among patients with untreated hypothyroidism. Thyroxine therapy is considered to reduce AHI (apnea-hypopnea index) significantly. A study of 20 successive hypothyroid patients was undertaken to investigate the occurrence of sleep apneas, and response to thyroxine therapy after achieving euthyroid state.

METHODS

Sleep studies were conducted in 20 consecutive hypothyroid patients at our sleep centre while they were hypothyroid. All were restudied during euthyroid state subsequent to three months of thyroxine therapy.

RESULTS

Nine (45%) of untreated 20 patients had obstructive sleep apnea syndrome (OSAS). Restudy of them during euthyroid state showed complete recovery in six, partial improvement in two and no change in one. Besides them, three other patients developed sleep apnea syndrome of central origin after euthyroid state was achieved. Central respiratory drive improved in 17 patients, while it was reduced among three of nine patients with OSAS who did not show recovery.

CONCLUSION

Our experience suggests that there is high incidence of sleep apnea among hypothyroid patients. Thyroxine treatment could achieve disappearance of these apneas in majority of them. Few hypothyroids may develop sleep apnea despite the achievement of euthyroid state. Central respiratory drive probably plays an insignificant role in the pathogenesis of sleep apnea among hypothyroids.