Normal VLDL metabolism despite altered lipoprotein composition in type 1 diabetes mellitus.

OBJECTIVES: Patients with type 1 diabetes are at increased risk of cardiovascular disease, which may be related to abnormal lipid metabolism. Secretion and clearance of VLDL apolipoprotein B100 (apoB) are important determinants of plasma lipid concentrations and are known to be influenced by hormones, including insulin and growth hormone. PATIENTS: This study examined overnight VLDL apoB metabolism and VLDL composition in six lean patients with type 1 diabetes during euglycaemia (controlled by a varying insulin infusion) and in six age-, sex- and BMI-matched control subjects. METHODS: VLDL apoB kinetics were determined using a primed constant 1-13C leucine infusion, and VLDL apoB enrichment was measured by gas-chromatography mass-spectrometry. Fasting lipid profile, IGF-I, IGFBP-3, overnight GH profiles and free insulin concentrations were also assessed. RESULTS: Fasting concentrations of triglycerides (TG), total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C) were similar in both groups. The VLDL apoB secretion and metabolic clearance rates were not significantly different between the two groups, but the VLDL-TGNLDL apoB and the VLDL-CNLDL apoB ratios were significantly increased in those with diabetes (P < 0.02 and P < 0.03, respectively). Total IGF-I concentrations were similar between the two groups; however, the GH area under the curve and free insulin concentrations were increased in patients with type 1 diabetes (GH: diabetes: 94.8 +/- 15.1 vs. controls: 45.6 +/- 10-6, mU/L/h, P < 0.04; free insulin: diabetes: 78.4 +/- 5.0 vs. controls: 28.3 +/- 3.26, pmol/l, P < 0.001). IGFBP-3 concentrations were lower in diabetic patients (diabetes: 2,454.2 +/- 68.7 vs. controls: 3,219.4 +/- 76.4, ng/ml, P < 0.001). In the control group overnight GH secretion correlated negatively with fasting TC (P < 0.01) and LDL-C (P < 0.03) concentrations, whereas free insulin concentrations correlated positively with fasting TG concentrations (P < 0.009). No significant correlations were found in the patients with diabetes. CONCLUSION: This study suggests that in euglycaemic conditions patients with type 1 diabetes mellitus have normal VLDL apoB kinetics but altered VLDL composition. The altered VLDL composition may be associated with accelerated atherogenesis. We speculate that the disrupted hormonal balance and, in particular, the increased GH secretion might be responsible for the compositional changes of VLDL particles in type 1 diabetes mellitus.

Effects of growth hormone (GH) replacement therapy on very low density lipoprotein apolipoprotein B100 kinetics in patients with adult GH deficiency: a stable isotope study.

Patients with adult GH deficiency are often dyslipidemic and may have an increased risk of cardiovascular disease. The secretion and clearance of very low density lipoprotein apolipoprotein B 100 (VLDL apoB) are important determinants of plasma lipid concentrations. This study examined the effect of GH replacement therapy on VLDL apoB metabolism using a stable isotope turnover technique. VLDL apoB kinetics were determined in 14 adult patients with GH deficiency before and after 3 months GH or placebo treatment in a randomized double blind, placebo-controlled study using a primed constant [1-(13)C]leucine infusion. VLDL apoB enrichment was determined by gas chromatography-mass spectrometry. GH replacement therapy increased plasma insulin-like growth factor I concentrations 2.9 +/- 0.5-fold (P < 0.001), fasting insulin concentrations 1.8 +/- 0.6-fold (P < 0.04), and hemoglobin A1C from 5.0 +/- 0.2% to 5.3 +/- 0.2% (mean +/- SEM; P < 0.001). It decreased fat mass by 3.4 +/- 1.3 kg (P < 0.05) and increased lean body mass by 3.5 +/- 0.8 kg (P < 0.01). The total cholesterol concentration (P < 0.02), the low density lipoprotein cholesterol concentration (P < 0.02), and the VLDL cholesterol/VLDL apoB ratio (P < 0.005) decreased. GH therapy did not significantly change the VLDL apoB pool size, but increased the VLDL apoB secretion rate from 9.2 +/- 2.0 to 25.9 +/- 10.3 mg/kg x day (P < 0.01) and the MCR from 11.5 +/- 2.7 to 20.3 +/- 3.2 mL/min (P < 0.03). No significant changes were observed in the placebo group. This study suggests that GH replacement therapy improves lipid profile by increasing the removal of VLDL apoB. Although GH therapy stimulates VLDL apoB secretion, this is offset by the increase in the VLDL apoB clearance rate, which we postulate is due to its effects in up-regulating low density lipoprotein receptors and modifying VLDL composition.

Growth hormone therapy may benefit protein metabolism in mitochondrial encephalomyopathy.

Mitochondrial encephalomyopathy is a genetic disorder for which there is at present no cure. Conventional treatment regimes may not be effective in preventing weight loss and muscle wasting in many patients. Recombinant human GH has been shown to have anabolic effects on protein metabolism and to reduce muscle wasting in various diseases. We have treated a patient known to have myoclonus, epilepsy with ragged red fibres (MERRF) with a high protein diet for 1 month followed by a high protein diet and GH therapy for 1 month. To assess the benefit of these treatments the patient underwent whole body protein turnover, myometric and body composition studies at baseline, following the high protein diet (100 g/day) and following GH therapy. Whole body protein synthesis (and protein breakdown) increased following a high protein intake and was further enhanced by treatment with GH and in a high protein diet. Body composition did not change significantly following treatment with either the high protein diet or GH but there was an improvement in muscle performance following GH treatment. Mitochondrial encephalomyopathy, a wasting disorder, may be a disease in which the known protein anabolic effect of GH may have a therapeutic benefit.

Abnormalities of very low density lipoprotein apolipoprotein B-100 metabolism contribute to the dyslipidaemia of adult growth hormone deficiency.

Increased cardiovascular mortality in adult growth hormone deficiency (GHD) may be, in part, explained by the dyslipidaemia associated with this condition. It is possible that abnormalities of very low density lipoprotein apolipoprotein B-100 (VLDL apoB) metabolism contribute to this dyslipidaemia. To test this hypothesis, we measured VLDL apoB kinetics in adult GH deficient patients (4 females, 3 males; age 50.1 +/- 4.7 yr (mean +/- SEM); BMI 28.2 +/- 1.1 kg/m2; total cholesterol (TC) 6.6 +/- 0.3 mmol/l; triglyceride (TG) 2.8 +/- 0.6 mmol/l; HDL cholesterol 1.1 +/- 0.1 mmol/l) and in control subjects (4 females, 3 male; age 47.0 +/- 4.7 yr; BMI 27.0 +/- 2.6 kg/m2; TC 5.0 +/- 0.4 mmol/l; TG 0.9 +/- 0.2 mmol/l; HDL cholesterol 1.4 +/- 0.1 mmol/l). [1-(13)C] leucine was administered by a primed (1 mg/kg), constant intravenous infusion (1 mg/kg/hr) and VLDL apoB enrichment with 13C leucine was determined using gas-chromatography mass-spectrometry. The GHD patients had a significantly higher hepatic secretion rate of VLDL apoB (15.5 +/- 1.8 mg/kg/day vs 9.4 +/- 0.6 mg/kg/day p = 0.007) and reduced catabolism ofVLDL apoB (metabolic clearance rate; 12.3 +/- 1.7 ml/min vs 24.3 +/- 4.8 ml/min p < 0.05) compared with control subjects. These findings suggest that GH is integrally involved in the regulation of VLDL apoB metabolism.