Am J Physiol Endocrinol Metab 282: E1154–E1162, 2002.
First published January 2, 2002; 10.1152/ajpendo.00470.2001.
Effect of IGF-I therapy on VLDL apolipoprotein B100metabolism in type 1 diabetes mellitus EMANUEL R. CHRIST,1 PAUL V. CARROLL,2 ELAINE ALBANY,2A. MARGOT UMPLEBY,2 PETER J. LUMB,3 ANTHONY S. WIERZBICKI,3PETER H. SO 1Department of Endocrinology and Diabetology of the Adult, University Hospital of Bern,Inselspital, CH-3010 Bern, Switzerland; and Departments of 2Medicine and 3Chemical Pathology,King’s College London, St. Thomas’ Hospital Campus, London SE1 7EH, United Kingdom Received 18 October 2001; accepted in final form 17 December 2001 Christ, Emanuel R., Paul V. Carroll, Elaine Albany,
ute to the observed excess cardiovascular risk. Usually, A. Margot Umpleby, Peter J. Lumb, Anthony S. Wier-
the lipid profiles in well-controlled patients with type 1 zbicki, Peter H. So
¨ nksen, and David L. Russell-Jones.
diabetes mellitus are similar to those seen in matched, Effect of IGF-I therapy on VLDL apolipoprotein B100 metab- healthy control subjects (17). Poor diabetic control, olism in type 1 diabetes mellitus. Am J Physiol Endocrinol however, is often associated with an increase in total Metab 282: E1154–E1162, 2002. First published January 2, cholesterol, triglycerides, and a decrease in high-den- 2002; 10.1152/ajpendo.00470.2001.—Abnormal lipid metab-olism may be related to the increased cardiovascular risk in sity lipoprotein (HDL)-cholesterol (C; see Ref. 17).
type 1 diabetes. Secretion and clearance rates of very low Important determinants of the lipid profile are the density lipoprotein (VLDL) apolipoprotein B100 (apoB) de- secretion and clearance rates of the apolipoprotein 100 termine plasma lipid concentrations. Type 1 diabetes is char- (apoB)-containing lipoproteins [very low density li- acterized by increased growth hormone (GH) secretion and poprotein (VLDL), intermediate density lipoprotein decreased insulin-like growth factor (IGF) I concentrations.
(IDL), low density lipoprotein (LDL); see Ref. 36]. Be- High-dose IGF-I therapy improves the lipid profile in type 1 cause VLDL apoB is the precursor of IDL and LDL, diabetes. This study examined the effect of low-dose (40 plasma lipid concentrations are dependent on VLDL ␮g⅐kgϪ1⅐dayϪ1) IGF-I therapy on VLDL apoB metabolism, apoB metabolism (36). Hepatic overproduction of VLDL composition, and the GH-IGF-I axis during euglyce- VLDL apoB has been demonstrated in type 2 diabetes mia in type 1 diabetes. Using a stable isotope technique, mellitus and in several hyperlipidemic conditions as- VLDL apoB kinetics were estimated before and after 1 wk of sociated with premature atherosclerosis (14, 15, 29, IGF-I therapy in 12 patients with type 1 diabetes in adouble-blind, placebo-controlled trial. Fasting plasma triglyc- 30). VLDL apoB is constitutively expressed (20), and eride (P Ͻ 0.03), VLDL-triglyceride concentrations (P Ͻ VLDL apoB secretion is essentially regulated by intra- 0.05), and the VLDL-triglyceride-to-VLDL apoB ratio (P Ͻ hepatic lipid substrate availability (triglycerides and 0.002) significantly decreased after IGF-I therapy, whereas cholesterol esters; see Ref. 40), whereas VLDL apoB VLDL apoB kinetics were not significantly affected by IGF-I clearance depends on a complex interaction between an therapy. IGF-I therapy resulted in a significant increase in enzyme (lipoprotein lipase) and receptors (LDL recep- IGF-I and a significant reduction in GH concentrations. The tors; see Ref. 36). Insulin-like growth factor I (IGF-I) is mean overnight insulin concentrations during euglycemia known to promote lipid oxidation (25), which may lead decreased by 25% after IGF-I therapy. These results indicate to a decrease in hepatic lipid supply and consequently that low-dose IGF-I therapy restores the GH-IGF-I axis in to a reduced VLDL apoB secretion. By increasing in- type 1 diabetes. IGF-I therapy changes fasting triglyceride sulin sensitivity, IGF-I may increase lipoprotein lipase concentrations and VLDL composition probably because of activity and therefore VLDL apoB clearance (46). In contrast, VLDL remnant clearance is unlikely to be type 1 diabetes mellitus; insulin-like growth factor I; growth influenced by IGF-I, since studies in rats suggest that hormone secretion; very low density lipoprotein apolipopro- IGF-I does not significantly affect hepatic expression of tein B turnover study; stable isotope technique LDL receptor (3), although growth hormone (GH) hasbeen shown to upregulate hepatic LDL receptors inhumans (39).
TYPE 1 DIABETES MELLITUS is associated with an increased The GH-IGF-I axis is disordered in type 1 diabetes, risk of atherosclerosis (31). Although type 1 diabetes resulting in low levels of IGF-I and, consequently, appears to be an independent risk factor for cardiovas- decreased feedback in GH hypersecretion (2). The ele- cular disease, abnormalities in lipoprotein metabolism vated GH concentrations, in particular at night, are (17) and lipoprotein composition (26, 42) may contrib- The costs of publication of this article were defrayed in part by the Address for reprint requests and other correspondence: E. Christ, payment of page charges. The article must therefore be hereby Dept. of Endocrinology and Diabetology of the Adult, Inselspital, marked ‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734 CH-3010 Bern, Switzerland (E-mail: Emanuel.Christ@insel.ch).
0193-1849/02 $5.00 Copyright 2002 the American Physiological Society thought to contribute to the reduced insulin sensitivity UK) and were injected with 40 ␮g ⅐ kgϪ1 ⅐ dayϪ1 IGF-I/placebo (16) and have been associated with diabetic microvas- subcutaneously at night (10:00 P.M.) for seven consecutive cular complications (18). Exogenous IGF-I administra- tion has been shown to decrease GH concentrations in Identical metabolic investigations were performed before adolescents (1, 4, 10, 44) and in adults (9) with type 1 (study 1) and after (study 2) 1 wk of IGF-I/placebo treatment.
On each occasion, all long-acting insulin had been discontin- diabetes and to improve insulin sensitivity (1, 4, 9, 10, ued at least 16 h before admission. Empirically with the first 44). Furthermore, IGF-I treatment results in a de- dose of IGF-I/placebo, the usual dose of evening isophane crease in fasting triglycerides, total cholesterol, and (NPH) insulin was decreased by 50%. The patients remained LDL-C concentrations in patients with type 1 diabetes in daily contact with the investigators, and the insulin doses (9). The mechanism, however, remains unknown.
were adjusted on a daily basis according to blood glucose Using a stable isotope technique, we aimed, there- fore, to investigate overnight VLDL apoB kinetics dur- On the days of study, the subjects were admitted to the ing euglycemic conditions in 12 patients with type 1 metabolic ward at 7:00 PM, having last eaten a snack at 3:00 diabetes before and after 1 wk of IGF-I treatment in a PM. They were studied in a semirecumbent position and randomized, double-blind, placebo-controlled trial. In were allowed to drink water. An indwelling cannula was addition, VLDL composition, the overnight GH secre- placed in a superficial vein of the antecubital fossa for ad-ministration of infusions (isotope tracer and insulin), and tion profile, and insulin concentrations were assessed another venous cannula was placed in the contralateral arm to determine the relationship between these variables for blood sampling. Insulin infusion was started at 7:30 PM, and euglycemia was obtained by 10:00 PM.
At 10:00 PM, baseline blood samples were taken to mea- sure isotope background enrichment and hemoglobin A1C.
Experimental subjects. Twelve adult patients with type 1 [1-13C]leucine (15 mg/ml, 13C enrichment 99%; Tracer Tech- diabetes mellitus participated in the study. Their clinical and nologies, Somerville, MA) was administered as a primed metabolic characteristics are summarized in Table 1. All (1 mg/kg) constant infusion (1 mg ⅐ kgϪ1 ⅐ hϪ1) for 10 h. Blood patients had stable metabolic control and were on subcuta- glucose concentrations were measured every 15–30 min neous soluble and isophane insulin. The patients were in throughout the night, and insulin infusion was adapted to good general health without evidence of diabetic complica- maintain glucose concentrations between 5 and 7 mmol/l.
tions and had normal thyroid, renal, and hepatic function. All EDTA-plasma (5 ml) samples were collected for VLDL apoB of the patients had a C-peptide concentration of Ͻ0.3 nmol/l, enrichment at baseline, at 30-min intervals for 2 h, and and the female patients were taking the combined oral con- hourly thereafter. Lithium heparin samples (5 ml) were traceptive pill. St. Thomas’ Hospital Ethics Committee ap- taken at baseline and after 0.5, 1, 2, 4, and 10 h to determine proved the study, and all patients provided informed written 13C enrichment of ␣-ketoisocaproate (␣-KIC), the deaminated consent. The effects of IGF-I therapy on glucose and pro- product of leucine that provides a measure of intracellular tein metabolism in these patients have been reported previ- leucine enrichment (33). At baseline and after 2, 4, 6, 8, and 10 h of infusion, 10-ml EDTA-plasma samples were collected Study protocol. The study was randomized, double blind, to determine free fatty acids (FFA), VLDL-triglycerides and placebo controlled. Patients were instructed in self-ad- (VLDL-TG), VLDL-C, and VLDL apoB concentrations. GH ministration of IGF-I (Pharmacia & Upjohn, Milton-Keynes, concentrations were measured every 30 min from 10:00 PM Table 1. Clinical characteristics of patients with type 1 diabetes mellitus BMI, body mass index; apo, apolipoprotein; F, female; M, male; IGF-I, insulin-like growth factor I. Unpaired t-testing and ␹2 analysis (*) were used to compare clinical characteristics of the patients in the placebo and the IGF-I groups.
AJP-Endocrinol Metab • VOL 282 • MAY 2002 • www.ajpendo.org until 7:30 AM, and insulin, IGF-binding protein-1 (IGFBP-1), the equation of Friedewald et al. (19). HbA1C was measured and IGF-binding protein-3 (IGFBP-3) concentrations were by anion exchange liquid chromatography (interassay CV determined at baseline and two times hourly thereafter. At 8%; Primus). GH was measured by an in-house double-anti- 8:00 AM the next morning, 10-ml EDTA-plasma samples body RIA with a detection limit of 0.3 mU/l. Intra-assay CV were collected for measurement of total cholesterol, triglyc- was 10, 4, and 5.4% at 1.7, 12.1 and 22.2 mU/l, respectively.
erides, apolipoprotein E phenotype, and HDL-C, and 5 ml of Serum IGF-I concentrations were measured by a double- serum were collected for measurement of total IGF-I concen- antibody RIA after an ethanol/hydrochloric acid extraction (intra-assay CV 6%; see Ref. 43). Plasma immunoreactive Body composition. Body weight was measured on an elec- insulin concentration was determined by double-antibody tronic balance with subjects wearing light clothes and without RIA (interassay CV 6%; see Ref. 41). An immunoradiometric shoes at the beginning of each study. Height was assessed by a assay was used for the measurement of IGFBP-1 and stadiometer. Bioelectrical impedance analysis was measured in IGFBP-3 [IRMA (Diagnostics Systems Laboratories); inter- the erect position after voiding using a TBF-105 body fat ana- assay CV for IGFBP-1 was 5%; interassay CV for IGFBP-3 lyzer (Tanita, Chicago, IL). Fat mass and lean body mass were was 1%]. Plasma FFA concentrations were measured enzy- calculated using a preprogrammed equation based on densito- matically [FFA kit (Wako Chemicals); interassay CV 3.6%].
metric data in a healthy population (6).
The apoE phenotype was determined by Western blotting Isolation and measurement of isotopic enrichment of VLDL after isoelectric focusing on a Pharmacia Phast system (Am- apoB. All EDTA-plasma samples were stored at 4°C and ersham-Pharmacia, Beaconsfield, UK; see Ref. 34).
analyzed within 24 h of collection. A 2-ml aliquot of plasma Calculation of VLDL apoB secretion and clearance rates. was overlaid with 3 ml of sodium chloride density solution VLDL apoB enrichment with [13C]leucine and [13C]KIC en- (1.006 kg/l) and ultracentrifuged for 16 h at 147,000 g (Cen- richment (precursor pool) was calculated using the following trikon T-2070 ultracentrifuge; Kontron Instruments, Zurich, formula (12): Et ϭ [Rt Ϫ R0/(1 ϩ Rt Ϫ R0)] ϫ 100, where Rt is Switzerland). The supernatant containing VLDL was iso- the 13C-to-12C ratio at time t and R0 is the 13C-to-12C ratio at lated by aspiration. ApoB was precipitated by the tetra- baseline before tracer infusion. Fractional catabolic rate methylurea method, which is highly specific (specificity 97%) (FCR) and fractional secretion rate (FSR) of VLDL were for apoB (15). The precipitate was delipidated by incubation estimated by a multicompartmental model with an intrahe- with 3 ml ether-ethanol solution (1:3, vol/vol) at Ϫ20°C for patic delay function by use of SAMM II software (SAMM, 12 h. After recentrifugation (2,000 revolutions/min, 30 min, Seattle, WA). The precursor compartment for the incorpora- 4°C), the supernatant was removed by aspiration. The delipi- tion of [13C]leucine into the VLDL particles (forcing function) dated apoB precipitate was dried under oxygen-free nitrogen was the steady-state tracer-to-tracee ratio of ␣-KIC. FSR of (OFN; BOC, Guildford, UK) for 20 min at 25°C and then VLDL is subject to an intrahepatic delay. The catabolic rate hydrolyzed in 2 ml of 6 M hydrochloric acid. The samples of VLDL apoB from plasma is expressed as FCR. Throughout were heated for 24 h at 115°C to ensure complete hydrolysis the study, the patients were in steady state, as shown by and reconstituted in 0.5 ml of 50% acetic acid. Amino acids constant VLDL apoB concentrations (data not shown). In this were eluted by cation-exchange chromatography [70 ␮m fil- case, FSR equals FCR. The model parameters (intrahepatic ter plastic columns (Bioconnections, Leeds, UK) and Hϩ form delay and FCR) were estimated from the tracer-to-tracee cation-exchange resin (Bio-Rad, Richmond, VA)] using 2 ml ratio of VLDL apoB. A total of 13 time points over the 10-h of 3 M ammonia. The eluted amino acids were frozen tracer infusion was included in the mathematical analysis.
(Ϫ70°C), lyophilized, and then stored at Ϫ20°C until deriva- The absolute VLDL apoB secretion rate was calculated as tization. The samples were derivatized using 100 ␮l acetoni- the product of FCR and the VLDL apoB pool size divided by trile and 100 ␮l N-(tert-butyldimethylsilyl)-N-methyltriflu- body weight. Pool size was determined as the product of oroacetamide (Aldrich, Dorset, UK) to form the bis(tert- plasma volume and VLDL apoB concentration (mean of 6 butyldimethylsilyl) derivative. Excess reagent was removed samples taken during the study). The plasma volume was by blowing down under OFN, and the sample was reconsti- derived as 4.5% of body weight (22), and metabolic clearance tuted in 100 ␮l decane for gas chromatography-mass spec- rate was calculated as the product of FCR and plasma trometry. Isotopic enrichment was determined by selected ion monitoring of fragments with a mass-to-charge ratio Statistical analyses. Results are expressed as means Ϯ SE.
(m/z) of 303 and 302 by use of a gas chromatograph-mass Skewed variables (plasma total and VLDL-TG concentra- spectrometer (VG Biotech TRIO-2; VG Biotech) in the elec- tions) were examined after log transformation. Baseline tron impact ionization mode. The quinoxalinol-tert-butyldim- characteristics between the placebo and the IGF-I groups ethylsilyl derivative of ␣-KIC was prepared, and isotope were compared using unpaired t-testing and, where appro- enrichment was determined by selected ion monitoring of priate, ␹2-analysis. The responses of each parameter (⌬ val- fragments at m/z 259 and 260 (GC-MS analysis; Hewlett ues) in the placebo and the IGF-I groups were analyzed for Packard 5890A, Bracknell, UK). Analytical precision of the between-group comparison using unpaired t-testing or, method [coefficient of variation (CV)] has been shown to be where appropriate, nonparametric testing (kinetic data). For Ͻ8% for isotopic enrichment (E) of leucine and ␣-KIC (15).
analysis of data from more than two time points, ANOVA Quantification of VLDL apoB and other analytes. Glucose was performed. Analysis of GH secretion was performed concentrations were measured using the glucose oxidase using Pulsar analysis (9) with nonparametric testing for method (glucose analyzer, YSI model 23AM; Yellow Springs comparisons of variables. P values Ͻ0.05 were considered Instruments). VLDL apoB concentration was determined us- ing the Lowry method (13). Plasma total cholesterol andtriglyceride concentrations were measured by an enzymatic method (Boehringer-Mannheim, Mannheim, Germany) usinga Cobas Fara II analyzer (Roche, Welwyn Garden City, UK).
Patients. The clinical and metabolic characteristics HDL-C was separated by precipitation of apoB-containing were similar in the placebo and IGF-I groups. All lipoproteins with dextran sulfate/magnesium chloride and subjects did not experience any side effects during the measured enzymatically. LDL-C was calculated according to study period except subject 9 (randomized to placebo), AJP-Endocrinol Metab • VOL 282 • MAY 2002 • www.ajpendo.org who had a hypoglycemic episode the day after study 1.
and VLDL-TG-to-VLDL-apoB ratios (P Ͻ 0.002), Total body weight and body composition did not change whereas no significant changes were observed after placebo treatment. The reduction in nonesterified free Mean overnight glucose concentrations were similar fatty acid (NEFA) concentrations after IGF-I therapy in both groups on both occasions (IGF-I group 5.4 Ϯ 0.1 did not reach statistical significance (P ϭ 0.09; Tables vs. 5.6 Ϯ 0.1 mmol/l, pre- vs. posttreatment, ANOVA P ϭ 0.49; placebo group 6.3 Ϯ 0.3 vs. 6.5 Ϯ 0.2 mmol/l, Kinetic characteristic of VLDL apoB metabolism. As pre- vs. posttreatment, ANOVA P ϭ 0.25). In the IGF-I shown in Figs. 1 and 2, apoB kinetics were in steady group, one patient was heterozygous for apoE2 and one state, since VLDL apoB concentrations did not show a for apoE4. In the placebo group, two patients were significant change at the selected time points through- heterozygous for apoE2 and two for apoE4. The re- out the study. Precursor pool enrichment as measured maining patients presented the phenotype apoE3/E3 by ␣-[13C]KIC remained constant throughout the study periods (Fig. 1, A and B). Because of technical problems IGF-I and insulin concentrations. Pretreatment se- (insufficient enrichment of VLDL apoB), we were not rum IGF-I concentrations were similar in the two able to include turnover data of subjects 4 (placebo groups. IGF-I therapy led to a significant rise in circu- group) and 12 (IGF-I group). The calculated values of lating IGF-I within the normal range, whereas there all the kinetic measurements were not statistically were no changes in the placebo group (IGF-I group different between the groups before treatment. After 28.2 Ϯ 2.4 vs. 42.7 Ϯ 3.8 nmol/l, pre- vs. posttreatment; IGF-I or placebo therapy, VLDL apoB pool size, FCR, placebo group 34.2 Ϯ 4.0 vs. 29.3 Ϯ 3.2 nmol/l, pre- vs.
VLDL apoB secretion, and clearance rate did not change significantly in either group (Figs. 1 and 2 and Pretreatment overnight insulin concentrations dur- ing euglycemia were not significantly different be- Overnight GH secretion. Mean overnight GH concen- tween the IGF-I and placebo groups. IGF-I therapy trations were significantly decreased after IGF-I ther- resulted in a 25% decrease in mean overnight insulin apy, whereas no change was observed after placebo concentrations, whereas no significant change was ob- (IGF-I group 23.6 Ϯ 3.8 vs. 10.5 Ϯ 1.3 mU/l pre- vs.
served in the placebo group (IGF-I group 35.6 Ϯ 6.7 vs.
posttreatment; placebo group 13.5 Ϯ 1.8 vs. 14.3 Ϯ 1.6 27.0 Ϯ 7.0 mU/l, pre- vs. posttreatment; placebo group mU/l pre- vs. posttreatment, P Ͻ 0.007). With the use 29.9 Ϯ 4.6 vs. 29.4 Ϯ 3.1 mU/l, pre- vs. posttreatment, of pulsar analysis, this reduction was attributable to a reduction in GH peak amplitude (IGF-I group 31.7 Ϯ Lipid profile. There were no statistically significant 6.3 vs. 21.5 Ϯ 7.2 mU/l, pre- vs. posttreatment; placebo differences in fasting plasma lipid profiles between the group 23.0 Ϯ 3.9 vs. 30.4 Ϯ 5.2 mU/l, pre- vs. posttreat- two groups before treatment. IGF-I therapy signifi- ment, P Ͻ 0.02) and peak length (IGF-I group 1.5 Ϯ 0.3 cantly decreased total plasma triglyceride concentra- vs. 1.3 Ϯ 0.2 h, pre- vs. posttreatment, placebo group tions (P Ͻ 0.03), VLDL-TG concentrations (P Ͻ 0.05), 1.3 Ϯ 0.1 vs. 1.7 Ϯ 0.2 h, pre- vs. posttreatment, P Ͻ Table 2. Fasting lipid profile in patients with type 1 diabetes mellitus before (study 1)and after (study 2) IGF-I or placebo therapy Mean Ϯ SE 4.16 Ϯ 0.28 4.03 Ϯ 0.39 2.55 Ϯ 0.24 2.44 Ϯ 0.35 1.17 Ϯ 0.10 1.14 Ϯ 0.09 0.95 Ϯ 0.15 1.01 Ϯ 0.16 0.80 Ϯ 0.05 0.93 Ϯ 0.11 Mean Ϯ SE 4.30 Ϯ 0.51 4.22 Ϯ 0.35 2.11 Ϯ 0.56 2.11 Ϯ 0.39 1.60 Ϯ 0.30 1.53 Ϯ 0.24 1.30 Ϯ 0.26 0.95 Ϯ 0.17 0.86 Ϯ 0.18 0.74 Ϯ 0.13P value TC, total cholesterol; TG, triglycerides; LDL-C, LDL-cholesterol; HDL-C, HDL-cholesterol; NEFA, nonesterified fatty acid. At baseline, the placebo- and the IGF-I groups were not statistically different. P values shown here correspond to the results of a comparison of the responses(delta values) of each parameter between the placebo and the IGF-I groups using unpaired t-testing. TG results were analyzed after logtransformation.
AJP-Endocrinol Metab • VOL 282 • MAY 2002 • www.ajpendo.org Table 3. VLDL lipid composition before (study 1) and after (study 2) IGF-I/placeboin patients with type 1 diabetes mellitus C, cholesterol; VLDL, very low density lipoprotein. At baseline, the placebo- and the IGF-I groups were not statistically different. P values correspond to the results of a comparison of the responses (delta values) of each parameter between the placebo and the IGF-I groups usingunpaired t-testing. TG results were analyzed after log transformation. * Mean of six pooled samples.
0.03). No change was observed in either the frequencyof peaks or the length of intervals between peaks ineither group. Total area under the GH curve was sig-nificantly decreased by IGF-I, whereas no significantchanges were observed in the placebo group (IGF-Igroup 131.6 Ϯ 46.5 vs. 67.3 Ϯ 25.8 mU ⅐ lϪ1 ⅐ hϪ1 pre- vs.
posttreatment; placebo group 82.4 Ϯ 11.9 vs. 91.1 Ϯ15.4 mU ⅐ lϪ1 ⅐ hϪ1 pre- vs. posttreatment, P Ͻ 0.04).
IGFBP. Before treatment, IGFBP-1 and IGFBP-3 concentrations were similar in the IGF-I-treated andplacebo groups. Mean IGFBP-1 concentrations in-creased 1.5-fold after IGF-I therapy (IGF-I group82.1 Ϯ 10.1 vs. 124.9 Ϯ 15.8 ng/ml pre- vs. posttreat-ment; placebo group 71.5 Ϯ 13.7 vs. 87.5 Ϯ 13.0 ng/mlpre- vs. posttreatment, ANOVA P Ͻ 0.001). IGFBP-3concentrations did not change significantly in eithergroup (IGF-I group 2,311.4 Ϯ 196.0 vs. 2,541 Ϯ 168.8ng/ml pre- vs. posttreatment; placebo group 2,611.6 Ϯ273.9 vs. 2,694.3 Ϯ 239.9 ng/ml pre- vs. posttreatment,ANOVA P ϭ 0.12).
This study demonstrates that low-dose IGF-I ther- apy in adult patients with type 1 diabetes significantlydecreases fasting triglyceride and VLDL-TG concen-trations without affecting VLDL apoB kinetics. AfterIGF-I, overnight GH secretion and mean overnightinsulin concentrations decreased, whereas IGFBP-I Fig. 1. Mean very low density lipoprotein (VLDL) apolipoprotein(apo) B enrichment with [13C]leucine in patients with type 1 diabetes concentrations significantly increased.
before (study 1) and after (study 2) 1 wk of insulin-like growth factor Decreased fasting triglyceride concentrations after (IGF) I (A) or placebo (B) therapy. Precursor pool enrichment of IGF-I therapy are consistent with findings in patients ␣-[13C]ketoisocaproate (␣-[13C]KIC) before (KIC study 1) and after with type 2 (47) and type 1 diabetes mellitus (9).
(KIC study 2) IGF-I (A) or placebo therapy (B) is also shown. Based Increasing evidence suggests that triglyceride concen- on the individual curve of each patient’s kinetic parameters of VLDL,apoB metabolism was calculated. No statistically significant differ- trations may be a significant risk factor for cardiovas- ences were observed after IGF-I or placebo therapy. APE, atom cular disease (24) and that lowering triglycerides (32, AJP-Endocrinol Metab • VOL 282 • MAY 2002 • www.ajpendo.org crease in insulin sensitivity. Therefore, it is likely thatthe IGF-I-induced improvement in insulin sensitivityhas led to the reduction of triglyceride and VLDL-TGconcentrations. In contrast to previous studies, totalcholesterol and LDL-C did not change significantlyafter IGF-I therapy in this study (9, 47). This may bebecause only 40% of the previous dose of IGF-I wasadministered in this study. Alternatively, the smallsample size did not have enough statistical power todetect statistically significant differences in fastingcholesterol concentrations.
It has been shown previously (26) that, even in well-controlled diabetic patients, fasting VLDL compo-sition is altered with an increase in lipid content (inparticular triglycerides) within the VLDL fraction com-pared VLDL-TG concentrations have been associated with aparallel increase in small dense LDL, a subfraction ofLDL particles that are known to be particularly athero-genic (26, 36, 42). In this study after IGF-I therapy,VLDL-TG concentration decreased, as did the VLDL- Fig. 2. A: VLDL apoB concentrations (means TG-to-VLDL-apoB ratio. This may indicate a reversal type 1 diabetes mellitus before (■) and after (ᮀ) IGF therapy.
of the impaired VLDL composition and may be associ- B: VLDL apoB concentrations (means Ϯ SE) in patients with type 1 ated with improvements in the LDL subfraction profile diabetes mellitus before (Œ) and after (‚) placebo. No significant (26, 36, 42). A possible explanation of the findings of changes in VLDL apoB concentrations were observed during theVLDL apoB turnover studies, indicating a steady-state condition.
this study is that the decrease in GH secretion leads toa reduction in peripheral lipolysis and a decrease in 38) can reduce this risk. These clinical findings are NEFA flux to the liver (6). The reduced hepatic NEFA supported by the fact that triglyceride-rich lipoproteins content, in turn, may result in decreased lipid esterifi- (i.e., VLDL and IDL) have been identified in human cation and lower incorporation of triglycerides into atherosclerotic plaques, and these particles are associ- VLDL particles (40). This hypothesis is supported by ated with progression of coronary lesions (45). In- the tendency for a reduction in NEFA concentrations creased triglyceride concentrations are associated with with IGF-I therapy seen here. In addition, administra- decreased insulin sensitivity (42). A decrease in insulin tion of GH to healthy subjects in a dose mimicking the concentrations for a similar glycemic control (euglyce- increased GH secretion in type 1 diabetes results in a mia) measured in the current study suggests an in- compositional change of VLDL particles with an in- Table 4. Kinetic characteristics of VLDL apoB metabolism in patients with type 1 diabetes mellitusbefore (study 1) and after (study 2) IGF-I/placebo therapy PV, plasma volume; FCR, fractional catabolic rate; ASR, absolute secretion rate; MCR, metabolic clearance rate. At baseline, the placebo and IGF-I groups were not statistically different. P values correspond to the results of the comparison of responses (delta values) of eachparameter between the placebo and IGF-I groups using nonparametric testing.
AJP-Endocrinol Metab • VOL 282 • MAY 2002 • www.ajpendo.org crease in triglyceride content (35), supporting our hy- and the IGF-I groups were not ideally matched for the apoE phenotype; hence, we cannot exclude that this The finding of unchanged VLDL apoB kinetics de- may have influenced our findings. However, differ- spite a decrease in fasting triglyceride concentrations ences in VLDL apoB kinetics have been shown only in is intriguing. It may be related to the small number of apoE2 homozygous patients (37), not included in the patients included in this study. A mean reduction in current study. It is therefore unlikely that the present VLDL apoB secretion of 33% after IGF-I therapy, al- results were confounded by the differences in apoE though not significant statistically, may support this hypothesis. Alternatively, it is well known that the In conclusion, the current results indicate that low- VLDL fraction is heterogeneous, consisting of triglyc- dose IGF-I therapy (40 ␮g ⅐ kgϪ1 ⅐ dayϪ1) is well toler- eride-rich (large VLDL) and cholesterol-rich (small ated and restores the disordered GH-IGF-I axis in type VLDL) subfractions that are independently secreted by 1 diabetes. IGF-I therapy does not significantly influ- the liver (36). Insulin is known to act primarily on the ence VLDL apoB kinetics but changes fasting triglyc- triglyceride-rich VLDL subfraction (36). The observed eride concentrations and the composition of VLDL par- increase in insulin sensitivity may, therefore, primarily ticles probably because of an increase in insulin affect the kinetics of triglyceride-rich VLDL subfractions, sensitivity. The decreased triglyceride content within which were not assessed separately in this study.
In patients with adult GH deficiency, GH replace- the VLDL particles leading to a reduction in athero- ment therapy has been demonstrated to increase whole genic small dense LDL particles and an increase in VLDL apoB turnover (11). The current study, however, IGFBP-1 concentrations may favorably influence the suggests that VLDL apoB metabolism is unchanged macrovascular risk profile in type 1 diabetes. In addi- after IGF-I therapy despite a reduction in GH secre- tion, by reducing GH secretion, IGF-I may have a tion. A possible explanation for this effect includes the beneficial effect on microvascular complications. Fur- fact that insulin is a powerful regulator of VLDL apoB ther long-term studies are required to investigate a metabolism, and, if euglycemia is maintained, it out- possible role of low-dose IGF-I therapy in the manage- weighs any possible effects of GH. Alternatively, he- ment of patients with type 1 diabetes mellitus.
patic GH resistance may occur, as has been suggested,especially in adolescents with type 1 diabetes (1, 4, 10, We thank Dr. R. Jones, St. Thomas’ Hospital, London, and R. W.
James, Geneva, for reviewing the manuscript.
44). GH is the principal regulator of hepatic synthesis E. R. Christ was supported by a grant from the Swiss National of IGFBP-3 (6). Unchanged IGFBP-3 concentrations Foundation and the Walther and Margarethe Lichtenstein Founda- after IGF-I therapy despite a decrease in GH secretion tion (Basel, Switzerland). P. V. Carroll was supported by the Special are consistent with previous results (28, 44) and sup- Trustees of St. Thomas’ Hospital. The study was supported by a port the hypothesis of GH resistance. Possible mecha- grant from the Juvenile Diabetes Foundation.
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PATIENT PAIN ASSESSMENT Part A: Body and Pain Scale Please mark, on the drawings below, the areas where you feel pain. Write “E” if external or “I” if internal. Write “EI” if both external and internal. Please use numbered pain scores and additional descriptive words like: neuropathic, intense (deep or surface), sharp, hot, dull, cold, sensitive, tender, itchy, shooti

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