Metabolism of chylomicrons in patients with congenital lipoatrophic diabetes: a study with emulsion models of chylomicrons.
BACKGROUND
Lipoatrophic diabetes is characterized by the near absence of adipose tissue and the presence of insulin-resistant diabetes. Fasting hypertriglyceridaemia and increased postprandial lipidaemia are also present, but the metabolism of chylomicrons, the triglyceride-rich lipoproteins in the circulation that carry the dietary fats absorbed by the intestine, was not specifically investigated. Because both the activity of insulin-dependent lipoprotein lipase that catalyses the chylomicron lipolysis and the storage of the lipolysis products are affected in the disease, it is important to evaluate how those changes may ultimately affect the chylomicron lipolysis and removal of chylomicron remnants from the circulation.


OBJECTIVE
The aim of the study was to evaluate the chylomicron intravascular metabolism in patients with lipoatrophic diabetes.


METHODS
Six patients with lipoatrophic diabetes (four females, two males) aged 22.2 +/- 4.4 years, with body mass index (BMI) 21.6 +/- 3.6 kg/m(2), were compared with 12 healthy control subjects (seven females, five males) aged 24.3 +/- 2.1 years with BMI 22.5 +/- 2.7 kg/m(2).


METHODS
The plasma kinetics of intravenously injected chylomicron-like emulsions labelled with (3)H-triglycerides ((3)H-TG) and with (14)C-cholesteryl esters ((14)C-CE) were determined, the former tracing the chylomicron lipolysis by lipoprotein lipase and the latter the removal of chylomicron remnants from the plasma.


RESULTS
Triglyceride values (8.3 +/- 9.2 mmol/l) in the patients were higher (P < 0.005) and high density lipoprotein (HDL) cholesterol values (0.8 +/- 0.2 mmol/l) lower (P < 0.0005) than in controls (0.7 +/- 0.2 and 1.3 +/- 0.4 mmol/l, respectively) whereas total cholesterol, apoprotein B (apo B) and apo A1 were similar. The fractional clearance rate (FCR, in min(-1)) of (3)H-TG was 0.014 +/- 0.016 and the FCR of (14)C-CE was 0.008 +/- 0.012 in the patients and 0.046 +/- 0.024 and 0.024 +/- 0.012 in the controls, respectively (P < 0.05). Thus FCRs of both emulsion labels were markedly reduced in the patients, indicating that lipolysis and remnant removal were diminished. Diminished remnant removal may be due to either deficient lipolysis or deficient removal mechanisms.


CONCLUSIONS
The metabolism of chylomicrons tested by the emulsion method is impaired in lipoatrophic diabetes.
Wajchenberg
Bernardo L
BL
Diabetes Section and Lipid Metabolism Laboratory, Heart Institute (InCor), University of São Paulo Medical School, Brazil.
Amâncio
Rosângela F
RF
Santomauro
Ana T
AT
Maranhão
Raul C
RC
D000328:Adult; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics; D016022:Case-Control Studies; D002788:Cholesterol Esters / Q000493:pharmacokinetics*; D002914:Chylomicrons / Q000493:pharmacokinetics*; D003923:Diabetes Mellitus, Lipoatrophic / Q000378:metabolism*; D004655:Emulsions; D005260:Female; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D018709:Statistics, Nonparametric; D014280:Triglycerides / Q000493:pharmacokinetics*; D014316:Tritium / Q000493:pharmacokinetics
D002250:Carbon Radioisotopes; D002788:Cholesterol Esters; D002914:Chylomicrons; D004655:Emulsions; D014280:Triglycerides; D014316:Tritium