Supplemental information on Methods for on-line appendix
Belonging to manuscript:
PANCREATIC FAT CONTENT AND Β-CELL FUNCTION IN MEN WITH AND
WITHOUT TYPE 2 DIABETES
Running title: Pancreatic Fat and β-Cell Dysfunction
Maarten E. Tushuizen, MD1, Mathijs C. Bunck, MD1, Petra J. Pouwels, PhD2, Saskia
Bontemps, MSc1, Jan Hein T. van Waesberghe, MD, PhD3, Roger K. Schindhelm, MD,
PhD1, Andrea Mari, PhD4, Robert J. Heine, MD, PhD, FRCP,1 and Michaela Diamant, MD,
PhD1
1
Department of Endocrinology / Diabetes Center; 2Department of Physics & Medical
Technology; 3Department of Radiology; VU University Medical Center, Amsterdam, The
Netherlands; 4Institute of Biomedical Engineering, National Research Council, Padova,
Italy
Correspondence to:
M. Diamant, MD, PhD
Department of Endocrinology / Diabetes Center
VU University Medical Center
PO Box 7057
1007 MB Amsterdam, The Netherlands
Phone: +31-204440534; Fax: +31-204440530
E-mail address: m.diamant@vumc.nl
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Supplemental information on methods for on-line appendix
Section 1.
MR-Spectroscopy. MR examinations were performed using a 1.5-T whole-body system
(Sonata; Siemens, Erlangen, Germany) in the supine position with the body-array coil
positioned at the upper abdominal region. MR imaging and spectroscopy were performed
using the body-coil for RF-transmission and spine-array and body-array coils for signal
receiving. Axial and coronal steady-state free precession (SSFP) MR images (repetition
time TR 3.8 ms, echo time TE 1.9 ms) during free breathing were employed for
localization of the volume-of-interest (VOI). Single voxel spectra were recorded by using
the stimulated-echo acquisition mode (STEAM) sequence with TR 5000 ms, TE 20 ms,
and mixing time 30 ms. A total of 8 acquisitions were obtained, and stored and processed
for each coil element separately (yielding typically 24 to 40 spectra – depending on the
number of coil elements selected). The short TE and long TR were chosen to ensure
optimal detectability of both lipid and water, which was used as an internal standard.
User-independent spectral quantification was performed with LCModel (version 6.1)(12).
This model is based on simulated lipid and water spectra (with resonances at 0.9 ppm
(lipid methyl groups) and 1.3 ppm (lipid methylene groups) and at 4.65 ppm (water),
respectively. After processing, the individual spectra were reviewed by an experienced
observer, who was blinded for the group variable, in order to discard occasional poorquality spectra, e.g. due to deep breathing. Subsequently, the individual phase-corrected
raw time-domain data were added (taking into account corresponding coil sensitivities
(13)), yielding one time-domain dataset per VOI, which was quantified again with
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LCModel. Spectroscopic lipid content is expressed as the percentage of the area under
the methyl and methylene peaks relative to that under the water peak.
Section 2.
Modeling of -cell function parameters. The model consists of three blocks: a) a model
for fitting the glucose concentration profile, the purpose of which is to smooth and
interpolate plasma glucose concentrations; b) a model describing the dependence of
insulin (or C-peptide) secretion on glucose concentrations; and c) a model of C-peptide
kinetics, i.e. the two-exponential model proposed by Van Cauter et al (16), in which the
model parameters are individually adjusted to the subject’s anthropometric data.
The model expresses insulin secretion as the sum of two components. The first component
represents the relationship between insulin secretion and absolute glucose concentration
at any time-point, i.e. a dose-response function. The mean slope of the dose-response
function is taken to represent β-cell glucose sensitivity. Insulin secretion at reference
glucose levels representing the average basal glucose concentration (5 mmol/l in nondiabetic and 7 mmol/l in diabetic subjects) was calculated from the β-cell dose-response.
The dose-response function is modulated by a time-varying factor, expressing a relative
potentiation effect on insulin secretion. The potentiation factor, which encompasses
various potentiating signals (glucose-induced potentiation, incretins, neural factors) was
set to have a mean value equal to unity over the 2 hours of the study. As the potentiation
factor typically increases during an OGTT, the ratio between the potentiation factor
value at 2-h and that at time 0 was used as a parameter quantifying potentiation. The
second insulin secretion component represents a dynamic dependence of insulin secretion
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on the rate of change of glucose concentration. It is proportional to the time-derivative of
glucose concentration when glucose rises and is zero otherwise. The proportionality
constant, termed rate sensitivity, accounts for anticipation of insulin secretion as glucose
levels rise. The potentiation factor and total insulin secretion (expressed in pmol/min per
square meter of body surface area) were calculated every 5 min for the whole 2-h period,
as detailed in (14,15).
References (cited above as well as in the printed text)
12. Provencher SW: Estimation of metabolite concentrations from localized in vivo
proton NMR spectra. Magn Reson Med 30:672-679, 1993
13. Wald LL, Moyher SE, Day MR, Nelson SJ, Vigneron DB: Proton spectroscopic
imaging of the human brain using phased array detectors. Magn Reson Med 34:
440-445, 1995
14. Mari A, Schmitz O, Gastaldelli A, Oestergaard T, Nyholm B, Ferrannini E: Meal
and oral glucose tests for assessment of beta -cell function: modeling analysis in
normal subjects. Am J Physiol Endocrinol Metab 283:E1159-E1166, 2002.
15. Pacini G, Mari A: Methods for clinical assessment of insulin sensitivity and betacell function. Best Pract Res Clin Endocrinol Metab 17:305-322, 2003
16. Van Cauter E, Mestrez F, Sturis J, Polonsky KS: Estimation of insulin secretion
rates from C-peptide levels. Comparison of individual and standard kinetic
parameters for C-peptide clearance. Diabetes 41:368-377, 1992
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