Association of exercise-induced hyperinsulinaemic hypoglycaemia with MCT1-expressing insulinoma.
OBJECTIVE
Exercise-induced hyperinsulinism (EIHI) is a hypoglycaemic disorder characterised by inappropriate insulin secretion following anaerobic exercise or pyruvate load. Activating promoter mutations in the MCT1 gene (also known as SCLA16A1), coding for monocarboxylate transporter 1 (MCT1), were shown to associate with EIHI. Recently, transgenic Mct1 expression in pancreatic beta cells was shown to introduce EIHI symptoms in mice. To date, MCT1 has not been demonstrated in insulin-producing cells from an EIHI patient.


METHODS
In vivo insulin secretion was studied during an exercise test before and after the resection of an insulinoma. The presence of MCT1 was analysed using immunohistochemistry followed by laser scanning microscopy, western blot analysis and real-time RT-PCR of MCT1. The presence of MCT1 protein was analysed in four additional insulinoma patients.


RESULTS
Clinical testing revealed massive insulin secretion induced by anaerobic exercise preoperatively, but not postoperatively. MCT1 protein was not detected in the patient's normal islets. In contrast, immunoreactivity was clearly observed in the insulinoma tissue. Western blot analysis and real-time RT-PCR showed a four- to fivefold increase in MCT1 in the insulinoma tissue of the EIHI patient compared with human pancreatic islets. MCT1 protein was detected in three of four additional insulinomas.


CONCLUSIONS
We show for the first time that an MCT1-expressing insulinoma was associated with EIHI and that MCT1 might be present in most insulinomas. Our data suggest that MCT1 expression in human insulin-producing cells can lead to EIHI and warrant further studies on the role of MCT1 in human insulinoma patients.
Department of General Paediatrics, Neonatology and Paediatric Cardiology, University Children's Hospital Düsseldorf, Moorenstrasse 5, 40225 Düsseldorf, Germany.
J
J
Marquard
A
A
Welters
T
T
Buschmann
W
W
Barthlen
S
S
Vogelgesang
D
D
Klee
M
M
Krausch
A
A
Raffel
S
S
Otter
L
L
Piemonti
E
E
Mayatepek
T
T
Otonkoski
E
E
Lammert
T
T
Meissner
D000293:Adolescent; D005080:Exercise Test; D005260:Female; D006801:Humans; D006946:Hyperinsulinism / Q000209:etiology* / Q000503:physiopathology; D007003:Hypoglycemia / Q000209:etiology* / Q000517:prevention & control; D050417:Insulin-Secreting Cells / Q000378:metabolism* / Q000473:pathology; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D027501:Monocarboxylic Acid Transporters / Q000235:genetics / Q000378:metabolism*; D009043:Motor Activity; D009363:Neoplasm Proteins / Q000378:metabolism*; D012894:Sleep Stages; D012893:Sleep Wake Disorders / Q000209:etiology / Q000517:prevention & control; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D016896:Treatment Outcome; D014474:Unconsciousness / Q000209:etiology / Q000517:prevention & control; D000099233:Monocarboxylate Transport Protein 1
D027501:Monocarboxylic Acid Transporters; D009363:Neoplasm Proteins; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1