Effects of thyroid hormone treatment on mitochondrial function, ectopic fat accumulation, insulin sensitivity and brown adipose tissue in type 2 diabetes mellitus

Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are known to
promote weight loss, which could be beneficial for treating obesity, and type 2
diabetes. Thyroid hormone treatment stimulates energy expenditure resulting in
increased body heat production, in which brown adipose tissue play an important
role. It is hypothesized that thyroid hormones would induce increased energy
expenditure via a process called mitochondrial uncoupling, thereby creating an
inefficient energy status. Indeed, an in vivo study showed a 70% increased flux
through the tricarboxylic acid cycle (TCA) and an unchanged ATP synthesis rate
upon T3 treatment in lean, healthy young men. The disproportionate increase in
TCA flux compared with ATP synthesis suggests increased mitochondrial
uncoupling. It is however unknown whether increased mitochondrial uncoupling
would increase fat oxidation and exerts favorable effects on insulin
sensitivity. There is compelling evidence that type 2 diabetic patients have
high levels of fat accumulation in non-adipose tissues, such as skeletal
muscle, heart and liver. Ectopic fat accumulation is related to insulin
resistance, however, why this fat accumulates in peripheral organs is not
known. Recently, studies reported compromised mitochondrial oxidative capacity
in type 2 diabetic patients and first-degree relatives of diabetic patients,
suggested to play an important role. Therefore, subjects suffering from
overweight and/or type 2 diabetes with overt hypothyroidism form an interesting
group for examining the metabolic effects of thyroid hormone treatment, as less
is known about the effects of thyroid hormone treatment in these groups.

The purpose of this study is to evaluate whether thyroid hormone replacement
therapy in type 2 diabetic patients suffering from overt hypothyroidism will
improve muscular mitochondrial function, lower ectopic fat accumulation in
muscle and liver, increase brown adipose tissue activity and enhance insulin
sensitivity.
furthermore, a group of patients with hypothyroidism, but without type 2
diabetes will be included to evaluate the effects of thyroid hormone on brown
adipose tissue activity.

Prospective intervention study in hypothyroidism patients (en type 2 diabetes),
who undergo hormone suppletion therapy.

Type 2 diabetic patients diagnosed with hypothyroidism will undergo 3 months of
thyroid hormone replacement therapy (THRT) (Euthyrox®, Merck, Germany).
Patients will be metabolically characterized (such as insulin sensitivity and
fat accumulation in peripheral tissues) before and after this thyroid hormone
replacement therapy. A dose of 25 µg per day of Euthyrox® will be administered
orally during the first week and will be increased to 50 µg per day during the
second week and to 75-100 µg per day in the third week depending on TSH, free
T4 and T3 concentrations monitored throughout the treatment period.

Risks of measurements
The placement of Teflon cannula*s, blood drawing and the muscle and fat
biopsies can cause bruises and hematomas. Anti-coagulants are excluded from the
study for this reason. Infections or continued bleeding are very rare. The
subjects will be instructed to refrain from heavy physical labour and not to
remove the pressure bandage for the biopsy at least 24 hours after the biopsy.
We take 1 biopsy every clamp. The incision length (0.5cm) and depth (viscera of
vastus lateralis muscle) of the biopsy are minimal, also to reduce risks. A
skilled medical doctor will take the biopsies. Furthermore, MRS is a safe
procedure, with no known health risk as long as no of the exclusion criteria
are met. Hyperinsulinemic-euglycemic clamping is a procedure routinely
performed in our laboratory without notable complications. In rare occasions
subjects exhibit symptoms of hypoglycaemia (even if their blood glucose levels
are still above 3 mmol). After successfully performing the clamp, blood glucose
values will be monitored for an additional 60 minutes with glucose infusion
stand-by if glucose levels happen to drop. Solid food and sugar-drinks will be
provided directly after finalising the clamp to avoid the experience of
hypoglycaemia. One week prior to the clamp, type 2 diabetic patients will be
withdrawn from their diabetic medication use. The withdrawal of diabetic oral
medication can lead to an increase in blood glucose levels in the type 2
diabetic patients. To minimize these effects we only include stable,
well-regulated diabetic patients who are on sulfonylurea (SU)-derivates or
metformin treatment. During this withdrawal period, subjects will be asked to
check and report their fasting glucose to monitor changes in plasma glucose. In
case they measure fasting glucoses > 13 mmol/L the study will be ended due to
medical reasons and in consultation with a medical doctor, the usual oral
anti-diabetic drugs are restarted again.
The advanced TF Gemini PET-CT scanner is equipped with time of flight
electronics, which allows the use of a relatively low amount of radioactivity
(2 mCi). The resulting total radiation dose from the low-dose CT scan and the
injected radioactive tracer is 2.8 mSv is considered as a low risk (47),
comparable with 2 times the yearly cosmic dose. The level of societal benefit
is considered to be substantial.


Risks of Treatment
In this study, no experimental products will be used. Euthyrox® is a registered
drug and prescription-based available. High dosage of Euthyrox® treatment could
cause tachycardia, arrhythmia, angina pectoris, headache and muscle cramp,
however, throughout the study these side-effects will be routinely checked by a
medical doctor.
Also, the withdrawal of diabetic oral medication can lead to an increase in
blood glucose levels in the type 2 diabetic patients. To minimize these effects
we only include stable, well-regulated diabetic patients who are on
sulfonylurea (SU)-derivates or metformin treatment. Their treating physician
will be informed about the subject*s participation in the study. During the
study the subjects will have to check their fasting glucose every morning to
monitor changes in plasma glucose. In case they measure fasting glucoses > 13
mmol/L the study will be ended due to medical reasons and in consultation with
a medical doctor, the usual oral anti-diabetic drugs are restarted again.

Benefits
Results of this study would be of great importance in evaluating thyroid
hormone treatment as strategy for treatment of type 2 diabetes. Some weight
loss could be a direct health benefit for the obese type 2 diabetic patients.