Nutrient sensing in response to starvation in obese and lean individuals

Supply of fuel is of critical importance for survival. Evolution therefore
provided highly conserved, sensitive cell autonomous and systemic *energy
gauges* to guard adequate availability of fuel. AMP activated protein kinase
(AMPK) plays a pivotal role at the cellular level. It is activated by nutrient
deprivation via a reduced intracellular ADP/AMP ratio and a variety of
endocrine cues (including insulin and leptin) and controls energy balance by
shutting off energy consuming processes while activating the machinery to
produce ATP (1). The sirtuins are a family of highly conserved nicotinamide
adenosine dinucleotide (NAD)+ dependent deacetylases that play similar roles by
histone modification of genes encoding proteins involved in energy metabolism
(2). Energy sensing neurons in the brain employ the same molecular machinery
(AMPK in particular) to sense the body*s energy status and coordinate a
multifaceted systemic neuroendocrine and behavioural response to nutrient
deprivation. Most of these neurons are located in the hypothalamus and the
nucleus of the solitary tract in the brain stem. They (in)directly control
autonomic nervous system activity and pituitary hormone release to adapt
metabolism, and higher cortical neural circuits to regulate appetite (3).
Within this framework, the hypothalamus-pituitary-adrenal (HPA) and -thyroid
(HPT) axes are particularly important for the control of energy balance and
metabolism.
Obesity is marked by an altered setting of energy balance. It is extremely
difficult to lose weight on a long term basis, as evidenced by the very
disappointing results of virtually every weight loss strategy that has been
developed in the last 50 years or so. Indeed, even after bariatric surgery
almost no obese patient ends up with a normal bodyweight (although considerable
amounts of weight are lost after these procedures). The above-mentioned energy
sensing system probably underlies this difficulty. We propose that the setting
of this system is different in obese humans. We specifically hypothesize that
the molecular and systemic response to calorie restriction is more explicit in
obese compared to normal weight individuals to explain there propensity to grow
obese. To test this hypothesis we will map the integrated molecular and
neuroendocrine response to fasting in obese vs normal weight humans. Muscle and
brain are exquisitely sensitive to fuel deprivation. Therefore, we will study
the (molecular) physiology of calorie restriction in these tissues. As
endocrine systems are dynamic by nature, multiple sequential blood samples will
be drawn to evaluate the status of the pituitary adrenal- and thyroid axes as
pivotal components of the systemic neuroendocrine response.

1. To compare the effects of fasting on energy sensing machinery in muscle of
obese vs normal weight subjects
2. To compare neuronal activity in the brain in response to fasting in obese vs
normal weight humans
3. To compare the activity of the HPA and HPT axes in response to fasting in
obese vs normal weight humans
4. To determine the effects of weight loss on energy sensing in obese humans

All participants will be screened prior to this intervention study. There will
be two groups in this study; lean and obese individuals.

All participants will be admitted to the clinical research unit of the
department of internal medicine for a 60 hour fast. The lean individuals serve
as a control group. Anthropometric measurements, a bioelectrical impedance
analysis (BIA) and indirect calorimetry will be performed. A basal blood sample
will be taken and a heart rate variability measurement will take place. Then a
structural MRI and resting-state FMRI will be performed on a 3T MRI scanner.
MRI scanning will take approximately 40 minutes. After MRI scanning a muscle
biopsy will be taken from the musculus vastus lateralis.
Subsequently subjects will be fasted for a total of 60 hours after which the
anthropometric measurements, the BIA, the indirect calorimetry, the blood
sampling, the heart rate variability, the MRI scan and the muscle biopsy will
be repeated.
Thereafter the obese participants will use a very low calorie diet (VLCD,
Prodimed) for 8 weeks to lose a substantial amount of weight. To monitor side
effects, participants will be seen and/or phoned on a regular basis. We will
see them after weeks 1, 2, 4 and 6 and phone them after weeks 3, 5 and 7. After
the very low calorie diet, all procedures described above will be repeated, but
the subjects will not fast.

The muscle biopsy regularly results in a hematoma and/or muscle ache at the
place of the biopsy. The first 2 days after the biopsy, patients can experience
a heavy feeling in the muscle.

From the use of Prodimed little side effects are expected. The most frequent
occuring side effect during the use of Prodimed is obstipation, which can be
released by increasing water intake. If this does not help, lactulose can be
used.

There is a risk that unexpected findings will occur on the MRI scans. These
will always be communicated to the patient and his/her general practioner. If a
patient does not want to be informed about eventual unexpected findings, he or
she will be excluded from participation in this study.