for Adipose Tissue DIabetes VAriants (fATDIVA)
Condition: Diabetes Mellitus
MeSH terms: Diabetes Mellitus; Insulin Resistance
Study type: Interventional

Summary: 
      The adipose (fat) cells under the skin are where individuals store excess fat. The more
      excess fat they have, the more "strain" they put on these cells which then get bigger and
      don't work as well as they should. Having some fat under the skin is important. People who
      have a genetic defect which results in them having almost no fat under their skin have a very
      high risk of a condition called insulin resistance (where the body does not respond as well
      to insulin and blood sugar levels rise). This can lead to diabetes and heart disease despite
      them not being overweight.

      Scientists have only recently started to understand the importance of fat in insulin
      resistance and how people unable to store fat very well can have insulin resistance despite
      not being obese. The investigators have also recently discovered that small changes in a
      person's genetic code (their body's instruction manual) may also affect their ability to
      store fat and would like to explore this in more detail. To do this, they will recruit
      volunteers from the Exeter 10,000 study who gave permission to contact them about further
      research. The investigators will collect detailed body size measures and blood samples taken
      before and after a special drink that is high in fat (similar to a thick milk shake), then
      compare the results between people with and without the particular genetic changes of
      interest.

      Knowing more about these genetic changes and how fat cells work could help to improve
      understanding about why some people develop diabetes and heart disease despite a relatively
      normal BMI.
    

Detailed description: 
      Hypothesis:

      Individuals carrying different genetic variations have different abilities to store fat under
      the skin.

      Aim: To improve understanding of "adipose tissue dysfunction" using human genetics, and
      demonstrate that lipid uptake into fat cells is compromised in subjects with 'polygenetic
      lipodystrophy' alleles.

      Objectives:

        -  Identify individuals with genetic risk variants of interest and controls matched for
           gender, age and BMI.

        -  Undertake detailed physiological assessments including an Oral Triglyceride Tolerance
           Test (OTTT) (blood samples before and after a fatty drink), detailed body size measures
           and an optional fat biopsy.

        -  Using the samples collected, test whether or not individuals carrying a high genetic
           load of "polygenic lipodystrophy" alleles:

             1. have larger subcutaneous fat cells.

             2. have higher circulating lipid levels 4 hours after a fatty meal challenge.

             3. have a gene expression profile normally associated with obesity, despite being of
                the same BMI as matched controls. This profile includes a downregulation of genes
                involved in fatty acid trafficking and an upregulation of genes involved in
                inflammation.

             4. have higher insulin resistance as measured by HOMAIR (calculated from fasting
                insulin and fasting glucose).

      Background:

      Diabetes is the most common chronic metabolic disease and is a major source of morbidity and
      mortality. It is one of the biggest healthcare challenges facing the UK NHS with more than
      2.6 million adults diagnosed in the UK, with the vast majority (90%) having type 2 Diabetes
      (T2D). It is anticipated the numbers will continue to rise, in part due to the increasing
      levels of obesity in the population.

      T2D is characterised by high blood glucose levels in the context of increasing insulin
      resistance and reduced beta cell function, and this can develop over several years with
      individuals unaware of the problem.

      Research groups in Exeter are leading efforts to identify the genetic factors that influence
      why some people develop T2D despite relative leanness, whilst many obese people do not get
      the disease. The investigators have identified many such factors but now wish to study them
      in more detail to understand the role of insulin.

      Introduction:

      Adipose tissue dysfunction Working with collaborators as part of ongoing genetic studies, the
      investigators have identified several genetic variations (DNA changes) associated with
      insulin resistance, and believe some of these genetic variants operate primarily through
      adipose tissue "dysfunction". Adipose tissue dysfunction is a relatively new concept and has
      resulted from detailed physiological studies that have revealed that obese individuals have
      larger fat cells, more inflamed fat tissue (often infiltrated with macrophages) poorer
      adipose tissue blood flow pre/post meal, and differential expression of genes involved in
      these processes (Alkhouli 2013). The failure of adipocytes, resulting in a limited capacity
      to take up free fatty acids (FFA), predispose to ectopic fat depositions which is a
      deposition of lipids in sites such as the liver, muscle with more omental tissue similar to
      subjects with lipodystrophy.

      The investigators are trying to understand how genetic variations cause differences in
      people's ability to store fat and wish to test the hypothesis that individuals carrying
      different genetic variations have different abilities to store fat under the skin as
      subcutaneous fat tissue. This could lead to an improved understanding of subcutaneous fat
      storage. It is very unlikely that the rising numbers of people becoming overweight or obese
      as they age will be substantially reversed, therefore the study's findings could be important
      in identifying how to reduce the risk of disease caused by obesity.

      Methods:

      Study design:

      This is a prospective "recruit by genotype" cohort study that will take place over a 2 year
      period (2015 to 2017).

      Study participants:

      All participants will be identified from existing research cohorts managed by the NIHR Exeter
      Clinical Research Facility (Exeter CRF) and recruitment will be facilitated within the Exeter
      CRF.

      Under over-arching ethical approval 09/H0106/75, approximately 7500 anonymised DNA samples
      have been genotyped for genetic variants related to insulin production. These variants occur
      in >1% of the population and have no direct consequences to individual health.

      There is no defined cut-off for having, or not having, polygenic lipodystrophy as it is not
      based on a single genetic variant. People will have between 0 and 22 polygenic lipodystrophy
      alleles and the investigators are looking for those with a combination of at least 11 genetic
      variants. They have identified approx 300 people in the EXTEND cohort who fit this criteria
      and will then recruit matched controls from those in the EXTEND cohort who have been
      identified as having the fewest number of risk alleles.

      Recruitment:

      The investigators will provide the Exeter Clinical Research Facility (Exeter CRF) with a list
      of the sample numbers that have been identified as having the Individuals identified with the
      "polygenic lipodystrophy" genetic variants of interest, together with control individuals
      carrying the average number of risk alleles. The Exeter CRF Data Manager will then identify
      50 individuals with the variants and 50 individuals matched for age, gender, diabetes status
      and BMI, who will be invited to a 5-hour visit to the Exeter CRF for data and sample
      collection. Interested participants will be contacted directly by a member of the study team
      who will be responsible for the recruitment process, providing more detailed verbal and
      written project-specific information.

      Procedure:

      All participants will be asked to refrain from strenuous exercise and from eating very fatty
      meals in the 48 hours prior to coming in to the clinic, and no alcohol (it has high energy
      content and affects the liver) but otherwise normal diet, then fast overnight prior to
      attending a morning visit at the Exeter CRF. Participants will be asked to sign a written
      consent form prior to any data collection.

      Data collection:

      Anthropometry:

        -  Baseline data including Ht (m), Wt (kg), Waist (cm) and Hip (cm) circumference will be
           recorded.

        -  Detailed body fat measures will be obtained from the BOD POD.

        -  Skin fold measurements (mm) from biceps, triceps, subscapular, and suprailiac regions.

      Medical history: including current medications and lifestyle information (smoking/alcohol).

      BODPOD TM :

      Detailed body composition measures will be obtained using the Body Composition Tracking
      System. This briefly comprises a BOD POD machine, electronic scales, and a computer. It uses
      the principles of body densitometry (measuring mass and volume) to calculate the
      participant's percentage and absolute amounts of fat and fat free mass. Participants will be
      asked to wear minimal clothing (e.g. swimming costume) and a close fitting swim hat. They
      stand on the electric scales to record their weight which is then calibrated with the BOD
      POD. Participants are asked to sit inside the BOD POD up to 1 minute at a time (max 3 times).
      The computer will then analyse and generate the results.

      Blood samples:

      Oral Triglyceride Tolerance Test (OTTT) (approx. 4 hours):

      A small cannula (thin plastic tube) will be inserted into a vein following standard clinical
      practice to minimize any potential trauma from repeat blood sampling.

        -  Fasting samples (at -5 and -2 minutes) will be obtained for baseline measures (including
           routine glucose and lipid measurement) plasma and serum for storage and future batched
           analysis, and pre-OTTT measures of glucose, insulin, standard lipids, and stored plasma
           for potential future metabolomic or lipidomic studies.

        -  Following the initial fasting blood sampling, the participant will be asked to drink
           approx 150 mls of Fresubin 5cal shot supplement drink over a 5 min period. The time of
           completion will be noted as T= 0. Further blood samples will be obtained at T=30, 60,
           120, 180 and 240 minutes post-ingestion. The calorific content and proportion of
           macronutrients in Fresubin is very similar to that described in publications performing
           the OTTT (Karamanos 2001; Carstensen 2003; Mohanlal 2004).

      At the end of this period the cannula will be removed and the participant will be offered a
      light lunch/refreshments.

      Optional abdominal fat biopsies (approx. 30 mins and undertaken during OTTT):

      For research volunteers that are happy to undergo a small fat biopsy, a sample of abdominal
      fat will be obtained by firstly injecting some local anaesthetic into an accessible area of
      the abdomen. Using a scalpel, a small incision (approx 2-3 cm) will be made to a depth of
      approx 15mm and two small pea-sized samples of fat will be removed. The wound will be closed
      with simple sutures or steristrips. One fat sample will be flash frozen in liquid nitrogen
      immediately after excision and stored at minus 80 degrees for RNA analyses. The other sample
      will be stored in formalin for later immunohistochemistry staining.
    

Intervention name(s): Oral Triglyceride Tolerance Test (OTTT); Abdominal fat biopsy (optional)
Intervention type(s): Other; Procedure
Intervention description(s): Participants consume a fatty drink. An intravenous catheter is inserted into the antecubital veins in one arm for intermittent sampling over the following 4 hours. The OTTT permits simple evaluation of postchallenge triglyceride levels and is acceptable to participants.; A sample of abdominal fat will be obtained by firstly injecting some local anaesthetic into an accessible area of the abdomen. Using a scalpel, a small incision (approx 2-3 cm) will be made to a depth of approx 15mm and two small pea-sized samples of fat will be removed. The wound will be closed with simple sutures or steristrips.
Other intervention name(s): OTTT
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Basic Science
Keywords: insulin resistance; physiology; genetics; gene variants; pathogenesis; type 2 diabetes; fat; polygenic lipodystrophy