Muscle Protein Synthesis in Dialysis Patients
Condition: Muscle Loss
Study type: Observational

Summary: 
      The most severe form of chronic renal failure is end-stage-renal-disease with maintenance
      hemodialysis (MHD) as the most common treatment strategy. MHD patients experience a number of
      metabolic and phenotypic derangements including skeletal muscle wasting. Previously, it has
      been demonstrated that dialysis treatment leads to increased rates of forearm phenylalanine
      uptake (proxy for 'muscle' protein synthesis) with an even greater rates of phenylalanine
      release (proxy for 'muscle' protein breakdown). Hence, the dialysis procedure itself is
      catabolic and induces a catabolic carryover for several hours after dialysis. This suggests
      prolonged post-dialysis disturbances in whole body- and skeletal muscle protein metabolism in
      MHD patients. Moreover, dialysis treatment in itself results in ~20 % losses of circulating
      amino acids in the dialysate. Collectively, this creates the need for replacement of amino
      acids by protein supplementation during and/or after dialysis. The ingestion of protein-dense
      meals in between dialysis treatments likely represents an important dietary strategy to
      counterbalance dialysis-induced catabolism and to achieve the current recommended protein
      intakes (set at 1.2 g/kg bodyweight/d) to limit muscle protein loss in MHD patients. However,
      the effectiveness of protein-rich meal ingestion to augment postprandial whole body and
      muscle protein metabolic responses in MHD patients outside of the dialysis period remain
      largely undefined.

      The purpose of this study is to compare basal and postprandial whole body leucine body
      kinetics, muscle anabolic sensing mechanisms, markers of muscle proteolysis, and myofibillar
      protein synthesis rates to mixed meal ingestion on a non-dialysis day in eight MHD patients,
      between 20-80 and to compare these outcomes to age- and BMI-matched controls. The
      investigators will use specifically produced intrinsically L-[5,5,5-2H3]leucine labeled eggs
      combined with primed constant amino acid tracer infusion methods and concomitant blood and
      muscle direct sampling to make direct assessments of in vivo protein digestion and absorption
      kinetics and subsequent postprandial muscle protein synthetic responses in MHD patents and
      controls. On the test day, subjects will remain sedentary for the determination of muscle
      protein synthesis in both the fasted state and after consumption of the meal.
    

Detailed description: 
      On the day of the infusion trial, participants will report to the laboratory at 0700 h after
      an overnight fast. MHD patients will be studied ~24 h after their dialysis treatment. A
      Teflon catheter will be inserted into an antecubital vein for baseline blood sample
      collection (t=-180 min) after which participants receive priming doses of NaH13CO2 (2.35
      µmol·kg), L-[1-13C]leucine (7.6 µmol·kg FFM), and L-[ring-2H5]phenylalanine (2.0 µmol·kg
      FFM). Subsequently, a continuous intravenous infusion of L-[1-13C]leucine (0.10 µmol·kg FFM
      ·min) and L-[ring-2H5]phenylalanine (0.05 µmol·kg-1 FFM·min) will be initiated (t=-180 min)
      and maintained until the end of the trial. A second Teflon catheter will be inserted into a
      heated dorsal hand vein of the same arm for repeated arterialized blood sampling and will
      remain patent by a 0.9% saline drip. In the postabsorptive state, muscle biopsies will be
      collected at t=-120 and -0 min of the infusion. Subsequently, participants will consume a
      mixed meal containing 20 grams of dietary protein and the completion of the meal will mark
      the start of the postprandial phase (t=0 min). An additional muscle biopsy will be collected
      at 300 min to determine postprandial myofibrillar protein synthesis rates. Biopsies will be
      collected from the middle region of the vastus lateralis (15 cm above the patella) with a
      Bergström needle modified for suction under local anesthesia (2% Lidocaine). The
      postabsorptive muscle biopsies will be collected from the same incision with the needle
      pointed to distal and proximal directions, respectively. The postprandial biopsy will be
      collected through a separate incision 2-3 cm above the postabsorptive incision. All biopsy
      samples will be freed from any visible blood, adipose, and connective tissue immediately
      frozen in liquid nitrogen, and stored at -80˚C until subsequent analysis.
    

Intervention name(s): Protein Meal; Stable Isotope Amino Acid Infusion
Intervention type(s): Other; Other
Intervention description(s): Ingestion of mixed meal containing 20 g of dietary protein; Continuous infusion of L-[1-13C]leucine (0.13 μmol⋅kg⋅min) and L-[ring- 2H5]phenylalanine (0.05 μmol⋅kg⋅min)
Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        In total, the investigators would like to recruit 8 maintenance hemodialysis patients (both
        male and female) and 8 healthy controls matched for gender, age and BMI.
      
Biospecimen description: 
      Plasma samples and skeletal muscle tissue biopsies