Insulin Resistance, Sarcopenia and Plasma BAIBA Levels
Condition: Sarcopenia; Insulin Resistance
MeSH terms: Sarcopenia; Insulin Resistance
Study type: Observational

Summary: 
      Insulin resistance (IR) is an early metabolic alteration in chronic kidney disease (CKD)
      patients, becoming almost universal in those who reach the end stage of kidney failure. The
      skeletal muscle represents the primary site of IR in CKD, and alterations at sites beyond the
      insulin receptor are recognized as the main defect underlying IR in this condition. The
      etiology of IR in CKD is multifactorial in nature and may be secondary to disturbances that
      are prominent in renal diseases, including physical inactivity, chronic inflammation,
      oxidative stress, vitamin D deficiency, metabolic acidosis, anemia, adipokine derangement,
      and altered gut microbiome.

      IR has been solidly associated with intermediate mechanisms leading to cardiovascular (CV)
      disease in CKD including left ventricular hypertrophy, vascular dysfunction, and
      atherosclerosis. Recent studies have identified a muscle factor β-aminoisobutyric acid
      (BAIBA), which is produced by skeletal muscle during physical activity. BAIBA have been found
      to link with sedentary life style, abdominal obesity, and impairments in carbohydrate and
      lipid metabolism. A few studies have shown that BAIBA can protect from diet-induced obesity
      in animal models. It induces transition of white adipose tissue to a "beige" phenotype, which
      induces fatty acids oxidation and increases insulin sensitivity. While the exact mechanisms
      of BAIBA-induced metabolic effects are still not well understood, the aim of this study is
      want to study its relationship with muscle wasting and insulin resistance in a group of
      non-diabetic hemodialysis patients.
    

Detailed description: 
      Study Design and Population

      Patients and Methods

      This study is an observational, cross-sectional and prospective cohort study. One hundred and
      fifty patients on non-diabetic hemodialysed patients will be included for the cross-sectional
      survey; Twenty healthy subjects will be elected as the controls. Prevalent adult HD patients
      with dialysis vintages over 3 months will be recruited. Patients are maintained on regular HD
      prescription, three times a week, for four-hour sessions. Subjects with significant comorbid
      conditions such as cancer, heart failure, or severe liver disease and chronic infection such
      diabetic foot will be excluded. This study is conducted according to the guidelines laid down
      in the Declaration of Helsinki, and all procedures were reviewed as well as approved by the
      Regional Hospital Ethics Committee. All subjects should give their written informed consent
      to participate in the study. Subjects' demographic and clinical characteristics, including
      age, gender, weight, height, body mass index (BMI), dialysis vintage, and Kt/V will be
      recorded, and comorbidities and current therapies will be collected.

      Anthropometric and biochemical assessments

      Systolic and diastolic blood pressures are taken with the subjects in the supine position. A
      measurement of height and weight was performed on all subjects. Waist circumference was
      measured at the midpoint between the lower border of the rib cage and the iliac bone. The
      concentration of plasma insulin was assayed by radioimmunoassay. Fasting plasma glucose was
      measured using the glucose oxidase method. HbA1c was measured by affinity chromatography.
      Total cholesterol, triglyceride, and HDL cholesterol levels were measured enzymatically using
      an autoanalyzer (Hitachi 747; Hitachi, Tokyo, Japan). Serum insulin concentrations are
      determined by IRMA. Adiponectin and leptin concentrations are measured using a commercially
      available ELISA kit.

      Sample preparation

      In each subject, the blood samples are drawn from the arteriovenous fistula in of each
      participant in the morning after fasting for at least 8 h and on the day of hemodialysis. The
      samples are properly processed, refrigerated at 2-8 C, and the plasma is separated
      immediately by centrifugation. Each serum sample is heat-inactivated by incubation at 65 C
      for 30 min. Fetal bovine serum (FBS; Gibco BRL, Grand Island, NY, USA), a negative control,
      is treated with activated charcoal (Sigma, St. Louis, MO, USA) overnight at 4 C and filtered
      to remove all small molecules and AhR agonists that might have been present. TCDD, a positive
      control for AhR agonists, was purchased from Sigma Co. Plasma BAIBA levels are assessed by a
      Liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, as previously described
      (15). Cell-based AhR ligand activity (CALA) assay and ELISA assay will be performed (16)

      HOMA-IR, HOMA-%B, HOMA-%S, and disposition index are calculated by the following formulae.

      HOMA-IR1 = [fasting insulin (mU/l) × fasting glucose(mg/dl)× 0.0555]/22.5 HOMA-%B1 = [20 ×
      fasting insulin (mU/l)]/[(fasting glucose(mg/dl) × 0.0555)-3.5] HOMA-%S1 = [1/ HOMA-IR1] ×
      100% Disposition index 1= (HOMA-%S1/100) × (HOMA-%B1/100)

      Dual-Energy X-ray Absorptiometry (DEXA)

      DEXA is a widely used reference method for body FFM and FM measurements.(10) DEXA was
      performed using a Lunar Prodigy (GE Medical Systems, Madison, WI). Whole-body scans were
      performed according to manufacturer's instructions, and body FM (FMDEXA), LTM (LTMDEXA) and
      bone mineral content were analyzed using the manufacturer's software. The DEXA method uses an
      X-ray tube with a filter to generate low-energy (40 kV) and high-energy (70 or 100 kV)
      photons. When photons at different energy levels pass through tissue, their absorptions can
      be expressed as a ratio of attenuation at lower or higher energy levels. DEXA estimate of FFM
      was calculated as a sum of LTMand bone mineral content estimates. All patients were examined
      by the same observer.

      Bioelectric Impedance Spectroscopy

      Whole-body bioelectric impedance spectroscopy (BIS) measurement using a body composition
      monitor (BCM: Fresenius Medical Care, Bad Homburg, Germany) was performed on each of the
      participants enrolled in the study by a specific member of the staff who had completed a
      training course in the BCM technique. The BCM measures the impedance spectroscopy at 50
      different frequencies between 5 kHz and 1 MHz. Measurements were taken on the day before
      dialysis with the patient calm, supine, and relaxed in the dialysis bed for 10minutes. Four
      electrodes were placed on the patient's hand and foot on the side contra lateral to their
      arteriovenous fistula. Specific exclusion criteria were dictated by the device and included
      history of a pacemaker, defibrillator, metallic sutures, or stent implantation and amputation
      of a major limb. As a multifrequency bioimpedance device, BCM not only provides extracellular
      (ECWBCM), intracellular (ICWBCM), and total body water (TBWBCM) measurements but also
      estimates the body composition in terms of lean tissue mass (LTMBCM-mainly muscle), fat mass
      (FATBCM), adipose tissue mass (ATMBCM-mainly fat), and overhydration (OH) according to the
      body compositionmodel.(17) This device combined BIS with the BCM model described in Chamney
      et al,11 and it takes into account the dissimilar hydration of relevant tissues. Briefly, the
      device was modified to reflect the presence of excess fluid accumulated due to pathologic
      reasons, that is, patients with kidney failure. It has therefore set constants for each of
      the body composition compartment. This device has been shown to be as precise as the gold
      standardreference methods and has been validated against reference methods for volume status
      and body composition assessments in healthy and HD populations, with methods frequently used
      in the 4-compartment model. The percentage proportions of LTMBCM, FATBCM, andATMBCM were
      denoted accordingly as pLTMBCM, pFATBCM, and pATMBCM.

      Muscle Strength

      The muscle function will be assessed on the same day of the recruitment immediately before
      starting the HD session by handgrip strength measurement, using a handle dynamometer. The
      test is performed conducting three attempts with each hand, and the mean of the strongest
      hand is used to determine muscle strength
    

Observational model: Case-Crossover
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        hemodialysis (HD) patients
      
Biospecimen description: 
      Plasma
    
Keywords: Insulin resistance; Sarcopenia; β-aminoisobutyric acid