Vitamin D and the Free Hormone Hypothesis
Condition: Arthrosis; Surgery
MeSH terms: Osteoarthritis
Study type: Observational

Summary: 
      The purpose of this study is to describe changes in vitamin D parameters before, during and
      after a well-defined elective surgical trauma (knee arthroplasty) and to compare these
      changes to other steroid hormones (testosterone and oestrogens). The hypothesis is that
      profound changes in free and total vitamin D will occur as a result of changes between
      intravascular vs extravascular protein compartments during surgical trauma.
    

Detailed description: 
      Introduction:

      Vitamin D is a versatile signaling molecule with a well-established role in the regulation of
      calcium homeostasis and bone health. The spectrum of vitamin D target-organs has expanded and
      it has been suggested that vitamin D influences the immune system, endocrine organs such as
      pancreas, testis and ovary and multiple other organs (Blomberg Jensen 2014). More recently
      attention has been paid to surgical patients suggesting hypovitaminosis D to increase
      postoperative morbidity. (Turan A et al, Zaloga et al). However, the perioperative literature
      is hindered by a mixture of acute and chronic diseases indicating surgery, different types of
      surgery and different time of vitamin-D assessments (pre- vs post-operatively) (Turan A et al
      Zaloga et al).

      Vitamin-D is a protein-bound steroid hormone and interpretation of vitamin-D surgical studies
      require knowledge about the effect of clinical surgical trauma per se on vitamin-D
      physiology, as has been demonstrated with cortisol, thyroid hormones and other steroid
      hormones (Kehlet, Brandt, Rem). Unlike other steroid hormones vitamin D depends on a two step
      activation process before it is able to bind and activate the vitamin D receptor (VDR). First
      by 25-hydroxylation (CYP2R1) in the liver, which forms 25-hydroxyvitamin D (25-OHD). 25-OHD
      is also biologically inactive but used clinically to determine vitamin D status because serum
      25-OHD levels are associated with rickets, bone health and calcium homeostasis. Circulating
      25-OHD is bound to vitamin D binding protein (DBP) (Prosser and jones 2004). This complex is
      filtered in the glomerulus and subsequently transported into the proximal tubules cells by
      megalin-mediated uptake (Nykjær 1999). Here, 25-OHD undergoes 1α-hydroxylation (CYP27B1) and
      the resulting 1,25(OH)2D3 binds and activates the vitamin D receptor (VDR). The fact that the
      protein bound fraction is taken up by megalin differs from the metabolic clearance and/or
      activation of other steroid hormones and questions whether the free hormone hypothesis is
      applicable to the vitamin D system. The fact that binding proteins are lost during surgical
      stress indicates that this patient group is ideal for studying total versus free hormone
      concentrations and possible secondary changes for instance in serum PTH and calcium due to
      functional hormonal aberrations.

      Aim of study:

      The purpose of this study is to describe changes in vitamin D parameters before, during and
      after a well-defined elective surgical trauma (knee arthroplasty) and to compare these
      changes to another steroid hormone (testosterone and oestrogens). The hypothesis is that
      profound changes in free and total vitamin D will occur as a result of changes between
      intravascular vs extravascular protein compartments during surgical trauma.

      DESIGN This is a prospective observational study

      Patients and methods 20 otherwise healthy patients (10 males and 10 females) age 50-75 years
      undergoing elective total knee arthroplasty in Department of Orthopaedic Surgery, Hvidovre
      Hospital. All patients undergo standard anesthesia and analgesic treatment in a fast-track
      set-up with discharge not earlier than 48-hours postoperatively.(Husted et al 2011) Exclusion
      criteria are

        -  intake of high dose vitamin D (above 10 microgram daily),

        -  serious co-morbidities such as previous Myocardial Infarction, heart, kidney or liver
           failure, severe rheumatological disorders, existing endocrine disorders in thyroid,
           pancreas, testis, adrenal,

        -  Disorders related to calcium metabolism, hypercalcemia,

        -  Granulomatous disease such as Wegener, tuberculosis, etc,

        -  Previous or present malignant disease, inflammatory bowel disease

        -  Current use of medication that influence protein binding and renal excretion
           (allopurinol, diuretics, hormones. immunosuppressive therapy)

        -  Elevated serum creatinine

        -  Non-european ethnicity

      SAMPLE SIZE CALCULATION AND STATISTICS In this association study with 20 participants we
      estimate based on the studies conducted with cortisol and other steroid hormones that the
      cohort size is sufficient to show the kinetics in vitamin D metabolism after surgery

      SCREENING AND TIME COURSE Men and women, who are investigated at Department of Orthopedics at
      Hvidovre hospital will be screened for eligibility to the study. Those who meet the criteria
      for participation will be informed, and if they consent allocated to the study. The study
      will be initiated January 2015 and ends when the last person has been included latest April
      2015.

      Each person will have one blood sampling performed prior to surgery and 2, 6, 24 and 48 hours
      postoperatively. Three weeks after inclusion the patients will have a final blood sample
      drawn .

      Blood samples Venus blood is drawn preoperatively before i.v. fluid administration, 2, 6,
      24,48 hours and 3 weeks postoperatively. Serum has to be frozen within 1 hour and will be
      stored at minus 20 degrees celsius until analysis.

      OUTCOME MEASUREMENTS

        -  Primary endpoints

           •Changes in total and calculated free 25-hydroxyvitamin D and 1,25dihydroxyvitamin D
           postoperatively.

        -  Secondary endpoints

             -  Serum concentrations of total calcium, albumin corrected calcium, phosphate,
                alkaline phosphatase, vitamin D binding protein and Parathyroid hormone (PTH)

             -  Total and calculated free testosterone and estradiol in males and females
                respectively.

             -  are the changes in sex hormones different from vitamin D

             -  Serum gonadotopin levels

             -  sex dependence. Are the changes in vitamin D availability dependent on sex.

             -  dependence on preoperative vitamin D status. Are the changes in vitamin D
                availability dependent on baseline serum vitamin D status

             -  Changes in serum concentrations of putative regulators and downstream signals
                osteocalcin, fibroblas growth factor 23 (FGF23), osteopontin, RANKL,
                osteoprotegerin (OPG), alpha Klotho, Sclerostin and IGF-1.

             -  Temporal changes in serum level of binding proteins. differences for vitamin D
                binding protein, albumin and sex hormone binding globulin.

      ANALYSIS AND INTERVENTION

      Reproductive hormones and growth factors will be analysed at dept. of GR, Rigshospitalet.
      Other serum analyses will be analysed at Department of clinical biochemistry, Holbæk and
      Aarhus Kommune Hospital

      ETHICS AND SIDE EFFECTS All the patients will have full-filled their investigation, before
      they are invited to the study. They will be informed of potential adverse effects, and they
      can leave the trial at any point without any consequences. All participants will be informed
      and counselling according to their VD status 3 weeks after the surgery. This study poses no
      additional risk to the patients except for the 5 perioperative blood samples (each 8 ml in
      total 40 ml per patient), as everything else is according to standard clinical practice.

      PUBLICATION OF RESULTS All results, positive or negative will be submitted to peer reviewed
      scientific journals. Data will successively be obtained and transferred to a statistical
      database.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        20 otherwise healthy patients (10 males and 10 females) age 50-75 years undergoing elective
        total knee arthroplasty in Department of Orthopaedic Surgery, Hvidovre Hospital. All
        patients undergo standard anaesthesia and analgesic treatment in a fast-track set-up with
        discharge not earlier than 48-hours postoperatively.
      
Biospecimen description: 
      serum
    
Keywords: vitamin d; free hormone; surgical stress