Immunoassay for Collagen Type VI
The present invention provides an immunological binding partner reactive with a C-terminal epitope of the C5 domain of the α3 chain of collagen Type 6, and a method of immunoassay using the immunological binding partner for detecting and quantifying the C-terminal epitope. The invention also provides a method of investigating the rate of formation of extracellular matrix and a method for identifying a subject suitable for treatment with an insulin sensitizer.
- 1. An immunological binding partner reactive with a C-terminal epitope of the C5 domain of the α
- 3 chain of collagen Type 6.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
The present invention relates to an antibody which binds to an epitope present at the C-terminus of the collagen type VI α3 chain and to immunoassays detecting said epitope.
Muscle mass and function is lost with age, a range of pathologies, and inactivity, and frequently due to a combination of the three. It is reported that individuals lose 1-2% skeletal muscle per year from 50th years old (Hughes), that 2-3% of muscle mass is lost per week during immobilization (Hortobagyi et al. 2000), and even quicker with cachexia. Impaired muscle function in elderly or hospitalized individuals is associated with (co)morbidity and mortality (Cruz-Jentoft). With the increasing population age in the industrialized world, maintaining functional independence is therefore becoming of increasing importance. The diagnosis and management methods for muscle loss still rely on the imaging examination, e.g. magnetic resonance imaging (MRI), computed tomography (CT) and dual-energy X-ray absorptiometry (DXA) (Cruz-Jentoft). However, such examinations are either expensive or inconvenient to be used in routine clinical practice. Urinary and serological biomarkers such as creatinine and 3-methylhistidine are also used to assist the management of muscle loss. However, high variation and poor validity of these assays limit their use (Nedergaard 2013). In summary, there is an urgent need for biomarkers which can be used in the diagnosing and prognosing muscle function as well as monitoring anti-catabolic treatment outcomes (Sharf).
Loss of muscle mass is driven by unbalanced turnover of muscle extracellular proteins (Rennie 2010 and Welle 2002). As protein turnover, particularly of extracellular proteins, can allow proteolytic fragments to escape into the circulation, quantitative or qualitative changes in protein metabolism can give rise to biomarker profiles that can be of use in monitoring muscle mass or function (Nedergaard 2013).
Collagens are important extracellular proteins of skeletal muscle, which could contribute to the passive tension of muscle (Granzier).
Type III collagen is expressed in most of the type I collagen containing tissues except for bone, and is an important components of connective tissues, muscle tissues and skin et al (Gelse). PIIINP is the N-terminal propeptide of collagen type III, which is removed during mature type III collagen synthesis (Niemela). It has been reported to be related to the anabolic response of hormone treatment (Bhasin 2009 and Chen 2011). Recently, a new ELISA kit was developed by applying monoclonal antibody targeting the N-protease cleavage site of N-terminal procollagen, which could assess the true synthesis of type III collagen (Nielsen 2013).
Collagen Type VI is a unique extracellular collagen which can form an independent microfibrillar network in the basement membrane of cells. It can interact with other matrix proteins including collagens, biglycan, and proteoglycans (Kuo 1997, Bidanset 1992 and Stallcup 1990). In muscle, type VI collagen is part of the sarcolemma and is involved in anchoring the muscle fiber into the intramuscular extracellular matrix, and so is involved in force transmission (Bonaldo 1990 and Keene 1988). Moreover, mutations in type VI collagen can cause Bethlem myopathy and Ullrich congenital muscular dystrophy (Lampe). It has been reported that C-terminal of type VI collagen α3 chain is cleaved off from the mature type VI microfibril after secretion (Aigner 2002 and Lamande 2006).
However, Type VI collagen is not just involved in muscles and muscle loss.
Chronic obstructive pulmonary disease (COPD) is a heterogeneous, slow progressing disease characterized by persistent airflow limitation resulting from chronic inflammation, structural changes, and small airway narrowing (Global initiative . . . ). The main structural proteins of the extracellular matrix (ECM) of the lung are collagens, elastin, and proteoglycans. ECM remodelling is part of healthy tissue maintenance, where old proteins are degraded and new proteins formed (Cox). However, excessive ECM remodelling drives the structural changes in COPD promoting loss of lung function. A key challenge in COPD is the identification of biomarkers of disease progression (Vestbo). ECM investigation by assessment of lung structural proteins may provide biomarkers of disease activity and prognosis.
Exacerbations are periods of increased disease activity that drive COPD progression by accelerating loss of lung function (Donaldson 2002)), reducing quality of life (Seemungal), and causing mortality (Sofer-Cataluna). Patients in all COPD stages may experience exacerbations, although they become more frequent with increasing disease severity (Hurst). It is difficult to predict their occurrence, and the best predictor of future exacerbations is an exacerbation history (Hurst 2010 and Donaldson 2006). Although exacerbations are key events in COPD pathogenesis, little is known regarding structural changes in lung tissue during these events. Matrix metalloproteinase 9 (MMP-9) levels are known to be elevated while tissue inhibitor of metalloproteinase 1 (TIMP-1) levels are decreased in sputum of COPD patients at time of exacerbation compared to stable COPD (Mercer), suggesting a destructive environment.
Recent research has revealed that the ECM harbors properties of an endocrine organ, with its structural proteins generating signaling molecules that can modulate cellular processes at distant sites, including cell migration, differentiation, and angiogenesis. These molecules include the potent anti-angiogenic peptide endostatin, which is derived from type XVIII collagen, as well as tumstatin, vastatin, and restin, which are released from types IV, VII, and XV collagens, respectively (Karsdal, 2015).
The microflamentous interstitial type VI collagen, a triple helical molecule composed of the constituent chains α1(VI), α2(VI), and α3(VI), is expressed in most connective tissues and prominently in adipose tissue (Park, 2012), where it anchors cells through its interconnections with other ECM proteins (Mak, 2012). During formation of the microfilaments, its triple-helical core is proteolytically released from its pro-peptide (Aigner, 2002; Lamande, 2006). Here, further cleavage of the C-terminal pro-peptide of the α3(VI) chain generates endotrophin (herein referred to as “Pro-C6”), a newly identified adipokine. Endotrophin is prominently produced by adipose tissue and induces upregulation of transforming growth factor beta (TGF-β), adipose tissue fibrosis, angiogenesis, inflammation and, in animal models, has been shown to unfavorably modulate several metabolic functions such as insulin sensitivity, food intake, energy balance, and adipose tissue inflammation (Sun, 2014; Dankel, 2014; Park, 2013; Khan, 2009; Pasarica, 2009). These findings suggest that levels of endotrophin in blood may be useful for classifying and/or monitoring patients with metabolic dysfunction, especially those with type 2 diabetes.
Thiazolidinediones (TZDs) are peroxisome proliferator-activated receptor gamma (PPARγ) agonists and have been used widely to treat type 2 diabetes due to their ability to improve insulin sensitivity, lower glucose levels, and reduce the need for insulin (Cho, 2008; Charbonnel, 2010). However, the use of TZDs such as pioglitazone has been limited substantially by associated adverse effects (AEs) such as heart failure (Home, 2009), weight gain (Takada, 2007), peripheral oedema (Karalliedde, 2007), and bone loss in women (Soroceanu, 2004). In an attempt to minimize the AEs of PPARγ agonists, partial activators of PPARγ that trigger only a subset of PPARγ downstream signals, such as balaglitazone, have been developed (Berger, 2005; Agrawal, 2012). Such partial agonists achieve good glycemic control with reduced AEs (Larsen, 2008). A serum biomarker that would optimally define treatment responders could further improve efficacy and safety of such glitazones.
We have now developed a monoclonal antibody and an ELISA kit targeting the C-terminal of α3 chain. We refer to this kit and to reactivity measured with it herein as ‘Pro-C6’.
We have established that levels of Pro-C6 reflect the rate of muscle turnover and also that ECM remodelling, assessed systemically by biomarkers of protein remodelling fragments, is accelerated during an exacerbation of COPD where disease activity is high.
We have also established that elevated serum levels of endotrophin (i.e. “Pro-C6”) predict response to two insulin sensitizers (Balaglitazone and Pioglitazone) and lower side-effects, identifying those patients with diabetes type II that profit from PPARγ agonist treatment.
The present invention now provides an immunological binding partner reactive with a C-terminal epitope of the C5 domain of the α3 chain of collagen Type VI.
Preferably said immunological binding partner specifically binds to a said C-terminal epitope comprised in a C-terminal amino acid sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1).
Said immunological binding partner is a monoclonal or polyclonal antibody. The immunological binding partner may be an antibody fragment with binding specificity as further explained below.
Preferably, said immunological binding partner does not recognise or bind an elongated version of said C-terminal amino acid sequence which is . . . KPGVISVMGTA (SEQ ID. NO:2)-COOH.
Preferably, said immunological binding partner does not recognise or bind (or also does not recognise or bind) a truncated version of said C-terminal amino acid sequence which is . . . KPGVISVMG-COOH (SEQ ID. NO:3).
Preferably still, the ratio of the affinity of said antibody for amino acid sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1) to the affinity of said antibody for elongated amino acid sequence . . . KPGVISVMGTA-COOH (SEQ ID. NO:2), and or to the truncated amino acid sequence . . . KPGVISVMG-COOH (SEQ ID. NO:3), is greater than 10 to 1,
More generally, the ratio of the affinity of said immunological binding partner for amino acid sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1) to the affinity of said immunological binding partner for said elongated amino acid sequence is preferably greater than 10 to 1, preferably greater than 50 to 1, preferably greater than 100 to 1, preferably greater than 500 to 1, preferably greater than 1000 to 1, and most preferably greater than 10,000 to 1.
Also preferably, the ratio of the affinity of said immunological binding partner for amino acid sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1) to the affinity of said immunological binding partner for said truncated amino acid sequence is greater than 10 to 1, preferably greater than 50 to 1, preferably greater than 100 to 1, preferably greater than 500 to 1, preferably greater than 1000 to 1, and most preferably greater than 10,000 to 1.
Preferably, said immunological binding partner is a monoclonal antibody or fragment thereof having specific binding affinity. Said monoclonal antibody or fragment thereof may preferably comprise one or more complementarity-determining regions (CDRs) selected from:
Preferably the antibody or fragment thereof comprises at least 2, 3, 4, 5 or 6 of the above listed CDR sequences.
Preferably the monoclonal antibody or fragment thereof has a light chain variable region comprising the CDR sequences
Preferably the monoclonal antibody or fragment thereof has a light chain that comprises framework sequences between the CDRs, wherein said framework sequences are substantially identical or substantially similar to the framework sequences between the CDRs in the light chain sequence below (in which the CDRs are shown in bold and underlined, and the framework sequences are shown in italics)
Preferably the monoclonal antibody or fragment thereof has a heavy chain variable region comprising the CDR sequences
Preferably the monoclonal antibody or fragment thereof has a heavy chain that comprises framework sequences between the CDRs, wherein said framework sequences are substantially identical or substantially similar to the framework sequences between the CDRs in the heavy chain sequence below (in which the CDRs are shown in bold and underlined, and the framework sequences are shown in italics)
As used herein, the framework amino acid sequences between the CDRs of an antibody are substantially identical or substantially similar to the framework amino acid sequences between the CDRs of another antibody if they have at least 70%, 80%, 90% or at least 95% similarity or identity. The similar or identical amino acids may be contiguous or non-contiguous.
The framework sequences may contain one or more amino acid substitutions, insertions and/or deletions. Amino acid substitutions may be conservative, by which it is meant the substituted amino acid has similar chemical properties to the original amino acid. A skilled person would understand which amino acids share similar chemical properties. For example, the following groups of amino acids share similar chemical properties such as size, charge and polarity: Group 1 Ala, Ser, Thr, Pro, Gly; Group 2 Asp, Asn, Glu, Gln; Group 3 His, Arg, Lys; Group 4 Met, Leu, Ile, Val, Cys; Group 5 Phe Thy Trp.
A program such as the CLUSTAL program to can be used to compare amino acid sequences. This program compares amino acid sequences and finds the optimal alignment by inserting spaces in either sequence as appropriate. It is possible to calculate amino acid identity or similarity (identity plus conservation of amino acid type) for an optimal alignment. A program like BLASTx will align the longest stretch of similar sequences and assign a value to the fit. It is thus possible to obtain a comparison where several regions of similarity are found, each having a different score. Both types of analysis are contemplated in the present invention. Identity or similarity is preferably calculated over the entire length of the framework sequences.
In certain preferred embodiments, the monoclonal antibody or fragment thereof may comprise the light chain variable region sequence:
and/or the heavy chain variable region sequence:
(CDRs bold and underlined; Framework sequences in italics)
The invention includes a method of immunoassay for detecting in a sample a C-terminal epitope of the α3 chain of collagen type VI, wherein said method comprises contacting a sample comprising said C-terminal epitope of the α3 chain of collagen type VI with an immunological binding partner as described above, and determining the amount of binding of said immunological binding partner.
Preferably said C-terminal epitope is comprised in a C-terminal amino acid sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1).
Said method may be used to quantify the amount of said C-terminal epitope of the α3 chain of collagen type VI in a biofluid.
Said biofluid may be for instance serum, plasma, urine or amniotic fluid.
Said immunoassay may be a competition assay or a sandwich assay such as a radioimmunoassay or an enzyme-linked immunosorbent assay (ELISA).
Such a method may further comprise correlating the quantity of said C-terminal epitope of the α3 chain of collagen type VI determined by said method with standard normal values of said C-terminal epitope of the α3 chain of collagen type VI to evaluate a change thereof from normal levels.
The invention includes a method of investigating the rate of formation of extracellular matrix comprising conducting an assay by a method as described above to obtain a measure of the level in a biofluid sample of collagen type VI α3 fragments comprising an epitope comprised in a C-terminal amino acid sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1).
Such a method may further comprise forming an index comparing the said measured level of collagen type VI α3 fragments with a measured level in the same sample of a biomarker of the degradation of collagen type VI. Such a biomarker of degradation may be a fragment of MMP degraded collagen type VI. Such an assay may be based on antibody reactivity to the N-terminal sequence YRGPEGPQGP . . . (SEQ ID No: 13) as described in Veidal 2011 and in WO2010/115749.
We have now investigated the modulation of serological collagen peptide biomarkers in response to long-term unloading in the form of bed rest and subsequent reloading and we have similarly studied these biomarkers in COPD exacerbation events.
In the bed rest investigation, subjects were immobilized through bed rest with or without a vibration device countermeasure for 8 weeks followed by remobilization through habitual physical activity. Both groups lost muscle mass and strength during the immobilization, with slightly more lost in the control group than in the rested group. Both groups regained muscle mass and strength during remobilization.
During immobilization, biomarkers of collagen type III pro-peptide (PRO-C3) and the collagen type VI biomarker of the invention (PRO-C6) display somewhat similar temporal patterns. While that of the invention initially drops slightly following the onset of immobilization, both PRO-C3 and PRO-C6 eventually increase with immobilization over time. At the onset of remobilization, a slight initial drop can again be observed followed by an increase that on the part of PRO-C6 was bigger in the CTRL than in the RVE group, followed by a return to baseline in both biomarkers.
The C6M biomarker is essentially unresponsive to bed rest unloading, but spikes briefly in response to reloading, with no significant difference between groups.
PRO-C6 can therefore be seen to be a biomarker of remodelling associated with changes in physical activity and changes in LBM (lean body mass). Low PRO-C6 at baseline is associated with a phenotype that is more prone to changes in LBM, both gain and loss. Thus, an assay for this sequence may be used to identify amongst individuals subjected to involuntary immobilization, e.g. from hospitalization, those who are at increased risk of muscle loss and thus qualify treatment decisions to counter LBM loss.
Furthermore, the assay may be used to monitor the rate of connective tissue remodeling, particularly muscle turnover, and to give information on the effectiveness of candidate treatments for modulating that rate.
This biomarker may be used to assist in the diagnosis of COPD exacerbation events, or to provide prognosis as to which patients are likely to suffer more rapid deterioration of their condition, which may make them more relevant patients to take into a clinical trial.
This biomarker may also be used to predict a response to insulin sensitizers, such as the class of compounds thiazolidinediones (e.g. balaglitazone or pioglitazone). This permits identification and monitoring of patients who will respond optimally to an insulin sensitizer, which improves the benefit to risk ratio of PPARγ agonists in the treatment of type 2 diabetes and/or non-alcoholic steatohepatitis (NASH). In this regard, the invention also provides a method for identifying a subject suitable for treatment with an insulin sensitizer, the method comprising the steps of:
- i) quantifying the amount of a C-terminal epitope of the C5 domain of the α3 chain of collagen type VI in a biofluid obtained from a subject using the Pro-C6 assay method of the invention; and
- ii) correlating an elevated value determined by step i) with a subject that is suitable for treatment with an insulin sensitizer.
A further aspect of the invention provides an assay kit for determining the quantity of a C-terminal epitope of the C5 domain of the α3 chain of collagen Type VI, preferably one comprised in a C-terminal amino acid sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1) in a biological sample, comprising an immunological binding partner of the invention and at least one of:
- a streptavidin coated 96 well plate
- a peptide which is reactive with said antibody, which may be a biotinylated peptide Biotin-L-KPGVISVMGT-COOH (SEQ ID. NO:4), wherein L is an optional linker
- an optionally biotinylated secondary antibody for use in a sandwich immunoassay
- a calibrator peptide comprising the C-terminal sequence . . . KPGVISVMGT-COOH (SEQ ID. NO:1)
- an antibody HRP labeling kit
- an antibody radiolabeling kit
- an assay visualization kit.
The term ‘immunological binding partner’ as used herein includes polyclonal and monoclonal antibodies and also specific binding fragments of antibodies such as Fab or F(ab′)2. Thus, said immunological binding partner may be a monoclonal antibody or a fragment of a monoclonal antibody having specific binding affinity.
We used the last 10 amino acids of the type VI collagen α3 chain (3168‘KPGVISVMGT’3177 (SEQ ID. NO:1)) as an immunogenic peptide to generate specific epitope monoclonal antibodies. The methods used for monoclonal antibody development were as previously described (Barascuk).
Briefly, 4-6-week-old Balb/C mice were immunized subcutaneously with 200 μl emulsified antigen with 60 μg of the immunogenic peptide. Consecutive immunizations were performed at 2-week intervals in Freund'"'"'s incomplete adjuvant, until stable sera titer levels were reached, and the mice were bled from the 2nd immunization on. At each bleeding, the serum titer was detected and the mouse with highest antiserum titer and the best native reactivity was selected for fusion. The selected mouse was rested for 1 month followed by intravenous boosting with 50 μg of immunogenic peptide in 100 μl 0.9% sodium chloride solution 3 days before isolation of the spleen for cell fusion.
The fusion procedure has been described elsewhere (Gefter). Briefly, mouse spleen cells were fused with SP2/0 myeloma fusion partner cells. The fusion cells were raised in 96-well plates and incubated in the CO2-incubator. Here standard limited dilution was used to promote monoclonal growth. Cell lines specific to the selection peptide and without cross-reactivity to neither elongated peptide (KPGVISVMGTA (SEQ ID. NO:2), Chinese Peptide Company, China) nor truncated peptide (KPGVISVMG (SEQ ID. NO:3), American Peptide Company, USA) were selected and sub-cloned. At last the antibodies were purified using an IgG column.
The antibodies generated were sequenced and the CDRs determined.
The sequence of the chains are as follows (CDRs underlined and in bold):
ELISA-plates used for the assay development were Streptavidin-coated from Roche (cat.: 11940279). All ELISA plates were analyzed with the ELISA reader from Molecular Devices, SpectraMax M, (CA, USA). We labeled the selected monoclonal antibody with horseradish peroxidase (HRP) using the Lightning link HRP labeling kit according to the instructions of the manufacturer (Innovabioscience, Babraham, Cambridge, UK). A 96-well streptavidin plate was coated with biotinylated synthetic peptide biotin-KPGVISVMGT (SEQ ID. NO:4) (Chinese Peptide Company, China) dissolved in coating buffer (40 mM Na2HPO4, 7 mM KH2PO4, 137 mM NaCl, 2.7 mM KCl, 0.1% Tween 20, 1% BSA, pH 7.4) and incubated 30 minutes at 20° C. 20 μL of standard peptide or samples diluted in incubation buffer (40 mM Na2HPO4, 7 mM KH2PO4, 137 mM NaCl, 2.7 mM KCl, 0.1% Tween 20, 1% BSA, 5% Liquid II, pH 7.4) were added to appropriate wells, followed by 100 μL of HRP conjugated monoclonal antibody 10A3, and incubated 21 hour at 4° C. Finally, 100 μL tetramethylbenzinidine (TMB) (Kem-En-Tec cat. 438OH) was added and the plate was incubated 15 minutes at 20° C. in the dark. All the above incubation steps included shaking at 300 rpm. After each incubation step the plate was washed five times in washing buffer (20 mM Tris, 50 mM NaCl). The TMB reaction was stopped by adding 100 μL of stopping solution (1% H2SO4) and measured at 450 nm with 650 nm as the reference.
The lowest limit of detection (LLOD) was determined from 21 zero samples (i.e. buffer) and calculated as the mean+3× standard deviation. The intra-assay variation and inter-assay variations were determined by 12 independent runs of 8 QC samples with each run consisting of double determinations of the samples. Dilution recovery was determined in 4 serum samples and 4 heparin plasma samples and was calculated as a percentage of recovery of diluted samples from the 100% sample.
The level of C-terminal of α3 chain is expected to reflect the level of newly formed mature type VI collagen. In order to investigate the synthesis of type VI collagen, we developed the Pro-C6 ELISA kit described above targeting the C-terminal of α3 chain. In addition, type VI collagen is also a substrate of MMPs (Veidal 2011). Previous studies showed that both MMP-2 and MMP-9 are relevant to muscle atrophy (Reznick 2003 and Giannelli 2005). Therefore, type VI collagen degradation fragments generated by MMP-2 and MMP-9 are of interest in such a process.
In this study, we measured three biomarkers Pro-C6 (measuring the C-terminal α3(VI) chain) and C6M (measuring type VI collagen fragment degraded by MMP-2 and MMP-9)(Veidal 2011), and Pro-C3 (measuring the true synthesis of type III collagen) (Nielsen), which directly measure the turnover of type III and VI collagen in the Berlin bed rest study—using bed rest immobilization and remobilization as a human model of muscle atrophy and hypertrophy.
The Berlin bed rest study has been described elsewhere (Rittweger 2006 and Belavy 2009). Briefly, 20 healthy young men were recruited and underwent a strict 8-week bed rest study. The 20 young men were then randomly divided into two groups. The resistive vibration exercise group (RVE) group was assigned to resistive vibration exercise 11 times per week. The resistive vibration exercises were performed by a vibration exercise apparatus at the end of the beds and pulling the subject towards the vibration plate with waist and shoulder straps and handles for the subjects to pull themselves towards the plate. The control group (CTRL) was not allowed to perform any exercise during the 8-week bed rest. Serum samples were obtained 2 days before the study (BDC-2), in the bed rest period (BR+) and in the following recovery period (R+). The serum samples were stored at −80° C. until further measurement. The muscle mass of both groups were assessed by MRI and DXA during the three periods.
The protocols of Pro-C3 and C6M assays have been described elsewhere (Nielsen 2013 and Kuo 1997). The Pro-C3 assay measures levels of a pro-peptide fragment of collagen type III. The C6M assay measures MMP degradation fragments of mature collagen type VI. Briefly, in Pro-C3 assay, a 96-well streptavidin plate was coated with biotinylated synthetic peptide and incubated 30 minutes at 20° C. 20 μL of standard peptide or 1:2 diluted serum samples were added to appropriate wells, followed by 100 μL of HRP conjugated monoclonal antibody NB61N-62, and incubated 20 hour at 4° C. Finally, 100 μL TMB was added and the plate was incubated 15 minutes at 20° C. in the dark. The TMB reaction was stopped by adding 100 μL of stopping solution (1% H2SO4) and measured at 450 nm with 650 nm as the reference. In C6M assay, biotinylated synthetic peptide is coated to a 96-well streptavidin plate. 20 μL of standard peptide or 1:2 diluted serum samples are added, followed by 100 μL of HRP conjugated monoclonal antibody, and incubated 1 hour at 20° C. The plate was read after the development by TMB.
The chosen antibody 10A3 specifically recognized the last 10 amino acids of C-terminal COL6A3 3168′KPGVISVMGT′3177 (SEQ ID. NO:1), but did not recognize elongated peptide KPGVISVMGTA nor truncated peptide KPGVISVMG (
The measurement range of Pro-C6 competitive ELISA was determined by LLOD and ULOD, providing the range from 0.15 ng/ml to 58.39 ng/ml. The inter- and intra-assay variability is 15.2% and 4.8%, respectively. The dilution recovery in human serum and heparin plasma were both within 100±20% (Table 1). The correlation between human serum and each of heparin plasma, citrate plasma and EDTA plasma was relatively high (
Samples were diluted in serial 2-fold dilution steps concentration was measured in these serial dilutions. Dilution recovery was obtained by multiplying measured concentrations with the dilution factor and expressed as percent of the concentration of the undiluted (starting) sample. The table shows that the signal dilutes linearly and stays within +/−20% within and 8-fold dilution range.
The levels of the three biomarkers referred to above measured in the Berlin Bed rest study (BBR) are seen in
As seen in
When we compared individual biomarker levels of PRO-C3 with LBM and changes therein, we found that individual levels of PRO-C3 correlated significantly with LBM at baseline (R2=0.2869, R=0.536, ρ=0.0149). Furthermore, we found that the level of biomarker at its peak at BR47, correlated significantly with the amount of LBM lost during immobilization (R2=0.2056, R=0.453, ρ=0.0447).
The PRO-C6 biomarker changed over time during the course of immobilization (significant time effect, p<0.0001) in the form of an increase after approximately one week of immobilization, reaching a peak level approximately 30% higher than baseline during the last couple of weeks of immobilization (being significantly higher than baseline from BR19 to R28, peaking at BR47, ρ=0.0002). There were no between-group differences during the immobilization period (no significant treatment effects or treatment*time interactions).
During re-mobilization, both time and time*treatment interaction effects manifested. This was in the form of an increase that peaked one week into remobilization (an 20% increase relative to the last day of immobilization, BR56, ρ=0.011), followed by a gradual return to baseline values. The interaction effect was not manifested in any post hoc tests, owing to high variation at the R7 time point.
When we compared individual biomarker levels of PRO-C6 with LBM and changes therein, we found that the level of PRO-C6 was not related to LBM at all, but positively related to change in LBM during immobilization (R2=0.2794, R=0.529, ρ=0.0166) meaning that higher levels of PRO-C6 were associated with less loss of LBM. We also found that PRO-C6 was negatively related to the amount of LBM (re)gained during remobilization (R2=0.3365, R=0.580, ρ=0.0073), meaning that higher levels were associated with less (re)gain of LBM during remobilization.
The C6M biomarker was essentially unaffected by immobilization (no time effect in the immobilization time period), but increased briefly 30-40% at the beginning of remobilization (a significant time effect at p<0.0001 during the immobilization period). There were no treatment effects during immobilization and although it may appear as if the increase in the C6M signal is bigger in the CTRL group than in the RVE group, this did not reach significance (the time*treatment interaction did not reach significance and thus no post hoc test was made). There were no differences between the groups.
When we compared individual biomarker levels of PRO-C6 with LBM and changes therein, we found that the level of PRO-C6 was not related to LBM at all, but positively related to muscle loss during immobilization (R2=0.2794, R=0.529, ρ=0.0166) and negative related to the amount of muscle (re)gained during remobilization (R2=0.3365, R=0.580, ρ=0.0073).
PRO-C6 is seen to be a biomarker of remodelling associated with changes in physical activity and changes in LBM. Low PRO-C6 at baseline is associated with a phenotype that is more prone to changes in LBM, both gain and loss.
Patients presenting with a hospital admission deemed by a medical consultant to be a COPD exacerbation during 2011 and 2012 were recruited within 24 hours of admission. Blood samples were collected at time of exacerbation and at recovery: a 4 week follow-up visit performed a median of 30 (IQR 28-34) days after admission. At follow-up visit, the patients underwent standard post-bronchodilator spirometry, and performed a six minute walking distance (6MWD). Patient-reported measures included assessments of dyspnoea, using the Medical Research Council (MRC) dyspnoea scale, at follow-up visit, and smoking history.
The inclusion criterion was a clinical diagnosis of acute COPD exacerbation at hospital admission made by a consultant physician. A physician diagnosis or radiological evidence of pneumonia was an exclusion criterion. The study comprised 69 patients with paired samples and with airflow obstruction (ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC) of <0.7) confirmed at follow-up visits.
ECM remodelling biomarkers:
Serum and heparin plasma samples were stored at −80° C. until analyzed. C3M, C4M, Pro-C3, P4NP 7S, ELM7, and EL-NE, were measured in serum, while C6M, Pro-C6, and VCANM were measured in heparin plasma. An overview of the assays used in this study to assess extracellular matrix remodelling appears in Table 3.
The reference level was provided by the manufacturer (Nordic Bioscience) and refers to the biomarker level of a healthy population in the relevant matrix, i.e. serum (C3M, C4M, Pro-C3, P4NP 7S, ELM7, EL-NE) or heparin plasma (C6M, Pro-C6, VCANM). SD, standard deviation; MMP, matrix metalloproteinase.
Patient demographics and clinical characteristics are summarised in Table 4. Patients were mostly men (71%) and ex-smokers (55%). They were hospitalised for a median [IQR] of 3 [2-6] days, and follow-up visit was performed at 30 [28-34] days after admission.
Variables are listed as mean (standard deviation) unless otherwise stated. IQR, interquartile range; BMI, body mass index; FEV1, forced expiratory volume in one second; FVC, forced vital capacity; 6MWD, 6 minute walking distance; MRC, Medical Research Council.
Circulating levels of protein fragments released at time of exacerbation and at a clinically stable disease period at 30-days follow-up are presented in Table 5.
Results are presented as geometric mean [95% confidence interval] and corresponding P values comparing circulating levels of protein fragments at time of exacerbation and follow-up.
Degradation fragments of collagen type III (C3M), collagen type IV (C4M), collagen type VI (C6M), and elastin (ELM7 and EL-NE) were significantly elevated at exacerbation compared to follow-up (all P<0.0001;
The balance between degradation and formation of collagens was investigated by calculating the ratio between fragments of degradation and formation for collagen types III, IV, and VI (
At follow-up, BMI was negatively associated with C3M (ρ=−0.271, P=0.029), Pro-C3 (ρ=−0.357, P=0.010), and Pro-C6 (ρ=−0.338, P=0.017). Age was negatively associated with C6M (ρ=−0.249, P=0.039) and Pro-C6 (ρ=−0.310, P=0.026). No associations were seen with smoking pack years, MRC score, length of hospitalisation, sputum production, or white blood cell counts. Pro-C3 levels were positively associated with FEV1% of predicted value (% pred) and FVC % pred, and these remained significant after correcting for age, gender, BMI, smoking pack years, and smoking status (Table 4). 6MWD was negatively associated with C3M, C4M, C6M, and P4NP 7S (Table 4). Following correction for age, gender, BMI, smoking pack years, and smoking status, associations with C3M and C6M remained significant, while C4M was borderline significant and P4NP 7S was non-significant (Table 6).
Results are presented as Spearman correlation coefficients (p) for each marker. In brackets are given multivariate correlation coefficients for markers showing significant p. The multivariate linear regression analysis included age, gender, BMI, smoking pack years, and smoking status as additional explanatory variables. Significance levels: £P<0.07, *P<0.05, **P<0.01. FEV1, forced expiratory volume in one second; % pred, percentage of predicted value; FVC, forced vital capacity; 6MWD, 6 minutes walking distance.
All assays employed a monoclonal antibody directed against either a protein fragment produced by MMP cleavage during degradation or formation or an internal protein sequence. An overview of the assays used in this study and their technical specifications is given in Table 3. All samples were measured within the quantification range of each assay and any sample with values below the lower limit of detection (LLOD) was assigned the value of LLOD.
The above results demonstrate that ECM remodelling, assessed systemically by biomarkers of protein remodelling fragments, is accelerated during an exacerbation of COPD where disease activity is high.
Treatment of diabetic patients with full agonists of peroxisome proliferator-activated receptor gamma (PPARγ) improves insulin sensitivity, but is associated with weight gain, heart failure, peripheral oedema, and bone loss. Endotrophin, the C-terminal fragment of the α3 chain of procollagen type VI (also called Pro-C6), is involved in both adipose tissue matrix remodeling and metabolic control. We established a serum assay for endotrophin to assess if this novel adipokine could identify type 2 diabetes (DM2) patients who respond optimally to PPARγ agonists, improving the risk to benefit ratio.
Testing Strategies) study was a phase III, randomized, double-blind, parallel-group, placebo and active comparator-controlled clinical study to determine the efficacy and safety of six months'"'"' treatment of balaglitazone or pioglitazone in subjects with type 2 diabetes on stable insulin therapy. The baseline demographics, CONSORT diagram as well as efficacy and safety data have previously been published (Henriksen, 2011). In the current study we used the per protocol population of the BALLETS study, which consisted of 299 subjects spread evenly over four groups (placebo, two doses of balaglitazone, and one dose of piogliatazone) as previously described (Henriksen, 2011), all with baseline and up to six follow-up parameters related to blood sugar control and Pro-C6 determinations under therapy.
The analysis included subjects from the per protocol population having a baseline measurement of serum Pro-C6. Subjects were grouped into one of three tertiles based on their baseline Pro-C6 value. Tertile 1 included subjects with baseline serum Pro-C6 of 6.2 ng/mL or below; tertile 2 had baseline serum Pro-C6 of 6.3 ng/mL to 7.7 ng/mL, and tertile 3 had baseline serum Pro-C6 of 7.8 ng/mL or above. Baseline characteristics between the three subgroups were compared by analysis of variance (ANOVA), and comparison of the proportion of genders in each tertile was compared by Fisher'"'"'s exact test.
Spearman'"'"'s ranked correlation was conducted on baseline levels of serum Pro-C6, fasting serum glucose (FSG), blood HbA1c, body mass index (BMI), and the derived parameters of insulin resistance (HOMA-IR) and fatty liver index (FLI). The HOMA-IR was calculated according to the homeostatis model assessment including serum glucose and insulin (Feigh, 2011) and FLI was calculated (as described by Bedogni et al, 2006) using the equation:
Changes from baseline in FSG, blood HbA1c, and serum Pro-C6 were studied as a function of time and treatment in each of the three tertiles. The least squares means (LS Means) and standard error were estimated from a mixed-effect repeated measure model with the change from baseline as the dependent variable; baseline level, visit (after 12 weeks on treatment) and end of treatment (after 26 weeks), and the baseline level vs visit and end of treatment vs visit interaction as fixed effects, and an unstructured covariance structure for subject.
For each subject the mean change from baseline was calculated as area under the curve by the trapezoidal method, and the LS means and standard error were estimated from an analysis of covariance model (ANCOVA) with the mean change as the dependent variable, the baseline level as the covariate, and treatments as fixed effects. Each tertile within each of the active treatment groups was compared with the placebo group with the level of significance adjusted for multiple comparisons by the Dunnett method. Assessment of whether mean change from baseline was different from 0 was based on the standard error of the LS means.
All statistical calculations were performed using the SAS software package. This study is registered with ClinicalTrials.gov identifier NCT00515632.
Efficacy of treatment as assessed by metabolic parameters and safety data in the BALLET trial have been published previously (Henriksen, 2011). The baseline correlations of endotrophin to parameters associated with the metabolic syndrome are presented in Table 7.
Endotrophin levels were significantly correlated to HOMA-IR, FLI, triglycerides, and BMI, but not to FSG and HbA1c, supporting that endotrophin is indeed an adipokine, related to adipocyte function, fat mass, and some aspects of insulin sensitivity. Endotrophin levels were not correlated to cholesterol levels or liver enzymes.
At the end of the six month treatment period, in the placebo group, the correlations between endotrophin and these metabolic parameters were maintained (Table 8, 9A). However, in those treated with either PPARγ agonist, the correlation between HOMA-IR and endotrophin was eliminated, while the correlation between endotrophin and BMI or FLI persisted and even showed a trend towards becoming stronger (Table 9B-9C).
Body weight and BMI were higher in the upper tertiles in all four treatment groups than in the lower tertile (Table 1). No differences were seen in glucose homeostasis between treatment groups.
Absolute levels of FSG and HbA1c decreased in all three treatment arms as compared to placebo, but only in the two upper tertiles of endotrophin as compared to the baseline set as zero during the study (
When assessing the mean absolute change over time from baseline to end of treatment (week 26) in FSG (
The effect on serum endotrophin as a function of treatment and time (to study midpoint and end of treatment), expressed as percent change relative to baseline, is shown in
Lower leg edema, when measured as volume increase due to water displacement, was correlated with baseline serum endotrophin tertiles. Glitazone therapy led to increased lower leg volume in the lower and middle tertile, while there were no differences between treatment and placebo groups in the upper tertile (
Serum endotrophin (Pro-C6) was predictive of a response to the insulin sensitizers, pioglitazone and balaglitazone, in patients with type 2 diabetes. Thus, patients with Pro-C6 serum levels in the two upper tertiles were 4 times more likely to have a treatment response when compared to patients in the lower tertile. As the glitazones are associated with safety concerns such as non-fatal heart failure and bone fractures, identifying the optimal responders who will gain the most treatment benefit with the fewest AEs is crucial for the continued use of these drugs, which still are considered highly effective insulin sensitizers. In direct agreement, patients in the upper tertiles of baseline Pro-C6 who responded with a decrease of FPG and HbA1c tertile developed no increase in lower leg oedema, one of the major AEs with glitazone treatment. These efficacy and safety data combined are highly relevant for an improved benefit to side effect prediction for patients treated with glitazones; this should also apply when their repurposing for other indications, especially the treatment of non-alcoholic steatohepatitis (NASH) is considered.
Endotrophin mediated metabolic dysfunction in obesity is likely induced via induction of a pro-inflammatory state and fibrosis in adipose tissue coupled with a reduction of energy expenditure. Accordingly, its suppression improved insulin sensitivity and attenuated adipose tissue inflammation (Sun, 2014), which correlates well with our findings that elevated serum endotrophin levels are indicative of a response to PPARγ agonists. Furthermore, mRNA levels of the endotrophin precursor, procollagen α3(VI), are upregulated in obese adipose tissue, again paralleling adipose tissue inflammation and fibrosis, supporting an important role of procollagen type VI as a modulator of adipocytes and adipose tissue in general (Dankel, 2014). The ECM and especially procollagen type VI and endotrophin may be of particular relevance in fatty liver disease and its severe expression, NASH, a metabolic-fibrotic disorder of the liver that shows at least a partial overlap with type 2 diabetes. Accordingly, we expect that this novel biomarker will also assist in the diagnosis and management of NASH patients, where insulin sensitizers may be beneficial for subpopulations, both for the treatment of insulin resistance and liver fibrosis. Here, the ECM, in particular collagens/collagen type VI, and their functional role in transition of fatty liver to overt fibrotic NASH needs to be further investigated. In agreement, in the current study, we observed a strong correlation to serum triglycerides and the FLI index that correlates with NASH inflammatory activity and predicts more severe liver fibrosis (Bedogni, 2006). In support of a role for type VI collagen in NASH-related fibrosis, prior studies demonstrated its prominent expression in areas of active scar formation (Burt, 1990; Griffiths, 1992) and elevated serum levels of the collagen VI core structure (which lacks the endotrophin domain) have been shown to be associated with advanced liver fibrosis in rodents (Veidal, 2011) and patients (Lebensztejn, 2006; Stickel, 2001), and with elevated portal pressure (Leeming, 2013). The expression of procollagen α3(VI) is regulated by PPARγ which is in direct alignment with our findings. In fact, procollagen α3(VI) mRNA is suppressed by PPARγ, as demonstrated by an increase in its mRNA in adipocyte cultures treated with a siRNA against PPARγ and by a decrease in its transcripts in subcutaneous adipose tissue of patients with type 2 diabetes treated with the PPARγ agonist pioglitazone, especially in patients with high baseline tissue levels of procollagen α3(VI) mRNA. These data may in part explain the change in correlations, from baseline to the end of treatment, between endotrophin/Pro-C6 serum levels and HbA1c or HOMA-IR, in particular the lack of a correlation between endotrophin and the metabolic parameters following glitazone treatment. Thus the expression of the endotrophin precursor (as measured by procollagen α3(VI) mRNA) in peripheral adipose tissue was not dependent on BMI or total fat mass in severely obese, insulin-resistant patients. In another clinical study tissue endotrophin levels in obese subjects correlated with chronic inflammation and systemic insulin resistance (Park, 2013). Further proof of the direct link between procollagen VI, adipose tissue fibrosis and impaired glucose sensitivity is provided by a study in ob/ob mice (that lack a functional leptin gene) in the absence of collagen VI in white adipose tissue. These mice had a significantly improved insulin sensitivity in the absence of adipose tissue fibrosis and inflammation (Khan, 2009). On a first view these data appear to contradict the strong correlation between serum endotrophin and BMI, FLI, and HOMA-IR, as found in our study. However, the presence of procollagen VI is only a necessary but not a sufficient precondition for the proteolytic generation of the adipokine endotrophin. Therefore, it will be of interest to identify the endotrophin generating protease and to characterize its upstream regulation. In addition, leptin induced the expression of type VI procollagen, which further supports a link between leptin resistance, metabolic dysfunction, and endotrophin.
As discussed before, the ECM has until now mostly been considered a passive scaffold. Type VI collagen has mostly been recognized through mutations in the genes COL6A1, COL6A2, and COL6A3 that encode its three constituent chains, which cause muscle disorders such as Bethlem myopathy, Ullrich congenital muscular dystrophy, limb-girdle muscular dystrophy, and autosomal recessive myosclerosis. (Lampe, 2005; Bonaldo, 1998; Bushby, 2014). This provides an interesting link to metabolic dysfunction since muscle represents an important regulator of insulin resistance. Therefore, all available evidence strongly suggests that collagen type VI is more than a passive ECM component, but an important mediator of adipose (and liver) metabolic dysfunction related to insulin resistance, type 2 diabetes, and NASH.
In conclusion, circulating endotrophin which prominently derives from adipocytes and adipose tissue is elevated in relation to insulin resistance and predictive of the response to insulin sensitizers. This permits identification and monitoring of patients who will respond optimally to an insulin sensitizer, which improves the benefit to risk ratio of PPARγ agonists in the treatment of type 2 diabetes and likely NASH.
In this specification, unless expressly otherwise indicated, the word ‘or’ is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator ‘exclusive or’ which requires that only one of the conditions is met. The word ‘comprising’ is used in the sense of ‘including’ rather than in to mean ‘consisting of’. All prior teachings acknowledged above are hereby incorporated by reference. No acknowledgement of any prior published document herein should be taken to be an admission or representation that the teaching thereof was common general knowledge in Australia or elsewhere at the date hereof.
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