|Ahead of print publication
Serum fatty acid-binding protein 3 levels differentiate active from inactive myositis and correlate with response to therapy
Latika Gupta1, Sanjukta Majumder1, Amita Aggarwal1, Ramnath Misra2, Able Lawrence1
1 Department of Clinical Immunology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
2 Department of Clinical Immunology and Rheumatology, Kalinga Institute of Medical Sciences, KIIT University, Bhubaneswar, Odisha, India
|Date of Submission||26-Mar-2020|
|Date of Acceptance||08-Jun-2020|
Department of Clinical Immunology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow - 226 014, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Background: Delay in the diagnosis of idiopathic inflammatory myopathies (IIMs) and resultant muscle wasting leads to a setting, wherein conventional biomarkers fail to identify inflammation amid damage. Fatty acid-binding protein 3 (FABP3) has a selective location and function lending unique potential as a specific biomarker in IIM.
Methods: Patients with IIM (ACR/EULAR criteria) prospectively evaluated for clinical features and laboratory data were screened to identify cases without ongoing infection, pregnancy, and renal disease. Clinical data and sera of patients and healthy controls were retrieved, and case details supplanted with standard outcome measures. For the inception cohort, 6-month follow-up sera were used for comparison of FABP3 using ELISA. Nonparametric tests were used for analysis and results expressed as median and interquartile range.
Results: One hundred and thirty two IIM patients (M:F 1:3.1) of age 38 (24.5–46.0) years and 0.9 (2.3–5.1) year long disease were compared with ten healthy controls. FABP3 levels were higher in active (5.73 vs. 2.91 ng/ml, P = 0.0351) disease, more so in early IIM (n = 16, 21, 3.84 vs. 0.00 ng/ml, P = 0.002). Levels fell with treatment in responders (n = 7, 14.5–7.5 ng/dl, P = 0.03) but not in nonresponders. A serum FABP3 ≥ 4.066 had a high specificity (80.6%) to distinguish active from inactive myositis, albeit lower than conventional biomarkers.
Conclusion: Serum FABP3 is elevated in active IIM, especially early disease, and decreases with treatment among responders. FABP3 has a favorable specificity but insufficient sensitivity, limiting role as a stand-alone biomarker. It might be useful in early IIM, without renal or cardiac involvement, pending further validation.
Keywords: Biomarker, India, metabolism, myositis, oxidation
|How to cite this URL:|
Gupta L, Majumder S, Aggarwal A, Misra R, Lawrence A. Serum fatty acid-binding protein 3 levels differentiate active from inactive myositis and correlate with response to therapy. Indian J Rheumatol [Epub ahead of print] [cited 2020 Oct 30]. Available from: https://www.indianjrheumatol.com/preprintarticle.asp?id=290268
| Introduction|| |
The idiopathic inflammatory myopathies (IIMs) incur significant morbidity as well as mortality. A delayed diagnosis is met with wasted muscle mass, wherein the conventional biomarkers such as muscle enzymes cannot identify ongoing inflammation amid damage. Moreover, muscle enzymes (i.e., creatine phosphokinase, serum glutamate oxaloacetate transaminase [SGOT], serum glutamate pyruvate transaminase, aldolase, and lactate dehydrogenase [LDH]) are not sufficiently sensitive, and correlations with disease activity are modest.
Thus, the ongoing quest for new biomarkers has led to the identification of various molecules using proteomics in animal models of muscle diseases. The fatty acid-binding protein 3 (FABP3) is one such protein that is preferentially expressed in slow-twitch skeletal muscle fibers, which are preferentially affected in IIM. FABP3 is a small (14–15 kDa) cytosolic protein involved in fatty acid transport to the mitochondria. Nonimmune mechanisms, including a switch to anaerobic metabolism, are the key inciting event for muscle weakness in IIM, even before the appearance of inflammatory infiltrates. Moreover, damage in IIM triggers the regeneration of Type I fibers, which are likely to overexpress FABP3. On the other hand, a failure of regeneration in chronic burnt-out muscle disease would potentially lead to the replacement of muscle with fibrofatty tissue, which might not express FABP3.
Therefore, FABP3 has the potential to be a sensitive biomarker of ongoing muscle disease, including identification of cases responsive to therapy versus burnt-out disease or inclusion body myositis. The FABPs usually are small enough to be filtered by renal glomerulus, and their levels increased in patients with chronic kidney disease, though this also sets them apart as potential urinary biomarkers with the advantage of noninvasive sampling.
Besides, Zhang et al. previously demonstrated an excellent correlation of serum FABP3 with muscle strength in 24 adults with active IIM. Thus, we validated the utility of FABP3 in a large cohort of children and adults with active as well as inactive IIM, followed by a longitudinal assessment after treatment. Further, the difference in levels in early and long-standing disease was explored.
| Methods|| |
Patients with IIM (ACR/EULAR criteria) prospectively evaluated for clinical features and laboratory data (including autoantibodies) in an institutional review board certified study (2017-41-IP-76) were screened to identify cases without an active ongoing infection, pregnancy, acute renal dysfunction, or chronic kidney disease. Clinical data and sera of patients and healthy controls were retrieved from the database and biobank, respectively.,, Case details were supplanted with standard outcome measures, as described by the International Myositis Assessment and Clinical Studies Group. Myositis disease activity assessment tool activity score ≥1 defined active disease.
For patients with myositis within 6 months of the first enrollment into the study (called the inception cohort), sera obtained at 6 months of therapy were also retrieved. A disease duration of ≤1 year was classified as early IIM. A polyphasic disease course was defined as previously described.
FABP3 levels were estimated using ELISA (R&D Systems, MN, USA). Myositis-specific and myositis-associated antibodies (MSAs/MAAs) were identified by the line immunoblot assay (G4 panel, Euro-Immune, Lubeck, Germany). Statistical analysis was done using GraphPad Prism© version 7.0 for Mac (GraphPad Software, SanDeigo, CA, USA). The data are presented as median with interquartile range, and nonparametric tests were used for analysis. P < 0.05 is deemed as statistically significant.
| Results|| |
One hundred and thirty-two (100 women and 32 men) IIM patients (12 juvenile dermatomyositis [jDM], 55 DM, 20 polymyositis [PM], 21 overlap [OM], and 24 antisynthetase syndrome [ASS]) of age 38 (24.5–46.0) years and disease duration 0.9 (2.3–5.1) years were compared with ten healthy controls. The MSA and MAAs are delineated in [Figure 1]a.
|Figure 1: (a) Myositis-specific and myositis-associated antibodies in the cohort (n = 128). (b) Serum fatty acid-binding protein 3 levels in active and inactive disease as defined by myositis disease activity assessment tool ≥1. (c) Serum fatty acid-binding protein 3 levels in early disease. (d) Predictive potential of fatty acid-binding protein 3 and conventional muscle biomarkers to distinguish active from inactive disease. (e) Fall in serum fatty acid-binding protein 3 levels with response to therapy|
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Serum FABP3 levels are similar in adults with IIM and children with jDM as well as healthy controls.
The serum FABP3 levels were comparable in IIM and healthy controls. The FABP3 values did not differ between adults (with PM/DM) and children (with jDM, P = 0.90).
Serum FABP3 levels are higher in active than an inactive disease.
FABP3 levels were higher in active (n = 26, 5.73 ng/ml) than inactive [n = 105, 2.9 ng/ml, P = 0.035, [Figure 1]b IIM, more so in early [Figure 1]c, n = 16 and 21, 3.84 vs. 0.00, P = 0.02].
Serum levels ≥4.07 ng/ml were poorly (38.5%) sensitive but fairly (80.6%) specific to identify active IIM, although aspartate aminotransferase (AST) ≥41 was more sensitive (82.6%) but less specific (73.3%). However, FABP3 was inferior than muscle enzymes at identifying active disease [Figure 1]d.
Moreover, FABP3 levels did not correlate with conventional markers of disease activity such as the physician global assessment (PGA), manual muscle testing (MMT8) scores, or SGOT/LDH.
FABP3 levels decline on follow-up in treatment responders.
Of those who followed up after 6 months, levels fell [Figure 1]e with treatment in responders (n = 7, 14.5–7.5 ng/dl, P = 0.03). In the two nonresponders, the levels did not change over the visits.
FABP3 levels do not differ in various subsets of IIM.
FABP3 did not differ between the various types of myositis or a polyphasic disease course from the rest.
| Discussion|| |
We found that FABP3 can distinguish active from inactive myositis, with a better discriminatory potential in early disease. It is elevated in inactive disease, too, albeit lower values. Levels fall with treatment in treatment responders. In a cross-sectional study of 24 patients with active inflammatory myositis and muscle weakness, Zhang et al. found an excellent inverse correlation of FABP3 levels with muscle strength (MMT8, coefficient − 0.927). However, its utility in OM, ASS, and jDM was explored for the first time, although levels were found to be comparable between in various types of IIM. This is also the first report of FABP3 levels in inactive disease upon longitudinal follow-up.
Contrary to published literature, a correlation with muscle strength was not found. This was noted in both active and inactive IIM, adults and children, and in the various subsets (PM/DM - which have more severe muscle weakness). The muscle strength could be a function of muscle mass, damage, and ongoing inflammation. Since FABP3 could, at best, be a reflection of the ongoing inflammation, it may not accurately reflect power alone though may potentially do so on using a composite biomarker with FABP3 being one component of it. Moreover, a large proportion of individuals had long-standing disease, where assessment of strength of more likely to be confounded by other factors. Thus, it may have been a better reflector of active disease in those with <1-year disease duration, suggesting that biomarker studies may assess early and established IIM separately.
Besides, underlying cardiac disease could confound elevated FABP3 levels, more so in the middle aged, especially since subclinical cardiac involvement has been described in IIM., Unfortunately, a formal cardiac evaluation was omitted in the absence of frank angina or other cardiovascular disease symptoms, precluding further interpretation.
In the current study, conventional muscle enzymes, particularly AST, were more sensitive marker to distinguish active from inactive IIM. However, FABP3 was reasonably specific, suggesting a potential utility in differentiating other muscle disorders from active IIM, pending further exploration.
We found lower levels of FABP3 in IIM as well as healthy in the current study, suggesting a possibly body composition of the Indian population as compared with the Chinese. Alternatively, the use of a different assay (they used an SS-J2 multifunctional tester) could explain this, although the possibility of genetic polymorphisms in FABP3 in the Indian population cannot be ruled out either. Moreover, interpretation in the current study is limited by the small number of healthy controls.,
This is the first prospective evaluation of treatment response using standard outcome measures in patients with IIM. It has the advantage of large numbers of various subsets of both active and inactive myositis. The use of ELISA for the current study offers the distinct advantage of a comparison with a different assay system for this biomarker. However, insights gained from the current study cast doubts on the utility of FABP3 as a stand-alone biomarker.
| Conclusion|| |
Serum FABP3 is elevated in active IIM, especially early disease, and decreases with treatment among responders. FABP3 has a favorable specificity but insufficient sensitivity, limiting role as a stand-alone biomarker. It might be useful in early IIM, without renal or cardiac involvement, pending validation in future studies.
Financial support and sponsorship
This study was funded by APLAR research grant.
Conflicts of interest
There are no conflicts of interest.
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