Inflammation factors

Inflammation factors

LASA filenames: LASAB861 / LASAC861 / LAS3B861

Contact: Natasja van Schoor


Background
Aging is associated with increases in systemic inflammatory processes, which is reflected by increased levels of inflammatory markers in the circulation(1). Subclinical – or low-grade – inflammation has been associated with several age-related diseases, of which atherosclerosis is the best known and to date probably the most important.

For background literature see Krabbe et al., 2004.(1)

In LASA we determined serum levels of the pro-inflammatory cytokine Interleukin-6 (IL-6), and of the acute-phase proteins C-reactive protein (CRP), and a1-antichymotrypsin (ACT).


Measurements in LASA

Blood collection first cohort
Blood samples were obtained in 1992/1993, and in 1995/1996. The blood samples were centrifuged and serum was stored at -80° C respectively -20° C until determination in 2002 to 2004.The serum levels of ACT, CRP, and IL-6 were determined using sensitive regular immunoassays (ELISA) at Sanquin Research, Amsterdam. The IL-6 ELISA was obtained from the Business Unit Immune Reagents of Sanquin, and performed according to manufacturer’s instructions. CRP levels were measured with a sandwich-type ELISA in which polyclonal rabbit anti-CRP antibodies were used as catching antibodies and a biotinylated mAb against CRP (CLB anti–CRP-2) as the detecting antibody(1). ACT was measured with an ELISA in which specific mAbs against ACT were used(2). Recombinant IL6, purified CRP and pooled human plasma were used as standards in the respective assays. Results were expressed as ug/mL for CRP, pg/mL for IL-6, and % of normal plasma for ACT. The normal human plasma pool (% NHP ) used as a standard for ACT contained ~300 mg ACT per L. The inter-assay coefficient of variation (CV) was less than 5.2% for ACT, less than 4.2% for CRP, and less than 5% for IL-6. The intra-assay CV was 4.1% for ACT, 3.2% for CRP, and 3.3% for IL-6. The detection limits were 0.8 ng/mL for CRP, and 5 pg/mL for IL-6. All values were measured in duplo, with averages being reported.

Please note that CRP levels have also been determined directly after blood sampling (both in 1992/93 and in 1995/96), but this has been done for respondents in the Zwolle region only (N=384; see “Docu bloedbepaling B en C). However, for complete use of all available CRP data, it is strongly recommended to use data from file B+C861 (inflammatory markers), because this file includes the measurements of respondents in all regions. Also, the CRP determination in Zwolle was performed with a less sensitive assay than the CRP determination in the blood samples from all regions.

Blood collection third cohort
Blood samples of the third cohort were obtained in 2012/2013. The blood samples were centrifuged and serum was stored at -80° C until determination in 2016. In this cohort CRP and IL-6 were measured. CRP was measured using a particle enhanced immunoturbidimetric assay (Modular analytics Cobas 6000, Roche diagnostics; Mannheim, Germany).
IL-6 was measured using the High Sensitivity Quantikine ELISA (R&D systems; Minneapolis, MN, USA). The detection range of this assay is 0.02 – 10 pg/ml – Reported inter-assay CV by the manufacturer was 7,8 %. Internal measured inter-assay CV was 12%.


Measurement procedure & variable information

Possible classification of inflammatory markers
Levels of inflammatory markers could be classified in tertiles, except for IL-6 levels. Given the rigid criteria applied to the IL-6 ELISA in the first cohort, dichotomization around the detection limit of 5 pg/mL was considered the best strategy for statistical analyses of IL-6 instead of using tertiles as was done for the other markers(4,5). From all respondents, 89.7% had IL-6 levels below the detection limit of 5 pg/mL. Another strategy used in LASA is to dichotomize IL-6 levels below the detection limit of 5 pg/mL at the median(6). In the third cohort, a high-sensitive assay has been used to measure IL-6. The detection range of this assay was 0.02 – 10 pg/mL. Only one respondent had an IL-6 level beyond the detection range (>246 pg/mL).

‘Chronic’ inflammation
The inflammatory markers were determined at two data measurement waves in the first cohort, three years apart, so that subjects who are susceptible to a high inflammation status could be distinguished more reliably. Therefore, because subjects with high inflammation at one measurement because of intercurrent disease such as flu can be excluded.


Availability of data per wave

Number of respondents per wave

B*

C

3B*
Pro-inflammatory cytokine
Interleukin-6 (IL-6)

1,745

1,287

638
Acute-phase proteins C-reactive
protein (CRP)

1,744

1,287

631
A1-antichymotrypsin (ACT)

1,743

1,287

–

* B=baseline first cohort (only Amsterdam and Zwolle region were involved);
3B=baseline third cohort


Previous use in LASA
In LASA, inflammatory markers have been associated with several age-related diseases and symptoms, such as cognitive decline (Dik et al., 2005), depression (Bremmer et al., 2008) sarcopenia (Schaap et al., 2006)and frailty (Puts et al., 2005). Research of Schaap (2010) investigated higher inflammatory marker concentrations and lower sex hormone concentrations as determinants of changes in muscle mass and muscle strength and decline in physical function in older persons. Van den Kommer et al. (2010) stated that only in the highest tertile of CRP, higher homocysteine was negatively associated with retention. In the middle tertile of ACT, higher homocysteine was associated with lower information processing speed and faster decline. Van Exel (2009) concluded that hypertension and the expression of an innate pro-inflammatory cytokine profile in middle age are early risk factors of Alzheimer disease in old age. Research of Den Uyl et al. (2015) showed that higher serum interleukin 6 (IL-6) and erythrocyte sedimentation rate (ESR) levels were associated with lower quantitative ultrasound values in older men, but not in women. No associations were found between inflammatory markers and the risk for fractures.


References

  1. Krabbe KS, Pedersen M, Bruunsgaard H. Inflammatory mediators in the elderly. Exp Gerontol 2004;39:687-699.
  2. Bruins P, te Velthuis H, Yazdanbakhsh AP, Jansen PG, van Hardevelt FW, de Beaumont EM, Wildevuur CR, Eijsman L, Trouwborst A, Hack CE. Activation of the complement system during and after cardiopulmonary bypass surgery: postsurgery activation involves C-reactive protein and is associated with postoperative arrhythmia. Circulation 1997;96:3542-8.
  3. Rozemuller JM, Abbink JJ, Kamp AM, Stam FC, Hack CE, Eikelenboom P. Distribution pattern and functional state of alpha 1-antichymotrypsin in plaques and vascular amyloid in Alzheimer’s disease. A immunohistochemical study with monoclonal antibodies against native and inactivated alpha 1-antichymotrypsin. Acta Neuropathol (Berl) 1991;82:200-7.


Date of last update: April 2, 2020