Characterization of serum amyloid A4 as a plasma apolipoprotein

The effect of the content of ApoA-I in peripheral blood on the state of immune homeostasis in people living in extreme climatic conditions of the Arctic

The paper presents data on the impacts of the content of ApoA-I in peripheral blood on the state of immune homeostasis in people living in extreme climatic conditions of the Arctic. From the village of Revda, Murmansk region, 191 people were examined, 160 women and 31 men, aged from 21 to 55 years. The analysis of the results was carried out depending on the level of ApoA-I content: 111 examined people had a low content of ApoA-I (< 115 mg/dl) and 80 people had a concentration of ApoA-I - within the physiological norm (115-220 mg/dl). Deficiency of ApoA-I is associated with an increase in plasma concentrations of total cholesterol in 37.5% and triglycerides in 62.5% of cases. Low content of ApoA-I is associated with a decrease in the content of neutrophilic granulocytes and an increase in the concentration of small lymphocytes, IL-10 and IgE. Deficiency of ApoA-I is associated with an increase in the content of CD45RA+, CD16+, CD56+ lymphocyte phenotypes in blood. Low concentrations of ApoA-I are associated with low expression activity of L-selectin gene and free L-selectin ligand. Due to deficiency of ApoA-I, no significant differences were detected in the content of transferrin, free transferrin receptor, haptoglobin, free calcium-dependent cell adhesion protein, and free pool of receptors involved in apoptosis. Conclusion: deficiency of ApoA-I in blood plasma is associated with increased migration of neutrophils into the tissue and cell-mediated cytotoxicity of lymphocytes and occurs because of the effect of decreased activity of the level of antioxidant defense, changes in the structure of cell membranes and the participation of adhesion molecules.

Proteins related to lipoprotein profile were identified using a pharmaco-proteomic approach as markers for growth response to growth hormone (GH) treatment in short prepubertal children

Background

The broad range in growth observed in response to growth hormone (GH) treatment is mainly caused by individual variations in both GH secretion and GH sensitivity. Individual GH responsiveness can be estimated using evidence-based models that predict the response to GH treatment; however, these models can be improved. High-throughput proteomics techniques can be used to identify proteins that may potentially be used as variables in such models in order to improve their predictive ability. Previously we have reported that proteomic analyses can identify biomarkers that discriminate between short prepubertal children with idiopathic short stature (ISS) who show good or poor growth in response to GH treatment. In this study we used a pharmaco-proteomic approach to identify novel factors that correlate with the growth response to GH treatment in prepubertal children who are short due to GH deficiency or ISS. The study included 128 short prepubertal children receiving GH treatment, of whom 39 were GH-deficient and 89 had ISS. Serum protein expression profiles at study start and after 1 year of GH treatment were analyzed using SELDI-TOF. Cross-validated regression and random permutation analyses were performed to identify significant correlations between protein expression patterns and the 2-year growth response to GH treatment.

Results

At start of treatment we identified a combination of seven protein peaks that correlated with the 2-year growth response in the GH-deficient group (R² = 0.73). After 1 year of treatment, a combination of four peaks in the GH-deficient group (R² = 0.64), eight peaks in the ISS group R² = 0.47) and eight peaks in the total study group correlated with the 2-year growth response R² = 0.38).

The peaks identified corresponded to apolipoproteins A-I, A-II, C-I, C-III, transthyretin and serum amyloid A 4, which are all part of the high-density lipoprotein.

Conclusion

Using a proteomic approach we identified biomarkers related to the lipoprotein profile that could be used to predict growth response to GH treatment in prepubertal children who are short as a result of GH-deficiency or who have ISS.

These results support our previous findings that apolipoproteins and transthyretin may have a role in GH sensitivity.

Lipoproteomics II: mapping of proteins in high-density lipoprotein using two-dimensional gel electrophoresis and mass spectrometry

High-density lipoprotein (HDL) is the most abundant lipoprotein particle in the plasma and a negative risk factor of atherosclerosis. By using a proteomic approach it is possible to obtain detailed information about its protein content and protein modifications that may give new information about the physiological roles of HDL. In this study the two subfractions; HDL(2) and HDL(3), were isolated by two-step discontinuous density-gradient ultracentrifugation and the proteins were separated with two-dimensional gel electrophoresis and identified with peptide mass fingerprinting, using matrix-assisted laser desorption/ionisation time of flight mass spectrometry. Identified proteins in HDL were: the dominating apo A-I as six isoforms, four of them with a glycosylation pattern and one of them with retained propeptide, apolipoprotein (apo) A-II, apo A-IV, apo C-I, apo C-II, apo C-III (two isoforms), apo E (five isoforms), the recently discovered apo M (two isoforms), serum amyloid A (two isoforms) and serum amyloid A-IV (six isoforms). Furthermore, alpha-1-antitrypsin was identified in HDL for the first time. Additionally, salivary alpha-amylase was identified as two isoforms in HDL(2), and apo L and a glycosylated apo A-II were identified in HDL(3). Besides confirming the presence of different apolipoproteins, this study indicates new patterns of glycosylated apo A-I and apo A-II. Furthermore, the study reveals new proteins in HDL; alpha-1-antitrypsin and salivary alpha-amylase. Further investigations about these proteins may give new insight into the functional role of HDL in coronary artery diseases.

Serum amyloid A and high-density lipoprotein cholesterol: serum markers of inflammation in sarcoidosis and other systemic disorders

Hypocholesterolemia has been observed in several inflammatory diseases such as rheumatoid arthritis, myeloproliferative disorders, systemic lupus erythematosus and sarcoidosis. Serum amyloid A is an acute-phase reactant that is related to the high-density lipoprotein cholesterol. This review discusses the relationship between the activation of the cells of the monocyte-macrophage system, determined by the serum amyloid A levels, and the lipid metabolism, measured as alterations in plasma lipoprotein concentrations. The mechanisms of this association during acute inflammation are also discussed in this review.

Further characterization of serum amyloid A4 as a minor acute phase reactant and a possible nutritional marker

A constitutive isotype of human serum amyloid A, serum amyloid A4 (SAA4), is distributed into plasma lipoproteins, primarily in high density lipoproteins. Its physiological function is unknown; its serum concentration has no relationship with those of other major apolipoproteins. In this study, changes in SAA4 concentrations were further characterized. Variations in healthy individuals were negligible. In subjects undergoing renal allograft transplantation, SAA4 changed in parallel with acute phase SAA, although its magnitude was not larger than a three-fold increase. This confirmed that SAA4 is a minor acute phase reactant in humans. SAA4 concentrations showed a good agreement with serum pseudocholinesterase activity in healthy subjects and patients with lowered pseudocholinesterase when patients with elevated acute phase SAA were excluded. These results suggest that SAA4 can be an indicator of nutrition or of hepatic protein synthesis in the absence of inflammation.

Serum amyloid A protein generates pre beta 1 high-density lipoprotein from alpha-migrating high-density lipoprotein

Serum amyloid A protein (SAA), an acute-phase reactant in reactive amyloidosis, has high affinity for high-density lipoprotein (HDL). When SAA is added to HDL, SAA displaces apolipoprotein A-I (apoA-I) and phospholipid from the HDL particles. These dissociated components may form prebeta1-HDL because free apoA-I can associate with phospholipid to become a lipoprotein having prebeta mobility. To determine whether SAA generates prebeta1-HDL from alpha-migrating HDL, we investigated the effects of recombinant SAA on HDL subfraction concentration using nondenaturing two-dimensional gradient gel electrophoresis. When we added SAA (0.5 mg/mL) to plasma, the prebeta1-HDL concentration increased by 164% (from 4.7% +/- 1.3% to 12.4% +/- 3.2% of apoA-I, p < 0.005). The increase in prebeta1-HDL was proportional to the dose of SAA. When we added SAA to a column of Sepharose beads coupled to the isolated HDL (alpha-migrating HDL), prebeta1-HDL was dissociated from the column together with the SAA-associated HDL. In summary, we demonstrate that SAA generates prebeta1-HDL from alpha-migrating HDL. We speculate that SAA-mediated HDL remodeling may take place in inflammation.

Serum amyloid A (SAA): a concise review of biology, assay methods and clinical usefulness

Serum amyloid A (SAA) is a family of proteins encoded in a multigene complex. Acute phase isotypes SAA1 and SAA2 are synthesized in response to inflammatory cytokines. SAA and C-reactive protein (CRP) are now the most sensitive indicators for assessing inflammatory activity. In viral infection and kidney allograft rejection, SAA proved more useful than CRP. Development of convenient assay methods for SAA will facilitate its use in clinical laboratories.

Effect of serum amyloid A on cellular affinity of low density lipoprotein

Serum amyloid A, an apolipoprotein of high density lipoproteins, is also present to a lesser degree in low density lipoproteins and is co-localized with apolipoprotein B in atherosclerotic lesions. This study examined the effect of serum amyloid A on cellular affinity of low density lipoprotein in vitro. 125I-labelled low density lipoprotein, when loaded with recombinant serum amyloid A1 (acute phase isotype) or recombinant serum amyloid A4 (constitutive isotype), had enhanced binding to both human skin fibroblasts and a murine macrophage cell line, J774, while its degradation was slightly increased in both cells. The binding of oxidized low density lipoprotein to J774 cells was also enhanced by addition of recombinant serum amyloid A1 or serum amyloid A4, and degradation of oxidized low density lipoprotein was moderately enhanced by recombinant serum amyloid A1. The effects of recombinant serum amyloid A on cellular binding of labelled low density lipoprotein were not competed by non-labelled low density lipoprotein and were diminished in the presence of high density lipoprotein. These findings suggest that serum amyloid A in low density lipoprotein may promote association of low density lipoprotein with cells by non-specific adsorption, and high density lipoprotein may prevent such interactions by removal of serum amyloid A.

Both acute phase and constitutive serum amyloid A are present in atherosclerotic lesions

The polymorphic protein, serum amyloid A (SAA), consists of acute phase isotypes and a constitutive isotype. Both are associated mostly with high density lipoproteins (HDL) in the circulation. In the present study, both SAA isotypes were detected by immunohistochemistry and immunoblotting using monoclonal antibodies in atherosclerotic lesions. As the distribution of SAA was identical with that of apolipoprotein B and SAA is known to be associated also with low density lipoproteins (LDL), SAA may also be delivered to the artery wall by LDL.