Development of monoclonal antibodies to pre-haptoglobin 2 and their use in an enzyme-linked immunosorbent assay (ELISA).

Haptoglobins (HPs) are alpha 2-globulin proteins that bind free hemoglobin in plasma to prevent oxidative damage. HPs are produced as preproteins that are proteolytically cleaved in the ER into alpha and beta chains prior to forming mature, functional tetramers. Two alleles exist in humans (HP1 and HP2), therefore three genotypes are present in the population, i.e., HP1-1, HP2-1, and HP2-2. A biochemical role for nascent haptoglobin 2 (pre-haptoglobin 2 or pre-HP2) as the only known modulator of intestinal permeability has been established. In addition, elevated levels of serum pre-HP2 have been detected in multiple conditions including celiac disease and type I diabetes, which are believed to result in part through dysregulation of the intestinal barrier. In this study, we report the development of a monoclonal antibody that is specific for pre-HP2 with a binding affinity in the nanomolar range. Additional antibodies with specificities for preHP but not mature haptoglobin were also characterized. A sandwich enzyme-linked immunosorbent assay (ELISA) was established and validated. The ELISA showed high specificity for pre-HP2 even in the presence of excess pre-HP1 or mature haptoglobins, and has excellent linearity and inter- and intra-assay reproducibility with a working range from 3.1ng/mL to 200ng/mL. Testing of sera from 76 healthy patients revealed a non-Gaussian distribution of pre-HP2 levels with a mean concentration of 221.2ng/mL (95% CI: 106.5-335.9ng/mL) and a median value of 23.9ng/mL. Compared to current approaches, this ELISA offers a validated, monoclonal-based method with high sensitivity and specificity for measuring pre-HP2 in human serum.

Cerebrospinal Aß11-x and 17-x levels as indicators of mild cognitive impairment and patients' stratification in Alzheimer's disease.

In the present work, the concentrations of Aß11-x and Aß17-x peptides (x=40 or 42), which result from the combined cleavages of ß-amyloid precursor protein (AßPP) by ß'/α or α/γ-secretases, respectively, were assessed in cerebrospinal fluid (CSF) samples from patients with Alzheimer's disease (AD) or mild cognitive impairment (MCI). Specific multiplexed assays were set up using new anti-40 and anti-42 monoclonal antibodies (mAbs) for the capture of these N-truncated Aß peptides and anti-11 or anti-17 mAbs for their detection. The specificity, sensitivity and reproducibility of such assays were assessed using synthetic peptides and human cell models. Aß11-x and Aß17-x were then measured in CSF samples from patients with AD (n=23), MCI (n=23) and controls with normal cognition (n=21). Aß11-x levels were significantly lower in patients with MCI than in controls. Compared with the combined quantification of Aß1-42, total Tau (T-Tau) and phosphorylated Tau (P-Tau; AlzBio3, Innogenetics), the association of Aß11-40, Aß17-40 and T-Tau improved the discrimination between MCI and controls. Furthermore, when patients with MCI were classified into two subgroups (MCI ≤1.5 or ≥2 based on their CDR-SB (Cognitive Dementia Rating-Sum of Boxes) score), the CSF Aß17-40/Aß11-40 ratio was significantly higher in patients with CDR-SB ≤1.5 than in controls, whereas neither Aß1-42, T-Tau nor P-Tau allowed the detection of this subpopulation. These results need to be confirmed in a larger clinical prospective cohort.

Inhibition of lecithin cholesterol acyltransferase by phosphatidylcholine hydroperoxides.

To gain insight into the nature of the lecithin-cholesterol acyltransferase inhibitory factor(s), we separated and collected the oxidation products from oxidized lipoproteins after lipoxygenase treatment. Isolated fractions identified by chemiluminescence, as hydroperoxides of phosphatidylcholine, were found to produce a significant reduction of lecithin-cholesterol acyltransferase activity. The reaction kinetics of lecithin-cholesterol acyltransferase with reconstitued high density lipoproteins were studied in the presence of 0.6 and 1.2 microM hydroperoxides of phosphatidylcholine. No significant changes in the apparent Vmax were observed but a concentration-dependent increase in slope of the reciprocal plots and in the apparent Km values was observed with increasing hydroperoxide concentrations. These results show that the active site of lecithin-cholesterol acyltransferase is not affected by the presence of phosphatidylcholine hydroperoxides. Nevertheless, hydroperoxides of phosphatidylcholine altered the reactivity of lecithin-cholesterol acyltransferase for reconstitued high density lipoproteins suggesting either an alteration of the binding of lecithin-cholesterol acyltransferase to the reconstitued high density lipoproteins or a competitive inhibition mechanism.