Rüdiger Siekmeier

Heterogeneous lipoprotein (a) size isoforms differ by their interaction with the low density lipoprotein receptor and the low density lipoprotein receptor-related protein/α2-macroglobulin receptor

Lipoprotein (a) (Lp(a)) is a complex of low density lipoprotein (LDL) with apolipoprotein (apo) (a). To examine the size distribution of Lp(a), plasma was separated by fast flow gel filtration and Lp(a): B complexes were determined in the eluate by enzyme immunoassays, in which detection was performed with monoclonal antibodies specific for apoB Lp(a): B particles displayed apparent molecular masses (Mr ) of 2 × 106 to at least 10 × 106. Lp(a) size isoforms differed by the expression of apoB epitopes and their interaction with cultured human skin fibroblasts. LDL was more effective in inhibiting binding, uptake, and degradation of low Mr , Lp(a) than of high Mr Lp(a). In contrast, Glu‐plasmmogen, α2‐macroglobulin and tissue‐type plasminogen activator were more effective in competing for the cellular degradation of high Mr Lp(a) than of low Mr Lp(a). Ligand blotting revealed that Lp(a) bound to the low density lipoprotein receptor, the low density lipoprotein receptor‐related protein/α2‐macroglobulin receptor (LRP) and to two other endosomal membrane proteins. We propose that the LDL receptor preferentially internalizes low Mr Lp(a), whereas LRP may have a role in the clearance of high Mr Lp(a).

Determination of lipoprotein(a): enzyme immunoassay and immunoradiometric assay compared

Lipoprotein(a) (Lp(a)) concentration in plasma is a strong independent risk factor for pre-mature atherosclerosis. Lp(a) closely resembles LDL. Its protein moiety contains apolipoprotein (apo) B-100 and apo(a). Two enzyme immunoassays (EIAs) for Lp(a) have been developed. In both, polyclonal antibodies for apo(a) are used as capturing antibodies. In the first, Lp(a) is detected with anti-apo(a) (apo(a)-EIA). In the second, detection is carried out with anti-apo B (Lp(a):B-EIA). Neither plasminogen nor LDL cross-reacted in the assays. Lp(a) was also measured using a commercial sandwich immunoradiometric assay (IRMA). This assay uses two monoclonal antibodies for apo(a). One of them, the solid phase antibody, cross-reacted with plasminogen. However, at physiological plasminogen concentrations there was no competition for solid phase binding sites. A quantity of plasma samples (201) were assayed for Lp(a) with the three methods. The best correlation was obtained between the IRMA and the Lp(a):B-EIA (r = 0.909). Correlations between the apo(a)-EIA and the IRMA or the Lp(a):B-EIA were 0.763 and 0.695, respectively. As compared to the EIAs, the IRMA overestimated Lp(a) by about 30%. It is concluded that both the Lp(a):B-EIA and the IRMA reflect the concentration of Lp(a) particles in plasma. In contrast, the apo(a)-EIA measures apo(a) antigen and may therefore be susceptible to the size polymorphism of apo(a).

Precipitation of LDL with sulfated polyanions: three methods compared

Three precipitation methods for the determination of low density lipoproteins have been evaluated. In n = 113 normolipidemic samples mean LDL-cholesterol levels have been 2.90 mmol/l, 2.77 mmol/l, 3.21 mmol/l after precipitation with heparin, dextran sulfate, and polyvinylsulfate, respectively. As compared to a combined ultracentrifugation and precipitation reference procedure (mean 3.22 mmol/l) two precipitation methods tend to underrate LDL-cholesterol. Elevated plasma triglycerides may interfere with the precipitation of LDL. The clinical relevance of the precipitation procedures has been studied by discriminant analysis in n = 28 consecutive patients admitted for coronary bypass operation and n = 28 controls. The data suggest that, statistically, the determination of LDL-cholesterol with either precipitation method only provides redundant information as in relation to the Friedewald approximation for LDL-cholesterol. Immunologically determined apolipoprotein B proved a better predictor for group separation than either precipitation method.

Deposition of inspired aerosol particles within the respiratory tract of patients with obstructive lung disease

Total deposition of monodisperse aerosol particles in the size range between 1 micron and 3 microns was measured in patients with obstructive lung disease and in normal people using equal breathing conditions for both groups. It turns out that for breathing conditions at rest, deposition for patients is higher, especially in the case of 1 micron particle: A second breathing pattern similar to forced exercise, but including a breath holding interval of 6 s after inhalation, is applied to throw some light on the effect of time-dependent deposition mechanisms. The results show less differences between both groups, indicating that enhanced gravitational deposition during respiratory pauses compensates for differences in lung morphometry.

Thirty month variability of aerosol pulse dispersion and conventional lung function parameters in healthy middle aged smokers and nonsmokers.

Chronic cigarette consumption is a generally accepted reason for the development of chronic obstructive pulmonary disease (COPD). COPD correlates to histomorphological parameters of lung structure as well as pulmonary function tests (PFT). COPD related changes affect PFT determined by conventional methods (bodyplethysmography, spirometry) as well as parameters of convective gas mixing. This study evaluates the diagnostic potential of a non-invasive aerosol method for the discrimination between healthy smokers and nonsmokers in comparison to conventional PFT. The aerosol method is based on the inhalation of small aerosol pulses suspended in particle free air and determines their changes during the breathing maneuver. Changes of aerosol pulse parameters (APP) are used to describe the convective component of gas mixing during ventilation. PFT and APP were determined in 40 healthy subjects (nonsmoker: 51.1 +/- 1.5 years; smoker: 49.6 +/- 1.5 years, 39.1 +/- 2.2 pack years) before and after a time interval of 30 months. Conventional PFT in smokers and nonsmokers showed no relevant differences between the values at the beginning and the end of the observation period. Thirty months later, at the end of the observation interval, a very similar behavior of the APP was obtained, which strongly confirmed the prior observed differences between smokers and nonsmokers. The data suggest that cigarette smoke-induced variations of lung function are also detectable in clinically asymptomatic smokers. Even in cases of normal PFT, most APP are able to discriminate between healthy smokers and nonsmokers. Since PFT showed only minor differences between both groups, it is indicated that APP are superior to PFT in the detection of early disturbances of lung ventilation in healthy smokers. Mean values of PFT and APP in smokers and nonsmokers showed a high reproducibility of the data obtained at the beginning of the study as well as at the end of the observation period. The data of our study further confirm that parameters of pulmonary gas exchange and gas mixing are affected by cigarette smoke at an earlier time than parameters of breathing mechanics.