High selectivity of a biomarker is a basic requirement when it is used for diagnosis, prognosis and treatment of a disease. The artificial gel antibodies, which we synthesise by a molecular imprinting method, have this property not only for proteins, but also for bioparticles, such as viruses and bacteria. However, diagnosis of a disease requires not only that the biomarker can be "fished out" from a body fluid with high selectivity, but also that its concentration in the sample can rapidly be determined and preferably by a simple technique. This paper deals primarily with the development of a spectrophotometric method, which is so simple and fast that it can be used with advantage in a Doctor's Office. The development of this method was not straight-forward. However, by modifications of the performance of these measurements we can now design standard curves in the form of a straight line, when we plot the true (not the recorded "apparent" absorption) against known protein concentrations. In an additional publication (see the following paper in this issue of JSS) we show an application of such a plot: determination of the concentration of albumin in serum and cerebrospinal fluid from patients with neurological disorders to investigate whether albumin is a biomarker for these diseases.

We have previously used the molecular-imprinting method for the synthesis of artificial gel antibodies, highly selective for various proteins. In the present work, we have synthesized artificial gel antibodies against human albumin with the aim to develop a simple and rapid procedure to measure the concentration of this protein in samples of clinical interest. The procedure, based on the design of a standard curve (see the preceding paper), was applied on a quantitative analysis of albumin in human plasma and cerebrospinal fluid (CSF). We found that our technique permitted detection of albumin in these body fluids with high precision and that the concentration of this protein was significantly enhanced in CSF from patients with amyotrophic lateral sclerosis (ALS), compared to control samples. This finding is in agreement with results from earlier studies, which confirms the validity of our analysis technique and suggests that the barrier permeability may be affected in ALS, perhaps also for other proteins. No enhancement in plasma levels of albumin was seen in patients with ALS, but rather a decrease. The results further indicate that our approach might also apply well to other biomarkers for the actual neurological disease and other disorders.

Artificial gel-antibodies were used to probe human growth hormone (GH) activity in hormone preparations purified from human pituitaries. A partially purified fraction containing differently sized forms of the hormone was further processed to yield monomeric and dimeric forms of GH activity suitable for synthesizing artificial polyacrylamide gel antibodies. These two types of GH antibodies were used for probing GH activity in experiments analyzing the two forms of the hormone by HPLC gel-permeation and ion-exchange chromatography. In the size-exclusion experiments both hormone fractions eluted as homogenous peaks, whereas the ion exchanger resolved the hormones in several active components. The antibodies towards the GH monomer were more potent to recognize monomeric GH compared to antibodies against dimeric GH. The opposite was found for the dimeric GH antibodies. It was concluded that these two sets of antibodies it might be useful for discriminating between dimeric and monomeric GH in samples of clinical origin.

Although protein biomarkers have a great potential as biomarkers for diagnosis of diseases, they are seldom used in hospitals. There are many reasons for this, for instance, the difficulties to (i) find a biomarker for which the concentration in body fluids clearly differs between patients and healthy subjects, (ii) attain purification of the biomarker close to 100%, which is required for production of conventional protein antibodies as well as artificial gel antibodies for selective capture of a biomarker, (iii) design a standard curve for rapid and accurate determination of the concentration of the biomarker in the body fluid because of adsorption of the biomarker onto vials, pipettes, etc., (iv) determine accurately the sample volume delivered by a pipette, (v) avoid polymerization of the biomarker upon storage and to decide whether it is in the form not only of monomers, but also of dimers, trimers, etc., in the native state, (vi) determine the degree of possible glycosylation and amidation of the biomarker and (vii) decide whether glycosylation and amidation positively or negatively affects the possibility to use the protein as a biomarker. In this article, we discuss in quantitative terms the difficulties (iii-vii) and how to overcome them, which also may help to overcome the difficulty (ti), which in turn minimizes difficulty (i).