Surface plasmon resonance immuno assays - A perspective

Label-Free Quantification of Anti-TNF-α in Patients Treated with Adalimumab Using an Optical Biosensor

This study describes the development of an immunosensory label-free quantification methodology based on surface plasmon resonance (SPR) and its applicability in measuring/evaluating therapeutic drug monitoring (TDM) of anti-TNF-α monoclonal antibody (adalimumab) in rheumatoid arthritis (RA) patients. The experimental parameters evaluated in this study were immobilising ligands by pre-concentration assays, sensor surface regeneration, ascertaining the method’s sensitivity and correlating the results from quantifying plasma samples by ELISA immunoassay. The results showed that TNF-α quantification values (in RU) were significantly different when comparing patients (~50–250 RU) to controls (~10–20 RU). Likewise, there was 0.97 correlation for patients and 0.91 for healthy volunteers using SPR and ELISA comparison methodologies. SPR immunosensory detection provided a precise, sensitive strategy, along with real-time determination, for quantifying adalimumab, having great potential for clinical routine regarding TDM.

Quantitative Detection of Weak D Antigen Variants in Blood Typing using SPR

Modern techniques for quantifying blood group antibody-antigen interactions are very limited, especially for weaker interactions which result from low antigen expression and/or partial expression of the antigen structure. Surface plasmon resonance (SPR) detection is often used to monitor and quantify bio-interactions. Previously, a regenerable, multi-fucntional platform for quantitative RBC phenotyping of normal antigen expression using SPR detection was reported. However, detection of weaker variants were not explored. Here, this sensitivity study used anti-human IgG antibodies immobilized to a gold sensor surface to two clinically important types of weaker D variants using SPR; weak D and partial D. Positive pre-sensitised cells bind to the anti-human IgG monolayer, and the response unit (RU) is reported (>100 RU). Unbound negative cells are directly eluted (<100 RU). Weak D cells were detected between a range of 180–580 RU, due to a lower expression of antigens. Partial D cells, category D VI, were also positively identified (352–1147 RU), similar to that of normal D antigens. The detection of two classes of weaker D variants was achieved for the first time using this fully regenerable SPR platform, opening up a new avenue to replace the current subjective and arbitrary methods for quantifying blood group antibody-antigen interactions.

Surface plasmon resonance imaging of pathogens: the Yersinia pestis paradigm

Background

Yersinia pestis, causing deadly plague, is classified as a group A bioterrorism bacterium. Some recent DNA-based methods were used for detection of bioterrorism agents.

Results

Y. pestis was used as a model organism to develop an immunosensor based on surface plasmon resonance imaging (SPRi) using monoclonal antibody against Y. pestis F1 antigen. The experimental approach included step-by-step detection of Y. pestis membrane proteins, lysed bacteria, intact bacteria, mock-infected powder and mock-infected clinical specimens. SPRi detected on average 10⁶ intact Y. pestis organisms in buffer, in mock-infected powder and in a 1:4 mixture with HEL cells.

Conclusions

This study offers the proof-of-concept of the SPRi-based detection of a human pathogen in both environmental and clinical specimens.

Affinity-based biosensors in sport medicine and doping control analysis

Affinity-based biosensors (ABBs) have started to be considered in sport medicine and doping control analysis because they are cheap, easy to use and sufficiently selective analytical devices, characterized by a reversible interaction with the analyte under investigation allowing the use of the same sensor for multiple analyses. In this review we describe the main categories of substances reported in the World Anti-Doping Agency Prohibited List and how ABBs may contribute to their detection. Although several ABBs proposed in the last few years display limit of detections that are in principle matching the World Anti-Doping Agency requirements, their application in the framework of 'traditional' antidoping tests seems quite unlikely, mainly because of the still insufficient selectivity especially in the case of 'pseudo-endogenous' compounds, and on the lack of complete information regarding potential matrix effects in real samples and following their routine use. At the same time, ABBs could contribute to fill a significant information gap concerning complementary evidence that can be obtained from their use 'on the spot', as well as to preselect a risk population of individuals to be targeted for a full antidoping test; while in sport medicine they could contribute to obtaining analytical information of physiological relevance from the measurement of specific parameters or markers before, during and after physical exercise.

Generation and characterization of nanobodies against rhGH expressed as sfGFP fusion protein

Growth hormone (GH) deficiencies are diagnosed in most children with short stature and treated with a long course of administrating expensive and daily doses of recombinant human GH (rhGH or Somatropin®). This work describes for the first time the production of several GH specific nanobodies with great potential in the field of GH production and detection. Nanobodies are the smallest intact antigen binders derived from heavy chain-only antibodies (HCAbs) of camelids. They are very stable, highly soluble and are produced as recombinant proteins in Escherichiacoli at an affordable cost for various biotechnological applications. To increase its solubility and immunogenicity, GH was produced as fusion with superfolder green fluorescent protein (sfGFP) and was used in this form to successfully immunize an adult camel. The active involvement of HCAbs in the specific camel immune response encouraged the preparation of large nanobody "immune" library. Phage display biopanning of this library against GH resulted in the isolation of five interesting and different nanobodies, referred to as NbGH01, 02, 03, 04 and 06. All nanobodies were able to recognize GH in its fusion and free formats and the detection sensitivity ranged from 0.5 to 10 ng/ml in sandwich ELISA. Pure rhGH was successfully purified by affinity chromatography, using immobilized NbGH06, from the cleavage reaction of fusion proteins with the tobaccos etch virus (TEV) protease. These specific molecular binders, especially NbGH06, provide valuable tools for rhGH diagnostic as well as for production purposes.

Implementation of a SPR immunosensor for the simultaneous detection of the 22K and 20K hGH isoforms in human serum samples

We have implemented a Surface Plasmon Resonance (SPR) immunosensor based on a sandwich assay for the simultaneous detection of the two main hGH isoforms, of 22 kDa (22K) and 20 kDa (20K). An oriented-antibody sensor surface specific for both hormone isoforms was assembled by using the biotin-streptavidin system. The immunosensor functionality was checked for the direct detection of the 22K hGH isoform in buffer, which gave high specificity and reproducibility (intra and inter-assay mean coefficients of variation of 8.23% and 9% respectively). The selective determination of the 22K and 20K hGH isoforms in human serum samples in a single assay was possible by using two specific anti-hGH monoclonal antibodies. The detection limit for both hormone isoforms was 0.9 ng mL(-1) and the mean coefficient of variation was below 7.2%. The excellent reproducibility and sensitivity obtained indicate the high performance of this immunosensor for implementing an anti-doping test.

Surface plasmon resonance shows a gender difference in circulating annexin A5 in human

The level of circulating anxA5 is correlated to various diseases such as acute myocardial infarction, trauma, thrombosis, inflammation and in some cancers. Our aim was to assess whether a direct approach using surface plasmon resonance (SPR) could be easily used to provide a rapid and cheap alternative to detect anxA5 in blood samples in human. Our results indicate that SPR permits to detect and quantify circulating anxA5 in serum with a minimum time of manipulation. Furthermore, we report here, for the first time, that the level of circulating anxA5 is significantly higher in male than in female (5.43 (± 0.02) and 4.41 (± 0.2)ng/ml, respectively). In conclusion, we found that SPR can be used to rapidly quantify anxA5 in patients and that a gender difference has to be taken into account to explain gender differences in the prevalence of some diseases.

Biochemical markers of bone turnover in tibia fracture patients randomly assigned to growth hormone (GH) or placebo injections: Implications for detection of GH abuse

CONTEXT

It has been argued that increased levels of bone remodelling markers are not suitable indicators of GH abuse, as bone injuries per se increase the expression levels of these markers.

OBJECTIVE

To investigate the impact of a recovering tibia fracture on circulating bone markers in subjects receiving placebo or GH treatment.

DESIGN AND SETTING

A randomised, double-blind, placebo-controlled trial of up to 16weeks GH treatment, followed by a 16-week washout.

PARTICIPANTS AND INTERVENTION

Subjects (406 adult males and females) with a tibia fracture were randomly allocated within three days after surgery, to either placebo or GH treatment (15, 30 or 60μg/kg daily) until fracture healing or 16weeks after treatment initiation.

MAIN OUTCOME MEASURES

IGF-I, serum C-terminal telopeptide of type I collagen (CTX), osteocalcin (OST) and bone-specific alkaline phosphatase (BAP) were measured during and after treatment.

RESULTS

Dose-dependent increases were observed in groups receiving GH, and mean levels in the highest GH dose group peaked at eight (IGF-I, CTX) or 12weeks (OST) after treatment initiation. Statistically significant differences between GH treatment and placebo were seen for IGF-I, CTX and OST in all GH dose groups throughout the treatment period, and persisted until eight (CTX) or 12 (OST) weeks after cessation of treatment.

CONCLUSION

IGF-I, CTX and OST are suitable candidate markers of prolonged, illicit administration of GH. Furthermore, CTX and OST have potentials to serve as markers also after cessation of GH administration.

Bioanalysis and Analytical Services Research Group at The Municipal Institute for Medical Research IMIM-Hospital del Mar, Spain

Analytical laboratories involved in health-related research are becoming a fundamental part of the advancement of science in this field. Of particular interest to clinical, legal, toxicological, forensic and environmental matters is the analysis of drugs and medications present in biological fluids of consumers or exposed subjects. The established sensitive and reliable work of sports drug-testing laboratories represents an interesting example of a multidisciplinarity approach toward widespread bioanalytical problems. The experiences reported in this article will be of general interest, especially for analysts studying the determination of substances in biological material.

Detecting growth hormone abuse in athletes

Catching athletes abusing human growth hormone (GH) by official antidoping tests is challenging because of specific properties of the hormone. Furthermore, the chemical structure of recombinant GH (rGH) is identical to that of the main GH isoform secreted by the pituitary, making it difficult to discriminate between endogenous and injected GH molecules by biochemical tests. The approaches developed to solve the problem include the "marker approach," which measures changes in concentration of GH-dependent proteins that are inappropriately elevated after rGH injection, and the "isoform approach," which detects changes in the spectrum of circulating GH isoforms after administration of rGH. A more widespread use of these tests in out-of-competition controls will enhance the likelihood to detect GH doping.