Radioimmunoassay for insulin-like growth factor-I in bovine milk

Development and validation of an enzyme-linked immunosorbent assay for the detection of circulating antibodies raised against growth hormone as a consequence of rbST treatment in cows

The recombinant bovine growth hormone (rbST) is used to increase lactating performances of dairy cows. Administration of rbST is banned in the European Union; nevertheless, its use is probable. Until now, efficient analytical strategies to detect such practice are based on the direct detection by mass spectrometry of the presence of rbST in biological fluids, which suits for confirmatory purposes. Current screening strategies do not offer satisfactory performances; therefore, alternative screening strategies are required. The aim of the present work is to develop and validate an ELISA to measure the production of specific antibodies upon rbST in bovine sera. In this immunoassay, rbST is absorbed onto microtiter plate. After specific purification of the antibodies in serum, samples are analysed and the presence of antibodies anti-rbST is detected by Protein G peroxidase conjugate and 2-2'-azino di-ethyl benz-thiazoline-6-sulphonic acid (ABTS). The mean reproducibility of the OD (λ=405 nm) measurement was calculated with a CV of 13%. The intra- and inter-assay CVs ranged from 0.79% to 7.91% and from 2.69% to 20% respectively. The test presents cross-reaction with other growth hormones such as the recombinant equine (reST) and porcine (pST) (100% and 80% respectively). The specificity of the test toward rbST anabolic treatment was confirmed through the analysis of sera samples collected on animals administered with other anabolic compounds (steroids). The performances of the present anti-rbST ELISA proves its efficiency as a new screening tool to highlight illegal administration of rbST in cattle up to at least 3 weeks after treatment.

Direct determination of recombinant bovine somatotropin in plasma from a treated goat by liquid chromatography/high-resolution mass spectrometry

Recombinant bovine somatotropin (rbST) is used in dairy cattle to enhance milk production. Despite the ban on this hormone in some countries, especially in Europe, there is so far no method available for the direct detection of rbST either in milk or in plasma. An analytical strategy has been developed to analyze rbST in plasma, including a purification procedure based on a precipitation with ammonium sulphate, followed by a solid-phase extraction (SPE)-based clean-up on C4 sorbent and precipitation with cold methanol. The hormone was then digested with trypsin and analyzed by liquid chromatography/high-resolution mass spectrometry (LC/HRMSn) on a linear ion trap coupled with an Orbitrap. The tryptic N-terminal peptide, specific to the difference between the endogenous and recombinant form of the somatotropin, was fragmented and product ions were analyzed at high mass resolution. Applying this approach to goat plasma allowed the direct detection of 10 ng mL(-1) of rbST in fortified samples. It also showed the presence of rbST in plasma collected from a goat treated with the hormone, even 2 days after administration. These results are of a great interest in the field of somatotropin control and undoubtedly constitute a first step in the development of a method for the detection of rbST not only in bovine plasma, but also in other biological matrices such as milk.

Measurement of bovine somatotropin (bST) and insulin-like growth factor-1 (IGF-1) in bovine milk using an electrochemiluminescent assay

Bovine somatotropin (bST) and insulin-like growth factor-1 (IGF-1) are peptide hormones that are involved in the regulation of milk production in dairy cows. Because these hormones are present at extremely low concentration in fresh and processed bovine milk, a highly sensitive and specific electrochemiluminescent immunoassay (ECLIA) has been developed to better estimate the concentration of these hormones in milk. The assay employs an imager, a capture antibody bound to a carbon electrode, and a detection antibody coupled to a ruthenium label. In the presence of tripropylamine and an electric pulse, ruthenium generates light proportional to the amount of antigen bound, and the light is captured as signal by a charge-coupled device (CCD) camera. Using bovine milk as the starting matrix, 99.69% of bST and 104.79% of IGF-1 were recoverable. The limit of detection (LOD) was <5 pg/mL for bST and <1 pg/mL for IGF-1. The limit of quantification (LOQ) was <14 pg/mL for bST in milk and <2 pg/mL of IGF-1. The assay is highly specific and shows <0.2% cross-reactivity with other peptide hormones found in bovine milk such as insulin and IGF-2. These data indicate this new, ECLIA is highly sensitive and specific for estimating the concentration of bST or IGF-1 in milk.

Comparison of a conventional immunoassay (ELISA) with a surface plasmon resonance-based biosensor for IGF-1 detection in cows' milk

Recombinant bovine somatotropin (rBST) treatment is adopted in dairy cows to augment milk yield. Previous studies showed that insulin-like growth factor-1 (IGF-1) is present in milk from cows treated with rBST. Since IGF-1 is a suspected carcinogen, its presence in milk for human consumption is potentially a health hazard. Therefore rBST use, still authorized in the United States, has been revoked in Canada and is under evaluation in the EU. The rising attention on IGF-1 presence in alimentary milk focused the necessity to develop specific, sensitive and rapid IGF-1 detection systems. We have developed a solid phase enzyme-linked immunoassay (ELISA) and also an automated surface plasmon resonance-based biosensor system (BIA-technology) for evaluating IGF-1 in fresh cow's milk. Hyperimmune polyclonal anti-IGF-1 antibodies were characterized with respect to their specific binding capacity to IGF-1. The results obtained with these two methods have been compared. This study shows the potential usefulness of the biosensor technology for biomolecular interaction analysis. The features of this technology (fully automated, measures in real time, sharpened yes/no response) offer several advantages compared to ELISA in the detection of compounds in fresh cows' milk (MURST 40%; CNR P.F. MADESS 2).

Somatotropin and insulin-like growth factor-I concentrations in plasma and milk after daily or sustained-release exogenous somatotropin administrations

Effects of daily injectable or sustained-release bovine somatotropin (bST) administrations on plasma and milk bST and insulin-like growth factor-I (IGF-I) concentrations were monitored in 74 lactating cows through early, mid- and late lactation. Treatments beginning at wk 4 of lactation were excipient (CO, 24 cows) at 2 wk intervals, daily injections of 10.3 mg bST (DI, 25 cows) and 350 mg sustained-release bST at 2 wk intervals (SR, 25 cows). The duration of treatments was 40 wk. Data were first analyzed for the overall mean concentrations covering the 40 wk treatment period. Overall mean plasma bST, milk bST and plasma IGF-I concentrations were significantly increased by both bST treatments (p < 0.05). On the other hand, milk IGF-I concentrations were significantly increased (p < 0.05) only in the DI group. Next, data were analyzed according to stage of lactation. The bST treatments resulted in significant increases (p < 0.05) in plasma and milk bST concentrations for all early, mid- and late lactation periods. Even though plasma IGF-I concentrations were higher (p < 0.05) in all lactation periods for bST treatment groups, higher milk IGF-I concentrations (p < 0.05) occurred only in mid- and late lactation periods for the DI group. The patterns of bST and IGF-I concentrations in milk follows those of the plasma after bST treatments.