Highly sensitive therapeutic drug monitoring of infliximab in serum by targeted mass spectrometry in comparison to ELISA data

BACKGROUND

Presently, antibody concentration measurements for patients undergoing treatment are predominantly determined by ELISA, which still comes with known disadvantages. Therefore, our aim was to establish a targeted mass-spectrometric assay enabling the reproducible absolute quantification of peptides from the hypervariable and interaction regions of infliximab.

METHODS

Peptides of infliximab were measured post-trypsin digestion and subsequent separation on a Vanquish Horizon UHPLC coupled to a TSQ Altis Triple-Quad mass spectrometer. Normalization and absolute quantification were conducted using stable isotope-synthesized peptides. Calibration curves covering a range of 0.25-50 µg/ml were employed for quantitation.

RESULTS

We demonstrated the substantial influence of peptide selection, choice of hydrolase for digestion, and digestion time on absolute peptide yield (28-44% for peptide 1 and 64-97% for peptide 2). Furthermore, we showed that the generated calibration curves for absolute quantification were highly reproducible and robust (LLOQ1 0.72 µg/ml and LLOQ2 1.00 µg/ml) over several months. In comparison to ELISA values, the absolute values obtained by mass spectrometry often yielded lower results for both targeted peptides.

CONCLUSIONS

In this study, a semi-automated workflow was employed and tested with 8 patients and corresponding replicates (n = 3-4). We demonstrated the robust implementation of calibration curves for the absolute quantification of infliximab in patient samples, with coefficients of variation ranging from 0.5 to 9%. Taken together, we have developed a platform enabling the rapid (2 days of sample preparation and 30 min of measurement time per sample) and robust quantification of Infliximab antibody concentration in patients. The use of mass spectrometry also facilitates the straightforward expansion of the method to include additional antibody peptides.

[Unusual IOL Calcification following Vitreoretinal Surgery with Silicone Oil Endotamponade]

PURPOSE

Calcification of intraocular lenses (IOL), although nowadays less frequent than in the past, is a well-documented complication that can still necessitate their explantation. Although mostly noted in hydrophilic materials it has been rarely reported in hydrophobic intraocular lenses. We wish to report on two unusual cases of intraocular lense (one hydrophobic and one hydrophilic with hydrophobic surface) calcification following vitrectomy and silicon oil endotamponade.

METHODS

In the course of treatment both patients underwent multiple ocular interventions due to re-detachment/persistent macular hole including local rt-PA or triamcinolone injection due to persistent postoperative anterior chamber inflammation/macular oedema. Finally and after thorough patient examination with characteristic visual complaints and difficulty in the retinal assessment the extraction of the calcified lenses was considered necessary. The configuration as well as the elemental analysis of the opacified surface of the IOLs was performed by means of high magnification microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Intraocular and systemic histories of both patients were summarised.

RESULTS

The scanning electron microscopy and EDX analysis demonstrated massive calcium-based deposits on the surface of the hydrophilic and a diffuse vacuolation and calcification consisting of oxygen (O), silicon (Si), magnesium (Mg), aluminium (Al), sulphur (S) and phosphorus (P) on the surface of the hydrophobic IOL.

CONCLUSION

The explantation of an IOL due to calcification represents an unusual event. The careful consideration of systemic and ocular factors that promote calcification processes can help reduce the incidence of calcification. Despite all efforts in material production and risk factor analysis, it is not always possible to define or even predict the exact cause of this phenomenon and in the presence of corresponding clinical symptoms IOL exchange remains as the sole option.