Investigation of the Solid-State Interactions in Lyophilized Human G-CSF Using Hydrogen-Deuterium Exchange Mass Spectrometry

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) previously elucidated the interactions between excipients and proteins for liquid granulocyte colony stimulating factor (G-CSF) formulations, confirming predictions made using computational structure docking. More recently, solid-state HDX mass spectrometry (ssHDX-MS) was developed for proteins in the lyophilized state. Deuterium uptake in ssHDX-MS has been shown for various proteins, including monoclonal antibodies, to be highly correlated with storage stability, as measured by protein aggregation and chemical degradation. As G-CSF is known to lose activity through aggregation upon lyophilization, we applied the ssHDX-MS method with peptide mapping to four different lyophilized formulations of G-CSF to compare the impact of three excipients on local structure and exchange dynamics. HDX at 22 °C was confirmed to correlate well with the monomer content remaining after lyophilization and storage at -20 °C, with sucrose providing the greatest protection, and then phenylalanine, mannitol, and no excipient leading to progressively less protection. Storage at 45 °C led to little difference in final monomer content among the formulations, and so there was no discernible relationship with total deuterium uptake on ssHDX. Incubation at 45 °C may have led to a structural conformation and/or aggregation mechanism no longer probed by HDX at 22 °C. Such a conformational change was observed previously at 37 °C for liquid-formulated G-CSF using NMR. Peptide mapping revealed that tolerance to lyophilization and -20 °C storage was linked to increased stability in the small helix, loop AB, helix C, and loop CD. LC-MS HDX and NMR had previously linked loop AB and loop CD to the formation of a native-like state (N*) prior to aggregation in liquid formulations, suggesting a similar structural basis for G-CSF aggregation in the liquid and solid states.

Food allergen analysis: A review of current gaps and the potential to fill them by matrix-assisted laser desorption/ionization

Food allergy remains a public health, business, and regulatory challenge. Risk analysis (RA) and risk management (RM) of food allergens are of great importance and analysis for food allergens is necessary for both. The current workhorse techniques for allergen analysis (enzyme linked immunosorbent assay [ELISA] and real-time polymerase chain reaction) exhibit recognized challenges including variable and antibody specific responses and detection of species DNA rather than allergen protein, respectively. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) enables protein identification, with potential for multiplex analysis and traceability to the System of International units (SI), aiding global measurement standardization. In this review, recent literature has been systematically reviewed to assess progress in LC-MS/MS and define the potential and benefits of matrix-assisted laser desorption/ionization-time-of-flight MS (MALDI-ToF-MS) technology for allergen analysis. MALDI-ToF-MS of initially intact protein is already applied to verify in silico-derived peptide sequences for LC-MS/MS analysis. We describe the origins of MALDI and its future perspectives, including affinity bead-assisted assays coupled to MALDI. Based on the proliferation of reliable and reproducible MALDI-based clinical applications, the technique should emulate the detection capability (sensitivity) of established allergen detection techniques, whilst reducing technical support and having equivalent multiplexing potential to competing techniques, for example, LC-MS/MS and ELISA. Although unlikely to offer inherent SI traceability, MALDI-based allergen analysis will complement existing MS approaches for allergens. Affinity bead-MALDI appears capable of higher throughput at lower cost per sample than almost any existing technique, enabling repeated sub-sampling as a way to reduce representative sampling issues.

Development of a candidate reference measurement procedure by ID-LC-MS/MS for total tau protein measurement in cerebrospinal fluid (CSF)

OBJECTIVES

In clinical pratice, tau protein measurement generally relies on immunoassays (IAs), whose major drawback is the lack of results comparability due to differences in selectivity and/or calibration. This underlines the importance of establishing a traceability chain for total tau (t-tau) measurements. The objective of this work is to develop a higher order candidate reference measurement procedure (RMP) for the absolute quantification of t-tau in cerebrospinal fluid (CSF).

METHODS

To calibrate the candidate RMP and establish metrological traceability to the SI units, a primary calibrator consisting in a highly purified recombinant protein was sourced. Its purity was evaluated by liquid chromatography coupled with high resolution mass spectrometry (LC-HRMS) and the protein mass fraction in solution was certified by amino acid analysis (AAA). An isotopically-labelled homologue was obtained to develop a candidate RMP by isotope dilution mass spectrometry (IDMS) for t-tau absolute quantification in CSF. Calibration blends and quality control (QC) materials were gravimetrically prepared and subjected to the same preparation workflow as CSF samples, followed by LC-HRMS analysis in Parallel Reaction Monitoring (PRM) mode.

RESULTS

A primary calibrator has been developed and an IDMS candidate RMP has been validated for CSF t-tau. The candidate RMP was used to certify t-tau concentration in three pools of CSF (low, medium, high).

CONCLUSIONS

The candidate RMP will pave the road towards global standardization of CSF t-tau measurements. Together with commutable Certified Reference Materials (CRMs), it will allow evaluating and improving the accuracy and comparability of results provided by IAs.

Impact of Bioconjugation on Structure and Function of Antibodies for Use in Immunoassay by Hydrogen-Deuterium Exchange Mass Spectrometry

Monoclonal antibodies (mAbs) are widely used as analytical components in immunoassays to detect target molecules in applications such as clinical diagnostics, food analysis and drug discovery. Functional groups are often conjugated to lysine or cysteine residues to aid immobilization of mAbs or to enable their detection in an antibody antigen complex. Good assay performance depends on the affinity and specificity of the mAbs for the antigen. The conjugation reaction however can cause higher order structural (HOS) changes and ultimately affect the assay performance. In this study, four differently conjugated mAbs were selected as model systems and characterized by mass spectrometry. Particularly, intact protein analysis by liquid-chromatography mass-spectrometry (LC-MS) was performed to determine the amount and distribution of conjugation. Hydrogen deuterium exchange mass spectrometry (HDX-MS) experiments were carried out for the structural characterization of the conjugated mAbs. Immunoassay experiments were performed to monitor the effects of conjugation on the binding properties of the antibodies selected. Good agreement between the mass spectrometry and binding experiment results was found. Particularly, it was noted that the overall structural flexibility of the antibodies increases upon cysteine conjugation and decreases for lysine conjugation. The conjugation of mAbs with bulky functional groups tends to decrease the deuterium uptake kinetics due to induced steric effects. Overall, this study shows correlations between conjugation, structure and function of immunoassay antibodies and the benefits of mass spectrometry to improve understanding of the conjugation reaction and provide insights that can predict immunoassay performance.

Effect of zinc imbalance and salicylic acid co-supply on Arabidopsis response to fungal pathogens with different lifestyles

In higher plants, Zn nutritional imbalance can affect growth, physiology and response to stress, with effect variable depending on host-pathogen interaction. Mechanisms through which Zn operates are not yet well known. The hormone salicylic acid (SA) can affect plant ion uptake, transport and defence responses. Thus, in this study the impact of Zn imbalance and SA co-supply on severity of infection with the necrotrophic fungal pathogen B. cinerea or the biotroph G. cichoracearum was assessed in A. thaliana Col-0. Spectrophotometric assays for pigments and malondialdehyde (MDA) content as a marker of lipid peroxidation, plant defensin 1.2 gene expression by semi-quantitative PCR, callose visualization by fluorescence microscopy and diseases evaluation by macro- and microscopic observations were carried out. Zinc plant concentration varied with the supplied dose. In comparison with the control, Zn-deficit or Zn-excess led to reduced chlorophyll content and PDF 1.2 transcripts induction. In Zn-deficient plants, where MDA increased, also the susceptibility to B. cinerea increased, whereas MDA decreased in G. cichoracearum. Zinc excess increased susceptibility to both pathogens. Co-administration of SA positively affected MDA level, callose deposition, PDF 1.2 transcripts and plant response to the two pathogens. The increased susceptibility to B. cinerea in both Zn-deficient and Zn-excess plants could be related to lack of induction of PDF 1.2 transcripts; oxidative stress could explain higher susceptibility to the necrotroph and lower susceptibility to the biotroph in Zn-deficient plants. This research shows that an appropriate evaluation of Zn supply according to the prevalent stress factor is desirable for plants.

Protein Engineering and HDX Identify Structural Regions of G-CSF Critical to Its Stability and Aggregation

The protein engineering and formulation of therapeutic proteins for prolonged shelf-life remain a major challenge in the biopharmaceutical industry. Understanding the influence of mutations and formulations on the protein structure and dynamics could lead to more predictive approaches to their improvement. Previous intrinsic fluorescence analysis of the chemically denatured granulocyte colony-stimulating factor (G-CSF) suggested that loop AB could subtly reorganize to form an aggregation-prone intermediate state. Hydrogen deuterium exchange mass spectrometry (HDX-MS) has also revealed that excipient binding increased the thermal unfolding transition midpoint (T_m) by stabilizing loop AB. Here, we have combined protein engineering with biophysical analyses and HDX-MS to reveal that increased exchange in a core region of the G-CSF comprising loop AB (ABI, a small helix, ABII) and loop CD packed onto helix B and the beginning of loop BC leads to a decrease in T_m and higher aggregation rates. Furthermore, some mutations can increase the population of the aggregation-prone conformation within the native ensemble, as measured by the greater local exchange within this core region.

Reference Protocol to Assess Analytical Performance of Higher Order Structural Analysis Measurements: Results from an Interlaboratory Comparison

Measurements of protein higher order structure (HOS) provide important information on stability, potency, efficacy, immunogenicity, and biosimilarity of biopharmaceuticals, with a significant number of techniques and methods available to perform these measurements. The comparison of the analytical performance of HOS methods and the standardization of the results is, however, not a trivial task, due to the lack of reference protocols and reference measurement procedures. Here, we developed a protocol to structurally alter and compare samples of somatropin, a recombinant biotherapeutic, and describe the results obtained by using a number of techniques, methods and in different laboratories. This, with the final aim to provide tools and generate a pool of data to compare and benchmark analytical platforms and define method sensitivity to structural changes. Changes in somatropin HOS, induced by the presence of zinc at increasing concentrations, were observed, both globally and at more localized resolution, across many of the methods utilized in this study and with different sensitivities, suggesting the suitability of the protocol to improve understanding of inter- and cross-platform measurement comparability and assess analytical performance as appropriate.

HDX and In Silico Docking Reveal that Excipients Stabilize G-CSF via a Combination of Preferential Exclusion and Specific Hotspot Interactions

Assuring the stability of therapeutic proteins is a major challenge in the biopharmaceutical industry, and a better molecular understanding of the mechanisms through which formulations influence their stability is an ongoing priority. While the preferential exclusion effects of excipients are well known, the additional presence and impact of specific protein-excipient interactions have proven to be more elusive to identify and characterize. We have taken a combined approach of in silico molecular docking and hydrogen deuterium exchange-mass spectrometry (HDX-MS) to characterize the interactions between granulocyte colony-stimulating factor (G-CSF), and some common excipients. These interactions were related to their influence on the thermal-melting temperatures (T_m) for the nonreversible unfolding of G-CSF in liquid formulations. The residue-level interaction sites predicted in silico correlated well with those identified experimentally and highlighted the potential impact of specific excipient interactions on the T_m of G-CSF.

First amyloid β1-42 certified reference material for re-calibrating commercial immunoassays

INTRODUCTION

Reference materials based on human cerebrospinal fluid were certified for the mass concentration of amyloid beta (Aβ)1-42 (Aβ₄₂ ). They are intended to be used to calibrate diagnostic assays for Aβ₄₂ .

METHODS

The three certified reference materials (CRMs), ERM-DA480/IFCC, ERM-DA481/IFCC and ERM-DA482/IFCC, were prepared at three concentration levels and characterized using isotope dilution mass spectrometry methods. Roche, EUROIMMUN, and Fujirebio used the three CRMs to re-calibrate their immunoassays.

RESULTS

The certified Aβ₄₂ mass concentrations in ERM-DA480/IFCC, ERM-DA481/IFCC, and ERM-DA482/IFCC are 0.45, 0.72, and 1.22 μg/L, respectively, with expanded uncertainties (k = 2) of 0.07, 0.11, and 0.18 μg/L, respectively. Before re-calibration, a good correlation (Pearson's r > 0.97), yet large biases, were observed between results from different commercial assays. After re-calibration the between-assay bias was reduced to < 5%.

DISCUSSION

The Aβ₄₂ CRMs can ensure the equivalence of results between methods and across platforms for the measurement of Aβ₄₂ .

Mass Spectrometry Characterization of Higher Order Structural Changes Associated with the Fc-glycan Structure of the NISTmAb Reference Material, RM 8761

As monoclonal antibodies (mAbs) rapidly emerge as a dominant class of therapeutics, so does the need for suitable analytical technologies to monitor for changes in protein higher order structure (HOS) of these biomolecules. Reference materials (RM) serve a key analytical purpose of benchmarking the suitability and robustness of both established and emerging analytical procedures for both drug producers and regulators. Here, two simple enzymatic protocols for generating Fc-glycan variants from the NISTmAb RM are described and both global and localized changes in HOS between the RM and these Fc-glycan variants are characterized using hydrogen deuterium exchange-mass spectrometry (HDX-MS) and ion mobility spectrometry-mass spectrometry (IMS-MS) measurements. An alternative statistical approach is described where measurement thresholds that differentiate between measurement variability and significant structural changes were established on the basis of experimental data. Measurements revealed decreases in structural stability correlating with the degree of Fc-glycan structure loss, especially at the C_H2/C_H3 domain interface. These data promote the use of this RM and these Fc-glycan variants for establishing the sensitivity of and validating analytical methods for the detection of HOS measurements of mAbs.

Is there long-term value of pathology scoring in immunoglobulin A nephropathy? A validation study of the Oxford Classification for IgA Nephropathy (VALIGA) update

Background

It is unknown whether renal pathology lesions in immunoglobulin A nephropathy (IgAN) correlate with renal outcomes over decades of follow-up.

Methods

In 1130 patients of the original Validation Study of the Oxford Classification for IgA Nephropathy (VALIGA) cohort, we studied the relationship between the MEST score (mesangial hypercellularity, M; endocapillary hypercellularity, E; segmental glomerulosclerosis, S; tubular atrophy/interstitial fibrosis, T), crescents (C) and other histological lesions with both a combined renal endpoint [50% estimated glomerular filtration rate (eGFR) loss or kidney failure] and the rate of eGFR decline over a follow-up period extending to 35 years [median 7 years (interquartile range 4.1–10.8)].

Results

In this extended analysis, M1, S1 and T1–T2 lesions as well as the whole MEST score were independently related with the combined endpoint (P &lt; 0.01), and there was no effect modification by age for these associations, suggesting that they may be valid in children and in adults as well. Only T lesions were associated with the rate of eGFR loss in the whole cohort, whereas C showed this association only in patients not treated with immunosuppression. In separate prognostic analyses, the whole set of pathology lesions provided a gain in discrimination power over the clinical variables alone, which was similar at 5 years (+2.0%) and for the whole follow-up (+1.8%). A similar benefit was observed for risk reclassification analyses (+2.7% and +2.4%).

Conclusion

Long-term follow-up analyses of the VALIGA cohort showed that the independent relationship between kidney biopsy findings and the risk of progression towards kidney failure in IgAN remains unchanged across all age groups and decades after the renal biopsy.

Almond or Mahaleb? Orthogonal Allergen Analysis During a Live Incident Investigation by ELISA, Molecular Biology, and Protein Mass Spectrometry

It is now well known that an incident investigated in the United Kingdom in 2015 of cumin alleged to be contaminated with almond, a risk for people with almond allergy, was caused by the Prunus species, Prunus mahaleb. In the United Kingdom, the Government Chemist offers a route of technical appeal from official findings in the food control system. Findings of almond in two official samples, cumin and paprika, which had prompted action to exclude the consignments from the food chain, were so referred. Herein are described the approaches deployed to resolve the analytical issues during the investigation of the incidents. The cross-reactivity of ELISA to Prunus species was confirmed, and although this is useful in screening for the genus, orthogonal techniques are required to identify the species and confirm its presence. Two novel PCR assays were developed: one specific for P. mahaleb and the other a screening method capable of identifying common Prunus DNA. Peptides unique to almond and mahaleb were identified, permitting LC-tandem MS and criteria were developed for peptide identification to forensic standards. This work enables a staged approach to be taken to any future incident thought to involve Prunus species and provides a template for the investigation of similar incidents.

A candidate liquid chromatography mass spectrometry reference method for the quantification of the cardiac marker 1-32 B-type natriuretic peptide

BACKGROUND

B-type natriuretic peptide (BNP) is a 32 amino acid cardiac hormone routinely measured by immunoassays to diagnose heart failure. While it is reported that immunoassay results can vary up to 45%, no attempt of standardization and/or harmonization through the development of certified reference materials (CRMs) or reference measurement procedures (RMPs) has yet been carried out.

METHODS

B-type natriuretic peptide primary calibrator was quantified traceably to the International System of Units (SI) by both amino acid analysis and tryptic digestion. A method for the stabilization of BNP in plasma followed by protein precipitation, solid phase extraction (SPE) and liquid chromatography (LC) mass spectrometry (MS) was then developed and validated for the quantification of BNP at clinically relevant concentrations (15-150 fmol/g).

RESULTS

The candidate reference method was applied to the quantification of BNP in a number of samples from the UK NEQAS Cardiac Markers Scheme to demonstrate its applicability to generate reference values and to preliminary evaluate the commutability of a potential CRM. The results from the reference method were consistently lower than the immunoassay results and discrepancy between the immunoassays was observed confirming previous data.

CONCLUSIONS

The application of the liquid chromatography-mass spectrometry (LC-MS) method to the UK NEQAS samples and the correlation of the results with the immunoassay results shows the potential of the method to support external quality assessment schemes, to improve understanding of the bias of the assays and to establish RMPs for BNP measurements. Furthermore, the method has the potential to be multiplexed for monitoring circulating truncated forms of BNP.

Online Hydrogen-Deuterium Exchange Traveling Wave Ion Mobility Mass Spectrometry (HDX-IM-MS): a Systematic Evaluation

Hydrogen-deuterium exchange mass spectrometry (HDX-MS) is an important tool for measuring and monitoring protein structure. A bottom-up approach to HDX-MS provides peptide level deuterium uptake values and a more refined localization of deuterium incorporation compared with global HDX-MS measurements. The degree of localization provided by HDX-MS is proportional to the number of peptides that can be identified and monitored across an exchange experiment. Ion mobility spectrometry (IMS) has been shown to improve MS-based peptide analysis of biological samples through increased separation capacity. The integration of IMS within HDX-MS workflows has been commercialized but presently its adoption has not been widespread. The potential benefits of IMS, therefore, have not yet been fully explored. We herein describe a comprehensive evaluation of traveling wave ion mobility integrated within an online-HDX-MS system and present the first reported example of UDMS^E acquisition for HDX analysis. Instrument settings required for optimal peptide identifications are described and the effects of detector saturation due to peak compression are discussed. A model system is utilized to confirm the comparability of HDX-IM-MS and HDX-MS uptake values prior to an evaluation of the benefits of IMS at increasing sample complexity. Interestingly, MS and IM-MS acquisitions were found to identify distinct populations of peptides that were unique to the respective methods, a property that can be utilized to increase the spatial resolution of HDX-MS experiments by >60%. Graphical Abstract ᅟ.

Thermodynamic and kinetic investigation of monoketo-aldehyde-peroxyhemiacetal (MKA), a stereolabile degradation product of dihydroartemisinin

Theβ⇆αepimerization process ofMKAhas been studied under a thermodynamic and kinetic point of view in several solvents. LSER analyses and molecular modeling calculations allowed an effective rationalization of the findings.

Middle and long-term outcomes of dual kidney transplant: a multicenter experience

INTRODUCTION

Dual kidney transplantation (DKTx) to reduce the disparity between demand and supply of organs was evaluated in two Italian centers (Bari and Novara).

MATERIALS AND METHODS

Between October 2000 and October 2011, we performed 97 DKT (26 ipsilateral/71 bilateral) following routine biopsy of all kidneys obtained from expanded criteria donors by Remuzzi-Karpinsky scores. The reference group was 379 single grafts from donors older than 60 years single kidney transplantation ([SKT] × > 60).

RESULTS

Good postoperative renal function was observed in 56 DKTx (57.7%); whereas acute tubular necrosis requiring dialysis was observed in 41 (42.3%) patients. After a mean follow-up of 60 months, DKTx graft survivals were 96%, 93%, and 90% and patient survivals, 96%, 91%, and 91% at 1, 3, and 5 years, respectively. Complications in expanded criteria donor kidney transplantations included a high rate of cytomegalovirus (CMV) disease especially dual kidney cases. DKTx represented the only independent risk factor for CMV disease upon multivariate analysis (odds ratio [OR] 2.33, 95% confidence interval [CI] 1.28-4.2; P = .006). We did not observe any significant difference in graft or patient survival between DKTx and SKTx > 60 years.

CONCLUSIONS

We observed good outcomes up to 5 years after transplantation in terms of graft and patient survival despite the use of inferior grafts. Comparing DKTx and SKT > 60, we noted that the mean Karpinski score for SKTx was significantly better than DKTx, although patient and graft survivals were similar. This trend confirms that the use of a biopsy to allocate expanded criteria donor kidneys may be too protective; therefore, the criteria to select DKTx require further refinement.

Schmallenberg virus in Italy: a retrospective survey in Culicoides stored during the bluetongue Italian surveillance program

Following the first case of Schmallenberg (SBV) in northern Italy in February 2012, virus detection was conducted on midges collected during the national entomological surveillance program for bluetongue (BT). Six cattle farms, within a radius of 50 km from the SBV case, were selected for a 12 month study, aiming to determine when the virus entered the area, if it was capable of overwintering, and the possible role played by each species of the Obsoletus complex in disseminating the infection. A total of 33,724 Culicoides were collected at the six sites between June 2011 and June 2012. Species belonging to the Obsoletus Complex were the most abundant (94.44%) and, within the complex, Culicoides obsoletus was the most prevalent species in the studying area (65.4%). Nearly 7000 Culicoides midges were screened, either in pools or individually, for SBV by real-time RT-PCR. Viral genome was detected in six pools of the Obsoletus complex, collected at three sites between September and November 2011, and in a single parous female of C. obsoletus, collected in May 2012. As a result of the BT surveillance program in Italy it was possible to demonstrate, retrospectively, that SBV has circulated in at least three Italian provinces since early September 2011, nearly 5 months prior and as far as 40 km away from the first detected case. Similarly, the survey confirmed the presence of SBV in the vector population 3 months after the outbreak, following a cold winter during which the blacklight traps failed to catch active adult midges.

Anti-IFI16 antibodies and their relation to disease characteristics in systemic lupus erythematosus

Objective

Several studies have shown the presence of anti-IFI16 antibodies in systemic lupus erythematosus (SLE), Sjögren Syndrome (SjS), systemic sclerosis (SSc) and other autoimmune diseases. However, the significance of anti-IFI16 antibodies in SLE has not been fully characterized. The aim of this study was to investigate associations between anti-IFI16 antibodies and clinical and serologic parameters of SLE.

Methods

An enzyme-linked immunosorbent assay (ELISA) kit was used to measure anti-IFI16 antibodies in the sera of 168 SLE patients, 46 patients with any type of primary glomerulonephritis (GN) and 182 healthy controls (HCs). Associations between anti-IFI16 antibodies and clinical and serologic parameters of SLE were statistically evaluated using both univariate and multivariate analysis.

Results

Significantly higher anti-IFI16 titres were observed in SLE patients compared to both non-SLE GN and HCs (median levels: 270.1 U/ml vs 132.1 U/ml, p = 0.001, and 52.9 U/ml, p < 0.0001, respectively). With cut-off levels corresponding to the 95th percentile of the control population (113 U/ml), 63% of the SLE patients tested positive for anti-IFI16 autoantibodies, compared to just 24% of patients with primary non-SLE GN and 5% of HCs. The presence of anti-IFI16 antibodies inversely correlated with proteinuria (univariate analysis) and C3 hypocomplementaemia (univariate and multivariate analyses).

Conclusions

The inverse correlations observed between anti-IFI16 positivity, proteinuria and C3 hypocomplementaemia suggest that anti-IFI16 antibodies do not contribute to renal inflammation in SLE; indeed they may even prevent complement consumption. Anti-IFI16 antibodies hold the potential to serve as a new biomarker of disease activity in SLE.

Severe acute nephrotoxicity in a kidney transplant patient despite low tacrolimus levels: a possible interaction between donor and recipient genetic polymorphisms

WHAT IS KNOWN AND OBJECTIVE

Tacrolimus has a narrow therapeutic index and shows large interindividual variations in pharmacokinetics, which may be partly explained by genetic variability in metabolic enzymes of the cytochrome P450 (mainly CYP3A4 and CYP3A5) and transport P-glycoprotein (encoded by the ABCB1 gene). Genetic variability in the expression of biotransformation enzymes and drug transporters may also predispose individuals to tacrolimus-induced nephrotoxicity.

CASE SUMMARY

We report a case of severe biopsy-proven Tacrolimus (TAC) nephrotoxicity that occurred 1 month after renal transplantation despite persistently low TAC levels. The donor genotype was CYP3A5*3/*3 (loss-of-function genotype), whereas that of the recipient was CYP3A5*1/*3. The donor and recipient genotypes did not differ with respect to either CYP3A4 rs35599367C>T (both were CC homozygotes) or ABCB1 gene polymorphisms (both TT homozygotes for the 1236C>T polymorphism and CT heterozygotes for the 3435C>T polymorphism).

WHAT IS NEW AND CONCLUSION

This case study suggests that donor/recipient genetic mismatch in metabolic enzymes may have an important role in modulating tacrolimus nephrotoxicity. It provides a possible explanation for the intriguing observation that for a subset of patients, cumulative TAC doses appear to correlate better with nephrotoxicity than trough levels.

Structure-function relationships of iodinated contrast media and risk of nephrotoxicity

Characteristics of CM have greatly changed over time. First-generation ionic CM have many-fold (5-7) greater osmolalities than plasma. Subsequently non ionic CM generations were looked for to reduce osmolality, and encompass nonionic monomers and nonionic dimers reaching osmolality as low as that of plasma (iso-osmolar CM) but paying however dear, as viscosity is considerably increased. Intrarenal microcirculation has its "Achilles" heel in the outer medulla, where the smallness of capillary lumen and the slackness of the capillary mesh render regular blood flow at high risk, mainly because it is the same area in which the only renal work needing oxygen is made and? Iodinated CM may exert their nephrotoxic effects in three different ways: by interfering with vascular hemodynamics, by interfering with intratubular fluid volume and composition, and by producing direct cytotoxic effects to glomerular and tubular cells due to iodine by-itself. Furthermore, effects of oxygen free radical can damage glomerular cells by increasing the permeability and tubular cells impairing specific function and leading to apoptosis. Although clinical nephrotoxicity has considerably improved over time, there is no evidence for an a priori superiority of a specific CM. In general, low-osmolar (2-3 times blood) and iso-osmolar (the same as blood) CM are recommended, keeping in mind that within last generation CM dimeric iso-somolar compounds reach viscosity values higher than monomeric low-osmolar compounds and hyperviscosity is a neglected mechanisms of nephrotoxicity. We suggest that CM should be classified not only by osmolality, but also by viscosity.