Superior vena cava syndrome in chronic intestinal failure patients: When the going gets tough

BACKGROUND & AIMS

Catheter-related venous thrombosis is a severe complication of home parenteral nutrition (HPN) with potentially devastating consequences such as superior vena cava syndrome (SVCS). Early recognition and awareness of factors leading to its development are of paramount importance. However, studies are lacking in HPN patients focusing on this topic. In this study, we aimed to determine the incidence of SVCS in HPN patients and describe SVCS-related outcomes.

METHODS

This retrospective cohort study comprised all adult HPN patients who developed SVCS between 2000 and 2022 at our national HPN referral center. Primary outcome was the incidence of SVCS. Secondary outcomes include SVCS-related symptoms, tip location of central venous access device (CVAD) post-insertion and at time of SVCS, diagnostics and treatment.

RESULTS

SVCS was diagnosed in 38 of 616 patients (6%), with an annual cumulative incidence rate ranging between 0 and 4.2%. Most common presenting symptoms were facial edema (82%) and arm edema (50%). Post-insertion, 17% (6/36) of patients had a correct position of the CVAD tip and 11% (4/36) during SVCS diagnosis. Computed tomography was the most used diagnostic imaging technique (66%). Sixty-three percent of patients started, 11% switched, and 21% continued anticoagulant treatment.

CONCLUSIONS

The incidence of SVCS is relatively high in our vulnerable HPN population. It is key to recognize whenever such patients present with vascular obstruction-related symptoms and treat them in an early stage by a multidisciplinary team.

High-throughput proteomics and in vitro functional characterization of the 26 medically most important elapids and vipers from sub-Saharan Africa

Venomous snakes are important parts of the ecosystem, and their behavior and evolution have been shaped by their surrounding environments over the eons. This is reflected in their venoms, which are typically highly adapted for their biological niche, including their diet and defense mechanisms for deterring predators. Sub-Saharan Africa is rich in venomous snake species, of which many are dangerous to humans due to the high toxicity of their venoms and their ability to effectively deliver large amounts of venom into their victims via their bite. In this study, the venoms of 26 of sub-Saharan Africa's medically most relevant elapid and viper species were subjected to parallelized toxicovenomics analysis. The analysis included venom proteomics and in vitro functional characterization of whole venom toxicities, enabling a robust comparison of venom profiles between species. The data presented here corroborate previous studies and provide biochemical details for the clinical manifestations observed in envenomings by the 26 snake species. Moreover, two new venom proteomes (Naja anchietae and Echis leucogaster) are presented here for the first time. Combined, the presented data can help shine light on snake venom evolutionary trends and possibly be used to further improve or develop novel antivenoms.

VHHs as tools for therapeutic protein delivery to the central nervous system

Background

The blood brain barrier (BBB) limits the therapeutic perspective for central nervous system (CNS) disorders. Previously we found an anti-mouse transferrin receptor (TfR) VHH (Nb62) that was able to deliver a biologically active neuropeptide into the CNS in mice. Here, we aimed to test its potential to shuttle a therapeutic relevant cargo. Since this VHH could not recognize the human TfR and hence its translational potential is limited, we also aimed to find and validate an anti-human transferrin VHH to deliver a therapeutic cargo into the CNS.

Methods

Alpaca immunizations with human TfR, and subsequent phage selection and screening for human TfR binding VHHs was performed to find a human TfR specific VHH (Nb188). Its ability to cross the BBB was determined by fusing it to neurotensin, a neuropeptide that reduces body temperature when present in the CNS but is not able to cross the BBB on its own. Next, the anti–β-secretase 1 (BACE1) 1A11 Fab and Nb62 or Nb188 were fused to an Fc domain to generate heterodimeric antibodies (1A11AM-Nb62 and 1A11AM-Nb188). These were then administered intravenously in wild-type mice and in mice in which the murine apical domain of the TfR was replaced by the human apical domain (hAPI KI). Pharmacokinetic and pharmacodynamic (PK/PD) studies were performed to assess the concentration of the heterodimeric antibodies in the brain over time and the ability to inhibit brain-specific BACE1 by analysing the brain levels of Aβ_1–40.

Results

Selections and screening of a phage library resulted in the discovery of an anti-human TfR VHH (Nb188). Fusion of Nb188 to neurotensin induced hypothermia after intravenous injections in hAPI KI mice. In addition, systemic administration 1A11AM-Nb62 and 1A11AM-Nb188 fusions were able to reduce Aβ_1-40 levels in the brain whereas 1A11AM fused to an irrelevant VHH did not. A PK/PD experiment showed that this effect could last for 3 days.

Conclusion

We have discovered an anti-human TfR specific VHH that is able to reach the CNS when administered systemically. In addition, both the currently discovered anti-human TfR VHH and the previously identified mouse-specific anti-TfR VHH, are both able to shuttle a therapeutically relevant cargo into the CNS. We suggest the mouse-specific VHH as a valuable research tool in mice and the human-specific VHH as a moiety to enhance the delivery efficiency of therapeutics into the CNS in human patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00374-4.

Advances in antibody phage display technology

Phage display technology can be used for the discovery of antibodies for research, diagnostic, and therapeutic purposes. In this review, we present and discuss key parameters that can be optimized when performing phage display selection campaigns, including the use of different antibody formats and advanced strategies for antigen presentation, such as immobilization, liposomes, nanodiscs, virus-like particles, and whole cells. Furthermore, we provide insights into selection strategies that can be used for the discovery of antibodies with complex binding requirements, such as targeting a specific epitope, cross-reactivity, or pH-dependent binding. Lastly, we provide a description of specialized phage display libraries for the discovery of bispecific antibodies and pH-sensitive antibodies. Together, these methods can be used to improve antibody discovery campaigns against all types of antigen. Teaser: This review provides an overview of the different strategies that can be exploited to improve the success rate of antibody phage display discovery campaigns, addressing key parameters, such as antigen presentation, selection methodologies, and specialized libraries.

AAV-mediated delivery of an anti-BACE1 VHH alleviates pathology in an Alzheimer's disease model

Single domain antibodies (VHHs) are potentially disruptive therapeutics, with important biological value for treatment of several diseases, including neurological disorders. However, VHHs have not been widely used in the central nervous system (CNS), largely because of their restricted blood-brain barrier (BBB) penetration. Here, we propose a gene transfer strategy based on BBB-crossing Adeno-associated virus (AAV)-based vectors to deliver VHH directly into the CNS. As a proof-of-concept, we explored the potential of AAV-delivered VHH to inhibit BACE1, a well-characterized target in Alzheimer's disease. First, we generated a panel of VHHs targeting BACE1, one of which, VHH-B9, shows high selectivity for BACE1 and efficacy in lowering BACE1 activity in vitro. We further demonstrate that a single systemic dose of AAV-VHH-B9 produces positive long-term (12 months plus) effects on amyloid load, neuroinflammation, synaptic function, and cognitive performance, in the App^NL-G-F Alzheimer's disease mouse model. These results constitute a novel therapeutic approach forneurodegenerative diseases, which is applicable to a range of CNS disease targets.

Applicability of cerebral open flow microperfusion and microdialysis to quantify a brain-penetrating nanobody in mice

The use of biologics in the therapeutic landscape has increased exponentially since the last 3 decades. Nevertheless, patients with central nervous system (CNS) related disorders could not yet benefit from this revolution because the blood-brain barrier (BBB) severely hampers biologics from entering the brain. Considerable effort has been put into generating methods to modulate or circumvent the BBB for delivery of therapeutics to the CNS. A promising strategy is receptor-mediated transcytosis (RMT). Recently, Wouters et al. (2020) discovered a mouse anti-transferrin receptor nanobody that is able to deliver a biologically active peptide to the brain via RMT. The present study aims to sample a derivative of this brain-penetrating nanobody (Nb105) in the CNS. Therefore, we compared the applicability of cerebral open flow microperfusion (cOFM) and microdialysis as sampling techniques to directly obtain high molecular weight substances from the cerebral interstitial fluid. A custom AlphaScreen™ assay was validated to quantify nanobody concentrations in the samples. In vitro microdialysis probe (AtmosLM™, 1 MDa cut-off) recovery by gain and by loss for Nb105 was 18.3 ± 3.2% and 27.0 ± 2.5% respectively, whereas for cOFM it was 87.2 ± 4.0% and 97.3 ± 1.6%. Although a large difference in in vitro recovery is observed between cOFM and microdialysis, in vivo similar results were obtained. Immunohistochemical stainings showed an astrocytic and microglial reaction in the immediate vicinity along the implantation track for both probe types. Coronal sections showed higher fluorescein isothiocyanate-dextran and immunoglobulin G extravasation around the microdialysis probe track than after cOFM sampling experiments, however this leakage was clearly limited compared to a positive control where the BBB was disrupted. This is the first study that samples a bispecific nanobody in the brain's interstitial fluid in function of time, providing a pharmacokinetic profile of nanobodies in the CNS. Furthermore, this is the first time a cOFM study is performed in awake freely moving mice, providing data on inflammation and blood-brain barrier integrity in the mouse brain. Overall, this work demonstrates that, while taking into account the (bio)analytical considerations, both microdialysis and cOFM are suitable in vivo sampling techniques for quantification of nanobodies in the CNS.

Identification and in vivo characterization of a brain-penetrating nanobody

Background

Preclinical models to determine blood to brain transport ability of therapeutics are often ambiguous. In this study a method is developed that relies on CNS target-engagement and is able to rank brain-penetrating capacities. This method led to the discovery of an anti-transferrin receptor nanobody that is able to deliver a biologically active peptide to the brain via receptor-mediated transcytosis.

Methods

Various nanobodies against the mouse transferrin receptor were fused to neurotensin and injected peripherally in mice. Neurotensin is a neuropeptide that causes hypothermia when present in the brain but is unable to reach the brain from the periphery. Continuous body temperature measurements were used as a readout for brain penetration of nanobody-neurotensin fusions after its peripheral administration. Full temperature curves were analyzed using two-way ANOVA with Dunnett multiple comparisons tests.

Results

One anti-transferrin receptor nanobody coupled to neurotensin elicited a drop in body temperature following intravenous injection. Epitope binning indicated that this nanobody bound a distinct transferrin receptor epitope compared to the non-crossing nanobodies. This brain-penetrating nanobody was used to characterize the in vivo hypothermia model. The hypothermic effect caused by neurotensin is dose-dependent and could be used to directly compare peripheral administration routes and various nanobodies in terms of brain exposure.

Conclusion

This method led to the discovery of an anti-transferrin receptor nanobody that can reach the brain via receptor-mediated transcytosis after peripheral administration. This method could be used to assess novel proteins for brain-penetrating capabilities using a target-engaging readout.

Randomised clinical trial: 2% taurolidine versus 0.9% saline locking in patients on home parenteral nutrition

BACKGROUND

The catheter lock solutions 2% taurolidine and 0.9% saline are both used to prevent catheter-related bloodstream infections (CRBSIs) in home parenteral nutrition patients.

AIMS

To compare the effectiveness and safety of taurolidine and saline.

METHODS

This multicentre double-blinded trial randomly assigned home parenteral nutrition patients to use either 2% taurolidine or 0.9% saline for 1 year. Patients were stratified in a new catheter group and a pre-existing catheter group. Primary outcome was the rate of CRBSIs/1000 catheter days in the new catheter group and pre-existing catheter group, separately.

RESULTS

We randomised 105 patients, of which 102 were analysed as modified intention-to-treat population. In the new catheter group, rates of CRBSIs/1000 catheter days were 0.29 and 1.49 in the taurolidine and saline arm respectively (relative risk, 0.20; 95% CI, 0.04-0.71; P = 0.009). In the pre-existing catheter group, rates of CRBSIs/1000 catheter days were 0.39 and 1.32 in the taurolidine and saline arm respectively (relative risk, 0.30; 95% CI, 0.03-1.82; P = 0.25). Excluding one outlier patient in the taurolidine arm, mean costs per patient were $1865 for taurolidine and $4454 for saline (P = 0.03). Drug-related adverse events were rare and generally mild.

CONCLUSIONS

In the new catheter group, taurolidine showed a clear decrease in CRBSI rate. In the pre-existing catheter group, no superiority of taurolidine could be demonstrated, most likely due to underpowering. Overall, taurolidine reduced the risk for CRBSIs by more than four times. Given its favourable safety and cost profile, taurolidine locking should be considered as an additional strategy to prevent CRBSIs.

TRIAL REGISTRATION

Clinicaltrials.gov, identifier: NCT01826526.

Affinity and kinetics study of anthranilic acids as HCA2 receptor agonists

Structure-affinity relationship (SAR) and structure-kinetics relationship (SKR) studies were combined to investigate a series of biphenyl anthranilic acid agonists for the HCA2 receptor. In total, 27 compounds were synthesized and twelve of them showed higher affinity than nicotinic acid. Two compounds, 6g (IC50=75nM) and 6z (IC50=108nM) showed a longer residence time profile compared to nicotinic acid, exemplified by their kinetic rate index (KRI) values of 1.31 and 1.23, respectively. The SAR study resulted in the novel 2-F, 4-OH derivative (6x) with an IC50 value of 23nM as the highest affinity HCA2 agonist of the biphenyl series, although it showed a similar residence time as nicotinic acid. The SAR and SKR data suggest that an early compound selection based on binding kinetics is a promising addition to the lead optimization process.