Anti-racism bystander training: A critical need in medical schools.

Despite increasing acknowledgment of racism in both the curricular and clinical spaces, it continues to pervade the medical field, with clear detrimental impacts to the health of our patients. The introduction of anti-racism bystander training (ARBT) may provide a unique opportunity to reduce inequitable care and health disparities that occur secondary to racism in healthcare. ARBT, in its various forms, has been shown to be an effective method to increase participants' confidence and efficacy in intervening on observed racist encounters. This training can take numerous forms, and the authors provide one successful template used with medical students at their own institution. If medical centers, educators, and leaders in the field of medicine truly hope to mitigate the individual racist behaviors that remain in healthcare, ARBT must be employed to a much wider degree in medical education.

Host biotin is required for liver stage development in malaria parasites.

Acetyl-CoA carboxylase (ACC) is a biotin-dependent enzyme that is the target of several classes of herbicides. Malaria parasites contain a plant-like ACC, and this is the only protein predicted to be biotinylated in the parasite. We found that ACC is expressed in the apicoplast organelle in liver- and blood-stage malaria parasites; however, it is activated through biotinylation only in the liver stages. Consistent with this observation, deletion of the biotin ligase responsible for ACC biotinylation does not impede blood-stage growth, but results in late liver-stage developmental defects. Biotin depletion increases the severity of the developmental defects, demonstrating that parasite and host biotin metabolism are required for normal liver-stage progression. This finding may link the development of liver-stage malaria parasites to the nutritional status of the host, as neither the parasite nor the human host can synthesize biotin.

Reversible Conformational Change in the Plasmodium falciparum Circumsporozoite Protein Masks Its Adhesion Domains.

The extended rod-like Plasmodium falciparum circumsporozoite protein (CSP) is comprised of three primary domains: a charged N terminus that binds heparan sulfate proteoglycans, a central NANP repeat domain, and a C terminus containing a thrombospondin-like type I repeat (TSR) domain. Only the last two domains are incorporated in RTS,S, the leading malaria vaccine in phase 3 trials that, to date, protects about 50% of vaccinated children against clinical disease. A seroepidemiological study indicated that the N-terminal domain might improve the efficacy of a new CSP vaccine. Using a panel of CSP-specific monoclonal antibodies, well-characterized recombinant CSPs, label-free quantitative proteomics, and in vitro inhibition of sporozoite invasion, we show that native CSP is N-terminally processed in the mosquito host and undergoes a reversible conformational change to mask some epitopes in the N- and C-terminal domains until the sporozoite interacts with the liver hepatocyte. Our findings show the importance of understanding processing and the biophysical change in conformation, possibly due to a mechanical or molecular signal, and may aid in the development of a new CSP vaccine.

A naturally variable residue in the S1 subsite of M1 family aminopeptidases modulates catalytic properties and promotes functional specialization.

M1 family metallo-aminopeptidases fulfill a wide range of critical and in some cases medically relevant roles in humans and human pathogens. The specificity of M1-aminopeptidases is dominated by the interaction of the well defined S1 subsite with the side chain of the first (P1) residue of the substrate and can vary widely. Extensive natural variation occurs at one of the residues that contributes to formation of the cylindrical S1 subsite. We investigated whether this natural variation contributes to diversity in S1 subsite specificity. Effects of 11 substitutions of the S1 subsite residue valine 459 in the Plasmodium falciparum aminopeptidase PfA-M1 and of three substitutions of the homologous residue methionine 260 in Escherichia coli aminopeptidase N were characterized. Many of these substitutions altered steady-state kinetic parameters for dipeptide hydrolysis and remodeled S1 subsite specificity. The most dramatic change in specificity resulted from substitution with proline, which collapsed S1 subsite specificity such that only substrates with P1-Arg, -Lys, or -Met were appreciably hydrolyzed. The structure of PfA-M1 V459P revealed that the proline substitution induced a local conformational change in the polypeptide backbone that resulted in a narrowed S1 subsite. The restricted specificity and active site backbone conformation of PfA-M1 V459P mirrored those of endoplasmic reticulum aminopeptidase 2, a human enzyme with proline in the variable S1 subsite position. Our results provide compelling evidence that changes in the variable residue in the S1 subsite of M1-aminopeptidases have facilitated the evolution of new specificities and ultimately novel functions for this important class of enzymes.

Shedding of TRAP by a rhomboid protease from the malaria sporozoite surface is essential for gliding motility and sporozoite infectivity.

Plasmodium sporozoites, the infective stage of the malaria parasite, move by gliding motility, a unique form of locomotion required for tissue migration and host cell invasion. TRAP, a transmembrane protein with extracellular adhesive domains and a cytoplasmic tail linked to the actomyosin motor, is central to this process. Forward movement is achieved when TRAP, bound to matrix or host cell receptors, is translocated posteriorly. It has been hypothesized that these adhesive interactions must ultimately be disengaged for continuous forward movement to occur. TRAP has a canonical rhomboid-cleavage site within its transmembrane domain and mutations were introduced into this sequence to elucidate the function of TRAP cleavage and determine the nature of the responsible protease. Rhomboid cleavage site mutants were defective in TRAP shedding and displayed slow, staccato motility and reduced infectivity. Moreover, they had a more dramatic reduction in infectivity after intradermal inoculation compared to intravenous inoculation, suggesting that robust gliding is critical for dermal exit. The intermediate phenotype of the rhomboid cleavage site mutants suggested residual, albeit inefficient cleavage by another protease. We therefore generated a mutant in which both the rhomboid-cleavage site and the alternate cleavage site were altered. This mutant was non-motile and non-infectious, demonstrating that TRAP removal from the sporozoite surface functions to break adhesive connections between the parasite and extracellular matrix or host cell receptors, which in turn is essential for motility and invasion.

Hybrid Stenting of Pulmonary Venous Baffle Stenosis: Subxiphoid Approach in Transposition of the Great Arteries.

A 31-year-old woman with transposition of the great arteries status post-Senning operation presents with severe pulmonary venous baffle obstruction. Both standards of care (percutaneous stenting or open repair) were deemed suboptimal and/or high risk. A multidisciplinary, hybrid approach via subxiphoid incision, guided by 3-dimensional modeling, provided a lower risk and minimally invasive intervention.

Durability of Aortic Homografts in Pulmonary Atresia and Major Aortopulmonary Collateral Arteries.

Objectives: It is well-known that right ventricle-to-pulmonary artery homograft conduit durability is worse for smaller conduits and smaller/younger patients. However, there is limited literature on age and conduit-size specific outcomes, or on the role of conduit oversizing. Methods: Patients diagnosed with tetralogy of Fallot and major aortopulmonary collateral arteries undergoing right ventricular outflow tract (RVOT) reconstruction with a valved aortic homograft conduit from November 2001 through March 2023, at our institution were included. Conduits were grouped and evaluated by diameter, diameter Z-score, and patient age at implant. The primary time-related outcome was freedom from RVOT reintervention. Factors associated with freedom from time-related outcomes were assessed with univariable Cox regression analysis. Results: A total of 863 RVOT conduits were implanted in 722 patients. On multivariable analysis, younger age, male sex, Alagille syndrome, smaller diameter of the conduit, and smaller Z-score were associated with shorter freedom from reintervention. Among patients with smaller diameter conduits, larger Z-scores were associated with longer freedom from conduit reintervention (P < .001). Transcatheter interventions were commonly used to extend conduit lifespan across ages and conduit sizes. Conclusions: Larger conduit diameter, older age, and higher conduit Z-score were associated with longer freedom from reintervention in patients undergoing RVOT reconstruction in this cohort. Oversizing of conduits, even beyond a Z-score of 4, is generally appropriate.

Temporary Microaxial Support in a Patient With Multiple Post-Myocardial Infarction Mechanical Complications: Bridge to Transplantation.

A 66-year-old man with post-myocardial infarction ventricular septal rupture, apical aneurysm, and pseudoaneurysm presenting in cardiogenic shock received a surgically placed temporary microaxial transvalvular left ventricular assist device. This stabilized hemodynamics and end-organ function, and he subsequently underwent successful heart transplantation. A temporary microaxial transvalvular left ventricular assist device can effectively bridge patients with select mechanical complications of myocardial infarction beyond ventricular septal rupture.

Short- and Mid-Term Results of Pulmonary Valve Replacement with the Inspiris Valve.

BACKGROUND: Various bioprosthetic valves are used off-label for pulmonary valve replacement (PVR), but there is no consensus on whether a particular valve is best for this application. Recently, the Inspiris Resilia valve (Edwards Lifesciences Inc) was approved for aortic valve replacement, and surgeons have begun using it for PVR. There is limited evidence on the performance of the Inspiris valve compared with other valves in the pulmonary position. METHODS: This study reviewed all patients who underwent PVR with a size 19- to 29-mm Inspiris valve or Mosaic valve (Medtronic Inc) from 2007 to 2022 at Lucile Packard Children's Hospital Stanford (Palo Alto, CA). Midterm outcomes included freedom from moderate or severe pulmonary regurgitation (PR), a maximum Doppler gradient ≥36 mm Hg, and freedom from reintervention. RESULTS: A total of 225 consecutive patients who underwent PVR with a size 19- to 29-mm Mosaic (n = 163) or Inspiris (n = 62) valve were included. There was no difference in baseline characteristics. Early postoperative gradients were low in both groups but higher in the Mosaic cohort, and neither group had more than mild PR on discharge. On univariable and multivariable analysis, Inspiris valves were significantly more likely to develop moderate or greater PR over time. There was no significant difference between the valves in freedom from reintervention or from a maximum gradient ≥36 mm Hg. CONCLUSIONS: Early and short-term gradients were similar in patients undergoing PVR with Inspiris and Mosaic valves, but significant PR was more common in patients who received an Inspiris valve. These preliminary findings suggest that the durability of the Inspiris valve in the pulmonary position may not be superior to that of other bioprosthetic valves used for PVR.

Minimally invasive adnexa-sparing surgery for benign ovarian and paratubal masses in children.

BACKGROUND: The precision of minimally invasive surgery (MIS) to resect benign ovarian and paratubal masses while preserving adnexa in children is unclear. This study evaluated the integrity of laparoscopy to spare adnexa while resecting benign pathologies in children. METHODS: The institutional pathology database was queried to identify patients aged 18 years and younger having any ovarian or tubal lesion resected at a comprehensive children's hospital between 2006 and 2021. Adnexa-sparing surgery was defined as preserving both the ovary and tube from which the lesion was resected. Postoperative ultrasounds were reviewed to document ovarian follicles, blood flow, volumes, and lesion recurrence. RESULTS: Adnexal preservation was implemented in 168 of 328 pathological resections. MIS approach was used in 149 cases. Median age was 13.4 [11.0-15.3]. Among sparing surgeries, MIS associated with benign pathology, shorter operative time (median minutes: 78 MIS [59-111.5]; 130 open [92.8-149.8]; 174 MIS-to-open [132.8-199.5]; p = 0.010), and reduced hospital stay (median days: 1 MIS (Lindfors, 1971; Lovvorn III et al., 1998) [1-2]; 2 open [2-2.9], 2 MIS-to-open [1-3.3]; p = 0.001). Postoperative ovarian volume ipsilateral to the MIS procedure (median, 7.6 ml [4.3-12.1]) was relatively smaller than the contralateral ovary (median, 9.1 ml [5.5-15.0]). Blood flow was documented to the ovary in 70/94 (74.4%) of patients after MIS adnexal-sparing surgery. Distinct follicles were detected in 48/74 (64.8%) of post-menarchal patients after MIS adnexal-sparing surgery. Five ovarian cysts recurred. CONCLUSIONS: MIS preserves adnexa reliably, with postoperative ovarian follicles and blood flow detected in most patients, and maintains ∼80% of contralateral volume, while achieving definitive tumor resection. LEVEL OF EVIDENCE: III.

Distribution and biochemical properties of an M1-family aminopeptidase in Plasmodium falciparum indicate a role in vacuolar hemoglobin catabolism.

Aminopeptidases catalyze N-terminal peptide bond hydrolysis and occupy many diverse roles across all domains of life. Here we present evidence that an M1-family aminopeptidase, PfA-M1, has been recruited to specialized roles in the human malaria parasite Plasmodium falciparum. PfA-M1 is abundant in two subcellular compartments in asexual intraerythrocytic parasites; that is, the food vacuole, where the catabolism of host hemoglobin takes place, and the nucleus. A unique N-terminal extension contributes to the observed dual targeting by providing a signal peptide and putative alternate translation initiation sites. PfA-M1 exists as two major isoforms, a nuclear 120-kDa species and a processed species consisting of a complex of 68- and 35-kDa fragments. PfA-M1 is both stable and active at the acidic pH of the food vacuole lumen. Determination of steady-state kinetic parameters for both aminoacyl-ß-naphthylamide and unmodified dipeptide substrates over the pH range 5.0-8.5 reveals that k(cat) is relatively insensitive to pH, whereas K(m) increases at pH values below 6.5. At the pH of the food vacuole lumen (5.0-5.5), the catalytic efficiency of PfA-M1 remains high. Consistent with the kinetic data, the affinity of peptidic competitive inhibitors is diminished at acidic pH. Together, these results support a catalytic role for PfA-M1 in the food vacuole and indicate the importance of evaluating the potency of peptidic inhibitors at physiologically relevant pH values. They also suggest a second, distinct function for this enzyme in the parasite nucleus.

Investigation of Cysteine Modifications in Recombinant Protein Tetanus Toxoid Heavy Chain Fragment C.

For conjugated HIV-1 fusion peptide vaccine development, recombinant Tetanus toxoid heavy chain fragment C (rTTHC) was applied as a carrier protein to boost peptide immunogenicity. Understanding the characteristics of rTTHC is the first step prior to the peptide conjugation. A comprehensive mass spectrometry (MS) characterization was performed on E. coli expressed rTTHC during its purification process. Intact mass along with peptide mapping analysis discovered the existence of three cysteine modification forms: glutathionylation, trisulfide bond modification, and disulfide bond shuffling, in correlation to a three-peak profile during a hydrophobic interaction chromatography (HIC) purification step. Coexistence of these multiple oxidative forms indicated that the active thiols underwent redox reaction in the rTTHC material. Identity confirmation of the rTTHC carrier protein by MS analysis provided pivotal guidance to assess the purification step and helped ensure that vaccine development could proceed.

Evidence for catalytic roles for Plasmodium falciparum aminopeptidase P in the food vacuole and cytosol.

The metalloenzyme aminopeptidase P catalyzes the hydrolysis of amino acids from the amino termini of peptides with a prolyl residue in the second position. The human malaria parasite Plasmodium falciparum expresses a homolog of aminopeptidase P during its asexual intraerythrocytic cycle. P. falciparum aminopeptidase P (PfAPP) shares with mammalian cytosolic aminopeptidase P a three-domain, homodimeric organization and is most active with Mn(II) as the cofactor. A distinguishing feature of PfAPP is a 120-amino acid amino-terminal extension that appears to be removed from the mature protein. PfAPP is present in the food vacuole and cytosol of the parasite, a distribution that suggests roles in vacuolar hemoglobin catabolism and cytosolic peptide turnover. To evaluate the plausibility of these putative functions, the stability and kinetic properties of recombinant PfAPP were evaluated at the acidic pH of the food vacuole and at the near-neutral pH of the cytosol. PfAPP exhibited high stability at 37 degrees C in the pH range 5.0-7.5. In contrast, recombinant human cytosolic APP1 was unstable and formed a high molecular weight aggregate at acidic pH. At both acidic and slightly basic pH values, PfAPP efficiently hydrolyzed the amino-terminal X-Pro bond of the nonapeptide bradykinin and of two globin pentapeptides that are potential in vivo substrates. These results provide support for roles for PfAPP in peptide catabolism in both the food vacuole and the cytosol and suggest that PfAPP has evolved a dual distribution in response to the metabolic needs of the intraerythrocytic parasite.

Longitudinal analysis of Plasmodium sporozoite motility in the dermis reveals component of blood vessel recognition.

Malaria infection starts with injection of Plasmodium sporozoites by an Anopheles mosquito into the skin of the mammalian host. How sporozoites locate and enter a blood vessel is a critical, but poorly understood process. In this study, we examine sporozoite motility and their interaction with dermal blood vessels, using intravital microscopy in mice. Our data suggest that sporozoites exhibit two types of motility: in regions far from blood vessels, they exhibit 'avascular motility', defined by high speed and less confinement, while in the vicinity of blood vessels their motility is more constrained. We find that curvature of sporozoite tracks engaging with vasculature optimizes contact with dermal capillaries. Imaging of sporozoites with mutations in key adhesive proteins highlight the importance of the sporozoite's gliding speed and its ability to modulate adhesive properties for successful exit from the inoculation site.

Engagement of the S1, S1' and S2' subsites drives efficient catalysis of peptide bond hydrolysis by the M1-family aminopeptidase from Plasmodium falciparum.

The M1-family aminopeptidase PfA-M1 catalyzes the last step in the catabolism of human hemoglobin to amino acids in the Plasmodium falciparum food vacuole. In this study, the structural features of the substrate that promote efficient PfA-M1-catalyzed peptide bond hydrolysis were analyzed. X-Ala and Ala-X dipeptide substrates were employed to characterize the specificities of the enzyme's S1 and S1' subsites. Both subsites exhibited a preference for basic and hydrophobic sidechains over polar and acidic sidechains. The relative specificity of the S1 subsite was similar over the pH range 5.5-7.5. Substrate P1 and P1' residues affected both K(m) and k(cat), revealing that sidechain-subsite interactions not only drive the formation of the Michaelis complex but also influence the rates of ensuing chemical steps. Only a small fraction of the available binding energy was exploited in interactions between substrate sidechains and the S1 and S1' subsites, which indicates a modest level of complementarity. There was no correlation between S1 and S1' specificities and amino acid abundance in hemoglobin. Interactions between PfA-M1 and the backbone atoms of the P1' and P2' residues as well as the P2' sidechain further contributed to the catalytic efficiency of substrate hydrolysis. By demonstrating the engagement of multiple, broad-specificity subsites in PfA-M1, these studies provide insight into how this enzyme is able to efficiently generate amino acids from highly sequence-diverse di- and oligopeptides in the food vacuole.