Biology subjects

Dharmaraj, T.

Publications and source records attributed to Dharmaraj, T..

6 recordsLinked to original sources

bioRxiv2025

Whole-body Bacteriophage Distribution Characterized by a Physiologically based Pharmacokinetic Model

In 2019 there were over 2.8 million cases of antibiotic-resistant bacterial infection in the US with gram negative organisms having up to a 6% rate of mortality. Bacteriophage (phage) therapy holds great promise to treat such infections. However, the biologic features which influence the pharmacokinetics (PK) of phage have been difficult to characterize due to a lack of standardized protocols of phage purification, tissue assay, and labeling. Here we present robust methods for ultrapure phage preparation as well as non-destructive highly stable attachment of radio-iodide to phage using the well described Sulfo-SHPP linker. We purified and radiolabeled the phage strains, PAML-31-1, OMKO1, and Luz24 lytic to drug-resistant Pseudomonas aeruginosa for biodistribution assay in normal young adult CD-1 mice injected via penile vein. Groups of 5 mice were euthanized and tissues/organs removed for weighing and scintillation well counting of I-125 activity at 30 min, 1h, 2h, 4h, 8h, and 24h. A physiologically based PK (PBPK) model was then constructed focusing on compartments describing blood, lung, muscle, bone, liver, stomach, spleen, small intestines, large intestines, and kidney. Model permeability coefficient (PS) was estimated across all organs as being 0.0227. Tissue partition coefficients (KP) were estimated for high perfusion organs (lung and kidney) as 0.000138, GI organs (liver, spleen, and stomach) as 0.627, and all other organs as 0.220. Elimination was governed by MPS-mediated elimination (TMPS,deg) and active secretion at epithelial barriers (CLActive), which were estimated as 0.00301 h and 0.0145 L/h/kg, respectively. Monte Caro simulations showed that the rapid elimination phage in humans is expected, resulting in phage blood concentrations being lower than 102 PFU/mL (limit of quantification by plaque assay) by 12 hours. As such, multi-dose regimens and continuous infusion regimens were the only strategies that allowed continuously detectible phage concentrations. Evaluation of different dose levels showed that at a maximum dose of 1012 PFU, phage concentrations are expected to be approximately 107 PFU/g. Our physiologically based PK model of phage represents the first rigorous pre-clinical assessment of phage PK utilizing contemporary pharmacometric approaches amenable to both pre-clinical and clinical study design.

microbiology↗

bioRxiv2024

Hydrogels for Local and Sustained Delivery of Bacteriophages to Treat Multidrug-Resistant Wound Infections

Lytic bacteriophages, viruses that lyse (kill) bacteria, hold great promise for treating infections, including wound infections caused by antimicrobial-resistant Pseudomonas aeruginosa. However, dosing and delivery strategies for phage therapy remain underdeveloped. In a mouse wound infection model, we investigated the impact of administration route, dose, and frequency on the efficacy of phage therapy. We find that topical but not systemic delivery is effective in this model. In vitro and in vivo data supported the use of high doses of phage. Repeated dosing achieves the highest eradication rates in vivo. Building on these insights, we developed "HydroPhage", a hyaluronan-based hydrogel system that uses dynamic covalent crosslinking to deliver high-titre phages over one week, a substantial improvement over existing burst-release systems. We conclude that hydrogel-based sustained phage delivery offers a practical, efficacious, and well-tolerated option for topical phage application.

bioengineering↗

bioRxiv2024

The contribution of neutrophils to bacteriophage clearance and pharmacokinetics in vivo

With the increasing prevalence of antimicrobial-resistant bacterial infections, there is great interest in using lytic bacteriophages (phages) to treat such infections. However, the factors that govern bacteriophage pharmacokinetics in vivo remain poorly understood. Here, we have examined the contribution of neutrophils, the most abundant phagocytes in the body, to the pharmacokinetics of intravenously administered bacteriophage in uninfected mice. A single dose of LPS-5, an antipseudomonal bacteriophage recently used in human clinical trials, was administered intravenously to both wild-type BALB/c and neutropenic ICR mice. Phage concentrations were assessed in peripheral blood and spleen at 0.5, 1, 2, 4, 8, 12, and 24 hours after administration by plaque assay and qPCR. We observed that the phage clearance is only minimally affected by neutropenia. Indeed, the half-life of phages in blood in BALB/c and ICR mice is 3.45 and 3.66 hours, respectively. These data suggest that neutrophil-mediated phagocytosis is not a major determinant of phage clearance. Conversely, we observed a substantial discrepancy in circulating phage levels over time when measured by qPCR versus plaque assay, suggesting that substantial functional inactivation of circulating phages occurs over time. These data indicate that circulating factors, but not neutrophils, inactivate intravenously administered phages.

pharmacology and toxicology↗

bioRxiv2023

Rapid assessment of changes in phage bioactivity using dynamic light scattering

Extensive efforts are underway to develop bacteriophages as therapies against antibiotic-resistant bacteria. However, these efforts are confounded by the instability of phage preparations and a lack of suitable tools to assess active phage concentrations over time. Here, we use Dynamic Light Scattering (DLS) to measure changes in phage physical state in response to environmental factors and time, finding that phages tend to decay and form aggregates and that the degree of aggregation can be used to predict phage bioactivity. We then use DLS to optimize phage storage conditions for phages from human clinical trials, predict bioactivity in 50-year-old archival stocks, and evaluate phage samples for use in a phage therapy/wound infection model. We also provide a web-application (Phage-ELF) to facilitate DLS studies of phages. We conclude that DLS provides a rapid, convenient, and non-destructive tool for quality control of phage preparations in academic and commercial settings. Significance StatementPhages are promising for use in treating antibiotic-resistant infections, but their decay over time in refrigerated storage and higher temperatures has been a difficult barrier to overcome. This is in part because there are no suitable methods to monitor phage activity over time, especially in clinical settings. Here, we show that Dynamic Light Scattering (DLS) can be used to measure the physical state of phage preparations, which provides accurate and precise information on their lytic function - the key parameter underlying clinical efficacy. This study reveals a "structure-function" relationship for lytic phages and establishes DLS as a method to optimize the storage, handling, and clinical use of phages.

biophysics↗

bioRxiv2020

Filamentous Bacteriophage Delay Healing of Pseudomonas-Infected Wounds

We have identified a novel role for filamentous bacteriophage in the delayed healing associated with chronic Pseudomonas aeruginosa (Pa) wound infections. Pf phage delays wound re-epithelialization in the absence of live Pa, indicative that Pf effects on wound healing are independent of Pa pathogenesis. Pf phage directly inhibits autocrine signaling of CXCL1 (KC) to impede keratinocyte migration and wound re-epithelization. In agreement with these studies, a prospective cohort study of 36 human patients with chronic Pa wound infections revealed that wounds infected with Pf positive strains of Pa took longer to heal and were more likely to increase in size compared to wounds infected with Pf negative strains. Together, these data implicate Pf phage in the delayed wound healing associated with Pa infection through direct manipulation of mammalian target cells. We propose that Pf phage may have potential as a biomarker and therapeutic target in delayed wound healing.

microbiology↗

bioRxiv2017

OGT (O-GlcNAc Transferase) selectively modifies multiple residues unique to lamin A

The LMNA gene encodes lamins A and C with key roles in nuclear structure, signaling, chromatin organization, and genome integrity. Mutations in LMNA cause >12 diseases, termed laminopathies. Lamins A and C are identical for their first 566 residues. However, they form distinct filaments in vivo with apparently distinct roles. We report that lamin A is O-GlcNAc modified in human hepatoma (Huh7) cells and in mouse liver. In vitro assays with purified OGT enzyme showed robust O-GlcNAcylation of recombinant mature lamin A tails (residues 385-646), with no detectable modification of lamin B1, lamin C, or progerin ({Delta}50) tails. Using mass spectrometry, we identified 11 O-GlcNAc sites in a sweet spot unique to lamin A, with up to seven sugars per peptide. Most sites were unpredicted by current algorithms. Double-mutant (S612A/T643A) lamin A tails were still robustly O-GlcNAc-modified at seven sites. By contrast, O-GlcNAcylation was undetectable on tails bearing deletion {Delta}50, which causes Hutchinson-Gilford progeria syndrome, and greatly reduced by deletion {Delta}35, suggesting this region is required for substrate recognition or modification by OGT in vitro. These results suggest OGT, an essential protein and master regulator, regulates partners or function(s) unique to lamin A that are lost in progeria.

biochemistry↗