Antibiotic Treatment Prior to Injury Improves Post-Traumatic Osteoarthritis Outcomes in Mice.

Osteoarthritis (OA) is a painful and debilitating disease characterized by the chronic and progressive degradation of articular cartilage. Post-traumatic OA (PTOA) is a secondary form of OA that develops in ~50% of cases of severe articular injury. Inflammation and re-occurring injury have been implicated as contributing to the progression of PTOA after the initial injury. However, there is very little known about external factors prior to injury that could affect the risk of PTOA development. To examine how the gut microbiome affects PTOA development we used a chronic antibiotic treatment regimen starting at weaning for six weeks prior to ACL rupture, in mice. A six-weeks post-injury histological examination showed more robust cartilage staining on the antibiotic (AB)-treated mice than the untreated controls (VEH), suggesting slower disease progression in AB cohorts. Injured joints also showed an increase in the presence of anti-inflammatory M2 macrophages in the AB group. Molecularly, the phenotype correlated with a significantly lower expression of inflammatory genes Tlr5, Ccl8, Cxcl13, and Foxo6 in the injured joints of AB-treated animals. Our results indicate that a reduced state of inflammation at the time of injury and a lower expression of Wnt signaling modulatory protein, Rspo1, caused by AB treatment can slow down or improve PTOA outcomes.

Naphthalene DNA Adduct Formation and Tolerance in the Lung.

Naphthalene (NA) is a respiratory toxicant and possible human carcinogen. NA is a ubiquitous combustion product and significant component of jet fuel. The National Toxicology Program found that NA forms tumors in two species, in rats (nose) and mice (lung). However, it has been argued that NA does not pose a cancer risk to humans because NA is bioactivated by cytochrome P450 monooxygenase enzymes that have very high efficiency in the lung tissue of rodents but low efficiency in the lung tissue of humans. It is thought that NA carcinogenesis in rodents is related to repeated cycles of lung epithelial injury and repair, an indirect mechanism. Repeated in vivo exposure to NA leads to development of tolerance, with the emergence of cells more resistant to NA insult. We tested the hypothesis that tolerance involves reduced susceptibility to the formation of NA-DNA adducts. NA-DNA adduct formation in tolerant mice was examined in individual, metabolically-active mouse airways exposed ex vivo to 250 µΜ 14C-NA. Ex vivo dosing was used since it had been done previously and the act of creating a radioactive aerosol of a potential carcinogen posed too many safety and regulatory obstacles. Following extensive rinsing to remove unbound 14C-NA, DNA was extracted and 14C-NA-DNA adducts were quantified by AMS. The tolerant mice appeared to have slightly lower NA-DNA adduct levels than non-tolerant controls, but intra-group variations were large and the difference was statistically insignificant. It appears the tolerance may be more related to other mechanisms, such as NA-protein interactions in the airway, than DNA-adduct formation.

Disposition of the Dietary Mutagen 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline in Healthy and Pancreatic Cancer Compromised Humans.

Pancreatic cancer is the fourth leading cause of cancer death in the U.S. Once diagnosed, prognosis is poor with a 5-year survival rate of less than 5%. Exposure to carcinogenic heterocyclic amines (HCAs) derived from cooked meat has been shown to be positively associated with pancreatic cancer risk. To evaluate the processes that determine the carcinogenic potential of HCAs for human pancreas, 14-carbon labeled 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), a putative human carcinogenic HCA found in well-done cooked meat, was administered at a dietary relevant dose to human volunteers diagnosed with pancreatic cancer undergoing partial pancreatectomy and healthy control volunteers. After (14)C-MeIQx exposure, blood and urine were collected for pharmacokinetic and metabolite analysis. MeIQx-DNA adducts levels were quantified by accelerator mass spectrometry from pancreatic tissue excised during surgery from the cancer patient group. Pharmacokinetic analysis of plasma revealed a rapid distribution of MeIQx with a plasma elimination half-life of approximately 3.5 h in 50% of the cancer patients and all of the control volunteers. In 2 of the 4 cancer patients, very low levels of MeIQx were detected in plasma and urine suggesting low absorption from the gut into the plasma. Urinary metabolite analysis revealed five MeIQx metabolites with 2-amino-3-methylimidazo[4,5-f]quinoxaline-8-carboxylic acid being the most abundant accounting for 25%-50% of the recovered 14-carbon/mL urine. There was no discernible difference in metabolite levels between the cancer patient volunteers and the control group. MeIQx-DNA adduct analysis of pancreas and duodenum tissue revealed adduct levels indistinguishable from background levels. Although other meat-derived HCA mutagens have been shown to bind DNA in pancreatic tissue, indicating that exposure to HCAs from cooked meat cannot be discounted as a risk factor for pancreatic cancer, the results from this current study show that exposure to a single dietary dose of MeIQx does not readily form measurable DNA adducts under the conditions of the experiment.

Determining the pharmacokinetics and long-term biodistribution of SiO2 nanoparticles in vivo using accelerator mass spectrometry.

Biodistribution is an important factor in better understanding silica dioxide nanoparticle (SiNP) safety. Currently, comprehensive studies on biodistribution are lacking, most likely due to the lack of suitable analytical methods. Accelerator mass spectrometry was used to investigate the relationship between administered dose, pharmacokinetics (PK), and long-term biodistribution of (14)C-SiNPs in vivo. PK analysis showed that SiNPs were rapidly cleared from the central compartment, were distributed to tissues of the reticuloendothelial system, and persisted in the tissue over the 8 week time course, raising questions about the potential for bioaccumulation and associated long-term effects.

Development of a CNS-permeable reactivator for nerve agent exposure: an iterative, multi-disciplinary approach.

Nerve agents have experienced a resurgence in recent times with their use against civilian targets during the attacks in Syria (2012), the poisoning of Sergei and Yulia Skripal in the United Kingdom (2018) and Alexei Navalny in Russia (2020), strongly renewing the importance of antidote development against these lethal substances. The current standard treatment against their effects relies on the use of small molecule-based oximes that can efficiently restore acetylcholinesterase (AChE) activity. Despite their efficacy in reactivating AChE, the action of drugs like 2-pralidoxime (2-PAM) is primarily limited to the peripheral nervous system (PNS) and, thus, provides no significant protection to the central nervous system (CNS). This lack of action in the CNS stems from their ionic nature that, on one end makes them very powerful reactivators and on the other renders them ineffective at crossing the Blood Brain Barrier (BBB) to reach the CNS. In this report, we describe the use of an iterative approach composed of parallel chemical and in silico syntheses, computational modeling, and a battery of detailed in vitro and in vivo assays that resulted in the identification of a promising, novel CNS-permeable oxime reactivator. Additional experiments to determine acute and chronic toxicity are ongoing.

Atomic force microscopy differentiates discrete size distributions between membrane protein containing and empty nanolipoprotein particles.

To better understand the incorporation of membrane proteins into discoidal nanolipoprotein particles (NLPs) we have used atomic force microscopy (AFM) to image and analyze NLPs assembled in the presence of bacteriorhodopsin (bR), lipoprotein E4 n-terminal 22k fragment scaffold and DMPC lipid. The self-assembly process produced two distinct NLP populations: those containing inserted bR (bR-NLPs) and those that did not (empty-NLPs). The bR-NLPs were distinguishable from empty-NLPs by an average increase in height of 1.0 nm as measured by AFM. Streptavidin binding to biotinylated bR confirmed that the original 1.0 nm height increase corresponds to br-NLP incorporation. AFM and ion mobility spectrometry (IMS) measurements suggest that NLP size did not vary around a single mean but instead there were several subpopulations, which were separated by discrete diameters. Interestingly, when bR was present during assembly the diameter distribution was shifted to larger particles and the larger particles had a greater likelihood of containing bR than smaller particles, suggesting that membrane proteins alter the mechanism of NLP assembly.

Cell-free co-expression of functional membrane proteins and apolipoprotein, forming soluble nanolipoprotein particles.

Here we demonstrate rapid production of solubilized and functional membrane protein by simultaneous cell-free expression of an apolipoprotein and a membrane protein in the presence of lipids, leading to the self-assembly of membrane protein-containing nanolipoprotein particles (NLPs). NLPs have shown great promise as a biotechnology platform for solubilizing and characterizing membrane proteins. However, current approaches are limited because they require extensive efforts to express, purify, and solubilize the membrane protein prior to insertion into NLPs. By the simple addition of a few constituents to cell-free extracts, we can produce membrane proteins in NLPs with considerably less effort. For this approach an integral membrane protein and an apolipoprotein scaffold are encoded by two DNA plasmids introduced into cell-free extracts along with lipids. For this study reported here we used plasmids encoding the bacteriorhodopsin (bR) membrane apoprotein and scaffold protein Delta1-49 apolipoprotein A-I fragment (Delta49A1). Cell free co-expression of the proteins encoded by these plasmids, in the presence of the cofactor all-trans-retinal and dimyristoylphosphatidylcholine, resulted in production of functional bR as demonstrated by a 5-nm shift in the absorption spectra upon light adaptation and characteristic time-resolved FT infrared difference spectra for the bR --> M transition. Importantly the functional bR was solubilized in discoidal bR.NLPs as determined by atomic force microscopy. A survey study of other membrane proteins co-expressed with Delta49A1 scaffold protein also showed significantly increased solubility of all of the membrane proteins, indicating that this approach may provide a general method for expressing membrane proteins enabling further studies.

Manipulation of the Gut Microbiome Alters Acetaminophen Biodisposition in Mice.

The gut microbiota is a vast and diverse microbial community that has co-evolved with its host to perform a variety of essential functions involved in the utilization of nutrients and the processing of xenobiotics. Shifts in the composition of gut microbiota can disturb the balance of organisms which can influence the biodisposition of orally administered drugs. To determine how changes in the gut microbiome can alter drug disposition, the pharmacokinetics (PK), and biodistribution of acetaminophen were assessed in C57Bl/6 mice after treatment with the antibiotics ciprofloxacin, amoxicillin, or a cocktail of ampicillin/neomycin. Altered PK, and excretion profiles of acetaminophen were observed in antibiotic exposed animals. Plasma Cmax was significantly decreased in antibiotic treated animals suggesting decreased bioavailability. Urinary metabolite profiles revealed decreases in acetaminophen-sulfate metabolite levels in both the amoxicillin and ampicillin/neomycin treated animals. The ratio between urinary and fecal excretion was also altered in antibiotic treated animals. Analysis of gut microbe composition revealed that changes in microbe content in antibiotic treated animals was associated with changes in acetaminophen biodisposition. These results suggest that exposure to amoxicillin or ampicillin/neomycin can alter the biodisposition of acetaminophen and that these alterations could be due to changes in gut microbiome composition.

Hydrogen production by a hyperthermophilic membrane-bound hydrogenase in water-soluble nanolipoprotein particles.

Hydrogenases constitute a promising class of enzymes for ex vivo hydrogen production. Implementation of such applications is currently hindered by oxygen sensitivity and, in the case of membrane-bound hydrogenases (MBHs), poor water solubility. Nanolipoprotein particles (NLPs) formed from apolipoproteins and phospholipids offer a novel means of incorporating MBHs into a well-defined water-soluble matrix that maintains the enzymatic activity and is amenable to incorporation into more complex architectures. We report the synthesis, hydrogen-evolving activity, and physical characterization of the first MBH-NLP assembly. This may ultimately lead to the development of biomimetic hydrogen-production devices.

Immobilization of His-tagged proteins on nickel-chelating nanolipoprotein particles.

Nanolipoprotein particles (NLPs) are nanometer-sized, discoidal particles that self-assemble from purified apolipoprotein and phospholipid. Their size and facile functionalization suggest potential application of NLPs as platforms for the presentation and delivery of recombinant proteins. To this end, we investigated incorporation of nickel-chelating lipids into NLPs (NiNLPs) and subsequent sequestration of polyhistidine (His)-tagged proteins. From initial lipid screens for NLP formation, the two phospholipids DMPC and DOPC were identified as suitable bulk lipids for incorporation of the nickel-chelating lipid DOGS-NTA-Ni into NLPs, and NiNLPs were successfully formed with varying amounts of DOGS-NTA-Ni. NiNLPs consisting of 10% DOGS-NTA-Ni with 90% bulk lipid (either DMPC or DOPC) were thoroughly characterized by size exclusion chromatography (SEC), non-denaturing gradient gel electrophoresis (NDGGE), and atomic force microscopy (AFM). Three different His-tagged proteins were sequestered on NiNLPs in a nickel-dependent manner, and the amount of immobilized protein was contingent on the size and composition of the NiNLP.