An improved pre-clinical model of sepsis incorporating vasopressor support

Published on 20 Nov 2022.
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A new article was recently published that I participated in during my time at NIH. The study was led by Tetsushi Yamashita and focuses on changes in blood pressure and heart rate during sepsis. Unlike previous articles that focused on the pathways involved in the progression of sepsis this study examined some of the treatment options that are typically used in patients.

Although this study built on our knowledge of the complex response to sepsis it also developed an existing mouse model of sepsis closer to what humans might experience during routine care. The more accurately our models can simulate human disease the more likely we are to successfully translate therapies from mice into humans.

Mice are widely used as models of disease including kidney disease and sepsis despite differences between these mouse models and humans. There are a variety of reasons for these differences with medical care being one we can reduce.

When sepsis is diagnosed common medical treatments include giving fluids, antibiotics and vasopressors such as norepinephrine (also called noradrenaline in the UK) to treat low blood pressure. Each of these treatments alter disease progression in humans but are relatively new developments in mouse models. Our lab had a long history of using fluids and antibiotics but vasopressors were not used.

The reason for this is simple: their use is technically very challenging. While fluids and antibiotics can be administered intermittently and via common injection routes vasopressors would need to be administered:

  1. directly into a vein
  2. continuously
  3. and with careful monitoring

The experimental procedures necessary for this model were first brought together by Brianna Halasa and then finalised when Tetsushi joined the lab. Each mouse undergoes approximately one hour of surgery in which the jugular vein is catheterised to enable the infusion of a vasopressor and then the carotid artery is catheterised to implant a pressure transducer to monitor blood pressure. Although the exact procedures are slightly different these videos demonstrate the jugular vein and carotid artery catheterisations. Only when the mice have recovered does the more usual sepsis model surgeries begin.

I would like to congratulate Tetsushi on publishing this study. If you are interested in learning more the complete article is now freely available in PLoS One.

Predicting progression in acute kidney injury

Published on 17 Jun 2020.
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Last month the final study from my time at NIH was published. This study explored a promising, and relatively new, biomarker for acute kidney injury during critical illness. Although the biomarker had been previously tested in humans we were able to develop a potential refinement in a preclinical model.

During critical illness, such as sepsis, organ failure is a major complication increasing the risk of death. For the kidneys, treatment is limited to more focused management. This means avoiding further harm and keeping the patient alive long enough for kidney function to return.

The sooner kidney injury is detected the better the likely outcome but this can be surprisingly difficult. Some significantly improved options have been developed but further, even better, options are still desired. A new approach is giving the kidney something to do and measuring how well it performs. This idea is similar to the treadmill stress test commonly used to detect cardiovascular disease such as angina.

The test that was developed gave a dose of a drug called furosemide that is actively excreted by the kidneys and stimulates urine production. If the kidneys are healthy, the furosemide will be excreted and the amount of urine produced will increase. In a human clinical study this approach performed very well and there have been several subsequent studies in different settings.

Urine volume is altered by a variety of factors and we decided to investigate whether further improvements in performance would be possible by measuring furosemide excretion directly. When used in ideal conditions results were comparable. However, when we gave a drug called vasopressin that is commonly used to manage blood pressure during critical illness measuring urine volume gave erroneous results while furosemide excretion remained reliable.

The study is published in Critical Care Explorations and is freely available.

Circadian rhythm and variation in small extracellular vesicles

Published on 25 Aug 2019.
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Exosomes have been an ongoing interest for several years. Beginning with my PhD in Edinburgh and continuing in my current position I have published several articles on exosomes. The field is also maturing with a growing appreciation for the complexities of exosomes and related vesicles. Exosomes are formed and released by a specific mechanism from cells. Once released exosomes are difficult to distinguish from other sources of similar vesicles. In many experimental settings it would be difficult to confirm an exosomal origin. To reflect this uncertainty the use of the term small extracellular vesicles was suggested following a broad consultation by the International Society for Extracellular vesicles.

We have recently published an article on two related investigations:

  1. the circadian pattern of small extracellular vesicle release in the urine
  2. possible methods for normalizing biomarkers derived from small extracellular vesicles

Circadian patterns, or rhythms, are natural oscillations in biological processes that repeat roughly every 24 hours. They are widely seen in biological systems but little is known about variations in exosome, or small extracellular vesicle, release. A circadian rhythm is just one source of variation that may contribute to the wide variability seen in biomarker studies of small extracellular vesicles. In this article we suggest that normalization by small extracellular vesicle number may help correct for some of the variability encountered.

Exploring the onset of acute kidney injury during sepsis

Published on 16 Jun 2018.
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In an earlier post I discussed the damage sepsis can do. It has been a focus of many of the projects I have been involved with for the past few years even though the group I am with is tasked with studying kidney disease. We are interested in sepsis because it is a major cause of acute kidney injury.

We do not yet know all the details of this link. Knowing exactly when kidney function falls after sepsis and what triggers the fall could be very important. It would help in developing clinical procedures and therapies to manage patients with sepsis at risk of acute kidney injury.

I recently published a study exploring one potential cause of falling kidney function during sepsis. The kidney filters the blood and removes excess fluid, solutes, and toxins from the body. The blood passes through the glomerulus where fluid can leak out. The volume at this stage is very large and includes many good things the body wants to keep. This fluid then passes through other specialized structures including the tubules where most of the fluid and useful solutes are re-absorbed. To prevent the body from losing too much fluid if the tubules are not working there is a feedback loop that stops the glomeruli producing filtrate.

Using a genetic model I tested whether this feedback loop is activated during sepsis. The results have just been published in the American Journal of Physiology. Renal Physiology.

Technique and review articles on exosomes

Published on 13 Aug 2017.
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I've studied exosomes since the Summer of 2007 when I did my MSc dissertation project and then PhD in the laboratory of James Dear. When it came time to move on I was fortunate in finding my current position where I could explore new areas without moving away entirely from the exosome field where I had so much experience.

An opportunity to revisit the exosomal field came at the beginning of 2016 when we were invited to write three separate book chapters and review articles on exosomes. The third manuscript, a chapter in the book "Drug Safety Evaluation", has just been published online.

Inevitably the manuscripts have some overlap but they each focus on different aspects of exosomes and their study. The highlight was having a figure from our article in the journal of cellular physiology on the front cover of the issue.

The three manuscripts are:

Urine Exosome Isolation and Characterization is focused on the methods we use to collect, process, and characterize exosomes.

Urine Exosomes: An Emerging Trove of Biomarkers is a review of the potential and challenges in bringing exosome based biomarkers into clinical use.

Quantification of Exosomes is a review of the options available for determining the concentration of exosomes.