Indiana University-Purdue University Indianapolis (IUPUI) / Acute kidney injury (AKI) affects millions of patients worldwide yet has few treatment options. There is a critical need to identify novel interventions for AKI, especially approaches targeting cell types that are central to the disease, such as neutrophils. Neutrophils are professional phagocytic cells that respond early to tissue injury. In rodent models of severe ischemic-reperfusion-injury AKI, neutrophils transiently infiltrate the injured kidney, appearing within 6 hours, and are gone by 72 hours. These infiltrating neutrophils are considered proinflammatory and harmful to tissue repair and recovery of kidney function. However, neutrophils can exhibit atypical activity such as antigen presentation and have a central role in recovery from myocardial ischemic injury. Furthermore, little is known of neutrophil polarization, atypical activity, or neutrophil diversity in AKI. Lastly, the kidney generated and renal-protective immunomodulatory protein uromodulin (Tamm-Horsfall Protein, THP) regulates granulopoiesis. In the absence of uromodulin, there is a systemic increase in neutrophils and mouse kidneys are sensitive to injury in AKI. To elucidate neutrophil diversity in AKI and their sensitivity to uromodulin, I performed a series of single-cell sequencing experiments to generate transcriptional profiles of neutrophils from the blood and kidneys of wild-type and THPknockout mice after renal ischemic-reperfusion-injury (IRI). Neutrophil diversity was detected following IRI of the mouse kidney in the blood and kidney. The distribution of subpopulations was sensitive to the kidney milieu. Within the kidney, this diversity and the transcriptional programs of neutrophil subpopulations was sensitive to the severity of ischemic injury. Lastly, Cxcl3 was uniquely upregulated in specific neutrophils after severe ischemic injury. Using single-cell sequencing of uromodulin knock-out mice, I detected the upregulation of toll-like receptor pathways and complement cascades across neutrophil subpopulations in a THP sensitive manner. Furthermore, CXCR2 ligand expression was a combination of moderate and severe injury in wild-type mice. This confirmed previously reported cytokine dysregulation in the uromodulin knock-out mouse after IRI and uncovers a novel role for Cxcl3. Thus, upon revisiting the well-studied neutrophil, I have uncovered novel neutrophil diversity that correlates with recovery of kidney function in AKI and suggests new roles for an old player.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18503号 / 医博第3923号 / 新制||医||1005(附属図書館) / 31389 / 京都大学大学院医学研究科医学専攻 / (主査)教授 山下 潤, 教授 斎藤 通紀, 教授 小川 修 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21263号 / 医博第4381号 / 新制||医||1029(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 柳田 素子, 教授 福田 和彦, 教授 木村 剛 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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Thesis (M.Med.(General Surgery)--University of the Witwatersrand, Faculty of Health Sciences, 2014. / Background. Renal insufficiency is increasingly common in end-stage liver disease and allocation of livers to this category of patient has escalated. The frequency of combined liver-kidney transplantation (CLKT) has consequently increased. Indications for CLKT in children differ from those for adults and typically include rare congenital conditions; subsequently limited numbers of this procedure have been performed in paediatric patients worldwide. Scant literature exists on the subject. Methods. Subsequent to institutional approval, a retrospective chart analysis of all paediatric CLKTs performed at the Transplant Unit, Wits Donald Gordon Medical Centre, University of the Witwatersrand, Johannesburg, South Africa between January 2005 and July 2013 was conducted. Results. Defining children as younger than 18 years of age, 43 patients had received a liver transplant since 2005, of whom 8 received a CLKT. Indications included autosomal recessive polycystic kidney disease (n=3), primary hyperoxaluria type 1 (n=4) and heterozygous factor H deficiency with atypical haemolytic uraemic syndrome (n=1). Graft combinations included whole liver and one kidney (n=5), whole liver and two kidneys (n=1) and left lateral liver segment and one kidney (n=2), all from deceased donors. Patient age ranged from 4 to 17 years (median 9) and included 4 females and 4 males. Weight ranged from 13 to 42 kg (median 22.5). We describe one in-hospital mortality. The remaining 7 patients were long-term survivors with a survival range from 6 to 65 months. Conclusions. Although rarely indicated in children, CLKT is an effective treatment option, appropriately utilising a scarce resource and significantly improving quality of life in the recipient.

Understanding how a therapy will impact the injured kidney before being administered would be an asset to the clinical world. The work in this thesis advances the field of mathematical modeling of the kidneys to aid in this cause. The objectives of this work are threefold: 1) to develop and personalize a model to specific patients in different diseased states, via parameter estimation, in order to test therapeutic trajectories, 2) to use parameter estimation to understand the cause of different kidney diseases, differentiate between potential kidney diseases, and facilitate targeted therapies, and 3) to push forward the understanding of kidney physiology via physiology-based mathematical modeling techniques. To accomplish these objectives, we have developed two models of the kidneys: 1) a broad, steady-state, closed-loop model of the entire kidney with human physiologic parameters, and 2) a detailed, dynamic model of the proximal tubule, an important part of kidney, with rat physiologic parameters. To readily aid physicians, a human model would easily fit into the clinical workflow. Since there is a lack of invasive human renal data for validation and parameter estimation, we employ a minimal modeling approach. However, to aid in deeper understanding of renal function for future applications, targeted therapy testing, and potentially replace invasive measures, we develop a more detailed model. The development of such a model requires invasive data for validation and parameter estimation, and hence we model for rodents, where such invasive data are more readily available. The kidneys are composed of approximately one million functional units known as nephrons. The glomerular filtration rate (GFR) is the rate at which the kidney filters blood at the start of the nephron. This filtration rate is highly regulated via several control mechanisms and needs to be maintained within a small range in order to maintain a proper water and electrolyte balance. Hence, fluctuations of GFR are indicative of overall kidney health. In developing the human kidney model, we also sought to understand the relationship between blood pressure and GFR since many therapies affect blood pressure and subsequently GFR. This model describes steady-state conditions of the entire kidney, including renal autoregulation. Model validation is performed with experimental data from healthy subjects and severely hypertensive patients. The baseline model’s GFR simulation for normotensive and the manually tuned model’s GFR simulation for hypertensive intensive care unit patients had low root mean squared errors (RMSE) of 13.5 mL/min and 5 mL/min, respectively. These values are both lower than the error of 18 mL/min in GFR estimates, reported in previous studies. It has been shown that vascular resistance and renal autoregulation parameters are altered in severely hypertensive stages, and hence, a sensitivity analysis is conducted to investigate how changes in these parameters affect GFR. The results of the sensitivity analysis reinforce the fact that vascular resistance is inversely related to GFR and show that changes to either vascular resistance or renal autoregulation cause a significant change in sodium concentration in the descending limb of Henle. This is an important conclusion as it quantifies the mapping between hypertension parameters and two important kidney states, GFR and sodium urine levels. Glomerulonephritis is one of the two major intra-renal kidney diseases, characterized as a breakdown at the site of the glomerulus that affects GFR and subsequently other portions of the nephron. This disease accounts for 15% of all kidney injuries and one-fourth of end-stage renal disease patients. The human kidney model is used to estimate renal parameters of patients with glomerulonephritis. The model is an implicit system and in developing an optimization algorithm to use for parameter estimation, we modify in a novel way, the Levenberg-Marquardt optimization using the implicit function theorem in order to calculate the Jacobian and Hessian matrices needed. We further adapt the optimization algorithm to work for constrained optimization since our parameter values must be physiologically feasible within a certain range. The parameter estimation method we use is a three-step process: 1) manually adjusting parameters for the hypertension comorbidity, 2) iteratively estimating parameters that vary from person to person using no-kidney- injury (NKI) data, and 3) iteratively estimating parameters that are affected by glomerulonephritis using labeled diseased data. Such a process generates a model that is personalized to each given patient. This patient-specific model can then be used to simulate and evaluate outcomes of potential therapies (e.g., vasodilators) on the model in lieu of the patient, and observe how alterations in blood pressure or sodium level affect renal function. Parameter estimation in the presence of glomerulonephritis is a challenging task due to the complexity of the kidney physiology and the number of parameters to estimate. This is further complicated by comorbidities such as hypertension, cardiac arrythmia, and valvular disease, because they alter kidney physiology and hence, increase the number of parameters to estimate. We chose to focus on hypertension since it is very prevalent in hospitals and intensive care units. It was found that over all patients, average model estimates of GFR and urine output rate (UO) were within 9.2 mL/min and 0.71 mL/min for NKI data. These results are expectedly better than those achieved from the non-personalized model since the parameters are now specific to each patient. The results also demonstrate our ability to non-invasively estimate GFR with less error than the 18 mL/min currently possible. The estimations were validated by ensuring that the estimated parameter values were physiologically sound and matched the literature in terms of expected values for different demographic groups. It is vital for a properly functioning kidney to maintain solute transport throughout the nephron. Kidney diseases in the nephron can manifest themselves via the solute transport mechanisms. To understand how these diseases affect the kidney and to simulate transporter- targeting therapies, we have developed a detailed model, starting from the human model previously developed, of one portion of the kidneys, the proximal tubule. The proximal tubule is the site of the most active transport within the nephron and the target for several therapies. Our goal is to study and understand the dynamic behavior of the proximal tubule when solute transporters breakdown and to investigate treatment therapies targeting certain solute transporters. The proposed model is dynamic and includes several solutes’ transport mechanisms, with parameters for rats. We chose to investigate diabetic nephropathy and the associated sodium-transporter alteration (knockout) therapy. Diabetic nephropathy is characterized as kidney damage due to diabetes and affects 30% of diabetics. In terms of reducing hyperfiltration, a potential cause of diabetic nephropathy where an overabundance of solutes and fluid are filtered at the glomerulus, the model demonstrates that knockout of this transporter results in a reduction in sodium and chloride reabsorptions in the proximal tubule, thereby preventing hyperfiltration. Further, we conclude that vital flows for maintaining kidney homeostasis, fluid and ammonium reabsorptions, are corrected to healthy values by a 50% knockout (impairment) of the sodium-hydrogen transporter. Next, we use the dynamic model to detect different diseased states of the proximal tubule transporters. We have accomplished this task by using Bayesian estimation to estimate transporter density parameters (a metric for kidney health) using measured signals from the proximal tubule. This approach is validated with experimental rat data, while further investigations are conducted into the performance of the estimation in the presence of varied input signals, signal resolutions, and noise levels. Estimation accuracy within 20% of true transporter density and within 4% of true fluid and solute reabsorption was achieved for all combinations of diseased transporters. We concluded that including chloride and bicarbonate concentrations improved estimation accuracy, whereas including formic acid did not. This is an important conclusion as it can help physicians determine which blood tests to order for diagnosing kidney disease; to our knowledge, this is a first. It was also found that sodium and glucose proximal tubule concentrations are most affected by changes in the sodium-hydrogen and sodium-bicarbonate transporters. This conclusion provides insight into the interplay between solute transporter density and sodium and glucose concentrations in the proximal tubule. Such knowledge paves the way for new transporter targeted therapies.

Many drugs and environmental chemicals, such as antibiotics and chemotherapeutic agents, are nephrotoxic (toxic to the kidney) and are a common cause of acute kidney injury and chronic kidney disease. Conventional tissue models for assessment of drug-induced nephrotoxicity rely on animals or simple cell culture models, which lack tissue characteristics of the human kidney required to accurately predict a drug’s effect in clinical trials. Microfluidic kidney-on-chips can generate tissue with improved human relevance compared to traditional models, however, generally lack high-throughput and multiparametric data collection capabilities for evaluation of nephrotoxic drug exposures. Standard data collection techniques remain limited to fluorescent imaging or colorimetric assays that often focus on single endpoints, are invasive due to the addition of labels, and fail to capture dynamic changes in tissue function. Additionally, conventional toxicological readouts rely on bulk measures of injury, such as cell death, which are less sensitive than sub-lethal changes in cell function and morphology that occur prior to cell death. Due to the challenges above, there is a need for new measurement approaches that enable collection of kinetic, multi-parametric, and sub-lethal readouts of injury in kidney-on-chip systems. In this work, we developed and characterized several measurement approaches for evaluation of tissue function in kidney-on-chip systems and assessment of drug-induced nephrotoxicity. In chapter 2, we developed a novel optical-based oxygen sensing technique for measurement of sub-lethal mitochondrial dysfunction in an array of kidney-on-chips. In chapter 3, we investigated an approach for simultaneous transepithelial electrical resistance (TEER) sensing and flow control to enable near-continuous monitoring of tissue barrier function under different flow conditions. In chapter 4, we demonstrated the use of different data collection modalities, including multiple sensors, fluorescent imaging, and colorimetric-based assays, to generate multi-parametric readouts for evaluation of drug-induced nephrotoxicity in kidney-on-chips. / 2024-05-24T00:00:00Z

This cross-sectional study aims to evaluate the association of caffeine intake with renal function among adults between ages 18-55. Participants of the National Health and Nutritional Examination Survey (NHANES) survey for the three consecutive years (2013-2014, 2015-2016, and 2017-2018) were used. A weighted multivariable linear regression analysis of the caffeine concentration was conducted. Greater intake was associated with lowered renal function. This association persisted when limiting the daily caffeine intake to 2000 mg/day or less. Among younger adults, ages 18 to 39 the beta coefficient was about 50 percent larger than the beta coefficient for individuals ages 40 to 55. This suggests that caffeine intake may have a greater impact on renal function among younger adults. While greater caffeine intake was associated with reduced renal function in this cross-sectional study, further investigation such as an experimental study should be performed to confirm the findings of this thesis. / Epidemiology

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