Flow-dependent endothelial function and kidney dysfunction

The post-cardiac arrest syndrome: A case for lung-brain coupling and opportunities for neuroprotection

Systemic inflammation and multi-organ failure represent hallmarks of the post-cardiac arrest syndrome (PCAS) and predict severe neurological injury and often fatal outcomes. Current interventions for cardiac arrest focus on the reversal of precipitating cardiac pathologies and the implementation of supportive measures with the goal of limiting damage to at-risk tissue. Despite the widespread use of targeted temperature management, there remain no proven approaches to manage reperfusion injury in the period following the return of spontaneous circulation. Recent evidence has implicated the lung as a moderator of systemic inflammation following remote somatic injury in part through effects on innate immune priming. In this review, we explore concepts related to lung-dependent innate immune priming and its potential role in PCAS. Specifically, we propose and investigate the conceptual model of lung-brain coupling drawing from the broader literature connecting tissue damage and acute lung injury with cerebral reperfusion injury. Subsequently, we consider the role that interventions designed to short-circuit lung-dependent immune priming might play in improving patient outcomes following cardiac arrest and possibly other acute neurological injuries.

Failed Tubule Recovery, AKI-CKD Transition, and Kidney Disease Progression

The transition of AKI to CKD has major clinical significance. As reviewed here, recent studies show that a subpopulation of dedifferentiated, proliferating tubules recovering from AKI undergo pathologic growth arrest, fail to redifferentiate, and become atrophic. These abnormal tubules exhibit persistent, unregulated, and progressively increasing profibrotic signaling along multiple pathways. Paracrine products derived therefrom perturb normal interactions between peritubular capillary endothelium and pericyte-like fibroblasts, leading to myofibroblast transformation, proliferation, and fibrosis as well as capillary disintegration and rarefaction. Although signals from injured endothelium and inflammatory/immune cells also contribute, tubule injury alone is sufficient to produce the interstitial pathology required for fibrosis. Localized hypoxia produced by microvascular pathology may also prevent tubule recovery. However, fibrosis is not intrinsically progressive, and microvascular pathology develops strictly around damaged tubules; thus, additional deterioration of kidney structure after the transition of AKI to CKD requires new acute injury or other mechanisms of progression. Indeed, experiments using an acute-on-chronic injury model suggest that additional loss of parenchyma caused by failed repair of AKI in kidneys with prior renal mass reduction triggers hemodynamically mediated processes that damage glomeruli to cause progression. Continued investigation of these pathologic mechanisms should reveal options for preventing renal disease progression after AKI.

The conundrum of protection from AKI by adenosine in rodent clamp ischemia models

Kim et al. show that isoflurane uses a tubule-based transforming growth factor-β/CD73-dependent process that generates adenosine to protect mice from ischemic acute kidney injury (AKI) with effects to prevent the 'no-reflow phenomenon' and decrease inflammation. While direct cytoprotection occurred in culture, extensive research suggests that in vivo adenosine protection from rodent ischemic AKI is mediated by a mutually cooperative mechanism involving blood flow, inflammation, and innate immunity through multiple adenosine receptors with promiscuous actions on diverse cell types.

The relationship between pulmonary emphysema and kidney function in smokers

BACKGROUND

It has been reported that the prevalence of kidney dysfunction may be increased in patients exposed to tobacco with airflow obstruction. We hypothesized that kidney dysfunction would associate with emphysema rather than with airflow obstruction measured by the FEV₁.

METHODS

Five hundred eight current and former smokers completed a chest CT scan, pulmonary function tests, medical questionnaires, and measurement of serum creatinine. Glomerular filtration rates (eGFRs) were estimated using the method of the Chronic Kidney Disease Epidemiology Collaboration. Quantitative determinants of emphysema and airway dimension were measured from multidetector chest CT scans.

RESULTS

The mean age was 66 ± 7 years, and mean eGFR was 101 ± 22 mL/min/1.73 m². Univariate and multivariate analysis showed a significant association between radiographically measured emphysema and eGFR: Participants with 10% more emphysema had an eGFR that was lower by 4.4 mL/min/1.73 m² (P = .01), independent of airflow obstruction (FEV₁), age, sex, race, height, BMI, diabetes mellitus, hypertension, coronary artery disease, patient-reported dyspnea, pack-years of smoking, and current smoking. There was no association between eGFR and either FEV₁ or quantitative CT scan measures of airway dimension.

CONCLUSIONS

More severe emphysema, rather than airflow obstruction, is associated with kidney dysfunction in tobacco smokers, independent of common risk factors for kidney disease. This finding adds to recent observations of associations between emphysema and comorbidities of COPD, including osteoporosis and lung cancer, which are independent of the traditional measure of reduced FEV₁. The mechanisms and clinical implications of kidney dysfunction in patients with emphysema need further investigation.