Cystatin C-based estimated glomerular filtration rate and risk of stroke in the general population: a prospective cohort study

Background

Previous results on the association between the estimated glomerular filtration rate (eGFR) and stroke are mixed. Most studies derived the eGFR from serum creatinine, which is affected by non-kidney determinants and thus has possibly biased the association with stroke risk.

Methods

In this cohort study, we included 429 566 UK Biobank participants (94.5% white, 54% women, age 56 ± 8 years) free of stroke at enrollment. The eGFRcys and eGFRcr were calculated with serum cystatin C and creatinine, respectively. Outcomes of interest were risk of total stroke and subtypes. We investigated the linear and nonlinear associations using Cox proportional hazards models and restricted cubic splines, corrected for regression dilution bias.

Results

During an average follow-up of 10.11 years, 4427 incident strokes occurred, among which 3447 were ischemic and 1163 were hemorrhagic. After adjustment for confounders, the regression dilution-corrected hazard ratios (95% confidence intervals) for every 10 mL/min/1.73 m2 decrement in eGFRcys were 1.10 (1.05-1.14) for total stroke and 1.11 (1.08-1.15) for ischemic stroke. A similar pattern was observed with eGFRcr, although the association was weaker. When either type of eGFR was below 75 mL/min/1.73 m2, the risks of total and ischemic stroke increased exponentially as eGFR decreased. A U-shaped relationship was witnessed if eGFRcr was used instead. There was a null association between eGFR and hemorrhagic stroke.

Conclusions

The risks of total stroke and ischemic stroke increased exponentially when the eGFRcys fell below 75 mL/min/1.73 m2.

Altered Cerebral Blood Flow in the Progression of Chronic Kidney Disease

Background: In chronic kidney disease (CKD), cognitive impairment is a definite complication. However, the mechanisms of how CKD leads to cognitive impairment are not clearly known. Methods: Cerebral blood flow (CBF) information was collected from 37 patients with CKD (18 in stage 3; 19 in stage 4) and 31 healthy controls (HCs). For CKD patients, we also obtained laboratory results as well as neuropsychological tests. We conducted brain perfusion imaging studies using arterial spin labeling and calculated the relationship between regional CBF changes and various clinical indicators and neuropsychological tests. We also generated receiver operator characteristic (ROC) curves to explore whether CBF value changes in certain brain regions can be used to identify CKD. Results: Compared with HCs, CBF decreased in the right insula and increased in the left hippocampus in the CKD4 group; through partial correlation analysis, we found that CBF in the right insula was negatively correlated with the number connection test A (NCT-A) (r = −0.544, p = 0.024); CBF in the left hippocampus was positively correlated with blood urea nitrogen (r = 0.649, p = 0.005) and negatively correlated with serum calcium level (r = −0.646, p = 0.005). By comparing the ROC curve area, it demonstrated that altered CBF values in the right insula (AUC = 0.861, p < 0.01) and left hippocampus (AUC = 0.862, p < 0.01) have a good ability to identify CKD. Conclusions: Our study found that CBF alterations in the left hippocampus and the right insula brain of adult patients with stage 4 CKD were correlated with disease severity or laboratory indicators. These findings provide further insight into the relationship between altered cerebral perfusion and cognitive impairment in patients with non-end-stage CKD as well as, additional information the underlying neuropathophysiological mechanisms.

Cerebral Autoregulation in Ischemic Stroke: From Pathophysiology to Clinical Concepts

Ischemic stroke (IS) is one of the most impacting diseases in the world. In the last decades, new therapies have been introduced to improve outcomes after IS, most of them aiming for recanalization of the occluded vessel. However, despite this advance, there are still a large number of patients that remain disabled. One interesting possible therapeutic approach would be interventions guided by cerebral hemodynamic parameters such as dynamic cerebral autoregulation (dCA). Supportive hemodynamic therapies aiming to optimize perfusion in the ischemic area could protect the brain and may even extend the therapeutic window for reperfusion therapies. However, the knowledge of how to implement these therapies in the complex pathophysiology of brain ischemia is challenging and still not fully understood. This comprehensive review will focus on the state of the art in this promising area with emphasis on the following aspects: (1) pathophysiology of CA in the ischemic process; (2) methodology used to evaluate CA in IS; (3) CA studies in IS patients; (4) potential non-reperfusion therapies for IS patients based on the CA concept; and (5) the impact of common IS-associated comorbidities and phenotype on CA status. The review also points to the gaps existing in the current research to be further explored in future trials.

Enhanced Renal Clearance in Patients With Hemorrhagic Stroke

OBJECTIVES

To evaluate enhanced renal clearance over time in patients with aneurysmal subarachnoid hemorrhage or intracerebral hemorrhage via measured creatinine clearance and to compare measured creatinine clearance to creatinine clearance calculated by the Cockcroft-Gault equation and estimated glomerular filtration rate calculated by the Modification of Diet in Renal Diseases equation.

DESIGN

Prospective, observational study.

SETTING

Neurosciences ICU in a tertiary care academic medical center.

PATIENTS

Study participants had an admission diagnosis of aneurysmal subarachnoid hemorrhage or intracerebral hemorrhage, an expected neurosciences ICU length of stay greater than 48 hours, no evidence of renal dysfunction (admission serum creatinine < 1.5 mg/dL), and no history of chronic kidney disease.

INTERVENTIONS

Eight-hour urine collections to measure creatinine clearance were collected daily as the primary method of measuring renal function. Creatinine clearance was also calculated using the Cockcroft-Gault equation and estimated glomerular filtration rate was calculated using the Modification of Diet in Renal Disease equation. Enhanced renal clearance was defined as a measured creatinine clearance greater than the calculated creatinine clearance via Cockcroft-Gault and estimated glomerular filtration rate via Modification of Diet in Renal Disease. Augmented renal clearance was defined by a measured creatinine clearance greater than or equal to 130 mL/min/1.73 m. Relevant demographic, clinical, and outcome data were recorded.

MEASUREMENTS AND MAIN RESULTS

Fifty aneurysmal subarachnoid hemorrhage patients and 30 intracerebral hemorrhage patients were enrolled, contributing 590 individual measurements. Patients with aneurysmal subarachnoid hemorrhage had a higher mean measured creatinine clearance compared with the mean calculated creatinine clearance based on the Cockcroft-Gault equation (147.9 ± 50.2 vs 109.1 ± 32.7 mL/min/1.73 m; p < 0.0001) and higher mean measured creatinine clearance compared with the mean calculated estimated glomerular filtration rate based on the Modification of Diet in Renal Disease equation (147.9 ± 50.2 vs 126.0 ± 41.9 mL/min/1.73 m; p = 0.04). Ninety-four percent of participants with aneurysmal subarachnoid hemorrhage experienced augmented renal clearance on at least 1 day. In patients with intracerebral hemorrhage, there was a higher mean measured creatinine clearance over the study period compared with the mean calculated creatinine clearance (119.5 ± 57.2 vs 77.8 ± 27.6 mL/min/1.73 m; p < 0.0001) and higher mean measured creatinine clearance compared with the mean calculated estimated glomerular filtration rate based on the Modification of Diet in Renal Disease equation (119.5 ± 57.2 vs 93.0.0 ± 32.8 mL/min/1.73 m; p = 0.02). Fifty percent of participants with intracerebral hemorrhage experienced augmented renal clearance on at least 1 day.

CONCLUSIONS

A substantial group of patients with aneurysmal subarachnoid hemorrhage or intracerebral hemorrhage experienced enhanced renal clearance, which may be otherwise unknown to clinicians. Enhanced renal clearance may lead to increased renal solute elimination over what is expected, resulting in subtherapeutic renally eliminated drug concentrations. This may result in underexposure to critical medications, leading to treatment failure and other medical complications.

Autonomic dysfunction following traumatic brain injury: translational insights

Although there is a substantial amount of research on the neurological consequences of traumatic brain injury (TBI), there is a knowledge gap regarding the relationship between TBI and the pathophysiology of organ system dysfunction and autonomic dysregulation. In particular, the mechanisms or incidences of renal or cardiac complications after TBI are mostly unknown. Autonomic dysfunction following TBI exacerbates secondary injury and may contribute to nonneurologial complications that prolong hospital length of stay. Gaining insights into the mechanisms of autonomic dysfunction can guide advancements in monitoring and treatment paradigms to improve acute survival and long-term prognosis of TBI patients. In this paper, the authors will review the literature on autonomic dysfunction after TBI and possible mechanisms of paroxysmal sympathetic hyperactivity. Specifically, they will discuss the link among the brain, heart, and kidneys and review data to direct future research on and interventions for TBI-induced autonomic dysfunction.

Mangiferin ameliorates collateral neuropathy in tBHP induced apoptotic nephropathy by inflammation mediated kidney to brain crosstalk

The kidneys and brain share similarities in anatomy and vaso-regulation and exhibit clinical interactions in various diseases. To investigate the probable mechanism of kidney to brain crosstalk, we developed an in vivo model of renal injury in mice through intoxication with the oxidative stress inducer, tBHP. Proteinuria, abnormalities in the renal tubules and KIM1 activation were found in tBHP intoxicated animals. Due to this renal pathophysiology, various pro-inflammatory molecules (TNF-α, IL-1β, IL-6, ICAM-1, VCAM-1) especially TNF-α, entered into the brain from kidneys, triggering cerebral inflammatory cascades leading to behavioral anomalies in association with membrane lipid peroxidation, BBB disruption and brain morphological alterations. Moreover, increased levels of reactive oxygen species, decreased antioxidant enzyme activity and an altered GSH/GSSG ratio were found in both these organs. Here, we introduced mangiferin as a protective molecule because of its anti-inflammatory and antioxidant properties. Mangiferin via inhibition of apoptosis and activation of the PI3K/Akt pathway protected the kidneys. It restored the deleterious phenomena in the damaged brain by downregulating the JNK and p38MAPK mediated pro-apoptotic cascade and activating the intracellular antioxidant thioredoxin, thereby protecting against tBHP induced nephropathy mediated neuropathophysiology.

Kidney-brain link in traumatic brain injury patients? A preliminary report

BACKGROUND

Kidney hyperfiltration with augmented renal clearance is frequently observed in patients with traumatic brain injury. The aim of this study is to report preliminary findings about the relationship between brain autoregulation impairment, estimated kidney glomerular filtration rate and outcome in critically ill patients after severe traumatic brain injury.

METHODS

Data collected from a cohort of 18 consecutive patients with severe traumatic brain injury managed with ICP monitoring in a Neurocritical Care Unit, were retrospectively analyzed. Early morning blood tests were performed for routine chemistry assessments and we analyzed creatinine and estimated creatinine clearance, osmolarity, and sodium. Daily norepinephrine dose, protein intake, and water balance were documented. Time average of brain monitoring data (intracranial pressure, cerebral perfusion pressure, and cerebrovascular reactivity pressure index--PRx) were calculated for 6 h before blood sample tests. Patient outcome was evaluated using Glasgow outcome scale at 6-month follow-up, considering nonfatal outcome if GOS ≥ 3 and fatal outcome if GOS < 3. Multiple linear regression models were used to study the crude and adjusted effects of the above variables on PRx throughout time.

RESULTS

A total of 199 complete daily observations from 18 adult consecutive multiple trauma patients with severe traumatic brain injury were analyzed. At hospital admission, the median post-resuscitation Glasgow coma score was 6 (range 3-12), mean SAPSII score was 44.65 with predicted mortality of 36 %. Hospital mortality rate was 27 % and median GOS at 6 month after discharge was 3. Creatinine clearance (CrCl) was found to have a negative correlation with PRx (Pearson correlation--0.82), with statistically significant crude (p < 0.001) and adjusted (p = 0.001) effects. For each increase of 10 ml/min in CrCl (estimated either by the Cockcroft-Gault or by Modification of Diet in Renal Disease Study equations) a mean decrease in PRx of approximately 0.01 was expected. Amongst possible confounders only norepinephrine was shown to have a significant effect. Mean PRx value for outcome fatal status was greater than mean PRx for nonfatal status (p < 0.05), regardless of the model used for the CrCl estimation.

CONCLUSIONS

Better cerebral autoregulation evaluated with cerebrovascular PRx is significantly correlated with augmented renal clearance in TBI patients and associates with better outcome.

Kidney Function and Cerebral Blood Flow: The Rotterdam Study

CKD is linked with various brain disorders. Whereas brain integrity is dependent on cerebral perfusion, the association between kidney function and cerebral blood flow has yet to be determined. This study was performed in the framework of the population-based Rotterdam Study and included 2645 participants with mean age of 56.6 years (45% men). We used eGFR and albumin-to-creatinine ratio to assess kidney function and performed phase-contrast magnetic resonance imaging of basilar and carotid arteries to measure cerebral blood flow. Participants had an average (SD) eGFR of 86.3 (13.4) ml/min per 1.73 m(2) and a median (interquartile range) albumin-to-creatinine ratio of 3.4 (2.2-6.1) mg/g. In age- and sex-adjusted models, a higher albumin-to-creatinine ratio was associated with lower cerebral blood flow level (difference in cerebral blood flow [milliliters per minute per 100 ml] per doubling of the albumin-to-creatinine ratio, -0.31; 95% confidence interval, -0.58 to -0.03). The association was not present after adjustment for cardiovascular risk factors (P=0.10). Each 1 SD lower eGFR was associated with 0.42 ml/min per 100 ml lower cerebral blood flow (95% confidence interval, 0.01 to 0.83) adjusted for cardiovascular risk factors. Thus, in this population-based study, we observed that lower eGFR is independently associated with lower cerebral blood flow.

Of heart and kidney: a complicated love story

The multiple connections that exist between the cardiovascular system and the kidney lead to a complex cardiovascular and renal medicine relationship. It is well established in the literature that chronic kidney disease (CKD) is an important and independent risk factor for cardiovascular disease (CVD). The prevalence of CKD in the general population is about 7%, comparable with the prevalence of diabetes. The main causes of CKD are diabetes and hypertension, worldwide. The prevalence of CVD in the CKD population ranges between 7 and 85% according to the CKD stage and type, and the patient diagnosed with CKD has a higher risk of dying of CVD than of starting renal replacement therapy. There are some particular aspects of CVD in CKD patients that differ from the general population, making its prevention and treatment a challenge for both cardiologists and nephrologists.

Epigenetic bystander-like effects of stroke in somatic organs

Clinical evidence suggests that stroke may lead to damage of somatic organs. This communication of damage is well- established in the case of exposure to genotoxic agents is termed a bystander effect. Genotoxic stress-induced bystander effects are epigenetically mediated. Here we investigated whether stroke causes epigenetic bystander-like effects in the liver, kidney and heart. We found a significant increase in the levels of H3K3 acetylation and H3K4 trimethylation, as well as a decrease in the H3K9 trimethylation in the kidney tissue of stroked rats. Furthermore, here we for the first time show changes in the gene and microRNA expression profile in the kidney tissues of stroked rats, as compared to intact control animals. Interestingly, the observed changes were somewhat similar to those reported earlier in kidney injury, inflammation, and acute renal failure. Our data explain the recent epidemiological evidence for the increased incidence of acute kidney injury post-stroke and provide an important roadmap for the future analysis of the mechanisms and cellular repercussions of the stroke-induced bystander-like effects in distal somatic organs.

Traditional and nontraditional risk factors as predictors of cerebrovascular events in patients with end stage renal disease

OBJECTIVES AND METHODS

End stage renal disease (ESRD) patients exhibit a higher risk of cerebrovascular events as compared with the general population. In 283 ESRD patients followed up for 10 years, we investigated the long-term predictive value for stroke and transient ischemic attacks of traditional and nontraditional risk factors. Data analysis was performed by a modified Cox regression analysis for repeated events and by a competing risks analysis.

RESULTS

During the follow-up, 61 cerebrovascular events occurred in 47 patients. On univariate Cox analysis, the risk of cerebrovascular outcomes was directly related to age, smoking, diabetes, BMI, systolic and pulse pressures, triglycerides, hemoglobin, history of stroke/transient ischemic attacks, arrhythmia and left ventricular mass index. Nontraditional risk factors in ESRD such as norepinephrine, homocysteine, interleukin-6 and asymmetric dimethylarginine failed to predict these events. In a multivariate Cox model for repeated events only smoking [hazard ratio: 2.45, 95% confidence interval (CI): 1.29-4.65], age (hazard ratio: 1.05, 95% CI: 1.01-1.08), hemoglobin (hazard ratio: 1.28, 95% CI 1.06-1.54), triglycerides (hazard ratio: 1.04, 95% CI 1.01-1.08), pulse pressure (hazard ratio: 1.53, 95% CI 1.01-2.23) and left ventricular mass index (hazard ratio: 1.02, 95% CI 1.01-1.04) maintained an independent relationship with cerebrovascular events. The direct link between hemoglobin and cerebrovascular events was significantly stronger (P < 0.05) than that of the same variable and death.

CONCLUSION

The risk of stroke in ESRD depends mainly on traditional risk factors, high hemoglobin and left ventricular hypertrophy. Multiple interventions aimed to reduce arterial stiffness, left ventricular mass and smoking as well as to maintain hemoglobin within the recommended therapeutic range may have beneficial effects on the risk of cerebrovascular events in ESRD patients.

Microvascular disease and its role in the brain and cardiovascular system: a potential role for uric acid as a cardiorenal toxin

Arteriolosclerosis (microvascular disease) may have a key role not only in driving salt-sensitive hypertension but also in mediating the development of chronic kidney disease, vascular dementia, stroke and coronary heart disease. In this paper, we review the evidence that these latter conditions result from the altered autoregulation that occurs when arterioles become diseased. We also discuss the increasing evidence that dietary intake of sugars rich in fructose may be driving the development of microvascular disease as a consequence of raising intracellular uric acid. We hypothesize that the treatment of microvascular disease may require a multifaceted approach by utilizing agents which aim at blocking of the renin-angiotensin system, reducing oxidative stress, stimulating endothelial nitric oxide production and lowering uric acid levels. Paradoxically, agents that only stimulate nitric oxide, such as oestrogens, may increase the risk of poor outcomes if microvascular disease is not reversed.