Bioinspired Gradient Covalent Organic Framework Membranes for Ultrafast and Asymmetric Solvent Transport

Gradients play a pivotal role in membrane technologies, e.g., osmotic energy conversion, desalination, biomimetic actuation, selective separation, and more. In these applications, the compositional gradients are of great relevance for successful function implementation, ranging from solvent separation to smart devices; However, the construction of functional gradient in membranes is still challenging both in scale and directions. Inspired by the specific function-related, graded porous structures in glomerular filtration membranes, a general approach for constructing gradient covalent organic framework membranes (GCOMx) applying poly (ionic liquid)s (PILs) as template is reported here. With graded distribution of highly porous covalent organic framework (COF) crystals along the membrane, GCOMx exhibts an unprecedented asymmetric solvent transport when applying different membrane sides as the solvent feed surface during filtration, leading to a much-enhanced flux (10-18 times) of the "large-to-small" pore flow comparing to the reverse direction, verified by hydromechanical theoretical calculations. Upon systematic experiments, GCOMx achieves superior permeance in nonpolar (hexane ≈260.45 LMH bar-1) and polar (methanol ≈175.93 LMH bar-1) solvents, together with narrow molecular weight cut-off (MWCO, 472 g mol-1) and molecular weight retention onset (MWRO, <182 g mol-1). Interestingly, GCOMx shows significant filtration performance in simulated kidney dialysis, revealing great potential of GCOMx in bionic applications.

Estimation of GFR in Patients With Cystic Fibrosis: A Cross-Sectional Study

Background

Patients with cystic fibrosis (CF) have frequent infectious complications requiring nephrotoxic medications, necessitating monitoring of renal function. Although adult studies have suggested that cystatin C (CysC)-based estimated glomerular filtration rate (eGFR) may be preferable due to reduced muscle mass of patients with CF, pediatric patients remain understudied.

Objective

Our objective was to determine which eGFR formula is best for estimating glomerular filtration rate (GFR) in pediatric patients with CF.

Methods

A total of 17 patients with CF treated with nephrotoxic antibiotics were recruited from the Children's Hospital at London Health Sciences Centre, London, Ontario, Canada. ⁹⁹Tc DTPA GFR (measured GFR [mGFR]) was measured with 4-point measurements starting at 120 minutes using a 2-compartmental model with Brøchner-Mortensen correction, with simultaneous measurement of creatinine, urea, and CysC. The eGFR was calculated using 16 known equations based on creatinine, urea, CysC, or combinations of these. Primary outcome measures were correlation with mGFR, and agreement within 10% for various eGFR equations.

Results

Mean mGFR was 136 ± 21 mL/min/1.73 m². Mean creatinine, CysC, and urea were 38 ± 10 μmol/L, 0.72 ± 0.08 mg/L, and 3.9 ± 1.4 mmol/L, respectively. The 2014 Grubb CysC eGFR had the best correlation coefficient (r = 0.75, P = .0004); however, only 35% were within 10%. The new Schwartz formula with creatinine and urea had the best agreement within 10%, but a relatively low correlation coefficient (r = 0.63, P = .0065, 64% within 10%).

Conclusions

Our study suggests that none of the eGFR formulae work well in this small cohort of pediatric patients with CF with preserved body composition, possibly due to inflammation causing false elevations of CysC. Based on the small numbers, we cannot conclude which eGFR formula is best.

Educational review: measurement of GFR in special populations

IMPORTANCE

Changes in kidney function are typically followed by the sequential estimation of glomerular filtration rate (eGFR). Formulae for eGFR work well on a population basis, but there are well-known conditions where they do not work.

OBJECTIVE

The purpose of this review is to summarize the existing literature on special populations in the pediatric age range and provide recommendations on how to estimate GFR in these populations.

FINDINGS

The reliability of creatinine depends on muscle mass, while cystatin C (not widely available) is limited by inflammation and changes in protein catabolism. Various dietary factors can alter eGFR. Renal function in neonates changes drastically every day, and there are currently no satisfactory reference intervals for routine pediatric use. Gender effects and conditions such as wasting disease and obesity require alternative ways to obtain eGFR. In oncology patients, chemotherapy may negatively affect renal function, and nuclear GFR measurements may be necessary. For body builders, high muscle mass may lead to underestimation of eGFR using creatinine.

CONCLUSIONS AND RELEVANCE

Clinicians should be aware of special populations that may yield misleading eGFRs with conventional creatinine-based formulae, and that the alternative methods may be more appropriate for some populations.

Capillary Hysteresis in Neutrally Wettable Fibrous Media: A Pore Network Study of a Fuel Cell Electrode

Hysteresis in the saturation versus capillary pressure curves of neutrally wettable fibrous media was simulated with a random pore network model using a Voronoi diagram approach. The network was calibrated to fit experimental air-water capillary pressure data collected for carbon fibre paper commonly used as a gas diffusion layer in fuel cells. These materials exhibit unusually strong capillary hysteresis, to the extent that water injection and withdrawal occur at positive and negative capillary pressures, respectively. Without the need to invoke contact angle hysteresis, this capillary behaviour is re-produced when using a pore-scale model based on the curvature of a meniscus passing through the centre of a toroid. The classic Washburn relation was shown to produce erroneous results, and its use is not recommended when modelling fibrous media. The important effect of saturation distribution on the effective diffusivity of the medium was also investigated for both water injection and withdrawal cases. The findings have bearing on the understanding of both capillarity in fibrous media and fuel cell design.

Impact of lean mass and bone density on glomerular filtration rate estimation in people living with HIV/AIDS

Context

Chronic kidney disease is a frequent complication in persons living with HIV/AIDS. Although previous studies have suggested that the CKD-EPI formula is appropriate to estimate glomerular filtration rate (GFR) in HIV-positive adults with normal kidney function, the optimal way to estimate GFR in those with Stage 3 chronic kidney disease is not known. Moreover, the impact of muscle mass on creatinine level and GFR estimation is unknown.

Aim and methods

Our study aimed to evaluate the accuracy of different diagnostic tests available compared to the gold standard measurement of GFR. A group of 44 HIV-1 patients with an estimated GFR between 60 and 30 ml/min/1.73 m² were included in a single-center cross-sectional study. Serum creatinine and cystatin C were measured. GFR was estimated using Cockcroft-Gault, MDRD, sMDRD, CKD-EPI, CKD-EPIcyst, and CKD-EPIcyst/creat formulae and was measured using isotopic Chrome₅₁ EDTA clearance. Bone density and muscle mass were measured by DXA scan.

Results

Mean age was 62±10 years. Mean BMI was 23±4 kg/m². Prevalence of diabetes was 30% and of hypertension was 47%. Viral load was <40 copies/ml for 90% of the patients, and mean CD₄ count was 446±191 cells/mm³. Mean measured GFR was 63.4±16.5 ml/min/1.73 m². All formulae under-estimated GFR. The best relative precision and accuracy were provided by the CKP-EPI formula. sMDRD, CKD-EPIcyst, and CKD-EPIcyst/creat performed worse than the CKD-EPI formula. Body composition did not significantly influence accuracy or precision of GFR estimation.

Conclusion

In HIV-infected patients in stable immunovirologic conditions with CKD stage 3 and high prevalence of metabolic associated conditions, the CKD-EPI formula performed best, although all formulae under estimate GFR.

Advanced mortar coatings for cultural heritage protection. Durability towards prolonged UV and outdoor exposure

In the present work, two kinds of hybrid polymeric-inorganic coatings containing TiO₂ or SiO₂ particles and prepared starting from two commercial resins (Alpha®SI30 and Bluesil®BP9710) were developed and applied to two kinds of mortars (an air-hardening calcic lime mortar [ALM] and a natural hydraulic lime mortar [HLM]) to achieve better performances in terms of water repellence and consequently damage resistance. The two pure commercial resins were also applied for comparison purposes. Properties of the coated materials and their performance were studied using different techniques such as contact angle measurements, capillary absorption test, mercury intrusion porosimetry, surface free energy, colorimetric measurements and water vapour permeability tests. Tests were also performed to determine the weathering effects on both the commercial and the hybrid coatings in order to study their durability. Thus, exposures to UV radiation, to UV radiation/condensed water cycles and to a real polluted atmospheric environment have been performed. The effectiveness of the hybrid SiO₂ based coating was demonstrated, especially in the case of the HLM mortar.

Racial Disparities in Creatinine-based Kidney Function Estimates Among HIV-infected Adults

OBJECTIVE

The aim of our study was to investigate whether current eGFR equations in clinical use might systematically over-estimate the kidney function, and thus misclassify CKD status, of Black Americans with HIV. Specifically, we evaluated the impact of removing the race coefficient from the MDRD and CKD-EPI equations on comparisons between Black and White HIV-infected veterans related to: 1) the prevalence of reduced eGFR; 2) the distribution of eGFR values; and 3) the relationship between eGFR and all-cause mortality.

DESIGN

Retrospective cohort study.

SETTING

The Department of Veterans Affairs (VA) HIV Clinical Case Registry (CCR), which actively monitors all HIV-infected persons receiving care in the VA nationally.

PATIENT/PARTICIPANTS

21,905 treatment-naïve HIV-infected veterans.

MAIN OUTCOME MEASURES

Estimated glomerular filtration rate (eGFR) using the abbreviated Modification of Diet in Renal Disease (MDRD) formula with and without (MDRD-RCR) the race coefficient and all-cause mortality.

RESULTS

Persons with eGFR <45 mL/min/1.73m(2) had a higher risk of death compared with those with eGFR >80 mL/min/1.73m(2) among both Blacks (HR=2.8, 95%CI: 2.4-3.3) and Whites (HR=1.9, 95%CI: 1.4-2.6), but the association appeared to be stronger in Blacks (P=.038, test for interaction). Blacks with eGFR 45-60 mL/min/1.73m(2) also had a higher risk of death (HR=1.7, 95%CI: 1.4-2.1) but Whites did not (HR=.86, 95%CI: .67-1.10; test for interaction: P<.0001). Racial differences were substantially attenuated when eGFR was re-calculated without the race coefficient.

CONCLUSIONS

Our findings suggest that clinicians may want to consider estimating glomerular filtration rate without the race coefficient in Blacks with HIV.

Individualizing pharmacotherapy in patients with renal impairment: the validity of the Modification of Diet in Renal Disease formula in specific patient populations with a glomerular filtration rate below 60 ml/min. A systematic review

Background

The Modification of Diet in Renal Disease (MDRD) formula is widely used in clinical practice to assess the correct drug dose. This formula is based on serum creatinine levels which might be influenced by chronic diseases itself or the effects of the chronic diseases. We conducted a systematic review to determine the validity of the MDRD formula in specific patient populations with renal impairment: elderly, hospitalized and obese patients, patients with cardiovascular disease, cancer, chronic respiratory diseases, diabetes mellitus, liver cirrhosis and human immunodeficiency virus.

Methods and Findings

We searched for articles in Pubmed published from January 1999 through January 2014. Selection criteria were (1) patients with a glomerular filtration rate (GFR) < 60 ml/min (/1.73m²), (2) MDRD formula compared with a gold standard and (3) statistical analysis focused on bias, precision and/or accuracy. Data extraction was done by the first author and checked by a second author. A bias of 20% or less, a precision of 30% or less and an accuracy expressed as P₃₀% of 80% or higher were indicators of the validity of the MDRD formula. In total we included 27 studies. The number of patients included ranged from 8 to 1831. The gold standard and measurement method used varied across the studies. For none of the specific patient populations the studies provided sufficient evidence of validity of the MDRD formula regarding the three parameters. For patients with diabetes mellitus and liver cirrhosis, hospitalized patients and elderly with moderate to severe renal impairment we concluded that the MDRD formula is not valid. Limitations of the review are the lack of considering the method of measuring serum creatinine levels and the type of gold standard used.

Conclusion

In several specific patient populations with renal impairment the use of the MDRD formula is not valid or has uncertain validity.

The validity of the modification of diet in renal disease formula in HIV-infected patients: a systematic review

RATIONALE, AIMS AND OBJECTIVES

Renal dysfunction is highly prevalent in HIV-infected patients and may require dose adjustment of renally excreted antiretroviral drugs. The Modification of Diet in Renal Disease (MDRD)-4 formula is frequently used in daily practice to estimate patients' renal function. The aim of this systematic review was to assess the validity of the MDRD-4 formula in HIV-infected patients.

METHOD

A systematic search in Pubmed and EMBASE was done to identify studies which compared MDRD-4 with measured glomerular filtration rate (mGFR) in HIV-infected patients.

RESULTS

Five studies were included, which provided data from 464 HIV-infected patients with mean mGFR ranging from 87 to 118 ml/min/1.73 m(2). In all studies, results from the MDRD-4 gave an underestimation of the mGFR. Mean bias ((MDRD-4) - mGFR) ranged from -6 to -11 ml/min/1.73 m(2) across studies. The accuracy expressed in terms of P 30 ranged from 64 to 89 %.

CONCLUSIONS

The MDRD-4 formula is as valid in HIV-positive as in HIV-negative patients. Because the available studies comprised mainly HIV-infected patients with mildly impaired to good renal function (GFR ≥ 60 ml/min/1.73 m(2)), more research is needed to validate the MDRD-4 formula in HIV-infected patients with moderate to severe renal impairment.

Use of glomerular filtration rate estimating equations for drug dosing in HIV-positive patients

BACKGROUND

Current HIV treatment guidelines recommend using the Cockcroft-Gault equation for drug dosing adjustments. The use of newer glomerular filtration rate (GFR) estimating equations for drug dosing and the appropriateness of physician antiretroviral dosing based on estimated kidney function have not been studied in an HIV-positive population.

METHODS

We evaluated concordance between measured and estimated GFR for the assignment of kidney function categories designated by the US Food and Drug Administration (FDA) Guidance for industry for pharmacokinetic studies, and appropriateness of physician antiretroviral drug dosing for level of kidney function in 200 HIV-positive patients on stable antiretroviral therapy. Estimated kidney function was determined using the Chronic Kidney Disease-Epidemiology collaboration (CKD-EPI), Modification of Diet in Renal Disease (MDRD) Study and Cockcroft-Gault equations.

RESULTS

For assignment of FDA-designated kidney function categories, concordance rates between measured and estimated GFR using the CKD-EPI, MDRD Study and Cockcroft-Gault equations were 79%, 71% and 77%, respectively. This pattern was consistent across most subgroups. When actual prescribed dosages were compared with recommended dosages based on the level of estimated kidney function, 3-19% of study participants were prescribed higher than recommended dosages. The largest discordance between prescribed and recommended dosages was observed for the Cockcroft-Gault equation.

CONCLUSIONS

The CKD-EPI equation has the highest concordance with measured GFR for the assignment of FDA-designated kidney function categories. Its use may lead to lower dosing-related errors in HIV-infected US adults on stable antiretroviral therapy. More education is required with respect to dose adjustment for level of kidney function.

Performance of creatinine and cystatin C-based glomerular filtration rate estimating equations in a European HIV-positive cohort

OBJECTIVE

To validate glomerular filtration rate (GFR) estimating equations in white HIV-infected patients based on serum creatinine and/or serum cystatin C.

DESIGN

Single-center, cross-sectional evaluation of the predictive performance of GFR estimators.

METHODS

GFR was measured by iohexol plasma clearance. Serum creatinine (Scr) and serum cystatin C (Scyst) were measured by traceable and standardized methods. We evaluated the performance of the Modification of Diet in Renal Disease (MDRD) and the Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) equations. We also studied the performance of the cystatin C-based equation (CKD-EPI Scyst) and the combined cystatin and creatinine-based equation (CKD-EPI combined), as recently proposed by the CKD-EPI group.

RESULTS

Two hundred and three participants (18% of women) were included. Mean age was 49 ± 10 years. Mean measured GFR (mGFR) was 95 ± 24 ml/min per 1.73 m². CKD-EPI and CKD-EPI combined significantly outperformed the MDRD equation. The percentage of estimating results within 30% of mGFR was 75, 82 and 81% for the MDRD, CKD-EPI and CKD-EPI combined equation, respectively. Results favoring the CKD-EPI and CKD-EPI combined equation were especially observed for patients with mGFR over 90 ml/min per 1.73 m².

CONCLUSION

In our European HIV cohort, we confirmed that the creatinine-based CKD-EPI equation should replace the MDRD study equation. However, global performance of this equation remains worse than the performance observed in the general population. This lesser performance is particularly relevant in patients with measured GFR under and around 60 ml/min per 1.73 m². Moreover, the specific interest of Scyst-based equations is not confirmed in this population.

Performance of creatinine and cystatin C GFR estimating equations in an HIV-positive population on antiretrovirals

OBJECTIVE

To evaluate the performance of Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine, cystatin C, and creatinine-cystatin C estimating equations in HIV-positive patients.

METHODS

We evaluated the performance of the Modification of Diet in Renal Disease (MDRD) Study and CKD-EPI creatinine 2009, CKD-EPI cystatin C 2012, and CKD-EPI creatinine-cystatin C 2012 glomerular filtration rate (GFR) estimating equations compared with GFR measured using plasma clearance of iohexol in 200 HIV-positive patients on stable antiretroviral therapy. Creatinine and cystatin C assays were standardized to certified reference materials.

RESULTS

Of the 200 participants, median (IQR) CD4 count was 536 (421) and 61% had an undetectable HIV viral load. Mean (SD) measured GFR (mGFR) was 87 (26) mL/min per 1.73 m. All CKD-EPI equations performed better than the MDRD Study equation. All 3 CKD-EPI equations had similar bias and precision. The cystatin C equation was not more accurate than the creatinine equation. The creatinine-cystatin C equation was significantly more accurate than the cystatin C equation, and there was a trend toward greater accuracy than the creatinine equation. Accuracy was equal or better in most subgroups with the combined equation compared to either alone.

CONCLUSIONS

The CKD-EPI cystatin C equation does not seem to be more accurate than the CKD-EPI creatinine equation in patients who are HIV-positive, supporting the use of the CKD-EPI creatinine equation for routine clinical care for use in North American populations with HIV. The use of both filtration markers together as a confirmatory test for decreased estimated GFR based on creatinine in individuals who are HIV-positive requires further study.

Cystatin C as a marker of glomerular filtration rate: prospects and limitations

PURPOSE OF REVIEW

There is much interest in cystatin C to replace or supplement serum creatinine to estimate the glomerular filtration rate (GFR). Here we review the performance of cystatin C and combined creatinine-cystatin C estimating equations compared to creatinine-based estimating equations in chronic and acute kidney disease.

RECENT FINDINGS

Drift in the cystatin C assay has had a large effect on the results reported using cystatin C, but these issues are not routinely considered in evaluation of GFR-estimating equations. The recently released primary reference material for cystatin C will allow less difference among assays in the future. There does not appear to be a consistent message among published studies as to whether cystatin C-based equations are better than creatinine-based equations in the general population or those with chronic kidney disease (CKD), as well as those with reduced muscle mass or chronic illness, or acute kidney injury. Cystatin C could be used in combination with creatinine as a confirmatory test for estimated GFR from creatinine.

SUMMARY

Cystatin C may have a role to estimate GFR in selected circumstances, and the next set of studies should be directed at developing implementation strategies for its use.

Chronic kidney disease and estimates of kidney function in HIV infection: a cross-sectional study in the multicenter AIDS cohort study

BACKGROUND

Cystatin C has been proposed as an alternative marker of kidney function among HIV-infected persons in whom serum creatinine is affected by extrarenal factors.

METHODS

In this cross-sectional study, we compared estimated glomerular filtration rates (eGFR) using serum creatinine versus cystatin C between 150 HIV-uninfected and 783 HIV-infected men. We evaluated the prevalence of chronic kidney disease (CKD; eGFR less than 60 mL/min/1.73 m) and examined the influence of extrarenal factors on GFR estimates among HIV-infected men.

RESULTS

Estimated GFRSCR was similar by HIV serostatus, but eGFRCYSC was lower in HIV-infected men. A higher proportion of HIV-infected men were classified as having CKD when using eGFRCYSC versus eGFRSCR (7% vs 5%, P < 0.01). In HIV-infected individuals without CKD, eGFRSCR was higher than eGFRCYSC, whereas it was lower than eGFRCYSC in persons with CKD. In HIV-infected men, older age, proteinuria, and prior clinical AIDS were inversely associated with both GFR estimates. Higher serum albumin levels and angiotensin-converting enzyme inhibitor/angiotensin receptor blocker use were associated with lower eGFRSCR. HIV viral load, hepatitis C coinfection, and serum alkaline phosphatase were inversely associated with eGFRCYSC.

CONCLUSION

Among HIV-uninfected and HIV-infected men of similar social risk behaviors, GFR estimates differed by biomarker and kidney function level. Estimated GFRCYSC classified a larger proportion of HIV-infected men with CKD compared with eGFRSCR. Differences between these GFR-estimating methods may be the result of the effects of extrarenal factors on serum creatinine and cystatin C. Until GFR-estimating equations are validated among HIV-infected individuals, current GFR estimates based on these biomarkers should be interpreted with care in this patient population.