Sergio Luis-Lima

Glycolate Oxidase Is a Safe and Efficient Target for Substrate Reduction Therapy in a Mouse Model of Primary Hyperoxaluria Type I.

Primary hyperoxaluria type 1 (PH1) is caused by deficient alanine-glyoxylate aminotransferase, the human peroxisomal enzyme that detoxifies glyoxylate. Glycolate is one of the best-known substrates leading to glyoxylate production, via peroxisomal glycolate oxidase (GO). Using genetically modified mice, we herein report GO as a safe and efficient target for substrate reduction therapy (SRT) in PH1. We first generated a GO-deficient mouse (Hao1(-/-)) that presented high urine glycolate levels but no additional phenotype. Next, we produced double KO mice (Agxt1(-/-) Hao1(-/-)) that showed low levels of oxalate excretion compared with hyperoxaluric mice model (Agxt1(-/-)). Previous studies have identified some GO inhibitors, such as 4-carboxy-5-[(4-chlorophenyl)sulfanyl]-1,2,3-thiadiazole (CCPST). We herein report that CCPST inhibits GO in Agxt1(-/-) hepatocytes and significantly reduces their oxalate production, starting at 25 µM. We also tested the ability of orally administered CCPST to reduce oxalate excretion in Agxt1(-/-) mice, showing that 30-50% reduction in urine oxalate can be achieved. In summary, we present proof-of-concept evidence for SRT in PH1. These encouraging results should be followed by a medicinal chemistry programme that might yield more potent GO inhibitors and eventually could result in a pharmacological treatment for this rare and severe inborn error of metabolism.

Estimated Glomerular Filtration Rate in Renal Transplantation: The Nephrologist in the Mist.

Background Formulas do not estimate renal function with acceptable precision and accuracy. Methods We compared 51 creatinine-based and/or cystatin c–based formulas with a gold standard (iohexol plasma clearance) in 193 renal transplant recipients using concordance correlation coefficient, total deviation index, coverage probability and the error in chronic kidney disease (CKD) stage classification. Results No formula showed a concordance correlation coefficient greater than 0.90 (average for creatinine-based formulas: ∼0.70 and for cystatin c–based formulas: ∼0.85). A wide total deviation index was observed: approximately 70% (creatinine-based) and approximately 50% (cystatin c–based), indicating that 90% of the estimations showed bounds of error of ±70% or ±50%, respectively, compared with the gold standard. No formula included 90% of the estimations within a coverage probability of ±10%. Half the CKD stages classified by creatinine-based formulas were incorrect, mainly due to overestimation of renal function. One of 3 CKD stages diagnosed by cystatin c–based formulas was incorrect, with both overestimation and underestimation. Overall, the formulas showed very low precision and accuracy and a high degree of error in reflecting real renal function. Conclusions In conclusion, formulas do not properly reflect renal function in kidney transplantation, which makes their use in clinical practice unreliable. Moreover, their use in clinical trials should be avoided.

A Simple Method to Measure Renal Function in Swine by the Plasma Clearance of Iohexol

There is no simple method to measure glomerular filtration rate (GFR) in swine, an established model for studying renal disease. We developed a protocol to measure GFR in conscious swine by using the plasma clearance of iohexol. We used two groups, test and validation, with eight animals each. Ten milliliters of iohexol (6.47 g) was injected into the marginal auricular vein and blood samples (3 mL) were collected from the orbital sinus at different points after injection. GFR was determined using two models: two-compartment (CL2: all samples) and one-compartment (CL1: the last six samples). In the test group, CL1 overestimated CL2 by ~30%: CL2 = 245 ± 93 and CL1 = 308 ± 123 mL/min. This error was corrected by a first-order polynomial quadratic equation to CL1, which was considered the simplified method: SM = −47.909 + (1.176xCL1) − (0.00063968xCL12). The SM showed narrow limits of agreement with CL2, a concordance correlation of 0.97, and a total deviation index of 14.73%. Similar results were obtained for the validation group. This protocol is reliable, reproducible, can be performed in conscious animals, uses a single dose of the marker, and requires a reduced number of samples, and avoids urine collection. Finally, it presents a significant improvement in animal welfare conditions and handling necessities in experimental trials.

An Overview of Errors and Flaws of Estimated GFR versus True GFR in Patients with Diabetes Mellitus

The determination of renal function is crucial in patients with type 2 diabetes (T2DM), a population at risk for chronic kidney disease (CKD). Glomerular filtration rate (GFR) can be measured (mGFR) with gold standard methods or estimated (eGFR) with formulas. Since 1957, when Effersoe published the first formula, more than 50 equations have been developed to estimate GFR. In this review, we examined the studies that compared mGFR and eGFR in patients with T2DM to analyze the performance of those formulae in this population. In cross-sectional studies, the average error of eGFR was ±30% of mGFR. Thus, in a patient with mGFR of 60 mL/min, eGFR may vary from 42 to 78 mL/min. Moreover, many patients were misclassified according to CKD stages. Formulas failed to detect glomerular hyperfiltration. In longitudinal studies, eGFR poorly reflected real GFR decline over time. All studies showed that eGFR decline was slower than mGFR decline. Notably, no major improvement in accuracy and precision has been observed since 1957 despite the use of cystatin-c. Thus, formulas are not reliable indicators of GFR in patients with T2DM. In clinical studies, where GFR is the main outcome measure of the study, eGFR should be avoided.