Joaquín Arenas

Sirolimus does not exhibit nephrotoxicity compared to cyclosporine in renal transplant recipients.

Sirolimus and cyclosporine (CsA) prevent acute rejection in man when used as primary therapies in triple drug regimens. Sirolimus does not act via the calcineurin pathway and therefore is not expected to produce the same renal side‐effects. This paper presents the pooled 2‐year data analysis of renal function parameters from two open‐label, randomized, multicenter studies. Patients (18–68 years) receiving a primary renal allograft were randomized to receive concentration‐controlled sirolimus (n = 81) or CsA (n = 80), in combination with azathioprine and steroids (n = 83), or mycophenolate mofetil (MMF) and steroids (n = 78). From week 10 through year 2, calculated glomerular filtration rate (GFR) was significantly higher in sirolimus‐ than in CsA‐treated patients (69.3 vs. 56.8 mL/min, at 2 years, p = 0.004). Serum uric acid was significantly higher in the CsA‐treated patients and magnesium was significantly lower; these parameters were more likely to be within normal limits in the sirolimus group. Mean serum potassium and phosphorus were lower in sirolimus‐treated patients. In conclusion, sirolimus, when administered as primary therapy in combination with azathioprine or MMF, has a favorable safety profile compared to CsA with regards to renal function.

Mitochondrial complex I plays an essential role in human respirasome assembly.

The biogenesis and function of the mitochondrial respiratory chain (RC) involve the organization of RC enzyme complexes in supercomplexes or respirasomes through an unknown biosynthetic process. This leads to structural interdependences between RC complexes, which are highly relevant from biological and biomedical perspectives, because RC defects often lead to severe neuromuscular disorders. We show that in human cells, respirasome biogenesis involves a complex I assembly intermediate acting as a scaffold for the combined incorporation of complexes III and IV subunits, rather than originating from the association of preassembled individual holoenzymes. The process ends with the incorporation of complex I NADH dehydrogenase catalytic module, which leads to the respirasome activation. While complexes III and IV assemble either as free holoenzymes or by incorporation of free subunits into supercomplexes, the respirasomes constitute the structural units where complex I is assembled and activated, thus explaining the significance of the respirasomes for RC function.

Mitochondrial DNA background modulates the assembly kinetics of OXPHOS complexes in a cellular model of mitochondrial disease

Lebers hereditary optic neuropathy (LHON), the most frequent mitochondrial disorder, is mostly due to three mitochondrial DNA (mtDNA) mutations in respiratory chain complex I subunit genes: 3460/ND1, 11778/ND4 and 14484/ND6. Despite considerable clinical evidences, a genetic modifying role of the mtDNA haplogroup background in the clinical expression of LHON remains experimentally unproven. We investigated the effect of mtDNA haplogroups on the assembly of oxidative phosphorylation (OXPHOS) complexes in transmitochondrial hybrids (cybrids) harboring the three common LHON mutations. The steady-state levels of respiratory chain complexes appeared normal in mutant cybrids. However, an accumulation of low molecular weight subcomplexes suggested a complex I assembly/stability defect, which was further demonstrated by reversibly inhibiting mitochondrial protein translation with doxycycline. Our results showed differentially delayed assembly rates of respiratory chain complexes I, III and IV amongst mutants belonging to different mtDNA haplogroups, revealing that specific mtDNA polymorphisms may modify the pathogenic potential of LHON mutations by affecting the overall assembly kinetics of OXPHOS complexes.

X‐linked NDUFA1 gene mutations associated with mitochondrial encephalomyopathy

Mitochondrial complex I deficiency is the commonest diagnosed respiratory chain defect, being genetically heterogeneous. The male preponderance of previous patient cohorts suggested an X‐linked underlying genetic defect. We investigated mutations in the X‐chromosomal complex I structural genes, NDUFA1 and NDUFB11, as a novel cause of mitochondrial encephalomyopathy.

Mitochondrial respiratory chain dysfunction: implications in neurodegeneration.

For decades mitochondria have been considered static round-shaped organelles in charge of energy production. In contrast, they are highly dynamic cellular components that undergo continuous cycles of fusion and fission influenced, for instance, by oxidative stress, cellular energy requirements, or the cell cycle state. New important functions beyond energy production have been attributed to mitochondria, such as the regulation of cell survival, because of their role in the modulation of apoptosis, autophagy, and aging. Primary mitochondrial diseases due to mutations in genes involved in these new mitochondrial functions and the implication of mitochondrial dysfunction in multifactorial human pathologies such as cancer, Alzheimer and Parkinson diseases, or diabetes has been demonstrated. Therefore, mitochondria are set at a central point of the equilibrium between health and disease, and a better understanding of mitochondrial functions will open new fields for exploring the roles of these mitochondrial pathways in human pathologies. This review dissects the relationships between activity and assembly defects of the mitochondrial respiratory chain, oxidative damage, and alterations in mitochondrial dynamics, with special focus on their implications for neurodegeneration.

Genotypic and phenotypic features of McArdle disease: insights from the Spanish national registry

Background Published genotype/phenotype data on McArdle disease are limited in sample size. A single national (Spanish) registry of patients with McArdle disease was created with the purpose of analysing their genotypic and phenotypic characteristics. Methods A cross sectional study was conducted, collecting demographic, family history, clinical, genotype and functional capacity data from all patients diagnosed with McArdle disease in the Spanish National Health System up to December 2010. Results 239 cases were recorded (all of Caucasian descent, 102 women; mean±SD age 44±18 years (range 9, 93)); prevalence of ∼1/167 000 people. Two mutant PYGM alleles were identified in 99.6% of cases. Although there was heterogeneity in the severity of symptoms, there were four common diagnostic features: (1) 99.5% of patients reported a history of acute crises of exercise intolerance (accompanied by recurrent myoglobinuria in 50% of cases); (2) in 58% of patients, symptoms started in the first decade of life; (3) 86% of patients repeatedly experienced the ‘second wind’ phenomenon over life; and (4) 99% of patients had a high basal serum level of total creatine kinase (>200 U/l). Clinical presentation of the disease was similar in men and women and worsened with age. Patients who were physically active had higher levels of cardiorespiratory fitness (by 23%, p=0.003) and were more likely to improve their clinical course over a 4 year period compared with inactive patients (OR 225; 95% CI 20.3 to 2496.7). Conclusions The main clinical features of McArdle disease are generally homogeneous and frequently appear during childhood; clinical condition deteriorates with ageing. Active patients have a better clinical outcome and functional capacity.

Molecular heterogeneity of myophosphorylase deficiency (McArdle's disease): a genotype-phenotype correlation study.

We report on 54 Spanish patients with McArdles disease from 40 unrelated families. Molecular analysis revealed that the most common R49X mutation was present in 70% of patients and 55% of alleles. The G204S mutation was less frequent and found in 14.8% of patients and 9% of mutant alleles. The W797R mutation was observed in 16.5% of patients, accounting for 13.7% of mutant alleles. Moreover, 78% of mutant alleles among Spanish patients can be identified by using polymerase chain reaction‐restriction fragment length polymorphism analysis for the R49X, G204S, and W797R mutations, which makes noninvasive diagnosis possible through molecular genetic analysis of blood DNA. Six novel mutations were found. Three were missense mutations, E348K, R601W, and A703V; two nonsense mutations, E124X and Q754X; and one single base pair deletion, 533 delA. No clear genotype‐phenotype correlation emerges from our study. Most of the mutations of uncharged and solvent inaccessible residues and the truncations must disrupt the basic structure of the protein. The mutations of charged residues would be expected to interfere with internal hydrogen bonding networks, introducing severe incompatible partnering that is caused by poor packing or electrostatic repulsions.

Mitochondrial DNA haplogroups: Role in the prevalence and severity of knee osteoarthritis

OBJECTIVE Some studies indicate that the mitochondrion is implicated in osteoarthritis (OA). To test the hypothesis that mitochondrial DNA (mtDNA) haplogroups contribute to the prevalence and severity of knee OA, we analyzed the European mtDNA haplogroups in a Spanish population of patients with knee OA and healthy control subjects. METHODS We combined the single-base extension assay with the polymerase chain reaction-restriction fragment length polymorphism technique to obtain the different single-nucleotide polymorphisms that characterize the European haplogroups in 457 patients with knee OA and 262 radiologic controls. Knee OA radiographs had previously been classified as grades 1-4 according to Kellgren/Lawrence (K/L) scoring system. RESULTS Individuals carrying haplogroup J showed a significantly decreased risk of knee OA (odds ratio [OR] 0.460 [95% confidence interval (95% CI) 0.282-0.748], P = 0.002). In terms of K/L scores, patients carrying haplogroup J had a less severe progression of knee OA (OR 0.351 [95% CI 0.156-0.787], P = 0.012), while those carrying haplogroup U had a more severe progression (OR 1.788 [95% CI 1.094-2.922], P = 0.025). CONCLUSION People carrying haplogroup J may be at a lower risk of developing knee OA, and those carrying this haplogroup in whom knee OA does not develop may have a less severe progression of the disease. Patients with knee OA carrying haplogroup U may have a more severe progression of the disease. These results indicate that mtDNA haplogroups contribute to the pathogenesis of OA.

Renal pathology in children with mitochondrial diseases

We studied renal involvement in 42 children with mitochondrial diseases (MDs). The diagnosis of MD was established by morphological, biochemical, and molecular genetic criteria. Renal disease was considered when patients had renal failure, nephrotic syndrome, Fanconi’s syndrome or any symptomatic renal alteration. Mild tubular disorder was established if they had abnormal laboratory findings with no apparent clinical symptom. Renal involvement was found in 21 children (50%), of whom 8 had an apparent clinical picture and 13 a mild tubular disorder. Five patients with renal disease showed Debré–Toni–Fanconi’s syndrome, 2 of them with decreased glomerular filtration rate (GFR). One case had nephrotic syndrome, another one presented decreased GFR, and the last one had a neurogenic bladder and bilateral hydronephrosis. Patients with mild renal disease showed tubular dysfunction with normal GFR. Renal involvement is frequent and present in about half of the children with MD. Thus, studies for evaluating kidney function should be performed on children with MD. Conversely, patients with tubulopathy of unknown origin or progressive renal disease should be investigated for the existence of MD, especially if associated with involvement of other organs or tissues. Southern blot analysis to search for large-scale mitochondrial DNA (mtDNA) rearrangements should be performed for patients with MD and kidney involvement.

Nephrotic Proteinuria Without Hypoalbuminemia: Clinical Characteristics and Response to Angiotensin-Converting Enzyme Inhibition

Although hypoalbuminemia is a fundamental characteristic of nephrotic syndrome (NS), there are many patients with massive proteinuria that do not develop hypoalbuminemia. We have studied the clinical and biochemical characteristics of 19 patients with persistent massive proteinuria (greater than 5 g/d) and normal serum albumin (group I) in comparison with 16 patients with similar proteinuria excretion, but persistent hypoalbuminemia (group II). Most of group I patients had diagnoses suggesting glomerular hyperfiltration (focal glomerulosclerosis [FGS] associated with vesicoureteral reflux [VUR], reduction of renal mass, proteinuria associated with obesity, sclerotic phase of idiopathic crescentic glomerulonephritis [GN] in contrast with those of group II, in which membranous GN was the most frequent diagnosis. We prospectively investigated differences in the antiproteinuric effect of captopril, an antiotensin-converting enzyme inhibitor (ACEI); after 6 months of treatment, proteinuria decreased clearly in group I (7.1 +/- 1.7 to 3.7 +/- 1.7 g/d; P less than 0.001), whereas no significant changes were observed in group II (8.1 +/- 2.4 to 8.8 +/- 4 g/d). Serum creatinine (Scr) remained stable during captopril treatment in group I, whereas three patients in group II showed a worsening of renal function.(ABSTRACT TRUNCATED AT 250 WORDS)