Arginase upregulation and eNOS uncoupling contribute to impaired endothelium-dependent vasodilation in a rat model of intrauterine growth restriction.

Individuals born after intrauterine growth restriction (IUGR) are at increased risk of developing cardiovascular diseases in adulthood, notably hypertension (HTN). Alterations in the vascular system, particularly impaired endothelium-dependent vasodilation, may play an important role in long-term effects of IUGR. Whether such vascular dysfunction precedes HTN has not been fully established in individuals born after IUGR. Moreover, the intimate mechanisms of altered endothelium-dependent vasodilation remain incompletely elucidated. We therefore investigated, using a rat model of IUGR, whether impaired endothelium-dependent relaxation precedes the development of HTN and whether key components of the l-arginine-nitric oxide (NO) pathway are involved in its pathogenesis. Pregnant rats were fed with a control (CTRL, 23% casein) or low-protein diet (LPD, 9% casein) to induce IUGR. Systolic blood pressure (SBP) was measured by tail-cuff plethysmography in 5- and 8-wk-old male offspring. Aortic rings were isolated to investigate relaxation to acetylcholine, NO production, endothelial NO synthase (eNOS) protein content, arginase activity, and superoxide anion production. SBP was not different at 5 wk but significantly increased in 8-wk-old offspring of maternal LPD (LP) versus CTRL offspring. In 5-wk-old LP versus CTRL males, endothelium-dependent vasorelaxation was significantly impaired but restored by preincubation with l-arginine or the arginase inhibitor S-(2-boronoethyl)-l-cysteine; NO production was significantly reduced but restored by l-arginine pretreatment; total eNOS protein, dimer-to-monomer ratio, and arginase activity were significantly increased; superoxide anion production was significantly enhanced but normalized by pretreatment with the NO synthase inhibitor Nω-nitro-l-arginine. In this model, IUGR leads to early-impaired endothelium-dependent vasorelaxation, resulting from arginase upregulation and eNOS uncoupling, which precedes the development of HTN.

Homocysteine modulates the proteolytic potential of human arterial smooth muscle cells through a reactive oxygen species dependant mechanism.

Pathological levels of homocysteine induce a dramatic degradation of arterial elastic structures. This severe metalloproteinase-dependant elastolysis affects elastic structures all over the media suggesting that smooth muscle cells (SMC) may participate to this process induced by homocysteine. Therefore, we investigated the effect of physiological (10 microM) and pathological (50, 100, and 500 microM) concentrations of homocysteine on the metalloproteinase-dependant proteolytic potential of human arterial SMC in culture. Pathological levels of homocysteine increased concomitantly the secretion of latent MMP-2 and TIMP-2 while the secretion of other elastolytic matrix metalloproteinases (MMPs) and expression of MT1-MMP were not altered. The increased secretion of latent MMP-2 induced by homocysteine was associated with an increased production of reactive oxygen species (ROS). Moreover, the increased secretion of latent MMP-2 induced by homocysteine was inhibited by antioxidant superoxide dismutase alone or in combination with catalase. These results suggest that SMC could participate, through an oxidative stress dependant secretion of elastolytic MMP-2, to the metalloproteinase-dependant degradation of arterial elastic structures induced by homocysteine.

An Efficient and Reproducible Protocol for Distraction Osteogenesis in a Rat Model Leading to a Functional Regenerated Femur.

This protocol describes the use of a newly developed external fixator for distraction osteogenesis in a rat femoral model. Distraction osteogenesis (DO) is a surgical technique leading to bone regeneration after an osteotomy. The osteotomized extremities are moved away from each other by gradual distraction to reach the desired elongation. This procedure is widely used in humans for lower and upper limb lengthening, treatment after a bone nonunion, or the regeneration of a bone defect following surgery for bone tumor excision, as well as in maxillofacial reconstruction. Only a few studies clearly demonstrate the efficiency of their protocol in obtaining a functional regenerated bone, i.e., bone that will support physiological weight-bearing without fracture after removal of the external fixator. Moreover, protocols for DO vary and reproducibility is limited by lack of information, making comparison between studies difficult. The aim of this study was to develop a reproducible protocol comprising an appropriate external fixator design for rat limb lengthening, with a detailed surgical technique that permits physiological weight-bearing by the animal after removal of the external fixator.

Determination of uremic solutes in biological fluids of chronic kidney disease patients by HPLC assay.

During chronic kidney disease (CKD), solutes called uremic solutes, accumulate in blood and tissues of patients. We developed an HPLC method for the simultaneous determination of several uremic solutes of clinical interest in biological fluids: phenol (Pol), indole-3-acetic acid (3-IAA), p-cresol (p-C), indoxyl sulfate (3-INDS) and p-cresol sulfate (p-CS). These solutes were separated by ion-pairing HPLC using an isocratic flow and quantified with a fluorescence detection. The mean serum concentrations of 3-IAA, 3-INDS and p-CS were 2.12, 1.03 and 13.03 µM respectively in healthy subjects, 3.21, 17.45 and 73.47 µM in non hemodialyzed stage 3-5 CKD patients and 5.9, 81.04 and 120.54 µM in hemodialyzed patients (stage 5D). We found no Pol and no p-C in any population. The limits of quantification for 3-IAA, 3-INDS, and p-CS were 0.83, 0.72, and 3.2 µM respectively. The within-day CVs were between 1.23 and 3.12% for 3-IAA, 0.98 and 2% for 3-INDS, and 1.25 and 3.01% for p-CS. The between-day CVs were between 1.78 and 5.48% for 3-IAA, 1.45 and 4.54% for 3-INDS, and 1.19 and 6.36% for p-CS. This HPLC method permits the simultaneous and quick quantification of several uremic solutes for daily analysis of large numbers of samples.

Changes in the physical structure and chain dynamics of elastin network in homocysteine-cultured arteries.

The thermal and dielectric properties of the elastin network were investigated in arteries cultured with physiological and pathological concentrations of homocysteine, an aminoacid responsible of histological impairments in human arteries. The physical structure of this amorphous protein was investigated by differential scanning calorimetry (DSC). To explore the molecular dynamics of the elastin network in the nanometer range, we used thermally stimulated currents (TSC), a dielectric technique running at low frequency, and measuring the dipolar reorientations in proteins subjected to a static electrical field. Combining DSC and TSC experiments reveals the molecular mobility of the proteins, both in the glassy state and in the liquid state. Significant differences are evidenced in the physical structure and relaxation behavior of elastin network in cultured arteries (physiological and pathological concentrations of homocysteine) and discussed.

Binding of p-cresylsulfate and p-cresol to human serum albumin studied by microcalorimetry.

p-Cresylsulfate, a metabolite of p-cresol, is reported as prototypic protein-bound uremic toxin, inefficiently removed by haemodialysis. The binding between p-cresylsulfate or p-cresol and human serum albumin was studied using microcalorimetry. The results confirm that the two molecules are protein-bound. However, the affinity of p-cresylsulfate and p-cresol toward human serum albumin is moderate at 25 degrees C and becomes relatively weak at physiological temperature, 37 degrees C. The binding principally involves van der Waals type interactions, and the binding sites of the two molecules are the same or very close. The low fraction of bound toxin (13-20%) appears to be insufficient to link strong binding to poor removal of this toxin by hemodialysis.

Homocysteine modulates the proteolytic potential of human vascular endothelial cells.

Pathological levels of homocysteine induce a metalloproteinase-dependent degradation of the elastic structures in arterial wall. This elastolytic process is preferentially localized toward the internal elastic laminae and in the first layers of the media, suggesting endothelium could participate in extracellular matrix degradation induced by homocysteine. Therefore, we studied the effects of homocysteine on proteolytic potential of endothelial cells. Human umbilical vein endothelial cells were cultured with concentrations of homocysteine matching human physiological (10 microM) and pathological (50, 100, and 250 microM) plasma homocysteine levels. Pathological levels of homocysteine increased the secretion of elastolytic metalloproteinase-2 and -9, but not of metalloproteinase-3 and -7. Homocysteine also increased the expression of human tissue kallikrein, a potential activator of matrix metalloproteinase-2 and -9, while the expression of urokinase plasminogen activator was not altered. These results suggest vascular endothelial cells could participate in the subendothelial degradation of the arterial elastic structures occurring in hyperhomocysteinemia.