Calcium uptake into enterocyte brush-border membrane vesicles is greater in spontaneously hypertensive than in normotensive control rats

Arterial hypertension in the SHR is associated with disturbances of calcium homeostasis, compared with its normotensive control, the WKY. In order to study intestinal Ca2+ handling at the subcellular level, we examined 45Ca2+ uptake kinetics in isolated brush-border membrane vesicles (BBMV). Experiments were conducted in male, 12- to 14-week-old rats on a 1% Ca diet. BBMV were purified by the method of Forstner et al. No difference in BBMV enrichment was observed between SHR and WKY. Ca2+ uptake was studied at various Ca2+ concentrations in the incubation medium (0.025-1.0 mM) and could be separated into a nonsaturable and a saturable component. The saturable component followed Michaelis-Menten kinetics. Vmax in the SHR was greater than in the WKY: 0.576 +/- 0.186 (n = 6) vs. 0.346 +/- 0.10 nmol/mg protein x 10 s (n = 6), mean +/- SD, p less than 0.05. However, Km was not different in the two animal strains. In conclusion, mediated Ca2+ transport into duodenal BBMV was increased in the adolescent SHR. When considering that the transcellular duodenal Ca2+ flux is decreased in the SHR at this age, the rate-limiting step of perturbed transeptithelial Ca2+ transport is probably localized at the site of the basolateral membrane.

Definition, evaluation, and classification of renal osteodystrophy: a position statement from Kidney Disease: Improving Global Outcomes (KDIGO)

Disturbances in mineral and bone metabolism are prevalent in chronic kidney disease (CKD) and are an important cause of morbidity, decreased quality of life, and extraskeletal calcification that have been associated with increased cardiovascular mortality. These disturbances have traditionally been termed renal osteodystrophy and classified based on bone biopsy. Kidney Disease: Improving Global Outcomes (KDIGO) sponsored a Controversies Conference on Renal Osteodystrophy to (1) develop a clear, clinically relevant, and internationally acceptable definition and classification system, (2) develop a consensus for bone biopsy evaluation and classification, and (3) evaluate laboratory and imaging markers for the clinical assessment of patients with CKD. It is recommended that (1) the term renal osteodystrophy be used exclusively to define alterations in bone morphology associated with CKD, which can be further assessed by histomorphometry, and the results reported based on a unified classification system that includes parameters of turnover, mineralization, and volume, and (2) the term CKD-Mineral and Bone Disorder (CKD-MBD) be used to describe a broader clinical syndrome that develops as a systemic disorder of mineral and bone metabolism due to CKD, which is manifested by abnormalities in bone and mineral metabolism and/or extra-skeletal calcification. The international adoption of these recommendations will greatly enhance communication, facilitate clinical decision-making, and promote the evolution of evidence-based clinical practice guidelines worldwide.

Hyporesponsiveness to recombinant human erythropoietin

The introduction of recombinant human erythropoietin (rh-Epo, epoetin) as a treatment for the anaemia of renal failure has transformed the management of this condition. Nevertheless, a significant number of patients fail to respond. There are many different possible causes of inadequate response to epoetin. Iron deficiency, whether absolute or functional, is considered to be the most important, and it is widely accepted that maintaining adequate iron levels reduces rh-Epo dosage requirement and improves efficacy in haemodialysis patients. Infection and inflammation have been shown to influence responsiveness to rh-Epo by disrupting iron metabolism and eliciting the release of cytokines that inhibit erythropoiesis. Another factor for consideration is severe hyperparathyroidism, which can lead to a reduced number of responsive erythroid progenitor cells. Inadequate dialysis can also negatively impact on rh-Epo therapy, and aluminium overload interferes with iron metabolism and reduces the efficacy of rh-Epo. Deficiencies in vitamin B(12), folic acid and potentially vitamin C can all reduce the efficacy of treatment with rh-Epo. Optimizing patient response to rh-Epo therapy, therefore, requires consideration of many factors, some well established and others that are more controversial, and the list continues to grow with the identification of new factors.

Inhibition of nitric oxide synthesis attenuates insulin-mediated sympathetic activation in rats

BACKGROUND AND OBJECTIVES

Infusion of insulin produces sympathoexcitation, nitric oxide (NO) generation and NO-mediated vasodilation. Because central nervous system NO may inhibit sympathetic outflow, the present study was designed to determine whether NO synthase blockade would enhance insulin-mediated sympathetic activation. We additionally aimed to determine whether augmented sympathoexcitation and reduced NO-mediated vasodilation, during combined NO synthase blockade and hyperinsulinemia, would result in a blood pressure increase.

DESIGN AND METHODS

We infused vehicle (Control; n = 7) or insulin (10 mU/min) in anaesthetized rats receiving either no pretreatment (Insulin; n = 7) or after pretreatment with the NO blocker, NG-monomethyl-L-arginine (L-NMMA-insulin; 0.25 mg/kg per min; n = 7), while measuring mean arterial pressure (MAP), heart rate and lumbar sympathetic nerve activity (SNA) during euglycemic clamp. An additional control group received L-NMMA (L-NMMA; n = 7).

RESULTS

Insulin rats had large SNA increases (190 +/- 22% from 100% baseline), contrasting with small increases in the Control (136 +/- 10%) and L-NMMA (135 +/- 20%) groups. Unexpectedly, NO blockade abolished insulin-induced SNA increases in the L-NMMA-insulin group (96 +/- 12%). In agreement with the SNA findings, Insulin rats had heart rate increases while no heart rate changes were observed in the L-NMMA-insulin, Control, or L-NMMA groups. In addition, there was an unexpected was a lack of MAP increase in L-NMMA-insulin rats. MAP also did not change in the Control, L-NMMA or Insulin groups.

CONCLUSIONS

These findings suggest that NO is necessary for insulin to exert its sympathoexcitatory effects, and that insulin-induced NO release may play a role in activating increases in lumbar SNA.

Human parathyroid cell proliferation in response to calcium, NPS R-467, calcitriol and phosphate

It remains uncertain how calcium, phosphate and calcitriol regulate parathyroid cell growth. The present study was aimed at examining possible direct effects of these modulators and of the calcimimetic NPS R-467 on parathyroid cell growth in vitro. Cell proliferation was determined by [3H]thymidine incorporation and cell cycle antigen Ki 67 expression in a parathyroid cell culture model derived from uraemic patients. The effect of NPS R-467 on parathyroid hormone (PTH) secretion and intracellular [Ca2+]i response was also examined. Increasing the [Ca2+] in the medium from 0.5 to 1.7 mM increased DNA synthesis (P < 0.005) and the number of Ki 67-positive cells (P < 0.005). However, NPS R-467 (0.01-1 microM) inhibited 3[H]thymidine incorporation by 35% in the presence of 0.5 mM [Ca2+]e. Exposure of cells to Ca2+ or NPS R-467 led to a rapid increase of intracellular Ca2+, although the pattern of increase differed. Addition of calcitriol (10-10-10-7 M) to the culture medium suppressed [3H]thymidine incorporation dose-dependently. Finally, high levels of phosphate (3.5 mM) in the medium led to a significant (P < 0.05) increase in [3H]thymidine incorporation. The observed stimulatory effect of Ca2+ in the medium in vitro appears to be at variance with the inhibitory effect of calcimimetic NPS R-467 in vitro. In an attempt to solve these apparent discrepancies, and based on the notion of a reduced calcium-sensing receptor (CaR) expression in parathyroid tissues of uraemic patients, we hypothesize that Ca2+ may regulate parathyroid cell proliferation via two different pathways, with predominant growth inhibition in cases of high CaR expression or activation, but prevailing stimulation of proliferation in cases of low CaR expression.

Dialysis-induced oxidative stress: biological aspects, clinical consequences, and therapy

Oxidative stress, which results from a rupture in the natural balance between pro- and antioxidant systems, is considered as a major factor in dialysis-associated morbidity and mortality. Emerging pharmacologic and dialytic antioxidant therapeutic and dialysis strategies should enable us to reduce the harmful consequences of oxidative stress in dialysis patients. Moreover, since there is increasing evidence of oxidative stress long before the initiation of maintenance dialysis, antioxidant therapeutic strategies should probably be developed very early in the course of renal failure.

[Refractory ascites in hemodialysis: treatment by paracentesis- reinjection during dialysis]

Two hemodialysis patients, one male and one female, aged 46 and 54 years, were treated with preceed respectively for refractory ascites secondary to hepatic cirrhosis and for large polycystic liver. Preceed was decided because of the rapid reappearance of effusion following repeated puncture and albumin infusion, the poor tolerance to ultrafiltration (UF) and the poor nutritional status of the patients, with severe hypoalbuminemia. Abdominal paracentesis was performed on initiation of the dialysis session. Reinjection of the ascites fluid was made into the arterial line, allowing its UF and control of its flow. The procedure was performed whenever necessary, i.e., when inter-dialysis weight gain and ascites volume were high. In both cases, improvement was quickly obtained, with less rapid and less severe reappearance of the effusion and correction of albuminemia. Dialysis sessions with UF were better tolerated. No notable side effect was observed. The first patient was treated for 2 months, when he died of an unrelated cause. The other patient was treated for 6 months and then could be transferred to a dialysis center near her home. Twenty five months after start of dialysis treatment, kidney and liver transplantation were performed in this same patient. After transplantation, reappearance of moderate ascites and oedema is attributed to e degradation of renal function, without liver dysfunction. Five weeks after transplantation, improvement of renal function and ascites regression were noted. Preceed is an effective method of treating refractory ascites in the hemodialysis patient. Compared to classical paracentesis, it has the advantage of good tolerance, patient comfort and moderate cost.

High serum apolipoprotein AIV levels in renal transplant recipients

BACKGROUND

Human apolipoprotein (apo) AIV might play a role in post-transplant reverse cholesterol transport, which appears to be comparable to that seen in healthy subjects. However, there may be subtle differences between healthy individuals and renal transplant recipients, given the other abnormalities of lipoprotein metabolism in the latter. Therefore, the aim of the present study was to investigate possible changes of serum apo AIV levels in renal transplant recipients, and to evaluate potential factors influencing these levels.

PATIENTS AND METHODS

Total and free serum apo AIV was determined in 36 clinically stable renal transplant recipients and in 20 sex- and age-matched healthy control subjects.

RESULTS

Mean total serum apo IV concentrations (+/- SD) were significantly higher in renal transplant recipients than in control subjects (202 +/- 102 vs 79 +/- 45 mg/l, p < 0.01). The percentage of lipoprotein-free fractions of apo AIV was comparable in both groups. The elevated total serum concentrations of apo AIV were mainly related to creatinine clearance and partially to serum triglyceride levels in renal transplant recipients.

CONCLUSION

Our data suggest that the observed elevation of serum apo AIV concentrations in renal transplant recipients is essentially related to the presence of impaired renal function.

[(99m)Tc]-sestamibi parathyroid scintigraphy in chronic haemodialysis patients: static and dynamic explorations

BACKGROUND

The place of parathyroid gland imaging by [(99m)Tc](technetium)-sestamibi scintigraphy in uraemic patients with secondary hyperparathyroidism remains a matter of debate. The purpose of the present study was (i) to assess its value with respect to plasma intact parathyroid hormone (iPTH) levels and to surgical parathyroidectomy (PTx), and (ii) to explore the possibility of suppressing parathyroid [(99m)Tc]-sestamibi uptake by calcitriol.

METHODS

In a first cross-sectional, static study 52 chronic haemodialysis (HD) patients with plasma iPTH levels between 14 and 2791 pg/ml (normal, 10-65 pg/ml) had a [(99m)Tc]-sestamibi scan, and 21 of them underwent surgical PTx. In a second longitudinal, dynamic study 14 chronic HD patients with advanced secondary hyperparathyroidism received short-term calcitriol treatment in an attempt to suppress [(99m)Tc]-sestamibi imaging of parathyroid glands. Calcitriol was given intravenously for 2 weeks, 2 microg after each haemodialysis session. Scintigraphy was carried out before and at the end of this inhibition test.

RESULTS

[(99m)Tc]-Sestamibi scan led to imaging of one or more (maximum three) parathyroid glands in most, but not all, HD patients with plasma iPTH values >600 pg/ml. Based on surgical findings, overall sensitivity of [(99m)Tc]-sestamibi scan in correctly locating parathyroid glands was only 50%, whereas specificity was 100%. In contrast, its sensitivity was 100% in locating single glands in the subgroup of five patients with recurrent hyperparathyroidism. The calcitriol inhibition test showed suppression of [(99m)Tc]-sestamibi uptake by at least one parathyroid gland in eight patients (57%), with complete suppression in five of them (36%). Basal plasma iPTH or decrease of plasma iPTH in response to calcitriol was not predictive of suppressible [(99m)Tc]-sestamibi uptake in the individual case, although mean iPTH was markedly higher in patients with non-suppressible parathyroid glands.

CONCLUSION

Because of its relatively low sensitivity the [(99m)Tc]-sestamibi scan is of limited help in the exploration of uraemic patients with severe secondary hyperparathyroidism before a first surgical PTx. However, it is very useful in locating the remaining parathyroid gland(s) in case of reoperation. The novel calcitriol inhibition test of [(99m)Tc]-sestamibi uptake could help to better distinguish parathyroid glands with non-suppressible, autonomous activity from glands whose activity might be amenable to long-term suppression.

[Factors determining the choice of a modality of treatment by dialysis: a study of nine dialysis centers]

BACKGROUND

The objective of this cross-sectional study in a population of 1472 dialysis patients was to identify the main factors involved in the choice of a specific option for dialysis therapy, taking into account three different types of criteria such as medical dependence (DM), nurse care requirement (SI) and independence for dialysis therapy (CA).

METHODS

Each patient has been analysed, independently of present treatment modality, according to the above three criteria, namely DM, SI and CA. For each type of parameter, patients have been allocated to one of three levels, each level being established to evaluate whether dialytic treatment should be undertaken as hospital centre dialysis (HDC) or in a facility off the hospital. Level 3 of any one category corresponded to the inability of doing haemodialysis at home (HHD) or in self-care unit (AD). Level 2 included patients who could be treated in AD or by peritoneal dialysis (PD) with the assistance of a nurse. CAPD or HHD were considered as potential treatment modalities only in patients qualifying for level 1 of each criterion.

RESULTS

In the patient population as a whole, the following treatment options were observed: HHD 3.6%, CAPD 6%, PD 1.8%, AD 16.3% and HDC 72.2%. For medical dependence (DM) there was a relatively even distribution for the three levels in six centres. In contrast, two centres were characterized by a predominance of DM level 3. Differences in DM levels between centres were greatly reduced when considering separately only those patients who were actually treated by CAPD, HDC and AD. SI levels were more uniformly distributed within all centres, and this was true for HCD and AD patients. When considering CA levels in HDC patients, a large predominance of CA level 3 was observed in all centres whereas CA level 1 was nearly in existent.

CONCLUSION

The major finding of this study was that the inability or the refusal of dialysis patients to participate at treatment, independently of medical condition and nurse care requirement, was the main factor in the choice of hospital centre dialysis.

Osteoporosis and salt intake

AIM

Recently, it has been hypothesized that salt intake may be related to the risk of osteoporosis. The aim of this review was to summarize the evidence for such relationship and to discuss possible mechanisms.

DATA SYNTHESIS

We performed a review of the scientific literature on osteoporosis, particularly its etiology, and then focussed on studies addressing the relation between salt intake on the one hand, and calcium balance, bone resorption, bone mineral density and fractures on the other. Although a relation between high salt intake and increased bone loss is biologically plausible, the most pertinent studies relating salt intake to bone mineral density are only suggestive of high salt consumption as a risk factor for osteoporosis. Unfortunately, studies on fracture risk and salt intake are lacking.

CONCLUSION

The relationship between salt intake and osteoporosis is still controversial. A possible relation between salt intake and fracture risk should be addressed in future studies.

Effective correction of hyperhomocysteinemia in hemodialysis patients by intravenous folinic acid and pyridoxine therapy

Effective correction of hyperhomocysteinemia in hemodialysis patients by intravenous folinic acid and pyridoxine therapy.

BACKGROUND

Folic acid supplementation is only partially efficacious in correcting moderate elevation of plasma total homocysteine (tHcy) concentrations observed in hemodialysis (HD) patients. Experimental and clinical data have suggested that this partial efficacy may be due to impairment of folic acid metabolism to 5-methyltetrahydrofolate (MTHF) and of MTHF transmembrane transport as well. To bypass these difficulties, we assessed the efficacy of intravenous (i.v.) folinic acid, a ready precursor of MTHF, on reducing plasma tHcy concentrations in HD patients.

METHODS

In a cohort of 37 patients on intermittent HD treatment, plasma tHcy concentrations were determined before and during i.v. supplementation of folinic acid (50 mg once per week), together with i.v. pyridoxine (250 mg 3 times per week), to prevent vitamin deficiency, particularly in those treated by recombinant erythropoietin.

RESULTS

Folinic acid and pyridoxine i.v. supplementation was given for 11.2 +/- 2.45 months (range 7.5 to 17 months). The mean plasma tHcy levels decreased significantly from 37. 3 +/- 5.8 microM at baseline to 12.3 +/- 5.4 microM on folinic acid treatment (P < 0.001). Moreover, 29 of the 37 patients (78%) had normal plasma tHcy levels at the end of follow-up (that is, <14.1 microM, mean 9.8 microM, range 6.2 to 13 microM). No adverse effects attributable to folinic acid treatment were observed during this time.

CONCLUSIONS

Intravenous folinic acid therapy (50 mg) once per week associated with pyridoxine supplementation appears to be an effective and safe strategy to normalize plasma tHcy levels in the majority of chronic HD patients.

Oxidized low-density lipoprotein induces macrophage respiratory burst via its protein moiety: A novel pathway in atherogenesis?

Oxidized low-density lipoproteins (oxLDL) play a crucial role in atherogenesis mainly via their capacity to bind and to activate macrophages. However, the role of the protein LDL moiety in this process is not yet established. In this study, human LDL were exposed to hypochlorous acid (HOCl), a selective protein oxidant, or copper sulfate (CuSO(4)), a major lipid oxidant, and tested for their capacity to activate the NADPH-oxidase of human THP-1- and U937-derived macrophages as measured by lucigenin chemiluminescence (CL). Compared to native LDL which had no effect, HOCl-oxLDL triggered potent CL responses in both U937 and THP-1 cells but only when these were fully differentiated into macrophages by phorbol myristate acetate. In contrast, Cu-oxLDL only triggered a moderate CL response of U937 cells and had little effect on THP-1 cells. While delipidation did not affect HOCl-oxLDL-induced CL response it abolished that induced by Cu-oxLDL. Interestingly, U937 cells showed higher CL responses to both types of oxLDL than THP-1 cells, a finding which could be related to their higher expression of the scavenger receptor CD36. Taken together these results strongly support the role of the protein moiety in oxLDL-induced macrophage activation.

Alpha-1-microglobulin: inhibitory effect on calcium oxalate crystallization in vitro and decreased urinary concentration in calcium oxalate stone formers

In the past few years, alpha-1-microglobulin (alpha1m) has been copurified from human urine with bikunin, a potent inhibitor of calcium oxalate (CaOx) crystallization in vitro. In this study, we have purified alpha1m without bikunin contamination and investigated its possible role in CaOx crystallization by in vitro and in vivo studies. Alpha-1m was purified with an anti-alpha1m antibodies CNBr-activated sepharose column. Two molecular species of alpha1m of respectively 30 and 60 kDa were purified. For each protein, two blots of 30 and 60 kDa cross-reacted with anti-alpha1m antibodies, suggesting that these two forms were derived one from the other. Both protein species inhibited CaOx crystallization in a dose-dependent manner in two in vitro tests. In the first test, the presence of alpha1m of 30 kDa (8 microg/ml) in a medium containing 0. 76 mM CaCl(2) (with (45)Ca) and 0.76 mM Ox(NH(4))(2) inhibited CaOx crystallization by 38% as estimated by supernatant radioactivity after 1 h of agitation. In the second test, CaOx kinetics were examined for 3 to 10 min in a turbidimetric model at 620 nm. The presence of alpha1m of 30 kDa in a medium containing 4 mM CaCl(2) and 0.5 mM Na(2)Ox inhibited CaOx crystallization by 41.5%, as estimated by the slope modification of turbidimetric curve. Alpha-1m can be considered as another inhibitor of urinary CaOx crystal formation, as shown by the present in vitro studies. Using an ELISA assay, we found that urinary alpha1m concentration was significantly lower in 31 CaOx stone formers than in 18 healthy subjects (2.95 +/- 0.29 vs 5.34 +/- 1.08 mg/l respectively, P = 0.01). The decreased concentration of alpha1m in CaOx stone formers could be responsible in these patients, at least in part, for an increased risk of CaOx crystalluria.

Inhibitory effect of bikunin on calcium oxalate crystallization in vitro and urinary bikunin decrease in renal stone formers

Two proteins of 17 and 24 kDa, respectively, which were immunologically related to bikunin, were purified from urine of healthy men, using in the last step a trypsin CNBr-sepharose affinity column. These proteins strongly inhibited calcium oxalate (CaOx) crystallization in two in vitro models. In the first model, the presence of 8 microg/ml protein in a medium containing 0.76 mM CaCl2 (with 45Ca) and 0.76 mM ammonium oxalate inhibited the crystallization process by 80%, as estimated by supernatant radioactivity after 60 min of incubation. A similar inhibition was observed in the second turbidimetric model, where the CaOx crystallization kinetics were followed for 10 min at 620 nm in a medium containing 4 mM CaCl2 and 0.5 mM Na2Ox. These proteins were used as standard protein for the development of an enzyme-linked immunosorbent assay (ELISA) in urine. Mean (+/-SEM) urinary bikunin concentration in 18 healthy subjects was 5.01 +/- 0.91 microg/ml. This was a concentration range of strong inhibitory activity in vitro. Bikunin values were nearly 50% lower (2.54 +/- 0.42 microg/ml, P=0.007) in 31 CaOx renal stone formers (having weddelite crystals in their first morning urine) than in the healthy volunteers. A correlation was found between urinary bikunin and alpha-1 microglobulin concentrations in the control group (y=0.73x + 1.09, r2=0.8) while no such correlation existed in the lithiasis group. In conclusion, bikunin exerts a strong inhibitory action of CaOx crystallization in vitro. Its involvement in urinary CaOx crystallization of stone formers is highly probable, based on the significant decrease in its urinary concentration in the majority of stone formers studied.

Role of transcellular pathway in ileal Ca2+ absorption: stimulation by low-Ca2+ diet

The present study was performed to determine the respective involvement of the cellular and paracellular routes in ileal Ca2+ transport. Two groups of rats were either fed a normal Ca2+ diet (1. 0%) or a Ca2+-deficient diet (0.02%) for 14 days. Ileal Ca2+ absorption was determined using both an in situ method of continuous luminal perfusion and an in vitro method (Ussing chamber model). The low-Ca2+ diet stimulated net Ca2+ flux in the ileum twofold, associated with a twofold increase of the mucosal-to-serosal Ca2+ flux in both models. This effect was observed in the absence of concomitant changes in Na+ or water flux in the in situ model or mannitol flux in the in vitro model, excluding the participation of the paracellular pathway in Ca2+ transport. Thus only cellular Ca2+ flux was stimulated. These data suggest that the ileum plays a major role in the adaptation to low dietary Ca2+. Whereas under physiological conditions with usual Ca2+ intakes the transcellular pathway of Ca2+ transport is negligible, it becomes of major importance in the case of Ca2+ deficiency, at least under the present conditions of severe Ca2+ deprivation.

Advanced oxidation protein products as novel mediators of inflammation and monocyte activation in chronic renal failure

We previously demonstrated the presence of advanced oxidation protein products (AOPP), a novel marker of oxidative stress in the plasma of uremic patients receiving maintenance dialysis. The present study in a cohort of 162 uremic patients showed that plasma concentrations of AOPP increased with progression of chronic renal failure and were closely related to advanced glycation end products (AGE)-pentosidine (r = 0.52, p < 0.001), taken as a marker of AGE. In vivo, the relevance of AOPP and AGE-pentosidine in monocyte-mediated inflammatory syndrome associated with uremia was evidenced by close correlations between AOPP or AGE-pentosidine and monocyte activation markers, including neopterin, IL-1R antagonist, TNF-alpha, and TNF soluble receptors (TNF-sR55 and TNF-sR75). To determine the mechanisms by which AOPP and AGE could be directly involved in monocyte activation, AOPP-human serum albumin (HSA) and AGE-HSA were produced in vitro by treating HSA with oxidants or glucose, respectively. Spectroscopic analysis confirmed that AOPP-HSA contains carbonyls and dityrosine. Both AOPP-HSA and AGE-HSA, but not purified dityrosine, were capable of triggering the oxidative burst of human monocytes in cultures. The AOPP-HSA-induced respiratory burst was dependent on the chlorinated nature of the oxidant and on the molar ratio HSA/HOCI. Collectively, these data first demonstrate that AOPP act as a mediator of oxidative stress and monocyte respiratory burst, which points to monocytes as both target and actor in the immune dysregulation associated with chronic uremia.

Carotid atherosclerosis in renal transplant recipients

BACKGROUND

Cardiovascular accidents are the major cause of morbidity and mortality in renal transplant recipients. However, there is little information concerning carotid atherosclerotic wall changes in renal transplant recipients, their relationship with cardiovascular accidents and their possible association with cardiovascular risk factors in such patients.

METHODS

Between April 1991 and December 1997, we prospectively assessed cardiovascular accidents in 79 renal transplant recipients who had received a transplant at our institution before January 1, 1986. Carotid morphology by B-mode ultrasonography, relevant clinical and laboratory cardiovascular risk factors, including lipid abnormalities and total homocyst(e)ine, were determined at the start of the follow-up period. Seventeen healthy subjects matched for age and sex with renal transplant recipients served as controls who volunteered for ultrasonographic examination of carotid arteries.

RESULTS

Nine patients experienced cardiovascular events during the period of follow-up. Compared with healthy, age- and sex-matched control subjects (n = 17), the frequency of carotid plaques was higher in renal transplant recipients with cardiovascular events (n = 9), but not in those without such events (n = 70). The frequency of cardiovascular accidents was related to the number of carotid plaques (4, 17 and 24% for no plaque, one plaque and > 1 plaque respectively, P < 0.04). However, by multivariate analysis, serum total cholesterol [odds ratio (OR) of 1.8 for each 1.0 mM, P < 0.07) and the presence of diabetes mellitus (OR of 28.4 for presence, P < 0.01) were the only predictors of cardiovascular events in such patients, whereas the presence of carotid plaques was not. Moreover, neither serum lipoprotein (a) nor total homocyst(e)ine concentrations could be identified as risk factors.

CONCLUSIONS

This prospective study shows that although a close association exists between asymptomatic carotid atherosclerosis and cardiovascular accidents in renal transplant recipients with long-term follow-up and relatively good renal function, other potentially modifiable risk factors appear to be better predictors of cardiovascular events. Consequently, the assessment of carotid atherosclerosis may not be clinically useful for the systematic identification of renal transplant recipients with an increased risk of developing cardiovascular events.

Persistence of Ca2+-sensing receptor expression in functionally active, long-term human parathyroid cell cultures

An original human parathyroid cell culture model from uremic patients with IIo hyperparathyroidism has been developed, with its main feature being long-term functionally active viability up to 5 months, as assessed by persistent responsiveness to changes of extracellular Ca2+ concentrations ([Ca2+]e). In addition to the inhibitory effect of increasing [Ca2+]e, increasing extracellular phosphate exerted a biphasic effect on parathyroid hormone (PTH) secretion. The presence of the Ca2+-sensing receptor (CaR), on which depends the response to [Ca2+]e and its persistence, has been demonstrated in our culture system both by direct detection and by inhibition of its activity. CaR protein was detected by Western blot analysis with a specific anti-CaR antibody. CaR gene transcripts have been identified by reverse transcription-polymerase chain reaction analysis. mRNA (by in situ hybridization) and protein (by immunocytochemistry) expression were detected for both CaR and PTH. Adding a specific anti-CaR antibody to the medium induced a marked reduction of low [Ca2+]e-stimulated PTH release, which decreased to levels equivalent to those obtained in high [Ca2+]e medium. The described long-term functionality could be due to several factors, including the clustered cell type of culture yielded by our preparation procedure, the growth characteristics of hyperplastic uremic tissue, and the use of a phosphate-rich medium. The present model, because of its long-term functionality, is a unique tool for the exploration of PTH synthesis and secretion and for studies of parathyroid cell growth in vitro.

Stimulation by citric acid of calcium and phosphorus bioavailability in rats fed a calcium-rich diet

The effect of dietary citric acid supplementation on calcium (Ca) and phosphorus (P) bioavailability was studied in rats fed 3 different diets containing 0.1, 0.5 or 1.0 g/100g Ca during 7 weeks. Citric acid supplementation increased intestinal Ca and P absorption and the Ca and P retention/intake ratio only in rats fed the 1% Ca diet. It also increased the P concentration of bone ashes in rats fed the 0.5% Ca diet (18.9 +/- 0.2 vs 17.5 +/- 0.5%) and the 1% Ca diet (20 +/- 0.1 vs. 19 +/- 0.3%), and the Ca bone ash concentration in rats fed the 1% Ca diet (36.7 +/- 0.4 vs. 35.7 +/- 0.5%). In rats fed the 1% Ca diet, plasma P concentration was decreased by citric acid supplementation (2.09 +/- 0.10 vs. 2.45 +/- 0.08 mmol/l) while urinary P excretion was increased (18.2 +/- 2.3 vs. 2.0 +/- 0.3 mmol/4 days), together with a decrease in plasma calcitriol concentration (54.4 +/- 2.6 vs. 79.6 +/- 2.5 ng/l), but no change of the circulating parathyroid hormone level. This study indicates that citric acid supplementation together with a Ca-rich diet allows to obtain an increased retention of Ca and P in bone. The prolonged administration of Ca citrate supplements may therefore help to increase bone mineral concentration.

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilage growth plate of uraemic rats

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilage growth plate of uraemic rats. Growth retardation, hypocalcaemia, hyperphosphataemia, and skeletal resistance to the action of PTH are well known features of advanced chronic renal failure (CRF). It has been suggested that the downregulation of renal and skeletal PTH receptors (PTH/PTHrP-R) could play an important role in the occurrence of these abnormalities. In the present study, four uraemic (4 weeks after 5/6 nephrectomy) and four control (sham-operated) rats were analysed for PTH/PTHrP-R mRNA expression at the proximal femoral and tibial growth plates by in situ hybridization. Uraemic rats had plasma biochemical abnormalities of advanced CRF including high creatinine, phosphate, and PTH, and low calcium and calcitriol levels. The femoral and tibial bones of uraemic animals were shorter in length than those of control rats, and had reduced width and cellularity of the epiphyseal cartilage growth plate. Mean (+/- SD) tibia growth plate width was 152 +/- 30 microns in uraemic rats, compared with 170 +/- 35 microns in control rats. The difference was mostly due to a marked reduction of the zone expressing PTH/PTHrP-R (mature chondrocytes) which was 30 +/- 5 microns in tibias from uraemic versus 44 +/- 10 microns in tibias from control rats. The hybridization signals of PTH/PTHrP-R per individual cell were quantified on dark field images using a computer-assisted image analysis system. The number of grains in PTH/PTHrP-R positive cells was also decreased in uraemic rats, 103 +/- 13 compared with 123 +/- 14 arbitrary units (dark pixel density)/cell in control rats (P < 0.005). In conclusion, these data indicate that rats with severe CRF and secondary hyperparathyroidism have reduced epiphyseal cartilage PTH/PTHrP-R mRNA expression. This alteration may be relevant in the pathogenesis of growth retardation in uraemia.

Mechanism of the enhancing effect of sorbitol on ileal Ca uptake in rat enterocytes

The effect of sorbitol on Ca uptake by isolated ileal epithelial cells was investigated. Intestinal cells were isolated from rat ileum by mechanical vibration. 45Ca uptake was approximately 2 times higher in cells exposed to 200 mM sorbitol of D-alanine than in control cells. This enhancing effect of sorbitol on percentage Ca uptake decreased with increasing Ca concentrations in the incubation medium suggesting an effect on Ca entry velocity. The addition of 10 microM nifedipine or 200 microM verapamil to the incubation medium was devoid of any effect on Ca uptake in ileal cells, whereas 100 microM trifluoperazine or chlorpromazine abolished the stimulatory effect of sorbitol. Finally, the effect of sorbitol on isolated cells was independent of a measurable change of cellular ATP content. In conclusion, the stimulatory effect of sorbitol on ileal Ca uptake is probably exerted through mechanisms other than an increase in intracellular ATP concentration. Sorbitol may enhance enterocyte Ca transport via a direct interaction with calmodulin and/or the Ca pump. It may also exert its effect through an inhibition of the basolateral Na Ca exchanger.

Dialysis-associated amyloidosis

Dialysis-related arthropathy represents a major complication of uremic patients treated by hemodialysis or other renal replacement therapies. Nearly 10 years ago, this syndrome was shown to be associated with a new type of amyloid, mainly composed of beta-2 microglobulin (beta 2-M). Retention of the beta 2-M protein due to chronic renal failure, although unquestionably a prerequisite for the occurrence of beta 2-M amyloidosis, appears not to be the unique pathogenetic factor involved in this complication. A role has also been attributed to an enhanced local or systemic generation of inflammatory mediators, an increased production of beta 2-M, and an altered metabolism of the molecule including partial proteolysis and glycation. It is possible that factors related to renal replacement therapy such as dialysis membrane biocompatibility also play a role. However, the clarification of the precise underlying mechanism(s) awaits further study. Because dialysis technology has progressed considerably during the last decade, a significant beta 2-M removal can be achieved at present using high-flux dialyzers. Moreover, a marked reduction in bioincompatibility during the dialysis procedure as manifested by activation of complement and stimulation of mononuclear blood cells can now be attained. Future studies will tell whether technical progress in dialysis technique results in a decrease in the incidence of symptomatic dialysis-associated amyloidosis.

[Mitogenic effect of erythropoietin on cultured aortic myocytes]

The administration of recombinant erythropoietin (rHuEpo) to anemic chronic renal failure patients may be associated with an increase in blood pressure, possibly by direct effects on peripheral blood vessels. In the present study, experiments were designed to explore the hypothesis that rHuEpo could enhance vascular resistance through mitogenic effect on vascular smooth muscle cells (VSMCs), and that preexisting hypertension might be a predisposing condition. Cultured VSMCs from the thoracic aortae of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats were studied for DNA synthesis, phospholipase C activity, and cell growth related proto-oncogene expression in the presence of rHuEpo. In cells from both strains, rHuEpo dose-dependently increased DNA synthesis and stimulated phospholipase C activity, as indicated by 3H-thymidine incorporation and 3H-inositol phosphate formation, respectively (EC50 approximately 4 U/ml). Exposure of VSMCs to rHuEpo for various times gradually increased the levels of c-myc and junB and transiently induced c-fos expression, as determined by Northern analysis. rHuEpo-induced DNA synthesis was markedly enhanced in VSMCs from SHR compared to those from WKY. In contrast, rHuEpo-induced phospholipase C activity and proto-oncogene expression did not differ between the two strains. Taken together, these results suggest that rHuEpo may function as a vascular smooth muscle cell growth promoting factor through activation of the phospholipase C cascade and modulation of proto-oncogene expression. It could thereby contribute to vascular hypertrophy and arterial hypertension.

The renal PTH/PTHrP receptor is down-regulated in rats with chronic renal failure

Hypocalcemia, hyperphosphatemia, and resistance to the action of PTH are well characterized features in the setting of advanced chronic renal failure (CRF). Although the underlying mechanisms are ill-understood, clinical and experimental evidence points to both PTH receptor down-regulation and post-receptor abnormalities in their pathogenesis. In the present study we have examined the effect of advanced CRF in rats on the renal expression of PTH/PTHrP receptor (PTH-R). CRF was created by a standard two-step operation (5/6 nephrectomy). Four weeks thereafter, 19 uremic rats were compared with 23 sham-operated rats. Uremic rats had higher mean (+/- SD) plasma creatinine levels than control rats, 164 +/- 107 microM versus 43 +/- 5 microM, respectively. They also had higher plasma phosphorus and iPTH levels, 4.70 +/- 1.71 mM versus 2.59 +/- 0.37 mM and 561 +/- 336 versus 27 +/- 18 pg/ml, respectively. Mean plasma total calcium and blood ionized calcium were significantly lower in uremic than in control rats, 2.13 +/- 0.06 mM versus 2.61 +/- 0.10 mM and 1.07 +/- 0.11 versus 1.31 +/- 0.06 mM, respectively. Mean plasma calcitriol concentration was also significantly lower in uremic than in control rats, 39.8 +/- 14.6 and 80.4 +/- 15.2 pg/ml, respectively. Nine out of the 19 rats were examined for renal PTH-R gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of various calcium intakes on calcium-oxalate crystalluria in rats on sodium-oxalate diet

Forty adult male Wistar rats were placed in metabolic cages on a Ca-deficient diet (0.1%) for 7 days and then on a Ca-deficient, Na-oxalate (NaOx) enriched diet (20 mg/100 g) for another 14 days. The animals were subdivided into three groups receiving three different types of mineral water: group I (n = 13), Badoit (Ca 222 mg/l); group II (n = 14), Contrexéville (Ca 467 mg/l); and group III (n = 13), Evian (Ca 78 mg/l). Another series of 25 rats (group I, n = 9; group II, n = 8; group III, n = 8) underwent the same study protocol, except that they received a normal Ca diet (1%). On the low-Ca diet, urinary Ca-Ox monohydrate (COM) crystals were observed only under the Na-Ox diet, with a mean crystal number significantly greater in group III (16.7 +/- 4.5 crystals/mm3) than in group I or II rats (2.5 +/- 1.5 or 4.1 +/- 1.5 crystals/mm3, respectively). Urinary Ca concentrations decreased in all groups (P < 0.001) under the Na-Ox diet, while urinary oxalate concentrations increased in all groups (P < 0.001). On the normal Ca diet, COM crystal excretion was observed only with the Na-Ox-enriched diet, but in this case feeding the Na-Ox diet did not modify urinary oxalate excretion. Ca/Ox ratio was significantly lower under 0.1% Ca diet than under normal Ca diet, related with the type and the number of crystals observed, demonstrating that assessment of crystalluria can provide an index of disease severity. Moreover, the hardness of the drinking water influences urinary COM crystal excretion only under a low-Ca, oxalate-rich diet, suggesting that the total calcium intake rather than the water calcium content is an important factor in the occurrence of Ca-Ox nephrolithiasis.