Accelerated atherosclerosis in ANCA-associated vasculitis

OBJECTIVES

Cardiovascular disease, including myocardial infarction and stroke, is a major cause of mortality in ANCA-associated vasculitis (AAV). Although AAV affects small vessels, an accelerated atherosclerosis not explained by traditional cardiovascular risk factors (CVRF) has been demonstrated. We aimed to investigate the association of atherosclerosis measured by carotid intima-media thickness (CIMT) and cerebral small vessel disease in AAV-patients.

MATERIALS & METHODS

Twenty-three AAV-patients in complete remission were recruited. Carotid ultrasonography (US), transcranial Doppler (TCD), brain magnetic resonance imaging (MRI), and SPECT after intravenous administration of tracer 99mTc-HMPAO (dose: 720MBq) were performed.

RESULTS

AAV-patients presented higher CIMT compared to normative population. Multivariate linear regression analysis demonstrated an association of higher CIMT with increased pulsatility index in middle cerebral artery (PI-MCA) (P=.011), higher lesion load on ARWMC scale (P=.011) and abnormal SPECT (P=.008). No association between higher CIMT and CVRF (diabetes or hypertension) was demonstrated. Increasing internal carotid artery pulsatility index (PI-ICA) was associated with decreasing mean flow velocity (MFV)-MCA (P=.038), increasing PI-MCA (P=.008) and increasing white matter lesions on MRI (P=.011).

CONCLUSIONS

Our study adds weight to the presence of increased atherosclerosis in AAV-patients. The association observed between CIMT and PI-ICA with small vessel cerebral disease, points the possible association of easy to use carotid US in predicting microvascular brain injury.

Lanthanum activates calcium-sensing receptor and enhances sensitivity to calcium

BACKGROUND

The aim of this study was to investigate whether nanomolar concentrations of lanthanum could influence the calcium-sensing receptor (CaSR) response.

METHODS

Embryonic kidney (HEK-293) cells transiently transfected with the human CaSR were used to test the ability of lanthanum to activate the CaSR, either alone or in combination with calcium. CaSR activation was measured by flow cytometry. Parathyroid glands from 4-month-old male Wistar rats with normal renal function (n = 60) were also cultured ex vivo with different concentrations of lanthanum to measure parathyroid hormone (PTH) secreted to the medium and PTH mRNA.

RESULTS

The maximal CaSR activation induced by 1 muM lanthanum chloride (LaCl(3)) was similar to that induced by 16 mM calcium chloride (CaCl(2) 16 mM: 294 +/- 14%; LaCl(3) 1 muM: 303 +/- 11%). Lanthanum half effective concentration (EC(50)) was 77.28 nM, lower than the 2.30 mM obtained for calcium, supporting the concept that this metal is a strong agonist of the CaSR. Moreover, lanthanum was also able to enhance CaSR sensitivity to calcium. The presence of 1 nM LaCl(3) significantly left-shifted the CaSR response curve, changing the EC(50) value for calcium from 2.30 mM (calcium alone) to 1.26 mM (calcium + 1 nM lanthanum). The parathyroid glands cultured with lanthanum showed a trend to secrete less PTH compared to the control glands: 1.51 +/- 0.23 (control), 0.91 +/- 0.17 (La 100 nM) and 1.04 +/- 0.18 (La 400 nM) [(pg/h)/(pg/h), mean +/- SEM] (ANOVA P = 0.0145). A similar trend was also observed in PTH synthesis measured by PTH mRNA levels.

CONCLUSIONS

These in vitro findings demonstrate that lanthanum, at nanomolar concentrations, is an agonist of the CaSR able to activate it in the absence of calcium. In addition, it can also enhance CaSR sensitivity to calcium, modulating PTH synthesis and secretion.

Residue 826 in the calcium-sensing receptor is implicated in the response to calcium and to R-568 calcimimetic compound

Within the extracellular loops of the seven-transmembrane domain of the calcium-sensing receptor (CaR) there is a region (I819-E837) relevant for calcimimetic activity. As the naturally occurring variant Ala826Thr is within this important region, it may be postulated that this change may influence the CaR response to calcium and R-568. Human embryonic kidney (HEK-293) cells transiently transfected with three different human CaRs (wild-type [A826], variant allele [T826], and artificial mutant [W826]) were used to test the ability of calcium alone or in combination with the calcimimetic R-568 to modulate CaR activity. CaR activation was detected by flow cytometry using a fluorescent probe. Intracellular calcium changes were measured in response to changes in extracellular calcium alone or with different R-568 concentrations. The change of the alanine in the 826 position (A826) for threonine (T826) worsened calcium sensitivity, increasing the EC(50) value from 2.34 +/- 0.48 mM (A826, wild-type) to 2.96 +/- 0.75 mM (T826) (P < 0.05). The T826 receptor reached a similar response with 1 muM R-568 compared with the wild-type receptor. On the contrary, the artificial introduction of a tryptophan in the same position (W826) did not affect calcium sensitivity (EC(50) = 2.64 +/- 0.81 mM) but reduced the ability of the receptor to respond to R-568. The results demonstrate the importance of the 826 residue in the CaR response to calcium and calcimimetics. Since the A826T change was described as a natural variant, the differences in the calcium and calcimimetic responses observed between the alleles could have potential clinical impact.

Viability and functionality of fresh and cryopreserved human hyperplastic parathyroid tissue tested in vitro

BACKGROUND/AIMS

This study aimed to test the viability and functionality of fresh and cryopreserved human hyperplastic parathyroid glands cultured in vitro.

METHODS

Small fragments of 18 parathyroid glands from 18 patients with secondary hyperparathyroidism were cultured in vitro, freshly or after cryopreservation, during 60 h. Cell viability and functionality of the parathyroid fragments exposed to calcium and calcitriol were studied.

RESULTS

Human parathyroid glands obtained from renal patients with secondary hyperparathyroidism maintained their viability and functionality for 60 h in culture. Sixty percent of the fresh but only 10% of the cryopreserved parathyroid glands showed the expected response with higher intact parathyroid hormone secretion when cultured with 0.6 mM calcium compared to 1.2 mM calcium. On the contrary, 44 of fresh and 40% of cryopreserved glands behaved in the same manner, showing a similar decrease in intact parathyroid hormone synthesis and secretion when cultured with calcitriol (10(-8)M).

CONCLUSION

These results demonstrate differences in the response to calcium between fresh and cryopreserved glands and no differences in the response to calcitriol. This in vitro culture method may be useful to discriminate between responsive and nonresponsive hyperplastic human parathyroid glands.

Aluminum posttranscriptional regulation of parathyroid hormone synthesis: A role for the calcium-sensing receptor

BACKGROUND

Calcium regulates parathyroid hormone (PTH) gene expression by a posttranscriptional mechanism, as well as parathyroid gland growth through the activation of the calcium-sensing receptor. Aluminum decreases both parathyroid cell proliferation and PTH levels by an unknown mechanism.

METHODS

To investigate the possible role of calcium-sensing receptor in the aluminum-induced PTH inhibition we used human embryonic kidney (HEK-293) cells transiently transfected with the human calcium-sensing receptor. We used a parathyroid gland tissue culture model to investigate whether the effect of aluminum in PTH mRNA was a transcriptional mechanism and also its possible role in calcium-sensing receptor expression.

RESULTS

We found that Al activated the calcium-sensing receptor with higher efficiency than calcium, its biologic ligand. Aluminum inhibited PTH gene expression by a posttranscriptional mechanism, but only when low calcium is present in the medium. Finally, we found that aluminum is also able to decrease calcium-sensing receptor mRNA levels by a posttranscriptional mechanism; however, no effect was observed on calcium-sensing receptor protein.

CONCLUSION

These findings indicate that aluminum impairs parathyroid function through a calcium-like mechanism due to the lack of specificity of the calcium-sensing receptor. Additionally, aluminum decreases parathyroid calcium-sensing receptor mRNA levels, and the regulatory mechanism was posttranscriptional. These findings demonstrate for the first time a regulatory effect in the calcium-sensing receptor by one of its ligands.

Effect of aluminium on calcium-sensing receptor expression, proliferation, and apoptosis of parathyroid glands from rats with chronic renal failure

BACKGROUND

To assess the effect of aluminium on the calcium-sensing receptor expression, proliferation, and apoptosis in parathyroid glands from rats with chronic renal failure, 2(1/2)-month-old male Wistar rats were 7/8 nephrectomized.

METHODS

Eight weeks after surgery the rats were divided into two groups, one receiving intraperitoneal AlCl3 for 8 weeks and the other receiving intraperitoneal placebo. Serum Al, Ca, P, creatinine, and PTH were measured. Parathyroid glands were removed, formaldehyde-fixed, and paraffin-embedded. Calcium-sensing receptor and proliferation were detected by immunohistochemistry and apoptosis by TUNEL and propidium iodide uptake.

RESULTS

At the end of the study, despite higher levels of serum P in the aluminium group (6.27 +/- 0.63 vs. 5.56 +/- 0.58 mg/dL; P = 0.045), serum PTH was lower (89.6 +/- 57.7 vs. 183.1 +/- 123.8 pg/mL; P = 0.059). No significant differences were found in the calcium-sensing receptor expression between groups (aluminium: 27.1 +/- 7.6; placebo: 25.4 +/- 3.5 RU). Rats receiving aluminium showed a significantly lower cell proliferation rate than the control rats (0.54 +/- 0.69 vs. 4.43 +/- 3.10 cells/mm2; P = 0.003). No apoptotic events were detected.

CONCLUSION

Aluminium was able to reduce the cell proliferation of the parathyroid glands. Due to the low apoptosis rate, however, it was not possible to find any change. Aluminium had no effect on the calcium-sensing receptor expression.