Atorvastatin inhibits calcification and enhances nitric oxide synthase production in the hypercholesterolaemic aortic valve

OBJECTIVE

To study in a rabbit model the expression of endothelial nitric oxide synthase (eNOS) in association with the development of calcification of the aortic valve, and to assess the effects of atorvastatin on eNOS expression, nitrite concentration, and aortic valve calcification.

METHODS

Rabbits (n = 48) were treated for three months: 16, forming a control group, were fed a normal diet; 16 were fed a 0.5% (wt/wt) high cholesterol diet; and 16 were fed a 0.5% (wt/wt) cholesterol diet plus atorvastatin (2.5 mg/kg/day). The aortic valves were examined with eNOS immunostains and western blotting. Cholesterol and high sensitivity C reactive protein (hsCRP) concentrations were determined by standard assays. Serum nitrite concentrations were measured with a nitric oxide analyser. eNOS was localised by electron microscopy and immunogold labelling. Calcification in the aortic valve was evaluated by micro-computed tomography (CT).

RESULTS

Cholesterol, hsCRP, and aortic valve calcification were increased in the cholesterol fed compared with control animals. Atorvastatin inhibited calcification in the aortic valve as assessed by micro-CT. eNOS protein concentrations were unchanged in the control and cholesterol groups but increased in the atorvastatin treated group. Serum nitrite concentrations were decreased in the hypercholesterolaemic animals and increased in the group treated with atorvastatin.

CONCLUSION

These data provide evidence that chronic experimental hypercholesterolaemia produces bone mineralisation in the aortic valve, which is inhibited by atorvastatin.

Human aortic valve calcification is associated with an osteoblast phenotype

BACKGROUND

Calcific aortic stenosis is the third most common cardiovascular disease in the United States. We hypothesized that the mechanism for aortic valve calcification is similar to skeletal bone formation and that this process is mediated by an osteoblast-like phenotype.

METHODS AND RESULTS

To test this hypothesis, we examined calcified human aortic valves replaced at surgery (n=22) and normal human valves (n=20) removed at time of cardiac transplantation. Contact microradiography and micro-computerized tomography were used to assess the 2-dimensional and 3-dimensional extent of mineralization. Mineralization borders were identified with von Kossa and Goldner's stains. Electron microscopy and energy-dispersive spectroscopy were performed for identification of bone ultrastructure and CaPO4 composition. To analyze for the osteoblast and bone markers, reverse transcriptase-polymerase chain reaction was performed on calcified versus normal human valves for osteopontin, bone sialoprotein, osteocalcin, alkaline phosphatase, and the osteoblast-specific transcription factor Cbfa1. Microradiography and micro-computerized tomography confirmed the presence of calcification in the valve. Special stains for hydroxyapatite and CaPO4 were positive in calcification margins. Electron microscopy identified mineralization, whereas energy-dispersive spectroscopy confirmed the presence of elemental CaPO4. Reverse transcriptase-polymerase chain reaction revealed increased mRNA levels of osteopontin, bone sialoprotein, osteocalcin, and Cbfa1 in the calcified valves. There was no change in alkaline phosphatase mRNA level but an increase in the protein expression in the diseased valves.

CONCLUSIONS

These findings support the concept that aortic valve calcification is not a random degenerative process but an active regulated process associated with an osteoblast-like phenotype.

Centrin-2 is required for centriole duplication in mammalian cells

BACKGROUND

Centrosomes are the favored microtubule-organizing framework of eukaryotic cells. Centrosomes contain a pair of centrioles that normally duplicate once during the cell cycle to give rise to two mitotic spindle poles, each containing one old and one new centriole. However, aside from their role as an anchor point for pericentriolar material and as basal bodies of flagella and cilia, the functional attributes of centrioles remain enigmatic.

RESULTS

Here, using RNA interference, we demonstrate that "knockdown" of centrin-2, a protein of centrioles, results in failure of centriole duplication during the cell cycle in HeLa cells. Following inhibition of centrin-2 synthesis, the preexisting pair of centrioles separate, and functional bipolar spindles form with only one centriole at each spindle pole. Centriole dilution results from the ensuing cell division, and daughter cells are "born" with only a single centriole. Remarkably, these unicentriolar daughter cells may complete a second and even third bipolar mitosis in which spindle microtubules converge onto unusually broad spindle poles and in which cell division results in daughter cells containing either one or no centrioles at all. Cells thus denuded of the mature or both centrioles fail to undergo cytokinesis in subsequent cell cycles, give rise to multinucleate products, and finally die.

CONCLUSIONS

These results demonstrate a requirement for centrin in centriole duplication and demonstrate that centrioles play a role in organizing spindle pole morphology and in the completion of cytokinesis.

Atorvastatin inhibits hypercholesterolemia-induced cellular proliferation and bone matrix production in the rabbit aortic valve

BACKGROUND

Despite the common occurrence of aortic stenosis, the cellular causes of the disorder are unknown, in part because of the absence of experimental models. We hypothesized that atherosclerosis and early bone matrix expression in the aortic valve occurs secondary to experimental hypercholesterolemia and that treatment with atorvastatin modifies this transformation.

METHODS AND RESULTS

To test this hypothesis, we developed an experimental hypercholesterolemic rabbit model. New Zealand White rabbits (n=48) were studied: group 1 (n=16), normal diet; group 2 (n=16), 1% (wt/wt) cholesterol diet; and group 3 (n=16), 1% (wt/wt) cholesterol diet plus atorvastatin (3 mg/kg per day). The aortic valves were examined with hematoxylin and eosin stain, Masson trichrome, macrophage (RAM 11), proliferation cell nuclear antigen (PCNA), and osteopontin immunostains. Cholesterol and highly sensitive C-reactive protein (hsCRP) serum levels were obtained by standard assays. Computerized morphometry and digital image analysis were performed for quantifying PCNA (% area). Electron microscopy and immunogold labeling were performed for osteopontin. Semiquantitative RT-PCR was performed for the osteoblast bone markers [alkaline phosphatase, osteopontin, and osteoblast lineage-specific transcription factor (Cbfa-1)]. There was an increase in cholesterol, hsCRP, PCNA, RAM 11, and osteopontin and osteoblast gene markers (alkaline phosphatase, osteopontin, and Cbfa-1) in the cholesterol-fed rabbits compared with control rabbits. All markers except hsCRP were reduced by atorvastatin.

CONCLUSIONS

These findings of increased macrophages, PCNA levels, and bone matrix proteins in the aortic valve during experimental hypercholesterolemia provide evidence of a proliferative atherosclerosis-like process in the aortic valve associated with the transformation to an osteoblast-like phenotype that is inhibited by atorvastatin.

Experimental hypercholesterolemia induces apoptosis in the aortic valve

BACKGROUND AND AIM OF THE STUDY

Aortic valve disease is presently the number one indication for valve replacement in the United States, yet its molecular mechanisms remain unknown. As apoptosis (programmed cell death) occurs in degenerative disease states, it was postulated that experimental hypercholesterolemia is associated with apoptosis in rabbit aortic valves.

METHODS

New Zealand White rabbits (n = 8) were fed a 1% cholesterol diet for 12 weeks; control rabbits (n = 8) were fed a normal diet. After sacrifice of the animals, the aortic valves were dissected. Apoptosis was identified in the valvular lesion by TdT-mediated dUTP-biotin nick end-labeling (TUNEL) technique, and confirmed with transmission electron microscopy. The number of apoptotic cells was measured by computed morphometry.

RESULTS

Valves from hypercholesterolemic rabbits showed an increase in apoptosis. TUNEL staining was identified in the atherosclerotic layer of hypercholesterolemic valves (0.1% of cells), but not in the cells of controls (p <0.0001).

CONCLUSION

Apoptosis is increased in rabbit aortic valves during experimental hypercholesterolemia. If fatal cellular degeneration occurs in hypercholesterolemic valve disease, these data suggest that apoptosis may play a role in the mechanism of valvular disease.

Regulation and processing of a precursor form of eosinophil granule major basic protein (ProMBP) in differentiating eosinophils

The cDNA for eosinophil granule major basic protein (MBP) encodes a prepromolecule with a total length of 222 amino acids (preproMBP). PreproMBP includes a secretory leader of 15 amino acids, an acidic propiece of 90 amino acids, and a basic MBP portion of 117 amino acids. The function of the propiece, which has a predicted pI of 3.9, is unknown, but it gives proMBP an overall acidic charge. Because proMBP is not found in mature eosinophils, we analyzed eosinophil differentiation in interleukin-5 (IL-5)-stimulated umbilical cord stem cells cultured for 24 days. By immunofluorescence, proMBP appeared by day 6 and peaked on day 18, whereas MBP was prominent at days 12 to 24. By day 6, Western blots detected heterogeneous glycosylated 33-kD proMBP; its peak expression occurred on day 12. Western blots showed sequential processing of 33-kD proMBP to an 18-kD intermediate form and finally to 14-kD MBP. By dual label immunoelectron microscopy, proMBP was localized primarily to large uncondensed eosinophil granules, whereas MBP was localized to granules containing a condensed central area. Thus, proMBP is likely expressed and processed as the granule condenses in a multistep process to 14-kD MBP in differentiating eosinophils.