Vascular enzyme activity changes accompanying the induction of experimental atherosclerosis. 2. Rats fed excess vitamin D

Vitamin D in inflammatory diseases

Changes in vitamin D serum levels have been associated with inflammatory diseases, such as inflammatory bowel disease (IBD), rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis (MS), atherosclerosis, or asthma. Genome- and transcriptome-wide studies indicate that vitamin D signaling modulates many inflammatory responses on several levels. This includes (i) the regulation of the expression of genes which generate pro-inflammatory mediators, such as cyclooxygenases or 5-lipoxygenase, (ii) the interference with transcription factors, such as NF-κB, which regulate the expression of inflammatory genes and (iii) the activation of signaling cascades, such as MAP kinases which mediate inflammatory responses. Vitamin D targets various tissues and cell types, a number of which belong to the immune system, such as monocytes/macrophages, dendritic cells (DCs) as well as B- and T cells, leading to individual responses of each cell type. One hallmark of these specific vitamin D effects is the cell-type specific regulation of genes involved in the regulation of inflammatory processes and the interplay between vitamin D signaling and other signaling cascades involved in inflammation. An important task in the near future will be the elucidation of the regulatory mechanisms that are involved in the regulation of inflammatory responses by vitamin D on the molecular level by the use of techniques such as chromatin immunoprecipitation (ChIP), ChIP-seq, and FAIRE-seq.

Vitamin D and the vasculature: can we teach an old drug new tricks?

BACKGROUND

Vitamin D is a steroid hormone known for its role in regulating levels of calcium and phosphorus. Vitamin D has important autocrine/paracrine roles and it is involved in vascular biology. Clinical studies have shown a relationship between vitamin D levels and cardiovascular health, and low levels of vitamin D metabolites have been associated with higher incidence of congestive heart failure and increases in mortality.

OBJECTIVE

To summarise the effect of vitamin D on cardiovascular pathology, the leading cause of death in chronic kidney disease patients.

CONCLUSIONS

All results indicate a potential effect of vitamin D on cardiovascular health. Therefore, maintaining optimum levels of circulating vitamin D is critical for a healthy cardiovascular system. In patients with low vitamin D status, like renal patients, supplementation with vitamin D metabolites has shown beneficial cardiovascular effects.

Tissue calcification and alkaline phosphatase activity in uraemic rats

The activity and localization of alkaline phosphatase activity (AP) in aorta and heart, and the incidence of calcifications in aorta, heart and kidney as well as cardial fibrosis were studied in uraemic rats treated with 1,25-dihydroxycholecalciferol (1,25-DCHH) and Nifedipine. 1,25-DHCC treatment elevated the serum Ca x P product and aggravated the development of renal and aortic calcifications and cardial fibrosis. Nifedipine did not protect against calcifications, but decreased the incidence of cardial fibrosis. The activity of AP was increased in the thoracic aorta in uraemia independent of 1,25-DHCC or Nifedipine treatment or presence of calcification. No changes of the AP activity were found in the heart.

The aortic content of glycosaminoglycans, hydroxyproline and calcium in experimental uraemia with special reference to parathyroidectomy and vitamin-D treatment

The contents of the various glycosaminoglycan (GAG) fractions, hydroxyproline and calcium in the thoracic aorta from the rat were studied. The effect on these contents of induced uraemia (3/4 kidney resection) combined with parathyroidectomy and/or 1-alpha-hydroxycholecalciferol (1-alpha-OH-D3) treatment was evaluated. Confirming earlier results increased levels of GAGs (predominately of chondroitin and dermatan sulphate) were found in the aortae of uraemic rats. The present study showed that parathyroidectomy or treatment with 1-alpha-OH-D3 did not significantly further alter the aortic content of GAGs in uraemic rats. Arteriosclerotic changes (calcifying medial necrosis) were only found in non-parathyroidectomized uraemic rats given 1-alpha-OH-D3. The aorta from these rats had a lower total content of GAGs, mainly due to a decrease in hyaluronic acid, than that from uraemic rats without calcifications. The aortic content of calcium was lowest in uraemic parathyroidectomized rats. Treatment with 1-alpha-OH-D3 increased this content, which was augmented 100-200-fold when calcifications were present. No correlation between the aortic contents of calcium and GAGs was found. There was a statistically significant correlation between the aortic content of calcium and the serum calcium X phosphate product. A significantly lower content of hydroxyproline was found in uraemic non-parathyroidectomized rats given 1-alpha-OH-D3, especially in those with arteriosclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of acid and alkaline phosphatase activities in the blood vessels of normotensive and hypertensive rats

Samples of aortae and caudal arteries from normotensive and hypertensive rats were studied for cytochemical and biochemical determinations of acid and alkaline phosphatase activities. Cytochemical examination revealed an increased amount of acid phosphatase reaction product in hypertensive samples, with extensive localization to the extracellular matrix. Alkaline phosphatase activity was localized to the plasma membrane of fibroblasts and vascular smooth muscle cells and to the extracellular matrix. Biochemical assays of enzyme activities supported the cytochemical findings, showing increased activity in aortae from hypertensive rats.

Aortic medial calcification in progeria-like syndrome

Aortic medial calcification was investigated in rats in which the progeria-like syndrome (PLS) was evoked by administering dihydrotachysterol. In 35 experimental rats and 15 controls, calcification was studied morphologically by light and electron microscopy, and by enzyme histochemistry. Body weight, food intake and serum calcium levels were also determined. Calcification occurred along and on the elastic lamellae in association with the accumulation of ground substance. In the smooth-muscle cells surrounding the calcified foci, the activities of various lysosomal enzymes increased concomitantly with a tendency toward transformation of smooth-muscle cells to a modified form. From these observations, the role of ground-substance formation by smooth-muscle cells is postulated, and participation in the catabolism of ground substance by the lysosomal enzymes of these cells is suggested. It appears the increased activity of adenosine monophosphatase should be linked to the calcification. The etiology of weight loss, skin manifestations and aortic calcification in PLS rats seems to be different from that in human progeric diseases. Therefore, the PLS rat should not be readily accepted as an animal model for the study of progeric diseases.