Coronary calcium quantification is an excellent method of assessing atherosclerotic plaque presence at individual artery sites. Moreover, the amount of calcium correlates with the overall magnitude of atherosclerotic plaque burden. This study suggests that the remodeling phenomenon is the likely explanation for the lack of a good predictive value between lumen narrowing and quantification of mural calcification.

IntroductionCoronary atherosclerosis is frequently associated with calcification of arterial plaque.

Atherosclerotic lesions are composed of cellular elements that have migrated from the vessel lumen and wall to form the cellular component of the developing plaque. The cellular elements are influenced by various growth-regulatory molecules, cytokines, chemoattractants, and vasoregulatory molecules that regulate the synthesis of the extracellular matrix composing the plaque. Because vascular smooth muscle cells (VSMC) constitute the major cellular elements of the atherosclerotic plaque and are thought to be responsible for the extracellular matrix that becomes calcified in mature plaques, immunostaining for collagenous and noncollagenous proteins typically associated with bone matrix was conducted on VSMC grown in vitro. VSMC obtained from human aorta were grown in chambers on glass slides and immunostained for procollagen type I, bone sialoprotein, osteonectin, osteocalcin, osteopontin, decorin, and biglycan. VSMC demonstrated an intense staining for procollagen type I, and a moderately intense staining for the noncollagenous proteins, bone sialoprotein and osteonectin, two proteins closely associated with bone mineralization. Minimal immunostaining was noted for osteocalcin, osteopontin, decorin, and biglycan. The presence in VSMC of collagenous and noncollagenous proteins associated with bone mineralization suggest that the smooth muscle cells in the developing atherosclerotic plaque play an important role in the deposition of the extracellular matrix involved in calcification of developing lesions.

Long bone calcification in chick embryos acutely- or chronically-treated with aluminum (Al) citrate was investigated. Acutely treated embryos received 100 microl of 60 mM Al citrate, 60 mM sodium (Na) citrate, or 0.7% sodium chloride on day 8 of incubation. Chronically treated embryos received a daily 25 microl dose of the above solutions beginning on day 8. Following 2-8 days of additional incubation, blood was collected, embryos killed, hind limbs radiographed, and tibias collected. Radiography indicated that Al administration resulted in a persistent angulation in the mid-diaphysis of tibias and femurs and a transient mineralization defect during the 10- to 12-day period of incubation. Tibias from 10- to 12-day embryos which were administered Al contained significantly less (P < 0.005) bone calcium (Ca) compared with tibias from NaCl-treated embryos. By day 14 there were no significant differences among the Ca content of tibias from embryos acutely treated with Al citrate, Na citrate or NaCl. Similarly, the rate of (45)Ca uptake by tibias of embryos treated with Al was significantly lower on days 10 (acute) and 12 (chronic) with no significant differences in Ca uptake rate among the three treatment groups by day 16. In each treatment group bone alkaline phosphatase (ALPase) activity increased approximately tenfold between days 10 and 16. At all stages, bone ALPase activity was consistently higher and significantly different (chronic) compared with levels in NaCl-treated embryos. In contrast, Al had no significant effect on the rate of tibia collagen and noncollagenous protein synthesis or serum levels of procollagen carboxy-terminal propeptide (PICP), osteocalcin, and parathyroid hormone (PTH).

Experimental evidence accumulated in recent years suggests that the osteoclast is derived from the fusion of mononuclear precursors which are of hematopoietic origin. Mononuclear cells were isolated from the spleen and bone marrow of young rats in order to examine osteoclast formation. The isolated cells were placed in diffusion chambers containing devitalized bone fragments freed of soft tissue, and the chambers sealed and placed in the peritoneal cavity of host rats. The host animals were killed after 4 days, and the bone removed from the chambers for examination. Light-microscopic examination demonstrated two types of cells adjacent to the bone surface, one a flattened and elongated mononuclear cell, and the other a larger and frequently multinucleated cell which had the morphological appearance of an osteoclast. Scanning electron microscopy demonstrated numerous flattened and elongated cells adjacent to the bone surface, as well as a second cell type which had dorsal membrane specializations and numerous lateral microprojections attaching to the bone surface. The second cell type was thought to correspond to the osteoclast-like cells seen with light microscopy. The observations suggest that osteoclast-like cells differentiate from mononuclear precursor cells of hematopoietic tissue.

The effects of aluminum exposure on bone formation employing the demineralized bone matrix (DBM) induced bone development model were studied using 4-week-old Sprague-Dawley rats injected with a saline (control) or an aluminum chloride (experimental) solution. After 2 weeks of aluminum treatment, 20-mg portions of rat DBM were implanted subcutaneously on each side in the thoracic region of the control and experimental rats. Animals were killed 7, 12, or 21 days after implantation of the DBM and the developing plaques removed. No morphological, histochemical, or biochemical differences were apparent between plaques from day 7 control and experimental rats. Plaques from day 12 control and experimental rats exhibited cartilage formation and alkaline phosphatase activity localized in osteochondrogenic cells, chondrocytes, osteoblasts, and extracellular matrix. Unlike the plaques from control rats that contained many osteoblastic mineralizing fronts, the plaques from the 12-day experimental group had a preponderance of cartilaginous tissue, no evidence of mineralization, increased levels of alkaline phosphatase activity, and a reduced calcium content. Plaques developing for 21 days in control animals demonstrated extensive new bone formation and bone marrow development, while those in the experimental rats demonstrated unmineralized osteoid-like matrix with poorly developed bone marrow. Alkaline phosphatase activity of the plaques continued to remain high on day 21 for the control and experimental groups. Calcium levels were significantly reduced in the experimental group. These biochemical changes correlated with histochemical reductions in bone calcification.(ABSTRACT TRUNCATED AT 250 WORDS)

Feeding rats a high-sucrose, fat-free diet after two days of starvation resulted in an initial accumulation of hepatic lipid and an increased activity of those enzymes which catalyze and support the formation of fatty acids from acetyl precursors. Rats starved for 48 hours were refed a highcarbohydrate, fat-free diet for 1, 2, 3, 5, 7 and 14 days. Frozen sections of liver were stained with Oil Red 0 for lipids. In adjacent sections glucose-6-phosphate dehydrogenase (GDH) and malate enzyme (ME) were localized and the relative enzyme activity evaluated. Enlargement and yellowing of the liver were noted after two to three days feeding of the fat-free diet, but subsequently the liver appeared normal. Oil Red 0 staining demonstrated a progressive accumulation of lipid from the periportal to the centrilobular area during the first three days of refeeding. After the seventh day on the fat-free diet, however, the lipid accumulation was less and the distribution appeared similar to that of animals maintained on a balanced diet. A marked increase in both GDH and ME activity was noted throughout the liver lobule after two days on the fat-free diet. Enzyme activity remained high throughout the lobule during the balance of the experimental period, with maximum activity in the centrilobular area.

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