Ritva Ylitalo

Bisphosphonates and atherosclerosis.

Bisphosphonates are used for the treatment of bone resorption, hypercalcemia, osteoporosis and Pagets disease. Etidronate, pamidronate and clodronate also inhibit the development of experimental atherosclerosis without altering serum lipid profile. Bisphosphonates inhibit the arterial calcification, lipid accumulation and fibrosis. They accumulate extensively in arterial walls and suppress macrophages in atheromatous lesions. In macrophage cultures, bisphosphonates inhibit the cellular accumulation and degradation of atherogenic LDL-cholesterol and foam cell formation. Further, they inhibit various enzymes involved in cell signal transduction and cholesterol biosynthesis. Recently, etidronate has been shown to inhibit the thickening of carotid arterial wall even in man.

Accumulation of bisphosphonates in the aorta and some other tissues of healthy and atherosclerotic rabbits

Clodronate, etidronate, and pamidronate are highly hydrophilic bisphosphonates used for the treatment of bone resorption and hypercalcemia. They also inhibit the development of experimental atherosclerosis without influencing serum cholesterol level. We studied the distribution and the accumulation of the carbon 14-labeled bisphosphonates in the aorta and some other tissues of healthy rabbits and in rabbits with diet-induced atherosclerosis. After intravenous injection, clodronate and pamidronate disappeared from circulation more slowly in atherosclerotic than in healthy rabbits, and the drug concentrations in the peripheral tissues were generally lower in atherosclerotic than in healthy animals. At 24 hours after dosing in healthy rabbits, the mean aorta to plasma ratios of clodronate, etidronate, and pamidronate were, respectively, 2.4 to 2.8, 2.4 to 4.0, and 8.6 to 10. The corresponding ratios in atherosclerotic rabbits were, respectively, 13 to 22, 1.5 to 2.2, and 13 to 24. Seven days after the injection the mean clodronate concentration in the aortas of healthy rabbits was 0.5% to 0.9% of the dose given per tissue weight, and the concentration in those of atherosclerotic animals was 3.8% to 5.2% of the dose given per tissue weight. The results indicate that hydrophilic bisphosphonates, known to inhibit the atherogenesis, concentrate markedly in the aortas of healthy and atherosclerotic rabbits.

Effects of liposome-encapsulated bisphosphonates on acetylated LDL metabolism, lipid accumulation and viability of phagocyting cells.

Bisphosphonates, the drugs used for the treatment of e.g. osteoporosis, inhibit the development of experimental atherosclerosis. When encapsulated in liposomes, they also inactivate macrophages, which have a key role in atherogenesis. We studied the effects of three clinically used bisphosphonates, i.e. clodronate, etidronate and pamidronate, on 1) the viability of mouse peritoneal macrophages and macrophage-like RAW 264 cells, 2) the degradation of 125I-labeled acetylated LDL by RAW 264 cells, and 3) the formation of LDL-derived foam cells in vitro. Liposome-encapsulated clodronate and pamidronate, but not etidronate, decreased the fraction of viable peritoneal macrophages in a concentration-dependent manner, whereas RAW 264 cells were much more resistant to the cytotoxic effects of bisphosphonates. Preincubation with liposomal clodronate and etidronate inhibited in a concentration-dependent manner the degradation of acetylated LDL in RAW 264 cells, but non-cytotoxic concentrations of liposomal pamidronate had only a weak inhibitory effect. The inhibition was more pronounced by liposomal clodronate than by liposomal etidronate. At high concentrations (500 microg protein/ml) of acetylated and aggregated LDL, RAW 264 cells transformed to foam cells. Preincubation with liposomal clodronate and etidronate reduced the cellular accumulation of acetylated LDL-derived lipids, but the drugs had no effect on the lipid accumulation caused by aggregated LDL. The results suggest that liposomal clodronate and etidronate inhibit the activity of phagocyting cells in internalizing and degrading atherogenic modified LDL.

Influences of nonselective, β1-selective and vasodilatory β1-selective β-blockers on arterial pulse wave velocity in normotensive subjects

β-Adrenoceptor blockers with disparate properties may have differential influences on arterial pulse wave velocity (PWV). Therefore, influences of single medium doses of bisoprolol, propranolol and celiprolol on PWV were compared in healthy subjects. Arterial PWV was obtained from the time delay between flow pulses measured from the root of the aorta and the popliteal artery. Bisoprolol and propranolol decreased arterial PWV more than placebo (P≤.002) and celiprolol (P<.0001). In conclusion, the acute effects of bisoprolol and propranolol on arterial PWV in normotensive subjects seem to differ from that of celiprolol.

Metabolism of modified LDL and foam cell formation in murine macrophage-like RAW 264 cells.

The uptake of modified low density lipoprotein (LDL) by arterial macrophages is a key event in the atherogenesis. We studied 1) the uptake and degradation of modified LDL, 2) LDL recognition by specific receptors, and 3) the foam cell formation with murine macrophage-like RAW 264 cells in vitro. The cells took up and degraded effectively 125I-labeled acetylated LDL (Ac-LDL) and aggregated LDL (Aggr-LDL). Also oxidized LDL (Ox-LDL) was taken up but it was degraded poorly. The degradation of 125I-Ac-LDL was efficiently competed by both unlabeled Ac-LDL and Ox-LDL, whereas the degradation of 125I-Ox-LDL was partially competed by unlabeled Ox-LDL and Aggr-LDL but not at all by unlabeled Ac-LDL. The incubation with increasing concentrations of Ac-LDL, Aggr-LDL or Ox-LDL resulted in marked foam cell formation in the RAW 264 cells. Ox-LDL was cytotoxic at 500 to 1000 microg/ml concentrations. The results show that RAW 264 cells have at least two classes of receptors for modified lipoproteins: one that recognizes both Ox-LDL and Ac-LDL, and is similar to the scavenger receptors, and another that recognizes Ox-LDL but not Ac-LDL. RAW 264 cells are a convenient model cell line for examining the metabolism of modified lipoproteins, not only that of Ac-LDL but also that of Ox-LDL and Aggr-LDL, and cellular accumulation of lipids derived from modified LDL.