Statins, other cholesterol depletors, may disrupt hypertension development

Novel calcium block attacks cause, rather than symptoms, of idiopathic pulmonary hypertension (IPAH), also called primary pulmonary hypertension

Cholesterol-lowering agents, such as the widely-prescribed statin drugs, and cholesterol-blocking agents may prove to be “novel therapeutic agents to modify cellular calcium that contributes to the development of pulmonary hypertension,” according Hemal H. Patel who lead a multidisciplinary team of researchers at the University of California, San Diego (UCSD).

In studying idiopathic pulmonary hypertension (PPH), formerly called primary pulmonary hypertension, the UCSD team found “a previously unappreciated cellular and molecular mechanism for the disease process,” Patel said, “which may be amenable to treatment with current and future therapies and might provide more substantial, long-term and efficacious benefit to those that have IPAH.”

Patel is presenting the research at the 35th Congress of the International Union of Physiological Sciences in San Diego, March 31 – April 5, 2005.

*Paper presentation: “Cholesterol-depleting drugs, including statins, lower intracellular Ca2+ and inhibit proliferation in pulmonary artery smooth muscle cells in primary pulmonary hypertension,” 12:30 p.m.-3 p.m. Tuesday April 5, Physiology 933.6/board #A446. On view 7:30 a.m. – 4 p.m.

*Featured topic: Patel will participate in Session 898, “Overview: From organelles to organ,” a featured topic of the IUPS Calcium Signaling Track, Tuesday beginning at 10:30 a.m., Convention Center room 29C. Patel’s presentation is scheduled for noon.

All researchers involved in the study are from UCSD: Hemal H. Patel, Fiona Murray and Paul A. Insel, Department of Pharmacology; Shen Zhang and Jason X-J Yuan, Dept. of Medicine, and Patricia A. Thistlethwaite, Dept. of Surgery.

Research aimed at cellular calcium-dependent aspects of hypertension

IPAH is a severe clinical disease. The prognosis of PPH is poor with untreated disease leading to heart failure and death in two to eight years, Patel noted. Because of limited understanding of the cellular and molecular determinants of the disease process, current therapy is limited and aimed towards symptomatic relief.

He said two factors that contribute to the disease are dependent on cellular calcium: constriction of vessels, and uncontrolled cell growth resulting in thickening of vessels. “We sought to determine, 1.) if IPAH has altered caveolae, which in Latin means “little caves,” on the membrane composed of cholesterol that control the intake of calcium into cells, and 2.) if agents that modify cellular cholesterol might limit calcium intake and ultimately limit the two factors (constriction and growth) in vessels that contribute to the disease process. These drugs then might provide for a novel therapy that not merely provides temporary relief of disease symptoms, but helps alleviate the underlying cause of IPAH,” Patel explained.

Lovostatin, MBCD significantly reduce calcium entry, cut cell proliferation

In their research, the team saw that “smooth muscle cells isolated from pulmonary arteries of patients with IPAH indeed had more caveolae on the cell membrane compared to cells from normal individuals, and also that there was a higher calcium intake into the diseased cells,” Patel reported. Subsequent treatment of the IPAH cells with an agent that depletes cholesterol (methyl-beta-cyclodextrin, or MBCD), or “a statin (in this case, lovostatin, sold as Mevacor by Merck), which blocks cholesterol synthesis, resulted in a disruption of the caveolae and reduced the amount of calcium that entered the cells.

“Additionally, these two treatments also decreased the growth rate of the diseased cells,” Patel said. Taken together, the results “mean that the micro-structure of the cell membrane is involved in controlling the intake of calcium and that the cholesterol modifiers of these structures may serve as novel therapeutics to reduce vessel constriction and cell growth associated with increased calcium intake in IPAH,” Patel stated.

Next steps: Determine caveolae proteins and how they influence calcium intake

The next steps, Patel explained, are to understand the nature of the proteins located on the caveolae and how these structures communicate with the internal regions of cells to influence calcium intake into the cell. He said the UCSD researchers “already have begun looking at the expression and localization of ion channels into caveolae that may further explain the increased calcium intake into cell.”