The American Heart Association has said that 105 million U.S. citizens have cholesterol levels high enough to cause an elevated risk of cardiovascular disease. With Halloween now past, leaving in its wake massive piles of fatty sweets, and Thanksgiving approaching, followed shortly by the holiday season, that doesn't seem surprising.

The AHA recommends that people with elevated cholesterol first try to lower their levels through lifestyle changes. But there are those who can't or won't make sufficient changes, and they have made Lipitor (atorvastatin) and Zocor (simvastatin) the two top-selling drugs in the U.S., according to pharmaceutical market research done by IMS Health.

Both drugs, as well as Pravachol, No. 16 on the list, are statins; they interfere with cholesterol biosynthesis through inhibiting the enzyme HMG-CoA reductase. Of course, statins work better for some patients than others, and other methods of lowering cholesterol are being studied. Recently, two papers were published that report statin-independent approaches to treating the problem.

Taking RNAim At Apolipoprotein B

In the Nov. 11, 2004, issue of Nature, researchers from Alnylam Pharmaceuticals Inc., headquartered in Cambridge, Mass., report on lowering cholesterol via RNA-mediated silencing of the apoB gene. ApoB is a critical protein required for the formation of low-density lipoproteins (LDL), and blocking apoB interferes with the transport and metabolism of both dietary and endogenous "bad" LDL cholesterol.

Alnylam scientists first worked to "design and engineer drug-like properties" into short interfering RNAs, or siRNAs, to prevent their degradation in the blood and enable their efficient delivery, Hans-Peter Vornlocher said at a press conference. Vornlocher is vice president of research at Alnylam Europe AG and senior author of the Nature paper.

The scientists achieved their goal by conjugating the apoB-siRNA to, of all things, cholesterol. Vornlocher called cholesterol conjugation a "Trojan horse" that prevents degradation of a siRNA.

"You can take the same chemistry and use it with other siRNA molecules," he said.

The researchers identified mouse and human apoB siRNAs that were able to strongly reduce the levels of apoB mRNA and protein in cell culture. When mice were injected with the cholesterol-conjugated siRNAs, those siRNAs were detected in the liver and the jejunum (a part of the small intestine) after administration, and reduced both apoB mRNA and protein levels. A cholesterol test showed that the critters had 40 percent reduced LDL cholesterol, with levels of HDL cholesterol reduced to a lesser degree and VLDL cholesterol levels unaffected.

When mice transgenic for human apoB were tested, expression of both the mouse and the human gene were reduced - an important control, given that the siRNA ultimately will target the human gene.

Alnylam has not officially decided whether to advance apoB into the clinic, but Alnylam's CEO, John Maraganore, told BioWorld Today that "apoB is certainly of interest to us, but we want to further optimize the short interfering RNA technology before we launch a formal clinical program."

Eastern Herbal Remedy, Western-Style Inquiry

Berberine is at the opposite end of the clinical trials spectrum from apoB - it already is being used to treat bacterial diarrhea. The catch is that berberine originally was a folk medicine.

Nevertheless, rigorous scientific questions can - and should - be asked about molecules that are isolated from herbal remedies, as well as those that are cooked up by synthetic chemists. And in the article, "Berberine is a novel cholesterol-lowering drug working through a unique mechanism distinct from statins," the authors - from the Institute of Medicinal Biotechnology, part of the Chinese Academy of Medical Sciences; Peking Union Medical College, Beijing; Nanjing Medical University in China; the Veterans Affairs Health Care System in Palo Alto, Calif.; and Mount Sinai School of Medicine in New York City - do just that.

The scientists focused their attention on medicines that are in use in China and have clinical safety records, and that have active compounds with a known molecular structure. Of the molecules that fit the bill, the alkaloid berberine was found to be most potent at up-regulating LDL receptors in liver cell cultures. Co-treatment of cells with berberine and a statin had additive effects, suggesting the two compounds were active via different mechanisms.

The authors found that berberine acted by stabilizing LDL receptor mRNA, which lasted three times longer than its counterpart in untreated cells. The increased longevity was independent of intracellular cholesterol levels, which play a key role in statin's mechanism of lowering serum cholesterol. Instead, berberine appears to stimulate binding proteins to interact with and stabilize the messenger RNA. When the scientists fattened up hamsters, a well-characterized animal model for studying excess blood fat and LDL cholesterol, treatment with berberine reduced the levels of both.

In clinical research carried out in Nanjing, China, 91 patients received either berberine or placebo twice daily for three months. The treatment reduced serum cholesterol, triglycerides and LDL cholesterol, while having no effect on HDL cholesterol. The results were confirmed by analyzing a subgroup of patients that did not take other drugs, to check for possible effects of drug-drug interactions.

Details of the study design are not what one would expect to see in a U.S. clinical trial; of the 91 patients, 63, or roughly two-thirds, were assigned to the experimental group, and only a single dose - the dose used for diarrhea treatment, which is known to be safe - was evaluated.

Jian-Dong Jiang now is assistant professor of medicine at Mount Sinai School of Medicine and senior author of the study. He was a professor at the Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences, Beijing, when the discoveries reported in Nature Medicine were made. Jiang told BioWorld Today that "this was a clinical study, but not a formal clinical trial." The researchers are working on finding funding and industrial collaborators to conduct full clinical trials in both China and the U.S.

"We are not very familiar with the U.S. FDA, so an American collaborator would be necessary for us to conduct clinical trials in the U.S.," Jiang said. "But we hope that this could be a contribution to the whole world, not just China."