Featured Research

from universities, journals, and other organizations

Sex Differences In Heart Disease May Be Due To Enzyme That Breaks Down Fat

Date:
March 25, 1998
Source:
American Heart Association
Summary:
Sex-related differences in an enzyme that breaks down blood fats -- particularly "bad cholesterol" known as LDL -- may explain why men develop heart disease earlier than women, say scientists at the American Heart Association's epidemiology and prevention conference.

SANTA FE, N.M., March 20 -- Sex-related differences in an enzyme that breaks down blood fats -- particularly "bad cholesterol" known as LDL -- may explain why men develop heart disease earlier than women, said scientists March 20 at the American Heart Association's epidemiology and prevention conference.

"There are gender differences in the risk of coronary artery disease, the cause of heart attack. Pre-menopausal women have lower cholesterol levels and higher HDL levels (the good cholesterol) and lower heart disease rates than men," says the study's lead author, John E. Hokanson, Ph.D.

"We have observed in the past that there are higher levels of the enzyme hepatic lipase in men than in women. We asked the question, does hepatic lipase account for these lipid differences in men and women, and, if so, to what extent?" adds Hokanson, research scientist in the department of medicine at the University of Washington, Seattle.

Hokanson's research -- the first to focus on hepatic lipase and gender in heart disease -- could point to a new mechanism for increased risk for heart disease that characterizes men, when compared to women, before age 55. The research could suggest new ways to intervene to reduce that risk, he says.

In the study, scientists tested 25 men, 21 to 59 years old, and 39 pre-menopausal women, 21 to 51 years old. Both groups had normal cholesterol levels. Hepatic lipase activity was 53.4 percent higher in men than in women.

"The differences in the type of cholesterol we see in men and women appear to be related to hepatic lipase, and differences in this enzyme's activity may account for much of the difference in heart disease risk between men and pre-menopausal women," Hokanson says.

Researchers have in recent years been studying what they call the atherogenic phenotype, also called LDL subclass pattern B, which is characterized by predominantly small, dense LDL, low levels of the protective HDL cholesterol component and high triglycerides. The researchers found that men had significantly lower amounts of HDL, higher triglyercides and more small, compact LDL.

"One of the regulators of hepatic lipase appears to be estrogen," he says. "A crucial question would be to look at post-menopausal women, because women's heart disease risk increases after menopause, and some women have changes in their lipoproteins like those associated with higher hepatic lipase. It would be very interesting to know whether hepatic lipase is involved in the difference in coronary disease risk between pre-menopausal and post-menopausal women. We are, in fact, looking into issues related to that question.

"Another very interesting question is how estrogen replacement therapy might affect HDL and small dense LDL in post-menopausal women," he adds. Evidence is mounting that small, dense LDL particles are the "baddest of the bad" because they are most likely to clog the arteries, Hokanson says. Having a predominance of small, compact LDL particles causes about a three-fold increase in a person's risk of heart disease compared to people whose LDL particles tend to be the larger kind.

"The density of LDL is crucial," he says. "Small, dense LDL is more atherogenic (likely to clog blood vessels), but the mechanism is unclear." Cholesterol and other fats cannot dissolve in the blood and must be transported by special carriers made in the liver called lipoproteins -- fats surrounded by proteins. Enzymes such as hepatic lipase, which is also made in the liver, break down the lipoproteins so the fats can be metabolized or used by the body.

Cholesterol metabolism has many steps. First, the liver turns food ingested into fatty acids, carbohydrates, alcohol and some cholesterol into very low-density lipoprotein (VLDL), the largest type of lipoprotein. VLDL is transported through the bloodstream to the body's tissues, which release triglycerides, fats used for energy or stored in muscle or fat cells. Lipoprotein lipase breaks down the VLDL into intermediate-density lipoprotein. Hepatic lipase is the enzyme that breaks the intermediate-density particles down into LDL, which carries 60 to 80 percent of the cholesterol in the blood.

Some lipoproteins are more dangerous than others. LDL is called the "bad" cholesterol because excess LDL particles stick to the inner walls of the blood vessels to form plaque. These particles help form the plaque obstructions in the blood vessels that can block blood flow and trigger heart attacks and strokes. LDL comes in different sizes, or densities, and everyone's cholesterol profile contains different ratios of the different sizes of LDL.

Reverse cholesterol transport doesn't sound very heroic, but that's the role of high-density lipoprotein (HDL), the so-called "good" cholesterol. HDL clears fragments of proteins, fats and cholesterol from the bloodstream before they can damage arteries. Low levels of HDL have been linked to increased heart disease risk.

Researchers have been able to show that they can intervene in men and change hepatic lipase levels, he says. In a previous study, co-author Alberto Zambon, a senior researcher at the University of Washington, found that intensive therapy with lipid-lowering drugs decreases hepatic lipase in men and causes coronary artery disease regression.

Hepatic lipase activity must be measured in a test tube and requires more than a simple blood test. Because it binds to the endothelium, the inner lining of blood vessels, people must first submit to an injection of the blood thinner heparin to release hepatic lipase into the bloodstream. The complexity of the test, which temporarily thins a person's blood but has no other side effects, makes large studies difficult, he says. "That has been an important limitation to the research."

This study was presented at the American Heart Association's 38th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.

Hokanson and Zambon's co-author was John D. Brunzell, M.D.


Story Source:

The above story is based on materials provided by American Heart Association. Note: Materials may be edited for content and length.


Cite This Page:

American Heart Association. "Sex Differences In Heart Disease May Be Due To Enzyme That Breaks Down Fat." ScienceDaily. ScienceDaily, 25 March 1998. <www.sciencedaily.com/releases/1998/03/980325074521.htm>.
American Heart Association. (1998, March 25). Sex Differences In Heart Disease May Be Due To Enzyme That Breaks Down Fat. ScienceDaily. Retrieved August 20, 2014 from www.sciencedaily.com/releases/1998/03/980325074521.htm
American Heart Association. "Sex Differences In Heart Disease May Be Due To Enzyme That Breaks Down Fat." ScienceDaily. www.sciencedaily.com/releases/1998/03/980325074521.htm (accessed August 20, 2014).

Share This




More Health & Medicine News

Wednesday, August 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Possible Ebola Patient in Isolation at California Hospital

Possible Ebola Patient in Isolation at California Hospital

Reuters - US Online Video (Aug. 20, 2014) — A patient who may have been exposed to the Ebola virus is in isolation at the Kaiser Permanente South Sacramento Medical Center. Linda So reports. Video provided by Reuters
Powered by NewsLook.com
Raw: World's Oldest Man Lives in Japan

Raw: World's Oldest Man Lives in Japan

AP (Aug. 20, 2014) — A 111-year-old Japanese was certified as the world's oldest man by Guinness World Records on Wednesday. Sakari Momoi, a native of Fukushima in northern Japan, was given a certificate at a hospital in Tokyo. (Aug. 20) Video provided by AP
Powered by NewsLook.com
Do More Wedding Guests Make A Happier Marriage?

Do More Wedding Guests Make A Happier Marriage?

Newsy (Aug. 20, 2014) — A new study found couples who had at least 150 guests at their weddings were more likely to report being happy in their marriages. Video provided by Newsy
Powered by NewsLook.com
Ebola-Hit Sierra Leone's Freetown a City on Edge

Ebola-Hit Sierra Leone's Freetown a City on Edge

AFP (Aug. 19, 2014) — Residents of Sierra Leone's capital voice their fears as the Ebola virus sweeps through west Africa. Duration: 00:56 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins