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Lipid and Atherosclerosis Research

The role of cholesterol in cardiovascular disease has come a long way since the Russian Ignatowski reported in 1908 that feeding cholesterol to rabbits caused marked hardening of the arteries (or atherosclerosis). Since then, 13 Nobel Prizes in medicine and physiology have been rewarded for work in the cholesterol field. Cholesterol in the body is now known to be made in the liver or to come from the diet. Cholesterol is carried in blood on three particles: very low-density lipoproteins (VLDL), low-density lipoproteins (LDL) and high-density lipoproteins (HDL). These lipoproteins transport cholesterol (and other lipids like triglycerides) back and forth from the liver and the intestine to peripheral cells. When cholesterol in LDL (also called “bad cholesterol”) is present in elevated amounts, cardiovascular disease increases dramatically. A similar pattern is found when the cholesterol (and triglycerides) in VLDL are elevated. Conversely, high levels of HDL protects against cardiovascular disease while low levels of HDL promote atherosclerosis and cardiovascular disease.

Coronary Primary Prevention Trial

In the 1970s and early 1980s, it was known that high cholesterol was associated with coronary heart disease, but it was not known if lowering LDL cholesterol would decrease the incidence of coronary disease. To address this question, the Lipid Research Clinics program designed a clinical trial. About 250,000 healthy men were screened for high cholesterol to identify a final group of almost 4,000 men. Each man had to agree to drink four to six packets of“yellow sand” mixed with water for up to sevenyears. However, there was only a fifty-fifty chance that a participant was drinking the active preparation that significantly lowered LDL cholesterol, while the other half were drinking a placebo that had no effect on lowering LDL cholesterol. In addition, because this was a placebo-controlled double blind study, in which neither the patient nor the doctor knew whether he was taking the active or placebo forms, each man had to agree not to have his cholesterol tested for seven years. In 1984, Timemagazine covered the results of the study: on its front cover was a cartoon character with two eggs for eyes and two frowning strips of bacon for a mouth with the headline, “And now the bad news.” Thus, it was shown for the first time that lowering LDL cholesterol decreased heart attacks and death from heart attacks!

Other Seminal Observations Made in the Lipid Research Clinic 

Hyperapobetalipoproteinemia (HyperapoB)

In 1981, Dr. Kwiterovich co-discovered with Dr. Allan Sniderman of the Royal Victoria Hospital in Montreal, Canada, the disorder called hyperapoB. Many patients with coronary heart disease had elevated amounts of the major protein in LDL, called apoB, but the LDL cholesterol level was either normal or borderline. This phenotype was found to be due to an increased number of small, dense LDL particles that was underestimated by simply measuring LDL cholesterol. Through a series of papers over the next 25 years, it was found that this disorder was expressed in children, common in coronary disease and was often associated with high triglycerides, low HDL cholesterol, insulin resistance, diabetes, hypertension and obesity. Its metabolic and biochemical basis are understood but the molecular defecthas remained elusive.

The Johns Hopkins Cord Blood Study

The cord blood study researches elevated levels of a large HDL at birth. Research in this area started serendipitously when Dr. Kwiterovich was studying hyperapoB in small-for-date infants, who have been shown to be at increased risk of coronary disease in middle age. While performing this study in 163 infants born at The Johns Hopkins Hospital, he observed that one out of five of all infants had very elevated levels of a large HDL, while one in five had no large HDL, with the other infants having trace or small amounts. Of interest, those with the large HDL had lower levels of apoB and triglycerides, while those with no large HDL had higher levels of apoB and triglycerides.

Triad Heart Study

The Triad Heart Study (beginning with father, pregnant mother and infant at birth) is designed to examine genetic factors that may explain the phenotype of elevated versus low levels of a large HDL, first described above in the Johns Hopkins Cord Blood Study.Despite all the previous and ongoing research in HDL, there is little work on inherited factors in families that may influence HDL levels, particularly starting early in life, even at birth.We have found in initial analyses that the level of the large HDL in infants at birth predict the levels at two months of age, indicating that the elevated amount of HDL at birth has physiological significance and is not simply a phenomenon only expressed at birth. We also discovered that the levels of large HDL in the pregnant mother predict the HDL levels at birth and at two months of age. Genetic analyses in the parents and their infants have indicated that this trait of an elevated large HDL particle is heritable.

We have found a striking inverse relationship between the levels of the large HDL and LDL particle number, both at birth, in the infant and in the mother. Thus, we believe that we have discovered a common genetic trait that is expressed at birth and early in life either as high large HDL, low apoB and triglycerides or no or little large HDL, higher apoBand triglycerides.

Frozen plasma and DNA from the parents and children will answer more definitive questions regarding the fundamental cause of the elevated large HDL phenotype. The foundation for the study has been established and we are anxious to perform the next series of experiments. We now wish to employ modern techniques of molecular biology and protein chemistry to discover the fundamental cause of the high HDL phenotype. For example, we will determine if special candidate genes may be responsible for the phenotype. As well, certain proteins and enzymes in blood, such as LCAT, CETP and apoC-I, may influence the expression of this trait. Finally, there are novel candidate genes associated strongly with coronary disease whose functions are unknown. To cut across disciplines may lead to fascinating new insights present even at birth. 

These more sophisticated but critical experiments will be labor intensive and expensive but most critical and promising. For example, the results of these experiments promise to point the way to the development of new drugs to increase the levels of the large HDL levels in blood and reduce apoB and triglycerides, leading to significantly less cardiovascular disease. Such effects will expand significantly the current known effect of statins on reducing LDL and cardiovascular disease.

Dietary Intervention Study in Children (DISC)

Pediatricians and other health care professionals had expressed concern about the safety and efficacy of a diet low in cholesterol and saturated fat. Starting in 1987, DISC examined over three years whether such a low fat diet was safe and lowered LDL in rapidly growing adolescents with moderately elevated LDL cholesterol. Dr. Kwiterovich was the principal investigator for the Johns Hopkins site and chairman of the steering committee of principal investigators. The diet was found to support normal growth and development and to be effective in the 300 children so treated, compared to a control group who were simply followed by their doctors.

Phytosterolemia

Dr. Kwiterovich has followed an Amish family for over 25 years ascertained through a 10-year-old boy who suddenly died in a barn from a heart attack and was found to have the atherosclerosis of an old man. Of the 12 surviving siblings, five had elevated LDL cholesterol but not to the extent expected based on their large golf ball cholesterol deposits (xanthomas) on their knees and elsewhere. He found that they had the disorder phytosterolemia. For over two decades he did clinical biochemical and metabolic research on this disorder in this family and the original family reported by Dr. Bill Connor. In 2001, in collaboration with Dr. Helen Hobbs from the University of Texas Southwestern, a report was published in Science elucidating the molecular defect in this disorder and leading also to the discovery of two new transporters in lipid metabolism, ABCG5 and ABCG8, both of which normally work in concert to pump excess cholesterol and plant sterols from the intestinal cell back into intestinal lumen and also sterols from the liver into bile.

Glycosphingolipids

Subroto Chatterjee, Ph.D., has published extensively on the potential role of sugar-lipids, called glycosphingolipids. He has over a dozen patents related to these and other research results. Several of his more important observations include: 

  • Prevention of restenosis following balloon angioplasty
  • Novel herbal compounds to lower cholesterol
  • Prevention of plaque ruptures

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