[MUSIC] This is the first of a series of modules. Each one of which discusses a case in personalized medicine. The first three modules we'll actually focus on the same case and different aspects of that case. And the problem is, in brief, a 42 year old man who routine physical examination and laboratory work is discovered to have an LDL cholesterol of 352. That's an extraordinarily high value and is a cause for some concern. So what I want to talk about in this module, and the subsequent modules, is the by chemical basis for a very high cholesterol. How that story evolved and understanding the genetic and molecular basis of an abnormally high cholesterol has informed drug therapies and has informed a new drug development. So this looks like a genetic problem, and in fact, is a genetic problem. The proband, the patient, is indicated by the red square and the rest of his family is shown here. Now, on further questioning, he has a very strong family history of premature coronary artery disease. He has, his father developed a myocardial infarction, an MI at age 42, he has an aunt who developed angina in her 30s, and his fraternal grandmother died suddenly at age 38. The common is cause for sudden death is coronary occlusion. So it sounds like he has pretty advanced coronary disease in his family. Let's look at the LDL cholesterol. His LDL cholesterol was 352, his father's is 408, also extraordinarily high. He has two siblings that have normal LDL cholesterol, both 92. His mother's cholesterol is also normal, at 110. The aunt with angina has an LDL cholesterol that's quite high, 210. And he has a cousin who has an LDL cholesterol of 280. So based on the pattern shown here, we would anticipate that as this is a genetic disease, it's probably autosomal dominant, male to female and female to male transmission. And the basis remains obscure. So. The story that I want to tell you today starts with these two investigators, Joseph Goldstein and Michael Brown, who were young faculty members that were recruited to go from Boston to Dallas in the early 1970s. They had trained in internal medicine, they had trained in genetics and they had trained in biochemistry. And the problem that they set out to solve was the problem of familial hypercholesterolemia. Now, the family that I've just shown you is a family with autosomal dominant, the autosomal dominant form of the disease. And I showed a small pedigree that indicates that. The disease, in its most full-blown form, actually occurs in patients who carry two abnormal alleles. The genetics had actually been reasonably well worked out. The familial hypercholesterolemia that occurs in patients with two abnormal alleles, the so called recessive form, that is an extraordinarily rare disease, one in a million. Literally, one in a million. Those patients present with extraordinarily high LDL cholesterol values, usually over a thousand, and a number of other manifestations including heart attacks, myocardial infarctions, often in their teenager years or before. And then deposits of cholesterol in pretty characteristic locations around the body. These lumps that are shown on the hands are called xanthomas. The xanthomas occur in the achilles tendon, on the hands. And then xanthelasma around the eyelids as in panel d, and then ocorcynalis, pretty typically, in panel c. So what Goldstein and Brown did was try to understand the fundamental about chemical basis for this disease. And in doing so, they defined a new pathway, they defined a new mechanism and won the Nobel Prize for medicine or physiology in 1985. Their story starts with, how do we make cholesterol? We make cholesterol from acyl-CoA as the initial precursor, through a number of steps that are shown on this slide all the way down to cholesterol. And the rate limiting enzyme in the formation of cholesterol is HMG CoA Reductase, shown on this pathway. So they knew that already. So they started the story by culturing skin fibroblasts from patients with homozygous familial hypercholesterolemia. That's one patient in a million. They start with the very, very extreme case and compare it to the normals. And what's shown on this slide is, they cultured skin fiber blasts and measured HMG CoA Reductase activity. So you can see immediately that the homozygote have enormously elevated values of this enzyme. And therefore, you can infer that that's the mechanism where by they're making lots, and lots, and lots of cholesterol and in a presumably unregulated fashion. So this is an experiment that occurred in culture, and what they did was they removed, they cultured the cells in serum, but then they removed LDL cholesterol, the cholesterol that is carried around in these tiny protein particles called LDL from the medium. And they watched what happened over time to both the normal and the homozygous. So here's the result of that experiment. And you can see the normal person, over time, and it's hours, and hours, and hours, the HMG CoA Reductase activity rises over time. It's as though the cell says, wait a second I'm not seeing any cholesterol, so I need to make more, and it up regulates the activity of the critical enzyme involved in cholesterol biosynthesis. The homozygotes don't care whether LDL's there or not, and they make a huge amount of HMG CoA Reductase regardless. So that's an interesting observation, why the time delay? And it's as though the cell sort of understands how much cholesterol there is outside the cell from intracellular signaling. So then they did the next, the flip side experiment. Basically, they took those normal cells, and the homozygous cells, and they expose them back to LDL. And as they expose them back to LDL, over time, the cells said look, I have enough cholesterol now, and I don't need to make this HMG CoA Reductase anymore, and they go back to normal. So, the really interesting part's where, this part where the cell somehow sensed extra cellular cholesterol and made it an enzyme intracellularly, and that there was peculiar time course that took several hours to develop and then resolve. So the story, in a nutshell, is that LDL cholesterols carried, in a number of particles, cholesterol is carried in a number of particles, the most important of which is LDL. And LDL approaches a cell, usually a liver cell, they were working with skin fiber blasts, but liver cells is where the action, much of the action is. And the cell carries, on it's cell surface, a receptor for LDL. The LDL binds to the receptor and then enters the cell through a process called receptor mediated endocytosis. And actually, this is the very first example of the process called, of receptor mediated endocytosisin, and is one of the many contributions that Goldstein and Brown made to this field and our understanding of basic cellular biochemistry. Then the LDL particle is processed inside the cell. The cholesterol then feeds back to the synthetic apparatus in ways that they haven't quite defined yet. And cholesterol then turns off HMG CoA Reductase. Now the problem in patients with familial homozygous hypercholesterolemia is that they absolutely lack LDL receptor activity. No receptor means that there's a huge amount LDL floating around outside the cell. Left free to do all the bad things, including generate premature atherosclerosis. Because there's no cholesterol inside the cell to turn off HMG-CoA Reductase. So what we have is the story of a very rare disease. A one in a million disease. That then leads to the understanding of LDL physiology Pharmacology and makes us understand how high LDL in the circulation then results and premature atherosclerosis and most importantly identifies the important. Target for drug action. So understanding that HMG-CoA reductase is the critical step in this, a Japanese investigator in the early 1970s started a very, very long process of Of developing drugs that inhibit HMG CoA reductase Goldstein and Brown participated in that process. And Simvastatin, one of the most widely prescribed HMG CoA reductase drugs or statin drugs had world-wide sales of almost $7,000,000,000 in 2010. Lots and lots of randomized clinical trials have shown that statin treatment in patients with Familial Hypercholesterolemia and patients with garden variety elevations of LDL cholesterol and even patients in whom there's modest elevation of LDL cholesterol have fewer heart attacks When they take statin drugs compared to when they take placebos and it's been one of the great advances in modern medicine and probably accounts for some of the reduction in coronary artery disease that we've seen over the last several decades. The other major contributor of course is the decrease in smoking. OK so the take home message is from this first module that focuses on hypercholesterol. Is the study of basic mechanisms in the biochemical space in the cellular biology is really really an important part of personalizing medicine. The studies here identified a drug target, identified a mechanism for a very rare disease as well as for a common disease and, notably, very few patients ever get their LDL receptor gene sequenced. We have other ways of detecting patients at risk such as measuring LDL cholesterol and other lipid particles that circulate. But the genetics has informed the way in which we approach this disease. [NOISE] >> [APPLAUSE]
