Atherosclerosis and gene therapy treatments essay PDF

Preview

Summary

exam answer essay style question...

Description

Atherosclerosis and gene therapy treatments essay Discuss the pathophysiology of atherosclerosis Briefly explain current treatments Introduction- what is atherosclerosis? Atherosclerosis, a type of arteriosclerosis- thickening of the walls of the arteries, is an inflammatory disease of the blood vessel walls caused by a build up of plaques and lipids and fibrous elements in the walls of large arteries. Early lesions of atherosclerosis consist of sub endothelial accumulation of cholesterol engorged macrophages known as foam cells due to their appearance. The walls of the arteries thicken due to invasion of the macrophages which are triggered in response to inflammation from HDL-C. This leads to the formation of a fatty streak. Fatty streaks are the precursors to more advanced lesions characterised by accumulation of lipids and necrotic debris and proliferation of smooth muscle cells. Such fibrous lesions have a fibrous cap consisting of smooth muscle cells and extracellular matrix that encloses a lipid rich necrotic core. Plaques become increasingly complex with calcification, ulceration at the luminal surface and haemorrhage from small vessels that grow into the lesion from the media of the blood vessel wall. Although advanced lesions can grow sufficiently large to block blood flow, the most important clinical complication is an acute occlusion due to the formation of a thrombus or blood clot resulting in myocardial infarction or stroke. Usually the stroke is associated with rupture or erosion of the lesion. Atherosclerosis is asymptomatic for decades because the arteries enlarge at all plaque locations, thus there is no effect on blood flow. Even most plaque ruptures do not produce symptoms until enough narrowing or closure of an artery, due to clots, occurs. Signs and symptoms only occur after severe narrowing or closure impedes blood flow to different organs enough to induce symptoms.[10] Most of the time, patients realize that they have the disease only when they experience other cardiovascular disorders such as stroke or heart attack. These symptoms, however, still vary depending on which artery or organ is affected. A large artery consists of three morphologically distinct layers, the intima is the innermost layer and is bounded by a monlayer of endothelial cells on the luminal surface and a sheet of elastic fibres the internal elastic lamina on the peripheral side. The normal intima is a very thin region and consists of extracellular connective tissue matrix, primarily proteoglycans and collagen. The media, the middle layer consists of smooth muscle cells. The adventitia, the outer layer consists of connective tissue with interspersed fibroblasts and smooth muscle cells. There are many factors that can lead to atherosclerosis in humans including environmental factors, genetic factors and personal factors. Also nonmodifiable factors such as being male, advanced age and having a close relative that has had cardiovascular disease. Turbulent blood flow around areas of vessels that have high flow around bifurcations. Blood vessel thicken to be more resistant but then get lipids moving into areas of intimal thickening. They develop into advanced plaques- stable plaques or unstable plaques. Unstable plaques- think fibrous caps more likely to rupture and then form a clot. Can cause myocardial infarction. Endothelial dysfunction and oxidative stress. Endothelium becomes dysfunctional in reactive oxygen species environment.

Initially endothelium a barrier- dysfunction causes gaps, circulating leukocytes get into gaps, adhesion markers are expressed by endothelium, inflammatory cells come in to repair, this quickly progresses- response to the dysfunction. Fatty streak, cells within vessel wall respond, LDL-c can get through the gaps, gets oxidised. Monocytes come in and differentiate into macrophages, take up the lipid and become foam cells. Become huge and mop up oxidised LDL. Die and then spill out lipid which drives more inflammation- cascade. Thrombi form. T cells come in to deal with inflammatory state. Smooth muscle cells migrate and proliferate to form a cap over all the inflammation and fatty streak which contributes to the thickening but also helps to stabilise the plaque. Complex plaque- heightened inflammation and protrusions into the lumen, build up of debris and necrotic core. Cap thickness and size of necrotic core is critical to integrity if plaque. What leads to the thinning of the cap? SMC apoptosis, loss of matrix supporting proteins. Reduced matrix synthesis due to loss of SMC. Structure on the surface becomes weak and splits. The necrotic core becomes exposed to blood flow which is thrombogenic. Matrix degrading metalloproteinase. Important for breaking down the matrix. TIMP is important to stop the MDMP from breaking down the fibrous cap. Options Surgery Angioplasty- stents Drugs for antiproliferation Surgery- mechanical to get around the blockage. Angiogram to find out where the blockage is. Saphenous vein commonly used. Internall mammary artery, cant often do multiple grafts. Radial artery another. But all in all limited in what to use. Balloon out the problem- catheter to get in a balloon to push out the blockage but when deflate the balloon the artery can just elastically recoil. So this is why we use a stent! Stents crucial to remember. Chicken wire structure. reblocking (restenosis) the big problem. Vein grafts even show restenosis. Stents can become restenosed. Inimtal thickening. In restenosis the big thing is smooth muscle cell migration and proliferation. What can we do? Inhibit plaques from the start? make plaques more stable? Inhibition of restenosis? Regress restenosis? We will concentrate on plaque stabilisation and inhubtion of restenosis. Therefore statins Good for plaque stabilisation. Statins come from a shroom. Mevalonate pathway! Mevalonate inhibits cholesterol production. So block mevalonate synthesis you block cholesterol production. Liver cells respond to increase LDL receptor which draws even more bad LDL out of the blood! Double whammy positive! Boom.

Statins are awesome and do something beneficial for all the negative involved in atherosclerosis. They stop progression to unstable plaque they help shift to stable phenotype. However limitations, statin intolerant people and in others fails to prevent restenosis. Giving more statins isn’t the answer and they are expensive. Some patients get sever side effects. Restenosis drugs Rapamysin. E2F and RB binding. If smooth muscle cell is going through cell cycle it needs topass through the binding stage of e2f and rb. Rb needs to be hyperphosporylated which allows e2f to go and make the cell cycle carry on. Stent placement or vein graft could be used to put in the rapamysin. Stents are useful for being coated with rapamysin. Enhanced thrombosis from this treatment which is bad as you are casuing the endothelium to stop growing too. You want the endothelium to repair but this can prevent it. Its non selective. So looking for new therapies that can have same benefit of rapamysin but that don’t prohibit the endothelium regrowth. Solutions Tools for vascular gene therapy. Describe the structure and principles behind the various gene therapy tools. Highlight the advantages and disadvantages of the various gene therapy tools. Main learning objective discuss the available gene therapy delivery vectors and methods

But even with these there is room for gene therapy. Aims to inhibit target gene expression or insert gene into cells. Atherosclerosis is polygenic disease. Not just one gene to fix. So we need to find a gene maybe at the top of a cascade. Small complementary sequnces of genes- inhibit gene transcription and translation using antisense or ribozymes, transcripton factor decoys. If you want to overexpress a gene you need the full length gene code. You may want to introduce a dysfunctional gene. Or maybe over express a natural inhibitor like NMPS… endogenous inhibitors are TIMPS! May want to overexpress TIMPS!! Antisense DNA transcribed in Mrna and then translation into protein. Antisense disrupts Mrna translation into proteins. Ribozymes

Act as molecular scissors. Chop up messenger RNA and by changing the sequence you engineer the specficicity. Cleave the mrna and protein production is reduced or stopped. Transcription factor decoy Stops mrna being made in the first place. Need to know more about the gene of interest. Need to know the transcription factors are required to activate the gene promoter. When a receptor is activated by its ligand the transcription factor is activated. Overexpression cassette Need the entire gene. Need a poly a tail. Can decide want high expression so will choose viral promoter and clone the genetic code. No control or specificity. Which cell type want it to be expressed in. cell specific such as FLT-1 or SM22-alpha (this is for smooth muscle cells)

How do we get them into the cell? Need to cross the cell membrane. Naked delivery- oligonucleotides Package in a lipsome. If you put the oligonueclotide in a lipid bubble it will cross the membrane easuer.

Best way is by viral transporters. Retrovirus and adenovirus Naked DNA Lipid transport is better than naked but not good in vivo. Retrovirus Oncogenic viruses because of the way they integrate into our DNA. Retrovirus carry 2 single strands of RNA. Don’t want the second part of life cycle if used in gene therapy so want to stop the cell cycle at replication. we modify its genome

adenovirus efficient at infecting cells. Lots of different types. AD5 good for smooth muscle cells. Natural adenoviral replication- keeps replicating and lyse and infect other cells. Not good for gene therapy so we make it genetically unable to replicate outside of the cell.

Angioplasty balloons. Double balloon- allows the virus to be put into a part of the vessel while blood flow is occluded. Perforated balloon Hydrogel- coated balloon. Gene eluting stent Gene delivery for vein grafts Surgeon takes out saphenous vein, therapeutic window with the vein for about 30 mins to put gene treatment on that specific piece of vein and then wash away the virus. The vein then goes into patient without virus....