Lipids & Lipoproteins Part 2 Lecture 13

Lipid and Lipoprotein Population Distributions Serum lipoprotein concentrations differ between adult men and women, Primarily as a result of differences in sex hormone levels, Women having, on average, higher HDL cholesterol levels and lower total cholesterol and triglyceride levels than men. The difference in total cholesterol, however, disappears after menopause as estrogen decreases

Diagnosis of Lipid Disorders Diseases associated with abnormal lipid concentrations can be caused: directly by genetic abnormalities or through environmental/lifestyle imbalances, or they can develop secondarily, as a consequence of other diseases. Generally defined by the clinical characteristics of patients and the results of laboratory tests Many, but not all, lipid disorders, regardless of etiology, are associated with coronary heart disease (CHD), or arteriosclerosis. Secondarily diseases: Pregnancy, Diabetes mellitus, infection, liver disease

Arteriosclerosis Deposition of lipids, mainly, esterified cholesterol in artery walls = fatty streaks Small damage to walls - macrophages & platelets move in to repair LDL brings cholesterol for new cell membranes LDL can also be taken up by macrophages = foam cells Accumulation of foam cells deposit in artery walls = fatty streaks Fatty streaks can develop over time into plaques which can partially block or occlude blood flow. Arteriosclerosis is a general term describing any hardening (and loss of elasticity) of medium or large arteries Therefore, atherosclerosis is a form of arteriosclerosis.

Arteriosclerosis Increased LDL and decreased HDL associated with increased plaque formation 1% decrease in LDL drops CHD risk 2% Treatment to reduce LDL below 100 mg/dL is effective in the stabilization and sometimes regression of plaques

Peripheral vascular disease (PVD) When plaque develops in arteries of the arms or legs Coronary artery disease (CAD) when it develops in the heart Cerebrovascular disease (CVD) when it develops in the vessels of the brain

Adult Reference Ranges For Lipids ANALYTE REFERENCE RANGE Total cholesterol 140-200 mg/dL HDL cholesterol 40-75 mg/dL LDL cholesterol 50-130 mg/dL Triglyceride 60-150 mg/dL

Urine excretion of albumin is increased

Cardiac enzyme CK and CK isoenzyme and LD and LD isoenzyme would be useful. Fasting total cholesterol, triglycerides, and HDL and LDL cholesterol could also be performed, but the values should be interpreted with caution because the patient is under stress and may have suffered a MI. The fasting lipids should be repeated after he has been released from the hospital. If he had a MI, it will be approximately 6 weeks before the values represent true levels.

With a total cholesterol level of approximately 280 mg/dL and normal triglycerides and HDL cholesterol, his LDL cholesterol is estimated to be >190 mg/dL, which is extremely elevated. His physician presumably would have started him on a Step II diet prior to leaving the hospital, based on the in-hospital values. If the 6- to 8-week values do not show significant improvement, the physician would probably start him on medication. The patient has a family history of CHD, and, presumably, the patient has now been diagnosed with CHD. Therefore, the goal would be to reduce LDL cholesterol values to <100 mg/dL. Step 2 diet (30% of calories or less as total fat, less than 7% saturated fat, and less than 200 mg cholesterol per day) 

Dyslipidemias Dyslipidemia is a disorder of lipoprotein metabolism. Include both the overproduction and deficiency of lipoproteins. Dyslipidemia can manifest as the elevation of plasma cholesterol, triglycerides, or both. It can also be manifested by: the elevation of LDL cholesterol and the decrease of HDL cholesterol in the blood.

Dyslipidemias Disease states are generally caused by: malfunction in synthesis, transport, or catabolism of lipoproteins Dyslipidemias can be subdivided into two major categories Hyperlipoproteinemia Hypercholesterolemia Hypertriglyceridemia Combined hyperlipoproteinemia Hyolipoproteinemia

Hypercholesterolemia Familial hypercholesterolemia (FH) Homozygotes rare 1/million Total cholesterol 800-1000 mg/dl Heart attack as early as teenage years Heterozygotes cholesterols 300-600 mg/dl Heart attacks 20-50 years

Hypercholesterolemia Familial hypercholesterolemia (FH) Primarily LDL elevations Synthesis is normal but decrease or lack LDL receptors Therefore LDL builds-up in serum Since cells cannot acquire from LDL increase internal synthesis

Hypertriglyceridemia Triglycerides Borderline = 150-200 mg/ dl High 200-500 mg/dl Very High > 500 mg/dl Familial hypertriglyceridemia Genetic Secondary hypertriglyceridemia Hormonal imbalances Imbalance between synthesis and clearance of VLDL hormonal abnormalities associated with the pancreas, adrenal glands, and pituitary,

Hypertriglyceridemia Generally caused by deficiency of LPL or LPL cofactor. LPL hydrolyzes triglycerides in chylomicrons and VLDL Deficiency prevents processing and clearing Elevated even with fasting

Combined Hyperlipoproteinemia Presence of elevated levels of serum total cholesterol and triglycerides Genetic form of this condition Familial combined hyperlipoproteinemia (FCH) Type III hyperlipoproteinemia an accumulation of cholesterol-rich VLDL and chylomicron remnants as a result of defective catabolism of those particles Rare form of apo E, called apo E2/2

Hypolipoproteinemia Low levels of lipoproteins Hypo alpha or hypobetalipoproteinemias Hypobetalipoproteinemia Associated with low LDL Not associated with CHD

Hypolipoproteinemia Hypoalphalipoproteinemia Several genetic defects decrease in circulating HDL (<40mg/dl) without hypertriglyceridemia Premature CHD An extreme form -Tangier Disease may have HDL 1-2 mg/dl People with Tangier disease have defective ABCA1 transporters

Hypolipoproteinemia Hypoalphalipoproteinemia Acute transient hypoalphalipoproteinemia Severe physiologic stress Infection, surgery, generalized illness Therefore samples taken during hospitalization interpret with caution Return to normal after recovery

Yes, she has diabetes mellitus. Eruptive xanthomas; triglycerides Yes Yes, she has diabetes mellitus. Cessation of estrogen replacement therapy, with consideration of transdermal estrogen therapy, triglyceride- lowering diet and medication, hypoglycemic medication. Most acute risk is pancreatitis.

Lipid and Lipoprotein Analyses Lipids and lipoproteins are important indicators of CHD risk, This is the major reason for their measurement in research, as well as in clinical practice. Diagnosis of dyslipidemia is dependent upon the measurement of: 1- Total cholesterol 2- Triglycerides 3- HDL cholesterol 4- and LDL cholesterol Lipid Panel or profile

Cholesterol Enzymatic Method Cholesterol esterase cleaves the fatty acid residue from cholesteryl esters, Comprise about two thirds of circulating cholesterol, Converting them to unesterified or free cholesterol. The free cholesterol is reacted by cholesterol oxidase, producing hydrogen peroxide, A common enzymatic color reaction using horseradish peroxidase to couple two colorless chemicals into a colored compound. The intensity of the resulting color, proportional to the amount of cholesterol

Cholesterol Enzymatic Method

Triglyceride measurement Several enzymatic reaction sequences are available for triglyceride measurement, All including lipases to cleave fatty acids from the glycerol backbone. The freed glycerol participates in any one of several enzymatic reactions. The last reaction include: conversion of NADH to NAD+ Or produce a colored product

Triglyceride measurement +

HDL Methods CDC reference method Three step process Ultracentrifugation to remove VLDL Heparin manganese precipitation to remove LDL activity Then analysis Two-step method with precipitation of non- HDL fractions (apo-B) then analysis on supernatant Enzymatic cholesterol method on remaining CDC = center for disease control and prevention Apo B in VLDL and LDL is rich in positively charged amino acids,

LDL = Total Cholesterol – HDL – Trig/5 LDL Methods Friedewald calculation Determine total cholesterol, total triglycerides and HDL as before VLDL is estimated as triglycerides/5 400 mg/dl is the upper limit for TG LDL = Total Cholesterol – HDL – Trig/5 It assumes, first, that virtually all of the plasma TG is carried on VLDL, and second, that the TG:cholesterol ratio of VLDL is constant at about 5:1

Lipoprotein Methods Must separate fractions Electrophoresis – agarose or polyacrylamide Chromatographic Precipitation Ultracentrifugation Immunochemical

Apolipoprotein Methods Primarily a research method or specialty cardiac service center Usually done by Immunoassay – Turbidimetric ELISA, RIA