Lipids & Lipoproteins

1. Lipids & Lipoproteins Part 2

2. 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 M. Zaharna Clin. Chem. 2009

3. 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 CHD, or arteriosclerosis. M. Zaharna Clin. Chem. 2009

4. 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. M. Zaharna Clin. Chem. 2009

5. 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 M. Zaharna Clin. Chem. 2009

6. 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 M. Zaharna Clin. Chem. 2009

7. Adult Reference Ranges For Lipids M. ZaharnaClin. Chem. 2009

8. 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. M. Zaharna Clin. Chem. 2009

9. 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 M. Zaharna Clin. Chem. 2009

10. 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 M. Zaharna Clin. Chem. 2009

11. 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 M. Zaharna Clin. Chem. 2009

12. 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 M. Zaharna Clin. Chem. 2009

13. 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 M. Zaharna Clin. Chem. 2009

14. 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 M. Zaharna Clin. Chem. 2009

15. Hypolipoproteinemia • Low levels of lipoproteins • Hypo alpha or hypobetalipoproteinemias • Hypobetalipoproteinemia • Associated with low LDL • Not associated with CHD M. Zaharna Clin. Chem. 2009

16. 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 M. Zaharna Clin. Chem. 2009

17. 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 M. Zaharna Clin. Chem. 2009

18. 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 M. Zaharna Clin. Chem. 2009

19. 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 M. Zaharna Clin. Chem. 2009

20. Cholesterol Enzymatic Method M. Zaharna Clin. Chem. 2009

21. 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 M. Zaharna Clin. Chem. 2009

22. Triglyceride measurement + M. Zaharna Clin. Chem. 2009

23. 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 M. Zaharna Clin. Chem. 2009

24. 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 M. Zaharna Clin. Chem. 2009

25. Lipoprotein Methods • Must separate fractions • Electrophoresis – agarose or polyacrylamide • Chromatographic • Precipitation • Ultracentrifugation • Immunochemical M. Zaharna Clin. Chem. 2009

26. Apolipoprotein Methods • Primarily a research method or specialty cardiac service center • Usually done by Immunoassay – • Turbidimetric • ELISA, RIA M. Zaharna Clin. Chem. 2009