Hyperlipoproteinemia
Hyperlipidemia, hyperlipoproteinemia or dyslipidemia
is the presence of elevated or abnormal levels of lipids and/or low-density lipoproteins in the blood. Lipids (fatty molecules)
are transported in a protein capsule, and the density of the lipids and type of protein determines the fate of the particle
and its influence on metabolism. Abnormal
levels of certain lipids, particularly cholesterol, triglycerides, and low-density lipoproteins are risk factors for atherosclerosis
which elevates the risk for coronary heart disease and strokes.
Deaths from CHD, cerebrovascular disease, and peripheral vascular disease account
for 38.5% of the 2.4 million deaths in the United States in 200. Two-thirds of atherosclerosis
deaths were due to CHD. About 85% of CHD deaths occurred in individuals over
65 years of age. Among the 15% dying prematurely, 80% died during their first
CHD event. Among those dying of sudden cardiac death in 1997, 50% of the men
and 64% of the women had previously been asymptomatic. It is estimated that an
average of 11.5 years of life are lost as a consequence of having a myocardial infraction (G&G 940).
Modifiable
risk factors account for 85% of excess risk (risk over and above that of individuals with optimal risk-factor profiles) for
premature CHD. The presence of one or more conventional risk factor in 90% of
patients with CHD belies claims that a large percentage of CHD, perhaps as much as 50%, is not attributable to conventional
risk factors. Studies indicate that when total cholesterol levels are below 160
mg/dl, CHD risk is markedly attenuated, even in the presence of additional risk factors.
Risk factors: LDL, low density lipoprotein
are associated with coronary heart disease (CHD). Statins lower primarily LDL. However, many patients with coronary heart disease (CHD) do not have substantially
elevated LDL, instead, low high-density lipoprotein (HDL) [thus the ratio of LDL to HDL is important]. HDL greater than 60 is a negative risk factor. Other lipid
abnormalities associated with CHD risk are elevations of triglyceride and lipoprotein(a), and a preponderance of small, dense
LDL particles. Oxidized LDL is central to the process. Low HDL increases CHD risk and is the primary lipid abnormality in many patients with CHD.
Hypertriglyceridemia is an independent risk
factor for CHD, but is often associated with low HDL levels, insulin resistance, and hyperinsulinemia. LDL poses
a risk for cardiovascular disease when it invades the endothelium and becomes oxidized since the oxidized form is more easily
retained by the proteoglycans. A complex set of biochemical reactions regulates the oxidation of LDL, chiefly stimulated by
presence of free radicals in the endothelium. Nitric oxide down-regulates this oxidation process catalyzed by L-arginine.
Correspondingly when there are high levels of asymmetric dimethylarginine in the endothelium, production of nitric oxide is
inhibited and more LDL oxidation occurs.
LDL particles actually vary in
size and density, and studies have shown that a pattern that has more small dense LDL particles—called "Pattern B"—equates
to a higher risk factor for coronary heart disease(CHD) than does a pattern with more of the larger and less dense LDL particles
("Pattern A"). This is because the smaller particles are more easily able to penetrate the endothelium. "Pattern I", meaning
"intermediate", indicates that most LDL particles are very close in size to the normal gaps in the endothelium (26 nm). Because of difficulty in acquiring the measurement of these two types of LDLs, these
values are not routinely obtained. {Given the cost, side effects, and inconvenience
of most drug treatments for high LDL, such measurement ought to be made, even thought it is not in the economic interest of
the physician—jk} If the LDL is elevated, the primary goal of therapy is to
lower LDL, with the reduction of triglyceride by nicotinic acid; a fibrate is a secondary consideration.
Inflammation which runs unchecked can also lead to a host of
diseases such as hay fever, atherosclerosis, and rheumatoid arthritis. Prolonged
inflammation (chronic) leads to a progressive shift in the type of cells which are present at the site of inflammation and
is characterized by a simultaneous destruction and healing of the tissue from inflammatory process. Causes: burns, chemical irritants, frostbite, toxins, infection,
necrosis, physical injury, immune reaction due to hypersensitivity, ionizing radiation, and foreign bodies.
Moderately elevated triglycerides (150-400 mg/dl) are of concern
because they often occur as part of the metabolic syndrome, which includes insulin resistance, obesity, hypertension, low
HDL levels, and substantially increased CHD risk. The metabolic syndrome affects
~25% of adults and is common in CHD patients; hence identification of moderate Hypertriglyceridemia should trigger an evaluation
to identify this disorder.
DRUG
INTERVENTIONS
There are 5 principle types of drug intervention. Most used are the statins which are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-COA) reductase inhibitors
(they also reduce blood clotting); bile acid-binding resins, nicotinic acid, fibric acid derivatives, the cholesterol absorption
inhibitior ezetimibe. (Statins primary
reduction in cardiac events is not, as big PHARMA suggests, through their effect on LDLs, but rather through the reduction
of thrombosis. This effect can be obtained through daily aspirin.) Drug intervention can reduce CHD and strokes in the high-at-risk populace by 30-40%.
http://www.aspirin-foundation.com/uses/cardio/thrombosis.html
Aspirin and Coronary Thrombosis
Once the anti-aggregant effect of aspirin
on platelets had been described in the mid 1960s, calls for trials of aspirin in myocardial infarction were made by John O’Brien
in the UK (19) and by Harvey Weiss and others in the USA.21
In
fact, these calls had been anticipated. Laurence Craven, a family practitioner in Glendale, California, published a series
of three papers on aspirin in the early 1950’s (22-24). Each of these focused
on some aspect of bleeding.
In the first, Craven pointed out that women take aspirin rather often for their pains and
aches, while men tend to scorn such an ‘effeminate’ remedy and he went on to wonder if this difference might explain
the sex difference in the incidence of heart attacks. (22) In his second paper,
Craven described bleeding in tonsillectomy
patients given Aspergum, a mint flavoured gum impregnated with aspirin. (23) His third paper reports uncritically a remarkable
benefit of aspirin on heart attacks and strokes (see panel). Craven’s ideas were however so unacceptable at that time,
and his experimental work so flawed that he had difficulty reporting his findings and had to submit his papers to a rather
obscure journal. (24)
The calls of O’Brien and Weiss
were however heard in the MRC Epidemiology Unit in Cardiff, and in 1969 a double-blind placebo-controlled
randomised trial of low-dose aspirin was commenced. (25) Men who had been recently discharged from local hospitals following
an MI were invited to cooperate. Those who agreed were randomised to receive either 300 mg aspirin in a gelatine capsule or
a placebo capsule.
Two points about the published report on this first trial are worth noting (see panel below). First, the journal published
it under the headline: ‘For debate’. This was totally appropriate. Clinical practice should never be based on
the results of a single trial, however convincing these are.
Replication is essential and if a drug or a preventive
measure truly works then it will show in different patient groups, in different situations and in trials run by different
trialists. Secondly, the results of the trial were evaluated only in terms of a reduction in total deaths. The inclusion of
non-fatal events gives opportunity for bias due to a possible differential reporting of symptoms. Cardiovascular disease makes
a substantial contribution to all-cause deaths, and if a measure does reduce it, an effect on total mortality should be seen.
A Randomised Controlled Trial of Acetyl Salicylic Acid in the Secondary
Prevention of Mortality from Myocardial Infarction.
P.C.Elwood, A.L.Cochrane, M.L.Burr, P.M.Sweetnam, G.Williams, E Welsby, S.J.Hughes, R.Renton British
Medical Journal 1974,1, 436-440
The results of a randomised controlled trial of a single daily dose of
acteyl salicylic acid (aspirin) in the prevention of re-infarction in 1,239 men who had had a recent myocardial infarct were
statistically inconclusive. Nevertheless, they showed a reduction in total mortality of 12% at six months and 12% at twelve
months after admission to the trial. Further trials are urgently needed to establish whether or not the effect is real.
Naturally,
clinicians at that time were somewhat more than sceptical of the whole situation, and there was no detectable change in clinical
practice. However research groups around the world took note, a number of trials were set up and by 1980 six trials had been
reported. (25-30)
An early overview (Seoul conference on aspirin 1980)
Cardiff 1 (1974)25 1239
26% n.s. CDP (1976) 26 1529 30% n.s. Cardiff 2(1979)27 1725 30% n.s. German (1979)28 626
18% n.s. AMIS (1980)29 4524 10% n.s. PARIS (1980)30 1216 18% n.s.
23% reduction by aspirin (P < 0.0001)
Each of these early trials
suggested a beneficial effect of aspirin, but the results of none achieved an acceptable level of statistical significance.
Overall, however, there is clearly convincing evidence of benefit.
The reporting of overviews of the results from
all relevant published trials relating to a particular clinical intervention is becoming increasingly common throughout clinical
practice and the first such overview, or meta-analysis, based on these six trials was presented by Richard Peto and his colleagues
of Oxford to the inaugural meeting of the Society for Clinical Trials in Philadelphia in 1980.(31)
This overview was
one strand in the thinking that led eventually to the setting up of the Cochrane Collaboration, the worldwide initiative that
aims to conduct overviews within every area of clinical activity. (32)
Since that first report, the Oxford group have produced several monumental overviews
of aspirin and cardiovascular disease: in 1988 (33) ,1994 (34). and 1997 (35).
The following is based on the overview published in 1994, which combines results from 145 RCTs, with a total of 102,459
patients and 10,943 outcome events. A remarkably consistent reduction in vascular events is demonstrated (22 to 32%).
An
overview of RCT's of aspirin and cardiovascular disease
(BMJ 1994;308:81-106)
Prior MI 11
25% Acute MI 9 29% Prior stroke/TIA 18 22% Other high risk 104 32%
All trials 25%
Non-fatal MI
122 34% Non-fatal stroke 124 25% Vascular death 144 17% All-cause death 144 16%
Also considering the following factors male/female; under/over 65yrs; hypertensive / normotensive; diabetic / non-diabetic
gave no evidence of any significant differences in benefit.
An overview of studies with such a large number of clinical
outcomes enables the drawing of conclusions from sub-group analyses with a fair degree of confidence. The benefit of aspirin
is similar in all groups of patients whatever the prior indication for prophylaxis. Furthermore, there is no evidence of differences
in the proportionate reduction by aspirin in different patient groups: males and females, older and younger subjects, diabetic
and non-diabetic, hypertensive and normotensive subjects etc.
Together with this overview a Press Release by the group
in Oxford was widely reported by the media. (36) This gave the estimate that around 100,000 premature deaths
from cardiovascular disease could be prevented world-wide by the appropriate use of low-dose aspirin together with at least
this number of non-fatal heart attacks and strokes.
Nicotinic Acid (Niacin, B3)
Nicotinic acid
has been used to treat hyperlipidemias for 40 years. Niacin is a water-soluble
B-complex vitamin that functions as a vitamin only after its conversion to NAD or NADP (in the energy production cycle), in
which it occurs as an amide (acid COOH, amide CONH2). Both niacin and its amide
may be given orally as a source of niacin for its functions as a vitamin, but only
niacin affects lipid levels, and at very large doses. It is the best agent
available for increasing HDL—the good cholesterol. In addition to improving
LDL, HDL, and triglyceride, niacin is one of the few agents know to reduce Lp(a). Niacin
is especially effective in treating patients with mixed dyslipidemia. Niacin reduces the production and release of VLDL and thereby leads to a reduction in IDL and LDL. Niacin also decreases the release of free fatty
acids, a substrate of triglyceride synthesis, from adipose tissue into the circulation.
Niacin may also decrease HDL catabolism. The mechanism by which niacin
reduces Lp(a) is not known.
Efficacy, Niacin
at a dosage of 1.5 to 6g/d decreases LDL by approximately 20-30%, increases HDL by 30-40%, and decrease triglyceride by 35-50%;
and Lp(a) by 40% (G&G, p. 955). Combination therapy with resins can reduce
LDL levels by as much as 40-60% (G&G 956).
Absorption, fate, and excretion: Niacin is almost complete absorbed, and peak plasma concentratioins
are achieved within30 to 60 minutes. The half-life is about 60 minutes, which
accounts for the necessity of twice- or thrice-daily dosing. At lower doses,
most niacin is taken up by the liver; only the major metabolite, nicotinuric acid is found in the urine. At higher doeses, a greater proportion of the drug is excreted in the urine as unchanged nicotinic acid
(G&G 956).
Mechanism of action: In adipose tissue, niacin inhibits the lipolysis of triglycerides by hormone-sentive lipase, which reduces transport
of free fatty acids to the liver and decreases hepatic triglyceride synthesis. IT
may exert tis effect on lipolysis by inhibiting adipocyte adenylyl cyclase. Niacin
may also inhibigt a rate-limiting enzyme of triglyceride synthesis. In the liver,
niacin reduces triglyceride synthesis by inhibiting both the synthesis and esterification of fatty acids. This reduction of triglyceride synthesis reduces hepatic VLDL production, which accounts for the reduced
LDL levels. HDL levels (good Cholesterol) are raised by decreasing the fractional
clearance of apoA-1, but not of cholesteryl esters, thereby increasing the apoA-1 content of plasma and augmenting reverse
cholesterol transport. The net effect of niacin on monocytic cells (foam cells) is HDL-mediated reduction of cellular cholesterol content.
Immediate-release
(crystalline) niacin is typically started at a dosage of 100 mg once or twice daily and gradually titrated up to 2 to 3 g/d over a period of 1-3 weeks, often with a schedule of 1 g two or three times daily. (Niaspan is a sustained release formulation).
Side Effects & Drug Interactions: Cutaneous flushing and pruritis
(itching) of the trunk and face limit patient compliance. Flushing is worse when therapy is initiated
or the dosage increased, but ceases in most patients after 1 to 2 weeks. It can
reoccur if one to two doses are missed, and it is more likely to occur when niacin is consumed with hot beverages or ethanol. Flushing and prutitis is minimized if therapy is initiated
with low doses, are taken with meals, and by concomitant administration of aspirin
(325 mg ½ hour prior). Dry skin,
a frequent complain, can be dealt with by using skin moisturizers. Acanthosis nigricans
(brown, poorly defined, velvety hyperpigmentation of the skin) can be dealt with by suing lotions or creams containing salicylic
acid.. Increased hepatic transaminases occur in 1-2% of patients. Combining niacin with a statin increases the risk of hepatitis and myopathy (muscle disease). Niacin can cause uric acid elevations and occasionally precipitates gout, and may activate peptic ulcers. The most common, medically serioius
side effects are hepatotoxicity, manifested as elevated serum transaminase and
hyperglycemia. Affected patients experience flu-like fatigue and weakness. A reduction of LDL of 50% or more should be viewed as a sign of niacin toxicity. High doses of niacin may also elevate blood sugar.
Niacin can adversely affect glucose metabolism, particularly in patients with underlying insulin resistance--about
4% of type 2 diabetics.
Therapeutic Uses: Crystalline niacin tablets are available over the counter. To minimize the flushing and pruritus, it is best to start with a low dose (100 mg. Twice daily taken after
breakfast and supper). The dose may be increased stepwise every 7 days by 100
to 200 mg to a total dose of 1.5 to 2 g. After 2 to 4 weeks at this dose, transaminases,
serum albumin, fasting glucose, and uric acid levels should be measured. Lipid
levels shoud be checked and doses increased further until the desired effect on plasma lipids is achieved. After a stable dose is attained blood should be drawn every 3 to 6 months.
All doses of sustained-relase niacin, but particlulary doses above 2 g per day, have been reported to cause hepatotoxicity
(G&G 956).
One popular form of dietary supplement is inositol hexanicotinate, usually sold as "flush-free" or "no-flush" niacin (although those terms are also used for regular sustained-release.) While
this form of niacin does not cause the flushing associated with the nicotinic acid form, it is not clear whether it is pharmacologically
equivalent in its positive effect.
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