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Hepatic mRNA levels for the LDL receptor and HMG-CoA reductase show coordinate regulation in vivo.

A sensitive solution hybridization assay using autologous cRNA probes was developed with the aim to study the simultaneous regulation of hepatic mRNA levels, on a quantitative basis, for the LDL receptor (LDLr), HMG-CoA reductase, and cholesterol 7 alpha-hydroxylase (Cho-7-hx) in C57BL/6J mice. With the purpose to suppress and stimulate transcript levels respectively, animals received established high fat diets, cholesterol-enriched diets, and a diet supplemented with mevinolin and colestipol. One hundred nineteen animals were investigated in six separate experiments. In spite of an eightfold increase in hepatic cholesterol induced by a high fat diet, the LDLr and the HMG-CoA reductase mRNA levels were only reduced to 60-70% and 25-50% of control values, respectively. When the data from all animals were analyzed, a strong positive correlation was obtained between the mRNA levels for the LDLr and HMG-CoA reductase (r = 0.79, P less than 0.001). A significant relation remained when control animals only were analyzed (n = 42, r = 0.59, P less than 0.001). Cho-7-hx mRNA showed a regulatory pattern that differed from that of the LDLr and HMG-CoA reductase; feeding cholesterol at 1.7% and 5% but not at 0.4% elevated the mRNA levels for Cho-7-hx while the LDLr and HMG-CoA reductase mRNA levels were maximally suppressed already at 0.4% of dietary cholesterol. The results show that the mRNA levels for the LDLr and HMG-CoA reductase are regulated in parallel in the liver in vivo during various metabolic perturbations as well as at normal physiologic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Bile acid sequestrants: mechanisms of action on bile acid and cholesterol metabolism.

Interruption of the enterohepatic circulation of bile acids by cholestyramine or colestipol influences the hepatic metabolism of cholesterol in many ways. The synthesis of bile acids is increased, as reflected by a several-fold increase in the activity of the cholesterol 7 alpha hydroxylase, the rate-determining enzyme in bile acid synthesis. The increased metabolism of cholesterol to bile acids causes an enhanced demand of cholesterol in the hepatocytes which respond with both new synthesis of cholesterol, as reflected in a several-fold increase of the HMG-CoA reductase activity, and increased expression of LDL receptors. As a consequence, the plasma level of LDL-cholesterol is lowered. The hepatic secretion rate of VLDL particles is increased. Cholestyramine therapy does not affect the output of biliary lipids or the cholesterol saturation of bile, indicating that treatment with bile acid sequestrants should not be associated with any increased risk of gallstone formation.

Bile↗

Reducing high blood cholesterol level with drugs. Cost-effectiveness of pharmacologic management.

We performed a cost-effectiveness analysis of pharmacologic treatment of high blood cholesterol levels. Agents modeled were cholestyramine, colestipol, gemfibrozil, lovastatin, niacin, and probucol. Pharmacologic effectiveness was estimated from reported studies. Cost estimates reflect societal resource consumption. Annual costs for therapy ranged from $327 (niacin) to $1881 (lovastatin, 80 mg/d). Niacin was the most efficient agent for reducing low-density lipoprotein cholesterol levels, having an average cost over 5 years of $139 per percent reduction in low-density lipoprotein cholesterol level. Lovastatin (20 mg/d) was also efficient ($177 per percent reduction). Cholestyramine was least efficient at $347. For high-density lipoprotein cholesterol, niacin was most efficient, at $116 per percent increase in high-density lipoprotein cholesterol level, followed by gemfibrozil at $271. Analyses combining low-density lipoprotein cholesterol and high-density lipoprotein cholesterol effects suggest that niacin and lovastatin (20 mg/d) were most efficient for reducing cardiovascular risk.

Anticholesteremic Agents↗

Treatment of heterozygous familial hypercholesterolemia with lipid-lowering drugs.

Patients with heterozygous familial hypercholesterolemia (FH) constitute a unique population at high risk for the premature development of coronary artery disease (CAD) and in whom long-term hypocholesterolemic therapy to reduce elevated levels of low density lipoprotein (LDL) cholesterol is most clearly indicated. Optimal therapy invariably requires diet regulation plus hypolipidemic drug therapy. When used as single agents, the bile-acid sequestrants, cholestyramine and colestipol, lower LDL cholesterol concentrations by 20% to 35% in compliant patients, whereas decreases of 20% to 30% can be achieved with nicotinic acid in doses of 3 to 6 g/day. Bezafibrate, fenofibrate, and ciprofibrate have also been shown to lower LDL cholesterol levels by 20% to 30%, and these drugs are more effective than gemfibrozil and clofibrate. Probucol, neomycin, and D-thyroxine reduce LDL cholesterol concentrations by 10% to 15% in single-drug use. Clinical trials with a new class of drugs that inhibit the rate-limiting enzyme in cholesterol biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, and that includes lovastatin, simvastatin, and pravastatin indicate that these drugs lower LDL cholesterol concentrations by 30% to 50% in patients with heterozygous FH. Combined drug therapy with a bile-acid sequestrant and nicotinic acid lowers LDL cholesterol by 40% to 55%, whereas fenofibrate, bezafibrate, or probucol plus a bile-acid sequestrant results in reductions varying from 25% to 50%. The combinations of an HMG CoA reductase inhibitor with either a bile-acid sequestrant or nicotinic acid appears to be the most promising, and these regimens reduce LDL cholesterol levels by 45% to 60%. With appropriate use, the currently available hypocholesterolemic drugs have the potential to markedly change the natural history of premature atherosclerosis that occurs in untreated patients with FH.

Butyrates↗

Antibiotic-associated pseudomembranous colitis.

All antibiotics, except parenteral aminoglycosides, sulfonamides and vancomycin, can induce pseudomembranous colitis. The worst offenders are clindamycin, ampicillin, amoxicillin and the cephalosporins. The cytotoxin produced by Clostridium difficile has been identified as the cause of pseudomembranous colitis. Treatment includes an antimicrobial to eradicate the organism and cholestyramine or colestipol to bind the toxin.

Amoxicillin↗

[Drug therapy of hypercholesterinemias (author's transl)].

Every permanent substantiated primary hypercholesterolemia which does not respond adequately to diet must be treated with drugs. For monotherapy first of all fenofibrate, bezafibrate and nicotinic acid derivatives are suitable for the treatment of adult patients. For supportive therapy colestyramine and colestipol come into consideration as well as beta-sitosterol. D-thyroxine and etiroxate should be reserved for refractory cases. Drug therapy is only given for secondary hypercholesterolemias in justifiable exceptions.

Adult↗

Hyperlipidemia - a diabetic emergency.

Treating hyperlipidemia in diabetics requires distinguishing between hypercholesterolemia, with its high risk of cardiovascular disease, and hypertriglyceridemia, which, if severe, may cause pancreatitis. Hypercholesterolemia is best managed with diet and, if necessary, colestipol and niacin. Hypertriglyceridemia with chylomicrons responds best to diabetic control, weight loss, and low-fat diet.

Adolescent↗

[Pharmacokinetics of fenofibrate in man (author's transl)].

The active metabolite of fenofibrate is fenofibric acid, which is strongly bound to serum proteins. Following a single oral dose of 300 mg fenofibrate there is a diphasic decrease in plasma levels of fenofibric acid, and most of the drug is excreted as conjugate in the urine. Following daily oral administration of 300 mg during 10 days, a state of equilibrium is obtained within 2 to 3 days and persists throughout the observation period; the mean elimination half-life and urinary excretion rate are very similar to those measured after a single dose, and the drug does not accumulate. In patients with renal insufficiency, the plasma half-life of fenofibric acid is very substantially prolonged and considerable accumulation takes place, as the compound is virtually not dialyzable. Doses of 100 mg/day produce plasma levels similar to those obtained with 300 mg/day. The lipid-lowering activity mostly affects triglycerides. Concomitant administration of colestipol has no effect on blood kinetics and urinary excretion of fenofibrate but results in very important reduction of all lipoprotein fractions.

Colestipol↗

Discordant regulation of proteins of cholesterol metabolism during the acute phase response.

Recent studies have shown that the administration of endotoxin (LPS) and cytokines to Syrian hamsters increases serum cholesterol levels, hepatic cholesterol synthesis, and the activity, protein levels, and mRNA levels of hepatic HMG-CoA reductase. Despite the greater than 10-fold increase in HMG-CoA reductase mRNA levels, LPS had only minimal effects on hepatic LDL receptor mRNA levels. In the present study, we demonstrate that LPS increases the transcription rate in the liver of HMG-CoA reductase mRNA approximately 4- to 5-fold without affecting LDL receptor mRNA transcription. Most stimuli that regulate HMG-CoA reductase and LDL receptor mRNA levels also regulate, in parallel, HMG-CoA synthase and farnesyl pyrophosphate (FPP) synthetase. However, in chow-fed animals, LPS and cytokines (TNF, IL-1, TNF + IL-1) increased hepatic HMG-CoA reductase mRNA levels without increasing LDL receptor, HMG-CoA synthase, or FPP synthetase mRNA levels. The feeding of cholesterol or bile resin binders regulates the mRNA levels of HMG-CoA reductase, LDL receptor, HMG-CoA synthase, and FPP synthetase. In both cholesterol- and colestipol-fed animals, LPS increased HMG-CoA reductase mRNA levels while either decreasing or causing minimal increases in the mRNA levels of the other proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute-Phase Reaction↗

Endotoxin, TNF, and IL-1 decrease cholesterol 7 alpha-hydroxylase mRNA levels and activity.

Endotoxin (LPS) and cytokines increase cholesterol synthesis and the secretion of lipoproteins by the liver in rodents resulting in hypercholesterolemia. Cholesterol 7 alpha-hydroxylase (CAH) is the rate-limiting enzyme in the conversion of cholesterol to bile acids in the liver, the major regulated pathway by which cholesterol is eliminated from the body. Decreases in CAH would increase the quantity of cholesterol available for lipoprotein production. In the present study, we demonstrate that LPS, TNF, or IL-1 administration to Syrian hamsters produces a marked decrease in the levels of CAH mRNA in the liver. This marked decrease occurred even when the basal level of CAH expression was increased by feeding the bile acid sequestrant, colestipol. Additionally, a marked decrease was also observed when the animals were fed a cholesterol-enriched diet. Moreover, the decrease in CAH mRNA occurred very rapidly (decreased 66% by 90 min after LPS administration) and required relatively small doses of LPS (100 ng/100 g body weight). Lastly, the decrease in mRNA levels was accompanied by a decrease in CAH activity. This decrease in CAH could contribute to the increase in hepatic lipoprotein production induced by LPS and cytokines. CAH can be added to the growing list of proteins that regulate lipid metabolism and that are altered during the acute phase response.

Animals↗

Endotoxin, tumor necrosis factor, and interleukin-1 decrease hepatic squalene synthase activity, protein, and mRNA levels in Syrian hamsters.

Recent studies have shown that endotoxin (LPS) administration to Syrian hamsters markedly increased hepatic HMG-CoA reductase activity, protein mass, and mRNA levels, but only produced a modest increase in hepatic cholesterol synthesis, suggesting that LPS may also influence other key enzymes involved in the regulation of cholesterol metabolism. In the present study, we have examined the effect of LPS and cytokines on the activity, protein mass, and mRNA level of squalene synthase, which is the first committed enzyme in cholesterol biosynthesis and is located at a branch point in the mevalonate pathway. Our results demonstrate that LPS administration produces a marked decrease in the mRNA levels of squalene synthase. This decrease in squalene synthase mRNA occurred very rapidly (90 min after LPS) and required relatively small doses of LPS (1 microg/100 gm body weight). LPS also significantly decreased squalene synthase activity and protein mass. Finally, LPS produced a marked decrease in squalene synthase mRNA, activity, and protein levels when the basal levels of squalene synthase expression were increased 4-fold by prior treatment with bile acid binding resin, colestipol. Tumor necrosis factor and interleukin-1, which mediate many of the metabolic effects of LPS, also decreased hepatic squalene synthase activity and mRNA levels. Taken together, our results suggest that the discordant regulation of HMG-CoA reductase and squalene synthase during the host response to infection and inflammation may have substantial effects on the regulation of substrate flux into the non-sterol pathways of mevalonate metabolism.

Animals↗

Management of blood lipid abnormalities in coronary heart disease patients.

Information obtained from clinical and laboratory research strongly supports a causal relationship between hyperlipidemia (dyslipidemia) and coronary heart disease (CHD), and provides an impetus to develop strategy for control of dyslipidemia. Some recent developments in the field may include the use of: (1) colestipol-niacin to control hypercholesterolemia and induce regression of coronary atherosclerosis; (2) limited amounts of foods rich in stearic or oleic fatty acids to enhance the appeal of cholesterol-lowering regimen; (3) gemfibrozil or lovastatin to inhibit cholesterol synthetic activity; and (4) gemfibrozil to raise atherosclerosis-protective plasma high-density lipoprotein levels. These and other newer developments will stimulate interest in research on dyslipidemia and its control to facilitate primary and secondary prevention of CHD.

Clinical Trials as Topic↗

Dyslipidemia and coronary artery disease.

Genetically determined and metabolically induced disturbances in lipid metabolism, as manifested in several types of dyslipidemia, have been shown to be causally related to the development of coronary artery disease (CAD). A diversity of clinical and angiographic studies has been made to evaluate the linkage between plasma lipid-control therapy in the development of initial and recurrent cardiovascular events. The plan of treatment invariably begins with a low-fat, low-cholesterol diet before initiation of drug therapy. However, many patients have difficulty in adhering to the low-fat diet. Fortunately, metabolic studies show that foods which contain fats rich in stearic (saturated) and oleic (monounsaturated) fatty acids may be given in limited amounts to boost patients' compliance to a low-fat diet and to prevent their blood lipids from rising to abnormal levels. A bile acid sequestrant (cholestyramine or colestipol) is the first-line drug for control of hypercholesterolemia. Either gemfibrozil or gemfibrozil plus niacin is prescribed to raise high-density lipoprotein (HDL) levels of CAD patients. Approval of two HMG CoA reductase inhibitors, pravastatin and simvastatin, by the FDA gives physicians the additional flexibility of employing a single or a combination drug therapy for optimal control of dyslipidemia. The association of low serum cholesterol level (< 160 mg/dl) with increase in noncardiac mortality has prompted health professionals to consider modifying the universal screening and treatment of serum cholesterol in children and young women and to use hypolipidemic drugs in patients judiciously.

Arteriosclerosis↗

Adverse effects of hypolipidaemic drugs.

Cholestyramine, colestipol, clofibrate, gemfibrozil, nicotinic acid (niacin), probucol, neomycin, and dextrothyroxine are the most commonly used drugs in the treatment of hyperlipoproteinaemic disorders. While adverse reaction data are available for all of them, definitive data regarding the frequency and severity of potential adverse effects from well-controlled trials using large numbers of patients (greater than 1000) are available only for cholestyramine, clofibrate, nicotinic acid and dextrothyroxine. In adult patients treated with cholestyramine, gastrointestinal complaints, especially constipation, abdominal pain and unpalatability are most frequently observed. Continued administration along with dietary manipulation (e.g. addition of dietary fibre) and/or stool softeners results in diminished complaints during long term therapy. Large doses of cholestyramine (greater than 32 g/day) may be associated with malabsorption of fat-soluble vitamins. Most significantly, osteomalacia and, on rare occasions, haemorrhagic diathesis are reported with cholestyramine impairment of vitamin D and vitamin K absorption, respectively. Paediatric patients have been reported to experience hyperchloraemic metabolic acidosis or gastrointestinal obstruction. Concurrent administration of acidic drugs may result in their reduced bioavailability. Serious adverse reactions to clofibrate will probably limit its role in the future. Of particular concern are ventricular arrhythmias, induction of cholelithiasis and cholecystitis, and the potential for promoting gastrointestinal malignancy which far outweigh the reported benefits in preventing new or recurrent myocardial infarction, cardiovascular death and overall death. Patients with renal disease are particularly prone to myositis, secondary to alterations in protein binding and impaired renal excretion of clofibrate. Drug interactions with coumarin anticoagulants and sulphonylurea compounds may produce bleeding episodes and hypoglycaemia, respectively. Nicotinic acid produces frequent adverse effects, but they are usually not serious, tend to decrease with time, and can be managed easily. Dermal and gastrointestinal reactions are most common. Truncal and facial flushing are reported in 90 to 100% of treated patients in large clinical trials. Significant elevations of liver enzymes, serum glucose, and serum uric acid are occasionally seen with nicotinic acid therapy. Liver enzyme elevations are more common in patients given large dosage increases over short periods of time, and in patients treated with sustained release formulations.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

[Role of lipid lowering therapy in patients with peripheral arterial occlusive disease].

BACKGROUND: Peripheral arterial occlusive disease (PAOD) is common in older age. PAOD is associated with an increased risk of vascular events (e. g. myocardial infarction or stroke). Therefore, the prevention and treatment of PAOD is important, especially at a time when the elderly population is increasing. There is an association between lipid abnormalities and the risk of developing PAOD. However, it is not yet definitively established if early intervention with lipid lowering drugs prevents the development of PAOD and improves outcome. RESULTS OF STUDIES: In a 5-year follow-up study, in which hypercholesterolemia was treated by partial ileal bypass (POSCH study), the incidence of claudication was reduced to 19% (n = 126) in the surgical treatment group vs. 33.6% (n = 119) in the control group (p < 0.01). Direct imaging of peripheral atherosclerosis was not performed and a partial ileal bypass operation is followed by considerable changes in nutrition. A 2-year follow-up study of 153 patients with femoral atherosclerosis treated with colestipol-niacin demonstrated a decreased progression of angiographically assessed femoral atherosclerosis (p < 0.02). A subgroup analysis of the Scandinavian Simvastatin Survival Study (n = 4,444) reported worsening symptoms in 3.6% in the placebo group as compared to 2.3% in the simvastatin group (p = 0.008). In an open trial lipid-lowering therapy with statins did not improve functional outcomes including 6 minutes walking distance and 4 minutes walking velocity in 392 men and women with an ankle-brachial-index (ABI) < 0.90. A summary performance score combined performance in walking speed, standing balance, and time for five repeated chair rises into an ordinal score ranging from 0 to 12 (12 = best) was improved (p < 0.001). A randomized placebo controlled prospective study with simvastatin including 43 patients in each group demonstrated an improved painfree and total walking distance as well as an increased ABI after 6 months. A second placebo controlled study investigated the effect of 10 mg and 80 mg atorvastatin in 354 patients after 12 months. Painfree walking time was only improved by 80 mg atorvastatin, maximum walking time and ABI remained unchanged. A questionnaire regarding physical activity showed improved results already for 10 mg atorvastatin, whereas quality of life did not change. Pathomechanistic explanations, such as regression of peripheral atherosclerosis, were not described. CONCLUSION: All in all the association between the progression of PAOD and lipid abnormalities is surprisingly inconclusive and the effects of lipid-lowering are not defined. Well designed long-term studies assessing primary and secondary prevention of PAOD with defined endpoints, such as amputation rate or number of vascular interventions are missing. The mechanisms improving physical activity whithout affecting PAOD outcome have to be investigated.

Anticholesteremic Agents↗

Treatment of Biliary Problems in Inflammatory Bowel Disease.

The most common biliary problem in patients with inflammatory bowel disease is primary sclerosing cholangitis (PSC). The treatment of this disease is multifaceted and frequently requires a multidisciplinary approach involving internists, nutritionists, gastroenterologists, and surgeons. Unfortunately, other than liver transplantation, no therapy that is currently available has been proven to alter the natural history of PSC or prolong survival. Ursodeoxycholic acid is currently the most promising pharmacologic treatment option for slowing disease progression and should be used in higher than usual doses (20 to 30 mg/kg/d). Treatment of symptoms due to cholestasis, such as pruritis and steatorrhea, is an important aspect of the medical care of patients with PSC. Our preferred treatment of pruritis due to cholestasis is with bile acid binding exchange resins such as cholestyramine or colestipol (which is generally better tolerated than cholestyramine). Endoscopic therapy should be reserved for patients with obstructive jaundice, cholangitis, or symptomatic dominant biliary strictures. We recommend dilation of dominant strictures with graduated or balloon dilators followed by temporary stenting if the postdilation cholangiographic appearance is not improved or adequate biliary drainage cannot be assured. There is indirect evidence that the combination of ursodeoxycholic acid and endoscopic therapy to maintain biliary patency may improve transplant-free survival in patients with PSC, although this remains to be proven. Liver transplantation remains the only effective treatment of advanced PSC, and should be considered in patients with complications of cirrhosis or intractable pruritis or fatigue.

Journal Article↗

Chronic Diarrhea.

Chronic diarrhea can be due to any of several hundred conditions. When investigation fails to uncover a specific cause that can be treated successfully, nonspecific therapy is implemented. This includes dietary alterations if specific aggravating foods can be identified, enteral or parenteral nutrition if nutritional status is compromised, and use of oral rehydration solutions if diarrhea produces volume depletion. Strategic use of dietary fiber can improve stool consistency and can be of special value when fecal incontinence is present concurrently. Medications of value include opiate antidiarrheal drugs, clonidine, octreotide, and bile acid-binding agents. Less potent opiates such as loperamide and diphenoxylate should be tried first, with more potent agents such as codeine, opium, and morphine used in refractory cases. Clonidine has both proabsorptive and motility effects that facilitate its antidiarrheal effect, but its antihypertensive action limits its utility. Octreotide is of great value in treating diarrhea due to endocrine tumors and dumping syndrome; its efficacy in other conditions or in nonspecific diarrhea is less well established. Bile acid binders such as cholestyramine or colestipol have several specific uses but have limited utility in nonspecific chronic diarrhea.

Journal Article↗

Lymphocytic and Collagenous Colitis: Medical Management.

When possible, patients taking nonsteroidal anti-inflammatory medications should discontinue them when the diagnosis of microscopic colitis is made. Although there is no direct evidence of its efficacy, a trial of elimination of caffeine or lactose or both should be undertaken. Nonspecific antidiarrheal agents (eg, loperamide, diphenoxylate) may be administered, but appear to be largely ineffective in this population. An aminosalicylate should be initiated at full therapeutic dose (2 to 4 g daily) as the first-line therapy. Because sulfasalazine appears to be associated with a high incidence of adverse effects in patients with microscopic colitis, other derivatives of 5-aminosalicylate (5-ASA) are preferred. Bile salt-binding agents such as cholestyramine or colestipol appear to be effective alternatives for patients who are either unresponsive to or intolerant of aminosalicylates. Systemic corticosteroids are an effective treatment for microscopic colitis, but may offer only transient improvement in symptoms. Given their potential adverse effects, corticosteroids should be reserved for patients with refractory disease in whom aminosalicylates and bile salt-binding agents have failed. Other agents that may be effective include antibiotics, bismuth subsalicylate, budesonide, pentoxifylline, octreotide, and methotrexate. Although these agents can be considered in unusual cases, the cumulative clinical experience with them in this setting is relatively limited. Surgical intervention, with either fecal stream diversion or subtotal colectomy, shows promise as an intervention of last resort. In refractory cases of microscopic colitis, strong consideration should be given to excluding a concomitant diagnosis of celiac disease, bacterial overgrowth, or chronic infection.

Journal Article↗