Cerebrotendinous xanthomatosis without neurological involvement

BACKGROUND

Cerebrotendinous xanthomatosis (CTX) is an autosomal recessively inherited inborn error of metabolism. Neurological symptoms are considered to be a clinical hallmark of untreated adult patients. We describe a 'milder CTX phenotype', without neurological involvement.

METHODS

We performed a retrospective patient file study in 79 genetically confirmed Dutch patients with CTX (55 patients aged ≥ 21 years) to study the clinical heterogeneity of CTX. We studied the frequency of adult patients with CTX without neurological involvement at diagnosis, in our Dutch cohort, and included a family from South Africa and patients from Italy, USA, Chile and Asia from the literature.

RESULTS

In total, we describe 19 adult patients with CTX from 16 independent families, without neurological symptoms at diagnosis. A relatively small percentage (21%, n = 4) had a history of cataract. The majority, 84% (n = 16), presented with tendon xanthomas as the sole or predominant feature. The majority of patients showed increased plasma cholesterol levels. No correlation was found between this 'milder phenotype', the cholestanol levels and the CYP27A1 genotype. In addition, we describe three novel mutations in the CYP27A1 gene.

CONCLUSIONS

This study shows the clinical heterogeneity of CTX, highlighting the existence of a 'milder phenotype', that is without neurological involvement at diagnosis. Adult patients with CTX may present with tendon xanthomas as the sole or predominant feature, mimicking familial hypercholesterolemia. It is important to realize that the absence of neurological symptoms does not rule out the development of future neurological symptoms. As CTX is a treatable disorder, early diagnosis and initiation of treatment when additional clinical signs occur is therefore essential.

P5364Safety profile of bempedoic acid: pooled analysis of 4 phase 3 clinical trials

Background/Introduction

Bempedoic acid (BA), an oral, first-in-class, ATP-citrate lyase inhibitor, lowers low-density lipoprotein cholesterol (LDL-C) in patients who do not achieve sufficient lipid lowering with guideline-recommended first-line therapies.

Purpose

We evaluated the safety profile of BA in phase 3 trials.

Methods

Data were pooled from 4 randomised, double-blind, placebo-controlled studies that enrolled patients with hyperlipidaemia who were receiving stable lipid-lowering therapy (LLT; maximally tolerated statins +/− nonstatin therapies) and required additional LDL-C lowering. Patients were randomised (2:1) to BA 180 mg or placebo daily for 12 to 52 weeks.

Results

Median exposure for 3621 patients (2424 BA, 1197 placebo) was 363 days. Background LLT included a statin +/− other LLT (83.8%), nonstatin LLT alone (9.4%), or none (6.8%). Adverse event (AE) and serious AE rates were similar between groups (Table). The most common AEs in the BA and placebo groups were nasopharyngitis (7.4% vs 8.9%), myalgia (4.9% vs 5.3%), and urinary tract infection (4.5% vs 5.5%). Rates of new-onset/worsening diabetes were 4.0% for BA and 5.6% for placebo. No AEs leading to discontinuation differed by ≥0.5% between treatments. All fatal AEs were judged by the investigator as unrelated to treatment. A trend was observed for a lower 3-component major adverse cardiac event rate with BA vs placebo (hazard ratio, 0.85; 95% confidence interval: 0.53 to 1.37). Changes in uric acid, creatinine, and haemoglobin were apparent at week 4, stable over time, and reversible after stopping BA. Gout occurred in 1.4% and 0.4% of patients in the BA and placebo groups, respectively. The safety profile of BA was consistent across background therapies, demographics, and disease characteristics.

Table 1. Safety summary Placebo (n=1197) BA (n=2424) Any AE / SAE, % (n) 72.5 (868) / 13.3 (159) 73.1 (1171) / 14.1 (341) Drug discontinuation due to an AE, % (n) 7.8 (93) 11.3 (273) AE with a fatal outcome, % (n) 0.3 (4) 0.8 (19) Aminotransferase elevation >3 x ULN, % (n) 0.3 (3) 0.7 (18) Aminotransferase elevation >5 x ULN, % (n) 0.2 (2) 0.2 (6) Creatine kinase elevation >5 x ULN, % (n) 0.2 (2) 0.3 (8) Creatinine, mean change at week 12, mg/dL −0.002±0.11 0.046±0.12 Uric acid, mean change at week 12, mg/dL −0.02±0.82 0.82±0.97 Haemoglobin, mean change at week 12, g/dL 0.06±0.69 −0.31±0.71

Conclusion(s)

BA added to LLT was well tolerated, with a safety profile comparable to placebo.

Volanesorsen for treatment of patients with familial chylomicronemia syndrome

Familial chylomicronemia syndrome (FCS) is a rare autosomal recessive disorder typically caused by mutations in genes for lipoprotein lipase (LPL), apolipoprotein C-II (Apo-CII), apolipoprotein A-V (Apo-AV), lipase maturation factor 1 (LMF1) and glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPI-HBP1). FCS is associated with severe morbidity that includes recurrent pancreatitis and other problems. Effective treatment to reliably prevent complications has been unavailable, so there is a quest to identify novel interventions to achieve sustained triglyceride lowering and prevention of pancreatitis. Apolipoprotein C-III (Apo-CIII) interferes with triglyceride clearance by blocking LPL and alternative pathways. Volanesorsen is an experimental antisense oligonucleotide that inhibits translation of Apo-CIII mRNA, thereby substantially lowering plasma levels of Apo-CIII and triglycerides. It is being developed for treatment of patients with FCS and refractory hypertriglyceridemia. Data from a variety of clinical trials have been very encouraging, with documentation of excellent triglyceride-lowering efficacy, but there have been concerns about the risk of drug-related thrombocytopenia and bleeding that contributed to the recent decision by the Food and Drug Administration (FDA) to not approve the drug for clinical use. Clinical trials testing the safety and efficacy of volanesorsen are ongoing, so there is hope that the drug ultimately will be approved and available for treatment of high-risk patients with FCS.

Short-term folic acid supplementation induces variable and paradoxical changes in plasma homocyst(e)ine concentrations

Folic acid is presently the mainstay of treatment for most subjects with elevated plasma homocyst(e)ine concentrations [Plasma or serum homocyst(e)ine, or total homocysteine, refers to the sum of the sulfhydryl amino acid homocysteine and the homocysteinyl moieties of the disulfides homocystine and homocystein-cysteine, whether free or bound to plasma proteins.] Changes in homocyst(e)ine in response to folic acid supplementation are characterized by considerable interindividual variation. The purpose of this study was to identify factors that contribute to heterogeneity in short-term responses to folic acid supplementation. The effects of folic acid supplementation (1 or 2 mg per day) for 3 wk on plasma homocyst(e)ine concentrations were assessed in 304 men and women. Overall, folic acid supplementation increased mean plasma folate 31.5 +/- 98.0 nmol/L and decreased mean plasma homocyst(e)ine concentrations 1.2 +/- 2.4 micromol/L. There was evidence of substantial interindividual variation in the homocyst(e)ine response from -18.5 to +7.1 micromol/L, including an increase in homocyst(e)ine in 20% of subjects (mean increase 1.5 +/- 1.4 micromol/L). Basal homocyst(e)ine, age, male gender, cigarette smoking, use of multivitamins, methylene tetrahydrofolate reductase, and cystathionine beta-synthase polymorphisms accounted for 47.6% of the interindividual variability in the change in homocyst(e)ine after folic acid supplementation, but about 50% of variability in response to folic acid was not explained by the variables we studied.

High plasma homocyst(e)ine levels in elderly Japanese patients are associated with increased cardiovascular disease risk independently from markers of coagulation activation and endothelial cell damage

Elevated plasma homocyst(e)ine is a risk factor for cardiovascular disease (CVD) in many populations, but the relationship between homocyst(e)ine and CVD in Japanese subjects has been unclear. It has been hypothesized that the link between homocyst(e)ine and CVD may be mediated in part by activation of coagulation and endothelial cell injury in the elderly Japanese subjects. To further evaluate this hypothesis, the present cross-sectional study was designed to assess the relationships among plasma homocyst(e)ine concentrations, risk of CVD, and markers of coagulation (fibrinogen, FVII, F1+2, FVIIa and FXIIa) and endothelial cell damage (vWF and thrombomodulin) in 146 elderly Japanese subjects (79 healthy controls and 67 patients with CVD). The geometric mean (range) of plasma homocyst(e)ine concentrations was 10.2 (3.2--33) micromol/l in 79 Japanese healthy elderly subjects. As expected, healthy female and male elderly subjects had homocyst(e)ine levels that were 2.5 and 5.3 micromol/; higher, respectively, compared to healthy young control subjects (n=62). Healthy young and elderly men had homocyst(e)ine levels that were 1.7 and 4.5 micromol/l higher, respectively, compared to values in women. This higher plasma homocyst(e)ine levels in the elderly subjects were negatively correlated with levels of folic acid, albumin and total cholesterol, but were not significantly related to markers of coagulation or endothelial cell-damage. The results of multiple logistic regression analyses suggested that high homocyst(e)ine levels were independently related to CVD risk. In addition, levels of FVIIa, and F1+2 were significantly higher in elderly Japanese patients with CVD compared to elderly subjects without CVD, but were unrelated to plasma homocyst(e)ine concentrations. In summary, elevated plasma concentrations of homocyst(e)ine, FVIIa, and F1+2 were associated with increased risk of CVD in elderly male and female Japanese subjects, but the association between homocyst(e)ine and CVD was unrelated to abnormalities in markers of coagulation and endothelial cell damage in this population.

Increased plasma homocyst(e)ine after withdrawal of ready-to-eat breakfast cereal from the diet: prevention by breakfast cereal providing 200 microg folic acid

OBJECTIVE

We tested the hypothesis that cessation of habitual ingestion of breakfast cereals would be associated with elevated plasma homocyst(e)ine concentrations. We anticipated that those subjects who reported consuming breakfast cereals containing 100 to 400 ,microg of folic acid per serving before entering the study would achieve higher plasma homocyst(e)ine concentrations if, in addition to their regular diet, they began ingesting a daily serving of breakfast cereal that contained less than 10 microg of folic acid per serving.

DESIGN

Seventy-nine subjects consumed a daily serving of breakfast cereal containing either < 10 microg or folic acid per serving (placebo) or breakfast cereal containing 200 microg of folic acid per serving (folic acid fortified).

RESULTS

Cessation of intake of commercially available breakfast cereal was associated with homocyst(e)ine elevation. Breakfast cereal containing 200 microg folic acid per day was sufficient to maintain the homocyst(e)ine lowering effects of commercial cereals.

CONCLUSIONS

Habitual consumption of commercially available fortified breakfast cereals, usually containing 100 to 400 microg folic acid per serving, had significant homocyst(e)ine lowering effects as shown by the homocyst(e)ine increase after cessation of habitual intake of commercial breakfast cereal. Substitution of breakfast cereal containing only 200 microg folic acid per day was sufficient to maintain the homocyst(e)inelowering effects of commercial cereals.

Polymorphisms in the CBS gene associated with decreased risk of coronary artery disease and increased responsiveness to total homocysteine lowering by folic acid

Elevated total plasma homocysteine (tHcy) is an established risk factor for the development of vascular disease and neural tube defects. Total homocysteine levels can be lowered by folic acid supplements but individual response is highly variable. In this case-control study, involving 142 coronary artery disease (CAD) patients and 102 controls, we have typed six genetic polymorphisms in three homocysteine metabolizing genes and examined their relationship to the incidence of CAD, tHcy levels, and lowering of tHcy levels in response to folic acid supplementation. We found that two single nucleotide polymorphisms in the cystathionine beta synthase (CBS) gene, 699C --> T and 1080T --> C, are associated with decreased risk of CAD and increased responsiveness to the tHcy lowering effects of folic acid. Individuals homozygous for 699T were significantly underrepresented in CAD patients as compared to controls (4.9% vs 17.3%, P = 0.0015), as were individuals homozygous for the 1080C (29.6% vs 44.2%, P = 0.018). Additionally, 699T and 1080C homozygous individuals were the most responsive to folate supplementation. 699T homozygotes lowered tHcy levels 13.6% on average, compared to 4.8% lowering in 699C homozygotes (P = 0.009), while 1080C homozygotes lowered 12.9% compared to just 2.7% for 1080T homozygotes (P = 0.005). The two polymorphisms in CBS are third codon changes and would not be predicted to affect the underlying protein. However, there is strong linkage disequilibrium between these two positions, suggesting that they may also be linked to other as yet unidentified polymorphisms within the CBS gene. These observations suggest that specific CBS alleles are a risk factor for the development of vascular disease and that genetic information could be predictive of individual response to folic acid supplementation.

Homocysteine and atherosclerosis

Elevated plasma total homocysteine is an independent risk factor for atherosclerotic vascular disease. Risk rises continuously across the spectrum of homocysteine concentrations and may become appreciable at levels greater than 10 mumol/l. A compelling case can be made for screening all individuals with atherosclerotic disease or at high risk. A reasonable, but unproven, goal for treatment is a plasma total homocysteine concentration less than 10 mumol/l. Folic acid is the mainstay of treatment, but vitamins B12 and B6 may have added benefit in selected patients. The results of ongoing randomized placebo-controlled trials will not be available for several years, but will help determine whether homocysteine lowering reduces the risk of cardiovascular disease.

Inhibition of LDL oxidation by melatonin requires supraphysiologic concentrations

Melatonin has been suggested as a potent antioxidant that may protect against development of atherosclerosis and cancer; however, these effects are unproven and controversial. The antioxidant capacity of melatonin was tested in comparison with alpha-tocopherol, ascorbic acid, and the melatonin precursors tryptophan and serotonin, by measuring inhibition of metal ion-mediated and human macrophage-mediated oxidation of LDL. Melatonin had weak antioxidant activity that was detectable only at concentrations 10000- to 100000-fold higher than physiologic concentrations. These results were comparable with published data showing that the radical scavenging activity of melatonin requires markedly supraphysiologic concentrations. In contrast, alpha-tocopherol was 50- to 100-fold more potent and was efficacious at physiologic concentrations. Ascorbic acid and tryptophan also were active at physiologic concentrations and were significantly more potent than melatonin. In summary, extremely supraphysiologic concentrations of melatonin had only weak antioxidant activity, which was surpassed by alpha-tocopherol, ascorbic acid, and tryptophan.

Reduction of plasma homocyst(e)ine levels by breakfast cereal fortified with folic acid in patients with coronary heart disease

BACKGROUND

The Food and Drug Administration (FDA) has recommended that cereal-grain products be fortified with folic acid to prevent congenital neural-tube defects. Since folic acid supplementation reduces levels of plasma homocyst(e)ine, or plasma total homocysteine, which are frequently elevated in arterial occlusive disease, we hypothesized that folic acid fortification might reduce plasma homocyst(e)ine levels.

METHODS

To test this hypothesis, we assessed the effects of breakfast cereals fortified with three levels of folic acid, and also containing the recommended dietary allowances of vitamins B6 and B12, in a randomized, double-blind, placebo-controlled, crossover trial in 75 men and women with coronary artery disease.

RESULTS

Plasma folic acid increased and plasma homocyst(e)ine decreased proportionately with the folic acid content of the breakfast cereal. Cereal providing 127 microg of folic acid daily, approximating the increased daily intake that may result from the FDA's enrichment policy, increased plasma folic acid by 31 percent (P=0.045) but decreased plasma homocyst(e)ine by only 3.7 percent (P= 0.24). However, cereals providing 499 and 665 microg of folic acid daily increased plasma folic acid by 64.8 percent (P<0.001) and 105.7 percent (P=0.001), respectively, and decreased plasma homocyst(e)ine by 11.0 percent (P<0.001) and 14.0 percent (P=0.001), respectively.

CONCLUSIONS

Cereal fortified with folic acid has the potential to increase plasma folic acid levels and reduce plasma homocyst(e)ine levels. Further clinical trials are required to determine whether folic acid fortification may prevent vascular disease. Until then, our results suggest that folic acid fortification at levels higher than that recommended by the FDA may be warranted.

Rhabdomyolysis after taking atorvastatin with gemfibrozil

The findings in this case indicate that atorvastatin, like other DL-3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, may increase the risk of myositis and rhabdomyolysis when used in combination with gemfibrozil.

The relationship between maternal and neonatal umbilical cord plasma homocyst(e)ine suggests a potential role for maternal homocyst(e)ine in fetal metabolism

OBJECTIVE

Data on fetal blood homocyst(e)ine concentrations are not available. We tested the hypothesis that homocyst(e)ine crosses the maternal/placental/fetal interphases and is sequestered by the fetus.

STUDY DESIGN

The concentration of homocyst(e)ine was determined at parturition in peripheral venous plasma from 35 nulliparous healthy pregnant women and umbilical arterial and venous plasma from their conceptus.

RESULTS

Findings demonstrated a descending concentration gradient of plasma homocyst(e)ine from maternal vein to umbilical vein and to umbilical artery; the decrease at each interphase approximated 1 micromol/L. The neonate weight and gestational age were inversely related to maternal homocyst(e)ine concentrations.

CONCLUSION

The umbilical vein to umbilical artery homocyst(e)ine decrement suggests that uptake of homocyst(e)ine occurs in the fetus. The likely incorporation of homocyst(e)ine into the fetal metabolic cycle may implicate maternal homocyst(e)ine as having a potential nutritional role in the fetus. Further studies are required to explain the role of homocyst(e)ine in fetal metabolism and development.

Differential effects of subcutaneous estrogen and progesterone on low-density lipoprotein size and susceptibility to oxidation in postmenopausal rhesus monkeys

OBJECTIVE

To study the differential effects of subcutaneous E2 alone or in combination with P on the susceptibility of low-density lipoprotein (LDL) cholesterol to oxidation in naturally postmenopausal diet-controlled rhesus monkeys.

DESIGN

Prospective, longitudinal controlled study.

SETTING

Oregon Health Sciences University, Portland, Oregon, and Oregon Regional Primate Research Center, Beaverton, Oregon.

PATIENT(S)

Five naturally postmenopausal rhesus monkeys.

INTERVENTION(S)

Estradiol was administered subcutaneously for the first 4 weeks, followed by E2 plus P for 4 weeks, followed by a third 4-week washout period.

MAIN OUTCOME MEASURE(S)

Changes in plasma lipoprotein levels and oxidation of LDL and serum concentrations of E2 and P.

RESULT(S)

Levels of LDL cholesterol fell after 4 weeks of treatment with E2, compared with baseline. The lag time to half maximal light absorbancy after 4 weeks of E2 treatment was significantly increased compared with baseline. The maximal absorbance values and the slope of the propagation phase after 4 weeks of treatment with E2 were decreased compared with baseline. After 4 weeks of combined E2 and P treatment, all values were comparable to baseline.

CONCLUSION(S)

These results suggest that subcutaneous E2 therapy appears to enhance LDL resistance to oxidation and that this effect is attenuated by the addition of the P.

The effects of folic acid supplementation on plasma total homocysteine are modulated by multivitamin use and methylenetetrahydrofolate reductase genotypes

Elevated concentration of plasma total homocysteine (tHcy) is a common risk factor for arterial occlusive diseases. Folic acid (FA) supplementation usually lowers tHcy levels, but initial tHcy and vitamin levels, multivitamin use, and polymorphisms in the gene for 5, 10-methylenetetrahydrofolate reductase (MTHFR) may contribute to variability in reduction. We tested the effects of a 3-week daily intake of 1 or 2 mg of FA supplements on tHcy levels in patients with and without coronary heart disease (CHD) who were analyzed for the C677T MTHFR mutation. Prior multivitamin intake and baseline vitamin and tHcy levels were also compared with responsiveness to folate supplementation. Both dosages of FA lowered tHcy levels similarly, regardless of sex, age, CHD status, body mass index, smoking, or plasma creatinine concentration. In non-multivitamin users, FA supplements reduced tHcy by 7% in C/C homozygotes and by 13% or 21% in subjects with one or two copies of the T677 allele, respectively; the corresponding reductions were smaller in users of multivitamins. Moreover, T/T homozygotes had elevated tHcy and increased susceptibility to high levels of tHcy at marginally low plasma folate levels, as well as enhanced response to the tHcy-lowering effects of FA. Although other factors are probably involved in the responsiveness of tHcy levels to FA supplementation, about one third of heterogeneity in responsiveness was attributable to baseline tHcy and folate levels and to multivitamin use.

Effect of fasting, refeeding, and dietary fat restriction on plasma leptin levels

The factors responsible for the variability in plasma leptin levels observed among individuals with similar body compositions remain unclear. To examine the impact of dietary variables, we compared the changes in leptin levels induced by fasting and dietary fat restriction with the expected decrease following a significant loss in adipose mass. A 21.4 +/- 3.7% weight loss led to a 76.3 +/- 8.1% decrease in mean plasma leptin level (25.2 +/- 9.3 to 6.1 +/- 3.4 ng/mL, P = 0.0001) in a group of 9 obese males. Despite a weight loss of only 2.6 +/- 0.8%, mean plasma leptin levels fell by 61.9 +/- 25.2% (8.5 +/- 4.5 to 2.4 +/- 0.5 ng/mL, P < 0.01) in 7 nonobese females subjected to 3 days of fasting. Leptin levels in fasted subjects returned to baseline within 12 h of refeeding. Individual high- and low-fat meals given to 19 subjects after an overnight fast had no effect on plasma leptin levels. Reduction in dietary fat content from 37-10% of total calories for 7 weeks was also without effect on plasma leptin levels in these subjects. We conclude that plasma leptin levels primarily reflect total adipose mass, rather than meal consumption or dietary energy source, but that the reduction in leptin levels with ongoing fasting is disproportionate to the reduction in adipose mass. The ability of fasting to deactivate this presumed physiological satiety system may have been advantageous in environments characterized by rapid changes in food availability.

Homocyst(e)ine: an important risk factor for atherosclerotic vascular disease

Homocysteine is an intermediate compound formed during metabolism of methionine. The results of many recent studies have indicated that elevated plasma levels of homocyst(e)ine are associated with increased risk of coronary atherosclerosis, cerebrovascular disease, peripheral vascular disease, and thrombosis. The plasma level of homocyst(e)ine is dependent on genetically regulated levels of essential enzymes and the intake of folic acid, vitamin B6 (pyridoxine), and vitamin B12 (cobalamin). Impaired renal function, increased age, and pharmacologic agents (e.g. nitrous oxide, methotrexate) can contribute to increased levels of homocyst(e)ine. Plausible mechanisms by which homocyst(e)ine might contribute to atherogenesis include promotion of platelet activation and enhanced coagulability, increased smooth muscle cell proliferation, cytotoxicity, induction of endothelial dysfunction, and stimulation of LDL oxidation. Levels of homocysteine can be reduced with pharmacologic doses of folic acid, pyridoxine, vitamin B12, or betaine, but further research is required to determine the efficacy of this intervention in reducing morbidity and mortality associated with atherosclerotic vascular disease.

Prevention of atherosclerosis with dietary antioxidants: fact or fiction?

The notion that oxidation of lipids and lipoproteins may contribute to the pathogenesis of atherosclerosis is supported by a large body of evidence. It is hypothesized that dietary antioxidants may help prevent development and progression of atherosclerosis. The available evidence helps substantiate this hypothesis but is not yet conclusive. The results of several ongoing large randomized intervention trials will provide valuable information about the efficacy and safety of supplemental dietary antioxidants in prevention of atherosclerosis.

Inappropriate thyroid gland ablation in patients with generalized resistance to thyroid hormone. A common sequela of a rare disorder

Generalized resistance to thyroid hormone is one of several rare disorders of thyroid metabolism that can be associated with confusing symptoms and signs. Five cases of generalized resistance to thyroid hormone that were misdiagnosed with thyrotoxicosis, leading to unnecessary thyroid gland ablation and iatrogenic hypothyroidism, are reviewed herein. These cases illustrate the point that a careful review of the history, physical examination, and laboratory data, as well as an understanding of hormonal feedback relationships, will greatly benefit the practitioner in evaluating the patients with thyroid dysfunction. Consultation with an endocrinologist may be helpful to establish the correct diagnosis and avoid unnecessary treatments.

The relationship between serum lipoprotein(a) and insulinemia in healthy nondiabetic adult men

OBJECTIVE

To test the hypothesis that variations in serum insulin concentrations and insulin action may influence serum concentrations of lipoprotein(a) [Lp(a)].

RESEARCH DESIGN AND METHODS

A cross-sectional analysis of fasting serum insulin and Lp(a) concentrations were conducted in a group of 54 healthy adult men 23-61 years of age. Measures of dietary intake, exercise, smoking, alcohol ingestion, body mass index (BMI), fasting plasma lipoprotein lipid concentrations, and serum sex hormone and fasting glucose levels were also determined.

RESULTS

The fasting serum concentrations of insulin and Lp(a) were negatively correlated (r = -0.339, P = 0.014) by univariate regression analysis. Several confounding variables were also significantly correlated with Lp(a) concentrations: testosterone (r = 0.348, P = 0.012), strenuous exercise (r = 0.287, P = 0.041), and BMI (r = -0.276, P = 0.050). As expected, these additional variables and serum insulin concentrations were highly interrelated. In a stepwise regression model, the serum insulin level was identified as the single best predictor of Lp(a) levels. Nearly 25% of the heterogeneity in serum concentrations of Lp(a) could be predicted by serum levels of insulin and testosterone, BMI, and the amount of strenuous exercise.

CONCLUSIONS

The results of these studies have shown that serum concentrations of insulin and testosterone, BMI, and strenuous exercise appear to account for the majority of predicted nongenetic variability in serum levels of Lp(a). These observations suggest the possibility in this group of healthy men that serum concentrations of Lp(a) may be modulated by a complex interplay between insulin action, obesity, androgen levels, and strenuous exercise.

A new point mutation (C446R) in the thyroid hormone receptor-beta gene of a family with resistance to thyroid hormone

Resistance to thyroid hormone (RTH) is a condition of impaired end-organ responsiveness to thyroid hormone characterized by goiter and elevated thyroid hormone levels with an inappropriately normal TSH. RTH has been associated with mutations in the thyroid hormone receptor-beta (TR beta) gene. We report studies carried out in 21 members of a family (F119), 12 of whom exhibited the RTH phenotype. A point mutation was detected in the T3-binding domain of the TR beta gene. It resulted in replacement of the normal cysteine-446 with an arginine (C446R) that has not been previously reported. The clinical characteristics of this family are similar to those reported in other families with RTH, namely goiter, tachycardia, and learning disabilities. Thyroid function tests are also typical of other subjects with RTH. The mean values (+/- SD) in untreated affected subjects compared to those in unaffected family members were: free T4 index, 250 +/- 21 vs. 108 +/- 13; total T3, 4.3 +/- 0.4 vs. 2.4 +/- 0.4 nmol/L; and TSH, 4.5 +/- 1.1 vs. 2.4 +/- 1.1 mU/L. DNA samples from 18 family members were screened for the TR beta mutation, which results in the loss of a BsmI restriction site, and each of the 11 subjects with abnormal thyroid function tests were heterozygous for the mutant allele. The mutant TR beta expressed in Cos-I cells did not bind T3 (Ka of C446R/wild-type, < 0.05). T3 at a concentration up to 100 nmol/L failed to enhance the transactivation of a reporter gene, and the mutant receptor inhibited the T3-mediated transcriptional activation of the wild-type TR beta.

Exacerbation of rheumatoid arthritis by sodium fluoride treatment of osteoporosis

Recent studies have suggested that sodium fluoride therapy may be an effective treatment for vertebral osteoporosis. Unfortunately, the high frequency of side effects may limit the use of this treatment modality. This report documents the repeated exacerbation of rheumatoid arthritis on three occasions after the initiation of sodium fluoride therapy. This apparent complication of sodium fluoride treatment may be mediated by stimulation of leukocyte production of reactive oxygen species and other mediators of the acute inflammatory response. We suggest that sodium fluoride should be used cautiously in patients with rheumatoid arthritis.

Nonenzymatic glycosylation of HDL and impaired HDL-receptor-mediated cholesterol efflux

Previous studies have shown that nonenzymatic glycosylation of high-density lipoprotein (HDL) inhibits high-affinity binding to cultured cells and the candidate HDL-receptor protein. Because binding of HDL to its receptor is required for HDL-receptor-mediated cholesterol efflux from cells, we hypothesized that glycosylated HDL3 would have reduced ability to remove cholesterol from cells. HDL3 was glycosylated in vitro to achieve up to 40-50% reductions in free-lysine residues. Glycosylated HDL3 had a slightly greater ability than control HDL3 to sequester cholesterol directly from the plasma membrane, as predicted by changes in lipid composition. This process is independent of HDL-receptor binding and should not be influenced by reduced binding of HDL3. In contrast, efflux of intracellular cholesterol from cells, which is HDL-receptor dependent, was reduced 25-40%. The ability of glycosylated HDL3 to diminish cholesterol esterification was significantly reduced, indicating reduced net cholesterol efflux. Steady-state efflux of LDL-derived cholesterol was also markedly reduced. These findings suggest that nonenzymatically glycosylated HDL is functionally abnormal and might contribute to the accelerated development of atherosclerosis in patients with diabetes mellitus.

Potential role of insulin in the clearance of remnant lipoproteins in dysbetalipoproteinaemia

Dysbetalipoproteinaemia is a genetic disorder characterized by accumulation of lipoprotein remnant particles in the plasma, accelerated atherosclerosis, and the abnormal apoprotein E2. Uncontrolled diabetes mellitus can aggravate the hyperlipidaemia associated with this disorder, presumably by increasing triglyceride synthesis and reducing very low density lipoprotein catabolism by lipoprotein lipase. This report documents the gradual amelioration of dysbetalipoproteinaemia in uncontrolled diabetes mellitus following therapy with exogenous insulin alone. Although the beneficial effects of insulin therapy in this patient may include inhibition of triglyceride synthesis and improved triglyceride catabolism, we propose that insulin may also stimulate clearance of atherogenic remnant lipoprotein particles.

High glucose levels do not directly impair cellular binding of HDL3 or HDL-mediated efflux of cholesterol from human skin fibroblasts

The excess risk of atherosclerosis that is associated with diabetes mellitus cannot be completely accounted for by other known risk factors. Recent studies have suggested that increased glycation of high density lipoproteins (HDL) at high glucose concentrations causes functional abnormalities that might contribute to accelerated atherosclerosis. Other investigators also have shown that elevated glucose concentrations can stimulate the activity of protein kinase C in cultured cells. Because protein kinase C appears to be involved in HDL receptor-mediated efflux, the hypothesis that a high glucose concentration in vitro might modulate HDL-mediated efflux of cholesterol from human fibroblasts was tested. These studies indicate that a high glucose level alone does not affect the interaction of normal HDL3 with cultured human skin fibroblasts.

The relationship between sex hormones and high-density lipoprotein cholesterol levels in healthy adult men

The objective of this study was to clarify the complex and uncertain relationship between endogenous sex hormones and high-density lipoprotein (HDL) cholesterol levels in healthy men. Fifty-five healthy adult men were consecutively recruited from an ongoing cross-sectional study of cardiovascular disease risk factors from a lipid research clinic at the University of Washington, Seattle. Subjects receiving medication were excluded. Multiple linear regression analysis identified several factors that correlated highly significantly with HDL cholesterol levels, including alcohol intake; frequency of strenuous exercise; age; levels of total cholesterol, low-density lipoprotein cholesterol, and triglyceride; and carbohydrate intake. Nearly 80% of the heterogeneity in HDL cholesterol levels could be accounted for by these factors. Despite finding significant correlations with factors known to influence HDL cholesterol levels, no correlation with estradiol level, testosterone level, or the ratio of estradiol to testosterone levels was apparent. In conclusion, endogenous sex hormones do not appear to influence HDL cholesterol levels in healthy adult men. Alternatively, a large proportion of the heterogeneity in HDL levels in this group of men can be accounted for by environmental factors. The disparity between this conclusion and others may be partially due to differences in accounting for these confounding variables.

Nonenzymatic glycosylation of HDL resulting in inhibition of high-affinity binding to cultured human fibroblasts

Nonenzymatic glycosylation of plasma proteins may contribute to the excess risk of developing atherosclerosis in patients with diabetes mellitus. Because high-density lipoprotein (HDL) is believed to protect against atherosclerosis and is glycosylated at increased levels in diabetic individuals, the effects of nonenzymatic glycosylation of HDL3 on binding of HDL3 to cultured fibroblasts and to the candidate HDL-receptor protein were examined. HDL3 was glycosylated in vitro with glucose alone or in combination with sodium cyanoborohydride. With this catalyst, up to 40-50% of the lysine residues could be glycosylated, resulting in a progressive drop to nearly 60% in high-affinity binding to cultured fibroblasts at 4 degrees C. Binding to the 110,000-Mr candidate HDL-receptor protein was reduced by almost 75%. At levels of HDL glycosylation equivalent to the 3-5% observed in diabetes, high-affinity binding to fibroblasts at 4 degrees C was diminished by up to 15-20%. Binding kinetic studies paradoxically suggested that glycosylated HDL3 binds with higher affinity to a reduced number of binding sites. The findings in this study suggest that nonenzymatically glycosylated HDL may be functionally abnormal and might contribute to the development of atherosclerosis in patients with diabetes mellitus.

Henoch-Schönlein purpura following thiram exposure

Henoch-Schönlein purpura (HSP) is an uncommon, nonthrombocytopenic hypersensitivity vasculitis that is often idiopathic, but may be induced by infectious agents, drugs, foods, environmental chemicals, or insect bites. To our knowledge, we report the first recognized case of HSP following exposure to the widely used industrial and agricultural agent, tetramethylthiuram disulfide. Few reports of HSP or other vasculitides resulting from exposure to structurally similar compounds are available. Despite the widespread use of tetramethylthiuram disulfide, many cases of exposure may remain unrecognized, resulting in a subsequent failure to properly identify sequelae.