Effect of menopause on plaque morphologic characteristics in coronary atherosclerosis

Terrein: a new melanogenesis inhibitor and its mechanism

Terrein is a bioactive fungal metabolite whose effects are almost unknown. In this study, we found for the first time that terrein has a strong hypopigmentary effect in a spontaneously immortalized mouse melanocyte cell line, Mel-Ab. Treatment of Mel-Ab cells with terrein (10-100 microM) for 4 days significantly reduced melanin levels in a dose-dependent manner. In addition, terrein at the same concentration also reduced tyrosinase activity. We then investigated whether terrein influences the extracellular signal-regulated protein kinase (ERK) pathway and the expression of microphthalmia-associated transcription factor (MITF), which is required for tyrosinase expression. Terrein was found to induce sustained ERK activation and MITF down-regulation, and luciferase assays showed that terrein inhibits MITF promoter activity in a dose-dependent manner. To elucidate the correlation between ERK pathway activation and a decreased MITF transcriptional level, PD98059, a specific inhibitor of the ERK pathway, was applied before terrein treatment and found to abrogate the terrein-induced MITF attenuation. Terrein also reduced the tyrosinase protein level for at least 72 h. These results suggest that terrein reduces melanin synthesis by reducing tyrosinase production via ERK activation, and that this is followed by MITF down-regulation.

Postmenopausal hormone therapy: Critical reappraisal and a unified hypothesis

OBJECTIVE

To reconcile apparently conflicting evidence regarding the use of hormone therapy as a health-preserving strategy in postmenopausal women in light of that fact that findings from animal studies, human observation studies, and human clinical trials are consistent for outcomes such as fracture and breast cancer but differ for coronary heart disease (CHD).

DESIGN

Literature review and generation of a unified hypothesis consistent with all of the data.

SETTING

Animal trials, human observational studies, human studies of biologic intermediates, and human clinical trials.

PATIENT(S)

Premenopausal and postmenopausal women with or without antecedent CHD.

MAIN OUTCOME MEASURE(S)

Coronary heart disease events, proxies, risk factors, and related mechanisms.

RESULT(S)

The complex CHD responses to hormone therapy in recent human trials likely reflect a combination of [1] early erosion/rupture of "vulnerable" coronary plaque, which is made worse by hormone therapy, [2] long-term reduction in plaque formation, which is improved by hormone therapy, and [3] modulation of the vasculoprotective actions of estrogens by systemic progestogens.

CONCLUSION(S)

The unified hypothesis predicts that hormone therapy initiated at the time of menopause should produce a decrease in CHD over time. In contrast, hormone therapy begun years after menopause should produce an increase in CHD events shortly after therapy is begun, followed later by benefit. In women who require progestogens for endometrial protection, there should be greater CHD benefit from use of progestogens with less systemic activity. The unified hypothesis is consistent both with plausible biologic mechanisms and with evidence from animal studies, human observational studies, and human clinical trials such as the Women's Health Initiative. In the absence of evidence from human trials that specifically involve initiation of hormone therapy in perimenopausal women, practitioners and patients can use the unified hypothesis as a rational tool to guide decisions about clinical management.

Vulnerable plaque: the pathology of unstable coronary lesions

Vulnerable plaques have been defined as precursors to lesions that rupture. However, coronary thrombosis may occur from other lesions like plaque erosion and calcified nodules, although to a lesser frequency than rupture. Therefore, the definition of vulnerable plaque should be all-inclusive. Using descriptive terminology, the authors define the precursor lesion of plaque rupture as "thin-cap fibroatheroma" (TCFA). Morphologically, TCFAs have a necrotic core with an overlying thin fibrous cap (< 65 mm) consisting of collagen type I, which is infiltrated by macrophages. These lesions are most frequent in the coronary tree of patients dying with acute myocardial infarction and least common in those with plaque erosion. TCFAs are more common in patients with high serum total cholesterol (TC) and a high TC to high density cholesterol ratio, in women > 50 years, and in those patients with elevated levels of high sensitivity C-reactive protein. TCFAs are mostly found in the proximal left anterior descending coronary arteries and less commonly in the proximal right or the proximal left circumflex coronary arteries. In TCFAs, necrotic core length is approximately 2-17 mm (mean 8 mm) and the underlying cross-sectional luminal narrowing in over 75% of cases is < 75% (< 50% diameter stenosis). The area of the necrotic core in at least 75% of cases is < or = 3 mm2. Clinical studies of TCFAs are limited as angiography and intravascular ultrasound (IVUS) catheters cannot precisely identify these lesions. Newer catheters and other techniques are at various stages of development and will play a significant role in the understanding of plaque progression and the development of symptomatic coronary artery disease.

Angioscopic evaluation of the effect of estrogen on ovariectomized Japanese monkeys

Using angioscopy to study the atheroprotective effect of estrogen, atherosclerotic changes in surgically postmenopausal Japanese monkeys were observed for a long period. Changes in serum lipids and estradiol were also followed. About 3-6 months after the 2% cholesterol diet, serum cholesterol increased up to three times normal value, and atheroma was first found at the orifice of major branches of the abdominal aorta. However, in the other group of 2% cholesterol including an oral estrogen diet, the appearance of atheroma was inhibited until 12 months, although serum cholesterol increased gradually. The chronologic investigation was continued over 3 years. From these results we concluded that the most important atheroprotective effect of estrogen is the direct inhibition of atherosclerosis in the arterial wall, and improvement in lipid metabolism is of secondary importance.

Hormone replacement therapy for prevention of coronary heart disease: current evidence

Postmenopausal estrogen replacement, with or without progestin therapy, has a generally favorable impact on lipids, improves endothelial function, and has anti-inflammatory and antioxidant effects. These properties should favorably impact coronary risk; indeed, epidemiologic studies have consistently associated hormone replacement therapy with reduced coronary risk. Nonetheless, the Heart & Estrogen/progestin Replacement Study (HERS), a randomized, placebo-controlled, secondary prevention trial of conjugated estrogen with progestin, found no overall reduction in coronary events among women assigned to active hormone treatment. This review explores the role of estrogen replacement among interventions intended to prevent coronary heart disease in the post-HERS era.

Postmenopausal oestrogen replacement therapy and atherosclerosis: can current compounds provide cardiovascular protection?

The natural oestrogen, 17 beta-oestradiol, has been implicated in protection from atherosclerosis, a chronic systemic vascular disease with an inflammatory component accounting for the majority of morbidity and mortality in Western countries. Despite the protective effects of 17 beta-oestradiol in premenopausal women and experimental evidence demonstrating inhibitory effects of oestrogen on atherosclerosis progression, it is currently unclear whether hormone replacement therapy can affect cardiovascular morbidity and mortality in postmenopausal women. The recent advances in understanding the mechanisms of oestrogen action demonstrated roles for different oestrogen receptors and oestrogen metabolites in the pathogenesis of vascular injury and endothelial cell dysfunction. However, their respective role in the process of atherogenesis remains yet to be elucidated. Moreover, the availability of novel drugs with tissue- and/or receptor-specific actions will help to understand the role of oestrogen in cardiovascular diseases. Several ongoing large-scale clinical trials using opposed or unopposed replacement therapy with natural or synthetic oestrogens, or selective oestrogen receptor modulators (SERMs) will resolve the question whether the drugs currently available have therapeutic potential to interfere with the progression of atherosclerosis and its complications.