(18)F-Florbetapir PET may be a promising technique to image light chain and transthyretin cardiac amyloidosis. Its role in diagnosing amyloid in other organ systems and in assessing response to therapy needs to be further studied.

Objectives We sought to test the hypothesis that coronary microvascular function is impaired in subjects with cardiac amyloidosis. Background Effort angina is common in subjects with cardiac amyloidosis even in the absence of epicardial coronary artery disease (CAD). Methods Thirty one subjects were prospectively enrolled in this study including 21 subjects with definite cardiac amyloidosis without epicardial CAD and 10 subjects with hypertensive left ventricular hypertrophy (LVH). All subjects underwent rest and vasodilator stress N-13 ammonia positron emission tomography and 2D echocardiography. Global LV myocardial blood flow (MBF) was quantified at rest and during peak hyperemia, and coronary flow reserve (CFR) was computed (peak stress MBF / rest MBF) adjusting for rest rate pressure product. Results Compared to the LVH group, the amyloid group showed lower rest MBF (0.59 ± 0.15 vs. 0.88 ± 0.23 ml/g/min, P = 0.004), stress MBF (0.85 ± 0.29 vs. 1.85 ± 0.45 vs. ml/min/g, P < 0.0001), CFR (1.19 ± 0.38 vs. 2.23 ± 0.88, P < 0.0001), and higher minimal coronary vascular resistance (111 ± 40 vs. 70 ± 19 mm Hg/mL/g/min, P = 0.004). Of note, almost all amyloid subjects (> 95%) demonstrated significantly reduced peak stress MBF (< 1.3 mL/g/min). In multivariable linear regression analyses, a diagnosis of amyloidosis, increased LV mass and age were the only independent predictors of impaired coronary vasodilator function. Conclusions Coronary microvascular dysfunction is highly prevalent in subjects with cardiac amyloidosis even in the absence of epicardial CAD, and may explain their anginal symptoms. Further study is required to understand whether specific therapy directed at amyloidosis may improve coronary vasomotion in amyloidosis.

The first major step of cysteine catabolism, the oxidation of cysteine to cysteine sulfinic acid, is catalyzed by cysteine dioxygenase (CDO). In the present work, we utilize recombinant rat liver CDO and cysteine derivatives to elucidate structural parameters involved in substrate recognition and x-ray absorption spectroscopy to probe the interaction of the active site iron center with cysteine. Kinetic studies using cysteine structural analogs show that most are inhibitors and that a terminal functional group bearing a negative charge (e.g. a carboxylate) is required for binding. The substrate-binding site has no stringent restrictions with respect to the size of the amino acid. Lack of the amino or carboxyl groups at the ␣-carbon does not prevent the molecules from interacting with the active site. In fact, cysteamine is shown to be a potent activator of the enzyme without being a substrate. CDO was also rendered inactive upon complexation with the metal-binding inhibitors azide and cyanide. Unlike many non-heme iron dioxygenases that employ ␣-keto acids as cofactors, CDO was shown to be the only dioxygenase known to be inhibited by ␣-ketoglutarate.The first major step in cysteine catabolism involves its conversion to cysteine sulfinic acid by cysteine dioxygenase (CDO), 2 which is a nonheme iron-containing dioxygenase present in mammalian tissues. CDO plays an important role in the formation of essential metabolites such as taurine and sulfate. Because cysteine is toxic at high levels (1), CDO assists in maintaining low intracellular cysteine levels without compromising its availability for incorporation into proteins and synthesis of major metabolites.Since the early studies on CDO by Sörbo and Ewetz (2), there have been great advances in understanding the regulation and biochemical properties of this enzyme. However, there is little information regarding the active site of CDO and its specificity for the only known substrate, L-cysteine (3).Herein we report the results of probing the active site requirements of CDO with cysteine structural analogs and the substrate binding mode with x-ray absorption spectroscopy. In addition to exploring the features required for enzyme inhibition, using substrate derivatives has attracted attention in the development of potent and target-specific drugs (4, 5). Because CDO is at a crucial branching point of cysteine catabolism, and several diseases have been linked to this metalloenzyme (6 -8), information about substrate recognition also provides insights for drug design. Many of the cysteine analogs utilized in our current work are metabolites that are present in mammalian cells, and their interaction with CDO could aid in unraveling thiol homeostasis and regulation. MATERIALS AND METHODSChemicals-Cysteine, cysteine sulfinic acid, and heptafluorobutyric acid were obtained from Aldrich Chemical Co. Sodium phosphate, sodium chloride, and ferrous sulfate were purchased from Fisher Scientific. Yeast extract, Tryptone, phenylmethylsulfonyl fluoride, ampicillin, chloramphenicol...