Biogenesis of the secretory granule: chromogranin A coiled-coil structure results in unusual physical properties and suggests a mechanism for granule core condensation

The secretory pro-hormone chromogranin A (CHGA) is densely packed into storage granules along with catecholamines, playing a catalytic role in granule biogenesis. 3-Dimensional structural data on CHGA are lacking. We found a superfamily structural homology for CHGA in the tropomyosin family of alpha-helical coiled-coils, even in mid-molecule regions where primary sequence identity is only modest. The assignment was confirmed by an independent algorithm, suggesting approximately 6-7 such domains spanning CHGA. We provide additional physiochemical evidence (chromatographic, spectral, microscopic) consistent with this unusual structure. Alpha-helical secondary structure (at up to approximately 45%) was confirmed by circular dichroism. CHGA molecular mass was estimated by MALDI-TOF mass spectrometry at approximately 50 kDa and by denaturing gel filtration at approximately 50-61 kDa, while its native Stokes radius was approximately 84.8 A, as compared to an expected approximately 30 A; the increase gave rise to an apparent native molecular weight of approximately 578 kDa, also consistent with the extended conformation of a coiled-coil. Small-angle X-ray scattering (SAXS) on CHGA in solution best fit an elongated cylindrical conformation in the monodisperse region with a radius of gyration of the rod cross-section (Rt) of approximately 52 A, compatible with a coiled-coil in the hydrated, aqueous state, or a multimeric coiled-coil. Electron microscopy with negative staining revealed an extended, filamentous CHGA structure with a diameter of approximately 94 +/- 4.5 A. Extended, coiled-coil conformation is likely to permit protein "packing" in the secretory granule at approximately 50% higher density than a globular/spherical conformation. Natural allelic variation in the catestatin region was predicted to disrupt the coiled-coil. Chromaffin granule ultrastructure revealed a approximately 108 +/- 6.3 A periodicity of electron density, suggesting nucleation of a binding complex by the CHGA core. Inhibition of CHGA expression, by siRNA, disrupted regulated secretory protein traffic by approximately 65%, while targeted ablation of the CHGA gene in the mouse reduced chromaffin granule cotransmitter concentrations by approximately 40-80%. These results suggest new roles for secretory protein tertiary structure in hormone and transmitter storage, with implications for secretory cargo condensation (or dense core "packing" structure) within the regulated pathway.

Severe preeclampsia with fulminant and extreme elevation of aspartate aminotransferase and lactate dehydrogenase levels: high risk for maternal death

We report a subgroup of patients with fulminant hemolysis, elevated liver enzymes, low platelet count (HELLP) syndrome, manifesting extreme elevation of aspartate aminotransferase (AST; SGOT) and lactate dehydrogenase (LDH) levels and abnormal mental status. These gravidas are at high risk for mortality. Only four patients treated by the authors over a 10-year period have had AST more than 2000 IU/L and LDH more than 3000 IU/L in the HELLP syndrome. This report is based on retrospective chart review. All patients manifested disordered mental status, jaundice, intense hemolysis, and extreme hypertension. One patient had developed multiple organ system failure, was moribund at initial perinatal consultation, and died. The three others were treated with aggressive afterload reduction and plasma infusion or plasmapheresis; two survived. Fulminant HELLP syndrome occurs rarely, but marks a group of patients at high risk for mortality. Optimal therapy is unclear; early intervention, including afterload reduction, volume expansion, and consideration of plasma infusions or plasmapheresis, is recommended.

Bilateral renal artery stenosis: presenting as a case of scleroderma renal crisis

A patient with long-standing scleroderma who developed malignant hypertension is presented. Renal insufficiency aggravated by the use of angiotensin-converting-enzyme inhibition prompted renal angiography. The latter demonstrated bilateral renal artery stenosis, an uncommon coexistence of two infrequent disorders.

Thrombotic thrombocytopenic purpura in human immunodeficiency (HIV)-seropositive males

Two male patients with thrombotic thrombocytopenic purpura (TTP) were found to have antibodies to the human immunodeficiency virus (HIV). In one patient, platelet-associated antibody levels were measured serially and were found to be initially elevated, but the levels decreased with initiation of successful therapy. The simultaneous occurrence of these two conditions in two of three patients admitted for TTP within the previous 2 years at this institution suggests an association between the two diseases. The precise nature of this association remains speculative inasmuch as the pathogenesis of TTP remains uncertain.

Contrasting renal haemodynamic responses to the angiotensin converting enzyme inhibitor enalapril and the beta-adrenergic antagonist metoprolol in essential hypertension

The individual target organ response to blood pressure reduction is an important criterion in the selection of appropriate antihypertensive therapy. We assessed both the renal and the systemic haemodynamic responses to antihypertensive monotherapy (five to seven weeks) with the angiotensin converting enzyme (ACE) inhibitor enalapril (n = 12), in contrast to the cardioselective beta-adrenergic blocker metoprolol (n = 11) in subjects with essential hypertension. Enalapril lowered systolic and diastolic blood pressure, and the fall in blood pressure was mediated haemodynamically by a 34% fall in systemic vascular resistance. In the kidney, glomerular filtration rate, renal plasma flow and renal blood flow were maintained by a 23% fall in renal vascular resistance. The disproportionate fall in systemic resistance versus renal resistance actually reduced the renal fraction of cardiac output. By contrast, metoprolol lowered predominantly diastolic blood pressure, with an associated 25% fall in cardiac output, without significant changes in overall systemic vascular resistance. In the renal circulation, renal perfusion was well maintained by a 20% fall in renal vascular resistance, perhaps at the efferent arteriole, without change in the renal fraction of cardiac output. Neither drug altered weight, plasma volume or total blood volume. Thus, each drug represents effective antihypertensive monotherapy, with a generally favourable, though different, renal haemodynamic profile, characterized by effective autoregulation of renal perfusion even in the face of a fall in perfusion pressure.

Diabetic neuropathic pain: control by amitriptyline and fluphenazine in renal insufficiency

Seven patients with diabetes of ten to 24 years' duration and renal insufficiency were treated with fluphenazine and amitriptyline in an attempt to control severe pain in the extremities. Six patients had relief of pain within five days of initiation of therapy. One patient had no pain relief despite mood alteration. The relief of pain persisted whether renal function was stable or declining. This form of therapy is safe and as effective in patients with neuropathic pain and mild to moderate renal insufficiency as in patients with normal renal function.

Successful medical management of bilateral ureteral obstruction due to acute uric acid nephropathy

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