Xestospongins: potent membrane permeable blockers of the inositol 1,4,5-trisphosphate receptor.

Xestospongins (Xe's) A, C, D, araguspongine B, and demethylxestospongin B, a group of macrocyclic bis-1-oxaquinolizidines isolated from the Australian sponge, Xestospongia species, are shown to be potent blockers of IP3-mediated Ca2+ release from endoplasmic reticulum vesicles of rabbit cerebellum. XeC blocks IP3-induced Ca2+ release (IC50 = 358 nM) without interacting with the IP3-binding site, suggesting a mechanism that is independent of the IP3 effector site. Analysis of Pheochromocytoma cells and primary astrocytes loaded with Ca2+-sensitive dye reveals that XeC selectively blocks bradykinin- and carbamylcholine-induced Ca2+ efflux from endoplasmic reticulum stores. Xe's represent a new class of potent, membrane permeable IP3 receptor blockers exhibiting a high selectivity over ryanodine receptors. Xe's are a valuable tool for investigating the structure and function of IP3 receptors and Ca2+ signaling in neuronal and nonneuronal cells.

Specific caspase interactions and amplification are involved in selective neuronal vulnerability in Huntington's disease.

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder resulting in selective neuronal loss and dysfunction in the striatum and cortex. The molecular pathways leading to the selectivity of neuronal cell death in HD are poorly understood. Proteolytic processing of full-length mutant huntingtin (Htt) and subsequent events may play an important role in the selective neuronal cell death found in this disease. Despite the identification of Htt as a substrate for caspases, it is not known which caspase(s) cleaves Htt in vivo or whether regional expression of caspases contribute to selective neuronal cells loss. Here, we evaluate whether specific caspases are involved in cell death induced by mutant Htt and if this correlates with our recent finding that Htt is cleaved in vivo at the caspase consensus site 552. We find that caspase-2 cleaves Htt selectively at amino acid 552. Further, Htt recruits caspase-2 into an apoptosome-like complex. Binding of caspase-2 to Htt is polyglutamine repeat-length dependent, and therefore may serve as a critical initiation step in HD cell death. This hypothesis is supported by the requirement of caspase-2 for the death of mouse primary striatal cells derived from HD transgenic mice expressing full-length Htt (YAC72). Expression of catalytically inactive (dominant-negative) forms of caspase-2, caspase-7, and to some extent caspase-6, reduced the cell death of YAC72 primary striatal cells, while the catalytically inactive forms of caspase-3, -8, and -9 did not. Histological analysis of post-mortem human brain tissue and YAC72 mice revealed activation of caspases and enhanced caspase-2 immunoreactivity in medium spiny neurons of the striatum and the cortical projection neurons when compared to controls. Further, upregulation of caspase-2 correlates directly with decreased levels of brain-derived neurotrophic factor in the cortex and striatum of 3-month YAC72 transgenic mice and therefore suggests that these changes are early events in HD pathogenesis. These data support the involvement of caspase-2 in the selective neuronal cell death associated with HD in the striatum and cortex.

Renal involvement in Behçet's syndrome.

A retrospective study of 77 cases of Behçet's syndrome showed that, of the 33 patients in whom urinalysis was done (including three with systemic amyloidosis reported earlier), 17 had pathological results. A prospective study of 51 of these patients uncovered eight additional subjects with urinary abnormalities, bringing the total to 25. The urinary abnormality was, as a rule, discrete, consisting of proteinuria and/or microhematuria. These occurred in some patients persistently, in some intermittently, in some alternatingly, and in some simultaneously. The initial finding was proteinuria in 10 patients, hematuria in 11, and both in 4. Over the years, eight showed only hematuria, seven only proteinuria and ten, both. The urinary sediment contained neither leukocytes nor casts. Pyelographies were unrevealing when performed and rectal biopsies uncovered no new instance of amyloidosis. These data suggest that a benign renal lesion occurs in Behçet's syndrome, whose pathological substrate, though not yet defined, is not amyloid deposition.

Proximal renal tubular acidosis: association with familial normaldosteronemic hyperpotassemia and hypertension.

Further investigation of a family with normaldosteronemic hyperpotassemia and low-renin hypertension showed seven members from three generations, who ranged in age from 4 to 56 years, to be affected. Results of earlier studies had established a normally functioning renin-aldosterone system and normal renal handling of potassium. Constant, albeit mild and asymptomatic, metabolic acidosis in all those affected prompted bicarbonate loading in both the propositus and his brother, which revealed a maximal renal tubular excretory capacity for bicarbonate reabsorption at serum levels of 18 mmole/liter and proved proximal renal tubular acidosis (PRTA). Further, a linear increase in urinary fractional potassium excretion accompanied that of bicarbonate in both, as in normal individuals. Dextrose-insulin infusion in the brother failed to reduce hyperpotassemia. These data support the hypothesis that a generalized cell membrane defect that specifically impedes potassium influx (as opposed to an isolated renal tubular defect) underlies this autosomal dominant disorder.

Renal transplantation in the amyloidosis of familial Mediterranean fever. Experience in ten cases.

Ten patients with familial Mediterranean fever (FMF) and histologically confirmed amyloidosis received cadaver kidney transplants for treatment of terminal renal disease. Colchicine, 1 mg daily, was included in the routine postoperative regimen from 1974 for amyloidotic patients. Graft and patient survival were compared with ten nonamyloidotic recipients of renal grafts matched for age, sex, type of allograft, and HLA compatibility. In the FMF group, five of ten grafts have survived from 20 to 64 months; in the control group, six of ten. While only recipients with functioning grafts survived in the FMF group, patient survival in the control group is eight of ten after one year. In all five FMF survivors, graft function is satisfactory, proteinuria is absent, and blood creatinine levels are normal. Amyloid involvement of an allograft was documented 16 months after transplantation in the only patient whose maintenance colchicine dosage had been reduced to 0.5 mg daily.

Familial hyperpotassemia and hypertension accompanied by normal plasma aldosterone levels: possible hereditary cell membrane defect.

Hypertension and hyperpotassemia that were accompanied by normal plasma aldosterone and low renin levels and were responsive to chlorothiazide administration were found in a 29-year-old patient and two decades later in his 21-year-old son. Their renal function is normal, including response to sodium sulfate, mannitol, and aldosterone infusions. Adrenal insufficiency was excluded. The renin-aldosterone system was proved intact by physiological and pharmacologic stress and angiotensin-II infusion. Also normal were values for blood counts, blood volumes, and erythrocyte and exchangeable body potassium. The postulation of a defective cell membrane impeding potassium influx is supported by the failure of glucose and insulin infusions to substantially reduce hyperpotassemia. In the context of a hereditary disorder (the pedigree, compatible with autosomal dominant inheritance, includes five affected in two generations), hypertension is a second phenotypic character of a single defective pleiotropic gene although its pathogenesis remains unclear.

Controlled trial of propranolol in intermittent claudication.

Seven patients (5 with arteriosclerosis obliterans and 2 with Buerger's disease) completed a two-phase double-blind crossover trial of propranolol in intermittent claudication. Performance was measured on a moving treadmill. In the initial phase, the patients were hospitalized in order to determine an "effective" dose of propranolol. Improvement was noted in all: after 1,600 mg in 5 and after 240 mg and 600 mg in the others. The controlled phase was carried out on an outpatient basis over 8 weeks, the patients receiving propranolol and placebo in a random manner, each for two 2-week periods. Comparison of matched periods of drug and placebo revealed no advantage for propranolol. Patients' performances deteriorated with time. None of the patients evidenced deterioration of occlusive peripheral arterial disease that could be attributed to propranolol, in spite of the high doses used.

Incidence and origin of non-systemic microdeposits of amyloid.

In a general hospital, 391 consecutive necropsies in which at least seven organs were available, were examined retrospectively by polarizing microscopy of Congo-red-stained sections for the presence of local amyloid deposits.Non-systemic microdeposits of amyloid were encountered in 72 cases, an overall incidence of 18.4%. They were usually small and frequently detectable only by virtue of polarizing microscopy. There is no indication that these microdeposits of amyloid are of pathogenetic significance. Although they sometimes occur in more than one organ, such deposits can be readily distinguished from those of systemic amyloidosis by their histological features.

Brain infarction is not reduced in SOD-1 transgenic mice after a permanent focal cerebral ischemia.

Using a mouse model with intraluminal blockade of the middle cerebral artery (MCA) which produced both cortical and striatal infarction, the effect that superoxide radicals have on cerebral infarction, local cerebral blood flow, and neurological deficits after 24 h of permanent focal cerebral ischemia in transgenic mice (Tg) overexpressing human CuZn-superoxide dismutase (SOD-1) was examined. There were no difference between SOD-1 Tg mice and non-Tg littermates observed in the infarct areas of brain slices, the infarct volume, the local cerebral blood flow, or the neurological deficits. These data suggest that pre-existing high levels of antioxidant enzyme failed to provide neuronal protection against permanent focal cerebral ischemia.

Mild intraischemic hypothermia suppresses consumption of endogenous antioxidants after temporary focal ischemia in rats.

Oxidative damage by free radicals has been proposed as a mechanism of cerebral injury due to ischemia and reperfusion. Hypothermia protects against ischemic necrosis; however, its effect on oxidative stress has not been investigated. In this study, the effects of hypothermia on oxidative stress were studied by determining consumption of endogenous antioxidants after temporary focal ischemia in rats. Thirty-two Sprague-Dawley rats anesthetized with 1.5% isoflurane underwent 3 h of middle cerebral artery occlusion under hypothermic (33 degrees C) or normothermic (37 degrees C) conditions followed by 3 h of normothermic reperfusion. In the first study (n = 8 per group), intraischemic hypothermia suppressed the reduction of tissue concentrations of endogenous antioxidants, ascorbate (P < or = 0.05), and glutathione (P < or = 0.05) in ischemic cortex but not in caudoputamen. In a parallel study (n = 8 per group), hypothermia reduced tissue damage in ischemic frontoparietal cortex (P < or = 0.05), but not in caudoputamen. Laser-Doppler estimates of cortical blood flow showed that intraischemic hypothermia significantly attenuated early postischemic hyperperfusion (P < or = 0.01) and delayed postischemic hypoperfusion (P < or = 0.01). These results demonstrate that intraischemic mild hypothermia reduces oxidative stress and cell injury after prolonged focal ischemia followed by reperfusion. The reduction of oxidative stress by hypothermia may be related indirectly to attenuation of postischemic blood flow changes.