An iron-sulfur cluster plays a novel regulatory role in the iron-responsive element binding protein

Post-transcriptional regulation of genes important in iron metabolism, ferritin and the transferrin receptor (TfR), is achieved through regulated binding of a cytosolic protein, the iron-responsive element binding protein (IRE-BP), to RNA stem-loop motifs known as iron-responsive elements (IREs). Binding of the IRE-BP represses ferritin translation and represses degradation of the TfR mRNA. The IRE-BP senses iron levels and accordingly modifies binding to IREs through a novel sensing mechanism. An iron-sulfur cluster of the IRE-BP reversibly binds iron; when cytosolic iron levels are depleted, the cluster becomes depleted of iron and the IRE-BP acquires the capacity to bind IREs. When cytosolic iron levels are replete, the IRE-BP loses RNA binding capacity, but acquires enzymatic activity as a functional aconitase. RNA binding and aconitase activity are mutually exclusive activities of the IRE-BP, and the state of the iron-sulfur cluster determines how the IRE-BP will function.

A regulated RNA binding protein also possesses aconitase activity

A clone for the iron-responsive element (IRE)-binding protein (IRE-BP) has been transfected and expressed in mouse fibroblasts. The IRE-BP gene product binds IREs with high affinity and specificity. Amino acid alignments reveal that the IRE-BP is 30% identical to mitochondrial aconitase. The 18 active site residues of mitochondrial aconitase are identical to those in the IRE-BP, suggesting that the IRE-BP may possess aconitase activity. After purification of native IRE-BP and immunoaffinity purification of transfected and expressed IRE-BP, we demonstrate that the purified IRE-BP has aconitase activity.

Assessing the residential care needs of nursing home applicants

In a study of nursing home applicants, residential care decisions made by a multidisciplinary assessment team were examined. The team agreed that of the 296 applicants assessed, 54 per cent required the high level of physical and supportive care provided in a nursing home. Hostel care was recommended for 17 per cent, continuing care at home for 17 per cent, hospice care for 1 subject, and in 13 per cent of cases the team postponed their decision. A decision for nursing home care was associated with low Barthel Index of Activities of Daily Living scores, dementia, incontinence and the absence of a carer willing to continue care. A decision to delay was associated, in most cases, with a requirement for further in-patient assessment and/or rehabilitation, and therefore with a potential for functional improvement. A decision for hostel care instead of home care was associated with a low level of informal support and the absence of a carer who was a spouse or daughter. The findings suggest that a program of geriatric assessment will accurately identify the differing care needs of nursing home applicants. The initial value of such an assessment program may be to contribute to the planning of residential and other long-term care services rather than to reduce inappropriate nursing home admissions.

Differences in red blood cell choline and lipid-bound choline between patients with Alzheimer disease and control subjects

The concentrations of red blood cell choline, glycerophosphocholine, phosphocholine and lipid-bound choline were measured in patients with Alzheimer disease (AD) and in normal elderly controls. Red blood cell choline in the Alzheimer group (41.4 +/- 9.2 nmol/ml) was significantly higher (p less than 0.023) than in the elderly controls (18.7 +/- 2.3 nmol/ml). Red blood cell lipid-bound choline (1387 +/- 58 nmol/ml) in the AD group was significantly lower (p less than 0.0022) than in the age-matched controls (1667 +/- 65), while there were no significant differences in glycerophosphocholine or phosphocholine. Plasma choline and lipid-bound choline did not differ significantly between the groups. The mechanisms for these changes still need further study, although the finding of decreased lipid-bound choline supports the concept of altered phospholipid metabolism in patients with AD.

Changes in red blood cell choline and choline-bound lipids with oral lithium

The influence of oral lithium on the concentration of red blood cell choline (Ch), lecithin, glycerophosphorylcholine (GPCh) and phosphorylcholine (PCh) was studied. The concentration of RBC Ch was significantly elevated and the concentration of lecithin, GPCh and PCh significantly depressed in 16 patients on oral lithium compared to 9 age-matched controls. We conclude that lithium markedly depletes the red blood cell of choline containing compounds including lecithin. These changes may be responsible for both the therapeutic efficacy and the toxicity of lithium.

Atrial structure and plasma ANF levels in rats with chronic diabetes mellitus

The effect of streptozocin-induced diabetes (STZ-D) on right atrial structure was investigated in male Wistar rats. STZ (55 mg/kg) or saline (1 ml/kg) was administered by intravenous injection 12 wk before the experimental studies. Tissue was sampled from four regions of the atrium, processed, and embedded in plastic. Quantitative stereological analysis indicated that in STZ-D rats, there was a significant diminution in size of the musculi pectinati (muscular ridges), which form a network making up the wall of the atrium. In addition, within the muscular ridges, there was a significant reduction in the relative proportion of cardiocytes within the cardiac tissue. The rest of the cardiac tissue consisted of interstitial regions, connective tissue, and blood vessels, which correspondingly increased. This suggests there was some form of cardiomyopathy. When atrial granularity was determined relative to cardiocyte volume density, a significant decrease (54%) was found in tissue from STZ-D rats. The blood pressure of conscious STZ-D rats was significantly lower than control rats, whereas right atrial pressure was not different. The level of resting plasma immunoreactive atrial natriuretic factor (ANF) in conscious STZ-D rats (98 +/- 5 pg/ml) was significantly higher than in control rats (52 +/- 7 pg/ml). The decreased atrial granularity could be related to the higher resting plasma ANF levels, suggesting a more rapid turnover or increased synthesis bypassing storage in the granular form.

Changes in the somatosensory evoked potential during and immediately following temporary middle cerebral artery occlusion predict somatosensory cortex ischemic lesions in monkeys

Somatosensory evoked potentials (SEP) were recorded during and immediately following temporary middle cerebral artery (MCA) occlusion to determine whether they can be used to predict ischemic lesions to the somatosensory cortex (SI). Twenty-one cynomolgus female monkeys were subjected to four different MCA occlusion durations (15-60 min) during hypotension (45-50 mm Hg mean arterial blood pressure). The amplitude and central conduction time (CCT) of the median nerve SEP were recorded preceding, during, and following occlusion. Two groups were established based on the development of SI ischemic lesions: animals developing SI lesions formed the SI-lesion group (n = 9), and animals without ischemic lesions or with lesions outside the SI cortex formed the SI-spared group (n = 12). Changes in the SEP during and following MCA occlusion under conditions of hypotension were similar to those reported by others. The SEP disappeared in all animals within 15 min of occlusion and reappeared 5 min following reperfusion. Several differences were observed between the SI-lesion and SI-spared groups. The SI-lesion group had a more rapid decrease in SEP amplitude during the first 5 min of occlusion and had smaller SEP amplitudes and longer CCTs during reperfusion. These results suggest that changes in SEP amplitude and latency during and immediately following temporary MCA occlusion predict development of SI ischemic lesions.

Association of DOCA hypertension with induction of atherosclerosis in rats with short-term diabetes mellitus

We investigated the effect of deoxycorticosterone acetate (DOCA)-induced hypertension on plasma lipid and cholesterol levels and the development of vascular atherosclerotic changes in male Wistar rats injected with streptozotocin (STZ) or saline (CON). Rats given STZ alone demonstrated a mild hyperlipidemia and hypercholesterolemia without any change in blood pressure. One week of DOCA administration was without effect on blood pressure in CON and STZ groups, but at 3 and 6 wk caused a significant and similar elevation in both groups. This DOCA-induced elevation in blood pressure appeared to be associated with the increase in plasma lipid and cholesterol levels seen in both CON and STZ groups at 3 and 6 wk, although the elevation in lipid and cholesterol levels was significantly more pronounced in the STZ rats. Both CON and STZ groups injected with DOCA developed significant pathological changes in all vessels under investigation. However, the degree of atherosclerosis appeared, from a semiquantitative analysis, to be worse in the thoracic aortas and renal arteries of the STZ group. Neither normotensive group developed any atherosclerosis. It is concluded that hypertension is associated with atherosclerosis in normal rats and rats with short-term STZ-induced diabetes mellitus, although the higher plasma lipid and cholesterol levels of the latter group may potentiate the degree of vascular damage.

Low-grade B-cell lymphoma of mucosa-associated lymphoid tissue arising in the thymus. A thymic lymphoma mimicking myoepithelial sialadenitis

We describe two cases of primary low-grade B-cell lymphoma of the thymus that showed histological features of low-grade B-cell lymphoma arising in mucosa-associated lymphoid tissue (MALT). The appearances most closely resembled MALT lymphoma arising in myoepithelial sialadenitis (MESA). In both cases, the tumor was excised. In one case, there has been no recurrence in 4 years of follow-up without further treatment; in the second case, the tumor has involved an axillary lymph node. Immunohistochemistry showed light-chain restriction in both cases, and the B-cell phenotype was similar to that previously described in MALT lymphomas. The occurrence of MALT lymphoma in the thymus is consistent with the presence of mucosal structures (Hassall's corpuscles) and with recent descriptions of a native B-cell population in this organ. The relationship of this previously undescribed thymic low-grade B-cell MALT lymphoma arising in the thymus has not yet been clarified.

Primate brain tolerance to temporary focal cerebral ischemia during isoflurane- or sodium nitroprusside-induced hypotension

Isoflurane has properties that suggest it may provide cerebral protection from ischemia. This study compared, in primates, neurologic outcome after a 45-min period of temporary focal ischemia during hypotension induced with either isoflurane or sodium nitroprusside (SNP). Fourteen macaque monkeys were studied. Seven animals received halothane and seven isoflurane anesthesia during surgical preparation. After transorbital exposure of the middle cerebral artery (MCA), in the halothane group, the inspired halothane was reduced to 0.75% and the mean blood pressure (BP) reduced to 50 mmHg by the infusion of SNP. In the isoflurane group, the isoflurane was titrated to reduce mean BP to 50 mmHg. Stable hypotension was maintained for 90 min, which included a 45-min period of MCA occlusion. Monitoring included intraarterial blood pressure, arterial blood gases, EEG, somatosensory evoked potentials (SEP), and temperature. After the procedure the animals were allowed to awaken and were assessed neurologically every 8 h. On the third postoperative day, they were reanesthetized and underwent magnetic resonance imaging (MRI) and SEP recording. Thereafter, they were killed with iv KCl and the brains fixed for neuropathology. All animals survived the surgical procedure, but two animals receiving halothane and none receiving isoflurane died prematurely (P less than 0.2). The SEP disappeared in all animals within 10 min of MCA occlusion and then returned partially or completely. There was no difference between groups in neurologic scores, in the size of the lesion as assessed by MRI (isoflurane 15.7 +/- 6%, halothane/SNP 10.5 +/- 4%), or in the extent or severity of the neuropathologic lesions.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors influencing erythrocyte choline concentrations

Choline concentrations in human erythrocytes increase after freezing and thawing, during incubation in Krebs-phosphate for 30 min or on storage at 0 degrees C for 3-24 hr. The increase is prevented by protein precipitation by 10% perchloric acid, 10% zinc hydroxide, 10% sodium tungstate or boiling in water. It is not prevented by EDTA (10 mM) and is increased by oleate (5 mM). We suggest that the increase is due to the action of phospholipase D on erythrocyte phospholipids.

Pharmacokinetics of vasopressin and atrial natriuretic peptide in anesthetized rabbits

The elimination from plasma of the peptide hormones vasopressin (VP) and atrial natriuretic peptide (ANP) as well as the time course of release and elimination of these hormones after a physiological stimulus were studied in anesthetized rabbits. As an inverse relationship was found to exist between carotid sinus pressure and plasma IR-ANP, a decrease in carotid sinus pressure to 60 mm Hg was used to stimulate ANP as well as VP release. The elimination of VP after iv injection involved a rapid initial phase and a slow late component, with corresponding half-life (t1/2) values of 0.9 and 5.4 min, respectively. After reduction of carotid sinus pressure to 60 mm Hg, plasma VP increased significantly within 1 min and reached a maximum at 10 min. When carotid sinus pressure was increased to 160 mm Hg to inhibit VP release, the t1/2 of VP was 1.3 min. The t1/2 of immunoreactive (IR) ANP after iv infusion was 1.2 min. Plasma IR-ANP was significantly increased 2 min after carotid sinus pressure was decreased, and a maximum was observed at 10 min. The t1/2 of IR-ANP after elevation of carotid sinus pressure to 160 mm Hg was 3.2 min. These studies indicate that both VP and IR-ANP are rapidly eliminated in the anesthetized rabbit.

Brain tolerance to middle cerebral artery occlusion during hypotension in primates

The aim of this study was to determine the duration of middle cerebral artery occlusion required to produce significant ischemic damage when the occlusion occurs during controlled systemic hypotension. In 21 anesthetized cynomolgus monkeys, an IV infusion of sodium nitroprusside was used to lower the mean arterial blood pressure to 45-50 mmHg for 90 minutes. Middle cerebral artery occlusion for 15, 30, 45, or 60 minutes was performed during the hypotensive period. Neurological function was then evaluated every 8 hours for a total of 72 hours. At the end of the observation period, the monkeys were again anesthetized, magnetic resonance imaging was performed, and the brain was perfused with 10% buffered formalin. Neurological deficits were observed after 30 minutes, but not after 15 minutes, of middle cerebral artery occlusion, and rapidly increased in incidence and severity when the duration of occlusion was increased. After 60 minutes of occlusion, all the monkeys exhibited severe deficits. Four monkeys died during the observation period--two in each of the 45- and 60-minute occlusion groups. Histopathological examination revealed that little or no ischemic damage resulted from a 15-minute occlusion during hypotension. However, severe ischemic damage began to occur after only 30 minutes of occlusion, and all monkeys subjected to middle cerebral artery occlusion for 60 minutes developed extensive regions of infarction. The size and incidence of these infarctions correlated well with the lesions observed in the magnetic resonance images. These results demonstrate that the duration of middle cerebral artery occlusion that produces cerebral infarction in primates is drastically reduced when the occlusion occurs at hypotensive levels commonly employed during neurovascular surgical procedures.