Amiloride directly inhibits growth factor receptor tyrosine kinase activity

Addition of amiloride to A431 human epidermoid carcinoma cell membranes inhibited autophosphorylation of the epidermal growth factor (EGF) receptor. The tyrosine phosphorylation of histone H2B catalyzed by an affinity-purified preparation of EGF receptor was also inhibited by amiloride. The inhibition was noncompetitive with respect to histone but competitive with ATP, suggesting that amiloride may act as an ATP analogue which causes the formation of nonproductive enzyme-substrate complexes. The tyrosine phosphorylation of histone H2B catalyzed by the purified EGF receptor was inhibited by amiloride at concentrations identical to those previously reported to block EGF action on cell proliferation (Ki = 350 microM). Amiloride similarly inhibited the tyrosine phosphorylation of the human placental insulin receptor and the platelet-derived growth factor receptor of Swiss 3T3 cells. Immunoprecipitation of the EGF receptor from A431 cells labeled for 24 h with [32P]phosphate demonstrated that amiloride decreased the phosphorylation of the EGF receptor on serine and threonine residues and blocked the effect of EGF to cause phosphorylation of the receptor on tyrosine residues. Phosphoamino acid analysis of total cell proteins indicated that amiloride inhibited the increase in phosphotyrosine levels caused by EGF. We conclude that amiloride directly inhibits the tyrosine kinase activity of the receptors for EGF, insulin, and platelet-derived growth factor in in vitro and can mediate such actions in vivo. This effect of amiloride demonstrates that it is unsuitable as a drug to test the hypothesis that the stimulation of the Na+/H+ antiporter is essential for mitogenic signaling by growth factor receptors.

sn-1,2-Dioctanoylglycerol. A cell-permeable diacylglycerol that mimics phorbol diester action on the epidermal growth factor receptor and mitogenesis

The cell-permeable diacylglycerol, sn-1,2-dioctanoylglycerol (DiC8), is shown to mimic the effect of tumor promoting phorbol diesters on epidermal growth factor (EGF) binding and action in intact cells. DiC8 inhibited the binding of [3H]phorbol dibutyrate to A431 cell monolayers indicating that the diacylglycerol interacts with the phorbol diester receptor. At 0.3 microM, DiC8 half-maximally inhibited the high affinity binding of 125I-EGF to A431 human epidermoid carcinoma cells. Scatchard analysis indicated that the inhibition of 125I-EGF binding was very similar to that observed in the presence of 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). DiC8 also mimicked the action of PMA to increase the phosphorylation state of the EGF receptor in 32P-labeled cells. Phosphoamino acid analysis demonstrated that DiC8 and PMA caused an increase in the level of EGF-receptor phosphoserine and phosphothreonine, whereas EGF caused an increase in the level of phosphoserine, phosphothreonine, and phosphotyrosine. Phosphopeptide mapping of the EGF receptor showed that DiC8 and PMA enhanced the phosphorylation of the same tryptic peptides. DiC8 inhibited the EGF-dependent tyrosine phosphorylation of the EGF receptor in A431 cells in a similar manner to that observed with PMA. In further experiments with quiescent Swiss 3T3 fibroblasts, DiC8 mimicked the ability of PMA to stimulate the incorporation of [methyl-3H]thymidine synergistically with low concentrations of EGF. This result indicates that DiC8 will mimic the long-term effects of PMA to regulate mitogenesis and raises the possibility that it may be active in two stage carcinogenesis. As both DiC8 and PMA stimulate the Ca2+- and phospholipid-dependent protein kinase (C-kinase) in vitro, the results support the hypothesis that the activation of C-kinase is a critical component of phorbol diester action on EGF receptor modulation and cell proliferation.

Tumor-promoting phorbol diesters mediate phosphorylation of the epidermal growth factor receptor

4 beta-Phorbol 12 beta-myristate 13 alpha-acetate (PMA) markedly inhibited the binding of low concentrations (less than 10(-9 m) of 125I-epidermal growth factor (EGF) to A431 human epidermoid carcinoma cells. However, very little change in the binding of 125-I-EGF at high concentrations (greater than 10(-8) M) was observed in response to PMA. Affinity labeling of the 170,000-dalton EGF receptor with 125I-EGF and disuccinimidyl suberate was also decreased by the tumor promoter at low, but not high, concentrations of 125I-EGF. In order to examine this action of PMA on the EGF receptor, the receptor phosphorylation state was evaluated in A431 cells that had been incubated with [32P]phosphate for 3 h prior to the addition of PMA. The 32P content of the EGF receptor purified with EGF-Sepharose was increased by 38% compared with the same amount of receptor isolated from control cells. The increase in EGF receptor phosphorylation was dose-dependent with a half-maximal effect between 0.1 and 1 nM PMA and was specific for tumor promoting analogues of phorbol diesters. Phosphoamino acid analysis indicated that the increase in the 32P content of the EGF receptor was mainly due to phosphoserine. These results demonstrate that the EGF receptor is a target for PMA action and suggest that the mechanism of PMA action on the response of cells to epidermal growth factor may be mediated in part by phosphorylation of the EGF receptor.

Multiple cerebral hemorrhages following chymopapain chemonucleolysis. Case report

A case of multiple cerebral hemorrhages following chymopapain chemonucleolysis is reported. The authors believe the probable etiology was intrathecal extravasation of chymopapain after injection of the drug into a lumbar disc space.

Porous polysulfone coatings for fixation of femoral stems by bony ingrowth

Sixteen porous polysulfone-coated canine femoral stems were inserted into 14 dogs. Coatings were approximately 40% porous, with an average pore size of 125 or 250 microns. Bone was formed within at least about 30% of the surface pores of the implants. The tissue ingrowths filling the pores included marrow and fibrous tissue. Correlated roentgenographic and histologic observations revealed a trabecular "lamina dura" at the coating-bone interface and relatively dense trabeculae distal to the stem tip. These observations support the concept of coating femoral prostheses with porous material for cement-free stabilization.

Activation of a procollagenase by low-molecular-weight angiogenesis factor

Avascular tumours have the ability to establish a blood supply for themselves by secreting a humoral factor which stimulates their host's endothelial cells to proliferate and to migrate towards the tumour source. The mechanism of action of such a humoral angiogenesis factor is more than that of an endothelial-cell growth factor since it requires an oriented migration of cells towards the tumour. We report here the activation of pure skin-fibroblast procollagenase by a low-molecular-weight angiogenesis factor capable of stimulating endothelial-cell growth in vitro. The activation was observed when either Type I or III collagen was used as substrate. It is suggested that at least one function of angiogenesis factor is to promote limited degradation of the connective tissue through which it passes causing channeling in the matrix along which stimulated endothelial cells may migrate.

The effect of beta-adrenergic agonists on the membrane potential of fat-cell mitochondria in situ

1. The accumulation of [3H]methyltriphenylphosphonium by isolated fat-cells was used to estimate the membrane potential of mitochondria in situ. 2. Adrenaline caused a large decrease in the accumulation of [3H]methyltriphenylphosphonium. Mitochondria in fat-cells incubated in the presence of adrenaline had a very low calculated membrane potential. This effect was also given by isoprenaline (a beta-adrenergic agonist) and was blocked by propranolol (a beta-adrenergic antagonist). 3. The effect of isoprenaline could be partially antagonized by the use of media with high albumin concentrations. Addition of sodium oleate to saturate the fatty acid-binding sites on the albumin reversed this antagonism. 4. It is proposed that the decrease in the calculated mitochondrial membrane potential is due to the uncoupling effect of the non-esterified fatty acids released by the stimulation of lipolysis observed in the presence of beta-adrenergic agonists.

The effect of alpha-adrenergic agonists on the membrane potential of fat-cell mitochondria in situ

1. The accumulation of [3H]methyltriphenylphosphonium by isolated fat-cells was used to estimate the membrane potential of mitochondria in situ. 2. An alpha-adrenergic receptor-mediated decrease in the apparent accumulation of [3H]methyltriphenylphosphonium was observed. Methoxamine, clonidine and low concentrations of phenylephrine decreased the calculated mitochrondrial membrane potential without significantly raising cyclic AMP levels, adenylate cyclase activity or stimulating lipolysis. The agonist potency order was phenylephrine greater than methoxamine greater than clonidine. 3. The decrease in the calculated mitochondrial membrane potential caused by phenylephrine, clonidine and methoxamine was blocked by the alpha-adrenergic antagonist prazosin but not by yohimbine nor by the beta-antagonist propranolol. This suggests that the effect on the calculated mitochondrial membrane potential may be mediated by alpha 1-like receptors.

Warfarin-induced skin necrosis: report of four cases

Four cases of warfarin-induced skin necrosis are reported, and previous reports of this adverse drug reaction are summarized. A 53-year-old man experienced two episodes of skin necrosis on his left flank and buttock, following the initiation of warfarin therapy for acute thrombophlebitis and after a dose adjustment. The lesion formed multiple hemorrhagic bullae that ruptured, and an eschar formed that did not heal and eventually required skin grafting. Seven days after the initiation of warfarin therapy, an area of erythema surrounded by a halo was noted on the left thigh of a 79-year-old woman. Following the typical pattern, the erythematic area turned to a blue-black color and rapidly formed an eschar deep into the subcutaneous tissue that required debridement. A 70-year-old man was given a warfarin dose of 10 mg daily that was reduced to 2.5 mg daily. It was discontinued when bullous violaceous lesions were discovered on his lower left leg and foot. His prothrombin times never exceeded 20 seconds with a control of 10.6 seconds. A 37-year-old woman was admitted with an erythematous area on her right thigh that turned blue-black and subsequently formed an eschar. Her prothrombin time was 21 seconds with a control of 10.6 seconds. Of the 50 reports of warfarin-induced skin necrosis in the literature (including the four here), 74% of the cases involved women. The mean age of the patients was 54 years, and 60% of the lesions occurred on the thigh, breast, or buttock. Usually the onset of the lesion was noted on days 3--5 of warfarin therapy. Sixty percent of the patients were hypocoagulated. The etiology of warfarin-induced skin necrosis has not been definitively established. In the event of this unusual complication, warfarin therapy should be discontinued, vitamin K should be administered to reverse the effects of warfarin, and heparin should be used to provide anticoagulation.

The effect of insulin on plasma-membrane and mitochondrial-membrane potentials in isolated fat-cells

1. A recently developed technique for the measurement of plasma-membrane and mitochondrial-membrane potentials in intact cells by using the distribution of 86Rb+ and [3H]methyltriphenylphosphonium+ has enabled us to characterize a novel insulin effect on fat-cell mitochondria. For control cells the plasma-membrane and mitochondrial-membrane potentials were 75 mV and 152 mV respectively. Insulin (10 mu units/ml) caused a 9 mV hyperpolarization of the plasma membrane and a 19 mV depolarization of the mitochondrial membrane. 2. The insulin-dependent mitochondrial depolarization was observed at physiological insulin concentrations (10 mu units/ml) and was apparent when the cells metabolized a wide variety of substrates. 3. Evidence from the uptake of the weak acid 5,5-dimethyloxazolidine-2,4-dione by fat-cells was interpreted as indicating that the mitochondrial pH gradient was increased by insulin. 4. Insulin alters the balance between the electrical and pH-gradient components that form the mitochondrial protonmotive force. A model is proposed.

Ankle arthrodesis in the management of traumatic ankle arthrosis: a long-term retrospective study

A retrospective study was carried out of 48 patients who underwent ankle arthrodesis for tramatic arthritis from January 1967 through January 1976. Following ankle fusion, the most common complaint was subtalar pain and the most frequent finding was limitation of subtalar motion (56%). Subtalar or triple arthrodesis was required in 12 patients, with good results in the majority of the cases. An infection rate of 22% was encountered, felt to be consequent to the failure to properly employ prophylactic antibiotics; which, when employed, were associated with less than 6% incidence of sepsis 69% of patients were improved from their status before ankle arthrodesis; 12% had come to below-knee amputation (three for resistant pain, two for chronic osteomyelitis, and one for vascular insufficiency). Fusion of the subtalar joint seems curative, and early mobilization of the subtalar joint, by ankle fusion techniques that do not immobilize the entire foot may play a preventive role.

Cardiac conduction in myotonic dystrophy

Cardiac conduction abnormalities are frequent in myotonic dystrophy and can result in complete heart block. In a study of 26 patients with myotonic dystrophy, first degree heart block was found to precede clinical presentation of the disease in 7 patients. His bundle electrocardiography in 11 patients demonstrated abnormalities throughout the entire conducting system, even in patients with only first degree heart block. In patients with block of the right bundle branch or anterior fascicle of the left bundle branch, slowing in the remaining fascicles was always present. Therapy of myotonia with procainamide significantly lengthened the P-R interval, and treatment with diphenylhydantoin significantly shortened the P-R interval suggesting that diphenylhydantoin may be preferable for therapy of myotonia in patients with myotonic dystrophy.