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T C Hohman

Publications and source records attributed to T C Hohman.

46 records · Page 3Linked to original sources
PubMed1986

Vacuolar pH is one factor that regulates hydrolase secretion.

Lysosomal hydrolases are continually secreted by Acanthamoeba as a consequence of membrane cycling between the vacuolar compartment and the cell surface. In pinocytosing amoebae acid hydrolases can be separated into two groups on the basis of their secretion kinetics. We have previously shown that in Acanthamoeba acid hydrolases are almost exclusively restricted to a single compartment, digestive vacuoles, and that pH-dependent differential binding of hydrolases to vacuolar membrane can account for the different rates of hydrolase secretion from this compartment. In this report we show that the hydrolase secretion pattern changes and that all of the hydrolases are released with the same kinetics after phagocytosis of yeast or in growth media supplemented with ammonium acetate or chloroquine, but not after phagocytosis of polystyrene beads. The changes in the pattern of hydrolase secretion correlate with changes in vacuolar pH. The vacuolar pH of pinocytosing amoebae and amoebae saturated with beads is about 4.8. This value is increased to 6.8 by accumulation of weak bases and to about 6.1 when digestive vacuoles are saturated with yeast. These results indicate that vacuolar pH modulates hydrolase transport and secretion.

Acetates↗
PubMed1984

Hydrolase secretion is a consequence of membrane recycling.

Acanthamoeba releases lysosomal hydrolases continuously into the culture medium. This release is specific for lysosomal hydrolases, but not other cellular proteins, and is energy dependent. The secreted hydrolases can be separated into two groups on the basis of their secretion kinetics: one is secreted at approximately 15% of the cellular activity per hour and the other at approximately 5%. Intracellularly the lysosomal hydrolases are restricted almost exclusively to secondary lysosomes where the hydrolases demonstrate a differential pH-dependent binding to membrane. Hydrolase secretion is not the result of secondary lysosomes' fusing with the plasma membrane since soluble and particulate lysosomal contents are not released at the same rate. Together the data suggest that the secreted hydrolases are trapped in shuttle vesicles that cycle membrane from secondary lysosomes to the cell surface. The inner membrane and content of these vesicles undergo a marked pH shift when, following fragmentation from lysosomes, these vesicles fuse with plasma membrane. This rapid pH shift and the differential pH-dependent membrane binding of hydrolases appear to account for the heterogeneous hydrolase secretion kinetics.

Amoeba↗
PubMed1982

Phagosome-lysosome fusion inhibited by algal symbionts of Hydra viridis.

Certain species of Chlorella live within the digestive cells of the fresh water cnidarian Hydra viridis. When introduced into the hydra gut, these symbiotic algae are phagocytized by digestive cells but avoid host digestion and persist at relatively constant numbers within host cells. In contrast, heat-killed symbionts are rapidly degraded after phagocytosis. Live symbionts appear to persist because host lysosomes fail to fuse with phagosomes containing live symbionts. Neither acid phosphatase nor ferritin was delivered via lysosomes into phagosomes containing live symbionts, whereas these lysosomal markers were found in 50% of the vacuoles containing heat-killed symbionts 1 h after phagocytosis. Treatment of symbiotic algae before phagocytosis with polycationic polypeptides abolishes algal persistence and perturbs the ability of these algae to control the release of photosynthate in vitro. Similarly, inhibition of photosynthesis and hence of the release of photosynthetic products as a result of prolonged darkness and 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) treatment also abolishes persistence. Symbiotic algae are not only protected from host digestive attack but are also selectively transported within host cells, moving from the apical site of phagocytosis to a basal position of permanent residence. This process too is disrupted by polycationic polypeptides, DCMU and darkness. Both algal persistence and transport may, therefore, be a function of the release of products from living, photosynthesizing symbionts. Vinblastine treatment of host animals blocked the movement of algae within host cells but did not perturb algal persistence: algal persistence and the transport of algae may be initiated by the same signal, but they are not interdependent processes.

Acid Phosphatase↗
PubMedDate not supplied

Minalrestat and leukocyte migration in diabetes mellitus.

BACKGROUND: We recently demonstrated that aldose reductase inhibition was effective in restoring the reduced migratory capacity of leukocytes in diabetic rats. To investigate the mechanism(s) involved in the restoring effect, we used minalrestat, an aldose reductase inhibitor. METHODS: In sodium pentobarbital-anesthetized (40 mg/kg, intraperitoneally) alloxan-diabetic or galactosemic male Wistar rats, the internal spermatic fascia was exteriorized, and the number of leukocytes rolling along the venular endothelium and the number of leukocytes sticking to the vascular wall after topical application of zymosan-activated plasma or leukotriene B(4) (1 ng/ml), as well as after the application of a local irritant stimulus (carrageenan, 100 microg), were determined using intravital microscopy. Data from animals that were treated with and those that were not treated with minalrestat (10 mg/kg/d by gavage) were compared. RESULTS: The reduced number of leukocytes rolling along the venular endothelium (by about 70%) and the number of adhered and migrated leukocytes in postcapillary venules (by 60%) were significantly restored to control values after minalrestat treatment. Total or differential leukocyte counts, venular blood flow velocity or wall shear rate were not altered by minalrestat treatment. The expression of ICAM-1 and P-selectin, cell adhesion molecules involved in the interaction of leukocyte-endothelium, reduced in diabetic rats was restored by minalrestat treatment. CONCLUSION: We conclude that an enhanced flux through the polyol pathway might be involved in the reduced expression of ICAM-1 and P-selectin contributing to the impaired leukocyte-endothelial interactions in diabetes mellitus and that aldose reductase inhibition restores the defect, restoring the reduced expression.

Aldehyde Reductase↗
PubMedDate not supplied

Effect of hyperglycemia and the aldose reductase inhibitor tolrestat on sural nerve biochemistry and morphometry in advanced diabetic peripheral polyneuropathy. The Tolrestat Study Group.

Tolrestat is a well tolerated nonhydantoin aldose reductase inhibitor that has been reported to improve nerve conduction in diabetic animals and humans. Its effects on nerve biochemistry and structure have not been studied in patients with diabetic neuropathy. Patients with advanced diabetic neuropathy treated with long-term open-label tolrestat were randomly assigned to continuation on drug treatment or to placebo-controlled drug withdrawal for 12 months. At the end of this period, sural nerve biopsies were obtained for measurement of glucose, sorbitol, and fructose content, and for detailed morphometric analysis. Tolrestat ameliorated the glucose-mediated increase in sorbitol and fructose in sural nerve tissue. No statistically significant differences in nerve morphometry emerged between the two groups; however, both treatment groups exhibited increased nerve-fiber regeneration and normalization of axo-glial dysfunction and segmental demyelination following long-term tolrestat treatment. These findings are similar to those previously reported in a placebo-controlled sequential nerve biopsy study with the aldose reductase inhibitor sorbinil. Thus tolrestat is a biochemically effective aldose reductase inhibitor in human diabetic nerve with potential therapeutic efficacy for diabetic neuropathy.

Aldehyde Reductase↗
PubMedDate not supplied

Aminoguanidine does not inhibit aldose reductase activity in galactose-fed rats.

Aminoguanidine, nucleophilic hydrazine derivative, has been shown to inhibit diamine oxidase, the formation of advanced glycation endproducts, nitric oxide synthase, and catalase. Prompted by the reports that aminoguanidine also inhibits aldose reductase (AR), we have investigated the effect of aminoguanidine, 1,3-diaminoguanidine, and methylguanidine on AR activity in vitro, and in vivo. In vitro, we have measured the inhibition of AR isolated from bovine lenses; in vivo, we have examined the effect on the galactitol levels in the red blood cells, sciatic nerve, retina, and lens of rats administered the test compounds for 11 days in the drinking water and, for the last 4 days, given access to a 20% galactose diet. Two known, structurally distinct AR inhibitors, tolrestat and compound WAY-121,509, were used as reference. In vitro, at concentrations up to 1.0 mmol/L, none of the tested guanidine derivatives had any effect on AR. As a corollary, in vivo, at doses ranging from 201 to 349 mg/kg/day, none of the guanidine derivatives affected tissular galactitol levels. We conclude that, in short-term galactose-fed rats, at the doses tested, aminoguanidine, 1,3-diaminoguanidine, and methylguanidine do not inhibit AR.

Aldehyde Reductase↗
PubMedDate not supplied

Reversal of defective peripheral nerve conduction velocity, nutritive endoneurial blood flow, and oxygenation by a novel aldose reductase inhibitor, WAY-121,509, in streptozotocin-induced diabetic rats.

The main aim was to investigate whether 1 month of aldose reductase inhibitor treatment could correct a deficit in sciatic nerve nutritive blood flow following 1 month of untreated streptozotocin-induced diabetes in rats. Treatment was with two doses of WAY-121,509, both of which completely blocked neuronal sorbitol accumulation. The high dose fully corrected a motor conduction velocity deficit, whereas the low dose caused 51.3% amelioration. Nutritive endoneurial blood flow, monitored by hydrogen clearance, was 43.4% reduced after 1 month of diabetes. This was completely corrected by the high dose of WAY-121,509. In addition, vascular conductance was supranormal and there was a decrease in arteriovenous shunt flow. Low dose treatment caused a 55.6% improvement of the nutritive endoneurial blood flow deficit, paralleling the conduction velocity effect. WAY-121,509 did not alter nerve perfusion in nondiabetic rats. Data from multiple sciatic nerve penetrations by oxygen sensitive microelectrodes revealed a 42.0% deficit in mean endoneurial oxygen tension with diabetes, whereas tensions were in the nondiabetic range for high dose WAY-121,509 treatment. Thus, the data highlight neurovascular actions of aldose reductase inhibition, and suggest that neuronal polyol pathway metabolite levels are a poor predictor of functional efficacy.

Aldehyde Reductase↗
PubMedDate not supplied

Effect of the aldose reductase inhibitor tolrestat on nerve conduction velocity, Na/K ATPase activity, and polyols in red blood cells, sciatic nerve, kidney cortex, and kidney medulla of diabetic rats.

Long-term prospective studies comparing the effects of conventional and intensive insulin therapy have linked diabetic hyperglycemia to the development of diabetic retinopathy, nephropathy, and neuropathy. The mechanisms through which glucose metabolism leads to the development of these secondary complications, however, are incompletely understood. In animal models of diabetic neuropathy, the loss of nerve function in myelinated nerve fibers has been related to a series of biochemical changes. Nerve glucose, which is in equilibrium with plasma glucose levels, rapidly increases during diabetic hyperglycemia because glucose entry is independent of insulin. This excess glucose is metabolized in large part by the polyol pathway. Increased flux through this pathway is accompanied by the depletion of myo-inositol, a loss of Na/K ATPase activity and the accumulation of sodium. Supportive evidence linking these biochemical changes to the loss of nerve function has come from studies in which aldose reductase inhibitors block polyol pathway activity, prevent the depletion of myo-inositol and the accumulation of sodium and preserve Na/K ATPase activity, as well as nerve function. The kidney and red blood cells (RBCs) are two additional sites of diabetic lesions that have been reported to develop biochemical changes similar to those in the nerve. We observed that polyol levels in the kidney cortex, medulla, and RBCs increased two- to ninefold in rats following 10 weeks of untreated diabetes. Polyol accumulation was accompanied by a 30% decrease in myo-inositol levels in the kidney cortex, but no change in RBCs or the kidney medulla. Na/K ATPase activity was decreased by 59% in RBCs but was unaffected in the kidney cortex or medulla. Aldose reductase inhibitor treatment that preserved myo-inositol levels, Na/K ATPase, and conduction velocity in the sciatic nerve also preserved Na/K ATPase activity in RBCs. Our results suggest that the pathophysiologic mechanisms underlying diabetic neuropathy are different from those of diabetic nephropathy. Our results also suggest that RBCs maybe a surrogate tissue for the assessment of diabetes-induced changes in nerve Na/K ATPase activity.

Aldehyde Reductase↗
PubMedDate not supplied

Hydrolase compartmentalization limits rate of digestion in Acanthamoeba.

The kinetics of lysosomal enzyme acquisition by newly formed phagosomes was studied by following the rate of digestion of radiolabeled yeast fed to Acanthamoeba. The distribution of hydrolases among phagosomes was assessed by electron microscopic acid phosphatase cytochemistry and by measurement of three glycosidases in isolated early and late phagosomes. The results show that compartmentalization of hydrolases limit the digestion of large phagocytic loads. The hydrolases appear to be sequestered into the early phagosomes and not to be distributed either by small vesicle transport or phagosome-phagosome fusion to those formed later. We infer from these results that newly internalized surface membrane in phagosomes is not rapidly randomized with internal pools, but is recycled to the surface as a function of the digestive process.

Acanthamoeba↗