Search

Transition metal-catalysed oxidations have been implicated in the complications of diabetes. We report here that some experimental inhibitors of the enzyme aldose reductase (implicated in diabetes mellitus via its ability to catalyse glucose reduction to sorbitol) are also potent inhibitors of transition metal-catalysed ascorbate oxidation. The inhibition appears to be dependent upon the presence of a spirohydantoin group. It is conceivable that the copper- and iron-binding capacity of these compounds may contribute to some of their observed biological effects and may provide a starting point for a new generation of experimental drugs for the treatment of diabetes mellitus.

Hyperglycemia is increasingly regarded as the cause of the diabetic complications, in particular via the ability of glucose to glycate proteins and generate Maillard browning products which cross-link proteins and render them brown and fluorescent in vitro. Similar changes occur in vivo to long-lived proteins in diabetes mellitus as well as in ageing. The evidence supporting this route of glucose toxicity is discussed in the context of the ability of glucose to oxidize in vitro (catalyzed by trace amounts of transition metal) generating hydrogen peroxide, highly reactive oxidants, and protein-reactive ketoaldehyde compounds. It is suggested that protein browning in vivo may not result from the reactions of glucose with protein but from the transition metal-catalyzed reactions of other small autoxidisable substrates, such as ascorbate, with protein. Overall, studies of glycation and protein browning suggest a critical role for oxidative processes perhaps involving decompartmentalized transition metals and a variety of low molecular weight reducing agents in diabetes mellitus and ageing.

The accumulation of hydrogen peroxide (H2O2) during incubations of protein with glucose (experimental glycation) has previously been too low for direct measurement although it is suggested to be the precursor of protein-damaging hydroxylating agents. We have thus developed a simple H2O2-measuring technique which relies upon the rapid peroxide-mediated oxidation of Fe2+ to Fe3+ (catalysed by sorbitol) under acidic conditions followed by reaction of the latter cation with the dye, xylenol orange. We have used the method to demonstrate that incubation mixtures of protein and glucose generates nanomolar levels of hydrogen peroxide in the presence of protein under physiological conditions of pH and temperature.

We have isolated recombinant lambda-phage clones that contain sequences complementary to the 3' half of the cDNA encoding human topoisomerase I (hTOP1). These lambda clones belong to three distinct classes: class-I clones contain sequences from the active gene located on human chromosome 20. Class-II and class-III clones contain sequences corresponding to the cDNA encoding hTOP1 from nucleotide (nt) 2208 to 3434 and from nt 1639 to 3434, respectively. These sequences exhibit the characteristic features of retroposons or retrosequences. They are most likely derived from truncated mRNA transcripts of the active gene. We propose to designate the truncated hTOP1 sequence located on chromosome 1 as the pseudogene 1 (psi 1-hTOP1) and the sequence on chromosome 22 as the pseudogene 2 (psi 2-hTOP1). Pseudogene psi 1-hTOP1 has two unique properties: it is flanked by upstream sequences which display promoter activity in transient expression assays, and it contains an open reading frame which could code for the 211 C-terminal amino acids of hTOP1. Pseudogene psi 2-hTOP1 is located within an AluI repetitive element and is flanked on one side by a (CA)21 stretch.

A549, a human lung cancer cell line, spontaneously produces a tumor-derived immunosuppressive factor (TDSF) which inhibits the production and action of interleukin 1 (IL-1). After exposure of macrophages to TDSF for 5 h, the production of IL-1 by macrophages was significantly inhibited. The inhibition was much stronger if TDSF existed continuously in macrophage culture. The response of thymocytes treated with nylon wool to exogenous IL-1 was significantly suppressed in the presence of TDSF, suggesting that TDSF can inhibit the action of IL-1. The thymocytes untreated with nylon wool could proliferate after being stimulated with Con A. The proliferation was significantly suppressed by TDSF in a dose-dependent manner. These results suggest that the inhibitory action of TDSF on T cell activation is associated with IL-1, and that TDSF might exert an inhibitory action on other reactions mediated by IL-1. Furthermore, TDSF can reduce the supplementation of new T cells by inhibiting the proliferation of thymocytes.

In 18 urethane-anesthetized ovariectomized female rats, 54 neurons in and around the hypothalamic ventromedial nucleus were transynaptically activated by electrical stimulation of the mesencephalic central gray matter. Ventromedial nucleus afferents from either the dorsal longitudinal fascicle (N = 10) or the medial forebrain bundle (N = 8) were disrupted by a small knife cut. In animals which lacked inputs from the dorsal longitudinal fascicle by a cut posterior to the ventromedial nucleus, transynaptic activation followed central gray stimulation in 20 cells; 26 cells were driven from the central gray in animals deprived of afferents through the medial forebrain bundle by a cut placed laterally to the ventromedial nucleus. Two patterns of synaptic activation followed electrical stimulation at 0.5 Hz: one type of response occurred during a latency range of 4 to 20 ms with fluctuation of each response less than 5 ms, the other type was characterized by diffuse activation for 50 ms following central gray stimulation. It was noted that the former time-locked response occurred in 19 among 20 cells in the posterior-cut animals, and the latter diffuse response was seen in 20 of 26 cells in the lateral-cut animals. Electrical stimulation of the ventromedial nucleus in another group of seven animals with the posterior cut caused antidromic activation of 19 central gray cells at latencies of 4.8 to 21.0 ms. Thus, central gray axons in the medial forebrain bundle were shown to have direct access to the ventromedial nucleus and multisynaptic pathways intervened for those in the dorsal longitudinal fascicle.

Effects of toxins III and IV (ATX III and IV) from the sea anemone Anemonia sulcata on the Na current of crayfish giant axons were studied. Both toxins slowed the inactivation of Na channels, producing a maintained Na current during a depolarizing voltage pulse. Using the intensity of the toxin-induced maintained current as an index for the fraction of Na channels to which toxin is bound, the toxin association and dissociation kinetics were analyzed. The dissociation rate of ATX III was increased by two orders of magnitudes by depolarizing the membrane from -70 to -40 mV. This increase of the dissociation rate caused a marked decrease in the binding rate of ATX III to Na channels in the same potential range. ATX IV exhibited association and dissociation kinetics that had a potential dependency quite similar to that of ATX III in spite of different ionic charge distribution in these two toxins. The results support the view that the potential-dependent kinetics of these toxins are not due to an electrostatic interaction between the ionic charges of toxins and the membrane potential but result from a modulation of the binding energy depending on the gate configuration of the Na channel.

The effect of taste stimuli on the efferent discharges in the gastric branch of the vagus nerve was studied in rats anesthetized with urethane-chloralose. An increase in discharge rate following taste stimulation with 5% NaCl over the tongue for 5 min, and a decrease of it following an application of 10% sucrose for the same duration were observed in normal as well as in decerebrated rats. The results indicate the existence of a pathway from the taste receptors to the gastric vagus nerve via the brainstem. The reflex effects of taste stimuli on gastric vagal outflow may be related to gastric acid output.

The afferent nerve activity was recorded from a nerve filament isolated from the peripheral cut end of the gastric branch of the vagus nerve. The gastric perfusion of 4 ml of two different concentrations (0.04% and 0.08%) of CuSO4 solution provoked an increase in afferent activity. The stimulating effect of the 0.08% solution was stronger than that of the 0.04% solution, and lasted for a longer period of time. The observations suggest a possible mechanism by which CuSO4 elicits emesis.

In the present study, antidromically activated raphe-spinal neurons in the nucleus raphe magnus are found to exhibit a wide range of conduction velocities and spontaneous discharge rates. The unit activities observed in control rats have been compared with those in 5,6-dihydroxytryptamine (a specific neurotoxin to serotonergic cells)-pretreated animals. It is found that the units conducting at slower than 12 m/sec and discharging at rates of less than 3 Hz often found in control rats are not found in drug-pretreated animals, and are thus presumed to be serotonergic. In addition, the regularity of spontaneous discharges of units has been evaluated by testing the coefficient of variability of spike intervals. These results indicate that the slow-conducting units discharge less regularly than the fast-conducting ones.

To investigate the possible existence of arginine sensors in the liver and their reflex effects, afferent discharges from the hepatic branch of the vagus nerve and efferent discharges from the pancreatic branches of the splanchnic and vagus nerves were recorded. Intraportal injection of arginine increased afferent discharge rate of the hepatic branch of the vagus nerve, slightly depressed the efferent discharge rate of the pancreatic vagal branch, and increased the efferent discharge rate of the pancreatic splanchnic branch. The results suggest the existence of arginine sensors in the hepato-portal system that exert reflex regulation of the pancreatic neuroendocrine system.