Neuroblastoma: a neurochemical approach.

Neuroblastoma is among the most common malignancies of childhood. Despite greatly improved therapy for some pediatric tumors, the prognosis for children with metastatic neuroblastoma has not changed significantly in the past 10 years. With conventional chemotherapy, radiation therapy, and surgery, children with metastatic neuroblastoma have a 20% long-term survival rate. We describe here approaches to neuroblastoma that target its neuronal characteristics. On the one hand, the neurotransmitter receptors on the surface of the neuroblastoma cells and, on the other hand, specific isozymes that distinguish neuroblastoma cells from their normal counterparts are the focus of these experimental therapies. In the former case, specificity for tumor cells is effected by (1) selective protection of normal neuronal elements from toxicity, or (2) selective potentiation of toxicity for neural tumor cells. It is hoped that these strategies will be generalizable to other neural crest-derived tumors.

Trypanocidal effects of catecholamines and indolealkylamines.

Catecholamines, indolealkylamines and their analogues are oxidized at neutral or alkaline pH, producing hydrogen peroxide, quinones and free radicals. Several of these amines were tested for trypanocidal effects on Trypanosoma brucei, which possess a well-documented vulnerability to such oxidation products. Dopamine, 5-hydroxydopamine (5-OHDA), 6-hydroxydopamine (6-OHDA), 5-hydroxytryptamine (5-HT), 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT) killed the parasites in vitro, using a fibroblast feeder layer cell culture system, in four to 48 hours at concentrations of 10(-5)-10(-7) M. The 5-OHDA, 6-OHDA, 5,6-DHT and 5,7-DHT were also effective in vivo when tested by intraperitoneal injection of infected mice.

Xylazine antinociception in mice: evidence for mediation by postsynaptic adrenoceptors.

The influence of 6-hydroxydopamine (6-OHDA) pretreatment on xylazine (XLZ)-induced antinociception was studied in mice using the writhing test (60 mg/kg acetic acid, ip, as the algogenic compound administered 10 min after 0.5 and 0.75 mg/kg XLZ, sc). 6-OHDA (100 mg kg-1 injection-1 administered ip on days 1, 3, 5, 7, 9 and 11 after birth) did not modify XLZ-induced antinociception, suggesting that this effect is mediated by postsynaptic alpha-2 adrenoceptors.

Xylazine antinociception in mice: evidence for mediation by postsynaptic adrenoceptors

The influence of 6-hydroxydopamine (6-OHDA) pretreatment on zylazine (XLZ)-induced antinociception was studied in mice using the writhing test (60 mg/Kg acetic acid, ip, as the algogenic compound administered 10 min after 0.5 0.75 mg/Kg XLZ, sc). 6-OHDA (100 mgKg-1 injection-1 administered ip on days 1, 3, 5, 7, 9 and 11 after bith) did not modify XLZ- induced antinociception, suggesting that effects is mediated by postsynaptic alpha-2 adrnoceptors

Central catecholamine neurotoxin administration. 1. Immunological changes associated with the suppression of experimental autoimmune encephalomyelitis.

Central nervous system (CNS) depletion of norepinephrine (NE) using 6-hydroxydopamine (6-OHDA) prior to disease induction suppressed the clinical signs of experimental autoimmune encephalomyelitis (EAE). This treatment did not have an effect on the degree of mononuclear cell infiltration when spinal cord sections were examined and stained with hematoxylin and eosin, nor on serum levels of anti-myelin basic protein antibodies. However, investigation of the subpopulations of lymphoid cells within the perivascular lesions showed an increase in cells bearing the T suppressor cell phenotype, OX8+, in the 6-OHDA-treated EAE rats when compared to saline-control-treated EAE rats. Examination of other cellular subsets showed no differences in the numbers of T helper cells, macrophages, or B cells within the lesions of the two groups. Furthermore, histofluorescent estimation of catecholamines in spinal cord sections from 6-OHDA- and saline-control-treated EAE rats demonstrated that catecholamines were indeed depleted in the rats with suppressed clinical EAE. These findings suggest that 6-OHDA depletion of CNS NE may remove an effector amplification mechanism, or trigger a T suppressor cell mechanism, or both, leading to suppression of the effector phase of EAE, clinical paralysis.

Adjunctive use of ethiofos (WR-2721) with free radical-generating chemotherapeutic agents in mice: new caveats for therapy.

The neurotransmitter analogue 6-hydroxydopamine has been proposed as a selective chemotherapeutic agent for peripheral neural crest tumors. It exerts its action through the generation of cytotoxic oxygen free radicals. Unfortunately, it is toxic to normal peripheral neurons as well. Ethiofos (WR-2721) is a free radical scavenger which appears to be preferentially taken up by normal cells relative to some tumor cells. WR-2721 has been assayed as a protector of the normal autonomic nervous system in mice treated with 6-hydroxydopamine. Although WR-2721 has some activity in this regard, its therapeutic window is narrowed by its depletion of glutathione, a phenomenon which has not previously been noted with this drug. These findings raise issues regarding the safety of adjunctive use of WR-2721 with oxygen free radical-generating chemotherapeutic agents.

Peripheral adrenergic stimulation and indomethacin in experimental ocular shedding of HSV.

The application of 6-hydroxydopamine to the cornea by iontophoresis, followed by topical epinephrine, effectively induces herpes simplex virus (HSV) shedding from the external eye of latently infected rabbits. In this study the beta adrenergic blocker, Timolol, reduced virus shedding when applied immediately before the epinephrine, but continued administration resulted in increased viral shedding. While indomethacin, a prostaglandin synthesis inhibitor decreased HSV replication in cell culture, it failed to decrease virus shedding when applied topically to the eye in adrenergically stimulated animals. Timolol may act then by its effect on the peripheral cells of the eye rather than by stimulation of virus production in ganglionic neurons. These same animals were subsequently tested for latent infection of the trigeminal and superior cervical ganglia and corneas 14 months after primary infection. Only 2 of 14 animals had virus in the trigeminal ganglia, a finding which suggests that latent virus may be depleted by repeated reactivations. Virus was recovered from corneas of five rabbits by co-cultivation so it is possible that corneal latency occurs in this rabbit model as it does in humans.

Inhibition of carrageenin-induced pedal oedema in rats by immobilisation stress.

The effect of immobilisation stress on acute pedal inflammation induced by carrageenin, and the mechanism of stress-induced anti-inflammatory effect, were investigated in male Wistar strain albino rats. Carrageenin-induced pedal inflammation oedema was attenuated by immobilisation stress in a time-dependent manner, when the rats were restrained for 30 min, 1 h, and 2 h immediately after the induction of the inflammation. Pentobarbitone exhibited significant anti-inflammatory effect of its own in an anaesthetic dose and also inhibited stress (1 h)-induced attenuation of the inflammation. Likewise, lignocaine, injected behind the knee joint of the inflamed limb, attenuated the inflammation and also inhibited the stress-induced anti-inflammatory effect. These findings indicate the importance of the central nervous system (CNS) and the afferent/efferent neural pathways from and to the inflammatory site, in inflammation and in stress-induced anti-inflammatory effect. Earlier studies from this laboratory have shown that the central noradrenergic, histaminergic, serotonergic and GABA-ergic neurotransmitter systems have a modulatory anti-inflammatory effect on carrageenin-induced pedal oedema. Since all these neurotransmitter systems have been reported to be activated by stress, their role was assessed in the inflammation-attenuation effect of immobilisation stress. The present studies indicate that, of these neurotransmitters, only the central noradrenergic system is involved in the anti-oedema effect of stress. Endogenous opioid peptides may also be involved in the stress-inflammation interaction, since naloxone inhibited the stress effect. Bilateral adrenalectomy and peripheral chemical sympathectomy, induced by i.p. administration of 6-hydroxydopamine, augmented carrageenin oedema and antagonised the stress-induced anti-inflammatory effect. However, metyrapone, an inhibitor of endogenous corticoid synthesis, failed to inhibit the stress effect. These findings indicate that the sympatho-medullary system, which is known to be activated during stress, is responsible for the observed anti-inflammatory effect of immobilisation stress, rather than augmented release of adrenal corticoids. It is suggested that the observed inflammation reducing effect of immobilisation stress is a consequence of increased central noradrenergic and peripheral sympatho-medullary activity.

Drugs and recurrent ocular herpes.

There are two types of ocular herpes simplex virus (HSV), type 1 and type 2, and infections can be primary or recurrent. This paper reviews characteristics of herpes infections, the prevalence of the disease, virus latency and reactivation, types of ocular involvement, and current concepts for the management of ocular HSV. Various exogenous factors associated with recurrent herpes of the eye are covered with an emphasis placed on corticosteroids, epinephrine, and medroxyprogesterone. Mechanisms of drug action, and reactivation/exacerbation of ocular herpes are discussed. Clinical guidelines for potential drug contraindications are discussed.

Patterns of destruction of mouse neuroblastoma cells by extracellular hydrogen peroxide formed by 6-hydroxydopamine and ascorbate.

The patterns of the cytolytic effects of 6-hydroxydopamine (6-OHDA), with/without ascorbate, on C-1300 and three other cloned mouse neuroblastoma cell lines (N1E-115, NS-20, N-18) were studied in vitro. The sensitivity to 6-OHDA differed and the three cloned cell lines were more sensitive than the wild type C-1300 cell line. Ascorbate synergistically potentiated the cytolytic effect of 6-OHDA to all four cell lines. The 6-OHDA cytotoxicity was eliminated by the addition of exogenous catalase but not by addition of other oxygen free radical scavengers, thereby suggesting that the hydrogen peroxide formed might influence the cells, extracellularly. In addition, the critical time for tumor cell lysis was the first 60 min of the reaction. The cytotoxicity induced by the unmasked cyclophosphamide, 4-hydroperoxycyclophosphamide, was synergistically enhanced in the presence of a nontoxic concentration of 6-OHDA and ascorbate. These data suggest that reactive oxygen intermediates may prove to be a good tool for destroying neuroblastoma cells.

Convulsive thresholds in mice: action of 6-hydroxydopamine and eboracin.

The neurotoxin, 6-hydroxydopamine, when injected intraperitoneally, protected mice from seizures induced by pentylenetetrazol (Metrazol) and altered the nature of the convulsive response induced by an auditory stimulus. Conversely, the indenopyrrole, eboracin, protected mice from seizures induced by auditory stimulation and altered the response to Metrazol. In each case the altered response was characterized by a marked prolongation of the clonic component without progression to the generalized tonic phase. It appeared, therefore, that 6-hydroxydopamine raised the threshold to tonus in audiogenic seizures, and eboracin raised it in Metrazol seizures. Eboracin raised threshold to clonic phase in audiogenic seizures whereas 6-hydroxydopamine raised it in Metrazol seizures. Our findings showed that in Metrazol and audiogenic seizures thresholds to clonus and progression to the tonic phase were mediated by different biochemical mechanisms and suggested that agents controlling induction of clonic manifestations in one seizure model may be those involved in controlling seizure spread in the other.

Use of recombinant interferon to prevent recurrent herpesvirus shedding.

Iontophoresis with 6-hydroxydopamine was performed in rabbits previously infected with herpes simplex virus, McKrae strain. Viral shedding into the tear film was significantly decreased by the use of recombinant alpha interferon subtype D given as one drop qid. Interferon was noted in the tear film of rabbits 16-18 hours after the last placement of interferon drops into the inferior cul-de-sac.

A single gene error of noradrenergic axon growth synchronizes central neurones.

One strategy for deciphering inherited neurological disease is to examine the expression of individual genes controlling the assembly and physiology of specific cell groups within the developing mammalian central nervous system (CNS). This neurogenetic approach, using defined single-locus mutations arising on coisogeneic mouse strains, has recently been used to analyse a major class of neuronal membrane diseases involving abnormal excitability, the epilepsies, and to identify examples of hereditary variation in signalling properties at central synapses. An interesting mutation, the Tottering (tg) gene, causes a delayed onset, recessive neurological disorder in the mouse featuring a stereotyped triad of ataxia, intermittent myoclonus and cortical spike-wave discharges accompanied by behavioural absence seizures which resemble petit mal epilepsy. Axon branches of the locus coeruleus, a noradrenergic brain-stem nucleus, hyperinnervate specific target regions of the tg brain. The number of parent coerulean perikarya is unaffected, indicating a true proliferation of the terminal axonal arbor. With the exception of this unusually precise error of axonal growth, no other cytopathology has been identified in the tg brain. Here I present evidence that selective lesions of the central noradrenergic axons early in development limit the expression of the disease.

Vasoactive drugs in acute pancreatitis.

Experimental evidence has shown that pancreatic blood flow is severely diminished during acute pancreatitis, but it is unclear whether a decrease in blood flow is a critical event in the evolution of complications of this disease. When an episode of edematous pancreatitis is complicated by necrosis of part of the gland, there is a risk of both acute and chronic complications, including sepsis, hemorrhage, and abscess. One of the questions that remains is whether the decreases in blood flow alluded to are primary or secondary causes. If primary, treatments that preserve pancreatic blood flow during pancreatitis might have a salutary effect on observed morbidity and mortality. This study determined whether two vasoactive drugs, oxidopamine (6-hydroxydopamine) and dihydroergotamine tartrate, given prior to experimentally induced pancreatitis in rats, affected observed mortality. After oxidopamine treatment, rats had a higher survival rate and greater pancreatic blood flow than untreated controls. The association of greater pancreatic blood flow and reduced mortality did not exclude other possible effects of oxidopamine treatment but was consistent with the hypothesis that vasoactive therapy may have a role in this disease.

Treatment of glaucoma.

In the past five years, new therapeutic modalities have been discovered that have revolutionized the medical and surgical management of glaucoma. New methods of drug delivery have been developed for pilocarpine and epinephrine. Timolol maleate has become the most widely used drug in the treatment of glaucoma since it was approved for general use in 1978. This chapter reviews the pharmacology of the newer antiglaucoma medications and gives a perspective on the role of laser surgery in open-angle glaucoma.

6-hydroxydopamine in the treatment of open-angle glaucoma.

We evaluated the effectiveness of subconjunctival injections of 6-hydroxydopamine in conjunction with epinephrine in lowering ocular tension in 63 eyes of 61 patients with open-angle glaucoma. A single injection caused a peak median reduction in ocular tension of 6 mm Hg four weeks after the injection. Ten eyes (16%) showed no significant decrease in ocular tension. A single injection significantly decreased the ocular tension for 12 weeks in 40 (63%) and for 20 weeks in 21 (33%) of the eyes. The fellow control eyes showed a slight but not significant decrease in ocular tension.