CHEMOTHERAPY OF TRYPANOSOME AND SPIROCHETE INFECTIONS : CHEMICAL SERIES. I. N-PHENYLGLYCINEAMIDE-p-ARSONIC ACID

Recent Advances in the Aetiology and Treatment of Neurosyphilis

During the first two decades of this century important advances were made in our knowledge of syphilis. Wassermann in 1904 introduced the serological reaction which bears his name; Schaudinn and Hoffmann discovered the spirochaete in 1905; Plaut in 1908 extended the application of the Wassermann test to the cerebro-spinal fluid; Ehrlich in 1909 synthesized “606”; Noguchi in 1913 demonstrated spirochaetes in the brains of general paralytics, and Wagner-Jauregg in 1918 inaugurated malaria therapy. During the second two decades no outstanding discoveries have been made, but there has been in these last twenty years a large amount of verification and elaboration; more sensitive serological tests have been devised, new chemo-therapeutic drugs have been manufactured, the histology of parenchymatous neurosyphilis has been more fully studied, and many methods of pyretotherapy have been tried. A review of the vast literature which has been published soon reveals the fact, however, that there are still numerous outstanding problems awaiting solution, many of which were already being discussed 20 and 30 years ago.

Drug resistance in African trypanosomiasis: the melarsoprol and pentamidine story

Melarsoprol and pentamidine represent the two main classes of drugs, the arsenicals and diamidines, historically used to treat the diseases caused by African trypanosomes: sleeping sickness in humans and Nagana in livestock. Cross-resistance to these drugs was first observed over 60 years ago and remains the only example of cross-resistance among sleeping sickness therapies. A Trypanosoma brucei adenosine transporter is well known for its role in the uptake of both drugs. More recently, aquaglyceroporin 2 (AQP2) loss of function was linked to melarsoprol-pentamidine cross-resistance. AQP2, a channel that appears to facilitate drug accumulation, may also be linked to clinical cases of resistance. Here, we review these findings and consider some new questions as well as future prospects for tackling the devastating diseases caused by these parasites.

ARSENICAL COMPOUNDS IN THE TREATMENT OF BLACKHEAD IN TURKEYS

The natural form of blackhead, although very fatal to young turkeys, is favorably influenced by treatment with certain of the newer arsenical compounds. Neoarsphenamine injected intravenously in toxic doses has a somewhat favorable effect on the course of the spontaneous disease and evidently lowers the mortality. Its instability, its pronounced toxicity for young turkeys, as well as the difficulty of obtaining amounts suitable for the cases to be treated on any one occasion, serve to make its employment impracticable. Less favorable results were obtained with atoxyl. Arsenious acid fed daily in small doses failed to prevent blackhead and possibly increased the incidence of infection. In larger doses it failed to cure spontaneous blackhead. Tryparsamide may be injected in cases of spontaneous blackhead in doses as high as 1 gm. per kilo of body weight either intravenously or subcutaneously without serious toxic effect. Prompt clinical improvement usually follows and the mortality is undoubtedly greatly lowered. With inoculated blackhead recovery is more difficult to obtain. Birds treated by injections of either neoarsphenamine or atoxyl failed to recover. There were two recoveries among three tryparsamidetreated cases. An attempt to cure inoculated blackhead at an advanced stage by the injection of tryparsamide failed. The study of the lesions of treated turkeys shows that tryparsamide, and to some extent neoarsphenamine, have a more pronounced effect on the liver lesions than on the disease in the lung, which accounts for the discrepancy in the results of the treatment of spontaneous and inoculated blackhead. There is histological evidence of prompt absorption of necrotic liver parenchyma; moreover, the protozoa are destroyed more rapidly in the liver than in the lung. Tryparsamide has the most pronounced curative action on blackhead infection of any of the drugs thus far tested. Either intravenous or subcutaneous injection of appropriate doses of this drug at the first appearance of symptoms should serve to cure the majority of cases of blackhead.

CHEMOTHERAPY OF TRYPANOSOME AND SPIROCHETE INFECTIONS : BIOLOGICAL SERIES. I. THE TOXIC ACTION OF N-PHENYLGLYCINEAMIDE-p-ARSONIC ACID

The essential facts to be gathered from these studies of the toxicologic action of N-phenylglycineamide-p-arsonic acid may be summarized very briefly. The substance is one which lends itself well to almost any method of administration and can be given to animals in very large doses. The tolerance of different animal species varies rather widely but with one exception the reaction of laboratory animals to toxic doses of the drug is of favorable character. That is, toxic effects are confined to doses relatively close to the minimum lethal dose and the recovery of animals from sublethal intoxications is remarkably rapid and complete. This feature of the action of the drug makes possible the repeated administration of even very large doses at comparatively short intervals of time without incurring the dangers incident to cumulative action or to superposition of toxic effects. On the contrary, by taking advantage of this peculiarity of action, it is possible to develop such a degree of tolerance on the part of animals that the dose of the drug administered can be progressively increased to a point well above that which is fatal to the normal animal, and this stands out as the feature of the toxicologic action of N-phenylglycineamide-p-arsonic acid which is of greatest significance in the use of the drug for therapeutic purposes.

STUDIES ON THE TREATMENT OF HUMAN TRYPANOSOMIASIS WITH TRYPARSAMIDE (THE SODIUM SALT OF N-PHENYLGLYCINEAMIDE-p-ARSONIC ACID)

The present study of the action of tryparsamide in human trypanosomiasis concludes a series of chemical and biological investigations in a particular problem of chemotherapy and thus represents the final step in a logical method of approach to such a problem. It has been shown that tryparsamide, the sodium salt of N-phenylglycineamide-p-arsonic acid, possesses a marked trypanocidal activity in human trypanosomiasis caused by Tr. gambiense. Single doses of from 0.5 to 5.0 gm. produced a peripheral sterilization of lymph glands and blood in an average of 6 to 12 hours. The duration of the peripheral sterilization following single doses of 17 to 83 mg. per kilo ranged from 17 to 58 days in patients who ultimately showed a return of trypanosomes to the peripheral blood. In a number of patients, however, treated with single doses of 9 to 68 mg. per kilo, no such relapse was detected during an observation period of from 40 to 111 days. The drug is extremely soluble in water and may be administered intramuscularly as well as intravenously. The immediate trypanocidal action after intramuscular administration was as rapid as that following the intravenous route while the duration of peripheral sterilization was appreciably longer. Relatively few repeated doses produced in advanced cases a marked and rapid diminution of the cells of the spinal fluid and were associated with definite improvement of mental and nervous symptoms. The occurrence of visual disturbances in certain advanced cases was the only untoward effect detected during the course of the work, and was apparently related to a too frequent administration of the drug. The condition was transitory in the majority of instances and resumption of treatment was not followed by a recurrence of this symptom. The general beneficial effect of the drug was a noticeable feature of its action in both early and advanced cases as shown by the disappearance of subjective symptoms, by the return of the pulse and temperature to normal limits, by the pronounced improvement of the blood picture, and by well marked gains in weight.

Transporters in African trypanosomes: role in drug action and resistance

Sleeping sickness is an increasing problem in many parts of sub-Saharan Africa. The problems are compounded by the lack of new medication, and the increasing resistance against traditional drugs such as melarsoprol, berenil and isometamidium. Over the last few years, much progress has been made in understanding how drug action, and the development of resistance, is related to the mechanisms by which the parasite ingests the drugs. In some cases novel transporters have been identified. In other cases, transporters do not appear to be involved in drug uptake, and selectivity must lie with other parasite features, such as a specific target or activation of the drug. Lessons learned from studying the uptake of drugs currently in use may assist the design of a much needed new generation of trypanocides.

General paralysis of the insane

Images