Dietary supplemented 2-mercaptoethanol prevents spontaneous and delays virally-induced murine mammary tumorigenesis

Potential alteration of tumor microenvironments by β-mercaptoethanol

The therapeutic effectiveness of immune checkpoint inhibitors in cancer patients is quite profound. However, it is generally accepted that further progress is curtailed by accompanying adverse events and by low cure rates linked to the tumor microenvironment. The multitudes of immune processes altered by low-molecular-weight thiols published over the past decades suggest they have potential to alter tumor microenvironment processes which could result in an increase in immune checkpoint inhibitor survival rates. Based on one of the most studied and most potent low-molecular-weight thiols, β-mercaptoethanol (BME), it is proposed that clinical assessment be undertaken to identify any BME benefits with relevance for proliferation/differentiation of immune cells, lymphocyte exhaustion, immunogenicity of tumor antigens and inactivation of suppressor cells/factors. The BME alterations projected to be most effective are: maintenance/replacement of glutathione in lymphocytes via facilitation of cysteine uptake, inhibition of suppressor cells/soluble factors and inactivation of free-radical, reactive oxygen species.

Thiosulfoxide (sulfane) sulfur: new chemistry and new regulatory roles in biology

The understanding of sulfur bonding is undergoing change. Old theories on hypervalency of sulfur and the nature of the chalcogen-chalcogen bond are now questioned. At the same time, there is a rapidly expanding literature on the effects of sulfur in regulating biological systems. The two fields are inter-related because the new understanding of the thiosulfoxide bond helps to explain the newfound roles of sulfur in biology. This review examines the nature of thiosulfoxide (sulfane, S0) sulfur, the history of its regulatory role, its generation in biological systems, and its functions in cells. The functions include synthesis of cofactors (molybdenum cofactor, iron-sulfur clusters), sulfuration of tRNA, modulation of enzyme activities, and regulating the redox environment by several mechanisms (including the enhancement of the reductive capacity of glutathione). A brief review of the analogous form of selenium suggests that the toxicity of selenium may be due to over-reduction caused by the powerful reductive activity of glutathione perselenide.

Sulfur amino acids in diet-induced fatty liver: a new perspective based on recent findings

The relationship of sulfur amino acids to diet-induced fatty liver was established 80 years ago, with cystine promoting the condition and methionine preventing it. This relationship has renewed importance today because diet-induced fatty liver is relevant to the current epidemics of obesity, non-alcoholic fatty liver disease, metabolic syndrome, and type 2 diabetes. Two recent papers provide the first evidence linking sulfane sulfur to diet-induced fatty liver opening a new perspective on the problem. This review summarizes the early data on sulfur amino acids in fatty liver and correlates that data with current knowledge of sulfur metabolism. Evidence is reviewed showing that the lipotropic effect of methionine may be mediated by sulfane sulfur and that the hepatosteatogenic effect of cystine may be related to the removal of sulfane sulfur by cysteine catabolites. Possible preventive and therapeutic strategies are discussed.

Alteration of radiation-sensitive processes associated with cancer and longevity by dietary 2-mercaptoethanol

BACKGROUND

Previous results demonstrated dietary 2-mercaptoethanol (2-ME) delayed appearance of cancer in certain murine strains. In addition, it had a benefit not found with other organosulfurs, in that it completely prevented spontaneous development of cancer in BXSB-Yaa + over an entire lifespan.

AIMS

These benefits raise the question: What, if any, alteration of radiation-induced tumorigenesis would 2-ME impart that may differ from that of other sulfur antioxidants? This is relevant based on the extensive use of radiation in diagnoses and therapy and 2-ME's superior in vitro and in situ immune enhancement properties.

MATERIALS AND METHODS

This was addressed by exposing long-lived, B10.A (4R) mice to sublethal, 5.5 Gy ionizing gamma-rays and then tumor development monitored over a lifetime.

STATISTICAL ANALYSIS

Two-tailed P-values were determined using the Fischer's Exact Test.

RESULTS

The only tumors detected were mammary and only in animals that were both exposed to radiation and not treated with 2-ME. The 43% incidence differed significantly from the absence of tumors in non-irradiated mice that were or were not exposed to 2-ME and in those irradiated and treated daily with 2-ME, irrespective of whether treatment was started prior to or post irradiation. However, quite unexpectedly, radiation shortened longevity 29% from undefined causes, including cancer, in animals pretreated with 2-ME; longevity was not altered in those not pretreated or if treatment was started post-irradiation.

CONCLUSIONS

The findings have relevance for cancer prevention and the controversy relative to ''long term survival/safety'' of currently used antioxidants as free radical scavengers in humans undergoing radiotherapy.

Anticancer activity and chemoprevention of xenobiotic organosulfurs in preclinical model systems

There seems to be little doubt that xenobiotic and plant derived organosulfur compounds have enormous benefits for in vitro cellular functions and for a multitude of diseases, including cancer. Since there are numerous reviews on anticancer activities of plant organosulfurs, the focus herein will be on alterations associated with xenobiotic organosulfurs. Benefits of 2-mercaptoethanol (2-Me), N-Acetyl-cysteine, cysteamine, thioproline, piroxicam, disulfiram, amifostine, sulindac, celecoxib, oltipraz and their derivates on transplanted homologous tumors and on autochthonous cancers with a viral-, radiation-, chemical carcinogen-, and undefined-etiology are assessed. Because all organosulfurs were not tested for activity in each of the etiology categories, comparative evaluations are restricted. In general, all ‘appeared’ to lower the incidence of cancer irrespective of etiology; however, since most of these values were determined at ages much younger than at a natural-end-of-life-age, differences most likely, instead, reflect a delayed initiation and/or a slowed progression of tumorigenesis. The poorest, long-term benefits of early intervention protocols occurred for viral- and chemical carcinogen-induced cancers. In addition, once tumorigenesis was beyond the initiation stage, outcomes of organosulfur therapies were extremely poor, indicating that they will not be of significant value as stand alone treatments. More importantly, except for the lifetime prevention of spontaneous and radiation-induced mammary tumors by daily dietary 2-Me, similar life long prevention of tumorigenesis was not achieved with other xenobiotics or any of nature’s plant organosulfurs. These results raise an interesting question: Is the variability in incidence found for different organosulfurs associated with (a) their structure, (b) the length of the untreated latency period, (c) treatment duration/dose, and/or (d) the etiology-inducing agent?