Cell surface thiols, but not intracellular glutathione, are essential for cytolysis by a cloned murine natural killer cell line

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.

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?

Obesity, longevity, quality of life: alteration by dietary 2-mercaptoethanol

Previous investigations demonstrated that optimization of murine immunological reactivity in tissue culture required a sulfhydryl compound; the most effective being 2-mercaptoethanol (2-Me). Since these reports, 2-Me was found beneficial for both growth/function of other cell-types in vitro, including those of other species, and when fed orally, it impeded and/or reversed some in situ physiological changes associated with aging. More recently, thiol-containing compounds possessing oxidation-reduction potentials weaker than 2-Me were found to impart beneficial effects for many other, including human, diseases. Based on these effects, the research herein addressed the question: What consequences might dietary 2-Me impart on health and disease of mice other than those associated with aging? The main parameters monitored over the lifetime of individual animals exposed to dietary 10⁻³ M 2-Me in their drinking water were: quality of life (obesity and development of recumbent, emaciated and/or cachectic health); longevity; and appearance of tumors. Instead of anticipated toxic attributes, the following unique benefits were found; mean survival of a moderately-lived strain (A/J) was increased 40.8%, high-fat-diet obesity was curtailed in C57BL/10 mice, and a goal of aging intervention protocols, namely preventing loss of quality of life during aging (recumbent, emaciated and/or cachectic) was achieved. Various mechanisms are discussed as they pertain to these findings.

Visualization of proteins in acrylamide gels using ultraviolet illumination

Proteins in polyacrylamide gels can be rapidly visualized by soaking in trichloroacetic acid or chloroform followed by illumination with UV light. The UV-light-driven reaction of tryptophan in the presence of trichlorocompounds yields products that emit sufficiently in the visible region to identify the location of the protein bands on the gel. This method can be used to rapidly identify protein bands on a gel in less than 20 min. On thin polyacrylamide gels, 1.0 microg of protein can easily be detected for proteins with typical tryptophan percentages.

Cell-surface protein disulfide isomerase catalyzes transnitrosation and regulates intracellular transfer of nitric oxide

Since thiols can undergo nitrosation and the cell membrane is rich in thiol-containing proteins, we considered the possibility that membrane surface thiols may regulate cellular entry of NO. Recently, protein disulfide isomerase (PDI), a protein that catalyzes thio-disulfide exchange reactions, has been found on the cell-surface membrane. We hypothesized that cell-surface PDI reacts with NO, catalyzes S-nitrosation reactions, and facilitates NO transfer from the extracellular to intracellular compartment. We observed that PDI catalyzes the S-nitrosothiol-dependent oxidation of the heme group of myoglobin (15-fold increase in the rate of oxidation compared with control), and that NO reduces the activity of PDI by 73.1 +/- 21.8% (P < 0.005). To assess the role of PDI in the cellular action of NO, we inhibited human erythroleukemia (HEL) cell-surface PDI expression using an antisense phosphorothioate oligodeoxynucleotide directed against PDI mRNA. This oligodeoxynucleotide decreased cell-surface PDI content by 74.1 +/- 9.3% and PDI folding activity by 46.6 +/- 3.5% compared with untreated or "scrambled" phosphorothioate oligodeoxynucleotide-treated cells (P < 0.0001). This decrease in cell-surface PDI was associated with a significant decrease in cyclic guanosine monophosphate (cGMP) generation after S-nitrosothiol exposure (65.4 +/- 26.7% reduction compared with control; P < 0.05), with no effect on cyclic adenosine monophosphate (cAMP) generation after prostaglandin E1 exposure. These data demonstrate that the cellular entry of NO involves a transnitrosation mechanism catalyzed by cell-surface PDI. These observations suggest a unique mechanism by which extracellular NO gains access to the intracellular environment.

Penicillamine-induced bullous dermatoses

The successful therapeutic use of D-penicillamine (DPA) has been hindered by its many adverse effects. Autoimmune bullous syndromes are among the less common adverse DPA reactions; they are not dose dependent and appear late in the treatment of diseases of altered immunity, most often rheumatoid arthritis. The majority of the DPA-induced bullous syndromes belong to the pemphigus spectrum, usually pemphigus foliaceus or erythematosus, have a lower prevalence of demonstrable tissue-fixed or circulating antibodies than spontaneously occurring pemphigus, display abnormal direct immunofluorescent patterns, and have a generally favorable prognosis. However, many cases do exhibit a full-blown chronic disease, unaffected by DPA withdrawal. DPA-induced cicatricial pemphigoid is a severe disease of both mucous and cutaneous involvement with a prognosis similar to the spontaneous disease. Cases of DPA-induced epidermolysis bullosa acquisita and DPA-induced bullous pemphigoid were not sufficiently substantiated by immunofluorescence or immunoprecipitation criteria.

Structural analysis and demonstration of the 29 kDa antigen of pathogenic Entamoeba histolytica as the major accessible free thiol-containing surface protein

The 29 kDa protein of pathogenic Entamoeba histolytica is a cysteine-rich surface antigen which we recently characterized by cDNA sequencing and by using monoclonal antibodies which differentiated between pathogenic and non-pathogenic clinical isolates. To determine the structure and biochemical attributes of this protein, a repertoire of immunological techniques using monoclonal antibodies, and radiolabelling were employed. We demonstrated that the 29 kDa protein forms a 60 kDa dimer and a high-molecular-mass oligomer(s) on the surface of the organism through disulphide bonds, and is the major accessible free thiol-containing surface protein of E. histolytica. The deduced amino acid sequence encoding the 29 kDa protein was found to share a common amino acid domain with sequences reported for Helicobacter pylori, Salmonella typhimurium, MER5 gene expressed in murine erythroleukemia cells, Clostridium pasteurianum, and a Bacillus spp.

Dichotomy of glutathione regulation of the activation of resting and preactivated lymphocytes

The present study has examined the effect of GSH on two lines of IL-2-dependent activated killer cells, LAK cells and alpha CD3-activated killer (CD3-AK) cells. We found that GSH added during first 24 hr decreased the generation of LAK and CD3-AK cells from resting lymphocytes, whereas after 48 hr of activation, the addition of GSH increased the killer cell activity. In addition, BSO, an inhibitor of GSH biosynthesis, decreased the proliferation and cytotoxic activities of activated killer cells, and the inhibitory effect was reversed by GSH. These results indicate that GSH downregulates the generation of LAK or CD3-AK cells from resting lymphocytes, but it upregulates the further differentiation of preactivated killer cells. The effect of GSH thus varied with the state of activation of the killer cells. Culturing CD3-AK cells in GSH did not change the distribution of T cell subsets, did not affect the cells' ability to produce lymphokine (IL-2), and did not induce suppressor cells. One striking change as revealed by flow cytometry analysis was that the levels of IL-2 receptor and TCR (alpha/beta)-CD3 were reduced by 80 and 30%, respectively, after 48 hr culturing in GSH. Determination of the mRNA of IL-2 receptor suggests that a post-transcriptional block existed. It appears that the negative effect of GSH on the function of surface IL-2 receptors or T cell receptors on resting lymphocytes severely affected the signal transduction through these receptors and thus abrogated or reduced LAK or CD3-AK cell response. In contrast, for preactivated killer cells, upregulation by intracellular GSH of IL-2 utilization is a dominant effect, thus allowing further differentiation of these killer cells. Our results indicate that the balance between the activation signal (IL-2 or alpha CD3) and the immunoregulatory signal (induced by GSH) may determine the outcome of the immune response.

D-penicillamine

D-Pen represents an effective treatment for a proportion of patients with RA and PSS. Its status in the treatment of juvenile RA is uncertain. The best results will be obtained by a skillful, careful physician maintaining careful surveillance for toxicity. Neither the mode of action nor the mechanisms of toxicity are well understood in RA. Consequently, safer and more effective analogues of D-pen have not been produced.

Role of thiols in human peripheral blood natural killer and killer lymphocyte activities

The thiol reagents, dithiothreitol, diethyldithiocarbamate and reduced glutathione were each found to inhibit Natural Killer and Killer lymphocyte-mediated cytotoxicities. A biphasic aspect to the inhibition with increasing concentration was observed with diethyldithiocarbamate and reduced glutathione. The inhibition observed in response to reduced glutathione, a non-permeant compound, suggests that cell surface thiols may be critical functional groups in the processes of NK and K lymphocyte-mediated cytotoxicities.