Protective action of methylglyoxal bis (guanylhydrazone) on the mitochondrial membrane

The effect of methylglyoxal-bis(guanylhydrazone) on mitochondrial Ca(2+) fluxes

Methylglyoxal-bis(guanylhydrazone) (MGBG) induces a dose-dependent inhibition of the electrophoretic Ca(2+) uptake by rat liver mitochondria (RLM) without affecting the electrical membrane potential. MGBG is also able to inhibit the electroneutral Ca(2+) release from mitochondria. These effects result in a progressive increase of Ca(2+) level in suspending medium indicating that Ca(2+) uptake is inhibited at higher extent than Ca(2+) efflux. Spermine instead, induces a lowering of external Ca(2+) concentration. This action is reversed by MGBG which again raises the external Ca(2+) concentration then in the absence of spermine, though at a lower extent. The mechanism of MGBG effects and their implications on energy metabolism are discussed.

Aroclor 1254 inhibits the mitochondrial permeability transition and release of cytochrome c: a possible mechanism for its in vivo toxicity

The mitochondrial permeability transition (MPT) occurs in several forms of necrotic cell death induced by various insults, including oxidative stress, ischemia/reperfusion injury Ca(2+)-ionophore toxicity, and apoptosis. In fact, the release of an apoptogenic factor such as cytochrome c is often associated with the opening of the transition pore. The present study shows that Aroclor 1254, a mixture of polychlorinated biphenyls that was banned in the U.S. in 1977 but is still present in the environment, inhibits the MPT in a dose-dependent manner in a concentration range of 1 to 25 nmol/mg protein. The compound prevents key phenomena associated with the MPT, including colloid-osmotic swelling, the collapse of membrane potential, nonspecific bidirectional traffic of solutes through the transition pore, and the oxidation of pyridine nucleotides. In contrast, Aroclor 1254 does not inhibit uptake of Ca(2+) or P(i). The effects of Aroclor 1254 are evident both in sucrose-based media and in saline and are observed when the compound is added before the opening of the pore. Aroclor 1254 prevents MPT induction provoked by a variety of agents, including phosphate, menadione, tert-butylhydroperoxide, and atractyloside. Aroclor 1254 also inhibits the specific release of cytochrome c, a correlate of MPT induction. These effects reveal a possible toxicological mechanism of action of this compound. The possibility that its effect on mitochondrial function is linked to its action as a tumor promoter is discussed.

Guanidino-containing drugs in cancer chemotherapy: biochemical and clinical pharmacology

The pharmacology and clinical application of three guanidino-containing compounds are reviewed in this commentary with special focus on a new member of this group of drugs, CHS 828 [N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine]. m-Iodobenzylguanidine (MIBG) and methylglyoxal bis(guanylhydrazone) (MGBG) have been extensively studied, preclinically as well as clinically, and have established use as anticancer agents. MIBG has structural similarities to the neurotransmitter, norepinephrine, and MGBG is a structural analog of the natural polyamine spermidine. CHS 828 is a pyridyl cyanoguanidine newly recognized as having cytotoxic effects when screening antihypertensive compounds. Apart from having the guanidino groups in common, there are many differences between these drugs in both structure and their mechanisms of action. However, they all inhibit mitochondrial function, a seemingly unique feature among chemotherapeutic drugs. In vitro in various cell lines and primary cultures of patient tumor cells and in vivo in various tumor models, CHS 828 has cytotoxic properties unlike any of the standard cytotoxic drugs with which it has been compared. Among these are non-cross-resistance to standard drugs and pronounced activity in tumor models acknowledged to be highly drug-resistant. Similar to MIBG, CHS 828 induces an early increase in extracellular acidification, due to stimulation of the glycolytic flux. Furthermore, ATP levels decrease, and the syntheses of DNA and protein are shut off after approximately 30 hr of exposure, indicating active cell death. CHS 828 is now in early clinical trials, the results of which are eagerly awaited.

Cellular pharmacodynamics of the cytotoxic guanidino-containing drug CHS 828. Comparison with methylglyoxal-bis(guanylhydrazone)

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine (CHS 828) is a new guanidino-containing compound with antitumoral activity both in vitro and in vivo. Its activity profile differs from those of standard cytotoxic drugs but the mechanism of action is not yet fully understood. CHS 828 is presently in early phase I and II clinical trials. In the present study, the pharmacodynamic effects at the cellular level of CHS 828 was compared to another compound containing two guanidino groups, methylglyoxal-bis(guanylhydrazone) (MGBG). MGBG is known to inhibit the synthesis of polyamines, which are important in, e.g., proliferation and macromolecular synthesis. The concentration-response relationship of CHS 828 closely resembled that of MGBG and the drugs were similar with respect to inhibition of DNA and protein synthesis. On the other hand, CHS 828 induced a significant increase in cellular metabolism while MGBG did not. The cytotoxic effect of MGBG was reversed by the addition of exogenous polyamines, while that of CHS 828 was unaffected. Unlike MGBG, there was also no effect of CHS 828 on the levels of decarboxylating enzymes in the polyamine biosynthesis. In conclusion, CHS 828 does not appear to share any major mechanisms of action with the polyamine synthesis inhibitor MGBG. Further studies will be required to define the exact mechanism of action of CHS 828.

The effects of methylglyoxal-bis(guanylhydrazone) on spermine binding and transport in liver mitochondria

This study evaluated the effect of the anticancer drug methylglyoxal-bis(guanylhydrazone) (MGBG) on the binding of the polyamine spermine to the mitochondrial membrane and its transport into the inner compartment of this organelle. Spermine binding was studied by applying a new thermodynamic treatment of ligand-receptor interactions (Di Noto et al., Macromol Theory Simul 5: 165-181, 1996). Results showed that MGBG inhibited the binding of spermine to the site competent for the first step in polyamine transport; the interaction of spermine with this site, termed S1, also mediates the inhibitory effect of the polyamine on the mitochondrial permeability transition (Dalla Via et al., Biochim Biophys Acta 1284: 247-252, 1996). In the presence of 1 mM MGBG, the binding capacity and affinity of this site were reduced by about 2.6-fold; on the contrary, the binding capacity of the S2 site, which is most likely responsible for the internalization of cytoplasmic proteins (see Dalla Via et al., reference cited above), increased by about 1.3-fold, and its binding affinity remained unaffected. MGBG also inhibited the initial rate of spermine transport in a dose-dependent manner by establishing apparently sigmoidal kinetics. Consequently, the total extent of spermine accumulation inside mitochondria was inhibited. This inhibition in transport seems to reflect a conformational change at the level of the channel protein constituting the polyamine transport system, rather than competitive inhibition at the inner active site of the channel, thereby excluding the possibility that the polyamine and drug use the same transport pathway. Furthermore, it is suggested that, in the presence of MGBG, the S2 site is able to participate in residual spermine transport. MGBG also strongly inhibits deltapH-dependent spermine efflux, resulting in a complete block in the bidirectional flux of the polyamine and its sequestration inside the matrix space. The effects of MGBG on spermine accumulation are consistent with in vivo disruption of the regulator of energy metabolism and replication of the mitochondrial genome.

Mutagenic and carcinogenic effects of waste oil of frying bean cake on Saccharomyces cerevisiae and Schizosaccharomyces pombe

The present investigation was conducted to study the genotoxic effects of waste oil of frying bean cake (Taamiah oil) using Saccharomyces cerevisiae and Schizosaccharomyces pombe as test organisms. The results showed that the different concentrations of Taamiah oil exert different toxicity on yeast cells. the induced toxicity in both organisms was gradually increased with rising the concentration of Taamiah oil While, the differences between cellular survival and respiratory deficient mutants in treated and untreated samples were significant. Though Taamiah oil induced a concentration-dependent toxicity, it did not exert an induction of recombination. Thus, it seems likely that there was a cytotoxic effect and a weak effect on the induction of cytoplasmic petite mutations in yeast. The results suggest that Taamiah oil does not seem to induce lesions in DNA that are subject to excision repair. However, in Schizosaccharomyces pombe some point mutations seem to be induced in addition to toxicity. The conclusion is straight forward that waste oil of frying bean cake is mutagenic and may be carcinogenic in humans.

Mitochondrial effects of the guanidino group-containing cytostatic drugs, m-iodobenzylguanidine and methylglyoxal bis (guanylhydrazone)

The involvement of mitochondrial damage in the antiproliferative effects of m-iodobenzylguanidine [MIBG] and methylglyoxal bis (guanylhydrazone) [methylGAG] was studied in human neuroblastoma SK-N-SH, mouse neuroblastoma N1E115 and mouse lymphosarcoma S49 cells. Proliferation of SK-N-SH cells was insensitive to MIBG (100 microM gave 15% inhibition), but sensitive to methylGAG (IC50 = 50 microM). MIBG and methylGAG were approximately equitoxic to N1E115 cells (IC50 of 92 and 87 microM, respectively). S49 cells were most sensitive to both MIBG (IC50 = 11 microM) and methylGAG (IC50 = 5 microM). In isolated sonicated mitochondria, MIBG inhibited respiration a complex I of the respiratory chain (EC50 = 0.5 mM), whereas methylGAG was much less effective (EC50 greater than 15 mM). In intact cells, MIBG at 31 microM impaired mitochondrial respiration and stimulated the glycolytic flux. In contrast, equimolar concentrations of methylGAG had no effect on oxygen consumption, ATP content, glucose consumption and lactate production. MethylGAG significantly increased putrescine levels in N1E115 and S49 cells within 12 hr via inhibition of S-adenosylmethionine decarboxylase. No such effects were seen in SK-N-SH cells for up to 48 hr. Equimolar concentrations of MIBG had no effect on the putrescine levels in the various cell lines, suggesting that MIBG did not inhibit S-adenosylmethionine decarboxylase. It is concluded that the antiproliferative mechanisms of the guanidino compounds are essentially different. MIBG inhibited mitochondrial respiration at complex I with concomitant stimulation of the glycolytic flux but was essentially without effect on polyamine levels. On the other hand, cytotoxicity of methylGAG was not associated with mitochondrial dysfunction.