Bruce S. Hass

Does caloric restriction induce hormesis

The question of whether caloric restriction (CR) is hormetic is addressed in terms of two common defini-tions of the term. In terms of the older definition, i.e., a growth-stimulatory effect when lower doses of a compound which resulted in growth inhibition at higher doses, CR is better characterized as a co-hormetic (i.e., a paradigm which at relatively “low doses,” in combina-tion with some stimulus, will evince increased growth (proliferation) and at higher “doses” will inhibit this increased proliferation) rather than a hormetic agent. Mechanisms such as cellular selection of cellular subpopulations, increases in receptor efficiency, and preservation of cellular proliferative potential can inter-act with agents and produce increased growth as long as the CR is not too severe. In terms of a broader definition, i.e., nonmonotonic dose-response behavior of a compound for any adverse response, CR appears to be hormetic, both as a result of body weight (BW) loss and other potential mechanisms. The impact of changes in BW, or frank CR, can be considered a component of every test for hormesis, and is thus capable for interaction with any other agent. The changes that BW loss (or CR) induce are so profound that any aspect of an agents action-metabolism, pharmacokinetics, pharmacodynamics-can modulate the response of an organism to an agent. Similarly, other effects of a chemical that induce BW loss, e.g., physical activity or temperature dysregulation, can also induce dose-response curves that appear hormetic. The interaction of the hormetic agents of BW loss and CR can influence agent tests. Controlling these factors may make it possible to dissect the key components of a hormetic response. In addition, the effects of CR or BW loss appear to extrapolate well across species [Colman R, Kemnitz JW. Aging experi-ments using nonhuman primates. In: Yu BP (Ed), Methods in Aging Research. CRC Press, Boca Raton, FL, 1999, pp. 249-267]. Thus there is some reason to believe that these hormetic factors may be important for humans, and may already be a factor for tests of potentially adverse agents already conducted in humans.

Hormesis - Implications for risk assessment caloric intake (body weight) as an exemplar

Hormesis can be considered as a parameter which has a non-monotonic relationship with some endpoint. Since caloric intake is such a parameter, and the impact of this parameter on risk assessment has been fairly well characterized, it can provide clues as to how to integrate the information from a hormetic parameter into risk assessments for toxicants. Based on the work with caloric intake, one could: (a) define a biomarker for hormetic effect; (b) integrate specific information on when in the animals lifespan the parameter is active to influence parameters such as survival; (c) evaluate component effects of the overall hormetic response; and (d) address the consequences of a non-monotonic relationship between the hormetic parameter and endpoints critical for risk assessment. These impacts on risk assessments have been characterized for chronic tests, but are also true for short-term tests. A priority is the characterization of the dose-response curves for hormetic parameters. This quantification will be critical in utilizing them in risk assessment. With this information, one could better quantitatively address the changes one expects to result from the hormetic parameter, and limit the uncertainty and variability which occurs in toxicity testing.

Protective effect of magnesium on DNA strand breaks induced by nickel or cadmium

Magnesium, an essential metal that is important in the normal functioning of DNA, has been shown to interact with some of the toxic heavy metals in respect to biochemical and molecular mechanisms and in altering the tumorigenic process. This study examined the influence of magnesium in combination with nickel and cadmium in respect to damage of the DNA molecule. The purpose of this study was to evaluate the influence of magnesium on the amelioration of the toxic metals nickel and cadmium in respect to sustaining DNA damage. Two types of lymphocytes were used, i.e., primary Fischer 344 rat splenocytes and AHH-1 TK+/-, a human B-lymphoblastoid cell line that has been spontaneously transformed. These cells were grown in either a magnesium-free or magnesium-supplemented RPMI 1640 medium that was specifically formulated for this study. A 2x2 factorial design was employed with magnesium and either nickel or cadmium serving as the two factors. The experimental groups were as follows: +Mg+Ni, +Mg−Ni, −Mg+Ni, −Mg−Ni, with cadmium alternating for the nickel in the subsequent studies. The nickel or cadmium was added at a concentration of 50 μmol/L. The presence of double-stranded DNA was determined in each of the respective treatment groups with the two types of cell lines. Based on the results of this study, nickel is not directly toxic to DNA, whereas cadmium produces damage directly on the DNA molecule. The magnesium has little or no direct influence on the occurrence of DNA damage from nickel since the toxicity of nickel appears to be manifested in areas other than the DNA molecule, such as in the heterochromatin. The presence of cadmium in the treatment group resulted in DNA damage, which in turn was reduced significantly by the presence of magnesium.

Reduced levels of catalase activity potentiate MPP+-induced toxicity: comparison between MN9D cells and CHO cells.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to be toxic by inducing oxygen free radicals in the mammalian nervous system, especially in the nigrostriatal dopaminergic system. The present study was designed to compare the toxic effects of MPP+, the active metabolite of MPTP, in MN9D neuronal cells that exhibit relatively low levels of catalase activity, as compared to CHO cells, which exhibit high levels of catalase activity. The survival of the MN9D cells in the presence of 250 microM MPP+ was less than 10%, whereas CHO cells exhibited 70% survival at the same concentration of MPP+. The ED50 values of MPP+ in MN9D and CHO cell lines were 60-600 microM, respectively. MN9D cells contain less catalase, an enzyme believed to be involved in the detoxification of free radicals compared to CHO cells. The catalase activity was 2 Units/mg protein in MN9D cells and 30 U/mg protein in CHO cells. The catalase activity in CHO cells increased with increasing MPP+ concentrations from 100-500 microM, however, it decreased at 1 mM MPP+. In contrast, catalase activity in MN9D remained the same at all MPP+ concentrations. When the CHO cells were pre-treated with 10-25 mM 3-aminotriazole (3-AT), which inhibits catalase activity, and exposed to MPP+ at various concentrations, they became susceptible to MPP+. It is evident from these data that the differential susceptibility to MPP+ in these two cell lines are due to differences in catalase activity. In addition, the inhibition of constituentive catalase activity in CHO cells by 3-AT treatment enhances their susceptibility. In conclusion, the study demonstrates that catalase activity represents an important defence mechanism in MPTP-induced toxicity.

EFFECT OF MAGNESIUM ON THE GROWTH AND CELL CYCLE OF TRANSFORMED AND NON-TRANSFORMED EPITHELIAL RAT LIVER CELLS IN VITRO

The effects of magnesium (Mg) restriction on cell growth and the cell cycle were determined in transformed (TRL-8) and non-transformed (TRL-12-15) epithelial-like rat liver cells. Cells were cultured in RPMI 1640 medium in which the Mg concentration was reduced to 0.5, 0.1, and 0 × the concentration in the regular RPMI 1640 media (100mg/l). Cell growth in the transformed cells was not influenced by the Mg restriction as greatly as in the non-transformed cell line. Transit through the cell cycle also exhibited an independence of the Mg in the medium in the transformed cells. When transformed cells were grown for two generations in Mg-limited medium, the growth rate slowed to a rate similar to that demonstrated by the non-transformed cells. Analysis by flow cytometry showed that transit through the cell cycle was minimally slowed in Mg deficient transformed cells; however, transit through the G1 and S phases in the non-transformed cells was slowed. The TRL-8 cells in Mg-limited medium resulted in fewer nuclei in G1 with subsequent increases in the percentages of S-phase nuclei. The TRL 12-15 cells reacted oppositely with the number of G1 nuclei increased and the number of S-phase nuclei decreased. In respect to growth, these results show that epithelial cells respond in a similar manner to Mg-limitation as do fibroblast cells. The transformed cells exhibited a level of independence from Mg in respect to growth, reproduction, and cell-cycle kinetics.

Neoplastic pathology in male Sprague-Dawley rats fed AIN-93M diet ad libitum or at restricted intakes.

The primary purpose of this study was to evaluate the effects of age and long-term dietary reduction on neoplastic diseases in rats fed the AIN-93M purified diet. Second, pathologic profiles are critical to comprehensive dietary evaluation. Male Sprague-Dawley rats assigned to 2 groups, ad libitum (AL) and dietary restricted (DR), were fed the AIN-93M (casein protein) diet free choice and reduced in amount by 31%, respectively. At 58 weeks of age, the predominant types of lesions in AL and DR rats were pituitary and skin tumors. At 114 weeks of age, the most common lesions were pituitary, adrenal gland, skin, mammary, brain, and pancreatic tumors and mononuclear cell leukemia. However, DR had no significant effect on these lesions. Primary findings demonstrate that DR significantly reduced the total number of tumors per rat and incidence of benign and primary tumors (all organs) but did not reduce the incidence of malignant tumors (all organs). Dietary restriction increased the percentage of unknown deaths. These results may explain why survival rates for AL and DR rats were not significantly different at 114 weeks (43.3 vs 57.5%, respectively). These findings differ from previous studies using NIH-31 cereal diet (Aging Clin Exp Res 2001;13:263; J Nutr 2002;132:101; Aging Clin Exp Res 2003;16(6):68; Aging Clin Exp Res 2004;16:448) where neoplastic lesions rather than nonneoplastic lesions were linked to a significant increase in survival rate among cohorts of DR-fed rats (J Nutr 2002;132:101). Factors such as diet composition and digestibility, although not independent of body weight, may have contributed to differences in rat mortality and may affect humans in a similar manner.

Nonneoplastic pathology in male Sprague-Dawley rats fed the American Institute of Nutrition-93M purified diet at ad libitum and dietary-restricted intakes ☆

This study evaluates the effects of age and chronic dietary restriction (DR) on nonneoplastic diseases in rats that were fed the American Institute of Nutrition (AIN)-93M purified diet. Male Sprague-Dawley (SD) rats were divided into an ad libitum (AL) group and a DR group that was fed the AIN-93M diet with intake reduced by 31%. Nonneoplastic disease profiles were developed to clarify whether the AIN-93M diet fulfills long-term nutritional requirements of rats. Subsets of rats were killed at 58 and 114 weeks of age, and histopathology was performed. At 58 weeks of age, the 2 main types of nonneoplastic diseases in AL rats were liver vacuolization and cardiomyopathy. Dietary restriction reduced the severity and incidence of both lesions. At 114 weeks of age, the most common lesions in AL rats were cardiomyopathy, nephropathy, liver vacuolization, and degeneration with renal failure and genitourinary infections causing the greatest mortality. Dietary restriction reduced the incidence and severity of these lesions. Nonneoplastic diseases accounted for 28.9% and 0.0% of total mortalities in the AL and DR groups, respectively; however, there was a higher incidence of unknown deaths in the DR rats (52.6%) compared to AL rats (28.9%), which may have limited the success of DR to improve survival. Although the AIN-93M diet supported chronic rat growth, alterations in some dietary component concentrations may be required to lower body weight in chronic rodent and human studies. Factors such as diet composition and digestibility may alter nonneoplastic diseases and mortality in rats and humans in a similar fashion.