Human & Experimental Toxicology

This paper introduces an issue of the BELLE Newsletter that is designed to reflect on the role of BELLE in affecting how the concept of hormesis is perceived and accepted by the biomedical and toxicological communities. A brief overview of how BELLE was created is provided.

This paper summarizes numerous conceptual and experimental advances over the past two decades in the study of hormesis. Hormesis is now generally accepted as a real and reproducible biological phenomenon, being highly generalized and independent of biological model, endpoint measured and chemical class/physical stressor. The quantitative features of the hormetic dose response are generally highly consistent, regardless of the model and mechanism, and represent a quantitative index of biological plasticity at multiple levels of biological organization. The hormetic dose-response model has been demonstrated to make far more accurate predictions of responses in low dose zones than either the threshold or linear at low dose models. Numerous therapeutic agents widely used by humans are based on the hormetic dose response and its low dose stimulatory characteristics. It is expected that as low dose responses come to dominate toxicological research that risk assessment practices will incorporate hormetic concepts in the standard setting process.

Personal reflections on radiation hormesis for the past 50 years are presented. The causes of ignoring and rejections of this phenomenon by international and national bodies and by radiation protection establishment are analyzed. The opposition against nuclear weapons and preparations for nuclear war was probably the main factor in inducing the concern for adverse effects of low doses of ionizing radiation, a byproduct of activism against the nuclear weapon tests. UNSCEAR was deeply involved in preparation of the scientific basis for cessation of nuclear test, and contributed to elaboration of the LNT assumption, which is in contradiction with the hormetic phenomenon. However, this authoritative body recognized also the existence of radiation hormesis, termed as ‘adaptive response.’ The political and vested interests behind exclusion of hormesis from the current risk assessment methodology are discussed.

The concept of hormesis, or low-dose U-shaped responses, is now well established in toxicology and pharmacology but requires development in medicine and therapeutics. In doing so, care must be taken to not confuse metaphorical and chemical uses of the term hormesis. Low dose, continuous adaptive responses are fundamentally different than conventional pharmacology, and they may improve the scientific underpinning for complementary medicine, nutrition and lifestyle therapies.

This paper briefly reviewed recent reports on the epidemiological and experimental data on low dose radiation effects that support the concept of radiation hormesis. These reports point to the possibility of existence of a threshold dose in cancer induction by ionizing radiation and in some cases the occurrence of hormetic effects with stimulation of host defense mechanisms. The possibility of the use of low dose radiation in cancer treatment to improve the outcome of conventional radiotherapy was raised by citing previous reports on experimental studies, which showed increased efficacy in tumor control with significant reduction of total dose of radiation when low dose radiation was used in the combined treatment protocol.

Change comes as a surprise because things do not happen in a straight line. Concepts often evolve haphazardly, reacting to specific events. Assumptions are made but are not challenged, sometimes for political or social expedience. It has long been recognized that the dose makes the poison. Concepts of the relationship evolved from both events and the availability of exploratory tools. There are consequences to risk aversion. The general concept of hormesis is perhaps not unexpected. The acceptance of multiphasic dose-responses has the potential to unleash additional and productive insights into this relationship. The activities of BELLE and its Newsletter provide an excellent example of what can be achieved when dogmas are challenged by the accrual of information that has not been previously examined to see whether additional insights are possible. A forthcoming challenge will be the critical examination of all the inputs and assumptions that will be used in the increasing sophistication of biological modeling.

Regarding the role of free radicals in pathogenesis of inflammatory bowel disease (IBD), we were interested to investigate the effects of Teucrium persicum with approved antioxidant and anti-inflammatory properties in an experimental model of colitis. Immunologic colitis was induced by rectal administration of a mixture of 2,4,6-trinitrobenzene sulphonic acid (TNBS) and ethanol through rubber cannula into rats. Three different doses of Teucrium (100, 200, and 400 mg/kg) were gavaged in a duration of 10 days to rats. Endpoint markers of colitis included macroscopic and microscopic examination of colon tissue and measuring colonic cells concentrations of tumor necrosis factor-α (TNF-α), interlukin-1β (IL-1β), total antioxidant power as ferric reducing antioxidant power (FRAP), myeloperoxidase (MPO), and lipid peroxidation as thiobarbitoric acid-reactive substance (TBARS). Teucrium at all doses improved both macroscopic and histological damages of rats with colitis. Teucrium reduced colonic MPO activity and concentrations of cellular lipid peroxides, TNF-α, and IL-1β, with a concomitant increase in FRAP value in rats with colitis. It is concluded that beneficial effects of Teucrium in experimental colitis is mediated through its antioxidant and anti-inflammatory potentials. Examination of this herbal medicine in patients with IBD as a supplement would further reveal the potential of Teucrium.

Imipramine (IMI) and desipramine (DES) are two drugs widely used for the treatment of depression as well as for other diseases. In the present study, we determined their capacity to induce chromosomal aberrations in mouse bone marrow cells. Three doses of each compound were tested and their results were compared with the frequency of chromosomal aberrations obtained in a control group as well as with a group treated with cyclophosphamide. Our results showed a significant increase in chromosome damage with the doses tested for each compound: 7, 20, and 60 mg/kg in the case of IMI, and 2, 20, and 60 mg/kg as regards DES. This last drug induced stronger chromosomal damage than IMI. Our results agree with previous studies regarding the induction of micronuclei and sister chromatid exchanges by the drugs in mouse and suggest caution with respect to their use in long-term treatments.

Clivorine is an otonecine-type hepatotoxic pyrrolizidine alkaloid (HPAs), to which humans are exposed when consuming herbs containing such components. In the present study, we investigated clivorine-induced oxidative stress injury on primary cultured rat hepatocytes. Rat hepatocytes were treated with various concentrations of clivorine (1—100 μM) for 48 hours, and then cell viability was detected by 3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay, while lipid peroxidation (LPO) level, glutathione peroxidase (GPx), glutathione-S-transferase (GST), glutathione reductase (GR), catalase (CAT) and superoxide dismutase (SOD) activities were determined to evaluate the oxidative injury. The results of MTT assay showed that clivorine decreased cell viability in a concentration-dependent manner. Clivorine also increased LPO amounts in rat hepatocytes at the concentrations of 50 μM and 100 μM. Further results showed that clivorine decreased GPx, GST and GR activities, which are all reduced glutathione (GSH)-related antioxidant enzymes. CAT and SOD are both important antioxidant enzymes, and the results showed that clivorine increased CAT activity at the low concentration of 5 μM and decreased cellular SOD activity at all concentrations. Taken together, our results demonstrated that clivorine induced toxicity on primary cultured rat hepatocytes by causing the damage on cellular redox balance.

Cypermethrin (CM) is an important type II pyrethroid pesticide used extensively in pest control and is reported to cause hepatic and renal toxicity. Oxidative stress and lipid peroxidation (LPO) has been implicated in the toxicology of pyrethroids. Fenugreek is known for its antitoxic and antioxidant potential. We have investigated the protective effect of aqueous extract of germinated fenugreek seeds in CM-induced hepatic and renal toxicity. Male Wistar rats were treated with 1/10 LD₅₀ (25 mg/kg body weight) of CM and 10% aqueous extract of fenugreek (GFaq) for 60 days. CM treatment caused increased thiobarbituric acid reactive substances (TBARS), depletion in glutathione (GSH) and reduction in the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST) in liver and kidneys. There was a significant reduction in total phospholipids and increased activities of phospholipases A (PLA) and C (PLC) in liver and kidneys and increased activities of serum marker enzymes, aspartate transaminase (AST), alanine tansaminase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and gamma glutamyl transferase (GGT). Treatment with 10% GFaq showed replenishment of antioxidant status and brought all the values to near normal, indicating the protective effect of fenugreek. Phytochemicals present in fenugreek could play an important role in ameliorating the pesticide-induced toxicity.

Inflammatory bowel disease (IBD) is a chronically relapsing inflammation of the gastrointestinal tract, of which the definite etiology remains ambiguous. Considering the adverse effects and incomplete efficacy of currently administered drugs, it is indispensable to explore new candidates with more desirable therapeutic profiles. 5-HT ₃ receptor antagonists have shown analgesic and anti-inflammatory properties in vitro and in vivo. This study aims to investigate granisetron, a 5-HT ₃ receptor antagonist, in acetic acid-induced rat colitis and probable involvement of 5-HT₃ receptors. Colitis was rendered by instillation of 1 mL of 4% acetic acid (vol/vol) and after 1 hour, granisetron (2 mg/kg), dexamethasone (1 mg/kg), meta-chlorophenylbiguanide (mCPBG, 5 mg/kg), a 5-HT ₃ receptor agonist, or granisetron + mCPBG was given intraperitoneally. Twenty-four hours following colitis induction, animals were sacrificed and distal colons were assessed macroscopically, histologically and biochemically (malondialdehyde, myeloperoxidase, tumor necrosis factor-alpha, interleukin-1 beta and interleukin-6). Granisetron or dexamethasone significantly (p < .05) improved macroscopic and histologic scores, curtailed myeloperoxidase activity and diminished colonic levels of inflammatory cytokines and malondialdehyde. The protective effects of granisetron were reversed by concurrent administration of mCPBG. Our data suggests that the salutary effects of granisetron in acetic acid colitis could be mediated by 5-HT₃ receptors.

To investigate the role of nitric oxide (NO) in acute lung inflammation and injury secondary to acute necrotizing pancreatitis (ANP), 5% sodium taurocholate was retrogradely injected into the biliopancreatic duct of rats to ANP model. These ANP rats were given L-Arginine (L-Arg, 100 mg/kg), L-NAME (10 mg/kg), or their combination by intraperitoneal injection 30 min prior to ANP induction. At 1, 3, 6, and 12 hours after ANP induction, lung NO production, and inducible NO synthase (iNOS) expression were measured. Lung histopathological changes, bronchoalveolar lavage (BAL) protein concentration, proinflammatory mediators tumor necrotic factor alpha (TNF-α), and lung tissue myeloperoxidase (MPO) activity were examined. Results showed that NO production and iNOS mRNA expression in alveolar macrophages (AMs) were significantly increased along with significant increases in lung histological abnormalities and BAL proteins in the ANP group, all of which were further enhanced by pretreatment with L-Arg and attenuated by pretreatment with L-NAME, respectively. These markers were slightly attenuated by pretreatment with combination of L-Arg + L-NAME, suggesting that NO is required for initiating the acute lung damage in ANP rats, and also that L-Arg-enhanced lung injury is mediated by its NO generation rather than its direct effect. MPO activity and TNF-α expression in lung were upregulated in the ANP rats and further enhanced by pretreatment with L-Arg and attenuated by pretreatment with L-NAME, respectively. These results suggest that overproduction of NO mediated by iNOS in the lung is required for the acute lung inflammation and damage secondary to ANP.