Hormetic effect

Given the problems associated with using standard animal bioassays and doses above the level where hormetic effects might be observed (which... 

Hormetic effects of low-dose stimulatory and high-dose inhibitory response include parameters of good health such as growth rate, fecundity, and longevity. The dose-response curve for this type of hormetic effect is the inverted U, see Figure 4.3. 

For adverse effects such as carcinogenicity, mutagenicity, and disease incidence, a hormetic effect means low-dose reduction and high-dose enhancement of response. The dose-response curve is the J-shape, see Figure 4.4. 

Low concentrations of carcinogenic polycyclic aromatic hydrocarbons (PAHs) have also been evaluated for a potential hormetic effect. Exposure of grunion embryos (Leuresthes tenuis-, a freshwater tel-eost) to 7ppb of benzo [a]pyrene resulted in significantly increased respiration rates compared with unexposed controls, whereas at higher concentrations of 24.2, 361, or 868.8 ppb, respiration rates were not... 

The implications of hormetic effects for chemotherapeutics also extend to the domain of peptide biology and its relationship to the human genome. Numerous hormetic-like biphasic dose responses exist for peptides, further displaying the broad generalizability of the hormetic concept. Recent assessments of both chemotherapeutic (57) and peptide (58) examples of hormetic effects have been completed. 

If hormetic effects are an evolutionary/biological/toxicological expectation, then it implies that hazard assessment strategies include a protocol to assess its possible occurrence. This has practical importance because hormetic effects may affect both the concept and derivation of the NOAEL. The derivation of the NOAEL could change if the low-dose stimulation were determined to be an adverse effect. The hormetic dose-response continuum in this instance (i.e., both the increase at low doses and the decrease at high doses from the control) could be viewed as adverse. However, if the low-dose stimulation were deemed as beneficial, it would have little direct effect on the concept of the NOAEL, but could affect how the traditional NOAEL is derived (59) as well as challenging the basic goal of the risk assessment process from the exclusive focus on the avoidance of potential harm to also include the concept of benefit. 

Appleby AP. 1998. The practical implications of hormetic effects of herbicides on plants. BELLE Newsl. 6 23-24... 

Calabrese EJ, Baldwin LA. 1999. Implementing hormetic effects in the risk assessment process differentiating beneficial and adverse hormetic effects in the RfD derivation process. Hum. Ecol. Risk Assess. 5 965-71... 

The probit model does not adequately describe the growth-response curve produced when G is fed to H. virescens larvae due to the hormetic effect observed at lower dosages, which causes a mean weight increase instead of the steady decrease required by probit model. We propose a new exponential/probit model described by the equation ... 

Simple probit analysis does not reflect the hormetic effect of G, and a new exponential/probit model which more accurately describes this effect has been proposed. 

Hormesis is not unique to EMs. It has been reported for several plant and animal species exposed to heavy metals, pesticides, polycyclic aromatic hydrocarbons, and other organic chemicals [67-69], Stebbing [68] suggested that hormesis is the cumulative consequence of transient and sustained overcorrections of biosynthesis, that is, a rate-controlled process controlled by the end-product inhibition. To date, however, no studies have identified the mechanisms responsible for hormetic effects of explosives at specific concentrations. 

Hormesis is a dose-response phenomenon characterized by low-dose stimulation and high-dose inhibition. The determination of whether the hormetic stimulation is beneficial or not should be decoupled from a decision as to whether the response is hormetic or not. Hormetic effects themselves can be beneficial, neutral, or harmful depending on the specific circumstances. For example, a low-level exposure to an antibiotic may stimulate the growth of harmful bacteria that could be harmful to human patients yet theoretically... 

Calabrese, E.J. (2001). Overcompensation stimulation A mechanism for hormetic effects. Critical Reviews in Toxicology, 31, 425—470. 

In addition to the negative effects of radiation at high doses, there is evidence that a hormetic effect occurs in some plants at lower doses. This tends to increase the yield in erop species when seeds are irradiated with ganuna doses np to 10 Gy. However, the growth stimulation is often inconsistent among experiments, with other envi-romnental variables exhibiting control. Therefore the phenomenon has not been widely nsed cormnercially. 

The above examples are just a few of the many studies that have shown that radiation health effects demonstrate a hormetic effect, a characteristic of most pharmaceuticals and even to many foods. Hormesis is the concept that large doses of a substance may be detrimental to health, but small doses are beneficial. The evidence for this knowledge was effectively presented in a text published in 1980, titled Radiation Hormesis, by Dr. T.D. Luckey, and in 1991 followed by the second edition [7]. This text included over 1000 references of data on radiation hormesis. 

Figure 26.1, derived from the work of T.D. Luckey, represents the nominal hormetic effect of low levels of radiation on human beings. The ordinate axis indicates nominal negative... 

Nominal hormetic effect of low levels of radiation on human beings. 

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