title: Temporal stability of chemical hormesis (CH): Is CH just a temporary stop on the road to thresholds and toxic responses?
abstract: Chemical hormesis (CH) is currently described as a nonmonotonic, bidirectional dose-response relationship for chemicals, where a stimulatory, (beneficial?) response at low dose or exposure is followed by an inhibitory response at higher doses/exposures (or vice-versa). CH is depicted as U(J)-shaped or inverse U(J)-shaped curves, i.e., curve slopes change sign. Some describe CH as a homeostasis-preserving response; others view CH as adaptive or (pre)conditioning responses to chemical stress. One aspect of CH and stress hormesis in general that has not been researched is its temporal stability, i.e., persistence, particularly in experimental animals and humans having long-term chemical stressing. Once maximized, does the CH response remain operative over the entire time of chemical exposure? One possible reason for the question's neglect is that temporal stability, e.g., 'steady-state hormesis,' has been assumed. Another is that CH temporality is not well understood or has been under-appreciated as to its importance. Available data, mainly for simpler biological systems, describe cases of transitory CH. Other examples, in human and experimental animal studies, show transitory existence of CH and, in some specialized cases, persisting CH. Also, certain disease state-induced hormetic responses are transitory over time in humans. The question requires resolution if CH is to be considered (i) a stable and beneficial or adverse response, (ii) a stable dose-response model competitive with stable threshold and linear, nonthreshold (LNT) dose-response models, and (iii) a model having any impact on, or role in, regulatory and public health policies.
authors.affiliation: PB Associates, 4036 Nottaway Road, Durham, NC, USA. Electronic address: pandbmushak@cs.com.
authors.forename: Paul
authors.initials: P
authors.lastname: Mushak
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D059165:Hormesis; D006801:Humans; D018570:Risk Assessment; D013997:Time Factors
keywords: Chemical hormesis; Hormesis mechanisms; Nonmonotonic dose-response relationships