Response to letters to the editor: Caldwell et al. [2008]

Reply: We would like to respond to two letters to the editor (Schoeb et al. and Goodman et al.) regarding our article ‘‘Evaluating the evidence for infection as a mode of action for the induction of rat lymphomas [Caldwell et al., 2008]. ’’ Some of the substantive comments contained in these letters have been addressed by Dr. Soffritti and colleagues in the publication of a second study of Aspartame [Soffritti et al., 2007, 2008] and in his responses to other letters and reviews [Soffritti et al., 2006, 2007, 2008; Magnuson et al., 2007; Magnuson and Williams, 2008; Soffritti, 2008]. In regard to the publication cited by Schoeb et al. that has been submitted to another journal, we cannot comment on a paper to which we do not have access. We agree with Goodman et al. that the best evidence regarding presence or absence of Mycoplasma Pulmonis (Mycoplasma P.) would be relevant serological data, although detection of Mycoplasma P. can be difficult. Schoeb et al. have argued why they believe the pattern of available data leads them to conclude that they believe it is ‘‘essentially certain’’ that the rats used in the bioassays at the European Ramazzini Foundation (ERF) had Mycoplasma P. infections. Interactions have been reported as described in our original article. However, there is certainly no existing evidence that shows the need for Mycoplasma P. to be present for these specific chemicals to induce the very specific response. There is no evidence that these particular chemicals exacerbate Mycoplasma P. disease. That a number of environmental conditions such as poor hygienic conditions and increased ammonia exposure can exacerbate Mycoplasma P. infection and effects is never disputed by our article but is in fact described therein. Schoeb [2000] states that animals can carry organisms without the causation of overt disease but that stress, poor nutrition, concurrent infections, advanced age, and environment and other factors can cause clinical disease. However, there is no mention in that report of Mycoplasma P. causing neoplasia but rather that Mycoplasma P. usually causes rhinitis and otitis media in rats. Descriptions of environmental conditions in the ERF are that such conditions that exacerbate mycoplasmosis (e.g., excessive ammonia levels) do not appear to be present at the ERF. The most detailed description of laboratory protocols and practices of the ERF [Maltoni et al., 1986] are consistent with acceptable care. Maltoni et al. [1986] have documented the careful attention paid to the conditions in which the animals are kept at the ERF, including the handling procedures designed to minimize stress, which can also be a factor in disease response. The same general procedures were reported by Soffritti et al. [2007] as well as compliance with Italian law regulating the use and humane treatment of animals for scientific purposes [Decreto Legistlativo N. 116, 1992]. As discussed in the US. EPA Cancer Guidelines [U.S. EPA, 2005], EPA policy is that ‘‘care should be taken to include studies that provide some evidence bearing on carcinogenicity or that help interpret effects noted in other studies, even if these studies have some limitations of protocol or conduct. ’’ Bioassays and associated reports by ERF and other laboratories such as the Bushy Run Research Center (BRRC) and the New Energy Development Organization (NEDO) may use different paradigms and/or quality and completeness than the NTP bioassays and reports. The differences in standard practices among laboratories can impart uncertainty into the assessment of a chemical’s cancer potency. However, the unique ERF protocol, including lifespan observation and use of Sprague-Dawley rats, appears to impart advantages too, increasing the sensitivity of the bioassay in some cases, such as for the lymphoma endpoint. Contrary to the negative view of full lifespan studies voiced by Goodman et al., this study protocol has been credited as the primary reason that ERF was the first laboratory to associate carcinogenic responses with chemicals that are now recognized as known human carcinogens, such as vinyl chloride [Maltoni and Cotti, 1988], acrylonitrile [Maltoni et al., 1988], and benzene [Maltoni et al., 1989]. When Schoeb et al. make reference to what is normally observed in rat studies, it must be also kept in mind that the ERF conducts studies for the lifetime of