Type 1 diabetes (T1D) animal models such as the nonobese diabetic (NOD) mouse have improved our understanding of disease pathophysiology, but many candidate therapeutics identified therein have failed to prevent/cure human disease. We have performed a comprehensive evaluation of disease-modifying agents tested in the NOD mouse based on treatment timing, duration, study length, and efficacy. Interestingly, some popular tenets regarding NOD interventions were not confirmed: all treatments do not prevent disease, treatment dose and timing strongly influence efficacy, and several therapies have successfully treated overtly diabetic mice. The analysis provides a unique perspective on NOD interventions and suggests that the response of this model to therapeutic interventions can be a useful predictor of the human response as long as careful consideration is given to treatment dose, timing, and protocols; more thorough investigation of these parameters should improve clinical translation.

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The tick-transmitted hemoparasite Babesia bovis causes an acute infection that results in persistence and immunity against challenge infection in cattle that control the initial parasitemia. Resolution of acute infection with this protozoal pathogen is believed to be dependent on products of activated macrophages (M), including inflammatory cytokines and nitric oxide (NO) and its derivatives. B. bovis stimulates inducible nitric oxide synthase (iNOS) and production of NO in bovine M, and chemical donors of NO inhibit the growth of B. bovis in vitro. However, the induction of inflammatory cytokines in M by babesial parasites has not been described, and the antiparasitic activity of NO produced by B. bovis-stimulated M has not been definitively demonstrated. We report that monocyte-derived M activated by B. bovis expressed enhanced levels of inflammatory cytokines interleukin-1␤ (IL-1␤), IL-12, and tumor necrosis factor alpha that are important for stimulating innate and acquired immunity against protozoal pathogens. Furthermore, a lipid fraction of B. bovis-infected erythrocytes stimulated iNOS expression and NO production by M. Cocultures of M and B. bovis-infected erythrocytes either in contact or physically separated resulted in reduced parasite viability. However, NO produced by bovine M in response to B. bovis-infected erythrocytes was only partially responsible for parasite growth inhibition, suggesting that additional factors contribute to the inhibition of B. bovis replication. These findings demonstrate that B. bovis induces an innate immune response that is capable of controlling parasite replication and that could potentially result in host survival and parasite persistence.

Tolvaptan is a selective vasopressin V2 receptor antagonist, approved in several countries for the treatment of hyponatremia and autosomal dominant polycystic kidney disease (ADPKD). No liver injury has been observed with tolvaptan treatment in healthy subjects and in non-ADPKD indications, but ADPKD clinical trials showed evidence of drug-induced liver injury (DILI). Although all DILI events resolved, additional monitoring in tolvaptan-treated ADPKD patients is required. In vitro assays identified alterations in bile acid disposition and inhibition of mitochondrial respiration as potential mechanisms underlying tolvaptan hepatotoxicity. This report details the application of DILIsym software to determine whether these mechanisms could account for the liver safety profile of tolvaptan observed in ADPKD clinical trials. DILIsym simulations included physiologically based pharmacokinetic estimates of hepatic exposure for tolvaptan and2 metabolites, and their effects on hepatocyte bile acid transporters and mitochondrial respiration. The frequency of predicted alanine aminotransferase (ALT) elevations, following simulated 90/30  mg split daily dosing, was 7.9% compared with clinical observations of 4.4% in ADPKD trials. Toxicity was multifactorial as inhibition of bile acid transporters and mitochondrial respiration contributed to the simulated DILI. Furthermore, simulation analysis identified both pre-treatment risk factors and on-treatment biomarkers predictive of simulated DILI. The simulations demonstrated that in vivo hepatic exposure to tolvaptan and the DM-4103 metabolite, combined with these 2 mechanisms of toxicity, were sufficient to account for the initiation of tolvaptan-mediated DILI. Identification of putative risk-factors and potential novel biomarkers provided insight for the development of mechanism-based tolvaptan risk-mitigation strategies.

The drug development industry faces multiple challenges in the realization of safe effective drugs. Computational modeling approaches can be used to support these efforts. One approach, mechanistic modeling, is new to the realm of drug safety. It holds the promise of not only predicting toxicity for novel compounds, but also illuminating the mechanistic underpinnings of toxicity. To increase the scientific community's familiarity with mechanistic modeling in drug safety, this article seeks to provide perspective on the type of data used, how they are used and where they are lacking. Examples are derived from the development of DILIsym ® software, a mechanistic model of drug-induced liver injury (DILI). DILIsym ® simulates the mechanistic interactions and events from compound administration through the progression of liver injury and regeneration. Modeling mitochondrial toxicity illustrates the type and use of in vitro data to represent biological interactions, as well as insights on key differences between in vitro and in vivo conditions. Modeling bile acid toxicity illustrates a case in which the over-arching mechanism is well accepted, but many mechanistic details are lacking. Modeling was used to identify measurements predicted to strongly impact toxicity. Finally, modeling innate immune responses illustrates the importance of time-series data, particularly in the presence of positive and negative feedback loops, as well as the need for data from different animal species for better translation. These concepts are germane to most mechanistic models, although the details will vary. The use of mechanistic models is expected to improve the rational design of new drugs.