Effects of hepatic drug-metabolizing enzyme induction on clinical pathology parameters in animals and man.

Hepatic drug-metabolizing enzyme (DME) induction is an adaptive response associated with changes in preclinical species; this response can include increases in liver weight, hepatocellular hyperplasia and hypertrophy, and upregulated tissue expression of DMEs. Effects of DME induction on clinical pathology markers of hepatobiliary injury and function in animals as well as humans are not well established. This component of a multipart review of the comparative pathology of xenobiotically mediated induction of hepatic metabolizing enzymes reviews pertinent data from retrospective and prospective preclinical and clinical studies. Particular attention is given to studies with confirmation of DME induction and concurrent evaluation of liver and/or serum hepatobiliary marker enzyme activities and histopathology. These results collectively indicate that in the rat, when histologic findings are limited to hepatocellular hypertrophy, DME induction is not expected to be associated with consistent or substantive changes in serum or plasma activity of hepatobiliary marker enzymes such as alanine aminotransferase, alkaline phosphatase, and gamma glutamyltransferase. In the dog and the monkey, published studies also do not demonstrate a consistent relationship across DME-inducing agents and changes in these clinical pathology parameters. However, increased liver alkaline phosphatase or gamma glutamyltransferase activity in dogs treated with phenobarbital or corticosteroids suggests that direct or indirect induction of select hepatobiliary injury markers can occur both in the absence of liver injury and independently of induction of DME activity. Although correlations between tissue and serum levels of these hepatobiliary markers are limited and inconsistent, increases in serum/plasma activities that are substantial or involve changes in other markers generally reflect hepatobiliary insult rather than DME induction. Extrahepatic effects, including disruption of the hypothalamic-pituitary-thyroid axis, can also occur as a direct outcome of hepatic DME induction in humans and animals. Importantly, hepatic DME induction and associated changes in preclinical species are not necessarily predictive of the occurrence, magnitude, or enzyme induction profile in humans.

Differentiating spontaneous from drug-induced vascular injury in the dog.

When vascular injury is observed in dogs used in preclinical toxicology studies, careful evaluation of the lesions is warranted, especially when differentiating drug-induced vascular changes from spontaneous findings, such as idiopathic canine polyarteritis. The clinical signs as well as the nature and distribution of lesions can often be distinguishing, as is the case with vasoactive drugs, including vasodilators and/or positive inotropes (hydralazine, minoxidil, endothelin receptor antagonists, and phosphodiesterase III inhibitors). For most types of vasodilator-induced vascular injury, the lesion is often restricted to coronary arteries, whereas in idiopathic canine polyarteritis, arterial lesions not only involve coronary arteries, but also medium to small arteries of other organs. In addition, the nature of the changes in vessels yields important clues. Medial and adventitial hemorrhage is generally associated with vasodilator-induced arterial lesion, whereas hemorrhage is generally absent in idiopathic polyarteritis. Although idiopathic canine polyarteritis can generally be differentiated from vasoactive-induced vascular injury in dogs, there are increasing incidences of this type of polyarteritis in dogs receiving any 1 of a number of unrelated classes of compounds, suggestive of an exacerbation of the spontaneous disease. Therefore, in order to differentiate drug-induced injury from idiopathic canine polyarteritis, it is critical that examination of the vascular pathology be conducted with good understanding of clinical, pharmacological, and mechanistic data associated with the drug.

Analysis of rat bone marrow by flow cytometry following in vivo exposure to cyclohexanone oxime or daunomycin HCl.

The purpose of these studies was to evaluate bone marrow from male CD rats following exposure to known hematotoxins using flow cytometry (FC) and a monoclonal antibody to the cell surface antigen CD71. Rats were treated with either CHO (300 mg/kg for 10 days) or DAUN (10 mg/kg for 1 day). Control groups received the appropriate vehicle. Half of the animals from each group were euthanized at the end of the dosing schedule and the remaining animals were euthanized after a recovery period. Hematology analyses were completed prior to the onset of each study and on the day of necropsy. Marrow was isolated from the tibia, stained with R-phycoerythrin-conjugated mouse anti-rat CD71 (transferrin receptor on proliferating cells) monoclonal antibody, and then analyzed by FC for myeloid:erythroid (M:E) ratios. FC determinations of myeloid and erythroid population percentages and M:E ratios from untreated rats were confirmed by microscopic examination of marrow cytospins and selected flow cell sorts. M:E ratios for control animals determined by FC were not significantly different between the two studies (1.83 vs 1.89). CHO treatment caused a significant (p < 0.01) decrease in M:E ratios (0.96 for CHO vs 1.48 for control) at day 11 due to increased erythroid cells. M:E ratios were significantly increased (p < 0.05) with DAUN treatment at day 3 (5.07 for DAUN vs 1.70 for control) and corresponded to generalized depletion of all marrow cell lines, especially erythroid cells. After recovery, M:E ratios of CHO and DAUN rats were similar to controls. Hematological values corroborated changes in marrow myeloid and erythroid populations evaluated by this FC technique. Using FC and a monoclonal antibody to the cell surface antigen CD71, this study confirmed the reversible selective toxicity on myeloid and erythroid marrow populations following in vivo exposure to CHO or DAUN. This FC procedure provides a rapid, sensitive method for bone marrow analysis compared to conventional cytological examination.