Zucker Lean Rats With Hepatic Steatosis Recapitulate Asymptomatic Metabolic Syndrome and Exhibit Greater Sensitivity to Drug-Induced Liver Injury Compared With Standard Nonclinical Sprague-Dawley Rat Model

Abstract

Fatty liver disease is a potential risk factor for drug-induced liver injury (DILI). Despite advances in nonclinical in vitro and in vivo models to assess liver injury during drug development, the pharmaceutical industry is still plagued by idiosyncratic DILI. Here, we tested the hypothesis that certain features of asymptomatic metabolic syndrome (namely hepatic steatosis) increase the risk for DILI in certain phenotypes of the human population. Comparison of the Zucker Lean (ZL) and Zucker Fatty rats fed a high fat diet (HFD) revealed that HFD-fed ZL rats developed mild hepatic steatosis with compensatory hyperinsulinemia without increases in liver enzymes. We then challenged steatotic HFD-fed ZL rats and Sprague-Dawley (SD) rats fed normal chow, a nonclinical model widely used in the pharmaceutical industry, with acetaminophen overdose to induce liver injury. Observations in HFD-fed ZL rats included increased liver injury enzymes and greater incidence and severity of hepatic necrosis compared with similarly treated SD rats. The HFD-fed ZL rats also had disproportionately higher hepatic drug accumulation, which was linked with abnormal hepatocellular efflux transporter distribution. Here, we identify ZL rats with HFD-induced hepatic steatosis as a more sensitive nonclinical in vivo test system for modeling DILI compared with SD rats fed normal chow.

Leptin Receptors Are Not Required for Roux-en-Y Gastric Bypass Surgery to Normalize Energy and Glucose Homeostasis in Rats

“…Finally, to determine if leptin receptors are required for RYGB to normalize liver health, we performed H&E staining on paraffin-embedded liver sections and also measured circulating levels of the liver enzymes ALT and AST as indicators of liver damage. This revealed that obese rats had markedly more hepatic lipid deposits than lean rats ( Figure 4 a), in line with previous studies [ 57 , 59 ], whereas RYGB-treated rats had similar hepatic lipid deposits compared with lean rats ( Figure 4 a). Interestingly, although circulating levels of ALT were higher in obese rats compared with lean rats (0.92 ± 0.03 mg/mL vs. 0.52 ± 0.05 mg/mL; p < 0.0001), again in line with previous studies [ 57 , 59 ], they remained elevated in RYGB-treated rats (0.91 ± 0.06 mg/mL) ( Figure 4 b).…”

“…This revealed that obese rats had markedly more hepatic lipid deposits than lean rats (Figure 4a), in line with previous studies [57,59], whereas RYGB-treated rats had similar hepatic lipid deposits compared with lean rats (Figure 4a). Interestingly, although circulating levels of ALT were higher in obese rats compared with lean rats (0.92 ± 0.03 mg/mL vs. 0.52 ± 0.05 mg/mL; p < 0.0001), again in line with previous studies [57,59], they remained elevated in RYGBtreated rats (0.91 ± 0.06 mg/mL) (Figure 4b). In contrast, circulating levels of AST were similar between groups (Figure 4c).…”

“…Zucker fatty fa/fa rats are another genetic model of leptin receptor deficiency since they harbor an autosomal recessive point mutation in the leptin receptor gene—distinct from the db/db point mutation—which causes an inhibitory amino acid substitution in the extracellular domain common to all leptin receptor subtypes (a–f) [ 53 , 54 , 55 ]. As a result, Zucker fatty fa/fa rats are obese and hyperlipidemic [ 56 , 57 ] and exhibit markedly impaired oral glucose tolerance [ 57 , 58 ] as well as fatty liver [ 57 , 59 ]. Numerous studies have been performed aimed at assessing the metabolic effects of RYGB on Zucker fatty fa/fa rats [ 60 , 61 , 62 , 63 , 64 ] and on the inbred [ 65 ] Zucker diabetic fatty fa/fa rat strain [ 38 , 62 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 ], but their descriptions on food intake are generally either incomplete [ 60 , 61 , 62 , 63 , 64 , 66 , 67 , 68 , 71 , 78 , 79 , 81 ] or, in many studies, entirely missing […”