We have reported that obese leptin-deficient mice (ob/ob) lacking the
low-
density lipoprotein receptor (LDLR
−/−) develop severe hyperlipidemia and spontaneous atherosclerosis. In the present study, we show that obese leptin
receptor-deficient mice (db/db) lacking LDLR have a similar phenotype, even in the presence of elevated plasma leptin levels. We investigated the mechanism for the hyperlipidemia in obese LDLR
−/− mice by comparing
lipoprotein production and clearance rates in C57BL/6, ob/ob, LDLR
−/− and ob/ob;LDLR
−/− mice. Hepatic triglyceride production rates were equally increased (
1.4-fold,
P<.05) in both LDLR
−/− and ob/ob;LDLR
−/− mice compared to C57BL/6 and ob/ob mice. LDL clearance was decreased (
1.3- fold,
P<.01) to a similar extent in LDLR
−/− and ob/ob;LDLR
−/− mice compared to C57BL/6 and ob/ob controls. While VLDL clearance was delayed in LDLR
−/− compared to C57BL/6 and ob/ob mice (2-fold,
P<.001), this delay was exaggerated in ob/ob;LDLR
−/− mice (3.8-fold,
P<001). The VLDL clearance defects were due to decreased hepatic uptake compared to C57BL/6 (54%and 26%for LDLR
−/− and ob/ob;LDLR
−/−, respectively,
P<.001). When VLDL was collected from C57BL/6, ob/ob, LDLR
−/−, and ob/ob;LDLR
−/− donors and injected into LDLR
−/− recipient mice, counts remaining in the liver were 1.4-fold elevated in mice receiving LDLR
−/− VLDL and 2-fold increased in mice receiving ob/ob;LDLR
−/− VLDL compared to controls receiving C57BL/6 VLDL (
P<.01). Thus, the increase in plasma
lipoproteins in ob/ob;LDLR
−/− mice is caused by delayed VLDL clearance. This appears to be due to defects in both the liver and the
lipoproteins themselves in these obese mice.