Lipodystrophy with high nonesterified
fatty acid (FA) efflux is reported in humans receiving
highly active antiretroviral therapy (
HAART) to treat
HIV infection.
Ritonavir, a common component of
HAART, alters adipocyte FA efflux, but the mechanism for this effect is not established. To investigate
ritonavir-induced changes in FA flux and recycling through
acylglycerols, we exposed differentiated murine 3T3-L1 adipocytes to
ritonavir for 14 d. FA efflux, uptake, and incorporation into
acylglycerols were measured. To identify a mediator of FA efflux, we measured adipocyte
triacylglycerol lipase (ATGL) transcript and
protein. To determine whether
ritonavir-treated adipocytes increased
glycerol backbone synthesis for FA reesterification, we measured labeled
glycerol and
pyruvate incorporation into
triacylglycerol (TAG).
Ritonavir-treated cells had increased FA efflux, uptake, and incorporation into TAG (all P < 0.01).
Ritonavir increased FA efflux without consistently increasing
glycerol release or changing TAG mass, suggesting increased partial TAG hydrolysis.
Ritonavir-treated adipocytes expressed significantly more ATGL
mRNA (P < 0.05) and
protein (P < 0.05).
Ritonavir increased
glycerol (P < 0.01) but not
pyruvate (P = 0.41), utilization for TAG backbone synthesis. Consistent with this substrate utilization,
glycerol kinase transcript (required for
glycerol incorporation into TAG backbone) was up-regulated (P < 0.01), whereas
phosphoenolpyruvate carboxykinase transcript (required for
pyruvate utilization) was down-regulated (P < 0.001). In 3T3-L1 adipocytes, long-term
ritonavir exposure perturbs FA metabolism by increasing ATGL-mediated partial TAG hydrolysis, thus increasing FA efflux, and leads to compensatory increases in FA reesterification with
glycerol and
acylglycerols. These changes in FA metabolism may, in part, explain the increased FA efflux observed in
ritonavir-associated
lipodystrophy.