Highly active antiretroviral therapy dysregulates proliferation and differentiation of human pre-adipocytes

AIM To investigate the mechanism(s) by which potential effects of multi-drug highly-active antiretroviral therapy contributes to lipodystrophy syndrome. METHODS Preadipocytes from healthy donors were assessed for proliferation and differentiation in the presence of nucleoside reverse transcriptase inhibitors(NRTIs), nonnucleoside reverse transcriptase inhibitors(NNRTIs), and protease inhibitors(PIs) individually and in combination. Effects on proliferation were assessed with a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay and effects on differentiation were assessed from glycerol-3-phosphate dehydrogenase(GPDH) activity and quantitation of Oil Red O staining for intracellular lipid. Data were analyzed with a randomized block ANOVA with post-hoc Fisher's Least Significant Difference test. RESULTS Preadipocyte proliferation was inhibited by a combination of NNRTI + NRTI(14% at 48 h, P < 0.001) and PI + NRTI(19% at 48 h, P < 0.001) with additional suppression when ritonavir(RTV) was added(26% at 48 h). The drug combination of atazanavir(ATV) + RTV + emtricitabine(FTC) + tenofovir(TDF) had the greatest inhibitory effect on proliferation at 48 h. Preadipocyte differentiation was most significantly reduced by the efavirenz + FTC + TDF assessed either by GPDH activity(64%) or lipid accumulation(39%), P < 0.001. Combining NRTIs with a PI(ATV + FTC + TDF) significantly suppressed differentiation(GPDH activity reduced 29%, lipid accumulation reduced by 19%, P < 0.01). This effect was slightly greater when a boosting amount of RTV was added(ATV + FTC + TDF + RTV, P < 0.001). CONCLUSION Although combination antiretroviral therapy is clinically more efficacious than single drug regimens, it also has a much greater inhibitory effect on preadipocyte proliferation and differentiation.

Circadian rhythms of hormone secretion and obesity

The adipose tissue homeostasis is profoundly affected by circadian rhythms of corticosteroid secretion and chronic loss of hormonal oscillations is associated with obesity. How adipose tissue differentially responds to pulsatile vs continuous presence of glucocorticoids is poorly defined. To address this question, Bahrami-Nejad et al studied differentiation of pre-adipocytes, containing endogenously tagged CCAAT/enhancer binding protein and peroxisome proliferator-activated receptor(PPAR) γ(key regulators of adipocyte differentiation), in response to corticosteroids that were delivered either in an oscillatory fashion or continuously. The authors show that the bi-stable state of differentiation of pre-adipocytes and adipocytes was regulated by a combination of fast and slow positive feedback networks, that determined unique threshold of PPARγ in these cells. Evidently, pre-adipocytes used the fast feedback loop to reject differentiation cues of oscillating pulses of glucocorticoids and failed to differentiate into fat cells. In contrast, when glucocorticoids were delivered continuously, precursor cells exploited the slow feedback loop to embark on a path of maximal differentiation. This differential differentiation response of pre-adipocytes to pulsatile vs continuous exposure to glucocorticoids was corroborated in vivo. Thus, mice receiving non-oscillating doses of exogenous glucocorticoids, for 21 d, elicited excessive accumulation of visceral and subcutaneous fat. These data shed new light on the mechanisms of obesity caused by putative misalignment of circadian secretion of glucocorticoids or their persistently high levels due to chronic stress or Cushing's disease.