 |
|
|
| |
Effects of Reyataz & Reyataz+ RTV on Lipids In Vitro
|
| |
| |
Reported by Jules Levin
This study was reported by BMS in a poster at the Lipodystrophy Workshop (October 2004). This study was conducted in vitro meaning in the laboratory. The researchers reported: Atazanavir as a single drug up to 10 µM or in combination with ritonavir (<=2 µM: boosted equivalent concentration) had little effect on triglyceride or cholesterol synthesis in HepG2 hepatoma cells or adipocytes (< 15% effect). These findings are encouraging and are in sync with observations in patients in studies, that Reyataz does not cause elevations in lipids for most people. Questions remain regarding boosted Reyataz, which is boosted by 100 mg of ritonavir per day. Anecdotal reports of patients with elevated lipids who switch to Reyataz/r are that dramatic improvements in lipids for some patients occurs. Study data suggests Reyataz/r can have a favorable lipid profile for patients on other HAART regimens who switch. But doubts remain regarding the effects of ritonavir boosted Reyataz on lipids, thus this study. Still, this study is in vitro, so further study in patients are anticipated. The authors concluded that confirmatory clinical data are needed.
"Comparative Effects of Atazanavir Alone and in Combination with Low Concentration of Ritonavir on Triglyceride and Cholesterol Synthesis in vitro"
MA Noor, R Mulvey, C. Elosua, F. Wang, RA Parker and OP Flint.
Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton NJ USA
ABSTRACT
Objectives: Treatment with some protease inhibitors (PIs) is associated with dyslipidemia. Proposed mechanisms include effects on lipid and lipoprotein production in hepatocytes and adipocytes. Atazanavir is a potent once-daily PI that in combination with low-dose ritonavir, showed comparable clinical efficacy to lopinavir/ritonavir in treatmentexperienced patients. Compared to ritonavir and lopinavir, atazanavir is associated with less or no dyslipidemia clinically and less effect on lipogenesis in vitro. We hypothesized whether combining atazanavir with ritonavir at low concentration (<=2 µM) would negate the favorable in vitro effect of atazanavir on lipogenesis reported previously.
Lipogenesis defined: production of fat, either fatty degeneration or fatty infiltration. Also called adipogenesis. An alternate use of lipogenesis is: the normal deposition of fat or the conversion of carbohydrate or protein to fat.
Methods: Lipogenesis was assayed as [14C]2-acetate incorporation into triglyceride and cholesterol in human primary adipocytes and HepG2 hepatoma cells. Triglyceride and cholesterol synthesis were quantified in triplicates in the presence of atazanavir and lopinavir alone or in combination with ritonavir at various doses approximating therapeutic and boosted PI levels expected in vivo. Comparisons are by t-test versus control.
Results: As a single drug at boosted-equivalent concentration (<=2 µM), ritonavir did not affect lipogenesis in either cell line. At 3 µM, ritonavir modestly inhibited (15-30%) triglyceride and cholesterol synthesis in adipocytes (P<0.05 for both). At 3 µM, ritonavir inhibited triglyceride synthesis in adipocytes and increased triglyceride synthesis in HepG2 cells. Atazanavir as a single drug up to 10 µM or in combination with ritonavir (<=2 µM) had little effect on triglyceride or cholesterol synthesis in HepG2 or adipocytes (< 15% effect, P>0.2). In contrast, lopinavir as a single drug at 10 µM increased (~50%) triglyceride synthesis in HepG2, and inhibited synthesis of triglycerides (~30%) and cholesterol (~50%) in adipocytes (P<0.01 for all).
Conclusions: Atazanavir as a single drug at 10 µM or combined with ritonavir up to 2 µM has very little effect on lipogenesis, whereas lopinavir as a single drug at 10 µM or combined with ritonavir up to 2 µM affects lipogenesis. The data are consistent with the current hypothesis that ritonavir-boosted atazanavir used clinically will maintain the favorable lipid profile of unboosted atazanavir. Confirmatory clinical data are needed.
INTRODUCTION
PI-associated atherogenic lipid profile manifests as elevated triglyceride (TG) and VLDL levels with increased LDL-cholesterol and low HDL. These lipid disturbances appear to result from hepatic overproduction and delayed clearance of triglyceride-rich VLDL, which tends to promote formation of small-dense LDL and reduce HDL. PIs also are associated with lipoatrophy, observed as the progressive loss of normal lipid stores in adipose tissue (note from Jules Levin: studies find associations between the use of certain nukes & lipoatrophy. The association between PIs and lipoatrophy is not well established, based on studies performed. However, it is believed by some that PIs may be associated with lipoatrophy, however, some believe they may not be. Studies suggest that regardless of regimen some patients develop lipoatrophy on HAART. At the Lipo Wksp, study of a regimen of amprenavir/r (SOLO Study) with tenofivir+3TC resulted in 3% of study patients developing lipoatrophy. The best way to deal with lipoatrophy is to carefully select your firstline regimen). Current PIs exhibit varying potencies in cell-based assays of lipid and glucose metabolism in liver and adipocyte models, including disruption of lipogenesis and triglyceride storage in adipocytes and overproduction of hepatic cholesterol and triglyceride (and under some conditions) increased VLDL secretion.
Compared to ritonavir and lopinavir, atazanavir is associated with less dyslipidemia clinically. Previously we reported that in HepG2 cells, PIs such as NFV and RTV promote TG synthesis while ATV has little or no effect. In adipocytes, LPV, RTV and SQV suppress TG synthesis while ATV has little effect. Clinically, many patients are being treated with combination of low-dose ritonavir (RTV) (mean Cmax ~ 0.5 to 1.5 µM) added on to ATV to take advantage of the enhanced pharmacokinetic profile. We tested the hypothesis that low dose RTV would negate the favorable in vitro lipid metabolic profile of ATV previously reported.
RESULTS
RITONAVIR AT 1, 2 and 3 µM
At concentrations of 1, 2 µM, ritonavir had no significant* effect on TG or CHOL synthesis in a human hepatocyte cell line (HepG2), or primary cultures of human adipocytes. At 3 µM, ritonavir significantly* inhibited cholesterol synthesis (63% control values) in human adipocytes. A non-significant reduction in TG synthesis was also observed in human adipocytes treated with 3 µM ritonavir. At 3 µM, ritonavir significantly increased both TG and CHOL synthesis in human hepatocytes.
*Means compared by Anova and Tukey-Kramer post-hoc analysis
(Significance at P < 0.05).
1. Selection of Ritonavir Concentrations for Combination Studies:
Because 3 µM ritonavir appeared to significantly affect both TG and CHOL synthesis in hepatocytes and adipocytes, in subsequent experiments we combined atazanavir or lopinavir with 1 or 2 µM ritonavir. The selected concentrations of ritonavir are equivalent to the Cmax observed in treatment with "boosted" PIs.
2. In general, there were only small, non-significant differences between cultures exposed to the PI alone or to the combination of ritonavir (1 or 2 µM) with the PI.
3. Human Adipocytes: Atazanavir slightly inhibited TG and CHOL synthesis at the highest concentration tested. In contrast, lopinavir, strongly inhibited adipocyte TG and CHOL synthesis over the full range of concentrations tested, and in a concentration-dependent manner.
4. Human Hepatocytes (HepG2): There were marked differences in the effect of the PIs on TG and CHOL synthesis. As in the adipocyte cultures, lopinavir strongly inhibited hepatocyte cholesterol synthesis in a concentration-dependent manner, while atazanavir only slightly inhibited hepatocyte cholesterol synthesis at the highest concentration tested. In contrast, both PIs tended to induce hepatocyte TG synthesis at the two lowest concentrations tested (3, and 10 µM). Lopinavir induced hepatocyte TG synthesis more strongly than atazanavir. At the highest concentration tested (30 µM) lopinavir inhibited TG synthesis by up to 50%.
DISCUSSION & CONCLUSIONS BY AUTHORS
--Ritonavir alone (1 or 2 µM) had no effect on either TG or CHOL synthesis over the range of concentrations tested in combination with atazanavir or lopinavir. At 3 µM, ritonavir slightly inhibited TG and CHOL synthesis in adipocytes, but induced lipid synthesis in hepatocytes. --ATV combined with low-concentration of RTV (<2 µM) exhibited weaker effects in preclinical assays of lipid biosynthesis in the HepG2 human hepatocyte cell line, and in human primary adipocytes, as compared to lopinavir combined with ritonavir. --Increased TG synthesis in hepatocytes (increased lipid production) but reduced TG synthesis in adipocytes (diminished fat storage), which was most significant in the case of lopinavir, is a potential mechanism for clinically-observed hyperlipidemia. Suppression of TG synthesis in the adipocyte may contribute to insulin resistance due to elevated free fatty acids, and in the long term promote clinical lipoatrophy. --The differences in the effect of PIs, especially lopinavir, on TG and CHOL synthesis in hepatocytes (induction vs inhibition) suggest that the key transcription factors regulating TG and CHOL synthesis (respectively, SREBP1 and SREBP2) are differently affected in hepatocytes following exposure to PIs. This appears not to be the case in adipocytes where both TG and CHOL synthesis were inhibited by the PIs tested.
--Data are consistent with the maintenance of ATV's favorable lipid profile when combined with a low-concentration of RTV suggesting that ritonavir-boosted atazanavir used clinically will maintain the favorable lipid profile of unboosted atazanavir.
--Confirmatory clinical data in patients are needed.
|
| |
|
|
|
|
|
