Evaluation of the Properties of Encapsulated Stavudine Microparticulate Lipid-based Drug Delivery System in Immunocompromised Wistar Rats.

BACKGROUND: Lipid-based formulations have been confirmed to lower some side effects of drugs and can be tailor-made to offer sustained drug release of drugs with short half-life like stavudine. AIM: This study aimed to evaluate the immunomodulatory properties of stavudine-loaded solid lipid microparticles (SLMs) using immunocompromised Wistar rats. METHODS: The SLMs were formulated by the homogenization method. The optimized batches were used for further in vivo studies. The effect of formulation on the CD4 count and the haematological properties of immunocompromised Wistar rats were studied. RESULTS: The particle size range was 4 -8 µm, EE range was 85-93 % and maximum drug release was observed at 10 h. The CD4 cells increased from 115 ± 3.17 cell/mm3 at day zero to 495 ± 5.64 cell/mm3 at day 14 of treatment and 538 ± 6.31 cell/mm3 at day 21. The red blood cells increased from 2.64 ± 1.58 (x 106/mm3) at day zero to 6.96 ± 3.47 (x 106/mm3) at day 14 and 7.85 ± 3.64 (x 106/mm3) at day 21. PCV increased significantly (p < 0.05) to about 42-50 % at day 21 in the groups that received the SLMs formulations. White blood cells (WBC) also were 12 x 103/mm3, for SLM formulations, while the rats that received plain stavudine exhibited WBC of 9.6 x 103/mm3 at day 21. The histopathological studies revealed that oral stavudine-loaded SLMs had no significant damage to the kidney, liver, spleen and the brain of Wistar rats. CONCLUSION: The formulations exhibited significantly higher immunomodulatory properties than plain stavudine (p<0.05) and showed good properties for once daily oral administration and could be a better alternative to plain stavudine tablets for the management of patients living with HIV.

Effect of change in nucleoside structure on the activation and antiviral activity of phosphoramidate derivatives.

Changing the nucleoside group of a series of phosphoramidate derivatives affects the enzyme mediated hydrolysis rate of the compounds. d4T and AZT-substituted analogs were activated by enzymes such as lipases, esterases, and proteases. On the other hand, 3dT-substituted derivatives were comparatively less prone to hydrolysis under similar experimental conditions. From the experimental results, we propose that the most preferable nucleoside group for enzyme activation is d4T rather than AZT or 3dT. Additionally, we also observed that depending on the enzymes used the chiral selectivity of the enzymes for the phosphorus center of these phosphoramidate derivatives differed, demonstrating the importance of the nucleoside structure for this class of compounds.

ATP-dependent removal of nucleoside reverse transcriptase inhibitors by human immunodeficiency virus type 1 reverse transcriptase.

Removal of nucleoside chain terminator inhibitors mediated by human immunodeficiency virus (HIV) reverse transcriptase (RT) using ATP as an acceptor molecule has been proposed as a novel mechanism of HIV resistance. Recombinant wild-type and mutant HIV type 1 (HIV-1) RT enzymes with thymidine analog resistance mutations D67N, K70R, and T215Y were analyzed for their ability to remove eight nucleoside reverse transcriptase inhibitors in the presence of physiological concentrations of ATP. The order for the rate of removal of the eight inhibitors by the mutant RT enzyme was zidovudine (AZT) > stavudine (d4T) >> zalcitabine (ddC) > abacavir > amdoxovir (DAPD) > lamivudine (3TC) > didanosine (ddI) > tenofovir. Thymidine analogs AZT and d4T were the most significantly removed by the mutant enzyme, suggesting that removal of these inhibitors by the ATP-dependent removal mechanism contributes to the AZT and d4T resistance observed in patients with HIV expressing thymidine analog resistance mutations. ATP-dependent removal of tenofovir was 22- to 35-fold less efficient than removal of d4T and AZT, respectively. The addition of ATP and the next complementary deoxynucleoside triphosphate caused a reduction of ATP-mediated removal of d4T, ddC, and DAPD, while AZT and abacavir removal was unaffected. The reduction of d4T, ddC, and DAPD removal in the presence of the deoxynucleoside triphosphate could explain the minor changes in susceptibility to these drugs observed in conventional in vitro phenotypic assays using cells that have higher deoxynucleoside triphosphate pools. The minimal removal of abacavir, ddC, DAPD, 3TC, ddI, and tenofovir is consistent with the minor changes in susceptibility to these drugs observed for HIV mutants with thymidine analog resistance mutations.

Differential removal of thymidine nucleotide analogues from blocked DNA chains by human immunodeficiency virus reverse transcriptase in the presence of physiological concentrations of 2'-deoxynucleoside triphosphates.

Removal of 2',3'-didehydro-3'-deoxythymidine-5'-monophosphate (d4TMP) from a blocked DNA chain can occur through transfer of the chain-terminating residue to a nucleotide acceptor by human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). ATP-dependent removal of either d4TMP or 3'-azido-3'-deoxythymidine-5'-monophosphate (AZTMP) is increased in AZT resistant HIV-1 RT (containing D67N/K70R/T215F/K219Q mutations). Removal of d4TMP is strongly inhibited by the next complementary deoxynucleoside triphosphate (50% inhibitory concentration [IC(50)] of approximately 0.5 microM), whereas removal of AZTMP is much less sensitive to this inhibition (IC(50) of >100 microM). This could explain the lack of cross-resistance by AZT-resistant HIV-1 to d4T in phenotypic drug susceptibility assays.