Blockade of HERG channels by HIV protease inhibitors

The HIV protease inhibitor class of antiretroviral drug causes unpredicted adverse effects by changing elements of normal cellular metabolism. A case of QT prolongation in a patient receiving protease inhibitors made us question whether these drugs might be responsible. We identified 24 patients with QT prolongation or torsade de pointes, or both, associated with protease inhibitors, using the Food and Drug Administration's voluntary adverse event reporting system. Attending physicians thought that protease inhibitors were the most probable cause of these symptoms in 14 of the patients. Drug-induced QT prolongation is usually caused by block of human ether-a-go-go-related gene (HERG) potassium channels, and we showed that lopinavir, nelfinavir, ritonavir, and saquinavir caused dose-dependent block of HERG channels heterologously expressed in HEK293 cells in vitro. We also recorded block by lopinavir of repolarising potassium current (I(Kr)) channels in neonatal mouse cardiac myocytes. Our data show that four protease inhibitors block HERG channels, suggesting that protease inhibitors could predispose individuals to QT prolongation and torsade de pointes.     

Dyslipidemia in the era of HIV protease inhibitors

Human immunodeficiency virus protease inhibitors are associated with metabolic abnormalities that may increase risk of atherosclerotic vascular disease, including dyslipidemia, insulin resistance, and central obesity. Dyslipidemia, characterized by hypercholesterolemia and hypertriglyceridemia, small low- and high-density lipoprotein particles, and in some cases lipoprotein(a) excess, can be severe and has been associated with endothelial dysfunction and carotid atherosclerosis. The mechanisms underlying protease inhibitor-associated dyslipidemia have not been elucidated completely, but appear to involve hepatic overproduction of very low-density lipoproteins and to a lesser extent, impaired clearance. Insulin resistance appears to mediate part of the adverse lipoprotein changes observed in patients taking protease inhibitors. Ongoing epidemiological and surrogate endpoint studies are investigating the atherogenicity of these medications. Until the risk associated with use of protease inhibitors is better understood, identifying patients at high risk for adverse vascular events such as heart attacks, cardiac death, and stroke is a high priority. This article reviews the lipid and lipoprotein abnormalities associated with use of protease inhibitors, possible mechanisms for protease inhibitor-associated dyslipidemia, its potential atherogenicity, and use of the National Cholesterol Education Program Adult Treatment Panel III Guidelines for the management of patients with dyslipidemia.     

Sequencing of protease inhibitor therapy: insights from an analysis of HIV phenotypic resistance in patients failing protease inhibitors

OBJECTIVE: To characterize the pattern of HIV-1 susceptibility to protease inhibitors in patients failing an initial protease inhibitor-containing regimen. DESIGN: A cross-sectional analysis of antiretroviral susceptibility. SETTING: HIV clinics in six metropolitan areas. PATIENTS: Eighty-eight HIV-infected adults with HIV RNA > 400 copies/ml after > or = 6 months of antiretroviral therapy, including the use of one protease inhibitor for > or = 3 months. MEASUREMENTS: The frequency and magnitude of decreased susceptibility, measured with a phenotypic assay using recombinant constructs, to five protease inhibitors. Decreased susceptibility was defined as > 2.5-fold increase in the 50% inhibitory concentration (IC50) compared with drug sensitive control virus. RESULTS: At study entry, patients were being treated with nelfinavir (63%), indinavir (25%), or another protease inhibitor (11%). HIV isolates from these patients were susceptible (fold change < 2.5) to all five protease inhibitors in 18% of patients and to none in 8%. Isolates from patients receiving nelfinavir were less likely to have reduced susceptibility to other protease inhibitors than isolates from patients treated with indinavir (P < 0.001) or one of the other three agents (P < 0.001), even after adjustment for the duration of prior protease inhibitor use. Reduced susceptibility to saquinavir and amprenavir was observed significantly less frequently than for the other protease inhibitors. CONCLUSION: The frequency of protease inhibitor cross-resistance and the magnitude of changes in susceptibility varied according to the initial protease inhibitor used in the failing treatment regimen. Significantly less protease inhibitor cross-resistance was demonstrated for isolates from patients failing a nelfinavir-containing regimen compared with those from patients receiving other protease inhibitors.     

The HIV type 1 protease L10I minor mutation decreases replication capacity and confers resistance to protease inhibitors

The effect of minor mutations in PR on treatment outcome has not been well established. We characterized the HIV protease minor mutations, L10I, compared to the minor mutation, L63P, and the major mutation D30N and their impact on viral fitness and resistance to protease inhibitors. Mutations were introduced individually and in combination by site-directed mutagenesis into the provirus pNL4.3ren and constructs used for replication capacity (RC) and resistance assays. A structure prediction of the protease carrying the L10I mutation was determined. The prevalence of the minor mutation L10I had a pattern similar to that found for major mutations D30N, with a low prevalence (4.9%) in naive patients and significantly higher prevalence in treated patients. Furthermore, viruses carrying the major mutation D30N or the minor mutation L10I showed a significant decrease in RC (p-value <0.05), whereas viruses carrying the minor mutation L63P had RC similar to wild-type virus. In addition, the L10I mutation conferred resistance to saquinavir, which was supported by the higher prevalence in the cohort of the L10I mutation among patients with SQV resistance. The molecular modeling suggests that L10I may affect the conformation of Leu-23, a critical residue in the substrate binding site. In conclusion, the L10I mutation impairs RC and confers resistance to SQV, similarly to other major mutations, which may be related with changes in the conformation in the protease binding site. The presence of this mutation in the genotype of HIV from patients should be taken into consideration when designing new optimize treatments.     

From nonpeptide toward noncarbon protease inhibitors: metallacarboranes as specific and potent inhibitors of HIV protease

HIV protease (PR) represents a prime target for rational drug design, and protease inhibitors (PI) are powerful antiviral drugs. Most of the current PIs are pseudopeptide compounds with limited bioavailability and stability, and their use is compromised by high costs, side effects, and development of resistant strains. In our search for novel PI structures, we have identified a group of inorganic compounds, icosahedral metallacarboranes, as candidates for a novel class of nonpeptidic PIs. Here, we report the potent, specific, and selective competitive inhibition of HIV PR by substituted metallacarboranes. The most active compound, sodium hydrogen butylimino bis-8,8-[5-(3-oxa-pentoxy)-3-cobalt bis(1,2-dicarbollide)]di-ate, exhibited a K(i) value of 2.2 nM and a submicromolar EC(50) in antiviral tests, showed no toxicity in tissue culture, weakly inhibited human cathepsin D and pepsin, and was inactive against trypsin, papain, and amylase. The structure of the parent cobalt bis(1,2-dicarbollide) in complex with HIV PR was determined at 2.15 A resolution by protein crystallography and represents the first carborane-protein complex structure determined. It shows the following mode of PR inhibition: two molecules of the parent compound bind to the hydrophobic pockets in the flap-proximal region of the S3 and S3' subsites of PR. We suggest, therefore, that these compounds block flap closure in addition to filling the corresponding binding pockets as conventional PIs. This type of binding and inhibition, chemical and biological stability, low toxicity, and the possibility to introduce various modifications make boron clusters attractive pharmacophores for potent and specific enzyme inhibition.     

The effects of HIV protease inhibitors atazanavir and lopinavir/ritonavir on insulin sensitivity in HIV-seronegative healthy adults

BACKGROUND: Therapy with some HIV protease inhibitors (PI) contributes to insulin resistance and type 2 diabetes mellitus, by inhibition of insulin-sensitive glucose transporters. Atazanavir (ATV) is a new PI with substantially less in vitro effect on glucose transport than observed with other PI, including lopinavir (LPV) or ritonavir (RTV). METHODS: Randomized, double-blind, crossover study of the effect of 5 days of administering ATV, lopinavir/ritonavir (LPV/r) or placebo on insulin-stimulated glucose disposal in 30 healthy HIV-negative subjects. Each subject was studied on two of three possible treatments with a wash-out period between treatments. RESULTS: The mean insulin-stimulated glucose disposal (mg/min per kg body weight) per unit insulin (microU/ml) (M/I) was 9.88, 9.80 and 7.52 for placebo, ATV and LPV/r, respectively (SEM, 0.84 for all). There was no significant difference between ATV and placebo. The M/I for LPV/r was 23% lower than that for ATV (P = 0.010) and 24% lower than that for placebo (P = 0.008). The mean glycogen storage rates were 3.85, 4.00 and 2.54 mg/min per kg for placebo, ATV and LPV/r, respectively (SEM, 0.39 for all). There was no significant difference between ATV and placebo. The glycogen storage rate for LPV/r was 36% lower than ATV (P = 0.003) and 34% lower than placebo (P = 0.006). CONCLUSIONS: ATV given to healthy subjects for 5 days did not affect insulin sensitivity, while LPV/r induced insulin resistance. This observation is consistent with differential in vitro effects of these PI on glucose transport. Further data are needed to assess clinical implications for body composition.     

Attitudes toward HIV protease inhibitors and medication adherence in an inner city HIV population

The objective of this pilot study was to examine attitudes toward protease inhibitors (PIs) among HIV-infected individuals and to assess the relationship between PI attitudes and adherence to PIs. Respondents were recruited from four AIDS service organizations in New York City; the total sample consisted of 97 HIV-infected individuals who were taking a PI. The sample consisted largely of African Americans and Latinos from inner city areas, and most had a low level of education. Adherence was suboptimal, with more than 50% of respondents failing to take their PI medications exactly as prescribed within the previous month. Individuals who had recently used illegal drugs within the past 6 months were more likely to be nonadherent to PIs. Those who were not adherent to PI medications reported greater concern about the side effects of PIs and were more likely to believe that it was acceptable to skip doses of PIs.     

Diabetes, insulin resistance, and HIV

The transformation of HIV infection into a chronically managed illness through the widespread use of highly active antiretroviral therapy has brought with it comorbid conditions such as increased risk of cardiovascular disease. Diabetes and insulin resistance have emerged as important comorbidities associated with HIV infection and the use of antiretroviral therapy. Significant inroads have been made towards understanding the etiology of insulin resistance and diabetes in association with HIV and highly active antiretroviral therapy, and there are also emerging data on the prevalence and incidence of this problem. The recognition and management of diabetes mellitus, insulin resistance, and related complications will be an important part of long-term health maintenance for HIV-infected patients.     

HIV, insulin resistance and cardiovascular disease

Individuals treated for HIV infection are at increased risk for accelerated cardiovascular disease. Treatment of HIV infection confers the significant benefits of improved clinical outcomes, quality of life, and survival. However, a number of metabolic complications have emerged as a consequence of treatment, including often severe, mixed hyperlipidemia, body fat partitioning disorders, and increased risk of type 2 diabetes. Treatment-induced insulin resistance underlies and contributes to these metabolic complications. This review examines the contribution of insulin resistance to increased cardiovascular disease rates in healthy and HIV-infected populations, mechanisms by which treatment of HIV infection exacerbates insulin resistance, and the effect of insulin resistance-modulating interventions on cardiovascular risk factors.