Effects of HIV protease inhibitors on barrier function in the human intestinal cell line HT-29/B6

Aspartyl Protease Inhibitors as Anti-Filarial Drugs

The current treatments for lymphatic filariasis and onchocerciasis do not effectively kill the adult parasitic nematodes, allowing these chronic and debilitating diseases to persist in millions of people. Thus, the discovery of new drugs with macrofilaricidal potential to treat these filarial diseases is critical. To facilitate this need, we first investigated the effects of three aspartyl protease inhibitors (APIs) that are FDA-approved as HIV antiretroviral drugs on the adult filarial nematode, Brugia malayi and the endosymbiotic bacteria, Wolbachia. From the three hits, nelfinavir had the best potency with an IC₅₀ value of 7.78 µM, followed by ritonavir and lopinavir with IC₅₀ values of 14.3 µM and 16.9 µM, respectively. The three APIs have a direct effect on killing adult B. malayi after 6 days of exposure in vitro and did not affect the Wolbachia titers. Sequence conservation and stage-specific gene expression analysis identified Bm8660 as the most likely primary aspartic protease target for these drug(s). Immunolocalization using antibodies raised against the Bm8660 ortholog of Onchocerca volvulus showed it is strongly expressed in female B. malayi, especially in metabolically active tissues such as lateral and dorsal/ventral chords, hypodermis, and uterus tissue. Global transcriptional response analysis using adult female B. pahangi treated with APIs identified four additional aspartic proteases differentially regulated by the three effective drugs, as well as significant enrichment of various pathways including ubiquitin mediated proteolysis, protein kinases, and MAPK/AMPK/FoxO signaling. In vitro testing against the adult gastro-intestinal nematode Trichuris muris suggested broad-spectrum potential for these APIs. This study suggests that APIs may serve as new leads to be further explored for drug discovery to treat parasitic nematode infections.

Diarrhea in the immunocompromised patient

Diarrhea is a common problem in patients with immunocompromising conditions. The etiologic spectrum differs from patients with diarrhea who have a normal immune system. This article reviews the most important causes of diarrhea in immunocompromised patients, ranging from infectious causes to noninfectious causes of diarrhea in the setting of HIV infection as a model for other conditions of immunosuppression. It also deals with diarrhea in specific situations, eg, after hematopoietic stem cell or solid organ transplantation, diarrhea induced by immunosuppressive drugs, and diarrhea in congenital immunodeficiency syndromes.

HIV protease inhibitors induce endoplasmic reticulum stress and disrupt barrier integrity in intestinal epithelial cells

The integrity of the intestinal epithelial barrier plays a crucial role in maintaining symbiotic homeostasis between microbes in the gut lumen and eukaryotic cells. Disruption of intestinal epithelial barrier function occurs commonly under various pathological conditions, including trauma, inflammatory bowel disease, and drug-induced gastrointestinal toxicity, exhibiting increased intestinal epithelial paracellular permeability or "leakiness" of the intestinal mucosa. Endoplasmic reticulum (ER) stress has recently been linked to various pathological conditions, including intestinal inflammation. Our previous studies have shown that HIV protease inhibitors (PIs) induce ER stress and activate the unfolded protein response (UPR) in different types of cells, and HIV PI-induced UPR activation contributes to the disruption of barrier function in intestinal epithelial cells and the increase of intestinal permeability. This chapter will discuss the commonly used methods for analysis of ER stress activation and epithelial barrier function. Both in vitro cell culture models and in vivo animal models are useful tools to examine general drug-induced ER stress and intestinal barrier dysfunction.

Development of a novel self-microemulsifying drug delivery system for reducing HIV protease inhibitor-induced intestinal epithelial barrier dysfunction

The development of HIV protease inhibitors (PIs) has been one of the most significant advances of the past decade in controlling HIV infection. Unfortunately, the benefits of HIV PIs are compromised by serious side effects. One of the most frequent and deleterious side effects of HIV PIs is severe gastrointestinal (GI) disorders including mucosal erosions, epithelial barrier dysfunction, and leak-flux diarrhea, which occurs in 16-62% of patients on HIV PIs. Although the underlying mechanisms behind HIV PI-associated serious adverse side effects remain to be identified, our recent studies have shown that activation of endoplasmic reticulum (ER) stress response plays a critical role in HIV PI-induced GI complications. The objective of this study was to develop a novel self-microemulsifying drug delivery system (SMEDDS) using various antioxidants as surfactants and cosurfactants to reduce the GI side effects of the most commonly used HIV PI, ritonavir. The biological activities of this SMSDDS of ritonavir were compared with that of Norvir, which is currently used in the clinic. Rat normal intestinal epithelial cells (IEC-6) and mouse Raw 264.7 macrophages were used to examine the effect of new SMEDDS of ritonavir on activation of ER stress and oxidative stress. Sprague-Dawley rats and C57/BL6 mice were used for pharmacokinetic studies and in vivo studies. The intracellular and plasma drug concentrations were determined by HPLC analysis. Activation of ER stress was detected by Western blot analysis and secreted alkaline phosphatase (SEAP) reporter assay. Reactive oxygen species (ROS) was measured using dichlorodihydrofluorescein diacetate as a probe. Cell viability was determined by Roche's cell proliferation reagent WST-1. Protein levels of inflammatory cytokines (TNF-alpha and IL-6) were determined by enzyme-linked immunosorbent assays (ELISA). The intestinal permeability was assessed by luminal enteral administration of fluorescein isothiocyanate conjugated dextran (FITC-dextran, 4 kDa). The pathologic changes in intestine were determined by histological examination. The results indicated that incorporation of antioxidants in this new SMEDDS not only significantly reduced ritonavir-induced ER stress activation, ROS production and apoptosis in intestinal epithelial cells and macrophages, but also improved the solubility, stability and bioavailability of ritonavir, and significantly reduced ritonavir-induced disruption of intestinal barrier function in vivo. In conclusion, this new SMEDDS of ritonavir has less GI side effects compared to Norvir. This new SMEDDS can be used for other HIV PIs and any insoluble antiviral drug with serious GI side effects.

HIV protease inhibitors induce endoplasmic reticulum stress and disrupt barrier integrity in intestinal epithelial cells

BACKGROUND & AIMS

Human immunodeficiency virus (HIV) protease inhibitor (PI)-induced adverse effects have become a serious clinical problem. In addition to their metabolic and cardiovascular complications, these drugs also frequently cause severe gastrointestinal disorders, including mucosal erosions, epithelial barrier dysfunction, and diarrhea. However, the exact mechanisms underlying gastrointestinal adverse effects of HIV PIs remain unknown. This study investigated whether HIV PIs disrupt intestinal epithelial barrier integrity by activating endoplasmic reticulum (ER) stress.

METHODS

The most commonly used HIV PIs (lopinavir, ritonavir, and amprenavir) were used; their effects on ER stress activation and epithelial paracellular permeability were examined in vitro as well as in vivo using wild-type and CHOP(-)/(-) mice.

RESULTS

Treatment with lopinavir and ritonavir, but not amprenavir, induced ER stress, as indicated by a decrease in secreted alkaline phosphatase activities and an increase in the unfolded protein response. This activated ER stress partially impaired the epithelial barrier integrity by promoting intestinal epithelial cell apoptosis. CHOP silencing by specific small hairpin RNA prevented lopinavir- and ritonavir-induced barrier dysfunction in cultured intestinal epithelial cells, whereas CHOP(-)/(-) mice exhibited decreased mucosal injury after exposure to lopinavir and ritonavir.

CONCLUSIONS

HIV PIs induce ER stress and activate the unfolded protein response in intestinal epithelial cells, thus resulting in disruption of the epithelial barrier integrity.

Diarrhea in patients with AIDS

Diarrhea in patients with AIDS is a worldwide problem that can have a devastating impact on quality of life for the patient. Chronic diarrhea, usually defined as at least 4 weeks' duration, is more common in patients with low CD4-positive T-lymphocyte counts, signaling advanced immunosuppression. Some organisms, such as Microsporidia, usually cause diarrhea only in the immunosuppressed; others, such as Cryptosporidium, Salmonella, Shigella, and Campylobacter, which are capable of causing diarrhea in the immunocompetent population, produce more severe or prolonged infections in people living with AIDS. Familiarity with the most common pathogens in the clinician's region will help with diagnosis and treatment. Because treatment options vary widely depending upon the infectious agent, thorough microbiologic evaluation is warranted. A stepped diagnostic approach of stool cultures and specialized microscopy and stains for protozoa, followed by sigmoidoscopy or colonoscopy and duodenoscopy with biopsies for histopathological examination is recommended in all patients with persistent, disabling diarrhea who have a CD4 count of less than 200/mm3, and should be considered for those with higher counts on an individual basis. Treatment, tailored to the specific pathogen, may need to be prolonged in the most severely immunocompromised patients to prevent relapse or recrudescence. For patients taking antiretroviral therapy (especially protease inhibitors) in whom no infectious agent can be found, diarrhea may be due to the medications. Nonspecific antidiarrheal agents should be tried until one that suits the patient is found. The most essential component of any therapeutic strategy for a patient with AIDS-associated diarrhea is restoration of the underlying immunologic defect using highly active antiretroviral therapy.

The Effect of Cell Culture Conditions on Saquinavir Transport Through, and Interactions with, MDCKII Cells Overexpressing hMDR1

MDCK cells are cultured using wide-ranging conditions and can produce variable results. To develop a standard protocol for studying saquinavir transport using MDCKII cells, stably transfected MDCKII cells overexpressing human Pgp (MDCKII-PGP) and MDCKII wild-type cells (MDCKII/wt) were used to evaluate the combined effects of seeding density (6.9 x 10(5) or 5 x 10(4) cells/cm2), substratum (polycarbonate +/- collagen coating) and saquinavir presence on monolayer integrity, Pgp expression, and saquinavir transport. The saquinavir efflux ratio (ratio of BL --> AP/AP --> BL permeability) for MDCKII-PGP cells (6.9 x 10(5) cells/cm2) was 57 with variable mannitol permeabilities. Consistent mannitol permeabilities and higher saquinavir efflux ratios were obtained with 5 x 10(4) cells/cm2 on polycarbonate (78) or collagen-coated polycarbonate (126). The MDCKII/wt saquinavir efflux ratio was 9. Saquinavir presence increased paracellular permeability for all treatments relative to cells seeded onto collagen-coated membranes. Collagen coating caused increased Pgp expression and saquinavir efflux ratios correlated (r2 = 0.96) with Pgp expression levels [MDCKII-PGP (on collagen-coated polycarbonate) > MDCKII-PGP (on polycarbonate) > MDCKII/wt (on collagen-coated polycarbonate)]. These results directly and quantitatively link interrelated differences in cell culture conditions to changes in monolayer integrity, transporter expression, and active transport; and emphasize the critical application of controls in cell culture models.

Calpain regulates enterocyte brush border actin assembly and pathogenic Escherichia coli-mediated effacement

This study identifies calpain as being instrumental for brush border (BB) microvillus assembly during differentiation and effacement during bacterial pathogenesis. Calpain activity is decreased by 25-80% in Caco 2 lines stably overexpressing calpastatin, the physiological inhibitor of calpain, and the effect is proportional to the calpastatin/calpain ratio. These lines exhibit a 2.5-fold reduction in the rate of microvillus extension. Apical microvillus assembly is reduced by up to 50%, as measured by quantitative fluorometric microscopy (QFM) of ezrin, indicating that calpain recruits ezrin to BB microvilli. Calpain inhibitors ZLLYCHN2, MDL 28170, and PD 150606 block BB assembly and ezrin recruitment to the BB. The HIV protease inhibitor ritonavir, which inhibits calpain at clinically relevant concentrations, also blocks BB assembly, whereas cathepsin and proteasome inhibitors do not. Microvillus effacement is inhibited after exposure of calpastatin-overexpressing cells to enteropathogenic Escherichia coli. These results suggest that calpain regulates BB assembly as well as pathological effacement, and indicate that it is an important regulator involved in HIV protease inhibitor toxicity and host-microbial pathogen interactions.