Analysis of the interactions of SDZ PSC 833 ([3'-keto-Bmt1]-Val2]-Cyclosporine), a multidrug resistance modulator, with P-glycoprotein

Multidrug resistance (MDR) is considered to be an important impediment to the effective treatment of cancer. P-glycoprotein, the drug efflux pump that mediates this resistance, can be inhibited by a wide variety of pharmacological agents, resulting in the circumvention of the MDR phenotype. SDZ PSC 833 ([3'-keto-Bmt1]-Val2]-cyclosporine), a nonimmunosuppressive cyclosporine D derivative, was identified to be a potent MDR modulator (Gaveriaux et al. J. Cell Pharmacol. 2:225-234; 1991). In this study, the interactions of P-glycoprotein with two cyclosporine derivatives, SDZ PSC 833 and cyclosporine A (CsA, Sandimmune), were analyzed. SDZ PSC 833 enhanced the sensitivity of the MDR cells to anticancer drugs by increasing the accumulation and inhibiting the efflux of cytotoxic agents from resistant cells more efficiently than CsA. The two cyclosporine analogs competed with the labeling of P-glycoprotein by a photoactive cyclosporine derivative. In addition, membrane vesicles derived from resistant cells bound SDZ PSC 833. However, CsA was transported by P-glycoprotein, whereas SDZ PSC 833 was not actively transported. This resulted in a prolonged inhibitory effect by SDZ PSC 833. The studies suggest that the binding of SDZ PSC 833 to P-glycoprotein in the absence of its transport from MDR cells mediated its high potency as an MDR reversing agent. In addition, the comparison of the two cyclosporine analogs indicated that limited chemical modifications of MDR reversing agents can affect their potential to inhibit P-glycoprotein function.     

Uptake and metabolism of lipoproteins from patients with diabetes mellitus type II by glomerular epithelial cells

BACKGROUND: Recent studies suggest that dyslipidaemia accelerates the progression of diabetic nephropathy, but the various pathomechanisms underlying such abnormalities are not completely delineated. METHODS: We isolated, radiolabelled, and characterized very-low-density lipoproteins (VLDL) and low-density lipoproteins (LDL) from eight diabetic patients with moderate impairment of renal function and dyslipidaemia and studied their interaction with LDL receptors in human glomerular epithelial cells. RESULTS: While diabetic VLDL showed no compositional changes, LDL particles contained a higher proportion of triglycerides at the expense of cholesterol in comparison with healthy controls. Despite differences in composition, both VLDL and LDL from patients exhibited reduced receptor affinity and cellular uptake capacity by glomerular epithelial cells. Since LDL composition was altered intracellular cholesterol homeostasis was investigated. Due to reduced cholesterol content and lower uptake capacity, diabetic LDL were less effective in suppressing intracellular sterol synthesis and in activating acylcholesterol acyltransferase than LDL from controls. Electrophoretic mobility of apoB from diabetic patients was enhanced as compared to controls, most probably due to the higher degree of glycation (17 + 1.7 versus 11 + 1%, P < 0.05) but not to oxidation (TBARS 0.5 + 0.2 versus 0.2 + 0.1 mumol/1). Oxidized LDL was not taken up in significant amounts, indicating no scavenger receptor activity in glomerular epithelial cells. CONCLUSION: The receptor-specific uptake of diabetic VLDL and LDL by glomerular epithelial cells is impaired. Compositional changes of the LDL particle and glycation of the protein moiety may contribute to altered glomerular uptake. However, glycation of the protein moiety may be superior to compositional changes. Because glomerular structures like mesangial matrix and endothelial cells are known for preferential binding of modified lipoproteins, further studies are required to elucidate their potential role in the progression of diabetic glomerulosclerosis.     

Intraglomerular foam cells and human focal glomerulosclerosis

Experimental evidence suggests a pathogenetic role for lipids in focal glomerulosclerosis (FGS) analogous to atherosclerosis. As foam cells (FC) are an important factor in atherosclerosis, a retrospective comparative study was done to evaluate the significance of intraglomerular FC in human FGS. Glomerular FC infiltration was evaluated in 115 biopsies of FGS, 120 biopsies of membranous glomerulonephritis (MGN) and 50 biopsies of minimal-change disease (MCD). Selected clinical and laboratory data collected at about the time of biopsy were reviewed. The proportion of biopsies showing glomerular FC was much higher in FGS (70%) than in either MGN (12%) or MCD (0%) p less than 0.001. The mean percent (+/- SD) of glomeruli with FC per biopsy was significantly greater in FGS (7.9 +/- 9.9) than in MGN (2.0 +/- 7.8; p less than 0.0001). Of the 14 MGN biopsies with FC, 13 showed superimposed FGS. Mean serum total cholesterol and triglyceride were not significantly higher in FGS than in either MGN or MCD. The results demonstrate a close association of glomerular FC infiltration with FGS.     

Potency of mixtures of polychlorinated biphenyls as inducers of dioxin receptor-regulated CYP1A activity in rat hepatocytes and H4IIE cells

Among the polychlorinated biphenyls (PCBs), a family of widespread environmental pollutants, the most toxic non-ortho-substituted coplanar (non-ortho coplanar) congeners are thought to act as strong dioxin (aryl hydrocarbon) receptor agonists leading to adverse effects, such as body weight loss, immunosuppression, thymic atrophy, hepatotoxicity, tumor promotion, and disturbances of steroid hormone action. Since PCBs are present in environmental and tissue samples as complex mixtures, we investigated the possible interaction of non-ortho coplanar congeners with other major PCBs, which are less active or inactive as dioxin receptor agonists. As a parameter for dioxin receptor activation, induction of CYP1A-catalyzed 7-ethoxyresorufin O-deethylase (EROD) was determined in rat hepatocytes in primary culture and in the rat hepatoma cell line H4IIE. In rat hepatocytes, individual EC50-values and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalency factors (TEFs) for the non-ortho and mono-ortho coplanar PCBs 126, 169, 105, 118 and 156, were in good agreement with published data from in vivo experiments, while in H4IIE cells coincidence was lower. However, in both cell systems TEFs for PCB 77 were significantly higher than reported from experiments in rats. In an approximately equipotent mixture the six potent PCB congeners showed perfect additive behaviour in both cell systems. In contrast, addition of a tenfold surplus of abundant mono- and di-ortho PCBs (28, 52, 101, 138, 153 and 180) led to an almost threefold higher TEF than predicted. This finding suggests a moderate synergistic enhancement of the inducing potency of potent PCBs by less potent congeners, present in abundance in environmental and tissue samples.     

The regional distribution of myelin oligodendrocyte glycoprotein (MOG) in the developing rat CNS: an in vivo immunohistochemical study

Using an immunohistochemical approach we have characterized the in vivo developmental distribution of myelin oligodendrocyte glycoprotein within the rat CNS. Myelin oligodendrocyte glycoprotein expression emerged in a non-uniform manner during the first 3 postnatal weeks. Although it was absent throughout the CNS of the newborn rat at postnatal day 0(P0), it had appeared in the spinal cord and brainstem by P7. The forebrain and cerebellum remained devoid of immunoreactivity until after P14. Myelin oligodendrocyte glycoprotein emerged at different times within the closely associated fasciculi of the dorsal funiculus. It appeared in the fasciculus cuneatus during the first postnatal week and in the fasciculus gracilis and corticospinal tracts during weeks 2 and 3 respectively. Myelin oligodendrocyte glycoprotein expression developed along a caudo-rostral gradient from spinal cord to forebrain and along an antero-posterior gradient within the CNS in general. The relationship between the onset of myelin oligodendrocyte glycoprotein expression and myelinogenesis was also investigated. In most regions, myelin oligodendrocyte glycoprotein expression lagged behind the initial appearance of myelin basic protein and Luxol Fast Blue-stained myelin by at least 1 week. These observations support the idea that myelin oligodendrocyte glycoprotein is the latest myelin protein to appear in development, only being expressed during the final stages of oligodendrocyte differentiation. Furthermore, the pattern of staggered expression within the dorsal columns indicates that localized, region-specific interactions may comprise a key element in the control of the terminal phases of oligodendrocyte differentiation.