Identification of tight junction modulating lipids.

Tight junctions (TJs) play an important role in regulating paracellular drug transport. The aim of this study was to identify lipids that rapidly and reversibly alter transepithelial electrical resistance (TER) and/or TJ permeability in epithelial tissue. In this study, we developed a screen for identifying lipids that alter TJ properties. Measurement of TER was used to monitor TJ activity on bronchial/tracheal epithelial tissues using a microtiter format. Among seven groups of lipids tested, four classes were identified as TJ modulators (sphingosines, alkylglycosides, oxidized lipids and ether lipids). Individual lipids within these four classes showed up to 95% TER reduction at noncytotoxic concentrations. Alkylglycosides, however, showed high cytotoxicity and low viability at concentrations (0.2-0.4%) reported to enhance transmucosal absorption (Ahsan et al., 2003, Int J Pham 251: 195-203). Several active lipids also showed enhanced permeation of FITC-labeled dextran (m.w. 3000). Immunofluorescence staining of PGPC-treated cells with antibodies against ZO-1, occludin and claudin 4 showed no detectable changes in TJ structural morphology, indicating that a nondestructive, submicroscopic alteration in TJ function may be involved in TER reduction and permeation enhancement. This study demonstrates that three new classes of lipids, excluding alkylglycosides, show potential utility for transmucosal drug delivery.

Hyperlipidemia in concert with hyperglycemia stimulates the proliferation of macrophages in atherosclerotic lesions: potential role of glucose-oxidized LDL.

Hyperglycemia and hyperlipidemia are important risk factors for diabetes-accelerated atherosclerosis. Macrophage proliferation has been implicated in the progression of atherosclerosis. We therefore investigated the effects of hyperglycemia and hyperlipidemia on macrophage proliferation in murine atherosclerotic lesions and isolated primary macrophages. Hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-free diet for 12 weeks did not have elevated cholesterol levels compared with nondiabetic mice, and there was no evidence of increased macrophage proliferation in atherosclerotic lesions. Moreover, elevated glucose levels did not increase proliferation of isolated mouse peritoneal macrophages. In contrast, hyperglycemic LDL receptor-deficient mice that were fed a cholesterol-rich diet showed increased cholesterol levels concomitant with macrophage proliferation in atherosclerotic lesions. Glucose promoted lipid and protein oxidation of LDL in vitro. Glucose-oxidized LDL resulted in phosphorylation of extracellular signal-regulated kinase and protein kinase B/Akt and stimulated proliferation of isolated macrophages. The mitogenic effect of glucose-oxidized LDL was mediated by CD36 and by extracellular signal-regulated kinase activation induced by protein kinase C-dependent and phosphatidylinositol 3-kinase-dependent pathways. Thus, hyperglycemia is not sufficient to stimulate macrophage proliferation in lesions of atherosclerosis or in isolated macrophages. A combination of hyperglycemia and hyperlipidemia, however, stimulates macrophage proliferation by a pathway that may involve the glucose-dependent oxidation of LDL.

Diabetes and diabetes-associated lipid abnormalities have distinct effects on initiation and progression of atherosclerotic lesions.

Diabetes in humans accelerates cardiovascular disease caused by atherosclerosis. The relative contributions of hyperglycemia and dyslipidemia to atherosclerosis in patients with diabetes are not clear, largely because there is a lack of suitable animal models. We therefore have developed a transgenic mouse model that closely mimics atherosclerosis in humans with type 1 diabetes by breeding low-density lipoprotein receptor-deficient mice with transgenic mice in which type 1 diabetes can be induced at will. These mice express a viral protein under control of the insulin promoter and, when infected by the virus, develop an autoimmune attack on the insulin-producing beta cells and subsequently develop type 1 diabetes. When these mice are fed a cholesterol-free diet, diabetes, in the absence of associated lipid abnormalities, causes both accelerated lesion initiation and increased arterial macrophage accumulation. When diabetic mice are fed cholesterol-rich diets, on the other hand, they develop severe hypertriglyceridemia and advanced lesions, characterized by extensive intralesional hemorrhage. This progression to advanced lesions is largely dependent on diabetes-induced dyslipidemia, because hyperlipidemic diabetic and nondiabetic mice with similar plasma cholesterol levels show a similar extent of atherosclerosis. Thus, diabetes and diabetes-associated lipid abnormalities have distinct effects on initiation and progression of atherosclerotic lesions.

Polymorphic markers in the 5alpha-reductase type II gene and the incidence of prostate cancer.

In the prostate, the enzyme encoded by the SRD5A2 gene (5alpha-reductase) converts testosterone to dihydrotestosterone, a potent androgen that has been hypothesized to play a role in the genesis of prostate cancer. Several polymorphisms have been identified in the SRD5A2 gene, including a valine-to-leucine substitution (V89L) at codon 89, a variable number of TA dinucleotide repeats and a missense substitution at codon 49 resulting in an amino acid substitution of alanine with threonine (A49T). To investigate the influence of these polymorphisms on prostate cancer risk, we conducted a case-control study nested within the Beta-Carotene and Retinol Efficacy Trial. Genotypes were determined by PCR-based capillary electrophoresis using genomic DNA isolated from 300 cases and 300 controls matched on the basis of race, age at enrollment (within 5 years), enrollment study center and year of randomization. There was no association between V89L genotypes and prostate cancer risk. The age- and race-adjusted odds ratio (OR) associated with the VL and LL genotypes were 1.06 (95% confidence interval (CI) = 0.75-1.49) and 0.99 (95% CI = 0.57-1.73), respectively, as compared to the VV genotype. The age- and race-adjusted odds ratio for men having 1 TA(9) or TA(18) allele was 0.98 (95% CI = 0.64-1.48) when compared to men without TA repeats. The corresponding odds ratio for men without the TA(0) alleles was 0.68 (95% CI = 0.21-2.19). The age- and race-adjusted odds ratio associated with having at least 1 T allele at codon 49 was 1.11 (95% CI = 0.58-2.11), as compared to the AA genotype. Our results do not support the hypothesis that the V89L and A49T polymorphisms in the SRD5A2 gene are related to the risk of prostate cancer, but are compatible with the suggestion from earlier studies that men who are homozygous for the TA(9) or (18) alleles and men who have the TA(9)/TA(18) genotype are at a modestly reduced risk.

Androgen receptor polymorphisms and the incidence of prostate cancer.

The human androgen receptor gene contains polymorphic CAG and GGC repeats in exon 1. We investigated whether the number of CAG and/or GGC repeats is related to prostate cancer risk in a case-control study nested within the beta Carotene and Retinol Efficacy Trial. Among 300 cases and 300 controls, we did not observe any increase in risk associated with fewer CAG or GGC repeats. We observed a nonsignificant decrease in risk associated with each unit of decrease in CAG length [odds ratio (OR), 0.98; 95% confidence interval (CI), 0.93-1.03). Men with CAG <22 had a relative risk of prostate cancer of 0.89 (95% CI, 0.65-1.23) compared with men with CAG > or =22. There was no appreciable difference in the mean number of GGC repeats between cases and controls; the estimated change in the risk of prostate cancer associated with one fewer GGC repeat was 0.97 (95% CI, 0.88-1.06). The risk in men at or below the mean number of GGC repeats (17) was 0.80 (95% CI, 0.57-1.12). In contrast to prior reports, men with both short CAG (<22) and short GGC (< or =17) repeats were not at increased risk of prostate cancer (OR, 0.56; 95% CI, 0.32-0.98), compared with men with > or =22 CAG repeats and >17 GGC repeats. Our results do not support the hypothesis that a small number of CAG or GGC repeats in the androgen receptor gene increases a man's risk of prostate cancer.