Effects of substitutions D73E, D73N, D103N and V106M on signaling and pH titration of sensory rhodopsin II

Several mutations in the repellent phototaxis receptor sensory rhodopsin II (SRII), in residues homologous to residues important in the related proton pump bacteriorhodopsin, were expressed in Pho81Wr-, a Halobacterium salinarum strain deficient in production of SRII and its transducer protein HtrII. The lack of production of SRII and HtrII is shown to be due to insertion of an ISH2 transposon into the promoter region upstream of the htrII-sopII gene pair. Near wild-type phototaxis responses are rescued in Pho81Wr- by expression of HtrII with D73E, D103N or V106M receptors. Partial responses are restored by the HtrII-D73N pair. From absorption spectroscopy of his-tag-purified receptor protein from mutants D73N and D73E we conclude that Asp73 is the primary counterion to the protonated Schiff base in SRII, like the corresponding Asp85 in bacteriorhodopsin. The absorption maximum of SRII (487 nm) is shifted to 514 nm in mutant D73N, a 1080 cm-1 shift identical to that caused by D85N in bacteriorhodopsin. Acid titration of SRII also induces the red shift with a pK of 3.0 in wild type. The absorption shift and the pK are nearly the same in V106M and D103N, but the pK is raised to 5.1 in D73E, confirming that Asp73 is the residue responsible for this spectral transition.

Simultaneous arterial and urinary bladder pressure recordings in multiple system atrophy and in spinal disorders with detrusor hyperreflexia

Simultaneous arterial and urinary bladder pressure measurements were recorded during bladder filling in 21 patients with urinary bladder symptoms; seven patients had autonomic failure due to multiple system atrophy (MSA), seven had spinal cord disease of different aetiology with detrusor hyperreflexia (DH) and seven had no neurological abnormalities. A significant increase in average systolic blood pressure (BP) was recorded on bladder filling in the neurologically intact patients (from 110 to 137 mmHg) and in the patients with spinal cord disease and DH (from 109 to 129 mmHg). In those with MSA, the BP rose in four and fell in three patients. The vesicopressor response during cold receptor-mediated DH was not significantly higher when compared with room-temperature saline and when compared with the BP response during bladder filling in the neurologically intact patients. Finally, intravesical lignocaine retained in the bladder for 15 min did not influence the BP response to cold receptor stimulation in patients with spinal cord disease and DH. These findings and their pathophysiological and clinical implications are discussed.

Antiinflammatory and antipyretic activity of Michelia champaca Linn., (white variety), Ixora brachiata Roxb. and Rhynchosia cana (Willd.) D.C. flower extract

Methanolic extracts of the flowers of M. champaca, I. Brachiata and R. cana were found to possess antiinflammatory activity against cotton pellet granuloma in rats at a dose level of 100 mg/kg body weight, sc. The latter two drugs showed higher activity (AIA) as compared to that of M. champaca. They reduced the protein content, acid phosphatase, glutamate pyruvate transaminase and glutamate oxalo-acetate transaminase activities in liver and serum. A significant reduction in the ascorbic acid content in adrenals was also observed in drug-treated animals. R. cana was recorded to possess significant antipyretic activity from the first hour of administration. These pharmacological properties may be traced to the presence of flavonoids in the flowers of these plants.

Pulsus alternans in diastolic left ventricular dysfunction--a case report

Pulsus alternans is usually found in patients with reduced systolic ventricular function. We describe a patient with recurrent pulmonary edema, hypertension, bilateral renal artery stenosis, but with normal systolic function. Pulsus alternans was demonstrated in both pulmonary artery, right ventricle, and left ventricle pressures. After successful renal artery revascularization, the pulsus alternans disappeared. This case illustrates that pulsus alternans can be present with diastolic dysfunction of the left ventricle in the absence of systolic dysfunction.

Lobucavir is phosphorylated in human cytomegalovirus-infected and -uninfected cells and inhibits the viral DNA polymerase

Lobucavir (LBV) is a deoxyguanine nucleoside analog with broad-spectrum antiviral activity. LBV was previously shown to inhibit herpes simplex virus (HSV) DNA polymerase after phosphorylation by the HSV thymidine kinase. Here we determined the mechanism of action of LBV against human cytomegalovirus (HCMV). LBV inhibited HCMV DNA synthesis to a degree comparable to that of ganciclovir (GCV), a drug known to target the viral DNA polymerase. The expression of late proteins and RNA, dependent on viral DNA synthesis, was also inhibited by LBV. Immediate-early and early HCMV gene expression was unaffected, suggesting that LBV acts temporally coincident with HCMV DNA synthesis and not through cytotoxicity. In vitro, the triphosphate of LBV was a potent inhibitor of HCMV DNA polymerase with a Ki of 5 nM. LBV was phosphorylated to its triphosphate form intracellularly in both infected and uninfected cells, with phosphorylated metabolite levels two- to threefold higher in infected cells. GCV-resistant HCMV isolates, with deficient GCV phosphorylation due to mutations in the UL97 protein kinase, remained sensitive to LBV. Overall, these results suggest that LBV-triphosphate halts HCMV DNA replication by inhibiting the viral DNA polymerase and that LBV phosphorylation can occur in the absence of viral factors including the UL97 protein kinase. Furthermore, LBV may be effective in the treatment of GCV-resistant HCMV.

An agarose-in-plug bridge method to study chemotaxis in the Archaeon Halobacterium salinarum

A simple agarose-in-plug bridge method was developed to study chemotaxis in the Archaeon Halobacterium salinarum. Preheated liquid agarose solution with chemoeffectors is pipetted in the middle of a microscope slide bridge, constructed by placing two plastic strips 16 mm apart. A coverslip is immediately placed over the agarose. The solidified agarose plug is completely encircled with the halobacterial cell suspension. Within a certain time concentrated halobacteria were seen as a ring at the edge of the agarose plug containing attractant amino acids and the control growth medium. Chemotaxis mutant Pho60 cells do not accumulate either around the attractants or around the growth medium. The kinetics of the ring formation can be readily videotaped or photographed using either phase-contrast or dark-field microscopy.

Pitfalls in the echocardiographic diagnosis of aortic dissection

The authors studied 25 patients with transthoracic echocardiography (TTE) and/or transesophageal echocardiography (TEE) for suspected aortic dissection. Of these, aortic dissection was diagnosed correctly in 19 patients, but in 6 the echocardiographic findings for dissection were atypical or false-positive. In patient 1, the TEE revealed a dilatated proximal aortic root. TEE showed a possible flap but was nondiagnostic. The diagnosis was made by computed tomography (CT) and confirmed at surgery to be type 1 dissection. In patient 2, the TTE depicted flail aortic cusps, questionable vegetations, and dilatated aortic root. In patient 3, TTE demonstrated moderate pericardial effusion with hematoma but no dissection. Type 1 dissection was subsequently confirmed at autopsy in both. Patient 4 had TEE diagnosis of type 3 dissection. However, reevaluation of the study by a senior sonographer just prior to surgery led to the correct diagnosis of type 1 dissection. Patients 5 and 6 had dilatated ascending aortas with linear echoes within the lumen on TEE and were reported as having type 1 dissections. CT and/or angiography did not reveal dissection in either patient. In conclusion, TTE and TEE are vaulable tests in diagnosing aortic dissection. However, atypical features, misdiagnosis of the site of dissection, or false-positive studies can occur.

Sulphasalazine, olsalazine and sulphapyridine induce mitogenic actions in the rat intestinal epithelium

Our aim was to study the influence of sulphasalazine (SASP), olsalazine (ADS) and sulphapyridine (SP) on the cell kinetics of the intestinal epithelium in conventional rats. Groups of rats were treated with SASP, ADS or SP for 9 days. After an intraperitoneal injection of a metaphase blocker, the rats were killed and the jejunum, ileum and colon were examined in histological sections by means of the cumulative mitotic index (MI), growth fraction and number of cells in crypts and villi. SP increased both the MI in the jejunum, ileum and colon and the number of crypt cells (p < 0.05 vs controls). In contrast, SASP and ADS increased the MI only in the colonic epithelium (p < 0.05 vs controls). The growth fraction was essentially unaffected. Our results suggest that SASP, SP and ADS have a selective compartment-dependent proliferative action on the epithelium of the intestinal tract.

Vibrio mimicus attaches to the intestinal mucosa by outer membrane hemagglutinins specific to polypeptide moieties of glycoproteins

Vibrio mimicus is the closest organism to Vibrio cholerae. V. mimicus E-33, which is a highly adhesive and enteropathogenic strain, is known to produce three types of hemagglutinins (HAs), i.e., a 31-kDa exocellular metalloprotease (Vm-HA/protease), lipopolysaccharide (Vm-LPSHA), and a 39-kDa major outer membrane protein (Vm-OMPHA). Hemagglutination induced by Vm-LPSHA and Vm-OMPHA was inhibited by glycoproteins, including mucin, fetuin, and asialofetuin, but not by monosaccharides, disaccharides, or N-acetylated saccharides. The inhibitory potential of each glycoprotein for Vm-OMPHA was greatly augmented by treatment with a glycolytic enzyme such as beta-D-galactosidase or beta-D-glucosidase, while pronase treatment achieved complete abolition of the inhibitory potential. The inhibitory ability of the glycoproteins for Vm-LPSHA was also abolished by pronase treatment; however, glycolytic enzyme treatment showed no effect. Hence, the polypeptide portion of glycoproteins may directly associate with Vm-OMPHA and Vm-LPSHA, but the sugar moiety may act as a barrier to interaction with Vm-OMPHA. The glycoproteins as well as Fab antibodies against Vm-OMPHA and Vm-LPSHA eliminated the ability of E-33 cells to agglutinate rabbit erythrocytes and to attach to rabbit intestinal mucosa. Additionally, expression of the hemagglutinating ability by the bacterial cells was accompanied by efficient bacterial adherence to the intestinal mucosa. Finally, the hemagglutinating activity of Vm-OMPHA was markedly increased by incubation with Vm-HA/protease. These results indicate that all three HAs may have significant roles in the glycoprotein-mediated intestinal adherence of V. mimicus E-33.

Hemagglutination is a novel biological function of lipopolysaccharide (LPS), as seen with the Vibrio cholerae O139 LPS

It has been generally thought that the polysaccharide moiety of lipopolysaccharide (LPS) maintains only serological specificity, while the lipid A portion determines various biological functions. However, we found that hemagglutination was a common function of the polysaccharide moiety of LPSs from important human enteropathogenic bacteria. Of the LPSs examined, Vibrio cholerae O139 LPS showed the highest hemagglutinating activity. Glycoproteins, such as mucin and fetuin, showed efficient inhibition of the hemagglutinating ability. Since cell-mediated hemagglutination is known to be correlated with bacterial adherence, hemagglutination induced by the polysaccharide moiety is interpreted to indicate that cell-surface LPS is a potential adhesin.

Endogenous prostaglandins and microflora modulate DNA synthesis and neuroendocrine peptides in the rat gastrointestinal tract

BACKGROUND

Previous studies suggest that E2 prostaglandins and the microflora may participate in the regulation of endocrine cells and of gastrointestinal cell kinetics. Our aim is to examine the actions of endogenous prostaglandins and of the microflora on gastrointestinal cell proliferation and tissue levels of neuroendocrine peptides.

METHODS

Germfree and ex-germfree rats were treated with subcutaneous placebo or 1.5 mg/kg indomethacin for 3 days. All rats were labeled with 3H-methyl-thymidine, and biopsy specimens from different parts of the gastrointestinal tract were processed for autoradiography. DNA synthesis was estimated by the labeling index, except in the oxyntic mucosa, where the total number of labeled cells present in 7.5 mm mucosa was used. The concentration of neuroendocrine peptides was determined by radioimmunoassay.

RESULTS

In the germfree rat, indomethacin reduced DNA synthesis in the fundus, duodenum, and proximal jejunum (P < 0.05) and the number of villous cells throughout the small intestine (P < 0.05). Exposure to microflora increased DNA synthesis in the proximal and distal jejunum, ileum, and colon (P < 0.05 versus germfree controls) and the number of crypt cells in the distal small intestine and colon (P < 0.05) and reduced the number of villous cells in the small intestine (P < 0.05) but did not affect tissue concentrations of neuroendocrine peptides. Indomethacin increased the concentration of somatostatin in the stomach, duodenum, and colon of germfree rats (P < 0.001), the concentration of calcitonin gene-related peptide (CGRP) and enteroglucagon in the proximal and distal jejunum and ileum (P < 0.001), and the concentration of glucagon in the colon (P < 0.05). The concentrations of somatostatin, CGRP, and glucagon were lower in indomethacin-treated ex-germfree rats than in indomethacin-treated germfree rats (P < 0.01).

CONCLUSIONS

Indomethacin selectively reduced DNA synthesis in the upper gastrointestinal tract of germfree rats, indicating a basal stimulatory role for endogenous prostaglandins on cell proliferation. Endogenous prostaglandins modulate synthesis or release of gastrointestinal neuroendocrine peptides. Somatostatin may mediate indomethacin-induced reduction of DNA synthesis. The microflora stimulates cell proliferation and influences tissue levels of neuroendocrine peptides in a manner opposite to that of indomethacin.

Indomethacin influences regulatory peptides and increases DNA synthesis in the gastrointestinal tract of the rat

OBJECTIVE

To examine the effect of long-term administration of indomethacin on regulatory peptides and DNA synthesis.

DESIGN

Sprague-Dawley rats were treated with 1 mg/kg indomethacin subcutaneously or indomethacin and 500 micrograms/kg oral prostaglandin E2 or solvents for 2 months before labelling with methyl-3H-thymidine.

METHODS

The labelling index, growth fraction and the number of epithelial cells were determined on autoradiographs of the stomach small intestine and colon. Plasma and gastrointestinal tissue concentrations of regulatory peptides were analysed by radioimmunoassay.

RESULTS

Indomethacin increased the concentration of somatostatin in the gastric fundus and ileum and reduced it in the colon. Prostaglandin E2 reduced the somatostatin concentration in the duodenum and colon. Indomethacin increased the concentration of neurotensin neurokinin A and glucagon in the distal small intestine and reduced the glucagon level in the colon. Prostaglandin E2 prevented such changes. Indomethacin increased DNA synthesis in the small intestine and produced hypoplasia of the villi. These changes were prevented by prostaglandin E2, except for the villous hypoplasia observed in the distal small intestine. Prostaglandin E2 reduced the labelling index in the antrum and colon.

CONCLUSION

Endogenous prostaglandins selectively modulate the synthesis and/or release of regulatory peptides and regulate the outflow of cells from the epithelial surface. Indomethacin induces hypoplasia, which triggers a secondary trophic reaction in the epithelium that may, at least partially, be mediated by regulatory peptides.

Invasive retroperitoneal infection due to Basidiobolus ranarum with response to potassium iodide--case report and review of the literature

We report a case of invasive retroperitoneal zygomycotic infection caused by Basidiobolus ranarum in a healthy 8-year-old boy. The youngster responded dramatically to potassium iodide. The clinical and pathological features are reviewed to highlight the problems encountered in the management of this rare infection.

Constitutive signaling by the phototaxis receptor sensory rhodopsin II from disruption of its protonated Schiff base-Asp-73 interhelical salt bridge

Sensory rhodopsin II (SRII) is a repellent phototaxis receptor in the archaeon Halobacterium salinarum, similar to visual pigments in its seven-helix structure and linkage of retinal to the protein by a protonated Schiff base in helix G. Asp-73 in helix C is shown by spectroscopic analysis to be a counterion to the protonated Schiff base in the unphotolyzed SRII and to be the proton acceptor from the Schiff base during photoconversion to the receptor signaling state. Coexpression of the genes encoding mutated SRII with Asn substituted for Asp-73 (D73N) and the SRII transducer HtrII in H. salinarum cells results in a 3-fold higher swimming reversal frequency accompanied by demethylation of HtrII in the dark, showing that D73N SRII produces repellent signals in its unphotostimulated state. Analogous constitutive signaling has been shown to be produced by the similar neutral residue substitution of the Schiff base counterion and proton acceptor Glu-113 in human rod rhodopsin. The interpretation for both seven-helix receptors is that light activation of the wild-type protein is caused primarily by photoisomerization-induced transfer of the Schiff base proton on helix G to its primary carboxylate counterion on helix C. Therefore receptor activation by helix C-G salt-bridge disruption in the photoactive site is a general mechanism in retinylidene proteins spanning the vast evolutionary distance between archaea and humans.

Primary structure and functional analysis of the soluble transducer protein HtrXI in the archaeon Halobacterium salinarium

Signal transduction in the archaeon Halobacterium salinarium is mediated by a family of 13 soluble and membrane-bound transducers. Here, we report the primary structure and functional analysis of one of the smallest halobacterial putative transducers, HtrXI. Hydropathy plot analysis of the primary structure predicts no membrane-spanning segments in HtrXI. The fractionation of the H. salinarium proteins confirmed that HtrXI is a soluble protein. Capillary assay with an HtrXI deletion mutant and a complemented strain revealed that this soluble transducer is involved in Asp and Glu taxis. In vivo analysis of the methylesterase activity of the htrXI-1 deletion mutant suggests that HtrXI plays an important role in the adaptation of the chemotactic responses to His, Asp, and Glu, which are attractants for halobacteria. Stimulation by Asp and Glu causes demethylation of HtrXI and of another putative transducer, HtrVII. But addition of His to halobacterial cells increases HtrXI methylation together with that of other putative transducers. In the absence of HtrXI, stimulation by either Glu or His does not decrease or increase the methylation of any putative transducers. Therefire, the HtrXI transducer appears to have a complex role in chemotaxis signal transduction.

Left atrial myxoma presenting with embolism to the aorta

We present a patient with left atrial myxoma embolizing to the ascending aorta. The features have not been reported previously and were diagnosed with transesophageal echocardiography.

Chronic invasive aspergillosis in apparently immunocompetent hosts

Seventeen cases of invasive aspergillosis occurring since 1987 in apparently immunologically normal hosts have been reviewed: 9 of invasive sinus aspergillosis, 2 of isolated brain abscesses, 3 of pneumonia (1 in a patient who developed mediastinitis), 2 of lymph node aspergillosis, and 1 of osteomyelitis of the foot. Two of the 9 patients with sinus aspergillosis died; the rest were stable up to March 1993. They responded initially to combined surgical and medical therapy. Both patients with brain abscesses survived following surgery, but one had neurological sequelae. Both patients with pneumonia were well following therapy with amphotericin B; one also received itraconazole. The patient with mediastinitis died, but this disease was diagnosed late. The patients with lymph node involvement were lost to follow-up, as was the patient with osteomyelitis. Invasive aspergillosis may be common in Pakistan. Greater awareness would allow earlier diagnosis and therapy, thereby improving the outcome.

Cell kinetic events in early indomethacin-induced gastrointestinal ulcerations in the rat

OBJECTIVE

To follow the sequence of cell kinetic events leading to the development of ulcerations in the gastrointestinal mucosa to better define primary actions of the drug and secondary phenomena mediated by the mucosal regulatory mechanisms.

DESIGN

Sprague-Dawley rats were given 4 mg/kg indomethacin subcutaneously as a single dose and killed 4h later. Additional rats were given three and five doses, twice daily, and were killed at 24h and 48h, respectively. Other groups were treated with indomethacin and oral prostaglandin E2 or placebo. All rats were killed 3h after mitotic arrest with vincristine.

METHODS

Histological sections from the oxyntic mucosa and proximal and distal jejunum were evaluated using a light microscope. The total number of arrested mitoses were counted in 250 microm width area of 30 consequent fields. In addition, the thickness and proliferative zone of the mucosa were determined. The cumulative mitotic index (MI%) and the number of cells in the left column of 30 well oriented crypts and villi were estimated in the proximal and distal small intestine.

RESULTS

The vast majority of rats given five doses of indomethacin developed small intestinal ulcerations and peritonitis and most of them showed haemorrhagic lesions in the oxyntic mucosa. Indomethacin reduced the number of mitotic cells in the oxyntic mucosa after three and five doses compared to controls (P<0.05). In addition, the thickness was significantly reduced in rats given five doses of indomethacin (P<0.05). These changes were prevented by the concomitant administration of prostaglandin E2. The MI% of the jejunal crypts was not affected by indomethacin but the number of villous cells was significantly lower in rats given five doses of indomethacin than in controls (P<0.05). A slight villous hyperplasia was observed in animals given three doses of indomethacin with prostaglandin E2 (P<0.05). The number of crypt cells was unaffected by treatments.

CONCLUSION

Indomethacin reduced cell proliferation in the oxyntic and jejunal epithelium, and increased epithelial cell losses, which are cell kinetic mechanisms leading to development of ulcerations. The regulatory mechanisms that increase DNA synthesis need longer periods of time to be triggered and they were not apparent in this model, in which the marked cell kinetic changes induced by indomethacin produced ulcerations within 48 h.

Purification and characterization of novel hemagglutinins from Vibrio mimicus: a 39-kilodalton major outer membrane protein and lipopolysaccharide

Two hemagglutinins (HAs) mediating the agglutinability to rabbit erythrocytes were isolated from 32-h culture supernatant of enterotoxigenic strain E-33 of Vibrio mimicus by ultrafiltration followed by gel filtration and anion-exchange column chromatography. The HAs were designated R-HA and C-HA on the basis of specific hemagglutinating activity towards rabbit erythrocytes only (R-HA) and towards chicken and rabbit erythrocytes (C-HA). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subsequent staining with Coomassie brilliant blue revealed no detectable protein band and a single band of Mr 39,000 in the case of R-HA and C-HA, respectively. However, silver staining of the gel containing R-HA revealed the appearance of low-molecular-weight material. These two HAs differed from each other and from previously reported HA/protease in receptor specificity, molecular composition, and biochemical and immunochemical properties. No simple sugar other than glycoproteins, including mucin, inhibited hemagglutinating activities of both C-HA and R-HA. Rabbit antibody against R-HA or C-HA could agglutinate E-33 whole cells, implying a possible cell surface origin of the two HAs. The isolated E-33 lipopolysaccharide (LPS) or its polysaccharide moiety conferred biochemical and immunochemical properties identical to those of R-HA, confirming that the R-HA represents polysaccharide of LPS. The LPS preparations from heterologous strains of Vibrio mimicus and Vibrio cholerae non-O1 confirmed that the hemagglutinating ability is a common function of LPS. On the other hand, the antibody against C-HA specifically recognized a major outer membrane protein (OMP) with an Mr of around 39,000 in both homologous and heterologous strains of V. mimicus, suggesting an OMP origin of C-HA. Furthermore, the antibody recognized a major OMP with an Mr of around 37,000 in V. cholerae. Although the immunogenicity of LPS and OMP is well documented for important intestinal pathogens, the hemagglutinating properties of such attractive cell surface components are hitherto unrecognized and will definitely contribute towards understanding their role in bacterial adherence.

Harziphilone and fleephilone, two new HIV REV/RRE binding inhibitors produced by Trichoderma harzianum

During the screening of the natural products for their ability to inhibit the binding of REV (regulation of virion expression) protein to [33P] labeled RRE (REV responsive element) RNA, two novel fungal metabolites, harziphilone and fleephilone, were isolated from the butanol-methanol (1:1) extract of the fermentation broth of Trichoderma harzianum by bioassay guided fractionation. The structures of these two new compounds were established by spectroscopic methods. Harziphilone and fleephilone showed inhibitory activity against the binding of REV-protein to RRE RNA with IC50 values of 2.0 microM and 7.6 microM, respectively. However both compounds did not protect CEM-SS cells from acute HIV infection at concentration levels up to 200 micrograms/ml using an XTT dye reduction assay. In addition, harziphilone demonstrated cytotoxicity at 38 microM against the murine tumor cell line M-109.

Expression of virulence-related properties by, and intestinal adhesiveness of, Vibrio mimicus strains isolated from aquatic environments

A study of the major pathogenic characteristics of Vibrio mimicus was carried out with 77 strains isolated from aquatic environments in Okayama, Japan. Of the strains tested, 96% demonstrated in vitro adherence to the rabbit intestinal mucosa, of which 36, 20, and 43% belonged to the strongly, moderately, and weakly adhesive groups, respectively. Of the 27 strains which appeared to be enterotoxigenic in the experiments using rabbit ileal loops, 74% belonged to the strongly adhesive group. All strains of V. mimicus at early log phase showed cell-mediated hemagglutination, and 70% of strongly hemagglutinative strains belonged to the strongly adhesive group, implying a possible correlation between cell-mediated hemagglutination and bacterial adherence. However, no significant correlation could be detected in the production of putative exocellular pathogenic factors and bacterial adherence or enterotoxigenicity.

Conformationally defined 6-s-trans-retinoic acid analogs. 3. Structure-activity relationships for nuclear receptor binding, transcriptional activity, and cancer chemopreventive activity

We recently demonstrated that conformationally defined 6-s-trans-retinoic acid (RA) analogs were effective in the prevention of skin papillomas (Vaezi et al. J. Med. Chem. 1994, 37, 4499-4507) and selective agonists for nuclear receptor binding and activation (Alam et al. J. Med. Chem. 1995, 38, 2302-2310). In order to probe important structure-activity relationships, we evaluated a homologous series of four 6-s-trans-retinoids that are 8-(2'-cyclohexen-1'-ylidene)-3,7-dimethyl-2,4,6-octatrienoic acids with different substituents at 2' (R2) and 3' (R1) positions on the cyclohexene ring. UAB1 (R1 = R2 = H), UAB4 (R1 = R2 = Me), UAB7 (R1 = Me, R2 = iPr), and UAB8 (R1 = Et, R2 = iPr) contain alkyl R groups that mimic, to different extents, portions of the trimethylcyclohexenyl ring of RA. Both 9Z- and all-E-isomers of these retinoids were evaluated in binding assays for cellular retinoic acid-binding proteins (CRABP-I and CRABP-II), a nuclear retinoic acid receptor (RAR alpha), and a nuclear retinoid X receptor (RXR alpha). The all-E-isomers of UAB retinoids bound tightly to CRABPs and RAR alpha, the binding affinity of the all-E-isomer increased systematically from UAB1 to UAB8, and binding for the latter was comparable to that of all-E-RA. In contrast to RA, the (9Z)-UAB retinoids were at least 200-fold less active than the all-E-isomers in binding to RAR alpha. The (9Z)-UAB isomers exhibited increasingly stronger binding to RXR alpha, and (9Z)-UAB8 was nearly as effective as (9Z)-RA in binding affinity. The retinoids were also evaluated in gene expression assays mediated by RAR alpha and RXR alpha homodimers or RAR alpha/RXR alpha heterodimers. Consistent with the binding affinities, the (all-E)-UAB retinoids activated gene transciption mediated by RAR alpha homodimers or RAR alpha/RXR alpha heterodimers, while the (9Z)-UAB isomers activated only the RXR alpha homodimer-mediated transcription. The all-E- and 9Z-isomers of the UAB retinoids were further evaluated for their capacity to prevent the induction of mouse skin papillomas. When compared to RA, only the (all-E)-UAB retinoids containing bulky R1 and R2 groups were effective in this chemoprevention assay. (9Z)-RA displayed equal capacity as RA to prevent papillomas, while the 9Z-isomers of the UAB retinoids were much less effective. Taken together, these studies demonstrate that the cyclohexenyl ring substituents of 6-s-trans-UAB retinoids are important for their biological activities and that the chemopreventive effect of the all-E-isomers of these retinoids correlates well with their capacity to bind to RARs and activate RAR/RXR-mediated transcription.