Two-dimensional strain imaging of controlled rabbit hearts

Ultrasound strain imaging using 2-D speckle tracking has been proposed to quantitatively assess changes in myocardial contractility caused by ischemia. Its performance must be demonstrated in a controlled model system as a step toward routine clinical application. In this study, a well-controlled 2-D cardiac elasticity imaging technique was developed using two coplanar and orthogonal linear probes simultaneously imaging an isolated retroperfused rabbit heart. Acute ischemia was generated by left anterior descending (LAD) artery ligation. An excitation-contraction decoupler, 2,3-butanedione monoxime, was applied at a 4-mM concentration to reversibly reduce myocardial contractility. Results using a single probe demonstrate that directional changes in the in-plane principal deformation axes can help locate the bulging area as a result of LAD ligation, which matched well with corresponding Evans Blue staining, and strains or strain magnitude, based on principal stretches, can characterize heart muscle contractility. These two findings using asymmetric displacement accuracy (i.e., normal single-probe measurements with good axial but poor lateral estimates) were further validated using symmetric displacement accuracy (i.e., dual-probe measurements using only accurate axial tracking estimates from each). However, the accuracy of 2-D cardiac strain imaging using a single probe depends on the probe's orientation because of the large variance in lateral displacement estimates.

Dynamics of microbubble generation and trapping by self-focused femtosecond laser pulses

Different from conventional optical tweezers used for trapping high refractive index micron-sized particles, bubble generation and trapping by femtosecond laser offer a unique strategy to manipulate microbubbles. Using high frequency ultrasound imaging and fast-frame optical video microscopy, we obtained results revealing the spatiotemporal characteristics of bubble generation and trapping by self-focused femtosecond laser pulses at multiple locations along the laser beam. We detected distinct acoustic signals associated with the laser focus and measured the trapping force by using acoustic radiation force to detrap the bubble from the laser beam.

Characterization of pancreatic cancer and intra-abdominal lymph node malignancy using spectrum analysis of endoscopic ultrasound imaging

This study assessed the ability of spectral analysis of endoscopic ultrasound (EUS) RF signals acquired in humans in vivo to distinguish between (1) benign and malignant intraabdominal and mediastinal lymph nodes and (2) pancreatic cancer, chronic pancreatitis, and normal pancreas. Mean midband fit, slope, intercept, and correlation coefficient from a linear regression of the calibrated RF power spectra were computed over regions of interest defined by the endoscopist. Linear discriminant analysis was then performed to develop a classification of the resulting spectral parameters. For lymph nodes, classification based on the midband fit and intercept provided 67% sensitivity, 82% specificity, and 73% accuracy for malignant vs. benign nodes. For pancreas, classification based on midband fit and correlation coefficient provided 95% sensitivity, 93% specificity, and 93% accuracy for diseased vs. normal pancreas and 85% sensitivity, 71% specificity, and 85% accuracy for pancreatic cancer vs. chronic pancreatitis. These promising results suggest that mean spectral parameters can provide a non-invasive method to quantitatively characterize pancreatic cancer and lymph malignancy in vivo.

Creation of an effective and reproducible nonsurvival porcine model that simulates actively bleeding peptic ulcers

BACKGROUND

Efforts to develop improved endoscopic therapeutic methods for upper GI bleeding require an effective animal model.

OBJECTIVE

To develop a nonsurvival porcine model that simulates acute peptic ulcer bleeding.

DESIGN

Prospective animal (porcine) study.

SETTING

Animal laboratory.

INTERVENTIONS

A surgical seromyotomy was created along the external surface of the greater curvature of the stomach in anesthesized pigs. A submucosal plane was developed and the gastroepiploic bundle, in continuity, was placed adjacent to the mucosa, and the seromuscular tissues were re-approximated over the vascular bundle. By using EGD, a needle-knife with electrocautery was then used to incise the mucosal tissue overlying the vascular bundle. Standard endoscopic methods for bleeding control were then tested in this animal model.

MAIN OUTCOME MEASUREMENTS

To evaluate whether successful bleeding that simulates submucosal arterial bleeding from peptic ulcer disease could be achieved in a porcine animal model.

RESULTS

Successful simulation of active peptic ulcer bleeding was achieved with this nonsurvival porcine model in a total of 5 sequential pigs. Other porcine models for bleeding were tested and found to be unsatisfactory. Hemoclips and combination injection-thermal therapy were used to stop bleeding over Doppler-positive areas, with subsequent endoscopic nonimaging Doppler US probe examination of the ulcer bed revealing a negative Doppler signal.

LIMITATIONS

This was an animal laboratory study. Further human studies would be ideal once any future endoscopic interventions are proven to be safe in animals.

CONCLUSIONS

This active bleeding ulcer model can be used to develop future endoscopic therapies and for training purposes.

The risk of exposure to diagnostic ultrasound in postnatal subjects: thermal effects

This review evaluates the thermal mechanism for ultrasound-induced biological effects in postnatal subjects. The focus is the evaluation of damage versus temperature increase. A view of ultrasound-induced temperature increase is presented, based on thermodynamic Arrhenius analyses. The hyperthermia and other literature revealed data that allowed for an estimate of a temperature increase threshold of tissue damage for very short exposure times. This evaluation yielded an exposure time extension of the 1997 American Institute of Ultrasound in Medicine Conclusions Regarding Heat statement (American Institute of Ultrasound in Medicine, Laurel, MD) to 0.1 second for nonfetal tissue, where, at this exposure time, the temperature increase threshold of tissue damage was estimated to be about 18 degrees C. The output display standard was also evaluated for soft tissue and bone cases, and it was concluded that the current thermal indices could be improved to reduce the deviations and scatter of computed maximum temperature rises.

EUS spectrum analysis for in vivo characterization of pancreatic and lymph node tissue: a pilot study

BACKGROUND

EUS is limited by variability in the examiner's subjective interpretation of B-scan images to differentiate among normal, inflammatory, and malignant tissue. By using information otherwise discarded by conventional EUS systems, quantitative spectral analysis of the raw radiofrequency (RF) signals underlying EUS images enables tissue to be characterized more objectively.

OBJECTIVE

Our purpose was to determine the feasibility of using spectral analysis of EUS data for characterization of pancreatic tissue and lymph nodes.

DESIGN AND SETTING

A pilot study of eligible patients was conducted to analyze the RF data obtained during EUS by using spectral parameters.

PATIENTS

Twenty-one subjects who underwent EUS of the esophagus, stomach, pancreas, and surrounding intra-abdominal and mediastinal lymph nodes.

MAIN OUTCOME MEASUREMENTS

Linear regression parameters of calibrated power spectra of the RF signals were tested to differentiate normal pancreas from chronic pancreatitis and from pancreatic cancer as well as benign from malignant-appearing lymph nodes.

RESULTS

The mean intercept, slope, and midband fit of the spectra differed significantly among normal pancreas, adenocarcinoma, and chronic pancreatitis when all were compared with each other (P < .01). On direct comparison, mean midband fit for adenocarcinoma differed significantly from that for chronic pancreatitis (P < .05). For lymph nodes, mean midband fit and intercept differed significantly between benign- and malignant-appearing lymph nodes (P < .01 and P < .05, respectively).

LIMITATIONS

Small sample population and spatial averaging inherent to this technique.

CONCLUSIONS

Mean spectral parameters in EUS imaging can provide a noninvasive method to discriminate normal from diseased pancreas and lymph nodes.

Effects of extracellular calcium on cell membrane resealing in sonoporation

Sonoporation has been exploited as a promising strategy for intracellular drug and gene delivery. The technique uses ultrasound to generate pores on the cell membrane to allow entry of extracellular agents into the cell. Resealing of these non-specific pores is a key factor determining both the uptake and post-ultrasound cell survival. This study examined the effects of extracellular Ca(2+) on membrane resealing in sonoporation, using Xenopus oocytes as a model system. The cells were exposed to tone burst ultrasound (1.06 MHz, duration 0.2 s, acoustic pressure 0.3 MPa) in the presence of 0.1% Definity at various extracellular [Ca(2+)] (0-3 mM). Sonoporation inception and resealing in a single cell were monitored in real time via the transmembrane current of the cell under voltage clamp. The time-resolved measurements of transmembrane current revealed the involvement of two or more Ca(2+) related processes with different rate constants and characteristics. Rapid resealing occurred immediately after ultrasound application followed by a much slower resealing process. Complete resealing required [Ca(2+)] above 0.54 mM. The cells resealed in 6-26 s at 1.8 mM Ca(2+), but took longer at lower concentrations, up to 58-170 s at 0.54 mM Ca(2+).

Ultrasound-induced calcium oscillations and waves in Chinese hamster ovary cells in the presence of microbubbles

This study investigated the effects of ultrasound on the intracellular [Ca(2+)] of Chinese hamster ovary cells in the presence of albumin-encapsulated Optison microbubbles. Cells were exposed to 1 MHz ultrasound (tone burst of 0.2 s duration, 0.45 MPa peak pressure) while immersed in solution of 0.9 mM Ca(2+). Calcium imaging of the cells was performed using digital video fluorescence microscopy and Ca(2+)-indicator dye fura-2AM. Experimental evidence indicated that ultrasound caused a direct microbubble-cell interaction resulting in the breaking and eventual dissolution of the microbubble and concomitant permeabilization of the cells to Ca(2+). These cells exhibited a large influx of Ca(2+) over 3-4 s and did not return to their equilibrium levels. Subsequently, some cells exhibited one or more Ca(2+) oscillations with the onset of oscillations delayed by 10-80 s after the ultrasound pulse. A variety of oscillations were observed including decaying oscillations returning to the baseline value over 35-100 s, oscillations superimposed on a more gradual recovery over 150-200 s, and oscillations continued with increased amplitude caused by a second ultrasound tone burst. The delays in onset appeared to result from calcium waves that propagated across the cells after the application of the ultrasound pulse.

Sonoporation is an efficient tool for intracellular fluorescent dextran delivery and one-step double-crossover mutant construction in Fusobacterium nucleatum

Studies of microorganisms are often hindered by a lack of effective genetic tools. One such example is Fusobacterium nucleatum, a gram-negative anaerobe associated with various human infections, including those causing periodontal disease and preterm birth. The first double-crossover allelic-exchange mutant in F. nucleatum was recently constructed using sonoporation, a novel ultrasound-mediated intracellular delivery method, demonstrating potential for bacterial gene transfection. To better unveil its mechanism, the current study examines the factors affecting the outcome of sonoporation. Delivery of Texas Red-conjugated dextran into F. nucleatum by sonoporation was at least twice as efficient as that by electroporation, and sonoporation was nonbactericidal, unlike electroporation. The delivery efficiency was affected by the acoustic pressure amplitude, the duty cycle, and the quantity of microbubbles used to initiate cavitation but not by the pulse repetition frequency of ultrasound application. To examine the involvement of homologous recombination in sonoporation-mediated mutant construction, the highly conserved recA gene, which carried most of the consensus residues, including the P loop, was identified in F. nucleatum, and a double-crossover recA mutant of F. nucleatum 12230, US1610, was constructed by sonoporation. The mutant exhibited increased sensitivity to UV exposure compared with that of the wild type, indicating that the RecA function in F. nucleatum was conserved. Interestingly, US1610 was also sensitive to ultrasound treatment, suggesting the likely involvement of RecA in postsonoporation repair and survival. Since sonoporation has consistently generated one-step double-crossover mutants in F. nucleatum by use of intact suicide plasmids, this technology may be developed into an efficient tool for streamlining mutant construction in bacteria.

Fluorescence imaging for real-time monitoring of high-intensity focused ultrasound cardiac ablation

Side effects and limitations of radio-frequency ablation of cardiac arrhythmias prompted search for alternative energy sources and means of their application. High-intensity focused ultrasound (HIFU) is becoming an increasingly attractive modality for ablation because of its unique ability for non-invasive or minimally invasive, non-contact focal ablation in 3D volume without affecting intervening and surrounding cells. The purpose of this study is to develop a real-time monitoring technique to elucidate HIFU-induced modifications of electrical conduction in cardiac tissues and to investigate the HIFU cardiac ablation process to help to achieve optimal HIFU ablation outcome. We conducted experimental studies applying HIFU at 4.23 MHz to ablate the atrio-ventricular (AV) node and ventricular tissue of Langendorff-perfused rabbit hearts. We employed fluorescent voltage-sensitive dye imaging and surface electrodes to monitor the electrical conduction activity induced by HIFU application in real time. In ventricular epicardium HIFU ablation, fluorescent imaging revealed gradual reduction of the plateau phase and amplitude of the action potential. Subsequently, conduction block and cell death were observed at the site of ablation. When HIFU was applied to the AV node, fluorescent imaging and electrograms revealed the development of the AV block. The study establishes that real-time fluorescent imaging provides novel monitoring and assessment to study HIFU cardiac ablation, which may be able to provide improved understanding of HIFU cardiac ablation process and mechanism useful for development of successful clinical applications.

Identification and characterization of a novel adhesin unique to oral fusobacteria

Fusobacterium nucleatum is a gram-negative anaerobe that is prevalent in periodontal disease and infections of different parts of the body. The organism has remarkable adherence properties, binding to partners ranging from eukaryotic and prokaryotic cells to extracellular macromolecules. Understanding its adherence is important for understanding the pathogenesis of F. nucleatum. In this study, a novel adhesin, FadA (Fusobacterium adhesin A), was demonstrated to bind to the surface proteins of the oral mucosal KB cells. FadA is composed of 129 amino acid (aa) residues, including an 18-aa signal peptide, with calculated molecular masses of 13.6 kDa for the intact form and 12.6 kDa for the secreted form. It is highly conserved among F. nucleatum, Fusobacterium periodonticum, and Fusobacterium simiae, the three most closely related oral species, but is absent in the nonoral species, including Fusobacterium gonidiaformans, Fusobacterium mortiferum, Fusobacterium naviforme, Fusobacterium russii, and Fusobacterium ulcerans. In addition to FadA, F. nucleatum ATCC 25586 and ATCC 49256 also encode two paralogues, FN1529 and FNV2159, each sharing 31% identity with FadA. A double-crossover fadA deletion mutant, F. nucleatum 12230-US1, was constructed by utilizing a novel sonoporation procedure. The mutant had a slightly slower growth rate, yet its binding to KB and Chinese hamster ovarian cells was reduced by 70 to 80% compared to that of the wild type, indicating that FadA plays an important role in fusobacterial colonization in the host. Furthermore, due to its uniqueness to oral Fusobacterium species, fadA may be used as a marker to detect orally related fusobacteria. F. nucleatum isolated from other parts of the body may originate from the oral cavity.

Study of sonoporation dynamics affected by ultrasound duty cycle

Sonoporation is the ultrasound-induced membrane porosity and has been investigated as a means for intracellular drug delivery and nonviral gene transfection. The dynamic characteristics of sonoporation, such as formation, duration and resealing of the pores in the cell membrane, determine the process of intracellular uptake of molecules or agents of interest that are otherwise obstructed by the cell membrane barrier. Sonoporation dynamics is also important for postultrasound cell survival. In this study, we investigated the effects of ultrasound duty cycle on sonoporation dynamics using Xenopus oocyte as a model system. Transducer with a center frequency of 0.96 MHz was used to generate pulsed ultrasound of desired duty cycle (5%, 10% and 15%) at a pulse repetition frequency of 1 Hz and an acoustic pressure of 0.4 MPa in our experiments. Employing voltage clamp techniques, we measured the transmembrane current as the direct result of decreased membrane resistance due to pore formation induced by ultrasound application. We characterized the sonoporation dynamics from these time-resolved recordings of transmembrane current to indicate cell membrane status, including pore formation, extension and resealing. We observed that the transmembrane current amplitude increased with increasing duty cycle, while the recovering process of membrane pores and cell survival rate decreased at higher duty cycles.

A feasibility study of high intensity focused ultrasound for liver biopsy hemostasis

This study was conducted to demonstrate the feasibility of high intensity focused ultrasound (HIFU) application to control post-liver-biopsy hemorrhage. Anesthetized Yorkshire pigs (n = 3; mean weight = 23.0 kg) were used and the liver organ was exposed surgically by an open laparotomy. Core biopsies were performed on the hepatic parenchyma with 14-gauge (n = 41) and 18-gauge (n = 33) core biopsy needles. The focus of HIFU (4.23 MHz) field was applied for 15 to 45 s to the needle entry site in the liver immediately after needle retraction. Blood loss from a biopsy site was determined using surgical sponges as absorbent applied at the site. Mean blood loss for control sites was 6.16 g (14-gauge, n = 20) and 1.22 g (18-gauge, n = 10). Virtually no blood loss was measured for biopsies after HIFU application (n = 44) for using needles of both sizes. Our results indicate that intraoperative HIFU application could successfully induce hemostasis after liver biopsy in a porcine model.

Ultrasound-induced cell membrane porosity

Recent studies of ultrasound (US) methods for targeted drug delivery and nonviral gene transfection revealed new, advantageous possibilities. These studies utilized US contrast agents, commonly stabilized microbubbles, to facilitate delivery and suggested that US delivery resulted from cell sonoporation, the formation of temporary pores in the cell membrane induced by US. Using voltage clamp techniques, we obtained real-time measurements of sonoporation of single Xenopus oocyte in the presence of Optison trade mark, an agent consisting of albumin-shelled C(3)F(8) gas bubbles (mean diameter 3.2 microm). Ultrasound increased the transmembrane current as a direct result of decreased membrane resistance due to pore formation. We observed a distinct delay of sonoporation following US activation and characteristic stepwise increases of transmembrane current throughout US duration. We discovered that the resealing of cell membrane following US exposure required Ca(2+) entering the cell through US-induced pores.

Emerging ultrasound technologies for early markers of disease

Ultrasound has been a popular clinical imaging modality for decades. It is well established as a means of displaying the macroscopic anatomy of soft-tissue structures. While conventional ultrasound methodologies (i.e., B-mode and Doppler methods) are well proven and continue to advance technically on a daily basis, e.g. by extending into higher frequencies and taking advantage of harmonic phenomena in tissues, fundamentally new ultrasound technologies also are emerging and offer exciting promise for making significant improvements in the clinical imaging of disease. These emerging methods include spectrum analysis, elasticity imaging, contrast-agent methods, and advanced flow detection and measurement techniques. Each provides independent information and, used alone, each can provide powerful new imaging capabilities; combined with each other, their capabilities may be even greater in many applications; and all in principle can be used in concert with other imaging modalities to offer the possibility of further improvements in disease detection, evaluation, and monitoring.

Radiation-force technique to monitor lesions during ultrasonic therapy

This report describes a monitoring technique for high-intensity focused ultrasound (US), or HIFU, lesions, including protein-denaturing lesions (PDLs) and those made for noninvasive cardiac therapy and tumor treatment in the eye, liver and other organs. Designed to sense the increased stiffness of a HIFU lesion, this technique uniquely utilizes the radiation force of the therapeutic US beam as an elastographic push to detect relative stiffness changes. Feasibility was demonstrated with computer simulations (treating acoustically induced displacements, concomitant heating, and US displacement-estimation algorithms) and pilot in vitro experimental studies, which agree qualitatively in differentiating HIFU lesions from normal tissue. Detectable motion can be induced by a single 5 ms push with temperatures well below those needed to form a lesion. Conversely, because the characteristic heat diffusion time is much longer than the characteristic relaxation time following a push, properly timed multiple therapy pulses will form lesions while providing precise control during therapy.

A review of physical phenomena associated with ultrasonic contrast agents and illustrative clinical applications

Successful clinical applications of contrast agents involve an understanding of the physical interaction of ultrasound (US) with contrast agents. This paper reviews the physical phenomena involved in these interactions and discusses the relevant theoretical background for modeling US-contrast agent interactions. Measurement techniques using US to obtain information regarding contrast agents are summarized. Illustrative clinical applications are given in the second part of the paper. Recent developments in nonlinear imaging techniques and transient techniques are reviewed. New methods, such as depletion perfusion measurement, and high-frequency applications are included.

Cholinergic dilation of cerebral blood vessels is abolished in M(5) muscarinic acetylcholine receptor knockout mice

The M(5) muscarinic receptor is the most recent member of the muscarinic acetylcholine receptor family (M(1)-M(5)) to be cloned. At present, the physiological relevance of this receptor subtype remains unknown, primarily because of its low expression levels and the lack of M(5) receptor-selective ligands. To circumvent these difficulties, we used gene targeting technology to generate M(5) receptor-deficient mice (M5R(-/-) mice). M5R(-/-) mice did not differ from their wild-type littermates in various behavioral and pharmacologic tests. However, in vitro neurotransmitter release experiments showed that M(5) receptors play a role in facilitating muscarinic agonist-induced dopamine release in the striatum. Because M(5) receptor mRNA has been detected in several blood vessels, we also investigated whether the lack of M(5) receptors led to changes in vascular tone by using several in vivo and in vitro vascular preparations. Strikingly, acetylcholine, a powerful dilator of most vascular beds, virtually lost the ability to dilate cerebral arteries and arterioles in M5R(-/-) mice. This effect was specific for cerebral blood vessels, because acetylcholine-mediated dilation of extra-cerebral arteries remained fully intact in M5R(-/-) mice. Our findings provide direct evidence that M(5) muscarinic receptors are physiologically relevant. Because it has been suggested that impaired cholinergic dilation of cerebral blood vessels may play a role in the pathophysiology of Alzheimer's disease and focal cerebral ischemia, cerebrovascular M(5) receptors may represent an attractive therapeutic target.

Multiple genetic changes are associated with mammary tumorigenesis in Brca1 conditional knockout mice

Germline mutations in the tumor suppressor gene BRCA1 predispose women to breast cancer, however somatic mutations in the gene are rarely detected in sporadic cancers. To understand this phenomenon, we examined mouse models carrying conditional disruption of Brca1 in mammary epithelium in either p53 wild type (wt) or heterozygous backgrounds. Although a p53(+/-) mutation significantly accelerated tumorigenesis, both strains developed mammary tumors in a stochastic fashion, suggesting that multiple factors, in addition to p53 mutations, may be involved in Brca1 related tumorigenesis. A unique feature of Brca1 mammary tumors is their highly diverse histopathology accompanied by severe chromosome abnormalities. The tumors also display extensive genetic/molecular alterations, including overexpression of ErbB2, c-Myc, p27 and Cyclin D1 in the majority of tumors, while they were virtually ERalpha and p16 negative. Translocations involving p53 were also identified which lead to abnormal RNA and protein products. In addition, we generated cell lines from mammary tumors and found that the cells retained many of the genetic changes found in the primary tumors, suggesting that these genes may be players in Brca1-associated tumorigenesis. Despite their distinct morphology, all cultured tumor cells were Tamoxifen resistant but highly sensitive to Doxorubicin or gamma-irradiation, suggesting that these methods would be effective in treatment of this disease.

Fibroblast growth factor receptor 2 (Fgfr2) plays an important role in eyelid and skin formation and patterning

Initiating as protruding ridges above and below the optic vesicle, the eyelids of mice grow across the eye and temporarily fuse in fetal life. Mutations of a number of genes disrupt this developmental process and result in a birth defect, "open-eyelids at birth." Here we show that a critical event for eyelid induction occurs at embryonic day 11.5 (E11.5) when the single cell-layered ectoderm in the presumptive eyelid territory increases proliferation and undergoes morphologic transition to form cube-shaped epithelial cells. Using embryos lacking the Fgfr2 Ig domain III (Fgfr2(DeltaIII/DeltaIII)) generated by tetraploid rescue and chimeric embryo formation approaches, we demonstrate that this event is controlled by Fgfr2 signals as the Fgfr2(DeltaIII/DeltaIII) mutation blocks these changes and results in embryos without eyelids. Fgfr2 and its ligands are differentially expressed in the ectoderm and underlying mesenchyme and function in a reciprocal interacting loop that specifies eyelid development. We also demonstrate that similar defects account for failure of skin formation at early stages. Interestingly, Fgfr2-independent skin formation occurs at E14.5 mutant embryos, resulting in much thinner, yet well-differentiated epidermis. Notably, mutant skin remains thin with decreased hair density after transplantation to wild-type recipients. These data demonstrate an essential role of Fgfr2 in eyelid and skin formation and patterning.

BRCA1-associated tumorigenesis: what have we learned from knockout mice?

A series of allelic mutations in the tumor suppressor Brca1 have been created to study mechanisms underlying BRCA1-associated tumorigenesis. Brca1 is essential in maintaining genome integrity through its involvement in DNA damage repair, G(2)-M cell-cycle checkpoint and centrosome duplication. The loss of Brca1 is not sufficient for malignant transformation, rather, it triggers multiple genetic alterations, including the inactivation of p53 and activation of a number of oncogenes, that ultimately result in mammary tumorigenesis.

Knockout mouse models and mammary tumorigenesis

The generation of transgenic mice overexpressing activated forms of oncogenes has greatly advanced our understanding into their roles in mammary tumor initiation, promotion and progression. However, targeted disruption of tumor suppressor genes often results in lethality at stages prior to mammary tumor formation. This obstacle can now be overcome using several approaches including conditional knockouts that delete genes of interest in a spatial and temporal manner. This review summarizes recent studies on tumor suppressor genes, including APC, ATM, BRCA1, BRCA2, PTEN and p53, in knockout mouse models and our understanding of the possible mechanisms underlying mammary tumorigenesis.

Safety levels for exposure of cornea and lens to very high-frequency ultrasound

OBJECTIVE

Very high-frequency (50-MHz) ultrasound is widely used for imaging the anterior segment of the eye. Our aim was to determine whether exposures to ultrasound at and above those used in diagnostic imaging systems might cause bioeffects in ocular tissues.

METHODS

We characterized the output parameters of a polyvinylidene difluoride transducer using a needle hydrophone. We exposed sites on the cornea or lens of rabbits for up to 30 minutes at a 10-kHz pulse repetition frequency. Tissue obtained immediately or 24 hours after exposure was examined by light microscopy. A numeric model was implemented to calculate expected temperature elevations in the cornea and lens under experimental conditions.

RESULTS

No tissue changes were observed directly or by slit lamp. Light microscopy showed no abnormalities attributable to ultrasound exposure. Simulations showed that even long-term exposures should produce temperature elevations of less than 1 degree C in both the cornea and lens.

CONCLUSION

With the use of exposure parameters 4 to 5 orders of magnitude greater than encountered in a clinical situation, no tissue changes were observed. This is consistent with the small (0.2 degrees C) temperature rises computed in simulations. The lack of biological effects is attributable to the small dimensions of the focal zone, allowing rapid dissipation of heat, and the low total acoustic power produced by the transducer.

Smad proteins and hepatocyte growth factor control parallel regulatory pathways that converge on beta1-integrin to promote normal liver development

Smads serve as intracellular mediators of transforming growth factor beta (TGF-beta) signaling. After phosphorylation by activated type I TGF-beta receptors, Smad proteins translocate to the nucleus, where they serve as transcription factors and increase or decrease expression of TGF-beta target genes. Mice lacking one copy each of Smad2 and Smad3 suffered midgestation lethality due to liver hypoplasia and anemia, suggesting essential dosage requirements of TGF-beta signal components. This is likely due to abnormal adhesive properties of the mutant hepatocytes, which may result from a decrease in the level of the beta1-integrin and abnormal processing and localization of E-cadherin. Culture of mutant livers in vitro revealed the existence of a parallel developmental pathway mediated by hepatocyte growth factor (HGF), which could rescue the mutant phenotype independent of Smad activation. These pathways merge at the beta1-integrin, the level of which was increased by HGF in the cultured mutant livers. HGF treatment reversed the defects in cell proliferation and hepatic architecture in the Smad2(+/-); Smad3(+/-) livers.