Current Pharmaceutical Biotechnology - Volume 14, Issue 4, 2013

Metallothionein (MT) is a low molecular weight metal-binding protein induced by endogenous and exogenous stimuli such as cytokines and heavy metals. In 1993 and 1994, two research groups (Choo et al. and Palmiter et al., respectively) produced MT-I/II double-knockout mice (MT-I/II null mice) with null mutations of the MT-I and MT-II genes. Subsequently, MT-I/II null mice have been used to clarify the biological function, physiological role, and pathophysiological relevance of MT by many research groups. Recent studies using MT-I/II null mice to investigate the role of MT in metal toxicity and distribution, oxidative stress, and some disease were reviewed. In addition, several research groups including our laboratory have reported that MT-I/II null mice are highly susceptible to several carcinogenesis caused by 7,12-dimethylbenz[a]anthracene, X-ray, benzo[a]pyrene, N-butyl-N-(4-hydroxybutyl) nitrosamine, lead, and cisplatin. These results suggest that MT is an important protective factor against not only metal toxicity and oxidative stress but also chemical and radiation carcinogenesis. In this review, we present the findings of MT-I/II null mice with regard to the protective role of MT in carcinogenesis and mutagenesis caused by chemical agents and X-ray.

Methallothionein (MT) is a low molecular weight cysteine rich metalloprotein. In mammals, there are four isoforms (MT-1, -2, -3, and -4) and they have multiple roles, such as the detoxification of heavy metals, regulating essential metal homeostasis, and protecting against oxidative stress. Recently, accumulating studies have suggested that MTs (especially MT-1, -2, and -3) are an important neuroprotective substance for cerebral ischemia and retinal diseases, such as age-related macular degeneration (AMD) and retinitis pigmentosa (RP), that are characterized by a progressive retinal degeneration. Oxidative stress and/or zinc toxicity has been implicated as part of the common pathway in these diseases. Studying the expression patterns and functions of MTs may broaden our understanding of the endogenous molecular responses that these diseases trigger, and may help us to develop new therapeutic strategies to treat them. However, the precise roles of MTs within the brain and retina are not fully understood in terms of neuropathological conditions. In this review, we discuss the recent findings focusing on MTs’ functions following cerebral ischemia, AMD, and RP.

Metallothionein (MT) is a small molecular and multi-functional protein containing four atoms of copper (Cu) and three atoms of zinc (Zn) per molecule. It was isolated from the horse kidney in 1957 and half a century has passed since then. Although MT was found to work as a modulator of Zn and induce anti-oxidant reaction, the precise functions and its functional mechanisms remain to be elucidated. Over the years, a new isoform of MT, MT-III (also called growth inhibitory factor (GIF)), has been found in the brain, which was markedly diminished in the brain of Alzheimer's disease (AD). Many new findings on MT have been discovered in neurodegenerative diseases other than AD such as amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), prion disease, brain trauma, brain ischemia, and psychiatric diseases. In ALS in particular, MTs were markedly diminished in the spinal cord of patients with ALS. Initially, MT, which easily binds to cadmium (Cd) and copper (Cu), was considered to be toxic to our bodies. Molecular biological technologies enabled the production of recombinant MT saturated with zinc (Zn). MT has a high potential for the treatment of neurodegenerative diseases such as ALS, AD, and PD owing to its various functions including anti-oxidant properties and modulators not only for Zn but for Cu in the extra- and intracellular spaces. On the other hand, there are still various problems on MT to be elucidated in detail, including their binding proteins and functional mechanisms.

The integration of knowledge concerning the regulation of metallothionein (MT) with research on its proposed functions is necessary to clarify how MT affects cellular processes. MT expression is induced/enhanced in various tissues by a number of physiological mediators through several response elements in the MT gene promoter. The cellular accumulation of MT depends on the availability of cellular zinc derived from the diet. MT modulates: 1) the binding and exchange/ transport of heavy metals such as zinc, cadmium, or copper under physiological conditions and cytoprotection from their toxicities, and 2) the release of gaseous mediators such as hydroxyl radicals or nitric oxide. In addition, MT reportedly affects a number of cellular processes, such as gene expression, apoptosis, proliferation, and differentiation. Given the genetic approach, the apparently healthy status of MT-deficient mice argues against an essential biological role for MT; however, the molecule may be critical in cells/tissues/organs in times of stress, since MT expression is also evoked/enhanced by various stresses. In particular, because metallothionein (MT) is induced by inflammatory stress, its roles in inflammation are implied. Also, MT expression in the lung can be enhanced by inflammatory stimuli, suggesting that its expression correlates with inflammatory pulmonary diseases. In this paper, we review the role of MT of various inflammatory conditions in the airway.

Hepatic metallothionein (MT) expression, with various isoforms, and varying cellular localizations is a useful marker for clinico-pathogenesis of liver diseases. In acute liver toxicity caused by cadmium, carbon tetrachloride, or acetaminophen, MT plays a protective role, via the scavenging of radical species. In chronic hepatitis C patients, hepatic MT levels appear to be a biological factor associated with the severity of HCV infection, and are associated with a better response to IFN therapy. Transgenic mice that express HBsAg in the liver show hepatocellular damage, inflammation, regeneration, hyperplasia, and, eventually, neoplasia. The MT isoform, MT-1 help mitigate HBV-induced hepatitis. Analysis of MT gene expression in the livers of chronic hepatitis B patients is useful for understanding the features of distinct liver diseases and for judging disease progression. A profound down-regulation of isoform MT-1G in hepatocellular carcinoma was observed in 63% of tumors relative to the adjacent nonmalignant liver. MT has been implicated in the control of p53 folding with zinc exchange. Therefore, it appears MT may play a role in the pathogenesis of hepatocellular carcinoma. Overall MT is linked to a variety of liver diseases.

We have developed a competitive ELISA using a polyclonal antibody that showed specificity to both metallothionin (MT)-1 and MT-2 isoforms in human and animal specimens. The advantage of this ELISA depends on the characteristics of the polyclonal antibody. The NH2 terminal peptide of MT with acetylated methionine was shown to be the epitope of this antibody. The reactivity of this ELISA system with liver, kidney, and brain extracts worked very well for MT1,2 in wild type mice. Extracts of MT-3 knock-out mice also react well this ELISA, as expected, very low in MT 1,2 but in MT1/2 knock-out mice. Detection limits, the ranges of linearity, and reliability coefficients of MT quantification of the ELISA were suitable for determination of MT. From the preliminary study of normal reference ranges, we found that normal MT levels were between approximately 10-30 ng/ml in human serum. We expect in the future to detect cases with low (MT deficiency) and high serum MT concentrations in patients with various diseases, such as brain/liver disorders, and cancers, using this MT ELISA.

The development of obesity consists of 3 distinct processes: differentiation of new adipocytes from precursor preadipocytic cells, formation of mature adipocytes, and excess accumulation of lipids in the adipocytes resulting in cell enlargement. This review aims to discuss the possible role of metallothionein (MT) in adipose tissue in the development of obesity. MT is induced in adipose tissue during the development of obesity. In addition, MT plays a preventive role against obesity in female mice. Although the detailed mechanism is presently unknown, one of the factors involved is the mesoderm-specific transcript (MEST/Peg1), adipocyte enlargement factor. MT has a potential to prevent obesity-related diseases, at least in part, through suppression of disease-induced generation of superoxide and endoplasmic reticulum stress and associated damage. Studies on the development of a MT inducer will encourage potential clinical use for obesity- related diseases.

Monitoring translational diffusion of single molecules in solution or in a living cell, particularly DNA and proteins brings valuable information unperturbed by interaction with an artificial surface. The article derives theoretical relationships for time intervals during which just one molecule in the effective probe region can be studied, the time we call meaningful time. This time is greater than the transit time of the molecule through the detection volume, as a single molecule will likely reenter the detection volume several times during measurement. From the infinitely stretched molecular Poisson distribution of single molecules or particles, we select the contribution of the selfsame molecule or particle by applying rules for choosing appropriate statistics for the single-molecule trajectories. The results point to a useful and sensitive predictive power of the derived relationships. The meaningful time relationships are the criteria to check the experimental single molecule data measured under conditions of normal and anomalous Brownian diffusion of the molecules of interest. At femtomolar bulk concentration, it would be possible to observe an individual molecule over a second time interval or longer during which biological processes — and not conformational biophysical changes — are just starting.

Acute lung injury is a life-threating condition characterized by surfactant dysfunction and raised secretory phospholipase A2 (sPLA2) activity. Varespladib is a sPLA2 inhibitor shown to be effective in animal models of acute lung injury. We aimed at investigating the effect of co-administration of surfactant and varespladib on sPLA2 activity. Alveolar macrophages were cultured and stimulated with lipopolysaccharide and then treated with either varespladib, surfactant, varespladib followed by surfactant or nothing. sPLA2 activity, free fatty acids, tumour necrosis factor-α (TNF-α) and protein concentrations were measured in culture supernatants. Treatment with varespladib (p=0.019) and varespladib + surfactant (p=0.013), reduced the enzyme activity by approximately 15% from the basal level measured in the untreated cultures. Surfactant, varespladib and varespladib + surfactant, respectively decreased free fatty acids by -45% (p=0.045), - 62% (p=0.009) and -48% (p=0.015), from the baseline concentration of the untreated cultures. Varespladib and poractant- α co-administration reduces sPLA2 activity and free fatty acids release in cultured rat alveolar macrophages, although a clear drug synergy was not evident. Since co-administration may be useful to reduce inflammation and surfactant inactivation in acute lung injury, further in vivo studies are warranted to verify its clinical usefulness.

The survival of pediatric patients with cancer entities including osteosarcoma and Ewing’s sarcoma (ES), remains extremely low hence novel treatment approaches are urgently needed. Therefore, based on the concept of targeted therapy, numerous potential targets for the treatment of these cancers have been evaluated pre-clinically or in some cases even clinically during the last decade. In ES the CD99 protein is an attractive target antigen. In this respect, a new entry site for therapeutic intervention may derive from specific human antibodies against CD99. Human scFvC7 was isolated from a semi-synthetic ETH-2 antibody phage library panned on the extracellular portion of recombinant human CD99 protein. The scFvC7 was genetically sequenced, tested for CD99 recognition on an array of recombinant CD99 fragments and measured for binding affinity by ELISA. Finally, it was tested for staining CD99 antigen on a large panel of tumor and normal cells and tissues by cytofluorimetric and immunohystochemical assays. The new antibody scFvC7 recognizes the CD99 extracellular domain included between residues 50 and 74 with a binding affinity of 2.4 x 10-8 M. In contrast with all other antibodies to CD99 so far isolated, scFvC7 shows a unique specificity in cancer cell recognition: It stained prevalently ES cells while no or weak reactivity was observed on the majority of the other tumor and normal cells and tissues. Thanks to its properties the new anti-CD99 antibody here described represents the first step towards the construction of new selective ES therapeutics.

Potency and activity of SR13668 in cancer prevention have been proven in several in vitro and in vivo cancer models. However, the compound is highly hydrophobic and its limited oral bioavailability has hindered its clinical translation. In this study, we encapsulated SR13668 into polymeric nanoparticles to increase compound aqueous solubility and therefore bioavailability. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles (100-200nm) encapsulating SR13668 with narrow size distribution and high drug loading were generated by a continuous and scalable process of flash nanoprecipitation integrated with spray dry. A single gavage dose of SR13668-PLGA nanoparticles at 2.8 mg/kg was administered in eight beagle dogs. Drug levels in animal whole blood and plasma were measured over 24 hours. Enhanced bioavailability of SR13668 using nanoparticles compared with formulations of Labrasol® and neat drug in 0.5% methylcellulose is reported. This is the first attempt to study pharmacokinetics of SR13668 in large animals with orally administrated nanoparticle suspension.

Elevated hyaluronidase levels are found in the urine of bladder and prostate cancer patients. Therefore, HA-ase is regarded as an important biomarker for the detection of these cancers. In this report, we use a FRET based ratiometric sensing approach to detect the level of HA-ase in synthetic urine. For this, we have used a HA-FRET probe (hyaluronan) labeled with fluorescein as a donor and rhodamine as an acceptor. We monitor the digestion of our HA-FRET probe with different concentrations of HA-ase in synthetic urine via fluorescence emission. The extent to which FRET is released depends on the concentration of HA-ase. Our fluorescence intensity results are also supported with time resolved fluorescence decay data. This assay can be used to develop a non-invasive technique for the detection of bladder and/or prostate cancer progression.