A quantum biological hypothesis of human secondary dentinogenesis

It is hypothesized that human coronal secondary dentin (SD) is a final classical mechanical (CM) response to a chain of prior quantum mechanical (QM) transductions of the information of initial CM occlusal loadings of enamel. Such CM energy is transduced into QM quanta (as protons) that are translocated centripetally via clustered water (CW), (as "proton wires"), that is structurally related to both enamel prism sheath and hydroxyapatite crystal hydration shells. These quanta pass into odontoblastic cell processes (OP), lying within dentinal tubules (DT). OP's contain abundant parallel arrays of cylindrical microtubules (MT). These are the sites of two further CW-related QM events: (i) proton translocation associated with conformal changes of MT tubulin protein dimers; and (ii) coherent energetic oscillations within the CW filling the MT's hollow cores. Finally, these quanta pass into the odontoblastic soma, where QM wave function collapse transduces this information into a final CM state that initiates the processes of SD formation. A critical portion of this hypothesis may be experimentally tested.

Therapeutic benefits from targeting of ADAM family members

Members of the ADAM (a disintegrin and metalloproteinase) family of proteolytic enzymes are implicated in the processing of many single transmembrane-bound proteins ranging from cell surface receptors to growth factors and cytokines. Because of the biological significance of these processing events, a recurring theme in studying ADAM biology is that they are involved in physiological processes that can go awry and lead to disease states. This review provides a comprehensive look at ADAM family members and their role in pathology and provides a pathway for determining whether an enzyme is a physiological convertase for a given protein. In addition, ADAMs are discussed as potential therapeutic targets.

Use of a Multiple-Enzyme/Multiple-Reagent Assay System To Quantify Activity Levels in Samples Containing Mixtures of Matrix Metalloproteinases

Matrix metalloproteinases (MMPs) are a family of enzymes that are up-regulated in many diseases, including osteoarthritis (OA) and rheumatoid arthritis (RA). Here we report on a novel technique that can be used to simultaneously measure activity levels for a panel of enzymes, such as the MMPs. The technique, termed the multiple-enzyme/multiple-reagent assay system (MEMRAS), relies on the use of reagents such as substrates with varying selectivity profiles against a group of enzymes. When reaction rates are measured by following a change in fluorescence with time, for mixtures of enzymes, an equation with unknown concentrations for each activity is generated for each reagent used. Simultaneously solving the set of equations leads to a solution for the unknown concentrations. We have applied this mathematical technique to measure activity levels for mixtures of MMPs such as collagenase 3 and gelatinase A. In addition, because we were most interested in determining collagenase 3 levels as a potential biological marker for OA, we developed highly selective substrates for this enzyme by using results found in previous bacteriophage substrate-mapping experiments. Some of the best substrates tested have specific activities for collagenase 3 that are 37,000-, 17,000-, 90-, and 200-fold selective over stromelysin 1, collagenase 1, and gelatinases A and B, respectively.

Shedding of membrane proteins by ADAM family proteases

Many membrane-bound proteins undergo proteolytic release from the membrane, a process known as 'shedding'. Some of the processing events are carried out by enzymes of the ADAM (a disintegrin and metalloproteinase) family, which are also membrane bound. One of the most well known ADAM family members is TACE (tumour necrosis factor-alpha-converting enzyme. TACE was the first ADAM family member to have a known physiological substrate, namely, precursor tumour necrosis factor-alpha. Inhibitors of TACE block the release of the soluble form of this inflammatory cytokine, and are currently being studied in drug discovery projects for the treatment of arthritis. Since the discovery of TACE, physiological substrates for other ADAMs have been determined. This review focuses on the shedding events carried out by TACE and other ADAM family proteinases.

Multiple metalloproteinases process protransforming growth factor-alpha (proTGF-alpha)

Shedding of TNF-alpha requires a single cleavage event, whereas the ectodomain of proTGF-alpha is cleaved at N-proximal (N-terminal) and membrane proximal (C-terminal) sites to release mature TGF-alpha. Tumor necrosis factor-alpha converting enzyme (TACE) was shown to have a central role in the shedding of both factors. Here we show that cleavage of the proTGF-alpha C-terminal site, required for release of mature growth factor, is less sensitive to a panel of hydroxamates than TNF-alpha processing. Recombinant TACE cleaves TNF-alpha and N-terminal TGF-alpha peptides 50-fold more efficiently than the C-terminal TGF-alpha peptide. Moreover, fractionation of rat liver epithelial cell membranes yields two populations: one contains TACE and cleaves peptides corresponding to TNF-alpha and both proTGF-alpha processing sites, while the other lacks detectable TACE and cleaves only the C-terminal proTGF-alpha processing site. Activities in both fractions are inhibited by hydroxamates and EDTA but not by cysteine, aspartate, or serine protease inhibitors. Both membrane fractions also contain ADAM 10. ADAM 10 correctly cleaves peptides and a soluble form of precursor TGF-alpha (proTGFecto) at the N-terminal site but not the C-terminal site. However, the kinetics of N-terminal peptide cleavage by ADAM 10 are 90-fold less efficient than TACE. Our findings indicate that while TACE is an efficient proTGF-alpha N-terminal convertase, a different activity, distinguishable from TACE, exists that can process proTGF-alpha at the C-terminal site. A model that accounts for these findings and the requirement for TACE in TGF-alpha shedding is proposed.

Endotoxin induces rapid metalloproteinase-mediated shedding followed by up-regulation of the monocyte hemoglobin scavenger receptor CD163

CD163, a monocyte and macrophage-specific surface glycoprotein, which is increased by interleukin-10 and glucocorticoids, is a scavenger receptor for hemoglobin/haptoglobin complexes. We report a rapid and highly reproducible rise in soluble CD163 in the plasma of human volunteers given intravenous lipopolysaccharide (LPS). We also show that LPS induces shedding of CD163 from the surface of isolated monocytes, identifying shedding from monocytes and macrophages as a likely mechanism for the endotoxemia-associated rise in plasma CD163 in vivo. Studies using the inhibitor TAPI-0 indicate that a metalloproteinase is responsible for LPS-mediated shedding of CD163. Finally, we demonstrate a marked increase in surface CD163 expression on circulating monocytes 24 h following experimental endotoxemia. These findings show that CD163 is rapidly mobilized in response to bacterial endotoxin. As hemoglobin can bind LPS and enhance its toxicity, it will be important to determine how cell surface and soluble CD163 influence inflammatory processes during sepsis.

The tumor necrosis factor-alpha converting enzyme (TACE): a unique metalloproteinase with highly defined substrate selectivity

TNF alpha converting enzyme (TACE) processes precursor TNF alpha between Ala76 and Val77, yielding a correctly processed bioactive 17 kDa protein. Genetic evidence indicates that TACE may also be involved in the shedding of other ectodomains. Here we show that native and recombinant forms of TACE efficiently processed a synthetic substrate corresponding to the TNF alpha cleavage site only. For all other substrates, conversion occurred only at high enzyme concentrations and prolonged reaction times. Often, cleavage under those conditions was accompanied by nonspecific reactions. We also compared TNF alpha cleavage by TACE to cleavage by those members of the matrix metalloproteinase (MMP) family previously implied in TNF alpha release. The specificity constants for TNF alpha cleavage by the MMPs were approximately 100-1000-fold slower relative to TACE. MMP 7 also processed precursor TNF alpha at the correct cleavage site but did so with a 30-fold lower specificity constant relative to TACE. In contrast, MMP 1 processed precursor TNF alpha between Ala74 and Gln75, in addition to between Ala76 and Val77, while MMP 9 cleaved this natural substrate solely between Ala74 and Gln75. Additionally, the MMP substrate Dnp-PChaGC(Me)HK(NMA)-NH(2) was not cleaved at all by TACE, while collagenase (MMP 1), gelatinase (MMP 9), stromelysin 1 (MMP 3), and matrilysin (MMP 7) all processed this substrate efficiently. All of these results indicate that TACE is unique in terms of its specificity requirements for substrate cleavage.

Design of selective and soluble inhibitors of tumor necrosis factor-alpha converting enzyme (TACE)

A program to improve upon the in vitro, in vivo, and physicochemical properties of N-hydroxyformamide TACE inhibitor GW 3333 (1) is described. Using the primary structure of pro-TNF-alpha, along with a homology model of the catalytic domain of TACE based on the X-ray diffraction coordinates of adamalysin, we synthesized N-hydroxyformamide TACE inhibitors containing a P2' arginine side chain. Introduction of nitro and sulfonyl electron-withdrawing groups covalently bound to the P2' guanidine moiety rendered the inhibitors electronically neutral at cellular pH and led to potent inhibition of TNF-alpha release from stimulated macrophages. Inhibitors containing these arginine mimetics were found to have increased solubility in simulated gastric fluid (SGF) relative to 1, allowing for the incorporation of lipophilic P1' side chains which had the effect of retaining potent TACE inhibition, but reducing potency against matrix metalloproteases (MMPs) thus increasing overall selectivity against MMP1, MMP3, and MMP9. Selected compounds showed good to excellent in vivo TNF inhibition when administered via subcutaneous injection. One inhibitor, 28a, with roughly 10x selectivity over MMP1 and MMP3 and high solubility in SGF, was evaluated in the rat zymosan-induced pleuisy model of inflammation and found to inhibit zymosan-stimulated pleural TNF-alpha elevation by 30%.

N-hydroxyformamide peptidomimetics as TACE/matrix metalloprotease inhibitors: oral activity via P1' isobutyl substitution

N-Hydroxyformamide-class metalloprotease inhibitors were designed and synthesized, which have potent broad-spectrum activity versus matrix metalloproteases and TNF-alpha converting enzyme (TACE). Compound 13c possesses good oral and intravenous pharmacokinetics in the rat and dog.

The nature of human craniofacial growth studied with finite element analytical approach

The purpose of this study was to elucidate the nature of human craniofacial growth by means of finite element method (FEM), and to compare the results with the current concept derived from morphometric studies with roentgenographic cephalometry (RCM). Lateral cephalograms were taken of 20 males and 20 females, and traced on acetate paper. On the tracing, the craniofacial complex was divided into seven areas or elements. Growth analysis was executed with FEM for changes in the size and shape of each area during six developmental periods from 4 to 18 years old. The size change in the male group exhibited a peak from 10 to 12 years old for the cranial base and upper facial skeleton, from 8 to 10 years old for the maxillary complex, and from 12 to 14 years old for the mandible. On the other hand, in the females, the size change was almost invariable from 4 to 12 years old and completed suddenly at 12 years old, which was earlier by a few years than in the males. An interesting finding is that changes in the size and shape were the most substantial in the maxillary complex, followed by those in the mandible, and the smallest in the cranial base and upper facial skeleton. It is shown that growth of the cranial base lasted up to 14 years old and the maxillary complex exhibited the greatest growth changes in the size among various anatomic structures. These findings may provide a new concept of human craniofacial growth, somewhat different from the previously established principles by RCM.

Substrate specificity of human collagenase 3 assessed using a phage-displayed peptide library

The substrate specificity of human collagenase 3 (MMP-13), a member of the matrix metalloproteinase family, is investigated using a phage-displayed random hexapeptide library containing 2 x 10(8) independent recombinants. A total of 35 phage clones that express a peptide sequence that can be hydrolyzed by the recombinant catalytic domain of human collagenase 3 are identified. The translated DNA sequence of these clones reveals highly conserved putative P1, P2, P3 and P1', P2', and P3' subsites of the peptide substrates. Kinetic analysis of synthetic peptide substrates made from human collagenase 3 selected phage clones reveals that some of the substrates are highly active and selective. The most active substrate, 2, 4-dinitrophenyl-GPLGMRGL-NH(2) (CP), has a k(cat)/K(m) value of 4.22 x 10(6) m(-)(1) s(-)(1) for hydrolysis by collagenase 3. CP was synthesized as a consensus sequence deduced from the preferred subsites of the aligned 35 phage clones. Peptide substrate CP is 1300-, 11-, and 820-fold selective for human collagenase 3 over the MMPs stromelysin-1, gelatinase B, and collagenase 1, respectively. In addition, cleavage of CP is 37-fold faster than peptide NF derived from the major MMP-processing site in aggrecan. Phage display screening also selected five substrate sequences that share sequence homology with a major MMP cleavage sequence in aggrecan and seven substrate sequences that share sequence homology with the primary collagenase cleavage site of human type II collagen. In addition, putative cleavage sites similar to the consensus sequence are found in human type IV collagen. These findings support previous observations that human collagenase 3 can degrade aggrecan, type II and type IV collagens.

Specific sequence elements are required for the expression of functional tumor necrosis factor-alpha-converting enzyme (TACE)

The tumor necrosis factor-alpha-converting enzyme (TACE) is a membrane-anchored zinc metalloprotease involved in precursor tumor necrosis factor-alpha secretion. We designed a series of constructs containing full-length human TACE and several truncate forms for overexpression in insect cells. Here, we demonstrate that full-length TACE is expressed in insect cells inefficiently: only minor amounts of this enzyme are converted from an inactive precursor to the mature, functional form. Removal of the cytoplasmic and transmembrane domains resulted in the efficient secretion of mature, active TACE. Further removal of the cysteine-rich domain located between the catalytic and transmembrane domains resulted in the secretion of mature catalytic domain in association with the precursor (pro) domain. This complex was inactive and function was only restored after dissociation of the complex by dilution or treatment with 4-aminophenylmercuric acetate. Therefore, the pro domain of TACE is an inhibitor of the catalytic domain, and the cysteine-rich domain appears to play a role in the release of the pro domain. Insect cells failed to secrete a deletion mutant encoding the catalytic domain but lacking the inhibitory pro domain. This truncate was inactive and extensively degraded intracellularly, suggesting that the pro domain is required for the secretion of functional TACE.

Metalloprotease-disintegrin MDC9: intracellular maturation and catalytic activity

Metalloprotease disintegrins are a family of membrane-anchored glycoproteins that are known to function in fertilization, myoblast fusion, neurogenesis, and ectodomain shedding of tumor necrosis factor (TNF)-alpha. Here we report the analysis of the intracellular maturation and catalytic activity of the widely expressed metalloprotease disintegrin MDC9. Our results suggest that the pro-domain of MDC9 is removed by a furin-type pro-protein convertase in the secretory pathway before the protein emerges on the cell surface. The soluble metalloprotease domain of MDC9 cleaves the insulin B-chain, a generic protease substrate, providing the first evidence that MDC9 is catalytically active. Soluble MDC9 appears to have distinct specificities for cleaving candidate substrate peptides compared with the TNF-alpha convertase (TACE/ADAM17). The catalytic activity of MDC9 can be inhibited by hydroxamic acid-type metalloprotease inhibitors in the low nanomolar range, in one case with up to 50-fold selectivity for MDC9 versus TACE. Peptides mimicking the predicted cysteine-switch region of MDC9 or TACE inhibit both enzymes in the low micromolar range, providing experimental evidence for regulation of metalloprotease disintegrins via a cysteine-switch mechanism. Finally, MDC9 is shown to become phosphorylated when cells are treated with the phorbol ester phorbol 12-myristate 13-acetate, a known inducer of protein ectodomain shedding. This work implies that removal of the inhibitory pro-domain of MDC9 by a furin-type pro-protein convertase in the secretory pathway is a prerequisite for protease activity. After pro-domain removal, additional steps, such as protein kinase C-dependent phosphorylation, may be involved in regulating the catalytic activity of MDC9, which is likely to target different substrates than the related TNF-alpha-convertase.

The functional matrix hypothesis revisited. 4. The epigenetic antithesis and the resolving synthesis

In two interrelated articles, the current revision of the functional matrix hypothesis extends to a reconsideration of the relative roles of genomic and of epigenetic processes and mechanisms in the regulation (control, causation) of craniofacial growth and development. The dialectical method was chosen to analyze this matter, because it explicitly provides for the fuller presentation of a genomic thesis, an epigenetic antithesis, and a resolving synthesis. The later two are presented here, where the synthesis suggests that both genomic and epigenetic factors are necessary causes, that neither alone is also a sufficient cause, and that only the two, interacting together, furnish both the necessary and sufficient cause(s) of ontogenesis. This article also provides a comprehensive bibliography that introduces the several new, and still evolving, disciplines that may provide alternative viewpoints capable of resolving this continuing controversy; repetition of the present theoretical bases for the arguments on both sides of these questions seems nonproductive. In their place, it is suggested that the group of disciplines, broadly termed Complexity, would most likely amply repay deeper consideration and application in the study of ontogenesis.

The functional matrix hypothesis revisited. 3. The genomic thesis

Although the initial versions of the functional matrix hypothesis (FMH) theoretically posited the ontogenetic primacy of "function," it is only in recent years that advances in the morphogenetic, engineering, and computer sciences provided an integrated experimental and numerical data base that permitted recent significant revisions of the FMH--revisions that strongly support the primary role of function in craniofacial growth and development. Acknowledging that the currently dominant scientific paradigm suggests that genomic, instead of epigenetic (functional) factors, regulate (cause, control) such growth, an analysis of this continuing controversy was deemed useful. Accordingly the method of dialectical analysis, is employed, stating a thesis, an antithesis, and a resolving synthesis based primarily on an extensive review of the pertinent current literature. This article extensively reviews the genomic hypothesis and offers a critique intended to remove some of the unintentional conceptual obscurantism that has recently come to surround it.

The functional matrix hypothesis revisited. 2. The role of an osseous connected cellular network

Intercellular gap junctions permit bone cells to intercellularly transmit, and subsequently process, periosteal functional matrix information, after its initial intracellular mechanotransduction. In addition, gap junctions, as electrical synapses, underlie the organization of bone tissue as a connected cellular network, and the fact that all bone adaptation processes are multicellular. The structural and operational characteristics of such biologic networks are outlined and their specific bone cell attributes described. Specifically, bone is "tuned" to the precise frequencies of skeletal muscle activity. The inclusion of the concepts and databases that are related to the intracellular and intercellular bone cell mechanisms and processes of mechanotransduction and the organization of bone as a biologic connected cellular network permit revision of the functional matrix hypothesis, which offers an explanatory chain, extending from the epigenetic event of muscle contraction hierarchically downward to the regulation of the bone cell genome.

The functional matrix hypothesis revisited. 1. The role of mechanotransduction

The periodic incorporation of advances in the biomedical, bioengineering, and computer sciences allow the creation of increasingly more comprehensive revisions of the functional matrix hypothesis. Inclusion of two topics, (1) the mechanisms of cellular mechanotransduction, and (2) biologic network theory, permit this latest revision; presented here in two interrelated articles. In this first article, the several possible types of intracellular processes of mechanotransduction are described. These translate the informational content of a periosteal functional matrix stimulus into a skeletal unit (bone) cell signal. The correlation between the strengths of the endogenous electrical fields produced by muscle skeletal muscle activity, and those to which bone cells maximally respond are stressed. Further, a physical chain of macromolecular levers, connecting the extracellular matrix to the bone cell genome is described, suggesting another means of epigenetic regulation of the bone cell genome, including its phenotypic expression.

Cloning of a disintegrin metalloproteinase that processes precursor tumour-necrosis factor-alpha

Tumour-necrosis factor-alpha (TNF-alpha) is a cytokine that contributes to a variety of inflammatory disease states. The protein exists as a membrane-bound precursor of relative molecular mass 26K which can be processed by a TNF-alpha-converting enzyme (TACE), to generate secreted 17K mature TNF-alpha. We have purified TACE and cloned its complementary DNA. TACE is a membrane-bound disintegrin metalloproteinase. Structural comparisons with other disintegrin-containing enzymes indicate that TACE is unique, with noteable sequence identity to MADM, an enzyme implicated in myelin degradation, and to KUZ, a Drosophila homologue of MADM important for neuronal development. The expression of recombinant TACE (rTACE) results in the production of functional enzyme that correctly processes precursor TNF-alpha to the mature form. The rTACE provides a readily available source of enzyme to help in the search for new anti-inflammatory agents that target the final processing stage of TNF-alpha production.

Structural features and biochemical properties of TNF-alpha converting enzyme (TACE)

Tumor necrosis factor-alpha is a potent cytokine, secreted primarily by activated monocytes and macrophages, that possesses a broad range of immunomodulating properties. Involvement of this cytokine has been validated in disease states such as arthritis and Crohn's disease and implicated in diverse neuroimmunological pathologies such as multiple sclerosis, Alzheimers and stroke. TNF-alpha is initially synthesized as a 26 kDa precursor molecule that is subsequently processed to the mature form by cleavage of the Ala76 Val77 bond. The 17 kDa carboxy-terminal protein is then secreted to function in a paracrine manner. The enzyme that processes precursor TNF-alpha has previously been identified as a microsomal metalloprotease called TNF-alpha converting enzyme (TACE). We have now purified and partially cloned the enzyme. TACE represents a novel target for therapeutic intervention in a variety of inflammatory and neuroimmunological diseases.