Functional characterization of a unique liver gene promoter

Human phenylalanine hydroxylase (PAH) is specifically expressed in the liver to convert L-phenylalanine to L-tyrosine. Deficiency of the PAH enzyme causes classic phenylketonuria, a common genetic disorder. The human PAH gene has a TATA-less promoter with multiple transcriptional initiation sites. A 9-kilobase DNA fragment 5'-flanking to the human PAH gene is sufficient to confer tissue- and developmental stage-specific expression of a reporter gene in transgenic mice. Deletion studies showed that the -121-base pair proximal promoter still retained a significant level of activity in hepatic cells. At least two protein binding sites, PAH-A and PAH-B, were identified in the proximal region of the human PAH promoter using rat liver nuclear extract. The PAH-A site covers a unique palindromic sequence, and the PAH-B site contains CCCTCCC repeats. Both elements are ubiquitous and essential regulatory elements for transcriptional activity. Nuclear protein factors that bind to the PAH-A and -B sites are detected in different cell types and are distinct from previously characterized transcription factors. No tissue-specific transcription factor binding sites have been detected within the proximal promoter region of the human PAH gene. These results suggest that the PAH gene promoter has a unique organization of regulatory elements for its tissue-specific expression in comparison with other liver gene promoters.

Origins of hyperphenylalaninemia in Israel

Mutations and polymorphisms at the phenylalanine hydroxylase (PAH) gene were used to study the genetic diversity of the Jewish and Palestinian Arab populations in Israel. PAH mutations are responsible for a large variety of hyperphenylalaninemias (HPAs), ranging from the autosomal recessive disease phenylketonuria to various degrees of nonclinical HPA. Seventy-two Jewish and 36 Palestinian Arab families with various HPAs, containing 115 affected genotypes, were studied by haplotype analysis, screening for previously known PAH lesions and a search for novel mutations. Forty-one PAH haplotypes were observed in this sample. Four mutations previously identified in Europe (IVS10nt546, R261Q, R408W and R158Q) were found, and were associated with the same haplotypes as in Europe, indicating possible gene flow from European populations into the Jewish and Palestinian gene pools. Of particular interest is a PAH allele with the IVS10nt546 mutation and haplotype 6, that might have originated in Italy more than 3,000 years ago and spread during the expansion of the Roman Empire. These results, together with previous identification of three PAH mutations unique to Palestinian Arabs [IVSnt2, Edel(197-205) and R270S], indicate that the relatively high genetic diversity of the Jewish and Palestinian populations reflects, in addition to genetic events unique to these communities, some gene flow from neighboring and conquering populations.

Hepatic gene therapy: efficient gene delivery and expression in primary hepatocytes utilizing a conjugated adenovirus-DNA complex

Receptor-mediated endocytosis is an effective method for gene delivery into target cells. We have previously shown that DNA molecules complexed with asialoglycoprotein can be efficiently endocytosed by primary hepatocytes and the internalized DNA can be released from endosomes by the use of a replication-defective adenovirus. Because the DNA and virus enter target cells independently, activity enhancement requires high concentrations of adenoviral particles. In this study, adenoviral particles were chemically conjugated to poly(L-lysine) and bound ionically to DNA molecules. Quantitative delivery to primary hepatocytes was achieved with significantly reduced viral titer when the asialoorosomucoid-poly(L-lysine) conjugate was included in the complex. The conjugated adenovirus was used to deliver a DNA vector containing canine factor IX to mouse hepatocytes, resulting in the expression of significant concentrations of canine factor IX in the culture medium. The results suggest that receptor-mediated endocytosis coupled with an efficient endosomal lysis vector should permit the application of targeted and efficient gene delivery into the liver for gene therapy of hepatic deficiencies.

Mathematical modeling of ligaments and tendons

Ligaments and tendons serve a variety of important functions in maintaining the structure of the human body. Although abundant literature exists describing experimental investigations of these tissues, mathematical modeling of ligaments and tendons also contributes significantly to understanding their behavior. This paper presents a survey of developments in mathematical modeling of ligaments and tendons over the past 20 years. Mathematical descriptions of ligaments and tendons are identified as either elastic or viscoelastic, and are discussed in chronological order. Elastic models assume that ligaments and tendons do not display time dependent behavior and thus, they focus on describing the nonlinear aspects of their mechanical response. On the other hand, viscoelastic models incorporate time dependent effects into their mathematical description. In particular, two viscoelastic models are discussed in detail; quasi-linear viscoelasticity (QLV), which has been widely used in the past 20 years, and the recently proposed single integral finite strain (SIFS) model.

Biology and biomechanics of the anterior cruciate ligament

With detailed information concerning the role of the anterior cruciate ligament in the overall kinematic response of the knee during external loading, current clinical management of the orthopedic injuries to this joint may be improved upon and refined. Among the largest challenges to be met will be elucidation of the effects of various levels and types of muscular stabilization concurrent with a precise determination of the roles of passive knee restraints.

Quadriceps/anterior cruciate graft interaction. An in vitro study of joint kinematics and anterior cruciate ligament graft tension

The Oxford Rig, a device that simulates active knee extension during stance, was used to study the effects of quadriceps force on AP tibial displacement and axial tibial rotation in vitro. Human anatomic specimen knees were tested with the anterior cruciate ligament (ACL) intact, sectioned, and reconstructed. Patellar tendon grafts used in the ACL-reconstructed state were attached distally to a load cell, allowing direct measurement of graft tension. Both ACL status and quadriceps force had significant effects on anterior tibial displacement, limits of AP displacement, axial tibial rotation, and graft tension, as shown by analysis of variance. Anterior cruciate ligament sectioning led to anterior tibial displacement in the absence of quadriceps force, whereas ACL reconstruction led to posterior tibial displacement. In the ACL-intact, quadriceps-stabilized state, anterior displacement of the tibia was observed between 95 degrees flexion and full extension, with a maximum displacement (3.5 +/- 0.2 mm) between 30 degrees and 45 degrees flexion. After ACL sectioning, anterior tibial displacement resulting from quadriceps force was accentuated relative to the intact state by as much as 4.5 mm +/- 0.9 mm at 20 degrees and 25 degrees flexion. Anterior tibial displacement in the ACL-intact and reconstructed specimens was similar when quadriceps force was present. In the quadriceps-stabilized state, graft tension increased between 5 degrees and 80 degrees flexion. The maximum increase in graft tension due to quadriceps force was at 35 degrees flexion.

Determination of the in situ loads on the human anterior cruciate ligament

A noncontact, kinematic method was used to determine the lengths and in situ loads borne by portions of the human anterior cruciate ligament (ACL) by the combination of kinematic data from the intact knee and load-length curves of the isolated ACL. Specimens from knees of cadavers of young people were tested in passive flexion and extension as well as with 100 N of anterior tibial drawer at 0, 30, 45, and 90 degrees of flexion. The results showed that the in situ load on the whole ACL (as much as 129 N) can exceed the magnitude of the applied anterior tibial drawer. The load distribution within the ligament changes with flexion of the knee. The anterior and posterior portions share the anterior drawer force equally toward full extension. However, at flexion > 45 degrees, the anterior portion supports 90-95% of the load. This information is important for the determination of the function of the entire ACL and of its subportions in response to external loading of the intact knee. In particular, the preferential loading found for one of the portions of the ACL demonstrates that successful operative reconstruction of this ligament may not be achieved simply by reproduction of its gross anatomy; consideration of the role of the ligament in the overall kinematics of the knee is necessary.

Hepatic gene therapy: efficient retroviral-mediated gene transfer into rat hepatocytes in vivo

The rat is an excellent model for gene therapy because there are many rat models for human diseases. We have developed a simple and efficient method to deliver genes to the rat liver using recombinant retroviral vectors. A 70% partial hepatectomy followed by retroviral infusion into the portal vein results in 10-15% hepatocyte transduction in vivo. This is 10 times more efficient than in the mouse due partially to the observation that the rat livers have much more synchronous hepatocyte replication after partial hepatectomy. Using a recombinant retroviral vector containing the human alpha 1-antitrypsin cDNA, persistent expression of the human protein in recipient rat plasma was observed for at least six months and at a level that is 10 times greater than the mouse. Thus, rats can serve as an excellent model for gene therapy of metabolic disorders secondary to hepatic deficiencies.

The use of robotics technology to study human joint kinematics: a new methodology

Robotics technologies have been modified to control and measure both the force and position of synovial joints for the study of joint kinematics. One such system was developed to perform kinematic testing of a human joint. A 6-axis articulated robotic manipulator with 6 degrees of freedom (DOF) of motion was designed and constructed; a mathematical description for joint force and position was devised; and hardware and software to control forces applied to the joint, as well as position of the joint, were developed. The new methodology was utilized to simulate physiological loading conditions and to perform an anterior-posterior (A-P) translation test on a human cadaveric knee. Testing showed that this new system can stimulate complex loading conditions and also measure the resulting joint kinematics.

Assessment of recombinant adenoviral vectors for hepatic gene therapy

Recombinant adenoviral vectors have recently been used to transfer genes into a number of different cell types in vitro and in vivo. A recombinant adenoviral vector bearing the Escherichia coli beta-galactosidase (beta-gal) gene was used to quantitate the frequency of hepatocyte transduction in the mouse after direct viral infusion into the portal vein. When 10(10) adenoviral particles were infused, over 95% of the hepatocytes were transduced in vivo as determined by x-gal staining. The transduction protocol is relatively safe in that there is no detectable helper virus production in transduced animals and that very few extrahepatic cells are transduced by this method. There is also no evidence of significant liver pathology unless substantially greater quantities of virus are used. However, the transduced hepatocytes do not appear to persist in vivo because the percentage of hepatocytes expressing beta-gal declined over time. Four months after the procedure, 0.5-10% of the hepatocytes contain detectable beta-gal activity in vivo. The change in beta-gal-positive cells correlates with decreasing amounts of adenoviral DNA. Thus, current recombinant adenoviral vectors may have clinical applications in gene therapy for acute hepatic disorders.

In vitro biomechanical analysis of suture methods for flexor tendon repair

This study was designed to compare five different suture methods that are used clinically for tendon repair. The flexor digitorum profundus tendons from the digits of adult mongrel dogs and adult human cadavers were used as models. The tendons in zone II of the hand, defined as the region from the distal palmar crease to the insertion of the flexor digitorum superficialis tendon at the middle phalanx, were transected and then were repaired by one of the suture methods developed by Kessler, Tsuge, Tajima, Savage, or Lee. The gliding function and tensile properties of the repaired tendons were evaluated biomechanically at time zero. The Tajima and Savage methods produced better gliding function than the other techniques. In the canine specimens that had been repaired by one of these two methods, the rotation of the distal interphalangeal joint was more than 60% of the rotation of the canine control specimens; only the Savage technique produced a rotation 124% that of the human control specimens. After the Tajima repair, the rotation of the proximal interphalangeal joint was 113% that of the canine control specimens and 157% that of the human controls. In the canine specimens that had had the Tajima or Savage repair, excursion of the tendon was greater than 55% that of the controls. The tendons repaired by the Savage method tolerated a significantly higher ultimate load to failure (14 and 25% that of the canine and human control specimens, respectively) than the other methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Autogenous flexor-tendon grafts. A biomechanical and morphological study in dogs

Intrasynovial and extrasynovial donor autogenous flexor-tendon grafts were placed in the synovial sheaths of the medial and lateral digits of the forepaw in twenty dogs (forty tendons). Postoperatively, the dogs were managed with early, controlled, passive mobilization. Histological and ultrastructural evaluations were carried out at ten days, three weeks, and six weeks, and biomechanical analyses were performed at three and six weeks. The intrasynovial and extrasynovial tendon grafts showed different healing processes histologically. The extrasynovial tendon grafts healed with early ingrowth of peripheral adhesions, which appeared to become larger and more dense over time. These grafts exhibited decreased cellularity and early neovascularization at ten days, and there was evidence of progressive revascularization and cellular repopulation at three and six weeks. In contrast, the intrasynovial tendon grafts demonstrated minimum adhesions, and both cellularity and collagen organization were normal at each time-interval. The intrasynovial grafts had significantly more angular rotation at the proximal interphalangeal joint at three and six weeks than did the extrasynovial grafts (p < 0.05).

A single polymorphic STR system in the human phenylalanine hydroxylase gene permits rapid prenatal diagnosis and carrier screening for phenylketonuria

Phenylketonuria (PKU) is an autosomal recessive genetic disorder caused by phenylalanine hydroxylase (PAH) deficiency. Individuals afflicted with PKU develop irreversible mental retardation that can be largely prevented by the administration of a low-phenylalanine diet. A number of restriction fragment-length polymorphisms (RFLPs) have been identified in the PAH gene. Combinations of RFLPs constitute unique haplotypes that can be used to identify mutant PAH chromosomes for prenatal diagnostic purpose in PKU families. Unfortunately, the utility of haplotype analysis is limited in populations with a single predominant haplotype. We have identified a novel short tandem repeat (STR) within the PAH gene that has an average level of heterozygosity of about 75% in Orientals and about 80% in European Caucasian populations. This single marker is as informative as haplotype analysis in Europeans and nearly twice as informative as haplotype analysis in Orientals. Although there is statistically significant disequilibrium between STR alleles and RFLP-based haplotypes, there is a relatively low degree of disequilibrium between STR alleles and certain RFLP sites. Nevertheless, the combined use of the STR and RFLP haplotype systems increases the informativity of linkage-based tests for prenatal diagnosis and carrier screening in PKU families.

Phenylketonuria: variable phenotypic outcomes of the R261Q mutation and maternal PKU in the offspring of a healthy homozygote

Phenylketonuria (PKU) and benign hyperphenylalaninaemia (HPA) result from a variety of mutations in the gene for the hepatic enzyme phenylalanine hydroxylase. PKU has been found in the Israeli population in two variants, classical and atypical. The two are clinically indistinguishable and require treatment with low phenylalanine diet to prevent mental retardation, but show differences in serum phenylalanine levels and in tolerance to this amino acid. Maternal PKU is a syndrome of congenital anomalies and mental retardation that appears in offspring of PKU mothers as a result of fetal exposure to the high phenylalanine level in the maternal blood. We studied a family in which two children with severe, classical PKU and their unaffected brother showed mild signs of maternal PKU. Their mother had no clinical signs of PKU, but the phenylalanine concentration in her serum reached a level that usually characterises PKU patients. This woman represents a rare phenotype, benign atypical PKU. Such 'hidden' PKU in women may lead to maternal PKU in the offspring, similar to overt PKU. Special attention should therefore be paid to women having children with any of the clinical hallmarks of maternal PKU, and to children born to women known to have benign HPA. The mother was also found to be homozygous for a missense mutation at the phenylalanine hydroxylase locus, R261Q, which does not abolish enzymatic activity completely. In two other families, homozygosity for this mutation resulted in atypical PKU in four children. This observation suggests that mutations that do not completely destroy phenylalanine hydroxylase activity may exhibit variable phenotypic expression which is unpredictable. Compound heterozygosity for R261Q and other mutations led in other patients either to classical PKU or to mild benign HPA.

On the viscoelastic properties of the anteromedial bundle of the anterior cruciate ligament

The nonlinear viscoelastic properties of the anteromedial (AM) bundle of porcine anterior cruciate ligament (ACL) were characterized by using a new analytical approach based on the quasi-linear viscoelastic theory. Stress relaxation and cyclic tensile tests were performed. Using the solution derived from this approach, we curve-fitted data from the stress relaxation test to determine the viscoelastic coefficients for the ligament bundles. The coefficients were verified by comparison of the predicted and the experimental results from the cyclic tensile test. The ACL AM bundle exhibited significant stress relaxation with time; a reduction of more than 50% of the peak value occurred during the 2-h experiment. Also, the reduced relaxation function for the ACL AM bundle was not a linear function of logarithmic time, as is commonly assumed for many soft tissues. The new approach, which takes into account the finite strain rate of the ramp function used in the stress relaxation test, provides an accurate description of this nonlinear stress relaxation behavior.

Hepatic gene therapy: adenovirus enhancement of receptor-mediated gene delivery and expression in primary hepatocytes

We have combined a receptor-mediated DNA delivery system with the endosomal lysis ability of adenovirus and shown that DNA can be delivered into primary hepatocytes, resulting in a high level of gene expression. When asialoorosomucoid conjugated with poly(L-lysine) was used to deliver the Escherichia coli beta-galactosidase gene into primary hepatocytes through binding with the hepatic asialoglycoprotein receptor, only a low level of beta-galactosidase was detectable, with less than 0.1% of the hepatocytes being transfected. This level of activity can be greatly enhanced by the cointernalization of the DNA.protein complex with a replication-defective adenovirus, resulting in 100% of the hepatocytes staining blue with 5-bromo-4-chloro-3-indolyl beta-D-galactoside. Quantitative analysis of beta-galactosidase expression also showed a 1000-fold enhancement of activity. To test the applicability of this DNA delivery system for the correction of phenylketonuria, a metabolic disorder that causes severe mental retardation in children, we have delivered the human phenylalanine hydroxylase (PAH) gene to hepatocytes derived from a PAH-deficient mouse strain and demonstrated complete reconstitution of enzymatic activity. This method shows great promise for efficient gene delivery to the liver for correction of hepatic disorders.

Hamstrings--an anterior cruciate ligament protagonist. An in vitro study

A cadaveric model that incorporated quadriceps and hamstrings muscle loads was developed to simulate the squat exercise. The addition of hamstrings load affected knee kinematics in two ways. First, anterior tibial translation during flexion ("femoral roll-back") was significantly reduced (P = 0.003) and second, internal tibial rotation during flexion was reduced (P = 0.008). However, quadriceps force was unaffected by the addition of hamstrings load. Thus, it seems likely that hamstrings muscle activity that has been observed in vivo during a squat probably functions synergistically with the anterior cruciate ligament to provide anterior knee stability. After the ACL was sectioned, anterior tibial translation was significantly increased during the squat (P = 0.04). The anterior cruciate ligament was then reconstructed using a graft instrumented with a load cell. During passive motion, maximal graft tension was at full extension. During simulated squat exercise, the addition of hamstrings caused a significant decrease in graft load (P = 0.006). During the squat, maximal graft tension was at full extension, and was equal to the graft tension at full passive extension. Thus, the squat exercise may be useful in the early stages of anterior cruciate ligament rehabilitation.

Methods for electrophoretic karyotyping of filamentous fungi in the genus Trichoderma

Methods for electrophoretic karyotyping of filamentous fungi in the genus Trichoderma were developed. These techniques permitted the separation and visualization of intact chromosomes from viable protoplasts. Three strains were analyzed: Trichoderma harzianum strains T12 his-2 and T95 lys-1, and a prototrophic strain (1295-22) produced by protoplast fusion of T12 his-2 with T95 lys-1. Four chromosome bands ranging in size from 2.2 Mb (megabase pairs) to 5.4 Mb were visualized with strain T95 lys-1, whereas two chromosome bands were visualized for strains T12 his-2 and 1295-22. The largest chromosome of all three strains seems to be similar in size and has been estimated to be approximately 5.4 Mb. All remaining chromosomes observed were dissimilar in size. Methods for protoplast isolation, protoplast embedding, and electrophoretic conditions useful for separation of intact chromosomes ranging in size from 50 kb (kilobase pairs) up to approximately 6.0 Mb utilizing transverse alternating field electrophoresis (TAFE) will be discussed. The techniques provided should be applicable to a variety of lower eukaryotic organisms when using the TAFE system.

A missense mutation, S349P, completely inactivates phenylalanine hydroxylase in north African Jews with phenylketonuria

The majority of hyperphenylalaninemias (HPAs) result from mutations at the gene for phenylalanine hydroxylase (PAH). The broad phenotypic variability of these conditions, ranging from phenylketonuria (PKU) to mild benign HPA, is underlain by a wide spectrum of mutations giving rise to various genotypic combinations. Mutant PAH alleles, labeled by specific polymorphic haplotypes and mutations, are becoming useful markers in human population genetics. We report here a mutant PAH allele found in Jews from Morocco and Tunisia, marked by haplotype 4 and a missense mutation, TCASer-->CCAPro, at codon 349 in exon 10 of the gene. In vitro expression of the mutation showed normal levels of mRNA with virtually no enzymatic activity or protein immunoreactivity, pointing to a highly unstable protein. A homozygote for this mutation showed the most severe ("classical") type of PKU, while compound heterozygotes showed two other types of HPA--"atypical" PKU and "high benign" HPA--illustrating the interplay between different mutations that gives rise to various HPAs.

Relation between genotype and phenotype in Swedish phenylketonuria and hyperphenylalaninemia patients

Phenylketonuria (PKU) and hyperphenylalaninemia (HPA) are caused mostly by an inherited (autosomal recessive) deficiency in hepatic phenylalanine hydroxylase (PAH) activity. More than 50 PAH mutations have ben reported. The goal of the present study was to examine the molecular basis for the clinical heterogeneity of Swedish PKU and HPA patients. Mutations were identified through allele-specific oligonucleotide hybridization or DNA sequencing on 128 of the 176 mutant alleles (73%). Three mutations (R408W, Y414C and IVS12) together accounted for 56% of all mutant alleles and ten relatively infrequent mutations were found on another 17% of all mutant alleles. Patients from 50 of the 88 families (57%) had identified mutations in both PAH genes and allowed use to compare the clinical effects of different combinations of PAH mutations. The in vitro activity of all of these mutations, including the newly identified G272X and delta L364, have been tested in a eukaryotic expression system. There was a strong relationship between the average in vitro PAH activity of the two mutant enzymes and both the phenylalanine tolerance and the neonatal pretreatment serum phenylalanine concentration. This confirms previous observations in Danish and German PKU patients that disease phenotype is a consequence of the nature of the mutations at the PAH locus and not significantly influenced by other loci. The sample population in the previous study did not, however, include mild HPA patients, and the observed correlation is thus restricted to severe and moderate mutant alleles. Since a comparatively high proportion of the Swedish patients were mildly affected, we have provided additional evidence that this correlation is valid throughout a continuous spectrum of clinical varieties.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanical properties of skeletally mature rabbit anterior cruciate ligament and patellar tendon over a range of strain rates

The effect of strain rate on the mechanical properties of the rabbit anterior cruciate ligament (ACL) and patellar tendon (PT) was evaluated. The medial portion of the ACL was loaded to tensile failure at rates of 0.003, 0.3, and 113 mm/s, and the middle third of the PT was loaded at rates of 0.008, 0.8, and 113 mm/s. The load was recorded with a high-speed measurement plotting system, and each test was videotaped for strain analysis. The nonlinear portion of the stress-strain curve was curve-fit to an exponential function having two nonlinear constants, representing the initial modulus and rate of change of the modulus. The modulus of the rabbit PT was found to be 89% higher than that of the ACL. The initial modulus and rate of change of the modulus also were greater for the PT than for the ACL. The modulus of the PT was shown to be more sensitive to strain rate than that of the ACL; a 94% increase was observed for the PT, and a 31% increase was observed for the ACL. There was no effect of strain rate on the mode of failure of either the ACL or the PT; all but three of the specimens failed at the insertion site.

Three polymorphisms but no disease-causing mutations in the proximal part of the promoter of the phenylalanine hydroxylase gene

The proximal promoter region of the human phenylalanine hydroxylase (PAH) gene was analyzed for the presence of mutations in 122 European phenylketonuria (PKU) and hyperphenylalaninemia patients having altogether 187 uncharacterized mutant PAH alleles. This promoter fragment, which contained the most 5' transcription start site and about 300 bp upstream, was sequenced directly from polymerase-chain-reaction-amplified genomic DNA. No disease-causing mutations but three neutral nucleotide substitutions were found. A -195 T-to-C transition was present on 1% of 441 normal and 0.3% of 653 mutant chromosomes. All chromosomes that carried this transition and to which a restriction fragment length polymorphism (RFLP) haplotype had been assigned were of haplotype 1. A -71 G-to-A change and a +7 C-to-T change were always observed together and were found on 1% of 425 normal and 4% of 681 mutant chromosomes. In addition, these two transitions were found in seven heterozygote samples where the phase could not be established due to incomplete family samples. In individuals where RFLP haplotypes were known and phase could be established, these linked substitutions were associated with RFLP haplotype 9. The relatively high frequency (10-20%) of these two polymorphisms on PKU chromosomes from Great Britain, Ireland and France may reflect a relative concentration of haplotype 9 alleles among PKU chromosomes from these countries compared to the rest of Europe. The absence of disease-causing mutations within a region of the PAH gene that possesses basal promoter activity suggests that transcriptional mutations are not likely causes of PKU in Caucasian populations.

Morphologic and biomechanical comparison of tendons used as free grafts

The palmaris longus (n = 10), plantaris (n = 11), and extensor digitorum longus (n = 10) tendons were harvested from cadaver limbs for morphologic and biomechanical comparisons. Eleven flexor digitorum profundus tendons from the index finger were also harvested for comparison of biomechanical properties of the free graft tendons with those of a typical digital flexor. Maximal tendon length, cross-sectional area, volume, stiffness, and modulus of elasticity were determined by measurement, laser micrometry, and tensile testing. The plantaris and extensor digitorum longus yielded the longest grafts, 334 and 325 mm, respectively, compared with the palmaris longus, which yielded only 161 mm of length. Cross-sectional areas were as follows: palmaris longus, 3.1 mm2; plantaris, 1.4 mm2; extensor digitorum longus, 3.3 mm2; and flexor digitorum profundus, 10.6 mm2. Mean volumes were as follows: palmaris longus, 529 mm3; plantaris, 557 mm3; and extensor digitorum longus, 1006 mm3. The palmaris longus and the extensor digitorum longus showed greater stiffness, 42.0 and 47.8 N/mm, respectively, than the plantaris, which had a stiffness of 25.5 N/mm. However, the flexor digitorum profundus showed significantly greater stiffness than all of the graft tendons. The modulus of elasticity ranged from 1161.6 to 1673.0 MPa, with no significant difference between tendons tested. The findings in this study provide data that may be useful in the selection of a specific donor for free tendon grafting.

Hepatic gene therapy: persistent expression of human alpha 1-antitrypsin in mice after direct gene delivery in vivo

The liver represents an excellent target organ for gene therapy. The current strategy for hepatic gene therapy involves the isolation of primary hepatocytes from a resected liver lobe, transduction of therapeutic genes in vitro followed by autologous hepatocellular transplantation. This ex vivo approach is a rather complex procedure in its entirety; thus, a simple method for direct gene delivery into hepatocytes in vivo has been developed. The procedure involves partial hepatectomy followed by the portal vein infusion of recombinant retroviral vectors. Histological analysis of hepatocytes after in vivo delivery of a recombinant retrovirus bearing the E. coli beta-galactosidase gene showed that 1-2% of the parenchymal cells were transduced. Direct hepatic transfer of human alpha 1-antitrypsin cDNA under the transcriptional direction of the albumin promoter-enhancer led to constitutive expression of the human protein in the sera of recipients at concentrations of 30-1,400 ng/ml for at least 6 months. The experimental animals showed no signs of illness and histologic analysis of the liver revealed no evidence of pathologic abnormalities. The results suggest that the in vivo approach is an attractive alternative for hepatic gene therapy.

Structural characterization of the 5' regions of the human phenylalanine hydroxylase gene

Human phenylalanine hydroxylase (PAH) is expressed in a liver-specific manner and catalyzes the enzymatic conversion of phenylalanine to tyrosine. Genetic deficiency of PAH results in the autosomal-recessive disorder phenylketonuria (PKU). Through the application of genomic and cDNA cloning, primer extension studies, SI mapping experiments, and PCR methodologies, the transcription initiation (CAP) site has been identified and the 5'-flanking region determined. The most upstream CAP site for the human hepatic PAH gene transcript is located 154 nucleotides upstream of the first translation codon. The genomic and cDNA sequences analyzed demonstrated that the previously reported cDNA sequence, phPAH247 [Kwok et al. (1985) Biochemistry 24, 556-561], contained a 164-nucleotide cloning artifact at its 5'-end. The 319 base pair region immediately upstream of the CAP site is characterized by the lack of a proximal TATA box and the presence of sequences similar to GC boxes, CACCC boxes, CCAAT boxes, activator protein 2 (Ap-2) sites, partial glucocorticoid response elements (GREs), and partial cyclic AMP response elements (CREs). This suggests that the human PAH gene has a TATA-less promoter regulated by multiple transcription factors.

Associations between mutations and a VNTR in the human phenylalanine hydroxylase gene

The HindIII RFLP in the human phenylalanine hydroxylase (PAH) gene is caused by the presence of an AT-rich (70%) minisatellite region. This region contains various multiple of 30-bp tandem repeats and is located 3 kb downstream of the final exon of the gene. PCR-mediated amplification of this region from haplotyped PAH chromosomes indicates that the previously reported 4.0-kb HindIII allele contains three of these repeats, while the 4.4-kb HindIII allele contains 12 of these repeats. The 4.2-kb HindIII fragment can contain six, seven, eight, or nine copies of this repeat. These variations permit more detailed analysis of mutant haplotypes 1, 5, 6, and, possibly, others. Kindred analysis in phenylketonuria families demonstrates Mendelian segregation of these VNTR alleles, as well as associations between these alleles and certain PAH mutations. The R261Q mutation, associated with haplotype 1, is associated almost exclusively with an allele containing eight repeats; the R408W mutation, when occurring on a haplotype 1 background, may also be associated with the eight-repeat VNTR allele. Other PAH mutations associated with haplotype 1, R252W and P281L, do not appear to segregate with specific VNTR alleles. The IVS-10 mutation, when associated with haplotype 6, is associated exclusively with an allele containing seven repeats. The combined use of this VNTR system and the existing RFLP haplotype system will increase the performance of prenatal diagnostic tests based on haplotype analysis. In addition, this VNTR may prove useful in studies concerning the origins and distributions of PAH mutations in different human populations.

Molecular biology and genetics of alpha 1-antitrypsin deficiency

The use of advanced recombinant DNA technology has provided an improved understanding of the human AAT deficiency phenotype by providing the amino acid sequence of several variant proteins and by allowing for the production of various cell and animal models to study the molecular and biochemical components of the retention, degradation, and accumulation of these variants in the hepatic ER. Human AAT deficiency will continue to serve as an excellent model for enhancing our current understanding of mechanisms utilized in regulating protein "traffic" in the ER and in elucidating the pathophysiologic components of AAT-related liver disease.

Biomechanics of the human anterior cruciate ligament. Muscle stabilization and ACL reconstruction

Several topics of debate surround the surgical reconstruction of the anterior cruciate ligament (ACL), including graft selection, reconstructive technique, and postoperative rehabilitation. The tensile properties of the human ACL and the role of this ligament in the normal kinematics of the knee have been addressed in the first part of this two-part review. This portion of the review will focus on the effects of reconstruction technique, initial graft tension, and muscular stabilization on knee kinematics.

Tissue- and development-specific expression of the human phenylalanine hydroxylase/chloramphenicol acetyltransferase fusion gene in transgenic mice

Human phenylalanine hydroxylase (PAH) catalyzes the conversion of L-phenylalanine to L-tyrosine. Deficiency of this enzyme results in phenylketonuria, a common genetic disorder of amino acid metabolism that causes severe mental retardation. In primates, PAH is expressed specifically in the liver, while in rodents PAH activity is also present in kidney, although at a much lower level. A 9-kilobase genomic DNA fragment at the 5' end of the hPAH gene (hPAH) was fused to the bacterial chloramphenicol acetyltransferase (CAT) gene. The hPAH/CAT minigene was used to generate multiple transgenic mouse lines. In all expressing lines, CAT activity was detected predominantly in the liver and at much lower levels in the kidney. By immunohistochemical staining, CAT expression was localized to hepatocytes and renal epithelial cells, both of which also express the endogenous mouse PAH enzyme. Furthermore, both the transgene and the endogenous mouse PAH were activated at about the same stage of embryonic development in the mouse liver. These results suggest that the 9-kilobase DNA fragment flanking the 5' end of the human PAH gene contains all the necessary cis-acting elements to direct tissue- and developmental-specific expression in vivo.

Healing of the medial collateral ligament following a triad injury: a biomechanical and histological study of the knee in rabbits

The effect of a partial medial meniscectomy and anterior cruciate ligament (ACL) transection on medial collateral ligament (MCL) healing was studied in skeletally mature rabbits. Two groups of animals, group I (isolated MCL rupture) and group II (MCL rupture with ACL transection and partial medial meniscectomy), were examined. At 6 and 12 weeks postoperatively, histological examination of the healing MCL and biomechanical evaluation of the varus-valgus (V-V) knee rotation and tensile properties of the femur-MCL-tibia complex (FMTC) were performed. Group II animals experienced substantial joint degeneration by 6 weeks. Progressive osteophyte formation was observed adjacent to the MCL insertions along with proximal migration of the MCL tibial insertion between 6 and 12 weeks. Histologic examination of the healing MCL substance from both groups showed disorganized collagen, inflammation, and fibroblast proliferation that decreased over time. For group II knees, the V-V knee rotation was found to be significantly elevated (4.7 to 5.2 times the contralateral control), and did not decrease with time. In contrast, the V-V knee rotations of the group I specimens were 1.8 times greater than control immediately following injury, and approached control values by 12 weeks. Tensile testing of the FMTCs revealed that the ultimate load increased with time for both groups, but group I had significantly higher values than group II. The linear stiffness in group I was not different than that group II and did not increase with time. For the mechanical (material) properties of the healed MCL substance, the modulus of the healing tissue for group II was only 40% that of group I. The structural properties of the FMTC and the mechanical properties of the MCL substance from both groups at 6 and 12 weeks were significantly different from the contralateral controls. We further demonstrated that immediately after ACL reconstruction, the V-V rotation of group II knees could be restored to group I levels. Recent clinical studies of MCL healing following isolated complete ligament tears have suggested that nonoperative management without immobilization leads to excellent treatment outcome. However, in more severe injuries involving additional tissues, poor quality of the healed ligament tissue and articular degeneration are observed. Our results demonstrate the deleterious effects of an untreated triad injury on the healing of the MCL substance and its insertions. Examination of the MCL substance suggests that a much larger healing mass is formed following a triad injury, which partially compensates for inferior ligament mechanical properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of three novel missense PKU mutations among Chinese

Three novel missense mutations have been identified in the phenylalanine hydroxylase (PAH) genes of Chinese individuals afflicted with various degrees of phenylketonuria (PKU). A T-to-C transition was observed in exon 5 of the gene, resulting in the substitution of Phe161 by Ser161. Two substitutions, G-to-T and T-to-G, were observed in exon 7, resulting in the substitution of Gly247 by Val247 and Leu255 by Val255, respectively. Expression analysis demonstrated that these mutant proteins produced between 0 and 15% of normal PAH enzyme activity. Population screening of a Chinese sample population indicates that these mutations are quite rare, together accounting for only about 4% of all PKU alleles among the Chinese. The P161S and G247V mutations were each present on a single PAH RFLP haplotype 4 chromosome in patients form Northern China, while the L255V mutation was present on chromosomes of both haplotypes 18 and 21 in patients from Southern China. These results suggest that the remaining 30% of uncharacterized PKU alleles in the Chinese population may bear a large number of relatively rare PAH mutations.

Biomechanics of the human anterior cruciate ligament. ACL structure and role in knee motion

Surgical reconstruction of the anterior cruciate ligament (ACL) to restore knee stability has introduced many subjects of debate, including graft selection, reconstructive technique, and postoperative rehabilitation. In the first part of this two-part review, the tensile properties of the human ACL and the role of the ACL in knee kinematics are discussed. Reconstructive techniques for ACL replacement with regard to the biomechanics of the ACL in normal and ACL-deficient knees will be addressed in Part II.

Molecular characterization of two galactosemia mutations and one polymorphism: implications for structure-function analysis of human galactose-1-phosphate uridyltransferase

We report here the molecular characterization of two galactosemia mutations, L74P and F171S, and one polymorphism, S135L, in human galactose-1-phosphate uridyltransferase (GALT). Both galactosemia mutations result in reduced enzymatic activity when reconstructed in the cDNA and overexpressed. The polymorphism, in contrast, has near normal activity. Both mutations affect evolutionarily conserved residues, suggesting that they are functionally important, while the polymorphism occurs in a nonconserved domain which is presumably not critical for enzymatic function. The F171S mutation is close to the putative active-site nucleophile. Our data further support the notion of molecular heterogeneity of galactosemia and suggest that galactosemia mutations and GALT polymorphisms may be useful tools in highlighting different functional domains in human GALT.

Screw fixation in the human sacrum. An in vitro study of the biomechanics of fixation

A load-to-failure test was used to study the biomechanical properties of sacral screw fixation in human cadaveric specimens. The goals of this study were 1) to determine the effects of the two commonly chosen sacral screw orientations of fixation characteristics; 2) to determine the effects of selected screw-instrumentation linkages on the biomechanics of sacral screw fixation; 3) to correlate the biomechanical properties with a noninvasive assessment of sacral bone density; and 4) to correlate the torque during screw insertion with these biomechanical properties. The bone density of each specimen was measured with quantitative computed tomography. A screw was inserted from the dorsal surface either anteromedially or anterolaterally into the body of S1, and the torque needed to insert each screw was measured. The screw head was attached to a constrained or semiconstrained loading linkage. Force was applied to the screw in an inferior direction until the maximum load was achieved. The maximum load, screw translation, rotation at maximum load, and initial compliance of the bone-screw interface were determined. It was found that the anteromedial screw orientation, combined with a rigidly constrained loading linkage, resulted in the greatest maximum load to failure, the least screw rotation, and the least initial compliance of the four groups studied. The maximum load and the initial stiffness of bone-screw fixation increased significantly with bone density. Torque measurements correlated significantly with maximum load to failure, initial interface stiffness, and bone density. It was therefore concluded that bone density and torque measurements can be useful in assessing sacral screw fixation.

Human gene therapy: present and future

The hematopoietic system and the liver are two primary target organs for attempting somatic gene therapy of hereditary deficiencies. Several leading laboratories have recently been able to demonstrate that bone marrow cells from rodents and non-human primates can be successfully transduced with foreign genes, resulting in the functional expression of these genes in culture. The genetically reconstituted cells can subsequently be transplanted into X-irradiated recipients, and expression of the transduced genes is observed in the recipients for more than 6 months. Subsequently, gene transfer into peripheral T-lymphocytes in humans has been attempted, and the clinical trials are currently in progress. The liver is the other major organ under intensive investigation. Primary hepatocytes can be isolated from rodents, rabbits, and dogs, and successfully transduced with recombinant retroviruses. After autologous transplantation, long term survival of the engrafted cells in vivo has been observed. More recently, it has been shown that human hepatocytes can also be efficiently transduced with recombinant retroviruses. These experimental results have laid the foundation for somatic gene therapy of hereditary deficiencies in humans in the future.

DNA sequencing with dye-labeled terminators and T7 DNA polymerase: effect of dyes and dNTPs on incorporation of dye-terminators and probability analysis of termination fragments

The incorporation of fluorescently labeled dideoxynucleotides by T7 DNA polymerase is optimized by the use of Mn2+, fluorescein analogs and four 2'-deoxyribonucleoside 5'-O-(1-thiotriphosphates) (dNTP alpha S's). The one-tube extension protocol was tested on single-stranded templates, as well as PCR fragments which were made single-stranded by digestion with T7 gene 6 exonuclease. Dye primer sequencing using four dNTP alpha S's was shown to give uniform termination patterns which were comparable to four dNTPs. Efficiency of the polymerase also appeared to improve with the dNTP alpha S's. A mathematical model was developed to predict the pattern of termination based on enzyme activity and ratios of ddNTP/dNTPs. This method can be used to optimize sequencing reactions and to estimate enzyme discrimination constants of chain terminators.

Identification of three novel PKU mutations among Chinese: Evidence for recombination or recurrent mutation at the PAH locus

Three novel mutations have been identified in the phenylalanine hydroxylase (PAH) genes of Chinese classical phenylketonuria (PKU) patients. Two of these substitutions (W326X and Y356X) result in the generation of a premature stop codon, while the third (IVS-7nt2) alters an invariant dinucleotide splicing signal. These mutations together account for about 10% of all PKU alleles in the Chinese population. The W326X mutation is associated with PAH RFLP haplotype 4, the most common haplotype in Orientals, while the IVS-7nt2 mutation occurs once on a haplotype 7 chromosome. The Y356X mutation is associated with multiple haplotypes, possibly due to crossover, gene conversion, or recurrent mutation.

A comparative evaluation of the mechanical properties of the rabbit medial collateral and anterior cruciate ligaments

The biomechanical properties of the medial collateral and anterior cruciate ligaments from 30 New Zealand White rabbits were measured. Because of its complex geometry, the ACL was divided into two portions (medial and lateral) to provide uniform loading. This allowed an examination of the intra-ligamentous properties. A laser micrometer system was used to measure the cross-sectional area for tensile stress and a video dimension analyzer was used to measure the strain. The mechanical properties (stress-strain curves) of the MCL and ACL were different, with the modulus (determined between 4 and 7% strain) in the MCL (1120 +/- 153 MPa) more than twice that of either portion of the ACL (516 +/- 64 and 516 +/- 69 MPa for the medial and lateral portions, respectively). This higher modulus correlated with the more uniform and dense appearance of the collagen fibrils examined with scanning electron microscopy (SEM).

Characterization of two missense mutations in human galactose-1-phosphate uridyltransferase: Different molecular mechanisms for galactosemia

We report the molecular characterization of two novel galactosemia mutations that exhibit different molecular phenotypes. Both are of the missense type with low or no residual enzyme activity. The R148W mutation results in an unstable protein, although messenger RNA is still produced. In contrast, the L195P mutation produces stable but inactive immunoreactive protein. The R148W mutation alters an amino acid that is not evolutionarily conserved, while the L195P mutation affects a well-conserved residue nine amino acids down-stream from the putative active site nucleophile. These mutations provide evidence that different mechanisms can result in galactosemia: destabilizing mutations in any given area of the protein and missense mutations in conserved domains of the enzyme resulting in low or no activity. These two mutant alleles represent the fifth and sixth galactosemia mutations and confirm the hypothesis that galactosemia results from a multiplicity of mutations at the molecular level.

Rib perichondrial autografts in full-thickness articular cartilage defects in rabbits

This study investigated the resurfacing of full-thickness articular defects in the adult rabbit medial femoral condyle using a rib perichondrial graft. The graft was secured to a 4-mm-diameter bone core removed from the femoral condyle. Two postoperative treatment protocols were studied: one group had ad libitum cage activity (CAGE; n = 95) and the other group received two weeks of passive motion (PM; n = 73; eight hours per day, five days per week) followed by cage activity. Animals in both groups were killed at six, 12, 26, and 52 weeks. Repair tissue resembling hyaline cartilage formed in a majority of animals at all time periods and in both postoperative treatment groups. The overall success rates in which repair tissue formed were 58% in the CAGE group and 56% in the PM group. However, over time, a maturation of the neocartilage into nearly normal hyaline articular cartilage was noted with the percentage of Type II collagen increasing from 55% at six weeks to 82% at one year. The complex shear modulus of the repair tissue for both groups became similar to normal cartilage with increased healing time. There was no statistical difference in shear moduli between the two treatment modalities. These results show that cartilage repair tissue derived from rib perichondrium could mature into hyaline articular cartilage over time and would not degrade by one year after repair.

The effect of storage on the biomechanical behavior of articular cartilage--a large strain study

The transplantation of stored shell osteochondral allografts is a potentially useful alternative to total joint replacements for the treatment of joint ailments. The maintenance of normal cartilage properties of the osteochondral allografts during storage is important for the allograft to function properly and survive in the host joint. Since articular cartilage is normally under large physiological stresses, this study was conducted to investigate the biomechanical behavior under large strain conditions of cartilage tissue stored for various time periods (i.e., 3, 7, 28, and 60 days) in tissue culture media. A biphasic large strain theory developed for soft hydrated connective tissues was used to describe and determine the biomechanical properties of the stored cartilage. It was found that articular cartilage stored for up to 60 days maintained the ability to sustain large compressive strains of up to 40 percent or more, like normal articular cartilage. Moreover, the equilibrium stress-strain behavior and compressive modulus of the stored articular cartilage were unchanged after up to 60 days of storage.