Recombinant collagen and gelatin for drug delivery

The tools of recombinant protein expression are now being used to provide recombinant sources of both collagen and gelatin. The primary focus of this review is to discuss alternatives to bovine collagen for biomedical applications. Several recombinant systems have been developed for production of human sequence collagens. Mammalian and insect cells were initially used, but were thought to be too costly for commercial production. Yeast have been engineered to express high levels of type I homotrimer and heterotrimer and type II and type III collagen. Co-expression of collagen genes and cDNAs encoding the subunits of prolyl hydroxylase has lead to the synthesis of completely hydroxylated, thermostable collagens. Human types I and III collagen homotrimers have been expressed in transgenic tobacco plants, while transgenic mice have been engineered to produce full-length type I procollagen homotrimer as well as a alpha2 (I) homotrimeric mini-collagen. Most recently, a transgenic silkworm system was used to produce a fusion protein containing a collagenous sequence. Each of these transgenic systems holds great promise for the cost-effective large-scale production of recombinant human collagens. As seen in other recombinant expression systems, transgenic silkworms, tobacco, and mice lack sufficient endogenous prolyl hydroxylase activity to produce fully hydroxylated collagen. In mice and tobacco, this was overcome by over-expression of prolyl hydroxylase, analogous to what has been done in yeast and insect cell culture. In addition to recombinant alternatives to bovine collagen, other sources such as fish and sponge collagen are discussed briefly. Recombinant gelatin has been expressed in Pichia pastoris and Hansenula polymorpha in both non-hydroxylated and hydroxylated forms. Pichia was shown to be a highly productive system for gelatin production. The recombinant gelatins produced in yeast are of defined molecular weight and physio-chemical properties and represent a new biomaterial not previously available from animal sources. Genetic engineering has made great progress in the areas of recombinant collagen and gelatin expression, and there are now several alternatives to bovine material that offer an enhanced safety profile, greater reproducibility and quality, and the ability of these materials to be tailored to enhance product performance.

Simplified endoproteinase assays using gelatin or azogelatin

Endoproteinase assays with gels containing incorporated gelatin have shown that gelatin is an exceptional substrate for studying enzymes from different sources. However, due to its solubility in trichloroacetic acid, gelatin is not suited to "in-solution" assays carried out in the classic manner (by reading the absorbance of supernatants of hydrolysis reactions after the substrate has been precipitated with trichloroacetic acid). In this paper we demonstrate that gelatin can be used for such analyses by using isopropanol as precipitating reagent. Alternatively, azogelatin, which is precipitated by trichloroacetic acid, can be used. Azogelatin also serves as a very good substrate. One problem with using gelatin (or any nonderivatized protein) as substrate for measuring the activity of crude enzyme preparations is that protein contaminants in the enzyme preparation are hydrolyzed. The resulting peptides are impossible to differentiate from those released from the gelatin substrate. This problem is obviated when azogelatin is used, since its peptides are detected at 440 nm, where nonderivatized peptides do not absorb. Unlike some azo-derivatized proteins, azogelatin is soluble from pH 3.0 to 9.0. This, together with the fact that it is hydrolyzed by many different endoproteinases, makes it suitable for many applications.

Fixation strength of a biodegradable screw in anterior cruciate ligament reconstruction

We compared the strength of fixation of a biodegradable screw with that of two metal screws in a bone-patellar-tendon-bone (BPTB) graft in the bovine knee. We used 33 fresh BPTB specimens with a circular tibial bone plug of 9 mm in diameter which were anchored in a tibial metaphyseal bone tunnel with either an interference screw (n = 11), an AO cancellous screw (n = 11) or a fibrillated, self-reinforced biodegradable poly-L-lactide screw (n = 11). The mean force to failure (+/- SD) in the three groups was 1358 +/- 348 N, 1081 +/- 331 N and 1211 +/- 362 N, respectively. There was no significant difference in the groups with regard to the linear load or the elastic moduli of the fixation. We conclude that the biodegradable screw is as good as either of the two metal screws in the fixation of a BPTB graft in the bovine knee and can be recommended for ACL reconstruction using this type of graft.

Anterior cruciate ligament reconstruction using quadriceps patellar tendon graft. Part II. A specific sport review

Eighty-three patients, from a 10 year follow-up study, who underwent ACL reconstruction with a quadriceps patellar tendon graft were reviewed. A questionnaire qualifying their sports performance in 20 possible sports compared their preinjury status to postinjury and postreconstructive surgery. Successful and unsuccessful patients, as determined by our previous investigation, were likewise compared. Sports performance, regardless of the sport or level of competition, decreased substantially postinjury and then rose significantly to near but not equal to patient preinjury status. The most strenuous sports dipped to the lowest performance level after injury and returned with a correspondingly more modest gain after the reconstruction. Not surprisingly, successful patients had a more impressive return in performance than unsuccessful patients, mirroring their clinical grading. Of those deemed unsatisfactory (N = 20), graft failures were no worse off in performance rating than those that were classified as unsatisfactory because of persistent symptoms.

Anterior cruciate ligament reconstruction using quadriceps patellar tendon graft. Part I. Long-term followup

Eighty-three patients with ACL reconstructions using the quadriceps patellar tendon graft were evaluated in a 10 year (mean, 5.5 years) follow-up study. A five-part analysis, consisting of physical examination, questionnaire, Genucom analysis, operative note review, and radiographs, was performed. Seventy-six percent were categorized as satisfactory. Ninety-two percent were content with their results, while only 4% were unsatisfied. Ninety-three percent of the patients had no significant pain and 95% had no giving way postreconstruction. Ninety-two percent had no more than a mild functional deficit. Eighty-seven percent and 90% of the patients had no significant Lachman or pivot shift by examination, respectively. Our results showed no increase in failure over time (1 to 10 years), although those operated on during the initial 5 years showed more radiographic degenerative changes. Plotting our results in classification systems of other authors yielded success rates as good as or better than those using our own criteria. An objective means by which to quantify laxity did not reliably correlate with the quantifying of laxity made by physical examination. Only the lack of a formal rehabilitation program greater than 4 months postoperatively and repaired tears of the medial or lateral collateral ligaments proved to be significant risk factors for poor recovery.

Keratin classes: molecular markers for different types of epithelial differentiation

Keratins are a group of water-insoluble proteins (molecular weight range 40-70 K) that form 10-nm tonofilaments in a wide variety of epithelial cells. The subunit composition of the keratin filaments varies with cell type, period of embryonic development, stage of histologic differentiation, cellular growth environment, and disease state. To better understand the functional significance of individual keratin species, we have generated three monoclonal antikeratin antibodies to different subsets of keratins and used these antibodies to localize specific keratins in normal human epidermis by a combination of immunohistochemical and biochemical techniques. The results indicate that the 50 K and 58 K keratins are present in all cell layers including the relatively undifferentiated basal layer, whereas the 56.5 K and 65-67 K keratins are associated only with the more differentiated cells above the basal layer. In a separate series of experiments, we used the monoclonal antibodies to survey the keratins expressed by various nonepidermal epithelia. The data show that keratins can be divided into at least seven major classes according to their immunologic reactivity and size. Among the keratin classes, the 50 K and 58 K classes appear to be characteristic of all stratified squamous epithelia, whereas the 56.5 K and 65-67 K classes are unique to the keratinized epidermis. These findings suggest that specific keratin classes, as defined by monoclonal antibodies, may serve as useful markers for different types of epithelial differentiation (simple versus stratified, keratinized versus nonkeratinized).