Effect of sugar metabolite methylglyoxal on equine lamellar explants: An ex vivo model of laminitis

Laminitis is one of the most devastating diseases in equine medicine, and although several etiopathogenetic mechanisms have been proposed, few clear answers have been identified to date. Several lines of evidence point towards its underlying pathology as being metabolism-related. In the carbonyl stress pathway, sugars are converted to methylglyoxal (MG)-a highly reactive α-oxoaldehyde, mainly derived during glycolysis in eukaryotic cells from the triose phosphates: D-glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. One common hypothesis is that MG could be synthesized during the digestive process in horses, and excessive levels absorbed into peripheral blood could be delivered to the foot and lead to alterations in the hoof lamellar structure. In the present study, employing an ex vivo experimental design, different concentrations of MG were applied to hoof explants (HE), which were then incubated and maintained in a specific medium for 24 and 48 h. Macroscopic and histological analyses and a separation force test were performed at 24 and 48 h post-MG application. Gene expression levels of matrix metalloproteinase (MMP)-2 and -14 and tissue inhibitor of metalloproteinase (TIMP)-2 were also measured at each time point for all experimental conditions. High concentrations of MG induced macroscopic and histological changes mimicking laminitis. The separation force test revealed that hoof tissue samples incubated for 24 h in a high concentration of MG, or with lower doses but for a longer period (48 h), demonstrated significant weaknesses, and samples were easily separated. All results support that high levels of MG could induce irreversible damage in HEs, mimicking laminitis in an ex vivo model.

The Trichohyalin-Like Protein Scaffoldin Is Expressed in the Multilayered Periderm during Development of Avian Beak and Egg Tooth

Scaffoldin, an S100 fused-type protein (SFTP) with high amino acid sequence similarity to the mammalian hair follicle protein trichohyalin, has been identified in reptiles and birds, but its functions are not yet fully understood. Here, we investigated the expression pattern of scaffoldin and cornulin, a related SFTP, in the developing beaks of birds. We determined the mRNA levels of both SFTPs by reverse transcription polymerase chain reaction (RT-PCR) in the beak and other ectodermal tissues of chicken (Gallus gallus) and quail (Coturnix japonica) embryos. Immunohistochemical staining was performed to localize scaffoldin in tissues. Scaffoldin and cornulin were expressed in the beak and, at lower levels, in other embryonic tissues of both chickens and quails. Immunohistochemistry revealed scaffoldin in the peridermal compartment of the egg tooth, a transitory cornified protuberance (caruncle) on the upper beak which breaks the eggshell during hatching. Furthermore, scaffoldin marked a multilayered peridermal structure on the lower beak. The results of this study suggest that scaffoldin plays an evolutionarily conserved role in the development of the avian beak with a particular function in the morphogenesis of the egg tooth.

Effects of insulin on IGF-1 receptors in equine lamellar tissue in vitro

Although it is understood that equine endocrinopathic laminitis can be triggered by high concentrations of insulin, it is unclear whether this represents a direct action on lamellar tissue via insulin receptors (InsR), an interaction with IGF-1 receptors (IGF-1R), or some other, indirect action. This uncertainty is because of the reported scarcity of InsR in lamellar tissue and the low affinity of insulin for equine IGF-1R. In the present study, the effects of insulin and IGF-1 (as a positive control) were examined using lamellar explants isolated from the hooves of healthy horses and incubated in cell culture medium for between 2 min and 48 h. In this system, a low physiological concentration of IGF-1 (10 nM; 1.31 ng/mL) caused a marked increase in the appearance of phosphorylated IGF-1R after 5 min (P < 0.05), and this effect was blocked by a human anti-IGF-1R monoclonal antibody (mAb). However, a high concentration of insulin (10 nM; 1,430 μIU/mL) appeared to cause dephosphorylation of the IGF-1R after 5 min (P < 0.01), 15 min, and 30 min (P < 0.001). Using ³H-thymidine as a marker, it was also demonstrated that insulin and IGF-1-stimulated cell proliferation in lamellar explants over the same concentration range as each other (1-100 nM), implying that each peptide acts via its own receptor (P < 0.001). Conversely, the effect of both peptides could be blocked using a selective anti-IGF-1R mAb (P < 0.001), implying that insulin acts via IGF1-R (either directly or indirectly). Notwithstanding this conundrum, the results demonstrate that insulin acts directly on lamellar tissue and suggest that a therapeutic anti-IGF-1R mAb could be useful in treating or preventing endocrinopathic laminitis.

Potential of Naftifine Application for Transungual Delivery

Naftifine is used to treat fungal skin infections as it inhibits dermatophytes, which are the cause of onychomycosis. However, naftifine's ability to permeate the human nail barrier has not been investigated, thus, the antimycotic potential is not clearly established. This work aims to evaluate the effect of penetration enhancing factors on the accumulation of naftifine hydrochloride through human nail clippings. Naftifine polymeric nail lacquers with Eudragit RL100 were developed as a suitable delivery system. Low penetration of naftifine into nail has been determined as less than 10% of applied drug dose accumulated in the nail layers. Incorporation of thioglycolic acid into formulations resulted in increased accumulation of antifungal agent in the nail layers by 100% compared with a control group. Salicylic acid did not effect naftifine accumulation in the human nail. The permeation of naftifine through the nail increased by threefold when the thioglycolic acid-containing formulation was applied and the nail was pretreated with a fractional CO2 laser. Structural changes of the nail barrier, induced by fractional CO2 laser, were visualized by microscopy. The results suggest, that naftifine nail penetration could be significantly increased when physical and chemical enhancing factors are applied.

The expression of equine keratins K42 and K124 is restricted to the hoof epidermal lamellae of Equus caballus

The equine hoof inner epithelium is folded into primary and secondary epidermal lamellae which increase the dermo-epidermal junction surface area of the hoof and can be affected by laminitis, a common disease of equids. Two keratin proteins (K), K42 and K124, are the most abundant keratins in the hoof lamellar tissue of Equus caballus. We hypothesize that these keratins are lamellar tissue-specific and could serve as differentiation- and disease-specific markers. Our objective was to characterize the expression of K42 and K124 in equine stratified epithelia and to generate monoclonal antibodies against K42 and K124. By RT-PCR analysis, keratin gene (KRT) KRT42 and KRT124 expression was present in lamellar tissue, but not cornea, haired skin, or hoof coronet. In situ hybridization studies showed that KRT124 localized to the suprabasal and, to a lesser extent, basal cells of the lamellae, was absent from haired skin and hoof coronet, and abruptly transitions from KRT124-negative coronet to KRT124-positive proximal lamellae. A monoclonal antibody generated against full-length recombinant equine K42 detected a lamellar keratin of the appropriate size, but also cross-reacted with other epidermal keratins. Three monoclonal antibodies generated against N- and C-terminal K124 peptides detected a band of the appropriate size in lamellar tissue and did not cross-react with proteins from haired skin, corneal limbus, hoof coronet, tongue, glabrous skin, oral mucosa, or chestnut on immunoblots. K124 localized to lamellar cells by indirect immunofluorescence. This is the first study to demonstrate the localization and expression of a hoof lamellar-specific keratin, K124, and to validate anti-K124 monoclonal antibodies.

A natural energy absorbent polymer composite: The equine hoof wall

The equine hoof has been considered as an efficient energy absorption layer that protects the skeletal elements from impact when galloping. In the present study, the hierarchical structure of a fresh equine hoof wall and the energy absorption mechanisms are investigated. Tubules are found embedded in the intertubular matrix forming the hoof wall at the microscale. Both tubules and intertubular areas consist of keratin cells, in which keratin crystalline intermediate filaments (IFs) and amorphous keratin fill the cytoskeletons. Cell sizes, shapes and IF fractions are different between tubular and intertubular regions. The structural differences between tubular and intertubular areas are correlated to the mechanical behavior of this material tested in dry, fresh and fully hydrated conditions. The stiffness and hardness in the tubule areas are higher than that in the intertubular areas in the dry and fresh samples when loaded along the hoof wall; however, once the samples are fully hydrated, the intertubular areas become stiffer than the tubular areas due to higher water absorption in these regions. The compression behavior of hoof in different loading speed and directions are also examined, with the isotropy and strain-rate dependence of mechanical properties documented. In the hoof walls, mechanistically the tubules serve as a reinforcement, which act to support the entire wall and prevent catastrophic failure under compression and impact loading. Elastic buckling and cracking of the tubules are observed after compression along the hoof wall, and no shear-banding or severe cracks are found in the intertubular areas even after 60% compression, indicating the highly efficient energy absorption properties, without failure, of the hoof wall structure. STATEMENT OF SIGNIFICANCE: The equine hoof wall is found to be an efficient energy absorbent natural polymer composite. Previous studies showed the microstructure and mechanical properties of the hoof wall in some perspective. However, the hierarchical structure of equine hoof wall from nano- to macro-scale as well as the energy absorption mechanisms at different strain rates and loading orientations remains unclear. The current study provides a thorough characterization of the hierarchical structure as well as the correlation between structure and mechanical behaviors. Energy dissipation mechanisms are also identified. The findings in the current research could provide inspirations on the designs of impact resistant and energy absorbent materials.

Characterization of insulin and IGF-1 receptor binding in equine liver and lamellar tissue: implications for endocrinopathic laminitis

Although it is well established that equine laminitis can be triggered by extreme hyperinsulinemia, the mechanism of insulin action is not known. High concentrations of insulin lead to separation of the weight-bearing apparatus from the hoof wall and are associated with an increased cycle of cell death and proliferation in the lamellae. Gene expression and immunohistochemistry studies have indicated that the lamellae are sparsely populated with insulin receptors, whereas IGF-1 receptors (IGF-1R) are abundant, suggesting that the action of insulin may be mediated by insulin binding to the IGF-1R. To investigate this possibility, cell membrane fragments containing IGF-1R were extracted from the livers of 6 horses and the lamellae of >50 horses euthanized for nonresearch purposes at an abattoir. Radioligand-binding studies using ¹²⁵I-IGF-1 and ¹²⁵I-insulin confirmed an abundance of high-affinity IGF-1R in the liver (K_D 0.11 nM, B_max 223 fmol/mg protein) and lamellae (K_D 0.16 nM, B_max 243 fmol/mg protein). However, the affinity of insulin for binding to the lamellar IGF-1R (K_i 934 nM) was >5,800 fold less than that of IGF-1, suggesting that insulin is unlikely to bind to equine IGF-1R at physiological concentrations. Although insulin receptors could be detected in the liver (K_D 0.48 nM, B_max 123 fmol/mg protein), they were barely detectable in lamellae (estimated B_max 14 fmol/mg protein). There was no evidence to support the presence of insulin/IGF-1 hybrid receptors in either tissue. These findings suggest that insulin does not act directly through IGF-1 receptors and that an alternative theory is required to explain the mechanism of insulin action in laminitis.

Influence of dietary zinc on the claw and interdigital skin of sheep

Claw diseases like interdigital dermatitis and footrot threaten sheep health and are major welfare issues. Several studies mainly done in cattle suggested that zinc (Zn) supplementation may improve claw integrity. However, Zn supplements may differ markedly regarding Zn bioavailability. Zn bound to single amino acids has been shown to be more bioavailable than inorganic Zn sources. The aim of this study was to determine the effect of different Zn supplements on the integrity of the claw and interdigital skin of healthy sheep. At weaning 30 Merino lambs were randomly allocated to three different dietary treatments which were provided through the pelleted concentrates as follows: 1) no supplemental Zn (Zn0); 2) addition of 40 mg/kg Zn as Zn sulphate (ZnS); 3) addition of 40 mg/kg organic Zn as Zn amino acid complex (CZn). Barley straw and pelleted concentrates were given ad-libitum. The calculated Zn concentration of the total diet (roughage and concentrate) without supplemental Zn (Zn0) was 38 mg Zn/kg DM. The concentrates were formulated to meet the nutritional requirements for growing lambs and contained 207 g/kg DM crude protein and 12.4 MJ/kg DM metabolizable energy. After 8 weeks the lambs were slaughtered and the following specimens were collected: blood serum, liver, sole and coronary band of the claw, and interdigital skin. Serum and tissue Zn and copper (Cu) concentrations and claw hardness were determined. Routine pathohistology and electron microscopy were conducted. Franz diffusion cell system and Ki-67 immunostaining were used to determine the permeability of the interdigital skin and the keratinocyte proliferation in the basal layer of sole horn, coronary band and interdigital skin, respectively. The concentrations of Zn and Cu in serum and liver tissue as well as the Zn concentration in claw horn were not affected by dietary treatment. Zn0 lambs showed higher (p < 0.05) Cu concentrations in claw horn compared to both Zn supplemented groups. Routine pathohistology as well as electron microscopy did not show significant morphological differences between the three groups. Franz diffusion cell system proved to be a suitable method examining the interdigital skin permeability, but the group differences in this study were not significant. Dietary treatment did not affect keratinocyte proliferation in the coronary band. In the sole keratinocyte proliferation was significantly higher (p < 0.05) in the Zn0 group compared to CZn with ZnS being intermediate. Keratinocyte proliferation in the interdigital skin was significantly higher (p < 0.05) in the CZn group compared to the Zn0 with ZnS being intermediate. The results of the current experiment indicate that serum and tissue Zn concentrations and horn hardness are not affected by adding a moderate amount of Zn sulphate or Zn amino acid complex to a basal diet. However, supplemental Zn amino acid complex seems to affect keratinocyte proliferation of interdigital skin and sole horn of lambs. Effects on skin permeability should be retested using a higher number of animals prospectively.

Ultrasound-Enhanced Drug Delivery for Treatment of Onychomycosis

OBJECTIVES

The aim of our study was to determine the effectiveness of using ultrasound (US) to increase the permeability of the nail, with the goal of improving outcomes in the treatment of onychomycosis.

METHODS

Porcine nails were used because of their similarity to human nails. A hydrophilic blue dye was used as a drug-mimicking compound. Two sets of experiments were performed: luminosity experiments to assess the dye levels inside the nail after US and sham treatments and diffusion cell experiments for determination of changes in nail permeability due to US application. In both sets of experiments, planar US transducers were used to sonicate the nails at frequencies of 400, 600, and 800 kHz and 1 MHz, an intensity of 1 W/cm² , and a duration of 5 min in a continuous mode. Modeling studies were also performed to assess the safety of US application to the human toe for later clinical studies.

RESULTS

In the luminosity experiments, application of US at frequencies of 600 and 800 kHz led to statistically significant results (P < .05), with an increase in dye delivery into the nail of up to 95% compared to control values. The diffusion cell results found statistical significance (P < .05) at all applied frequencies, with up to a 70% increase in the nail permeability compared to the control. Safety modeling studies found a maximal temperature increase of 4.4 °C in the bone.

CONCLUSIONS

Our proposed US method may offer an alternative for improved treatment of onychomycosis. The current maximal temperature increase was found to be at the safety limit, and so pulsing and other alternatives will be investigated to minimize this temperature increase.

Fumonisin B₁ (FB₁) Induces Lamellar Separation and Alters Sphingolipid Metabolism of In Vitro Cultured Hoof Explants

One of the most important hoof diseases is laminitis. Yet, the pathology of laminitis is not fully understood. Different bacterial toxins, e.g. endotoxins or exotoxins, seem to play an important role. Additionally, ingestion of mycotoxins, toxic secondary metabolites of fungi, might contribute to the onset of laminitis. In this respect, fumonsins are of special interest since horses are regarded as species most susceptible to this group of mycotoxins. The aim of our study was to investigate the influence of fumonisin B₁ (FB₁) on primary isolated epidermal and dermal hoof cells, as well as on the lamellar tissue integrity and sphingolipid metabolism of hoof explants in vitro. There was no effect of FB₁ at any concentration on dermal or epidermal cells. However, FB₁ significantly reduced the separation force of explants after 24 h of incubation. The Sa/So ratio was significantly increased in supernatants of explants incubated with FB₁ (2.5–10 µg/mL) after 24 h. Observed effects on Sa/So ratio were linked to significantly increased sphinganine concentrations. Our study showed that FB₁ impairs the sphingolipid metabolism of explants and reduces lamellar integrity at non-cytotoxic concentrations. FB₁ might, therefore, affect hoof health. Further in vitro and in vivo studies are necessary to elucidate the effects of FB₁ on the equine hoof in more detail.

Trichohyalin-like proteins have evolutionarily conserved roles in the morphogenesis of skin appendages

S100 fused-type proteins (SFTPs) such as filaggrin, trichohyalin, and cornulin are differentially expressed in cornifying keratinocytes of the epidermis and various skin appendages. To determine evolutionarily conserved, and thus presumably important, features of SFTPs, we characterized nonmammalian SFTPs and compared their amino acid sequences and expression patterns with those of mammalian SFTPs. We identified an ortholog of cornulin and a previously unknown SFTP, termed scaffoldin, in reptiles and birds, whereas filaggrin was confined to mammals. In contrast to mammalian SFTPs, both cornulin and scaffoldin of the chicken are expressed in the embryonic periderm. However, scaffoldin resembles mammalian trichohyalin with regard to its expression in the filiform papillae of the tongue and in the epithelium underneath the forming tips of the claws. Furthermore, scaffoldin is expressed in the epithelial sheath around growing feathers, reminiscent of trichohyalin expression in the inner root sheath of hair. The results of this study show that SFTP-positive epithelia function as scaffolds for the growth of diverse skin appendages such as claws, nails, hair, and feathers, indicating a common evolutionary origin.

Use of stable isotopes to investigate keratin deposition in the claw tips of ducks

Stable isotopes derived from the claws of birds could be used to determine the migratory origins of birds if the time periods represented in excised sections of claws were known. We investigated new keratin growth in the claws of adult female Lesser Scaup (Aythya affinis) by estimating the equilibration rates of stable isotopes (δ¹³C, δ¹⁵N, and δ²H) from the breeding grounds into 1 mm claw tips. We sampled birds on their breeding ground through time and found that it took approximately 3–3.5 months for isotope values in most claw tips to equilibrate to isotope values that reflected those present in the environment on their breeding grounds. Results from this study suggest that isotopes equilibrate slowly into claw tips of Lesser Scaup, suggesting isotopes could potentially be used to determine the wintering grounds of birds. We suggest using controlled feeding experiments or longitudinal field investigations to understand claw growth and isotopic equilibration in claw tips. Such information would be valuable in ascertaining whether claw tips can be used in future studies to identify the migratory origins of birds.

Distribution of purinergic P2X receptors in the equine digit, cervical spinal cord and dorsal root ganglia

Purinergic pathways are considered important in pain transmission, and P2X receptors are a key part of this system which has received little attention in the horse. The aim of this study was to identify and characterise the distribution of P2X receptor subtypes in the equine digit and associated vasculature and nervous tissue, including peripheral nerves, dorsal root ganglia and cervical spinal cord, using PCR, Western blot analysis and immunohistochemistry. mRNA signal for most of the tested P2X receptor subunits (P2X1-5, 7) was detected in all sampled equine tissues, whereas P2X6 receptor subunit was predominantly expressed in the dorsal root ganglia and spinal cord. Western blot analysis validated the specificity of P2X1-3, 7 antibodies, and these were used in immunohistochemistry studies. P2X1-3, 7 receptor subunits were found in smooth muscle cells in the palmar digital artery and vein with the exception of the P2X3 subunit that was present only in the vein. However, endothelial cells in the palmar digital artery and vein were positive only for P2X2 and P2X3 receptor subunits. Neurons and nerve fibres in the peripheral and central nervous system were positive for P2X1-3 receptor subunits, whereas glial cells were positive for P2X7 and P2X1 and 2 receptor subunits. This previously unreported distribution of P2X subtypes may suggest important tissue specific roles in physiological and pathological processes.

Ultrasound-mediated nail drug delivery system

A novel ultrasound-mediated drug delivery system has been developed for treatment of a nail fungal disorder (onychomycosis) by improving delivery to the nail bed using ultrasound to increase the permeability of the nail. The slip-in device consists of ultrasound transducers and drug delivery compartments above each toenail. The device is connected to a computer, where a software interface allows users to select their preferred course of treatment. In in vitro testing, canine nails were exposed to 3 energy levels (acoustic power of 1.2 W and exposure durations of 30, 60, and 120 seconds). A stereo -microscope was used to determine how much of a drug-mimicking compound was delivered through the nail layers by measuring brightness on the cross section of each nail tested at each condition, where brightness level decreases coincide with increases in permeability. Each of the 3 energy levels tested showed statistical significance when compared to the control (P < .05) with a permeability factor of 1.3 after 30 seconds of exposure, 1.3 after 60 seconds, and 1.5 after 120 seconds, where a permeability factor of 1 shows no increase in permeability. Current treatments for onychomycosis include systemic, topical, and surgical. Even when used all together, these treatments typically take a long time to result in nail healing, thus making this ultrasound-mediated device a promising alternative.

Epidermal cell proliferation in the equine hoof wall

REASONS FOR PERFORMING STUDY

Current theories explaining how the hoof wall 'grows' and moves past the stationary distal phalanx are speculative and based on incomplete evidence. Movement in the lamellar region could occur by cell proliferation or an enzyme-based remodelling process. Since laminitis pathogenesis appears to involve increased transcription and activation of enzymes normally involved in tissue remodelling, it is important to know precisely which process dominates the lamellar region of the hoof..

OBJECTIVES

To investigate epidermal cell proliferation in the equine hoof wall and calculate a proliferative index (PI) for the coronet, lamellae and toe.

METHODS

An analogue of thymidine, 5-bromo-2'-deoxyuridine (BRdU), was infused i.v. into 5 ponies. After tissue harvesting, BRdU (and therefore basal cell proliferation) was detected immunohistochemically using mouse anti-BRdU. PIs were calculated for the coronet and 10 levels of the dorsal hoof wall lamellae.

RESULTS

The highest PIs (mean +/- s.e.) were in the coronet; 12.04% +/- 1.59 and proximal lamellae (7.13% +/- 1.92) and are therefore growth zones of the proximal hoof wall. PIs of more distal lamellae were 0.11% +/- 0.04 to 0.97% +/- 0.29; significantly lower (P = 0.05) than the lamellar growth zone.

CONCLUSIONS

A 20-fold PI decrease between proximal and more distal lamellae suggests that the majority of the normal lamellae are nonproliferative and their main function is to suspend the distal phalanx within the hoof capsule. Remodelling within the hoof wall epidermal lamellae, which must occur as the hoof wall moves past the stationary distal phalanx, is a process not requiring epidermal cell proliferation.

POTENTIAL RELEVANCE

A hoof lamellar epidermis that remodels using the same MMPs involved in laminitis pathogenesis implies that laminitis is a normal process out of control. Understanding MMP control and how the normal lamellar epidermis achieves this will help in the development of better laminitis preventative and treatment strategies.

Increased expression of MAIL, a cytokine-associated nuclear protein, in the prodromal stage of black walnut-induced laminitis

REASONS FOR PERFORMING STUDY

The mediators and signalling cascades important in the initiation of laminitis remain unclear. We therefore wanted to explore the genes and overall signalling mechanisms that play an important role in the developmental stage of laminitis.

OBJECTIVE

To use a broad genomic screening technique to identify novel genes that are differentially regulated in the equine lamellae during the developmental period of laminitis.

METHODS

Differential mRNA display (DRD) was performed to discover regulated genes, and real-time quantitative polymerase chain reaction (RT-qPCR) was then used to evaluate lamellar mRNA levels of a regulated gene (MAIL) and mediators related to that gene (IL-1beta and IL-6) in control horses (n = 5) and horses administered black walnut extract (BWE; n = 5).

RESULTS

Using DRD, MAIL was identified as a regulated gene. RT-qPCR indicated a 4-fold increase in expression of the MAIL mRNA in BWE lamellae compared to controls. A 30-fold increase in IL-1beta, and a 160-fold difference in IL-6 mRNA expression was present in BWE lamellae. Differences in MAIL, IL-1beta and IL-6 mRNA expression were statistically significant between groups (P < 0.05).

CONCLUSIONS AND POTENTIAL RELEVANCE

The data strongly support a role for inflammatory cytokines in the developmental stages of laminitis, possibly inducing the vascular and metabolic alterations reported to occur in the affected digit. These results potentially support the use of anti-inflammatory drugs in horses at risk of laminitis, and warrant further investigation of the link between systemic disease processes associated with laminitis and the reported digital inflammation.

Chronic equine laminitis is characterised by loss of GLUT1, GLUT4 and ENaC positive laminar keratinocytes

REASONS FOR PERFORMING STUDY

Equine laminitis is a multifactorial connective tissue disorder with major implications for the welfare of horses. There are few published studies on phenotypic markers for identification of equine laminar keratinocytes using immunohistochemical techniques.

OBJECTIVES

To establish whether the epithelial sodium channel (ENaC) and the GLUT1 and GLUT4 facilitative glucose transporters may be used as phenotypic markers for identification of equine laminar keratinocytes using immunohistochemical techniques to monitor changes in the keratinocyte population in laminitis.

METHODS

Histology and immunohistochemistry using polyclonal antibodies to the alpha subunit of ENaC (alphaENaC), GLUT1 and GLUT4 were used to compare the distribution of these proteins in normal and laminitic equine laminae.

RESULTS

Immunohistochemistry with antibodies to alphaENaC, GLUT1 and GLUT4 confirmed the abundant expression of all 3 membrane proteins in healthy laminar keratinocytes. However, in laminitis, the Haematoxylin Van Gieson (HVG) technique revealed disordered laminar arrays and replacement with fibrous scar tissue. Immunostaining of laminitic samples confirmed the loss of alphaENaC, GLUT1 and GLUT4 positive keratinocytes. Other connective tissue cells did not stain positive for these proteins.

CONCLUSIONS

This is the first report of alphaENaC and GLUT1/GLUT4 protein expression in equine laminar keratinocytes, which also confirms that the loss of laminar structure and function in chronic laminitis is accompanied by the loss of laminar keratinocytes.

POTENTIAL RELEVANCE

alphaENaC, GLUT1 and GLUT4 may be used as phenotypic markers of metabolically active, differentiated equine laminar keratinocytes. Further in vitro studies are necessary to determine the effects of hypoxia, bacterial endotoxins, vasoactive amines, lactic acid and prostaglandins on the expression and activity of these plasma membrane keratinocyte markers.

Effects of ammonia and hydrogen sulfide on physical and biochemical properties of the claw horn of Holstein cows

The effects of ammonia and hydrogen sulfide on the physical and biochemical properties of the claw horn of Holstein cows were evaluated. Significant (P < 0.05, 0.01) decreases in hardness and elasticity were found in claw horns soaked in ammonia (NH(3)) and hydrogen sulfide (H(2)S) solutions compared with those that were soaked in water for 12, 24, and 48 h. Water absorption rate, as a indicator of permeability barrier function, increased significantly (P < 0.05) over time during the soaking period and was found to be dependent on the concentrations of NH(3) and H(2)S in the solutions. The contents of ceramide, the main lipid component for the permeability barrier system of the stratum corneum, were significantly decreased in claw horns soaked in NH(3) and H(2)S solutions compared with the values before soaking. Quantities of eluted protein released from claw horns treated with NH(3) and H(2)S solutions were approximately 20 times and 30 to 40 times greater than those released from claw horns treated with water alone. Interestingly, the quantities of cytokeratin 10, the main cytoskeletal protein of the stratum corneum, eluted from claw horns treated with NH(3) and H(2)S solutions were markedly greater than the quantity released from horns soaked in water. Our results suggest that abnormal changes in the physical property of claw horn caused by NH(3) and H(2)S treatment are due to disruption of the biochemical property of the claw horn induced by these chemical agents derived from slurry.

Effects of housing, parturition and diet change on the biochemistry and biomechanics of the support structures of the hoof of dairy heifers

This study investigated effects of housing, diet and parturition on the biochemistry, biomechanics and pathology of feet of maiden, pregnant and lactating dairy heifers. Strength/laxity, laminar morphology, connective tissue (CT) biochemistry and sole lesions were assessed. Although no animals became clinically lame, severity of sole lesions was significantly greater in heifers housed in cubicles vs. straw yards, and in lactating/pregnant heifers vs. maidens. These effects were additive. Cubicle housing and parturition each increased CT metabolism (and were additive), and altered CT composition. Similarly, both impaired the biomechanical resilience of the hoof. There were no effects for diet. The results indicate that parturition/lactation causes non-inflammatory changes in CT that impair resilience of the feet to external stresses associated with poor housing. This "parturition effect" appears to be unrelated to change in diet and relatively brief, unless exacerbated by additional stresses of housing. Thus heifer lameness may be significantly reduced through short-term, low-cost improvements in husbandry around the time of calving.

Muscle-specific calpain is localized in regions near motor endplates in differentiating lobster claw muscles

Calpains are Ca2+-dependent proteinases that mediate protein turnover in crustacean skeletal muscles. We used an antibody directed against lobster muscle-specific calpain (Ha-CalpM) to examine its distribution in differentiating juvenile lobster claw muscles. These muscles are comprised of both fast and slow fibers early in development, but become specialized into predominantly fast or exclusively slow muscles in adults. The transition into adult muscle types requires that myofibrillar proteins specific for fast or slow muscles to be selectively removed and replaced by the appropriate proteins. Using immunohistochemistry, we observed a distinct staining pattern where staining was preferentially localized in the fiber periphery along one side of the fiber. Immunolabeling with an antibody directed against synaptotagmin revealed that the calpain staining was greatest in the cytoplasm adjacent to synaptic terminals. In complementary analyses, we used sequence-specific primers with real-time PCR to quantify the levels of Ha-CalpM in whole juvenile claw muscles. These expression levels were not significantly different between cutter and crusher claws, but were positively correlated with the expression of fast myosin heavy chain. The anatomical localization of Ha-CalpM near motor endplates, coupled with the correlation with fast myofibrillar gene expression, suggests a role for this intracellular proteinase in fiber type switching.

Nail swelling as a pre-formulation screen for the selection and optimisation of ungual penetration enhancers

INTRODUCTION

Targeting drug treatment to fungal infections that reside within or below the nail plate is problematic due to the highly restrictive barrier of the human nail. To optimise topical formulations for ungual drug delivery, inclusion of an effective penetration enhancer (PE) is imperative. At present, in vitro nail permeation studies can take weeks or months in order to obtain any meaningful data because the lack of a simple in vitro model to identify and develop nail PEs makes the selection and optimisation of novel PEs an empirical and inefficient process. The aim of this study was to compare three methods for pre-formulation screening of putative ungual PEs and then to select the most suitable technique for screening candidates that may enhance the permeation of therapeutic agents through the human nail.

METHODS

Three screening techniques were evaluated; nail swelling (weight increase of human nail clippings), horse hoof swelling (weight increase of horse hoof clippings) and nail penetration of a radiolabelled permeability probe. Four test PEs were evaluated using each screening method and nail swelling was identified as a simple, rapid, economic, relevant and reliable technique. This screen was then used to evaluate 20 potential PEs. Thioglycolic acid (TA), hydrogen peroxide (H(2)O(2)) and urea H(2)O(2) produced the greatest nail weight increases; 71.0+/-4.6%, 69.2+/-6.6%, and 69.0+/-9.9 respectively. To confirm the relationship between human nail swelling and altered ungual barrier function, a permeation study was performed in human nails using caffeine as a model penetrant.

RESULTS AND DISCUSSION

Human nails pre-treated with TA in vitro had a 3.8-fold increase in caffeine flux compared to the control (TA-free solution). This study illustrated the potential to use human nail clipping swelling as a surrogate marker of PE activity for topical ungual drug delivery.

An investigation into keratinolytic enzymes to enhance ungual drug delivery

The topical therapy of nail diseases is limited by the low permeability of drugs through the nail plate. To increase drug penetration, the integrity of the nail plate must be compromised to a certain extent. We hypothesised that keratinolytic enzymes might decrease the barrier properties of the nail plate by hydrolysing the nail keratins, and thereby enhance ungual drug permeation. To determine enzyme action on nail plates, nail clippings were incubated at 35 degrees C, in the presence of keratinase at optimal pH for 48h, after which the nail plates were examined using scanning electron microscopy. It was found that the enzyme acted on the intercellular matrix which holds nail cells together, such that corneocytes on the dorsal surface separated from one another and 'lifted off' the nail plate. In addition, the surface of the corneocytes was corroded. Permeation studies using modified Franz diffusion cells and bovine hoof membranes as a model for the nail plate showed that the enzyme enhanced drug permeation through the hoof membrane. The permeability and partition coefficients, and the drug flux were found to be significantly increased in the presence of the enzyme. We can conclude that the enzyme, via its hydrolytic action on nail plate proteins, could increase ungual drug delivery.

In vitro antimycotic activity and nail permeation models of a piroctone olamine (octopirox) containing transungual water soluble technology

Several in vitro studies with a new medical device (Myfungar) containing 0.5% of piroctone olamine (CAS 68890-66-4, octopirox) in a hydroxypropyl chitosan hydroalcoholic solution were performed. The chemical name of the active ingredient is 1-hydroxy-4-methyl-6 (2,4,4-trimethylpentyl)-2(1H)-pyridone; combination with 2-amino-ethanol (1:1). The antimycotic activity was determined in the most common fungi responsible of nail infections such as Candida parapsilosis, Scopulariopsis brevicaulis or Trichophyton rubrum. The minimum inhibitory concentration (MIC), found by means of the broth dilution susceptibility method, ranged between 0.0003% and 0.006% for all pathogens considered. The in vitro permeation study was performed by using bovine hoof membranes inserted in a modified Gummer vertical permeation cell. The experiment showed, at 30 h, a retention of the product in the nail membranes by 11.1% of the applied dose. No piroctone permeation through bovine hoof membranes could be detected by HPLC due to the limit of quantitation of this method. On the other hand, permeation of nail membranes has been demonstrated by a biological assay: the study of in vitro permeation through bovine hoof membranes, performed by biological assay, showed dose-dependent inhibition rings of T. rubrum growth by the tested device, placed either on disks for antibiogram or on nail fragments. The placebo did not show any inhibition. In vitro experimental infection by T. rubrum showed a preventive activity of the tested device on fungal growth as well as a curative activity, as the pathogen was eradicated by the tested solution in previously infected nails.

Bioadhesive patch-based delivery of 5-aminolevulinic acid to the nail for photodynamic therapy of onychomycosis

The in vitro penetration of 5-aminolevulinic acid (ALA) across human nail and into neonate porcine hoof when released from a novel bioadhesive patch containing 50 mg cm(-2) ALA is described. ALA is a naturally occurring precursor of the photosensitiser protoporphyrin IX (PpIX). Topical application of excess ALA bypasses negative feedback inhibition and yields photosensitising concentrations of PpIX at the application site. ALA-based photodynamic therapy (PDT) has been extensively investigated in the topical treatment of various skin neoplasias. Recently, its use has been extended to the microbiological field. If sufficient concentrations of ALA could be achieved within the nail matrix, and at the nail bed, PDT may prove to be a useful treatment for onychomycosis. Patch application for 24 h allowed an ALA concentration of 2.8 mM to be achieved on the ventral side of excised human nail. Application for 48 h induced a concentration of 6.9 mM. Application time had no significant effect on the ALA concentration at mean depths of 2.375 mm in neonate porcine, with application times of 24, 48 and 72 h all producing concentrations of 0.1 mM. Incubation of Candida albicans and Trichophyton interdigitale with ALA concentrations of 10.0 mM for 30 min and 6 h, respectively, caused reductions in viability of 87% and 42%, respectively, following irradiation with red light. Incubation with 0.1 mM ALA for 30 min and 6 h, respectively, caused reductions in viability of 32% for Candida albicans and 6% for Trichophyton interdigitale, following irradiation. Drug penetration across nail may be improved using penetration enhancers, or by filing of the impenetrable dorsal surface of the nail. Moreover, iron chelators can be used to increase PpIX production for a given ALA dose. Therefore, with suitable modifications, ALA-PDT may prove to be a viable alternative in the treatment of onychomycosis.

Equine laminitis: glucose deprivation and MMP activation induce dermo-epidermal separation in vitro

REASONS FOR PERFORMING STUDY

Acute laminitis is characterised by hoof lamellar dermal-epidermal separation at the basement membrane (BM) zone. Hoof lamellar explants cultured in vitro can also be made to separate at the basement membrane zone and investigating how this occurs may give insight into the poorly understood pathophysiology of laminitis.

OBJECTIVES

To investigate why glucose deprivation and metalloproteinase (MMP) activation in cultured lamellar explants leads to dermo-epidermal separation.

METHODS

Explants, cultured without glucose or with the MMP activator p-amino-phenol-mercuric acetate (APMA), were subjected to tension and processed for transmission electron microscopy (TEM).

RESULTS

Without glucose, or with APMA, explants under tension separated at the dermo-epidermal junction. This in vitro separation occurred via 2 different ultrastructural processes. Lack of glucose reduced hemidesmosomes (HDs) numbers until they disappeared and the basal cell cytoskeleton collapsed. Anchoring filaments (AFs), connecting the basal cell plasmalemma to the BM, were unaffected although they failed under tension. APMA activation of constituent lamellar MMPs did not affect HDs but caused AFs to disappear, also leading to dermo-epidermal separation under tension.

CONCLUSIONS

Natural laminitis may occur in situations where glucose uptake by lamellar basal cells is compromised (e.g. equine Cushing's disease, obesity, hyperlipaemia, ischaemia and septicaemia) or when lamellar MMPs are activated (alimentary carbohydrate overload).

POTENTIAL RELEVANCE

Therapies designed to facilitate peripheral glucose uptake and inhibit lamellar MMP activation may prevent or ameliorate laminitis.

Nail and Bone Surface as Biomarkers for Acute Fluoride Exposure in Rats

When acute exposure to fluoride is thought to be the cause of death, confirmation often depends on the analysis of some body fluid or tissue. The aim of this study was to evaluate the use of nails and the periosteal surface of bone as indicators of acute exposure to fluoride. Six groups of rats were given a single oral dose of fluoride (50 mg/kg body weight), while the control group was given deionized water. The rats were killed at 2, 4, 8, 16, 24, and 48 h after fluoride administration. Plasma and nails (the proximal halves) were collected and analyzed for fluoride with an ion-specific electrode after hexamethyldisiloxane-facilitated diffusion. A circular area of the femur (4.52 mm(2)) was etched with 0.5M HCl for 15 s, and, after the addition of a buffer, the solution was analyzed with an ion-specific electrode. Peak plasma concentration occurred at 2 h, followed by progressively declining concentrations. Peak nail fluoride concentrations occurred at 8 h. The mean nail concentrations at 8, 16, and 24 h were significantly higher than that of the control group. Bone surface concentrations were significantly higher than that of the control group at 4 h and thereafter. Thus, the proximal portion of nails and bone surface are suitable biomarkers for acute fluoride exposure in rats.

Effects of biotin supplementation on serum biotin levels and physical properties of samples of solar horn of Holstein cows

Effects of dietary biotin supplementation on serum biotin levels and physical properties of sole horn of 40 Holstein cows were evaluated. The mean serum biotin level in biotin-supplemented cows after 10 mo of biotin supplementation (1163.2 +/- 76.2 pg/mL) was significantly higher (P = 0.007) than that in control cows (382.0 +/- 76.2 pg/mL). The sole horn of biotin-supplemented cows was significantly harder (P = 0.026) and had a significantly lower moisture content (P = 0.021) than that of control cows. No morphologic differences in horn tubules or intertubular horn were found between the biotin-supplemented and control cows. The total lipid content of sole horn was significantly higher (P = 0.030) in the biotin-supplemented cows than in the control cows. These results suggest that dietary biotin supplementation causes increases in serum biotin levels and changes in physical properties and fat content of sole horn.

Invited Review: Formation of Keratins in the Bovine Claw: Roles of Hormones, Minerals, and Vitamins in Functional Claw Integrity

Keratins are the characteristic structural proteins of the highly cornified epidermis of the skin, feathers, and hoof. Keratin proteins provide the structural basis for the unique properties of the biomaterial horn and its protective function against a wide range of environmental factors. Hoof horn is produced through a complex process of differentiation (keratinization) of epidermal cells. Formation and biochemical binding of keratin proteins and synthesis and exocytosis of intercellular cementing substance (ICS) are the hallmarks of keratinization. It is finalized by the programmed death of the living epidermal cells, i.e., cornification, that turns the living epidermal cells into dead horn cells. The latter become connected by the intercellular cementing substance. The functional integrity of hoof horn essentially depends on a proper differentiation, i.e., keratinization of hoof epidermal cells. Keratinization of hoof epidermis is controlled and modulated by a variety of bioactive molecules and hormones. This process is dependent on an appropriate supply of nutrients, including vitamins, minerals, and trace elements. Regulation and control of differentiation and nutrient flow to the epidermal cells play a central role in determining the quality and, consequently, the functional integrity of hoof horn. Decreasing nutrient supply to keratinizing epidermal cells leads to horn production of inferior quality and increased susceptibility to chemical, physical, or microbial damage from the environment. A growing body of evidence suggests that hormones, vitamins, minerals, and trace elements play critical roles in the normal development of claw horn and correct keratin formation.

Permeation of ciclopirox across porcine hoof membrane: effect of pressure sensitive adhesives and vehicles

The purpose of this study was to investigate the effects of various pressure sensitive adhesives (PSA) on the penetration of ciclopirox across porcine hoof membrane. In addition, the influence of various vehicles on the permeation of ciclopirox from a PSA matrix across porcine hoof membrane was evaluated using a plastic penetration chamber containing poloxamer gel at 32 degrees C. Ciclopirox in poloxamer gel was extracted, derivatized and analyzed by HPLC. Ciclopirox showed highest permeability from an acrylic adhesive with a hydroxyl functional group, and this was followed by styrene-isoprene-styrene, styrene-butadiene-styrene, silicone and polyisobutylene adhesives in order. In addition, N-methyl-2-pyrrolidone (NMP), polypropylene glycol 400 (PPG 400), dimethylsulfoxide (DMSO), Labrasol, mercaptoethanol and Transcutol showed excellent permeation enhancing effects in a styrene-isoprene-styrene adhesive. A porcine hoof membrane treated with NMP changed from the non-helical phase to the helical phase, and another treated with DMSO showed a S=O peak shift to lower wavelength.

Physiological changes in the concentrations of biotin in the serum and milk and in the physical properties of the claw horn in Holstein cows

Physiological changes in the concentrations of biotin in the serum and milk and in the physical properties of the claw horn were examined in Holstein cows. A lower concentration of biotin in the serum and a higher concentration of biotin in milk were found during early and late lactation and during the dry period, and a significant (p<0.05) inverse correlation was found between serum and milk biotin concentrations. A high moisture content and a low level of hardness of the claw horn were found during mid-lactation. Our results indicate that change in the serum biotin concentration probably results from the loss of biotin in the milk of cows during each stage of lactation and also confirm that the moisture content and hardness of the claw horn undergo physiological changes.

Activity levels of 137Cs and 40K in the skin and the cutaneous organs of a cow

We have performed an extensive study to determine the activity distributions of radiocesium (137Cs) and of the radioisotope 40K of potassium in the whole body of a cow. ICRP assumes that cesium and potassium are distributed homogeneously throughout the whole body of an organism. The current investigation measured concentrations of 137Cs and 40K in components of the skin, horns, and hooves of a cow. Activity levels of 137Cs were caused by the long-term ingestion following the Chernobyl fallout, whereas the naturally occurring potassium (40K) is an essential part of cow's normal diet. The cow was born at the time of the fallout following the Chernobyl accident and had ingested heavily contaminated forage during its entire lifetime. Activities of 137Cs and 40K were determined simultaneously by gamma spectrometry. All activities are related to the day of slaughter and include also corrections for self attenuation of photons caused by the different densities of the samples. Radionuclide concentrations in samples were corrected for moisture losses incurred during freezing and sample preparation. Surface contamination on the skin was estimated by rinsing it in heated water followed by removal of the epidermis and hair. In comparison with the activities of the components of the skin we observed a considerable amount of external contamination on the surface of the skin. But with respect to whole body countings of the animal this amount of external contamination appears to be negligible. It was found that activity ratios of 137Cs to 40K are greater than 1 in all measured components. The average activity concentrations of 137Cs and 40K in the common integument are 23.3 Bq kg(-1) and 13.3 Bq kg(-1), respectively. The highest activity concentrations of 137Cs and 40K were measured in clean hair and hypodermis. Despite being its largest organ, the cow's skin contains probably less than 1% of the animal's whole body 137Cs activity.

Basement membrane integrity and keratinization in healthy and ulcerated bovine hoof tissue

Damage to, or deterioration of, the keratinized horn tissue of the bovine hoof claw culminates ultimately in the development of solear ulceration. We have observed abnormal keratin distribution at the site of solear ulceration in the bovine claw that may be due to alteration of the positional cues of the keratinocytes. In this study we have characterized key cell biological changes associated with ulceration in the claw that may precipitate abnormal keratinization. Loss of basement membrane at sites of ulceration was found by immunofluorescent detection of laminin and integrins. In other tissues, basement membrane breakdown results from degradation by matrix metalloproteinases (MMPs). Similarly, elevated levels of MMPs 2 and 9 were observed in ulcerated bovine claw tissue both by zymography and, quantitatively, by assay of enzyme activity. In the sole of claws that contained an ulcer, tissue distal to the ulcer site also had elevated MMP 2 when compared with healthy sole tissue from the same animals, as did sole tissue of claws recovering from ulceration. Tissue inhibitor of metalloproteinase 2 (TIMP 2) was detected by ELISA in healthy tissue. TIMP 2 tended to be lower in diseased tissue distal to ulcer sites, and was significantly lower in ulcerated tissue. MMP 2 was located by immunofluorescence in the dermal and basal epidermal region of sole tissue, in the region of the basement membrane. Increased punctate staining of material in the dermis was associated with ulcerated material. ELISA of TIMP 2 in tissue extracts enriched for dermis or epidermis confirmed that the inhibitor was located predominantly in the dermis. To investigate a possible causal relationship between basement membrane anchorage and epidermal keratinization, the effect of function-blocking antibodies to laminins and integrins was tested in tissue explant cultures prepared from healthy sole tissue. Anti-integrin antibody treatment had no effect on either protein or DNA synthesis. In contrast, in the presence of anti-laminin antibody, protein synthesis was decreased in a concentration-dependent manner, a significant effect being observed at the highest concentration after treatment for 24 h. At this concentration, DNA synthesis was also decreased after 48 h of culture, an effect that may be relevant to a hibernal reduction in claw cell turnover, and the associated seasonal vulnerability of cows to claw damage. The results provide evidence for basement membrane disruption at ulcer sites, and an increased potential for disruption in the diseased claw, and a causal link between this and abnormal epidermal keratinization. Basement membrane disruption is in turn associated with reciprocal changes in MMPs and their inhibitors, favouring extracellular proteolysis. Whether MMP activation is the primary cause of dermal-epidermal deterioration and, if so, how MMP activation is triggered, remains to be determined.

Biomechanical and histopathological changes in the support structures of bovine hooves around the time of first calving

Hooves were removed from heifers killed two weeks before calving (C-2), and four and twelve weeks post-calving (C+4 and C+12), and from age-matched maiden heifers. Segments were dissected from the anterior walls of lateral hind claws, to include horn, corium and bone, and the biomechanical properties were measured. There was reduced rigidity, both overall and at a physiologically appropriate displacement of 2 mm, and a greater displacement was required to reach initial and maximum support in the hooves of calving, compared with maiden, heifers. Histological examination revealed widened and distorted interdigitating laminae, progressing to C+12 in the hind claws, but with evidence of recovery in the front claws after C+4. Increased connective tissue strength from dorsal to ventral hoof segments was correlated with protein, proteoglycan, pro- and activated matrix metalloproteinase-2, and tissue inhibitors of metalloproteinases, and was inversely correlated with fat, water and collagen content. This implies that mechanical changes reflect alterations in the biochemistry of the connective tissue. This evidence supports the hypothesis that primary causal events associated with calving weaken the connective tissue of the hoof suspensory apparatus, leading to increased susceptibility to clinical lameness associated with sole ulcers and white line disease.

Diffusion of mepivacaine between adjacent synovial structures in the horse. Part 1: forelimb foot and carpus

This paper tests the hypothesis that the local analgesic agent mepivacaine diffuses between adjacent equine synovial structures in the forelimb and with greater frequency than latex, gelatine dye or contrast media. We report the incidence of diffusion of mepivacaine between the distal interphalangeal joint (DIPJ) and navicular bursa (NB) of the forelimbs and between the intercarpal (IC) and radiocarpal (RC) joints of 31 fresh equine cadavers. The DIPJ of one forelimb and the NB of the contra lateral forelimb and the RC joint of one forelimb and the IC joint of the contra lateral forelimb were injected with mepivacaine. After flexion and extension of the joints, synovial fluid was obtained from the synovial structures adjacent to the injected synovial structures. The concentration of mepivacaine in these samples was determined using an enzyme linked immunosorbent assay. For samples obtained by dilution of synovial fluid, the concentration of mepivacaine was determined by comparing the concentrations of urea in the diluted synovial fluid and the concentration of serum urea. Mepivacaine diffused from the DIPJ to the NB or from the NB to the DIPJ in 25/25 (100%) limbs. Mepivacaine diffused from the IC to RC joints in 24/25 (96%) limbs and from the RC to IC joints in 21/25 (84%) limbs. It was detected at concentrations >0.3 mg/l in 9/25 (36%) of IC joints after RC joint injection and in 25/25 (100%) of the NB after DIPJ injection; at concentrations >100 mg/l in 2/25 (8%) of IC and RC joints and 12/25 (48%) of NB following DIPJ injection; and at concentrations >300 mg/l in 1/25 (4%) in the IC joints following RC joint injection and in 11/25 (44%) of DIPJ following NB injection. The results show greater diffusion of mepivacaine between adjacent synovial structures than assumed from previous anatomical, latex injection and contrast arthrographic studies. This study showed that commonly performed intrasynovial analgesic techniques in the forelimb of the horse are not as specific as previously reported.

Comparison of two hard keratinous substrates submitted to the action of a keratinase using an experimental design

The influence of temperature, pH, keratinase concentration, substrate concentration and incubation time on the soluble proteins released by a new keratinase from Doratomyces microsporus was studied with a second-order experimental design. Only 15 or 18 spectrophotometric analyses were required to determine the optimal experimental conditions for this keratinase on nail and hoof. This study was carried out by measuring, according to Smith's method, the concentration of soluble proteins released by the enzyme on two substrates: nails and sheep hooves. Results give optimum conditions for the keratinase to release the soluble proteins: pH 8.2, keratinase concentration 0.14% (weight of keratinase lyophilisate/final volume) and substrate concentration 5% (weight of nail powder/final volume) for nails; temperature 38.8 degrees C, pH 9, substrate concentration 5% (weight of hoof powder/final volume) and a 5 h 55 min incubation time for hooves.

Expression of interleukin-1beta in the digital laminae of horses in the prodromal stage of experimentally induced laminitis

OBJECTIVE

To study expression of interleukin-1beta (IL-1beta) in the digital laminae of horses in the prodromal stage of experimentally induced laminitis.

ANIMALS

8 healthy adult horses with no signs of laminitis.

PROCEDURES

Black walnut extract was administered via nasogastric tube to 4 horses, and water was administered to the remaining 4 (controls). Complete blood counts and physical examinations were performed every 30 minutes after administration of black walnut extract or water. General anesthesia was induced when total WBC count decreased by 30% in horses given the black walnut extract and 3 hours after water administration in control horses. The left forefoot was perfusion fixed with neutral-buffered 10% formalin, and paraffin-embedded sections of the digit were used for in situ hybridization with an equine-specific IL-1beta probe.

RESULTS

IL-1beta mRNA expression was observed in perivascular cells of the small laminar venules and capillaries in all 4 horses given black walnut extract and in interstitial cells remote from the microvasculature in 1 of the 4. Other cellular components of the laminar tissue and cellular components of the digital arterioles and veins did not exhibit IL-1beta mRNA expression. Expression of IL-1beta mRNA was not detected in laminae from control horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that IL-1beta mRNA is expressed by perivascular cells in the laminar tissues of horses in the prodromal stage of experimentally induced laminitis. This provides evidence of an inflammatory process during the prodromal stage of laminitis, indicating that local digital proinflammatory cytokine expression may be an initiating factor in laminitis.

Cytokeratins of the matrices of the chestnut (torus carpeus) and periople in horses with acute laminitis

OBJECTIVES

To determine whether there is a change in the expression of cytokeratins in the epidermal cells of the non-weight-bearing parts of the limb in horses with acute laminitis and thus determine whether the morphologic changes that develop in the periople and chestnut (torus carpeus) of horses early in acute laminitis are caused by inhibition of keratinocyte differentiation.

ANIMALS

8 horses with acute laminitis.

PROCEDURE

Tissue specimens were obtained from the chestnuts of all 8 horses and from the stratum externum of the hoof wall of 3 horses. Tissue specimens were obtained within 48 hours of the first clinical signs of laminitis. The cytokeratins were characterized by 1- and 2-dimensional gel electrophoresis, and the tissue distribution of the cytokeratins was studied by immunohistochemical staining.

RESULTS

The biochemical findings indicated that the epidermal cells of tissues from horses affected by laminitis contained the same set of cytokeratins as corresponding tissues from clinically normal horses. Immunohistochemistry on sections from specimens of horses with laminitis versus clinically normal horses indicated a difference in the expression of cytokeratin in the basal cells in the matrix of the stratum externum of the hoof wall and in the matrix of the chestnut of horses with laminitis in which the most severe morphologic changes were observed.

CONCLUSIONS

Inhibition of keratinocyte differentiation, as observed by immunohistochemical changes, in cells in parts of the chestnut and periople may indirectly indicate that the observed epidermal changes in horses with laminitis are primary and are unaffected by weight-bearing.

Dermatopharmacology of ciclopirox nail lacquer topical solution 8% in the treatment of onychomycosis

Ciclopirox is a synthetic hydroxypyridone antifungal agent. In contrast to the azoles, glucuronidation is the main metabolic pathway of ciclopirox; therefore interactions with drugs metabolized via the cytochrome P450 system are unlikely Ciclopirox is also distinct from the common systemic agents, which interfere with sterol biosynthesis. In fact, ciclopirox chelates trivalent cations (such as Fe3+), inhibits metal-dependent enzymes that are responsible for degradation of toxic metabolites in the fungal cells, and targets diverse metabolic (eg, respiratory) and energy producing processes in microbial cells. Ciclopirox is a broad spectrum antimicrobial with activity against all the usual dermatophytes as well as yeast and nondermatophyte molds. It has demonstrated activity against gram positive and negative bacteria, including resistant strains of Staphlococcus aureus. Ciclopirox exhibits fungal inhibitory activity (minimum inhibitory concentration < 4 microg/mL for dermatophytes) as well as fungicidal activity; to date resistance to the drug has not been identified. Ciclopirox has been formulated in a nail lacquer delivery system. After evaporation of volatile solvents in the lacquer, the concentration of ciclopirox in the remaining lacquer film reaches approximately 35%, providing a high concentration gradient for penetration into the nail. Radiolabel data demonstrate penetration into infected nails after only 1 application of the lacquer. Ciclopirox nail lacquer is a topical product that provides an active fungicidal agent in a delivery system capable of promoting nail penetration. With repeated applications, the antifungal agent is homogeneously distributed through all layers of the toenail achieving concentrations of ciclopirox in excess of inhibitory and fungicidal concentrations for most pathogens. Although ciclopirox readily penetrates nails, very low levels of ciclopirox are recoverable systemically, even after chronic use. Ciclopirox nail lacquer 8% is a topical product that provides an active fungicidal agent in a delivery system capable of penetrating nails.

Cytokeratins of the stratum medium and stratum internum of the equine hoof wall in acute laminitis

The cytoskeleton of living keratinocytes consists mainly of cytokeratins that have polymerised into intermediate filaments. The aim of this study was to describe the expression of cytokeratins in the living epidermal cells of the weight-bearing parts of the equine hoof wall during acute spontaneous laminitis. A total of 9 hooves from 3 horses subjected to euthanasia within 48 h of the first clinical signs of laminitis were sectioned and examined. The cytokeratins in the stratum medium and stratum internum of the hoof wall were characterized by 1- and 2-dimensional gel electrophoresis, and the tissue distribution of the cytokeratins was studied by immunohistochemical staining. The biochemical results showed the same set of cytokeratins as was seen in 8 normal horses, reported on previously, used as controls. The immunohistochemical results indicated a difference between normal horses and horses with acute laminitis in the content of cytokeratins in the basal cells of the matrix of the stratum medium of the hoof wall and in the basal and suprabasal cells in the stratum internum at the mid level of the hoof wall. However, no conclusion could be drawn as to whether this change in the cytokeratin distribution in laminitis was primary or was caused by the initiation of the local tissue-repairing process.

Chromatographic approach to study beta-cyclodextrin as a promoter of the penetration of bifonazole into keratinic tissue

A high-performance liquid chromatographic method for the determination of bifonazole in dimethyl sulfoxide solvent was developed to study its penetration into sheephoof. The analytical method was linear over the concentration range studied, i.e., from 0.1 mg/ml to 1 mg/ml. The relative standard deviation was less than 2%. The data obtained showed that complex forming with beta-cyclodextrin greatly improved the penetration of bifonazole.

The digital pathologies of chronic laminitis

This review indicates that the patient-to-patient uniqueness commonly seen in chronic laminitis represents the variable presence of the digital pathologies. Although some degree of mechanical failure is always present, the secondary metabolic and growth dysplasias, vascular pathologies, and sepsis may or may not be evident. The presence and severity of these pathologies appear to have a more significant impact on the prognosis of individual cases than does the displacement of the distal phalanx. It should be reiterated that it is often the combined presence of these individual pathologies that gives rise to the patient that is totally refractory to treatment. In the absence of these pathologies, many horses with significant displacement of the distal phalanx are not in pain and are not in need of treatment. It thus follows that a key to the improved rehabilitation of difficult patients is focusing research on the physiopathology and diagnosis of these nonmechanical problems.

Expression of endothelin in equine laminitis

Biosynthesis of endothelin-1 (ET-1), the most potent endogenous vasoconstrictor yet identified, is increased following myocardial infarction (MI) in man. Pathological events which occur in the connective tissues of the equine hoof during laminitis are similar in some respects, to changes occurring in the myocardial connective tissues following MI in man. The objective of this study was to determine whether ET-1 expression in connective tissues obtained from the hoof of laminitic horses is increased compared with tissues obtained from healthy horses. Expression of ET-1 in connective tissues of the equine hoof was measured following tissue extraction from 3 groups of horses: horses in which acute laminitis had been induced by the administration of starch; chronically foundered horses; nonlaminitic horses. The concentration of ET-1 in laminar connective tissues obtained from all laminitic horses (1573.0 +/- 392.8 pg/g of tissue; n = 10) was increased when compared with tissues obtained from nonlaminitic horses (392.5 +/- 117.4 pg/g of tissue; n = 5) (P<0.05). The concentration of ET-1 in laminar connective tissues obtained from the experimentally induced, acute laminitic horses (1043.6 +/- 254.4 pg/g of tissue; n = 7) and from the spontaneously affected, chronic laminitic horses (2808.3 +/- 878.6 pg/g of tissue; n = 3) was increased compared with the control group (P<0.05, P<0.01, respectively). The concentration of ET-1 in laminar connective tissues obtained from the chronic laminitic horses was greater than that of the experimentally induced, acute laminitic group (P<0.05). It is suggested that the data provide a strong argument that increased ET-1 expression in the connective tissues of the equine hoof represent a potentially important and hitherto unrecognised component of the pathophysiology of equine laminitis. Further studies are needed to determine whether inhibitors of ET-1 converting enzyme or antagonists of ET-1 receptors might be useful in the treatment and prevention of laminitis in horses.

Effect of endocrine and paracrine factors on protein synthesis and cell proliferation in bovine hoof tissue culture

Laminitis is a major cause of lameness in dairy cattle, and is widely attributed to a defect in the horny tissue that gives the hoof its mechanical strength. Defective horn is associated with, and may be preceded by, impaired keratin deposition in the hoof epidermis. The cause of abnormal keratin deposition is not easily identified but, like epidermal keratinization in other tissues, is likely to be controlled by hormones and the paracrine action of locally produced growth factors. The hormonal regulation of keratin synthesis and cell proliferation in the bovine hoof was studied using tissue explants in organ culture. As the highest incidence of laminitis is in early lactation, the study focused on insulin, cortisol and prolactin, three hormones implicated in lactogenesis and galactopoiesis. Incubation of tissue explants for 24 h in medium containing insulin (10-5000 ng/ml) stimulated protein synthesis measured by incorporation of 35S-labelled amino acids. Histochemical examination showed that insulin binding co-localized with the site of protein synthesis. Insulin also stimulated DNA synthesis, an index of cell proliferation, which was measured by incorporation of [3H]methyl thymidine. Cortisol (10-5000 ng/ml) decreased protein synthesis, whereas prolactin (10-5000 ng/ml) had no significant effect on protein or DNA synthesis. Epidermal growth factor (10-200 ng/ml), a potent inhibitor of keratinization in other tissues, stimulated protein synthesis compared with untreated controls. Epidermal growth factor binding was located microscopically to the germinal and differentiating epidermal layers. SDS-PAGE and fluorography showed that the population of proteins synthesized in the presence of any hormone or growth factor combination did not differ from that in untreated controls and included the keratins involved in horn deposition. The results show that bovine hoof keratinization is under endocrine and growth factor control, and suggest that systemic changes in lactogenic hormones may act to inhibit keratin deposition.

Decreased glucose metabolism causes separation of hoof lamellae in vitro: a trigger for laminitis?

Explants of horses' hooves remained intact for up to 8 days when incubated in Dulbecco's modified Eagle medium (D-MEM) containing 25 mmol/l glucose but separated within 36 h when incubated in saline. The separation occurred between the basal epidermal cells and their basement membrane which is characteristic of the hoof separation that occurs in laminitis. Separation of hoof explants was prevented by addition of glucose to saline and was induced by adding 2-deoxyglucose or aminophenylmercuric acetate to D-MEM. Glucose consumption by the hoof explants was inhibited by 2-deoxyglucose and aminophenylmercuric acetate. The explants consumed relatively large amounts of glucose during the first 2 days of incubation and then little over the next 6 days. Despite the reduced glucose consumption, the hoof explants did not separate over 8 days of incubation. The results indicated that the integrity of the hoof explants was initially dependent on consumption of glucose and provide a possible explanation for the development of laminitis caused by conditions such as carbohydrate overload, acute inflammatory conditions, corticosteroid therapy and hyperlipidaemia. It would be expected that these conditions would induce a major hormonally-mediated metabolic shift away from glucose consumption by many peripheral tissues. It is suggested, therefore, that if the metabolic change occurred faster than the hoof tissue could adapt to an alternative energy substrate, then hoof separation and laminitis would occur.

A permeability barrier in the dorsal wall of the equine hoof capsule

The permeability barrier in the dorsal wall of the equine hoof capsule was studied by means of horseradish peroxidase (HRP) in 0.9 N saline solution as a water soluble tracer. Section were treated with 3'3'-diaminobenzidine tetrachloride (DAB) and before dissection the quality of the horn of feet from 10 horses was assessed and given a subjective grade as either good or poor. Blocks of tissue from each horse were left in either an oven at 60 degrees C or in water for 2 weeks before treatment in HRP, sectioning and DAB solution. Regions observed were i) outer surface, ii) outermost layers of the horn, iii) cut edge of the outer layer, iv) inner layer of horn, v) cut edge of the inner layer and vi) laminae. Horn deemed to be normal horn and of good 'quality' showed very slight penetration of HRP 3-5 cell layers deep in the outer layer. The cut edge of the outer layer of the wall of the 'normal' horn also showed minimal penetration of HRP through the intercellular spaces. The cut edge of the inner layers of the wall of normal, good quality horn showed penetration of the tracer up to 20 cell layers deep, with HRP in both the intercellular spaces and within the cells. In contrast, sections of horn from horses with brittle feet showed deep cracks in the outer surface into which the HRP had penetrated. Good quality horn showed no change in the position of the permeability barrier after soaking in water for 14 days, but the brittle horn showed an increase in permeability to HRP. In brittle horn, reaction product was seen deep within the section in the intercellular spaces of the intertubular horn only. Placing horn in an oven had no effect on the permeability barrier. The permeability barrier of the dorsal wall of the equine hoof capsule differs with the layer of the wall. Horn considered to be of poor quality had a weaker permeability barrier than horn of good quality.

In-vitro permeability of the human nail and of a keratin membrane from bovine hooves: prediction of the penetration rate of antimycotics through the nail plate and their efficacy

In contrast to the partition coefficient octanol/water the molecular size of penetrating drugs has a noticeable influence on the permeability of the human nail plate and a keratin membrane from bovine hooves. The relationship between permeability and molecular weight is founded on well-established theories. The correlation between the permeability of the nail plate and that of the hoof membrane allows a prediction of the nail permeability after determination of the drug penetration through the hoof membrane. The maximum flux of ten antimycotics (amorolfine, bifonazole, ciclopirox, clotrimazole, econazole, griseofulvin, ketoconazole, naftifine, nystatin and tolnaftate) through the nail plate was predicted on the basis of their penetration rates through the hoof membrane and their water solubilities. An efficacy coefficient against onychomycoses was calculated from the maximum flux and the minimum inhibitory concentration. Accordingly, amorolfine, ciclopirox, econazole and naftifine are expected to be especially effective against dermatophytes, whereas in the case of an infection with yeasts only, amorolfine and ciclopirox are promising.

Cellular features of differentiation in the nail

Biochemical analysis indicated that the human nail plate contains two distinct types of keratin (skin-type and hair-type keratins), and several population of keratinocytes are thought to be associated with development of the nail. To elucidate the nature of the differentiation occurring in nail development, we examined the patterns of molecular markers relevant to the course of differentiation in the skin and hair in the nail matrix as well as in cultured nail cells. The nail matrix was characterized by the mutually exclusive localization of skin-type and hair-type markers, while in the apical matrix the localization of two groups of keratins partially overlapped. Double-label immunofluorescence showed the existence of unusual cells coexpressing both keratins, thereby indicating that the nail matrix consists of skin-type and hair-type and additionally intermediate-type differentiating cells. The cultured cells taken from the ventral matrix which develop under hair-type differentiation in vivo were found to express skin-type along with hair-type keratins, suggesting alteration of the pathway of differentiation in vitro. The cellular diversification as seen in in vitro cultured cells provides further insight into nail differentiation which is related to the multiple patterns of keratin expression that generate in the nail matrix.