Zinc chloride inhibits lysine decarboxylase production from Eikenella corrodens in vitro and its therapeutic implications.

OBJECTIVES: Dentifrices containing zinc reduce gingival inflammation and bleeding better than control dentifrices (no zinc). How zinc might work is not understood. We have shown that lysine decarboxylase (LdcE), an enzyme from Eikenella corrodens, converts lysine to cadaverine in dental biofilms. The lack of lysine impairs the dentally attached cell barrier to biofilm, causing biofilm products to leak into junctional epithelium and stimulate inflammation. In year-old beagle dogs, immunization with LdcE, induces antibodies that inhibit LdcE activity and retard gingivitis development. We therefore examined whether a zinc-mediated loss of LdcE activity could explain the beneficial effect of zinc dentifrices. METHODS: We grew E. corrodens in modified tryptic soy broth with or without zinc chloride, and extracted LdcE from the cell surface using a Potter Elvehjem homogenizer. RESULTS: Up to 0.96 mM zinc chloride in the bacterial growth medium did not change cell yield, but reduced the extracted protein content by 41% (R2 = 0.27, p < 0.05) and LdcE activity/mg extracted protein by 85% (R2 = 0.90, p < 0.001). In extracts from cells grown without zinc, 78 times this zinc chloride concentration (73 mM) was required to reduce LdcE activity by 75%. CONCLUSIONS: Zinc ions inhibit the production of protein with LdcE activity at E. corrodens cell surfaces. The zinc ions may attach to cysteine residues that are unique to the N-terminal region of LdcE by interfering with the non-covalent polypeptide assembly that produces enzyme activity. CLINICAL SIGNIFICANCE: Zinc ion-mediated inhibition of LdcE assembly may provide a rationale for the improved control of gingival inflammation by zinc dentifrices.

Biofilm Lysine Decarboxylase, a New Therapeutic Target for Periodontal Inflammation.

BACKGROUND: Lysine, a nutritionally essential amino acid, enters the oral cavity in gingival crevicular fluid (GCF). During oral hygiene restriction (OHR), lysine decarboxylase (LDC) in dento-gingival biofilms converts lysine to cadaverine. Lysine depletion impairs the dental epithelial barrier to bacterial proinflammatory products. Antibodies to LDC from Eikenella corrodens (Ecor-LDC) inhibit LDC activity and retard gingival inflammation in beagle dogs. Whether E. corrodens is the major source of LDC in dental biofilms and whether the lysine analog tranexamic acid (TA) inhibits LDC activity, biofilm accumulation, and GCF exudation in a human gingivitis model were examined. METHODS: Antibodies raised in goats to LDC-rich extracts from E. corrodens cell surfaces were used to inhibit Ecor-LDC and detect it in biofilm extracts using Western blots. Ecor-LDC activity was measured at pH 4.0 to 11.0 and its TA dissociation constant (Ki) at pH 7.0. Young adults used a 5% or 10% TA mouthwash three times daily during OHR for 1 week. RESULTS: Ecor-LDC antibodies and TA inhibited biofilm LDC. Ki of TA for Ecor-LDC was 940 µM. TA reduced plaque index (PI) by downshifting the PI correlation with biofilm lysine content after OHR without TA. GCF was correspondingly suppressed. However, greater TA retention in saliva partially relieved GCF suppression but not biofilm lysine depletion. CONCLUSIONS: TA slightly inhibits LDC but strongly reduces biofilm by inhibiting bacterial lysine uptake. Unfortunately, TA may impair dental epithelial attachments by also inhibiting lysine transporter uptake. Ecor-LDC inhibitors other than lysine analogs may maintain sufficient lysine levels and attachment integrity to prevent periodontal inflammation.

Effects of immunization with natural and recombinant lysine decarboxylase on canine gingivitis development.

Periodontal disease, gingival inflammation (gingivitis) and periodontal attachment loss (periodontitis), causes tooth loss and susceptibility to chronic inflammation. Professionally scaling and cleaning the teeth regularly controls the disease, but is expensive in companion animals. Eikenella corrodens is common in canine oral cavities where it is a source of lysine decarboxylase (LDC). In human dental biofilms (plaques), LDC converts lysine to cadaverine and impairs the gingival epithelial barrier to bacteria. LDC vaccination may therefore retard gingivitis development. Year-old beagle dogs provided blood samples, and had weight and clinical measurements (biofilm and gingivitis) recorded. After scaling and cleaning, two dogs were immunized subcutaneously with 0.2mg native LDC from E. corrodens and 2 sets of four dogs with 0.2mg recombinant LDC purified from Escherichia coli. A third set of 4 dogs was immunized intranasally. Rehydragel(®), Emulsigen(®), Polygen™ or Carbigen™ were used as adjuvant. Four additional pairs of dogs were sham-immunized with each adjuvant alone (controls). Immunizations were repeated twice, 3 weeks apart, and clinical measurements were obtained after another 2 weeks, when the teeth were scaled and cleaned again. Tooth brushing was then stopped and the diet was changed from hard to soft chow. Clinical measurements were repeated after 1, 2, 3, 4, 6 and 8 weeks. Compared with sham-immunized dogs, gingivitis was reduced over all 8 weeks of soft diet after subcutaneous immunization with native LDC, or after intranasal immunization with recombinant LDC in Carbigen™, but for only 6 of the 8 weeks after subcutaneous immunization with recombinant LDC in Emulsigen(®) (repeated measures ANOVA). Subcutaneous vaccination induced a strong serum IgG antibody response that decreased during the soft diet period, whereas intranasal immunization induced a weak serum IgA antibody response that did not decrease. Immunization with recombinant LDC may provide protection from gingivitis if procedures are optimized.

Social anhedonia and schizotypy in a community sample: the Maryland longitudinal study of schizotypy.

Social anhedonia has been employed in psychometric high-risk studies to identify putative schizotypes. To date, this research has focused almost exclusively on college samples. The current study sought to examine the validity of social anhedonia as an indicator of risk for schizophrenia-spectrum disorders within a community sample. Furthermore, we evaluated the role of other individual difference variables in accounting for variable clinical severity within the social anhedonia group including trait affectivity, social support, and family environment. Following the mailed questionnaire screening of 2434 eighteen-year olds, laboratory assessments were conducted with individuals identified as being high in social anhedonia (n=86) and a comparison sample (n=89). Compared with the control group, individuals in the social anhedonia group were found to have higher rates of mood disorders, elevated schizophrenia-spectrum personality disorder characteristics, greater negative symptom characteristics, and lower global functioning. Individuals within the social anhedonia group also reported greater trait negative affectivity, lower positive affectivity, less social support, and more family conflict. Low social support and problematic family environment were found to be related to elevations in spectrum personality disorder characteristics and poorer functioning within the social anhedonia group. These cross-sectional findings from a community sample provide further support for social anhedonia as a possible indicator of schizotypy.

Behavioral signs of schizoidia and schizotypy in social anhedonics.

Social anhedonia appears to be a promising indicator of Meehl's construct of schizotypy. While findings from diagnostic, cognitive, and psychophysiological studies have supported the validity of social anhedonia as an indicator of schizotypy, the behavioral characteristics of these putative schizotypes are not yet fully understood. This study utilized a rating system for behavioral signs of schizoidia and schizotypy to determine whether atypical interpersonal behaviors were observable in social anhedonics and to examine if these behavioral signs provide unique information, beyond traditional symptom ratings, in the identification of putative schizotypes. A community sample of 170 18-19-year-olds (85 social anhedonics, 85 controls) received diagnostic evaluations which were videotaped and subsequently rated for behavioral signs of schizoidia and schizotypy. Compared to controls, the social anhedonia group displayed significantly more behavioral signs characteristic of schizoid and schizotypal personality disorders. Behavioral signs of schizoidia accounted for a significant amount of group variance even after controlling for clinical symptom ratings. These results indicate that social anhedonics display interpersonal behaviors consistent with risk for schizophrenia-spectrum disorders and that these behavioral signs convey information about group status that is not accounted for by traditional clinical interview ratings of symptomatology.

Examining the latent structure of negative symptoms: is there a distinct subtype of negative symptom schizophrenia?

Negative symptoms have emerged as a replicable factor of symptomatology within schizophrenia. Although rating scales provide assessments along dimensions of severity, categorization into a negative symptom subtype is typically conducted. A categorical view of negative symptoms is best reflected in the proposal that enduring, primary negative symptoms, or deficit symptoms, reflect a distinct subtype of schizophrenia . Despite an accumulation of findings that support a categorical conceptualization, the data are also consistent with a dimensional-only model where negative symptom subtypologies simply reflect an extreme on a continuum of severity. Using taxometric statistical methods , the present study examined whether a taxonic, or latent class, model best describes negative symptoms in a sample of 238 schizophrenia patients. In order to obtain more stable estimates of symptoms, ratings on the Scale for the Assessment of Negative Symptoms [Andreasen, N.C., 1982. Negative symptoms in schizophrenia: Definition and reliability. Arch. Gen. Psychiatry 39, 784-788.] were averaged across two assessments over a 6-month period. Two taxometric methods, maximum covariance analysis (MAXCOV) and mean above minus below a cut (MAMBAC) identified a latent class or taxon with a base rate of approximately 28-36%. Members of the negative symptom taxon differed from the nontaxon class in that taxon members were more likely to be male and demonstrated poorer social functioning. Taxon and nontaxon schizophrenia patients did not differ in psychotic or affective symptoms. The findings converge to provide support for a categorical view of negative symptoms. Further research is required to replicate the present taxonic findings and to examine characteristics (including possible etiological factors) associated with this negative symptom taxon.

Affectivity in the problem-solving interactions of schizophrenia patients and their family members.

This study sought to examine the relationship between symptomatology and the affect expressed between individuals with schizophrenia and their family members. It was hypothesized that, because of their impact on patient social behavior and potential burden on relatives, greater negative symptoms would be associated with less emotional expression in patients but would be related to the greater expression of negative emotions in their relatives within a problem-solving discussion. Informed by research on the structure of emotion, a broad assessment of affect, including Negativity, Positivity, and Disengagement, was utilized to examine affect expressed by patients with schizophrenic disorders (N=91) and their family members during videotaped problem-solving discussions. Although individuals with schizophrenia were comparable to their family members in displays of Negativity, patients displayed less Positivity and greater Disengagement. Greater negative symptoms (in particular blunted or flat affect) were related to a general diminution of affective expression in the schizophrenia group. However, negative symptoms were unrelated to the emotional expression of family members. Other symptoms such as thought disorder and mood symptoms of anxiety, depression, and hostility were not related to displays of affect by either patients or their family members. The findings indicate the importance of examining domains of affect other than negativity and demonstrate that negative symptoms are related to interpersonal displays of affect in schizophrenia. Additionally, these results suggest that schizophrenic symptoms, by themselves, may contribute little to the conflict between patients and their family members.