Effect of adjuvant arthritis on collagenase and certain lysosomal enzymes in relation to the catabolism of collagen

A novel endogenous corticotropin release inhibiting factor

ACTH is the major regulator of the body's adaptive response to stress and the physiological stimulus for glucocorticoid secretion. A hypothalamic corticotropin release inhibiting factor (CRIF) that inhibits ACTH synthesis and secretion has long been postulated but was not characterized until recently. We have recently identified a 22 amino acid peptide, prepro-thyrotropin releasing hormone (TRH) 178-199 that inhibits basal and stimulated ACTH synthesis and secretion in vitro and stress-induced ACTH secretion in vivo. Prepro-TRH 178-199 is abundant in several brain regions, including the external zone of the median eminence, where its concentration changes in response to stress. We propose that this peptide is a physiological regulator of ACTH production: an endogenous CRIF. Because prepro-TRH 178-199 is encoded within the same precursor as TRH, its expression is likely to be negatively regulated by thyroid hormones leading to changes in endogenous glucocorticoid levels. Streptococcal cell wall (SCW)-induced inflammation, a model of rheumatoid arthritis (RA), was alleviated after long-term thyroxine treatment. Inversely, a hypothyroid milieu led to decreased basal hypothalamic-pituitary-adrenal activity, but increased expression of IL-1 beta and MIP-1 alpha, specific markers for RA in humans. These results suggest that this putative CRIF may be an important component in the development of RA and that regulation of prepro TRH may be highly relevant to the development of other autoimmune diseases that are also exacerbated by low endogenous glucocorticoid levels.

Thyroxine administration prevents streptococcal cell wall-induced inflammatory responses

Administration of streptococcal cell wall (SCW) preparation induces an inflammatory response in susceptible animals that is a model frequently used for rheumatoid arthritis. The degree of inflammation produced by SCW is greatly enhanced by low endogenous levels of glucocorticoids due to diminished hypothalamic-pituitary-adrenal activity. Because decreased glucocorticoid production is known to occur in the hypothyroid state, we tested whether hypothyroidism would increase, and conversely, whether hyperthyroidism would decrease, the inflammatory responses to SCW. Adult female Sprague Dawley rats were fed a regular diet (control), L-T4 (T4; hyperthyroid), or 6-propyl-thiouracil (hypothyroid) in drinking water for 7 weeks. Hypothyroidism resulted in elevated plasma levels of TSH and hypothalamic preproTRH messenger RNA (mRNA) while reducing anterior pituitary POMC mRNA and plasma ACTH and corticosterone levels. In contrast, hyperthyroid rats produced opposite results: decreased measures of central thyroid function but increased pituitary-adrenal function. Three days after administration of SCW, macrophage inflammatory protein-1alpha and interleukin-1beta mRNA expression increased dramatically in controls and even further in hypothyroid animals, as measured by Northern blot analysis. In contrast, T4-treated rats showed significant inhibition of these inflammatory markers. Thus, the hyperthyroid state combined with increased endogenous glucocorticoid levels is protective against inflammatory challenges. The inverse relationship between preproTRH expression and pituitary-adrenal function suggests the possibility of a direct inhibitory link connecting the hypothalamic-pituitary-adrenal and thyroid axes, and suggests alternative sites of therapeutic intervention for rheumatoid arthritis and other inflammatory associated disorders.

Adjuvant polyarthritis in rats: is this a satisfactory model for screening anti-arthritic drugs?

The pathological and biochemical features of the polyarthritis in rats induced by Freund's adjuvant are briefly reviewed. The object of this is to highlight recent studies that provide a basis for specifically improving procedures employed in screening the activity and mode of action of anti-inflammatory/antiarthritic drugs--especially those with possible disease modifying activity. Current screening procedures involve the simple measurement of hind-paw or joint swelling. This may not reflect the extent of degradation or systemic changes in arthritis. It is suggested that it is possible to more precisely measure the extent of joint degradation by the following: (1) X-ray monitoring of joints afflicted with the disease, (2) Histological and morphological examination (the latter in alkali cleared--Alizarin stained preparations) of hindlimbs, (3) Quantitative histoenzymic and biochemical analysis of degradative enzymes and inflammatory mediators. Additional to this specific immunological and systemic (blood, liver) changes should be measured in primary screening in recognition that arthritis is a disease not only of joints but involving the immune, hepatic and possibly other organ systems and that these systemic components clearly have effects on joints. Only by a combined analysis of both local joint and systemic changes during drug treatment will it be possible to discriminate new drugs with disease-modifying activity.

Levels of collagenolytic activity, beta-glucuronidase, and collagen prolyl hydroxylase in paws from rats with developing adjuvant arthritis

The collagenolytic activity associated with insoluble collagen fibers separated from homogenates of inflamed paws from rats with adjuvant arthritis was quantitated using EDTA-sensitive solubilization of hydroxyproline as a measure of activity. Approximately 60% of the solubilized hydroxyproline was associated with dialyzable products. The level of collagenolytic activity in the paws increased with time after the induction of adjuvant arthritis and paralleled to a large extent the development of inflammation in both the adjuvant injected (right) hind paw and in the non-injected, contralateral paw. By day 26, the level of free collagenolytic activity in the injected paw had increased to a level 30 times normal while that in the contralateral paw had increased to a level 10 times normal. Treatment of the residues from the injected paws with trypsin resulted in the activation of a latent collagenolytic activity which, on day 26, accounted for approximately 50% of the total activity. The elevated level of collagen prolyl hydroxylase in the inflamed paw suggested that the rate of collagen synthesis was also increased. The activity of beta-glucuronidase increased in the inflamed paw with time after the induction of adjuvant arthritis while that of cathepsin G was elevated as compared to normal in paws removed, 5 but not 22 days after the induction of adjuvant arthritis. The inflamed paw of the adjuvant rat may represent a useful system in which to study the role of collagenolytic enzymes in the destruction of connective tissue by inflammatory lesions.

Effect of adjuvant induced arthritis on the mechanical properties and thermal behavior of skin and tendon

In rats with adjuvant induced arthritis, the mechanical properties and thermal behavior of the skin and tendon were studied during the acute and chronic phase of the disease. Among the mechanical properties, the tensile strength and elastic modulus were found to decrease markedly both in the skin and tendon of arthritic rats while the extensibility did not show any significant change during the course of the disease. The thermal behavior, namely, shrinkage temperature, denaturation temperature, isometric tension and the temperature at isometric tension were decreased appreciably both in the skin and tendon of arthritic rats, the decrease being prominent during the chronic phase of arthritis. Both the mechanical properties and thermal behavior were correlated with biochemical parameters such as total collagen content and the ratio of the total activity of 14C-hydroxyproline of soluble collagens to insoluble collagen. The results support the concept of impaired collagen crosslinking in adjuvant induced arthritis. Prednisolone and L-thyroxine were administered to arthritic rats and the changes in the mechanical properties and thermal behavior of the skin and tendon of arthritic rats were studied. Both prednisolone and L-thyroxine increased the decreased values of tensile strength and elastic modulus of the skin and tendon in adjuvant induced arthritis. Similarly the decreased values in the thermal behavior of arthritic rats were found to be increased by treatment with prednisolone and L-thyroxine. Results indicated correlations with the beneficial action of prednisolone and L-thyroxine on the impaired collagen crosslinking in adjuvant induced arthritis.

Influence of prostaglandins E1 and E2 on collagen metabolism in adjuvant induced arthritis

In rats with adjuvant induced arthritis, the ihnfluence of PGE1 and PGE2 on collagen metabolism was investigated after an injection of 3H-proline, both the specific and total radioactivity of 3H-ydroxyproline being determined in skin collagen fractions and in urine. In untreated animals with adjuvant induced arthritis, a decrease in the collagen synthesis accompanied by a retardation in the conversion of soluble to insoluble collagen was observed. It was also found that the catabolism of collagen is intensified. Subcutaneous administration of PGE1 (1 mg/kg body weight twice daily) to arthritic animals accelerated the conversion of soluble to insoluble collagen and inhibited the catabolism of collagen, but remained ineffective on the decreased synthesis of collagen observed in arthritic animals. PGE2 normalised on the changes in collagen metabolism - accelerated the synthesis of collagen and the conversion of soluble to insoluble collagen and inhibited the catabolism of collagen.

Influence of prednisolone and L-thyroxine on the changes in collagen metabolism in rats with adjuvant-induced arthritis

In rats with adjuvant-induced arthritis the effects of prednisolone and L-thyroxine on the changes in collagen metabolism were investigated both in the skin and tendon during the acute and chronic phase of the arthritis. In untreated animals with adjuvant-induced arthritis, a decrease in the collagen synthesis accompanied by an increase in the catabolism of collagen and a retardation in the conversion of soluble to insoluble collagen were noted both in the skin and tendon during the course of the disease. Prednisolone was found to accelerate the conversion of soluble to insoluble collagen and to inhibit the enhanced catabolism of collagen in rats with adjuvant-induced arthritis. L-Thyroxine accelerated the conversion of soluble to insoluble collagen in adjuvant-induced arthritic rats more effectively than prednisolone but was less effective with regard to the inhibition of enhanced catabolism of collagen. However, the synthesis of collagen in adjuvant-induced arthritis was improved by both prednisolone and L-thyroxine.