Increased glycation and pigmentation of collagen in aged and young parabiotic rats and mice

Surgical approaches to create murine models of human wound healing

Wound repair is a complex biologic process which becomes abnormal in numerous disease states. Although in vitro models have been important in identifying critical repair pathways in specific cell populations, in vivo models are necessary to obtain a more comprehensive and pertinent understanding of human wound healing. The laboratory mouse has long been the most common animal research tool and numerous transgenic strains and models have been developed to help researchers study the molecular pathways involved in wound repair and regeneration. This paper aims to highlight common surgical mouse models of cutaneous disease and to provide investigators with a better understanding of the benefits and limitations of these models for translational applications.

Skin aging: postulated mechanisms and consequent changes in structure and function

Aging is a complex process influenced by telomere shortening and damage to cellular DNA. New insights into age-associated decrements in DNA damage repair are reviewed. Age-associated gross, histologic, and functional cutaneous deficits are delineated. Different treatment options for aged skin are examined.

Changes in biomechanical properties, composition of collagen and elastin, and advanced glycation endproducts of the rat aorta in relation to age

During ageing and senescence the aorta becomes stiffer and its elasticity is reduced. The mechanism causing this increased stiffness of the aortic wall was studied using a rat model. Ring-shaped samples were prepared from the thoracic aorta of three groups of rats aged 4.5, 14 and 27 months, representing young, adult and old animals. Analysis of the static biomechanical properties showed increased diameter (2.20 +/- 0.03 mm) and increased stiffness (4.0 +/- 0.2 mN) of aortic samples from old rats compared with adult rats (1.82 +/- 0.02 mm and 3.0 +/- 0.1 mN, respectively). The total hydroxyproline and elastin content per sample was not changed. However, the hydroxyproline content/mm2 of the aortic wall was reduced by 20% and the elastin content/mm2 of the aortic wall was reduced by 19% comparing the old with the adult rats. No differences were found in the pyridinoline concentrations between old and adult rats. The collagen- and elastin-associated fluorescence was determined as a marker of advanced glycation endproducts (AGE). Both parameters were increased in the old rats compared with the adult rats by 42% and 17%, respectively, and positively correlated with stiffness at physiological loads. A positive correlation between collagen-associated fluorescence and maximum stiffness was found as well. In conclusion, the age-related increase in stiffness of the aorta was associated with increased diameter, reduced collagen and elastin contents/mm2 of the aortic wall, increased fenestration of elastic laminae and accumulation of fluorescent material in collagen and elastin.

Longevity effect of chromium picolinate--'rejuvenation' of hypothalamic function?

The first rodent longevity study with the insulin-sensitizing nutrient chromium picolinate has reported a dramatic increase in both median and maximal lifespan. Although the observed moderate reductions in serum glucose imply a decreased rate of tissue glycation reactions, it is unlikely that this alone can account for the substantial impact on lifespan; an effect on central neurohormonal regulation can reasonably be suspected. Recent studies highlight the physiological role of insulin as a modulator of brain function. I postulate that aging is associated with a reduction of effective insulin activity in the brain, and this contributes to age-related alterations of hypothalamic functions that result in an 'older' neurohormonal milieu; consistent with this possibility, diabetes leads to changes of hypothalamic regulation analogous to those seen in normal aging. Conversely, promoting brain insulin activity with chromium picolinate may help to maintain the hypothalamus in a more functionally youthful state; increased hypothalamic catecholamine activity, sensitization of insulin-responsive central mechanisms regulating appetite and thermogenesis, and perhaps trophic effects on brain neurons may play a role in this regard. Since both the pineal gland and thymus are dependent on insulin activity, chromium may aid their function as well. Thus, the longevity effect of chromium picolinate may depend primarily on delay or reversal of various age-related changes in the body's hormonal and neural milieu. A more general strategy of hypothalamic 'rejuvenation' is proposed for extending healthful lifespan.

Ultrastructural morphometry of matrical changes induced by exercise and food restriction in the rat calcaneal tendon

The ultrastructural morphometry of collagen fibril populations in 24 calcaneal tendons obtained from 12 Fischer 344 rats were studied to elucidate matrical changes induced by food restriction and/or endurance exercise. Rats were randomly assigned to four equal groups: ad libitum control (AC), ad libitum exercise (AE), restricted diet control (RC) and restricted diet exercise (RE) groups. Beginning from 6 weeks of age, animals in the two food restriction groups were fed 60% of the mean food consumption of ad libitum fed rats. Then, starting from 6-7 months of age, the rats in the two exercise groups performed 40-50 min of treadmill running at 1.2-1.6 miles h-1 every day for a total of 10 weeks. Endurance training did not significantly alter body weight, but food restriction with or without exercise resulted in a significant loss of body weight. In ad libitum fed controls, food restriction alone did not significantly alter the mean collagen fibril CSA, but predisposed a preponderance of small-sized collagen fibrils. Endurance training per se induced a significant (32%) increase in mean fibril CSA (P less than 0.05), but this adaptive response to exercise was prevented by food restriction, as indicated by a 33% decline in fibril CSA (P less than 0.05). These findings demonstrate that dietary restriction modifies the adaptation of tendon collagen morphometry in response to endurance training, and that weight loss is better achieved with food restriction than endurance exercise.

Change with age of UV absorbance and fluorescence of collagen and accumulation of epsilon-hexosyllysine in collagen from Wistar rats living on different food restriction regimes

Accumulation of glycation products (as revealed by the thiobarbituric test and hexosyllysine assay) and the pigmented products (350 nm UV absorbance and 370ex/440em nm fluorescence) in aortal and skin collagen was investigated under the conditions of different nutritional regimes. Four groups of animals were tested: (1) ad libitum fed controls, (2) animals which were food restricted throughout their whole life (50% food intake), (3) animals fed ad libitum during their first year of life and then food restricted and (4) animals food restricted when young and fed ad libitum from the age of 1 year onwards. It was shown that all food-restricted animals showed lower levels of glycation and pigmentation products in collagen preparations from skin and aorta. The lowest accumulation was observed in group 4 which exhibited the longest 50% survival (29.4 months, as compared with 18.3 months in normally-fed controls). Of particular interest is the fact that in this group the decreased rate of accumulation of the glycated and pigmented products was preserved even after 1 year of life, i.e., when the animals had a free access to food. Though not directly supporting the glycation theory of aging (Cerami, 1985), our data are indicative of the involvement of glucose metabolism in the ageing process. Correlation between the levels of glycated and pigmented products in aortal and skin collagen as well as the correlation between the rate of accumulation of these products and 50% survival was impossible to establish. Nevertheless, each time that food restriction was imposed on the animals it always resulted in decreased accumulation of glycated and pigmented products and increased 50% survival. Possible mechanisms for this process are discussed.