The influence of aging and low zinc nutrition on the choroid in the pig: II. The melanosome

Abstract

The effects of low zinc nutrition and aging on central choroidal melanosomes were examined in the pig. Melanosomes of central choroidal melanocytes were morphologically and morphometrically examined in three populations of pigs (young, pregnant and aged), that were maintained on either control (C) or low zinc (LZ) diets. In C groups, the typical melanosomes decreased in size with age, although a subpopulation of larger melanosomes occurred in the oldest group. In contrast, the melanosomes of the animals on LZ diets increased in size significantly in the adult groups. The melanosomes in the pregnant and aged groups were 65% and 30-40% greater than those of the age-matched C groups. Extremely large melanosomes were frequently encountered in adult LZ choroidal melanocytes. Melanogenesis of these large bodies included the formation of one or more outer shells. Fusion of adjacent large melanosomes was also observed. Melanolysosomal-like bodies were observed, particularly among the pigmented cells in the large blood vessel region of C and LZ adults. Melanin dynamics, i.e. its production and breakdown, occurred within choroidal melanocytes throughout much of the lifespan of the pig. This dynamic was greatly influenced by low zinc nutrition, resulting in unusual and aberrant melanin activity.

Zinc Deficiency Leads to Lipofuscin Accumulation in the Retinal Pigment Epithelium of Pigmented Rats

“…We assume that melanosomes without adequate uptake of zinc change their structural and probably functional properties, which was shown before in pig eyes [31]–[32]. Here we found that this mechanism also applies for rat eyes.…”

“…However, while Samuelson et al [32] described them as melanocytes by ultrastructure, we found that they are ED-1 positive macrophages.…”

“…The large melanosomes that appeared can be the result of reduced normal cellular function and/or fusion of altered melanosomes. It has been reported that a zinc deficient diet results in an “ageing-like” process, with melanosomal morphological changes [31]–[32], severe degeneration of the photoreceptor outer segments and osmiophilic inclusion bodies in the RPE [33]–[34]. Such alterations are typically found in pigmentary disorders [35]–[36].…”

Zinc and the Eye

“…Samuelson et al have reported ultrastructural changes in the RPE and choroidal melanocytes of adult pigs when they were maintained on diets deficient in zinc. These included displacement of cone nuclei towards the RPE, swollen outer segments of photoreceptors and altered choroidal melanosomes [31,38,39,82,83]. Cataracts and exophthalmos have been reported in trout and salmon associated with zinc deficiency [64 -67].…”

Potential vascular mechanisms in an ex vivo functional pig bladder model

“…Although advanced age is associated with increasing prevalence of detrusor underactivity in the clinical setting, 1 we do not believe that this was a significant factor in this study given that the lifespans of these animals are typically >10 years and previous studies involving domestic pigs have considered ages up to 2 years as subadult and >5 years as aged. [27][28][29] Finally, we were unable to accurately assess the role of influential factors including the kinetic features of slow venous drainage and potential autoregulatory changes in compliance and capacitance which may occur in the absence of vascular flow. Thus, the non-zero pressure values witnessed at zero flow reflect an estimate of the bladder vascular filling pressure.…”