Vitamin D3 in Tilapia mossambica: Relevance of Photochemical Synthesis.

Abstract

SummaryThe capability of fish to synthesize vitamin D on exposure to ultraviolet (UV) light was examined. Purposeful exposure of the freshwater fish Tilapia mossambica (Tilapia) to artificial UV light (300 nm) resulted in a significant increase of vitamin D3 with a concomitant decrease in provitamin D3 ], indicating that provitamin D3 was coverted to vitamin D3. However, only 0.13% of the intraperitoneally injected 4-14C cholesterol was recovered in the vita min D3 and 25-hydroxyvitamin D3 (25-OH-D3) fractions after 15h of irradiation. Thus, although fish is capable of photosynthesizing vitamin D through constant, prolonged exposure to UV light of appropriate wave length, the contribution of this mode of synthesis is unlikely to be of any significance in its natural habitat. Key Words photochemical, Tilapia, vitamin D3, 7-dehydrocholesterol, 25-OH-D3It is well known that vitamin D3 in land animals is mainly derived from photochemical conversion of provitamin D3 (7-DHC) in the skin (1-4). On exposure to sunlight, the 5,7-diene of 7-DHC (steroid) absorbs ultraviolet (UV) energy (spectral range 290-315nm) that causes the cleavage of C9-C10 bond in the "B ring" to form vitamin D3 (secosteroid) (5-7) . Thus, "sunlight" is the chief energy source for breaking the B-ring of steroid in land animals.Interestingly, certain fish liver oils are rich sources of vitamin D [25,000 250,000IU/g oil (8-11)] when compared to mammals [<1IU/g oil (12)], inspite of the non-availability of enough UV light in their natural habitats (13).Earlier studies reported a lack of any relation between provitamin D3 and vitamin D3 contents in several fish (10,11,14) and also that the levels of these two compounds in the skin of fish were lower than those of rats (15), suggesting that the photochemical synthesis of vitamin D3 might not be significant in fish. It has been * To whom correspondence should be addressed . Abbreviations 7-DHC, 7-dehydrocholesterol; 25-OH-D3, 25-hydroxy vitamin D3; UV, ultraviolet; HPLC, high-performance liquid chromatography. (16) that UV exposure to the muscle of Katsuwonus pelamis (Skipjack) in vitro resulted in the conversion of provitamin D3 to vitamin D3 (20%), indicating that photochemical formation of vitamin D3 is possible in fish when exposed to UV light. However, direct evidence for the capability of fish to photosynthesize vitamin D needs to be established. This aspect was studied in the freshwater column feeder fish Tilapia mossambica (Tilapia) and reported in this paper.

From 7-dehydrocholesterol to vitamin D3: Optimization of UV conversion procedures toward the valorization of fish waste matrices

“…This could suggest that the photoproduced pre-VD3, heated just for 5 min, does not receive enough energy to thermoisomerize to VD3, therefore, when it is put back under UVB light it converts into by-product such as DHT. As mentioned before, the intermediate, if not properly heated, can further produce by-product or return in 7-DHC form ( Jasinghe & Perera, 2006 ; Sunitarao & Raghuramulu, 1997 ). Accordingly, in 4-cycles strategy, not only the DHT concentration is higher than in 2-cycles, but also the residual 7-DHC resulted in higher and statistically significant values (292.04 ± 8.76 μg/mL and 242.3 ± 4.569 μg/mL respectively) ( Fig.…”

“…Initial evidences of 7-DHC conversion to VD3 in fish matrices were reported in 1997 ( Sunitarao & Raghuramulu, 1997 ). In particular, the study focused on the exposing alive Oreochromis mossambicus ( Tilapia mossambica ) to UVB light (300 nm) for 15 h and subsequent quantification of VD3 in the meat of the sacrificed animal.…”

“…To the best of our knowledge, the production of vitamin D 3 has been poorly studied in fish using UV radiation although 7-DHC occurs in fish tissues at a high level ( Mgbechidinma et al, 2023 ; Pierens & Fraser, 2015 ). The scarce scientific literature mainly focuses on vitamin D 3 production without planning an experimental optimization of all the parameters involved and without giving attention to the by-products that are certainly produced ( Hidaka, Suzuki, Hayakawa, Okazaki, & Wada, 1989 ; Murthy, Phadke, Jeyakumari, & Vijayakumar, 2023 ; Sunitarao & Raghuramulu, 1997 ) or focuses on the irradiation of alive fish to obtain vitamin D 3 rich fish meat ( Ding, Jin, Fu, Zhang, & Guan, 2019 ). In this scenario, fish waste can be considered a great natural substrate available for the production of vitamin D 3 -rich extracts that can be further used in food functionalization or supplement formulation.…”